Abstract: The method to control the uncompensatable pose error of a class of 3-DOF parallel kinematic machines with parallelogram struts is investigated. The error mapping function is formulated which allows the geometric errors affecting the orientation accuracy of the moving platform to be found. It is observed that the orientation error is uncompensatable and the results of accuracy synthesis show that it is impossible to control such error by allocating the manufacturing tolerances to each related components since they are too tight to be realized. Consequently, two schemes are proposed that allow the orientation pose error to be effectively minimized by adding an adjustable bush between two components of the carriages.

Key words: Accuracy synthesis, Assembly process, Error modeling, Parallel kinematic machine