JPS59151720A - Photoelectric switch - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to improvements in photoelectric switches.Prior art Photoelectric switches can be used as non-contact detectors even in cases where mechanical switches such as microswitches and limit switches cannot be used. However, since it uses light, it has the advantage of not being limited in what it can detect, whereas proximity switches are limited to detecting objects such as conductors and magnetic materials. Systems using photoelectric switches have the disadvantage that the light emitting and light receiving parts of the receiver gradually become cloudy due to the accumulation of dust, making it impossible to perform normal detection operations, and that they are subject to disturbance by external light. There are concerns about the reliability of operation. To overcome this drawback, photoelectric switches have traditionally been fitted with dust-proof and external light-preventing hoods, but although this can slow down the adhesion of dust, it cannot completely prevent it, and it is difficult to effectively block only external light. I couldn't even say anything.

OBJECTS OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the conventional photoelectric switch and to improve the reliability of a system including the photoelectric switch.

Structure of the Invention The present invention provides a photoelectric switch light receiver consisting of a light emitter and a light receiver.As shown in FIG. An auxiliary light-receiving element 3 is arranged around the main light-receiving element 2, and this auxiliary light-receiving element detects the scattered light S in the condenser lens or the disturbance that enters the lens from a direction different from the light flux that enters the lens from the projector. It is characterized in that the light N is received, and the signal processing section 4 detects that the output of the auxiliary light receiving element 3 exceeds a certain level and issues a warning signal or the like.

According to the above configuration, the auxiliary light receiving element receives the light scattered by the condensing lens, but since the scattering of light by the condensing lens increases due to the adhesion of dust, the output level of the auxiliary light receiving element may cause the condensing lens to become cloudy due to dust. Adjustment can be detected. Furthermore, it is obvious that the auxiliary light receiving element is capable of detecting disturbance light based on its arrangement.

Embodiment 2 FIG. 2 shows a light receiver in a basic embodiment of the present invention. 2 is a main light receiving element arranged at the focal point of the condenser lens 1;
3 is an auxiliary light-receiving element, which is connected to the main light-receiving element 2 as shown in FIG.
are arranged around the circuit and connected in parallel to the amplifier 42. Reference numeral 41 denotes an amplifier for amplifying the output noise of the main light receiving element 2. The outputs of the amplifiers 41142 are compared with reference levels Vr and Vr' by level discrimination circuits 43 and 44, respectively, and the level discrimination circuit 43 outputs an object detection signal when the amount of light received by the main light receiving element 2 falls below a certain level. The level discrimination circuit 44 outputs a signal when the amount of light received by the auxiliary light receiving element 3 exceeds a certain level. This signal becomes a warning signal. A flat beam F is emitted from the projector 5, and if an object that is focused onto the main light receiving element 2 by the condenser lens 1 blocks the beam F, an object detection signal is output from the level discrimination circuit 43. . In a normal case, the light scattered by the lens 1 is extremely small, so the output of the light receiving probe 3 is almost O. When dust adheres to the lens 1, a part of the luminous flux F incident on the lens 1 is scattered and enters the light receiving element 3, and when the intensity of this scattered light exceeds a certain level, a warning signal is output from the level discrimination circuit 44. Ru. Even if the light flux F is still blocked by the object to be detected, the output of the light receiving element 2 may not be sufficiently reduced and an object detection signal may not be output. In such a case, since the disturbance light has a direction different from that of the light flux F, it also enters the auxiliary light receiving element 3, so that a warning signal is output. Note that the warning signal is not a warning that the object cannot be detected, but a notice that the object cannot be detected, and the object detection signal is issued even when the warning signal is being issued.

Figure 4 shows another embodiment of the signal processing circuit.

The light receiving elements 2, 3, the amplifiers 4'l-, 42, and the level discrimination circuit 43 correspond to those with the same numbers in FIG. 2, so their explanations will be omitted. In this embodiment, variable resistors 11 and 13 are adjusted so that the ratio of the gains of amplifiers 41 and 42 becomes a predetermined ratio. A comparator 45 compares the output of the amplifier 41 (corresponding to the output level of the main light receiving element 2) and the output of the amplifier 42 (corresponding to the output level of the auxiliary light receiving element 3), so that the output level of the auxiliary light receiving element is equal to that of the main light receiving element. When the output level is higher than a certain ratio to the output level, the comparator 45 outputs a no-level signal, and this signal is output through the AND gate 47 as a warning signal. The meaning of this configuration is that when the output of the auxiliary light-receiving element 3 is greater than a certain percentage of the output of the main light-receiving element 2, it means that the lens l is cloudy or that outside light is entering.
A warning signal is issued through the AND gate 47. In this case, a signal that is output when the amount of light incident on the auxiliary light receiving element 3 exceeds a certain level is sent to the AND gate 47 from the level discriminator 44'', and the AND gate 47 opens. The configurations of the circuit 44' and the AND gate 47 are functionally redundant, and the reason for this is as follows.

When ambient light is incident to a level that does not interfere with object detection When an object is detected, the output of the main light receiving element 2 drops near the edge aO, but the output of the auxiliary light receiving element does not drop much, so the comparator 45 The output will become low level and a warning signal will be issued, but in this case the amplifier 42
The output of the level discriminator 44 is lower than the reference level Vr'' set in the level discriminator 44, and the output of the level discriminator 441 is at a low level, and the AND gate 47 is closed to prevent the output of a warning signal.

Main light receiving element 2. Amplifier 41. When an object is detected by the channel of the level discrimination circuit 43, the object detection signal outputted from the level discrimination circuit 4-3 is outputted through the inhibition gate 46. Inhibit gate 46 remains open whenever switch 18 is open. When the switch 18 is closed, the prohibition gate 46 is closed when a warning signal is output by the comparator 45, and the output of the object detection signal is stopped. The meaning of doing this is that when a shining object 2 that is different from the original object to be detected passes between the emitter and the light receiver, the scattered light from that object will be transmitted to the auxiliary light receiving element. 3, a warning signal is issued, but an object detection signal is also issued, so in such a case, only the warning signal is issued, so that the object detection signal does not pile up.

FIG. 5 is a modification of the embodiment shown in FIG.
Instead of adjusting each gain of 1.42 to set the ratio of the gains to a predetermined ratio, the potentiometer 20 is used to set the ratio of the gains of each amplifier to a predetermined ratio when input to the comparator 45. It is something.

The difference between the embodiments shown in FIGS. 4 and 5 described above and the embodiment shown in FIG. 2 described above is that in the embodiment shown in FIG. While it detects dirt on the lens, the 4th. In the embodiment shown in FIG. 5, dirt on the condenser lens is detected based on the ratio between the output of the main light receiving element 2 and the output of the auxiliary light receiving element 3. If dirt on the condenser lens is detected based on the absolute value of the output of the auxiliary light receiving element 3 as in the embodiment shown in FIG. Since the scattered light also becomes weaker, the scattered light detection output of the auxiliary light receiving element for the same degree of condensing lens contamination also decreases, and a warning signal will not be issued until the condensation has progressed further. By detecting dirt on the condenser lens based on the ratio of the outputs of the light receiving elements, even if the intensity of the light emitted from the projector side decreases, it is possible to issue a warning signal if the condenser lens is dirty to a certain extent.

Although each of the above-mentioned embodiments relates to a transmission type photoelectric switch, the present invention can also be implemented with a reflection type photoelectric switch. Although the above description focuses on dirt on the condenser lens, it goes without saying that if a protective glass or filter is placed in front of the lens, these dirts can be detected with the above configuration.

Effects With the above-described configuration, the present invention uses the auxiliary light-receiving element to detect the degree of blurring of the focal image of the projector's light beam due to dirt on the lens, etc., and the disturbance light. Unlike detecting dirt on the lens, etc., it can distinguish between a decrease in the brightness of the light source on the projector side and a decrease in the received light output due to dirt on the lens, etc., and issue a warning signal only when the lens, etc. is dirty. It is also possible to issue a warning against disturbances caused by external light.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the principle of the photoelectric switch of the present invention.
FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 3 is a front view of the arrangement of light receiving elements in the same embodiment, and FIG.
5 are circuit diagrams of other embodiments of the present invention. DESCRIPTION OF SYMBOLS 1... Condenser lens, 2... Main light receiving element, 3... Auxiliary light receiving element, 4... Signal processing section, 43. 44...
Level discrimination circuit. Agent Patent Attorney Kosuke Ne

Claims (1)

[Claims] (11) Object detection based on a change in the output of the main light-receiving element, the main light-receiving element arranged at the condensing position of the emitted light, and the auxiliary light-receiving element arranged around it. output a signal,
A photoelectric switch comprising a signal processing circuit that outputs a warning signal based on the output of an auxiliary light receiving element. (2) The signal processing circuit is configured to level-discriminate the output change of the main light-receiving element and issue an object detection signal, and to level-discriminate the output of the auxiliary light-receiving element and issue a warning signal. Photoelectric switch. (3) The signal processing circuit distinguishes the level of the output change of the main light receiving element, outputs an object detection signal, compares the ratio of the output of the main light receiving element and the auxiliary light receiving element with a predetermined level, and outputs a condemnation signal. A photoelectric switch according to claim 1, wherein: