JPH04175009A - Photoelectric switch - Google Patents

Abstract

PURPOSE:To reduce a delay time of an electric signal resulting from light receiving with simple constitution and to prevent malfunction due to noise by providing a waveform shaping circuit for a pulse voltage from a pulse generating circuit and using an output signal of the waveform shaping circuit so as to drive an LED drive circuit. CONSTITUTION:A rectangular pulse voltage from a pulse generating circuit 13 is waveform-shaped into a triangular wave whose leading is steep by a waveform shaping circuit 14, and a light radiates from an LED 11 via an LED drive circuit 12. The light radiating from the LED 11 is received by a light receiving element 2 of a light receiving circuit section 2, in which the light is converted into an electric signal and its level is compared with a reference voltage by a comparator circuit 23 via an amplifier 22. Through the constitution above, a delay time of a binarizing signal (d) from the comparator circuit 23 with respect to a pulse voltage of the circuit 13 is reduced. Thus, the delay time is reduced without decreasing the reference voltage of the circuit 23 and malfunction due to noise is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a light emitting circuit section that emits pulsed light and a light receiving circuit section that receives the pulsed light from the light emitting circuit section and outputs an electrical signal. The present invention relates to a photoelectric switch that detects the presence or absence of an object to be detected existing between the light emitting circuit section and the light receiving circuit section.

[Conventional technology]

A conventional device of this kind is shown in the block diagram of FIG.

In FIG. 5, reference numeral 1 denotes a pulse generation circuit 13 that generates a pulse voltage, an LED drive circuit 12 driven by the output of this pulse generation circuit 13, and an LED drive circuit 12 that is driven by the output of this pulse generation circuit 13.
LED that emits light by the LED drive current from
11 is a light projecting circuit section, and 2 is a light receiving element 21 that receives light from the LED 11 and converts it into an electrical signal.

The light receiving circuit section includes an amplifier circuit that amplifies the electrical signal from the light receiving element 21, and a signal processing circuit that determines the presence or absence of an object to be detected based on the output of the amplifier circuit n. The operation of this photoelectric switch will be explained using the waveform diagram in FIG.

#! When the pulse generating circuit 13 outputs a rectangular pulse voltage at a predetermined period as shown in FIG. 6 1al, the LED driving circuit 12 outputs an LED driving current as shown in FIG. 6 1b+. When an LED drive current flows through L E D n , light is emitted from L E D 11 . L E
When the light receiving element 21 receives 9 from D11 directly or the reflected light reflected by the object to be detected, the light receiving element 21
Light 1! The electrical signal is amplified by the amplifier circuit η. The output signal from amplifier circuit n is shown in Fig. 6, 1c.
It has a waveform as shown in FIG. 6, is compared with a reference voltage Vo of a predetermined level, and is output as a 12-valued signal as shown in FIG. 6, 1dl J. 2 from comparison circuit B
The value signal 1dl is subjected to processing such as detection to determine whether it is synchronized with the pulse voltage 1al from the pulse generation circuit 13 and counting to determine whether it has continued for a predetermined number of times by each signal processing circuit, and then processed by the load etc. The signal is output as a switching signal for the switching transistor that drives the signal.

[Problem to be solved by the invention]

In the conventional device described above, LEDll is a rectangular LE.
It is driven by the DIIA dynamic current 1bl, and the level of the electric signal received by the light receiving circuit section 2 increases in a rate of 1 KM as time passes. This state is shown in Figure 6 1c),
The peak value of the level of the electric signal is delayed from the falling time of the rectangular wave of the LED drive current of 1 bl. As the electric signal received increases linearly with the passage of time, the binary signal 1dl from the comparison circuit okara is generated by the pulse generation circuit 13.
The pulse voltage 1a) from 1a) is delayed by a time t. This delay time must be made small in order to prevent mutual interference with adjacent photoelectric switches when a plurality of photoelectric switches are arranged in parallel. Therefore, if the level of the reference voltage Vo of each comparison circuit is lowered, malfunctions due to noise L will increase.

Note that when a large drive current flows when driving the LED, a temporary voltage drop occurs in the power supply voltage, which affects the signal of the light receiving circuit section. Also, in the case of a waveform such as a rectangular pulse voltage or pulse current that has a steep slope above π and a steep fall, the rise and fall of V will be different!
The downward noise mixes as noise from the light emitter circuit section to the light receiver circuit section due to stray capacitance between printed wiring boards and electromagnetic induction.

In order to prevent malfunctions caused by this noise, a special and expensive component such as a noise removal circuit must be provided.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks of the conventional device, to easily shorten the delay of the electric signal received with respect to the pulse voltage of the light emitting circuit with a simple configuration, and to provide a photovoltaic device that does not malfunction due to noise. The purpose is to provide a switch.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the first invention provides a pulse generation circuit that generates a rectangular pulse voltage, and an LED drive driven by the pulse voltage l output from the pulse generation circuit. A light emitting circuit section consisting of an LED that emits light using an output current from the LED drive circuit, a light receiving element that receives the light emitted from the LED and converts it into an electrical signal, and amplifying the electrical signal from the light receiving element. A light-receiving circuit section includes an amplifier circuit for detecting an object to be detected, a comparison circuit for comparing an output signal from the amplifier circuit with a reference voltage of a predetermined level, and a signal processing circuit for determining the presence of an object to be detected based on the output of the comparison circuit. The photoelectric switch is characterized in that a waveform shaping circuit is provided to transform the pulse voltage of the pulse generating circuit into a triangular wave with a steep rise, and an output signal of this waveform shaping circuit drives an LED driving circuit.

The second invention is a projection system comprising a pulse generation circuit that generates a rectangular pulse voltage, an LEDIA driving circuit that is driven by the pulse voltage output from this pulse generation circuit, and an LED that emits light by the output current from this LED driving circuit. an optical circuit section, a light receiving element that receives light emitted from the LED and converts it into an electrical signal, a comparison circuit that compares the electrical signal from the element with a reference voltage of a predetermined level, and an output of this comparison circuit. A photoelectric switch is provided with a waveform shaping circuit that converts the pulse voltage of the pulse generating circuit into a triangular wave with a steep rise, and the photoelectric switch is equipped with a light receiving circuit section consisting of a signal processing circuit that determines the presence of a detected object based on the signal processing circuit. A synchronization circuit synchronizes the output of the comparison circuit and the output of the pulse generation circuit with the pulse voltage delayed by the delay circuit.
The waveform shaping circuit in the first and second inventions is characterized by comprising a detection circuit and an output determination circuit that determines the presence of a detected object based on the output of the synchronization/detection circuit. It is characterized by being a circuit.

[Effect]

In the first invention, the electric signal received by the light receiving circuit grows exponentially by driving the LED by converting the rectangular pulse voltage from the pulse generating circuit into a steeply rising triangular wave of V using the waveform shaping circuit. The pulse voltage from the pulse generation circuit reaches its peak before V drops 2, and this electric signal grows exponentially and reaches its peak, resulting in a short delay time without lowering the level of the reference voltage of the comparator circuit 2 A valued signal is obtained.

Also#! In the second invention, a waveform shaping circuit is provided to make the pulse voltage of the pulse generation circuit a triangular wave with a steep rise! Naturally, the descent will be a gentle waveform. Therefore, the noise that enters the light receiving circuit from the light emitting circuit is only at the rising edge of this triangular wave, and is less likely to enter the XL falling direction. Therefore, by slightly transporting the pulse voltage of the pulse generator circuit through a delay circuit and synchronizing it with the output of the comparator circuit, it is possible to eliminate this noise and the influence of fluctuations in the power supply voltage that occur when the triangular wave V rises. .

〔Example〕

Embodiments of the photoelectric switch according to the present invention will be described below in detail based on FIGS. 1 to 4, and the same parts as in FIG. .

FIG. 1 is a block diagram showing an embodiment of the photoelectric switch according to the first invention, and the difference from the conventional device shown in FIG. The point is that a waveform shaping circuit 14 consisting of a capacitor 15 and a resistor 16 is provided between them.

The waveform shaping circuit 14 has a function of shaping the rectangular pulse voltage from the pulse generation circuit 13 into a steep triangular wave.

The operation of this photoelectric switch will be explained using the waveform diagram shown in FIG. @2 As shown in Figure 1al, pulse generation circuit 1
3 outputs a rectangular pulse voltage at a predetermined period as in the conventional device, and the waveform shaping circuit 14 shapes this pulse voltage into a triangular wave with a steep rise. This results in L
As shown in FIG. 2, 1b+, a steeply rising triangular wave (0) LED drive current flows from the ED drive circuit 12 to the LED11, and light is emitted from the LEDn. L E
The original light emitted from D 11 is received by the light receiving circuit section 2, and is converted into an electrical signal by the receiver 21 and sent to the amplifier circuit η.
is amplified by The electrical signal amplified by the amplifier circuit n is compared with a reference voltage Vo at a predetermined level by a comparison circuit B. Here, since Kan II L E D 11 is driven by a triangular wave LED drive current with a steep rise, it grows exponentially, and its peak is also equal to before the V drop of the pulse voltage 1al of the pulse generation circuit 13. Become. Therefore, the delay time ti of the binary signal 1dl from the comparator Okara with respect to the pulse voltage of the pulse generating circuit 13 is also shorter than the delay time t2 of the conventional device, and the reference voltage V of the comparator circuit B.

The delay time can be shortened without lowering the level.

FIG. 3 is a block diagram showing an embodiment of the photoelectric switch according to the second invention. In FIG. 3, pulse generation circuit 1
The output terminal of 3 is the capacitor 15. This is similar to the first invention in that the waveform is shaped into a steeply rising triangular wave by a waveform shaping circuit 14 comprising a resistor 16.

Below is the LED drive circuit 12. LED II is the light emitting circuit part 1
It consists of Further, the light receiving element 2], the amplifier circuit n, and the comparison circuit n constituting the light receiving circuit section 2 are also the same as those in the first invention. However, in the second invention, the pulse voltage of the pulse generation circuit 13 is sent to the synchronization/detection circuit via the delay circuit δ, and only the signal from the comparison circuit B that is synchronized with the output of the delay circuit section is sent to the output determination circuit n. It will be done.

The operation of this photoelectric switch will be explained using the waveform diagram shown in FIG. As shown in FIG. 4 1al, the pulse generation circuit 1
3 outputs a rectangular pulse voltage at a predetermined period as in the first invention or the conventional device, and this pulse voltage is waveform-shaped into a steeply rising triangular wave by the waveform shaping circuit 1jH. As a result, the LED body rotation circuit 12L E D 1
1, a steeply rising triangular wave LED drive current flows as shown in w14 in FIG. 1b+, and light is emitted from the LEDll. When V of this triangular wave rises, a large current flows from a power supply (not shown), so the power supply voltage temporarily decreases by voltage Vd as shown in Figure 11K4 (c). L E D 11
The light emitted from the light receiving circuit section 2 is received by the light receiving element 21 and converted into an electric signal. The output signal amplified by amplifier n contains noise Vn as shown in FIG. 4 1dl. Therefore, the binary value number compared with the reference voltage 0 in the comparison circuit n is inputted to the synchronization/detection circuit A as two continuous rectangular waves as shown in FIG. 4 1al. Here, the pulse voltage 1a of the pulse generation circuit 13
l is determined by the delay circuit 5 at a time t as shown in FIG.
The pulse voltage is delayed by 3 and is input to the synchronization/detection circuit, and the width Wc4 (Fig. f) synchronized with this pulse voltage 1fl is generated.
Only the pulse voltage shown at gl is sent to the output determination circuit υ. Signal 1 received in this way and converted into an electrical signal
The output judgment circuit receives a normal pulse signal from which the noise that tends to appear at the rise of dl has been removed.

After performing processing such as counting to determine whether the number of pulses is continuous a predetermined number of times, it is output as a switching signal for a switching transistor that drives a load or the like.

[Effects of the Invention j] As explained above, according to the present invention, a waveform shaping circuit is provided which changes the pulse voltage of the pulse generation circuit into a steeply rising triangular wave of V, and the output signal of this waveform shaping circuit is used to generate an LED & driving circuit metal circuit. With this configuration, it is possible to shorten the delay time of the electric signal received by the light receiving circuit section with respect to the pulse voltage of the light emitting circuit section, and furthermore, the light is received by the light receiving element, converted to an electric signal, and then sent to the comparison circuit. The binary code obtained by comparing with the reference voltage is synchronized with the pulse signal obtained by delaying the output of the pulse generator circuit, and the signal due to noise that tends to appear when the binary code increases again is synchronized. This has the advantage that it is possible to provide an inexpensive photoelectric switch with good noise resistance.

[Brief explanation of drawings]

1 to 4 show an embodiment of a photoelectric switch according to the present invention, FIG. 1 is a block diagram showing an embodiment of the first invention, FIG. 2 is a waveform diagram explaining the operation of FIG. 1, FIG. 3 is a block diagram showing an embodiment of the second invention, FIG. 4 is a waveform diagram explaining the operation of FIG. 3, FIGS. 5 and 6 show an example of a conventional charging switch, and FIG. Figure 5 is a block diagram, Figure 6
The figure is a waveform diagram showing the operation of FIG. 5. l: light emitting circuit section, 2: light receiving circuit section, u: LED. 12: LED drive circuit, 13: Pulse generation circuit, 14
: [Shaping circuit, 15: Capacitor% 16: Resistor. 2]: receiver ft, receiver, 22 = amplifier circuit, mu: comparison circuit. 24: signal processing circuit, 5: delay circuit, 26 two synchronization/detection circuits, 27 two output determination circuits. 1st mouth 3rd (21

Claims (1)

[Claims] 1) A pulse generation circuit that generates a rectangular pulse voltage, an LED drive circuit that is driven by the pulse voltage output from this pulse generation circuit, and emits light by the output current from this LED drive circuit. A light projecting circuit section consisting of an LED, a light receiving element that receives light emitted from the LED and converts it into an electrical signal, an amplifier circuit that amplifies the electrical signal from this light receiving element, and an output signal from this amplifier circuit that adjusts the output signal to a predetermined level. In a photoelectric switch, the photoelectric switch is equipped with a comparison circuit that compares the voltage with a reference voltage of the pulse generator, and a light receiving circuit section that includes a signal processing circuit that determines the presence of a detected object based on the output of the comparison circuit. 1. A photoelectric switch characterized in that a waveform shaping circuit is provided to form a steep triangular wave, and an output signal of the waveform shaping circuit drives an LED driving circuit. 2) A light projection circuit consisting of a pulse generation circuit that generates a rectangular pulse voltage, an LED drive circuit that is driven by the pulse voltage output from this pulse generation circuit, and an LED that emits light by the output current from this LED drive circuit. a light receiving element that receives the light emitted from the LED and converts it into an electrical signal; a comparison circuit that compares the electrical signal from the light receiving element with a reference voltage of a predetermined level; and a detection target based on the output of the comparison circuit. a photoelectric switch comprising a light receiving circuit section comprising a signal processing circuit for determining the presence of a signal processing circuit; and a synchronization/detection circuit that synchronizes the output of the pulse generation circuit with the pulse voltage delayed by a delay circuit, and an output determination circuit that determines the presence of a detected object based on the output of the synchronization/detection circuit. A photoelectric switch featuring 3) The photoelectric switch according to claim 1 or 2, wherein the waveform shaping circuit is a differentiating circuit comprising a capacitor and a resistor.