Self-excited vibration of a 3-PRR planar parallel robot

Abstract

Self-excited vibration of parallel robots can seriously affect the motion performance and damage the mechanical structure. In order to study the self-excited vibration characteristics of a 3-PRR (where P and R represent the prismatic and revolute joints respectively and the underlined letter represents the actuated joint) planar parallel robot, dynamic model is firstly established and the singularity is analyzed theoretically. Then the dynamic characteristics at internal and boundary singularities are both explored experimentally. The motion form and generating mechanism of the self-excited vibration are researched. The influencing factors on vibration frequency are obtained and the self-excited vibration during trajectory tracking motion is analyzed. Finally, a singularity escaping strategy is proposed and tested. Theoretical analysis and experimental results show that the performance of parallel robot deteriorates dramatically at singularities. Nevertheless, the parallel robot can pass through the internal singularity successfully with optimized load and motion speed so that the workspace can be expanded. The 3-PRR planar parallel robot exhibits self-excited vibration at internal singularities, which is mainly caused by the singularity, self-regulation of motors and the closed-chain coupling effect. The vibration frequency is mainly determined by singular configuration and the structural parameters. The parallel robot can maintain self-excited vibration state while carrying out trajectory tracking under a singular attitude angle. Moreover, the proposed singularity escaping strategy is verified to be feasible so that the self-excited vibration can be eliminated effectively.