Due to the thermal effects, the airflow disturbance and the platform vibration, the random jitters of laser axis are caused, which have a serious impact on the laser coherent combining. If the conventional PID controller is used to reject the disturbance, the control bandwidth will be lager, but the high frequency noise of the system will be significantly amplified, so that the control error increases. The open-loop disturbance data spectrum is analyzed to add a lag compensator. The results show that the system has a good effect on rejecting the jitters of the middle-and-low frequency optical axis, while the high frequency noise has on amplification effect, which decreases the control error of the system.
A design of optical axis closed-loop control system for multi beam lasers coherent combining based on FPGA was introduced. The system uses piezoelectric ceramics Fast Steering Mirrors (FSM) as actuator, the Fairfield spot detection of multi beam lasers by the high speed CMOS camera for optical detecting, a control system based on FPGA for real-time optical axis jitter suppression. The algorithm for optical axis centroid detecting and PID of anti-Integral saturation were realized by FPGA. Optimize the structure of logic circuit by reuse resource and pipeline, as a result of reducing logic resource but reduced the delay time, and the closed-loop bandwidth increases to 100Hz. The jitter of laser less than 40Hz was reduced 40dB. The cost of the system is low but it works stably.
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