Abstract:
A conveyor apparatus which allows a workpiece to be carried in and out of a desired process and lends itself to easy maintenance as well is provided. A conveyor apparatus ( 13 ) includes a first conveyance mechanism ( 13 A) capable of carrying a board ( 7 ) into a desired process and a second conveyance mechanism ( 13 B) capable of carrying the board ( 7 ) out of the desired process. The first conveyance mechanism ( 13 A) includes a first conveying rod ( 18 ) adapted to reciprocate, a first pusher piece ( 19 ) fixed to the first conveying rod ( 18 ) and configured to protrude from the rod, and a switching mechanism adapted to switch the first pusher piece ( 19 ), by turning the first conveying rod ( 18 ) a predetermined angle, between an engaged position where the first pusher piece ( 19 ) engages with the board ( 7 ) and a retracted position where the pusher piece ( 19 ) is separated from the board ( 7 ), and the second conveyance mechanism ( 13 B) includes a second conveying rod ( 32 ) adapted to reciprocate, a pusher piece ( 19 ) fixed to the second conveying rod ( 32 ) and configured to protrude from the rod, and a switching mechanism adapted to switch the second pusher piece ( 19 ), by turning the second conveying rod ( 32 ) a predetermined angle, between an engaged position where the pusher piece ( 19 ) engages with the board ( 7 ) and a retracted position where the pusher piece ( 19 ) is separated from the board.

Description:
The present application is a National Stage Application of PCT/JP2012/071621, filed Aug. 27, 2012, which claims priority from Japanese Patent Application No. 2011-185644, filed Aug. 29, 2011. 
     FIELD OF THE INVENTION 
     The present invention relates to a conveyor apparatus, which, for example, is effectively used for a reflow soldering apparatus provided with a decompression process for degassing a soldered portion during soldering. 
     BACKGROUND OF THE INVENTION 
     The reflow soldering apparatus solders, for example, a printed circuit board on which electronic components have been mounted using cream solder, solder paste, or the like while conveying the board on a conveyor, inside a furnace having a preheating process, a reflow process, and a cooling process in sequence (See Patent Document 1). 
     Patent Document 2 discloses a method for conveying a board in a reflow furnace. A conveyor system disclosed in Patent Document 2 includes a main endless conveyor belt configured to extend from an inlet to an outlet of a reflow furnace and operated at a constant speed. A board conveyance path is formed to convey boards from the inlet to the outlet of the reflow furnace on the main endless conveyor belt. On the board conveyance path, plural pushers are placed, being spaced away from each other in a workpiece conveyance direction, and each of the pushers reciprocates in directions the same as and opposite to the workpiece conveyance direction. The pusher can push the board on the main endless conveyor belt upward and convey the board in the workpiece conveyance direction at a controlled speed. An endless belt has been adopted to reciprocate the pushers attached to the endless belt. When the endless belt rotates in a forward direction, the pusher moves in the workpiece conveyance direction, and when the endless belt rotates in a reverse direction, the pusher moves in the direction opposite to the workpiece conveyance direction. 
     A first pusher included in the plural pushers is used to send a board into a reflow process of the reflow furnace. A second pusher is used to send the board out of the reflow process and convey the board from the reflow process to a cooling process. The first and second pushers are controlled to move independently of the main endless conveyor belt at a speed faster than that of the main endless conveyor belt. 
     In soldering using a reflow furnace, preferably a degassing process is applied in advance to avoid foaming in accompanying with heating. For example, in the reflow soldering apparatus shown in Patent Document 1, when a decompression chamber capable of reducing ambient pressure is installed on a board conveyance path such that a soldered portion formed on the board and molten by heating will be degassed in the decompression chamber, a single conveyor (main endless conveyor belt) cannot be installed over the entire board conveyance path including the decompression chamber because the decompression chamber needs to be enclosed hermetically during decompression. Therefore, separate conveyors are installed in the decompression chamber and in conveyance paths in processes preceding and succeeding the decompression chamber. In this case, if a conveyor is installed in the decompression chamber, there is a problem in that mechanical components of the conveyor become expensive to withstand a decompressed atmosphere and that maintenance frequency is increased. 
     With the board conveyance method described in Patent Document 2, air cylinders are used to move the pushers up and down, resulting in increased maintenance frequency. Also, the air cylinders themselves need to be moved in the conveyance direction. 
     Patent Document 1 
     Japanese Patent Laid-Open No. 2000-188467 
     Patent Document 2 
     Japanese Patent Laid-Open No. 11-40941 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a conveyor apparatus capable of carrying a workpiece in and out of a desired process. 
     A further object of the present invention to provide a conveyor apparatus which lends itself to easy maintenance as well. 
     A still further object of the present invention is to provide a conveyor apparatus which is suitable for a reflow furnace provided with a degassing process. 
     A conveyor apparatus according to the present invention comprises a first conveyance mechanism capable of carrying a workpiece into a desired process on a conveyance path along which the workpiece is conveyed; and a second conveyance mechanism capable of carrying the workpiece out of the desired process, characterized in that 
     the first conveyance mechanism includes: 
     a first conveying rod adapted to reciprocate along the conveyance path, 
     a first pusher member fixed to the first conveying rod and configured to protrude from the first conveying rod, and 
     a first switching mechanism adapted to switch the first pusher member, by turning the first conveying rod a predetermined angle, between an engaged position where the first pusher member engages with the workpiece and a retracted position where the first pusher member is separated from the workpiece, and 
     the second conveyance mechanism includes: a second conveying rod adapted to reciprocate along the conveyance path, 
     a second pusher member fixed to the second conveying rod and configured to protrude from the second conveying rod, and 
     a second switching mechanism adapted to switch the second pusher member, by turning the second conveying rod a predetermined angle, between an engaged position where the second pusher member engages with the workpiece and a retracted position where the second pusher member is separated from the workpiece. 
     The conveyor apparatus according to the present invention allows a workpiece to be carried in and out of a desired process and lends itself to easy maintenance as well. The conveyor apparatus according to the present invention is suitably applied to a reflow furnace. 
     Preferably the first switching mechanism of the first conveyance mechanism includes a guide member. The guide member includes a guiding portion adapted to guide a guided portion protruding from the first conveying rod. The guiding portion is formed into a closed loop by a first guiding portion and a second guiding portion configured to extend in parallel to each other in a conveyance direction by being spaced away from each other and a coupling guide portion configured to couple the first and second guiding portions to each other. The guided portion is configured to make a round of the guiding portion of the closed loop through a reciprocating motion of the first conveying rod by being guided by the guiding portion. When the guided portion is guided by the first guiding portion, the pusher members are positioned so as to push the workpiece. When the guided portion moves from the first guiding portion to the second guiding portion, the first conveying rod is turned a predetermined angle and the pusher members are preferably placed at a position retracted from the workpiece. Preferably a switching mechanism of the second conveyance mechanism is configured similarly. Preferably the guiding portion comprises a guide hole or a guide groove. 
     The first conveying rod and the second conveying rod may be driven by either of the following methods. Specifically, the first conveying rod and the second conveying rod may be driven by common driving means or first driving means adapted to reciprocate the first conveying rod and second driving means adapted to reciprocate the second conveying rod may be independent of each other. 
     Preferably the first conveying rod and the first switching mechanism are placed on both sides of the conveyance path, the first conveying rod having the first pusher member; and the second conveying rod and the second switching mechanism are placed on both sides of the conveyance path, the second conveying rod having the second pusher member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall configuration diagram showing a reflow soldering apparatus equipped with a conveyor apparatus according to an embodiment of the present invention; 
         FIGS. 2(A) to 2(D)  are explanatory diagrams showing operation of the conveyor apparatus; 
         FIG. 3  is a sectional view showing the conveyor apparatus; 
         FIGS. 4(   a ) and  4 ( b ) are plan views showing guide members, where  FIG. 4(   a ) shows a guide member on the right side as viewed from an outlet side to an inlet side of a furnace while  FIG. 4(   b ) shows a guide member on the left side; 
         FIG. 5  is a longitudinal section view showing a guide member; and 
         FIG. 6  is an overall configuration diagram of a reflow soldering apparatus equipped with a modification of a drive system for first and second conveying rods. 
     
    
    
     DESCRIPTION OF SYMBOLS 
     
         
           1  . . . Furnace;  2 A,  2 B . . . Preheating chamber;  3 A,  3 B . . . Reflow chamber;  4  . . . Cooling chamber;  5  . . . Decompression chamber;  5 A . . . Upper housing;  5 B . . . Lower housing;  6  . . . Partition wall;  7  . . . Printed board with electronic components mounted thereon;  8 ,  9 ,  10  . . . Board conveyance rail;  11  . . . Inlet;  12  . . . Outlet;  13  . . . Conveyor apparatus;  13 A . . . First conveyance mechanism;  13 B . . . Second conveyance mechanism;  14 ,  15 ,  16  . . . Heater;  17  . . . Cooling device;  18  . . . First conveying rod;  19  . . . Pusher piece;  20  . . . Rod support member;  20   a  . . . Rod bearing hole;  20   b  . . . Guiding portion;  21  . . . Support wall;  21   a  . . . Guide groove;  22  . . . Guide rod;  23  . . . Guide member;  23   a  . . . Guide member body;  24  . . . Guide hole;  25  . . . First guide hole;  26  . . . Second guide hole;  27  . . . Coupling guide hole;  28  . . . Blocking piece;  29  . . . Pivot pin;  30  . . . Linking piece;  31  . . . Return spring;  32  . . . Second conveying rod;  33  . . . Upright member;  34  . . . Coupling rod;  35  . . . Chain conveyor;  36  . . . Coupling rod 
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. 
     Overall Configuration of Reflow Furnace: 
     As shown in  FIG. 1 , a reflow soldering apparatus (reflow furnace) includes plural chambers partitioned in a workpiece conveyance direction and lined up in series within the furnace  1 . Specifically, the reflow furnace  1  includes, in order in the workpiece conveyance direction; two preheating chambers  2 A and  2 B located on the right side of the drawing, two reflow chambers  3 A and  3 B located in the center of the drawing, and one cooling chamber  4  located on the left side of the drawing. Furthermore the reflow furnace  1  includes a decompression chamber  5  in the reflow chamber  3 B. Reference number  6  denotes a partition wall adapted to partition adjacent chambers. An inert gas—nitrogen gas according to the present embodiment—is supplied as an ambient gas into the reflow furnace  1  to prevent oxidation of solder. 
     A printed circuit board (hereinafter referred to simply as a “board”)  7  with electronic components mounted thereon is conveyed on conveyance rails laid linearly in the reflow furnace  1 . The conveyance rails are made up of three pairs of rails  8 ,  9 , and  10  which are arranged in series in the workpiece conveyance direction, forming a pair of linear workpiece conveyance paths by being placed in a same horizontal plane in the reflow furnace  1 . The first conveyance rails  8  are disposed horizontally from a position in front of an inlet  11  of the furnace  1  to an inlet of the decompression chamber  5  in the furnace  1 . The second conveyance rails  9  are disposed horizontally in the decompression chamber  5 . The third conveyance rails  10  are disposed horizontally from an outlet of the decompression chamber  5  to an outlet  12  of the furnace  1 . The rails in each of the conveyance rail pairs  8 ,  9 , and  10  are installed on right and left sides of the conveyance path of the board  7 , supporting right and left edges of a bottom face of the board  7 . 
     Cream solder has been applied to soldering locations on a top face of the board  7  which is input to the reflow furnace  1  and electronic components have been put on the cream solder. The board  7  with electronic components placed thereon via the cream solder are moved along the conveyance rails  8 ,  9 , and  10  by the conveyor apparatus  13 . 
     That is, the board  7  is conveyed intermittently by the conveyor apparatus  13  from a position in front of the inlet  11  of the furnace  1 . First, the board  7  is sent to the first preheating chamber  2 A and heated there in a first preheating process for a predetermined period of time in an ambient gas heated by a heater  14 . Next, the board  7  is sent to the adjacent preheating chamber  2 B next by the conveyor apparatus  13  and heated there in a preheating process for a predetermined period of time in an ambient gas heated by a heater  14 . Next, the board  7  is sent to the first-stage reflow chamber  3 A by the conveyor apparatus  13 , and a soldered portion is molten by being heated there in a reflow process for a predetermined period of time in an ambient gas heated by a heater  15 . 
     The decompression chamber  5  in the second-stage reflow chamber  3 B is divided horizontally into an upper housing  5 A and lower housing  5 B, and the lower housing  5 B is fixedly placed in the reflow chamber  3 B. In contrast, the upper housing  5 A is configured to be able to move up and down by means of an actuator-specifically, a cylinder device (not shown)—and able to assume two states: a tightly closed state (see  FIG. 1 ) in which the upper housing  5 A is placed in close contact with the lower housing  5 B by moving down and an open state (not shown) in which the upper housing  5 A is placed above and spaced away from the lower housing  5 B by moving up. 
     Thus, the board  7  is carried into the decompression chamber  5  in the reflow chamber  3 B from the reflow chamber  3 A by the conveyor apparatus  13 , in open state in which the upper housing  5 A of the decompression chamber  5  is placed above and spaced away from the lower housing  5 B. On the other hand, the tightly closed state is achieved in a decompression process in which the decompression chamber  5  is depressurized to degas the cream solder on the board  7 . In the decompression process, the soldered portion is heated and degassed for a predetermined period of time. That is, the soldered portion on the board  7  is heated and molten in an ambient gas heated by a heater  16 , the decompression chamber  5  is subsequently put in the tightly closed state and depressurized by a vacuum pump (not shown) to a predetermined decompressed atmosphere in which the soldered portion is degassed, and the molten soldered portion on the board  7  is degassed in the predetermined decompressed atmosphere. 
     Subsequently, the decompression chamber  5  is put in the open state, the board  7  is sent by the conveyor apparatus  13  to the cooling chamber  4  through the reflow chamber  3 B heated by the heater  15 , and the soldered portion solidifies in the cooling process there by being cooled by a cooling device  17  for a predetermined period of time. Then, the board  7  is carried outside from the cooling chamber  4  through the outlet  12  of the furnace  1  by the conveyor apparatus  13 . 
     Conveyor Apparatus  13 : 
     Next, the conveyor apparatus  13  will be described below. The conveyor apparatus  13  includes a first conveyance mechanism  13 A and second conveyance mechanism  13 B. 
     First, the first conveyance mechanism  13 A will be described. The first conveyance mechanism  13 A includes first conveying rods  18  ( FIGS. 1 and 3 ). The first conveying rods  18  are placed horizontally along the first conveyance rails  8 , extending in the furnace  1  from a position in front of the inlet  11  of the furnace  1  to a position in front of the decompression chamber  5  ( FIG. 3 ). Four pusher pieces  19  are positioned at intervals on the first conveying rod  18 . The left and right pusher pieces  19  are fixedly attached to the respective first conveying rods  18 . As described later, as the first conveying rod  18  is axially rotated, each pusher piece  19  can assume an engaged position (position indicated by a solid line in  FIG. 3 ) where the pusher piece  19  abuts the board  7  and a retracted position (position indicated by a virtual line in  FIG. 3 ) spaced away from the board  7 . 
     An end of each first conveying rod  18  on the side of the furnace inlet  11  is inserted in a bearing hole  20   a  of a rod support member  20 . The first conveying rod  18  is supported by the rod support member  20  axially rotatably, but immovably in an axial direction. The rod support member  20  has a guiding portion  20   b  on an outer surface thereof. A support wall  21  is elected on an outer side of the rod support member  20 . The guiding portion  20   b  of the rod support member  20  is fitted in a horizontal guide groove  21   a  formed in an inner surface of the support wall  21 . The rod support member  20  is configured to be able to move horizontally by being guided by the guide groove  21   a  provided with one end and another end. Thus, the first conveying rod  18  can move horizontally in the furnace  1  in a conveyance direction of the board  7  along with the rod support member  20 . 
     When the first conveying rod  18  advances from the side of the inlet  11  of the furnace  1  to the side of the outlet  12  (hereinafter referred to as “forward movement”), the pusher piece  19  (see  FIG. 3 ) is positioned at a place (engaged position) where the pusher piece  19  engages with a rear face of the board  7  on the conveyance rails  8 , and when the first conveying rod  18  advances from the side of the outlet  12  of the furnace  1  to the side of the inlet  11  (hereinafter referred to as “backward movement”), the pusher piece  19  is positioned at a place (retracted position) retracted to above the board  7 . The pusher piece  19  is switched between the engaged position and the retracted position by axially rotating the first conveying rod  18  a predetermined angle. 
     Switching Mechanism for Switching Pusher Piece  19  Between Engaged Position and Retracted Position: 
     The switching mechanism includes a guide rod  22  (see  FIGS. 1 and 3 ) fixed in position to an end (front end) of the first conveying rod  18  on the side of the furnace inlet  11 . The guide rod  22  extends downward from the first conveying rod  18 . The switching mechanism includes a guide member  23  (see  FIGS. 1 and 3  to  5 ) placed in connection with the guide rod  22  and placed below the guide rod  22 . The guide member  23  has a body  23   a  which is a box-shaped member, and a guide hole  24  is formed in a top face of the box-shaped body  23   a . The guide rod  22  protruding from the first conveying rod  18  has its lower end inserted in the guide hole  24 . 
       FIGS. 4(   a ) and  4 ( b ) are plan views showing the guide members  23 , where  FIG. 4(   a ) shows the guide member on the right side as viewed from the outlet side to the inlet side of the furnace while  FIG. 4(   b ) shows the guide member on the left side. Referring to  FIG. 4 , the guide hole  24  includes a first guide hole  25  adapted to place the pusher piece  19  of the first conveying rod  18  at the engaged position, a second guide hole  26  adapted to place the pusher piece  19  at the retracted position, and a coupling guide hole  27  adapted to couple the two guide holes  25  and  26 . The first guide hole  25  and second guide hole  26  extend linearly along the conveyance direction of the board  7 . Also, the first and second guide holes  25  and  26  extend in parallel to each other by being spaced away from each other. Also, the first and second guide holes  25  and  26  are joined together at both ends, i.e., at a front end and rear end in the workpiece conveyance direction via the coupling guide holes  27  described above. 
     Continuing to refer to  FIG. 4 , the rear end (end in upper part of  FIG. 4 ) of the first guide hole  25  is coupled to the rear end (end in upper part  FIG. 4 ) of the second guide hole  26  via a slant coupling guide hole  27  extending linearly in a diagonal direction. On the other hand, a front end portion (end in lower part of  FIG. 4 ) of the first guide hole  25  is coupled to the front end (end in lower part of  FIG. 4 ) of the second guide hole  26  via another slant coupling guide hole  27  extending linearly in a diagonal direction. In this way, the ends of the first and second guide holes  25  and  26  are coupled to each other via the coupling guide holes  27 , forming the closed-loop guide hole  24 , which in conjunction with the guide rod  22  inserted into the guide hole  24 , makes up a cam mechanism adapted to swing the pusher piece  19  between the engaged position and the retracted position. 
     As described above, the pusher piece  19  assumes an engaged position and retracted position. The first guide hole  25  is a cam groove adapted to place the pusher piece  19  at the engaged position. The board  7  located on rails has its rear end engaged with the pusher piece  19 , and when the first conveying rod  18  moves forward, the board  7  is pushed by the pusher, piece  19  and thereby conveyed from one processing position to another processing position. When the conveyance is finished, the first conveying rod  18  moves backward and returns to its original position. When the first conveying rod  18  moves backward, the pusher piece  19  is positioned at the retracted position. 
     When the guide rod  22  is located in the first guide hole  25 , the pusher piece  19  assumes the engaged position. On the other hand, when the guide rod  22  is located in the second guide hole  26 , the pusher piece  19  assumes the retracted position. Therefore, with the first conveying rod  18 , when the guide rod  22  moves forward by being guided by the first guide hole  25  (direction of arrow A in  FIG. 4 ), the pusher piece  19  is positioned at the engaged position (see  FIG. 3 ) and moves the board  7  forward by pushing the rear face of the board  7 . On the other hand, with the first conveying rod  18 , when the guide rod  22  moves backward by being guided by the second guide hole  26  (direction of arrow B in  FIG. 4 ), the pusher piece  19  is positioned at the retracted position (see  FIG. 3 ) above the board  7  so as not to interfere with the board  7 . 
     The following means is provided such that the guide rod  22  will move forward by being guided by the first guide hole  25  during forward movement of the first conveying rod  18  and move backward by being guided by the second guide hole  26  during backward movement of the first conveying rod  18 . 
     As shown in  FIGS. 4 and 5 , on a back face in upper part of the body  23   a  ( FIG. 5 ) of the guide member  23 , blocking pieces  28  are placed at opposite ends of the closed-loop guide hole  24 . One of the blocking pieces  28  is placed, intersecting the first guide hole  25  while the other blocking piece  28  is placed, intersecting the second guide hole  26 . Each of the blocking pieces  28  is fixed at one end to a pivot pin  29 . The pivot pin  29  is turnably installed between the first guide hole  25  and second guide hole  26 , perpendicularly penetrating the body  23   a  of the guide member  23 . A linking piece  30  is placed on a bottom face in lower part of the body  23   a  of the guide member  23 . The linking piece  30  is fixed at one end to a lower end of the pivot pin  29  and fixed at the other end to one end of a return spring  31  made up of a tension spring. The return spring  31  is fixed at the other end to the lower part of the body  23   a  of the guide member  23 . 
     As described above, the blocking piece  28  coupled with the linking piece  30  via the pivot pin  29  is located at such a height position as to interfere with the guide rod  22  while the linking piece  30  is located at such a height position as not to interfere with the guide rod  22 . 
     Therefore, during forward movement of the first conveying rod  18 , as the guide rod  22  moves forward and advances to the front end of the first guide hole  25  by being guided by the first guide hole  25 , the guide rod  22  comes into contact with the first blocking piece  28  illustrated in lower part of  FIG. 4 . As the guide rod  22  further moves forward, the first blocking piece  28  turns against the spring force of the return spring  31 . Then, the guide rod  22  reaches the front end (end in lower part of  FIG. 4 ) of the first guide hole  25 . When the guide rod  22  passes the first blocking piece  28 , the blocking piece  28  is returned to its original position by the return spring  31 . In a forward movement process of the first conveying rod  18 , i.e., in the process of advancing to the bottom end illustrated in  FIG. 4  by being guided by the first guide hole  25 , the pusher piece  19  is located at the engaged position (see  FIG. 3 ) as described above. Therefore, the pusher piece  19  engages with the board  7  and pushes the board  7  one process forward to an adjacent, next process (e.g., from the reflow process to the decompression process). 
     Next during backward movement of the first conveying rod  18 , as the guide rod  22  moves backward from the front end of the first guide hole  25  (moves upward from the lower end of the first guide hole  25  illustrated in  FIG. 4 ) by being guided by the first guide hole  25 , the guide rod  22  collides with the blocking piece  28  located across the first guide hole  25 . As can be seen well from  FIG. 4 , the blocking piece  28  diagonally crosses the first guide hole  25 . Preferably, the blocking piece  28  has an inclination angle equal to that of the coupling guide hole  27 . In  FIG. 4 , when the guide rod  22  collides with the blocking piece  28  by moving upward from the lower end of the first guide hole  25 , the guide rod  22  enters the slant coupling guide hole  27  by being guided by the slanted lateral edge of the blocking piece  28  and moves to the second guide hole  26  by passing through the coupling guide hole  27 . 
     With the first conveying rod  18 , when the guide rod  22  moves backward by being guided by the second guide hole  26 , the guide rod  22  comes into contact with the second blocking piece  28  illustrated in upper part of  FIG. 4 . As the guide rod  22  further moves backward, the second blocking piece  28  turns against the spring force of the return spring  31  illustrated in the upper part of  FIG. 4 . Then, the guide rod  22  reaches an end of the second guide hole  26  (upper end of the second guide hole  26  in  FIG. 4 ). When the guide rod  22  passes the second blocking piece  28 , the blocking piece  28  is returned to its original position by the return spring  31 . In a backward movement process of the first conveying rod  18 , i.e., in a process in which the first conveying rod  18  moves backward by being guided by the second guide hole  26 , the pusher piece  19  is located at the retracted position (see  FIG. 3 ) as described above. Therefore, being positioned at the retracted position above the board  7  so as not to interfere with the board  7 , the pusher piece  19  moves one process backward. 
     Next, with the first conveying rod  18 , when the guide rod  22  moves forward by being guided by the second guide hole  26 , (moves downward from the upper end of the second guide hole  26  in  FIG. 4 ), the guide rod  22  collides with the blocking piece  28  located across the second guide hole  26 . As can be seen well from  FIG. 4 , the blocking piece  28  illustrated in upper part of  FIG. 4  diagonally crosses the second guide hole  26 . Preferably, the blocking piece  28  has an inclination angle equal to that of the coupling guide hole  27 . In  FIG. 4 , when the guide rod  22  collides with the blocking piece  28  by moving downward from the upper end of the second guide hole  26 , the guide rod  22  enters the slant coupling guide hole  27  by being guided by the slanted lateral edge of the blocking piece  28  and moves to the first guide hole  25  by passing through the coupling guide hole  27 . That is, the guide rod  22  enters the coupling guide hole  27  by being guided by the blocking piece  28  having the lateral edge slanted in the traveling direction of the guide rod  22 . The coupling guide hole  27  is slanted in the traveling direction of the guide rod  22 , and the guide rod  22  enters the first guide hole  25  by being guided by the slanted coupling guide hole  27 . The operation described above is repeated subsequently. 
     Thus, through one reciprocating motion (forward movement and backward movement) of the first conveying rod  18 , the board  7  can be conveyed one process forward, i.e., to the next process. Note that the slant coupling guide hole  27  may be straight as described above or may be curved to some extent. 
     Note that the plural pusher pieces  19  for respective ones of plural processes are fixed to the first conveying rod  18  ( FIG. 2 ). This allows the boards  7  in respective processes to be sent to the next processes through a single forward motion of the first conveying rod  18 . That is, by the first conveying rod  18 , the board  7  located in front of the inlet  11  of the reflow furnace  1  is conveyed to the first preheating chamber  2 A (preheating process), the board  7  located in the first preheating chamber  2 A is conveyed to the next preheating chamber  2 B (preheating process), the board  7  located in the preheating chamber  2 B is conveyed to the reflow chamber  3 A (reflow process), and the board  7  located in the reflow chamber  3 A is sent to the decompression chamber  5  (decompression process). 
     Next, the second conveyance mechanism  13 B will be described. The second conveyance mechanism  13 B has a configuration similar to that of the first conveyance mechanism  13 A. That is, the second conveying rod  32  (see  FIG. 1 ) is placed horizontally, extending in the furnace  1  from immediately behind the decompression chamber  5  of the furnace  1  to a position ahead of the outlet  12  of the furnace  1 . Two pusher pieces  19  are fixed to the second conveying rod  32  at a distance from each other. Each pusher piece  19  protrudes from the rod  32 . As with the first conveying rod  18 , the second conveying rod  32  is supported by the rod support member  20  axially rotatably, but immovably in an axial direction. The rod support member  20  is configured to be able to move horizontally by being guided by the guide groove in the support wall. Thus, the second conveying rod  32  is also configured to be able to move horizontally in the furnace  1  in a conveyance direction of the board  7  along with the rod support member  20 . 
     Using the same switching mechanism as the one installed on the first conveying rod  18 , the second conveying rod  32  is configured such that the pusher piece  19  is placed at such a position (engaged position) as to push the rear face of the board  7  on the conveyance rails  10  when the second conveying rod  32  advances (moves forward) from the side of the inlet  11  of the furnace  1  to the side of the outlet  12 , and is placed at a position (retracted position) retracted to above the board  7  when the second conveying rod  32  moves backward from the side of the outlet  12  of the furnace  1  to the side of the inlet  11 . Consequently, through one reciprocating motion (forward movement and backward movement) of the second conveying rod  32 , the board  7  is conveyed one process forward, i.e., to the next process. Also, the plural pusher pieces  19  for respective ones of plural processes are fixed to the second conveying rod  32  as well, allowing the boards  7  in respective processes to be sent to the next processes. That is, by the second conveying rod  32 , the board  7  located in the decompression chamber  5  is sent to the cooling chamber  4  (cooling process) and the board  7  located in the cooling chamber  4  is sent outside through the outlet  12  of the furnace  1 . 
     As shown in  FIG. 3 , a pair of the first conveying rod  18  and switching mechanism is installed on both right and left sides of the conveyance path so as to push the right and left ends of the board  7 , the first conveying rod  18  having the pusher piece  19 , and upright members  33  erected on top faces of the right and left rod support members  20  are coupled by a coupling rod  34  so that the right and left first conveying rods  18  will operate together. The second conveying rod  32  is configured similarly. 
     Means for making the first conveying rod  18  and second conveying rod  32  reciprocate (move forward and move backward) will be described next. As shown in  FIG. 1 , a chain conveyor  35  is disposed outside the furnace  1  on the side of the outlet  12 . The chain conveyor  35  is placed horizontally, parallel to the conveyance direction of the board  7 . The rod support member  20  of the second conveying rod  32  is fixed to a chain portion of the chain conveyor  35 . The rod support member  20  of the first conveying rod  18  and rod support member  20  of the second conveying rod  32  are coupled via a coupling rod  36 . The coupling rod  36  penetrates the furnace  1  and is placed outside the decompression chamber  5 . 
     The first conveying rod  18  and second conveying rod  32  move a predetermined distance (equivalent to one process) forward when the chain conveyor  35  rotates a predetermined angle forward in the direction of arrow A in  FIG. 4 , and move a predetermined distance (equivalent to one process) backward when the chain conveyor  35  rotates a predetermined angle backward in the direction of arrow B in  FIG. 4 . In this way, as the chain conveyor  35  rotates a predetermined angle forward and backward, the first conveying rod  18  and second conveying rod  32  is reciprocated a predetermined distance (equivalent to one process). 
     Operation of the conveyor apparatus  13  will be described below with reference to  FIG. 2 .  FIG. 2(A)  shows how the board  7  is placed in each process and processed there for a predetermined period of time.  FIGS. 2(B) to 2(D)  show how the board  7  is transferred to the next process after being processed in the state of  FIG. 2(A)  for the predetermined period of time. 
     In  FIG. 2(C) , the first conveying rod  18  and second conveying rod  32  are in states described below. That is, the pusher pieces  19  of the first conveying rod  18  are at the engaged position, being located on the upstream side of the respective boards  7  located in the reflow chamber  3 A (reflow process), in the preheating chamber  2 B (preheating process), in the preheating chamber  2 A (preheating process), and in front of the furnace  1  inlet, respectively. The pusher pieces  19  of the second conveying rod  32  are at the engaged position, being located on the upstream side of the respective boards  7  in the decompression chamber  5  (decompression process) and cooling chamber  4  (cooling process), respectively. 
     As the first conveying rod  18  and second conveying rod  32  move forward after the state of  FIG. 2(C) , with the guide rod  22  being guided by the first guide hole  25  as a result of forward rotation of the chain conveyor  35 , the board  7  in each process is sent to the next step by the pusher piece  19  as shown in  FIGS. 2(C) to 2(D) . 
     That is, by the first conveying rod  18 , the board  7  located in front of the inlet  11  of the furnace  1  is conveyed to the first preheating chamber  2 A (preheating process), the board  7  located in the first preheating chamber  2 A is conveyed to the next preheating chamber  2 B (preheating process), the board  7  located in the preheating chamber  2 B is conveyed to the reflow chamber  3 A (reflow process), and the board  7  located in the reflow chamber  3 A is sent to the decompression chamber  5  (decompression process). Also, by the second conveying rod  32 , the board  7  located in the decompression chamber  5  is sent to the cooling chamber  4  (cooling process) and the board  7  located in the cooling chamber  4  is sent outside through the outlet  12  of the furnace  1 . 
     Next, as a result of backward rotation of the chain conveyor  35 , the first conveying rod  18  and second conveying rod  32  are transferred from the state of  FIG. 2(D)  to the state of  FIG. 2(A) . That is, as the first conveying rod  18  and second conveying rod  32  move backward, the guide rod  22  enters the second guide hole  26  by being guided by the coupling guide hole  27  and the pusher pieces  19  are placed at the retracted position. 
     In  FIG. 2(A) , the first conveying rod  18  and second conveying rod  32  are in states described below. That is, the first conveying rod  18  and second conveying rod  32  are placed outside the decompression chamber  5 , the pusher pieces  19  are at the retracted position, and the pusher pieces  19  at the heads of the rods  18  and  32  are placed on opposite sides of the decompression chamber  5 . In this state, the boards  7  are processed in respective processes for a predetermined period of time. 
     After the boards  7  are processed in respective processes in the state of  FIG. 2(A)  for the predetermined period of time, the first conveying rod  18  and second conveying rod  32  move backward as a result of backward rotation of the chain conveyor  35 , shifting from the state of  FIG. 2(A)  to the state of  FIG. 2(B) . That is, with the guide rods  22  being guided by the second guide holes  26  and with the pusher pieces  19  being placed at the retracted position, the first conveying rod  18  and second conveying rod  32  move backward by approximately one process. 
     In  FIG. 2(   b ), the first conveying rod  18  and second conveying rod  32  are in states described below. That is, the pusher pieces  19  of the first conveying rod  18  are at the retracted position, being located on the upstream side of the respective boards  7  located in the reflow chamber  3 A (reflow process), in the preheating chamber  2 B (preheating process), in the preheating chamber  2 A (preheating process), and in front of the furnace  1  inlet, respectively. The pusher pieces  19  of the second conveying rod  32  are at the retracted position, being positioned on the upstream side (rear end) of the respective boards  7  located in the decompression chamber  5  (decompression process) and cooling chamber  4  (cooling process). 
     Next, as a result of forward rotation of the chain conveyor  35 , the first conveying rod  18  and second conveying rod  32  are transferred from the state of  FIG. 2(B)  to the state of  FIG. 2(C) . That is, as the first conveying rod  18  and second conveying rod  32  move forward, the guide rod  22  enters the first guide hole  25  by being guided by the coupling guide hole  27 , the pusher pieces  19  are placed at the engaged position, and transferring the first conveying rod  28  and second conveying rod  32  to the state of  FIG. 2(C) . Subsequently, the above-described operation is repeated, beginning with the state of  FIG. 2(C)  described above. 
     In this way, through one reciprocating motion (forward movement and backward movement) of the first conveying rod  18  and second conveying rod  32 , the boards  7  are sent to next processes, respectively, and processed in respective processes for a predetermined period of time. 
     Regarding the decompression process, the board  7  can be carried into the decompression process by the first conveyance mechanism  13 A and carried out of the decompression process by the second conveyance mechanism  13 B. 
     Therefore, the printed circuit board  7  on which electronic components have been mounted via cream solder is conveyed from a position in front of the inlet  11  of the furnace  1  by the conveyor apparatus  13  going through processes one by one including the decompression process in the reflow furnace  1 , and processed in each process for a predetermined period of time. Consequently, the board  7  on which the electronic components have been soldered is carried out of the furnace  1  through the outlet  12  of the furnace  1 . 
     Note that the operations of the first conveying rod  18  and second conveying rod  32  are performed by controlling a driving motor of the chain conveyor  35  according to a predetermined sequence. 
     The first conveying rod  18  and second conveying rod  32  may be driven by respective chain conveyors independent of each other. That is, although the first conveying rod  18  and second conveying rod  32  are driven by the common chain conveyor  35  in the above embodiment, two chain conveyors  35  may be installed to drive the first conveying rod  18  and second conveying rod  32  separately as a modification ( FIG. 6 ). According to this modification, the first conveying rod  18  and second conveying rod  32  are driven independently by separate chain conveyors  35 ,  35 . 
     That is, as shown in  FIG. 6 , the rod support members  20  of the first conveying rod  18  and second conveying rod  32  are separated instead of being coupled via a coupling rod and the chain conveyor  35  adapted to drive the first conveying rod  18  is installed on the inlet side of the furnace  1  while the chain conveyor  35  adapted to drive the second conveying rod  32  is installed on the outlet side of the furnace  1 . The first conveying rod  18  and second conveying rod  32  are coupled to the respective chain conveyors  35  via the respective rod support members  20 , which are fixed to the chain portions of the respective chain conveyors  35 , as with the above embodiment. The operations of the first conveying rod  18  and second conveying rod  32  are the same as those described with reference to  FIGS. 2(A) to 2(D) . 
     Although an example of guiding the guide rod  22  using the guide hole  24  has been described in the above embodiment, this is not restrictive, and the guide rod  22  may be configured to be guided, for example, by a guide groove. 
     Although in the above embodiment, the first conveyance mechanism  13 A has a pair of the first conveying rods  18  and the second conveyance mechanism  13 B has a pair of second conveying rods  32 , each of the conveyance mechanisms may be configured to have a single conveying rod. 
     Although the common chain conveyor  35  is used in the above embodiment as driving means adapted to reciprocate the first conveying rod  18  and second conveying rod  32 , this is not restrictive, and a belt conveyor or the like may be used alternatively. Of course, the first and second conveying rods  18  and  32  may be driven by separate belt conveyors. 
     Although an example in which the decompression chamber is installed in the reflow chamber has been described in the above embodiment, the decompression chamber may be installed independently of the reflow chamber, or installed on the board conveyance path. 
     Also, although nitrogen gas is used as a furnace gas in the above embodiment, the gas is not limited to nitrogen gas. For example air may be used.