Abstract
High line-of-sight (LOS) pointing precision is a prerequisite for improving the laser confrontation capability of a photoelectric interference pod. In a traditional photoelectric pod, the time delay in TV tracking reduces the system phase margin, system stability and LOS pointing precision. In view of this deficiency, a normalized LMS algorithm is introduced to compensate for the TV camera delay in the inner gimbal position loop of a two-axis and four-gimbal structure, which can allow a pod to avoid system phase margin reduction. Meanwhile, a fast steering mirror (FSM) system is used to improve the LOS pointing precision. First, this paper proposes a normalized LMS algorithm. Second, a compound control structure, with an outer gimbal analog controller and an inner gimbal lag–lead controller, is designed. Finally, the FSM beam control precision is analyzed. The experimental results show that the normalized LMS algorithm yields almost no delay; moreover, the azimuth and pitch beam control accuracies are greater by a factor of 15 and 3, respectively, compared with those of a conventional photoelectric pod.
Highlights
Photoelectric pods mounted on aircraft for detection and tracking tasks and as inertial navigation platforms with laser interference are important components of UAVs [1, 2]
In a traditional photoelectric pod, the time delay in TV tracking reduces the system phase margin, system stability and LOS pointing precision. In view of this deficiency, a normalized LMS algorithm is introduced to compensate for the TV camera delay in the inner gimbal position loop of a two-axis and four-gimbal structure, which can allow a pod to avoid system phase margin reduction
We present only the stable condition of the inner gimbal control system; the stable conditions of the other systems are similar
Summary
Photoelectric pods mounted on aircraft for detection and tracking tasks and as inertial navigation platforms with laser interference are important components of UAVs [1, 2]. The adaptive fuzzy PID controller has been applied to the two-axis tracking platform. The cascading, fractional-order, internal model PID controller is only suitable for fractional-order control objects and cannot be applied to integer-order photoelectric pod control systems [9]. To improve the anti-interference ability of a system, some studies have put forward sliding mode control. The design of the disturbance observer is attributed to the Q-filter design It enhances the system anti-interference performance; the phase seriously lags, resulting in a low damping characteristic [14]. The outer gimbal analog regulator control method and the inner gimbal lag-lead controller are applied; the linkage mode is that the outer gimbal follows the movement of the inner gimbal, the characteristics of which are simple structure and convenient control.
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