Abstract:
A work conveying apparatus is comprised of a conveying rail for moving carriages with works and a returning rail for returning the carriages without works to the conveying rail. The returning rail is disposed along the conveying rail while being perpendicularly inclined from the conveying rail. Selector rails are disposed at both ends of the conveying rail, respectively. The selector rails are swingable between a horizontal position extending from the conveying rails and a vertical position extending from the returning rail. The selector rails are swung to transfer the carriages between the conveying rail and the returning rail.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method and apparatus for continuously conveying works by circulatingly moving a plurality of conveying carriages for supporting the works. 
     Various work conveying apparatuses have been proposed and in practical use. A typical work conveying apparatus has been arranged to dispose a conveying rail above a returning rail. A plurality of conveying carriages are circulated between the conveying rail and the returning rail through a pair of lifter mechanisms. More specifically, a conveying carriage conveyed on the conveying rail is transferred to the returning rail through a carriage receiving base, a carriage put-out mechanism, the lifter mechanism and a carriage put-in mechanism. Similarly, the conveying carriage conveyed on the returning rail is transferred to the conveying rail through a carriage receiving base, a carriage put-out mechanism, the lifter mechanism and a carriage put-in mechanism. 
     SUMMARY OF THE INVENTION 
     However, such a conventional work conveying apparatus is complicated in structure and operation, and therefore a cycle time of this apparatus is limited by these complicated structure and operation. 
     It is an object of the present invention to provide an improved work conveying apparatus and method which is simplified in structure and operation and improves its operation speed thereby to decrease a cycle time in operation. 
     An aspect of the present invention resides in a work conveying apparatus which comprises a conveying rail and a returning rail, a starting-stage selector rail, a terminating-stage selector rail, a plurality of conveying carriages and a carriage drive mechanism. The returning rail is disposed along the conveying rail. The starting-stage selector rail is parallel to the conveying rail and is swingable between a first position straightly extending from an end of the conveying rail and a second position straightly extending from an end of the returning rail. The terminating-stage selector rail is parallel to the conveying rail and is swingable between a third position straightly extending from the other end of the conveying rail and a fourth position straightly extending from the other end of the returning rail. A plurality of conveying carriages are conveyed on the conveying rail and the returning rail to convey works from the starting-stage selector rail through the conveying rail. A carriage drive mechanism moves the conveying carriages on the conveying rail, the return rail, the starting-stage selector rail and the terminating-stage selector rail. The carriage drive mechanism comprises a reciprocating member and a supporting member, the reciprocating member being disposed along the conveying rail and being reciprocatingly movable along the conveying rail, the supporting member is connected to the reciprocating member and being selectively connected to a portion of each of the conveying carriages. 
     Another aspect of the present invention resides in a work conveying apparatus comprising a conveying rail, a returning rail disposed along the conveying rail, and a starting-stage selector rail parallel to the conveying rail. The starting-stage selector rail is swingable between a first position straightly extending from an end of the conveying rail and a second position straightly extending from an end of the returning rail. A terminating-stage selector rail is parallel to the conveying rail, the terminating-stage selector rail being swingable between a third position straightly extending from the other end of the conveying rail and a fourth position straightly extending from the other end of the returning rail. The apparatus also includes a plurality of conveying carriages moved on the conveying rail and the returning rail, the conveying carriage conveying a work from the starting-stage selector rail to the terminating-stage selector rail through the conveying rail. The apparatus further includes a carriage drive mechanism moving the conveying carriages on the conveying rail, the return rail, the starting-stage selector rail and the terminating-stage selector rail, the carriage drive mechanism comprising a carriage conveying mechanism which moves the conveying carriages disposed on the conveying rail and the starting-stage selector rail set at the first position in a conveying direction, and a carriage returning mechanism which moves the conveying carriages disposed on the returning rail and the terminating-stage selector rail set at the fourth position in a returning direction. The carriage conveying mechanism comprises a conveying finger lever connected to the conveying carriage and a carriage transfer mechanism which is disposed under the conveying rail, the carriage transfer mechanism reciprocatingly moving the conveying finger lever along the conveying direction. 
     Yet another aspect the present invention resides in a work conveying apparatus which comprises a conveying rail, a returning rail disposed along the conveying rail, and a starting-stage selector rail parallel to the conveying rail. The starting-stage selector rail is swingable between a first position straightly extending from an end of the conveying rail and a second position straightly extending from an end of the returning rail. A terminating-stage selector rail is parallel to the conveying rail, the terminating-stage selector rail being swingable between a third position straightly extending from the other end of the conveying rail and a fourth position straightly extending from the other end of the returning rail. The apparatus also includes a plurality of conveying carriages moved on the conveying rail and the returning rail, the conveying carriage conveying a work from the starting-stage selector rail to the terminating-stage selector rail through the conveying rail. The apparatus further includes a carriage drive mechanism moving the conveying carriages on the conveying rail, the return rail, the starting-stage selector rail and the terminating-stage selector rail. The carriage drive mechanism comprises a carriage conveying mechanism which moves the conveying carriages disposed on the conveying rail and the starting-stage selector rail set at the first position in a conveying direction, and a carriage returning mechanism which moves the conveying carriages disposed on the returning rail and the terminating-stage selector rail set at the fourth position in a returning direction. The carriage returning mechanism comprises a returning finger lever connected to the conveying carriage and a carriage transfer mechanism which is disposed under the conveying rail, the carriage transfer mechanism reciprocatingly moving the returning finger lever along the returning direction. 
     Still another aspect of present invention resides in a work conveying apparatus which comprises a conveying rail, a returning rail disposed along the conveying rail, and a starting-stage selector rail parallel to the conveying rail. The starting-stage selector rail is swingable between a first position straightly extending from an end of the conveying rail and a second position straightly extending from an end of the returning rail. A terminating-stage selector rail is parallel to the conveying rail, the terminating-stage selector rail being swingable between a third position straightly extending from the other end of the conveying rail and a fourth position straightly extending from the other end of the returning rail. The apparatus also includes a plurality of conveying carriages moved on the conveying rail and the returning rail, the conveying carriage conveying a work from the starting-stage selector rail to the terminating-stage selector rail through the conveying rail. The apparatus further includes a carriage drive mechanism moving the conveying carriages on the conveying rail, the return rail, the starting-stage selector rail and the terminating-stage selector rail. The carriage drive mechanism comprises a carriage conveying mechanism which moves the conveying carriages disposed on the conveying rail and the starting-stage selector rail set at the first position in a conveying direction, and a carriage returning mechanism which moves the conveying carriages disposed on the returning rail and the terminating-stage selector rail set at the fourth position in a returning direction. The carriage returning mechanism comprises a starting-stage sprocket disposed in the vicinity of said starting-stage selector rail, a terminating-stage sprocket in the vicinity of the terminating-stage selector rail, an endless chain wound around the starting-stage sprocket and the terminating-stage sprocket, a return projection which is projected from each of the conveying carriages, and a plurality of fixing projections installed to the endless chain at predetermined intervals, the fixing projections being in contact with the return projections, respectively, when the conveying carriages are returned from the terminating stage to the starting stage. 
     Another aspect of the present invention resides in a work conveying method which comprises a step for moving a plurality of conveying carriages continuously set on a conveying rail and a starting-stage selector rail by one pitch in a conveying direction; a step for detaching a work from the conveying carriage set on the terminating-stage selector rail; a step for displacing the starting-stage selector rail and a terminating-stage selector rail from first positions straightly extending from ends of the conveying rail to second positions straightly extending from ends of a returning rail; a step for moving the plurality of the conveying carriages continuously set on the returning rail and the terminating-stage selector rail by one pitch in a returning direction; a step displacing the starting-stage selector rail and the terminating-stage selector rail from the second positions to the first positions; and a step for attaching a work to the conveying carriage set on the starting-stage selector rail. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, like reference numerals denote like elements and components throughout all figures, in which: 
     FIG. 1 is a partial side view showing a starting stage of a work conveying apparatus of a first embodiment according to the present invention; 
     FIG. 2 is a top view showing the work conveying apparatus including the starting stage and a terminating stage and a part of conveying stages therebetween; 
     FIG. 3 is a partial top view of the work conveying apparatus of the first embodiment; 
     FIG. 4 is a cross-sectional view taken in the direction of arrows substantially along the line IV—IV of FIG. 1; 
     FIG. 5 is a cross-sectional view taken in the direction of arrows substantially along the line V—V of FIG. 1; 
     FIG. 6 is a view taken in the direction of the arrow VI of FIG. 5; 
     FIG. 7 is a view taken in the direction of the arrow VII of FIG. 6; 
     FIG. 8 is a partial side view showing a starting stage of the work conveying apparatus of a second embodiment according to the present invention; 
     FIG. 9 is a partial top view of the work conveying apparatus of the second embodiment; 
     FIG. 10 is a cross-sectional view taken in the direction of arrows substantially along the line X—X of FIG. 9; 
     FIG. 11 is a cross-sectional view taken in the direction of arrows substantially along the line XI—XI of FIG. 9; 
     FIG. 12 is a view taken in the direction of the arrow XII of FIG. 11; 
     FIG. 13 is a view taken in the direction of the arrow XIII of FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 to  7 , there is shown a first embodiment of a method and apparatus for conveying works in accordance with the present invention. 
     As shown in FIGS. 1 and 3, the work conveying apparatus according to the present invention is arranged to linearly extend from a left hand side toward a right hand side to convey works W from a starting stage shown in FIG. 1 toward a terminating stage located at a leftmost side in FIG.  2 . The work conveying apparatus is horizontally provided on a flat ground G through a base. A plurality of conveying carriages  41  for respectively supporting works W thereon are continuously disposed on guide rails  67  along a conveying direction of the work conveying apparatus. These conveying carriages  41  are conveyed toward the left hand side direction of FIGS. 2 and 3 by one pitch corresponding to a length of each stage of the work conveying apparatus. 
     The conveyed work W in this embodiment is a body side-panel of an automotive vehicle to be worked on each stage of the work conveying apparatus. The conveying carriage  41  comprises two work supporting tools  43  and  45  for supporting lower end portions of the work W, a pair of opening supporting tools  47  and  49  for supporting an opening Wa of the work W in the fore-and-aft direction, a rear supporting tool  51  for supporting a lower and rear end portion of the work W and a base plate  53 . These supporting tools  43 ,  45 ,  47 ,  49  and  51  are installed on the base plate  53 . 
     The opening supporting tools  47  and  49  are installed on the base plate  52  through a mount  55  and are extendable in the fore-and-aft direction by means of air-cylinder drive. The rear supporting tool  51  is installed at an end portion of a swing arm  57  which is installed on a bracket  59  mounted on the base plate  53 . The swing arm  57  is swingable on the bracket  59  along a vertical plane corresponding to a paper surface of FIG. 1 so as to be able to adjust the height of the rear and lower end portion of the work W. By vertically moving the other end portion of the swing arm  57  by means of an air-cylinder  63  installed to the base plate  53 , the rear supporting tool  51  is vertically moved to vary the height level of the rear end portion of the work W. 
     The conveying carriage  41  comprises a plurality of roller units  69  which clamp a pair of guide rails  67  disposed along a work conveying direction. Each roller unit  69  rotatably clamps the guide rails  67  of a plate shape in the vertical direction as shown in FIG.  1 . The guide rails  67  in the starting stage is divided at a boundary Ss between the starting stage and a second state as shown in FIGS. 2 and 3. The divided rails of the starting stage are starting-stage selector rails  71   a . Further, the guide rails  67  are divided at a boundary St between the terminating stage and its adjacent stage as shown in FIG.  2 . The divided rails  67  of the terminating stage are terminating-stage selector rails  71   b . The guide rails  67  located between the boundaries Ss and St are conveying rails  73 . Therefore, each conveying carriage  41  is moved from the starting-stage selector rails  71   a  through the conveying rails  73  to the terminating-stage rails  71   b  while supporting the work W. 
     A pair of returning rails  75  having the form as same as that of the guide rails  65  are disposed on a vertical plane which is parallel with and perpendicular to the plane including the guide rails  67 , as shown in FIG.  2 . The returning rails  75  function to guide the conveying carriage  41  without the work W from the terminating stage to the starting stage. 
     As shown in FIG. 4, the starting-stage selector rails  71   a  are swingable on a pair of supporting shafts  77  directed along the conveying direction. The starting-stage selector rails  71   a  are swung between a horizontal position represented by continuous lines and a vertical position represented by two-dot chain lines. When the starting-stage selector rails  71   a  are positioned at the horizontal position, they are positioned on the line extending from the conveying rails  73 . Further, when the starting-stage selector rails  71   a  are positioned at the vertical position, they are positioned on the line extending from the returning rails  75 . Each supporting shaft  77  is supported by a pair of supporting brackets  81  set on a base  79 , as shown in FIG.  1 . The starting-stage selector rails  71   a  are fixed to intermediate portions of a pair of rotation supporting members  83  rotatably supported by the supporting brackets  81  through connecting members  85 , as shown in FIG.  1 . 
     As shown in FIGS. 3 and 4, a pair of air-cylinders  89  for rotating the starting-stage selector rails  71   a  are installed to the base  79  through cylinder brackets  87 , respectively. A tip end of a piston rod  91  of the air-cylinder  89  is rotatably connected through a pin  95  to a bracket  93  disposed at a laterally side portion of the connecting member  85 . Therefore, by moving the piston rod  91  toward the right hand side direction in FIG. 4, the starting-stage selector rails  71   a  are swung from the horizontal position represented by the continuous lines to the vertical position represented by the two-dot chain lines shown in FIG.  4 . 
     The terminating-stage selector rails  71   b  are also swingable between a horizontal-position extending from the conveying rails  73  and a vertical position extending from the returning rails  75 . 
     A plurality of carriage conveying mechanisms  97  are provided in the plurality of stages corresponding to the conveying carriages  41  set on the conveying rails  73  between the starting-stage rails  71   a  and the terminating-stage rails  71   b , respectively. As shown in FIG. 5, the carriage conveying mechanism  97  is disposed under the conveying rails  73  and on a base  101  of the work conveying apparatus so that a direct guide rail  99  is parallel to the conveying rails  73  and that a work supporting mechanism  103  reciprocatingly moves on the direct guide rails  99  along the work conveying direction. 
     The work supporting mechanism  103  comprises a conveying finger lever  107  and a returning finger lever  111 . The conveying finger lever  107  functioning as a swing lever is connectable to a conveying projection  105  installed at a front end portion of each conveying carriage  41  to support the conveying carriage  41 . The returning finger lever  111  functioning as a swing lever is connectable to a returning projection  109  installed at a front end portion of each conveying carriage  41  to support the conveying carriage  41  in the returning stages. 
     When the conveying carriage  41  is located on the starting-stage selector rails  71   a  or the terminating-stage selector rails  71   b  which is positioned at the horizontal position extending from the conveying rails  73 , the conveying finger lever  107  is connected to the conveying projection  105 . Further, when the conveying carriage  41  is located on the starting-stage selector rails  71   a  or the terminating-stage selector rails  71   b  which is positioned at the vertical position extending from the returning rails  75 , the returning finger lever  111  is connected to the returning projection  109 . 
     In addition to the conveying and returning projections  105  and  109  installed at the front end portion of the conveying carriage  41 , other projections similar to the projections  105  and  109  are installed at rear end portions of the conveying carriage  41  although not shown in Figures. When the conveying carriage  41  is conveyed from the foremost stage on the conveying rails  73  to the terminating stage, the other work supporting mechanism  103   b  supports the other projections  105   b  and  109   b . If the conveying carriage  41  is conveyed to the terminating-stage selector rails  71   b  by supporting the projections  103   a  and  105   a  provided at the front end portions of the conveying carriage  41  by means of the work supporting mechanism  103   a  provided at the front end portions of the conveying carriage  41 , the work supporting mechanism  103   a  interferes with a rail selector mechanism of the terminating-stage selector rails  71   b . Therefore, these projections  105   b  and  109   b  and the work supporting mechanism  103   b  are provided. 
     The conveying finger lever  107  is swingably supported at a pine  115  fixed to the supporting bracket  113 , and a depressed portion  107   a  is formed at a tip end portion of the conveying finger lever  107  so as to be connected to the conveying projection  105 . The other end portion of the conveying finger lever  107  is connected to a piston rod  127  of a lever selector cylinder  123  through a joint  119 . Similarly, the returning finger lever  111  is swingably supported at a pin  117  fixed to the supporting bracket  113 , and a depressed portion  111   a  is formed at a tip end portion of the returning finger lever  107  so as to be connected to the returning projection  109 . The other end portion of the returning finger lever  111  is connected to a piston rod  129  of a lever selector cylinder  125  through a joint  121 . Accordingly, by elongating or shortening a projecting amount of each of the piston rods  127  and  129 , each of the finger levers  107  and  111  is swung on each of pins  115  and  117 . By these swing movements of the finger levers  107  and  111 , the finger levers  107  and  111  are connected to and disconnected from the projections  105  and  109 , respectively. 
     As shown in FIG. 5, the swing supporting bracket  113  is fixed through a conveying bar  133  to an upper portion of the direct drive guide  131  which is engaged with the direct guide rail  99 . The lever selector cylinders  123  and  125  are fixed to the conveying bar  133  through a cylinder bracket  135 . 
     A rack  137  is fixed to the conveying bar  133  along the longitudinal direction of the conveying bar  133  and is meshed with a pinion  139 . The pinion  139  is meshed with a drive gear  143  driven by a drive motor  141 . The drive gear  143  is rotatably supported to a supporting member  147  through a motor bracket  149 . The supporting member  147  is fixed to the base  101 . 
     The conveying bar  133  is reciprocated in the work conveying direction according to the right and reverse rotations of the drive motor  141 . According to the movement of the conveying bar  133 , the work supporting mechanism  103  is reciprocated to convey the conveying carriage  41  with the work W and to return the conveying carriage  41  without the work W. 
     Next, the manner of operation of the work conveying apparatus of the first embodiment will be discussed. 
     Under the condition shown in FIG. 1, the starting-stage selector rails  71   a  and the terminating-stage selector rails  71   b  are located at the horizontal positions extending from the conveying rails  73 , respectively. Under this condition, the rearmost conveying carriage  41  is set on the starting-stage selector rails  71   a , and the foremost conveying carriage  41  is set on the conveying rails  73  adjacent to the terminating-stage selector rails  71   b . Further, the other conveying carriages  41  are continuously set on the conveying rails  73  between the foremost and rearmost conveying carriages  41 . That is, under this condition, no conveying carriage  41  is set on the terminating-stage selector rails  71   b . Of course, the other conveying carriages  41  are continuously set on the returning rails  75 . 
     First, the conveying finger levers  107  and the returning finger levers  111  are set such that the projections  105  of the conveying carriages  41  on the conveying rails  73  and the starting-stage selector rails  71   a  are supported to the conveying finger levers  107 , respectively, and that the returning projections  109  of the conveying carriages  41  on the returning rails  51  are not supported to the returning finger levers  111 . Then, the drive motor  141  is rotated in the right direction. By these operations, the pinion  139  is rotated and the rack  137  is moved by one pitch toward the conveying direction together with the conveying bar  133 . Due to this one-pitch movement, each conveying carriage  41  on the guide rails  67  is conveyed in the conveying direction by one-pitch. According to this one-pitch movement of the conveying carriage  41 , the foremost carriage  41  on the conveying rails  73  adjacent the terminating-stage selector rails  71   b  is moved to the terminating-stage selector rails  71   b , and the work W set on the conveying carriage  41  of the terminating state is then detached from the conveying carriage  41 . The conveying carriage  41  on the starting-stage selector rails  71   a  is moved to the conveying rails  73  adjacent to the starting-stage selector rails  71   a . Therefore, as a result of this operation, no conveying carriage  41  exists on the starting-stage selector rails  71   a.    
     Next, the rail selecting cylinder  89  shown in FIG. 3 is operated to rotate the starting-stage selector rails  71   a  by 90 degrees from the horizontal position represented by continuous lines in FIG. 4 to the vertical position represented by the two-dot chain lines in FIG.  4 . Similarly, the terminating-stage selector rails  71   b  are rotated by 90 degrees from the horizontal position to the vertical position. 
     Thereafter, the returning projections  109  of the conveying carriages  41  set on the returning rails  75  without the work W are supported to the returning finger levers  111 , respectively. On the other hand, the conveying finger levers  107  are released from the projections  105  of the conveying carriages  41  set on the conveying rails  73 . Next, the drive motor  141  is rotated in the reverse direction. By these operations, the pinion  139  is rotated and the rack  137  is moved by one pitch toward the returning direction together with the conveying bar  133 . Due to this one-pitch returning movement, each conveying carriage  41  on the returning rails  75  is conveyed in the returning direction by one-pitch. According to this one-pitch returning movement of the conveying carriage  41 , the conveying carriage  41  on the terminating-stage selector rails  71   b  is moved to the returning rails  75  adjacent to the terminating-stage selector rails  71   b , and the conveying carriage  41  on the conveying rails  73  adjacent to the terminating state is moved to the terminating-stage selector rails  71   b.    
     Under this condition, the rail selector cylinder  89  is then operated to rotate the starting-stage selector rails  71   a  with the conveying carriage  41  from the vertical position to the horizontal position by 90 degrees. Then, the new work W is installed to the conveying carriage  41  set on the starting-stage selector rails  71 . 
     Thereafter, each conveying carriage  41  on the conveying rails  73  is again moved in the conveying direction by one pitch as mentioned above. By repeatedly executing the above-mentioned operations, the works W are continuously conveyed by the work conveying apparatus according to the present invention. 
     With the thus arranged work conveying apparatus of the first embodiment according to the present invention, the conveying carriage  41  of the returning rails  75  is moved to the conveying rails  73  by rotating the starting-stage selector rails  71   a  by 90 degrees, and the conveying carriage  41  set on the conveying rails  73  is moved to the returning rails  75  by rotating the terminating-stage selector rails  71   b  by 90 degrees. This arrangement simplifies the total structure of this conveying system. Therefore, it becomes possible to decrease the production cost of this apparatus. Further, since the cycle time of the apparatus is shortened, the work conveying time is shortened. Furthermore, the arrangement of the conveying rails  73  and the returning rails  75  enables the size of the apparatus to be decreased as compared with the conventional apparatuses. 
     Referring to FIGS. 8 to  13 , there is shown a second embodiment of the work conveying apparatus and method thereof according to the present invention. 
     The construction of the second embodiment is basically the same as that of the first embodiment except for a construction of a carriage returning mechanism  151  of the carriage drive mechanism  97 . Therefore, in this embodiment like reference numeral denote like parts and elements of the first embodiment as shown in FIGS. 8 to  13 , and the explanation thereof will be omitted herein. Herein, only the carriage returning mechanism  151  and the manner of operation of the work conveying apparatus of the second embodiment will be discussed. 
     The carriage returning mechanism  151  shown in FIG. 10 functions to return the conveying carriage  41  without the work W toward the starting stage. The carriage returning mechanism  151  comprises an endless chain  153  which is disposed at a position laterally adjacent to the returning rails  75  and along the work conveying direction. The work returning mechanism  151  shown in FIG. 10 is practically disposed in the vicinity of the terminating stage. The endless chain  153  is wound around a starting-stage sprocket  155  disposed in the vicinity of the frond end of the starting stage selector rails  71   a . The sprocket  155  is rotatably supported to a rotation supporting bracket  157 . 
     The other side of the endless chain  153  is wound around a terminating-stage sprocket  159  disposed in the vicinity of the rear end of the terminating stage. The terminating-stage sprocket  159  is rotatably supported to a rotation supporting bracket  161 . The terminating-stage sprocket  159  is driven by a returning drive motor  165  supported to a cylinder bracket  163 . 
     A return projection  167  is projected from each conveying carriage  41  toward the chain  153  as shown in FIG.  10 . The chain  153  is provided with a plurality of fixing projections  169  at predetermined intervals corresponding to the interval of the conveying carriages  41 . 
     The fixing projections  169  are engaged with the return projections  167  according to the reverse rotation of the terminating-stage sprocket  159  to move the chain  153  in contact with the return projection  157  through the fixing projection  159 , the conveying carriage  41  is moved in the returning direction. 
     Next, the manner of operation of the work conveying apparatus of the second embodiment according to the present invention will be discussed. 
     Under the condition shown in FIG. 8, the starting-stage selector rails  71   a  and the terminating-stage selector rails  71   b  are located at the horizontal positions extending from the conveying rails  73 . Under this condition, the rearmost conveying carriage  41  is set on the starting-stage selector rails  71   a , and the foremost conveying carriage  41  is set on the conveying rails  73  adjacent to the terminating-stage selector rails  71   b . Further, the other conveying carriages  41  are continuously set on the conveying rails  73  between the foremost and rearmost conveying carriages  41 . That is, under this condition, no conveying carriage  41  is set on the terminating-stage selector rails  71   b . The other conveying carriages  41  are continuously set on the returning rails  75 . 
     First the conveying finger levers  107  are set such that the projections  105  of the conveying carriages  41  on the conveying rails  73  and the starting-stage selector rails  71   a  are supported to the conveying finger levers  107 , respectively, and that the projections  109  of the conveying carriages  41 . 
     Next, the drive motor  141  is rotated in the right direction. By these operations, the pinion  139  is rotated and the rack  137  is moved by one pitch toward the conveying direction together with the conveying bar  133 . Due to this one-pitch movement, each conveying carriage  41  on the guide rails  67  is conveyed in the conveying direction by one-pitch. According to this one-pitch movement of the conveying carriage  41 , the foremost conveying carriage  41  on the conveying rails  73  adjacent the terminating-stage selector rails  71   b  is moved to the terminating-stage selector rails  71   b , and the work W set on the conveying carriage  41  of the terminating state is then detached from the conveying carriage  41 . The conveying carriage  41  on the starting-stage selector rails  71   a  is moved to the conveying rails  73  adjacent to the starting-stage selector rails  71   a . Therefore, as a result of this operation, no conveying carriage  41  exists on the starting-stage selector rails  71   a.    
     Next, the rail selecting cylinder  89  shown in FIG. 10 is operated to rotate the starting-stage selector rails  71   a  by 90 degrees from the horizontal position represented by continuous lines in FIG. 10 to the vertical position represented by the two-dot chain lines in FIG.  10 . Similarly, the terminating-stage selector rails  71   b  are rotated by 90 degrees from the horizontal position to the vertical position. 
     Thereafter, the return drive motor  165  is driven to rotate the sprocket  159 . By this rotation of the sprocket  159 , the fixing projections  169  provided to the chain  153  are in contact with the return projections  167  of the conveying carriages  41  set on the returning rails  75  and the terminating stage selector rails  71   b  set at the vertical position, and move the return projections  167  toward the returning direction to move the conveying carriages  41  set at the vertical position toward the returning direction by one-pitch. By this one-pitch return movement, the conveying carriage  41  on the terminating-stage selector rails  71   b  is moved to the return rails  75  adjacent to the terminating stage, and the conveying carriage  41  set on the return rails  75  adjacent to the starting stage is moved to the starting state selector rails  71   a  set at the vertical position. 
     Under this condition, the rail selecting cylinder  89  is operated to rotate the starting-stage selector rails  71   a  with the conveying carriage  41  from the vertical position to the horizontal position by 90 degrees. Then, the new work W is installed to the conveying carriage  41  set on the starting-stage selector rails  71 . 
     Then, each conveying carriage  41  on the conveying rails  73  is moved in the conveying direction by one pitch as mentioned above. 
     With the thus arranged work conveying apparatus of the second embodiment according to the present invention, the movement of the conveying carriages  41  between the returning rails  75  and the conveying rails  73  is executed by rotating the starting-stage selector rails  71   a  and the terminating-stage selector rails  71   b  by 90 degrees as same in the first embodiment. Therefore, advantages gained by the first embodiment are also ensured by the arrangement of the second embodiment. 
     The entire contents of Japanese Patent Applications No. 11-8263 and 11-8274 respectively filed on Jan. 14, 1999 in Japan are incorporated herein by reference. 
     Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teaching. The scope of the invention is defined with reference to the following claims.