Kinematic Calibration for Redundantly Actuated Parallel Mechanisms

Abstract

In this paper we present simulation and experimental results for kinematic calibration algorithms using a planar seven-bar 2-d.o.f. redundantly actuated parallel mechanism. Although simple in appearance and identical to the non-redundant case, random joint errors due to the internal forces generated by the additional actuators make kinematic calibration more difficult. With a few exceptions, previous works in kinematic calibration ignored this issue and concentrated on the common non-redundant situation. Force redundancy aspects in closed chain mechanisms have also been extensively presented in the scientific community, however calibration related concerns have not been specifically addressed. Kinematic calibration for our mechanism is performed in state of redundant actuation within the enlarged workspace of the mechanism. Tool plate information is acquired using a laser ball bar and the mechanism’s kinematic calibration parameters are identified using an optimization algorithm. For the constant joint offsets case introduced by internal forces the accuracy of the tool plate after kinematic calibration improved by 25%.