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.