A Large-Aperture Variable Iris Directly Driven by a V-Shaped Mode-Coupled Ultrasonic Motor: Design, Optimization, and Experimental Validation

Large-aperture variable irises must provide continuous aperture regulation within a restricted axial space. This study presents a laboratory prototype of a 20-blade iris directly driven by a V-shaped mode-coupled ultrasonic motor. The iris was geometrically designed for a 5.5 mm– 98 mm clear-aperture range. A wave-spring–bearing compliant preload mechanism was designed to maintain blade compression while permitting low-resistance actuating-ring rotation. Under a 3 N axial load, finite-element analysis showed that a representative three-blade overlap unit was approximately 7.6 times stiffer axially than the preload mechanism, so deformation occurred mainly in the latter. Taguchi design and multi-objective optimization produced a flexibly clamped stator with simulated working modes at 121.93 kHz and 122.10 kHz, separated by 170 Hz; the measured frequencies were 120.7 kHz and 121.5 kHz. At 121.8 kHz and 300Vpp, the 5.74 g stator generated bidirectional maximum thrusts of 3.91 N and 4.11 N, corresponding to a maximum thrust-to-mass ratio of 716 N/kg. A separate short-cycle test yielded a minimum observed stable tangential displacement of 3.23m. Quantitative opening and closing tests over a local 10 mm– 20 mm interval yielded mean absolute actuating-ring angle errors of 0.087∘ and 0.13∘, respectively. Model-extrapolation tests from a 20 mm reference yielded an aperture MAE of 0.183 mm over 10 mm– 80 mm, while errors of +1.7 mm and −1.2 mm were measured at the 5.5 mm and 98 mm targets. These results support the functional feasibility of the proposed direct-drive architecture and identify an increased prediction error near the travel limits.