JP2004342334A - Proximity switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proximity switch for improving performance, dispensed from investment for a die, abolishing expensive pressed goods, reducing an assembly cost, and achieving a high quality, an inexpensive price and static electricity-resistance. <P>SOLUTION: The switch has a case 10; a conductive cover 30 attached to the case 10 detachably; and a printed board 20 housed in a housing composed of the case 10 and the cover 30. The cover is made of conductive resin obtained by mixing conductive filler into a thermoplastic resin and has a passing through hole 31 for a Pachinko ball. The case 10 has a passing through hole 11 for the Pchinko ball. The printed board 20 has a detecting coil 26 wounded with a bobbin 25 having a passing through hole 27 for the Pchinko ball. A static electricity connecting pole 32 is disposed inside the cover 30 and a static electricity ground hole 22 is formed on the printed board 20 corresponding to the connecting pole 32. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a proximity switch that prevents electrostatic damage due to static electricity when detecting or counting a metal object charged with very high static electricity of tens of thousands of volts, for example, a pachinko ball.
[0002]
[Prior art]
Pachinko balls in a pachinko machine flow through a long and complicated path made of metal or plastic with repeated friction and impact, and are used for the purpose of playing. At this time, the pachinko balls charge static electricity up to several tens of kV. When the charged pachinko ball is detected by the proximity switch, the power of the proximity switch is DC-isolated to ground, but high-frequency or electrostatically equal to ground through a large distributed capacitance in the transformer and wiring. Potential.
[0003]
Therefore, the pachinko ball charged with extremely high static electricity discharges a portion connected to a power source such as a coil or a printed circuit board when passing through the detection surface of the proximity switch or the penetration detection hole. When static electricity of several tens of kV is discharged to a portion other than the ground portion of the power supply, the charge eventually reaches the ground portion of the power supply and disappears on the ground. However, all the semiconductors to which the charge is applied are destroyed, and the proximity switch Function cannot be exhibited. In order to prevent the damage due to the static electricity, the following various methods are implemented.
B) A method of filling all parts of the proximity switch with epoxy resin or polyurethane resin and solidifying it.
[0004]
In this case, there is a problem that the processing cost becomes extremely high.
B) A method of increasing the creepage distance at the fitting portion between the case and the cover (the housing as a whole).
[0005]
In this case, the structure of the mold is complicated and expensive, and the shape of the proximity switch becomes large, so that the size cannot be reduced.
C) A method in which a shield plate is provided at the combination of the case and the cover to discharge static electricity to the ground of the power supply. This method is common.
[0006]
As a conventional pachinko ball detection proximity switch employing this method, there is one having a structure as shown in FIGS. 5 (exploded perspective view) and FIG. 6 (a plan view as viewed from the case side) (for example, Patent Reference 1).
[0007]
This proximity switch includes a case 50, a cover 60 detachably attached to the case 50, a shield plate 70 and a printed circuit board 80 housed in a housing constituted by the case 50 and the cover 60. The case 50 has a through hole 51 for a pachinko ball, a detection coil mounting portion 52 provided around the through hole 51, and two through holes 53. The cover 60 has a pachinko ball passage hole 61. The shield plate 70 has a passage hole 71 for a pachinko ball. Various electronic components 81 are mounted on the printed circuit board 80, and a detection coil (not shown) is also connected thereto. The shield plate 70 is mainly formed by pressing a very thin pure copper plate with a press die, and is provided at a joint between the case 50 and the cover 60.
[0008]
Further, as shown in FIG. 8 (exploded perspective view), there is a proximity switch in which a side plate 72 is provided in a shield plate 70 instead of forming two through holes 53 in the case 50 as shown in FIG. 8 (exploded perspective view).
[0009]
In the proximity switch of FIG. 5, in FIG. 7 (a cross-sectional view taken along the line AA in FIG. 6), the static electricity of the pachinko ball is guided from the surface of the case 50 to the shield plate 70 through the through hole 53 as indicated by the dotted line. Further, discharge is performed to the ground of the printed circuit board 80. In addition, in the proximity switch of FIG. 8, as shown by a dotted line in FIG. 9, the lead is guided from the surface of the case 50 to the side plate 72 of the shield plate 70 through the joint between the case 50 and the cover 60, and further to the ground of the printed circuit board 80. It is discharging.
[0010]
[Patent Document 1]
Japanese Utility Model Publication No. 4-22515
[Problems to be solved by the invention]
However, the conventional proximity switch has various problems (1) to (5) as follows.
{Circle around (1)} The shield plate 70 is used in close contact with the detection coil mounting portion 52. However, since the configuration is inconsistent in terms of increasing the detection sensitivity, the detection distance characteristics of the metal body and the hysteresis, which is the difference between the detection distance and the return distance. The characteristics (difference between ON and OFF) are much worse than those without a shield plate, which is the characteristic of the original proximity switch, and the detection sensitivity varies greatly. Has led to a decline in sex.
(2) For the reason (1), the shield plate 70 needs to reduce high-frequency loss. Therefore, in practice, a thin pure copper plate having a thickness of several tens μm to several hundreds μm and having no rigidity is used. This pure copper plate is punched out with a press die, but when the press product falls from the die in press processing, when the press product is put in cardboard and transported, and the press product is taken out from the cardboard during assembly processing At times, pressed products are easily bent by a small force, are difficult to handle, and the yield of usable pressed products is very poor.
{Circle around (3)} In order to manufacture the shield plate 70, investment of a very expensive mold is required, and the shield plate 70 becomes very expensive for the above-mentioned reason 2).
{Circle around (4)} The assembling cost for carefully assembling the shield plate 70 which is difficult to handle is required, and if a bent shield plate is used, a short circuit accident with other parts may occur.
{Circle around (5)} The proximity switch for detecting pachinko balls is extremely inexpensive at 1/10 to 1/15 of the price of the same product sold for industrial use, and is a highly competitive market. Therefore, a proximity switch that amortizes such an expensive mold, uses a shield plate that is an expensive pressed product, and performs assembly that is difficult to handle cannot meet the market.
[0012]
Therefore, the present invention has been made by focusing on such problems (1) to (5).
a) Improvement of characteristics b) Elimination of investment in molds c) Elimination of expensive press parts d) Reduction of assembly cost e) High quality and low price f) Objective to provide a proximity switch which realizes anti-static property And
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the proximity switch of the present invention includes a high-frequency oscillation circuit and a detection coil connected to the high-frequency oscillation circuit incorporated in a housing to detect a metal body. It is characterized in that the whole is made of conductive resin.
[0014]
The proximity switch of the present invention achieves the above objects a to f by forming a part or the whole of the housing with a conductive resin, and at the same time, places where the static electricity of the charged metal body is weak against the static electricity in the housing ( In particular, it can be prevented from being applied to the electronic components in the detection circuit.
[0015]
Here, the conductive resin is obtained by mixing a conductive filler into a thermoplastic resin. Thermoplastic resins include polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polybutylene terephthalate (PBT), polyacetal resin (POM), acrylonitrile butadiene styrene (ABS), and the like. The conductive filler is a carbon filler, a metallic (for example, brass) filler, or the like. The thermoplastic resin is mixed with a conductive filler to form a conductive resin, and this conductive resin constitutes a part or all of the housing.
[0016]
Of the above conductive fillers, the use of carbon fillers in particular improves the slidability with respect to a metal body, and is caused by a large number of metal bodies (hundreds of millions of pachinko balls) passing through the detection surface or through hole of the proximity switch. Wear of the housing can be reduced.
[0017]
In the above basic configuration, as a more specific configuration, when a detection circuit board equipped with a high-frequency oscillation circuit and a detection coil is provided, and a part of the housing is brought into contact with or close to a ground portion of the detection circuit board via a capacitor, It is suitable for use in places where this proximity switch may come into contact with other electronic devices (especially conductive parts). In other words, the conductive housing is insulated DC from the ground portion of the internal detection circuit board, but is connected electrostatically, so that the ground portion of the detection circuit board is electrically conductive. Even if it comes into contact with a conductive part of another electronic device via the electronic device, a short circuit or an electrical malfunction does not occur.
[0018]
In addition, when a detection circuit board equipped with a high-frequency oscillation circuit and a detection coil is provided, and a part of the housing is directly contacted or brought close to the ground portion of the detection circuit board, the proximity switch electrically connects to another electronic device. Suitable for use where there is no risk of contact. That is, since the conductive housing is directly connected to the ground portion of the internal detection circuit board, the proximity switch is less expensive because no capacitor is used.
[0019]
In the present invention, part or all of the housing is made of a conductive resin. However, when the housing is made up of a case and a cover detachably attached to the case, the cover and / or the case may be made of a conductive resin. It consists of.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to embodiments.
[0021]
FIG. 1 is an exploded perspective view of the proximity switch according to the embodiment, and FIG. 2 is an exploded perspective view of each component as viewed from the opposite side.
[0022]
The proximity switch includes a case 10, a conductive cover 30 detachably attached to the case 10, and a printed circuit board (detection circuit board) 20 housed in a housing constituted by the case 10 and the cover 30. .
[0023]
The case 10 has a through hole 11 for a pachinko ball and a detection coil mounting portion 12 provided around the through hole 11. The cover 30 has a pachinko ball passage hole 31. Various electronic components 21 are mounted on the printed circuit board 20. Here, the detection coil 26 is wound around an octagonal annular bobbin 25 and connected to the printed circuit board 20. The inside of the bobbin 25 is a passage hole 27 for a pachinko ball. An electrostatic connection pole 32 is provided inside the cover 30, and an electrostatic ground hole 22 is formed in the printed circuit board 20 corresponding to the pole 32.
[0024]
In this embodiment, the cover 30 is made of a conductive resin. That is, for example, the cover 30 is formed by resin molding using a conductive resin obtained by mixing a carbon filler into the thermoplastic resin of the previous example. Regarding this conductivity, the volume resistivity is from 1 × 10 ² to 1 × 10 ⁵ Ω by the ASTM method depending on the mixing ratio of the thermoplastic resin and the conductive filler, and is extremely large according to the amount of the electrostatic charge. The width can be selected arbitrarily.
[0025]
The circuit configuration of the printed circuit board 20 is, for example, as shown in FIG. 3 or FIG. The circuit of FIG. 3 is suitable for use in a place where there is no risk that the proximity switch will make electrical contact with other electronic devices (especially conductive parts), and the circuit of FIG. 4 will allow the proximity switch to be electrically connected to other electronic devices. Suitable for use where there is a risk of contact with
[0026]
3 and 4, the detection coil 26 is connected to the oscillation circuit 41, and the oscillation circuit 41 is further connected to the switching circuit 42 and the output circuit 43. In the ground portion, the electrostatic connection pole 32 of the cover 30 and the electrostatic ground hole 22 of the printed circuit board 20 are directly connected in FIG. 3 and connected via a capacitor 45 in FIG.
[0027]
The assembling is performed such that the bobbin 25 is disposed on the detection coil mounting portion 12 of the case 10, the printed board 20 is accommodated in a predetermined position of the case 10, and the pole 32 of the cover 30 is inserted into the hole 22 of the printed board 20. This is performed by fitting the engagement piece 35 of the cover 30 into the recess 15 of the case 10. As a result of the assembly, the passage hole 11 of the case 10, the passage hole 27 of the bobbin 25, and the passage hole 31 of the cover 30 are aligned to form a path for the pachinko balls.
[0028]
In the proximity switch configured as described above, when a pachinko ball as a metal body tries to pass through the passage hole 31 from the cover 30 side (in the direction of the arrow in FIG. 1), the charged static electricity of the pachinko ball is discharged by the conductive cover 30. Discharge from the electrostatic connection pole 32 to the power ground via the electrostatic ground hole 22 of the printed circuit board 20 directly (the circuit in FIG. 3) or via the capacitor 45 (the circuit in FIG. 4).
[0029]
This proximity switch is characterized in that the cover 30 is conductive. For example, if the cover 30 is made of a conductive filler using a carbon filler as a conductive filler, it is more effective than a conventional shield plate. Other characteristics can be improved. This will be described.
(1) This type of proximity switch emits electromagnetic waves from a detection coil using a high-frequency oscillation circuit and stops or reduces the oscillation gain due to eddy current loss generated by a metal body. The cover 30 made of a conductive resin mixed with a filler does not generate an eddy current unlike a copper plate (shield plate) or the like. This is because the carbon filler has conductivity, but has a low content and is a powder. Therefore, there is no loss of the detection coil 26, and there is no influence even if the conductive cover 30 is in the immediate vicinity of the detection coil 26.
[0030]
Accordingly, the proximity switch has a good yield without a decrease in the detection sensitivity, the temperature characteristic, and the voltage characteristic and little variation in the operation sensitivity.
{Circle around (2)} The conductive cover 30 is basically used on the side where a metal body (pachinko ball) enters, and the static electricity of the charged pachinko ball is removed to protect the proximity switch. The ball passes through the passage holes 11, 27, 31. For this reason, the pachinko ball hits the passage hole 31 of the cover 30 which becomes the entrance of the pachinko ball, and the peripheral portion of the passage hole 31 is extremely worn.
[0031]
However, when a carbon filler is used as the conductive filler, good sliding properties of carbon are exhibited, the specific wear amount is reduced to 1/2 to 1/5 as compared with the inorganic filler, and the life of the proximity switch can be greatly extended. .
{Circle around (3)} In the product cost, the depreciation cost of the mold has a large weight, but it is only necessary to add a protrusion for the electrostatic connection pole 32 to the mold of the cover 30, and a press mold is not required. In addition, since an expensive and difficult-to-handle shield plate is not required, the assembling cost is not required, and the product can be made highly cost-competitive.
[0032]
In the above embodiment, only the cover 30 is made conductive, but the case 10 may be made conductive. In this case, it is preferable that an electrostatic connection pole is also formed inside the case 10 corresponding to the electrostatic ground hole 22 of the printed circuit board 20. This makes it easier to discharge static electricity.
[0033]
In this regard, a metal case and / or a metal cover can be considered the same as the conductive resin, but the metal case and the metal cover generate high-frequency eddy current loss as described above, and as a proximity switch, Stop functioning.
[0034]
【The invention's effect】
The proximity switch of the present invention has the following effects because it is configured as described above.
(1) Since no eddy current loss occurs due to electromagnetic waves of the detection coil,
(A) Variation in detection sensitivity is small.
[0035]
(B) Good temperature and voltage characteristics.
[0036]
(C) Good quality.
(2) Since no shield plate is required,
(D) Investment in a mold for the shield plate is not required.
[0037]
(E) The component cost of the shield plate is unnecessary.
[0038]
(F) The cost of assembling and processing the shield plate is eliminated.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a proximity switch according to one embodiment.
FIG. 2 is an exploded perspective view of the proximity switch when viewed from the opposite side.
FIG. 3 is a block diagram showing an example of a circuit configuration of a printed circuit board incorporated in the proximity switch.
FIG. 4 is a block diagram showing another example of a circuit configuration of a printed circuit board incorporated in the proximity switch.
FIG. 5 is an exploded perspective view of a proximity switch according to a conventional example.
FIG. 6 is a plan view of the proximity switch of FIG. 5 viewed from a case side.
FIG. 7 is a sectional view taken along line AA in FIG. 6;
FIG. 8 is an exploded perspective view of a proximity switch according to another conventional example.
FIG. 9 is a sectional view of the proximity switch of FIG. 8;
[Explanation of symbols]
10. Case (housing)
11 Passing hole for pachinko balls 12 Detector coil mounting part 20 Printed circuit board (detection circuit board)
DESCRIPTION OF SYMBOLS 21 Electronic component 22 Static electricity ground hole 25 Bobbin 26 Detection coil 27 Pachinko ball passage hole 30 Cover (housing)
31 Pachinko ball passage hole 32 Electrostatic connection pole

Claims (5)

In a proximity switch that detects a metal body by incorporating a high-frequency oscillation circuit and a detection coil connected to the high-frequency oscillation circuit in a housing,
A proximity switch characterized in that part or all of a housing is made of a conductive resin. The proximity switch according to claim 1, wherein the conductive resin is obtained by mixing a conductive filler into a thermoplastic resin. 3. A detection circuit board on which the high-frequency oscillation circuit and the detection coil are mounted, and a part of the housing is brought into contact with or close to a ground portion of the detection circuit board via a capacitor. Proximity switch as described. 3. The proximity device according to claim 1, further comprising a detection circuit board on which the high-frequency oscillation circuit and the detection coil are mounted, wherein a part of the housing is directly in contact with or close to a ground portion of the detection circuit board. switch. 4. The housing according to claim 1, wherein the housing comprises a case and a cover detachably attached to the case, and the cover and / or the case are made of a conductive resin. Or the proximity switch according to claim 4.

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