Miniaturized Dual-Stage Rotary Actuator for Fast and Precise Positioning by Overcoming the Cogging Torque

The existing piezoelectric actuators (PEA) are difficult to increase the speed, and the cross-scale dual-stage precision drive technology usually adopts the tandem transmission configuration, which has the problems of insufficient positioning accuracy, low device stiffness and large structure size. This article proposes a novel miniaturized parallel dual-stage rotary actuator, driven by a permanent magnet synchronous motor (PMSM) and a PEA, and develops a corresponding dual-stage closed-loop control method to achieve fast and precise positioning. PEA consists of the drive unit and the clutch unit. The drive unit overcomes the cogging torque to realize precise positioning, and the clutch unit realizes flexible switching of electromagnetic/piezoelectric power. Mathematical models are constructed to analyze the inherent cogging torque of the PMSM and the feasibility of overcoming the cogging torque by the PEA to achieve precise positioning compensation. The prototype is fabricated, with the outer diameter of Ø38 mm and the drive component mass of 48 g, and the output performance is tested. The experimental results show that the proposed dual-stage rotary actuator can achieve a speed of 4700 r/min and a resolution of 0.127 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i>rad, and the steady state error is reduced by 93% compared to the PMSM driving alone.