Method for detecting defect in bottle

The present invention relates to a method for detecting a defect in a barrel portion of a bottle. The defect in the barrel portion of the bottle includes a thin blister and a longitudinal streak. The defect in the bottle barrel is detected by imaging the bottle barrel with a CCD camera based on light which has passed through a light shield plate having a plurality of oblique slits and the bottle barrel, and processing the image of the bottle barrel generated by the CCD camera to determine whether or not the defect is present.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a method for detecting a defect in a
 bottle based on an imaging technology, and more particularly to a method
 for detecting a refractive defect in a barrel portion of the bottle.
 2. Description of the Related Art
 Defects in a barrel portion of a glass bottle are classified into shading
 defects which block applied light to prevent the light from passing
 therethrough and refractive defects which refract applied light. The
 applicant of the present application has proposed a method of detecting
 both shading defects and refractive defects as disclosed in Japanese
 patent publication No. 6-90150. According to the disclosed method, a light
 shield plate (referred to as an obliquely slit plate in the specification)
 having a plurality of oblique slits is positioned between a source of
 diffused light and a bottle under test. Diffused light from the source
 passes through the light shield plate and the barrel portion of the
 bottle, producing an image of a striped pattern. The image of the striped
 pattern is scanned to compare the levels of brightness at three closely
 positioned spots in the image for flaw detection.
 If the bottle suffers large wall thickness variations, then the striped
 pattern tends to be so irregular that it is difficult to detect defects in
 the barrel portion of the bottle. The inventors of the present invention
 have made efforts to develop a method of processing images of irregular
 striped patterns particularly for the detection of thin blisters among
 different types of blisters which are one kind of refractive defects. The
 thin blister refers to a blister in the form of a thin lens on a surface
 of the glass bottle or in the glass bottle.
 Further, the inventors of the present invention have made efforts to
 develop a method of processing images of irregular striped patterns
 particularly for the detection of longitudinal streaks. The longitudinal
 streak refers to a linear recess that appears partly in the longitudinal
 direction of the bottle.
 SUMMARY OF THE INVENTION
 It is therefore a first object of the present invention to provide a method
 for detecting a defect, which is referred to as a thin blister, in a
 barrel portion of a bottle.
 It is a second object of the present invention to provide a method for
 detecting a defect, which is referred to as a longitudinal streak, in a
 barrel portion of a bottle.
 In order to accomplish the first object, according to a first aspect of the
 present invention, there is provided a method for detecting defect in
 bottle, comprising: imaging a barrel portion of a bottle with a CCD camera
 based on light which has passed through a light shield plate having a
 plurality of oblique slits and the barrel portion; generating a binary
 image having a striped pattern of bright and dark areas within a window
 having a certain area from an image of the barrel portion generated by the
 CCD camera; scanning the binary image in a longitudinal direction of the
 barrel portion to generate a labeled image in which labels are assigned to
 the bright and dark areas of the striped pattern, respectively; and
 scanning the labeled image in a longitudinal direction of the barrel
 portion to determine a defect in the barrel portion if there is a label
 which is not in contact with any one of sides of the window or if one
 label appears more than a preset number of times along a scanning line.
 With the above method, the barrel portion of the bottle is imaged by the
 CCD camera, and a generated image of a striped pattern is processed into a
 binary image having a striped pattern of bright and dark areas. In the
 binary image, a defect in the form of a thin blister is represented by an
 image of branched stripes or an isolated stripe. Then, a labeled image in
 which labels are assigned to the bright and dark areas of the striped
 pattern is produced from the binary image. Thereafter, the labeled image
 is scanned to determine an image of branched stripes or an isolated stripe
 for thereby detecting a thin blister if there is a label which is not in
 contact with any one of sides of the window or if one label appears more
 than a preset number of times along a scanning line.
 In order to accomplish the second object, according to a second aspect of
 the present invention, there is provided a method for detecting defect in
 bottle, comprising: imaging a barrel portion of a bottle with a CCD camera
 based on light which has passed through a light shield plate having a
 plurality of oblique slits and the barrel portion; generating a binary
 image having a striped pattern of bright and dark areas within a window
 having a certain area from an image of the barrel portion generated by the
 CCD camera; scanning the binary image in a longitudinal direction of the
 barrel portion to determine the number of successive bright or dark pixels
 along a first scanning line; determining the number of area-changing
 points where a bright area changes to a dark area or a dark area changes
 to a bright area between a start point and an end point of pixels which
 are equal to the successive pixels whose number has exceeded the first
 preset number along the first scanning line, along a second scanning line
 which precedes the first scanning line by a second preset number, if the
 determined number of successive bright or dark pixels exceeds a first
 preset number; and determining the presence of a defect if the determined
 number of area-changing points is equal to or greater than a third preset
 number.
 With the above method, the barrel portion of the bottle is imaged by the
 CCD camera, and a generated image of a striped pattern is processed into a
 binary image having a striped pattern of bright and dark areas. In the
 binary image, a defect in the form of a longitudinal streak is represented
 by a longitudinal succession of bright or dark pixels. The number of
 successive bright or dark pixels along a first scanning line (L) is
 determined from the binary image. If the determined number of successive
 bright or dark pixels exceeds a first preset number (K1), then the number
 of area-changing points where a bright area changes to a dark area or a
 dark area changes to a bright area is determined between a start point and
 an end point of pixels which are equal to the successive pixels whose
 number has exceeded the first preset number (K1) along the first scanning
 line (L), along a second scanning line (L') which precedes the first
 scanning line (L) by a second preset number (K2). If the determined number
 of area-changing points is equal to or greater than a third preset number
 (K3), then the distance between adjacent stripes along the second scanning
 line (L') is normal, and a defect in the form of a longitudinal streak is
 present along the first scanning line (L). If the determined number of
 area-changing points is smaller than the third preset number (K3), then
 the distance between adjacent stripes along the first and second scanning
 lines (L and L') is normal, and a defect in the form of a longitudinal
 streak is not present along the first and second scanning lines (L and
 L').
 The above and other objects, features, and advantages of the present
 invention will become apparent from the following description when taken
 in conjunction with the accompanying drawings which illustrate a preferred
 embodiment of the present invention by way of example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 A method for detecting defect in bottle according to a first embodiment of
 the present invention will be described with reference to FIGS. 1 through
 10.
 As shown in FIG. 1, an inspection apparatus for carrying out a method for
 detecting a defect in a barrel portion of a bottle comprises a diffused
 light source 3 for emitting diffused light and applying the diffused light
 to a glass bottle 2 placed on a turntable 1, a light shield plate 10
 disposed between the diffused light source 3 and the glass bottle 2 and
 having a plurality of oblique slits, a CCD (Charge-Coupled Device) camera
 4 positioned on one side of the glass bottle 2 remotely from the diffused
 light source 3 for imaging the glass bottle 2 from one side thereof, i.e.,
 horizontally, and an image processor 5 for processing an image of the
 glass bottle 2 which has been generated by the CCD camera 4. The diffused
 light source 3 comprises a light source 3a and a light diffuser plate 3b.
 An optical axis of the CCD camera 4 is horizontal or substantially
 horizontal.
 FIG. 2 shows the light shield plate 10 which has a plurality of oblique
 slits 10s.
 While the glass bottle 2 is being rotated about its vertical axis by the
 turntable 1, the CCD camera 4 images the glass bottle 2 from one side
 thereof to generate a number of images thereof. When diffused light
 emitted from the diffused light source 3 is applied through the slits 10s
 in the light shield plate 10 to the glass bottle 2, a part of the applied
 light passes through the glass bottle 2 and reaches the CCD camera 4.
 FIG. 3 shows an image of the glass bottle 2 which has been generated by the
 CCD camera 4. As shown in FIG. 3, when the barrel portion of the glass
 bottle 2 is imaged by the CCD camera 4 with light that has passed through
 the light shield plate 10, an image 7 containing a striped pattern is
 generated by the CCD camera 4. Since the glass bottle 2 has wall thickness
 variations or irregularities, the striped pattern is deformed in some
 parts thereof. A window 8 is established centrally in the image 7, and
 image data in the window 8 is processed by the image processor 5.
 Specifically,, the image processing by the image processor 5 is carried
 out as follows:
 The image processing is composed of a number of steps. In step 1, a binary
 image is generated from the striped pattern in the window 8 of the image
 7. FIG. 4A shows an original image, in the window 8 produced by the CCD
 camera 4, and FIG. 4B shows a binary image generated from the original
 image shown in FIG. 4A. As shown in FIG. 4A, the original image in the
 window 8 includes a dark light-shielded area (indicated by "x" in square
 pixels), a bright light-transmitted area (indicated by blank square
 pixels), and boundary areas (indicated by "/" in square pixels) which are
 of an intermediate shade between the dark and bright areas. When the
 brightness data of the pixels are converted into binary data using a
 threshold representing a certain level of brightness, those pixels which
 are brighter than the threshold become bright pixels (represented by 1,
 for example), and those pixels which are darker than the threshold become
 dark pixels (represented by 0, for example). Therefore, the image
 represented by the binary data comprises a matrix of data "1" and "0". A
 change from the bright area to the dark area of the original image is
 equivalent to a change from the data "1" to the data "0" of the binary
 image. In FIG. 4B, the blank square pixel has the bright data "1", and the
 square pixel marked with "x" has the dark data "0".
 In step 2, the binary image in the window 8 generated in step 1 is scanned
 in a vertical direction of the glass bottle 2 to label bright areas and
 dark areas of the striped pattern.
 FIGS. 5A and 5B show images which have been labeled in step 2. In each of
 FIGS. 5A and 5B, the image is scanned downwardly from the origin at an
 upper right corner thereof, and scanned horizontally from the right to the
 left.
 A thin blister, which is a type of defect contained in the glass bottle 2,
 is represented by an image of plural stripes. In the original image
 captured by the CCD camera 4, part of the plural stripes has an
 intermediate shade between dark and bright areas. In the binary image,
 therefore, depending on the brightness in the original image, the thin
 blister is represented by an image of joined and branched stripes as
 indicated by &lt;7&gt; in FIG. 5A or an image of an isolated stripe which
 is not in contact with the window 8 as indicated by &lt;11&gt; in FIG. 5B.
 While the images shown in FIGS. 5A and 5B are given for illustrative
 purpose, the images of thin blisters are characterized in that part of
 stripes is branched or isolated. This is because the thin blister has a
 lens effect by which an incident light is refracted more intensely than
 the normal portion. Therefore, depending on the degree of refraction, the
 thin blister converges light to cause a whole area corresponding to the
 thin blister to become a bright area in the binary image, or the thin
 blister forms image of small slits thereon to cause areas corresponding to
 the image of small slits to become dark areas in the binary image. The
 defect detecting method according to the present invention is based on the
 extraction of such a feature.
 In step 2 the binary image is labeled by scanning the binary image to
 detect continuity of the stripes and assign identification numbers to the
 bright areas and the dark areas. One area is composed of pixels having the
 same identification number. The labeling is carried out by labeling with
 8-neighbours. In FIGS. 5A and 5B, labels are represented by &lt;1&gt;,
 &lt;2&gt;, . . . , &lt;10&gt;(in FIG. 5A) or &lt;12&gt;(in FIG. 5B) for
 dark areas, and (1), (2), . . . , (11) (in FIG. 5A) or (13) (in FIG. 5B)
 for bright areas. When focusing on the dark area, the labeled image is
 composed of dark areas &lt;1&gt;, &lt;2&gt;, . . . , &lt;10&gt; and bright
 areas 0 (bright areas are assumed to be denoted by 0). When focusing on
 the bright area, the labeled image is composed of bright areas (1), (2), .
 . . , (11) (in FIG. 5A) or (13) (in FIG. 5B) and dark areas 0 (dark areas
 are assumed to be denoted by 0). These two kinds of images are generated.
 In step 3, the labeled images produced in step 2 are scanned in the
 longitudinal direction thereof, and a defect is determined to be present
 in the bottle if a label that is not in contact with either one of the
 four sides of the window 8 is present or if one label appears more than a
 preset number of times along a scanning line. Specifically, when the image
 of the dark labels is scanned in FIG. 5B, a label &lt;11&gt; that is not
 in contact with either one of the four sides of the window 8 is present on
 or near a scanning line L, and hence the presence of a defect is
 determined. Since the label &lt;11&gt; is not present in either one of the
 four sides of the window 8 when the image is scanned, it is determined
 that the label &lt;11&gt; is not in contact with either one of the four
 sides of the window 8.
 When the image of the bright labels is scanned in FIG. 5B, the label (9)
 appears twice on or near the scanning line L. When the image of the dark
 labels is scanned in FIG. 5A, the label &lt;7&gt; appears three times on
 or near the scanning line L. When the image of the bright labels is
 scanned in FIG. 5A, the label (6) appears twice on or near the scanning
 line L, and the label (7) also appears twice on or near the scanning line
 L. Depending on wall thickness variations of the bottle, a substantially
 S-shaped stripe may appear as shown in FIG. 6 though it does not represent
 a defect. When the image shown in FIG. 6 is scanned, one label appears
 twice along each of scanning lines L.sub.1 and L.sub.2. If the preset
 number of times for determining the appearance of one label is "2", then
 since the label &lt;7&gt; appears three times in FIG. 5A, it can be
 distinguished from the substantially S-shaped stripe (which is not a
 defect) shown in FIG. 6, and can be determined as a defect.
 Images in which bright areas and dark areas of striped patterns are
 labeled, respectively are generated because one label appears different
 numbers of times for bright areas and dark areas, and the appearance of
 one label by a greater number of times is to be recognized. In FIG. 5A,
 the label (6) or (7) appears twice, and the label &lt;7&gt; appears three
 times. However, the label (6) or (7) may appear three times, and the label
 &lt;7&gt; may appear twice. While the preset number of times for
 determining the appearance of one label is "2" in the illustrated
 embodiment, it is not limited "2" because images change from bottle to
 bottle. The preset number of times for determining the appearance of one
 label is determined based on the results of many sample tests.
 There is one phenomenon which should be taken into account in carrying out
 the method according to the present invention. A glass bottle has a
 vertical ridge referred to "seam line". Some bottles have gentle ridges,
 and some bottles have sharp ridges. FIGS. 7, 8A, and 8B fragmentarily show
 binary images of the barrel portion of the bottle including the seam line
 in the window 8. If the vertical ridge of the seam line of the bottle
 barrel is gently protrusive, then stripes are continuous as shown in FIG.
 7, and the method of the present invention is directly applicable to the
 bottle barrel. If the vertical ridge of the seam line of the bottle barrel
 is sharply protrusive, then bright areas and dark areas are interrupted as
 indicated by images shown in FIGS. 8A and 8B. Whether the image shown in
 FIG. 8A or the image shown in FIG. 8B is generated depends on the
 threshold used to convert the brightness data of the original image into
 binary data. In FIGS. 8A and 8B, since one label appears more than the
 preset number of times, the seam line is determined as a defect. To avoid
 the determination of the seam line as a defect, it is necessary to mask
 the image of the seam line, i.e., to keep the seam line out of the defect
 detecting process.
 FIG. 9 shows a binary image including a portion of the seam line. In FIG.
 9, dark areas are shown hatched only in edge portions, but not in a
 central portion, of the window 8 for the convenience of illustration, and
 A and B represent an area corresponding to the seam line in the window 8.
 FIG. 10 shows the area A and B as being positioned adjacent to each other.
 A process of masking the area A and B corresponding to the seam line will
 be described below with reference to FIGS. 9 and 10. In step S1, the
 binary image is scanned in the longitudinal direction of the bottle to
 determine the number of successive pixels in bright or dark areas along a
 scanning line L. Then, in step S2, if the number of successive pixels
 determined in step S1 exceeds a preset number K1, then along a scanning
 line L' that precedes the scanning line L by a preset number K2, the
 number of area-changing points where a bright area changes to a dark area
 or a dark area changes to a bright area is determined between a start
 point Ps and an end point Pe of pixels which are equal to the successive
 pixels whose number has exceeded the preset number K1 along the scanning
 line L. In step S3, if the number of area-changing points is equal to or
 greater than a preset number K3, then the number of the scanning line L is
 stored. In step S4, an image extending from a scanning line Ls that
 precedes, by a preset number K4, a scanning line Lm whose number was the
 first number stored in step S3 to a scanning line Le that precedes, by a
 preset number K5, a scanning line Lm whose number was the last number
 stored in step S3, is masked.
 If there is a scanning line L along which there are successive pixels in
 excess of the ordinary gap between adjacent stripes in step S1, then a
 seam line is present along the scanning line L. However, as indicated by
 an area C in FIG. 9, there is an instance where bright pixels are
 successively present as with the area A though no seam line is actually
 present in the area C. Therefore, in step S2, the number of area-changing
 points where a bright area changes to a dark area or a dark area changes
 to a bright area is determined along the scanning line L' that precedes
 the scanning line L by a certain number. In step S3, the areas A, C are
 distinguished from each other by determining whether or not the number of
 area-changing points is equal to or greater than the preset number K3. In
 FIG. 9, the number of area-changing points in the area A is 5, and the
 number of area-changing points in the area C is 2. If the preset number K3
 is 3, then the area A corresponding to the seam line and the area C are
 distinguished from each other.
 As shown in FIGS. 9 and 10, if there is an area corresponding to the seam
 line in the image, then bright or dark areas in a binary image containing
 the seam line are horizontally interrupted by the area corresponding to
 the seam line. The bright or dark areas may be interrupted over different
 distances. In FIG. 10, the bright or dark areas are interrupted over
 different distances by the areas A, B, with the interrupted distance in
 the area B being greater than the interrupted distance in the area A.
 Therefore, in step S4, as shown in FIG. 10, the image extending from the
 scanning line Ls that precedes, by the preset number K4, the scanning line
 Lm whose number was the first number for the determined seam line to the
 scanning line Le that precedes, by the preset number K5, the scanning line
 Lm whose number was the last number for the determined seam line, is
 masked. In this manner, the image of the interrupted areas is masked to
 keep the seam line out of the defect detecting process.
 Since binary images generated from bottles vary from bottle to bottle, the
 preset numbers K1 through K5 are determined as the results of many sample
 tests, and may be changed if necessary.
 The method for detecting defect in bottle according to the first embodiment
 of the present invention is capable of reliably detecting thin blisters in
 the bottle barrel as it extracts features of stripe irregularities in
 binary images of the bottle which are caused by the thin blisters.
 Next, a method for detecting defect in bottle according to a second
 embodiment of the present invention will be described with reference to
 FIG. 11. The second embodiment of the present invention is directed to a
 method for detecting a longitudinal streak in a barrel portion of a
 bottle. The inventors of the present application made the second invention
 directed to a method for detecting the longitudinal streak by utilizing a
 preprocessing function of the first invention described above.
 FIG. 11 shows a binary image generated by the above binarizing process
 shown in FIGS. 1 through 4B. That is, the binary image shown in FIG. 11 is
 generated from the striped pattern in the window 8 of the image 7 through
 the step 1. In FIG. 11, the image is scanned downwardly from the origin at
 an upper right corner thereof, and scanned horizontally from the right to
 the left. In FIG. 11, dark areas are shown hatched only in edge portions,
 but not in a central portion, of the window 8 for the convenience of
 illustration.
 In step 2, the binary image generated in step 1 is scanned in the
 longitudinal direction of the bottle to determine the number of successive
 pixels in bright or dark areas along a scanning line L. In the original
 image captured by the CCD camera, a longitudinal streak is represented by
 a succession of pixels which are of an intermediate shade between the dark
 and bright areas and extend beyond the ordinary distance between adjacent
 stripes. In the binary image, as shown in FIG. 11, depending on the
 brightness in the original image, the longitudinal streak is represented
 by a longitudinal succession of bright or dark pixels as indicated in an
 area A or B. This is because the longitudinal streak is not a simple
 recess but a recess around which ridges are formed, and the surface of the
 streak has an arcute angle, differently from the thin blister. Therefore,
 the streak forms image of a portion around the streak thereon to cause an
 area corresponding to the streak to become an intermediate shade between
 dark and bright areas which is converted into either a bright area or a
 dark area in the binary image.
 If there is a scanning line along which there is a succession of pixels
 which extend beyond the ordinary distance between adjacent stripes, then
 there is a longitudinal streak along the scanning line. The number of
 successive bright or dark pixels is determined along the scanning line L.
 However, as indicated by an area C in FIG. 11, there is an instance where
 bright pixels are successively present as with the area A though no
 longitudinal streak is actually present in the area C.
 In step 3, if the number of successive pixels determined in step 2 exceeds
 a preset number K1, then along a scanning line L' that precedes the
 scanning line L by a preset number K2, the number of area-changing points
 where a bright area changes to a dark area or a dark area changes to a
 bright area is determined between a start point Ps and an end point Pe of
 pixels which are equal to the successive pixels whose number has exceeded
 the preset number K1 along the scanning line L. In FIG. 11, the number of
 area-changing points in the area A is 5, and the number of area-changing
 points in the area C is 2.
 Then, in step 4, if the number of area-changing points determined in step 3
 is equal to or greater than the preset number K3, then a defect is
 determined. In an example of FIG. 11, if the preset number K3 is 3, then
 the area A (defective area) and the area C (no defective area) are
 distinguished from each other.
 Since binary images generated from bottles vary from bottle to bottle, the
 preset numbers K1 through K3 are determined as the results of many sample
 tests, and may be changed if necessary.
 The method for detecting defect in bottle according to the second
 embodiment of the present invention is capable of reliably detecting
 longitudinal streaks in the bottle barrel as it extracts features of
 longitudinal streaks in binary images of the bottle as distinguished from
 stripe irregularities.
 Although a certain preferred embodiment of the present invention has been
 shown and described in detail, it should be understood that various
 changes and modifications may be made therein without departing from the
 scope of the appended claims.