A calibration method of redundantly actuated parallel mechanism machines based on projection technique

This paper presents a new calibration method for redundantly actuated parallel mechanism machines without measuring stiffness of actuating joints directly. The stiffness measurement of the actuating joints was a mandatory procedure to calibrate the redundantly actuated parallel mechanism in previous works. A new error propagation formula by using projection technique is established, which projects the constraint force terms onto the orthogonal complementary terms, in order to remove the need to know joint stiffness. Two sets of experimental verification are presented: (1) a two d.o.f. Gosselin's mechanism manipulator with three actuators and (2) a three d.o.f. parallel platform with four actuators.