A Stiffness-controlled Robotic Palm based on a Granular Jamming Mechanism

This paper presents a new type of a robotic palm based on a granular jamming mechanism to improve grasping performance. The granular jamming principle is adopted to alter the shape and stiffness of the robotic palm by controlling a transition between a solid-state and a fluid-state of a granular material used. The robotic palm incorporates a specifically designed granular chamber that is optimized for dealing with large volume change. The control system is also developed for the proposed granular jamming mechanism to be electrically operated without any pneumatic components. In addition, the stiffness of the palm can be precisely regulated by the feedback control of the negative pressure applied to the granular chamber. We evaluate the shape-adaptability of the robotic palm for various objects. As a result, the robotic palm could accommodate the various shapes of the testing objects by conformably altering its shape during contact. Moreover, the stiffness-controllability is also investigated for the three different sizes of granular materials. The stiffness increases up to 30 fold under fully jammed state for the small size of the grain. Finally, we evaluate the grasping performance of the robotic palm with a commercially available robot hand. 1.7 times higher grasping force was attained with the conformably deformed and stiffened surface, compared to the flat skin of the rigid palm. Therefore, the stiffness-controlled robotic palm can improve grasping performance with the enhanced shape-adaptability and stiffness-controllability.