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

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.