为了进一步提高光电跟踪系统的目标捕获和跟踪性能, 提出了一种基于变增益趋近律的级联滑模控制方法。基于反双曲正弦函数和幂次项设计了新型变增益滑模趋近律, 在提高滑模面趋近速度的同时抑制滑模抖振现象; 基于变增益滑模趋近律设计速度环和位置环滑模控制器构成级联滑模控制, 以提高系统的动态响应性能和鲁棒性, 提高系统对目标的捕获能力和跟踪精度。最后, 以某球形光电跟踪系统的方位轴作为控制对象, 进行了传统级联PI控制和级联滑模控制方法的对比分析。实验结果表明, 相比于传统级联PI控制, 捕获速度为1 (°)/s的目标时, 级联滑模控制可以将目标捕获时间减小32%; 跟踪等效最大速度为4 (°)/s和最大加速度为2 (°)/s2的正弦引导信号, 可将跟踪误差RMS值减小31%, 采用级联滑模控制可有效提高跟踪系统的控制性能。

A cascade sliding mode control method based on a variable gain reaching law was proposed to improve the target acquisition and tracking performance of a photoelectric tracking system. First, to reduce sliding mode chattering and improve the dynamic response speed, a novel sliding mode reaching law with variable gains was designed. The variable gains were designed based on the inverse sine and exponential functions. Then, based on the novel reaching law with variable gain, the speed and position sliding mode controllers of the system were presented. The speed and position sliding mode controllers include cascade sliding mode control, which was designed to enhance the dynamic and robust performance of the system and further improve the system target acquisition and tracking accuracy. Finally, a comparison was made between the control performance of a traditional cascade PI control and the proposed cascade sliding mode control, based on the azimuth axis of a photoelectric tracking system. The experimental results show that compared to traditional cascade PI control, cascade sliding mode control can reduce the acquisition time by 32% when detecting a target with a speed of 1 (°)/s. Moreover, it can reduce the RMS of the tracking error by 31% when tracking the position sine signal with a maximum speed of 4 (°)/s and a maximum acceleration of 2 (°)/s2. These results indicate that cascade sliding mode control can improve the control performance of the tracking system.