Friction Compensation And Oscillation Suppression Technology For Full-closed Position Servo System

Reducing the position tracking error and improving the positioning accuracy are the main control targets of the position servo system.In the field of high-precision position control,in order to improve the positioning accuracy,the position information on the load side is used as the position feedback to form a full-closed loop control.Full-closed control can eliminate the influence of backlash,pitch nonlinearity,screw thermal expansion and other mechanical links.Then friction nonlinearity and elastic shape become the main factors that restrict the full-closed position performance.The frictional nonlinearity causes the speed lag when the position is reversed,which leads to the distortion of the position tracking error.The elastic deformation causes the full-closed loop to oscillate.Usually,the position gain is reduced to suppress the oscillation,but the position tracking error is increased.Actual demand.Therefore,this paper studies the friction and elastic links in the mechanical transmission link to improve the position performance of the full closed-loop control.In this paper,the mechanical transmission is firstly analyzed.According to the number of degrees of freedom,the mechanical transmission is divided into a single inertia model and a double inertia elastic model.Next,the backlash,pitch error and friction nonlinearity in the mechanical transmission are analyzed.Finally,the electrical control part is equivalent,and a full-closed-feed servo system model is established.For the position error caused by the friction link in the full-closed loop control,the torque feedforward based on the static friction model is used to eliminate the error.First,the friction error mechanism is analyzed in combination with the friction characteristics.The Coulomb friction force and the viscous friction coefficient are integrated by integrating the torque command,and the torque feedforward control method is proposed based on the static friction model to realize nonlinear friction compensation.Finally,experiments were carried out on the feed platform to verify that the proposed method can eliminate the error bulging caused by friction and reduce the position tracking error.Aiming at the position oscillation caused by the elastic link in the full-closed loop control,dual-position feedback control is proposed to suppress the oscillation.Firstly,the transfer function of the full closed-loop control is derived by using the two-inertia elastic model,and then the full-closed oscillation mechanism is analyzed according to the frequency domain characteristics.Through research,it is found that the resonance point brought by the elastic link to the system causes the system gain margin to decrease,and then the oscillation problem occurs.In order to suppress full-closed position oscillation,the introduction of the motor position constitutes a dual-position feedback control.Finally,experiments were carried out on the elastic feed platform to verify that the dual-position feedback control can suppress the full-closed oscillation and ensure the position gain and positioning accuracy of the system.