Hybrid Soft Electrostatic Metamaterial Gripper for Multi-surface, Multi-object Adaptation

TL;DR

The paper tackles the challenge of universal soft gripping by addressing residual peeling forces and limited payload in electroadhesive grippers. It introduces the Soft Electrostatic Metamaterial (SEM) gripper, which combines metamaterial cut patterns with electroadhesion to achieve directional adhesion and controlled preloading, enabling rapid release and higher lifting capability. Through design, optimization (NSGA-II), layer-by-layer fabrication, and extensive experiments, the SEM system demonstrates adhesion directionality up to $65.5\times$ and lifting up to $1617\times$ its weight while handling diverse flat and curved surfaces and deformable objects. This approach yields a lightweight, scalable, multi-surface gripper with practical potential for delicate-to-heavy object manipulation in soft robotics.

Abstract

One of the trendsetting themes in soft robotics has been the goal of developing the ultimate universal soft robotic gripper. One that is capable of manipulating items of various shapes, sizes, thicknesses, textures, and weights. All the while still being lightweight and scalable in order to adapt to use cases. In this work, we report a soft gripper that enables delicate and precise grasps of fragile, deformable, and flexible objects but also excels in lifting heavy objects of up to 1617x its own body weight. The principle behind the soft gripper is based on extending the capabilities of electroadhesion soft grippers through the enhancement principles found in metamaterial adhesion cut and patterning. This design amplifies the adhesion and grasping payload in one direction while reducing the adhesion capabilities in the other direction. This counteracts the residual forces during peeling (a common problem with electroadhesive grippers), thus increasing its speed of release. In essence, we are able to tune the maximum strength and peeling speed, beyond the capabilities of previous electroadhesive grippers. We study the capabilities of the system through a wide range of experiments with single and multiple-fingered peel tests. We also demonstrate its modular and adaptive capabilities in the real-world with a two-finger gripper, by performing grasping tests of up to $5$ different multi-surfaced objects.

Figures (9)

• Figure 1: (a) Soft Electrostatic Metamaterial (SEM) gripper. (b) The SEM adhesive. The scale bar is 20 mm.
• Figure 2: Adhesion Simulation in COMSOL. a) The metamaterial is first evaluated by lifting in the forward direction until the material releases the substrate [Top], then repeated in the reverse direction [Bottom]. Results of (b) 3 Point Polygon, (c) 5 Point Polygon, and (d) 7 Point Polygon optimizations, showing high-performing shapes and optimization chronology. The color bar shows the sequence of design evaluations, with brighter colors occurring later. The clustering of bright numbers at the top right is indicative of optimizer progress.
• Figure 3: Fabrication process. a-i) First dielectric mixture layer is blade-casted by a film applicator. a-ii) Laser cut interdigitated electrodes are attached to the pre-cured dielectric layer onto a PET sheet. a-iii) Second dielectric mixture layer is blade-casted. a-iv) Metamaterial cut lines are created using laser cutter. Conductive tapes are attached. b) Prototyped SEM adhesive [Left]. An electrostatic adhesion is generated by applying high voltage. [Right]
• Figure 4: SEM gripper Mechanism. a) A parallel gripper controlled with a single servo motor [Top]. The mechanism of the parallel gripper [Bottom]. b) The bistable gripper mechanism consists of two arms connected by a hinge joint. Two rubberbands are connected at the top and bottom of the arm in order to create the bistable mechanism. The tendon assists in pulling it back to its initial state. c) The gripper snaps onto the object as soon as on contact with object, voltage is then applied to enhance adhesion between the object and the adhesive [Top]. The two-arm symmetrical SEM adhesive. Note that the grasping stress applied to SEM adhesive is the same direction for maximum peeling force enduring large payload [Bottom].
• Figure 5: a) Normalized adhesion directionality of simulation vs experiment. b) Experimental normalized forward adhesion stress of different shapes.