Corrugated cardboard sheet defect detection device and method, and box making machine

Abstract

To provide a device and method for detecting a defect in a cardboard sheet, and a cardboard box manufacturing machine capable of appropriately detecting defects in a conveyance state of the cardboard sheet.SOLUTION: There is provided a cardboard sheet defect detection device in which a recessed portion of a first ruled line is formed on one surface in a thickness direction, and a recessed portion of a second ruled line is formed on the other side in the thickness direction, a depth of which is smaller than the recess of the first ruled line. The defect detection device comprises: a measuring device that is disposed facing one side or the other side, and measures a distance from a placement position to a tip of the cardboard sheet or a distance to the recessed portion of the first ruled line or the recessed portion of the second ruled line to obtains a measured distance; a storage device that stores a preset threshold value; and a determination device that compares a threshold value with the measured distance by using a prescribed determination range set in advance from the tip of the cardboard sheet towards a rear end, thereby identifying a magnitude relation between the measured distance and the threshold value, and determines front and back defects or forward and rear defects of the cardboard sheet.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a cardboard sheet defect detection device and method for determining whether a cardboard sheet is oriented properly during transport, and to a box making machine. [Background technology]

[0002] The corrugated cardboard sheet manufacturing device processes the corrugated core and attaches a back liner to form a single-faced cardboard sheet, and then attaches a front liner to the single-faced cardboard sheet to form a double-faced cardboard sheet. The double-faced cardboard sheet is cut to a predetermined width and a predetermined length to form a plate-shaped cardboard sheet. Finally, the corrugated cardboard sheet manufacturing device forms scores to form flaps in the cardboard sheet.

[0003] A box-making machine processes cardboard sheets produced by a cardboard sheet manufacturing device to produce boxes (cardboard boxes). That is, the box-making machine prints on the surface of the cardboard sheets, forms creases that serve as fold lines in the cardboard sheets, and processes grooves that form flaps and adhesive strips for joining. The cardboard sheets with the creases and grooves formed have glue applied to the adhesive strips before being folded to form a flat cardboard box.

[0004] The corrugated board sheet manufacturing device produces corrugated board sheets by laminating a back liner, a corrugated core, and a front liner in layers. At this time, the corrugated board sheets are transported with the back liner facing up. On the other hand, the box making machine transports the sheets with the front liner facing up, producing flat corrugated board boxes. The corrugated board sheet manufacturing device and the box making machine have a 90-degree difference in the horizontal transport direction of the corrugated board sheets. Furthermore, the corrugated board sheets are reversed in both the front and back sides when transported. Therefore, the corrugated board sheets produced by the corrugated board sheet manufacturing device are supplied to the box making machine after the transport direction of the corrugated board sheets is changed and the front and back sides are reversed.

[0005] Therefore, when a cardboard sheet is fed to a box-making machine, the conveying direction or front and back may not be changed properly. For example, the conveying direction of the cardboard sheet may be reversed, or the front and back may be reversed. For example, a technology for detecting imperfections in the conveying direction of a cardboard sheet is described in Patent Document 1 below. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-115839 Summary of the Invention [Problem to be solved by the invention]

[0007] The defective product occurrence detection method described in Patent Document 1 detects the leading edge of a cardboard sheet and the recessed part of a ruled line, converts the transport time from detecting the leading edge of the cardboard sheet to detecting the recessed part of the ruled line into the distance between the leading edge of the cardboard sheet and the recessed part of the ruled line, and determines whether the recessed part of the ruled line is in the correct position. However, while conventional defective product occurrence detection methods can detect defects on both the front and back of a cardboard sheet in the transport direction, they have the problem of not being able to detect defects on the reverse side.

[0008] The present disclosure is intended to solve the above-mentioned problems, and aims to provide a cardboard sheet defect detection device and method, as well as a box making machine, that can properly detect defects in the transport state of cardboard sheets. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the defect detection device for cardboard sheets of the present disclosure has a first line recess formed on one side in the thickness direction and a second line recess formed on the other side in the thickness direction that is deeper than the first line recess, and is equipped with a measuring device that is arranged opposite the one side or the other side and measures the distance from the arrangement position to the leading edge of the cardboard sheet and the distance to the first line recess or the second line recess to obtain measured distances, a memory device that stores a preset threshold value, and a judgment device that compares the measured distance with the threshold value in a predetermined judgment area that is set in advance from the leading edge to the rear edge of the cardboard sheet to determine whether the measured distance is larger or smaller than the threshold value and judges whether the cardboard sheet is defective on the front or back side or front or back.

[0010] Furthermore, the disclosed method for detecting defects in cardboard sheets has a first line recess formed on one side in the thickness direction and a second line recess formed on the other side in the thickness direction that is deeper than the first line recess, and includes the steps of measuring the distance from a predetermined position facing the one side or the other side to the leading edge of the cardboard sheet and the distance to the first line recess or the second line recess, and obtaining these as measured distances; comparing the measured distance with a predetermined threshold value in a predetermined judgment area extending from the leading edge to the trailing edge of the cardboard sheet; and determining whether the measured distance is larger or smaller than the threshold value to judge whether the cardboard sheet has a front / back defect or a front / back defect.

[0011] The box making machine of the present disclosure also includes a defect detection device for the cardboard sheets. [Effects of the Invention]

[0012] According to the cardboard sheet defect detection device and method and box making machine of the present disclosure, defects in the conveying state of cardboard sheets can be properly detected. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing a corrugating machine. [Figure 2] FIG. 2 is a plan view of a cardboard sheet produced by a corrugating machine. [Figure 3] FIG. 3 is a schematic diagram showing a box-making machine. [Figure 4] FIG. 4 is a plan view of a cardboard sheet produced by a box-making machine and before folding. [Figure 5] FIG. 5 is a schematic diagram showing the configuration of a defect detection device for cardboard sheets according to the first embodiment. [Figure 6] FIG. 6 is an explanatory diagram for explaining a method for detecting defects in cardboard sheets. [Figure 7] FIG. 7 is an explanatory diagram for explaining the first threshold value and the second threshold value. [Figure 8] FIG. 8 is an explanatory diagram for explaining a method for detecting a defective cardboard sheet that is upside down. [Figure 9] FIG. 9 is an explanatory diagram for explaining a method for detecting a defective cardboard sheet that is upside down. [Figure 10] FIG. 10 is a flowchart showing the judgment control of the method for detecting defects in cardboard sheets. [Figure 11] FIG. 11 is a schematic diagram showing the configuration of a defect detection device for cardboard sheets according to the second embodiment. [Figure 12] FIG. 12 is a flowchart showing the judgment control of the method for detecting defects in cardboard sheets. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to these embodiments, and when there are multiple embodiments, the present disclosure also includes configurations that combine the embodiments. Furthermore, the components in the embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially identical, and those that are within the so-called equivalent range.

[0015] [First embodiment] <Corrugating machine> FIG. 1 is a schematic diagram showing a corrugating machine.

[0016] As shown in Figure 1, corrugating machine (cardboard sheet manufacturing device) 10 includes mill roll stands 11 and 12, a single facer 13, a bridge 14, mill roll stands 15 and 16, a single facer 17, a bridge 18, a mill roll stand 19, a preheater 20, a glue machine 21, a double facer 22, a rotary shear 23, a slitter scorer 24, a cutoff 25, a defective product discharge device 26, and a stacker 27.

[0017] The mill roll stand 11 holds a roll of paper with a core C1 wound in a roll shape, and as the roll paper rotates, the core C1 is continuously supplied. The mill roll stand 12 holds a roll of paper with a back liner B1 wound in a roll shape, and as the roll paper rotates, the back liner B1 is continuously supplied. The single facer 13 processes the core C1 into a corrugated shape and bonds it to the back liner B1 to form a single-faced cardboard sheet D1. The bridge 14 absorbs the speed difference between the single facer 13 and the double facer 22, and thus the single-faced cardboard sheet D1 is continuously supplied. temporary Let it remain there.

[0018] The mill roll stand 15 holds a roll of paper with a core C2 wound in a roll shape, and as the roll paper rotates, the core C2 is continuously supplied. The mill roll stand 16 holds a roll of paper with a back liner B2 wound in a roll shape, and as the roll paper rotates, the back liner B2 is continuously supplied. The single facer 17 processes the core C2 into a corrugated shape and bonds it to the back liner B2 to form a single-faced cardboard sheet D2. The bridge 18 absorbs the speed difference between the single facer 17 and the double facer 22, and thus the single-faced cardboard sheet D2 is continuously supplied. temporary Let it remain there.

[0019] Mill roll stand 19 holds roll paper with front liner A wound into a roll, and as the roll paper rotates, it continuously supplies front liner A. Preheater 20 preheats single-faced corrugated cardboard sheets D1, D2, and front liner A, respectively. Glue machine 21 glues the tops of the corrugations C1, C2 in single-faced corrugated cardboard sheets D1, D2. Double facer 22 stacks single-faced corrugated cardboard sheets D1, D2, and front liner A and heats them while applying pressure, bonding them together to form a continuous double-faced corrugated cardboard sheet E.

[0020] The rotary shear 23 cuts the double-sided corrugated cardboard sheet E in the entire width direction or in parts, while the lamination is still stabilizing in the initial stage of operation. The slitter scorer 24 cuts the double-sided corrugated cardboard sheet E in the conveying direction to a predetermined width and processes scores extending in the conveying direction. The cutoff 25 cuts the double-sided corrugated cardboard sheet E in the width direction to a predetermined length. The slitter scorer 24 and cutoff 25 form a plate-shaped double-sided corrugated cardboard sheet F. The defective product ejector 26 ejects double-sided corrugated cardboard sheets F that have been determined to be defective from the conveying line. The stacker 27 stacks double-sided corrugated cardboard sheets F that have been determined to be non-defective and ejects them as products.

[0021] In the above description, the corrugating machine 10 has been described as laminating a single-faced corrugated cardboard sheet D1, a single-faced corrugated cardboard sheet D2, and a front liner A to produce a double-faced corrugated cardboard sheet F. However, the corrugating machine 10 may also be used to laminate a single-faced corrugated cardboard sheet D1 or a single-faced corrugated cardboard sheet D2 and a front liner A to produce a double-faced corrugated cardboard sheet F. Double-sided corrugated cardboard sheet Therefore, in the following description, the back liners B1 and B2 will be referred to as back liners B, the cores C1 and C2 will be referred to as cores C, and the double-sided corrugated cardboard sheet F and the flat-shaped double-sided corrugated cardboard sheet will be referred to as corrugated cardboard sheet S.

[0022] FIG. 2 is a plan view of a cardboard sheet produced by a corrugating machine.

[0023] As shown in Figure 2, a plate-shaped cardboard sheet S is formed by bonding a front liner A and a back liner B to both thickness-wise sides of a corrugated core C. The corrugating machine 10 conveys the cardboard sheet S along the conveying direction X. The cardboard sheet S is conveyed so that the back liner B is positioned on the upper surface in the vertical direction and the front liner A is positioned on the lower surface in the vertical direction. The corrugating machine 10 then forms a crease 101 and a crease 102 in the cardboard sheet S.

[0024] Here, the length of the cardboard sheet S from one end (the left end in FIG. 2) to the crease 101 is shorter than the length from the other end (the right end in FIG. 2) to the crease 102. However, the length from one end to the crease 101 and the length from the other end to the crease 102 differ depending on the specifications of the cardboard sheet S. For example, the length from one end to the crease 101 of the cardboard sheet S may be longer than the length from the other end to the crease 102, or the length from one end to the crease 101 may be the same as the length from the other end to the crease 102.

[0025] <Box making machine> FIG. 3 is a schematic diagram showing a box-making machine.

[0026] As shown in FIG. 3, the box former 30 includes a paper feed unit 31, a printing unit 32, a paper discharge unit 33, a die cut unit , a folder gluer unit 35, and a counter ejector unit .

[0027] The paper feed unit 31 feeds out cardboard sheets S one by one and transports them horizontally at a constant speed. The printing unit 32 performs multi-color printing on the surface of the cardboard sheets S. The paper discharge unit 33 has the functions of scoring, cutting, and grooving the cardboard sheets S. The die-cut unit 34 punches holes and other shapes into the cardboard sheets S1 to form the cardboard sheets S1. The folder-gluer unit 35 folds the cardboard sheets S1 and joins both widthwise ends to form flat cardboard boxes G. The counter-ejector unit 36 ​​counts and stacks the cardboard boxes G, then sorts them into a predetermined number of batches and discharges them.

[0028] FIG. 4 is a plan view of a cardboard sheet produced by a box making machine.

[0029] [Corrugated cardboard sheet] FIG. 4 is a plan view of a cardboard sheet produced by a box-making machine and before folding.

[0030] As shown in Figure 4, the cardboard sheet S1 is in a state before folding, in which the cardboard sheet S (dotted line in Figure 4) produced by the corrugating machine 10 has been printed, scored, cut, grooved, and punched by the box-making machine 30.

[0031] The box making machine 30 conveys the cardboard sheet S (S1) along the conveying direction Y. The conveying direction X of the cardboard sheet S by the corrugating machine 10 and the conveying direction Y of the cardboard sheet S by the box making machine 30 are both horizontal, but are 90 degrees apart horizontally. The cardboard sheet S (S1) is conveyed so that the front liner A is positioned on the upper surface in the vertical direction and the back liner B is positioned on the lower surface in the vertical direction.

[0032] The cardboard sheet S1 has creases 101 and 102 formed thereon by the corrugating machine 10. The creases 101 and 102 are used to fold flaps when assembling the cardboard box G manufactured by the box making machine 30.

[0033] The cardboard sheet S1 has cutting line 111 and creases 112, 113, 114, and 115 formed at predetermined intervals in the width direction relative to the conveyance direction Y. The cardboard sheet S1 has grooves 121, 122, and 123 and a notch 124 formed on the crease 101 side at predetermined intervals in the width direction relative to the conveyance direction Y. Furthermore, the cardboard sheet S1 has grooves 131, 132, and 133 and a notch 134 formed on the crease 102 side at predetermined intervals in the width direction relative to the conveyance direction Y. Furthermore, the cardboard sheet S1 has hand holes 141 and 142 formed therein.

[0034] <Defect detection device> FIG. 5 is a schematic diagram showing the configuration of a defect detection device for cardboard sheets according to the first embodiment.

[0035] As shown in Figure 5, the defect detection device 50 is disposed upstream of the folder-gluer unit 35 of the box former 30 in the conveying direction Y of the cardboard sheet S. The defect detection device 50 detects front / back defects and front / rear defects in the cardboard sheet S during conveyance. A crease 101 is formed on the cardboard sheet S downstream in the conveying direction Y, and a crease 102 is formed upstream of the crease 101 in the conveying direction Y. The length of the cardboard sheet S from the leading edge Sa to the crease 101 is La, and the length from the leading edge Sa to the crease 102 is Lb.

[0036] The cardboard sheet S has creases 101 formed as depressions by being pinched and crushed by a pair of upper and lower rollers in the thickness direction in the slitter scorer 24 of the corrugating machine 10. One roller has a single ring shape, and the other roller has a double ring shape. The cardboard sheet S is pressed by one roller forming a single ring shape and the other roller forming a double ring shape, forming one first crease 101a on one side and two second creases 101b on the other side. That is, the cardboard sheet S is conveyed by the box-making machine 30 with the back liner B arranged on one side (bottom) and the front liner A arranged on the other side (top). Therefore, the cardboard sheet S has one first crease 101a formed on the back liner B on the bottom surface and two second creases 101b formed on the front liner A on the top surface. The first ruled lines 101a and the second ruled lines 101b are positioned slightly offset in the conveyance direction Y.

[0037] The ruled lines 101 and 102 have the same shape. Therefore, the ruled lines 102 are also formed as one first ruled line 102a on the back liner B on the lower surface and two second ruled lines 102b on the front liner A on the upper surface.

[0038] A front-back defect of the cardboard sheet S is a defect in which the cardboard sheet S is conveyed with the front and back sides reversed. That is, this is a defect in which the cardboard sheet S is conveyed with the back liner B located on the upper surface side and the front liner A located on the lower surface side. In this case, the first creases 101a and 102a are located on the upper surface side of the cardboard sheet S, and the second creases 101b and 102b are located on the lower surface side. A front-back defect of the cardboard sheet S is a defect in which the cardboard sheet S is conveyed with the leading edge Sa and trailing edge Sb reversed. That is, this is a defect in which the cardboard sheet S is conveyed with the trailing edge Sb located on the downstream side (leading edge side) and the leading edge Sa located on the upstream side (trailing edge side). In this case, the cardboard sheet S has the crease 102 located on the downstream side and the crease 101 located on the upstream side. Note that a cardboard sheet S may have both a front-back defect and a front-back defect at the same time.

[0039] The defect detection device 50 includes a distance measurement sensor (measuring device) 51, a rotary encoder 52, a determination device 53, a storage device 54, and a display device 55.

[0040] The distance measurement sensor 51 is disposed opposite the back liner B, which is one side of the conveyed cardboard sheet S, at a predetermined distance in the thickness direction of the cardboard sheet S. The distance measurement sensor 51 measures at least the distance to the leading edge of the cardboard sheet S on the downstream side and the distance to the recesses of the ruled lines 101, 102 formed on the cardboard sheet S.

[0041] The distance measurement sensor 51 is a common distance measurement sensor that measures both the distance to the leading edge of the cardboard sheet S and the distance to the recesses of the ruled lines 101 and 102. However, the distance measurement sensor 51 may be a different distance measurement sensor that measures both the distance to the leading edge of the cardboard sheet S and the distance to the recesses of the ruled lines 101 and 102. Here, the recesses of the ruled lines 101 and 102 refer to the recesses of the first ruled lines 101a and 102a or the recesses of the second ruled lines 101b and 102b. The distance measurement sensor 51 acquires, for example, the maximum distance from the position of the distance measurement sensor 51 to the recesses of the first ruled lines 101a and 102a of the cardboard sheet S or the maximum distance from the position of the distance measurement sensor 51 to the recesses of the second ruled lines 101b and 102b as the measured distance.

[0042] The distance measuring sensor 51 is positioned on the rear liner B side of the cardboard sheet S, spaced a distance H from the rear liner B. In other words, the distance H is the distance from the distance measuring sensor 51 to the plane of the cardboard sheet S. Therefore, when the distance measuring sensor 51 measures the distance H, it measures the leading edge Sa or the trailing edge Sb of the cardboard sheet S. As shown in FIG. 7 (described later), the recess depth of the first ruled lines 101a and 102a is a depth H1, and the recess depth of the second ruled lines 101b and 102b is a depth H2. The depth H1 of the first ruled lines 101a and 102a is greater than the depth H2 of the second ruled lines 101b and 102b. In other words, the relationship between the depth H1 of the first ruled lines 101a and 102a and the depth H2 of the second ruled lines 101b and 102b is H1>H2. Therefore, when the distance measuring sensor 51 measures the distance H+H1 obtained by adding the depth H1 to the distance H, it is considered to have measured the first ruled lines 101a, 102a (depth H1). Also, when the distance measuring sensor 51 measures the distance H+H2 obtained by adding the depth H2 to the distance H, it is considered to have measured the second ruled lines 101b, 102b (depth H2).

[0043] The distance measurement sensor 51 is preferably, for example, a laser displacement meter, but is not limited to a laser displacement meter and may be an ultrasonic sensor, etc. Furthermore, the measurement device is not limited to a non-contact sensor and may be a contact sensor.

[0044] The distance measuring sensor 51 is connected to the determination device 53. The distance measuring sensor 51 outputs the measurement result to the determination device 53.

[0045] The rotary encoder 52 functions as a position detector that detects the conveying position of the cardboard sheet S. The rotary encoder 52 detects, for example, the number of rotations (rotational speed) and rotational position of a rotating member in a drive device that conveys the cardboard sheet S along the conveying direction Y. The rotary encoder 52 is connected to a determination device 53. The rotary encoder 52 outputs the detection result to the determination device 53.

[0046] The judgment device 53 compares the measured distance in a predetermined judgment area from the leading edge to the trailing edge in the conveying direction Y of the cardboard sheet S with a predetermined threshold value, thereby determining whether the measured distance is larger or smaller than the threshold value and judging whether the cardboard sheet S is defective on the front or back or front or back.

[0047] The threshold values ​​include a first threshold value HA and a second threshold value HB. The first threshold value HA and the second threshold value HB determine the distance H+H1 to the first ruled lines 101a, 102a formed on the back liner B (one side) of the cardboard sheet S and the distance H+H2 to the second ruled lines 101b, 102b formed on the front liner A (the other side) of the cardboard sheet S. Here, the second threshold value HB is smaller than the first threshold value HA. In other words, since the relationship between the depth H1 of the first ruled lines 101a, 102a and the depth H2 of the second ruled lines 101b, 102b is H1>H2, the relationship between the first threshold value HA and the second threshold value HB is HA>HB.

[0048] The determination device 53 compares the distance measured by the distance measurement sensor 51 with the first threshold value HA and the second threshold value HB to determine whether the cardboard sheet S is defective on the front or back side or front or back side. The determination method will be described in detail later.

[0049] The determination device 53 is a control device, which is a controller, and is realized by, for example, a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) executing various programs stored in a memory unit using RAM as a working area.

[0050] The memory device 54 is connected to the determination device 53. The memory device 54 stores a first threshold value HA and a second threshold value HB. The memory device 54 also stores the determination result of the determination device 53. The display device 55 is connected to the determination device 53. The display device 55 displays the determination result of the determination device 53. In other words, when the cardboard sheet S is determined to be defective, the display device 55 displays whether the front and back are defective or the front and back are defective.

[0051] <Method for detecting defects in cardboard sheets> FIG. 6 is an explanatory diagram for explaining a method for detecting defects in cardboard sheets, and FIG. 7 is an explanatory diagram for explaining the first threshold value and the second threshold value.

[0052] The method for detecting defects in cardboard sheets according to the first embodiment is as shown in FIG. 6, in which the distance to the leading edge of the cardboard sheet S and the First ruled lines 101a, 102a The method includes a step of measuring the distance to the recess or the second ruled line 101b, 102b of the cardboard sheet S and acquiring the measured distance; a step of comparing the measured distance with a preset first threshold value HA in predetermined judgment areas A1, A2 set in advance from the front end to the rear end of the cardboard sheet S; a step of comparing the measured distance with a second threshold value HB that is smaller than the first threshold value HA in the judgment areas A1, A2; and a step of determining whether the measured distance is larger or smaller than the first threshold value HA and the second threshold value HB to determine whether the cardboard sheet S is defective on the front or back side or front or rear side.

[0053] More specifically, the distance measurement sensor 51 measures the distance to the cardboard sheet S, and acquires the measured distance of the cardboard sheet S at least in a determination area A1 before and after the leading edge of the cardboard sheet S being conveyed by a length La, and outputs the measured distance to the determination device 53. In other words, the distance measurement sensor 51 acquires the measured distance regardless of whether or not the cardboard sheet S is present on the conveying line of the box making machine 30.

[0054] 6, when the cardboard sheet S is conveyed in the correct orientation along the conveyance direction Y, the leading edge Sa is located downstream and the trailing edge Sb is located upstream, with the back liner B located on the bottom side and the front liner A located on the top side. Up to length L0, at which the leading edge Sa of the cardboard sheet S reaches the measurement position of the distance measurement sensor 51, the distance between the distance measurement sensor 51 and the cardboard sheet S indicates, for example, a value outside the measurement range. When the leading edge Sa of the cardboard sheet S reaches the measurement position of the distance measurement sensor 51, the distance measurement sensor 51 measures the distance H (measured distance) at the leading edge Sa at length L0, measures the distance H+H1 (measured distance) of the first ruled line 101a at length L1 from the leading edge Sa, measures the distance H+H1 (measured distance) of the first ruled line 102a at length L2 from the leading edge Sa, and measures the distance H (measured distance) at the trailing edge Sb at length L3. Then, the distance measurement sensor 51 outputs the measured distance obtained by measurement to the determination device 53. The determined device 53 receives the measured distance from the distance measurement sensor 51 and the conveying position of the cardboard sheet S from the rotary encoder 52. That is, the determination device 53 obtains the measured distance at the position of length L1 corresponding to the determination area A1, i.e., the distance H+H1 of the first ruled line 101a, and the measured distance at the position of length L2 corresponding to the determination area A2, i.e., the distance H+H1 of the first ruled line 102a.

[0055] In this case, the determination area A1 is the length of the area obtained by adding a predetermined margin on the upstream and downstream sides in the conveying direction Y to the length La from the leading edge Sa of the cardboard sheet S. The determination area A2 is the length of the area obtained by adding a predetermined margin on the upstream and downstream sides in the conveying direction Y to the length Lb from the leading edge Sa of the cardboard sheet S. Note that the length La from the leading edge Sa to the first ruled line 101a and the length Lb from the leading edge Sa to the first ruled line 102a can be determined in advance based on design values ​​associated with the specifications of the cardboard sheet S. Therefore, the determination areas A1 and A2 can be set in advance before measurement by the distance measurement sensor 51.

[0056] The determination device 53 determines that the cardboard sheet S is defective on both sides when the measured distance (here, distance H+H1) in the determination areas A1, A2 input from the distance measurement sensor 51 is smaller than the first threshold value HA and larger than the second threshold value HB. Furthermore, the determination device 53 determines that the cardboard sheet S is defective on both sides when the measured distance (here, distance H+H1) in the determination areas A1, A2 input from the distance measurement sensor 51 is smaller than the second threshold value HB.

[0057] As shown in FIG. 7, the first threshold value HA is set to a value obtained by adding a value Ha that is 60% to 70% of the design depth H1 of the first creases 101a and 102a to the distance H from the distance measurement sensor 51 to the plane of the cardboard sheet S, i.e., the back liner B without the first creases 101a and 102a. The second threshold value HB is set to a value obtained by adding a value Hb that is 20% to 30% of the design depth H1 of the first creases 101a and 102a to the distance H from the distance measurement sensor 51 to the plane of the cardboard sheet S, i.e., the back liner B without the first creases 101a and 102a. In this case, the design depth can be determined in advance from the specifications of the cardboard sheet S. Therefore, the first threshold value HA and the second threshold value HB can be set in advance before the determination by the determination device 53.

[0058] In other words, when the cardboard sheet S is transported in the correct orientation along the transport direction Y, the judgment device 53 determines that the cardboard sheet S is not defective on either the front or back, or on the front or back, and is a good product, because the measured distance H+H1 in the judgment areas A1 and A2 is greater than the first threshold value HA.

[0059] FIG. 8 is an explanatory diagram for explaining a method for detecting a defective cardboard sheet that is upside down.

[0060] 8, when a cardboard sheet S is conveyed in the conveying direction Y with its front and back sides facing inversely, the leading edge Sa is located downstream and the trailing edge Sb is located upstream, but the rear liner B is located on the upper surface side and the front liner A is located on the lower surface side. In this case, the distance measuring sensor 51 measures the distance H (measured distance) at the leading edge Sa at a position of length L0, measures the distance H+H2 (measured distance) of the second ruled line 101b at positions of lengths L11 and L12 from the leading edge Sa, measures the distance H+H2 (measured distance) of the second ruled line 102b at positions of lengths L13 and L14 from the leading edge Sa, and measures the distance H (measured distance) at the trailing edge Sb at a position of length L15. Then, the distance measurement sensor 51 outputs the measured distance at the position of lengths L11, L12 corresponding to the judgment area A1 obtained by measurement, i.e., the distance H+H2 of the second ruled line 101b, to the judgment device 53, and also outputs the measured distance at the position of lengths L13, L14 corresponding to the judgment area A2, i.e., the distance H+H2 of the second ruled line 102b, to the judgment device 53.

[0061] The determination device 53 determines that the cardboard sheet S is defective on both sides when the measured distance (here, distance H+H2) in the determination areas A1, A2 input from the distance measurement sensor 51 is smaller than the first threshold value HA and larger than the second threshold value HB. Furthermore, the determination device 53 determines that the cardboard sheet S is defective on both sides when the measured distance (here, distance H+H2) in the determination areas A1, A2 input from the distance measurement sensor 51 is smaller than the second threshold value HB.

[0062] In other words, when the cardboard sheet S is transported in the transport direction Y with the front and back facing backwards, the judgment device 53 judges that the cardboard sheet S is defective on both sides because the measured distance H+H2 in the judgment areas A1 and A2 is smaller than the first threshold value HA and larger than the second threshold value HB.

[0063] FIG. 9 is an explanatory diagram for explaining a method for detecting a defective cardboard sheet that is upside down.

[0064] 9, when a cardboard sheet S is conveyed in the conveying direction Y with its front and rear facing in opposite directions, the leading edge Sa is located upstream, the trailing edge Sb is located downstream, the back liner B is located on the bottom side, and the front liner A is located on the top side. Then, the distance measuring sensor 51 measures the distance H (measured distance) at the trailing edge Sb at a position of length L0, measures the distance H+H1 (measured distance) of the first ruled line 102a at a position of length L21 from the trailing edge Sb, measures the distance H+H1 (measured distance) of the first ruled line 101a at a position of length L22 from the trailing edge Sb, and measures the distance H (measured distance) at the leading edge Sa at a position of length L23. The distance measuring sensor 51 then outputs the measured distance at the position corresponding to the determination area A1, i.e., the distance H of the cardboard sheet S, to the determination device 53, and also outputs the measured distance at the position corresponding to the determination area A2, i.e., the distance H of the cardboard sheet S, to the determination device 53.

[0065] The determination device 53 determines that the cardboard sheet S has a front / back defect when the measured distance (here, distance H) in the determination areas A1 and A2 input from the distance measurement sensor 51 is smaller than the first threshold value HA and larger than the second threshold value HB. Furthermore, the determination device 53 determines that the cardboard sheet S has a front / back defect when the measured distance (here, distance H) in the determination areas A1 and A2 input from the distance measurement sensor 51 is smaller than the second threshold value HB.

[0066] In other words, when the cardboard sheet S is transported in the conveying direction Y with the front and back facing in the opposite direction, the judgment device 53 judges that the cardboard sheet S is defective in the front and back because the measured distance H in the judgment areas A1 and A2 is smaller than the second threshold value HB.

[0067] FIG. 10 is a flowchart showing the judgment control of the method for detecting defects in cardboard sheets.

[0068] 5 and 10, in step S11, the determination device 53 determines whether the leading edge of the cardboard sheet S has been detected based on information input from the distance measurement sensor 51. Here, the leading edge of the cardboard sheet S is the leading edge on the downstream side, and is the leading edge Sa or the trailing edge Sb. If the determination device 53 determines that the leading edge of the cardboard sheet S has not been detected (No), it continues processing in step S11. On the other hand, if the determination device 53 determines that the leading edge of the cardboard sheet S has been detected (Yes), it proceeds to step S12.

[0069] In step S12, the determination device 53 acquires the measured distance of the cardboard sheet S in the determination areas A1 and A2 measured by the distance measurement sensor 51. In step S13, the determination device 53 determines whether the measured distance is greater than a first threshold value HA. If the determination device 53 determines that the measured distance is greater than the first threshold value HA (Yes), in step S14, the determination device 53 determines that the cardboard sheet S is a non-defective product.

[0070] On the other hand, if the determination device 53 determines that the measured distance is not greater than the first threshold value HA (No), the process proceeds to step S15. In step S15, the determination device 53 determines whether the measured distance is greater than the second threshold value HB. If the determination device 53 determines that the measured distance is greater than the second threshold value HB (Yes), the determination device 53 determines in step S16 that the cardboard sheet S is a defective product and that both the front and back are defective.

[0071] On the other hand, if the determining device 53 determines that the measured distance is not greater than the second threshold value HB (No), then in step S17, it determines that the cardboard sheet S is a defective product and that the front and rear are defective.

[0072] In the above description of the determination method, two determination areas A1 and A2 are provided, and the measurement distances measured in the respective determination areas A1 and A2 are compared with the first threshold value HA and the second threshold value HB to determine whether the defect is present. However, if the measurement distances measured in at least one of the two determination areas A1 and A2 are compared with the first threshold value HA and the second threshold value HB, the defect is determined. One In the determination region A1 (A2), the measured distance may be compared with the first threshold value HA and the second threshold value HB to determine whether the defect is present.

[0073] [Second embodiment] 11 is a schematic diagram showing the configuration of a defect detection device for cardboard sheets according to the second embodiment. Note that components having the same functions as those in the above-described embodiments are given the same reference numerals, and detailed descriptions thereof will be omitted.

[0074] The defect detection device 50A includes a distance measurement sensor (measuring device) 51, a rotary encoder 52, a determination device 53A, a storage device 54, and a display device 55. The distance measurement sensor 51, the rotary encoder 52, the storage device 54, and the display device 55 are the same as those in the first embodiment.

[0075] The distance measuring sensor 51 is disposed so as to face the front liner A, which is the other side of the conveyed cardboard sheet S, at a predetermined distance in the thickness direction of the cardboard sheet S. Downstream side and the distance to the recesses of the ruled lines 101 and 102 formed on the cardboard sheet S. The distance measuring sensor 51 has the same function as in the first embodiment, but its location differs from that in the first embodiment.

[0076] The judgment device 53A judges whether the cardboard sheet S is defective by comparing the distance from the leading edge to the trailing edge of the cardboard sheet S in the conveying direction Y to the recesses of the ruled lines 101, 102 in a predetermined judgment area set in advance with a predetermined threshold value.

[0077] When the cardboard sheet S is conveyed in the correct orientation along the conveying direction Y, the leading edge Sa is located downstream and the trailing edge Sb is located upstream, with the back liner B located on the bottom side and the front liner A located on the top side. Then, the distance measuring sensor 51 measures the distance H (measured distance) at the leading edge Sa, measures the distance H+H2 (measured distance) of the second ruled line 101b in the determination area A1, measures the distance H+H2 (measured distance) of the second ruled line 102b in the determination area A2, and measures the distance H (measured distance) at the trailing edge Sb. Then, the distance measuring sensor 51 calculates the measured distances obtained by measuring. Judgment device 53A Output to. Judgment device 53A The measured distance is input from the distance measurement sensor 51, and the conveying position of the cardboard sheet S is input from the rotary encoder 52. Judgment device 53A obtains the measured distance at the position corresponding to the judgment area A1, i.e., the distance H+H2 of the second ruled line 101b, and the measured distance at the position corresponding to the judgment area A2, i.e., the distance H+H2 of the second ruled line 102b.

[0078] In this case, similar to the first embodiment, the determination areas A1 and A2 are lengths La and Lb with a predetermined margin added on the upstream and downstream sides in the conveyance direction Y. However, the determination areas A1 and A2 may also be lengths from the leading edge Sa of the cardboard sheet S to the second ruled lines 101b and 102b with a predetermined margin added on the upstream and downstream sides in the conveyance direction Y.

[0079] Judgment device 53A If the measured distance (here, the distance H+H2) in the determination areas A1 and A2 input from the distance measurement sensor 51 is greater than the first threshold value HA, it is determined that the cardboard sheet S has a defect on both sides. Make a judgment. Also, Judgment device 53A If the measured distance is smaller than the second threshold value HB, the cardboard sheet S is determined to be defective in the front and rear directions.

[0080] FIG. 12 is a flowchart showing the judgment control of the method for detecting defects in cardboard sheets.

[0081] As shown in FIGS. 11 and 12, in step S21, Judgment device 53ABased on the information input from the distance measurement sensor 51, it is determined whether or not the leading edge of the cardboard sheet S has been detected. Judgment device 53A If it is determined that the leading edge of the cardboard sheet S has not been detected (No), the process of step S21 continues. Judgment device 53A If it is determined that the leading edge of the cardboard sheet S has been detected (Yes), the process proceeds to step S22.

[0082] In step S22, Judgment device 53A In step S23, the distance measurement sensor 51 measures the distance of the cardboard sheet S in the determination areas A1 and A2. Judgment device 53A determines whether the measured distance is greater than a first threshold value HA. Judgment device 53A If it is determined that the measured distance is greater than the first threshold value HA (Yes), then in step S24, it is determined that the cardboard sheet S is a defective product and that both the front and back are defective.

[0083] on the other hand, Judgment device 53A If it is determined that the measured distance is not greater than the first threshold value HA (No), the process proceeds to step S25. Judgment device 53A determines whether the measured distance is greater than a second threshold value HB. Judgment device 53A If it is determined that the measured distance is greater than the second threshold value HB (Yes), then in step S26, the cardboard sheet S is determined to be a non-defective product.

[0084] on the other hand, Judgment device 53A If it is determined that the measured distance is not greater than the second threshold value HB (No), then in step S27, it is determined that the cardboard sheet S is a defective product and that the front and rear are defective.

[0085] [Effects of this embodiment] The cardboard sheet defect detection device of the first embodiment is equipped with a distance measurement sensor (measurement device) 51 that is arranged facing one or the other side of the cardboard sheet S and measures the distance from the arrangement position to the leading edge of the cardboard sheet S and the distance to the recesses of the first ruling lines 101a, 102a or the second ruling lines 101b, 102b, and acquires the measured distance; a memory device 54 that stores preset threshold values ​​HA, HB; and a judgment device 53 that compares the measured distance with the threshold values ​​HA, HB in predetermined judgment areas A1, A2 that are set in advance from the leading edge to the trailing edge of the cardboard sheet S, thereby determining whether the measured distance is larger or smaller than the threshold values ​​HA, HB and judging whether the cardboard sheet S is defective on the front or back side or front or back sides.

[0086] According to the cardboard sheet defect detection device of the first aspect, the depth H1 of the recesses of the first ruled lines 101a, 102a formed on one side of the cardboard sheet S is different from the depth H2 of the recesses of the second ruled lines 101b, 102b formed on the other side, so by comparing the measured distance with the thresholds HA, HB, it is possible to determine whether the cardboard sheet is defective on the front or back side or the front or back side. As a result, defects in the conveying state of the cardboard sheet S can be properly detected.

[0087] When the box former 30 produces cardboard boxes G, it sorts them into a predetermined number of batches and discharges them in bundles. A worker then removes defective cardboard boxes G from the discharged bundle. If the defect detection device 50 can detect front-to-back defects and front-to-back defects in the cardboard sheet S as different defects, the worker can easily remove defective cardboard boxes G (cardboard sheets S) from the bundle of cardboard boxes G. In other words, for a bundle of cardboard boxes G, front-to-back defects are caused by the positions of the creases 101, 102 in the conveyance direction Y being different from those of non-defective boxes, so the worker can easily find cardboard boxes G with front-to-back defects. On the other hand, for a bundle of cardboard boxes G, front-to-back defects are caused by the positions of the creases 101, 102 in the conveyance direction Y being the same as those of non-defective boxes, so the worker has difficulty finding cardboard boxes G with front-to-back defects. However, if it is known that a bundle of cardboard boxes G contains a mixture of front-to-back defects and front-to-back defects, the worker can easily find cardboard boxes G with front-to-back defects and front-to-back defects. As a result, it becomes easier for workers to remove defective cardboard boxes G from a bundle of cardboard boxes G, shortening the work time and reducing the number of defective cardboard boxes G that are missed.

[0088] The cardboard sheet defect detection device according to the second aspect is the cardboard sheet defect detection device according to the first aspect, further comprising a first threshold value HA and a second threshold value HB smaller than the first threshold value HA, and the determination device 53 compares the measured distance with the first threshold value HA and the second threshold value HB to determine whether the measured distance is larger or smaller than the first threshold value HA and the second threshold value HB, thereby determining whether the cardboard sheet S is front / back defective or front / back defective. This makes it possible to separately determine whether the measured distance is front / back defective or front / back defective by comparing the measured distance with the different threshold values ​​HA and HB.

[0089] The cardboard sheet defect detection device according to the third aspect is the cardboard sheet defect detection device according to the second aspect, further comprising: a distance measurement sensor 51 disposed opposite one side of the cardboard sheet S; and a determination device 53 determining whether the measured distance is smaller than a first threshold value HA and larger than a second threshold value HB. Corrugated cardboard sheet SAs a result, when the distance measurement sensor 51 is placed on one side of the cardboard sheet S on which the first ruled lines 101a and 102a are formed, the determination device 53 can easily determine whether the cardboard sheet S is a good product or a defective product on both sides by comparing the measured distance with the first threshold value HA and the second threshold value HB.

[0090] The cardboard sheet defect detection device according to the fourth aspect is the cardboard sheet defect detection device according to the third aspect, and further, the determination device 53 determines that the cardboard sheet S has a front-to-back defect when the measured distance is smaller than the second threshold value HB. This makes it easy to determine whether the cardboard sheet S has a front-to-back defect.

[0091] The cardboard sheet defect detection device according to the fifth aspect is the cardboard sheet defect detection device according to the second aspect, and further, the distance measurement sensor 51 is arranged facing the other side of the cardboard sheet S, and when the measured distance is greater than the first threshold value HA, Corrugated cardboard sheet S As a result, when the distance measurement sensor 51 is placed on the other side of the cardboard sheet S on which the second ruled lines 101b and 102b are formed, the determination device 53 can easily determine whether the cardboard sheet S is a good product or a defective product on both sides by comparing the measured distance with the first threshold value HA.

[0092] The cardboard sheet defect detection device according to the sixth aspect is the cardboard sheet defect detection device according to the fifth aspect, and further, the determination device 53 determines that the cardboard sheet S has a front-to-back defect if the measured distance is smaller than the second threshold value HB. This makes it easy to determine whether the cardboard sheet S is a good product or a front-to-back defect.

[0093] The seventh aspect of the defect detection device for cardboard sheets is the same as any one of the first to sixth aspects, except that the measuring device is a common distance measurement sensor 51 that measures the distance from the placement position to the leading edge of the cardboard sheet S and the distance to the recesses of the first ruled lines 101a and 102a or the recesses of the second ruled lines 101b and 102b. This simplifies the device and reduces costs.

[0094] The method for detecting defects in cardboard sheets according to the eighth aspect is a method for detecting defects in cardboard sheets by measuring the distance from a predetermined position facing one side or the other side of the cardboard sheet S to the leading edge of the cardboard sheet S and First ruled lines 101a, 102a The method includes a step of measuring the distance to the recess or the second ruled line 101b, 102b and acquiring the measured distance, a step of comparing the measured distance with preset thresholds HA, HB in predetermined judgment areas A1, A2 set in advance from the leading edge to the trailing edge of the cardboard sheet S, and a step of determining whether the measured distance is a front / back defect or a front / rear defect of the cardboard sheet S by determining which is larger or smaller between the measured distance and the thresholds HA, HB. In this way, by comparing the measured distance with the thresholds HA, HB, it is possible to determine whether the cardboard sheet S is a front / back defect or a front / rear defect. As a result, it is possible to properly detect defects in the conveying state of the cardboard sheet S.

[0095] A cardboard sheet defect detection method according to a ninth aspect is the cardboard sheet defect detection method according to the eighth aspect, and further includes a step of comparing the measured distance with a first threshold value HA in the determination areas A1 and A2, a step of comparing the measured distance with a second threshold value HB that is smaller than the first threshold value HA in the determination areas A1 and A2, and a step of determining whether the measured distance is a front / back defect or a front / back defect of the cardboard sheet S by determining whether the measured distance is a front / back defect or a front / back defect by comparing the measured distance with the different threshold values ​​HA and HB. As a result, it is possible to properly detect defects in the conveyance state of the cardboard sheet S.

[0096] The box making machine according to the tenth aspect is equipped with a defect detection device 50. This makes it possible to determine whether a front / back defect or a front / back defect is present by comparing the measured distance with thresholds HA and HB. As a result, defects in the conveyance state of the cardboard sheet S can be properly detected. This also makes it easier to remove defective cardboard boxes G from a bundle of cardboard boxes G discharged from the box making machine 30, shortening the work time and reducing the number of defective cardboard boxes G that are missed.

[0097] In the above-described embodiment, the threshold values ​​HA and HB are set by adding values ​​Ha and Hb, which take into account the design value for the depth of the recesses of the ruled lines 101a, 101b, 102a, and 102b, to the distance H from the distance measurement sensor 51 to the plane of the cardboard sheet S, and a defect is determined by comparing the measured distance to the cardboard sheet S acquired by the distance measurement sensor 51 with the threshold values ​​HA and HB, but the method is not limited to this. For example, the threshold values ​​HA and HB may be set to values ​​Ha and Hb, which take into account the design value for the depth of the recesses of the ruled lines 101a, 101b, 102a, and 102b, and a defect may be determined by comparing the value obtained by subtracting the distance H from the measured distance to the cardboard sheet S acquired by the distance measurement sensor 51 with the threshold values ​​Ha and Hb.

[0098] In the above-described embodiment, the cardboard sheet S has a ruled line 101 formed downstream in the conveying direction Y and a ruled line 102 formed upstream of the ruled line 101 in the conveying direction Y, and two judgment areas A1 and A2 are provided. The measured distances in the respective judgment areas A1 and A2 are compared with the first threshold value HA and the second threshold value HB to determine whether the cardboard sheet is defective. However, this configuration is not limited to this. Depending on the specifications, the cardboard sheet S may have one, three, or four ruled lines. In this case, a judgment area corresponding to each ruled line may be provided, and the measured distances in the respective judgment areas may be compared with the first threshold value HA and the second threshold value HB to determine whether the cardboard sheet is defective. Furthermore, the measured distances in at least one of the judgment areas may be compared with the first threshold value HA and the second threshold value HB to determine whether the cardboard sheet is defective.

[0099] Furthermore, in the description of the above embodiment, the box former 30 includes the paper feed unit 31, the printing unit 32, the paper discharge unit 33, the die-cut unit 34, the folder-gluer unit 35, and the counter ejector unit 36, but is not limited to this configuration. The box former 30 may be configured to include, for example, the paper feed unit 31, the printing unit 32, and the paper discharge unit 33. The box former 30 may be configured to include, for example, the paper feed unit 31, the printing unit 32, the paper discharge unit 33, and the die-cut unit 34. The box former 30 may be configured to include, for example, the paper feed unit 31, the printing unit 32, and the die-cut unit 34. [Explanation of symbols]

[0100] 10 Corrugating Machine 11, 12, 15, 16, 19 Mill roll stand 13,17 Single Facer 14,18 Bridge 20 Preheater 21 Glue Machine 22 Double Facer 23 Rotary Shaft 24 Slitta Scorara 25 cutoff 26 Defective product ejection device 27 Stacker 30 Box making machine 31 Paper feed section 32 Printing Department 33 Paper output section 34 Die-cut section 35 Folder gluer section 36 Counter ejector section 50,50A Defective Detector 51 Distance measurement sensor (measuring device) 52 rotary encoder 53,53A Judgment device 54 Storage device 55 Display device 101 Ruled Lines 101a First ruled line 101b Second ruled line 102 Ruled Lines 102a First ruled line 102b Second ruled line 111 Cutting line 112,113,114,115 Ruled lines 121,122,123 Groove 124 Notch 131,132,133 Groove 134 Notch A Front liner B, B1, B2 back liner C,C1,C2 center core D1, D2 single-sided corrugated cardboard sheet E,F Double-sided corrugated cardboard sheet G. Cardboard box S, S1 Corrugated cardboard sheet

Claims

1. A defect detection device for cardboard sheets having a first crease recess formed on one surface in the thickness direction and a second crease recess formed on the other surface in the thickness direction, the second crease recess being smaller in depth than the first crease recess, A measuring device is arranged opposite the one surface or the other surface, and measures the distance from the arrangement position to the leading edge of the cardboard sheet and the distance to the recess of the first ruled line or the recess of the second ruled line, and acquires the measured distance; a storage device that stores a threshold value that is set in advance according to the distance from the arrangement position to the recessed portion of the first ruled line or the recessed portion of the second ruled line; A judgment device that compares the measured distance with the threshold value in a predetermined judgment area set in advance from the leading edge to the trailing edge of the cardboard sheet to determine the magnitude relationship between the measured distance and the threshold value and judges whether the cardboard sheet is defective on the front or back side or front or back side; A cardboard sheet defect detection device comprising:

2. The threshold values ​​include a first threshold value and a second threshold value that is smaller than the first threshold value, and the determination device compares the measured distance with the first threshold value and the second threshold value to determine whether the measured distance is larger or smaller than the first threshold value and the second threshold value, thereby determining whether the cardboard sheet is front / back defective or front / back defective. The cardboard sheet defect detection device according to claim 1.

3. The measuring device is disposed opposite to the one surface of the cardboard sheet, and the determining device determines that the cardboard sheet has a front / back defect when the measured distance is smaller than the first threshold value and larger than the second threshold value. The cardboard sheet defect detection device according to claim 2.

4. The determination device determines that the cardboard sheet has a front-to-back defect when the measured distance is smaller than the second threshold value. The cardboard sheet defect detection device according to claim 3.

5. The measuring device is disposed opposite the other surface of the cardboard sheet, and the determining device determines that the cardboard sheet has a front / back defect when the measured distance is greater than the first threshold value. The cardboard sheet defect detection device according to claim 2.

6. The determination device determines that the cardboard sheet has a front-to-back defect when the measured distance is smaller than the second threshold value. The cardboard sheet defect detection device according to claim 5.

7. The measuring device is a common distance measuring sensor that measures the distance from the placement position to the leading edge of the cardboard sheet and the distance to the recess of the first ruled line or the recess of the second ruled line. The cardboard sheet defect detection device according to any one of claims 1 to 6.

8. A method for detecting defects in a cardboard sheet in which a recessed portion of a first crease is formed on one surface in the thickness direction and a recessed portion of a second crease that is smaller in depth than the recessed portion of the first crease is formed on the other surface in the thickness direction, A process of measuring the distance from a predetermined position facing the one surface or the other surface to the leading edge of the cardboard sheet and the distance to the recess of the first ruled line or the recess of the second ruled line, and acquiring the measured distances; A step of comparing the measured distance in a predetermined judgment area set in advance from the leading edge to the trailing edge of the cardboard sheet with a threshold value set in advance according to the distance from the predetermined position to the recess of the first ruled line or the recess of the second ruled line; A step of determining whether the measured distance is greater or smaller than the threshold value to determine whether the cardboard sheet is defective on the front or back or front or back; A method for detecting defects in cardboard sheets.

9. comparing the measured distance with a first threshold value in the determination region; comparing the measured distance with a second threshold value that is smaller than the first threshold value in the determination region; a step of determining whether the measured distance is greater than the first threshold value or the second threshold value and determining whether the cardboard sheet is defective on the front or back side or front or back side; 9. The method for detecting defects in cardboard sheets according to claim 8, further comprising:

10. A box making machine comprising the cardboard sheet defect detection device according to claim 1.

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