Design and Preliminary Evaluation of a Torso Stabiliser for Individuals with Spinal Cord Injury

TL;DR

Torso instability after spinal cord injury severely impairs activities of daily living, and existing stabilisers are often rigid. This work proposes a purely mechanical 1-DoF torso stabiliser that remains transparent during ADL and engages compliant blocking on incipient falls, motivated by centrifugal-clutch and seat-belt mechanisms. Using MoCap data and OpenSim, the authors identify design targets, including $55-60$ cm of unrestricted cable travel and a blocking threshold of $80-100$ cm/s, and validate a prototype with MoCap demonstrating non-restrictive movement and a compliant block at the trigger velocity. Preliminary hardware tests confirm the concept but reveal blocking at a somewhat lower velocity than simulations, indicating a need to tune the trigger and improve robustness. If further validated, the low-cost mechanical approach could offer a practical stabilization solution for SCI patients, with potential applicability in low- and middle-income settings, pending broader testing.

Abstract

Spinal cord injuries generally result in sensory and mobility impairments, with torso instability being particularly debilitating. Existing torso stabilisers are often rigid and restrictive. We present an early investigation into a non-restrictive 1 degree-of-freedom (DoF) mechanical torso stabiliser inspired by devices such as centrifugal clutches and seat-belt mechanisms. First, the paper presents a motion-capture (MoCap) and OpenSim-based kinematic analysis of the cable-based system to understand the requisite device characteristics. The evaluation in simulation resulted in the cable-based device to require 55-60\,cm of unrestricted travel, and to lock at a threshold cable velocity of 80-100\,cm/s. Next, the developed 1-DoF device is introduced. The proposed mechanical device is transparent during activities of daily living, and transitions to compliant blocking when incipient fall is detected. Prototype behaviour was then validated using a MoCap-based kinematic analysis to verify non-restrictive movement, reliable transition to blocking, and compliance of the blocking.

Figures (4)

• Figure 1: The proposed torso stabiliser system. (i) incorporated as a device attached to the wheelchair, and the cable from the device anchored to a back-support vest. (ii) Section view of the developed prototype.
• Figure 2: Overview of the virtual prototyping setup and results: (i). Setup for MoCap experiments, (ii). Musculoskeletal model in OpenSim with path actuators, (iii). Torso stabiliser cable displacement and velocity (filtered) v/s time during a trial (blue line - left device, and orange line - right device).
• Figure 3: An exploded view and list of components of the developed device that enables both non-restrictive ADL movement and responsive compliant blocking. The mechanism that triggers compliant blocking is presented in the inset figure.
• Figure 4: An overview of the (i). MoCap setup and (ii). results of preliminary validation of the prototype. The results show device transparency during low-to-medium cable velocities (green shaded regions), and the transition to blocking, and compliant blocking above a certain threshold (red shaded regions).