Method for detecting pinhole and device for detecting pinhole

Abstract

An event-based vision sensor (15) outputs, to a determination device (16), event data including the position of a pixel (50a) that has detected an event, the occurrence time of the event, and the polarity of the luminance change of the event indicating whether the event is a P-type event in which luminance increases or an N-type event in which the luminance decreases. The determination device (16) determines, on the basis of the event data, whether or not: an event number condition in which the number of events, which is an integrated value of the number of occurrences of events in a prescribed integration period (T), is equal to or greater than a first event number threshold value; or an event distribution condition in which events are distributed in the conveyance direction of metal foil (100), is satisfied. When the event number condition or the event distribution condition is satisfied, the determination device (16) determines that a pinhole (PH) has occurred in the metal foil (100).

Description

Pinhole detection method and pinhole detection device

[0001] The present disclosure relates to a pinhole detection method and a pinhole detection device.

[0002] Patent Document 1 describes a pinhole detection device that detects pinholes that occur in an object to be inspected. The pinhole detection device includes a light source, an optical lens, and a detector. The light source irradiates the object to be inspected with light. The optical lens is disposed between the light source and the object to be inspected. The light from the light source is converged by the optical lens and then passes through a pinhole in the object to be inspected. The detector has a detection element such as a photomultiplier tube. The detector detects the light that has passed through the pinhole.

[0003] Japanese Patent Application Laid-Open No. 2022-173728

[0004] In detecting such pinholes, there is a demand for the ability to detect pinholes with smaller diameters. However, in the case of pinhole detection using a photomultiplier tube as in Patent Document 1, even if the illuminance of the light source is increased, the detection performance cannot be improved as the noise simply increases.

[0005] A pinhole detection method for solving the above problems is a pinhole detection method for detecting a pinhole that has occurred in an object being transported, wherein the Y direction, which is the transport direction of the object being inspected, is perpendicular to the Z direction, which is the thickness direction of the object being inspected, and the pinhole detection method comprises: a light source irradiating light toward the object being inspected in the Z direction; and an event-based vision sensor, which is arranged on the opposite side of the object being inspected in the Z direction from the light source, capturing an image of the object being transported; the event-based vision sensor has a plurality of pixels that can detect a change in brightness as an event; and a position of the pixel that detected the event. outputting event data to a determination device, the event data including the occurrence time of the event and the polarity of the luminance change of the event, indicating whether the event is a P-type event in which luminance increases or an N-type event in which luminance decreases; determining by the determination device, based on the event data, whether an event number condition, where the number of events, which is an integrated value of the number of occurrences of the events in a predetermined integration period, is equal to or greater than a first event number threshold, or an event distribution condition, where the events are distributed in the Y direction, is satisfied; and if the event number condition or the event distribution condition is satisfied, the determination device determines that the pinhole has occurred in the object being inspected.

[0006] If a pinhole exists in the object being inspected, the luminance of light from the light source changes as it passes through the pinhole. Furthermore, as the object being inspected is transported, the position of the pinhole moves in the Y direction, and the position at which the luminance changes also moves in the Y direction. Each pixel of the event-based vision sensor detects an event caused by light passing through the pinhole. As the pinhole approaches each pixel, the luminance increases, and each pixel detects a P-type event. On the other hand, as the pinhole moves away from each pixel, the luminance decreases, and each pixel detects an N-type event. Therefore, when a pinhole exists in the object being inspected, the number of P-type events and N-type events increases compared to when the object being inspected does not have a pinhole. Furthermore, when a pinhole exists in the object being inspected, events are distributed in the Y direction.

[0007] According to the above method, the determination device determines that a pinhole has occurred in the object to be inspected when an event number condition that the number of events is equal to or greater than a first event number threshold or an event distribution condition that the events are distributed in the Y direction is satisfied, thereby making it possible to detect a pinhole that has occurred in the object to be inspected.

[0008] When detecting pinholes using an event-based vision sensor in this way, the higher the illuminance of the light source, the wider the distribution range of events in the Y direction and the greater the number of events. This makes it possible to detect pinholes with smaller diameters, thereby improving pinhole detection performance.

[0009] In the pinhole detection method, the number of pixel columns in which the event was detected during the integration period among the plurality of pixel columns aligned in the Y direction may be the number of pixel columns in the Y direction, and the event distribution condition may include a first event distribution condition in which the number of pixel columns in the Y direction is equal to or greater than a Y direction pixel column number threshold.

[0010] As described above, if a pinhole occurs in the object being inspected, the pinhole moves in the Y direction, causing events to be distributed in the Y direction. Therefore, if the transport speed of the object being inspected is fast, the number of pixel columns in the Y direction will be large. If the event detected by the event-based vision sensor is an event caused by light passing through a pinhole, the number of pixel columns in the Y direction will be larger than if the event is caused by noise.

[0011] According to the above method, the event distribution condition includes a first event distribution condition that the number of pixel columns in the Y direction is equal to or greater than a threshold value for the number of pixel columns in the Y direction. This allows the determination device to determine whether events distributed in the Y direction are caused by light transmitted through a pinhole or by noise. This improves the accuracy of pinhole detection.

[0012] In the pinhole detection method, the number of pixel columns in which the event was detected during the integration period among a plurality of pixel columns aligned in an X direction orthogonal to both the Y direction and the Z direction may be the number of pixel columns in the X direction, and the number of pixel columns in which the event was detected during the integration period among a plurality of pixel columns aligned in the Y direction may be the number of pixel columns in the Y direction, and the event distribution condition may include a first event distribution condition in which a ratio of the number of pixel columns in the Y direction to the number of pixel columns in the X direction is equal to or greater than a ratio threshold.

[0013] As described above, if a pinhole occurs in the object being inspected, the pinhole moves in the Y direction, causing events to be distributed in the Y direction. Therefore, if the transport speed of the object being inspected is fast, the number of pixel columns in the Y direction will be large. If the event detected by the event-based vision sensor is an event caused by light passing through a pinhole, the number of pixel columns in the Y direction will be larger than if the event is caused by noise.

[0014] On the other hand, because the pinhole hardly moves in the X direction, the distribution range of events in the X direction is small. Therefore, if the event detected by the event-based vision sensor is an event caused by light passing through a pinhole, the number of pixel columns in the X direction will be smaller than if the event is caused by noise. Therefore, if the event detected by the event-based vision sensor is an event caused by light passing through a pinhole, the ratio of the number of pixel columns in the Y direction to the number of pixel columns in the X direction will be larger than if the event is caused by noise.

[0015] According to the above method, the event distribution condition includes a first event distribution condition that the ratio of the number of pixel columns in the Y direction to the number of pixel columns in the X direction is equal to or greater than a ratio threshold. This allows the determination device to determine whether events distributed in the Y direction are events caused by light transmitted through a pinhole or events caused by noise. This improves the accuracy of pinhole detection.

[0016] In the pinhole detection method, the event distribution condition may include a second event distribution condition that the integration period during which the number of events is equal to or greater than a second event number threshold occurs a predetermined number of times in succession.

[0017] As described above, if a pinhole occurs in the object being inspected, events are distributed in the Y direction. Therefore, if the transport speed of the object being inspected is slow, an event will occur in each of multiple consecutive integration periods. If the event detected by the event-based vision sensor is an event caused by light passing through a pinhole, the number of consecutive integration periods in which the event occurs will be greater than if the event is caused by noise.

[0018] According to the above method, the event distribution conditions include a second event distribution condition that the number of events is equal to or greater than the second event threshold and that the accumulation period is a predetermined number of consecutive periods. This allows the determination device to determine whether an event detected by the event-based vision sensor is an event caused by light passing through a pinhole or an event caused by noise, thereby improving pinhole detection accuracy.

[0019] In the above pinhole detection method, the determination device may determine whether the event number condition or the event distribution condition is satisfied by using only events that occur consecutively in the Y direction at the same position in the X direction perpendicular to both the Y direction and the Z direction, among the events detected by the event-based vision sensor.

[0020] If the events detected by the event-based vision sensor are caused by white noise with a short occurrence time, they will not occur consecutively in the Y direction at the same position in the X direction. On the other hand, if the events detected by the event-based vision sensor are not caused by white noise, they will occur consecutively in the Y direction at the same position in the X direction.

[0021] According to the above method, the determination device determines whether the event number condition or the event distribution condition is satisfied by using only events that occur consecutively in the Y direction at the same position in the X direction. That is, the determination device determines whether the event number condition or the event distribution condition is satisfied by using only events that are not caused by white noise, in other words, excluding events caused by white noise. Therefore, the pinhole detection accuracy can be improved.

[0022] In the above pinhole detection method, the light source and the event-based vision sensor may be provided in multiple locations in the Y direction, and the determination device may determine that the pinhole has occurred in the inspected object when the event number condition or the event distribution condition is satisfied in each of the multiple event-based vision sensors.

[0023] According to the above method, the determination device determines that a pinhole has occurred when the event count condition or event distribution condition is satisfied in each of the multiple event-based vision sensors. This improves pinhole detection accuracy compared to when the determination device determines that a pinhole has occurred when the event count condition or event distribution condition is satisfied in a single event-based vision sensor.

[0024] In the above pinhole detection method, the determination device may determine that the pinhole has occurred in the inspected object if the event number condition is satisfied in each of the multiple event-based vision sensors and the events in the multiple event-based vision sensors occur at the same position in the X direction, which is perpendicular to both the Y direction and the Z direction.

[0025] Even when the object to be inspected is transported, the position of the pinhole hardly moves in the X direction. Therefore, if an event is caused by light that has passed through the pinhole, the event will occur at the same position in the X direction. According to the above method, the determination device determines that a pinhole has occurred in the object to be inspected if events occur at the same position in the X direction in multiple event-based vision sensors. This further improves the accuracy of pinhole detection.

[0026] In the above pinhole detection method, the illuminance of the light source may be set to be different for each light source, and the determination device may determine that the pinhole has occurred in the inspected object if the event number condition is satisfied in each of the multiple event-based vision sensors and the event-based vision sensor arranged with the light source having higher illuminance has a larger number of events.

[0027] The higher the illuminance of the light source, the more events occur, and therefore the number of events increases. According to the above method, the determination device determines that a pinhole has occurred when the number of events is greater for an event-based vision sensor located near a light source with higher illuminance. This further improves the accuracy of pinhole detection.

[0028] In the above pinhole detection method, the detection range of the event-based vision sensor may be set differently for each event-based vision sensor, and the determination device may determine that the pinhole has occurred in the inspected object if the event number condition is satisfied in each of the multiple event-based vision sensors and the larger the detection range of the event-based vision sensor, the greater the number of consecutive accumulation periods that satisfy the event number condition.

[0029] The larger the detection range of the event-based vision sensor, the longer it takes for a pinhole to pass through the detection range, and therefore the greater the number of consecutive integration periods that satisfy the event count condition. According to the above method, the determination device determines that a pinhole has occurred when the number of consecutive integration periods that satisfy the event count condition is greater for an event-based vision sensor with a larger detection range. This further improves the accuracy of pinhole detection.

[0030] In the pinhole detection method, the object to be inspected may be a long strip that is transported in a longitudinal direction. In the pinhole detection method, the first event number threshold may include two types of event number thresholds: a center event number threshold and an edge event number threshold that is greater than the center event number threshold, the event number condition may include a first event number condition under which the number of events at a center in a widthwise direction of the object to be inspected is equal to or greater than the center event number threshold, and a second event number condition under which the number of events at an edge in the widthwise direction of the object to be inspected is equal to or greater than the edge event number threshold, and the determination device may determine that the pinhole has occurred in the object to be inspected if at least one of the first event number condition and the second event number condition is satisfied.

[0031] Light from the light source may pass outside the ends of the object's width, and may find its way around to the event-based vision sensor. In this case, noise-induced events are more likely to occur at the ends of the object's width than at the center, making the number of events more likely to increase at the ends than at the center.

[0032] According to the above method, the first event number threshold includes two types: a center event number threshold and an edge event number threshold that is greater than the center event number threshold. The determination device determines that a pinhole has occurred in the object to be inspected when at least one of the first event number condition, under which the number of events at the center in the widthwise direction of the object to be inspected is equal to or greater than the center event number threshold, and the second event number condition, under which the number of events at the edge in the widthwise direction of the object to be inspected is equal to or greater than the edge event number threshold, is satisfied.

[0033] This allows pinhole detection to be performed while taking into consideration that the number of events is more likely to increase at each end of the object in the lateral direction than at the center. Therefore, the accuracy of pinhole detection can be improved. Furthermore, if a pinhole occurs in the object, it can be detected whether the pinhole occurs in the center or at an end of the object in the lateral direction.

[0034] In the above pinhole detection method, a marking device arranged downstream of the light source and the event-based vision sensor in the Y direction may apply a mark to the object to be inspected at a position corresponding to the pinhole in the Y direction when the determination device determines that the pinhole has occurred in the object to be inspected.

[0035] According to the above method, when the determination device determines that a pinhole has occurred in the object to be inspected, the marking device applies a mark to the object to be inspected at a position corresponding to the pinhole in the Y direction. The mark makes it easier to identify the pinhole that has occurred in the object to be inspected.

[0036] In the above pinhole detection method, a plurality of inspection areas are set on the object to be inspected so as to be aligned in an X direction perpendicular to both the Y direction and the Z direction, the determination device determines individually whether or not the pinhole has occurred in each of the plurality of inspection areas, and the marking device may apply the mark only to the inspection area determined by the determination device to have the pinhole.

[0037] For example, a portion of an object to be inspected that has a mark applied thereto may be discarded as it is determined that a pinhole has occurred. In this case, if the position of the pinhole in the X direction cannot be determined, the entire object to be inspected in the X direction is discarded. In contrast, according to the above method, the object to be inspected has multiple inspection areas arranged in the X direction. The determination device individually determines whether or not a pinhole has occurred in each of the multiple inspection areas. The marking device applies a mark only to the inspection area that has been determined by the determination device to have a pinhole. This makes it possible to determine which of the multiple inspection areas arranged in the X direction has a pinhole. Therefore, only the inspection areas to which a mark has been applied are discarded, thereby improving yield.

[0038] In the pinhole detection method, the light source may emit light having a peak in the wavelength range of 600 to 660 nm. According to the method, the light from the light source is more likely to be diffracted, causing events to occur over a wider range, thereby widening the distribution range of events in the Y direction and increasing the number of events. Therefore, it becomes easier to detect small-diameter pinholes.

[0039] The pinhole detection device that solves the above problem is a pinhole detection device configured to detect pinholes that occur in an object being transported for inspection, wherein the Y direction, which is the transport direction of the object being inspected, is perpendicular to the Z direction, which is the thickness direction of the object being inspected, and the pinhole detection device includes a light source configured to irradiate light toward the object being inspected in the Z direction, and an event-based vision sensor that is placed on the opposite side of the object being inspected from the light source in the Z direction, sandwiching the object being inspected, in order to capture an image of the object being transported, and the pinhole detection device has a plurality of pixels that can detect a change in luminance as an event, and the position of the pixel that detected the event and the time when the event occurred are recorded. and the polarity of the luminance change of the event, indicating whether the event is a P-type event in which luminance increases or an N-type event in which luminance decreases; and a determination device, wherein the determination device is configured to determine, based on the event data, whether an event number condition, where the number of events, which is the integrated value of the number of occurrences of the events in a predetermined integration period, is equal to or greater than a first event number threshold, or an event distribution condition, where the events are distributed in the Y direction, is satisfied, and if the event number condition or the event distribution condition is satisfied, determine that the pinhole has occurred in the object being inspected.

[0040] According to the above configuration, the determination device determines that a pinhole has occurred in the object to be inspected when an event count condition that the number of events is equal to or greater than a first event count threshold or an event distribution condition that the events are distributed in the Y direction is satisfied, thereby making it possible to detect a pinhole that has occurred in the object to be inspected.

[0041] When detecting pinholes using an event-based vision sensor in this way, the higher the illuminance of the light source, the wider the distribution range of events in the Y direction and the greater the number of events. This makes it possible to detect pinholes with smaller diameters, thereby improving pinhole detection performance.

[0042] According to the present invention, it is possible to improve the pinhole detection performance.

[0043] FIG. 1 is a plan view of a pinhole detection device. FIG. 2 is a plan view of a bipolar electrode of FIG. 1. FIG. 3 is a cross-sectional view of the bipolar electrode of FIG. 2. FIG. 4 is a cross-sectional view of the pinhole detection device of FIG. 1. FIG. 5 is a cross-sectional view of the pinhole detection device of FIG. 1. FIG. 6 is a schematic diagram showing the configuration of the event-based vision sensor of FIG. 1. FIG. 7 is a perspective view of the pinhole detection device of FIG. 1. FIG. 8 is a plan view showing the detection range of the event-based vision sensor of FIG. 1. FIG. 9 is a block diagram showing the configuration of the pinhole detection device of FIG. 1. FIG. 10 is a diagram showing the correspondence relationship between the pinhole diameter and the metal foil conveyance speed and the judgment condition. FIG. 11 is a flowchart showing the judgment process executed by the judgment device. FIG. 12 is a graph showing an example of the change in the number of P-type events over time. FIG. 13 is a diagram showing an example of the event detection result by the event-based vision sensor. FIG. 14 is a distribution diagram of events. FIG. 15 is a graph showing an example of the change in the number of N-type events over time. FIG. 16 is a graph showing an example of the change in the total number of events over time. Fig. 17 is a graph showing an example of the number of P-type events at each coordinate in the short-side direction of the metal foil. Fig. 18 is a cross-sectional view showing a pinhole detection device in a modified example. Fig. 19 is a plan view showing the detection range of the event-based vision sensor in Fig. 18. Fig. 20 is a graph showing an example of the change in the number of P-type events over time. Fig. 21 is a plan view showing a pinhole detection device in a modified example. Fig. 22 is a cross-sectional view showing a pinhole detection device in a modified example.

[0044] An embodiment of a pinhole detection method and a pinhole detection device will be described below with reference to Figures 1 to 15. The pinhole detection method and the pinhole detection device of this embodiment are applied to the detection of pinholes occurring in a metal foil, which is an object to be inspected.

[0045] Before describing the pinhole detection method and device, the metal foil to be inspected will be described. As shown in FIG. 1 , the metal foil 100 is in the form of a long strip. The metal foil 100 of this embodiment is a nickel-plated steel sheet in which the surface of the steel sheet is nickel-plated. The metal foil 100 of this embodiment is used in a nickel-metal hydride battery. The nickel-metal hydride battery is formed by stacking multiple electrodes 200 shown in FIGS. 2 and 3 .

[0046] 2 and 3 , the electrode 200 includes a current collector 210, a negative electrode active material layer 211 provided on a first surface 210a of the current collector 210, and a positive electrode active material layer 212 provided on a second surface 210b of the current collector 210. In other words, the electrode 200 is a bipolar electrode in which active material layers are provided on both surfaces of the current collector 210.

[0047] The current collector 210, the negative electrode active material layer 211, and the positive electrode active material layer 212 each have a rectangular shape. The longitudinal and lateral dimensions of the negative electrode active material layer 211 are larger than the longitudinal and lateral dimensions of the positive electrode active material layer 212, respectively. The pair of long sides 211a and the pair of short sides 211b of the negative electrode active material layer 211 are located outside the pair of long sides 212a and the pair of short sides 212b of the positive electrode active material layer 212, respectively. The longitudinal and lateral dimensions of the negative electrode active material layer 211 are smaller than the longitudinal and lateral dimensions of the current collector 210. The pair of long sides 211a and the pair of short sides 211b of the negative electrode active material layer 211 are located inside the pair of long sides 210c and the pair of short sides 210d of the current collector 210, respectively. The current collector 210 has exposed portions 210e between each long side 211a of the negative electrode active material layer 211 and each long side 210c of the current collector 210, where the negative electrode active material layer 211 and the positive electrode active material layer 212 are not formed.

[0048] The metal foil 100 of this embodiment is used as the current collector 210 of such an electrode 200. Therefore, if a pinhole PH occurs in the metal foil 100, a pinhole PH also occurs in the current collector 210. If a pinhole PH occurs in the current collector 210, there is a risk of a short circuit between the positive electrode and the negative electrode via the pinhole PH.

[0049] The manufacturing method of the electrode 200 includes an inspection process for inspecting the metal foil 100, an anode active material layer forming process for forming the anode active material layer 211, a cathode active material layer forming process for forming the cathode active material layer 212, and a cutting process for cutting the metal foil 100.

[0050] In the inspection step, the metal foil 100 is inspected for pinholes PH. The pinhole detection method of this embodiment is used in this inspection step. In the anode active material layer formation step, a cathode active material mix is ​​applied to the first surface 100a of the metal foil 100. In FIG. 1 , the coated area Ac to which the anode active material mix is ​​applied is indicated by a rectangular frame with two-dot chain lines. The anode active material mix is ​​applied in four rows at predetermined intervals in the lateral direction of the metal foil 100. Furthermore, the anode active material mix is ​​applied in each row at predetermined intervals in the longitudinal direction of the metal foil 100. Then, as the anode active material mix dries, a cathode active material layer 211 is formed on the first surface 100a of the metal foil 100.

[0051] In the positive electrode active material layer forming step, a positive electrode active material mix is ​​applied to the second surface 100b (see FIG. 4 ), which is the surface opposite to the first surface 100a of the metal foil 100. The positive electrode active material mix is ​​applied to a position corresponding to the negative electrode active material layer 211. That is, the positive electrode active material mix is ​​applied in four rows at predetermined intervals in the short direction of the metal foil 100. Furthermore, the positive electrode active material mix is ​​applied in each row at predetermined intervals in the long direction of the metal foil 100. Then, as the positive electrode active material mix dries, a positive electrode active material layer 212 is formed on the second surface 100b of the metal foil 100.

[0052] In the cutting step, the metal foil 100 having the negative electrode active material layer 211 formed on the first surface 100a and the positive electrode active material layer 212 formed on the second surface 100b is cut into a desired shape. In this embodiment, the metal foil 100 is cut into a rectangular shape.

[0053] Specifically, the metal foil 100 is cut along a first cutting line L1, a second cutting line L2, a third cutting line L3, a fourth cutting line L4, and a fifth cutting line L5 that extend in the longitudinal direction of the metal foil 100. The first cutting line L1, the second cutting line L2, the third cutting line L3, the fourth cutting line L4, and the fifth cutting line L5 are arranged at equal intervals in this order from one side to the other in the widthwise direction of the metal foil 100. The distance between two adjacent cutting lines L1, L2, L3, L4, and L5 in the widthwise direction of the metal foil 100 is larger than the dimension of a coated area Ac in the widthwise direction of the metal foil 100. The coated area Ac is located midway between two adjacent cutting lines L1, L2, L3, L4, and L5 in the widthwise direction of the metal foil 100.

[0054] The metal foil 100 is cut along a plurality of sixth cutting lines L6 that extend in the short direction of the metal foil 100 and are arranged at equal intervals in the longitudinal direction of the metal foil 100. The distance between two adjacent sixth cutting lines L6 in the longitudinal direction of the metal foil 100 is greater than the dimension of the coated area Ac in the longitudinal direction of the metal foil 100. The coated area Ac is located midway between two adjacent sixth cutting lines L6 in the longitudinal direction of the metal foil 100.

[0055] The metal foil 100 is cut along the first to sixth cutting lines L1 to L6, thereby forming a plurality of electrodes 200 from one metal foil 100. At this time, both ends of the metal foil 100 in the short direction, specifically the portions of the metal foil 100 located outside the first cutting line L1 and the fifth cutting line L5 in the short direction, are discarded. Furthermore, of the formed plurality of electrodes 200, any electrode 200 in which a pinhole PH occurs in the current collector 210 is discarded.

[0056] Next, the pinhole detection device 10 will be described. <Conveying Device> As shown in FIG. 4 , the pinhole detection device 10 includes a conveying device 11 that conveys the metal foil 100. The Y direction, which is the conveying direction of the metal foil 100, is perpendicular to the Z direction, which is the thickness direction of the metal foil 100. The conveying device 11 of this embodiment conveys the metal foil 100 in the longitudinal direction. Therefore, in this embodiment, the Y direction is parallel to the longitudinal direction of the metal foil 100. Furthermore, the X direction, which is perpendicular to both the Y direction and the Z direction, is parallel to the width direction of the metal foil 100. The conveying device 11 of this embodiment includes a payout roller 11a and a take-up roller 11b. The metal foil 100 is wound around the payout roller 11a. As the take-up roller 11b rotates, the metal foil 100 unwound from the payout roller 11a is wound around the take-up roller 11b, thereby conveying the metal foil 100. In this embodiment, the metal foil 100 is conveyed so that the first surface 100a is positioned on the upper side and the second surface 100b is positioned on the lower side. The conveying speed of the metal foil 100 in this embodiment is, for example, 50 to 500 m / min.

[0057] 4 and 5 , the pinhole detection device 10 includes a box-shaped housing 12. The housing 12 in this embodiment is made of aluminum or SUS. The housing 12 in this embodiment is composed of a first housing portion 12a disposed above the metal foil 100 and a second housing portion 12b disposed below the metal foil 100. The first housing portion 12a has an upper wall 121 and a cylindrical first peripheral wall 122 extending downward from the upper wall 121 toward the metal foil 100. The second housing portion 12b has a lower wall 123 and a cylindrical second peripheral wall 124 extending upward from the lower wall 123 toward the metal foil 100. The interior of the housing 12, i.e., the space surrounded by the first housing portion 12a and the second housing portion 12b, is a darkroom. In order to enhance the function as a darkroom, the tip of the first peripheral wall 122 and the tip of the second peripheral wall 124 are each positioned as close as possible to the metal foil 100 without coming into contact with the metal foil 100 .

[0058] <Light Source> The pinhole detection device 10 includes a light source 13. The light source 13 is configured to irradiate light toward the metal foil 100 in the Z direction. The light source 13 is disposed within the housing 12. The light source 13 is a line light. The light source 13 extends along the short direction of the metal foil 100, i.e., the X direction. In this embodiment, the light source 13 is disposed below the metal foil 100 within the second housing portion 12b. The light source 13 irradiates light toward the second surface 100b of the metal foil 100. The light source 13 of this embodiment is a white LED. That is, the light source 13 irradiates the metal foil 100 with white light. The illuminance of the light source 13 of this embodiment may be 2 to 10,000,000 lx. The illuminance of the light source 13 is preferably 4 to 8,000,000 lx. The illuminance of the light source 13 is more preferably 5 to 6,000,000 lx. In order to ensure a sufficient luminous flux to be irradiated onto the metal foil 100, it is preferable that the distance from the light source 13 to the metal foil 100 is short.

[0059] 5, the pinhole detection device 10 includes two masks 14. One of the two masks 14 is disposed at one end of the metal foil 100 in the lateral direction within the housing 12, and the other is disposed at the other end of the metal foil 100 in the lateral direction within the housing 12. The mask 14 prevents light from the light source 13 from passing outside both ends of the metal foil 100 in the lateral direction, thereby preventing the light from circulating from the side facing the second surface 100b to the side facing the first surface 100a.

[0060] Each mask 14 in this embodiment has a brush holder 41 and a brush 42 held by the brush holder 41. The two brush holders 41 are positioned outside both ends of the metal foil 100 in the lateral direction. The brush 42 is formed of bristles made of highly heat-resistant synthetic fibers. The synthetic fibers are, for example, polyester or nylon. The brush 42 extends from the brush holder 41 toward the metal foil 100. Both ends of the metal foil 100 in the lateral direction, specifically, the portions of the metal foil 100 located outside the first cutting line L1 and the fifth cutting line L5 in the lateral direction, pass through the brush 42 as the metal foil 100 is transported.

[0061] The brush holder 41 is fixed to a bracket 43. The bracket 43 is fixed to the housing 12. Therefore, the mask 14 is fixed to the housing 12 via the bracket 43. In this embodiment, the bracket 43 is made of aluminum or SUS. In this embodiment, the bracket 43 is U-shaped. The bracket 43 has a base 43a extending in the vertical direction, a first extension 43b extending from the upper end of the base 43a, and a second extension 43c extending from the lower end of the base 43a. The brush holder 41 is located between the base 43a and the brush 42 in the short-side direction of the metal foil 100. The mask 14 is located between the first extension 43b and the second extension 43c. The first extension 43b is located above the mask 14. The second extension 43c is located below the mask 14. The second extending portion 43c is interposed between the light source 13 and the brush 42. The tip of the second extending portion 43c is located at a position that protrudes further than the tip of the brush 42. The second extending portion 43c covers the brush 42 from below.

[0062] 1 and 5 , the pinhole detection device 10 includes an event-based vision sensor (hereinafter referred to as "EVS") 15. The pinhole detection device 10 of this embodiment includes 12 EVSs 15.

[0063] As shown in FIG. 6 , the EVS 15 has an image sensor 50. The image sensor 50 is composed of a plurality of pixels 50a. The plurality of pixels 50a are arranged in a two-dimensional grid pattern. The number of pixels in the image sensor 50 of this embodiment is several hundred to several thousand pixels by several hundred to several thousand pixels. Each pixel 50a has a light receiving unit 51 and a luminance change detection unit 52. The light receiving unit 51 converts light incident on the pixel 50a into an input voltage Vin. The luminance change detection unit 52 detects luminance changes as events. The luminance change detection unit 52 can detect P-type events in which luminance increases and N-type events in which luminance decreases. The "P" in P-type events stands for positive. The "N" in N-type events stands for negative.

[0064] Specifically, the luminance change detection unit 52 calculates the difference |Vin-Vr| between the input voltage Vin and the reference voltage Vr. If the calculated difference |Vin-Vr| is equal to or greater than the difference threshold Vt and the input voltage Vin is greater than the reference voltage Vr, the luminance change detection unit 52 detects a P-type event. If the calculated difference |Vin-Vr| is equal to or greater than the difference threshold Vt and the input voltage Vin is less than the reference voltage Vr, the luminance change detection unit 52 detects an N-type event. If the calculated difference |Vin-Vr| is less than the difference threshold Vt, the luminance change detection unit 52 does not detect either a P-type event or an N-type event. When the luminance change detection unit 52 detects a P-type event or an N-type event, it sets the input voltage Vin at that time as a new reference voltage Vr.

[0065] The plurality of pixels 50 a independently detects such events. The EVS 15 generates event data including the coordinates of the pixel 50 a that detected the event, the time of the event occurrence, and the polarity of the luminance change of the event, which indicates whether the event is a P-type event or an N-type event, and outputs the event data to the determination device 16, which will be described later.

[0066] 4 and 5 , the EVS 15 is disposed on the opposite side of the metal foil 100 from the light source 13 in the thickness direction of the metal foil 100, i.e., in the Z direction. In this embodiment, the EVS 15 is disposed above the metal foil 100 in the first housing part 12a. The EVS 15 captures an image of the first surface 100a of the metal foil 100. The pixels 50a are arranged in the longitudinal direction and lateral direction of the metal foil 100. In other words, the pixels 50a are arranged in the Y direction and the X direction.

[0067] 1 and 5, the twelve EVSs 15 are arranged in a row along the short-side direction of the metal foil 100, i.e., the X direction. When distinguishing between the twelve EVSs 15, they are referred to as first to twelfth EVSs 15a to 15l from one side to the other in the short-side direction of the metal foil 100.

[0068] As shown in FIG. 1 , the metal foil 100 of this embodiment has a first inspection area A1, a second inspection area A2, a third inspection area A3, and a fourth inspection area A4. Each of the inspection areas A1 to A4 extends in the longitudinal direction of the metal foil 100. The first inspection area A1 is a portion located between the first cutting line L1 and the second cutting line L2 in the lateral direction of the metal foil 100. The second inspection area A2 is a portion located between the second cutting line L2 and the third cutting line L3 in the lateral direction of the metal foil 100. The third inspection area A3 is a portion located between the third cutting line L3 and the fourth cutting line L4 in the lateral direction of the metal foil 100. The fourth inspection area A4 is a portion located between the fourth cutting line L4 and the fifth cutting line L5 in the lateral direction of the metal foil 100. The first inspection area A1, the second inspection area A2, the third inspection area A3, and the fourth inspection area A4 are aligned in the widthwise direction of the metal foil 100, that is, the X direction.

[0069] In this embodiment, three EVSs 15 are provided for each inspection area A1 to A4. The first to third EVSs 15a to 15c are provided to detect pinholes PH that occur in the first inspection area A1. The fourth to sixth EVSs 15d to 15f are provided to detect pinholes PH that occur in the second inspection area A2. The seventh to ninth EVSs 15g to 15i are provided to detect pinholes PH that occur in the third inspection area A3. The tenth to twelfth EVSs 15j to 15l are provided to detect pinholes PH that occur in the fourth inspection area A4.

[0070] As shown in FIGS. 7 and 8 , each EVS 15 has a detection range Ad in which an event can be detected. Light from the light source 13 is irradiated onto at least an area of ​​the second surface 100b of the metal foil 100 that is located inside the detection range Ad. FIG. 7 illustrates only one of the twelve EVSs 15. As shown in FIG. 8 , the end of the detection range Ad in the short-side direction of the metal foil 100 overlaps with the end of another detection range Ad adjacent in the short-side direction of the metal foil 100. The metal foil 100 passes through the detection range Ad of each EVS 15 by being transported by the transport device 11. In this embodiment, the time it takes for the metal foil 100 to pass through the detection range Ad (hereinafter simply referred to as the "passing time") is, for example, 10 to 2000 milliseconds.

[0071] <Determination Device> As shown in FIG. 9 , the pinhole detection device 10 includes a determination device 16. The determination device 16 includes a processor 16a and a storage unit 16b. The processor 16a may be, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a digital signal processor (DSP). The storage unit 16b includes a random access memory (RAM) and a read-only memory (ROM). The storage unit 16b stores program code or instructions configured to cause the processor 16a to execute processing. The storage unit 16b, i.e., a computer-readable medium, includes any available medium accessible by a general-purpose or dedicated computer. The determination device 16 may be configured as a hardware circuit such as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). The determination device 16, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or FPGA, or a combination thereof.

[0072] The determination device 16 is connected to the 12 EVSs 15. Event data is output from each EVS 15 to the determination device 16. The determination device 16 determines whether or not a pinhole PH has occurred in the metal foil 100 based on the event data output from the EVSs 15.

[0073] <Marking Device> The pinhole detection device 10 includes a marking device 17. The pinhole detection device 10 of this embodiment includes four marking devices 17. The four marking devices 17 are connected to the determination device 16.

[0074] 1, the marking device 17 is disposed downstream of the EVS 15 in the conveying direction of the metal foil 100, i.e., the Y direction. The marking device 17 is disposed outside the housing 12. In this embodiment, the marking device 17 is disposed above the metal foil 100. The four marking devices 17 are arranged in a row at intervals in the short direction of the metal foil 100, i.e., the X direction. When distinguishing between the four marking devices 17, they are referred to as first to fourth marking devices 17a to 17d from one side of the metal foil 100 to the other.

[0075] The marking device 17 is configured to be able to provide a mark M indicating the occurrence of a pinhole PH on the metal foil 100. The marking device 17 in this embodiment is a laser irradiation device. In this embodiment, the marking device 17 provides the mark M on the metal foil 100 by irradiating the metal foil 100 with a laser.

[0076] <Pinhole Detection Method> A pinhole detection method executed by the pinhole detection device 10 will be described.

[0077] 8, when a pinhole PH occurs in the metal foil 100, the position of the pinhole PH in the longitudinal direction of the metal foil 100, i.e., in the Y direction, moves as the metal foil 100 is transported. On the other hand, the position of the pinhole PH in the lateral direction of the metal foil 100, i.e., in the X direction, hardly moves.

[0078] When light from the light source 13 passes through the pinhole PH, the luminance changes on the first surface 100a side of the metal foil 100, i.e., on the EVS 15 side. Furthermore, as the metal foil 100 is transported, the position of the pinhole PH moves in the longitudinal direction of the metal foil 100, i.e., in the Y direction, and the position at which the luminance changes also moves in the Y direction.

[0079] Each pixel 50a of the EVS 15 detects an event caused by light transmitted through the pinhole PH. When the pinhole PH approaches each pixel 50a, the brightness increases, and therefore each pixel 50a detects a P-type event. On the other hand, when the pinhole PH moves away from each pixel 50a, the brightness decreases, and therefore each pixel 50a detects an N-type event. Each pixel 50a detects a P-type event and then an N-type event. When a pinhole PH occurs in the metal foil 100, the number of P-type events and N-type events increases compared to when no pinhole PH occurs in the metal foil 100. Furthermore, when a pinhole PH occurs in the metal foil 100, the P-type events and N-type events are distributed in the Y direction.

[0080] The determination device 16 determines whether or not a pinhole PH has occurred in the metal foil 100 based on the event data output from the EVS 15. In this embodiment, the determination conditions for determining whether or not a pinhole PH has occurred in the metal foil 100 are an event number condition and an event distribution condition. The event number condition determines whether or not a pinhole PH has occurred in the metal foil 100 by utilizing the fact that the number of events occurring increases when a pinhole PH has occurred in the metal foil 100. The event distribution condition determines whether or not a pinhole PH has occurred in the metal foil 100 by utilizing the fact that the events are distributed in the Y direction when a pinhole PH has occurred in the metal foil 100.

[0081] As shown in Fig. 10, the event number condition is a condition for detecting a large-diameter pinhole PH. The event number condition is that "the number of events, which is the integrated value of the number of events occurring in a predetermined integration period T, is equal to or greater than a first event number threshold." The integration period T in this embodiment is, for example, 5 milliseconds. The event number condition in this embodiment is that "the number of P-type events Xp, which is the integrated value of the number of P-type events occurring in the integration period T, is equal to or greater than a first P-type event number threshold Xpt1."

[0082] The smaller the diameter of the pinhole PH, the less light passes through the pinhole PH, and therefore the fewer the number of events. Therefore, even if a pinhole PH occurs in the metal foil 100, if the diameter of the pinhole PH is small, the number of events may be less than the first event number threshold, i.e., the event number condition may not be satisfied. The event distribution condition is a condition for detecting small-diameter pinholes PH that cannot be detected by the event number condition. The event distribution condition of this embodiment includes a first event distribution condition and a second event distribution condition.

[0083] The first event distribution condition is a condition for detecting small-diameter pinholes PH when the conveying speed of the metal foil 100 is fast. When the conveying speed of the metal foil 100 is fast, the movement speed of the pinholes PH also becomes fast, and therefore, of the multiple pixel rows aligned in the Y direction, the number of pixel rows in which an event is detected during the integration period T increases.

[0084] The first event distribution condition in this embodiment is that "the ratio R (= Ny / Nx) of the number of pixel columns Ny in the Y direction to the number of pixel columns Nx in the X direction is equal to or greater than a predetermined ratio threshold Rt." The number of pixel columns Nx in the X direction is the number of pixel columns in which an event was detected during the integration period T, among the multiple pixel columns lined up in the X direction. Each of the multiple pixel columns lined up in the X direction is made up of multiple pixels 50a lined up in a line in the Y direction. The number of pixel columns Ny in the Y direction is the number of pixel columns in which an event was detected during the integration period T, among the multiple pixel columns lined up in the Y direction. Each of the multiple pixel columns lined up in the Y direction is made up of multiple pixels 50a lined up in a line in the X direction.

[0085] The second event distribution condition is a condition for detecting small-diameter pinholes PH when the conveying speed of the metal foil 100 is slow. When the conveying speed of the metal foil 100 is slow, the moving speed of the pinholes PH also becomes slow, and therefore an event occurs in each of a plurality of consecutive integration periods T.

[0086] The second event distribution condition is that "the accumulation period T in which the number of events is equal to or greater than the second event number threshold occurs a predetermined number of times in succession." In this embodiment, the second event distribution condition is that "the accumulation period T in which the number of P-type events Xp is equal to or greater than the second P-type event number threshold Xpt2 occurs a predetermined number of times in succession."

[0087] The determination device 16 determines whether the event number condition or the event distribution condition is satisfied based on the event data. In this embodiment, the determination device 16 determines that the event distribution condition is satisfied if either the first event distribution condition or the second event distribution condition is satisfied. If the event number condition or the event distribution condition is satisfied, the determination device 16 determines that a pinhole PH has occurred in the metal foil 100. If the event number condition and the event distribution condition are not satisfied, the determination device 16 determines that a pinhole PH has not occurred in the metal foil 100.

[0088] A detailed description will now be given of a series of determination processes executed by the determination device 16. As shown in Fig. 11, the determination device 16 first determines whether or not the event number condition is satisfied (step S1).

[0089] As shown in FIG. 12 , the determination device 16 calculates the number of P-type events Xp from the event data output from the EVS 15. In this embodiment, the determination device 16 adds up the number of P-type events that occur in all pixels 50 a of each EVS 15 during an integration period T. If a pixel 50 a detects a P-type event multiple times during the integration period T, the determination device 16 counts each of the multiple P-type events individually. For example, if a pixel 50 a detects a P-type event three times during the integration period T, the determination device 16 counts the number of P-type events that occur in that pixel 50 a as three. The determination device 16 repeatedly calculates the number of P-type events Xp in this manner every time the integration period T elapses. That is, the determination device 16 calculates the number of P-type events Xp for multiple integration periods T.

[0090] The determination device 16 compares the calculated number of P-type events Xp with a preset first P-type event number threshold Xpt1. The first P-type event number threshold Xpt1 is set to a value that enables determination of whether a P-type event is an event caused by light transmitted through the pinhole PH or an event caused by noise. Specifically, if the P-type events and N-type events are events caused by noise, increasing the illuminance of the light source 13 does not significantly change the number of P-type events and N-type events. On the other hand, if the P-type events and N-type events are events caused by light transmitted through the pinhole PH, increasing the illuminance of the light source 13 increases the number of P-type events and N-type events. The first P-type event number threshold Xpt1 is set by utilizing this property.

[0091] 11 , if the calculated P-type event number Xp is equal to or greater than the first P-type event number threshold Xpt1, i.e., if the event number condition is satisfied (YES in step S1), the determination device 16 determines that a pinhole PH has occurred in the metal foil 100 (step S2). In this embodiment, if the P-type event number Xp is equal to or greater than the first P-type event number threshold Xpt1 in one integration period T among multiple integration periods T, i.e., if the event number condition is satisfied in one integration period T, the determination device 16 determines that a pinhole PH has occurred in the metal foil 100. If the P-type event number Xp is less than the first P-type event number threshold Xpt1, i.e., if the event number condition is not satisfied (NO in step S1), the determination device 16 determines whether the event distribution condition is satisfied.

[0092] Before determining whether the event distribution condition is satisfied, the determination device 16 of this embodiment determines whether the event detected by the EVS 15 is an event caused by white noise (step S3).

[0093] Because the generation time of white noise is short, if the events detected by the EVS 15 are events caused by white noise, the events do not occur continuously in the Y direction at the same position in the X direction. On the other hand, if the events detected by the EVS 15 are events not caused by white noise, the events occur continuously in the Y direction at the same position in the X direction. Events not caused by white noise are events caused by light that has passed through the pinhole PH or events caused by spike noise. The generation time of spike noise is longer than the generation time of white noise. Therefore, events caused by spike noise occur continuously in the Y direction at the same position in the X direction.

[0094] The determination device 16 determines that, among the events detected by the EVS 15, events that do not occur consecutively in the Y direction at the same position in the X direction are events caused by white noise. The determination device 16 determines that, among the events detected by the EVS 15, events that occur consecutively in the Y direction at the same position in the X direction are events not caused by white noise.

[0095] FIG. 13 shows an example of the results of event detection by the EVS 15. In FIG. 13, pixels 50a in which no event was detected during the integration period T are indicated by open squares, and pixels 50a in which an event was detected one or more times during the integration period T are indicated by hatched squares. For ease of explanation, in FIG. 13, the number of pixels in the image sensor 50 is assumed to be 10 x 10, or 100 pixels. The X-coordinates of the pixels 50a are assumed to be 1, 2, 3, ..., 10 from left to right on the page. The Y-coordinates of the pixels 50a are assumed to be 1, 2, 3, ..., 10 from top to bottom on the page.

[0096] For example, a first pixel 501 located at (X, Y) = (5, 6) detects an event. A second pixel 502 located at (X, Y) = (5, 7) adjacent to the first pixel 501 in the Y direction does not detect an event. In this case, the events detected by the first pixel 501 do not occur consecutively in the Y direction at the same position in the X direction. Therefore, the determination device 16 determines that the event detected by the first pixel 501 is an event caused by white noise.

[0097] A third pixel 503 located at (X, Y) = (2, 3) detects an event. A fourth pixel 504 located at (X, Y) = (2, 4) adjacent to the third pixel 503 in the Y direction detects an event. In this case, the events detected by the third pixel 503 occur consecutively in the Y direction at the same position in the X direction. Therefore, the determination device 16 determines that the event detected by the third pixel 503 is an event not caused by white noise.

[0098] 11 , the determination device 16 determines whether the first event distribution condition is satisfied (step S4). The determination device 16 of this embodiment determines whether the first event distribution condition is satisfied using only events determined in step S3 to be events not caused by white noise. That is, the determination device 16 determines whether the first event distribution condition is satisfied using only events that occur consecutively in the Y direction at the same position in the X direction among the events detected by the EVS 15.

[0099] The determination device 16 recognizes pixels 50a that detected an event during the integration period T from the event data output from the EVS 15. The determination device 16 calculates the number of pixel columns in the X direction Nx by counting the number of pixel columns in which an event was detected during the integration period T among multiple pixel columns aligned in the X direction. The determination device 16 calculates the number of pixel columns in the Y direction Ny by counting the number of pixel columns in which an event was detected during the integration period T among multiple pixel columns aligned in the Y direction. The determination device 16 calculates the ratio R (= Ny / Nx) of the number of pixel columns Ny in the Y direction to the number of pixel columns Nx in the X direction by dividing the number of pixel columns Ny in the Y direction by the number of pixel columns Nx in the X direction.

[0100] 13, the number of pixel columns Nx in the X direction is 3. The number of pixel columns Ny in the Y direction is 8. Therefore, the ratio R of the number of pixel columns Ny in the Y direction to the number of pixel columns Nx in the X direction is 8 / 3.

[0101] The determination device 16 compares the calculated ratio R with a ratio threshold Rt. The ratio threshold Rt is set to a value that enables determination of whether an event is caused by light transmitted through the pinhole PH or by spike noise. In this embodiment, the ratio threshold Rt is set as follows:

[0102] 14 shows a distribution diagram of events, with the vertical axis representing the ratio R and the horizontal axis representing the number of pixel columns Ny in the Y direction. In FIG. 14, events caused by light transmitted through the pinhole PH are indicated by white circles, and events caused by spike noise are indicated by black circles. As is clear from this distribution diagram, the number of pixel columns Ny in the Y direction and the ratio R are larger for events caused by light transmitted through the pinhole PH than for events caused by spike noise.

[0103] A boundary line L is set between the group of events caused by light transmitted through the pinhole PH and the group of events caused by spike noise. In this embodiment, the boundary line L is expressed by a function f(Ny) = -aNy + b (a and b are constants). When the ratio R is greater than or equal to the function f(Ny), the event is caused by light transmitted through the pinhole PH. The ratio threshold value Rt is set to a value obtained by substituting the number of pixel columns Ny in the Y direction calculated by the determination device 16 into the function f(Ny).

[0104] 11 , if the calculated ratio R is equal to or greater than the ratio threshold Rt, i.e., if the first event distribution condition is satisfied (YES in step S4), the determination device 16 determines that a pinhole PH has occurred in the metal foil 100 (step S2). If the ratio R is less than the ratio threshold Rt, i.e., if the first event distribution condition is not satisfied (NO in step S4), the determination device 16 determines whether the second event distribution condition is satisfied.

[0105] The determination device 16 determines whether the second event distribution condition is satisfied (step S5). The determination device 16 of this embodiment determines whether the second event distribution condition is satisfied using only the events determined in step S3 to be events not caused by white noise. That is, the determination device 16 determines whether the second event distribution condition is satisfied using only events that occur consecutively in the Y direction at the same position in the X direction among the events detected by the EVS 15.

[0106] 12 , the determination device 16 calculates the number of P-type events Xp from the event data output from the EVS 15. The determination device 16 of this embodiment counts the number of P-type events determined in step S3 to be events not caused by white noise. The determination device 16 of this embodiment does not count the number of P-type events determined in step S3 to be events caused by white noise. The determination device 16 repeatedly calculates the number of P-type events Xp in this manner every time the integration period T elapses. That is, the determination device 16 calculates the number of P-type events Xp for multiple integration periods T.

[0107] The determination device 16 compares the calculated P-type event count Xp with a preset second P-type event count threshold Xpt2 for each of the multiple integration periods T. The second P-type event count threshold Xpt2 is set to a value smaller than the first P-type event count threshold Xpt1.

[0108] In this embodiment, the second P-type event count threshold Xpt2 is set to 2. In this case, if an event not caused by white noise occurs during the integration period T, the P-type event count Xp is 2 or more, and therefore the P-type event count Xp is equal to or greater than the second P-type event count threshold Xpt2.

[0109] The value of the second P-type event count threshold Xpt2 may be changed as appropriate. For example, if step S3 is omitted, the second P-type event count threshold Xpt2 may be set to a value greater than the number of events due to white noise that are expected to occur during the integration period T.

[0110] The determination device 16 determines whether the integration period T during which the P-type event count Xp is equal to or greater than the second P-type event count threshold Xpt2 occurs a predetermined number of times in succession. The predetermined number is set to an integer equal to or greater than 2 based on the expected occurrence time of spike noise and the integration period T. In this embodiment, the maximum occurrence time of spike noise is assumed to be 6 milliseconds. As described above, the integration period T is 5 milliseconds. In this case, the maximum number of consecutive integration periods T during which the P-type event count Xp is equal to or greater than the second P-type event count threshold Xpt2 due to P-type events caused by spike noise is three. In other words, the number of consecutive integration periods T during which the P-type event count Xp is equal to or greater than the second P-type event count threshold Xpt2 due to P-type events caused by spike noise will not exceed four or more. Therefore, the predetermined number in this embodiment is set to four.

[0111] 11 , if the accumulation period T during which the P-type event count Xp is equal to or greater than the second P-type event count threshold Xpt2 occurs four or more consecutive times, i.e., if the second event distribution condition is satisfied (YES in step S5), the determination device 16 determines that a pinhole PH has occurred in the metal foil 100 (step S2). If the accumulation period T during which the P-type event count Xp is equal to or greater than the second P-type event count threshold Xpt2 does not occur four or more consecutive times, i.e., if the second event distribution condition is not satisfied (NO in step S5), the determination device 16 ends the series of processes.

[0112] In this embodiment, the determination device 16 determines whether or not pinholes PH have occurred in the first to fourth inspection areas A1 to A4 of the metal foil 100. That is, the determination device 16 determines whether or not the event number condition or the event distribution condition is satisfied in the first to fourth inspection areas A1 to A4 of the metal foil 100.

[0113] The determination device 16 determines whether a pinhole PH has occurred in the first inspection area A1 based on the event data output from the first to third EVSs 15a to 15c. Specifically, when the determination device 16 determines that the event number condition or the event distribution condition is satisfied based on the event data output from the first EVS 15a, it determines that a pinhole PH has occurred in the first inspection area A1. When the determination device 16 determines that the event number condition or the event distribution condition is satisfied based on the event data output from the second EVS 15b, it determines that a pinhole PH has occurred in the first inspection area A1. When the determination device 16 determines that the event number condition or the event distribution condition is satisfied based on the event data output from the third EVS 15c, it determines that a pinhole PH has occurred in the first inspection area A1.

[0114] The determination device 16 determines whether a pinhole PH has occurred in the second inspection area A2 based on the event data output from the fourth to sixth EVSs 15d to 15f. Specifically, when the determination device 16 determines that the event number condition or the event distribution condition is satisfied based on the event data output from the fourth EVS 15d, it determines that a pinhole PH has occurred in the second inspection area A2. When the determination device 16 determines that the event number condition or the event distribution condition is satisfied based on the event data output from the fifth EVS 15e, it determines that a pinhole PH has occurred in the second inspection area A2. When the determination device 16 determines that the event number condition or the event distribution condition is satisfied based on the event data output from the sixth EVS 15f, it determines that a pinhole PH has occurred in the second inspection area A2.

[0115] The determination device 16 determines whether a pinhole PH has occurred in the third inspection area A3 based on the event data output from the seventh to ninth EVSs 15g to 15i. Specifically, if the determination device 16 determines that the event number condition or the event distribution condition is satisfied based on the event data output from the seventh EVS 15g, it determines that a pinhole PH has occurred in the third inspection area A3. If the determination device 16 determines that the event number condition or the event distribution condition is satisfied based on the event data output from the eighth EVS 15h, it determines that a pinhole PH has occurred in the third inspection area A3. If the determination device 16 determines that the event number condition or the event distribution condition is satisfied based on the event data output from the ninth EVS 15i, it determines that a pinhole PH has occurred in the third inspection area A3.

[0116] The determination device 16 determines whether a pinhole PH has occurred in the fourth inspection area A4 based on the event data output from the tenth to twelfth EVSs 15j to 15l. Specifically, if the determination device 16 determines that the event number condition or the event distribution condition is satisfied based on the event data output from the tenth EVS 15j, it determines that a pinhole PH has occurred in the fourth inspection area A4. If the determination device 16 determines that the event number condition or the event distribution condition is satisfied based on the event data output from the eleventh EVS 15k, it determines that a pinhole PH has occurred in the fourth inspection area A4. If the determination device 16 determines that the event number condition or the event distribution condition is satisfied based on the event data output from the twelfth EVS 15l, it determines that a pinhole PH has occurred in the fourth inspection area A4.

[0117] In this embodiment, the marking device 17 operates in accordance with the determination result by the determination device 16. If the determination device 16 determines that a pinhole PH has occurred in the metal foil 100, the marking device 17 applies a mark M to the metal foil 100. If the determination device 16 determines that a pinhole PH has not occurred in the metal foil 100, the marking device 17 does not apply a mark M to the metal foil 100.

[0118] 1 , the mark M is provided at a position corresponding to the pinhole PH in the longitudinal direction of the metal foil 100, i.e., the Y direction. The mark M in this embodiment is a straight line extending in the lateral direction of the metal foil 100, i.e., the X direction, but the shape of the mark M may be changed as appropriate. The mark M in this embodiment is provided on a portion of the metal foil 100 that will later become the exposed portion 210e.

[0119] In this embodiment, the marking device 17 applies marks M individually to the first to fourth inspection areas A1 to A4 of the metal foil 100. Fig. 1 illustrates the case where a mark M is applied to the second inspection area A2.

[0120] Specifically, when the determination device 16 determines that a pinhole PH has occurred in the first inspection area A1, the first marking device 17a applies a mark M to the first inspection area A1. In the first inspection area A1, the portion located between the coated area Ac and the first cutting line L1 and the portion located between the coated area Ac and the second cutting line L2 in the short direction of the metal foil 100 are the portions that will later become the exposed portion 210e. Therefore, the first marking device 17a applies a mark M to, for example, the portion of the first inspection area A1 that is located between the coated area Ac and the first cutting line L1 in the short direction of the metal foil 100.

[0121] When the determination device 16 determines that a pinhole PH has occurred in the second inspection area A2, the second marking device 17b applies a mark M to the second inspection area A2. In the second inspection area A2, the portion located between the coated area Ac and the second cutting line L2 and the portion located between the coated area Ac and the third cutting line L3 in the short direction of the metal foil 100 will later become the exposed portion 210e. Therefore, the second marking device 17b applies a mark M to, for example, the portion of the second inspection area A2 located between the coated area Ac and the second cutting line L2 in the short direction of the metal foil 100.

[0122] When the determination device 16 determines that a pinhole PH has occurred in the third inspection area A3, the third marking device 17c applies a mark M to the third inspection area A3. In the third inspection area A3, the portion located between the coated area Ac and the third cutting line L3 in the short direction of the metal foil 100 and the portion located between the coated area Ac and the fourth cutting line L4 are the portions that will later become the exposed portion 210e. Therefore, the third marking device 17c applies a mark M to, for example, the portion of the third inspection area A3 that is located between the coated area Ac and the third cutting line L3 in the short direction of the metal foil 100.

[0123] When the determination device 16 determines that a pinhole PH has occurred in the fourth inspection area A4, the fourth marking device 17d applies a mark M to the fourth inspection area A4. In the fourth inspection area A4, the portion located between the coated area Ac and the fourth cutting line L4 and the portion located between the coated area Ac and the fifth cutting line L5 in the short direction of the metal foil 100 will later become the exposed portion 210e. Therefore, the fourth marking device 17d applies a mark M to, for example, the portion of the fourth inspection area A4 located between the coated area Ac and the fourth cutting line L4 in the short direction of the metal foil 100.

[0124] As described above, in this embodiment, the mark M is applied only to the inspection areas A1 to A4 of the metal foil 100 where pinholes PH have occurred. As described above, the metal foil 100 is cut in the cutting process to form a plurality of electrodes 200. At this time, of the plurality of electrodes 200 formed, the electrode 200 in which pinholes PH have occurred in the current collector 210 is applied with the mark M, as shown in FIG. 2. The electrode 200 with the mark M applied is discarded as a defective product in which pinholes PH have occurred. In other words, the electrode 200 in which pinholes PH have occurred cannot be used as a nickel-metal hydride battery.

[0125] [Actions and Effects of the Present Embodiment] The actions and effects of the present embodiment will be described. (1) When a pinhole PH occurs in the metal foil 100, the number of P-type events and N-type events increases compared to when no pinhole PH occurs in the metal foil 100. Furthermore, when a pinhole PH occurs in the metal foil 100, the pinhole PH moves in the Y direction, causing the P-type events and N-type events to be distributed in the Y direction.

[0126] The determination device 16 of this embodiment determines whether an event count condition, in which the number of events, which is the integrated value of the number of events occurring in a predetermined integration period T, is equal to or greater than a first event count threshold, or an event distribution condition, in which the events are distributed in the Y direction, is satisfied. If the event count condition or the event distribution condition is satisfied, the determination device 16 determines that a pinhole PH has occurred in the metal foil 100. This makes it possible to detect a pinhole PH that has occurred in the metal foil 100.

[0127] When pinholes PH are detected using the EVS 15 in this way, the higher the illuminance of the light source 13, the wider the distribution range of events in the Y direction and the greater the number of events. Therefore, pinholes PH with smaller diameters can be detected. In other words, the pinhole PH detection performance can be improved.

[0128] (2) For example, when pinhole PH is detected based on an image of the metal foil 100 captured by an imaging device, an imaging device capable of capturing images at high speed and a high-performance image processing device for processing the captured images are required. In contrast, the EVS 15 of this embodiment outputs only event data to the determination device 16, thereby reducing the amount of data. Therefore, the load on the pinhole PH detection process can be reduced and high-speed processing becomes possible.

[0129] Furthermore, when pinhole PH is detected based on an image of the metal foil 100 captured by an imaging device, improving pinhole PH detection performance while maintaining the detection range requires narrowing the imaging range, which necessitates increasing the number of imaging devices. Increasing the number of imaging devices also increases the number of image processing devices, resulting in a significant increase in costs. In contrast, in this embodiment, pinhole PH detection performance can be improved by increasing the illuminance of the light source 13, thereby avoiding a significant increase in costs.

[0130] (3) As described above, when a pinhole PH occurs in the metal foil 100, the pinhole PH moves in the Y direction, distributing events in the Y direction. Therefore, when the conveyance speed of the metal foil 100 is fast, the number of pixel columns Ny in the Y direction increases. When the event detected by the EVS 15 is an event caused by light transmitted through a pinhole PH, the number of pixel columns Ny in the Y direction increases compared to when the event is caused by noise.

[0131] On the other hand, because the pinhole PH hardly moves in the X direction, the distribution range of events in the X direction is small. Therefore, when an event detected by the EVS 15 is an event caused by light that has passed through the pinhole PH, the number of pixel columns Nx in the X direction is smaller than when an event is caused by noise. Therefore, when an event detected by the EVS 15 is an event caused by light that has passed through the pinhole PH, the ratio R of the number of pixel columns Ny in the Y direction to the number of pixel columns Nx in the X direction is larger than when an event is caused by noise.

[0132] According to the above method, the event distribution conditions include a first event distribution condition in which the ratio R is equal to or greater than the ratio threshold Rt. This allows the determination device 16 to determine whether an event detected by the EVS 15 is an event caused by light transmitted through the pinhole PH or an event caused by noise. This improves the accuracy of pinhole PH detection.

[0133] (4) As described above, when a pinhole PH occurs in the metal foil 100, the pinhole PH moves in the Y direction, causing events to be distributed in the Y direction. Therefore, when the conveyance speed of the metal foil 100 is slow, an event occurs in each of multiple consecutive integration periods T. When the event detected by the EVS 15 is an event caused by light transmitted through the pinhole PH, the number of consecutive integration periods T in which the event occurs is greater than when the event is caused by noise.

[0134] In this embodiment, the event distribution condition includes a second event distribution condition that the accumulation period T during which the number of events is equal to or greater than the second event number threshold occurs a predetermined number of times in succession. This allows the determination device 16 to determine whether the event detected by the EVS 15 is an event caused by light transmitted through the pinhole PH or an event caused by noise. This improves the accuracy of pinhole PH detection.

[0135] (5) The determination device 16 determines whether the event distribution condition is satisfied using only events that occur consecutively in the Y direction at the same position in the X direction among the events detected by the EVS 15.

[0136] If the events detected by the EVS 15 are events caused by white noise with a short occurrence time, they do not occur consecutively in the Y direction at the same position in the X direction. On the other hand, if the events detected by the EVS 15 are events not caused by white noise, they occur consecutively in the Y direction at the same position in the X direction.

[0137] In this embodiment, the determination device 16 determines whether the event distribution condition is satisfied by using only events that occur consecutively in the Y direction at the same position in the X direction. That is, the determination device 16 determines whether the event distribution condition is satisfied by using only events that are not caused by white noise, in other words, excluding events caused by white noise. Therefore, the detection accuracy of pinholes PH can be improved.

[0138] (6) In this embodiment, a marking device 17 is disposed downstream of the EVS 15 in the Y direction. When the determination device 16 determines that a pinhole PH has occurred in the metal foil 100, the marking device 17 applies a mark M to the metal foil 100 at a position in the longitudinal direction, i.e., the Y direction, that corresponds to the pinhole PH. The mark M makes it easier to identify the pinhole PH that has occurred in the metal foil 100.

[0139] (7) In this embodiment, first to fourth inspection areas A1 to A4 are set on the metal foil 100 so as to be aligned in the short direction, i.e., the X direction. The determination device 16 determines whether or not pinholes PH have occurred in the first to fourth inspection areas A1 to A4 individually. The marking device 17 applies marks M only to the inspection areas A1 to A4 determined by the determination device 16 to have pinholes PH.

[0140] As described above, an electrode 200 bearing mark M is discarded as a defective product containing a pinhole PH. If the position of the pinhole PH in the widthwise direction of the metal foil 100 cannot be determined, it is unclear which of the four electrodes 200 aligned in the widthwise direction of the metal foil 100 contains the pinhole PH, and all four electrodes 200 are discarded. In contrast, in this embodiment, the marking device 17 marks M only on the inspection areas A1 to A4 determined by the determination device 16 to contain the pinhole PH. This makes it possible to determine which of the multiple inspection areas A1 to A4 aligned in the widthwise direction of the metal foil 100 contains the pinhole PH. In this case, only the electrodes 200 including the inspection areas A1 to A4 with mark M are discarded, thereby improving yield.

[0141] (8) In this embodiment, the mark M is provided on a portion of the metal foil 100 that will later become the exposed portion 210e. Therefore, the mark M can be confirmed even after the negative electrode active material layer 211 and the positive electrode active material layer 212 are formed on the metal foil 100.

[0142] (9) The determination device 16 of this embodiment adds up the number of P-type events that have occurred in all of the pixels 50 a included in the EVS 15. Therefore, for example, by adding up the number of P-type events that have occurred in a plurality of pixels 50 a that are aligned in a line in the Y direction for each of a plurality of pixel columns aligned in the X direction during the integration period T, the load on the calculation process for the number of P-type events Xp can be reduced compared to when the number of P-type events Xp is calculated for each coordinate in the X direction.

[0143] (10) When detecting light transmitted through the pinhole PH using a photomultiplier tube as in the prior art, an optical lens for converging the light must be disposed between the light source 13 and the metal foil 100. In contrast, when detecting light transmitted through the pinhole PH using the EVS 15 as in the present embodiment, there is no need to converge the light, and therefore no optical lens needs to be disposed between the light source 13 and the metal foil 100. This allows the light source 13 to be disposed closer to the metal foil 100, making it easier to ensure a luminous flux irradiating the metal foil 100.

[0144] (11) Two masks 14 are disposed at both ends in the lateral direction of the metal foil 100. The two masks 14 cause the light from the light source 13 to pass outside the both ends in the lateral direction of the metal foil 100, thereby preventing the light from escaping toward the EVS 15. Therefore, it is possible to reduce noise caused by the light from the light source 13 escaping toward the EVS 15 side of the metal foil 100.

[0145] (12) In this embodiment, the second extension 43c of the bracket 43 is interposed between the brush 42 of the mask 14 and the light source 13. This prevents the light from the light source 13 from directly irradiating the brush 42. This prevents the brush 42 from melting.

[0146] (13) Radiant heat from the light source 13 may cause the ambient temperature inside the housing 12 to become high, which may result in thermal expansion of the brush 42. In this embodiment, the tip of the second extension 43c is positioned to protrude further than the tip of the brush 42. This makes it less likely that the brush 42 will come into contact with the light source 13 even if the brush 42 thermally expands.

[0147] [Modifications] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0148] The number of EVSs 15 arranged in the widthwise direction of the metal foil 100, i.e., in the X direction, may be changed as appropriate depending on the size of the metal foil 100 in the widthwise direction, the detection range Ad of the EVSs 15, and the like.

[0149] The number of EVSs 15 provided for each of the inspection areas A1 to A4 of the metal foil 100 may be changed as appropriate depending on the dimensions of the inspection areas A1 to A4 in the short direction of the metal foil 100 and the detection range Ad of the EVSs 15.

[0150] The illuminance of the light source 13 may be changed as appropriate depending on the transit time, the diameter of the pinhole PH to be detected, etc. The integration period T may be changed as appropriate depending on the illuminance of the light source 13, the transit time, the diameter of the pinhole PH to be detected, etc.

[0151] The determination device 16 may generate an event image from the event data and determine whether the event number condition or the event distribution condition is satisfied based on the generated event image.

[0152] In the above embodiment, the event count condition is that "the number of P-type events Xp is equal to or greater than the first P-type event count threshold Xpt1," but this is not limited to this. As described above, an N-type event occurs after a P-type event. Therefore, the determination device 16 may determine whether the event count condition is satisfied using an N-type event. In this case, the event count condition is that "the number of N-type events Xn, which is the cumulative value of the number of N-type events occurring during the accumulation period T, is equal to or greater than the first N-type event count threshold Xnt1."

[0153] For example, as shown in FIG. 15 , the determination device 16 calculates the number of N-type events Xn. The determination device 16 determines that the event number condition is satisfied when the number of N-type events Xn is equal to or greater than the first N-type event number threshold Xnt1. Ideally, the number of P-type events Xp and the number of N-type events Xn should be the same number of events, but in reality, due to the influence of afterimages or a small amount of light passing through the pinhole PH, the number of N-type events Xn may be smaller than the number of P-type events Xp. In this case, the first N-type event number threshold Xnt1 is set to a value smaller than the first P-type event number threshold Xpt1.

[0154] The determination device 16 may determine whether the event count condition is satisfied by using both P-type events and N-type events. In this case, the event count condition is that "the total event count Xs, which is the sum of the number of P-type events Xp and the number of N-type events Xn, is equal to the first total event count threshold Xst1."

[0155] 16, the determination device 16 calculates the total number of events Xs. If the total number of events Xs is equal to or greater than a first total event number threshold Xst1, the determination device 16 determines that the event number condition is satisfied.

[0156] In the above embodiment, the determination device 16 sums up the number of P-type events occurring in all pixels 50a of the EVS 15 during the integration period T, but this is not limited to this. As described above, the position of the pinhole PH hardly moves in the short direction of the metal foil 100, i.e., in the X direction. Therefore, if the P-type events and the N-type events are events caused by light transmitted through the pinhole PH, the P-type events and the N-type events occur at the same position in the X direction. Therefore, the number of P-type events Xp and the number of N-type events Xn also increase at the same position in the X direction. Specifically, the number of P-type events Xp and the number of N-type events Xn increase at the position corresponding to the pinhole PH in the X direction. On the other hand, if the P-type events and the N-type events are events caused by noise, the P-type events and the N-type events are unlikely to occur at the same position in the X direction.

[0157] "P-type events and N-type events occur at the same position in the X direction" includes not only the cases where they occur at exactly the same position in the X direction, but also the cases where they occur at different positions within a predetermined range in the X direction. Even when P-type events and N-type events are events caused by light transmitted through the pinhole PH, the positions at which the P-type events and N-type events occur may actually vary slightly in the X direction due to vibrations during transport of the metal foil 100, etc. However, the amount of variation is smaller than when the P-type events and N-type events are events caused by noise. The predetermined range is set to a range that allows for determining whether the P-type events and N-type events are events caused by light transmitted through the pinhole PH or events caused by noise. The predetermined range may be, for example, several pixels aligned in the X direction, or a range of 1, 3, 5, or 10 mm in width in the short direction of the metal foil 100.

[0158] For example, as shown in FIG. 17 , the determination device 16 may calculate the number of P-type events Xp at each coordinate in the X direction by adding up the number of P-type events occurring in a plurality of pixels 50 a arranged in a line in the Y direction during an integration period T for each of a plurality of pixel columns aligned in the X direction. The determination device 16 determines that the event number condition is satisfied, for example, when the number of P-type events Xp at one coordinate in the X direction is equal to or greater than a first P-type event number threshold Xpt1. In this modified example, the first P-type event number threshold Xpt1 is set to a value smaller than the first P-type event number threshold Xpt1 in the above embodiment. In this case, it is possible to detect not only whether a pinhole PH has occurred in the metal foil 100 but also the position of the pinhole PH in the short direction of the metal foil 100.

[0159] In this modified example, the marking device 17 may apply a mark M to the metal foil 100 at a position corresponding to the pinhole PH in the short direction of the metal foil 100, i.e., the X direction. In this case, the mark M allows the position of the pinhole PH in the short direction of the metal foil 100 to be ascertained, as well as the position of the pinhole PH in the long direction of the metal foil 100.

[0160] As described above, when P-type events and N-type events are events caused by light transmitted through the pinhole PH, the number of P-type events Xp and the number of N-type events Xn increase not only in one integration period T but also in multiple consecutive integration periods T. For example, in the example shown in Fig. 12, there are three consecutive integration periods T in which the number of P-type events Xp is equal to or greater than the first P-type event number threshold Xpt1.

[0161] The determination device 16 may determine that a pinhole PH has occurred in the metal foil 100 when the accumulation period T satisfies the event number condition multiple times in succession. This improves the accuracy of pinhole PH detection compared to when it is determined that a pinhole PH has occurred when the event number condition is satisfied in one accumulation period T.

[0162] P-type events and N-type events may be detected throughout the entire passage time, but may also be detected during part of the passage time depending on the illuminance of the light source 13, the angle of incidence of the light, etc. When P-type events and N-type events are events caused by light transmitted through the pinhole PH, the period during which the number of occurrences of P-type events and N-type events increases is longer than when P-type events and N-type events are events caused by noise. When P-type events and N-type events are events caused by light transmitted through the pinhole PH, the period during which the number of occurrences of P-type events and N-type events increases is, for example, 50% or more of the passage time.

[0163] Therefore, the determination device 16 may determine that a pinhole PH has occurred in the metal foil 100 when the cumulative period T that satisfies the event number condition occurs multiple times in a row and the total time of the cumulative period T that satisfies the event number condition (the time when the condition is met) is 50% or more of the passing time. This makes it possible to suppress erroneous determination due to noise, thereby further improving the accuracy of pinhole PH detection.

[0164] "50%" is just an example. The ratio of the condition-fulfilled time to the passing time may be set to a ratio that allows for determining whether P-type events and N-type events are events caused by light transmitted through the pinhole PH or events caused by noise. The ratio of the condition-fulfilled time to the passing time may be, for example, 10% or 25%.

[0165] When the P-type events and N-type events are events caused by light transmitted through the pinhole PH, the P-type events and N-type events occur continuously in the Y direction at the same position in the short-side direction of the metal foil 100, i.e., the X direction. On the other hand, when the P-type events and N-type events are events caused by noise, the P-type events and N-type events are unlikely to occur continuously in the Y direction at the same position in the short-side direction of the metal foil 100, i.e., the X direction.

[0166] Therefore, the determination device 16 may determine that a pinhole PH has occurred in the metal foil 100 when the event number condition is satisfied and at least one of a P-type event and an N-type event occurs consecutively in the Y direction at the same position in the X direction during at least one integration period T. This makes it possible to suppress erroneous determinations due to noise, thereby improving the accuracy of pinhole PH detection.

[0167] The determination device 16 may determine that a pinhole PH has occurred in the metal foil 100 when the event number condition is repeatedly satisfied over multiple consecutive integration periods T and at least one of a P-type event and an N-type event occurs consecutively in the Y direction at the same position in the X direction. In this case, erroneous determination due to noise can be suppressed, thereby further improving the detection accuracy of the pinhole PH.

[0168] Before determining whether the event number condition is satisfied, the determination device 16 may determine whether the events detected by the EVS 15 are events caused by white noise. In this case, the determination device 16 may determine whether the event number condition is satisfied using only events that occur consecutively in the Y direction at the same position in the X direction, i.e., only events that are determined not to be caused by white noise.

[0169] The determination device 16 may determine whether the event distribution condition is satisfied without determining whether the event detected by the EVS 15 is an event caused by white noise.

[0170] The first event distribution condition may be "the number of pixel columns Ny in the Y direction is equal to or greater than a threshold value Nyt for the number of pixel columns in the Y direction." As long as it is possible to determine whether an event is caused by light passing through the pinhole PH or by spike noise, the method for setting the threshold value Nyt for the number of pixel columns in the Y direction may be changed as appropriate.

[0171] For example, the Y-direction pixel column number threshold Nyt may be set based on the distribution diagram shown in Fig. 14. The Y-direction pixel column number threshold Nyt may be set to the smallest Y-direction pixel column number Ny for which the ratio R≧function f(Ny) holds.

[0172] Since the ratio R is Ny / Nx, R>0. When the number of pixel columns in the Y direction Ny>b / a, the ratio threshold Rt is Rt=f(b / a)<0. Therefore, when the number of pixel columns in the Y direction Ny>b / a, the ratio R>ratio threshold Rt holds. From the above, the Y-direction pixel column number threshold Nyt may be set to b / a.

[0173] The Y-direction pixel column number threshold Nyt may be set based on the amount of movement of the metal foil 100 in the Y direction during the integration period T. For example, if the metal foil 100 moves n pixels in the Y direction during the integration period T, the Y-direction pixel column number threshold Nyt may be set to n.

[0174] As described above, when a pinhole PH occurs in the metal foil 100, the pinhole PH moves in the Y direction, causing events to be distributed in the Y direction. Therefore, when the conveyance speed of the metal foil 100 is fast, the number of pixel columns Ny in the Y direction increases. When the event detected by the EVS 15 is an event caused by light that has passed through the pinhole PH, the number of pixel columns Ny in the Y direction increases compared to when the event is caused by spike noise.

[0175] In this modified example, the first event distribution condition is that "the number of pixel columns Ny in the Y direction is equal to or greater than the Y direction pixel column number threshold Nyt." This allows the determination device 16 to determine whether events distributed in the Y direction are events caused by light transmitted through the pinhole PH or events caused by spike noise. This improves the accuracy of pinhole PH detection.

[0176] Furthermore, the determination device 16 can determine whether the first event distribution condition is satisfied without calculating the number of pixel columns Nx in the X direction and the ratio R, thereby reducing the load on the pinhole PH detection process.

[0177] The number of pixel columns Nx in the X direction may be the number of pixel columns that are consecutive in the X direction and for which an event is detected during the integration period T, among a plurality of pixel columns aligned in the X direction. The number of pixel columns Ny in the Y direction may be the number of pixel columns that are consecutive in the Y direction and for which an event is detected during the integration period T, among a plurality of pixel columns aligned in the Y direction.

[0178] In the above embodiment, the second event count condition is that the accumulation period T in which the P-type event count Xp is equal to or greater than the second P-type event count threshold Xpt2 occurs a predetermined number of times in succession. However, the second event count condition is not limited to this.

[0179] The second event count condition may be "a predetermined number of consecutive integration periods T in which the number of N-type events Xn is equal to or greater than the second N-type event count threshold Xnt2." The second event count condition may be "a predetermined number of consecutive integration periods T in which the total number of events Xs is equal to or greater than the second total event count threshold Xst2."

[0180] As shown in Fig. 18 , a plurality of light sources 13 and EVSs 15 may be provided in the Y direction. In the example shown in Fig. 18 , two light sources 13 and two EVSs 15 are provided with a gap in the Y direction. In the following description, of the two light sources 13 and two EVSs 15, the light source 13 and the EVS 15 located upstream in the Y direction are referred to as the upstream light source 131 and the upstream EVS 151, and the light source 13 and the EVS 15 located downstream are referred to as the downstream light source 132 and the downstream EVS 152. In this case, the determination device 16 may determine whether or not a pinhole PH has occurred in the metal foil 100, for example, as in the following specific examples 1 to 4.

[0181] <Specific Example 1> When the event number condition or the event distribution condition is satisfied in each of the plurality of EVSs 15, the determination device 16 determines that a pinhole PH has occurred in the metal foil 100.

[0182] 18 , the determination device 16 determines, from the event data from the upstream EVS 151, whether or not the event count condition is satisfied in the upstream EVS 151. The determination device 16 determines, from the event data from the downstream EVS 152, whether or not the event count condition is satisfied in the downstream EVS 152.

[0183] Specifically, the determination device 16 calculates the number Xp of P-type events detected by the upstream EVS 151 from the event data from the upstream EVS 151. The determination device 16 also calculates the number Xp of P-type events detected by the downstream EVS 152 from the event data from the downstream EVS 152. If the number Xp of P-type events detected by the upstream EVS 151 is equal to or greater than the first P-type event count threshold Xpt1 and the number Xp of P-type events detected by the downstream EVS 152 is equal to or greater than the first P-type event count threshold Xpt1, the determination device 16 determines that the event count condition is satisfied in each of the upstream EVS 151 and the downstream EVS 152.

[0184] Although detailed description will be omitted, the determination device 16 determines, from the event data from the upstream EVS 151, whether or not the event distribution condition is satisfied in the upstream EVS 151. The determination device 16 determines, from the event data of the downstream EVS 152, whether or not the event distribution condition is satisfied in the downstream EVS 152.

[0185] If the event number condition or the event distribution condition is satisfied in each of the upstream EVS 151 and the downstream EVS 152, the determination device 16 determines that a pinhole PH has occurred in the metal foil 100.

[0186] In this case, the accuracy of pinhole PH detection can be improved compared to when the determination device 16 determines that a pinhole PH has occurred when the event number condition or event distribution condition is satisfied in one EVS 15.

[0187] <Specific Example 2> The determination device 16 may determine that a pinhole PH has occurred in the metal foil 100 when the event number condition is satisfied in each of the multiple EVSs 15 and at least one of a P-type event and an N-type event occurs in the multiple EVSs 15 at the same position in the short direction of the metal foil 100, i.e., in the X direction.

[0188] In the example shown in Figure 18, the determination device 16 determines that a pinhole PH has occurred in the metal foil 100 if the number of P-type events Xp in each of the upstream EVS 151 and the downstream EVS 152 is greater than or equal to the first P-type event number threshold Xpt1, and if the P-type events occur at the same position in the X direction in both the upstream EVS 151 and the downstream EVS 152.

[0189] As described above, when a P-type event and an N-type event are events caused by light transmitted through a pinhole PH, the P-type event and the N-type event occur at the same position in the X direction. Therefore, the determination device 16 determines that a pinhole PH has occurred when at least one of a P-type event and an N-type event occurs at the same position in the X direction in a plurality of EVSs 15, thereby further improving the accuracy of pinhole PH detection.

[0190] <Specific Example 3> The illuminance of the light source 13 may be set to be different for each light source 13. In this case, the determination device 16 determines that a pinhole PH has occurred in the metal foil 100 when the event number condition is satisfied for each of the plurality of EVSs 15 and the number of events is greater for an EVS 15 arranged with a light source 13 having a higher illuminance.

[0191] 18 , the illuminance of the upstream light source 131 is set higher than the illuminance of the downstream light source 132. In this case, the determination device 16 determines that a pinhole PH has occurred in the metal foil 100 when the number of P-type events Xp is equal to or greater than the first P-type event number threshold Xpt1 in each of the upstream EVS 151 and the downstream EVS 152, and the number of P-type events Xp detected by the upstream EVS 151 is greater than the number of P-type events Xp detected by the downstream EVS 152.

[0192] The higher the illuminance of the light source 13, the more the number of P-type events and N-type events that occur, and therefore the number of P-type events Xp and the number of N-type events Xn increase. Therefore, when the EVS 15 arranged with a light source 13 having a higher illuminance has a larger number of events, the determination device 16 determines that a pinhole PH has occurred in the metal foil 100, thereby further improving the detection accuracy of the pinhole PH.

[0193] <Specific Example 4> The detection range Ad of the EVS 15 may be set differently for each EVS 15. In this case, the determination device 16 determines that a pinhole PH has occurred in the metal foil 100 if the event number condition is satisfied in each of the multiple EVSs 15 and the larger the detection range Ad of the EVS 15, the greater the number of consecutive accumulation periods T that satisfy the event number condition.

[0194] 19 , the detection range Ad1 of the upstream EVS 151 is set larger than the detection range Ad2 of the downstream EVS 152. The determination device 16 calculates the number of consecutive integration periods T during which the P-type event count Xp is equal to or greater than the first P-type event count threshold Xpt1 for the upstream EVS 151. The determination device 16 also calculates the number of consecutive integration periods T during which the P-type event count Xp is equal to or greater than the first P-type event count threshold Xpt1 for the downstream EVS 152. The determination device 16 determines that a pinhole PH has occurred in the metal foil 100 when the number of consecutive integration periods T during which the P-type event count Xp is equal to or greater than the first P-type event count threshold Xpt1 for the upstream EVS 151 is longer than the number of consecutive integration periods T during which the P-type event count Xp is equal to or greater than the first P-type event count threshold Xpt1 for the downstream EVS 152.

[0195] The larger the detection range Ad of the EVS 15, the longer the passing time, and therefore the longer the number of consecutive integration periods T that satisfy the event number condition. Therefore, the larger the detection range Ad of the EVS 15, the more consecutive integration periods T that satisfy the event number condition, and therefore the more accurately the pinhole PH is detected, as determined by the determination device 16 when the number of consecutive integration periods T that satisfy the event number condition is large.

[0196] For example, as the brush 42 becomes worn, light from the light source 13 may pass outside the two ends of the metal foil 100 in the lateral direction, and may find its way around to the EVS 15. In this case, noise-induced P-type events and N-type events are more likely to occur at the ends of the metal foil 100 in the lateral direction than at the center, and therefore the number of P-type events Xp and the number of N-type events Xn are more likely to increase at the ends of the metal foil 100 in the lateral direction than at the center. Therefore, different first event count thresholds may be set for the center and the ends of the metal foil 100 in the lateral direction. Specifically, different first P-type event count thresholds Xpt1, first N-type event count thresholds Xnt1, and first total event count thresholds Xst1 may be set for the center and the ends of the metal foil 100 in the lateral direction.

[0197] For example, the first P-type event number threshold Xpt1 may include two types of P-type event number thresholds: a center P-type event number threshold Xptc and an edge P-type event number threshold Xpte. The center P-type event number threshold Xptc is a P-type event number threshold Xpt for detecting pinholes PH occurring in the center in the short-side direction of the metal foil 100. The edge P-type event number threshold Xpte is a P-type event number threshold Xpt for detecting pinholes PH occurring at the edges in the short-side direction of the metal foil 100. The edge P-type event number threshold Xpte is set to a value greater than the center P-type event number threshold Xptc. The event number conditions include a "first event number condition in which the number of P-type events Xp at the center of the metal foil 100 in the short direction is equal to or greater than a center P-type event number threshold Xptc," and a "second event number condition in which the number of P-type events Xp at the end of the metal foil 100 in the short direction is equal to or greater than an end P-type event number threshold Xpte."

[0198] The determination device 16 calculates the number of P-type events Xp separately for the central portion and each end portion of the metal foil 100 in the widthwise direction. For example, assume that one EVS 15 detects events across the entire widthwise direction of the metal foil 100. In this case, the determination device 16 calculates the number of P-type events Xp at the central portion of the widthwise direction of the metal foil 100 by adding up the number of P-type events occurring in pixel rows located at the central portion of the widthwise direction of the metal foil 100 among multiple pixel rows aligned in the X direction. The determination device 16 calculates the number of P-type events Xp at each end portion of the widthwise direction of the metal foil 100 by adding up the number of P-type events occurring in pixel rows located at each end portion of the widthwise direction of the metal foil 100 among multiple pixel rows aligned in the X direction. The determination device 16 determines that a pinhole PH has occurred in the metal foil 100 when at least one of the first event number condition and the second event number condition is satisfied.

[0199] In this case, pinhole PH detection can be performed taking into consideration that the number of P-type events Xp and the number of N-type events Xn are more likely to increase at each end in the lateral direction of the metal foil 100 than at the center. Therefore, the accuracy of pinhole PH detection can be improved. Furthermore, if a pinhole PH occurs in the metal foil 100, it can be detected whether the pinhole PH occurs in the center or at an end in the lateral direction of the metal foil 100.

[0200] Similarly, the first N-type event number threshold Xnt1 may include two types of event number conditions: a center N-type event number threshold Xntc and an edge N-type event number threshold Xnte that is greater than the center N-type event number threshold Xntc. The event number conditions include a "first event number condition in which the number of N-type events Xn at the center in the widthwise direction of the metal foil 100 is equal to or greater than the center N-type event number threshold Xntc," and a "second event number condition in which the number of N-type events Xn at the edge in the widthwise direction of the metal foil 100 is equal to or greater than the edge N-type event number threshold Xnte."

[0201] The first total event number threshold Xst1 may include two types of event number conditions: a center total event number threshold Xstc and an edge total event number threshold Xste that is greater than the center total event number threshold Xstc. The event number conditions include a "first event number condition in which the total event number Xs at the center in the widthwise direction of the metal foil 100 is equal to or greater than the center total event number threshold Xstc" and a "second event number condition in which the total event number Xs at the edge in the widthwise direction of the metal foil 100 is equal to or greater than the edge total event number threshold Xste."

[0202] When a plurality of EVSs 15 are arranged in the lateral direction of the metal foil 100 as in the above embodiment, the determination device 16 may calculate the number of P-type events Xp at the central portion of the lateral direction of the metal foil 100 from event data from the EVSs 15 located at the central portion of the lateral direction of the metal foil 100. The determination device 16 may calculate the number of P-type events Xp at each end portion of the lateral direction of the metal foil 100 from event data from the EVSs 15 located at each end portion of the lateral direction of the metal foil 100.

[0203] The first event count threshold may be set in multiple stages. Specifically, the first P-type event count threshold Xpt1, the first N-type event count threshold Xnt1, and the first total event count threshold Xst1 may each be set in multiple stages.

[0204] 20 , for example, the first P-type event count threshold Xpt1 may be set in two stages: a small diameter P-type event count threshold Xpta, and a large diameter P-type event count threshold Xptb that is greater than the small diameter P-type event count threshold Xpta. In this case, the event count condition includes a "first event count condition in which the P-type event count Xp is equal to or greater than the small diameter P-type event count threshold Xpta and less than the large diameter P-type event count threshold Xptb," and a "second event count condition in which the P-type event count Xp is equal to or greater than the large diameter P-type event count threshold Xptb."

[0205] Similarly, the first N-type event count threshold Xnt1 may be set in two stages: a small diameter N-type event count threshold Xnta, and a large diameter N-type event count threshold Xntb that is greater than the small diameter N-type event count threshold Xnta. In this case, the event count condition includes a "first event count condition in which the N-type event count Xn is equal to or greater than the small diameter N-type event count threshold Xnta and less than the large diameter N-type event count threshold Xntb," and a "second event count condition in which the N-type event count Xn is equal to or greater than the large diameter N-type event count threshold Xntb."

[0206] The first total event number threshold Xst1 may be set in two stages: a small diameter total event number threshold Xsta and a large diameter total event number threshold Xstb that is greater than the small diameter total event number threshold Xsta. In this case, the event number condition includes a "first event number condition in which the total event number Xs is equal to or greater than the small diameter total event number threshold Xsta and less than the large diameter total event number threshold Xstb" and a "second event number condition in which the total event number Xs is equal to or greater than the large diameter total event number threshold Xstb."

[0207] When the determination device 16 determines that the first event number condition or the second event number condition is satisfied, it determines that a pinhole PH has occurred in the metal foil 100. When the first event number condition is satisfied, the determination device 16 determines that the pinhole PH occurring in the metal foil 100 is a small-diameter pinhole PH among the pinholes PH with diameters detectable by the event number condition. When the second event number condition is satisfied, the determination device 16 determines that the pinhole PH occurring in the metal foil 100 is a large-diameter pinhole PH among the pinholes PH with diameters detectable by the event number condition.

[0208] As described above, the larger the diameter of the pinhole PH, the more light passes through the pinhole PH, and therefore the larger the number of P-type events Xp and the number of N-type events Xn. Therefore, by setting the first P-type event count threshold Xpt1, the first N-type event count threshold Xnt1, and the first total event count threshold Xst1 in two stages, it is possible to determine not only the presence or absence of a pinhole PH, but also whether the pinhole PH is a small-diameter pinhole PH or a large-diameter pinhole PH among pinholes PH with diameters that can be detected based on the event count condition.

[0209] In the above example, the first P-type event count threshold Xpt1, the first N-type event count threshold Xnt1, and the first total event count threshold Xst1 were each set in two stages, but they may also be set in three or more stages.

[0210] In this modified example, the marking device 17 may apply the mark M to the metal foil 100 as follows: When the determination device 16 determines that a pinhole PH occurring in the metal foil 100 is a small-diameter pinhole PH among pinholes PH with diameters detectable under the event number condition, the marking device 17 applies a first mark M1, which is the mark M, to the metal foil 100. As shown in FIG. 1 , the first mark M1 is, for example, a straight line extending in the short direction of the metal foil 100, similar to the mark M in the above embodiment.

[0211] 21 , when the determination device 16 determines that a pinhole PH occurring in the metal foil 100 is a large-diameter pinhole PH among pinholes PH with diameters detectable under the event number condition, the marking device 17 applies a second mark M2, which is a mark M, to the metal foil 100. The second mark M2 is a mark M different from the first mark M1. The second mark M2 is, for example, a cross formed by a line extending in the short direction of the metal foil 100 and a line extending in the long direction of the metal foil 100 intersecting at right angles. The first mark M1 and the second mark M2 may be changed as appropriate as long as they are different marks M from each other.

[0212] In this case, the first mark M1 or the second mark M2 applied to the metal foil 100 can be used to determine not only whether a pinhole PH has occurred in the metal foil 100, but also whether the pinhole PH has a large diameter or a small diameter.

[0213] When the metal foil 100 is used as the current collector 210 of the bipolar electrode 200 as in the above embodiment, if large-diameter pinholes PH are present, there is a risk that the negative electrode active material mixture applied to the first surface 100a of the metal foil 100 may reach the second surface 100b through the pinholes PH during the negative electrode active material layer formation process. In this case, if the second marks M2 are provided on the metal foil 100, the negative electrode active material mixture can be applied in the negative electrode active material layer formation process while avoiding the areas where the large-diameter pinholes PH exist. Therefore, it is easier to prevent the negative electrode active material mixture applied to the first surface 100a of the metal foil 100 from reaching the second surface 100b through the pinholes PH.

[0214] For example, the first P-type event number threshold Xpt1 may include four types of P-type event number thresholds: a central small diameter P-type event number threshold Xptca, a central large diameter P-type event number threshold Xptcb, an end small diameter P-type event number threshold Xptea, and an end large diameter P-type event number threshold Xpteb. The central large diameter P-type event number threshold Xptcb is greater than the central small diameter P-type event number threshold Xptca. The end large diameter P-type event number threshold Xpteb is greater than the end small diameter P-type event number threshold Xptea. The end small diameter P-type event number threshold Xptea is greater than the central small diameter P-type event number threshold Xptca. The end large diameter P-type event number threshold Xpteb is greater than the central large diameter P-type event number threshold Xptcb.

[0215] The event number conditions include a first event number condition, a second event number condition, a third event number condition, and a fourth event number condition. The first event number condition is that "the number of P-type events Xp at the central portion of the metal foil 100 in the short-side direction is equal to or greater than a P-type event number threshold Xptca for a central small diameter and less than a P-type event threshold Xptcb for a central large diameter." The second event number condition is that "the number of P-type events Xp at the end portions of the metal foil 100 in the short-side direction is equal to or greater than a P-type event number threshold Xptea for an end small diameter and less than a P-type event number threshold Xpteb for an end large diameter." The third event number condition is that "the number of P-type events Xp at the central portion of the metal foil 100 in the short-side direction is equal to or greater than a P-type event number threshold Xptcb for a central large diameter." The fourth event number condition is that "the number of P-type events Xp at the end portions of the metal foil 100 in the short-side direction is equal to or greater than a P-type event number threshold Xpteb for an end large diameter."

[0216] When the determination device 16 determines that any one of the first event number condition, the second event number condition, the third event number condition, and the fourth event number condition is satisfied, the determination device 16 determines that a pinhole PH has occurred in the metal foil 100. Furthermore, when the first event number condition is satisfied, the determination device 16 determines that the detected pinhole PH is located in the center of the metal foil 100 in the short side direction and is a pinhole PH with a small diameter among pinholes PH with diameters detectable by the event number condition. When the determination device 16 determines that the second event number condition is satisfied, the determination device 16 determines that the detected pinhole PH is located at an end of the metal foil 100 in the short side direction and is a pinhole PH with a small diameter among pinholes PH with diameters detectable by the event number condition. If the third event number condition is satisfied, the determination device 16 determines that the detected pinhole PH is located at the center of the metal foil 100 in the short direction and is a large-diameter pinhole PH among pinholes PH with diameters detectable by the event number condition. If the fourth event number condition is satisfied, the determination device 16 determines that the detected pinhole PH is located at an end of the metal foil 100 in the short direction and is a large-diameter pinhole PH among pinholes PH with diameters detectable by the event number condition.

[0217] In this case, pinhole PH detection can be performed taking into consideration that the number of P-type events Xp and the number of N-type events Xn are more likely to increase at each end of the metal foil 100 in the lateral direction than at the center. Therefore, the accuracy of pinhole PH detection can be improved. Furthermore, if a pinhole PH occurs in the metal foil 100, it can be detected whether the pinhole PH occurs in the center or end of the metal foil 100 in the lateral direction. Furthermore, it can be determined whether the pinhole PH is a small-diameter pinhole PH or a large-diameter pinhole PH among pinholes PH with diameters detectable under the event number condition.

[0218] The first N-type event count threshold Xnt1 and the first total event count threshold Xst1 may also be set as described above. In the above embodiment, the determination device 16 individually determines whether pinholes PH have occurred in the first to fourth inspection areas A1 to A4 of the metal foil 100, but this is not limited to this. For example, the determination device 16 may collectively determine whether pinholes PH have occurred in the entire area from the first cutting line L1 to the fifth cutting line L5 in the short direction of the metal foil 100. In this case, only one marking device 17 is required.

[0219] The conveying speed of the metal foil 100 may be changed as appropriate. The slower the conveying speed of the metal foil 100, the more light passes through the pinholes PH, and therefore the number of P-type events Xp and the number of N-type events Xn increase. Therefore, in order to improve the detection accuracy of pinholes PH, it is preferable to ensure the number of P-type events Xp and the number of N-type events Xn by slowing down the conveying speed of the metal foil 100. On the other hand, if the conveying speed of the metal foil 100 is slow, the inspection time for the metal foil 100 increases, thereby reducing productivity. Therefore, it is preferable to set the conveying speed of the metal foil 100 taking into consideration the detection accuracy of pinholes PH and productivity.

[0220] The value obtained by dividing the illuminance of the light source 13 by the conveying speed of the metal foil 100 is R1. The higher the illuminance of the light source 13, the larger R1 becomes. The slower the conveying speed of the metal foil 100, the larger R1 becomes. In other words, the larger R1 becomes, the easier it is to ensure the number of P-type events Xp and the number of N-type events Xn. For example, the conveying speed of the metal foil 100 is 200 m / min. The maximum value of the illuminance of the light source 13 is 6.16 million lx, the minimum value is 5.54 million lx, and the median value is 5.6 million lx. In this case, the minimum value R1min of R1 is 2.77.

[0221] Furthermore, the value obtained by dividing the diameter of the pinhole PH by R1 is R2. The larger the diameter of the pinhole PH, the larger R2 becomes. The larger R1 becomes, the smaller R2 becomes. The higher the illuminance of the light source 13, the smaller R2 becomes. The slower the conveying speed of the metal foil 100, the smaller R2 becomes. In other words, the smaller R2 is, the easier it is to ensure the number of P-type events Xp and the number of N-type events Xn.

[0222] The diameter of the pinhole PH and the maximum value R2max of R2 suitable for detecting pinholes PH of that diameter are shown in Table 1. The maximum value R2max of R2 is the value obtained by dividing the diameter of the pinhole PH by the minimum value R1min of R1.

[0223] As shown in Table 1, to detect a pinhole PH having a diameter of 0.01 μm, R2 is preferably 0.004 or less. To detect a pinhole PH having a diameter of 0.1 μm, R2 is preferably 0.036 or less. To detect a pinhole PH having a diameter of 0.15 μm, R2 is preferably 0.054 or less. To detect a pinhole PH having a diameter of 0.2 μm, R2 is preferably 0.072 or less. To detect a pinhole PH having a diameter of 1 μm, R2 is preferably 0.361 or less. To detect a pinhole PH having a diameter of 5 μm, R2 is preferably 1.804 or less. To detect a pinhole PH having a diameter of 10 μm, R2 is preferably 3.608 or less. To detect a pinhole PH having a diameter of 200 μm, R2 is preferably 72.150 or less.

[0224] The conveying device 11 may convey the metal foil 100 so that the first surface 100a is located on the lower side and the second surface 100b is located on the upper side. If the entire pinhole detection device 10 is provided in a darkroom, the housing 12 may be omitted.

[0225] The light source 13 may be disposed above the metal foil 100, and the EVS 15 may be disposed below the metal foil 100. In short, the EVS 15 may be disposed on the opposite side of the metal foil 100 from the light source 13 in the thickness direction of the metal foil 100, i.e., in the Z direction.

[0226] In the above embodiment, the light source 13 irradiates the metal foil 100 with white light. However, the present invention is not limited to this. The light source 13 may irradiate the metal foil 100 with light of a color other than white.

[0227] The light source 13 preferably emits light with a relatively long wavelength, such as red light. Specifically, the light source 13 preferably emits light having a peak in the wavelength range of 600 to 660 nm. The light source 13 more preferably emits light having a peak in the wavelength range of 630 to 650 nm.

[0228] 22, the light from the light source 13 is more likely to be diffracted, causing events to occur over a wider range, which in turn widens the distribution range of events in the Y direction and increases the number of events, making it easier to detect small-diameter pinholes PH.

[0229] The configuration of the mask 14 in the above embodiment is an example. The configuration of the mask 14 may be changed as appropriate as long as the light from the light source 13 passes outside both ends of the metal foil 100 in the short direction and is thereby prevented from leaking into the EVS 15.

[0230] The marking device 17 may be omitted. The method by which the marking device 17 applies the mark M to the metal foil 100 is not limited to laser irradiation, and other methods such as attaching tape, applying ink, and punching may also be used.

[0231] The marking device 17 may be disposed below the metal foil 100. In the above embodiment, the same number of marking devices 17 as the inspection areas A1 to A4 of the metal foil 100 are provided, but this is not limited to this. For example, the pinhole detection device 10 may be provided with one marking device 17. One marking device 17 is configured to be able to apply marks M individually to the first to fourth inspection areas A1 to A4 of the metal foil 100.

[0232] The number of cutting lines extending in the longitudinal direction of the metal foil 100 may be changed as appropriate depending on the widthwise dimension of the metal foil 100 and the dimensions required for the current collector 210. The metal foil 100 may be used in batteries other than nickel-metal hydride batteries. The metal foil 100 may be used in, for example, lithium-ion batteries.

[0233] The metal foil 100 may be used in an electrode in which an active material layer is formed on only one side of a current collector. The metal foil 100 may be used for purposes other than as a current collector.

[0234] The object to be inspected to which the pinhole detection method is applied is not limited to the metal foil 100. The object to be inspected to which the pinhole detection method is applied does not have to be in the shape of a long strip.

[0235] [Notes] The technical ideas that can be understood from the above embodiments and modifications are described below. <Note 1> A pinhole detection method for detecting a pinhole that has occurred in an object being transported to be inspected, wherein a Y direction, which is a transport direction of the object to be inspected, is perpendicular to a Z direction, which is a thickness direction of the object to be inspected, and the pinhole detection method comprises: a light source irradiating light toward the object to be inspected in the Z direction; and an event-based vision sensor, which is arranged on the opposite side of the object to be inspected in the Z direction from the light source, capturing an image of the object to be inspected as it is being transported; the event-based vision sensor has a plurality of pixels that can detect a change in brightness as an event, and records the position of the pixel that detected the event, the time when the event occurred, and the image of the event. and polarity of a luminance change of the event, indicating whether the vent is a P-type event in which luminance increases or an N-type event in which luminance decreases, to a determination device; and determining by the determination device, based on the event data, whether an event number condition, where the number of events, which is an integrated value of the number of occurrences of the events in a predetermined integration period, is equal to or greater than a first event number threshold, or an event distribution condition, where the events are distributed in the Y direction, is satisfied; and if the event number condition or the event distribution condition is satisfied, the determination device determines that the pinhole has occurred in the object being inspected.

[0236] <Supplementary Note 2> The pinhole detection method according to Supplementary Note 1, wherein the number of pixel columns in which the event has been detected during the integration period among the plurality of pixel columns aligned in the Y direction is the number of pixel columns in the Y direction, and the event distribution condition includes a first event distribution condition in which the number of pixel columns in the Y direction is equal to or greater than a Y direction pixel column number threshold.

[0237] <Supplementary Note 3> The pinhole detection method according to Supplementary Note 1, wherein, of a plurality of pixel columns aligned in an X direction orthogonal to both the Y direction and the Z direction, the number of pixel columns in which the event has been detected during the integration period is the number of pixel columns in the X direction; and, of a plurality of pixel columns aligned in the Y direction, the number of pixel columns in which the event has been detected during the integration period is the number of pixel columns in the Y direction; and the event distribution condition includes a first event distribution condition in which a ratio of the number of pixel columns in the Y direction to the number of pixel columns in the X direction is equal to or greater than a ratio threshold.

[0238] <Supplementary Note 4> The pinhole detection method according to any one of Supplementary Notes 1 to 3, wherein the event distribution condition includes a second event distribution condition that the integration period during which the number of events is equal to or greater than a second event number threshold occurs a predetermined number of times in succession.

[0239] <Supplementary Note 5> The pinhole detection method according to any one of Supplementary Notes 1 to 4, wherein the determination device determines whether the event number condition or the event distribution condition is satisfied by using only events that occur consecutively in the Y direction at the same position in the X direction orthogonal to both the Y direction and the Z direction, among the events detected by the event-based vision sensor.

[0240] <Supplementary Note 6> The pinhole detection method according to any one of Supplementary Notes 1 to 5, wherein a plurality of the light sources and the event-based vision sensors are provided in the Y direction, and the determination device determines that the pinhole has occurred in the inspected object when the event number condition or the event distribution condition is satisfied in each of the plurality of event-based vision sensors.

[0241] <Supplementary Note 7> The pinhole detection method according to Supplementary Note 6, wherein the determination device determines that the pinhole has occurred in the inspected object if the event number condition is satisfied in each of the plurality of event-based vision sensors and the events in the plurality of event-based vision sensors occur at the same position in the X direction, which is orthogonal to both the Y direction and the Z direction.

[0242] <Supplementary Note 8> The pinhole detection method according to Supplementary Note 6, wherein the illuminance of the light source is set to be different for each of the light sources, and the determination device determines that the pinhole has occurred in the inspected object if the event number condition is satisfied in each of the plurality of event-based vision sensors and the number of events is greater for an event-based vision sensor arranged with a light source having a higher illuminance.

[0243] <Supplementary Note 9> The pinhole detection method according to Supplementary Note 6, wherein the detection range of the event-based vision sensor is set to be different for each of the event-based vision sensors, and the determination device determines that the pinhole has occurred in the inspected object if the event number condition is satisfied in each of the plurality of event-based vision sensors and the larger the detection range of the event-based vision sensor, the greater the number of consecutive accumulation periods that satisfy the event number condition.

[0244] <Supplementary Note 10> The pinhole detection method according to any one of Supplementary Notes 1 to 9, wherein the object to be inspected is a long strip that is transported in the longitudinal direction.

[0245] <Supplementary Note 11> The pinhole detection method according to Supplementary Note 10, wherein the first event number threshold includes two types of event number thresholds: a center event number threshold and an end event number threshold that is greater than the center event number threshold; the event number conditions include a first event number condition under which the number of events at a center in a widthwise direction of the object to be inspected is equal to or greater than the center event number threshold, and a second event number condition under which the number of events at an end of the object to be inspected in the widthwise direction is equal to or greater than the end event number threshold; and the determination device determines that the pinhole has occurred in the object to be inspected when at least one of the first event number condition and the second event number condition is satisfied.

[0246] <Supplementary Note 12> The pinhole detection method according to any one of Supplementary Notes 1 to 11, wherein a marking device arranged downstream of the light source and the event-based vision sensor in the Y direction applies a mark to the object to be inspected at a position corresponding to the pinhole in the Y direction when the determination device determines that the pinhole has occurred in the object to be inspected.

[0247] <Supplementary Note 13> The pinhole detection method according to Supplementary Note 12, wherein a plurality of inspection areas are set on the inspection object so as to be aligned in an X direction perpendicular to both the Y direction and the Z direction, the determination device determines individually whether or not the pinhole has occurred in each of the plurality of inspection areas, and the marking device applies the mark only to the inspection area determined by the determination device to have the pinhole.

[0248] <Supplementary Note 14> The pinhole detection method according to any one of Supplementary Notes 1 to 13, wherein the light source irradiates light having a peak in a wavelength region of 600 to 660 nm.

[0249] <Supplementary Note 15> A pinhole detection device configured to detect pinholes occurring in an object to be inspected that is being transported, wherein a Y direction that is a transport direction of the object to be inspected is perpendicular to a Z direction that is a thickness direction of the object to be inspected, and the pinhole detection device includes a light source configured to irradiate light toward the object to be inspected in the Z direction, and an event-based vision sensor that is arranged on the opposite side of the object to the light source in the Z direction across the object to be inspected in order to capture an image of the object to be inspected that is being transported, the event-based vision sensor having a plurality of pixels that can detect a luminance change as an event, and a position of the pixel that detected the event, a time when the event occurred, and an event when the event occurred and a determination device, wherein the determination device is configured to determine, based on the event data, whether an event count condition, where the number of events, which is the integrated value of the number of occurrences of the events in a predetermined integration period, is equal to or greater than a first event count threshold, or an event distribution condition, where the events are distributed in the Y direction, is satisfied, and to determine that the pinhole has occurred in the object being inspected if the event number condition or the event distribution condition is satisfied.

[0250] 13...light source, 15...event-based vision sensor (EVS), 16...judgment device, 17...marking device, 50a...pixel, 100...metal foil as object to be inspected, A1...first inspection area as inspection area, A2...second inspection area as inspection area, A3...third inspection area as inspection area, A4...fourth inspection area as inspection area, Ad...detection range, M...mark, PH...pinhole, T...accumulation period.

Claims

1. A pinhole detection method for detecting pinholes occurring in an object being transported, wherein a Y direction, which is a transport direction of the object being transported, is perpendicular to a Z direction, which is a thickness direction of the object being transported, and the pinhole detection method comprises: a light source irradiating light towards the object being inspected in the Z direction; an event-based vision sensor, which is disposed on the opposite side of the object being inspected in the Z direction from the light source, images the object being transported, the event-based vision sensor having a plurality of pixels capable of detecting a luminance change as an event, and outputting event data to a determination device, the event data including the position of the pixel that detected the event, the time of occurrence of the event, and the polarity of the luminance change of the event, which indicates whether the event is a P-type event in which luminance increases or an N-type event in which luminance decreases; and the determination device determining, based on the event data, whether an event number condition, which is an integrated value of the number of occurrences of the events in a predetermined integration period, is equal to or greater than a first event number threshold, or an event distribution condition, which indicates that the events are distributed in the Y direction, is satisfied. and when the event number condition or the event distribution condition is satisfied, the determination device determines that the pinhole has occurred in the inspected object.

2. A pinhole detection method as described in claim 1, wherein, among the multiple pixel columns lined up in the Y direction, the number of pixel columns in which the event is detected during the integration period is the number of Y-direction pixel columns, and the event distribution condition includes a first event distribution condition in which the number of Y-direction pixel columns is equal to or greater than a Y-direction pixel column number threshold.

3. The pinhole detection method of claim 1, wherein, among a plurality of pixel columns aligned in an X direction perpendicular to both the Y direction and the Z direction, the number of pixel columns in which the event is detected during the integration period is the number of pixel columns in the X direction, and, among a plurality of pixel columns aligned in the Y direction, the number of pixel columns in which the event is detected during the integration period is the number of pixel columns in the Y direction, and the event distribution condition includes a first event distribution condition in which a ratio of the number of pixel columns in the Y direction to the number of pixel columns in the X direction is equal to or greater than a ratio threshold.

4. A pinhole detection method according to claim 1, wherein the event distribution conditions include a second event distribution condition that the integration period during which the number of events is equal to or greater than a second event number threshold continues for a predetermined number of times or more.

5. A pinhole detection method according to any one of claims 1 to 4, wherein the determination device determines whether or not the event number condition or the event distribution condition is satisfied using only those events that occur consecutively in the Y direction at the same position in the X direction perpendicular to both the Y direction and the Z direction, among the events detected by the event-based vision sensor.

6. The pinhole detection method of claim 1, wherein the light source and the event-based vision sensor are provided in multiple locations in the Y direction, and the determination device determines that the pinhole has occurred in the inspected object when the event number condition or the event distribution condition is satisfied in each of the multiple event-based vision sensors.

7. The pinhole detection method of claim 6, wherein the determination device determines that the pinhole has occurred in the inspected object when the event number condition is satisfied in each of the multiple event-based vision sensors and when the event occurs at the same position in the X direction perpendicular to both the Y direction and the Z direction in the multiple event-based vision sensors.

8. The pinhole detection method of claim 6, wherein the illuminance of the light source is set differently for each of the light sources, and the determination device determines that the pinhole has occurred in the inspected object when the event number condition is satisfied in each of the plurality of event-based vision sensors and the event-based vision sensor arranged with the light source having a higher illuminance has a larger number of events.

9. The pinhole detection method of claim 6, wherein the detection range of the event-based vision sensor is set differently for each of the event-based vision sensors, and the determination device determines that the pinhole has occurred in the inspected object when the event number condition is satisfied in each of the multiple event-based vision sensors and the event-based vision sensor with the larger detection range has a greater number of consecutive accumulation periods that satisfy the event number condition.

10. The pinhole detection method according to claim 1, wherein the object to be inspected is a long strip transported in the longitudinal direction.

11. The pinhole detection method according to claim 10, wherein the first event number threshold includes two types of event number thresholds: a center event number threshold, and an end event number threshold that is greater than the center event number threshold; the event number conditions include a first event number condition under which the number of events at a center in the short side direction of the object to be inspected is equal to or greater than the center event number threshold, and a second event number condition under which the number of events at an end portion of the object to be inspected in the short side direction is equal to or greater than the end event number threshold; and the determination device determines that the pinhole has occurred in the object to be inspected if at least one of the first event number condition and the second event number condition is satisfied.

12. A pinhole detection method as described in claim 1, wherein a marking device arranged downstream of the light source and the event-based vision sensor in the Y direction applies a mark to the object being inspected at a position corresponding to the pinhole in the Y direction when the judgment device judges that the pinhole has occurred in the object being inspected.

13. A pinhole detection method as described in claim 12, wherein a plurality of inspection areas are set on the object to be inspected so as to be aligned in an X direction perpendicular to both the Y direction and the Z direction, the judgment device judges individually whether or not the pinhole has occurred in each of the plurality of inspection areas, and the marking device applies the mark only to the inspection area judged by the judgment device to contain the pinhole.

14. The pinhole detection method according to claim 1, wherein the light source irradiates light having a peak in the wavelength region of 600 to 660 nm.

15. A pinhole detection device configured to detect pinholes occurring in an object being transported, wherein a Y direction, which is a transport direction of the object being transported, is perpendicular to a Z direction, which is a thickness direction of the object being transported, the pinhole detection device comprises: a light source configured to irradiate light toward the object being inspected in the Z direction; and an event-based vision sensor disposed on the opposite side of the object being inspected from the light source in the Z direction, in order to capture an image of the object being transported, the event-based vision sensor having a plurality of pixels capable of detecting a luminance change as an event, and configured to generate event data including a position of the pixel that detected the event, a time of occurrence of the event, and a polarity of the luminance change of the event, which indicates whether the event is a P-type event in which luminance increases or an N-type event in which luminance decreases; and a determination device, wherein the determination device determines based on the event data whether an event number condition is satisfied, where the event number, which is an integrated value of the number of occurrences of the events in a predetermined integration period, is equal to or greater than a first event number threshold, or an event distribution condition where the events are distributed in the Y direction, The pinhole detection device is configured to determine that the pinhole has occurred in the inspected object when the event number condition or the event distribution condition is satisfied.

Images