JPH0487418A - Proximity switch - Google Patents

Abstract

PURPOSE:To prevent the malfunction of an oscillating circuit caused by an action of a magnetic field by providing two pieces of oscillation coils on an LC resonance circuit, and shielding magnetically one oscillation coil, in the proximity switch in which the oscillating circuit containing the LC resonance circuit is used CONSTITUTION:When a strong magnetic field works upon the proximity switch, a first oscillation coil 25 loses a function as a coil since its core is magnetized. However, a second oscillation coil 24 is not influenced by the magnetic field since it is shielded magnetically. An IC resonance circuit 22 becomes a form that two pieces of capacitors 25, 26 are connected in parallel against a second oscillation coil 24, and is resonated by L2 of a second oscillation coil 24 and the composite capacity C1+C2 of two pieces of caracitors 25, 26. As a result, an oscillating circuit 20 executes an oscillating operation by a frequency omega3 irrespective of whether a metallic body approaches or not, and an output VOUT of a comparing circuit 21 becomes a high level.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a proximity switch that detects the approach of a metal object without contact.
The present invention relates to a proximity switch using an oscillation circuit including a resonant circuit.

<Prior Art> For example, in a pachinko machine, an electromagnetic induction type pachinko ball sensor using a proximity switch is used to detect when a pachinko ball enters a winning slot. This type of pachinko ball sensor uses electromagnetic induction to detect when a metal pachinko ball has passed through a prize opening without contact. An example is illustrative.

In the case shown in the figure, a detection hole 3 having a diameter that allows a pachinko ball 6 to pass through a thin plate-like case body 2 made of synthetic resin is opened in the thickness direction.

In this case body 1, a detection circuit section 4 of a proximity switch is incorporated in an example part of a detection hole 3, and an oscillation coil 5 of an oscillation circuit forming a part of the detection circuit section 4 is installed around the detection hole 3 through a ball passage. It is arranged to surround the

However, this type of structure has a problem in that when two or more pachinko ball sensors are placed close to each other, malfunctions occur due to mutual induction between the oscillation coils.

FIG. 7 shows an improvement plan that solves this problem, in which an oscillation coil 7 is arranged in one example of the detection hole 3 facing 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 end of this core 8 is open to form an open magnetic path (indicated by a broken line in the figure), and the open end is connected to the detection hole 3.
placed towards.

When no pachinko ball approaches this oscillation coil 7,
The oscillation circuit performs an oscillation operation, but when the pachinko ball 6 passes through the detection hole 3 and approaches the oscillation coil 7, the pachinko ball 6 receives the magnetic field lines of the oscillation coil 7 and generates 1 inside it.
! Eddy currents are generated due to magnetic induction. Therefore, the oscillation coil 7
When the resistance becomes large (the oscillation stops), it is possible to detect the passage of the pachinko ball 6.

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

This oscillation circuit IO has an amplification transistor R6,
An LC resonant circuit 11 consisting of an oscillation coil 7 and a capacitor 12 is electrically connected to a resistor R, and is compensated by a constant current source Is and a bias voltage E shown in the figure so that the operating point of the transistor TR is in the active region. ing. Further, the transistors TR, TR constitute a mirror circuit, and feed back the same current as the collector current of the transistor TR to the LC resonant circuit 11. Note that VCC is the power supply voltage,
v out indicates output, and G indicates ground.

In the oscillation circuit 10, as shown in FIG.
If the conductance on the side of the resonance circuit IIO is 01 and the negative conductance on the side of the amplifier circuit section 13 is G, then the pachinko ball 6 passes through the detection hole 3 when the metal body 14 is not close to the oscillation coil 7. In the state where it is not done,
The relationship G,<G is established, and the oscillation circuit 10 enters an oscillation state. On the other hand, when the metal 14 approaches the oscillation coil 7, that is, when the pachinko ball 6 passes through the detection hole 3, the conductance G increases and the relationship c>Gi is established, and the oscillation circuit 10 oscillates. Stop operation.

FIG. 11 shows a relationship 15 between the distance between the oscillation coil 7 and the metal body 14 and the conductance G on the LC resonance circuit 11 side. In the figure, when the distance exceeds a predetermined value D0, G<G=, and the oscillation circuit 10 operates in oscillation, while the distance remains at the predetermined value. When it becomes smaller, G>c, and the oscillation circuit 10 stops its oscillation operation.

<Problems to be Solved by the Invention> In a pachinko machine in which the pachinko ball sensor 1 described above is used, some players commit fraudulent acts and cause the pachinko ball sensor 1 to malfunction, causing the pachinko balls to be stolen illegally. is defrauding.

In other words, by bringing a permanent magnet close to the pachinko ball sensor 1 located in the winning opening and applying a strong magnetic field, it is possible to detect whether the pachinko ball sensor 1 has detected a pachinko ball even though no pachinko ball has entered the winning opening. This causes the system to malfunction. The magnetic field from the permanent magnet causes the oscillation coil 7
, the core 8 is magnetized and the conductance G increases, even though the pachinko ball 6 has not passed through the detection hole 3.

This is because the relationship GL is established and the oscillation operation of the oscillation circuit 10 is stopped.

In FIG. 11, 16 indicates the relationship between the distance between the metal body 14 and the oscillation coil 7 and the conductance G on the LC resonance circuit 11 side when the core 8 is magnetized by a permanent magnet. According to the figure, regardless of the distance, C,>
It can be seen that the relationship C always holds true.

The present invention was made in view of the above-mentioned problem, and an object of the present invention is to provide a proximity switch that correctly detects the approach of metal without being adversely affected by the approach of a permanent magnet.

<Means for Solving the Problems> The present invention provides a proximity switch using an oscillation circuit including an LC resonance circuit, wherein the LC resonance circuit includes two oscillation coils, and the - oscillation coil is It is magnetically shielded.

<Effect> An oscillation coil that is not magnetically shielded responds similarly to the approach of metal and the action of a magnetic field, but an oscillation coil that is magnetically shielded does not respond to the action of a magnetic field. Therefore, the operation of the oscillation circuit can be maintained in a state where metal does not come close to it, and malfunction of the oscillation circuit due to the action of the magnetic field can be prevented.

<Embodiment> 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. In FIG.

The illustrated example 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 resonant circuit 22.

Therefore, corresponding components are given the same reference numerals and their explanations will be omitted here.

The LC resonance circuit 22 consists of two oscillation coils 23, 24 and two capacitors 25, 26. The first oscillation coil 23 is used as a metal detection coil, and the second oscillation coil 23 is used as a metal detection coil.
The oscillation coil 24 is used for the purpose of providing magnetic shielding and assisting the first oscillation coil 23.

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

The output of the oscillation circuit 20 is given to a comparator circuit 21, which rectifies and smoothes the input and then compares it with a predetermined threshold value to produce a binarized output (2). Generate Il+1.

FIG. 2 shows the principle of the invention, with the horizontal axis representing the distance to the metal body, and the vertical axis representing the conductance Ge on the LC resonance circuit 22 side.

In the figure, 27 indicates the relationship between the distance to the metal body and the conductance Ge under normal conditions where no magnetic field is applied, and 28 indicates the relationship between the distance to the metal body and the conductance Gi under a strong magnetic field. It shows the relationship between

In the same figure, under normal conditions where no magnetic field is acting, when the distance exceeds a predetermined value D0, C0<C,
Therefore, the oscillation circuit 20 operates in oscillation, and when the distance becomes smaller than a predetermined value, C,>C, and the oscillation circuit 20 stops its oscillation operation.

However, under the action of a strong magnetic field, the relationship G<c holds regardless of the distance to the metal object, and the oscillation circuit 2
0 maintains the oscillation state and creates a state in which no metal objects are close to each other.

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

When the proximity switch is currently in a state where no magnetic field is acting, the LC resonant circuit 22 of the oscillation circuit 20 operates as shown in FIG.
) As shown in (2), C composite capacitances of the second oscillation coil 24 and two capacitors 25.26 are connected in parallel to the first oscillation coil 23, and the potential at the midpoint of the capacitor 25.26 is vLc will be applied to the oscillation circuit 20.

In this case, if the inductance of the second oscillation coil 24 is Lx, the capacitance of one capacitor 25 is CI+the capacitance of the other capacitor 26 is Ct, then the above-mentioned combined capacitance Cx
is expressed as follows.

jωCx JωC1 therefore ・・・・■ It is.

When the proximity switch is in a state where no magnetic field is acting as described above, the first oscillation coil 23 and the composite capacitance CX described above resonate.

As a result, when the metal body is separated, the oscillation circuit 20 oscillates at the frequency ω2, as shown in FIG. 3, and the output of the comparison circuit 21 is . υa will be at a high level. Furthermore, when a metal object approaches, the first oscillation coil 23 responds to this and the oscillation circuit 20 stops its oscillation operation, so the output of the comparison circuit 21 is -. u7 becomes low level.

Next, when a strong magnetic field acts on the proximity switch, the core of the first oscillation coil 23 is magnetized and it loses its function as a coil, but the second oscillation coil 24 is magnetically shielded and is not affected by the magnetic field. do not have. In this case, the LC resonance circuit 22 has a configuration in which two capacitors 25 and 26 are connected in parallel to the second oscillation coil 24, and L2 and two capacitors 25 and 26 are connected in parallel to the second oscillation coil 24, as shown in FIG. It resonates with the combined capacitance (C, 107) of the capacitors 25 and 26.

As a result, the oscillation circuit 20 oscillates at the frequency ω3, regardless of whether the metal object approaches, and the output V of the comparison circuit 21
. tlT becomes high level.

In this way, the output V of the comparator circuit 21 is generated only when a metal object approaches under normal conditions where no magnetic field is applied. U becomes a low level, and the output (■) of the comparator circuit 21 occurs not only when the metal body separates, but also when a magnetic field is applied. . , is at a high level. Therefore, when the proximity switch of the present invention is used, for example, in a pachinko ball sensor, it is possible to prevent the pachinko machine from malfunctioning due to fraudulent activities using permanent magnets.

<Effects of the Invention> As described above, the present invention provides a proximity switch using an oscillation circuit including an LC resonant circuit, in which the LC resonant circuit includes two oscillation coils, and one of the oscillation coils is magnetically shielded. Therefore, the magnetically shielded oscillation coil is not sensitive to the action of the magnetic field, and the operation of the oscillation circuit can be maintained in a state where metal does not come close to it. Therefore, the oscillation circuit can be prevented from malfunctioning due to the action of the magnetic field, and a highly reliable proximity switch can be obtained, achieving the remarkable effects of achieving the purpose of the invention.

[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 explaining the principle of the present invention, and FIG. 3 is a time chart showing the operation of the proximity switch. Figures 4 and 5 are electric circuit diagrams showing LC resonance circuits, Figures 6 and 7 are oblique views of conventional pachinko ball sensors, Figure 8 is an explanatory diagram of the structure of the oscillation coil, and Figure 9 is the conventional The electric circuit diagram of the proximity switch, FIG. 1θ, and FIG. 11 are diagrams explaining the principle of the proximity switch. 20...Oscillation circuit 22...LC resonant circuit 2
3, 24...Oscillation coil

Claims (1)

[Claims] A proximity switch using an oscillation circuit including an LC resonance circuit, wherein the LC resonance circuit includes two oscillation coils,
One of the oscillation coils is a proximity switch that is magnetically shielded.