Method and system for the determination of a quality of bonded area in a boxmaking blank

A method and system for determining the bonding quality of a bonded area of a flapped boxmaking blank in a boxmaking apparatus at an assembling station of a production line, where opposite end portions of the blank are bonded together with confronting edges of companion end flaps defining a required gap, in terms of the outline of the gap. The quality determination is accomplished by irradiating sheetlike light onto the bonded area across the gap, forming an image of the irradiated light as a light image line composed of discrete segments which are arranged along a reference line for the flap portions and include at least one line segment located off the reference line, computing a ratio of a length of the off-line segment to the entire length of the light image line to obtain a width of the gap, and comparing the width of the gap with a preset reference value.

BACKGROUND OF THE INVENTION 
a) Field of the Invention 
This invention relates to a method and system for the determination of a 
quality of a bonded area in a boxmaking blank with opposite end portions 
thereof bonded together at the bonded area. In a boxmaking apparatus for 
continuously assembling boxes from such blanks, the above method and 
system makes, based on a width of a gap formed in the bonded area of the 
boxmaking blank, a determination as to whether the bonded area is good or 
bad. 
b) Description of the Related Art 
In a boxmaking process for producing boxes (corrugated fibreboard 
containers) from corrugated cardboard blanks (corrugated fibreboard 
blanks), it has been the conventional practice to fold each corrugated 
cardboard blank of a predetermined size, which includes slots formed 
therein and carries ruled lines, prints and the like applied thereon, to 
apply a glue on an overlap formed on one of opposite end portions of the 
corrugated cardboard blank and then to bond the opposite end portions 
together via the glued overlap, all by a folder gluer. 
After the corrugated cardboard blanks already folded and bonded by the 
folder gluer are corrected in squareness at a squaring unit, they are fed 
out box after box from a lower part of the squaring unit to a counter 
unit, where they are bundled in a desired number per bundle and are then 
ejected. 
As is shown in FIG. 13A, for example, each corrugated cardboard blank 1 is 
provided with gaps 1D in parts of a top flap 1A and bottom flap 1B, 
respectively, at locations corresponding to a bonded area 1C between 
opposite end portions of the blank. It is to be noted that, concerning the 
bonded area 1C and the gaps 1D, the overlapping back-side blank is shown 
with a portion thereof cut away in FIG. 13B because the bonded area 1C and 
the gaps 1D are located on the back side of the bonded blank and are 
hardly visible. 
Upon bonding the corrugated cardboard blank at the area 1C, control is 
performed so that, as is illustrated in FIGS. 13A and 13B, width a,b of 
the gaps 1D have a predetermined constant value. Namely, production of a 
corrugated cardboard box of an accurate shape free of off-squareness 
requires to bond opposite end portions of a blank together in a proper 
positional relationship. Whether the bonded area of the blank is good or 
bad can be determined depending on the width of the gap corresponding to 
the bonded area. It is therefore important to control the gap at a 
predetermined width. 
Attempts have therefore been made to measure the width of such gaps in an 
automated contactless manner in the course of boxmaking. For example, 
Prime Technology Inc., Maryland, U.S.A. has already commercialized a 
system under the name of "Gap Watch system". Further, JP kokai 9-22464 
discloses a gap quality determination system making use of a CCD (charged 
coupled device) camera. 
According to such conventional technology, a still image of a bonded area 
is formed by using a stroboscope or the electronic shutter function of a 
CCD camera and is then subjected to so-called image processing to extract 
necessary information. 
Described specifically, the system disclosed in JP kokai 9-22464 forms a 
varied-density image of the bonded area and, based on differences in 
density, detects edges in the bonded area and determines the width of the 
gap in the bonded area. In other words, when light is irradiated onto a 
corrugated cardboard blank, stronger reflection of light is available from 
a gap-free area of a corrugated cardboard blank, while weaker reflection 
of light is obtained from its gap-containing area. This system therefore 
detects a gap by making use of this difference in the intensity of 
reflection of light occurred for the existence and non-existence of the 
gap. 
However, an attempt to detect a gap from a varied-density image of a bonded 
area of a corrugated cardboard blank involves a potential problem that, 
when there is a print on a surface of the corrugated cardboard blank, the 
printed area may also be extracted erroneously as a gap depending on the 
color of the print because the printed area is also different in color 
density and hence in the intensity of reflection of light from a ground 
color of (a color of a liner on) the corrugated cardboard blank. 
Accordingly, this system must further perform accurate distinction of a 
true gap from the gap information so obtained. 
Further, the liner color is available with considerably wide variations in 
color tone, ranging from a very light tone called "white liner" to a 
significantly dark tone called "K liner". This may result in a variation 
in the quantity of reflection of light from the surface of a liner in a 
gap and hence in the density of the surface of the liner in the gap, 
thereby possibly making it difficult to accurately discriminate a 
difference from the density of the gap. As a consequence, the measurement 
of the width of a gap in a bonded area, said measurement performing image 
processing such as edge extraction by using a varied-density image of the 
bonded area, has difficulty in making determination at high reliability. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide, by an improvement on the 
manner of formation of an image of the bonded area in a boxmaking blank, a 
method for the determination of a quality of a bonded area in a boxmaking 
blank, which permits an easy determination as to whether the bonded area 
is good or bad. 
Another object of the present invention is to provide, by an improvement on 
the manner of formation of an image of the bonded area in a boxmaking 
blank, a system for the determination of a quality of a bonded area in a 
boxmaking blank, which permits an easy determination as to whether the 
bonded area is good or bad. 
To achieve these objects, a method and system according to the present 
invention for the determination of a quality of a bonded area in a 
boxmaking blank have characteristic features to be described hereinafter. 
Namely, the method according to the present invention is provided for the 
determination of a quality of a bonded area in a boxmaking blank with 
opposite end portions thereof bonded together at the bonded area. The 
method is suited for application to a boxmaking apparatus adapted to 
continuously assemble boxes from such boxmaking blanks. The method 
includes irradiating light from a light source onto the bonded area of the 
blank travelling on and along a production line, forming an image of the 
bonded area by image pick-up means, computing a width of a gap formed in 
the bonded area on a basis of information of the image so formed, and from 
the results of the computation, making a determination as to whether the 
bonded area is good or bad. The light is irradiated in the form of a sheet 
from the light source toward the bonded area so that the sheetlike light 
extends across the gap. The image pick-up means is arranged with an image 
pick-up direction thereof extending at an angle relative to a direction of 
an optical axis of the sheetlike light from the light source, and an image 
of the bonded area irradiated by the sheetlike light from the light source 
is formed by the image pick-up means so arranged. The width of the gap in 
the bonded area is computed based on information of the image formed by 
the image pick-up means so arranged. The results of the computation are 
then compared with a preset upper limit and lower limit to determine 
whether the bonded area is good or bad. 
Owing to the above-described characteristic features, the method of the 
present invention can easily measure the bonded area in the blank 
irrespective of the density, and can also easily measure the bonded area 
in the blank without being affected by the color of a liner or a printed 
area on the blank. This method therefore has an advantage that the 
performance and reliability of a boxmaking line making use of such blanks 
can be substantially improved. 
In the above-described method for the determination of the quality of the 
bonded area in the boxmaking blank, before the irradiation of the 
sheetlike light from the light source and the subsequent formation of the 
image by the image pick-up means, the light source and the image pick-up 
means may be adjusted in position so that the light source and the image 
pick-up means are directed toward a position of the bonded area of the 
blank travelling on and along the production line. 
Further, the computation of the width of the gap in the bonded area, the 
computation being conducted based on the information of the image formed 
by the image pick-up means, may be conducted by a projection method or a 
sequential comparison method. 
In addition, the system according to the present invention is provided for 
the determination of a quality of a bonded area in a boxmaking blank with 
opposite end portions thereof bonded together at the bonded area. The 
system is suited for arrangement in association with a boxmaking apparatus 
adapted to continuously assemble boxes from such boxmaking blanks, whereby 
a width of a gap formed in the bonded area of the blank is measured to 
determine whether the quality of the bonded area is good or bad. The 
system comprises a light source for irradiating light in the form of a 
sheet toward the bonded area travelling on and along a production line so 
that the sheetlike light extends across the gap; image pick-up means for 
forming an image of the bonded area irradiated by the sheetlike light from 
the light source, the image pick-up means being arranged with an image 
pick-up direction thereof extending at an angle relative to a direction of 
an optical axis of the sheetlike light from the light source; and 
computation and determination means for computing the width of the gap in 
the bonded area on a basis of information of the image from the image 
pick-up means and comparing the results of the computation with a preset 
upper limit and lower limit to determine whether the bonded area is good 
or bad. 
Owing to the above-described characteristic features, the system of the 
present invention can easily measure the bonded area in the blank 
irrespective of the density, and can also easily measure the bonded area 
in the blank without being affected by the color of a liner or a printed 
area on the blank. This system therefore has an advantage that the 
performance and reliability of a boxmaking line making use of such blanks 
can be substantially improved. 
The above-described system for the determination of the quality of the 
bonded area in the boxmaking blank may further comprise a positioning 
device for setting states of arrangement of the light source and the image 
pick-up means in correspondence with a position of the bonded area of the 
blank travelling on and along the production line. 
In the above-described system for the determination of the quality of the 
bonded area in the boxmaking blank, the computation and determination 
means may compute the width of the gap by the projection method or the 
sequential comparison method on the basis of the information of the image 
from the image pick-up means. 
In the above-described system for the determination of the quality of the 
bonded area in the boxmaking blank, the light source and the image pick-up 
means may be suited for arrangement above or below the production line, 
and additional light source and image pick-up means as defined above may 
be included for arrangement below or above the production line so that the 
additional light source and image pick-up means are located on a side 
opposite to the light source and the image pick-up means with respect to 
the production line. 
In the above-described system for the determination of the quality of the 
bonded area in the boxmaking blank, the blank may travel with a widthwise 
direction of the gap directed at a right angle relative to or in parallel 
with a longitudinal direction of the production line.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to the drawings, a description will hereinafter be made 
about the construction of the system according to the preferred embodiment 
of the present invention for the determination of the quality of the 
bonded area in the boxmaking blank. 
As is illustrated in FIG. 2, the system according to this embodiment for 
the determination of the quality of the bonded area of the boxmaking blank 
is provided with the light source 10 having an optical axis and the 
photosensor 11, and these light source 10 and photosensor 11 are arranged 
between a squaring unit 30 and a counter unit 31 disposed in a boxmaking 
production line for corrugated cardboard boxes. 
Namely, each corrugated cardboard blank 1 as a material for the corrugated 
cardboard box is bonded at opposite end portions thereof and, subsequent 
to correction into a square form at the squaring unit 30, the corrugated 
cardboard blank 1 is transported to the counter unit 31. At this time, the 
corrugated cardboard blank 1 is fed out from a lower part of the squaring 
unit 30 and is then transported to the counter unit 31 (in the direction 
of a leftward arrow in FIG. 2) by a first conveyor 32 and a second 
conveyor 33. 
The first conveyor 32 and the second conveyor 33 are arranged with an 
interval left therebetween, and the light source 10 and photosensor 11 of 
the system are arranged below a transport line between the first conveyor 
32 and the second conveyor 33. 
In addition to the light source 10 and the photosensor 11, the system for 
the determination of the quality of the bonded area in the boxmaking blank 
is also provided, as is shown in FIG. 1, with a positioning device 12, a 
blank pass detection sensor 13, a computation and determination unit 14 
and a display unit 15. The positioning device 12 and the computation and 
determination unit 14 are controllable by a computer numerical control 
(CNC) 20 of the boxmaking apparatus. 
Here, the corrugated cardboard blank 1 is transported in the direction of 
arrow C on and along the production line with a top flap 1A and a bottom 
flap 1B directed forward and rearward, respectively, and with a bonded 
area 1C facing downward. The light source 10 irradiates sheetlike light 
(sectorally-flaring laser beam) onto the gap 1D in the bonded area 1C of 
the corrugated cardboard blank 1, which is travelling on and along the 
production line, so that the sheetlike light is directed extending across 
the gap 1D. In FIG. 1, the direction of the sheetlike light from the light 
source 10 is not set in a direction perpendicular to a lower side of the 
corrugated cardboard blank 1 but is set in a direction aslant relative to 
the travelling direction of the corrugated cardboard blank 1 as indicated 
by arrow c. 
Incidentally, the sectorally-flaring laser beam is used as the light source 
10 as mentioned above. Besides such a laser beam, it is also possible to 
use a strong sheetlike light source constructed of a strong metal halide 
light source, a cylindrical lens and the like. 
Further, the photosensor (camera) 11 as the image pick-up means is adapted 
to form an image of the bonded area 1C irradiated by the sheetlike light 
from the light source 10. It forms the image of the bonded area 1C at a 
timing corresponding to a detection signal by the blank pass detection 
sensor 13 to be described subsequently herein. As is illustrated in FIG. 
2, the photosensor is arranged in a direction perpendicular to the 
corrugated cardboard blank 1. The photosensor 11 shown in FIG. 2 will 
hereinafter be called the "camera" as it is constructed of a matrix-array 
CCD camera. 
Although the camera 11 is arranged with its image-forming direction toward 
the corrugated cardboard blank 1 extending in a direction perpendicular to 
the lower side of the corrugated cardboard blank 1 in FIG. 2, this 
image-forming direction is not limited to such a direction. It is 
sufficient if the image-forming direction is set to form an angle relative 
to the direction of an optical axis of the sheetlike light from the light 
source 10. 
Accordingly, the optical axis of the sheetlike light from the light source 
10 may extend at a right angle relative to the lower side of the 
corrugated cardboard blank 1 when the image-forming direction is set 
aslant relative to the lower side of the corrugated cardboard blank 1. By 
the way, these light source 10 and camera 11 are constructed integrally as 
a sensing device in this embodiment. 
The positioning device 12 is to adjust the state of arrangement of the 
sensing device, which is composed of the light source 10 and the camera 
11, in correspondence with the position of the bonded area 1C of the 
corrugated cardboard blank 1 travelling on and along the production line. 
This positional adjustment is effected based on a signal from the control 
20 which will be described subsequently herein. Incidentally, these 
positioning device 12 and sensing device 10,11 make up a gap width sensor 
head. Further, the term "state of arrangement" as used herein means 
"position or location" and/or "angle or spatial position". 
The blank pass detection sensor 13 detects a timing at which the sheetlike 
light is irradiated onto the bonded area 1C, and generates a detection 
signal indicative of the timing. This blank pass detection sensor detects 
the leading edge and trailing edge of the corrugated cardboard blank 1 
while distinguishing these edges from each other. At the timing based on 
the detection signal from the blank pass detection sensor 13, the 
irradiation of the light from the light source 10 and the image formation 
by the camera 11 are performed. 
As the blank pass detection sensor 13 is arranged on an upstream side, as 
viewed in the direction of transportation (see the arrow c), of the camera 
11 by a predetermined distance, the detection of the trailing edge of the 
corrugated cardboard blank 1 by the blank pass detection sensor 13 also 
means the concurrent existence of the gap 1D, which is formed in the 
bonded area 1C on the side of the bottom flap 1B, within a detection area 
of the camera 11. 
When the blank pass detection sensor 13 has detected the leading edge of 
the corrugated cardboard blank 1, however, the gap 1D in the bonded area 
1C on the side of the top flap 1A has not reached yet the inside of the 
detection area of the camera 11. Subsequent to elapse of a predetermined 
time from this time point, the gap 1D on the side of the top flap 1A 
reaches the detection area of the camera 11. The time required from the 
detection of the forward edge of the corrugated cardboard blank 1 until 
the arrival of the gap 1D in the detection area is determined by a 
positional relationship between the blank pass detection sensor 13 and the 
camera 11, a positional relationship between the leading edge of the 
corrugated cardboard blank 1 and the gap 1D on the side of the top flap 1A 
and the traveling speed of the corrugated cardboard blank 1. 
When the blank pass detection sensor 13 outputs a leading edge detection 
signal upon detection of the leading edge of the corrugated cardboard 
blank 1, the width of the gap 1D in the bonded area 1C on the side of the 
leading edge (on the side of the top flap 1A) is measured at a timing 
delayed by a predetermined time. When the blank pass detection sensor 13 
outputs a trailing edge detection signal upon detection of the trailing 
edge of the corrugated cardboard blank 1, on the other hand, the width of 
the gap 1D in the bonded area 1C on the side of the trailing edge (on the 
side of the bottom flap 1B) is measured concurrently with the output of 
the trailing edge detection signal. 
The computation and determination unit (good/bad determination unit) 14 
computes the width of the gap 1D on the basis of the signal from the 
camera 11 and then compares the results of the computation with a preset 
upper limit and lower limit to make a determination as to whether the 
bonded area 1C is good or bad. The computation and determination unit is 
controlled by the control 20 which will be described subsequently herein. 
Further, the display unit (determination results display unit) 15 serves 
to display the results of the determination which has been made at the 
computation and determination unit 14. 
The control (CNC) 20 controls the above-mentioned positioning device 12 and 
computation and determination unit 14, and is constructed as a control for 
the entire boxmaking apparatus. Specifically, the control 20 first 
performs a positional adjustment of the sensing device (the light source 
10 and the camera 11) before the initiation of an operation (job) so that 
the light source 10 and the camera 11 can irradiate and detect the bonded 
area 1C of each corrugated cardboard blank 1 travelling on and along the 
production line. 
In other words, positional information of the bonded area 1C is sent from 
the control 20 to the positioning device 12, and the positioning device 12 
then performs positional adjustments of the light source 10 and camera 11 
in accordance with the positional information so that their states of 
arrangement can be set corresponding to the passing position of the bonded 
area 1C. 
After the initiation of the operation, the sheetlike light is irradiated 
responsive to a command signal from the control 20 from the light source 
10 toward the bonded area 1C so that the sheetlike light extends across 
the gap 1D, an image of the bonded area 1C irradiated by the light from 
the light source 10 is formed by the camera 11, and the width of the gap 
1D in the bonded area 1C is then computed based on information of the 
image formed by the camera 11. The results of the computation are compared 
with the preset upper limit and lower limit, whereby a determination is 
made as to whether the bonded area 1C is good or bad. By the way, the 
above-mentioned control by the control 20 is performed lot by lot. 
With reference to FIGS. 3A and 3B, a detailed description will now be made 
about the principle of the above-mentioned detection of the width of the 
gap in the bonded area 1C by the light source 10 and the camera 11. It is 
to be noted that FIG. 3A is a diagram schematically illustrating the light 
source 10 and the camera 11 as viewed from the side of the conveyor line 
but the positions and directions of the light source 10 and camera 11 as 
shown in FIGS. 1 and 2 are vertically reversed in FIG. 3A. 
As is depicted in FIG. 3A, when an image of the bonded area 1C irradiated 
at an angle by the sheetlike laser beam from the light source 10 is formed 
by the camera 11 arranged with its detecting direction extending at a 
right angle relative to the corrugated cardboard blank 1, a plan view 
image d is obtained at the camera 11 as shown in FIG. 3B. 
Incidentally, FIG. 3B illustrates by way of example the image formed by the 
camera 11 in connection with the gap 1D in the bonded area 1C on the side 
of the trailing edge (on the side of the flap 1B) of the corrugated 
cardboard blank 1. In FIG. 3B, a straight line d1 indicates the trailing 
edge of the corrugated cardboard blank 1, dashed lines d2,d3 represent 
lines of light formed on the corrugated cardboard blank 1 as a result of 
the irradiation by the laser beam, and a region d4 with hatching 
designates the part of the gap 1D. 
Among these, the dashed lines d2 correspond to the lines of light formed on 
the surface of the corrugated cardboard blank 1, while the dashed line d3 
corresponds to the line of light formed at the part of the gap (the region 
d4 with the hatching) in the bonded area 1C. As is readily appreciated 
from this diagram, a difference arises in the position of a line of light 
between the gap part d4 and the other parts on the image d. 
Reasons for the occurrence of this positional difference will be explained 
hereinafter with reference to FIG. 3A. In the neighborhood of the gap 1D 
as the detection target in the bonded area 1C of the corrugated cardboard 
blank 1, the gap-free part is irradiated by the light at a liner on the 
surface of a blank portion on a side closer to the light source 10 and the 
camera 11 but the gap part is irradiated by the light at a liner on the 
surface of a blank portion on a side farther from the light source 10 and 
the camera 11. A difference therefore arises in the point of irradiation 
by the laser beam between the gap-free parts and the gap part. 
The lines of light formed at the respective parts are hence shifted from 
each other on the image d formed by the camera 11 from the oblique 
direction relative to the irradiated direction of the light. 
Namely, when a sheetlike laser beam impinges an object having a concavity 
or convexity at a surface thereof like the corrugated cardboard blank 1 
containing the gap 1D, a line of light is formed as a non-continuous line 
along the edge of the concavity or convexity. Making use of this 
characteristic phenomenon of noncontinuity, the gap part can be 
ascertained. This method is called the "light cutting method" and is used 
for the measurement of three-dimensional shapes. In this embodiment, the 
gap part and the other parts are discriminated from each other by using 
this method. 
As has already been mentioned above, a similar image can also be obtained 
when the bonded area vertically irradiated by a sheetlike laser beam is 
taken by the camera 11 arranged at an upper left or right position. 
A specific description will now be made about an extraction method of the 
gap in the bonded area 1C and a measuring method of its width. 
When a laser beam is irradiated onto the bonded area 1C, an image e 
containing mutually-shifted lines of light as shown in FIG. 4A is obtained 
at the camera 11. As is indicated in FIG. 4A, the width of the gap in the 
bonded area 1C can be determined as the length M2 of a line segment 
P.sub.3 -P.sub.4 or as the distance M.sub.1 between points P.sub.1 and 
P.sub.2. In FIG. 4A, letter "G" indicates a barycenter of the line segment 
P.sub.3 -P.sub.4 and letter "D" designates an X coordinate of the 
barycenter G. From the image information, the length M2 of the line 
segment P.sub.3 -P.sub.4 or the distance M1 between the points P.sub.1 and 
P.sub.2 is thus determined as will be described next. 
In this embodiment, the image information is first processed by the 
labeling method, followed by the calculation of the width of the gap by 
the projection method or the sequential comparison method. 
(a) Processing of the image data by the labeling method: 
According to the processing by the labeling method, bi-level digitization 
processing is first conducted, namely, individual pixels in a 
varied-density image formed at the camera 11 are compared pixel by pixel 
with a predetermined constant density level and to each pixel, 0 (black) 
is allotted when the density of the pixel is lower than the predetermined 
constant density level or 1 (white) is allotted when the density of the 
pixel is higher than the predetermined constant density level. 
The bi-level digitized data obtained by the bi-level digitization 
processing are then subjected to elimination processing of isolated points 
and continuation processing of noncontinuous points. Subsequent to 
elimination of a noise and the like, labeling processing is performed 
further to take each continuous line as a single group. From the data so 
labeling processed, line segment data of the gap are extracted. 
(b) Calculation of the width of the gap by the projection method (the first 
detection method): 
According to the projection method, the bi-level digitized image data are 
first projected in X direction. Because each pixel has a value of 1 or 0 
in the bi-level digitized image data, the values (1 or 0) of individual 
pixels in each row are successively added by the projection in X 
direction. By performing this computation over the entire rows, the 
numbers of pixels in the respective rows (Y coordinate points) can be 
determined. By conducting projection of the bi-level digitized data in X 
direction (in the direction of the lines of light), a maximum peak is 
determined from the results of this projection. 
By searching the maximum peak Y.sub.p as described above, a line position 
at which the sheetlike light crosses the surfaces of the corrugated 
cardboard blank 1 can be extracted. Another search is then conducted for a 
peak Y.sub.g which is located at a position adjacent to the maximum peak 
Y.sub.p. This makes it possible to extract the gap part. Namely, the width 
of the gap can be obtained by choosing data closer to the Y.sub.g 
coordinate point from the above-mentioned labeling processed segment data 
and determining the length of the line segment (the number of pixels). 
When lines of light are horizontal, two peaks Y.sub.p,Y.sub.g are obtained 
by adding individual pixels line after line, for example, as shown in FIG. 
4B. In the diagram, the peak Y.sub.p is the maximum peak in the image e. 
This peak Y.sub.p indicates the results (the number of pixels) of addition 
of the data of the segment line passing through the point P.sub.1 with the 
data of the segment line extending through the point P.sub.2. On the other 
hand, the peak Y.sub.g represents the results of addition of the data of 
the line segment between the points P.sub.3 and P.sub.4, and the results 
of the addition correspond to the length M2 of the line segment P.sub.3 
-P.sub.4. 
(c) Calculation of the width of the gap by the sequential comparison method 
(the second detection method): 
In the projection method described above under (b), projection is conduced 
in X direction, a peak is detected from the results of the projection, and 
the width of the gap in the bonded area 1C is then determined from the 
height of the peak. According to the sequential comparison method, 
however, distances between labeling processed data of line segments and an 
end of an image are measured and, based on the data at which a difference 
arises in the distance, the width of the gap in the bonded area 1C is 
determined. 
Described specifically, as is illustrated in an image f of FIG. 5, the 
distances Y.sub.i between labeling processed data of line segments 
(f.sub.1 to f.sub.3) and the end of the image f (the upper edge of the 
image f in FIG. 5) are used as position data of lines of light at 
individual X coordinate points. These distances Y.sub.i are measured in 
the order of pixel units (Y.sub.1 .fwdarw.Y.sub.n) toward the X-axis. 
In the course of this measurement (Y.sub.1 .fwdarw.Y.sub.n), a difference 
between each position data Y.sub.i and its adjacent position data 
Y.sub.i+1 is determined. Assuming that there is a continuous line segment 
when this difference is not greater than a predetermined value, a line 
segment which is not in continuation with the other line segments is 
formed exclusively corresponding to the gap part. If a line segment which 
is not in continuation with other line segments is extracted and the 
number of pixels in the thus-extracted line segment is determined, the 
number of the pixels indicates the length of the line segment, that is, 
the width of the gap. 
From a theoretical standpoint, data on such distances Y.sub.i should appear 
as shown in FIG. 6, corresponding to lines of light at the gap-free part 
(see f.sub.1 and f.sub.3 in FIG. 5) and a line of light at the gap part 
(see f.sub.2 in FIG. 5). It is to be noted that, compared with FIG. 5., 
FIG. 6 shows the lines of light upside down. 
Described specifically, distances Y.sub.1 -Y.sub.j of a first pixel to a 
j-th pixel have continuity with each other (the differences between the 
adjacent distance data are not greater than the predetermined value) and 
are around Y.sub.a. Between the j-th pixel and a (j+1)-th pixel, however, 
there is noncontinuity (the difference between the adjacent distance data 
Y.sub.j and Y.sub.j+1 is greater than the predetermined value). Further, 
distances of the (j+1)-th pixel to a k-th pixel have continuity with each 
other (the differences between the adjacent distance data are not greater 
than the predetermined value) and are around Y.sub.b. Moreover, there is 
noncontinuity between the k-th pixel and a (k+1)-th pixel (the difference 
between the adjacent distance data Y.sub.k and Y.sub.k+1 is greater than 
the predetermined value), but distances Y.sub.k+1 -Y.sub.n of the (k+1)-th 
pixel to an n-th pixel have continuity with each other (the differences 
between the adjacent distance data are not greater than the predetermined 
value) and are around Y.sub.a. 
Actual image data, however, do not always appear as shown in FIG. 5 due to 
the influence of a noise, the machined shape of such edge portions 1E of 
the corrugated cardboard blank 1 as shown in FIG. 9, said edge portions 
forming peripheral edge portions of the gap 1D, a detection failure of 
light by the camera 11, and/or a like cause. Likewise, distance data do 
not necessarily appear as illustrated in FIG. 6, due to the influence of a 
noise, the machined shape of the edge portions 1E of the corrugated 
cardboard blank 1, a detection failure of light, and/or a like cause. 
Instead, the data on the distances Y.sub.i are considered to appear in 
rather varied forms as shown in FIGS. 7A to 7C and FIGS. 8A and 8B. 
Signs L.sub.1 -L.sub.7 shown in FIGS. 7A to 7C and FIGS. 8A and 8B are 
labels allotted to data groups which were recognized as line segments as a 
result of determination of differences. Although the labels L.sub.1 
-L.sub.5 are commonly used in at least two of FIGS. 7A to 7C and FIGS. 8A 
and 8B, each label in one of these drawings has no relevance to the 
corresponding label in one or more of the remaining drawings. 
The determination of continuity or noncontinuity among the distances 
Y.sub.i is therefore conducted with the following matters in mind. 
First, a noise is dealt with. Assuming that a noise basically appears as a 
single-shot signal, it is designed that, upon occurrence of a noise, 
noncontinuity is determined to exist between a pixel detected at the time 
of the occurrence of the noise and each of pixels detected before and 
after the occurrence of the noise. As is shown in FIG. 7A, for example, if 
there is data R.sub.2 greater than a constant value of label L.sub.1 
between two data (R.sub.1,R.sub.2) determined to fall in label L.sub.1, 
this data R.sub.2 is determined to be a noise and is included in label 
L.sub.1. 
As is shown in FIG. 7B, for example, between a data group determined to be 
label L1 and another data group determined to be label L2, in other words, 
in a transition state from label L1 to label L2 or from label L2 to label 
L1, data R.sub.4 which is remote from any of the predetermined constant 
values of the respective labels, is neglected. Data R.sub.5 situated 
between label L2 and label L3 is neglected likewise. 
As has been described above, a measurement data is either neglected or 
included in an adjacent label provided that it is not continuous with any 
of its adjacent data. 
When, as is shown in FIG. 7C, for example, two noncontinuous data 
[(R.sub.6,R.sub.7) or (R.sub.8,R.sub.9)] are successively situated between 
label L1 and label L2 or label L2 and label L3, these two data are not 
registered but are neglected as in the case of FIG. 7B because they are 
remote from any of the labels. 
Although the two noncontinuous measurement data are successively situated 
in the above case, there is a difference greater than a certain constant 
value between the values of these two data. Accordingly, they cannot be 
put together in a single label and are neglected. 
When data similar to those shown in the above-described FIG. 7B or 7C are 
obtained, the line segment data (equivalent to f.sub.2 in FIG. 5) of the 
bonded area 1C can be obtained by subtracting the line segment data of 
labels L1,L3 from the overall line segment data (label data) (see spans 
SP1,SP2 in FIGS. 7B and 7C). 
Next, as is shown in FIG. 8A, for example, measurement data may be obtained 
in a stepwise pattern. This indicates the occurrence of a cutting failure 
in the gap part of the corrugated cardboard blank 1. Namely, if a cutter 
deteriorates and its sharpness changes, a core part of the corrugated 
cardboard blank 1 may not be cut in specified dimensions, for example, as 
illustrated in FIG. 9 (see 1E). In such a case, measurement data similar 
to those shown in FIG. 8A occur. 
The above case means the existence of plural labels. Nonetheless, the line 
segment data of the bonded area 1C can be obtained by subtracting the line 
segment data of labels L1,L7 from the overall line segment data (label 
data) (see a span SP3 in FIG. 8A). 
Further, as is illustrated in FIG. 8B, for example, measurement data may be 
partially cut off as indicated by labels L2,L4. Data similar to those 
shown in this diagram occur if the quantity of light is reduced due to 
oblique impingement or the like of a laser beam and no light can be 
detected as data on an image. 
In the above case, the line segment data of the bonded area 1C can be 
obtained likewise by subtracting the line segment data of labels L1,L5 
from the overall line segment data and hence taking into consideration 
portions failed to be detected on the image (see a span SP4 in FIG. 8B). 
Incidentally, as is illustrated in FIG. 8B, the positions of available 
data vary depending on the mounting position (direction) of the camera 11 
(see labels L3,L3'). 
Further, the above-described values subtracted from the overall line 
segment data, that is, the individual line segment data of labels L1,L7 
(FIG. 8A) and labels L1,L5 (FIG. 8B) are obtained in such a manner that 
their values become equal to the maximum value and the value next to the 
maximum value, respectively, of the label data (namely, L1 and L7 in FIG. 
8A; and L1 and L5 in FIG. 8B). 
The system according to the embodiment of the present invention for the 
determination of the quality of the bonded area in the boxmaking blank is 
constructed as described above, and procedures of a quality determination 
by the system (i.e, the method according to the present invention for the 
determination of the quality of the bonded area in the boxmaking blank) is 
performed, for example, as shown in the flow chart of FIG. 10. 
First, the positions of the light source 10 and camera 11 are adjusted by 
the positioning device 12 so that the light source 10 and the camera 11 
are set at such positions as enabling them to irradiate light onto the 
bonded area 1C in each corrugated cardboard blank 1 travelling on and 
along the production line and to form an image of the bonded area 1C. 
From the light source 10 toward the bonded area 1C, sheetlike light is then 
irradiated extending across the gap 1D, whereby an image of the bonded 
area 1C irradiated by the light from the light source 10 is formed. In 
other words, lines of light are extracted by such bi-level digitization as 
mentioned above (step a1). 
Labeling processing is then applied to the thus-extracted lines of light to 
classify the resulting line segment data into groups (step a2). Described 
specifically, the classified line segment data can be obtained by using 
one of the two methods as described above. Based on the line segment data, 
the width of the gap 1D in the bonded area 1C is extracted (step a3). 
Afterwards the thus-extracted width of the gap 1D is then compared with the 
preset upper limit and lower limit to determine whether the bonded area 1C 
is good or bad, the width of the gap 1D is calculated (step a4). 
Two methods are available for the execution of the processing in these 
steps a3,a4, namely, for the determination of the width of the gap 1D in 
the bonded area 1C. These two methods will hereinafter be described in 
detail with reference to the flow charts of FIGS. 11 and 12. 
(a) Execution by the projection method: 
A description will be made in accordance with the flow chart shown in FIG. 
11. Upon initiation of a measurement, the black and white image of a 
monochrome image formed by the camera 11 is first subjected to smoothing 
(step b1), and bi-level digitization is conducted based on a preset 
threshold level as described above (step b2). As a result, the position of 
a line at which sheet-like light crosses a surface of a corrugated 
cardboard blank is extracted. 
Subsequent to elimination of noncontinuous isolated points from the 
bi-level digitized data obtained by the bi-level digitization (step b3), 
continuation processing of noncontinuous points is performed (step b4). 
Referring to FIG. 4A, for example, the points P.sub.3,P.sub.4 which are 
noncontinuous with the point P.sub.1 and the point P.sub.2 are rendered 
continuous to form the line segment P.sub.3 -P.sub.4. Labeling processing 
is then conducted on the line segment obtained by the continuation 
processing as described above. (step b5). 
At this time, the bi-level digitized data are projected in X direction 
(step b6) and, from the results of the projection, the maximum peak 
Y.sub.p is searched, followed by the search for the peak Y.sub.g located 
at the position adjacent the maximum peak (step b7). 
A Y.sub.g coordinate is then determined from the peak Y.sub.g and, from 
labeling data obtained beforehand, data close to the Y.sub.g coordinate is 
selected. The length of its line segment (the number of pixels) is then 
determined to detect the width of the gap of the bonded area (step b8). 
(b) Execution by the sequential comparison method: 
A description will be made in accordance with the flow chart shown in FIG. 
12. Upon initiation of a measurement, with respect to i (pixel number)=1 
(step S1), its distance Y.sub.1 from the end of the image is inputted 
(step S2). Concerning i=2 (i=i+1) (step S3), Y.sub.2 is then inputted 
(step S4). For the confirmation of continuity, a determination is next 
made as to whether or not the difference between Y.sub.1 and Y.sub.2 is 
not greater than a predetermined value (.vertline.Y.sub.i -Y.sub.i-1 
.vertline..ltoreq.DELTA?; step 5). 
If the difference (Y.sub.i -Y.sub.i-1) is not determined to be greater than 
the predetermined value (the YES route from step S5) as a result, the 
existence of continuity is determined and a determination is then made as 
to whether or not a flag F has been set (F=1 ?; step S6). The flag F has 0 
as its initial value but, when noncontinuity is determined, is changed to 
1. Since no flag F has been set yet at a time point shortly after the 
initiation of the measurement (namely, F=0) (the NO route from step S6), 
pixels are simply counted (step S8) and then, i is incremented by 1 (step 
S9). 
Subsequently, continuity with Y.sub.2 is checked with respect to the next 
value, Y.sub.3. If there is continuity, Y.sub.3 is also registered in the 
same label (group) [the term "label" as used herein means the group of the 
first line segment (f.sub.1 in FIG. 5)]. 
When i becomes, for example, equal to j (i=j), the following inequality is 
established: .vertline.Y.sub.i -Y.sub.i-1 .vertline.=.vertline.Y.sub.j 
-Y.sub.j-1 .vertline.&gt;DELTA, resulting in determination of noncontinuity. 
The routine then advances along the NO route from step S5, and a 
determination is made as to whether or not this value Y.sub.j is a noise 
(subsequent steps S11 to S17). 
Described specifically, a determination is first made as to whether or not 
the flag has been set (F=1?; step S11). Unless F=1 (the NO route from step 
S11), the flag F is set as F=1 (step S12). 
Next, i is incremented by 1 (step S13), Y.sub.i =Y.sub.j+1 is inputted 
(step S4), and continuity is checked based on the difference, Y.sub.j+1 
-Y.sub.j (step S5). If continuity is found to exist here (the YES route 
from step S5), a determination is made as to whether F=1 or not (step S6). 
If F=1, the label is then changed to a new label (the group of the second 
line segment) and 1 is counted as the number of pixel(s) in the new label 
(step S7). Subsequently, pixels are additionally counted (step S8) and, 
after i is incremented by 1 (step S9), F=0 is set (step S10). 
If a lack of continuity is found (the NO route from step S5), a 
determination is again made as to whether F=1 or not (step S11). Since F=1 
this time, the routine advances along the YES route from step S11 to step 
S14, and a determination is then made as to whether or not the difference 
between the current Y.sub.i value (Y.sub.i =Y.sub.j+1) and the second 
preceding value (Y.sub.i-2 =Y.sub.j-1) is not greater than a predetermined 
value (DELTA2) (.vertline.Y.sub.i -Y.sub.i-2 
.vertline.=.vertline.Y.sub.j+1 -Y.sub.j-1 .vertline..ltoreq.DELTA2?; step 
S14). 
If the determination results in YES (the YES route from step S14), Y.sub.j 
is determined to have occurred due to a noise and, assuming that the 
distance Y.sub.i of the second preceding pixel (i=j-1) still remains 
unchanged now (i=j+1), 2 is added as a pixel number to the preceding group 
(label) of the first line segment (step S15). After F=0 is set (step S17), 
i is incremented by 1 (step S13). Namely, if there is continuity with the 
second preceding data, the first preceding data is determined as a noise 
and is registered in the group (label) of the first line segment. 
If the difference is found to be greater than predetermined value as a 
result of the determination in step S14 (the NO route from step S14), in 
other words, there is no continuity, the second preceding data does not 
have continuity either. This determination of noncontinuity is thus not 
interpreted as a determination of noncontinuity caused by a noise, and 
both of the data are registered as a new group (the group of the second 
line segment) different from the above-mentioned group and 2 is then added 
as a pixel number (step S16). After F=0 is set (step S17), i is 
incremented by 1 (step S13). 
By these processing, the numbers of pixels in the first line segment 
(f.sub.1 in FIG. 5), the second segment (f.sub.2 in FIG. 5, which 
corresponds to the gap part), and the third or last line segment (f.sub.3 
in FIG. 5) can be determined. The width of the gap can then be determined 
by subtracting the numbers of the pixels in the first line segment and the 
third or last line segment from the total number of the pixels (a known 
value). As a consequence, the gap widths (SP1 to SP4) can be properly 
determined even if Y.sub.i data are as shown in FIGS. 7B and 7C and FIGS. 
8A and 8B. 
As has been described above, the method and system according to the present 
invention for the determination of the quality of a bonded area in each 
boxmaking blank conduct measurements by using a pattern of light no matter 
whether the measurements are made by the projection method or the 
sequential comparison method. Irrespective of the quantity level of light, 
the quality of the bonded area 1C of each corrugated cardboard blank 1 can 
therefore be determined. Further, owing to the use of strong light 
condensed in the form of a sheet as a light source, the quality of the 
bonded area of each corrugated cardboard blank 1 can also be determined 
easily without being affected by the color of a liner and/or printed parts 
of the corrugated cardboard blank 1. The method and system according to 
the present invention therefore have an advantage in that they can 
significantly improve the performance and reliability of a boxmaking 
production line of corrugated cardboard boxes. 
In the above-described embodiment, the system is constructed for 
arrangement under the production line. It may however be constructed for 
arrangement above a production line. In such a construction, a similar 
advantage can be brought about. It is also possible to arranged two 
systems of the above-described construction, one above and the other under 
a production line. In this case, the quality of the bonded area 1C of each 
corrugated cardboard blank 1 can be determined no matter whether the 
bonded area 1C is on the upper side or on the lower side. 
Further, in the above-described embodiment, each corrugated cardboard blank 
1 is travelling with the width of the gap 1D in the bonded area 1C thereof 
directed at a right angle relative to the lengthwise direction of the 
production line. As an alternative, the corrugated cardboard blank 1 may 
be caused to travel with the width of the gap 1D of the bonded area 1C 
thereof directed in parallel with the lengthwise direction of the 
production line. In this alternative case, it is desired to arrange two 
systems of the above-described construction, one on one side of the 
production line and the other on the opposite side of the production line, 
so that they correspond to the gaps 1D in the top flap 1A and the bottom 
flap 1B, respectively. 
Corrugated cardboard blanks are employed as boxmaking blanks in the 
above-described embodiment. However, the boxmaking blanks are not limited 
to such corrugated cardboard blanks. Further, the projection method or the 
sequential comparison method is used as an extraction method of the bonded 
area 1C. The extraction method is however not limited to such methods. The 
present invention can therefore be practiced by changing or modifying the 
above-described embodiment in various ways to such extent as not departing 
from the spirit of the present invention.