Clearance and manufacturing errors' effects on the accuracy of the 3-RCC Spherical Parallel Manipulator

This paper deals with the analysis of a Spherical Parallel Manipulator (3-RCC) with clearance and manufacturing errors. The objective of this study is to determine the error on the pose of the platform in presence of these imperfections. The assumption of the manufacturing errors and clearance as small displacements allowed using the screw method to calculate the pose error of the platform for 10(7) combinations spanning the workspace of the robot. The stochastic results are presented at 95% confidence of likelihood. We showed that the superposition principle does not work when we consider both the manufacturing errors and the clearance despite the assumption of small displacements. We also showed that the pose error is configuration dependent and it reaches high values near singular configurations. The axial displacement in the C joints is also determined as a function of the manufacturing errors and the clearance. It is shown that this displacement is also configuration dependent and it can reach high values, which justifies the need to release the axial displacement in the 3-RRR overconstrained architecture. (C) 2012 Elsevier Masson SAS. All rights reserved.