| The submicron precision stage is widely applied in precision manufacturing and detection equipment.With the continuous improvement of equipment performance indicators,the requirements for the control accuracy of the stage are more stringent.The H-type air floating motion platform has symmetrical structure,large overall stiffness and minimal guiding friction,which can be used as a structural carrier to realize submicron control precision.The inherent time delay in control system affects the response speed,and the disturbance rejection ability of the one-direction dual-drive synchronous model in the air floating platform is poor,which poses a great challenge to further improve the performance of position control and one-direction dualdrive synchronous control.Relying on the major national scientific research project,this thesis studies the motion characteristics analysis and modeling of the platform,high-speed and highprecision motion control and precise synchronous control,so as to meet the urgent demand of precision equipment for submicron precision stage.According to the requirement of submicron control precision,an H-type air floating platform is adopted.In order to effectively reduce the influence of eccentric disturbance on motion control during driving,the method is adopteded to coincide the force of motor and guide rail with the moving parts’ centroid.Meanwhile,the influence of air floating characteristics on control accuracy is analyzed.The driving mathematical models of platform along the X,Y translation direction and Rz rotation direction are established,which eliminates the displacement coupling caused by the beam connection,and provides a model basis for the formulation of the precision motion control strategy.In order to realize the submicron precision,a high-precision motion control model is established.The feedback parameters tuning method is proposed to ensure the system bandwidth and stability margin,and the influence of feedback parameters on motion accuracy is analyzed.In order to improve the system response speed,the feedforward control is introduced and an accurate parameter tuning method of feedforward controller with time-delay compensation is proposed.Based on the measured data of finite-time task,the objective function of the update vector of feedforward dynamic parameters and delay time is established.An optimization strategy combining the Gauss-Newton Iterative(GNI)scheme and instrumental variable(IV)independent of disturbance is proposed to eliminate identification bias and the feedforward controller can be turned accurately.With the identified parameters,the system time-delay which is non-integral multiple of the sampling period is compensated with accurate path planning time-shift in the implementation.Finally,the stability time of the system response is reduced and the near-zero error position tracking control is realized.The one-direction dual-drive synchronization performance has a great influence on the system control accuracy.A synchronous control model is established and a synchronous control method based on model decoupling and the fractional order notch filter is proposed.In order to solve the problem of system instability caused by the oscillation model in synchronous loop,the fractional order notch filter is introduced to improve the phase of the system at resonance frequency and reduce the amplitude frequency peak value of the process sensitive transfer function,which can increase the control gain and quickly attenuate external disturbance.The advantages of fractional order filter over integer order filter are clarified.The order is added as an adjustable parameter and the system disturbance rejection ability is improved.Feedforward control is introduced to compensate the eccentric torque caused by the cross axis movement of the worktable,and the precise synchronous control of one-direction dual-drive is realized.The precision stage experimental system is set up.In order to verify the effectiveness of feedback parameter tuning method,the open-loop transfer function reflecting the system control performance is tested,which meet the requirements of frequency characteristics and ensure the system bandwidth and stability.The feedforward parameter tuning method is analyzed,and the feedforward parameters and delay time is identified with the measured data.The feedforward controller can be adjusted to match the inverse plant model and the feedforward control goal is realized.In the synchronous control loop,the proposed method can quickly attenuate the external disturbance and suppress the synchronization error caused by eccentric torque,which proves the effectiveness of the proposed synchronous control method.The experimental results show that the positioning accuracy of single-drive direction is 80.0nm and that of dual-drive direction is 45.0nm,the proposed method realizes the submicron control precision of the stage. |
