**5. Experiment and discussions**

This hand was made for gestures like human hand not grasping, so experiments are very simple. From this purpose, the experiments were taken to check how this hand can realize gestures like the one of human similarly and verify the torque of hand is enough or not to move under the resistance of skin. Even if some experiments were taken to know the resistance of skin by pieces of silicon, there are great differences between pieces of skin and hand shaped skin. The exact experiments can be taken by material engineering area, so it was not efficient way to check the resistance of skin, tests to the real model was taken. The performed experiments to gestures are basically to express rock-paper-scissors posture. The 6 postures are performed including rock-paper-scissors and during these postures, how the shapes are natural like the shape of hand of human in same posture was checked. The tearing and wrinkle at the surface, adequateness of torque are also checked. Fig. 12 shows 6 postures with the completed hand. The gear ratio was 1/30 at first, but it is not enough to bend the finger fully, so the gear ratio was changed to 1/50 and it worked well. In addition to change of the gear ratio, the thickness of skin was thinner and this made problem. Because the transmittance becomes high, the inner mechanical part can be shown even if there is make-up to the skin. The mixture ratio among silicon, pigments and an emulsion should be more researched. There are no barometers for a point of similarity between presented hand and human hand, so the evaluation of this hand is subjectively. The esthetic valuation basis should be needed as future works. There are some needs of improvement after experiments. Firstly, the exact measure of the resistance of skin is needed. It is not easy to know the resistance of the real shape, but trial-error ways are not efficient. Secondly, the cost of hand is too expensive. This hand is not just for researches, the cost is one of the most important factors. The small and exquisite parts caused high cost, so the more simple structure and parts should be designed. Thirdly, the 1 D.O.F thumb finger and no spread of fingers are not enough to gesture like human. Even if there are not enough spaces in hand, the spread fingers and abduction-adduction motion of thumb finger should be added to make natural gestures like human.

Fig. 12. The 6 postures with completed hand.
