DESIGN OPTIMIZATION OF AN ACTUATION MECHANISM FOR A DUAL-ARM ROBOTIC MANIPULATOR

摘要

The design optimization of an actuation mechanism for a dual-arm scara-type robotic manipulator is presented. The manipulator is to be used in a vacuum environment for wafer handling applications in the semi-conductor manufacturing industry. The actuation mechanism consists of a pivoting platform that serves as the common driver link for two four-bar mechanisms each of which drives a scara-type arm. Each of the scara-type arms has a substrate carrying end-effector to pick from or place substrates on a process module. When the pivoting platform is in its neutral position, both of the arms are retracted. When the platform swings to one side, the arm on that side extends while the arm on the other side remains close to retracted position. The actuation mechanism is unique in that it uses just one motor to control the extension of both arms in contrast to the conventional design where each arm requires a motor of its own. However, the design needs to be optimized in order to minimize the effects of kinematic coupling between the two arms and, at the same time, keep the motor torque requirements and encoder resolution requirements to within practical limits. In this article, the relationships between the link lengths of the actuation mechanism, the kinematic coupling between the two arms, maximum encoder resolution requirements and motor torque requirements are described. These relationships are presented in the context of motion profiles characterized by limits on substrate acceleration - a typical requirement in wafer handling applications in vacuum. A methodology for determining link lengths to minimize motor torques and kinematic coupling between arms is presented.