JP3055717B2 - Output circuit of 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 an output circuit of a photoelectric switch for outputting detection signals having different levels depending on the presence or absence of an object.

[0002]

2. Description of the Related Art In general, a photoelectric switch is provided with a light receiver so as to receive light from a light emitter, and when light from the light emitter is blocked by an object, the amount of light incident on the light receiver changes. And outputs a detection signal having a voltage level of "H" level or "L" level.

In order to reduce the size of the light emitter and the light receiver, a controller for transmitting and receiving signals to and from the light emitter and the light receiver via a signal transmission path is provided. And a configuration in which a detection signal from a light receiver is received. This allows
A controller installed at a place distant from the light receiving device and the light emitting device may perform control of the device based on the "H" level or "L" level detection signal obtained from the light receiving device via the signal transmission path. it can.

[0004]

However, in such a photoelectric switch, the transmission of the detection signal can be carried out with a simple structure, but on the other hand, a failure such as a failure of the photodetector or a short circuit or disconnection of the signal transmission line occurs. In such a case, there is a possibility that the signal output state at the receiving end of the signal transmission path is fixed to either the “H” level or the “L” level. And if you are using the photoelectric switch for safety purposes,
If such a failure state occurs, there is a risk that the failure may occur on the dangerous side, and there is a problem that the reliability for safety use is lacking.

In the conventional configuration, even if the signal output state at the receiving end of the signal transmission path is fixed at either the "H" level or the "L" level due to such a failure, the state is not changed. Since it is not possible to determine whether or not it is in a failure state, there is a possibility that the discovery of the failure may be delayed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to determine whether a signal reception state at a receiving end of a signal transmission path is normal or not and to ensure a reliable detection state. Another object of the present invention is to provide an output circuit of a photoelectric switch that can quickly detect a failure.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to a photoelectric switch which outputs a detection signal having a different level depending on the presence or absence of an object, and a modulation system comprising a pulse train having a different duty ratio according to the level of the detection signal. A modulation unit that outputs a signal, a signal transmission line for transmitting the modulation signal, a demodulation unit that demodulates the modulation signal provided via the signal transmission line and extracts a detection signal, and the signal transmission line And an abnormality judging unit for detecting a pulse train of the modulation signal given via the control unit and judging an abnormal state without detecting the pulse train.

[0008]

According to the output circuit of the photoelectric switch of the present invention, the detection signal output from the photoelectric switch is modulated into a pulse train signal having a different duty ratio by the modulator in accordance with the level, and is output to the signal transmission line. . On the contrary,
The demodulation unit demodulates the modulation signal given through the signal transmission path and extracts a detection signal. At this time, the abnormality determination unit detects the pulse train of the modulation signal at the same time. judge. As a result, occurrence of a failure such as disconnection or short circuit of the signal line, or an abnormal state due to a failure of the photoelectric switch or the like can be quickly detected, and occurrence of a malfunction can be prevented as much as possible.

[0009]

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1 showing the electrical configuration, the photoelectric switch is composed of a light emitting unit and a light receiving unit 1 (not shown), and the light receiving unit 1 is connected to a controller 3 via a signal line 2 serving as a signal transmission path.

The light receiving unit 1 includes a detection circuit 4, a self-diagnosis circuit 5, and a modulation circuit 6 as a modulation unit.
The detection circuit 4 receives light from a projector (not shown) and outputs an “H” level voltage signal as a detection signal when an object is detected, and an “L” level voltage signal when no object is detected. The self-diagnosis circuit 5 outputs an “H” level signal when the operation state of the light receiving unit 1 is normal,
When an abnormal state is diagnosed, an "L" level signal is output.

In the modulation circuit 6, two input terminals of the XOR circuit 7 are connected to an output terminal of the pulse generation circuit 8 and an output terminal of the detection circuit 4, respectively. AND circuit 9-2
The two input terminals are connected to the output terminal of the XOR circuit 7 and the output terminal of the self-diagnosis circuit 5, respectively. The output terminal of the AND circuit 9 is connected to the signal line 2. The pulse generation circuit 8 outputs a pulse train having a duty ratio of, for example, 10%. The output terminal of the self-diagnosis circuit 5 is connected to a DC power supply terminal 12 via a light emitting diode 10 for abnormality notification and a resistor 11.

Next, in the controller 3, the signal line 2
Is connected to an input terminal a of a detection signal demodulation circuit 13 as a demodulation unit and to an input terminal b of a pulse train detection circuit 14 as an abnormality determination unit. In the detection signal demodulation circuit 13, the input terminal a is connected to a resistor 13a and a capacitor 13b.
Is connected to the input terminal of the comparator 13c via an integrating circuit S composed of The detection signal demodulation circuit 13 outputs an "H" level signal by the comparator 13c when the signal supplied to the input terminal a exceeds a predetermined level after passing through the integration circuit S. .

In the pulse train detecting circuit 14, an input terminal b is connected to a detecting circuit 14c via a differentiating circuit D comprising a capacitor 14a and a resistor 14b. The detection circuit 14c has a configuration using a retrigger type one-shot multivibrator, and outputs a signal of “H” level for a certain period of time when a pulse signal is given from the differentiation circuit D,
When a pulse signal is supplied even during the output period of the “H” level signal, the output state of the “H” level signal is held again for a fixed time from that point.

The two input terminals of the AND circuit 15 are connected to the output terminal of the comparator 13c and the output terminal of the detection circuit 14c, respectively. The output terminal of the AND circuit 15 is connected to the output terminals 3a, 3a via an output relay 16 for outputting a detection signal. The output terminal of the detection circuit 14c is
It is connected to the DC power supply terminal 12 via a light emitting diode 17 and a resistor 18 for abnormality notification.

Next, the operation of this embodiment will be described with reference to FIG.

Now, the detection signal of the detection circuit 4 is shown in FIG.
The following describes an example of a case where it changes as shown in FIG.
The pulse generation circuit 8 has a duty ratio of 10% as described above.
(See FIG. 2 (c)).
When the light receiving unit 1 is operating normally, the self-diagnosis circuit 5 outputs an "H" level signal (see FIG. 2B). Note that the self-diagnosis circuit 5 is "H"
While the signal of the level is being output, the light emitting diode 10 is off.

In the modulation circuit 6, the XOR circuit 7 includes 2
Since the result of calculating the exclusive OR of the signals applied to the two input terminals is used as the output signal, when the level of the detection signal of the detection circuit 4 is "L" level, the pulse train signal from the pulse generation circuit 8 is output as it is. When the level of the detection signal is "H" level, the pulse train signal is inverted and outputted, that is, outputted as a pulse train signal having a duty ratio of 90%. Since the AND circuit 9 receives the “H” level signal from the self-diagnosis circuit 5, the output of the XOR circuit 7 is output as it is to the signal line 2 as a modulation signal (see FIG. 2D).

Next, in the controller 3, the detection signal demodulation circuit 13 demodulates the detection signal of the detection circuit 4 in accordance with the modulation signal (see FIG. 2 (e)) given through the signal line 2. That is, the pulse train signal input as the modulation signal is integrated by the integrating circuit S. When the duty ratio of the pulse train signal is 10%, the terminal voltage of the capacitor 13b is low, so that the comparator 13c outputs "L" level, When the duty ratio is 90%, the capacitor 13b
Since the terminal voltage of the comparator 13c becomes sufficiently high, the comparator 13c outputs an "H" level (see FIG. 6F). Thereby, a demodulated signal corresponding to the detection signal of the detection circuit 4 is extracted.

On the other hand, in the pulse train detection circuit 14,
In accordance with the modulation signal supplied via the signal line 2, the differentiating circuit D makes a pulse signal irrelevant to the duty ratio of the pulse train signal (see FIG. 2 (g)), and the pulse signal is used as a trigger signal to keep the detection circuit 14c constant. The signal at the “H” level is output during the period. In this case, the fixed period during which the “H” level signal is output is set longer than the period of the pulse signal. Therefore, during the period when the pulse signal is supplied from the differentiating circuit D, the detection circuit 14c is retriggered. ,
The output state of the "H" level signal is held (see FIG. 3H).

As a result, the AND circuit 15 operates the comparator 1
The output signal from 3c is output as it is, and as a result, an output corresponding to the detection signal of the detection circuit 4 is given to the output terminal 3a via the output relay 16 (see FIG. 2 (i)). still,
In this state, since the output state of the detection circuit 14c is at the “H” level, the light emitting diode 17 for abnormality notification is in the off state.

Next, when an abnormality occurs in the light receiving unit 1, the self-diagnosis circuit 5 detects the abnormality and outputs an "L" level signal (see FIG. 2B).
Then, the light emitting diode 10 is supplied with power from the DC power supply terminal 12 and lights up, thereby reporting an abnormal state. As a result, the output of the AND circuit 9 is fixed at the “L” level (see FIG. 4D), and the transmission state of the signal line 2 also becomes the “L” level.

In the controller 3, the pulse signal is not supplied to the pulse train detection circuit 14, so that
The output state of the detection circuit 14c becomes "L" level (see FIG. 3H). Further, since no modulation signal is input to the detection signal demodulation circuit 13 as well, the output of the comparator 13c becomes "L" level, and the output of the output terminal 3a of the controller 3 is stopped.

On the other hand, since the output of the detection circuit 14c is at the "L" level, the light emitting diode 17 is supplied with power from the DC power supply terminal 12, lights up, and reports an abnormal state.
In such a state, the light emitting diode 10 is also lit together with the light emitting diode 17, so the controller 3
It can be understood that the abnormality occurrence detected on the side is caused by the abnormality occurrence in the light receiving unit 1.

Next, a case where the signal line 2 is short-circuited and fixed at the "H" level irrespective of the presence or absence of the modulation signal while the function in the light receiving unit 1 is normally maintained will be described. That is, in this state, the input to the controller 3 is always at the “H” level (see FIG. 2E). Therefore,
The detection signal demodulation circuit 13 outputs an "H" level signal indicating the detection state (see FIG. 3 (f)).

On the other hand, since the pulse train signal is not input to the pulse train detection circuit 14, the output state of the detection circuit 14c becomes "L" level (see FIG. 2 (h)), and the light emitting diode 17 is turned on (see FIG. 2 (h)). At the same time, the output of the AND circuit 15 is set to the “L” level, and the output of the controller 3 is set to the “L” level (see FIG. 11I).

Thus, since only the light emitting diode 17 of the controller 3 is turned on, it can be seen that an abnormality has occurred in the signal line 2.

When the signal line 2 is disconnected, the input to the controller 3 is fixed at the "L" level, and the pulse train detection circuit 14 sets the "L" level in the same manner as in the case of the short circuit described above. A level signal is output to set the output of the controller 3 to the “L” level, and an abnormal state is notified by lighting the light emitting diode 17.

According to the present embodiment, the detection signal transmitted from the light receiving unit 1 to the controller 3 via the signal line 2 is a pulse train signal modulated by the modulation circuit 6, so that the controller 3 detects the pulse train. If not, it is possible to detect that an abnormality has occurred, so that it is possible to determine whether the signal reception state is normal and to ensure a reliable detection state, and to quickly detect an abnormal state such as a failure. Can be found in

According to the present embodiment, the light receiving unit 1
The self-diagnosis circuit 5 is provided to stop the output of the detection signal when the occurrence of an abnormality in the light receiving unit 1 is detected and to notify the abnormality by the light emitting diode 10. Therefore, when the controller 3 detects the abnormality, It is possible to distinguish between an abnormality of the light receiving unit 1 and an abnormality of the signal line 2, and therefore, it is possible to easily and quickly identify an abnormal location.

[0031]

As described above, according to the output circuit of the photoelectric switch of the present invention, the detection signal is output by the modulation section as a modulation signal of a pulse train having a different duty ratio in accordance with the level, and the abnormality is determined by the abnormality determination section. Since the abnormal state is determined when the pulse train of the modulation signal supplied via the signal transmission path is in the non-detection state, a signal whose level has been fixed due to an abnormality due to a failure or the like is input to the demodulation unit. In this case, there is an excellent effect that the abnormal state is determined by the abnormality determining unit and erroneous detection is eliminated, and that the occurrence of the abnormality can be quickly detected.

[Brief description of the drawings]

FIG. 1 is an electrical configuration diagram showing one embodiment of the present invention.

FIG. 2 is a time chart showing a signal output state of each unit.

[Explanation of symbols]

1 is a light receiving unit, 2 is a signal line (signal transmission line), 3 is a controller, 4 is a detection circuit, 5 is a self-diagnosis circuit, 6 is a modulation circuit (modulation unit), 7 is an XOR circuit, 8 is a pulse generation circuit, 9 is an AND circuit, 10 is a light emitting diode, 13 is a detection signal demodulation circuit (demodulation unit), 13c is a comparator, 14 is a pulse train detection circuit (abnormality judgment unit), 14c is a detection circuit,
5 is an AND circuit, and 17 is a light emitting diode.

Claims (1)

(57) [Claims] 1. A photoelectric switch for outputting a detection signal having a different level in accordance with the presence or absence of an object, a modulator for outputting a modulation signal comprising a pulse train having a different duty ratio in accordance with the level of the detection signal, and the modulation signal A signal transmission line for transmitting a signal, a demodulation unit that demodulates the modulation signal given through the signal transmission line and extracts a detection signal, and a pulse train of the modulation signal given through the signal transmission line An output circuit for a photoelectric switch, comprising: an abnormality determination unit that detects and determines an abnormal state when a pulse train is not detected.