M. S. Thesis Abstract

Control of a Three-Link In-Parallel Manipulator

Christopher Yien

June 1989


This thesis describes the implementation of position and trajectory control on a three degree-of-freedom in-parallel manipulator. The manipulator has inherent non-linearities that challenge the robustness of its controller. These include actuator saturation, link friction (static and Coulomb friction), and the effects of over-constrained forces on the manipulator links. The effects of these non-linearities were investigated as several different control schemes were tested. A full-state feedback control system with a full-order observer was implemented for positioning. In addition, a hybrid digital/analog controller was implemented that contours the static actuator output characteristics. This controller, with an analog velocity feedback loop and a digital position feedback loop, effectively negates the influence of nonlinear friction without requiring prior or on-line modeling of friction. Both types of controllers were implemented with integral as well as zero phase error tracking control for trajectory control. The effects of payload and payload direction on the performance of each controller were also investigated.