In the satellite-to-ground laser communication, the beacon light is affected by atmospheric turbulence, atmospheric scattering and atmospheric absorption, so there is a coupling error. And the receiving end of ATP system is affected by random disturbance which lead to the initial coupling place change. The above reasons resulting in the fiber coupling energy decline. The efficiency of fiber coupling directly affects the success rate of decoding, so it is important to improve the efficiency of fiber coupling. This paper uses a tilt mirror which has cheaper cost and simple structure compared to wavefront corrector as the actuator for optical fiber coupling alignment and use the two-dimensional stochastic parallel gradient descent algorithm (SPGD algorithm) widely used in the field of adaptive optics to correct the coupling errors caused by atmospheric turbulence and random disturbance at the receiving end. The SPGD algorithm is affected by the initial coupling position, when the initial coupling position is unreasonable, the SPGD algorithm cannot be used for effective coupling. Therefore, the CCD camera is used as a position sensor to obtain a reasonable initial coupling position and improve the fiber coupling efficiency of the system.
In classical electro-optical control systems, the double closed-loop control including speed feedback and position feedback is often used to enhance the closed-loop performance. As the system is subject to internal detection delays and external disturbances, the stability and tracking accuracy of system are greatly challenged. MEMS gyroscopes inertial sensor are widely used in electro-optical control systems due to their advantages of light weight, high resonant frequency, and short response time. However, the Analog-to-Digital conversion and self-filtering characteristics of the sensors determine that there is a certain detection delay, and the system also faces the interference caused by the mechanical resonance. To solve this problem, an improved Smith Predictor method based on inertial sensor-MEMS gyroscope is proposed. The original Smith Predictor is only used to eliminate the effect of delay. Base of that, we modify the predictor’s structure and add a branch of disturbance observer to compensate the external disturbance. The control strategy and the formula derivation is given out. The experimental results show that the closed-loop bandwidth of the system’s speed loop are significantly improved, and the method effectively improves the system’s disturbance suppression performance.
The optical tracking system mainly encounters the problems of sensor delay and external physical disturbance. We propose a method combining Smith predictor and disturbance observer based on Micro-Electro-Mechanical System (MEMS) gyroscope to improve velocity closed-loop bandwidth and disturbance suppression ability. The experimental results demonstrate that the velocity closed-loop bandwidth is increased by about 10 Hz and the disturbance suppression ability is increased by about 11 dB in the low and middle frequency domain.
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