Patent Publication Number: US-2020298426-A1

Title: Rotary actuator and robot

Description:
TECHNICAL FIELD 
     The present invention relates to a hollow-type rotary actuator including a hollow motor and a hollow reduction gear which are disposed coaxially with each other. The present invention also relates to a robot having such a rotary actuator. 
     BACKGROUND ART 
     Conventionally, a hollow-type rotary actuator including a hollow motor and a hollow reduction gear is known (for example, refer to Patent Document 1). In the hollow-type rotary actuator described in Patent Document 1, the hollow reduction gear is a hollow wave gear device and includes an annular device housing, a rigid internal gear fixed to an inner circumferential portion of the device housing, a cup-shaped flexible external gear disposed inside the rigid internal gear, and a wave generator disposed inside the flexible external gear. The flexible external gear is rotatably supported by the device housing via a cross roller bearing. A part of the wave generator is fixed to an outer circumferential surface of a hollow motor shaft of the hollow motor. 
     Further, in the hollow-type rotary actuator described in Patent Document 1, the hollow motor and the hollow reduction gear are disposed coaxially with each other. A sleeve formed in a cylindrical shape is disposed on the inner circumferential side of the hollow motor and hollow reduction gear. The sleeve is fixed by laser welding to a boss forming a part of the flexible external gear. Therefore, the sleeve rotates with the flexible external gear when the flexible external gear rotates. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1 
     Japanese Unexamined Patent Application Publication No. 2014-206265 
     SUMMARY OF INVENTION 
     Technical Problem 
     The hollow-type rotary actuator described in Patent Document 1 is used, for example, in a joint part of an industrial robot. When the hollow-type rotary actuator described in Patent Document 1 is used in the joint part of an industrial robot, in general, various types of wiring or piping are arranged to pass through the inner circumferential side of the sleeve. In the hollow-type rotary actuator described in Patent Document 1, since the sleeve is fixed to the flexible external gear and the sleeve rotates as the flexible external gear rotates, when this hollow-type rotary actuator is used in the joint part of the industrial robot, an inner circumferential surface of the rotating sleeve may be brought into contact with the wiring or the piping, and the wiring or the piping may be damaged. 
     Therefore, an objective of the present invention is to provide a hollow-type rotary actuator capable of minimizing damage to wiring or piping passing through an inner circumferential side of the rotary actuator more than before when used in a joint part of a robot. Further, another objective of the present invention is to provide a robot having such a rotary actuator. 
     Solution to Problem 
     To solve the above-described problems, a rotary actuator of the present invention includes a hollow motor having a hollow rotary shaft, a hollow reduction gear having a hollow input shaft disposed coaxially with the rotary shaft and connected to the rotary shaft, a cylindrical tubular member disposed on an inner circumferential side of the rotary shaft and the input shaft, and a holding member which holds one end side of the tubular member, wherein the holding member includes a holding portion in which a through-hole communicating with an inner circumferential side of the tubular member is formed, one end side of the tubular member is held by the holding portion, and the other end side of the tubular member is loosely fitted to an output side portion of the hollow reduction gear. 
     In the rotary actuator of the present invention, one end side of the cylindrical tubular member disposed on the inner circumferential side of the rotary shaft of the hollow motor and the input shaft of the hollow reduction gear is rotatably held by the holding portion of the holding member, and the other end side of the tubular member is loosely fitted to the output side portion of the hollow reduction gear. That is, the other end side of the tubular member is held in a state in which it is not fixed to the output side portion of the hollow reduction gear. Thus, in the present invention, even when the output shaft of the hollow reduction gear rotates, the tubular member does not necessarily rotate. Therefore, in the present invention, for example, when the rotary actuator is used in a joint part of a robot, even when wiring or piping is disposed to pass through the inner circumferential side of the tubular member, it is possible to minimize damage to the wiring or the piping passing through the inner circumferential side of the rotary actuator more than before. Further, in the present invention, since the other end side of the tubular member is not fixed to the output side portion of the hollow reduction gear, assembling work of the rotary actuator becomes easier than, for example, a case in which the other end side of the tubular member is fixed to the output side portion of the hollow reduction gear by welding, adhering or the like. 
     In the present invention, the rotary actuator may further include a fixed member fixed to an output shaft of the hollow reduction gear, the fixed member may have an inserted portion which is inserted into an inner circumferential side of the other end side portion of the tubular member, and an inner circumferential surface of the tubular member and an outer circumferential surface of the inserted portion may be in contact with each other. That is, the other end side of the tubular member is held on the output side portion of the hollow reduction gear by the inner circumferential surface of the tubular member and the outer circumferential surface of the inserted portion coming into contact with each other. In this case, it is possible to hold the other end side of the tubular member to the output side portion of the hollow reduction gear with a relatively simple configuration. 
     In the present invention, preferably, the inserted portion may be disposed on an inner circumferential side of the input shaft. With such a configuration, it is possible to reduce a size of the rotary actuator in the axial direction of the input shaft, as compared with a case in which the input shaft and the inserted portion are disposed in a state in which they are displaced from each other in the axial direction of the input shaft. 
     In the present invention, the rotary actuator may further include a fixed member fixed to an output shaft of the hollow reduction gear, the fixed member may include an insertion portion into which the other end side portion of the tubular member is inserted, and an outer circumferential surface of the tubular member and an inner circumferential surface of the insertion portion may be in contact with each other. That is, the other end side of the tubular member may be held on the output side portion of the hollow reduction gear by the outer circumferential surface of the tubular member and the inner circumferential surface of the insertion portion coming into contact with each other. In this case as well, it is possible to hold the other end side of the tubular member to the output side portion of the hollow reduction gear with a relatively simple configuration. 
     In the present invention, the tubular member may be formed of a resin, or the inner circumferential surface of the tubular member may be coated with a resin. With such a configuration, for example, when the rotary actuator is used in the joint part of the robot and the wiring is disposed to pass through the inner circumferential side of the tubular member, it is possible to prevent a short circuit between the tubular member and the wiring even if the wiring slides on the inner circumferential surface of the tubular member and the coating of the wiring disposed on the inner circumferential side of the tubular member is broken. 
     The rotary actuator of the present invention can be used in a robot including a joint part configured by a rotary actuator, and wiring disposed to pass through the inner circumferential side of the tubular member. In this robot, it is possible to minimize the damage to the wiring passing through the inner circumferential side of the rotary actuator more than before. 
     Advantageous Effects of Invention 
     As described above, in the present invention, in the hollow-type rotary actuator, for example, when the rotary actuator is used in the joint part of the robot, damage to the wiring or piping passing through the inner circumferential side of the rotary actuator can be minimized more than before. Further, in the robot of the present invention, it is possible to minimize damage to the wiring passing through the inner circumferential side of the rotary actuator more than before. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front view of an industrial robot according to an embodiment of the present invention. 
         FIG. 2(A)  is a perspective view of the industrial robot shown in  FIG. 1 , and  FIG. 2(B)  is a perspective view showing a state in which the industrial robot shown in  FIG. 2(A)  is operating. 
         FIG. 3  is a longitudinal cross-sectional view of a joint part shown in  FIG. 1 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 
     Schematic Configuration of Industrial Robot 
       FIG. 1  is a front view of an industrial robot  1  according to an embodiment of the present invention.  FIG. 2(A)  is a perspective view of the industrial robot  1  shown in  FIG. 1 , and  FIG. 2(B)  is a perspective view showing a state in which the industrial robot  1  shown in  FIG. 2(A)  is operating.  
     The industrial robot  1  (hereinafter referred to as “robot  1 ”) of the embodiment is an articulated robot used for assembling or manufacturing predetermined products and is installed and used in an assembly line or a manufacturing line. The robot  1  includes a plurality of joint parts  2  and a plurality of arms  3 . In this embodiment, the robot  1  includes six joint parts  2  and two anus  3 . Hereinafter, when the six joint parts  2  are distinguished from each other, the six joint parts  2  are referred to as a “first joint part  2 A,” a “second joint part  2 B,” a “third joint part  2 C,” a “fourth joint part  2 D,” a “fifth joint part  2 E,” and a “sixth joint part  2 F.” Further, in the following description, when the two arms  3  are distinguished from each other, the two arms  3  are referred to as a “first arm  3 A” and a “second arm  3 B.” 
     Further, the robot  1  includes a support member  4  which is connected to the first joint part  2 A to be relatively rotatable. The support member  4  is formed in a flanged cylindrical shape having a flange portion  4   a,  and a through-hole (not shown) penetrating in the axial direction of the support member  4  is formed on the inner circumferential side of the support member  4 . The flange portion  4   a  is formed in an annular shape and forms a bottom surface portion of the robot  1 . The arm  3  is formed in an elongated cylindrical shape. 
     The first joint part  2 A and the second joint part  2 B are connected to be relatively rotatable in the robot  1 , and the second joint part  2 B and a base end of the first arm  3 A are fixed. Further, a tip end of the first arm  3 A and the third joint part  2 C are fixed, the third joint part  2 C and the fourth joint part  2 D are connected to be relatively rotatable, the fourth joint part  2 D and a base end of the second aim  3 B are connected to be relatively rotatable, a tip end of the second arm  3 B and the fifth joint part  2 E are fixed, and the fifth joint part  2 E and the sixth joint part  2 F are connected to be relatively rotatable. A hand, a tool, or the like can be installed on the sixth joint part  2 F to be relatively rotatable. 
     Hereinafter, a specific configuration of the joint part  2  will be described. As shown in  FIG. 1 , in the embodiment, the first joint part  2 A, the second joint part  2 B, and the third joint part  2 C are formed to have the same size, and the fourth joint part  2 D, the fifth joint part  2 E, and the sixth joint part  2 F are formed to have the same size. In addition, the sizes of the first joint part  2 A, the second joint part  2 B, and the third joint part  2 C are larger than the sizes of the fourth joint part  2 D, the fifth joint part  2 E, and the sixth joint part  2 F. However, the first joint part  2 A, the second joint part  2 B, the third joint part  2 C, the fourth joint part  2 D, the fifth joint part  2 E, and the sixth joint part  2 F are formed to have the same configuration, except for the difference in size. 
     Configuration of Joint Part 
       FIG. 3  is a longitudinal cross-sectional view of the joint part  2  shown in  FIG. 1 . Hereinafter, for the sake of convenience of explanation, a Z 1  direction side in  FIG. 3  will be referred to as the “upper” side, and a Z 2  direction side opposite thereto will be referred to as the “lower” side. 
     The joint part  2  includes a motor  7 , a reduction gear  8  connected to the motor  7 , a circuit board  10  to which the motor  7  is electrically connected, and a case body  11  in which the motor  7 , the reduction gear  8 , and the circuit board  10  are accommodated, and the joint part  2  itself is a rotary actuator. That is, the joint part  2  is configured by a rotary actuator. 
     The motor  7  is a hollow motor in which a through-hole is formed in a center in the radial direction and has a hollow rotary shaft  13 . Further, the motor  7  includes a rotor  14  and a stator  15 . The reduction gear  8  is a hollow reduction gear in which a through-hole is formed in a center in the radial direction. The motor  7  and the reduction gear  8  are disposed to overlap in the vertical direction. Specifically, the motor  7  is disposed on the upper side, and the reduction gear  8  is disposed on the lower side. Further, the motor  7  and the reduction gear  8  are disposed coaxially. 
     The reduction gear  8  of the embodiment is a hollow wave gear device and includes a rigid internal gear  16 , a flexible external gear  17 , a wave generating portion  18 , and a cross roller bearing  19 . The wave generating portion  18  includes a hollow input shaft  20  connected to the rotary shaft  13 , and a wave bearing  21  installed on the outer circumference side of the input shaft  20 . In the embodiment, the rigid internal gear  16  serves as an output shaft of the reduction gear  8 . Further, the joint part  2  includes a tubular (more specifically, cylindrical) member  26  disposed on the inner circumferential side of the rotary shaft  13  and the input shaft  20 , and an output side member  27  fixed to the rigid internal gear  16 . 
     As described above, the motor  7  includes the rotor  14  and the stator  15 . The rotor  14  includes the rotary shaft  13 , and a driving magnet  29  fixed to the rotary shaft  13 . The rotary shaft  13  is formed in a substantially cylindrical shape elongated in the vertical direction and disposed so that the axial direction of the rotary shaft  13  and the vertical direction coincide with each other. That is, the vertical direction is the axial direction of the rotary shaft  13  and the axial direction of the rotor  14 . The rotary shaft  13  serves as a back yoke and is formed of a soft magnetic material. The rotary shaft  13  of the embodiment is formed of an iron-based metal such as a steel material. 
     The driving magnet  29  is formed in a cylindrical shape. A length of the driving magnet  29  (a length in the vertical direction) is shorter than that of the rotary shaft  13 , and the driving magnet  29  is fixed to an outer circumferential surface of a lower end side portion of the rotary shaft  13 . In the embodiment, the driving magnet  29  is fixed to the outer circumferential surface of the rotary shaft  13  so that a lower end surface of the rotary shaft  13  and a lower end surface of the driving magnet  29  coincide with each other. 
     The stator  15  is formed in a substantially cylindrical shape as a whole and is disposed on the outer circumferential side of the driving magnet  29  to cover an outer circumferential surface of the driving magnet  29 . An upper end side portion of the rotary shaft  13  protrudes upward from an upper end surface of the stator  15 . The stator  15  includes a driving coil, and a stator core having a plurality of salient poles around which a driving coil is wound via an insulator. The salient poles of the stator core are formed to protrude toward the inner circumferential side, and tip end surfaces of the salient poles face the outer circumferential surface of the driving magnet  29 . The stator  15  is fixed to the case body  11 . 
     As described above, the reduction gear  8  includes the rigid internal gear  16 , the flexible external gear  17 , the wave generating portion  18 , and the cross roller bearing  19 . The rigid internal gear  16  is formed in a substantially flat cylindrical shape and disposed so that the axial direction of the rigid internal gear  16  and the vertical direction coincide with each other. That is, the vertical direction is the axial direction of the rigid internal gear  16  which is the output shaft of the reduction gear  8 . The rigid internal gear  16  is fixed to an inner ring  19   a  of the cross roller bearing  19 . An outer ring  19   b  of the cross roller bearing  19  is fixed to a lower end side portion of the case body  11 , and the rigid internal gear  16  is rotatably held by the lower end side portion of the case body  11  via the cross roller bearing  19 . 
     The flexible external gear  17  is formed in a flanged substantially cylindrical shape having a flange portion  17   a  at an upper end thereof. The flange portion  17   a  is formed in a substantially annular shape, and an outer circumferential side portion of the flange portion  17   a  is fixed to the case body  11 . The rigid internal gear  16  forms a lower end side portion of the reduction gear  8 . The flange portion  17   a  forms an upper end side portion of the reduction gear  8 . Internal teeth are formed on an inner circumferential surface of the rigid internal gear  16 . External teeth meshing with the internal teeth of the rigid internal gear  16  are formed on an outer circumferential surface of the flexible external gear  17  on the lower end side. 
     As described above, the wave generating portion  18  includes the input shaft  20  and the wave bearing  21 . The input shaft  20  is formed in a tubular shape which is elongated as a whole in the vertical direction and is disposed so that the axial direction of the input shaft  20  and the vertical direction coincide with each other. The input shaft  20  is formed of a material having a specific gravity smaller than that of the soft magnetic material forming the rotary shaft  13 . Further, the input shaft  20  is formed of a non-magnetic material. Specifically, the input shaft  20  is formed of an aluminum alloy. A portion of the input shaft  20  other than the lower end side portion is formed in a substantially elongated cylindrical shape. A lower end side portion of the input shaft  20  is an elliptical portion  20   a  in which a shape of an inner circumferential surface thereof when seen in the axial direction of the input shaft  20  is circular and a shape of an outer circumferential surface thereof when seen in the axial direction of the input shaft  20  is elliptical. The input shaft  20  may be formed of a material other than an aluminum alloy as long as it is formed of a material having a specific gravity smaller than that of the soft magnetic material forming the rotary shaft  13 . 
     The rotary shaft  13  and the input shaft  20  are disposed coaxially, and the inner circumferential side of the input shaft  20  communicates with the inner circumferential side of the rotary shaft  13 . An upper end side portion of the input shaft  20  is inserted and fixed into the inner circumferential side of the lower end side portion of the rotary shaft  13 . Specifically, the upper end side portion of the input shaft  20  is inserted and fixed into the inner circumferential side of a portion of the rotary shaft  13  to which the driving magnet  29  is fixed. That is, the rotary shaft  13  has a tubular (more specifically, cylindrical) magnet fixing portion  13   a,  to which the driving magnet  29  is fixed on the outer circumferential side, at the lower end side of the rotary shaft  13 , and the upper end side of the input shaft  20  is inserted and fixed into the inner circumferential side of the magnet fixing portion  13   a.  In addition, the upper end side portion of the input shaft  20  is fixed to the rotary shaft  13  by bonding. In the embodiment, an upper end surface of the driving magnet  29  and an upper end surface of the input shaft  20  are disposed at the same position in the vertical direction. 
     A center portion of the input shaft  20  in the vertical direction is rotatably supported by a bearing  30 . The bearing  30  is a ball bearing. The bearing  30  is installed at a bearing holding member  31 , and the bearing holding member  31  is fixed to the case body  11 . That is, the input shaft  20  is rotatably supported by the bearing  30  installed at the case body  11  via the bearing holding member  31 . The bearing holding member  31  is formed in an annular and flat plate shape and is fixed to the case body  11  to overlap the flange portion  17   a  of the flexible external gear  17  in the vertical direction. 
     The wave bearing  21  is a ball bearing having a flexible inner ring and an outer ring. The wave bearing  21  is disposed along an outer circumferential surface of the elliptical portion  20   a  and is flexed in an elliptical shape. The lower end side portion of the flexible external gear  17  on which the external teeth are formed is disposed on the outer circumferential side of the wave bearing  21  to surround the wave bearing  21 , and this portion is flexed in an elliptical shape. The external teeth of the flexible external gear  17  mesh with the internal teeth of the rigid internal gear  16  at two places of the lower end side portion of the flexible external gear  17 , which is flexed in the elliptical shape, in the long axis direction. 
     The output side member  27  is formed in a flanged substantially cylindrical shape having a flange portion  27   a  and a cylindrical portion  27   b.  The output side member  27  is disposed so that the axial direction of the output side member  27  and the vertical direction coincide with each other, and a through-hole  27   c  penetrating in the vertical direction is formed on the inner circumferential side of the output side member  27 . The flange portion  27   a  is formed in a flat plate shape and an annular shape and is connected to a lower end of the cylindrical portion  27   b.  The flange portion  27   a  is fixed to the rigid internal gear  16  so that an upper surface of the flange portion  27   a  is in contact with a lower surface of the rigid internal gear  16 . Further, the flange portion  27   a  is disposed below a lower end of the case body  11  and disposed outside the case body  11 . 
     A small diameter portion  27   d  having an outer diameter smaller than that of the lower end side portion of the cylindrical portion  27   b  is formed on the upper end side of the cylindrical portion  27   b,  and an annular stepped surface  27   e  orthogonal in the vertical direction is formed on the outer circumferential side of an upper end side portion of the cylindrical portion  27   b.  The small diameter portion  27   d  is inserted into the inner circumferential side of a lower end side portion of the tubular member  26 , and a lower end surface of the tubular member  26  faces the stepped surface  27   e.  Further, the through-hole  27   c  communicates with the inner circumferential side of the tubular member  26 . 
     In the embodiment, an inner circumferential surface of the tubular member  26  and an outer circumferential surface of the small diameter portion  27   d  are in contact with each other. Further, as the inner circumferential surface of the tubular member  26  and the outer circumferential surface of the small diameter portion  27   d  come into contact with each other, the lower end side of the tubular member  26  is held by the output side member  27 . That is, as the inner circumferential surface of the tubular member  26  and the outer circumferential surface of the small diameter portion  27   d  come into contact with each other, the lower end side of the tubular member  26  is held by an output side portion of the reduction gear  8  which is configured with the rigid internal gear  16  as the output shaft of the reduction gear  8  and the output side member  27 , and the lower end side of the tubular member  26  is loosely fitted to the output side portion of the reduction gear  8 . The output side member  27  of the embodiment is a fixed member fixed to the rigid internal gear  16  which is the output shaft of the reduction gear  8 , and the small diameter portion  27   d  is an inserted portion which is inserted into the inner circumferential side of the other end side portion of the tubular member  26 . The loosely fitted state is that the lower end side of the tubular member  26  is held in a state in which it is not fixed to the output side portion of the reduction gear  8 . 
     The upper end side portion of the cylindrical portion  27   b  is disposed on the inner circumferential side of the lower end side portion of the input shaft  20 . That is, the small diameter portion  27   d  is disposed on the inner circumferential side of the lower end side portion of the input shaft  20 . The bearing  34  is disposed between an outer circumferential surface of the cylindrical portion  27   b  and an inner circumferential surface of the lower end side portion of the input shaft  20 . The bearing  34  is a ball bearing. 
     The tubular member  26  is formed of an aluminum alloy. Further, the tubular member  26  is formed in a cylindrical shape elongated in the vertical direction and disposed so that the axial direction of the tubular member  26  and the vertical direction coincide with each other. That is, the vertical direction is the axial direction of the tubular member  26 . The tubular member  26  may be formed of a metal other than an aluminum alloy. 
     As described above, the tubular member  26  is inserted into the inner circumferential side of the rotary shaft  13  and the input shaft  20 . An upper end surface of the tubular member  26  is disposed above an upper end surface of the rotary shaft  13 , and the lower end surface of the tubular member  26  is disposed above a lower end surface of the input shaft  20 . Also, as described above, the small diameter portion  27   d  of the output side member  27  is inserted into the inner circumferential side of the lower end side portion of the tubular member  26 , the lower end surface of the tubular member  26  faces the stepped surface  27   e,  and the lower end side of the tubular member  26  is held by the output side member  27 . Specifically, the lower end side of the tubular member  26  is held by the output side member  27  to enable relative rotation of the tubular member  26  with respect to the output side member  27  with the vertical direction as the axial direction of the rotation. 
     The upper end side of the tubular member  26  is held by the holding member  32 . The holding member  32  is fixed to a support column  33 , and the support column  33  is fixed to the case body  11 . That is, the holding member  32  is fixed to the case body  11  via the support column  33 . The holding member  32  has a cylindrical holding portion  32   a  which holds the upper end side of the tubular member  26 . The holding portion  32   a  is disposed so that the axial direction of the holding portion  32   a  and the vertical direction coincide with each other, and a through-hole  32   b  penetrating in the vertical direction is formed on the inner circumferential side of the holding portion  32   a.  The support column  33  may be fixed to the circuit board  10 . 
     A large diameter portion  32   c  having an inner diameter larger than that of the upper end side of the holding portion  32   a  is formed on the lower end side of the holding portion  32   a,  and an annular stepped surface  32   d  orthogonal in the vertical direction is formed on the inner circumferential side of a lower end side portion of the holding portion  32   a.  The upper end side of the tubular member  26  is inserted into the inner circumferential side of the large diameter portion  32   c,  and the upper end surface of the tubular member  26  faces the stepped surface  32   d.  In addition, the upper end side of the tubular member  26  is held by the holding portion  32   a  to enable rotation of the tubular member  26  with the vertical direction as the axial direction of the rotation. The through-hole  32   b  of the holding portion  32   a  communicates with the inner circumferential side of the tubular member  26 . That is, the through-hole  32   b  communicating with the inner circumferential side of the tubular member  26  is formed in the holding member  32 . 
     The case body  11  includes a case main body  41  in which upper and lower ends thereof open, and a cover  42  which closes an opening on the upper end side of the case main body  41 . The opening on the lower end side of the case main body  41  is closed by the reduction gear  8 . An opening portion  41   a  opening in a direction orthogonal to the vertical direction is formed in a side surface of the case main body  41 . That is, the opening portion  41   a  opening in the direction orthogonal to the vertical direction is formed in the case body  11 . The opening portion  41   a  is formed to pass through the side surface portion of the case main body  41 . 
     The circuit board  10  is a rigid board such as a glass epoxy board and is formed in a flat plate shape. This circuit board  10  is fixed to the case body  11  so that the thickness direction of the circuit board  10  and the vertical direction coincide with each other. Further, the circuit board  10  is fixed to the upper end side of the case body  11 . An upper end of the tubular member  26  is disposed above an upper surface of the circuit board  10 . A motor driving circuit for driving the motor  7 , and so on is mounted on the circuit board  10 . 
     In addition, at least two connectors (not shown) are mounted on the circuit board  10 . Wiring  60  connected to one of the two connectors is disposed to pass through the inner circumferential side of the tubular member  26  and then is drawn out from the through-hole  27   c  of the output side member  27 . That is, the wiring  60  is disposed to pass through the inner circumferential side of the rotary shaft  13  and the input shaft  20  and then drawn out from the through-hole  27   c  of the output side member  27 . Further, the wiring  61  connected to the other one of the two connectors is drawn out from the opening portion  41   a  of the case body  11 . 
     Connecting Structure of Joint Part  2  and Arm  3  of Robot  1   
     As a connecting structure of the joint part  2  and the arm  3  of the robot  1 , for example, each of the joint parts  2  and the arms  3  are connected as described below so that the robot  1  can perform an operation shown in  FIG. 2(B) . 
     In the following description, the axial direction of the rigid internal gear  16  of the first joint part  2 A is referred to as “the axial direction of the first joint part  2 A,” the axial direction of the rigid internal gear  16  of the second joint part  2 B is referred to as “the axial direction of the second joint part  2 B,” the axial direction of the rigid internal gear  16  of the third joint part  2 C is referred to as “the axial direction of the third joint part  2 C,” the axial direction of the rigid internal gear  16  of the fourth joint part  2 D is referred to as “the axial direction of the fourth joint part  2 D,” the axial direction of the rigid internal gear  16  of the fifth joint part  2 E is referred to as “the axial direction of the fifth joint part  2 E,” and the axial direction of the rigid internal gear  16  of the sixth joint part  2 F is referred to as “the axial direction of the sixth joint part  2 F.” 
     First, the support member  4  and the first joint part  2 A are connected to each other by fixing an end surface of the support member  4  on the side, at which the flange portion  4   a  is not formed, to the flange portion  27   a  of the first joint part  2 A. That is, the support member  4  and the first joint part  2 A are connected so that the axial direction of the first joint part  2 A and the axial direction of the support member  4  coincide with each other. The first joint part  2 A and the second joint part  2 B are connected so that the axial direction of the first joint part  2 A and the axial direction of the second joint part  2 B are orthogonal to each other. Also, the side surface of the case main body  41  of the first joint part  2 A on which the opening portion  41   a  is formed is fixed to the flange portion  27   a  of the second joint part  2 B. 
     The second joint part  2 B and the first arm  3 A are connected so that the axial direction of the second joint part  2 B and the longitudinal direction (axial direction) of the first arm  3 A are orthogonal to each other. Also, the base end of the first arm  3 A is fixed to the side surface of the case main body  41  of the second joint part  2 B in which the opening portion  41   a  is formed. The first arm  3 A and the third joint part  2 C are connected so that the longitudinal direction of the first arm  3 A and the axial direction of the third joint part  2 C are orthogonal to each other. Further, the tip end of the first arm  3 A is fixed to the side surface of the case main body  41  of the third joint part  2 C in which the opening portion  41   a  is formed. 
     The third joint part  2 C and the fourth joint part  2 D are connected so that the axial direction of the third joint part  2 C and the axial direction of the fourth joint part  2 D are orthogonal to each other. Also, the side surface of the case main body  41  of the fourth joint part  2 D in which the opening portion  41   a  is formed is fixed to the flange portion  27   a  of the third joint part  2 C. More specifically, the side surface of the case main body  41  of the fourth joint part  2 D in which the opening portion  41   a  is formed is fixed to the flange portion  27   a  of the third joint part  2 C via a connecting member  63  fixed to the side surface of the case main body  41  of the fourth joint part  2 D in which the opening portion  41   a  is formed. The connecting member  63  is formed in a flanged cylindrical shape having a flange portion  63   a  fixed to the flange portion  27   a  of the third joint part  2 C. 
     The fourth joint part  2 D and the second arm  3 B are connected so that the axial direction of the fourth joint part  2 D and the longitudinal direction of the second arm  3 B coincide with each other. Also, the base end of the second arm  3 B is fixed to the flange portion  27   a  of the fourth joint part  2 D. A flange portion  3   a  for fixing the base end of the second arm  3 B to the flange portion  27   a  of the fourth joint part  2 D is formed at the base end of the second arm  3 B, and the flange portion  27   a  of the fourth joint part  2 D and the flange portion  3   a  are fixed to each other. 
     The second arm  3 B and the fifth joint part  2 E are connected so that the longitudinal direction of the second arm  3 B and the axial direction of the fifth joint part  2 E are orthogonal to each other. Also, the tip end of the second arm  3 B is fixed to the side surface of the case main body  41  of the fifth joint part  2 E in which the opening portion  41   a  is formed. The fifth joint part  2 E and the sixth joint part  2 F are connected so that the axial direction of the fifth joint part  2 E and the axial direction of the sixth joint part  2 F are orthogonal to each other. Further, the side surface of the case main body  41  of the sixth joint part  2 F in which the opening portion  41   a  is formed is fixed to the flange portion  27   a  of the fifth joint part  2 E. 
     Main Effect of This Embodiment 
     As described above, in the embodiment, the upper end side of the tubular member  26  is held by the holding portion  32   a  to enable the rotation of the tubular member  26  with the vertical direction as the axial direction of the rotation. Further, in the embodiment, the lower end side of the tubular member  26  is loosely fitted to the output side member  27 . Thus, in the embodiment, even when the output side member  27  fixed to the rigid internal gear  16  rotates together with the rigid internal gear  16 , the tubular member  26  does not necessarily rotate. Therefore, in the embodiment, damage to the wiring  60  passing through the inner circumferential side of the tubular member  26  can be minimized more than before. Further, in the embodiment, since the lower end side of the tubular member  26  is not fixed to the output side member  27 , an assembling work of the joint part  2  becomes easier than a case in which the lower end side of the tubular member  26  is fixed to the output side member  27  by welding, adhering or the like. 
     In the embodiment, the lower end side of the tubular member  26  is held by the output side member  27  by the inner circumferential surface of the tubular member  26  and the outer circumferential surface of the small diameter portion  27   d  of the output side member  27  coming into contact with each other. Thus, in the embodiment, it is possible to hold the lower end side of the tubular member  26  to the output side member  27  with a relatively simple configuration. Further, in the embodiment, since the small diameter portion  27   d  is disposed on the inner circumferential side of the lower end side portion of the input shaft  20 , the joint part  2  can be downsized in the vertical direction as compared with a case in which the small diameter portion  27   d  and the input shaft  20  are disposed in a state in which they are displaced from each other in the vertical direction. 
     Another Embodiment 
     The above-described embodiment is an example of a preferred embodiment of the present invention, but the present invention is not limited thereto, and various modifications can be made without changing the gist of the present invention. 
     In the above-described embodiment, the tubular member  26  is formed of a metal such as an aluminum alloy, but the tubular member  26  may be formed of a resin. Further, a resin may be coated on the inner circumferential surface of the metallic tubular member  26 . In this case, even when the wiring  60  slides on the inner circumferential surface of the tubular member  26  and the coating of the wiring  60  disposed on the inner circumferential side of the tubular member  26  is broken, it is possible to prevent a short circuit between the tubular member  26  and the wiring  60 . 
     Also, when the tubular member  26  is formed of a resin, it is preferable that the tubular member  26  be formed of a resin having excellent slidability. For example, the tubular member  26  is preferably formed of polytetrafluoroethylene or polyacetal. Further, when the inner circumferential surface of the tubular member  26  is coated with a resin, it is preferable that a resin having excellent slidability such as polytetrafluoroethylene be coated on the inner circumferential surface of the tubular member  26 . In this case, even when the wiring  60  slides on the inner circumferential surface of the tubular member  26 , the coating of the wiring  60  is not easily broken. In the case in which the tubular member  26  is formed of a resin, the tubular member  26  and the holding member  32  may be integrally molded. 
     In the above-described embodiment, as the inner circumferential surface of the tubular member  26  and the outer circumferential surface of the small diameter portion  27   d  of the output side member  27  come into contact with each other, the lower end side of the tubular member  26  is held by the output side member  27 . Besides this, for example, as an insertion portion into which the lower end side portion of the tubular member  26  is inserted is formed on the upper end side of the cylindrical portion  27   b  of the output side member  27  and an inner circumferential surface of the insertion portion and the outer circumferential surface of the lower end side portion of the tubular member  26  come into contact with each other, the lower end side of the tubular member  26  may be held by the output side member  27 . Even in this case, it is possible to hold the lower end side of the tubular member  26  to the output side member  27  with a relatively simple configuration. 
     In the above-described embodiment, although the lower end side of the tubular member  26  is loosely fitted to the output side member  27 , the lower end side of the tubular member  26  may be loosely fitted to the rigid internal gear  16  which is the output shaft of the reduction gear  8 . Further, in the above-described embodiment, the small diameter portion  27   d  of the output side member  27  is disposed on the inner circumferential side of the lower end side portion of the input shaft  20 , but the small diameter portion  27   d  may be disposed below the input shaft  20 . 
     In the above-described embodiment, the rigid internal gear  16  serves as the output shaft of the reduction gear  8 , but the flexible external gear  17  may serve as the output shaft of the reduction gear  8 . In this case, the rigid internal gear  16  is fixed to the case body  11 , and the flexible external gear  17  is fixed to the inner ring  19   a  of the cross roller bearing  19 . Further, in the above-described embodiment, the reduction gear  8  is a hollow wave gear device, but the reduction gear  8  may be a hollow reduction gear other than the hollow wave gear device. Furthermore, in the above-described embodiment, the motor  7  is a so-called inner rotor type motor, but the motor  7  may be an outer rotor type motor. 
     In the above-described embodiment, although the robot  1  includes six joint parts  2 , the number of the joint parts  2  provided in the robot  1  may be five or less or may be seven or more. Further, in the above-described embodiment, although the robot  1  includes two arms  3 , the number of the arms  3  provided in the robot  1  may be one or may be three or more. Furthermore, in the above-described embodiment, an air piping may be disposed to pass through the inner circumferential side of the joint part  2  (that is, the inner circumferential side of the tubular member  26  (the inner circumferential side of the rotary shaft  13  and the input shaft  20 )). 
     In the above-described embodiment, although the joint part  2  of the robot  1  is configured by the rotary actuator having the motor  7 , the reduction gear  8  and so on, the rotary actuator may be used other than for the joint part  2  of the robot  1 . For example, the rotary actuator may be used in a driving part of a θ stage (rotary stage) or the like. Further, in the above-described embodiment, the robot  1  is an industrial robot, but the robot  1  can be applied to various uses. For example, the robot  1  may be a service robot. 
     REFERENCE SIGNS LIST 
       1  Robot (industrial robot) 
       2  Joint part (rotary actuator) 
       7  Motor (hollow motor) 
       8  Reduction gear (hollow reduction gear) 
       13  Rotary shaft 
       16  Rigid internal gear (output shaft of hollow reduction gear, a part of output side portion of hollow reduction gear) 
       20  Input shaft 
       26  Tubular member 
       27  Output side member (fixed member, a part of output side portion of hollow reduction gear) 
       27   d  Small diameter portion (inserted portion) 
       32  Holding member 
       32   a  Holding portion 
       32   b  Through-hole 
       60  Wiring