Figure 2. The gripper’s schematic structure and operating principle of the gripper. a) The blue silicone balloon is held using an orange holder. Granules are kept inside the balloon. The electroadhesive pad is located on the bottom surface of the gripper and is connected to the ground and high voltage electrodes. The gripper is lowered to the flat surface (in grey) of a grasping object. b) The applied potential difference causes the generation of electrostatic forces attraction between the bottom surface of the gripper and the substrate surface of a grasping object. c-e) The working principle of a granular jamming mode. c) The gripper is lowered on an object. d)The gripper deforms and takes shape of the manipulated object. e) The air is evacuated by turning on the vacuum pump. f) The object can be released by applying positive pressure and changing the curvature of the bottom layer of the gripper.
The GJ mode relies on a bag filled with the granules, which is soft when the gripper approaches the target object (Figure 2c). As the gripper lowers against the object, the soft bag deforms and takes the shape of the object (Figure 2d); at this point, the bag is stiffened by evacuating the air and jamming the tightly packed granules (Figure 2e). This stiff state fixes the object against the bag such that it can be lifted. Pumping air back into the bag makes it soft by enabling movement of the granules, thereby causing the release of the object (Figure 2f).
In the combined mode, the simultaneous activation of GJ and EA enhances the grasping force of the gripper. In the soft state, granules flow around the object increasing the contact surface between the object and the gripper. After activation GJ and EA, EA enhances the adhesive forces of the contact surface.[1,28]

Fabrication

The fabrication procedure consists of layer-by-layer and molding techniques, as illustrated in Figure 3 . First, an EA pad was fabricated by encapsulating a conductive silicone layer with a laser-engraved interdigitated electrode in-between two dielectric layers made of silicone (Figure 3a-i,ii,iii). All the layers were fabricated using a blade-casting technique and cured onto each other. Then, the fabricated EA pad was placed in an empty mold, which consists of an external, internal, and bottom part (Figure 3b-i). Liquid silicone was poured into the mold to form the silicone bag and connect the EA pad, resulting in a monolithic structure. After curing the silicone, the gripper was removed from the mold (Figure 3b-ii). Finally, the silicone bag was filled with coffee granules with diameters of 0.2 mm (Figure 3b-iii). A detailed explanation of the fabrication process is available in the Experimental Methods section. The resulting gripper had a weight of 13 g and the diameter of the grasping surface was 36 mm (the diameter of the interdigitated electrode structure was 30 mm).