Proximity sensor and amplifier

Abstract

The invention provides a proximity sensor and an amplifier. The proximity sensor detects a detection object. The proximity sensor includes a detection coil, a head housing, a power supply cable, a control circuit, an amplifier substrate, and an amplifier housing. The head housing accommodates the detection coil. A power supply cable is connected to the head housing to supply power to the detection coil. A pulsed excitation current is supplied to a detection coil for generating a magnetic field, and a control circuit outputs a result of detecting a detection target on the basis of a reception signal. The amplifier housing accommodates an amplifier substrate on which a control circuit is implemented. The amplifier housing is arranged outside a head housing having a detection surface, a connection portion, and a fixed portion.

Description

Technical Field

[0001] This invention relates to proximity sensors and amplifiers. Background Technology

[0002] Chinese Utility Model Patent 202853631 discloses a proximity sensor for detecting an object. In the proximity sensor described in Chinese Utility Model Patent 202853631, a head substrate 16 (main circuit substrate) is housed within a head shaft (housing 11). When the head shaft (housing 11) is shorter, it is easier to arrange the head shaft even in environments with obstacles, while the distance between the head shaft (housing 11) and the object being detected increases. As the distance between the head shaft (housing 11) and the object being detected increases, the change in the magnetic field used to detect the object weakens.

[0003] To capture this subtle change, a pulsed type (the type that applies a pulsed excitation current) can be used.

[0004] In the proximity sensor described in Chinese Utility Model Patent 202853631, even when a pulse-type sensor is used, the calculation based on the change in magnetic field becomes complex, even if a slight change in magnetic field can be detected. Therefore, as the size of the substrate of the control circuit used to perform the calculation increases, the size of the head shaft (housing 11) that houses the substrate inevitably increases as well. Summary of the Invention

[0005] The present invention was made in view of the above-mentioned problems, and the object of the present invention is to provide a proximity sensor and amplifier housing that can achieve a long detection distance while miniaturizing the head shaft.

[0006] A proximity sensor according to an embodiment of the present invention detects a target object. The proximity sensor includes a detection coil, a head housing, a power supply cable, a transmitting circuit, a receiving circuit, a control circuit, an amplifier substrate, and an amplifier housing. The detection coil generates a magnetic field for detection. The head housing houses the detection coil. The power supply cable is a cable connected to the head housing to supply power to the detection coil. The transmitting circuit supplies a pulsed excitation current to the detection coil. The receiving circuit detects the detection current generated in the detection coil. The control circuit outputs a result of detecting the target object based on a received signal from the receiving circuit that has detected the detection current. The control circuit is implemented on the amplifier substrate. The amplifier housing houses the amplifier substrate. The head housing includes a detection surface, a connecting portion, and a fixed portion. The connecting portion is located on the opposite side of the head housing relative to the detection surface in the normal direction of the detection surface, and the power supply cable is connected to the connecting portion. The fixed portion is located between the detection surface and the connecting portion in the normal direction of the detection surface, and contacts a fastener used to fix the head housing to the external component when the head housing is fixed to the external component. The amplifier housing is disposed outside the head housing.

[0007] An amplifier according to another embodiment of the present invention is included in a proximity sensor. The proximity sensor includes a head, a power supply cable, an amplifier, a transmitting circuit, a receiving circuit, and a control circuit. The head includes a head housing for housing a detection coil used to generate a magnetic field for detection. The power supply cable is connected to the head housing. The transmitting circuit supplies a pulsed excitation current to the detection coil. The receiving circuit detects the detection current generated in the detection coil. The control circuit outputs a result of detecting an object based on a received signal from the receiving circuit that has detected the detection current. The amplifier is electrically connected to the head via the power supply cable. The amplifier includes: an amplifier substrate connected to a core wire included in the power supply cable, and having the control circuit implemented thereon; and an amplifier housing for housing the amplifier substrate.

[0008] The proximity sensor and amplifier housing according to the present invention enable miniaturization of the head shaft. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the proximity sensor structure;

[0010] Figure 2 This is a 3D view of an L-shaped proximity sensor;

[0011] Figure 3 This is a 3D view of a cylindrical proximity sensor;

[0012] Figure 4 This is a 3D view of a flat proximity sensor;

[0013] Figure 5 This is a longitudinal cross-sectional view of an L-shaped proximity sensor;

[0014] Figure 6 This is an enlarged three-dimensional view of the longitudinal cross-section of the front part of the head shell;

[0015] Figure 7 It is a double logarithmic curve plotting frequency-skin depth with the horizontal and vertical axes as the axes, and a schematic diagram used to illustrate the double logarithmic curve plot.

[0016] Figure 8 This is a three-dimensional view of the longitudinal cross-section of the head shell;

[0017] Figure 9 This is an enlarged perspective view illustrating the detection coil and the device associated with the detection coil;

[0018] Figure 10A It is a graph representing the zeroed received waveform when there are no external components and the object being detected is not within the detection range;

[0019] Figure 10B It is a graph representing the zeroed received waveform when there are no external components and the object being detected is within the detection range;

[0020] Figure 11A It is a graph representing the zeroed received waveform when there are external components and the object being detected is not within the detection range;

[0021] Figure 11B It is a graph representing the zeroed received waveform when there are external components and the object being detected is within the detection range;

[0022] Figure 12 It is a 3D view of a partial cut of a cylindrical proximity sensor; and

[0023] Figure 13 This is a magnified 3D view of the longitudinal cross-section of a flat proximity sensor. Detailed Implementation

[0024] In the following description, embodiments of the invention will be illustrated with reference to the accompanying drawings. Note that in the drawings, the same or corresponding parts are indicated by the same reference numerals, and their description will not be repeated.

[0025] In the following description, terms such as “front” and “rear” that indicate position or direction may be used. These terms are used for convenience in understanding the embodiments and, unless otherwise explicitly stated, are not related to the actual direction of the action.

[0026] In the following description, a proximity sensor 100 according to an embodiment of the present invention will be explained with reference to the accompanying drawings. First, reference will be made to... Figure 1To illustrate the general outline of proximity sensor 100. Figure 1 This is a schematic diagram of the proximity sensor 100. Figure 1 The illustrations indicate three mutually orthogonal directions: arrows X, Y, and Z. The directions indicated by arrows X, Y, and Z all correspond to the arrangement orientation of the proximity sensor 100, with the direction indicated by arrow X referred to as the X-axis direction, the direction indicated by arrow Y as the Y-axis direction, and the direction indicated by arrow Z as the Z-axis direction. One direction along the X-axis is called the +X direction, and the other is called the -X direction. One direction along the Y-axis is called the +Y direction, and the other is called the -Y direction. One direction along the Z-axis is called the +Z direction, and the other is called the -Z direction.

[0027] The proximity sensor 100 is a sensor that detects the presence, absence, or position of the object D. For example... Figure 1 As illustrated, the proximity sensor 100 includes a head 100H, an amplifier 100A, and a power supply cable 2 connecting the head 100H and the amplifier 100A. The head 100H includes a detection coil 1 and a head housing 3 housing the detection coil 1. The amplifier 100A includes a transmitting circuit 5, a receiving circuit 6, a control circuit 7, an amplifier substrate 70 on which the transmitting circuit 5, the receiving circuit 6, and the control circuit 7 are disposed, and an amplifier housing 8 housing the amplifier substrate 70.

[0028] The detection coil 1 generates the magnetic field used for detection. The power supply cable 2 is a component for supplying power to the detection coil 1, and power is supplied from a power source (not shown) via the power supply cable 2 to the detection coil 1. The head housing 3 houses the detection coil 1. The head housing 3 is arranged such that the normal direction of the detection surface 30 (described later) is along the Y-axis direction, and the detection surface 30 faces the +Y direction side. In this embodiment, the head housing 3 has a shape where the long side direction is along the Y-axis direction, and includes a connecting portion 34 that guides the power supply cable 2 to the -Y direction side.

[0029] The transmitting circuit 5 supplies a pulsed excitation current to the detection coil 1. The receiving circuit 6 detects the detection current generated in the detection coil 1. The control circuit 7 detects the presence, absence, or location of the detection object D based on the received signal from the receiving circuit 6, which has already detected the detection current. Since the detection current changes according to the magnetic field, the change in the magnetic field is reflected in the received signal from the receiving circuit 6. The control circuit 7 outputs the result of detecting the presence, absence, or location of the detection object D.

[0030] The transmitting circuit 5, receiving circuit 6, and control circuit 7 are implemented on the amplifier substrate 70. The power supply cable 2 electrically connects the detection coil 1 and the amplifier substrate 70. Although the transmitting circuit 5, receiving circuit 6, and control circuit 7 are implemented on the amplifier substrate 70 in this embodiment, at least the control circuit 7 can be implemented. For example, the substrate implementing the transmitting circuit 5 and receiving circuit 6 can be housed in the head housing 3.

[0031] The head housing 3 includes a detection surface 30 disposed at the end of the head housing 3 on the +Y direction side, and a cylindrical head portion 32 having a circumferential shape with its centerline along the Y-axis direction. The cylindrical head portion 32 has a fixed portion 31. The fixed portion 31 is disposed between the connecting portion 34 in the Y-axis direction and the detection surface 30, and is the portion to which a fastening member, such as a nut (not shown), is fastened when the head housing 3 is fixed to the external member E.

[0032] The amplifier housing 8 houses the amplifier substrate 70. The amplifier housing 8 is located outside the head housing 3.

[0033] Generally, proximity sensors using induced current are products with a detection distance so short that they collide with the detected object D when the detected object D deviates from its assumed movement path. Therefore, achieving a long detection distance in a proximity sensor using induced current reduces the risk of collision with the detected object D. The proximity sensor 100 using induced current includes a sinusoidal type that applies a sinusoidal excitation current to the detection coil 1 and a pulsed type that applies a pulsed excitation current to the detection coil 1. Both types detect changes in the current generated in the detection coil 1, but the current change becomes weaker as the distance between the detected object D and the detection coil 1 increases. That is, to achieve a long detection distance, it is necessary to capture minute changes, but in the sinusoidal type, it is difficult to distinguish between the detected object D and a metallic object (external component E) other than the detected object D. In the type that supplies a pulsed excitation current to the detection coil 1, more information can be obtained compared to the sinusoidal type because a signal with characteristic changes along a time axis starting from the excitation timing can be obtained as the received signal based on the excitation current. For example, the detection object D can be distinguished from a metal body other than the detection object D by calculating the decay time from the peak of the received signal, or by matching the time axes of multiple received signals generated in multiple detection coils 1. Therefore, the pulse type has the advantage of improving the detection accuracy by calculation compared to the sinusoidal type. The proximity sensor 100 of this embodiment is a pulse type proximity sensor that supplies a pulse-shaped excitation current to the detection coil 1. The pulse type requires complex processing, such as controlling the timing of the application of the pulse-shaped excitation current to the coil and processing the current generated in the coil. Therefore, in order to achieve a long detection distance, when the detection object D is to be detected using the pulse type, a relatively complex control circuit 7 is required, and the amplifier board 70 of the control circuit 7 is enlarged.

[0034] 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 substrate 70 in an amplifier housing 8 separate from the head housing 3. In particular, in this embodiment, since the size in the Y-axis direction can be reduced, the proximity sensor 100 can be arranged even if sufficient mounting space is not provided in the Y-axis direction relative to the external member E.

[0035] As in Figure 1The power supply cable 2, illustrated in an enlarged manner, includes a core wire 21 through which the detection current flows and a shielding sleeve 20 covering the core wire 21 using a shielding element. The shielding sleeve 20 is electrically connected to an electrical shielding element 43, which will be described later. Note that the shielding sleeve 20 and the electrical shielding element 43 can be electrically connected, and can be directly or indirectly connected. Since the core wire 21 through which the detection current flows is covered by the shielding sleeve 20, changes in the detection current are almost unaffected by external factors. As mentioned above, the longer the distance between the object being detected (D) and the detection coil 1, the weaker the change in the detection current. In particular, in such cases, by employing a structure where the detection current is almost unaffected by external factors, the detection accuracy of the object being detected (D), which is further away from the detection coil 1, is improved. Therefore, based on the structure in which the core wire 21 is shielded, the detection accuracy of the proximity sensor 100 is improved.

[0036] Amplifier 100A includes a display unit 9 (e.g., an indicator light) for displaying the results output from control circuit 7. The display unit 9 is disposed on the front surface of amplifier housing 8. Because the display unit 9 is disposed on the front surface of amplifier housing 8, the user can easily grasp the detection results using proximity sensor 100 by visually recognizing amplifier housing 8.

[0037] The cylindrical head portion 32 is made of metal, and a portion thereof is machined as the fixed portion 31. A circumferential threaded groove is formed in the fixed portion 31 on a circumference with the Y-axis as its centerline. A threaded hole is provided in the outer member E, with a threaded groove corresponding to the threaded groove formed in the fixed portion 31. If the fixed portion 31 has an external thread, the threaded hole in the outer member E has an internal thread. The outer member E and the fixed portion 31 are fixed by a threaded engagement. With the outer member E and the fixed portion 31 threadedly engaged, a nut (not shown) can be threadedly engaged with the fixed portion 31 to further stabilize the positional relationship between the outer member E and the head housing 3 in the Y-axis direction. In particular, when the head housing 3 is arranged such that it does not protrude relative to the outer member E towards the +Y direction side (that is, the path side of the detection object D in the Y-axis direction), the outer member E and the fixed portion 31 are often fixed by a threaded engagement. Therefore, it is preferable to assemble the nut to the fixed portion 31 located on the -Y direction side relative to the outer member. Note that in this embodiment, a threaded hole is provided in the outer member E, and the head housing 3 is fixed to the outer member E by threading the fixing part 31 into the threaded hole. However, with the head housing 3 arranged in the through hole provided in the outer member E, the head housing 3 can be configured to be fixed to the outer member E by clamping the outer member E between a nut that is threadedly engaged with the fixing part 31 located on the +Y direction side relative to the outer member E and a nut that is threadedly engaged with the fixing part 31 located on the -Y direction side relative to the outer member E.

[0038] Therefore, the metal fixing part 31 is a threaded groove, which allows the proximity sensor 100 to be easily fixed to the external member E. In this embodiment, the threaded groove is provided in the fixing part 31, but it can 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. The head housing 3 can be fixed to the external member E by attaching a clamp to the metal fixing part 31 and fixing the clamp to the external member E.

[0039] In the following text, reference will be made to Figures 2 to 4 To illustrate the deformation of proximity sensor 100. Figure 2 This is a 3D view of the L-shaped proximity sensor 100. Figure 3 This is a 3D view of the cylindrical proximity sensor 100. Figure 4 This is a 3D view of the flat proximity sensor 100.

[0040] Since the side view of the head housing 3, which includes the head 100H (not shown) and has a detection surface 30, is L-shaped, therefore Figure 2 The illustrated proximity sensor 100 is also referred to as L-type. Because the structure with the detection surface 30 is cylindrical, therefore... Figure 3 The illustrated proximity sensor 100 is also referred to as cylindrical. Because the structure with the detection surface 30 is box-shaped (having a flat surface), therefore... Figure 4 The illustrated proximity sensor 100 is also referred to as a flat type.

[0041] Figures 2 to 4 The illustrated proximity sensors 100 include a head housing 3 as a structure having a detection surface 30, and an amplifier housing 8 separate from the head housing 3. For example... Figure 2 and Figure 3 As illustrated, in the L-shaped proximity sensor 100 and the cylindrical proximity sensor 100, the head housing 3 includes a detection surface 30 and a cylindrical head portion 32 with the normal direction of the detection surface as its center line. The head housing 3 of both the L-shaped and cylindrical proximity sensors 100 has an elongated shape, such that the axial direction of the cylindrical head portion 32 is the direction of its longer side. On the other hand, as... Figure 4 As illustrated, the flat proximity sensor 100 includes a box-shaped head housing 3B, and the head housing 3B has a detection surface 30.

[0042] In the following text, reference will be made to Figures 5 to 9 To illustrate the L-type proximity sensor 100, first, refer to... Figure 5 Let me explain the L-type proximity sensor 100 in detail. Figure 5 This is a longitudinal cross-sectional view of the L-shaped proximity sensor 100.

[0043] like Figure 5 As illustrated, the proximity sensor 100 includes a detection coil 1, a power supply cable 2, and a head housing 3.

[0044] The detection coil 1 generates the magnetic field used for detection. The power supply cable 2 is a component used to supply power to the detection coil 1. The head housing 3 houses the detection coil 1. The head housing 3 is arranged such that the normal direction of the detection surface 30 is along the Y-axis direction, and the detection surface 30 faces the +Y direction side. In this embodiment, the head housing 3 has an elongated shape with its long side along the Y-axis direction, and includes a connecting portion 34 that guides the power supply cable 2 to the -Y direction side.

[0045] The head housing 3 has a detection surface 30 made of metal on the +Y direction side. Since the detection coil 1 is arranged near the detection surface 30, it is positioned on the +Y direction side of the head housing 3. The head housing 3 has an elongated shape in the Y-axis direction, and the detection coil 1 is arranged such that its -Y direction end is located on the +Y direction side relative to the connecting portion 34; in other words, the detection coil 1 and the connecting portion 34 are separated from each other in the Y-axis direction.

[0046] The connecting part 34 is arranged on the -Y direction side of the head housing 3 and guides the power supply cable 2 in the -Z direction.

[0047] In the following text, for convenience, the -Y direction side of the head housing 3 may be referred to as one end side of the head housing 3 in the long side direction (in other words, the connecting part 34 side), and the +Y direction side of the head housing 3 may be referred to as the other end side of the head housing 3 in the long side direction (in other words, the detection surface 30 side). In addition, the -Y direction side may be referred to as the rear side, and the +Y direction side may be referred to as the front side.

[0048] Figure 5 The illustrated head housing 3 has a shape in which the connecting portion 34 guides the power supply cable 2 in the -Z direction, so the head housing has an L-shape in the side view (as viewed in the X-axis direction). That is, the connecting portion 34 does not extend rearward along the Y-axis direction, which is the normal direction of the detection surface 30, but extends in a direction that intersects the front-back direction (long side direction), which is the Y-axis direction.

[0049] Therefore, an L-shaped proximity sensor 100 with an L-shaped head housing 3 is suitable when there is an obstacle behind the head housing 3. This is because, compared to a proximity sensor 100 where the head housing 3 is not L-shaped, the head housing 3 hardly interferes with the obstacle located behind the external member E when it is fixed to the external member E. However, when the distance between the external member E and the obstacle located on the -Y direction side relative to the external member E in the Y-axis direction (that is, the front-to-back direction) is short, even in an L-shaped proximity sensor 100, the head 100H needs to be arranged close to the +Y direction side (front side). That is, since the head housing 3 is arranged such that the detection surface 30 of the head housing 3 is closer to the path of the detected object D, the possibility of collision between the detected object D and the detection surface 30 increases. Here, the detection surface 30, which has the risk of colliding with the detected object D, is made of metal, thus increasing its strength. As a result, the failure of the head 100H due to collision with the detected object D can be reduced. Therefore, the proximity sensor 100 can achieve both the freedom of installation, even in environments where obstacles are located behind the external component E, and the reduction of failures of the head 100H.

[0050] Note that in this embodiment, the connecting portion 34 is configured to guide the power supply cable 2 in the -Z direction, but it can also 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 connecting portion 34 is preferably closer to the Y-axis direction (that is, a direction orthogonal to the long side direction (front-back direction)). Therefore, the head housing 3 will hardly interfere with obstacles located behind the head housing 3.

[0051] Next, refer to Figure 6 Let’s describe in detail the head housing 3 of the proximity sensor 100. Figure 6 This is a perspective view of the longitudinal cross-section of the head shell 3 on the +Y direction side (the other end). Figure 6 For convenience, components other than the detection coil 1 are omitted from the head housing 3.

[0052] like Figure 6 As illustrated, the head housing 3 includes a cylindrical head portion 32 (main body) made of metal and a cover portion 35 made of metal. The cylindrical head portion 32 is a cylindrical member having a peripheral surface on its circumference along the Y-axis and an opening facing the +Y direction. The cover portion 35 is attached to the cylindrical head portion 32 from the +Y direction side (front end side) to cover the opening of the cylindrical head portion 32. The cover portion 35 attached to the cylindrical head portion 32 is located on the front end side of the head housing 3. The cover portion 35 includes a detection surface 30 made of metal.

[0053] Since the cover 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 of the head cylindrical portion 32 but also its front end is open. Therefore, the inner peripheral surface of the head cylindrical portion 32 can be cut (thinned) from both ends of the front and rear ends. Compared to a structure where the detection surface 30 is integrally provided with the head cylindrical portion 32, the manufacturing difficulty is reduced because cutting can be performed from both ends in the Y-axis direction.

[0054] More specifically, cutting (recessing) is generally performed by inserting the drill bit, which acts as a cutting disc, into the head tube 32 while rotating the drill bit. The longer the drill bit, the greater the deflection of the drill bit tip.

[0055] In the structure where the detection surface 30 and the head cylindrical portion 32 are integrally formed, the drill bit is inserted only from the rear end side of the head cylindrical portion 32. For this reason, a long drill bit is required to cut the front end side of the head cylindrical portion 32, and the deflection of the drill bit tip is large. Therefore, it is difficult to maintain cutting (thinning) accuracy at the front end of the head cylindrical portion.

[0056] Since the front end of the head tube is where the detection coil 1 is located, high precision is required for cutting (thinning). Therefore, the head tube, which is only open at the rear end, is difficult to manufacture.

[0057] On the other hand, in such Figure 6 In the illustrated head cylindrical portion 32, a cover portion 35, including the detection surface 30, is separately provided, into which a drill bit is inserted that rotates from both ends of the head cylindrical portion 32, at its front and rear ends. Therefore, even when cutting at the front end of the head cylindrical portion 32, the drill bit can be inserted from the front end of the head cylindrical portion 32. Thus, since a relatively short drill bit, whose tip side is easily swung during cutting, can be selected, the cutting (thinning) accuracy is improved. As a result, in the proximity sensor 100, the head housing 3 includes the detection surface 30 and the cover portion 35, which is separate from the head cylindrical portion 32, so that the front and rear ends of the head cylindrical portion 32 are open. As a result, manufacturing difficulty can be reduced.

[0058] The head cylindrical portion 32 has an abutting portion 33 on its inner peripheral surface. The abutting portion 33 abuts against the cover portion 35, which is properly attached to the head cylindrical portion 32. The cover portion 35 is fixed to the head cylindrical portion 32 by adhesive while abutting against the abutting portion 33.

[0059] Therefore, since the cover 35 can be easily and properly attached to the head cylindrical portion 32, the manufacturing difficulty of the proximity sensor 100 is reduced.

[0060] The abutment portion 33 has a circumferential groove of predetermined width on the inner peripheral surface of the head cylindrical portion 32, extending from the +Y direction side 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 cover 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 cover portion 35 (the amount of adhesive entering). Therefore, the circumferential groove, as the abutment portion 33, serves as a positioning element for the cover portion 35.

[0061] The cover portion 35 has a bottom 36 including a detection surface 30 and a peripheral portion 37 standing upright from the outer periphery of the bottom 36. When the cover portion 35 is attached to the head cylindrical portion 32, the end of the peripheral portion 37 on the -Y direction (connecting portion 34) side (the rear end of the peripheral portion 37) is located on the +Y direction side (that is, the front side) relative to the end of the detection coil 1 on the -Y direction (connecting portion 34) side (the rear end 56 of the detection coil 1).

[0062] Since the cover 35 does not become longer than required in the front-rear direction, the difficulty of cutting the cover 35 itself is almost negligible. Therefore, the manufacturing difficulty of the proximity sensor 100 is reduced.

[0063] In the head tube portion 32, the portion of the detection coil 1 on the -Y direction side (connection portion 34 side) (that is, the portion on the +Y direction side (front portion) relative to the rear end 56 of the detection coil 1) is a thinner portion than the other portions.

[0064] Therefore, since the head cylindrical portion 32 is formed relatively thin around the outer periphery of the detection coil 1, the magnetic field from the detection coil 1 is hardly hindered by the head cylindrical portion 32. Furthermore, since the head cylindrical portion 32 has a relatively thick portion on its outer periphery relative to the detection coil 1 in the -Y direction, it is easy to maintain the strength of the head cylindrical portion 32. As a result, the proximity sensor 100 can improve detection accuracy while maintaining mechanical strength. Additionally, since the head cylindrical portion 32 is separate from the cover portion 35 including the detection surface 30, the difficulty of processing the portion of the head cylindrical portion 32 with the cover portion 35 attached to it in the +Y direction is reduced. Moreover, the inner periphery of the end of the head housing 3 in the +Y direction is used for positioning the detection coil 1. The positional accuracy of the detection coil 1 relative to the head housing 3 greatly affects the detection distance based on the detection surface 30. Therefore, when the head housing 3 can be machined with high precision at the end of the head housing 3 on the +Y direction side using a structure in which the head cylindrical part 32 and the cover part 35 are separated from each other, the detection distance of the proximity sensor 100 can be increased.

[0065] The detection coil 1 preferably generates a magnetic field at an effective frequency equal to or greater than 2 kHz and equal to or less than 200 kHz. The portion including the detection surface 30 preferably has a thickness of 1.0 mm or less.

[0066] Next, refer to Figure 7 The reasons for the preferred effective frequency of the magnetic field (equal to or greater than 2kHz and equal to or less than 200kHz) and the preferred thickness (1.0mm or less than 1.0mm) of the portion including the detection surface 30 are explained in detail. Figure 7 This is a double logarithmic graph with the horizontal and vertical axes representing frequency versus skin depth, and a schematic diagram illustrating the double logarithmic graph.

[0067] like Figure 7 As illustrated by the double logarithmic graph, the higher the frequency, the smaller the skin depth. In other words, the lower the frequency, the greater the skin depth. Since the skin depth indicates the length of a magnetic flux line of a certain intensity that is directed toward a component made of a certain material, it is less likely to decay at a certain frequency, and thus the skin depth increases. Furthermore, the easier it is for magnetic flux lines to pass through a component, the less likely they are to decay, and therefore the skin depth increases.

[0068] To reduce the attenuation of magnetic flux caused by the detection surface 30 made of metal, it is preferable to generate a magnetic field at a low frequency. However, when the frequency of the generated magnetic field is low, it is difficult to control the change in the magnetic field as the magnetic flux passes through the object being detected, and there is a risk of the number of objects being detected decreasing.

[0069] On the other hand, pulsed or relatively low-frequency sinusoidal pulses generally have an effective frequency of 200kHz or less. With an upper limit of 200kHz for the effective frequency, that is, at a frequency of 200kHz (… Figure 7 At point B) or below 200 kHz, the skin depth of stainless steel (SUS304) exceeds 1 mm. Therefore, when the portion including the detection surface 30 is made of stainless steel (SUS304) with relatively high mechanical strength, both mechanical strength and a reduction in magnetic flux attenuation due to the components constituting the detection surface 30 can be achieved with a maximum thickness of 1 mm. Note that in this embodiment, SUS304 is used as the stainless steel, but stainless steel is not limited to SUS304, and other stainless steels can be used.

[0070] Next, refer to Figure 8 To explain in detail the filler filling the head shell 3. Figure 8 This is a perspective view of the longitudinal cross-section of the head shell 3. Figure 8 In this drawing, examples and reference numerals for the filler are omitted for priority of visibility, but the filler is filled in the portion inside the head housing 3 that is indicated as a space.

[0071] like Figure 8As illustrated, the proximity sensor 100 includes a detection coil 1, a power supply cable 2, and a metal head housing 3, with the head housing 3 filled with a filler.

[0072] The detection coil 1 generates the magnetic field used for detection. The power supply cable 2 is a component used to supply power to the detection coil 1. The head housing 3 is made of metal and houses the detection coil 1. The head housing 3 is filled with a filler, and the filler is filled in such a way that it fills the periphery of the detection coil 1 housed in the head housing 3. As a filler, an adhesive and an additive having a relative permittivity lower than that of the adhesive are mixed together.

[0073] The proximity sensor 100 is a sensor that detects a metal object D by using an induced current. The presence or absence of the object D and its position are detected 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. Therefore, to increase the detection distance of the proximity sensor 100, it is necessary to capture even small changes in the detection current. When a noise current component is added to the detection current, there is a risk of decreased detection accuracy, even if the noise current is weak.

[0074] More specifically, since power is supplied to the detection coil 1 via the power supply cable 2 for the head 100H, the power supply cable 2 is electrically connected to the detection coil 1. Therefore, the power supply cable 2 can be a path for noise current to flow in, affecting the change in the detection current of the detection coil 1.

[0075] On the other hand, the external component E to which the head housing 3 is fixed is often grounded to the grounding terminal G. This is because, in this embodiment, the external component E is often part of a device including the proximity sensor 100, and such a device is often connected to the grounding terminal G for accident prevention. Therefore, in many cases, the head housing 3 fixed to the external component E is grounded to the grounding terminal G, and the current generated within the head housing 3 flows to the grounding terminal G. When the head housing 3 is grounded, the power supply cable 2 and the head housing become a circuit via the grounding terminal G, and there is a risk of noise current flowing from the power supply cable 2 into the head 100H. Therefore, it is preferable to minimize capacitive coupling between the head housing 3, the power supply cable 2, and the current circuit from the power supply cable 2 to the detection coil 1. For example, air may be present.

[0076] However, the head housing 3 is filled with a filler to improve mechanical strength. The capacitive coupling of this filler poses a risk of current flowing 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 the 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 forming a current circuit via the grounding terminal G, create a risk of noise current flowing into the head 100H from the power supply cable 2. When this noise current affects the change in the detection current flowing through the detection coil 1, there is a risk of decreased accuracy in detection using the proximity sensor 100.

[0077] The proximity sensor 100 of this embodiment has a lower relative permittivity than the case where the filler consists only of adhesive. Therefore, almost no capacitive coupling occurs between the head housing 3 and the current circuit between the power supply cable 2 and the detection coil 1. Consequently, noise current hardly flows into the head 100H. Thus, the proximity sensor 100 achieves both mechanical strength and detection accuracy utilizing the filler. Note that in this embodiment, the head housing 3 is filled with filler, but the head housing 3 is not limited to the entire head housing 3. In the head housing 3, only the portion including the detection coil 1 on the +Y direction side may be filled. Furthermore, it is not necessary to fill the entire head housing 3 in the circumferential direction with the Y-axis as the centerline, and at least the inner space including the detection coil 1 may be filled. In this case, an air layer may exist between the filled portion and the head housing 3.

[0078] The filler has a relative permittivity of 3.7 or less. Because the relative permittivity of the filler is 3.7 or less, almost no capacitive coupling occurs between the head housing 3 and the current circuit between the power supply cable 2 and the detection coil 1. Therefore, the proximity sensor 100 can reduce the decrease in detection accuracy caused by noise flowing in from the power supply cable 2.

[0079] The internal space of the head housing 3 has a first space including the detection coil 1 in the Y-axis direction, and a second space excluding the detection coil 1 and located on the -Y-direction side relative to the first space. The filler filling the first space has a lower relative permittivity than the filler filling the second space.

[0080] In other words, when the filler filling the first space is the first filler and the filler filling the second space is the second filler, the relative permittivity of the first filler is lower than that of the second filler.

[0081] With this structure, capacitive coupling between the current circuit between the power supply cable 2 and the detection coil 1, which is prone to occur in the second space filled with the second filler (that is, the space excluding the detection coil 1), and the head housing 3 is eliminated. Therefore, even if a current circuit including the power supply cable 2, the head housing 3, and the grounding terminal is formed, the current tends to flow through the path excluding the detection coil 1. Therefore, even if noise current enters the head 100H from the power supply cable 2, the noise current hardly flows near the detection coil 1. Thus, the influence of noise current flowing from the power supply cable 2 on the detection current is reduced. In addition, since the material of the second filler can be selected with preference for hardness rather than relative permittivity, the overall durability of the head 100H can be improved.

[0082] The head housing 3 has a detection surface 30, which serves as a surface for detecting the object D. The end of the second space on the +Y direction side is filled with a first filler and a second filler, so that it is located on the -Y direction side (rear side) relative to the -Y axis direction end (rear end) 56 of the detection coil 1.

[0083] Therefore, even if noise current enters from the power supply cable 2, it hardly flows near the detection coil 1. Thus, the influence of noise current flowing from the power supply cable 2 on the detection current can be reduced.

[0084] The proximity sensor 100 also includes a conductive electrical shield 43. The electrical shield 43 covers the detection coil 1 in the circumferential direction with the Y-axis as its centerline. The +Y direction side of the second space is filled with a first filler and a second filler, so as to be located on the -Y direction side (rear side) relative to the -Y direction side (rear side) 54 of the electrical shield 43.

[0085] An electrical shield 43 is provided to prevent external noise from reaching the detection coil 1. Therefore, the electrical shield 43 is arranged to fully cover the detection coil 1 in the Y-axis direction. Consequently, the boundary between the first space and the second space is located on the -Y-direction side relative to the -Y-direction side end of the electrical shield 43, and the distance between the detection coil 1 and the boundary between the first space and the second space in the Y-axis direction becomes longer. Therefore, the influence of noise current flowing from the power supply cable 2 on the detection current can be reduced.

[0086] The space filled with filler in the head housing 3 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 the space inside the head housing 3 on the front side (+Y direction side) relative to the rear end 56, which serves as the -Y direction side end of the detection coil 1. The middle space 52 is the space inside the head housing 3 on the rear side (-Y direction side) relative to the rear end 56 of the detection coil 1 and on the front side (+Y direction side) relative to the rear end 54, which serves as the -Y direction side end of the electrical shield 43. The rear space 53 is the space inside the head housing 3 on the rear side (-Y direction side) relative to the rear end 54 of the electrical shield 43.

[0087] As an example, the front space 51 is filled with a first filler, and the middle space 52 and the rear space 53 are filled with a second filler. 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.

[0088] As another example, the front space 51 and the middle space 52 are filled with a first filler, and the rear space 53 is filled with a second filler. 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.

[0089] The filler is a mixture of binder and additive. The binder is, for example, silicone, urethane, or polyethylene. The additive has a lower relative permittivity than the binder. The additive material is, for example, at least one of fluorine, polyimide, chlorine, polyethylene, acrylic, urethane, boron nitride, air, and vacuum fillers. Examples of additive shapes include flake-shaped primary particles, agglomerated granules, and sheet-like structures.

[0090] The Shore hardness of the filler after curing is preferably D0 or greater, and more preferably D80 or greater. This is because the Shore hardness of the filler after curing is D80 or greater, which sufficiently improves the mechanical strength of the proximity sensor 100.

[0091] The proximity sensor 100 may also include a member 46 for fixing the head base plate 13 inside the head cylindrical portion 32. The proximity sensor 100 can be assembled stably by using the member 46 for fixing the head base plate 13 inside the head cylindrical portion 32.

[0092] The following will be referenced Figure 9 Let me explain the details of detection coil 1. Figure 9This is an enlarged perspective view illustrating detection coil 1 and related devices. Figure 9 In the middle, the part about... is omitted. Figure 9 The unnecessary structures are visualized first.

[0093] like Figure 9 As illustrated, the detection coil 1 includes a coil wire 1L. The power supply cable 2 has a core wire 21. The proximity sensor 100 also includes a head substrate 13. The head substrate 13 is housed in the head housing 3 and extends along its long side (front-to-back direction). Circuitry for electrically connecting the coil wire 1L and the core wire 21 is provided in the head substrate 13. That is, the head substrate 13 can be considered as a component for electrically connecting the coil wire 1L and the core wire 21.

[0094] Since both the coil wire 1L and the core wire 21 are flexible linear components, the handling during assembly becomes complex. However, since 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 rigidity, the assembly of the proximity sensor 100 is easily stabilized.

[0095] The proximity sensor 100 also includes a ferrite core 23 and a core holder 24. A coil wire 1L is wound around the ferrite core 23. The core holder 24 holds the ferrite core 23. A head substrate 13 is fixed to the core holder 24. When the ferrite core 23 and the head substrate 13 are not fixed to each other and are freely movable, there is a risk that during assembly, the coil wire 1L may break due to applying a load by separating the ferrite core 23 and the head substrate 13 by a certain amount. Since the ferrite core 23 and the head substrate 13 are fixed via the core holder 24, the risk of the coil wire 1L breaking during assembly is reduced.

[0096] The coil wire 1L includes a first coil wire 11L and a second coil wire 12L, which is different from the first coil wire 11L. The detection coil 1 has a first coil 11 wound with the first coil wire 11L, and a second coil 12 wound around the first coil 11 with the second coil wire 12L. Note that there are two first coil wires 11L extending from the first coil 11, one of which is as follows: Figure 9 The example shows a first coil line 11L connected to the face of the head substrate 13 on the +Z direction side, and another first coil line 11L connected to the face of the head substrate 13 on the -Z direction side. In this embodiment, the two first coil lines 11L are connected to different faces of the head substrate 13, but can be connected to the same face. Additionally, there are two second coil lines 12L extending from the second coil 12, one of which is as follows: Figure 9The illustrated second coil line 12L is connected to the face of the head substrate 13 on the +Z direction side, and another second coil line 12L is connected to the face of the head substrate 13 on the -Z direction side. In this embodiment, the two second coil lines 12L are connected to different faces of the head substrate 13, but can be connected to the same face.

[0097] Because of the different positional relationships between the first coil 11 and the second coil 12, the detection current generated in the first coil 11 and the detection current generated in the second coil 12 are affected in different ways by surrounding metal bodies such as the detection object D and the external component E. In other words, the first coil 11 and the second coil 12 have unique characteristics. Therefore, the proximity sensor 100 includes the first coil 11 and the second coil 12 as detection coil 1, thereby improving detection accuracy.

[0098] In the proximity sensor 100, which includes a first coil 11 and a second coil 12 as detection coil 1, there is a risk that the detection accuracy may be affected by the relative positional relationship between the first coil 11 and the second coil 12. Since the first coil 11 and the second coil 12 are often located on the inner surface of the portion of the head housing 3 on the +Y direction side, high machining precision is required for the +Y direction side portion of the head housing 3 to ensure detection accuracy. As described above, when the head cylindrical portion 32 and the metal cover 35 (metal cover portion 35) including the detection surface 30 are constructed from different components, the difficulty of high-precision machining of the +Y direction side portion of the head housing is reduced, which is particularly effective in the proximity sensor 100 structure including the first coil 11 and the second coil 12. Furthermore, since the second coil 12 is located outside the first coil 11, the second coil 12 is positioned close to the inner peripheral surface of the head housing 3 (that is, the inner surface of the head cylindrical portion 32). Therefore, the portion of the head housing 3 on the +Y direction side is required to have machining accuracy not only near the centerline of the head cylindrical portion 32, but also up to the periphery about that centerline. As described above, when the head cylindrical portion 32 and the metal cover 35 including the detection surface 30 are composed of different components, the difficulty of high-precision machining of the portion of the head housing on the +Y direction side is reduced, thus the structure of the proximity sensor 100 including a first coil 11 and a second coil 12 arranged outside the first coil 11 is particularly effective.

[0099] The proximity sensor 100 includes a transmitting circuit 5, a receiving circuit 6, and a control circuit 7. The transmitting circuit 5 supplies a pulsed excitation current to a 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, absence, or location of the object D based on the received signal from the receiving circuit 6, which has detected the detection current. Since the detection current changes according to the magnetic field, the change in the magnetic field is reflected in the received signal from the receiving circuit 6. The control circuit 7 outputs the result of detecting the presence, absence, or location of the object D.

[0100] The detection coil 1 includes a first coil 11 and a second coil 12, which is different from the first coil 11. Since the first coil 11 and the second coil 12 are separate from each other, their arrangements within the head housing 3 are different. Therefore, the change in detection current caused by the 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 receiving circuit 6 sends 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 an independent manner. The control circuit 7 detects the presence or absence of the detection object D and its position based on a first received signal based on the first detection current and a second received signal based on the second detection current. At this time, the first received signal and the second received signal have different signal changes relative to a change in a certain magnetic field. For example, even when the magnetic field changes due to both the detection object D of the metal body and the external component E of the metal body, multiple coils with different arrangements can be used as the detection coil 1, so that the change in the magnetic field caused by the detection object D of the metal body is easily reflected in the first received signal, and the change in the magnetic field caused by the external component E of the metal body is easily reflected in the second received signal, thus allowing various information about the area around the head housing 3 to be acquired. Therefore, in the detection in the proximity sensor 100, the control circuit 7 takes into account the characteristics of the first coil 11 and the second coil 12 to process 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, thereby improving the detection accuracy.

[0101] The receiving circuit 6 includes a first receiving circuit 61 for detecting the detection current generated in the first coil 11 and a second receiving circuit 62 for detecting the detection current generated in the second coil 12. According to this structure, the first and second detection currents can be sent to the control circuit 7 simultaneously and independently. Therefore, since the time period during which the control circuit 7 receives the first receiving signal and the time period during which the control circuit 7 receives the second receiving signal can be the same time period, the time required to detect the presence or absence and position of the object D using the first and second receiving signals is shortened. Furthermore, calculations for correcting the difference between the time periods for acquiring the first and second receiving signals are no longer necessary. Therefore, the receiving circuit 6, including the first receiving circuit 61 and the second receiving circuit 62, can improve the detection accuracy of the proximity sensor 100.

[0102] Here, we will refer to Figures 10A to 11B This section details the suppression of the influence of metallic bodies other than the detected object D. In the following text, the time variation of the first received signal may be referred to as the first received waveform, and the time variation of the second received signal may be referred to as the second received waveform. Furthermore, the first and second received waveforms may be collectively referred to as received waveforms.

[0103] Figures 10A to 11B Examples of the first received waveform (symbol ΔR1) and the second received waveform (symbol ΔR2) after zeroing are shown. Zeroing in this embodiment means zeroing the signal strength when there is no external component E of the metal body and the detection object D of the metal body is not within the detection range. Note that in Figure 10A and Figure 11B In the diagram, the horizontal axis represents time, and the vertical axis represents the signal strength of the received waveform.

[0104] Figure 10A This is a graph showing the zeroed received waveform when the external component E of the metal body is absent and the detection object D is not within the detection range. As described above, since the waveform adjusted so that the value indicated by the waveform becomes zero when the external component E of the metal body is absent and the detection object D is not within the detection range is a zeroed waveform, both the first and second received waveforms indicate zero on the graph.

[0105] Figure 10B This is a graph representing the zeroed received waveform when no external component E is present and the object being detected, D, is within the detection range. For example... Figure 10BAs illustrated, the change in signal strength of the first received waveform is greater than the change in signal strength of the second received waveform. This is because the first coil 11 and the second coil 12 are arranged such that the first detection current generated in the first coil 11 is more susceptible to changes in the magnetic field caused by the detected object D within the detection range, compared to the second detection current generated in the second coil 12.

[0106] Figure 11A This is a graph representing the received waveform after zeroing, when an external component E is present and the object being detected, D, is not within the detection range. For example... Figure 11A As illustrated, both the change in signal strength of the first received waveform and the change in signal strength of the second received waveform are 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 easily affected by changes in the magnetic field of the external component E to which the head 100H is fixed. However, despite Figure 10B The change in signal strength of the first received waveform illustrated is related to Figure 11A The change in signal strength of the first received waveform illustrated is similar, but Figure 11A The variation in signal strength of the second received signal illustrated is significantly greater than Figure 10B The amount of change in the signal strength of the second received signal illustrated. Additionally, in Figure 11A In this case, the change in the signal strength of the second received signal is greater than the change in the signal strength of the first received signal. This is because the first coil 11 and the second coil 12 are arranged such that the second detection current generated in the second coil 12 is more susceptible to the influence of the external component E compared to the first detection current generated in the first coil 11.

[0107] Figure 11B This is a graph representing the zeroed received waveform when an external component E is present and the object being detected, D, is within the detection range. (Compared to...) Figure 11A Similarly, since the head 100H is fixed to the external component E, therefore, as Figure 11B As illustrated, both the change in signal strength of the first received waveform and the change in signal strength of the second received waveform are large. However, unlike... Figure 11A The change in signal strength of the first received signal is greater than the change in signal strength of the second received signal. Figures 10A to 11BIn the case of a magnetic field change caused by at least one of the external component E and the detection object D, the change in the signal strength of the first received signal increases. Therefore, it becomes difficult to detect the presence or absence of the detection object D and its position solely based on the first received signal. In particular, when the distance between the detection object D and the first coil 11 is long, the change in the signal strength of the first signal caused by the magnetic field change due to the detection object D is similar to the change in the signal strength of the second signal caused by the magnetic field change caused by the external component E, thus easily leading to a decrease in detection accuracy. On the other hand, in Figures 10A to 11B In the presence of magnetic field changes caused by external component E, the change in the signal strength of the second received signal increases significantly. Therefore, combining the first and second received signals can improve the detection accuracy of the presence or absence of the object D and its position.

[0108] More specifically, the difference is calculated using the difference between a first received waveform that has been zeroed and a second received waveform that has been zeroed. The difference mentioned herein is a value obtained by subtracting the second received waveform that has been zeroed from the first received waveform. Based on this process, the received signal in the case where the detection object D is absent is... Figure 10A and Figure 11A In the example, the calculation result is negative, and the received signal is shown in the case where the detection object D is present. Figure 10B and Figure 11B In this case, the calculation result is positive. As mentioned above, this can improve the detection accuracy of the proximity sensor 100.

[0109] In the following text, reference will be made to Figure 12 To illustrate other examples of the detection surface 30. Figure 12 This is a three-dimensional view of a section cut from a cylindrical proximity sensor 100. Figure 12 In order to Figure 8 Prioritizing visibility, examples and reference numerals for the filler are omitted, but the filler is shown filling the portion inside the head housing 3 that is indicated as a space. Figure 12The arrows X, Y, and Z are shown as indicating three mutually orthogonal directions. The directions indicated by arrows X, Y, and Z all correspond to the arrangement orientation of the proximity sensor 100, and the direction indicated by arrow X is called the X-axis direction, the direction indicated by arrow Y is called the Y-axis direction, and the direction indicated by arrow Z is called the Z-axis direction. One direction along the X-axis is called the +X direction, and the other is called the -X direction. One direction along the Y-axis is called the +Y direction, and the other is called the -Y direction. One direction along the Z-axis is called the +Z direction, and the other is called the -Z direction. The normal direction of the detection surface 30 is the Y-axis direction, and the direction in which the detection surface 30 faces is the +Y direction.

[0110] Figure 12 The illustrated detection surface 30 is made of resin. In a proximity sensor 100 using induced current, when the detection surface 30 is made of metal, there is a risk of decreased detection accuracy due to the following reasons: eddy currents generated on the detection surface 30 itself due to the magnetic field can generate noise; and changes in the detection current can occur due to changes in the magnetic field caused by the detection surface 30 itself. Therefore, when the detection surface 30 is made of resin, the detection accuracy is prone to decrease. On the other hand, resin components have lower strength compared to metal components. Therefore, by filling the head housing 3 with a filler, the mechanical strength is improved. As a result, both detection accuracy and strength can be achieved. Note that the head 100H is easily capacitively coupled between the component including the detection surface 30 and the detection coil 1. Therefore, by using a resin component as the detection surface 30, it is easier to prevent noise current from flowing into the vicinity of the detection coil 1.

[0111] However, as described above, when the head housing 3 is filled with filler, there is a risk of capacitive coupling of the filler and a decrease in the detection accuracy of the sensor 100. More specifically, in the case of capacitive coupling of the filler, a current circuit is formed by the power supply cable 2, the head housing 3, and the grounding terminal connected to the head housing 3, thus posing a risk of noise current flowing into the head 100H from the power supply cable 2. Therefore, from the viewpoint of the detection accuracy of the sensor 100 and the strength of the head 100H, it is particularly effective to fill the head housing 3, which has a detection surface 30 made of resin, with a filler containing additives having a relatively low relative permittivity. Furthermore, the front space 51 of the head housing 3, which is located on the +Y direction side and includes the detection coil 1 in the Y-axis direction, is filled with a first filler containing additives having a low relative permittivity, and the rear space 53, which does not include the detection coil 1 in the Y-axis direction, is filled with a second filler having a higher relative permittivity and higher hardness compared to the first filler. According to this structure, it is easy to prevent the decrease in detection accuracy caused by the influence of noise flowing into the head housing 3 on the detection current, as well as to improve the mechanical strength of the head 100H.

[0112] In the following text, reference will be made to Figure 13 To illustrate the flat proximity sensor 100. Figure 13 This is a magnified three-dimensional view of the longitudinal cross-section of the flat proximity sensor 100.

[0113] exist Figure 13 In the illustrated flat proximity sensor 100, the flat, box-shaped head housing 3B is filled with a filler. The filler is in... Figure 13 The figure is indicated by reference numeral 38 in the attached figure.

[0114] The box-shaped head housing 3B is not limited to a strictly box-shaped form, but may be generally box-shaped. The box-shaped head housing 3B has a first surface 101 and a second surface 102 that is different from the first surface 101. The first surface 101 includes a detection surface 30, which serves as the surface for detecting the object D. The second surface 102 is mounted (fixed) to contact the surface of the external component E.

[0115] The proximity sensor 100 also includes a head substrate 13. The head substrate 13 is housed in a box-shaped head housing 3B and extends along the first surface 101. The head substrate 13 electrically connects the detection coil 1 and the power supply cable 2.

[0116] When noise current affects the detection current generated in the detection coil 1, there is a risk that the inflow of noise current from the power supply cable 2 to the head 100H due to the capacitive coupling of the filler will reduce the detection accuracy of the proximity sensor 100. Therefore, the portion where capacitive coupling of the filler occurs and which can form a noise current circuit is separated from the detection coil 1. However, in the head housing 3B, the circuit (corresponding to the head substrate 13) electrically connecting the power supply cable 2 and the detection coil 1 is arranged near the detection coil 1. Therefore, in the flat proximity sensor 100, compared to other types of proximity sensors 100, the possibility of noise current affecting the detection current when noise current flows from the power supply cable 2 into the head 100H is higher. Therefore, a structure that reduces the relative permittivity of the filler so that noise current from the power supply cable 2 hardly flows into the head 100H is particularly effective.

[0117] Incidentally, the embodiments are illustrative in all respects and are not limiting. The scope of the invention is indicated not by the foregoing description but by the claims, and is intended to include the meaning equivalent to the claims and all modifications within that scope. In the structures described in the embodiments, structures other than those described as an aspect of the invention in "Means for Solving the Problem" are arbitrary structures and can be appropriately deleted and modified.

[0118] This invention provides a flat proximity sensor that is industrially applicable.

Claims

1. A proximity sensor for detecting a detection object, the proximity sensor comprising: a detection coil for generating a magnetic field for detection; a head case for accommodating the detection coil; a power supply cable connected to the head case to supply electric power to the detection coil; a transmission circuit for supplying a pulse-shaped excitation current to the detection coil; a reception circuit for detecting a detection current generated in the detection coil; a control circuit for outputting a result of detecting the detection object based on a reception signal from the reception circuit that has detected the detection current; an amplifier substrate on which the control circuit is implemented; and an amplifier case for accommodating the amplifier substrate, wherein the head case includes: a detection surface; a connection portion located on an opposite side of the head case with respect to the detection surface in a normal direction of the detection surface, the connection portion being connected to the power supply cable; and a fixed portion located between the detection surface and the connection portion in the normal direction of the detection surface and contacting a fixing member for fixing the head case to an external member when the head case is fixed to the external member, and the amplifier case is disposed outside the head case. The power supply cable includes a core wire through which the detection current flows, and a shield cover for covering the core wire with a shield.

2. The proximity sensor of claim 1, wherein, 3. The proximity sensor according to claim 1, further comprising: a head substrate connected to a coil wire of the detection coil and a core wire of the power supply cable, the head substrate electrically connecting the coil wire and the core wire.

4. The proximity sensor according to claim 3, further comprising: a ferrite core wound with the coil wire; and a core holder for holding the ferrite core and fixed to the head substrate. The connection portion guides the power supply cable in a direction intersecting the normal direction. The detection surface is made of metal.

5. The proximity sensor of claim 1, wherein, a head including a head case for accommodating a detection coil for generating a magnetic field for detection; 6. The proximity sensor of claim 1, wherein, a power supply cable connected to the head case; 7. An amplifier in a proximity sensor, the proximity sensor comprising: an amplifier electrically connected to the head via the power supply cable; a transmission circuit for supplying a pulse-shaped excitation current to the detection coil; a reception circuit for detecting a detection current generated in the detection coil; and a control circuit for outputting a result of detecting a detection object based on a reception signal from the reception circuit that has detected the detection current, wherein the amplifier includes: an amplifier substrate connected to a core wire included in the power supply cable and on which the control circuit is implemented; and an amplifier case for accommodating the amplifier substrate. ​ ​

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