Research On Type Synthesis And Optimal Design Of A Class Of Parallel Mechanisms With 2R1T DOFs

According to the practical demands for 2R1T(Two Rotational and One Translational DOFs)spatial parallel mechanisms,this dissertation proposes two novel parallel mechanism: the new 3PUU mechanism and the new 3UPU mechanism(where P denotes Prismatic joint,U denotes Universal joint).Then this paper focuses on the new 3PUU mechanism,and systematically carries out research on it at the following aspects: mobility calculation,kinematics analysis and size optimization,flexible dynamics modeling of the whole machine and topology optimization for key parts.Last,the effectiveness of the proposed theory and the practicability of the proposed mechanism are validated with experiments.The main research works can be described as follows:The coordinate transformation rule of screws is acquired based on the screw theory.Combining the coordinate transformation rule of screws and mechanism topology,we put forward a kind of mobility analysis theory called “one core principle and two key techniques”.The theory is applied to the analysis of five typical parallel mechanisms,such as the 3PRS mechanism,the 4PUU mechanism,the Orthoglide mechanism,the classical 3PUU mechanism and the classical 3UPU mechanism.The analysis results indicate that the mobility analysis method is rigorous on mathematics,has strong versatility,and is able to avoid the analysis error brought by subjective judgement and personal experience.Moreover,the proposed theory makes it’s easy to realize automatic calculation of full-cycle DOFs of a mechanism,and the theory can also provide us multiple information about DOFs,such as the quantity,direction,properties and mutual coupling relationship of DOFs of a mechanism.Based on the above-mentioned mobility analysis theory,we come up with a structure synthesis strategy for parallel mechanisms with 2R1 T DOFs,with which we obtain two novel parallel mechanisms with 2R1 T DOFs: the new 3PUU mechanism and the new 3UPU mechanism.Then this paper focuses on the new 3PUU mechanism.The geometry constraint condition and forward/inverse kinematics of it are studied.We find that the manipulator possesses two kinds of inverse kinematics solutions: the one is with 2R1 T DOFs,when the translations along x-axis and y-axis are the parasitic motions;the other is with 3T DOFs,when the rotations about xaxis and y-axis are the parasitic motions.Corresponding motion modes can be utilized for hybrid machine tools and goods sorting robots fields,respectively.Then we adopt the atlas method to optimize structural sizes of the 3PUU mechanism for these two different demands.The guide-weight method is extended and improved,and combining it with the Submodel method and the Substructure method,a new topology optimization strategy for flexible dynamics optimization of key parts of mechanisms is proposed.Optimization examples indicates that the optimization strategy owns a high accuracy when extracting the boundary conditions of parts,and it could greatly improves the computation efficiency at the same time.Thus,the proposed method can solve this kind of problems,whose loads have both design-independence and time-independence,very well.With servo motors and motion controllers,we build an experimental prototype of the new 3PUU mechanism.Then,the DOF properties of the proposed mechanism and the effectiveness of the proposed optimization methods are validated with corresponding experiments,i.e.,the DOFs experiments,the kinematics experiments,and the dynamics experiments.The outcome of this dissertation will provide theoretical guidance and technical support for designing and developing hybrid machine tools and goods sorting robots with this kind of parallel manipulators.