Proximity sensor

Abstract

To provide a proximity sensor that sufficiently extends the detection distance by suppressing the influence of embedded metal.SOLUTION: A proximity sensor 100 comprises a coil 20, a transmitter circuit 70, a ferrite core 30, a receiver circuit 60, and a control circuit 76. The coil 20 generates a magnetic field through excitation current. The transmitter circuit 70 periodically supplies the pulsed excitation current to the coil 20. The ferrite core 30 guides the magnetic field generated by the coil 20. The coil 20 comprises a first coil 21 and a second coil 22 arranged concentrically with respect to the first coil 21. The transmitter circuit supplies the excitation current to either the first coil or the second coil. The receiver circuit 60 detects the voltage or current generated in each of the first coil 21 and the second coil 22 when the magnetic field changes due to the detected object D. The control circuit 76 detects the detected object D based on changes in the voltage or current detected in the receiver circuit 60, which occur in the first coil 21 and the second coil 22 respectively.SELECTED DRAWING: Figure 6

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 transmitting circuit, and a ferrite core. The coil generates a magnetic field by an excitation current. The transmitting circuit periodically passes a pulsed excitation current through the coil. The ferrite core guides the magnetic field generated from the coil. The coil includes a first coil and a second coil. The second coil is arranged concentrically with the first coil. The transmitting circuit passes an excitation current through one of the first coil and the second coil. The proximity sensor further includes a receiving circuit and a control circuit. The receiving 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 each of the first coil and the second coil detected by the receiving circuit. [Effects of the Invention]

[0008] 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]

[0009] [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. 2 is an exploded perspective view of the proximity sensor from the coil to the substrate. [Figure 4] FIG. 2 is an exploded perspective view of parts housed in a case of the proximity sensor. [Figure 5] FIG. 2 is a central vertical cross-sectional view of the proximity sensor. [Figure 6] FIG. 2 is a block diagram illustrating a main circuit configuration of a proximity sensor. [Figure 7] FIG. 2 is a block diagram illustrating in detail the main circuit configuration of the proximity sensor. [Figure 8A] 10 is a graph showing an image of a received waveform when there is no embedded metal and no object to be detected within the detection range. [Figure 8B]10 is a graph showing an image of a received waveform when there is no embedded metal and the object to be detected is within the detection range. [Figure 9A] 10 is a graph showing an image of a received waveform when there is embedded metal and the object to be detected is not within the detection range. [Figure 9B] 10 is a graph showing an image of a received waveform when there is embedded metal and the object to be detected is within the detection range. [Figure 10A] 10 is a graph showing an image of a zero-adjusted received waveform when there is no embedded metal and no object to be detected within the detection range. [Figure 10B] 10 is a graph showing an image of a zero-adjusted received waveform when there is no buried metal and the object to be detected is within the detection range. [Figure 11A] 10 is a graph showing an image of a zero-adjusted received waveform when there is embedded metal and the object to be detected is not within the detection range. [Figure 11B] 10 is a graph showing an image of a zero-adjusted received waveform when there is embedded metal and the object to be detected is within the detection range. [Figure 12] 3A and 3B are diagrams illustrating the sizes and arrangements of the first coil and the second coil. [Figure 13A] FIG. 10 is a central vertical cross-sectional view showing a state in which the influence of the embedded metal is slightly suppressed. [Figure 13B] FIG. 10 is a central vertical cross-sectional view showing a state in which the influence of the embedded metal is further suppressed. [Figure 14] FIG. 5 is an exploded perspective view illustrating the magnetic shield shown in FIG. 4 in detail. [Figure 15] This is an exploded view of the electrical shield. [Figure 16] This is a development view of an electric shield having a different shape of the cutout on the detection surface side from that of FIG. [Figure 17] FIG. 3 is a central vertical cross-sectional view of a first coil and a ferrite core. [Figure 18] 10 is a graph showing the results of an electromagnetic field simulation. [Figure 19] This is a magnetic flux line diagram when the shaft body of the ferrite core is thin. [Figure 20] FIG. 10 is a magnetic flux line diagram when the shaft of the ferrite core is not thin. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] Hereinafter, a proximity sensor according to an embodiment of the present invention will be described with reference to the drawings.

[0012] 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.

[0013] As shown in FIG. 1, the proximity sensor 100 has an external thread 12 formed on its side, making it shaped (shielded) so that it can be fixed with a nut or the like. As shown in FIG. 2, when in use, 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 is not its intended detection target. Therefore, the proximity sensor 100 according to an embodiment of the present invention is configured to suppress the influence of the embedded metal E in order to sufficiently extend the detection distance.

[0014] The configuration of the main components of the proximity sensor 100 will be described below with reference to Figs. 3 to 5. Fig. 3 is an exploded perspective view of components from the coil 20 to the substrate 50 that make up the proximity sensor 100. Fig. 4 is an exploded perspective view of components housed in the case 10 of the proximity sensor 100. Fig. 5 is a central vertical cross-sectional view of the proximity sensor 100.

[0015] 3, the proximity sensor 100 includes a coil 20, a ferrite core 30, a core holder 40, and a substrate 50. Hereinafter, the coil 20, the ferrite core 30, the core holder 40, and the substrate 50 may be collectively referred to as a sensor unit 25.

[0016] 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 core holder 40 holds the ferrite core 30. The substrate 50 is electrically connected to the coil 20 via a lead wire 23.

[0017] 3 and 4, there are a plurality of lead wires 23 (four in the illustrated example) extending from the coil 20. None of the lead wires 23 are arranged in positions that are point-symmetric with respect to the axis of the coil 20. In other words, none of the lead wires 23 are arranged in positions that are not directly opposite each other at 180° with respect to the axis of the coil 20.

[0018] 4, this arrangement allows the plurality of lead wires 23 to be collected and soldered on one surface of the substrate 50. Therefore, the proximity sensor 100 can be easily manufactured by collecting the plurality of lead wires 23 and soldering them on one surface of the substrate 50. The plurality of lead wires 23 run from the coil 20 through gaps between the ferrite core 30 and the core holder 40 to the substrate 50.

[0019] In addition to the sensor unit 25, the proximity sensor 100 further includes an electric shield 80, a magnetic shield 90, and a case 10.

[0020] 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.

[0021] 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 substrate 50.

[0022] The case 10 has a case main body 11 on which an external thread 12 is formed. As shown in Figures 4 and 5, the case main body 11 completely covers the magnetic shield 90, the electric shield 80, and the sensor unit 25. As shown in Figure 5, the case 10 further has a case base end 13 on which a cable attachment port 14 is formed. The case base end 13 is inserted into the case main body 11 from the circuit board 50 side.

[0023] The proximity sensor 100 further includes a cable 19. The cable 19 is electrically connected to the substrate 50. The cable 19 extends from inside the case 10 to outside through the cable attachment port 14 at the case base end 13.

[0024] The main circuit configuration of the proximity sensor 100 will be described below with reference to Fig. 6. Fig. 6 is a block diagram illustrating the main circuit configuration of the proximity sensor 100.

[0025] As shown in FIG. 6, the proximity sensor 100 further includes a transmitting circuit 70, a receiving circuit 60, and a control circuit 76 as main circuit components.

[0026] The transmission 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 outward from the first coil 21. The second coil 22 may be disposed concentrically with the first coil 21. In this example, "disposed 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 disposed concentrically with the first coil 21, it may be disposed on the side (or opposite side) from which the detection object D is detected relative to the first coil 21.

[0027] 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.

[0028] 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. By detecting voltages or currents with different characteristics, calculations for suppressing the influence of the embedded metal E become more efficient. 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.

[0029] The control circuit 76 detects the object D to be sensed based on a change in voltage or current detected by the receiving circuit 60. It is preferable that the control circuit 76 detects the object D to be sensed 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 effect of the embedded metal E.

[0030] In the example shown in FIG. 6 , 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 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. As described above, the detection results by the first coil 21 and the second coil 22 differ. However, to extend the detection distance, it is preferable that both detection results be susceptible to the influence of 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 susceptible to the influence of 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.

[0031] 6, the transmitter circuit 70, the receiver circuit 60, and the control circuit 76 are provided on the substrate 50. Providing the transmitter circuit 70, the receiver circuit 60, and the control circuit 76 on the 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 substrate 50. For example, the transmitter circuit 70, the receiver circuit 60, and the control circuit 76 may be provided on separate members. Alternatively, one or two of the transmitter circuit 70, the receiver circuit 60, and the control circuit 76 may be provided on the substrate 50, and the other circuits may be provided on a separate substrate or member (a substrate or member disposed inside or outside the case 10).

[0032] 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.

[0033] 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.

[0034] The transmitter circuit 70, receiver circuit 60, and control circuit 76 will be described in detail below with reference to Fig. 7. Fig. 7 is a block diagram illustrating the main circuit configuration of the proximity sensor 100 in detail.

[0035] The transmission circuit 70 includes an excitation circuit 71. The excitation circuit 71 generates a pulsed excitation current based on a signal from a control circuit 76 and passes the generated current through the first coil 21.

[0036] The control circuit 76 has an arithmetic circuit 77 and an output circuit 78. The arithmetic circuit 77 performs calculations to detect the object D to be detected based on at least one of the first received waveform and the second received waveform. The arithmetic circuit 77 performs calculations based on both the first received waveform and the second received waveform. The output circuit 78 outputs the results of the calculations by the arithmetic circuit 77 to the outside via cable 19. Note that the arithmetic circuit 77 may be configured to perform calculations to detect the object D to be detected based on at least one of the first received waveform and the second received waveform, and the response speed increases when calculations are performed based on only one of them.

[0037] The first and second received waveforms will be described below with reference to Figures 8A, 8B, 9A, and 9B. In Figures 8A to 9B, the first received waveform is indicated by the symbol R1, and the second received waveform is indicated by the symbol R2.

[0038] FIG. 8A is a graph showing an image of a received waveform when there is no embedded metal E and the detection target D is not within the detection range. FIG. 8B is a graph showing an image of a received waveform when there is no embedded metal E and the detection target D is within the detection range. FIG. 9A is a graph showing an image of a received waveform when there is embedded metal E and the detection target D is not within the detection range. FIG. 9B is a graph showing an image of a received waveform when there is embedded metal E and the detection target D is within the detection range. In the graphs of FIGS. 8A to 9B, the horizontal axis represents time and the vertical axis represents the signal strength of the received waveform.

[0039] 8A and 8B are graphs showing the case where there is no embedded metal E. As shown in FIG. 8A, when the object to be detected D is not within the detection range, the proximity sensor 100 itself is slightly detected, and the first and second received waveforms reflecting this detection appear. As shown in FIG. 8B, when the object to be detected D is within the detection range, the detection of the object to be detected D results in larger changes in both the first and second received waveforms compared to when the object to be detected D is not within the detection range. In particular, the first received waveform, which is more susceptible to the influence of the object to be detected D than the second received waveform, has a larger change than the second received waveform.

[0040] 9A and 9B are graphs showing the case where embedded metal E is present. As shown in FIG. 9A, when the detection target D is not within the detection range, the embedded metal E is detected, resulting in larger changes in both the first and second received waveforms compared to the case in FIG. 8A where embedded metal E is not present and the detection target D is not within the detection range. In particular, the second received waveform, which is more susceptible to the influence of embedded metal E than the first received waveform, has a larger change than the first received waveform. As shown in FIG. 9B, when the detection target D is present within the detection range, the detection target D is also detected, resulting in larger changes in both the first and second received waveforms compared to the case where the detection target D is not within the detection range. In particular, the first received waveform, which is more susceptible to the influence of the detection target D than the second received waveform, has a larger difference in change from the change when the detection target D is not within the detection range than the second received waveform.

[0041] Although the first received waveform is more susceptible to the influence of the detection object D than the second received waveform, when the embedded metal E is present, the difference in the amount of change in the waveform depending on whether the detection object D is present within the detection range is smaller, as shown in FIGS. 9A and 9B, compared to when the embedded metal E is not present as shown in FIGS. 8A and 8B. In particular, the difference in the amount of change in the waveform depending on whether the detection object D is present within the detection range becomes smaller as the distance between the detection object D and the coil 20 increases. However, as shown in FIGS. 8A to 9B, the first received waveform is more susceptible to the influence of the detection object D than the second received waveform, and the second received waveform is more susceptible to the influence of the embedded metal E than the first received waveform, and the difference in the amount of change in the second received waveform tends to differ from that of the first received waveform. More specifically, the difference in the amount of change in the waveform depending on whether the detection object D is present within the detection range is smaller for the second received waveform than for the first received waveform, and the difference in the amount of change in the waveform depending on whether the embedded metal E is present is larger for the first received waveform. Therefore, by performing calculations based on both the first received waveform and the second received waveform, the object D to be detected can be detected while efficiently suppressing the influence of the embedded metal E.

[0042] The zero-adjusted first and second received waveforms will be described below with reference to Figures 10A, 10B, 11A, and 11B. In Figures 10A to 11B, the zero-adjusted first received waveform is indicated by the symbol ΔR1, and the zero-adjusted second received waveform is indicated by the symbol ΔR2.

[0043] FIG. 10A is a graph showing an image of a zero-adjusted received waveform when there is no embedded metal E and the object to be detected D is not within the detection range. FIG. 10B is a graph showing an image of a zero-adjusted received waveform when there is no embedded metal E and the object to be detected D is within the detection range. FIG. 11A is a graph showing an image of a zero-adjusted received waveform when there is embedded metal E and the object to be detected D is not within the detection range. FIG. 11B is a graph showing an image of a zero-adjusted received waveform when there is embedded metal E and the object to be detected D is within the detection range. In the graphs of FIGS. 10A to 11B, the horizontal axis represents time and the vertical axis represents the signal strength of the received waveform.

[0044] 10A and 10B are graphs showing the case where there is no embedded metal E. As shown in FIG. 10A, when the object to be detected D is not within the detection range, the measurement value is calibrated to zero (zero adjustment), and therefore the zero-adjusted first received waveform and second received waveform do not appear. As shown in FIG. 10B, when the object to be detected D is within the detection range, the detection of the object to be detected D increases the amount of change in both the zero-adjusted first received waveform and the zero-adjusted second received waveform. In particular, the zero-adjusted first received waveform, which is more susceptible to the influence of the object to be detected D than the zero-adjusted second received waveform, exhibits a larger amount of change than the zero-adjusted second received waveform.

[0045] 11A and 11B are graphs showing the case where embedded metal E is present. As shown in FIG. 11A, when the detection target D is not within the detection range, the detection of embedded metal E results in a larger change in both the zero-adjusted first received waveform and the zero-adjusted second received waveform. In particular, the zero-adjusted second received waveform, which is more susceptible to the influence of embedded metal E than the zero-adjusted first received waveform, has a larger change than the zero-adjusted first received waveform. As shown in FIG. 11B, when the detection target D is present within the detection range, the detection of the detection target D also results in a larger change in both the zero-adjusted first received waveform and the zero-adjusted second received waveform compared to when the detection target D is not within the detection range. In particular, the zero-adjusted first received waveform, which is more susceptible to the influence of the detection target D than the zero-adjusted second received waveform, has a larger difference in change from the change when the detection target D is not within the detection range than the zero-adjusted second received waveform.

[0046] 10A to 11B, the zero-adjusted first received waveform is easily affected by the object to be detected D, and the zero-adjusted second received waveform is easily affected by the embedded metal E. Therefore, by performing calculations based on both the zero-adjusted first received waveform and the zero-adjusted second received waveform, the object to be detected D can be detected while efficiently suppressing the influence of the embedded metal E.

[0047] This calculation is, for example, the difference between the zero-adjusted first received waveform and the second received waveform. The difference is the subtraction of the zero-adjusted second received waveform from the zero-adjusted first received waveform (ΔR1-ΔR2).

[0048] The size and arrangement of the first coil 21 and the second coil 22 will be described in detail below with reference to Fig. 12. Fig. 12 is a diagram for explaining the size and arrangement of the first coil 21 and the second coil 22.

[0049] As shown in FIG. 12, the radial direction of the first coil 21 and the radial direction of the second coil 22 are in the same direction (the left-right direction in FIG. 12). Therefore, hereinafter, the radial direction of the first coil 21 or the second coil 22 may simply be referred to as the radial direction.

[0050] The axial direction of the first coil 21 and the axial direction of the second coil 22 are in the same direction (the up-down direction in FIG. 12). Therefore, hereinafter, the axial direction of the first coil 21 or the second coil 22 may simply be referred to as the axial direction. The radial direction (the left-right direction in FIG. 12) and the axial direction (the up-down direction in FIG. 12) are orthogonal.

[0051] Hereinafter, among the axial directions, the side where the detection object D is detected (the upper side in FIG. 12) may be referred to as the tip side, and the opposite side of the tip side (the lower side in FIG. 12) may be referred to as the base end side.

[0052] The second coil 22 is shorter than the first coil 21 in the direction orthogonal to its radial direction (axial direction). That is, the axial length L2 of the second coil 22 is shorter than the axial length L1 of the first coil 21 (L2 < L1). The fact that the axial length L2 of the second coil 22 is shorter than the axial length L1 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. Also, by adopting such a configuration, the sensitivity of the second coil 22 to magnetic flux with respect to the first coil 21 decreases. It is preferable that the influence of the magnetic flux passing through both the detection object D and the embedded metal E is reduced from the detection result of the second coil 22. By reducing the sensitivity of the second coil 22 to magnetic flux with respect to the first coil 21, the influence of the magnetic flux passing through both the detection object D and the embedded metal E is reduced.

[0053] The second coil 22 is located closer to the tip of the object D than the first coil 21. Specifically, the second coil 22 is located a predetermined distance ΔL closer to the tip than the first coil 21. Positioning the second coil 22 closer to the tip than the first coil 21 reduces the number of 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.

[0054] 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.

[0055] The magnetic field and its magnetic flux lines will be described below with reference to Figures 13A and 13B. Figure 13A is a central vertical cross-sectional view in a state where the influence of the embedded metal E is slightly suppressed. Figure 13B is a central vertical cross-sectional view in a state where the influence of the embedded metal E is further suppressed.

[0056] 13A and 13B, 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.

[0057] The core holder 40 preferably has a structure for fixing the substrate 50. By using the core holder 40 to fix the substrate 50, the positioning accuracy between the substrate 50 and the coil 20 is improved, and it becomes easier to manufacture the proximity sensor 100 in a space-saving manner. The core holder 40 is made of, for example, resin.

[0058] Next, the magnetic flux lines of the magnetic field received by coil 20 will be described with reference to a comparison of FIGS. 13A and 13B.

[0059] In Figures 13A and 13B, 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.

[0060] 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.

[0061] 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.

[0062] 13B, compared to Fig. 13A, 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. Therefore, compared to Fig. 13A, the magnetic flux lines (dotted lines: symbol C) received by both the first coil 21 and the second coil 22 are reduced in Fig. 13B. To achieve the state shown in Fig. 13B, a magnetic shield 90 and a ferrite core 30 are appropriately provided.

[0063] 13B, 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.

[0064] 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.

[0065] The magnetic shield 90 will now be described in detail with reference to Figures 13B and 14. Figure 14 is an exploded perspective view illustrating the magnetic shield 90 shown in Figure 4 in detail.

[0066] 13B, 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.

[0067] 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 case 10). The magnetic shield 90 may also constitute the case 10.

[0068] As shown in FIG. 14, the magnetic shield 90 is made of a sheet member into which ferromagnetic powder 91 is kneaded. Because the magnetic shield 90 is made of a sheet member into which ferromagnetic powder 91 is kneaded, it has a relative permeability higher than that of air (above a certain level) and low electrical conductivity. 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 treatment. Suppressing 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 sufficiently extend the detection distance.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] The electric shield 80 will be described in detail below with reference to Figures 14 to 16. 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.

[0073] 14, the electric shield 80 is disposed radially outward of the second coil 22. The electric shield 80 has a cut 81 (slit) formed therein. The cut 81 crosses a direction 88 around the axis of the electric shield 80. Specifically, the longitudinal direction of the cut 81 intersects (preferably perpendicular to) the direction 88 around the axis.

[0074] 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.

[0075] The electric shield 80 has a peripheral portion 84 and a detection surface portion 87. The peripheral portion 84 covers the second coil 22 from the outside in the radial direction. The detection surface portion 87 is located on the side that detects the detection target D. The detection surface portion 87 closes the tip side, which is one end of the peripheral portion 84.

[0076] 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.

[0077] 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.

[0078] 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 is made of sheet metal, the shape of the electric shield 80 remains stable even if the strength is reduced by the notches 81.

[0079] 15 and 16 show the metal sheet before being bent into the electric shield 80. Fig. 15 is a development view of the electric shield 80. Fig. 16 is a development view of the electric shield 80 in which the shape of the detection surface side notch 83 is different from that in Fig. 15.

[0080] As shown in Figures 15 and 16, a metal sheet is punched before being bent into the electric shield 80. The metal sheet is punched so that notches 81 are also formed at the same time. The punched metal sheet is pressed to form the electric shield 80 into the three-dimensional cylindrical shape with a bottom shown in Figure 14. In other words, the electric shield 80 is a press-formed product of the punched metal sheet. Even if the strength of such an electric shield 80 is reduced by the notches 81, the shape of the electric shield 80 is more stable. The metal sheet constituting the electric shield 80 is, for example, copper foil or brass foil.

[0081] The peripheral portion 84 has a left semi-circular portion 85 and a right semi-circular portion 86. The left semi-circular portion 85 and the right semi-circular portion 86 are connected to the detection surface portion 87 from the left and right sides, respectively. The left semi-circular portion 85 and the right semi-circular portion 86 are bent so as to be perpendicular to the detection surface portion 87. Furthermore, the left semi-circular portion 85 and the right semi-circular portion 86 are roll-bent and pressed so that the edges on the side closer to the detection surface portion 87 are aligned with the edges of the detection surface portion 87.

[0082] The peripheral portion side cutout 82 is a gap between the left semi-peripheral portion 85 and the right semi-peripheral portion 86. The detection surface portion side cutout 83 is a gap that radiates from the center of the detection surface portion 87.

[0083] 15, in a clock position in which the top of FIG. 15 is 0 o'clock, radial gaps extending in the directions of 0 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock pass through the center of the detection surface 87 but do not reach the edges of the detection surface 87. Radial gaps extending in the directions between 1 o'clock and 2 o'clock, between 4 o'clock and 5 o'clock, between 7 o'clock and 8 o'clock, and between 10 o'clock and 11 o'clock do not pass through the center of the detection surface 87 but reach the edges of the detection surface 87.

[0084] 16 , the radial gaps extending in the 0 o'clock and 6 o'clock directions do not pass through the center of the detection surface 87 but reach the edges of the detection surface 87. The linear gaps extending in the 3 o'clock and 9 o'clock directions pass through the center of the detection surface 87 but do not reach the edges of the detection surface 87. The radial gaps extending between 1 o'clock and 2 o'clock, between 4 o'clock and 5 o'clock, between 7 o'clock and 8 o'clock, and between 10 o'clock and 11 o'clock do not pass through the center of the detection surface 87 and do not reach the edges of the detection surface 87.

[0085] The electric shields 80 shown in Figures 15 and 16 both suppress eddy current loops to the same extent. Compared to Figure 15, the electric shield 80 shown in Figure 16 has a shorter current path, which reduces electrical resistance and improves resistance to external noise.

[0086] The electric shield 80 is not limited to being made of sheet metal. For example, the electric shield 80 may be a coated or vapor-deposited molded product. A coated or vapor-deposited molded product is formed by coating or vapor-depositing a conductive material onto a cylindrical resin mold with a bottom.

[0087] The ferrite core 30 will be described in detail below with reference to Figs. 17 to 20. Fig. 17 is a central vertical cross-sectional view of the first coil 21 and the ferrite core 30. Fig. 18 is a graph showing the results of an electromagnetic field simulation. Fig. 19 is a magnetic flux line diagram when the shaft body 31 of the ferrite core 30 is thin. Fig. 20 is a magnetic flux line diagram when the shaft body 31 of the ferrite core 30 is not thin.

[0088] 17, 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.

[0089] In order to understand the relationship between the relative shaft width w / W and the influence of the embedded metal E, an electromagnetic field simulation was carried out under the following conditions.

[0090] As a condition for the electromagnetic field simulation, the overall width W (outer diameter) of the ferrite core 30 in the radial direction was set to 7 mm. The following seven widths w of the shaft 31 in the radial direction were set. Specifically, the widths w of the shaft 31 in the radial direction were set to 3.5 mm, 3 mm, 2.5 mm, 2 mm, 1.5 mm, 1 mm, and 0.5 mm. For each of these seven widths, the signal strength Ve of the received waveform based on the embedded metal E was divided by the signal strength Vd of the received waveform based on the detection object D to calculate the intensity ratio Vd / Ve. Note that the signal strengths Vd and Ve of each received waveform were defined as the voltages at both ends of the coil 20.

[0091] The results of the electromagnetic field simulation are shown in Figure 18. In the graph shown in Figure 18, the horizontal axis is the relative shaft width w / W and the vertical axis is the intensity ratio Vd / Ve. As is clear from the graph shown in Figure 18, as the relative shaft width w / W became smaller, the intensity ratio Vd / Ve increased. However, once the relative shaft width w / W became smaller to a certain extent, the intensity ratio Vd / Ve remained flat.

[0092] In particular, when the relative shaft width w / W was 30% or less, the intensity ratio Vd / Ve was greater than or equal to 1. In other words, when the relative shaft width w / W was 30% or less, the signal intensity Vd of the received waveform based on the detection object D was greater than or equal to the signal intensity Ve of the received waveform based on the embedded metal E.

[0093] When the relative shaft width w / W is less than 15%, the intensity ratio Vd / Ve remains flat. Furthermore, when the relative shaft width w / W is less than 15%, it is difficult to manufacture the ferrite core 30. In other words, when the relative shaft width w / W is 15% or more, the intensity ratio Vd / Ve is high and manufacturing is easy.

[0094] If the intensity ratio Vd / Ve is high, the signal intensity Vd of the received waveform based on the object to be detected D will be relatively high. In other words, if the intensity ratio Vd / Ve is high, the signal intensity Ve of the received waveform based on the embedded metal E will be relatively low. Therefore, by having the relative shaft width w / W of 30% or less, the proximity sensor 100 can suppress the influence of the embedded metal E and sufficiently extend the detection distance. Furthermore, by having the relative shaft width w / W of 15% or more, the proximity sensor 100 can sufficiently extend the detection distance and facilitate manufacturing.

[0095] From the above, it can be said from the results of the electromagnetic field simulation that the relative shaft width w / W is preferably 30% or less, and more preferably 15% or more and 30% or less.

[0096] Next, magnetic flux lines in an electromagnetic field simulation are shown in Figures 19 and 20. Figure 19 shows the case where the width w of the shaft body 31 in the radial direction is 1.5 mm, and Figure 20 shows the case where the width w of the shaft body 31 in the radial direction is 3 mm.

[0097] In the example shown in Fig. 19, 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. 19, three magnetic flux lines m1 to m3 pass through the embedded metal E.

[0098] On the other hand, in the example shown in Fig. 20, 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. 20, four magnetic flux lines M1 to M4 pass through the embedded metal E.

[0099] 19 and 20, in FIG. 19 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. 20 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 said from FIG. 19 and 20 that the influence of the embedded metal E is suppressed when the relative shaft width w / W is 30% or less.

[0100] 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.

[0101] (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.

[0102] (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.

[0103] (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]

[0104] The present invention provides a proximity sensor and has industrial applicability. [Explanation of symbols]

[0105] E Embedded metal D. Object to be detected 20 coils 21 First coil 22 Second coil 30 Ferrite Core 31 Axial body 40 Core holder 50 boards 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

Claims

1. a coil that generates a magnetic field by an excitation current; a transmission circuit that periodically applies a pulsed excitation current to the coil; a ferrite core that guides the magnetic field generated from the coil; Equipped with The coil is A first coil; a second coil arranged concentrically with respect to the first coil; and the transmission circuit causes an excitation current to flow through one of the first coil and the second coil; a receiving circuit that detects a voltage or a current generated in each 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 generated in each of the first coil and the second coil, which change is detected by the receiving circuit; The proximity sensor further comprises:

2. the second coil is disposed radially outward of the first coil, The proximity sensor according to claim 1 , wherein the first coil generates the magnetic field when the pulsed excitation current is periodically applied from the transmission circuit.

3. The proximity sensor according to claim 1 or 2, further comprising a substrate on which the transmitting circuit, the receiving circuit, and the control circuit are provided.

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 or 2, 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 or 2, wherein the second coil is shorter than the first coil in a direction perpendicular to a radial direction of the second coil.

7. The proximity sensor according to claim 1 or 2, wherein the second coil is positioned closer to the first coil than the first coil in order to detect the object to be detected.

8. Further provided is a core holder for holding the ferrite core, The proximity sensor according to claim 1 or 2, wherein the core holder positions the second coil.

9. The proximity sensor according to claim 1 or 2, further comprising a magnetic shield disposed radially outside the second coil.

10. The proximity sensor according to claim 9 , wherein the magnetic shield is made of a sheet member having ferromagnetic powder kneaded therein.

11. further comprising an electric shield disposed radially outside the second coil; The proximity sensor according to claim 1 or 2, wherein the electric shield has a notch formed therein that crosses the direction around the axis of the electric shield.

12. 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 11 , wherein the notch is formed in the sensing surface portion.

13. The proximity sensor according to claim 12 , wherein the notch is formed in the periphery.

14. The proximity sensor of claim 11 , wherein the electrical shield is of sheet metal construction.

15. 15. The proximity sensor of claim 14, wherein the electrical shield is a stamped sheet metal pressing.

16. the ferrite core has a shaft passing through a hollow portion of the first coil, 3. 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.

17. The proximity sensor according to claim 16 , 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.

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