A Miniaturized Multi-Drum Magnetorheological Actuator with Shared Magnetic Flux for Enhanced Torque Output

Reducing the size of magnetorheological (MR) actuators imposes severe constraints on magnetic volume and excitation efficiency, thereby limiting the achievable torque output, particularly at the 20 mm-class outer-diameter scale. To address this limitation, a miniaturized multi-drum MR actuator is proposed for enhanced torque output. It features multiple concentric annular shear gaps operating in radial shear mode and a shared magnetic flux path to improve flux utilization. Finite-element analysis is conducted to guide the magnetic circuit design, revealing a radial field distribution inherent to flux-sharing architectures and motivating an optimization strategy that drives the inner shear gap and magnetic paths close to saturation simultaneously. An optimized actuator prototype with an outer diameter of 20.8 mm, a height of 21.7 mm, and a total mass of 42.2 g was fabricated. Experimental characterization demonstrates that the actuator delivers a maximum torque of 91 mN·m with a low off-state torque of approximately 2 mN·m, achieving a substantial performance improvement over representative prior designs of comparable dimensions.