Abstract: Based on the structure of 6-TPS parallel kinematic machine tools, the mapping from machine’s kinematics errors to tool’s motion errors is formulated, and the relations between input errors and output errors of both single kinematic link and whole machine are analyzed. The singular values of Jacobian matrix are used to define three error sensitivity measures, which are comprehensive error sensitivity, absolute error sensitivity and directional error sensitivity. According to these, two terms are defined, which are named comprehensive error coefficient and comprehensive error degree, and used to evaluate the precision of various configurations of this type of mechanisms. At last, based on a real parallel kinematic machine tool – VAMT1Y, the kinematic precisions under various tool trajectories are compared, and a relatively optimal trajectory is chosen.

Key words: Stewart platform, Parallel kinematic machine tool (PKMT), Precision measure Comprehensive error coefficient Comprehensive error degree