JP2680977B2 - 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 light projecting circuit for causing a light projecting element to carry out a light projecting operation based on a periodic light projecting pulse, and a signal received by a light receiving element is inputted via an amplifying circuit. The present invention relates to a photoelectric switch having a light receiving circuit that performs synchronous detection based on a synchronization signal corresponding to a light emitting pulse.

[0002]

2. Description of the Related Art This type of photoelectric switch applies a light emitting pulse to a light emitting element to output pulsed light, receives light reflected by an object or the like by a light receiving element, and amplifies the light receiving signal through an amplifier circuit. The presence of an object is detected when there is a predetermined level or more, and for example, the reflected light with respect to its own pulsed light is detected by synchronously detecting the received light signal based on a synchronization signal synchronized with the light projection pulse. There is a structure for preventing erroneous detection due to interference light as a configuration for receiving the light.

In this case, if the light emitting pulse is simply synchronized with the light emitting pulse, when a similar photoelectric switch is installed in the vicinity of the light emitting pulse, a light emitting cycle substantially the same as the light emitting cycle of the light emitting pulse is set. If so, the pulsed light from the photoelectric switch will be received. Therefore, in the prior art, in order to reliably detect the reflected light due to its own pulsed light as a received light signal, if it is already in the light receiving state at the output start timing of the projected light pulse, it is regarded as interference light and the projected light pulse The output is stopped and the output of the next light emitting pulse is delayed by a certain delay time. In this case, the delay time is set to be longer than the time when the reception time of the interference light is actually measured.

As a result, when the light receiving signal already exists at the output start timing of the light projecting pulse, the output of the light projecting pulse is delayed by a certain delay time, assuming that it is the interference light, so that the light receiving state of the interference light is surely achieved. After the end, it can output its own pulsed light, and even if another photoelectric switch with the same light emission cycle is placed in the vicinity, the output state of the subsequent light emission pulse is Since it is shifted from the light projection cycle of the switch, the detection operation can be surely performed in synchronization with the pulsed light from the own light projection element.

[0005]

However, in the photoelectric switch described above, for example, one used as a collision prevention sensor for an automated guided vehicle or the like, there are the following problems.

That is, the automatic guided vehicle is an automatic guided vehicle that automatically moves along a track drawn on the floor or the like to carry members and the like, and obstacles or people present in the traveling direction or other automatic guided vehicles. In order to prevent the collision with the, a photoelectric switch is arranged on the front face portion in the traveling direction. Then, the obstacles and the like are detected in advance by a photoelectric switch, and a detection signal is given to the automatic guided vehicle to control the traveling state such as the slow driving or the driving stop, thereby preventing a collision accident in advance. It is a thing.

By the way, in general, a large number of unmanned guided vehicles are often used at the same time in a factory or the like, and each location in the factory is moved. Various interference light such as pulsed light from the photoelectric switch arranged in the automatic guided vehicle is frequently incident. That is, even in such a situation, the photoelectric switch must reliably receive only the reflected light by its own projection pulse and detect the object while avoiding the light receiving period of the interference light.

On the other hand, since the interference light randomly enters the light receiving element, it is uncertain at which timing the received interference light enters at the output start timing of the light projection pulse. Therefore, in the photoelectric switch, the output of the light projection pulse at that time is delayed by the fixed time set as described above, so that the light output is performed when the light receiving state of the interference light is surely ended.

However, in this case, even if the interference light which is just before the end of the output of the light projection pulse is detected, the output start timing of the next light projection pulse is delayed by a certain delay time, so that the interference light is delayed. The time from immediately after the end of the light receiving period to the end of the delay time elapses as a wasteful time in which no operation is performed. Therefore, in such a photoelectric switch, when it is attempted to detect the reflected light due to its own light-emitting pulse while passing through the intervals of frequently incident interference light, it becomes impossible to effectively use the period without interference light. However, there is a problem that the interference prevention rate is lowered due to delay in detection or erroneous detection.

The present invention has been made in view of the above circumstances, and an object thereof is to reliably prevent interference by effectively utilizing a period between the interference lights even when the interference lights frequently enter. Another object of the present invention is to provide a photoelectric switch capable of performing a detecting operation.

[0011]

According to the present invention, a light projecting circuit for causing a light projecting element to carry out a light projecting operation based on a periodic light projecting pulse given from a light projecting control means, and a signal received by a light receiving element. light receiving means for performing synchronous detection based on the through the amplifier circuit and the input synchronizing signal corresponding to the light projection pulse, the
Based on the output signal of the light receiving means, the light receiving state detection is judged.
A first object of the present invention is to detect a positive signal of a predetermined level or more among the outputs from the amplifier circuit and input it to the light emission control means.
And a second detection circuit for detecting a negative signal of a predetermined level or more out of the output from the amplifier circuit and inputting it to the light projecting control means. When the first detection circuit is outputting the detection signal at the output start timing of the light pulse, the output of the light projection pulse at that time is stopped and the light projection pulse is output with a delay of the first delay time, When the second detection circuit is outputting the detection signal at the output start timing of the light projection pulse, the output of the light projection pulse at that time is stopped and the second delay time shorter than the first delay time It is characterized in that it is configured to output a light projection pulse with a delay only.

[0012]

According to the photoelectric switch of the present invention, at the output start timing of the light emitting pulse, when the first detecting circuit is outputting a positive signal, the light emitting control means outputs the light emitting pulse at that time. When the output is stopped and the light emitting pulse is output with a delay of the first delay time, and the second detection circuit outputs a negative signal, the output of the light emitting pulse at that time is stopped. At the same time, the light projection pulse is output with a delay of the second delay time.

In this case, first, at the output start timing of the light projection pulse, since the reflected light due to the light to be projected has not yet reached the light receiving element, the first detection circuit or the second detection circuit is set at that timing. The detection circuit of (1) outputs a signal because it receives interference light from other than its own light projecting element. When the light received by the light receiving element is amplified through the amplifier circuit, the first half of the output signal is output as a positive signal and the second half is output as a negative signal, and thus is output from the amplifier circuit. When the level of the signal corresponding to the interference light has reached the predetermined level for exhibiting the light receiving state, the positive signal and the negative signal are sequentially output from each of the first and second detection circuits.

Therefore, when the positive signal is output from the first detection circuit at the output start timing of the light projection pulse, it indicates that the output of the amplifier circuit corresponds to the first half of the interference light. The output start timing of the light projection pulse is delayed by the first delay time until the interference light ends. Similarly, when a negative signal is output from the second detection circuit at the output start timing of the light projection pulse, it indicates that the output of the amplification circuit corresponds to the latter half of the interference light. As the time until the latter half of the interference light ends, the output start timing of the light projection pulse is delayed by the second delay time which is shorter than the first delay time.

As a result, the light emitting means emits a light emitting pulse.
By performing synchronous detection based on the synchronous signal according to
Based on the output signal obtained
Can be determined, and at this time,
Since the output start timing of the light projection pulse is not unnecessarily delayed, it is possible to make effective use of the period during which the interfering light is not incident on the light receiving element for reliable detection operation. The prevention rate can be improved.

A first embodiment in which the present invention is applied to a collision prevention sensor will be described below with reference to FIGS. 1 to 4. In FIG. 1 showing the outline of the electrical configuration,
A light emitting diode 1 as a light projecting element is adapted to be supplied with a drive current from a light projecting circuit 2 connected between terminals, and outputs pulsed light toward a detection area. The light projecting circuit 2 is provided with a light projecting pulse Sp at a light projecting cycle set by the control circuit 3, and generates a drive current to be given to the light emitting diode 1 based on the light projecting pulse Sp. Has become. The control circuit 3 includes a CPU and RO
Those M and RAM or the like comprising a built-in example 1-chip microcomputer, described below detection program is stored in advance, receiving the hand referred to in the present invention
It also has the functions of a step, a determination means, and a light emission control means.

The photodiode 4 as a light receiving element is
It receives light from the detection area and converts it into a received light signal as an electric signal, and an amplifier circuit 5 connected between the output terminals.
A light receiving signal is given to. The amplifier circuit 5
The received light signal from the photodiode 4 is amplified and its amplified output So is given to the positive signal detection circuit 6 and the negative signal detection circuit 7 as the first and second detection circuits.

The positive signal detection circuit 6 detects the "H" level detection signal as a positive signal when the magnitude of the amplified output So given from the amplification circuit 5 exceeds a preset positive level. It outputs Sa, and its output terminal is connected to the input terminal A of the control circuit 3. The negative signal detection circuit 7 outputs an “H” level signal Sb as a negative signal when the magnitude of the amplified output So given from the amplification circuit 5 falls below a preset negative predetermined level. The output terminal is connected to the input terminal B of the control circuit 3.

The control circuit 3 has a detection signal S supplied from each of the positive signal detection circuit 6 and the negative signal detection circuit 7.
The object detection and the interference light determination are performed based on a and Sb as will be described later. When the object detection is determined, the external output terminal P is connected via the output circuit 8 connected to the output terminal. The object detection signal Sx is output to.

Next, referring to the flow charts of the programs shown in FIGS. 2 and 3 and the time chart shown in FIG. 4, the operation of the present embodiment will be described. (1) Detection operation in the absence of interference light and (2) The interference prevention operation when there is interference light will be described separately.

(1) Detection operation when there is no interference light The control circuit 3 performs a detection operation according to the detection program shown in FIGS. 2 and 3, and starts the program when power is supplied from a power source (not shown). First, the initialization process is performed in step P1, and then the process proceeds to step P2 to set a preset light projection period T0 in the internally set timer 1.

Next, the control circuit 3 starts the timer 1 in step P3 and starts the timer 1 in step P4.
After waiting for the light projecting cycle T0 as the set time of (1) to proceed to Step P5, the light projecting pulse Sp is output to the light projecting circuit 2. As a result, the light projecting circuit 2 applies a drive current to the light emitting diode 1 based on the applied light projecting pulse Sp, and the light emitting diode 1 outputs pulsed light toward the detection area.

At this time, the control circuit 3 detects the detection signal Sa or Sb from the positive signal detection circuit 6 or the negative signal detection circuit 7 in step P6 or the following step P7.
Is output. Now, for example, when the interference light is not incident, the amplified output So from the amplifier circuit 5 is 1 as shown in the left end portion of FIG.
Since the second projection pulse Sp1 is not output at the output start timing, the detection signals Sa and Sb are also not output as shown in FIGS.

In this case, the reflected light of the pulsed light output from the light emitting diode 1 is incident on the photodiode 4, and the first light projection pulse Sp1 is generated.
The amplified output So from the amplifying circuit 5 appears a little later than the output start timing of 1., and in response to this, the positive signal detecting circuit 6 and the negative signal detecting circuit 7 sequentially output the detection signals Sa and Sb of "H" level. It is being output. That is, when the reflected light from the object is incident on the pulsed light of the light emitting diode 1, the light reception delay time Δt from the light projection to the light reception.
It will be after the passage of.

As a result, the control circuit 3 causes the step P6.
And P7 both determine "NO" and step P8
To the timer 2 provided inside, and the light receiving delay time Δt
After setting, the timer 2 is started in steps P9 and P10 to wait for the light receiving delay time Δt to elapse. After that, the control circuit 3 proceeds to step P11 to determine whether or not there is a positive light reception signal. That is,
The control circuit 3 determines whether or not the "H" level detection signal Sa from the positive signal detection circuit 6 is input to the input terminal A. When the control circuit 3 determines "YES", it proceeds to step P12 and outputs. The object detection signal Sx is output via the circuit 8, and when it is determined to be "NO", the process proceeds to step P13 to stop the output of the object detection signal Sx.

In this case, for example, as shown at the left end of FIG. 4, the light emitting diode 1 is driven by the first light projecting pulse Sp1.
When the pulsed light output from the object is reflected by the object and the reflected light is incident on the photodiode 4, as described above, the positive signal is generated after the light receiving delay time Δt has elapsed from the output start timing of the light projecting pulse Sp1. Since the detection signal Sa is output from the detection circuit 6, the control circuit 3 determines “YES” in step P11, and the object detection signal S
x is output to the output circuit 8.

The control circuit 3 executes the step P12 or P
After passing 13, the process proceeds to step P14 to stop the output of the first light projecting pulse Sp1, and then returns to step P2, and thereafter, in the same manner as described above, steps P2 to P14.
By repeating the above, the second light projection pulse Sp2 is output and the detection operation is continued.

(2) Interference prevention operation against interference light When the interference light is incident on the photodiode 4 from the outside during the detection operation as described above, the control circuit 3 performs the following operation. Interference prevention operation comes to be performed. Now, as shown in FIG. 4A, when the interference light A whose output is a positive signal is incident at the output start timing of the third light projection pulse Sp3, and subsequently to this An example will be described in which the interference light B whose output is a negative signal is incident at the output start timing of the fourth light projection pulse Sp4.

That is, the control circuit 3 outputs the "H" level detection signal Sa from the positive signal detection circuit 6 when the interference light A is incident at the output start timing of the third light projection pulse Sp3. Since it is given to the input terminal A, it is determined to be "YES" in step P6 and the process proceeds to step P15 (see FIG. 3). In this step P15,
The control circuit 3 adds a new light projecting cycle T1 (= T0) to the light projecting cycle T of the light projecting pulse Sp by adding the light projecting cycle T0 set in step P1 with the delay time t as the first delay time.
+ T).

Subsequently, the control circuit 3 shifts to step P16, and the new projection period T1 set in step P15 is set.
Does not exceed the upper limit value Tmax. If it does not exceed the upper limit value Tmax, the determination is “NO”, the process proceeds to step P17, where the third light-emission pulse Sp3 started to be output in step P5. Will come to a stop. At this time,
A thin whisker-shaped light emitting pulse Sp3 is a control circuit
However, in reality, the light projecting circuit 2 and
Due to the response delay of the light projecting element 1, the light projecting element 1 does not emit light,
Pulsed light that becomes interference light with other photoelectric switches
Is never sent. The control circuit 3 stores the newly set light projecting period T1 in the following step P18, and subsequently sets the delay time t in the internal timer 3 in step P19. Then, the control circuit 3 performs steps P20 and P2.
The timer 3 is started at 1 and the delay time t, which is the timer time, is waited for, and then step P5
Will come back to.

As a result, as shown in FIG.
The output of the th projection pulse Sp4 is delayed from the time when the interference light A is detected until the delay time t elapses. The delay time t set at this time is a value set in advance so as to be equal to or longer than a time corresponding to the light receiving time of the interference light by actually measuring the light receiving time of the interference light, and after the delay time t elapses. When the fourth light projection pulse Sp4 is output, the light receiving period of the interference light A has ended, and the detection operation can be performed without any trouble if no other interference light is incident.

After returning to step P5, the control circuit 3 performs the detection operation in the same manner as described above, but when it returns to step P2 through steps P5 to P14, it sets it in the timer 1. The value of the light projection period is the new light projection period T1 (= T0 stored in step P18).
+ T). That is, in the subsequent detection operation, the light projecting operation is performed at the light projecting cycle T1.

Next, when the interference light B is incident on the photodiode 4, that is, when the fifth light projection pulse Sp5 is output, the output period of the amplification circuit 5 by the interference light B has already exceeded half. If it has changed to a negative signal, the control circuit 3 causes the negative signal detection circuit 7 to detect the detection signal Sb.
Has been input, the "YE
When it is determined to be "S", the process proceeds to step P22.
Here, the control circuit 3 sets a new light projecting cycle T2 to a time T2 (= T1 + 0.5t) obtained by adding a delay time 0.5t as a second delay time to the current projecting cycle T1. .

Subsequently, the control circuit 3 shifts to step P23, and the new light projecting period T2 set in step P22 is set.
Does not exceed the upper limit value Tmax. If it does not exceed the upper limit value Tmax, the determination is “NO” and the process proceeds to step P24, where the fifth light-emission pulse Sp5 started to be output in step P5. The output of will be stopped. The control circuit 3 stores the projection cycle T2 (= T1 + 0.5t) newly set in the following step P25, and then, the step P25.
At 26, a delay time of 0.5 t is set in the internal timer 3. Then, the control circuit 3 starts the timer 3 in steps P20 and P21 and waits for the delay time 0.5t, which is the timer time, to elapse, and then, in step P20.
I will come back to 5.

As a result, as shown in FIG.
The output of the th light projection pulse Sp6 is delayed from the time when the interference light B is detected until a delay time of 0.5 t elapses. The delay time 0.5t at this time is half the above-mentioned delay time t, that is, a time corresponding to a half or more of the maximum value of the actual measurement value of the light reception time of the interference light. Is a value set as the time from when the amplified output So output as a negative signal changes to a negative signal to when the light receiving period ends, and the sixth light emitting pulse Sp6 is generated after the delay time 0.5t elapses. If it outputs, the light receiving period of the interference light B has ended, and if no other interference light is incident, the detection operation can be performed without trouble.

After returning to step P5, the control circuit 3 performs the detection operation in the same manner as described above, but when it returns to step P2 through steps P5 to P14, it sets it in the timer 1. The value of the light projection period is the new light projection period T2 (= T1) stored in step P15.
+ 0.5t). That is, in the subsequent detection operation, the light projection pulse Sp is output at the light projection cycle T2.

When the interference light A or the interference light B is detected, the new projection period T1 or T2 set in step P15 or P22 is set as the upper limit value of the projection period T, Tmax. If it exceeds, the control circuit 3 determines “YES” in step P16 or P23 and proceeds to step P27. Then, in step P27, the control circuit 3 sets the light projection period T to the preset minimum light projection period Tmin, stores the minimum light projection period Tmin in the subsequent step P28, and proceeds to step P8. return,
After that, the detection operation is performed in the same manner as described above. As a result, the light projecting cycle T starts again from the state where the light projecting cycle T is set to a short time. Therefore, even when the light projecting cycle T is set to be long each time the interference light is detected, the light projecting cycle T becomes infinitely long. Disappears.

According to the present embodiment as described above, the positive signal detection circuit 6 and the negative signal detection circuit 7 are provided, and the control circuit 3 outputs signals from these detection circuits 6 and 7 at the output start timing of the light projection pulse Sp. In response to the detection signal, the output start timing of the light projection pulse Sp at that time is delayed by delay time t or delay time 0.5t, and the subsequent light projection cycle T is delayed by the delay time t at that time.
Alternatively, the new projection period is set by adding 0.5t, so that the detection operation can be performed after delaying the required minimum time according to the state of the incident interference light. Even in a use environment in which light is frequently incident, it is possible to catch a gap between the interference lights and perform a detection operation quickly and reliably without waiting unnecessarily long, and it is possible to improve the interference prevention rate as a whole.

FIG. 5 shows a second embodiment of the present invention. Hereinafter, parts different from the first embodiment will be described. That is, in the first embodiment, this is the light projecting period T corresponding to the detection signal Sa or Sb every time the interference light is detected at the output start timing of the light projecting pulse Sp.
Is increased by t or 0.5t to perform the subsequent light projecting operation. When the interference light is not detected, the light projecting cycle T is shortened so that the light projecting cycle is constantly changed. The configuration is different.

In the control circuit 3 of this embodiment, the positive signal detection circuit 6 detects the detection signal Sa or the negative signal detection circuit 7 detects the detection signal Sb at the output start timing of the light projection pulse Sp.
Is not input, that is, when the interference light is not detected, the projection cycle T at that time is set as a new projection cycle T (= T-ta) shortened by the time ta. There is.

When the detection signal Sa is input at the output start timing of the light projecting pulse Sp, the control circuit 3 immediately stops the light projecting pulse Sp and outputs the first signal.
Delay time 3 which is obtained by multiplying the above-mentioned time ta by 3
The output start timing of the next light projection pulse Sp is delayed by ta, and the delay time 3t is added to the projection cycle T up to that point.
A new light projection period T (= T + 3ta) to which a is added is set.

When the detection signal Sb is input at the output start timing of the light projecting pulse Sp, the control circuit 3 immediately stops the light projecting pulse Sp, and the above-mentioned time ta as the second delay time. Delay time 2t
The output start timing of the next light emitting pulse Sp is delayed by a, and the delay time 2ta is added to the light emitting cycle T until then.
A new projection period T (= T + 2ta) is added. The delay time 3ta at this time is preset as a value corresponding to the delay time t corresponding to the first delay time in the first embodiment.

With such a configuration, as shown in FIG. 5, for example, when the interference light is not detected at the output start timing of the first light projection pulse Sp1, that is, the positive signal detection circuit 6 and the negative signal detection are performed. When none of the circuits 7 outputs the detection signal Sa or Sb, the control circuit 3 sets a new light projection cycle T1 in which the next and subsequent light projection cycles T are shortened by the time ta.

If the interference light is not detected again when the second light projecting pulse Sp2 is output after the light projecting cycle T1 has elapsed, the control circuit 3 sets the light projecting cycle T for a time ta. It is set as a shortened new projection period (T1-ta), and when the projection period (T1-ta) elapses, the output of the third projection pulse Sp3 is started. At this time, for example, when the detection signal Sa is output from the positive signal detection circuit 6, that is, when the interference light A is incident, the control circuit 3 stops the output of the third light projection pulse Sp3 and , The light emitting cycle T from the next time onward is delayed by 3ta with respect to the light emitting cycle (T1-ta) set at that time.
Is newly set as the light projection cycle T2 (= T1 + 2ta), and when the delay time 3ta elapses, the fourth light projection pulse Sp4 is output.

At this time, for example, the fourth projection pulse S
When the interference light is not detected with respect to the output of p4, the projection period T is not shortened by the time ta as described above, and the projection period T2 set previously is maintained. This is because after the interference light is detected by the output of the third light emitting pulse Sp3, the once light emitting cycle has already been set to T2 at the time of the output of the fourth light emitting pulse Sp4. Regarding the output of the optical pulse Sp5, the light projecting period T is not changed again even when the interference light is not detected.

Now, when the light projecting period T2 elapses after the output of the fourth light projecting pulse Sp4, the control circuit 3 starts outputting the fifth light projecting pulse Sp5. Then, at this time, when the detection signal Sb is output from the negative signal detection circuit 7, that is, when the interference light B is incident, the control circuit 3 stops the output of the fifth light projection pulse Sp5 and , The light emitting cycle T3 from the next time onward is the light emitting cycle T3 obtained by adding the delay time 2ta to the light emitting cycle T2 set at that time.
(= T2 + 2ta) is newly set, and the delay time is 2t.
When a has passed, the sixth light emitting pulse Sp6 is output.

Even when the interference light is not detected at the output start timing of the sixth light emitting pulse Sp6, the light emitting cycle is not changed twice as described above, so that when the light emitting cycle T3 elapses, 7th light emission pulse S
p7 is output. The output start timing of the next light projection pulse Sp is the new light projection cycle T.
4 (= T3-ta). Thereafter, the detection operation and the interference prevention operation are performed by the control circuit 3 in the same manner as described above.

Note that the control circuit 3 changes the light projecting cycle T one after another as described above, and when the light projecting cycle T to be set becomes a long time exceeding the upper limit value Tmax while it is being changed. Is set to the lower limit value Tmin for the projection cycle T at that time, and the projection cycle T to be set is set.
When the time becomes shorter than the lower limit value Tmin, the light projection period T at that time is set to the upper limit value Tmax.

According to the present embodiment as described above, the same effect as that of the first embodiment can be obtained, and in addition, the projection period T
Is frequently changed between Tmin and Tmax, the probability of being synchronized with the projection cycle of the photoelectric switch of another automated guided vehicle can be reduced, and a more reliable detection operation can be performed. As a result, it is possible to improve the interference prevention rate as a whole.

FIG. 6 shows a third embodiment of the present invention. Hereinafter, parts different from the first embodiment will be described. That is, in the first embodiment, this is the light projecting period T corresponding to the detection signal Sa or Sb every time the interference light is detected at the output start timing of the light projecting pulse Sp.
In the present embodiment, the light projecting period T is set to a constant value as the basic light projecting period T, and the interference light is detected. The output of the light projecting pulse Sp at that time is immediately stopped only at that time, and the output of the next light projecting pulse Sp is delayed by a predetermined delay time t or 0.5t from that time point and output. .

For example, in FIG. 6, the control circuit 3 is
1st light emission pulse Sp1, 2nd light emission pulse Sp2
Since the interference light was not detected at the time of outputting
The third light projection pulse Sp3 is output at the basic light projection cycle T. When the detection signal Sa is input from the positive signal detection circuit 6 at the output start timing of the third light projecting pulse Sp3, the control circuit 3 causes the light projecting pulse Sp to be output.
The output of No. 3 is immediately stopped, delayed by the first delay time t, and the next fourth projection pulse Sp4 is output. Then, when the interference light is not detected at the output start timing of the light projection pulse Sp4, the control circuit 3 again outputs the next fifth light projection pulse Sp5 in the basic light projection cycle T.

When the detection signal Sb is input from the negative signal output circuit 7 at the output start timing of the fifth light emitting pulse Sp5, the control circuit 3 outputs the fifth light emitting pulse Sp5. Is immediately stopped, the second delay time is delayed by 0.5 t, and the sixth light projection pulse Sp6 is output. When the interference light is not detected at the output start timing of the light projection pulse Sp6, the control circuit 3
Again outputs the seventh light-emission pulse Sp7 in the basic light-emission cycle T. Therefore, also with this embodiment, the same effect as that of the first embodiment can be obtained.

In each of the above embodiments, the first extension time is time t and the second delay time is half the time 0.5t, or the first delay time is 3ta.
Although the case where the second delay time is set to the time 2ta has been described, the present invention is not limited to this, and the second delay time may be set in an appropriate relationship as long as it is set shorter than the first delay time. .

In each of the above embodiments, the detection of the object in the detection area is judged by one-time detection, and the object detection signal Sx is output. However, the present invention is not limited to this.
It is also possible to adopt a configuration in which the object detection signal is output by determining the detection state that has been repeated a plurality of times by analog integration or digital integration.

[0055]

As described above, in the photoelectric switch of the present invention, the first and second detection circuits are provided and the first and second detection signals are detected when the signal from the amplifier circuit is positive or negative. When the first or second detection circuit is outputting a detection signal at the projection start timing by the projection pulse, the projection control means stops the projection pulse output at that time, and The first delay time,
Alternatively, the light projecting pulse is output after being delayed by the second delay time which is shorter than the first delay time. This makes it possible to set the output start timing of the next light emitting pulse without unnecessarily delaying it in a state where the interference light is incident on the light receiving element at the light emitting start timing of the light emitting pulse. , The detection operation can be performed efficiently by effectively utilizing the non-reception period of the interference light,
It has an excellent effect that the interference prevention rate can be improved as a whole.

[Brief description of the drawings]

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

FIG. 2 is a flowchart of a detection program (No. 1)

FIG. 3 is a flowchart of a detection program (No. 2)

FIG. 4 is a time chart showing a signal output state of each part.

FIG. 5 is a view corresponding to FIG. 4 showing a second embodiment of the present invention.

FIG. 6 is a view corresponding to FIG. 4, showing a third embodiment of the present invention.

[Explanation of symbols]

1 is a light emitting diode (light emitting element), 2 is a light emitting circuit, 3 is a control circuit ( light receiving means, determination means, light emitting control means), 4 is a photodiode (light receiving element), 5 is an amplifier circuit, and 6 is positive. A signal detection circuit (first detection circuit), 7 is a negative signal detection circuit (second detection circuit), and 8 is an output circuit.

Claims (1)

(57) [Claims] 1. A light projecting circuit for causing a light projecting element to perform a light projecting operation based on a periodic light projecting pulse given from a light projecting control means, and a signal received by a light receiving element is inputted via an amplifier circuit. A light receiving means for performing synchronous detection based on a synchronizing signal corresponding to the light emitting pulse, and an output signal from the light receiving means
A first detection circuit for detecting a positive signal of a predetermined level or higher among the outputs from the amplification circuit and inputting it to the light emission control means. A second detection circuit for detecting a negative signal of a predetermined level or more out of the output from the amplifier circuit and inputting the negative signal to the light projecting control means, wherein the light projecting control means When the first detection circuit is outputting the detection signal at the output start timing, the output of the light emitting pulse at that time is stopped, and the light emitting pulse is output with a delay of the first delay time. When the second detection circuit is outputting the detection signal at the pulse output start timing, the output of the light projection pulse at that time is stopped, and the second delay shorter than the first delay time Photoelectric switch, characterized in that only delays between being configured to output a light projection pulse.