Kinetostatics and Retention Force Analysis of Soft Robot Grippers With External Tendon Routing

Soft robots (SR) are a class of continuum robots that enable safe human interaction with task versatility beyond rigid robots. This has resulted in their rapid adoption in a number of applications that require manipulation of delicate and irregular objects. Despite their advantages, SR grippers typically require case-specific experimental characterization for shape and gripper retention force estimation. This letter presents a kinetostatic modeling approach based on strain energy minimization subject to mechanics and geometric constraints for shape estimation of SR grippers with external tendon routing (ETR), including those with composite structures. Additionally, Castigliano's First Theorem is used to estimate the retention force of the gripper. These models are evaluated across four different ETR SR grippers. The mechanics model predicted the fingertip position and orientation with an accuracy of 1.06 $\pm$ 0.62 mm (1.79% $\pm$ 1.05% of length) and 3.58$^{\circ } \pm \text{2.82}^{\circ }$ with respect to tendon force and 0.72 $\pm$ 0.45 mm (1.22% $\pm$ 0.76% of length) and 2.86$^{\circ } \pm \text{2.11}^{\circ }$ with respect to tendon retraction. The retention force of the gripper was predicted with an average error of 0.20 $\pm$ 0.12 N.