Abstract
When a fast-steering mirror (FSM) system is designed, satisfying the performance requirements before fabrication and assembly is vital. This study proposes a structural parameter design approach for an FSM system based on the quantitative analysis of the required closed-loop bandwidth. First, the open-loop transfer function of the FSM system is derived. In accordance with the transfer function, the notch filter and proportional-integral (PI) feedback controller are designed as a closed-loop controller. The gains of the PI controller are determined by maximizing the closed-loop bandwidth while ensuring the robustness of the system. Then, the two unknown variables of rotational radius and stiffness in the open-loop transfer function are optimized, considering the bandwidth as a constraint condition. Finally, the structural parameters of the stage are determined on the basis of the optimized results of rotational radius and stiffness. Simulations are conducted to verify the theoretical analysis. A prototype of the FSM system is fabricated, and corresponding experimental tests are conducted. Experimental results indicate that the bandwidth of the proposed FSM system is 117.6 Hz, which satisfies the minimum bandwidth requirement of 100 Hz.
Highlights
A fast-steering mirror (FSM) is a rotational positioning stage that plays an important role in optical beam control systems to achieve pointing, tracking, and acquisition [1].Received April 5, 2019; accepted May 4, 2019✉ Guozhen CHEN, Pinkuan LIU ( ), Han DINGFSMs have been widely used in many fields, such as imaging [2,3] and laser processing systems [4], free-space optical communications [5,6], and laser weaponry [7,8]
The FSM is generally designed for a target application for which the bandwidth requirement is specific
If the FSM’s structural parameters are poorly designed, the final bandwidth may fail to satisfy the practical requirements of the target application
Summary
A fast-steering mirror (FSM) is a rotational positioning stage that plays an important role in optical beam control systems to achieve pointing, tracking, and acquisition [1]. Developing a structural parameter design approach, which can ensure that the FSM can satisfy the bandwidth requirement for a given target application, is crucial. Eng. 2020, 15(1): 55–65 addressing bandwidth challenges, the two major determinants of final bandwidth are the open-loop transfer function of the stage and the corresponding closed-loop control strategy. To conduct the quantitative analysis of the bandwidth, the open-loop transfer function, resonant modes’ damping methods, and feedback controller should all be considered. The rest of this paper is organized as follows: Section 2 presents the mechanical design of the FSM; Section 3 presents the open-loop transfer function of the stage and the closedloop control strategy; Section 4 determines the structural parameters; Sections 5 and 6 detail the conducted simulations and experimental testing, respectively; Section 7 concludes the study
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