Triangulation-based 3D imaging and processing method and system

• US 5,546,189 A
• Filed: 05/19/1994
• Issued: 08/13/1996
• Est. Priority Date: 05/19/1994
• Status: Expired due to Term

• Current Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Original Assignee: View Engineering, Inc. (Quality Vision International, Inc.)
• Inventors: Svetkoff, Ronald J., Rohrer, Donald K., Kelley, Robert W.
• Primary Examiner(s): EVANS, FANNIE L
• Application Number:
  US08/245,864
• Time in Patent Office: 817 Days
• Field of Search: 356/375, 356/376, 250/559.22, 250/559.23, 250/559.29, 250/559.31
• US Class Current: 356/602
• CPC Class Codes: G01B 11/24 for measuring contours or curvatures

Abstract

A triangulation-based method and system for high speed 3D and gray scale imaging and associated pre-processing of digitized information allows for estimation or filtering of height and gray scale values based upon the confidence level of the information obtained from a pair of sensors and also based upon knowledge of the object structure and its reflectance characteristics. A modulated laser beam is scanned across the object to create a plurality of spots which are viewed by a pair of well-matched receivers. Each receiver includes a light collection and delivery system, a position sensitive detector, and an associated ratio-metric signal processor, or similar means for extraction of height and intensity information or data by triangulation. An optional automatic light control sub-system provides greatly extended dynamic range with control inputs derived from an amplifying detector included in each receiver to maximize occurrences of valid data points. Prior to image processing, each point in the digitized 3D and gray scale data is transformed based upon the digital values of the gray scale and height values. The multi-channel pointwise transformation produces an improved estimate of intensity and height at a point of interest, or is used to filter the data for improvements in the 3D and gray scale contrast prior to image processing and measurement analysis. Either linear or non-linear transformations are utilized, based on the match between 3D and gray values, and other conditions which determine the confidence level of the information.

Claims

1. A triangulation-based 3D processing method for generating transformed height and gray scale values, the method comprising the steps of:

generating a first pair of data values represented by height data and intensity data obtained from a first direction with respect to an object;

generating a second pair of data values represented by height data and intensity data obtained from a second direction with respect to the object;

controllably selecting at least one control algorithm adapted to process the height and intensity data;

processing the intensity data from the first and second directions to obtain transformed intensity data;

processing the height data from the first and second directions and the intensity data from the first and second directions with the at least one control algorithm to obtain transformed height data; and

transmitting the transformed height and intensity data which are adapted to be processed by an image processing computer, the transformed height data representing at least one transformed height value and the transformed intensity data representing at least one transformed gray scale value.

2. A triangulation-based 3D imaging and processing method for generating transformed height and gray scale values regarding an object located at an inspection station, the method comprising the steps of:

positioning the object at the inspection station;

transmitting a beam of controlled radiant energy to a surface of the object to obtain first and second reflected beams of radiant energy;

receiving and focusing the first reflected beam to obtain a first focused spot of radiant energy at a first imaging area and receiving and focusing the second reflected beam to obtain a second focused spot of radiant energy at a second imaging area;

detecting the position and intensity of the first focused spot of radiant energy at the first imaging area to provide a first signal;

processing the first signal to generate a first set of height data and a first set of intensity data;

detecting the position and intensity of the second focused spot of radiant energy at the second imaging area to obtain a second signal;

processing the second signal to generate a second set of height data and a second set of intensity data;

controllably selecting at least one control algorithm adapted to process the sets of height and intensity data;

processing the first and second sets of intensity data to obtain a transformed set of intensity data;

processing the first and second sets of height data and the first and second sets of intensity data with the at least one control algorithm to obtain a transformed set of height data; and

transmitting the transformed sets of height and intensity data which are adapted to be processed by an image processing computer, the transformed set of intensity data representing at least one transformed gray scale value and the transformed set of height data representing at least one transformed height value.

3. The method as claimed in claim 2 wherein the step of transmitting a beam of controlled radiant energy includes the step of scanning the beam and wherein the beam of controlled radiant energy is a modulated beam of coherent light.

4. The method as claimed in claim 2 further comprising the steps of generating first and second feedback signals based on the first and second reflected beams, respectively, and utilizing the first and second feedback signals to control the intensity of the beam of controlled radiant energy.

5. The method as claimed in claim 2 wherein the step of focusing the first and second beams is accomplished with a pair of anamorphic magnification and field lens systems wherein each of the focused spots of radiant energy is an enlarged elongated spot of radiant energy.

6. The method as claimed in claim 5 wherein the steps of detecting the positions of the first and second focused spots of radiant energy are accomplished by a pair of small area position detectors, each of the position detectors having a position-sensitive axis for determination of height by position detection and triangulation and is capable of determining intensity of its respective focused spot of radiant energy.

7. The method as claimed in claim 2 wherein the transformed height and gray scale values represent a gray scale digital image containing the object.

8. The method as claimed in claim 2 wherein the step of transmitting includes the step of projecting or scanning the beam to create a plurality of points in the form of a line focused onto the object.

9. The method as claimed in claim 6 wherein each of the position detectors is a lateral effect photodiode or a detector array.

10. The method as claimed in claim 4 wherein the step of generating the first and second feedback signals includes the step of splitting the first and second reflected beams to obtain first and second split portions and detecting the first and second split portions to obtain the first and second feedback signals.

11. The method of claim 10 wherein the step of detecting the first and second split portions is accomplished with a pair of amplifying avalanche photodiodes.

12. The method as claimed in claim 6 wherein the step of processing the first signal includes the step of creating a first height value representing a centroid of the intensity distribution of the first focused spot and wherein the step of processing the second signal includes the step of creating a second height value representing a centroid of the intensity distribution of the second focused spot.

13. The method as claimed in claim 2 wherein the step of processing the first and second sets of intensity data includes the steps of comparing values represented by the first and second sets of intensity data with each other and determining whether the values represented by the first and second sets of intensity data are within a preprogrammed dynamic range.

14. The method of claim 13 wherein the preprogrammed dynamic range has upper and lower limits wherein the upper limit is as small as three times larger than the lower limit.

15. The method of claim 13 wherein the preprogrammed dynamic range has upper and lower limits wherein the upper limit is up to 10⁶ times larger than the lower limit.

16. The method as claimed in claim 13 wherein the step of processing the first and second sets of intensity data includes the step of encoding each datum of the transformed set of intensity data with a predetermined value if the values represented by the first and second sets of intensity data are both outside the preprogrammed dynamic range.

17. The method as claimed in claim 13 wherein the step of processing the first and second sets of height data includes the step of determining the mathematical difference between corresponding values represented by the first and second sets of height data and, if the values represented by the first and second sets of intensity data are inside the preprogrammed dynamic range, comparing the mathematical difference to a predetermined match tolerance.

18. The method as claimed in claim 2 wherein the step of processing the first and second sets of intensity data includes the steps of determining if a first data value is outside a predetermined range and a second data value is inside the predetermined range and selecting the second data value as a valid value.

19. The method as claimed in claim 17 further including the step of selecting a predetermined function based on the step of comparing the mathematical difference with the predetermined match tolerance.

20. The method as claimed in claim 19 wherein the function is a logical function including the minimum or maximum of the height and gray scale values.

21. The method as claimed in claim 19 wherein the function is a numeric function including the average value or difference of the height and gray scale values.

22. A triangulation-based 3D processing system for generating transformed height and gray scale values, the system comprising:

means for generating a first pair of data values represented by height data and intensity data obtained from a first direction with respect to an object;

means for generating a second pair of data values represented by height data and intensity data obtained from a second direction with respect to the object;

means for controllably selecting at least one control algorithm adapted to process the height and intensity data;

means for processing the intensity data from the first and second directions to obtain transformed intensity data;

means for processing the height data from the first and second directions and the intensity data from the first and second directions with the at least one control algorithm to obtain transformed height data; and

means for transmitting the transformed height and intensity data which are adapted to be processed by an image processing computer, the transformed height data representing at least one transformed height value and the transformed intensity data representing at least one transformed gray scale value.

23. A triangulation-based 3D imaging and processing system for generating transformed height and gray scale values regarding an object located at an inspection station, the system comprising:

means for transmitting a beam of controlled radiant energy to a surface of the object to obtain first and second reflected beams of radiant energy;

means for receiving and focusing the first reflected beam to obtain a first focused spot of radiant energy at a first imaging area and means for receiving and focusing the second reflected beam to obtain a second focused spot of radiant energy at a second imaging area;

means for detecting the position and intensity of the first focused spot of radiant energy at the first imaging area to provide a first signal;

means for processing the first signal to generate a first set of height data and a first set of intensity data;

means for detecting the position and intensity of the second focused spot of radiant energy at the second imaging area to provide a second signal;

means for processing the second signal to generate a second set of height data and a second set of intensity data;

means for selecting at least one control algorithm;

means for processing the first and second sets of intensity data to obtain a transformed set of intensity data;

means for processing the first and second sets of height data and the first and second sets of intensity data with the at least one control algorithm to obtain a transformed set of height data; and

means for transmitting the transformed sets of height and intensity data which are adapted to be processed by an image processing computer, the transformed set of intensity data representing at least one transformed gray scale value and the transformed set of height data representing at least one transformed height value.

24. The system as claimed in claim 23 wherein the means for transmitting includes means for scanning the beam and wherein the beam of controlled radiant energy is a modulated beam of coherent light.

25. The system as claimed in claim 23 further comprising first and second feedback means for generating first and second feedback signals, respectively, based on the first and second reflected beams, respectively, and control means for utilizing the first and second feedback signals to control the intensity of the beam of controlled radiant energy.

26. The system as claimed in claim 23 wherein the means for focusing the first and second beams includes a pair of anamorphic magnification and field lens systems wherein each of the focused spots of radiant energy is an enlarged elongated spot of radiant energy.

27. The system as claimed in claim 26 wherein the means for detecting the positions of the first and second focused spots of radiant energy includes a pair of small area position detectors, wherein each of the position detectors has a position-sensitive axis for determination of height by position detection and triangulation and is capable of determining intensity of its respective focused spot of radiant energy.

28. The system as claimed in claim 23 wherein the transformed height and gray scale values represent a gray scale digital image containing the object.

29. The system as claimed in claim 23 wherein the means for transmitting a beam of controlled radiant energy includes means for projecting or scanning the beam to create a plurality of points in the form of a line focused onto the object.

30. The system as claimed in claim 27 wherein each of the position detectors is a lateral effect photodiode or a detector array.

31. The system as claimed in claim 25 wherein the means for generating the first and second feedback signals includes means for splitting the first and second reflected beams to obtain first and second split portions and means for detecting the first and second split portions to obtain the first and second feedback signals.

32. The system of claim 31 wherein the means for detecting includes a pair of amplifying avalanche photodiodes.

33. The system as claimed in claim 27 wherein the means for processing the first signal includes means for creating a first height value representing a centroid of the intensity distribution of the first focused spot and wherein the means for processing the second signal includes means for creating a second height value representing a centroid of the intensity distribution of the second focused spot.