Theoretical And Experimental Research On Motion Reliability Of Planar Parallel Mechanisms

In the trend of the development of modern manufacturing equipment towards high speed and high precision,it has a higher requirement for the motion accuracy of the core mechanism.An actual mechanism comprises inherent uncertainties,such as manufacturing tolerances,assembly errors,joint clearances and input errors,leading to deviations between its ideal motion and its actual motion.Motion reliability is a performance index which can be used to evaluate the motion accuracy of a mechanism under the influence of uncertainties.Thus,the introduction of motion reliability into the design and performance evaluation of the mechanism is conducive to improving its motion performance.With the characteristics of high stiffness,good load-carrying capacities and high accuracy,planar parallel mechanisms(PPMs)are widely used in modern precision manufacturing equipment.In this thesis,the theoretical and experimental research on the motion reliability of the PPM is carried out.The main work of the thesis is as follows:First,a modeling method for the motion error of the PPM with joint clearances is proposed,and the effectiveness of the proposed modeling method is verified.On this basis,a new hybrid method of motion reliability analysis is proposed based on the FOSM,interval method and MCS method,incorporating both random and interval variables simultaneously.Through analyzing the motion reliability problems of two typical PPM,3-RRR PPM and 3-PRR PPM,the effectiveness of the proposed method is verified.Second,the influence of each uncertain parameter on the motion reliability of PPM is studied.A reliability sensitivity analysis method of PPM based on AFOSM method is proposed.In order to verify the analysis accuracy of the proposed method,a numerical analysis model of reliability sensitivity based on MCS method is established.The simulation results show that the proposed model is effective and can also obtain higher precision.Third,taking the 3-RRR PPM as a special object,the motion reliability-based optimal designed for the PPM is studied.Based on a 3-RRR PPM whose geometric parameters are obtained from a deterministic optimization design,the motion reliability optimization design is carried out.The motion reliability,the sizes of PPM's parameters and workspace based on reliability optimization and traditional deterministic optimization are compared and analyzed.Further,a 3-RRR PPM optimization design model with the goal of maximizing the working space and the constraint of the motion reliability being greater than a given value is established,and the motion reliability simulation analysis is carried out for the optimized mechanism.Finally,the experimental research on the motion reliability of planar parallel mechanism based on 3-RRR PPM is carried out.The kinematic parameters of the 3-RRR mechanism are calibrated using a laser tracker.On this basis,the revolute joints of the moving platform of the PPM is replaced with revolute joints having larger joint clearances.The multi-directional repeated positioning experiment of the PPM with joint clearances is made to verify the validity of the established motion error model of the PPM.Then,based on the machine vision,a long-term and real-time monitoring visualization system of motion reliability of the PPM is built,which provides an experimental basis for further research on data analysis and data mining of the process of motion degradation.