Independent tube position verification system

• US 6,282,461 B1
• Filed: 07/09/1999
• Issued: 08/28/2001
• Est. Priority Date: 07/15/1998
• Status: Expired due to Term

• Current Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Katz, Jeffrey S., Gan, Zhongxue, Fitzgibbons, Lance T.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): NGUYEN, THU V
• Application Number:
  US09/349,981
• Time in Patent Office: 781 Days
• Field of Search: 700/245, 700/247, 700/255, 700/259, 345/433, 345/438, 382/103, 382/106, 382/153, 382/154, 382/170, 382/181, 382/190, 382/203, 382/291
• US Class Current: 700/258
• CPC Class Codes: B25J 9/1697 Vision controlled systems
• CPC Class Codes: G05B 2219/37614 Number of workpieces, counter
• CPC Class Codes: G05B 2219/40613 Camera, laser scanner on end effector, hand eye manipulator, local
• CPC Class Codes: G05B 2219/4701 Edge detector, project line, inclined camera detects discontinuity
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: G06T 7/74 involving reference images or patches
• CPC Class Codes: G06T 7/80 Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration

Abstract

An independent tube position verification system includes a TV camera (16) mounted on an end effector (EE) of a robotic arm (20) mounted in a steam generator (10) beneath the tube sheet (12) to visually track changes in position as the end effector (EE) is moved across the tube sheet (12) by a robotic arm (20). The tube sheet (12) and the tube ends (14) thereof are illuminated by one or more light sources (18) at an oblique angle to cause the desirable presence of shadows in the field of view. The TV camera (16) outputs successive image frames so that displacement of a artifact in the image field in successive frames yields physical displacement information which is converted into velocity and direction information. Changes in position determined by the verification system are compared against position information maintained by the robotic arm (20); any mis-match indicates a loss of tracking integrity requiring a system re-calibration.

Claims

1. A tube position verification system for use in the inspection and service of the tube sheets of steam generators (10) of the type having a plurality of tube ends (14) in a tube sheet (12) arranged pursuant to a predetermined coordinate system and a robotic arm (20) for moving an end effector EE adjacent to the surface of the tube sheet (12) to successive tube end positions, characterized by:

an imaging device (16) connected to the robotic arm (20) for imaging successive image frames as the robotic arm (20) moves an end effector (EE) across the surface of the tube sheet (12);

a light source (18) for illuminating the tube sheet (12) so as to create shadow effects within the field of view of the imaging device (16);

an image processor (104,106) for processing successive images from the imaging device (16) to discern relative displacement of image artifacts from frame to successive frame; and

position coordinate registers (108) for registering displacement changes from the image processor (104,106) to track changes in the coordinates of the end effector (EE),

and further characterized by a control function to maintain the imaging device (16) a selected optimum spacing distance z(n) from the surface of the tube sheet (12) under observation, wherein the control function is characterized by observing an apparent angle of convergence between objects in an image frame, comparing the observed angle to an optimum value, and moving the end effector (EE) toward the optimum spacing distance z(n).

2. The tube position verification system of claim 1, wherein the robotic arm (20) includes position coordinate indicators separate from the position coordinate registers (108) and further characterized by a comparator for the comparison of the position coordinate values of the image processor and the robotic arm (20) to determine tracking integrity of the robotic arm (20).

3. The tube position verification system of claim 1, further characterized in that the robotic arm (20) includes an actuator (24) for moving the end effector (EE) toward the surface of the tube sheet (12) or for moving the end effector (EE) away from the surface of the tube sheet (12).

4. The tube position verification system of claim 1, further characterized in that the imaging device (16) is a television camera.

5. The tube position verification system of claim 1, further characterized in that the light source (18) is aligned at an angle of about 45-55 degrees relative to the plane of the tube sheet (12).

6. The tube position verification system of claim 1, further characterized in that the image device (16) is aligned at an angle of about 45-55 degrees relative to the plane of the tube sheet (12).

7. The tube position verification system of claim 1, further characterized in that the light source (18) creates a shadow effect in which the shadow is at least 40% of the image of each shadow producing feature and its shadow in the image field.

8. The tube position verification system of claim 1, further characterized in that the light source (18) is mounted on the image device (16).

9. A tube position verification method for use in the inspection and service of the tube sheet (12) of steam generators (10) of the type having a plurality of tube ends (14) in a tube sheet (12) arranged pursuant to a predetermined coordinate system and a robotic arm (20) for moving an end effector (EE) adjacent to the surface of the tube sheet (12) to successive specified tube end positions, characterized by:

illuminating the tube sheet (12) so as to create shadow effects thereon;

taking successive image frames of the tube sheet (12) from the robotic arm (20);

processing the successive images from the imaging device (16) to discern relative displacement of image artifacts from frame to successive frame; and

updating position coordinate registers for registering displacement changes from the relative displacement of image artifacts from frame to successive frame,

wherein the processing step is further characterized by a control function to maintain the imaging device (16) at a selected optimum spacing distance z(n) from the surface of the tube sheet (12) under observation, and further characterized by observing an apparent angle of convergence between objects in an image frame, comparing the observed angle to an optimum value, and moving the end effector (EE) toward the optimum spacing distance z(n).

10. The tube position verification method of claim 9, wherein said processing step is further characterized by converting any perceived elliptical artifacts within an image to circular artifacts.

11. An end effector (EE) positioning system for use in the inspection and service of the tube sheets of steam generators (10) of the type having a plurality of tube ends (14) in a tube sheet (12) arranged pursuant to a predetermined coordinate system and a robotic arm (20) for moving an end effector (EE) adjacent to the surface of the tube sheet (12) to successive specified tube end positions, characterized by:

a imaging device (16) connected to the robotic arm (20) for imaging successive image frames as the robotic arm (20) moves an end effector (EE) across the surface of the tube sheet (12), the imaging device (16) positioned to provide image frames with a perspective view of objects within the image frame, the perspective view such that objects appear to converge toward a distant vanishing point;

a light source (18) for illuminating the tube sheet (12) so as to create shadow effects within the field of view of the imaging device (16);

an image processor (104,106) for processing successive images from the imaging device (16) to discern an apparent angle of convergence of image artifacts from frame to successive frame; and

an actuator for effecting movement of the end effector (EE) toward or away from the tube sheet (12) to maintain an optimal spacing distance z(n) as a function of the apparent angle of convergence.

12. The end effector (EE) positioning system of claim 11, further characterized in that the light source (18) is aligned at an angle of about 45-55 degrees relative to the plane of the tube sheet (12).

13. The end effector (EE) positioning system of claim 11, further characterized in that the image device (16) is aligned at an angle of about 45-55 degrees relative to the plane of the tube sheet (12).

14. The end effector (EE) positioning system of claim 11, further characterized in that the light source (18) creates a shadow effect in which the shadow is at least 40% of the image of each shadow producing feature and its shadow in the image field.

15. The end effector (EE) positioning system of claim 11, further characterized in that the light source (18) is mounted on the image device (16).

16. An end effector (EE) positioning method for use in the inspection and service of the tube sheet (12) of steam generators (10) of the type having a plurality of tube ends (14) in a tube sheet (12) arranged pursuant to a predetermined coordinate system and a robotic arm (20) for moving an end effector (EE) adjacent to the surface of the tube sheet (12) at an optimum spacing distance z(n) to successive specified tube end positions, characterized by:

illuminating the tube sheet (12) so as to create shadow effects thereon;

taking successive image frames of the tube sheet (12) from the robotic arm (20), the successive image frames taken at an angle relative to the surface of the tube sheet (12) to provide a perspective view thereof in which objects in the image frame appear to converge toward a distant vanishing point;

processing the successive images from the imaging device (16) to discern an apparent angle of convergence of objects within the image frame; and

maintaining the imaging device (16) a selected optimum spacing distance z(n) from the surface of the tube sheet (12) under observation as a function of the apparent angle of convergence of objects within the image frame.

17. The end effector (EE) positioning method of claim 16, wherein the control function is characterized by measuring an apparent angle of convergence α

between objects in an image frame;

comparing the measured angle α

to an optimum value, and moving the end effector (EE) toward the optimum spacing distance z(n).

18. The end effector (EE) positioning method of claim 16, further characterized in that the robotic arm (20) includes an actuator (24) for moving the end effector (EE) toward the surface of the tube sheet (12) or for moving the end effector (EE) away from the surface of the tube sheet (12).