JPH0520713B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention includes a light-emitting element and a light-receiving element, and emits pulsed light that is pulse-modulated from the light-emitting element, and reflects or transmits it to an object. The present invention relates to a light modulation type detection device such as a photoelectric switch or a photointerrupter that detects the presence or absence of an object by detecting the presence or absence of pulsed light incident on a light receiving element.

[Prior art]

Conventional optical modulation type detection devices photoelectrically convert the pulsed light projected from the light emitting element by being driven by a pulse drive signal using the light receiving element, and then amplify this photoelectrically converted pulse signal using an AC amplifier. It is generally known that sampling is performed using a sampling pulse synchronized with the pulse drive signal, and the signal is processed by a signal processing circuit to produce a detection signal. This type of light modulation type detection device has a configuration as shown in FIG. 6, for example, and its operation is as follows.

By receiving the pulse signal generated from the timing generation circuit 22, the light emitting element drive circuit 23
A light emission signal is output from. By receiving this light emission signal, the light emitting element 24 is pulse-driven.
Projects pulse-modulated light. This light may be blocked from entering the light receiving element 25 by the object S passing between the light emitting element 24 and the light receiving element 25 (in the case of a transmission type detection device), or it may be reflected by the object S and enter the light receiving element 25. incident (in the case of a reflective detection device). Therefore, the pulsed light incident on the light receiving element 25 is turned on and off by the passage of the object S. As a result, the pulsed light incident on the light receiving element 25 is photoelectrically converted by the light receiving element 25,
The signal photocurrent obtained by this photoelectric conversion is further converted into a voltage by a preamplifier 26. and,
The received light signal converted to this voltage is sent to the AC amplifier 2.
7 and input to the determination circuit 28. The received light signal whose waveform has been shaped by the determination circuit 28 is input to the signal processing circuit 29 shown in FIG.
Output through 0. Then, the presence or absence of the object S is determined based on this output.

However, in addition to the pulsed light from the light emitting element, DC or pulsed disturbance light may be incident on the light receiving element 25. As a result, in the conventional structure described above, as shown in FIG.
DC disturbance light is removed by the AC amplifier 27, and pulse disturbance light is removed by the signal processing circuit 29. However, if the disturbance light is very strong, the preamplifier 27 removes the disturbance light.
6's output is saturated, and the next stage AC amplifier 2
The situation is the same as when the signal is not transmitted to 7 and the light is blocked. In other words, the state is the same as when an object is detected by this strong disturbance light. This does not normally occur, but if strong ambient light is turned on and off intentionally or accidentally, it may lead to malfunctions such as an object detection signal being output even though there is no object. There is a risk.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned conventional problems, and is capable of detecting an object even when there is no object by turning strong disturbance light on and off intentionally or accidentally. The object of the present invention is to provide a light modulation type detection device that can prevent malfunctions that occur when a signal is output, and can improve the reliability of object detection.

[Structure of the invention]

In order to achieve the above object, the light modulation type detection device of the present invention uses a light receiving element to receive pulsed light projected from a light emitting element in synchronization with a pulse signal, and uses a light receiving signal obtained from the light receiving element to In a light modulation type detection device that detects an object intervening in the optical path between a light emitting element and a light receiving element, when the DC level of the incident light entering the light receiving element exceeds a certain value, this is detected and a saturation detection signal is generated. A signal processing circuit connected to the saturation detection circuit is provided, and when the saturation detection signal is input, the output of the signal processing circuit is converted into a direct current of the incident light incident on the light receiving element. Configure it to hold the level before it exceeds a certain value,
At the disturbance light detection timing between one light emission timing and the next light emission timing, even if the DC level of the incident light exceeds a certain value at the same time as pulsed disturbance light is detected, this is considered as DC disturbance light. Another feature of the present invention is that the light modulation type detection device is configured to be able to prevent malfunctions caused by strong disturbance light.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 to 5.

As shown in FIG. 1, the light modulation type detection device according to the present invention includes a timing generation circuit 1 that generates a pulse signal, a light emitting element drive circuit 2 that drives a light emitting element 3 in response to the pulse signal, and a light emitting element drive circuit 2 that drives a light emitting element 3 in response to the pulse signal. a light-emitting element 3 for projecting light, a light-receiving element 4 for receiving the pulsed light and photoelectrically converting it, a preamplifier 5 for converting the photocurrent of this light-receiving element 4 into voltage, an AC amplifier 6 for amplifying the output of this preamplifier 5, A determination circuit 7 that shapes the output of this AC amplifier 6 into a determination output IN1, a signal processing circuit 8 that samples the determination output IN1 of this determination circuit 7 and outputs a detection output, and detects the saturation of the preamplifier 5. The saturation detection circuit 9 outputs a saturation detection signal IN2, and an output circuit 10. As shown in FIG. 2, the preamplifier 5 includes an amplifier 11, a feedback resistor 12, and a feedback resistor 1.
It consists of two series clamp diodes 13, 13 connected in parallel to 2. Here, the clamp diode 13 is designed to clamp the signal amplitude when the received light signal is very strong, thereby preventing the amplifier 11 from becoming saturated to a certain extent. Further, as shown in FIG. 3, the saturation detection circuit 9 includes a diode 14, resistors 15, 16,
and an amplifier 17, which operates when the received light signal is strong enough to be clamped by the clamp diodes 13, 13, and outputs a saturation detection signal.
IN2 is input to a flip-flop 19 in the signal processing circuit 8, which will be described later. Further, the signal processing circuit 8 has two detection points A and B that are synchronized with the pulse signal of the timing generation circuit 1 and have different timings,
It is configured as shown in Figure 4. That is, two flip-flops 18 and 19 each take in and hold data at the detection points A and B, a shift register type digital integration circuit 20 (hereinafter simply referred to as shift register 20) that counts the same detection state, and this shift register. It consists of a control circuit 21 that controls the state of 20. This control circuit 21 includes three AND circuits 21a and 21b.
and 21c, and the shift register 20 consists of three flip-flops.
Further, the flip-flop 18 has an AND circuit 18a connected to its S (set) terminal.
One gate of this AND circuit 18a is connected to the determination circuit 7, and the other gate and the R (reset) terminal of the flip-flop 18 are connected to the timing generation circuit 1. The flip-flop 19 also has an AND circuit 19a connected to its S terminal.
One gate of this AND circuit 19a is OR circuit 1
The determination circuit 7 and the saturation detection circuit 9 are connected via 9b.
, the other gate and flip-flop 19 R
The terminal is connected to a timing generation circuit 1.
Here, the detection point A in this signal processing circuit 8 is a disturbance light detection point between a light emission timing and the next light emission timing, and the detection point B is an object detection point that coincides with the light emission timing. Further, the detection timing of the detection point A is the pulse signal c (sampling timing A) output from the timing generation circuit 1, and the detection timing of the detection point B is the pulse signal a output from the timing generation circuit 1. (sampling timing B).

In the above configuration, the pulse signal b of the timing generation circuit 1 causes the light emitting element drive circuit 2 to
A light emitting signal is output from the light emitting element 3 in synchronization with this signal b, and in response to this, pulsed light is projected from the light emitting element 3. Due to the passage of the object S between the light emitting element 3 and the light receiving element 4 and the disturbance light, the judgment output IN1 shown in FIG. 5b is obtained through the light receiving element 4, the preamplifier 5, the AC amplifier 6, and the judgment circuit 7. . This determination output IN1 is then input to the next stage signal processing circuit 8 shown in FIG. Here, the DC component and low frequency component of the disturbance light are removed by the AC amplifier 6, leaving only the high frequency component comparable to the signal. Also, when the ambient light is very strong,
A saturation detection signal IN2 shown in FIG. 5c is outputted from the saturation detection circuit 9 to the flip-flop 19.
From the timing generation circuit 1, the signals d, e,
Pulse signals a, c, d shown in h and a pulse signal e (not shown) are output, and among these, pulse signal a is set as sampling timing B above.
The pulse signal c is sent to one gate of the AND circuit 19a as the R terminal of the flip-flop 18 and the sampling timing A, and the pulse signal d is sent to one gate of the AND circuit 21a of the control circuit 21 as the clock pulse d. The pulse signal e is applied to the gate of flip-flop 1.
They are input to the R terminals of 9, respectively. Also,
The Q terminal of the flip-flop 18 outputs a signal shown in the figure f, and the flip-flop 19 outputs a signal shown in the figure g. In addition, cl (clock) in the shift register 20
A signal shown in the figure i is input to the terminal, a signal shown in the figure j is inputted from the AND circuit 21c in the control circuit 21, and a signal shown in the figure k is inputted from the AND circuit 21b.
The signals shown in are output respectively. Then, from the Q terminal of the final stage flip-flop of the shift register 20, the output shown in FIG.
(referred to as OUT) is output.

At sampling timing B at detection point B for object detection, if this device is a transmission type, as shown in FIG.
In other words, in the null state, the judgment output IN1 goes high in synchronization with sampling timing B, so the flip-flop 18 is in the set state.
Therefore, the Q terminal output is held at high level and the terminal output is held at low level. At this time, assuming that the output OUT of the shift register 20, that is, the output shown in FIG. 1, is at high level and the terminal output of the final stage flip-flop is at low level,
The AND circuit 21c outputs the output OUT of the shift register 20 when the clock pulse d is at high level.
is output, and since the output of the AND circuit 21b is always at a low level, the shift register 20 is in the set state, and this shift register 2
The output OUT of 0 is always held at a high level.
Therefore, this light modulation type detection device determines that there is no object.

When the object S is located between the light emitting element 3 and the light receiving element 4, the pulsed light from the light emitting element 3 is blocked by the object S. As a result, the light reception signal becomes low level, and the determination output IN1 becomes low level. Therefore, at sampling timing B, the flip-flop 18 is reset, and its Q terminal output becomes low level and its terminal output becomes high level.
Therefore, the output of the AND circuit 21c becomes low level, and the set signal to the shift register 20 becomes
It becomes "0". On the other hand, the AND circuit 21b remains at a low level while the output OUT of the shift register 20 is at a high level.
The data is shifted in response to the clock pulse d from the AND circuit 21a. shift register 20
The first flip-flop has shift register 2.
Since the output of the final stage of 0 is input, the shift register 2 is input to this first flip-flop.
When the output OUT of 0 is at a high level, a low level output is being input. Therefore, when the data is shifted by the number of stages of the shift register 20 (here, three times), the output of the shift register 20
OUT changes from high level to low level.
As a result, the AND circuit 21b outputs a high level when the clock pulse d is at a high level.
Since the output of the AND circuit 21b is input to the reset terminal of the shift register 20, the shift register 20 is held in the reset state. Thereby, this light modulation type detection device determines that the object S is present.

When disturbance light is incident on the light receiving element 4 when the object S is present, the judgment output IN1 becomes high level as when the pulsed light from the light receiving element 3 is received, but at the sampling timing A, the flip-flop Since the output of 19 becomes low level, the clock pulse d is cut off by the AND circuit 21a. Therefore, at sampling timing B, the judgment output IN1 is at a high level, and the flip-flop 18 is set.
Even if the Q terminal output becomes high level, AND
The output of circuit 21c remains at low level, and shift register 20 is not set. Therefore, the output OUT of the shift register 20, that is, the detection output does not change and the previous state is maintained. This results in
This prevents it from being determined that the object S does not exist even though the object S exists.

When the object S has passed, the light reception signal becomes high level again at sampling timing B, the judgment output IN1 also becomes high level, the flip-flop 18 is set, and its Q terminal output becomes high level and its terminal output becomes low level. Therefore, the output of the AND circuit 21b becomes low level, and the reset signal to the shift register 20 becomes "0". When the data is shifted by the number of stages of the shift register (three times here), the output OUT of the shift register 20 changes from low level to high level, a set signal is input to the set terminal of the shift register 20, and the output of the shift register 20 changes from low level to high level. is always maintained at a high level. Therefore, this light modulation type detection device determines that the object S has passed.

When disturbance light is incident on the light receiving element 4 in the absence of the object S, the following operation is performed. Before the disturbance light enters, flip-flop 1
8 has its Q terminal output at a high level, its terminal output at a low level, and flip-flop 19 has its terminal output at a high level. When disturbance light is incident here, if the disturbance light is pulsed disturbance light, the light reception signal is input to the signal processing circuit 8 through the AC amplifier 6 and the determination circuit 7.
At sampling timing A, the light reception signal is at a high level and the judgment output IN1 is at a high level, so the flip-flop 19 is set. Therefore, the terminal output becomes low level, and the clock pulse d is blocked by the AND circuit 21a. Therefore, even if the light reception signal becomes high level at sampling timing B, the flip-flop 18 is set, and its Q terminal output becomes high level, the output of the AND circuit 21c remains low level, so the shift register 20 does not operate. First, the output OUT, that is, the detection output does not change and the previous state is maintained. Therefore, such a light modulation type detection device is not affected by ambient light. In addition, in the case of DC or low frequency disturbance light,
The received light signal is blocked by the AC amplifier 6.

Here, if the preamplifier 5 becomes saturated due to the extremely strong disturbance light level, the judgment output IN1 becomes low level, but in this case, the saturation detection circuit 9 operates and outputs the saturation detection signal IN2. Therefore, at sampling timing A, the flip-flop 19 remains set. Therefore, as mentioned earlier, the AND circuit 2
1c remains at low level, the shift register 20 also does not operate, and the output of the shift register 20
OUT, that is, the detection output also does not change and the previous state is maintained. In this way, the output circuit 10 can provide the output shown in FIG. 1, which is not affected by normal disturbance light or very strong disturbance light.

〔Effect of the invention〕

As described above, the light modulation type detection device of the present invention has the following features:
A light modulation type in which a light receiving element receives pulsed light projected from a light emitting element in synchronization with a pulse signal, and detects an object intervening in the optical path between the light emitting element and the light receiving element using the light reception signal obtained from the light receiving element. The detection device is provided with a saturation detection circuit that detects when the DC level of the incident light entering the light receiving element exceeds a certain value and outputs a saturation detection signal, and a signal processing circuit connected to the saturation detection circuit. The circuit is configured such that when the saturation detection signal is input, the output of the signal processing circuit is maintained at a state before the DC level of the incident light incident on the light receiving element exceeds a certain value. be. This can prevent the light modulation type detection device from malfunctioning due to intentional or accidental ON/OFF of strong disturbance light. Then,
This has the effect of improving the reliability of object detection by the light modulation type detection device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Fig. 2 is a circuit diagram of the preamplifier in Fig. 1, Fig. 3 is a circuit diagram of the saturation detection circuit in Fig. 1, Fig. 4 is a circuit diagram of the signal processing circuit in Fig. 1, and Fig. 5 a to l are A timing chart showing the signals of each part shown in FIGS. 1 and 4, FIG. 6 a block diagram showing a conventional example, FIG. 7 a circuit diagram of the signal processing circuit shown in FIG. 6, and FIG. A to k are timing charts showing signals of each part shown in FIG. 1 is a timing generation circuit, 2 is a light emitting element drive circuit, 3 is a light emitting element, 4 is a light receiving element, 5 is a preamplifier, 6 is an AC amplifier, 7 is a determination circuit, 8 is a signal processing circuit, 9 is a saturation detection circuit, 10 is the output circuit, 1
8 and 19 are flip-flops, 20 is a shift register, and 21 is a control circuit.

Claims (1)

[Claims] 1. Optical modulation in which a light receiving element receives pulsed light projected from a light emitting element in synchronization with a pulse signal, and detects an object intervening in the optical path between the light emitting element and the light receiving element using the light reception signal obtained from the light receiving element. In the mold detection device, a saturation detection circuit is provided which detects when the DC level of the incident light incident on the light receiving element exceeds a certain value and outputs a saturation detection signal, and a signal connected to this saturation detection circuit is provided. The processing circuit is configured to maintain the output of the signal processing circuit at a state before the DC level of the incident light entering the light receiving element exceeds a certain value when the saturation detection signal is input. An optical modulation detection device characterized by: