Kinematics optimization for high positioning accuracy of a 4-DOF parallel manipulator for semiconductor applications

The end-effector kinematics error of a manipulator is caused by variations in machining accuracy of linkages. In most manipulators, the structural design results in an error magnification from the linkage variation to the end-effector position. In this paper, an optimization approach for suppressing kinematics error magnification is considered for a 4-DOF parallel manipulator. Two objective functions are developed for characterizing the error magnification effect. The kinematic parameters are then determined by minimizing these objective functions. It is shown that the proposed approach can reduce the error magnification to such a degree that the magnification factor is reduced to close to one. This means that the end-effector kinematics error can be made to match the error tolerance allowed in the manufacturing of the linkages.