JP3719485B2 - Can lid score remaining thickness measurement method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is to measure the remaining thickness of a score groove that is engraved on the surface of a can lid so that the easy-open can lid is fastened and fastened to the can body as the top side wall of the easy open can. relates to a method, in particular, as the consumer touching the sharp break end of mouthpiece by fracture of the score groove is not injured, along the edge of the portion to be the opening piece of the panel portion of the can lid, the panel portion multilayer portion overlaid triply folded in S-shaped cross-section is formed, about the score residual thickness measuring method suitable for opening easy can lid with safety.
[0002]
[Prior art]
A can lid that is fastened to the can body as the top side wall of the easy open can, that is, a score groove that can be broken is engraved on the surface of the can lid, and the score groove is operated by operating a tab attached to the can lid. For easy-to-open can lids that can be opened by breaking the can, beverage canned foods can be partially opened with a portion of the can lid as a spout, but also for various solid foods, jelly, pudding, etc. In food canning that requires a wide opening, a full-opening type in which the panel portion of the can lid is cut out almost entirely has been used in general.
[0003]
In addition, with the easy opening can lid of the full opening type, the panel portion is folded in an S-shaped cross section so that the consumer is not injured by touching the sharply broken end of the portion (opening piece) that is removed when the can lid is opened. The multi-layered part overlapped on the top of the can is formed in an annular shape along the edge of the part that becomes the opening piece of the panel part of the can lid, and an annular score line that defines the opening piece is engraved on the uppermost layer of the multi-layer part Such structures are conventionally known (see, for example, JP-A-48-989889, JP-A-49-73285, JP-A-49-118589, etc.).
[0004]
In such an easy-to-open can lid, the score groove engraved on the surface of the can lid is strong enough not to break due to impact during transportation, etc. Also, if the tab at the time of opening the can is pulled up, it must be weak enough to break easily. For that purpose, the depth of the score groove from the plate thickness of the can lid (including the coating film on the inner and outer surfaces) It is necessary to confirm that the score remaining thickness obtained by subtracting is within a predetermined range in design.
[0005]
Therefore, it has been conventionally performed to measure the remaining score of each can lid by using a conventional apparatus for measuring the thickness of a sample obtained by extracting the can lid at an appropriate interval. In the measurement of the remaining thickness of the score, not only the work efficiency is poor by manually removing the can lid and the subsequent measurement, but also the work of pushing the measuring needle against the bottom of the score groove of the can lid is a manual operation In this case, skillful techniques are required to accurately drop the tip of the measuring needle into the bottom surface of the score groove, and the error for each measurer is large, resulting in a large variation in measurement accuracy. is there.
[0006]
In addition, in an easy-to-open can lid, an aluminum alloy is usually used as a material for the can lid, and the score groove is a thin groove having a minimum width of about 40 μm. For this, the tip of the measuring needle needs to be smaller than the groove width and about 20 μm in diameter, and the tip of the measuring needle cannot be made too hard in order not to damage the bottom surface of the score groove. Therefore, since the tip of the measuring needle is thin and soft, it wears out early, and its thickness is larger than the width of the score groove, making accurate measurement impossible.Therefore, the measuring needle must be frequently replaced or polished. There is also the problem of having to.
[0007]
On the other hand, a method of measuring the score remaining thickness based on the reflected light by irradiating light (slit light or beam light) around the score groove and its surroundings has been conventionally known (for example, , Japanese Patent Laid-Open No. 4-122808, Japanese Patent Laid-Open No. 8-136232, etc.), according to a method of measuring the score remaining thickness in a non-contact state using such light (slit light or beam light), The problem in the case of the remaining score thickness measurement using the measuring needle as described above can be solved.
[0008]
[Problems to be solved by the invention]
However, in any of the conventionally known methods for measuring the remaining thickness of the score of the can lid as described above, irradiation light (slit light or beam light) is projected onto the can lid, and the reflected thickness of the score remaining thickness is projected. Since the measurement is performed, a light projecting unit (light projector) and a light receiving unit (light receiver) are required, and the thickness of the panel portion of the can lid and the depth of the score groove are measured for each can lid ( That is, for each can lid, the reflected light is detected by projecting light to the bottom surface of the score groove and the surface of the surrounding panel portion), so that the remaining score thickness of many can lids can be measured efficiently and quickly. Can not be done.
[0009]
Further, the light projecting unit and the light receiving unit are arranged with a parallax (cutting angle), and the light cutting method is used to inspect the unevenness of the surface of the object to be inspected by the reflected light of the light projected at a predetermined angle. Therefore, depending on the depth and shape of the score groove, the reflected light of the projected light may interfere with the inner wall of the score groove, resulting in a problem that the cross-sectional shape of the score groove cannot be measured accurately. . That is, the light cutting method is generally used to measure a three-dimensional shape in a non-contact manner, and the light passing through the slit is projected onto the surface of the object to be inspected through a lens at an angle of 45 ° and reflected. It is possible to check the surface condition of the inspection object by observing the surface irregularities drawn in detail by light, but the points to note are the light projecting part and the light receiving part. Are arranged with a parallax (cutting angle), and in the deep part such as a groove on the surface of the object to be inspected, the surrounding area may be overhanged, resulting in an invisible region that cannot be measured. A typical example is the problem in measuring the remaining score of the lid.
[0010]
Further, the panel portion is formed in an S-shaped cross section along the edge of the portion that becomes the opening piece of the panel portion of the can lid so that the consumer is not injured by touching the sharply broken end of the opening piece due to the breaking of the score groove. With easy-to-open can lids that are folded and triple-layered, if the overhanging amount of the multi-layered part with respect to the score groove is small, the broken edge of the open piece projects outward from the multi-layered part, causing a safety problem. On the other hand, if the overhanging amount of the multi-layered portion with respect to the score groove is large, when the initially broken opening piece is pulled up, the broken edge remaining on the can body side and the multi-layered portion of the opening piece come into contact with each other. Therefore, it is necessary to determine in advance the amount of overhang of the multi-layered portion with respect to the score groove, and to remove the can lid with an inappropriate overhang amount from the manufacturing process. In the method for measuring the remaining thickness of the score, the quality of the overhang of the layered portion of the can lid is judged. It can not be.
[0011]
An object of the present invention is to solve the above-described problems. Specifically, for safety, a multilayer portion is formed along the edge of the portion that becomes the opening piece of the panel portion of the can lid. For the easy-to-open can lid, when measuring the score remaining thickness of the can lid in a non-contact state by light, by allowing the score remaining thickness to be measured only by projecting irradiation light regardless of reflected light, It is not necessary to provide a light receiving part for reflected light, and the remaining score thickness of many can lids can be measured accurately and efficiently quickly regardless of the depth and shape of the score groove of the can lid to be measured. At the same time, it is an object to make it possible to determine the quality of the overhanging amount of the multilayer portion with respect to the score groove .
[0012]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides an illuminating unit that irradiates light so that a contact is formed at a constant distance with respect to a contact formed on a flat surface whose axis is oblique and whose apex is minute. By installing the contactor so as to be movable in the axial direction with a line perpendicular to the top plane of the contact as an axis, a breakable score groove is formed on the surface , and an opening piece is formed by breaking the score groove. For the can lid where the panel part is folded in an S-shape along the edge of the part and the multi-layered part is formed , the top surface of the contact is irradiated with the can lid not set. Move the illumination means to the position where the light is in focus, set that position as the origin, then bring the tip of the contact into contact with the side surface of the multilayer portion on the back side of the can lid, and score The top end of the contact is brought into contact with the back surface of the can lid corresponding to the bottom surface of the groove. At setting the urchin can lid, by moving the illumination means to a position where the focal point of the irradiation light is focused on the bottom of the score groove, it is characterized in that it has to indicate the movement distance as a score residual thickness.
[0013]
According to the method for measuring the remaining thickness of the can lid as described above, it is possible to easily measure the remaining thickness of the score by only projecting the irradiation light by the illuminating means without providing a light receiving unit for the reflected light. In addition, once the origin position of the illumination means is set, the score remaining thickness of many can lids can be efficiently and quickly obtained by simply focusing the irradiation light on the score groove of each can lid. In addition to being able to measure, the remaining score thickness is accurately measured regardless of the depth and shape of the score groove because the remaining score thickness is measured by the focus of the irradiated light projected from the direction perpendicular to the bottom surface of the score groove. can do. Further, when measuring the remaining score of the score, the tip of the contact is brought into contact with the side surface (panel bent portion) of the multilayer portion to position the can lid. Whether or not the overhang amount of the multi-layered portion with respect to the score groove can be determined.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a method for measuring a score remaining thickness of a can lid according to the present invention will be described in detail based on the drawings.
[0015]
FIG. 1 schematically shows the entire apparatus as an example of an apparatus for carrying out the score remaining thickness measuring method of the present invention. For such a score remaining thickness measuring apparatus, FIG. 2 (A) shows a state in which the scale is calibrated to the origin (zero point) with the focus of irradiation light on the top end of the contact before setting the can lid, 2 (B) shows a state in which the remaining score of the score is measured by setting the can lid and then focusing the irradiation light on the bottom surface of the score groove. FIGS. 3A and 3B are partially enlarged views showing the main parts of the respective states shown in FIGS. 2A and 2B.
[0016]
In this score remaining thickness measuring apparatus 1, a contact 2 having a tapered top and a microscope unit 3 are respectively installed on a table 4 movable in the front-rear and left-right directions. On the other hand, a can lid positioning table 5 for positioning and setting the can lid is installed on the side of the table 4 so as to be movable in the vertical and horizontal directions.
[0017]
The contact 2 is fixed at a fixed position on the table 4 by the fixing jig 6 with the axis inclined so that the upper part approaches the can lid positioning table 5, as shown in FIG. As shown, a minute plane (horizontal plane) 2 a having a maximum width of about 50 μm is formed at the top end of the contact 2 that is fixed with the axis inclined.
[0018]
The microscope unit 3 is a unit in which a coaxial illumination device 9 for projecting irradiation light downward from the objective lens side is integrated with a microscope 7 having a CCD camera 8 attached to the eyepiece. The axis of the microscope 7 passing through the center of each of the eyepiece lens and the objective lens is vertically movable above the contact 2 so that the axis of the microscope 7 is perpendicular to the top surface of the contact 2. ing.
[0019]
That is, the microscope unit 3 is moved in the vertical direction by the coarse / fine movement handle 10 in which the coarse movement and the fine movement are separated so that the moving direction is perpendicular to the plane of the top end of the contact 2. In order to obtain the amount of movement of the microscope unit 3 which is installed at a fixed position on the table 4 so as to be arbitrarily movable and moves up and down by the rotation of the coarse / fine movement handle 10, a scale device (linear gauge) ) 11 is provided as a part of the microscope unit 3.
[0020]
The coaxial illumination device 9 of the microscope unit 3 is based on high-intensity cold-light illumination using a halogen lamp. Light from the illumination lamp (halogen lamp) is transmitted from the lower end of the microscope 7 through each reflector 9a, 9b. Light is irradiated toward the contact 2 through the objective lens of the microscope 7 so that the irradiation light is focused at a certain distance (a position where the microscope is in focus).
[0021]
In the present embodiment, a target mark method generally used for non-contact position measurement and distance measurement using image processing is incorporated in the coaxial illumination device 9, and specifically, the target mark A translucent filter plate 9c provided with a slit for revealing is incorporated in the coaxial illumination device 9 so that the target mark appears at a position where the irradiation light from the coaxial illumination device 9 is in focus. It is configured. Further, when the top surface 2a of the contact 2 and the bottom surface of the score groove 25 are not parallel, the thickness of the line of the target mark is different (not uniform).
[0022]
The microscope unit 3 in which the CCD camera 8, the coaxial illumination device 9, and the scale device 11 are integrated into the microscope 7 as described above, and the power source 12 for the CCD camera 8 and the illumination for the coaxial illumination device 9. A power display 13 for the monitor, a monitor display 14 for displaying an image taken by the CCD camera 8 on a screen, and a scale indicator 15 for displaying the movement amount of the microscope obtained by the scale device 11 in numbers. It is installed at an appropriate place in a state where it is connected to each part of the microscope unit 3 via a cable.
[0023]
One embodiment of the remaining score measuring method of the present invention using the remaining score measuring apparatus as described above will be described below.
[0024]
In the present embodiment, the can lid 20 that is the target of the remaining score measurement is a full-open-type easy-open can lid having a safety structure, and a thin plate of aluminum alloy is used as shown in FIG. An opening operation tab 23 is integrally fixed to the panel portion 21 with a rivet portion 24 with respect to the main body in which the flange portion 22 is integrally formed on the outer periphery of the panel portion 21 by press molding. The score groove 25 and the multi-layered portion 26 are respectively formed in the peripheral portion of the panel portion 21 along the ring so as to form an annular shape (endless shape) that defines an opening piece (a portion that is broken and removed when the can lid is opened). Is formed.
[0025]
That is, as shown in FIG. 4B, a score groove 25 that can be broken is engraved on the front side of the can lid 20, and a sharp break of the broken score groove 25 is made on the back side of the can lid 20. A multi-layered portion 26 is formed by folding the metal plate of the panel portion 21 into an S-shaped cross section so that the consumer may not be injured by touching the end. The multi-layered portion 26 is formed on the side of the can lid ( The side continuing to the flange portion 22 side) is the uppermost layer 26a, the side continuing to the can lid center side is the lowermost layer 26c, and the score groove 25 is formed on the upper surface side of the uppermost layer 26a of the multilayer portion 26.
[0026]
When the score remaining thickness of the easy opening can lid 20 (plate thickness at the bottom surface of the score groove 25) is measured by the score remaining thickness measuring apparatus as described above, first, FIG. 2 (A) and FIG. As shown in (A), a microscope taken with a CCD camera 8 by irradiating light from the coaxial illumination device 9 of the microscope unit 3 toward the top end of the contact 2 without setting the can lid 20. 7, the microscope unit 3 is moved up and down by the coarse / fine movement handle 10 to the position where the target mark appears on the screen while viewing the image of the field of view 7 on the monitor display 14, and the focus of the irradiation light is contacted. 2, the display of the scale display 15 displaying the measurement result of the scale device (linear gauge) 11 of the microscope unit 3 is reset to zero at the time when it is set to the top end (plane 2a) of the microscope unit 3. (Zero point) perform the calibration.
[0027]
Next, as shown in FIGS. 2B and 3B, the can lid 20 placed on the can lid positioning table 5 is placed on the bottom end of the score groove 25 with the top end (plane 2 a) of the contact 2. The coarse / fine adjustment handle 10 is used until the target mark appears on the screen while viewing the image of the field of view of the microscope 7 taken by the CCD camera 8 on the monitor display 14 after being set to be positioned on the back side. The microscope unit 3 is moved up and down, and the table 5 is moved up and down, left and right so that the line thickness of the target mark is uniform so that the top surface 2a of the contact 2 and the bottom surface of the score groove 25 are parallel. At the time when the irradiation light is focused on the bottom surface of the score groove 25 by moving in the direction, the numerical value displayed on the scale display 15 is read as the score remaining thickness. That is, the movement amount d in the vertical direction shown in FIG. 3 is the score remaining thickness, and this is displayed on the scale display 15 as a number.
[0028]
In addition, in the case of the can lid 20 in which the multilayer portion 26 is formed on the panel portion 21 for the safety of the opening piece as shown in the present embodiment, the table 5 on which the can lid 20 is placed is first placed on the can lid. When the end of 20 is moved to an appropriate height so as to be placed on the contact 2 and then moved so as to approach the fixed table 4 as shown in FIG. In addition, the tip 2 of the contact 2 is brought into contact with the side surface (panel bent portion) of the multilayer portion 26 on the back side of the can lid 20, so that the top surface 2 a of the contact 2 is located behind the bottom surface of the score groove 25. The can lid 20 is automatically positioned so as to be positioned.
[0029]
According to the score remaining thickness measuring method of the can lid of the present embodiment as described above, the score remaining thickness can be obtained only by projecting the irradiation light by the coaxial illumination device 9 without providing a light receiving unit for reflected light. In addition to being able to measure and resetting the display of the scale display 15 by the scale device (linear gauge) 11 to zero, the origin (zero point) is calibrated only once at the beginning. Since the score remaining thickness of each can lid can be easily measured only by focusing the irradiation light of the coaxial illumination device 9 on the score groove of each can lid, the score remaining thickness measurement of a large number of can lids can be performed. It can be performed efficiently and quickly.
[0030]
In addition, since the score remaining thickness is measured by projecting the light irradiated by the coaxial illumination device 9 from the vertical direction with respect to the bottom surface of the score groove and focusing it, even if the depth and shape of the score groove are different, the score If the groove position is not misaligned, the irradiation light can always be focused on the bottom surface of the score groove, and the remaining score thickness of various can lids can be accurately measured regardless of the depth and shape of the score groove. it can.
[0031]
Further, in the present embodiment, unlike the score remaining thickness measurement using the reflected light, the CCD camera 8 and the monitor display 14 are used to view the real image of the bottom surface of the score groove entering the field of view of the microscope 7. It is closer to the visual inspection, and the state of the bottom surface of the score groove can be observed simultaneously with the measurement of the remaining score thickness, so that the quality of the product can be more reliably guaranteed.
[0032]
In the present embodiment, by incorporating the target mark method into the coaxial illumination device 9, the target mark appears on the screen of the monitor display 14 when the irradiation light from the coaxial illumination device 9 is in focus, By making it easier to recognize that the irradiation light is in focus, it is possible to process a large number of can lids at a higher speed, and to reduce measurement errors for each measurer. Can improve the reliability.
[0033]
Further, in the present embodiment, for the safety of the opening piece, the score remaining thickness is measured for the full-opening type can lid 20 in which the multilayer portion 26 is formed on the panel portion 21. In the case of measuring the score remaining thickness of the lid 20, the unique effect of being able to perform the pass / fail judgment by visual confirmation of the overhang amount of the multilayer portion 26 with respect to the score groove 25 simultaneously with the measurement of the score remaining thickness. Will play.
[0034]
That is, when the overhang amount of the multilayer portion 26 with respect to the score groove 25 is normal, the bottom surface of the score groove 25 appears at the center of the monitor screen (or within the range of the monitor screen) as shown in FIG. When the overhang amount of the multilayer portion 26 with respect to the score groove 25 is out of the normal value range, as shown in FIG. 5B or 5C, the bottom surface of the score groove 25 is the edge of the monitor screen. Partly appearing on the screen or completely off the edge of the monitor screen (out of the field of view of the CCD camera of the microscope), thereby making it possible to easily determine whether the overhanging amount of the multilayer portion 26 is good or bad. .
[0035]
As shown in FIG. 5B, when the bottom surface of the score groove 25 is disengaged from one end (left side) of the monitor screen and the overhanging amount of the multilayer portion 26 with respect to the score groove 25 is small, the can There is no problem in terms of opening of the can lid without contact between the broken edge remaining on the main body side and the multilayer portion 26 of the opening piece, but the broken edge of the opening piece projects outward in the radial direction from the multilayer portion 26. Therefore, it is determined that there is a problem in the safety of the opening piece to be removed by breakage (the safety is inferior to the design).
[0036]
On the other hand, as shown in FIG. 5C, when the bottom surface of the score groove 25 is disengaged from the other (right side) end of the monitor screen and the overhanging amount of the multilayer portion 26 with respect to the score groove 25 is large, the opening is opened. There is no problem with the safety of the piece (the safety is greater), but when the opening piece that has been initially broken is pulled up and removed, the broken edge remaining on the can body and the layered portion 26 of the opening piece come into contact with each other. Therefore, as a result, it is determined that the opening piece is unsuitable due to the large resistance when the opening piece is removed by breakage, making it difficult to open the can.
[0037]
As mentioned above, although the score residual thickness measuring method of the can lid of the present invention has been described by one embodiment, the present invention is not limited to the above embodiment, and specifically, for example, a certain distance It is also possible to implement without incorporating the target mark method into the illumination means that irradiates light so as to focus on the microscope, and without performing the visual field of the microscope as an image on the monitor display by the CCD camera. Of course, it is possible to change the focus of the irradiation light as appropriate, such as by observing it with a visual sensor rather than looking through a microscope. Nor.
[0038]
【The invention's effect】
According to the method for measuring the remaining score of the can lid according to the present invention as described above, it is possible to efficiently and easily measure the remaining score by using only the irradiation light from the illumination unit without the need for a light receiving unit for reflected light. In addition, once the origin position of the illumination means is set, the score remaining thickness of many can lids can be quickly obtained simply by focusing the irradiation light on the score groove of each can lid. In addition to being able to measure, the remaining score thickness is accurately measured regardless of the depth and shape of the score groove because the remaining score thickness is measured by the focus of the irradiated light projected from the direction perpendicular to the bottom surface of the score groove. can do. Furthermore, when measuring the remaining score, the can lid is positioned by bringing the tip of the contact into contact with the side surface of the multilayer portion. Depending on the positioning state of the can lid, the overhang of the multilayer portion with respect to the score groove is performed. The quality of the quantity can be determined.
[Brief description of the drawings]
FIG. 1 is a front explanatory view schematically showing the whole of an example of an apparatus for carrying out a method for measuring a score remaining thickness of a can lid according to the present invention.
FIG. 2 shows the score remaining thickness measuring apparatus shown in FIG. 1, (A) the scale is calibrated to the origin (zero point) with the irradiation light focused on the top of the contact before setting the can lid, and (B) Front explanatory drawing which shows the state which adjusted the focus of irradiation light to the bottom face of a score groove | channel, and measured the score remaining thickness after setting a can lid | cover.
FIG. 3 shows the score remaining thickness measuring apparatus shown in FIG. 1. (A) A state in which the irradiation light is focused on the top end of the contact before setting the can lid, and (B) after setting the can lid. The principal part expansion explanatory drawing which each shows the state which matches the focus of irradiated light with the bottom face of a score groove | channel.
4A is a cross-sectional view showing the entire can lid, and FIG. 4A is a cross-sectional view showing the entire can lid; FIG. B) Sectional drawing which expands and shows a part of can lid.
FIG. 5 is a graph showing the remaining amount of overhang with respect to the score groove at the same time as the measurement of the remaining score for the full-open-type can lid provided with the safety of the opening piece by the score remaining thickness measuring apparatus shown in FIG. When performing pass / fail judgment, (A) when the overhanging amount is normal, (B) when the overhanging amount is small, and (C) when the overhanging amount is large, an explanatory diagram showing a measurement state and a monitor screen .
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Can lid score remaining thickness measuring device 2 Contact 3 Microscope unit 5 Can lid positioning device 7 Microscope 8 CCD camera 9 Coaxial illumination device (illumination means)
9c Filter plate (means to show the target mark)
10 Coarse / Fine Handle 11 Scale Device (Scale Means)
14 Monitor display 15 Scale indicator (scale means)
20 Can lid 25 Score groove 26 Multi-layer part

Claims (4)

An illuminating means that irradiates light so as to focus at a fixed distance on a contact formed on a flat plane with the axis tilted obliquely and the apex is a line perpendicular to the plane of the apex of the contact. By installing so as to be movable in the direction, a score groove that can be broken is engraved on the surface , and the panel portion is folded in an S shape along the edge of the portion that becomes an opening piece by breaking the score groove For the can lid on which the multi-layered layered portion is formed , first, with the can lid not set, the illumination means is moved to a position where the irradiation light is focused on the plane of the top end of the contact. After the position is set as the origin , the contact tip is brought into contact with the side surface of the multilayer portion on the back side of the can lid, and the top end of the contact on the back surface of the can lid corresponding to the bottom surface of the score groove With the can lid set to contact the bottom of the score groove By moving the illumination means to a position where the focal point of the irradiation light is focused, the score residual thickness measurement method can lid, characterized in that in the manner shown that the movement distance as a score residual thickness. An illuminating unit that irradiates light so as to focus at a fixed distance on a microscope installed so as to be movable in the axial direction about a line perpendicular to the top surface of the contact as an axis is integrated to provide coaxial illumination By first unitizing the microscope unit, the microscope unit is moved to a position where the irradiation light is focused on the plane of the top of the contactor while looking at the field of view of the microscope without setting the can lid. The position is set as the origin on the scale means for indicating the movement distance of the contact point, and then the tip of the contact is brought into contact with the side surface of the multilayer portion on the back side of the can lid, and the bottom surface of the score groove With the can lid set in contact with the back of the corresponding can lid, move the microscope unit to the position where the irradiation light is focused on the bottom of the score groove while looking at the microscope field of view, The travel distance Score residual thickness measurement method can lid according to claim 1, characterized in that as shown as a score residual thickness by kale means.   The method for measuring the remaining thickness of a can lid according to claim 2, wherein the target mark appears at a position where the light irradiated by the illumination means is in focus.   The field of view of the microscope is displayed as an image on a monitor display through a CCD camera, and the amount of movement of the microscope unit is displayed numerically on a scale display via a scale device attached to the microscope unit. Item 4. The method for measuring the remaining score of a can lid according to Item 2 or 3.

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