Accuracy Analysis Considering Clearances and Elastic Deformations in Parallel Manipulators

Clearances at joints and deformability of links produce a loss of accuracy when positioning a mechanism. End-effector pose error depends on the mechanism configuration, the applied external wrenches, the nature and magnitude of clearances and the rigidity of the mechanical components. Clearance magnitudes and elastic deformations are much smaller than other dimensions and consequently they are assumed to be infinitesimal, which leads to a linear analysis. Under this assumption, velocity equations can be utilized instead of position ones, and they can be easily expressed by using screw coordinates. A general methodology for analyzing the pose accuracy of a parallel manipulator is presented, making use of the example of a 5R planar mechanism along a pick-and-place trajectory.