Patent Publication Number: US-2023142018-A1

Title: Rotating shaft structure comprising plurality of speed reducers, and manufacturing method therefor

Description:
TECHNICAL FIELD 
     The present invention relates to a rotating shaft structure and a manufacturing method therefor, in particular, relates to a rotating shaft structure having a plurality of speed reducers and a manufacturing method therefor. 
     BACKGROUND ART 
     Generally, for rotating shafts of machines such as robots, construction machines, vehicles, and aircraft, a large (large capacity) speed reducer is used because the load applied to the speed reducer positioned between the links increases w % ben a load of 1 ton or more is applied. Since the large-capacity speed reducer has a large outer shape, the rotating shaft structure of the machine also becomes large. As a method for miniaturizing the rotating shaft structure, a structure has been proposed in which two small (small capacity) speed reducers are arranged so as to sandwich one link from both sides thereof, and each speed reducer is connected to the other link. (e.g., see Patent Literature 1 and 2). With such a structure, the rotating shaft structure can be miniaturized without using a large-capacity speed reducer. 
     Patent Literature 3 describes that, in a wrist mechanism of an industrial robot, a first speed reducer and a second speed reducer are arranged on both sides of an arm, pulleys are fixed to input shafts of the first and second speed reducers, respectively, and the pulleys are configured to be driven by two drive motors via a timing belt wound around the pulley. 
     Patent Literature 4 describes that, in a deceleration drive device, a collar having a flange portion is fixed to a motor housing by a bolt, a bearing for holding a rotating hub is arranged on the collar, a support member is attached to the flange portion by a bolt, a shim is positioned between the support member and the flange portion, so that an attachment gap of the bearing is adjusted by adjusting the shim. 
     the parts and adjusting the shim. 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] WO 2007/072546 A1 
         [PTL 2] KR 10-1881350 A 
         [PTL 3] JP 1994 (H06)-312394 A 
         [PTL 4] JP 1986 (S61)-010238 U 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     When assembling a rotating shaft structure including a plurality of speed reducers, it is necessary to previously adjust the positional relationship between a plurality of attachment holes on the speed reducer side and attachment holes on the link side. However, when a drive shaft common to multiple reducers is inserted while being rotated, an input shaft of the reducer will be rotated and the positional relationship between the attachment hole on the speed reducer side and the attachment hole on the link side may be shifted. As a result, there arises a problem that the rotating shaft structure cannot be easily assembled. Even when a separate drive shaft is inserted into each of the multiple reducers, the input shaft of the reducer may be rotated by inserting the drive shaft while rotating, whereby the positional relationship between the speed reducer side attachment hole and the link side attachment hole may be shifted. 
     Therefore, there is a demand for a technique for improving the manufacturing efficiency of a rotating shaft structure having a plurality of speed reducers. 
     Solution to Problem 
     One aspect of the present disclosure provides a rotating shaft structure comprising: a first link; a second link connected to the first link; and a plurality of speed reducers positioned between the first link and the second link, wherein one of a speed reducer side attachment hole and a first link side attachment hole configured to connect the speed reducer to the first link is larger than the other attachment hole or an elongate hole. 
     Another aspect of the present disclosure provides a manufacturing method of a rotating shaft structure comprising a first link, a second link connected to the first link, and a plurality of speed reducers positioned between the first link and the second link, the method comprising the steps of forming one of a speed reducer side attachment hole and a first link side attachment hole configured to connect the speed reducer to the first link so that the one attachment hole is larger than the other attachment hole or an elongate hole; previously adjusting the positional relationship between the speed reducer side attachment hole and the first link side attachment hole by attaching the plurality of speed reducers to the second link; attaching one of the speed reducers attached to the second link to the first link; inserting a drive shaft configured to drive the speed reducer into the speed reducer while rotating the drive shaft; and attaching the remaining speed reducer to the first link while a position of the speed reducer side attachment hole is displaced due to the insertion of the drive shaft. 
     Advantageous Effects of Invention 
     According to the aspect of the present disclosure, the speed reducer can be attached to the first link even when the position of the speed reducer side attachment hole is displaced due to the insertion of the drive shaft. As a result, it is possible to improve the manufacturing efficiency of the rotating shaft structure having the plurality of speed reducers. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a side view showing an example of a machine having a rotating shaft structure. 
         FIG.  2 A  is a plan view showing an example of a speed reducer. 
         FIG.  2 B  is a cross-sectional view along a IIB-IIB line showing the example of the speed reducer. 
         FIG.  3    is a cross-sectional view showing a part of the rotating shaft structure according to an embodiment. 
         FIG.  4    is a side view along a IV-IV line showing the rotating shaft structure according to the embodiment. 
         FIG.  5    is a cross-sectional view showing a part of a modification of the rotating shaft structure. 
         FIG.  6    is a side view along a VI-VI line showing the modification of the rotating shaft structure. 
         FIG.  7    is a cross-sectional view showing a part of another modification of the rotating shaft structure. 
         FIG.  8    is a side view along a VIII-VIII line showing the other modification of the rotating shaft structure. 
         FIG.  9    is a cross-sectional view showing a part of a further modification of the rotating shaft structure. 
         FIG.  10    is a side view along a X-X line showing the further modification of the rotating shaft structure. 
         FIG.  11    is a cross-sectional view showing a part of a still further modification of the rotating shaft structure. 
         FIG.  12    is a cross-sectional view showing an example of the rotating shaft structure applied to another joint shaft. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The embodiments of the present disclosure will be described in detail below with reference to the attached drawings. In the drawings, identical or similar constituent elements have been assigned the same or similar reference signs. Furthermore, the embodiments described below do not limit the technical scope of the invention described in the claims or the definitions of the terms. 
       FIG.  1    shows an example of a machine  2  having a rotating shaft structure  1 . The rotating shaft structure  1  is, for example, a joint structure of a robot, but may be a rotating shaft structure in another machine  2  such as a construction machine, a vehicle, or an aircraft. The rotating shaft structure  1  includes a first link  10 , a second link  20  connected to the first link  10 , and a plurality of speed reducers  30  positioned between the first link  10  and the second link  20 . For example, the rotating shaft structure  1  is configured to rotate about a rotation axis J 2  of the robot, the first link  10  is a rotation base configured to rotate about a vertical axis, and the second link  20  is a first arm configured to rotate about a horizontal axis. Alternatively, note that the first link  10  and the second link  20  may be opposite members, in which case the first link  10  may be the first arm and the second link  20  may be the rotation base, for example. 
       FIGS.  2 A and  2 B  show an example of the speed reducer  30 . The speed reducer  30  includes an input shaft  31  and an output shaft  32 . The input shaft  31  is attached with an input shaft side wheel  33  and inputs power via the input shaft side wheel  33 . The input shaft side wheel  33  may be a gear configured to engage with a drive shaft side wheel described later, but may be a pulley or the like around which a belt, a cable, etc., is wound The output shaft  32  includes an inner output shaft  34  and an outer output shaft  35 . For example, the inner output shaft  34  may be a shaft configured to rotate inward, and the outer output shaft  35  may be a case configured to rotate outward. When the inner output shaft  34  is fixed so as not to rotate, the power of the input shaft  31  is transmitted to the outer output shaft  35  and the outer output shaft  35  is rotated to output. When the outer output shaft  35  is fixed so as not to rotate, the power of the input shaft  31  is transmitted to the inner output shaft  34  and the inner output shaft  34  is rotated to output. In order to attach the inner output shaft  34  or the outer output shaft  35  to the first link  10  or the second link  20 , the inner output shaft  34  or the outer output shaft  35  has one or more speed reducer side attachment hole  36  or  37 , respectively, to which a screw such as a bolt can be fastened. For example, the speed reducer side attachment holes  36  and  37  may be arranged at predetermined intervals in the circumferential direction of the speed reducer  30 . 
       FIGS.  3  and  4    show the rotating shaft structure  1  in the present embodiment. As shown in  FIG.  3   , the rotating shaft structure  1  has the first link  10 , the second link  20  connected to the first link  10 , and the plurality of speed reducers  30  positioned between the first link  10  and the second link  20 . For example, the first link  10  may have a U-shaped portion, and the second link  20  may have an I-shaped portion. The first link  10  has a first link side attachment hole  11  for connecting the speed reducer  30  to the first link  10 . The second link  20  has a second link side attachment hole  21  for connecting the speed reducer  30  to the second link  20 . Although the plurality of speed reducers  30  are arranged on both sides of the second link  20 , they may be arranged on one side of the second link  20 . When the plurality of speed reducers  30  are arranged on one side of the second link  20 , the first link  10  may have an L-shaped portion instead of the U-shaped portion. Further, two or more speed reducers  30  may be arranged on each of both sides of the second link  20 , or three or more speed reducers  30  may be arranged on one side of the second link  20 . 
     This rotating shaft structure  1  is a tandem drive type and further includes a drive shaft  40  common to the plurality of speed reducers  30 , but may be another type in which the plurality of speed reducers  30  are driven by separate drive shafts. The drive shaft  40  has a drive shaft side wheel (not shown) linked to the input shaft side wheel  33  of the speed reducer  30 . The drive shaft side wheel may be a gear configured to engage with the input shaft side wheel  33 , but may be a pulley or the like around which a belt, a cable, etc., is wound. The drive shaft  40  is inserted into the plurality of speed reducers  30  to transmit a common driving force to the plurality of speed reducers  30 . In this rotating shaft structure  1 , the inner output shafts  34  of the plurality of speed reducers  30  are fixed to the first link  10 , the outer output shafts  35  of the plurality of speed reducers  30  rotate, and the second link  20  rotates relative to the first link  10 . For example, when the drive shaft  40  is inserted into the plurality of speed reducers  30  from the left side of  FIG.  3    while being rotated, the input shaft  31  of the speed reducer  30  on the right side may be rotated, whereby the positional relationship between the speed reducer side attachment hole  36  and the first link side attachment hole  11  may be shifted. In order that the speed reducer  30  can be attached to the first link  10  even when the positional relationship between the speed reducer side attachment hole  36  and the first link side attachment hole  11  is deviated, it is preferable that the first link side attachment hole  11  be larger than the speed reducer side attachment hole  36  or an elongate hole as shown in  FIG.  4   , otherwise, the speed reducer side attachment hole  36  be larger than the first link side attachment hole  11  or an elongate hole. The location where these holes are formed into large or elongate holes may be only the place where the speed reducer  30  is finally fastened (in the example of  FIG.  3   , between the speed reducer  30  on the right side and the first link  10 ). Further, as shown in  FIG.  4   , it is preferable that the elongate hole be curved and extended in the circumferential direction of the speed reducer  30 . 
     The manufacturing method of the rotating shaft structure  1  shown in  FIG.  3    is, for example, as follows. It should be noted that  FIG.  3    shows the following step 5. 
     (Step 1) One of the speed reducer side attachment hole  36  and the first link side attachment hole  11  for connecting the speed reducer  30  to the first link  10  is formed larger than the other or an elongate hole. 
     (Step 2) The two speed reducers  30  are attached to the second link  20 , and the positional relationship between the speed reducer side attachment hole  36  and the first link side attachment hole  11  is previously adjusted. 
     (Step 3) One of the two speed reducers  30  attached to the second link  20  (the speed reducer  30  on the left side in the example of  FIG.  3   ) is attached to the first link  10 . 
     (Step 4) The drive shaft  40  for driving the speed reducer  30  is inserted into the speed reducer  30  while rotating the drive shaft  40 . The drive shaft  40  is common to the plurality of speed reducers  30 , but may be a separate drive shaft. 
     (Step 5) The remaining speed reducer of the two speed reducers  30  (the speed reducer  30  on the right side in the example of  FIG.  3   ) is attached to the first link  10 , while the position of the speed reducer side attachment hole  36  is displaced due to the insertion of the drive shaft  40 . In this regard, since one of the first link side attachment hole  11  and the speed reducer side attachment hole  36  is larger than the other or the elongate hole, the speed reducer  30  can be attached to the first link  10 , even when the positional relationship between the speed reducer side attachment hole  36  and the first link side attachment hole  11  is shifted. 
     Since the axial dimensions of the speed reducer  30  may vary depending on individual differences, the gap between the first link  10 , the second link  20  and the speed reducer  30  may be narrow, and thus the speed reducer  30  and the first link  10  may interfere with each other. For this reason, it is common to slightly increase the gap between the first link  10  and the second link  20 . However, when the speed reducer  30  is forcibly attached to the first link  10  with the gap formed, an excessive tensile force may be generated in the axial direction of the speed reducer  30 , resulting in early damage of the speed reducer  30 . Therefore, it is preferable that the rotating shaft structure  1  further have a shim  50  configured to adjust the gap between the first link  10 , the second link  20  and the speed reducer  30 . The shim  50  may be a disk shape or an annular shape, and may be provided with an insertion hole  51  through which a screw such as a bolt is inserted. The insertion hole  51  may have a diameter through which a screw such as a bolt can be inserted, but may have a large diameter or an elongated hole such as the first link side attachment hole  11  or the speed reducer side attachment hole  36 . 
     The shim  50  may be positioned at the place where the speed reducer  30  is finally fastened (between the speed reducer  30  on the right side and the first link  10  in the example of  FIG.  3   ), whereas the shim  50  may be positioned between the speed reducer  30  and the second link  20 . Alternatively, when the plurality of speed reducers  30  are provided on one side or both sides of the second link  20 , the shims  50  may be positioned between the plurality of speed reducers  30 . In the former case, shims  50  having different types of thicknesses may be prepared in advance, and then the shim  50  having the required thickness may be appropriately selected and positioned before the remaining speed reducer  30  is attached to the first link  10  (step 5). In the latter case, before manufacturing the rotating shaft structure  1 , the thickness required for the shim  50  is previously checked to prepare a predetermined shim  50 , and then the predetermined shim  50  may be positioned before the two speed reducers  30  are attached to the second link  20  (step 2). 
       FIGS.  5  and  6    show a modification of the rotating shaft structure  1 . This rotating shaft structure  1  is different from the above in that the speed reducer  30  is first attached to the first link  10  and then the second link  20  is attached. Further, this rotating shaft structure  1  is different from the above in that the first link  10  is configured to be separable into two portions so that the input shaft side wheel  33  of the speed reducer  30  does not interfere with the second link  20  when the second link  20  is attached. For example, in the example of  FIG.  5   , the two portions are an L-shaped portion and an I-shaped portion, but two L-shaped portions may be used. Further, in this rotating shaft structure  1 , the place where the speed reducer  30  is finally fastened is between the second link  20  and the speed reducer  30  (the speed reducer  30  on the right side in the example of  FIG.  5   ). Therefore, it is preferable that the second link side attachment hole  21  be larger than the speed reducer side attachment hole  37  or an elongate hole as shown in  FIG.  6   , or the speed reducer side attachment hole  37  be larger than the second link side attachment hole  21  or an elongate hole. 
     The manufacturing method of the rotating shaft structure  1  shown in  FIG.  5    is, for example, as follows. It should be noted that  FIG.  5    shows the following step 3-1. 
     (Step 0) The first link  10  is formed so that it can be separated into two portions. 
     (Step 1) One of the speed reducer side attachment hole  37  and the second link side attachment hole  21  for connecting the speed reducer  30  to the second link  20  is formed larger than the other or an elongate hole. 
     (Step 2) The two speed reducers  30  are attached to the first link  10 , and the positional relationship between the speed reducer side attachment hole  37  and the second link side attachment hole  21  is previously adjusted. 
     (Step 3) One of the two speed reducers  30  attached to the first link  10  (the speed reducer  30  on the left side in the example of  FIG.  5   ) is attached to the second link  20 . 
     (Step 3-1) The two portions of the first link  10  are contacted to each other. This step may be performed after the step of inserting the drive shaft  40  into the speed reducer  30  (step 4). In this case, the two portions of the first link  10  are contacted to each other during the drive shaft  40  is rotated. 
     (Step 4) The drive shaft  40  for driving the speed reducer  30  is inserted into the speed reducer  30  while rotating the drive shaft  40 . The drive shaft  40  is common to the plurality of speed reducers  30 , but may be a separate drive shaft. 
     (Step 5) The remaining speed reducer of the two speed reducers  30  (the speed reducer  30  on the right side in the example of  FIG.  5   ) is attached to the second link  20 , while the position of the speed reducer side attachment hole  37  is displaced due to the insertion of the drive shaft  40 . In this regard, since one of the speed reducer side attachment hole  37  and the second link side attachment hole  21  is larger than the other or the elongate hole, the speed reducer  30  can be attached to the second link  20 , even when the positional relationship between the speed reducer side attachment hole  37  and the second link side attachment hole  21  is shifted. 
     In the rotating shaft structure as shown in  FIG.  5   , before manufacturing the rotating shaft structure  1 , the thickness required for the shim  50  is previously checked to prepare a predetermined shim  50 , and then the predetermined shim  50  may be positioned before the two speed reducers  30  are attached to the first link  10  (step 2). Alternatively, when the shim  50  is positioned between the second link  20  and the speed reducer  30  (the speed reducer  30  on the right side in the example of  FIG.  5   ), shims  50  having different types of thicknesses may be prepared in advance, and then the shim  50  having the required thickness may be appropriately selected and positioned before the remaining speed reducer  30  is attached to the second link  20  (step 5). 
       FIGS.  7  and  8    show another modification of the rotating shaft structure  1 . This rotating shaft structure  1  is different from the above in that the outer output shaft  35  of the speed reducer  30  is fixed to the first link  10 , and the inner output shaft  34  is rotated. Further, in this rotating shaft structure  1 , since the speed reducer  30  is attached to the second link  20  in advance, the first link  10  is configured to be separable into two portions so that the input shaft side wheel  33  of the speed reducer  30  does not interfere with the first link  10 . Further, in this rotating shaft structure  1 , the place where the speed reducer  30  is finally fastened is between the first link  10  and the speed reducer  30  (the speed reducer  30  on the right side in the example of  FIG.  7   ). Therefore, it is preferable that the speed reducer side attachment hole  37  be larger than the first link side attachment hole  11  or an elongate hole as shown in  FIG.  8   , or the first link side attachment hole  11  be larger than the speed reducer side attachment hole  37  or an elongate hole. 
     The manufacturing method of the rotating shaft structure  1  shown in  FIG.  7    is, for example, as follows. It should be noted that  FIG.  7    shows the following step 3-1. 
     (Step 0) The first link  10  is formed so that it can be separated into two portions. Although the two portions are the L-shaped portion and the I-shaped portion in the example of  FIG.  7   , two L-shaped portions may be used. 
     (Step 1) One of the speed reducer side attachment hole  37  and the first link side attachment hole  11  for connecting the speed reducer  30  to the first link  10  is formed larger than the other or an elongate hole. 
     (Step 2) The two speed reducers  30  are attached to the second link  20 , and the positional relationship between the speed reducer side attachment hole  37  and the first link side attachment hole  11  is previously adjusted. 
     (Step 3) One of the two speed reducers  30  attached to the second link  20  (the speed reducer  30  on the left side in the example of  FIG.  7   ) is attached to the first link  10 . 
     (Step 3-1) The two portions of the first link  10  are contacted to each other. This step may be performed after the step of inserting the drive shaft  40  into the speed reducer  30  (step 4). In this case, the two portions of the first link  10  are contacted to each other during the drive shaft  40  is rotated. 
     (Step 4) The drive shaft  40  for driving the speed reducer  30  is inserted into the speed reducer  30  while rotating the drive shaft  40 . The drive shaft  40  is common to the plurality of speed reducers  30 , but may be a separate drive shaft. 
     (Step 5) The remaining speed reducer of the two speed reducers  30  (the speed reducer  30  on the right side in the example of  FIG.  7   ) is attached to the first link  10 , while the position of the speed reducer side attachment hole  37  is displaced due to the insertion of the drive shaft  40 . In this regard, since one of the speed reducer side attachment hole  37  and the first link side attachment hole  11  is larger than the other or the elongate hole, the speed reducer  30  can be attached to the first link  10 , even when the positional relationship between the speed reducer side attachment hole  37  and the first link side attachment hole  11  is shifted. 
     In the rotating shaft structure as shown in  FIG.  7   , before manufacturing the rotating shaft structure  1 , the thickness required for the shim  50  is previously checked to prepare a predetermined shim  50 , and then the predetermined shim  50  may be positioned before the two speed reducers  30  are attached to the second link  20  (step 2). Alternatively, when the shim  50  is positioned between the first link  10  and the speed reducer  30  (the speed reducer  30  on the right side in the example of  FIG.  7   ), shims  50  having different types of thicknesses may be prepared in advance, and then the shim  50  having the required thickness may be appropriately selected and positioned before the remaining speed reducer  30  is attached to the first link  10  (step 5). 
       FIGS.  9  and  10    show a further modification of the rotating shaft structure  1 . In this rotating shaft structure  1 , the outer output shaft  35  of the speed reducer  30  is fixed to the first link  10 , and the inner output shaft  34  of the speed reducer  30  is rotated. Further, in this rotating shaft structure  1 , the speed reducer  30  is attached to the first link  10  in advance, and then the second link  20  is attached, while the input shaft side wheel  33  of the speed reducer  30  does not interfere with the second link  20  when the second link  20  is attached. Therefore, this rotating shaft structure  1  is different from the above also in that the first link  10  is not configured to be separable into two portions. Further, in this rotating shaft structure  1 , the place where the speed reducer  30  is finally fastened is between the second link  20  and the speed reducer  30  (the speed reducer  30  on the right side in the example of  FIG.  9   ). Therefore, it is preferable that the second link side attachment hole  21  be larger than the speed reducer side attachment hole  36  or an elongate hole as shown in  FIG.  10   , or the speed reducer side attachment hole  36  be larger than the second link side attachment hole  21  or an elongate hole. 
     The manufacturing method of the rotating shaft structure  1  shown in  FIG.  9    is, for example, as follows. It should be noted that  FIG.  9    shows the following step 5. 
     (Step 1) One of the speed reducer side attachment hole  36  and the second link side attachment hole  21  for connecting the speed reducer  30  to the second link  20  is formed larger than the other or an elongate hole. 
     (Step 2) The two speed reducers  30  are attached to the first link  10 , and the positional relationship between the speed reducer side attachment hole  36  and the second link side attachment hole  21  is previously adjusted. 
     (Step 3) One of the two speed reducers  30  attached to the first link  10  (the speed reducer  30  on the left side in the example of  FIG.  9   ) is attached to the second link  20 . 
     (Step 4) The drive shaft  40  for driving the speed reducer  30  is inserted into the speed reducer  30  while rotating the drive shaft  40 . The drive shaft  40  is common to the plurality of speed reducers  30 , but may be a separate drive shaft. 
     (Step 5) The remaining speed reducer of the two speed reducers  30  (the speed reducer  30  on the right side in the example of  FIG.  9   ) is attached to the second link  20 , while the position of the speed reducer side attachment hole  36  is displaced due to the insertion of the drive shaft  40 . In this regard, since one of the speed reducer side attachment hole  36  and the second link side attachment hole  21  is larger than the other or the elongate hole, the speed reducer  30  can be attached to the second link  20 , even when the positional relationship between the speed reducer side attachment hole  36  and the second link side attachment hole  21  is shifted. 
     In the rotating shaft structure as shown in  FIG.  9   , shims  50  having different types of thicknesses may be prepared in advance, and then the shim  50  having the required thickness may be appropriately selected and positioned before the remaining speed reducer  30  is attached to the second link  20  (step 5). Alternatively, before manufacturing the rotating shaft structure  1 , the thickness required for the shim  50  is previously checked to prepare a predetermined shim  50 , and then the predetermined shim  50  may be positioned before the two speed reducers  30  are attached to the first link  10  (step 2). 
       FIG.  11    shows a still further modification of the rotating shaft structure  1 . The rotating shaft structure  1  further includes a deceleration mechanism  60  configured to transmit power to the drive shaft  40 , and a drive source  61  configured to supply power to the deceleration mechanism  60 . For example, the deceleration mechanism  60  may have a large wheel  63  and a small wheel  64 . The large wheel and the small wheel  64  may be gears configured to engage with each other, whereas the wheels may be pulleys or the like around which a belt or cable, etc., is wound. The large wheel  63  is attached to the drive shaft  40 , and the small wheel  64  is attached to a rotating shaft  62  of the drive source  61 . The deceleration mechanism  60  may be arranged within the first link  10 . By providing the deceleration mechanism  60 , the drive source  61  can be further miniaturized and reduced in power, and the rotating shaft structure  1  can be further miniaturized. 
     Although the rotating shaft  62  of the drive source  61  is positioned parallel to the drive shaft  40 , the rotating shaft  62  may be orthogonal to the drive shaft  40  by using a bevel gear, etc. Further, a plurality of the drive source  61  may be arranged in the first link  10 , and each drive source  61  may supply power to the deceleration mechanism  60 . By virtue of this, the output from the drive source  61  can be further increased or the drive source  61  can be further miniaturized. 
       FIG.  12    shows an example of the rotating shaft structure  1  applied to another joint structure. For example, the rotating shaft structure  1  may be applied to a rotating shaft structure configured to rotate about a rotation axis J 3  (see  FIG.  1   ) of the robot. In this case, the first link  10  is a first arm configured to rotate about a horizontal axis, and the second link  20  is a second arm configured to rotate about a horizontal axis. As described above, the rotating shaft structure  1  is not limited to the joint structure of the robot. Note that the rotating shaft structure  1  can be applied to other rotating shaft structures such as a crank mechanism, a steering mechanism, a door opening/closing mechanism, a wiper mechanism, and a four-node link mechanism provided to other machines such as construction machines, vehicles and aircrafts. 
     According to the above embodiments, the speed reducer  30  can be attached to the first link  10  even when the positions of the speed reducer side attachment holes  36 ,  37  are displaced due to the insertion of the drive shaft  40 . As a result, the manufacturing efficiency of the rotating shaft structure  1  having the plurality of speed reducers  30  can be improved. 
     Although the various embodiments are described herein, it should be noted that the present invention is not limited to the above embodiments, and various modifications can be performed within the scope of the claims. 
     REFERENCE SIGNS LIST 
     
         
           1  rotating shaft structure 
           2  machine 
           10  first link 
           11  first link side attachment hole 
           20  second link 
           21  second link side attachment hole 
           30  speed reducer 
           31  input shaft 
           32  output shaft 
           33  input shaft side wheel 
           34  inner output shaft 
           35  outer output shaft 
           36 ,  37  speed reducer side attachment hole 
           40  drive shaft 
           50  shim 
           51  insertion hole 
           60  deceleration mechanism 
           61  drive source 
           62  rotating shaft 
           63  large wheel 
           64  small wheel 
         J 2 , J 3  rotation axis