A displacement sensor for providing an indication of the position of a first body relative to a second body, the first body being displaceable relative to the second body in a displacement direction. The sensor is composed of: two magnets that are spaced from one another in the displacement direction to define therebetween a region containing a magnetic field; a magnetic field sensing element mounted in the region; and components for coupling at least one of the magnets to one of the bodies and the magnetic field sensing element to the other of the bodies to produce a relative displacement between the at least one magnet and the magnetic field sensing element in the displacement direction in response to displacement of the first body relative to the second body

Bahr, Joseph K.

Johnson, Mont A.

NASA Technical Reports Server

(12) United States Patent 
Bahr et al. 
(54) DISPLACEMENT SENSOR CONTAINING 
MAGNETIC FIELD SENSING ELEMENT 
BETWEEN A PAIR OF BIASED MAGNETS 
MOVABLE AS A UNIT 
(75) Inventors: Joseph K. Bahr, Elkhart, IN (US); 
Mont A. Johnson, Perry, UT (US) 
(73) Assignee: Alliant Techsystems Inc., Edina, MN 
(US) 
( * ) Notice: Subject to any disclaimer, the term of this 
patent is extended or adjusted under 35 
U.S.C. 154(b) by 0 days. 
(21) Appl. No.: 09/961,211 
(22) Filed: Sep. 21, 2001 
Related U.S. Application Data 
(60) Provisional application No. 601234,341, filed on Sep. 22: 
2000. 
(51) Int. Cl? ............................ G01B 7/00; GOlB 7/14; 
(52) U.S. C1. ................................ 324/207.2; 3241207.24 
(58) Field of Search ....................... 3241207.13, 207.15, 
GOlD 5/12 
3241207.2-207.24, 207.26, 251; 3351205-207; 
338132 H; 73DIG. 3, 722, 728, 735; 200182 E, 
83 L 
(56) References Cited 
U.S. PATENT DOCUMENTS 
3,777,273 A 1211973 Baba et al. 
4,361,805 A 1111982 Narimatsu et al. 
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20 
(io) Patent No.: 
(45) Date of Patent: 
US 6,670,805 B1 
Dec. 30,2003 
4,535,289 A 811985 Abe et al. 
4,665,362 A 511987 Abel et al. 
4,810,965 A * 311989 Fujiwara et al. ....... 3241207.22 
4,837,539 A * 611989 Baker ......................... 3351207 
5,231,352 A * 711993 Huber ................... 3241207.24 
5,313,182 A 511994 Blache 
5,325,869 A 711994 Stokes 
5,493,216 A 211996 Asa 
5,521,497 A * 511996 Schneider et al. ..... 3241207.22 
5,617,023 A 411997 Skalski 
5,670,876 A 911997 Dilger et al. 
6,060,969 A * 512000 Hufgard et al. ............. 3351207 
6,411,081 B1 * 6/2002 Spellman ............... 324/207.21 
* cited by examiner 
Primary Examinerqerard R. Strecker 
(74) Attorney, Agent, or Firm-TraskBritt 
(57) ABSTRACT 
A displacement sensor for providing an indication of the 
position of a first body relative to a second body, the first 
body being displaceable relative to the second body in a 
displacement direction. The sensor is composed of  two 
magnets that are spaced from one another in the displace- 
ment direction to define therebetween a region containing a 
magnetic field; a magnetic field sensing element mounted in 
the region; and components for coupling at least one of the 
magnets to one of the bodies and the magnetic field sensing 
element to the other of the bodies to produce a relative 
displacement between the at least one magnet and the 
magnetic field sensing element in the displacement direction 
in response to displacement of the first body relative to the 
second body. 
12 Claims, 2 Drawing Sheets 
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https://ntrs.nasa.gov/search.jsp?R=20080007456 2019-08-30T03:19:39+00:00Z
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FIG. 2 
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FIG. 3 
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U S .  Patent Dec. 30,2003 Sheet 2 of 2 US 6,670,805 B1 
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FIG. 5 
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FIG. 6 
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1 
DISPLACEMENT SENSOR CONTAINING 
MAGNETIC FIELD SENSING ELEMENT 
BETWEEN A PAIR OF BIASED MAGNETS 
MOVABLE AS A UNIT 
CROSS-REFERENCE TO RELATED 
APPLI CAT1 ON 
6,670,805 B3 
The benefit of priority is claimed of U.S. Provisional 
Application No. 601234,341 filed in the U.S. Patent & 
Trademark Office on Sep. 22,2000, the complete disclosure 
of which is incorporated herein by reference. 
GOVERNMENT LICENSE CLAUSE 
The U.S. Government has a paid-up license in this inven- 
tion and the right in limited circumstances to require the 
patent owner to license others on reasonable terms as 
provided for by the terms of contract NAS 8-97238 with the 
National Aeronautics and Space Administration (NASA). 
BACKGROUND OF THE INVENTION 
The present invention relates to displacement, or position, 
sensors of the type having a movable element capable of 
being placed in contact with a component whose displace- 
ment is to be monitored, and particularly relates to displace- 
ment sensors constructed to monitor small amplitude dis- 
placements of the order of a fraction of an inch. 
Displacement sensors of the type contemplated by the 
present invention are useful for a variety of purposes, one of 
which is the monitoring of movements experienced by parts 
of a structure for testing purposes. 
BRIEF SUMMARY OF THE INVENTION 
The invention provides a displacement sensor for provid- 
ing an indication of the position of a first body relative to a 
second body, the first body being displaceable relative to the 
second body in a displacement direction. The sensor com- 
prises two magnets that are spaced from one another in the 
displacement direction to define therebetween a region con- 
taining a magnetic field, with a magnetic field sensing 
element mounted in the region. The sensor further comprises 
means for coupling at least one of the magnets to one of the 
bodies and the magnetic field sensing element to the other of 
the bodies to produce a relative displacement between the at 
least one magnet and the magnetic field sensing element in 
the displacement direction in response to displacement of 
the first body relative to the second body. 
BRIEF DESCRIPTION OF THE SEVERAL 
VIEWS OF THE DRAWING 
The accompanying drawings are incorporated in and 
constitute a part of the specification. The drawings, together 
with the general description given above and the detailed 
description of the preferred embodiments and methods given 
below, serve to explain the principles of the invention. In 
such drawings: 
FIGS. 1, 2, and 3 are simplified pictorial views of three 
embodiments of the present invention; 
FIG. 4 is a cross-sectional view of a preferred embodi- 
ment of the invention; 
FIG. 5 is a detailed view of one component of the 
embodiment of FIG. 4; and 
FIG. 6 is a partial cross-sectional view of a further 
embodiment of the invention. 
DETAILED DESCRIPTION OF THE 
INVENTION 
Reference will now be made in detail to the presently 
preferred embodiments and methods of the invention. It 
2 
should be noted, however, that the invention in its broader 
aspects is not limited to the specific details, representative 
devices and methods, and illustrative examples shown and 
described in this section in connection with the preferred 
s embodiments and methods. The invention according to its 
various aspects is particularly pointed out and distinctly 
claimed in the attached claims read in view of this 
specification, and appropriate equivalents. 
It is to be noted that, as used in the specification and the 
10 appended claims, the singular forms “a,” ‘‘an,’’ and “the” 
include plural referents unless the context clearly dictates 
otherwise. 
FIG. 1 shows a first embodiment of the invention com- 
posed of a housing 12 which contains a first permanent 
magnet 14, a second permanent magnet 16 and a Hall effect 
sensor 18 interposed between magnets 14 and 16. Magnet 14 
and sensor 18 are fixed in position within housing 12, while 
magnet 16 is mounted to be movable along the longitudinal 
axis of housing 12, in the direction of arrows 20. As is 
2o apparent from the drawing, magnet 16 is movable only in the 
direction of arrows 20. 
A compression spring 22 is installed between magnet 16 
and sensor 18 in order to bias magnet 16 away from sensor 
18. 
Magnets 14 and 16 are installed so that their magnetiza- 
tion directions are opposite to one another in order to 
produce a magnetic field at the location of sensor 18 that will 
vary as magnet 16 moves toward and away from magnet 14. 
Housing 12 is fixed to a body 26 which includes a 
movable component whose displacement in the direction of 
arrows 20 relative to body 26 is to be measured. This 
component or an extension 28 thereof is coupled to the end 
of magnet 16 that is remote from sensor 18. Extension 28 
35 may simply be in contact with magnet 16 to exert a pushing 
force thereon. Magnet 16 is held in position relative to 
extension 28 by the action of spring 22 as well as by the 
magnetic repelling force existing between magnets 14 and 
16. Any movement of the part whose displacement is to be 
4o measured in the direction of arrows 20 produces a corre- 
sponding movement of magnet 16, thereby varying the 
distance between magnets 14 and 16. This produces a 
corresponding variation in the intensity of the magnetic field 
at the location of sensor 18. Sensor 18 produces a magnetic 
45 field sensing signal indicative of the distance between mag- 
nets 14 and 16, and thus indicative of the displacement of the 
part being monitored of extension 28. 
In the embodiment illustrated in FIG. 2, magnet 16 is 
replaced by a permanent magnet 30 which is fixed in 
50 position in housing 12, while sensor 18 is mounted to be 
movable within housing 12 in the direction of arrows 20. 
Sensor 18 is connected to a linkage, here in the form of a rod 
32, which extends through a passage formed in magnet 30. 
The end of rod 32 that is remote from sensor 18 is provided 
5s with an enlarged contact head 34 which engages extension 
28 of body 26. In order to maintain contact head 34 in 
contact with extension 28, a compression spring 36 is 
provided between magnet 30 and head 34. In this 
embodiment, both magnets 14 and 30 are fixed in position 
60 in housing 12, so that the distance therebetween is fixed, and 
the configuration of the magnetic field between magnets 14 
and 30 is such that the response of sensor 18 to its displace- 
ment between magnets 14 and 30 will be substantially linear 
over much of its displacement range. 
In place of, or in addition to, spring 36, contact head 34 
can be provided with a magnet and extension 28 made in 
whole or in part of a magnetizable material. Alternatively, 
25 
3o 
65 
US 6,670,805 B1 
3 4 
extension 28 can include a magnet and head 34 made of a 
magnetizable material. In either case, head 34 will be 
maintained in contact with extension 28 by a magnetic 
attractive force. According to a further possibility, spring 36 
can be installed between magnet 14 and sensor 18. 
In the embodiment shown in FIG, 3, housing 12 is 
are joined together by a suitable connecting element 44, such 
conventional permanent magnetic material, it having been 
noted that the particular field strength employed will effect 
the magnitude of the output of sensor 18, but not the linearity 
of the magnetic field variation. 
In order to improve the response of a displacement sensor 
according to the present invention, use can be made of Hall 
magnets with which they are associated, thus taking into 
account the fact that the magnetic field of any magnet varies 
5 
provided with an assembly of two magnets 40 and 42 which effect that are temperature for the 
as a rod' Magnets 40 and 42 are shown having polarities (N roughly linearly with temperature, The Hall effect sensor 
and arranged end-to-end a common longitudina1 lo may be programmed to for this temperature 
axis, with the polarities Of magnet 40 being arranged OPP0- variation in order to maintain linearity Over a reasonable 
site to the polarities of magnet 42. Magnets 40 and 42 and temperature range, for example, of -10 to 500 C, 
element 44 are installed for movement as a unit within While the description above refers to particular embodi- 
housing 12 in the direction of arrows 20, while sensor 18 is ments of the present invention, it will be understood that 
fixed in position with respect to housing 12. Magnet 42 15 many modifications may be made without departing from 
carries a contact head 46 which bears against extension 28 the spirit thereof, The accompanying claims are intended to 
and the assembly of magnets 40 and 42 and element 44 is cover such modifications as would fall within the true scope 
biased toward extension 28 by a compression spring 48 and spirit of the present invention. 
located between the base of housing 12 and magnet 40. This The presently disclosed embodiments are, therefore, to be 
embodiment operates in much the same manner as the 2o considered in all respects as illustrative and not restrictive, 
embodiment of FIG. 2 in that the spacing between magnets the scope of the invention being indicated by the appended 
40 and 42 is fixed and the position of sensor 18 in the claims, rather than the foregoing description, and all changes 
magnetic field between those magnets will vary as a function which come within the meaning and range of equivalency of 
of the displacement of extension 28. the claims are therefore intended to be embraced therein. 
Two forms of construction of the embodiment of FIG. 3 25 What is is: 
are illustrated in FIGS, 4-6, which also illustrate the signal- 
carrying conductors 50 that are connected to 18 and 
that extend through a passage in housing 12. Since placement direction, the displacement comprising: 
'. A for providing an indication Of 
to a fixed location, the body the position Of a body 
being displaceable relative to the fixed location in a dis- 
first and second magnets arranged along a longitudinal 
axis parallel to the displacement direction and spaced 
from one another by a fixed distance along the longi- 
tudinal axis to define therebetween a region containing 
a magnetic field, the first and second magnets each 
nal axis, the polarities of the first magnet arranged 
opposite to the polarities of the second magnet; 
a magnetic field sensing element mounted in the region 
between the first and second magnets; and 
a biasing member positioned and oriented to provide a 
bias against at least one of the first and second magnets 
toward the body in a direction parallel to the displace- 
ment direction, 
sensor 18 is fixed in position relative to housing 12, the 
feeding of conductors 50 out of housing 12 is a simple 30 
matter. 
The embodiment shown in FIGS. 4 and 5 includes a 
simple support structure 43 to hold sensor 18 at the desired 
housing 12 for supporting spring 48. 
The embodiment shown in FIG. 6 is functionally similar 
to that of the embodiment of FIGS. 4 and 5. However, in the 
embodiment of FIG. 6, the housing is composed of a main 
body 52 and an end cap 54 which is screwed into a threaded 4o 
passage in body 52, with a seal 56 interposed between body 
52 and cap 54 in order to hermetically seal the region 
enclosed by body 52. An actuator 58 extends through a 
position and a retaining clip 51 installed at the base of the 35 having respective polarities arranged on the longitudi- 
passage in the front end Of the housing, which passage is 
sealed by two sealing rings 60 which surround actuator 58. 45 
wherein the first and second magnets are mutually posi- 
tioned with an element extending therebetween so as to 
Actuator 58 is coupled to magnets 40 and 42 and the outer 
end of actuator 58 can be given any desired configuration in 
order to contact the component whose displacements are to 
be monitored. member. 
be displaceable as a unit in response to displacement of 
the body in the displacement direction relative to the 
fixed location against the bias provided by the biasing 
2. The displacement sensor according to claim 1, wherein 
made to operate Over a linear range by an appropriate a mechanical force sufficient to maintain contact between 
selection ofthe spacing between the two Permanent magnets the at least one of the first and second magnets and the body. 
and the physical size, or dimensions, of each magnet. 3. The displacement sensor according to claim 1, wherein 
are particularly useful for measuring displacements which 4. The displacement sensor according to claim 1, wherein 
occur over a small range, one application being for measur- the first and second magnets are permanent magnets. 
ing displacements that extend over a range of the order of 0.1 5 .  The displacement sensor according to claim 1, wherein 
inch. According to one preferred embodiment of the the element allows for the relative displacement between the 
invention, use can be made of magnets 40 and 42, each 60 first and second magnets and the magnetic field sensing 
having a diameter of 0.25 inch and a thickness of 0.06 inch element to occur only in the displacement direction. 
with a spacing between the magnets of the order of 0.2 inch. 6. The displacement sensor according to claim 1, wherein 
With this arrangement, it was found experimentally that the the biasing member includes a spring for urging the first and 
magnetic field over a displacement range of 0.01 inch at a second magnets toward the body. 
location midway between the magnets varied linearly with a 65 7. The displacement sensor according to claim 2, wherein 
deviation of less than 0.5% Each magnet 40, 42 can have a the biasing member includes a spring for urging the first and 
magnetic field strength that is typical for magnets made of second magnets toward the body. 
In Preferred embodiments of the Present invention, and SO 
particularly those illustrated in FIGS. 2-6, sensor 18 can be the biasing member is configured to provide a magnetic or 
Displacement sensors according to the present invention ss the magnetic field sensing element is a Hall effect sensor. 
US 6,670,805 B1 
5 6 
8. The displacement sensor according to claim 3, wherein 11. The displacement sensor according to claim 1, 
the biasing member includes a spring for urging the first and wherein at least one of the first and second magnets includes 
second magnets toward the body. a contact head configured and located to contact the body. 
9. The displacement sensor according to claim 4, wherein 12. The displacement sensor according to claim 1, 
the biasing member includes a spring for urging the first and s wherein the magnetic sensing element is attached to an 
second magnets toward the body. inside of a housing in which the first and second magnets are 
wherein the biasing member includes a spring for urging the 
10. The displacement sensor according to claim 5,  positioned to move along the longitudinal axis. 
first and second magnets toward the body. * * * * *  


Displacement sensor containing magnetic field sensing element between a pair of biased magnets movable as a unit

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