Smear-limit based system and method for controlling vision systems for consistently accurate and high-speed inspection

• US 7,499,584 B2
• Filed: 10/21/2004
• Issued: 03/03/2009
• Est. Priority Date: 10/21/2004
• Status: Active Grant

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: Delaney, Mark L.
• Primary Examiner(s): Mariam; Daniel G
• Application Number:
  US10/971,504
• Publication Number:
  US 20060088201A1
• Time in Patent Office: 1,594 Days
• Field of Search: 382141-152, 382/159, 348/92, 702 34- 35
• US Class Current: 382/152
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means

Abstract

A machine vision inspection system and method for generating a workpiece image acquisition/inspection program, which can be shared by different machine vision systems having different hardware capabilities. Each system includes a movable stage for scanning and measuring selected workpiece features, and preferably includes strobe lighting to control the effective exposure time of the workpiece image. The program provides for the determination of various image acquisition parameters, such as the stage velocity, strobe light power, strobe exposure time, etc., based on a functional limit related to image smear. Thus, the program automatically adapts to any specific system, by allowing determination of optimal image acquisition parameters for that system based on the functional limit. Accordingly, the same program is usable on different systems to consistently provide a desired level of accuracy as well as optimum or near-optimum throughput, regardless of which vision system is used.

Claims

1. A method for programming a workpiece inspection program on a first precision machine vision inspection system, the precision machine vision inspection system comprising an image acquisition system comprising at least a camera;

at least one light source;

a workpiece stage; and

a control system portion, wherein at least one of the workpiece stage and the camera is movable to provide relative motion with respect to each other, and wherein at least one of the camera and the light source defines a minimum effective exposure time of the precision machine vision inspection system, the method comprising;

(a) determining acceptable image acquisition exposure parameters for an image of a respective workpiece feature;

(b) recording at least one parameter indicative of an exposure energy corresponding to the determined image acquisition exposure parameters in the workpiece inspection program;

(c) recording at least one parameter indicative of an acceptable image smear for the image of the respective workpiece feature in the workpiece inspection program; and

(d) executing the workpiece inspection program on a current precision machine vision inspection system that is not the first precision machine vision inspection system and that has different specifications than the first precision machine vision inspection system, the current machine vision inspection system comprising an image acquisition system comprising at least a camera;

at least one light source;

a workpiece stage; and

a control system portion that is not the control system portion of the first precision machine vision inspection system, the executing of the workpiece inspection program on the current machine vision inspection system comprising the sub-steps of;

(i) receiving the at least one parameter indicative of an exposure energy recorded in the workpiece inspection program for the respective workpiece feature;

(ii) receiving the at least one parameter indicative of an acceptable image smear recorded in the workpiece inspection program for the respective workpiece feature; and

(iii) determining an operative combination of a light source power setting, an exposure time, and relative motion speed usable in conjunction with the exposure time on the current precision machine vision inspection system to provide an image smear not greater than the acceptable image smear.

2. The method of claim 1, wherein the at least one parameter indicative of an exposure energy defines a combination of a light source power setting and an exposure time.

3. The method of claim 2, wherein the first precision machine vision inspection system comprises a set of respective values usable to provide a respective exposure energy, determining the acceptable image acquisition exposure parameters comprises selecting one of the set of respective values, and recording at least one parameter indicative of an exposure energy corresponding to the determined image acquisition exposure parameters comprises recording the selected one of the set of respective values.

4. The method of claim 2, wherein the at least one parameter indicative of an acceptable image smear in the workpiece inspection program comprises one of (a) a relative motion speed usable in conjunction with the exposure time to provide an acceptable image smear and (b) an image smear parameter that defines an acceptable relative motion displacement during the exposure time.

5. The method of claim 2, wherein the exposure time is determined by one of (a) an effective light integration time duration of the camera, (b) an electronic shutter exposure duration of the camera, and (c) a strobe light time duration of the light source.

6. The method of claim 1, further comprising the sub-step of acquiring an image of the respective workpiece feature using the operative combination of light source power setting, exposure time, and relative motion speed.

7. A method for programming a workpiece inspection program on a first precision machine vision inspection system, the precision machine vision inspection system comprising an image acquisition system comprising at least a camera;

at least one light source;

a workpiece stage; and

a control system portion, wherein at least one of the workpiece stage and the camera is movable to provide relative motion with respect to each other, and wherein at least one of the camera and the light source defines a minimum effective exposure time of the precision machine vision inspection system, the method comprising;

(a) determining acceptable image acquisition exposure parameters for an image of a respective workpiece feature;

(b) recording at least one parameter indicative of an exposure energy corresponding to the determined image acquisition exposure parameters in the workpiece inspection program, wherein the at least one parameter indicative of an exposure energy defines a combination of a light source power setting and an exposure time;

(c) recording at least one parameter indicative of an acceptable image smear for the image of the respective workpiece feature in the workpiece inspection program, wherein the at least one parameter indicative of an acceptable image smear in the workpiece inspection program comprises one of (c1) a relative motion speed usable in conjunction with the exposure time to provide an acceptable image smear and (c2) an image smear parameter that defines an acceptable relative motion displacement during the exposure time; and

(d) executing the workpiece inspection program on a current precision machine vision inspection system that is one of (d1) the first precision machine vision inspection system and (d2) a precision machine vision inspection system that is not the first precision machine vision inspection system, comprising the sub-steps of;

(d-i) receiving the at least one parameter indicative of an exposure energy recorded in the workpiece inspection program for the respective workpiece feature;

(d-ii) receiving the at least one parameter indicative of an acceptable image smear recorded in the workpiece inspection program for the respective workpiece feature; and

(d-iii) determining an operative combination of a light source power setting, an exposure time, and relative motion speed usable in conjunction with the exposure time on the current precision machine vision inspection system to provide an image smear not greater than the acceptable image smear;

wherein the first precision machine vision inspection system comprises a first set of respective values usable to control an image exposure and each respective value is usable to provide a corresponding calibrated exposure energy, the current precision machine vision inspection system comprises a current set of respective values usable to control an image exposure and each respective value is usable to provide a corresponding calibrated exposure energy, and similar respective values from the first and current sets of respective values on the first and current machines are usable to provide similar corresponding calibrated exposure energies, wherein;

the step of receiving the at least one parameter indicative of an exposure energy recorded in the workpiece inspection program comprises receiving one of the first set of respective values; and

the step of determining an operative combination of a light source power setting, an exposure time, and relative motion speed comprises;

using one of the current set of respective values that is closest in value to the received one of the first set of respective values to determine the combination of a light source power setting and an exposure time in the current precision machine vision inspection system; and

determining the relative motion speed in conjunction with the determined exposure time to provide an image smear not greater than the acceptable image smear.

8. The method of claim 7, wherein the first precision machine vision inspection system comprises a set of respective values usable to provide a respective exposure energy, determining the acceptable image acquisition exposure parameters comprises selecting one of the set of respective values, and recording at least one parameter indicative of an exposure energy corresponding to the determined image acquisition exposure parameters comprises recording the selected one of the set of respective values.

9. The method of claim 7, further comprising the sub-step of acquiring an image of the respective workpiece feature using the operative combination of light source power setting, exposure time, and relative motion speed.

10. The method of claim 7, wherein the exposure time is determined by one of (a) an effective light integration time duration of the camera, (b) an electronic shutter exposure duration of the camera, and (c) a strobe light time duration of the light source.

11. A method for programming and executing a workpiece part program such that it will execute efficiently on a first machine vision inspection system or on a second machine vision system having different specifications than the first machine vision inspection system, each machine vision inspection system comprising an image acquisition system comprising at least a camera;

at least one light source;

a workpiece stage; and

a control system portion, wherein at least one of the workpiece stage and the camera is movable to provide relative motion with respect to each other, and wherein at least one of the camera and the light source defines a minimum effective exposure time of the precision machine vision inspection system, the method comprising;

(a) programming the workpiece part program on the first machine vision inspection system such that it will execute efficiently on the first machine vision inspection system or on a second machine vision system having different specifications than the first machine vision inspection system, comprising the sub-steps of;

(a-i) determining a value of a functional limit variable related to allowable image smear for an image of a respective workpiece feature and storing the value of the functional limit variable in the workpiece part program, for acquiring an image of the respective workpiece feature; and

(a-ii) determining an operable exposure time at a defined light power level for acquiring an image of the respective workpiece feature and storing at least one parameter indicative of the product of the operable exposure time multiplied by the defined light power level in the workpiece part program, for acquiring an image of the respective workpiece feature; and

(b) executing the workpiece part program on a current machine vision inspection system, comprising the sub-steps of;

(b-i) inputting from the current machine vision inspection system a maximum relative motion speed, a minimum effective exposure time and a maximum light power of the current machine vision inspection system;

(b-ii) inputting from the workpiece part program the value of the functional limit variable related to allowable image smear and the at least one parameter indicative of the product of the operable exposure time multiplied by the defined light power level, for acquiring an image of the respective workpiece feature;

(b-iii) determining an optimal exposure time for acquiring an image of the respective workpiece feature using the current machine vision inspection system, the optimal exposure time based on the at least one parameter indicative of the product of the operable exposure time multiplied by the defined light power level and a selected light power level that is equal to or less than the maximum light power of the current machine vision inspection system;

(b-iv) determining an operational relative velocity for acquiring the image of the respective workpiece feature using the current machine vision inspection system, the operational relative velocity based on the value of the functional limit variable and the optimal exposure time of the current machine vision inspection system for acquiring an image of the respective workpiece feature, wherein the operational relative velocity is equal to or less than the maximum relative motion speed of the current machine vision inspection system; and

(b-v) acquiring an image of the respective workpiece feature using the determined operational relative velocity, the optimal exposure time, and the selected light power on the current machine vision inspection system such that the image of the respective workpiece feature has approximately the allowable amount of image smear corresponding to the value of the functional limit variable.

12. The method of claim 11, wherein the value of the functional limit variable comprises a smear limit.

13. The method of claim 11, wherein the optimal exposure time multiplied by the selected light level is approximately equal to the operable exposure time multiplied by the defined light power level.

14. The method of claim 11, wherein the current machine vision inspection system comprises a second machine vision inspection system wherein a specification for at least one of the maximum relative motion speed, the minimum effective exposure time, and the maximum light power of the second machine vision inspection system is different from the corresponding specification of the first precision machine vision inspection system.

15. The method of claim 11, wherein, in sub-step (b-iii), the maximum light power of the current machine vision inspection system is the selected light power level.

16. The method of claim 11, wherein, in sub-step (b-iii), determining an optimal exposure time for the second machine vision inspection system further comprises sub-sub-steps of:

(1) calculating a tentative exposure time based on the at least one parameter indicative of the product of the operable exposure time multiplied by the defined light power level and the selected light power level;

(2) comparing the calculated tentative exposure time with the minimum effective exposure time of the current system to determine which one has a longer value;

(3) if the calculated tentative exposure time is longer, setting the calculated tentative exposure time as the optimal exposure time; and

(4) if the minimum effective exposure time is longer, setting the minimum effective exposure time as the optimal exposure time, and performing at least one of (a) re-calculating the selected light power level based on the at least one parameter indicative of the product of the exposure time multiplied by the defined light power level and the minimum effective exposure time and (b) re-calculating the operational relative velocity based on the value of the functional limit variable and the minimum effective exposure time.

17. The method of claim 11, wherein sub-step (b-iv) of calculating an operational relative velocity further comprises sub-sub-steps of:

(1) calculating a tentative relative velocity based on the value of the functional limit variable and the optimal exposure time;

(2) comparing the calculated tentative relative velocity with the maximum relative motion speed of the current system to determine which one has a lower value;

(3) if the calculated tentative relative velocity is lower, setting the calculated tentative relative velocity as the operational relative velocity; and

(4) if the maximum relative motion speed of the current system is lower, setting the maximum relative motion speed as the operational relative velocity.

18. The method of claim 11, wherein steps (a) and (b) are repeated for each of a set of workpiece inspection images corresponding to respective workpiece features.

19. The method of claim 18, wherein a first value of the functional limit variable corresponds to a first respective workpiece feature, a second value of the functional limit variable corresponds to a second respective workpiece feature, and the first and second values of the function limit variable are different.