JP4868779B2 - Photoelectric sensor - Google Patents

Description

  The present invention relates to a photoelectric sensor.

  For example, in order to prevent false alarms due to self-noise generated by circuit elements, the average value is calculated by sampling the signal output from the light receiving means at a predetermined cycle, and this average value exceeds the threshold value a predetermined number of times. A hot wire sensor that sometimes generates an alarm signal is known (see Patent Document 1). This heat ray sensor calculates the average value of the signal output from the light receiving means, thereby removing the self-noise superimposed on the signal and preventing false alarms.

By the way, the photoelectric sensor is desired to increase the detection distance of the object to be detected. This photoelectric sensor increases the detection sensitivity by amplifying the signal output from the light receiving means in order to increase the detection distance of the object to be detected.
JP-A-7-55952

  However, when the photoelectric sensor amplifies the signal output from the light receiving means in order to increase the detection sensitivity, the self-noise signal superimposed on the signal is also amplified. In this photoelectric sensor, when the reflectance of the object to be detected is low and the amount of light received by the light receiving means is small, the signal of the amount of received light may be buried in the self-noise signal and difficult to detect. In some cases, the detection distance of the object to be detected is increased while being detected.

  The present invention has been proposed in view of such a situation, and provides a photoelectric sensor that can increase the detection distance while reducing the influence of self-noise while increasing the detection sensitivity. Objective.

According to the first aspect of the present invention, there is provided light projecting means for projecting light onto an object to be detected, drive means for driving the light projecting means to project pulsed light, and pulsed light projected by the light projecting means. Light receiving means for receiving light, sampling means for sampling the amount of light received by the light receiving means in synchronization with the light projecting operation of each pulse light of the light projecting means, and the light projecting means does not project the object to be detected. A photoelectric sensor comprising: setting means for setting an addition value and a subtraction value according to the maximum received light amount and the minimum received light amount at the time of the light receiving means; and a detecting means for detecting the detected object, wherein the sampling The means is configured to sample the received light amount a plurality of times within a period corresponding to a half cycle of self-noise of the photoelectric sensor in each sampling operation of the light receiving means corresponding to the projecting operation of each pulsed light. And said Multiple received light quantities sampled by the sampling operation are increasing changes that increase over time, decreasing changes that decrease over time, increase / decrease changes that change from increasing to decreasing over time, or change from decreasing to increasing over time A discriminating unit for discriminating whether the change is an increase or decrease, an averaging process for calculating an average value of the plurality of received light amounts on the condition that the discriminating unit discriminates that the change is an increase or decrease, and the discrimination conditions and addition process of adding the additional value to the average value after calculating the average value on condition that it is judged that the reduced increase change by the means, that the change in increase and decrease by the discriminating means is detected wherein comprising from the average value after calculating the average value calculating means for performing a subtraction process for subtracting the subtraction value as the detection means is calculated by said calculation means And detecting the object to be detected based on the value.

  According to a second aspect of the present invention, in the first aspect, the sampling unit samples only the maximum received light amount at the light receiving unit and the received light amount before and after the received light amount, and the detecting unit includes the sampling unit that performs the sampling. The detected object is detected based on a value calculated using only the maximum received light amount and the received light amount before and after the received light amount.

  According to a third aspect of the present invention, in the second aspect, the detection unit is configured to detect the detection target based on a value calculated by the calculation unit at a timing determined for each light projection operation of each pulsed light of the light projection unit. Is detected.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the determination unit determines each change based on at least three received light amounts sampled by the sampling unit, and the calculation unit includes: The averaging process is performed using at least three sampled received light amounts.

<Invention of Claim 1>
According to the photoelectric sensor of the present invention, the calculating means calculates the received light amount that reduces the influence of self-noise according to the change over time determined by the determining means, and the detecting means detects the received light amount based on the calculated received light amount. Since the presence / absence of the detection object is detected, the detection distance of the detection object can be increased by reducing the influence of self-noise while increasing the detection sensitivity.
In addition, the addition value and the subtraction value used for the arithmetic processing can be set according to the maximum light reception amount and the minimum light reception amount at the light receiving means, and the detection means is based on the light reception amount whose influence is reduced according to the self-noise characteristics. Thus, the detection object can be detected, and the detection distance of the detection object can be increased.

<Invention of Claim 2>
According to the present invention, the detecting means detects the detection object based on the value calculated by the calculating means using only the maximum received light amount and the received light amount before and after the received light amount. And the value calculated using the amount of received light exceeding the threshold value can be compared, and the detected object can be reliably detected.

<Invention of Claim 3>
According to the present invention, the detection means detects the detection object based on the value calculated by the calculation means at a timing determined for each light projection operation of each pulse light of the light projection means. The detection object can be detected at a timing determined for each light projecting operation, and the efficiency of the detection process of the detection object can be increased.

<Invention of Claim 4 >
According to the present invention, by using at least three or more received light amounts, each temporal change (increase change, decrease change, increase / decrease change, decrease / increase change) is detected without sequentially storing the received light amount for determining the change over time. In addition, the accuracy of the average value of the calculated received light amounts can be improved.

<Embodiment>
An embodiment of the present invention will be described by taking a reflection type photoelectric sensor as an example with reference to FIGS. 1 to 5.
1. Configuration of Photoelectric Sensor As shown in FIG. 1, the photoelectric sensor 1 includes a light projecting element 11 composed of an LED, a light projecting circuit 12 for projecting the light projecting element 11, and a PD (photodiode). A light receiving element 13 that receives the light projected by the optical element 11 and reflected by the object to be detected and outputs a light receiving signal corresponding to the received light amount; and a light receiving circuit 14 that receives the light receiving signal output from the light receiving element 13. The amplifier circuit 15 receives and amplifies the signal output from the light receiving circuit 14, and the control circuit 20 controls the operation of the light projecting circuit 12.

  In the photoelectric sensor 1, the control circuit 20 transmits a light projecting circuit operation signal to the light projecting circuit 12. As shown in FIG. 2A, the light projecting circuit operation signal controls the light projecting element 11 to light up at a predetermined cycle T1. When receiving the light projecting circuit operation signal, the light projecting circuit 12 supplies a driving current to the light projecting element 11. The light projecting element 11 projects the pulsed lights P1 to P4 with the driving current.

  In the photoelectric sensor 1, the control circuit 20 transmits to the light receiving circuit 14 a switching element operation signal whose cycle and phase coincide with those of the light projecting circuit operation signal. When the control circuit 20 transmits the switching element operation signal, as shown in FIG. 2, the light projecting element 11 projects light for each light projecting time T <b> 2 and is reflected by the object to be detected. The amount of received light is compared with the threshold value H to determine the presence or absence of an object to be detected.

  The photoelectric sensor 1 includes an input unit 16 for inputting various types of information, a display unit 17 for displaying detection results of detected objects, an output unit 18 for transmitting a signal related to the detection results to an external device, and light reception And a memory 19 for storing received light signal information and the like of the element 13. Reference numeral 21 denotes an oscilloscope connected to measure the self-noise period. The self noise is generated by, for example, a switching operation of the light receiving circuit 14, or is generally formed by thermal noise (white noise) generated due to irregular thermal motion of electrons in a conductor or a semiconductor element, and the amount of generation increases as the temperature increases. It is thought that.

  In the photoelectric sensor 1, when an operator obtains a half-cycle value of the self noise from the waveform of the self noise measured by the oscilloscope 21 and sets the value by the input unit 16, the control circuit 20 transmits a signal transmitted from the input unit 16. , And the memory 19 stores the half-cycle value of its own noise. The light projecting element 11 is a light projecting means, the light projecting circuit 12 and the control circuit 20 are driving means, the light receiving element 13 and the light receiving circuit 14 are light receiving means, the control circuit 20 is a sampling means and an arithmetic means, a memory 19 and a control circuit. Reference numeral 20 corresponds to a detection unit and a determination unit.

  The memory 19 is configured by a flash memory, for example. Based on the signal output from the amplifier circuit 15, the control circuit 20 sequentially stores light reception signal information (here, the amount of received light) received by the light receiving element 13 in the memory 19. The control circuit 20 is configured by a microprocessor.

  Further, the control circuit 20 stores in the memory 19 light reception signal information received by the light receiving element 13 when the light projecting element 11 does not project light after the photoelectric sensor 1 is turned on. Here, the memory 19 stores light reception signal information (maximum light reception amount, minimum light reception amount) of light received for a predetermined time (reference numeral T3 in the figure). Further, the control circuit 20 causes the memory 19 to store the addition value and the subtraction value calculated by the control circuit 20 using the maximum received light amount and the minimum received light amount in order to reduce the influence of self noise. Furthermore, the memory 19 stores a threshold value for determining whether or not to detect an object to be detected in comparison with the amount of received light in which the influence of noise is reduced. This threshold value is appropriately set by the input unit 16 according to the type of the object to be detected. The memory 19 and the control circuit 20 correspond to the setting unit of the present invention.

2. Operation and Calculation Processing of Photoelectric Sensor As shown in FIG. 2A, in the photoelectric sensor 1 of the present embodiment, the light projecting element 11 projects pulsed lights P1 to P4. The received light signal of the light receiving element 13 is superimposed by amplifying the signal of self noise N by the amplifier circuit 15 as shown in FIG. As shown in the figure, when the control circuit 20 samples the maximum received light amount M of the self noise, the received light amount of the received light signal S of the light receiving element 13 exceeds the threshold value H and the detected signal of the self noise N is detected. Nevertheless, the control circuit 20 may determine that the threshold value H has not been exceeded, and may not notify that the detected object has been detected. This photoelectric sensor 1 performs the following processing to prevent erroneous notification.

  The photoelectric sensor 1 has a maximum light receiving element 13 in a period (reference numeral T3 in the figure) in which the light projecting element 11 does not project light after the control circuit 20 turns on the power of the photoelectric sensor 1 stored in the memory 19. Using the received light amount and the minimum received light amount, an addition value and a subtraction value for reducing the influence of the self noise N are calculated. The control circuit 20 calculates an addition value and a subtraction value by a process of dividing a difference value between the maximum light reception amount and the minimum light reception amount by 2.

  Next, in the photoelectric sensor 1, the control circuit 20 corresponds to each pulsed light P1 to P4 received by the light receiving element 13 from the received light signal information stored in the memory 19 for each light projection time T2. The light receiving element 13 receives light within a half cycle of the self-noise N and samples three received light amounts stored in the memory 19. The control circuit 20 samples the maximum received light amount of the light receiving element 13 and the received light amount having a value slightly larger or slightly smaller than the maximum received light amount as three received light amounts. In the photoelectric sensor 1, the control circuit 20 discriminates the temporal change of the received light amount from the three received light amounts sampled for each of the pulse lights P <b> 1 to P <b> 4.

  Further, the photoelectric sensor 1 uses only the maximum received light amount and the received light amount having a value slightly larger or slightly smaller than the maximum received light amount in response to the change with time determined by the control circuit 20, and the self-noise. The amount of received light with N reduced is calculated. The control circuit 20 calculates the amount of received light as follows in correspondence with each change over time (increase change, decrease change, increase / decrease change, decrease / increase change).

(1) Increase Change FIG. 3A is a partially enlarged view of the self-noise N superimposed on the light reception signal S (see FIG. 2B) of the light receiving element 13. Here, the control circuit 20 samples three received light amounts (A to C) within a half cycle (T / 2) of self-noise. The control circuit 20 determines that the received light amount has an A <B <C relationship, thereby determining that the received light amount shows an increasing change that increases with time. Then, the control circuit 20 performs an averaging process by determining that the amount of received light shows the increase change. In this averaging process, an average value ([A + B + C] / 3) of the received light amount is calculated. In the figure, symbol T is the self-noise period, and α is the self-noise amplitude.

(2) Decrease Change As shown in FIG. 3B, the control circuit 20 determines that the amount of received light sampled within the self-noise half-cycle (T / 2) has a relationship of A>B> C. Thus, it is determined that the amount of received light shows a decreasing change that decreases with time. Then, the control circuit 20 performs an averaging process by determining that the amount of received light shows the decrease change. In this averaging process, an average value ([A + B + C] / 3) of the received light amount is calculated.

(3) Increase / decrease change As shown in FIG. 3C, the control circuit 20 determines that the amount of received light sampled within the self-noise half-cycle (T / 2) has a relationship of A <B> C. Thus, it is determined that the amount of received light shows an increase / decrease change that increases and then decreases as time elapses. Then, the control circuit 20 performs a subtraction process when it is determined that the amount of received light indicates the increase or decrease. In this subtraction process, a value ({[A + B + C] / 3} −α / 2) obtained by subtracting a half value (α / 2, the subtraction value) of the amplitude α of the self noise from the average value of the received light amount is calculated. Note that the half value (α / 2, the subtraction value) of the amplitude α of the self noise is read from the memory 19 by the control circuit 20 when the subtraction process is performed.

(4) Increase / decrease change As shown in FIG. 3D, the control circuit 20 determines that the amount of received light sampled within the self-noise half-cycle (T / 2) has a relationship of A> B <C. By doing so, it is determined that the amount of received light shows a decrease / increase change that decreases after decreasing with time. Then, the control circuit 20 performs an addition process when it is determined that the amount of received light indicates the decrease and increase. In this addition process, a value ({[A + B + C] / 3} + α / 2) obtained by adding a half value (α / 2, the addition value) of the self-noise amplitude α to the average value of the received light amount is calculated. The half value (α / 2, the addition value) of the amplitude α of the self noise is read from the memory 19 by the control circuit 20 when the addition process is performed, similarly to the above-described increase / decrease change.

3. Control of Photoelectric Sensor The photoelectric sensor 1 detects a detected object and a self-noise detection process in which the control circuit 20 detects self-noise when the light emitting element 11 does not project light after the sensor 1 is turned on. The detection process is performed.

(1) Self-noise detection processing In the self-noise detection processing, the addition is performed based on a light-receiving signal of self-noise received by the light-receiving element 13 when the light-emitting element 11 does not emit light after the photoelectric sensor 1 is turned on. An addition value (α / 2) used for processing and a subtraction value (α / 2) used for the subtraction processing are calculated. In this self-noise calculation process, first, the control circuit 20 determines whether or not it has received a detection start instruction signal set by the input unit 16 (S1).

  When it is determined in S1 that the detection start instruction signal has been received, a received light signal information sampling process (S2) is performed. In this light reception signal information sampling process (S2), the control circuit 20 transmits a switching element operation signal Si (see FIG. 1) to turn on the switching element of the light reception circuit 14, and the amplification circuit 15 amplifies the self. Light reception signal information (light reception amount information) of noise is sampled over a predetermined time (reference T3 in FIG. 2). If it is determined in S1 that the detection start instruction signal is not received, the process is repeated until the signal is received.

  After the light reception signal information sampling process (S2), a light reception signal information storage process (S3) is performed. In this received light signal information storage process (S3), the control circuit 20 uses the received light signal information (received light quantity information) of the self noise sampled by the received light signal information sampling process (S2) for a predetermined time (reference T3 in FIG. 2). Are sequentially stored in the memory 19. Note that the predetermined time is set to an appropriate time according to the characteristics of self-noise.

  After the received light signal information storage process (S3), the maximum received light amount information extraction process (S4) is performed. In this maximum received light quantity information extraction process (S4), the control circuit 20 sequentially extracts the maximum received light quantity information (maximum received light quantity value) of its own noise stored in the received light signal information storage process (S3) and stores it in the memory. It is stored in the 19 maximum received light amount storage area.

  After the maximum received light amount information extraction process (S4), the minimum received light amount information extraction process (S5) is performed. In this minimum received light quantity information extraction process (S5), the control circuit 20 sequentially extracts the minimum received light quantity information (minimum received light quantity value) of the self-noise stored in the received light signal information storage process (S3) to obtain the memory 19. Is stored in the minimum received light amount information storage area.

  After the minimum received light amount information extraction process (S5), it is determined whether or not the predetermined time (symbol T3 in FIG. 2) has elapsed (S6). If it is determined in S6 that the predetermined time has elapsed, an addition value / subtraction value calculation process (S7) is performed. In the addition value / subtraction value calculation process (S7), the control circuit 20 uses the maximum and minimum light reception amount values stored by the maximum light reception amount information extraction process (S4) and the minimum light reception amount information extraction process (S5). Read from the memory 19. Further, in the addition value / subtraction value calculation process (S7), the difference value (self-noise amplitude α) between the read maximum value and the minimum value is divided by 2, and calculated as the addition value and the subtraction value. In S6, when it is determined that the predetermined time (the symbol T3 in FIG. 2) has not elapsed, the processing of S2 to S5 is continued until the predetermined time has elapsed.

  After the addition value / subtraction value calculation processing (S7), addition value / subtraction value storage processing (S8) is performed. In the addition value / subtraction value storage process (S8), the addition value (α / 2) and the subtraction value (α / 2) calculated by the addition value / subtraction value calculation process (S7) are added to the addition value / Store in the subtraction value storage area. The stored addition value and subtraction value are used to calculate the received light amount in which the self-noise N is reduced in accordance with each time-dependent change described above in the detection process described later.

(2) Detection process In the detection process, a process of detecting an object to be detected is performed by reducing the influence of the self-noise N signal superimposed on the light reception signal S of each pulsed light P1 to P4 received by the light receiving element 13. In this detection process, first, the control circuit 20 determines whether or not the operation start instruction signal set by the input unit 16 has been received (S11).

  When it is determined in S11 that the operation start instruction signal has been received, the light projection / reception signal information sampling process (S12) is performed. In the light projection / reception signal information sampling process (S12), the control circuit 20 transmits a switching element operation signal Sj (see FIG. 1) whose cycle and phase coincide with those of the light projection circuit operation signal to switch the light reception circuit 14. The device is turned on, and the received light signal information (received light amount information) reflected on the object to be detected, amplified by the amplifier circuit 15 and superimposed with the self-noise N signal is sampled over each projection time T2. In the light projection / reception signal information sampling process (S12), the sampled light reception signal information is stored in the memory 19. When it is determined in S11 that the operation start instruction signal is not received, the process is repeated until the signal is received.

  After the light transmission / reception signal information sampling processing (S12), light transmission / reception signal information extraction processing (S13) is performed. In this light projection / reception signal information extraction process (S13), the control circuit 20 uses the light projection / reception signal information sampling process (3) for the received light quantity information in the half cycle (T / 2) of the self-noise stored in the memory 19. In step S12), the received light amount information stored in the memory 19 is read. In this light projection / reception signal information extraction process (S13), the light reception amount information stored in the memory 19 corresponding to the time (reference numeral T5 in FIG. 2) determined for each light projection time T2 is read out. The maximum received light amount M1 of the light receiving element 13 and the received light amount having a value slightly larger or slightly smaller than the maximum received light amount M1 can be read. In this embodiment, the time set for each light projection time T2 (symbol T5 in FIG. 2) is set by the operator as half the time T2 by the input unit 16. In this light projection / reception signal information extraction process (S 12), the read three received light quantity information is stored in the read received light quantity storage area of the memory 19.

  After the light projection / reception signal information extraction process (S13), it is determined whether or not the three light reception amounts (A, B, C) have a relationship of A <B <C (S14). In S14, when the control circuit 20 determines that the relationship of A <B <C (see FIG. 3A) is obtained and determines that the increase is indicated, the received light amount average value calculation process (S15). )I do. In this received light amount average value calculation process (S15), the maximum received light amount M1 read out by the light projection / reception signal information extraction process (S13) and the received light having a value slightly larger or slightly smaller than the maximum received light amount M1. The average value ([A + B + C] / 3) of the received light amount is calculated using the amount. In this received light amount average value calculation process (S15), the calculated average value is stored in the calculated value storage area of the memory 19.

  After the received light amount average value calculation process (S15), the control circuit 20 calculates the average value calculated using the maximum received light amount M1 and the received light amount having a value slightly larger or slightly smaller than the maximum received light amount M1. Are compared with the threshold value stored in the memory 19 (S16). In S16, when the control circuit 20 determines that the calculated average value exceeds the threshold and the detected object is detected, a detection notification process (S17) is performed. In this detection notification process (S17), the control circuit 20 transmits a detection notification signal to the display unit 17 and controls the display unit 17 to light up.

  On the other hand, when the control circuit 20 determines in S16 that the calculated average value does not exceed the threshold value and does not detect the detected object, a non-detection notification process (S18) is performed. In the non-detection notification process (S18), the control circuit 20 transmits a non-detection notification signal to the display unit 17 and controls the display unit 17 to turn off.

  After the detection notification process (S17) and the non-detection notification process (S18), an initialization process (S19) is performed. In this initialization process (S19), the control circuit 20 performs a process of clearing received light signal information and the like stored in the memory 19.

  In S14, when the control circuit 20 determines that A <B <C does not have a relationship, does the three received light amounts (A, B, C) have a relationship of A> B> C? It is determined whether or not (S20). In S20, when the control circuit 20 determines that the relationship of A> B> C (see FIG. 3B) is present and determines that the decrease is indicated, the received light amount average value calculation processing ( S15) is performed. After this received light amount average value calculation processing (S15), the control circuit 20 performs the processing of S16, 17, 19 or S16, 18, 19 described above.

  In S20, when the control circuit 20 determines that there is no relationship of A> B> C, whether the three received light amounts (A, B, C) have the relationship of A <B> C or not. Is determined (S21). In S21, when the control circuit 20 determines that the relationship of A <B> C (see FIG. 3C) is present and determines that the increase / decrease change is indicated, the received light amount subtraction process (S22) is performed. Do. In the received light amount subtraction process (S22), after the control circuit 20 calculates the average value of received light quantity ([A + B + C] / 3), it is stored in the added value / subtract value storage process (S8) of the self-noise detection process. The subtracted value (α / 2) is read from the added value / subtracted value storage area of the memory 19 and the subtracted value (α / 2) is subtracted from the average value of the received light amount ({[A + B + C] / 3} − α / 2) is calculated. In the received light amount subtraction process (S22), the calculated value ({[A + B + C] / 3} −α / 2) is stored in the calculated value storage area of the memory 19. After the received light amount subtraction process (S22), the control circuit 20 compares the calculated value with a threshold value (S16), and performs the above-described processes of S17 and S19 or S16, 18, and 19.

  In S21, when the control circuit 20 determines that there is no relationship of A <B> C, that is, three light reception amounts (A, B, C) have a relationship of A> B <C (FIG. 3D). If it is determined that there is a change in decrease, the received light amount addition process (S23) is performed. In this received light amount addition process (S23), after the control circuit 20 calculates the average value ([A + B + C] / 3) of the received light quantity, it is stored in the added value / subtract value storage process (S8) of the self-noise detection process. The obtained addition value (α / 2) is read from the addition value / subtraction value storage area of the memory 19, and the value obtained by adding the addition value (α / 2) to the average value of the received light amount ({[A + B + C] / 3}) + Α / 2) is calculated. In this received light amount addition processing (S23), the calculated value ({[A + B + C] / 3} + α / 2) is stored in the calculated value storage area of the memory 19. After the received light amount addition processing (S23), the control circuit 20 compares the calculated value with a threshold value (S16), and performs the above-described processing of S17 and S19 or S18 and S19.

4). Effects of this Embodiment In the photoelectric sensor 1 according to the embodiment, the control circuit 20 determines the temporal change in the amount of light received by the light receiving element 13 for each pulse P1 to P4, and the temporal change is the increase change or the decrease change. If it is determined that the change over time is the increase / decrease change, the received light amount subtraction process (S22), and if the change over time is the decrease change, the received light amount addition process is performed. Processing (S23) is performed. The photoelectric sensor 1 is configured to make the received light amount of the self-noise N close to the received light amount of the light-receiving element 13 by each processing (S15, S22, S23), and the signal of the self-noise N from the received light signal output from the amplifier circuit 15. The amount of received light that reduces the influence of the self-noise N can be calculated according to each change over time.

  In the photoelectric sensor 1, the control circuit 20 performs the detection notification process (S17) and the non-detection notification process (S18) by comparing the received light amount calculated by each process (S15, S22, S23) with a threshold value. . As a result, even when the light receiving circuit 14 outputs and superimposes the light reception signal on which the signal of the self noise N is superimposed in order to increase the detection sensitivity, the above process (S15, S22, S23) causes the self noise N. It is possible to calculate the amount of received light that reduces the influence of, and to reduce the influence of the self-noise N while increasing the detection sensitivity, and to increase the detection distance of the detected object.

  In the photoelectric sensor 1, the control circuit 20 receives light having a maximum light reception amount M1 of the light receiving element 13 and a value slightly larger or slightly smaller than the maximum light reception amount M1 by the light projection / reception signal information extraction process (S13). An amount is read out, and the detected object is detected by comparing the value calculated using the maximum received light amount M1 and the received light amount having a value slightly larger or slightly smaller than the maximum received light amount M1 with a threshold value. In the photoelectric sensor 1, the control circuit 20 compares the threshold value with the maximum received light amount M1 exceeding the threshold value and the received light amount having a value slightly larger or slightly smaller than the maximum received light amount M1. The detected object can be reliably detected.

  In the photoelectric sensor 1, the control circuit 20 uses the light projection / reception signal information extraction process (S13) to obtain the received light amount information stored in the memory 19 corresponding to the time T5 determined for each light projection time T2. The detected object is detected by comparing the value calculated by each process (S15, S22, S23) with the threshold value using the read received light amount information. In the photoelectric sensor 1, since the control circuit 20 reads only the received light amount information corresponding to the time T5 and compares it with the threshold value to detect the detected object, the light projection signal information extraction process (S13). And the efficiency of the detection processing of the detection object can be increased.

  In the photoelectric sensor 1, the control circuit 20 extracts the maximum received light amount information and the minimum received light amount information of the self-noise N by the maximum received light amount information extraction process (S4) and the minimum received light amount extraction process (S5). By the addition value / subtraction value calculation processing (S7) and the addition value / subtraction value storage processing (S8), the addition value and the subtraction value used for the light reception amount subtraction processing (S22) and the light reception amount addition processing (S23) are calculated. And can be stored in the memory 19. Accordingly, the addition value and the subtraction value can be calculated and set according to the characteristics of the self noise N. Further, since the control circuit 20 performs the detection notification process (S17) and the non-detection notification process (S18) by comparing the received light amount whose influence is reduced according to the characteristics of the self noise N and the threshold value, The detection distance of the detected object can be increased while detecting the presence or absence of the detected object by reducing the influence of the noise N.

  In the photoelectric sensor 1, after the control circuit 20 clears the memory 19 by the initialization process (S19) of the detection process, the light reception signal information is sampled by the light projection / reception signal information sampling process (S12) and the memory 19 The three received light amount information within the half cycle (T / 2) of the self-noise N is read from the memory 19 by the light projection / reception signal information extraction process (S13), and the magnitude relationship between the three received light amount information To determine each change with time (increase change, decrease change, increase / decrease change, decrease / increase change). Then, when executing the next detection cycle, the photoelectric sensor 1 clears the received light amount information stored in the memory 19 by the initialization process (S19). Thereby, the photoelectric sensor 1 does not need to sequentially store received light amount information for determining a change with time, and can prevent an increase in the storage capacity of the memory 19.

  Further, since the photoelectric sensor 1 determines the relationship between the three received light amount information and determines the respective temporal changes, the photoelectric sensor 1 determines the change in which the received light amount changes from increasing to decreasing or decreasing to increasing. The accuracy of detecting a change with time can be increased. Further, in the photoelectric sensor 1, since the control circuit 20 calculates the average value using the three received light quantity information by the received light quantity average value calculation process (S15), the multi-point received light quantity information is used. The accuracy of the calculated average value can be improved.

<Other embodiments>
The present invention is not limited to the embodiment described above, and can be implemented by appropriately changing a part of the configuration without departing from the spirit of the invention.
(1) The photoelectric sensor 1 is not limited to the reflective photoelectric sensor of the embodiment, and may be a transmissive photoelectric sensor.
(2) In this photoelectric sensor 1, the control circuit 20 determines the magnitude relationship between four or more received light amount information and discriminates each temporal change (increase change, decrease change, increase / decrease change, decrease / increase change), The received light amount average value calculating process (S15) may be performed using four or more received light amount information.
(3) In this photoelectric sensor 1, the control circuit 20 turns on the switching element of the light receiving circuit 14 for the time of the half cycle (T / 2) of its own noise N by the switching element operation signal, and receives the light receiving signal information. Instead of storing in the memory 19 over the respective light projection times T2, it is also possible to determine each temporal change while sampling three received light quantity information within a half cycle (T / 2) of the self-noise N. Good.
(4) The photoelectric sensor 1 may set the time T5 determined for each light projection time T2 to an appropriate position at which the received light amount exceeding the threshold value can be read from the memory 19. Further, the photoelectric sensor 1 may set the time T5 determined for each light projection time T2 to a plurality of positions where the received light amount exceeding the threshold value can be read from the memory 19.

The photoelectric sensor of the present invention may have the following configuration.
(5) The setting means is an addition value used for the addition processing according to the maximum received light amount and the minimum received light amount at the light receiving means from when the power is turned on until the light projecting element starts light projection. The photoelectric sensor according to claim 2, wherein a subtraction value used for the subtraction process is set. According to this configuration, the received light amount in which the influence of noise is reduced according to the maximum received light amount and the minimum received light amount in the light receiving unit from when the photoelectric sensor is turned on until the light projecting element starts projecting light. Since the addition value and the subtraction value used in the process of calculating the light amount can be set, the received light amount that reduces the influence of self-noise regularly generated by the switching operation of the light receiving circuit 14 even when the light projection is started is calculated. be able to.
(6) The setting means is responsive to the maximum light reception amount and the minimum light reception amount at the light reception means in a non-light projection time (for example, reference numeral T4 in FIG. 2) in the light projection operation of each pulsed light. The photoelectric sensor according to claim 2, wherein an addition value used for the addition process and a subtraction value used for the subtraction process are set. According to this configuration, the addition value and the subtraction value used for the process of calculating the received light amount in which the influence of noise is reduced according to the maximum received light amount and the minimum received light amount in the light receiving unit within the non-projection time are set. Therefore, it is possible to calculate the amount of received light in which the influence of self-noise that occurs irregularly after the start of light projection is reduced.

The block diagram which shows the electric constitution of the photoelectric sensor which concerns on embodiment Timing chart of the photoelectric sensor (A) The figure is a partial enlarged view of self-noise illustrating an increase change, (b) The figure is a partial enlarged view of self-noise illustrating a decrease change, (c) Figure is a partial enlarged view of self-noise illustrating an increase / decrease change. , (D) is a partially enlarged view of self-noise illustrating an increase / decrease change. Flow chart regarding processing for detecting self-noise Flow chart related to processing to detect the object to be detected

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Photoelectric sensor 11 ... Light projection element (light projection means)
12 ... Projection circuit (drive means)
13: Light receiving element (light receiving means)
14: Light receiving circuit (light receiving means)
19: Memory (detection means, discrimination means, setting means)
20 ... Control circuit (driving means, sampling means, detecting means, discriminating means, calculating means, setting means)
A, B, C: received light quantity P1 to P4: pulsed light

Claims (4)

A light projecting means for projecting light on the object to be detected;
Driving means for driving the light projecting means to project pulsed light; and
A light receiving means for receiving the pulsed light projected by the light projecting means;
Sampling means for sampling the amount of light received by the light receiving means in synchronization with the light projecting operation of each pulsed light of the light projecting means;
Setting means for setting an addition value and a subtraction value according to the maximum light reception amount and the minimum light reception amount at the light receiving unit when the light projecting unit does not project the object to be detected;
A photoelectric sensor comprising detection means for detecting the detected object,
The sampling means samples the received light amount a plurality of times within a period corresponding to a half cycle of self-noise of the photoelectric sensor in each sampling operation of the light receiving means corresponding to the light projection operation of each pulsed light. Composed of
The amount of received light sampled in each sampling operation is an increasing change that increases over time, a decreasing change that decreases over time, an increasing / decreasing change that changes from increasing to decreasing over time, or an increase from decreasing over time. A discriminating means for discriminating whether the increase or decrease changes to turn to
An average process for calculating an average value of the plurality of received light amounts on the condition that the determination means determines that the increase change or the decrease change, and the determination means determines that the decrease change an addition process of adding the additional value to the average value after calculating the average value on condition that, from the average value after calculating the average value on condition that the increase or decrease change is detected by said discriminating means and an arithmetic means for performing a subtraction process for subtracting the subtraction value,
The photoelectric sensor characterized in that the detection means detects the object to be detected based on a value calculated by the calculation means. The sampling unit samples only the maximum received light amount at the light receiving unit and the received light amount before and after the received light amount, and the detecting unit is configured to sample the maximum received light amount and the received light amount before and after the sampled light. The photoelectric sensor according to claim 1, wherein the detected object is detected based on a value calculated using only the amount of received light. 3. The detection unit according to claim 2, wherein the detection unit detects the object to be detected based on a value calculated by the calculation unit at a timing determined for each light projection operation of each pulsed light of the light projection unit. The photoelectric sensor as described. The determining means determines each change based on at least three or more received light amounts sampled by the sampling means,
It said calculating means includes a photoelectric sensor according to any one of claims 1 to 3, characterized in that the averaging process using at least three or more light-receiving amount of said sampled.

Images