Proximity sensor

Abstract

Provided is a proximity sensor capable of sufficiently extending a detection distance by suppressing the influence of an embedded metal. The coils of the proximity sensor include a first coil and a second coil. The second coil is arranged concentrically with the first coil. The proximity sensor detects a detection object based on a change in voltage or current generated in each of the first coil and the second coil. A coil wire of the first coil is electrically connected to the in-head substrate by direct bonding.

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 ferrite core, a head shell and an inner-head substrate. The coil generates a magnetic field by an excitation current. The ferrite core guides the magnetic field generated from the coil. The head shell accommodates the coil and the ferrite core. The inner-head substrate is accommodated in the head shell. 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 transmitting circuit, a receiving circuit and a control circuit. The transmitting circuit periodically applies a pulsed excitation current to the coil. The receiving circuit detects the voltage or current generated in each of the first coil and the second coil by the magnetic field changed by the detection object. The control circuit detects the detection object based on the change in voltage or current generated in at least one of the first coil and the second coil detected by the receiving circuit. The coil wire of the first coil is electrically connected to the inner-head substrate by direct bonding.

[0008] According to another aspect of the present invention, a proximity sensor includes a coil, a ferrite core, a head housing, a cable, and an amplifier housing. The coil generates a magnetic field by an excitation current. The ferrite core guides the magnetic field generated by the coil. The head housing accommodates the coil and the ferrite core. The cable extends from the head housing. The amplifier housing is connected to the head housing via a cable. 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 transmitting circuit, a receiving circuit, and a control circuit. The transmitting circuit periodically applies a pulsed excitation current to the coil. The receiving circuit detects a voltage or current generated in at least one of the first coil and the second coil by a magnetic field changed 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. The coil wire of the first coil is electrically connected to the cable by direct bonding.

[0009] According to another aspect of the present invention, a proximity sensor includes a coil, a ferrite core, and a head housing. The coil generates a magnetic field by an excitation current. The ferrite core guides the magnetic field generated by the coil. The head housing accommodates the coil and the ferrite core. The coil includes a first coil and a second coil. The second coil is arranged on the outside of the first coil in the radial direction. The proximity sensor also includes a transmitting circuit, a receiving circuit, and a control circuit. The transmitting circuit periodically applies a pulsed excitation current to the coil. The receiving circuit detects the voltage or current generated in each of the first coil and the second coil by the magnetic field changed by the detection object. The control circuit detects the detection object based on the change in voltage or current generated in at least one of the first coil and the second coil detected by the receiving circuit. In the head housing, the diameter of the surface facing the detection object is less than 8 mm. The number of windings of the first coil is 100 or more.

[0010] 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

[0011] Figure 1 This is the appearance diagram of the proximity sensor;

[0012] Figure 2 This is the appearance of the proximity sensor in use;

[0013] Figure 3 is a perspective view illustrating a bonding state between a coil wire and a substrate electrode;

[0014] Figure 4 It is along Figure 3 a cross-sectional view taken along line IV-IV;

[0015] Figure 5 is a diagram illustrating the wiring of the coil wire from the first coil to the substrate electrode;

[0016] Figure 6 is a diagram illustrating the wiring of the coil wire from the second coil to the substrate electrode;

[0017] Figure 7 This is an exploded perspective view from the coil that makes up the proximity sensor to the substrate inside the head;

[0018] Figure 8 is an exploded perspective view of components housed in a head housing of a proximity sensor;

[0019] Figure 9 This is a block diagram illustrating the main circuit structure of a proximity sensor.

[0020] Figure 10 is a diagram schematically illustrating magnetic flux lines around a first coil and a second coil;

[0021] Figure 11 It is an exploded perspective view for explaining the electric shield and the magnetic shield in detail;

[0022] Figure 12 is the flux diagram when the ferrite core has a thin axis; and

[0023] Figure 13 This is a magnetic flux diagram when the axis of the ferrite core is not thin. Specific embodiments

[0024] 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.

[0025] Hereinafter, a proximity sensor 100 according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0026] 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.

[0027] like Figure 1 As shown, 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. The external thread 12 is formed on the outer surface of the housing body 11 of the head housing 10 arranged near the detection object. The head housing 10 is made of metal and has a head front portion 11a ( Figure 1 If the head front portion 11a is made of metal, the proximity sensor 100 is less likely to be damaged even if the head front portion 11a comes into contact with an object in the surrounding environment such as a detection object.

[0028] In this embodiment, the head housing 10 has a cylindrical shape, and the head front portion 11a has a circular shape. The diameter of the head housing 10 of this embodiment is small (small diameter). For example, the diameter of the head front portion 11a (the surface facing the detection object) is less than 8mm.

[0029] Inside the head housing 10, a coil 20 for generating a magnetic field and an in-head substrate 50 electrically connected to the coil 20 are arranged. The proximity sensor 100 of this embodiment uses metal as a detection object. By receiving the magnetic field generated by the coil 20, eddy currents are induced in the metal detection object. The proximity sensor 100 detects the magnetic field (magnetic flux) generated by the eddy currents generated in the detection object.

[0030] The head inner substrate 50 is electrically connected to the cable 19. The cable 19 extends from the inside of the head housing 10 through the head base end 13 to the outside of the head housing 10. The cable 19 is connected to the amplifier housing 200. The amplifier housing 200 houses an amplifier unit 210. The amplifier unit 210 amplifies the electrical signal sent from the coil 20 through the cable 19 and sends the amplified electrical signal to an external device (such as a computer). In addition, the amplifier unit 210 supplies power to the coil 20 through the cable 19 to operate the coil 20.

[0031] like Figure 2 As shown, the proximity sensor 100 is secured to the mounting bracket E1 using, for example, 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.

[0032] In the following, reference will be made to Figure 3 、 Figure 4 、 Figure 5 and Figure 6 The structures of the coil 20 and the intra-head substrate 50 will be described. Figure 3It is a perspective view illustrating a joining state between the coil wires 21 a and 22 a and the substrate electrode 50 a . Figure 4 It is along Figure 3 A cross-sectional view taken along line IV-IV. Figure 5 1 is a diagram illustrating the wiring of the coil wire 21 a from the first coil 21 to the substrate electrode 50 a . Figure 6 : is a diagram illustrating the wiring of the coil wire 22a from the second coil 22 to the substrate electrode 50a. Note that Figure 5 One surface 50B of the head inner substrate 50 is illustrated, and Figure 6 The other surface 50F of the intra-head substrate 50 is illustrated.

[0033] Figure 3 、 Figure 4 、 Figure 5 and Figure 6 Example Figure 1 The coil 20 and the head inner substrate 50 are housed in the head shell 10 of the proximity sensor 100. The proximity sensor 100 includes the coil 20, the ferrite core 30, the core holder 40 and the head inner substrate 50. The coil 20, the ferrite core 30, the core holder 40 and the head inner substrate 50 are all housed in the head shell 10. Hereinafter, the coil 20, the ferrite core 30, the core holder 40 and the head inner substrate 50 may be collectively referred to as the sensor unit 25.

[0034] The coil 20 generates a magnetic field via an excitation current. The ferrite core 30 guides the magnetic field generated by the coil 20. The coil 20 includes a first coil 21 and a second coil 22. The second coil 22 is arranged radially outward from the first coil 21. The second coil 22 can be arranged concentrically with the first coil 21. In this example, "concentrically arranged" indicates that the arrangement of circles is not limited to objects on the same plane. Therefore, when the second coil 22 is arranged concentrically with respect to the first coil 21, the second coil 22 can be arranged on the side (or opposite side) of the first coil 21 that detects the detection object D. The first coil 21 is constructed by winding a coil wire 21a. The second coil 22 is constructed by winding a coil wire 22a. The magnetic field generated by the coil 20 is preferably directed toward the detection object. Because the ferrite core 30 includes a shaft 31 and the shaft 31 points toward the detection object, the magnetic field generated near the shaft 31 is easily guided toward the detection object. Therefore, it is preferable that the first coil 21, which is arranged closer to the shaft 31 than the second coil 22, generates a magnetic field via the excitation current. Note that the ferrite core 30 in this embodiment includes the shaft 31 around which the first coil 21 is wound, and a peripheral wall (outer peripheral portion) made of a magnetic material located between the first coil 21 and the second coil 22, but the ferrite core 30 may include only the shaft 31. Alternatively, the shaft 31 may be made of a magnetic material other than ferrite. Furthermore, since the magnetic field itself is generated even without the ferrite core 30, the proximity sensor 100 may have a structure without the ferrite core 30.

[0035] In order to ensure sufficient inductance, the number of windings of the first coil 21 is preferably 100 or more, and preferably 200 or more. In the case where the number of windings of the first coil 21 is large enough, the influence of the magnetic field generated from the first coil 21 by the pulsed excitation current passes through the head front portion 11a and reaches the detection object at a distance. Therefore, even if the surface of the head shell 10 facing the detection object is made of metal, the detection distance of the proximity sensor 100 becomes large enough. In the case where the linear shape of the coil wire 21a of the first coil 21 is thin enough (for example, 0.02 mm or less), even if the diameter of the head front portion 11a of the head shell 10 is less than 8 mm, the first coil 21 having 200 turns or more can be accommodated in the head shell 10.

[0036] The core holder 40 holds the ferrite core 30. The core holder 40 positions the second coil 22 and secures the ferrite core 30 to the in-head substrate 50. A substrate receiving portion 45 is formed in the core holder 40. When the end of the in-head substrate 50 is inserted into the substrate receiving portion 45, the in-head substrate 50 is secured to the core holder 40. While the core holder 40 holds the ferrite core 30, the core holder 40 secures the ferrite core 30 to the in-head substrate 50.

[0037] A slit 32 extending in the axial direction is formed in a portion of the outer periphery of the ferrite core 30. A slit 42 extending in the axial direction is also formed in a portion of the outer periphery of the core holder 40. The coil wire 21a of the first coil 21 and the coil wire 22a of the second coil 22 are led out to the head inner substrate 50 through the slit 32 of the ferrite core 30 and the slit 42 of the core holder 40.

[0038] The substrate electrodes 50a are arranged on each of the one face 50B and the other face 50F of the intra-head substrate 50. Figure 3 、 Figure 4 、 Figure 5 and Figure 6 In the embodiment, two substrate electrodes 50 a are arranged on each of one face 50B and the other face 50F.

[0039] At least the coil wire 21a of the first coil 21 is preferably electrically connected to the head substrate 50 by direct bonding. In this embodiment, both the coil wire 21a of the first coil 21 and the coil wire 22a of the second coil 22 are directly bonded to the substrate electrode 50a on the head substrate 50.

[0040] Direct bonding means that the components to be bonded are directly bonded to each other without intervening a brazing material such as solder. For example, direct bonding is performed by bonding the coil wire 21a and the coil wire 22a to the substrate electrode 50a using a method such as resistance welding, pressure welding, ultrasonic welding, or friction stir welding.

[0041] Direct bonding avoids the problem of copper corrosion caused by the copper in the wire dissolving into the solder, even for thin coil wires 21a and 22a (e.g., 0.02 mm or less). Furthermore, soldering thin coil wires 21a and 22a to substrate electrodes 50a is difficult, but direct bonding is generally less difficult than soldering.

[0042] For example, in resistance welding, direct joining can be performed simply by applying current while the coil wires 21 a and 22 a are in contact with the substrate electrode 50 a , and the work is easier than welding that requires soldering.

[0043] An intermediate member may be interposed between the coil wire 21a of the first coil 21 (or the coil wire 22a of the second coil 22) and the in-head substrate 50. Even in a case where the coil wire 21a or the coil wire 22a is directly bonded to the intermediate member and the intermediate member is electrically connected to the in-head substrate 50, it can be considered that the coil wire 21a or the coil wire 22a is electrically connected to the in-head substrate 50 by direct bonding.

[0044] When the coil wire 21a or the coil wire 22a is electrically connected to the head inner substrate 50 by direct bonding, the first coil 21 and the second coil 22 can be composed of a thin coil wire 21a and a thin coil wire 22a (for example, 0.02 mm or less). When the first coil 21 and the second coil 22 are composed of a thin coil wire 21a and a thin coil wire 22a, even if the number of windings of the first coil 21 and the second coil 22 is large (for example, 100 or more, or 200 or more), the diameter size of the coil 20 becomes smaller. When the diameter size of the coil 20 is small, the proximity sensor 100 can have a small diameter (for example, the diameter of the head front portion 11a is less than 8 mm). If the number of windings of the first coil 21 is large enough, the detection distance becomes large enough even if the head front portion 11a is made of metal.

[0045] The coil wire 21a and the coil wire 22a are electrically connected to the cable 19 via the substrate electrode 50a and the wiring (not illustrated) on the head inner substrate 50. The cable 19 includes a plurality of cable wires. Figure 3 、 Figure 4 、 Figure 5 and Figure 6 In the embodiment, the cable 19 includes two first cable wires 17 electrically connected to the coil wire 21 a of the first coil 21 and two second cable wires 18 electrically connected to the coil wire 22 a of the second coil 22 .

[0046] The first cable 17 is connected to one surface 50B of the intra-head substrate 50. The second cable 18 is connected to the other surface 50F of the intra-head substrate 50. The first and second cables 17 and 18 are connected to the intra-head substrate 50 by soldering using solder 50s.

[0047] Since the first cable wires 17 and the second cable wires 18 are separately arranged on one surface 50B and the other surface 50F, respectively, the first coil 21 and the second coil 22 can be electrically connected to the cable 19 even if the size of the head-in-substrate 50 is small. Therefore, even if the head shell 10 has a small diameter (for example, the diameter of the head front portion 11a is less than 8 mm), the size of the head-in-substrate 50 can be set to a size that can be accommodated in the head shell 10. One of the two first cable wires 17 can be electrically connected to one of the two coil wires 21a of the first coil 21, and the other first cable wire 17 can be electrically connected to one of the two coil wires 22a of the second coil 22. In this case, the remaining one of the coil wires 21a of the first coil 21 and the remaining one of the coil wires 22a of the second coil 22 are connected to each of the two second cable wires 18. That is, the first cable wire 17 connected to one side 50B is not limited to being electrically connected to the coil wire 21a of the first coil 21, and the first cable wire 17 is preferably electrically connected to the coil wire 21a of the first coil 21 or the coil wire 22a of the second coil 22. Similarly, the second cable wire 18 connected to the other side 50F is preferably electrically connected to the coil wire 21a of the first coil 21 or the coil wire 22a of the second coil 22.

[0048] Note that the coil wire 21a of the first coil 21 and the coil wire 22a of the second coil 22 can be electrically connected to the cable 19 via direct bonding without intervening the in-head substrate 50. For example, the coil wire 21a of the first coil 21 can be directly bonded to the first cable wire 17 without using solder 50s. In addition, an intermediate member may be interposed between the coil wire 21a of the first coil 21 (or the coil wire 22a of the second coil 22) and the cable 19. Even in the case where the coil wire 21a or the coil wire 22a is directly bonded to the intermediate member and the intermediate member is electrically connected to the cable 19, it can be considered that the coil wire 21a or the coil wire 22a is electrically connected to the cable 19 by direct bonding.

[0049] Next, refer to Figure 7 The structures of the coil 20 , the ferrite core 30 , the core holder 40 , and the head inner substrate 50 will be described. Figure 7 This is an exploded perspective view of the section from the coil 20 to the head inner substrate 50 that constitutes the proximity sensor 100 .

[0050] like Figure 7As illustrated, the first coil 21 and the second coil 22 are arranged concentrically, and the second coil 22 is arranged on the outside of the first coil 21 in the radial direction. In addition, 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 dimension of the second coil is smaller than the axial dimension of the first coil 21. With such a structure, the second coil 22 has a lower sensitivity to magnetic flux than the first coil 21. For example, in a case where the first coil 21 is used to detect the detection object and the second coil 22 is used to detect the embedded metal E, it is preferable to reduce the influence of the magnetic flux passing through both the detection object and the embedded metal E on the detection result of the second coil 22. By reducing the sensitivity of the second coil 22 to magnetic flux relative to the first coil 21, the influence of the magnetic flux passing through both the detection object and the embedded metal E is reduced.

[0051] like Figure 7 As 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.

[0052] A slit 32 extending in the axial direction is formed in a portion of the outer periphery of the ferrite core 30. Figure 7 In the embodiment, three slits 32 are formed. The coil wire 21a of the first coil 21 and the coil wire 22a of the second coil 22 pass through the slits 32. Figure 7 In the figure, two of the coil wires 21 a of the first coil 21 pass through the two slits 32 on the front side, and two of the coil wires 22 a of the second coil 22 pass through one slit 32 on the back side.

[0053] The core holder 40 is made of resin, for example. A slit 42 extending in the axial direction is formed in a portion of the outer periphery of the core holder 40. Figure 7 In the embodiment, three slits 42 are formed. The coil wire 21a of the first coil 21 and the coil wire 22a of the second coil 22 pass through the slits 42. Figure 7 In the figure, two of the coil wires 21 a of the first coil 21 pass through the two slits 42 on the front side, and two of the coil wires 22 a of the second coil 22 pass through one slit 42 on the back side.

[0054] The core holder 40 holds the ferrite core 30 while securing the ferrite core 30 to the in-head substrate 50 by receiving the in-head substrate 50 using the concave substrate receiving portion 45 formed on the lower surface. Note that a holder hole 46 is formed in the center of the substrate receiving portion 45, and a substrate protrusion 56 formed at the front end of the in-head substrate 50 is inserted into the holder hole 46, thereby securing the in-head substrate 50 to the core holder 40. When the core holder 40 secures the in-head substrate 50, the positioning accuracy between the in-head substrate 50 and the coil 20 is improved, and the proximity sensor 100 can be manufactured in a space-saving manner.

[0055] The upper surface 48 of the circumferential edge portion of the core holder 40 supports the second coil 22. Since the upper surface 48 of the circumferential edge portion supports the second coil 22, the core holder 40 positions the second coil 22.

[0056] Next, refer to Figure 8 The arrangement of the electric shield 80 and the magnetic shield 90 used in the proximity sensor 100 will be described. Figure 8 It is an exploded perspective view of components housed in the head housing 10 of the proximity sensor 100 .

[0057] In addition to the sensor unit 25 , an electric shield 80 and a magnetic shield 90 are further accommodated in the head housing 10 of the proximity sensor 100 .

[0058] 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 in-head substrate 50.

[0059] 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 in-head substrate 50.

[0060] The head housing 10 has a housing body 11 formed with an external thread 12. Figure 8 As illustrated, the housing body 11 completely covers the magnetic shield 90 , the electric shield 80 , and the sensor unit 25 .

[0061] In the following, reference will be made to Figure 9 The main circuit structure of the proximity sensor 100 will be described below. Figure 9 1 is a block diagram for explaining a main circuit configuration of the proximity sensor 100 .

[0062] like Figure 9 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.

[0063] The transmitting circuit 70 periodically applies a pulsed excitation current to the coil 20. The coil 20 generates a magnetic field by periodically flowing the pulsed excitation current. 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 transmitting circuit 70 may include, for example, an excitation circuit that generates a pulsed excitation current based on a signal from the control circuit 76 and causes the pulsed excitation current to flow to the first coil 21. Figure 9 As illustrated, a portion (outer peripheral portion) of the ferrite core 30 is located between the first coil 21 and the second coil 22, but a magnetic material different from the ferrite core 30 may be located between the first coil 21 and the second coil 22. In any case, since the magnetic material is arranged between the first coil 21 and the second coil 22, the size (diameter dimension) of the entire coil 20 includes not only the size of the first coil 21 and the second coil 22, but also the size of the magnetic material. However, in this embodiment, since the coil wire 21a of the first coil 21 and the coil wire 22a of the second coil 22 are thin, even if the number of windings is 100 or more (or 200 or more), the first coil 21 and the second coil 22 are small, and the entire coil 20 can be accommodated in a small head housing 10 having a diameter of less than 8 mm.

[0064] 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.

[0065] 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 have different configurations, the characteristics of the generated voltage or current are also different. By detecting voltages or currents with different characteristics, the operation for suppressing the influence of the embedded metal E becomes more efficient. The receiving circuit 60 may include, for example, a braking resistor for adjusting the current flowing from the coil 20, a filter circuit for filtering the analog signal of the received waveform, an amplifier circuit for amplifying the filtered analog signal, and an A / D conversion circuit for converting the amplified analog signal into a digital signal. 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.

[0066] 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. The control circuit 76 is connected to the amplifier unit 210 of the amplifier housing 200 via the cable 19. The control circuit 76 may include, for example, an operation circuit and an output circuit, the operation circuit being used to perform an operation operation for detecting the detection object D based on at least one of the first received waveform and the second received waveform, and the output circuit being used to output the result of the operation operation of the operation circuit to the outside (such as the amplifier unit 210) via the cable 19.

[0067] exist Figure 9 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 easily affected by the detection object D. 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.

[0068] exist Figure 9In the illustrated example, the transmitting circuit 70, the receiving circuit 60, and the control circuit 76 are provided on the in-head substrate 50. By providing the transmitting circuit 70, the receiving circuit 60, and the control circuit 76 on the in-head 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 in-head substrate 50. For example, the transmitting circuit 70, the receiving circuit 60, and the control circuit 76 may be provided in another component (for example, the amplifier housing 200). 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 in-head substrate 50, and the other circuits may be provided on another substrate (a substrate arranged inside or outside the head housing 10 (for example, a substrate in the amplifier housing 200)).

[0069] 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.

[0070] 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, the receiving circuit 60 includes the first receiving circuit 61 and the second receiving circuit 62, and can therefore 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.

[0071] In the following, reference will be made to Figure 10 to illustrate the magnetic field and its flux lines. Figure 10 2 is a diagram schematically illustrating magnetic flux lines around the first coil 21 and the second coil 22 .

[0072] like Figure 10 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.

[0073] In addition, since the axial dimension of the second coil 22 is smaller than that of the first coil 21 , the magnetic flux lines passing through the embedded metal E are reduced. Therefore, the proximity sensor 100 can substantially extend the detection distance by suppressing the influence of the embedded metal E.

[0074] The second coil 22 is located on the side (distal side) that detects the detection object D relative to the first coil 21. Since the second coil 22 is located distally from 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.

[0075] 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 .

[0076] exist Figure 10 , 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.

[0077] 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.

[0078] 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.

[0079] and Figure 10 In contrast, 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. In order to achieve Figure 10 In the illustrated state, the magnetic shield 90 and the ferrite core 30 are appropriately provided.

[0080] like Figure 10As 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.

[0081] 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.

[0082] In the following, reference will be made to Figure 10 and Figure 11 The magnetic shield 90 will be described in detail. Figure 11 It is an exploded perspective view for explaining the electric shield 80 and the magnetic shield 90 in detail.

[0083] like Figure 10 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.

[0084] 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 head housing 10). The magnetic shield 90 may constitute the head housing 10.

[0085] like Figure 11 As illustrated, the magnetic shield 90 includes a sheet member kneaded with ferromagnetic powder 91 (for example, metal powder). Since the magnetic shield 90 is formed by a sheet member kneaded with ferromagnetic powder 91, the magnetic shield has a relative magnetic permeability that is higher (to a certain extent or greater) than that of air and a low electrical conductivity. The sheet member can be formed by compacting the ferromagnetic powder 91. The magnetic shield 90 appropriately guides the magnetic flux lines with a relative magnetic permeability that is higher than that of air. The magnetic shield 90 has a low electrical conductivity, so that the eddy current loop in the magnetic shield 90 can be suppressed without performing insulation treatment. By suppressing the eddy current loop, the noise to the received waveform is suppressed. Therefore, the proximity sensor 100 including such a magnetic shield 90 can substantially extend the detection distance by improving the detection accuracy.

[0086] 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 entire magnetic shield 90 may be amorphous.

[0087] Note that permalloy sheets or cobalt sheets are not suitable as magnetic shielding member 90. This is because permalloy sheets or cobalt sheets have high relative magnetic permeability (approximately 1000 to tens of thousands), but also high electrical conductivity, which generates eddy current loops.

[0088] 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.

[0089] In the following, reference will be made to Figure 11 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.

[0090] like Figure 11 As shown, the electric shield 80 is arranged radially outward from the second coil 22. A cutout 81 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 long side direction of the cutout 81 intersects (preferably is perpendicular to) the direction 88 around the axis.

[0091] 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.

[0092] 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 closes the distal end side, which is one end of the peripheral portion 84. The detection surface portion 87 is located on the side where the detection object D is detected.

[0093] 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.

[0094] 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.

[0095] The electric shield 80 has a sheet metal structure. That is, the electric shield 80 is obtained by bending a thin metal plate. Because the electric shield 80 has a sheet metal structure, even if the strength is reduced by the cutout 81, the shape is stable. The thin metal plate before being bent as the electric shield 80 can be stamped. The electric shield 80 has a bottom cylindrical three-dimensional shape by pressing the stamped thin metal plate. In other words, the electric shield 80 can be a pressed product of the stamped thin metal plate. Even if the strength is reduced by the cutout 81, the shape of such an electric shield 80 is further stabilized. The thin metal plate constituting the electric shield 80 can be, for example, copper foil or brass foil. The electric shield 80 is not limited to a sheet metal structure. For example, the electric shield 80 can be a coated molded product or a vapor deposited molded product. Coated molded products or vapor deposited molded products are formed by coating or vapor depositing a conductive material on a bottomed cylindrical resin mold. Since current flows through the electric shield 80, the electric shield 80 is preferably electrically connected to the ground terminal (GND, reference potential). In the present embodiment, for example, a shielded cable (not illustrated) serving as a reference potential is included in the first cable line 17 , and the shielded cable is electrically connected to the electric shield 80 .

[0096] In the following, reference will be made to Figure 12 and Figure 13 The ferrite core 30 will be described in detail. Figure 12 This is a magnetic flux diagram when the shaft 31 of the ferrite core 30 is thin. Figure 13 This is a magnetic flux diagram when the shaft 31 of the ferrite core 30 is not thin. Figure 12 Magnetic flux lines are exemplified when the width w of the shaft body 31 in the radial direction is 1.5 mm in the electromagnetic field simulation, and Figure 13 Magnetic flux lines in a case where the width w of the shaft body 31 in the radial direction is 3 mm in electromagnetic field simulation are exemplified.

[0097] exist Figure 12 In the illustrated example, 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, and the relative shaft width w / W is 21.4%. That is, the relative shaft width w / W is 30% or less. Figure 12 As illustrated, three magnetic flux lines m1 to m3 pass through the embedded metal E.

[0098] On the other hand, Figure 13 In the illustrated example, 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, and the relative shaft width w / W is 42.9%. That is, the relative shaft width w / W is greater than 30%. Figure 13 As illustrated, four magnetic flux lines M1 to M4 pass through the embedded metal E.

[0099] As from Figure 12 and Figure 13 The comparison between the two clearly shows that when the relative axis width w / W is 30% or less Figure 12 The number of magnetic flux lines passing through the embedded metal E is as small as 3 and the relative axis width w / W is greater than 30%. Figure 13 , the number of magnetic flux lines passing through the embedded metal E is as large as 4. Therefore, it was found that when the relative axial width w / W is 30% or less, the influence of the embedded metal E is suppressed.

[0100] When the relative axial width w / W is less than 15%, it is difficult to manufacture the ferrite core 30. Therefore, it is considered that the relative axial width w / W is preferably 30% or less, and more preferably 15% or more and 30% or less.

[0101] 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.

[0102] (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.

[0103] (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.

[0104] (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.

[0105] 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 ferrite core for guiding the magnetic field generated from the coil; a head housing for accommodating the coil and the ferrite core; as well as an inner head substrate housed in the head housing, 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 sending circuit, configured to periodically apply a pulsed excitation current to the coil; 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; and a control circuit for detecting the detection object based on the change in voltage or current detected by the receiving circuit, and The coil wire of the first coil is electrically connected to the in-head substrate via direct bonding.

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

3. The proximity sensor according to claim 1 , further comprising: a cable extending from the head housing; as well as an amplifier housing connected to the head housing via the cable, The transmitting circuit, the receiving circuit and the control circuit are arranged in the amplifier housing.

4. The proximity sensor according to any one of claims 1 to 3, 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 4 , 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. 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.

7. The proximity sensor according to claim 6, wherein: The second coil is arranged outside the first coil in a radial direction. 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, The core holder positions the second coil and fixes the ferrite core to the in-head substrate. 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, further comprising: an electric shield arranged outside the second coil in a radial direction, The electric shield is formed with a cutout that crosses a direction around an axis of the electric shield.

13. The proximity sensor according to claim 12, wherein: 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, and The cutout is formed in the detection face portion. The proximity sensor according to claim 13 , wherein: The cutout is formed in the peripheral portion.

15. The proximity sensor according to claim 12, wherein The electric shield has a sheet metal structure.

16. The proximity sensor according to claim 15, wherein The electric shield is a pressed product of a stamped thin metal sheet.

17. 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.

18. The proximity sensor according to claim 17, 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 greater.

19. The proximity sensor according to claim 3, wherein: The cable includes: a first cable wire electrically connected to the coil wire of the first coil or the coil wire of the second coil; and a second cable wire electrically connected to the coil wire of the first coil or the coil wire of the second coil. The first cable is connected to one surface of the head inner substrate, and The second cable is connected to the other surface of the in-head substrate.

20. A proximity sensor comprising: a coil for generating a magnetic field by an excitation current; a ferrite core for guiding the magnetic field generated from the coil; a head housing for accommodating the coil and the ferrite core; as well as a cable extending from the head housing, 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 sending circuit, configured to periodically apply a pulsed excitation current to the coil; 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; and a control circuit for detecting the detection object based on the change in voltage or current detected by the receiving circuit, and The coil wire of the first coil is electrically connected to the cable via direct bonding.

21. A proximity sensor comprising: a coil for generating a magnetic field by an excitation current; a ferrite core for guiding the magnetic field generated from the coil; as well as a head housing for accommodating the coil and the ferrite core, Wherein, the coil comprises: First coil; a second coil arranged outside the first coil in a radial direction; and a magnetic material located between the first coil and the second coil, The proximity sensor further includes: a sending circuit, configured to periodically apply a pulsed excitation current to the coil; 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; and a control circuit, configured to detect the detection object based on a change in voltage or current detected by the receiving circuit, The diameter of the surface of the head housing that can face the detection object is less than 8 mm, and The number of windings of the first coil is 100 or greater.

22. The proximity sensor according to claim 21, wherein The surface of the head housing that can face the detection object is made of metal.

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

24. The proximity sensor of claim 21, further comprising: an inner head substrate housed in the head housing, The coil wire of the first coil is electrically connected to the in-head substrate via direct bonding.

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