A novel high resolution, fast response speed, and long-stroke hybrid flexible focusing mechanism of advanced optical imaging system driven by an ultrasonic motor

Focusing mechanisms are critical components of optical systems, such as airborne remote sensing, deep space exploration, and biomedical engineering. Traditional focusing mechanisms driven by electromagnetic motors or piezoelectric stack actuators struggle to achieve high resolution, fast response speed, and long stroke simultaneously, falling short of meeting the requirements for high-resolution and high-speed imaging mainly because electromagnetic motors have poor precision and piezoelectric stack actuators have limited stroke. To address these challenges, this study proposes a novel flexible focusing mechanism driven by an ultrasonic motor, integrating a double-bending mode ultrasonic motor with a long-stroke flexible mechanism. First, a compact double-bending mode ultrasonic motor is designed and optimized to accommodate limited vertical space. The design prioritizes a reduced height while maintaining stable performance. Second, based on the pseudo-rigid-body model, the parametric and structural design of the flexible mechanism is completed using a hybrid configuration that incorporates a parallelogram flexible mechanism. Third, the dynamic model of the moving platform is established. Through simulation, it is observed that driving the flexible mechanism improves stability by 83.34 % compared to a rigid body. This helps to improve the accuracy of the focusing mechanism. A prototype of the focusing mechanism is fabricated and tested. The experimental results show that the focusing mechanism's response time, resolution, and stroke are 40 ms, 90 nm, and ±5 mm. The proposed focusing mechanism demonstrates the capability of nanometer-scale focusing with nanometer precision in a millimeter stroke.