JP4731636B1 - Magnetic switch - Google Patents

Abstract

A highly sensitive magnetic switch with a small number of parts is provided.
A rectangular wave is supplied to a circuit in which a saturable coil with a yoke and a reference coil are connected in series. A saturation phenomenon is generated in the yoke within the period of the rectangular wave, and a voltage change of the reference coil L105 that occurs at that time is detected. Unlike the prior art, the external magnetic field required to cause the saturation phenomenon may be weaker than that of the prior art, so that a highly sensitive magnetic switch 201 can be realized.
[Selection] Figure 4

Description

The present invention relates to a magnetic switch.
More specifically, the present invention relates to a magnetic switch having no mechanical contact, which is improved in magnetic detection performance and the like from the prior art, and which is turned on or off by approaching a magnet.

  The applicant manufactures and sells an active magnetic switch using a saturable coil. Hereinafter, the operation principle of this active magnetic switch will be described.

FIGS. 7A, 7B, and 7C are a circuit diagram of a magnetic switch disclosed in Patent Document 1 and graphs for explaining various characteristics of the circuit.
FIG. 7A is a circuit diagram for explaining the principle of the magnetic switch, FIG. 7B is a graph showing the voltage of the base of the transistor 706 in the circuit of FIG. 7A, and FIG. It is a graph which shows the voltage of the collector of the transistor 711 of the circuit of Fig.7 (a).

A configuration of the magnetic switch circuit 701 will be described with reference to FIG.
A resistor R703 and a saturable coil L704 having a yoke are connected in series to the AC voltage source 702, and a connection point between the saturable coil L704 and the AC voltage source 702 is grounded.
A base of a transistor 706 that is an NPN transistor is connected to a connection point between the resistor R703 and the saturable coil L704 via a resistor R705. The collector of the transistor 706 is pulled up at the power supply voltage + Vcc through the resistor R707. On the other hand, the emitter of the transistor 706 is grounded. Therefore, when the transistor 706 is turned on, the collector voltage becomes zero.

A capacitor C708 is connected to the collector of the transistor 706. The other terminal of the capacitor C708 is grounded.
A base of a transistor 711 which is an NPN transistor is connected to a connection point between the collector of the transistor 706 and the capacitor C708 via a resistor R709. A resistor R710 is connected to the base of the transistor 711, and the other terminal of the resistor R710 is grounded. Resistor R710 serves to discharge capacitor C708. The emitter of the transistor 711 is grounded.
The collector of the transistor 711 becomes the output terminal of the magnetic switch. That is, the transistor 711 constitutes an open collector output.

With reference to FIGS. 7B and 7C, the operation of the magnetic switch circuit 701 in FIG. 7A will be described.
Prior to time t713 in FIG. 7B, the voltage waveform of the base of the transistor 706 in a state where the magnet 712 is not in proximity to the saturable coil L704. After time t713, the magnet 712 is present in the saturable coil L704. It is a voltage waveform of the base of the transistor 706 in a state of being close to each other.
Before time t713 in FIG. 7C, the voltage waveform of the collector of the transistor 711 in a state where the magnet 712 is not in proximity to the saturable coil L704. After time t713, the magnet 712 is present in the saturable coil L704. It is a voltage waveform of the collector of the transistor 711 in a state of being close to each other. In FIG. 7A, since the transistor 711 is an open collector, FIG. 7C shows a voltage waveform in a state where a predetermined voltage is applied to the collector of the transistor 711.

In a state where the magnet 712 is not close to the saturable coil L704, the saturable coil L704 exhibits high inductance because the yoke is not saturated. Therefore, an AC voltage obtained by dividing the voltage of the AC voltage source 702 by the resistor R703 and the saturable coil L704 is applied to the base of the transistor 706 through the resistor R705. Since current flows only in one direction between the base and emitter of the transistor, a half-wave rectified voltage having the waveform of FIG. 7B is output to the collector of the transistor 706.
The half-wave rectified voltage is integrated by an integrating circuit including a capacitor C708 and a resistor R709. As a result, the potential output from the resistor R709 is lowered. This voltage is input to the base of the transistor 711.

  On the other hand, when the magnet 712 is close to the saturable coil L704, the saturable coil L704 shows a low inductance because the yoke is saturated. For this reason, a voltage close to ground is applied to the base of the transistor 706 through the resistor R705. For this reason, the base current of the transistor 706 hardly flows, and as a result, substantially the same voltage as the power supply voltage + Vcc is output to the collector of the transistor 706. For this reason, the voltage divided by the series combined resistance of the resistors R707, R709, and R710 is applied to the base of the transistor 711.

  By appropriately setting the values of the resistors R707, R709, and R710, the transistor 711 is turned off when the magnet 712 is not close to the saturable coil L704, and the transistor 711 is set when the magnet 712 is close to the saturable coil L704. The magnetic switch circuit 701 can be configured to be turned on. This is the waveform of FIG.

JP 61-172077 A

  Since the magnetic switch circuit 701 described with reference to FIG. 7 has to saturate the saturable coil L704 only with the external magnetic field generated by the magnet, a relatively strong magnetic field must be applied to the saturable coil. That is, a strong magnet must be brought as close as possible to the saturable coil L704, and therefore the sensitivity is inferior.

  An object of the present invention is to solve such problems and to provide a magnetic switch having a high sensitivity with a small number of parts.

In order to solve the above problems, a magnetic switch of the present invention includes a saturable coil with a yoke, a reference coil connected in series to the saturable coil , a saturable coil and a reference coil, and a predetermined cycle. When a rectangular wave having a predetermined voltage is output and a predetermined external magnetic field is applied to the yoke during a period in which the predetermined voltage is maintained, the yoke causes magnetic saturation to flow into the saturable coil. A rectangular wave voltage source that outputs a rectangular wave that is set so that an increase in current is steeper than before magnetic saturation occurs, and a voltage detector that detects a change in the voltage between terminals of the reference coil.

A rectangular wave is supplied to a circuit in which a saturable coil with a yoke and a reference coil are connected in series. A saturation phenomenon is generated in the yoke within the period of the rectangular wave, and a voltage change of the reference coil that occurs at that time is detected.
Unlike the prior art, the external magnetic field required to cause the saturation phenomenon may be weaker than that of the prior art, so that a highly sensitive magnetic switch can be realized.

  According to the present invention, a highly sensitive magnetic switch can be provided with a small number of parts.

FIG. 2 is a circuit diagram and a waveform diagram of a magnetic detection circuit for explaining the operation principle of the present invention. 1 is an external perspective view of a magnetic switch according to a first embodiment of the present invention. 1 is a block diagram of a magnetic switch according to a first embodiment of the present invention. It is a circuit diagram of a magnetic detection circuit, and a waveform diagram of each part of a circuit. It is the schematic of a magnetic switch. It is a circuit diagram and a wave form diagram of a magnetic switch concerning a second embodiment of the present invention. It is a circuit diagram and a waveform diagram of a conventional magnetic switch.

[Operating principle]
Before describing the embodiment of the present invention, the operating principle of the magnetic switch will be described.
1A, 1B, 1C, and 1D are a circuit diagram and a waveform diagram of a magnetic detection circuit for explaining the operation principle of the present invention.
FIG. 1A is a circuit diagram of the magnetic detection circuit 101.
In the magnetic detection circuit 101, a switch 103, a saturable coil L104 having a yoke, and a reference coil L105 are connected in series to a DC power source 102. A free wheel diode D106 is connected to the saturable coil L104 and the reference coil L105. Connected in parallel. As the material of the yoke, a material having a high magnetic permeability such as permalloy or ferrite is suitable. The switch 103 has an on-time controlled by a control circuit (not shown).

FIG. 1B is a waveform diagram showing the logic state of the switch 103 of the magnetic detection circuit 101.
FIG. 1C is a waveform diagram of currents flowing through the saturable coil L104 and the reference coil L105 of the magnetic detection circuit 101.
FIG. 1D is a waveform diagram of a voltage appearing at the midpoint of connection between the saturable coil L104 and the reference coil L105 of the magnetic detection circuit 101.

As is well known, when the DC power source 102 is connected to the coil (t111 to t112 in FIG. 1B), no current flows at that moment, and the current gradually increases (t111 in FIG. 1C). ~ T112). From the viewpoint of direct current, this can be considered that the direct current resistance gradually decreases.
Assume that saturable coil L104 and reference coil L105 in a state where no magnetic field is applied have the same inductance. Then, a voltage that is ½ of the power supply voltage appears at the midpoint of connection between the saturable coil L104 and the reference coil L105 (t111 to t112 in FIG. 1D). Since the inductance is the same, both the saturable coil L104 and the reference coil L105 can be considered to have a DC resistance that decreases with time.

  If the DC power source 102 is left connected, the current increases and the coil may burn out. Therefore, when the current increases to some extent, the switch 103 is turned off (t112 to t114 in FIG. 1B). Then, since a counter electromotive force is generated from the coil (t112 to t113 in FIG. 1D), a free wheel diode D106 is provided in order to flow a current and prevent destruction of the circuit elements and the like. Through this free wheel diode D106, the current decreases with time (t112 to t113 in FIG. 1C).

Next, a magnetic field is applied to the saturable coil L104, and the switch 103 is turned on in the same manner (t114 to t116 in FIG. 1B). At this time, the magnetic field applied to the saturable coil L104 applies a magnetic field in the same direction as the magnetic field generated from the saturable coil L104.
In the saturable coil L104, the magnetic field becomes stronger as the current increases (t114 to t115 in FIG. 1C). When the magnetic field generated by the saturable coil itself and the magnetic field applied by the magnet saturate the yoke of the saturable coil L104, the inductance of the saturable coil L104 decreases at that time. Then, at this time, the DC resistance of the saturable coil L104 is the same as that decreased. As a result, the current flowing through the saturable coil L104 and the reference coil increases rapidly (t115 to t116 in FIG. 1C), and the potential at the midpoint of connection between the saturable coil L104 and the reference coil increases (FIG. 1 (d)). ) T115 to t116).

  Compared with the prior art circuit of FIG. 7, the principle of the present invention uses not only the external magnetic field generated by the magnet 107 but also the magnetic field generated in the saturable coil L104 by the DC power source 102 for saturation of the yoke. It can be seen that a saturation phenomenon can be caused in the saturable coil L104 even with a weak external magnetic field. Furthermore, by taking a long ON time of the switch 103, it becomes possible to cause a saturation phenomenon even by applying a slight magnetic field. That is, the sensitivity can be adjusted by turning on the switch 103.

The ON time of the switch 103 is a cycle of the pulse power source, that is, a frequency.
Furthermore, when the direction of the magnetic field applied by the magnet is opposite to the magnetic field generated by the saturable coil L104, the saturation phenomenon does not occur or is difficult to occur. That is, the magnetic detection circuit 101 of the present invention has polarity and corresponds to the direction of the magnetic field.

[First embodiment / Appearance and internal configuration]
FIG. 2 is an external perspective view of the magnetic switch according to the first embodiment of the present invention.
The magnetic switch 201 is resin-molded, and a saturable coil L104 is embedded in the detection protrusion 201a. When the magnet 107 is brought close to the detection protrusion 201a, an ON output is obtained through the cable 202.

FIG. 3 is a block diagram of the magnetic switch 201.
The saturable coil L104 having the yoke 301 is connected to the magnetic detection circuit 302. Both the saturable coil L104 and the magnetic detection circuit 302 are resin-molded. The end surface of the yoke 301 fits into the detection protrusion 201a.
Note that the shape of FIG. 2 is merely an example, and as can be seen from the circuit configuration described later, there is no factor that hinders the mounting mode of the magnetic switch 201 in the circuit configuration. Be free.
Although the saturable coil L <b> 104 is illustrated separately from the magnetic detection circuit 302 in FIG. 3, the saturable coil L <b> 104 is also a component of the magnetic detection circuit 302.

[Circuit and operation]
4A, 4B, 4C, 4D, and 4E are a circuit diagram of the magnetic detection circuit 302 and waveform diagrams of each part of the circuit.
FIG. 4A is a circuit diagram of the magnetic detection circuit 302.
The pulse signal source 401 is input to the gate of an FET 402 that is a P-channel MOS-FET. The source of the FET 402 is connected to the power supply voltage + Vcc. A saturable coil L104 and a reference coil L105 are connected in series to the drain of the FET 402, and the other terminal of the reference coil L105 is grounded. A free wheel diode D106 is also connected to the drain of the FET 402.

The positive terminal of the comparator 403 is connected to the midpoint of connection between the saturable coil L104 and the reference coil L105. A reference voltage Vref obtained by dividing the power supply voltage + Vcc by resistors R404 and R405 is applied to the negative terminal of the comparator 403.
The output signal of the pulse signal source 401 is also supplied to the Cp terminal of a D flip-flop (hereinafter “D-FF”) 406. The output terminal of the comparator 403 is connected to the D terminal of the D-FF 406.
The base of an open collector transistor 408 is connected to the Q terminal of the D-FF 406 via a resistor R407.

FIG. 4B is a waveform diagram of the output signal of the pulse signal source 401.
FIG. 4C is a waveform diagram of the potential at the midpoint between the saturable coil L104 and the reference coil L105.
FIG. 4D is a waveform diagram of the output voltage of the comparator 403.
FIG. 4E is a waveform diagram of the Q terminal of the D-FF 406.

The FET 402 is turned on when the potential of the pulse signal source 401 is low, and is turned off when the potential of the pulse signal source 401 is high.
In a state where a positive magnetic field is not applied to the saturable coil L104 (before time t413), no saturation phenomenon occurs in the saturable coil L104, so the potential at the midpoint between the saturable coil L104 and the reference coil L105. Does not exceed the reference voltage Vref (time points t411 to t412 in FIG. 4C).

  On the other hand, in a state where a positive magnetic field having a predetermined strength is applied to the saturable coil L104 (after time t413), the period of the pulse signal source 401 is such that a saturation phenomenon occurs in the saturable coil L104. Since it is determined, the potential at the midpoint between the saturable coil L104 and the reference coil L105 exceeds the reference voltage Vref (time points t415 to t416 in FIG. 4C).

The comparator 403 compares the potential at the midpoint between the saturable coil L104 and the reference coil L105 with the reference voltage Vref, and captures and outputs the potential when the saturation phenomenon occurs (time t415 in FIG. 4D). ~ T416).
The D-FF 406 holds the logic (P423 and P424 in FIG. 4D) of the D terminal of the Cp terminal up-edge (P421 and P422 in FIG. 4B), so that the saturable coil L104 has a positive external When a magnetic field is not applied, a low potential that is a logic “false” is output (P425 in FIG. 4E), and when a positive external magnetic field is applied to the saturable coil L104, a logic “true” is output. Is output (P426 in FIG. 4E).

  Among the components of the magnetic detection circuit 302 in FIG. 4A, the comparator 403 and the reference voltage source (resistors R404 and R405) include a voltage detection unit for detecting a change in the voltage between the terminals of the reference coil L105. Constitute.

  In the magnetic detection circuit 302 in FIG. 4A, the pulse signal source 401, the comparator 403, the reference voltage sources (resistors R404 and R405), and the D-FF 406 can be replaced by a microcomputer. Since it is only necessary to measure the potential at the midpoint between the saturable coil L104 and the reference coil L105 and capture the change in potential when the saturable coil L104 is saturated, the comparator 403 is not necessarily used. As an example, a method is conceivable in which a midpoint between the saturable coil L104 and the reference coil L105 is converted into a digital value by an A / D converter and then numerical comparison is performed. In this case, it can be said that the A / D converter constitutes a voltage detection unit.

The pulse signal source 401 and the D-FF 406 can also be realized by a microcomputer program.
Since the pulse signal source 401 can be realized by counting and outputting the operation clock of the microcomputer, as described above, it is possible to easily adjust the pulse width in order to realize the desired sensitivity.

The conditions of the elements constituting the magnetic switch 201 of the present embodiment will be described.
Elements constituting the magnetic switch 201 of the present embodiment are a rectangular wave voltage source (FET 402 and DC voltage + Vcc), a saturable coil L104 having a yoke, a reference coil L105, a freewheel diode D106, and a voltage detector. (Comparator 403 and reference voltage source).

The rectangular wave voltage source must be a rectangular wave voltage source because a constant DC voltage must be applied to the saturable coil L104 and the reference coil L105 for a predetermined time. A voltage source such as a sine wave or a sawtooth wave whose voltage continuously changes with time cannot be used.
Since the saturable coil L104 needs to cause a saturation phenomenon, a yoke is essential.
As with the saturable coil L104, the reference coil L105 must be a coil because it must cause a phenomenon in which the direct current resistance decreases as the current increases. However, the inductance may not be the same as that of the saturable coil L104. Further, the yoke may or may not be provided, but it is desirable that there is no yoke in order to prevent a saturation phenomenon. If a yoke is used, the reference coil L105 needs to be magnetically shielded or sufficiently separated from the saturable coil L104 so that the influence of the external magnetic field on the saturable coil L104 is not exerted.
The voltage detection part should just be able to catch the change of the voltage between the terminals of the reference coil L105, when the saturable coil L104 is not saturated and when it is saturated.

[About polarity]
The conventional saturable coil L704 shown in FIG. 7 causes a saturation phenomenon only with an external magnetic field. On the other hand, the magnetic switch 201 of the present embodiment has a saturable coil that is influenced by an external magnetic field in addition to a magnetic field generated in the saturable coil L104 by applying a rectangular wave voltage to the saturable coil L104. L104 saturation occurs. That is, the external magnetic field required to cause the saturation phenomenon may be weaker than that of the prior art. Instead, the saturation phenomenon does not appear unless a magnetic field in the same direction as the magnetic field generated by the current flowing through the saturable coil L104 is applied. For this reason, in the magnetic switch 201 of this embodiment, the polarity of the external magnetic field affects the sensitivity.

5A and 5B are schematic diagrams of the magnetic switch 201. FIG.
In the magnetic switch 501 a in FIG. 5A, a saturable coil L <b> 104 a is connected to the magnetic detection circuit 302.
In the magnetic switch 501b of FIG. 5B, a saturable coil L104b that is wound in the reverse direction to the winding direction of the saturable coil L104a is connected to the magnetic detection circuit 302.
When a saturable coil having a reverse winding direction is connected to the same magnetic detection circuit 302, a magnetic switch that reacts to a magnetic field having a reverse polarity can be formed. In this way, the magnetic switch can be easily polarized. For example, a magnet having N and S poles is scanned in a predetermined movement direction to detect the movement direction of the magnet. Can be considered.

[Second Embodiment / Circuit Configuration and Operation]
A plurality of magnetic switches 201 according to the first embodiment shown in FIGS. 2 to 4 can be connected in parallel for scanning.
6A, 6B, 6C, 6D, and 6E are a circuit diagram and a waveform diagram of the magnetic switch according to the second embodiment.
FIG. 6A is a circuit diagram of the magnetic switch 601. As can be seen at a glance, the magnetic switch 601 includes a plurality of FETs 402, saturable coils L104, and free wheel diodes D106 of the magnetic switch 201 of the first embodiment. The plurality of saturable coils L104 are connected to one reference coil L105.

FIG. 6B shows a voltage waveform at the gate of the first FET 402a.
FIG. 6C shows a voltage waveform of the gate of the second FET 402b.
FIG. 6D shows the voltage waveform of the gate of the n-th FET 402n.
FIG. 6E shows a voltage waveform of the reference coil L105.
The microcomputer 602 sequentially applies pulsed signals to the first FET 402a, the second FET 402b,..., The n-th FET 402n (FIGS. 6B, 6C, and 6D). Then, by measuring the voltage of the reference coil L105 (FIG. 6E), it can be determined which of the saturable coils L604a, L604b... L604n is saturated.
Among the circuit elements constituting the magnetic switch 601, the first FET 402a can be said to be a first rectangular wave voltage source. Similarly, it can be said that the second FET 402b is a second rectangular wave voltage source, and the nth FET 402n is an nth rectangular wave voltage source.

  The magnetic switch 601 according to the second embodiment is used as a non-contact switch for detecting the position of a moving body described in Patent Document 1, for example, and a membrane switch or a mechanical switch cannot be used. It can be used as a switch for a keyboard used in a special environment.

In addition to the embodiment described above, the following application examples are conceivable.
(1) Although the voltage applied to the switch is the power supply voltage, this need not necessarily be the power supply voltage. How to determine the voltage applied to these elements is a matter of design.

  (2) The yoke 301 is permalloy, but is not limited to this as long as the material has a high magnetic permeability and a low saturation magnetic flux density. For example, an amorphous alloy etc. are mentioned. Further, as described above, since the magnetic switch 201 of this embodiment has high sensitivity, it can be practically used even if the saturation magnetic flux density is somewhat high like ferrite.

In the present embodiment, a magnetic switch has been disclosed.
A rectangular wave is supplied to a circuit in which a saturable coil L104 with a yoke and a reference coil L105 are connected in series. A saturation phenomenon is generated in the yoke within the period of the rectangular wave, and a voltage change of the reference coil L105 that occurs at that time is detected.
Unlike the prior art, the external magnetic field required to cause the saturation phenomenon may be weaker than that of the prior art, so that a highly sensitive magnetic switch can be realized.

  The embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiment, and other modifications may be made without departing from the gist of the present invention described in the claims. Includes application examples.

  DESCRIPTION OF SYMBOLS 101 ... Magnetic detection circuit, 102 ... DC power supply, 103 ... Switch, L104 ... Saturable coil, L104a ... Saturable coil, L104b ... Saturable coil, L105 ... Reference coil, D106 ... Freewheel diode, 107 ... Magnet, 201 ... magnetic switch, 201a ... detection protrusion, 202 ... cable, 301 ... yoke, 302 ... magnetic detection circuit, 401 ... pulse signal source, 402 ... FET, 402a ... first FET, 402b ... second FET, 402n ... nth FET, 403 ... Comparator, R404 ... Resistance, 406 ... D flip-flop, R407 ... Resistance, 408 ... Transistor, 501a ... Magnetic switch, 501b ... Magnetic switch, 601 ... Magnetic switch, 602 ... Microcomputer, L604a ... Saturable coil, 701 ... Magnetic Switch circuit, 702 ... AC Pressure source, R703 ... resistance, L704 ... saturable coils, R705 ... resistors, 706 ... transistor, R707 ... resistors, C708 ... capacitor, R709 ... resistors, R710 ... resistors, 711 ... transistor, 712 ... magnet

Claims (3)

A saturable coil with a yoke ;
A reference coil connected in series to the saturable coil;
A rectangular wave connected to the saturable coil and the reference coil and having a predetermined period and a predetermined voltage is output, and a predetermined external magnetic field is applied during the period in which the predetermined voltage of the period is maintained. When applied to the yoke, a rectangular wave voltage source that outputs a rectangular wave that is defined such that an increase in current flowing through the saturable coil is steeper than before the magnetic saturation occurs due to magnetic saturation of the yoke. When,
A magnetic switch comprising: a voltage detection unit that detects a change in voltage between terminals of the reference coil. Furthermore,
A freewheel diode connected in parallel to the rectangular wave voltage source together with a series connection of the saturable coil and the reference coil ;
Comprising a magnetic switch according to claim 1, wherein. A first rectangular wave voltage source that outputs a rectangular wave;
A first saturable coil with a yoke connected to the first rectangular wave voltage source;
A first freewheeling diode connected to the first rectangular wave voltage source;
A second rectangular wave voltage source that outputs a rectangular wave having a period exclusive to the first rectangular wave voltage source;
A second saturable coil with a yoke connected to the second rectangular wave voltage source;
A second freewheeling diode connected to the second rectangular wave voltage source;
A reference coil connected to the first saturable coil and the second saturable coil;
A magnetic switch comprising: a voltage detection unit that detects a change in voltage between terminals of the reference coil.

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