Abstract:
A link drive structure includes a first arm constituting a parallel link on one side, a second arm constituting a parallel link on the other side, a coupling base interposed between end portions, at which the first arm is coupled with the second arm, to couple the end portions of both the parallel links, and a drive motor with a harmonic gear reducer disposed to the coupling end portion of the arm on the one side. The harmonic gear reducer has two output shafts rotating in the same direction, a first output shaft is coupled with the end portion of the other arm, and a second output shaft is coupled with the coupling base. With this arrangement, there can be provided a link drive structure having a high positioning accuracy and an excellent sealing property and an industrial robot using the link drive structure.

Description:
[0001]     The entire disclosure of Japanese Patent Application No. 2004-363918, filed Dec. 16, 2004, is expressly incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a link drive structure, and more particularly, to a link drive structure preferably used to an industrial robot.  
         [0004]     2. Description of the Related Art  
         [0005]     Recently, industrial robots are required to cope also with unusual environments in which particular gases, chemicals, and the like are used, in addition to fields of production in which high speed, high accuracy, and a high level of cleanness are required. Most of vertical shaft structures of, for example, current SCARA (Selective Compliance Assembly Robot Arm) type robots constitute a direct drive shaft using a ball screw. In this structure, a protection member such as a bellows and the like is necessary to prevent dusts and grease from scattering from the insides of arms. However, when the bellows is used, a material thereof is limited due to fluctuation of the internal pressure of a robot caused by contraction of the bellows and from a point of view of durability and the like of the bellows. Accordingly, when a high level of cleanness is required and when a job in an unusual environment is required, it is difficult for the bellows to cope with the requirements.  
         [0006]     In contrast, there is an industrial robot employing a link type vertical shaft structure (refer to, for example, Japanese Unexamined Patent Application Publication No. 2002-326182). The link type vertical shaft structure is arranged such that a pair of first right and left-arms that constitute a parallel link on one side are coupled with a base and a link base, a pair of second right and left arms that constitute a parallel link on the other side are coupled with the link base and an arm base, a drive motor is mounted on the link base, a transmission mechanism using a bevel gear is employed to apply rotation force to a coupling shaft of the first and second arms on both the right and left sides, and the transmission mechanism is accommodated in the inside of the link base together with a reducer.  
         [0007]     The parallel link type vertical shaft structure as shown in patent document 1 can constitute a so-called bellowsless vertical shaft structure without using a bellows. However, since the vertical shaft structure employs a transmission mechanism using a bevel gear to rotate the coupling shaft of the first and second arms, it is disadvantageous in that a positional accuracy is deteriorated by the effect of backlash of the bevel gear. Further, in a bevel gear mechanism, since right and left coupling shafts must be rotated in an opposite direction each other in such a manner that a coupling shaft of a first arm on a left side is rotated clockwise and a coupling shaft of a second arm on a right side is rotated counterclockwise, the structure of the coupling portions of the first and second arms are made very complex, and assembling of the coupling portions is very difficult. Further, a seal structure of the coupling portions is also very complex.  
         [0008]     Further, an end effector such as a hand unit and the like is mounted on the extreme end of a robot arm to cause the end effector to execute a robot job. However, in a structure in which wiring or piping of a driving device of the end effector, robot arms, and the like are exposed to the vicinity of the robot arms, a layout of the wiring or the piping must be determined such that the motion of the robot arms is not restricted by it and that it does not interfere with an external object and the like, in addition to that an outside appearance is not good.  
         [0009]     An object of the present invention, which was made in view of the above circumstances, is to provide a link drive structure having a high positional accuracy and an excellent sealing property and an industrial robot using the structure.  
         [0010]     Further, an object of the present invention is to provide an industrial robot which does not expose wiring and piping of a driving device of an end effector, robot arms, and the like to the outside.  
       SUMMARY  
       [0011]     A link drive structure according to the present invention is characterized by comprising a first arm constituting a parallel link on one side, a second arm constituting a parallel link on the other side, a coupling base interposed between end portions, at which the first arm is coupled with the second arm, to couple the end portions of both the parallel links, and a drive motor with a harmonic gear reducer disposed to the coupling end portion of the arm on the one side, wherein the harmonic gear reducer has two output shafts rotating in the same direction, a first output shaft of them is coupled with the end portion of the other arm, and a second output shaft is coupled with the coupling base.  
         [0012]     The link drive structure of the present invention is composed of the parallel links including the first and second arms through the coupling base. Thus, a position can be completely controlled by only the rotational motion of rotary shafts. Further, since the harmonic gear reducer having the two output shafts, which rotate in the same direction, is used, no backlash arises, thereby pinpoint position accuracy can be realized. Further, since a seal mechanism is simple and excellent in a sealing property because the rotary shafts are employed, the link drive structure can easily cope with various unusual environments such as a clean environment and the like.  
         [0013]     Note that, in the present invention, when the drive motor with the harmonic gear reducer is mounted on the coupling end portion of the first arm, a first output shaft of the harmonic gear reducer is coupled with the coupling end portion of the second arm, and a second output shaft is coupled with the coupling base. Inversely, when the drive motor with the harmonic gear reducer is mounted on the coupling end portion of the second arm, the first output shaft of the harmonic gear reducer is coupled with the coupling end portion of the first arm, and the second output shaft is coupled with the coupling base likewise.  
         [0014]     Further, in the present invention, a ratio between speed reduction of the first and second output shafts in the harmonic gear reducer is set to 1:2.  
         [0015]     With this arrangement, a movable base coupled with the second arm constituting the parallel link can be moved linearly.  
         [0016]     Further, in the present invention, the first and second output shafts are preferably disposed concentrically. With this arrangement, the length of the harmonic gear reducer can be reduced, thereby a drive unit can be formed compactly.  
         [0017]     Further, in the present invention, the inside of the link drive structure has a hollow structure, and wiring and/or piping passes through the inside.  
         [0018]     With this arrangement, the wiring/piping can be concealed in the insides of the first and second arms, no restriction is applied to the motions of the first and second arms and a robot arm, and no interference with an external object and the like arises. Further, a neat and tidy impression is given to an outside appearance.  
         [0019]     Further, an ordinary industrial robot can be arranged by using the link drive structure of the present invention. In particular, the link drive structure can be preferably used as a vertical shaft structure of a SCARA type robot. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a side elevational view of a SCARA type robot having a link drive structure of the present invention;  
         [0021]      FIG. 2  is an upper surface view of the SCARA type robot;  
         [0022]      FIG. 3  is a sectional view showing a schematic arrangement of a link drive structure;  
         [0023]      FIG. 4  is a sectional view of a drive unit; and  
         [0024]      FIG. 5  is a view explaining operation of the link drive structure. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]     An example of an embodiment to which the present invention is applied will be explained below with reference to drawings. Although an example in which the link drive structure of the present invention is used as a vertical shaft structure of a SCARA type robot is shown here, the present invention is by no means limited thereto.  
         [0026]      FIG. 1  is a side elevational view of an industrial robot (SCARA type robot) of the present invention, and  FIG. 2  is an upper surface view of the SCARA type robot.  
         [0027]     A link drive structure (vertical shaft structure)  10  of the SCARA type robot is arranged such that an intermediate coupling base  3  is interposed between a fixed base  1  installed on a floor surface or the like and an upper movable base  2 , and two sets of parallel link structures are coupled with each other in a shape bent to a “&lt;” state through the coupling base  3 .  
         [0028]     A first arm  11  on one side constitutes a parallel link together with a first link  13 , an end (lower end portion) of the first arm  11  is rotatably coupled with the fixed base  1  through a shaft  15 , a drive motor with a harmonic gear reducer to be described later is attached to the other end (upper end portion) thereof, and a second output shaft (refer to FIGS.  3  to  5 ) of the harmonic gear reducer is rotatably coupled with the coupling base  3 .  
         [0029]     Both the ends of the first link  13  are rotatably coupled with the fixed base  1  and the coupling base  3  through shafts  17   a ,  17   b.    
         [0030]     A second arm  12  on the other side constitutes a parallel link together with a second link  14 , an end (lower end portion) of the second arm  12  is coupled with a first output shaft of the harmonic gear reducer, and the other end (upper end portion) thereof is rotatably coupled with the movable base  2  through a shaft  16 .  
         [0031]     Both the ends of the second link  14  are rotatably coupled with the coupling base  3  and the movable base  2  through shafts  18   a ,  18   b.    
         [0032]     Further, the drive motor is directly attached to the harmonic gear reducer. The coupling base  3  is interposed between the upper end portion of the first arm  11  and the lower end portion of the second arm  12 .  
         [0033]     As described above, the fixed base  1 , the coupling base  3 , the first arm  11 , and the first link  13  constitute a parallel link structure that is formed in a parallelogram when the coupling points thereof are connected to each other, and further the movable base  2 , the coupling base  3 , the second arm  12 , and the second link  14  also constitute a parallel link structure that is formed in a parallelogram when the coupling points thereof are connected to each other likewise. The movable base  2  is kept in a predetermined posture (for example, horizontal) by the two sets of the parallel link structures at all times regardless a rotational angle of the first arm  11 .  
         [0034]     A robot arm structure as an upper structure  20  is mounted on the movable base  2 . In the SCARA type robot, a robot arm structure mainly composed of a first horizontal arm  21  and a second horizontal arm  22  is mounted on the movable base  2 . The first horizontal arm  21  can rotate about a first joint shaft (not shown) for coupling the first horizontal arm  21  with the movable base  2 , and the second horizontal arm  22  can rotate about a second joint shaft (not shown) for coupling the first horizontal arm  21  with the second horizontal arm  22 . Further, a working shaft  23  (refer to  FIG. 2 ) is rotatably mounted on the extreme end of the second horizontal arm  22 , and an end effector (not shown) such as a hand unit and the like is attached to the working shaft.  
         [0035]     Further, the link drive structure  10  described above will be described in detail based on FIGS.  3  to  5 .  FIG. 3  is a sectional view showing a schematic arrangement of the link drive structure  10 , and  FIG. 4  is a sectional view of a drive unit of the link drive structure  10 . Note that the lower half portion of the harmonic gear reducer  30  is omitted in  FIG. 4 . Further,  FIG. 5  is a view explaining operation of the link drive structure  10 .  
         [0036]     The drive unit  4  of the link drive structure  10  is composed of the drive motor  50  with the harmonic gear reducer  30 , and mounted on the upper end portion of the first arm  11 , that is, a coupling end portion coupled with the second arm  12 .  
         [0037]     The harmonic gear reducer  30  is mainly composed of an input shaft  31 , a wave generator  32 , flexsplines  33 ,  34 , circular splines  35 ,  36 , a first output shaft  37 , and a second output shaft  38 .  
         [0038]     A motor shaft  51  of the drive motor  50  is firmly coupled with the input shaft  31  through, for example, a flange joint (illustration of which is omitted) and the like so that no looseness arises in a rotational direction. The wave generator  32  is secured to the input shaft  31  by screws, an adhesive, and the like and has two bearings  32   a ,  32   b  which generate a wave motion by being engaged with the inner peripheries of the circular splines  35 ,  36 , respectively.  
         [0039]     The teeth of the flexspline  33  on one side are partly meshed with the circular spline  35  as well as the flexspline  33  is secured to the first output shaft  37  by not shown attachment screws and the like.  
         [0040]     The teeth of the flexspline  34  on the other side are partly meshed with the circular spline  36  as well as the flexspline  34  is secured to the second output shaft  38  by not shown attachment screws and the like together with the circular spline  35 . The circular spline  36  on the other side is secured to a reducer case  40 .  
         [0041]     Then, the first output shaft  37  is secured to an end of the second arm  12 , and the second output shaft  38  is secured to the coupling base  3 .  
         [0042]     The first and second output shafts  37 ,  38  are disposed concentrically with this arrangement, the length of the harmonic gear reducer  30  can be reduced, which can make the drive unit  4  compact.  
         [0043]     The first output shaft  37  is attached to the lower end portion of the second arm  12  by attachment screws  41   a ,  41   b  through an arm connecting member  39 . Further, the second output shaft  38  is attached to the coupling base  3  by an attachment screw  41   c.    
         [0044]     The harmonic gear reducer  30  is attached to the upper end portion of the first arm  11  by an attachment screw  41   d.    
         [0045]     The drive motor  50  is attached to the harmonic gear reducer  30  by an attachment screw  41   e  through a motor flange  52 .  
         [0046]     As described above, the harmonic gear reducer  30  is arranged as a one-input/two-outputs reducer having the one input shaft  31  and the two output shafts  37 ,  38  as well as the first and second output shafts  37 ,  38  rotate in the same direction. Further, the first and second output shafts  37 ,  38  have a reduction ratio of 1:2. The above reduction ratio can be achieved by changing the number of teeth of the flexsplines  33  and  34  or the number of teeth of the circular splines  35  and  36 .  
         [0047]     Accordingly, since no backlash arises, the first and second arms  11 ,  12  can be turned with pinpoint accuracy, thereby the position of the movable base  2  can be controlled with pinpoint accuracy.  
         [0048]     Further, the link drive structure  10  has a hollow structure as shown in  FIGS. 3 and 4 . More specifically, all of the movable base  2 , the shaft  16 , the drive motor  50  with the harmonic gear reducer  30 , the first arm  11 , and the shaft  15  have the hollow structure. Further, the drive motor  50  is composed of a hollow motor, and a sleeve  53  is disposed at the center of the drive motor  50  with the harmonic gear reducer  30  entirely passing therethrough. Note that reference numeral  54  denotes a sleeve attachment member, and  55  denotes a slide bearing interposed between the sleeve  53  and the arm connecting member  39 . Further, in  FIG. 3 , reference numeral  11   a  denotes a first arm cover,  12   a  denotes a second arm cover,  15   a  denotes a bearing of the hollow shaft  15 , and  16   a  denotes a bearing of the hollow shaft  16 .  
         [0049]     Wiring/piping  60  of the upper structure  20 , wiring (not shown) of the drive motor  50 , and the like can be disposed in the inside of the link drive structure  10  by arranging the link drive structure  10  as the hollow structure as described above. The wiring/piping  60 , and the like are connected to a wiring board, a valve, and the like in an accommodation box  61  disposed on the fixed base  1 .  
         [0050]     As a result, according to the arrangement of the link drive structure  10 , since the wiring/piping  60  and the like are accommodated in the inside of the link drive structure  10  and are not exposed to the outside, the robot gives a neat and tidy impression in the outside appearance thereof as well as the link drive structure  10 , the robot arms and like are not restricted in motion and has no possibility of interference with an external object and the like.  
         [0051]     Further, the first and second arms  11 ,  12  are hermetically closed by the first arm cover  11   a  and the second arm cover  12   a , respectively, and the arm connecting member  39  for connecting the second arm  12  to the first output shaft  37 , the coupling base  3  of the second output shaft  38  and the reducer case  40 , the attachment portions of the hollow arms  15  and  16 , and the like are sealed by not shown O-rings and the like. Accordingly, the robot can be easily applied to various unusual environments such as a clean environment and the like because it is excellent in a sealing property, and dusts, grease, and the like do not scatter from the insides of the arms.  
         [0052]     Next, the operation of the harmonic gear reducer  30  will be explained based on a schematic view of  FIG. 5 .  
         [0053]     In  FIG. 5 , when the movable base  2  is moved (raised) from a position A shown by a solid line to a position B shown by a dotted line, both the first and second output shafts  37 ,  38  of the harmonic gear reducer  30  are rotated in the same counterclockwise direction. Since the coupling base  3  is kept horizontal by the two sets of upper and lower parallel link structures and further the first and second output shafts  37 ,  38  have the reduction ration set to 1:2, the second arm  12  rotates at an angle θ between it and the first arm  11  that is twice the horizontal angle α of the first arm  11 . More specifically, since the first and second arms  11 ,  12  have the same rotation angle (horizontal angle), the movable base  2  moves linearly.  
         [0054]     Further, when the movable base  2  is lowered from the position B to the position A, both the first and second output shafts  37 ,  38  are rotated in an opposite clockwise direction.  
         [0055]     Although a case in which the drive motor  50  with the harmonic gear reducer  30  is mounted on the upper end portion of the first arm  11  in the embodiment described above, the drive motor  50  with the harmonic gear reducer  30  may be mounted on the lower end portion of the second arm  12  by an inverted mounting method. In this case, the first output shaft  37  is coupled with the first arm  11 , and the second output shaft  38  is coupled with the coupling base  3 .  
         [0056]     Further, since the link drive structure of the present invention need not arrange the first and second arms  11 ,  12  as a pair on the right and left sides as shown in the patent document 1, the link drive structure can be formed compact.  
         [0057]     Further, when the link drive structure of the present invention is installed, for example, horizontally, it can be used as an expansion/contraction structure in a right/left direction. The movable base  2  may be guided as a sliding member. Accordingly, the link drive structure of the present invention can be applied to a wide region.