Wave-based control of suspended cable driven parallel manipulators

Abstract

This paper provides a conceptual framework through wave-based strategy to control suspended cable driven parallel manipulators. Since these manipulators usually take up large workspaces, the inclusion and investigation of the effects of cable mass and flexibility on the robot performance is inevitable. Due to modeling complexity, researchers have not paid enough effort on studying the sagging effect on designing controllers. In a large suspended cable robot, stiffness decreases significantly, causing the motion of end effector to undergo unwanted vibration. In this paper, wave based control (WBC), as a newly developed method for mechanical flexible systems is proposed and applied to cable driven parallel manipulators to perform position control and active vibration damping at the same time. The control approach assumes actuator motion as launching a mechanical wave into the flexible system which is absorbed on its return to the actuator, while the launching and absorbing proceed simultaneously. This simple, intuitive idea lets controllers to act rapid and almost vibration free repositioning of the system, using only sensors collocated at the actuator system interface. To accomplish this, the mathematical model of the robot which takes the mass and flexibility of the cable into account is developed first. Then the control method is adapted and presented to prevent or minimize any undesirable sway in the system.