Biomimetic skin structure with a crease which is unobstructive to the manipulation

Abstract

The skin structure is one of the key part of robotic manipulator. To increase the surface friction or to achieve compliant characteristics, various skin structures have been developed. When these skin structures are applied to the skeletal structure, the joint is the most difficult part. Under the joint motion, the skin structure which covers the joint is exposed to high compressional or tensile pressure. This pressure leads to the high resistance force to the skeletal structure. This resistance force causes the increase of required joint torque for the same range of motion. Therefore in this paper, the novel skin structure was developed to reduce the resistance force due to the skin structure. The developed skin structure has three layers which represent the outer skin layer (epidermis and dermis), the subcutaneous fat layer, and the inner muscle layer of the human skin structure. Based on this three-layer structure, the crease of human skin was conducted. Figure 1a shows the skin structure for the palmar part of the robotic hands. It has about 15mm thickness. To reduce the resistance force during the joint motion, the developed skin structure is floated above the joint. In general, it causes instability of the skin structure. However, the biomimetic skin structure has stiff muscle layer at the bottom. Therefore even if the outer skin layer and the subcutaneous fat layer is highly compliant, the stiff muscle layer holds the entire structure. To compare this structure to the conventional structure, by using the motion capture system and the force sensor attached on the skeletal structure, the resistance torque depending on the posture was measured. As shown in the figure 1b, biomimetic structure has about 40% decreased resistance force. Through this biomimetic design and connection method, we could apply the skin structure with less resistance force.