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Switch-based Independent Antagonist Actuation with a Single Motor for a Soft Exosuit

Atharva Vadeyar, Rejin John Varghese, Etienne Burdet, Dario Farina

TL;DR

The paper addresses the actuator count challenge in cable-driven soft exosuits designed for multi-DoF control by introducing a switch-based mechanism that enables independent antagonist actuation with a single motor across arbitrary cable paths. A lightweight prototype demonstrates spool independence and practical switching between antagonistic directions, with average switching times around 0.3 s at ~120 rpm, highlighting generalizability and low-cost advantages. The approach offers a simple, safe, and scalable alternative to dual motors or complex underactuation schemes, though the switching delay and absence of on-demand torque/stiffness modulation remain limitations. Overall, the work provides a viable pathway toward more compact, affordable multi-DoF soft exosuits suitable for rehabilitation and activities of daily living, with clear directions for optimization and future enhancements.

Abstract

The use of a cable-driven soft exosuit poses challenges with regards to the mechanical design of the actuation system, particularly when used for actuation along multiple degrees of freedom (DoF). The simplest general solution requires the use of two actuators to be capable of inducing movement along one DoF. However, this solution is not practical for the development of multi-joint exosuits. Reducing the number of actuators is a critical need in multi-DoF exosuits. We propose a switch-based mechanism to control an antagonist pair of cables such that it can actuate along any cable path geometry. The results showed that 298.24ms was needed for switching between cables. While this latency is relatively large, it can reduced in the future by a better choice of the motor used for actuation.

Switch-based Independent Antagonist Actuation with a Single Motor for a Soft Exosuit

TL;DR

The paper addresses the actuator count challenge in cable-driven soft exosuits designed for multi-DoF control by introducing a switch-based mechanism that enables independent antagonist actuation with a single motor across arbitrary cable paths. A lightweight prototype demonstrates spool independence and practical switching between antagonistic directions, with average switching times around 0.3 s at ~120 rpm, highlighting generalizability and low-cost advantages. The approach offers a simple, safe, and scalable alternative to dual motors or complex underactuation schemes, though the switching delay and absence of on-demand torque/stiffness modulation remain limitations. Overall, the work provides a viable pathway toward more compact, affordable multi-DoF soft exosuits suitable for rehabilitation and activities of daily living, with clear directions for optimization and future enhancements.

Abstract

The use of a cable-driven soft exosuit poses challenges with regards to the mechanical design of the actuation system, particularly when used for actuation along multiple degrees of freedom (DoF). The simplest general solution requires the use of two actuators to be capable of inducing movement along one DoF. However, this solution is not practical for the development of multi-joint exosuits. Reducing the number of actuators is a critical need in multi-DoF exosuits. We propose a switch-based mechanism to control an antagonist pair of cables such that it can actuate along any cable path geometry. The results showed that 298.24ms was needed for switching between cables. While this latency is relatively large, it can reduced in the future by a better choice of the motor used for actuation.

Paper Structure

This paper contains 9 sections, 5 figures.

Table of Contents

  1. Introduction
  2. The Switch-based Actuation Mechanism
  3. Validation Experiments & Results
  4. Experimental Setup
  5. Experimental Protocol
  6. Spool Independence Test
  7. Switching Time Test
  8. Results
  9. Discussion & Conclusion

Figures (5)

  • Figure 1: The proposed actuation mechanism capable of independently facilitating antagonist actuation.
  • Figure 2: Schematic of the switch-based actuation mechanism: A). CAD rendering of the mechanism with labelled components, B). Geometrical configuration of the pitch circles of different gears and their placement. It is to be noted that the driven gears are spring-loaded.
  • Figure 3: The test rig to test the switching mechanism. It consists of a motor with the switching mechanism. The capstans in the mechanism are connected to both the string potentiometers and the simulated 1-DoF joint with different tendon paths.
  • Figure 4: Spool Independence Test Results
  • Figure 5: Switching Time Test Results