Proximity sensor

Abstract

To provide a proximity sensor that sufficiently extends the detection distance by suppressing the influence of embedded metal.SOLUTION: A coil 20 of a proximity sensor 100 comprises a first coil 21 and a second coil 22. The second coil 22 is arranged concentrically with respect to the first coil 21. The proximity sensor 100 detects the detected target based on changes in voltage or current generated in each of the first coil 21 and the second coil 22. The coil wire 21a of the first coil 21 is electrically connected to a head internal substrate 50 via direct bonding.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a proximity sensor. [Background technology]

[0002] Patent Document 1 discloses a proximity sensor. The proximity sensor described in Patent Document 1 reduces the effects of changes in coil characteristics, etc. As shown in FIG. 3 of Patent Document 1, the proximity sensor of Patent Document 1 is embedded in nuts and washers denoted by reference numerals 7 to 9 when used. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-152320 Summary of the Invention [Problem to be solved by the invention]

[0004] However, proximity sensors may malfunction if they come into contact with the object to be detected (hereinafter referred to as the detection object) or its surrounding components. For this reason, proximity sensors are required to have an extended detection distance (hereinafter referred to as the detection distance) to avoid contact with the object to be detected, etc.

[0005] To extend the detection distance, the proximity sensor needs to detect even weak changes in the received waveform. However, the proximity sensor described in Patent Document 1 cannot detect weak changes in the received waveform due to the influence of embedded nuts, washers, etc. (hereinafter referred to as embedded metal), and therefore the detection distance cannot be sufficiently extended.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to provide a proximity sensor that can sufficiently extend the detection distance by suppressing the influence of the embedded metal. [Means for solving the problem]

[0007] According to one aspect of the present invention, a proximity sensor includes a coil, a ferrite core, a head housing, and a substrate within the head. The coil generates a magnetic field by an excitation current. The ferrite core guides the magnetic field generated by the coil. The head housing accommodates the coil and the ferrite core. The substrate within the head is accommodated in the head housing. The coil includes a first coil and a second coil. The second coil is arranged concentrically with the first coil. The proximity sensor further includes a transmitter circuit, a receiver circuit, and a control circuit. The transmitter circuit periodically passes a pulsed excitation current through the coil. The receiver circuit detects a voltage or current generated in each of the first coil and the second coil as a result of a change in the magnetic field caused by a detection object. The control circuit detects the detection object based on the change in voltage or current generated in at least one of the first coil and the second coil, detected by the receiver circuit. The coil wire of the first coil is electrically connected to the substrate within the head via a direct bond.

[0008] According to another aspect of the present invention, a proximity sensor includes a coil, a ferrite core, a head housing, a cable, and an amplifier housing. The coil generates a magnetic field by an excitation current. The ferrite core guides the magnetic field generated by the coil. The head housing accommodates the coil and the ferrite core. A cable extends from the head housing. The amplifier housing is connected to the head housing via the cable. The coil includes a first coil and a second coil. The second coil is arranged concentrically with the first coil. The proximity sensor further includes a transmitter circuit, a receiver circuit, and a control circuit. The transmitter circuit periodically passes a pulsed excitation current through the coil. The receiver circuit detects a voltage or current generated in at least one of the first coil and the second coil due to a change in the magnetic field caused by a detection object. The control circuit detects the detection object based on the change in voltage or current generated in each of the first coil and the second coil detected by the receiver circuit. The coil wire of the first coil is electrically connected to the cable via a direct joint.

[0009] According to yet another aspect of the present invention, a proximity sensor includes a coil, a ferrite core, and a head housing. The coil generates a magnetic field by an excitation current. The ferrite core guides the magnetic field generated by the coil. The head housing accommodates the coil and the ferrite core. The coil includes a first coil and a second coil. The second coil is disposed radially outward of the first coil. The proximity sensor further includes a transmitter circuit, a receiver circuit, and a control circuit. The transmitter circuit periodically passes a pulsed excitation current through the coil. The receiver circuit detects a voltage or current generated in each of the first coil and the second coil as a result of a change in the magnetic field caused by a detection object. The control circuit detects the detection object based on the change in voltage or current generated in at least one of the first coil and the second coil, detected by the receiver circuit. The head housing has a diameter of less than 8 mm on the surface facing the detection object. The first coil has 100 or more turns. [Effects of the Invention]

[0010] According to the proximity sensor of the present invention, the influence of the embedded metal is suppressed, thereby making it possible to sufficiently extend the detection distance. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an outline drawing of a proximity sensor. [Figure 2] FIG. 2 is an outline drawing of the proximity sensor in use. [Figure 3] FIG. 4 is a perspective view showing a state in which a coil wire and a substrate electrode are joined together. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3. [Figure 5] 10 is a diagram showing the wiring of a coil wire from a first coil to a substrate electrode. FIG. [Figure 6] 10 is a diagram showing the wiring of the coil wire from the second coil to the substrate electrode. FIG. [Figure 7] FIG. 2 is an exploded perspective view of the proximity sensor from the coil to the substrate in the head. [Figure 8]FIG. 2 is an exploded perspective view of parts housed in a head housing of the proximity sensor. [Figure 9] FIG. 2 is a block diagram illustrating a main circuit configuration of a proximity sensor. [Figure 10] 3 is a diagram schematically showing magnetic flux lines around a first coil and a second coil. FIG. [Figure 11] FIG. 2 is an exploded perspective view illustrating the electric and magnetic shields in detail. [Figure 12] This is a magnetic flux line diagram when the shaft body of the ferrite core is thin. [Figure 13] FIG. 10 is a magnetic flux line diagram when the shaft of the ferrite core is not thin. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or equivalent parts will be designated by the same reference numerals, and description thereof will not be repeated. In the following description, terms indicating positions or directions, such as "upper," "lower," "left," and "right," may be used. These terms are used for convenience to facilitate understanding of the embodiments, and unless otherwise clearly stated, do not relate to directions in actual implementation.

[0013] A proximity sensor 100 according to an embodiment of the present invention will be described below with reference to the drawings.

[0014] First, a situation in which the proximity sensor 100 is used will be described with reference to Figures 1 and 2. Figure 1 is an external view of the proximity sensor 100. Figure 2 is an external view of the proximity sensor 100 in a state in which it is used.

[0015] As shown in FIG. 1, the proximity sensor 100 has an external thread 12 formed on its side, and is shaped (shielded type) so that it can be fixed with a nut or the like. The external thread 12 is formed on the outer surface of a housing main body 11 of a head housing 10 that is placed near the detection target. The head housing 10 is made of metal, and the head front surface 11a (the upper end in FIG. 1) that faces the detection target is also made of metal. If the head front surface 11a is made of metal, there is little risk of the proximity sensor 100 being damaged even if the head front surface 11a comes into contact with an object in the surrounding environment, such as the detection target.

[0016] In this embodiment, the head housing 10 has a cylindrical shape, and the head front surface 11a is circular. The head housing 10 in this embodiment has a small diameter. For example, the diameter of the head front surface 11a (the surface facing the object to be detected) is less than 8 mm.

[0017] A coil 20 for generating a magnetic field and an internal head substrate 50 electrically connected to the coil 20 are arranged inside the head housing 10. The proximity sensor 100 of this embodiment detects metal as a detection object. Eddy currents are induced in the metal detection object when it receives the magnetic field generated by the coil 20. The proximity sensor 100 detects the magnetic field (magnetic flux) generated from the eddy currents generated in the detection object.

[0018] The internal head substrate 50 is electrically connected to a cable 19. The cable 19 extends from inside the head housing 10, through the head base end 13, and to the outside of the head housing 10. The cable 19 is connected to an amplifier housing 200. The amplifier housing 200 houses an amplifier unit 210. The amplifier unit 210 amplifies the electrical signal transmitted from the coil 20 through the cable 19 and transmits it to an external device (such as a computer). The amplifier unit 210 also supplies power to the coil 20 through the cable 19 to operate the coil 20.

[0019] 2, the proximity sensor 100 is fixed to a mounting bracket E1 with a double nut E2, for example. That is, the proximity sensor 100 is embedded in the mounting bracket E1 and the double nut E2. In this state, the proximity sensor 100 detects embedded metal E, such as the mounting bracket E1 and the double nut E2, which are not intended to be detected by the proximity sensor 100. Therefore, the proximity sensor 100 according to the embodiment of the present invention is configured to suppress the influence of the embedded metal E in order to sufficiently extend the detection distance.

[0020] The configuration of the coil 20 and the internal-head substrate 50 will be described below with reference to Figures 3, 4, 5, and 6. Figure 3 is a perspective view showing the state in which the coil wires 21a, 22a are joined to the substrate electrode 50a. Figure 4 is a cross-sectional view taken along line IV-IV in Figure 3. Figure 5 is a diagram showing the wiring of the coil wire 21a from the first coil 21 to the substrate electrode 50a. Figure 6 is a diagram showing the wiring of the coil wire 22a from the second coil 22 to the substrate electrode 50a. Note that Figure 5 shows one surface 50B of the internal-head substrate 50, and Figure 6 shows the other surface 50F of the internal-head substrate 50.

[0021] 3, 4, 5, and 6 show the coil 20 and the internal-head substrate 50 housed in the head housing 10 of the proximity sensor 100 in FIG. 1. The proximity sensor 100 includes the coil 20, a ferrite core 30, a core holder 40, and the internal-head substrate 50. The coil 20, the ferrite core 30, the core holder 40, and the internal-head substrate 50 are all housed in the head housing 10. Hereinafter, the coil 20, the ferrite core 30, the core holder 40, and the internal-head substrate 50 may be collectively referred to as a sensor unit 25.

[0022] The coil 20 generates a magnetic field by an excitation current. The ferrite core 30 guides the magnetic field generated by the coil 20. The coil 20 has a first coil 21 and a second coil 22. The second coil 22 is arranged radially outward of the first coil 21. The second coil 22 may be arranged concentrically with the first coil 21. In this example, "arranged concentrically" refers to an arrangement that is not limited to an arrangement in which the circles are on the same plane. Therefore, when the second coil 22 is arranged concentrically with the first coil 21, the second coil 22 may be arranged on the side of the first coil 21 where the detection target is detected (or on the opposite side). The first coil 21 is configured by winding a coil wire 21a. The second coil 22 is configured by winding a coil wire 22a. It is preferable that the magnetic field generated by the coil 20 be guided toward the detection target. The ferrite core 30 has a shaft 31, which is oriented toward the object to be sensed, so that a magnetic field generated near the shaft 31 is easily guided to the object to be sensed. Therefore, it is preferable that the first coil 21, which is configured closer to the shaft 31 than the second coil 22, generates a magnetic field by an excitation current. Note that the ferrite core 30 in this embodiment has the shaft 31 around which the first coil 21 is wound and a peripheral wall (outer periphery) made of a magnetic material located between the first coil 21 and the second coil 22. However, the ferrite core 30 may have only the shaft 31. Alternatively, a shaft 31 made of a magnetic material other than ferrite may be disposed. Furthermore, because a magnetic field itself is generated even without the ferrite core 30, the proximity sensor 100 may be configured without the ferrite core 30.

[0023] To ensure sufficient inductance, the number of turns of the first coil 21 should be 100 or more, preferably 200 or more. If the number of turns of the first coil 21 is sufficiently large, the influence of the magnetic field generated from the first coil 21 by the pulsed excitation current penetrates the head front surface 11a and reaches a distant detection target. Therefore, even if the surface of the head housing 10 facing the detection target is made of metal, the detection distance of the proximity sensor 100 will be sufficiently large. Note that if the wire length of the coil wire 21a of the first coil 21 is sufficiently thin, for example, 0.02 mm or less, a first coil 21 with 200 or more turns can be accommodated within the head housing 10 even if the diameter of the head front surface 11a of the head housing 10 is less than 8 mm.

[0024] The core holder 40 holds the ferrite core 30. The core holder 40 also positions the second coil 22 and fixes the ferrite core 30 to the in-head substrate 50. A substrate receiving portion 45 is formed in the core holder 40. The in-head substrate 50 is fixed to the core holder 40 by inserting an end of the in-head substrate 50 into the substrate receiving portion 45. The core holder 40 holds the ferrite core 30, thereby fixing the ferrite core 30 to the in-head substrate 50.

[0025] A slit 32 extending in the axial direction is formed in a portion of the outer periphery of the ferrite core 30. A slit 42 extending in the axial direction is also formed in a portion of the outer periphery of the core holder 40. The coil wire 21 a of the first coil 21 and the coil wire 22 a of the second coil 22 are drawn out to the head internal substrate 50 through the slit 32 of the ferrite core 30 and the slit 42 of the core holder 40.

[0026] A substrate electrode 50a is arranged on each of one surface 50B and the other surface 50F of the head internal substrate 50. In Figures 3, 4, 5, and 6, two substrate electrodes 50a are arranged on each of one surface 50B and the other surface 50F.

[0027] It is preferable that at least the coil wire 21a of the first coil 21 is electrically connected to the internal head substrate 50 via direct bonding. In this embodiment, both the coil wire 21a of the first coil 21 and the coil wire 22a of the second coil 22 are directly bonded to the substrate electrode 50a on the internal head substrate 50.

[0028] Direct bonding refers to bonding of components directly to each other without using a brazing material such as solder, etc. For example, direct bonding is achieved by bonding the coil wires 21 a and 22 a to the board electrode 50 a by methods such as resistance welding, pressure welding, ultrasonic bonding, and friction stir welding.

[0029] Direct bonding avoids the problem of copper erosion, whereby the copper of the conductor dissolves into the solder, even for thin coil wires 21a and 22a (for example, 0.02 mm or less). Furthermore, soldering thin coil wires 21a and 22a to board electrodes 50a is a difficult task, but direct bonding is often easier than soldering.

[0030] For example, resistance welding allows direct joining by simply passing current through the coil wires 21a and 22a while they are in contact with the board electrode 50a, making the process easier than soldering, which requires the handling of a soldering iron and solder.

[0031] An intermediate member may be interposed between the coil wire 21a of the first coil 21 (or the coil wire 22a of the second coil 22) and the internal head substrate 50. Even when the coil wire 21a or the coil wire 22a is directly joined to the intermediate member and the intermediate member is electrically connected to the internal head substrate 50, it can be said that the coil wire 21a or the coil wire 22a is electrically connected to the internal head substrate 50 via a direct joint.

[0032] When the coil wire 21a or the coil wire 22a is electrically connected to the head internal substrate 50 via direct bonding, the first coil 21 and the second coil 22 can be formed using thin coil wires 21a and 22a (e.g., 0.02 mm or less). When the first coil 21 and the second coil 22 are formed using thin coil wires 21a and 22a, the diameter of the coil 20 can be small even if the number of turns of the first coil 21 and the second coil 22 is large (e.g., 100 or more, or even 200 or more). If the diameter of the coil 20 is small, the proximity sensor 100 can be made small (e.g., the diameter of the head front surface 11a is less than 8 mm). Furthermore, if the number of turns of the first coil 21 is sufficiently large, the detection distance can be sufficiently large even if the head front surface 11a is made of metal.

[0033] The coil wire 21a and the coil wire 22a are electrically connected to the cable 19 via the board electrode 50a and wiring (not shown) on the head internal board 50. The cable 19 includes a plurality of cable wires. In Figures 3, 4, 5, and 6, the cable 19 includes two first cable wires 17 electrically connected to the coil wire 21a of the first coil 21 and two second cable wires 18 electrically connected to the coil wire 22a of the second coil 22.

[0034] The first cable wire 17 is connected to one surface 50B of the internal head substrate 50. The second cable wire 18 is connected to the other surface 50F of the internal head substrate 50. The connection between the first cable wire 17, the second cable wire 18 and the internal head substrate 50 may be performed by soldering using solder 50s.

[0035] By arranging the first cable wire 17 and the second cable wire 18 separately on one surface 50B and the other surface 50F, respectively, it is possible to electrically connect the first coil 21 and the second coil 22 to the cable 19 even if the internal head substrate 50 is small in size. Therefore, even if the head housing 10 has a small diameter (for example, the diameter of the head front surface 11a is less than 8 mm), the internal head substrate 50 can be made large enough to be accommodated in the head housing 10. Note that one of the two first cable wires 17 may be electrically connected to one of the two coil wires 21a of the first coil 21, and the other first cable wire 17 may be electrically connected to one of the two coil wires 22a of the second coil 22. In this case, the remaining coil wire 21a of the first coil 21 and the remaining coil wire 22a of the second coil 22 are connected to the two second cable wires 18, respectively. That is, the first cable wire 17 connected to one surface 50B is not limited to being electrically connected to the coil wire 21a of the first coil 21, and the first cable wire 17 may be electrically connected to either the coil wire 21a of the first coil 21 or the coil wire 22a of the second coil 22. Similarly, the second cable wire 18 connected to the other surface 50F may be electrically connected to either the coil wire 21a of the first coil 21 or the coil wire 22a of the second coil 22.

[0036] Note that the coil wire 21a of the first coil 21 and the coil wire 22a of the second coil 22 may be electrically connected to the cable 19 via direct bonding without using the internal head substrate 50. For example, the coil wire 21a of the first coil 21 may be directly bonded to the first cable wire 17 without using solder 50s. Also, an intermediate member may be interposed between the coil wire 21a of the first coil 21 (or the coil wire 22a of the second coil 22) and the cable 19. Even when the coil wire 21a or the coil wire 22a is directly bonded to the intermediate member and the intermediate member is electrically connected to the cable 19, it can be said that the coil wire 21a or the coil wire 22a is electrically connected to the cable 19 via direct bonding.

[0037] Next, the configuration of the coil 20, ferrite core 30, core holder 40, and in-head substrate 50 will be described with reference to Fig. 7. Fig. 7 is an exploded perspective view of the components constituting the proximity sensor 100, from the coil 20 to the in-head substrate 50.

[0038] As shown in FIG. 7 , the first coil 21 and the second coil 22 are concentrically arranged, with the second coil 22 positioned radially outward of the first coil 21. The second coil 22 is also shorter than the first coil 21 in a direction perpendicular to the radial direction (axial direction). In other words, the axial dimension of the second coil is smaller than that of the first coil 21. This configuration reduces the sensitivity of the second coil 22 to magnetic flux relative to the first coil 21. For example, when the first coil 21 is used to detect a detection target and the second coil 22 is used to detect embedded metal E, it is preferable to reduce the influence of magnetic flux passing through both the detection target and the embedded metal E on the detection results of the second coil 22. By reducing the sensitivity of the second coil 22 to magnetic flux relative to the first coil 21, the influence of magnetic flux passing through both the detection target and the embedded metal E is reduced.

[0039] 7, the ferrite core 30 has a shaft 31. The shaft 31 passes through the hollow portion of the first coil 21. Hereinafter, the ratio of the width w of the shaft 31 to the overall width W of the ferrite core 30 in the radial direction may be referred to as the relative shaft width w / W.

[0040] Axial-extending slits 32 are formed in part of the outer periphery of the ferrite core 30. In Fig. 7, three slits 32 are formed. The coil wire 21a of the first coil 21 and the coil wire 22a of the second coil 22 are passed through the slits 32. In Fig. 7, two of the coil wires 21a of the first coil 21 are passed through two slits 32 on the front side of the drawing, and both of the coil wires 22a of the second coil 22 are passed through one slit 32 on the back side.

[0041] The core holder 40 is made of, for example, resin. A slit 42 extending in the axial direction is formed in part of the outer periphery of the core holder 40. In FIG. 7, three slits 42 are formed. The coil wire 21 a of the first coil 21 and the coil wire 22 a of the second coil 22 are passed through the slits 42. In FIG. 7, two of the coil wires 21 a of the first coil 21 are passed through two slits 42 on the front side of the drawing, and both of the coil wires 22 a of the second coil 22 are passed through one slit 42 on the back side.

[0042] The core holder 40 holds the ferrite core 30 and receives the intra-head substrate 50 in a concave substrate receiving portion 45 formed on the underside thereof, thereby fixing the ferrite core 30 to the intra-head substrate 50. A holder hole 46 is formed in the center of the substrate receiving portion 45, and a substrate protrusion 56 formed on the tip of the intra-head substrate 50 is inserted into the holder hole 46, thereby fixing the intra-head substrate 50 to the core holder 40. Fixing the intra-head substrate 50 by the core holder 40 improves the positioning accuracy between the intra-head substrate 50 and the coil 20, and enables the proximity sensor 100 to be manufactured in a space-saving manner.

[0043] Additionally, the upper surface 48 of the circumferential edge of the core holder 40 supports the second coil 22. By supporting the second coil 22 with the upper surface 48 of the circumferential edge, the core holder 40 positions the second coil 22.

[0044] Next, the arrangement of the electric shield 80 and magnetic shield 90 used in the proximity sensor 100 will be described with reference to Fig. 8. Fig. 8 is an exploded perspective view of the components housed in the head housing 10 of the proximity sensor 100.

[0045] In addition to the sensor unit 25, an electric shield 80 and a magnetic shield 90 are further housed inside the head housing 10 of the proximity sensor 100.

[0046] The electric shield 80 covers the sensor unit 25. The electric shield 80 completely covers the coil 20, the ferrite core 30, and the core holder 40 of the sensor unit 25, and partially covers the substrate 50 within the head.

[0047] The magnetic shield 90 covers the sensor unit 25 together with the electric shield 80. The magnetic shield 90 partially covers the electric shield 80. The magnetic shield 90 completely covers the coil 20, the ferrite core 30, and the core holder 40 of the sensor unit 25, and partially covers the in-head substrate 50.

[0048] The head housing 10 has a housing main body 11 on which an external thread 12 is formed. As shown in FIG. 8, the housing main body 11 completely covers the magnetic shield 90, the electric shield 80, and the sensor unit 25.

[0049] The main circuit configuration of the proximity sensor 100 will be described below with reference to Fig. 9. Fig. 9 is a block diagram illustrating the main circuit configuration of the proximity sensor 100.

[0050] As shown in FIG. 9, the proximity sensor 100 further includes a transmitting circuit 70, a receiving circuit 60, and a control circuit 76 as main circuit components.

[0051] The transmitter circuit 70 periodically passes a pulsed excitation current through the coil 20. The coil 20 generates a magnetic field when the pulsed excitation current is periodically passed through it. The coil 20 includes a first coil 21 and a second coil 22. The second coil 22 is disposed radially outside the first coil 21. The transmitter circuit 70 may include, for example, an excitation circuit that generates a pulsed excitation current and passes it through the first coil 21 based on a signal from a control circuit 76. As shown in FIG. 9 , a portion (outer periphery) of the ferrite core 30 is positioned between the first coil 21 and the second coil 22. Alternatively, a magnetic material other than the ferrite core 30 may be positioned between the first coil 21 and the second coil 22. In either case, since a magnetic material is disposed between the first coil 21 and the second coil 22, the overall size (diameter dimension) of the coil 20 includes not only the size of the first coil 21 and the second coil 22 but also the size of the magnetic material. However, in this embodiment, since the coil wire 21a of the first coil 21 and the coil wire 22a of the second coil 22 are thin, even if the number of turns is 100 or more (or 200 or more), the first coil 21 and the second coil 22 are small, and the entire coil 20 can be housed in a small head housing 10 with a diameter of less than 8 mm.

[0052] When the object to be detected D is within the detection range, the magnetic field generated by the coil 20 generates an eddy current in the object to be detected D. The eddy current in the object to be detected D generates a magnetic field from the object to be detected D. Here, because the excitation current flowing through the coil 20 is pulsed, the magnetic field generated from the coil 20 weakens rapidly. Therefore, the eddy current in the object to be detected D also weakens, and accordingly the magnetic field generated from the object to be detected D also weakens. In an attempt to prevent the weakening of the magnetic field generated from the object to be detected D, a voltage or current is generated in the coil 20.

[0053] The receiving circuit 60 detects the voltage or current generated in each of the first coil 21 and the second coil 22. Since the first coil 21 and the second coil 22 are arranged differently, the characteristics of the generated voltage or current are also different. Detecting voltages or currents with different characteristics makes it possible to efficiently perform calculations to suppress the influence of the embedded metal E. The receiving circuit 60 may include, for example, a damping resistor that adjusts the current flowing from the coil 20, a filter circuit that filters the analog signal of the received waveform, an amplifier circuit that amplifies the filtered analog signal, and an A / D conversion circuit that converts the amplified analog signal into a digital signal. Note that the receiving circuit 60 may be configured to detect the voltage or current generated in at least one of the first coil 21 and the second coil 22.

[0054] The control circuit 76 detects the object to be detected D based on a change in voltage or current detected by the receiving circuit 60. The control circuit 76 preferably detects the object to be detected D based on a change in voltage or current generated in each of the first coil 21 and the second coil 22. This allows the proximity sensor 100 to sufficiently extend the detection distance by suppressing the influence of the embedded metal E. The control circuit 76 is connected to the amplifier unit 210 of the amplifier housing 200 via a cable 19. The control circuit 76 may include, for example, an arithmetic circuit that performs calculations to detect the object to be detected D based on at least one of the first received waveform and the second received waveform, and an output circuit that outputs the results of the calculations of the arithmetic circuit to an external device (such as the amplifier unit 210) via the cable 19.

[0055] In the example shown in FIG. 9 , the first coil 21 generates a magnetic field by periodically passing a pulsed excitation current from the transmission circuit 70. In this embodiment, only the first coil 21 generates a magnetic field by the excitation current. However, the coil 20 that generates a magnetic field by the excitation current may be only the second coil 22, or may be both the first coil 21 and the second coil 22. When a magnetic field is generated by passing an excitation current through only one of the first coil 21 and the second coil 22, it is preferable to pass an excitation current through only the first coil 21 to generate the magnetic field. As described above, the detection results by the first coil 21 and the second coil 22 differ. However, in order to extend the detection distance, it is preferable that both detection results be easily influenced by the detection target D. When the magnetic field generated by the coil 20 is directed toward the range in which the detection target D may be located, i.e., the detection range, the detection result by the coil 20 is easily influenced by the detection target D. The coil 20 through which the excitation current flows is preferably a coil wound close to the shaft body 31 of the ferrite core 30, as this makes it easier for the generated magnetic field to be directed toward the detection range, and therefore it is preferable to generate the magnetic field by passing an excitation current through the first coil 21. Furthermore, when a magnetic field is generated by passing an excitation current through both the first coil 21 and the second coil 22, for example, by directing the magnetic field of the first coil 21 toward the detection object D and the magnetic field of the second coil 22 toward the embedded metal E, the magnetic fields of the first coil 21 and the second coil 22 will interfere with each other, and a detection result in which the influence of the embedded metal E is reduced can be obtained.

[0056] 9, the transmitter circuit 70, the receiver circuit 60, and the control circuit 76 are provided on the internal head substrate 50. Providing the transmitter circuit 70, the receiver circuit 60, and the control circuit 76 on the internal head substrate 50 provides a stable circuit configuration. The transmitter circuit 70, the receiver circuit 60, and the control circuit 76 are not limited to being provided on the internal head substrate 50. For example, the transmitter circuit 70, the receiver circuit 60, and the control circuit 76 may be provided in a separate member, such as the amplifier housing 200. Alternatively, one or two of the transmitter circuit 70, the receiver circuit 60, and the control circuit 76 may be provided on the internal head substrate 50, and the other circuits may be provided on a separate board (a board located inside or outside the head housing 10, such as a board within the amplifier housing 200).

[0057] The receiving circuit 60 has a first receiving circuit 61 and a second receiving circuit 62. The first receiving circuit 61 detects the voltage or current generated in the first coil 21. The second receiving circuit 62 detects the voltage or current generated in the second coil 22. Hereinafter, the change in voltage or current over time detected by the receiving circuit 60 may also be referred to as a received waveform. Furthermore, the change in voltage or current over time detected by the first receiving circuit 61 and the second receiving circuit 62 may also be referred to as a first received waveform and a second received waveform, respectively.

[0058] Because the receiving circuit 60 has the first receiving circuit 61 and the second receiving circuit 62, it is not necessary to switch the receiving circuit 60 between detecting the voltage or current generated in the first coil 21 and detecting the voltage or current generated in the second coil 22. In other words, because the receiving circuit 60 has the first receiving circuit 61 and the second receiving circuit 62, it is possible to simultaneously detect the voltage or current generated in the first coil 21 and the voltage or current generated in the second coil 22. Therefore, the proximity sensor 100 can sufficiently extend the detection distance by improving the detection accuracy.

[0059] The magnetic field and its magnetic flux lines will be described below with reference to Fig. 10. Fig. 10 is a diagram schematically showing magnetic flux lines around the first coil 21 and the second coil 22.

[0060] 10, the core holder 40 holds the ferrite core 30 and also positions the second coil 22. By using the core holder 40 to position the second coil 22, the arrangement of the second coil 22 is stabilized regardless of the ferrite core 30. The stable arrangement of the second coil 22 allows for stable detection of the second received waveform. Therefore, the proximity sensor 100 can sufficiently extend the detection distance by suppressing the influence of the embedded metal E.

[0061] Furthermore, the axial dimension of the second coil 22 being smaller than the axial dimension of the first coil 21 leads to a reduction in the magnetic flux lines passing through the embedded metal E. Therefore, the proximity sensor 100 can sufficiently extend the detection distance by suppressing the influence of the embedded metal E.

[0062] The second coil 22 is located closer to the side (tip side) that detects the object to be detected D than the first coil 21. Positioning the second coil 22 closer to the tip side than the first coil 21 reduces the magnetic flux lines that pass through the embedded metal E. Therefore, the proximity sensor 100 can sufficiently extend the detection distance by suppressing the influence of the embedded metal E.

[0063] It is preferable that the second coil 22 is located closer to the tip. This is because the more the second coil 22 is located closer to the tip, the fewer magnetic flux lines pass through the embedded metal E. Therefore, it is more preferable that the second coil 22 is disposed against the most tip-side member of the proximity sensor 100.

[0064] In Figure 10, magnetic flux lines received only by the first coil 21 are shown by thick lines with symbol A, magnetic flux lines received only by the second coil 22 are shown by dashed lines with symbol B, and magnetic flux lines received by both the first coil 21 and the second coil 22 are shown by dotted lines with symbol C.

[0065] The magnetic flux lines (thick line: symbol A) received only by the first coil 21 tend to produce a received waveform based on the object to be detected D. The magnetic flux lines (dashed line: symbol B) received only by the second coil 22 tend to produce a received waveform based on the embedded metal E. The magnetic flux lines (dotted line: symbol C) received by both the first coil 21 and the second coil 22 tend to produce a received waveform based on both the object to be detected D and the embedded metal E.

[0066] Therefore, by reducing the magnetic flux lines (dotted lines: symbol C) received by both the first coil 21 and the second coil 22, the respective proportions of the received waveform based on the detection object D and the received waveform based on the embedded metal E increase relatively. If the respective proportions of the received waveform based on the detection object D and the received waveform based on the embedded metal E increase, it becomes easier to grasp the received waveform based on the embedded metal E, which leads to a reduction in the influence of the embedded metal E.

[0067] 10, the magnetic flux lines (dotted lines: symbol C) received by both the first coil 21 and the second coil 22 are routed in a way that avoids the embedded metal E. To achieve the state shown in FIG. 10, a magnetic shield 90 and a ferrite core 30 are appropriately provided.

[0068] 10, by appropriately positioning the magnetic shield 90, the magnetic flux lines (dotted lines: symbol C) received by both the first coil 21 and the second coil 22 are directed along a path that further avoids the embedded metal E. This is because the magnetic shield 90 guides the magnetic flux lines due to a relative permeability above a certain level.

[0069] By appropriately shaping the ferrite core 30, the magnetic flux lines (dotted lines: symbol C) received by both the first coil 21 and the second coil 22 are routed in a way that further avoids the embedded metal E. This is because the shape of the ferrite core 30 causes the magnetic flux lines to be more oriented toward the tip side.

[0070] The magnetic shield 90 will now be described in detail with reference to Figures 10 and 11. Figure 11 is an exploded perspective view illustrating the electric shield 80 and the magnetic shield 90 in detail.

[0071] 10, the magnetic shield 90 is disposed radially outward of the second coil 22. With this arrangement, the magnetic flux lines (dotted lines: symbol C) received by both the first coil 21 and the second coil 22 are guided along the magnetic shield 90, thereby forming a path that further avoids the embedded metal E. Therefore, the proximity sensor 100 can sufficiently extend the detection distance by suppressing the influence of the embedded metal E.

[0072] The magnetic shield 90 is preferably located radially outward in the proximity sensor 100. This is because the magnetic flux lines (dotted lines: symbol C) received by both the first coil 21 and the second coil 22 are guided in a direction that further avoids the embedded metal E. The magnetic shield 90 is, for example, located radially outward of the electric shield 80 (and inward of the head housing 10). The magnetic shield 90 may form part of the head housing 10.

[0073] As shown in FIG. 11 , the magnetic shield 90 is made of a sheet member into which ferromagnetic powder 91 (e.g., metal powder) is kneaded. The magnetic shield 90 is made of a sheet member into which ferromagnetic powder 91 is kneaded, and thus has a relative permeability higher than that of air (above a certain level) and low electrical conductivity. The sheet member may also be made of compressed ferromagnetic powder 91. The magnetic shield 90 appropriately guides magnetic flux lines due to its higher relative permeability than that of air. The magnetic shield 90 has low electrical conductivity, so eddy current loops in the magnetic shield 90 are suppressed without the need for insulation. The suppression of eddy current loops suppresses noise in the received waveform. Therefore, a proximity sensor 100 equipped with such a magnetic shield 90 can improve detection accuracy and thereby sufficiently extend the detection distance.

[0074] The ferromagnetic powder 91 constituting the magnetic shield 90 is, for example, iron powder. The magnetic shield 90 is made of a sheet material with iron powder mixed in, and therefore has a relatively high relative magnetic permeability (approximately 200 to 300). The sheet material with iron powder mixed in is, for example, an electromagnetic wave absorbing sheet. In this example, a sheet material with ferromagnetic powder 91 mixed in is used as the magnetic shield 90, but the magnetic shield 90 as a whole may be made of a non-crystalline ferromagnetic material. For example, it may be made of an amorphous material.

[0075] It should be noted that permalloy sheets, cobalt sheets, etc. are not suitable for the magnetic shield 90. This is because permalloy sheets, cobalt sheets, etc. have high relative magnetic permeability (approximately 1,000 to tens of thousands), but also high electrical conductivity. High electrical conductivity leads to the generation of eddy current loops.

[0076] The magnetic shield 90 is wrapped around the outer periphery of a cylindrical resin cap 95 with a bottom. The resin cap 95 has the function of protecting the components housed inside the resin cap 95. By wrapping the magnetic shield 90 around the outer periphery of the resin cap 95, its radially outward positioning is stabilized. Note that instead of the resin cap 95, which is made of resin, a cap made of a material other than resin may be used. The magnetic shield 90 is arranged on the outside of the cap, regardless of whether the cap is made of resin or not.

[0077] The electric shield 80 will be described in detail below with reference to Fig. 11. The electric shield 80 is a cylindrical metal body with a bottom that protects the coil 20 and the ferrite core 30 from external noise.

[0078] 11 , the electric shield 80 is disposed radially outward of the second coil 22. The electric shield 80 has a notch 81 formed therein. The notch 81 crosses a direction 88 around the axis of the electric shield 80. Specifically, the longitudinal direction of the notch 81 intersects (preferably perpendicular to) the direction 88 around the axis.

[0079] The notches 81 that intersect with the axial direction 88 of the electric shield 80 suppress eddy current loops, which are currents around the axis, in the electric shield 80. Suppressing eddy current loops suppresses noise in the received waveform. Therefore, the proximity sensor 100 equipped with such an electric shield 80 can improve detection accuracy and sufficiently extend the detection distance.

[0080] The electric shield 80 has a circumferential portion 84 and a detection surface portion 87. The circumferential portion 84 covers the second coil 22 from the outside in the radial direction. The detection surface portion 87 closes the tip side, which is one end of the circumferential portion 84. The detection surface portion 87 is located on the side that detects the object D to be detected.

[0081] The notches 81 have peripheral portion-side notches 82 and detection surface portion-side notches 83. The peripheral portion-side notches 82 are formed in the peripheral portion 84. The detection surface portion-side notches 83 are formed in the detection surface portion 87.

[0082] The peripheral cutouts 82 suppress eddy current loops in the peripheral portion 84. The peripheral cutouts 82 facilitate the manufacture of the electric shield 80. The detection surface cutouts 83 efficiently suppress eddy current loops in the detection surface portion 87.

[0083] The electric shield 80 is made of sheet metal. That is, the electric shield 80 is obtained by bending a thin metal plate. Because the electric shield 80 has a sheet metal structure, its shape is stable even if its strength is reduced by the notches 81. The thin metal plate before being bent into the electric shield 80 is preferably punched. The punched thin metal plate is then pressed to form the electric shield 80 into a three-dimensional, bottomed, cylindrical shape. That is, the electric shield 80 is preferably a press-formed product of the punched thin metal plate. Such an electric shield 80 has a more stable shape even if its strength is reduced by the notches 81. The thin metal plate forming the electric shield 80 is preferably copper foil or brass foil, for example. The electric shield 80 is not limited to a sheet metal structure. For example, the electric shield 80 may be a coated or vapor-deposited product. A coated or vapor-deposited product is formed by coating or vapor-depositing a conductive material on a bottomed, cylindrical resin mold. It is preferable that the electric shield 80 be electrically connected to ground (GND, reference potential) because a current flows through the electric shield 80. In this embodiment, for example, a shielded cable (not shown) that serves as a reference potential is included in the first cable line 17, and the shielded cable is electrically connected to the electric shield 80.

[0084] The ferrite core 30 will be described in detail below with reference to Fig. 12 and Fig. 13. Fig. 12 is a magnetic flux line diagram when the shaft body 31 of the ferrite core 30 is thin. Fig. 13 is a magnetic flux line diagram when the shaft body 31 of the ferrite core 30 is not thin. Fig. 12 shows the magnetic flux line when the width w of the shaft body 31 in the radial direction is set to 1.5 mm in the electromagnetic field simulation, and Fig. 13 shows the magnetic flux line when the width w of the shaft body 31 in the radial direction is set to 3 mm in the electromagnetic field simulation.

[0085] In the example shown in Fig. 12, the width w of the shaft 31 in the radial direction is 1.5 mm, and the width W of the entire ferrite core 30 is 7 mm, so the relative shaft width w / W is 21.4%. In other words, the relative shaft width w / W is 30% or less. As shown in Fig. 12, three magnetic flux lines m1 to m3 pass through the embedded metal E.

[0086] 13, the width w of the shaft 31 in the radial direction is 3 mm, and the width W of the entire ferrite core 30 is 7 mm, so the relative shaft width w / W is 42.9%. In other words, the relative shaft width w / W is more than 30%. As shown in FIG. 13, four magnetic flux lines M1 to M4 pass through the embedded metal E.

[0087] 12 and 13, in FIG. 12 where the relative shaft width w / W is 30% or less, there are only three magnetic flux lines passing through the embedded metal E, whereas in FIG. 13 where the relative shaft width w / W is more than 30%, there are four magnetic flux lines passing through the embedded metal E. Therefore, it can be seen that when the relative shaft width w / W is 30% or less, the influence of the embedded metal E is suppressed.

[0088] If the relative shaft width w / W is less than 15%, it becomes difficult to manufacture the ferrite core 30. Therefore, it can be said that the relative shaft width w / W is preferably 30% or less, and more preferably 15% or more and 30% or less.

[0089] The embodiments are illustrative in all respects and are not limiting. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. Among the configurations described in the embodiments, those other than those described as one aspect of the present invention in the "Means for Solving the Problems" are optional configurations and may be deleted or modified as appropriate.

[0090] (1) In the embodiment, the magnetic shield 90 and the electric shield 80 are illustrated as being cylindrical, but they may be in other shapes, such as a rectangular tube.

[0091] (2) Although the mounting bracket E1 and double nut E2 have been described as the embedded metal E in which the proximity sensor 100 is embedded, other metals may also be used. Examples of other metals include a single nut or a metal block with an internal thread. The embedded metal E is merely the metal in which the proximity sensor 100 is embedded, and is not a component of the proximity sensor 100 itself.

[0092] (3) In the embodiment, the transmitter circuit 70 is illustrated as a single circuit, but the transmitter circuit 70 may include a first transmitter circuit and a second transmitter circuit. The first transmitter circuit periodically supplies a pulsed excitation current to the first coil 21, and the second transmitter circuit periodically supplies a pulsed excitation current to the second coil 22. [Industrial Applicability]

[0093] The present invention provides a proximity sensor and has industrial applicability. [Explanation of symbols]

[0094] E Embedded metal D. Object to be detected 10 Head housing 19 Cable 20 coils 21 First coil 21a coil wire 22 Second coil 22a coil wire 30 Ferrite Core 31 Axial body 40 Core holder 50 Head internal circuit board 50a Substrate electrode 60 Receiving circuit 61 First receiving circuit 62 Second receiving circuit 70 Transmitting circuit 76 Control Circuit 80 Electric Shield 81 Cut 82 Peripheral cut 83 Detection surface side notch 84 Periphery 87 Detection surface 88 Directions around an axis 90 Magnetic Shield 91 Ferromagnetic powder 100 Proximity Sensor 200 Amplifier Case

Claims

1. a coil that generates a magnetic field by an excitation current; a ferrite core that guides the magnetic field generated from the coil; a head housing that houses the coil and the ferrite core; a head internal substrate accommodated in the head housing; Equipped with The coil is A first coil; a second coil arranged concentrically with respect to the first coil; and a transmission circuit that periodically applies a pulsed excitation current to the coil; a receiving circuit that detects a voltage or a current generated in at least one of the first coil and the second coil when the magnetic field is changed by an object to be detected; a control circuit that detects the object to be detected based on a change in the voltage or the current detected by the receiving circuit; Furthermore, A proximity sensor, wherein the coil wire of the first coil is electrically connected to the substrate within the head via direct bonding.

2. The proximity sensor according to claim 1 , wherein the transmitting circuit, the receiving circuit, and the control circuit are provided on the substrate within the head.

3. a cable extending from the head housing; an amplifier housing connected to the head housing via the cable, The proximity sensor according to claim 1 , wherein the transmitting circuit, the receiving circuit, and the control circuit are provided within the amplifier housing.

4. The receiving circuit a first receiving circuit that detects a voltage or a current generated in the first coil; a second receiving circuit that detects a voltage or a current generated in the second coil; The proximity sensor according to claim 1 , further comprising:

5. The proximity sensor according to claim 4, wherein the control circuit detects the object to be detected based on a difference between the voltage or the current detected by the first receiving circuit and the voltage or the current detected by the second receiving circuit.

6. The proximity sensor according to claim 1 , wherein the second coil is shorter than the first coil in a direction perpendicular to the radial direction of the second coil.

7. The proximity sensor according to claim 6 , wherein the second coil is disposed radially outward of the first coil.

8. The proximity sensor according to claim 1 , wherein the second coil is positioned closer to the first coil than the first coil in order to detect the object to be detected.

9. Further provided is a core holder for holding the ferrite core, The proximity sensor according to claim 1 , wherein the core holder positions the second coil and fixes the ferrite core to the substrate within the head.

10. The proximity sensor according to claim 1 , further comprising a magnetic shield disposed radially outward of the second coil.

11. The proximity sensor according to claim 10 , wherein the magnetic shield is made of a sheet member having ferromagnetic powder kneaded therein.

12. further comprising an electric shield disposed radially outside the second coil; The proximity sensor according to claim 1 , wherein the electric shield has a notch formed therein that extends transversely in a direction around the axis of the electric shield.

13. The electrical shield a peripheral portion that covers the second coil from the outside in the radial direction; a detection surface portion located on the side where the object to be detected is to be detected; and The proximity sensor according to claim 12 , wherein the notch is formed in the sensing surface portion.

14. The proximity sensor according to claim 13 , wherein the notch is formed in the periphery.

15. The proximity sensor of claim 12 , wherein the electrical shield is of sheet metal construction.

16. 16. The proximity sensor of claim 15, wherein the electrical shield is a stamped sheet metal pressing.

17. the ferrite core has a shaft passing through a hollow portion of the first coil, The proximity sensor according to claim 1 , wherein a ratio of a width of the shaft body to an overall width of the ferrite core in a radial direction of the first coil is 30% or less.

18. The proximity sensor according to claim 17 , wherein a ratio of a width of the shaft body to an overall width of the ferrite core in a radial direction of the first coil is 15% or more.

19. the cable includes a first cable wire electrically connected to either the coil wire of the first coil or the coil wire of the second coil, and a second cable wire electrically connected to either the coil wire of the first coil or the coil wire of the second coil, the first cable is connected to one surface of the substrate within the head; The proximity sensor according to claim 1 , wherein the second cable wire is connected to the other surface of the substrate within the head.

20. a coil that generates a magnetic field by an excitation current; a ferrite core that guides the magnetic field generated from the coil; a head housing that houses the coil and the ferrite core; a cable extending from the head housing; Equipped with The coil is A first coil; a second coil arranged concentrically with respect to the first coil; and a transmission circuit that periodically applies a pulsed excitation current to the coil; a receiving circuit that detects a voltage or a current generated in at least one of the first coil and the second coil when the magnetic field is changed by an object to be detected; a control circuit that detects the object to be detected based on a change in the voltage or the current detected by the receiving circuit; Furthermore, A proximity sensor, wherein the coil wire of the first coil is electrically connected to the cable via a direct joint.

21. a coil that generates a magnetic field by an excitation current; a ferrite core that guides the magnetic field generated from the coil; a head housing that houses the coil and the ferrite core; Equipped with The coil is A first coil; a second coil disposed radially outside the first coil; a magnetic material positioned between the first coil and the second coil; and a transmission circuit that periodically applies a pulsed excitation current to the coil; a receiving circuit that detects a voltage or a current generated in at least one of the first coil and the second coil when the magnetic field is changed by an object to be detected; a control circuit that detects the object to be detected based on a change in the voltage or the current detected by the receiving circuit; Furthermore, the head housing has a surface facing the object to be detected that has a diameter of less than 8 mm; The first coil has 100 or more turns.

22. The proximity sensor according to claim 21 , wherein the head housing has a surface that faces the object to be sensed that is made of metal.

23. 22. The proximity sensor according to claim 21, wherein the wire diameter of the coil wire of the first coil is 0.02 mm or less.

24. a head internal substrate accommodated in the head housing, The proximity sensor according to claim 21 , wherein the coil wire of the first coil is electrically connected to the substrate within the head via direct bonding.

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