Control a Manipulator with a Passive Joint

Hirohiko Arai

Video Proceedings of 1992 IEEE International Conference on Robotics and Automation, 1992.


This video shows dynamic control of a manipulator with a passive joint. The passive joint has a holding brake instead of an actuator. When the brake is engaged, the active joint can be controlled without affecting the state of the passive joint. When the holding brake is released, the passive joint can rotate freely and is controlled indirectly by using the coupling characteristics of manipulator dynamics. The position of the manipulator is controlled by combining these two control modes. In point to point control, mode switching is performed twice. First, the passive joint is fixed and the active joint is accelerated. Next, the passive joint is released and the passive joint is positioned to the desired angle. Finally, the passive joint is fixed again the active joint is positioned. This method is extended to path tracking control. The manipulator is controlled to follow a geometrically specified path. A "path coordinate system" is defined in operational space. The path coordinates consist of a component parallel to the path and a component normal to the path. The component normal to the desired path is controlled to suppress tracking error. This in turn keeps the manipulator on the desired path.