Macro-Mini Linear Actuator Using Electrorheological-Fluid Brake for Impedance Modulation in Physical Human–Robot Interaction

Abstract

Robots designed to interact physically with humans are typically characterized by low impedance and low output force, but in many circumstances, high force is needed. Integrated to a high-torque velocity source, antagonistic designs of electrorheological (ER)-fluid or magnetorheological (MR)-fluid clutches enabled a range of achievable impedances for rotational uses. This letter presents an alternative novel concept of linear actuator which uses a rotary ER-fluid brake to engage the highly backdrivable unit to the high force unit. The end effector driven by a mini motor is connected to the brake rotor. Since the brake rotation allows the relative translation between the endpoint and the high-force actuator, the mechanical impedance can be modulated by controlling the brake friction through the applied voltage. The ER-fluid brake using multiple concentric cylinders for high torque-to-inertia ratio was characterized experimentally. The macro-mini linear actuator with an intrinsic failsafe can be applied for active body weight support systems requiring antigravity high force.