Research On Designing Theory And Method Of Stewart-Platform Based Machine Tool

In 1960's, Stewart platfonn was invented to flight simulator. In 1990's, Stewart platform wasused to reconstruct conventional machine tool, some prototype parallel machine tools are produced inUnited States, Japan , Russia and so on, there are also some prototype parallel machine tools were produced in our country. Parallel machine tool has simplified mechanism and has much agility and specified on the processing of the curved surface, but it also has some shortcoming such as its workspace is strait and influenced much by the orientation of the moving platform, moreover, there is not a conclusion now whether it can attain the accuracy at level of the traditional machine tool in the academy and engineering. All these factors are influencing the research and development of the parallel machine tool in our country. By the study made in this paper, some theories basis are provided for the design of the parallel machine tool, which enables its performance to become better than before.The parameter model of the Stewart platfonn is founded firstly in mis paper, based on which we analyze the kinematics performance of the Stewart platform, all these works are the basis of the structure design and the accuracy design of Stewart platform.During the work of designing the structure of parallel machine tool, in allusion to the main shortcoming of Stewart platform mat its workspace is strait, we decide to design a Stewart type parallel machine tool which fulfill the given spherical position workspace and have the best dexterity, genetic Algorithm is used in this paper. Because the calculation of the fitness function is complex, BackPropagation arithmetic is used to approach fitness function. The results show that mis method has good accuracy and computing efficiency.In this paper, accuracy design is completed through two steps: first, we analyze the error of parallel machine tool, the joints' gap are considered by using Monte Carlo method, also in mis part, three kinds of error sensitivity are established to wholly reflect the error of moving platform. Secondly, accuracy synthesis is carried out to reasonably allocate the tolerance of the struts and the joints according to moving platform's position error. In the process of accuracy synthesis, Monte Carlo method is used for calculating the moving platform's mean error. The results show that this method is simply and easy to program.In this paper, two computer aided design software of the parallel machine tool are developed One is the movement simulation software of me Stewart platform based on OpenGL, the other is the error analysis software of the Stewart platform based on VB and Matiab, these two software are helpful to design the parallel machine tool.