Study Of Electromagnetic Levitation Grip For CNC With The Cutting Force Disturbance

Electromagnetic levitation system has many good quality characteristics such as no pollution, no mechanical contact, no friction, no lubrication, high precision positioning and high feed speed and acceleration. Therefore electromagnetic levitation technology is adopted in gantry NC machine tool to eliminate the friction between the crossbeam and guide, namely the crossbeam is levitated upon the guide without contact in order to achieve finishing-cut. First, on the basis of reading many foreign and domestic references, it summarizes the structure and the principle of operation of the gantry NC machine tool moving crossbeam to analyze the levitation theory. The mathematic model is built. The output feedback adaptive backstepping control is applied in the electromagnetic levitation nonlinear system based on this. Second, the nonlinear model is linearzed by using feedback linearization method and linear voltage control and current control model are obtained respectively. On the basis of the model, sliding mode controller is designed, the simulation result shows it has advantage of strong robustness and rapidity but there is chattering as well. In order to eliminate the chattering of sliding mode surface, we designed the dynamic integral sliding mode control, the simulation result shows that, because of bringing in the dynamic sliding mode control, it reduce to litter the chattering probiem,and the same time, it has advantage of strong robustness and rapidity. For dealing with the controlled object mathematical model, choosing a coordinate transform method directly to nonlinear controlled object to undertake handling, it has altered the need for nonlinear controlled object first linearization. And then to design the controller of trivial process, but also eliminates but their system error of system of nonlinear mathematical model, in this paper, nonlinear dynamic integral sliding mode control and inversion adaptive dynamic integral sliding mode control are put forward. System simulation show that:although the inversion adaptive dynamic integral sliding mode control can achieve real-time online estimation for the uncertain parameters of the controlled object, and obtain the corresponding controller parameters, due to online estimation calculation process is quite complicated, computational comparison is big, so the rapidity is relatively poor. The advantages of the nonlinear dynamic integral sliding mode control is that:it does not need to determine the mathematical model of controlled object, and it has a small steady state error and high robustness, the system can quickly achieve the requirements of exact suspension, to meet the control requirements.