Multimode attitude motion control of triplet stator-based spherical piezoelectric motor

Abstract In spherical piezoelectric motors (SPM) attitude control ensures precise rotor orientation, thereby improving reliability, minimizing errors, and optimizing efficiency. The existing studies about the SPM system have mainly focused on multi-axial torque output while neglecting the techniques for controlling the spherical motor’s rotor attitude. Most of the SPM systems are limited to their range of orientations and can achieve rotations only along the x , y , and z directions. Except for a few systems capable of providing multi-axial moments, such systems are typically confined to a single 2D-plane or their axial movement ranges are not well-defined and mostly rely on open-loop control systems without model-based control methods. To tackle these issues, in this article, a feedback-control framework for rotor attitude control has been proposed. The rotor’s driving torques are specifically configured to attain omnidirectional capability. This is achieved through a linear combination of six elementary torque orientations, achieved by adjusting the positions of the contact points between the stators and the rotor. This study adopts a quaternion-based dynamic framework to effectively eliminate singularities in the manipulation of omnidirectional rotors and systematically derives independent control commands for each stator using a computed torque control approach, making it suitable for motor systems that function across all axial orientations. The study implements the developed rotor attitude control strategy in general motion control applications, which are broadly classified into three operational categories: positioning, spin, and hybrid modes. A priority level-based switching algorithm is developed to facilitate torque trajectory generation and reduce the dynamic effects caused by switching rotor contact positions. Finally, a simulation is conducted to validate the proposed rotor attitude control algorithm. The results confirm that the introduced approach delivers consistent and flexible performance suitable for a wide spectrum of motion control scenarios. Simulation analyses further demonstrate that the integration of the switching algorithm enables the rotor to consistently achieve its target orientations throughout different spatial regions.