JPS626416B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention provides a floodlight connected to an AC power source;
An AC 3-wire system consisting of a switching section that is connected to an AC power source separately from the emitter through a load in series, and a light receiver that is made up of a circuit that receives power from the AC power source and controls opening and closing of the switching section. This article relates to a transmissive type photoelectric switch.

A through-beam type photoelectric switch turns on the load switching element depending on the presence or absence of a detection signal generated when the light emitted from the projector toward the object to be detected is blocked or transmitted depending on the presence or absence of the object to be detected.・It is to be turned off. Therefore, a detection circuit has a means for projecting light toward an object to be detected, a means for receiving the transmitted light, a means for generating a detection signal based on the received light, and a load switching device controlled by this detection circuit. It consists of a switching element. Furthermore, circuitry for supplying power to these devices is usually provided.

A typical example of a conventional AC three-wire transmission type photoelectric switch is constructed as shown in FIG. That is, the projector 1 includes a full-wave rectifier circuit 13', a constant voltage circuit 11', an oscillation circuit 5, and a light emitting diode 6.
It is connected to an AC power source 4'. The receiver 2 is connected to an AC power source 4 separately from the projector 1 through a load 3 in series, and has a terminal directly connected to receive power from the AC power source 4. a full-wave rectifier circuit 13 and a switching thyristor 12, a light-receiving diode 7, an AC amplifier circuit 8, a waveform processing circuit 9, which are necessary for controlling on/off of the thyristor 12 in response to optical input.
Trigger circuit 10, rectifier 14 and constant voltage circuit 1
1.

As shown in FIG. 2, the light emitting diode 6 of the projector 1 is driven by the output of the oscillation circuit 5 regardless of the phase of the voltage of the AC power source 4', and the projector 1 emits light at a repetition frequency of several hundred to several KHz. A pulse is projected, and if this optical pulse is blocked by an object or the like, the arrangement is such that the light receiving input pulse input to the light receiving diode 7 disappears (see the waveform diagram in FIG. 2). The waveform processing circuit 9 generates an output signal and triggers the trigger circuit 10 only when this optical input disappears.
is driven to produce an output on its output side, turning on the thyristor 12. At this time, the output terminal of the full-wave rectifier circuit 13 is short-circuited by the thyristor 12, so a large current flows through the load and the load is turned on. When a light reception input is generated in the light receiving diode 7, the output signal of the waveform processing circuit 9 disappears, the output of the trigger circuit 10 also disappears, the half wave of the voltage of the AC power supply 4 ends, the instantaneous value becomes zero, and the thyristor 12 The anode voltage of thyristor 1 also becomes zero.
2 is turned off to cut off the load current flowing to the load 3.

By the way, in the conventional photoelectric switch, as described above, the light projector 1 emits light pulses with a repetition frequency of several hundred to several KHz. This is because when the repetition frequency of the optical pulse becomes low, its phase is completely unrelated to the phase of the AC power supply 4, so the thyristor 12 cannot be turned on at the required phase, so the conduction angle of the load current is not sufficient. This is because there is a possibility that the repetition frequency of the optical pulses approaches the frequency of the AC power source, and beat disturbances may occur and the instability of the conduction angle of the load current may become even worse. Therefore, by using optical pulses with a repetition frequency of several hundred to several KHz, the triggering of the thyristor 12 is reliably controlled at an early phase within a half cycle of the AC power supply.

However, increasing the driving frequency of the light emitting diode 6 in this manner deteriorates the duty factor, and from the viewpoint of reliability of the light emitting diode 6, the peak value of the driving current cannot be increased. Therefore, when the projector 1 and the light receiver 2 are used with a large distance between them, the amount of light at the peak value of the optical pulse will be insufficient.

Conventionally, this problem has been dealt with by improving the inside of the light receiver, such as increasing the amplification degree of the AC amplifier circuit 8. However, a small peak value of the projected optical pulse originally means a poor signal-to-noise ratio, and increasing the amplification degree in the receiver 2 will conversely cause operational instability, and will also cause problems with the circuit. This method has drawbacks such as being complicated and likely to be expensive.

In view of the above-mentioned drawbacks, this invention allows the driving current of the light emitting diode to flow once every half cycle at a specific phase of the AC power supply, and on the receiver side, the switching element for switching the load is activated at the timing when the light pulse is received. It is an object of the present invention to provide an AC three-wire transmissive photoelectric switch which can be turned on, thereby increasing the peak value of the optical pulse and improving the signal-to-noise ratio.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows one embodiment.

In the following description, the same parts as in FIG. 1 are described using the same reference numerals.

In FIG. 3, the floodlight 1 is a full-wave rectifier circuit 13'.
and a Zener diode 2 forming a constant voltage circuit 11'.
1. A capacitor 22, a current limiting resistor 23, a light emitting element such as a light emitting diode 6, an instantaneous current limiting coil 25 connected in series, a thyristor 24 which is a switching element, and applying a gate voltage to the thyristor 24. Voltage dividing resistor 2 for
7, 28, instantaneous current limiting coil 25
A back electromotive force absorbing diode 26 is connected to both terminals of the . The light receiver 2 has a light receiving element such as a light receiving diode 7, a constant voltage circuit 11, an AC amplifier circuit 8, a trigger circuit 10, a switching element such as a thyristor 12, and a full wave rectifier circuit 13. The constant voltage circuit 1 is composed of a half-wave rectifier 44, a resistor 43, a Zener diode 41, and a capacitor 42, and is connected to one end of the AC power supply 4 and the full-wave rectifier circuit 13.
Connected between the negative side output terminal of the The AC amplifier circuit 8 includes a transistor 45 and resistors 47, 48, 49.
It amplifies the input from the light receiving diode 7 and outputs it to the trigger circuit 10. The trigger circuit 10 is composed of a transistor 46, resistors 50, 51, and a capacitor 55, and is connected to output a pulse voltage across an output termination resistor 52 when an input is received from the AC amplifier circuit 8. Furthermore, one input side of the full-wave rectifier circuit 13 is connected to one end of the AC power source 4 through the load 3, and the other end is directly connected to the other end of the AC power source. The output side of the full-wave rectifier circuit 13 is connected to the cathode and anode of the thyristor 12, and the gate of the thyristor 12 is connected to receive the output of the trigger circuit 10.

Next, the operation of the projector 1 will be explained with reference to FIG. When the rectified half-wave of the AC power source 4' begins to be applied through the full-wave rectifier circuit 13', the capacitor 22 starts to be charged, and at the same time the terminal voltage of the capacitor 22 is divided by the resistors 27 and 28, and the terminal voltage of the resistor 28 is applied to the thyristor. 24 between the gate and cathode. As the instantaneous value of the rectified wave further rises, the terminal voltage of the capacitor 22 rises, and when the terminal voltage of the resistor 28 reaches the trigger voltage of the thyristor 24, the thyristor 24 is turned on. When thyristor 24 turns on, capacitor 2
The charged charges of 2 are rapidly discharged through the light emitting diode 6, the coil 25, and the thyristor 24, and the light emitting diode 6 emits light due to the instantaneous discharge current, and emits light toward the object to be detected. The coil 25 is connected to prevent this instantaneous discharge current from becoming excessive. After light is emitted, a circuit consisting of resistor 23 - light emitting diode 6 - coil 25 - thyristor 24 is constructed, but the current is limited by resistor 23 .
When the half-wave of the rectified wave supplied from the full-wave rectifier circuit 13' ends and the anode voltage of the thyristor 24 becomes zero, the thyristor 24 is turned off and the circuit returns to its initial state. Eventually, when the next rectified half wave is added, the above operation is repeated. As is clear from the above explanation, the light emitting diode 6 emits light once every half cycle of the AC power source 4', and its drive current uses the instantaneous discharge current of the capacitor 22, so the duty of the drive current is The factor is small and can therefore be set to make the peak value of the drive current sufficiently large. Depending on the case, it can be set from several hundred mA to several A.

Next, the operation of the light receiver 2 will be explained. When there is no object to be detected at the detection position and the projected light passes through the light receiving diode 7 and receives light input to the light receiving diode 7, the internal resistance of the light receiving diode 7 decreases, the passing current increases, and the resistor 47 The voltage at the terminals of transistor 45 increases, causing transistor 45 to conduct. When the transistor 45 becomes conductive, its output causes the transistor 46 of the trigger circuit 10 to conduct, and a pulsed output voltage is obtained at the terminal of the output termination resistor 52 of the trigger circuit 10. This pulse output voltage is applied as a trigger voltage between the gate and cathode of the thyristor 12, turning the thyristor 12 on. When the thyristor 12 turns on, the output terminal of the full-wave rectifier circuit 13 is short-circuited, and the AC power supply 4 - load 3 - full-wave rectifier circuit 13 - thyristor 1
A load current flows through the load 3 through the path 2-full-wave rectifier circuit 13-AC power supply 4. Due to the self-holding property of the thyristor 12, this load current continues until the half wave ends even if there is no optical input to the photoreceiver 2. When the current half-wave of the AC power source 4 ends and the instantaneous value becomes zero, the output terminal voltage of the full-wave rectifier circuit 13 also becomes zero, and therefore the anode voltage of the thyristor 12 also becomes zero, so the thyristor 12 is turned off. All circuits are restored to their initial state. Eventually, the next half-wave begins to join,
If there is light input to the light receiving diode 7, the above operation is repeated and a load current flows to the load 3, and if there is no light input to the light receiving diode 7, the thyristor 12 is in an OFF state and no load current flows to the load 3.

Since the AC power supplies 4' and 4 connected to the emitter 1 and the receiver 2 belong to the same commercial power supply, they are in phase or synchronized with a phase difference of 180°, so the above explanation is completely correct in any half wave. Repeat the same action. If the transmitted light is blocked by an object etc. on the way to the transmitted light, the light receiving diode 7
Since there is no light receiving input, the thyristor 12 is not triggered and no current flows to the load 3. The relationship between them is shown in FIG.

As mentioned above, although the operation of the thyristor 12 is unidirectional, by using it together with the full-wave rectifier circuit 13, the device as seen from the AC power source 4 and the load 3 is controlled and turned on depending on the presence or absence of the detected object.・It can be thought of as a switch that turns off.

As explained above, AC 3 according to this invention
A wire-type through-beam photoelectric switch consists of a full-wave rectifier circuit connected to an AC power source, a series circuit of a current-limiting resistor and a capacitor connected between the output terminals of this full-wave rectifier circuit, and a series circuit consisting of a current-limiting resistor and a capacitor connected between the output terminals of this full-wave rectifier circuit. A series circuit of a switching element and a light emitting element connected in parallel, and a trigger circuit that turns on the switching element at the timing of the rising edge of a rectified half wave by triggering the switching element according to the charging potential of the capacitor. a full-wave rectifier circuit connected to an AC power source via a load, a load switching element connected between the output terminals of the full-wave rectifier circuit, and a rectifier circuit and a constant voltage circuit from the AC power source. and an amplifier circuit that amplifies the output of the light receiving element by receiving power through the light receiving element and generates a trigger signal for triggering the load switching element. Therefore, the light emission repetition frequency of the light emitting element of the floodlight is twice the frequency of the AC power supply, that is, it emits light once every half cycle of the AC power supply, and the driving current of the light emitting element is determined by using the instantaneous discharge current of the capacitor and by using the power supply. Since the current from the side is limited by the current limiting resistor, the time width is narrow and the duty factor is small, and as a result, the peak value of the drive current can be made sufficiently large. Furthermore, since the switching element is triggered to emit light when the charging potential of the capacitor becomes constant, the driving current of the light emitting element can be kept constant and large without being affected by the power supply voltage. Since the peak of light emission can be increased and the time width can be narrowed in this way, the signal-to-noise ratio can be improved. That is, the amplification gain of the amplifier can be set small on the photoreceiver side, and it can be made stable against induced noise caused by disturbance light and the like. Therefore, as illustrated in FIG. 3, the control signal circuit for controlling the switching element in the light receiver can be configured as a very simple amplifier circuit, and therefore can be manufactured at low cost. In addition, the emitter and receiver are synchronized via an AC power source, and the light emitted from the emitter occurs at the rising edge of the rectified half-wave, so when the receiver receives this light, it receives the light reception signal as is. If the signal is amplified and used as a trigger signal for a load switching element, a current can be applied to the load from around zero volts of the AC waveform, and power can be efficiently and stably supplied to the load with a simple circuit. Furthermore, as mentioned above, since it emits light at a constant peak without being affected by the power supply voltage, it can be used with the same constant amount even with different AC power supplies such as 100V and 200V AC.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional AC 3-wire transmission type photoelectric switch, Fig. 2 is a waveform diagram explaining the operation of Fig. 1, and Fig. 3 is a circuit showing the configuration of an embodiment according to the present invention. 4 are waveform diagrams showing the operation of FIG. 3. 1... Emitter, 2... Receiver, 3... Load,
4, 4'... AC power supply, 5... Oscillation circuit, 6...
Light emitting element, 7... Light receiving element, 8... Amplifying circuit, 9
... Waveform processing circuit, 10 ... Trigger circuit, 11,
11'... Constant voltage circuit, 12... Switching element, 13, 13'... Full wave rectifier circuit.

Claims (1)

[Claims] 1. A full-wave rectifier circuit connected to an AC power source, a series circuit of a current-limiting resistor and a capacitor connected between the output terminals of this full-wave rectifier circuit, and a switching element connected in parallel to both ends of this capacitor. A floodlight consisting of a series circuit with a light emitting element, and a trigger circuit that turns on the switching element at the timing of the rising edge of a rectified half wave by triggering the switching element according to the charging potential of the capacitor, and an AC power supply. A full-wave rectifier circuit connected via a load, a load switching element connected between the output terminals of the full-wave rectifier circuit, and a switching element that receives power from the AC power source through the rectifier circuit and the constant voltage circuit. An AC 3-wire transmissive photoelectric switch comprising a light receiver and an amplifier circuit that amplifies the output of the light receiving element and generates a trigger signal to trigger the load switching element.