JP3351816B2 - Photoelectric switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronous detector for detecting reflected light by a light receiving element by a detection object of pulsed light emitted from light emitting means, and detecting a received light signal based on a synchronous signal from a light emitting circuit. The present invention relates to a method for preventing a malfunction due to noise light in a photoelectric switch.

[0002]

2. Description of the Related Art In a conventional photoelectric switch, reflected light is received by a light receiving element by an object to be detected of a pulse light emitted from a light emitting means, and a light receiving signal is synchronized based on a synchronization signal from a light emitting circuit. There is something to detect. This type of photoelectric switch has a problem that, for example, it receives pulsed light from the same type of photoelectric switch or the like and malfunctions.

Therefore, the following method has been proposed as a malfunction preventing method for improving this point. Now, when the detection target object does not exist and the noise light does not exist, the light emission cycle is cyclically varied within a predetermined range, and the light emission cycle is set as the direction in which the light emission cycle becomes shorter. In some devices, when pulse light is emitted from the element and noise light is detected, the light emission cycle is lengthened to reverse the light emission cycle of the noise light and the light emission cycle of its own pulse light. If the light emission cycle is long and the light emission cycle coincides with the noise light emission cycle, the light emission of the pulse light is stopped once, and the light emission of the pulse light is stopped when the light emission cycle is further lengthened. The light was going to start.

[0004]

[0007] Incidentally, in the case of the photoelectric switch, in the rise and fall time of the pulse signal applied to generate a pulsed light, and detecting the presence or absence of noise light, falling time When the noise light is detected at the rising edge, the light emission cycle is simply extended. The way to start the light is taking.

However, in this case, when there are many noise sources that emit extraneous noise light, or when a different type of photoelectric switch having a shorter pulse light projection cycle than the above photoelectric switch is a noise source, In addition, there are few timings when there is no noise light, so that the operation of once stopping the emission of the pulse light and starting the emission of the pulse light when the emission period is further extended is often performed. Here, the point in time when the emission of the pulse light is started is not necessarily the point in time when no noise light exists, and therefore, there is a problem that the operation of the photoelectric switch becomes rather unstable.

The present invention has been made in view of the above points, and has as its object the case where there are a large number of noise sources emitting extraneous noise light, and the fact that pulse light is projected more than the above photoelectric switch. An object of the present invention is to provide a photoelectric switch capable of preventing malfunction when a different type of photoelectric switch having a short light cycle is a noise source.

[0007]

According to the present invention, in order to achieve the above object, there is provided a pulse generating means for generating a pulse signal having a variable generation period, and a projection apparatus for projecting a pulse light in accordance with the pulse signal. A light means, a light receiving means for receiving the pulse light from the light emitting means and detecting the light in synchronization with a generation cycle of the pulse signal, and a noise detection for detecting the presence or absence of the noise light from the light receiving output when the pulse signal is generated Means, a cycle varying means for varying the generation cycle of the pulse light output from the pulse generating means in accordance with the result of detection of the noise light by the noise detecting means, and judging the presence or absence of the detection target from the output of the light receiving means. and a discriminating means, when said noise detection means detects the presence or absence of the noise light in the rise and fall time of the pulse signal, the noise light to the falling time is detected, the period changing means is a pulse In addition to controlling the generation cycle of the pulse signal from the generating means to be longer, when noise light is detected at the rising time, the cycle variable means temporarily stops the generation of the pulse signal from the pulse generating means, and stops at the falling time. when the noise light is detected to generate a pulse signal at longer the period the generation period of a pulsed signal from a case where the detection object by the determination means is not detected, the sense target
The noise detection sensitivity of the noise detection means
The that has been changed.

[0008] More specifically, a first comparator that generates an output when the received light output of the noise light is equal to or higher than a predetermined level;
A second comparator which generates an output when the received light output goes to a negative level, and a noise process which determines that noise light exists when the outputs of these comparators are obtained at the rise and fall of the pulse signal When the detection target is not detected by the circuit and the determination unit, the output of the second comparator is prevented from being input to the noise processing circuit, and when the detection target is detected by the determination unit, The noise detection means can be constituted by input control means for inputting the output of the second comparator to the noise processing circuit.

[0009]

According to the present invention, the object to be detected is determined by the determination means as described above .
Is not detected and when the target is detected
In the case, more this <br/> and change the noise detection sensitivity of the noise detecting means, when the detection subject absent, or when, the photoelectric switch noise source that emits external noise light exists many When a different type of photoelectric switch having a shorter light emission cycle than the noise source is a noise source, the light emission of the pulse light is temporarily stopped, and the light emission of the pulse light is started when the light emission cycle is further lengthened. Such operations are prevented from being performed frequently, and unstable operation states are avoided to reduce malfunctions.

[0010]

1 to 3 show an embodiment of the present invention. The photoelectric switch of the present embodiment detects an object by receiving light reflected from an object to be detected from light emitted from a light emitting element. Do it with a reflective photoelectric switch. The light emitting section 4 of the photoelectric switch includes a light emitting element 1 composed of a light emitting diode, a driving circuit 2 for driving the light emitting element 1, an oscillation circuit 3 for supplying a pulse signal for driving the light emitting element 1 to the driving circuit 2. It consists of.

Here, as the oscillating circuit 3, a circuit in which the generation period of the pulse signal is variable is used. In order to change the generation period of the pulse signal, the period changing means 1 is used.
7 is provided. This cycle changing means 17 includes
A delay circuit 15 that generates a delay output that goes low when the pulse width of the pulse signal is equal to or greater than a predetermined width, and a fall detection circuit 1 that detects the fall of the output of the delay circuit 15
6 and a counter 14 for increasing the count value when the output of the rising detection circuit 16 is given.

In the oscillation circuit 3, the generation period of the pulse signal is determined by the count value of the counter 14. For example, when the count value of the counter 14 is gradually increased, the generation period of the pulse signal is gradually shortened accordingly. Light receiving unit 1
Reference numeral 1 denotes a light receiving element 5 composed of a photodiode for receiving the reflected light of the pulse light from the light emitting element 1 reflected by the detection target, an amplification circuit 6 for amplifying the light receiving output of the light receiving element 5, and an amplification circuit 6 A comparison circuit 7 for comparing the output of the detection circuit with a predetermined level to remove a signal of a minute level, a detection circuit 8 for detecting the output of the comparison circuit 7, and integrating the output of the detection circuit 8 to determine whether the integrated value exceeds a predetermined value. It comprises a discriminating circuit 9 for discriminating the presence of a detection target depending on whether the detection circuit is present, and an output circuit 10 for appropriately outputting a detection signal according to the discrimination result of the discriminating circuit 9. The detection circuit 8 performs synchronous detection based on the synchronization signal provided from the delay circuit 15 so as to detect only the reflected light synchronized with the projection pulse.

In this photoelectric switch, a noise processing means 19 is provided in order to prevent malfunction due to pulse light (noise light) from another photoelectric switch of the same type. The noise processing means 19 determines that the output of the amplifier circuit 6 is equal to or higher than the noise detection level lower than the level of the comparison circuit 7
A comparator 12a for detecting the Rukoto, output of the amplifying circuit 6 is
Negative level (undershoot)
12b that detects the output of the comparator 12b and the output of the discriminating circuit 9; and the counter 14 according to the outputs of the comparator 12a, the AND circuit 18, and the oscillation circuit 3. And a noise processing circuit 13 for controlling the counting operation.

Here, in the noise processing circuit 13, when a high level output from the comparator 12a or the AND circuit 18 is input at the rising or falling timing of the output of the oscillation circuit 3, two pulses are counted. 14 Counter 1 receiving this pulse
In 4, when the output from the noise processing circuit 13 is received, the count value decreases.

The operation of this embodiment will be described below.
First, when the detection target does not exist and there is no noise, the light emitting element 1 is driven by the drive circuit 2 in accordance with the output of the oscillation circuit 3 and emits pulse light. In a state where the detection target does not exist and no noise exists, the light receiving element 5 does not receive any noise light. Therefore, no amplified output is generated in the amplifier circuit 6, and no output is generated from the noise processing circuit 13.

At this time, a delay output is obtained from the delay circuit 15 in accordance with the output of the oscillation circuit 3. Each time the fall of the delay output is detected by the fall detection circuit 16, the count value of the counter 14 is increased. And the generation cycle of the pulse signal output from the oscillation circuit 3 is gradually shortened. However, the pulse signal generation cycle is limited to a predetermined range. When the lowest pulse signal generation cycle is reached, the pulse signal generation cycle returns to the highest pulse signal generation cycle. Is variable.

Next, a case will be described where extraneous noise light is received by the light receiving element 5 in a state where no detection target exists. The output of the amplifier circuit 6 at this time has a waveform shown in FIG. In the comparator 12a, the output of the amplifying circuit 6 goes high while exceeding the noise detection level.
An output shown in (c) is generated.
Specified to detect that the output of the
Figure 2 (d), which goes high while below the level
Produces the output shown in

In this case, when the incident time of the noise light coincides with the falling timing of the pulse signal output from the oscillation circuit 3, and the high-level time of the comparator 12a becomes the falling timing of the pulse signal. The noise processing circuit 13 outputs two pulses to the counter 14 as shown in FIG. As a result, the count value of the counter 14 decreases by two. After that, the falling edge of the delay output of the delay circuit 15 shown in FIG.
6, and the detection output is input to the counter 14. As a result, the count value of the counter 14 increases by one. Therefore, the count value of the counter 14 is reduced by one overall. Thereby, at this time, the generation cycle of the pulse signal output from the oscillation circuit 3 becomes longer.

As described above, the erroneous detection is prevented by shifting the light emission cycle of its own pulse light so that the light emission cycles with other noise sources do not overlap. This reduces the possibility that the noise light is reflected by the detection target and is received by the light receiving element 5. Here, when the incident time of the noise light coincides with the falling timing of the pulse signal output from the oscillation circuit 3 and the high-level time point of the comparator 12a becomes the falling timing of the pulse signal. Further shifts the light emission cycle of the pulsed light.

By the way, when the light emission cycle of the pulse light is lengthened in this way, it is conceivable that the light emission cycle of the noise light and the light emission cycle of its own pulse light are opposite to each other. At this time, at the time when the pulse signal of the oscillation circuit 3 rises, a state occurs in which the comparator 12a goes high. For this reason, another count value is input to the oscillation circuit 3 immediately after the pulse signal rises according to the count value of the counter 14. At this point, the oscillation circuit 3
Stops the output of the pulse signal. Therefore, the pulse width of the pulse signal of the oscillation circuit 3 does not reach the predetermined value, and the delay circuit 15
Does not occur, and therefore the output of the rise detection circuit 16 is not input to the counter 14. In this case, the count value of the counter 14 is decremented by two, and the light emitting cycle of the pulse light is made longer than that in the above-mentioned case to shift the synchronization state of the light emitting cycle with the noise light.

[0021] When the further noise light is received by the rising time, shifting the synchronization state by repeating the same operation. In this way, erroneous detection when no detection target exists is prevented. Next, an operation in a state where the detection target is detected will be described. In this case, since the output of the determination circuit 9 is at the high level, the output of the comparator 12b is also input to the noise processing circuit 13 through the AND circuit 18 as shown in FIG. In this case, the undershoot portion in the output of the noise light amplifying circuit 6 is also a target of noise light detection. Therefore, once the detection target is detected, the sensitivity of the above-described operation of shifting the cycle with respect to the noise light increases. In this way, it is possible to prevent the output state of the determination circuit 9 from changing unstably.

When the object to be detected does not exist as described above, the operation of shifting the synchronization of the light emission cycle is performed only by the output of the comparator 12a, so that the pulse of the oscillation circuit 3 is generated at the rising cycle of the pulse signal. Stops outputting the signal, and then sets the counter 1 regardless of the presence or absence of noise light.
An unstable operation of outputting a pulse signal at a cycle determined by the count value of 4 can be minimized.

The above operation can also be executed by the processing shown in the flowchart of FIG. 3. Therefore, the noise processing section may be constituted by a logical operation circuit, and may be processed by software.

[0024]

As described above, the present invention provides a pulse generating means for generating a pulse signal having a variable generation period, a light emitting means for emitting a pulse light in accordance with the pulse signal, and a light emitting means. A light receiving means for receiving the pulse light from the light source and detecting the light in synchronization with a generation cycle of the pulse signal; a noise detecting means for detecting the presence or absence of the noise light from a light receiving output at the time of generating the pulse signal; A period varying unit that varies a generation period of the pulse light output from the pulse generation unit in accordance with a detection result of the noise light; and a determination unit that determines presence or absence of a detection target from an output of the light receiving unit. detecting means detects the presence or absence of the noise light in the rising and falling <br/> time of the pulse signal, the noise light to the falling time is detected, the period changing means is a pulse signal from the pulse generating means While controlling so as to lengthen the live cycle, when noise light is detected at the rising point, the cycle variable means temporarily stops the generation of the pulse signal from the pulse generating means, and the noise light is detected at the falling time. A pulse signal is generated at a period that is longer than the generation period of the pulse signal , and noise detection is performed when the detection target object is not detected by the above-described determination means and when the detection target object is detected.
Since the noise detection sensitivity of the informing means is changed, when there is no detection target, there are many noise sources emitting extraneous noise light, or the light emission cycle of pulse light is shorter than that of the photoelectric switch. When a different type of photoelectric switch is a noise source, it is possible to prevent the operation of stopping the light emission of the pulse light once and starting the light emission of the pulse light when the light emission cycle is further extended. In addition, an unstable operation state can be avoided to reduce malfunctions.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of an embodiment of the present invention.

FIG. 2 is an operation explanatory view of the above.

FIG. 3 is a flowchart in a case where processing of a main part of the above is executed by software.

[Explanation of symbols]

 Reference Signs List 3 oscillation circuit 4 light emitting section 9 discriminating circuit 11 light receiving section 12a, 12b comparator 13 noise processing circuit 17 period changing means 18 AND circuit 19 noise processing means

Claims (2)

(57) [Claims] 1. A pulse generating means for generating a pulse signal having a variable generation period, a light emitting means for emitting a pulse light according to the pulse signal, and a light receiving means for receiving the pulse light from the light emitting means. A light receiving means for detecting in synchronization with a pulse signal generation cycle; a noise detecting means for detecting the presence or absence of noise light from a light receiving output at the time of generation of the pulse signal; and a detecting means for detecting the noise light by the noise detecting means. A period varying unit that varies a generation period of the pulse light output from the pulse generation unit; and a determination unit that determines the presence or absence of a detection target from the output of the light receiving unit. and detecting the presence or absence of noise light in a falling point, noise light falling time is detected, control so that the period changing means is to increase the generation period of the pulse signal from the pulse generating means When the noise light is detected at the rising time, the cycle variable means temporarily stops the generation of the pulse signal from the pulse generating means, and the generation cycle of the pulse signal is further increased than when the noise light is detected at the falling time. A pulse signal is generated at a cycle that is longer than the detection target object.
The noise detection sensitivity of the noise detection means
A photoelectric switch characterized by being changed . 2. A first comparator for generating an output when a received light output of noise light is equal to or higher than a predetermined level;
A second comparator that generates an output when the pulse signal becomes high, a noise processing circuit that determines that noise light exists when the outputs of these comparators are obtained at the rise and fall of the pulse signal, Means for preventing the output of the second comparator from being input to the noise processing circuit when the detection target is not detected by the means, and performing the second comparison when the detection target is detected by the determination means. 2. The photoelectric switch according to claim 1, wherein said noise detecting means is constituted by input control means for inputting an output of the detector to a noise processing circuit.