Research For The Electro-mechanical Coupling Of The Parallel Mechanism Of Virtual Axis Polishing Machine

Commonly the principal part of the complex Electro-mechanical system is made up of mechanism and electric control part. Finally the system will transform the control signal to corresponding mechanic transmission. The whole transform process includes multi-physics process.Kinds of the transfer and transform of energy is implemented through the pluralistic and multidimensional movement. All dynamic process are interactional acted by various coupling.The relation between input and output becomes clearly by decoupling.The research information shows that researhing on the coupling principle of machanism and the servo motor of NC and then instructing the optimizing designing of servo system and machine is the best method to improve the precision and speed of the NC machine when there is no change on the hardware.Servo system is not only the main component of the NC machine, but also the character that distinguish NC machine from normal tool machine.The excellenet performance index of servo system of the NC machine can be concluded as high orientation precision, quick response of command signal and well stability of the system.In this paper, the reasearch object is the parallel mechanism of virtual axis polishing machine. The mathematics model of the electro-mechanical coupling system of the NC machine is built up by researching on the dynamics character of the mechanism,the statics and dynamics character of the serve motor,the transfer function of the electric system and the control method.The optimal design of the serve system is done by various control methods based on the mathematics model.1.The entity model is built up by the CATIA software.And the transfer function of the system is worked out based on the interrelated data of the NC machine. Then the connected software is used to transfer the CATIA model to ADAMS.The rigid body of the ball screw is replaced by flexible box.The flexible box dynamics analyses is done to the screw. The departure of the ball screw center and the stress nephogram of the flexible are obtained.2.The ANSYS software is used to do the statics and mode analysis of the ball screw. The transmutation nephogram and stress nephogram under the static impose are obtained. And the first seven ranks of the mode shape and frequency are obtained by the ANSYS software. During the process of building the FEM model, to build the reasonable and precise model and improve the calculate efficiency and quality of the FEM analysis, suitable predigestion is done based on the movement and structure character of the feed system. The main predigestion content is considering the local structure that is less influence to the whole character as entity, ignoring some local structure such as tool escape, chamfering and blends.3.MATLAB and ADAMS software are used to do co-simulation for the servo- control system .The complicated control is added to the mechanism prototype model, then co-simulation is done for the Electro-mechanical system. The simulation model of mechanism of the control system could be built up by the program directly. Simultaneity the simulation result gained from the co-simulation can be analyzed in MATLAB environment.4.The decoupling control simulation to the servo feed system is done based on the PID method with repeated compensate. The PID controller is a kind of linear controller. The control error is based on the input constant rin (t) and the output constant yout (t)The control rule of PID could be expressed as the transfer function format: where k P the proportion coefficient, T I the integral time coefficient, T D the differential time coefficient.The action of the proportion link is to reflect the error signal error (t) proportionately. As soon as the error appears, the controller performs the controlling action to reduce the error. The action of the integral link is to eliminate the static error and improve the indiscrimination degree of system. The degree of the integral action lies on the integral time coefficient. The integral action will become weak when T I increases. The differential link reflects the change trend of the error signal. And an effective early correct signal is imported to the system before the signal error becomes oversize to accelerate the system action and reduce the adjusting time.A simulation analysis is done to the whole structure control of the parallel mech- anism of virtual axis polishing machine based on the PID method with repeated co- mpensate. The parameter of PID is confirmed using Ziegler-Nichols method. The control block diagrams of sine wave input and step wave input are build up. The block diagrams and the curve of position tracing when the input is step wave are shown as Fig. 1 and 2, separately. Sliding mode variable structure control requires the perfect sliding mode ,excellent dynamic quality and great robustness. Sliding mode variable structure control system has two steps, so the design of sliding mode variable structure controller has two steps, too. The block diagram of the whole system is built up by the sliding mode variable structure controller which has Stribeck friction model and based on Exponential Approach Law. The simulation result curve is shown in Fig.3.It indicates that trace precision could meet the qualification from the tracking curve.