Objective The photoelectric load system under the airborne platform is the basis of aerial photography, aerial mapping, and aerial communication in China. With the diversified application scenarios, the new photoelectric tracking platform characterized by small volume and shape, hidden and flexible installation mode, and high tracking accuracy is more suitable for applications in the new generation of aviation field than the traditional photoelectric platform. Therefore, a photoelectric tracking platform based on dual liquid crystal polarization gratings (LCPGs) is proposed to meet the above application requirements. Meanwhile, the control method is studied to provide theoretical support and technical references for the new tracking system under the airborne platform. Methods First, the dual-LCPG beam solution model is built with the location information of the target location information. The solution model is divided into the forward model and the reverse model. Forward model solution analysis is the premise and foundation for the application of rotating dual-grating beam pointing. The reverse model is a key one that must be addressed in optical tracking and target-directed applications. To achieve high-precision target tracking of dual-LCPC photoelectric follow aim systems, we design a controller combining the solution model and MPC based on the beam solution model. Meanwhile, by employing the servo system controller of dual-grating control, beam deflection, and target tracking, MPC can predict the system model in the future for a certain time to improve the tracking accuracy. Finally, to verify the tracking performance of the system, we build the platform as shown in Fig. 4 for dynamic tracking experiments. Employing dual-grating diffraction characteristics, we place the two gratings in parallel by the servo motor, with the encoder displaying the angle position information of the motor as the feedback signal of the control system. After the incident beam diffraction, the deflection angle is derived from the positive and negative solution calculation model. Additionally, the outgoing beam is received by the camera after the beam, and the image processing unit can process the target off amount. Then, the feedback platform position attitude of the inertial measurement unit is installed on the platform. After establishing the experimental platform, the dynamic tracking accuracy under 2 degrees @0.5 Hz and 5 degrees @0.2 Hz interference respectively. Finally, the overhead time is tested. Results and Discussions According to the disturbance in the simulated aircraft flight, the maximum angular velocity and angular acceleration are calculated, and similar sinusoidal signals of 2 degrees@0.5 Hz and 5 degrees@0.2 Hz are selected to simulate the airborne disturbance. Therefore, the photoelectric tracking platform is mounted on the six-degree-of-freedom swing platform, and the swing platform is set up simultaneously by swinging around the X axis and the Z axis, with the sinusoidal sine phase difference of 90 degrees . The experimental system is shown in Fig. 5. To verify the tracking effect of the MPC controller, we select the traditional control algorithm PID, and apply the PID controller and the MPC controller respectively to track the target, with the spot stable tracking shown in Fig. 6. The experimental results are shown in Figs. 8 and 9. By adopting the upper machine to record 3000 orientation and elevation target data, the statistical tracking accuracy RMS values of the system under the case of biaxial 2 degrees@0.5 Hz and 5 degrees@0. 2 Hz perturbation are 132.56 mu rad and 126.69 mu rad respectively, and the system tracking performance is significantly improved compared with the traditional PID algorithm. Conclusions By studying the tracking performance of a dual-grating photoelectric tracking platform based on the MPC algorithm, the dual-grating beam solution model is built and introduced into the servo control system. The MPC controller is designed to realize the high-precision tracking of the target under the dynamic platform. The experimental platform is built to verify the dual-grating tracking platform. The experimental results show that the MPC algorithm improves the tracking accuracy by more than 23.76% compared with the traditional PID algorithm, and the tracking accuracy is less than 150 mu rad. The experimental results verify the effectiveness and excellence of the dual-LCPC photoelectric tracking system based on the MPC algorithm. The results prove that the system can realize high-precision dynamic tracking under the airborne platform. Additionally, the system has sound application significance and provides certain theoretical references and technical support for the development of new light and miniaturized photoelectric tracking technology.
