Design, Simulation, and Experimental Validation of a Soft Robotic Finger with Variable Stiffness and Embedded Sensing

This work presents a soft finger designed, simulated, and experimentally tested, combining pneumatic actuation, variable stiffness, and embedded sensing. The finger integrates a fiber-reinforced pneumatic actuator that generates single-input underactuated bending through three interconnected chambers located at the MCP, PIP, and DIP finger joints. The design methodology follows bioinspired principles and cost-effective manufacturing constraints, producing a prototype via silicone casting with 3D-printed molds and incorporating a bio-based granular substrate for variable stiffness that allows post-deformation stiffening without compromising flexibility. Bending under pressurization is simulated utilizing the Finite Element Method (FEM) in ANSYS software, with the finger modeled using hyperelastic and fiber-composite material properties. Comparison of simulated and experimental results reveals an average deviation of approximately 8°. The adjustment of stiffness properties is achieved via vacuum-induced granular jamming, increasing the applied forces by up to 60% relative to the unstiffened state. An embedded sensing system (microphone) in the fingertip enables discrimination of contact surfaces based on captured vibration signals. These results indicate that finger deformation and stiffness can be controlled with minimal hardware and a simple design, supporting the use of this finger as a component in soft grippers or robotic hands.