Error Compensation for Continuous Path Operation of 3-RRR Planar Parallel Manipulator with Clearance in the Joints

In this paper, we study continuous path operation of a 3-RRR planar parallel manipulator whose joints have clearance. During continuous path operation end-effector must go through a predefined path. However, clearance introduces an additional uncontrollable degree of freedom to the manipulator. Therefore it causes error and should not be neglected in a successful path operation. In this paper, inverse and direct kinematicswith and without considering clearances, of the manipulator have been utilized. The direct kinematics in the presence of clearance is complicated and has no analytical solution. Therefore, a Neural Network is used to tackle this problem. The clearances are modelled as mass-less virtual links whose angular displacement are obtained from dynamic analysis of the manipulator. We have shown that the errors in the path can be efficiently compensated by appropriate modifications of the inputs for both vertical and horizontal planes. Perhaps surprisingly, the flexibility and generality of the proposed method makes it applicable to any parallel manipulator with revolute joints by just modifying the actuator inputs and without any changes in the design of manipulator.