Modular one-to-many clutchable actuator for a soft elbow exosuit

Abstract

Exoskeletons have been developed for a wide range of applications, from the military to the medical field, with the aim of augmenting human performance or compensating for neuromuscular deficiencies. However, to empower the high number of degrees of freedom of the human body, they often employ a high number of motors, increasing the size, weight and power consumption of the system. We hereby present an actuation strategy to empower our elbow exosuit that adopts a single motor to drive multiple, independently actuated, degrees of freedom. This paradigm, known as One-to-many, is achieved using a modular design where each module comprises a clutchable mechanism that allows to convert a single directional motion from the prime mover to a selectable bidirectional output. Moreover, the mechanism has a locking feature that enables the wearer of the exoskeleton to hold a static load with a minimal power consumption. We present a simple controller for the clutchable unit based on a finite-state machine model, and evaluate its performance for varying input velocities. The system is shown to have a bandwidth of 1.5 Hz, sufficient for daily elbow movements, whilst retaining a compact design.

Development and validation of a soft robotic exosuit for assistance of the upper limbs

“…tained for 45 rad/s. This result echoes our previous findings, where [131] tested the same device for higher input velocity and found a saturation effect of its bandwidth for higher velocities of the prime mover. This suggests that the limiting dynamic at high frequencies is not given by the rotating speed of the prime mover but by the engaging dynamics of the clutches [127].…”

“…In [131], we proposed a heuristic control approach that consisted in a feedback state machine to keep the measured trajectory as close as possible to a reference profile. This strategy, although being simple, presented fundamental limitations in accuracy and stability.…”

“…This paradigm is shown in Figure 6 Figure 6.2: OTM actuator to power two elbow exosuits with one electric motor. This system, that we proposed in [131], consists in one prime mover, transmitting power to two clutchable DOF Modules connected to two elbow exosuits via Bowden cables. Each module independently controls the position of its corresponding DoF.…”

“…The encouraging results of OTM systems, applied to drive manipulators and robotic hands, led us to investigate their feasibility in the field of wearable assistive devices, increasingly in need of novel, efficient actuation paradigms. We previously proposed an OTM system, consisting of 2 clutchable modules, to actuate the tendons driving a soft exosuit for the elbow joints [131], shown in Figure 6.2.…”

Design and Validation of a Modular One-To-Many Actuator for a Soft Wearable Exosuit

“…The encouraging results of OTM systems, applied to drive manipulators and robotic hands, led us to investigate their feasibility in the field of wearable assistive devices, increasingly in need of novel, efficient actuation paradigms. We previously proposed an OTM system, consisting of 2 clutchable modules, to actuate the tendons driving a soft exosuit for the elbow joints (Canesi et al, 2017), shown in Figure 2. Each module followed a working principle similar to the one presented in Chen and Xie (1999): this design has the advantage, over the spring-ratchet design in Hunt et al (2013), of not being limited in the amount of energy that can be stored in each module and it results in a simpler and lighter architecture than the designs employing MR clutches or IVTs.…”