Variable Kinematics enabled by Layer Jamming Transition in a Soft Bending Actuator

In soft robotics, variable stiffness is typically employed to solve the trade-off between compliance and the ability to exert high forces. However, modulating the stiffness of a soft actuator can also provide control over its deformation and enhance its adaptability. This latter concept has not been thoroughly investigated in literature and this work aims at demonstrating variable kinematics enabled by the integration of variable stiffness modules into the structure of a soft finger. We have augmented a segmented pneumatic bending actuator with two-layer jamming modules integrated into its proximal and distal sections and proposed an actuation strategy designed through finite element modeling to control its shape in terms of angle of attack and grasping radius. The presented soft finger exhibited a grasping width in the range of about 40 mm to 75 mm while simultaneously keeping the angle of attack around $90^{\circ}$. Different activations of the two-layer jamming modules also produced an alteration of the forces exerted by the finger which were characterized in terms of blocking and grasping force for different configurations. The results show an interesting and less explored use of variable stiffness, relevant for the development of adaptive soft grippers and manipulators. Moreover, the proposed concept and control strategy is independent of the actuation technologies used to produce finger bending.