Objective Fast Steering Mirrors (FSMs) are critical components in high-dynamic military optoelectronic systems for precise beam pointing, tracking, and stabilization. Traditional Voice Coil Motor (VCM) driven FSMs offer large travel ranges but are inherently limited by low bandwidth due to high inertia. Conversely, Piezoelectric (PZT) driven FSMs provide high bandwidth and precision but are typically constrained by small angular strokes. Furthermore, scaling PZT-FSMs to large apertures (e.g., >50 mm) presents significant challenges, as the increased mirror mass significantly degrades system stiffness and dynamic response. Existing designs often struggle to simultaneously achieve large clear apertures, wide angular scanning ranges, and high structural stiffness. This study addresses these trade-offs by designing and implementing a high-performance FSM system based on a rhombic Amplified Piezoelectric Actuator (APA), tailored for a large-aperture (65 mm) application to ensure both large travel and robust dynamic performance.
Methods We propose a novel FSM configuration driven by a rhombic displacement amplification mechanism (Fig.4) to address the stroke limitations of PZT actuators. To accommodate a large-aperture 65 mm Silicon Carbide (SiC) mirror, the structural parameters of the APA (Fig.6) were systematically optimized (L_1=9.3 \mathrm~mm,\; \theta=7.6^\circ ), increasing the theoretical displacement amplification factor from 3.75 to 5.71 to compensate for the increased load inertia. Unlike traditional adhesive bonding, a bolt-connection method was adopted to secure the large mirror, thereby enhancing structural reliability and minimizing assembly stress. A multi-physics coupled modeling approach combined with topology optimization was employed to synergistically optimize the static and dynamic performance. To accurately predict system behavior, a high-fidelity dynamic model (Fig.14) accounting for the nonlinear effects of flexure hinges was established, and an explicit transfer function from driving voltage to angular displacement was derived. The design was validated through Finite Element Analysis (FEA) and comprehensive experimental testing on a prototype.
Results and Discussions Experimental characterization of the rhombic APA demonstrated excellent linear displacement amplification within the 0-120 V driving range, achieving an amplification factor of 5.71±0.08 with a nonlinear error of less than 0.3% (Fig.8). The assembled FSM system achieved a mechanical deflection range (angular stroke) of ±3.75 mrad in the X-axis and ±3.68 mrad in the Y-axis, significantly exceeding standard PZT-FSM capabilities (Fig.19). High-precision angular resolutions of 2.9 μrad (X-axis) and 1.0 μrad (Y-axis) were realized (Fig.20-Fig.21). Modal analysis and testing revealed that the first-order (pitch) and second-order (yaw) resonant frequencies reached 558.34 Hz and 558.96 Hz, respectively (Fig.15), representing an approximate 35% improvement in system stiffness compared to similar products. In closed-loop control tests, the system exhibited high linearity, with errors as low as 0.71% for the X-axis and 0.52% for the Y-axis (Fig.22-Fig.23). The measured –3 dB closed-loop bandwidth was 28 Hz, confirming stable dynamic response capabilities under large-load conditions (Fig.24-Fig.25).
Conclusions This study successfully developed a large-aperture, piezo-driven FSM system that effectively mitigates the conflict between large angular stroke and high structural stiffness. By integrating an optimized rhombic APA with a rigid supporting structure, the system achieves microradian-level precision and milliradian-level travel for a 65 mm aperture mirror. The significant improvements in stiffness and linearity, combined with the robust bolt-connected design, validate the efficacy of the proposed technical path. This design provides a viable engineering solution for next-generation high-performance optoelectronic systems requiring both wide-range scanning and high-bandwidth stabilization.
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