JPS61139776A - Photoelectric switch - Google Patents

Abstract

PURPOSE:To prevent erroneous operation due to disturbance noise without using a condenser or a coil, by providing a presettable incremental and decremental counter and applying light receiving detection output when the predetermined number or more of pulses were counted. CONSTITUTION:A light emitting element driving circuit 2 drives a light emitting element 3 or the basis of the oscillation output of a pulse oscillator 1 and the output of a light receiving element 4 receiving pulse light L is amplified by an amplifying circuit 5 and a latch circuit 7 latches the pulse signal of a wave form shaping circuit 6 in synchronous relation to the pulse output of the oscillator 1. The output of a presettable incremental and decremental counter 8 for counting the oscillation output of the pulse oscillator 1 is applied to a first logical circuit 9 which, in turn, applies a light receiving detection signal to an output circuit 10 when the counter 8 counted the predetermined number or more of pulses. A second logical circuit 11 resets the count output of the light receiving element 4 when pulse light L continuously received by the light receiving element 4 was short of a predetermined number and presets the output of the counter 8 when pulse light not received continuously was short of a predetermined number.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application This invention relates to a so-called pulse modulation type photoelectric switch in which a light receiving element detects pulsed light emitted from a light projecting element.

(B) Prior Art Conventionally, in this type of pulse modulation sculptural switch, in order to prevent malfunctions caused by electrical noise or pulsed light emitted from a fluorescent lamp, a light reception signal is fed to an integrating circuit, and this integrated value is combined with a predetermined value. The switching output is obtained by comparing and determining the level of .

However, since a conductance element such as a capacitor or a coil is required to constitute the integration circuit, the conventional photoelectric switch has a problem in that it is difficult to miniaturize it, especially to integrate it into an integrated circuit.

Furthermore, since the time constant of the integrating circuit is determined by a resistor and a capacitor or a resistor and a coil, there is a drawback that the operating time of the photoelectric switch becomes non-uniform due to variations in the characteristics of these components.

In order to solve the above problem, a method for counting pulses using a shift register number (Japanese Patent Laid-Open No. 52-82
0665) has been proposed and implemented. However, according to this method, it is possible to eliminate the capacitors, coils, etc. that constitute the integration circuit, but on the other hand, flip-flop circuits for the set count number are required, which increases the number of parts and increases integration. A drawback arises in that the area of the device increases when circuitized.

(c) Purpose This invention aims to provide a photoelectric switch that can prevent malfunctions due to disturbance noise without using actance elements such as capacitors or coils, and is suitable for integration into an integrated circuit.

(d) Configuration The photoelectric switch according to the present invention has a presettable up/down switch that counts the oscillation output given to the light emitting element.
A counter is provided, and a light reception detection output is provided when the counter counts a predetermined number or more of pulses. When the number of pulsed lights that are received is less than a predetermined number, or when the number of pulsed lights that are not consecutively received is less than a predetermined number, the count output at that time is reset or preset.

On the other hand, the photoelectric switch according to the second invention, in addition to the features of the photoelectric switch according to the first invention, - reduces the output current when the output current of the cough photoelectric switch exceeds a predetermined value. The present invention is characterized in that it includes an overcurrent protection circuit that controls the counter in both directions.

(e) Embodiment FIG. 1 is a block diagram schematically showing the configuration of a photoelectric switch according to the first invention, and FIG. 2 is a specific circuit diagram of the photoelectric switch shown in FIG. 1.

In FIG. 1, reference numeral 1 indicates a pulse oscillator that provides an oscillation output of a predetermined frequency. 2 is a light emitting element drive circuit that drives the light emitting element 3 by the oscillation output of the pulse oscillator 1.
Reference numeral 4 indicates a light receiving element that receives the pulsed light emitted from the light projecting element 3. The light receiving output of the light receiving element 4 is transmitted to the amplifier circuit 5.
After being amplified, the signal is provided to the waveform shaping circuit 6. The output of the waveform shaping circuit 6 is given to a latch circuit 7. This latch circuit 7 latches the pulse signal of the waveform shaping circuit 6 in synchronization with the pulse output of the pulse oscillator 1.

Reference numeral 8 indicates a presettable up/down counter that counts the oscillation output of the pulse oscillator 1. The output of the counter 8 is given to a first logic circuit 9 at the next stage. 1st
The logic circuit 9 provides a light reception detection signal to the output circuit 10 when the counter 8 counts a predetermined number or more of pulses.

Reference numeral 11 indicates a second logic circuit to which each output signal of the latch circuit 7 and the first logic circuit 9 is applied. This logic circuit 11 resets the count output of the counter 8 when the number of pulsed lights continuously received by the light receiving element 4 is less than the predetermined number. Further, when the number of pulsed lights that are not consecutively received is less than the predetermined number, the output of the counter 8 at that time is preset.

Next, the configuration of the specific circuit shown in FIG. 2 will be explained. Second
In the figure, the same parts as in FIG. 1 are indicated by the same reference numerals.

However, the light emitting element drive circuit 2, the light emitting element 3, shown in FIG.
The light receiving element 4 and the amplifier circuit 5 are omitted. In the figure, the latch circuit 7 is a D flip-flop (delayed
flip-flop). Presettable up/down counter 8 has three D
Flip-flops 81 to 83 are connected in cascade to form an octal counter.

The first logic circuit 9 includes logic circuits 91 and 92, and a flip-flop 93 to which the outputs of the logic circuits 91 and 92 are applied. Thus, flip-flop 93 is connected to an output circuit (not shown). The logic circuit 91 is given the ζ output of the flip-flop 81 and the ζ output of the flip-flop 82.

R circuit, the output of the NOR circuit, and the flip-flop 8
It is composed of a NAND circuit that is given three ζ outputs. The logic circuit 92 is composed of a NOR circuit to which the ζ output of the flip-flop 81 and the ζ output of the flip-flop 82 are applied, and a NAND circuit to which the output of the NOR circuit 92 and the ζ output of the flip-flop 83 are applied.

The logic circuit 91 outputs L only when all the ζ outputs of the flip-flops 81 to 83 are H, and the logic circuit 92 outputs L only when all the ζ outputs are L.

On the other hand, the second logic circuit 11 is composed of two NOR circuits 111 and 112. The NOR circuit 111 receives the ζ output of the latch circuit 7 as one input, and the ζ output of the flip-flop 93 as the other input.

The NOR circuit 112 receives the ζ output of the latch circuit 7 as one input, and receives the ζ output of the flip-flop 93 as the other input.

Thus, the output of the NOR circuit 111 is applied to each preset terminal PR of the flip-flops 81-83 constituting the counter 8, while the output of the NOR circuit 112 is applied to the clear terminal CL of the flip-flops 81-83.

Next, the operation of the photoelectric switch shown in Figure 2 is explained in Figures 3 to 6.
Let's explain according to the operation waveform diagram of each part shown in the figure.

First, the light receiving element 4 that is not receiving pulsed light is 7+1i.
The operation when one or more consecutive pulsed lights are received will be explained based on FIG. 3. When the light receiving element 4 does not receive pulsed light, the waveform shaping circuit 6 outputs H as shown in FIG. 3 (C1). 1, the output of the waveform shaping circuit 6 is latched in synchronization with the rise of the oscillation output given from 1. Therefore, the output terminal Q of the latch circuit 7 becomes H as shown in FIG. Same figure (
Output L as shown in e).

By the way, the flip-flop 93 of the first logic circuit 9 is
When the light receiving element is not receiving pulsed light, it outputs H to the output terminal Q and L to the output terminal d. Therefore, in the NOR circuit 111 in the second logic circuit, the re-input is H.
Therefore, the output of the NOR circuit 112 becomes L, and since the re-input of the NOR circuit 112 becomes L, its output becomes H. Therefore counter 8
H is applied to the clear terminals of flip-flops 81 to 83,
Since L is input to each preset terminal, the counter 8 is forcibly reset. Therefore, the output terminals Q of the flip-flops 81 to 83 all output L, and all the output terminals output H. As a result, logic circuit 91 in first logic circuit 9 outputs H, and logic circuit 92 outputs L. Therefore, at this time, the output terminal Q of the flip-flop circuit 93 outputs L and the output terminal d outputs H, thereby indicating that the pulsed light is not being received.

Next, the operation when continuous pulsed light is incident on the light receiving element 4 will be explained.

The light emitting element 3 is driven to emit light in the pulse output state shown in FIG. This received light signal is applied to the waveform shaping circuit 6, where it is shaped into a pulse signal C as shown in FIG. , at the rise of the oscillation output a applied to the clock pulse input terminal CP, the pulse signal C is in the L state, so the latch circuit 7 outputs the L state to the output terminal Q.
and output H to the mouth, respectively. As a result, one input of the NOR circuit 112 becomes H, so its output becomes L, and the clear state of the counter 8 is released.

The counter 8 whose clear state has been released starts counting in synchronization with the oscillation output of the pulse oscillator 1.

As a result, the output terminal Q of the flip-flop 81 rises from L to H, and the logic circuit 92 changes from L to H. However, since the output of logic circuit 91 is maintained in the H state, the output of flip-flop/op 93 is not inverted. Note that the Q output of the flip-flop 93 is fed back to the counter 8, so that the counter 8 is controlled to operate as an up counter or a down counter. However, in this case, since the Q output is provided, the counter 8 operates as an up counter.

While the pulsed light is continuously incident, the counter 8 counts the number of input pulses. Then, at the same time that the seventh clock pulse enters the counter 8, the flip-flops 81 to 8
Since each output terminal Q of 3 outputs H, the logic circuit 91 inverts its output from H to L. As a result, the output of the flip-flop 93 is inverted, and the output terminal Q outputs H and the output terminal outputs L, thereby indicating that the light receiving element 4 has received the pulsed light.

At the same time as the output of flip-flop 93 is inverted, NOR
The output of the circuit 111 changes from L to H, and the preset terminals PR of the flip-flops 81 to 83 are maintained at H. As a result, the counter 8 is forcibly preset, and the flip-flops 81 to 83 are
The output terminal Q of outputs H. Also flip flop 9
When the output terminal Q of the counter 3 becomes H, the mode of the counter 8 is switched from an up counter to a down counter.

Next, a case where the light receiving element 4 that has been receiving pulsed light no longer receives pulsed light continuously will be described with reference to FIG. 4.

When the pulsed light is no longer incident on the light receiving element, the waveform shaping circuit 6
Since the output signal C of the latch circuit 7 is maintained at H, the output terminal Q of the latch circuit 7 is inverted to H and the output terminal is inverted to L. As a result, NOR
Since one input of the circuit 111 becomes H, its output becomes L and the preset of the counter 8 is canceled. Although the counter 8 has been switched to a down counter as described above, the counter 8 starts counting down in synchronization with the input oscillation output a. At the same time as starting the down count, the output terminal of the flip-flop 81. is to L,
Low is reversed to H. As a result, the logic circuit 91 outputs an H level, but in this state, the flip-flop 93 does not output a reverse signal.

During the period when the light receiving element is not receiving pulsed light, the counter 8 continues to count down, and at the same time as the 71st pulse is input, the output terminals Q of the flip-flops 81 to 83 output L. As a result, the logic circuit 92 becomes L, so the output of the flip-flop 93 is inverted, the output terminal Q becomes L, and the output terminal becomes H, indicating that no pulsed light is being received.

Since the NOR circuit 112 outputs H due to the inversion of the flip-flop 93, the counter 8 is forcibly reset and the counting mode is switched to amplifier counting.

The operation described above is for a state in which the photoelectric switch shown in FIG. 2 is not affected by noise.

Next, the operation when the charging switch is affected by noise will be explained. First, a case will be described with reference to FIG. 5 in which the light-receiving element is affected by noise while receiving pulsed light and a portion of its output signal is missing.

As mentioned above, when receiving pulsed light, the output terminal Q of the flip-flop 93 outputs H and the output terminal Q outputs L, respectively, and the output terminals of each flip-flop 11 to 83 of the counter 8 All Q outputs H, NO
The R circuit 111 outputs H, and the NOR circuit 112 outputs L. Further, since the output terminal 9 of the flip-flop 93 is in the H state, the mode of the counter 8 is a down counter.

When a pulse is missing, the output signal C of the waveform shaping circuit 6 in that part becomes H, so the output Q of the latch circuit in that part becomes H and ζ becomes L. As a result, the NOR circuit 111 is inverted to L as shown in FIG. 4(g), so that the preset of the counter 8 is canceled. As a result, the counter 8 starts counting down. During the period when the pulsed light is missing, the power 67 and 8 continue to count down in synchronization with the oscillation output a, but the number of pulses counted by the counter 8 is 7 (
If even one pulsed light is received when the
As shown in (di and e) in the same figure, the output of the latch circuit 7 is inverted. Therefore, the output of the NOR circuit 111 becomes H, the counter 8 is forcibly preset, and the output Q of each flip-flop 81 to 83 is All return to H. If pulsed light is missing again, counting down from the initial value is started again.

In this way, if the number of pulsed lights that are consecutively dropped due to the influence of noise is less than 7, the counter will be forcibly preset when a new pulsed light is received, so 7 pulsed lights will be missed in a row. Flip-flop 9 unless more than one is missing
The output of 3 is not inverted.

However, since it is extremely rare for seven or more pulsed lights to be missing in succession due to the influence of noise, it can be said that this photoelectric switch is highly reliable against dropouts of pulsed light due to the influence of noise.

Next, a case where a noise pulse is superimposed on the output signal of the light receiving element 4 due to the influence of noise while the light receiving element is not receiving pulsed light will be described with reference to FIG.

In a state where pulsed light is not being received, the output Q of the flip-flop 93 is maintained at L, the output terminal d is maintained at H, and the output Q of each flip-flop 81 to 83 of the counter 8 is maintained at L.
are all L. In addition, the NOR circuit 111 has L,
The NOR circuits 112 each output H, and the mode of the counter 8 is an up counter.

Suppose that the light receiving element outputs a noise pulse as shown in the figure (bl) due to the influence of noise.This signal is waveform-shaped and a signal C as shown in the figure (C>) is given to the latch circuit 7. It will be done.

By being given the prayer sign C, the latch circuit 7 operates as shown in the figure (d
Invert its output as shown in l and (el).

Therefore, the output of the NOR circuit 112 becomes L, and the clearing of the counter 8 is canceled. As a result, the counter 8 starts counting up the oscillation output of the pulse oscillator 1. However, when the number of consecutively input noise pulses is less than 7, at the rise of the oscillation output a input to the clock pulse input terminal CP after the noise pulses,
Since the signal C becomes H, the output terminal Q of the latch circuit 7 becomes H.
Then, the output terminal Q is inverted to L. Therefore, NOR circuit 1
Since the counter 12 outputs H as shown in the top view (f), the output of the counter 8 is cleared. Therefore, if the number of consecutively input noise pulses is less than seven, the output of the flip-flop 93 will not be inverted. However, in reality, it is almost impossible for seven or more noise pulses to occur in succession in synchronization with the rise of the oscillation output a, and therefore, this photoelectric switch is extremely reliable even when such noise occurs. can be said to be high.

As explained above, the photoelectric switch shown in FIG. 2 outputs H to the output terminal Q of the flip-flop 93 when seven or more pulsed lights are received continuously, and Flip-flop 93 when pulsed light is missing
Inverts the output of , and outputs H to its output terminal d. In this way, this photoelectric switch has the same operating time for light reception and non-light reception. Of course, such operating time can be arbitrarily set by changing the logic of the counter output, the number of counting flip-flow knobs, the oscillation period of the pulse oscillator, etc.

In addition, in the above embodiment, in order to set the operation time of light reception and non-light reception to be the same, the number of pulsed lights that are consecutively received when resetting or presetting the counter, and the number of pulsed lights that are not consecutively received The numbers were set to be the same.

However, if it is not necessary to set the operating time to be the same, the number of pulsed lights that are received and the number of pulsed lights that are not consecutively received may be set to different numbers.

Next, a photoelectric switch according to a second invention will be explained.

FIG. 7 is a circuit diagram showing the specific structure of the photoelectric switch according to one embodiment of the invention shown in FIG.

In this figure, the same parts as in FIG. 2 are indicated by the same reference numerals.

Reference numeral 12 denotes an output transistor whose heel is connected to the output terminal Q of the flip-flop 93. 13 is a 2Ω resistor connected between the emitter of output transistor 12 and ground.
The front and rear resistors are provided to convert the output current flowing through the output transistor 12 into a voltage. Reference numeral 14 indicates a comparator whose one input terminal is connected to the emitter of the output transistor 12 and the other input terminal is connected to the reference voltage source 15. Output of comparator 14 and NOR circuit 12
The output of is given to the clear terminal CL of each flip-flop 81 to 83 of the counter 8 via the OR circuit 16. Thus, the above-described resistor 13, comparator 14, reference voltage source 15, and OR circuit 16 form an overcurrent protection circuit. The operation will be explained below.

Assume that the light receiving element is now receiving pulsed light, and therefore the output terminal Q of the clip-flop 93 is outputting H. Therefore, the output transistor 12 is in an ON state.

When an overcurrent flows through the output transistor 12, the emitter voltage of the transistor 12 becomes higher than the set voltage of the reference voltage source 15, and the comparator 14 outputs an H level. As a result of this output H being applied to the clear terminal CL of the counter 8 via the OR circuit 16, the counter 8 is forcibly reset.

As a result, the output of the flip-flop 93 is inverted and the output terminal Q becomes L, so the output transistor 12 is turned off.
state. When the pulsed light is continuously received, the flip-flop 93 is inverted again and the output terminal Q becomes H.
Therefore, the output transistor 12 is turned on. If overcurrent still flows at this point, the counter 8 is instantly cleared and the above-described operation is repeated.

In such a repeated operation, the transistor 12 is turned on for a moment after seven consecutive pulsed lights are received until it is reset. Therefore, the power consumed by the output transistor 12 is equal to the value obtained by integrating the instantaneously consumed power, so that the integrated value does not exceed the allowable power. Therefore, even if the collector of the output transistor 12 is mistakenly connected directly to the power supply without connecting a load, the transistor 12 will not be destroyed.

(f) Effect The photoelectric switch according to the first invention can presetably up/down the output of the pulse oscillator that drives the light projecting element.
When a predetermined number or more of pulsed lights are received consecutively, a light reception detection output is given based on the count output at that time, and when the number of pulsed lights received is less than the predetermined number, The count output is reset or precented when the number of pulsed lights that are not received is less than the predetermined number.

Therefore, unlike the conventional photoelectric switch, the photoelectric switch according to the present invention does not use a reactance element to remove noise, and is therefore suitable for integration into an integrated circuit.

Furthermore, since a presettable up/down counter is used to count the pulses of the pulse oscillator, the number of components is reduced compared to conventional photoelectric switches that use shift registers, etc., and the circuit configuration can be made simpler. Therefore, when this is integrated into an integrated circuit, the chip size can be reduced.

On the other hand, a photoelectric switch according to a second invention, in addition to the configuration of the first invention, controls the counter in a direction to decrease the output current when the output current of the photoelectric switch exceeds a predetermined value. Equipped with an overcurrent protection circuit.

Therefore, according to the present invention, the protection function of the output circuit can be easily realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram schematically showing the configuration of a photoelectric switch according to an embodiment of the first invention, FIG. 2 is a circuit diagram showing a specific configuration of the photoelectric switch shown in FIG. 1, and FIG. 6 is an operational waveform diagram of each part of the photoelectric switch shown in FIG. 2, and FIG. 7 is a circuit diagram showing a specific configuration of the photoelectric switch according to an embodiment of the second invention. DESCRIPTION OF SYMBOLS 1...Pulse oscillator, 3...Light emitting element, 4...Light receiving element, 7...Latch circuit, 8...P'no sestable up/counter, 9...First logic circuit , 11
...Second logic circuit, 13...Resistor, 14...Comparator, 15...Reference voltage source, 16...OR circuit

Claims (2)

[Claims] (1) A pulse oscillator that provides an oscillation output of a predetermined frequency, a light emitting element driven by the oscillation output, a light receiving element that receives pulsed light emitted from the light emitting element, and an oscillation output of the pulse oscillator. A latch circuit that synchronously latches the output signal of the light receiving element and a presettable up/down circuit that counts the oscillation output of the pulse oscillator.
a counter; a first logic circuit that provides a detection output based on a count output when the counter counts a predetermined number of pulses or more; a second unit that resets or presets the count output of the counter when the number of pulsed lights that are continuously received by the light receiving element is less than a predetermined number, and when the number of pulsed lights that are not continuously received is less than a predetermined number; A photoelectric switch characterized by comprising a logic circuit. (2) a pulse oscillator that provides an oscillation output of a predetermined frequency; a light emitting element driven by the oscillation output; a light receiving element that receives the pulsed light emitted from the light emitting element; and an oscillation output of the pulse oscillator. A latch circuit that synchronously latches the output signal of the light receiving element and a presettable up/down circuit that counts the oscillation output of the pulse oscillator.
a counter; a first logic circuit that provides a detection output based on a count output when the counter counts a predetermined number of pulses or more; a second unit that resets or presets the count output of the counter when the number of pulsed lights that are continuously received by the light receiving element is less than a predetermined number, and when the number of pulsed lights that are not continuously received is less than a predetermined number; and an overcurrent protection circuit that controls the counter in a direction to decrease the output current when the output current of the photoelectric switch exceeds a predetermined value.