Research On Self-excited Vibration And Working Mode Conversion Of Planar 3-(?)RR Parallel Manipulator

The parallel manipulator has been widely used in precision positioning,high-speed movement and trajectory tracking.It also has been widely used in the field of precision manufacturing,such as semiconductor processing,micro-nano operation and medical engineering.The special topology structure of parallel manipulator causes singular configurations in the working space,which results in losing some constraints of the parallel manipulator,losing control of the moving platform and causing self-excited vibration.The working space and the singular configuration of the 3-(?)RR planar parallel manipulator(PPM)are analyzed.Based on the experiment,the self-excited vibration and working mode conversion of the 3-(?)RR PPM are studied.The aspects of the paper are listed as follows:The physical significance and practical configurations of singularities have been studied in detail.The singular configuration of the 3-(?)RR PPM is analyzed,which includs the classification and the detection of the singular configuration.The singular configuration is determined by kinematic Jacobian matrix,and the singular configuration of the 3-(?)RR PPM can be divided into the forward Jacobian matrix singular configuration and the reverse Jacobian matrix singular configuration.The characteristics of forward Jacobian matrix singular configuration are different in eight working modes.However,the characteristic of the reverse Jacobian matrix singular configuration are same in different working modes.The effect of singular configurations on the movement of the 3-(?)RR PPM is studied by experiments.Through experiments,the conclusion could be obtained that the movement of the end moving platform is uncertain in forward Jacobian matrix singular configurations.The reason of self-excited vibration of the 3-(?)RR PPM is analyzed under different experimental conditions.The effect of singularity configuration and servo gain of drive motors on self-excited vibration are researched.The self-excited vibration is respectively tested in the singular configurations and non-singular configurations.The input position,velocity and acceleration of active joints are tested by sensors,the position and acceleration of the moving platform could be obtained by forward kinematic solutions.The accelerations of the moving platform obtained by forward kinematic solutions agree with the experimental results tested by accelerometers in the non-singular configuration.Finally,the self-excited vibration could be avoided by adjusting the servo gain in the non-singular configuration.The working mode conversion of the 3-(?)RR PPM is studied.For the free positioning in the global working space,the best combination of working modes is determined to avoid the forward Jacobian matrix singular area in the working space.By comparing the similarity and differences of the working space and singular properties among eight working modes,the conversion strategies of eight working modes have been proposed.Finally,the validity of the working mode conversion of the 3-(?)RR PPM is verified by experiments.