Machine vision method for the inspection of a material for defects

• US 6,531,707 B1
• Filed: 04/27/2001
• Issued: 03/11/2003
• Est. Priority Date: 12/29/2000
• Status: Active Grant

• Current Assignee: Ametek Incorporated
• Original Assignee: Cognex Corporation
• Inventors: Favreau, Patrice, Wolinsky, Jeffrey, Jaaskelainen, Markku E.
• Primary Examiner(s): Allen, Stephone B.
• Assistant Examiner(s): Spears, Eric J
• Application Number:
  US09/842,842
• Time in Patent Office: 683 Days
• Field of Search: 250/205, 250/559.45, 250/559.46, 250/559.01, 250/559.07, 250/559.08, 356/429, 356/430, 382/112, 382/141, 348/83, 348/370, 348/362, 348/364, 348/125
• US Class Current: 250/559.46
• CPC Class Codes: G01N 2021/8909 Scan signal processing specially adapted for inspection of running sheets
• CPC Class Codes: G01N 21/8901 Optical details; Scanning details per se G02B

Abstract

A machine vision method and system for inspecting a material. The system comprises a light source arranged to illuminate the material and an imaging device configured to acquire image data corresponding to at least one characteristic of the material while the material is being illuminated by the light source. An image processor is configured to normalize the image data and to control adjustment of an exposure control level for the imaging device based upon the normalized image data. An exemplary method of implementing the machine vision system may include illuminating a material using a light source and obtaining image data corresponding to the material using an imaging device. The image data may be normalized and the adjustment of an exposure control level of the imaging device may be controlled based on the normalized image data.

Claims

1. A method comprising:

illuminating a material using a light source, the material having at least one characteristic;

obtaining image data corresponding to the material using an imaging device;

normalizing the image data to provide normalized image data;

processing the normalized image data to detect defects in the material; and

controlling the adjustment of an exposure control level of the imaging device based on the image data.

2. The method of claim 1, wherein the exposure control level is set based on the at least one characteristic of the material.

3. The method of claim 1, the at least one characteristic of the material indicates a grade of the material.

4. The method of claim 1, the at least one characteristic of the material indicates multiple grades of the material.

5. The method of claim 1, wherein obtaining image data comprises setting an initial exposure control level of the imaging device for the material based on the at least one characteristic of the material.

6. The method of claim 1, wherein obtaining image data comprises obtaining a measured intensity level based on the at least one characteristic of the material.

7. The method of claim 1, wherein normalizing the image data implements adaptive normalization or static normalization.

8. The method of claim 1, wherein normalizing the image data comprises obtaining an average intensity level based on the at least one characteristic of the material.

9. The method of claim 8, wherein controlling the adjustment of the exposure control level comprises comparing a measured intensity level of the material to the average intensity level of the material.

10. The method of claim 1, wherein the at least one characteristic of the material is determined based on optical properties of the material.

11. The method of claim 10, wherein the optical properties include reflectivity properties, transmissivity properties, or reflectivity and transmissivity properties.

12. A method for inspecting multiple grades of a material, comprising:

illuminating a material using a light source;

obtaining image data corresponding to the multiple grades of the material using an imaging device, a certain grade of the material being used to define an exposure control level;

normalizing the image data;

processing the normalized image data to detect defects in the material; and

controlling the adjustment of the exposure control level of the imaging device based on the image data.

13. The method of claim 12, wherein normalizing the image data implements adaptive normalization or static normalization.

14. The method of claim 12, wherein the adjustment of the exposure control level is optional.