A wearable arm with controllable light force based on hydro-magnetic actuation

Supernumerary Robotics Limbs (SRL) can help hold heavy objects, support the user’s arm, reach unreachable objects, or act as a co-worker. However, the existing powertrains used in wearable robotlike geared motors, are not suitable for SRL applications in terms of their mechanical bandwidth, backdriveand force density.

The proposed 2-DOF flat wearable supersonic robotic arm. Image credit: arXiv: 2206.13361 [cs.RO]

A recent article on arXiv.org explores an alternative transmission method that involves using a magnetic clutch in combination with a low-friction hydrostatic transmission. The robotic arm was developed to minimize the total user-wearing mass, friction and reflected inertia, and to maximize the bandwidth and controllability of the interaction force.

The results showed that the demonstrator was light enough to be worn for long periods of time without strain. A relatively constant force can be applied to the work object while the person exhibits natural motion.

Supernumerary Robotic Limbs (SRL) are wearable robots that enhance human abilities by acting as a co-worker, approaching objects, assisting human arm, etc. However, existing SRLs lacks the mechanical capability and bandwidth required for tasks where interaction forces must be controlled such as painting, manipulating fragile objects, etc. Has high back-processing capability with large bandwidth while minimizing weight poses a major technological challenge due to the limited performance of conventional electromagnetic actuators. This paper investigates the feasibility of using a dynamic magnetic clutch (MR) in combination with a low-friction hydrostatic transmission to provide an Ostia with high force control, but light yet light. A 2.7 kg 2-DOF wearable robotic arm is designed and built. The shoulder and elbow joints are designed to deliver 39 and 25 Nm, with 115 and 180° range of motion. Experimental studies conducted on a single DOF and analytically validated test bench have demonstrated high force bandwidth (>25 Hz) and good control of the interaction force even when interacting with impedance outside. Furthermore, three approaches to force control are studied and experimentally proven: open-loop, force-closed, and pressure-closed. All three methods have been shown to be effective. Overall, the proposed MR-Hydrostatic drive system is well suited for a lightweight SRL that interacts with both people and the environment causing unpredictable turbulence.

Research articles: Véronneau, C., Denis, J., Lebel, L.-P., Denninger, M., Plante, J.-S. and Girard, A., “A controllable lightweight wearable arm based on hydro-magnetic-hydrostatic actuators”, 2022. Link: https://arxiv.org/abs/2206.13361

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