Design and Analysis of a Preload-Controllable Lead Screw Linear Ultrasonic Motor Based on Model-Free Adaptive Control

Conventional monolithic lead-screw linear ultrasonic motors exhibit poor output performance due to their lack of adjustable preload mechanisms and inadequate drive-control frameworks. To address these issues, this study proposes a novel split-rotor structure featuring adjustable preload capability and develops comprehensive friction models to characterize preload–interface–thrust and preload–thrust–velocity relationships. Moreover, integrating a model-free adaptive control (MFAC) approach, we design an advanced lead-screw linear ultrasonic motor system. An experimental platform was constructed to validate the accuracy of the proposed preload friction models and MFAC strategy. Experimental results indicate optimal performance at a resonance frequency of 30,890Hz, achieving a maximum velocity of approximately 7.5 mm/s and a peak thrust of around 25 N, with the optimal preload identified between 10 N and 40N. This research effectively resolves intrinsic limitations in thrust output and control precision, thereby laying a solid foundation for precision-driven applications in high-end manufacturing, aerospace, and related fields.