Patent Publication Number: US-2022234322-A1

Title: Folder-gluer

Description:
RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2021-010978, filed on Jan. 27, 2021, the entire content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a folder-gluer, and more particularly to a folder-gluer for folding and gluing a corrugated paperboard sheet having four panels and a joint flap. 
     2. Description of the Related Art 
     Generally, a corrugated paperboard box making machine is configured to perform slotting and creasing to thereby form, in a corrugated paperboard sheet, a plurality of slots and crease lines each extending in a conveyance direction. The corrugated paperboard sheet is designed to be formed as a box, i.e., has four panels and a joint flap. A folder-gluer is one processing unit comprised in the corrugated paperboard box making machine, and configured to fold endmost two of the four panels of the corrugated paperboard sheet by 180 degrees, and glue one of the folded panels to the joint flap. During conveyance of the corrugated paperboard sheet at high speed, each of the two endmost panels is folded through contact between an outside surface of the panel and a bending bar or bending belt. 
     With reference to  FIGS. 21 to 23 , one example of a conventional folder-gluer will be described. A conventional folder-gluer  90  comprises: a frame  92 ; a conveyance device (upper conveyor belt and a lower conveyor belt)  94  for conveying a corrugated paperboard sheet SS comprising first to fourth panels P 1  to P 4 ; a first bending station  96  for bending each of the endmost first and fourth panels P 1 , P 4  of the corrugated paperboard sheet SS from 0 degree to about 90 degrees; and a second bending station (not illustrated) for bending each of the endmost panels from about 90 degrees to 180 degrees. 
     In order to bend the two endmost panels P 1 , P 4  of the corrugated paperboard sheet SS from 0 degree to about 90 degrees, the first bending station  96  illustrated in  FIGS. 21 and 22  employs a pair of bending bars  98  configured to come into contact with respective outside surfaces of the endmost first and fourth panels P 1 , P 4 , and a pair of bending plates  100  each configured to allow a respective one of the two endmost panels to be bent along an associated crease line. Each of the bending plates  100  tends to be arranged such that a distal end (upper end) thereof is located slightly inwardly in a width direction with respect to a position of the crease line along which the first and fourth panels P 1 , P 4  is to be bent. The reason is as follows. Since the corrugated paperboard sheet SS has a certain thickness, if the distal end of the bending plate  100  is located just at the position of the crease line, the corrugated paperboard sheet SS bulges along with the bending, the distal end is pinched between edges of the bulged portion of the corrugated paperboard sheet SS, and resulting friction makes it impossible to successfully convey the corrugated paperboard sheet SS. The above arrangement is intended to prevent the occurrence of this situation. 
     As above, there is a slight distance between the distal end of the bending die plate  100  and the position of the crease line, so that, due to contact frictional resistance between respective ones of the bending bars  98  and conveyance-directional leading edge regions (downstream edge regions) of the endmost first and fourth panels P 1 , P 4  of the corrugated paperboard sheet SS being conveyed, a fold line of each of the first and fourth panels P 1 , P 4  is shifted inwardly in the width direction with respect to the position of the crease line, in the leading edge region of the corrugated paperboard sheet SS, and thereby each of the endmost first and fourth panels P 1 , P 4  has a posture where it is inclined outwardly in the width direction (see  FIG. 22 ). 
     Then, the corrugated paperboard sheet having the endmost first and fourth panels P 1 , P 4  bent in the inclined posture is introduced into a last-half (downstream) zone of the folder-gluer, and each of the first and fourth panels P 1 , P 4  is further bent from about 90 degrees to 180 degrees, while being guided by a corresponding one of two sets of a plurality of gauge rollers (guide rollers) disposed on both sides of the corrugated paperboard sheet. In this case, the bending is progressed while each of the first and fourth panels P 1 , P 4  is kept in the inclined posture, so that a box is formed such that the fold lines of the first and fourth panels P 1 , P 4  are inclined (skewed) in a fishtail shape toward an upstream side in the conveyance direction. This “fishtail” problem is more likely to occur, as the corrugated paperboard sheet has a larger box depth dimension in the conveyance direction. 
       FIG. 23  illustrates a folded corrugated paperboard sheet SS produced by the above folder-gluer, wherein the fishtail occurs in this corrugated paperboard sheet SS. In particular, a gap between edge regions of the two endmost panels on a downstream side in the conveyance direction is “A” (especially, “−A”), and a gap between edge regions of the two endmost panels on the upstream side is “B”, so that a difference between the upstream-side and downstream-side gaps between the two endmost panels is “A+B”. That is, in the folded corrugated paperboard sheet SS, the fold lines obliquely extend in a direction from the downstream side to the upstream side to form a fishtail shape. 
     With a view to preventing the occurrence of the fishtail in a corrugated paperboard sheet, various techniques have heretofore been proposed. For example, a folder-gluer disclosed in JP 5895316 B (Patent Document 1) pushes and moves a bending member outward in the width direction for a predetermined period of time after a sensor detects a passage of the corrugated paperboard sheet on the upstream side of the bending member, and therefore extends the downstream portions of the first and fourth panels in the width direction, so that a box having no fishtail shape can be made. 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     The folder-gluer described in Patent Document 1 controls the timing of pushing the bending member outward in the width direction so as to extend only the downstream portions of the first and fourth panels in the width direction, and so as not to extend only the upstream portions of the first and fourth panels in the width direction, such that the occurrence of the fishtail is prevented. Therefore, in order to accurately control the timing of pushing out the bending member, the folder-gluer uses the sensor for detecting the passage of the corrugated paperboard sheet on the upstream side of the bending member and the control device for controlling the operation of the device for pushing out the bending member outward in the width direction. Accordingly, in the folder-gluer in Patent Document 1, there is a problem that using such a sensor and control device increases the costs of the apparatus. 
     The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a folder-gluer capable of appropriately producing boxes having no fishtail while avoiding an increase in costs of an apparatus. 
     Solution to Problem 
     In order to achieve the above object, the present invention provides a folder-gluer for, with respect to a corrugated paperboard sheet having first to fourth panels and a joint flap serially connected together through respective connection regions, folding each of the first panel and the fourth panel in the connection region thereof and gluing the folded first and fourth panels together through the joint flap, comprising: a conveyance device configured to convey the corrugated paperboard sheet; a pair of first bending members which extend in a conveyance direction of the corrugated paperboard sheet by the conveyance device, and respectively come into contact with outside surfaces of the first and fourth panels of the corrugated paperboard sheet being conveyed by the conveyance device, so as to bend the first and fourth panels from 0 degree to about 90 degrees; a pair of second bending members which extend in the conveyance direction, and are disposed inwardly in a width direction (sheet width direction) perpendicular to the conveyance direction, with respect to each of the first bending members, respectively, wherein the pair of second bending members are configured such that distal ends thereof come into contact, respectively, with a crease line formed in a reverse surface of the first panel or a vicinity of this crease line, and a crease line formed in a reverse surface of the fourth panel or a vicinity of this crease line, so as to bend the first and fourth panels of the corrugated paperboard sheet being conveyed by the conveyance device in cooperation with the pair of first bending members; and a push-out device configured to add a push-out force to each of the second bending members to push and move each of the second bending members outwardly in the width direction, wherein the push-out force by the push-out device is set such that: (1) when downstream portions of the first and fourth panels are passing through the pair of second bending members, the pair of second bending members are set to a state of being pushed outwardly in the width direction by the push-out force, and the downstream portions of the first and fourth panels are extended in the width direction by the pair of second bending members in this state; (2) next, when upstream portions relative to the downstream portions of the first and fourth panels are passing through the pair of second bending members, the pair of second bending members are set to a state of being pushed back inwardly in the width direction by a resistance force applied to the pair of second bending members by the first and fourth panels which are passing, and the upstream portions of the first and fourth panels are not extended in the width direction by the pair of second bending members; and (3) next, when the first and fourth panels have finished passing through the pair of second bending members, the pair of second bending members are returned to a state of being pushed outwardly in the width direction by the push-out force, wherein the push-out force is not varied by a control while the first and fourth panels are passing through the pair of second bending members. 
     According to the above present invention, the occurrence of the fishtail in the corrugated paperboard sheet can be prevented by extending only the downstream portions of the first and fourth panels in the width direction by the second bending member without extending the upstream portions of the first and fourth panels in the width direction WD by the second bending member, for the corrugated paperboard sheet to be conveyed. Especially, according to the present invention, an extension operation of the first and fourth panels can be realized by using the push-out force which is set to a desired amount as described above and which is not varied by the control while the first and fourth panels are passing through the second bending member. Therefore, it is not necessary to use the sensor(s) and the control device as described in Patent Document 1, in order to realize the extension operation of the first and fourth panels. Specifically, while the first and fourth panels are passing through the second bending member, it is not necessary to control the push-out force applied to the second bending member by the control device according to the detection result of the sensor. Accordingly, according to the present invention, it is possible to appropriately produce boxes having no fishtail while avoiding an increase in cost of an apparatus. 
     Preferably, in the folder-gluer of the present invention, when a length of each of the second bending members along the conveyance direction is defined as “L”, and a distance between leading edges of two adjacent corrugated paperboard sheets in the conveyance direction is defined as “N”, and a box depth dimension of a box produced by the corrugated paperboard sheet is defined as “F”, each of the second bending members is configured such that the length thereof satisfies an equation “L≤N−F”. 
     According to the above present invention, when the downstream end of the panel portion of the corrugated paperboard sheet to be conveyed reaches the upstream end of the second bending member, it is possible to avoid that the second bending member is maintained in a state of being pushed back to a substantially initial position by a resistance applied by the panel portion of the adjacent preceding corrugated paperboard sheet. Therefore, when each of the panel portions in the corrugated paperboard sheets continuously conveyed reaches the second bending member, the second bending member can be reliably returned to the state of being pushed outwardly in the width direction by the push-out force by the push-out device. Accordingly, the downstream portions of the first and fourth panels can be reliably extended in the width direction by the second bending member, for each of the corrugated paperboard sheets continuously conveyed. 
     Preferably, in the folder-gluer of the present invention, the push-out device comprises a push-out spring which applies the push-out force to each of the second bending members by elasticity. 
     According to the above present invention, since the push-out spring has a characteristic of high agility when returning from a compressed state, the push-out force can be quickly applied to the second bending member when the first and fourth panels have finished passing through the second bending member. Therefore, the second bending member can be quickly returned to the state of being pushed outwardly in the width direction. 
     Preferably, in the folder-gluer of the present invention, the push-out device comprises an air cylinder which applies the push-out force to each of the second bending members by high-pressure air. 
     Since the push-out force of the air cylinder is less affected by a widthwise position of the second bending member, the air cylinder has such a characteristic that it is easy to maintain a desired push-out force. Therefore, according to the above present invention, by using the air cylinder, it is possible to accurately realize the desired push-out force to be applied to the second bending member for performing the extension operation of the first and fourth panels, when the first and fourth panels are passing through the second bending member. 
     Preferably, in the folder-gluer of the present invention, the push-out device comprises: a push-out spring which applies the push-out force to each of the second bending members by elasticity; and an air cylinder which applies the push-out force to each of the second bending members by high-pressure air. 
     According to the above present invention, by using both the air cylinder and the push-out spring, it is possible to accurately perform the desired extension operation by the first and fourth panels when the first and fourth panels are passing through the second bending member, and it is possible to quickly the second bending member to the state of being pushed outwardly in the width direction when the first and fourth panels have finished passing through the second bending member. 
     Preferably, the folder-gluer of the present invention further comprises a mechanism capable of adjusting an initial compression amount of the push-out spring of the push-out device to vary a magnitude of the push-out force. 
     According to the above present invention, it is possible to accurately vary the push-out force applied by the push-out spring by adjusting the initial compression amount of the push-out spring, in accordance with the characteristics of the corrugated paperboard sheet to be conveyed, for example, the size, weight and material. 
     Preferably, the folder-gluer of the present invention further comprises a mechanism capable of adjusting a pressure of the high-pressure air supplied to the air cylinder of the push-out device to vary a magnitude of the push-out force. 
     According to the above present invention, it is possible to accurately vary the push-out force applied by the air cylinder by adjusting the pressure of the high-pressure air supplied to the air cylinder, in accordance with the characteristics of the corrugated paperboard sheet to be conveyed, for example, the size, weight and material. 
     Preferably, in the folder-gluer of the present invention, the push-out spring of the push-out device is housed in a housing and one or both ends of the push-out spring are secured. 
     According to the above present invention, the push-out spring is not disposed to be biased downward in the gravity direction, in the housing. Therefore, it is possible to prevent a friction between the push-out spring and the bottom surface inside the housing in accordance with the expansion and contraction in the width direction. 
     Preferably, the folder-gluer of the present invention further comprises a frame to which each of the second bending members is attached, and which comprises a support member for supporting each of the second bending members, wherein each of the second bending members comprises a guide member which engages with the support member of the frame and slides with respect to the support member so that each of the second bending members can move in the width direction, and wherein a surface of the guide member engaged with the support member is made of a material softer than a material of the support member. 
     According to the above present invention, since the second bending member moves in the width direction with the guide member thereof engaged with the support member of the frame, it is possible to ensure the accuracy of the movement in a traveling direction. Additionally, according to the present invention, since the surface (in other words, an abutting surface, or a sliding surface) of the guide member engaged with the support member is made of the material softer than the material of the support member, the wear of the support member can be suppressed by wearing only the guide member. Therefore, it is not necessary to replace the frame which is a large component, and only the guide member may be replaced. Accordingly, time and effort required for a replacement work can be reduced, and costs of the replacement work can be reduced at low cost. 
     Preferably, in the folder-gluer of the present invention, the guide member is further configured by a member which does not require lubrication by oiling. 
     According to the above present invention, it is possible to eliminate a need for periodic oiling of the surface of the guide member engaged with the support member. 
     Preferably, the folder-gluer of the present invention further comprises a frame to which each of the second bending members is attached, and which comprises a support member for supporting each of the second bending members, wherein each of the second bending members comprises a guide member which engages with the support member of the frame and includes a rolling part configured to roll over the support member so that each of the second bending members can move in the width direction. 
     According to the above present invention, since the second bending member moves in the width direction with the guide member thereof engaged with the support member of the frame, it is also possible to ensure the accuracy of the movement in the traveling direction. Also, according to the present invention, since the rolling part of the guide member rolls over the support member during the movement of the second bending member in the width direction, the wear of the support member can be suppressed. Therefore, it is not necessary to replace the frame which is a large component, and only the guide member (especially, the rolling part) may be replaced. Accordingly, time and effort required for a replacement work can be reduced, and costs of the replacement work can be reduced at low cost. 
     Preferably, in the folder-gluer of the present invention, each of the second bending members is configured such that a distal end part including a distal end can be removed and replaced from a main body part. 
     According to the above present invention, only the distal end part including the distal end which is prone to wear can be replaced. Therefore, even if the distal end wears, since it is not necessary to replace the entire second bent member which is a large component, time and effort required for a replacement work can be reduced, and costs of the replacement work can be reduced at low cost. 
     The folder-gluer of the present invention makes it possible to appropriately produce the boxes having no fishtail while avoiding the increase in the costs of the apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating an overall structure of a folder-gluer according to one embodiment of the present invention. 
         FIG. 2  is a top plan view illustrating a both-side flap type corrugated paperboard sheet. 
         FIG. 3  is a side view illustrating a first bending station of the folder-gluer according to this embodiment. 
         FIG. 4  is a top plan view illustrating the first bending station in  FIG. 3 . 
         FIG. 5  is a side view illustrating the first bending station in a state where the corrugated paperboard sheet is being bent by the folder-gluer according to this embodiment. 
         FIG. 6  is a top plan view illustrating the first bending station in  FIG. 5 . 
         FIG. 7  is a schematic top plan view illustrating a swinging movement of a second bending plate in the first bending station of the folder-gluer according to this embodiment. 
         FIG. 8  is an enlarged side view illustrating the second bending plate in the folder-gluer according to this embodiment. 
         FIG. 9  is an enlarged top plan view illustrating the second bending plate in  FIG. 8 . 
         FIG. 10  is an enlarged cross-sectional view of the folder-gluer according to this embodiment, taken along the line X-X in  FIG. 8 . 
         FIG. 11  is an enlarged cross-sectional view of the folder-gluer according to this embodiment, taken along the line XI-XI in  FIG. 8 . 
         FIG. 12  is an enlarged side view illustrating the distal end part of the second bending plate according to this embodiment. 
         FIG. 13  is an explanatory diagram of the extension operation of the corrugated paperboard sheet by the second bending plate according to this embodiment. 
         FIG. 14  is an explanatory diagram of the force applied to the corrugated paperboard sheet by the second bending plate according to this embodiment. 
         FIG. 15A  is a block diagram schematically showing the adjustment mechanism of the push-out force by the air cylinder according to this embodiment, and  FIG. 15B  is a block diagram schematically showing the adjustment mechanism of the push-out force by the push-out spring mechanism according to this embodiment. 
         FIG. 16  is an explanatory diagram of the length of the second bending plate in the conveyance direction, according to this embodiment. 
         FIG. 17  is a top plan view illustrating a second bending station of the folder-gluer according to this embodiment. 
         FIG. 18A  is a sectional view illustrating a bent state of the corrugated paperboard sheet at a downstream end of the first bending station, and  FIGS. 18B ,  18 C and  18 D are, respectively, sectional views illustrating bent states of the corrugated paperboard sheet in the second bending station. 
         FIG. 19A  shows a result of the corrugated paperboard sheet bent by the folder-gluer according to the comparative example, and  FIG. 19B  shows a result of the corrugated paperboard sheet bent by the folder-gluer according to this embodiment of the present invention. 
         FIG. 20  is an enlarged cross-sectional view of the folder-gluer according to the modification of this embodiment. 
         FIG. 21  is a side view of a first bending station of a conventional folder-gluer, illustrating a state in which the corrugated paperboard sheet is being bent by the conventional folder-gluer. 
         FIG. 22  is a top plan view illustrating the first bending station in  FIG. 20 . 
         FIG. 23  is a back plan view illustrating fishtail occurring in the corrugated paperboard sheet folded by the conventional folder-gluer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the accompanying drawings, a folder-gluer of the present invention will now be described based on one embodiment thereof. 
     At first, the folder-gluer is a part of a corrugated paperboard box making machine in which a large number of processing units including the folder-gluer are disposed along a conveyance direction of a corrugated paperboard sheet. The corrugated paperboard box making machine comprises, on an upstream side of the folder-gluer, a corrugated paperboard sheet feeding unit, a printing unit, and a creaser-slotter unit for creasing and slotting a corrugated paperboard sheet, and further comprises, on a downstream side of the folder-gluer, a counter-ejector unit for accumulating and ejecting a plurality of folded and glued corrugated paperboard sheets. 
     With reference to  FIGS. 1 and 2 , an overall structure of the folder-gluer according to this embodiment will be described.  FIG. 1  is a schematic diagram illustrating an overall structure of the folder-gluer according to this embodiment, and  FIG. 2  is a top plan view illustrating a both-side flap type corrugated paperboard sheet. 
     As illustrated in  FIG. 1 , the folder-gluer  1  according to this embodiment is disposed along a conveyance direction PD and configured to fold and glue a both-side flap type corrugated paperboard sheet SS (see  FIG. 2 ). 
     As illustrated in  FIG. 2 , the both-side flap type corrugated paperboard sheet SS has first to fourth panels P 1  to P 4  along a width direction WD (sheet width direction) perpendicular to the conveyance direction PD; and a joint flap GS on a left side of the first panel P 1 . The creaser-slotter unit (not illustrated) disposed on the upstream side of the folder-gluer  1  is operable to form four crease lines K 1  to K 4 , respectively, in a connection region between the first panel P 1  and the joint flap GS, and three connection regions between respective adjacent ones of the first to fourth panels P 1  to P 4 , and to form three slit-like slots S 1  to S 3  in a region adjacent to a leading edge FE of the corrugated paperboard sheet SS, and three slit-like slots S 4  to S 6  in a region adjacent to a trailing edge RE of the corrugated paperboard sheet SS. Each of the connection regions has a given box depth dimension F in a direction parallel to the conveyance direction PD, and a distance between the connection region formed with the crease line K 2  and the connection region formed with the crease line K 4  is a given widthwise distance CNW along the sheet width direction WD. The crease lines K 1  to K 4  are formed in respective reverse surfaces of the first to fourth panels P 1  to P 4 . On the other hand, the “corrugated paperboard sheet” in the present invention may be a sheet having the first to fourth panels and the joint flap, and is not limited to a sheet having flaps connected to the first to fourth panels. For example, the corrugated paperboard sheet may be a sheet which does not have either one or both of the upstream side and downstream side flaps connected to the first to fourth panels. 
     As illustrated in  FIG. 1 , the folder-gluer  1  comprises: a frame  2 ; a conveyance device  4  for conveying the corrugated paperboard sheet SS along a conveyance pathway PL; a glue application device  6  for applying glue to the joint flap GS of the corrugated paperboard sheet SS; a first bending station  8  for bending the endmost, first and fourth panels P 1 , P 4  of the corrugated paperboard sheet SS from its flat state (0 degree) to about 90 degrees; and a second bending station  10  for bending the first and fourth panels P 1 , P 4  from about 90 degrees to 180 degrees. 
     The frame  2  comprises an upper frame  2   a  and a lower frame  2   b , which are configured to allow aforementioned various components to be attached thereto. 
     The conveyance device  4  comprises a pair of upper conveyor belts  12  provided on right and left sides of the conveyance pathway PL, in a tensioned state. The upper conveyor belts  12  are disposed along and above the conveyance pathway PL, over the overall length of the folder-gluer  1 , and only a part thereof corresponding to the second bending station  10  is formed as a suction type configured to convey the corrugated paperboard sheet SS while suction-holding an upper surface of the corrugated paperboard sheet SS. A conveyance motor  14  is provided to drive the upper conveyor belts  12 , and a conveyance amount detector  16  is coupled to a rotary shaft of the conveyance motor  14  to detect a conveyance amount by the upper conveyor belts  12 . A distance between the upper conveyor belts  12  in the width direction WD is adjustable depending on the given widthwise distance CNW of the corrugated paperboard sheet SS. 
     The glue application device  6  is disposed adjacent to a feed port of the folder-gluer  1  through which the corrugated paperboard sheet SS is fed into the folder-gluer  1 . The glue application device  6  is configured to apply glue to the joint flap GS of the corrugated paperboard sheet SS being conveyed from the feed port. The joint flap GS applied with glue is bonded to the fourth panel P 4  by a joining roller, when the corrugated paperboard sheet SS is discharged from the folder-gluer  1 . 
     With reference to  FIGS. 3 to 12 , the first bending station  8  of the folder-gluer  1  will be described below.  FIG. 3  is a side view illustrating the first bending station, and  FIG. 4  is a top plan view illustrating the first bending station in  FIG. 3 .  FIG. 5  is a side view illustrating the first bending station in a state where the corrugated paperboard sheet is being bent, and  FIG. 6  is a top plan view illustrating the first bending station in  FIG. 5 .  FIG. 7  is a schematic top plan view illustrating a swinging movement of a second bending plate in the first bending station.  FIG. 8  is an enlarged side view illustrating the second bending plate in the folder-gluer according to this embodiment, and  FIG. 9  is an enlarged top plan view illustrating the second bending plate in  FIG. 8 .  FIG. 10  is an enlarged cross-sectional view of the folder-gluer taken along the line X-X in  FIG. 8 .  FIG. 11  is an enlarged cross-sectional view of the folder-gluer taken along the line XI-XI in  FIG. 8 .  FIG. 12  is an enlarged side view illustrating the distal end part of the second bending plate. 
     The first bending station  8  is designed to bend the endmost, first and fourth panels P 1 , P 4  of the corrugated paperboard sheet SS from its flat state (0 degree) to about 90 degrees. The first bending station  8  is equipped with a pair of bending bars  20  disposed on both sides of the conveyance pathway PL, and a pair of lower conveyor belts  22  for conveying the corrugated paperboard sheet SS while supporting the corrugated paperboard sheet SS from therebelow. 
     Each of the bending bars  20  is disposed to extend from the corrugated paperboard sheet feed port of the folder-gluer  1  to an upstream region of the second bending station  10 , and fixed to the upper frame  2   a  of the folder-gluer  1 . An upstream portion of the bending bar  20  is located above the conveyance pathway PL, and the bending bar  20  is gradually lowered toward an upstream side to a position below the conveyance pathway PL. Thus, when an outer surface of each of the first and fourth panels P 1 , P 4  comes into contact with a corresponding one of the bending bars  20 , each of the first and fourth panels P 1 , P 4  is bent from 0 degree to about 90 degrees. Each of the lower conveyor belts  22  are provided between the corrugated paperboard sheet feed port of the folder-gluer  1  and the upstream region of the second bending station  10 , in a tensioned state, and configured to be driven by a drive pulley  23  so as to convey the corrugated paperboard sheet SS in cooperation with the pair of upper conveyor belts  12 . 
     As illustrated in  FIGS. 3, 4, 7, 10 and 11 , in the first bending station  8 , a pair of bending plates  26  are attached to the lower frame  2   b  at respective positions on both sides of the conveyance pathway PL. Each of the bending plates  26  comprises a first bending plate  28  disposed on an upstream side, and a second bending plate  30  disposed on a downstream side in continuous relation to the first bending plate  28 . 
     Each of the first bending plates  28  is fixedly installed to the lower frame  2   b , and configured such that a distal end  28   a  thereof has an edged shape, and comes into contact with a respective one of the crease line formed in a reverse surface of the first panel P 1  or a vicinity of the crease line, and the crease line formed in a reverse surface of the fourth panel P 4  or a vicinity of the crease line, to thereby facilitate bending an associated one of the first and fourth panels P 1 , P 4  along the crease line formed in the reverse surface thereof, in cooperation with a corresponding one of the bending bars  20 . Each of the first bending plates  28  is not limited to be configured by one plate, but may be configured by connecting a plurality of plates (for example, 3 plates) arranged along the conveyance direction PD. 
     As with the first bending plates  28 , each of the second bending plates  30  is configured such that a distal end  30   a  thereof has an edged shape, and comes into contact with a respective one of the crease line K 2  of the first panel P 1  or a vicinity thereof, and the crease line K 4  of the fourth panel P 4  or a vicinity thereof, to thereby facilitate bending an associated one of the first and fourth panels P 1 , P 4  along the crease line thereof, in cooperation with a corresponding one of the bending bars  20 . 
     The bending bar  20  corresponds to an example of the “first bending member” in the present invention, and the second bending plate  30  corresponds to an example of the “second bending member” in the present invention. Although the bending bar  20  and the second bending plate  30  are each configured by a pair of members, only one of the pair of members will be described for convenience of explanation. 
     In the second bending plate  30 , as shown in  FIG. 12 , a distal end part  30   b , including the distal end  30   a  in contact with the first and fourth panels P 1 , P 4 , and a main body part  30   c  are separately configured. Specifically, the distal end part  30   b  and the main body part  30   c  have their respective ends formed in an uneven shape, and are engaged with each other in the uneven-shaped portion and connected by a bolt  30   d . By configuring the second bending plate  30  in this way, only the distal end part  30   b  can be removed from the main body part  30   c  and replaced. The first bending plate  28  may also be configured so that the distal end part can be removed from the main body part in the same way as the second bending plate  30 . 
     Next, as illustrated in  FIGS. 7 to 11 , each of the second bending plates  30  is configured such that a downstream portion thereof is swingingly movable outwardly in the width direction by a given distance (for example, 2 mm), about an upstream end thereof serving as a support point  30   b  (rotational center). The lower frame  2   b  is fixedly provided with a rib  31  as a support member, which extends along each of the bending plates  28  horizontally and outwardly from the lower frame  2   b . A plurality of guide members  33  are connected to the inside in the width direction of each of the second bending plates  30 , and each of the guide members  33  engages with the rib  31  of the lower frame  2   b . Specifically, the pair of guide members  33  arranged in the vertical direction are disposed so as to sandwich the rib  31  from opposite sides thereof (see  FIGS. 8 and 10 ), in such a manner that they can be slidingly moved in the width direction WD with respect to the rib  31 . In this case, the surface of the guide members  33  contacting the rib  31  is configured by a material softer than the material of the rib  31 , and a so-called slide plate which does not require lubrication by oiling is applied to the guide members  33 . 
     When each of the second bending plates  30  is slidingly moved outwardly in the width direction, the guide member  33  connected to the second bending plate  30  is slidingly moved with respect to the rib  31  fixed to the lower frame  2   b  in a horizontal posture. Thus, the second bending plate  30  is allowed to be moved only in a horizontal direction. Preferably, a movement distance (given distance) of each of the second bending plates  30  toward an outward side in the width direction is approximately one-half of a widthwise dimension of each of the slit-like slots S 1 , S 3 , S 4 , S 6  of the corrugated paperboard sheet SS. Each of the first bending plates  28  and the second bending plates  30  is configured such that a width direction WD position thereof can be adjusted depending on the widthwise distance CNW of the corrugated paperboard sheet SS by a widthwise positioning mechanism (not illustrated). 
     As illustrated in  FIG. 10 , in order to push each of the second bending plates  30  outwardly in the width direction to swingingly move it, an air cylinder  32  which applies the push-out force to the second bending plates  30  is attached to the lower frame  2   b  in the vicinity of a downstream end of the second bending plate  30  (see also  FIGS. 8 and 9 ). The vicinity of the downstream end of the second bending plate  30  is a zone in which a bending angle of each of the first and fourth panels P 1 , P 4  of the corrugated paperboard sheet SS reaches about 90 degrees. The air cylinder  32  is operable, according to an on-off operation of a solenoid valve (not illustrated), to send high-pressure air into a cylinder  32   a  to thereby move a piston so as to cause a rod  32   b  to protrude outwardly in the width direction. Thus, by applying the push-out force of the air cylinder  32  to the second bending plates  30  in the width direction, the second bending plate  30  is moved outwardly in the width direction along with a sliding movement of the guide member  33  on a surface of the rib  31 . 
     Further, a stopper mechanism  36  for regulating an amount of push-out (widthwise movement) of the second bending plate  30  by the air cylinder  32  is provided near a connection point with the lower frame  2   b  in the air cylinder  32 . The stopper mechanism  36  is configured by a bolt and screw mechanism, and provided with a nut  36   b  that functions as a stopper to regulate the movement of the piston  32   b  and the rod  32   c  in the air cylinder  32 . By adjusting the position of the nut  36   b  in the width direction, it is possible to variously set an amount for regulating a protrusion amount (i.e., a movement amount of the second bending plate  30  outward in the width direction) of the rod  32   c  in the air cylinder  32 . 
     Further, as illustrated in  FIG. 11 , two return spring mechanisms  34  for returning the second bending plate  30  inwardly in the width direction and a push-out spring mechanism  37  for pushing the second bending plate  30  outwardly in the width direction are provided in the position of the second bending plate  30  and the lower frame  2   b  on the downstream side of the air cylinder  32  (see also  FIGS. 8 and 9 ). The return spring mechanism  34  comprises: a rod member  34   a  having a distal end fixed to the inner surface of the second bending plate  30  and movable integrally with the swinging movement of the second bending plate  30 ; and a return spring  34   b  interposed between the rod member  34   a  and the lower frame  2   b . The return spring mechanism  34  generates an elastic force to bias the second bending plate  30  inwardly in the width direction, when the return spring  34   b  is compressed, typically when the second bending plate  30  is pushed outwardly in the width direction. 
     The push-out spring mechanism  37  includes a push-out spring  37   a  which applies a push-out force to the second bending plate  30  to push the second bending plate  30  outwardly in the width direction and swingingly move it. Additionally, the push-out spring mechanism  37  includes: a housing  37   b  which houses the push-out spring  37   a ; a block member  37   c  which fixes the housing  37   b  to the second bending plate  30  and to which an end portion of the push-out spring  37   a  outwardly in the width direction is attached; a spacer member  37   d  to which an end portion of the push-out spring  37   a  inwardly in the width direction is attached; and a bolt and screw mechanism  37   e , a tip end of which is attached to the spacer member  37   d . The push-out spring mechanism  37  generates an elastic force to bias the second bending plate  30  outwardly in the width direction, when the push-out spring  37   a  is compressed, typically when the second bending plate  30  is pushed inwardly in the width direction. 
     Further, by adjusting the position of the bolt and screw mechanism  37   e  so as to change the position of the spacer member  37   d  in the width direction, the push-out spring mechanism  37  can vary an initial compression amount (specifically, a compression amount of the push-out spring  37   a  in a state where the second bending plate  30  is not pushed outwardly in the width direction by the air cylinder  32 ) of the push-out spring  37   a , one end portion of which is attached to the spacer member  37   d . Thus, the elastic force applied to the second bending plate  30  by the push-out spring  37   a  (i.e., the push-out force for pushing the second bending plate  30  outwardly in the width direction) can be varied. 
     The air cylinder  32  and the push-out spring mechanism  37  correspond to an example of the “push-out device” in the present invention. 
     Next, with reference to  FIG. 13 , an operation in which the second bending plate  30  extends the first and fourth panels P 1 , P 4  of the corrugated paperboard sheet SS in this embodiment will be described.  FIG. 13  is an enlarged cross-sectional view of the folder-gluer taken along the line X-X in  FIG. 8 , as with  FIG. 10 . In  FIG. 13 , “F 1 ” indicates a force (push-out force, in other words, thrust) applied to the second bending plate  30  by the air cylinder  32  (not shown in  FIG. 13 ) outwardly in the width direction. “F 2 ” indicates a force (push-out force, in other words, elastic force) applied to the second bending plate  30  by the push-out spring mechanism  37  outwardly in the width direction. “F 3 ” indicates a force (elastic force) applied to the second bending plate  30  by each of the two return spring mechanisms  34  inwardly in the width direction. “F 4 ” indicates a force (resistance force due to bending) applied to the second bending plate  30  by the first and fourth panels P 1 , P 4  which are being bent, inwardly in the width direction. 
     First, before a production of the corrugated paperboard box is started, the air cylinder  32  is operated, and thereby the second bending plate  30  is set to a state of being pushed outwardly in the width direction by a predetermined distance from the initial position (this means the same position as the first bending plate  28  in the width direction WD (the same shall apply hereinafter)), by the push-out force F 1  of the air cylinder  32  and the push-out force F 2  of the push-out spring mechanism  37 . In the state, the production of the corrugated paperboard box is started, and the corrugated paperboard sheet SS is conveyed from the upstream side of the folder-gluer  1 . When the first and fourth panels P 1 , P 4  of the corrugated paperboard sheet SS to be conveyed reach the second bending plate  30 , the first and fourth panels P 1 , P 4  are extended in the width direction WD by the second bending plate  30  which is pushed outwardly in the width direction, and fold lines of the first and fourth panels P 1 , P 4  are moved outwardly in the width direction. At this time, the first and fourth panels P 1 , P 4  are bent at about 90 degrees by the bending bar  20  of the folder-gluer  1 . 
     When the first and fourth panels P 1 , P 4  are bent by the second bending plate  30 , the resistance force F 4  is applied to the second bending plate  30  inwardly in the width direction, by the first and fourth panels P 1 , P 4  which are being bent. Specifically, when the downstream portions of the first and fourth panels P 1 , P 4  (typically the downstream half of the first and fourth panels P 1 , P 4 ) are passing through the second bending plate  30 , the magnitude of the resistance force F 4  is relatively small. Therefore, at this time, the second bending plate  30  is maintained in a state of being pushed outwardly in the width direction, by the push-out forces F 1  and F 2  outwardly in the width direction by the air cylinder  32  and the push-out spring mechanism  37 , and the downstream portions of the first and fourth panels P 1 , P 4  are extended in the width direction WD by the second bending plate  30  in this state. 
     Thereafter, as the downstream end of the corrugated paperboard sheet SS is advanced to the downstream side in the conveyance direction PD and the bending angles of the first and fourth panels P 1  and P 4  increase, and accordingly, the resistance force F 4  applied to the second bending plate  30  by the first and fourth panels P 1 , P 4  which are being bent increases. Therefore, when the upstream portions relative to the above downstream portions of the first and fourth panels P 1 , P 4  (typically, the upstream half of the first and fourth panels P 1 , P 4 ) are passing through the second bending plate  30 , the second bending plate  30  is pushed back inwardly in the width direction, by the increased resistance force F 4  by the first and fourth panels P 1 , P 4  inwardly in the width direction and the force F 3  by each of the return spring mechanisms  34  inwardly in the width direction (see an arrow A 1  in  FIG. 13 ). Typically, the second bending plate  30  is pushed back to the above initial position or a position close to the initial position. Hence, the upstream portions of the first and fourth panels P 1 , P 4  are not extended in the width direction WD by the second bending plate  30 . 
     Then, when the first and fourth panels P 1 , P 4  have finished passing through the second bending plate  30 , that is, when the upstream ends of the crease line portions of the first and fourth panels P 1 , P 4  pass through the downstream ends of the second bending plate  30 , the resistance force F 4  is no longer applied to the second bending plate  30  from the first and fourth panels P 1 , P 4 . Therefore, the second bending plate  30  quickly returns to the state of being pushed outwardly in the width direction by the predetermined distance, by the push-out forces F 1 , F 2  outwardly in the width direction by the air cylinder  32  and the push-out spring mechanism  37 . Thereafter, the operation of extending the downstream portions of the first and fourth panels P 1 , P 4  of the corrugated paperboard sheet SS conveyed to the folder-gluer  1  is repeated in the same manner as described above, until the production of the corrugated paperboard box is completed. 
     As described above, in this embodiment, the upstream portions of the first and fourth panels P 1 , P 4  are not extended in the width direction WD by the second bending plate  30 , and only the downstream portions of the first and fourth panels P 1 , P 4  are extended in the width direction WD by the second bending plate  30 . The extension operation of the first and fourth panels P 1 , P 4  by the second bending plate  30  is realized by appropriately setting the push-out forces F 1  and F 2  by the air cylinder  32  and the push-out spring mechanism  37 . 
     In the folder-gluer  1  of this embodiment, the push-out forces F 1  and F 2  by the air cylinder  32  and the push-out spring mechanism  37  are set such that: (1) when the downstream portions of the first and fourth panels P 1 , P 4  are passing through the second bending plate  30 , the second bending plate  30  is set to a state of being pushed outwardly in the width direction by the push-out forces F 1  and F 2 , and the downstream portions of the first and fourth panels P 1 , P 4  are extended in the width direction WD by the second bending plate  30  in this state; (2) next, when the upstream portions relative to the above downstream portions of the first and fourth panels P 1 , P 4  are passing through the second bending plate  30 , the second bending plate  30  is set to a state of being pushed back inwardly in the width direction by the resistance force F 4  applied to the second bending plate  30  by the first and fourth panels P 1 , P 4  which are passing, and the upstream portions of the first and fourth panels P 1 , P 4  are not extended in the width direction WD by the second bending plate  30 ; and (3) next, when the first and fourth panels P 1 , P 4  have finished passing through the second bending plate  30 , the second bending plate  30  is returned to the state of being pushed outwardly in the width direction by the push-out forces F 1  and F 2 , wherein the push-out forces F 1  and F 2  are not varied by a control while the first and fourth panels P 1 , P 4  are passing through the second bending plate  30 . 
     For example, by experiments, predetermined arithmetic expressions or simulations, the resistance force F 4  applied to the second bending plate  30  by bending the first and fourth panels P 1 , P 4  may be calculated, derived or estimated from the various corrugated paperboard sheets SS, and the push-out forces F 1  and F 2  to be applied to the second bending plate  30  by the air cylinder  32  and the push-out spring mechanism  37  may be determined based on the resistance force F 4 , so that the state of the second bending plate  30  in each of the above-mentioned situations (1) and (2) is appropriately realized. In this case, since the push-out forces F 1  and F 2  vary in accordance with the widthwise position of the second bending plate  30  while the first and fourth panels P 1 , P 4  are passing through the second bending plate  30 , as an example, on the basis of the time when the first and fourth panels P 1 , P 4  are not passing through the second bending plate  30  (that is, the time when the second bending plate  30  is moved outwardly in the widthwise direction by the predetermined distance), the push-out forces F 1  and F 2  to be applied at this time may be determined. Further, the total value of the push-out forces F 1  and F 2  to be applied to the second bending plate  30  may be determined, and the total value may be distributed to the push-out force F 1  of the air cylinder  32  and the push-out force F 2  of the push-out spring mechanism  37 . The push-out forces F 1  and F 2  thus determined can be realized in each of the air cylinder  32  and the push-out spring mechanism  37  by using adjustment mechanisms ( FIG. 15 ) described later. In order to determine the push-out forces F 1  and F 2  based on the resistance force F 4 , the force F 3  by each of the return spring mechanisms  34  may also be determined. That is, the magnitude of the force F 3  to be applied in each of the return spring mechanisms  34  may be determined so as to ensure an appropriate balance between the resistance force F 4  and the push-out forces F 1  and F 2 . 
     According to this embodiment, similarly to the technique described in Patent Document 1, the occurrence of the fishtail can be prevented, since the upstream portions of the first and fourth panels P 1 , P 4  are not extended in the width direction WD by the second bending plate  30 , but only the downstream portions of the first and fourth panels P 1 , P 4  are extended in the width direction WD by the second bending plate  30 . In particular, according to this embodiment, the extension operation of the first and fourth panels P 1 , P 4  can be realized by the push-out forces F 1  and F 2  which are set to the desired magnitude and are not varied by the control during the passage of the first and fourth panels P 1 , P 4 . That is, it is not necessary to use the sensor(s) and the control device as described in Patent Document 1, in order to realize the extension operation of the first and fourth panels P 1 , P 4 . Specifically, while the first and fourth panels P 1 , P 4  are passing through the second bending plate  30 , it is not necessary to control the push-out forces F 1  and F 2  applied to the second bending plate  30  by the control device according to the detection result of the sensor. Therefore, according to this embodiment, it is possible to appropriately produce the boxes having no fishtail while avoiding the increase in the cost of the apparatus. 
     The “downstream portion(s)” of the first and fourth panels P 1 , P 4  which is extended in the width direction WD by the second bending plate  30  is not limited to the downstream half of the first and fourth panels P 1 , P 4 . In other words, the “upstream portion(s)” of the first and fourth panels P 1 , P 4  which is not extended in the width direction WD by the second bending plate  30  is not limited to the upstream half of the first and fourth panels P 1 , P 4 . The “downstream portion(s)” only means that, when a portion which is not extended in the width direction WD by the second bending plate  30  is used as a comparative criterion, a portion which is extended in the width direction WD by the second bending plate  30  is located on the downstream side of portion corresponding to the comparative criterion. The same is true for the upstream portion(s). 
     Next, with reference to  FIG. 14 , a force applied to the corrugated paperboard sheet SS by the second bending plate  30  in this embodiment will be described. In  FIG. 14 , a horizontal axis shows time (corresponding to an advancing amount of the corrugated paperboard sheet SS), and a vertical axis shows a force applied to the first and fourth panels P 1 , P 4  of the corrugated paperboard sheet SS by the second bending plate  30  in the vicinity of the downstream end. Solid line graphs G 1  show time variations of forces applied by the second bending plate  30  to the first and fourth panels P 1 , P 4  of a N-th sheet and a N+1-th sheet, in this embodiment. In contrast, broken line graphs G 2  show time variations of forces applied by the second bending plate  30  to the first and fourth panels P 1 , P 4  of a N-th sheet and a N+1-th sheet, in a comparative example. In the comparative example, the second bending plate  30  does not move and is maintained at the same position as the first bending plate  28  in the width direction WD. 
     According to the comparative example, from time t 11  when the first and fourth panels P 1 , P 4  of the corrugated paperboard sheet SS to be conveyed reach the second bending plate  30  to time t 13  when the first and fourth panels P 1 , P 4  have finished passing through the second bending plate  30 , the force applied to the first and fourth panels P 1 , P 4  by the second bending plate  30  in the vicinity of the downstream end gradually rises from 0. When such a force is applied to the first and fourth panels P 1 , P 4 , the fishtail tends to occur as mentioned above (See  FIGS. 22 and 23 ). 
     On the other hand, according to this embodiment, at the time t 11  when the first and fourth panels P 1 , P 4  of the corrugated paperboard sheet SS to be conveyed reach the second bending plate  30 , the force applied to the first and fourth panels P 1 , P 4  by the second bending plate  30  in the vicinity of the downstream end becomes maximum by the push-out forces F 1  and F 2  by the air cylinder  32  and the push-out spring mechanism  37 . This is because, at the time t 11 , the resistance force F 4  by the first and fourth panels P 1 , P 4  has not yet been applied to the second bending plate  30 . When the first and fourth panels P 1 , P 4  are being bent after the time t 11 , the resistance force F 4  applied to the second bending plate  30  by the first and fourth panels P 1 , P 4  increases. Accordingly, the force applied to the first and fourth panels P 1 , P 4  by the second bending plate  30  in the vicinity of the downstream end decreases. In this case, the second bending plate  30  is gradually pushed back inwardly in the width direction by the force F 3  by the return spring mechanism  34  in addition to the resistance force F 4  by the first and fourth panels P 1 , P 4 . 
     Thereafter, at time t 12  when the downstream portions of the first and fourth panels P 1 , P 4  have finished passing through the second bending plate  30 , i.e., when the downstream ends of the upstream portions of the first and fourth panels P 1 , P 4  reaches the downstream end of the second bending plate  30 , the second bending plate  30  is set to a state of being pushed back to the substantially initial position by the forces F 4  and F 3  inwardly in the width direction from the first and fourth panels P 1 , P 4  and the return spring mechanism  34 . This state is the same as the state of the second bending plate  30  in the comparative example. Therefore, after the time t 12 , the force in this embodiment which is applied to the first and fourth panels P 1 , P 4  by the second bending plate  30  in the vicinity of the downstream end is the same as in the comparative example. 
     Next, with reference to  FIGS. 15A and 15B , an adjustment of the push-out force applied to the second bending plate  30  by the air cylinder  32  and the push-out spring mechanism  37  will be described.  FIG. 15A  is a block diagram schematically showing an adjustment mechanism of the push-out force by the air cylinder  32 . As shown in  FIG. 15A , an electropneumatic regulator  32   e  is connected to a cylinder  32   a  of the air cylinder  32  via a switching valve (solenoid valve)  32   d  for switching between supply and non-supply of high-pressure air to the cylinder  32   a . The electropneumatic regulator  32   e  adjusts the pressure of the high-pressure air to be supplied to the air cylinder  32  by using a pressure sensor (not shown) provided on a supply path of the high-pressure air, thereby adjusting the push-out force applied to the second bending plate  30  by the air cylinder  32 . In this case, the pressure of the high-pressure air to be supplied to the air cylinder  32  is determined based on the characteristics of the corrugated paperboard sheet SS to be conveyed, for example, the size, the weight and the material, and the electropneumatic regulator  32   e  is controlled so as to realize the determined pressure of the high-pressure air. Preferably, since a resistance applied to the second bending plate  30  increases as the basis weight (weight per square meter of the base paper) of the corrugated paperboard sheet SS to be conveyed increases, the electropneumatic regulator  32   e  may be controlled to increase the high-pressure air so as to increase the push-out force by the air cylinder  32  as the basis weight increases. 
       FIG. 15B  is a block diagram schematically showing an adjustment mechanism of the push-out spring mechanism  37 . As shown in  FIG. 15B , a rack and pinion mechanism  37   f  having a rack and a pinion capable of adjusting a position of a bolt and screw mechanism  37   e  is connected to the bolt and screw mechanism  37   e  of the push-out spring mechanism  37 , and an electric actuator  37   g  having a robotic cylinder and a servomotor is connected to the rack and pinion mechanism  37   f . The electric actuator  37   g  operates the rack and pinion mechanism  37   f  to adjust the position of the bolt and screw mechanism  37   e . Therefore, an initial compression amount of the push-out spring  37   a  whose one end is connected to the bolt and screw mechanism  37   e  via the spacer member  37   d  is varied (see  FIG. 11 ), so that the push-out force applied to the second bending plate  30  by the push-out spring mechanism  37  is adjusted. In this case, the initial compression amount (corresponding to an initial elastic force to be generated by the push-out spring  37   a ) to be set for the push-out spring  37   a  is determined based on the characteristics of the corrugated paperboard sheet SS to be conveyed, for example, the size, the weight and the material, and the electric actuator  37   g  is controlled so as to realize the determined initial compression amount. Preferably, since the resistance applied to the second bending plate  30  increases as the basis weight of the corrugated paperboard sheet SS to be conveyed increases, the electric actuator  37   g  may be controlled to increase the initial compression amount of the push-out spring  37   a  so as to increase the push-out force by the push-out spring mechanism  37  as the basis weight increases. 
     Next, with reference to  FIG. 16 , a length in the conveyance direction applied to the second bending plate  30  in this embodiment will be described. In this embodiment, as shown in  FIG. 16 , the second bending plate  30  is configured such that the length L of the second bending plate  30  in the conveyance direction is equal to or less than a length obtained by subtracting the box depth dimension F from a distance N (corresponding to a circumferential length of a printing cylinder of the printing unit provided on the upstream side of the folder-gluer  1  in the corrugated paperboard box making machine) between the leading edges of the two adjacent corrugated paperboard sheets SS in the conveyance direction, that is, a conditional equation “L≤N−F” is satisfied. The right side “N−F” of the conditional equation corresponds to a distance between the upstream end of the panel portion of the preceding corrugated paperboard sheet SS and the downstream end of the panel portion of the following corrugated paperboard sheet SS in the two adjacent corrugated paperboard sheets SS in the conveyance direction PD. Preferably, the box depth dimension of the corrugated paperboard box having the largest box depth dimension among the various corrugated paperboard boxes produced by the corrugated paperboard box making machine is applied to the box depth dimension F in the conditional equation. 
     By applying the length L in the conveyance direction satisfying the above conditional equation, when the downstream end of the panel portion of the corrugated paperboard sheet SS to be conveyed reaches the upstream end of the second bending plate  30 , it is possible to avoid that the second bending plate  30  is maintained in a state of being pushed back to a substantially initial position by the resistance applied by the panel portion of the adjacent preceding corrugated paperboard sheet SS. Therefore, when each of the panel portions in the corrugated paperboard sheets SS continuously conveyed reaches the second bending plate  30 , the second bending plate  30  can be reliably returned to the state of being pushed outwardly in the width direction by the push-out forces F 1 , F 2  by the air cylinder  32  and the push-out spring mechanism  37 . Accordingly, the downstream portions of the first and fourth panels P 1 , P 4  can be reliably extended in the width direction WD by the second bending plate  30 , for each of the corrugated paperboard sheets SS continuously conveyed. 
     With reference to  FIGS. 1, 17 and 18 , the second bending station  10  of the folder-gluer  1  according to this embodiment will be described below. 
     As illustrated in  FIG. 1 , the second bending station  10  is equipped with a pair of panel bending belts  50  disposed, respectively, on left and right sides of the conveyance pathway PL, and configured to be driven so as to bend the first and fourth panels P 1 , P 4  of the corrugated paperboard sheet SS, respectively, from about 90 degrees to 180 degrees; and two sets of a pair of guiding and regulating mechanisms  52  arranged along the conveyance direction PD, and configured to guide and regulate the bent connection regions of the first and fourth panels P 1 , P 4 . 
     Each of the panel bending belts  50  is disposed to extend over the overall length of the second bending station  10 , wherein it has a contact surface contactable with an outer surface of an associated one of the first and fourth panels P 1 , P 4 . Each of the panel bending belts  50  is wound around a large number of rollers  50   a  in a tensioned state, in such a manner that the contact surface of the panel bending belt  50  positioned in a vertically standing posture at an upstream end of the second bending station  10  in the conveyance direction PD is gradually inclined as being moved toward a downstream side, and finally positioned in a horizontal posture (see  FIGS. 18B, 18C and 18D ). A distance between the panel bending belts  50  in the width direction WD can be adjusted depending on the given widthwise distance CNW of the corrugated paperboard sheet SS. 
     As illustrated in  FIG. 17 , the two sets of a pair of guiding and regulating mechanisms  52  are provided, respectively, on upstream and downstream sides of the second bending station  10 . The upstream and downstream sets are structurally the same, and the pair of guiding and regulating mechanisms  52  on the right and left sides in the conveyance line PL are also structurally the same. Each of the pair of guiding and regulating mechanisms  52  comprises: a support plate  54  fixed to the frame  2  of the folder-gluer  1 ; a group of eight gauge rolls  56  supported by the support plate  54 ; and a positioning mechanism (not illustrated) for variably positioning the support plate  54  in the width direction WD. 
     The eight gauge rolls  56  are arranged in a line along the conveyance direction PD, and rotatably supported by a lower surface of the support plate  54 . The eight gauge rolls  56  are configured to be rotated by a drive motor (not illustrated) via a timing belt  58  and three tension pulleys  60 . The support plate  54  is configured to be moved in the width direction WD (right-left direction) and positioned depending on the given widthwise distance CNW of the corrugated paperboard sheet SS. As illustrated in  FIGS. 17 and 18 , a pair of the groups of gauge rolls  56  are configured such that, during the operation of bending the corrugated paperboard sheet SS from about 90 degrees to 180 degrees, they come into contact with respective fold lines of the panels P 1 , P 4  to regulate a widthwise movement of the corrugated paperboard sheet SS, and smoothly convey the corrugated paperboard sheet SS along the conveyance direction PD. 
     Next, with reference to  FIGS. 19A and 19B , functions and effects according to the folder-gluer in this embodiment will be described.  FIG. 19A  shows a result of the corrugated paperboard sheet SS which is bent by the folder-gluer according to the comparative example, and  FIG. 19B  shows a result of the corrugated paperboard sheet SS which is bent by the folder-gluer according to this embodiment. In  FIGS. 19A and 19B , a horizontal axis shows a gap (corresponding to the gap with the reference numeral A in  FIG. 23 , hereinafter referred to as “A gap”) between the edge regions of the first and fourth panels P 1 , P 4  on the downstream side in the corrugated paperboard sheet SS bent by the folder-gluer, and a vertical axis shows a gap (corresponding to the gap with the reference numeral B in  FIG. 23 , hereinafter referred to as “B gap”) between the edge regions of the first and fourth panels P 1 , P 4  on the upstream side in the corrugated paperboard sheet SS bent by the folder-gluer. Specifically,  FIGS. 19A and 19B  show scatter plots of points corresponding to the A gaps and the B gaps, for each of samples of the plurality of corrugated paperboard sheets SS bent by the folder-gluer according to the comparative example and this embodiment, respectively. The folder-gluer according to the comparative example does not move the second bending plate  30  but maintains it at the same position as the first bending plate  28  in the width direction WD. 
     As shown in  FIG. 19A , in the corrugated paperboard sheets SS bent by the folder-gluer according to the comparative example, it can be seen that the gap of each sample is largely varied and that the B gap is too large relative to the A gap. That is, according to the comparative example, the fishtail occurs in a large number of corrugated paperboard sheets SS. On the other hand, in the corrugated paperboard sheets SS bent by the folder-gluer according to this embodiment, it can be seen that the gap variation of each sample is within a small range, especially that there are not too-small A gap and too-large B gap. That is, according to this embodiment, almost no fishtail occurs. 
     As mentioned above, in the folder-gluer  1  of this embodiment, the push-out forces F 1  and F 2  by the air cylinder  32  and the push-out spring mechanism  37  are set such that: (1) when the downstream portions of the first and fourth panels P 1 , P 4  are passing through the second bending plate  30 , the second bending plate  30  is set to a state of being pushed outwardly in the width direction by the push-out forces F 1  and F 2 , and the downstream portions of the first and fourth panels P 1 , P 4  are extended in the width direction WD by the second bending plate  30  in this state; (2) next, when the upstream portions relative to the above downstream portions of the first and fourth panels P 1 , P 4  are passing through the second bending plate  30 , the second bending plate  30  is set to a state of being pushed back inwardly in the width direction by the resistance force F 4  applied to the second bending plate  30  by the first and fourth panels P 1 , P 4  which are passing, and the upstream portions of the first and fourth panels P 1 , P 4  are not extended in the width direction WD by the second bending plate  30 ; and (3) next, when the first and fourth panels P 1 , P 4  have finished passing through the second bending plate  30 , the second bending plate  30  is returned to the state of being pushed outwardly in the width direction by the push-out forces F 1  and F 2 , wherein the push-out forces F 1  and F 2  are not varied by the control while the first and fourth panels P 1 , P 4  are passing through the second bending plate  30 . 
     Therefore, according to this embodiment, the occurrence of the fishtail in the corrugated paperboard sheet SS can be prevented by extending only the downstream portions of the first and fourth panels P 1 , P 4  in the width direction WD by the second bending plate  30  without extending the upstream portions of the first and fourth panels P 1 , P 4  in the width direction WD by the second bending plate  30 , for the corrugated paperboard sheet SS to be conveyed. Especially, according to this embodiment, the extension operation of the first and fourth panels P 1 , P 4  can be realized by using the push-out forces F 1  and F 2  which are set to the desired amount as described above and which are not varied by the control while the first and fourth panels P 1 , P 4  are passing through the second bending plate  30 . Therefore, it is not necessary to use the sensor(s) and the control device as described in Patent Document 1, in order to realize the extension operation of the first and fourth panels P 1 , P 4 . Specifically, while the first and fourth panels P 1 , P 4  are passing through the second bending plate  30 , it is not necessary to control the push-out forces F 1  and F 2  applied to the second bending plate  30  by the control device according to the detection result of the sensor. Accordingly, according to this embodiment, it is possible to appropriately produce the boxes having no fishtail while avoiding the increase in the cost of the apparatus. 
     Further, in this embodiment, the second bending plate  30  is configured such that the length L of the second bending plate  30  in the conveyance direction of the second bending plate  30  is equal to or less than the length obtained by subtracting the box depth dimension F from the distance N between the leading edges of the two adjacent corrugated paperboard sheets SS in the conveyance direction (L≤N−F). Hence, when the downstream end of the panel portion of the corrugated paperboard sheet SS to be conveyed reaches the upstream end of the second bending plate  30 , it is possible to avoid that the second bending plate  30  is maintained in a state of being pushed back to a substantially initial position by the resistance applied by the panel portion of the adjacent preceding corrugated paperboard sheet SS. Therefore, when each of the panel portions in the corrugated paperboard sheets SS continuously conveyed reaches the second bending plate  30 , the second bending plate  30  can be reliably returned to the state of being pushed outwardly in the width direction by the push-out forces F 1 , F 2  by the air cylinder  32  and the push-out spring mechanism  37 . Accordingly, the downstream portions of the first and fourth panels P 1 , P 4  can be reliably extended in the width direction WD by the second bending plate  30 , for each of the corrugated paperboard sheets SS continuously conveyed. 
     Further, in this embodiment, both the air cylinder  32  and the push-out spring mechanism  37  are used to apply the push-out force to the second bending plate  30  outwardly in the width direction. First, the push-out spring mechanism  37  is more agile than the air cylinder  32 , when the push-out spring mechanism  37  returns from a compressed state. Therefore, by using the push-out spring mechanism  37 , when the first and fourth panels P 1 , P 4  have finished passing through the second bending plate  30 , the push-out force can be quickly applied to the second bending plate  30 , and therefore the second bending plate  30  can be quickly returned to the state of being pushed outwardly in the width direction. Next, the air cylinder  32  has less variation in push-out force according to the widthwise position of the second bending plate  30 , compared to the push-out spring mechanism  37 , that is, the push-out force of the air cylinder  32  is less affected by the widthwise position of the second bending plate  30 . Therefore, by using the air cylinder  32 , it is possible to accurately realize a desired push-out force to be applied to the second bending plate  30  for performing the extension operation of the first and fourth panels P 1 , P 4  as described above. Thus, by using both the air cylinder  32  and the push-out spring mechanism  37 , it is possible to accurately perform a desired extension operation by the first and fourth panels P 1 , P 4  when the first and fourth panels P 1 , P 4  are passing through the second bending plate  30 , and it is possible to quickly return the second bending plate  30  to the state of being pushed outwardly in the width direction when the first and fourth panels P 1 , P 4  have finished passing through the second bending plate  30 . 
     In a modification of this embodiment, only one of the air cylinder  32  and the push-out spring mechanism  37  may be used to apply the push-out force to the second bending plate  30  outwardly in the width direction. In such a case of using only the air cylinder  32 , it is possible to accurately realize the push-out force to be applied to the second bending plate  30  for performing a desired extension operation of the first and fourth panels P 1 , P 4 , when the first and fourth panels P 1 , P 4  are passing through the second bending plate  30 . On the other hand, in such a case of using only the push-out spring mechanism  37  is used, it is possible to quickly return the second bending plate  30  to the state of being pushed outwardly in the width direction, when the first and fourth panels P 1 , P 4  have finished passing through the second bending plate  30 . 
     Further, in this embodiment, the initial compression amount of the push-out spring  37   a  of the push-out spring mechanism  37  is adjusted by using the electric actuator  37   g  to vary the push-out force by the push-out spring mechanism  37 . Therefore, it is possible to accurately vary the push-out force by the push-out spring mechanism  37  by adjusting the initial compression amount of the push-out spring  37   a  according to the characteristics of the corrugated paperboard sheet SS to be conveyed, for example, the size, weight and material. Additionally, since the initial compression amount of the push-out spring  37   a  can be mechanically and accurately adjusted by the bolt and screw mechanism  37   e , it is possible to appropriately equalize the push-out force between the operation side and the drive side. 
     Further, in this embodiment, the pressure of the high-pressure air supplied to the air cylinder  32  is adjusted by using the electropneumatic regulator  32   e  to vary the push-out force by the air cylinder  32 . Therefore, it is possible to accurately vary the push-out force by the air cylinder  32  by adjusting the pressure of the high-pressure air supplied to the air cylinder  32  according to the characteristics of the corrugated paperboard sheet SS to be conveyed, for example, the size, weight and material. 
     By the way, when both the adjustment for varying the push-out force by the push-out spring mechanism  37  and the adjustment for varying the push-out force by the air cylinder  32  are performed, a plurality of combination patterns of the push-out force by the push-out spring mechanism  37  and the push-out force by the air cylinder  32  arise, and therefore the adjustment tends to be complicated. However, if the adjustment for varying the push-out force by the push-out spring mechanism  37  is not performed (that is, the initial compression amount of the push-out spring  37   a  is set to be constant) and only the adjustment for varying the push-out force by the air cylinder  32  is performed, the adjustment can be simplified. 
     Further, in this embodiment, the push-out spring  37   a  of the push-out spring mechanism  37  is housed in the housing  37   b , and both ends of the push-out spring  37   a  are fixed. Therefore, the push-out spring  37   a  is not disposed to be biased downward in the gravity direction, in the housing  37   b . Accordingly, it is possible to prevent a friction between the push-out spring  37   a  and the bottom surface inside the housing  37   b  in accordance with the expansion and contraction in the width direction WD. 
     It is not limited to fix both ends of the push-out spring  37   a , but as another example, only one end of the push-out spring  37   a  may be fixed. According to the example, it is also possible to prevent the friction between the push-out spring  37   a  and the bottom surface inside the housing  37   b.    
     Further, in this embodiment, the second bending plate  30  is provided with the guide member  33  which is engaged with the rib  31  of the lower frame  2   b  and slides with respect to the rib  31  so that the second bending plate  30  can move in the width direction. Therefore, since the second bending plate  30  moves in the width direction with the guide member  33  engaged with the rib  31  of the lower frame  2   b , it is possible to ensure the accuracy of the movement in the traveling direction (substantially horizontal direction). Additionally, according to this embodiment, since the surface (in other words, the abutting surface, or the sliding surface) of the guide member  33  engaged with the rib  31  is made of a material softer than the material of the rib  31 , the wear of the rib  31  can be suppressed by wearing only the guide member  33 . Therefore, it is not necessary to replace the lower frame  2   b  which is a large component, and only the guide member  33  may be replaced. Accordingly, the time and effort required for the replacement work can be reduced, and the cost of the replacement work can be reduced at low cost. 
     Further, in this embodiment, the guide member  33  is configured by the member (so-called the slide plate) which does not require lubrication by oiling. Therefore, it is possible to eliminate the need for periodic oiling of the surface of the guide member  33  engaged with the rib  31 . 
     In a modification of this embodiment, instead of using the guide member  33  as described above, a guide member which is engaged with the rib  31  of the lower frame  2   b  and includes a rolling part configured to roll over the rib  31  so that the second bending plate  30  can move in the width direction may be used. With reference to  FIG. 20 , a guide member according to a modification of this embodiment will be described.  FIG. 20  is an enlarged cross-sectional view of the folder-gluer viewed from the same direction as in  FIGS. 10 and 11 . As shown in  FIG. 20 , the guide member  33   x  according to the modification comprises a base part  30   xa  which has an end portion fixed to the second bending plate  30  and extends in the width direction, and a rolling part  33   xb  as a bearing (rolling bearing) attached to the base part  33   xa . Specifically, the rolling part  33   xb  comprises: a shaft  33   xc  which is attached to the base part  33   xa  and extends in the conveyance direction PD; an inner ring  33   xd  fixed to the shaft  33   xc ; a plurality of rolling elements (balls)  33   xe  which is positioned outside the inner ring  33   xd  and arranged in an annular shape; and an outer ring  33   xf  (see an arrow A 2 ) which is positioned outside the plurality of rolling elements  33   xe  and rolls over the rib  31  by abutting on the surface of the rib  31 . A pair of the guide members  33   x  including the above rolling part  33   xb  is used, and the pair of guide members  33   x  are arranged to sandwich the rib  31  in the vertical direction. 
     According to the modification, since the second bending plate  30  moves in the width direction with the guide member  33   x  engaged with the rib  31  of the lower frame  2   b , it is possible to ensure the accuracy of the movement in the traveling direction (substantially horizontal direction). Also, according to this modification, since the rolling part  33   xb  of the guide member  33   x  rolls over the rib  31  during the movement of the second bending plate  30  in the width direction, the wear of the rib  31  can be suppressed. Therefore, it is not necessary to replace the lower frame  2   b  which is a large component, and only the guide member  33   x  (especially, the rolling part  33   xb ) may be replaced. Accordingly, the time and effort required for the replacement work can be reduced, and the cost of the replacement work can be reduced at low cost. 
     In a further modification, a so-called free ball bearing (in other words, a ball caster) may be used as the rolling part of the guide member. The free ball bearing comprises one or more balls freely rotatable by 360 degrees, and a holding part (ball receiver) rotatably holding the one or more balls to abut them on the surface of the rib  31 , and the free ball bearing rolls the one or more balls over the rib  31 . 
     Further, in this embodiment, the second bending plate  30  is configured such that the distal end part  30   b  including the distal end  30   a  can be removed from the main body part  30   c . Therefore, only the distal end part  30   b  including the distal end  30   a  which is prone to wear can be replaced. Accordingly, even if the distal end  30   a  wears, since it is not necessary to replace the entire second bent plate  30  which is a large component, the time and effort required for the replacement work can be reduced, and the cost of the replacement work can be reduced at low cost.