Magnetic sensor and foreign object detection system using the same

Abstract

To provide a magnetic sensor which has high accuracy of detection, and is suitable for use in a foreign matter detection system.SOLUTION: A magnetic sensor 5 comprises: a first magnetic shield 10 which has an inner wall enclosing housing space and has at least an upper opening 15; a positioning member 20 which is housed in the housing space in such a way as to be in contact with the inner wall; and a sensor chip 40 which is located at a prescribed position in the housing space by the positioning member 20 in such a way as to be exposed from the upper opening 15. Thus, the sensor chip 40 is positioned at the prescribed position of the sensor chip 40 in the housing space using the positioning member 20, so that variation in the position of the sensor chip 40 is reduced. Therefore, it is possible to reduce a variation in the accuracy of detection due to the positional variation of the sensor chip 40.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a magnetic sensor, and more particularly to a magnetic sensor suitable for use in a foreign object detection system, and also to a foreign object detection system using such a magnetic sensor. [Background technology]

[0002] Patent Document 1 discloses a foreign object detection system that includes a transmitter coil that applies a magnetic field to an object to be inspected and a receiver coil that receives the magnetic field. In the foreign object detection system described in Patent Document 1, the transmitter coil and receiver coil are housed in a magnetically shielded housing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-091664 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the foreign object detection system described in Patent Document 1 has a problem in that the detection accuracy varies greatly depending on the positions of the transmitting coil and receiving coil within the magnetic shield housing.

[0005] Therefore, an object of the present invention is to provide a magnetic sensor with high detection accuracy and a foreign object detection system using the same. [Means for solving the problem]

[0006] The magnetic sensor according to the present invention is characterized by comprising a first magnetic shield having an inner wall surrounding an accommodating space and having at least an upper opening, a positioning member accommodated in the accommodating space so as to be in contact with the inner wall, and a sensor chip positioned at a predetermined position in the accommodating space by the positioning member so as to be exposed from the upper opening.

[0007] According to the present invention, the sensor chip is positioned at a predetermined position within the accommodation space using the positioning member, which reduces the positional variation of the sensor chip, thereby making it possible to reduce the variation in detection accuracy caused by the positional variation of the sensor chip.

[0008] The magnetic sensor according to the present invention may further include a sensor substrate on which a sensor chip is mounted, and a magnetic collector mounted on the sensor substrate and collecting magnetic flux toward the sensor chip, and the positioning member may have a slit into which the sensor substrate is inserted to position the sensor chip. This increases the magnetic flux density applied to the sensor chip, and enables the sensor chip to be correctly positioned in a predetermined position within the accommodation space, even if the sensor chip is small.

[0009] In the present invention, the top surface of the first magnetic shield surrounding the upper opening and the top surface of the sensor chip exposed through the upper opening may be substantially flush with each other, thereby achieving high detection sensitivity while suppressing the effects of external noise.

[0010] The magnetic sensor according to the present invention further includes a second magnetic shield fixed to the positioning member and covering the sensor chip from the side opposite the upper opening when viewed from the sensor chip. The first magnetic shield may be a cylindrical body further having a lower opening located opposite the upper opening, and wiring connected to the sensor chip may be drawn out of the housing space through the lower opening. This facilitates drawing out the wiring and enables the second magnetic shield to block external noise entering through the lower opening. In this case, the first magnetic shield may be made of ferrite, and the second magnetic shield may be made of a metallic magnetic material. This allows the first magnetic shield to be produced inexpensively and the second magnetic shield to be easily fixed to the positioning member.

[0011] The foreign matter detection system according to the present invention is characterized by comprising a magnetizing mechanism that applies a magnetic field to an object to be inspected, the magnetic sensor described above, and a transport mechanism that transports the object to be inspected from the magnetizing mechanism to the magnetic sensor, thereby enabling highly accurate detection of the presence of magnetizable metallic foreign matter such as iron (Fe). [Effects of the Invention]

[0012] As described above, according to the present invention, it is possible to provide a magnetic sensor with high detection accuracy and a foreign object detection system using the same. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of a foreign object detection system 1 according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic perspective view showing the appearance of the magnetic sensor 5. As shown in FIG. [Figure 3] FIG. 3 is a schematic exploded perspective view for explaining the configuration of the magnetic sensor 5 in more detail. [Figure 4] 4A and 4B are diagrams for explaining the structure of the positioning member 20, and (a) and (b) are schematic perspective views seen from different angles. [Figure 5] FIG. 5 is a schematic perspective view for explaining the structure of the sensor chip 40 and magnetic collectors 51 to 53 mounted on the sensor substrate 30. As shown in FIG. [Figure 6] FIG. 6 is a schematic exploded perspective view for explaining the structure of the sensor chip 40 and magnetic collectors 51 to 53 mounted on the sensor substrate 30. As shown in FIG. [Figure 7] FIG. 7 is a schematic cross-sectional view for explaining the positional relationship between the first magnetic shield 10 and the sensor chip 40 in the z direction. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0015] FIG. 1 is a schematic diagram illustrating the configuration of a foreign object detection system 1 according to one embodiment of the present invention.

[0016] As shown in FIG. 1, a foreign matter detection system 1 according to this embodiment is a system that detects whether or not metallic foreign matter is present in an inspection object 3 while transporting the inspection object 3 using a transport mechanism consisting of multiple motor rollers 2 arranged in the x direction. The motor rollers 2 rotate around their axes of rotation in the y direction, and the inspection object 3 placed on the motor rollers 2 is transported in the x direction by the rotation of multiple motor rollers 2 arranged in the x direction in one direction. In the example shown in FIG. 1, the inspection object 3 is transported using the motor rollers 2, but the method of transporting the inspection object 3 is not limited to this, and the inspection object 3 may be transported using other transport mechanisms such as a belt conveyor or a linear motor.

[0017] A magnetizing mechanism 4 that applies a magnetic field to the object 3 to be inspected and a plurality of magnetic sensors 5 located downstream of the magnetizing mechanism 4 are disposed along the conveying path made up of multiple motor rollers 2. The magnetizing mechanism 4 serves to at least temporarily magnetize metallic foreign matter such as iron (Fe) that may be contained in the object 3 to be inspected by applying a magnetic field to the object 3 to be inspected. The magnetic sensors 5 are disposed downstream of the magnetizing mechanism 4, so that the object 3 to which the magnetic field has been applied by the magnetizing mechanism 4 passes over the magnetic sensors 5. Therefore, if the object 3 to be inspected contains metallic foreign matter such as iron (Fe), the metallic foreign matter will be magnetized by the magnetizing mechanism 4, and the magnetic field emitted from the magnetized metallic foreign matter can be detected by the magnetic sensors 5 to detect the presence of the metallic foreign matter.

[0018] 1, multiple magnetic sensors 5 are arranged in the y direction, which makes it possible to inspect the object 3 over its entire width in the y direction. The number of magnetic sensors 5 may be selected appropriately depending on the width of the motor rollers 2 in the y direction. Furthermore, instead of transporting the object 3 using a transport mechanism such as the motor rollers 2, inspection may be performed by scanning the magnetizing mechanism 4 and magnetic sensors 5 while the object 3 is stationary.

[0019] FIG. 2 is a schematic perspective view showing the appearance of the magnetic sensor 5. As shown in FIG.

[0020] As shown in FIG. 2, the magnetic sensor 5 is mounted on a support substrate 6 having an xy plane. As will be described in detail later, the magnetic sensor 5 includes a first magnetic shield 10 made of a magnetic material such as ferrite, a positioning member 20 made of a non-magnetic material such as resin, and a sensor substrate 30. The first magnetic shield 10 is a cylindrical body with openings on both sides in the z direction, and houses the positioning member 20 and the sensor substrate 30 inside. A sensor chip including a magnetic sensing element and a magnetic collector are mounted on the sensor substrate 30, but in the example shown in FIG. 2, these are molded with a molding member 31 and are not visible in the external view shown in FIG. 2. Wiring 32 connected to the sensor substrate 30 is drawn out to the surface of the support substrate 6 from the lower opening of the first magnetic shield 10.

[0021] FIG. 3 is a schematic exploded perspective view for explaining the configuration of the magnetic sensor 5 in more detail.

[0022] As shown in FIG. 3 , the first magnetic shield 10 included in the magnetic sensor 5 is a cylindrical body having an upper opening 15 and a lower opening 16 that open in the z direction. The plate-shaped portions 11 and 12 that form a yz plane and are located on both sides in the x direction and an xz plane and are located on both sides in the y direction. The plate-shaped portions 11 to 14 that form the first magnetic shield 10 are preferably integral blocks made of ferrite or the like. The area surrounded by the inner walls of the plate-shaped portions 11 to 14 forms a housing space, and the positioning member 20 is accommodated in this housing space so as to contact the inner walls of the plate-shaped portions 11 to 14. While the positioning member 20 does not need to contact all the inner walls of the plate-shaped portions 11 to 14, contact with at least two of the inner walls allows it to be positioned within the housing space by frictional force. This can be achieved by designing the size of the positioning member 20 in the x or y direction to be the same as or slightly smaller than the size of the housing space surrounded by the inner walls of the plate-shaped portions 11 to 14 in the x or y direction.

[0023] 4A and 4B are diagrams for explaining the structure of the positioning member 20, and (a) and (b) are schematic perspective views seen from different angles.

[0024] 4, the positioning member 20 includes a main body 21 having a slit SL and legs 22 located on the x-direction side of the main body 21. The main body 21 and the legs 22 may be separate members or may be integrated. In this embodiment, the main body 21 and the legs 22 are an integrated block made of resin or the like, and their total size in the x-direction is designed to be the same as or slightly smaller than the size in the x-direction of the accommodation space of the first magnetic shield 10. As a result, when the positioning member 20 is accommodated in the accommodation space of the first magnetic shield 10, the main body 21 contacts the inner wall of the plate-like portion 11, and the legs 22 contact the inner wall of the plate-like portion 12, thereby positioning the positioning member 20 within the accommodation space.

[0025] The top surface 21a of the main body 21, which forms the xy plane, is flat and is substantially flush with the top surface of the molded member 31 shown in FIG. 2. The bottom surface 21b, located opposite the top surface 21a, and the side surfaces 21c and 21d, which form the xz plane, are covered with a second magnetic shield 60 shown in FIG. 3. The second magnetic shield 60 is made of a magnetic metal such as permalloy and serves to block external noise that enters through the lower opening 16 of the first magnetic shield 10. The boundary between the bottom surface 21b and the side surfaces 21c and 21d of the main body 21 is curved, which makes it easier for the second magnetic shield 60, made of permalloy or the like, to cover the main body 21. Furthermore, if the second magnetic shield 60 has spring properties, it is biased against the inner walls of the plate-like portions 13 and 14, making the second magnetic shield 60 less likely to fall off.

[0026] A slit SL is provided in the main body 21, and the sensor substrate 30 is positioned relative to the positioning member 20 by inserting it into the slit SL and sliding it in the x direction. The sensor chip 40 and magnetic collectors 51 to 53 shown in Fig. 3 are mounted on the sensor substrate 30. Notches are provided in the main body 21 so that the sensor chip 40 and magnetic collectors 51 to 53 do not interfere with the main body 21 when the sensor substrate 30 is inserted into the slit SL.

[0027] 5 and 6 are diagrams for explaining the structure of the sensor chip 40 and magnetic collectors 51 to 53 mounted on the sensor substrate 30, with FIG. 5 being a schematic perspective view and FIG. 6 being a schematic exploded perspective view.

[0028] As shown in FIGS. 5 and 6 , the sensor chip 40 mounted on the surface of the sensor substrate 30 has a substantially rectangular parallelepiped shape and includes an element-forming surface 41 and a back surface 42 that form the yz plane, an upper surface 43 and a lower surface 44 that form the xy plane, and side surfaces 45 and 46 that form the xz plane. The element-forming surface 41 is the surface on which a magnetic-sensing element is formed. The sensor chip 40 is mounted on the sensor substrate 30 so that the lower surface 44 faces the sensor substrate 30 and the element-forming surface 41 is perpendicular to the surface of the sensor substrate 30. Magnetic yokes M1 to M3 made of permalloy or the like are formed on the element-forming surface 41 of the sensor chip 40, and a magnetic-sensing element (not shown) is disposed near the magnetic gap formed by the magnetic yoke M1 and the magnetic yokes M2 and M3. This allows magnetic flux passing through the magnetic gap to be applied to the magnetic-sensing element.

[0029] The magnetic collectors 51 to 53 are blocks made of a magnetic material such as ferrite, and each serves to collect the magnetic field emitted from the object 3 to be inspected toward the sensor chip 40. The magnetic collectors 51 to 53 overlap with the magnetic yokes M1 to M3, respectively, when viewed from the x-direction. Furthermore, the magnetic collector 52 has a portion covering the side surface 45 and rear surface 42 of the sensor chip 40, and the magnetic collector 53 has a portion covering the side surface 46 and rear surface 42 of the sensor chip 40. In the example shown in FIGS. 5 and 6, a compensation coil C is wound around the magnetic collector 51. A canceling current flows through the compensation coil C to cancel the magnetic field applied to the magnetic sensing element. The compensation coil C and the magnetic sensing element provided on the sensor chip 40 are connected to the wiring 32 shown in FIG. 2 via a connector 33 provided on the rear surface of the sensor substrate 30.

[0030] 2 is formed on the surface of the sensor substrate 30 so that the sensor chip 40 and the magnetic collectors 51 to 53 are embedded. The molding member 31 is exposed from the upper opening 15 of the first magnetic shield 10. The molding member 31 is made of a non-magnetic material and is provided to protect the sensor chip 40 and the magnetic collectors 51 to 53. Although it is not essential to use such a molding member 31 in the present invention, by covering the sensor chip 40 and the magnetic collectors 51 to 53 with the molding member 31, it is possible to prevent contact between the object to be inspected 3 and the sensor chip 40, for example.

[0031] As described above, the sensor substrate 30 having such a configuration is positioned relative to the positioning member 20 by being inserted into the slit SL of the positioning member 20. As a result, the sensor chip 40 mounted on the sensor substrate 30 is also positioned relative to the positioning member 20. The positioning member 20 itself is positioned within the accommodation space by contacting the inner wall of the first magnetic shield 10, and as a result, the sensor chip 40 is positioned at a predetermined position within the accommodation space of the first magnetic shield 10.

[0032] Furthermore, when the sensor substrate 30 is inserted into the slit SL of the positioning member 20, the sensor chip 40 completely overlaps the second magnetic shield 60 when viewed from the z direction. This makes it difficult for disturbance noise, even if it enters through the lower opening 16 of the first magnetic shield 10, to reach the sensor chip 40. Moreover, in this embodiment, the first magnetic shield 10 is a cylindrical body and has not only the upper opening 15 that magnetically exposes the sensor chip 40 but also the lower opening 16 through which the wiring 32 is drawn out, so there is no need to provide through holes or the like in the plate-like portions 11 to 14 for drawing out the wiring 32.

[0033] 7 is a schematic cross-sectional view for explaining the positional relationship in the z direction between the first magnetic shield 10 and the sensor chip 40. In FIG. 7, the molding member 31 is omitted.

[0034] 7, the top surface 15a of the first magnetic shield 10 surrounding the upper opening 15 and the top surface 43 of the sensor chip 40 exposed through the upper opening 15 form the same plane. In this way, by positioning the top surface 15a of the first magnetic shield 10 and the top surface 43 of the sensor chip 40 so that they form the same plane, it is possible to reduce the distance in the z direction between the sensor chip 40 and the object to be inspected 3 while suppressing the effects of disturbance noise entering through the upper opening 15, and it is possible to obtain high detection sensitivity. However, the two do not need to form a completely coplanar surface, and it is acceptable for there to be a slight deviation in their positions in the z direction due to errors that inevitably occur due to manufacturing variations and the like. In other words, it is sufficient for the two to form approximately the same plane.

[0035] 7, the height of magnetic collector 51 in the z direction is slightly lower than that of sensor chip 40, and the height of magnetic collectors 52 and 53 in the z direction is slightly higher than that of sensor chip 40. In this way, the heights of sensor chip 40 and magnetic collectors 51 to 53 do not necessarily have to match.

[0036] The above describes a preferred embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention. [Explanation of symbols]

[0037] 1 Foreign object detection system 2 motor rollers 3. Inspection object 4 Magnetizing mechanism 5 Magnetic Sensor 6 Support substrate 11~14 Plate-shaped part 15 Top opening 15a Top side 16 Lower opening 20 Positioning member 21 Main body 21a Top surface 21b Bottom side 21c,21d side 22 Legs 30 Sensor board 31 Molded parts 32 Wiring 33 Connector 40 sensor chips 41 Element formation surface 42 Back side 43 Top surface 44 Bottom surface 45,46 Side 51~53 Magnetic collector C Compensation coil M1~M3 magnetic yoke SL Slit

Claims

1. A cylindrical first magnetic shield made of a magnetic material, having an inner wall surrounding an accommodation space, and having an upper opening and a lower opening located opposite the upper opening, the first magnetic shield having openings on both sides in a first direction; a positioning member made of a non-magnetic material and accommodated in the accommodation space so as to be positioned in position by frictional force when in contact with the inner wall; a sensor chip exposed from the upper opening; a sensor substrate on which the sensor chip is mounted and which is positioned at a predetermined position in the accommodation space by the positioning member; a second magnetic shield having spring properties, the second magnetic shield being fixed to the positioning member and covering the sensor chip from the side opposite to the upper opening when viewed from the sensor chip; the positioning member has a slit, the sensor substrate is inserted into the slit by sliding it in a second direction perpendicular to the first direction, thereby positioning the sensor substrate on which the sensor chip is mounted; A magnetic sensor characterized in that wiring connected to the sensor chip is drawn out from the lower opening to the outside of the accommodation space.

2. A magnetic sensor as described in claim 1, further comprising a magnetic collector mounted on the sensor substrate for collecting magnetic flux to the sensor chip.

3. 3. The magnetic sensor according to claim 1, wherein an upper surface of the first magnetic shield surrounding the upper opening and an upper surface of the sensor chip exposed through the upper opening form substantially the same plane.

4. 4. The magnetic sensor according to claim 1, wherein the first magnetic shield is made of ferrite, and the second magnetic shield is made of a metallic magnetic material.

5. a magnetizing mechanism that applies a magnetic field to the object to be inspected; A magnetic sensor according to any one of claims 1 to 4; a transport mechanism that transports the object to be inspected from the magnetizing mechanism to the magnetic sensor.

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