JP2008241649A - Inner surface inspection method of can - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a paint defect or a change state of an inner surface which are difficult to be detected by a conventional inspection method, and to thereby improve the accuracy of inner surface inspection, when inspecting the inner surface state of a can having the painted inner surface. <P>SOLUTION: Image data of the can inner surface are acquired by imaging the inner surface of the can 1 by a camera 32 before a paint film formed by painting applied to the inner surface of the can 1 is dried, and the inner surface state of the can 1 is determined based on the image data. Normal image data wherein the inner surface state of the can 1 after being painted is normal are converted into a gradation numerical value showing a density difference and held beforehand, and a difference is checked by comparing a normal numerical value with a numerical value based on inspection image data acquired by the camera 32. The can 1 is discriminated to be nondefective one in the case where the difference is within a prescribed range, and to be defective one in the case of out of the prescribed range. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for inspecting an inner surface of a can in which beverage food such as water, juice, and alcoholic beverages is enclosed, and in particular, an inner surface inspection of a can that inspects the state of the inner surface of the can after the inner surface of the can has been painted. Regarding the method.

  This type of can has a configuration in which an opening of a cylindrical can body having a bottom portion is closed with a can lid, and an aluminum alloy, steel, or the like is a common material. In the can manufacturing process, the inner surface of the can body is coated for the purpose of protecting the inner surface of the can body and preventing the change of the inclusion. As a paint for the inner surface coating, a synthetic resin paint such as a thermosetting resin or a thermoplastic resin is used, and enamel is a typical example. After coating the inner surface, check whether the inner surface has been reliably coated, or check whether the coating is in a healthy state that does not suffer from so-called foreign matter or uneven coating. Inspection is being conducted.

Conventional methods for inspecting the inner surface of a can include a method called an enamellator method (Patent Document 1) for detecting a change state such as a coating defect from a current measurement value passed through the can, and a method using a photoelectric sensor (Patent Document 2). there were. However, in these methods, since the inspection time for one can takes a long time, in a facility that manufactures a large number of cans in a flow operation, for example, a sampling inspection in which cans are extracted and inspected at a rate of, for example, one out of 100 cans. The form is taken. In addition, a method for judging the coating state from image data obtained by imaging the inner surface of the can with a camera has been developed (Patent Document 3), and this method enables 100% inspection instead of sampling inspection.
Japanese Patent Laid-Open No. 2003-14679 JP-A-6-134364 JP 2005-315698 A

  By the way, the conventional inner surface inspection of the can described in each of the above-mentioned documents and the like is performed after drying the coating film of the inner surface coating in any case. However, some types of coating defects cannot be clearly detected by the conventional method, or some time and effort are required for detection. Furthermore, there are cases where such a change in the inner surface coating is tolerated even if it is within an allowable range and cannot be said to be a defect.

  Therefore, the present invention can reliably and quickly detect coating defects and changes in the inner surface that are difficult to detect by the conventional method when inspecting the inner surface state of a can that has been internally coated. As a result, the accuracy of the inner surface inspection is improved. The object is to provide a method for inspecting the inner surface of a can.

  The present invention relates to a can inner surface inspection method for inspecting the state of an inner surface of a can after coating, and before the coating film formed by coating applied to the inner surface of the can dries, the inner surface of the can Is picked up by an image pickup means to obtain image data of the inner surface of the can, and the inner surface state of the can is determined based on the image data.

  That is, the present invention is a method in which the coating film is not yet dried and is inspected by a predetermined method at a stage where the coating film is wet and the wet state is maintained after the coating is applied. This is based on the knowledge that excellent detection accuracy can be obtained. The inspection is performed based on image data obtained by imaging the inner surface of the can with the imaging means. Therefore, it is possible to grasp the coating defects and the change state of the inner surface, which are difficult to understand after drying, with high accuracy. In addition, since the inner surface inspection by the imaging means can be performed for each can in a short time including judgment of the inspection result (inspection pass / fail) during the production line, 100% inspection is possible even for equipment.

  As a specific method of the inner surface inspection by the imaging means of the present invention, normal image data in which the state of the inner surface of the can after coating is normal is stored in advance, and this normal image data and the inspection image data of the captured inner surface of the can And the difference between the two data is found, and if the difference is within a predetermined range, a pass / fail judgment is made for a product such as a non-defective product, and when the difference is outside the predetermined range, a product is judged as acceptable.

  Examples of the image data include numerical values of image shading. In this case, a numerical value in which the gradation difference is displayed with 256 gradations is preferably used, and in this case, the gradation of the inner surface of the can which is inspected with respect to the gradation of the normal coating is the same, or an allowable range. An inspection is made based on the judgment of whether it is within. Further, a can to be inspected in the present invention is the above-mentioned can body that is cylindrical and has one end opened in the axial direction. In this case, the image pickup means has one end with the optical axis aligned with the axis of the can. It is used in the form of imaging the inner surface of the can through the opening on the side. In the case where the density of the image is used as a judgment material in this way, the paint is not transparent but has a color.

  When imaging the inner surface of the can in this way, even though the inner surface of the can has a constant density difference according to the coating thickness, the amount of reflected light, that is, the amount of light received by the imaging means depends on the angle with respect to the optical axis of the imaging means. Come different. That is, the image picked up by the image pickup means has a light / dark difference corresponding to the amount of reflected light even if there is no light / dark difference on the inner surface of the can. Specifically, the amount of reflected light is the largest from the bottom almost perpendicular to the optical axis of the imaging means, and therefore the bottom is the darkest. Further, the inclination of the inner wall surface of the can with respect to the optical axis increases from the bottom side toward the opening side, and the darkness increases as the amount of reflected light decreases in proportion to this. The inspection by the imaging means must be made appropriately according to the difference in the amount of light reflection according to the location of the inner surface of the can, and therefore the present invention moves the inner surface of the can from the bottom to the opening. In the axial direction, it is preferable to divide into three areas, a bottom area, an intermediate area, and an upper area, and to process the image data obtained by the imaging means for each of these areas.

  According to the present invention, when inspecting the inner surface state of an internally coated can, it is possible to detect coating defects and changes in the inner surface that are difficult to detect after drying, resulting in improved accuracy of the inner surface inspection. There are effects such as.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
<1> Inner surface inspection line of can FIG. 1 is a part of a production line of a can (which is a can body but hereinafter referred to as a can) 1 and shows a process part related to an inner surface inspection process. An upper and lower triple turret index mechanism 10 is disposed at the most upstream part of the line in FIG. The mechanism 10 is composed of three turrets 11, 12, and 13 incorporated in the vertical direction. Each of the turrets 11 to 13 rotates in a rotating state around the horizontal rotation axis in the arrow direction in the figure.

  A plurality of pockets 11a, 12a, 13a for holding each can 1 horizontally are provided at equal intervals in the circumferential direction on the outer peripheral portion of each turret 11-13. In the pocket 11a that reaches the top of the turret 11 on the upper side of the turret mechanism 10, the can 1 whose outer surface is printed and whose inner surface is to be coated is successively carried and held. Is done. The can 1 held in the pocket 11a of the upper turret 11 is swirled and transferred to the pocket 12a of the intermediate turret 12, and is placed on the inner surface at a position indicated by an arrow P in FIG. Paint is applied. Internal coating is performed by spraying paint with a spray gun. In this case, a synthetic resin paint such as enamel, which is relatively slow to dry, is used for the inner surface coating. In this case, the paint is not transparent but has a color. The can 1 coated on the inner surface is transferred from the intermediate turret 12 to the pocket 13 a of the lower turret 13.

  Each can 1 held by the lower turret 13 is swirled and transferred to a descending conveying path 21 extending in the vertical direction, and the descending conveying path 21 is lowered. Further, the can 1 is moved from the descending conveyance path 21 to a belt conveyor type horizontal conveyance path 22, and is conveyed along the horizontal conveyance path 22 from the left to the right in FIG. 1. Next, each can 1 is moved to the ascending conveyance path 23 extending in the vertical direction, and the ascending conveyance path 23 is raised. An inner surface inspection device 30 is disposed in the middle of the ascending conveyance path 23.

  After the inner surface of the can 1 has been inspected by the inner surface inspection device 30, a product that has passed the inspection is continuously moved up the ascending conveyance path 23, carried into an oven device (not shown), and subjected to a drying treatment of the inner surface coating. The Further, the can that is determined to be unacceptable by the inner surface inspection apparatus 30 is discharged from the ascending conveyance path 23 by the discharge mechanism 40 after the inspection. Although each can 1 in FIG. 1 rotates around its axis, it is transported so that its posture is consistently horizontal, that is, its own axis is horizontal during transportation.

<2> Inner Surface Inspection Device The inner surface inspection device 30 includes an illumination 31, a camera (imaging means) 32, and a control unit 33, as partially enlarged in FIG. The illumination 31 is, for example, a ring-shaped one arranged on the opening side of the can 1 in order to illuminate the inner surface of the can 1, and an LED or the like is preferably used. The camera 32 takes an image of the inner surface of the can 1 illuminated by the illumination 31, and is arranged at a position sandwiching the illumination 31 on the opening side of the can 1. A camera 32 having an element such as a CCD is used. The camera 32 is set so that the optical axis coincides with the axis of the can 1 and the inner surface of the can 1 is imaged from the opening of the can 1.

  The conveyance time of the can 1 from the inner surface coating position P to the inner surface inspection apparatus 30 is about 20 seconds or so, and about 30 seconds at the latest. This is because the coating film coated on the inner surface does not dry and is still sufficient. It is the time when the wet state is secured. The inner surface of the can 1 is inspected by the inner surface inspection device 30 as follows, with the coating film being undried.

<3> Inner surface inspection method
As described above, when the inner surface is applied at the inner surface coating position P and the coating film is left in an undried state, that is, in a wet state, the inner surface coating apparatus 30 is illuminated, as shown in FIG. The inner surface of the can 1 is imaged by the camera 32. The conveyance of the can 1 stops instantaneously only when the inner surface is imaged by the camera 32. The image data of the inner surface of the can 1 captured by the camera 32 is supplied to the control unit 33 (FIG. 1).

  Based on the supplied image data, the control unit 33 converts the data into 256 gradation numerical values (density: represented by X / 256) indicating a difference in light and shade. The control unit 33 holds the numerical value of the normal inner surface state of the painted can inner surface when the coating film is undried, and the control unit 33 compares the normal value with the inspection value.

  Then, the control unit 33 determines whether the normal value and the inspection value match or are within a preset allowable range, and if they match or are within a predetermined allowable range. Then, it is determined that the inner surface state is good, and the ascending conveyance path 23, which is a regular conveyance path, is further raised as it is. On the other hand, when the inspection value deviates from the allowable range with respect to the normal value (abnormal value), it is determined that the inner surface is defective or has some change, and an operation signal is sent to the discharge mechanism 40. Thus, the can determined to be defective is discharged from the ascending conveyance path 23 by the discharge mechanism 40 immediately after passing through the inner surface inspection apparatus 30.

  By the way, even when the inner surface of the can 1 is normally painted, the shade of the image of the painted inner surface captured by the camera differs depending on the amount of reflection from the portion of the inner surface of the can (the amount of light received by the camera 32). The bottom and inner sides are very different. Therefore, in this case, as shown in FIG. 2, the inner surface of the can is divided into three regions of a bottom region 1A, an intermediate region 1B, and an upper region 1C along the axial direction from the bottom of the can 1 to the opening. Each time, the image data captured by the camera 32 is processed separately. As shown in the upper diagram of FIG. 2, the concentrations of the bottom region 1A, the intermediate region 1B, and the top region 1C are concentrically divided.

  In the lower diagram of FIG. 2, the angles of light reflected from the bottom region 1A, middle region 1B, and top region 1C of the inner surface of the can and incident on the camera 32 are indicated by dotted arrows. The inner surface of the can 1 shown in FIG. 2 is normally coated and has no defects, and the concentrations of the regions 1A, 1B, and 1C show normal values. These normal values are stored and held by the control unit 33. Incidentally, the normal values in this case are the bottom region 1A: 150/256, the intermediate region 1B: 120/256, and the upper region 1C: 100/256 {the smaller the value, the thinner (= brighter)}.

  Further, the control unit 33 divides the bottom region 1A, the intermediate region 1B, and the top region 1C into a large number in the circumferential direction, and determines the density of each divided region. As a result, in each of the regions 1A, 1B, and 1C, local changes in the inner surface are also grasped, and if the circumferential density difference deviates from the allowable range, the can is also discharged. As a result, extremely local defects such as so-called foreign matter and uneven coating can be detected with high accuracy.

<4> Types of Defective Products FIGS. 3 (a) to 3 (c) show examples of defects in the inner surface coating of the can 1, each of which is a defective product including an abnormal value in the inspection value. To be judged. The can 1 shown in FIG. 3A is not painted at all on the inner surface, and the material cloth is exposed on the entire inner surface. The inspection values in this case are abnormal values in the bottom region 1A: 200/256, the intermediate region 1B: 180/256, and the upper region 1C: 150/256. 3B, the upper region 1C was normally painted, but the intermediate region 1B and the bottom region 1A were thinly coated. In this case, the inspection value is the bottom region 1A: 180/256 ( Abnormal value), middle region 1B: 150/256 (abnormal value), upper region 1C: 100/256 (normal value). The can 1 of FIG. 3 (c) is one in which the bottom region 1A and the intermediate region 1B are normally painted but the top region 1C is not painted at all, and the inspection value in this case is the bottom region 1A: 150/256 ( Normal value), intermediate region 1B: 120/256 (normal value), and upper region 1C: 150/256.

  As described above, the entire inner surface of the can 1 after the inner surface coating is inspected one by one by the inner surface inspection device 30 in the middle of the production line. According to the present embodiment, the inner surface inspection of the can is performed immediately after the coating is performed, and the coating film is not yet dried, and the coating film is wet and the wet state is maintained. Then, the inner surface of the can is imaged and the inner surface of the can is inspected based on the image data at that time.

  Therefore, it is possible to grasp the coating defects and the change state of the inner surface, which are difficult to understand after drying, with high accuracy. In particular, according to the present invention, as described above, the state of the inner surface of the can is imaged by the camera 32 before the coating film dries, and is determined based on the image data. As a result, it is possible to reliably and promptly detect even a defect that cannot be detected after the paint is dried or is difficult to detect. Further, the inner surface inspection by the camera 32 can be performed in a short time for each can including the result of the inspection in the middle of the production line. Therefore, 100% inspection is possible even for mass production equipment.

It is the figure which drawn roughly the can manufacturing line to which the inner surface inspection method concerning one embodiment of the present invention was applied. It is a figure which shows the inner surface inspection method which concerns on one Embodiment. (A)-(c) is the figure which showed the example of the type of the defect of the inner surface coating of a can, and the measured numerical value with respect to each defect, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Can 1A ... Bottom area | region 1B ... Intermediate | middle area | region 1C ... Upper area | region 30 ... Inner surface inspection apparatus 31 ... Illumination 32 ... Camera (imaging means)
33 ... Control unit

Claims (5)

A method for inspecting the inner surface of a can after inspecting the inner surface of the can after being coated,
Before the coating film formed on the inner surface of the can dries, the inner surface of the can is imaged by an imaging means to obtain image data of the inner surface of the can, and the inner surface state of the can is determined based on this image data A method for inspecting the inner surface of a can.   Preliminarily holding normal image data that the inner state of the can after painting is normal, and comparing the normal image data with the inspection image data obtained by the imaging means, find the difference between the two data, 2. The method for inspecting an inner surface of a can according to claim 1, wherein if the difference is within a predetermined range, it is judged as a non-defective product, and if it is outside the predetermined range, it is judged as a defective product.   The method for inspecting an inner surface of a can according to claim 1 or 2, wherein the image data is obtained by digitizing the density of an image.   The can is cylindrical and has an opening on one end in the axial direction, and the imaging means takes an image of the inner surface of the can from the opening on the one end while the optical axis is aligned with the axial center of the can. The inner surface inspection method for a can according to any one of claims 1 to 3.   The inner surface of the can is divided into three regions, a bottom region, an intermediate region, and an upper region, in an axial direction from the bottom to the opening, and image data obtained by the imaging unit is processed for each region. The inner surface inspection method for a can according to claim 4.

Images