Abstract:
A manipulator includes a first arm having a first reduction gear unit built therein, a second arm fitted through the first arm and having a second reduction gear unit built therein, and a third arm fitted through the second arm and having a third reduction gear unit built therein. To avoid any possible interference between, for example, a welding torch, and a portion of the manipulator during operation of the manipulator, the drive axis of the third reduction gear unit is spaced apart a distance from a drive axis of the second reduction gear unit.

Description:
BACKGROUND OF THE INVENTION 
     1. (Field of the Invention) 
     The present invention relates to an industrial manipulator, particularly a manipulator wrist structure, and a method of controlling the manipulator. 
     2. (Description of the Prior Art) 
     Industrial manipulators are currently employed in various industries. Although manipulators are many in type, most of the manipulators largely employed to accomplish factory automation are of a type resembling a human hand, an example of which is shown in FIGS. 4 to  5 C for discussion of the prior art to which the present invention pertains. 
     Referring particularly to FIG. 4, the prior art manipulator arm shown therein comprises a first tubular shell (a first driving articulate element)  31 , a second tubular shell (a second driving articulate element)  35   a , an intermediate tubular shell (a driven articulate element)  35   b  positioned between the first tubular shell  31  and the second tubular shell  35   a  and a third tubular shell (a third driving articulate element)  39  positioned adjacent one of the opposite ends of the second tubular shell  35   a  remote from the intermediate tubular shell  35   b.    
     The first tubular shell  31  includes a first reduction gear unit  32  incorporated therein and having a first drive axis  33 , and a first drive motor  34  housed within the first tubular shell  31  and drivingly coupled with an input side of the first reduction gear unit  32 . The intermediate tubular shell  35   b  has one end coupled with an output side of the first reduction gear unit  32  and the opposite end coupled with the second tubular shell  35   a.    
     The second tubular shell  35   a  includes a second reduction gear unit  36  incorporated therein and having a second drive axis  37 , and a second drive motor  38  housed within the second tubular shell  35   a  and adapted to drive an input side of the second reduction gear unit  36  through a drive transmission element. On the other hand, the third tubular shell  39  includes a third reduction gear unit  40  incorporated therein and having a third drive axis  41 , a third drive motor  42  housed within the second tubular shell  35   a  and drivingly coupled with an input side of the third reduction gear unit  40  through a drive transmission element. 
     The third tubular shell  39  has a safety holder  14  fixedly coupled with an output side of the third reduction gear unit  40  for carrying a welding torch  13  which can revolve together with the safety holder  14  about the third drive axis  41 . The welding torch  13  is connected with a cable  15  having an electric power line, a conduit and a gas hose bundled together. 
     In order for the manipulator arm to allow the welding torch  13  to gain access to a workpiece of a relatively complicated shape during a welding operation without interfering with a manipulator wrist, the second and third tubular shells  35   a  and  39  must have a size as small as possible and, particularly, the dimension L 3  shown in FIGS. 5B and 5C affects the accessibility of the welding torch  13  to the workpiece. Accordingly, how small the dimension L 3  is designed is one of the factors determinative of the range of application in which the welding manipulator can be effectively utilized to accomplish an intended job. For this reason, the prior art manipulator is so designed and so configured that the first and second drive axes  33  and  37  lie perpendicular to each other; the second and third drive axes  37  and  41  lie perpendicular to each other; and both of the second and third drive motors  38  and  42  are housed within the second tubular shell  35 . 
     The operation of the prior art manipulator arm of the structure discussed above will now be described with reference to FIG.  4 . 
     When the first drive motor  34  drives the input side of the first reduction gear unit  32  accommodated within the first tubular shell  31 , the second and intermediate tubular shells  35   a  and  35   b  rotate about the first drive axis  33  in one of the opposite directions shown by θ1. The third tubular shell  39  can rotate about the second drive axis  37  in one of the opposite directions shown by θ2 when the second drive motor  38  drives the input side of the second reduction gear unit  36 , accommodated within the second tubular shell  35   a , through the drive transmission element. On the other hand, when the third drive motor  42  drives the input side of the third reduction gear unit  40 , accommodated within the third tubular shell  39 , through the drive transmission element, the safety holder  14  carrying the welding torch  13  rotates about the third drive axis  41  in one of the opposite directions shown by θ3. 
     Accordingly, it is theoretically possible for the welding torch  13  to assume any position and/or orientation relative to the workpiece by suitably selecting and/or combining directions of movement θ1, θ2 and θ3. 
     However, in the prior art manipulator arm of the type discussed above, and so long as the freedom of movement in either of the opposite directions θ3 is concerned, the angle through which the safety holder  14  carrying the welding torch  13  can rotate relative to the third tubular shell  39  is limited and, thus, the prior art manipulator arm is necessarily incapable of continuously assuming an arbitrarily chosen orientation. This is because, in the case of the welding manipulator such as discussed above or a paint applying manipulator, the cable  15  extending outwardly from the welding torch  13  interferes with the second tubular shell  35   a  when the safety holder  14  rotates in one of the opposite directions θ3 about the third drive axis  41 . 
     Considering that all of the second reduction gear unit  36 , the second drive motor  38 , the third drive motor  42 , the drive transmission element connecting the second reduction gear unit  36  and the second drive motor  38  together and the drive transmission element connecting the third reduction gear unit  40  and the third drive motor  42  together are housed within the second tubular shell  35   a , the second tubular shell  35   a  necessarily has a square outer appearance, that is, a generally rectangular sectioned shape, as shown in FIG.  5 C. Accordingly, when the cable  15  interferes with the second tubular shell  35   a , the cable  15  is considerably bent with its outer sheath  15   a  damaged and, consequently, weld padding tends to be considerably adversely affected. 
     By way of example, where a welding line along which welding is desired to be effected at the workpiece lies at a location shown by B in FIG. 4, the cable  15  when moved to a position shown by  13   b  about the third drive axis  41  interferes with the second tubular shell  35   a  and, accordingly no beautiful weld padding can be obtained. Thus, the prior art welding manipulator has a problem in that the position and/or orientation of the workpiece to be welded relative to the welding manipulator have been limited. 
     Moreover, when it comes to effecting a fillet welding continuously along a circular welding line  19  defined between a cylindrical workpiece  17  and a base plate  18  as shown in FIG. 6 to eventually form a circular fillet joint by which the cylindrical workpiece  17  is rigidly connected to the base plate  18 , the welding torch  13  has to be revolved so as to follow the circular welding line  19 . In this instance, even though the workpiece is disposed in an optimum layout, interference between the cable  15  and the second tubular shell  35   a  necessarily takes place and, consequently, no beautiful weld padding that continues along the circular welding line  19  can be obtained. 
     The foregoing problems discussed in connection with the welding manipulator are equally found in the paint applying manipulator. 
     In view of the foregoing, it is suggested to position the cable at a location distant from the second drive axis  37  and towards the third drive axis  41 . However, to position the cable at a location distant from the second drive axis  37  may result in enhancement of an angular transmission error of any one of the first and second reduction gear units  32  and  36 , which in turn brings about reduction in positioning accuracy with which the tip of the welding torch  13  is positioned relative to the welding line. 
     To downsize or eliminate a cable guard  15   a  which directly interferes with the second tubular shell  35   a  would adversely affect the freestanding property of the cable  15  to such an extent as to result in a severe bending of a welding wire bundled in the cable  15  which would in turn bring about an adverse influence on the eventually formed weld padding. 
     It may be contemplated to lessen the interference by downsizing the second tubular shell  35   a . However, considering that all of the second reduction gear unit  36 , the second and third drive motors  38  and  42  and the drive transmission elements connecting the second and third reduction gear units  36  and  40  respectively with the second and third drive motors  38  and  43  are housed within the second tubular shell  35   a , the dimensions L 2  and L 3  shown in FIGS. 5A to  5 C can no longer be reduced economically and rationally. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been devised with an aim at substantially eliminating the problems inherent in the prior art manipulator of the kind discussed hereinbefore and is intended to provide an improved manipulator capable of performing an intended welding operation without allowing the cable to interfere with a portion of the manipulator, to thereby form a beautiful, stabilized weld padding. 
     It is a related object of the present invention to provide a method of controlling the improved manipulator of the type referred to above. 
     To this end, the present invention according to a broad aspect thereof provides a manipulator which comprises at least two manipulator arms each including a reduction gear unit built therein and having a respective drive axis. The drive axis of the reduction gear unit in one of the manipulator arms is uniquely displaced from the drive axis of the other of the manipulator arms. In a preferred embodiment of the present invention, the manipulator arm is comprised of a driving articulate element having the reduction gear unit built therein, and a driven articulate element coupled with the driving articulate element. 
     Preferably, the other of the manipulator arms has a tool fitted thereto for a particular job. Also, preferably, the drive axis of the reduction gear unit in such one of the manipulator arms is displaced from the drive axis of the reduction gear unit in such other of the manipulator arms a distance not smaller than the radial dimension of the reduction gear unit in such other of the manipulator arms. 
     A method of controlling the manipulator of the type referred to above comprises rotating one of the manipulator arms in one of vertical and horizontal directions, and rotating the other of the manipulator arms through an angle not smaller than 90° in the other of the vertical and horizontal directions, to thereby allow such one of the manipulator arms to approach a workpiece to be acted on. 
     Alternatively, the method of controlling the manipulator of the type referred to above may comprise rotating one of the manipulator arms in a direction away from a workpiece to be acted on, and rotating the other of the manipulator arms through an angle not smaller than 90° in a direction perpendicular to the direction in which such one of the manipulator arms is rotated, to thereby allow such one of the manipulator arms to approach the workpiece. 
     In a specific embodiment of the present invention, the manipulator comprises a first arm having a first reduction gear unit built therein, a second arm fitted through the first arm and having a second reduction gear unit built therein, and a third arm fitted through the second arm and having a third reduction gear unit built therein, wherein the third reduction gear unit has a drive axis displaced from a drive axis of the second reduction gear unit. In this specific embodiment, the first arm may be comprised of a driving articulate element having the reduction gear unit built therein, and a driven articulate element coupled with the driving articulate element, whereas the third arm may have a tool fitted thereto for a particular job. 
     In addition, in such specific embodiment, the drive axis of the third reduction gear unit is preferably (i.e. spaced apart) from the drive axis of the second reduction gear unit by a distance not smaller than the radial dimension of the second reduction gear unit. 
     When it comes to the control of the manipulator according to the specific embodiment of the present invention, the third arm is first rotated in one of vertical and horizontal directions, and the second arm is subsequently rotated through an angle not smaller than 90° in the other of the vertical and, to thereby allow the third arm to approach a workpiece to be acted on. Alternatively, the third arm may be rotated in a direction away from a workpiece to be acted on, and the second arm subsequently rotated through an angle not smaller than 90° in a direction perpendicular to the direction of rotation of the third arm, to thereby allow the third arm to approach the workpiece. 
     According to the present invention, the manipulator and the controlling method therefor outlined above and described in detail hereinafter are effective to avoid any possible interference between the tool, for example, a welding torch, and a portion of the manipulator during operation of the manipulator being, to thereby provide a beautiful, stabilized weld padding on the workpiece. 
     In addition, the second arm can have an outer dimension reduced to enhance the accessibility of the third arm to the workpiece to be welded. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become readily understood from the following description of a preferred embodiment thereof made with reference to the accompanying drawings, in which like parts are designated by like reference numeral and in which: 
     FIG. 1 is a schematic side view of a welding manipulator embodying the present invention, showing an outer appearance thereof; 
     FIG. 2 is a fragmentary side view of the welding manipulator shown in FIG. 1, showing a manipulator arm thereof; 
     FIG. 3A is a fragmentary side view of the manipulator arm; 
     FIG. 3B is a fragmentary top plan view of the manipulator arm; 
     FIG. 3C is a fragmentary front view of the manipulator arm; 
     FIG. 4 is a side view of a prior art welding manipulator; 
     FIG. 5A is a fragmentary side view of a manipulator arm in the prior art welding manipulator; 
     FIG. 5B is a fragmentary top plan view of the manipulator arm in the prior art welding manipulator; 
     FIG. 5C is a fragmentary front view of the manipulator arm in the prior art welding manipulator; and 
     FIG. 6 is a schematic perspective view showing the relationship in position between a workpiece to be welded and the welding manipulator. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring first to FIG. 1, there is shown a welding manipulator to which the present invention is applied for illustration purposes. The welding manipulator shown therein comprises a first arm constituted by a first tubular shell (a first driving articulate element)  1 , and a second arm constituted by a second tubular shell (a second driving articulate element)  5   a  and an intermediate tubular shell (a driven articulate element)  5   b  positioned between the first tubular shell  1  and the second tubular shell  5   a  and a third arm constituted by a third tubular shell (a third driving articulate element)  9  positioned adjacent one of opposite ends of the second tubular shell  5   a  remote from the intermediate tubular shell  5   b.    
     The first tubular shell  1  includes a first reduction gear unit  2  incorporated therein and having a first drive axis  3 , a first drive motor  4  housed within the first tubular shell  1  and drivingly coupled with an input side of the first reduction gear unit  2 . The intermediate tubular shell  5   b  has one end coupled with an output side of the first reduction gear unit  2  and the opposite end coupled with the second tubular shell  5   a . It is to be noted that the intermediate tubular shell  5   b  is of a generally cylindrical shape having a smooth outer peripheral surface. 
     The second tubular shell  5   a  includes a second reduction gear unit  6  incorporated therein and having a second drive axis  7  lying perpendicular to the first drive axis  3 , and a second drive motor  8  housed within the second tubular shell  5   a  in coaxial relation with the first drive axis  3  and adapted to drive an input side of the second reduction gear unit  6 . On the other hand, the third tubular shell  9  includes a third reduction gear unit  10  incorporated therein and having a third drive axis  11 , and a third drive motor  12  drivingly coupled with an input side of the third reduction gear unit  10 . 
     The third tubular shell  9  has a safety holder  14  fixedly coupled with an output side of the third reduction gear unit  10  for carrying a welding torch  13  which can revolve together with the safety holder  14  about the third drive axis  11 . The welding torch  13  and a control unit  16  therefor are connected with each other through a cable  15  which is a bundle of an electric power line, a conduit and a gas hose bundled together. 
     The second and third drive axes  7  and  11  are so positioned relative to each other that those drive axes  7  and  11  may lie perpendicular to each other, but may not lie in the same plane, having been offset a distance L 1  from each other. In other words, the second tubular shell  5   a  and the third tubular shell  9  are so pivotally connected with each other that the third drive axis  11  of the third reduction gear unit  10  within the third tubular shell  9  can extend perpendicular to the second drive axis  7  of the second reduction gear unit  6  within the second tubular shell  5   a , but be displaced a distance L 1  from the second drive axis  7  in a direction away from the second tubular shell  5   a.    
     Preferably, the drive axes  7 ,  11  of the second and third reduction gear units  6 ,  10  are spaced apart by the predetermined distance L 1  which is not smaller than the radial dimension of the second reduction gear unit  6 . 
     By this unique design, the third tubular shell  9  has an interior space available for accommodating therein the third drive motor  12  for driving an input side of the third reduction gear unit  10  and accordingly, the third drive motor  12  within the third tubular shell  9  is so disposed as to be directly coupled with the input side of the third reduction gear unit  10  in a manner coaxially of the third drive axis  11 . 
     The operation of the prior art manipulator arm of the structure discussed above in accordance with the present invention will now be described with reference to FIG.  2 . 
     When the first drive motor  4  drives the input side of the first reduction gear unit  2  accommodated within the first tubular shell  1 , the second and intermediate tubular shells  5   a  and  5   b  rotate about the first drive axis (or rotation axis)  3  in one of the opposite directions shown by θ1 (see FIG.  2 ). The third tubular shell  9  can rotate about the second drive axis  7  in one of the opposite directions shown by θ2 when the second drive motor  8  drives the input side of the second reduction gear unit  6 , accommodated within the second tubular shell  5   a , through a drive transmission element. On the other hand, when the third drive motor  12  drives the input side of the third reduction gear unit  10 , accommodated within the third tubular shell  9 , the safety holder  14  carrying the welding torch  13  rotates about the third drive axis  11  in one of the opposite directions shown by θ3. Accordingly, it is clear that the welding torch  13  can assume any position and/or orientation relative to the workpiece by suitably selecting and/or combining directions of movement θ1, θ2 and θ3. 
     By way of example, where a welding line along which welding is desired to be effected at the workpiece lies at a location shown by B in FIG. 2, the welding torch  13  can be brought to a position in the vicinity of the welding line B without the cable  15  interfering with the second tubular shell  5   a , provided that the third tubular shell  9  is rotated about the second drive axis  7  in one of the opposite directions θ2 to thereby orient the welding torch  13  upwardly and the second tubular shell  5   a  is subsequently rotated at least 90° about the first drive axis  3  in one of the opposite directions θ1 to thereby bring the welding torch  13  to a position shown by  13   b . Although at this time the cable  15  may interfere with the intermediate tubular shell  5   b , neither is the cable  15  considerably bent nor its outer sheath damaged since the intermediate tubular shell  5   b  contains therein neither a drive transmission element nor a reduction gear unit and has a smooth outer peripheral surface. 
     When it comes to effecting a fillet welding continuously along a circular welding line  19  defined between a cylindrical workpiece  17  and a base plate  18  as shown in FIG. 6 to eventually form a circular fillet joint by which the cylindrical work  17  is rigidly connected to the base plate  18 , the welding torch  13  can be moved to the position shown by  13   b  by actuating the second and third tubular shells  5   a  and  9  in the manner described above and, in such case, even though the welding torch  13  then moved to the position  13   b  is moved so as to follow the circular welding line  19 , the cable  15  does not interfere with the second tubular shell  5   a , to thereby accomplish a continuous fillet welding along the welding line  19  to form a beautiful weld padding. 
     As hereinbefore described, by positioning the second and third drive axes  7  and  11  such that the drive axes  7  and  11  lie perpendicular to each other but do not lie in the same plane and are offset (i.e. spaced apart) a distance L 1  from each other and by sequentially rotating the third tubular shell  9  so as to cause it to be orient upwardly and rotating the second tubular shell  5   a  at least 90° in a left or right direction to bring the third tubular shell  9  and the welding torch  13  to a position close to the workpiece to be welded, a continuous fillet welding can be accomplished along the circular welding line  19  to form a beautiful weld padding without allowing the cable  15  to interfere with the second tubular shell  5   a  even when the welding line  19  in the workpiece is positioned close to the manipulator arm. 
     Also, the arrangement in which the second drive motor  8  is disposed within the intermediate tubular shell  5   b  in coaxial relation with the first drive axis  3  and the third drive motor  12  is disposed within the third tubular shell  9  in coaxial relation with the third drive axis  11  in a manner coupled directly with the input side of the third reduction gear unit  10  is effective to reduce the outer dimensions (length and width) L 2  and L 3  of the second tubular shell  5   a  as shown in FIGS. 3A to  3 C. Accordingly, even though the workpiece to be welded is of a complicated shape, the accessibility of the welding torch  13  to the intended welding line on the workpiece can advantageously be increased to thereby increase the welding performance of the welding manipulator remarkably. 
     Moreover, the direct connection of the third drive motor  12  with the third reduction gear unit  10  is advantageous in that no drive transmission element which would otherwise be necessary to connect the third drive motor  12  with the third reduction gear unit  10  can be eliminated, thereby resulting in reduction in noise level generated when the third drive axis is operated. 
     Although the present invention has been described in connection with the preferred embodiments thereof, it should be noted that various changes and modifications are apparent to those skilled in the art. By way of example, although in the foregoing embodiment of the present invention the manipulator arm has been shown and described as having the first to third driving articulate elements, that is, the first to third tubular shells, the present invention can be equally applicable where any other driving articulate element is employed on one side of the first driving articulate element opposite to the second driving articulate element. 
     Accordingly, such changes and modifications so far as encompassed by the appended claims are to be understood as included within the scope of the present invention.