JPH03213013A - Optoelectric switch - Google Patents

Abstract

PURPOSE:To prevent mis-detection of an object to be detected when an external disturbance light enters a photodetector section by connecting a high frequency filter eliminating a modulation optical component to the output terminal of a photodetection circuit and connecting an abnormal level detection circuit supplying an output when the output of the filter exceeds a prescribed value to the output terminal equipment of the filter. CONSTITUTION:A high frequency cut filter 13 is connected to the output terminal of a photodetection circuit eliminating the modulation signal outputted from the photodetection circuit and an abnormal level detection circuit 14 having a prescribed threshold level is connected to the output terminal Since the high frequency cut filter 13 eliminates a modulation signal from the output of the photodetection circuit, that is, the synthesis value of the modulation signal and an external disturbance light, when a signal exceeds threshold level VSH of the abnormal level detection circuit 14, the output of an abnormal state display circuit 15 is inverted from OFF to ON, thereby activating the external abnormal state display circuit 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a photoelectric switch, and particularly to a circuit for preventing malfunction of the switch due to ambient light.

[Prior art]

Generally, as shown in Fig. 4, a photoelectric switch emits frequency-modulated light from a light emitter 1, receives this light in a light receiver 2 at ℃, and outputs an output depending on the strength of the light. If strong light from an incandescent lamp or sunlight enters the light receiving section while the switch is operating, it may cause malfunction. The malfunction is mainly due to light shielding.

That is, if disturbance light is incident while modulated light is incident on the light receiving section 2, electric signals 1.
, Jt changes as shown in FIG. 5(A).As the value further increases, the modulated light l, exceeds a certain value ■CC. Then, as shown in FIG. 5(b), this modulated light substantially attenuates at time t and thereafter, and finally disappears. Therefore, as shown in FIG. 4, when detecting the detected object 16 moving on the conveyor 20, when the disturbance light enters the light receiving section, the plate detection object 16 moves into the light projecting section l and the light receiving section 2.
The photoelectric switch determines that the light is blocked even though there is no light in between, and thereby outputs an output as if the detected object 16 were present between the light projector l and the light receiver s2. In other words, a malfunction occurs.

[Purpose of the invention]

In view of these conventional drawbacks, the present invention has been developed to provide a system in which when external light, particularly incandescent lamps or sunlight, is projected onto the light receiving section, light other than the original frequency modulated light enters the output side. The purpose is to output that.

[Summary of the invention]

In order to achieve the object, this invention provides a high frequency cut filter for removing high frequency components of modulated light at the output end of the light receiving circuit, and outputs an abnormal output when the output from this filter exceeds a certain threshold. This is what I did.

〔Example〕

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

In other words, in FIG. 1, only a resistor 4, a light emitting element 5, such as a light emitting diode, and a drive circuit 7 for modulating and driving the light emitting element are shown in the light projecting section l. Since they are the same, their details will be omitted.In the light receiving section 2, a series circuit of a light receiving element 6 and a resistor 80 is connected between the power terminals CC and G, and this resistor forms a light receiving circuit.

An amplifier circuit 11 is connected to the output end of this light receiving circuit, that is, the connection point between the resistor 8 and the light receiving element 6 via a capacitor 9. Furthermore, a switching output circuit 12 as a photoelectric switch is connected to the output end of this amplifier circuit, but its configuration is well known and will therefore be omitted.

First, a high frequency cut filter 13 is connected to the output end of the light receiving circuit for removing the modulated signal output from the light receiving circuit. Furthermore, an abnormal potential detection circuit 14 having a predetermined threshold value is connected to the output end of this filter. Further, an abnormal state display circuit 15 such as a light emitting circuit or a buzzer is connected to the output terminal of this detection circuit.

In the above configuration, when the light emitting element 5 of the light projecting section 1 is modulated and driven by the drive circuit 7, the light emitting element emits modulated light having a predetermined high frequency. This modulated light is received by the light receiving element 6. At this time, if there is an object 16 to be detected between the light emitting part l, that is, the light emitting cable 5, and the light receiving part 2, that is, the light receiving element 6, the light emitted from the light emitting element 5 will not reach the light receiving element 6, and therefore the output of the light receiving circuit The potential at point A changes. Furthermore, the output of this light receiving circuit is waveform-shaped by passing through a capacitor 9, amplified by an amplifier circuit 11, and sent to a switching circuit 12.

The waveform diagram in Figure 2 shows the waveforms at points A, B, and C in Figure 1, and now '! If disturbance light enters the light receiving element 6 shown in Figure IPJ1, the modulated light from the light emitting cable 5 fluctuates as shown in Figure 2 (A) along with the disturbance light.This signal is converted to Figure 2 (B) by the condenser 9. As shown in FIG. 2, only the disturbance light component is smoothed and input to the amplifier circuit 11.

On the other hand, the high frequency cut filter 13 removes the f harmonic signal from the output of the light receiving circuit, that is, the composite value of the modulated wave signal and the disturbance light, that is, the waveform at point A (therefore, the waveform becomes as shown in FIG. 2 e1. The waveform is mainly a signal corresponding to disturbance light 1, and this signal is input to the abnormal potential detection circuit 14.Then, as shown in FIG. If the threshold value exceeds V8H,
The output of the abnormal output circuit 15 is O as shown in Fig. 3 (b).
The signal is reversed from FF to ON, which also activates the external abnormal state display circuit 15.

〔Effect of the invention〕

As described above, this invention connects a high frequency cut filter for removing modulated light components to the output end of the light receiving circuit, and outputs an output to the output end of this filter when the output from this filter exceeds a predetermined value. Since the abnormal potential detection circuit is connected, the object to be detected will not be abnormally detected when ambient light enters the light receiving section.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a block diagram showing one embodiment of the photoelectric switch according to the present invention, FIG. 2 is a waveform diagram at each point in FIG. 1,
Figure 3 (a) is an operation waveform diagram for explaining the operation of the abnormal potential detection circuit, Figure 3 (10) is an operation waveform diagram for explaining the operation of the abnormal state display circuit, and Figure 4 is a transmission waveform diagram for explaining the operation of the abnormal state display circuit. A perspective view showing how the room switch is used, ′! Figure 1%5 is a waveform diagram for explaining the operation of a conventional photoelectric switch.
b) respectively. l...Light emitter, 2...Light receiver, 4...Resistor, 5...
...Light emitting element, 6... Light receiving element, 7... Drive circuit,
8...Resistor, 9...Capacitor ll...Amplification circuit, 12...Switching output circuit, 13...High frequency cut filter 14...Abnormal potential detection circuit, 15
...Abnormal state display circuit, 16...Detected object, 20
···Conveyor. Applicant: Yamatake Newell Co., Ltd.
−〒〒2＝

Claims (1)

[Claims] A light-receiving element (6) that optically corresponds to a light-emitting element (5) that emits modulated light, a light-receiving circuit that converts an optical signal incident on the light-receiving element into an electrical signal, and an amplifier circuit that amplifies the output of this light-receiving circuit. (11) and a switching output circuit (12) for guiding the output of the amplifying circuit to the outside, wherein a high frequency signal is provided at the output end of the light receiving circuit to remove a high frequency component of the modulated light emitted by the light emitting element (5). A photoelectric switch connected to a cut filter (13) and an abnormal potential detection circuit (14) that outputs an output signal when the output from the filter exceeds a predetermined value.