U.S. patent application number 10/585012 was filed with the patent office on 2008-12-25 for methods and apparatuses for magnetizing an object and for calibrating a sensor device.
Invention is credited to Lutz May.
Application Number | 20080313886 10/585012 |
Document ID | / |
Family ID | 34744009 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080313886 |
Kind Code |
A1 |
May; Lutz |
December 25, 2008 |
Methods and Apparatuses for Magnetizing an Object and for
Calibrating a Sensor Device
Abstract
A method and an apparatus for magnetizing an object, a method
and an apparatus for calibrating a force and torque sensor device,
a use of an apparatus for magnetizing an object in particular
fields, and a use of an apparatus for calibrating a force and
torque sensor device in particular fields. A method for magnetizing
a first object and/or a second object comprises the steps of
arranging a first object in such a manner that the first object
encloses a second object, and applying a first electrical signal to
the second object, wherein the first electrical signal is adapted
such that at least a portion of the first object and/or of the
second object is magnetized.
Inventors: |
May; Lutz;
(Gelting/Geretsried, DE) |
Correspondence
Address: |
FAY KAPLUN & MARCIN, LLP
150 BROADWAY, SUITE 702
NEW YORK
NY
10038
US
|
Family ID: |
34744009 |
Appl. No.: |
10/585012 |
Filed: |
December 29, 2004 |
PCT Filed: |
December 29, 2004 |
PCT NO: |
PCT/EP04/14797 |
371 Date: |
June 22, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60533276 |
Dec 30, 2003 |
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60598111 |
Aug 2, 2004 |
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60612562 |
Sep 23, 2004 |
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60617890 |
Oct 12, 2004 |
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60626359 |
Nov 9, 2004 |
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60629589 |
Nov 19, 2004 |
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Current U.S.
Class: |
29/607 ; 324/174;
324/207.22; 73/1.09 |
Current CPC
Class: |
F16H 59/70 20130101;
Y10T 29/49075 20150115; G01L 3/102 20130101; H01F 13/006 20130101;
G01L 3/103 20130101; G01D 5/145 20130101 |
Class at
Publication: |
29/607 ; 73/1.09;
324/174; 324/207.22 |
International
Class: |
G01L 3/10 20060101
G01L003/10; G01L 25/00 20060101 G01L025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 30, 2003 |
EP |
03030030.5 |
Claims
1. A method for magnetizing at least one of a first object and a
second object, comprising: arranging a first object in such a
manner that the first object encloses a second object; and applying
a first electrical signal to the second object, wherein the first
electrical signal is adapted such that at least a portion of at
least one of the first object and the second object is
magnetized.
2. The method according to claim 1, wherein the first electrical
signal is one of a first pulse signal and a sequence of subsequent
pulse signals.
3. The method according to claim 2, wherein, in a time versus
current diagram, the first pulse signal has a fast raising edge
which is essentially vertical and has a slow falling edge.
4. The method according to claim 1, wherein the first electrical
signal is one of a current and a voltage.
5. The method according to claim 1, wherein a second electrical
signal is applied to the second object after having applied the
first electrical signal, wherein the second electrical signal is
adapted such that at least a portion of at least one of the first
object and the second object is magnetized, and wherein the second
electrical signal differs from the first electrical signal
concerning at least one of the group consisting of amplitude, sign,
signal shape and duration.
6. The method according to claim 5, wherein the second electrical
signal is one of a second pulse signal and a sequence of subsequent
pulse signals.
7. The method according to claim 6, wherein, in a time versus
current diagram, the second pulse signal has a fast raising edge
which is essentially vertical and has a slow falling edge.
8. The method according to claim 5, wherein at least one of the
first object and the second object is magnetized by applying the
first electrical signal and the second electrical signal such that
in a direction essentially perpendicular to a surface of the first
object and/or of the second object, a magnetic field structure is
generated such that there is a first magnetic flow in a first
direction and a second magnetic flow in a second direction, and
wherein the first direction is opposite to the second
direction.
9. The method according to claim 5, wherein the second electrical
signal is one of a current and a voltage.
10. An apparatus for magnetizing at least one of a first object and
a second object, comprising: a first object; a second object; and
an electrical signal source; wherein the first object is arranged
in such a manner that the first object encloses the second object;
and wherein the electrical signal source applies a first electrical
signal to the second object, and wherein the first electrical
signal is adapted such that at least a portion of at least one of
the first object and the second object is magnetized.
11. The apparatus according to claim 10, wherein the first object
is a hollow tube.
12. The apparatus according to claim 10, wherein the second object
is one of the group consisting of a shaft, a wire and a hollow
tube.
13. The apparatus according to claim 10, wherein the second object
is arranged at a center of the first object.
14. The apparatus according to claim 10, wherein the electrical
signal source comprises a capacitor bank.
15. The apparatus according to claim 10, wherein the first object
has a first electrical connection and a second electrical
connection, wherein the second object has a first electrical
connection and a second electrical connection, and wherein the
second electrical connection of the first object is coupled to the
first electrical connection of the second object.
16. The apparatus according to claim 15, wherein the electrical
signal source is connected such that a first electrical signal is
applyable between the first electrical connection of the first
object and the second electrical connection of the second
object.
17. The apparatus according to claim 15, wherein the first object
has a third electrical connection, wherein the second object has a
third electrical connection.
18. The apparatus according to claim 17, wherein the electrical
signal source is connected such that a first electrical signal is
applyable between the first electrical connection of the first
object and the second electrical connection of the second object,
and such that a second electrical signal is applyable between the
third electrical connection of the first object and the third
electrical connection of the second object.
19. The apparatus according to claim 15, further comprising: an
electrically conductive coupling element arranged to couple the
second electrical connection of the first object to the first
electrical connection of the second object.
20. The apparatus according to claim 19, wherein the coupling
element is one of an electrically conductive plate and an
electrically conducting liquid.
21. The apparatus according to claim 10, wherein the second object,
in addition to the first object, is adapted to be magnetized when
the first electrical signal is applied.
22. The apparatus according to claim 10, wherein the second object
comprises a first connection and a second connection, and wherein
the electrical signal source is connected between the first
connection and the second connection of the second object.
23. The apparatus according to claim 10, wherein the electrical
signal source is disconnected from the first object.
24. The apparatus according to claim 22, wherein a portion of the
second object is free from an enclosure with the first object, and
wherein the apparatus further comprising: a shielding element which
is arranged and adapted to electromagnetically shield the portion
of the second object being free from an enclosure with the first
object from the first object.
25. The apparatus according to claim 24, wherein the shielding
element is arranged between the first element and the portion of
the second object being free from an enclosure with the first
object.
26. The apparatus according to claim 24, wherein the shielding
element is a tube which is arranged to enclose the portion of the
second object being free from an enclosure with the first
object.
27. The apparatus according to claim 24, wherein the shielding
element comprises a plurality of sub-elements which are arranged
surrounding the portion of the second object being free from an
enclosure with the first object.
28. A method for calibrating a force and torque sensor device,
comprising: providing a force and torque sensor device having a
magnetically encoded region on an object and a magnetic field
detector adapted to detect a signal resulting from one of a force
and a torque applied to the object; applying a pre-known force to
the object; detecting a signal resulting from the pre-known force
applied to the object; and calibrating the force and torque sensor
device as a function of a correlation between the pre-known force
and the detected signal resulting from the pre-known force.
29. An apparatus for calibrating a force and torque sensor device,
comprising a force and torque sensor device; a pre-known force
generating element; and a calibrating unit; wherein the force and
torque sensor device has a magnetically encoded region on an object
and a magnetic field detector detecting a signal resulting from one
of a force and a torque applied to the object; wherein the
pre-known force generating element applies a pre-known force to the
object; and wherein the calibrating unit calibrates the force and
torque sensor device as a function of a correlation between a
pre-known force and a detected signal resulting from the pre-known
force.
30. The apparatus according to claim 29, wherein the pre-known
force generating element is a pre-known weight.
31. The apparatus according to claim 29, wherein the pre-known
force generating element applies a pre-known shear stress.
32. The apparatus according to claim 29, wherein the pre-known
force generating element is a pre-known torque.
33. The apparatus according to claim 29, wherein the magnetically
encoded region on the object of the force and torque sensor device
is manufactured in accordance with the following manufacturing
steps: applying a first current pulse to the magnetizable object;
wherein the first current pulse is applied such that there is a
first current flow in a first direction along a longitudinal axis
of the magnetizable object; and wherein the first current pulse is
such that the application of the current pulse generates the
magnetically encoded region on the object.
34. The apparatus according to claim 33, wherein a second current
pulse is applied to the magnetizable object; wherein the second
current pulse is applied such that there is a second current flow
in a second direction along the longitudinal axis of the
magnetizable object.
35. The apparatus according to claim 34, wherein each of the first
and second current pulses has a raising edge and a falling edge;
wherein the raising edge is steeper than the falling edge.
36. The apparatus according to claim 34, wherein the first
direction is opposite to the second direction.
37. The apparatus according to claim 33, wherein the magnetizable
object has a circumferential surface surrounding a core region of
the magnetizable object; wherein the first current pulse is
introduced into the magnetizable object at a first location at the
circumferential surface such that there is the first current flow
in the first direction in the core region of the magnetizable
object; wherein the first current pulse is discharged from the
magnetizable object at a second location at the circumferential
surface; and wherein the second location is at a distance in the
first direction from the first location.
38. The apparatus according to claim 34, wherein the second current
pulse is introduced into the magnetizable object at the second
location at the circumferential surface such that there is the
second current flow in the second direction in the core region of
the magnetizable object; and wherein the second current pulse is
discharged from the magnetizable object at the first location at
the circumferential surface.
39-41. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method and an apparatus
for magnetizing an object, to a method and an apparatus for
calibrating a force and torque sensor device, to a use of an
apparatus for magnetizing an object in particular technical fields,
and to a use of an apparatus for calibrating a force and torque
sensor device in particular technical fields.
DESCRIPTION OF THE RELATED ART
[0002] Magnetic transducer technology finds application in the
measurement of torque and position. It has been especially
developed for the non-contacting measurement of torque in a shaft
or any other part being subject to torque or linear motion. A
rotating or reciprocating element or an element which is subject to
an axial load or to shear forces can be provided with a magnetized
region, i.e. a magnetic encoded region, and when the shaft is
rotated or reciprocated, such a magnetic encoded region generates a
characteristic signal in a magnetic field detector (like a magnetic
coil) enabling to determine torque, force or position of the
shaft.
[0003] For such kind of sensors which are disclosed, for instance,
in WO 02/063262, it is important to have an accurately defined
magnetically encoded region which can be manufactured and
calibrated with low cost.
SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to provide a sensor
device having a magnetically encoded region, wherein the sensor
device shall be manufacturable and operable with low cost.
[0005] This object may be achieved by providing a method and an
apparatus for magnetizing an object, a method and an apparatus for
calibrating a force and torque sensor device, a use of an apparatus
for magnetizing an object in particular technical fields, and a use
of an apparatus for calibrating a force and torque sensor device in
particular technical fields according to the independent
claims.
[0006] According to an exemplary embodiment of the invention, a
method for magnetizing a first object and/or a second object is
provided, the method comprising the steps of arranging a first
object in such a manner that the first object encloses a second
object, and applying a first electrical signal to the second
object, wherein the first electrical signal is adapted such that at
least a portion of the first object and/or of the second object is
magnetized.
[0007] According to another exemplary embodiment of the invention,
an apparatus is provided for magnetizing a first object and/or a
second object. The apparatus comprises a first object, a second
object, and an electrical signal source. The first object is
arranged in such a manner that the first object encloses the second
object. The electrical signal source is adapted to apply a first
electrical signal to the second object, wherein the first
electrical signal is adapted such that at least a portion of the
first object and/or of the second object is magnetized.
[0008] Moreover, according to another exemplary embodiment of the
invention, a method for calibrating a force and torque sensor
device is provided, the method comprising the steps of providing a
force and torque sensor device having a magnetically encoded region
on an object and a magnetic field detector adapted to detect a
signal resulting from a force or a torque applied to the object,
applying a pre-known force to the object, detecting a signal
resulting from the pre-known force applied to the object, and
calibrating the force and torque sensor device based on a
correlation between the pre-known force and the detected signal
resulting from the pre-known force.
[0009] Beyond this, according to another exemplary embodiment of
the invention, an apparatus for calibrating a force and torque
sensor device is provided, the apparatus comprising a force and
torque sensor device, a pre-known force generating element, and a
calibrating unit. The force and torque sensor device has a
magnetically encoded region on an object and a magnetic field
detector adapted to detect a signal resulting from a force or a
torque applied to the object. The pre-known force generating
element is adapted to apply a pre-known force to the object, and
the calibrating unit is adapted to calibrate the force and torque
sensor device based on a correlation between a pre-known force and
a detected signal resulting from the pre-known force.
[0010] According to another exemplary embodiment of the invention,
an apparatus having the above-mentioned features is used for
magnetizing one of the group consisting of a mining shaft, a
concrete processing cylinder, a push-pull rod in a gearbox, and a
shaft of an engine.
[0011] According to another exemplary embodiment of the invention,
an apparatus having the above-mentioned features is used for
calibrating a force and torque sensor device of the group
consisting of a mining shaft, a concrete processing cylinder, a
push-pull rod in a gearbox, and a shaft of an engine.
[0012] Within this specification, the expression "magnetizing"
particularly has the meaning that microscopic or elementary magnets
like magnetic moments, grains or domains which are present within a
magnetizable material are treated such that at least a part of them
becomes aligned along a particular direction, so that a random
magnetic orientation is at least partially removed.
[0013] The method for magnetizing a first object and the apparatus
for magnetizing a first object according to the exemplary
embodiments mentioned above have the advantage that a first object
can be magnetized by applying an electrical signal to a second
object which is surrounded by the first object. For instance, a
wire or a shaft or a rod as the second element can be surrounded by
a hollow cylinder as the first object. Applying an appropriate
electrical signal to the second object then allows to generate a
magnetized region in the first object due to a physical effect
which is similar like the physical effects occurring in the case of
a transformator. In other words, a time-dependent electrical
signal, like a current pulse, flowing through the second object
generates a magnetic field which influences magnetizable material
of the first object in such a manner that it becomes magnetized.
The magnetization scheme of the invention allows a cheap and easy
magnetization even of large hollow cylinders--as they occur
particularly in the field of mining and drilling equipment. Thus, a
magnetically encoded region can be formed in an already existing
industrial steel hollow cylinder or tube. This allows that also
already existing magnetizable objects, for instance a drilling
shaft, may be provided with a magnetically encoded region so that a
torque, a bending force and an axial load applied to such an object
can be measured by a simple magnetic field detector like a coil
arranged adjacent to the magnetized object.
[0014] According to the described embodiment, particularly the
outer first object is magnetized. However, in case that also the
inner second object is made of a magnetizable material, the second
object is magnetized simultaneously.
[0015] Another advantage related to the method and the apparatus
for magnetizing a second object according to exemplary embodiments
of the invention is the opportunity to connect the first object to
the second object at a selected position, for instance at an end
portion of the first object and at an end portion of the second
object. According to such an architecture, the current flowing
through the second object is injected also in the first object to
form a counter magnetic field there, which stabilizes the current
distribution in the objects. Thus, a high quality magnetically
encoded region may be formed in the second object, yielding a
sensor with more reproducible and reliable properties.
[0016] According to the described embodiment, particularly the
inner second object is magnetized. However, in case that also the
outer first object is made of a magnetizable material, the first
object is magnetized simultaneously.
[0017] In the following, the method and the apparatus for
calibrating a force and torque sensor device will be explained. One
idea of this calibrating method is to simply apply a pre-known
calibrating force, for instance a known mass or weight, to an
object having a magnetically encoded region (which may be
generated, for instance, according to the method of the invention
of magnetizing an object). Such a weight or gravity force applied
to a torque and force sensor results in a magnetic signal which can
be detected by a magnetic field detector arranged in the vicinity
of the magnetically encoded region. Therefore, the correlated data
pair of the applied force and the resulting detection signal of the
magnetic field detector can be stored. The magnetically encoded
region can be encoded, for instance, according to the above
described method of magnetizing an object, or to the technology
mentioned in WO 02/063262, or according to the so-called PCME
technology which will be described below in detail.
[0018] The thus measured correlation between an axial load and a
detected signal of the magnetic field detector can then be used for
a calibration of the sensor. When the object calibrated in this
manner is practically used (for instance as a drilling shaft), a
measured detection signal can be associated with an corresponding
axial load force, using the calibration data pair estimated using
the known mass. It is also possible, during calibration, to measure
a plurality of calibration data pairs to refine the
calibration.
[0019] Further, the data pair of a known axial load and a
corresponding detecting signal may also serve as an calibration
information which may be used with a sensor which is subject of an
applied torque during practical use. In other words, an axial load
calibration calibrates a torque sensor. This aspect is particularly
advantageous in an application in which a very heavy object is
used, for example in the context of a drilling shaft in a mining
application, when the torque applied to such a drilling shaft shall
be measured. In this case, it is very easy just to place the
drilling shaft, for example a tube, on a stable ground base and to
put a known mass element on the upper end of the drilling shaft. In
contrast to this, it would be very difficult to apply a calibration
torque to such a drilling shaft for calibrating a torque sensor. It
is easier to calibrate a torque sensor by using a calibrating axial
force.
[0020] According to further aspects of the invention, the methods
and apparatuses mentioned above may be implemented in the frame of
a mining shaft, a concrete processing cylinder, a push-pull rod in
a gearbox, or a shaft of an engine. In all of these applications,
the magnetization and the calibration of such a torque, force and
position sensor is highly advantageous, since it allows to
manufacture a highly accurate and reliably calibrated force,
position and torque sensor with low costs. Particularly, mining and
drilling equipment may be provided with the systems of the
invention, and may be used for monitoring a drilling direction and
drilling forces. Further applications of the invention are the
recognition and the analysis of engine knocking.
[0021] Thus, a real-time measurement of actual mechanical forces
applied and being effective "on the job" of large mining and
drilling equipment is enabled according to the invention. The harsh
outdoor conditions and dealing with abrasive materials is something
traditional sensing technologies have difficulties to deal with,
whereas the systems of the invention are compatible with such
conditions without any problems. Mechanical forces which may be
measured according to the invention are torque, bending, axial load
and potential mining equipment overloads.
[0022] By the magnetization method of the invention, a unique
power-shaft encoding process is employed which allows utilizing the
magnetic properties of many types of industrial steel so that a
standard drilling shaft turns into a high precision force sensor.
The actual time required to apply the encoding process is a
fraction of a second and is permanent. After the desired section of
the drilling shaft has been treated with the process of the
invention, this part of the shaft is emanating a specific signal in
relation to the applied mechanical forces to the shaft. This signal
can be detected, for instance, by a passive electrical component
that is placed several millimetres away from the shaft surface.
Nothing needs to be attached to the shaft and nothing needs to
touch the shaft, therefore the mean time between failure is very
high (i.e. the invention provides a very reliable sensing
solution). This non-contact mechanical force measurement principle
relies only on the ferromagnetic properties of the drilling or
power-transmitting shaft. It provides real-time information of any
mechanical force that is travelling through the encoded section of
the shaft, including rotational torque, bending forces, shearing
forces and axial push-pull load. The overall signal bandwidth of
the force-sensing technology is, according to an embodiment, 29 kHz
or around 100,000 measurement samples per second. In addition, a
distinct signal will be emitted when the drilling shaft has been
exposed to mechanical overload and is about to fail.
[0023] In large equipment it is often the case that the mechanical
forces do not travel symmetrically or even distributed through the
power or drilling shaft. Therefore, the magnetic field detector for
instance "looks" at several critical locations at the shaft to get
a larger picture. However, particularly in statically operating
equipment (where the shaft does not rotate) it is often
recommendable to work with one magnetic detecting device only.
[0024] The sensor of the invention can operate under water, in oil,
or even in very dusty environment (like in concrete pumps or
concrete mixing stations). The sensor can withstand temperatures in
a very large range, particularly from -50.degree. C. to
+210.degree. C.
[0025] The sensor signal detection units may be connected to a
custom specific electronic circuit that can be placed several
metres away from the magnetic field detectors itself. Only two
wires ("twisted pair") may be implemented to connect a magnetic
field detector with a corresponding electronic circuit. The output
signal of such an electronic circuit can be a buffered analogue +5V
signal, whereby +2500V may equal to zero torque. The overall
electrical current consumption for a torque, axial load, or bending
sensor is less than 5 mA per sensor channel.
[0026] The magnetic field detectors may be placed outside or inside
a magnetically encoded hollow shaft. Assuming that mechanical
forces transmitted through such a shaft are not passing through the
magnetically encoded section symmetrically, several magnetic field
detectors may be placed geometrically around the shaft to be able
to capture a highly resolved "force picture".
[0027] The encoding of large drilling shafts may be done "at site"
to eliminate the potential need of shipping the heavy shaft to a
specific factory location. The encoding equipment may be
portable/mobile and can be used under almost all weather
conditions. Under ideal circumstances, the drilling shaft can be
placed on its own onto the ground for the encoding process.
However, under the correct circumstances, the drilling shaft can be
encoded while still placed in the drilling or mining equipment.
This is particularly possible if the shaft can be accessed and is
not hidden away. Such a mobile magnetizing and calibration unit can
be brought very close to a drilling shaft.
[0028] A feature of the sensing technology according to the
invention is the way the permanent encoding drilling shaft may be
calibrated. In case of a one meter diameter drilling shaft which is
capable to deal with one million Nm torque, it will be normally be
difficult to apply a "beam and weight" method for the shaft torque
sensor calibration. When placing upright on a horizontal and
structurally sound surface, the measurement performances of the
magnetically encoded shaft can be defined within a relative short
time by relying on the way the "permanently" embedded signal source
is behaving. This is particularly of interest when the drilling
equipment has to be serviced and maintained at remote and difficult
to reach locations.
[0029] The mechanical force sensing technology according to the
invention can be implemented in large-scale oil drilling equipment
to detect the direction the drilling head is moving, and to measure
the drilling pipes axial load (forward thrust) at the drilling
heads location. In this application, the entire sensor system may
be exposed to pressures of >1,500 bars and to temperatures
>200.degree. C. In another application, the sensing principle is
measuring the mechanical forces applied to large-scale
mobile/moving cranes. Here, the magnetically encoded sensor has the
task to prevent the crane from falling (falling over or tilting)
when critical load situations occur. Other applications of the
invention are wind power plants, large extruder equipment, abrasive
material pumping station, and large-scale industrial gear box
systems.
[0030] It is mentioned that a second object (e.g. a shaft) enclosed
by a first object (e.g. a hollow tube) can be magnetized by
applying an electrical signal to the first object. This aspect is
related to a method for magnetizing a second object, the method
comprising the steps of arranging a first object in such a manner
that the first object encloses the second object, and applying an
electrical signal to the first object, wherein the electrical
signal is adapted such that at least a portion of the second object
is magnetized. The method works particularly fine when end portions
of the second object outside the first object are short-circuited,
for instance if two such end portions are connected with each other
electrically be a wire guided outside of the first object.
[0031] Referring to the dependent claims, further exemplary
embodiments of the invention will be described in the
following.
[0032] In the following, exemplary embodiments of the method for
magnetizing an object will be described. However, these embodiments
also apply for the apparatus for magnetizing an object, for the
method and the apparatus for calibrating a force and torque sensor
device, for the use of an apparatus for magnetizing an object in
particular technical fields, and for the use of an apparatus for
calibrating a force and torque sensor device in particular
technical fields.
[0033] The first electrical signal may be a first pulse signal or a
sequence of subsequent pulse signals. Such a pulse signal can
particularly be a signal which is different from zero only for a
defined interval of time.
[0034] For instance, in a time versus current diagram, the first
pulse signal has a fast raising edge which is essentially vertical
and has a slow falling edge. With such a pulse signal, the
magnetically encoded region obtained has a high quality. It is also
possible that a plurality of such pulses are subsequently applied
to form a magnetically encoded region.
[0035] A second electrical signal may be applied to the second
object after having applied the first electrical signal, wherein
the second electrical signal may be adapted such that at least a
portion of the first object and/or of the second object is
magnetized, and wherein the second electrical signal differs from
the first electrical signal concerning at least one of the group
consisting of amplitude, sign, signal shape and duration.
[0036] According to this embodiment, two pulses with opposite
flowing direction of the electrical current may be applied to the
second object.
[0037] The second electrical signal may be a second pulse signal or
a sequence of subsequent pulse signals, which, in a time versus
current diagram may have a fast raising edge which is essentially
vertical and may have a slow falling edge.
[0038] According to an embodiment of the method of the invention,
the first object may be magnetized by applying the first electrical
signal and the second electrical signal such that in a direction
essentially perpendicular to a surface of the first object and/or
of the second object, a magnetic field structure is generated such
that there is a first magnetic flow in a first direction and a
second magnetic flow in a second direction, wherein the first
direction is opposite to the second direction. This geometrical
orientation of the two layers of magnetization results from two
different pulses applied to the magnetizable material, so that a
PCME-like sensor according to the below described technology may be
manufactured.
[0039] The second electrical signal may also be an electrical
current or an electrical voltage.
[0040] In the following, exemplary embodiments of the apparatus for
magnetizing an object will be described. However, these embodiments
also apply for the method for magnetizing an object, for the method
and the apparatus for calibrating a force and torque sensor device,
for the use of an apparatus for magnetizing an object in particular
technical fields, and for the use of an apparatus for calibrating a
force and torque sensor device in particular technical fields.
[0041] The first object may be a hollow tube. For instance, the
first object enclosing the second object may be a hollow cylinder
or the like. This structure provides a very symmetric geometry and
is easy to manufacture. However, the first object being arranged as
a hollow tube does not necessarily have to have a circular
cross-section, but may also have a cross-section with the geometry
of a polygon (e.g. a triangle or a square). Such a more asymmetric
configuration may be used to refine sensing properties.
[0042] The second object may be a wire or a shaft or a hollow tube.
Such a shaft or wire may be arranged along a symmetry axis of the
first object, particularly of the first object embodied as a hollow
tube. In an embodiment in which the second object is a hollow tube,
the radius of the hollow tube as the second object is smaller than
the radius of the hollow tube as the first object so that the
second object can be surrounded by the first object. The second
object being arranged as a hollow tube does not necessarily have to
have a circular cross-section, but may also have a cross-section
with the geometry of a polygon (e.g. a triangle or a square). Such
a more asymmetric configuration may be used to refine sensing
properties.
[0043] The second object may be arranged at a centre of the first
object. In this configuration, a very symmetric current and
magnetic field distribution is achieved.
[0044] The electrical signal source may comprise a capacitor bank.
Such a capacitor bank comprises a plurality of capacitors which
together may generate a pulse signal with a very high current
amplitude and a small time duration, particularly for magnetizing
large objects, as they may occur in the field of mining and
drilling equipment. Such a capacitor bank may, for instance, have a
capacity of 0.5 F. As an alternative to a capacitor bank, the
electrical signal source/electrical power source may comprise a
conventional power supply unit or power pack.
[0045] The first object may have a first connection and may have a
second connection, and the second object may have a first
electrical connection and a second electrical connection. The
second electrical connection of the first object may be coupled to
the first electrical connection of the second object. According to
this embodiment, the two objects are coupled in a manner that a
portion, for instance an end portion, of the first object is
coupled to a portion, for instance an end portion, of the second
object. By this configuration, the current flowing through the
second object is injected into the first object, so that a
"feedback" of the magnetic field generating current is achieved. By
this feedback, a counter magnetic field is generated in the first
object which, together with the current flowing through the second
object, provides a very symmetric configuration and yields an
advantageous current distribution within the object. A torque and
force sensor with a magnetic encoding of this kind, has a very high
signal to noise ratio and only a small hysteresis behaviour.
[0046] Referring to the previously described embodiment, the
electrical signal source may be connected such that a first
electrical signal is applyable between the first electrical
connection of the first object and the second electrical connection
of the second object. According to this circuitry, the current is
flowing from the first electrical connection of the first object to
the second electrical connection of the first object, from there to
the first electrical connection of the second object, and from
there to the second electrical connection of the second object.
[0047] The first object may have a third electrical connection, and
the second object may have a third electrical connection.
[0048] Referring to this embodiment, the electrical signal source
may be connected such that a first electrical signal is applyable
between the first electrical connection of the first object and the
second electrical connection of the second object, and such that a
second electrical signal is applyable between the third electrical
connection of the first object and the third electrical connection
of the second object. This configuration allows to apply
magnetizing currents from both end portions of the first and second
objects, whereas the first and second objects are coupled
electrically at their centre portions with each other.
[0049] The apparatus may further comprise an electrically
conductive coupling element arranged to couple the second
electrical connection of the first object to the first electrical
connection of the second object. Such a coupling element may be an
electrically conductive plate, like a metal plate, which may be
coupled with an end portion of a shaft as the second object and
coupled with an end surface of a hollow tube as the first object.
However, the electrically conductive coupling element may also be
realized as a simple wire or the like. The electrically conductive
coupling element may also be realized as an electrically conducting
liquid, e.g. on the basis of mercury.
[0050] The second object, in addition to the first object, may be
adapted to be magnetized when the first electrical signal is
applied. In other words, according to the described arrangement of
the first object enclosing the second object, both of the objects
can be magnetized and used as magnetized objects of a torque or
force sensor.
[0051] The second object may comprise a first connection and a
second connection, wherein the electrical signal source may be
connected between the first connection and the second connection of
the second object. According to this circuitry, the electrical
signal source may be disconnected from the first object. In other
words, this configuration can be considered as a transformator-like
arrangement, wherein the first object surrounding the second object
can be magnetized without any direct ohmic contact between the two
objects. In this context, the magnetization of the first object is
generated by the electrical signal propagating through the second
object and forcing elementary magnets of the material of the first
object to become aligned.
[0052] According to an exemplary embodiment, a portion of the
second object may be free from an enclosure with the first object,
and the apparatus may further comprise a shielding element which is
arranged and adapted to electromagnetically shield the portion of
the second object being free from an enclosure with the first
object from the first object. This embodiment takes into account
that a wiring of the second object back to the electrical signal
source may also produce a magnetic field which influences the first
object in a way that the magnetization generated by the part of the
second object being enclosed or surrounded by the first object is
weakened. In order to avoid such an undesired weakening and to
achieve a homogeneous and reproducible magnetization of the first
object, the shielding element shields the magnetic field generated
by the part of the wiring of the second object which is not covered
by the first object.
[0053] Such a shielding element may be an element, for instance a
tube, which may be optionally made of a magnetizable material which
is arranged between the first object and the portion of the second
object being from an enclosure with the first object. In this
configuration, the shielding element forms some kind of magnetic
"shadow" to magnetically decouple the first object from the part of
the second object which is not covered by the second object.
[0054] Alternatively, the shielding element may be a tube
(optionally made of a magnetizable material) which is arranged to
enclose the portion of the second object being free from an
enclosure with the first object. According to this embodiment, the
shielding tube surrounds at least a part of the part of the second
object which is not surrounded by the first element.
[0055] As a further alternative, the shielding element may comprise
a plurality of tubes (optionally made of a magnetizable material)
which are arranged surrounding at least a part of the portion of
the second object being free from an enclosure with the first
object. Such shielding tubes may be arranged symmetrically around
the part of the first object to be shielded.
[0056] In the following, embodiments of the apparatus for
calibrating a force and torque sensor device. However, these
embodiments also apply for the method and apparatus for magnetizing
an object, for the method for calibrating a force and torque sensor
device, for the use of an apparatus for magnetizing an object in
particular technical fields, and for the use of an apparatus for
calibrating a force and torque sensor device in particular
technical fields.
[0057] In the calibrating apparatus, the pre-known force generating
element may be a pre-known weight. This pre-known weight, for
instance 1000 kg, may be simply put on the top of a hollow
cylinder-like force and torque sensor device to be calibrated and
forms a constant and pre-known axial load applied to the sensor
device, so that a highly accurate calibration is possible.
[0058] Alternatively, the pre-known force generating element may be
adapted to apply a pre-known shear stress. Also by applying a shear
stress, a pair of data values (force; resulting magnetic signal)
can be obtained as a basis for a calibration.
[0059] Alternatively, the pre-known force generating element may be
adapted to be a pre-known torque, particularly a pre-known reactive
torque.
[0060] The above and other aspects, objects, features and
advantages of the present invention will become apparent from the
following description and the appended claim, taken in conjunction
with the accompanying drawings in which like parts or elements are
denoted by like reference numbers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] The accompanying drawings, which are included to provide a
further understanding of the invention and constitute a part of the
specification illustrate embodiments of the invention.
[0062] FIG. 1 shows a torque sensor with a sensor element according
to an exemplary embodiment of the present invention for explaining
a method of manufacturing a torque sensor according to an exemplary
embodiment of the present invention.
[0063] FIG. 2a shows an exemplary embodiment of a sensor element of
a torque sensor according to the present invention for further
explaining a principle of the present invention and an aspect of an
exemplary embodiment of a manufacturing method of the present
invention.
[0064] FIG. 2b shows a cross-sectional view along AA' of FIG.
2a.
[0065] FIG. 3a shows another exemplary embodiment of a sensor
element of a torque sensor according to the present invention for
further explaining a principle of the present invention and an
exemplary embodiment of a method of manufacturing a torque sensor
according to the present invention.
[0066] FIG. 3b shows a cross-sectional representation along BB' of
FIG. 3a.
[0067] FIG. 4 shows a cross-sectional representation of the sensor
element of the torque sensor of FIGS. 2a and 3a manufactured in
accordance with a method according to an exemplary embodiment of
the present invention.
[0068] FIG. 5 shows another exemplary embodiment of a sensor
element of a torque sensor according to the present invention for
further explaining an exemplary embodiment of a manufacturing
method of manufacturing a torque sensor according to the present
invention.
[0069] FIG. 6 shows another exemplary embodiment of a sensor
element of a torque sensor according to the present invention for
further explaining an exemplary embodiment of a manufacturing
method for a torque sensor according to the present invention.
[0070] FIG. 7 shows a flow-chart for further explaining an
exemplary embodiment of a method of manufacturing a torque sensor
according to the present invention.
[0071] FIG. 8 shows a current versus time diagram for further
explaining a method according to an exemplary embodiment of the
present invention.
[0072] FIG. 9 shows another exemplary embodiment of a sensor
element of a torque sensor according to the present invention with
an electrode system according to an exemplary embodiment of the
present invention.
[0073] FIG. 10a shows another exemplary embodiment of a torque
sensor according to the present invention with an electrode system
according to an exemplary embodiment of the present invention.
[0074] FIG. 10b shows the sensor element of FIG. 10a after the
application of current surges by means of the electrode system of
FIG. 10a.
[0075] FIG. 11 shows another exemplary embodiment of a torque
sensor element for a torque sensor according to the present
invention.
[0076] FIG. 12 shows a schematic diagram of a sensor element of a
torque sensor according to another exemplary embodiment of the
present invention showing that two magnetic fields may be stored in
the shaft and running in endless circles.
[0077] FIG. 13 is another schematic diagram for illustrating PCME
sensing technology using two counter cycle or magnetic field loops
which may be generated in accordance with a manufacturing method
according to the present invention.
[0078] FIG. 14 shows another schematic diagram for illustrating
that when no mechanical stress is applied to the sensor element
according to an exemplary embodiment of the present invention,
magnetic flux lines are running in its original paths.
[0079] FIG. 15 is another schematic diagram for further explaining
a principle of an exemplary embodiment of the present
invention.
[0080] FIG. 16 is another schematic diagram for further explaining
the principle of an exemplary embodiment of the present
invention.
[0081] FIGS. 17-22 are schematic representations for further
explaining a principle of an exemplary embodiment of the present
invention.
[0082] FIG. 23 is another schematic diagram for explaining a
principle of an exemplary embodiment of the present invention.
[0083] FIGS. 24, 25 and 26 are schematic diagrams for further
explaining a principle of an exemplary embodiment of the present
invention.
[0084] FIG. 27 is a current versus time diagram for illustrating a
current pulse which may be applied to a sensor element according to
a manufacturing method according to an exemplary embodiment of the
present invention.
[0085] FIG. 28 shows an output signal versus current pulse length
diagram according to an exemplary embodiment of the present
invention.
[0086] FIG. 29 shows a current versus time diagram with current
pulses according to an exemplary embodiment of the present
invention which may be applied to sensor elements according to a
method of the present invention.
[0087] FIG. 30 shows another current versus time diagram showing an
exemplary embodiment of a current pulse applied to a sensor element
such as a shaft according to a method of an exemplary embodiment of
the present invention.
[0088] FIG. 31 shows a signal and signal efficiency versus current
diagram in accordance with an exemplary embodiment of the present
invention.
[0089] FIG. 32 is a cross-sectional view of a sensor element having
a preferred PCME electrical current density according to an
exemplary embodiment of the present invention.
[0090] FIG. 33 shows a cross-sectional view of a sensor element and
an electrical pulse current density at different and increasing
pulse current levels according to an exemplary embodiment of the
present invention.
[0091] FIGS. 34a and 34b show a spacing achieved with different
current pulses of magnetic flows in sensor elements according to
the present invention.
[0092] FIG. 35 shows a current versus time diagram of a current
pulse as it may be applied to a sensor element according to an
exemplary embodiment of the present invention.
[0093] FIG. 36 shows an electrical multi-point connection to a
sensor element according to an exemplary embodiment of the present
invention.
[0094] FIG. 37 shows a multi-channel electrical connection fixture
with spring loaded contact points to apply a current pulse to the
sensor element according to an exemplary embodiment of the present
invention.
[0095] FIG. 38 shows an electrode system with an increased number
of electrical connection points according to an exemplary
embodiment of the present invention.
[0096] FIG. 39 shows an exemplary embodiment of the electrode
system of FIG. 37.
[0097] FIG. 40 shows shaft processing holding clamps used for a
method according to an exemplary embodiment of the present
invention.
[0098] FIG. 41 shows a dual field encoding region of a sensor
element according to the present invention.
[0099] FIG. 42 shows a process step of a sequential dual field
encoding according to an exemplary embodiment of the present
invention.
[0100] FIG. 43 shows another process step of the dual field
encoding according to another exemplary embodiment of the present
invention.
[0101] FIG. 44 shows another exemplary embodiment of a sensor
element with an illustration of a current pulse application
according to another exemplary embodiment of the present
invention.
[0102] FIG. 45 shows schematic diagrams for describing magnetic
flux directions in sensor elements according to the present
invention when no stress is applied.
[0103] FIG. 46 shows magnetic flux directions of the sensor element
of FIG. 45 when a force is applied.
[0104] FIG. 47 shows the magnetic flux inside the PCM encoded shaft
of FIG. 45 when the applied torque direction is changing.
[0105] FIG. 48 shows a 6-channel synchronized pulse current driver
system according to an exemplary embodiment of the present
invention.
[0106] FIG. 49 shows a simplified representation of an electrode
system according to another exemplary embodiment of the present
invention.
[0107] FIG. 50 is a representation of a sensor element according to
an exemplary embodiment of the present invention.
[0108] FIG. 51 is another exemplary embodiment of a sensor element
according to the present invention having a PCME process sensing
region with two pinning field regions.
[0109] FIG. 52 is a schematic representation for explaining a
manufacturing method according to an exemplary embodiment of the
present invention for manufacturing a sensor element with an
encoded region and pinning regions.
[0110] FIG. 53 is another schematic representation of a sensor
element according to an exemplary embodiment of the present
invention manufactured in accordance with a manufacturing method
according to an exemplary embodiment of the present invention.
[0111] FIG. 54 is a simplified schematic representation for further
explaining an exemplary embodiment of the present invention.
[0112] FIG. 55 is another simplified schematic representation for
further explaining an exemplary embodiment of the present
invention.
[0113] FIG. 56 shows an application of a torque sensor according to
an exemplary embodiment of the present invention in a gear box of a
motor.
[0114] FIG. 57 shows a torque sensor according to an exemplary
embodiment of the present invention.
[0115] FIG. 58 shows a schematic illustration of components of a
non-contact torque sensing device according to an exemplary
embodiment of the present invention.
[0116] FIG. 59 shows components of a sensing device according to an
exemplary embodiment of the present invention.
[0117] FIG. 60 shows arrangements of coils with a sensor element
according to an exemplary embodiment of the present invention.
[0118] FIG. 61 shows a single channel sensor electronics according
to an exemplary embodiment of the present invention.
[0119] FIG. 62 shows a dual channel, short circuit protected system
according to an exemplary embodiment of the present invention.
[0120] FIG. 63 shows a sensor according to another exemplary
embodiment of the present invention.
[0121] FIG. 64 illustrates an exemplary embodiment of a secondary
sensor unit assembly according to an exemplary embodiment of the
present invention.
[0122] FIG. 65 illustrates two configurations of a geometrical
arrangement of primary sensor and secondary sensor according to an
exemplary embodiment of the present invention.
[0123] FIG. 66 is a schematic representation for explaining that a
spacing between the secondary sensor unit and the sensor host is
preferably as small as possible.
[0124] FIG. 67 is an embodiment showing a primary sensor encoding
equipment.
[0125] FIG. 68A shows a magnetizing apparatus without involving an
object enclosing another object.
[0126] FIG. 68B shows a magnetizing apparatus according to the
invention involving an object enclosing another object.
[0127] FIG. 68C shows a schematic view of a torque and force
sensing device with a magnetically encoded region formed according
to the invention.
[0128] FIG. 68D shows a signal versus torque diagram of a torque
and force sensing device magnetized with the magnetizing apparatus
shown in FIG. 68A.
[0129] FIG. 68E shows a signal versus torque diagram of a torque
and force sensing device magnetized with the magnetizing apparatus
shown in FIG. 68B.
[0130] FIG. 69 is a schematic view illustrating the principle of a
method for magnetizing an object according to the invention.
[0131] FIGS. 70A and 70B are schematic views illustrating an
apparatus for magnetizing an object according to the invention.
[0132] FIG. 70C is a schematic view illustrating another apparatus
for magnetizing an object according to the invention.
[0133] FIG. 701D is a diagram illustrating a pulse signal for
magnetizing a object according to an apparatus as shown in FIGS.
70A to 70C.
[0134] FIGS. 71A, 71B illustrate another embodiment of an apparatus
for magnetizing an object according to the invention.
[0135] FIG. 72 illustrates still another apparatus for magnetizing
an object according to an embodiment of the invention.
[0136] FIGS. 73A to 73D show top views of different apparatuses for
magnetizing an object according to embodiments of the
invention.
[0137] FIG. 74 shows another apparatus for magnetizing an object
according to the invention.
[0138] FIGS. 75A, 75B show different views of an apparatus for
calibrating a force and torque sensor device according to the
invention.
[0139] FIGS. 76A, 76B show schematic views of force and torque
sensor devices according to the invention.
[0140] FIG. 77 shows different views of magnetically encoded hollow
cylinders.
[0141] FIG. 78 shows views of a sensing device according to the
invention.
[0142] FIG. 79 illustrates still another apparatus for magnetizing
an object.
[0143] FIG. 80 illustrates still another apparatus for magnetizing
an object according to an embodiment of the invention.
[0144] FIG. 81 shows another apparatus for calibrating a force and
torque sensor device according to the invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION
[0145] It is disclosed a sensor having a sensor element such as a
shaft wherein the sensor element may be manufactured in accordance
with the following manufacturing steps [0146] applying a first
current pulse to the sensor element; [0147] wherein the first
current pulse is applied such that there is a first current flow in
a first direction along a longitudinal axis of the sensor element;
[0148] wherein the first current pulse is such that the application
of the current pulse generates a magnetically encoded region in the
sensor element.
[0149] It is disclosed that a further second current pulse may be
applied to the sensor element. The second current pulse may be
applied such that there is a second current flow in a direction
along the longitudinal axis of the sensor element.
[0150] It is disclosed that the directions of the first and second
current pulses may be opposite to each other. Also, each of the
first and second current pulses may have a raising edge and a
falling edge. For instance, the raising edge is steeper than the
falling edge.
[0151] It is believed that the application of a current pulse may
cause a magnetic field structure in the sensor element such that in
a cross-sectional view of the sensor element, there is a first
circular magnetic flow having a first direction and a second
magnetic flow having a second direction. The radius of the first
magnetic flow may be larger than the radius of the second magnetic
flow. In shafts having a non-circular cross-section, the magnetic
flow is not necessarily circular but may have a form essentially
corresponding to and being adapted to the cross-section of the
respective sensor element.
[0152] It is believed that if no torque is applied to a sensor
element, there is no magnetic field or essentially no magnetic
field detectable at the outside. When a torque or force is applied
to the sensor element, there is a magnetic field emanated from the
sensor element which can be detected by means of suitable coils.
This will be described in further detail in the following.
[0153] A torque sensor may have a circumferential surface
surrounding a core region of the sensor element. The first current
pulse is introduced into the sensor element at a first location at
the circumferential surface such that there is a first current flow
in the first direction in the core region of the sensor element.
The first current pulse is discharged from the sensor element at a
second location at the circumferential surface. The second location
is at a distance in the first direction from the first location.
The second current pulse may be introduced into the sensor element
at the second location or adjacent to the second location at the
circumferential surface such that there is the second current flow
in the second direction in the core region or adjacent to the core
region in the sensor element. The second current pulse may be
discharged from the sensor element at the first location or
adjacent to the first location at the circumferential surface.
[0154] As already indicated above, the sensor element may be a
shaft. The core region of such shaft may extend inside the shaft
along its longitudinal extension such that the core region
surrounds a center of the shaft. The circumferential surface of the
shaft is the outside surface of the shaft. The first and second
locations are respective circumferential regions at the outside of
the shaft. There may be a limited number of contact portions which
constitute such regions. For instance, real contact regions may be
provided, for example, by providing electrode regions made of brass
rings as electrodes. Also, a core of a conductor may be looped
around the shaft to provide for a good electric contact between a
conductor such as a cable without isolation and the shaft.
[0155] The first current pulse and also the second current pulse
may be not applied to the sensor element at an end face of the
sensor element. The first current pulse may have a maximum between
40 and 1400 Ampere or between 60 and 800 Ampere or between 75 and
600 Ampere or between 80 and 500 Ampere. The current pulse may have
a maximum such that an appropriate encoding is caused to the sensor
element. However, due to different materials which may be used and
different forms of the sensor element and different dimensions of
the sensor element, a maximum of the current pulse may be adjusted
in accordance with these parameters. The second pulse may have a
similar maximum or may have a maximum approximately 10, 20, 30, 40
or 50% smaller than the first maximum. However, the second pulse
may also have a higher maximum such as 10, 20, 40, 50, 60 or 80%
higher than the first maximum.
[0156] A duration of those pulses may be the same. However, it is
possible that the first pulse has a significant longer duration
than the second pulse. However, it is also possible that the second
pulse has a longer duration than the first pulse.
[0157] The first and/or second current pulses may have a first
duration from the start of the pulse to the maximum and may have a
second duration from the maximum to essentially the end of the
pulse. The first duration may be significantly longer than the
second duration. For example, the first duration may be smaller
than 300 ms wherein the second duration may be larger than 300 ms.
However, it is also possible that the first duration is smaller
than 200 ms whereas the second duration is larger than 400 ms.
Also, the first duration may be between 20 to 150 ms wherein the
second duration may be between 180 to 700 ms.
[0158] As already indicated above, it is possible to apply a
plurality of first current pulses but also a plurality of second
current pulses. The sensor element may be made of steel whereas the
steel may comprise nickel. The sensor material used for the primary
sensor or for the sensor element may be 50NiCr13 or X4CrNi13-4 or
X5CrNiCuNb16-4 or X20CrNi17-4 or X46Cr13 or X20Cr13 or 14NiCr14 or
S155 as set forth in DIN 1.2721 or 1.4313 or 1.4542 or 1.2787 or
1.4034 or 1.4021 or 1.5752 or 1.6928.
[0159] The first current pulse may be applied by means of an
electrode system having at least a first electrode and a second
electrode. The first electrode is located at the first location or
adjacent to the first location and the second electrode is located
at the second location or adjacent to the second location.
[0160] Each of the first and second electrodes may have a plurality
of electrode pins. The plurality of electrode pins of each of the
first and second electrodes may be arranged circumferentially
around the sensor element such that the sensor element is contacted
by the electrode pins of the first and second electrodes at a
plurality of contact points at an outer circumferential surface of
the shaft at the first and second locations.
[0161] As indicated above, instead of electrode pins laminar or
two-dimensional electrode surfaces may be applied. For instance,
electrode surfaces are adapted to surfaces of the shaft such that a
good contact between the electrodes and the shaft material may be
ensured.
[0162] At least one of the first current pulse and at least one of
the second current pulse may be applied to the sensor element such
that the sensor element has a magnetically encoded region such that
in a direction essentially perpendicular to a surface of the sensor
element, the magnetically encoded region of the sensor element has
a magnetic field structure such that there is a first magnetic flow
in a first direction and a second magnetic flow in a second
direction. The first direction may be opposite to the second
direction.
[0163] In a cross-sectional view of the sensor element, there may
be a first circular magnetic flow having the first direction and a
first radius and a second circular magnetic flow having the second
direction and a second radius. The first radius may be larger than
the second radius.
[0164] Furthermore, the sensor elements may have a first pinning
zone adjacent to the first location and a second pinning zone
adjacent to the second location.
[0165] The pinning zones may be manufactured in accordance with the
following manufacturing method. According to this method, for
forming the first pinning zone, at the first location or adjacent
to the first location, a third current pulse is applied on the
circumferential surface of the sensor element such that there is a
third current flow in the second direction. The third current flow
is discharged from the sensor element at a third location which is
displaced from the first location in the second direction.
[0166] For forming the second pinning zone, at the second location
or adjacent to the second location, a forth current pulse may be
applied on the circumferential surface to the sensor element such
that there is a forth current flow in the first direction. The
forth current flow is discharged at a forth location which is
displaced from the second location in the first direction.
[0167] A torque sensor may be provided comprising a first sensor
element with a magnetically encoded region wherein the first sensor
element has a surface. In a direction essentially perpendicular to
the surface of the first sensor element, the magnetically encoded
region of the first sensor element may have a magnetic field
structure such that there is a first magnetic flow in a first
direction and a second magnetic flow in a second direction. The
first and second directions may be opposite to each other.
[0168] The torque sensor may further comprise a second sensor
element with at least one magnetic field detector. The second
sensor element may be adapted for detecting variations in the
magnetically encoded region. More precisely, the second sensor
element may be adapted for detecting variations in a magnetic field
emitted from the magnetically encoded region of the first sensor
element.
[0169] The magnetically encoded region may extend longitudinally
along a section of the first sensor element, but does not extend
from one end face of the first sensor element to the other end face
of the first sensor element. In other words, the magnetically
encoded region does not extend along all of the first sensor
element but only along a section thereof.
[0170] The first sensor element may have variations in the material
of the first sensor element caused by at least one current pulse or
surge applied to the first sensor element for altering the
magnetically encoded region or for generating the magnetically
encoded region. Such variations in the material may be caused, for
example, by differing contact resistances between electrode systems
for applying the current pulses and the surface of the respective
sensor element. Such variations may, for example, be burn marks or
color variations or signs of an annealing.
[0171] The variations may be at an outer surface of the sensor
element and not at the end faces of the first sensor element since
the current pulses are applied to outer surface of the sensor
element but not to the end faces thereof.
[0172] A shaft for a magnetic sensor may be provided having, in a
cross-section thereof, at least two circular magnetic loops running
in opposite direction. Such shaft is believed to be manufactured in
accordance with the above-described manufacturing method.
[0173] Furthermore, a shaft may be provided having at least two
circular magnetic loops which are arranged concentrically.
[0174] A shaft for a torque sensor may be provided which is
manufactured in accordance with the following manufacturing steps
where firstly a first current pulse is applied to the shaft. The
first current pulse is applied to the shaft such that there is a
first current flow in a first direction along a longitudinal axis
of the shaft. The first current pulse is such that the application
of the current pulse generates a magnetically encoded region in the
shaft. This may be made by using an electrode system as described
above and by applying current pulses as described above.
[0175] An electrode system may be provided for applying current
surges to a sensor element for a torque sensor, the electrode
system having at least a first electrode and a second electrode
wherein the first electrode is adapted for location at a first
location on an outer surface of the sensor element. A second
electrode is adapted for location at a second location on the outer
surface of the sensor element. The first and second electrodes are
adapted for applying and discharging at least one current pulse at
the first and second locations such that current flows within a
core region of the sensor element are caused. The at least one
current pulse is such that a magnetically encoded region is
generated at a section of the sensor element.
[0176] The electrode system may comprise at least two groups of
electrodes, each comprising a plurality of electrode pins. The
electrode pins of each electrode are arranged in a circle such that
the sensor element is contacted by the electrode pins of the
electrode at a plurality of contact points at an outer surface of
the sensor element.
[0177] The outer surface of the sensor element does not include the
end faces of the sensor element.
[0178] FIG. 1 shows an exemplary embodiment of a torque sensor
according to the present invention. The torque sensor comprises a
first sensor element or shaft 2 having a rectangular cross-section.
The first sensor element 2 extends essentially along the direction
indicated with X. In a middle portion of the first sensor element
2, there is the encoded region 4. The first location is indicated
by reference numeral 10 and indicates one end of the encoded region
and the second location is indicated by reference numeral 12 which
indicates another end of the encoded region or the region to be
magnetically encoded 4. Arrows 14 and 16 indicate the application
of a current pulse. As indicated in FIG. 1, a first current pulse
is applied to the first sensor element 2 at an outer region
adjacent or close to the first location 10. For instance, as will
be described in further detail later on, the current is introduced
into the first sensor element 2 at a plurality of points or regions
close to the first location and for instance surrounding the outer
surface of the first sensor element 2 along the first location 10.
As indicated with arrow 16, the current pulse is discharged from
the first sensor element 2 close or adjacent or at the second
location 12 for instance at a plurality or locations along the end
of the region 4 to be encoded. As already indicated before, a
plurality of current pulses may be applied in succession they may
have alternating directions from location 10 to location 12 or from
location 12 to location 10.
[0179] Reference numeral 6 indicates a second sensor element which
is for instance a coil connected to a controller electronic 8. The
controller electronic 8 may be adapted to further process a signal
output by the second sensor element 6 such that an output signal
may output from the control circuit corresponding to a torque
applied to the first sensor element 2. The control circuit 8 may be
an analog or digital circuit. The second sensor element 6 is
adapted to detect a magnetic field emitted by the encoded region 4
of the first sensor element.
[0180] It is believed that, as already indicated above, if there is
no stress or force applied to the first sensor element 2, there is
essentially no field detected by the second sensor element 6.
However, in case a stress or a force is applied to the secondary
sensor element 2, there is a variation in the magnetic field
emitted by the encoded region such that an increase of a magnetic
field from the presence of almost no field is detected by the
second sensor element 6.
[0181] It has to be noted that according to other exemplary
embodiments of the present invention, even if there is no stress
applied to the first sensor element, it may be possible that there
is a magnetic field detectable outside or adjacent to the encoded
region 4 of the first sensor element 2. However, it is to be noted
that a stress applied to the first sensor element 2 causes a
variation of the magnetic field emitted by the encoded region
4.
[0182] In the following, with reference to FIGS. 2a, 2b, 3a, 3b and
4, a method of manufacturing a torque sensor according to an
exemplary embodiment of the present invention will be described. In
particular, the method relates to the magnetization of the
magnetically encoded region 4 of the first sensor element 2.
[0183] As may be taken from FIG. 2a, a current I is applied to an
end region of a region 4 to be magnetically encoded. This end
region as already indicated above is indicated with reference
numeral 10 and may be a circumferential region on the outer surface
of the first sensor element 2. The current I is discharged from the
first sensor element 2 at another end area of the magnetically
encoded region (or of the region to be magnetically encoded) which
is indicated by reference numeral 12 and also referred to a second
location. The current is taken from the first sensor element at an
outer surface thereof, for instance circumferentially in regions
close or adjacent to location 12. As indicated by the dashed line
between locations 10 and 12, the current I introduced at or along
location 10 into the first sensor element flows through a core
region or parallel to a core region to location 12. In other words,
the current I flows through the region 4 to be encoded in the first
sensor element 2.
[0184] FIG. 2b shows a cross-sectional view along AA'. In the
schematic representation of FIG. 2b, the current flow is indicated
into the plane of the FIG. 2b as a cross. Here, the current flow is
indicated in a center portion of the cross-section of the first
sensor element 2. It is believed that this introduction of a
current pulse having a form as described above or in the following
and having a maximum as described above or in the following causes
a magnetic flow structure 20 in the cross-sectional view with a
magnetic flow direction into one direction here into the clockwise
direction. The magnetic flow structure 20 depicted in FIG. 2b is
depicted essentially circular. However, the magnetic flow structure
20 may be adapted to the actual cross-section of the first sensor
element 2 and may be, for example, more elliptical.
[0185] FIGS. 3a and 3b show a step of the method according to an
exemplary embodiment of the present invention which may be applied
after the step depicted in FIGS. 2a and 2b. FIG. 3a shows a first
sensor element according to an exemplary embodiment of the present
invention with the application of a second current pulse and FIG.
3b shows a cross-sectional view along BB' of the first sensor
element 2.
[0186] As may be taken from FIG. 3a, in comparison to FIG. 2a, in
FIG. 3a, the current I indicated by arrow 16 is introduced into the
sensor element 2 at or adjacent to location 12 and is discharged or
taken from the sensor element 2 at or adjacent to the location 10.
In other words, the current is discharged in FIG. 3a at a location
where it was introduced in FIG. 2a and vice versa. Thus, the
introduction and discharging of the current I into the first sensor
element 2 in FIG. 3a may cause a current through the region 4 to be
magnetically encoded opposite to the respective current flow in
FIG. 2a.
[0187] The current is indicated in FIG. 3b in a core region of the
sensor element 2. As may be taken from a comparison of FIGS. 2b and
3b, the magnetic flow structure 22 has a direction opposite to the
current flow structure 20 in FIG. 2b.
[0188] As indicated before, the steps depicted in FIGS. 2a, 2b and
3a and 3b may be applied individually or may be applied in
succession of each other. When firstly, the step depicted in FIGS.
2a and 2b is performed and then the step depicted in FIGS. 3a and
3b, a magnetic flow structure as depicted in the cross-sectional
view through the encoded region 4 depicted in FIG. 4 may be caused.
As may be taken from FIG. 4, the two current flow structures 20 and
22 are encoded into the encoded region together. Thus, in a
direction essentially perpendicular to a surface of the first
sensor element 2, in a direction to the core of the sensor element
2, there is a first magnetic flow having a first direction and then
underlying there is a second magnetic flow having a second
direction. As indicated in FIG. 4, the flow directions may be
opposite to each other.
[0189] Thus, if there is no torque applied to the first torque
sensor element 2, the two magnetic flow structures 20 and 22 may
cancel each other such that there is essentially no magnetic field
at the outside of the encoded region. However, in case a stress or
force is applied to the first sensor element 2, the magnetic field
structures 20 and 22 cease to cancel each other such that there is
a magnetic field occurring at the outside of the encoded region
which may then be detected by means of the secondary sensor element
6. This will be described in further detail in the following.
[0190] FIG. 5 shows another exemplary of a first sensor element 2
according to an exemplary embodiment of the present invention as
may be used in a torque sensor according to an exemplary embodiment
which is manufactured according to a manufacturing method according
to an exemplary embodiment of the present invention. As may be
taken from FIG. 5, the first sensor element 2 has an encoded region
4 which is for instance encoded in accordance with the steps and
arrangements depicted in FIGS. 2a, 2b, 3a, 3b and 4.
[0191] Adjacent to locations 10 and 12, there are provided pinning
regions 42 and 44. These regions 42 and 44 are provided for
avoiding a fraying of the encoded region 4. In other words, the
pinning regions 42 and 44 may allow for a more definite beginning
and end of the encoded region 4.
[0192] In short, the first pinning region 42 may be adapted by
introducing a current 38 close or adjacent to the first location 10
into the first sensor element 2 in the same manner as described,
for example, with reference to FIG. 2a. However, the current I is
discharged from the first sensor element 2 at a first location 30
which is at a distance from the end of the encoded region close or
at location 10. This further location is indicated by reference
numeral 30. The introduction of this further current pulse I is
indicated by arrow 38 and the discharging thereof is indicated by
arrow 40. The current pulses may have the same form shaping maximum
as described above.
[0193] For generating the second pinning region 44, a current is
introduced into the first sensor element 2 at a location 32 which
is at a distance from the end of the encoded region 4 close or
adjacent to location 12. The current is then discharged from the
first sensor element 2 at or close to the location 12. The
introduction of the current pulse I is indicated by arrows 34 and
36.
[0194] The pinning regions 42 and 44 may be such that the magnetic
flow structures of these pinning regions 42 and 44 are opposite to
the respective adjacent magnetic flow structures in the adjacent
encoded region 4. As may be taken from FIG. 5, the pinning regions
can be coded to the first sensor element 2 after the coding or the
complete coding of the encoded region 4.
[0195] FIG. 6 shows another exemplary embodiment of the present
invention where there is no encoding region 4. In other words,
according to an exemplary embodiment of the present invention, the
pinning regions may be coded into the first sensor element 2 before
the actual coding of the magnetically encoded region 4.
[0196] FIG. 7 shows a simplified flow-chart of a method of
manufacturing a first sensor element 2 for a torque sensor
according to an exemplary embodiment of the present invention.
[0197] After the start in step S1, the method continues to step S2
where a first pulse is applied as described as reference to FIGS.
2a and 2b. Then, after step S2, the method continues to step S3
where a second pulse is applied as described with reference to
FIGS. 3a and 3b.
[0198] Then, the method continues to step S4 where it is decided
whether the pinning regions are to be coded to the first sensor
element 2 or not. If it is decided in step S4 that there will be no
pinning regions, the method continues directly to step S7 where it
ends.
[0199] If it is decided in step S4 that the pinning regions are to
be coded to the first sensor element 2, the method continues to
step S5 where a third pulse is applied to the pinning region 42 in
the direction indicated by arrows 38 and 40 and to pinning region
44 indicated by the arrows 34 and 36. Then, the method continues to
step S6 where force pulses applied to the respective pinning
regions 42 and 44. To the pinning region 42, a force pulse is
applied having a direction opposite to the direction indicated by
arrows 38 and 40. Also, to the pinning region 44, a force pulse is
applied to the pinning region having a direction opposite to the
arrows 34 and 36. Then, the method continues to step S7 where it
ends.
[0200] In other words, two pulses may be applied for encoding of
the magnetically encoded region 4. Those current pulses for
instance have an opposite direction. Furthermore, two pulses
respectively having respective directions are applied to the
pinning region 42 and to the pinning region 44.
[0201] FIG. 8 shows a current versus time diagram of the pulses
applied to the magnetically encoded region 4 and to the pinning
regions. The positive direction of the y-axis of the diagram in
FIG. 8 indicates a current flow into the x-direction and the
negative direction of the y-axis of FIG. 8 indicates a current flow
in the y-direction.
[0202] As may be taken from FIG. 8 for coding the magnetically
encoded region 4, firstly a current pulse is applied having a
direction into the x-direction. As may be taken from FIG. 8, the
raising edge of the pulse is very sharp whereas the falling edge
has a relatively long direction in comparison to the direction of
the raising edge. As depicted in FIG. 8, the pulse may have a
maximum of approximately 75 Ampere. In other applications, the
pulse may be not as sharp as depicted in FIG. 8. However, the
raising edge should be steeper or should have a shorter duration
than the falling edge.
[0203] Then, a second pulse is applied to the encoded region 4
having an opposite direction. The pulse may have the same form as
the first pulse. However, a maximum of the second pulse may also
differ from the maximum of the first pulse. Although the immediate
shape of the pulse may be different.
[0204] Then, for coding the pinning regions, pulses similar to the
first and second pulse may be applied to the pinning regions as
described with reference to FIGS. 5 and 6. Such pulses may be
applied to the pinning regions simultaneously but also successfully
for each pinning region. As depicted in FIG. 8, the pulses may have
essentially the same form as the first and second pulses. However,
a maximum may be smaller.
[0205] FIG. 9 shows another exemplary embodiment of a first sensor
element of a torque sensor according to an exemplary embodiment of
the present invention showing an electrode arrangement for applying
the current pulses for coding the magnetically encoded region 4. As
may be taken from FIG. 9, a conductor without an isolation may be
looped around the first sensor element 2 which is may be taken from
FIG. 9 may be a circular shaft having a circular cross-section. For
ensuring a close fit of the conductor on the outer surface of the
first sensor element 2, the conductor may be clamped as shown by
arrows 64.
[0206] FIG. 10a shows another exemplary embodiment of a first
sensor element according to an exemplary embodiment of the present
invention. Furthermore, FIG. 10a shows another exemplary embodiment
of an electrode system according to an exemplary embodiment of the
present invention. The electrode system 80 and 82 depicted in FIG.
10a contacts the first sensor element 2 which has a triangular
cross-section with two contact points at each phase of the
triangular first sensor element at each side of the region 4 which
is to be encoded as magnetically encoded region. Overall, there are
six contact points at each side of the region 4. The individual
contact points may be connected to each other and then connected to
one individual contact points.
[0207] If there is only a limited number of contact points between
the electrode system and the first sensor element 2 and if the
current pulses applied are very high, differing contact resistances
between the contacts of the electrode systems and the material of
the first sensor element 2 may cause burn marks at the first sensor
element 2 at contact point to the electrode systems. These burn
marks 90 may be color changes, may be welding spots, may be
annealed areas or may simply be burn marks. According to an
exemplary embodiment of the present invention, the number of
contact points is increased or even a contact surface is provided
such that such burn marks 90 may be avoided.
[0208] FIG. 11 shows another exemplary embodiment of a first sensor
element 2 which is a shaft having a circular cross-section
according to an exemplary embodiment of the present invention. As
may be taken from FIG. 11, the magnetically encoded region is at an
end region of the first sensor element 2. According to an exemplary
embodiment of the present invention, the magnetically encoded
region 4 is not extend over the full length of the first sensor
element 2. As may be taken from FIG. 11, it may be located at one
end thereof. However, it has to be noted that according to an
exemplary embodiment of the present invention, the current pulses
are applied from an outer circumferential surface of the first
sensor element 2 and not from the end face 100 of the first sensor
element 2.
[0209] In the following, the so-called PCME
("Pulse-Current-Modulated Encoding") Sensing Technology will be
described in detail, which can, according to an exemplary
embodiment of the invention, be implemented to magnetize a
magnetizable object which is then partially demagnetized according
to the invention. In the following, the PCME technology will partly
described in the context of torque sensing. However, this concept
may implemented in the context of position sensing as well.
[0210] In this description, there are a number of acronyms used as
otherwise some explanations and descriptions may be difficult to
read. While the acronyms "ASIC", "IC", and "PCB" are already market
standard definitions, there are many terms that are particularly
related to the magnetostriction based NCT sensing technology. It
should be noted that in this description, when there is a reference
to NCT technology or to PCME, it is referred to exemplary
embodiments of the present invention.
[0211] Table 1 shows a list of abbreviations used in the following
description of the PCME technology.
TABLE-US-00001 TABLE 1 List of abbreviations Acronym Description
Category ASIC Application Specific IC Electronics DF Dual Field
Primary Sensor EMF Earth Magnetic Field Test Criteria FS Full Scale
Test Criteria Hot-Spotting Sensitivity to nearby Ferro magnetic
Specification material IC Integrated Circuit Electronics MFS
Magnetic Field Sensor Sensor Component NCT Non Contact Torque
Technology PCB Printed Circuit Board Electronics PCME Pulse Current
Modulated Encoding Technology POC Proof-of-Concept RSU Rotational
Signal Uniformity Specification SCSP Signal Conditioning &
Signal Electronics Processing SF Single Field Primary Sensor SH
Sensor Host Primary Sensor SPHC Shaft Processing Holding Clamp
Processing Tool SSU Secondary Sensor Unit Sensor Component
[0212] The magnetic principle based mechanical-stress sensing
technology allows to design and to produce a wide range of
"physical-parameter-sensors" (like Force Sensing, Torque Sensing,
and Material Diagnostic Analysis) that can be applied where
Ferro-Magnetic materials are used. The most common technologies
used to build "magnetic-principle-based" sensors are: Inductive
differential displacement measurement (requires torsion shaft),
measuring the changes of the materials permeability, and measuring
the magnetostriction effects.
[0213] Over the last 20 years a number of different companies have
developed their own and very specific solution in how to design and
how to produce a magnetic principle based torque sensor (i.e. ABB,
FAST, Frauenhofer Institute, FT, Kubota, MDI, NCTE, RM, Siemens,
and others). These technologies are at various development stages
and differ in "how-it-works", the achievable performance, the
systems reliability, and the manufacturing/system cost.
[0214] Some of these technologies require that mechanical changes
are made to the shaft where torque should be measured (chevrons),
or rely on the mechanical torsion effect (require a long shaft that
twists under torque), or that something will be attached to the
shaft itself (press-fitting a ring of certain properties to the
shaft surface,), or coating of the shaft surface with a special
substance. No-one has yet mastered a high-volume manufacturing
process that can be applied to (almost) any shaft size, achieving
tight performance tolerances, and is not based on already existing
technology patents.
[0215] In the following, a magnetostriction principle based
Non-Contact-Torque (NCT) Sensing Technology is described that
offers to the user a whole host of new features and improved
performances, previously not available. This technology enables the
realization of a fully-integrated (small in space), real-time (high
signal bandwidth) torque measurement, which is reliable and can be
produced at an affordable cost, at any desired quantities. This
technology is called: PCME (for Pulse-Current-Modulated Encoding)
or Magnetostriction Transversal Torque Sensor.
[0216] The PCME technology can be applied to the shaft without
making any mechanical changes to the shaft, or without attaching
anything to the shaft. Most important, the PCME technology can be
applied to any shaft diameter (most other technologies have here a
limitation) and does not need to rotate/spin the shaft during the
encoding process (very simple and low-cost manufacturing process)
which makes this technology very applicable for high-volume
application.
[0217] In the following, a Magnetic Field Structure (Sensor
Principle) will be described.
[0218] The sensor life-time depends on a "closed-loop" magnetic
field design. The PCME technology is based on two magnetic field
structures, stored above each other, and running in opposite
directions. When no torque stress or motion stress is applied to
the shaft (also called Sensor Host, or SH) then the SH will act
magnetically neutral (no magnetic field can be sensed at the
outside of the SH).
[0219] FIG. 12 shows that two magnetic fields are stored in the
shaft and running in endless circles. The outer field runs in one
direction, while the inner field runs in the opposite
direction.
[0220] FIG. 13 illustrates that the PCME sensing technology uses
two Counter-Circular magnetic field loops that are stored on top of
each other (Picky-Back mode).
[0221] When mechanical stress (like reciprocation motion or torque)
is applied at both ends of the PCME magnetized SH (Sensor Host, or
Shaft) then the magnetic flux lines of both magnetic structures (or
loops) will tilt in proportion to the applied torque.
[0222] As illustrated in FIG. 14, when no mechanical stresses are
applied to the SH the magnetic flux lines are running in its
original path. When mechanical stresses are applied the magnetic
flux lines tilt in proportion to the applied stress (like linear
motion or torque).
[0223] Depending on the applied torque direction (clockwise or
anti-clockwise, in relation to the SH) the magnetic flux lines will
either tilt to the right or tilt to the left. Where the magnetic
flux lines reach the boundary of the magnetically encoded region,
the magnetic flux lines from the upper layer will join-up with the
magnetic flux lines from the lower layer and visa-versa. This will
then form a perfectly controlled toroidal shape.
[0224] The benefits of such a magnetic structure are: [0225]
Reduced (almost eliminated) parasitic magnetic field structures
when mechanical stress is applied to the SH (this will result in
better RSU performances). [0226] Higher Sensor-Output Signal-Slope
as there are two "active" layers that compliment each other when
generating a mechanical stress related signal. Explanation: When
using a single-layer sensor design, the "tilted" magnetic flux
lines that exit at the encoding region boundary have to create a
"return passage" from one boundary side to the other. This effort
effects how much signal is available to be sensed and measured
outside of the SH with the secondary sensor unit. [0227] There are
almost no limitations on the SH (shaft) dimensions where the PCME
technology will be applied to. The dual layered magnetic field
structure can be adapted to any solid or hollow shaft dimensions.
[0228] The physical dimensions and sensor performances are in a
very wide range programmable and therefore can be tailored to the
targeted application. [0229] This sensor design allows to measure
mechanical stresses coming from all three dimensions axis,
including in-line forces applied to the shaft (applicable as a
load-cell). Explanation: Earlier magnetostriction sensor designs
(for example from FAST Technology) have been limited to be
sensitive in 2 dimensional axis only, and could not measure in-line
forces.
[0230] Referring to FIG. 15, when torque is applied to the SH, the
magnetic flux lines from both Counter-Circular magnetic loops are
connecting to each other at the sensor region boundaries.
[0231] When mechanical torque stress is applied to the SH then the
magnetic field will no longer run around in circles but tilt
slightly in proportion to the applied torque stress. This will
cause the magnetic field lines from one layer to connect to the
magnetic field lines in the other layer, and with this form a
toroidal shape.
[0232] Referring to FIG. 16, an exaggerated presentation is shown
of how the magnetic flux line will form an angled toroidal
structure when high levels of torque are applied to the SH.
[0233] In the following, features and benefits of the PCM-Encoding
(PCME) Process will be described.
[0234] The magnetostriction NCT sensing technology from NCTE
according to the present invention offers high performance sensing
features like: [0235] No mechanical changes required on the Sensor
Host (already existing shafts can be used as they are) [0236]
Nothing has to be attached to the Sensor Host (therefore nothing
can fall off or change over the shaft-lifetime=high MTBF) [0237]
During measurement the SH can rotate, reciprocate or move at any
desired speed (no limitations on rpm) [0238] Very good RSU
(Rotational Signal Uniformity) performances [0239] Excellent
measurement linearity (up to 0.01% of FS) [0240] High measurement
repeatability [0241] Very high signal resolution (better than 14
bit) [0242] Very high signal bandwidth (better than 10 kHz)
[0243] Depending on the chosen type of magnetostriction sensing
technology, and the chosen physical sensor design, the mechanical
power transmitting shaft (also called "Sensor Host" or in short
"SH") can be used "as is" without making any mechanical changes to
it or without attaching anything to the shaft. This is then called
a "true" Non-Contact-Torque measurement principle allowing the
shaft to rotate freely at any desired speed in both directions.
[0244] The here described PCM-Encoding (ACME) manufacturing process
according to an exemplary embodiment of the present invention
provides additional features no other magnetostriction technology
can offer (Uniqueness of this technology): [0245] More then three
times signal strength in comparison to alternative magnetostriction
encoding processes (like the "RS" process from FAST). [0246] Easy
and simple shaft loading process (high manufacturing through-putt).
[0247] No moving components during magnetic encoding process (low
complexity manufacturing equipment=high MTBF, and lower cost).
[0248] Process allows NCT sensor to be "fine-tuning" to achieve
target accuracy of a fraction of one percent. [0249] Manufacturing
process allows shaft "pre-processing" and "post-processing" in the
same process cycle (high manufacturing through-putt). [0250]
Sensing technology and manufacturing process is ratio-metric and
therefore is applicable to all shaft or tube diameters. [0251] The
PCM-Encoding process can be applied while the SH is already
assembled (depending on accessibility) (maintenance friendly).
[0252] Final sensor is insensitive to axial shaft movements (the
actual allowable axial shaft movement depends on the physical
"length" of the magnetically encoded region). [0253] Magnetically
encoded SH remains neutral and has little to non magnetic field
when no forces (like torque) are applied to the SH. [0254]
Sensitive to mechanical forces in all three dimensional axis.
[0255] In the following, the Magnetic Flux Distribution in the SH
will be described.
[0256] The PCME processing technology is based on using electrical
currents, passing through the SH (Sensor Host or Shaft) to achieve
the desired, permanent magnetic encoding of the Ferro-magnetic
material. To achieve the desired sensor performance and features a
very specific and well controlled electrical current is required.
Early experiments that used DC currents failed because of luck of
understanding how small amounts and large amounts of DC electric
current are travelling through a conductor (in this case the
"conductor" is the mechanical power transmitting shaft, also called
Sensor Host or in short "SH").
[0257] Referring to FIG. 17, an assumed electrical current density
in a conductor is illustrated.
[0258] It is widely assumed that the electric current density in a
conductor is evenly distributed over the entire cross-section of
the conductor when an electric current (DC) passes through the
conductor.
[0259] Referring to FIG. 18, a small electrical current forming
magnetic field that ties current path in a conductor is shown.
[0260] It is our experience that when a small amount of electrical
current (DC) is passing through the conductor that the current
density is highest at the centre of the conductor. The two main
reasons for this are: The electric current passing through a
conductor generates a magnetic field that is tying together the
current path in the centre of the conductor, and the impedance is
the lowest in the centre of the conductor.
[0261] Referring to FIG. 19, a typical flow of small electrical
currents in a conductor is illustrated.
[0262] In reality, however, the electric current may not flow in a
"straight" line from one connection pole to the other (similar to
the shape of electric lightening in the sky).
[0263] At a certain level of electric current the generated
magnetic field is large enough to cause a permanent magnetization
of the Ferro-magnetic shaft material. As the electric current is
flowing near or at the centre of the SH, the permanently stored
magnetic field will reside at the same location: near or at the
centre of the SH. When now applying mechanical torque or linear
force for oscillation/reciprocation to the shaft, then shaft
internally stored magnetic field will respond by tilting its
magnetic flux path in accordance to the applied mechanical force.
As the permanently stored magnetic field lies deep below the shaft
surface the measurable effects are very small, not uniform and
therefore not sufficient to build a reliable NCT sensor system.
[0264] Referring to FIG. 20, a uniform current density in a
conductor at saturation level is shown.
[0265] Only at the saturation level is the electric current density
(when applying DC) evenly distributed at the entire cross section
of the conductor. The amount of electrical current to achieve this
saturation level is extremely high and is mainly influenced by the
cross section and conductivity (impedance) of the used
conductor.
[0266] Referring to FIG. 21, electric current travelling beneath or
at the surface of the conductor (Skin-Effect) is shown.
[0267] It is also widely assumed that when passing through
alternating current (like a radio frequency signal) through a
conductor that the signal is passing through the skin layers of the
conductor, called the Skin Effect. The chosen frequency of the
alternating current defines the "Location/position" and "depth" of
the Skin Effect. At high frequencies the electrical current will
travel right at or near the surface of the conductor (A) while at
lower frequencies (in the 5 to 10 Hz regions for a 20 mm diameter
SH) the electrical alternating current will penetrate more the
centre of the shafts cross section (E). Also, the relative current
density is higher in the current occupied regions at higher AC
frequencies in comparison to the relative current density near the
centre of the shaft at very low AC frequencies (as there is more
space available for the current to flow through).
[0268] Referring to FIG. 22, the electrical current density of an
electrical conductor (cross-section 90 deg to the current flow)
when passing through the conductor an alternating current at
different frequencies is illustrated.
[0269] The desired magnetic field design of the PCME sensor
technology are two circular magnetic field structures, stored in
two layers on top of each other ("Picky-Back"), and running in
opposite direction to each other (Counter-Circular).
[0270] Again referring to FIG. 13, a desired magnetic sensor
structure is shown: two endless magnetic loops placed on top of
each other, running in opposite directions to each other:
Counter-Circular "Picky-Back" Field Design.
[0271] To make this magnetic field design highly sensitive to
mechanical stresses that will be applied to the SH (shaft), and to
generate the largest sensor signal possible, the desired magnetic
field structure has to be placed nearest to the shaft surface.
Placing the circular magnetic fields to close to the centre of the
SH will cause damping of the user available sensor-output-signal
slope (most of the sensor signal will travel through the
Ferro-magnetic shaft material as it has a much higher permeability
in comparison to air), and increases the non-uniformity of the
sensor signal (in relation to shaft rotation and to axial movements
of the shaft in relation to the secondary sensor.
[0272] Referring to FIG. 23, magnetic field structures stored near
the shaft surface and stored near the centre of the shaft are
illustrated.
[0273] It may be difficult to achieve the desired permanent
magnetic encoding of the SH when using AC (alternating current) as
the polarity of the created magnetic field is constantly changing
and therefore may act more as a Degaussing system.
[0274] The PCME technology requires that a strong electrical
current ("uni-polar" or DC, to prevent erasing of the desired
magnetic field structure) is travelling right below the shaft
surface (to ensure that the sensor signal will be uniform and
measurable at the outside of the shaft). In addition a
Counter-Circular, "picky back" magnetic field structure needs to be
formed.
[0275] It is possible to place the two Counter-Circular magnetic
field structures in the shaft by storing them into the shaft one
after each other. First the inner layer will be stored in the SH,
and then the outer layer by using a weaker magnetic force
(preventing that the inner layer will be neutralized and deleted by
accident. To achieve this, the known "permanent" magnet encoding
techniques can be applied as described in patents from FAST
technology, or by using a combination of electrical current
encoding and the "permanent" magnet encoding.
[0276] A much simpler and faster encoding process uses "only"
electric current to achieve the desired Counter-Circular
"Picky-Back" magnetic field structure. The most challenging part
here is to generate the Counter-Circular magnetic field.
[0277] A uniform electrical current will produce a uniform magnetic
field, running around the electrical conductor in a 90 deg angle,
in relation to the current direction (A). When placing two
conductors side-by-side (B) then the magnetic field between the two
conductors seems to cancel-out the effect of each other (C).
Although still present, there is no detectable (or measurable)
magnetic field between the closely placed two conductors. When
placing a number of electrical conductors side-by-side (D) the
"measurable" magnetic field seems to go around the outside the
surface of the "flat" shaped conductor.
[0278] Referring to FIG. 24, the magnetic effects when looking at
the cross-section of a conductor with a uniform current flowing
through them are shown.
[0279] The "flat" or rectangle shaped conductor has now been bent
into a "U"-shape. When passing an electrical current through the
"U"-shaped conductor then the magnetic field following the outer
dimensions of the "U"-shape is cancelling out the measurable
effects in the inner halve of the "U".
[0280] Referring to FIG. 25, the zone inside the "U"-shaped
conductor seem to be magnetically "Neutral" when an electrical
current is flowing through the conductor.
[0281] When no mechanical stress is applied to the cross-section of
a "U"-shaped conductor it seems that there is no magnetic field
present inside of the "U" (F). But when bending or twisting the
"U"-shaped conductor the magnetic field will no longer follow its
original path (90 deg angle to the current flow). Depending on the
applied mechanical forces, the magnetic field begins to change
slightly its path. At that time the magnetic-field-vector that is
caused by the mechanical stress can be sensed and measured at the
surface of the conductor, inside and outside of the "U"-shape.
Note: This phenomena is applies only at very specific electrical
current levels.
[0282] The same applies to the "O"-shaped conductor design. When
passing a uniform electrical current through an "O"-shaped
conductor (Tube) the measurable magnetic effects inside of the "O"
(Tube) have cancelled-out each other (G).
[0283] Referring to FIG. 26, the zone inside the "O"-shaped
conductor seem to be magnetically "Neutral" when an electrical
current is flowing through the conductor.
[0284] However, when mechanical stresses are applied to the
"O"-shaped conductor (Tube) it becomes evident that there has been
a magnetic field present at the inner side of the "O"-shaped
conductor. The inner, counter directional magnetic field (as well
as the outer magnetic field) begins to tilt in relation to the
applied torque stresses. This tilting field can be clearly sensed
and measured.
[0285] In the following, an Encoding Pulse Design will be
described.
[0286] To achieve the desired magnetic field structure
(Counter-Circular, Picky-Back, Fields Design) inside the SH,
according to an exemplary embodiment of a method of the present
invention, unipolar electrical current pulses are passed through
the Shaft (or SH). By using "pulses" the desired "Skin-Effect" can
be achieved. By using a "unipolar" current direction (not changing
the direction of the electrical current) the generated magnetic
effect will not be erased accidentally.
[0287] The used current pulse shape is most critical to achieve the
desired PCME sensor design. Each parameter has to be accurately and
repeatable controlled: Current raising time, Constant current
on-time, Maximal current amplitude, and Current falling time. In
addition it is very critical that the current enters and exits very
uniformly around the entire shaft surface.
[0288] In the following, a Rectangle Current Pulse Shape will be
described.
[0289] Referring to FIG. 27, a rectangle shaped electrical current
pulse is illustrated.
[0290] A rectangle shaped current pulse has a fast raising positive
edge and a fast falling current edge. When passing a rectangle
shaped current pulse through the SH, the raising edge is
responsible for forming the targeted magnetic structure of the PCME
sensor while the flat "on" time and the falling edge of the
rectangle shaped current pulse are counter productive.
[0291] Referring to FIG. 28, a relationship between rectangles
shaped Current Encoding Pulse-Width (Constant Current On-Time) and
Sensor Output Signal Slope is shown.
[0292] In the following example a rectangle shaped current pulse
has been used to generate and store the Couter-Circilar
"Picky-Back" field in a 15 mm diameter, 14CrNi14 shaft. The pulsed
electric current had its maximum at around 270 Ampere. The pulse
"on-time" has been electronically controlled. Because of the high
frequency component in the rising and falling edge of the encoding
pulse, this experiment can not truly represent the effects of a
true DC encoding SH. Therefore the Sensor-Output-Signal Slope-curve
eventually flattens-out at above 20 mV/Nm when passing the
Constant-Current On-Time of 1000 ms.
[0293] Without using a fast raising current-pulse edge (like using
a controlled ramping slope) the sensor output signal slope would
have been very poor (below 10 mV/Nm). Note: In this experiment
(using 14CrNi14) the signal hysteresis was around 0.95% of the FS
signal (FS=75 Nm torque).
[0294] Referring to FIG. 29, increasing the Sensor-Output
Signal-Slope by using several rectangle shaped current pulses in
succession is shown.
[0295] The Sensor-Output-Signal slope can be improved when using
several rectangle shaped current-encoding-pulses in successions. In
comparisons to other encoding-pulse-shapes the fast falling
current-pulse signal slope of the rectangle shaped current pulse
will prevent that the Sensor-Output-Signal slope may ever reach an
optimal performance level. Meaning that after only a few current
pulses (2 to 10) have been applied to the SH (or Shaft) the
Sensor-Output Signal-Slope will no longer rise.
[0296] In the following, a Discharge Current Pulse Shape is
described.
[0297] The Discharge-Current-Pulse has no Constant-Current ON-Time
and has no fast falling edge. Therefore the primary and most felt
effect in the magnetic encoding of the SH is the fast raising edge
of this current pulse type.
[0298] As shown in FIG. 30, a sharp raising current edge and a
typical discharging curve provides best results when creating a
PCME sensor.
[0299] Referring to FIG. 31, a PCME Sensor-Output Signal-Slope
optimization by identifying the right pulse current is
illustrated.
[0300] At the very low end of the pulse current scale (0 to 75 A
for a 15 mm diameter shaft, 14CrNi14 shaft material) the
"Discharge-Current-Pulse type is not powerful enough to cross the
magnetic threshold needed to create a lasting magnetic field inside
the Ferro magnetic shaft. When increasing the pulse current
amplitude the double circular magnetic field structure begins to
form below the shaft surface. As the pulse current amplitude
increases so does the achievable torque sensor-output
signal-amplitude of the secondary sensor system. At around 400 A to
425 A the optimal PCME sensor design has been achieved (the two
counter flowing magnetic regions have reached their most optimal
distance to each other and the correct flux density for best sensor
performances.
[0301] Referring to FIG. 32, Sensor Host (SH) cross section with
the optimal PCME electrical current density and location during the
encoding pulse is illustrated.
[0302] When increasing further the pulse current amplitude the
absolute, torque force related, sensor signal amplitude will
further increase (curve 2) for some time while the overall
PCME-typical sensor performances will decrease (curve 1). When
passing 900 A Pulse Current Amplitude (for a 15 mm diameter shaft)
the absolute, torque force related, sensor signal amplitude will
begin to drop as well (curve 2) while the PCME sensor performances
are now very poor (curve 1).
[0303] Referring to FIG. 33, Sensor Host (SH) cross sections and
the electrical pulse current density at different and increasing
pulse current levels is shown.
[0304] As the electrical current occupies a larger cross section in
the SH the spacing between the inner circular region and the outer
(near the shaft surface) circular region becomes larger.
[0305] Referring to FIG. 34, better PCME sensor performances will
be achieved when the spacing between the Counter-Circular
"Picky-Back" Field design is narrow (A).
[0306] The desired double, counter flow, circular magnetic field
structure will be less able to create a close loop structure under
torque forces which results in a decreasing secondary sensor signal
amplitude.
[0307] Referring to FIG. 35, flattening-out the current-discharge
curve will also increase the Sensor-Output Signal-Slope.
[0308] When increasing the Current-Pulse discharge time (making the
current pulse wider) (B) the Sensor-Output Signal-Slope will
increase. However the required amount of current is very high to
reduce the slope of the falling edge of the current pulse. It might
be more practical to use a combination of a high current amplitude
(with the optimal value) and the slowest possible discharge time to
achieve the highest possible Sensor-Output Signal Slope.
[0309] In the following, Electrical Connection Devices in the frame
of Primary Sensor Processing will be described.
[0310] The PCME technology (it has to be noted that the term `PCME`
technology is used to refer to exemplary embodiments of the present
invention) relies on passing through the shaft very high amounts of
pulse-modulated electrical current at the location where the
Primary Sensor should be produced. When the surface of the shaft is
very clean and highly conductive a multi-point Cupper or Gold
connection may be sufficient to achieve the desired sensor signal
uniformity. Important is that the Impedance is identical of each
connection point to the shaft surface. This can be best achieved
when assuring the cable length (L) is identical before it joins the
main current connection point (I).
[0311] Referring to FIG. 36, a simple electrical multi-point
connection to the shaft surface is illustrated.
[0312] However, in most cases a reliable and repeatable multi-point
electrical connection can be only achieved by ensuring that the
impedance at each connection point is identical and constant. Using
a spring pushed, sharpened connector will penetrate possible
oxidation or isolation layers (maybe caused by finger prints) at
the shaft surface.
[0313] Referring to FIG. 37, a multi channel, electrical connecting
fixture, with spring loaded contact points is illustrated.
[0314] When processing the shaft it is most important that the
electrical current is injected and extracted from the shaft in the
most uniform way possible. The above drawing shows several
electrical, from each other insulated, connectors that are held by
a fixture around the shaft. This device is called a
Shaft-Processing-Holding-Clamp (or SPHC). The number of electrical
connectors required in a SPHC depends on the shafts outer diameter.
The larger the outer diameter, the more connectors are required.
The spacing between the electrical conductors has to be identical
from one connecting point to the next connecting point. This method
is called Symmetrical-"Spot"-Contacts.
[0315] Referring to FIG. 38, it is illustrated that increasing the
number of electrical connection points will assist the efforts of
entering and exiting the Pulse-Modulated electrical current. It
will also increase the complexity of the required electronic
control system.
[0316] Referring to FIG. 39, an example of how to open the SPHC for
easy shaft loading is shown.
[0317] In the following, an encoding scheme in the frame of Primary
Sensor Processing will be described.
[0318] The encoding of the primary shaft can be done by using
permanent magnets applied at a rotating shaft or using electric
currents passing through the desired section of the shaft. When
using permanent magnets a very complex, sequential procedure is
necessary to put the two layers of closed loop magnetic fields, on
top of each other, in the shaft. When using the PCME procedure the
electric current has to enter the shaft and exit the shaft in the
most symmetrical way possible to achieve the desired
performances.
[0319] Referring to FIG. 40, two SPHCs (Shaft Processing Holding
Clamps) are placed at the borders of the planned sensing encoding
region. Through one SPHC the pulsed electrical current (I) will
enter the shaft, while at the second SPHC the pulsed electrical
current (I) will exit the shaft. The region between the two SPHCs
will then turn into the primary sensor.
[0320] This particular sensor process will produce a Single Field
(SF) encoded region. One benefit of this design (in comparison to
those that are described below) is that this design is insensitive
to any axial shaft movements in relation to the location of the
secondary sensor devices. The disadvantage of this design is that
when using axial (or in-line) placed MFS coils the system will be
sensitive to magnetic stray fields (like the earth magnetic
field).
[0321] Referring to FIG. 41, a Dual Field (DF) encoded region
(meaning two independent functioning sensor regions with opposite
polarity, side-by-side) allows cancelling the effects of uniform
magnetic stray fields when using axial (or in-line) placed MFS
coils. However, this primary sensor design also shortens the
tolerable range of shaft movement in axial direction (in relation
to the location of the MFS coils). There are two ways to produce a
Dual Field (DF) encoded region with the PCME technology. The
sequential process, where the magnetic encoded sections are
produced one after each other, and the parallel process, where both
magnetic encoded sections are produced at the same time.
[0322] The first process step of the sequential dual field design
is to magnetically encode one sensor section (identically to the
Single Field procedure), whereby the spacing between the two SPHC
has to be halve of the desired final length of the Primary Sensor
region. To simplify the explanations of this process we call the
SPHC that is placed in the centre of the final Primary Sensor
Region the Centre SPHC (C-SPHC), and the SPHC that is located at
the left side of the Centre SPHC: L-SPHC.
[0323] Referring to FIG. 42, the second process step of the
sequential Dual Field encoding will use the SPHC that is located in
the centre of the Primary Sensor region (called C-SPHC) and a
second SPHC that is placed at the other side (the right side) of
the centre SPHC, called R-SPHC. Important is that the current flow
direction in the centre SPHC (C-SPHC) is identical at both process
steps.
[0324] Referring to FIG. 43, the performance of the final Primary
Sensor Region depends on how close the two encoded regions can be
placed in relation to each other. And this is dependent on the
design of the used centre SPHC. The narrower the in-line space
contact dimensions are of the C-SPHC, the better are the
performances of the Dual Field PCME sensor.
[0325] FIG. 44 shows the pulse application according to another
exemplary embodiment of the present invention. As my be taken from
the above drawing, the pulse is applied to three locations of the
shaft. Due to the current distribution to both sides of the middle
electrode where the current I is entered into the shaft, the
current leaving the shaft at the lateral electrodes is only half
the current entered at the middle electrode, namely 1/2 I. The
electrodes are depicted as rings which dimensions are adapted to
the dimensions of the outer surface of the shaft. However, it has
to be noted that other electrodes may be used, such as the
electrodes comprising a plurality of pin electrodes described later
in this text.
[0326] Referring to FIG. 45, magnetic flux directions of the two
sensor sections of a Dual Field PCME sensor design are shown when
no torque or linear motion stress is applied to the shaft. The
counter flow magnetic flux loops do not interact with each
other.
[0327] Referring to FIG. 46, when torque forces or linear stress
forces are applied in a particular direction then the magnetic flux
loops begin to run with an increasing tilting angle inside the
shaft. When the tilted magnetic flux reaches the PCME segment
boundary then the flux line interacts with the counterflowing
magnetic flux lines, as shown.
[0328] Referring to FIG. 47, when the applied torque direction is
changing (for example from clock-wise to counter-clock-wise) so
will change the tilting angle of the counterflow magnetic flux
structures inside the PCM Encoded shaft.
[0329] In the following, a Multi Channel Current Driver for Shaft
Processing will be described.
[0330] In cases where an absolute identical impedance of the
current path to the shaft surface can not be guaranteed, then
electric current controlled driver stages can be used to overcome
this problem.
[0331] Referring to FIG. 48, a six-channel synchronized Pulse
current driver system for small diameter Sensor Hosts (SH) is
shown. As the shaft diameter increases so will the number of
current driver channels.
[0332] In the following, Bras Ring Contacts and Symmetrical "Spot"
Contacts will be described.
[0333] When the shaft diameter is relative small and the shaft
surface is clean and free from any oxidations at the desired
Sensing Region, then a simple "Bras"-ring (or Copper-ring) contact
method can be chosen to process the Primary Sensor.
[0334] Referring to FIG. 49, bras-rings (or Copper-rings) tightly
fitted to the shaft surface may be used, with solder connections
for the electrical wires. The area between the two Bras-rings
(Copper-rings) is the encoded region.
[0335] However, it is very likely that the achievable RSU
performances are much lower then when using the Symmetrical "Spot"
Contact method.
[0336] In the following, a Hot-Spotting concept will be
described.
[0337] A standard single field (SF) PCME sensor has very poor
Hot-Spotting performances. The external magnetic flux profile of
the SF PCME sensor segment (when torque is applied) is very
sensitive to possible changes (in relation to Ferro magnetic
material) in the nearby environment. As the magnetic boundaries of
the SF encoded sensor segment are not well defined (not "Pinned
Down") they can "extend" towards the direction where Ferro magnet
material is placed near the PCME sensing region.
[0338] Referring to FIG. 50, a PCME process magnetized sensing
region is very sensitive to Ferro magnetic materials that may come
close to the boundaries of the sensing regions.
[0339] To reduce the Hot-Spotting sensor sensitivity the PCME
sensor segment boundaries have to be better defined by pinning them
down (they can no longer move).
[0340] Referring to FIG. 51, a PCME processed Sensing region with
two "Pinning Field Regions" is shown, one on each side of the
Sensing Region.
[0341] By placing Pinning Regions closely on either side the
Sensing Region, the Sensing Region Boundary has been pinned down to
a very specific location. When Ferro magnetic material is coming
close to the Sensing Region, it may have an effect on the outer
boundaries of the Pinning Regions, but it will have very limited
effects on the Sensing Region Boundaries.
[0342] There are a number of different ways, according to exemplary
embodiments of the present invention how the SH (Sensor Host) can
be processed to get a Single Field (SF) Sensing Region and two
Pinning Regions, one on each side of the Sensing Region. Either
each region is processed after each other (Sequential Processing)
or two or three regions are processed simultaneously (Parallel
Processing). The Parallel Processing provides a more uniform sensor
(reduced parasitic fields) but requires much higher levels of
electrical current to get to the targeted sensor signal slope.
[0343] Referring to FIG. 52, a parallel processing example for a
Single Field (SF) PCME sensor with Pinning Regions on either side
of the main sensing region is illustrated, in order to reduce (or
even eliminate) Hot-Spotting.
[0344] A Dual Field PCME Sensor is less sensitive to the effects of
Hot-Spotting as the sensor centre region is already Pinned-Down.
However, the remaining Hot-Spotting sensitivity can be further
reduced by placing Pinning Regions on either side of the Dual-Field
Sensor Region.
[0345] Referring to FIG. 53, a Dual Field (DF) PCME sensor with
Pinning Regions either side is shown.
[0346] When Pinning Regions are not allowed or possible (example:
limited axial spacing available) then the Sensing Region has to be
magnetically shielded from the influences of external Ferro
Magnetic Materials.
[0347] In the following, the Rotational Signal Uniformity (RSU)
will be explained.
[0348] The RSU sensor performance are, according to current
understanding, mainly depending on how circumferentially uniform
the electrical current entered and exited the SH surface, and the
physical space between the electrical current entry and exit
points. The larger the spacing between the current entry and exit
points, the better is the RSU performance.
[0349] Referring to FIG. 54, when the spacings between the
individual circumferential placed current entry points are
relatively large in relation to the shaft diameter (and equally
large are the spacings between the circumferentially placed current
exit points) then this will result in very poor RSU performances.
In such a case the length of the PCM Encoding Segment has to be as
large as possible as otherwise the created magnetic field will be
circumferentially non-uniform.
[0350] Referring to FIG. 55, by widening the PCM Encoding Segment
the circumferentially magnetic field distribution will become more
uniform (and eventually almost perfect) at the halve distance
between the current entry and current exit points. Therefore the
RSU performance of the PCME sensor is best at the halve way-point
between of the current-entry/current-exit points.
[0351] Next, the basic design issues of a NCT sensor system will be
described.
[0352] Without going into the specific details of the PCM-Encoding
technology, the end-user of this sensing technology need to now
some design details that will allow him to apply and to use this
sensing concept in his application. The following pages describe
the basic elements of a magnetostriction based NCT sensor (like the
primary sensor, secondary sensor, and the SCSP electronics), what
the individual components look like, and what choices need to be
made when integrating this technology into an already existing
product.
[0353] In principle the PCME sensing technology can be used to
produce a stand-alone sensor product. However, in already existing
industrial applications there is little to none space available for
a "stand-alone" product. The PCME technology can be applied in an
existing product without the need of redesigning the final
product.
[0354] In case a stand-alone torque sensor device or position
detecting sensor device will be applied to a motor-transmission
system it may require that the entire system need to undergo a
major design change.
[0355] In the following, referring to FIG. 56, a possible location
of a PCME sensor at the shaft of an engine is illustrated.
[0356] FIG. 56 shows possible arrangement locations for the torque
sensor according to an exemplary embodiment of the present
invention, for example, in a gear box of a motorcar. The upper
portion of FIG. 56 shows the arrangement of the PCME torque sensor
according to an exemplary embodiment of the present invention. The
lower portion of the FIG. 56 shows the arrangement of a stand alone
sensor device which is not integrated in the input shaft of the
gear box as is in the exemplary embodiment of the present
invention.
[0357] As may be taken from the upper portion of FIG. 56, the
torque sensor according to an exemplary embodiment of the present
invention may be integrated into the input shaft of the gear box.
In other words, the primary sensor may be a portion of the input
shaft. In other words, the input shaft may be magnetically encoded
such that it becomes the primary sensor or sensor element itself.
The secondary sensors, i.e. the coils, may, for example, be
accommodated in a bearing portion close to the encoded region of
the input shaft. Due to this, for providing the torque sensor
between the power source and the gear box, it is not necessary to
interrupt the input shaft and to provide a separate torque sensor
in between a shaft going to the motor and another shaft going to
the gear box as shown in the lower portion of FIG. 56.
[0358] Due to the integration of the encoded region in the input
shaft it is possible to provide for a torque sensor without making
any alterations to the input shaft, for example, for a car. This
becomes very important, for example, in parts for an aircraft where
each part has to undergo extensive tests before being allowed for
use in the aircraft. Such torque sensor according to the present
invention may be perhaps even without such extensive testing being
corporated in shafts in aircraft or turbine since, the immediate
shaft is not altered. Also, no material effects are caused to the
material of the shaft.
[0359] Furthermore, as may be taken from FIG. 56, the torque sensor
according to an exemplary embodiment of the present invention may
allow to reduce a distance between a gear box and a power source
since the provision of a separate stand alone torque sensor between
the shaft exiting the power source and the input shaft to the gear
box becomes obvious.
[0360] Next, Sensor Components will be explained.
[0361] A non-contact magnetostriction sensor (NCT-Sensor), as shown
in FIG. 57, may consist, according to an exemplary embodiment of
the present invention, of three main functional elements: The
Primary Sensor, the Secondary Sensor, and the Signal Conditioning
& Signal Processing (SCSP) electronics.
[0362] Depending on the application type (volume and quality
demands, targeted manufacturing cost, manufacturing process flow)
the customer can chose to purchase either the individual components
to build the sensor system under his own management, or can
subcontract the production of the individual modules.
[0363] FIG. 58 shows a schematic illustration of components of a
non-contact torque sensing device. However, these components can
also be implemented in a non-contact position sensing device.
[0364] In cases where the annual production target is in the
thousands of units it may be more efficient to integrate the
"primary-sensor magnetic-encoding-process" into the customers
manufacturing process. In such a case the customer needs to
purchase application specific "magnetic encoding equipment".
[0365] In high volume applications, where cost and the integrity of
the manufacturing process are critical, it is typical that NCTE
supplies only the individual basic components and equipment
necessary to build a non-contact sensor: [0366] ICs (surface mount
packaged, Application-Specific Electronic Circuits) [0367]
MFS-Coils (as part of the Secondary Sensor) [0368] Sensor Host
Encoding Equipment (to apply the magnetic encoding on the
shaft=Primary Sensor)
[0369] Depending on the required volume, the MFS-Coils can be
supplied already assembled on a frame, and if desired, electrically
attached to a wire harness with connector. Equally the SCSP (Signal
Conditioning & Signal Processing) electronics can be supplied
fully functional in PCB format, with or without the MFS-Coils
embedded in the PCB.
[0370] FIG. 59 shows components of a sensing device.
[0371] As can be seen from FIG. 60, the number of required
MFS-coils is dependent on the expected sensor performance and the
mechanical tolerances of the physical sensor design. In a well
designed sensor system with perfect Sensor Host (SH or magnetically
encoded shaft) and minimal interferences from unwanted magnetic
stray fields, only 2 MFS-coils are needed. However, if the SH is
moving radial or axial in relation to the secondary sensor position
by more than a few tenths of a millimeter, then the number of
MFS-coils need to be increased to achieve the desired sensor
performance.
[0372] In the following, a control and/or evaluation circuitry will
be explained.
[0373] The SCSP electronics, according to an exemplary embodiment
of the present invention, consist of the NCTE specific ICs, a
number of external passive and active electronic circuits, the
printed circuit board (PCB), and the SCSP housing or casing.
Depending on the environment where the SCSP unit will be used the
casing has to be sealed appropriately.
[0374] Depending on the application specific requirements NCTE
(according to an exemplary embodiment of the present invention)
offers a number of different application specific circuits: [0375]
Basic Circuit [0376] Basic Circuit with integrated Voltage
Regulator [0377] High Signal Bandwidth Circuit [0378] Optional High
Voltage and Short Circuit Protection Device [0379] Optional Fault
Detection Circuit
[0380] FIG. 61 shows a single channel, low cost sensor electronics
solution.
[0381] As may be taken from FIG. 61, there may be provided a
secondary sensor unit which comprises, for example, coils. These
coils are arranged as, for example, shown in FIG. 60 for sensing
variations in a magnetic field emitted from the primary sensor
unit, i.e. the sensor shaft or sensor element when torque is
applied thereto. The secondary sensor unit is connected to a basis
IC in a SCST. The basic IC is connected via a voltage regulator to
a positive supply voltage. The basic IC is also connected to
ground. The basic IC is adapted to provide an analog output to the
outside of the SCST which output corresponds to the variation of
the magnetic field caused by the stress applied to the sensor
element.
[0382] FIG. 62 shows a dual channel, short circuit protected system
design with integrated fault detection. This design consists of 5
ASIC devices and provides a high degree of system safety. The
Fault-Detection IC identifies when there is a wire breakage
anywhere in the sensor system, a fault with the MFS coils, or a
fault in the electronic driver stages of the "Basic IC".
[0383] Next, the Secondary Sensor Unit will be explained.
[0384] The Secondary Sensor may, according to one embodiment shown
in FIG. 63, consist of the elements: One to eight MFS (Magnetic
Field Sensor) Coils, the Alignment-& Connection-Plate, the wire
harness with connector, and the Secondary-Sensor-Housing.
[0385] The MFS-coils may be mounted onto the Alignment-Plate.
Usually the Alignment-Plate allows that the two connection wires of
each MFS-Coil are soldered/connected in the appropriate way. The
wire harness is connected to the alignment plate. This, completely
assembled with the MFS-Coils and wire harness, is then embedded or
held by the Secondary-Sensor-Housing.
[0386] The main element of the MFS-Coil is the core wire, which has
to be made out of an amorphous-like material.
[0387] Depending on the environment where the Secondary-Sensor-Unit
will be used, the assembled Alignment Plate has to be covered by
protective material. This material can not cause mechanical stress
or pressure on the MFS-coils when the ambient temperature is
changing.
[0388] In applications where the operating temperature will not
exceed +110 deg C. the customer has the option to place the SCSP
electronics (ASIC) inside the secondary sensor unit (SSU). While
the ASIC devices can operated at temperatures above +125 deg C. it
will become increasingly more difficult to compensate the
temperature related signal-offset and signal-gain changes.
[0389] The recommended maximal cable length between the MFS-coils
and the SCSP electronics is 2 meters. When using the appropriate
connecting cable, distances of up to 10 meters are achievable. To
avoid signal-cross-talk in multi-channel applications (two
independent SSUs operating at the same Primary Sensor location
=Redundant Sensor Function), specially shielded cable between the
SSUs and the SCSP Electronics should be considered.
[0390] When planning to produce the Secondary-Sensor-Unit (SSU) the
producer has to decide which part/parts of the SSU have to be
purchased through subcontracting and which manufacturing steps will
be made in-house.
[0391] In the following, Secondary Sensor Unit Manufacturing
Options will be described. When integrating the NCT-Sensor into a
customized tool or standard transmission system then the systems
manufacturer has several options to choose from: [0392] custom made
SSU (including the wire harness and connector) [0393] selected
modules or components; the final SSU assembly and system test may
be done under the customer's management. [0394] only the essential
components (MFS-coils or MFS-core-wire, Application specific ICs)
and will produce the SSU in-house.
[0395] FIG. 64 illustrates an exemplary embodiment of a Secondary
Sensor Unit Assembly.
[0396] Next, a Primary Sensor Design is explained.
[0397] The SSU (Secondary Sensor Units) can be placed outside the
magnetically encoded SH (Sensor Host) or, in case the SH is hollow,
inside the SH. The achievable sensor signal amplitude is of equal
strength but has a much better signal-to-noise performance when
placed inside the hollow shaft.
[0398] FIG. 65 illustrates two configurations of the geometrical
arrangement of Primary Sensor and Secondary Sensor.
[0399] Improved sensor performances may be achieved when the
magnetic encoding process is applied to a straight and parallel
section of the SH (shaft). For a shaft with 15 mm to 25 mm diameter
the optimal minimum length of the Magnetically Encoded Region is 25
mm. The sensor performances will further improve if the region can
be made as long as 45 mm (adding Guard Regions). In complex and
highly integrated transmission (gearbox) systems it will be
difficult to find such space. Under more ideal circumstances, the
Magnetically Encoding Region can be as short as 14 mm, but this
bears the risk that not all of the desired sensor performances can
be achieved.
[0400] As illustrated in FIG. 66, the spacing between the SSU
(Secondary Sensor Unit) and the Sensor Host surface, according to
an exemplary embodiment of the present invention, should be held as
small as possible to achieve the best possible signal quality.
[0401] Next, the Primary Sensor Encoding Equipment will be
described.
[0402] An example is shown in FIG. 67.
[0403] Depending on which magnetostriction sensing technology will
be chosen, the Sensor Host (SH) needs to be processed and treated
accordingly. The technologies vary by a great deal from each other
(ABB, FAST, FT, Kubota, MDI, NCTE, RM, Siemens, . . . ) and so does
the processing equipment required. Some of the available
magnetostriction sensing technologies do not need any physical
changes to be made on the SH and rely only on magnetic processing
(MDI, FAST, NCTE).
[0404] While the MDI technology is a two phase process, the FAST
technology is a three phase process, and the NCTE technology a one
phase process, called PCM Encoding.
[0405] One should be aware that after the magnetic processing, the
Sensor Host (SH or Shaft), has become a "precision measurement"
device and has to be treated accordingly. The magnetic processing
should be the very last step before the treated SH is carefully
placed in its final location.
[0406] The magnetic processing should be an integral part of the
customer's production process (in-house magnetic processing) under
the following circumstances: [0407] High production quantities
(like in the thousands) [0408] Heavy or difficult to handle SH
(e.g. high shipping costs) [0409] Very specific quality and
inspection demands (e.g. defense applications)
[0410] In all other cases it may be more cost effective to get the
SH magnetically treated by a qualified and authorized
subcontractor, such as NCTE. For the "in-house" magnetic processing
dedicated manufacturing equipment is required. Such equipment can
be operated fully manually, semi-automated, and fully automated.
Depending on the complexity and automation level the equipment can
cost anywhere from EUR 20 k to above EUR 500 k.
[0411] FIG. 68A shows a magnetizing apparatus 140 for magnetizing a
shaft 150 to form a magnetically encoded region on the shaft 150.
The magnetizing apparatus 140 does not involve a shaft which is
enclosed by another object. When a current signal is applied
between different ends of the shaft 150, the shaft 150 is
magnetized.
[0412] FIG. 68B shows a magnetizing apparatus 160 according to the
invention involving a hollow tube 121 enclosing a shaft 150 (not
shown in FIG. 68B) to be magnetized. An end portion of the shaft
150 is coupled with an end portion of the hollow tube 121 enclosing
the shaft 150. When a current signal is applied to the shaft 150,
the current is injected in the hollow tube 121. The magnetic field
generated by the current flowing in the hollow tube 121 stabilizes
the current distribution in the shaft 150. Thus, the shaft 150 is
magnetized in a very homogenous manner.
[0413] FIG. 68C shows a schematic view of a torque and force
sensing device 170 with a magnetically encoded region 122 formed
according to the magnetization generation process carried out with
the magnetizing apparatus 160. The length of the magnetically
encoded region 122 is defined by the length along which the current
flows during the magnetization procedure (i.e. depends on the
geometry of the contacts for injecting a magnetizing current).
[0414] FIG. 68C shows the torque sensor 170 having the shaft 150
which may rotate with a predetermined value of torque, wherein a
portion of the shaft 150 is magnetized to form a magnetically
encoded region 122. When the shaft 150 rotates, the magnetically
encoded region 122 generates a magnetic signal in a magnetic field
detecting coil 123.
[0415] FIG. 68D shows a signal versus torque diagram 100 (an
experimentally measured curve and a schematic curve emphasizing the
features of the measured curve) of a torque and force sensing
device magnetized with the magnetizing apparatus 140 shown in FIG.
68A.
[0416] FIG. 68E shows a signal versus torque diagram 110 (an
experimentally measured curve and a schematic curve emphasizing the
features of the measured curve) of a torque and force sensing
device 170 magnetized with the magnetizing apparatus 160 shown in
FIG. 68B.
[0417] The diagrams 100, 110 of FIG. 68D and FIG. 68E each have an
abscissa 101 along which a torque is shown which is applied to a
shaft with a magnetically encoded region. FIGS. 68D and 68E show
along an ordinate 102 the signal as detected by coil 123 when a
particular value of the torque as plotted along the abscissa 101 is
applied.
[0418] FIGS. 68D and 68E show a hysteresis loop 103 and a best fit
line 104, for both cases. As can be seen, the slope of the best fit
line 104 is larger in FIG. 68E than in FIG. 68D, and the hysteresis
properties are suppressed in FIG. 68E even better than in FIG.
68D.
[0419] One of the big challenges of the magnetic field encoding
process according to the invention is to achieve a uniform
electrical current distribution around a "to be encoded" shaft 150,
i.e. to have a properly magnetized region 122. Failing to do so
will result in a poor rotational signal uniformity performance and
in a poor signal linearity.
[0420] FIG. 68D shows the sensors torque signal when the shaft 150
has been processed according to FIG. 68A. The sensor
characteristics as shown in FIG. 68D shows some non-linearity which
has a negative impact on the sensor signal hysteresis
performance.
[0421] Processing the shaft 150 to form the magnetically encoded
region 122 with the method as shown in FIGS. 68B, 69, 70, greatly
improves the sensors signal linearity and has a positive impact on
the sensors signal hysteresis, which will become much smaller (see
FIG. 68E).
[0422] The magnetically encoded sensor corresponding to FIG. 68A
has a slope of the best fit line 104 of 13.8 mV/Nm, and a
hysteresis of 3.72%. In contrast to this, the torque sensor
magnetized according to FIG. 68B has, as shown in FIG. 68E, a slope
of 15.1 mV/Nm and a hysteresis with only 2.59%.
[0423] Thus, the signal-to-noise ratio is significantly improved
when the magnetically encoded region 122 is generated according to
the invention.
[0424] A basic principle of the method for magnetizing an object
according to the invention, which can also be denoted as a
self-adjusting process, is to generate a counter magnetic field
during the actual magnetization process, whereby this counter
magnetic field ensures that the electrical signal passes through
the shaft 150 very uniformly through the "to be encoded" sensing
region 122.
[0425] By passing back the electrical signal for magnetizing a part
of the shaft 150 to form the magnetically encoded region 122
through the conductive tube 121 enclosing the shaft 150, the
magnetic field that develops at the inner side of the tube 121 can
work hand in hand with the magnetic field that is developing at the
outside of the shaft 150. The shaft 150 is placed at the centre,
inside the tube 121, and is not allowed to contact the tube 121,
except at desired locations.
[0426] FIG. 69 shows a scheme which may be useful for a further
understanding of the invention. Thus, the arrangement shown in FIG.
69 shows the solid shaft 150 and the hollow tube 121. An electrical
current I is injected in the solid shaft 150 to form a magnetic
field around the solid shaft 150, as shown in FIG. 69. When this
current I flows through the hollow tube 121, a further magnetic
field is also generated in the material of the hollow tube 121.
Thus, FIG. 69 is a schematic view illustrating a principle of a
method for magnetizing an object according to the invention.
[0427] FIGS. 70A and 70B are schematic views illustrating an
apparatus for magnetizing an object according to the invention.
[0428] In order to magnetize the shaft 150, the hollow tube 121 is
arranged to enclose the solid shaft 150. Further, an electrical
signal I is applied to the solid shaft 150. As shown in a diagram
310 of FIG. 70D having a time abscissa 301 and having a current
ordinate 302, the pulsed current signal 300 has a fast raising edge
which is essentially vertical and has a slow falling edge.
[0429] As can be further seen in FIG. 70A, the solid shaft 150 is
arranged at the centre of the hollow tube 121. The hollow tube 121
has first electrical connection 201 and has a second electrical
connection 202, wherein the second electrical connection 202 of the
hollow tube 121 is coupled to a first electrical connection 203 of
the solid shaft 150. Further, the solid shaft has a second
electrical connection 204. An electrical signal source (not shown)
is connected such that the current signal I can be applied between
the first connection 201 of the hollow tube 121 and the second
connection 204 of the solid shaft 150.
[0430] FIG. 70B shows another view of the configuration of FIG.
70A.
[0431] Because the magnetic flux direction at the inside of the
hollow tube 121 (caused by the return electrical current flow
direction) is the same rotational direction as the magnetic field
that goes around the solid shaft 150 (because of the forward
electrical current flow direction), the magnetic field density will
distribute itself uniformly in the space between the tube 121 and
the shaft 150. Consequently, the electrical current that flows in
the solid shaft 150 and the tube 121 will be evenly distributed in
both items.
[0432] The resulting solution is that the rotational signal
uniformity performance of the sensor signal improves greatly (see
FIG. 68E), and with this the signal non-linearity and signal
hysteresis (will become smaller), and in addition the signal slope
increases (more signal at an applied torque).
[0433] Particular at the electrical connections between the
electrical supply cables and the "to be encoded" shaft 150 the
results are very challenging. Even the slightest differences in
impedance where the cable connects with the shaft (or tube surface)
will cause that the electrical current will be not uniformly
distributed around the shaft 150 at this particular area.
[0434] As the current is flowing further in the shaft 150, the
electrical current density will become more and more uniformly
around the shaft 150. If it would be possible to ensure that the
electrical current enters uniformly around the shaft 150 right
where the electrical wires are connected, then the useful sensing
area will become larger (moves nearer to the point where the wires
connect with the shaft 150).
[0435] The method of magnetizing the shaft according to the
invention is exactly doing that: it forces the electrical current
to flow most uniformly (in respect when monitoring the current flow
density 360.degree. around the shaft).
[0436] Thus, the invention has the benefits that it simplifies the
way the electrical connections need to be made to the shaft 150.
Further, the invention improves greatly several sensor
performances. Moreover, the encoding equipment is simplified, and
with this the manufacturing equipment costs are reduced.
[0437] FIG. 70C shows an alternative arrangement of an apparatus
for magnetizing the shaft 150. In addition to the first and the
second connections 201, 202, the hollow tube 121 further has a
third electrical connection 351, and the solid shaft 150 has a
third electrical connection 352. In the case of FIG. 70C, two
different pulses I1 and I2 are applied to the array in the manner
as shown in FIG. 70C. The first electrical signal I1 is applied
between the first electrical connection 201 of the hollow tube 121
and the second electrical connection 204 of the solid shaft 150. A
second electrical signal I2 is applied between the third electrical
connection 351 of the hollow tube 121 and the third electrical
connection 352 of the solid shaft 150.
[0438] Further, an electrically conductive coupling element 350 is
provided to couple the second electrical connection 202 of the
hollow tube 121 to the first electrical connection 203 of the solid
shaft 150. The current distribution shown in FIG. 70C achieves a
magnetic field distribution which yields a homogeneous current
profile in elements 121, 150, thus achieving a sensor with a
well-defined magnetization, i.e. a well-defined magnetically
encoded region 122.
[0439] FIGS. 71A, 71B illustrate another embodiment of an apparatus
for magnetizing a shaft 150 according to the invention,
[0440] FIG. 71A shows a configuration in which the coupling between
the connection 202 of the hollow tube 121 and the connection 203 of
the conductive solid shaft 150 are realized by a conductive based
plate 400 as a coupling element.
[0441] FIG. 71B shows the apparatus of FIG. 71A in a state in which
a current is applied. The current flows through the shaft 150,
through the plate 400 and from there--in opposite direction
compared to the flowing direction in the shaft 150--through the
tube 121. As can be seen in FIG. 71B, the current is applied to the
tube 121 via a plurality of electrical connection cables which are
arranged circumferentially along the perimeter of the upper
circular surface of the tube 121. Such an arrangement with--for
instance six or eight--cables yields a very homogeneous current
distribution.
[0442] As an alternative to the provision of a conductive plate 400
for coupling the tube 121 to the shaft 150, the tube 121 can remain
uncoupled from the shaft 150 (i.e. the plate 400 can be omitted),
and two oppositely oriented current signals can be flown through
the shaft 150 and through the tube 121, wherein the current in the
shaft 150 may serve to magnetize the shaft 150, and the current in
the tube 121 may serve to provide a counter magnetic field to
increase the homogeneity of magnetizing the shaft 150. Thus, two
signals are applied simultaneously, one to the tube 121 and the
other one to the shaft 150.
[0443] In the following, referring to FIG. 72, an apparatus 500 for
magnetizing a magnetizable tube 501 according to another embodiment
of the invention will be described.
[0444] The apparatus 500 comprises the magnetizable tube 501,
namely a hollow cylinder, a wire 502 having a first part 502a, a
second part 502b and a third part 502c, wherein a current can flow
through the wire 502. An electrical power source 503 is provided
which can inject an electrical current in the wire 502 in an
operation state in which a switch 504 is closed. Thus, by closing
the switch 504, a pulse current 505 can be injected in wire 502.
However, alternatively to the pulse current 505, a pulse as shown
in FIG. 70D, for instance, can also be injected in the wire 502.
Although a pulse as the one shown in FIG. 70D is preferred, any
other appropriate pulse shape like the one shown in FIG. 72 can be
injected in the wire 502.
[0445] The magnetizable tube 501 is made of industrial steel and
has a wall thickness of 4 cm, a diameter of 88 cm and a length of
several metres. The tube 501 to be magnetized is arranged in such a
manner that the tube 501 encloses the first part 502a of the wire
502. The electrical power source 503 is adapted to apply a pulsed
current 505 to the wire 502, wherein the pulsed current 505 is
adapted such that the magnetizable tube 501 becomes magnetized.
When such a current pulse 505 is applied to the first part 502a of
the wire 502, a magnetic field is generated in the vicinity and
around the first part 502a of the wire 502 which influences,
similar like in the case of a transformator, the elementary magnets
within the magnetizable tube 501. Consequently, the pulse 505 will
cause the tube 501 to become magnetized.
[0446] As can be seen in FIG. 72, the first part 502a of the wire
502 is arranged at the centre of the hollow tube 501. In contrast
to the configuration shown in FIG. 70A to 70D, the electrical power
source 503 is connected to the wire 502, but is disconnected from
the magnetizable tube 501. Further, a hollow shielding cylinder 506
is provided which is manufactured similarly to the magnetizable
tube 501. As can be further seen, particularly the third part 502c
of the wire 502 is free from an enclosure with the magnetizable
tube 501, i.e. is not surrounded by the magnetizable tube 501. The
shielding cylinder 506 is arranged and adapted to
electromagnetically shield (i.e. decouple) the third part 502c of
the wire 502 being free from an enclosure with the magnetizable
tube 501 from the magnetizable tube 501. The shielding tube 506
made of magnetizable material is arranged between the magnetizable
tube 501 and the third part 502c of the wire 502. Thus, the current
pulse 505 flowing through all parts 502a, 502b, 502c of the wire
502 acts on the magnetizable tube 501 essentially only at the first
part 502a which is enclosed by the magnetizable tube 501, whereas
the current flowing in a counter direction compared to the first
part 502a through the third part 502c is avoided to negatively
influence, particularly to weaken, the magnetization generated in
the magnetizable tube 501.
[0447] Also the second part 502b of the wire 502 can be shielded
from the magnetizable tube 501 by a similar shielding element like
the shielding cylinder 506.
[0448] FIG. 73A shows a schematic top view of the apparatus 500. As
can be seen, the shielding cylinder 506 efficiently shields the
third part 502c of the wire 502 from the tube 501.
[0449] FIGS. 73B to 73D show further embodiments of shielding
elements.
[0450] FIG. 73B shows a configuration in which four shielding
cylinders 600 to 603 are arranged around the third part 502c of the
wire 502. Thus, the shielding cylinders 600 to 603 made of
magnetizable material are arranged surrounding the portion 502c of
the wire 502 which is free from an enclosure with the magnetizable
tube 501.
[0451] FIG. 73C shows a plurality of cylindrical shafts 610 to 617
which are arranged around the third part 502c of the wire 502 to
shield the third part 502 being free of an enclosure with the
magnetizable tube 501 from the magnetizable tube 501.
[0452] FIG. 73D shows a six tubes 620 to 625 which are arranged to
surround the third part 502c.
[0453] In the following, referring to FIG. 74, an apparatus 700 for
magnetizing a magnetizable tube 501 according to another embodiment
of the invention will be described.
[0454] According to the embodiment of FIG. 74, the shielding
cylinder 506 is arranged to surround the third part 502c of the
wire 502. Further, the electrical signal source 503 is realized as
a bank of (charged) capacitors 701 which may be discharged by
closing the switch 504 to generate a pulse as the one shown in FIG.
71D. The magnetizing apparatus 700 is "mobile" which is illustrated
by means of a vehicle 702 which transports the capacitor banks 701
to a place at which a magnetizable tube 501 (i.e. drilling
equipment at a mining place) shall be magnetized.
[0455] Thus, the mobile processing unit of FIG. 74 can be brought
closest to drilling or large tooling shafts.
[0456] In the following, referring to FIG. 75A and FIG. 75B, an
apparatus 800 for calibrating a force and torque sensor device 810
will be described.
[0457] The apparatus 800 comprises the force and torque sensor
device 810, a pre-known mass 811 with a weight of 1000 kg and a
calibrating unit 818. The force and torque sensor device 810 has a
magnetically encoded region 812 on a hollow tube 813 and four
magnetic field detecting coils 814 to 817.
[0458] The pre-known weight 811 is put on the top of the force and
torque sensor device 810 to apply a pre-known axial force to the
magnetized hollow tube 813. The calibrating unit 818 which is
connected to the magnetic field detecting coils 814 to 817 is
adapted to calibrate the force and torque sensor 810 based on a
correlation between the pre-known mass 811 and a detecting signal
resulting from the pre-known force of the mass 811.
[0459] Thus, a pre-known mass 811 is applied on the top of the
horizontally arranged hollow tube 813 which stands on a horizontal
and stable base 819. As a consequence of the mass 811 applied to
the top of the force and torque sensor device 810 (which may be
magnetized in a manner as shown in FIG. 74), the magnetic field
generated by the magnetically encoded region 812 changes so that a
signal in the magnetic field detecting coils 814 to 817 occurs.
Thus, this signal which is processed in the calibration unit 818 is
correlated to the pre-known axial force applied to the magnetized
tube 813 by the known mass 811. This pair of data pairs, namely the
known axial force and the detected signal, can be stored in the
calibration unit 818.
[0460] The upper surface of the hollow tube 813 (onto which the
mass 811 is put) is for instance arranged horizontally so that the
vector of the force generated by the mass 811 on the top of the
tube 813 is oriented essentially perpendicular to the surface of
the hollow tube 813 (or is directed towards the center of the
earth). In case that the upper surface of the tube 813 and/or the
base 819 is/are not oriented in a horizontal manner, an angular
correction calculation may be necessary or desirable.
[0461] When the drilling shaft 813 is brought back in the ground
and is used for drilling, axial forces and torque applied to the
drilling shaft 813 can be measured by the magnetic field detecting
coils 814 to 817 and may be compared to the calibration signal.
Thus, an absolute measurement of torque and force can be carried
out based on a calibration with an axial load 811.
[0462] For the calibration, the coils 814 to 817 have to be
arranged such that an axial force can be measured. For the torque
sensing operation, the coils 814 to 817 have to be arranged such
that torque can be measured. Thus, the axes of the coils 814 to 817
may have to be re-oriented, accordingly, when switching from a
calibration mode to a measuring mode.
[0463] FIGS. 76A and 76B show two possible configurations for
arranging the magnetic field detecting coils 814 to 817.
[0464] FIG. 77 shows three possible configurations of drilling
shafts 1000 having magnetically encoded regions 1001, 1002 or
1003.
[0465] The markings 1001 to 1003 symbolize where the drilling shaft
1000 (or rotational power transmitting shaft 1000) have
magnetically encoded regions. In real life, the encoding 1001 to
1003 is optically invisible and does not change or interfere with
any of the mechanical properties of the shaft 1000. The drilling
shaft 1000 can be encoded at a specific location 1001, or at a
section 1002, or in its entirety 1003. In many cases, the encoding
at a specific location 1001 is advisable for a static system
operation only. The encoding options 1002, 1003 are particularly
dedicated for applications where the drilling shaft 1000 is
rotating or in motion in some ways.
[0466] FIG. 78 shows two configurations how magnetic field
detecting coils 1100 to 11103 may be arranged around the drilling
shaft 1000.
[0467] In the following, referring to FIG. 79, an apparatus 6800
for magnetizing an object will be explained.
[0468] As shown in FIG. 79, the shaft 150 enclosed by the hollow
tube 121 can be magnetized by applying an electrical signal
generated by the electrical power source 503 to the hollow tube
121. The apparatus 6800 allows magnetizing the shaft 150 by
arranging the hollow tube 121 in such a manner that the hollow tube
121 encloses the shaft 150, and by applying an electrical signal
via a plurality of circumferentially arranged contacts to the
hollow tube 121. The electrical signal generated by the electrical
power source 503 is for instance a pulsed signal such that at least
a portion of the shaft 150 is magnetized. As shown in FIG. 79, two
end portions of the shaft 150 outside the hollow tube 121 are
short-circuited by a wire 6801 located outside the hollow tube
121.
[0469] FIG. 80 illustrates still another apparatus 6900 for
magnetizing an object according to an embodiment of the
invention.
[0470] The function of the apparatus 6900 is very similar to the
function of the apparatus shown in FIG. 72A, FIG. 72B with the
difference that the electrically conductive plate 400 is
substituted by an electrically conductive fluid 6902 (e.g. mercury)
which serves to electrically contact the shaft 150 to the hollow
tube 121.
[0471] In the following, it is described how the apparatus 6900 is
operated. A (for instance electrically insulating) spacer element
6901 in the form of a hollow cylinder with an inside diameter which
essentially equals to the diameter of the shaft 150 and with an
outside diameter which essentially equals to the inside diameter of
the hollow tube 121 is arranged to seal and space the volume
between the hollow tube 121 and the shaft 150 located within the
hollow tube. Subsequently, the electrically conductive fluid 6902
is injected in the array 6900 to fill the space delimited by the
hollow tube 121 and the shaft 150 and the spacer element 6901 to
electrically couple the hollow tube 121 and the shaft 150 in a very
flexible manner.
[0472] In the following, referring to FIG. 81, an apparatus 7000
for calibrating a force and torque sensor device according to the
invention will be explained.
[0473] The apparatus 7000 comprises a base 7001 for receiving a
shaft 7002 of a torque sensing device. The torque sensing device
further includes two magnetic field detection coils 7004 and a
magnetically encoded region 7003 which may be formed, for instance,
by the above-described PCME technology. The base 7001 receives the
shaft 7002 in such a manner that the shaft cannot be moved or
rotated by an applied force. A motor 7005 is adapted to drive a
rotatable element 7006 (e.g. a flywheel) which in term can rotate
in a controllable manner and which is coupled to the shaft 7002
such that a mechanical impulse of the rotatable element 7006 can be
transferred to the shaft 7002 to apply a (reactive) torque to the
shaft 7002. As a response to such a calibrating torque of a known
value, a signal can be detected by the coils 7004 which can serve
for a calibration of the torque sensing device. Thus, the apparatus
7000 has the driven rotatable element 7006 as a pre-known torque
generating element. Particularly, a sudden change of the rotation
state of the rotatable element 7006 (e.g. a sudden brake signal) is
useful as a source of (reactive) torque applied as a calibrating
signal to the torque sensing device.
[0474] It should be noted that the term "comprising" does not
exclude other elements or steps and the "a" or "an" does not
exclude a plurality. Also elements described in association with
different embodiments may be combined.
* * * * *