JPH0575420A - Photoelectric switch - Google Patents

Abstract

PURPOSE:To reduce the power consumption of a photoelectric switch circuit by activating a light receiving circuit and a signal processing circuit only for a period when a signal light is received with a light emitting pulse emitted intermittently. CONSTITUTION:A light emitting element 3 is driven by an intermittent light emitting pulse from an oscillator circuit 1 via a light emitting circuit 2, a light obtained from the light emitting element 3 via an object sensing area is received by a light receiving element 4 and amplified by a preamplifier 5 and a main amplifier 6. In this case, the output of the oscillator circuit 1 is given to an analog switch 21. The analog switch 21 is a power supply switching means to control the power supply to the preamplifier 5, the main amplifier 6 and a comparator circuit 7 to emit the light to the oscillator circuit 1 as a power supply control signal. That is, the power supply is supplied to the preamplifier 5, the main amplifier 6 and the comparator circuit 7 only when the light emitting pulse is received.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric switch, and more particularly to a photoelectric switch designed to reduce the current consumption on the light receiving portion side thereof.

[0002]

2. Description of the Related Art A conventional photoelectric switch, for example, as shown in FIG. 10, generates a periodic light projecting pulse from an oscillation circuit 1 and intermittently drives a light projecting element 3 via a light projecting circuit 2. .. If there is an object in the irradiation area of the light projecting element 3, the light receiving element 4
The reflected light is received by and is amplified through the preamplifier 5 and the main amplifier 6 and given to the comparison circuit 7. The comparison circuit 7 discriminates the amplified output by a predetermined threshold value and gives the comparison output to the gate circuit 8. The gate circuit 8 gives only the signal synchronized with the oscillation clock of the oscillation circuit 1 to the integration circuit 9 at the next stage.
The integrating circuit 9 is a signal processing circuit that outputs an object detection signal to the outside via the output circuit 10 when a signal exceeding a predetermined level is continuously obtained a plurality of times.

[0003]

However, in such a photoelectric switch, it is necessary to reduce the current consumption in order to reduce the amount of heat generation and reduce the size. Especially in a two-wire type photoelectric switch, it is necessary to make the leakage current below a predetermined value, for example, 1 mA or less when the switch is turned off. As described above, the light projecting section intermittently drives the light projecting element 3 in accordance with the oscillation output of the oscillation circuit 1, and the light receiving section processes the light receiving signal only during this period. I'm wearing a gate. However, in the conventional photoelectric switch, the current is always supplied to the preamplifier 5, the main amplifier 6, the comparator 7 and the signal processing circuit of the subsequent stage regardless of the oscillation timing of the oscillation circuit 1, and a wasteful current is generated. It had the drawback of consuming it.

The present invention has been made in view of the above problems of the conventional photoelectric switch, and supplies a current to the block of the light receiving circuit including the comparison circuit only in a necessary time zone to reduce the power consumption. It is a technical task to be able to achieve

[0005]

According to the invention of claim 1 of the present application, a light projecting element for irradiating light to a detection area, an oscillation circuit for intermittently driving the light projecting element, and an object detecting area from the light projecting element. A light receiving element for receiving an optical signal obtained through the amplifier, an amplifier for amplifying the output of the light receiving element, a comparison circuit for comparing the output of the amplifier with a predetermined threshold level, and an output of the oscillation circuit for the amplifier and the comparison circuit. And a power switch means for controlling power supply.

The invention of claim 2 of the present application can be obtained by a light projecting element for irradiating light to the detection area, an oscillation circuit for intermittently driving the light projecting element, and an object detecting area from the light projecting element. A light receiving element that receives an optical signal, an amplifier that amplifies the output of the light receiving element, a comparison circuit that compares the output of the amplifier with a predetermined threshold level, and an I ² L logic circuit that processes the output of the comparison circuit. It is characterized by comprising a signal processing circuit and power switch means for controlling power supply to the signal processing circuit by the output of the oscillation circuit.

Further, the invention of claim 3 of the present application has a pulse width expanding circuit for expanding the pulse width of the oscillation circuit, and drives the power supply switch means of claim 1 through the pulse width expanding circuit. It is characterized by having done.

[0008]

According to the invention of claim 1 of the present application having such a feature, the light projecting element is intermittently driven by the output of the oscillation circuit. The power supply to the amplifier circuit for amplifying the optical signal obtained from the light receiving element and the comparison circuit for discriminating its output is controlled by the light emitting pulse of the oscillator circuit. In the invention of claim 2 of the present application, the signal processing circuit is I
^{In the} photoelectric switch composed of ² L, the injection current of the I ² L logic circuit is controlled by the output of the oscillating circuit, and the current is supplied only during the period when the light receiving signal is obtained, so that the current consumption as a whole is reduced. I have to. Further, in the invention of claim 3, the pulse width of the light projecting pulse of the oscillation circuit is expanded, and the power supply of the comparison circuit, the amplifier or the signal processing circuit is controlled based on the expanded power supply control signal.

[0009]

1 is a block diagram showing the overall construction of a photoelectric switch according to a first embodiment of the present invention. The same parts as those of the conventional example described above are designated by the same reference numerals and detailed description thereof will be omitted.
Also in this embodiment, the light projecting element 3 is driven through the light projecting circuit 2 by the intermittent light projecting pulses from the oscillation circuit 1, and the light obtained from the light projecting element 3 through the object detection area is generated. The light is received by the light receiving element 4 and amplified through the preamplifier 5 and the main amplifier 6. The amplified output is the comparison circuit 7
Are discriminated by a predetermined threshold value and given to the gate circuit 8. The integration circuit 9 detects whether or not the output of the gate circuit 8 is continuously obtained in a predetermined cycle, and outputs the object detection signal to the outside through the output circuit 10 as in the conventional example described above.

In this embodiment, the output of the oscillator circuit 1 is given to the analog switch 21. Analog switch 2
Reference numeral 1 is a power switch means for controlling the supply of power to the preamplifier 5, the main amplifier 6 and the comparison circuit 7,
The light emitting pulse of the oscillation circuit 1 is intermittently used as a power supply control signal. That is, power is supplied to the preamplifier 5, the main amplifier 6 and the comparison circuit 7 only while the light emitting pulse is being applied.

FIG. 2 is a circuit diagram showing the detailed structure of the main part of this embodiment. In the figure, each of the preamplifier 5 and the main amplifier 6 is composed of an NPN type transistor as shown, and the comparison circuit 7 is composed of an operational amplifier 7a. In this way, as shown in FIG. 2B, the light emitting pulse is generated because the light emitting pulse to the light emitting circuit 2 interrupts the power supply to the preamplifier 5, the main amplifier 6, and the comparison circuit 7. The supply of unnecessary power is stopped while there is no power supply, and the effect of reducing the power consumption of the entire photoelectric switch can be obtained.

Next, a second embodiment of the present invention will be described. In the above-described first embodiment, the light projection pulse of the oscillation circuit 1 is directly applied to the analog switch 21 as a gate signal. FIG. 3 (a) shows this light emission pulse signal, and FIG. 3 (b).
Shows the output waveforms of the inverting input terminal (-) and the non-inverting input terminal (+) of the operational amplifier 7a of the comparison circuit 7. As shown in this figure, in the first embodiment, since the analog switch 21 performs switching in synchronization with the light projection pulse, switching noise may be superimposed on the non-inverting input terminal, which inverts the comparison output. There is a risk that Therefore, in the second embodiment, as shown in FIG. 4, the analog switch 21 is driven via the pulse width expansion circuit 22 for expanding the pulse width of the light projection pulse before and after the light projection. FIG. 5 is a circuit diagram showing a detailed configuration of the oscillation circuit 1 and the pulse width expansion circuit 22. As shown in the figure, in the oscillator circuit 1, a clock generator 31 and a plurality of, for example, four D-type flip-flops 32 to 35 are connected in cascade. The clock generator 31 outputs the clock signal shown in FIG. 6A, and the flip-flops 32 to 35.
Divides each output as shown in FIGS. 6 (b) to 6 (e). The output of the clock generator 31 and the outputs Q1 to Q4 of the flip-flops 32 to 35 are given to the AND circuit 36. The AND circuit 36 generates a light projecting gate as shown in FIG. 6F by taking the logical product of the clock signal and the outputs of the flip-flops 32 to 35. Further, the pulse width expansion circuit 22 has Q2, Q3 and Q4
And AND circuit 38 for taking the logical product of Q2 bar, Q3 bar and Q4 bar. The outputs of the AND circuits 37 and 38 are supplied to the analog switch 21 via the OR circuit 39 as in the first embodiment.
Connected to the gate terminal of. The AND circuit 37 is shown in FIG.
As shown in (g), a signal for the first four clock cycles of the light projecting pulse, that is, a signal of the T1 period is obtained, and the AND circuit 38 obtains a signal for time T2 after the end of the light projecting pulse. is there. The OR circuit 39 outputs the power supply control signal shown in FIG. In this way, the ON time of the analog switch 21 is extended for a predetermined period before and after the light projection pulse. Therefore, after the power supply to the preamplifier 5, the main amplifier 6 and the comparison circuit 7 is turned on for a predetermined time, the light receiving signal corresponding to the light emitting pulse is obtained after the power supply is stabilized, and the operation is stabilized. be able to. In this embodiment, the on-time of the analog switch 21 is extended even after the light emitting pulse ends, but since the gate circuit 8 gates the light emitting pulse as shown in FIG. 6 (i). The falling edge of the power supply control signal of the analog switch 21 may be matched with the light projection pulse.

Next, a third embodiment of the present invention will be described. FIG. 7 is a circuit diagram showing the configuration of the light receiving circuit portion according to the third embodiment. Also in this embodiment, the power supply to the light receiving amplifier circuit 41 and the comparison circuit 7b is interrupted by the light emitting pulse signal of the oscillation circuit 1 or the power control signal obtained by expanding the pulse width of the light emitting pulse of the oscillation circuit. In this embodiment, the power supply control signal is applied to the base of the transistor Q1 as shown. The emitter of the transistor Q1 is grounded, and the collector is connected to the base / collector common connection end of the transistor Q2 via a resistor. Transistor Q2
Together with the transistors Q3 and Q4 of the light receiving amplifier circuit 41 and the transistors Q5 and Q6 of the comparison circuit 7b constitute a current mirror circuit. In this embodiment, the transistor Q1 is turned on / off by the power supply control signal, and the transistor Q2 is turned on / off. Therefore transistor Q
When Q1 and Q2 are in the ON state, the same current as the current I1 flowing through the transistor Q2 is the same as that of the transistors Q3, Q4 and Q.
5 and Q6, power is supplied to the light receiving amplifier circuit 41 and the comparison circuit 7b. Here, the current mirror circuit of the transistor Q1 and the transistors Q2 to Q6 constitutes power switch means for controlling the power supply to the amplifier and the comparison circuit based on the power control signal. In this way, it is possible to directly connect the power source by using the analog switch 21 unlike the first and second embodiments.
Low power consumption can be achieved. In the present embodiment, power is supplied to a part of the circuit such as the high impedance part of the light receiving amplifier circuit and the comparison circuit, and the other parts are selectively configured to interrupt the current by the power supply control signal. You can

Next, a fourth embodiment of the present invention will be described with reference to FIG. In FIG. 8, the same parts as those in the third embodiment are designated by the same reference numerals and detailed description thereof will be omitted. In this embodiment, a second current mirror circuit is provided in addition to the transistors Q1 to Q6 which are intermittently driven by the power supply control signal. This current mirror circuit is a transistor Q7 that supplies current to the transistor Q7 and the light receiving amplifier circuit 41.
8 and Q9, and transistors Q10 and Q11 for supplying power to the comparison circuit 7b. The second current mirror circuit has a current I of the first current mirror circuit.
A minute current I2 smaller than 1 is always supplied to the light receiving amplifier circuit 41 and the comparison circuit 7b. This makes it easy to charge the coupling capacitor C and stabilize the fluctuation of the power supply.

Next, a fifth embodiment of the present invention will be described. In the above-described first to fourth embodiments, the power supply of the light receiving amplifier circuit and the comparison circuit in the light receiving circuit is reduced, but the signal processing circuit side always supplies a constant power supply. In the fifth embodiment, the electric current of the I ² L logic circuit used when integrated into an analog element in a signal processing circuit to form a one-chip IC is reduced.
FIG. 9A is a circuit diagram showing a part of the integrating circuit 9 in the signal processing circuit, and the output of the comparing circuit 7 is given to the integrating circuit 9 including the RS flip-flop 51 via the gate circuit 8. Here, it is assumed that the RS flip-flop 51 is configured in the chip of the I ² L logic circuit. I ²
In the L logic circuit, if an injection current is not sufficiently supplied, a delay occurs and the L logic circuit does not operate normally. Therefore, in this embodiment, the injection current of the I ² L logic circuit is the same as the light emission pulse width of the oscillation circuit 1 as in the first embodiment, or the power is supplied only before and after the light emission pulse as in the second embodiment. To supply. FIG. 9B is a schematic diagram showing the configuration of a part of this I ² L logic circuit. As shown in the figure, the transistor Q12 and the transistor Q1 operated by the power control signal are operated.
I ² L by the current mirror circuit composed of 3, Q14
An injection current is supplied to the logic circuit, such as the RS flip-flop 51 shown in FIG. In this way, the injection current is supplied only during the required signal processing period, and the injection current is stopped during the time period when the signal processing is not required to be performed, thereby reducing the power consumption.

[0016]

As described in detail above, according to the inventions of claims 1 to 3, the light receiving circuit and the signal are received only during the period when the signal is received by the light emitting pulse of the light emitting circuit which intermittently emits light. The processing circuit is operated. Therefore, the effect that the current consumption of the photoelectric switch circuit can be greatly reduced as a whole can be obtained. Therefore, if the reduced current is increased, for example, by increasing the drive current of the light projecting element, it is possible to increase the detection distance.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a photoelectric switch according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a detailed configuration of an amplifier circuit and a comparison circuit of the first embodiment.

FIG. 3 is a waveform diagram showing a waveform of each part of the first embodiment.

FIG. 4 is a block diagram showing an overall configuration of a photoelectric switch according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing configurations of an oscillator circuit and a pulse width expansion circuit according to a second embodiment of the present invention.

FIG. 6 is a waveform diagram showing the waveform of each part according to the second embodiment of the present invention.

FIG. 7 is a circuit diagram showing a configuration of a light receiving circuit section according to a third embodiment of the present invention.

FIG. 8 is a circuit diagram showing a configuration of a light receiving circuit section according to a fourth embodiment of the present invention.

9A is a circuit diagram showing a part of a photoelectric switch, and FIG. 9B is a schematic diagram showing an internal circuit according to a fifth embodiment of the present invention.

FIG. 10 is a block diagram showing an overall configuration of a conventional photoelectric switch.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 oscillator circuit 2 light emitting circuit 3 light emitting element 4 light receiving element 5 preamplifier 6 main amplifier 7,7b comparison circuit 8 gate circuit 9 integrating circuit 10 output circuit 21 analog switch 22 pulse width expansion circuit 31 clock generation unit 32 to 35 flip-flop 36-38 AND circuit 39 OR circuit 41 Light receiving amplifier circuit 51 RS flip-flop Q1-Q14 Transistor

Claims (3)

[Claims] 1. A light projecting element for irradiating light to a detection region, an oscillation circuit for intermittently driving the light projecting element, and a light receiving device for receiving an optical signal obtained from the light projecting element through an object detection region. An element, an amplifier that amplifies the output of the light receiving element, a comparison circuit that compares the output of the amplifier with a predetermined threshold level, and a power switch that controls the power supply to the amplifier and the comparison circuit by the output of the oscillation circuit A photoelectric switch comprising: 2. A light projecting element for irradiating light to a detection region, an oscillation circuit for intermittently driving the light projecting element, and a light receiving device for receiving an optical signal obtained from the light projecting element via an object detection region. An element, an amplifier that amplifies the output of the light receiving element, a comparison circuit that compares the output of the amplifier with a predetermined threshold level, and a signal processing circuit configured by an I ² L logic circuit that processes the output of the comparison circuit And a power switch means for controlling the power supply to the signal processing circuit according to the output of the oscillation circuit. 3. A pulse width expansion circuit for expanding the pulse width of the oscillation circuit, wherein the power switch means is driven through the pulse width expansion circuit. The described photoelectric switch.