Study On Design Theory And Key Technology Of 2UPS-UPR Parallel Machine Tool

Parallel machine tool is the combination of parallel robot and modern CNC machine tool technology. It is a kind of new type manufacturing equipment emerging from the end of last century. Compared to conventional machine tools, parallel machine tool is characterized by high ratio of stiffness to weight, fast response speed, strong environmental adaptation, high technology added value and suitable for machining complex surfaces and so on. Thus it has wide application prospect in manufacturing filed. Among these, due to its own advantages, No-full DOF Parallel Machine Tool has become a significant tendency in the field of parallel machining equipment’s development.Although many people in the worldwide range have resorted to develop parallel machine tool, and even to achieve a little progress, the current overall focuses of parallel machine tool research are still in research, trial-production and probation stage. In the P.R. China, although domestic scholars and designers have gotten some research fruits, most of he parallel machine tools which we have developed have not yet reached the level of practical products and have common problems of low dynamic stiffness and machining precision. This reflects that there is still a wide gap between the domestic and abroad research on the key technology of the theory, design and application of parallel machine tool. Thus, systematically studying the design theory of parallel machine tool and effectively resolving the key technical problems during the design can provide a theoretical basis for the design of parallel machine tool, which has the important significance in promoting the industrialization of China’s parallel machine tool.In this paper, the main research content is to develop a new 2UPS-UPR parallel machine tool. According to the basic design theory of parallel machine tool, it is deeply studied from kinematic design, dynamic design, stiffness design, structural dynamic modeling and digital prototype simulation. It is specifically included as follows:(1) Kinematic design of 2UPS-UPR parallel machine tool is studied. According to the structure of machine tools, kinematic analysis of parallel mechanism and parallel restriction mechanism of machine tools is conducted, the normal and converse solutions of position analysis of parallel mechanism and parallel restriction mechanism of machine tools, Jacobian matrix and the speeds of the components of parallel restriction mechanism are also given. On this basis, the Influence Factors and the composition of the workspace of machine tools are analyzed. Finally, the law of the influence of structural parameters and motion parameters on the workspace of machine tools and the variation of the influence of design parameters on dimensional synthesis performance index are analyzed and obtained.(2) Dynamic optimization of rigid body of 2UPS-UPR parallel machine tool is studied. First, rigid body dynamic model of this machine tool is established with Lagrange’s equation. On this basis, to obtain the minimum value of the maximum driving force among the three drive rods of this machine tool, mathematical model of optimization design of dynamic parameters is established. Meanwhile, the law of the influence of design parameters on dynamic design index is gained by simulation analysis. Then, from a more meaningful point of view of partial balancing, dynamic equilibrium structure is given based on parallel constraint structure, the establishment of optimization mathematical model of dynamic equilibrium is proposed with a linear weighting method, optimization solution and calculation comparison are conducted with MATLAB software, thus the positive effect which dynamic equilibrium structure has had on shaking force and shaking moment of parallel constraint structure is proved.(3) Static stiffness of 2UPS-UPR parallel machine tool is analyzed and optimized. On the basis of establishing the stiffness model of machine tool, the formula of axial stiffness is given and simulation analysis and calculation are conducted, thus axial stiffness distribution in the work space and axial stiffness values in typical working conditions are obtained. Then, Static stiffness performance design index is separately defined from axial stiffness and stiffness matrix condition numbers of parallel machine tool. By conducting simulation analysis with MATLAB software, the law of the influence of design parameters of parallel machine tool on the two design indexes is given and the consistency of the two design indexes in measuring stiffness properties is proved. Finally, the static stiffness optimization design is fulfilled.(4) Study on structural dynamic modeling of 2UPS-UPR parallel machine tool and natural frequency solution of the organization are conducted, the structural dynamic equations of the whole machine tool organization are established, the subspace iteration method is given for solving the former five-order calculation steps of machine structure natural frequency and the value of the first-order natural frequency in the typical location is calculated. (5) By means of the digital prototype of 2UPS-UPR parallel machine tool, static stiffness and modal simulation analysis of the machine tool is conducted in the ANSYS Workbench Environment, static stiffness values of directions x, y and z in the three typical positions are obtained, The fact that the static stiffness simulation results are consistent with the theoretical analysis results is proved by analysis. With modal simulation analysis of natural frequency and vibration modes of the machine tool, the fact that the machine tool has relatively stable dynamic characteristics is proved.(6) Drive rods and spindle parts of the machine tool are structurally designed. The calculation process of the design parameters of the drive rod components and the criterion of the movement interference of the spindle components are given. Solid model and assembly drawings of the drive rods and spindle components are gained. According to this, corresponding parts can be manufactured.(7) By means of the physical prototype of 2UPS-UPR parallel machine tool, static stiffness and modal analysis experiments of the machine tool are conducted, the value of the static stiffness and the first-order natural frequency in the typical location are gained, thus the accuracy of the theoretical study and simulation analysis of machine tool static stiffness and modal simulation analysis of machine tool is verified. Besides, compared with 3-TPT parallel machine tool pre-developed,2UPS-UPR parallel machine tool is proved to have much better sports, stiffness and precision performance.In this paper, the research results of a number of issues such as kinematic design, dynamic design, static stiffness design provide foundational theoretical basis and data reference for the development of the physical prototype for the parallel machine tool and also provide a reference for parallel machine tool design of other configurations. However, because of the complexity of dynamic characteristic design of parallel machine tool and the rapid development of digital prototyping technology, to improve and develop the design theory of 2UPS-UPR parallel machine tool, a lot more and deeper research work is needed in the dynamic characteristic design and the digital prototype parameters design of the machine tool.