The Design Of Iterative Learning Controller Based On Zero Phase Filter

With the development of the information age,consumer demand for smart phones is increasing.And the appearance of the phone shell,comfort and other requirements are also getting higher and higher.Among them,metal cell phone shell with its excellent texture,wear resistance and good thermal conductivity and other advantages is getting more and more popular by the public.CNC(Computer Numerical Control)machine tools currently used in metal processing intelligent mobile phone for traditional machine tool,does not take the same workpiece mass repeated processing into account,batch processing tasks will still lead to production as a single,resulting in high defect rate.In order to solve the above problems,this paper puts forward the concept of iterative learning process,so that the machine tool can be used to optimize the subsequent processing to improve the machining accuracy.Iterative learning control as the core control algorithm,this project will be on its convergence,stability and engineering applications in the process of overshoot phenomenon,and puts forward the corresponding solutions.The main control object is the power system composed of servo drive and servo motor.The servo motor control system is usually composed of three loops,which are position loop,speed and current loop.We will adjust the servo drive into speed closed loop mode,and the controller to complete the position loop.Based on the d SPACE1103 control card,the speed loop frequency sweep experiment is designed,and the mathematical model of the speed closed loop is obtained by using the obtained data.In engineering practice,the control mode of position loop is always set up as the proportion(P)control.The control parameter P is needed to be optimized in order to make the control system obtain good dynamic characteristics.Data driven based iterative feedback tuning(IFT)method is used to execute the parameter tuning.The phenomenon where the system error appears convergence then divergence and convergence finally often occurs in the application process of iterative learning control.Research from two perspectives of time domain and frequency domain analysis on this phenomenon,and draws the conclusion: with the iterative learning process,the high frequency components in the error spectrum would gradually accumulate,eventually lead to overshoot.In order to solve this problem,it is needed to design the filter to filter out the high frequency component.But the common filter has the phase difference which means introducing new error,so we design the zero phase filter to complete the filter.The convergence rate of iterative learning and the final convergence error are affected by many factors.In many optimization methods,the advance compensation of the error is simple and feasible.Introducing a line phase lead is always off-line,and the error will be stored in the operation process,and then applied to the next iteration process.Whether it is zero phase filtering or introducing a linear phase lead can't work in real time.However in the middle of the two iteration process will exist offline time,zero phase filtering and introducing a linear lead is done in this offline time.As for the specific optimal number of linear phase lead steps corresponding to the maximum cut-off frequency,it is determined by the relevant simulation experiments based on algorithm design.Based on the analysis of the cause of the overshot phenomenon and the related filtering and compensation mechanism,the simulation experiment based on Simulink is carried out,and the expected effect is obtained.Based on the theoretical derivation and simulation experiment,the paper designs a specific numerical control machine tool experiment,and the error decreases monotonically.The results show that the effect of zero phase filter and phase lead compensation is verified.And the error spectrum of the iterative operation process is analyzed,which can directly reflect the effect of zero phase filtering.