Abstract:
The object is to provide a universal joint that, has a secure range of motion, does not deviate from the center of rotation, and does not generate bending moments between itself and a joint that links a plurality of movable members. A plurality of movable members ( 3 A- 3 F and  3   a - 3   f ) and a spherical member ( 2 ) that links the plurality of movable members are provided, curved node sections (q) are formed on the movable members and are brought into contact with the spherical member ( 2 ), and by causing one of the plurality of movable members ( 3 A) to rotate such that the curved node section thereof rotates along the surface of the spherical member ( 2 ), another one of the plurality of movable members ( 3 B) is caused to rotate along the surface of the spherical member.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a universal joint and particularly relates to a universal joint that links a plurality of movable members and a variable structure connected to the universal joint. 
       BACKGROUND ART 
       [0002]    Universal joints have been widely used for machine control technology such a steering techniques. Universal joints have two members joined at a variable angle. Such universal joints include a hook joint such a Cardin joint having two movable member ends connected with a cross pin, a ball universal joint including a ball and socket joint, and a ball joint magnet having a ball and a movable member that are joined by a magnetic force. 
       PRIOR ART DOCUMENT 
     Patent Document 
       [0000]    
       
         Patent Document 1 describes that a ball joint configured to be swaged over a ball formed on the end of a movable member, e.g., a piston. Patent Document 2 describes a pin joint that moves a movable member with a curved member. Patent Document 3 describes a running torque transmission joint that connects one shaft to the other shaft to transmit a running torque. Moreover, known a truss structure called variable geometry trust (VGT) applied to a building structure. 
         Patent Document 1 is U.S. Pat. No. 2,708,591 
         Patent Document 2 is JP-H07-228960A1 
         Patent Document 3 is JP-H09-060649A1 
         Non-Patent Literature 1: System/control/information, Vol. 45, No. 2, pp 82-89, 2001 
       
     
       BRIEF SUMMARY OF THE INVENTION 
     Problems the Invention Intends to Solve 
       [0008]    However, conventional universal joints cannot obtain a range of motion for a large number of movable members. Furthermore, in a conventional universal joint, a large axial force disadvantageously generates a bending moment at a nodal point. 
         [0009]    Specifically, the number of movable members cannot be increased to four, eight, twelve, and so on. Even if the number of movable members can be increased, a bending moment may be generated at a nodal point. For example, in application of a VGT (a variable geometry truss: a metallic framework) to a nodal portion, a plurality of frames are connected at the top of the VGT and thus generate a bending moment at the top. Unfortunately, a metallic structure like a frame may cause a metal fatigue between the structure and a spherical member because of driving of a driving member. 
         [0010]    In view of the above, the present invention to provide a universal joint that, even if multiple movable members are provided, can obtain a range of motion without deviating from the center point of rotation or generating a bending moment between the movable members and a joint for linking the movable members, and a variable structure including the multiple connected universal joints. 
       Means for Solving the Problems 
       [0011]    In order to solve the problems, a universal joint, comprising: a plurality of movable members; a spherical member that links the movable members; a cover member that brings the movable members into contact with the spherical member; wherein the movable member has a curved nodal portion in contact with the spherical member, and any one of the movable members is moved or rotated along the surface of the spherical member with the curved nodal portion. 
         [0012]    According to the present invention, the curved nodal portion is formed on the engaging surface of the movable member and is in contact with the spherical member. In the case of a large number of movable members, using a large spherical member allows the provision of the corresponding number of movable members. The curved nodal portion of one of the movable members is moved or rotated along the spherical member. Thus, even a large number of movable members can be driven without deviating from the center point of movement or rotation. 
         [0013]    The universal joint according to the present invention is characterized in that the curved nodal portion of the movable member is larger in diameter than the movable member and the cover member is movable or rotatable along the surface of the curved nodal portion. In this case, some of the curved nodal portions of the movable members may be brought into contact with the spherical member with the cover member while the curved nodal portions of the other movable members may not be brought into contact with the spherical member. Alternatively, the cover member may operate with the movable members. 
         [0014]    According to the present invention, depending upon the location of the cover member, one of the movable members can be rotated while another one of the movable members is not rotated. If the movable member operates with the cover member, the cover member can be rotated along the surface of the curved nodal portion. Thus, the movable member linked with the cover member and the other movable members move or rotate along the surface of the spherical member without interfering with each other. 
         [0015]    The universal joint according to the present invention is characterized in that the movable members include at least two pairs of members: a first pair of movable members and a second pair of movable members, and the cover member includes a first cover member that brings one of the movable members of the first pair and the other movable member of the second pair into contact with the spherical member, and a second cover member that brings the other movable member of the first pair and one of the movable members of the second pair into contact with the spherical member. 
         [0016]    According to the present invention, for example, in case of the two pairs of members, which are the first pair of movable members and the second pair of movable members, are disposed at intervals of 90 degree on the surface of the spherical members such the pairs are respectively located along a vertical line and a horizontal line of the spherical member, only one of the first and second pairs of movable members can be rotated. 
         [0017]    The universal joint according to the present invention is characterized in that further comprising: a cylindrical member covering each of the movable members; wherein the cylindrical member is connected that is allowed a rotation of the cover member. 
         [0018]    According to the present invention, the cylindrical member covering one of the movable members is operated so as to rotate the other movable members with the cover member connected to the cylindrical member. 
         [0019]    The universal joint according to the present invention is characterized in that the universal joint according to claim  1 , wherein the movable members are disposed radially around the spherical member, or the movable members are disposed with point symmetry around the spherical member, or the movable members are disposed with line symmetry around the spherical member. 
         [0020]    According to the present invention, the movable members disposed radially or with point symmetry or line symmetry can be moved in a coordinated manner. Specifically, when one of the movable members is rotated, another one of the movable members is preferably moved or rotated with respect to the spherical member in response to the rotation. 
       Effects of the Invention 
       [0021]    According to the present invention, even a large number of movable members can be rotated along the surface of the spherical member without deviating from the center point of rotation. The number of movable members can be increased and a range of motion can be ensured by expanding the surface area of the spherical member. 
         [0022]    According to the present invention, the movable members are radially disposed with respect to the spherical member or are disposed with point symmetry or line symmetry. Thus, the movable members can be moved by an equal angle, the movable members can be driven so as to transform in a certain direction, the pair of opposed movable members can be symmetrically driven, one of the pairs of opposed movable members can be driven while the other pair of movable members is not driven, or the movable members can be freely and driven in a separate manner. This can achieve a structure generating no bending moment between the movable members and the spherical member linked with the movable members, regardless of how the movable members are driven. 
         [0023]    According to the present invention, since the nodal points as contact points are free, for example, even if the movable members and the spherical member are made of metals, the free nodal points as contact points do not generate a bending moment. For example, if a three-dimensionally transformed component like a dome ceiling is formed in a tent supported with a frame, a durable truss structure can be provided for an extendable building structure. Furthermore, the nodal points such curved nodal portions are free and thus even in application to a damping/base isolation structure or like, the present invention can be effectively used for an active control technique involving the transformation of the structure. 
         [0024]    The following advantages can be obtained: 
       (Productivity) 
       [0025]    The number of kinds of curved structure members can be reduced. Even if a curved structure is designed with varying angles of members at all nodal points, the curved structure can be composed of an identical joint mechanism. 
       (Work Efficiency) 
       [0026]    The number of temporary works can be reduced. A three-dimensional dome building to be constructed is temporarily assembled on a flat surface to adjust the lengths of the members, allowing the three-dimensional construction of the dome building. 
       (Expandability) 
       [0027]    An additional structure can be optionally produced using the freely changing angles of the movable members. Since a bending moment is not generated, a longer life cycle can be obtained. 
       (Adaptability) 
       [0028]    A structure changing depending upon the environment can be produced. If a structure is designed with a varying internal volume, the internal volume is reduced in a summer period having a large energy load. Thus, the structure can change depending upon the environment. 
       (Efficiency) 
       [0029]    The present invention is suitable for the joints of a parallel-link mechanism. The mechanism can be controlled by the direct action of the movable member unlike in a serial link mechanism under torque control. This can efficiently transform the universal joint. 
       (Novelty) 
       [0030]    An organic shape can be formed with an extended range of design. A durable structure, e.g., the large roof of a spacious construction can be obtained while attracting publicity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  is an explanatory drawing of the principle and configuration of a universal joint according to the present invention. 
           [0032]      FIG. 2  is an explanatory drawing of the principle and configuration of the universal joint according to the present invention. 
           [0033]      FIG. 3  is an explanatory drawing of the principle and configuration of the universal joint according to the present invention. 
           [0034]      FIG. 4  is an explanatory drawing of the principle and configuration of the universal joint according to the present invention. 
           [0035]      FIG. 5A  is a perspective view illustrating a universal joint according to a first embodiment of the present invention. 
           [0036]      FIG. 5B  is a perspective view showing the component configuration of the universal joint. 
           [0037]      FIG. 6  is an explanatory drawing of the relationship between a movable member and a cover member according to the first embodiment. 
           [0038]      FIG. 7  is an explanatory drawing of the internal configuration of a cylindrical member according to the first embodiment. 
           [0039]      FIG. 8  is an explanatory drawing of a layout example of the movable member according to the first embodiment. 
           [0040]      FIG. 9  is a perspective view illustrating a comparative example for explaining the effect of the first embodiment. 
           [0041]      FIG. 10A  is a perspective view for explaining an application example according to the first embodiment. 
           [0042]      FIG. 10B  is a perspective view showing the component configuration of the application example. 
           [0043]      FIG. 11  is an explanatory drawing of the relationship between the movable member and the cover member according to the first embodiment. 
           [0044]      FIG. 12A  is a perspective view illustrating a universal joint according to a second embodiment of the present invention. 
           [0045]      FIG. 12B  is a perspective view showing the component configuration of the universal joint. 
           [0046]      FIG. 13A  is a bottom view of a universal joint according to a third embodiment of the present invention. 
           [0047]      FIG. 13B  is a side view of the universal joint according to a third embodiment of the present invention. 
           [0048]      FIG. 13C  is a perspective view of the universal joint according to a third embodiment of the present invention. 
           [0049]      FIG. 13D  is a plan view of the universal joint according to a third embodiment of the present invention. 
           [0050]      FIG. 14  is a perspective view for explaining the operation of the universal joint according to the third embodiment. 
           [0051]      FIG. 15  is a perspective view showing the component configuration of the third embodiment. 
           [0052]      FIG. 16  is an explanatory drawing of an application example of the embodiment. 
           [0053]      FIG. 17  is an explanatory drawing of an application example of the embodiment. 
           [0054]      FIG. 18  is an explanatory drawing of an application example of the embodiment. 
           [0055]      FIG. 19  is an explanatory drawing of a variable geometry truss structure. 
           [0056]      FIG. 20  is an explanatory drawing of a variable geometry truss structure. 
           [0057]      FIG. 21  is an example according to the second embodiment. 
           [0058]      FIG. 22A  is an explanatory drawing showing motions according to the second embodiment, in which short movable members move or rotate along a spherical member while keeping a constant distance from long movable members such that the long movable members come closer to each other in a sliding manner. 
           [0059]      FIG. 22B  is an explanatory drawing showing motions according to the second embodiment, in which short movable members move or rotate along a spherical member while keeping a constant distance from long movable members such that the long movable members come close to each other in a sliding manner. 
           [0060]      FIG. 22C  is an explanatory drawing showing motions according to the second embodiment, in which the short movable members move or rotate along the spherical member while keeping a constant distance from the long movable members such that the long movable members come closer to each other in a sliding manner. 
           [0061]      FIG. 22D  is an explanatory drawing showing motions according to the second embodiment, in which the short movable members move or rotate along the spherical member while keeping a constant distance from the long movable members such that the long movable members come closer to each other in a sliding manner. 
           [0062]      FIG. 22E  is an explanatory drawing showing motions according to the second embodiment, in which the short movable members move or rotate along the spherical member while keeping a constant distance from the long movable members such that the long movable members come closer to each other in a sliding manner. 
           [0063]      FIG. 23  is an explanatory drawing of the motions of a structure including connected universal joints according to the second embodiment. 
           [0064]      FIG. 24A  is an explanatory drawing of the motions of a variable structure including the connected universal joints according to the second embodiment of the present invention. 
           [0065]      FIG. 24B  is an explanatory drawing of the motions of the variable structure including the connected universal joints according to the second embodiment of the present invention. 
           [0066]      FIG. 24C  is an explanatory drawing of the motions of the variable structure including the connected universal joints according to the second embodiment of the present invention. 
           [0067]      FIG. 24D  is an explanatory drawing of the motions of the variable structure including the connected universal joints according to the second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0068]    Hereinafter, specific modes for carrying out the present invention will be explained by using drawings. 
         [0069]    (The Principle and Configuration of the Present Invention) 
         [0070]      FIG. 1  shows the principle and configuration of a universal joint according to the present invention. 
         [0071]    The present invention includes a spherical member  2  and a plurality of movable members  3 A,  3 B, and so on. The movable member  3 A is driven by the movable member  3 B with the spherical member  2 . In this explanation, the two movable members  3 A and  3 B are provided. The number of movable members may be two or more and an even number or an odd number. 
         [0072]    The movable members  3 A and  3 B each have a curved nodal portion q with a predetermined curvature on one end. In this case, the curvature of the curved nodal portion q on each of the movable members  3 A and  3 B is larger than that of the spherical shape of the spherical member  2 . The curvature of the curved nodal portion q may be equal to or smaller than that of the spherical member  2 . As shown in  FIG. 2A  and  FIG. 2B , the curved nodal portion q may be larger in diameter than the movable members  3 A and  3 B and come into contact with the spherical member  2 . 
         [0073]    The curved nodal portions q of the movable members  3 A and  3 B are pressed to the surface of the spherical member  2  by a cover member  4 , which will be described later. Thus, the movable member  3 A driven in contact with the spherical member  2  (arrows F 1 , F 2 ) is rotated along the surface of the spherical member  2 . Arrows F 1  and F 2  indicate the opposite rotation directions of the movable members  3 A and  3 B. The movable members  3 A and  3 B rotated along F 1  and F 2  come closer to each other from the positions of  FIG. 1 . 
         [0074]    The ball-like spherical member  2  has the effect of transmitting the compressive force like a sliding force of the movable member. The spherical member  2  does not move. The movable members  3 A and  3 B and the spherical member  2  can come into contact with each other but are not connected to each other, generating no bending moment between the movable members  3 A and  3 B and the spherical member  2  linked with the movable members  3 A and  3 B. 
         [0075]    In  FIG. 2 , the two movable members  3 A and  3 B each have a ring as curved nodal portion  6 . Both surfaces of the ring as curved nodal portion  6  are curved and are larger than the diameters of the movable members  3 A and  3 B. Thus, the movable member  3 A is rotated along the surface of the spherical member  2  direction arrows F 1  and F 2  and is brought closer to or separated from the movable member  3 B with respect to the rotation of the spherical member  2 . A pair of movable members  3 C and  3 D is provided in addition to the pair of movable members  3 A and  3 B and they are structured to behave in a similar manner. Specifically, an angle between the movable member  3 A and the movable member  3 B that is next to the movable member  3 C adjacent to the movable member  3 A is freely changed while keeping an equal angle between the movable member  3 A and the movable member  3 C adjacent to the movable member  3 A. The present inventor calls the joint “alternately universal joint” because a rotation is allowed for the pair of movable members  3 A and  3 B. In the alternately universal joint, the pair of movable members  3 A and  3 B and the pair of movable members  3 C and  3 D are rotated with an equal traveling distance. According to this principle, subsequent embodiments will be also configured as alternately universal joints. 
         [0076]    In  FIG. 4 , the pairs of four movable members  3 A to  3 D with the rings as curved nodal portions  6  are provided on the surface of the spherical member  2 . The pair of movable members  3 A and  3 B and the pair of movable members  3 C and  3 D are evenly spaced so as to have point symmetry with respect to the spherical member  2 . From this position, the movable members come closer to each other or return to the original positions. A cover member  4  ( 4   a ,  4   b ) is disposed between the pair of movable members  3 A and  3 B and the pair of movable members  3 C and  3 D. The cover member  4  is rotatably provided along the surfaces of the rings as curved nodal portions  6  and is connected to the pair of movable members  3 A and  3 B or the pair of movable members  3 C and  3 D. For example, the pair of movable members  3 A and  3 B are rotated so as to approach each other while the pair of movable members  3 C and  3 D are stopped. In other words, a rotation direction arrow F 1  of the movable member  3 A of the pair of movable members  3 A and  3 B also rotates the movable member  3 B direction arrow F 2  through the cover member  4 , bringing the movable members  3 A and  3 B closer to each other. Thus, at least two movable members can be provided. As the ball-like spherical member  2  increases in size, a larger number of movable members  3 A to  3 D can be provided on the surface of the spherical member  2 . The movable members  3 A and  3 B linked with the cover member  4  that further explaining the four first and second cover members  4   a  and  4   b  evenly spaced on the outer periphery of the spherical member  2 ) are configured to rotate along the surfaces of the rings as curved nodal portions  6 . Thus, the movable members  3 A and  3 B and the movable members  3 C and  3 D rotate along the surface of the spherical member  2  without interfering with each other. 
         [0077]    As shown in  FIG. 3 , without the rings as curved nodal portions  6 , the movable member  3 A can be rotated along the surface of the spherical member  2  direction arrows F 1 , F 2  so as to approach or separate from the movable member  3 B with respect to a rotation of the spherical member  2 . 
       First Embodiment 
       [0078]      FIG. 5A  is a perspective view showing a universal joint  11  according to a first embodiment.  FIG. 5B  is a component configuration diagram of the universal joint  11  according to the first embodiment. 
         [0079]    In the present embodiment, the universal joint  11  includes four movable members  3 A to  3 D, a spherical member  2  that links the movable members  3 A to  3 D, and cover members  4  that bring the movable members  3 A to  3 D into contact with the spherical member  2 . The movable members  3 A to  3 D have curved nodal portions as rings  6  near the spherical member. The shaft center of each of the movable members  3 A to  3 D has a rod member as shaft  3 . The cover member  4  has a V-shaped member as wing on one end. The cover member  4  is disposed among the movable members  3 A to  3 D with its V-shaped left and right sides pressing the curved members as rings  6  of the movable members  3 A to  3 D, which are adjacent to the cover member  4 , to the spherical member  2 . Moreover, cylindrical members as pipes  5  cover the respective movable members  3 A to  3 D. The cylindrical member as pipe  5  and the cover member  4  are connected to each other while allowing a rotation of the cover member. The cover member  4  and the curved nodal portion  6  are not connected to each other and the cover member  4  presses the adjacent curved nodal portion  6  from the outer periphery. The ring as curved nodal portion  6  has a cylindrical protrusion  6   a  at the center of the ring  6  and a protrusion  6   b  around the outer circumference of the ring  6 . The movable member  3  cannot be removed between the protrusions  6   a  and  6   b . The top and bottom of the spherical member  2  have areas as gaps not containing the cover member  4 , allowing a rotation of the cover member  4 . 
         [0080]    According to the present embodiment, at a nodal point where the four movable members  3 A to  3 D are connected, an equal angle is kept between one of the movable members and the adjacent movable member; meanwhile, an angle between the movable member and the movable member next to the adjacent movable member can be freely changed. In other words, a rotation direction arrow F 1  of the movable member  3 A of the pair of movable members  3 A and  3 B also rotates the movable member  3 B direction arrow F 2  through the cover member  4 , bringing the movable members  3 A and  3 B closer to each other, while the pair of movable members  3 C and  3 D are stopped. Furthermore, a rotation direction arrow F 1  of the movable member  3 C of the pair of movable members  3 C and  3 D also rotates the movable member  3 D direction arrow F 2  through the cover member  4 , bringing the movable members  3 C and  3 D closer to each other, while the pair of movable members  3 A and  3 B are stopped. The present inventor calls such a rotation “the relationship of a rotational sliding pair”. 
         [0081]    The constituent elements as component configurations do not need to be independent from one another and are preferably combined. For example, the cylindrical member  5  and the rod member  3  are preferably combined so as to be aligned with each other in the transformation of the movable members  3 A to  3 D. One of the wings  4  and the cylindrical member  5  may be joined to each other but in this case, the other wing  4  needs to be independent from the cylindrical member  5 . Furthermore, the curved nodal portion  6  and the rod member  3  may be combined. 
         [0082]      FIG. 7  shows an example of the curved member  6  and the rod member  3 . A plurality of wings evenly spaced around the rod member  3  may be covered with the cylindrical member  5 . 
         [0083]    The present embodiment described an example of the four movable members (see  FIG. 8A ). Alternatively, six shafts (see  FIG. 8B ), five shafts, or an odd or even number of shafts may be provided (see  FIG. 8C ). Symbol  9  is spacers. 
         [0084]    Engagement such protrusion and groove for transmitting a tensile force applied to the movable member as rod member needs to be prepared between the cylindrical member  5  and the wing  4 . Preferably, the cylindrical member  5  is a protrusion and the wing is a groove in consideration of the thickness of the member. 
         [0085]    A coil introduced into the cylindrical member  5  can achieve a mechanism with a restoring force. Alternatively, a viscous fluid introduced into the cylindrical member  5  can achieve a mechanism with a buffer effect. 
         [0086]    In the present embodiment, the wing  4  is a member resistant to a tensile force applied to the movable member. The wings  4  are disposed around the cylindrical member  5 , and at least two of the wings  4  are considered to be resistant due to a shearing resistance on two surfaces as symbol r along dotted lines (see  FIG. 6 ). 
         [0087]    One end faces of the movable members  3 A to  3 D can be formed as nodal points q having curved shapes, allowing the movable members  3 A to  3 D to be connected via the cover members. 
         [0088]      FIG. 9  is a perspective view showing a hinge joint  1 H as a comparative example. The hinge joint  1 H is a comparative example of the first embodiment and includes four movable members Hb and a spherical member Ha that are connected to each other. The four movable members Hb and the spherical member Ha are made of metals. The four movable members Hb driven in the comparative example generates a bending moment at a connected point. The metallic movable members Rb may cause a metal fatigue. 
         [0089]    Unlike the hinge joint  1 H, the universal joint  11  of the present embodiment brings the curved nodal portion q into contact with the spherical member  2 , thereby preventing a bending moment on the curved nodal portion q without deviating from the center of rotation. 
         [0090]      FIG. 10  and  FIG. 11  illustrate a universal joint  21  according to an application example of the first embodiment. 
         [0091]    In the application example  21 , a cover member  14  includes a first cover  14   a  and a second cover  14   b  having a through hole  14   c  through which another adjacent one of the movable members passes. The cover member  14  has the effect of suppressing the opening of the movable member  3  moving on the surface of the spherical member  2  such like in a transformation process. The cover member  14  is configured like a chain with a spherical outer periphery connecting all the movable members  3 A to  3 D. Specifically, the cover member  14  having an initial flat shape connects one of the movable members  3  and another adjacent one of the movable members  3  and connects all the adjacent movable members so as to cover the spherical member  2 . The cover member  14  like a chain does not connect the cover member  14  and the ring as curved nodal portion  16  but presses the adjacent rings  16  from the outer periphery (see  FIG. 5 ), allowing the rotations of the pair of movable members  3 A and  3 B and the movable members  3 C and  3 D. In this application example, one surface as symbol r of the chain  14  is considered to be resistant to a tensile force applied to the movable member unlike in the first embodiment (see  FIG. 11 ). 
         [0092]    According to the present embodiment, a feature of the present embodiment is that the cover member  14  has a larger area with a larger sliding surface or sliding contact surface with the surface of the spherical member  2  than in the first embodiment. Since the cover member  14  is a circular chain member or chain, a tension ring is formed around the spherical member  2 , allowing sliding between the spherical member  2  and the chain  14 . The present inventor calls such sliding “the relationship of a rotational sliding pair”. 
         [0093]    Engagement such protrusion and groove for transmitting a tensile force applied to the movable member needs to be prepared between the cylindrical member  5  and the wing  4 . Preferably, the cylindrical member  5  is a protrusion and the wing is a groove in consideration of the thickness of the member. 
       Second Embodiment 
       [0094]      FIG. 12A  shows an example of multi-axis universal joints  11  according to the present embodiment.  FIG. 12B  is a perspective view showing the component configuration of the universal joint. 
         [0095]    The universal joint  11  of the present embodiment includes six large movable members  3 A to  3 F and six small movable members  3   a  to  3   f , totaling  12  movable members. The number of movable members is not particularly limited and thus may be smaller than or larger than 12. 
         [0096]    The large movable members  3 A to  3 F and the small movable members  3   a  to  3   f  each include a cylindrical member containing the movable member  3 , a cover member as wing  4  provided around the rod member  3 , and the cylindrical member  5  that contains the rod member  3  and the wing  4 . The cover member as wing  4  is V-shaped and is fan-shaped in cross section as shown like a spread wing. The movable members  3 A to  3 F and the small movable members  3   a  to  3   f  each have a curved nodal portion as ring  6  near the spherical member. In this configuration, the V-shaped member as wing  4  and the cylindrical member  5  press the curved nodal portion as ring  6  that is provided on the end of the movable member, to the spherical member  2 . A fitting portion  4   a  is provided on the other end of the cylindrical member  5 . The curved nodal portion  6  has a concave shape. The center of the curved nodal portion  6  is connected to the rod member  3  and is fitted to the end  4   a  of the V-shaped wing  4 . The range of motion of the spherical member  2  changes depending upon the relationship between the size of the spherical member  2  and the diameter of the movable member, the fan shape of the wing in cross section and center angle, and so on. 
         [0097]    The large movable members  3 A to  3 F and the small movable members  3   a  to  3   f  are vertically disposed in pairs with respect to the spherical member  2  and are horizontally spaced at intervals of 90 degree. The movable members  3  are directed to the center of the spherical member  2  and are evenly spaced. The movable members  3  can be radially disposed or disposed with point symmetry or line symmetry with respect to the spherical member  2 . Thus, the multiple movable members at equal intervals are efficiently disposed. 
         [0098]    For example, if the V-shaped wing  4  and the cylindrical member  5  only press the curved nodal portion as ring  6  of each of the large movable members  3 A to  3 F to the spherical member  2 , only the large movable members  3 A to  3 F can be rotated. 
         [0099]    The curved nodal portions  6  of the large movable members  3 A to  3 F and the curved nodal portions as rings  6  of the small movable members  3 A to  3 F can be varied in size so as to change a contact area with the spherical member  2 . 
         [0100]    The universal joint  31  according to the first embodiment can freely change an angle formed by one spaced consecutive movable members. The second embodiment is composed of the large movable members  3 A to  3 F and the small movable members  3   a  to  3   f . The relationship among the large movable members  3 A to  3 F is identical to that can freely change an angle formed by one spaced consecutive movable members, including the small movable members  3   a  to  3   f . Thus, an angle formed by the large movable members can be freely changed. 
         [0101]    The second embodiment is applicable to a construction for efficiently constructing a temporarily assembled two-dimensional structure on the ground into a three-dimensional dome such lifting a tent into a dome roof, a bridge, a joint of a structure, and so on. 
         [0102]      FIG. 21  and  FIG. 22A  to  FIG. 22E  show an application example of the second embodiment. The universal joint  11  includes the three long movable members  3 A to  3 C and the six short movable members  3   a  to  3   f . These movable members are connected at equal intervals via a cover member as wing  4  so as to approach one another or separate from one another. The universal joint  11  of the present embodiment is configured to move the long movable members  3 A to  3 C. The short movable members  3   a  to  3   f  are only used for moving the long movable members  3 A to  3 C and thus are not connected to other joints. In other words, the connected state of the short movable members  3   a  to  3   f  to other joints is a state of a structure including joints connected via spacers S as shown in  FIG. 17 . The long movable members  3 A and  3 B constitute the structure including the joints connected via the spacers S as shown in  FIG. 17 . 
         [0103]    The cover members as wings  4  of the present embodiment are connected at predetermined intervals around the respective long movable members  3 A to  3 C. The length of the cover member allows an end  4   a  of the cover member to approach the cylindrical member  5  of each of the short movable members  3   a  to  3   f . The cover members are unconnected to allow movements of the six short movable members  3   a  to  3   f  and press curved nodal portions q of the six short movable members  3   a  to  3   f  from above. Thus, as shown in  FIG. 22A  to  FIG. 22E , the movable members  3 A to  3 C and  3   a  to  3   f  can rotate about the center of the spherical member  2  serving as the center point of rotation. Furthermore, the movable members can move in contact with the outer periphery of the spherical member  2 . The cylindrical member  5  and so on of the movable member connected to the cover member as wing  4  is identical to that of the second embodiment. 
         [0104]      FIG. 21  shows arrows of motions. If the long movable members  3 A to  3 C are moved along a long arrow Y 1 , the short movable members  3   a  to  3   c  are rotated along a second longest arrow Y 2 . Further explaining the second longest arrow Y 2  rotation is made with respect to the center point of a sphere. A short arrow Y 3  indicates the rotation of the cover member  4 . Further explaining the center of rotation of the short arrow Y 3  is the central axis of the rod member  3 . The movable members are simultaneously rotated by a movement along the long arrow Y 1 . If the direction of the movement is reversed from the long arrow Y 1 , the directions of all the arrows are reversed. 
         [0105]    Thus, as shown in  FIG. 22A  to  FIG. 22E , the three short movable members  3   a  to  3   c  can be moved to the center in this order. In order to move the long movable members  3 A and  3 B, the three short movable members  3   a  to  3   c  are moved to the center as shown in  FIG. 22A  to  FIG. 22E , relocating the long movable members  3 A to  3 C to the center as one side of the spherical member  2  in a sliding manner. As shown in  FIG. 22E , the relocation increases the intervals of the short movable members  3   d  to  3   f  on the other side. 
         [0106]      FIG. 23  is an explanatory drawing of motions of an variable structure  51  including the connected universal joints according to the second embodiment. Specifically,  FIG. 23  shows an example of a numerical analysis on the variable structure or adjustable movement of the structure  51  that uses the multi-axis universal joint  11  corresponding to  FIG. 12A .  FIG. 23  sequentially shows the motions. The structure  51  is transformed like amoeba. Further explaining, the rolls with a changing rectangular shape and moves forward from the left to the right in  FIG. 23 . In this example, a rover is a driving member that travels forward on a bad road and is expected to be developed for motor vehicles that can move under adverse conditions such as roads with long rocks and holes. Programs have been developed to examine the variable structure  51  according to a numerical analysis example on a two-dimensional plane and determine the length of a shaft member as an input value by a numerical analysis. Thus, the examination of the analysis and motions was confirmed. 
       Third Embodiment 
       [0107]      FIG. 13  shows a universal joint  41  according to a third embodiment.  FIG. 14  is an explanatory drawing of a driven state.  FIG. 15  is a component configuration diagram.  FIG. 16  shows an example applied to the ceiling of a construction. The third embodiment is different from the first embodiment in its three-dimensional initial shape. 
         [0108]    An application example of the universal joint  41  according to the present embodiment is an adjustable three-dimensional truss frame. In the present embodiment, four movable members  3  as  3 A to  3 D are disposed at equal intervals with the spherical member  2  located on top of the movable members. The movable members  3 A to  3 D include cylindrical members  5  that store the respective movable members  3 A to  3 D, cover members  44  connecting the cylindrical members  5  to each other, and the spherical member  2 . The cover member  44  has a curved nodal portion  44   q  for locating the spherical member  2  on the top of the V shape of the cover member  44 , and curved portions  44   p  for locating the movable members  3  on the left and right sides of the V shape of the cover member  44 . 
         [0109]    Moreover, the four movable members  3 A to  3 D at equal intervals are rotated from its positions such that the pair of movable members  3 A and  3 B (or  3 C and  3 D) is brought closer to each other or returned to the original positions. A feature of the movable members is that even if these operations are repeated, the curved nodal portion q formed in contact with the spherical member  2  on the ends of the movable members  3 A to  3 D does not generate a bending moment. Another feature is that the cover member  44  having the curved nodal portion  44   q  does not generate a bending moment even if the cover member  44  is rotated. 
         [0110]      FIG. 15  shows an application example of the universal joint  41  according to the present embodiment. The third embodiment is applicable to a construction for efficiently constructing a temporarily assembled two-dimensional structure on the ground into a three-dimensional dome such lifting a tent into a dome roof, a bridge, a joint of a structure, and so on. 
         [0111]      FIG. 24  shows an example of a numerical analysis on the variable structure  52  that uses the universal joint  41  corresponding to a numerical analysis example on the variable structure of  FIG. 16A . The variable structure  52  of  FIG. 24  can be manufactured using the universal joint  11  of  FIG. 5A  and the universal joint  21  of  FIG. 10A . A morphological analysis program was prepared to trace how the variable structure  52  is transformed into a stable shape. It is verified that a target shape can be designed. 
         [0112]      FIG. 17  shows an application example of the third embodiment. 
         [0113]    In this application example, a structure uses a connecting member as spacer S that connects the spherical members  2  to each other with the same diameter as the cylindrical member  5 . A wing  4  or the cylindrical member  5  does not need to be contained in all lines. The spherical member  2  only needs to be configured around a nodal point. Pipes or rod-like connecting members as spacers connecting nodal points are introduced to form a large number of connecting structures. 
         [0114]    A conventional truss structure is called variable geometry trust (VGT). In a diagram of a VGT, a nodal point having concentrated lines serves as a joint and a multi-axis universal joint is used (see  FIG. 19 ). In the case of a VGT called a helical mast in  FIG. 20 , a multi-axis universal joint having six axes is used. 
         [0115]    It is however quite difficult to achieve such a joint in an actual three-dimensional VGT. Thus, a nodal point offset can not be avoided between the rotation centers of multiple joints that join the members (see the marginal notes of Non-patent Literature). 
         [0116]    In contrast, the present embodiment can provide a durable truss structure and avoid the nodal point offset. 
         [0117]      FIG. 18  shows another application example of the third embodiment. The spherical member  2  at the top has another movable member  3  according to the third embodiment. In  FIG. 18 , a universal joint unit is composed of the three movable members  3 A to  3 C, each having the spherical member  2  on the top, and the movable member  3 . In this configuration, the three movable members  3 A to  3 C are disposed at the intervals of 60 degree and the additional movable member  3  and the movable members  3 A and  3 C are disposed at the intervals of 120 degree. Furthermore, the movable members  3 A to  3 C can be driven by a predetermined angle with respect to the movable member  3  via the spherical member  2 . The multiple movable members in a connected state are applied to, for example, a truss structure for a construction. 
         [0118]    The foregoing embodiments described building structures as specific examples, but the embodiments may be applied as follows: 
       (Construction) 
       [0119]    The embodiments are applicable to transformed constructions such as a variable structure and a developed structure unlike a conventional static construction. The embodiments are applicable to a construction for efficiently constructing a temporarily assembled two-dimensional structure on the ground into a three-dimensional dome in a construction process. Preferably, a developed structure has a rigid surface with mechanism properties such as a constant surface area and a varying internal volume. Moreover, constructions specifically for designs having organic forms can be efficiently produced by a uniform component configuration. For example, joints for constructions requiring multi-axis pin joints can be produced. Such constructions with expandability take advantage of free nodal points. Furthermore, such constructions are usable as damping/base isolation. Because of its free nodal points, such constructions are effective for active damping techniques involving transformation of structures. 
       (Machine) 
       [0120]    A machine operation (steering) technique is considered to be effective in the case where multiple operation targets are three-dimensionally provided. A mechanism for transmitting the motions of multiple members can be achieved by a small number of members. This technique is applicable to the joints of a parallel-link mechanism having multiple links, a flight simulator, and so on. 
         [0121]    This technique is applicable to robots using curving motions like geometers (Multi-legged walking creature) instead of robots operated by a serial link mechanism with robot hands and legs. Direct acting control can achieve efficient robots unlike in torque control. This technique is also applicable to a device for damping an impact on a surface. Since spacers S are springs, large sporting apparatuses such as a trampoline can be provided. Furthermore, this technique is widely applicable to apparatuses for precisely keeping the coordinate position of a target of base isolation, medical technology, and so on in combination with a base isolating device for vibrations in multiple directions and a system control technique. 
       (Engineering Works) 
       [0122]    The embodiments are applicable to, for example, the joints of structures such as bridges requiring multi-axis pin joints. Such structures as bank protection works or temporary works take advantage of tracking performance on irregular shapes of natural objects. 
       (Space Structure) 
       [0123]    The embodiments are applicable to developed structures with adjusting performance, solar panels, and so on. Such structures have free nodal points and thus can be easily extended into structures for a space station. 
       (Other Applications) 
       [0124]    The embodiments are applicable to various products such as the joints of toys, products having folding structures, and products using adjustable mechanisms.