Apparatus and method for detecting magnetic foreign particles

Abstract

The present invention provides a magnetic foreign matter particle detection device and detection method that can appropriately detect whether or not magnetic foreign matter particles contained in a transported object are passing through. [Solution] A detection device for detecting the passage of magnetic foreign matter particles contained in an object being transported in the transport direction comprises: a first magnetic sensor positioned at a first transport position and outputting a change in the magnetic force of the transported object as a first sensor signal; a third magnetic sensor positioned at the first transport position opposite the first magnetic sensor via the object being transported and outputting a change in the magnetic force of the transported object as a third sensor signal; second and fourth magnetic sensors that output changes in external magnetism as second and fourth sensor signals; a difference signal pair acquisition unit that acquires two difference signals between two sensor signals and between other two sensor signals; and a foreign matter detection unit that uses the two difference signals to detect the passage of magnetic foreign matter particles at the first transport position.

Description

Technical Field

[0001] The present invention relates to a detecting device and a detecting method for magnetic foreign matter particles that detect magnetic foreign matter particles contained in an object to be inspected conveyed in a conveying direction.

Background Art

[0002] Patent Document 1 discloses a metal foreign matter detecting device that includes a magnetized unit, two magnetic sensors, a differential calculation unit, and a determination unit as a metal foreign matter detecting device for an inspection object conveyed along a conveyance path.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when detecting the presence or absence of passage of magnetic foreign matter particles contained in a conveyed object such as paste, the direction of magnetization of the contained magnetic foreign matter particles is indefinite, and when conveyed through a pipe, it may pass near the center of the pipe or near the periphery. For this reason, the strength of the sensor signal generated when the magnetic foreign matter particles detected by the magnetic sensor pass is likely to vary. In addition, since noise due to changes in external magnetic fields arriving from the outside is also added to the sensor signal, it is likely to be difficult to detect when the magnetic foreign matter particles are small and have a slight magnetization.

[0005] The present invention has been made in view of such a situation, and provides a detecting device and a detecting method for magnetic foreign matter particles that can appropriately detect the presence or absence of passage of magnetic foreign matter particles contained in a conveyed object.

Means for Solving the Problems

[0006] (1) One aspect of the present invention for solving the above problems is a magnetic foreign matter particle detection device for detecting whether or not magnetic foreign matter particles contained in an object to be inspected are passing through an object being transported from the upstream side to the downstream side in the transport direction, comprising: a first magnetic sensor positioned at a first transport position in the transport direction and outputting a change in the magnetic force of the object being transported as a first sensor signal; a second magnetic sensor that outputs a change in external magnetic field arriving from the outside as a second sensor signal; and a magnetic foreign matter particle detection device positioned at the first transport position opposite the first magnetic sensor via the object to be inspected and detecting the passage of magnetic foreign matter particles contained in an object being transported. The magnetic foreign object detection device comprises: a third magnetic sensor that outputs a change in the magnetic force of an object being inspected as a third sensor signal; a fourth magnetic sensor that outputs a change in the external magnetic field as a fourth sensor signal; a difference signal pair acquisition unit that acquires two difference signals from the first, second, third, and fourth sensor signals: a difference signal between two of the sensor signals and a difference signal between the other two of the sensor signals; and a foreign object detection unit that uses the two difference signals to detect whether or not the magnetic foreign object has passed through the first transport position.

[0007] In this detection device, the difference signal pair acquisition unit acquires two (a pair) difference signals from four sensor signals. Furthermore, the foreign object detection unit uses these two difference signals to detect whether or not magnetic foreign particles have passed through. Both difference signals are obtained by subtracting one sensor signal from the other, thereby suppressing noise components caused by changes in external magnetism that are thought to be commonly present. Therefore, by using two difference signals, it is possible to sensitively detect whether or not magnetic foreign particles have passed through the first transport position while suppressing noise components caused by changes in external magnetism contained in the first sensor signal and the third sensor signal from the first magnetic sensor and the third magnetic sensor opposite it.

[0008] The objects to be transported include slurries such as active material paste, liquids such as electrolytes, powders and granules such as active material particles, aggregates of clay-like or solid pellets, strip-shaped films such as electrode plates and separators, individual clay-like or solid pellets, and individual components, all of which are transported inside pipes or on conveyors.

[0009] The second and fourth magnetic sensors are preferably positioned near the first and third magnetic sensors in order to cancel out external magnetic field changes (external noise) entering the first and third magnetic sensors through differential detection. Furthermore, it is desirable that the second and fourth magnetic sensors also be able to detect changes in the magnetic field of the object being inspected. For example, they may be positioned downstream or upstream of the first and third magnetic sensors positioned at the first transport position, or at the same first transport position as the first and third magnetic sensors.

[0010] External magnetic field changes are changes in the magnetic field that reach the detection range of each magnetic sensor from the outside. Examples include alternating magnetic fields of 50Hz or 60Hz emitted from nearby power lines, and changes in the surrounding magnetic field caused by the rotation of motors located near each magnetic sensor. Often, white noise-like magnetic changes are also present.

[0011] Examples of pairs of difference signals include a 1-2 difference signal between the first and second sensor signals, and a 3-4 difference signal between the third and fourth sensor signals, or a 1-3 difference signal between the first and third sensor signals, and a 2-4 difference signal between the second and fourth sensor signals.

[0012] When using two difference signals to detect the presence or absence of magnetic foreign particles passing through the first transport position, it is advisable to consider the arrangement of the second and fourth magnetic sensors, in addition to the first and third magnetic sensors which are positioned facing each other across the object under inspection. Specifically, it is advisable to select a processing method for the two difference signals by considering the presence or absence of signal components other than noise components due to changes in external magnetism, such as signal components due to the passage of magnetic foreign particles, in the second and fourth sensor signals detected by these second and fourth magnetic sensors.

[0013] For example, if the second and fourth magnetic sensors generate the same external magnetic field changes as the first and third magnetic sensors placed at the first transport position, but are positioned at a distance from the first and third magnetic sensors (for example, at the second transport position downstream of the first transport position), the following can be done: a second-order difference signal is obtained, which is the difference between the 1-2 difference signal between the first and second sensor signals and the 3-4 difference signal between the third and fourth sensor signals. Then, this second-order difference signal is compared with an upper or lower threshold to detect the passage of magnetic foreign particles at the first transport position. Alternatively, if the period during which the second-order difference signal exceeds a predetermined upper threshold or falls below a predetermined lower threshold is within a predetermined period range (exceeding the first period and less than the second period), the passage of magnetic foreign particles during that period can be detected. If the period during which the upper threshold is exceeded is too short, it is considered to be noise. On the other hand, if the period is too long, it is considered to be a signal due to some malfunction rather than the passage of magnetic foreign particles. Alternatively, the passage of magnetic foreign particles at the first transport position may be detected when the absolute value of the second-order difference signal exceeds the threshold. Another method is to detect the passage of magnetic foreign particles when the period during which the absolute value of the second-order difference signal exceeds the threshold is within a predetermined period range (exceeding the first period but less than the second period).

[0014] Furthermore, if the second and fourth magnetic sensors are positioned at the same first transport position as the first and third magnetic sensors, but in a second direction perpendicular to the transport direction and perpendicular to the first direction connecting the first and third magnetic sensors—that is, rotated 90 degrees in the circumferential direction—then the second and fourth magnetic sensors will experience magnetic field changes from external magnetism similar to the first and third magnetic sensors, as well as magnetic field changes associated with the passage of magnetic foreign particles at the same timing as the first and third magnetic sensors. Therefore, a 1-3 difference signal between the first and third sensor signals and a 2-4 difference signal between the second and fourth sensor signals are acquired. In addition, a second-order difference signal, which is the difference between these two difference signals, and a difference-sum signal, which is the sum of these two difference signals, are acquired. Then, by comparing these second-order difference signals and difference-sum signals with thresholds, if either exceeds the threshold, a method can be adopted in which the passage of magnetic foreign particles at the first transport position is detected.

[0015] Another method involves obtaining the squared difference signals for each of the two difference signals, and then obtaining the sum of these squared signals. If this sum of squared signals exceeds a threshold, it is considered that the passage of magnetic foreign particles at the first transport position has been detected. Another method involves detecting the passage of magnetic foreign particles if the period during which the sum of squared signals exceeds the threshold is within a predetermined period range (greater than the first period but less than the second period).

[0016] (2) A magnetic foreign particle detection device as described in (1), wherein the second magnetic sensor is positioned at a second transport position downstream of the first transport position and outputs a second sensor signal that also detects a change in the magnetic force of the object being transported, the fourth magnetic sensor is positioned at the second transport position opposite the second magnetic sensor via the object being inspected and outputs a fourth sensor signal that also detects a change in the magnetic force of the object being inspected, the difference signal pair acquisition unit acquires a 1-2 difference signal between the first sensor signal and the second sensor signal and a 3-4 difference signal between the third sensor signal and the fourth sensor signal, and the foreign object detection unit has a second-order difference acquisition unit that acquires an upstream-downstream second-order difference signal which is the difference between the 1-2 difference signal and the 3-4 difference signal, and a determination unit 5 that uses the upstream-downstream second-order difference signal to determine whether or not the magnetic foreign particle has passed through the first transport position.

[0017] In this inspection device, the first and third magnetic sensors are positioned facing each other at the first transport position, and the second and fourth magnetic sensors are positioned facing each other at the second transport position. A difference signal pair acquisition unit then obtains a 1-2 difference signal and a 3-4 difference signal. Even if the first magnetic sensor detects the passage of magnetic foreign particles at the first transport position and the signal of the first sensor changes accordingly, the signal of the second sensor downstream is not affected by the magnetic foreign particles. Therefore, in the 1-2 difference signal, noise caused by changes in external magnetism that enter both the first and second magnetic sensors is subtracted and suppressed, while the signal change due to the passage of magnetic foreign particles at the first transport position can be retained. Similarly, in the 3-4 difference signal, noise common to the third and fourth magnetic sensors can be suppressed, while the signal change due to the passage of magnetic foreign particles at the first transport position can be retained. Moreover, the signal change due to the passage of magnetic foreign particles is in opposite phase between the 1-2 difference signal and the 3-4 difference signal. The second-order difference acquisition unit then acquires the upstream / downstream second-order difference signal, which is the difference between the 1-2 difference signal and the 3-4 difference signal. Therefore, in this upstream / downstream second-order difference signal, in-phase noise components that could not be removed at the stage when the 1-2 difference signal or 3-4 difference signal was obtained are also removed. In addition, a large change can be obtained by adding the signal changes that occur in the first sensor signal and the third sensor signal due to the passage of magnetic foreign matter particles at the first transport position. Therefore, the determination unit can use this upstream / downstream second-order difference signal to more reliably determine whether or not magnetic foreign matter particles have passed at the first transport position.

[0018] Preferably, the second transport position where the second and fourth magnetic sensors are positioned is spaced away from the first transport position to such an extent that the detection ranges of the second and fourth magnetic sensors do not overlap with those of the first and third magnetic sensors positioned at the first transport position. This is to prevent situations where, if magnetic foreign particles are present, signals due to the magnetic foreign particles are simultaneously generated in the first and second sensor signals, and in the third and fourth sensor signals, and when acquiring the 1-2 difference signal and the 3-4 difference signal, the magnitude of the difference signal due to the magnetic foreign particles is reduced.

[0019] In the determination unit, a method for determining whether or not magnetic foreign particles have passed through the first transport position using the upstream-downstream second-order difference signal is to determine that magnetic foreign particles have passed through the first transport position if the upstream-downstream second-order difference signal exceeds a predetermined upper threshold or falls below a predetermined lower threshold. Alternatively, a method can be adopted in which, if the period during which the upstream-downstream second-order difference signal exceeds a predetermined upper threshold or falls below a predetermined lower threshold is within a predetermined period range (exceeding the first period and less than the second period), it is determined that magnetic foreign particles have passed through during that period. This is because if the period during which the upper threshold is exceeded is too short, it is considered to be noise, while if the period is too long, it is considered to be a signal due to some kind of malfunction rather than the passage of magnetic foreign particles. Furthermore, a method can be adopted in which, if the absolute value or squared value of the upstream-downstream second-order difference signal exceeds a predetermined threshold, it is determined that magnetic foreign particles have passed through. Furthermore, another method involves determining that magnetic foreign particles have passed through if the absolute or squared value of the upstream-downstream second-order difference signal exceeds a predetermined threshold for a period within a predetermined time range.

[0020] (3)(2) A magnetic foreign particle detection device, wherein the foreign object detection unit further comprises a foreign object confirmation unit that uses the upstream-downstream two-order difference signal to confirm the passage of the magnetic foreign particle detected at the first transport position to the second transport position.

[0021] In this inspection device, the second and fourth magnetic sensors are positioned opposite each other at the second transport position. Therefore, after the first timing when the magnetic foreign particle passes the first transport position, the second and fourth magnetic sensors also detect the passage of the magnetic foreign particle at the second timing when it passes the second transport position, and the signals from the second and fourth sensors change accordingly. Consequently, just as when the magnetic foreign particle passes the first transport position, the presence or absence of the magnetic foreign particle passing at the second transport position can be reliably determined using the upstream-downstream two-order difference signal. Moreover, since the passage of the magnetic foreign particle at the first transport position has already been detected at the first timing, by determining whether or not the magnetic foreign particle passed at the second timing when it should have passed the second transport position, it is possible to further confirm the presence of magnetic foreign particles that passed through both the first and second transport positions.

[0022] Furthermore, even if the upstream-downstream double-order difference signal determines that a magnetic foreign particle passed the first transport position at the first timing, it is possible that the passage of the magnetic foreign particle to the second transport position may not be detected from the upstream-downstream double-order difference signal at the subsequent second timing. In this case, for example, it is advisable to perform a process that considers the determination that a magnetic foreign particle passed at the first timing to be a false determination. Alternatively, the processing may be changed depending on the magnitude of the upstream-downstream double-order difference signal obtained at the first timing. For example, if the upstream-downstream double-order difference signal exceeds a definitive threshold greater than the upper threshold at the first timing, it may be assumed that a magnetic foreign particle was detected regardless of the result at the second timing. On the other hand, if, at the first timing, the absolute value of the upstream-downstream second-order difference signal exceeds the upper threshold but also exceeds the definitive threshold, and at the second timing, the passage of the magnetic foreign particle to the second transport position is not detected from the upstream-downstream second-order difference signal, then the determination that the magnetic foreign particle has passed the first transport position due to the absolute value of the upstream-downstream second-order difference signal exceeding the upper threshold at the first timing may be considered a false determination.

[0023] When the conveying distance from the first conveying position to the second conveying position is L and the conveyed object is conveyed at a constant conveying speed V, the delay time (conveying time) TL from the first timing to the second timing is given by TL = L / V.

[0024] Furthermore, the magnetic foreign particle detection device according to (2) or (3), wherein the inspection object is conveyed through a pipe, the first magnetic sensor and the second magnetic sensor are arranged at a first circumferential position in the circumferential direction of the pipe, and the third magnetic sensor and the fourth magnetic sensor are arranged at a second circumferential position on the opposite side of the first circumferential position in the circumferential direction. It is preferable to be a magnetic foreign particle detection device.

[0025] Thus, when conveying the inspection object through a pipe, the four magnetic sensors are arranged in the circumferential direction of the pipe as described above. Thereby, when magnetic foreign particles are conveyed together with the inspection object in the pipe, the changes in the first and third sensor signals and the changes in the second and fourth sensor signals due to the magnetic foreign particles are likely to have the same pattern, and the processing of each sensor signal, such as confirming the magnetic foreign particles at the second conveying position, becomes easy.

[0026] (4) Furthermore, the magnetic foreign particle detection device according to (2) or (3), which is arranged at a third conveying position upstream of the first conveying position in the conveying direction, and applies a magnetic field directed in a first direction connecting the first magnetic sensor and the third magnetic sensor that are orthogonal and opposed to each other in the conveying direction, and further includes a magnetization unit that magnetizes metal foreign particles contained in the inspection object to form the magnetic foreign particles. It is good to be a magnetic foreign particle detection device.

[0027] In this detection device, the magnetization unit is arranged at a third conveying position upstream of the first conveying position. Moreover, in this magnetization unit, the metal foreign particles are magnetized by a magnetic field directed in the first direction to form magnetic foreign particles. Therefore, when this magnetic foreign particle reaches the first conveying position, a large signal change due to the magnetic foreign particle can be caused in the first and third sensor signals. Thus, it is possible to more reliably determine the presence or absence of the passage of the magnetic foreign particle.

[0028] (5) Or, a magnetic foreign particle detection device as described in (1), wherein the second magnetic sensor is positioned at the first transport position on one side of a second direction perpendicular to the first direction connecting the first magnetic sensor and the third magnetic sensor which are opposite to each other and perpendicular to the transport direction, and outputs a second sensor signal that also detects a change in the magnetic force of the object being transported, and the fourth magnetic sensor is positioned at the first transport position on the other side of the second direction opposite to the second magnetic sensor via the object being transported, and outputs a fourth sensor signal that also detects a change in the magnetic force of the object being transported, and the difference signal pair acquisition The unit acquires a 1-3 difference signal between the first sensor signal and the third sensor signal, and a 2-4 difference signal between the second sensor signal and the fourth sensor signal. The foreign object detection unit is a magnetic foreign object detection device having a counter-second-order difference acquisition unit that acquires a counter-second-order difference signal which is the difference between the 1-3 difference signal and the 2-4 difference signal, a counter-second-order difference sum acquisition unit that acquires a counter-second-order difference sum signal which is the sum of the 1-3 difference signal and the 2-4 difference signal, and a determination unit that determines whether or not the magnetic foreign object particles have passed through the first transport position based on the second-order difference signal and the counter-second-order difference sum signal.

[0029] In this inspection device, the four magnetic sensors are positioned at the same first transport position. Furthermore, the second and fourth magnetic sensors are positioned opposite each other on one side and the other side of a second direction perpendicular to the first direction, with respect to the first direction connecting the first and third magnetic sensors, which are perpendicular to the transport direction and face each other. As a result, when a magnetic foreign particle passes through the first transport position, all four sensor signals from the four magnetic sensors change. Moreover, the passage of the magnetic foreign particle through the first transport position causes the first and third sensor signals to change in opposite phases. Similarly, the second and fourth sensor signals also change in opposite phases. Therefore, in the 1-3 difference signal and the 2-4 difference signal, noise caused by changes in external magnetism common to each magnetic sensor is subtracted and suppressed, while the signal changes due to the passage of the magnetic foreign particle at the first transport position can be added together and increased. Furthermore, depending on the direction of the magnetic field generated by the magnetic foreign particles, one of the opposing second-order difference signal and the opposing difference summation signal obtained from the 1-3 difference signal and the 2-4 difference signal will become even larger as the changes in the sensor signal due to the passage of the magnetic foreign particles through the first transport position are added together. Therefore, the determination unit can more reliably determine whether or not magnetic foreign particles have passed through the first transport position by using the opposing second-order difference signal and the opposing difference summation signal.

[0030] Furthermore, in the determination unit, a method for determining whether or not magnetic foreign particles have passed at the first transport position using the second-order difference signal and the opposing difference summation signal is to determine that magnetic foreign particles have passed if the second-order difference signal exceeds a predetermined upper threshold, falls below a predetermined lower threshold, or if the opposing difference summation signal exceeds an upper threshold or falls below a predetermined lower threshold. Alternatively, a method is to determine that magnetic foreign particles have passed if any of the periods during which the second-order difference signal exceeds the upper threshold, falls below the lower threshold, or if the opposing difference summation signal exceeds the upper threshold or falls below the lower threshold are within a predetermined period range (greater than the first period but less than the second period).

[0031] Another method involves detecting the passage of magnetic foreign particles when either the absolute value of the opposing second-order difference signal exceeds a predetermined threshold, or when the absolute value of the opposing difference sum signal exceeds a predetermined threshold. Furthermore, another method involves detecting the passage of magnetic foreign particles when the period during which the absolute value of the opposing second-order difference signal or the absolute value of the opposing difference sum signal exceeds a threshold falls within a predetermined period range.

[0032] One method involves detecting the passage of magnetic foreign particles when the sum of squares, which is the sum of the squares of the opposing second-order difference signals and the opposing sum of difference signals, exceeds a predetermined threshold. Another method involves detecting the passage of magnetic foreign particles when the period during which the sum of squares signal exceeds the threshold falls within a predetermined time range.

[0033] It is preferable that the magnetic foreign particle detection device described in (5) is such that the object to be inspected is transported inside a pipe, the first magnetic sensor is positioned at a first circumferential position in the circumferential direction of the pipe, the third magnetic sensor is positioned at a second circumferential position opposite to the first circumferential position in the circumferential direction, the second magnetic sensor is positioned at a third circumferential position deflected by 90 degrees from the first and second circumferential positions in the circumferential direction, and the fourth magnetic sensor is positioned at a fourth circumferential position opposite to the third circumferential position in the circumferential direction of the pipe.

[0034] Thus, when transporting the object to be inspected through piping, the four magnetic sensors are arranged circumferentially around the piping as described above. This ensures reliable detection of magnetic foreign particles if they are transported along with the object to be inspected within the piping.

[0035] Furthermore, it is preferable to have a magnetic foreign particle detection device according to any one of (1) to (5), which further comprises a magnetization unit that is located at a third transport position upstream of the first transport position in the transport direction, applies a magnetic field oriented perpendicular to the transport direction, and magnetizes metallic foreign particles contained in the object to be inspected to become magnetic foreign particles.

[0036] In this detection device, the magnetization unit is positioned at a third transport position upstream of the first transport position. Furthermore, in this magnetization unit, metallic foreign matter particles are magnetized with a magnetic field oriented perpendicular to the transport direction to become magnetic foreign matter particles. Therefore, when these magnetic foreign matter particles reach the first transport position, a large signal change due to the magnetic foreign matter particles can be generated in the signals of the first to fourth sensors. Thus, the presence or absence of magnetic foreign matter particles can be determined more reliably. In particular, it is preferable to position the magnetic field obliquely at a 45-degree angle to the first direction connecting the first and third magnetic sensors and the second direction perpendicular to this first direction. When magnetic foreign matter particles reach the first transport position, a large signal change due to the magnetic foreign matter particles can be generated in any of the signals of the first to fourth sensors.

[0037] (6) Another solution is a method for detecting magnetic foreign matter particles, which detects whether or not magnetic foreign matter particles contained in an object to be inspected are passing through an object being transported from the upstream side to the downstream side in the transport direction, comprising: a first magnetic sensor positioned at a first transport position in the transport direction and outputting a first sensor signal for changes in the magnetic force of the object being transported; a second magnetic sensor that outputs a second sensor signal for changes in the magnetic force of an external magnetic field arriving from the outside; a third magnetic sensor positioned at the first transport position opposite the first magnetic sensor via the object to be inspected and outputting a third sensor signal for changes in the magnetic force of the object being transported; and the external magnetic field A method for detecting magnetic foreign particles, comprising: a fourth magnetic sensor that outputs a change in magnetic force as a fourth sensor signal; a sensor signal acquisition step that acquires the first sensor signal, the second sensor signal, the third sensor signal, and the fourth sensor signal using a fourth magnetic sensor; a difference signal pair acquisition step that acquires two difference signals from the first sensor signal, the second sensor signal, the third sensor signal, and the fourth sensor signal: a difference signal between two of the sensor signals and a difference signal between the other two of the sensor signals; and a foreign object detection step that uses the two difference signals to detect the passage of the magnetic foreign particles at the first transport position.

[0038] In this detection method, two (a pair) difference signals are acquired from four sensor signals in the difference signal pair acquisition step, and in the foreign object detection step, these two difference signals are used to detect whether or not magnetic foreign particles have passed. Both difference signals are obtained by subtracting the other sensor signal from the signal of one sensor, thereby suppressing noise components caused by changes in external magnetism that are thought to be commonly present. Therefore, by using two difference signals, it is possible to sensitively detect whether or not magnetic foreign particles have passed at the first transport position while suppressing noise components caused by changes in external magnetism contained in the first sensor signal and the third sensor signal from the first magnetic sensor and the third magnetic sensor opposite it.

[0039] (7) Furthermore, a method for detecting magnetic foreign particles as described in (6), wherein the second magnetic sensor is positioned at a second transport position downstream of the first transport position and outputs a second sensor signal that also detects a change in the magnetic force of the object being transported, the fourth magnetic sensor is positioned at the second transport position opposite the second magnetic sensor via the object being transported and outputs a fourth sensor signal that also detects a change in the magnetic force of the object being transported, the difference signal pair acquisition step acquires a 1-2 difference signal between the first sensor signal and the second sensor signal and a 3-4 difference signal between the third sensor signal and the fourth sensor signal, and the foreign object detection step comprises a second-order difference acquisition step that acquires an upstream-downstream second-order difference signal which is the difference between the 1-2 difference signal and the 3-4 difference signal, and a determination step that uses the upstream-downstream second-order difference signal to determine whether or not the magnetic foreign particles have passed through the first transport position.

[0040] In this inspection method, the first and third magnetic sensors are positioned facing each other at the first transport position, and the second and fourth magnetic sensors are positioned facing each other at the second transport position. Then, in the difference signal pair acquisition step, the 1-2 difference signal and the 3-4 difference signal are obtained. The 1-2 difference signal and the 3-4 difference signal are suppressed by subtracting noise from external magnetism, while the signal change due to the passage of magnetic foreign particles at the first transport position can be retained. Moreover, the signal change due to the passage of magnetic foreign particles is in opposite phase between the 1-2 difference signal and the 3-4 difference signal. Then, in the second difference acquisition step, the upstream / downstream second difference signal, which is the difference between the 1-2 difference signal and the 3-4 difference signal, is obtained. As a result, in-phase noise components that could not be removed at the stage of the 1-2 difference signal and the 3-4 difference signal are also removed in this upstream / downstream second difference signal. In addition, the signal change due to the passage of magnetic foreign particles can be increased. Therefore, in the determination step, this upstream-downstream second-order difference signal can be used to more reliably determine whether or not magnetic foreign particles have passed through the first transport position.

[0041] (8) Furthermore, the method for detecting magnetic foreign particles as described in (7) is preferable, wherein the foreign object detection step includes a foreign object confirmation step that uses the upstream-downstream two-order difference signal to confirm that the magnetic foreign particles detected at the first transport position have passed through the second transport position.

[0042] Furthermore, the method for detecting magnetic foreign particles described in (7) or (8) is preferable in which the object to be inspected is transported inside a pipe, the first magnetic sensor and the second magnetic sensor are positioned at a first circumferential position in the circumferential direction of the pipe, and the third magnetic sensor and the fourth magnetic sensor are positioned at a second circumferential position on the opposite side of the circumferential direction from the first circumferential position.

[0043] (9) A method for detecting magnetic foreign particles as described in (7) or (8), further comprising a foreign object magnetization step, wherein a magnetization unit is positioned at a third transport position upstream of the first transport position in the transport direction, and applies a magnetic field directed in a first direction connecting the first magnetic sensor and the third magnetic sensor which are perpendicular to the transport direction and facing each other, to magnetize the metallic foreign particles contained in the object to be inspected into magnetic foreign particles, and delivers the object to the first transport position.

[0044] (10) or (6) is a method for detecting magnetic foreign particles, wherein the second magnetic sensor is positioned at the first transport position on one side of a second direction perpendicular to the first direction connecting the first magnetic sensor and the third magnetic sensor which are opposite to each other and perpendicular to the transport direction, and outputs a second sensor signal that also detects a change in the magnetic force of the object being transported, and the fourth magnetic sensor is positioned at the first transport position on the other side of the second direction opposite to the second magnetic sensor via the object being transported, and outputs a fourth sensor signal that also detects a change in the magnetic force of the object being transported inside the pipe, and the difference signal pair acquisition stage The step may also be a method for detecting magnetic foreign matter particles that includes a step to acquire a 1-3 difference signal between the first sensor signal and the third sensor signal, and a 2-4 difference signal between the second sensor signal and the fourth sensor signal, and the foreign matter detection step includes a second-order difference acquisition step to acquire a counter-second-order difference signal which is the difference between the 1-3 difference signal and the 2-4 difference signal, a difference-sum acquisition step to acquire a counter-difference-sum signal which is the sum of the 1-3 difference signal and the 2-4 difference signal, and a determination step to determine whether or not the magnetic foreign matter particles have passed through the first transport position based on the second-order difference signal and the counter-difference-sum signal.

[0045] In this inspection method, the four magnetic sensors are positioned at the same first transport position. Furthermore, the second and fourth magnetic sensors are positioned opposite each other on one side and the other side of a second direction perpendicular to the first direction connecting the first and third magnetic sensors, which face each other. As a result, when a magnetic foreign particle passes through the first transport position, all four sensor signals of the four magnetic sensors change. Moreover, the passage of the magnetic foreign particle through the first transport position causes the first and third sensor signals to change in opposite phases. Similarly, the second and fourth sensor signals also change in opposite phases. Therefore, in the 1-3 difference signal and the 2-4 difference signal, noise caused by changes in the external magnetism that commonly enters each magnetic sensor is subtracted and suppressed, while the signal changes caused by the passage of the magnetic foreign particle at the first transport position can be added together and increased. Furthermore, depending on the direction of the magnetic field generated by the magnetic foreign particles, one of the opposing second-order difference signal and the opposing difference summation signal obtained from the 1-3 difference signal and the 2-4 difference signal will become even larger as the changes in the sensor signal due to the passage of the magnetic foreign particles through the first transport position are added together. Therefore, the determination unit can more reliably determine whether or not the magnetic foreign particles have passed through the first transport position using the opposing second-order difference signal and the opposing difference summation signal.

[0046] Furthermore, the method for detecting magnetic foreign particles described in (10) is preferable in which the object to be inspected is transported inside a pipe, the first magnetic sensor is positioned at a first circumferential position in the circumferential direction of the pipe, the third magnetic sensor is positioned at a second circumferential position opposite to the first circumferential position in the circumferential direction, the second magnetic sensor is positioned at a third circumferential position deflected by 90 degrees from the first and second circumferential positions in the circumferential direction, and the fourth magnetic sensor is positioned at a fourth circumferential position opposite to the third circumferential position in the circumferential direction of the pipe.

[0047] Furthermore, a method for detecting magnetic foreign particles MP as described in any one of items (6) to (10) is preferable, further comprising a foreign matter magnetization step in which a magnetization unit is located at a third transport position upstream of the first transport position in the transport direction, applies a magnetic field oriented perpendicular to the transport direction, and magnetizes metallic foreign particles contained in the object to be inspected to become magnetic foreign particles, thereby delivering the object to the first transport position. [Brief explanation of the drawing]

[0048] [Figure 1] This is an explanatory diagram relating to Embodiment 1, Modified Forms 1 and 2, showing how magnetic foreign matter particles, which are metal foreign matter particles contained in a paste flowing through a pipe and have been magnetized, are detected by two pairs of magnetic sensors positioned on the upstream and downstream sides. [Figure 2] This is a cross-sectional diagram taken along the line AA in Figure 1, showing the circumferential arrangement of the first and third magnetic sensors at the first transport position of the piping, relating to Embodiment 1 and Modified Forms 1 and 2. [Figure 3] This is a cross-sectional diagram taken along the BB arrow in Figure 1, showing the circumferential arrangement of the second and fourth magnetic sensors at the second transport position of the piping, relating to Embodiment 1 and Modified Forms 1 and 2. [Figure 4] This is a block diagram showing the configuration of the detection device according to Embodiment 1, Modified Forms 1 and 2. [Figure 5] This flowchart shows the processing flow of the detection method related to Embodiment 1, Modification Forms 1 and 2. [Figure 6] This graph shows the time evolution of four sensor signals, two difference signals, and upstream / downstream second-order difference signals, relating to Embodiment 1, Modified Forms 1 and 2. [Figure 7] This is an explanatory diagram illustrating Embodiment 2, in which magnetic foreign particles contained in paste flowing inside a pipe are detected by two pairs of magnetic sensors placed around the pipe. [Figure 8]This is a cross-sectional diagram taken along the CC arrow in Figure 7, relating to Embodiment 2, showing the circumferential arrangement of the first to fourth magnetic sensors at the first transport position of the piping, and an example of the magnetic foreign particles being transported. [Figure 9] This is a cross-sectional diagram taken along the CC arrow in Figure 7, relating to Embodiment 2, showing the circumferential arrangement of the first to fourth magnetic sensors at the first transport position of the piping, and another example of the magnetic foreign particles being transported. [Figure 10] This is a block diagram showing the configuration of the detection device according to Embodiment 2. [Figure 11] This is a flowchart showing the processing flow of the detection method according to Embodiment 2. [Figure 12] This graph, relating to Embodiment 2, shows the time evolution of four sensor signals, two difference signals, a second-order difference signal, and a summation of the difference signals.

[0049] (Embodiment 1) Hereinafter, an embodiment 1 of the present invention will be described, with reference to Figures 1 to 6, of a detection device 10 and a detection method for detecting magnetic foreign particles MP flowing inside a pipe PP. As shown in Figure 1, a positive electrode paste IM, which is the object to be inspected, may be transported by flowing it through a cylindrical pipe PP. Such a positive electrode paste IM is, for example, applied to an electrode foil and dried to form a positive electrode layer. An electrode plate having such a positive electrode layer is used to form a wound or laminated electrode body, which is then used to form an energy storage device such as a lithium-ion battery.

[0050] However, the positive electrode paste IM, which is the object under inspection and flows through the cylindrical PP pipe, may contain metallic foreign particles KP such as stainless steel particles or iron particles. If metallic foreign particles KP are present in the positive electrode layer that makes up the battery, they may dissolve in the electrolyte and precipitate as needle-shaped dendrites on the negative electrode plate, potentially causing malfunctions such as short circuits between the negative and positive electrode plates.

[0051] Therefore, it is desirable to detect the presence or absence of metallic foreign particles KP in the positive electrode paste IM being transported through the piping PP. The portion of the transported positive electrode paste IM containing metallic foreign particles KP is removed and discarded. Alternatively, the metallic foreign particles KP may be removed through a foreign matter removal filter (not shown) before being transported again through the piping PP.

[0052] In this embodiment 1, the detection device 10 detects metallic foreign particles KP contained in the positive electrode paste IM flowing through the piping PP toward the downstream side HHD in the transport direction HH. Note that the metallic foreign particles KP are not necessarily magnetized. Therefore, in this embodiment 1, as shown in Figure 1, the magnetization unit 90 is placed in the piping PP upstream of the magnetic sensors 1 to 4 described later in the transport direction HH, HHU. This magnetization unit 90 consists of an upper magnetization unit 90A consisting of an air-core coil 91 and a drive power supply 93 connected thereto, and a lower magnetization unit 90B consisting of an air-core coil 92 paired with the air-core coil 91 and a drive power supply 94 connected thereto. By passing current through the air-core coils 91 and 92, a magnetic field MF is generated in the piping PP that is perpendicular to the transport direction HH and directed toward the upper side DH1a of the first direction DH1 connecting the first magnetic sensor 1 and the third magnetic sensor 3 described later. As a result, when metallic foreign particles KP flow through the piping PP together with the positive electrode paste IM, the metallic foreign particles KP are magnetized and become magnetic foreign particles MP. Specifically, as shown in Figure 1, the magnetic field MF generated in the magnetization section 90 magnetizes the metallic foreign particles KP into magnetic foreign particles MP with the upper side being the north pole and the lower side being the south pole. Furthermore, the positive electrode paste IM flows in a laminar flow within the piping PP. Therefore, when the positive electrode paste IM is transported downstream HHD (to the right in Figure 1) in the transport direction HH, as shown in Figure 1, the magnetic foreign particles MP are transported without rotating, maintaining their orientation with the upper side being the north pole and the lower side being the south pole.

[0053] In the piping PP, at the first transport position HH1 in the transport direction HH (see Figure 1), the first magnetic sensor 1 is positioned at the first circumferential position CH1 (upper side in Figure 2) in the circumferential direction CH of the piping PP. Furthermore, at the second transport position HH2 (see Figure 1), which is downstream from the first transport position HH1, the second magnetic sensor 2 is positioned at the same first circumferential position CH1 (upper side in Figure 3) in the circumferential direction CH of the piping PP as the first magnetic sensor 1.

[0054] Furthermore, in the piping PP, at the first transport position HH1 in the transport direction HH, the third magnetic sensor 3 is positioned opposite the first magnetic sensor 1 via the positive electrode paste IM and piping PP at the second circumferential position CH2 (lower side in Figure 2), which is on the opposite side of the first circumferential position CH1 in the circumferential direction CH of the piping PP. Also, at the second transport position HH2, which is downstream of the first transport position HH1, the fourth magnetic sensor 4 is positioned opposite the second magnetic sensor 2 via the positive electrode paste IM and piping PP at the same second circumferential position CH2 (lower side in Figure 3) as the third magnetic sensor 3 in the circumferential direction CH of the piping PP.

[0055] Furthermore, at the third transport position HH3 (see Figure 1), the aforementioned air-core coil 91 is positioned at the upper first circumferential position CH1 of the circumferential direction CH of the piping PP, while the air-core coil 92 is positioned at the lower second circumferential position CH2.

[0056] The magnetic foreign particle MP (metal foreign particle KP) detection device 10 of this embodiment 1 has, in addition to the magnetization unit 90 and the first to fourth magnetic sensors 1 to 4 mentioned above, a difference signal pair acquisition unit 20 and a foreign object detection unit 30 (see Figure 4). The first to fourth magnetic sensors 1 to 4 continuously output first to fourth sensor signals S1(t) to S4(t) corresponding to the magnetic changes at each location. Specifically, the first magnetic sensor 1 is located at the first transport position HH1 and the first circumferential position CH1, and outputs the change in magnetic force at the first transport position HH1 of the transported positive electrode paste IM as the first sensor signal S1(t). The second magnetic sensor 2 is located at the second transport position HH2 and the first circumferential position CH1 downstream of the first transport position HH1, and outputs the change in magnetic force at the second transport position HH2 of the transported positive electrode paste IM as the second sensor signal S2(t). Furthermore, the third magnetic sensor 3 is positioned at the first transport position HH1 and at the second circumferential position CH2 facing the first magnetic sensor 1, and outputs the change in magnetic field of the transported positive electrode paste IM at the first transport position HH1 as the third sensor signal S3(t). The fourth magnetic sensor 4 is positioned at the second transport position HH2 and at the second circumferential position CH2 facing the second magnetic sensor 2, and outputs the change in magnetic field of the transported positive electrode paste IM at the second transport position HH2 as the fourth sensor signal S4(t). Note that the first to fourth sensor signals S1(t) to S4(t) all have a noise component NZ superimposed on them, which is a change in the external magnetic field OM arriving from the outside, i.e., the external magnetic field OM (see Figures 1 and 6).

[0057] The differential signal pair acquisition unit 20 consists of a 1-2 differential acquisition unit 21 and a 3-4 differential acquisition unit 22. Of these, the 1-2 differential acquisition unit 21 acquires the 1-2 differential signal D12(t), which is the difference between the first sensor signal S1(t) and the second sensor signal S2(t) (D12(t) = S1(t) - S2(t)). In this 1-2 differential signal D12(t), by taking the difference between the first sensor signal S1(t) and the second sensor signal S2(t), much of the noise component NZ due to the foreign magnetic OM commonly included can be canceled, and the noise component included in the 1-2 differential signal D12(t) can be suppressed. Conversely, the signal-to-noise ratio is increased, and the signal change associated with the passage of magnetic foreign particles MP at the first transport position HH1 can be clearly obtained in the 1-2 differential signal D12(t) (see the 1st, 2nd, and 5th stages of Figure 6). Furthermore, in this embodiment, since the second magnetic sensor 2 is placed at the second transport position HH2, it is possible to clearly obtain the signal change associated with the passage of magnetic foreign matter particles MP at this second transport position HH2.

[0058] On the other hand, the 3-4 difference acquisition unit 22 acquires the 3-4 difference signal D34(t), which is the difference between the third sensor signal S3(t) and the fourth sensor signal S4(t) (D34(t) = S3(t) - S4(t)). In this 3-4 difference signal D34(t), by taking the difference between the third sensor signal S3(t) and the fourth sensor signal S4(t), many of the common noise components NZ can be canceled, so the noise components contained in the 3-4 difference signal D34(t) can be suppressed. Conversely, the signal-to-noise ratio becomes larger, and the signal change associated with the passage of magnetic foreign particles MP at the first transport position HH1 can be clearly obtained in the 3-4 difference signal D34(t) (see stages 3, 4, and 6 of Figure 6). Furthermore, in this embodiment, since the fourth magnetic sensor 4 is placed at the second transport position HH2, the signal change associated with the passage of magnetic foreign particles MP at this second transport position HH2 can also be clearly obtained.

[0059] Therefore, by using these two difference signals D12(t) and D34(t), it is possible to sensitively detect whether or not magnetic foreign particles MP have passed through the first transport position HH1 while suppressing noise components NZ caused by changes in the external magnetic field OM included in the first sensor signal S1(t) and the third sensor signal S3(t) from the first magnetic sensor 1 and the third magnetic sensor 3 facing it.

[0060] Specifically, the foreign object detection unit 30, which detects the passage of magnetic foreign particles MP at the first transport position HH1, includes an upstream / downstream second-order difference acquisition unit 40 and a determination unit 50. Of these, the upstream / downstream second-order difference acquisition unit 40 acquires the upstream / downstream second-order difference signal DDc(t), which is the difference between the 1-2 difference signal D12(t) and the 3-4 difference signal D34 (DDc(t)=D12(t)-D34(t)=(S1(t)-S2(t))-(S3(t)-S4(t))). By acquiring the upstream / downstream second-order difference signal DDc(t) from the two difference signals D12(t) and D34(t) in this way, noise components that occur in phase with both signals, which could not be removed at the stage of acquiring the 1-2 difference signal D12(t) and the 3-4 difference signal D34(t), are also removed. In addition, by adding the signal changes that occur in the first sensor signal S1(t) and the third sensor signal S3(t) due to the passage of magnetic foreign particles MP at the first transport position HH1, a large signal change can be obtained. Therefore, the determination unit 50 described below can use this upstream-downstream two-order difference signal DDc(t) to more reliably determine whether or not magnetic foreign particles MP have passed through the first transport position HH1 (see stages 5 to 7 of Figure 6).

[0061] Specifically, the determination unit 50 monitors the upstream-downstream second-order difference signal DDc(t), and determines that the magnetic foreign particle MP has passed the first transport position HH1 if the upstream-downstream second-order difference signal DDc(t) exceeds the first threshold TH1 (TH1>0), which is the upper threshold, or falls below the second threshold TH2 (TH2<0), which is the lower threshold.

[0062] In this manner, if magnetic foreign particles MP are detected in the transported positive electrode paste IM, it is advisable to discard the portion of the positive electrode paste IM near where the magnetic foreign particles MP were detected, or to remove the magnetic foreign particles MP by passing it through a separate foreign matter removal filter before returning it as positive electrode paste IM.

[0063] Next, the method for detecting magnetic foreign particles MP (metallic foreign particles KP) in this embodiment 1 will be described (see Figure 5). First, in step ST0, the magnetization unit 90 generates a magnetic field MF inside the piping PP at the third transport position HH3. This magnetizes the metallic foreign particles KP that were transported together with the positive electrode paste IM, turning them into magnetic foreign particles MP.

[0064] In the subsequent sensor signal acquisition step ST1, the sensor signals S1(t) to S4(t) of each magnetic sensor 1 to 4 are continuously acquired in the four sensor acquisition step signals ST1a to ST1d included therein.

[0065] In the subsequent difference signal pair acquisition step ST2, the two difference signal pair acquisition steps ST2a and ST2b include the acquisition of the 1-2 difference signal D12(t), which is the difference between the first sensor signal S1(t) and the second sensor signal S2(t), and the 3-4 difference signal D34(t), which is the difference between the third sensor signal S3(t) and the fourth sensor signal S4(t).

[0066] In the subsequent foreign object detection step ST3, the passage of magnetic foreign object particles MP at the first transport position HH1 is detected. The foreign object detection step ST3 includes a second-order difference acquisition step ST4 and a determination step ST6. Specifically, the second-order difference acquisition step ST4 acquires the upstream / downstream second-order difference signal DDc(t), which is the difference between the 1-2 difference signal D12(t) and the 3-4 difference signal D34(t). Furthermore, in the determination step ST6, the upstream / downstream second-order difference signal DDc(t) is used to determine whether or not magnetic foreign object particles MP have passed through the first transport position HH1. Specifically, if the upstream / downstream second-order difference signal DDc(t) exceeds the first threshold TH1 or falls below the second threshold TH2, it is determined that magnetic foreign object particles MP have passed through the first transport position HH1.

[0067] The following explanation uses examples of each signal in Figure 6. In this explanation, we assume that magnetic foreign particles MP magnetized by the magnetization unit 90 pass through the first transport position HH1 at the first timing t1, and then pass through the second transport position HH2 at the second timing t2. The positive electrode paste IM transported through the pipe PP is transported in a laminar flow manner at a constant transport speed (flow velocity) Vh, and the distance from the first transport position HH1 to the second transport position HH2 is defined as the distance between sensors L12. Therefore, the second timing t2 arrives after the first timing t1 by a delay time TD (TD = L12 / Vh).

[0068] The top four graphs in Figure 6 show the first to fourth sensor signals S1(t) to S4(t) obtained from the first to fourth magnetic sensors 1 to 4. As mentioned above, the magnetic foreign particle MP passes through the first transport position HH1 at the first timing t1. Therefore, the first sensor signal S1(t) and the third sensor signal S3(t) have foreign component signals SG and SG' before and after the first timing t1. Each magnetic sensor 1 to 4 has the characteristic of generating a positive signal when the north pole of the magnetic foreign particle MP approaches and a negative signal when it moves away, and a negative signal when the south pole approaches and a positive signal when it moves away.

[0069] Therefore, in the first sensor signal S1(t), before the first timing t1 when the magnetic foreign particle MP passes the first transport position HH1, the north pole first approaches the first magnetic sensor 1 (see Figures 1 and 2), so a positive signal is obtained. Subsequently, at the first timing t1, the north pole moves away from the first magnetic sensor 1, so a negative signal is obtained. That is, a foreign object component signal SG is generated (see the first stage of Figure 6). Conversely, in the third sensor signal S3(t), before the first timing t1, the south pole approaches the third magnetic sensor 3, so a negative signal is obtained first. Subsequently, at the first timing t1, the south pole moves away from the third magnetic sensor 3, so a positive signal is obtained. That is, a foreign object component signal SG' is generated, which is in the opposite phase to the foreign object component signal SG (see the third stage of Figure 6). Furthermore, there is no change in the second sensor signal S2(t) and the fourth sensor signal S4(t) before and after the first timing t1 (see the second and fourth panels of Figure 6). This is because, from the perspective of the second and fourth magnetic sensors 2 and 4, the magnetic foreign particle MP has not yet approached. In addition, the first to fourth sensor signals S1(t) to S4(t) are always accompanied by a noise component NZ caused by the external magnetic field OM.

[0070] On the other hand, in the second sensor signal S2(t), before the second timing t2 when the magnetic foreign particle MP passes the second transport position HH2, the north pole approaches the second magnetic sensor 2 (see Figures 1 and 2), so a positive signal is first obtained. Then, at the second timing t2, the north pole moves away from the second magnetic sensor 2, so a negative signal is obtained. That is, a foreign object component signal SG is generated (see the second panel of Figure 6). Conversely, in the fourth sensor signal S4(t), before the second timing t2, the south pole approaches the fourth magnetic sensor 4, so a negative signal is first obtained. Then, at the second timing t2, the south pole moves away from the fourth magnetic sensor 4, so a positive signal is obtained. That is, a foreign object component signal SG' is generated (see the fourth panel of Figure 6). Note that there is no change in the first sensor signal S1(t) and the third sensor signal S3(t) before and after the second timing t2. From the perspective of the first and third magnetic sensors 1 and 3, the magnetic foreign particles MP have already passed through.

[0071] The fifth graph in Figure 6 shows the 1-2 difference signal D12(t) obtained by subtracting the second sensor signal S2(t) from the first sensor signal S1(t). In the 1-2 difference signal D12(t), the noise component NZ that is common to both the first sensor signal S1(t) and the second sensor signal S2(t) is subtracted, and the noise component is suppressed. On the other hand, the foreign matter component signal SG that occurs in the first sensor signal S1(t) around the first timing t1, and the foreign matter component signal SG that occurs in the second sensor signal S2(t) around the second timing t2, remain in the 1-2 difference signal D12(t). Therefore, as shown in Figure 6, the signal-to-noise ratio of the 1-2 difference signal D12(t) is significantly improved compared to the first sensor signal S1(t) and the second sensor signal S2(t).

[0072] The sixth graph in Figure 6 shows the 3-4 difference signal D34(t) obtained by subtracting the fourth sensor signal S4(t) from the third sensor signal S3(t). In the 3-4 difference signal D34(t), the noise component NZ, which is common to the third and fourth sensor signals S3(t) and S4(t), is subtracted, and the noise component is suppressed. On the other hand, the foreign matter component signal SG' that occurs in the third sensor signal S3(t) around the first timing t1, and the foreign matter component signal SG' that occurs in the fourth sensor signal S4(t) around the second timing t2, remain in the 3-4 difference signal D34(t). Therefore, as shown in Figure 6, the signal-to-noise ratio of the 3-4 difference signal D34(t) is significantly improved compared to the third sensor signal S3(t) and the fourth sensor signal S4(t).

[0073] The graph in the seventh row (bottom row) of Figure 6 shows the upstream-downstream second-order difference signal DDc(t) obtained by subtracting the 3-4 difference signal D34(t) from the 1-2 difference signal D12(t). In this upstream-downstream second-order difference signal DDc(t), the in-phase noise components remaining in the 1-2 difference signal D12(t) and the 3-4 difference signal D34(t) are further subtracted, resulting in further suppression of the noise component. On the other hand, around the first timing t1, a foreign component signal SG' with the opposite phase is subtracted from the foreign component signal SG, resulting in a larger foreign component signal SG+SG'.

[0074] Therefore, as shown in the seventh step of Figure 6, the upstream-downstream second-order difference signal DDc(t) is monitored, and if the upstream-downstream second-order difference signal DDc(t) exceeds the upper threshold, the first threshold TH1 (TH1>0), or falls below the lower threshold, the second threshold TH2 (TH2<0), it is determined that the magnetic foreign particle MP has passed the first transport position HH1. This makes it possible to reliably determine that the magnetic foreign particle MP has passed the first transport position HH1 around the first timing t1.

[0075] Furthermore, since the second and fourth magnetic sensors 2 and 4 are positioned at the second transport position HH2, as can be easily understood by looking at the graphs shown in Figure 6, foreign matter component signals SG and SG' are obtained in the second and fourth sensor signals S(t) and S4(t) at the second timing t2 when the magnetic foreign matter particle MP passes through the second transport position HH2. As a result, around the second timing t2, the upstream-downstream second-order difference signal DDc(t) exceeds the first threshold TH1 or falls below the second threshold TH2. Therefore, in this embodiment, if the determination unit 50 (determination step ST6) has already detected the passage of the magnetic foreign matter particle MP at the first timing t1, it ignores the case where the upstream-downstream second-order difference signal DDc(t) exceeds the first threshold TH1 or falls below the second threshold TH2 around the second timing t2, which arrives with a delay of the aforementioned delay time TD.

[0076] (Transformation form 1) In Embodiment 1, the upstream-downstream second-order difference signal DDc(t) was compared with a first threshold TH1 and a second threshold TH2 to determine whether or not magnetic foreign matter particles MP had passed through the first transport position HH1.

[0077] Alternatively, as shown by the dashed line in Figure 4, an absolute value acquisition unit 60 may be provided between the upstream / downstream second-order difference acquisition unit 40 and the determination unit 50. Also, as shown by the dashed line in Figure 5, an absolute value acquisition step ST7 may be provided between the second-order difference acquisition step ST4 and the determination step ST6.

[0078] As a result, in the graph of the seventh row (bottom row) in Figure 6, as shown by the dashed line, the absolute value of the upstream-downstream second-order difference signal DDc(t) is obtained, and if the absolute value of the upstream-downstream second-order difference signal DDc(t) exceeds the first threshold TH1, it is determined that the magnetic foreign particle MP has passed through the first transport position HH1. By using the absolute value of the upstream-downstream second-order difference signal DDc(t) in this way, it is sufficient to use the first threshold TH1 as the threshold for determination, and comparison with the threshold becomes easy.

[0079] (Transformation form 2) In Embodiment 1, the upstream-downstream second-order difference signal DDc(t) was compared with a first threshold TH1 and a second threshold TH2 to determine whether or not a magnetic foreign particle MP had passed the first transport position HH1 at the first timing t1. On the other hand, if the passage of a magnetic foreign particle MP had already been detected at the first timing t1, the upstream-downstream second-order difference signal DDc(t) would be ignored even if it exceeded the first threshold TH1 or fell below the second threshold TH2 before or after the second timing t2, which arrives with a delay of the aforementioned delay time TD.

[0080] However, since the second and fourth magnetic sensors 2 and 4 are positioned at the second transport position HH2, as can be easily understood by looking at the graphs shown in Figure 6, foreign matter component signals SG and SG' are obtained in the second and fourth sensor signals S(t) and S4(t) at the second timing t2 when the magnetic foreign matter particle MP passes through the second transport position HH2. As a result, the upstream-downstream second-order difference signal DDc(t) exceeds the first threshold TH1 or falls below the second threshold TH2 around the second timing t2, indicating that the magnetic foreign matter particle MP passed through the second transport position HH2.

[0081] Therefore, in this modified form 2, as shown by the dashed line in Figure 4, a foreign object detection unit 70 may be provided between the upstream / downstream second-order difference acquisition unit 40 and the determination unit 50. Also, as shown by the dashed line in Figure 5, a foreign object detection step ST8 may be provided between the second-order difference acquisition step ST4 and the determination step ST6.

[0082] In this foreign object detection unit 70 and foreign object detection step ST8, as shown in the graph of the 7th stage (bottom stage) in Figure 6, if the upstream-downstream second-order difference signal DDc(t) exceeds the first threshold TH1 or falls below the second threshold TH2 at the first timing t1, it is tentatively determined that the magnetic foreign object particle MP passed the first transport position HH1 at the first timing t1. Then, the determination unit 50 (determination step ST6) confirms that, around the time of the second timing t2, which arrives with a delay time TD from the first timing t1, the upstream-downstream second-order difference signal DDc(t) exceeds the first threshold TH1 or falls below the second threshold TH2. In this case, it is determined that the magnetic foreign particle MP passed the second transport position HH2 at the second timing t2.

[0083] In this modified form 2, the foreign object detection unit 70 (foreign object detection step ST8) tentatively determined that the magnetic foreign object particle MP passed the first transport position HH1 at a certain timing (first timing t1) because the upstream-downstream double-order difference signal DDc(t) exceeded the first threshold TH1 or fell below the second threshold TH2. However, if the upstream-downstream double-order difference signal DDc(t) did not exceed the first threshold TH1 or fall below the second threshold TH2 before or after the second timing t2, which is delayed by a delay time TD from the first timing t1, the determination unit 50 (determination step ST6) determined that the magnetic foreign object particle MP did not pass the second transport position HH2.

[0084] In this modified form 2, it is confirmed that the upstream-downstream second-order difference signal DDc(t) exceeds the first threshold TH1 or falls below the second threshold TH2 at two intervals, the first timing t1 and the second timing t2. Therefore, it is possible to determine that the magnetic foreign particle MP has reliably passed through the first transport position HH1 and the second transport position HH2.

[0085] (Embodiment 2) Next, a detection device 110 and detection method for detecting magnetic foreign particles MP flowing through the piping PP will be described with reference to Figures 7 to 12, relating to the second embodiment. In both Embodiment 1 and Modifications 1 and 2, the first and third magnetic sensors 1 and 3 are placed at the first transport position HH1, while the second and fourth magnetic sensors 2 and 4 are placed at the second transport position HH2, which is downstream of the first transport position HH1. Two difference signals D12(t) and D34(t) are obtained from the four sensor signals S1(t) to S4(t), and a second-order upstream / downstream difference signal DDc(t) is obtained to determine whether or not magnetic foreign particles MP have passed through the first transport position HH1 or the second transport position HH2.

[0086] In contrast, the detection device 110 and detection method of this embodiment 2 are similar in that they use four magnetic sensors 1, 12, 3, and 14, but all four magnetic sensors 1, 12, 3, and 14 are placed at the first transport position HH1. Furthermore, they differ in that they obtain two difference signals D13(t) and D24(t) from the four sensor signals S1(t), S12(t), S3(t), and S14(t), and further obtain a counter-second-order difference signal DDo(t) and a counter-difference summation signal DAo(t) to determine whether or not magnetic foreign matter particles MP have passed through the first transport position HH1.

[0087] In other words, in the detection device 110 of this embodiment 2, the first magnetic sensor 1 is positioned at the first circumferential position CH1 (upper side in Figures 8 and 9) in the circumferential direction CH of the pipe PP, at the first transport position HH1 (see Figure 7) in the transport direction HH of the pipe PP through which the positive electrode paste IM is transported. Also, at the same first transport position HH1, the third magnetic sensor 3 is positioned at the second circumferential position CH2 (lower side in Figures 8 and 9) in the circumferential direction CH, opposite to the first circumferential position CH1, and is positioned opposite the first magnetic sensor 1 via the positive electrode paste IM and the pipe PP.

[0088] Furthermore, in the detection device 110 of this embodiment 2, at the same first transport position HH1, the second magnetic sensor 12 is positioned at the third circumferential position CH3 (to the left in Figures 8 and 9), which is 90 degrees deflected from the first circumferential position CH1 and the second circumferential position CH2 (to the left in Figures 8 and 9), and is perpendicular to the first direction DH1 (up and down in Figure 8) that connects the first magnetic sensor 1 and the third magnetic sensor 3, which are facing each other, at the same first transport position HH1, and perpendicular to the first direction DH1 (up and down in Figure 8). Also, the fourth magnetic sensor 14 is positioned opposite the second magnetic sensor 12 at the third circumferential position CH3, which is 90 degrees deflected from the first circumferential position CH1 and the second circumferential position CH2, respectively, at the same first transport position HH1, which is perpendicular to the transport direction HH (direction perpendicular to the plane of the paper in Figures 8 and 9), and perpendicular to the first direction DH1 (up and down in Figure 8) that connects the first magnetic sensor 1 and the third magnetic sensor 3, which are facing each other, at the third circumferential position CH3 in the circumferential direction CH.

[0089] In the detection device 110 of this embodiment 2, the arrangement of the magnetic poles of the magnetic foreign particle MP passing through the first transport position HH1 results in differences in the patterns generated in the opposing second-order difference signal DDo(t) and the opposing difference summation signal DAo(t), which will be described later. Therefore, the following will examine the two cases shown in Figures 8 and 9. Of these, Figure 8 shows the case in which the magnetic foreign particle MP is transported with the S pole positioned to the upper right and the N pole to the lower left among the magnetic poles generated around the magnetic foreign particle MP. On the other hand, Figure 9 shows the case in which the magnetic foreign particle MP is transported with the S pole positioned to the upper left and the N pole to the lower right among the magnetic poles generated around the magnetic foreign particle MP. The following will examine these two cases.

[0090] Furthermore, within the piping PP, the positive electrode paste IM flows in a laminar flow, and the magnetic foreign particles MP contained in the positive electrode paste IM are transported without rotation, maintaining the orientation of the magnetic poles as shown in Figures 7 and 8, or Figures 7 and 9.

[0091] The detection device 110 of this second embodiment includes, in addition to the first to fourth magnetic sensors 1, 12, 3, and 14 described above, a difference signal pair acquisition unit 120 and a foreign object detection unit 130 (see Figure 10). The first to fourth magnetic sensors 1, 12, 3, and 14 each continuously output first to fourth sensor signals S1(t), S12(t), S3(t), and S14(t) corresponding to the magnetic change at the first transport position HH1 of the transported positive electrode paste IM. Note that all of the first to fourth sensor signals S1(t), S12(t), S3(t), and S14(t) are superimposed with a noise component NZ caused by an external magnetic field OM, i.e., an external magnetic field OM (see Figures 7, 8, and 12).

[0092] The difference signal pair acquisition unit 120 consists of a 1-3 difference acquisition unit 121 and a 2-4 difference acquisition unit 122. Of these, the 1-3 difference acquisition unit 121 acquires the difference between the first sensor signal S1(t) and the third sensor signal S3(t), which is the 1-3 difference signal D13(t) (D13(t) = S1(t) - S3(t)). In this 1-3 difference signal D13(t), by taking the difference between the first sensor signal S1(t) of the first magnetic sensor 1 and the third sensor signal S3(t) of the opposing third magnetic sensor 3, much of the noise component NZ due to the external magnetic OM commonly included can be canceled, and the noise component included in the 1-3 difference signal D13(t) can be suppressed. Furthermore, the 1-3 difference signal D13(t) allows for the summation and amplified effect of the signal changes of the first sensor signal S1(t) and the third sensor signal S3(t) that occur as magnetic foreign matter particles MP pass through the first transport position HH1, further improving the signal-to-noise ratio.

[0093] On the other hand, the 2-4 difference acquisition unit 122 acquires the 2-4 difference signal D24(t), which is the difference between the second sensor signal S12(t) and the fourth sensor signal S14(t) (D24(t) = S12(t) - S14(t)). In this 2-4 difference signal D24(t), by taking the difference between the second sensor signal S12(t) of the second magnetic sensor 12 and the fourth sensor signal S14(t) of the opposing fourth magnetic sensor 14, much of the noise component NZ due to the foreign magnetic OM commonly included can be canceled, and the noise component included in the 2-4 difference signal D24(t) can be suppressed. Moreover, in the 2-4 difference signal D24(t), the signal changes that occur in the second sensor signal S12(t) and the fourth sensor signal S14(t) as the magnetic foreign particle MP passes through at the first transport position HH1 can be added together and increased, further improving the signal-to-noise ratio.

[0094] Therefore, by using these two difference signals D13(t) and D24(t), it is possible to sensitively detect whether or not magnetic foreign particles MP have passed through the first transport position HH1 while suppressing noise components NZ caused by changes in the external magnetic field OM contained in the four sensor signals S1(t) etc. from the four magnetic sensors 1, 12, 3, and 14.

[0095] Specifically, the foreign object detection unit 130, which detects the passage of magnetic foreign particles MP at the first transport position HH1, includes a counter-second-order difference acquisition unit 140, a counter-second-order difference sum acquisition unit 145, and a determination unit 150. Of these, the counter-second-order difference acquisition unit 140 acquires the counter-second-order difference signal DDo(t), which is the difference between the 1-3 difference signal D13(t) and the 2-4 difference signal D24 (DDo(t)=D13(t)-D34(t)=(S1(t)-S3(t))-(S12(t)-S14(t))). Furthermore, the opposing difference sum acquisition unit 145 acquires the opposing difference sum signal DAo(t), which is the sum of the 1-3 difference signal D13(t) and the 2-4 difference signal D24 (DAo(t)=D13(t)+D34(t)=(S1(t)-S3(t))+(S12(t)-S14(t))).

[0096] For example, as shown in Figures 8 and 9, depending on the orientation of the magnetic poles of the passing magnetic foreign particle MP, either the opposing second-order difference signal DDo(t) or the opposing difference summation signal DAo(t) can be increased by summing the signal changes that occur in the four sensor signals S1(t), etc., due to the passage of the magnetic foreign particle MP at the first transport position HH1, resulting in a large signal change. Conversely, the other signal can only be increased by canceling out the signal changes that occur in the sensor signals S1(t), etc., resulting in a small signal change. Therefore, the determination unit 150, described below, can use these opposing second-order difference signals DDo(t) and opposing difference summation signals DAo(t) to more reliably determine whether or not the magnetic foreign particle MP has passed through the first transport position HH1.

[0097] Specifically, the determination unit 150 monitors the opposing second-order difference signal DDo(t) and the opposing difference summation signal DAo(t), and determines that the magnetic foreign particle MP has passed the first transport position HH1 if the opposing second-order difference signal DDo(t) or the opposing difference summation signal DAo(t) exceeds the upper threshold, the third threshold TH3 (TH3>0), or falls below the lower threshold, the fourth threshold TH4 (TH4<0).

[0098] In this manner, if magnetic foreign particles MP are detected in the transported positive electrode paste IM, it is preferable, as in Embodiment 1, to discard the portion of the positive electrode paste IM near where the magnetic foreign particles MP were detected, or to remove the magnetic foreign particles MP separately through a foreign matter removal filter before returning it as positive electrode paste IM.

[0099] Next, the method for detecting magnetic foreign particles MP in this second embodiment will be described (see Figure 11). In the sensor signal acquisition step ST1, the sensor signals S1(t) to S4(t) of each magnetic sensor 1 to 4 are continuously acquired in the four sensor acquisition step signals ST1a to ST1d included therein.

[0100] In the subsequent difference signal pair acquisition step ST12, the two difference signal pair acquisition steps ST12a and ST12b include the acquisition of the 1-3 difference signal D13(t), which is the difference between the first sensor signal S1(t) and the third sensor signal S3(t), and the 2-4 difference signal D24(t), which is the difference between the second sensor signal S12(t) and the fourth sensor signal S14(t).

[0101] Furthermore, in the foreign object detection step ST13, the passage of magnetic foreign object particles MP at the first transport position HH1 is detected. The foreign object detection step ST13 includes a second-order difference acquisition step ST14, a difference sum acquisition step ST15, and a determination step ST16. Specifically, the second-order difference acquisition step ST14 acquires the opposing second-order difference signal DDo(t), which is the difference between the 1-3 difference signal D13(t) and the 2-4 difference signal D24(t). On the other hand, the difference sum acquisition step ST15 acquires the opposing difference sum signal DAo(t), which is the sum of the 1-3 difference signal D13(t) and the 2-4 difference signal D24(t). Furthermore, in the determination step ST16, the opposing second-order difference signal DDo(t) and the opposing difference sum signal DAo(t) are used to determine whether or not magnetic foreign object particles MP have passed at the first transport position HH1. Specifically, if either the opposing second-order difference signal DDo(t) or the opposing difference summation signal DAo(t) exceeds the third threshold TH3, or falls below the fourth threshold TH4, it is determined that the magnetic foreign particle MP has passed the first transport position HH1.

[0102] The following explanation uses examples of each signal in Figure 12. In this explanation, we assume that the magnetic foreign particle MP passes through the first transport position HH1 at the first timing t1. The upper four graphs in Figure 12 show the first to fourth sensor signals S1(t), S12(t), S3(t), and S14(t) obtained from the first to fourth magnetic sensors 1, 12, 3, and 14. As mentioned above, the magnetic foreign particle MP passes through the first transport position HH1 at the first timing t1. Therefore, the four sensor signals S1(t), etc., have foreign component signals SGa, SGb, SGc, and SGd generated before and after the first timing t1. As in Embodiment 1, each magnetic sensor 1, etc., has the characteristic of generating a positive signal when the N pole approaches the magnetic foreign particle MP and a negative signal when it moves away, and a negative signal when the S pole approaches and a positive signal when it moves away.

[0103] Therefore, when a magnetic foreign particle MP passes through the first transport position HH1, regardless of whether the orientation of the magnetic poles of the passing magnetic foreign particle MP is as shown in Figure 8 or Figure 9, the south pole of the magnetic foreign particle MP approaches the first magnetic sensor 1, so a negative signal is first obtained in the first sensor signal S1(t) before the first timing t1. Then, at the first timing t1, the south pole moves away from the first magnetic sensor 1, so a positive signal is obtained. That is, a foreign matter component signal SGa is generated (see the first panel of Figure 12). Conversely, the north pole of the magnetic foreign particle MP approaches the third magnetic sensor 3 first, so a positive signal is first obtained in the third sensor signal S3(t) before the first timing t1. Then, at the first timing t1, the north pole moves away from the third magnetic sensor 3, so a negative signal is obtained. That is, a foreign matter component signal SGc is generated (see the second panel of Figure 12).

[0104] On the other hand, the second sensor signal S12(t) and the fourth sensor signal S14(t) have different patterns depending on whether the magnetic pole orientation of the magnetic foreign particle MP is as shown in Figures 8 and 9. In the case of Figure 8, the north pole of the magnetic foreign particle MP approaches the second magnetic sensor 12 first, so a positive signal is obtained in the second sensor signal S12(t) before the first timing t1. Then, at the first timing t1, the north pole moves away from the second magnetic sensor 12, so a negative signal is obtained. That is, a foreign component signal SGb is generated (see the thick solid line in the third stage of Figure 12). Conversely, the south pole approaches the fourth magnetic sensor 14 first, so a negative signal is obtained in the fourth sensor signal S14(t) before the first timing t1. Then, at the first timing t1, the south pole moves away from the fourth magnetic sensor 14, so a positive signal is obtained. In other words, it generates a foreign substance component signal SGd (see the thick solid line in the fourth row of Figure 12).

[0105] However, when the magnetic pole orientation of the magnetic foreign particle MP is as shown in Figure 9, the south pole of the magnetic foreign particle MP approaches the second magnetic sensor 12 first, so a negative signal is obtained in the second sensor signal S12(t) before the first timing t1. Then, at the first timing t1, the south pole moves away from the second magnetic sensor 12, so a positive signal is obtained. That is, a foreign component signal SGb' is produced that is in the opposite phase to the foreign component signal SGb mentioned above (see the dashed line in the third row of Figure 12). Similarly, with the fourth magnetic sensor 14, the north pole approaches the fourth magnetic sensor 14 first, so a positive signal is obtained in the fourth sensor signal S14(t) before the first timing t1. Then, at the first timing t1, the north pole moves away from the fourth magnetic sensor 14, so a negative signal is obtained. In other words, it generates a foreign object component signal SGd' that is in the opposite phase to the aforementioned foreign object component signal SGd (see the dashed line in the fourth row of Figure 12). Furthermore, each of the four sensor signals S1(t), etc., is always superimposed with a noise component NZ caused by the external magnetic field OM.

[0106] The fifth graph in Figure 12 shows the 1-3 difference signal D13(t) (=S1(t)-S3(t)) obtained by subtracting the third sensor signal S3(t) from the first sensor signal S1(t). This 1-3 difference signal D13(t) is the same regardless of whether the magnetic pole orientation of the magnetic foreign particle MP is as shown in Figure 8 or Figure 9. In the 1-3 difference signal D13(t), the noise component NZ that is commonly added to the first sensor signal S1(t) and the third sensor signal S3(t) is subtracted, and the noise component is suppressed. On the other hand, the foreign object component signal SGa that occurs in the first sensor signal S1(t) around the first timing t1, and the foreign object component signal SGc that occurs in the third sensor signal S3(t) and is in the opposite phase to the foreign object component signal SGa, are treated as foreign object component signals SGa-SGc in the 1-3 difference signal D13(t), and their magnitudes are added together. Therefore, as shown in Figure 12, the 1-3 difference signal D13(t) provides a large foreign matter component signal SGa-SGc around the first timing t1, and the signal-to-noise ratio is significantly improved compared to the first sensor signal S1(t) and the third sensor signal S3(t).

[0107] The sixth graph in Figure 12 shows the 2-4 difference signal D24(t) (=S12(t)-S24(t)) obtained by subtracting the fourth sensor signal S14(t) from the second sensor signal S12(t). This 2-4 difference signal D24(t) has different patterns depending on whether the magnetic pole orientation of the magnetic foreign matter particle MP is as shown in Figure 8 or Figure 9. When the magnetic pole orientation of the magnetic foreign matter particle MP is as shown in Figure 8, the foreign matter component signal SGd, which is generated in the fourth sensor signal S14(t) and is in the opposite phase to the foreign matter component signal SGb, is subtracted from the foreign matter component signal SGb generated in the second sensor signal S12(t) around the first timing t1. As a result, the foreign matter component signals SGb-SGd are obtained in the 2-4 difference signal D24(t), and their magnitudes are added together and become larger (see the thick solid line in the sixth graph of Figure 12).

[0108] On the other hand, when the magnetic pole orientation of the magnetic foreign particle MP is as shown in Figure 9, the foreign component signal SGd', which is generated in the fourth sensor signal S14(t) and is in the opposite phase to the foreign component signal SGb', is subtracted from the foreign component signal SGb' generated in the second sensor signal S12(t) around the first timing t1. As a result, the 2-4 difference signal D24(t) is obtained as foreign component signal SGb'-SGd', and their magnitudes are added together and become larger (see the dashed line in the 6th row of Figure 12). However, the foreign component signal SGb'-SGd' shown by the dashed line is in the opposite phase to the foreign component signal SGb-SGd. In either case, the 2-4 difference signal D24(t) has the noise component NZ, which is commonly added to the second and fourth sensor signals S12(t) and S14(t), subtracted, thus suppressing the noise component. Therefore, with the 2-4 difference signal D24(t), a large foreign matter component signal SGb-SGd or foreign matter component signal SGb'-SGd' is obtained around the first timing t1, and the signal-to-noise ratio is significantly improved compared to the second sensor signal S2(t) and the fourth sensor signal S4(t).

[0109] The graph in the seventh row of Figure 12 shows the opposing second-order difference signal DDo(t) (=D13(t)-D24(t)=(S1(t)-S3(t))-(S12(t)-S14(t))) obtained by subtracting the 2-4 difference signal D24(t) from the 1-3 difference signal D13(t). This opposing second-order difference signal DDo(t) also shows different patterns depending on whether the magnetic pole orientation of the magnetic foreign matter particle MP is as shown in Figure 8 or Figure 9. When the magnetic pole orientation of the magnetic foreign matter particle MP is as shown in Figure 8, the opposing second-order difference signal DDo(t) yields foreign matter component signals (SGa-SGc)-(SGb-SGd) around the first timing t1, and the four foreign matter component signals SGa~SGd are added together to form an even larger foreign matter component signal (see the thick solid line in the seventh row of Figure 12).

[0110] However, when the magnetic pole orientation of the magnetic foreign particle MP is as shown in Figure 9, the opposing second-order difference signal DDo(t) yields the foreign component signal (SGa-SGc)-(SGb'-SGd') around the first timing t1. However, since the in-phase foreign component signal SGb'-SGd' is subtracted from the foreign component signal SGa-SGc, the foreign component signals cancel each other out, and only a small foreign component signal is obtained (see the dashed line in the 7th stage of Figure 12).

[0111] The graph in the eighth row of Figure 12 shows the opposing difference summation signal DAo(t) (=D13(t)+D24(t)=(S1(t)-S3(t))+(S12(t)-S14(t))) obtained by adding the 1-3 difference signal D13(t) and the 2-4 difference signal D24(t). This opposing difference summation signal DAo(t) also shows different patterns depending on whether the magnetic pole orientation of the magnetic foreign matter particle MP is as shown in Figure 8 or Figure 9. When the magnetic pole orientation of the magnetic foreign matter particle MP is as shown in Figure 8, the opposing difference summation signal DAo(t) yields the foreign matter component signal (SGa-SGc)+(SGb-SGd) around the first timing t1. However, since the foreign matter component signal SGa-SGc is added to the foreign matter component signal SGb'-SGd' which is out of phase, only a small foreign matter component signal is obtained (see the thick solid line in the eighth row of Figure 12).

[0112] On the other hand, when the magnetic pole orientation of the magnetic foreign particle MP is as shown in Figure 9, the opposing difference summation signal DAo(t) yields the foreign component signal (SGa-SGc)+(SGb'-SGd') around the first timing t1. However, since the foreign component signal SGa-SGc and the in-phase foreign component signal SGb'-SGd' are added together, an even larger foreign component signal is obtained (see the dashed line in the 8th stage of Figure 12).

[0113] Therefore, as shown in the 7th and 8th steps of Figure 12, the opposing second-order difference signal DDo(t) and the opposing difference summation signal DAo(t) are monitored, and if either the opposing second-order difference signal DDo(t) or the opposing difference summation signal DAo(t) exceeds the third threshold TH3 (TH3>0) or falls below the fourth threshold TH4 (TH4<0), it is determined that the magnetic foreign particle MP has passed the first transport position HH1. This makes it possible to more reliably determine that the magnetic foreign particle MP has passed the first transport position HH1 around the first timing t1.

[0114] The present invention has been described above in accordance with Embodiments 1 and 2 and Modified Embodiments 1 and 2. However, it goes without saying that the present invention is not limited to the embodiments, and can be applied with appropriate modifications without departing from the spirit of the invention.

[0115] For example, in Embodiment 2, the presence or absence of magnetic foreign matter particles MP passing through the first transport position HH1 was determined without using the magnetization unit 90. However, as shown by the dashed line in Figure 7, similar to Embodiment 1, the metal foreign matter particles KP may be pre-magnetized using the magnetization unit 90 to become magnetic foreign matter particles MP, and then these magnetic foreign matter particles MP may be detected.

[0116] When using the magnetization unit 90, it is preferable to direct the magnetic field MF generated by the magnetization unit 90 perpendicular to the transport direction HH and towards the upper side DH1a of the first direction DH1, as in Embodiment 1. However, in this case, when the magnetic foreign matter particles MP pass through the first transport position HH1, the foreign matter component signals generated in the second sensor signal S12(t) and the fourth sensor signal S14(t) become very small. Therefore, it is preferable to direct the magnetic field MF perpendicular to the transport direction HH and obliquely intersect the first direction DH1 and the second direction DH2. Furthermore, it is even better to direct the magnetic field MF obliquely intersect the first direction DH1 and the second direction DH2 at a 45-degree angle. In this case, when the magnetic foreign particle MP passes the first transport position HH1, the foreign matter component signals generated in the first sensor signal S1(t) and the third sensor signal S3(t), as well as the foreign matter component signals generated in the second sensor signal S12(t) and the fourth sensor signal S14(t), become larger. Consequently, the foreign matter component signals generated in the 1-3 difference signal D13(t) and the 2-4 difference signal D24(t) also become larger. The foreign matter component signals generated in the opposing second-order difference signal DDo(t) or the opposing difference summation signal DAo(t) also become larger, making it possible to more reliably determine whether or not the magnetic foreign particle MP has passed the first transport position HH1.

[0117] Furthermore, in Embodiment 2, it was determined that the magnetic foreign particle MP had passed the first transport position HH1 if either the opposing second-order difference signal DDo(t) or the opposing difference summation signal DAo(t) exceeded the third threshold TH3 or fell below the fourth threshold TH4.

[0118] Alternatively, similar to modified form 1, the absolute value of the opposing second-order difference signal DDo(t) and the opposing difference summation signal DAo(t) may be obtained, and if either of these exceeds the third threshold TH3, it may be determined that a magnetic foreign particle MP has passed through the first transport position HH1. By using the absolute values ​​of the opposing second-order difference signal DDo(t) and the opposing difference summation signal DAo(t), it is sufficient to use the third threshold TH3 as the threshold for determination, making comparison with the threshold easier.

[0119] Alternatively, the sum of the squares of the squares of the opposing second-order difference signal DDo(t) and the opposing difference sum signal DAo(t) may be obtained, and if this sum of squares signal exceeds a predetermined threshold, it may be determined that the magnetic foreign particle MP has passed through the first transport position HH1. By using the sum of squares signal in this way, it is possible to appropriately detect whether or not the magnetic foreign particle MP has passed through the first transport position HH1, even if the direction of the magnetic field of the magnetic foreign particle MP is parallel to the first direction DH1 or the second direction DH2, or even if it is oblique to the first direction DH1 and the second direction DH2.

[0120] Furthermore, in the aforementioned embodiments 1 and 2, and modified embodiments 1 and 2, it was determined that the passage of magnetic foreign particles MP at the first transport position HH1 was detected when the upstream / downstream second-order difference signal DDc(t), the opposing second-order difference signal DDo(t), and the opposing difference sum signal DAo(t) exceeded the first threshold TH1, etc.

[0121] However, in Embodiment 1, as shown by the dashed line in the graph of the upstream-downstream second-order difference signal DDc(t) in the seventh stage (bottom stage) of Figure 6, the period TP1 in which the upstream-downstream second-order difference signal DDc(t) exceeds the first threshold TH1 and the period TP2 in which it falls below the second threshold TH2 are also measured. Furthermore, if period TP1 or period TP2 falls within a predetermined period range (exceeding the first period and less than the second period), it may be determined that the passage of magnetic foreign matter particles MP at the first transport position HH1 has been detected. The same applies to Embodiment 2 and modified forms 1 and 2. [Explanation of symbols]

[0122] PP piping HH Conveying direction HHU (Upstream side in the transport direction) HHD (downstream side in the transport direction) HH1 First transport position HH2 Second transport position CH circumferential direction CH1,CH2,CH3,CH4 circumferential position DH1 1st direction DH2 2nd direction DH2a (one side in the second direction) DH2b (the other side in the second direction) IM positive electrode paste (object under inspection) MP magnetic foreign particles OM (External Magnetic Field) 10,110 detection device 1. First magnetic sensor 2.12 Second Magnetic Sensor 3. Third magnetic sensor 4.14 Fourth Magnetic Sensor S1(t) First sensor signal S2(t), S12(t) Second sensor signal S3(t) Third sensor signal S4(t), S14(t) 4th sensor signal t1 First Timing t2 Second timing SG,SG',SGa,SGb,SGc,SGd,SGb',SGd' Foreign object signal component NZ noise component D12(t) 1-2 difference signal D34(t) 3-4 difference signal D13(t) 1-3 difference signal D24(t) 2-4 difference signal DDc(t) Upstream / downstream second-order differential signal ADDc(t) Difference absolute value signal DDo(t) Opposite second-order difference signal DAo(t) Opposing difference sum signal TH1, TH2, TH3, TH4 thresholds 20,120 Differential signal pair acquisition unit 21 1-2 Difference acquisition part 22 3-4 Difference acquisition part 121 1-3 Difference acquisition part 122 2-4 Difference acquisition part 30,130 Foreign object detection unit 40 Upstream / downstream second-order difference acquisition section 140 Opposite second-order difference acquisition unit 145 Opposing difference summation acquisition part 50,150 Judgment section 60 Absolute Value Acquisition Section 70 Foreign object detection section 90 Magnetization part MF magnetic field ST0 Foreign Matter Magnetization Step ST1, ST1a~ST1d Sensor signal acquisition steps ST2, ST2a, ST2b, ST12, ST12a, ST12b Differential signal pair acquisition step ST3, ST13 Foreign object detection step ST4, ST14 Steps to obtain the second-order difference ST15 Step to obtain difference sum ST6, ST16 Judgment Step ST7 Absolute Value Acquisition Step ST8 Foreign object detection step

Claims

1. A magnetic foreign object particle detection device that detects whether or not magnetic foreign object particles containing magnetized magnetic foreign object particles are passing through an object being transported from the upstream side to the downstream side in the transport direction, A first magnetic sensor is positioned at a first transport position in the transport direction and outputs the change in the magnetic force of the object being transported as a first sensor signal. A second magnetic sensor outputs a second sensor signal that detects changes in external magnetic fields arriving from the outside, A third magnetic sensor is positioned at the first transport position, facing the first magnetic sensor via the object to be inspected, and outputs the change in the magnetic force of the transported object to be inspected as a third sensor signal. A fourth magnetic sensor that outputs the aforementioned change in external magnetic field as a fourth sensor signal, A difference signal pair acquisition unit acquires two difference signals from among the first sensor signal, the second sensor signal, the third sensor signal, and the fourth sensor signal: the difference signal between two of the sensor signals and the difference signal between the other two of the sensor signals. The system includes a foreign object detection unit that uses the two difference signals to detect whether or not the magnetic foreign object particles have passed through the first transport position. A device for detecting magnetic foreign particles.

2. A magnetic foreign particle detection device according to claim 1, The second magnetic sensor is The second sensor is positioned downstream of the first transport position and outputs a second sensor signal that also detects changes in the magnetic force of the object being transported. The fourth magnetic sensor is, The fourth sensor is positioned opposite the second magnetic sensor via the object to be inspected at the second transport position and outputs a signal that also detects changes in the magnetic force of the object to be inspected. The difference signal pair acquisition unit is, The 1-2 difference signal between the first sensor signal and the second sensor signal, and the 3-4 difference signal between the third sensor signal and the fourth sensor signal are acquired. The aforementioned foreign object detection unit is A second-order difference acquisition unit acquires an upstream / downstream second-order difference signal, which is the difference between the 1-2 difference signal and the 3-4 difference signal, and The system includes a determination unit 5 that uses the upstream-downstream two-order difference signal to determine whether or not the magnetic foreign particles have passed through the first transport position. A device for detecting magnetic foreign particles.

3. A magnetic foreign particle detection device according to claim 2, The aforementioned foreign object detection unit is The system further includes a foreign object detection unit that uses the aforementioned upstream-downstream two-order difference signal to confirm the passage of the magnetic foreign object particles detected at the first transport position through the second transport position. A device for detecting magnetic foreign particles.

4. A magnetic foreign particle detection device according to claim 2 or claim 3, It is positioned at a third transport position upstream of the first transport position in the transport direction, The magnetization unit further comprises a magnetization unit that applies a magnetic field directed in a first direction connecting the first magnetic sensor and the third magnetic sensor, which are perpendicular to the transport direction and facing each other, thereby magnetizing the metallic foreign matter particles contained in the object to be inspected and converting them into magnetic foreign matter particles. A device for detecting magnetic foreign particles.

5. A magnetic foreign particle detection device according to claim 1, The second magnetic sensor is At the first transport position, the second sensor is positioned on one side of a second direction perpendicular to the first direction connecting the first magnetic sensor and the third magnetic sensor, which are perpendicular to the transport direction and face each other, and outputs a second sensor signal that also detects the change in the magnetic force of the object being transported. The fourth magnetic sensor is, At the first transport position, the fourth sensor is positioned opposite the second magnetic sensor on the other side of the second direction via the object to be inspected, and outputs a signal that also detects the change in the magnetic force of the object to be inspected as it is being transported. The difference signal pair acquisition unit is, The 1-3 difference signal between the first sensor signal and the third sensor signal, and the 2-4 difference signal between the second sensor signal and the fourth sensor signal are acquired. The aforementioned foreign object detection unit is Opposite second-order difference acquisition unit acquires an opposite second-order difference signal which is the difference between the 1-3 difference signal and the 2-4 difference signal. A unit for acquiring a counter-counter-counter-counter-counter-sum signal, which is the sum of the 1-3 difference signal and the 2-4 difference signal, and The system includes a determination unit that determines whether or not the magnetic foreign particles have passed through the first transport position based on the second-order difference signal and the opposing difference summation signal. A device for detecting magnetic foreign particles.

6. A method for detecting magnetic foreign matter particles, which detects whether or not magnetic foreign matter particles containing magnetized particles are passing through an object being transported from the upstream side to the downstream side in the transport direction, A first magnetic sensor is positioned at a first transport position in the transport direction and outputs the change in the magnetic force of the object being transported as a first sensor signal. A second magnetic sensor outputs a second sensor signal that detects changes in the magnetic field of an external magnetic field arriving from the outside, A third magnetic sensor is positioned at the first transport position, facing the first magnetic sensor via the object to be inspected, and outputs the change in the magnetic force of the transported object to be inspected as a third sensor signal. Using a fourth magnetic sensor that outputs the change in the magnetic field of the aforementioned external magnetic field as a fourth sensor signal, A sensor signal acquisition step of acquiring the first sensor signal, the second sensor signal, the third sensor signal, and the fourth sensor signal, A difference signal pair acquisition step in which two difference signals are obtained from among the first sensor signal, the second sensor signal, the third sensor signal, and the fourth sensor signal, namely the difference signal between two of the other two sensor signals, The foreign object detection step includes detecting the passage of the magnetic foreign object particles at the first transport position using the two difference signals mentioned above. A method for detecting magnetic foreign particles.

7. A method for detecting magnetic foreign particles according to claim 6, The second magnetic sensor is The second sensor is positioned downstream of the first transport position and outputs a second sensor signal that also detects changes in the magnetic force of the object being transported. The fourth magnetic sensor is, The fourth sensor is positioned opposite the second magnetic sensor at the second transport position via the object to be inspected, and outputs a signal that also detects the change in the magnetic force of the object to be inspected as it is being transported. The step of acquiring the difference signal pair is as follows: The 1-2 difference signal between the first sensor signal and the second sensor signal, and the 3-4 difference signal between the third sensor signal and the fourth sensor signal are acquired. The aforementioned foreign object detection step is: A second-order difference acquisition step to acquire an upstream / downstream second-order difference signal, which is the difference between the 1-2 difference signal and the 3-4 difference signal, and The system includes a determination step that uses the upstream-downstream two-order difference signal to determine whether or not the magnetic foreign matter particles have passed through the first transport position. A method for detecting magnetic foreign particles.

8. A method for detecting magnetic foreign particles according to claim 7, The aforementioned foreign object detection step is: The system includes a foreign object confirmation step that uses the upstream-downstream two-order difference signal to confirm that the magnetic foreign object particles detected at the first transport position have passed through to the second transport position. A method for detecting magnetic foreign particles.

9. A method for detecting magnetic foreign particles according to claim 7 or claim 8, It is positioned at a third transport position upstream of the first transport position in the transport direction, The system further includes a foreign object magnetization step, in which a magnetic field is applied to the object to be inspected at the third transport position to magnetize the metallic foreign particles contained in the object to be inspected into magnetic foreign particles, using a magnetization unit that applies a magnetic field oriented in a first direction connecting the first magnetic sensor and the third magnetic sensor which are perpendicular to the transport direction and facing each other, thereby magnetizing the metallic foreign particles contained in the object to be inspected into magnetic foreign particles, and delivering the object to the first transport position. A method for detecting magnetic foreign particles.

10. A method for detecting magnetic foreign particles according to claim 6, The second magnetic sensor is At the first transport position, the second sensor is positioned on one side of a second direction perpendicular to the first direction connecting the first magnetic sensor and the third magnetic sensor, which are perpendicular to the transport direction and face each other, and outputs a second sensor signal that also detects the change in the magnetic force of the object being transported. The fourth magnetic sensor is, At the first transport position, and positioned opposite the second magnetic sensor via the object under inspection on the other side of the second direction, the fourth sensor outputs a signal that also detects the change in the magnetic force of the object under inspection as it is transported within the piping. The step of acquiring the difference signal pair is as follows: The 1-3 difference signal between the first sensor signal and the third sensor signal, and the 2-4 difference signal between the second sensor signal and the fourth sensor signal are acquired. The aforementioned foreign object detection step is: A second-order difference acquisition step in which a counter-second-order difference signal is obtained, which is the difference between the 1-3 difference signal and the 2-4 difference signal. A difference-sum acquisition step to acquire a counter-difference-sum signal which is the sum of the 1-3 difference signal and the 2-4 difference signal, and The determination step includes determining whether or not the magnetic foreign matter particles have passed through the first transport position based on the second-order difference signal and the opposing difference summation signal. A method for detecting magnetic foreign particles.

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