Proximity sensor

Abstract

To provide a proximity sensor capable of suppressing generation of noise.SOLUTION: The proximity sensor 100 senses an object to be sensed D. The proximity sensor 100 includes a detection coil 1, a head housing 3 made of metal, and a power supply cable 2. The detection coil 1 generates a detection current. The head housing 3 made of metal houses the detection coil 1. The power supply cable 2 has an electrical connection with the detection coil 1 and is connected to the head housing 3. A filler is filled so that the detection coil 1 is buried in at least a part of the internal space of the head housing 3. The filler is a mixture of an adhesive and an additive having a lower relative dielectric constant than the adhesive.SELECTED DRAWING: Figure 8

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a proximity sensor that detects a detection target. In the proximity sensor described in Patent Document 1, a power supply cable (cord 150) is electrically connected to a detection coil 121 housed in a head shaft body (case bodies 111, 113). The head shaft body (case bodies 111, 113) is filled with a filler (sealing resin layer 180). The filler (sealing resin layer 180) improves mechanical strength. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-297828 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the detection distance of a proximity sensor, including that described in Patent Document 1, is increased, the change in the magnetic field used to detect an object to be detected becomes weaker. Therefore, even a small amount of noise introduced into the detection current due to the change in the magnetic field may reduce the detection accuracy.

[0005] Noise currents that cause noise can enter the head shaft from the power supply cable. If the head shaft is grounded (connected to ground), a large amount of noise current flows via the ground, which can generate noise near the detection coil. Even if an insulating member is placed inside the head shaft to block the noise current, if a filler is filled in as mentioned above, the noise current can penetrate the insulating member due to capacitive coupling of the filler, generating noise.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to provide a proximity sensor that can suppress the generation of noise. [Means for solving the problem]

[0007] A proximity sensor according to a first aspect of the present invention detects a detection target. The proximity sensor includes a detection coil, a metal head housing, and a power supply cable. The detection coil generates a detection current. The metal head housing houses the detection coil. The power supply cable is electrically connected to the detection coil and is connected to the head housing. A filler is filled into at least a portion of the internal space of the head housing so that the detection coil is buried. The filler is a mixture of an adhesive and an additive having a lower dielectric constant than the adhesive. [Effects of the Invention]

[0008] According to the proximity sensor of the present invention, it is possible to suppress the generation of noise. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram illustrating the configuration of a proximity sensor. [Figure 2] FIG. 1 is a perspective view of an L-shaped proximity sensor. [Figure 3] FIG. 1 is a perspective view of a cylinder-type proximity sensor. [Figure 4] FIG. 1 is a perspective view of a flat-type proximity sensor. [Figure 5] FIG. 1 is a vertical cross-sectional view of an L-shaped proximity sensor. [Figure 6] FIG. 2 is an enlarged perspective view of a vertical cross section of the front part of the head housing. [Figure 7] 1 is a double logarithmic graph in which the horizontal axis and the vertical axis represent frequency and skin depth, and a schematic diagram illustrating this double logarithmic graph. [Figure 8] FIG. 2 is a perspective view of a vertical cross section of a head housing. [Figure 9] FIG. 2 is an enlarged perspective view showing a detector coil and related equipment. [Figure 10A]10 is a graph showing an image of a zero-adjusted received waveform when there is no external member and no object to be detected within the detection range. [Figure 10B] 10 is a graph showing an image of a zero-adjusted received waveform when there is no external component and an object to be detected is within the detection range. [Figure 11A] 10 is a graph showing an image of a zero-adjusted received waveform when an external member is present and the object to be detected is not within the detection range. [Figure 11B] 10 is a graph showing an image of a zero-adjusted received waveform when an external member is present and an object to be detected is within the detection range. [Figure 12] FIG. 2 is a partially cutaway perspective view of a cylinder-type proximity sensor. [Figure 13] FIG. 2 is an enlarged perspective view of a vertical cross section of a flat-type proximity sensor. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters, and description thereof will not be repeated.

[0011] In the following description, terms indicating positions or directions such as "front" and "rear" may be used. These terms are used for convenience to facilitate understanding of the embodiments, and unless otherwise clearly stated, do not relate to the directions in which the devices are actually implemented.

[0012] A proximity sensor 100 according to an embodiment of the present invention will be described below with reference to the drawings. First, an overview of the proximity sensor 100 will be described with reference to FIG. 1. FIG. 1 is a schematic configuration diagram of the proximity sensor 100. FIG. 1 illustrates arrows X, Y, and Z indicating three mutually perpendicular directions. The directions indicated by the arrows X, Y, and Z all correspond to the placement orientation of the proximity sensor 100, and the direction indicated by the arrow X is referred to as the X-axis direction, the direction indicated by the arrow Y is referred to as the Y-axis direction, and the direction indicated by the arrow Z is referred to as the Z-axis direction. Of the directions along the X-axis direction, one is referred to as the +X direction, and the other is referred to as the -X direction. Of the directions along the Y-axis direction, one is referred to as the +Y direction, and the other is referred to as the -Y direction. Of the directions along the Z-axis direction, one is referred to as the +Z direction, and the other is referred to as the -Z direction.

[0013] The proximity sensor 100 is a sensor that detects the presence or position of a detection target D. As shown in FIG. 1, the proximity sensor 100 includes a head 100H, an amplifier 100A, and a power supply cable 2 that connects the head 100H and the amplifier 100A. The head 100H includes a detection coil 1 and a head housing 3 that houses the detection coil 1. The amplifier 100A includes a transmission circuit 5, a reception circuit 6, a control circuit 7, an amplifier board 70 on which the transmission circuit 5, the reception circuit 6, and the control circuit 7 are provided, and an amplifier housing 8 that houses the amplifier board 70.

[0014] The detector coil 1 generates a magnetic field for detection. The power supply cable 2 is a member for supplying power to the detector coil 1, and power is supplied to the detector coil 1 via the power supply cable 2 from a power supply (not shown). The head housing 3 houses the detector coil 1. The head housing 3 is arranged so that the normal direction of a detection surface 30 (described later) is along the Y-axis direction, and the detection surface 30 faces the +Y direction. The head housing 3 in this embodiment is shaped so that its longitudinal direction is along the Y-axis direction, and has a connection part 34 that guides the power supply cable 2 on the -Y direction side.

[0015] The transmitting circuit 5 supplies a pulsed excitation current to the detecting coil 1. The receiving circuit 6 detects the detecting current generated in the detecting coil 1. The control circuit 7 detects the presence or position of the object to be detected D based on the received signal from the receiving circuit 6 that detected the detecting current. Because the detecting current changes in accordance with changes in the magnetic field, the received signal from the receiving circuit 6 reflects the change in the magnetic field. The control circuit 7 outputs the result of detecting the presence or position of the object to be detected D.

[0016] The amplifier board 70 is mounted with a transmitter circuit 5, a receiver circuit 6, and a control circuit 7. A power supply cable 2 electrically connects the detector coil 1 and the amplifier board 70. The amplifier board 70 in this embodiment is mounted with the transmitter circuit 5, the receiver circuit 6, and the control circuit 7, but it is sufficient that at least the control circuit 7 is mounted on it. For example, the board on which the transmitter circuit 5 and the receiver circuit 6 are mounted may be housed in the head housing 3.

[0017] The head housing 3 has a detection surface 30 located at the end of the head housing 3 on the +Y direction side, and a circumferential head cylindrical portion 32 whose center line is along the Y axis direction. The head cylindrical portion 32 has a fixed portion 31. The fixed portion 31 is provided between the connection portion 34 and the detection surface 30 in the Y axis direction, and is a portion to which a fastening member such as a nut (not shown) is fastened when the head housing 3 is fixed to an external member E.

[0018] The amplifier housing 8 houses the amplifier board 70. The amplifier housing 8 is disposed outside the head housing 3.

[0019] Generally, proximity sensors using induced current have a short detection distance, so that they may collide with the object to be detected D if the object to be detected D deviates from its expected movement path. Therefore, achieving a long detection distance in a proximity sensor using induced current reduces the risk of collision with the object to be detected D. Proximity sensors 100 using induced current include a sine wave type that applies a sine wave excitation current to the detection coil 1, and a pulse type that applies a pulse-shaped excitation current to the detection coil 1. Both types detect changes in the current generated in the detection coil 1, but the change in current becomes weaker the longer the distance between the object to be detected D and the detection coil 1. In other words, to achieve a long detection distance, it is necessary to detect weak changes, but with the sine wave type, it is difficult to distinguish between the object to be detected D and metal objects other than the object to be detected D (such as external components E). A method that supplies a pulsed excitation current to the detector coil 1 provides a received signal that exhibits a characteristic change on the time axis starting from the excitation timing, enabling more information to be obtained than with a sinusoidal wave method. For example, it is possible to perform calculations using the decay time from the peak of the received signal to distinguish between the detection target D and metal objects other than the detection target D, or to process the time axes of multiple received signals generated by multiple detector coils 1. Therefore, compared to a sinusoidal wave method, the pulse method offers the advantage of improved detection accuracy through calculations. The proximity sensor 100 of this embodiment is a pulsed proximity sensor that supplies a pulsed excitation current to the detector coil 1. The pulse method requires complex processing, such as controlling the timing of applying the pulsed excitation current to the coil and processing the current generated in the coil. Therefore, if a pulsed method is used to detect the detection target D in order to achieve a long detection distance, a control circuit 7 that performs relatively complex processing is required, and the amplifier board 70 on which the control circuit 7 is mounted becomes large.

[0020] Therefore, the proximity sensor 100 according to this embodiment can achieve a long detection distance while miniaturizing the head housing 3 by housing the amplifier board 70 in an amplifier housing 8 separate from the head housing 3. In particular, in this embodiment, the dimension in the Y-axis direction can be reduced, so the proximity sensor 100 can be placed even when there is not enough installation space in the Y-axis direction for the external member E.

[0021] As shown enlarged in FIG. 1 , the power supply cable 2 includes a core 21 through which a detection current flows and a shield sheath 20 that shields and covers the core 21. The shield sheath 20 is electrically connected to an electric shield 43 (described later). The shield sheath 20 and the electric shield 43 may be electrically connected either directly or indirectly. Because the core 21 through which the detection current flows is covered by the shield sheath 20, changes in the detection current are less susceptible to external influences. As described above, the longer the distance between the detection object D and the detection coil 1, the weaker the changes in the detection current. Therefore, by configuring the detection current to be less susceptible to external influences, the detection accuracy of the detection object D that is far from the detection coil 1 is improved. Therefore, a configuration in which the core 21 is shielded improves the detection accuracy of the proximity sensor 100.

[0022] The amplifier 100A has a display unit 9 (for example, an indicator light) that displays the result output by the control circuit 7. The display unit 9 is provided on the surface of the amplifier housing 8. By providing the display unit 9 on the surface of the amplifier housing 8, the user can easily understand the detection result by the proximity sensor 100 by visually checking the amplifier housing 8.

[0023] The head cylindrical portion 32 is made of metal, and a portion thereof is machined as the fixed portion 31. The fixed portion 31 has a circumferential thread formed on its circumference with the Y-axis direction as its centerline. The external member E has a threaded hole with a thread corresponding to the thread formed on the fixed portion 31. If the fixed portion 31 is male-threaded, the threaded hole formed in the external member E is female-threaded. The fixed portion 31 is fixed to the external member E by screwing. When the external member E and the fixed portion 31 are screwed together, a nut (not shown) may be screwed onto the fixed portion 31 to further stabilize the positional relationship between the external member E and the head housing 3 in the Y-axis direction. In particular, the external member E and the fixed portion 31 are often fixed together by screwing when the head housing 3 is positioned so that the head housing 3 does not protrude toward the +Y direction relative to the external member E, i.e., toward the path of the detection target object D in the Y-axis direction. For this reason, it is preferable that the nut be screwed onto the fixed portion 31 located on the -Y direction side of the external member. In this embodiment, a screw hole is provided in the external member E, and the fixed portion 31 is screwed into the screw hole to fix the head housing 3 to the external member E, but the head housing 3 may be fixed to the external member E by sandwiching the external member E between a nut screwed onto the fixed portion 31 located on the +Y direction side of the external member E and a nut screwed onto the fixed portion 31 located on the -Y direction side of the external member E, with the head housing 3 placed in a through-hole provided in the external member E.

[0024] Therefore, the proximity sensor 100 can be easily fixed to the external member E because the metal fixed portion 31 has a thread groove. In this embodiment, the fixed portion 31 is provided with a thread groove, but it may be made of metal so that the positional relationship between the external member E and the head housing 3 is stable when the head housing 3 is fixed to the external member E. A clamp may be attached to the metal fixed portion 31, and the clamp may be fixed to the external member E, thereby fixing the head housing 3 to the external member E.

[0025] Variations of the proximity sensor 100 will be described below with reference to Figs. 2 to 4. Fig. 2 is a perspective view of an L-shaped proximity sensor 100. Fig. 3 is a perspective view of a cylinder-type proximity sensor 100. Fig. 4 is a perspective view of a flat-type proximity sensor 100.

[0026] The proximity sensor 100 shown in Fig. 2 is also called an L-type sensor because the structure having the sensing surface 30, which is the head housing 3 of the head 100H equipped with the sensing coil 1 (not shown), is L-shaped in side view. The proximity sensor 100 shown in Fig. 3 is also called a cylindrical type sensor because the structure having the sensing surface 30 is cylindrical. The proximity sensor 100 shown in Fig. 4 is also called a flat type sensor because the structure having the sensing surface 30 is box-shaped (has a flat surface).

[0027] Each of the types of proximity sensors 100 shown in FIGS. 2 to 4 includes a head housing 3, which is a structure having a sensing surface 30, and an amplifier housing 8 that is a separate pair from the head housing 3. As shown in FIGS. 2 and 3, the L-shaped proximity sensor 100 and the cylinder-type proximity sensor 100 include a head housing 3 that includes a sensing surface 30 and a cylindrical head portion 32 whose center line is the normal to the sensing surface. The head housing 3 of the L-shaped proximity sensor 100 and the head housing 3 of the cylinder-type proximity sensor 100 are elongated, with the axial direction of the head cylindrical portion 32 being the longitudinal direction. On the other hand, as shown in FIG. 4, the flat-type proximity sensor 100 includes a box-shaped head housing 3B, which has a sensing surface 30.

[0028] The L-shaped proximity sensor 100 will be described below with reference to Figures 5 to 9. First, the L-shaped proximity sensor 100 will be described in detail with reference to Figure 5. Figure 5 is a vertical cross-sectional view of the L-shaped proximity sensor 100.

[0029] As shown in FIG. 5, the proximity sensor 100 includes a detection coil 1, a power supply cable 2, and a head housing 3.

[0030] The detector coil 1 generates a magnetic field for detection. The power supply cable 2 is a member for supplying power to the detector coil 1. The head housing 3 houses the detector coil 1. The head housing 3 is arranged so that the normal direction of the detector surface 30 is along the Y-axis direction, and the detector surface 30 faces the +Y direction. The head housing 3 of this embodiment has an elongated shape with its longitudinal direction along the Y-axis direction, and has a connection part 34 on the -Y direction side that guides the power supply cable 2.

[0031] The head housing 3 has a metal detection surface 30 on the +Y direction side of the head housing 3. The detection coil 1 is disposed near the detection surface 30, and is therefore disposed on the +Y direction side of the head housing 3. The head housing 3 is elongated in the Y axis direction, and the detection coil 1 is disposed so that the -Y direction end of the detection coil 1 is located on the +Y direction side of the connection part 34, in other words, so that the detection coil 1 and the connection part 34 are spaced apart in the Y axis direction.

[0032] The connection portion 34 is disposed on the −Y direction side of the head housing 3, and guides the power supply cable 2 in the −Z direction.

[0033] Hereinafter, for convenience, the -Y side of the head housing 3 may be referred to as one end side in the longitudinal direction of the head housing 3, in other words, the connection portion 34 side, and the +Y side of the head housing 3 may be referred to as the other end side in the longitudinal direction of the head housing 3, in other words, the detection surface 30 side. The -Y side may also be referred to as the rear side, and the +Y side may also be referred to as the front side.

[0034] 5 has an L-shape in side view (viewed in the X-axis direction) because the connection portion 34 is shaped to guide the power supply cable 2 in the -Z direction. That is, the connection portion 34 does not extend rearward along the Y-axis direction which is the normal direction to the detection surface 30, but extends in a direction intersecting the front-rear direction (longitudinal direction) which is the Y-axis direction.

[0035] For this reason, an L-shaped proximity sensor 100 with an L-shaped head housing 3 is suitable for cases where there is an obstacle behind the head housing 3. This is because, compared to a proximity sensor 100 with a non-L-shaped head housing 3, an L-shaped proximity sensor 100 is less likely to interfere with an obstacle located behind the external member E when the head housing 3 is fixed to the external member E. However, when the distance between the external member E and an obstacle located on the -Y direction side of the external member E in the Y-axis direction, i.e., the front-to-rear direction, is short, even an L-shaped proximity sensor 100 requires the head 100H to be positioned closer to the +Y direction (front). In other words, since the head housing 3 is positioned so that the detection surface 30 of the head housing 3 is closer to the path of the detection target D, the possibility of a collision between the detection target D and the detection surface 30 increases. Here, the detection surface 30, which may collide with the detection target D, is made of metal, which increases its strength and reduces damage to the head 100H due to a collision with the detection target D. Therefore, the proximity sensor 100 can achieve both freedom of placement, allowing it to be installed in an environment where an obstacle is located behind the external member E, and reduction in failure of the head 100H.

[0036] In this embodiment, the connection portion 34 is configured to guide the power supply cable 2 in the -Z direction, but it may be configured to guide the power supply cable 2 in a direction intersecting the normal direction of the detection surface 30. Furthermore, the direction in which the power supply cable 2 is guided by the connection portion 34 is preferably as close to the Y-axis direction, that is, the direction perpendicular to the longitudinal direction (front-to-back direction). This makes it even less likely that the head housing 3 will interfere with obstacles located behind it.

[0037] Next, the head housing 3 of the proximity sensor 100 will be described in detail with reference to Fig. 6. Fig. 6 is an enlarged perspective view of a vertical cross section of the +Y direction side (other end) of the head housing 3. For convenience, Fig. 6 omits components inside the head housing 3 other than the detector coil 1.

[0038] As shown in FIG. 6, the head housing 3 has a metallic head cylindrical portion 32 (main body portion) and a metallic cap portion 35. The head cylindrical portion 32 is a tubular member having a peripheral surface on a circumference whose centerline is along the Y-axis direction and an opening facing the +Y direction side. The cap portion 35 is attached to the head cylindrical portion 32 from the +Y direction side (front end side) of the head cylindrical portion 32 so as to cover the opening of the head cylindrical portion 32. The cap portion 35 attached to the head cylindrical portion 32 is located on the front end side of the head housing 3. The cap portion 35 includes a metallic detection surface 30.

[0039] Because the cap portion 35, which is separate from the head cylindrical portion 32, includes the detection surface 30, the head cylindrical portion 32 has a shape in which not only the rear end but also the front end of the head cylindrical portion 32 is open. Therefore, the inner circumferential surface of the head cylindrical portion 32 can be machined (thinned) from both ends of the front end and rear end. Compared to a configuration in which the detection surface 30 is provided integrally with the head cylindrical portion 32, the ability to machine from both ends in the Y-axis direction reduces the difficulty of manufacturing.

[0040] More specifically, cutting (thickness reduction) is generally performed by inserting a drill, which is a cutting blade, while rotating it into the cylindrical head portion 32. The longer the drill, the greater the deflection of the tip of the drill.

[0041] In a configuration in which the detection surface 30 is integral with the cylindrical head portion 32, the drill is inserted only from the rear end side of the cylindrical head portion 32. This requires the use of a long drill to cut the front end side of the cylindrical head portion 32, which increases the deflection of the drill tip. This makes it difficult to maintain the accuracy of the cutting process (thinning process) at the front end of the cylindrical head portion.

[0042] The front end of the cylindrical head is where the detector coil 1 is located, so high precision is required for cutting (thinning) the front end. Therefore, it is difficult to manufacture a cylindrical head with only the rear end open.

[0043] On the other hand, in a configuration in which a cap portion 35 including the detection surface 30 is separately provided, such as the cylindrical head portion 32 shown in FIG. 6 , a rotating drill is inserted from both the front and rear ends of the cylindrical head portion 32. Therefore, even when cutting the front end side of the cylindrical head portion 32, the drill can be inserted from the front end side of the cylindrical head portion 32. Therefore, a relatively short drill, whose tip side is less likely to vibrate while rotating, can be selected for cutting, improving the accuracy of the cutting process (thinning process). As a result, the proximity sensor 100 is easier to manufacture because the head housing 3 has a cap portion 35 that includes the detection surface 30 and is separate from the cylindrical head portion 32, leaving the front and rear ends of the cylindrical head portion 32 open.

[0044] The cylindrical head portion 32 has an abutment portion 33 on its inner circumferential surface. The abutment portion 33 abuts against the cap portion 35 when the cap portion 35 is properly attached to the cylindrical head portion 32. The cap portion 35 is fixed to the cylindrical head portion 32 with an adhesive while abutting against the abutment portion 33.

[0045] Therefore, the cap portion 35 can be easily attached to the cylindrical head portion 32 appropriately, and the difficulty of manufacturing the proximity sensor 100 is reduced.

[0046] The abutment portion 33 is a circumferential groove on the inner peripheral surface of the head cylindrical portion 32, having a predetermined width from the +Y direction end (front end) of the head cylindrical portion 32 toward the -Y direction side (rear side). The predetermined width of the circumferential groove corresponds to the dimension of the cap portion 35 attached to the head cylindrical portion 32 in the Y axis direction (front-rear direction). The inner diameter of the circumferential groove is slightly larger than the outer diameter of the cap portion 35 (by an amount sufficient to accommodate adhesive). Therefore, the circumferential groove, which is the abutment portion 33, functions to position the cap portion 35.

[0047] The cap portion 35 has a bottom portion 36 including the detection surface 30, and a peripheral portion 37 standing upright from the outer periphery of the bottom portion 36. When the cap portion 35 is attached to the head cylindrical portion 32, the end of the peripheral portion 37 on the -Y direction (connection portion 34) side (rear end of the peripheral portion 37) is located closer to the +Y direction, i.e., forward, than the end of the detection coil 1 on the -Y direction (connection portion 34) side (rear end 56 of the detection coil 1).

[0048] Since the cap portion 35 does not become longer in the front-rear direction than necessary, the difficulty of cutting the cap portion 35 itself is unlikely to increase. Therefore, the difficulty of manufacturing the proximity sensor 100 is reduced.

[0049] The head cylindrical portion 32 has a thin portion that is thinner than other portions, including the end of the detector coil 1 on the -Y side (connection portion 34 side), i.e., the portion on the +Y side (front portion) of the detector coil 1 relative to the rear end 56.

[0050] Therefore, because the head cylindrical portion 32 is relatively thin around the outer periphery of the detector coil 1, the magnetic field from the detector coil 1 is less likely to be obstructed by the head cylindrical portion 32. Furthermore, because the head cylindrical portion 32 includes a relatively thick portion around the outer periphery on the -Y side of the detector coil 1, the strength of the head cylindrical portion 32 is easily maintained. As a result, the proximity sensor 100 can improve detection accuracy while maintaining mechanical strength. Furthermore, because the head cylindrical portion 32 and the cap portion 35 including the detection surface 30 are separate bodies, it is easier to thin the portion of the head cylindrical portion 32 on the +Y side where the cap portion 35 is attached. Furthermore, the inner periphery of the end of the head housing 3 on the +Y side is used to position the detector coil 1. The positional accuracy of the detector coil 1 relative to the head housing 3 significantly affects the detection distance based on the detection surface 30. Therefore, if the head cylindrical portion 32 and the cap portion 35 are configured as separate bodies and the end portion of the head housing 3 on the +Y direction side can be processed with high precision, the detection distance of the proximity sensor 100 can be increased.

[0051] The detection coil 1 preferably generates a magnetic field with an effective frequency of 2 kHz or more and 200 kHz or less. The portion including the detection surface 30 preferably has a thickness of 1.0 mm or less.

[0052] Next, the reasons for the preferred effective frequency of the magnetic field (2 kHz or more and 200 kHz or less) and the preferred thickness of the portion including the detection surface 30 (1.0 mm or less) will be explained in detail with reference to Fig. 7. Fig. 7 is a double logarithmic graph with frequency versus skin depth on the horizontal and vertical axes, and a schematic diagram for explaining this double logarithmic graph.

[0053] As shown in the double logarithmic graph in Figure 7, the higher the frequency, the smaller the skin depth. In other words, the lower the frequency, the greater the skin depth. Skin depth indicates the length over which magnetic flux lines of a certain strength heading towards a material of a certain material attenuate to a certain strength, so the lower the frequency, the less attenuation there is and the greater the skin depth. Also, the more easily magnetic flux lines pass through a material, the less attenuation there is and the greater the skin depth.

[0054] It is preferable to generate a magnetic field at a low frequency in order to reduce attenuation of the magnetic flux due to the metal detection surface 30. However, if the frequency of the generated magnetic field is low, it becomes difficult to detect changes in the magnetic field when the magnetic flux passes through the detection object D, and there is a risk that the detection object will be reduced.

[0055] On the other hand, pulse-type and relatively low-frequency sine wave-type sensors generally have an effective frequency of 200 kHz or less. If the upper limit of the effective frequency is set to 200 kHz, that is, at frequencies below 200 kHz (point B in Figure 7), the skin depth of stainless steel (SUS304) exceeds 1 mm. Therefore, if the portion including the detection surface 30 is made of stainless steel (SUS304), which has relatively high mechanical strength, setting the upper limit of the thickness to 1 mm can achieve both mechanical strength and reduced magnetic flux attenuation due to the materials that make up the detection surface 30. Note that, although SUS304 is used as the stainless steel in this embodiment, other stainless steels may also be used.

[0056] Next, the filler filled in the head housing 3 will be described in detail with reference to Fig. 8. Fig. 8 is a perspective view of a vertical cross section of the head housing 3. In Fig. 8, for ease of viewing, the illustration and reference numerals of the filler are omitted, but the filler is filled in the portion shown as a space inside the head housing 3.

[0057] As shown in FIG. 8, the proximity sensor 100 includes a detection coil 1, a power supply cable 2, and a metal head housing 3, and the head housing 3 is filled with a filler.

[0058] The detector coil 1 generates a magnetic field for detection. The power supply cable 2 is a member for supplying power to the detector coil 1. The head housing 3 is made of metal and houses the detector coil 1. The head housing 3 is filled with a filler so as to fill the space around the detector coil 1 housed in the head housing 3. The filler is a mixture of an adhesive and an additive with a lower dielectric constant than the adhesive.

[0059] The proximity sensor 100 is a sensor that detects a metal object D using an induced current. It detects the presence and position of the object D based on changes in the detection current generated in the detection coil 1. The longer the distance between the detection coil 1 and the object D, the weaker the change in the detection current becomes. Therefore, to increase the detection distance of the proximity sensor 100, it is necessary to capture weak changes in the detection current. If a noise current component is added to the detection current, there is a risk that the detection accuracy will decrease, even if the noise current is weak.

[0060] More specifically, in the head 100H, power is supplied to the detection coil 1 via the power supply cable 2, and the power supply cable 2 is therefore electrically connected to the detection coil 1. Therefore, the power supply cable 2 can become a path through which a noise current that affects changes in the detection current of the detection coil 1 flows.

[0061] Incidentally, the external member E to which the head housing 3 is fixed is often grounded to ground G. This is because the external member E is often part of a device including the proximity sensor 100 of this embodiment, and such devices are often connected to ground G when used to prevent accidents. For this reason, the head housing 3 fixed to the external member E is often grounded to ground G, and a configuration is used in which the current generated in the head housing 3 itself flows to ground G. When the head housing 3 is grounded, the power supply cable 2 and the head housing form a circuit via ground G, and there is a risk that noise current will flow from the power supply cable 2 into the head 100H. Therefore, it is preferable to minimize the capacitive coupling between the head housing 3 and the power supply cable 2 and between the power supply cable 2 and the current circuit from the detection coil 1. For example, a configuration in which air is present.

[0062] However, the head housing 3 is filled with a filler to improve its mechanical strength. Due to capacitive coupling of the filler, there is a risk that a current will flow between the head housing 3 and the current circuit between the power supply cable 2 and the detection coil 1. In other words, due to capacitive coupling of the filler, the power supply cable 2, the current circuit between the power supply cable 2 and the detection coil 1, and the head housing 3 form a current circuit via ground G, and there is a risk that a noise current will flow from the power supply cable 2 to the head 100H. If this noise current affects changes in the detection current flowing through the detection coil 1, there is a risk that the detection accuracy of the proximity sensor 100 will decrease.

[0063] The proximity sensor 100 of this embodiment has a lower dielectric constant than a sensor composed solely of adhesive. Therefore, capacitive coupling is less likely to occur between the current circuit between the power supply cable 2 and the detector coil 1 and the head housing 3. Therefore, noise current is less likely to flow into the head 100H. Therefore, the proximity sensor 100 can achieve both mechanical strength provided by the filler and detection accuracy. While this embodiment is configured such that the filler is filled in the head housing 3, this does not necessarily mean the entire head housing 3. It may also be configured such that only the portion of the head housing 3 on the +Y direction side, including the detector coil 1, is filled. Furthermore, the head housing 3 does not need to be filled entirely around the circumference of the head housing 3, with the Y-axis direction as its centerline. It is sufficient that at least the inner space, including the detector coil 1, is filled. In this case, an air layer may exist between the filled portion and the head housing 3.

[0064] The filler has a relative dielectric constant of 3.7 or less. Since the filler has a relative dielectric constant of 3.7 or less, capacitive coupling is unlikely to occur between the current circuit between the power supply cable 2 and the detection coil 1 and the head housing 3. Therefore, the proximity sensor 100 can reduce a decrease in detection accuracy caused by noise flowing in from the power supply cable 2.

[0065] The internal space of the head housing 3 has a first space in the Y-axis direction that includes the detector coil 1, and a second space that is located on the -Y-direction side of the first space and does not include the detector coil 1. The filler filled in the first space has a lower relative dielectric constant than the filler filled in the second space.

[0066] That is, when the filler filled in the first space is the first filler and the filler filled in the second space is the second filler, the relative dielectric constant of the first filler is lower than the relative dielectric constant of the second filler.

[0067] With this configuration, capacitive coupling between the current circuit between the power supply cable 2 and the detector coil 1 and the head housing 3 is likely to occur in the second space filled with the second filler, i.e., the space that does not include the detector coil 1. Therefore, even if a current circuit is formed that includes the power supply cable 2, the head housing 3, and the ground, the current is likely to flow through a path that passes through the second space that does not include the detector coil 1. Therefore, even if a noise current enters the head 100H from the power supply cable 2, the noise current is unlikely to flow near the detector coil 1. Therefore, the effect of the noise current flowing from the power supply cable 2 on the detection current is reduced. Furthermore, because the second filler can be selected from a material that prioritizes hardness over dielectric constant, the durability of the entire head 100H can be improved.

[0068] The head housing 3 has a detection surface 30 that is a surface for detecting the detection object D. The first filler and the second filler are filled so that the end on the +Y direction side of the second space is located on the −Y axis direction side (rear side) of the −Y axis direction end (rear end) 56 of the detection coil 1.

[0069] Therefore, even if a noise current flows in from the power supply cable 2, the noise current is unlikely to flow near the detection coil 1. This reduces the effect of the noise current flowing in from the power supply cable 2 on the detection current.

[0070] The proximity sensor 100 further includes a conductive electric shield 43. The electric shield 43 covers the detection coil 1 in a circumferential direction with the Y-axis direction as its centerline. The first filler and the second filler are filled so that the +Y-direction side end of the second space is located on the -Y-direction side (rear side) of the -Y-direction side end (rear end) 54 of the electric shield 43.

[0071] The electric shield 43 is provided to prevent external noise from reaching the detector coil 1. For this reason, the electric shield 43 is provided so as to sufficiently cover the detector coil 1 in the Y-axis direction. Therefore, by positioning the boundary between the first space and the second space on the -Y-axis side of the -Y-axis end of the electric shield 43, the distance in the Y-axis direction between the boundary between the first space and the second space and the detector coil 1 becomes longer. Therefore, the effect of noise current flowing in from the power supply cable 2 on the detection current is reduced.

[0072] The space in the head housing 3 that is filled with the filler is divided into a front space 51, a middle space 52, and a rear space 53 in the Y-axis direction. The front space 51 is a space inside the head housing 3 that is forward (in the +Y direction) of a rear end 56, which is the end of the detector coil 1 in the -Y direction. The middle space 52 is a space inside the head housing 3 that is rear (in the -Y direction) of the rear end 56 of the detector coil 1 and forward (in the +Y direction) of a rear end 54, which is the end of the -Y direction of the electric shield 43. The rear space 53 is a space inside the head housing 3 that is rear (in the -Y direction) of the rear end 54 of the electric shield 43.

[0073] As an example, the first filler is filled in the front space 51, and the second filler is filled in the middle space 52 and the rear space 53. In this case, the first space is the front space 51, and the second space is the middle space 52 and the rear space 53. That is, the boundary between the first space and the second space is the boundary 56 between the front space 51 and the middle space 52.

[0074] As another example, the first filler is filled in the front space 51 and the middle space 52, and the second filler is filled in the rear space 53. In this case, the first space is the front space 51 and the middle space 52, and the second space is the rear space 53. That is, the boundary between the first space and the second space is the boundary 54 between the middle space 52 and the rear space 53.

[0075] The filler is a mixture of an adhesive and an additive. Examples of the adhesive include silicone-based, urethane-based, and polyethylene-based adhesives. The additive has a lower dielectric constant than the adhesive. The additive material is, for example, at least one of fluorine, polyimide, chlorine, polyethylene, acrylic, urethane, boron nitride, air, and vacuum filler. The additive shape includes, for example, primary particle platelet type, granulated agglomerate type, and flake type.

[0076] The Shore hardness of the filler after hardening is preferably D0 or more, and more preferably D80 or more. This is because when the Shore hardness of the filler after hardening is D80 or more, the mechanical strength of the proximity sensor 100 can be sufficiently improved.

[0077] The proximity sensor 100 may further include a member 46 that fixes the head substrate 13 inside the cylindrical head portion 32. The member 46 that fixes the head substrate 13 inside the cylindrical head portion 32 allows the proximity sensor 100 to be assembled stably.

[0078] The detector coil 1 will be described in detail below with reference to Fig. 9. Fig. 9 is an enlarged perspective view of the detector coil 1 and related devices. In Fig. 9, configurations that are not necessary for the description of Fig. 9 are omitted to prioritize clarity.

[0079] As shown in FIG. 9, the detection coil 1 has a coil wire 1L. The power supply cable 2 has a core wire 21. The proximity sensor 100 further includes a head substrate 13. The head substrate 13 is housed in the head housing 3 and extends along the longitudinal direction (front-to-back direction). The head substrate 13 is provided with a circuit that electrically connects the coil wire 1L and the core wire 21. In other words, the head substrate 13 can be said to be a member that electrically connects the coil wire 1L and the core wire 21.

[0080] The coil wire 1L and the core wire 21 are both flexible linear members, which makes handling them cumbersome during assembly. However, because the coil wire 1L and the core wire 21 are housed in the head housing 3 via the head substrate 13, which has a certain degree of hardness, assembly of the proximity sensor 100 is easy and stable.

[0081] The proximity sensor 100 further includes a ferrite core 23 and a core holder 24. The coil wire 1L is wound around the ferrite core 23. The core holder 24 holds the ferrite core 23. The head substrate 13 is fixed to the core holder 24. If the ferrite core 23 and the head substrate 13 were not fixed to each other and were freely movable, the ferrite core 23 and the head substrate 13 might be separated by more than a certain distance during assembly, which might apply a load to the coil wire 1L and cause the coil wire 1L to break. By fixing the ferrite core 23 and the head substrate 13 via the core holder 24, the risk of the coil wire 1L breaking during assembly is reduced.

[0082] The coil wire 1L has a first coil wire 11L and a second coil wire 12L that is different from the first coil wire 11L. The detection coil 1 has a first coil 11 around which the first coil wire 11L is wound, and a second coil 12 around which the second coil wire 12L is wound outside the first coil 11. There are two first coil wires 11L extending from the first coil 11, and one first coil wire 11L is connected to the surface of the head substrate 13 on the +Z direction side as shown in FIG. 9, while the other first coil wire 11L is connected to the surface of the head substrate 13 on the -Z direction side. In this embodiment, the two first coil wires 11L are connected to different surfaces of the head substrate 13, but they may also be connected to the same surface. 9, one second coil wire 12L is connected to the surface on the +Z direction side of the head substrate 13, and the other second coil wire 12L is connected to the surface on the −Z direction side of the head substrate 13. In this embodiment, the two second coil wires 12L are connected to different surfaces of the head substrate 13, but they may also be connected to the same surface.

[0083] Since the first coil 11 and the second coil 12 are positioned differently, the detection current generated in the first coil 11 and the detection current generated in the second coil 12 are affected differently by surrounding metal objects such as the detection object D and the external member E. In other words, the first coil 11 and the second coil 12 have their own characteristics. Therefore, by including the first coil 11 and the second coil 12 as the detection coil 1, the proximity sensor 100 can improve detection accuracy.

[0084] In a configuration in which the proximity sensor 100 includes the first coil 11 and the second coil 12 as the detection coil 1, the relative positional relationship between the first coil 11 and the second coil 12 may affect detection accuracy. Because the first coil 11 and the second coil 12 are often positioned on the inner surface of the +Y direction portion of the head housing 3, high processing accuracy is required for the +Y direction portion of the head housing 3 to ensure detection accuracy. As described above, when the head cylindrical portion 32 and the metal cap 35 (metal cap portion 35) including the detection surface 30 are made of different materials, the difficulty of highly accurate processing of the +Y direction portion of the head housing is reduced, making the proximity sensor 100 including the first coil 11 and the second coil 12 particularly effective. Furthermore, because the second coil 12 is positioned outside the first coil 11, it is positioned close to the inner circumferential surface of the head housing 3, i.e., the inner surface of the head cylindrical portion 32. Therefore, the +Y direction side portion of the head housing 3 requires high processing accuracy not only near the center line of the head cylindrical portion 32 but also around the periphery of the center line. As described above, if the head cylindrical portion 32 and the metal cap 35 including the detection surface 30 are made of different materials, the difficulty of highly accurate processing of the +Y direction side portion of the head housing is reduced, and therefore it is particularly effective to configure the proximity sensor 100 to have the first coil 11 and the second coil 12 arranged outside the first coil 11.

[0085] The proximity sensor 100 comprises a transmitting circuit 5, a receiving circuit 6, and a control circuit 7. The transmitting circuit 5 supplies a pulsed excitation current to the first coil 11. The receiving circuit 6 detects the detection current generated in both the first coil 11 and the second coil 12. The control circuit 7 detects the presence or position of a detection object D based on a reception signal from the receiving circuit 6 that detected the detection current. Because the detection current changes in response to changes in the magnetic field, the reception signal from the receiving circuit 6 reflects the change in the magnetic field. The control circuit 7 outputs the detection result of the presence or position of the detection object D.

[0086] The detector coil 1 has a first coil 11 and a second coil 12 that is different from the first coil 11. Because the first coil 11 and the second coil 12 are separate bodies, their arrangements in the head housing 3 are different. As a result, the change in the detection current due to a change in the magnetic field differs between the detection current of the first coil 11 and the detection current of the second coil 12. The receiver circuit 6 transmits the detection current generated in the first coil 11 (hereinafter referred to as the first detection current) and the detection current generated in the second coil 12 (hereinafter referred to as the second detection current) to the control circuit in a mutually independent state. The control circuit 7 detects the presence or absence and position of the object D to be detected based on a first reception signal based on the first detection current and a second reception signal based on the second detection current. At this time, the first reception signal and the second reception signal exhibit different signal changes in response to a certain change in the magnetic field. For example, even if the magnetic field changes due to both the metal object D to be detected and a member E external to the metal object, the first received signal is likely to reflect the magnetic field change due to the metal object D to be detected, and the second received signal is likely to reflect the magnetic field change due to the member E external to the metal object, and in this way, by using multiple coils with different arrangements as the detector coil 1, it is possible to acquire various information about the surroundings of the head housing 3. Therefore, in detection by the proximity sensor 100, the first received signal based on the detection current generated in the first coil 11 and the second received signal based on the detection current generated in the second coil 12 are processed by the control circuit 7 taking into account the respective characteristics of the first coil 11 and the second coil 12, thereby improving the detection accuracy.

[0087] The receiver circuit 6 includes a first receiver circuit 61 that detects the detection current generated in the first coil 11 and a second receiver circuit 62 that detects the detection current generated in the second coil 12. This configuration allows the first and second detection currents to be transmitted to the control circuit 7 simultaneously while being independent of each other. This allows the control circuit 7 to receive the first reception signal for the same period as the second reception signal, thereby reducing the time required to detect the presence or distance of the object D using the first and second reception signals. This also eliminates the need for calculations to correct for a discrepancy between the period for acquiring the first reception signal and the period for acquiring the second reception signal. Therefore, the receiver circuit 6 including the first receiver circuit 61 and the second reception circuit 62 can improve the detection accuracy of the proximity sensor 100.

[0088] 10A to 11B, the suppression of the influence of metal objects other than the detection target D will be described in detail. Hereinafter, the time change of the first reception signal may be referred to as the first reception waveform, and the time change of the second reception signal may be referred to as the second reception waveform. Furthermore, the first reception waveform and the second reception waveform may be collectively referred to as the reception waveform.

[0089] 10A to 11B show a zero-adjusted first received waveform (reference symbol ΔR1) and a zero-adjusted second received waveform (reference symbol ΔR2). In this embodiment, zero adjustment refers to adjusting the signal strength to zero when there is no external metal member E and no metal detection target D within the detection range. In FIGS. 10A to 11B, the horizontal axis represents time and the vertical axis represents the signal strength of the received waveform.

[0090] 10A is a graph showing an image of a zero-adjusted received waveform when there is no external metal member E and no detection target D within the detection range. As described above, a zero-adjusted waveform is a waveform that has been adjusted so that the value shown by the waveform becomes zero when there is no external metal member E and no detection target D within the detection range, so both the first and second received waveforms show zero on the graph.

[0091] 10B is a graph showing an image of the zero-adjusted received waveform when there is no external member E and a detection target D is within the detection range. As shown in FIG. 10B, the change in signal strength of the first received waveform is larger than the change in signal strength of the second received waveform. This is because first coil 11 and second coil 12 are arranged so that the first detection current generated in first coil 11 is more susceptible to the influence of magnetic field changes caused by detection target D within the detection range than the second detection current generated in second coil 12.

[0092] FIG. 11A is a graph showing an image of a zero-adjusted received waveform when an external member E is present and the detection target D is not within the detection range. As shown in FIG. 11A, the change in signal strength of both the first received waveform and the second received waveform is large. This is because both the first detection current generated in the first coil 11 and the second detection current generated in the second coil 12 are susceptible to changes in the magnetic field caused by the external member E to which the head 100H is fixed. However, while the change in signal strength of the first received waveform shown in FIG. 10B is similar to the change in signal strength of the first received waveform shown in FIG. 11A, the change in signal strength of the second received signal shown in FIG. 10B is clearly larger than the change in signal strength of the second received signal shown in FIG. 11A. Also, in FIG. 11A, the change in signal strength of the second received signal is larger than the change in signal strength of the first received signal. This is because the first coil 11 and the second coil 12 are arranged so that the second detection current generated in the second coil 12 is more susceptible to the influence of the external member E than the first detection current generated in the first coil 11.

[0093] FIG. 11B is a graph showing an image of a zero-adjusted received waveform when an external member E is present and the detection target D is within the detection range. Because the head 100H is fixed to the external member E, as in FIG. 11A, the change in signal intensity of both the first and second received waveforms is large, as shown in FIG. 11B. However, unlike FIG. 11A, the change in signal intensity of the first received signal is larger than the change in signal intensity of the second received signal. In FIGS. 10A to 11B, the change in signal intensity of the first received signal increases when there is a change in the magnetic field due to at least one of the external member E and the detection target D. This makes it difficult to detect the presence or distance of the detection target D from the first received signal alone. Particularly when the distance between the detection target D and the first coil 11 is long, the change in signal intensity of the first signal due to the change in magnetic field due to the detection target D and the change in signal intensity of the second signal due to the change in magnetic field due to the external member E are similar, which tends to reduce detection accuracy. 10A to 11B, the signal strength of the second reception signal changes significantly when there is a change in the magnetic field due to an external member E. Therefore, by combining the first reception signal and the second reception signal, it is possible to improve the accuracy of detecting the presence or absence and position of the detection target D.

[0094] More specifically, the calculation is performed using the difference between the zero-adjusted first received waveform and the zero-adjusted second received waveform. The difference here refers to the value obtained by subtracting the zero-adjusted second received waveform from the zero-adjusted first received waveform. According to this processing, the calculation result is a negative value in Figures 10A and 11A, which show the received signal when the detection target D is not present, and a positive value in Figures 10B and 11B, which show the received signal when the detection target D is present. In this way, the detection accuracy of the proximity sensor 100 can be improved.

[0095] Another example of the sensing surface 30 will be described below with reference to FIG. 12 . FIG. 12 is a partially cutaway perspective view of a cylinder-type proximity sensor 100. As with FIG. 8 , the filler is not shown or referenced in FIG. 12 to prioritize clarity. However, the filler fills the space inside the head housing 3. FIG. 12 also shows arrows X, Y, and Z indicating three mutually orthogonal directions. The directions indicated by the arrows X, Y, and Z correspond to the orientation of the proximity sensor 100. The direction indicated by the arrow X is referred to as the X-axis direction, the direction indicated by the arrow Y is referred to as the Y-axis direction, and the direction indicated by the arrow Z is referred to as the Z-axis direction. One of the directions along the X-axis direction is referred to as the +X direction, and the other is referred to as the −X direction. One of the directions along the Y-axis direction is referred to as the +Y direction, and the other is referred to as the −Y direction. One of the directions along the Z-axis direction is referred to as the +Z direction, and the other is referred to as the −Z direction. The normal direction of the sensing surface 30 is the Y-axis direction, and the direction in which the sensing surface 30 faces is the +Y direction.

[0096] The sensing surface 30 shown in FIG. 12 is made of resin. In a proximity sensor 100 that uses induced current, if the sensing surface 30 is made of metal, the sensing accuracy may be reduced due to factors such as noise generated by eddy currents due to the magnetic field of the sensing surface 30 itself, or changes in the sensing current due to changes in the magnetic field caused by the sensing surface 30 itself. For this reason, a resin sensing surface 30 is less likely to reduce the sensing accuracy. On the other hand, resin members have lower strength than metal members. For this reason, filling the head housing 3 with a filler improves the mechanical strength, achieving both high sensing accuracy and strength. Note that capacitive coupling is likely to occur between the member including the sensing surface 30 and the sensing coil 1 in the head 100H. Therefore, making the sensing surface 30 out of a resin member makes it easier to prevent noise currents from flowing near the sensing coil 1.

[0097] However, as described above, if the head housing 3 is filled with a filler, the filler may cause capacitive coupling, which may reduce the detection accuracy of the proximity sensor 100. More specifically, if the filler causes capacitive coupling, a current circuit is formed among the power supply cable 2, the head housing 3, and the ground connected to the head housing 3, which may cause noise current to flow from the power supply cable 2 to the head 100H. For this reason, filling the head housing 3 having a resin detection surface 30 with a filler containing an additive with a relatively low dielectric constant is particularly effective from the perspectives of the detection accuracy of the proximity sensor 100 and the strength of the head 100H. Furthermore, the front space 51 located on the +Y direction side of the head housing 3 and including the detector coil 1 in the Y-axis direction is filled with a first filler containing an additive with a low dielectric constant, and the rear space 53 in the Y-axis direction that does not include the detector coil 1 is filled with a second filler that has a higher dielectric constant and higher hardness than the first filler. This configuration makes it easy to prevent a decrease in detection accuracy due to the influence of noise flowing into the head housing 3 on the detection current, while also ensuring the mechanical strength of the head 100H.

[0098] The flat-type proximity sensor 100 will be described below with reference to Fig. 13. Fig. 13 is an enlarged perspective view of the vertical cross section of the flat-type proximity sensor 100.

[0099] 13, a flat-type proximity sensor 100 has a flat box-shaped head housing 3B filled with a filler. The filler is indicated by reference numeral 38 in FIG.

[0100] The box-shaped head housing 3B is not limited to a strict box shape, but may be approximately box-shaped. The box-shaped head housing 3B has a first surface 101 and a second surface 102 different from the first surface 101. The first surface 101 includes a detection surface 30 that detects a detection target D. The second surface 102 is installed (fixed) in contact with a surface of an external member E.

[0101] The proximity sensor 100 further includes a head substrate 13. The head substrate 13 is housed in a box-shaped head housing 3B and is disposed along the first surface 101. The head substrate 13 electrically connects the detection coil 1 and the power supply cable 2.

[0102] The aforementioned inflow of noise current from the power supply cable 2 to the head 100H due to capacitive coupling of the filler may affect the detection current generated in the detector coil 1, potentially reducing the detection accuracy of the proximity sensor 100. Therefore, it is sufficient to separate the portion of the filler that may become a noise current circuit due to capacitive coupling from the filler from the detector coil 1. However, in the head housing 3B, the circuit (corresponding to the head substrate 13) that electrically connects the power supply cable 2 and the detector coil 1 is located near the detector coil 1. Therefore, compared to other types of proximity sensors 100, the flat-type proximity sensor 100 is more likely to affect the detection current when noise current flows from the power supply cable 2 to the head 100H. Therefore, a configuration that reduces the dielectric constant of the filler to make it more difficult for noise current from the power supply cable 2 to flow into the head 100H is particularly effective.

[0103] The embodiments are illustrative in all respects and are not limiting. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. Among the configurations described in the embodiments, those other than those described as one aspect of the present invention in the "Means for Solving the Problems" are optional configurations and may be deleted or modified as appropriate. [Industrial Applicability]

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

[0105] D. Object to be detected E. External components F magnetic flux lines 1 detection coil 1L coil wire 2 Power supply cables 3 Head housing 3B Box-shaped head housing 5. Transmitting circuit 6 Receiving circuit 7 Control Circuit 8 Amplifier enclosure 9 Display section 11 First coil 11L First coil wire 12 Second coil 12L Second coil wire 13 Head board 20 Shielded outer jacket 21 Core Wire 23 Ferrite core 24 Core holder 30 Detection surface 31 Fixed part 32 Head cylinder 33 Contact part 34 Connection 35 Cap part 36 Bottom 37 Periphery 39 Cable guide 43 Electrical Shield 45 Insulating material 51 Front space 52 Chubu space 53 Rear space 61 First receiving circuit 62 Second receiving circuit 70 Amplifier board 100 Proximity Sensor

Claims

1. A proximity sensor that detects a detection object, a detection coil generating a detection current; a metal head housing that houses the detection coil; a power supply cable electrically connected to the detection coil and connected to the head housing; a filler that is filled in at least a part of the internal space of the head housing so that the detection coil is buried; Equipped with The filler is a mixture of an adhesive and an additive having a lower dielectric constant than the adhesive.

2. The proximity sensor according to claim 1 , wherein the filler has a relative dielectric constant of 3.7 or less.

3. 3. The proximity sensor according to claim 1, wherein the filler has a Shore hardness of D0 degrees or more after hardening.

4. the detection coil is disposed on one side of the head housing in a predetermined direction, the power supply cable is connected to the head housing at the other side of the head housing in the predetermined direction, a first space including the detection coil is filled with a first filler as the filler; The proximity sensor according to claim 1 or 2, wherein a second filler having a higher dielectric constant than the first filler is filled on the other side of the first space in the predetermined direction.

5. the head housing has a detection surface whose normal direction is along the predetermined direction, The proximity sensor according to claim 4 , wherein the other end of the first space is located on the other side of the other end of the detection coil.

6. a conductive electrical shield covering the sensing coil; the head housing has a detection surface whose normal direction is along the predetermined direction, The proximity sensor according to claim 4 , wherein the other end of the first space is located on the other side of the other end of the electric shield.

7. The detection coil a first coil wound with a first coil wire; a second coil in which a second coil wire different from the first coil wire is wound outside the first coil; and a transmission circuit that supplies a pulsed excitation current to one of the first coil and the second coil; a receiving circuit for detecting a first sensed current generated in the first coil and a second sensed current generated in both the first coil and the second coil; a control circuit that detects the object to be detected based on a signal received from the receiving circuit that detects the first detection current and the second detection current; Furthermore, The proximity sensor according to claim 1 or 2, wherein the control circuit outputs a result of detecting the object to be detected.

8. The head housing includes: a detection surface that is located between the detection coil and the detection object when the detection object is detected and faces the detection object; 3. The proximity sensor according to claim 1, wherein the proximity sensor is configured by combining a metal body and a metal cap that is attached to an opening in the body and includes the sensing surface.

9. 3. The proximity sensor according to claim 1, wherein the head housing is positioned between the detection coil and the object to be detected when the object to be detected, and the detection surface facing the object to be detected is made of metal.

10. 3. The proximity sensor according to claim 1, wherein the head housing is positioned between the detection coil and the object to be detected when the object to be detected, and the detection surface facing the object to be detected is made of resin.

11. a head substrate accommodated in the head housing, the head housing is substantially box-shaped and has a first surface including a detection surface and a second surface different from the first surface and coming into contact with an external member when the head housing is installed on the external member, a part of a circuit that electrically connects the detection coil and the power supply cable is mounted on the head substrate; The proximity sensor according to claim 1 , wherein the head substrate is disposed along the first surface.

Images