Force and Torque Characterization in the Actuation of a Walking-Assistance, Cable-Driven Exosuit

Abstract

Soft exosuits stand out when it comes to the development of walking-assistance devices thanks to both their higher degree of wearability, lower weight, and price compared to the bulkier equivalent rigid exoskeletons. In cable-driven exosuits, the acting force is driven by cables from the actuation system to the anchor points; thus, the user’s movement is not restricted by a rigid structure. In this paper, a 3D inverse dynamics model is proposed and integrated with a model for a cable-driven actuation to predict the required motor torque and traction force in cables for a walking-assistance exosuit during gait. Joint torques are to be shared between the user and the exosuit for different design configurations, focusing on both hip and ankle assistance. The model is expected to guide the design of the exosuit regarding aspects such as the location of the anchor points, the cable system design, and the actuation units. An inverse dynamics analysis is performed using gait kinematic data from a public dataset to predict the cable forces and position of the exosuit during gait. The obtained joint reactions and cable forces are compared with those in the literature, and prove the model to be accurate and ready to be implemented in an exosuit control scheme. The results obtained in this study are similar to those found in the literature regarding the walking study itself as well as the forces under which cables operate during gait and the cable position cycle.

Sensing and Control Strategies for a Synergy-Based, Cable-Driven Exosuit via a Modular Test Bench

“…The basis for designing the exosuit was to use the torque curves of each leg segment and attempt to provide a fraction of the aforementioned torque at each segment. The torque curves were calculated from an inverse dynamics model [ 20 ] that received its kinematic input from publicly available human gait databases [ 22 ]; anthropometric data were estimated from [ 23 ] with the available information. The model estimated the motor torque required to assist 100% of the gait cycle for each segment; the final goal was to provide assistance (by about 30%) once the exosuit design was proposed.…”

“…To avoid overloading the motor/clutches, and considering the available torque, it was decided to decouple the knee joint from the others, thus increasing the assistance capabilities of the exosuit. An inverse-dynamics 3D model is used to predict the evolution of the biological joint torques, as better described in [ 20 , 24 ].…”

“…The reduction of weight in gait-assist devices is not an easy task. The synergies concept is often used to characterize the greatest number of possible movements with the least number of actuators [ 19 , 20 ]. Synergies provide a way to correlate the actuation of each segment with the number of actuators available.…”

Design, Control, and Assessment of a Synergy-Based Exosuit for Patients with Gait-Associated Pathologies

“…These clutches were connected to a clutch control board consisting of Panasonic AQV252 Solid State Relays. The inverse dynamics model introduced in [21], along with the study conducted in a target population (older adults of both genders) with gait data from a public dataset [22] and anthropometric parameters from [23], allowed the authors to estimate the maximum hip, knee, and ankle torques during gait and, thus, the shaft torques expected at the actuation unit, including the clutches, during the operation of the exosuit.…”