Research On Modeling And Compensation Of Machining Geometric Error For A Movable Parallel Machine Tool

Parallel machine tool, also known as virtual axis machine tool or parallel kinematics machine, integrates the technology of machine structure, robot and CNC. It is a kind of knowledge-intensive equipment. Compared with traditional machine tool, it has higher stiffness-weight ratio, faster response, stronger adaptability to environment, and higher added value of technology, but smaller working space, lower accuracy have been placing restrictions on putting it into industrial operation. In this thesis, the parallel machine tool is moveable, it has flexible working space. So, how to improve its accuracy is the urgent problem to be solved.In order to solve this problem, the thesis found the main factors that affect the machining error and detected the actual kinematic error. The error model based on the rules of kinematic error was established. The NC system was optimized to compensate the kinematic error, so that the accuracy could be improved.According to analyzing the principle of adaptive localization, the method to process the super-large flange was designed. By finding the error sources of the whole system, the main factors that affecting the accuracy was identified, which were geometric error and adaptive localization error. Simplified geometric error model was established based on the kinematic differential equations of shaft. When the machine tool moved in the mode of three degrees of freedom, the distribution law of kinematic error was analyzed by simulation. And it was corresponded with the actual law detected by laser tracker. Adaptive localization error model was also established. Compensated the error and used positive kinematics to evaluate the effect of compensation. Finally, modified the NC system and processed the super-larger flange. The experiments verified the feasibility of adaptive positioning processing and error compensation.The thesis verified using the small moveable parallel machine tools which adopted adaptive localization to process a super-large flange was possible, and found when the machine moved in the model of three degrees of freedom, circular error was nearly cosine curve distribution. After compensation experiment of the kinematic error, the machining flatness of the workpiece increased nearly doubled.