In order to maintain accurate tracking of a target, it is essential to counteract the effects of hull disturbances caused by waves. These disturbances lead to random movements—such as rolling, pitching, and yawing—which can cause the antenna to sway, thereby degrading the performance of narrow beam antennas and potentially causing the loss of the target. To ensure stable and precise tracking, an anti-disturbance stabilization system must be implemented. This system isolates the antenna from the hull's motion, allowing it to remain stable in the inertial space coordinate system and meet the required tracking performance.
Traditionally, this is achieved through multi-mode compensation techniques that require at least six rate gyros to detect three-dimensional disturbance information and active rotation data of the antenna. Based on the three axes (azimuth, pitch, and cross-cut), both feedforward open-loop and feedback closed-loop compensations are combined. However, this approach leads to complex designs, high gyro usage, and insufficient redundancy.
The influence of three-dimensional hull disturbances on the visual axis of a three-axis antenna system (transverse axis C, azimuth axis A, and pitch axis E) is significant. The system is based on a conventional AE-type frame, with the transverse axis perpendicular to the pitch axis. When the pitch angle is 0°, the transverse axis aligns with the azimuth axis, while at 90°, it becomes perpendicular. The angular velocity vector of the hull, ωz = (ωp, ωy, ωh), where ωy is roll speed, ωp is pitch speed, and ωh is heading speed, affects the antenna’s movement. These disturbances are converted into velocity components along the heel, azimuth, and pitch axes.
Through detailed analysis, equations are derived that reflect how these disturbances impact the three axes of the antenna. Open-loop compensation can be used to eliminate their influence, while closed-loop methods address the total rotational speeds in inertial space. Accurate measurement and appropriate control strategies are crucial for effective disturbance suppression and ensuring fast, stable target tracking.
Anti-disturbance design involves detecting interference signals introduced by the ship's motion and using either closed-loop or open-loop methods to reduce their impact. Feedforward compensation is preferred over closed-loop control because it allows for open-loop adjustments without affecting the system's bandwidth or stability. By adding measured disturbance information to the input of the speed loop, the antenna rotates in the opposite direction to the ship, effectively counteracting the disturbance.
The control implementation uses a speedometer for speed feedback and an encoder for position feedback, with disturbance information fed forward via rate gyros. This configuration ensures the system can handle both current and future disturbances, improving tracking accuracy. Engineering applications demonstrate that proper selection of feedforward coefficients and combination with the tracking loop can significantly enhance performance.
In real-world tests, a three-axis antenna system was evaluated under typical sea conditions, showing excellent isolation performance and high tracking accuracy. The results confirm that the open-loop compensation method meets all system requirements efficiently and reliably.
In conclusion, feedforward compensation enhances system performance without altering the original control structure, maintaining stability and bandwidth. Combined with feedback control, it simplifies the system, improves reliability, and extends device lifespan, making it an effective solution for marine antenna systems.
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