Research Of Parameter Self-tuning Technology For Cascade Control System

The main development directions of CNC system are high speed,high precision and intellectualization caused by the rapid progress of modern industrial technology.As the core of CNC system,servo system usually contains cascade PID controllers consisting of one current loop,one velocity loop and one position loop.The configuration of parameters of feedforward and feedback controllers within it determines the performance of motion control system.The way of adjusting parameters by workers is both time-consuming and laborious.However,automatic-tuning method is very fast and efficient.This function is integrated into many commercial servo drives made by foreign companies.But the research is still in the theoretical stage in China,and there rarely exist mature industrial products made by Chinese companies.A reliable,fast and accurate self-tuning scheme of servo-system parameters is then in urgent need of being studied and proposed.This article studies one self-tuning scheme and the current loop under torque-control mode is the controlled object.Firstly,the mechanism of mechanical resonance and nonlinear phenomena is discussed.The available scanning surveying method and power spectrum analysis method are chosen to obtain frequency-domain characteristics of controlled system.The maximum closed-loop bandwidth of both speed-loop and position-loop of the system is then derived from the vibration-characteristic analysis.Next,the method of identification of mathematical model of servo system with Coulomb friction force based on relay feedback is studied and improved,and test processes are proposed.The accuracy of algorithm,the effect of filtering and the stability of the identification method are analyzed.The principle of parameter configuration of relay test is also described.Then,on the basis of the foregoing,the structure of servo-system controller is designed considering the performance index of stability,following accuracy and bandwidth of the closed-loop system.The effect and necessity of the feedforward controller are also verified.Finally,summarize the above,the self-tuning scheme of parameters of cascade controllers for servo system is proposed based on the bandwidth of closed loop system.The feedforward and feedback control-parameters of the speed loop and position loop are then tuned automatically.The results of simulation experiment and engineering application prove that this tuning scheme is better than that of the servo system of Yaskawa under speed control mode,and can be applied to different load conditions.The tuning scheme can also be done accurately and efficiently on GSK servo drive platforms with a strong value and feasibility.