U.S. patent application number 09/785097 was filed with the patent office on 2001-10-25 for multi-turn, non-contacting rotary shaft position sensor.
Invention is credited to Glasson, Richard O..
Application Number | 20010033160 09/785097 |
Document ID | / |
Family ID | 22672129 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010033160 |
Kind Code |
A1 |
Glasson, Richard O. |
October 25, 2001 |
Multi-turn, non-contacting rotary shaft position sensor
Abstract
A multi-turn non-contacting rotary shaft position sensor that
determines a positional parameter of a rotating shaft. The sensor
converts the rotational movement of an input shaft to a linear
translational movement of a magnetic element. A magnetically
sensitive sensor is provided in a fixed location in close proximity
to the magnetic element within the flux field of that magnetic
element. As the input shaft rotates, the magnetic element moves
along that linear path toward or away from the magnetically
sensitive sensor so that the sensor detects the change in the
magnetic flux imposed by the magnetic element. That change in
magnetic flux is used to determining a positional parameter of the
input shaft.
Inventors: |
Glasson, Richard O.;
(Whippany, NJ) |
Correspondence
Address: |
GIBBONS, DEL DEO, DOLAN, GRIFFINGER & VECCHIONE
1 RIVERFRONT PLAZA
NEWARK
NJ
07102-5497
US
|
Family ID: |
22672129 |
Appl. No.: |
09/785097 |
Filed: |
February 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60183270 |
Feb 17, 2000 |
|
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|
Current U.S.
Class: |
324/207.25 ;
324/207.2; 324/207.21 |
Current CPC
Class: |
G01D 2205/26 20210501;
G01D 5/145 20130101; G01D 5/04 20130101; G01D 2205/22 20210501;
G01D 11/245 20130101 |
Class at
Publication: |
324/207.25 ;
324/207.2; 324/207.21 |
International
Class: |
G01B 007/30 |
Claims
What is claimed is:
1. A rotary shaft position sensor comprising: a housing; a magnetic
element producing a magnetic field and located within said housing,
said magnetic element adapted to be translatable along a linear
path within said housing but constrained from rotational movement;
said magnetic element having a threaded shaft extending therefrom;
a rotatable input shaft threadedly affixed to said threaded shaft,
said rotatable input shaft adapted to be rotated to translate said
magnetic element along said linear path within said housing, and a
sensor positioned in proximity to said magnetic element and within
said magnetic field, wherein said linear movement of said magnetic
element causes a change in the magnetic influence of said magnetic
field on said sensor.
2. A rotary shaft position sensor as defined in claim 1 wherein
said sensor is a Linear Hall Effect sensor.
3. A rotary shaft position sensor as defined in claim 1 wherein
said sensor is a Giant Magneto Resistive sensor.
4. A rotary shaft position sensor as defined in claim 1 wherein
said magnetic element is a permanent magnet.
5. A rotary shaft position sensor as defined in claim 1 wherein
said threaded shaft has external threads and said input shaft has
internal threads.
6. A rotary shaft position sensor comprising: a housing; a magnetic
element producing a magnetic field and located within said housing,
means to affix said magnetic element to said housing to allow said
magnetic element to move along a linear path but to prevent said
magnetic element from rotating with respect to said housing; said
magnetic element having a threaded shaft extending therefrom, said
threaded shaft extending outwardly from said housing a rotatable
input shaft threadedly affixed to said threaded shaft, said
rotatable input shaft adapted to be rotated to translate said
magnetic element along said linear path within said housing, and a
magnetically sensitive sensor; means to mount said magnetically
sensitive sensor within said housing in proximity to said magnetic
element and within said magnetic field, wherein said linear
movement of said magnetic element causes a change in the magnetic
influence of said magnetic field on said sensor.
7. A rotary shaft position sensor as defined in claim 6 wherein
said means to mount said magnetically sensitive sensor comprises a
recess formed in said housing, said magnetically sensitive sensor
configured to be fitted within said recess.
8. A rotary shaft position sensor as defined in claim 6 wherein
said housing has a pocket formed therein and wherein said magnetic
element has a specially configured outer portion and said means to
affix said magnetic element to said housing comprises interfitting
said magnetic element into said pocket.
9. A rotary shaft position sensor as defined in claim 8 wherein
specially configured outer portion of said magnetic element is a
prismatic shape.
10. A rotary shaft position sensor as defined in claim 6 wherein
said threaded shaft has external threads and said input shaft has
internal threads.
11. A rotary shaft position sensor as defined in claim 6 wherein
said magnetic element is a permanent magnet.
12. An instrument for determining a positional parameter of a
rotatable shaft, said instrument comprising; a housing; a magnetic
element producing a magnetic field and located within said housing,
said magnetic element adapted to be translatable along a linear
path within said housing but constrained from rotational movement;
said magnetic element having a threaded shaft extending therefrom;
a rotatable input shaft threadedly affixed to said threaded shaft,
said rotatable input shaft adapted to be rotated to translate said
magnetic element along said linear path within said housing, a
sensor positioned in close proximity to said magnetic element and
within said magnetic field, wherein said linear movement of said
magnetic element causes a change in the magnetic influence of said
magnetic field on said sensor; and means to derive a signal based
upon said change in the magnetic influence sensed by said sensor to
determine a positional parameter of said input shaft.
13. An instrument as defined in claim 12 wherein said rotational
parameter is the rotational travel of said input shaft.
14. An instrument as defined in claim 12 wherein said rotational
parameter is the angular position of said input shaft.
15. An instrument as defined in claim 12 wherein said rotational
parameter is the angular speed of said input shaft.
16. An instrument as defined in claim 12 wherein said means to
derive a signal comprises a means of determining a change in
resistance of said sensor based on said change in the magnetic
influence.
17. An instrument as defined in claim 12 where said means to derive
a signal comprises a means of sensing an electrical signal from
said sensor.
18. A method of detecting a positional parameter of a rotatable
shaft, said method comprising the steps of: providing a housing,
providing a magnetic element within the housing emitting a magnetic
field and having a shaft extending therefrom, providing a
magnetically sensitive sensor in a fixed position within the
housing within the magnetic field of the magnetic element, allowing
the magnetic element to move along a linear path with the housing
while constraining the magnetic element for rotational movement,
providing a input shaft threadedly engaged to the shaft, and
rotating the input shaft to translate the magnetic element to move
the magnetic element along the linear path toward and away from the
magnetically sensitive sensor to change the effect of the magnetic
field on the sensor.
19. A method of detecting a positional parameter of a rotatable
shaft as defined in claim 18 wherein said step of providing a
magnetic element comprises providing a permanent magnet.
20. A method of detecting a positional parameter of a rotatable
shaft as defined in claim 18 wherein said step of providing a
magnetically sensitive sensor in a fixed position comprises
locating the sensor in a recess formed in the housing.
21. A rotary shaft position sensor comprising: a housing; a
magnetic element producing a magnetic field and located within said
housing, said magnetic element adapted to be translatable along a
linear path within said housing but constrained from rotational
movement; said magnetic element having an shaft extending
therefrom; a rotatable input shaft operatively interconnected to
said magnetic element shaft, said rotatable input shaft adapted to
be rotated to translate said magnetic element along said linear
path within said housing, and a sensor positioned in proximity to
said magnetic element and within said magnetic field, wherein said
linear movement of said magnetic element causes a change in the
magnetic influence of said magnetic field on said sensor.
22. A rotary shaft position sensor as defined in claim 20 wherein
said operative interconnection between said magnetic element shaft
and said rotatable input shaft comprises a threaded
interengagement.
23. A rotary shaft position sensor as defined in claim 21 wherein
said magnetic element shaft has external threads and said rotatable
input shaft has internal threads.
24. A rotary shaft position sensor as defined in claim 20 wherein
said sensor produces an electrical signal dependent upon the
influence of the magnetic field on said sensor.
25. A rotary shaft position sensor as defined in claim 20 wherein
said sensor changes its internal resistance dependent upon the
influence of the magnetic field on said sensor.
Description
RELATED APPLICATIONS
[0001] The present application is based upon and claims the benefit
of U.S. Provisional Application Ser. No. 60/183,270 filed Feb. 17,
2000.
FIELD OF THE INVENTION
[0002] The invention generally relates to position sensors, and
more particularly, to a magnetically sensitive sensor that detects
a positional parameter of a rotating element.
BACKGROUND
[0003] Rotary sensors using contacting technology, such as
potentiometers, suffer from various disadvantages that have limited
their use. In applications requiring prolonged use over many years
or requiring many cycles, the contacting sensors develop dead zones
and non-uniform electrical behavior. Additionally, contacting
sensors, even when in good condition, exhibit a relatively high
degree of electrical noise during operation. This noise is a
problem in sensitive electronic circuits.
[0004] It has been suggested to use non-contacting angular sensors
to overcome the disadvantages of contacting sensors. Such sensors
are not as susceptible to wear and exhibit reduced electrical
noise. One barrier to the widespread use of non-contacting
transducers, however, is the restricted angular range of those
devices. Examples of such devices are shown in the U.S. Pat. Nos.
3,777,273; 3,988,710; 4,425,557 and 5,789,917. All of these devices
have an angular operating range of less than one-half turn.
[0005] Another barrier to the widespread use of non-contacting
sensors is the use of magnetic devices in such sensors. Magnetic
fields are short acting, thus magnetic sensors have limited range
and they exhibit undesirable signal-to-noise ratios (SNR) due to
outside magnetic disturbances. The problems with non-linearity and
SNR have been somewhat offset by the use of pole pieces, or flux
directors. Flux directors attempt to extend the usable linear range
of a magnetic field by advantageously shaping the field. The need
to improve the SNR has been cited in various publications,
including U.S. Pat. Nos. 5,444,369; 5,789,917; and 5,757,179.
[0006] There are contacting rotary sensors that exhibit extended
range, but these sensors suffer from the disadvantages discussed
above and are generally too complex and too costly for commercial
acceptance. Moreover, these multi-turn sensors provide only a
relative position indication, having no absolute reference.
SUMMARY OF THE INVENTION
[0007] The advantages of magnetic, non-contacting sensors over
contacting potentiometric types include virtually unlimited
operating life, owing to the fact that there are no physical
contacts. Non-contacting sensors according to the principles of the
invention do not suffer from the wear degradation and electrical
noise exhibited by contacting sensors. A sensor according to the
principles of the invention also offers a useful range of many full
revolutions. Such a range makes the present invention a suitable
replacement for absolute rotary encoders, angular sensors,
potentiometers, tuners, and robotic joint sensors. A sensor
according to the principles of the invention reduces SNR by
converting a relatively large rotational mechanical input to a
smaller linear mechanical translation of the magnet in the
measurement circuit. This technique allows the sensor to use a very
small portion of the magnetic field that is close to the magnet.
This field portion offers the highest magnetic flux density for a
given magnet and thus results in improved SNR. Also, the small size
of this field portion reduces dependence on linearity.
BRIEF DESCRIPTION OF THE DRAWING
[0008] A more complete understanding of the invention may be
obtained from consideration of the following description in
conjunction with the drawing in which:
[0009] The FIGURE is a perspective view, partially cut away,
showing the rotary shaft position sensor constructed in accordance
with the present invention.
DETAILED DESCRIPTION
[0010] Referring to FIG. 1, there is shown a perspective view,
partially cut away, of a rotary shaft position sensor 10
constructed in accordance with the present invention. As can be
seen, there is a housing 12 that may be of any variety of
materials, such as metals or plastic compositions. Within the
housing 12, there is formed a specially configured pocket 14 within
which is located a magnetic element 16. The magnetic element 16 may
be a permanent magnetic that emits a magnetic flux therefrom and
the purpose of the magnetic field flux will be later appreciated.
The exterior portion 18 of the magnetic element 16 is also
specially configured, and as shown, that exterior portion 18 may be
formed in a prismatic shape, it being of importance that the
exterior portion 18 of the magnetic element 16 be specially
configured so as to fit with the pocket 14 such that the magnetic
element 16 is prevented from rotating with respect to housing 12
but can move along a linear path within the housing 12 indicated by
the arrow A.
[0011] Extending outwardly from the magnetic element 16 is threaded
shaft 20, shown as externally threaded and the threaded shaft 20
extends external of the housing 12. The threaded shaft 20 may be a
separately formed part that is inserted into the magnetic element
16 or insert molded in the production of the magnetic element 16,
however, in any event, the threaded shaft 20 is firmly affixed to
that magnetic element 16.
[0012] An input shaft 22 is threadedly affixed to the threaded
shaft 20 external of the housing 12 by means of internal threads
24. Thus, the input shaft 22 and the threaded shaft 20 are
threadedly engaged together and, as stated, in the preferred
embodiment, the threaded shaft 20 has external threads and the
input shaft 22 has internal threads 24. The threaded shaft 20 and
the input shaft 22 are threadedly engaged together and, as can be
seen, the external and internal locations of the respective threads
on each of those components could readily be reversed and the
rotary shaft position sensor 10 still function in the manner to be
explained.
[0013] The input shaft 22 is rotatable affixed to the housing 12
such that the input shaft 22 can freely rotate with respect to the
housing 12 but is restrained from any axial movement with respect
thereto. In the FIGURE, the mounting of the input shaft 22 is
accomplished by means of a mounting bushing 26 that is fitted to
the housing 12 and that mounting bushing 26 has an inner end 28, an
outer end 30 and an exterior flange 32 that seats against the
housing 12. Mounting bushing 26 thus surrounds the input shaft 22
and provides a seal against the input shaft 22 while allowing the
input shaft 22 to freely rotate within the mounting bushing 26.
[0014] To prevent the input shaft 22 from moving axially with
respect to the housing 12, there is formed an inner flange 34 at
the inner end of the input shaft 22 and which rotatably engages the
inner end 28 of the mounting bushing 26 to prevent the input shaft
22 from moving axially outwardly from the housing 12. A further
device, such as a C-clip, not shown, can be inserted into a groove
36 formed in the input shaft 22 just proximate the outer end 30 of
the mounting bushing 26 such that the axial movement of the input
shaft 22 toward the housing 12 is also prevented, thus restraining
the input shaft 22 with respect to the housing 12 along either
axial direction while, at the same time, allowing the input shaft
22 to freely rotate within the housing 12.
[0015] A magnetically sensitive sensor 38 is mounted proximate the
magnetic element 16 and that mounting is preferably by means of a
recess 40 that is formed in the housing 12 and into which the
sensor 38 is fitted, thus retaining that sensor 38 firmly in a
fixed position with respect to the housing 12 so that the finite
distance between the magnetically sensitive sensor 38 and the
magnetic element 16 is affected only by the movement of the
magnetic element 16. As can be noted, however, it is important that
the magnetically sensitive sensor 38 be positioned within the
magnetic field of the magnetic element 16 and the precise finite
distance from that magnetic element 16 is dependent, of course, on
the strength of the magnetic field of that magnetic element 16.
[0016] The actual magnetically sensitive sensor 38 may be of a
variety of sensors provided that such sensors are capable of
detecting the changing magnetic field of the magnetic element 16 as
the distance between the magnetic element 16 and the sensor
changes. Typical of such magnetically sensitive sensors is a Hall
Effect sensor or a Giant Magneto Resistive (GMR) sensor, however
other sensors sensitive to magnetic flux may be used consistent
with the principles of the invention.
[0017] Accordingly, with the elements of the present invention
described, the operation of the rotary shaft position sensor 10 can
be described. As the input shaft 22 is rotated, that rotation
causes the magnetic element 16 to translate in the direction along
the axis of the threaded shaft 20 and thus the magnetic element 16
moves axially within the housing 12 dependent upon the amount of
angular rotation of the input shaft 22. The amount of such
translational movement per angular rotation of the input shaft 22
is, of course, dependent upon the threads per inch, thread pitch or
other parameter of the threaded interengagement between the input
shaft 22 and the threaded shaft 20 of the magnetic element 16. In
the design of a particular rotating shaft position sensor 10,
therefore, the amount of linear translation of the magnetic element
16 per the amount of angular rotation of the input shaft 22 can be
designed in accordance with the particular rotation of the input
shaft 22 depending upon the particular use of the device such that
the use of the rotary shaft position sensor 10 is applicable to a
wide variety of differing applications.
[0018] In any event, as the input shaft 22 is rotated, the magnet
element 16 is linearly translated by the interengement of the
threaded shaft 20 and the internal threads 24 of the input shaft 22
to change the distance between that magnetic 16 and the
magnetically sensitive sensor 38 such that the effect of the
magnetic flux field on sensor 38 changes in proportion thereto and
that change in magnetic field can be measured in order to determine
the rotation of the input shaft 22.
[0019] It should be noted here that the rotation of the input shaft
22 being measured by this invention is not limited to a 90, 180 or
even 360 degree rotation of the input shaft 22 but may be
applicable readily to multiple full rotations of the input shaft
22.
[0020] As indicated, the magnetically sensitive sensor 38
experiences the change in the magnetic field flux radiated by the
magnet element 16 and the sensor itself may be any one of a variety
of sensors, among such typical sensors is a Linear Hall Effect
sensor where the sensor produces an electrical change in a voltage
signal analogous to the angular position of the input shaft 22, or,
alternatively, the sensor 38 may be a Giant Magneto Resistive (GMR)
sensor that experiences a change in internal resistance responsive
to the change in the magnetic field and, in such case, that change
of resistance can be measured and which is also analogous to the
angular position of the input shaft 22. Other sensors may also be
utilized as long as the particular sensor is sensitive to a
changing of the magnetic flux field emitted by the magnetic element
16. In this way, a varying magnetic influence is imposed upon the
magnetically sensitive sensor, the magnetic influence being
dependent on the angular position of the input shaft.
[0021] As can now be seen, the rotary shaft position sensor 10
according to the principles of the invention can be used to detect
and measure various parameters of the rotational movement of the
input shaft 22 including, but not limited to, the angular position
of that input shaft 22, the amount of rotation of the input shaft
22 and even the angular velocity of the rotation by means of the
sensing and interpretation of the changing effect of the magnetic
field upon the magnetically sensitive sensor 38. The present
invention can even be used to determine the direction of rotation
of the input shaft 22, that is, whether it is moving in the
clockwise or counterclockwise directions by determining whether the
influence of the magnetic flux is increasing or decreasing upon the
magnetically sensitive sensor 38.
[0022] It is to be understood that the invention is not limited to
the illustrated and described forms of the invention contained
herein. It will be apparent to those skilled in the art that
various changes may be made without departing from the scope of the
invention and the invention is not considered limited to what is
shown in the drawing and described in the specification.
* * * * *