JPS6151812B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photoelectric switch, and particularly to an AC two-wire photoelectric switch.

A photoelectric switch (hereinafter explained using an AC 2-wire transmission type photoelectric switch) consists of a light emitter and a light receiver, and by receiving light from the emitter, it turns on a switching element (SCR, etc.) for switching a load.
This is to turn it off. Therefore, power must be supplied to each of the emitter and receiver. Furthermore, the receiver side must be constructed so that the current to be passed through the load (the current turned on and off by the switching element for switching on and off the load) is also passed therethrough. For this reason, conventionally, a so-called AC three-wire transmission type photoelectric switch has been used, in which a circuit for supplying power for operating the light receiver is provided separately from a circuit for supplying power to the load.

As shown in FIG. 1, this AC 3-wire transmission type photoelectric switch consists of a light emitter 11 and a light receiver 15.
The projector 11 includes a full-wave rectifier circuit for rectifying AC power, a constant voltage circuit 12, an oscillation circuit 13, and a light emitting diode 14. The photoreceiver 15 is composed of a photodiode 16, an AC amplifier circuit 17, a waveform processing circuit 18, a trigger circuit 19, and an SCR 21 which is a switching element for switching loads, and each circuit is supplied with electric power by a constant voltage circuit 20. A current flows through the SCR 21 from a full-wave rectifier circuit via a load. Floodlight 11
The light emitting diode 14 emits an optical pulse with a frequency of several hundred to several kHz, and the optical receiver 15 AC amplifies the input signal of this optical pulse, performs processing such as integration and detection, and generates a trigger signal for the SCR 21. It's on.

As shown in FIG. 2, when the light is blocked by an object or the like, the optical input pulse is no longer input, a trigger signal is generated, and the load is turned on.

Furthermore, as shown in FIG. 3, an AC two-wire transmission type photoelectric switch is also well known. In FIG. 3, the emitter 31 consists of a full-wave rectifier circuit, a constant voltage circuit 32, an oscillation circuit 33, and a light emitting diode 34, and the receiver 35 consists of a photodiode 36 and an AC amplifier circuit 3.
7, a signal processing circuit 38, and an SCR 39 which is a switching element for switching loads. The SCR 39, the transistor 41, the Zener diodes 40, 44, 47, the diode 45, the resistors 42, 43, 46, and the capacitor 48 are a switching circuit for opening and closing the load, and an AC amplifier circuit 37.
and a circuit that sends power to the signal processing circuit 38.

As shown in FIG. 4, when the light is not blocked, the trigger signal from the signal processing circuit 38 is off, so the transistor 41 is off and the SCR 39 is off. At this time, power is supplied to the AC amplifier circuit 37 and signal processing circuit 38 via the resistor 42, Zener diode 44, and resistor 46, so that a small load current flows through the load. When the light is blocked and the trigger signal from the signal processing circuit 38 is turned on, the transistor 41 is turned on and the SCR 39 is turned on, so that a large current flows through the load. At this time, the voltage generated across the Zener diode 40 is applied to the AC amplifier circuit 37 and the signal processing circuit 38 via the diode 45 and the resistor 46. Therefore, the voltage at point C has the same waveform in any case. The Zener diode 47 and the capacitor 48 constitute a constant voltage circuit.

By the way, in the conventional devices shown in FIGS. 1 and 3, the light emitting diode of the projector is turned on at a frequency of several hundred to several kHz in order to reliably trigger the switching element for switching the load. That is, if the frequency is low, there are problems such as beats occurring with the AC power supply and the firing phase of the SCR being shifted. Therefore, in terms of the reliability of the light emitting diode, for example, from the standpoint of the duty factor, its peak current can be kept low, and the amplification gain of the receiver can be increased to increase sensitivity and the distance between the emitter and receiver can be increased. It is being said. From the above, since the optical receiver receives high-frequency optical input pulses and turns on the switching element, waveform processing such as detection and amplification is required, which inevitably makes the circuit configuration complicated. Therefore, there was no need to worry about adding to the cost. In addition, by increasing the amplification gain of the photoreceiver, stability against external induced noise can be improved.
I didn't like it.

However, switching elements such as SCRs have self-retaining properties, so if one relatively short trigger pulse is applied for each half-wave of AC, they will continue to conduct during that half-wave. Therefore, the trigger signal to the switching element does not need to have a fairly long steady waveform width as shown in FIGS. 2 and 4.

In view of the above, the present invention lights up a light emitting diode once every half wave with a constant phase in synchronization with an AC power supply,
By configuring the light receiver to receive the light and trigger the switching element in synchronization with this light pulse, the peak current flowing through the light emitting element can be increased, simplifying the circuit configuration and reducing the cost of AC. The purpose of the present invention is to provide a two-wire transmission type photoelectric switch.

Embodiments of the present invention will be described below with reference to FIGS. 5 and 6.

As shown in FIG. 5, in the projector 51, voltage dividing resistors 52, 53 are connected between the positive and negative output terminals of the full-wave rectifier circuit.
54 are connected in series. A light emitting diode 55, a coil 56, and an SCR 57 are connected in series between the connection point of the resistors 52 and 53 and the negative output terminal of the full-wave rectifier circuit. A diode 58 is connected in parallel to both ends of the coil 56. resistance 52,
A constant voltage circuit consisting of a Zener diode and a smoothing capacitor 59 is connected between the connection point 53 and the negative output terminal of the full-wave rectifier circuit. The light receiver 61 includes a constant voltage circuit 62, an AC amplifier circuit 71, and a load switching circuit 82. The constant voltage circuit 62 consists of a Zener diode 63, a capacitor 64, and a resistor 65, and the AC amplifier circuit 71 consists of a photodiode 7.
2, capacitors 77, 73, resistors 74, 76, 7
8 and 81, and transistors 75 and 79. The load switching circuit 82 is composed of a differential circuit consisting of a resistor 84 and a capacitor 83, and an SCR 85. Note that other light receiving elements such as a phototransistor may be used in addition to the photodiode 72.

Next, the operation of the circuit shown in FIG. 5 will be explained.

When the rectified half-wave of the AC power source rises in the projector 51, voltage begins to be applied to the gate of the SCR 57 by the voltage dividing resistors 52, 53, and 54. At the same time, capacitor 59 is charged through resistor 52. The resistors 52, 53, and 54 are set so as to apply a voltage higher than the minimum trigger voltage to the gate of the SCR 57 in the early rise portion of the rectified half wave. Therefore, the SCR57 is triggered in synchronization with the timing of the early rising part of the rectified half wave,
Turn on. When the SCR 57 is triggered and turned on, the charge stored in the capacitor 59 is rapidly discharged through the SCR 57. After the charge of this capacitor 59 has finished discharging, the resistor 5
2, a current flows between the anode and cathode of the SCR57, so the SCR57 remains on until near the end of its half-wave cycle, and when the half-wave stabilized voltage approaches zero, it becomes less than the holding current and turns off. . While this SCR57 is on, the capacitor 59
Since both ends of the capacitor 59 are short-circuited, no charge is accumulated in the capacitor 59. SCR57
When the capacitor 59 is turned off, charging of the capacitor 59 starts again. The above operation is repeated every half wave of AC. In this way, as shown in FIG. 6(b), a light pulse generated once per AC half wave can be emitted from the light emitting diode 55 to provide a light input pulse to the photodiode 72. This light pulse is generated by a large current (several
100 mA) flows through the light emitting diode 55 in a pulsed manner. After that, when the SCR 57 continues to be on, the light emitting diode 55
A current flows through the resistor 52, but the resistor 52 is set to a relatively high resistance, and the current is small (several mA), which is about the holding current required to keep the SCR 57 on, and the light pulse is emitted. After that, the light emitting diode 55 hardly emits any light. In this way, a large current is passed through the light emitting diode 55 only once in an AC half wave for a short period of time, and the average current is made small, and the duty factor is also made small. Note that the coil 56 is connected to the capacitor 5.
The diode 58 is used to somewhat suppress the excessively steep rise of the discharge current of the coil 56, and the diode 58 is used to absorb the back electromotive force of the coil 56.

When the photoreceiver 61 detects an optical input pulse by the photodiode 72, the detection signal is amplified by the AC amplifier circuit 71, and the detected signal is amplified by the load switching circuit 82.
input to the differential circuit inside. The output of the differentiator circuit is
When the trigger current flows into the gate of the SCR 85, the SCR 85 is turned on. In the next rectification half-wave, when an optical input pulse is input, a similar operation is performed to turn on the SCR 85 and supply power to the load.

As shown in FIG. 6, when the light from the projector 51 is blocked, the optical input pulse is not input to the photodiode 72, so there is no output from the AC amplifier circuit 71.
Since the SCR 85 is not triggered, it does not provide power to the load and the load is in an off state.

The oscillation frequency of the light emitting diode 55 of the light projector 51 is twice the AC power frequency, its average current is quite small, and the duty factor is quite small. Therefore, it is possible to emit light with a peak current of several hundred mA or more. Therefore, since the peak current is high, the amplification gain of the AC amplifier circuit 71 can also be made small. It also becomes more stable against induced noise from the outside.

By setting the AC power supplies of the emitter and receiver shown in Figure 5 to be in phase or with a 180° phase difference, half waves with the same phase can be used.
Since the light emitting diode light emission timing of the light emitter is synchronized with the rectified half-wave timing in the light receiver, it is preferable that a constant power can be efficiently supplied to the load. Furthermore, the circuit configuration is simple and the cost can be reduced.

According to this invention, on the projector side, an instantaneous high current is applied to the light emitting element at the timing of the rising edge of each half wave of the AC power supply to turn on the light emitting element, and the emitted light is received. The brightness of the light is increased, and the gain for amplifying the output of the light-receiving element on the light-receiving side can be kept low, making the light receiver resistant to external fluctuation factors and preventing malfunctions. Further, since it is not necessary to increase the amplification gain of the light received by the light receiver, the circuit can be simplified and the cost can be reduced.

[Brief explanation of the drawing]

Figures 1 and 3 are circuit diagrams of conventional examples, Figure 2a,
b, c, d, e, f are waveform diagrams showing each operation in Fig. 1, Fig. 4 a, b, c, d are waveform diagrams showing each operation in Fig. 3, a, b, c,
FIG. 5 is a circuit diagram showing an embodiment of the present invention; FIG. 6 is a, b, c, d,
e is a waveform chart showing each operation in FIG. 5; 12, 20, 32, 62...constant voltage circuit, 13,
33...Oscillation circuit, 14,34,55...Light emitting diode, 16,36,72...Photodiode, 1
7, 37... AC amplifier circuit, 18... Waveform processing circuit,
19...Trigger circuit, 38...Signal processing circuit, 21,
39, 57, 85...SCR, 40, 44, 47,
60, 63... Zener diode, 45, 58... Diode, 41, 75, 79... Transistor.

Claims (1)

[Claims] 1. A switching element connected between a first full-wave rectifier circuit connected to an AC power supply and an output terminal of the first full-wave rectifier circuit and turned on at the timing of the rising edge of a rectified half-wave, and this switching element. a light emitter comprising a light emitting element connected in series to the light emitting element and a high current generating circuit that instantaneously flows a high current to the light emitting element at the timing when the switching element is turned on;
A second full-wave rectifier circuit connected to an AC power supply via a load, a load switching element and a constant voltage circuit connected between the output terminals of the second full-wave rectifier circuit, and light emitted from the light-emitting element. a light receiving element that receives light; and an amplifier circuit that receives power from the constant voltage circuit, amplifies the output of the light receiving element, and generates a trigger signal that triggers the load switching element. AC 2-wire photoelectric switch.