Magnetic detection system

Abstract

The technical problem of the present invention is to provide a magnetic detection system capable of detecting metal foreign matters with high sensitivity. As a technical means for solving the technical problem, a magnetism detection system (100) is provided with: a signal generation circuit (501) that generates an excitation signal (P); an excitation coil (250) to which an excitation signal (P) is supplied; a buffer circuit (503) connected between the signal generation circuit (501) and the excitation coil (250); magnetic sensors (40A, 40B) that are disposed on opposite sides of each other in the coil axis direction when viewed from the excitation coil (250); a sample stage (300) that holds a sample (310) between the excitation coil (250) and the magnetic sensor (40A); and a detection circuit that generates a detection signal (OUT) on the basis of the difference between the output signals (Pa, Pb) output from the magnetic sensors (40A, 40B). As a result, it is possible to suppress a disorder in the waveform of the excitation signal (P) by means of the snubber circuit (503), and thus it is possible to detect a metal foreign object with high sensitivity.

Description

Technical Field

[0001] This invention relates to magnetic detection systems, and more particularly to magnetic detection systems that can be used as foreign object detection systems. Background Technology

[0002] Patent Document 1 discloses an apparatus comprising: an excitation coil for applying a magnetic field to a sample, a magnetic sensor for detecting the magnetic field, and a cancellation coil for eliminating the magnetic field applied to the magnetic sensor. In the case where the sample contains a metallic foreign object, the magnetic sensor detects the magnetic field caused by eddy currents generated in the metallic foreign object. Existing technical documents Patent documents

[0003] Patent Document 1: Japanese Patent Application Publication No. 2015-102513 Summary of the Invention The technical problem that the invention aims to solve

[0004] However, to generate eddy currents in the metallic foreign matter contained in the sample, a large current needs to flow through the excitation coil. Therefore, if the driving capability of the signal generation circuit that generates the excitation signal is insufficient, the waveform of the excitation signal will be disordered, which can sometimes be a cause of measurement error.

[0005] Therefore, the purpose of this invention is to provide a magnetic detection system that can detect metallic foreign objects with high sensitivity by suppressing the waveform disturbance of the excitation signal. Technical means for solving technical problems

[0006] A magnetic detection system according to one embodiment of the present invention comprises: a signal generation circuit that generates an excitation signal; an excitation coil that supplies the excitation signal; a buffer circuit connected between the signal generation circuit and the excitation coil, having an output impedance lower than its input impedance; a first magnetic sensor and a second magnetic sensor disposed at positions where the amplitude of the excitation magnetic field generated by the excitation coil is the same; a sample stage that holds a sample between the excitation coil and the first magnetic sensor; and a detection circuit that generates a detection signal based on the difference between a first output signal output from the first magnetic sensor and a second output signal output from the second magnetic sensor. Invention Effects

[0007] According to the present invention, a magnetic detection system can be provided that can detect metallic foreign objects with high sensitivity because it can suppress waveform disturbances of the excitation signal by utilizing a buffer circuit. Attached Figure Description

[0008] Figure 1 This is a generally exploded perspective view showing the appearance of a magnetic detection system 100 according to one embodiment of the present invention. Figure 2This is a general perspective view used to illustrate the structure of the sensor body parts 10A and 10B. Figure 3 This is a roughly exploded perspective view used to illustrate the structure of the sensor body parts 10A and 10B. Figure 4 This is a rough three-dimensional diagram showing the state of the magnetic yokes M1~M3 after they have been removed from the magnetic sensors 40A and 40B. Figure 5 This is a circuit block diagram of the magnetic detection system 100. Figure 6 This is a circuit diagram of an example of a buffer circuit 503. Figure 7 This is a schematic diagram used to illustrate the magnetic field generated by the metallic foreign object 311. Detailed Implementation

[0009] In the following, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0010] Figure 1 This is a generally exploded perspective view showing the appearance of a magnetic detection system 100 according to one embodiment of the present invention.

[0011] like Figure 1 As shown, the magnetic detection system 100 of this embodiment includes an arm 110 with the Z-direction as its long side and arms 120, 130, and 140 fixed to the arm 110. Guide members 111 and 112 along the Z-direction are provided on the arm 110. Arms 120 and 130 are threadedly fixed to the guide members 111 and 112, respectively, using fixing screws 122 and 132. The Z-direction positions of the fixing screws 122 and 132 are respectively slidable along the guide members 111 and 112. Thus, arms 120 and 130 can move along the guide members 111 and 112 in the Z-direction. Furthermore, guide members 121, 131, and 141 along the Y-direction are provided on the arms 120, 130, and 140, respectively. The Y-direction positions of the fixing screws 122, 132, and 142 are respectively slidable along the guide members 121, 131, and 141. This allows arms 120, 130, and 140 to move in the Y direction along guides 121, 131, and 141.

[0012] Sensor body parts 10A and 10B are fixed to the front ends of arms 120 and 130 in the Y direction, respectively. In addition, a winding tube 251 with an excitation coil 250 wound on it is fixed to the front end of arm 140 in the Y direction. Figure 1 The image shows the arm 140 separated from the winding tube 251, but in actual use, the winding tube 251 is fixed to the front end of the arm 140.

[0013] The excitation coil 250 has its coil axis in the Z direction, and sensor bodies 10A and 10B are arranged on opposite sides of each other in the coil axis direction when viewed from the excitation coil 250. Furthermore, the position of the excitation coil 250 in the Y direction can be adjusted by sliding the arm 140 along the guide 141. Additionally, the Z-direction positions of the sensor bodies 10A and 10B can be adjusted by sliding the arms 120 and 130 along the guides 111 and 112 respectively, and the Y-direction positions of the sensor bodies 10A and 10B can be adjusted by sliding the arms 120 and 130 along the guides 121 and 131 respectively.

[0014] Therefore, the positions of the sensor bodies 10A and 10B in the XY plane can be adjusted so that the center of the coil shaft passes through the sensor bodies 10A and 10B. Furthermore, the distance between the excitation coil 250 and the sensor bodies 10A and 10B in the Z direction is adjusted to be the same. Thus, when current flows through the excitation coil 250, the magnetic field strength of the excitation magnetic field applied to the sensor body 10A is the same as the magnetic field strength of the excitation magnetic field applied to the sensor body 10B. The magnetic field strength can also be defined by the amplitude of the excitation magnetic field.

[0015] A sample stage 300 for holding the sample 310 is disposed between the excitation coil 250 and the sensor body 10A. Furthermore, during measurement, the position of the adjusting arm 120 in the Z direction is adjusted so that the distance between the sample 310 and the sensor body 10A in the Z direction is close. Therefore, the distance between the sample 310 and the sensor body 10A in the Z direction is significantly shorter than the distance between the sample 310 and the sensor body 10B in the Z direction.

[0016] Figure 2 and Figure 3 This is a diagram illustrating the structure of the sensor body sections 10A and 10B. Figure 2 It's a rough 3D diagram. Figure 3 It is a roughly disassembled 3D diagram.

[0017] like Figure 2 as well as Figure 3As shown, the sensor body 10A includes a chip-shaped magnetic sensor 40A and magnet collectors 51-53 mounted on the surface of the sensor substrate 30. Similarly, the sensor body 10B includes a chip-shaped magnetic sensor 40B and magnet collectors 51-53 mounted on the surface of the sensor substrate 30. The magnetic sensors 40A and 40B are generally cuboid in shape, having an element forming surface 41 and a back surface 42 constituting the YZ plane, an upper surface 43 and a lower surface 44 constituting the XY plane, and side surfaces 45 and 46 constituting the XZ plane. The element forming surface 41 is the surface on which the magnetic sensing element is formed. The magnetic sensors 40A and 40B are mounted on the sensor substrate 30 in such a way that the lower surface 44 faces the sensor substrate 30 and the element forming surface 41 is orthogonal to the surface of the sensor substrate 30. Magnetic yokes M1-M3 made of permalloy or the like are formed on the element forming surface 41 of the magnetic sensors 40A and 40B, and magnetic sensing elements are disposed near the magnetic gap formed by the magnetic yokes M1 and M2 and M3. Thus, magnetic flux through the magnetic gap is applied to the magnetic sensitive element.

[0018] Figure 4 This is a rough three-dimensional diagram showing the state of the magnetic yokes M1~M3 after they have been removed from the magnetic sensors 40A and 40B.

[0019] like Figure 4 As shown, magnetic sensing elements R1 to R4 are formed on the element forming surface 41 of magnetic sensors 40A and 40B. All magnetic sensing elements R1 to R4 use the Y direction as their magnetic sensing direction. Furthermore, magnetic sensing elements R1 and R2 are positioned near the magnetic gap formed by magnetic yokes M1 and M2, and magnetic sensing elements R1 and R2 are positioned near the magnetic gap formed by magnetic yokes M1 and M3. Magnetic sensing elements R1 to R4 are bridged between terminal electrodes 61 and 62, and differential signals corresponding to the magnetic field appear at terminal electrodes 63 and 64.

[0020] Magnetizers 51-53 are blocks made of magnetic materials such as ferrite, and all serve to concentrate the magnetic field generated by sample 310 onto magnetic sensors 40A and 40B. When viewed from the X direction, magnetizers 51-53 overlap with magnetic yokes M1-M3, respectively. That is, magnetizers 51-53 are arranged along the Y direction on the element forming surface 41. When viewed from the X direction, magnetic sensing elements R3 and R4 are arranged between magnetizers 51 and 52, and magnetic sensing elements R1 and R2 are arranged between magnetizers 51 and 53.

[0021] The magnet collector 51 has its length direction in the X direction and mainly serves to concentrate the magnetic field in the X direction onto the magnetic yoke M1. The magnet collector 52 has portions covering the sides 45 and back 42 of the magnetic sensors 40A and 40B, and the magnet collector 53 has portions covering the sides 46 and back 42 of the magnetic sensors 40A and 40B. Therefore, the magnetic field in the X direction concentrated by the magnet collector 51 is bent in the Y direction by the magnetic yoke M1 and flows to the magnet collectors 52 and 53 via the magnetic yokes M2 and M3. Furthermore, the magnetic field passing through the magnetic gap between the magnetic yokes M1 and M2 and M3 is detected by the magnetic sensing elements R1 to R4. Figure 2 as well as Figure 3 In the example shown, a compensation coil C is wound around the magnet 51. A canceling current flows in the compensation coil C to cancel the magnetic field applied to the magnetic sensing elements R1 to R4.

[0022] The sensor body 10A, having this structure, moves closer to the sample 310 by moving the arm 120 in the Z direction. The distance between the sample 310 and the sensor body 10A in the Z direction is preferably as close as possible without interference between them. There is a possibility that a metallic foreign object 311 may be mixed into the sample 310.

[0023] Figure 5 This is a circuit block diagram of the magnetic detection system 100 of this embodiment.

[0024] like Figure 5 As shown, the magnetic detection system 100 of this embodiment includes a signal generation circuit 501 that generates an excitation signal P having a predetermined frequency. The excitation signal P is supplied to one end of the excitation coil 250 via a digital filter 502 and a buffer circuit 503. The other end of the excitation coil 250 is grounded via a resistor 504. The excitation signal P can be a sine wave or a square wave. The digital filter 502 is a circuit used to remove unwanted frequency components contained in the excitation signal P and has a bandpass filter function. The buffer circuit 503 is a circuit that increases the current without changing the voltage waveform of the excitation signal P, and its output impedance is lower than its input impedance.

[0025] Figure 6 This is a circuit diagram of an example of a buffer circuit 503. Figure 6 In the example shown, the buffer circuit 503 is composed of multiple voltage follower circuits 510 connected in parallel. This allows the voltage waveform of the output excitation signal Pout to be maintained at the same waveform as the input excitation signal Pin, and allows more current to flow through the excitation coil 250. The amount of current flowing through the excitation coil 250 can be adjusted by the number of voltage follower circuits 510 connected in parallel. Depending on the required current and the capability of the voltage follower circuit 510, a single voltage follower circuit 510 may also be used.

[0026] Furthermore, when the excitation signal P flows through the excitation coil 250, a magnetic field is generated around the excitation coil 250, and this magnetic field is applied to the two magnetic sensors 40A and 40B. As described above, the magnetic field generated from the excitation coil 250 is applied equally to the magnetic sensors 40A and 40B. Therefore, in the absence of the sample 310, the output signal Pa output from the magnetic sensor 40A is at the same level as the output signal Pb output from the magnetic sensor 40B.

[0027] The output signals Pa and Pb are input to the differential amplifier 506 via the phase adjustment circuit 505. Here, since the excitation coil 250 and the magnetic sensors 40A and 40B are at the same distance in the Z direction, the output signals Pa and Pb should be in phase. However, if a phase difference occurs due to the position adjustment deviation of the arms 120 and 130, the phase adjustment circuit 505 is used to adjust the phase of the output signals Pa and Pb to make them in phase.

[0028] Differential amplifier 506 is a circuit that extracts the difference between output signal Pa and output signal Pb, and the resulting difference signal Va is supplied to lock-in amplifier 507. In the absence of sample 310, the output signals Pa and Pb are at the same level, so the difference signal Va output from differential amplifier 506 is zero.

[0029] Lock-in amplifier 507 uses the excitation signal P as a reference and extracts the frequency components in the difference signal Va that are identical to those in the excitation signal P to generate the detection signal OUT. The waveform of the detection signal OUT is displayed on oscilloscope 508. Differential amplifier 506 and lock-in amplifier 507 constitute a detection circuit that generates the detection signal OUT based on the difference between output signal Pa and output signal Pb. Figure 5 In the example shown, the detection circuit consists of a differential amplifier 506 and a lock-in amplifier 507, but the present invention is not limited thereto.

[0030] Furthermore, when a metallic foreign object is mixed into the sample 310, eddy currents are generated in the metallic foreign object due to the magnetic field from the excitation coil 250. These eddy currents generate a new magnetic field, which is detected by the magnetic sensor 40A. Here, since the sample 310 is positioned between the excitation coil 250 and the magnetic sensor 40A, and the distance between the sample 310 and the magnetic sensor 40B is sufficiently large, the magnetic field generated by the eddy currents is almost not applied to the magnetic sensor 40B. Therefore, when a metallic foreign object is mixed into the sample 310, a difference arises between the output signal Pa and the output signal Pb due to the magnetic field component generated by the eddy currents, which becomes the detection signal OUT.

[0031] Thus, by using the magnetic detection system 100 of this embodiment, it is possible to detect metallic foreign objects mixed in with the sample 310 with high sensitivity. Furthermore, since the magnetic sensor 40A detects the magnetic field caused by eddy currents, it can detect even metallic foreign objects made of non-magnetic materials such as aluminum or copper. In addition, in this embodiment, the excitation signal P output from the signal generation circuit 501 is not directly provided to the excitation coil 250, but rather supplied to the excitation coil 250 via a buffer circuit 503 with high driving capability. Therefore, even when the current flowing through the excitation coil 250 is large, the magnetic field generated by the excitation coil 250 is less prone to unnecessary fluctuations. As a result, measurement errors caused by unnecessary fluctuations in the magnetic field are reduced, and therefore, even if the metallic foreign object in the sample 310 is of a small size, it can be detected with high sensitivity.

[0032] Furthermore, although the positional relationship between the metallic foreign object 311 and the sensor body 10A is in the Z direction, by making the distance between the sample 310 and the sensor body 10A sufficiently close in the Z direction, as shown in the schematic diagram... Figure 7 As shown, magnetizers 51-53 can be used to focus the X-direction component of the magnetic field generated by the metallic foreign object 311 and apply it to the magnetic sensitive elements R1-R4. Figure 7 In the accompanying drawings, reference numeral 312 indicates the direction and intensity of the magnetic field generated by the metallic foreign object 311. By setting the length direction (X-direction) of the magnetizer 51 perpendicular to the separation direction (Z-direction) of the sample 310 and the sensor body 10A, the distance between the sample 310 and the magnetic sensing elements R1 to R4 can be brought closer, thereby achieving high detection sensitivity. In particular, if the center of the coil shaft of the excitation coil 250 passes between the element forming surface 41 of the magnetic sensor 40A and the magnetizer 51, and the center of the coil shaft of the excitation coil 250 passes between the element forming surface 41 of the magnetic sensor 40B and the magnetizer 51, even higher detection sensitivity can be obtained.

[0033] As explained above, in the magnetic detection system 100 of this embodiment, magnetic sensors 40A and 40B are arranged on opposite sides of each other in the axial direction of the excitation coil 250 when viewed from the excitation coil 250, and a sample 310 is arranged between the excitation coil 250 and the magnetic sensor 40A. Therefore, even if a metallic foreign object is mixed into the sample 310, the eddy current generated in the metallic foreign object can be detected. Thus, even if the metallic foreign object is made of a non-magnetic material, it can be detected with high sensitivity.

[0034] In addition, since the magnetic sensors 40A, 40B and the excitation coil 250 are fixed to the movable arms 120, 130 and 140 respectively, the relative positional relationship of the magnetic sensors 40A, 40B and the excitation coil 250 can be finely adjusted.

[0035] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. Various modifications can be made without departing from its spirit, and these are of course included within the scope of the present invention.

[0036] For example, in the above embodiment, when viewed from the excitation coil 250, the sensor body parts 10A and 10B are arranged on opposite sides of each other in the direction of the coil axis. However, as long as the amplitude of the excitation magnetic field generated by the excitation coil 250 is the same, the position of the sensor body parts 10A and 10B is not particularly limited.

[0037] The technology of this invention includes, but is not limited to, the following structural examples.

[0038] A magnetic detection system according to one embodiment of the present invention includes: a signal generation circuit that generates an excitation signal; an excitation coil that supplies the excitation signal; a buffer circuit connected between the signal generation circuit and the excitation coil, having an output impedance lower than its input impedance; a first magnetic sensor and a second magnetic sensor disposed at positions where the amplitude of the excitation magnetic field generated by the excitation coil is the same; a sample stage that holds a sample between the excitation coil and the first magnetic sensor; and a detection circuit that generates a detection signal based on the difference between a first output signal output from the first magnetic sensor and a second output signal output from the second magnetic sensor. Thus, because the buffer circuit can suppress waveform disturbances in the excitation signal, highly sensitive detection of metallic foreign objects is possible.

[0039] In the aforementioned magnetic detection system, the first and second magnetic sensors can also be positioned on opposite sides of the coil axis when viewed from the excitation coil. This allows it to easily ensure that the amplitudes of the excitation magnetic fields applied to the first and second magnetic sensors are the same.

[0040] In the aforementioned magnetic detection system, the buffer circuit may also include a single or multiple voltage follower circuits connected in parallel. This allows for easy adjustment of the current flowing through the excitation coil.

[0041] In the aforementioned magnetic detection system, it may also include: a first magnetizer and a second magnetizer that respectively focus magnetic flux onto the first magnetic sensor and the second magnetic sensor. Both the first and second magnetic sensors are configured such that the element forming surface of the magnetic sensing element is parallel to the coil axis. The first magnetizer is disposed on the element forming surface of the first magnetic sensor, and the second magnetizer is disposed on the element forming surface of the second magnetic sensor. The center of the coil axis is located between the element forming surface of the first magnetic sensor and the first magnetizer, and also between the element forming surface of the second magnetic sensor and the second magnetizer. This enables detection with higher sensitivity.

[0042] The aforementioned magnetic detection system may also include a phase adjustment circuit for adjusting the phase of the first and second output signals. This eliminates phase differences caused by position adjustment deviations, etc.

[0043] The aforementioned magnetic detection system may further include: a first arm having a first guide and a second guide along the coil axis; a second arm having a first magnetic sensor fixed thereon and movable along the first guide in the coil axis; and a third arm having a second magnetic sensor fixed thereon and movable along the second guide in the coil axis. This allows for changing the positions of the first and second magnetic sensors along the coil axis.

[0044] The aforementioned magnetic detection system may further include: a fourth arm on which an excitation coil is fixed, and the second to fourth arms being fixed to the first arm in a manner that allows them to move in a first direction perpendicular to the coil axis. This allows the positions of the first and second magnetic sensors and the excitation coil in the first direction to be changed. Explanation of reference numerals in the attached figures

[0045] 10A and 10B sensor body sections 30 sensor substrate 40A and 40B magnetic sensors 41 Component Forming Surface 42 Back 43 Upper surface 44 Lower surface Side views at 45 and 46 51~53 magnets 61~64 terminal electrodes 100 Magnetic Detection System 111, 112, 121, 131, 141 guide components 120, 130, 140 arms 122, 132, 142 fixing screws 250 excitation coil 300 sample stage 310 sample 311 Metal Foreign Object 312 magnetic field 501 signal generation circuit 502 Digital Filter 503 buffer circuit 504 resistor 505 phase adjustment circuit 506 Differential Amplifier 507 Lock-in Amplifier 508 Oscilloscope 510 voltage follower circuit C compensation coil M1~M3 Magnetic Yokes R1~R4 are magnetic sensitive elements.

Claims

1. A magnetic detection system, wherein, have: The signal generation circuit generates the excitation signal; An excitation coil, which is supplied with the excitation signal; A buffer circuit is connected between the signal generation circuit and the excitation coil, and its output impedance is lower than its input impedance. The first magnetic sensor and the second magnetic sensor are configured at positions where the amplitude of the excitation magnetic field generated by the excitation coil is the same. A sample stage, which holds the sample between the excitation coil and the first magnetic sensor; and The detection circuit generates a detection signal based on the difference between a first output signal from the first magnetic sensor and a second output signal from the second magnetic sensor.

2. The magnetic detection system according to claim 1, wherein, The first magnetic sensor and the second magnetic sensor are positioned on opposite sides of each other in the direction of the coil axis when viewed from the excitation coil.

3. The magnetic detection system according to claim 1, wherein, The buffer circuit includes a single or multiple voltage follower circuits connected in parallel.

4. The magnetic detection system according to claim 1, wherein, The magnetic detection system further comprises: a first magnet collector and a second magnet collector, which respectively focus magnetic flux onto the first magnetic sensor and the second magnetic sensor. Both the first magnetic sensor and the second magnetic sensor are configured such that the element forming surface on which the magnetic sensing element is formed is parallel to the coil axis. The first magnet is disposed on the element forming surface of the first magnetic sensor. The second magnet is disposed on the element forming surface of the second magnetic sensor. The center of the coil shaft is located between the element forming surface of the first magnetic sensor and the first magnet collector, and between the element forming surface of the second magnetic sensor and the second magnet collector.

5. The magnetic detection system according to claim 1, wherein, It also includes a phase adjustment circuit for adjusting the phase of the first output signal and the second output signal.

6. The magnetic detection system according to any one of claims 1 to 5, wherein, It also has: The first arm has a first guide and a second guide along the direction of the coil axis; The second arm is fixed with the first magnetic sensor and is movable along the first guide in the direction of the coil axis; and The third arm is fixed with the second magnetic sensor and is movable along the second guide in the direction of the coil axis.

7. The magnetic detection system according to claim 6, wherein, It also includes: a fourth arm, on which the excitation coil is fixed. The second to the fourth arms are all fixed to the first arm in a manner that allows them to move in a first direction perpendicular to the direction of the coil axis.

Images