Optical Linear and Rotation Displacement Sensor

• US 20090059206A1
• Filed: 08/30/2008
• Published: 03/05/2009
• Est. Priority Date: 08/30/2007
• Status: Active Grant

• Current Assignee: Hottinger Bruel & Kjaer Incorporated
• Original Assignee: MicroStrain, Inc. (Spectris PLC)
• Inventors: Arms, Steven W., Churchill, David L.
• Granted Patent: US 7,952,721 B2
• Time in Patent Office: Days
• US Class Current: 356/72
• CPC Class Codes: A61B 2017/3405 using mechanical guide means
• CPC Class Codes: A61B 2090/062 penetration depth
• CPC Class Codes: A61H 2201/5064 Position sensors
• CPC Class Codes: A61H 2201/5069 Angle sensors
• CPC Class Codes: A61H 39/086 Acupuncture needles
• CPC Class Codes: G01B 11/002 for measuring two or more coordinates
• CPC Class Codes: G01B 11/02 for measuring length, width or thickness G01B11/08 takes precedence
• CPC Class Codes: G01B 11/26 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: G01B 7/02 for measuring length, width or thickness G01B7/004, G01B7/12 take precedence

Abstract

A system includes a measuring tool, a fixture, and a rotatable target. The measuring tool includes a light source, an imaging device, and an electronic circuit. The fixture allows the rotatable target to rotate about an axis. The rotatable target includes a surface having microscopic asperities. The imaging device is mounted to provide a sequence of images derived from said microscopic asperities. The electronic circuit is connected to the imaging device for measuring rotation of the rotatable target from the sequence of images.

Claims

1. A system, comprising a measuring tool, a fixture, and a rotatable target, wherein said measuring tool includes a light source, an imaging device, and an electronic circuit, wherein said fixture allows said rotatable target to rotate about an axis, wherein said rotatable target includes a surface having microscopic asperities, wherein said imaging device is mounted to provide a sequence of images derived from said microscopic asperities, wherein said electronic circuit is connected to said imaging device for measuring rotation of said rotatable target from said sequence of images.

2. A system as recited in claim 1, wherein said light source is coherent.

3. A system as recited in claim 1, wherein said light source shining on said surface having said microscopic asperities provides a speckle pattern and wherein each image of said sequence of images includes said speckle pattern.

4. A system as recited in claim 1, wherein said electronic circuit includes a processor.

5. A system as recited in claim 1, wherein said electronic circuit includes calibration to convert a signal derived from said sequence of images to an angle.

6. A system as recited in claim 5, further comprising a memory device storing at least one from the group consisting of calibration coefficients and a look-up table, wherein said calibration is provided by said memory device.

7. A system as recited in claim 1, further comprising a reference feature on said target.

8. A system as recited in claim 7, wherein said reference feature includes a magnet.

9. A system as recited in claim 8, further comprising a magnetic sensor for determining absolute motion.

10. A system as recited in claim 9, wherein said magnetic sensor includes a Hall effect sensor.

11. A system as recited in claim 7, wherein said reference feature includes a mark.

12. A system as recited in claim 11, wherein said rotatable target includes an adhesive label, wherein said mark is on said label.

13. A system as recited in claim 11, further comprising a plurality of said marks.

14. A system as recited in claim 13, wherein said plurality of marks have different spacings there between.

15. A system as recited in claim 11, wherein said imaging device detects presence of said mark to correct for accumulated errors in output.

16. A system as recited in claim 1, wherein said rotatable target is constrained to translation along said axis and rotation about said axis.

17. A system as recited in claim 1 further comprising a circuit for determining at least one from the group consisting of angular velocity and angular acceleration of said target.

18. A system as recited in claim 1, wherein said target includes an actuator rod.

19. A system as recited in claim 18, wherein said actuator rod is an actuator rod of at least one from the group consisting of a hydraulic cylinder, a pneumatic cylinder, and a motor.

20. A system as recited in claim 1, wherein said target includes a portion of at least one from the group consisting of a string pot and a tape measure.

21. A system as recited in claim 1, wherein said target includes a portion of an acupuncture needle.

22. A system as recited in claim 1, wherein said target includes a portion of at least one from the group consisting of a wire, a chord, an optical cable, a string, a needle, and a pipe.

23. A system as recited in claim 1, further comprising a controller for controlling movement of said target, wherein data derived from said measuring tool is provided as feedback to said controller.

24. A system as recited in claim 1, further comprising a connector.

26. A system as recited in claim 1, wherein said measuring tool is connected to said fixture.

27. A system as recited in claim 26, wherein said fixture includes an opening for light from said light source to travel from said light source to said surface and for reflected light to enter said imaging device.

28. A system as recited in claim 1, wherein said imaging device is located a fixed distance from said moveable target.

29. A system as recited in claim 1, wherein said fixture allows said rotatable target to rotate about a first axis and to rotate about a second axis perpendicular to said first axis.

30. A system as recited in claim 1, wherein said fixture allows said rotatable target to translate along said axis.

31. A system as recited in claim 1, wherein said electronic circuit is programmed to use said rotation measurement to calculate another parameter.

32. A system as recited in claim 31, wherein said other parameter includes separation distance.

25. A system as recited in claim 25, wherein said connector includes pins for power, ground and digital data out.

33. A system, comprising a measuring tool, a first fixture, a moveable target, and a first axis, wherein said measuring tool includes a light source, an imaging device, and an electronic circuit, wherein said first fixture constrains said moveable target to at least one from the group consisting of translation along said first axis and rotation about said first axis, wherein said moveable target includes a surface having microscopic asperities, wherein said imaging device is mounted to provide a sequence of images derived from said microscopic asperities, wherein said electronic circuit is connected to said imaging device for measuring movement of said moveable target from said sequence of images.

34. A system as recited in claim 33, wherein said first fixture constrains said moveable target to translation along said first axis.

35. A system as recited in claim 33, wherein said first fixture constrains said moveable target to rotation about said first axis.

36. A system as recited in claim 33, wherein said first fixture constrains said moveable target to translation along said first axis and rotation about said first axis.

37. A system as recited in claim 33, further comprising a second fixture, wherein said first fixture is mounted on said second fixture, wherein said second fixture constrains said moveable target to translation along a second axis perpendicular to said first axis.

38. A system as recited in claim 33, wherein said target includes a portion of a roll of a material.

39. A system as recited in claim 38, wherein said material includes at least one from the group consisting of paper, metal, and plastic.

40. A system as recited in claim 33, wherein said target includes an actuator rod.

41. A system as recited in claim 40, wherein said actuator rod is an actuator rod of at least one from the group consisting of a hydraulic cylinder, a pneumatic cylinder, and a motor.

42. A system as recited in claim 33, wherein said target includes a portion of at least one from the group consisting of a string pot and a tape measure.

43. A system as recited in claim 33, wherein said target includes a portion of an acupuncture needle.

44. A system as recited in claim 33, wherein said target includes a portion of at least one from the group consisting of a wire, a chord, an optical cable, a string, a needle, and a pipe.

45. A system as recited in claim 33, wherein said measuring tool provides measurement of more than two degrees of freedom.

47. A system as recited in claim 45, wherein said elongate member includes one from the group consisting of a wire, a thread, a filament, a needle, a catheter, a tube, a pipe, a rod, and a tape.

48. A system as recited in claim 45, wherein said needle is an acupuncture needle.

49. A system as recited in claim 45, wherein said elongate member includes wire, further comprising a plurality of said wires, wherein said measuring tool measures at least one from the group consisting of translation along more than one axis and rotation around more than one axis.

50. A system as recited in claim 48, wherein said plurality of wires are non-parallel with respect to each other.

51. A system as recited in claim 45, wherein said surface has microscopic asperities, wherein said imaging device is mounted to provide a sequence of images derived from said microscopic asperities.

52. A system as recited in claim 45, wherein said elongate member has a length to width ratio of more than ten to one.

53. A system as recited in claim 45, wherein said elongate member has a length to width ratio of more than one hundred to one.

46. A system, comprising an elongate member and a measuring tool, wherein said measuring tool includes a light source, an imaging device, and an electronic circuit, wherein said elongate member has a surface, wherein said imaging device is mounted to image said surface, wherein said measuring tool measures at least one from the group consisting of translation and rotation of said elongate member from said images of said surface.

54. A system, comprising at least one fixture, a plurality of measuring tools and a plurality of moveable targets, wherein each said measuring tool includes a light source and an imaging device, wherein each said moveable target includes a surface having microscopic asperities, wherein each said imaging device is mounted to provide a sequence of images derived from said microscopic asperities, wherein said at least one fixture constrains movement of said moveable targets relative to said imaging devices for measuring movements of said moveable targets from said sequences of images.