Continuous Nonsingular Fast Terminal Sliding Mode Control for a Free Gyro Stabilized Mirror System

Optical sensor-based systems necessitate a pointing and stabilization mechanism to separate the line-of-sight (LOS) from the operating environment. A gyro-stabilized mirror system (GSMS) can fulfill this requirement. Although this configuration is cost-effective, structured and unstructured nonlinear disturbances, dynamic imbalances, and carrier vibrations deteriorate the system performance. Therefore, it is indispensable to design a control system that has a fast response, high control accuracy, and insensitivity to perturbations. To acquire these attributes for GSMS applications, an improved nonsingular fast terminal sliding mode-based control is proposed in this paper. The prime advantage of the investigated control scheme is that its realization requires only available measurements of the system and control gains without acquiring a priori knowledge of the bounds on system perturbations. Moreover, the developed controller alleviates the main drawback, chattering, in conventional sliding mode control while preserving its robustness to disturbances. The stability of the closed-loop system is proven via the Lyapunov method, and the effectiveness of the proposed control strategy is elucidated through comparative numerical studies. Note to Practitioners—This paper proposes an improved control system for GSMS used in optical sensors. These systems are susceptible to vibrations and disturbances that can degrade their performance. The proposed control method offers several advantages for practical applications: (i) Fast Response and High Accuracy: The controller achieves fast settling times and minimizes pointing errors, leading to improved overall system performance; (ii) Insensitivity to Disturbances: The controller is designed to handle external vibrations and other uncertainties without requiring precise knowledge of their characteristics. This makes it robust and adaptable to real-world operating conditions; (iii) Reduced Chattering: Unlike traditional sliding mode control, this method minimizes chattering, a high-frequency control output oscillation that can damage mechanical components. Implementing this control strategy requires only angular position measurements. Furthermore, unlike previous methods that typically employ artificial neural networks or fuzzy logic to obtain an approximate model for unknown disturbances, we use simple adaptive laws for adjusting control gains. These eliminate the need for complex system modeling, making it practical for real-world engineering applications. While the paper explores the effectiveness through simulations, real-world implementation can further illustrate closed-loop features. The focus of this paper is on GSMS. While the control method has broader applicability, its adaptation to other systems might require adjustments. Overall, this paper suggests that the proposed control scheme offers a promising approach for engineers working with GSMS or similar positioning systems that require high precision, fast response, and robustness to disturbances. Future research will focus on designing an event-triggered quantitative prescribed performance control scheme based on the proposed method for a GSMS.