JP2926927B2 - Proximity switch - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a proximity switch for detecting the approach of a metal body without contact, and in particular, the present invention relates to a proximity switch for detecting an approach of a metal body.
The present invention relates to a proximity switch using an oscillation circuit including a resonance circuit.

<Prior Art> For example, in a pachinko machine, an electromagnetic induction type pachinko ball sensor using a proximity switch is used to detect that a pachinko ball has entered a winning opening. The pachinko ball sensor of this type detects that a metal pachinko ball has passed through the winning opening without contact using an electromagnetic induction action, and FIG. 6 shows a conventional pachinko ball sensor 1.
Is shown.

FIG. 1 shows a case body 2 made of a synthetic resin having a thin plate shape.
A detection hole 3 having a hole diameter through which a pachinko ball 6 can pass is opened in the thickness direction. In this case body 1, a detection circuit 4 of a proximity switch is incorporated on one side of the detection hole 3 and an oscillation coil 5 of an oscillation circuit forming a part of the detection circuit portion 4 is provided around the detection hole 3 in a ball passage. Has been deployed to surround.

However, this type of structure has a problem that if two or more pachinko ball sensors are arranged close to each other, a malfunction occurs due to the mutual induction of the oscillation coil winding.

FIG. 7 shows an improvement that solves such a problem. The oscillation coil 7 is arranged on one side of the detection hole 3 so as to face the ball passage. As shown in FIG. 8, the oscillation coil 7 is wound around a central leg 9 of a core 8 having an E-shape as a whole. One of the cores 8 is open to form an open magnetic path (indicated by a broken line in the drawing), and the open end thereof is disposed with the open end facing the detection hole 3.

When the pachinko ball is not approaching the oscillation coil 7, the oscillating circuit performs an oscillating operation.
When approaching the oscillation coil 7 through the detection hole 3,
The pachinko ball 6 receives the magnetic field lines of the oscillation coil 7 and generates an eddy current due to electromagnetic induction therein. Therefore, the resistance of the oscillation coil 7 increases and the oscillation stops, whereby the passage of the pachinko ball 6 can be detected.

As the oscillation circuit, a separated Hartley oscillation circuit 10 as shown in FIG. 9 is used.

The oscillation circuit 10, the transistor TR ₁ for amplification, the LC resonance circuit 11 composed of the oscillation coil 7 and a capacitor 12 and a resistor R which was electrically connected, a constant current source of FIG I _S and the bias voltage E _S the operating point of the transistor TR ₁ is compensated to be the active region by. Transistors TR ₂ and TR
₃ constitute a mirror circuit, which is fed back to the same current as the collector current of the transistor TR ₁ to LC resonance circuit 11. Note that V
_CC is a power supply voltage, V _OUT is an output, and G is a ground.

In the oscillation circuit 10, as shown in FIG. 10, when the conductance on the LC resonance circuit 11 side is G _e and the negative conductance on the amplification circuit unit 13 side is G _i , the metal body 14 state not close, i.e. in the state in which the detection hole 3 pachinko ball 6 has not passed, a condition for resonance, established the relationship G _e <G _i, the oscillation circuit 10 becomes the oscillation state. On the other hand, when the metal 14 approaches the oscillation coil 7,
That is, in a state where the pachinko ball 6 passes through the detection hole 3,
The conductance G _e is increased established relationship G _e> G _i, the oscillation circuit 10 stops the oscillation operation.

FIG. 11 shows the distance D between the oscillation coil 7 and the metal body 14.
When shows the relationship 15 between the conductance G _e side of the LC resonant circuit 11. In the figure, when the distance D exceeds Tokoro stationary D _0, G _e <oscillation circuit 10 is oscillating operation becomes G _i, whereas the distance D is smaller than the predetermined value D _0, G _e> and G _i The oscillation circuit 10 stops the oscillation operation.

<Problems to be Solved by the Invention> In a pachinko machine using the above-mentioned pachinko ball sensor 1, some players perform wrongdoing, and the pachinko ball sensor 1 is caused to malfunction so that the pachinko ball is improperly used. Is fraudulent.

That is, by applying a strong magnetic field by bringing a permanent magnet close to the pachinko ball sensor 1 located at the winning opening, whether the pachinko ball sensor 1 has detected a pachinko ball even though the pachinko ball has not entered the winning opening. It causes a malfunction like this. When a magnetic field by the permanent magnets acts on the oscillator coil 7, the conductance G _e core 8 is magnetized increases, despite pachinko ball 6 does not pass through the detection hole 3, the relationship of G _e> G _i Is satisfied, and the oscillation operation of the oscillation circuit 10 stops.

In FIG. 11, reference numeral 16 denotes a distance D between the metal body 14 and the oscillation coil 7 when the core 8 is magnetized by a permanent magnet, and an LC resonance circuit.
Shows the relationship between the conductance G _e 11 side. According to the figure, the distance regardless is D, it can be seen that the relationship of G _e> G _i always holds.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a proximity switch that correctly detects the approach of metal without being adversely affected by the proximity of a permanent magnet.

<Means for Solving the Problems> The present invention includes an oscillation circuit including an LC resonance circuit and an amplification circuit, and performs resonance depending on whether a metal body approaches an oscillation coil of the LC resonance circuit. In the proximity switch in which the oscillation circuit is configured so that the condition (1) is satisfied or not satisfied, the oscillation coil of the LC resonance circuit is a first oscillation coil whose core is magnetized by the action of a magnetic field. And a second oscillation coil that is magnetically shielded, and the condition for the resonance is not affected by the action of the magnetic field on the oscillation coil in a state where the metal body is not approaching the oscillation coil. The oscillation circuit is configured so that the established and unsatisfied states are maintained in a state before the action of the magnetic field.

<Operation> When a magnetic field is applied from the outside by a permanent magnet or the like while the metal body is not approaching the oscillation coil, the core of the first oscillation coil is magnetized under the influence of this magnetic field, and the first oscillation coil is magnetized.
Oscillating coil loses its function as a sensitive element for metal detection. However, since the oscillation circuit is operated by the magnetically shielded second oscillation coil so that the state before the magnetic field is applied is maintained, it is not likely that the action of the magnetic field is erroneously detected as a metal object approaching. Absent.

FIG. 1 shows a circuit configuration of a proximity switch according to an embodiment of the present invention, which includes an oscillation circuit 20 and a comparison circuit 21.

The illustrated oscillation circuit 20 is a separate Hartley oscillation circuit, and has the same configuration as the conventional example shown in FIG. 9 except for the LC resonance circuit 22. Accordingly, the same reference numerals are given to the corresponding components, and the description thereof will be omitted.

The LC resonance circuit 22 is composed of two oscillation coils 23 and 24 and two capacitors 25 and 26.
3 is used as a metal detection coil, and the second oscillation coil 2
Reference numeral 4 is used for the purpose of providing a magnetic shield to assist the first oscillation coil 23.

The first oscillation coil 23 is connected in series with the capacitor 25,
The second oscillation coil 24 and another capacitor 26 are connected in parallel to this series circuit.

The output of the oscillation circuit 20 is supplied to a comparison circuit 21. The comparison circuit 21 rectifies and smoothes the input, compares it with a predetermined threshold value, and generates a binary output _VOUT .

FIG. 2 shows the principle of the present invention, in which the horizontal axis indicates the distance D from the metal body, and the vertical axis indicates the conductance Ge on the LC resonance circuit 22 side.

In the figure, 27 shows the relationship between the conductance Ge and the distance D to the metal body under a normal state where no magnetic field acts,
Numeral 28 indicates the relationship between the distance D from the metal body under a strong magnetic field and the conductance Gi.

In the figure, under normal conditions where the magnetic field is not acting, when the distance D exceeds a predetermined value D _0, a condition for resonance, the relationship of G _e <G _i is satisfied, the oscillation circuit 20 There was oscillation operation, whereas when the distance D is smaller than the predetermined value D _0, G _e
> G _i, and the oscillation circuit 20 stops the oscillation operation.

In However strong action of a magnetic field, regardless of the distance D between the metal body, the relationship of G _e <G _i is satisfied, the oscillation circuit 20 maintains the oscillation state, a state in which the metal body is not approaching Generate.

FIG. 3 is a time chart showing an example of the operation of the proximity switch.

If the proximity switch is under a state in which no magnetic field is acting, the LC resonance circuit 22 of the oscillation circuit 20 is switched to the state shown in FIG.
As shown in (2), the combined capacitance C _{x of} the second oscillation coil 24 and the two capacitors 25 and 26 is provided for the first oscillation coil 23.
Are connected in parallel, and the potential _{VLC at} the intermediate point between the capacitors 25 and 26 is _supplied to the oscillation circuit 20.

In this case, the inductance of the second oscillation coil 24 is L ₂ , the capacity of _one capacitor 25 is C ₁ , and the other capacitor is
When the capacity of 26 and C _2, is expressed as the composite capacitance C _x Hatsugi.

therefore It is.

When such a proximity switch is in a state where a magnetic field is not acting, resonance occurs between L1 of the _first oscillation coil 23 and the above-described combined capacitance _CX, and the potential corresponding to the capacitance ratio of the entire resonance oscillation is _VLC
It will be fed back to the terminal.

As a result, when the metal body is moved away, as shown in Figure 3, the oscillation circuit 20 oscillates at a frequency omega _2, the output V _OUT of the comparator circuit 21 becomes high level. When the metal body approaches, the first oscillation coil 23 responds to this and the oscillation circuit 20 stops the oscillation operation.
_OUT goes low.

Next, when a strong magnetic field acts on the proximity switch, the core of the first oscillating coil 23 is magnetized and loses its function as a coil. However, the second oscillating coil 24 is magnetically shielded and thus is affected by the magnetic field. Absent. LC resonance circuit 22 in this case
Is, as shown in FIG.
The capacitors 25 and 26 are connected in parallel, and resonate with L ₂ of the second oscillation coil 24 and the combined capacitance (C ₁ + C ₂ ) of the _two capacitors 25 and 26.

As a result, the oscillation circuit 20 oscillates at the frequency ω ₃ irrespective of the presence or absence of the approach of the metal body, and the output V _{OUT of the} comparison circuit 21 is output.
Becomes high level.

As described above, the output V _OUT of the comparison circuit 21 becomes low level only when the metal body approaches under the normal state where the magnetic field is not applied, and when the metal body is separated, as well as when the magnetic field is applied, the comparison circuit is output. The output V _OUT of 21 goes high. Therefore, when the proximity switch of the present invention is used, for example, in a pachinko ball sensor, it is possible to prevent a pachinko machine from malfunctioning in response to fraud using a permanent magnet.

<Effect of the Invention> As described above, the present invention provides an oscillation coil of an LC resonance circuit,
It is composed of a first oscillation coil whose core is magnetized by the action of a magnetic field and a second oscillation coil that is magnetically shielded, and a magnetic field applied to the oscillation coil when no metal body is close to the oscillation coil. Since the oscillation circuit is configured so that the condition for resonance is satisfied or not satisfied can be maintained in the state before the action of the magnetic field, in the state where the metal body does not approach the oscillation coil, Even when a magnetic field is applied from the outside by a permanent magnet or the like, the effect of the magnetic field is not erroneously detected as a metal object approaching, and a remarkable effect that a highly reliable proximity switch can be obtained.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of a proximity switch according to an embodiment of the present invention, FIG. 2 is a diagram illustrating the principle of the present invention, FIG. 3 is a time chart showing the operation of the proximity switch, FIG. 4 and FIG. 6 is an electric circuit diagram showing an LC resonance circuit, FIGS. 6 and 7 are perspective views of a conventional pachinko ball sensor, FIG. 8 is an explanatory view of the structure of an oscillation coil, and FIG. 9 is an electric circuit diagram of a conventional proximity switch. , FIG. 10 and FIG. 11 are explanatory diagrams of the principle of the proximity switch. 20 …… oscillation circuit, 22 …… LC resonance circuit 23,24 …… oscillation coil

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-199325 (JP, A) JP-A-58-96424 (JP, A) JP-A-2-60203 (JP, A) JP-A-2-96 56105 (JP, A) JP-A-51-9270 (JP, A) JP-A-2-268785 (JP, A) JP-A-49-111167 (JP, A) JP-A-62-272415 (JP, A) JP-A-61-199326 (JP, A) JP-A-4-25218 (JP, A) JP-A-1-175140 (JP, A) JP-A-4-12718 (JP, U) (58) Fields investigated (Int.Cl. ⁶ , DB name) H03K 17/78-17/98

Claims (1)

(57) [Claims] An oscillation circuit including an LC resonance circuit and an amplification circuit is provided, and a condition for resonance is established or not established depending on whether a metal body approaches an oscillation coil of the LC resonance circuit. As described above, in the proximity switch including the oscillation circuit, the oscillation coil of the LC resonance circuit includes a first oscillation coil whose core is magnetized by the action of a magnetic field, and a second shielded magnetic shield.
Oscillation coil of the above, the effect of the magnetic field on the oscillation coil in a state where the metal body is not approaching the oscillation coil, the condition for the resonance is satisfied, the state of the non-establishment of the magnetic field A proximity switch including the oscillation circuit configured to be maintained in a state before the operation.