Optical coordinate measuring machines and optical touch probes

• US 5,825,666 A
• Filed: 06/07/1995
• Issued: 10/20/1998
• Est. Priority Date: 06/07/1995
• Status: Expired due to Term

• Current Assignee: Visicon Technologies, Inc (MKS Instruments Incorporated)
• Original Assignee: Daniel Freifeld
• Inventors: Freifeld, Daniel
• Primary Examiner(s): Cosimano, Edward R.
• Application Number:
  US08/482,978
• Time in Patent Office: 1,231 Days
• Field of Search: 33/503, 33/504, 33/556, 33/559, 33/560, 33/561, 250/559.19, 250/559.22, 279/128, 356/2, 356/375, 356/376, 364/559, 364/560, 483/59, 382/201
• US Class Current: 702/153
• CPC Class Codes: G01B 11/005 coordinate measuring machines
• CPC Class Codes: G01B 11/007 feeler heads therefor
• CPC Class Codes: Y10T 279/23 with magnetic or electrostatic means
• CPC Class Codes: Y10T 483/1809 Matrix including means to latch tool

Abstract

The optical touch probe has a first target at the distal end thereof on the contact element in a standard probe. The probe is mounted to a video camera of an optical coordinate measuring machine to image the target on the camera. Movement and position of the target in the X and Y coordinates is indicated by the machine'"'"'s computer image processing system. A second target is mounted to the proximal end of the probe and indicates movement and position in the Z coordinate. The second target may obscure a photodetector, but preferably is parfocused on the camera by light beam parallel to the X,Y plane. Preferably there are two second targets illuminated by orthogonal beams parallel to the X,Y plane. Rotation around the Z axis then may be calculated by the computer when star probes are used. Auto changing racks are also disclosed for holding multiple probes, a probe holder, and lenses for selective mounting on the camera.

Claims

1. A coordinate measuring machine comprising:

A) a video based coordinate measuring system comprising;

a) a video camera producing a video signal having a first optical axis and a focal plane where an image of a part to be measured is focused, said camera being mounted to move with respect to said part to be measured and generating an image in the form of a plurality of pixels; and

b) a video monitor responsive to said video signal connected to said video camera for displaying an image of said part being on said focal plane; and

,

B) a touch probe mounted on support structure which allows it to be imaged by said video camera in said focal plane, said touch probe being adapted for mounting to said video camera and comprising;

a) a contact tip;

b) a target mounted to said contact tip in the field of view of said video camera, said video signal including an image of said target, said target being adapted to be imaged on said focal plane, the image of said target changing position in said focal plane in response to movement of said touch probe relative to said video camera from a central pixel having a first set of x and v coordinates; and

c) an electronic circuit for analyzing said video signal to determine changes in the coordinates of the position of said target relative to said video camera.

2. A coordinate measuring machine as in claim 1, said probe further comprising:

d) a second target on said probe, and

e) a light source outputting light along a second optical axis perpendicular to said first optical axis for parfocal imaging of said second target on said focal plane to enable said video signal to measure coordinates, along a z axis of said tip in a direction orthogonal to said x and y axes.

3. A coordinate measuring machine comprising:

A) an optical image to electronic signal converter comprising a focal plane and outputting a video signal;

B) first imaging optics having a first optical axis for focusing an object plane on said focal plane;

C) an optical touch probe mounted on support structure which allows said probe to be imaged by said electronic signal converter, said touch probe being adapted for mounting to said machine and comprising;

a) a first target located within the field of view of said focusing optics and substantially in said object plane,

b) a second target mounted to said probe, and

c) second imaging optics having a second optical axis transverse to said first optical axis for parfocal imaging of said second target on said focal plane, said video signal including an image of said first and second targets; and

D) an electronic circuit analyzing said video signal to determine changes in the coordinates of the position of said second target.

4. A machine as in claim 3 wherein said second target is located substantially on said first optical axis.

5. A machine as in claim 3 wherein said signal converter is the camera of an optical coordinate measuring machine.

6. A machine as in claim 3 wherein at least one of said targets comprises self illumination means.

7. A machine as in claim 3, wherein said second optical axis is orthogonal to said first optical axis.

8. A machine as in claim 3 wherein said touch probe is an elongated member mounted at a proximal end to said support structure, said first target being mounted to the distal end of said member and to a portion thereof configured and dimensioned for measuring contact with a workpiece.

9. A machine as in claim 8 wherein said elongated member extends in the same general direction as said optical axis and said first target is symmetrical when viewed parallel to said optical axis.

10. A machine as in claim 9 wherein said target comprises radially disposed indicia for indicating rotation thereof, said indicia also identifying said probe.

11. A machine as in claim 3 wherein said targets art located such that they define three mutually orthogonal axes.

12. A probe as in claim 11 wherein one of said axes becomes coaxial with said optical axis when said probe is mounted to a video based coordinate measuring machine.

13. A machine as in claim 12 wherein said electronic signal converter is a video camera.

14. A machine as in claim 3, further comprising:

d) a third target mounted to said probe, and

e) third imaging optics having a third optical axis transverse to said first optical axis for parfocal imaging of said target on said focal plane, wherein said electronic circuit determines the coordinates in space of said probe.

15. A machine as in claim 14 wherein said second and third optical axes are orthogonal to each other.

16. A machine as in claim 14, wherein said third optical axis is orthogonal to said first optical axis.

17. The machine as in claim 14 wherein said second and third targets are radially spaced away from said first optical axis.

18. A machine as in claim 17 wherein said second and third targets are equally spaced away from said first optical axis.

19. The method of utilizing a touch probe with a video based measuring machine comprising the steps of:

A) mounting a touch probe on said machine with its distal end located substantially on the optical axis of said machine;

B) focusing the image of said distal end on the focal plane of said machine;

C) measuring motion along Cartesian coordinates X and Y orthogonal to said optical axis by analyzing the video signal produced by motion of the image of said distal end;

D) parfocusing an image of a first target mounted on said probe that moves proportionally to movement of said probe along said optical axis such that the image of said first target also moves proportionally to said movement; and

,

E) measuring motion along Cartesian coordinate Z along said optical axis by analyzing the video signal produced by motion of the image of said first target.

20. The method defined in claim 19 wherein said first target is located substantially on said optical axis.

21. The method defined in claim 19 wherein said measuring of motion along Cartesian coordinate Z along said optical axis is accomplished by analyzing the video signals produced by motion of the parfocal images of said first target and a second target on said probe that also moves proportionally to movement of said probe along said optical axis such that the image of said second target also moves proportionally to said movement.

22. The method defined in claim 21 wherein said first target and a third target are located on radii from said optical axis parallel to Cartesian coordinates X and Y.

23. An optical coordinate machine comprising:

(a) a touch probe having a distal end;

(b) an imaging device having a focal plane and outputting a signal containing image information;

(c) a support structure holding said touch probe with said distal end in a nominal zero position while allowing said distal end to be displaced from said nominal zero position upon the application of force to said distal end;

(d) first imaging optics imaging said distal end in said focal plane;

(e) a computer for receiving said signal containing image position information from said imaging device having a focal plane and generating in response thereto indications of changes in the coordinates of said image of said distal end in said focal plane;

(f) a target mounted on said probe; and

,

(g) optics for imaging said target in said focal plane,

wherein said computer indicates changes in the vertical coordinate of said target.

24. An optical coordinate machine as in claim 23, further comprising,

(h) a pair of arms extending horizontally from a first position on said probe;

(i) a pair of targets each mounted at a respective point on its respective end of one of said arms at a position displaced from said first position; and

(j) optics for imaging said targets in said focal plane,

said computer calculating changes in the vertical position of said distal end of said probe.

25. An optical coordinate machine as in claim 23, further comprising:

(k) additional touch probe assemblies, said touch probe and said touch probe assemblies each comprising;

A) a touch probe;

B) a mounting assembly to which said touch probe is mounted comprising;

i) first cooperative magnetic means,

ii) first cooperative indexing means,

iii) cooperative key means; and

(l) a rack for storing each of said touch probe assemblies comprising;

A) multiple cooperative lock means each for receiving said key means of one touch probe assembly to store said assembly.

26. An optical coordinate measuring machine as in claim 25, further comprising

(m) a touch probe assembly head for securing one of said touch probes to said imaging device comprising:

A) second cooperative magnetic means for magnetically engaging and holding said first cooperative magnetic means,

B) second cooperative indexing means for engaging said first cooperative indexing means and establishing a fixed indexed position of a touch probe assembly in relation to said head when said magnetic means are engaged.

27. An optical coordinate measuring machine as in claim 26 wherein said imaging device comprises a video imaging head and said touch probe assembly head further comprises:

(n) means for removably mounting said assembly head to said imaging device.

28. An optical coordinate measuring machine as in claim 27 wherein said means for removably mounting said assembly head to said video imaging head comprises:

i) third cooperative magnetic means,

ii) third cooperative indexing means and

iii) second cooperative key means; and

said rack further comprises;

b) second cooperative lock means for receiving said second key means of said assembly head.

29. An optical coordinate measuring machine as in claim 28 wherein said lock means each comprises a horizontally disposed generally C-shaped channel and said key means each comprises a generally ovoid shape fitting into said channel and is mounted on an arm extending from each of said assemblies.

30. An optical coordinate measuring machine as in claim 25;

further comprising;

(m) a video imaging head; and

wherein said touch probe assembly is adapted for mounting to said video imaging head and further comprises;

i) means for resiliently holding a distal end of a touch probe in a nominal zero position;

ii) means for imaging said distal end in the focal plane of said video imaging head; and

iii) computer means for receiving information from said video imaging head and indicating changes in the coordinates of said image of said distal end in said focal plane.

31. An optical coordinate measuring machine as in claim 30 wherein said distal end of said probe is rigidly mounted to a rigid vertically oriented shaft and the proximal end of said shaft is resiliently mounted to said assembly.

32. An optical coordinate measuring machine as in claim 31, further comprising:

n) a shaft edge at the proximal end of said shaft; and

,

o) means for imaging said edge in the focal plane of said video imaging head; and

wherein said computer means also indicates changes in the vertical coordinate of said edge.

33. An optical coordinate measuring machine as in claim 32, and;

D) a pair of arms extending horizontally from the proximal end of said shaft;

E) a pair of sharp edges each mounted at the distal end of one of said arms;

F) means for imaging said edges in the focal plane of said video imaging head; and

,

wherein said computer means also indicates changes in the vertical position of said edges and rotation thereof about the vertical orientation of said shaft.

34. The method of measuring a workpiece using a video based coordinate measuring machine comprising a video camera, monitor and computer, said method comprising the steps of:

A) mounting a touch probe to said video camera with its contact tip imaged on said video camera and monitor; and

B) using said video camera and computer to determine the X, Y coordinates of the contact tip when it is in contact with a workpiece mounted in the machine.

35. The method of claim 34, wherein said video camera and computer determine said coordinates at the video refresh rate of said video camera.

36. The method of claim 34 further comprising the additional step of:

C) using said video camera and computer to determine the Z coordinate of the touch probe by illuminating a target on the probe with a beam of light parallel to said X, Y coordinates to form an image of the said target on the video camera.

37. The method of claim 36 said last step further comprising:

a) illuminating a second target on the touch probe with a beam of light parallel to said X,Y coordinates to form an image of said second target on the video camera.

38. The method of claim 37 further comprising the additional step of determining rotation of the touch probe by using said video camera and computer.

39. Apparatus for determining the position of a point in space comprising:

(a) a movable support system outputting information with indicates the position of said movable support system;

(b) a touch probe comprising;

i) a contacting portion; and

ii) an optical pattern including first and second imagable characteristics;

(c) probe supporting structure mounted on said moveable support system, said probe being mounted on said probe supporting structure, allowing said probe to be moved by said movable support system, said probe supporting structure supporting said probe while allowing said contacting portion and said optical pattern to be displaced along a path determined by said probe supporting structure upon the application of force to a contacting point on said contacting portion, the displacement of said optical pattern causing changes in said characteristics;

(d) an image generating system for receiving an image and outputting an image signal;

(e) first imaging optics imaging said first and second imagable characteristics on said image generating system to cause said image generating system to generate a signal containing an image of said first and second imagable characteristics, the changes in said characteristics caused in response to movement of said contacting portion indicating the position of said point of contact; and

(f) a computer for receiving said signal containing said images of said first and second imagable characteristics and the output of said movable support system, and calculating the position in three dimensional space of said point of contact.

40. Apparatus as in claim 39, further comprising a movement signal source controlling the movement of said movable support system to move it to a plurality of at least three points, and wherein said computer determines the orientation of a plane tangent to said object between said points, whereby the shape of an object is determined as a set of points with specific locations in three dimensions.

41. Apparatus as in claim 39, wherein said image generating system is a video camera operating at a frame rate in excess of thirty frames per second.

42. Apparatus as in claim 39, wherein said optical pattern is a reflective circle.

43. Apparatus as in claim 39, wherein said optical pattern is a pinhole.

44. Apparatus as in claim 39, wherein said image generating system is a multi-element CCD.

45. Apparatus as in claim 39, further comprising structure associated with said probe and including a third imageable characteristic imaged by said image generating system and analyzed by said computer to determine position.

46. Apparatus as in claim 39, wherein said such probe comprises a first arm extending from a mounting secured to said probe supporting structure, said optical pattern including first and second imagable characteristics being disposed at the other end of said first arm, said touch probe further comprising an extension extending from said mounting, said extension being mounted at one point adjacent said mounting and extending to a point remote from said point adjacent said mounting to a remote point, said remote point including said second imagable characteristic.

47. Apparatus as in claim 39, wherein said such probe comprises a first arm extending from a mounting secured to said probe supporting structure, said optical pattern including said first imagable characteristic being disposed at the other end of said first arm, said second imagable characteristic being mounted adjacent said mounting secured to said probe supporting structure.

48. Apparatus as in claim 39, wherein said probe has three points on its surface which generally defined an L shape, the corner of the L shape bearing an imagable characteristic, one end of said L-shape including a touch probe body for contacting a point to be measured, and the other end of said L shape including an a second imagable characteristic, said probe being mounted proximate said other end of said L shape.

49. Apparatus as in claim 39, further comprising a rack supporting a plurality of attachments adapted to be mounted on said probe supporting structure, said rack comprising structure for supporting a probe supporting structure or other attachment, and said rack further comprising retention structure adapted to retain and hold an attachment upon the application of force by said probe supporting structure in a direction resulting in disengagement of said attachment from said probe supporting structure, whereby said probe supporting structure may move to engage an attachment in said rack, pull away from said rack, leaving said attachment in place on said rack, and move into engagement with another attachment allowing said probe supporting structure to remove said other attachment from said rack.

50. Apparatus as in claim 49, wherein said rack supports an auxiliary lens for changing overall magnification of the image generating system, said lens including a precision reticle mounted on the rack below the auxiliary lens such that by viewing the reticle after the auxiliary lens is engaged by the probe supporting structure, the system can recalibrate itself for magnification and centering of the lens.

51. Apparatus as in claim 39, wherein said touch probe comprises a flexibly mounted arm secured to a mounting at one end of said arm.

52. Apparatus as in claim 51, wherein the other end of said flexible arm supports said optical pattern.

53. Apparatus as in claim 51, wherein said mounting is magnetically coupled to said probe supporting structure.

54. Apparatus as in claim 39, wherein said such probe comprises a first arm extending from a mounting secured to said probe supporting structure, said optical pattern including said first imagable characteristic being disposed at the other end of said first arm, said touch probe further comprising an extension extending from said mounting, said extension being mounted at one point adjacent said mounting and extending to a point remote from said point adjacent said mounting to a remote point, said remote point including said second imagable characteristic.

55. Apparatus as in claim 54, wherein said mounting is flexible and said arm is rigid.

56. Apparatus as in claim 55, further comprising a second extension being mounted at a point adjacent said mounting and extending to an other remote point remote from said point adjacent said mounting, said other remote point including a third imagable characteristic.

57. Apparatus as in claim 56, wherein said probe arm, and said first and second extensions form three members which extend in directions substantially across the directions of extension of said other members.

58. Apparatus as in claim 56, wherein said imaging optics comprises separate focusing members for each of said first, second and third imagable characteristic.

59. Apparatus as in claim 58, wherein said first imagable characteristic includes elements which define a closed shape, and said second imagable characteristic is formed by a pair of studs, one mounted on each of said extensions.

60. Apparatus for determining the position of a point in space comprising:

(a) a movable support system outputting information with indicates the position of said movable support system;

(b) a touch probe comprising;

i) a contacting portion; and

ii) an optical pattern including first and second imagable characteristics;

(c) a flexible probe supporting structure mounted on said moveable support system, said probe being mounted on said probe supporting structure, allowing said probe to be moved by said movable support system, said probe supporting structure supporting said probe while allowing said contacting portion and said optical pattern to be displaced along a path determined by said probe supporting structure upon the application of force to a contacting point on said contacting portion, the displacement of said optical pattern causing changes in said characteristics;

(d) an image generating system for receiving an image and outputting an image signal;

(e) first imaging optics imaging said first and second imagable characteristics on said image generating system to cause said image generating system to generate a signal containing an image of said first and second imagable characteristics, the changes in said characteristics caused in response to movement of said contacting portion indicating the position of said point of contact; and

(f) a computer for receiving said signal containing said images of said first and second imagable characteristics and the output of said movable support system, and detecting change in the position in three dimensional space of said point of contact.