Vibration Reduction in Slewing of a Very Flexible One-Link Manipulator Using Shaped Reference Inputs

Abstract

Future trends suggest that manipulators will be required to be light and to carry large payloads and this encourages the study of flexible-link robots. However, after more than three decades of investigation, vibration control of the flexible-link robot is still an unsolved problem. Researchers have made much progress using active and passive controls and with structural modification and new sensors and actuators, but a simple, effective and reliable vibration controller has yet to be found. To reduce vibration, shaping the reference input so that no energy is injected around the flexible modes can be performed in the time domain, by convolution of the input with a sequence of impulses or in the frequency domain, by optimally constructing a new input from suitable basis functions. While many researchers have applied the time-domain method to the flexible-link robot, the frequency-domain method is rarely seen with this type of robot. This paper investigated the results of applying the frequencydomain command shaping method to a flexible one-link robot. The closed-loop system consisted of a feed-forward, computed-torque loop and a feedback PID loop. As vital information for this method, the range of natural frequencies with respect to the robot’s parameters was obtained from an exact model, treating the flexible link as an Euler-Bernoulli’s beam. Using minimum a priori knowledge of the robot, the experimental results showed that the method is effective in reducing the vibration of a slewing flexible-link robot.