JPS61269522A - Photoelectric switch - Google Patents

Abstract

PURPOSE:To prevent generation of mis-detection by opening the 2nd gate circuit at a time zone where no light is irradiated from a light projection section and using an integration circuit to integrate a light signal during the zone thereby inhibiting the detection output when the output level reaches a prescribed value. CONSTITUTION:A light projection section 13 and a photodetector section 14 are provided to a photoelectric switch, a signal having a prescribed frequency from an oscillation circuit 11 is frequency-divided by a frequency division circuit 12, clocks a, b being at H level not at the same time, the light emitting section 13 is driven by a pulse of the clock (a) and irradiated to a detection region 24. The light signal from the region 24 is received by the light receiving section 14, amplified (15) into a prescribed level and fed to the 1st and 2nd gate circuits 16, 17. The circuit 17 is opened during the clock (b) when the light projection section 13 does not irradiate any light. Then the optical signal obtained during this period is integrated by an integration detection circuit 19 and a waveform shaping circuit 21, an inhibition signal is fed to an inhibition circuit 22 while regarding it as an external disturbance light so as to prevent mis-output of the detection signal from the region 24 through the circuit 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a photoelectric switch, and more particularly to a photoelectric switch that prevents malfunctions caused by ambient light.

[Summary of the invention]

The photoelectric switch according to the present invention drives a light emitting element with a large pulse signal and integrates a light reception signal obtained at a timing different from the driving timing, and when the integration level reaches a predetermined value or more, disturbance light from the outside is continuously generated. The detection output of the object is stopped as if the object was added to the object. In this way, the photoelectric switch will not output an object detection signal due to an erroneous signal, and the reliability of the photoelectric switch can be improved.

[Prior art and its problems]

In conventional photoelectric switches, the light emitting element is driven using clock pulses, and the pulsed light reception signal from the object is converted into a continuous reception level signal using an integral detection circuit, and at the same time, it is used to prevent malfunctions due to noise, etc. The time constant of the integrating circuit is set to, for example, five cycles of clock pulses, and noise below that value is removed to prevent malfunction.

FIG. 4 is a block diagram of such a conventional reflective photoelectric switch, and FIG. 5 is a waveform diagram of each part of the switch a' to e. In this photoelectric switch, the output of the clock pulse oscillation circuit 1 drives the light emitting part 2, and the received light output of the light receiving part 3 is amplified and applied to the gate circuit 5, which opens and closes at the same timing as the driving clock. Only the received light signal is fed to the integral detection circuit to prevent noise from entering.

The signal passed through the gate circuit 5 is then applied to an integral detection circuit 6, and its output is discriminated at a predetermined level to obtain an object detection signal. When disturbance light is continuously applied to such a photoelectric switch, the integral level may exceed the threshold and the photoelectric switch may malfunction, as shown in Figure 5 (C1, (dl). This possibility can be reduced by lengthening the time constant of the integrating circuit, but if it is made too long, the responsiveness of the photoelectric switch will decrease.Therefore, in the conventional photoelectric switch 1. There was a problem in that it was not possible to completely prevent malfunctions when the light receiving section was continuously irradiated with disturbance light when the light receiving section was not present.

[Purpose of the invention]

The present invention has been made in order to solve the problems of the conventional photoelectric switch, and provides a fast response and prevents malfunctions caused by ambient light without making the time constant of the integrating circuit too long. The purpose is to provide a photoelectric switch that can.

[Structure and effects of the invention]

The present invention is a photoelectric switch that has a light projecting section and a light receiving section, and detects an object by driving the light projecting section in pulses, and the gate timing corresponds to the drive signal of the light projecting section when a light reception signal is given from the light receiving section. a first gate circuit having a first gate circuit; a second gate circuit to which a light receiving signal is applied from a light receiving section and having a gate timing different from a pulse drive signal of the light projecting section; Second
The first one integrally detects the output of each gate circuit. a second integral detection circuit; a first integral detection circuit; A first waveform shaping circuit that discriminates and shapes the output of the second integral detection circuit by a predetermined threshold value, respectively; and a second waveform shaping circuit that outputs an object detection signal based on the output of the first waveform shaping circuit; and a prohibition circuit that prohibits the output of the first waveform shaping circuit based on the output of the first waveform shaping circuit.

According to the present invention having such characteristics, the second gate circuit is opened during the time period when no light is emitted from the light projecting section, and the optical signal obtained during that time is integrated by the integrating circuit, and the output level thereof is equal to or higher than a predetermined level. When it reaches , it is assumed that disturbance light has been continuously added and the detection output is prohibited. This eliminates the possibility of erroneously outputting an object detection output, and it is possible to improve the reliability of object detection without increasing the response time.

[Explanation of Examples]

(Overall Configuration of Embodiment) FIG. 1 is a block diagram showing an embodiment in which the present invention is applied to a diffuse reflection type photoelectric switch.

In the figure, an oscillation circuit 11 is an oscillator that generates a signal of a predetermined frequency, and its output is given to a frequency dividing circuit 12. The frequency dividing circuit 12 generates two clock signals that have the same period and do not reach the "H" level at the same time.
One of the clock signals is given to the light projector 13. The light projector 13 has a light emitting element such as a light emitting diode, and intermittently causes the light emitting element to emit light based on the clock signal thus applied, and irradiates the detection area. The light receiving section 14 receives reflected light from the detection object, and transmits its output to the amplifier circuit 15. The amplifier circuit 15 amplifies the reflected wave signal to a predetermined level and transmits its output to two gate circuits 16 and 17. The gate circuit 16 is connected to the light emitting unit 13 by the frequency dividing circuit 12.
The same clock signal as the drive signal of is given to the gate circuit 17, and the other clock signal of the frequency dividing circuit 12 is given to the gate circuit 17. By opening the gates at the respective timings, the gate circuit 16 allows the light reception signal given at the driving timing of the light projecting section 13 to pass through and gives it to the integral detection circuit 18, and the gate circuit 17 gives it at other timings. The received light signal is given to an integral detection circuit 19.

Integral detection circuit 1B.

Reference numeral 19 converts the output signal into a signal with a level corresponding to the amount of received light. The respective outputs of the integral detection circuits 18 and 19 are sent to the waveform shaping circuit 20. Given in '21. The waveform shaping circuits 20 and 21 each output an output when an input exceeding the threshold ThLTh3 is given, and the respective waveform shaping circuits 20 and 21 output an output when the input exceeds the threshold Th2 (<Th
1) This is a shaping circuit that converts the input signal into a binary signal by stopping the output when it becomes less than or equal to Th4 (<Th3), and its output is given to the inhibition circuit 22, respectively. The prohibition circuit 22 is further connected to the light emitter 1 from the frequency dividing circuit 12.
The same clock signal as the drive signal of No. 3 is given. The prohibition circuit 22 prohibits the output of the waveform shaping circuit 20 when the output is given from the waveform shaping circuit 21, and also uses the output of the waveform shaping circuit 20 as the clock of the frequency dividing circuit 12 when the output is not prohibited. It is synchronized and given to the outside. Further, an indicator light 23 is connected to the output end of the waveform shaping circuit 21 to indicate that noise has been added from the outside.

(Configuration of Prohibition Circuit) Next, the detailed configuration of the prohibition circuit 22 will be described with reference to FIG. 2. The output terminal of the waveform shaping circuit 20 is connected to the terminal 31, and the waveform shaping output is given to the D-type flip-flop 32 via the terminal 31. The D-type flip-flop 32 is a flip-flop for synchronizing the rise of its output with a clock signal, and its Q output is given to a D-type flip-flop 33, an AND circuit 34, and a NOR circuit 35. Also, the clock signal of the frequency divider circuit 12 is input from the terminal 36 to 2.
This signal is applied to the clock input terminals of two D-type flip-flops. The D-type flip-flop 33 is a flip-flop for synchronizing the falling edge of the output signal with a clock, and its Q output is given to an AND circuit 34 and a NOR circuit 35. Further, the output of the waveform shaping circuit 21 is applied to an inverter 38 via a terminal 37, and the output of the inverter 38 is applied to two AND circuits 39 and 40. Inverter 38 operates these AND circuits 39 and 4.0 as a gate circuit. The outputs of the AND circuits 39 and 40 are applied to an RS flip-flop 410 cent and a reset input terminal, respectively, and an object detection output is output from the RS flip-flop 41 to the outside.

(Operation of this embodiment) Next, the operation of this embodiment will be explained with reference to waveform diagrams. 'Figure 3 fa) to (nl are a in Figures 1 and 2.
It is a waveform diagram of the waveform of each part indicated by -n. The frequency dividing circuit 12 generates two clock signals shown in FIG. As shown in the figure, when the detection object 24 is present, reflected light is obtained in synchronization with this clock signal, and this signal passes through the gate circuit 16 as it is, as shown in Figure 3 (C1, (d)). The signal is transmitted to the integral detection circuit 18.The integral detection circuit 18 starts integrating based on the input signal as shown in FIG. Therefore, at time t2 when the integrated output exceeds the threshold level Thl, the waveform shaping circuit 20 provides an output as shown in FIG. Output stops.

Further, as shown in FIG. 3(C), even if an optical signal that is not synchronized with the light projection clock signal is applied to the light receiving section 14 at time t3, it does not pass through the gate circuit 16, so that the signal is not transmitted to the waveform shaping circuit 20. However, since the gate circuit 17 is open at this time, the signal is transmitted to the integral detection circuit 19 and integration is performed as shown in FIG. Assuming that disturbance light is added to the light receiving section 14, the amplifier circuit 15 and the gate circuit 16
．． It passes through both ITs and is transmitted to integral detection circuits 18 and 19 as shown in FIGS. 3(d) and (g). Therefore, the outputs of the integral detection circuits 18 and 19 gradually increase as shown in FIG. 3(h).

(As shown in 11, the output from the waveform shaping circuit 21 is given to the inhibition circuit 22 at time t5 when the threshold value Th3 is exceeded.

Similarly, as shown in FIG. 3 (el, (fl), the object detection output is transmitted from the waveform shaping circuit 20 to the inhibition circuit 22 due to the increase in the integral output at time t6, at time t7゜t.
8, the input to the inhibition circuit 22 is stopped due to a decrease in the integral output. If the time constant of the integral detection circuit 19 is set so that the rising time is faster than that of the integral detecting circuit 18 and the falling time is slower than that of the integral detecting circuit 18, as shown in FIG. 3(e),
As shown in (1), the output time of the waveform shaping circuit 21 can be made to include the output time of the waveform shaping circuit 20.

Now, the clock signal shown in FIG. 3 (al) is applied to the flip-flops 32 and 33 of the inhibit circuit 22.

Therefore, based on the output of the waveform shaping circuit 20, FIG.
, +11, AND circuit 34 and NOR circuit 3
5, an output synchronized with the clock signal can be obtained.

At this time, if the output from the waveform shaping circuit 21 is not applied, these signals pass through the AND circuit 39 and 40 as shown in FIG. As shown in 01, the object detection output is output to the outside.

However, due to the output of the waveform shaping circuit 20, as shown in FIG.
Even if an output synchronized with the clock signal is obtained as shown in (kl, tl), if an inhibit input signal is given from the waveform shaping circuit 21, the AND circuits 39 and 40 are closed, so the RS
No output is transmitted to the flip-flop 41. Therefore, as shown in Fig. 3+J), no object detection output is obtained, and there is no possibility of erroneously outputting the output.Also, the output of the waveform shaping circuit 21 is given to the indicator light 23, and the disturbance light is added to prevent the object from being detected. It will be displayed that it cannot be detected.

In this embodiment, the specific number of integrals of the integral detection circuit 19 is set to be shorter than the integral detection circuit 18 at the rising edge and longer than the integral detection circuit 18 at the falling edge, but the threshold t of the waveform shaping circuit 21, to z JtzTh3. T
h4ヲ Waveform shaping circuit 20 threshold level T
It is also possible to set them to be slightly lower than hl and Th2, respectively, so that disturbance light can be detected and the output can be reliably inhibited.

Furthermore, although this embodiment describes a diffuse reflection type photoelectric switch, if the clock signal is integrated to provide an object detection output when the output of the first gate circuit is not given, a transmission type photoelectric switch is used. It is also possible to apply the present invention to a retroreflective type photoelectric switch.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the photoelectric switch according to the present invention, FIG. 2 is a circuit diagram showing the detailed configuration of the inhibition circuit, and FIG. 3 is a waveform diagram showing waveforms of various parts of this embodiment. FIG. 4 is a block diagram showing an example of a conventional photoelectric switch, and FIG. 5 is a waveform diagram of each part thereof. Q1, 11-----One oscillation circuit 2.13--
-----One light emitting section 3, 111---One light receiving section 5, 16.17---Gate circuit 6. 18.
1! 1l --- Integral detection circuit 7, 20
, 21------One waveform shaping circuit 12------
---1 frequency division circuit 22-・-----1 inhibition circuit 3
2.33−・− type flip-flop 41 =−−
---RS flip-flop

Claims (4)

[Claims] (1) A photoelectric switch that has a light projecting section and a light receiving section and detects an object by driving the light projecting section in pulses, and a gate that receives a light reception signal from the light receiving section and corresponds to a driving signal for the light projecting section. a first gate circuit having a timing; a second gate circuit to which a light reception signal is applied from a light receiving section and having a gate timing different from a pulse drive signal of the light projecting section; and outputs of the first and second gate circuits. first and second integral detection circuits that perform integral detection, respectively; first and second waveform shaping circuits that discriminate and shape the outputs of the first and second integral detection circuits using predetermined threshold values, respectively; A prohibition circuit that outputs an object detection signal based on the output of the first waveform shaping circuit and prohibits the output of the first waveform shaping circuit based on the output of the second waveform shaping circuit. photoelectric switch. (2) The time constant of the second integral detection circuit is set such that the rise time is shorter and the fall time is longer than that of the first integral detection circuit. switch. (3) The photoelectric switch according to claim 1, wherein the threshold value of the second waveform shaping circuit is set lower than the threshold value of the first waveform shaping circuit. (4) Claim 1, further comprising a display that operates based on the output of the second waveform shaping circuit.
Photoelectric switch described in section.