A Variable-stiffness Soft Finger Based on Particle Jamming with Honeycomb Structure

Aiming at the shortcomings of the current soft fingers, such as poor actuating and loading performances, and uncertain structural shape due to the particle fluidity in the particle blocking structure, a variable-stiffness soft finger based on particle jamming is proposed. Firstly, a soft finger with the pneumatic-network actuator and the variable-stiffness structure is designed, according to the characteristics of particle jamming and honeycomb-shaped supporting structure. A mathematical model of the actuator is established by using the constant volume principle of the hyperelastic material and Ogden hyperelastic theory. A theoretical model of variable-stiffness structure is built, according to the packing and contacting characteristics of spherical particles in the particle blocking structure. Then the structural parameters influencing the bending angle of actuator are analyzed by the finite element method, and the optimal structure of the finger is obtained. Finally, the prototype of soft finger is prepared using the casting molds designed by 3D printing technology, and an experimental platform is built for finger characteristic test and three-finger soft gripper grasping performance test. The bending performance and variable-stiffness performance of the soft fingers are tested. Results show that, the maximum deflection angle is 153.2° under the driving air pressure of 30 kPa, and the stiffness is 0.1038 N/mm under the negative pressure of −50 kPa, which are obviously superior to the performance of the existing variable-stiffness structures. Gripping performance tests show that the soft gripper has a good shape adaptation and wrapping ability. Experimental results verify the theoretical model, bending performance, variable-stiffness capability and gripping performance of the designed finger, and the proposed design can solve the problem of shape uncertainty caused by particle reorganization.