Dynamic analysis of a 3-(P)under-barRR parallel mechanism by considering joint clearances

The joint clearance causes poor dynamic mechanism performance, and the effect of multiple clearance joints on many complex mechanisms is unclear. This paper therefore performs dynamic analysis of a 3-PRR parallel mechanism by considering joint clearances. A concise method based on Newton-Euler equations is presented for the planar multibody system, and the root mean square error (RMSE) of the angular acceleration is proposed as an index to quantify the effect of the joint clearance on the dynamic behaviour. To improve the performance of the mechanism, this paper discusses the dynamic response of three parameters: the clearance size, restitution coefficient of the material and movement trajectory. Moreover, the simulation results indicate that: (i) the maximum absolute value of the displacement deviation is approximately triple the clearance size, and the nonlinearity of the mechanism rises obviously with increasing clearance size; (ii) different movement trajectories have various dynamic responses, and the nonperiodic response decreases due to the coupling effect of certain special movement trajectories; and (iii) a material with a moderate value of coefficient restitution is beneficial to the dynamic response, because the trend curve of the RMSE of the angular acceleration appears similar to a bathtub curve with increasing restitution coefficient of the material. This study provides support for the design and control of the parallel mechanism in the field of precision machinery.