Research On Some Fundamental Problems Of Parallel Laser Cutting Machine Tool

This paper researched current laser processing equipment characterized by some natural drawbacks, such as poor stiffness, complex structure and large cumulative error, because the laser head is driven by traditional serial mechanism. As serial mechanism’s dual, parallel mechanism possesses a lot of virtues, for example high rigidity, high precision, simple structure, good quality at high speed, and so on. Therefore, for cutting spatial complex curved surface, a kind of parallel laser cutting machine tool was proposed in this paper, whose laser head would be driven by the vertical 6-PUS parallel mechanism.Firstly, the forward kinematics and singularity of the vertical 6-PUS parallel mechanism was studied. In this paper, the position and orientation variables of the moving platform were uncoupled for the first time in history and the semi-analytical forward kinematics was derived. The analytical expression of singularity loci was also acquired; the influence of three orientation angles on position singularity was inspected. The rule that position workspace would decrease with orientation angles increasing was found. Using singularity-free orientation sphere’s radius to evaluate the orientation ability of parallel mechanisms, the impact of several important mechanism parameters and position parameters on orientation ability is mainly discussed. A conclusion that the orientation ability decreases with the increase of the distance from the center was drawn, and linearly expressions between orientation ability and distance from the center was derived. Based on the above analysis, the workspace of 6-PUS parallel mechanism was calculated with the forward and inverse kinematics dependently.Secondly, the force transmission performance and the whole stiffness of the vertical 6-PUS parallel mechanism were researched. Based on this, the 6-PUS parallel mechanism was optimized with the dimensional synthesis of “performance-chart and optimum-region”, and the optimal parameters were derived. Then, the dissertation compared the motion/force transmission performance of the optimized mechanism with the original. The comparative result indicates that the motion/force transmission performance and the workspace would improve remarkably with the length of the linkage closer to the radius of the base platform.Thirdly, kinematics and dynamics of 6-PUS parallel mechanism prototype were analyzed based on optimized mechanism. Through motion simulation with RecurDyn software, the driving force on given conditions were determined to help select the motor. With the help of MFBD multi-deformable-body dynamics theory, the maximum stress and strain value in different motion models were obtained based on rigid-flexible coupling simulation, which provide reference for design.Finally, machining experiments on steel plate and curved surface were carried out on the 6-PUS parallel laser cutting machine prototype. Through single factor experiments and orthogonal experiments, the impact of the process factors on machining quality was discussed and the optimal process parameters in cutting steel plate were determined. Finally, through surface machining the impact of machine rigidity and isotropy on machining precision were investigated, which provides references for a further optimization of the parallel laser machine tool.