To enhance imaging stability across a wide temperature range for large-aperture parallel optical tubes, this paper designs a novel rigid-ring six-bar truss support structure with integrated passive thermal compensation for a Φ600 mm Cassegrain system. By introducing rigid rings, the force flow transmission of the six-bar truss was optimized. This achieved lightweighting while raising the first-order natural frequency of the primary/secondary mirror support structure to 146.9 Hz, meeting high dynamic stiffness requirements. To address mirror spacing drift caused by temperature fluctuations, a passive thermal compensation mechanism based on active matching of multi-material thermal expansion coefficients was proposed. This utilizes counter-displacement generated by high-expansion materials to offset positive thermal deformation in the system. Comprehensive validation using response surface methodology and thermo-structural coupled finite element analysis demonstrates that within a 20 °C to 40 °C temperature range, this compensation structure reduces primary-secondary mirror spacing variation to 37.6%–47.3% of the uncompensated state, effectively suppressing increases in system wavefront error. This work achieves synergistic design of high support structure stiffness and system thermal stability, providing an engineering-feasible solution for performance assurance of similar high-precision opto-mechanical instruments under variable temperature environments.
Cai et al. (2026) studied this question.