Dynamical analysis and control of rotatory manipulators with time varying mass loads

Abstract

Manipulators are widely used in industrial fields as automation equipment and robotic structures. Besides moving objects, manipulators often work with variable payloads, and the residual vibration significantly affects the position accuracy of manipulators. This paper mainly investigates the dynamic characteristics of flexible manipulators with time varying mass payloads and active control of the residual vibration is carried out. Finite element method is utilized to construct the dynamical model, and responses of the system are calculated by Bathe’s method. The influence of the time varying mass is analyzed in details, including an increasing mass case and a decreasing mass case. Then active control of the residual vibration is given based on a PID controller. To improve the control effect, genetic algorithm (GA) is applied to tune the parameters of the PID controller. Simulations demonstrate that the time varying mass affects the residual vibration of the system remarkably. For a decreasing mass system, a nonstructural negative damping is induced and the residual vibration may be strengthened, while for an increasing mass system, a nonstructural positive damping is caused and the residual vibration may be attenuated. The comparison of the control methods demonstrates that the GA-PID controller results in a significant improvement in the vibration reduction.