A Lightweight Force-Controllable Wearable Arm Based on Magnetorheological-Hydrostatic Actuators

TL;DR

This paper presents a lightweight, force-controllable wearable robotic arm using magnetorheological clutches and hydrostatic transmission, demonstrating high bandwidth and effective force control for human-robot interaction tasks.

Contribution

It introduces a novel MR-Hydrostatic actuation system for wearable robots, achieving high force bandwidth and lightweight design for improved human interaction capabilities.

Findings

Achieved force bandwidth >25 Hz in experiments

Designed a 2.7 kg 2-DOF robotic arm with high torque and range of motion

Validated three force-control methods successfully

Abstract

Supernumerary Robotic Limbs (SRLs) are wearable robots augmenting human capabilities by acting as a co-worker, reaching objects, support human arms, etc. However, existing SRLs lack the mechanical backdrivability and bandwidth required for tasks where the interaction forces must be controllable such as painting, manipulating fragile objects, etc. Being highly backdrivable with a high bandwidth while minimizing weight presents a major technological challenge imposed by the limited performances of conventional electromagnetic actuators. This paper studies the feasibility of using magnetorheological (MR) clutches coupled to a low-friction hydrostatic transmission to provide a highly capable, but yet lightweight, force-controllable SRL. A 2.7 kg 2-DOFs wearable robotic arm is designed and built. Shoulder and elbow joints are designed to deliver 39 and 25 Nm, with 115 and 180{\deg} of range of motion. Experimental studies conducted on a one-DOF test bench and validated analytically demonstrate a high force bandwidth (>25 Hz) and a good ability to control interaction forces even when interacting with an external impedance. Furthermore, three force-control approaches are studied and demonstrated experimentally: open-loop, closed-loop on force, and closed-loop on pressure. All three methods are shown to be effective. Overall, the proposed MR-Hydrostatic actuation system is well-suited for a lightweight SRL interacting with both human and environment that add unpredictable disturbances.