Precision study of a decoupled four degrees of freedom parallel robot including manufacturing and assembling errors

This paper presents a study of geometric errors due to assembly and manufacturing tolerance on the kinematic accuracy of a parallel robot with four degrees of freedom with decoupled motions and fully isotropic in translation - ISOGLIDE4-T3R1. The effects of geometric errors on the kinematic accuracy are analytically calculated under the hypothesis that the components are rigid bodies by using the ISOGLIDE4-T3R1 forward Jacobian. Analytic calculations give a general form for the pose accuracy in the workspace. They both give a form for the ISOGLIDE4-T3R1 sensitivity to geometric errors, which allows to quantify which defect is more harmful, and how the sensitivity varies in the workspace. In the second part in this paper, geometric error measurements on the robot prototype are presented. They are carried out using vision-based metrology. This system not only has the required capabilities but also has the advantage of measuring six degrees of freedom in the same coordinate system without contact. The metrology results and analytic calculations allow the hypothesis of rigid bodies to be quantified and open up prospects for the error influences on robot stiffness and accuracy with deformable bodies.