Figure 1. Structure of the gripper. a) The gripper consists of a silicone balloon with granules and a soft electrode layer at the bottom. The silicone bag is connected to an external vacuum pump and fixed by a holder. The electrode layer is plugged into an external power supply via conductive tape. b) The electrode layer consists of a circular interdigitated electrode structure made of conductive silicone. c) The gripper can change the geometry of the bottom layer from flat to hemisphere by applying a positive pressure via a vacuum pump. d) In the soft state, the gripper can take the shape of a grasped object (spherical object, as an example) and then maintain it after the air is evacuated.
Here we present a new soft gripper that combines granular jamming and electrodhesion technologies to enhance and complement the grasping capabilities of each technology used in isolation. The soft gripper consists of an inflatable balloon filled with granules and an integrated electroadhesive pad with an interdigitated electrode structure (Figure 1a,b ). This design enables activation of GJ and EA independently or in combination, thus offering three operation modes. In GJ mode, the gripper can hold and lift non-flat objects with negative air pressure (Figure 1d). Also, in GJ mode, the gripper can release objects by removing negative pressure or applying positive air pressure, which produces a convex curvature of the gripper’s surface (Figure 1c). In EA mode, the gripper is capable of grasping flat and delicate objects by applying a voltage. In combined GJ and EA mode, the gripper can grasp and release a variety of objects with different geometry and surface conditions (moistened, oily, porous, and powdered). Moreover, the gripper is able to perform forced releasing of objects stuck on the device surface (for example, sticky objects) by applying positive pressure that make the gripper bulge outwards.
We characterize the grasping performance of the gripper for different object sizes and analyze how grasping parameters such as bending angle, applied force, and activation of GJ and EA influence the grasping force. We also assess the impact of the combined mode on the grasping of objects with different geometries and deformable objects, including flat objects of different sizes. We characterize the gripper’s performance in picking up objects with different surface conditions determined by moisture, oiliness, porosity, and dust. Last, we show the use of the gripper in multi-stage grasping tasks consisting of a sequence of different grasping and releasing operations. In one case, the gripper opens a rigid book cover in GJ mode and then gently flip pages in EA mode. In the other case, the gripper grasps a tea bag in EA mode, picks up a plastic cup in GJ mode, dips the tea bag into the plastic cup in EA mode, and finally release the used tea bag by bulging out the gripper’s surface in GJ mode.
Results and Discussion

Working principle

The working principle of the dual gripper is illustrated inFigure 2. After reaching an object, one of three different working modes can be activated (Figure 2a). Applying a high potential difference to the interdigitated electrode structure activates the EA gripper, causing fringing electric fields that extend from the surface of the gripper. These fields induce electric charges on the surface of the object (Figure 2b), resulting in the electrostatic adhesion force between the gripper and object.