JPH02213220A - Reflection type photoelectric switch - Google Patents

Abstract

PURPOSE:To surely detect all light shield objects regardless of the color and position of an object to be detected by emitting a red light and an infrared ray with a different wavelength radiating from one light emitting element, giving the light to a recursive reflecting plate with one and same optical axis, absorbing the infrared ray with the recursive reflecting plate and reflecting the red light. CONSTITUTION:A light emitting diode of a light projection element 3 emits a red light and an infrared ray and the lights irradiates the recursive reflecting plate 7 provided to a position apart from a reflection type photoelectric switch main body via a condenser lens 5. The recursive reflection plate 7 absorbs the infrared ray and reflects only the red light in the same direction. When an object 8 shielding the optical path shields the light completely, the optical current of two photodiodes PD-a, PD-b of a light receiving element 4 is almost zero. When an object having a mirror surface exists between the photoelectric switch main body and the recursive reflection plate 7, a strong reflecting light is made incident in the light receiving element and the infrared ray is made incident in the light receiving element 4 at the same time. A constant reflected light is obtained independently of the wavelength in the case of a white object to be detected. Thus, the light shield object is accurately detected.

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention irradiates light from a light projector onto a retroreflector, receives the reflected light by a light receiver to form a light path, and the light path is blocked by a detection object. This invention relates to a retroreflective photoelectric switch that detects an object when it is touched.

[Conventional technology]

Conventionally, a retroreflective photoelectric switch is known in which a light emitting and receiving part is housed in a single case, and the light emitting part emits light onto a regressive reflector and receives the reflected light, while also obtaining a detection signal by blocking light from the detection object. ing. In such a retroreflective photoelectric switch, if the surface of the object to be detected has a mirror surface such as metallic luster, the light from the light emitter is reflected by the mirror surface and given to the light receiver. However, there is a problem in that it may not be possible to detect this regardless of the situation.

Therefore, as shown in Japanese Patent Application Laid-Open No. 59-119628, light of different wavelengths, for example, red light and infrared light, is irradiated onto the retroreflector plate using two light projecting elements. A retroreflective photoelectric switch has been proposed that reflects only external light and identifies a retroreflector and a detection object by comparing the levels of the reflected light.

[Problem to be solved by the invention]

However, such conventional reflective photoelectric switches have a drawback in that objects with printed colors such as blue or purple cannot be distinguished from the retroreflector. That is, objects with colors such as blue and violet absorb red light and reflect infrared light with longer wavelengths. Therefore, when a retroreflector that absorbs red light is used, there is a drawback that the retroreflector at a long distance and the blue printed matter at a short distance cannot be distinguished and cannot be detected. In addition, conventional reflective photoelectric switches require two sets of light emitters.
The disadvantage is that the number of parts in the optical system increases. Furthermore, since the optical axes of the two light emitting sections are slightly shifted, there is a problem that if a detection object blocks only the light beam on one of the optical axes, there is a risk of a detection signal being output erroneously. there were.

In addition, the applicant has already proposed a reflection method that detects an object regardless of its color by adding and subtracting the outputs of a light-receiving section that receives infrared light and red light, and distinguishing the outputs using a predetermined threshold value. We are proposing a type photoelectric switch (unpublished). However, such a photoelectric switch has a drawback in that when an object is close and the amount of reflected light is large, the output of the amplifier becomes saturated, making it impossible to accurately detect the object.

The present invention has been made in view of the problems of conventional reflective photoelectric switches, and is capable of reliably detecting all light-blocking objects regardless of the color or position of the detection object. The technical problem is to enable a simple optical system to accurately detect a detection object with a mirror surface without malfunction.

[Means for Solving the Problems] The invention of claim 1 of the present application includes a light projecting section and a light receiving section provided in the photoelectric switch main body, and a light projecting section and a light receiving section arranged at a position away from the photoelectric switch main body to reflect the irradiated light. A reflective photoelectric switch that detects an object by reciprocating light from a light projecting section via the regression reflector and having a detection object block the light path, the light projecting section has a light emitting element that emits red light and infrared light, the retroreflector is a reflector that reflects red light and absorbs infrared light, and the light receiving element emits red light and infrared light. The reflective photoelectric switch is a color sensor that has sensitivities for each of the first and second color sensors, and the reflective photoelectric switch has a first one that amplifies the output of each color sensor of the light receiving element. a second logarithmic amplifier; a first logarithmic amplifier; a first discriminator that adds the outputs of the second logarithmic amplifier and compares the sum with a predetermined threshold; a second determining means for detecting an output deviation of the second logarithmic amplifier and comparing it with a predetermined threshold; The present invention is characterized in that it comprises a logical product means for giving a logical product output of the second determining means, and the presence or absence of an object is determined based on the logical product output.

In addition, the invention of claim 2 of the present application sets the outputs of the color sensors to the first and second outputs, respectively. The second amplifier amplifies the amplified signal and supplies the amplified signal to the first and second discriminating means. An AGC circuit is provided to control the driving current of the light projecting element using the addition output of the second amplifier.

Further, the invention according to claim 3 of the present application is a reflective photoelectric switch in which the output of the color sensor is connected to the first . , %2 logarithmic amplifier and the first . An AGC circuit is provided to control the drive current of the light projecting element using the addition output of the second logarithmic amplifier.

[Effect]

According to the invention of claim 1 of the present application having such characteristics, red light and infrared light of different wavelengths are emitted from one light projecting element and applied to the retroreflector on the same optical axis. The 0-return reflector in the photoelectric switch absorbs infrared light and reflects red light, and the reflected light is given to a light receiving element provided within the photoelectric switch body and sensitive to light of both wavelengths. The output of each color sensor of the light receiving element is the first. amplified by a second logarithmic amplifier; is given to the second determining means.

1st. The second discrimination means adds and subtracts the outputs of the pair of logarithmic amplifiers and compares them with a predetermined threshold.

Then, the object is detected by the logical product of these discrimination means. Therefore, in the case of a general reflective object, the output of any color sensor is extremely low, so the presence of the object is detected by the first discrimination means. Since a deviation is obtained in the output, an object detection signal can be obtained from the second discrimination means by comparing the deviation with a threshold value.

Also, when a retroreflector or a specular object is nearby and the output level from the color sensor is high, the color sensor output will be the first. Since the output of the logarithmic amplifier is amplified by the second amplifier, the output of the logarithmic amplifier does not saturate. The information is transmitted to the second determining means.

Further, in the invention of claim 2 of the present application, a normal amplifier is used in place of the logarithmic amplifier, and the light projection level of the light projection element is controlled by the AGC circuit based on the addition output of the first determining means.

Further, in the invention of claim 3 of the present application, the output of the logarithmic amplifier is prevented from being saturated by using the logarithmic amplifier and the AGC circuit simultaneously.

〔Effect of the invention〕

Therefore, according to the inventions of claims 1 to 3 of the present application, it is possible to detect an object without malfunction even when a retroreflector or a specular object is located at a short distance. Furthermore, since a retroreflector that absorbs infrared light and reflects red light is used, it is possible to reliably detect all objects, including blue and violet objects. Furthermore, since one light projecting element emits light of different wavelengths, the configuration of the optical system is extremely simple and the entire photoelectric switch can be miniaturized. Furthermore, since the emission axes of the red light and infrared light emitted from the photoelectric switch do not separate, it is possible to prevent false detection of an object due to one of the optical axes being blocked. You can get the effect that you can.

[Explanation of Examples]

FIG. 1 is a diagram showing the structure of an optical system of a reflective photoelectric switch according to a first embodiment of the invention of claim 1 of the present application. In this figure, a light emitting element 3, such as a light emitting diode, and a light receiving element 4, such as a photodiode, are mounted on a printed circuit board 2 in a case l of a photoelectric switch. The light projecting element 3 is made of GaA as shown in FIG. 2(a), for example.
A light emitting diode having an ItAs heterojunction structure,
For example, the light emitting diode used in this example has a strong red light with a wavelength of 660 na+ and a weak light with a wavelength of 880 nm. It is a light emitting diode that emits infrared light at the same time. Now, the light emitting and receiving elements 3 and 4 are provided with condensing lenses 5 and 6 at opposing positions, respectively. The condensing lens 5 irradiates the light emitted from the light projecting element 3 onto a retroreflector plate 7 located a predetermined distance away from the photoelectric switch body. The retroreflector 7 is configured to absorb infrared light and reflect only red light, and is a collection of corner cubes made of acrylic resin mixed with paint that absorbs infrared light and transmits red light. Constructed by integrally molding the body. For example, as shown in FIG. 3, the retroreflector 7 has a spectral characteristic of reflecting almost no infrared light of 880nII but reflecting 60% or more of red light of 660nm.

A condensing lens 6 provided on the front surface of the photoelectric switch focuses reflected light onto the light receiving element 4.

The light-receiving element 4 is a color sensor that obtains signals by separating light of different wavelengths, and for example, as shown in FIG. Colors are determined using the differences in their spectral characteristics.

These photodiodes are equivalently displayed as two photodiodes PD-a and PD-b as shown in FIG. These photodiodes PD-a+P
D-b each has characteristics with respect to wavelength as shown in FIG. 4(C), for example.

Next, a first embodiment of a photoelectric switch embodying the first invention of the present application will be described with reference to FIG. First, the outputs of the two photodiodes PD-a and PD-su are given to logarithmic amplifiers 10 and 11, respectively. Logarithmic amplifier 1
The outputs Va and vb of 0.11 are respectively sent to adders 12. The subtracter 13 receives the subtractor 13. The adder 12 adds the outputs of the two amplifiers (Va+vb), and its output is the first
is applied to the comparator 14 of . Also, the subtracter 13 is the amplifier 10
The output vb of the amplifier 11 is subtracted from the output Va of (Va
-vb), the output of which is given to the second comparator 15. Comparators 14 and 15 each have a threshold value V thl
, V th2 are given, and when inputs exceeding these thresholds are given, rHJ level outputs are given to the AND and DO circuits 16, respectively. Here, the adder 12 and the comparator 14 are color sensors that are light receiving elements.

A subtracter 13 and a comparator 15 detect the output deviation of the color sensor, which is a light receiving element, and compare the two outputs at a predetermined threshold level. It constitutes a second discrimination means 19 for comparing with. The AND circuit 16 constitutes an AND means for taking these AND signals, and provides its output to the output circuit 17. The output circuit 17 outputs the presence or absence of object detection to the outside based on the output of the AND circuit 16'.

Further, this reflective photoelectric switch has a light emitter drive circuit 20 that drives the light emitter 3 continuously or intermittently, and is configured so that the light emitter 3 is driven by the light emitter drive circuit 20. .

The light emitting diode of the light projecting element 3 emits red light and infrared light with a spectrum as shown in FIG. The 0-recurrence reflector 7, which is irradiated onto the recursive reflector 7 provided at a distant position, absorbs infrared light and reflects only red light in the same direction. Therefore, only red light is applied to the photodiode, which is the light receiving element 4, via the condenser lens 6. Table 1 below shows the operating status of each part of the photoelectric switch.

(Leaving space below) Table 1 (1) No detected object When there is no detected object and does not block the optical path, the two photodiodes PD-a and PD-b of the light receiving element 4 are set as shown in Fig. 4 (C). PD-
In Table 1, the relative values of the photocurrent are shown as 5 and 1.5 when there is no detection object. Here, the logarithmic amplifiers 10 and 11 are provided so that the output is not saturated, and the amplification factor is set by the photodiode PD-a.
, PD-b variations and retroreflector 7. For example, it is assumed that the logarithmic amplifier 10 has an amplification factor of 201ogx with respect to the input X, and the logarithmic amplifier 11 has an amplification factor of 601ogx, which is set to absorb variations in the light projecting elements. Also comparator 1
4 reference voltage vth1・20. Reference voltage V of comparator 15
When th2=O, the photocurrent outputs of the two photodiodes are amplified by logarithmic amplifiers 10.11, respectively, and adders 12.11 as shown in Table 1. The output of the subtractor 13 is obtained.

Then, if discrimination is made using the threshold value mentioned above, the comparators 14 and 15 will be r
In order to output an HJ level output, the logical product condition is satisfied and the object detection output becomes null.

(If) General light-blocking object When the object 8 that blocks the light path completely blocks light, the photocurrents of the two photodiodes PD-a and PD-b both become almost zero. In this case, the logarithmic amplifiers 10 and 11 do not operate normally and are shown in Table 1, for example. Therefore, as shown in Table 1, the output of the comparator 14 is "L
”, the output of the comparator 15 becomes undefined, but the AND circuit 16
Since the AND output of is "L", the object can be detected.

(III) Object with a mirror surface When an object with a mirror surface exists between the photoelectric switch main body and the retroreflector 7, strong reflected light enters the light receiving element. However, since the reflectance of the mirror surface is constant regardless of the wavelength, infrared light also enters the light receiving element 4 at the same time. Therefore, from the optical system having the characteristics shown in FIG. 2(b), FIG. 3, and FIG. 4(C), for example, as shown in Table 1, PD-a, PD-b
For example, a photocurrent corresponding to 60.30 is obtained. In this case, the outputs of the logarithmic amplifiers 10 and 11 are amplified to r36J "89" without being saturated, and the adders 12 and 12. The output shown in Table 1 is obtained from the subtracter 13. Therefore, the output of the comparator 14 is "H", and the output of the comparator 15 is r
Since it becomes LJ, an object detection output can be obtained.

(IV) White detection object Also in this case, a constant amount of reflected light can be obtained regardless of the wavelength. Although the current level is small as shown in Table 1, an output similar to that of an object with a mirror surface can be obtained. Therefore, the logical product condition of the AND circuit 16 is satisfied, and an object detection output is obtained as in the case of a mirror surface.

Next, a second embodiment embodying the invention of claim 2 of the present application will be described with reference to FIG. 6. The first embodiment described above uses a logarithmic amplifier as an amplifier, but in this embodiment, the two photodiodes PD-a and PD-b are amplified by a pair of amplifiers 21 and 22 having amplification factors m and n, respectively. and is applied to the adder 12 and the subtracter 13. The output of the adder 12 is controlled by AGC to prevent saturation when an object with a mirror surface or the retroreflector 7 is close to each other.
The signal is supplied to the circuit 23. The AGC circuit 23 is supplied with a driving signal for the light projecting element 3 from an oscillator 24 . When the reflected light is extremely strong, such as from an object with a mirror surface, the AGC circuit 23 operates and reduces the light emission level of the light emitting element 3, so that the amplifiers 21 and 22 are not saturated and accurately detect the light blocking object. can do. Furthermore, when the object to be detected is located at a long distance, the current flowing through the light projecting element 3 increases and the light level becomes high, so that the object can be detected accurately regardless of fluctuations in the distance to the retroreflector 7. In this case, the time constant of the AGC circuit 23 is set to be about 10 times the response speed of the photoelectric switch (
This allows objects to be identified without being affected by AGC due to periodically passing objects.

Next, a third embodiment embodying the invention of claim 3 of the present application will be described with reference to FIG. 7. This example is the first example. This is a combination of the configurations of the second embodiment. That is, the outputs of the photodiodes PD-a and PD-b are given to the logarithmic amplifiers 10 and 11 as in the first embodiment, and the adder 1
The output of 2 is used as an AGC voltage to change the amount of light from the light projecting element 3. In this case as well, regardless of the position of the retroreflector, and even when a specular object passes close to the photoelectric switch body, the output of the amplifier will not be saturated, making it possible to accurately detect the light-blocking object.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure of an optical system of a reflective photoelectric switch according to an embodiment of the invention of claims 1 to 3 of the present application, and FIG.
a) is a diagram showing the structure of a multicolor light emitting diode used as a light emitting element, FIG. 2 is a graph showing its light emitting characteristics, and FIG.
Figure 4 (al) is a diagram showing the structure of a color sensor used as a light receiving element, Figure 4 (b) is a diagram showing an equivalent circuit of the color sensor, Figure 4 (C) is a graph showing its sensitivity characteristics, 5 is a block diagram showing the electrical configuration of a photoelectric switch according to an embodiment embodying the invention of claim 1 of the present application;
The figure shows the invention of claim 2 of the present application, and FIG. 7 shows the invention of claim 2 of the present application. FIG. 7 is a block diagram showing the electrical configuration of a photoelectric switch according to a third embodiment. 1−・−・Logarithmic amplifier 12−−−−・−Adder
13--...-Subtractor 14, 15--
-1.Comparator 16-...-AND circuit 17-
-------Output circuit 18-...-First discrimination means 19...-Second discrimination means 21.2
2--Amplifier 23-----A G C circuit patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Yoshiki Okamoto (and one other person) 3----------Light emitter 4 −・−・−・Photodetector 5.6−・・−Condensing lens 7−・・−
・-Regression reflector 10.1 Figure 3-----------Ichiyaku*-Bougo 4----L light collector 5.6-------- 8 Gun Izu 7 ----------・Day % snoring diagram (a) Diagram diagram (C) Clothes 5k (nm) *t (nm) Back and front (nm) 3------One throw is collected 4-----At a stroke, 9 serving tongues, 10 potatoes, 1, 1, 19, 1, 2, 1, 2 cow's sources, 3'l-'s roles, and 19 pieces.

Claims (3)

[Claims] (1) It has a light projecting part and a light receiving part provided in the photoelectric switch main body, and a regression reflector that is placed at a position away from the photoelectric switch main body and reflects the irradiated light, and the light projecting part In a reflective photoelectric switch that detects an object by reciprocating the light through the retroreflector and a detection object blocks the light path, the light projecting section includes a light projecting element that emits red light and infrared light. The retroreflector is a reflector that reflects the red light and absorbs the infrared light, and the light receiving element is a color sensor that is sensitive to the red light and the infrared light, respectively. , the reflective photoelectric switch includes: first and second logarithmic amplifiers that respectively amplify the output of each color sensor of the light receiving element; and the sum of the outputs of the first and second logarithmic amplifiers and comparison with a predetermined threshold value. a first discriminating means for detecting the output deviation of the first and second logarithmic amplifiers and comparing it with a predetermined threshold; and a logical product output of the first and second discriminating means. and a logical product means for giving
A reflective photoelectric switch characterized in that the presence or absence of an object is determined based on the AND output. (2) It has a light projecting part and a light receiving part provided in the photoelectric switch main body, and a regression reflector that is placed at a position away from the photoelectric switch main body and reflects the irradiated light, and the light projecting part In a reflective photoelectric switch that detects an object by reciprocating the light through the retroreflector and a detection object blocks the light path, the light projecting section includes a light projecting element that emits red light and infrared light. The retroreflector is a reflector that reflects the red light and absorbs the infrared light, and the light receiving element is a color sensor that is sensitive to the red light and the infrared light, respectively. , the reflective photoelectric switch includes: first and second amplifiers that respectively amplify the output of each color sensor of the light receiving element; and a second amplifier that adds the outputs of the first and second amplifiers and compares the sum with a predetermined threshold. 1, an AGC circuit that controls the light emission level of the light emission element based on the summed outputs of the first and second amplifiers; a second discriminating means for comparing with a threshold value, and an AND means for giving a logical product output of the first and second determining means, and is configured to determine the presence or absence of an object based on the logical product output. A reflective photoelectric switch characterized by: (3) It has a light projecting part and a light receiving part provided in the photoelectric switch main body, and a regression reflector that is placed at a position away from the photoelectric switch main body and reflects the irradiated light, and the light projecting part In a reflective photoelectric switch that detects an object by reciprocating the light through the retroreflector and a detection object blocks the light path, the light projecting section includes a light projecting element that emits red light and infrared light. The retroreflector is a reflector that reflects the red light and absorbs the infrared light, and the light receiving element is a color sensor that is sensitive to the red light and the infrared light, respectively. , the reflective photoelectric switch includes: first and second logarithmic amplifiers that respectively amplify the output of each color sensor of the light receiving element; and the sum of the outputs of the first and second logarithmic amplifiers and comparison with a predetermined threshold value. an AGC circuit that controls the light projection level of the light projection element based on the added outputs of the first and second logarithmic amplifiers; and an output deviation of the first and second logarithmic amplifiers. a second discriminating means for detecting and comparing with a predetermined threshold; and an AND means for providing an AND output of the first and second discriminating means,
A reflective photoelectric switch characterized in that the presence or absence of an object is determined based on the AND output.