| Parallel mechanism has the advantages of small inertia,compact spatial structure,small cumulative error and fast moving speed,get the attention of the scholars and industry,widely used in sorting pickup device,numerical control machine tool,rescue robot and rehabilitation training device,etc.Facing the occasion of grasping and sorting（small load,high or high speed,requiring three movements and one rotational degree of freedom）,a novel 3T1R planar symmetric parallel mechanism,named as 2PRPa U-2PSS PM,is proposed.2PRPaU-2PSS parallel mechanism is taken as the research object,and its structure,kinematics,workspace,scale synthesis and other aspects are analyzed and studied in detail,and a prototype is developed.The main research contents are as follows:（1）The 2PRPaU-2PSS PM for structure analysis.The constraint characteristics,degree of freedom and structural coupling degree of the mechanism are addressed through the position and orientation characteristic（POC）theory,and the rationality of driving pair selection is judged.The analysis shows that the mechanism has three degrees of freedom of movement and one rotation（rotation around the plumb axis）,the coupling degree of the mechanism isκ=2,and the selection of the driving pair of the mechanism is reasonable.（2）The 2PRPaU-2PSS PM for kinematics analysis.The mathematical models of displacement and orientation,velocity and acceleration analysis are derived by utilizing the vector method.The coupling degree of the mechanism isκ=2,which indicates that the positive solution of the mechanism position is more complicated.the nonlinear equations of forward displacement are transformed into one-dimensional equation,thus using the improved gray wolf optimization algorithm solve this problem.A numerical example of mechanism kinematics analysis is given.According to the theoretical model,displacement,velocity and acceleration are calculated by Matlab software,and Adams software is used for simulation verification.The comparison shows that the average errors of displacement,velocity and acceleration of theoretical analysis and numerical simulation are 3.085×10-5 mm,2.783×10-6 mm/s,and 5.2753×10-6 mm/s~2,and the maximum errors of angular displacement,angular velocity and angular acceleration are are 8.360×10-6°,1.663×10-6°/s,and 1.883×10-6°/s~2,and the error values are all small and negligible,indicating that the kinematic analysis model and calculation method given in this paper are correct and reliable,which lays a foundation for the subsequent parametric design of the mechanism.（3）The 2PRPaU-2PSS PM for work space analysis.The kinematic/force transfer performance index model of 2PRPaU-2PSS parallel mechanism is established.The definition and calculation method of Regular effective transmission workspace（RETW）for mechanism attitude determination rules are presented.A numerical example of workspace analysis of the mechanism is given.The ETW and RETW boundary curves of the mechanism at fixed attitude Angle are drawn by numerical search method with Matlab software.The results show that when the fixed attitude angleγof the mechanism is 30°,the RETW radius of the mechanism under the given scale parameters is 103.8281 mm,the AITI and AOTI within the RETW range are 0.5493 and 0.3748,respectively.The RETW radius of the mechanism is small and the transfer performance is poor.（4）The 2PRPaU-2PSS PM for dimension synthesis.Taking the 2PRPaU-2PSS parallel mechanism’s regular effective transmission workspace（RETW）as large as possible and its average input transfer index and average input transfer index as the objective function,a multi-objective optimization model of mechanism scale parameters was established by taking mechanism scale parameters and spherical hinge opening Angle as decision variables and combining with mechanism constraints.A numerical example of mechanism scale synthesis is given,and the NSGAⅡ-DE algorithm is used to solve the problem,and two sets of solutions obtained by the algorithm are selected for the optimal design of scale parameters.The results show that the optimized rule effective delivery workspace radius is increased by 56.5839%and 69.2250%,the rule space average input delivery index is increased by 3.0584%and 7.2038%,and the rule space average output delivery index is increased by 4.1507%and 9.4984%.It shows that the scale synthesis multi-objective optimization model and calculation method in this paper are correct and feasible.（5）The 2PRPaU-2PSS PM principle prototype research and development.Based on the parameters after the comprehensive optimization of the scale,the mechanism principle prototype structure design is carried out.Through the UG modeling and the finite element analysis of the key members of the mechanism using ANSYS software,the stress and strain values of the key members of the mechanism are obtained,and the size of the members is determined.For the selection of the driving pair of the mechanism and the rational design of the fixed/moving platform of the mechanism,the motion posture of the mechanism is verified by the principle prototype processing and overall assembly,which meets the expectations,which lay a foundation for practical application,and has certain theoretical and engineering value for the development of new industrial automation equipment. |
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