Study On A Tripod Parallel Universal Platform

With the development of number control machine tool, the parallel kinematics machine (PKM), as a novel machine tool,makes a very important role in many fields. But when it comes to the industrial period gradually, because its inherent structure features, the main problem of PKM, accuracy problem, has been a very key problem,to block it to widespread and make more development.Recent years, PKM with less than six freedoms is becoming the new research direction. A novel parallel mechanism, tripod parallel universal platform, is studied in this paper, it not only inherits the features of prophase PKM,such as high stiffness, high speed, large workspace, but also get some new characteristics.For the tripod parallel universal platform, the poses of moving platform are decided by 3 driving chains. Therefore, its accuracy influence factors are mainly from these error sources from 3 chains, including the design and manufacturing errors of the parts, clearance influence of the pairs, working force to the bars, and thermal influences. The total number of these factors is more than 100, so a full error analysis to tripod parallel universal platform and building a proper error model for it are very difficult.In this paper, based on the D-H parameters differential to the kinematics equations, the influences from all minor differences from 3 driving chains to the pose of moveable table and their mathematical model are gotten respectively. Based on these models, the influences from all these factors to the pose error of the moveable table are gotten. Combined with the kinematics inverse algorithm of 3-UPS PKM,a real time error analysis model is derived.Finally, establishing the 3D entity model and kinematics simulation by means of the software-Pro/E,then designing the detail structure of the machine, drawing the blueprint of assembly and parts, also we has participated in the building of the prototype of the tripod parallel universal platform.