Distance setting type photoelectric sensor

Abstract

To improve detection performance without using division.SOLUTION: A distance setting type photoelectric sensor includes: a light projection section 114; a light reception section 115 that has a light receiving element 105 extended and disposed up to an N-side light reception surface for detecting an object existing in a position nearer than setting distance and a F-side light reception surface for detecting an object existing in a position farther than the setting distance, and receives reflection light for light projected by the light projection section 114; an arithmetic section 107 for calculating a difference (N-F) in a light reception quantity between a light reception quantity N obtained by the N-side light reception surface and a light reception quantity F obtained by the F-side light reception surface; an arithmetic section 109 for calculating a light reception quantity sum (N+F) between the light reception quantity N and the light reception quantity F; a threshold generation section 110 for generating a threshold by multiplying (N+F) by a positive real number coefficient larger than 0 and smaller than 1; and a comparison section 111 for outputting a binary signal as a comparison result between (N-F) and the threshold.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a distance setting type photoelectric sensor that detects the presence or absence of an object within a set distance range. [Background technology]

[0002] Distance-setting photoelectric sensors that detect the presence or absence of an object within a set distance range have been known (see, for example, Patent Document 1). Distance-setting photoelectric sensors detect objects using the principle of triangulation. Figure 4 shows the configuration of a conventional distance-setting photoelectric sensor. A light-projecting circuit 101 drives a light-projecting element 102 such as an LED to emit light. A light-projecting optical system 103 collects light from the light-projecting element 102 and projects the light into a detection area. When an object 100 is present in the detection area, the light is reflected by the object 100.

[0003] The light receiving optical system 104 collects the light reflected by the object 100. The light receiving element 105 receives the light collected by the light receiving optical system 104 and converts it into an electrical signal. The light receiving element 105 may be a two-segment photodiode, a multi-segment photodiode, a PSD (Position Sensitive Detector), a one-dimensional CCD (Charge Coupled Device), or the like. Of the light receiving surfaces of the light receiving element 105, the light receiving surface farther from the detection area is called an N-side (Near side) light receiving surface for detecting the object 100 present at a position closer than a set distance, and the light receiving surface closer to the detection area is called an F-side (Far side) light receiving surface for detecting the object 100 present at a position farther than a set distance.

[0004] The amplifying unit 106-N amplifies the received light amount signal obtained by the N-side light receiving surface 105-N of the light receiving element 105, and the amplifying unit 106-F amplifies the received light amount signal obtained by the F-side light receiving surface 105-F of the light receiving element 105. The arithmetic unit 107 calculates the difference (N - F) between the received light amount N indicated by the N-side received light amount signal amplified by the amplifying unit 106-N and the received light amount F indicated by the F-side received light amount signal amplified by the amplifying unit 106-F. When the object 100 exists at a position farther than the set distance, the light receiving spot on the light receiving surface of the light receiving element 105 is biased toward the F-side light receiving surface 105-F, so the received light amount F becomes larger than the received light amount N (N < F). When the object 100 exists at a position closer than the set distance, the light receiving spot on the light receiving surface of the light receiving element 105 is biased toward the N-side light receiving surface 105-N, so the received light amount N becomes larger than the received light amount F (N > F).

[0005] The comparison unit 108 compares the received light amount difference (N - F) calculated by the arithmetic unit 107 with a predetermined threshold TH. The comparison unit 108 turns the output ON when the received light amount difference (N - F) is larger than the threshold TH, and turns the output OFF when the received light amount difference (N - F) is less than or equal to the threshold TH. Output ON indicates that the object 100 exists within the set distance range, and output OFF indicates that the object 100 does not exist within the set distance range.

[0006] In the distance setting type photoelectric sensor shown in FIG. 4, when the absolute light amount changes, the received light amount difference (N - F) also changes. For this reason, there has been a problem that the detection performance greatly changes depending on the reflectivity of the object 100. For example, when the reflectivity of the object 100 is low, there is a possibility that the output of the comparison unit 108 does not turn ON even when the object 100 exists within the set distance range.

[0007] Therefore, it has been proposed to divide the received light amount difference (N - F) by the sum (N + F) of the received light amount N and the received light amount F to eliminate the influence of the reflectivity of the object 100 (see Patent Documents 2 to 4). In the techniques disclosed in Patent Documents 2 to 4, it is expected to improve the detection performance by setting a reference distance (threshold) based on (N - F) / (N + F).

[0008] However, the techniques disclosed in Patent Documents 2 to 4 have a problem in that a division is required to calculate (NF) / (N+F). When the division is performed by hardware, the area of ​​the division circuit becomes large, and the photoelectric sensor cannot be made compact. When the division is performed by software, the calculation takes time. In addition, when (N+F) is 0, that is, when there is no reflected light, the calculation of (NF) / (N+F) cannot be performed. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 6767072 [Patent Document 2] JP 2006-226851 A [Patent Document 3] JP 2006-226853 A [Patent Document 4] JP 2006-226854 A Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made to solve the above-mentioned problems, and has an object to provide a distance setting type photoelectric sensor that can improve detection performance without using division. [Means for solving the problem]

[0011] The distance setting type photoelectric sensor of the present invention has a light-projecting section configured to project light, a light-receiving element extending to an N-side light-receiving surface for detecting an object located closer than a set distance, and an F-side light-receiving surface for detecting an object located farther than the set distance, and a light-receiving section configured to receive reflected light from the light projected by the light-projecting section, and a light-receiving difference (NF) or light-receiving difference (FN) between the amount of light received N obtained by the N-side light-receiving surface and the amount of light received F obtained by the F-side light-receiving surface. a first calculation unit configured to calculate a sum of the received light amounts N and F (N+F); a threshold generation unit configured to multiply the sum of the received light amounts (N+F) by a coefficient that is a positive real number greater than 0 and less than 1 to generate a first threshold; and a first comparison unit configured to output a first binary signal that is a comparison result between the difference in the received light amounts (NF) or the difference in the received light amounts (FN) and the first threshold. Furthermore, one configuration example of the distance setting type photoelectric sensor of the present invention is characterized in that it further includes a second comparison unit configured to output a second binary signal which is a comparison result between the sum of the received light amounts (N+F) and a second threshold value which is 0 or a positive real number close to 0, and a judgment unit configured to output a third binary signal which is a calculation result between the first binary signal and the second binary signal.

[0012] Furthermore, in one configuration example of the distance setting type photoelectric sensor of the present invention, the first comparison unit turns the first binary signal ON when the difference in the amount of received light (NF) is greater than the first threshold value, and turns the first binary signal OFF when the difference in the amount of received light (NF) is equal to or less than the first threshold value, the second comparison unit turns the second binary signal ON when the sum of the amounts of received light (N+F) is greater than the second threshold value, and turns the second binary signal OFF when the sum of the amounts of received light (N+F) is equal to or less than the second threshold value, and the judgment unit outputs the first binary signal as the third binary signal when the second binary signal is ON, and turns the third binary signal OFF when the second binary signal is OFF. Furthermore, in one configuration example of the distance setting type photoelectric sensor of the present invention, the first comparison unit turns the first binary signal ON when the difference in the amount of received light (FN) is greater than the first threshold value, and turns the first binary signal OFF when the difference in the amount of received light (FN) is equal to or less than the first threshold value, the second comparison unit turns the second binary signal ON when the sum of the amounts of received light (N+F) is greater than the second threshold value, and turns the second binary signal OFF when the sum of the amounts of received light (N+F) is equal to or less than the second threshold value, and the judgment unit outputs the first binary signal as the third binary signal when the second binary signal is ON, and turns the third binary signal ON when the second binary signal is OFF. Effect of the Invention

[0013] According to the present invention, by providing a first calculation unit, a second calculation unit, a threshold generation unit, and a first comparison unit, it is possible to eliminate the influence of the reflectance of an object without using division, and to solve the problem that the detection distance changes depending on the reflectance of an object. Since the present invention does not require the use of a division circuit, it is possible to realize a miniaturized photoelectric sensor. Furthermore, the present invention can increase the response speed of the photoelectric sensor compared to a case where the division is performed by software.

[0014] Furthermore, in the present invention, by providing the second comparing section and the determining section, it is possible to prevent the operation of the photoelectric sensor from becoming unstable. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram showing the configuration of a distance setting type photoelectric sensor according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing the configuration of a distance setting type photoelectric sensor according to a second embodiment of the present invention. [Diagram 3] FIG. 3 is a block diagram showing an example of the configuration of a computer that realizes the distance setting type photoelectric sensors according to the first and second embodiments of the present invention. [Figure 4]FIG. 4 is a block diagram showing the configuration of a conventional distance setting type photoelectric sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] [First Example] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram showing the configuration of a distance setting type photoelectric sensor according to a first embodiment of the present invention, and the same components as those in Fig. 4 are given the same reference numerals. The distance setting type photoelectric sensor includes a light projecting circuit 101, a light projecting element 102, a light projecting optical system 103, a light receiving optical system 104, a light receiving element 105, amplifiers 106-N and 106-F, calculation units 107 and 109, a threshold value generating unit 110, comparison units 111 and 112, and a judgment unit 113.

[0017] The light projecting element 102 and the light receiving element 105 are disposed at a predetermined interval. The light receiving element 105 is disposed such that an N-side light receiving surface 105-N and an F-side light receiving surface 105-F extend along a direction intersecting with the optical axis direction of the reflected light from the object 100. The light projecting circuit 101, the light projecting element 102, and the light projecting optical system 103 constitute a light projecting section 114. The light receiving optical system 104, the light receiving element 105, and the amplifiers 106-N and 106-F constitute a light receiving section 115.

[0018] As in the conventional case, the light-projecting circuit 101 drives the light-projecting element 102 to emit light. The light-projecting optical system 103 collects light from the light-projecting element 102 and projects the light onto a detection area. The light-receiving optical system 104 collects light reflected by the object 100. The light-receiving element 105 receives the light collected by the light-receiving optical system 104 and converts it into an electrical signal. The amplifier 106-N amplifies the light-receiving amount signal obtained by the N-side light-receiving surface 105-N of the light-receiving element 105, and the amplifier 106-F amplifies the light-receiving amount signal obtained by the F-side light-receiving surface 105-F of the light-receiving element 105.

[0019] The calculation unit 107 calculates the difference (NF) between the amount of received light N indicated by the N-side received light amount signal amplified by the amplifier 106-N and the amount of received light F indicated by the F-side received light amount signal amplified by the amplifier 106-F. Meanwhile, the calculation unit 109 calculates the sum (N+F) of the amount of received light N and the amount of received light F. The threshold generation unit 110 multiplies the sum of the amounts of received light (N+F) calculated by the calculation unit 109 by a predetermined coefficient α to generate a threshold α×(N+F). The coefficient α is a positive real number greater than 0 and less than 1.

[0020] The comparison unit 111 compares the difference in the amount of received light (NF) calculated by the calculation unit 107 with a threshold value α×(N+F). The comparison unit 111 turns on an output Y (first binary signal) when the difference in the amount of received light (NF) is greater than the threshold value α×(N+F), and turns off the output Y when the difference in the amount of received light (NF) is equal to or smaller than the threshold value α×(N+F).

[0021] On the other hand, the comparison unit 112 compares the sum of the received light amounts (N+F) calculated by the calculation unit 109 with a predetermined threshold value TH0. The threshold value TH0 is a positive real number of 0 or close to 0. The comparison unit 112 turns on an output X (second binary signal) when the sum of the received light amounts (N+F) is greater than the threshold value TH0, and turns off the output X when the sum of the received light amounts (N+F) is equal to or less than the threshold value TH0.

[0022] The judgment unit 113 outputs an output Z (third binary signal) indicating the final detection result of the distance setting type photoelectric sensor based on the output Y of the comparison unit 111 and the output X of the comparison unit 112. When the output X of the comparison unit 112 is OFF, the judgment unit 113 turns the output Z OFF regardless of the result of the output Y of the comparison unit 111. When the output X of the comparison unit 112 is ON, the judgment unit 113 outputs the output Y of the comparison unit 111 as the output Z without change. The output Z being ON indicates that the object 100 is present within the set distance range, and the output Z being OFF indicates that the object 100 is not present within the set distance range. Table 1 shows a truth table indicating the relationship between the inputs X, Y and the output Z of the judgment unit 113.

[0023] [Table 1]

[0024] Transforming the judgment equation (NF)>α×(N+F) in comparison unit 111 gives (NF) / (N+F)>α. Therefore, in this embodiment, the influence of the reflectance of object 100 can be eliminated without using division, and it is clear that the problem of the detection distance changing depending on the reflectance of object 100 can be solved.

[0025] In this embodiment, it is sufficient to use the calculation unit 107 (subtraction circuit), the calculation unit 109 (addition circuit), the threshold generation unit 110 (multiplication circuit), the comparison unit 111 (comparison circuit), the comparison unit 112 (comparison circuit), and the judgment unit 113 (AND circuit), and there is no need to use a division circuit, so that the circuit area can be reduced compared to when a division circuit is used, and the photoelectric sensor can be made smaller. Also, in this embodiment, when the processing after the calculation units 107 and 109 is performed by software, there is no need to perform division of (NF) / (N+F), so the response speed of the photoelectric sensor can be made faster compared to when division is performed.

[0026] Furthermore, in this embodiment, when the amount of reflected light becomes 0 or a value close to 0, the threshold value α×(N+F) becomes 0 or a value close to 0, and the determination operation of (NF)>α×(N+F) in comparison unit 111 becomes unstable. Therefore, in this embodiment, by providing comparison unit 112 and determination unit 113, when the sum of the amounts of received light (N+F) is 0 or a value close to 0, it is possible to turn off output Z of determination unit 113, thereby preventing the operation of the photoelectric sensor from becoming unstable.

[0027] [Second Example] In the first embodiment, the difference in the amount of received light (NF) was calculated and compared with the threshold value, but it is also possible to calculate (FN) instead of (NF). This type of photoelectric sensor is called FGS (Foreground Suppression).

[0028] Fig. 2 is a block diagram showing the configuration of a distance setting type photoelectric sensor according to a second embodiment of the present invention, and the same components as those in Fig. 1 and Fig. 4 are given the same reference numerals. The distance setting type photoelectric sensor of this embodiment includes a light projecting circuit 101, a light projecting element 102, a light projecting optical system 103, a light receiving optical system 104, a light receiving element 105, amplifiers 106-N and 106-F, a calculation unit 107a, a calculation unit 109, a threshold value generating unit 110, comparison units 111 and 112, and a judgment unit 113a.

[0029] The calculation unit 107a calculates the difference (FN) between the amount of received light F indicated by the F-side received light amount signal amplified by the amplification unit 106-F and the amount of received light N indicated by the N-side received light amount signal amplified by the amplification unit 106-N. The comparison unit 111 compares the received light amount difference (FN) calculated by the calculation unit 107a with a threshold value α×(N+F). The comparison unit 111 turns on an output Y (first binary signal) when the received light amount difference (FN) is greater than the threshold value α×(N+F), and turns off the output Y when the received light amount difference (FN) is equal to or less than the threshold value α×(N+F).

[0030] When output X of comparison unit 112 is OFF, judgment unit 113a turns output Z (third binary signal) ON regardless of the result of output Y of comparison unit 111. When output X of comparison unit 112 is ON, judgment unit 113a outputs output Y of comparison unit 111 as output Z without change. Output Z of judgment unit 113a being OFF indicates that object 100 is present within the set distance range, and output Z being ON indicates that object 100 is not present within the set distance range. Table 2 shows a truth table showing the relationship between inputs X, Y and output Z of judgment unit 113a. The other configurations are the same as those of the first embodiment.

[0031] [Table 2]

[0032] As explained in the first and second embodiments, the processing after the calculation units 107, 107a, and 109 may be realized by hardware or software. When using software, the calculation units 107 and 107a, the calculation unit 109, the threshold generation unit 110, the comparison units 111 and 112, and the judgment units 113 and 113a can be realized by a computer equipped with a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in FIG. 3.

[0033] The computer includes a CPU 200, a storage device 201, and an interface device (I / F) 202. Amplification units 106-N, 106-F, etc. are connected to the I / F 202. In such a computer, a program for implementing the detection method of the present invention is stored in the storage device 201. The CPU 200 executes the processes described in the first and second embodiments in accordance with the program stored in the storage device 201. [Industrial Applicability]

[0034] The present invention can be applied to a photoelectric sensor. [Explanation of symbols]

[0035] 101...light-projecting circuit, 102...light-projecting element, 103...light-projecting optical system, 104...light-receiving optical system, 105...light-receiving element, 106-N, 106-F...amplification section, 107, 107a, 109...calculation section, 110...threshold generation section, 111, 112...comparison section, 113, 113a...determination section, 114...light-projecting section, 115...light-receiving section.

Claims

1. A light projecting unit configured to project light; a light receiving section having a light receiving element extending to an N-side light receiving surface for detecting an object located closer than a set distance and an F-side light receiving surface for detecting an object located farther than the set distance, the light receiving section being configured to receive reflected light of light projected by the light projecting section; a first calculation unit configured to calculate a light receiving amount difference (N-F) or a light receiving amount difference (F-N) between an amount of light receiving N obtained by the N-side light receiving surface and an amount of light receiving F obtained by the F-side light receiving surface; a second calculation unit configured to calculate a sum (N+F) of the amount of received light N and the amount of received light F; a threshold value generating unit configured to generate a first threshold value by multiplying the sum of the received light amounts (N+F) by a coefficient that is a positive real number greater than 0 and less than 1; a first comparison unit configured to output a first binary signal which is a comparison result between the difference in the amount of received light (N-F) or the difference in the amount of received light (F-N) and the first threshold value.

2. 2. The distance setting type photoelectric sensor according to claim 1, a second comparator configured to output a second binary signal that is a result of comparing the sum of the received light amounts (N+F) with a second threshold value that is 0 or a positive real number close to 0; a determination unit configured to output a third binary signal which is a result of an operation performed on the first binary signal and the second binary signal.

3. 3. The distance setting type photoelectric sensor according to claim 2, the first comparison unit turns the first binary signal ON when the difference in the amount of received light (N-F) is greater than the first threshold value, and turns the first binary signal OFF when the difference in the amount of received light (N-F) is equal to or smaller than the first threshold value; the second comparison unit turns the second binary signal ON when the sum of the received light amounts (N+F) is greater than the second threshold value, and turns the second binary signal OFF when the sum of the received light amounts (N+F) is equal to or less than the second threshold value; A distance setting type photoelectric sensor characterized in that the judgment unit outputs the first binary signal as the third binary signal when the second binary signal is ON, and turns the third binary signal OFF when the second binary signal is OFF.

4. 3. The distance setting type photoelectric sensor according to claim 2, the first comparison unit turns the first binary signal ON when the difference in the amount of received light (F-N) is greater than the first threshold value, and turns the first binary signal OFF when the difference in the amount of received light (F-N) is equal to or less than the first threshold value; the second comparison unit turns the second binary signal ON when the sum of the received light amounts (N+F) is greater than the second threshold value, and turns the second binary signal OFF when the sum of the received light amounts (N+F) is equal to or less than the second threshold value; A distance setting type photoelectric sensor characterized in that the judgment unit outputs the first binary signal as the third binary signal when the second binary signal is ON, and turns the third binary signal ON when the second binary signal is OFF.

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