Movement control by a metrological instrument

• US 20020059041A1
• Filed: 11/26/2001
• Published: 05/16/2002
• Est. Priority Date: 05/28/1999
• Status: Active Grant

• Current Assignee: Taylor Hobson Limited (Ametek Incorporated)
• Original Assignee: Taylor Hobson Limited (Ametek Incorporated)
• Inventors: Mills, Michael
• Granted Patent: US 6,594,532 B2
• Time in Patent Office: Days
• US Class Current: 702/127
• CPC Class Codes: G01B 21/042 Calibration or calibration artifacts G01B3/30, G01B9/02072 take precedence
• CPC Class Codes: G01B 7/008 using coordinate measuring machines
• CPC Class Codes: G01B 7/28 for measuring contours or curvatures
• CPC Class Codes: G01B 7/34 for measuring roughness or irregularity of surfaces

Abstract

A measurement probe (8) is carried by a carriage (7) movable in a first direction (X) to cause the measurement probe (8) to traverse a measurement path across a surface of an object (RS) received by a support surface (4) to provide measurement data representing variations in a second direction (Z) different from the first direction of surface features along the measurement path. The support surface (4) is movable in a third direction (Y) different from the first and second directions. Measurement of a surface area is effected by controlling the carriage (7) to cause the measurement probe to traverse a plurality of measurement paths across an area of the surface of an object mounted on the support surface and by controlling the support surface (4) to move in said third direction after each measurement path traverse. Measurement data thus obtained for a reference sphere of previously known radius is used to determine the relative orientation of the first and third directions. Measurement data provided by the measurement probe may then be corrected in accordance with any errror in the determined relative orientations of the first and third directions.

Claims

1. An instrument, comprising:

means for receiving a measurement probe;

first moving means for effecting relative movement in a first direction between a support for receiving an object and the measurement probe receiving means so as to cause the measurement probe to traverse a measurement path across a surface of a reference object of known form received by the support to provide measurement data representing variations, in a second direction different from the first direction, of surface features of the object along the measurement path;

second moving means for effecting relative movement between the support and the measurement probe receiving means in a third direction different from the first and second directions;

control means for causing the first moving means to effect said relative movement in said first direction a plurality of times and for causing the second moving means to effect said relative movement in said third direction after each movement in said first direction for causing the measurement probe to traverse a plurality of measurement paths across an area of the surface of an object mounted on the support surface and to provide measurement data representing variations in the surface along each measurement path,

characterised by processor means comprising determining means for using measurement data provided by the measurement probe and representing variations across a surface area of the reference object to determine the relative orientation of the first and third directions.

2. An instrument according to claim 1, wherein the receiving means is arranged to receive a measurement probe or a machine tool component such that the instrument is operable as a metrological instrument when the measurement probe is received by the receiving means and is operable as a machine tool when the machine tool component is received by the receiving means.

3. An instrument according to claim 2, further comprising a machine tool component comprising a cutting or polishing device.

5. An instrument according to any one of the preceding claims, further comprising means for correcting measurement data provided by the measurement probe in accordance with any error in the determined relative orientations of the first and third directions.

6. An instrument according to any one of the preceding claims, wherein the reference object is such that each measurement path forms an arc and the determining means comprises first determining means for determining a central focus or axis of each arc and second determining means for using the determined central foci or axes to determine the relative orientation of the first and third directions.

7. An instrument according to claim 6, wherein the second determining means comprises means for fitting a line through the centers of the arcs to determine the orientation of the third direction to the first direction.

8. An instrument according to claim 6, wherein the second determining means comprises means for fitting a line through the centers of the arcs in the plane containing the first and third directions to determine the orientation of the third direction to the first direction.

9. An instrument according to any one of claims 1 to 6, wherein the determining means is arranged to use the measurement data provided by the measurement probe and representing variations across the surface area of the reference object of known form to determine the relative orientation of the first and third directions and the relative orientation of the second and third directions.

10. An instrument according to claim 9 when dependent on claim 5, wherein the correcting means is operable to correct measurement data provided by the measurement probe in accordance with any error in the relative orientations of the first and third directions and any error in the relative orientations of the second and third directions.

11. An instrument according to claim 9 or 10, wherein the reference object is such that each measurement path forms an arc and the determining means comprises first determining means for determining a central focus or axis of each arc and second determining means for using the determined central foci or axes to determine the relative orientation of the first and third directions and the second and third directions.

12. An instrument according to claim 11, wherein the second determining means comprises means for fitting a line through the centers of the arcs to determine the orientation of the first and third directions.

13. An instrument according to claim 11 wherein the second determining means comprises means for fitting a first line through the centers of the arcs in the plane containing the first and third directions to determine the orientation of the third direction to the first direction and for fitting a second line through the centers of the arcs in the plane containing the second and third directions to determine the orientation of the third direction to the second direction.

14. An instrument according to any one of the preceding claims, further comprising means for pivotably supporting the measurement probe so that the measurement probe pivots about a pivot axis in response to surface variations.

15. An instrument according to any one of the preceding claims, further comprising means for correcting start and end points of each measurement path for errors in the movement of the measurement probe.

16. An instrument according to claim 14 when dependent on any one of claims 6 to 13, further comprising means for correcting start and end points of each measurement path for arcuate errors in the movement of the measurement probe.

17. An instrument according to any one of the preceding claims, wherein the processor means further comprises means for fitting a three-dimensional form to the reference object measurement data, means for comparing a characteristic of the fitted three-dimensional form to the corresponding characteristic of the reference object, means for adjusting a value representing the distance of relative movement in the third direction between measurement paths to determine the value for that distance for which the characteristic of the fitted form most closely corresponds to the characteristic of reference object.

18. An instrument according to claim 17, further comprising means for correcting measurement data in accordance with the determined value.

19. An instrument according to claim 5 or claims 6 to 18 when dependent on claim 5, further comprising means for storing calibration data corresponding to corrections made by the correcting means.

20. An instrument according to any one of the preceding claims, further comprising means for removing surface form data from measurement data provided by the measurement probe.

21. An instrument according to any one of the preceding claims, further comprising means for outputting measurement data to a user.

22. An instrument according to claim 21, wherein the output means is arranged to provide a topographical or perspective representation of the measured surface area.

23. An instrument according to claim 21 or 22 when dependent on claim 19, wherein the processor means is arranged to output measurement data to a user after correction and surface form removal.

24. An instrument according to claim 21, 22 or 23, wherein the output means comprises a display.

25. An instrument according to any one of the preceding claims, wherein the first, second and third directions are mutually orthogonal.

29. Apparatus according to claim 27 or 28, further comprising means for correcting measurement data provided by the measurement probe in accordance with any error in the relative orientations of the first and third directions.

30. Apparatus according to claim 27, 28 or 29, wherein the reference object is such that each measurement path forms an arc and the determining means comprises first determining means for determining a central focus or axis of each arc and second determining means for using the determined central foci or axes to determine the relative orientation of the first and third directions.

31. Apparatus according to claim 30, wherein the second determining means comprises means for fitting a line through the centers of the arcs to determine the orientation of the third direction to the first direction.

32. Apparatus according to claim 30, wherein the second determining means comprises means for fitting a line through the centers of the arcs in the plane containing the first and third directions to determine the orientation of the third direction to the first direction.

33. Apparatus according to claim 27, 28 or 29, wherein the determining means is arranged to use the measurement data provided by the measurement probe and representing variations across the surface area of the reference object of known form to determine the relative orientation of the first and third directions and the relative orientation of the second and third directions.

34. Apparatus according to claim 33 when dependent on claim 29, wherein the correcting means is operable to correct measurement data provided by the measurement probe in accordance with any error in the relative orientations of the first and third directions and any error in the relative orientations of the second and third directions.

35. Apparatus according to claim 33 or 34, wherein the reference object is such that each measurement path forms an arc and the determining means comprises first determining means for determining a central focus or axis of each arc and second determining means for using the determined central foci or axes to determine the relative orientation of the first and third directions and the second and third directions.

36. Apparatus according to claim 35, wherein the second determining means comprises means for fitting a line through the centers of the arcs to determine the orientation of the first and third directions and the second and third directions.

37. Apparatus according to claim 35, wherein the second determining means comprises means for fitting a first line through the centers of the arcs in the plane containing the first and third directions to determine the orientation of the third direction to the first direction and for fitting a second line through the centers of the arcs in the plane containing the second and third directions to determine the orientation of the third direction to the second direction.

62. A storage medium carrying processor implementable instructions for configuring computing apparatus to provide the processor means set out in any one of claims 1 to 42.

63. A signal carrying processor implementable instructions for configuring computing apparatus to provide the processor means set out in any one of claims 1 to 42.

4. A metrological instrument for determining surface features comprising at least one of surface form and texture, comprising:

first moving means for effecting relative movement in a first direction between a support for receiving an object and a measurement probe so as to cause the measurement probe to traverse a measurement path across a surface of an object received by the support to provide measurement data representing variations, in a second direction different from the first direction, of surface features of the object along the measurement path;

second moving means for effecting relative movement between the support and the measurement probe in a third direction different from the first and second directions;

control means for causing the first moving means to effect said relative movement in said first direction a plurality of times and for causing the second moving means to effect said relative movement in said third direction after each movement in said first direction to cause the measurement probe to traverse a plurality of measurement paths across an area of the surface of an object mounted on the support and to provide measurement data representing variations in the surface along each measurement path; and

processor means for processing the measurement data provided by the measurement probe to produce data representing features of at least one of surface form and texture of the surface,

characterised in that the processor means further comprises determining means for using measurement data provided by the measurement probe and representing variations across a surface area of a reference object of known form to determine the relative orientation of the first and third directions.

26. A metrological instrument for determining surface features comprising at least one of surface form and texture, comprising:

first moving means for effecting relative movement in a first direction between a support for receiving an object and a measurement probe so as to cause the measurement probe to traverse a measurement path across a surface of an object received by the support to provide measurement data representing variations, in a second direction different from the first direction, of surface features along the measurement path;

second moving means for effecting relative movement between the support and the measurement probe in a third direction different from the first and second directions;

control means for causing the first moving means to effect said relative movement in said first direction a plurality of times and for causing the second moving means to effect said relative movement in said third direction after each movement in said first direction to cause the measurement probe to traverse a plurality of measurement paths across an area of the surface of an object mounted on the support and to provide measurement data representing variations in the surface along each measurement path; and

processor means for processing the measurement data provided by the measurement probe to produce data representing features of at least one of surface form and texture of the surface;

characterised in that the processor means further comprises determining means for using measurement data provided by the measurement probe and representing variations across a surface area of a reference object of known form to determine any difference between a measured value of a characteristic representing the form of the reference object and the actual value of that characteristic, means for adjusting a value representing the distance moved in the third direction between measurement paths to determine the distance value for which the measured value of the characteristic most closely matches the actual value and means for using the determined distance to correct or adjust measurement data.

27. Control apparatus for controlling an instrument, comprising:

means for causing first moving means to effect relative movement in a first direction between a support for receiving an object and a measurement probe so as to cause the measurement probe to traverse a measurement path across a surface of a reference object of known form received by the support to provide measurement data representing variations, in a second direction different from the first direction, of surface features along the measurement path a plurality of times;

means for causing second moving means to effect relative movement between the support surface and the measurement probe in a third direction different from the first and second directions after each movement in said first direction to cause the measurement probe to traverse a plurality of measurement paths across an area of the surface of the reference object and to provide measurement data representing variations in the surface along each measurement path; and

processor means comprising determining means for using measurement data provided by the measurement probe and representing variations across a surface area of the reference object to determine the relative orientation of the first and third directions.

38. Apparatus according to any one of claims 27 to 37, further comprising means for correcting start and end points of each measurement path for errors in the movement of the measurement probe.

39. Apparatus according to any one of claims 27 to 37, further comprising means for correcting start and end points of each measurement path for arcuate errors in the movement of the measurement probe.

40. Apparatus according to any one of claims 27 to 39, wherein the processor means further comprises means for fitting a three-dimensional form to the reference object measurement data, means for comparing a characteristic of the fitted three-dimensional form to the corresponding characteristic of the reference object and means for adjusting a value representing the distance of relative movement in the third direction between measurement paths to determine the value for that distance for which the characteristic of the fitted form most closely corresponds to the characteristic of reference object and means for correcting measurement data in accordance with the determined value.

41. An instrument according to any one of claims 27 to 40, further comprising means for removing surface form data from measurement data provided by the measurement probe.

42. Apparatus according to any one of claims 27 to 41, further comprising output means for providing a topographical or perspective representation of the measured surface area.

28. Control apparatus for a metrological instrument for determining surface features comprising at least one of surface form and texture, comprising:

means for causing first moving means to effect relative movement in a first direction between a support for receiving an object and a measurement probe so as to cause the measurement probe to traverse a measurement path across a surface of an object received by the support to provide measurement data representing variations, in a second direction different from the first direction, of surface features along the measurement path a plurality of times;

means for causing second moving means to effect relative movement between the support and the measurement probe in a third direction different from the first and second directions after each movement in said first direction to cause the measurement probe to traverse a plurality of measurement paths across an area of the surface of an object mounted on the support and to provide measurement data representing variations in the surface along each measurement path; and

processor means for processing the measurement data provided by the measurement probe to produce data representing features of at least one of surface form and texture of the surface,

characterised in that the processor means further comprises determining means for using measurement data provided by the measurement probe and representing variations across a surface area of a reference object of known form to determine the relative orientation of the first and third directions.

43. A method of determining the relative orientation of axes of an instrument having first moving means for effecting relative movement along a first axis in a first direction between a support for receiving an object and receiving means for receiving a measurement probe so as to cause the measurement probe to traverse a measurement path across a surface of an object received by the support to provide measurement data representing variations, in a second direction different from the first direction, of surface features along the measurement path, and second moving means for effecting relative movement between the support and the measurement probe receiving means along another axis in a third direction different from the first and second directions, the method comprising the steps of:

causing the first moving means to effect said relative movement in said first direction a plurality of times and causing the second moving means to effect said relative movement in said third direction after each movement in said first direction to cause the measurement probe to traverse a plurality of measurement paths across an area of the surface of a reference object of known form mounted on the support and to provide measurement data representing variations in the surface along each measurement path; and

determining the relative orientation of the first and third directions using measurement data provided by the measurement probe and representing variations across said surface area of said reference object.

45. A method according to claim 43 or 44, further comprising correcting measurement data provided by the measurement probe in accordance with any error in the determined relative orientations of the first and third directions.

46. A method according to claim 43, 44 or 45, wherein the reference object is such that each measurement path forms an arc and the determining step comprises determining a central focus or axis of each arc and using the determined central foci or axes to determine the relative orientation of the first and third directions.

49. A method according to claim 43, 44 or 45, wherein the determining step comprises using the measurement data provided by the measurement probe and representing variations across the surface are of the reference object of known form to determine the relative orientation of the first and third directions and the relative orientation of the second and third directions.

54. A method according to any one of claims 43 to 53, further comprising correcting start and end points of each measurement path for errors in the movement of the measurement probe.

55. A method according to any one of claims 43 to 54, further comprising fitting a three-dimensional form to the reference object measurement data, comparing a characteristic of the fitted three-dimensional form to the corresponding characteristic of the reference object, adjusting a value representing the distance of relative movement in the third direction between measurement paths to determine the value for that distance for which the characteristic of the fitted form most closely corresponds to the characteristic of reference object and correcting measurement data in accordance with the determined value.

56. A method according to any one of claims 43 to 55, further comprising removing surface form data from measurement data provided by the measurement probe.

57. A method according to any one of claims 43 to 56, further comprising outputting measurement data to a user as a topographical or perspective representation of the measured surface area.

59. A method according to any one of claims 43 to 58, further comprising supplying a signal carrying measurement data correction data.

60. A method according to any one of claims 43 to 59, further comprising storing measurement data correction data as calibration data on a storage medium.

61. A method of obtaining data representing surface features comprising at least one of surface form and texture using a metrological instrument having:

first moving means for effecting relative movement in a first direction between a support for receiving an object and a measurement probe so as to cause the measurement probe to traverse a measurement path across a surface of an object received by the support to provide measurement data representing variations, in a second direction different from the first direction, of surface features along the measurement path; and

second moving means for effecting relative movement between the support and the measurement probe in a third direction different from the first and second directions, the method comprising the steps of;

causing the first moving means to effect said relative movement in said first direction a plurality of times and causing the second moving means to effect said relative movement in said third direction after each movement in said first direction to cause the measurement probe to traverse a plurality of measurement paths across an area of the surface of an object mounted on the support surface and to provide measurement data representing variations in the surface along each measurement path; and

correcting the measurement data using correction data obtained using a method in accordance with any one of claims 43 to 60.

64. A storage medium carrying processor implementable instructions for causing processing means to carry out a method in accordance with any one of claims 43 to 61.

65. A signal carrying processor implementable instructions for causing processing means to carry out a method in accordance with any one of claims 43 to 61.

44. A method of obtaining calibration data using a metrological instrument having first moving means for effecting relative movement in a first direction between a support for receiving an object and a measurement probe so as to cause the measurement probe to traverse a measurement path across a surface of an object received by the support to provide measurement data representing variations, in a second direction different from the first direction, of surface features along the measurement path, and second moving means for effecting relative movement between the support and the measurement probe in a third direction different from the first and second directions, the method comprising the steps of:

causing the first moving means to effect said relative movement in said first direction a plurality of times and causing the second moving means to effect said relative movement in said third direction after each movement in said first direction to cause the measurement probe to traverse a plurality of measurement paths across an area of the surface of a reference object mounted on the support and to provide measurement data representing variations in the surface of known form along each measurement path; and

determining the relative orientation of the first and third directions using measurement data provided by the measurement probe and representing variations across said surface area of said reference object.

47. A method according to claim 46, which comprises determining the orientation of the third direction to the first direction by fitting a line through the centers of the arcs.

48. A method according to claim 46, which comprises determining the orientation of the third direction to the first direction by fitting a line through the centers of the arcs in the plane containing the first and third directions.

50. A method according to claim 49 when dependent on claim 45, further comprising correcting measurement data provided by the measurement probe in accordance with any error in the relative orientations of the first and third directions and any error in the relative orientations of the second and third directions.

51. A method according to claim 49 or 50, wherein the reference object is such that each measurement path forms an arc and the determining step comprises determining a central focus or axis of each arc and using the determined central foci or axes to determine the relative orientation of the first and third directions and the second and third directions.

52. A method according to claim 51, which comprises fitting a line through the centers of the arcs to determine the orientation of the first and third directions and the second and third directions.

53. A method according to claim 51, which comprises fitting a first line through the centers of the arcs in the plane containing the first and third directions to determine the orientation of the third direction to the first direction and fitting a second line through the centers of the arcs in the plane containing the second and third directions to determine the orientation of the third direction to the second direction.

58. A method of calibrating a metrological instrument for determining surface features comprising at least one of surface form and texture and having:

first moving means for effecting relative movement in a first direction between a support for receiving an object and a measurement probe so as to cause the measurement probe to traverse a measurement path across a surface of an object received by the support to provide measurement data representing variations, in a second direction different from the first direction, of surface features along the measurement path; and

second moving means for effecting relative movement between the support and the measurement probe in a third direction different from the first and second directions, the method comprising the steps of;

causing the first moving means to effect said relative movement in said first direction a plurality of times and causing the second moving means to effect said relative movement in said third direction after each movement in said first direction to cause the measurement probe to traverse a plurality of measurement paths across an area of the surface of a reference object of known form mounted on the support and to provide measurement data representing variations in the surface along each measurement path;

determining means using measurement data provided by the measurement probe and representing variations across said surface area of said reference object of known form any difference between a measured value of a characteristic representing the form of the reference object and the actual value of that characteristic; and

adjusting a value representing the distance moved in the third direction between measurement paths to determine the distance value for which the measured value of the characteristic most closely matches the actual value and using the determined distance value to correct or adjust measurement data.