OVERCOMING SINGULARITIES IN PARALLEL MANIPULATORS BY CHANGE IN BASE LENGTH

Abstract

The focus of this project is 5-bar parallel manipulator. There are many approaches to eliminate the singularities of this kind of manipulators, like redundant actuation, connecting two inverse kinematic solutions without a singularity, topology of self-motion manifolds of redundant manipulators, self-motion, extending the link length by prismatic joints etc. In this project, a novel approach is proposed to eliminate the singularities from the workspace. This investigation is proposed to be carried out for 2-DOF planar parallel manipulator to establish the concept. One of the base actuators (motors) is fixed to a linear actuator. This linear actuator extends when the end-effector is in the proximity of singularity loci. As the manipulator clears out of the singularity condition, then again, the parallel manipulator is reverted back to the original position by the linear actuator. Mathematically, when the manipulator attains a singularity condition, the Jacobian matrix loses/gains rank. A reconfiguration of the manipulator to a defined degree at this instance ensures a change in the determinant of the Jacobian matrix to a non-zero value, thereby avoiding the singularity condition. Once the singularity loci are avoided, the base length is reverted to its actual state by the linear actuator for the same trajectory of the end–effector within the defined workspace of the manipulator. As a result, the used trajectories remain unaffected by the effect of singularities and thus improve the efficiency of the parallel manipulator significantly.