Method and system for inspecting a low gloss surface of an object at a vision station

• US 6,239,436 B1
• Filed: 12/24/1998
• Issued: 05/29/2001
• Est. Priority Date: 04/22/1996
• Status: Expired due to Fees

• Current Assignee: Perceptron Incorporated (Atlas Copco AB)
• Original Assignee: Perceptron Incorporated (Atlas Copco AB)
• Inventors: Haven, Neil, Parker, Jeffrey B, Czubko, Myron
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): HANIG, RICHARD E
• Application Number:
  US09/171,504
• Time in Patent Office: 887 Days
• Field of Search: 250/341.8, 250/345, 250/339.05, 250/339.06, 250/339.11, 250/572, 356/32, 356/376, 356/371, 356/446, 348/128, 209/581
• US Class Current: 250/341.8
• CPC Class Codes: G01N 2021/8829 Shadow projection or structured background, e.g. for deflectometry three-dimensional metrology of surfaces G01B11/25
• CPC Class Codes: G01N 21/57 Measuring gloss
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features

Abstract

A method and system are provided for inspecting a low gloss surface (12) of an object (14) at a vision station utilizing a regular, extended pattern of infrared radiation. The system includes an infrared radiation source (10) and an infrared image converter and/or infrared cameras (16) to automatically locate a surface defect in the object. A signal processor processes a first set of electrical signals from the infrared cameras to obtain a second set of electrical signals which represent pattern distortions in the reflected infrared radiation signal caused by the surface defect in order to locate the surface defect in the object. The second set of electrical signals may be processed to classify the surface defect in the object as being an “in-dent” or an “out-dent”.

Claims

1. A method for inspecting a low gloss surface of an object at a vision station to automatically locate a surface defect in the object, the method comprising the steps of:

directing a regular, extended pattern of radiation, having a wavelength longer than the wavelength of visible light, but shorter than the dimensions of the surface defect, at the low gloss surface of the object to generate a corresponding reflected radiation signal;

imaging the reflected light signal at the vision station to generate a first set of electrical signals representing the surface defect to be located; and

processing the first set of electrical signals to obtain a second set of electrical signals representing pattern distortions in the reflected radiation signal caused by the surface defect to locate the surface defect in the object.

2. The method as claimed in claim 1 wherein the radiation is infrared radiation.

3. The method as claimed in claim 2 wherein the radiation is broadband infrared radiation.

4. The method as claimed in claim 1 further comprising the step of processing the second set of electrical signals to classify the surface defect in the object.

5. The method as claimed in claim 1 further comprising the steps of moving the object relative to the pattern of radiation at the vision station and generating a position signal representative of position of the object relative to the pattern of radiation at the vision station and wherein the first set of electrical signals are processed with the position signal to locate the surface defect in the object.

6. The method as claimed in claim 1 further comprising the step of generating a control signal based on location of the surface defect in the object and controllably moving a surface marking mechanism between a withdrawn position and a surface marking position in response to the control signal to mark the surface of the object as a function of the location of the surface defect.

7. The method of claim 1 wherein the step of processing includes the step of processing the second set of electrical signals together to correlate the pattern distortions.

8. A system for inspecting a low gloss surface of an object at a vision station to automatically locate a surface defect in the object, the system comprising:

a structured radiation source located at the vision station for directing a regular, extended pattern of radiation, having a wavelength longer than the wavelength of visible light, but shorter than the dimensions of the surface defect, at the low gloss surface of the object to generate a corresponding reflected radiation signal;

an imaging detector having an image plane located at the vision station for imaging the reflected radiation signal and to generate a first set of electrical signals representing the surface defect to be located; and

a signal processor coupled to the imaging detector for processing the first set of electrical signals to obtain a second set of electrical signals representing pattern distortions in the reflected radiation signal caused by the surface defect to locate the surface defect in the object.

9. The system as claimed in claim 8 wherein the radiation is infrared radiation, the structured radiation source is an infrared radiation source and the imaging detector is an infrared imaging detector.

10. The system as claimed in claim 9 wherein the infrared imaging detector is an infrared camera.

11. The system as claimed in claim 8 further comprising an optical element adapted to be focused at or near the low gloss surface for forming an image containing the surface defect in the image plane from the reflected radiation signal.

12. The system as claimed in claim 8 wherein the regular, extended pattern of radiation has a parallel line structure.

13. The system as claimed in claim 8 wherein the structured radiation source includes a plurality of electrically-heated resistive wires.

14. The system as claimed in claim 8 wherein the structured radiation source includes a plurality of strips of electrically-heated heat tape.

15. The system as claimed in claim 8 further comprising means for moving the object relative to the pattern of radiation at the vision station and a sensor coupled to the means for moving and the signal processor to generate a position signal representative of position of the object relative to the pattern of radiation at the vision station and wherein the first set of electrical signals are processed with the position signal by the signal processor to locate the surface defect in the object.

16. The system as claimed in claim 8 further comprising a controller coupled to the signal processor for generating a control signal based on location of the surface defect in the object and a surface marking mechanism movable between a withdrawn position and a surface marking position in response to the control signal to mark the surface of the object as a function of the location of the surface defect.

17. The system as claimed in claim 16 wherein the mechanism includes a robot and wherein the controller is a robot controller.

18. The system as claimed in claim 8 wherein the signal processor processes the second set of electrical signals to classify the surface defect in the object.

19. The system as claimed in claim 8 wherein the structured radiation source directs the pattern of radiation at a plurality of low gloss surfaces of the object to generate a plurality of corresponding reflected radiation signals and wherein the system further comprises a plurality of imaging detectors located at the vision station for imaging the plurality of reflected radiation signals.

20. The system of claim 8 wherein the signal processor processes the second set of electrical signals together to correlate the pattern distortions.

21. A method for inspecting a low gloss surface of an object located at a vision station, the method comprising the steps of:

(a) directing a regular, extended pattern of radiation, having a wavelength longer than the wavelength of visible light, but shorter than the dimensions of the surface defect, at the low gloss surface of the object to generate a corresponding reflected radiation signal; and

(b) converting the reflected radiation signal into a visible image for visual observation of pattern distortions in the reflected radiation signal caused by the surface defect.

22. The method of claim 21 wherein the radiation is infrared radiation.

23. The method of claim 21 wherein steps (a) and (b) are repeated to obtain a sequence of visible images and wherein the method further comprises the steps of storing the sequence of visible images and displaying the stored sequence of visible images so that visual observation may occur at a different time-rate than the reflected radiation signals are generated.

24. A system for inspecting a low gloss surface of an object located at a vision station, the system comprising:

a structured radiation source located at the vision station for directing a regular, extended pattern of radiation, having a wavelength longer than the wavelength of visible light, but shorter than the dimensions of the surface defect, at the low gloss surface of the object to generate a corresponding reflected radiation signal; and

an image converter located at the vision station for converting the reflected radiation signal into a visible image for visual observation of pattern distortions in the reflected radiation signal caused by the surface defect.

25. The system of claim 24 wherein the radiation is infrared radiation, the source is an infrared radiation source and the image converter is an infrared image converter.

26. The system of claim 24 further comprising a storage device coupled to the image converter for storing a sequence of visual images and a display coupled to the storage device for displaying the stored sequence of visible images so that visual observation may occur at a different time-rate than reflected radiation signals are generated.