Correction of Workpiece Frame for Robot-Assisted Ultrasonic Nondestructive Testing

Abstract

The combination of robot and ultrasonic nondestructive testing technology enables automated ultrasonic scanning of complex surfaces. Before the scanning, the robot needs to calibrate the workpiece frame by clamping the tip tool, thereby establishing the relationship between the offline programming trajectory and the actual placement of the workpiece. The tip will inevitably wear out during the using process, and the calibration error will be introduced into the calibration process, which will cause the actual movement track of the manipulator to deviate from the theoretical planning trajectory. Therefore, it is necessary to correct the workpiece frame. In this paper, target point cloud was collected based on ultrasonic propagation time and source point cloud was collected through joint angles. Using the improved ICP (iterative closet points) algorithm to calculate the coordinate conversion parameters. The ultrasonic testing proves that the improved ICP algorithm has higher registration accuracy and efficiency. The artificial flat bottom hole defect with a diameter of 0.5–1 mm can be clearly distinguished on the C-scan image.