Figure 6. Working principle and grasping demonstration. a)
Grasping is performed using a motorized linear stage, which raised and
lowered the gripper. The gripper acts as an end effector (see Video S1,
Supporting Information). (i) In the initial state, a soft silicone bag
with granules is soft. (ii) When the gripper touches the object, the
silicone bag deforms. After that, the pump and voltage are turned on.
The pump evacuates the air out of the bag triggering the granular
jamming (GJ) and making it stiff to hold the object. The applied voltage
(3 kV) triggers the generation of electroadhesion (EA) force on the
bottom surface of the gripper. (iii) The objects (two quail eggs with
the weight of 34 grams) are then picked up due to the grasping force
provided by the GJ and EA while the linear stage lifts up. Release of
the objects is achieved by a reverse of the operating procedure
explained above. b) With the same operating principle, a grasping
demonstration is performed for (i) a highly deformable water-filled
balloon (31 grams), (ii) a flat and delicate fabric (0.5 grams), and
(iii) a bottle with water (507 grams). c) The high compliance of the
gripper allows grasping objects from different sides broadening
potential grasping scenarios. The fork (32 grams) can be manipulated
from three different sides (i-iii).
(Figure 6a-I,ii); subsequently, the simultaneous activation of GJ and EA
modes allow the gripper to grasp the eggs (Figure 6a-ii) and lift them
up (Figure 6a-iii). In a second example, we pick up a highly deformable
water balloon with a size larger than the size of the gripper, a mass of
31 grams, and a membrane thickness less than 30 μm (Figure 6b-i). In a
third example, we pick up a flat tissue with the weight of 0.5 g and
thickness less than 60 μm, without deforming it (Figure 6b-ii). After
lifting the tissue, the gripper can release it by applying positive
pressure bulging out its surface (Video S1, Supporting Information). In
a fourth example, we lift a bottle of water with a mass of 507 grams,
which is 38 times heavier than the gripper (Figure 6b-iii). In addition,
the high deformability of the gripper allows it to grasp objects from
different sides broadening potential grasping scenarios. In a fifth
example, we pick up a fork of 32 grams from three different sides
(Figure 6c-i,ii,iii).
The ability to selectively operate in different modes allows the gripper
to be used for multi-stage complex operations, such as opening and
flipping through the pages of a book and making a cup of tea
(Figure 7 and Video S2 and S3, Supporting Information). In the
first example, the book hardcover weighs ~300 g
(~0.3 N) and requires GJ mode to open the book (Figure
7a-i); once the book is open, the pages can be gently flipped over in EA
mode (Figure 7a-ii). In the second the EA mode can be used to grasp
(Figure 7b-i,ii) and lift (Figure 7b-iii) a tea bag with a mass of 1.8
g. The GJ mode on the second gripper is used to grasp (Figure 7c-i,ii),
lift (Figure 7c-iii) and move (Figure 7c-iv) the plastic glass with a
mass of 8 g for the tea. Then, the tea bag is moved up and down (Figure
7d-i,ii) and changes the weight from 2 to 7.7 grams as it absorbs water.
The tea bag can be rapidly released by turning off EA and bulging out
the gripper’s surface by applying positive pressure (Figure 7d-iii).
Figure 7. Demonstration of complex manipulation scenarios. Each
black rectangular area corresponds to the use of a specific grasping
mode: granular jamming (GJ) or electroadhesion (EA). a) The gripper can
be used for complex manipulation such as an interaction with a book. (i)
The cover page can be opened by GJ mode. (ii) Then, the pages can be
gently turned over using EA mode. b) Another example of complex
manipulation is tea making. (i) The EA mode can be used to grasp (i,ii)
and lift (iii) the teabag (1.8 grams). c) The GJ mode of the second
gripper is used to grasp (i,ii), lift (iii) and move (iv) the plastic
glass (8 grams) for the tea. (d) (i,ii) The teabag is moved up and down
using linear stage. It changes the weight from 2 to 7.7 grams when
sopping. (iii) The tea bag can be rapidly released by turning off EA and
applying positive pressure to the gripper to change the curvature of the
grasping surface and detach the object. The gripper can grasp objects
with different surface conditions such as dry, oily porous, moistened,
and powdered. The grasping force for dry, oily, and moistened objects
are in four to five times higher compared to the objects with porous and
powdered surfaces due to the formation of a tightly sealed interface
between the gripper and the object surfaces, which leads to the suction
effect.
Conclusion
We showed that the combination of controlled stiffness by granular
jamming (GJ) and controlled adhesion by electroadhesion (EA) can lead to
versatile grippers capable of manipulating a broader range of objects
than currently existing GJ-based or EA-based
grippers.[5,11,12,17] The gripper is fabricated
out of commercially available and low-cost components such carbon
black-filled elastomer composite and silicone elastomer using common
fabrication techniques such as film-casting, laser ablation, and
molding. The GJ mode allows lifting objects with a weight 38 times
larger than the weight of the gripper. In addition, the application of
positive pressure bulges out the gripper’s surface to facilitate object
release. The EA mode enables manipulation of flat and delicate objects,
which would not be possible with GJ alone, with a weight of 20-80 grams.
The grasping force in the combined mode, when GJ and EA are activated
simultaneously, is higher for all the diameters of manipulated objects.
The difference between combined mode of GJ & EA versus the pure GJ mode
increases with the object sizes and achieves the maximum difference of
15.2% at the object size of 89% of the gripper’s diameter. The
generated grasping force correlates with the applied force before the
gripper activation and inversely correlates with the grasping angle in
the same manner shown in the literatures on conventional GJ
grippers.[5,11] The gripper is capable of
manipulating objects of various shape. The combined mode shows the
highest grasping force enhancement of 35%, 16%, and 15% compared to
GJ for a cylinder, pyramid, and parallelepiped shapes. The combined mode
is especially beneficial with the shapes that do not allow granules to
flow easily around the target object and grasp it from all sides.
The separate use of an EA, GJ, or combined modes makes the gripper
suitable for complex manipulation scenarios that require manipulations
of multiple objects with different sizes, shapes, softness, and surface
conditions. This gripper can be beneficial for agricultural applications
where picking fresh vegetables and fruits without damaging them remains
challenging.[32] Moreover, the gripper can be used
to address current challenges in industry such as the development of
adaptive industrial assembly robots capable of manipulating objects in
different ways such as twisting and re-grasping with a large variety of
different geometries.[33,34] The fabrication
process of the gripper combines molding and layer by layer fabrication
techniques that are both scalable. Thus, the proposed fabrication
approach can easily be adapted to produce grippers with various
dimensions suitable for the aforementioned applications.