Preload design and modal-analysis-based verification of a cam-driven opto-mechanical zoom mechanism for deep-space exploration

Accurate preload design is essential for the stiffness, dynamic stability, and driving reliability of precision opto-mechanical systems. This study investigates a cam-driven zoom mechanism with miniature ball bearings and spring preloading devices, and establishes a preload–stiffness–torque margin coupled model. Based on Hertzian contact theory, the relationships among preload, contact stiffness, and motor torque margin are derived. Sensitivity analysis is performed to identify the dominant parameters, and a multi-objective optimization is conducted to balance stiffness enhancement and torque safety margin, yielding an optimal preload of 29 N. Finite element modal analyses under different preload conditions show that both stiffness and natural frequency exhibit saturation beyond 29 N. The second-order natural frequency follows a sixth-root dependence on preload, consistent with the analytical prediction. For deep-space applications, the effects of thermally induced differential expansion on preload drift and contact clearance variation are further analyzed. Margin verification demonstrates that the mechanism remains stable and reliable within the controlled operational temperature range. The proposed framework provides theoretical support and engineering guidance for preload design in precision opto-mechanical systems for deep-space applications.