Sensitivity analysis of a smart soft composite robotic finger design using geometrically nonlinear laminated composite finite beam elements

Abstract

Soft robotics is an emerging research field that uses deformable materials to build compliant and adaptable systems, using simple integrated mechanisms, enabling biomimetic behavior. This paper presents a sensitivity analysis of a shape memory alloy (SMA)-driven smart soft composite (SSC) bending actuator that is used as an artificial finger in robots or prosthetics. This SSC structure is made of a flexible material, such as polydimethylsiloxane (PDMS), reinforced with some layers of glass fiber sheets, and actuated via SMA wires embedded in the flexible material. The SMA wires shrink when thermally activated, resulting in bending the three flexible hinges of the finger. Designing such smart soft structures involves optimizing large number of design parameters such as the flexible hinge length and thickness, the number of composite layers and their orientation, the number of SMA wires and their diameters. Hence an accurate and efficient computational tool is required to perform sensitivity analysis, and facilitate and accelerate the design process. The mathematical model should also account for geometric nonlinearity due to the large deformation and rotation of the structure in hand. A recently-developed accurate and efficient novel geometrically-nonlinear laminated composite beam finite element model is used in this work for analyzing the SSC robotic finger. The sensitivity analysis revealed that the effect of the flexible hinge thickness in the studied design is much more significant than the hinge length, and that the relationship between the fingertip rotation and the hinge thickness is nonlinear for the case of one glass fiber sheet and approaches linearity as the number of sheets increases to three.