Parallel Kinematic Machine Positioning Accuracy Assessment and Improvement

Although parallel kinematic machines potentially offer high force/torque capacity, structural rigidity, speeds, and dexterity, characterization of the first generation of hexapods has proven the need for improving the positioning accuracy before these new machines will be accepted for manufacturing applications. This paper proposes a systematic approach to assess the accuracy of a parallel kinematic machine subject to structural errors and then to effectively compensate for them. Analytical models were constructed for both the nominal and actual structures. Sensitivity analysis was performed, and it was determined-that of the 33 sources of error, only the six due to strut length deviations are significant. Simulations indicate that the accuracy of strut length calculations shows a discrepancy of at most ±4 micrometers. In summary, the simulation and preliminary experimental results show that the performance of parallel kinematic machines can be enhanced through error modeling and compensation.