Performance Validation of Joint Modular Soft Actuators for Finger Joint Stiffness Estimation

In hand telerehabilitation of stroke patients, it is important to accurately assess the finger joint stiffness and plan an optimal rehabilitation for the patient's joint condition. Our previous study proposed an analytical model-based joint stiffness estimation that adapted an analytical model originally proposed for a whole-finger soft actuator to a joint modular soft actuator with performance suitable for telerehabilitation. However, the estimation accuracy is low, necessitating improvements. For that, it is necessary to elucidate the crucial characteristics and influencing factors of stiffness estimation with joint modular soft actuators. In this study, we estimated the stiffness of multiple joints at various stiffness levels to better understand the characteristics of joint modular soft actuators in stiffness estimation. Additionally, the unique influencing factors of joint modular soft actuators were investigated by comparing their stiffness estimation performance with that of whole-finger soft actuators. The results show that factors that cannot be represented by the analytical models, such as the interaction between joint modular soft actuators and a finger, as well as, between joint modular soft actuators themselves, may affect the accuracy. This study provides new insights into the evaluation of finger joint stiffness suitable for telerehabilitation, contributing to the advancement of optimal rehabilitation strategies.