Multifunctional Remotely Actuated 3-DOF Supernumerary Robotic Arm Based on Magnetorheological Clutches and Hydrostatic Transmission Lines

Supernumerary robotic limbs (SRL) are wearable extra limbs intended to help humans perform physical tasks beyond conventional capabilities in domestic and industrial applications. However, unique design challenges are associated with SRLs as they are mounted on the human body. SRLs must 1) be lightweight to avoid burdening the user, 2) be fast enough to compensate for human unpredictable motions, 3) be strong enough to accomplish a multitude of tasks, 4) have high force-bandwidth and good backdrivability to control interaction forces between the user and the environment. This letter studies the potential of a remotely actuated 3-DOF supernumerary robotic arm equipped with a 3 fingers soft gripper, both powered by magnetorheological (MR) clutches and hydrostatic transmission lines. The tethered configuration allows the power-unit to be located on the ground, which minimizes the remote mass (4.2 kg) on the user. MR clutches minimize the actuation inertia in order to provide fast dynamics and good backdrivability. An experimental open-loop force-bandwidth of 18 Hz is obtained at each joint and the maximal speed reached by the device end-effector is 3.4 m/s, which is sufficient for compensating human motions. In addition, the two first joints provide 35 Nm and the third joint provides 29 Nm, which is strong enough to hold manual industrial tools. Finally, the SRL is put in real practical situations, as fruit and vegetables picking, painting, tools holding and badminton playing. The capability of the proposed MR-Hydrostatic SRL to perform successfully various tasks with high speed and smoothness suggests a strong potential of SRLs to become future commonly used devices.