JPH02202715A - Detection switch - Google Patents

Abstract

PURPOSE:To diagnose the trouble of an output circuit by comparing the output with the input of the output circuit via a comparator and using the result of comparison as a trouble diagnostic signal. CONSTITUTION:A light projecting element 2 produces the optical signals of the same waveform with a pulse signal received from an oscillation circuit 1. The light of the optical signal is reflected by a detected object 10 and received by a photodetecting element 3. The output signal of the element 3 is inputted to an integration circuit 5 via an amplifier circuit 4, and an integrated signal C is outputted. A comparator 6 compares the signal C with the threshold level and an H signal (d) is outputted when the signal C is higher than the threshold level. In other words, the output signal (d) is set at H when the object 10 is detected. While the output of a comparator 11 is set at L and no trouble detection output is transmitted since the output of an output circuit 7 is turned on and set at L. However the output of the circuit 7 is turned on and set at L in case an output element is turned on due to its destruction. In such a case, the output of the comparator 6 is also set at L with absence of the object 10 and therefore the comparator 11 outputs the trouble detection output (i) of H. Then a trouble pilot lamp 12 is also turned on.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to detection switches such as photoelectric switches, proximity switches, pressure switches, and ultrasonic switches.

(B) Conventional technology In general, a detection switch consists of a detection circuit that obtains a detection signal that changes in an analog manner depending on the detection target, a comparator that compares this detection signal with a predetermined reference value, and an ON state according to the output of this comparator. It is equipped with an output circuit including an output element that operates OFF/OFF, and turns ON10F depending on the presence or absence of a detection target.
Outputs F signal. A specific example of a conventional detection switch of this type will be explained using a modulated light photoelectric switch shown in FIG.

This photoelectric switch uses an oscillation circuit l that generates a pulse signal.
, 1. A light projecting element 2 that emits pulsed light in response to the pulse signal from the oscillation circuit 1. A light receiving element 3 that receives the pulsed light from the light projecting element 2 reflected by the detection object 10.
, an amplifier circuit 4 that amplifies the received light signal, an integration circuit 5 that integrates the pulse signal that is the output of the amplifier circuit 4, and this integration circuit 5.
a comparator 6 that compares an analog signal corresponding to the detected object output from the threshold level (reference signal); an output circuit 7 that outputs a signal according to the comparison result;
It consists of an operation indicator light 8 and a power supply circuit 9. The output circuit 7 includes an output transistor 71 as shown in FIG.
In this photoelectric switch, the oscillation circuit 1 emits a waveform pulse signal shown in FIG. 8A, and the light emitter 2 emits an optical signal having the same waveform. When the detection object 10 is present, light is reflected by the detection object 10 and enters the light receiving element 3 . The waveform of the light-receiving signal that has passed through the amplifier circuit 4 is shown in FIG. 8b. That is, when a detection object exists, a number of pulses corresponding to the size of the object are input from the amplifier circuit 4 to the integration circuit 5. The integrating circuit 5 integrates the input pulse signal, and its output waveform becomes C in FIG. The comparator 6 compares this integral output with a threshold level (see C in Figure 8), and if the detection signal exceeds the threshold level, the comparator 6 outputs a high signal as shown in d in Figure 8. Output. In response, the output circuit 7 outputs ONL (eighth
(see C in the figure), the operation indicator light 8 also lights up.

(c) Problems to be Solved by the Invention In the output circuit of the conventional photoelectric switch described above, when an excessive surge is applied, the Zener diode 72 cannot absorb it completely, and the voltage exceeding the withstand voltage of the transistor 71 is applied to the transistor 71. This may cause the transistor 71 to be destroyed. The output terminal and the power supply terminal are terminals that go out to the outside of the photoelectric switch, and are parts to which external surges are likely to be applied. Surge absorption is possible by inserting and connecting a capacitor to the power supply terminal, but since the output terminal is a switching device, a capacitor cannot be used, and surge absorption must be done by a Zener diode. If a surge exceeds the capacity of the
As described above, destruction of the transistor occurs. FIG. 8e shows a case in which the output transistor is normal, and the ON10 FF state of the output transistor changes in accordance with the output that switches and changes depending on the presence or absence of a detection object. f in FIG. 8 shows the case where the output transistor is destroyed at time A. In this case, after time A, regardless of whether there is any detected object,
The same signal will be output. Therefore, in this case, it is impossible to distinguish between normal object detection and a failure, and there is a risk that production lines using such photoelectric switches may produce defective products or, in some cases, lead to accidents that threaten human life. Ta.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a detection switch capable of turning on and off a failure in an output circuit.

(d) Means and operation for solving the problems The detection switch of the present invention includes a detection circuit that obtains a detection signal that changes in an analog manner depending on the detection target, and a comparator that compares the detection signal with a predetermined reference signal. , an output circuit including an output element that operates ON/OFF in response to the output of this comparator, and a comparison circuit that compares the output of this output circuit with the output of the comparator and outputs the comparison result as a failure diagnosis output. has been done.

In this detection switch, if the output element of the output circuit is operating normally, the output element will also be turned on by the output of the detected object of the comparator, and the input to the comparison circuit will be the expected logic, indicating a "failure". does not output a signal indicating this. However, if the output element is turned ON due to a surge, etc., even if the comparator does not detect the detection object, the output element of the output circuit is ON, and the comparison circuit becomes an input to an unplanned logic, that is, a failure logic, and outputs a signal indicating a failure. do.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a circuit block diagram of a photoelectric switch showing one embodiment of the present invention. This photoelectric switch has an oscillation circuit 1
, light emitting element 2, light receiving element 3, amplifier circuit 4, integrating circuit 5,
It includes a comparator 6, an output circuit 7, an operation indicator light 8, and a power supply circuit 9.

This configuration is similar to the photoelectric switch shown in FIG. However, this photoelectric switch includes a comparison circuit 11 that compares the output of the comparator 6 and the output of the output circuit 7, and a failure indicator light 12.

FIG. 2 shows operating waveforms of the photoelectric switch of this embodiment. A to e in FIG. 2 are cases in which the device is operating normally, and the operation is the same as that shown in FIG. 6. Furthermore, when a detection object is detected, the output of the comparator 6 becomes "high" as shown in d of FIG. The output becomes low and no fault diagnosis output is issued.However, if the output element is turned ON due to destruction, A of r in Fig. 2
As shown in the dot, the output of the output circuit 7 becomes ON (low). In this case, the output of the comparator 6 is also low since there is no detected object, so the comparator circuit 11 outputs a high fault diagnosis output i (see i in FIG. 2) and lights up the fault indicator lamp 12.

FIG. 3 shows a specific circuit example of the output circuit 7 and comparison circuit 11 of the photoelectric switch of this embodiment.

In the figure, 71 is an output transistor, and 72 is a Zener diode for absorbing surges. The output d of the comparator 6 is applied to the base of an output transistor 71 via a resistor 73.

In the comparator circuit 11, a current source 111 is connected to the collector of the output transistor 71, that is, an output terminal via a diode 112, and a current source 111 is connected to the collector of the output transistor 71, that is, the output terminal via a diode 113.
It is connected to the base of the transistor 114, the emitter of the transistor 114 is connected to the 0 line, and the collector is connected to one end of the exclusive 0R115. Also, the output d of the comparator 6 is exclusive 0R11
5 to the other input terminal.

When the output of comparator 6 is low, output transistor 7
1 is normal, the output transistor 7 is OFF and the output e is high. Therefore, the current of current source 111 is
It does not flow to the diode 112, but flows to the transistor 114 via the diode 113, and the transistor 114 is turned on.
becomes. Therefore, the human power of the exclusive 0R115 is low, low, and the output is also low. Further, when the output of the comparator 6 is high and the output transistor 71 is normal, the transistor 7e is on and the output e is low, and the current from the current source 111 flows to the transistor 71 via the diode 112. Therefore, transistor 114 is 0FFL, exclusive OR
Low and high signals are input to the input terminal of the circuit. Therefore, its output will be low. Output low means no fault.

However, the output transistor 71 was destroyed and turned on. In this case, when the comparator output is low, transistor 71 is ON and transistor 114 is OFF, which is exclusive OR.
The input of the circuit 115 is low-byed, and its output becomes high. In other words, a fault diagnosis output is output.

FIG. 4 is a circuit block diagram of a photoelectric switch showing another embodiment of the present invention. This photoelectric switch includes, in addition to what is shown in FIG. 1, a comparator 1113 and an OR circuit 14 that derives the output of the comparison circuit 12 or the comparator 1113 as a fault diagnosis output.

The comparator I[13 is a window comparator, and as shown in FIG. Threshold level ■A is set to a value that is in between.

In this embodiment of the photoelectric switch, when the amount of received light decreases due to fogging of the lens, for example, the output of the integrating circuit 5 decreases, and the output of the comparator [13.19. It becomes lower than . In this case, the comparator ■6 which is the output operation level
This results in an unstable operating condition because the voltage is close to the threshold level. Therefore, when the output of the integrating circuit 5 enters between the VTR and VTLO, the comparator l113 outputs a high signal (see j in FIG. 5), and outputs the failure diagnosis output k from the OR circuit 14 (see j in FIG. 5). ). On the other hand, if the output transistor of the output circuit 7 is destroyed, the comparator circuit 1
1 outputs a high signal (see i in FIG. 5). The OR circuit 14 is used when the detection signal is weak and falls between
1 outputs high, that is, when the output transistor of the output circuit 7 is destroyed, a failure diagnosis output is output.

This embodiment of the photoelectric switch does not only reduce the detection signal due to changes in the optical system, such as cloudiness, but also
It is also possible to monitor the deterioration of amplifier circuits, integration circuits, and oscillation circuits over time. Furthermore, since it is also possible to monitor the destruction of the output circuit, it is possible to almost completely determine the operating state of the photoelectric switch.

Although the above embodiment has been described using a photoelectric switch as an example, the present invention is not limited to photoelectric switches, but can also be applied to detection switches such as proximity paper, ultrasonic switches, pressure switches, and the like.

(F) Effects of the Invention According to this invention, the output of the output circuit and 1. The input of the output circuit is compared with the comparison circuit, and the comparison result is used as a failure diagnosis signal, so if the output element is destroyed due to a surge, etc., the failure diagnosis signal allows immediate measures such as stopping the machine. , the safety of the production line etc. will be improved.

[Brief explanation of the drawing]

Fig. 1 is a circuit block diagram of a photoelectric switch showing an embodiment of the present invention, Fig. 2 is a waveform time chart of each part to explain the operation of the photoelectric switch, and Fig. 3 is an output of the photoelectric switch. FIG. 4 is a circuit diagram showing a specific example of a circuit and a comparison circuit. FIG. 4 is a circuit block diagram of a photoelectric switch showing another embodiment of the present invention. FIG. 5 is a waveform of each part to explain the operation of the photoelectric switch. Time chart, Figure 6 is a circuit block diagram showing a conventional photoelectric switch, Figure 7 is a specific circuit diagram of the output circuit of the same photoelectric switch, and Figure 8 is for explaining the operation of the conventional photoelectric switch. This is a waveform time chart 1- for each part. 3: Light receiving element, 4: Amplifying circuit, 5: Integrating circuit,
6: Comparator, 7: Output circuit,
11: Comparison circuit. Patent Applicant Tateishi Electric Co., Ltd. Agent Patent Attorney Shigeru Nakamura

Claims (1)

[Claims] (1) A detection circuit that obtains a detection signal that changes in an analog manner depending on the detection target, a comparator that compares the detection signal with a predetermined reference signal, and an output element that turns ON/OFF according to the output of this comparator. A detection switch comprising: an output circuit including an output circuit; and a comparison circuit that compares the output of the output circuit with the output of the comparator and outputs the comparison result as a failure diagnosis output.