颗粒驱动软体驱动器设计及FEM-DEM运动分析

Design of soft actuator driven by granular matters and its kinematic analysis based on DEM-FEM

摘要:

颗粒物质具有流动传压和阻塞刚化的双相特性,是变刚度软体机器人的理想驱动介质. 由于颗粒物质复杂的力学特性,颗粒驱动软体机器人运动预测极具挑战性. 综合考虑颗粒物质的离散性和超弹软体型腔的连续性,本文提出了一种基于FEM-DEM耦合计算的软体驱动器运动分析方法. 为降低颗粒充入软体型腔时的局部径向膨胀,设计了具有径向增强约束的弯曲驱动器软体型腔结构. 利用FEM-DEM耦合计算方法对此驱动器的运动变形规律进行了分析,同时采用基于颗粒物质Mohr-Coulomb连续介质模型的FEM开展了对比计算. 利用 3D 打印和硅胶浇注技术制造驱动器样机,测试了软体驱动器的运动特性及变刚度能力. 研究结果表明:与基于Mohr-Coulomb模型的FEM相比,利用FEM-DEM耦合计算方法,可使驱动器弯曲角度的预测精度提高约 14.3% ；使用较小直径的颗粒介质可以提高机器人的变形能力；与前期研究中的原始方案相比,本文提出的径向增强约束驱动器在不削弱刚度调节能力的前提下,最大弯曲角度从 48.9°提升至了 72.7°.

Abstract:

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.