Photoelectric sensor

Abstract

To provide a photoelectric sensor that can prevent malfunctions caused by sunlight. [Solution] The photoelectric sensor 100 comprises a light emitter 10 that emits light toward a predetermined area, and a light receiver 20 that receives the light emitted from the light emitter 10 with a plurality of light receiving elements 22 and detects the presence or absence of an object to be detected in the predetermined area according to the amount of light received by each light receiving element 22. The light receiver 20 is connected to each light receiving element 22 and has a current limiting unit 41 that limits the current corresponding to the amount of light received by the light receiving element 22 that receives sunlight, according to the amount of sunlight received, and a current summing unit 42 that sums the currents from each current limiting unit 41 and outputs the summed current.

Description

Technical Field

[0001] The present disclosure relates to a photoelectric sensor for detecting the presence or absence of an object.

Background Art

[0002] Patent Document 1 discloses a photoelectric sensor. The photoelectric sensor disclosed in Patent Document 1 is a photoelectric sensor using the principle of triangulation. This photoelectric sensor detects the distance to the measurement object from the reflected light when light is projected toward the measurement object.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] [[ID=3,4]]<00000, The photoelectric sensor disclosed in Patent Document 1 has a plurality of photodiodes as light-receiving elements of the light receiver. And the photoelectric sensor disclosed in Patent Document 1 pre-sets the sensitivity of the photodiode that may be saturated by the light reflected by the measurement object to be low. For this reason, the photoelectric sensor disclosed in Patent Document 1 suppresses the reflected light reception amount from the measurement object located at a short distance from becoming excessive in the photodiode even when the measurement object is located at a short distance.

[0005] Here, if the photoelectric sensor disclosed in Patent Document 1 is installed outdoors, sunlight may be incident on the light-receiving element. In this case, since sunlight is strong light, even if the photodiode in the photoelectric sensor disclosed in Patent Document 1 has its sensitivity set to a low level beforehand, it will be saturated by sunlight. When a photodiode is saturated by sunlight in this way, it can no longer receive any more light. For this reason, the photoelectric sensor disclosed in Patent Document 1 will determine that it is in a light-blocking state even though the light receiver is in a light-receiving state. As a result, the photoelectric sensor disclosed in Patent Document 1 will detect the presence of a measurement target even though the measurement target does not exist.

[0006] This disclosure was made to solve the above-mentioned problems and aims to provide a photoelectric sensor that can prevent malfunctions caused by sunlight. [Means for solving the problem]

[0007] The photoelectric sensor according to this disclosure comprises a light emitter that emits light toward a predetermined area, and a light receiver that receives the light emitted from the light emitter with a plurality of light receiving elements and detects the presence or absence of an object to be detected in the predetermined area according to the amount of light received by each light receiving element, wherein each light receiver is connected to a light receiving element and has a current limiting unit that limits the current corresponding to the amount of light received by the light receiving element that receives sunlight according to the amount of sunlight received, and a current summing unit that sums the currents from each current limiting unit and outputs the summed current. [Effects of the Invention]

[0008] According to this disclosure, malfunctions caused by sunlight can be prevented. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the photoelectric sensor according to Embodiment 1. [Figure 2] This is an enlarged view of the main part of Figure 1. [Figure 3]This is a front view of the light-receiving surface formed by multiple light-receiving elements in a photodetector. Figure 3A shows the light-collecting position on the light-receiving surface. Figure 3B shows the position of sunlight incidence on the light-receiving surface. [Figure 4] This figure shows the angle of incidence of sunlight on the light-receiving surface. Figure 4A shows the case when sunlight does not incident on the light-receiving surface. Figure 4B shows the case when sunlight incident on the light-receiving surface. [Figure 5] This is an enlarged view of the main part of the photoelectric sensor according to Embodiment 2. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure will be described in detail below with reference to the drawings.

[0011] Embodiment 1. The photoelectric sensor 100 according to Embodiment 1 will be described with reference to Figures 1 and 2.

[0012] Figure 1 is a schematic diagram of the photoelectric sensor 100 according to Embodiment 1. The photoelectric sensor 100 according to Embodiment 1 shown in Figure 1 is, for example, a through-beam photoelectric sensor or a reflector-reflector photoelectric sensor (sometimes referred to as a retro-reflector photoelectric sensor) that detects the presence or absence of an object to be detected in a predetermined area set in advance. The photoelectric sensor 100 is installed, for example, indoors or outdoors in a location where sunlight is incident.

[0013] In this case, if the photoelectric sensor 100 according to Embodiment 1 shown in Figure 1 is a through-type photoelectric sensor, the photoelectric sensor 100 comprises a light emitter 10 and a light receiver 20. In the through-type photoelectric sensor 100, the light emitter 10 and the light receiver 20 are arranged facing each other across a predetermined area where an object to be detected can be placed.

[0014] In the transmissive photoelectric sensor 100, the light projector 10 projects light toward the light receiver 20. The light receiver 20 receives the transmitted light that is projected from the light projector 10 and transmits through a predetermined area, or the transmitted light that is projected from the light projector 10 and transmits through the detection target present in the predetermined area, and detects the amount of the received transmitted light. Then, based on the amount of received light, the light receiver 20 determines the presence or absence of the detection target in the predetermined area.

[0015] Further, when the photoelectric sensor 100 according to Embodiment 1 shown in FIG. 1 is a reflector reflection type photoelectric sensor, the photoelectric sensor 100 includes a light projector 10, a light receiver 20, and a reflector (not shown). The reflector reflection type photoelectric sensor 100 uses the integrated light projector 10 and light receiver 20 as a sensor body, and arranges the sensor body and the reflector to face each other with a predetermined area where the detection target can be arranged therebetween.

[0016] In the reflector reflection type photoelectric sensor 100, the light projector 10 projects light toward the reflector. The reflector reflects the transmitted light that is projected from the light projector 10 and transmits through a predetermined area, or the transmitted light that is projected from the light projector 10 and transmits through the detection target present in the predetermined area, as return reflected light toward the light receiver 20. The light receiver 20 receives the reflected light from the reflector and detects the amount of the received reflected light. Then, based on the amount of received light, the light receiver 20 determines the presence or absence of the detection target in the predetermined area.

[0017] The light projector 10 has a light projecting element 11, a light projecting lens 12, and a drive circuit 13.

[0018] The light projecting element 11 projects light. The light projecting element 11 is, for example, a light emitting diode (LED).

[0019] The light projecting lens 12 is a lens that receives the light projected from the light projecting element 11 and projects the received light toward the light receiver 20 or the reflector.

[0020] The drive circuit 13 is connected to the light-emitting element 11. The drive circuit 13 drives the light emission of the light-emitting element 11 by controlling the drive current of the light-emitting element 11 according to the applied drive voltage.

[0021] The light receiver 20 includes a light-receiving lens 21, a plurality of light-receiving elements 22, an I / V conversion circuit 23, an amplifier circuit 24, a signal processing circuit 25, a comparison circuit 26, an output circuit 27, a plurality of current limiting units 31, and a current totalizing unit 32. Details of the current limiting unit 31 and the current totalizing unit 32 will be described later.

[0022] The light-receiving lens 21 receives the transmitted light from the light emitter 10 in the transmissive type optical sensor 100 or the reflected light from the reflector in the reflector reflection type optical sensor 100, and condenses the received light toward the light-receiving element 22.

[0023] The light-receiving element 22 forms a flat light-receiving surface 22A in the light receiver 20. The light receiver 20 divides and forms one light-receiving surface 22A by a plurality of light-receiving elements 22. (See FIG. 3) The light-receiving element 22 is, for example, a photodiode.

[0024] The I / V conversion circuit 23 is connected to the light-receiving element 22 via a plurality of current limiting units 31 and one current totalizing unit 32. The I / V conversion circuit 23 performs I / V conversion on the current output by the light-receiving element 22 according to its light-receiving amount. I / V conversion is an operation of converting current into voltage. The I / V conversion circuit 23 converts a minute current signal (light-receiving signal) from the light-receiving element 22 into an easy-to-handle voltage signal (light-receiving signal). Further, the I / V conversion circuit 23 transmits the converted voltage signal to the amplifier circuit 24.

[0025] The amplifier circuit 24 is connected to the I / V conversion circuit 23. The amplifier circuit 24 receives and amplifies the received signal transmitted from the I / V conversion circuit 23. Further, the amplifier circuit 24 transmits the amplified received signal to the signal processing circuit 25.

[0026] The signal processing circuit 25 is connected to the amplification circuit 24. The signal processing circuit 25 receives the received signal transmitted from the amplification circuit 24 and converts it to digital. That is, the signal processing circuit 25 converts the received signal, which is analog data, into digital data. The signal processing circuit 25 then transmits the converted digital data to the comparison circuit 26.

[0027] The comparison circuit 26 is connected to the signal processing circuit 25. The comparison circuit 26 detects the presence or absence of an object to be detected in a predetermined area by comparing the digital data (signal level of the received signal) converted digitally by the signal processing circuit 25 with a predetermined threshold (voltage value). For example, if the signal level is above the threshold, the comparison circuit 26 detects that an object to be detected is present in the predetermined area. On the other hand, if the signal level is below the threshold, the comparison circuit 26 detects that an object to be detected is not present in the predetermined area. The comparison circuit 26 also transmits the detection result indicating the presence or absence of an object to be detected in the predetermined area to the output circuit 27.

[0028] The output circuit 27 is connected to the comparator circuit 26. The output circuit 27 receives the detection result transmitted from the comparator circuit 26 and outputs the received detection result to the outside of the photodetector 20. The output circuit 27 is, for example, a transistor.

[0029] Next, the details of the multiple current limiting units 31 and the current summing unit 32 will be explained using Figure 2. Figure 2 is an enlarged view of the main parts of Figure 1.

[0030] As shown in Figure 2, the photodetector 20 has multiple photodetectors 22, multiple current limiting units 31, and one current summing unit 32. There is a one-to-one relationship between the photodetectors 22 and the current limiting units 31, and the number of photodetectors 22 matches the number of current limiting units 31. That is, one current limiting unit 31 is connected to one photodetector 22. All current limiting units 31 are connected to one current summing unit 32. The current summing unit 32 is also connected to the I / V conversion circuit 23.

[0031] The current limiting unit 31 applies a limit to the current corresponding to the amount of light received by the corresponding light-receiving element 22, in accordance with the amount of sunlight received. When the light-receiving element 22 receives transmitted or reflected light, the current limiting unit 31 sends a current corresponding to the amount of light received to the current summing unit 32. Furthermore, when the light-receiving element 22 receives sunlight, the current limiting unit 31 reduces the current corresponding to the amount of light received to a preset current, and then sends that reduced current to the current summing unit 32. In this way, the current limiting unit 31 prevents current saturation in the I / V conversion circuit 23 and prevents malfunction of the I / V conversion circuit 23 by reducing the current according to the amount of sunlight received.

[0032] The current summing unit 32 sums the currents sent from the light-receiving element 22 via the current limiting unit 31, and sends the summed current to the I / V conversion circuit 23.

[0033] Next, the focusing of light onto the light-receiving surface 22A and the incidence of sunlight onto the light-receiving surface 22A will be explained using Figures 3 and 4. Figure 3 is a front view of the light-receiving surface 22A, which is divided and formed by a plurality of light-receiving elements 22 in the light receiver 20. Figure 4 is a diagram showing the incidence angle of sunlight Lb onto the light-receiving surface 22A. Note that Figure 4 shows only the through-type photoelectric sensor 100 as a representative example of the two types of photoelectric sensors 100: the through-type and the refrain-reflection type.

[0034] As shown in Figure 3, the light-receiving surface 22A of the light receiver 20 is divided and formed by multiple light-receiving elements 22. Figure 3 shows an example in which one light-receiving surface 22A is divided and formed by nine light-receiving elements 22. In this case, the light-receiving end faces of the light-receiving elements 22 are square, and each light-receiving element 22 is arranged so that the entire light-receiving surface 22A is square. However, the shape of the light-receiving surface 22A, and the shape, number, and arrangement of the light-receiving elements 22 can be adjusted as appropriate.

[0035] As shown in Figure 4A, when the angle of incidence of sunlight Lb to the light-receiving surface 22A is the same as the angle of focus of transmitted light La to the light-receiving surface 22A, the sunlight Lb attempting to enter the light-receiving surface 22A is blocked by the light emitter 10. Therefore, sunlight Lb does not enter the light-receiving surface 22A. In other words, only transmitted light La is focused onto the light-receiving surface 22A.

[0036] On the other hand, as shown in Figure 4B, if the angle of incidence of sunlight Lb to the light-receiving surface 22A is different from the angle of focus of transmitted light La to the light-receiving surface 22A, sunlight Lb will be incident on the light-receiving surface 22A without being obstructed by the light emitter 10. Therefore, both transmitted light La and sunlight Lb will be received by the light-receiving surface 22A. In other words, as shown in Figure 4B, when transmitted light La and sunlight Lb are received by the light-receiving surface 22A, there is a risk of malfunction due to sunlight Lb.

[0037] Therefore, as shown in Figures 3A and 3B, in the photoelectric sensor 100, the shape, number, and arrangement of the light-receiving elements 22 are predetermined so that the light-receiving elements 22 that focus transmitted light La and the light-receiving elements 22 that receive sunlight Lb are separate light-receiving elements 22. Figures 3A and 3B show examples in which the shape, number, and arrangement of the light-receiving elements 22 are predetermined so that there is one light-receiving element 22 that focuses transmitted light La and one light-receiving element 22 that receives sunlight Lb. Note that among the multiple light-receiving elements 22 that form the light-receiving surface 22A, there may be some light-receiving elements 22 that do not receive either transmitted light La or sunlight Lb.

[0038] In this case, as shown in Figures 3A and 3B, the size of the light-receiving area Sa that receives transmitted light La and the size of the light-receiving area Sb that receives sunlight Lb are different from each other. In order to distinguish between the collection position of transmitted light La and the incident position of sunlight Lb, the size of the light-receiving element 22 is set to be large enough to include the light-receiving areas Sa and Sb.

[0039] Furthermore, the light-receiving elements 22 that receive sunlight Lb need to change their arrangement on the light-receiving surface 22A depending on the position of the sun. For this reason, all the light-receiving elements 22 forming the light-receiving surface 22A can be changed to any one of the following: a light-receiving element 22 that receives only transmitted light La, a light-receiving element 22 that receives only sunlight Lb, or a light-receiving element 22 that receives no light at all. To accommodate such changes, a current limiting unit 31 is connected to all the light-receiving elements 22 forming the light-receiving surface 22A.

[0040] Furthermore, when a refrain-reflecting type photoelectric sensor 100 is used, a reflector is installed at the same location as the light receiver 20 in a transmissive type photoelectric sensor 100. Therefore, the shape, number, and arrangement of the light receiving elements 22 are predetermined so that the light receiving element 22 that collects the reflected light La transmitted by the reflector and the light receiving element 22 that receives the reflected light Lb of sunlight from the reflector are separate light receiving elements 22.

[0041] Therefore, when transmitted or reflected light and sunlight are received by separate light-receiving elements 22 on the light-receiving surface 22A, a current corresponding to the amount of transmitted or reflected light received and a limiting current corresponding to the amount of sunlight received flow through the I / V conversion circuit 23, thus preventing current saturation in the I / V conversion circuit 23. At this time, the limiting current corresponding to the amount of sunlight received is constant and does not change. In contrast, the current corresponding to the amount of transmitted or reflected light received fluctuates depending on the passage of the object to be detected. For this reason, the photoelectric sensor 100 facilitates the detection of the presence or absence of the object to be detected by the comparison circuit 26 by cutting the limiting current corresponding to the amount of sunlight received in the stage after the I / V conversion circuit 23 or after the amplification circuit 24.

[0042] In the photoelectric sensor 100 according to Embodiment 1 described above, an I / V conversion circuit 23 is provided after the current summing unit 32. However, an I / V conversion circuit 23 may be provided after each current limiting unit 31. In this case, the current summing unit 32 becomes a voltage summing unit and sums the voltages converted by each I / V conversion circuit 23.

[0043] As described above, the photoelectric sensor 100 according to Embodiment 1 is a photoelectric sensor comprising a light emitter 10 that emits light toward a predetermined area, and a light receiver 20 that receives the light emitted from the light emitter 10 with a plurality of light receiving elements 22 and detects the presence or absence of an object to be detected in the predetermined area according to the amount of light received by each light receiving element 22. The light receiver 20 is connected to each light receiving element 22 and has a current limiting unit 31 that limits the current corresponding to the amount of light received by the light receiving element 22 that receives sunlight, according to the amount of sunlight received, and a current summing unit 32 that sums the currents from each current limiting unit 31 and outputs the summed current. For this reason, the photoelectric sensor 100 according to Embodiment 1 can prevent malfunctions caused by sunlight.

[0044] In the photoelectric sensor 100 according to Embodiment 1, the light-receiving element 22 that receives light emitted from the light emitter 10 and the light-receiving element 22 that receives sunlight are different light-receiving elements 22. Therefore, the photoelectric sensor 100 according to Embodiment 1 can easily detect the presence or absence of an object to be detected in a predetermined area.

[0045] In the photoelectric sensor 100 according to Embodiment 1, the light-receiving element 22 is formed to a size that includes the light-receiving area Sa of light emitted from the light emitter 10 and the light-receiving area Sb of sunlight, respectively. Therefore, in the photoelectric sensor 100 according to Embodiment 1, it is possible to easily distinguish between the light-receiving element 22 that collects transmitted light La and the light-receiving element 22 into which sunlight Lb is incident.

[0046] Embodiment 2. The photoelectric sensor 200 according to Embodiment 2 will be described with reference to Figure 5. Figure 5 is an enlarged view of the main part of the photoelectric sensor 200 according to Embodiment 2. Components having the same function as those described in Embodiment 1 above are denoted by the same reference numerals, and their descriptions are omitted.

[0047] The photoelectric sensor 200 according to Embodiment 2 shown in Figure 5 is equipped with a current monitoring unit 41 in place of the current limiting unit 31 of the photoelectric sensor 100 according to Embodiment 1 shown in Figures 1 and 2.

[0048] The current monitoring unit 41 disables the output of the current from the corresponding light-receiving element 22 if the current corresponding to the amount of light received by that light-receiving element 22 exceeds a threshold corresponding to the amount of sunlight received. Conversely, the current monitoring unit 41 keeps the output of the current from the light-receiving element 22 enabled if the current corresponding to the amount of light received by that light-receiving element 22 does not exceed a threshold corresponding to the amount of sunlight received.

[0049] As described above, the photoelectric sensor 200 according to Embodiment 2 comprises a light emitter 10 that emits light toward a predetermined area, and a light receiver 20 that receives the light emitted from the light emitter 10 with a plurality of light receiving elements 22 and detects the presence or absence of an object to be detected in the predetermined area according to the amount of light received by each light receiving element 22. The light receiver 20 is connected to each light receiving element 22 and includes a current monitoring unit 41 that disables the output of current corresponding to the amount of light received by the light receiving element 22 that has received sunlight, and a current summing unit 32 that sums the currents from the light receiving elements 22 whose current output was not disabled by the current monitoring unit 41 and outputs the summed current. Therefore, the photoelectric sensor 200 according to Embodiment 2 can prevent malfunctions caused by sunlight.

[0050] Within the scope of this disclosure, it is possible to freely combine the embodiments, modify any component in each embodiment, or omit any component in each embodiment. [Explanation of Symbols]

[0051] 10 Floodlights 11 Light-emitting elements 12 Floodlight Lenses 13. Drive Circuit 20 Receiver 21 Light-receiving lens 22 Photodetector 22A light receiving surface 23 I / V conversion circuit 24 Amplifier Circuit 25 Signal Processing Circuits 26 Comparison circuit 27 Output Circuit 31 Current limiting section 32 Current summing section 41 Current monitoring section 100,200 photoelectric sensors La transmitted light Lb sunlight Sa Light-receiving area Sb light receiving area

Claims

1. A photoelectric sensor comprising a light emitter that emits light toward a predetermined area, and a light receiver that receives the light emitted from the light emitter with a plurality of light receiving elements and detects the presence or absence of an object to be detected in the predetermined area according to the amount of light received by each light receiving element, The aforementioned light receiver is, Each light-receiving element is connected to a current limiting unit that limits the current corresponding to the amount of light received by the light-receiving element, in accordance with the amount of sunlight received. It has a current summing unit that sums the currents from each current limiting unit and outputs the summed current. A photoelectric sensor characterized by the following features.

2. A photoelectric sensor comprising a light emitter that emits light toward a predetermined area, and a light receiver that receives the light emitted from the light emitter with a plurality of light receiving elements and detects the presence or absence of an object to be detected in the predetermined area according to the amount of light received by each light receiving element, The aforementioned light receiver is, Each light-receiving element is connected to a current monitoring unit that disables the output of the current corresponding to the amount of light received by the light-receiving element, The system includes a current summing unit that sums the currents from photodetectors whose current output was not disabled by the current monitoring unit and outputs the summed current. A photoelectric sensor characterized by the following features.

3. The light-receiving element that receives light emitted from the light emitter and the light-receiving element that receives sunlight are different light-receiving elements from each other. A photoelectric sensor according to claim 1 or 2, characterized in that it is a photoelectric sensor.

4. The aforementioned light-receiving element is It is formed to a size that includes the light-receiving area of ​​the light emitted from the aforementioned floodlight and the light-receiving area of ​​sunlight, respectively. A photoelectric sensor according to claim 1 or 2, characterized in that it is a photoelectric sensor.

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