Manufacturer of Nuclear Plants uses SmartVision™ Success Story
As a part of retrofitting a Nuclear Reactor, a number of very large (10+ ton) specialized tools needed to be mated with the reactor face. Each of these tools completed a specific operation on each pressure tube, and that operation needed to be performed once per tube (by many different operators) over the ~380 tubes per reactor face.
Several vision systems were required to aid the operators in aligning the tool with each tube (or thumb tack or end fitting which cover it at specific times). Over time, the positions (X, Y and Z) and lengths (along Z) of the tubes changed considerably because of the prolonged exposure within the reactor.
Three different vision systems performed similar docking operations, but with different targets in the field of view of the camera. The cameras were each positioned so that they viewed the target object at an angle. Once the camera was calibrated, feature points of each target were used to reconstruct the 3D pose of the object.
In the case of the thumbtack and end fittings, a triangle comprised of three features was used, while in the case of the tube, the two ellipses were used directly. The X and Y corrections that were reported back on the operator screens were reported in the tool coordinates, and could be used by the operator to control the motion stages of the tool.
To complicate matters, the application locating the tube had its camera mounted on a SmartVision controlled goniometer, allowing the camera to tilt. The effect of this tilting had to be considered when computing the X and Y corrections.
The most exciting technology used in this application was the camera calibration. The full 3D camera calibration consisted of computing the 4 intrinsic camera parameters (focal length, scaling, and the coordinates of the principal point) and 4 distortion coefficients (2 radial and 2 tangential). This calibration allowed the single camera to be used to measure real world 3D (six degree of freedom) coordinates using single images. The calibration routine used several somewhat arbitrary views of a flat checkerboard-like target.
Analog cameras were used in this application, primarily because of the price as they would be replaced as they degrade due to radiation exposure.
Initially, the customer was somewhat skeptical that these applications were possible. Now, the customer is very happy with the system functionality.
Internal testing of the end fitting setup has shown a positional accuracy (3s) in the 0.008” range, and an angular accuracy (3s) in the 0.13 degree range over the relevant work envelope. To put the target size into context, the centers of the white dots on the end fitting are 2.5” apart.