Proximity sensor

Abstract

Provided is a proximity sensor capable of sufficiently extending a detection distance by suppressing the influence of an embedded metal. The proximity sensor includes a first coil, a second coil, a transmitting circuit, a ferrite core, a receiving circuit, a control circuit, and an electrical shield. The second coil is disposed radially outward of the first coil. The transmission circuit periodically applies a pulsed excitation current to at least one of the coils. The control circuit detects the detection object D on the basis of a change in the detected voltage or current generated in at least one of the coils by the magnetic field. The electrical shield is a press-molded article having a bottomed cylindrical shape disposed on an outer side in a radial direction of the second coil, and has a peripheral portion and a detection surface portion in which a cutout that traverses a direction around the axis is formed in the peripheral portion and the detection surface portion.

Description

Technical Field

[0001] The present invention relates to proximity sensors. Background Art

[0002] Japanese Patent Application Laid-Open No. 2018-152320 discloses a proximity sensor. The proximity sensor described in Japanese Patent Application Laid-Open No. 2018-152320 reduces the influence of changes in coil characteristics, etc.

[0003] For example, Japanese Patent Application No. 2018-152320 Figure 3 As illustrated, the proximity sensor of Japanese Patent Application Laid-Open No. 2018-152320 is used by being embedded in the nuts and washers of reference numerals 7 to 9.

[0004] On the other hand, if the proximity sensor comes into contact with the object to be detected (hereinafter referred to as the detection object) and its surrounding components, the proximity sensor may malfunction. For this reason, the proximity sensor is required to extend the distance to be detected (hereinafter referred to as the detection distance) to avoid contact with the detection object, etc.

[0005] To extend the detection distance, the proximity sensor also needs to detect slight changes in the received waveform. However, the proximity sensor described in Japanese Patent Application Laid-Open No. 2018-152320 cannot detect slight changes in the received waveform due to the influence of embedded nuts or washers (hereinafter referred to as embedded metal), and therefore cannot fully extend the detection distance. Summary of the Invention

[0006] The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a proximity sensor capable of sufficiently extending a detection distance by suppressing the influence of embedded metal.

[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 via an excitation current. The transmitting circuit periodically applies a pulsed excitation current to the coil. The ferrite core guides the magnetic field generated by the coil. The coil includes a first coil and a second coil. The second coil is arranged concentrically with the first coil. The proximity sensor also includes a receiving circuit, a control circuit, and an electric shield. The receiving circuit detects a voltage or current generated in at least one of the first and second coils due to a magnetic field altered by a detection target. The control circuit detects the detection target D based on the change in voltage or current detected by the receiving circuit. The electric shield has a bottomed cylindrical shape arranged radially outward of the second coil. The electric shield includes a peripheral portion and a detection surface portion. The peripheral portion covers the second coil from the radial outward. The detection surface portion is located on the side that detects the detection target. The electric shield includes cutouts transverse to the winding axis in the detection surface portion and the peripheral portion. The electric shield is a pressed and formed product of a stamped thin metal plate having a sheet metal structure.

[0008] According to the proximity sensor of the present invention, the detection distance can be sufficiently extended by suppressing the influence of embedded metal. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is the appearance diagram of the proximity sensor;

[0010] Figure 2 This is the appearance of the proximity sensor in use;

[0011] Figure 3 This is an exploded perspective view of the proximity sensor, from the coil to the substrate.

[0012] Figure 4 is an exploded perspective view of components housed in a housing of a proximity sensor;

[0013] Figure 5 is a central longitudinal section of the proximity sensor;

[0014] Figure 6 This is a block diagram illustrating the main circuit structure of a proximity sensor;

[0015] Figure 7 This is a block diagram that details the main circuit structure of the proximity sensor.

[0016] Figure 8A is a graph illustrating an image of a reception waveform in a case where there is no embedded metal and the detection object is not within the detection range;

[0017] Figure 8B is a graph illustrating an image of a reception waveform in a case where there is no embedded metal and the detection object is within the detection range;

[0018] Figure 9A is a graph illustrating an image of a reception waveform in a case where embedded metal exists and the detection object is not within the detection range;

[0019] Figure 9B is a graph illustrating an image of a reception waveform in a case where embedded metal exists and a detection object is within a detection range;

[0020] Figure 10A is a graph illustrating an image of a reception waveform subjected to zero adjustment when there is no embedded metal and the detection object is not within the detection range;

[0021] Figure 10B is a graph illustrating an image of a reception waveform after zero adjustment when there is no embedded metal and the detection object is within the detection range;

[0022] Figure 11A is a graph illustrating an image of a reception waveform subjected to zero adjustment when embedded metal is present and the detection object is not within the detection range;

[0023] Figure 11B is a graph illustrating an image of a reception waveform after zero adjustment when embedded metal is present and a detection object is within the detection range;

[0024] Figure 12 is a diagram for explaining the size and arrangement of the first coil and the second coil;

[0025] Figure 13A It is a central longitudinal section with the influence of the embedded metal slightly suppressed;

[0026] Figure 13B It is a central longitudinal section in a state where the influence of the embedded metal is further suppressed;

[0027] Figure 14 It is used to explain in detail Figure 4 An exploded perspective view of the illustrated magnetic shield;

[0028] Figure 15 is an expanded view of the electric shield;

[0029] Figure 16 The shape of the cutout on the detection surface Figure 15 Expanded view of electric shielding components with different shapes of detection surface cutouts;

[0030] Figure 17is a central longitudinal section of the first coil and the ferrite core;

[0031] Figure 18 is a graph illustrating the results of an electromagnetic field simulation;

[0032] Figure 19 is the flux diagram when the ferrite core has a thin axis; and

[0033] Figure 20 This is a magnetic flux diagram when the axis of the ferrite core is not thin. DETAILED DESCRIPTION

[0034] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that in the drawings, identical or corresponding parts are denoted by the same reference numerals, and their description will not be repeated. In the following description, terms such as "upper," "lower," "left," and "right" may be used to indicate position or direction. These terms are used for convenience to facilitate understanding of the embodiments and, unless otherwise expressly stated, have no bearing on the directions in which these terms are actually implemented.

[0035] Hereinafter, a proximity sensor according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0036] First, refer to Figure 1 and Figure 2 A case where the proximity sensor 100 is used will be described. Figure 1 FIG. 1 is an external view of the proximity sensor 100 . Figure 2 FIG. 1 is an external view of the proximity sensor 100 in use.

[0037] like Figure 1 As illustrated, the proximity sensor 100 has a shape (shielded type) that can be fixed by a nut or the like by forming an external thread 12 on the side surface. Figure 2 As shown, the proximity sensor 100, in use, is secured to the mounting bracket E1, for example, via a double nut E2. 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 it would not otherwise detect. Therefore, the proximity sensor 100 according to an embodiment of the present invention is configured to suppress the effects of the embedded metal E, thereby substantially extending the detection distance.

[0038] In the following, reference will be made to Figures 3 to 5 1 and 2 to illustrate the main component structure of the proximity sensor 100. Figure 3 It is an exploded perspective view of the parts from the coil 20 to the substrate 50 that constitute the proximity sensor 100 . Figure 4 1 is an exploded perspective view of components housed in the housing 10 of the proximity sensor 100 . Figure 52 is a central longitudinal sectional view of the proximity sensor 100 .

[0039] like Figure 3 As illustrated, 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.

[0040] 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 the lead wire 23.

[0041] like Figure 3 and Figure 4 As illustrated, a plurality of (four in the illustrated example) lead wires 23 are provided from the coil 20. All of the plurality of lead wires 23 are arranged at positions that are not point-symmetrical with respect to the axis of the coil 20. In other words, all of the plurality of lead wires 23 are arranged at positions that do not face the axis of the coil 20 at 180°.

[0042] With this configuration, Figure 4 As illustrated, the plurality of lead wires 23 can be soldered together to one surface of the substrate 50. Therefore, the proximity sensor 100 can be easily manufactured by soldering the plurality of lead wires 23 together to one surface of the substrate 50. The plurality of lead wires 23 extend from the coil 20 through the gap between the ferrite core 30 and the core holder 40 to reach the substrate 50.

[0043] In addition to the sensor unit 25 , the proximity sensor 100 includes an electric shield 80 , a magnetic shield 90 and a housing 10 .

[0044] 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 in the sensor unit 25, and partially covers the substrate 50.

[0045] 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 in the sensor unit 25, and partially covers the substrate 50.

[0046] The housing 10 has a housing body 11 formed with an external thread 12. Figure 4 and Figure 5 As shown, the housing body 11 completely covers the magnetic shield 90, the electric shield 80 and the sensor unit 25. Figure 5 As shown in the example, the housing 10 further includes a housing base end 13 formed with a cable attachment port 14. The housing base end 13 is inserted into the housing body 11 from the substrate 50 side.

[0047] The proximity sensor 100 further includes a cable 19. The cable 19 is electrically connected to the substrate 50. The cable 19 extends from the inside of the housing 10 to the outside through the cable attachment port 14 of the housing base end 13.

[0048] In the following, reference will be made to Figure 6 The main circuit structure of the proximity sensor 100 will be described below. Figure 6 1 is a block diagram for explaining a main circuit configuration of the proximity sensor 100 .

[0049] like Figure 6 As shown, the proximity sensor 100 further includes a transmitting circuit 70 , a receiving circuit 60 , and a control circuit 76 as main circuit structures.

[0050] The transmitting circuit 70 periodically applies a pulsed excitation current to the coil 20. The coil 20 generates a magnetic field by causing the pulsed excitation current to flow periodically. The coil 20 includes a first coil 21 and a second coil 22. The second coil 22 is arranged on the outside of the first coil 21 in the radial direction. The second coil 22 can be arranged concentrically with the first coil 21. In this example, the “concentrically arranged” indication circle is not limited to the configuration relationship of objects on the same plane, and thus, when the second coil 22 is concentrically arranged relative to the first coil 21, the second coil 22 can be arranged on the side (or opposite side) where the detection object D is detected relative to the first coil 21.

[0051] When the detection object D is within the detection range, the magnetic field generated by coil 20 generates eddy currents in the detection object D. The eddy currents of the detection object D generate a magnetic field from the detection object D. Here, because the excitation current flowing through coil 20 is pulsed, the magnetic field generated by coil 20 is rapidly weakened. Consequently, the eddy currents of the detection object D are also weakened, and accordingly, the magnetic field generated from the detection object D is also weakened. To prevent the weakening of the magnetic field generated from the detection object D, a voltage or current is generated in coil 20.

[0052] The receiving circuit 60 detects the voltage or current generated in each of the first coil 21 and the second coil 22. Because the first coil 21 and the second coil 22 have different configurations, the characteristics of the generated voltage or current also differ. By detecting voltages or currents with different characteristics, the calculation operation for suppressing the influence of the embedded metal E becomes more efficient. Note that the receiving circuit 60 can be configured to detect the voltage or current generated in at least one of the first coil 21 and the second coil 22.

[0053] The control circuit 76 detects the detection object D based on the change in voltage or current detected by the receiving circuit 60. Preferably, the control circuit 76 detects the detection object D based on the change in voltage or current generated in each of the first coil 21 and the second coil 22. As a result, the proximity sensor 100 can substantially extend the detection distance by suppressing the influence of the embedded metal E.

[0054] exist Figure 6 In the illustrated example, the first coil 21 generates a magnetic field by periodically passing a pulsed excitation current from the transmitting circuit 70. In this embodiment, only the first coil 21 generates a magnetic field via the excitation current. However, the coil 20 generating a magnetic field via the excitation current may be only the second coil 22, or both coils 21 and 22. When applying an excitation current to only one of the first coil 21 and the second coil 22 to generate a magnetic field, it is preferable to apply the excitation current only to the first coil 21. As described above, the detection results using the first coil 21 differ from those using the second coil 22. However, to extend the detection distance, it is preferable that both detection results are easily affected by the detection object D. When the magnetic field generated by the coil 20 is directed toward a range where the detection object D can be located (that is, the detection range), the detection results using the coil 20 are easily affected by the detection object D. The coil 20 through which the excitation current flows is preferably wound close to the shaft 31 of the ferrite core 30. Because the generated magnetic field is more likely to be directed toward the detection range, the magnetic field generated by passing the excitation current through the first coil 21 is generated. In addition, when an excitation current is passed through both the first coil 21 and the second coil 22 to generate a magnetic field, for example, by directing the magnetic field of the first coil 21 toward the detection object D and directing the magnetic field of the second coil 22 toward the embedded metal E, a detection result can be obtained in which the magnetic fields of the first coil 21 and the second coil 22 interfere with each other and the influence of the embedded metal E is reduced.

[0055] exist Figure 6 In the illustrated example, the transmitting circuit 70, the receiving circuit 60, and the control circuit 76 are provided on the substrate 50. By providing the transmitting circuit 70, the receiving circuit 60, and the control circuit 76 on the substrate 50, the circuit structure is stabilized. The transmitting circuit 70, the receiving circuit 60, and the control circuit 76 are not limited to being provided on the substrate 50. For example, the transmitting circuit 70, the receiving circuit 60, and the control circuit 76 may be provided in different components. In addition, any one or two of the transmitting circuit 70, the receiving circuit 60, and the control circuit 76 may be provided on the substrate 50, and the other circuits may be provided on another substrate or component (a substrate or component arranged inside or outside the housing 10).

[0056] The receiving circuit 60 includes 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 temporal variation of the voltage or current detected by the receiving circuit 60 may be referred to as a received waveform. The temporal variation of the voltage or current detected by the first receiving circuit 61 and the second receiving circuit 62 may be referred to as a first received waveform and a second received waveform, respectively.

[0057] Because the receiving circuit 60 includes the first receiving circuit 61 and the second receiving circuit 62, there is no need 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 includes the first receiving circuit 61 and the second receiving circuit 62, it can 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 significantly extend the detection distance by improving detection accuracy.

[0058] In the following, reference will be made to Figure 7 The details of the transmission circuit 70, the reception circuit 60, and the control circuit 76 will be described. Figure 7 1 is a block diagram for explaining the main circuit configuration of the proximity sensor 100 in detail.

[0059] The transmission circuit 70 includes an excitation circuit 71 . The excitation circuit 71 generates a pulsed excitation current based on a signal from the control circuit 76 , and causes the pulsed excitation current to flow through the first coil 21 .

[0060] Control circuit 76 includes an arithmetic circuit 77 and an output circuit 78. Arithmetic circuit 77 performs an arithmetic operation for detecting object D based on at least one of the first and second received waveforms. Arithmetic circuit 77 performs an arithmetic operation based on both the first and second received waveforms. Output circuit 78 outputs the results of the arithmetic operation performed by arithmetic circuit 77 to the outside via cable 19. Arithmetic circuit 77 can be configured to perform an arithmetic operation for detecting object D based on at least one of the first and second received waveforms, and when performing an arithmetic operation based on only one of the first and second received waveforms, response speed is increased.

[0061] In the following, reference will be made to Figure 8A 、 Figure 8B 、 Figure 9A and Figure 9B To illustrate the images of the first reception waveform and the second reception waveform. Figures 8A to 9B, the first reception waveform is represented by symbol R1, and the second reception waveform is represented by symbol R2.

[0062] Figure 8A : is a graph illustrating an image of a reception waveform in a case where there is no embedded metal E and the detection object D is not within the detection range. Figure 8B : is a graph illustrating an image of a reception waveform in a case where there is no embedded metal E and the detection object D is within the detection range. Figure 9A : is a graph illustrating an image of a reception waveform in a case where the embedded metal E is present and the detection object D is not within the detection range. Figure 9B is a graph illustrating an image of a reception waveform in a case where there is an embedded metal E and the detection object D is within the detection range. Figures 8A to 9B In the graph of , the horizontal axis represents time, and the vertical axis represents the signal strength of the received waveform.

[0063] Figure 8A and Figure 8B is a graph in the absence of embedded metal E. Figure 8A As illustrated, when the detection object D is not within the detection range, the proximity sensor 100 itself is slightly detected, so that the first reception waveform and the second reception waveform reflecting the detection appear. Figure 8B As illustrated, when object D is within the detection range, the object D is detected, and thus both the amount of change in the first received waveform and the amount of change in the second received waveform are greater than when object D is not within the detection range. In particular, the first received waveform, which is more susceptible to the influence of object D than the second received waveform, has a greater amount of change than the second received waveform.

[0064] Figure 9A and Figure 9B is a graph in the presence of embedded metal E. Figure 9A As illustrated, when the detection object D is not within the detection range, the embedded metal E is detected, so that both the change amount of the first reception waveform and the change amount of the second reception waveform are greater than when the detection object D is not within the detection range. Figure 8A The two changes in the case where the embedded metal E is present and the detection object D is not within the detection range. In particular, the second reception waveform, which is more susceptible to the influence of the embedded metal E than the first reception waveform, has a larger change than the first reception waveform. Figure 9BAs illustrated, even when object D is within the detection range, object D is detected, resulting in both the amount of change in the first received waveform and the amount of change in the second received waveform being greater than when object D is not within the detection range. In particular, the first received waveform, which is more susceptible to the influence of object D than the second received waveform, has a greater difference in amount of change than the second received waveform relative to the amount of change when object D is not within the detection range.

[0065] Although the first reception waveform is more susceptible to the influence of the detection object D than the second reception waveform, Figure 9A and Figure 9B In the case of the presence of embedded metal E, as shown in the example Figure 8A and Figure 8B Compared to the case where the embedded metal E does not exist as illustrated, the difference in the amount of change in the waveform depending on whether the detection object D is within the detection range is small. In particular, the longer the distance between the detection object D and the coil 20, the smaller the difference in the amount of change in the waveform caused by whether the detection object D is within the detection range. However, as Figures 8A to 9B As illustrated, the first received waveform is more susceptible to the influence of the detection object D than the second received waveform, while the second received waveform is more susceptible to the influence of embedded metal E than the first received waveform. Furthermore, the difference in the amount of change in the second received waveform has a different trend than that of the first received waveform. More specifically, in the second received waveform, the difference in the amount of change due to the presence or absence of the detection object D within the detection range is smaller than that in the first received waveform, while the difference in the amount of change due to the presence or absence of embedded metal E is greater than that in the first received waveform. Therefore, through calculations based on both the first and second received waveforms, the detection object D is efficiently detected while suppressing the influence of embedded metal E.

[0066] In the following, reference will be made to Figure 10A 、 Figure 10B 、 Figure 11A and Figure 11B The first reception waveform and the second reception waveform that have undergone zeroing are shown in FIG. Figures 10A to 11B , the first reception waveform subjected to zero adjustment is indicated by symbol ΔR1 , and the second reception waveform subjected to zero adjustment is indicated by symbol ΔR2 .

[0067] Figure 10A 3 is a graph illustrating an image of a reception waveform after zero adjustment when there is no embedded metal E and the detection object D is not within the detection range. Figure 10B 3 is a graph illustrating an image of a reception waveform after zero adjustment when there is no embedded metal E and the detection object D is within the detection range. Figure 11A3 is a graph illustrating an image of a reception waveform after zero adjustment when an embedded metal E is present and the detection object D is not within the detection range. Figure 11B is a graph illustrating an image of a reception waveform subjected to zeroing in a case where an embedded metal E exists and a detection object D is within the detection range. Figures 10A to 11B In the graph of , the horizontal axis represents time, and the vertical axis represents the signal strength of the received waveform.

[0068] Figure 10A and Figure 10B is a graph in the absence of embedded metal E. Figure 10A As illustrated, when the detection object D is not within the detection range, the measurement value is calibrated to 0 (zero adjustment), so that the zero-adjusted first reception waveform and the second reception waveform do not appear. Figure 10B As illustrated, when a detection object D is within the detection range, detection of the detection object D causes both the amount of change in the first received waveform that has undergone zeroing and the amount of change in the second received waveform that has undergone zeroing to increase. In particular, the first received waveform that has undergone zeroing, which is more susceptible to the influence of the detection object D than the second received waveform that has undergone zeroing, has a greater amount of change than the second received waveform that has undergone zeroing.

[0069] Figure 11A and 11B is a graph in the presence of embedded metal E. Figure 11A As illustrated, when the detection object D is not within the detection range, the embedded metal E is detected, causing both the variation of the first reception waveform that has undergone zeroing and the variation of the second reception waveform that has undergone zeroing to increase. In particular, the second reception waveform that has undergone zeroing, which is more susceptible to the influence of the embedded metal E than the first reception waveform that has undergone zeroing, has a larger variation than the first reception waveform that has undergone zeroing. Figure 11B As illustrated, even when the object D is within the detection range, the object D is detected, so that both the amount of change in the first reception waveform that has undergone zeroing and the amount of change in the second reception waveform that has undergone zeroing are greater than those in the case where the object D is not within the detection range. In particular, in the first reception waveform that has undergone zeroing, which is more susceptible to the influence of the object D than the second reception waveform that has undergone zeroing, the difference in amount of change relative to the amount of change in the case where the object D is not within the detection range is greater than that in the second reception waveform that has undergone zeroing.

[0070] like Figures 10A to 11BAs illustrated, the first received waveform that has undergone zeroing is susceptible to the influence of the detection object D, and the second received waveform that has undergone zeroing is susceptible to the influence of the embedded metal E. Therefore, by performing arithmetic operations based on both the first received waveform that has undergone zeroing and the second received waveform, the detection object D can be efficiently detected while suppressing the influence of the embedded metal E.

[0071] The calculation operation is, for example, the difference between the first reception waveform and the second reception waveform that have undergone zero adjustment. The difference is obtained by subtracting the second reception waveform that has undergone zero adjustment from the first reception waveform that has undergone zero adjustment (ΔR1 - ΔR2).

[0072] In the following, reference will be made to Figure 12 The sizes and arrangements of the first coil 21 and the second coil 22 will be described in detail. Figure 12 1 and 2 are diagrams illustrating the sizes and arrangements of the first coil 21 and the second coil 22 .

[0073] like Figure 12 As illustrated, the radial direction of the first coil 21 and the radial direction of the second coil 22 are the same direction ( Figure 12 Therefore, hereinafter, the radial direction of the first coil 21 or the second coil 22 may be simply referred to as the radial direction.

[0074] The axial direction of the first coil 21 and the axial direction of the second coil 22 are the same direction ( Figure 12 Therefore, hereinafter, the axial direction of the first coil 21 or the second coil 22 may be referred to simply as the axial direction. Figure 12 in the left-right direction) and the axial direction ( Figure 12 The up and down directions in the image are orthogonal to each other.

[0075] Hereinafter, in the axial direction, the side ( Figure 12 The upper side in the figure) can be called the distal side, and the side opposite to the distal side ( Figure 12 The lower side in the figure can be called the proximal side.

[0076] The second coil 22 is shorter than the first coil 21 in a direction (axial direction) orthogonal to its radial 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). Since the axial length L2 of the second coil 22 is shorter than the axial length L1 of the first coil 21, the magnetic flux lines passing through the embedded metal E are reduced. Therefore, the proximity sensor 100 can fully extend the detection distance by suppressing the influence of the embedded metal E. In addition, through such a structure, the second coil 22 has a lower sensitivity to magnetic flux relative to the first coil 21. According to the detection result of the second coil 22, it is preferable to reduce the influence of the magnetic flux passing through both the detection object D and the embedded metal E. By reducing the sensitivity of the second coil 22 to magnetic flux relative 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.

[0077] The second coil 22 is located on the side (distal side) that detects the detection object D relative to the first coil 21. Specifically, the second coil 22 is located a predetermined distance ΔL distal to the first coil 21. Because the second coil 22 is located distal to the first coil 21, the magnetic flux lines passing through the embedded metal E are reduced. Therefore, the proximity sensor 100 can significantly extend the detection distance by suppressing the influence of the embedded metal E.

[0078] The second coil 22 is preferably located on the distal side because the magnetic flux lines passing through the embedded metal E decrease as the second coil 22 is located further distally. Therefore, it is more preferable that the second coil 22 abuts against the member on the distal side of the proximity sensor 100 .

[0079] In the following, reference will be made to Figure 13A and Figure 13B to illustrate the magnetic field and its flux lines. Figure 13A This is a central longitudinal sectional view in a state where the influence of the embedded metal E is slightly suppressed. Figure 13B This is a central longitudinal sectional view in a state where the influence of the embedded metal E is further suppressed.

[0080] like Figure 13A and Figure 13B As shown, the core holder 40 holds the ferrite core 30 and positions the second coil 22. When the core holder 40 positions the second coil 22, the configuration of the second coil 22 is stable regardless of the ferrite core 30. With the configuration of the second coil 22 stable, the second received waveform is stably detected. Therefore, the proximity sensor 100 can significantly extend the detection distance by suppressing the influence of the embedded metal E.

[0081] The core holder 40 preferably has a structure for fixing the substrate 50. By fixing the substrate 50 with the core holder 40, the positioning accuracy between the substrate 50 and the coil 20 is improved, and the proximity sensor 100 can be easily manufactured in a space-saving manner. The core holder 40 is made of resin, for example.

[0082] Next, in comparison Figure 13A and Figure 13B At the same time, the magnetic flux lines of the magnetic field received by the coil 20 are described.

[0083] exist Figure 13A and Figure 13B , the magnetic flux lines received only by the first coil 21 are indicated by the thick line of symbol A, the magnetic flux lines received only by the second coil 22 are indicated by the dotted line of symbol B, and the magnetic flux lines received by both the first coil 21 and the second coil 22 are indicated by the dotted line of symbol C.

[0084] The magnetic flux lines received only by the first coil 21 (bold line: symbol A) have a high rate of generating a received waveform based on the detection object D. The magnetic flux lines received only by the second coil 22 (dashed line: symbol B) have a high rate of generating a received waveform based on the embedded metal E. The magnetic flux lines received by both the first coil 21 and the second coil 22 (dotted line: symbol C) have a high rate of generating a received waveform based on both the detection object D and the embedded metal E.

[0085] Therefore, by reducing the magnetic flux lines received by both the first coil 21 and the second coil 22 (dotted line: symbol C), the respective ratios of the reception waveform based on the detection object D and the reception waveform based on the embedded metal E are relatively increased. When the ratio between the reception waveform based on the detection object D and the reception waveform based on the embedded metal E is increased, the reception waveform based on the embedded metal E can be easily grasped, which reduces the influence of the embedded metal E.

[0086] and Figure 13A In comparison, Figure 13B In the embodiment, the magnetic flux lines (dotted lines: symbol C) received by both the first coil 21 and the second coil 22 form a path that avoids the embedded metal E. Therefore, in Figure 13B In the figure, the magnetic flux lines (dotted lines: symbol C) received by both the first coil 21 and the second coil 22 are Figure 13A In order to achieve Figure 13B In the illustrated state, the magnetic shield 90 and the ferrite core 30 are appropriately provided.

[0087] like Figure 13BAs illustrated, by appropriately configuring the magnetic shield 90 , the magnetic flux lines (dotted lines: symbol C) received by both the first coil 21 and the second coil 22 form a path that further avoids the embedded metal E. This is because the magnetic shield 90 guides the magnetic flux lines with a certain degree or greater relative magnetic permeability.

[0088] By forming the ferrite core 30 into an appropriate shape, the magnetic flux lines (dotted lines: symbol C) received by both the first coil 21 and the second coil 22 form a path that further avoids the embedded metal E. This is because the shape of the ferrite core 30 causes the magnetic flux lines to face further toward the distal end side.

[0089] In the following, reference will be made to Figure 13B and Figure 14 The magnetic shield 90 will be described in detail. Figure 14 It is used to explain in detail Figure 4 An exploded perspective view of the illustrated magnetic shield 90 .

[0090] like Figure 13B As shown, the magnetic shield 90 is arranged radially outward from the second coil 22. With this configuration, 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 obtaining a path that further avoids the embedded metal E. Therefore, the proximity sensor 100 can substantially extend the detection distance by suppressing the influence of the embedded metal E.

[0091] In the proximity sensor 100, the magnetic shield 90 is preferably oriented radially outward. This is because the magnetic flux lines (dotted lines: symbol C) received by both the first coil 21 and the second coil 22 are directed in a direction that further avoids the embedded metal E. For example, the magnetic shield 90 is arranged radially outward from the electric shield 80 (and inside the housing 10). The magnetic shield 90 may constitute the housing 10.

[0092] like Figure 14 As shown, the magnetic shield 90 includes a sheet member kneaded with ferromagnetic powder 91. Since the magnetic shield 90 is formed from a sheet member kneaded with ferromagnetic powder 91, it has a relative magnetic permeability that is higher (to a certain extent or greater) than that of air and a low electrical conductivity. The magnetic shield 90 appropriately guides the magnetic flux lines with a relative magnetic permeability higher than that of air. The low electrical conductivity of the magnetic shield 90 makes it possible to suppress eddy current loops in the magnetic shield 90 without performing insulation treatment. By suppressing the eddy current loops, noise affecting the received waveform is suppressed. Therefore, the proximity sensor 100 including such a magnetic shield 90 can significantly extend the detection distance by improving the detection accuracy.

[0093] The ferromagnetic powder 91 that constitutes the magnetic shield 90 is, for example, iron powder. Since the magnetic shield 90 is formed from a sheet member kneaded from the iron powder, it has a relatively high relative magnetic permeability (approximately 200 to 300). The sheet member kneaded from the iron powder is, for example, an electromagnetic wave absorbing sheet. In this example, a sheet member kneaded from the ferromagnetic powder 91 is used as the magnetic shield 90, but the entire magnetic shield 90 may be an amorphous ferromagnetic member. For example, the magnetic shield 90 may be amorphous.

[0094] Note that permalloy sheets or cobalt sheets are not suitable as magnetic shield 90. This is because permalloy sheets or cobalt sheets have high relative magnetic permeability (approximately 1000 to tens of thousands), but high electrical conductivity, which generates eddy current loops.

[0095] The magnetic shield 90 is wrapped around the outer circumference of a bottomed cylindrical resin cap 95. Resin cap 95 protects the components housed within it. The magnetic shield 90 is wrapped around the outer circumference of resin cap 95, thereby stabilizing the radially outer configuration. Instead of resin cap 95, a cap other than resin may be used. Regardless of whether the cap is made of resin, the magnetic shield 90 is positioned outside the cap.

[0096] In the following, reference will be made to Figures 14 to 16 The details of the electric shield 80 will be described. The electric shield 80 is a bottomed cylindrical metal body that protects the coil 20 and the ferrite core 30 from external noise.

[0097] like Figure 14 As shown, the electric shield 80 is arranged radially outward from the second coil 22. A cutout 81 (slit) is formed in the electric shield 80. The cutout 81 is transverse to a direction 88 around the axis of the electric shield 80. Specifically, the longitudinal direction of the cutout 81 intersects (preferably is perpendicular to) the direction 88 around the axis.

[0098] Because the cutouts 81 intersect the direction 88 around the axis of the electric shield 80, the circulation of eddy currents, which are currents flowing around the axis, is suppressed within the electric shield 80. By suppressing the eddy current loops, noise in the received waveform is suppressed. Therefore, a proximity sensor 100 including such an electric shield 80 can significantly extend the detection range by improving detection accuracy.

[0099] The electric shield 80 includes 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 for detecting the detection object D. The detection surface portion 87 closes the distal end side, which is one end of the peripheral portion 84.

[0100] The cutout 81 includes a peripheral cutout 82 and a detection surface cutout 83. The peripheral cutout 82 is formed in the peripheral portion 84. The detection surface cutout 83 is formed in the detection surface portion 87.

[0101] The peripheral cutout 82 suppresses an eddy current loop in the peripheral portion 84. The peripheral cutout 82 facilitates the manufacture of the electric shield 80. The detection surface cutout 83 effectively suppresses an eddy current loop in the detection surface portion 87.

[0102] The electric shield 80 has a sheet metal structure. That is, the electric shield 80 is obtained by bending a thin metal plate. Since the electric shield 80 has a sheet metal structure, even if the strength is reduced by the cutouts 81, the shape is stable.

[0103] exist Figure 15 and Figure 16 exemplified in FIG. 8 is a thin metal plate before being bent as the electric shield 80 . Figure 15 1 is a developed view of the electric shield 80 . Figure 16 The shape of the detection surface cutout 83 is Figure 15 Developed view of the electric shield 80 with different shapes of the detection surface cutout 83 .

[0104] like Figure 15 and Figure 16 As illustrated, a thin metal plate is punched before being bent as an electric shield 80. The thin metal plate is stamped so that the cutouts 81 are also formed at the same time. The electric shield 80 has a shape obtained by pressing the punched thin metal plate. Figure 14 The illustrated three-dimensional shape is a bottomed cylindrical shape. That is, the electric shield 80 is a pressed, formed product of a thin metal plate. Even if the strength is reduced by the cutouts 81, the shape of the electric shield 80 is further stabilized. The thin metal plate constituting the electric shield 80 is, for example, copper foil or brass foil.

[0105] The peripheral portion 84 has a left semi-peripheral portion 85 and a right semi-peripheral portion 86. The left semi-peripheral portion 85 and the right semi-peripheral portion 86 are connected to the detection surface portion 87 from the left and right sides, respectively. The left semi-peripheral portion 85 and the right semi-peripheral portion 86 are bent in a manner perpendicular to the detection surface portion 87. In addition, the left semi-peripheral portion 85 and the right semi-peripheral portion 86 are subjected to roller bending and pressing in a manner such that the edges on the side close to the detection surface portion 87 are along the edges of the detection surface portion 87.

[0106] The peripheral cutout 82 is a gap between the left half peripheral portion 85 and the right half peripheral portion 86. The detection surface cutout 83 is a radial gap extending from the center of the detection surface portion 87.

[0107] exist Figure 15 In the example illustrated, in Figure 15In the clock position where the upward direction is 0:00 o'clock, the radial gaps extending in the directions of 0:00 o'clock, 3:00 o'clock, 6:00 o'clock, and 9:00 o'clock pass through the center of the detection surface 87 without reaching the edge of the detection surface 87. The radial gaps extending in the directions between 1:00 o'clock and 2:00 o'clock, between 4:00 o'clock and 5:00 o'clock, between 7:00 o'clock and 8:00 o'clock, and between 10:00 o'clock and 11:00 o'clock do not pass through the center of the detection surface 87 but reach the edge of the detection surface 87.

[0108] exist Figure 16 In the illustrated example, radial gaps extending in the directions between 0:00 and 6:00 o'clock do not pass through the center of the detection face 87 but reach the edge of the detection face 87. Linear gaps extending in the directions between 3:00 and 9:00 o'clock pass through the center of the detection face 87 and do not reach the edge of the detection face 87. Radial gaps extending in the directions between 1:00 and 2:00 o'clock, between 4:00 and 5:00 o'clock, between 7:00 and 8:00 o'clock, and between 10:00 and 11:00 o'clock do not pass through the center of the detection face 87 and do not reach the edge of the detection face 87.

[0109] Figure 15 and Figure 16 The electric shield 80 shown in FIG. 1 and FIG. 2 both equally suppress eddy current loops. Figure 16 The illustrated electric shield 80 is Figure 15 The path of the current is shorter than that of the conventional MOSFET, so the resistance is reduced, thereby improving the resistance to external noise.

[0110] The electric shield 80 is not limited to a sheet metal structure. For example, the electric shield 80 may be a coating molded product or a vapor deposition molded product. Coating molded products or vapor deposition molded products are formed by coating or vapor depositing a conductive material on a bottomed cylindrical resin mold.

[0111] In the following, reference will be made to Figures 17 to 20 The ferrite core 30 will be described in detail. Figure 17 It is a central longitudinal sectional view of the first coil 21 and the ferrite core 30 . Figure 18 is a graph illustrating the results of electromagnetic field simulation. Figure 19 This is a magnetic flux diagram when the shaft 31 of the ferrite core 30 is thin. Figure 20 This is a magnetic flux diagram when the shaft 31 of the ferrite core 30 is not thin.

[0112] like Figure 17As illustrated, the ferrite core 30 has an axial body 31. The axial body 31 passes through the hollow portion of the first coil 21. Hereinafter, the ratio of the width w of the axial body 31 to the entire width W of the ferrite core 30 in the radial direction may be referred to as a relative axial width w / W.

[0113] In order to understand the relationship between the relative axis width w / W and the influence of the embedded metal E, electromagnetic field simulations have been performed under the following conditions.

[0114] As a condition for electromagnetic field simulation, the entire width W (outer diameter) of the ferrite core 30 in the radial direction has been set to 7 mm. The width w of the shaft body 31 in the radial direction has been set to the following seven modes. Specifically, the width w of the shaft body 31 in the radial direction has been set to 3.5 mm, 3 mm, 2.5 mm, 2 mm, 1.5 mm, 1 mm and 0.5 mm. In each of these seven modes, the intensity ratio Vd / Ve has been calculated by dividing the signal intensity Vd of the received waveform based on the detection object D by the signal intensity Ve of the received waveform based on the embedded metal E. Note that the signal intensities Vd and Ve of the respective received waveforms are the voltages at both ends of the coil 20.

[0115] exist Figure 18 The results of electromagnetic field simulation are shown in . Figure 18 In the illustrated graph, the horizontal axis represents the relative axis width w / W, and the vertical axis represents the intensity ratio Vd / Ve. Figure 18 As is clear from the graph illustrated in FIG, as the relative axial width w / W decreases, the intensity ratio Vd / Ve increases. However, when the relative axial width w / W has decreased to a certain extent, the intensity ratio Vd / Ve has leveled off.

[0116] In particular, when the relative axial width w / W is already 30% or less, the intensity ratio Vd / Ve is already 1 or greater. That is, when the relative axial width w / W is already 30% or less, the signal intensity Vd based on the received waveform of the detection object D is already equal to or greater than the signal intensity Ve based on the received waveform of the embedded metal E.

[0117] When the relative axial width w / W is less than 15%, the strength ratio Vd / Ve becomes flat. Furthermore, when the relative axial width w / W is less than 15%, it becomes difficult to manufacture the ferrite core 30. In other words, when the relative axial width w / W is 15% or greater, the strength ratio Vd / Ve is high, making manufacturing easier.

[0118] When the intensity ratio Vd / Ve is high, the signal intensity Vd of the received waveform based on the detection object D becomes relatively high. In other words, when the intensity ratio Vd / Ve is high, the signal intensity Ve of the received waveform based on the embedded metal E becomes relatively low. Therefore, since the relative axis width w / W is 30% or less, the proximity sensor 100 can substantially extend the detection distance by suppressing the influence of the embedded metal E. Furthermore, since the relative axis width w / W is 15% or greater, the proximity sensor 100 can substantially extend the detection distance and can be easily manufactured.

[0119] From the results of electromagnetic field simulation, it can be considered that the relative axial width w / W is preferably 30% or less, and more preferably equal to or greater than 15% and less than or equal to 30%.

[0120] Then, in Figure 19 and Figure 20 , which illustrates magnetic flux lines in an electromagnetic field simulation. Figure 19 The case where the width w of the shaft body 31 in the radial direction is 1.5 mm is exemplified, and Figure 20 A case where the width w of the shaft body 31 in the radial direction is 3 mm is exemplified.

[0121] exist Figure 19 In the illustrated example, since the width w of the shaft body 31 in the radial direction is 1.5 mm and the width W of the entire ferrite core 30 is 7 mm, the relative shaft width w / W is 21.4%. That is, the relative shaft width w / W is 30% or less. Figure 19 As illustrated, three magnetic flux lines m1 to m3 pass through the embedded metal E.

[0122] On the other hand, Figure 20 In the example shown, since the width w of the shaft body 31 in the radial direction is 3 mm and the width W of the entire ferrite core 30 is 7 mm, the relative shaft width w / W is 42.9%. That is, the relative shaft width w / W is greater than 30%. Figure 20 As illustrated, four magnetic flux lines M1 to M4 pass through the embedded metal E.

[0123] from Figure 19 and Figure 20 The comparison between the two clearly shows that when the relative axis width w / W is 30% or less Figure 19 In the case of the embedded metal E, the number of magnetic flux lines passing through it is as small as 3, while in the case of the relative axis width w / W being greater than 30%, the number of magnetic flux lines passing through the embedded metal E is as small as 3. Figure 20 In the example, the number of magnetic flux lines passing through the embedded metal E is as large as 4. Therefore, according to Figure 19 and Figure 20, it can be considered that when the relative axis width w / W is 30% or less, the influence of the embedded metal E is suppressed.

[0124] The embodiments are illustrative in all respects and are non-restrictive. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning equivalent to the claims and the scope thereof. Among the structures described in the embodiments, structures other than those described as aspects of the present invention in the "means for solving the problem" are arbitrary structures and can be deleted or modified as appropriate.

[0125] (1) In the embodiment, the magnetic shield 90 and the electric shield 80 are exemplified as cylindrical shapes, but may have other shapes such as a square tube shape.

[0126] (2) Although the mounting bracket E1 and the double nut E2 are described as the embedded metal E embedded in the proximity sensor 100, other metals may be used. Other metals include a single nut or a metal block with an internal thread. The embedded metal E is simply the metal embedded in the proximity sensor 100 and is not a structure of the proximity sensor 100 itself.

[0127] (3) In the embodiment, the transmitting circuit 70 is illustrated as one, but the transmitting circuit 70 may include a first transmitting circuit that periodically applies a pulsed excitation current to the first coil 21 and a second transmitting circuit that periodically applies a pulsed excitation current to the second coil 22.

[0128] The present invention provides a proximity sensor and has industrial applicability.

Claims

1. A proximity sensor, comprising: a coil for generating a magnetic field by an excitation current; a sending circuit, configured to periodically apply a pulsed excitation current to the coil; as well as a ferrite core for guiding the magnetic field generated from the coil, Wherein, the coil comprises: a first coil; and a second coil, which is arranged concentrically with the first coil, The proximity sensor further includes: a receiving circuit for detecting a voltage or a current generated in at least one of the first coil and the second coil by a magnetic field changed by a detection object; a control circuit, configured to detect the detection object based on a change in voltage or current detected by the receiving circuit; and an electric shield having a bottomed cylindrical shape, which is arranged outside the second coil in the radial direction, The electric shielding member comprises: a peripheral portion that covers the second coil from an outer side in a radial direction of the second coil; and detecting a face located on a side of the detection object, wherein a cutout is formed in the detection surface portion and the peripheral portion, the cutout being transverse to a direction around the axis of the electric shield; and The electric shield is a pressed product of a stamped thin metal plate in a sheet metal structure.

2. The proximity sensor according to claim 1, wherein The receiving circuit detects a voltage or a current generated in each of the first coil and the second coil by a magnetic field changed by the detection object, and The control circuit detects the detection target based on changes in voltage or current generated in each of the first coil and the second coil detected by the receiving circuit.

3. The proximity sensor according to claim 1, wherein The second coil is arranged outside the first coil in a radial direction, and The first coil generates the magnetic field by periodically allowing the pulsed excitation current to flow from the transmission circuit. 4 . The proximity sensor according to claim 1 , further comprising a substrate on which the transmitting circuit, the receiving circuit, and the control circuit are provided. The proximity sensor according to claim 2 , wherein: The receiving circuit includes: a first receiving circuit for detecting a voltage or a current generated in the first coil; and The second receiving circuit is configured to detect a voltage or a current generated in the second coil. The proximity sensor according to claim 5 , wherein: The control circuit detects the detection object based on a difference between a voltage or current detected by the first receiving circuit and a voltage or current detected by the second receiving circuit.

7. The proximity sensor according to claim 1, wherein The second coil is shorter than the first coil in a direction orthogonal to a radial direction of the second coil. The proximity sensor according to claim 1 , wherein: The second coil is located closer to a side where the detection object is detected than the first coil.

9. The proximity sensor according to claim 1, further comprising: a core holder for holding the ferrite core, wherein the core holder positions the second coil. 10 . The proximity sensor according to claim 1 , further comprising a magnetic shield arranged outside the second coil in a radial direction. The proximity sensor according to claim 10 , wherein: The magnetic shield includes a sheet member kneaded with ferromagnetic powder.

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

13. The proximity sensor according to claim 12, wherein: A ratio of a width of the shaft relative to an entire width of the ferrite core in a radial direction of the first coil is 15% or more.

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