Sensor

Abstract

To enable stable detection of an object where the difference in signal amount is small depending on whether the object is present.SOLUTION: A sensor includes a light receiving unit 4, a correction value calculation unit 8 that performs statistical processing on the amount of light received by the light receiving unit 4 during a period in which the dispersion of the amount of light received by the light receiving unit 4 is below a dispersion threshold value and calculates a correction value for correcting long-term fluctuations in the amount of light received, a correction unit 9 that corrects the amount of light received using the correction value, and a determination unit 7 that detects the presence or approach of an object by comparing the amount of light received corrected by the correction unit 9 with the light receiving amount threshold value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a sensor for detecting the presence or absence of an object or the proximity of an object. [Background technology]

[0002] Conventionally, photoelectric sensors that detect the presence or absence of an object based on the amount of light have been known (see Patent Document 1). Fig. 15 is a block diagram showing the configuration of a conventional photoelectric sensor. The light projecting unit 1 emits light. When an object 100 is present, the light from the light projecting unit 1 is emitted onto the object 100 via a lens 2. The light receiving unit 4 receives the light focused by a lens 3 and converts it into an electrical signal. When an object 100 is present, the reflected light from the object 100 enters the light receiving unit 4.

[0003] The electrical signal output from the light receiving unit 4 is amplified by the amplifier circuit 5 and is AD converted by the AD conversion unit 6 . The determination unit 7 compares the amount of received light indicated by the data output from the AD conversion unit 6 with a threshold value to determine the presence or absence of an object.

[0004] In photoelectric sensors like those described above, the amount of light received gradually decreases over the course of several months due to dirt and deterioration of the LED in the light-emitting section 1. Also, the amount of light received fluctuates over a period of several days to several weeks due to dimensional changes in the device caused by humidity. Furthermore, the amount of light received fluctuates over a period of several hours due to changes in the circuit characteristics and LED characteristics caused by temperature.

[0005] Therefore, in the photoelectric sensor disclosed in Patent Document 1, in order to be able to set an appropriate threshold value even if the amount of received light changes over time, the threshold value is set based on the amount of received light during a period when it was determined that an object was present and the amount of received light during a period when it was determined that an object was not present.

[0006] However, in the case of objects such as transparent bodies, the difference in the amount of received light depending on whether an object is present or not is small, making it difficult to set the threshold value. In other words, when the difference in the amount of received light depending on whether an object is present or not is small, there is no room for setting the threshold value. Therefore, due to fluctuations in the amount of received light, there are cases where an object is judged to be present when it is not, or conversely, an object is judged to be absent when it is present.

[0007] The above problems also occur in the case of inductive proximity sensors. In the case of inductive proximity sensors, the oscillation amplitude changes depending on the type and size of the object, so care must be taken when setting the threshold value. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2021-145231 A Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the above-mentioned problems, and has an object to provide a sensor that can stably detect an object with only a small difference in signal amount depending on whether the object is present or not. [Means for solving the problem]

[0010] The sensor of the present invention is characterized in that it comprises a detection unit configured to detect a signal amount that changes depending on the presence or absence of an object or the approach of an object; a correction value calculation unit configured to statistically process the signal amount during a period in which the dispersion of the signal amount is equal to or less than a dispersion threshold value, and calculate a correction value for correcting long-term fluctuations in the signal amount; a correction unit configured to correct the signal amount using the correction value; and a determination unit configured to detect the presence or absence of an object or the approach of an object by comparing the signal amount corrected by the correction unit with a signal amount threshold value.

[0011] The sensor of the present invention is characterized in that it comprises a detection unit configured to detect a signal amount that changes depending on the presence or absence of an object or the approach of an object, a correction value calculation unit configured to statistically process the signal amount during a period in which the dispersion of the signal amount is equal to or less than a dispersion threshold value, and calculate a correction value for correcting long-term fluctuations in the signal amount, a correction unit configured to correct the signal amount threshold value using the correction value, and a determination unit configured to detect the presence or absence of an object or the approach of an object by comparing the signal amount with the signal amount threshold value corrected by the correction unit.

[0012] In addition, in one configuration example of the sensor of the present invention, the correction value calculation unit includes a first average value calculation unit configured to calculate a moving average value of the signal amount, a dispersion calculation unit configured to calculate the dispersion based on the moving average value, a second average value calculation unit configured to calculate the average value of the signal amount for a period excluding a period when the dispersion is equal to or less than the dispersion threshold value, and a correction value determination unit configured to determine the correction value as the difference between a known signal amount measured in the absence of a detection object and the average value calculated by the second average value calculation unit. Furthermore, in one configuration example of the sensor of the present invention, the correction value determination unit calculates the absolute value of the difference, and when the absolute value of the difference is equal to or less than a certain value, sets the difference as the correction value, and when the absolute value of the difference exceeds the certain value, does not update the correction value. In one configuration example of the sensor of the present invention, the degree of dispersion is a standard deviation or a variance. Effect of the Invention

[0013] According to the present invention, the signal amount during the period when the dispersion of the signal amount is equal to or less than the dispersion threshold value is statistically processed to calculate a correction value for correcting the long-term fluctuation of the signal amount, and the signal amount is corrected by the correction value, so that the margin of freedom in setting the signal amount threshold value can be increased, and therefore an object with a small difference in signal amount depending on the presence or absence of the object can be stably detected. Also, the present invention can correct the signal amount that varies depending on the temperature, humidity, etc. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a block diagram showing the configuration of a photoelectric sensor according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a flowchart illustrating the operation of the photoelectric sensor according to the first embodiment of the present invention. [Diagram 3] FIG. 3 is a diagram illustrating components included in the amount of received light. [Figure 4] FIG. 4 is a block diagram showing a configuration of a correction value calculation unit according to the first embodiment of the present invention. [Diagram 5] FIG. 5 is a diagram showing an example of long-term fluctuations in the amount of received light. [Figure 6] FIG. 6 is a diagram illustrating an example of the operation of the correction value calculation unit according to the first embodiment of the present invention. [Figure 7] FIG. 7 is a diagram for explaining the effect of the photoelectric sensor according to the first embodiment of the present invention. [Figure 8] FIG. 8 is a diagram for explaining the effect of the photoelectric sensor according to the first embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing an example in which the amount of received light fluctuates in a proximity sensor. [Figure 10] FIG. 10 is a diagram showing another example in which the amount of received light fluctuates in the proximity sensor. [Figure 11] FIG. 11 is a block diagram showing the configuration of a photoelectric sensor according to the second embodiment of the present invention. [Figure 12] FIG. 12 is a flowchart illustrating the operation of the photoelectric sensor according to the second embodiment of the present invention. [Figure 13] FIG. 13 is a block diagram showing the configuration of an inductive proximity sensor according to a third embodiment of the present invention. [Figure 14] FIG. 14 is a diagram showing an example of the configuration of a computer that realizes the photoelectric sensors according to the first to third embodiments of the present invention. [Figure 15] FIG. 15 is a block diagram showing the configuration of a conventional photoelectric sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [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 photoelectric sensor according to a first embodiment of the present invention. The photoelectric sensor includes a light projecting unit 1, lenses 2 and 3, a light receiving unit 4 (detecting unit), an amplifier circuit 5, an AD (Analog-to-digital) conversion unit 6, a determination unit 7, a correction value calculation unit 8, and a correction unit 9.

[0016] 2 is a flow chart for explaining the operation of the photoelectric sensor of this embodiment. The light projecting unit 1 emits light to an area where it is desired to detect the presence or absence of an object 100 (step S100 in FIG. 2). If the object 100 is present, the light from the light projecting unit 1 is irradiated onto the object 100 via the lens 2. The light receiving section 4 receives the light focused by the lens 3 and converts it into an electrical signal (Step S101 in FIG. 2).

[0017] The configuration in Fig. 1 shows an example of a reflective photoelectric sensor. In the reflective photoelectric sensor, when an object 100 is present, reflected light from the object 100 enters the light receiving unit 4, and when the object 100 is not present, the reflected light does not enter the light receiving unit 4, and only ambient light enters the light receiving unit 4.

[0018] On the other hand, in the case of a transmission type photoelectric sensor, the light-projecting unit 1 and the light-receiving unit 4 are arranged to face each other. When there is no object 100 between the light-projecting unit 1 and the light-receiving unit 4, the light emitted from the light-projecting unit 1 enters the light-receiving unit 4 as is, and when there is an object 100 between the light-projecting unit 1 and the light-receiving unit 4, the light that has passed through the object 100 enters the light-receiving unit 4.

[0019] There is also a reflector type (retro-reflective type) photoelectric sensor in which a light emitter / receiver housing a light emitter 1 and a light receiver 4 is arranged to face a reflector. In the case of a reflector type photoelectric sensor, if there is no object 100 between the light emitter / receiver and the reflector, the light from the light emitter 1 is reflected by the reflector and enters the light receiver 4. If there is an object 100 between the light emitter / receiver and the reflector, the light that has passed through the object 100 enters the light receiver 4.

[0020] The amplifier circuit 5 amplifies the electrical signal output from the light receiving unit 4 (Step S102 in FIG. 2). The AD conversion unit 6 performs AD conversion on the signal amplified by the amplifier circuit 5 (Step S103 in FIG. 2).

[0021] Fig. 3(A) shows an example of the change over time in the amount of received light D (signal amount) indicated by the data output from the AD conversion unit 6, and Figs. 3(B) to 3(D) show the components contained in the amount of received light D. Fig. 3(B) shows the noise components generated by the circuitry of the photoelectric sensor. The noise components cause the amount of received light to fluctuate in units of 1 μs to 10 ms.

[0022] FIG. 3(C) shows the fluctuation in the amount of received light caused by the appearance of an object. In this case, the amount of received light fluctuates in units of 10 ms to 1 s. Note that FIG. 3(C) shows an example in the case of a transmission type photoelectric sensor or a reflector type photoelectric sensor. FIG. 3(D) shows long-term fluctuations that change in units of 1 minute or more. In this embodiment, this long-term fluctuation is detected and corrected.

[0023] 4 is a block diagram showing the configuration of the correction value calculation unit 8. The correction value calculation unit 8 is made up of an average value calculation unit 80, a dispersion degree calculation unit 81, an average value calculation unit 82, and a correction value determination unit 83.

[0024] The average value calculation unit 80 calculates a moving average value A of the amount of received light D over an X period (e.g., 5 ms) (FIG. 2, step S104). The reason for calculating the moving average value A is to remove noise components, which are short-term fluctuations as shown in FIG. 3(B), from the amount of received light D. Next, the dispersion calculation unit 81 calculates the standard deviation B based on the amount of received light D during the X period and the moving average value A during the X period (Step S105 in FIG. 2).

[0025] The average value calculation unit 82 calculates the average value Z of the amount of received light D for a period Y (for example, a period of about 10 seconds) longer than the X period, excluding the period when the standard deviation B is equal to or less than a predetermined dispersion degree threshold value (FIG. 2, step S106). By excluding the period during which the standard deviation B exceeds the dispersion threshold from the calculation of the average value Z, it is possible to remove the fluctuation in the amount of received light D caused by the appearance of an object. In addition, by calculating the average value, it is possible to remove noise components, which are short fluctuations in time as shown in Figure 3(B), from the amount of received light D.

[0026] In addition, the dispersion calculation unit 81 may calculate the variance instead of the standard deviation, and the average value calculation unit 82 may calculate the average value Z of the amount of received light D for a period of Y excluding the period when the variance is equal to or less than the dispersion threshold value.

[0027] The correction value determination unit 83 calculates the absolute value |D0-Z| of the difference between a known amount of received light D0 measured in the absence of a detection object when the photoelectric sensor is shipped, for example, and the average value Z (step S107 in FIG. 2). If |D0-Z| is equal to or less than a certain value (YES in step 108 in FIG. 2), the correction value determination unit 83 determines the difference D0-Z between the amount of received light D0 and the average value Z as the correction value S (step S109 in FIG. 2). If |D0-Z| exceeds a certain value (NO in step 108), the correction value determination unit 83 does not update the current correction value S (step S110 in FIG. 2). The amount of received light D0 is set in advance in the correction value calculation unit 8. The initial value of the correction value S is 0.

[0028] By setting the difference D0-Z between the amount of received light D0 and the average value Z when |D0-Z| is equal to or less than a certain value as the correction value S, it is possible to extract a plausible value as the long-term fluctuation component. With this, the processing by the correction value calculation unit 8 is completed.

[0029] The correction unit 9 corrects the amount of received light D by adding the current correction value S determined based on the amount of received light D prior to the amount of received light D to be corrected, to the latest amount of received light D to be corrected indicated by the data output from the AD conversion unit 6 (step S111 in FIG. 2). The determination unit 7 compares the amount of received light D+S corrected by the correction unit 9 with a predetermined threshold value TH for the amount of received light (signal amount threshold value) to determine the presence or absence of the object 100 (Step S112 in FIG. 2).

[0030] In the case of a reflective photoelectric sensor, the determination unit 7 determines that the object 100 is present when the corrected amount of received light D+S exceeds the threshold value TH, and determines that the object 100 is not present when the amount of received light D+S is equal to or less than the threshold value TH. In the case of a transmissive photoelectric sensor or a reflector type photoelectric sensor, the determination unit 7 determines that the object 100 is present when the amount of received light D+S is less than the threshold value TH, and determines that the object 100 is not present when the amount of received light D+S is equal to or greater than the threshold value TH. The determination unit 7 outputs a signal indicating the determination result (Step S113 in FIG. 2). The photoelectric sensor repeatedly executes the processes of steps S100 to S113 described above.

[0031] Figures 5(A) and 5(B) are diagrams showing an example of long-term fluctuations in the amount of received light. Figure 5(A) shows the amount of received light (D0 above) at the time of shipment of a photoelectric sensor, for example. In contrast, Figure 5(B) shows that the amount of received light D has decreased over time.

[0032] 6(A) to 6(D) are diagrams showing an example of the operation of the correction value calculation unit 8 in this embodiment. Fig. 6(A) shows data on the amount of received light D output from the AD conversion unit 6. The sampling period of the AD conversion unit 6 is 0.1 ms. 6B shows the result of the average calculation unit 80 calculating the moving average A of 50 pieces of data. The length of the X period is 5 ms.

[0033] FIG. 6C shows the result of the dispersion calculation unit 81 calculating 50 standard deviations B of the moving average value A of 50 pieces of data. Fig. 6(D) shows the calculation result of the average value calculation unit 82. Here, the dispersion threshold is set to 4, and the average value Z is calculated by taking the average of data whose standard deviation is 4 or less. Note that the data marked with a circle 600 in Fig. 6(D) is excluded from the calculation of the average value Z because it is data whose standard deviation exceeds 4.

[0034] In this embodiment, the long-term fluctuation in the amount of received light shown in Fig. 3(D) can be corrected as shown in Fig. 7(A). As a result, the amount of received light D shown in Fig. 3(A) can be corrected as D+S in Fig. 7(B). V in Fig. 7(B) indicates the long-term fluctuation before correction, and Vc indicates the corrected long-term fluctuation.

[0035] According to this embodiment, it is also possible to cope with fluctuations in the amount of received light due to temperature. Fig. 8 shows data on the amount of received light D output from the AD conversion unit 6, and Fig. 8(B) shows data on the amount of received light D+S corrected according to this embodiment. It can be seen that according to this embodiment, the fluctuation of 2% is suppressed to 0.5% or less.

[0036] In this embodiment, the present invention has been described as being applied to a photoelectric sensor that detects the presence or absence of an object, but it may also be applied to a photoelectric sensor (proximity sensor) that detects the approach of an object. Fig. 9 shows an example in which the amount of light received varies with temperature in a proximity sensor. Fig. 10 shows an example in which the amount of light received varies in an environment with a temperature of 50°C and a humidity of 90%. The example in Fig. 10 shows the variation in the amount of light received for four different proximity sensors, #1 to #2.

[0037] In the case of a reflective proximity sensor, the determination unit 7 determines that the object 100 is within the set distance range when the corrected amount of received light D+S exceeds the threshold light-receiving amount TH, and determines that the object 100 is not within the set distance range when the amount of received light D+S is equal to or less than the threshold light-receiving amount TH. In the case of a transmissive proximity sensor or a reflector-type proximity sensor, the determination unit 7 determines that the object 100 is within the set distance range when the amount of received light D+S is less than the threshold light-receiving amount TH, and determines that the object 100 is not within the set distance range when the amount of received light D+S is equal to or more than the threshold light-receiving amount TH.

[0038] [Second Example] Next, a second embodiment of the present invention will be described. Fig. 11 is a block diagram showing the configuration of a photoelectric sensor according to the second embodiment of the present invention. The photoelectric sensor of this embodiment includes a light projecting unit 1, lenses 2 and 3, a light receiving unit 4, an amplifier circuit 5, an AD conversion unit 6, a determination unit 7a, a correction value calculation unit 8, and a correction unit 9a. As in the first embodiment, the configuration of Fig. 11 shows an example of a reflective photoelectric sensor, but this embodiment may also be applied to a transmissive photoelectric sensor or a reflector type photoelectric sensor.

[0039] 12 is a flow chart for explaining the operation of the photoelectric sensor of this embodiment. The operations of the light projecting unit 1, the light receiving unit 4, the amplifier circuit 5, the AD conversion unit 6, and the correction value calculation unit 8 (steps S100 to S110 in FIG. 12) are the same as those in the first embodiment.

[0040] The correction unit 9a corrects the threshold value TH of the amount of received light by subtracting the correction value S from the initial value of the threshold value TH of the amount of received light (Step S111a in FIG. 12). The determination unit 7a compares the latest amount of received light D indicated by the data output from the AD conversion unit 6 with the corrected threshold value TH for the amount of received light to determine the presence or absence of the object 100 or the approach of the object 100 (step S112 in FIG. 12).

[0041] In the case of a reflective photoelectric sensor, the determination unit 7a determines that the object 100 is present when the amount of received light D exceeds the corrected threshold value TH, and determines that the object 100 is not present when the amount of received light D is equal to or less than the corrected threshold value TH. In the case of a transmissive photoelectric sensor or a reflector type photoelectric sensor, the determination unit 7a determines that the object 100 is present when the amount of received light D is less than the corrected threshold value TH, and determines that the object 100 is not present when the amount of received light D is equal to or more than the corrected threshold value TH.

[0042] In addition, in the case of a reflective proximity sensor, the determination unit 7a determines that the object 100 is within the set distance range when the amount of received light D exceeds the corrected threshold value TH, and determines that the object 100 is not within the set distance range when the amount of received light D is equal to or less than the corrected threshold value TH. In the case of a transmissive proximity sensor or a reflector type proximity sensor, the determination unit 7a determines that the object 100 is within the set distance range when the amount of received light D is less than the corrected threshold value TH, and determines that the object 100 is not within the set distance range when the amount of received light D is equal to or more than the corrected threshold value TH.

[0043] [Third Example] Fig. 13 is a block diagram showing the configuration of an inductive proximity sensor according to a third embodiment of the present invention. In the first and second embodiments, a photoelectric sensor has been taken as an example, but the present invention may also be applied to an inductive proximity sensor. The inductive proximity sensor includes a detection coil 10 that generates a magnetic field, and an oscillation circuit 11 that generates a high-frequency current that flows through the detection coil 10. The detection coil 10 and the oscillation circuit 11 form a detection unit 12.

[0044] In the case of an induction type proximity sensor, when a metallic object 100 enters the detection area of ​​the detection coil 10, an induced current is generated in the object 100, causing the impedance of the detection coil 10 to change, and the oscillation amplitude of the oscillation circuit 11 to change. When the result of AD conversion of the oscillation amplitude by the AD conversion unit 6 is less than a threshold value, the determination unit 7 determines that the object 100 has approached. If this oscillation amplitude is applied to the first embodiment as the signal amount to be corrected, the same effect as that of the first embodiment can be obtained in the induction type proximity sensor. Furthermore, when this embodiment is applied to the second embodiment in which the threshold value is corrected, a detection coil 10 and an oscillation circuit 11 may be provided in place of the light projecting unit 1, the lenses 2 and 3, the light receiving unit 4 and the amplifier circuit 5.

[0045] The judgment units 7, 7a, the correction value calculation unit 8, and the correction units 9, 9a described in the first to third embodiments 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.

[0046] The computer includes a CPU 200, a storage device 201, and an interface device (I / F) 202. The I / F 202 is connected to an AD conversion unit 6 and the like. 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 to third embodiments in accordance with the program stored in the storage device 201. [Industrial Applicability]

[0047] The present invention can be applied to photoelectric or inductive proximity sensors. [Explanation of symbols]

[0048] 1...light-projecting unit, 2, 3...lens, 4...light-receiving unit, 5...amplification circuit, 6...AD conversion unit, 7, 7a...judgment unit, 8...correction value calculation unit, 9, 9a...correction unit, 10...detection coil, 11...oscillating circuit, 12...detection unit, 80, 82...average value calculation unit, 81...dispersion degree calculation unit, 83...correction value determination unit.

Claims

1. A detection unit configured to detect a signal amount that changes depending on the presence or absence of an object or the approach of the object; a correction value calculation unit configured to perform statistical processing on the signal amount during a period in which the dispersion of the signal amount is equal to or less than a dispersion threshold value, and to calculate a correction value for correcting a long-term variation in the signal amount; a correction unit configured to correct the signal amount by the correction value; a determination unit configured to detect the presence or absence of an object or the approach of an object by comparing the signal amount corrected by the correction unit with a signal amount threshold.

2. A detection unit configured to detect a signal amount that changes depending on the presence or absence of an object or the approach of the object; a correction value calculation unit configured to perform statistical processing on the signal amount during a period in which the dispersion of the signal amount is equal to or less than a dispersion threshold value, and to calculate a correction value for correcting a long-term variation in the signal amount; a correction unit configured to correct the signal amount threshold value by the correction value; a determination unit configured to detect the presence or absence of an object or the approach of an object by comparing the signal amount threshold value corrected by the correction unit with the signal amount.

3. 3. The sensor according to claim 1, The correction value calculation unit A first average value calculation unit configured to calculate a moving average value of the signal amount; a dispersion calculation unit configured to calculate the dispersion based on the moving average value; a second average value calculation unit configured to calculate an average value of the signal amount for a period excluding a period when the degree of dispersion is equal to or less than the degree of dispersion threshold; a correction value determination unit configured to determine the correction value as a difference between a known signal amount measured in the absence of a detection object and the average value calculated by the second average value calculation unit.

4. 4. The sensor according to claim 3, The correction value determination unit calculates the absolute value of the difference, and when the absolute value of the difference is equal to or less than a certain value, sets the difference as the correction value, and when the absolute value of the difference exceeds the certain value, does not update the correction value.

5. 3. The sensor according to claim 1, The sensor, wherein the dispersion is a standard deviation or a variance.

Images