Can internal pressure inspection device

Abstract

To accurately determine the quality of internal pressure by measuring a shape of a can deformed according to a change in internal pressure.SOLUTION: A can internal pressure inspection device irradiates a surface of a can lid for sealing a can with a laser beam, and relatively scans the laser beam in a conveying direction of the can to continuously measure a distance from a predetermined reference point to a surface by a laser displacement sensor, and obtains shape data on the surface based on a measured value of the continuous distance to determine the quality of an internal pressure of a can based on the shape data. The device includes: inclination calculation means for sequentially calculating inclination of a measurement value according to the shape data at two mutually preceding and subsequent points in a scanning direction in a predetermined region at a central section of the can lid in the shape data; and measurement point derivation means for deriving a portion where a change in amount of the calculated inclination becomes maximum as a measurement point. The device is configured to determine the quality of the internal pressure of the can based on a distance from the reference point of the measurement point.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an apparatus for inspecting the internal pressure of a can containing food or drink, and more particularly to an apparatus for inspecting the internal pressure of a so-called food can containing solid food based on the amount of deformation of the lid. [Background technology]

[0002] The internal pressure of cans containing food or drink can become positive (positive pressure) higher than atmospheric pressure or negative (negative pressure) depending on the properties of the contents and the temperature of the contents at the time the can lid is sealed. In a normal can, the internal pressure is maintained at a specified pressure according to the product, but if there is an abnormality such as a poor seal, the internal pressure will deviate from the normal value, which will appear as a deformation of the can lid.

[0003] Therefore, conventionally, the amount of deformation of a can lid in response to internal pressure is detected, and cans (products) whose detected value exceeds a predetermined reference value (threshold value) are rejected as defective. For example, Patent Document 1 describes a device configured to measure the distance to a container by irradiating the container with a laser beam from above during transport. The device described in Patent Document 1 aims to reduce measurement errors caused by vertical vibration or tilt of the container during transport. If the direction of container transport is defined as the vertical direction and the direction perpendicular to this is defined as the horizontal direction, three distance detectors such as laser length measuring devices are arranged horizontally to detect three distances between the center of the container and its two peripheral edges (distances from a reference position such as the distance detector). When the container vibrates vertically, all three detected values ​​change in magnitude. Therefore, the effect of the vertical vibration is eliminated or reduced by calculating the difference between these three detected values. Furthermore, when the container is tilted, one of the detection values ​​on the left and right will be larger and the other will be smaller, so the effect of the container tilt is eliminated or suppressed by taking the average of these two detection values ​​as the distance on both sides, or by taking the average of the difference with the distance at the center.

[0004] When detecting or measuring the deformation of a container such as a can lid as the distance from a sensor to the container, if an accessory such as a tab is placed on the measurement surface of the container such as a can lid, the detected distance value will include the dimension of the accessory, reducing the measurement accuracy or detection accuracy and making the device impractical. Therefore, the device described in Patent Document 2 is configured to determine the difference between the distance from a reference position, such as the installation position of the sensor, to the seam edge of the can and the distance to the center of the can lid, and to test the internal pressure using this difference as the deformation of the can lid. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-192646 [Patent Document 2] Special Publication No. 5-38891 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 exemplifies an apparatus configured to measure the deformation of the bottom surface of a so-called two-piece can. The apparatus measures the distance between the center and both of its two sides, a total of three points. In this case, since the left and right sides have a certain amount of space, the measurement accuracy does not particularly affect the accuracy of the internal pressure test. However, the measurement point in the center is limited to one point. Furthermore, if the top lid (top cover) with a tab is measured instead of the bottom lid, horizontal or vertical displacement of the can being inspected may result in the tab and the rivet securing it being measured as the can lid surface. In other words, the apparatus described in Patent Document 1 cannot be used to inspect lids with tabs, and can misalignment may significantly affect inspection accuracy.

[0007] In contrast, the device described in Patent Document 2 is configured so that the reference position for distance measurement is changed to the position of the sensor, and is therefore capable of measuring the amount of deformation of the can lid and conducting an internal pressure inspection even when a tab is provided. However, Patent Document 2 does not describe any specific means for eliminating or correcting the influence of the tab and the associated processing locations, and there are still issues to be resolved in order to conduct an internal pressure inspection that measures the distance on the surface of the lid where the tab is provided.

[0008] This invention has been made with an eye on the above-mentioned technical problems, and aims to provide a device that can accurately test the internal pressure of a can even if the can has a tab or other processing part associated with it on the measurement surface where the distance for determining the internal pressure is measured. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, this invention provides a can internal pressure inspection device that irradiates a laser beam onto the surface of a can lid that seals a can, and scans the laser beam relatively in the conveying direction of the can to continuously measure the distance from a predetermined reference point to the surface using a laser displacement sensor, obtains shape data about the surface based on the continuous distance measurements, and judges whether the internal pressure of the can is good or bad based on the shape data.The device is characterized by comprising: a slope calculation means that sequentially calculates, in accordance with the shape data, the slopes of the measurement values ​​at two points in the shape data that are adjacent to each other in the scanning direction in a predetermined area in the center of the can lid, and a measurement point derivation means that derives the point where the calculated change in slope is greatest as a measurement point, and is configured to judge whether the internal pressure of the can is good or bad based on the distance of the measurement point from the reference point.

[0010] In this invention, the device may further include a temperature sensor that detects the temperature of the can, a correction value calculation means that calculates a distance correction value based on a predetermined relationship between the temperature of the can and a distance correction value and the detected temperature of the can, and a distance correction means that corrects the distance of the measurement point from the reference point using the distance correction value calculated by the correction value calculation means, and may be configured to determine whether the internal pressure of the can is good or bad based on the distance of the measurement point from the reference point corrected by the distance correction value.

[0011] In addition, this invention may further include a height measurement means for measuring the height of the can while the distance is being measured by the laser displacement sensor, a height correction value calculation means for calculating a height correction value based on the height of the can measured by the height measurement means and a predetermined reference height, and a height correction means for correcting the height of the reference point or the distance measured by the laser displacement sensor using the height correction value. [Effects of the Invention]

[0012] According to this invention, the measurement point for determining the deformation of the can lid is set at a location in a predetermined region in the center of the can lid where the shape data changes abruptly, specifically, at a location where the change in the slope of the measured values ​​at two adjacent points is greatest. For example, in a can lid in which a tab is riveted to the periphery of the can lid, the finger grip is located near the center of the can lid, and the general surface of the can lid is raised so that the tab is lower than the general surface (the surface that occupies the majority of the can lid), the measurement point is near the boundary between the raised slope and the general surface. Therefore, even in a can lid with a tab, the measurement point in this invention is set at a location in the center of the can lid that avoids the tab. This allows the deformation of the can lid and the resulting internal pressure to be accurately measured and determined without being affected by the tab. Furthermore, the measurement point may be, for example, any point in a region that is somewhat wide and near the boundary between the raised slope and the general surface. In other words, since it is not a specific point or a narrow area close to it, there is little measurement error due to misalignment of the can, and in this sense too, the amount of deformation of the can lid and the internal pressure of the can based on that can be measured and determined with high accuracy. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a block diagram for explaining the configuration of a can internal pressure inspection device according to the present invention. [Figure 2] FIG. 1 is a plan view showing an example of a can lid of a can as an inspection target. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. [Figure 4] FIG. 10 is a diagram showing an example of shape data (displacement waveform). [Figure 5] FIG. 1 is a diagram showing actual measured values ​​of the internal pressure of the can and the amount of deformation thereof at the center of the can and at measurement points. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the present invention is shown in block diagram form in Figure 1. Note that the example shown here does not limit the present invention, and the device of the present invention may be configured with appropriate modifications as needed.

[0015] The cans to be inspected in this invention are cans containing sealed food or drink, more specifically, so-called food cans containing solid ingredients such as fish or meat. Therefore, can 1, the object to be inspected, is a sealed container with a can body 2 sealed at the open end with a lid (can lid) 3, and can 1 is subjected to an internal pressure inspection while being transported by conveyor 4. In FIG. 1, conveyor 4 is configured to transport can 1 in a direction perpendicular to the plane of the drawing, with can lid 3 facing upward. A first laser sensor 5 and a second laser sensor 6 are disposed above can 1 at a predetermined position during the transport. Note that first laser sensor 5 corresponds to the laser displacement sensor in this invention, and second laser sensor 6 corresponds to part of the height measuring means in this invention.

[0016] These laser sensors 5, 6 are configured to irradiate laser light toward cans 1 on conveyor 4, receive the reflected light, measure the distance to the surface of can lid 3 (more precisely, the point where the laser light is irradiated), and output a measurement signal. The installation height of these laser sensors 5, 6 is predetermined, so the height of the measurement point can be determined by subtracting the distance measured by the laser sensors 5, 6 from the installation height of the laser sensors 5, 6.

[0017] The first laser sensor 5 is positioned approximately along a straight line passing through the center of the can lid 3. The reason why it is said to be "approximately along" here is that even if the first laser sensor 5 is positioned along this straight line, the position of the can 1 being transported by the conveyor 4 may shift, so that when the can lid 3 on the can 1 being transported is used as a reference, the can lid 3 may not perfectly coincide with the straight line. The second laser sensor 6 is also provided at a position corresponding to the peripheral portion of the surface of the can lid 3 where the flat surface is continuous. This is to measure the actual height of the can 1 on the conveyor 4 and obtain a correction value for height correction, as will be explained later.

[0018] Distance measurement by each laser sensor 5, 6 is performed after the can 1 reaches below the laser sensor 5, 6. In order to detect when the can 1 has reached the measurement position, i.e., to start distance measurement by the laser sensors 5, 6, a position sensor (photoelectric sensor) 7 is provided to detect the position of the can 1. This photoelectric sensor 7 is a conventionally known sensor (switch) that outputs a detection signal when a light beam from a light emitter to a light receiver is interrupted. Furthermore, because the internal pressure of the can 1 is affected by the temperature of the can 1, a temperature sensor 8 is provided to detect the temperature of the can 1 on the conveyor 4 without contact. This temperature sensor 8 may be, for example, an infrared thermometer.

[0019] A controller 9 is provided which determines whether the internal pressure of the can 1 is good or bad based on the distance measurements obtained by the laser sensors 5 and 6. The controller 9 is an electronic control device comprising an arithmetic element, a memory element, an interface, a power supply, etc., and as shown in functional blocks in Figure 1, is mainly composed of an analog input / output circuit 10, a digital input / output circuit 11, an A / D converter 12, and a sequencer (PLC) 13. The laser sensors 5 and 6 and the temperature sensor 8 are connected to the analog input / output circuit 10, and their detection signals are input to the sequencer 13 via the A / D converter 12. The photoelectric sensor 7 is connected to the digital input / output circuit 11, and the temperature detection signal is input to the sequencer 13 via this digital input / output circuit 11.

[0020] Furthermore, a display / setting device 14 is connected to the sequencer 13, which displays the results of calculations and switches between ON and OFF, inputs preset values, etc. Also, when the sequencer 13 determines that a can is defective, the digital input circuit 11 outputs an instruction signal to a rejection device that rejects the defective can 1 from the conveyance path.

[0021] Next, an example of a can lid 3 for a can 1 used in the above-described internal pressure determination is shown in Figure 2. Figure 2 is a plan view, and Figure 3 is a cross-sectional view taken along line III-III in Figure 2. The can lid 3 shown here is a conventionally known full-open type can lid, and its peripheral portion forms a chuck wall 15 that is seamed to the can body 2 and rises into a cylindrical shape. The inner peripheral portion of the chuck wall 15 forms a panel portion 16, and a score line (easy-to-break line) 17 is formed on the outer periphery of the panel portion 16. The portion surrounded by the score line 17 forms an opening flap 18 that can be released when the score line 17 breaks.

[0022] Tabs 19 are fixed by rivets 20 to predetermined locations on the periphery of the opening piece 18. The tabs 19 act as levers using the portions fixed by the rivets 20 as fulcrums to cause an initial break in the score line 17, and then pull up the opening piece 18 to further the break in the score line 17. The tip of the tab 19 extending toward the outer periphery of the panel portion 16 is approximately aligned with the score line 17. In other words, the score line 17 is approximately circular overall, but the tip of the tab 19 is slightly curved inward toward the panel portion 16 so as to approach the tip. The opposite side (rear end side) of the tab 19 across from the portion fixed by the rivets 20 is formed in a ring shape to form a finger hook 21. A recess 22 is formed in the center of the panel portion 16 at a position corresponding to the outside of the finger hook 21 to provide space below the finger hook 21.

[0023] A wide area of ​​the panel portion 16, excluding the areas where the tab 19 and recessed portion 22 are provided and a portion of a predetermined width (countersink portion) inward from the score line 17, is slightly raised to form a height portion 23. This height portion 23 is a portion that is raised as much as possible around the thickness of the tab 19 so that only the tab 19 does not protrude upward from the panel portion 16, and therefore the height portion 23 is recessed (curved) on the rear end side of the tab 19 (toward the finger hook portion 21) so as to surround the outer periphery of the finger hook portion 21. The recessed portion 22 is located between the height portion 23 and the finger hook portion 21, which are curved in an arc.

[0024] The height portion 23 has a portion thereof inserted into the finger hook portion 21 of the tab 19 and surrounds approximately half of the rear end of the finger hook portion 21, so that the height portion 23 has an approximately arc-shaped overall shape in a plan view. The peripheral portion that separates the height portion 23 from the panel portion 16 is an inclined portion 24 that rises obliquely, as shown in Figure 3. The upper surface (surface) of the height portion 23 is approximately flat when no pressure is applied.

[0025] Next, we will explain how to measure the distance (measure the amount of deformation) to determine the internal pressure of the can 1. The can 1 is placed on the conveyor 4 and transported so that the center of the can lid 3 passes as directly below the first laser sensor 5 as possible. When the photoelectric sensor 7 detects the arrival of the can 1, the laser sensors 5 and 6 measure the distance. Specifically, a laser beam is irradiated onto the surface of the can lid 3 and the reflected light is captured by the light-receiving unit to measure the distance. The irradiation of the laser beam and the reception of the reflected light continue while the can 1 passes below the first laser sensor 5. Therefore, the laser beam is scanned in the diameter direction through the center of the can lid 3, and the distance is measured continuously.

[0026] When the can 1 is sealed with the can lid 3 immediately after being filled with the contents, the internal pressure of the can 1 becomes a negative pressure lower than atmospheric pressure if the can is normal. However, if the sealing by the can lid 3 is defective or the sealing is not tight enough, the negative pressure decreases and the internal pressure approaches atmospheric pressure (outside air pressure). The can lid 3 deforms in response to this internal pressure. This deformation causes the center of the can lid 3 to dent, and appears as the measurement value of the first laser sensor 5 described above. The measurement value thus obtained is obtained by linearly scanning the surface of the can lid 3 with laser light, and therefore becomes shape data that represents the uneven shape of the linearly arranged measurement points.

[0027] FIG. 4 shows an example of the shape data, which represents a predetermined range on both sides of the center of the can lid 3. The data shown here is the distance from the installation position of the laser sensor 5 or a reference point predetermined based on the installation position to the measurement point (the point of laser light irradiation) on the surface of the can lid 3. Therefore, the larger the amount of deformation (depression) due to negative pressure, the larger the value. As a result, the shape on the coordinate system becomes convex upward, as opposed to the actual shape, which is concave downward. The shape data shown in FIG. 4 is data for a range t of approximately equal dimensions from the center of the finger hook 21 through the center of the can lid 3 to the opposite side of that center. The symbol "CD" in FIG. 4 indicates the measurement value at the center of the can lid 3, which is the measurement value inside the aforementioned finger hook recess 22. Therefore, the amount of deformation (depression) in this part of the can lid 3 is the largest.

[0028] 4, the depth of recess 22 gradually decreases from recess 22 toward panel 16. This change in shape and the deformation due to the negative pressure combine to cause the amount of deformation in the recessed direction to gradually decrease on the left side. A small flat area exists between recess 22 and finger hook 21 (rear end of tab 19), and this flat area also deforms in accordance with the overall deformation of can lid 3. Therefore, the measurement value (shape data) at this flat area appears as a line sloping downward to the left in FIG. 4.

[0029] The adjacent finger hook 21 (rear end of tab 19) protrudes from the front side of the can lid 3, and therefore its measurement value (shape data) appears as a line that bends downward into a rectangular shape in Fig. 4. The portion further to the left in Fig. 4 is part of the panel 16 that is exposed inside the ring-shaped part of the finger hook 21, and therefore its measurement value (shape data) appears as a curved line that is nearly straight, with the amount of depression increasing toward the center of the can lid 3.

[0030] On the other hand, the portion on the opposite side of the center point indicated by the symbol "CD" in Figure 4 from the tab 19 is an inclined portion 24 rising from the bottom surface of the recess 22 toward the height portion 23. Therefore, the measurement value (shape data) of this portion is a superposition of the change in distance based on the shape and the change in distance due to the deformation of the recess caused by the negative pressure, and appears as a slightly convex curved line upward in Figure 4. The portion following this to the right in Figure 4 is the surface of the height portion 23, and although this portion is higher toward the surface of the can lid 3 than the panel portion 16, the deformation of this recess is similar to the deformation of the panel portion 16. Therefore, the measurement value or shape data of this portion appears as a curved line on the left side of Figure 4 that is approximately symmetrical to the measurement value (shape data) of the panel portion 16.

[0031] The internal pressure inspection device according to the present invention accurately measures the amount of deformation (or height) of can 1 according to the internal pressure based on shape data including measurement values ​​unrelated to deformation due to negative pressure such as the above-mentioned finger hook 21 (tab 19) or external disturbances, and determines the internal pressure based on the measurement results. An example of this control will be described below. The control described below is executed by the above-mentioned controller 9 (particularly its sequencer 13).

[0032] (i) The internal pressure of the can 1 appears as the amount of deformation of the panel portion 16 and the height portion 23 of the can lid 3, so first, a range t of large deformation suitable for judging the internal pressure is determined. The point of greatest deformation is the center of the can lid 3, and this point always appears in the shape data, so a predetermined range centered on the point of greatest deformation can be set as the measurement range. In this case, since the moving speed of the can 1 is known in advance, the above range can be set as a predetermined time width.

[0033] (ii) Data relating to the tab 19 is also excluded. The maximum value of the deformation amount within the distance range from the center point of the can lid 3 to a point slightly beyond the inclined portion 24 is almost fixed, as shown in FIG. 4. Therefore, by defining this range as a range that does not include the tab 19 (a predetermined range in this invention), it is possible to exclude the measurement values ​​caused by the tab 19. This range can be determined based on the conveying speed of the can 1, the elapsed time from the time the photoelectric sensor 7 detected the can 1, etc.

[0034] (iii) The maximum value within the above range (the measurement value at the most recessed point) is taken as the measurement value at the center of the can lid 3, and the relationship of the tab 19 to that measurement point can be determined from the time before and after each measurement was taken. Based on this relationship, it is possible to determine, for example, which data in the shape data shown in Figure 4 is on the tab 19 side and which data is on the opposite side, i.e., the side of the inclined portion 24 following the height portion 23. In other words, a data group including the measurement point of this invention is selected.

[0035] (iv) In the data group thus selected, the slope between two adjacent data points is calculated in sequence. This calculation process (control process) corresponds to the slope calculation means in this invention.

[0036] (v) The obtained slopes between two points are sequentially compared to determine the amount of change in slope, and the point where the amount of change is greatest is derived as the measurement point. This calculation process (control process) corresponds to the measurement point derivation means in this invention. The measurement point derived in this way is indicated by the symbol "PH" in Figure 4, and as can be seen from the displacement waveform shown in Figure 4, this is the boundary (bend) between the aforementioned slope portion 24 and the upper surface (surface) of the height portion 23.

[0037] (vi) Based on the measurement value at measurement point PH thus obtained, the displacement (deformation) corresponding to the internal pressure of can 1 is calculated. Specifically, the measurement value at measurement point PH (distance from the reference point) is corrected using a temperature-based distance correction value and a height correction value, and the resulting value is compared with a predetermined reference value. Here, the distance correction value is a correction value adopted based on the temperature of can 1 obtained by temperature sensor 8. In the case of food cans, the higher the temperature of can 1, the higher the internal pressure (decreasing the degree of vacuum) and the smaller the deformation. Therefore, if room temperature (or normal temperature) of approximately 25°C is used as the reference temperature, for example, the measurement value is corrected to match the measurement value at that reference temperature. Note that the relationship between the temperature of can 1 and the internal pressure can be determined in advance, and the distance correction value can be calculated based on this relationship and the detected can temperature. The height correction value is a correction value used to prevent any change in height of can 1 on conveyor 4 from affecting the measurement value used to determine internal pressure. In the example shown in Fig. 1, the difference between the height obtained by the second laser sensor 6 and a predetermined height reference value can be used as the height correction value. Note that in the example shown in Fig. 1, the area measured by the second laser sensor 6 is a countersink portion with a relatively large area, so the error in the measurement value is small. The calculation process (control process) for determining the temperature-dependent correction value corresponds to the distance correction value calculation means in this invention, the calculation process (control process) for correcting the measurement value using the correction value corresponds to the distance correction means in this invention, the calculation process (control process) for measuring the height of the can 1 as a measurement value obtained by the second laser sensor 6 corresponds to the height measurement means in this invention, and the calculation process (control process) for correcting the distance based on the measured height corresponds to the height correction means in this invention.

[0038] (vii) If the internal pressure is normal, in the case of a food can, it is within the reference value (or range) for judging the amount of depression deformation of the can lid 3 (measurement point PH described above). In contrast, if there is a sealing defect (poor sealing), the internal pressure increases (the degree of vacuum decreases), and the amount of deformation decreases. Therefore, the internal pressure is judged to be good or bad by comparing the data (distance) obtained by the above measurement and correction with a judgment threshold value prepared in advance. If the internal pressure is judged to be bad, in the example shown in Figure 1, a command signal is output from the controller 9 to the rejection device, and the can 1 judged to have bad internal pressure is rejected to a disposal location.

[0039] As described above, the internal pressure testing device of the present invention sequentially calculates the slope of data between two points within a predetermined region, determines the point where the slope is greatest as the measurement point, and judges the internal pressure of the can 1 based on the distance of the measurement point from a reference point, i.e., the amount of deformation. In the case of a can 1 in which the finger grip 21 for the tab 19 is located in the center of the can lid 3 and the corresponding recess 22 is provided, such a measurement point is the boundary (contour) of the slope 24 that defines the height section 23, which prevents the tab 19 from protruding beyond the surface of the can lid 3. Because this contour section is not a single point but has a certain length or extent, even if the position of the can 1 on the conveyor 4 shifts slightly during transport, there is no significant error or change in the measured distance from the reference point. In other words, the device of the present invention can accurately determine the internal pressure while minimizing the influence of positional shifts of the can 1 being tested.

[0040] Here, the reason why the deformation amount (distance) and the internal pressure can be accurately measured and determined based on it even when the point where the slope of the data from the two points is maximum is explained. Figure 5 shows the results of actual measurements of the internal pressure and deformation amount of the can, with the horizontal axis representing negative pressure (-kPa) and the vertical axis representing the depression deformation amount (mm). Line A represents the deformation amount measured at the center of the can lid, and line B represents the deformation amount measured at the aforementioned measurement point, i.e., the boundary (bend) between the sloped portion and the height portion. The deformation amount was calculated based on the distance from a reference point measured by placing a stylus on the surface of the can lid.

[0041] As can be seen from the measured values ​​in Figure 5, the amount of deformation for each internal pressure varies slightly for each can. However, the amount of deformation at the center of the can lid and the measurement points increases with increasing vacuum, and the amount of deformation saturates once the vacuum reaches a certain level. Furthermore, although the amount of deformation at the measurement points is smaller than that at the can center, the relationship between each can internal pressure and the amount of deformation is nearly the same. This indicates that the amount of deformation at the measurement points is correlated with and reflects the can internal pressure. Therefore, even when the device of this invention measures the amount of deformation at the measurement points described above to determine whether the can is in good condition, the accuracy of the determination is comparable to that of measuring the amount of deformation at the can center, and the internal pressure can be determined with high accuracy. In fact, because the device of this invention measures the distance between the measurement points, which are located in a somewhat spread-out area, the measurement accuracy is less affected by misalignment of the can. In this respect, the accuracy of distance measurement or internal pressure determination can be improved compared to conventional devices that measure the distance at the can center.

[0042] In this invention, the amount of deformation of the can lid may be calculated by various conventionally known calculation methods. That is, the reference point may be the installation position of the laser sensor, the top of the seam of the can lid, or a position obtained by correcting either of these, and the amount of deformation of the can lid may be calculated based on the reference point, the height of the can, and the measured distance. [Explanation of symbols]

[0043] 1 can 2 Can body 3 can lids 4 Conveyor 5,6 Laser sensors 7 Photoelectric Sensor 8 Temperature Sensor 9 Controller 10 Analog input / output circuit 11 Digital input / output circuit 12 A / D converter 13 Sequencer 14 Setting device 15 Chuck Wall 16 Panel section 17 Score Line 18 Opening piece 19 tabs 20 rivets 21 Finger rest 22 recess 23 Height section 24 Slope section PH measurement point

Claims

1. A can internal pressure inspection device that irradiates a surface of a can lid sealing a can with laser light, and scans the laser light relatively in a conveyance direction of the can to continuously measure the distance from a predetermined reference point to the surface using a laser displacement sensor, obtains shape data about the surface based on the continuous distance measurements, and judges whether the internal pressure of the can is good or bad based on the shape data, a gradient calculation means for sequentially calculating gradients of the measurement values ​​at two points adjacent to each other in the scanning direction in a predetermined region of the center of the can lid in accordance with the shape data; a measurement point derivation means for deriving a point where the calculated change in the slope is maximum as a measurement point; The apparatus is configured to determine whether the internal pressure of the can is good or bad based on the distance of the measurement point from the reference point. A can internal pressure inspection device characterized by:

2. 2. The can internal pressure inspection device according to claim 1, a temperature sensor for detecting the temperature of the can; a correction value calculation means for calculating a distance correction value based on a predetermined relationship between the temperature of the can and a distance correction value and the detected temperature of the can; a distance correction means for correcting the distance of the measurement point from the reference point using the distance correction value calculated by the correction value calculation means; Further provided with and determining whether the internal pressure of the can is good or bad based on the distance of the measurement point from the reference point corrected by the distance correction value. A can internal pressure inspection device characterized by:

3. 3. The can internal pressure inspection device according to claim 1 or 2, a height measuring means for measuring the height of the can when the laser displacement sensor is measuring the distance; a height correction value calculation means for calculating a height correction value based on the height of the can measured by the height measurement means and a predetermined reference height; a height correction means for correcting the height of the reference point or the distance measured by the laser displacement sensor using the height correction value; The can internal pressure inspection device further comprises:

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