Abstract:
Disclosed is a humanoid robot capable of improving power transmission efficiency of a wire and movement displacement of a wrist joint by modifying the structure of the wrist joint serving as a passage for wires. The humanoid robot includes a robot hand including a power transmission device for transferring gripping force to finger members. The power transmission device includes connection members connecting an actuator to finger joints and guide members for guiding the connection members. The guide members include a first guide member coupled to a robot arm and a second guide member coupled to a hand body. The connection members are alternately wound around the first and second guide members. The gripping force is enhanced whereby a length of the connection members provided between the first and second guide members is constantly maintained even if the second guide member is shifted from the first guide member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. § 119(a) from Korean Patent Application No. 10-2008-0069275 filed on Jul. 16, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present general inventive concept relates to a humanoid robot. More particularly, the present general inventive concept relates to a humanoid robot capable of improving power transmission efficiency and movement displacement by modifying a wrist joint of the humanoid robot. 
         [0004]    2. Description of the Related Art 
         [0005]    Robots are extensively used in various industrial and domestic fields. As a result, research and development concerning humanoid robots has accelerated in recent years. In order to enable a humanoid robot to perform housework in a manner done by a human hand, for example, a humanoid robot must be able to safely and rapidly grip and handle various objects of varying sizes used by human beings. 
         [0006]    Since the size of a robot hand is limited in a humanoid robot, many motors having large capacity may not be installed for the hand of the humanoid robot. For this reason, the robot hand tends to represent relatively low gripping force as compared with the gripping force of a human hand. In addition, since there are structural limitations in the use of a robot hand, the degree of freedom of movement of the robot hand has been very low as compared with the gripping force of the human hand. 
         [0007]    In order to increase the gripping force of a robot hand, a motor can be installed in an arm part near the forearm, apart from the robot hand, to transfer a driving force of the motor to the fingers using wires. The wires extend by passing through a wrist joint that connects the hand to the forearm part. In order to reduce friction when the wires pass through the wrist joint, the wires are supported by two pulleys. 
         [0008]    However, if the wrist joint is moved, the two pulleys are also moved, so that the length of the wires supported by the two pulleys may be altered. If the length of the wires are changed, the fingers may not be precisely controlled by the wires. Since the movement of the wrist joint exerts an influence upon the length of the wires, the motor driving the wires must be thus controlled in relation to the movement of the wrist joint. As a result, the driving mechanism of the motor for controlling the fingers may be hindered due to the movement of the wrist joint. 
         [0009]    To solve the above problem, there has been suggested a driving mechanism capable of preventing the length of the wire from being changed even if the wrist joint is moved. In such a driving mechanism, the wire passing through the wrist joint, which connects the robot hand to the forearm part, is inserted into a tube, so that the length of the wire can be constantly maintained even if the wrist joint is moved. The tube serves to keep the length of the wire unchanged regardless of the movement of the wrist joint. Since the length of the wire is not changed even if the wrist joint is moved, it is not necessary to control the motor driving the wire to compensate for the length of the wire. 
         [0010]    However, one problem with the above solution is that friction may occur between the tube and the wire inserted into the tube. Such friction may cause a great loss in the driving force of the motor, and this loss may become increased as movement displacement of the wrist joint is increased. If the movement displacement of the wrist joint is increased, the tube is excessively bent so that friction between the wire and the tube is further increased. When this happens, power transmission efficiency of the motor is remarkably lowered. To solve this problem, the movement displacement of the wrist joint must be restricted. 
       SUMMARY OF THE INVENTION 
       [0011]    The present general inventive concept provides a humanoid robot having a robot hand, capable of improving power transmission efficiency of a motor and ensuring movement displacement of a wrist joint by modifying the structure of the wrist joint serving as a passage for a wire. 
         [0012]    Additional features and/or utilities of the present general inventive concept will be set forth in part in the description which follows and, in part, will be apparent from the description herein, or may be learned by practice of the general inventive concept. 
         [0013]    An embodiment of the present general inventive concept provides a humanoid robot comprising a wrist joint connecting a robot arm to a hand body, a first actuator and a first power transmission device that drive the wrist joint to rotate the hand body relative to the robot arm, finger members comprising finger joints and knuckles, wherein the finger members are connected to the hand body, and a second actuator and a second power transmission device that drive the finger joints to rotate the finger members relative to the hand body, wherein the second power transmission device includes connection members connecting the finger joints to the second actuator, and guide members for guiding the connection members, wherein the guide members include a first guide member coupled with the robot arm and a second guide member coupled with the hand body, and wherein the connection members are alternately wound around the first and second guide members. 
         [0014]    Lengths of the connection members provided between the first and second guide members are constantly maintained even if the second guide member is shifted from the first guide member. The robot arm includes a first contact section making contact with the hand body, the hand body includes a second contact section making contact with the first contact section, and the second contact section is configured to slide on the first contact section. The first power transmission device includes a support member connecting the robot arm to the hand body and a belt for rotating the support member. 
         [0015]    The support member may include a first rotating section rotatably installed in the robot arm and a second rotating section rotatably installed in the hand body. The first guide member is rotatably coupled with the first rotating section and the second guide member is rotatably coupled with the second rotating section. 
         [0016]    The first contact section has a circular shape having a first radius, a second contact section has a circular shape having a second radius, wherein the first radius has the same length as the second radius. 
         [0017]    A ratio of the first radius to the second radius can be identical to a radius ratio of the first guide member to the second guide member when the first radius is different from the second radius. 
         [0018]    The first contact section has a planar shape, and the second contact section has a circular shape having a second radius about the second rotating section. A radius of the second guide member is the same length as the second radius of the second contact section. 
         [0019]    The first power transmission device includes a first rotating section rotatably inserted into the hand body and a belt for moving the first rotating section. The humanoid robot may further include a slot for guiding the first rotating section and a belt support member having a reel that supports the belt to allow the belt to guide the first support member along the slot. 
         [0020]    The hand body includes a pivot shaft rotatably coupled to the robot arm. The first power transmission device includes the pivot shaft and a belt for rotating the pivot shaft. A first reel is fitted around the pivot shaft and a second reel is coupled with the first actuator. 
         [0021]    The robot arm includes a first support member, to which the first guide member is rotatably coupled, and the hand body includes a second support member, to which the second guide member is rotatably coupled. The second support member rotates together with the pivot shaft. 
         [0022]    Portions of the connection members aligned between the first and second guide members are positioned in line with the pivot shaft rotatably coupled to the robot arm. 
         [0023]    Embodiments of the present general inventive concept provide a humanoid robot comprising a robot arm, a hand body connected to the robot arm through a wrist joint, finger members connected to the hand body through finger joints, a first actuator and a first power transmission device that drive the wrist joint to rotate the hand body relative to the robot arm, and a second actuator and a second power transmission device that drive the finger joints to rotate the finger members relative to the hand body, wherein the first power transmission device driving the wrist joint operates independently from the second power transmission device driving the finger joints. 
         [0024]    The second power transmission device includes connection members connecting the second actuator to the finger joints and guide members for guiding the connection members, wherein friction between the connection members and the guide members are constantly maintained when the wrist joint is driven by the first actuator and the first power transmission device. The guide members include a first guide member coupled to the robot arm and a second guide member coupled to the hand body, and the connection members are alternately wound around the first and second guide members. Lengths of the connection members provided between the first and second guide members are constantly maintained even if the second guide member is shifted from the first guide member. The connection members include wires and the guide members include pulleys. 
         [0025]    Embodiments of the present general inventive concept provide a humanoid robot including a robot arm, a hand body connected to the robot arm through a wrist joint, finger members comprising finger joints and knuckles, wherein the finger members are connected to the hand body, a first actuator and a first power transmission device that drive the wrist joint to rotate the hand body relative to the robot arm; and a second actuator and a second power transmission device that drive the finger joints to rotate the finger members relative to the hand body, wherein the second power transmission device includes connection members connecting the second actuator to the finger joints and guide members for guiding the connection members, and wherein the length of the connection members, which connects the actuator to the finger members, can be constantly maintained, so that the finger joints can move with sufficient movement displacement. 
         [0026]    The humanoid robot may also include a support member that connects the hand body to the robot arm, wherein the support member comprises a first rotating section inserted into the robot arm, a second rotating section inserted into the hand body; and a leg section connecting the first rotating section to the second rotation section. 
         [0027]    The humanoid robot may also include a first reel installed at the support member, a second reel installed adjacent the first actuator; and a belt that is wound around the first and second reels, wherein a driving force of the first actuator is transferred to the support member through the belt. 
         [0028]    According to the humanoid robot of the present general inventive concept, connection members are alternately wound around the first and second guide members, so that driving force of the actuator can be efficiently transferred to the finger joints. 
         [0029]    The length of the connection members, which connects the actuator to the finger members, can be constantly maintained, so that the finger joint can move with sufficient moving angle (or movement displacement). 
         [0030]    Further, the humanoid robot according to the present general inventive concept can be used as medical equipment, such as a surgery robot and an endoscope, a probe robot, and a working robot in dangerous fields to transfer power to an end effecter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    These and/or other features and utilities of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0032]      FIG. 1  is a schematic perspective view showing a joint structure of a humanoid robot according to the present general inventive concept; 
           [0033]      FIG. 2  is a perspective view showing a robot hand and a robot arm according to the present general inventive concept; 
           [0034]      FIG. 3  is a front view showing a robot hand and a robot arm according to the present general inventive concept; 
           [0035]      FIG. 4  is a side sectional view showing a wrist joint of a humanoid robot according to the present general inventive concept; 
           [0036]      FIG. 5  is a side sectional view showing a hand body, which is bent to the right, according to the present general inventive concept; 
           [0037]      FIG. 6  is a side sectional view showing a hand body, which is bent to the left, according to the present general inventive concept; 
           [0038]      FIG. 7  is a perspective view showing a robot hand and a robot arm according to a second embodiment of the present general inventive concept; 
           [0039]      FIG. 8  is a side sectional view showing a robot hand and a robot arm according to a second embodiment of the present general inventive concept; 
           [0040]      FIG. 9  is a side sectional view showing a hand body, which is bent to the right, according to the present general inventive concept; 
           [0041]      FIG. 10  is a side sectional view showing a hand body, which is bent to the left, according to the present general inventive concept; 
           [0042]      FIG. 11  is a perspective view showing a robot hand and a robot arm according to a third embodiment of the present general inventive concept; 
           [0043]      FIG. 12  is a front view showing a wrist joint according to a third embodiment of the present general inventive concept; 
           [0044]      FIG. 13  is a side sectional view showing a wrist joint according to a third embodiment of the present general inventive concept; 
           [0045]      FIG. 14  is a side sectional view showing a hand body, which is bent to the right relative to a robot arm, according to the present general inventive concept; and 
           [0046]      FIG. 15  is a side sectional view showing a hand body, which is bent to the left relative to a robot arm, according to the present general inventive concept. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0047]    Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present general inventive concept by referring to the figures. 
         [0048]    As shown in  FIGS. 1 and 2 , a robot arm of the humanoid robot according to an embodiment of the present general inventive concept includes a shoulder joint  1 , an elbow joint  2  and a wrist joint  3 . The shoulder joint  1  includes a first joint  4  rotating about an X axis, a second joint  5  rotating about a Y axis, and a third join  6  rotating about a Z axis. The shoulder joint  1  having the first to third joints  4  to  6  having three degrees of freedom, or the 3-DOF. 
         [0049]    The elbow joint  2  includes a fourth joint  7  rotating about the Y axis. The fourth joint  7  allows the robot arm to be folded. The elbow joint  2  having the fourth joint  7  has one degree of freedom, or 1-DOF. 
         [0050]    The wrist joint  3  includes a fifth joint  8  rotating about the X axis, a sixth joint  9  rotating about the Y axis, and a seventh joint  10  rotating about the Z axis. The wrist joint  3  having the fifth to seventh joints  8  to  10  has the 3-DOF. In particular, the sixth joint  9  rotating about the Y axis and the seventh joint  10  rotating about the Z axis allow a robot hand  12  to be bent relative to a robot arm  11   
         [0051]    As shown in  FIGS. 2 and 3 , the humanoid robot according to the present general inventive concept includes the robot arm  11  and the robot hand  12  connected to the robot arm  11  through a wrist joint  15 . 
         [0052]    A hand body  13  is connected to the robot arm  11  by a support member  20  such that the hand body  13  can rotate relative to the robot arm  11 . The support member  20  includes a first rotating section  21  inserted into the robot arm  11 , a second rotating section  22  inserted into the hand body  13 , and a leg section  23  connecting the first rotating section  21  to the second rotating section  22 . In addition, a first reel  24  is installed at the support member  20  and a second reel  26  is installed adjacent a first actuator  27  so that driving force of the first actuator  27  can be transferred to the support member  20  through a belt  25  that is wound around the first and second reels  24  and  26 . Since the first reel  24  that is installed at the support member  20  is positioned on the first rotating section  21 , the support member  20  rotates about the first rotating section  21 . The support member  20  and the belt  25  constitute a first power transmission device to transfer a driving force of the first actuator  27  to the wrist joint  15 . 
         [0053]    The robot hand  12  includes a hand body  13  and finger members  14  connected to the hand body  13 . The finger members  14  include a plurality of finger members and a thumb member, collectively referred to as finger members. Each finger member  14  includes a plurality of knuckles  17  wherein finger joints  16  are provided between the knuckles  17 . 
         [0054]    In operation, if the knuckles  17  are rotated by the finger joints  16 , the finger members  14  can grip articles. The finger members  14  must reliably grip the articles. If the finger members  14  drop the articles due to the lack of gripping force, accident may occur. In order to increase the gripping force of the finger members  14 , an actuator having a large capacity can be installed to provide a great driving force to the finger members  14 . However, if the driving force of the actuator is increased, the size of the actuator is enlarged so that such an actuator is not suitable for the robot hand  12 . 
         [0055]    For this reason, as shown in  FIG. 2 , a second actuator  43  is installed in the robot arm  11  and connection members  40  are provided to transfer driving force of the second actuator  43  to the finger joints  16 . The connection members  40  connect the second actuator  43  to the finger members  14 . The connection members  40  include wires and the number of connection members  40  corresponds to the number of finger members  14 . 
         [0056]    In the present embodiment, the finger joints  16  driven by the second actuator  43  can be operated independently from the wrist joint  15  that is driven by the first actuator  27 . In particular, when the robot hand  12  is folded due to the driving of the wrist joint  15  by the first actuator  27 , the length of the connection members  40 , which connects the finger members  14  to the second actuator  43 , must be constantly maintained. 
         [0057]    Guide members  30  are provided in the wrist joint  15  to guide the connection members  40 . The guide members  30  include first guide members  31  rotatably installed on the first rotating section  21  and second guide members  32  rotatably installed on the second rotating section  22 . The number of first and second guide members  31  and  32  correspond to the number of finger members  14 . The first and second guide members  31  and  32  may include pulleys. 
         [0058]    As shown in  FIG. 4 , the robot arm  11  and the hand body  13  of the humanoid robot according to the present embodiment are adjacent to each other. The robot arm  11  includes a first contact section  61 , and the hand body  13  includes a second contact section  62 . The first contact section  61  makes slide-contact with the second contact section  62 . The first contact section  61  has a first radius R 1  about the first rotating section  21 , and the second contact section  62  has a second radius R 2  about the second rotating section  22 . 
         [0059]    A radius R 3  of the first guide member  31  and a radius R 4  of the second guide member  32  may vary depending on the first radius R 1  of the first contact section  61  and the second radius R 2  of the second contact section  62 . That is, if the first radius R 1  of the first contact section  61  has the same length as the second radius R 2  of the second contact section  62 , the radius R 3  of the first guide member  31  has the same length as the radius R 4  of the second guide member  32 . In contrast, if the first radius R 1  of the first contact section  61  is different from the second radius R 2  of the second contact section  62 , then the ratio of the first radius R 1  to the second radius R 2  (that is, R 1 /R 2 ) will be equal to the ratio of the radius R 3  of the first guide member  31  to the radius R 4  of the second guide member  32  (that is, R 3 /R 4 ) 
         [0060]    A second power transmission device includes the guide members  30  and the connection members  40  that transfer a driving force of the second actuator  43  to the finger joints  16 . The connection members  40  may include first connection members  41  that are used to fold the finger members  14  and second connection members  42  that are used to unfold the finger members  14 . The connection members  40  are alternately wound around the first and second guide members  31  and  32 . That is, the first connection members  41  are alternately wound around a left portion of the first guide member  31  and a right portion of the second guide member  32 . In contrast, the second connection members  42  are alternately wound around a right portion of the first guide member  31  and a left portion of the second guide member  32 . This configuration enables the length of the first and second connection members  41  and  42 , which connect the finger members  14  to the second actuator  43 , can be constantly maintained even if the robot hand  12  is folded due to the driving of the wrist joint  15 . Since the first and second connection members  41  and  42  have the same structure, the following description will be made with reference to the first connection members  41 . 
         [0061]      FIG. 4  shows the hand body  13  before the hand body  13  is bent relative to the robot arm  11 , and  FIG. 5  shows the hand body  13  that is bent to the right relative to the robot arm  11  at an angle of 90 degrees. In  FIG. 4 , a contact point between the first and second contact sections  61  and  62  will be referred to as a first contact point  63 . In  FIG. 5 , a contact point between the first and second contact sections  61  and  62  will be referred to as a second contact point  64 . When the support member  20  (see,  FIGS. 2 and 3 ) rotates about the first rotating section  21 , the hand body  13  rotates relative to the robot arm  11 . In this case, the first contact section  61  slides on the second contact section  62  while the contact point between the first and second contact sections  61  and  62  is being shifted from the first contact point  63  of  FIG. 4  to the second contact point  64  of  FIG. 5 . Thus, the length of the first connection member  41  extending from first guide members  31  to second guide members  32  may not deviate from the distance between the first and second guide members  31  and  32 . Therefore, even if the hand body  13  is bent relative to the robot arm  11  due to the driving of the wrist joint  15 , the length of the first connection member  41  that connects the finger members  14  to the second actuator  43  can be constantly maintained. 
         [0062]      FIG. 6  is a side sectional view showing a hand body, which is bent to the left, according to the present invention.  FIG. 6  shows the hand body  13  that is bent to the left relative to the robot arm  11  at an angle of 90 degrees. In  FIG. 6 , a contact point between the first and second contact sections  61  and  62  will be referred to as a third contact point  65 . In this configuration, the first contact section  61  slides on the second contact section  62  while the contact point between the first and second contact sections  61  and  62  is being shifted from the first contact point  63  of  FIG. 4  to the third contact point  65  of  FIG. 6 . At this time, the length of the first connection member  41  between the first and second guide members  31  and  32  may not deviate from the distance between the first and second guide members  31  and  32 . Therefore, as mentioned above, the length of the first connection member  41  that connects the finger members  14  to the second actuator  43  can be constantly maintained even if the hand body  13  is bent relative to the robot arm  11  due to the driving of the wrist joint  15 . In this way, the movement of the wrist joint does not exert an influence upon the length of the wires. Therefore, the finger members are more precisely controlled and the gripping force of the robot hand is improved. 
         [0063]    Referring to  FIGS. 4 and 6 , the second actuator  43  and the second power transmission device can operate the finger members  14  independently from the first actuator  27  and the first power transmission device. In addition, since the length of the first connection member  41  wound around the first and second guide members  31  and  32  can be constantly maintained, friction between the guide members  30  and the connection members  40  can be constantly maintained. That is, a power transmission efficiency of the second power transmission device may not be lowered even if the hand body  13  is bent relative to the robot arm  11 . 
         [0064]      FIG. 7  is a perspective view showing the robot hand and the robot arm according to the second embodiment of the present invention, and  FIG. 8  is a side sectional view showing the robot hand and the robot arm according to a second embodiment of the present invention. 
         [0065]    As shown in  FIGS. 7 and 8 , the robot hand  12  of the humanoid robot includes a first rotating section  71  rotatably installed in the robot arm  11  and a second rotating section  72  rotatably installed in the hand body  13 . In addition, the first guide member  31  is rotatably installed around the first rotating section  71  and the second guide member  32  is rotatably installed around the second rotating section  72 . 
         [0066]    A belt support member  73  is provided in the robot arm  11 . The belt support member  73  has reels  74  which are positioned opposite to each other on either side of the second rotating section  72 . The first actuator  27  also has a reel  76 . A belt  75  is coupled with the second rotating section  72 , so that when the first actuator  27  is driven, the second rotating section  72  is moved together with the belt  75 . The second rotating section  72 , the belt  75  and the belt support member  73  constitute the first power transmission device. 
         [0067]      FIG. 8  shows the robot arm  11  and the hand body  13  are adjacent to each other. The robot arm  11  includes the first contact section  61 , and the hand body  13  includes the second contact section  62 . The first contact section  61  makes slide-contact with the second contact section  62 . If the second rotating section  71  moves together with the belt  75 , the second contact section  62  slides on the first contact section  61 . The second contact section  62  has a second radius R 2  about the second rotating section  72 . The first contact section  61  has a planar shape. 
         [0068]    In  FIG. 8  the first guide member  31  is rotatably installed around the first rotating section  71  and the second guide member  32  is rotatably installed around the second rotating section  72 . The radius R 3  of the second guide member  32  is the same length as the second radius R 2  of the second contact section  62 . 
         [0069]    The second power transmission device includes the guide member  30  and the connection member  40 . The connection member  40  may include a first connection member  41  used to fold the finger members  14  and a second connection member  42  used to unfold the finger members  14 . The first connection member is alternately wound around the first and second guide members  31  and  32 . That is, the first connection member  41  is alternately wound around a left portion of the first guide member  31  and a right portion of the second guide member  32 . In contrast, the second connection member  42  is alternately wound around a right portion of the first guide member  31  and a left portion of the second guide member  32 . The length of the first and second connection members  41  and  42 , which connect the finger members  14  to the second actuator  43 , can be constantly maintained even if the robot hand  12  is folded due to the driving of the wrist joint  15 . Since the first and second connection members  41  and  42  have the same structure, the following description will be made with reference to the first connection member  41 . 
         [0070]      FIG. 8  shows the hand body  13  before the hand body  13  is bent relative to the robot arm  11 , and  FIG. 9  shows the hand body  13  that is bent to the right relative to the robot arm  11  at an angle of 90 degrees. In  FIG. 8 , a contact point between the first and second contact sections  61  and  62  will be referred to as a first contact point  63 . In  FIG. 9 , a contact point between the first and second contact sections  61  and  62  will be referred to as a second contact point  64 . When the belt  75  (see,  FIG. 7 ) moves together with the second rotating section  72 , the hand body  13  rotates relative to the robot arm  11 . In this case, the first contact section  61  slides on the second contact section  62  while the contact point between the first and second contact sections  61  and  62  is being shifted from the first contact point  63  of  FIG. 8  to the second contact point  64  of  FIG. 9 . Thus, the length of the first connection member  41  between the first and second guide members  31  and  32  can be constantly maintained. Therefore, even if the hand body  13  is bent relative to the robot arm  11  due to the driving of the wrist joint  15 , the length of the first connection member  41  that connects the finger members  14  to the second actuator  43  can be constantly maintained. In this way, the movement of the wrist joint does not exert an influence upon the length of the wires. Therefore, the finger members are more precisely controlled and the gripping force of the robot hand is improved. 
         [0071]      FIG. 10  shows the hand body  13  that is bent to the left relative to the robot arm  11  at an angle of 90 degrees. In  FIG. 10 , a contact point between the first and second contact sections  61  and  62  will be referred to as a third contact point  65 . The first contact section  61  slides on the second contact section  62  while the contact point between the first and second contact sections  61  and  62  is being shifted from the first contact point  63  of  FIG. 8  to the third contact point  65  of  FIG. 10 . As a result, the length of the first connection member  41  between the first and second guide members  31  and  32  can be constantly maintained. 
         [0072]      FIG. 11  is a perspective view showing the robot hand and the robot arm according to the third embodiment of the present invention,  FIG. 12  is a front view showing the wrist joint according to the third embodiment of the present invention, and  FIG. 13  is a side sectional view showing the wrist joint according to the third embodiment of the present invention. 
         [0073]    As shown in  FIGS. 11 to 13 , the robot hand  12  of the humanoid robot according to another embodiment of the present general inventive concept includes a pivot shaft  80  rotatably coupled to the robot arm  11 . A first reel  84  is fitted around the pivot shaft  80  and a second reel  86  is coupled with the first actuator  27 . The first actuator  27  rotates the pivot shaft  80  using the belt  85 . The pivot shaft  80  and the belt  85  constitute the first power transmission device. 
         [0074]    A first support member  81 , to which the first guide member  31  is rotatably coupled as shown in  FIGS. 12 and 13 , is installed in the robot arm  11 , and a second support member  82 , to which the second guide member  32  is rotatably coupled, is installed in the hand body  13 . The second support member  82  is connected to the pivot shaft  80 , so that the second support member  82  rotates together with the pivot shaft  80 . The number of first and second guide members  31  corresponds to the number of second guide members  32  and corresponds to the number of finger members  14 . 
         [0075]    The connection members  40  are alternately wound around the first and second guide members  31  and  32  to transfer the driving force of the second actuator  43  to the finger members  14 . The connection members  40  include a first connection member  41  used to fold the finger members  14  and a second connection member  42  used to unfold the finger members  14 . For instance, the first connection member  41  is wound around the left portion of the second guide member  32  and then wound around the right portion of the first guide member  31 . 
         [0076]    According to this embodiment, a portion of the connection members  40  aligned between the first and second guide members  31  and  32  is positioned on the same line with the pivot shaft  80 . In this case, the length of the connection members  40  aligned between the first and second guide members  31  and  32  can be constantly maintained even if the hand body  13  is bent relative to the robot arm  11 . 
         [0077]      FIG. 14  is a side sectional view showing the hand body, which is bent to the right relative to the robot arm, according to this embodiment, and  FIG. 15  is a side sectional view showing the hand body, which is bent to the left relative to the robot arm, according to this embodiment. 
         [0078]      FIG. 13  shows the hand body  13  before the hand body  13  is bent relative to the robot arm  11 , and  FIG. 14  shows the hand body  13  that is bent to the right relative to the robot arm  11  at an angle of 90 degrees. In addition,  FIG. 15  shows the hand body  13  that is bent to the left relative to the robot arm  11  at an angle of 90 degrees. As shown in  FIGS. 13 to 15 , the first connection member  41  is provided on the same line with the pivot shaft  80 , so that the length of the first connection member  41  between the first and second guide members  31  and  32  can be constantly maintained even if the hand body  13  is bent relative to the robot arm  11 . 
         [0079]    Although few embodiments of the present general inventive concept have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the claims and their equivalents.