Modal-coupled dual-rotor ultrasonic motor with expandable configuration

Conventional sandwich-type ultrasonic motors suffer from structural complexity, limited design flexibility, and inefficient assembly when configured for dual-rotor operation, which restricts their application scope. To address these challenges, this study proposes a novel piezoelectric actuation mechanism, an expandable design scheme, and a cooperative assembly method tailored for sandwich-type dual-rotor ultrasonic motors. The principle of longitudinal-bending modal coupling is employed to replace the commonly adopted bending-bending mechanism in dual-rotor actuation, thereby simplifying the coupling elements. An expandable design method is established, enabling rapid iteration of transducer count, ring structure dimensions, and key vibration modes according to specific requirements, enhancing prototype development flexibility for engineering applications. A case study is presented accordingly, its core structural advantage lies in a synergistic assembly system formed by three components: the frame, prestressed nuts, and ring-horn composite structure, enabling efficient and stable multi-transducer cooperative assembly through single-step torque loading. This approach avoids the inefficiency and low reliability associated with conventional individual transducer assembly via standard bolts. The validity of the driving principle is verified through finite element analysis, and the structural parameters are optimized. The feasibility of the assembly strategy and design method is validated through impedance-phase and vibration measurements on the prototype. Mechanical performance tests show the prototype's output torque reaches 1.5 N·m (600 V in peak-to-peak value) with reliable continuous operation. Notably, the prototype exhibits exceptional stepping capability, achieving single-step angular displacements of 0.065/0.114μrad in single-/dual-rotor configurations. The study expands the design paradigm for sandwich-type dual-rotor ultrasonic motors, providing a systematic solution for engineering applications.