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Applying soft actuators to hand motion assist for rehabilitation has been receiving increasing interest in recent years. Pioneering research efforts have shown the feasibility of soft rehabilitation gloves (SRGs). However, one important and practical issue, the effects of users’ individual differences in finger size and joint stiffness on both bending performance (e.g., Range of motion (ROM) and torque) and the mechanical loads applied to finger joints when the actuators are placed on a patient’s hand, has not been well investigated. Moreover, the design considerations of SRGs for individual users, considering individual differences, have not been addressed. These, along with the inherent safety of soft actuators, should be investigated carefully before the practical use of SRGs. This work aimed to clarify the effects of individual differences on the actuator’s performance through a series of experiments using dummy fingers designed with individualized parameters. Two types of fiber-reinforced soft actuators, the modular type for assisting each joint and conventional (whole-finger assist) type, were designed and compared. It was found that the modular soft actuators respond better to individual differences set in the experiment and exhibit a superior performance to the conventional ones. By suitable connectors and air pressure, the modular soft actuators could cope with the individual differences with minimal effort. The effects of the individualized parameters are discussed, and design considerations are extracted and summarized. This study will play an important role in pushing forward the SRGs to real rehabilitation practice.

Studies have developed various types of soft robotic gloves for hand rehabilitation in recent years. Most soft actuators achieved a sufficient thumb flexion assist while lacking opposition support, which requires the coordination of thumb flexion and abduction-adduction. The difficulties for thumb support lie in the intrinsic complexity of thumb movements and spatial restriction of the hand. To realize multiple degrees of freedom of the thumb and make effective use of the limited space of the hand's dorsal side, we optimized and compared two approaches for thumb support. The combination approach used two independent soft actuators for thumb flexion and abduction-adduction support, respectively. The all-in-one approach used one single soft actuator to assist motions in different directions. We designed the soft actuators for each approach based on the thumb's biomechanical characteristics and evaluated their thumb flexion, abduction support performance in terms of the range of motion (RoM) and force output, and the opposition support performance using an enhanced Kapandji test. The results showed a larger abduction RoM and force output of the composition approach and a higher Kapandji score of the all-in-one approach, indicating that the two approaches might be applicable for thumb support but have the advantage in different rehabilitation stages.

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