Modeling a Hybrid Soft-and-Rigid Robotic Exo-digit with Varying Length Soft Segments Coupled to a Human Finger

This paper presents the kinematics and quasi-static analytical model of a soft robotic exo-digit that physically interacts with a human finger model in the middle contact points along each link (in the [Formula: see text]-direction), which is crucial for rehabilitation. The hybrid soft-and-rigid exo-digit consists of three soft segments between four semi-rigid blocks, modeled as a lumped quasi-static model with constant curvatures and variable arc lengths. The material is modeled using Yeoh’s third-order hyperelastic model. The human finger is modeled as a rigid multi-body structure with torsional springs to represent joint stiffness. Kinematic and quasi-static models describe the interaction at multiple contact points between the soft robot and the human finger. Experimental studies on single soft segments and the full exo-digit interacting with the human finger validate the analytical model, showing improved accuracy with the variable arc length model over the constant-length model.