Maximal strengths of dielectric elastomer fingers for a passive grip

Dielectric elastomer minimum energy structures (DEMESs) are useful as low-force robotic grippers; they can sweep a large angle but carry not much load. It was a design dilemma to reinforce the benders without compromising the stroke angle. As a stronger variant of DEMES, a dielectric elastomer (DE) finger can unbend the 'phalanges' of a load beam upon activation of the 'intrinsic muscles' of the dielectric elastomer actuator (DEA). The DE finger used a uniform tendon hood that raises the tension center of a single-layered DEA and thus enhances the moment generation and load capacity. In this work, we further optimize the structural design of a slender DE finger by mimicking the human thumb profile. This thumb-inspired DE finger has a tapered load beam for hood shaping of multi-layered DEAs with a blunter fingertip. This thumb-up profile greatly enhances the passive lift strength (against a tip weight) by 54% as compared to the earlier rectangular design, at the cost of a 13% reduction in the active stroke. Further, it exploited the axial stiffness to achieve an order-greater pull strength as compared to the lift strength. Finally, the optimized DEMES grippers carried a payload well exceeding the lift strength; they managed to pick an apple of nearly ten times the gripper weight. In addition, a foot of three DE toes hung upside-down to a branch of a horizontal tube while supporting a payload of close to ten times the foot's weight.