**1. Introduction**

18 Will-be-set-by-IN-TECH

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There have been many researches of robot hands in robot fields and they have been considered one of the most complicated area. There are many reasons why researches of robotic hand are difficult, and these are from complicated structures and functions of hands. There are many types of robotic hands in robotics area, but they can be classified to major two categories. The one is a robotic hand for an operation in industrial area and the other is an experimental hand like human hand. The most of robotic hands in industrial area are 1 D.O.F or 2 D.O.F gripers and they are designed for precise, repetitive operations. In the other area, human like robotic hands, main concerns are how the shape of robotic hands resembles human hands and how the robotic hands can operate like human hands. Most human like robotic hands have 3 ~ 5 fingers like human hands and their shape, size and functions are designed based on human hand. For a long time, major area in researches of robotic hand has been an industrial area, but the importance of human like robotic hands are getting more and more increasing, because the needs of robots will be changed from industrial fields to human friendly environment such as home, office, hospital, school and so on. In brief, the mainstream of robotics will be changed from industrial robots to service robots. One of the important factors for service robots in human friendly environment is their appearance. In general, most of humans are feeling friendly and comfortably to similar appearance like them, so the appearance of service robots should resemble human and their hands should imitate human hands, too. For this reason, there have been many researches for human like robotic hands.

Haruhisa Kawasaki developed Gifu hand 2 which has 5 independent fingers. It has 16 D.O.F and 20 joints, so it is one of the most complicated hands. It can operate all joint of each fingers and with attached tactile sensors, delicate grip can be operated. However, its size is big to install to the human size robot (Haruhisa Kawasaki. et al., 2002). F. Lotti used spring joint and tendon to make UBH 3. It has 5 fingers and human like skin and like Gifu hand, each finger has independent joint. The characteristics of this hand is using a spring to its joint and this make its structure simple, but this hand uses too many motors and they are located in other place, so this hand is not good to humanoid robot (F. Lotti. et al., 2005). Kenji KANEKO developed human size multi fingered hand. It has 13 D.O.F complicated fingers and all devices are located in hand but it has 4 fingers and the back of the hand is too big like glove. In this reason, the shape of this hand is a little bit different to human hand, so

Design of 5 D.O.F Robot Hand with an Artificial Skin for an Android Robot 83

mobile lower body and was controlled by wireless LAN. Fig.1 shows an android robot EveR 3 with skin, dress and mechanical drawing. Why this robot was made as a woman is to hide the mobile lower body. As an actress, moving on the stage is necessity, but its appearance is different to humans one, so we can hide this parts with long skirt and to wear a skirt, the woman robot is chosen not a man. There is already an android robot can walk, but it is not enough to fast, stable moving (Shin'ichiro Nakaoka. et al., 2009) (Kenji KANEKO. et al., 2009). To make a woman android robot is more difficult than a man android robot, because it has more curved body, narrow space and especially it is more sensitive in appearance. This android robot EveR 3 is based on Korean young woman. To play emotional acting, it has face which has 9 D.O.F and an artificial skin to make expressions. The full body was made by 3D data which is from real human scanning data and this data is also used to make hand, skin. The hand is designed by using this data, so the size and shape are decided from this reference. The artificial skin was also made by this data but little bit different, because the skin design needs making mold. To make mold for an artificial skin, RP (Rapid prototype) mock up was made from 3D data and the mold was made by using mock up. Silicon complex is used as an artificial skin. There are many materials which are reviewed for an artificial skin, but why silicon complex is selected is its characteristics are most like to human skin. The appearance is the most important factor to android robots, so these are

design policies for hands.

Fig. 1. The android robot EveR 3 and its mechanical drawing.

it can be used to humanoid robot not android robot (Kenji KANEKO. et al., 2007). The HONDA ASIMO is the most well-known humanoid robot in the world and its hand shape is like human. Its appearance and size is like human and all devices are included in hand but it has only 1 D.O.F, so it is impossible to express variable gestures (K. hirai. et al., 1998) (H. Hirose. et al., 2001). N.Dechev used spring, links and ball nut joint to make multi fingered prosthetic hand. This hand can passive adaptive grasp by using only one actuator and it has human like shape, 5 fingers but it can't express variable motions because there is only one active joint. This hand shows possibility that prosthetic hands can be applied to human like robot (N. Dechev. et al., 2000). Many of exist hands used motors as actuators but Feifei Zhao used pneumatic type actuators. This hand was made of rubber tube, so there are no links or wires and the structure is so simple. However, this hand can't make gesture of human finger and its shape is different to human hand (Feifei Zhao. et al., 2006).

The many existing researches of human like hands can be applied to humanoid robots but not matched to android robots. An android robot is one of humanoid robots but its appearance is more similar to human appearance than appearance of humanoid robot. When the android robot is designed, uncanny-vally must be concerned, in particular (Shimada M. et al., 2009). In this reason, the hand of an android required the nearest appearance to human hand than existing variable human like hands and the design is more difficult than one of humanoid hand. There are three required factors to the design of an android robot hands. Firstly, the size is very important, because it must be matched to whole body in proportion. It can be hard to make small size hand due to its complexity, but if the proportion is contrary to human body, it can look ugly. Secondly, even if the size of hand is satisfied, shape must be concerned. Most of humanoid robot hands satisfy the size policy, but the shape is not curved surface like human hand. Mechanical parts are generally angulate, so the space which can be used is narrow and this makes the design of an android robot hand hard. Thirdly, android robot hands need an artificial skin. The artificial skin is major difference between humanoid robot hands and android robot hands. The artificial skins which is used to android robot hands need human like touch, color and flexibility for driving.

In this research, an android robot hand for an android robot EveR 3 is presented. The EveR 3 is an android robot for stage performances as an actress, so the hand of EveR 3 was made for variable gestures as acting not grasping. This hand has five fingers with 5 D.O.F and artificial skin. DC motors and screw-nut are used as actuators and the hand is driven by links. The shape is based on 3D model which was made by scanning data from real human. The artificial skin was made by silicon complex and its shape was also based on 3D model, so its appearance is very similar to human hand.
