JPH01320818A - Photoelectric switch - Google Patents

Abstract

PURPOSE:To output the result of self-diagnosis and the result of detection of an object from one transistor(TR) by providing a delay circuit retarding the upper level of a voltage by a prescribed time to a power application section and a selection circuit receiving the output of a comparator and of a self- diagnosis circuit, selecting any of them and outputting it. CONSTITUTION:When a control power supply Vcc is applied, then the result of selection by a selection circuit 11 and subject to self-diagnosis is outputted from an output TR 9. Then a capacitor 18 is charged and reaches a prescribed voltage, then a low level signal is inputted to other input terminal of an AND circuit 15 via an inverter 13 to interrupt the AND circuit 15. When a high level signal is inputted to other input terminal of the AND circuit 14, the AND circuit 14 is opened and a signal received by a light receiving element 4 is discriminated by a comparator 6a and its output is fed to the base of the TR 9.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a photoelectric switch that determines the age of a target object based on the amount of light emitted from a light emitting element and reaching a light receiving element ζ.

(Prior Art) A conventional photoelectric switch shown in FIG. 2 is known. The circuit of FIG. 2 and its operation will be explained with reference to the waveform diagram of FIG. 3. In FIG. 2, the output end of the oscillation circuit 1 is connected to a light emitting element 3 via a resistor 2, and a pulse current Ip as shown in FIG. 3 is passed through the light emitting element 3 to cause it to emit pulsed light. A light-receiving element 4 facing the light-emitting element 3 is connected to an amplifier 51, and the amplifier 5 amplifies the output signal of the light-receiving element 4 into a waveform shown by a voltage Vp. The output terminal of the amplifier 5 is connected to a comparator 6al, which converts the waveform of the voltage Vp to a predetermined reference level vL.
0, and a digital signal Vd suitable for logic processing,
A detection signal V01 is obtained by a detection circuit 7 connected to the output terminal ζ of this comparator 6a, and an output transistor 9
The presence of a target object (not shown) is confirmed by applying a voltage to the base of the transistor 9 and turning the transistor 9 on and off. Further connected to the output terminal of the amplifier 5 are a comparator 6b having a predetermined reference level Vr, t higher than the comparator 6a, and a comparator 6c having a predetermined reference level VL2 lower than the comparator 6a, and each comparator 6b, 5c has a respective level Vjx. , VL2 to discriminate the output of the amplifier 5 and output voltages Vdl and Vd2. Comparator 6b.

A self-diagnosis circuit 8 to which the output end of 6C is connected diagnoses whether the received light signal is sufficient or whether there is no leakage light and the received light signal is completely blocked.

The reference level of the comparators 6b and 6C is determined by the amplifier 5.
When the output Vp of the amplifier 5 is below the reference level VL2 of the comparator 6C, the light emitted from the light emitting element 3 does not enter the light receiving element 4 and is sufficiently shielded, and the output Vp of the amplifier 5 is at the reference level of the comparator 6b. The self-diagnosis circuit 8 is selected so that the output Vp of the amplifier 5 is at the reference level V of the comparator 6c.
Although it exceeds L2, the reference level VL of comparator 6b
It is configured to output an output when the voltage does not exceed I. This can be obtained by performing a logical product of the output d2 of the comparator 6C and a signal obtained by inverting the output Vd1 of the comparator 6b. Here, the state in which the output Vp of the amplifier 5 is between the reference levels VLI and VL2 of the comparators 6b and 6c means that the light emitted from the light emitting element 3 is received by the light receiving element 4 and detected by the detection circuit 7. signal V
Although OI has been obtained and the sensor is in a detection state, there is not enough light reception output for the photoelectric switch to operate stably. Such a situation occurs, for example, when the lens surface of the light emitting/receiving lens becomes dirty while the photoelectric switch is in use. In such a case, the self-diagnosis circuit 8 issues an alarm before the function of the photoelectric switch is impaired, prompting cleaning of the lens surface, etc., thereby preventing failure of the entire device using the photoelectric switch.

(Problem to be solved by the invention) An optical switch having such a self-diagnosis circuit has the advantage of stable operation and high reliability, but on the other hand, in addition to the output transistor of the detection circuit, there is also a Since the photoelectric switch is equipped with several output transistors, the number of output elements increases, and the number of lead wires connected to external devices also increases, which causes problems such as increased wiring costs and hinders miniaturization. . Furthermore, in order to input these outputs to the sequence controller, the number of input circuits of the sequence controller must also be increased, which poses the problem of requiring a larger and more expensive sequence controller.

SUMMARY OF THE INVENTION An object of the present invention is to provide a photoelectric switch capable of transmitting self-diagnosis results to the outside in addition to the original output as a photoelectric switch from one output transistor.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention includes a light-receiving element that receives an optical signal emitted from a pulse-lit light-emitting element and converts it into an electric signal, and a light-receiving element that converts the output of the light-receiving element into a predetermined signal. a first comparator that discriminates and outputs based on the level; a second comparator that has a higher discrimination level than the first comparator; a third comparator that has a lower discrimination level than the first comparator; Second. A photoelectric switch equipped with a self-diagnosis circuit that diagnoses the input of the light receiving element-1 according to the output of a third comparator and outputs the result, a delay circuit that delays the rise of the power supply voltage for a predetermined period of time after power is turned on; A selection circuit is provided, which receives the output of the first comparator and the output of the self-diagnosis circuit, selects one of these inputs by the delay circuit, and outputs the selected one.

(Function) Since the attenuation of the light reception signal of the photoelectric switch does not progress rapidly, there is no need for constant self-diagnosis, and it is sufficient to perform the diagnosis once a day, for example, when the power is turned on. Immediately after the power is turned on, the second and third comparators and self-diagnosis circuit diagnose whether the photoelectric switch is operating properly, and the voltage of the delay circuit rises to a predetermined value. Output this diagnosis result until
When the voltage reaches a predetermined value, the selection circuit switches the original output of the photoelectric switch, and the 11 output transistors provide a photoelectric switch that outputs a detection output and a self-diagnosis result as a photoelectric switch.

(Example) An example of a photoelectric switch according to the present invention is shown in FIG.
Components that are the same as in FIG. 2 are given the same reference numerals as in FIG. 2.

In FIG. 1, a light emitting element 3 emits light using a pulse current generated by an oscillation circuit 1 as in the conventional device, and a light receiving element 4
It receives light. Amplification circuit on the light receiving side 5. Three comparators 6a, 6b, 6c detection circuit 7, self-diagnosis circuit 8
etc. are the same as the conventional one, so their explanation will be omitted. The present invention differs from the conventional one in that a selection circuit 11 and a delay circuit 12 are provided. The selection circuit 11 includes an inverter 13, two AND circuits 14, 15, and an OR circuit 16, the output of the detection circuit 7 is connected to one input terminal of the AND circuit 14, and the output of the self-diagnosis circuit 8 is connected to the AND circuit 16.
It is connected to one input end of the circuit 15. The output terminals of both AND circuits 14 and 15 are connected to respective input terminals of an OR circuit 16.

The output terminal of the OR circuit 16 is connected to the base of the output transistor 9. The delay circuit 12 is connected to the control power supply Vcc.
is connected to charge the capacitor 18 via the resistor 17, and the delay time for charging the capacitor 18 is determined by the resistance value of the resistor 17 and the capacitance of the capacitor 18. resistance 1
The connection point between 7 and the capacitor 18 is connected to the other input terminal of the AND circuit 14 and the other input terminal of the AND circuit 15 via the inverter 13 .

The original operation of this photoelectric switch as a photoelectric switch and the operation of the self-diagnosis circuit 8 are shown in FIG. 12 operations will be explained below.

Most of the photoelectric switches start immediately when the control power supply Vcc is turned on, but at this time, the voltage of the capacitor 18 is still low, so the input at the other input terminal of the AND circuit 14 is at a low level, and the detection circuit 7 The output is cut off and A
The output of the ND circuit 14 is at low level. But AND
Since the other input terminal of the circuit 15 becomes high level through the inverter 13, the output of the self-diagnosis circuit 8 becomes the AND circuit 1.
5 and the OR circuit 16 and is applied to the base of the output transistor 9. That is, this photoelectric switch is initially selected by the selection circuit 11 when the control power supply Vcc is turned on, and the result of diagnosis by the self-diagnosis circuit 8 is output from the output transistor 9. Next, when the capacitor 18 is charged and reaches a predetermined voltage, a low level signal is input to the other input terminal of the AND circuit 15 via the inverter 13, so the AND circuit 15 is cut off. However, since a high level signal is input to the other input terminal of the AND circuit 14, the AN
The D circuit 14 is opened, the signal received by the light receiving element 4 is discriminated by the comparator 6a, and its output is applied to the base of the output transistor 9. That is, after a predetermined period of time after the control power supply Vcc is turned on and the voltage rise is delayed by the delay circuit 12,
The selection circuit 11 switches to the original photoelectric switch operation.

As mentioned above, this photoelectric switch has a control power supply Vc on the light receiving side.
When the optical system c is first turned on, its optical system is self-diagnosed, and after a predetermined time, the selection circuit 18 switches it to its original operation. Therefore, at the beginning of the photoelectric switch start-up, as well as at any time, the control power supply Vcc is
can be diagnosed by blocking.

(Effects of the Invention) According to the present invention, this photoelectric switch switches the selection circuit using a power-on delay circuit, outputs a self-diagnosis result for a predetermined period of time after the power is turned on, and automatically detects the presence of a target object after a predetermined period of time. Since the original operation of detection is performed, the self-diagnosis result and the detection result of the target object can be output with one output transistor, and the number of external wirings can be reduced.

Moreover, the present invention has the advantage that diagnosis can be made without fail when starting the photoelectric switch, and furthermore, diagnosis can be made at any time. Furthermore, when connecting to a sequence controller, the number of input circuits may be small, and the sequence controller can also be made smaller.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram showing an example of a photoelectric switch according to the present invention, Fig. 2 is a wiring diagram showing an example of a conventional photoelectric switch, and Fig. 3 is a waveform diagram of various parts explaining the operation of such a photoelectric switch. It is. 3; Light emitting element, 4; Light receiving element, 6a, 6b, 6c: Comparator, 8; Self-diagnosis circuit, 11: Selection circuit, 12
;Delay circuit. −11=

Claims (1)

[Claims] 1) A light receiving element that receives an optical signal emitted by a pulse-lit light emitting element and converts it into an electrical signal, a first comparator that discriminates and outputs the output of this light receiving element at a predetermined level, and this first comparator. A second comparator having a higher discrimination level, a third comparator having a lower discrimination level than the first comparator, and diagnosing the input to the light receiving element according to the outputs of the second and third comparators. In a photoelectric switch equipped with a self-diagnosis circuit that outputs a result, the photoelectric switch has a delay circuit that delays the rise of the power supply voltage for a predetermined period of time after power is turned on, and the output of the first comparator and the output of the self-diagnosis circuit are input. A photoelectric switch comprising a selection circuit that selects and outputs either of the two inputs using the delay circuit.