JP2017127996A - Inspection method for fold and joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection method for fold and joint, capable of inspecting whether bonding a joint piece of a folded cardboard sheet is properly done to form a cylindrical shape, in parallel with production of cartons in a production line.SOLUTION: An inspection method for fold and joint in a box production line comprises; providing a displacement sensor at a position separated from a cardboard sheet moving path in a cardboard sheet folding direction between a fold joint part where the cardboard sheet with a glue-pasted joint piece 15 is gradually folded and jointed into a cylindrical shape and a discharge part where the folded cardboard sheets are discharged and stacked; detecting a distance to the cardboard sheet using the displacement sensor, on a path L1 where the joint piece 15 passes; and determining whether the joint piece 15 is positioned inside or outside the folded cardboard sheet on the basis of the detected distance.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fold joint inspection method for inspecting whether or not a joint in which a corrugated sheet is folded and formed into a cylindrical shape by bonding of joint pieces is properly performed in a corrugated board production line. is there.

  In the production line for cardboard boxes, a horizontal ruled line (score) is put and cut on the cardboard sheet formed by laminating the core and the front and back liners. ) Insertion, formation of notches (slots) and seam pieces, application of glue to the seam pieces, folding and bonding of the seam pieces are performed continuously. Then, a predetermined number of the corrugated cardboard sheets joined in a tubular shape by bonding of the joint strips are stacked and carried out from the downstream end of the box making line.

  In the above process, corrugated cardboard sheets (blanks) with glue applied to the seam piece are gradually folded and joined, but there are two types of joints: “inner” and “outer” There is. Using FIG. 6 and FIG. 7, the four surfaces constituting the side surface of the cardboard box are arranged in order from the surface adjacent to the joint piece 15, “first surface 11”, “second surface 12”, “third surface 13”, This will be described as “fourth surface 14”.

  As shown in FIG. 6, in the joint strip 15, the glue G is applied to the surface (illustrated, upper surface) opposite to the direction in which the corrugated cardboard sheet 10 is folded (illustrated, lower), and the first surface 11 is the fourth surface. Folding ahead of the surface 14 is “inner paste”. Thereby, as shown in the lower left of FIG. 6, the normal product B <b> 1 n is manufactured in which the joint piece 15 is joined to the inner peripheral surface of the fourth surface 14 to form a cylindrical shape.

  On the other hand, as shown in FIG. 7, in the joint piece 15, the glue G is applied to a surface (illustrated, lower surface) in the same direction as the direction in which the cardboard sheet 10 is folded, and the fourth surface 14 is ahead of the first surface 11. It is “outside paste” that is folded. Thereby, as shown in the lower left of FIG. 7, the normal product B2n of the corrugated cardboard box in which the joint piece 15 is joined to the outer peripheral surface of the fourth surface 14 into a cylindrical shape is manufactured.

  However, the first surface 11 and the fourth surface 14 may not be folded in a normal order due to warpage of the cardboard sheet 10 or the like. For example, when the fourth surface 14 is folded prior to the first surface 11 in spite of the production by the internal bonding, the joint piece 15 is joined as shown in the lower right of FIG. It becomes a defective product B1d that does not become cylindrical. Further, in this case, not only the corrugated cardboard sheet 10 becomes the defective product B1d but also when the predetermined number of sheets are stacked in the folded state, the seam piece 15 adheres to the adjacent normal product B1n. Corrugated cardboard sheets that are manufactured normally will be defective.

  Similarly, when the first surface 11 is folded before the fourth surface 14 in spite of being manufactured by external bonding, as shown in the lower right of FIG. It adheres to the inner peripheral surface of the other side surface (not shown, the third surface) that is not the fourth surface 14, resulting in a defective product B2d.

  Conventionally, an operator has visually inspected whether or not such defective products have occurred. Human visual inspections are labor intensive for workers, the production of cardboard boxes takes place at a high speed, but the inspection takes a long time, there is a risk that defective products will be missed if the inspection is performed in a short time, etc. Had various problems.

  Therefore, there is a demand for a method that can inspect whether the corrugated cardboard sheet is folded and joined into a cylindrical shape by bonding the joint piece in parallel with the production of the corrugated cardboard box in the production line. It had been.

  Therefore, in view of the above situation, the present invention determines whether or not the corrugated cardboard sheet is folded and joined in a cylindrical shape by bonding of joint pieces, in parallel with the production of the corrugated cardboard box in the production line. It is an object of the present invention to provide a folding joint inspection method that can be inspected.

In order to solve the above problems, the folding joint inspection method according to the present invention is:
“In the box making line, a corrugated cardboard sheet that has been glued to the joint piece is gradually folded and joined into a cylindrical shape, and a folded joint that discharges and stacks the folded corrugated sheet. In between, a displacement sensor is arranged at a position separated from the moving path of the cardboard sheet in the direction in which the cardboard sheet is folded,
On the path through which the joint piece passes, the displacement sensor detects the distance from the cardboard sheet,
Based on the detected distance, it is determined whether the joint piece is outside or inside in the folded corrugated cardboard sheet. "

  The distance detected by the displacement sensor is the distance between the outer peripheral surface of the folded cardboard sheet and the displacement sensor. Therefore, when the joint (hereinafter referred to as “folded joint”) in which the corrugated cardboard sheet is folded and formed into a tubular shape by bonding the joint strip is “inner bonding”, that is, in the folded corrugated cardboard sheet, When inside, there is no discontinuous change in the distance detected on the path through which the splice piece passes.

  On the other hand, when the folded joint of the corrugated cardboard sheet is “outside pasting”, that is, when the joint strip is on the outside in the folded corrugated cardboard sheet, from the portion where there is no joint strip on the path through which the joint strip passes. At the boundary with the portion where the joint piece is present, the detected distance is shortened by an amount corresponding to the thickness of the joint piece. In addition, at the boundary between the portion where the joint piece exists and the portion where there is no joint piece, the detected distance becomes longer by an amount corresponding to the thickness of the joint piece. That is, in any case, a discontinuous change corresponding to the thickness of the joint piece is observed in the detected distance.

  Therefore, in the process of manufacturing the cardboard box on the production line, by detecting the distance from the displacement sensor to the cardboard sheet on the path through which the joint piece passes, it is determined whether or not the folding joint is properly performed. Can do. In other words, in a production line in which corrugated cardboard boxes are manufactured by internal bonding, a discontinuous change in the detected distance should not occur, but a discontinuity corresponding to the thickness of the joint piece. If the change appears, it becomes a state where the fourth surface is folded before the first surface, as in the case of external bonding, in an inappropriate folding joint (hereinafter referred to as “external bonding state”). Can be determined. On the other hand, in a production line in which a corrugated cardboard box is manufactured by external bonding, a discontinuous change corresponding to the thickness of the seam piece should appear in the detected distance with the conveyance of the corrugated cardboard sheet. On the other hand, when there is no such change in the detected distance, an inappropriate folding joint in which the first surface is folded ahead of the fourth surface as in the case of the inner paste (hereinafter, “ It can be determined that it is referred to as “internally attached state”.

  Note that the “outer pasted state” is a state of a defective product B1d that is folded like the outer pasted but the joint piece 15 is not bonded to the specified part as shown in the lower right of FIG. It is distinguished from “outside pasting” done properly. Similarly, the “inner attachment state” is a state of the defective product B2d that is folded like the inner attachment, but the joint piece 15 is not bonded to the specified portion as shown in the lower right of FIG. It is distinguished from “internal pasting” that has been done properly.

  In other words, the fold joint inspection method of the present invention detects an externally applied state during the internal application process or an internal application state during the external application process as a state in which the folding connection is inappropriate.

The folding joint inspection method according to the present invention is the above-described configuration,
“A second displacement sensor is disposed at a position separated from the displacement sensor in a direction orthogonal to the movement path,
On the path through which the corrugated sheet of the portion without the joint piece passes, the distance from the corrugated sheet is detected by the second displacement sensor at the same timing as the detection by the displacement sensor,
Based on the difference between the distance detected by the displacement sensor and the distance detected by the second displacement sensor, it is determined whether the seam piece is outside or inside the folded cardboard sheet. Can be.

  When the folded joint of the corrugated cardboard sheet is “inner”, that is, when the joint piece is inside the folded corrugated cardboard sheet, the distance detected by the displacement sensor and the distance detected by the second displacement sensor are almost equal. The difference is almost zero. On the other hand, when the folding joint of the corrugated cardboard sheet is “outside pasting”, that is, when the joint piece is outside on the folded cardboard sheet, at the timing when the displacement sensor detects the distance from the joint piece, There is a difference corresponding to the thickness of the joint piece between the distance detected by the displacement sensor and the distance detected by the second displacement sensor.

  Therefore, it is possible to determine whether or not the folding joint is properly performed based on the difference between the distances detected by the two displacement sensors. In other words, in a production line where corrugated cardboard boxes are manufactured by external bonding, a difference corresponding to the thickness of the seam piece should appear at the distance originally detected by the two displacement sensors. If there is no such difference, it can be determined that the state is in the in-pasting state. On the other hand, in a production line where corrugated cardboard boxes are manufactured by internal bonding, the difference between the distances detected by the two displacement sensors should be essentially zero, whereas the difference is the thickness of the joint piece. When the value corresponds to the value, it can be determined that the externally attached state is set.

  As described above, as an effect of the present invention, it is possible to provide a folding joint inspection method capable of inspecting whether or not the folding joint is properly performed in parallel with the production of the cardboard box in the production line. .

(A) It is a figure which shows the position of the displacement sensor in the folding joining test | inspection method which is 1st embodiment of this invention, (b) It is explanatory drawing of the detection by a displacement sensor. It is explanatory drawing of the folding joining test | inspection method of 1st embodiment. It is explanatory drawing of the folding joining test | inspection method of 2nd embodiment. It is a figure explaining the shift of the position of a displacement sensor. (A) The block diagram of the apparatus which uses the folding joining test | inspection method of 1st embodiment, (b) The block diagram of the apparatus which uses the folding joining test | inspection method of 2nd embodiment. It is a figure explaining generation | occurrence | production of the folding joining and inferior goods by internal bonding. It is a figure explaining folding joining by external bonding, and generation | occurrence | production of inferior goods.

  Hereinafter, a folding joint inspection method according to a specific embodiment of the present invention will be described with reference to FIGS. 1 to 5. First, the folding joint inspection method of the first embodiment and the folding joint inspection apparatus 1 using the same will be described.

  The folding joint inspection apparatus 1 includes a displacement sensor 21 that measures the distance from the corrugated cardboard sheet 10 in the box making line, and a computer 50 that performs a process for determining whether or not the folding joint is properly performed based on detection by the displacement sensor 21. Is the main configuration.

  The box-making line is connected to the corrugated sheet 10 (blank) in which the core base paper formed into a corrugated shape is bonded to the front and back liners, and then provided with ruled lines and cut grooves to form the joint strip 15. Glue portion (not shown) where paste is applied to the blank piece 15, the cardboard sheet 10 is gradually folded, the folding piece 91 is joined by joining the seam piece 15, and the corrugated cardboard is folded It is a box making line in a box making machine (folder gluer) provided with a counter ejector section 92 that discharges while counting sheets 10. The box making machine may be a flexo folder gluer that is a multifunction machine with a flexo printing machine. Here, the folding portion 91 corresponds to the “folding joint portion” of the present invention, and the counter ejector portion 92 corresponds to the “discharge portion” of the present invention.

  As shown in FIG. 1A, the displacement sensor 21 is separated from the moving path 90 of the cardboard sheet 10 in the direction in which the cardboard sheet 10 is folded between the folding part 91 and the counter ejector part 92 in the box making line. It is arranged at the position. In the folding unit 91 of the present embodiment, the corrugated cardboard sheet 10 is folded downward, so that the displacement sensor 21 is disposed below the moving path 90 of the corrugated cardboard sheet 10.

  The displacement sensor 21 is a displacement sensor that projects light onto an object, receives reflected light with a light receiving element such as a PSD or CCD, and detects the distance between the sensor and the object from the light receiving position by a triangulation method. , A displacement sensor that detects the distance between the sensor and the object from the time it takes to project the light and receives the reflected light, the time it takes to project the ultrasonic wave onto the object and receive the reflected wave A displacement sensor that detects the distance between the sensor and the object can be used. Here, a displacement sensor that projects light onto a cardboard sheet is illustrated.

  Furthermore, an encoder 25 is attached to a portion synchronized with the drive unit in the mechanical configuration of the production line, for example, a rotation mechanism unit of a roller that drives a conveyor that conveys the cardboard sheet 10. An electrical signal from the encoder 25 is sent to the computer 50.

  The computer 50 includes a main storage device as a hardware configuration, a central processing unit (CPU) that performs processing according to a program stored in the main storage device, and an auxiliary storage device 53 such as a hard disk. Here, in the main storage device, based on detection of the distance by the displacement sensor 21, determination that causes the computer 50 to function as determination means 51 that performs determination processing as to whether or not the cardboard sheet 10 is properly folded and joined. The program is stored. Further, the determination means 51 is based on the electrical signal sent from the encoder 25 and the positional relationship between the displacement sensor 21 and the encoder 25, and the object detected by the displacement sensor 21 and the corrugated cardboard conveyed through the box making line. Association with the sheet 10 is performed.

  The auxiliary storage device 53 stores the distance data transmitted from the displacement sensor 21 and the thickness of the corrugated cardboard sheet 10 necessary for the determination process (the type of the cardboard, the basis weight of the base paper, the double-sided cardboard sheet, the double-sided cardboard sheet, And the like, the reference value such as the threshold used in the determination process, the result of the determination process, and the like can be stored.

  The fold joint inspection apparatus 1 also includes a keyboard and pointing device 61 for inputting the cardboard information and reference values to the computer 50, and a monitor for displaying the process and results of the process by the computer 50. And an output device 62 such as a printer, and an alarm device 65 that gives a notification by an alarm light or an alarm sound when it is determined that the folding joint is not properly performed as a result of processing by the computer 50.

  Further, the computer 50 is connected to the office computer 67 of the manufacturer of the corrugated cardboard sheet 10 and the production management device 68 of the production line so as to be capable of wired communication or wireless communication. The cardboard information and the reference value can be input from the office computer 67 to the computer 50, and the process and results of the processing by the computer 50 can be transmitted from the computer 50 to the office computer 67. Alternatively, the cardboard information and the reference value may be transmitted from the office computer 67 to the production management device 68, stored in the production management device 68, and transmitted from the production management device 68 to the computer 50.

  Next, the fold joint inspection method of the first embodiment performed using the fold joint inspection apparatus 1 having the above configuration will be described. In the folding joint inspection method of the first embodiment, the distance from the corrugated cardboard sheet 10 is detected by the displacement sensor 21 on the path L1 through which the joint piece 15 passes, and the corrugated cardboard sheet folded based on the detected distance. 10, it is determined whether the joint piece 15 is outside or inside.

  The displacement sensor 21 moves from the folding portion 91 toward the counter ejector portion 92 (in the direction of arrow A in FIG. 1), as shown in FIG. Light is projected onto L1. The displacement sensor 21 detects the distance from the cardboard sheet 10 at a fixed time interval or at a detection point P for each fixed movement distance of the cardboard sheet 10. The detected distance data is transmitted from the displacement sensor 21 to the computer 50.

  The distance detected by the displacement sensor 21 is the distance between the outer peripheral surface of the folded cardboard sheet 10 and the displacement sensor 21. Therefore, when the folding and joining of the corrugated cardboard sheet 10 is “inner bonding”, that is, when the seam piece 15 is inside the folded corrugated cardboard sheet 10, the distance when the detection point P is on the seam piece 15 The distance when the detection point P is not on the joint piece 15 is almost the same as shown in FIG. 2A, and no discontinuous change occurs.

  On the other hand, when the folding joining of the corrugated cardboard sheet 10 is “outside pasting”, that is, when the joint strip 15 is on the outside in the folded corrugated cardboard sheet 10, as shown in FIG. When the detection point P shifts from a portion where there is no joint piece 15 to a portion where the joint piece 15 exists, the detected distance is shortened discontinuously by an amount corresponding to the thickness of the joint piece 15. Further, when the detection point P moves from a portion where the joint piece 15 is present to a portion where the joint piece 15 is not present, the detected distance becomes discontinuously longer by an amount corresponding to the thickness of the joint piece 15.

  Therefore, in the first embodiment, the determination unit 51 calculates the difference ΔD between the distance at a certain detection point P and the distance at the previous detection point P. A threshold value is determined in advance in consideration of the thickness of the joint piece 15 and the magnitude of noise in detecting the distance. The determination means 51 can determine whether the joint strip 15 is on the outside or the inside in the folded cardboard sheet 10 by comparing the ΔD value with the threshold value. As a result, if an “inner attachment state” is detected while the outer bonding process is being performed on the production line, it is possible to detect that a defective product has occurred instead of proper folding joining, If the “outer pasting state” is detected while the inner pasting process is being performed, it is possible to detect that the folding joint is not appropriate and a defective product has occurred.

  If the computer 50 determines that the folding joint is not properly performed, a failure detection signal is sent from the computer 50 to the alarm device 65, and a notification is given by the alarm device 65. At the same time, information specifying the defective cardboard sheet 10, for example, information on the number of defective products in the plurality of cardboard sheets 10 stacked on the counter ejector unit 92 is output to the output device 62. Is output.

  The inspection point P by the displacement sensor 21 shifts from a portion where the cardboard sheet 10 does not exist to a portion where the cardboard sheet 10 exists and from a portion where the cardboard sheet 10 exists to a portion where the cardboard sheet 10 does not exist. In this case, the detected distance changes due to the step. However, since the change in the distance at this time is greatly different from the distance of the detection target, it can be clearly distinguished from the change in the distance due to the presence of the joint piece 15 and can be detected by setting the range of the distance to be detected. It can also be outside the possible range.

  Note that the threshold value can be stored in the auxiliary storage device 53 as a database associated with the cardboard information. Alternatively, a threshold value may be input to the computer 50 from the input device 61, or a threshold value may be input to the computer 50 via the office computer 67 or the production management device 68.

  Further, when the dimensions of the cardboard boxes to be manufactured are different as in the cardboard sheets 10 and 10b illustrated in FIG. 4, the path L1 through which the joint piece 15 passes in the moving path 90 is different. Therefore, the folding joint inspection apparatus 1 includes a mechanism that shifts the position of the displacement sensor 21 in a direction orthogonal to the moving path 90 (the width direction of the corrugated cardboard sheet). The displacement sensor 21 is moved in accordance with a path L1 through which 15 passes. Examples of the mechanism for shifting the position of the displacement sensor 21 include a mechanism using a ball screw, a mechanism using a rack and a pinion, and a mechanism using a cylinder rod.

  Next, the folding joint inspection method of the second embodiment and the folding joint inspection apparatus 2 using the same will be described. The difference between the folding joint inspection method of the second embodiment and the first embodiment is that the second displacement sensor 22 is used in addition to the displacement sensor 21. Similar to the displacement sensor 21, the second displacement sensor 22 is disposed between the folding portion 91 and the counter ejector portion 92 in the box making line and spaced apart from the moving path 90 in the direction in which the cardboard sheet 10 is folded. . In the second displacement sensor 22, the position of the detection target is separated from the position of the detection target of the displacement sensor 21 in a direction orthogonal to the movement path 90. Then, the second displacement sensor 22 detects the distance on the path L <b> 2 through which the corrugated cardboard sheet 10 of the portion without the joint piece 15 passes at the same timing as the displacement sensor 21, and transmits the detected distance data to the computer 50. To do.

  In the present embodiment, the displacement sensor 21 and the second displacement sensor 22 are arranged very close to each other, and the position where both sensors detect the distance is 5 cm to 15 cm apart in the width direction of the cardboard sheet 10. Yes. Here, the case where the displacement sensor 21 and the second displacement sensor 22 are separated from the moving path 90 by an equal distance is illustrated.

  In the second embodiment, the determination unit 51 calculates a difference D2-D1 between the distance D1 detected by the displacement sensor 21 and the distance D2 detected by the second displacement sensor 22 at the same timing. When the folded joint of the corrugated cardboard sheet 10 is “inner bonding”, that is, when the joint strip 15 is inside the folded corrugated cardboard sheet 10, the distance D1 detected by the displacement sensor 21 and the second displacement sensor 21 detect Since the distances D2 to be transmitted are substantially equal, the distance difference D2-D1 is substantially zero as shown in FIG.

  On the other hand, when the folding joining of the corrugated cardboard sheet 10 is “outside pasting”, that is, when the seam piece 15 is on the outer side in the folded corrugated cardboard sheet 10, as shown in FIG. The distance between the distance D1 detected by the displacement sensor 21 and the distance D2 detected by the second displacement sensor 22 at the timing when the distance to the joint piece 15 is detected corresponds to the thickness of the joint piece 15. There is a difference.

  Therefore, the determination means 51 calculates D2-D1 from the detected distances D1, D2, and compares this with a predetermined threshold value, so that the joint strip 15 is moved outward in the folded cardboard sheet 10. Whether it is inside or inside can be determined.

  As described above, according to the folding joint inspection method of the first embodiment and the second embodiment, only the distance from the corrugated cardboard sheet 10 in the process of moving from the folding portion 91 to the counter ejector portion 92 is measured by the displacement sensor. It is possible to easily detect the externally applied state in the internal application process or the internal application state in the external application process as a state in which folding joining is inappropriate.

  In the folding joint inspection method of the second embodiment, the two displacement sensors 21 and 22 are used, and the corrugated board sheet 10 on the path L1 through which the joint piece 15 passes and the portion without the joint piece 15 pass. Since the distance is simultaneously detected on the route L2 and the determination is made based on the distance difference D2-D1, it is not necessary to consider the step between the portion where the cardboard sheet 10 does not exist and the portion where the cardboard sheet 10 exists.

  Further, the distance from the displacement sensor may fluctuate due to vibration (flapping) of the corrugated cardboard sheet 10 conveyed on the box making line. The fold joint inspection method of the first embodiment uses a time-series distance difference (distance change) for determination, whereas the fold joint inspection method of the second embodiment uses the moving path 90 in the corrugated cardboard sheet 10. The difference in distance measured simultaneously for positions separated in a direction orthogonal to is used for the determination. Therefore, a variation in the distance of the displacement sensor due to the vibration of the cardboard sheet 10 has an advantage that does not affect the determination.

  The present invention has been described with reference to the preferred embodiments. However, the present invention is not limited to the above-described embodiments, and various improvements can be made without departing from the scope of the present invention as described below. And design changes are possible.

  For example, in the above embodiment, the “0201 format” that is commonly used as a corrugated cardboard sheet (blank) in which ruled lines and cut grooves are formed is illustrated by way of illustration. The present invention can be applied. In addition, it is not limited to corrugated cardboard sheets formed through the process of forming horizontal ruled lines, cutting, vertical ruled lines, cut grooves and joint pieces, and even cardboard sheets formed through a die cutting process, The present invention can be applied to any corrugated cardboard sheet that is joined by joint pieces.

  In the second embodiment, the displacement sensor 21 and the second displacement sensor 22 are illustrated as being equidistant from the moving path 90. However, the distance from the moving path 90 is determined by the displacement sensor and the second displacement sensor. And may be different. In that case, the difference between the distances detected by the two displacement sensors corresponds to the difference between the distances from the moving path 90 of the two displacement sensors in the part where the joint piece does not exist and the part where the joint piece is inside. To do. Therefore, if the determination unit performs a process of subtracting the difference in distance from the moving path 90 of the two displacement sensors from the difference in distance detected by the two displacement sensors, the determination process is the same as that described with reference to FIG. Can be determined.

10, 10b Corrugated cardboard sheet 15, 15b Joint piece 21 Displacement sensor 22 Second displacement sensor 90 Moving path 91 Folding part (folding joint part)
92 Counter ejector section (discharge section)
L1 A route through which the joint piece passes L2 A route through which the corrugated sheet of the portion without the joint piece passes

Claims (2)

In the box-making line, between the folding joint where the corrugated cardboard sheet glued to the joint piece is gradually folded and joined into a cylindrical shape, and the discharge part where the folded corrugated sheet is discharged and stacked Then, a displacement sensor is arranged at a position separated from the moving path of the cardboard sheet in the direction in which the cardboard sheet is folded,
On the path through which the joint piece passes, the displacement sensor detects the distance from the cardboard sheet,
A method for inspecting a folded joint, comprising: determining, based on the detected distance, whether the joint piece is on the outside or the inside in the folded cardboard sheet. A second displacement sensor is disposed at a position separated from the displacement sensor in a direction orthogonal to the movement path,
On the path through which the corrugated sheet of the portion without the joint piece passes, the distance from the corrugated sheet is detected by the second displacement sensor at the same timing as the detection by the displacement sensor,
Based on the difference between the distance detected by the displacement sensor and the distance detected by the second displacement sensor, it is determined whether the seam piece is outside or inside the folded cardboard sheet. The fold joint inspection method according to claim 1.

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