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.