Design, modeling, and testing of a soft actuator with variable stiffness using granular jamming

Abstract

Soft robots combine the load-bearing capability of rigid material with the resilience, shape-shifting capabilities of soft materials. This paper presents a novel soft actuator with stiffness variation using particulate jamming technology. We design a hybrid composite structure consisting of driving layer and jamming layer. The driving layer with the arc air chamber aim to achieve large bending deformation. A membrane containing particles is integrated with driving layer to module its stiffness. The influence factors of stiffness variation were analyzed from energy of point of view. The dependence of granular attributes on the stiffness of the actuator was studied. Furthermore, we illustrated influence of stiffness changes on the kinematic and dynamic performance of the soft actuator. The experimental results showed these performance indexes are twofold. On the one hand, the structural parameters have significant effect on the bending angle, but on the other hand they have little effect on the end force. We found that flow resistance inside air chamber results in bending morphology variation. The dynamic response subjected to a square-wave air pressure was analyzed to exhibit the actuator’s transient and steady vibration behavior. The actuator with greater stiffness has faster responsiveness, but smaller range of motion. These conclusions are helpful to adjust the stiffness behavior and to improve motion performance.

Intelligent Soft Robotic Grippers for Agricultural and Food Product Handling: A Brief Review with a Focus on Design and Control

“…However, it should be noted that granular jamming can also be utilized in grippers with finger configurations, serving as an inextensible layer to enable structural anisotropy. [131,132,148,149] Grippers featuring jamming Bioinspired 3D printable soft vacuum actuators [218] Thermoplastic polyurethane, TPU, (NinjaTek) À80-0 kPa 1.64 N Cup, kiwifruit, mandarin, apple High actuation speed, long lifetime…”

“…This unique capability has found extensive application in developing pneumatic grippers with variable stiffness. Starting from the classical PneuNets structure, Hu [ 131 ] developed a PneuNets SPA with a constrain layer composed of granular materials, endowing it with variable stiffness functionality. Furthermore, granular jamming has also been harnessed to empower FRSAs for achieving high surface texture adaptability.…”

“…However, it should be noted that granular jamming can also be utilized in grippers with finger configurations, serving as an inextensible layer to enable structural anisotropy. [ 131,132,148,149 ] Grippers featuring jamming technology have achieved successful grasping performance on diverse objects, including apples, eggs, [ 121,148 ] pears, pitayas, and pineapples, [ 138 ] effectively providing a firm grip and adjustable force through their stiffness variation functions.…”

Force analysis of a soft-rigid hybrid pneumatic actuator and its application in a bipedal inchworm robot

“…Soft fluidic actuators were categorized as a subset of soft actuators and exhibit excellent characteristics such as inherent compliance, good impact resistance, high energy-to-weight ratio, and safety interaction with humans [1,2]. Based on the mode of motion, they can be further classified mainly into linear actuators [3,4], bending actuators [5][6][7], and torsional actuators [8][9][10]. In particular, twisting actuators capable of the compound motion of rotation and contraction have also been developed and combined to achieve other motions, including linear, rotational, and radial movements [11,12].…”

Piston-like particle jamming for enhanced stiffness adjustment of soft robotic arm

“…Various stiffness adjusting techniques have been actively studied in recent years (Götz et al , 2022; Jadhav et al , 2022; Zhao et al , 2020), among which particle jamming is one of the most widely used principles (Fitzgerald et al , 2020). A pack of particles have a soft and fluid-like natural state, while being rigid on the solid-like jamming state under vacuum pressure or external forces (Hu et al , 2022; Wockenfus et al , 2022). The particle jamming method has quick response and excellent flexibility and is adaptable to various robotic structures.…”