Design and benchmarking of a two degree of freedom tendon driver unit for cable-driven wearable technologies

TL;DR

This work addresses the lack of transparent benchmarking for tendon driver units in cable-driven exosuits by introducing a modular $2$-DOF tendon driver unit (TDU) and a comprehensive test battery. It combines a practical hardware platform with benchmarking protocols across Open-Loop Static Torque, Closed-Loop Velocity Control, Thermal Cooling, Noise, and Battery Life to quantify performance. Key findings show accurate, repeatable torque, high- bandwidth velocity tracking with limited phase lag, effective active cooling, and acceptable noise levels under typical use, supporting day-long usability under moderate loading. By openly sharing the design and methodologies, the paper enables reproducibility and cross-study comparability, accelerating development of adaptable TDUs for both upper and lower limb exosuits.

Abstract

Exosuits have recently been developed as alternatives to rigid exoskeletons and are increasingly adopted for both upper and lower limb therapy and assistance in clinical and home environments. Many cable-driven exosuits have been developed but little has been published on their electromechanical designs and performance. Therefore, this paper presents a comprehensive design and performance analysis of a two degree of freedom tendon driver unit (TDU) for cable-driven wearable exosuits. Detailed methodologies are presented to benchmark the functionality of the TDU. A static torque output test compares the commanded and measured torques. A velocity control test evaluates the attenuation and phase shift across velocities. A noise test evaluates how loud the TDU is for the wearer under different speeds. A thermal stress test captures the cooling performance of the TDU to ensure safe operation at higher loads. Finally, a battery endurance test evaluates the runtime of the TDU under various loading conditions to inform the usable time. To demonstrate these tests, a modular TDU system for cable-driven applications is introduced, which allows components such as motors, pulleys, and sensors to be adapted based on the requirements of the intended application. By sharing detailed methodologies and performance results, this study aims to provide a TDU design that may be leveraged by others and resources for researchers and engineers to better document the capabilities of their TDU designs.

Figures (10)

• Figure 1: Three conceptual designs demonstrating examples of how a two DOF TDU may support multiple joints: (a) shoulder and elbow on one arm, (b) hip and/or knee on the legs, or (c) shoulder elevation on both arms.
• Figure 2: An example of how the TDU can be mounted on the body in real life. In this application, the TDU is used, along with a textile interface, to support the right and left shoulder joints against gravity during shoulder elevation.
• Figure 3: Rendering of an exploded view of the TDU. The numbers correspond to the system components in Table \ref{['tab:mass_breakdown']}.
• Figure 4: Aerial view of the assembled TDU
• Figure 5: Static torque test results demonstrating the relationship between commanded motor torque and measured output torque based on cable tension measurements.