Research On Sliding Mode Control For Long Stroke Linear Precision Platform

In lithography machine,there are massive moving components,they have unique form and norm,through coordinate they can accomplish complex movements like exposure,step forward,scanning and so on.But their essence is motion platform.In case of satisfies high performance,it is essential for us to special study motion platform,so this paper study on the most typical platform in lithography machine which is long stroke linear precision platform.So as to eliminate various disturbance on platform,sliding mode control had been implemented in this paper.Simulation and experiment shows the effective of controller,which can enhance system is tracking accuracy and rapidity.First of all,this paper introduce the platform is working features,performance index and structure.According to platform is work situation planning S curve as reference trajectory.Through analysis of disturb on platform,point out there are nonlinear disturbance force,parameter perturbation,model uncertainty and mechanical resonance which is harmful to control.At last obtain platform is frequency response curve via sweptfrequency experiment.And curve fitting the frequency response with 2nd order transfer function.Secondly,in order to get over the disadvantages on platform to improve performance.On the basis of the platform is transfer function,this paper presents a sliding mode control method based on parameter optimization through improved particle swarm algorithms.This method selects linear sliding surface,in order to eliminate chattering,boundary-layer technique is proposed to improve sliding mode part.Via the simulation sliding mode control method shows better disturbance resistance,response rapidity and tracking performance than PID control method.Thirdly,although the method proposed last chapter performance batter than traditional PID method,it still have the problem like: rapidity not perfect,chattering effect still serious,so it is necessary for us to improve control method.So as to improve rapidity this paper uses non-singular fast terminal sliding mode surface instead of linear sliding mode surface,that can make system is state convergence in finite time.So as to eliminate chattering effect,abandon boundary-layer technology taken before,but introduces second-order sliding mode control,which called second-order non-singular fast terminal sliding mode control method.This method can not only highly weaken the chattering without reduce the capability of resistance disturbance,but also make tracking accuracy batter than before.The comparison of three sliding mode control in simulation,verified the superior of.Ultimately,explained every link in control system of platform and implement the control algorithm above-mentioned in hardware and use this algorithm to control platform.Compare each control method from three aspects: tracking accuracy,rapidity and chattering effect.The experiments indicate that second-order non-singular fast terminal sliding mode control method have best effect,it is useful to improve system's performance.