Effect of the granular material on the maximum holding force of a granular gripper

Abstract

A granular gripper is a device used to hold objects by taking advantage of the phenomenon of Reynold's dilatancy. A membrane containing a granular sample is allowed to deform around the object to be held and then vacuum is used to jam the granular material inside the membrane. This allows to hold the object against external forces since deformation of the granular material is prevented by not allowing the system to increase its volume. The maximum holding force supported by the gripper depends on a number of variables. In this work, we show that in the regime of frictional holding (where the gripper does not interlock with the object), the maximum holding force does not depend on the granular material used to fill the membrane. Results for a variety of granular materials can be collapsed into a single curve if maximum holding force is plotted against the penetration depth achieved. The results suggest that the most important feature in selecting a particular granular material is its deformability to ensure an easy flow during the initial phase of the gripping process. IntroductionThe handling of objects is a regular task in the industry. Holding objects of well defined size, shape and hardness can be done by robotic arms that present a gripper with a matching shape that fits the object to hold (e.g., hooks). Also, magnets can be used with ferromagnetic objects, and suction systems with objects presenting smooth surfaces. However, matching some of the gripping charac-

A Soft Gripper with Granular Jamming and Electroadhesive Properties

“…[ 14 ] In this study, we chose different gripper design and material composition from already existing devices. [ 34 ] Thus, we performed characterization of the grasping force at different surface conditions in the combined mode (Figure 5c) as this mode shows the highest grasping force among all modes (Figure 4a). We used the hemisphere with a diameter of 28 mm, which corresponds to 78% of the gripper diameter, following the same setup and testing protocol as for Figure 4a.…”

Empirically adapted model for the Handling of Variable Geometries with Vacuum-based Granulate Grippers

“…When a vacuum is applied to these cushions, the granular material compacts, jams and enables a gripping force to be exerted on different kinds of objects through friction and interlocking with the respective surfaces. For these grippers, influences such as the stiffness of cushion membrane material, the granulate material, the object enclosure and the conditions of the granulate material have been examined [15][16][17][18].…”

Soft particles reinforce robotic grippers: robotic grippers based on granular jamming of soft particles

“…As there are no materials with infinite Young's modulus this solution seems artificial and not relevant at first glance, however, almost all experiments on granular grippers use granular particles from rather rigid materials such as glass beads, see e.g. [10,14,20,22], and compared to the forces resulting from the vacuum, i.e. the ambient air pressure, dense packings of glass or steel particles very well be considered as undeformable and rigid.…”