JPS6115421A - Photoelectric switch - Google Patents

Abstract

PURPOSE:To reduce the interference between photoelectric switches and influences due to external disturbance by driving a light projecting section of each photoelectric switch with a different code generator, allowing a photodetector section to take the correlation between the code generator and the photodetector output and apply signal processing. CONSTITUTION:Code setters 2, 9 of the light projecting section 1 and the photodetecting section 6 are made identical and the same code is generated from the code generators 3, 10. A signal corresponding to the code is given from the generator 3 to a code modulator 4, where pulse modulation is executed to drive the light projecting element 5. When any object exists, reflected light is received by a photodetector 7 of the photodetector section 6, the light is fed to a correlation device 8 as a signal the same as a signal subjected to pulse modulation and the correlation with the code from the generator 10 is taken. Even if the projected light of other photoelectric switch or an external light is received, since the codes are dissident, the correlation is low, and since only an output of a low level is given, the output does not exceed the reference value even when it is inputted to a comparator 12 via a band pass filter 11 and the output circuit 13 is inactivated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a photoelectric switch that reduces interference between photoelectric switches and the influence of disturbances.

Prior Art and Its Problems Conventional photoelectric switches use a light emitting diode or the like as a light emitting element, and the light emitting element is driven in pulses and applied to the light receiving element. Pulsing the light emitting element in this way makes it more resistant to disturbance light and has a longer detection distance than a photoelectric switch with a DC type light emitter. However, when multiple photoelectric switches are installed in parallel or used, In an environment where there are many signals and a poor S/N ratio, it is difficult to separate and receive the light emitted by the corresponding light emitting part. Therefore, in order to prevent mutual interference between photoelectric switches, for example, each photoelectric switch should be provided with a polarizing filter, etc., which has a different polarization angle (=J
There is a problem in that parts are required, and even in that case, it is not possible to sufficiently prevent the influence of ambient light.

Purpose of the Invention The present invention has been made in view of the problems of conventional photoelectric switches, and is capable of reliably detecting a light emitting signal even in an environment with a poor S/N ratio. The purpose of the present invention is to provide a photoelectric switch free from mutual interference.

Structure and Effects of the Invention The present invention provides a photoelectric switch formed of a pair of light emitting/receiving parts each having a light emitting element and a light receiving element, in which a code generating part that generates a unique code for each photoelectric switch is connected to the light emitting/receiving part. The light emitting section includes a code modulator that drives the light emitting element by the code generating section, and the light receiving section correlates the code output obtained from the code generating section with a certain light reception output from the light projecting section. The device is characterized in that it includes a correlator and a signal processing unit that processes a predetermined signal with a large correlation as a received light signal.

According to the photoelectric switch of the present invention having such characteristics, each photoelectric switch has a unique code that is common to the light emitting and receiving parts, and the light emitting element is modulated based on the code, and the light receiving signal and its The received light signal is discriminated based on the correlation with the code. Therefore, even if a signal from another photoelectric switch with a different sign is received, malfunction will not occur, and mutual interference can be reduced. Furthermore, since the effects of external light and the like can be removed at the same time, it is possible to provide a photoelectric switch that can extend the detection distance and perform reliable object detection even under conditions where the S/N ratio is poor.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 (al is a block diagram of a light projecting section showing an embodiment of the photoelectric switch according to the present invention. In this figure, the light projecting section 1
The code setting device 2 is a setting device that determines a unique code for each photoelectric switch consisting of a pair of light emitting/receiving sections.
It is formed by a switch or the like. The output of this code setter 2 is then given to a code generator 3. The code generator 3 is formed by a chirp filter using, for example, a surface acoustic wave device, and its code output is given to the code modulator 4. The code modulator 4 provides a modulated wave to a light projecting element 5, such as a light emitting diode, in accordance with a given code. In this way, the light projecting section 1 has a unique code pattern formed for each photoelectric switch, and based on the code pattern, an optical signal modulated by the code is provided from the light projecting section 1 to the light receiving section 6.

Next, FIG. 1 Tbl is a block diagram showing one embodiment of the light receiving section 6 of the photoelectric switch according to this embodiment. In this figure, the light receiving element 7 is arranged so as to face the detection area illuminated by the light projecting element 5, and its light receiving signal is guided to the next stage correlator 8. The light receiving section 6 has a code setter 9 to which the same code as that of the light emitting section 1 is set, and a code generator 10 that generates a predetermined pattern of codes based on the setting, and the output of the code generator IO is as follows. Correlator 8 is provided. The correlator 8 distinguishes between the signal from the light projecting section and the signal from the light projecting section of another photoelectric switch or disturbance light by correlating these input signals, and its output is based on the band. It is applied to a comparator 12 via a pass filter 11.

Comparator 12 compares the level of a given input signal with a predetermined reference level, and provides an output to output circuit 13 when the input signal exceeds reference level Vref. The output circuit 13 is composed of, for example, a relay, and transmits an output signal when an object is detected to the outside.

Next, the operation of this embodiment will be explained with reference to flowcharts and waveform diagrams. First, the code setters 2 and 9 of the light emitting unit 1 and the light receiving unit 6 are set to the same code, and when a plurality of photoelectric switches are used in parallel, a different code is set for each photoelectric switch. . Then, the light projector 1
A signal corresponding to the code is given from the code generator 3 to the code modulator 4. In steps 21 and 22 shown in FIG. 3, pulse modulation is performed according to this unique code, and the light emitting element 5
is driving. FIG. 4 is a waveform diagram showing an example of a clock signal and a code, and 0 and 1 signals modulated by the code. The light signal of the light projecting element 5 driven by such pulse modulation is irradiated in the detection direction of the object. Then, if an object is present, its reflected light is given to the light receiving section 6.

Now, in the light receiving section 6, the light receiving element 7 receives the reflected light, converts it into an electric signal, and supplies it to the correlator 8. As mentioned above, the light projecting section 1
The same code is given to the correlator 8 from the code generator lO by the code setter 9, which has the same code as .
The correlation between this code and the light-receiving signal obtained from the light-receiving element 7 is determined (step 23). If the signal received by the light receiving element 7 is a signal from the light emitting part of another photoelectric converter or is disturbance light, the code does not match the code of the code generator inside the light receiving part 6, so there is no correlation. is low, and a lower level output is obtained from the correlator 8. In the case of the light projection signal from the light projection section 1 of the corresponding photoelectric converter, a high level signal is obtained from the correlator 8 because there is a high correlation. The output of this correlator 8 is passed through a bandpass filter 11 to a comparator 12.
is given and compared with the standard darkness value level. If the correlation signal is higher than the dark value level, step 24 to step 2
Proceed to step 5, turn on the output from the output circuit 13, and step 2
Return to 3. If the correlation signal is lower than the dark value in step 24, the signal from the output circuit 13 is turned off (step 26) and the process returns to step 23. In this way, it is possible to eliminate mutual interference with other photoelectric switches and noise from disturbance light, and to operate the output circuit 13 by the signal from the corresponding light projector 1. Although a surface acoustic wave element is used as the correlator, it goes without saying that a digital correlator may also be used.

Furthermore, although this embodiment has described a diffuse reflection type photoelectric switch, if the output of the output circuit 13 is made to output an object detection output when the output from the comparator 12 is not obtained,
It goes without saying that the present invention can be applied to transmission type and retroreflection type photoelectric switches.

[Brief explanation of the drawing]

Figures 1(a) and (bl are block diagrams showing the electrical configuration of one embodiment of the light emitting/receiving part of the photoelectric switch according to the present invention, and Figure 2 is a surface acoustic wave device showing an example of a correlator used in the light receiving part. 3 is a flowchart showing the operation of the photoelectric switch according to the present embodiment, and FIG. 4 is a waveform diagram showing the symbols of the light projecting section and pulse signals corresponding to the symbols. 1. 1 light emitter 2. !l-, -----
Sign setter 3゜10----1 code generator 4-
・−・−Sign converter 5−−−−−11 Light emitting element
6-- Light receiving section 7-------- Light receiving element 8-
--------One correlator 11------Band pass filter 12---One comparator 13---
--One output circuit patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Yoshiki Okamoto (1 person) Figure 1 ('a) m-~'' Figure 1 (b) Figure 2 Figure 4 Figure 3

Claims (2)

[Claims] (1) In a photoelectric switch formed by a pair of light emitting/receiving sections each having a light emitting element and a light receiving element, each of the light emitting/receiving sections has a code generating section that generates a unique code for each photoelectric switch; The light projecting section includes a code modulating section that drives the light projecting element by the code generating section, and the light receiving section is configured to calculate the correlation between the code output obtained from the code generating section and a certain light reception output from the light projecting section. A correlator that takes
1. A photoelectric switch comprising: a signal processing unit that processes a predetermined signal with a high correlation as a received light signal. (2) The photoelectric switch according to claim 1, wherein the correlator is a surface acoustic wave device.