U.S. patent application number 11/406121 was filed with the patent office on 2007-10-18 for system and method for detecting an axial position of a shaft.
This patent application is currently assigned to Deere & Company, a Delaware corporation. Invention is credited to Ashley Elwood Greer, James Edward Lenz.
Application Number | 20070244665 11/406121 |
Document ID | / |
Family ID | 38265128 |
Filed Date | 2007-10-18 |
United States Patent
Application |
20070244665 |
Kind Code |
A1 |
Greer; Ashley Elwood ; et
al. |
October 18, 2007 |
SYSTEM AND METHOD FOR DETECTING AN AXIAL POSITION OF A SHAFT
Abstract
A shaft comprises a hardened outer metallic layer having a first
hardness level with a generally uniform radial depth. A first strip
extends in a generally longitudinal direction in the outer metallic
layer. The first strip has a second hardness level different from
the first hardness level. A second strip in the outer metallic
layer has the second hardness level. The first strip and the second
strip are spaced apart from each other over at least a longitudinal
region. A sensor senses an angular difference between a first
magnetic field associated with the first strip and a second
magnetic field associated with the second strip. A data processor
references an established relationship between a position of the
shaft and the angular difference between magnetic fields associated
with the first strip and the second strip to detect a Position of
the shaft with respect to a reference point.
Inventors: |
Greer; Ashley Elwood;
(Moline, IL) ; Lenz; James Edward; (Fargo,
ND) |
Correspondence
Address: |
DEERE & COMPANY
ONE JOHN DEERE PLACE
MOLINE
IL
61265
US
|
Assignee: |
Deere & Company, a Delaware
corporation
|
Family ID: |
38265128 |
Appl. No.: |
11/406121 |
Filed: |
April 18, 2006 |
Current U.S.
Class: |
702/151 ;
702/127; 702/150; 702/189 |
Current CPC
Class: |
G01D 5/145 20130101;
F15B 15/2846 20130101; C23C 8/80 20130101; F15B 15/2861
20130101 |
Class at
Publication: |
702/151 ;
702/127; 702/150; 702/189 |
International
Class: |
G01C 9/00 20060101
G01C009/00; G06F 19/00 20060101 G06F019/00 |
Claims
1. A method for detecting a position of a shaft, the method
comprising: providing a shaft comprising a hardened outer metallic
layer having a first hardness level with a generally uniform radial
depth, forming a first strip extending in a generally longitudinal
direction in the hardened outer metallic layer, the first strip
having a second hardness level different from the first hardness
level; forming a second strip in the hardened outer metallic layer
having the second hardness level, the first strip and the second
strip spaced apart from each other over a longitudinal region;
sensing an angular difference between a first magnetic field
associated with the first strip and a second magnetic field
associated with the second strip; and referencing an established
relationship between a position of the shaft and the angular
difference between the magnetic fields associated with the first
strip and the second strip to detect a position of the shaft with
respect to a reference point
2. The method according to claim 1 wherein the first hardness level
is greater than the second hardness level.
3. The method according to claim 1 wherein the first hardness
levels is less than the second hardness level.
4. The method according to claim 1 wherein the first strip
comprises a curved segment, and wherein the second strip comprises
a generally linear segment spaced apart from the curved
segment.
5. The method according to claim 1 wherein the first strip and the
second strip comprise generally linear segments, wherein the second
strip is generally parallel to a rotational axis of the shaft and
wherein the first strip is slanted with respect to the second
strip.
6. The method according to claim 1 wherein the first strip and the
second strip comprise a first generally sinusoidal wave and a
second generally sinusoidal wave, wherein the waves are offset in
frequency with respect to one another and cross one another at one
or more nodes.
7. The method according to claim 1 further comprising storing the
established relationship as angular differences and corresponding
axial positions of the shaft.
8. The method according to claim 1 further comprising storing the
established relationship as magnetic field patterns and
corresponding axial positions of the shaft.
9. A system for detecting a position of a shaft, the system
comprising: a shaft comprising a hardened outer metallic layer
having a first hardness level with a generally uniform radial
depth; a first strip extending in a generally longitudinal
direction in the hardened outer metallic layer, the first strip
having a second hardness level different from the first hardness
level; a second strip in the hardened outer metallic layer having
the second hardness level, the first strip and the second strip
spaced apart from each other over a longitudinal region; a sensor
assembly for sensing an angular difference between a first magnetic
field associated with the first strip and a second magnetic field
associated with the second strip; and a data processor for
referencing an established relationship between a position of the
shaft and the angular difference between the magnetic fields
associated with the first strip and the second strip to detect a
position of the shaft with respect to a reference point.
10. The system according to claim 9 wherein the first hardness
level is greater than the second hardness level.
11. The system according to claim 9 wherein the first hardness
level is less than the second hardness level.
12. The system according to claim 9 wherein the first strip
comprises a curved segment, and wherein the second strip comprises
a generally linear segment spaced apart from the curved
segment.
13. The system according to claim 9 wherein the first strip and the
second strip comprise generally linear segments, wherein the second
strip is generally parallel to a rotational axis of the shaft and
wherein the first strip is slanted with respect to the second
strip.
14. The system according to claim 9 wherein the first strip and the
second strip comprise a first generally sinusoidal wave and a
second generally sinusoidal wave, wherein the wave are offset in
frequency with respect to one another and cross one another at one
or more nodes.
15. The system according to claim 9 wherein the sensor assembly
comprises a group of magnetoresistive sensors radially aligned with
respect to the shaft.
16. The system according to claim 9 further comprising a data
storage device for storing the established relationship as angular
differences and corresponding axial positions of the shaft.
17. The system according to claim 9 further comprising a data
storage device for storing the established relationship as magnetic
field patterns and corresponding axial positions of the shaft.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a method and system for detecting
an axial position of a shaft.
BACKGROUND OF THE INVENTION
[0002] In the prior art, cylinder position sensing devices may use
a magnet embedded in a piston and one or more Hall effect sensors
that sense the magnetic field; hence, relative displacement of the
piston. However, in practice such cylinder position sensors are
restricted to cylinders with limited stroke and may require
expensive magnets with strong magnetic properties. Other prior art
cylinder position sensing devices may use magnetostrictive sensors
which require multiple magnets to be mounted in the cylinder. To
the extent that machining and other labor is required to prepare
for mounting of the magnets, the prior art cylinder position
sensing may be too costly and impractical for incorporation into
certain shafts. Thus, a need exists for a reliable and economical
technique for determining the position of a shaft.
SUMMARY OF THE INVENTION
[0003] In accordance with one embodiment of the invention, a shaft
comprises a hardened outer metallic layer having a first hardness
level with a generally uniform radial depth. A first strip extends
in a generally longitudinal direction in the outer metallic layer.
The first strip has a second hardness level different from the
first hardness level. A second strip in the outer metallic layer
has the second hardness level. The first strip and the second strip
are spaced apart from each other over at least a longitudinal
region. A sensor assembly senses an angular difference between a
first magnetic field associated with the first strip and a second
magnetic field associated with the second strip. A data processor
references an established relationship between an axial position of
the shaft and the sensed angular difference between magnetic fields
associated with the first strip and the second strip to detect the
axial position of the shaft with respect to a reference point.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a perspective view of one embodiment of a system
for detecting the axial position of a shaft in accordance with the
invention.
[0005] FIG. 2 is a cross-sectional view of the system of FIG.
1.
[0006] FIG. 3 shows a cross-sectional view of the shaft along
reference line 3-3 of FIG. 2.
[0007] FIG. 4 shows a cross-sectional view of the shaft along
reference line 4-4 of FIG. 2.
[0008] FIG. 5 shows a cross-sectional view of a sensor assembly and
a schematic of the data processing module of FIG. 1.
[0009] FIG. 6 is a perspective view of another embodiment of a
system for detecting the longitudinal position of a shaft in
accordance with the invention.
[0010] FIG. 7 is a perspective view of yet another embodiment of a
system for detecting the longitudinal position of a shaft in
accordance with the invention.
[0011] FIG. 8 is flow chart of a method for detecting the axial
position of a shaft.
[0012] Like reference numbers in different drawings indicate like
elements.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] In accordance with one embodiment, FIG. 1 shows a
perspective view of a system for detecting an axial position of a
shaft 28 (or a member 10 attached thereto) with respect to a
cylinder 12 (e.g., hydraulic cylinder). The cylinder 12 is cut away
to better reveal the components of FIG. 1. A member 10, such as a
piston, may be coupled to one end of the shaft 28. The member 10 is
slidable in an axial direction within the cylinder 12. The volume
bounded by the member 10 and the interior of the cylinder 12 is
referred to as the chamber 24. If the member 10 and shaft 28 are
part of a hydraulic cylinder or assembly, the chamber 24 would
contain hydraulic fluid or oil, for example.
[0014] A bushing 18 is associated with the cylinder 12. For
example, a bushing 18 is secured (e.g., press-fitted or threaded
into the interior of the cylinder 12) between the cylinder 12 and
the shaft 28. The bushing 18 houses one or more seals (e.g., inner
seal 14 and outer seal 16) and a sensor assembly 22. The bushing 18
or the cylinder 12 may support the mounting of an inner seal 14 and
an outer seal 16, for instance. In one embodiment, the seals
(14,16) are lubricated to reduce friction at the shaft-bushing
interface. The bushing 18 may function as a shaft guide for the
shaft 28. The bushing 18 supports longitudinal movement of the
shaft 28 with respect to the cylinder 12.
[0015] Although a sensor assembly 22 may be housed in the bushing
18 as shown in FIG. 1, in other embodiments the sensor assembly 22
may be mounted elsewhere in or on the cylinder 12. As shown, the
sensor assembly 22 may comprise a ring or annular member that is
placed around the shaft 28 and spaced apart from the shaft 28. In
an alternate embodiment, the sensor assembly 22 comprises a ring
that is integrated into the inner seal 14 or outer seal 16.
[0016] The sensor assembly 22 facilitates sensing of the axial
position of the shaft 28 with respect to the cylinder 12. The
sensor assembly 22 may comprise one or sensors 88 that sense
magnetic fields associated with a first strip and a second strip in
the shaft 28. In one embodiment, each sensor 88 comprises one or
more of the following: a magnetoresistive sensor, a Hall-effect
sensor, a digital position sensor, and another position sensor.
[0017] In one embodiment, the magnetoresistive sensor may be
operated in a saturated mode to measure or map the angle of
magnetic field lines, for example. A magnetoresistive sensor may
comprise a semiconductor that changes resistance based on the
magnetic field vector (e.g., magnetic field strength and its
direction) that is received by the magnetoresistive sensor. The
saturation mode may be attained by positioning one or more biasing
magnets (e.g., rare earth magnets or electromagnets) around the
sensor assembly 22. The biasing magnets may be positioned to
reinforce the magnetic fields of dipoles produced by the first
strip 91, the second strip 93, or both, for instance.
Advantageously, the sensor assembly 22 is not located with the
pressurized chamber of the cylinder 12 and does not need to
withstand any thermal stress or pressure associated with the
chamber 24.
[0018] The sensor assembly 22 or sensors 88 are coupled to a data
processing module 55. For example, the sensor assembly 22 may be
coupled to a data interface 84 of the data processing module 55.
The data processing module 55 comprises a data interface 84 which
is in communication with a data processor 82. In turn, the data
processor 82 is capable of communicating with a data storage device
80. The data processor 82 comprises a logic circuit, a
microprocessor, a microcontroller, programmable logic device, a
digital signal processor, or another data processing device. The
data storage device 80 may comprise memory (e.g., nonvolatile
memory, electronically erasable programmable read-only memory) or
the like. The data interface 84 may comprise a driver to convert a
ground closure, a semiconductor switch closure, a change in
resistance, or sink of one or more sensors 88 to a logic level
input (e.g., or voltage range) suitable for the data processor 82.
Further, the data interface 84 may comprise a latch, a flip-flop,
or buffer memory for storing or buffering input data from the data
interface 84.
[0019] The data processor 82 determines axial or longitudinal
position of the shaft 28 with respect to a cylinder 12 (at a
respective time) based on the sensed electromagnetic field or
magnetic field detected by the sensor assembly 22. The sensor
assembly 22 supports detection of a first magnetic field or first
magnetic dipole associated with the first strip 91 and a second
magnetic field or second magnetic dipole associated with the second
strip 93. The first magnetic field or first magnetic dipole
indicates a first angle of the first strip 91 on the shaft 28,
whereas the second magnetic field or second magnetic dipole
indicates a second angle of the second strip 93 on the shaft 28.
For the first strip 91 and the second strip 93, the angular
difference or separation between the first angle and the second
angle varies with the axial displacement or along the longitudinal
axis of the shaft 28. The data storage device 80 may store
relationships of angular differences to corresponding axial
positions or longitudinal positions of the shaft 28.
[0020] The shaft 28 comprises a core 30 and a metallic outer layer
26, which overlies a core 30 of the shaft 28. In one embodiment,
the metallic outer layer 26 has a generally cylindrical outer
surface 34. The thickness of the metallic outer layer 26 of the
shaft (e.g., shaft 28) may be generally uniform along a length of
the shaft 28. An induction hardening procedure or other case
hardening procedure may be used to create a first hardness level of
the metallic outer layer 26 of the shaft 28, for example. A laser
augmentation procedure may be used to retard or advance cooling of
the hardening procedure to produce one or more strips (e.g., 91,
93) with a second hardness level. The strips (e.g., 91, 93) may be
formed of the same metallic material as the outer layer 26, but
treated to a different hardness level. In FIG. 1, the first strip
91 comprises a generally linear segment, and the second strip 93
comprises a curved segment spaced apart from the linear
segment.
[0021] Hardening refers to any process (e.g., induction hardening)
which increases the hardness of a metal or alloy. For example, a
metal or alloy is heated to a target temperature or target
temperature range and cooled at a particular rate or over a
particular cooling time. Case hardening refers to adding carbon to
a surface of an iron alloy to produce a carburized alloy and
heat-treating (e.g., induction heating) all or part of a surface of
the carburized iron alloy. The hardening process may be used to
change the permeability of the carburized iron alloy, metal or
alloy, while leaving the electrical conductivity generally
unchanged, for instance. The difference between the first hardness
level and the second hardness level creates induced magnetic
dipoles or magnetic fields associated with the first strip 91 and
the second strip 93.
[0022] Induction hardening may be used to define the outer metallic
layer 26 by controlling a depth of hardening through varying the
induction current. In one example, the induction frequency may be
varied linearly as the induction coil travels axially along the
length of the shaft 28 to produce a non-linear depth of hardened
case along the length of the shaft 28. In another example, the
induction frequency may be varied to produce a linear variation of
hardened case depth along the length of the shaft 28. The following
variables may influence induction hardening of the shaft (e.g.,
shaft 28): (1) power density induced in a surface layer of the
shaft 28, (2) clearance between the induction coil and the shaft
28, (3) concentricity or coaxial alignment between the induction
coil and the shaft 28, (4) coil voltage, (5) coil design, (6) speed
of coil travel with respect to the surface of the shaft 28, and (7)
ambient conditions including room temperature, humidity and air
turbulence.
[0023] Although the shaft 28 may be constructed of various metals
or alloys that fall within the scope of the invention, in one
embodiment the shaft 28 represents a steel or iron-based alloy,
which may be plated with a protective metallic plating material
(e.g., nickel and chromium). The protective metallic plating
material is not shown in FIG. 1. If the metallic plating material
is applied to an exterior surface of the shaft 28, the thickness of
the plating should be kept substantially uniform to prevent
disturbances in the eddy current or electromagnetic field induced
by the sensor assembly 22.
[0024] FIG. 2 shows the shaft 28 at a second longitudinal position
40. In FIG. 2, the second angular difference (.theta..sub.2 of FIG.
4) is aligned with the sensing region associated with the sensor
assembly 22. The second angular difference (.theta..sub.2) is
associated with a second longitudinal position 40 of the shaft 28.
The second longitudinal position 40 of the shaft 28 is spaced apart
from the first longitudinal position 39. Like reference numbers in
FIG. 2 and FIG. 1 indicate like elements.
[0025] Referring to FIG. 1 and FIG. 2, the sensor assembly 22
senses the induced magnetic field or one or more magnetic dipoles
associated with the first strip 91 and the second strip 93 to
detect an axial alignment of the shaft 28 with a reference point
(e.g., a fixed point on the cylinder 12) at a particular time. For
example, the sensor assembly 22 senses a first angular difference
(.theta..sub.1 of FIG. 3) between magnetic fields associated with
the first strip 91 and the second strip 93 when the shaft 28 has a
first longitudinal position 39; the sensor assembly 22 senses a
second angular difference (.theta..sub.2 of FIG. 4) between
magnetic fields associated with the first strip 91 and the second
strip 93 when the shaft 28 has a second longitudinal position 40.
The change in the magnetic field between the first angular
difference (.theta..sub.1) and the second angular distance
(.theta..sub.2) indicates the movement or change in position of the
shaft 28. The data processing module 55 measures the change in the
angular magnetic field or electromagnetic field associated with the
axial displacement of the shaft 28. The data processor 82 may store
one or more of the following position reference data: a reference
table, a look-up table, axial position data versus detected
magnetic field, axial position data versus magnetic field patterns
(e.g., magnetic field vectors of field strength and direction) a
database of axial positions of the shaft 28 versus measured angular
difference values, or an equation or curve representing axial
positions of the shaft 28 versus measured angular difference
values. The sensed angular difference is compared to the reference
angular difference to determine the corresponding axial position of
the shaft 28.
[0026] FIG. 3 shows a cross-sectional view of the shaft 28 along
reference line 3-3 of FIG. 2. FIG. 3 illustrates the core 30 of the
shaft 28 and the metallic outer layer 26. In the metallic outer
layer 26 at a first longitudinal position 39, a first strip 91 is
positioned at a first angle on the shaft, whereas a second strip 93
is positioned at a second angle on the shaft 28. The first angle
and the second angle may be measured (e.g., in clockwise degrees)
from a common reference angle, for example. The common reference
angle may be established such that 0 degrees is generally upward or
at 12 o'clock with respect to the cross-section of the shaft 28 in
FIG. 3. The first angular difference (.theta..sub.1) represents the
angular displacement between the first angle and the second angle
of FIG. 3. At the first angle of the first strip 91, a first
magnetic field or first magnetic dipole is generally perpendicular
or normal to an outer surface of the shaft 28. At the second angle
of the second strip 93, a second magnetic field or second magnetic
dipole is generally perpendicular or normal to an outer surface of
the shaft 28. The sensor assembly 22 cooperates with the data
processing module 55 to determine the axial position (e.g., first
longitudinal position) of the shaft 28 associated with the first
angular difference (E,).
[0027] FIG. 4 shows a cross-sectional view of the shaft 28 along
reference line 4-4 of FIG. 2. FIG. 4 illustrates the core 30 of the
shaft 28 and the metallic outer layer 26. In the metallic outer
layer 26, a first strip 91 is positioned at a first angle on the
shaft 28, whereas a second strip 93 is positioned at a second angle
on the shaft 28. The first angle and the second angle may be
measured from a common reference angle. For example, the common
reference angle may represent where 0 degrees and 360 degrees are
generally upward in FIG. 4. The second angular difference
(.theta..sub.2) represents the angular displacement between the
first angle and the second angle of the first strip 91 and the
second strip 93, respectively, of FIG. 4. At the first angle of the
first strip 91, a first magnetic field or first magnetic dipole is
generally perpendicular or normal to an outer surface of the shaft
28. At the second angle of the second strip 93, a second magnetic
field or second magnetic dipole is generally perpendicular or
normal to an outer surface of the shaft 28. The sensor assembly 22
cooperates with the data processing module 55 to determine the
axial position (e.g., second longitudinal position) of the shaft 28
associated with the second angular difference (.theta..sub.2).
[0028] FIG. 5 shows a cross-sectional view of a sensor assembly 22
and an illustrative schematic of the data processing module 55 of
FIG. 1. Further, the data processing module 55 and the sensor
assembly 22 are associated with an energy source 90 (e.g., a
battery or direct current supply). The sensor assembly 22 may
comprises an array of sensors 88 embedded or retained by a
generally annular retainer 23. For example, the sensors 88 may be
aligned in a generally radial array about a common axis. In FIG. 5,
the generally annular retainer 23 is cut-away to reveal the sensors
88, which are aligned radially about a central axis or opening of
the sensor assembly 22. The data processing module 55 of FIG. 5
shows the illustrative data connections between the sensors 88 and
the data interface 84, and between the data interface 84 and the
data processor 82. Further, the data processing module 55 shows at
least one rail of the direct current power bus for powering the
sensors and the data processing module 55. Each sensor 88 may
provide a state or level indicating the presence of a detected
magnetic field at a certain angular orientation with respect to the
shaft 28 at the data output port 86. Each sensor 88 may provide a
"magnetic-field-detected" state and a "magnetic-field-not-detected"
state, for example.
[0029] In an alternate embodiment, the sensor 88 may provide a
signal or state representative of a magnetic field strength,
orientation, or both at data output port 86 or otherwise.
[0030] The configuration of FIG. 6 is similar to that of FIG. 1,
except the first strip 191 of FIG. 6 is generally linear or
rectangular and the second strip 193 of FIG. 6 is generally linear
or rectangular. Like reference numbers indicate like elements in
FIG. 1 and FIG. 6. The first strip 191 and the second strip 193
comprise generally linear segments, wherein the second strip 193 is
generally parallel to a rotational axis of the shaft and wherein
the first strip 191 is slanted with respect to the second strip
193.
[0031] The configuration of FIG. 7 is similar to that of FIG. 1,
except the first strip 291 of FIG. 7 comprises a first curve or
waveform (e.g., a generally sinusoidal curve) with a first
frequency and the second strip 293 comprises a second curve or
waveform (e.g., a generally sinusoidal curve) with a second
frequency, distinct from the first frequency. In general, the first
strip 291 and the second strip 293 comprise a first waveform (e.g.,
a first generally sinusoidal waveform) and a second waveform (e.g.,
second generally sinusoidal waveform) wherein the waveforms are
offset in frequency with respect to one another and intersect or
cross one another at one or more nodes. Here, as shown the first
frequency and the second frequency are related by a multiple of
two, although other multiples are possible and fall within the
scope of the invention.
[0032] The first frequency and the second frequency may be selected
with a corresponding wavelength to cover an axial region or
distance of interest of the shaft 28 with a desired resolution. For
example, the wavelength may be chosen such that the first strip 291
and the strip 293 only overlap or intersect at their ends. Here,
the first strip 291 extends over approximately one wavelength,
whereas the second strip 293 extends over approximately one-half
wavelength. Therefore, the axial region of interest may equal
approximately one wavelength for the first strip 291 and
approximately one-half wavelength for the second strip 293.
[0033] In an alternative embodiment, the first frequency and the
second frequency may be selected to have wavelengths that are
smaller than the axial distance or region of interest such that the
strips or curves overlap at one or more nodes. In such a case
ambiguity would potentially exist because the angular differences
would be equal at repetitive axial locations along the shaft 28
between different pairs of nodes. To the resolve this ambiguity,
various techniques may be applied alternatively or cumulatively.
Under a first technique, a third strip may be added or other
supplemental magnetic markings added to the shaft that differ along
its axial length with respect to different internodal locations.
Under a second technique, a supplemental sensor may determine the
direction of axial travel of the shaft 28 to resolve the ambiguity
between each equivalent angular difference between magnetic regions
associated with the shaft 28. Under a third technique, a
supplemental sensor may be used when the shaft 28 reaches travel
limit in one axial direction or when the shaft 28 reaches another
travel limit in an opposite axial direction. For example, a contact
sensor may be associated with the end of the bushing 18 to contact
the member 10 (e.g., piston) at its travel limit and provide an
electrical signal consistent with such contact.
[0034] FIG. 8 is flow chart of a method for detecting the axial
position of a shaft. The method of FIG. 8 begins in step S800.
[0035] In step S800, a shaft (e.g., 28) is provided that comprises
a hardened outer metallic layer (e.g., 26) having a first hardness
level with a generally uniform radial depth. The shaft 28 may be
induction hardened or otherwise treated to form the outer metallic
layer 26 associated with the first hardness level.
[0036] In step S802, a first strip (e.g., 91, 191 or 291) is formed
and extends in a generally longitudinal direction in the outer
metallic layer (e.g., 26). Further, the first strip has a second
hardness level different from the first hardness level. The first
strip may be formed by treating the hardened metallic outer layer
26 with a laser beam to thermally augment or modify the induction
hardening process. In one example, the laser beam can heat the
shaft 28 in a localized area to delay cooling to form the first
strip with a second hardness level less than the first hardness
level. In another example, the laser beam can heat the shaft 28 in
a localized area to a higher temperature than the remainder of the
outer layer to form the first strip with a second hardness level
greater than the first hardness level.
[0037] In step S804, a second strip (e.g., 93, 193, and 293) is
formed and extends in the outer metallic layer (e.g., 26). Further,
the second strip has the second hardness level and is spaced apart
from the first strip. The second strip may be formed by treating
the hardened metallic outer layer 26 with a laser beam to thermally
augment or modify the induction hardening process. In one example,
the laser beam can heat the shaft 28 in a localized area to delay
cooling to form the second strip with a second hardness level less
than the first hardness level. In another example, the laser beam
can heat the shaft 28 in a localized area to a higher temperature
than the remainder of the outer layer to form the second strip with
a second hardness level greater than the first hardness level.
[0038] In step S806, a sensor assembly 22, a data processing module
55, or both sense an angular difference between a first magnetic
field associated with the first strip (e.g., 91, 191, and 291) and
a second magnetic field associated with the second strip (e.g., 93,
193 and 293). The angular difference between the magnetic field
associated with the first strip and the second strip may differ in
accordance with various configurations.
[0039] Under a first configuration of FIG. 1, the first strip 91
comprises a generally linear segment, and the second strip 93
comprises a curved segment spaced apart from the linear segment.
Under a second configuration of FIG. 6, the first strip 191 and the
second strip 193 comprise generally linear segments, wherein the
second strip 193 is generally parallel to a rotational axis of the
shaft and wherein the first strip 191 is slanted with respect to
the second strip 193. Under a third configuration of FIG. 7, the
first strip 291 and the second strip 293 comprise a first generally
sinusoidal waveform and a second generally sinusoidal waveform,
wherein the waveforms are offset in frequency with respect to one
another and intersect or cross one another at one or more
nodes.
[0040] In step S808, a sensor assembly 22, a data processing module
55, or both reference an established relationship between a
position of the shaft and the angular difference between magnetic
fields associated with the first strip (e.g., 91,191 and 291) and
the second strip (e.g., 93,193 and 293) too detect a position of
the shaft with respect to a reference point. The established
relationships may be stored in a data storage device 80 of the data
processing module 55 as a look-up table, a database or otherwise.
In one example, the established relationship may comprise a stored
list of angular differences and corresponding axial positions of
the shaft 28. In another example, the established relationships may
comprise a stored list of magnetic field patterns (e.g., magnetic
field vectors) and corresponding axial positions of the shaft
28.
[0041] All of the foregoing embodiments of the system of method of
detecting a position of a shaft (or member attached thereto), use
sensors that are mounted external to the cylinder chamber.
Accordingly, no special sealing of the cylinder chamber is
required. The detection system and method operates by sensing
electromagnetic fields induced on the shaft surface and within a
penetration depth; does not need to contact the shaft and requires
no moving parts that might detract from reliability. The system and
method may be readily extended to determining torque or the number
of revolutions associated with a shaft by sensing the magnetic
field patterns associated with the spacing between the first strip
and the second strip.
[0042] Having described the preferred embodiment(s), it will become
apparent that various modifications can be made without departing
from the scope of the invention as defined in the accompanying
claims.
* * * * *