Modeling and Numerical Simulation of Variable Length Soft Fluidic Actuators for Wearable Rehabilitation Robots

This paper presents the dynamic and kinematic models of a soft fluidic actuator (SFA) during two types of motion: free motion and interaction with a human finger model. The soft exo-digit is divided into segments corresponding to the proximal phalanx (PP), intermediate phalanx (IP), and distal phalanx (DP), which form the foundational units of soft wearable robots. Developing and analyzing the model of a single segment aids in constructing an accurate model of the entire exo-digit. Each phalanx aligns with the corresponding human finger joint during constrained motion. In free motion, the SFA operates independently of the human finger. To derive the kinematic and dynamic equations, we assume a constant curvature and variable arc length for the SFA. This model is specifically intended for stroke rehabilitation, where slow, repetitive movements are crucial; therefore, the modeling emphasizes quasi-static motion. Rather than using a continuous model, a lumped model is employed, selecting discrete points at the base of the soft digit. Material properties are defined using Yeoh's third-order material model for RTV silicone. The model was simulated in MATLAB, where the space of solutions was explored through surface and contour plots of force and torque, and the model was validated through experimental studies.