Optical displacement sensor and method for sensing linear displacements in a shock absorber

• US 5,371,598 A
• Filed: 10/07/1993
• Issued: 12/06/1994
• Est. Priority Date: 10/07/1993
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Xue, Jie, Gerbetz, Kenneth S., Ghaem, Sanjar
• Primary Examiner(s): Evans, F. L.
• Application Number:
  US08/132,982
• Time in Patent Office: 425 Days
• Field of Search: 356/373, 356/374, 356/375, 250/222.1, 250/231.1, 33/707
• US Class Current: 356/617
• CPC Class Codes: G01D 5/347 using displacement encoding scales

Abstract

A device and method for sensing linear displacements between a first member (101) and a second member (102) on a same axis (108). The second member (102) substantially encompasses the first member (101). To sense the linear displacements, an optical code pattern (103) is placed on the first member (101) and an encircling optical sensor (104) is placed on the second member (102). The encircling optical sensor (104) includes light transmitting (106) and receiving (107) paths that transmit and receive light to/from the optical code pattern (103). The light received from the optical code pattern (103) is sent to a displacement calculation device (105) that determines the linear displacement of the first member (101) with respect to the second member (102). Using this technique, linear displacements of the first member (101) with respect to the second member (102) can be accurately measured in high temperature environments without adversely affecting electrical components associated with the displacement calculation device (105).

Claims

1. A device for sensing linear displacements between a first member and a second member, wherein the first member has a non-planar geometric shape, wherein the second member has a substantially similar non-planar geometric shape as the first member, wherein, from a first axis, the second member substantially encompasses the first member, and wherein the sensed linear displacements are along a first axis, the device comprises:

an optical code pattern disposed on a non-planar surface of the first member, wherein the optical code pattern at least partially encircles the first axis;

an encircling optical sensor arranged on the second member, wherein the encircling optical sensor at least partially encircles the optical code pattern, wherein the encircling optical sensor senses the optical code pattern, and wherein the encircling optical sensor includes;

at least one light transmitting path, wherein the at least one light transmitting path has a nonlinear geometry, and emits light on the optical code pattern to reflect off the optical code pattern to produce, at least a portion of the light off of the optical code pattern;

a plurality of light receiving paths, wherein each of the plurality of light receiving paths has a nonlinear geometry, and wherein at least one of the light receiving paths receives the at least a portion of the light reflected off the optical code pattern emitted from the at least one light transmitting path; and

a displacement calculation device, operably coupled to the encircling optical sensor, wherein the displacement calculation device calculates the displacement of the first member with respect to the second member.

2. A sensing device in accordance with claim 1 wherein the at least one light transmitting path comprises a fiber-optic waveguide.

3. A sensing device in accordance with claim 1 wherein each of the plurality of light receiving paths comprise fiber-optic waveguides.

4. A sensing device in accordance with claim 1 wherein the at least one light transmitting path and the plurality of light receiving paths are positioned on a common substrate.

5. A sensing device in accordance with claim 4 wherein each of the at least one light transmitting path and the plurality of light receiving paths are comprised of a first material and the common substrate is comprised of a second material, wherein the first and second materials have a different refractive index.

6. A sensing device in accordance with claim 5 wherein each of the at least one light transmitting path and the plurality of light receiving paths are formed by a groove on the substrate filled with a material comprising a molded plastic material.

7. A sensing device in accordance with claim 6 wherein the molded plastic material comprises a polysulphone plastic material.

8. A sensing device in accordance with claim 6 wherein the molded plastic material and the common substrate are formed with materials having substantially a same thermal coefficient of expansion.

9. A sensing device in accordance with claim 1 wherein said encircling optical sensor is constructed of a horseshoe geometry.

10. A sensing device in accordance with claim 1 wherein the optical code pattern comprises a Gray code.

11. A sensing device in accordance with claim 1 wherein each of the plurality of light receiving paths are formed of a substantially tubular geometry, wherein opposite the optical code pattern on the first member the substantially tubular geometry commences at a first cross-sectional area and progresses to a smaller cross-sectional area.

12. A sensing device in accordance with claim 1 wherein the device is mounted in a shock absorber.

13. A sensing device in accordance with claim 1 wherein the first member has a cylindrical shape.

14. A device for sensing linear displacements between a first member and a second member, wherein the first member has a non-planar geometric shape, wherein the second member has a substantially similar non-planar geometric shape as the first member, wherein, from a first axis, the second member substantially encompasses the first member, and wherein the sensed linear displacements are along a first axis, the device comprises:

an optical code pattern disposed on a non-planar surface of the first member, wherein the optical code pattern at least partially encircles the first axis;

an encircling optical sensor arranged on the second member, wherein the encircling optical sensor at least partially encircles the optical code pattern, wherein the encircling optical sensor senses the optical code pattern, and wherein the encircling optical sensor includes;

at least one light transmitting path, wherein the at least one light transmitting path has a nonlinear geometry, and wherein a termination of the at least one light transmitting path emits light on the optical code pattern to reflect, non-normal to the optical code pattern to produce, at least a portion of the light off of the optical code pattern, and wherein the termination has a smaller cross-sectional area than a cross-sectional area of the at least one light transmitting path;

a plurality of light receiving paths, wherein each of the plurality of light receiving paths has a nonlinear geometry, and wherein at least one of the light receiving paths receives the at least a portion of the light reflected off the optical code pattern emitted from the at least one light transmitting path; and

a displacement calculation device, operably coupled to the encircling optical sensor, wherein the displacement calculation device calculates the displacement of the first member with respect to the second member dependent on the transmission of light from the at least one light transmitting path, including the optical code pattern to at least one of the plurality of light receiving paths.

15. A method for sensing linear displacements between a first member and a second member, wherein the first member has a non-planar geometric shape, wherein the second member has a substantially similar non-planar geometric shape as the first member, wherein, from a first axis, the second member substantially encompasses the first member, and wherein the linear displacements are along the first axis, the method comprises the steps of:

disposing an optical code pattern on a non-planar surface of the first member, wherein the optical code pattern at least partially encircles the first axis and has a substantially similar non-planar surface as the first member;

positioning an encircling optical sensor on the second member to at least partially encircle the optical code pattern;

transmitting, by the encircling optical sensor, a light beam onto the optical code pattern;

receiving, by the encircling optical sensor, a reflected portion of the light beam; and

calculating the linear displacement of the first member with respect to the second member based on the reflected portion of the light.

16. A device for indicating an axial position of a shaft, the device comprising:

a coded longitudinal member principally oriented coincident with a first axis, said coded longitudinal member having a digitized pattern disposed thereon, wherein the digitized pattern comprises a plurality of tracks disposed along a portion of an outer surface of said coded longitudinal member, wherein the outer surface extends radially surrounding the first axis, wherein each of the plurality of tracks includes a plurality of reflective portions interdigitated with a plurality of non-reflective portions, the tracks extending along a portion of the outer surface longitudinally oriented with the first axis;

optical transceptive means oriented at least partially circumferentially surrounding said coded longitudinal member, said optical transceptive means including at least a light transmission path, and a plurality of light reception paths, wherein the plurality of light reception paths are positioned opposite the plurality of tracks such that a transception path is completed between the at least a light transmission path, the plurality of tracks of the digitized pattern, and the plurality of light reception paths; and

a displacement calculation device, operably coupled to the optical transceptive means, wherein said displacement calculation device calculates the displacement of the optical transceptive means along said coded longitudinal member dependent on the transception of light between the at least a light transmission path, the plurality of tracks of the digitized pattern, and the plurality of light reception paths.