JP4623267B2 - Can body inspection apparatus and can body inspection method - Google Patents

Description

  The present invention relates to a can body inspection apparatus and a can body inspection method for inspecting a can body in which irregularities are regularly formed.

When the manufactured can is loaded, transported, unpacked, transported in the factory, etc., there is a possibility that defects such as dents may occur in the can. For this reason, conventionally, an apparatus for inspecting the presence or absence of defects such as dents in such a can has been proposed (see, for example, Patent Document 1). This conventional inspection apparatus derives the density change, shape, etc. of an image (image data) obtained by photographing the inner surface of the can with a camera, and applies the image based on the density change, image shape, etc. of the image. It is determined whether there is a portion corresponding to a dent or the like.
JP-A-5-18909

  By the way, in recent years, irregularities 510 (so-called diamond cuts) have been regularly formed on the body as shown in FIG. 1 in order to maintain the strength while reducing the weight and to improve the degree of attention and aesthetics. A can 500 has been proposed.

  However, the above-described conventional inspection apparatus is intended for inspection of a can body having a body portion with a uniform curved surface. As shown in FIG. 1, the unevenness 510 formed on the body portion of the can body 500. When there is a defect such as a dent, it is difficult to detect the dent or the like that is a defect separately from the regular unevenness 510.

  The present invention has been made to solve the conventional problems, and a can inspection apparatus and can capable of accurately detecting defects such as dents in the body of a can body in which irregularities are regularly formed. The purpose is to provide a physical examination method.

The can body inspection apparatus according to the present invention is a can body inspection apparatus for inspecting a can body formed such that irregularities having the same shape regularly repeated on the body portion appear on the outer surface and the inner surface of the body. A light irradiating means for irradiating light on the inner surface of the light source, a photographing means for photographing the inner surface of the can body through the mouth and generating image data, and a portion in which the irregularities of the can body are formed based on the image data For each of a plurality of small areas obtained by equally dividing an image portion corresponding to the irregularities so as to include an image corresponding to the same irregular shape of the can body based on the regularity of the irregularities, an image of the entire small area Density deriving means for deriving density, and determination means for determining whether or not there is a defect in the uneven portion of the can body based on the image density of each small region derived by the density deriving means. Yes, and the determination means, the A density difference calculating means for calculating a difference in image density between two small areas having the same optical condition determined based on the irradiation means and the photographing means, and a difference in the image density obtained for each set of the two small areas. A portion having a maximum density difference determination means for determining whether or not the maximum value is less than or equal to a predetermined value, and the unevenness of the can body formed on the basis of the determination result of the maximum density difference determination means a configuration to determine whether there is a defect in.

With such a configuration, when a defect such as a dent is generated in a portion formed so that irregularities that are regularly repeated in the body shape of the can body appear on the outer surface and the inner surface thereof , the can body is formed on the can body. Among the small regions obtained by equally dividing the image portion corresponding to the can body portion on which the unevenness is formed based on the regularity of the unevenness into a plurality of equal parts so as to include an image corresponding to the same uneven shape of the can body The defect can be detected by utilizing the fact that the image density of the small area corresponding to the portion where the defect of the can body is normal is different from the case where there is no defect (when there is no defect) .

  Furthermore, in the can inspection apparatus according to the present invention, the determination means calculates a difference in image density between two small regions having the same optical condition determined based on the light irradiation means and the imaging means. Means for determining whether or not there is a defect in the uneven portion of the can body based on the difference in the image density obtained for each set of the two small regions. .

  As described above, the images correspond to the same uneven shape, and furthermore, the image density of the two small regions having the same optical condition is essentially the same if the can body is normal (if there is no defect). From this, it is determined whether or not there is a defect in the portion where the unevenness of the can body is formed based on the difference in image density obtained for each set of the two small regions.

  Thus, based on the difference in image density obtained for each set of two small regions for a single can body to be inspected, it is determined whether or not there is a defect in the uneven portion of the can body. Therefore, it is not necessary to compare the image density of each small region obtained for the can body to be inspected with the image density of the corresponding small region obtained for the can body determined as a non-defective product. That is, it is not necessary to prepare in advance the image density of each small region obtained for a can determined as a good product.

  Further, the can inspection apparatus according to the present invention can be configured such that the density difference calculation means calculates a difference in image density between two non-adjacent small regions.

  With such a configuration, it is unlikely that a defect such as a dent will occur in both of the can parts corresponding to two non-adjacent small areas. Therefore, the defect is more accurately determined based on the difference in image density between the two small areas. It is possible to detect the presence or absence of.

  In the can inspection apparatus according to the present invention, the determination means determines whether or not a maximum value of the difference in image density obtained for each set of the two small regions is equal to or less than a predetermined value. It can be set as the structure which has a means.

  With such a configuration, when the maximum value of the difference in image density obtained for each set of two small areas exceeds a predetermined value, there is a defect such as a dent in the portion where the unevenness of the can body is formed. Determined.

Further, the can body inspection apparatus according to the present invention, the irregularities, there is formed to regularly repeat in the circumferential direction of the depth direction and the can body of the can body, the concentration deriving means The optical conditions determined based on the plurality of light irradiation means and photographing means obtained by dividing the image portion corresponding to the uneven portion of the can body in a direction corresponding to the depth direction are the same. each inspection area by deriving a plurality of small areas each of image density obtained by equally dividing, based on the regularity in the direction corresponding to the circumferential direction in which the density difference calculation means, for each of the inspection area The difference between the image densities of the two small areas can be calculated.

  With such a configuration, in each of the plurality of inspection regions obtained by dividing the image portion corresponding to the portion where the unevenness of the can body is formed in a direction corresponding to the depth direction of the can body, The presence or absence of a defect is determined based on the difference in image density.

  Further, the can inspection apparatus according to the present invention detects that the cans sequentially transported on the transport path are at a predetermined inspection position included in the light irradiation area by the light irradiation means and the imaging area by the imaging means. When the inspection position detecting means and the inspection position detecting means detect that the can body is at the inspection position, the photographing means can photograph the inner surface of the can body.

  With such a configuration, it is possible to inspect whether or not there is a defect such as a dent in a portion where the unevenness of the can body is formed in the process of transporting the can body on the transport path.

  Moreover, the can inspection apparatus according to the present invention discharges the can from the transport path when the determination means determines that there is a defect in a portion where the unevenness of the can is formed. It can be set as the structure which has a discharge means.

  With such a configuration, it is possible to transport only a can body that is free of defects such as dents in the uneven portion to a subsequent processing step (for example, a content filling step).

The can body inspection method according to the present invention is a can body inspection method for inspecting a can body formed such that irregularities in which the same shape is regularly repeated on the body portion appear on the outer surface and the inner surface of the body. The inner surface of the can body is photographed through the mouth in a state where light is irradiated on the inner surface of the, and a photographing step for generating image data, corresponding to the portion where the irregularities of the can body are formed based on the image data For each of a plurality of small regions obtained by equally dividing the image portion so as to include images corresponding to the same uneven shape of the can body based on the regularity of the unevenness , the image density as a whole of the small regions is determined. a density deriving step of deriving, possess a determination step of determining whether or not there is a defect in the unevenness formed portion of the can body on the basis of the image density of each small region that is derived by the deriving step, The judgment step Is obtained for each set of the two small areas, and a density difference calculating step for calculating a difference in image density between two small areas having the same optical condition determined based on the light irradiation condition and the photographing condition. A maximum density difference determination step for determining whether or not a maximum value of the difference in image density is equal to or less than a predetermined value, and the unevenness of the can body is formed based on a determination result in the maximum density difference determination step. a configuration to determine whether there is a defect in the portion.

  Further, in the can inspection method according to the present invention, the determination step calculates a difference in image density between two small regions having the same optical condition determined based on the light irradiation condition and the imaging condition. A calculation step, and determining whether or not there is a defect in the uneven portion of the can body based on the difference in image density obtained for each set of the two small regions. it can.

  The can inspection method according to the present invention may be configured such that the density difference calculating step calculates a difference in image density between two non-adjacent small regions.

  Further, in the can inspection method according to the present invention, the determination step determines whether or not the maximum value of the difference in image density obtained for each set of the two small regions is equal to or less than a predetermined value. It can be set as the structure which has a difference determination step.

  According to the present invention, when a defect such as a dent occurs in a portion where irregularities are regularly formed in the body of the can body, the image density of the small region corresponding to the portion where the defect of the can body is normal is normal. It is possible to accurately detect the defect by utilizing the difference from the above case (when there is no defect).

  Hereinafter, a can body inspection apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 2 is a block diagram of the can inspection apparatus according to the embodiment of the present invention, FIG. 3 (a) is a front view, and FIG. 3 (b) is a side view. As shown in FIG. 1, each of the can bodies 500-1 to 500-4 (hereinafter referred to as inspection objects) in which irregularities such as so-called diamond cuts are regularly formed on the side surface, as shown in FIG. These can bodies 500-1 to 500-4 are collectively referred to as “can body 500” as appropriate), and the shape of the portion where the irregularities 510 are formed is inspected. Specifically, the unevenness 510 formed on the can body 500 is such that ridge lines and valley lines are regularly repeated in a triangular shape in the depth direction and the circumferential direction of the can body 500 (FIG. 1). reference).

  This can inspection apparatus includes a light irradiation apparatus 100 that irradiates light on the inner surface of the can 500, a camera 200 that performs image generation to generate image data, a controller 300 that controls the entire can inspection apparatus, The conveyance device 400 that conveys the can body 500, the can body detection unit 410 that detects that the can body 500 has reached the inspection position, and the defective can body 500 having a defect in shape are discharged from the conveyance device 400. And a discharge device 420 for performing the above operation. The controller 300 includes a frame memory 301, a monitor 302, a CPU 303, and a memory 304.

  The conveyance device 400 (including the conveyance path) is configured such that the can body 500 to be inspected is set to a predetermined inspection position so that the inspection object can body 500 is arranged in the light irradiation region by the light irradiation device 100 and the photographing region by the camera 200. Transport. The light irradiation apparatus 100 has an annular light irradiation surface such as an optical fiber or a xenon tube, and uniformly irradiates light to the inner surface of the can 500 at the inspection position. As shown in FIG. 3, the light irradiation apparatus 100 can be adjusted in position and light irradiation angle by an adjustment mechanism 102. Note that the casing of the can inspection device does not allow light (external light) other than light from the light irradiation device 100 to enter the inner surface of the can 500 from the viewpoint of performing inspection under uniform optical conditions. Thus, it is desirable to have a configuration that blocks external light.

  The camera 200 photographs the inner side surface of the can body 500 through the inner hole of the light irradiation apparatus 100 having an annular light irradiation surface and the mouth portion of the can body 500, and generates image data. As shown in FIG. 3, the camera 200 can be adjusted in position and shooting angle by an adjustment mechanism 102. As the camera 200, for example, a CCD camera having a predetermined effective number of pixels can be used. Image data generated by the camera 200 is sent to the CPU 303 in the controller 300.

  When the can body 500 transported by the transport device 400 reaches the inspection position, the can body detection unit 410 detects the can body 500 and outputs a can detection timing signal as a detection result to the CPU 303 in the controller 300. The can detection unit 410 includes a laser beam irradiation unit and a laser beam receiving unit that are opposed to each other with the conveying device 400 interposed therebetween. When the can 500 reaches between the laser beam irradiation unit and the laser beam receiving unit, the laser beam is blocked by the can 500, and the laser beam receiving unit cannot detect the laser beam from the laser beam irradiation unit. In this case, the can detection unit 410 outputs a can detection timing signal to the CPU 303 in the controller 300.

  A frame memory 301 in the controller 300 stores image data from the camera 200. The monitor 302 performs image display based on image data read from the frame memory 301 under the control of the CPU 303.

  When the can detection timing signal is input from the can detection unit 410, the CPU 303 calculates the density of each pixel based on the image data from the camera 200 representing the photographed image of the inner surface of the can 500 to be inspected. Image data (inspection image data) represented by multiple gradations (for example, 256 gradations where black is 0 and white is 255) is generated. The CPU 303 performs an inspection process based on the inspection image data to determine whether or not there is a defect such as a dent in a portion where the unevenness 510 of the can body 500 is formed.

  The inspection process is performed according to the procedure shown in FIG.

  In FIG. 4, the CPU 303 determines whether or not a can detection timing signal is input from the can body detection unit 410 in a state where light is irradiated from the light irradiation device 100 to a predetermined region including the inspection position. (S101). When the can body 500 transported by the transport device 400 reaches the detection position and the can detection timing signal from the can body detection unit 410 is input to the CPU 303 (YES in S101), the CPU 303 captures the image from the camera 200. Image data corresponding to the video is acquired, and the image data is taken into the frame memory 301 (S102). Then, based on the image data captured in the frame memory 301, the CPU 303 represents image data (inspection image data) representing the gradation of each pixel in multiple gradations (for example, 256 gradations where black is 0 and white is 255). Is generated (S103).

  This inspection image data represents, for example, an image I of the inner surface of the can body 500 viewed from the mouth of the can body 500 as shown in FIG. In this image I, the direction from the circular portion corresponding to the outer peripheral edge of the mouth of the can body 500 toward the center thereof corresponds to the depth direction of the can body 500, and the circumferential direction of the circular portion is the circumferential direction of the can body 500. It corresponds to. Further, the image I includes an image portion Ia corresponding to a portion where the unevenness (diamond cut) of the can 500 is formed as shown in FIG.

  As shown in FIGS. 7A and 7B, the CPU 303 that has generated the inspection image data as described above displays an image portion Ia corresponding to the portion where the unevenness of the can 500 is formed with respect to the image I. Three inspection regions (annular regions) 600, 610, 620 obtained by dividing in a direction corresponding to the depth direction of the can body 500 (a direction from the outer peripheral edge of the circular portion toward the center) are set, and each inspection is further performed. The regions 600, 610, and 620 are obtained by equally dividing the regions 600, 610, and 620 in accordance with the regularity of the unevenness (see FIG. 1) formed in the can body 500 in a direction corresponding to the circumferential direction of the can body 500 (circular circumferential direction). A plurality of small areas are set (S104). Accordingly, the inspection area 600 divided into a plurality of small areas 600 (1),..., 600 (4),..., A plurality of small areas 610 (1),. The inspection area 620 divided into the inspection area 610 and the small areas 620 (1), ..., 620 (4), ... are set on the image I. Each small region in each inspection region is, for example, a region corresponding to a repeating unit of unevenness of the can body 500.

  7A and 7B, the same inspection region and small region are set for the image I of the can 500 that has reached the inspection position in different directions. Each small region in each inspection region includes an image corresponding to the same uneven shape of the can 500 (for example, a repeating unit of unevenness).

  When three inspection areas 600, 610, and 620 divided into a plurality of small areas are set on the image I represented by the inspection image data in this way, the CPU 303 performs processing according to the procedure shown in FIG. Continue.

  In FIG. 5, the CPU 303 selects one inspection area, for example, the inspection area 600 from the three inspection areas (S105), and calculates the image density Di of each small area in the selected inspection area 600 (S106). ). For example, the sum of the gray values (represented by, for example, 256 gradations) of each pixel included in the small area is calculated as the image density Di. Each small region included in the same inspection region is an optical condition determined by the light irradiation device 100 and the camera 200 installed at the same position in the depth direction of the can 500, that is, on the axis of the can 500. Corresponds to the same part. In addition, as described above, each small region includes an image corresponding to the same uneven shape (for example, the repeating unit of the unevenness) of the can 500, so that the image density Di of each small region in the same inspection region is If the can 500 has no defects such as dents, it is essentially the same.

  When the image density Di of all the small areas in the selected inspection area 600 is calculated, the CPU 303 determines the difference ΔDj between the image densities Di of the two small areas (small area pairs) selected not to be adjacent to each other according to a predetermined rule. Is calculated (S107). For example, the image density difference ΔD1 between two small areas 600 (1) and 600 (4) arranged every two in the inspection area 600 is calculated. The CPU 303 determines whether or not the image density difference ΔDj exceeds the maximum density difference ΔDmax (initial value is, for example, zero) (S108), and if the image density difference ΔDj exceeds the maximum density difference ΔDmax (S108). (YES in S108), the maximum density difference Dmax is updated to the value of the image density difference ΔDj (S109). Then, the CPU 303 determines whether or not the processing for all the small region pairs in the inspection region 600 has been completed (S110).

  If the processing for all the small region pairs has not been completed (NO in S110), the CPU 303 selects the next small region pair according to the rule (for example, the rule that every other small region is arranged), and sets the small region pairs. An image density difference ΔDj for the region pair is calculated (S107). When the image density difference ΔDj exceeds the maximum density difference ΔDmax (YES in S108), the CPU 303 changes the maximum density difference ΔDmax to the value of the image density difference ΔDj (S109). Thereafter, the same processing (S107, S108, S109, S110) is executed for all small region pairs selected from the inspection region 600.

  When the processing for all the small areas selected from the inspection area 600 is completed, the CPU 303 determines whether or not the maximum density difference ΔDmax obtained at that time is equal to or less than the reference value ΔDo (S111). When it is determined that the maximum density difference ΔDmax is equal to or less than the reference value ΔDo (YES in S111), the CPU 303 initializes the maximum density difference ΔDmax (S112), and the processing for all inspection areas is completed. It is determined whether or not (S113).

  As described above, the image density Di of each small area in the same inspection area is essentially the same unless the can 500 has a defect such as a dent. Therefore, the can 500 corresponding to the inspection area 600 can be used. If there is no defect such as a dent, the maximum density difference ΔDmax is equal to or less than the reference value ΔDo.

  If the processing has not been completed for all the inspection areas (NO in S113), the CPU 303 selects the next inspection area, for example, the inspection area 610 (S105), and the above-described inspection area 610 has been described above. Similar processing (S106 to S112) is executed. The CPU 303 then performs the above-described processing until the processing for all the inspection areas is completed (YES in S113) unless the determination that the maximum density difference ΔDmax exceeds the reference value ΔDo (NO in S111) is made. Repeatedly. In the process, when it is determined that the maximum density difference ΔDmax exceeds the reference value ΔDo (NO in S111), the CPU 303 outputs a defect detection signal (S114). For example, as shown in FIG. 8, when there is a dent 650 in the portion of the can 500 corresponding to the small region 610 (1), that portion of the can 500 and the small region that is paired with the small region 610 (1) The light reflection conditions at the portion of the can 500 corresponding to 610 (4) are different. Therefore, the difference (image density difference) ΔD1 between the image density D1 of the small area 610 (1) and the image density D4 of the small area 610 (4) is larger than the image density difference for the other small area pairs. In this case, in the process of the inspection area 610, the image density difference ΔD1 is set as the maximum density difference ΔDmax (S108, S109), and it is determined that the maximum density difference ΔDmax exceeds the reference value ΔDo. (NO in S111). Then, a defect detection signal is output from the CPU 303.

  Upon receiving the defect detection signal from the CPU 303, the discharge device 420 installed downstream from the inspection position of the can body 500 has been transported from the inspection position to the position facing the discharge device 420 by the transport device 400. Compressed air is ejected at the same timing, and the can 500 is discharged from the transfer device 400 to a predetermined defective product storage box.

  As described above, the can body inspection apparatus according to the present embodiment is a portion in which the unevenness of the can body 500 is formed in the image I obtained by photographing the inner surface of the can body 500 to be inspected with light irradiated. A plurality of inspection areas equally divided into a plurality of small areas based on the regularity of the unevenness are set for the image portion Ia corresponding to the image portion Ia, and the image density difference between the non-adjacent small areas in each inspection area and the reference value Based on the comparison result, it is determined whether or not a defect such as a dent has occurred in the uneven portion of the can 500. The concave / convex shape of the can body 500 corresponding to each small region (for example, the repeating unit of the concave / convex) is the same, and when there are no defects such as dents in the concave / convex formation portion, the image density of each small region is It is essentially the same. By utilizing this fact, that is, when a shape defect such as a dent is formed in the uneven portion, the fact that the image density of each small region is different from the normal case is utilized. Defects can be accurately detected.

  In particular, since the image densities of two non-adjacent small regions are compared, even if a dent or the like extends over a portion corresponding to two adjacent small regions (such as a relatively large dent), the dent or the like is accurately detected. Can be detected.

  In the can inspection apparatus according to the above-described embodiment, each small region is made to correspond to the repeating unit of the concave and convex portions of the can 500, but is not limited to this, and the can 500 corresponding to each small region. If the uneven | corrugated shape of a part is the same, it can set arbitrarily.

  In addition, in the direction corresponding to the depth direction of the can body 500, a plurality of inspection regions 600, 610, and 620 corresponding to the portions where the unevenness is formed are set, but the image portion where the unevenness of the can body 500 is formed All of Ia may be a single inspection region. However, it is preferable to set a plurality of inspection areas from the viewpoint of resolution related to defect detection.

  Furthermore, the width | variety in the direction corresponding to the depth direction of the can 500 of the said some test | inspection area | region 600,610,620 may be the same, or may differ.

  In addition, the image density of each small area is the sum of the gray values of the pixels included in each small area, but the average value of the gray values of each pixel represents the overall density of the small area. If it exists, it may be obtained by another calculation method. However, in the case where a defect occurs, the image density difference of each pair of small areas can be made to appear larger, that is, from the viewpoint of resolution related to defect detection, the image density of each small area is It is preferable to set the sum of the gray values.

  In the above-described embodiment, the presence or absence of dents or the like is determined based on the image density difference between the two small regions (small region pairs) set in the image obtained from the can 500 to be inspected. Image data (reference image data) obtained by photographing the inner surface of a good can body 500 under the same conditions as the photographing conditions of the target can body 500 is stored in advance in the memory 304 of the controller 300 for inspection. It is also possible to determine the defect by comparing the above-described image of the target can 500 with the reference image represented by the reference image data. Specifically, the image density of each small region (see FIG. 7) set in the image portion corresponding to the uneven portion in the reference image and the uneven portion in the image I obtained from the can body to be inspected. Whether or not there is a defect can be determined based on whether or not the difference between the image density and the corresponding small area (see FIG. 7) set in the corresponding image portion Ia is equal to or less than a predetermined value. In this case, if each small region is set in the same way for the reference image and the image obtained from the can 500 to be inspected, the regularity of the irregularities formed on the can 500 is determined. It can be set arbitrarily regardless of. However, in order to accurately detect defects, the optical conditions for obtaining an image of the can 500 to be inspected are always the same as the optical conditions for obtaining a reference image (corresponding to a non-defective can). Need to be maintained.

  As described above, the can inspection apparatus and the can inspection method according to the present invention have the effect that it is possible to accurately inspect defects in the shape that occurs in the can body having irregularities formed on the side surfaces, It is useful as a can body inspection device and a can body inspection method.

It is a side view of the can in which the unevenness | corrugation was formed. It is a block diagram of a can body inspection apparatus. It is the front view and side view of a can inspection apparatus. It is a flowchart which shows the process sequence (the 1) of CPU in the controller of a can body test | inspection apparatus. It is a flowchart which shows the processing procedure (the 2) of CPU in the controller of a can body test | inspection apparatus. It is a figure which shows an example of the picked-up image of the inner surface of a can. It is a figure which shows the test | inspection area | region and small area | region set to the image part corresponding to the part in which the unevenness | corrugation of the can was formed. It is a figure which shows the state of the image of each small area | region when there exists a dent in the part in which the unevenness | corrugation of the can was formed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Light irradiation apparatus 200 Camera 300 Controller 301 Frame memory 302 Monitor 303 Memory 304 CPU
400 Conveying device 410 Can body detection unit 420 Discharge device 500-1 to 500-4 Can body 600, 610, 620 Inspection area 600 (1), 600 (4), 610 (1), 610 (4), 620 (1 ), 620 (4) Small area 650 Dented

Claims (7)

A can body inspection device that inspects a can body that is formed such that irregularities that are regularly repeated on the body portion appear on the outer surface and the inner surface thereof ,
A light irradiating means for irradiating the inner surface of the can with light;
Photographing means for photographing the inner surface of the can through the mouth and generating image data;
Based on the image data, the image portion corresponding to the portion where the unevenness of the can body is formed is equally divided so as to include an image corresponding to the same uneven shape of the can body based on the regularity of the unevenness. For each of the plurality of small areas obtained, density derivation means for deriving the image density as a whole of the small areas,
On the basis of the image density of each small area is derived by the concentration deriving means have a determination means for determining whether there is a defect in the unevenness formed portion of the can body,
The determination unit is a density difference calculation unit that calculates a difference in image density between two small regions having the same optical condition determined based on the light irradiation unit and the photographing unit;
Having maximum density difference determination means for determining whether or not the maximum value of the difference in image density obtained for each set of the two small areas is equal to or less than a predetermined value;
A can inspection apparatus characterized by determining whether or not there is a defect in a portion of the can where the irregularities are formed based on a determination result by the maximum density difference determination means . The density difference calculation means can body inspection apparatus according to claim 1, wherein the calculating the difference in image density of the two small regions that are not adjacent. The irregularities are formed so as to repeat regularly in the depth direction of the can body and the circumferential direction of the can body,
The density derivation means is an optical determined based on a plurality of the light irradiation means and the photographing means obtained by dividing an image portion corresponding to the uneven portion of the can body in a direction corresponding to the depth direction. Deriving the image density of each of a plurality of small areas obtained by equally dividing each of the inspection areas having the same general condition in the direction corresponding to the circumferential direction based on the regularity thereof,
3. The can inspection apparatus according to claim 1, wherein the density difference calculation unit calculates a difference between image densities of two small areas for each of the inspection areas. An inspection position detection means for detecting that the cans sequentially conveyed on the conveyance path are at a predetermined inspection position included in the light irradiation area by the light irradiation means and the imaging area by the imaging means;
When the can body at the test position detection means that is in the inspection position is detected, in any one of claims 1 to 3 wherein the imaging means is characterized by capturing the inner surface of the can body The can inspection apparatus as described. 5. The apparatus according to claim 4 , further comprising: a discharge unit that discharges the can body from the transport path when it is determined by the determination unit that there is a defect in the uneven portion of the can body. The can inspection apparatus as described. A can body inspection method for inspecting a can body formed such that irregularities that are regularly repeated on the body portion appear on the outer surface and the inner surface thereof ,
Photographing the inner surface of the can body through the mouth in a state where light is irradiated on the inner surface of the can body, and generating an image data,
Based on the image data, the image portion corresponding to the portion where the unevenness of the can body is formed is equally divided so as to include an image corresponding to the same uneven shape of the can body based on the regularity of the unevenness. A density deriving step for deriving an image density as a whole of each of the obtained small areas;
Have a a determination step of determining whether or not on the basis of the image density of each small area is defective unevenness formed portion of the can body to be derived by the deriving step,
The determination step includes a density difference calculation step for calculating a difference in image density between two small regions having the same optical condition determined based on the light irradiation condition and the imaging condition;
A maximum density difference determining step for determining whether or not a maximum value of the difference in image density obtained for each set of the two small regions is equal to or less than a predetermined value;
A can body inspection method comprising: determining whether or not a portion of the can body where the irregularities are formed has a defect based on a determination result in the maximum density difference determination step . 7. The can inspection method according to claim 6, wherein the density difference calculating step calculates a difference in image density between two non-adjacent small areas.

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