JPH03129919A - Self-diagnostic circuit for photoelectric switch - Google Patents

Abstract

PURPOSE:To prevent a malfunction caused by noise by providing a counting means for counting a pulse in a first circuit in which a photodetecting signal is outputted in a first level or above, resetting it in a second circuit for outputting it in a second level or above, and outputting a self-diagnostic signal by a prescribed counting value. CONSTITUTION:When a photodetecting signal is in the first level or above, a signal B is outputted from a comparator 23, and the signal B is counted by a counter 28. Subsequently, when the photodetecting signal exceeds a stable photodetecting level, both the comparators 23, 24 output outputs B, C, and a counting pulse is inputted to the counter 28, but it is reset by a signal C each time. When the photodetecting signal is below a stable light incident level, the counter 28 is brought to counting and stepping again. By counting a prescribed pulse, the comparator 28 counts up, and outputs a self-diagnostic signal (alarm signal) D.

Description

[Detailed description of the invention] (b) Industrial application field The present invention relates to a self-diagnosis circuit for a photoelectric switch.

(B) Conventional technology Generally, as shown in FIG. 6, a photoelectric switch receives light with a light receiving element 1, converts the light into an electrical signal, and amplifies it with an amplifier 2. The output is input into a Schmitt circuit 3. When the input signal exceeds a predetermined incident light level, the Schmitt circuit 3 outputs a switching signal via the output amplifier 4. This type of photoelectric switch outputs only when the input signal exceeds the incident light level but is within a predetermined range in order to prevent unstable operation or malfunction if the input signal does not exceed a predetermined stable level. The self-diagnosis circuit includes a comparator 5 and a timer 7 that outputs its output via a gate 6 after a predetermined delay time. In this self-diagnosis circuit, when the detection object is moving slowly, it takes a long time to transition from the light blocking state to the light receiving state or from the light receiving state to the light blocking state, resulting in an unstable state for a while. In order to prevent a self-diagnosis output from being erroneously output during this time, the timer 7 is constituted by an integrating circuit with a large time constant.

Another conventional self-diagnosis circuit is shown in FIG.

In this self-diagnosis circuit, the output of the amplifier 12 is applied to a comparison circuit 13 for object detection and a comparison circuit 14 for level-down detection, and the output of the comparison circuit 13 is differentiated by a differentiation circuit 15 to the set input terminal of R3-FF17. The output of the comparison circuit 14 is differentiated by the differentiation circuit 16 and becomes R3-FF l
It is applied to the reset input terminal R of 7. R3-FF17
The Q output of is applied to the input end of the D-FF 18, and the output of the comparator circuit 13 is inverted by the impark 20 and input to the D-FF.
18 input terminals CP. In this self-diagnosis circuit, when the input signal exceeds the incident light level, the output of the comparator circuit 13 becomes high, and the differentiator circuit 15 outputs an impulse accordingly, setting R3-FF 17. If the input is normal, the input signal will soon exceed the stable level. As a result, the output of comparator circuit]4 goes high, and the output of comparator circuit]4 goes high, and
6 outputs an impulse and resets R3-FF17.

Therefore, the input signal eventually becomes lower than the incident light level,
The output of the comparator circuit 13 becomes low, the output of the inverter 20 rises to high, and the R3-FF17 is transferred to the D-FF18.
When the Q output of R3-FF 17 is read, the Q of R3-FF 17 is read.
The output is low, so the D-FF 18 does not output a self-diagnosis signal (alarm signal). However, when the level of the input signal is down and the input signal exceeds the incident light level, it eventually becomes lower than the incident light level without exceeding the stable level, R3-FF 17 is set by the output of the differentiating circuit 15. The Q output remains high without being reset. Therefore, when the input signal becomes lower than the incident light level and the output of the comparator circuit 13 drops from high to low, at that point the D-FF 18 reads the high Q output of R3/FFL7, and sends a high alarm signal to the alarm circuit 19. Output.

(c) Problems to be Solved by the Invention Among the conventional self-diagnosis circuits mentioned above, the former circuit uses a timer time constant to prevent an erroneous self-diagnosis output from being output when the detected object moves slowly. is increasing. However, when using a reflective photoelectric switch and detecting a small object moving at high speed, there is a problem in that self-diagnosis output is not output even in an unstable state (level down). .

On the other hand, the latter circuit solves the above problem, but
As shown in Figure 8, when the light reception signal on which noise is superimposed transitions from the stable light incident level to the light blocking level, once it falls below the human light level as shown by signal a, the light incident level is changed again by noise b. If it exceeds R, this noise b causes R
Since 3-FF 17 is sent and then not reset, there is a problem in that a false alarm signal is output from D-FF 1B.

The present invention has been made in view of the above-mentioned problems, and is a self-contained photoelectric switch that is less susceptible to external noise and operates even when detecting minute objects moving at high speed using a reflective type. The purpose is to provide a diagnostic circuit.

(d) Means and operation for solving the problems The self-diagnosis circuit for a photoelectric switch of the present invention includes a first circuit that outputs a signal when a light reception signal of a light receiving element exceeds a predetermined first level;
a second circuit that outputs a signal when the light reception signal of the light receiving element exceeds a predetermined second level that is higher than the first level;
The counting means is driven by the output of the first circuit to count pulses, is reset by the output of the second circuit, and outputs a self-diagnosis signal when the counted value reaches a predetermined value.

In this self-diagnosis circuit, if the light reception signal exceeds the first level (light incident level), the first circuit outputs an output, and the counting means counts pulses in response to this output. The level of the received light signal is sufficient, and the second level (stable light incident level)
If it exceeds , not only the first circuit but also the second circuit outputs an output, and this output resets the counting means.

Therefore, the counting means does not count up and does not output a self-diagnosis signal.

If the level of the light reception signal decreases, it exceeds the first level and the counting means performs pulse counting. However, since the level does not exceed the second level due to the level down, the counting means is not reset and continues counting pulses. When a predetermined count value is reached, that is, when the count is up, a self-diagnosis signal is output.

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

<Embodiment 1> FIG. 1 is a circuit diagram of a self-diagnosis circuit for a photoelectric switch showing an embodiment of the present invention. In the same figure, power supply ■. A series circuit of resistors 25, 26, and 27 is connected between the terminal and GND. The connection point between the resistor 26 and the resistor 27 is connected to one end of the input of the comparator 23, and a reference voltage (light incident level) 1 is applied thereto. The connection point between resistor 25 and resistor 26 is comparator 2.
4, and a reference voltage (stable incident light level) Vl (Vl > Vl) is applied thereto.

The light-receiving element 21 converts the input pulsed optical signal into a light-receiving current, further converts it into a voltage signal with a current/voltage converter 22, and applies the light-receiving signal (voltage) to the other input end of the comparator 23.24. ing. The comparator 23 compares the light reception signal with the reference voltage (1), and outputs a "high" signal when the light reception signal is larger. This high degree signal is input to the counter 28 and counted.

Also, the "high" signal of the comparator 23 is derived as a control output signal. The comparator 24 compares the light reception signal and the reference voltage (2), and outputs a high signal when the light reception signal is larger. This "high" signal is input manually to the input terminal of the measuring device 28, and the count value of the counter 28 is reset. Counter 2
8 counts up when the count reaches 8 and outputs a self-diagnosis signal (alarm signal).

Next, the operation of the self-diagnosis circuit of the above embodiment will be explained with reference to the waveform diagram shown in FIG. In addition, in Figure 2,
A is the output of the current/voltage converter 22, that is, the received light signal;
B is the output of the comparator 23, C is the output of the comparator 24, and D
shows the waveform of the output of the counter 28, respectively.

First, a case where the received light signal is at a sufficient level will be described. If the received light signal A does not exceed the incident light level ■1,
Neither signals B nor C of the comparators 23 and 24 are output. Eventually, when the received light signal A exceeds the incident light level vI, the comparator 23 also outputs a signal B, and this signal B is counted by the counter 28.

In the waveform example A1 in FIG. 2, there are two light reception pulses that exceed the light incident level ■1, so the count value of the counter 28 becomes two. Next, when the light reception signal exceeds the stable light reception level V2, both the comparators 23 and 24 output outputs B and C, and a counting pulse is manually inputted to the counter 28, but each time it is reset by the signal C, it is counted. No progress will be made on the 2nd day. When the received light signal eventually becomes lower than the stable light incident level (2), the pulse from the comparator 23 is only applied to the counter 28 again, so that the counter 28 increments. However, if the received light signal immediately falls below the incident light level ■1, the output of the comparator 23 will no longer be output, and the count value of the counter 28 will not exceed 8.
Self-diagnosis signal is not output.

In addition, as shown in A in Figure 2, the received light signal goes from a stable input level ■2 to below the large light level as shown by pulse a, and then exceeds the light input level ■1 due to noise as shown in pulse b. However, since the counter 28 only counts I, no self-diagnosis signal is immediately output.

Next, a case where the level of the received light signal is lowered will be explained. Assuming that the light reception signals shown in Az and A3 in Fig. 2 are input, the light reception signal changes from a state in which it exceeds the stable light reception level ■2, to a state where the light reception signal exceeds the stable light reception level ■2, and becomes smaller than the level ■2, and the light reception level ■
When the pulse C exceeds , the counter 28 counts 1, the reset time is not applied, and the counter 28 counts 2 at the next pulse d, and is still not reset. Furthermore, the counter 28 counts from the pulse e in the next light receiving period of A3, and the sixth pulse 7<
) Count 8 in response f. During this period, the light reception signal does not exceed the stable light reception level, so the comparator 24 does not output an output C, and therefore the counter 28 is not reset.

Counter 28 counts up by counting eight pulses,
Outputs self-diagnosis signal (alarm signal) D.

For example, with a reflective photoelectric switch, even if the object to be detected is small and passes through at high speed, and the light incident time is short, unless the counter 28 is reset, the count will continue by adding up to the next bright light time, so the count will continue. When the pump ends, an alarm signal is output. For example, as shown in FIG. 3, when the level drops from A, the counter 28 counts up with one shot at At, four shots at A3, and three shots at A4, and an alarm signal is output.

<Embodiment 2> FIG. 4 is a circuit diagram of a self-diagnosis circuit for a photoelectric switch showing another embodiment of the present invention. In this embodiment circuit, the same numbers as in the circuit of FIG. 1 indicate the same components. The difference from the embodiment circuit in FIG. 1 is the comparator 2.
A signal stretching circuit 2 is connected between the output of 3 and the input of the counter 28.
9 was established. Specifically, for example, a shift register or an integrator+comparator is used as the signal extension circuit 29. The self-diagnosis circuit of this embodiment is capable of detecting errors when the detection object moves extremely slowly or stops at a position where the light reception signal is unstable (the light reception signal is between ■1 and ■2). A signal extension circuit 29 is provided in order to eliminate the possibility that an alarm ta signal may be output.

This signal extension circuit 29 responds to the pulses output from the comparator 23, shapes the waveform so that it outputs l pulses for each series of operations of light shielding → light entrance → light shielding, and uses the output to output l pulses. 28.

Next, the operation of the self-diagnosis circuit of this embodiment will be explained with reference to the waveform diagram shown in FIG. In FIG. 5, E is the output of the current/voltage converter 22, that is, the received light signal, F is the output of the comparator 23, G is the output of the signal extension circuit 29, and ■] is the output of the comparator 24. , 1 indicate the waveforms of the outputs of the counter 28, respectively.

As shown in IE+ in FIG.
If E exceeds the stable light receiving level V2, the output F is sent to the comparator 23 every time the light receiving signal is manually input, similarly to the circuit shown in Fig. 1.
is output, and an output I( is also output to the comparator 24, which sets the counter 28, so that the counter 2
8, the alarm signal I is not output.

If the signal extension circuit 29 is, for example, a 4-pin shift register, then the 4 consecutive pulses of the comparator 23 (
4 bits) makes the output G high, and when all 4 bits are 0, the output G becomes low. In other words, each of the light blocking, light entering, and light blocking E5, Ez, E3, . . . 1 every
outputs pulses G.

Counter 28 is set to 1 at the rising edge of pulse G at El.
is counted, but it is also reset by the output H of the comparator 24. However, assuming that the level of the received light signal decreases after Snake 2, the counter 28 is not reset by the output +( of the comparator 24, so it counts 1 with the pulse G corresponding to E2, and thereafter E2, E4, E Count the pulse G corresponding to
The counter 28 has a count value of 4 (in this embodiment, the counter 28 is set to count up by a count value of 4).
Amplifies the count and outputs an alarm signal.

In this self-diagnosis circuit, the moving speed of the detection object is slow, and even if the stable light incident level V is exceeded within one cycle of light shielding, human light, and light shielding, unstable light incidence (input between v2 and Even if the light) continues, the counter 28 does not advance at all, so
Do not output alarm signal■. Further, even if the object to be detected stops in an unstable light receiving state, the counter 28 does not perform any counting, so there is no risk of outputting the alarm signal I.

(f) Effects of the Invention According to the present invention, the first circuit outputs a signal when the light reception signal of the light receiving element exceeds the first predetermined level; A second circuit outputs a signal when the second level is exceeded, and is driven by the output of the first circuit to count pulses, is reset by the output of the second circuit, and when the counted value reaches a predetermined value, the pulse is counted. and a counting means for outputting a diagnostic signal, and outputs a self-diagnosis signal when a predetermined value is counted by the counting means during a period when the received light signal level is between the first level and the second level. A type photoelectric switch can also reliably detect a drop in the received light level, and can also prevent self-diagnosis signals from being erroneously output due to noise.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a self-diagnosis circuit for a photoelectric switch showing an embodiment of the present invention, FIG. 2 is a waveform diagram of each part to explain the operation of the self-diagnosis circuit, and FIG. FIG. 4 is a circuit diagram of a self-diagnosis circuit for a photoelectric switch showing another embodiment of the present invention;
FIG. 5 is a waveform diagram of each part to explain the operation of the self-diagnosis circuit, FIGS. 6 and 7 are circuit diagrams showing the self-diagnosis circuit of a conventional photoelectric switch, and FIG. This is a waveform circle to explain the problems of the self-diagnosis circuit. 21: Light receiving element, 23/24: Comparator, 2nd: Counter, 29: Signal extension circuit.

Claims (1)

[Claims] (1) A first circuit that outputs a signal when the light-receiving signal of the light-receiving element exceeds a predetermined first level; and a first circuit that outputs a signal when the light-receiving signal of the light-receiving element exceeds a predetermined second level that is higher than the first level. and a counting means that is driven by the output of the first circuit to count pulses, is reset by the output of the second circuit, and outputs a self-diagnosis signal when the counted value reaches a predetermined value. A self-diagnosis circuit for a photoelectric switch characterized by: