Statically balanced direct drive manipulator

SUMMARY A practical architecture, using a four-bar-linkage, is considered for the University of Minnesota direct drive rotot1. This statically-balanced direct drive robot has been constructed for stability analysis of the robot in constrained maneuvers.2-6 As a result of the elimination of the gravity forces (without any counter weights), 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, brush-less AC synchronous motors are used to power the robot. Graphite-epoxy composite material is used for the construction of the robot links. A 4-node parallel processor has been used to control the robot. The dynamic tracking accuracy-with the feedforward torque method as a control law- has been derived experimentally. KEYWORDS: Direct drive; Robot; Statically balanced; Tracking accuracy; Linkage. the arm is only under its static load. 4. Structural Stiffness. The structural stiffness of the direct drive arms is greater than the non-direct drive systems. About 80% of the total mechanical compliance in most non-direct drive industrial robots is caused by transmission systems9.IO. The high structural stiffness allows for wide bandwidth control. The low structural stiffness of non-direct drive arm$, due to the existence of IIlany mechanical elements in the transmission system, is a limiting factor on achievement of a relatively wide bandwidth control system. 5. Backlash and Friction. The direct drive arms are free from mechanical backlash and friction due to elimination of transmission systems. A small mechanical backlash in the transmission system would cause the gear teeth to wear faster. The high rate of wear in the gear would develop an even larger backlash. About 25% of the torque in non direct drive arms is used to overcome the friction. II 6. Performance and Control. Because of elimination of the transmission systems, and consequently backlash, the control and performance analysis of direct drive arms is more straightforward than the non-direct drive arms (not necessarily "easier"). 7. Accuracy. The accuracy of direct drive arms is questionable. The lack of the transmission system eliminates cogging, backlash, and its corresponding limit

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