| Laser beam is a very important measure in the field of high-precision measurement and processing because of its inherent excellent characteristics.However,due to various reasons,the measurement of the beam itself has unstable drift,which seriously affects the accuracy of laser measurement.The factors that affect the laser beam drift include the thermal deformation of the laser and its fixed frame,the air disturbance in the environment and the mechanical stability of the optical system.The drift form can be divided into angular drift and horizontal drift,and the separation and detection of horizontal drift and angular drift can be realized by convex lens.The drift form can be divided into angular drift and horizontal drift,and the separation and detection of horizontal drift and angular drift can be realized by convex lens.On this basis,a method of active restraint for measuring beam angular drift based on PZT(piezoelectric ceramics)is presented in this paper.Based on Labview and MATLAB,we analyze the dynamic characteristics of the actuator and get the transfer function.Finally,an experimental platform is built to suppress the angular drift of the measured beam.First of all,in view of the large number of high-frequency noises that exist in the measured data,spectrum analysis is carried out.It is found that the high frequency noise is concentrated above 10 HZ.Based on this,the design of digital filter is carried out in this paper.After applying elliptic filter and moving average filter,the noise of measured data has been greatly reduced.Then,based on the pitch angle and yaw angle of the mirrors controlled by PZT,the mathematical model between the PZT expansion and the direction vector of the reflected light is established by the homogeneous transformation method.The actuator of PZT adjusting mirror is designed and manufactured.The calibration experiment of the actuator was carried out.Next,the executive system is simplified as a series connection between the PZT system and the adjustment rack system.The dynamic characteristics of PZT system and adjusting rack system are analyzed respectively,and they are all two order systems,so the executing mechanism is a four order system.Based on MATLAB,the step response curve of actuator is analyzed and modeled.The four order transfer function of the actuator system is obtained.Finally,based on LabVIEW,the incremental PID algorithm and relay feedback PID parameter tuning program are written.In order to verify the feasibility of the proposed method for restraining the angular drift of the measuring beam,a four degree of freedom of guide measurement platform is built.The experimental results show that the proposed method can restrain the angular drift of the measured beam.After feedback control,the peak and peak value of QPDs decreased.After feedback control,the drift of QPD1 in X and Y directions was reduced by 96%,88%,respectively,and QPD2 was reduced by76%,83% respectively;QPD3 was reduced by 55%,78% respectively. |
