Granular matters have the biphasic characteristics of transmitting pressure while flowing and stiffening while jamming

which makes them the ideal driving medium of the soft robots. Yet with the complex mechanical properties of the granular matters

it is extremely challenging to predict the motion of granular matters-driven soft robots. Considering the discreteness of granular matters and the continuity of hyperelastic soft cavities

a motion analysis method of the soft actuator based on the coupling simulation of FEM-DEM is proposed in this paper. The structure of the soft cavity of bending actuator that has constraints of radial enhancement is optimized on basis of previous researches. Rules of the actuator’s deformation are analyzed using the coupling calculation method of FEM-DEM and the contrast calculation is conducted with the FEM simplifying granular matters to continuous medium using Mohr-Coulomb model. The actuator prototype is manufactured using technologies of 3D printing and silicone casting

and the kinetic characteristic and capacity of variable stiffness are tested. The experimental and simulation data show that

compared with the FEM based on the Mohr-Coulomb model

the coupling calculation method of FEM-DEM proposed in this paper is expected to increase the accuracy of predicting the actuator’s bending angle by about 14.3%. Using granular matters with smaller diameters can improve the deformation capacity. At the same time

compared with the original scheme in previous researches

the maximum bending angle of the actuator that has constraints of radial enhancement increases from 48.9°to 72.7° without weakening the capacity of stiffness tuning.