Design and analysis of the statically balanced direct-drive robot manipulator

Abstract A practical architecture, using a four-bar linkage, is considered for the University of Minnesota direct-drive robot (Kazerooni, H., Kim, S.: A new architecture for direct drive robots. In Proc. IEEE International Conference on Robotics and Automation, Philadelphia, Pennsylvania, April 1988). This statically balanced direct-drive robot has been constructed for stability analysis of the robot in constrained manipulation (Kazerooni, H. et al.: Fundamentals of robust compliant motion for robot manipulators. IEEE J. Robotics Automation 2: 1986; Kazerooni, H.: On the robot compliant motion control. ASME J. Dynamic Systems Msmt Control; 111 (3): September 1989. Kazerooni, H. et al.: Theory and experiments on robot compliant motion control. ASME J. Dynamic Systems Msmt Control, June 1990). As a result of the elimination of the gravity forces (without any counterweights), smaller actuators and, consequently, smaller amplifiers were chosen. The motors yield acceleration of 5 g at the robot end point without overheating. High torque, low speed, brushless AC synchronous motors are used to power the robot. Graphite-epoxy composite material is used for construction of the robot links. A 4-node parallel processor has been used to control the robot. A compliant motion control method has been derived and experimentally verified to guarantee stable constrained maneuvers for the robot. As part of the research work, a general criterion has been derived to guarantee the stability of robot manipulators in constrained maneuvers.