Path Tracking Control of a Manipulator with Passive Joints

Abstract

Each joint of a conventional manipulator has one actuator. Dynamic coupling among joints used to be regarded as a disturbance for control of the manipulator. However, it is possible to control a manipulator with passive joints, which have no actuators, by utilizing the dynamic coupling. In this paper, a method of path tracking control of a manipulator with passive joints is proposed. A desired path is geometrically specified in an operational space. The position of the manipulator is controlled to follow the desired path. In this method, a path coordinate system based on the desired path is defined in the operational space. The path coordinates consist of a component parallel to the desired path, and components normal to the desired path. The equations of motion of the manipulator are described in terms of the path coordinates. The accelerations of the components normal to the desired path can be controlled by using the dynamic coupling among components. This in turn keeps the manipulator on the desired path. Results of path tracking experiments by a two-degree-of-freedom manipulator with a passive joint are presented.