JP2012159292A - Foreign matter detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase magnetic signals from metallic foreign matter and reduce background signals from the checkup object.SOLUTION: Metallic foreign matter having stuck to or mixed into a checkup object 102 is caused to reach saturated magnetization in a relatively weak magnetic field by applying a magnetic field not less in intensity than the coercive force of the foreign matter in a plurality of directions, and the intensity of magnetic signals from the metallic foreign matter is thereby increased efficiently; further, the checkup object, demagnetized by applying an AC magnetic field after having been magnetized, is subjected to measurement of the residual magnetism therein.

Description

  The present invention relates to an inspection apparatus and an inspection method for magnetically detecting non-destructive metallic foreign matters mixed in foods, pharmaceuticals, industrial products and the like.

  As a method for detecting a metallic foreign object adhering to or mixed in a product during a manufacturing process, there is a method of measuring residual magnetism using a magnetic sensor after magnetizing an inspection object. In the metal foreign object detection technology using such a magnetic sensor, the sensitivity of metal foreign object detection determines the S / N ratio of the magnetic signal, that is, the signal from the metal foreign object and the background signal from the inspection object itself. Is the ratio. In order to improve this S / N ratio, in the magnetic detection device disclosed in Japanese Patent Application Laid-Open No. 9-54167, after magnetizing a target object with a magnetizing device, only a specific magnetic material is applied with a demagnetizing device. The background signal is reduced by demagnetizing.

JP-A-9-54167

  However, even with the above method, when the magnetic signal from the metal foreign object is very small and is buried in the background signal, it is difficult to detect the metal foreign object. Further, when the magnetic characteristics of the inspection object are not uniform, it becomes difficult to completely demagnetize the inspection object by applying a cancel magnetic field.

  The present invention increases a magnetic signal from a metal foreign object in the detection of the metal foreign object. Further, the background signal from the inspection object is reduced.

  One form of the foreign matter detection apparatus of the present invention measures residual magnetism of an inspection object after applying a magnetic field from a plurality of directions to the inspection object. The strength of the magnetic field to be applied is preferably set to be higher than the coercive force of the foreign matter that is considered to be attached to or mixed in the inspection object.

  In another embodiment of the foreign matter detection apparatus of the present invention, after magnetizing an inspection object, the residual magnetism is measured after demagnetizing by applying an alternating magnetic field. At this time, as a suitable condition, the intensity of the alternating magnetic field is set to be stronger than twice the holding force of the inspection object. As another suitable condition, the intensity of the alternating magnetic field is set to be weaker than the coercive force of a foreign substance that is considered to be attached to or mixed in the inspection object.

  According to the present invention, when a metal foreign object having magnetic anisotropy adheres to or is mixed in the inspection object, saturation magnetization can be performed with a relatively low magnetic field regardless of the direction of the magnetization easy axis of the metal foreign object. Therefore, the intensity of the magnetic signal from the metal foreign object can be efficiently improved.

Even if the magnetic properties of the inspection object are not uniform, the inspection object can be demagnetized by applying an alternating magnetic field. At that time, the inspection object can be effectively demagnetized by setting the intensity of the alternating magnetic field sufficiently higher than the holding force of the inspection object. In addition, by setting the strength of the alternating magnetic field to be weaker than the coercive force of the metal foreign object that is considered to be attached or mixed in the inspection object, only the inspection object is selectively demagnetized without demagnetizing the metal foreign object. I can do it. Thus, the background signal from the inspection object can be reduced while maintaining the magnetic signal from the metal foreign object.
Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is a schematic diagram illustrating a configuration example of a foreign object detection device according to Embodiment 1. FIG. The figure which shows the MH curve of the ferromagnetic material which has magnetic anisotropy. The figure which shows the change of the magnetization of a metal foreign material and a test target object. The flowchart which shows the procedure of the fluctuation | variation detection of the magnet for a magnet using a magnetic sensor. FIG. 6 is a schematic diagram illustrating a configuration example of a foreign object detection device according to a second embodiment. The figure which shows the change of the magnetization of a metal foreign material and a test target object. FIG. 9 is a schematic diagram illustrating a configuration example of a foreign object detection device according to a third embodiment. 9 is a time chart illustrating Example 3. FIG. Schematic which shows the structural example of the foreign material detection apparatus which concerns on Example 4. FIG. 9 is a time chart illustrating Example 4. 9 is a time chart illustrating Example 4. FIG. 10 is a schematic diagram illustrating a configuration example of a foreign object detection device according to a fifth embodiment. The figure which shows the change of the magnetization of a metal foreign material and a test target object. Schematic which shows the structural example of the foreign material detection apparatus which concerns on Example 6. FIG. The figure which shows the change of the magnetization of a metal foreign material and a test target object.

  Embodiments of the present invention will be described below with reference to the drawings.

[Example 1]
FIG. 1 is a schematic diagram showing a configuration example of a foreign object detection apparatus according to the first embodiment of the present invention. The inspection object 102 is placed on the conveyance belt 101 and conveyed from the left to the right on the paper surface. Here, the transport direction is defined as the Y axis, the vertical axis orthogonal to the Y axis is defined as the Z axis, and the axis orthogonal to the Y axis and the Z axis is defined as the X axis. The magnetizing magnets 103, 104, and 105 are electromagnets that generate magnetic fields in the X, Y, and Z axis directions, respectively. The demagnetizing magnet 107 is an electromagnet that generates a magnetic field in the same direction and in the opposite direction as the magnetizing magnet 105. Although not shown, a magnetic shield is provided between the magnetizing magnets 103, 104, and 105 so that the magnetic fields do not interfere with each other. Magnetic shields are also provided before and after the demagnetizing magnet 107 so that the magnetic field does not leak. The magnetizing magnets 103, 104, and 105 and the demagnetizing magnet 107 are supplied with power from the DC power supply 111 through the amplifier circuits 109a, 109b, 109c, and 110, respectively. The outputs of the amplifier circuits 109a, 109b, 109c and 110 are controlled in an integrated manner by the control computer 114.

  The magnetic sensor 106 is installed between the magnetizing magnet 105 and the demagnetizing magnet 107, and the detection circuit 112 measures a magnetic signal generated from the inspection object 102 immediately after passing through the magnetizing magnets 103, 104, 105. . The magnetic sensor 108 is installed on the downstream side of the demagnetizing magnet 107, and the detection circuit 113 measures a magnetic signal generated from the inspection object 102. The input / output device 115 is connected to the control computer 114, and setting of inspection conditions by the operator and display of detection results for the operator are performed via the input / output device 115. As the magnetic sensors 106 and 108, any magnetic sensor including a Hall element and a magnetoresistive effect element can be used.

  Here, the principle of magnetization of the foreign matter in the present embodiment will be described. In this embodiment, by using the magnetic anisotropy of a metal foreign object made of a ferromagnetic material, a metal foreign object accompanying the inspection object, that is, a metal foreign object adhering to or mixed in the inspection object is detected with high sensitivity. . Magnetic anisotropy is a property in which the magnetization vector of a ferromagnetic material is easily oriented in a specific direction (is easily magnetized). The direction that is easily magnetized is called the easy axis, and the direction that is hard to be magnetized is called the hard axis. FIG. 2 is an MH curve of a ferromagnetic material having magnetic anisotropy. The MH curve indicates a change in magnetization of the magnetic material when a sufficiently strong external magnetic field is applied, and is also called a major loop. FIG. 2A is an MH curve when an external magnetic field is applied in the direction of the easy axis of magnetization, and a loop close to a rectangle is drawn. That is, it has a feature that magnetization rises steeply with increasing external magnetic field and reaches saturation with a relatively low magnetic field. Further, after reaching the saturation magnetization by the external magnetic field in the easy axis direction, even if the external magnetic field is made zero, a large residual magnetization remains. In order to make the magnetization zero, a reverse external magnetic field must be applied. The strength of the external magnetic field when the magnetization becomes zero is called coercivity. On the other hand, when an external magnetic field is applied in the direction of the hard axis, as shown by the MH curve in FIG. Only then will saturation be reached. Further, after reaching the saturation magnetization by the external magnetic field in the hard axis direction, when the external magnetic field is zero, the residual magnetization is small. Accordingly, it can be said that the coercive force is small, and the magnetization is relatively easy to disappear.

  Most of the metal foreign matter adhering to or mixed in the product originates from the mechanical equipment used in the manufacturing process at the factory, and iron or stainless steel is the main component. In particular, SUS304 is a material often used as a member of a manufacturing apparatus and does not inherently have magnetism. However, SUS304 mixed as a metallic foreign object contains a martensite phase because it receives stress during wear and fracture, and has magnetism. it is conceivable that. In addition, since the metal foreign matter is generated by wear or breakage, it is considered that it has a magnetic anisotropy more easily than a highly symmetric shape such as a sphere and has a complicated and directional shape. On the other hand, industrial products that are inspection objects often have no magnetism or are magnetically isotropic even if they have magnetism.

  From the above, in the foreign object detection device that magnetizes the inspection object and detects the metal foreign object by its residual magnetism, the external magnetic field applied to the inspection object is set to the magnetization easy axis direction of the metal foreign object, thereby reducing the external The metal foreign matter can be magnetically saturated with a magnetic field efficiently, and the residual magnetization can be increased. However, it is considered that the direction of the easy axis of the metallic foreign object attached to the product is random, and it is difficult to know the direction of each easy axis and apply an external magnetic field in that direction.

  Therefore, in the present invention, an external magnetic field is applied to the easy axis of magnetization regardless of the direction of the easy axis of the metal foreign object, and a magnetic field is applied in a plurality of directions to reach saturation magnetization. . Once the magnetic material is magnetized in the easy axis direction, it is difficult to demagnetize even if an external magnetic field is applied to the hard axis.

  Next, the flow of foreign object detection in the present embodiment will be described using FIG. 1 again. The inspection object 102 sequentially passes through an external magnetic field in the X, Y, and Z axis directions formed by the magnetizing magnets 103, 104, and 105. Since any one of the three axes is in a direction close to the easy magnetization axis direction of the metal foreign matter mixed in or attached to the inspection object 102, all the metal foreign matters are magnetized on the easy magnetization axis. At this time, if the inspection object has magnetism, the inspection object is also magnetized. However, since the magnetic property of the inspection object is isotropic as described above, the magnetization direction is applied immediately before. The direction of the magnetic field. In the case of the present embodiment, since the magnetic field is applied in the order of the X, Y, and Z axes by the magnetizing magnets 103, 104, and 105, the magnetization direction of the inspection object 102 is the Z axis.

  The magnetic sensor 106 measures a magnetic signal generated by an inspection object that has passed through an external magnetic field created by the magnetizing magnets 103, 104, and 105. This signal is transmitted to the control computer 114 through the detection circuit 112, and the control computer 114 can determine the magnetic field strength of the demagnetizing magnet 107 based on this signal. A method for determining the magnetic field strength of the demagnetizing magnet 107 will be described in detail later.

  After passing through the magnetic sensor 106, the inspection object 102 is demagnetized by a demagnetizing magnet 107. As described above, since the direction of magnetization of the inspection object 102 is the direction of the magnetic field generated by the magnetizing magnet 105 that has passed through last, the demagnetizing magnet 107 has substantially the same direction as that of the magnetizing magnet 105 in the opposite direction. Designed to generate a DC magnetic field, the residual magnetization of the inspection object 102 becomes zero. At this time, the metallic foreign matter mixed in or attached to the inspection object 102 is also subjected to the action of the demagnetizing magnet 107, but the metallic foreign matter once magnetized in the direction of the easy magnetization axis is not easily degaussed. Therefore, if the magnetic sensor 108 installed downstream of the demagnetizing magnet 107 is used, the residual magnetization of the metallic foreign object can be measured with high sensitivity. The measurement result of the magnetic sensor 108 is transmitted to the control computer 114 through the detection circuit 113, and the control computer 114 compares the measured signal intensity with a predetermined threshold value to determine the presence or absence of a metallic foreign object. That is, the control computer 114 constitutes a foreign object detection unit.

Here, with reference to FIG. 3A, the setting of the intensity of the magnetic field in the present embodiment will be described.
FIG. 3A shows the change in the magnetization of the metal foreign object in the present embodiment, which is smaller than a major loop (shown by a broken line in FIG. 3) assuming a sufficiently large external magnetic field. Draw a minor loop. The direction in which the external magnetic field is applied is the easy axis of magnetization of the metal foreign object. In order to increase the sensitivity of metal foreign object detection, it is important to bring the magnetization of the metal foreign object close to saturation in order to increase the residual magnetization. Therefore, a stronger magnetic field strength is desirable, but there is a limit to the magnetic field strength that can be applied from the viewpoint of mounting and cost. For this reason, in this embodiment, by applying a magnetic field in a plurality of directions, the metal foreign object is magnetized in the direction in which it is most easily magnetized. Thereby, compared with the case where a magnetic field is applied in a single direction, metallic foreign matter can be magnetically saturated with a lower magnetic field. Specifically, as indicated by an arrow A in FIG. 3A, a magnetic field intensity sufficient to cause magnetization to rise is necessary and sufficient as the magnetization magnetic field. This magnetizing magnetic field is approximately the same as the coercive force in the first approximation, but in actuality, the operator or the control is based on the information of the inspection object, the metal foreign object to be detected, the past detection result, etc. It is desirable for the computer to set the strength of the magnetizing magnetic field.

Next, the demagnetizing field strength setting in the present embodiment will be described with reference to FIG.
FIG. 3B shows the change in magnetization of the inspection object in the present embodiment. The inspection object magnetized in the path indicated by the arrow A by applying the magnetizing magnetic field decreases its magnetization as indicated by the arrow B in FIG. Magnetized in the direction. Thereafter, when the magnetic field passes through the magnetic field region of the demagnetizing magnet and the external magnetic field becomes zero, as indicated by the arrow C, the magnetization of the inspection object slightly returns to the positive direction again. The finally left magnetization is the residual magnetization. It is desirable to set the strength of the demagnetizing magnetic field so that the residual magnetization becomes zero.

  Due to this demagnetizing magnetic field, the foreign metal also loses magnetization to some extent, but the residual magnetization is larger than that of the object to be inspected, as indicated by arrows B and C in FIG. This is because the MH curve in the direction of the easy axis draws a loop close to a rectangle, and the magnetization gradient is small for a demagnetizing magnetic field smaller than the coercive force. In other words, the demagnetizing magnetic field needs to be set smaller than the coercive force of the metal foreign matter.

  Since the optimum demagnetizing field strength is determined by the magnetic properties of the inspection object, it is preferable to determine the demagnetizing field strength by measurement using a test piece prior to inspection. Furthermore, since there is a possibility that the magnetic characteristics of the inspection object may vary with changes in materials and manufacturing processes, it is preferable to adjust the demagnetizing magnetic field for each material and for each lot.

  Even after the magnetization field and the demagnetization field are set as described above, the strength of the demagnetization field is reduced due to the offset fluctuation of the current supplied to the magnetization magnet and the demagnetization magnet and the magnetism fluctuation of the inspection object. The optimum value may vary over a long period.

  FIG. 4 is a flow for detecting fluctuations in the magnetizing magnet using the magnetic sensor 106. According to this flow, the magnetizing magnetic field is set (S11), and the measured value of the magnetic sensor 106 immediately after that is stored as a reference (S12). After starting the inspection, the output of the magnetic sensor 106 is measured to monitor long-period fluctuations in the magnetizing magnetic field (S13, S14), and the inspection is continued when the output fluctuation of the magnetic sensor 106 is equal to or less than the threshold (S15). When the fluctuation exceeds the threshold value, the magnetic field is readjusted (S16).

  Similarly, it is also possible to monitor long-period fluctuations of the demagnetizing magnetic field using the magnetic sensor 108. Since the low frequency component of the magnetic signal detected by the magnetic sensor 108 is considered to be a signal from the inspection object, feedback is sent to the amplifier circuit 110 via the control computer 114 so that this becomes zero on average. Just do it.

  In this embodiment, electromagnets are used as the magnetizing magnets 103, 104, 105 and the demagnetizing magnet 107. However, in principle, permanent magnets may be used. In this case, since the control by the amplifier circuit cannot be performed, the inspection condition is fixed, but the cost can be reduced. Alternatively, a combination of a permanent magnet and an electromagnet may be used for the magnetizing magnets 103, 104, 105 and the demagnetizing magnet 107 in order to achieve both cost and freedom of inspection conditions.

  In this embodiment, the direction of magnetization by the magnet for magnetizing is set to the sample transport direction and two directions orthogonal to the sample transport direction, but the same effect can be obtained even in three different directions. Also, it is difficult to magnetize in three directions from the viewpoint of mounting and cost, and when the magnetization direction is two directions, the effect is reduced compared to the case of three directions, but the foreign matter detection sensitivity is higher than that of the conventional magnetization method. can get.

[Example 2]
FIG. 5 is a schematic diagram showing a configuration example of a foreign object detection apparatus according to the second embodiment of the present invention. In addition, the same code | symbol was attached | subjected to the part same as FIG. Detailed descriptions of portions having the same functions as those of the foreign object detection device of FIG. 1 are omitted.

  In this embodiment, the inspection object 401 is a belt-like film, which is transported from the left side to the right side of the drawing. The definitions of the X axis, the Y axis, and the Z axis are the same as those in FIG. The magnetizing magnets 103, 104, and 105 are electromagnets that generate magnetic fields in the X, Y, and Z axis directions, respectively, and are supplied with current from the DC power supply 111 via the amplifier circuits 109a, 109b, and 109c, respectively. The demagnetizing magnet 402 is an electromagnet that can generate an alternating magnetic field, and is supplied with power by an alternating current power supply 404 via an amplifier circuit 403. The amplitude of the alternating magnetic field formed by the degaussing magnet 402 is constant over time. However, in terms of space, a magnetic shield or the like is designed so that it gradually attenuates as it moves away from the demagnetizing magnet.

  The magnetometer type magnetic sensor 405 and the planar type gradiometer type magnetic sensor 407 are installed on the downstream side of the demagnetizing magnet 402, and the detection circuits 406 and 408 respectively detect the inspection object 401 immediately after passing through the demagnetizing magnet 402. Measure the generated magnetic signal. Although not shown, a magnetic shield is provided between the demagnetizing magnet 402 and the magnetometer type magnetic sensor 405 so that the magnetic field does not leak. The output of the detection circuit 406 is transmitted to the control computer 114, and the control computer 114 determines the magnetic field strength of the demagnetizing magnet 402 based on this signal. The output of the detection circuit 408 is transmitted to the control computer 114, and the control computer 114 compares the signal intensity with a predetermined threshold value to determine the presence or absence of a metallic foreign object. The operation of the magnetometer type magnetic sensor 405 and the planar type gradiometer type magnetic sensor 407 will be described later.

  Here, the principle of AC demagnetization performed by the demagnetizing magnet 402 will be described using the MH curve in FIG. FIG. 6A shows the change in magnetization of the metallic foreign object in the present example, and shows that an alternating magnetic field that is attenuated thereafter is applied in the direction of the easy magnetization axis, starting from immediately after the application of the magnetic field. . At this time, even if the external magnetic field reciprocates around zero, the magnetization of the metal foreign matter is not greatly attenuated, and finally a large residual magnetization remains. This is because the MH curve of the metal foreign object draws a loop close to a rectangle on the easy magnetization axis. On the other hand, FIG. 6B shows a change in the magnetization of the inspection object in the present embodiment. The external magnetic field reciprocates around zero and the magnetization is greatly attenuated. The remanent magnetization becomes zero. This is because the MH curve of the inspection object has a large gradient in the vicinity of the zero magnetic field.

  The magnetic field strength of the demagnetizing magnet is determined as follows. FIG. 6C is an enlarged portion of the MH curve of the inspection object. In order for the magnetization to approach zero when the intensity of the alternating magnetic field is gradually attenuated, the center of the amplitude of the magnetization corresponding to the amplitude of the alternating magnetic field needs to be zero. Therefore, when the MH curve in the vicinity of the zero magnetic field is approximated by a straight line, it can be seen that the intensity of the alternating magnetic field needs to be about twice the coercive force of the inspection object.

  On the other hand, from the viewpoint of the magnetic signal level from the foreign matter, it is desirable that the intensity of the alternating magnetic field is small. The strength of the alternating magnetic field that is allowed in order not to attenuate the magnetization of the foreign matter by the alternating magnetic field is about the coercive force of the foreign matter.

  Thus, the degaussing of the inspection object and the magnetic signal level maintenance of the metal foreign object are in a trade-off relationship. Therefore, more preferably, the S / N ratio of the magnetic signal, that is, the ratio of the signal from the metal foreign object to the background signal from the inspection object itself is maximized by the measurement using the test piece prior to the inspection. It is desirable to obtain the following conditions.

  By appropriately setting the intensity of the alternating magnetic field formed by the demagnetizing magnet by the above method, only the magnetization of the inspection object can be selectively demagnetized.

  Next, the operation of the magnetometer type magnetic sensor 405 and the planar gradiometer type magnetic sensor 407 in the present embodiment will be described. The magnetometer type magnetic sensor is one in which a magnetic detection element is connected to a pickup coil wound in one turn or in a plurality of turns in the same direction. On the other hand, a planar gradiometer type magnetic sensor is one in which two coils having the same shape are wound in opposite directions, and those connected in series are connected to a magnetic detection element. In the present embodiment, the SQUID sensor is used as the magnetic detection element, but other magnetic detection elements such as a fluxgate sensor and an MR sensor may be used.

  The magnetometer type magnetic sensor measures the absolute value of the magnetic field entering the detection coil, whereas the planar gradiometer type magnetic sensor has the feature of erasing the magnetic field that is common to the two coils and measuring only the difference. .

  In this embodiment, since the inspection object 401 is a band-like film, it is expected that a certain magnetic signal is generated when it has magnetism. Therefore, the planar gradiometer type magnetic sensor has an effect of reducing the magnetic signal from the inspection object and detecting the signal from the metal foreign object with high sensitivity.

  On the other hand, the magnetometer type magnetic sensor has a function of monitoring a magnetic signal from an inspection object. Even after deciding the strength of the demagnetizing magnet, the optimum value of the demagnetizing magnetic field has a long period due to the offset fluctuation of the current supplied to the magnetizing magnet and the demagnetizing magnet and the magnetism fluctuation of the inspection object. May vary. In such a case, a magnetic signal is detected by the magnetometer type magnetic sensor 405, and feedback may be provided to the amplification circuit 403 via the control computer 114 so that the signal from the inspection object becomes zero on average. . In the present embodiment, the positional relationship between the magnetometer type magnetic sensor 405 and the planar gradiometer type magnetic sensor 407 is the upstream side of the magnetometer and the downstream side of the planar type gradiometer type magnetic sensor 407, but is reversed. However, the same effect can be obtained.

[Example 3]
FIG. 7 is a schematic diagram showing a configuration example of a foreign object detection apparatus according to the third embodiment of the present invention. In addition, the same code | symbol was attached | subjected to the part same as FIG. 1, FIG. Detailed descriptions of portions having the same functions as those of the foreign matter detection apparatus of FIGS. 1 and 5 are omitted.

  In this embodiment, the inspection object 102 is put into a mortar-shaped funnel 601, rotates in the funnel, and then falls on the conveyor belt 101 from an opening provided at the bottom of the funnel. The magnetizing magnet 602 is an electromagnet that forms a magnetic field that immerses the entire funnel, and is supplied with current from a DC power source 605 via an amplifier circuit 604. The magnetic shield 603 is a magnetic shield having an inlet and an outlet for an inspection object while surrounding the entire magnetizing magnet 602 and prevents leakage of a magnetic field. The output of the amplifier circuit 604 is controlled by the control computer 114. The optical sensor 606 is installed so as to look on the conveyor belt 101 and detects the passage of the inspection object 102. The demagnetizing magnet 402 is an electromagnet that can generate an alternating magnetic field, and is supplied with a voltage by an alternating current power supply 404 via a signal generating circuit 403. The magnetic sensor 108 is installed on the downstream side of the demagnetizing magnet 402, and the detection circuit 113 measures a magnetic signal generated from the inspection object 102. The input / output device 115 is connected to the control computer 114, and setting of inspection conditions by the operator and display of detection results for the operator are performed via the input / output device 115.

  The principle of the present embodiment is the same as that of the first embodiment, and after magnetizing a metal foreign object adhering to or mixed in the inspection object in the direction of the easy magnetization axis, a flow for demagnetizing the inspection object by applying an alternating magnetic field. It has become. One of the differences from the first embodiment is that, in the first embodiment, in order to magnetize the metal foreign object in the easy magnetization axis direction, a plurality of magnetized magnets are used to apply a magnetizing magnetic field in a plurality of directions to the inspection object. On the other hand, in this embodiment, the mortar-shaped funnel 601 is used to rotate the inspection object 102 in the magnetic field formed by the magnetizing magnet 602, so that the metal adhered to or mixed into the inspection object. The foreign matter is magnetized on the easy magnetization axis. As a result, the magnetizing magnet can be single, and the cost can be reduced.

  Another difference between the present embodiment and the first embodiment is that the demagnetizing magnetic field intensity is constant in time in the first embodiment, whereas the demagnetizing magnetic field is pulsed in the present embodiment. . This will be described with reference to the time chart of FIG. FIG. 8A shows the output of the optical sensor 606. The optical sensor 606 detects the passage of the inspection object and outputs a pulse signal. When this signal is transmitted to the control computer 114, the control computer 114 calculates the timing of applying an alternating magnetic field to the demagnetizing magnet 402 based on the speed of the conveyor belt 101, and a trigger signal as shown in FIG. Is generated. With this trigger signal as an input signal, the signal generating circuit 403 generates an alternating current that attenuates as shown in FIG. 8C and causes the demagnetizing magnet 402 to generate an alternating magnetic field.

  By generating the demagnetizing magnetic field in a pulse manner in this way, it is possible to generate the demagnetizing magnetic field only when the inspection object passes, so that it is possible to reduce power consumption and heat generation by the demagnetizing magnet. The optical sensor 606 may be replaced with any other sensor such as a capacitive sensor or an imaging device as long as it can detect the passage of the inspection object.

[Example 4]
FIG. 9 is a schematic diagram showing a configuration example of a foreign object detection device according to a fourth example of the present invention. In addition, the same code | symbol was attached | subjected to the part same as FIG. 1, FIG. Detailed descriptions of portions having the same functions as those of the foreign matter detection apparatus of FIGS. 1 and 7 are omitted.

  In this embodiment, the inspection object 102 is placed on the transport belt 101 and transported from the left to the right of the paper surface. The optical sensor 606 is installed so as to look on the conveyor belt 101 and detects the passage of the inspection object 102.

  The magnets 801a and 801b are electromagnets that generate a magnetic field in the X direction as a pair, and are supplied with current by the signal generation circuit 804a. The magnets 802a and 802b are electromagnets that generate a magnetic field in the Y direction as a pair, and are supplied with current by the signal generation circuit 804b. Magnets 803a and 803b are a pair of electromagnets that generate a magnetic field in the Z direction, and are supplied with current by a signal generation circuit 804c. The signal generation circuits 804a, 804b, and 804c are supplied with current by a power source 805.

  The magnetic sensor 108 is installed on the downstream side of the magnets 801a, 801b, 802a, 802b, 803a, and 803b, and the detection circuit 113 measures a magnetic signal generated from the inspection object 102. The input / output device 115 is connected to a control computer, and setting of inspection conditions by an operator and display of detection results for the operator are performed via the input / output device 115.

  The principle of the present embodiment is the same as that of the first and third embodiments, and after inspecting the metal foreign matter adhering to or mixed in the inspection object in the direction of the easy axis of magnetization, an AC magnetic field is applied to thereby inspect the inspection object. It has become a flow to demagnetize. One of the features of this embodiment is that magnetization in a plurality of directions is performed in a time division manner at a single site. Another feature of the present embodiment is that the same magnet is used for magnetization and demagnetization of the inspection object. This will be described with reference to the time chart of FIG.

  When the passage of the inspection object is detected by the optical sensor 606, the control computer 114 inputs a trigger signal to the signal generation circuits 804a, 804b, and 804c, whereby the signal generation circuits 804a, 804b, and 804c are respectively Signals such as those shown in FIGS. 10A, 10B, and 10C are generated. These signals correspond to magnetic fields in the X direction, Y direction, and Z direction, respectively. First, a direct current flows through the magnets 801a and 801b from T1 to T2, and a magnetic field for magnetization is applied in the X direction. Next, a direct current flows through the magnets 802a and 802b from T2 to T3, and a magnetic field for magnetization in the Y direction is formed. Next, a direct current flows through the magnets 803a and 803b from T3 to T4, and a magnetization magnetic field is applied in the Z direction. The above is the process of magnetization of the inspection object. Next, from T5 to T6, an alternating current that attenuates flows in the magnets 801a and 801b, and alternating current demagnetization is performed in the X direction. Subsequently, an alternating current that attenuates to the magnets 802a and 802b flows from T6 to T7, and alternating current demagnetization is performed in the Y direction. Further, from T7 to T8, an alternating current that attenuates flows in the magnets 803a and 803b, and AC demagnetization is performed in the Z direction. While the inspection object passes through the magnetic field generated by the magnets 801a, 801b, 802a, 802b, 803a, and 803b, the processing from T1 to T8 is performed.

  In the example of FIG. 10, the magnetization is performed in three directions. However, considering that the metal foreign matter adhering to or mixed in the inspection target can have an easy magnetization axis in any direction, the number of directions is further increased. Magnetization may be performed. For example, in the example of FIG. 11, magnetization is performed in seven directions. That is, a direct current flows through the magnets 801a and 801b from T1 to T2, and a magnetization magnetic field is applied in the positive direction of the X direction. Next, a direct current flows through the magnets 802a and 802b and the magnets 803a and 803b from T2 to T3, and a magnetization magnetic field is applied in a 45 degree direction from the positive direction in the X direction to the positive direction in the Y direction. Next, a direct current flows through the magnets 802a and 802b from T3 to T4, and a magnetic field for magnetization is applied in the positive direction of the Y direction. In the following, a magnetizing magnetic field is applied to seven directions by changing the strength of the magnet and the current flowing in order, and finally magnets 801a, 801b, 802a, 802b, 803a, from T9 to T10. When an alternating current that attenuates flows to 803b, alternating current demagnetization is performed on the inspection object. At this time, in order to uniformly demagnetize the inspection object in all directions, the alternating current flowing through the magnets 801a and 801b, the alternating current flowing through the magnets 802a and 802b, and the alternating current flowing through the magnets 803a and 803b have different frequencies. You may make it have. Thereby, since the magnetic field synthesized by the three types of alternating currents is directed in a random direction, demagnetization can be performed without leaving a specific magnetization component.

  When the sensor 606 detects the passage of the inspection object, the conveyance belt is at a timing when the inspection object advances to substantially the center of the magnetic field application space constituted by the magnets 801a, 801b, 802a, 802b, 803a, and 803b. 101 may be stopped and the process shown in FIG. 10 may be performed in a state where the inspection object is stationary. In this case, the inspection object 102 is placed on the conveyor belt 101 and is intermittently conveyed from the left to the right of the drawing.

[Example 5]
FIG. 12 is a schematic diagram showing a configuration example of a foreign object detection device according to a fifth example of the present invention. In addition, the same code | symbol was attached | subjected to the part same as FIG. Descriptions of portions having the same functions as those of the foreign object detection device in FIG. 5 are omitted.

  In this embodiment, the inspection object 401 is a belt-like film, which is transported from the left side to the right side of the drawing. The definitions of the X axis, the Y axis, and the Z axis are the same as those in FIG. The magnetizing magnets 103, 104, and 105 are electromagnets that generate magnetic fields in the X, Y, and Z axis directions, respectively, and are supplied with current from the DC power supply 111 via the amplifier circuits 109a, 109b, and 109c, respectively. The magnetic sensor array 1101 is installed on the downstream side of the magnetizing magnet 105, and the magnetic signal generated from the inspection object 401 is measured by the detection circuit 113. The magnetic sensor array 1101 includes magnetic sensors such as Hall elements and MR elements arranged in a straight line. The input / output device 115 is connected to a control computer, and setting of inspection conditions by an operator and display of detection results for the operator are performed via the input / output device 115. The demagnetizing magnet 1102 is an electromagnet capable of generating an alternating magnetic field, and is supplied with a voltage from an alternating current power source 1104 via an amplifier circuit 1103.

  The principle of the present embodiment is the same as that of the second embodiment. By applying a magnetic field for magnetization in a plurality of directions, the metal foreign matter adhering to or mixed into the object to be inspected is magnetized on the easy magnetization axis, and the residual magnetization of the metal foreign matter is magnetized. Is measured with high sensitivity. One of the features of this embodiment is that direct current or alternating current demagnetization is not performed before measuring a magnetic signal from an inspection object. This will be described with reference to FIG.

  FIG. 13A shows an MH curve of a metal foreign object, where a broken line indicates a major loop assuming a sufficiently large external magnetic field, and a solid line indicates a change in magnetization of the metal foreign object in the present embodiment. It is. On the other hand, FIG. 13B shows the MH curve of the inspection object, where the dotted line is a major loop assuming a sufficiently large external magnetic field, and the solid line is the change in magnetization of the inspection object in this embodiment. Is shown. Comparing FIG. 13A and FIG. 13B, it can be seen that the coercive force (the strength of the external magnetic field when the magnetization becomes zero) is close to each other. In such a case, if a magnetic field is applied to demagnetize the inspection object, the metal foreign object is also demagnetized, and thus a sufficiently high sensitivity may not be obtained. Therefore, in this embodiment, as shown by the solid lines in FIGS. 13A and 13B, the residual magnetization is measured without demagnetization. Thereby, compared with the case where demagnetization is performed, the difference in magnetization between the metal foreign object and the inspection object becomes larger, and the metal foreign object can be detected with higher sensitivity.

  Another feature of the present embodiment is that AC demagnetization is performed by the degaussing magnet 1102 after measuring the magnetic signal from the inspection object. The role of this AC demagnetization is to remove the influence that the DC magnetic field applied during the inspection magnetizes the inspection object on the process after the inspection or the performance of the inspection object after the shipment.

[Example 6]
FIG. 14 is a schematic diagram showing a configuration example of a foreign object detection device according to a sixth example of the present invention. In addition, the same code | symbol was attached | subjected to the part same as FIG. 1, FIG. Detailed descriptions of portions having the same functions as those of the foreign matter detection apparatus of FIGS. 1 and 5 are omitted.

  In this embodiment, the inspection object 401 is a belt-like film, which is transported from the left side to the right side of the drawing. The definitions of the X axis, the Y axis, and the Z axis are the same as those in FIG. The magnetizing magnet 105 is an electromagnet that generates a magnetic field in the Z-axis direction, and is supplied with a current from a DC power supply 111 via an amplifier circuit 109c. The demagnetizing magnet 402 is an electromagnet that can generate an alternating magnetic field, and is supplied with a voltage by an alternating current power supply 404 via an amplifier circuit 403. The amplitude of the alternating magnetic field formed by the degaussing magnet 402 is constant over time. However, in terms of space, a magnetic shield or the like is designed so that it gradually attenuates as it moves away from the demagnetizing magnet.

  The magnetometer type magnetic sensor 405 and the planar type gradiometer type magnetic sensor 407 are installed on the downstream side of the demagnetizing magnet 402, and the detection circuits 406 and 408 respectively detect the inspection object 401 immediately after passing through the demagnetizing magnet 402. Measure the generated magnetic signal. Although not shown, a magnetic shield is provided between the demagnetizing magnet 402 and the magnetometer type magnetic sensor 405 so that the magnetic field does not leak. The output of the detection circuit 406 is transmitted to the control computer 114, and the control computer 114 determines the magnetic field strength of the demagnetizing magnet 402 based on this signal. The output of the detection circuit 408 is transmitted to the control computer 114, and the control computer 114 compares the signal intensity with a predetermined threshold value to determine the presence or absence of a metallic foreign object. The operations of the magnetometer type magnetic sensor 405 and the planar type gradiometer type magnetic sensor 407 are as described in the second embodiment.

  One of the features of the present embodiment is that the inspection object is magnetized and demagnetized in a single direction. In Examples 1 to 5, a method for increasing the residual magnetization of a metal foreign object by magnetizing the inspection object in a plurality of directions and magnetizing the metal foreign object adhering to or mixed in the inspection object in the direction of the easy axis of magnetization. Was taken. However, it may be difficult to use a plurality of magnets for magnetization from the viewpoint of mounting and cost. On the other hand, if the magnetic properties of the inspection object and the metal foreign object to be detected satisfy certain conditions, even if the inspection object is magnetized in a single direction, by performing AC demagnetization after the magnetization, It is possible to detect metallic foreign matter with high sensitivity. The condition is a case where “the coercive force of the metal foreign matter to be detected is larger than the coercive force of the inspection object”.

  This will be described with reference to the MH curve in FIG. FIG. 15A shows the change in magnetization of the metallic foreign object in the present example, and shows that an alternating magnetic field that is attenuated thereafter is applied starting from immediately after the application of the magnetizing magnetic field. At this time, even if the external magnetic field reciprocates around zero, the magnetization of the metal foreign matter is not greatly attenuated, and finally a large residual magnetization remains. This is because the MH curve of the metal foreign object draws a loop close to a rectangle. On the other hand, FIG. 15B shows a change in the magnetization of the inspection object in this example, and the external magnetic field reciprocates around zero and the magnetization is greatly attenuated. The remanent magnetization becomes zero. This is because the MH curve of the inspection object has a large gradient in the vicinity of the zero magnetic field.

  The magnetic field strength of the demagnetizing magnet is determined as follows. FIG. 15C is an enlarged portion of the MH curve of the inspection object. In order for the magnetization to approach zero when the intensity of the alternating magnetic field is gradually attenuated, the center of the amplitude of the magnetization corresponding to the amplitude of the alternating magnetic field needs to be zero. Therefore, when the MH curve in the vicinity of the zero magnetic field is approximated by a straight line, it can be seen that the intensity of the alternating magnetic field needs to be about twice the coercive force of the inspection object.

  On the other hand, from the viewpoint of the magnetic signal level from the metal foreign matter, it is desirable that the intensity of the alternating magnetic field is small. The strength of the alternating magnetic field that is allowed in order not to attenuate the magnetization of the metallic foreign object by the alternating magnetic field is about the coercive force of the metallic foreign object.

  Thus, the degaussing of the inspection object and the magnetic signal level maintenance of the metal foreign object are in a trade-off relationship. Therefore, more preferably, the S / N ratio of the magnetic signal, that is, the ratio of the signal from the metal foreign object to the background signal from the inspection object itself is maximized by the measurement using the test piece prior to the inspection. It is desirable to obtain the following conditions.

  By appropriately setting the intensity of the alternating magnetic field formed by the demagnetizing magnet by the above method, only the magnetization of the inspection object can be selectively demagnetized.

  As described above, when the coercive force of the metal foreign object to be detected is larger than the coercive force of the inspection object, the strength of the alternating magnetic field is appropriately set even if the magnetization of the inspection object is in a single direction. Thus, only the magnetization of the inspection object can be selectively demagnetized.

  INDUSTRIAL APPLICABILITY The present invention is useful as a non-destructive inspection apparatus that detects a minute amount of metallic foreign matter mixed in a product containing a magnetic material, for example, an in-line inspection that detects a minute amount of metallic foreign matter mixed in an electrode of a lithium ion battery. It can be applied to the device.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. In addition, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 101 Conveyor belt 102 Inspection object 103,104,105 Magnetization magnet 106 Magnetic sensor 107 Demagnetization magnet 108 Magnetic sensor 109a, 109b, 109c, 110 Amplifier circuit 111 DC power supply 112 Detection circuit 114 Control computer 115 Input / output device 401 Inspection object Object 402 Demagnetizing magnet 403 Amplifier circuit 404 AC power source 405 Magnetometer type magnetic sensor 406 Detection circuit 407 Planar type gradiometer type magnetic sensor 408 Detection circuit 601 Funnel 602 Magnet for magnet 603 Magnetic shield 604 Amplification circuit 605 DC power source 606 Optical sensor 801a , 801b, 802a, 802b, 803a, 803b Magnet 804a, 804b, 804c Signal generation circuit 805 Power supply 1101 Magnetic sensor array 1102 Demagnetizing magnet 1103 Amplifying circuit 11 04 AC power supply

Claims (14)

A magnetic field application unit for applying a magnetic field to the inspection object;
A magnetic sensor for measuring a magnetic signal generated from an inspection object to which a magnetic field is applied by the magnetic field application unit;
A foreign matter detector that detects foreign matter associated with the inspection object using a signal from the magnetic sensor;
The said magnetic field application part applies the several DC magnetic field from which a direction differs with respect to the said test object in order, The foreign material detection apparatus characterized by the above-mentioned.   The foreign object detection device according to claim 1, wherein the plurality of DC magnetic fields include DC magnetic fields in three directions whose directions are substantially orthogonal to each other.   2. The foreign matter detection device according to claim 1, wherein the magnetic field application unit includes a plurality of magnets that generate magnetic fields having different directions and a transport device that transports the inspection object, and the inspection object is formed by the transport device. The foreign matter detection device is characterized in that the magnetic field region generated by the plurality of magnets is sequentially moved.   2. The foreign object detection device according to claim 1, wherein the magnetic field application unit includes a plurality of electromagnets and a signal generation circuit that sequentially energizes the plurality of electromagnets.   The foreign object detection device according to claim 1, wherein the magnetic field application unit includes a magnet and means for rotating the inspection object in a magnetic field generated by the magnet.   2. The foreign matter detection apparatus according to claim 1, wherein a direct-current magnetic field that is finally applied to the inspection object by the magnetic field application unit is substantially in the same direction as that of the direct-current magnetic field applied to the inspection object immediately before and opposite to the inspection object. A debris detection device characterized by having a demagnetizing magnetic field.   2. The foreign matter detection device according to claim 1, wherein the magnetic field application unit applies the alternating magnetic field substantially in the same direction as the last applied direct magnetic field after applying the plurality of direct magnetic fields to attenuate the alternating magnetic field. And measuring a magnetic signal generated from the inspection object by the magnetic sensor.   8. The foreign object detection device according to claim 7, wherein the maximum intensity of the alternating magnetic field is at least twice the coercive force of the inspection object.   The foreign object detection device according to claim 8, wherein the maximum intensity of the AC demagnetizing field is smaller than the coercive force of the foreign object to be detected.   The foreign object detection apparatus according to claim 1, wherein the inspection object is a belt-like continuous body, and the magnetic sensor is a flat-type gradiometer. A magnet for applying a magnetic field to the inspection object;
A magnetic sensor for measuring a magnetic signal generated from an inspection object to which a magnetic field is applied by the magnet;
A foreign matter detector that detects foreign matter associated with the inspection object using a signal from the magnetic sensor;
The magnetic field intensity generated by the magnet is equal to or greater than the coercive force on the easy magnetization axis of the foreign object to be detected. A magnetic field application unit for applying a magnetic field to the inspection object;
A magnetic sensor for measuring a magnetic signal generated from an inspection object to which a magnetic field is applied by the magnetic field application unit;
A foreign matter detector that detects foreign matter associated with the inspection object using a signal from the magnetic sensor;
The magnetic field application unit includes a DC magnetic field application unit that applies a DC magnetic field to the inspection object, and an AC demagnetization unit that applies an AC magnetic field to the inspection object after applying the DC magnetic field,
After the AC magnetic field is attenuated, a magnetic signal generated from the inspection object is measured by the magnetic sensor.   13. The foreign object detection device according to claim 12, wherein the maximum magnetic field strength generated by the AC demagnetizing means is at least twice the coercive force of the inspection object.   14. The foreign object detection device according to claim 13, wherein the maximum magnetic field strength generated by the AC demagnetizing means is smaller than the coercive force of the foreign object to be detected.

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