Electro-optical inspection

• US 4,576,482 A
• Filed: 06/02/1981
• Issued: 03/18/1986
• Est. Priority Date: 09/07/1979
• Status: Expired due to Term

• Current Assignee: LMI Technologies Inc.
• Original Assignee: Diffracto, Ltd. (LMI Technologies Inc.)
• Inventors: Pryor, Timothy R.
• Primary Examiner(s): Reeves, Robert B.
• Assistant Examiner(s): Wacyra, Edward M.
• Application Number:
  US06/269,614
• Time in Patent Office: 1,750 Days
• Field of Search: 209/538, 209/576, 209/577, 209/579, 209/586, 209/598, 250/252.1, 356/23, 356/376, 356/384, 356/385, 356/386, 356/387, 356/394, 356/398, 356/426, 358/96, 358/101, 358/106, 358/107, 358/166, 358/180, 358/199, 358/200, 358/205, 358/903, 364/515, 364/550, 364/551, 364/552, 364/560, 364/579, 364/571, 364/582, 382/51, 382/67
• US Class Current: 356/612
• CPC Class Codes: F01L 1/047 Camshafts
• CPC Class Codes: G01B 11/2433 for measuring outlines by shadow casting

Abstract

A method and apparatus for inspecting workpieces for rapid and accurate determination of dimensions and the like. The equipment is electro-optical in nature and there is no contact between the inspecting elements and the workpiece under inspection. An electro-optical sensor is utilized which includes a light source for illuminating at least one edge of a workpiece, a lens for forming an image of the illuminated edge, and an array of photosensitive elements, such as photodiodes, capable of producing an electrical signal in response to light incident thereon. The light, including the edge image, is impinged upon the array and the electrical signals produced correspond to the portion of the edge, its shape, etc. The signals can be rapidly analyzed to provide a determination of a dimension such as length, squareness, curvature, and the like.

Claims

1. Apparatus for determining a dimension of an object to an accuracy of at least ±

0.0004 inches comprising;

an electro-optical sensor unit for sensing the positon of a portion of an object, said sensor unit comprising;

light source means for illuminating an edge of said portion of an object;

lens means for forming an image of the illuminated edge of an object;

a photosensitive array comprising a plurality of light sensitive elements capable of producing a signal in response to light incident thereon, said array being positioned to receive the image of an illuminated edge of an object;

electronic means for magnifying the resolution provided by said photosensitive array to a fraction of an individual light sensitive element, said electronic means including means for producing a fractional distance signal having a value indicative of the fractional distance between adjacent light sensitive elements; and

means for analyzing the signals from said light sensitive elements and said fractional distance signal to determine a dimension of said portion of said object to an accuracy of at least 0.0004 inches.

2. Apparatus according to claim 1 for determining said dimension to an accuracy of at least ±

0.0001 inches.

3. Apparatus according to claim 1 for determining said dimension to an accuracy of at least ±

0.00005 inches.

4. Apparatus according to claim 1 wherein said object is a machined part and comprises a crankshaft, a valve, or a camshaft.

5. Apparatus according to claim 1 wherein said apparatus further comprises means for rotating a mounted elongate object.

6. Apparatus according to claim 5 wherein said light source means comprises means for strobing the light to effectively freeze the image of the edge of a rotating object on said photodiode array, said apparatus further comprising means for determining the angular position of a rotating object and means for actuating the strobe light pulse at an angular position determined by said angular position determining means.

7. Apparatus according to claim 6 wherein said light source means comprises a pulsed diode laser.

8. Apparatus according to claim 1 further comprising means for compensating for light fluctuations.

9. Apparatus according to claim 8 wherein said light compensation means comprises means for detecting the intensity of light incident on said array.

10. Apparatus according to claim 1 wherein said object comprises a camshaft and wherein said illuminated edge comprises an edge of a cam lobe or journal of said camshaft.

11. Apparatus according to claim 10 comprising means for monitoring the angular position of an illuminated cam lobe edge relative to a reference point on said camshaft.

12. Apparatus according to claim 11 wherein said dimension is cam lift and further means are provided to analyze the relationship between said dimension and said angular position so as to determine lobe contour.

13. Apparatus according to claim 10 wherein said dimension is base circle runout of a cam lobe.

14. Apparatus according to claim 10 further comprising a cylinder lens mounted adjacent said photodiode array to concentrate light from a range of positions along said edge onto said photodiode array.

15. Apparatus according to claim 10 wherein said sensor unit is positioned to sense an edge of a journal of a mounted camshaft and further comprising a further sensor unit for sensing a further edge of said journal of a mounted cam shaft, said further edge being diametrically opposite to the first mentioned journal edge for determining the diameter and center point location of said journal.

16. Apparatus according to claim 10 further comprising means for storing predetermined cam lobe lift data for a cam shaft type and wherein said analyzing means further comprises means for comparing the determined cam lobe lift data with said stored data.

17. Apparatus according to claim 16 wherein said storing means comprises means for storing predetermined cam lobe lift data for a plurality of cam shaft types and further comprising means for sensing the type of a cam shaft under inspection.

18. Apparatus according to claim 1 wherein said photodiode array comprises a linear array having at least 1000 discrete photodiodes.

19. Apparatus according to claim 1 wherein said electronic magnifying means comprises means for establishing a plurality of edge detection thresholds.

20. Apparatus according to claim 1 comprising a plurality of said sensor units.

21. Apparatus according to claim 1 further comprising means for moving said sensor unit relatively longitudinally of an object to predetermined locations.

22. Apparatus according to claim 21 further comprising a reference gage member located such that at one end of the relative movement of said sensor unit, said sensor unit senses the said reference gage.

23. Apparatus according to claim 1 wherein said light source means comprises a source of collimated light.

24. Apparatus according to claim 1 wherein said lens means comprises a telecentric lens system.

25. Apparatus according to claim 1 further comprising a lens stop positioned between said lens means and said photodiode array to block light reflected from an object'"'"'s surface.

26. Apparatus according to claim 1 wherein said electro-optical sensor unit comprises a single lens and photodiode array located in a common housing, said housing being moveably mounted to accomodate different object sizes.

27. Apparatus according to claim 1 wherein two diametrically opposite edges of said object are both imaged by a single lens onto a single photodiode array.

28. Apparatus according to claim 27 wherein said array comprises at least 1000 elements.

29. Apparatus according to claim 1 wherein said light source is located below an object and wherein a window is provided between said light source and said object.

30. Apparatus according to claim 1 wherein said light source is oriented to direct the illuminating light horizontally across an object.

31. Apparatus according to claim 1 wherein said object comprises a crankshaft and wherein said sensor means is positioned to sense the position of a pin journal diameter or fillet contour of a crankshaft.

32. Apparatus according to claim 1 further comprising fiber optic means for transmitting said image to a remote photodiode array.

33. Apparatus according to claim 1 wherein said light source means comprises fiber optic means for transmitting light to said edge of said object.

34. Apparatus according to claim 1 further comprising means for mounting said object in a mounted position.

35. Apparatus according to claim 34 further comprising transfer means for moving an object from a loading position adjacent said apparatus into said mounted position.

36. Apparatus according to claim 34 wherein said mounting means comprises centers or vee supports.

44. A method according to claim 32 further comprising compensating for light fluctuations.

45. A method according to claim 44 wherein said light compensation step comprises detecting the intensity of light incident on said array.

37. A method of determining a dimension of an object to an accuracy of at least ±

0.0004 inches comprising;

illuminating an edge of a portion of an object;

forming an optical image of the illuminated edge of the object;

detecting the image of the illuminated edge of the object on a photosensitive array of light sensitive elements capable of producing a signal in response to light incident thereon;

electronically magnifying the resolution provided by the photosensitive array to a fraction of an individual light sensitive element by producing a fractional distance signal having a value indicative of the fractional distance between adjacent light sensitive elements; and

analyzing the signals from said light sensitive elements and said fractional distance signal, so as to determine a dimension of said portion of said object to an accuracy of ±

of 0.0004 inches.

38. A method according to claim 37 for determining said dimension to an accuracy of at least ±

0.0001 inches.

39. A method according to claim 37 for determining said dimension to an accuracy of at least 0.00005 inches.

40. A method according to claim 37 wherein said object comprises a crankshaft, a valve, or a camshaft.

41. A method according to claim 37 wherein said method further comprises rotating a mounted elongate object.

42. A method according to claim 41 wherein said light source means comprises means for strobing the light to effectively freeze the image of a rotating object on said photosensitive array, said method further comprising the steps of determining the angular position of an object and actuating the strobe light at a determined angular position of said object.

43. A method according to claim 42 wherein said light source means comprises a pulsed diode laser.

46. A method according to claim 37 wherein said object comprises a camshaft and wherein said illuminated edge comprises an edge of a cam lobe or journaal of said camshaft.

47. A method according to claim 37 wherein said object comprises a camshaft, said method comprising the further step of monitoring the angular position of an illuminated cam lobe edge relative to a reference point on said camshaft.

48. A method according to claim 47 wherein said dimension is cam lift and further including the step of analyzing the relationship between said dimension and said angular position to determine lobe contour.

49. A method according to claim 48 wherein said dimension is a base circle runout of a cam lobe.

50. A method according to claim 37 further comprising concentrating light from a range of axial positions on an object onto said photosensitive array by means of a cylinder lens mounted adjacent to said photosensitive array.

51. A method according to claim 50 wherein said photosensitive array comprises a linear photodiode array having at least 1000 discrete photodiodes.

52. A method according to claim 50 wherein said lens and said photodiode array are located in a common housing and wherein said method includes the step of moving said housing to accomodate objects of different size.

53. A method according to claim 37 wherein said electronic magnifying step comprises establishing a plurality of edge detection thresholds.

54. A method according to claim 37 wherein said edge comprises an edge of a journal of camshaft and wherein said method further comprises the step of sensing a further edge of said journal, said further edge being diametrically opposite to the first mentioned journal edge for determining the diameter and center point location of said journal.

55. A method according to claim 37 wherein said object comprises a camshaft, said method further comprising the step of storing predetermined cam lobe lift data for a camshaft type and comparing the determined cam lobe lift data with said stored data.

56. A method according to claim 55 wherein said data storing step comprises storing predetermined cam lobe lift data for a plurality of camshaft types and further comprising the step of sensing the type of a camshaft under inspection.

57. A method according to claim 37 wherein said light source comprises a source of collimated light.

58. A method according to claim 37 wherein said object comprises a valve and wherein two diametrically opposite edges of said valve are both imaged by a single lens onto a single photosensitive array.

59. A method according to claim 37 wherein a window is provided between said light source and said object.

60. A method according to claim 37 further comprising the step of mounting said object on a support.

61. A method according to claim 60 further comprising the step of moving an object from a loading position into said mounted position.

62. A method according to claim 60 wherein said object comprises a valve and wherein said valve is transferred horizontally between a conveyor and said mounted position and wherein said light is projected upwardly from below a mounted valve.

63. A method according to claim 60 wherein said object comprises a crankshaft.

64. A method according to claim 63 wherein said step of mounting the crankshaft comprises automatically transferring the crankshaft between a position in which the crankshaft is located on a crankshaft conveyor and said mounted position.

65. A method according to claim 64 wherein said transferring step comprises lifting a crankshaft off a walking beam conveyor into said mounted position.

66. A method according to claim 63 wherein said edge comprises an edge of a pin journal of a crankshaft.

67. A method according to claim 63 wherein said edge comprises the edge of a fillet contour of a crankshaft.

68. A method according to claim 60 wherein said support comprises centers or vee supports.

69. A method according to claim 37 wherein said image is transmitted by fiber optic means to a remote photodiode array.

70. A method according to claim 37 wherein the incident light is transmitted by fiber optic means.