Abstract:In order to improve the grasping effect on complex shaped objects of the variable stiffness soft robotic arm with a single jamming medium, inspired by the structure of human fingers, a variable stiffness soft finger with hybrid jamming methods imitating the finger pulp structure was designed. It was a double-layer structure, where the outer layer was used for a pneumatic actuator, and the inner layer was used for a variable stiffness layer with hybrid jamming methods based on active layer jamming and passive particle jamming methods, which can facilitate the soft fingers to fit the profiles of objects grasped automatically, and achieve the effects of passive adaptation under active driving, and objects grasping reliably by stiffness adjustment. Based on the traditional sewing techniques, the soft fingers were manufactured with hyperelastic silicone material. A stiffness control model for multi-material soft fingers based on cantilever beam structure was established by using Euler-Bernoulli beam theory and virtual work principle, furthermore, a selection rule to increase the overall material stiffness was proposed based on the stiffness control model. Experimental results on bendability showed the excellent bendability of the soft fingers. Besides, the stiffness variation and objects grasping experimental results showed that the stiffness of the soft fingers with hybrid jamming method was increased by 4.6 times, and the maximum relative error of the stiffness control model established was only 3.4%. Despite of increasing the surface roughness of the objects grasped, the detachment force of the soft fingers was still increased by 17%, which reached 1.7N. Therefore, compared with the soft fingers with single jamming medium, the grasp success rate and load capacity were improved significantly.
