Experimental validation of the influence of kinematic redundancy on the pose accuracy of parallel kinematic machines

In this paper experimental results are presented to compare the performance of kinematically redundant parallel robots with respect to their non-redundant counterparts. The main purpose is to validate existing simulated, i.e. claimed, findings demonstrating the advantages of kinematic redundancy in terms of singularity avoidance and, therefore, accuracy and precision. Exemplarily, the kinematically redundant prototype of the Institute at Mechatronic Systems is introduced. It is based on the well known planar 3RRR mechanism. In order to achieve kinematic redundancy, a prismatic actuator is added to the structure allowing one base joint to move linearly. As a result, the mechanism is able to reconfigure, i.e. optimize, its geometry according to different performance criteria and motion strategies. While performing a geometrical reconfiguration and following several desired (optimized) trajectories the pose of the end-effector is determined using an external measurement device. Hence, in addition to the encoder data of the actuators the performance can be analyzed without using any (uncertain) kinematic models. This allows for a meaningful comparative evaluation of the performance of kinematically redundant mechanisms.