Designing Soft Pneumatic Actuators for Thumb Movements

Abstract

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.

Effects of Inflation Pressure and Wall Thickness on Gripping Force of Semi-Cylindrical Shaped Soft Actuator: Numerical Investigation

“…This variation of the gripping force tends to follow a sigmoidal nature of curve. Similar trends of the nonlinear gripping force variations (sigmoidal variation) has been observed in the study conducted by Wang et al [30].…”

“…The maximum gripping force achieved in the simulations were around 35 N at 300 kPa pressure for 5 mm thick RLT. In an experimental study of human thumb inspired semicylindrically shaped soft actuator, Wang et al [30] reported a comparable gripping force between 30 N -40 N having a nonlinear variation with respect to actuation pressure as observed in Figure 9(a). Although the shapes of their internal chamber were different, the forces were in the same order as in the present study.…”

“…The material constants of the Yeoh 2 nd order model used in the present numerical investigation with the constant values stated in Table 1 [34]. Using the strain-energy expression of Equation ( 1), the stress-strain relationship under uniaxial loading can be obtained as follows [30].…”

“…From the literature review on geometrical aspects of soft actuators it is observed that, comparatively fewer studies have investigated the semi-cylindrical shaped actuators [27][28][29][30]. Among these studies, Tan et al [28] and Wang et al [30] experimentally measured the forces generated by the soft gripppers.…”

“…From the literature review on geometrical aspects of soft actuators it is observed that, comparatively fewer studies have investigated the semi-cylindrical shaped actuators [27][28][29][30]. Among these studies, Tan et al [28] and Wang et al [30] experimentally measured the forces generated by the soft gripppers. However, as per the best information of the authors, the effects of restraining layer thicknesses on the gripping force generation has not been investigated.…”