Development Of Tripod Parallel Mechanism Control Module In PA CNC System

Tripod is a new type of series-parallel hybrid mechanism, it has both serial and parallel machine tool characteristics. It was developed on the basis of the Tricept mechanism which achieved a good success in business.The performance of Tripod has increased in differentl respects.In this paper, the main work is the development of the numeral control system(based on Power Automation) of Tripod parallel machine system. Specific work is discribed as follows:Frist of all, kinematics of the Tripod is analyzed. Considering the manufacturing and assemble error factors, more structural parameters are introduced in the kinematics model. Then the inverse kinematics and forward kinematics algorithm are completed. After this, the algorithm of interference check is developed, and the analysis of the nonlinear deviation of Tripod machine was also finished.After kinematics modeling, a control system is developed specially for Tripod machine. PA(Power Automation) CNC system is a soft CNC based on Windows platform, with a single CPU architecture. PA is an open CNC which has a good stability. Based on the real-time control open interface"Compile Cycles"provided by PA,the inverse and forward kinematics algorithm are programmed, and the transformation of virtual axes and actual axes is realized. Besides, a real-time interference check function is added to the system. In HMI, a page displaying the state of the machine is developed specially for Tripod. In PLC module, a program is developed to realize the measurement function. In addition, an integrated module was developed based on PA, in order to handle the control of different kind of PKMs. After all the development, an experiment was designed to test the system, and the result is proved to be good.Beforing the control system is fixed on the LINKS-EXE 700 Tripod machine in Harbin Measuring & Cutting Tool Works, whose CNC is Sinumerik 840d, a reconstruction plan based on PA is developed in this paper. To improve the accuracy of Tripod in case the system is fixed, two Calibration methods(Cocktail method & full posture method) are given. The Calibration methods were proved effective by an experiment on another PKM.After the analysis and research, the development of control system for Tripod machine in PA was proved to be a success. It can be a reference for future research of PKM.