Visual Servo Control for Ball-on-Plate Balancing: Effect of PID Controller Gain on Tracking Performance

Abstract

Ball-on-plate balancing is a popular challenge for the implementation of control systems. In this paper, the Universal Robots UR3 industrial arm is set up for the challenge. An acrylic plate is firmly grasped by the robot’s gripper. The pure rotation about three axes is achieved at the center of the plate by considering the offset of the plate from the tool frame. A web camera is mounted on the last link to observe the position of a ping pong ball moving on top of the plate. The color-based object detection is used with OpenCV and the coordinates of the ball are mapped to the pixel of the camera. At the beginning of each test, the ball was placed away from the center of the plate. Considering the x-axis and y-axis error of the ball position away from the center of the plate, the robot arm stabilizes the ball to the center according to the PID controller gain configurations. The effect of the proportional gain on reducing the rise time of the response is observed. The advantage of the derivative gain on reducing the response overshoot is observed. The advantage of the integral gain on reducing the steady-state error is not clearly observed for this ball-on-plate balancing problem. The implemented controller is robust against the small vibration of the camera with respect to the robot arm.