JP2014131170A - Photoelectric sensor - Google Patents

Abstract

In a photoelectric sensor configured to convert a received light amount into an electrical signal and determine a threshold value by a comparator, auto-tuning is quickly performed without increasing the circuit scale.
When tuning an OP threshold value of a comparator, a control unit outputs a set-off signal to reset a count value of an up / down counter to 0 to create a light-shielding state in a pseudo manner. 6 discriminates the received light signal with a tentative threshold value and outputs a pulse, and it is determined from the count value of the pulse of the up / down counter 9 whether it is a light incident state or a light shielding state. The control unit 11 sets the provisional threshold value of the boundary where the determination result changes from the light shielding state to the light incident state as the OP threshold value.
[Selection] Figure 1

Description

  The present invention particularly relates to sensitivity adjustment in a photoelectric sensor that converts a received light amount into an electrical signal and determines a threshold value by a comparator.

  In a conventional photoelectric sensor, a light projection pulse from a light projector is received by a light receiver, converted into an electric signal, amplified, and output as a light reception signal. When this received light signal exceeds the threshold, a pulse is output from the comparator, and the up / down counter counts up each time the pulse is input, otherwise it counts down, and the count value reaches the set maximum value Is set to the light incident state, and when the count value becomes 0, the light is blocked (see, for example, Patent Document 1).

  In order to prevent chattering, the actual operating point of the comparator is set by adding a hysteresis width to the threshold value. For example, in the case of a reflection type photoelectric sensor, when the light reception signal changes from the large side to the small side (RP when changing from the light incident state to the light shielding state) and when the light reception signal changes from the small side to the large side (light shielding). When the state changes to the light incident state, the threshold value differs from OP), and the OP threshold value is higher than the RP threshold value.

JP 2004-207770 A

  In the photoelectric sensor configured to convert the amount of received light into an electrical signal and determine the threshold value with a comparator, the amount of received light is not converted into a digital value, so that there has been a problem that the optimum threshold value cannot be calculated directly. Therefore, threshold auto-tuning (auto teaching) has not been performed.

On the other hand, when manually tuning the threshold value, it depends on whether the RP threshold value is tuned when changing from the light incident state to the light shielding state, or the OP threshold value tuning when changing from the light shielding state to the light incident state. Since the threshold values are different, it is necessary to make the photoelectric sensor recognize the state before the change.
Further, it is necessary to create a light incident / light shielding state in a pseudo manner and wait for the up / down counter to finish counting. Furthermore, a circuit for artificially entering / blocking light is also required.

  The present invention has been made to solve the above-described problems. In a photoelectric sensor having a configuration in which a received light amount is converted into an electric signal and a threshold value is determined by a comparator, automatic tuning can be quickly performed without increasing the circuit scale. The purpose is to implement.

  The photoelectric sensor according to the present invention includes a light projecting element that projects light to a detection region, a light receiving element that receives light from the light projecting element and outputs a light reception signal at a level corresponding to the amount of light received, and light reception from the light receiving element. Discriminating unit that discriminates and outputs signals with a predetermined threshold, up / down counter that counts up or down the output of the discriminating unit every predetermined period, and light entering state when the count value of the up / down counter is the maximum value When the threshold value of the discriminator is tuned based on the received light signal and the output control unit that outputs a signal indicating that the light is blocked at the minimum value, the count value of the up / down counter is reset to the maximum value or the minimum value. And a control unit.

  The photoelectric sensor according to the present invention includes a light projecting element that projects light to a detection region, a light receiving element that receives light from the light projecting element and outputs a light reception signal at a level corresponding to the amount of light received, and light reception from the light receiving element. Discriminating unit that discriminates and outputs signals with a predetermined threshold, up / down counter that counts up or down the output of the discriminating unit every predetermined period, and light entering state when the count value of the up / down counter is the maximum value When the output control unit that outputs a signal indicating that the light is blocked at the minimum value and the amplification degree of the amplification unit are tuned based on the comparison between the received light signal and the threshold value, the count value of the up / down counter is maximized. And a controller that resets the value to the minimum value.

  The photoelectric sensor according to the present invention includes a light projecting element that projects light to a detection region, a light receiving element that receives light from the light projecting element and outputs a light reception signal at a level corresponding to the amount of light received, and light reception from the light receiving element. Discriminating unit that discriminates and outputs signals with a predetermined threshold, up / down counter that counts up or down the output of the discriminating unit every predetermined period, and light entering state when the count value of the up / down counter is the maximum value The output control unit that outputs a signal indicating that the light is blocked at the minimum value, and the count value of the up / down counter when tuning the light projection amount of the light projecting element based on the comparison between the light reception signal and the threshold value. And a control unit that resets to a maximum value or a minimum value.

  According to the present invention, since the count value of the up / down counter is reset when adjusting the light receiving sensitivity, it is possible to create a light incident state or a light shielding state without waiting for the count of the up / down counter. Therefore, in the photoelectric sensor having a configuration in which the received light amount is converted into an electric signal and the threshold value is determined by the discrimination unit, auto-tuning can be performed quickly without increasing the circuit scale.

It is a circuit diagram which shows the structure of the reflection type photoelectric sensor which concerns on Embodiment 1 of this invention. It is a figure explaining the operation | movement at the time of count-up by the up / down counter of the reflection type photoelectric sensor which concerns on Embodiment 1. FIG. It is a figure explaining the operation | movement at the time of countdown by the up-down counter of the reflection type photoelectric sensor which concerns on Embodiment 1. FIG. It is a figure explaining the operation | movement at the time of set-on by the up-down counter of the reflection type photoelectric sensor which concerns on Embodiment 1. FIG. It is a figure explaining the operation | movement at the time of the set-off by the up-down counter of the reflection type photoelectric sensor which concerns on Embodiment 1. FIG. It is a flowchart which shows the auto tuning operation | movement of the reflective photoelectric sensor which concerns on Embodiment 1, and is an example of a bisection method. It is a graph explaining the auto-tuning of the reflective photoelectric sensor which concerns on Embodiment 1, and is an example of a bisection method. It is a conceptual diagram of the OP threshold value and the RP threshold value of the reflective photoelectric sensor according to Embodiment 1, and is an example of auto-tuning by the sequential method.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing a configuration of a reflective photoelectric sensor 1 according to Embodiment 1 of the present invention. The reflective photoelectric sensor 1 includes a light projecting element 2 (for example, a light emitting diode), a light projecting circuit 3, a light receiving element 4 (for example, a photodiode), an amplifier circuit 5, a comparator (discriminating unit) 6, The threshold setting circuit 7, the pulse detection circuit 8, the up / down counter 9, the output control circuit 10, the control unit 11, and the storage unit 12 are configured.

  In the case of the reflection type, a projector in which the light projecting element 2 and the light projecting circuit 3 are integrated, a light receiving element 4, an amplifier circuit 5, a comparator 6, a threshold setting circuit 7, a pulse detection circuit 8, an up / down counter 9, and an output control circuit 10. A light receiver in which the control unit 11 and the storage unit 12 are integrated is arranged side by side on the same side with respect to the detection region where the detection target exists, and light reflected from the detection target of the light emitted from the projector is received. When the light is received by the detector, it is determined from the change in the amount of received light whether the light is incident or light is blocked.

  The light projecting circuit 3 drives the light projecting element 2 to project a pulse having a predetermined light amount onto the detection area. The light receiving element 4 receives reflected light from the detection region and converts it into an electrical signal corresponding to the amount of received light to obtain a light receiving signal. The amplifier circuit 5 amplifies the received light signal and inputs it to one input terminal of the comparator 6. The threshold setting circuit 7 is composed of, for example, a variable resistor connected to the other input terminal of the comparator 6. When an on signal is input from the up / down counter 9, the threshold setting circuit 7 sets an RP threshold and the input of the on signal is interrupted. And set the OP threshold. The comparator 6 discriminates and outputs the light reception signal of the amplifier circuit 5 input to one input terminal by the threshold value (OP or RP) of the threshold setting circuit 7 input to the other input terminal. In the case of the reflection type, the comparator 6 compares the light reception signal when the value changes from the small side to the large side with the OP threshold value, and the detection target is present when the light reception signal is equal to or greater than the OP threshold value (light incident state). ) And outputs a pulse to the pulse detection circuit 8. The comparator 6 compares the light reception signal when the value changes from the larger side to the smaller side with the RP threshold value, and determines that there is no detection target (light shielding state) when the light reception signal is equal to or less than the RP threshold value. No pulse is output to the pulse detection circuit 8. These OP and RP threshold values are determined by auto-tuning described later.

  In the case of the reflection type, the light projecting circuit 3 on the light projector side and the pulse detecting circuit 8 on the light receiver side are synchronized based on the synchronization signal, and the pulse detecting circuit 8 receives the pulse input from the comparator 6 as the light projecting element 2. Whether or not the pulse is an effective pulse corresponding to the self-emitted light emitted from is determined using a synchronization signal, and the effective pulse is input to the up / down counter 9 as an up / down signal. A periodic count synchronized with the synchronization signal is input from the pulse detection circuit 8 to the up / down counter 9.

FIG. 2 shows the operation when the up / down counter 9 is counting up, and FIG. 3 shows the operation when counting down. Each horizontal axis in FIGS. 2 and 3 represents time.
The up / down counter 9 counts up when an up / down signal is input at every periodic count (FIGS. 2A and 3A) (FIG. 2C), and no pulse is input. In this case, it counts down (FIG. 3C). When the count value reaches the maximum value of 5, an ON signal is output as the light incident state (FIG. 2D), and when the count value reaches the minimum value of 0, the ON signal output is stopped as the light shielding state (FIG. 3 ( d)). The output control circuit 10 opens and closes the contacts according to whether or not an ON signal is input to the up / down counter 9.

FIG. 4 shows the set-on operation of the up / down counter 9, and FIG. 5 shows the set-off operation. Each horizontal axis in FIGS. 4 and 5 represents time.
When the set-on signal is input from the control unit 11 (FIG. 4E), the up / down counter 9 changes the count value to the maximum value (for example, 5) (FIG. 4C), Output (FIG. 4D). On the other hand, when a set-off signal is input from the control unit 11 (FIG. 5 (e)), the up / down counter 9 changes the count value to the minimum value 0 (FIG. 5 (c)) and stops the on signal output. (FIG. 5D).

  When the count value is reset by supplying a set-on signal or a set-off signal to the up / down counter 9, the count value can be reset immediately, and a pseudo light incident state or light shielding state can be created. On the other hand, when there is no such reset function, it is necessary to shift the current count value to 0 or 1 count at a time, so that a time corresponding to a maximum of 5 counts is required to create a pseudo light incident state or light shielding state. Have

  The light projecting element 2, the light projecting circuit 3, the light receiving element 4, the amplifying circuit 5, the comparator 6, the threshold setting circuit 7, the pulse detecting circuit 8, the up / down counter 9, and the output control circuit 10 are configured by analog circuits. On the other hand, the control unit 11 described below may be configured with an analog circuit or a digital circuit such as a microcomputer. The storage unit 12 includes a storage element such as an EEPROM (Electrically Erasable Programmable Read-Only Memory).

  The storage unit 12 stores various setting information (for example, the maximum count-up value) of the reflective photoelectric sensor 1, and the control unit 11 reads the information and sends a count stage number control signal to the up / down counter 9. The maximum count-up value is set by outputting. Further, the control unit 11 reads and executes the auto tuning program stored in the storage unit 12, and sets the OP threshold value and the RP threshold value obtained by using the ON signal output from the up / down counter 9 as the threshold level selection signal. Is output to the threshold value setting circuit 7 to adjust the light receiving sensitivity of the reflective photoelectric sensor 1. Further, during auto tuning, a set-on signal and a set-off signal are output from the control unit 11 to the up / down counter 9 as necessary, and the count value of the up / down counter 9 is set to a maximum value (for example, 5) or a minimum value. By forcibly shifting to (0), a pseudo light incident state or light blocking state is quickly created.

  Hereinafter, auto-tuning of the reflective photoelectric sensor 1 will be described. FIG. 6 is a flowchart for obtaining the OP threshold by the bisection method, and an operation example according to the flowchart will be described with reference to the graph of FIG. The vertical axis of the graph represents the light amount of the received light signal, and the horizontal axis represents the flow loop count. When performing auto-tuning, the light incident state where the detection target object exists in the detection region is maintained, and the OP threshold value and the RP threshold value are estimated from the light incident amount at this time.

  The control unit 11 sets the loop count i = N (for example, i = 8) among the setting information stored in the storage unit 12 (step ST1), and sets the maximum value that the threshold can take. The minimum value is initially set as the threshold lower limit as the threshold upper limit (step ST2). Subsequently, the control unit 11 sets an intermediate value that bisects the range from the upper threshold to the lower threshold as a temporary OP threshold (step ST3), outputs a set-off signal, and sets the count value of the up / down counter 9 to zero. Then, a light shielding state is set (step ST4). In FIG. 7, the threshold upper limit is represented by a triangle (Δ), the threshold lower limit is represented by a square (□), the provisional OP threshold is represented by a white circle (◯), and the incident light amount is represented by a broken line.

  Subsequently, the light incident state is determined (step ST5). First, the threshold setting circuit 7 notified of the temporary OP threshold from the control unit 11 sets the temporary OP threshold in the comparator 6. The comparator 6 outputs an up / down signal when the received light signal (incident light amount indicated by a broken line in FIG. 7) is equal to or larger than the temporary OP threshold, and the up / down counter 9 counts up the count value from 0 to the maximum value. An ON signal indicating the incident light state is output (step ST5 “ON”). Then, the control unit 11 receives this ON signal, and changes the threshold lower limit to a temporary OP threshold as in the case of i = 8 in FIG. 7 (step ST6).

  On the other hand, when the received light signal is smaller than the temporary OP threshold value, the up / down signal is not output from the comparator 6, and the count value of the up / down counter 9 remains 0 even when, for example, 5 counts have elapsed. No ON signal is output. In this case, after outputting the set-off signal and creating a pseudo light-shielding state, the control unit 11 does not receive an ON signal even if, for example, a time of 5 counts has elapsed (step ST5 “OFF”). Then, it is determined that the light shielding state continues, and the upper limit threshold is changed to a temporary OP threshold as in the case of i = 7 in FIG. 7 (step ST7).

  The controller 11 decrements the loop count i after changing the threshold upper limit or threshold lower limit to the temporary OP threshold (step ST8), and ends auto-tuning when i = 0 (step ST9 “YES”). The temporary OP threshold at that time is notified to the threshold setting circuit 7 as a formal OP threshold.

  If i = 0 is not satisfied (“NO” in step ST9), the process returns to step ST3 again, and an intermediate value that divides the range between the upper limit of the threshold value and the lower limit of the threshold value into two is set as a temporary OP threshold value to determine the light incident state. Repeat the process. By repeating this process, the temporary OP threshold can be made closer to the incident light amount, and the light receiving sensitivity can be adjusted.

  In the above description, the OP threshold value for detecting the change from the light-blocking state to the light-blocking state is auto-tuned. However, the RP threshold value for detecting the change from the light-blocking state to the light-blocking state is also auto-tuned by the same method. To do. When auto-tuning the RP threshold value, the control unit 11 sets a temporary RP threshold value (indicated by a black circle (●) in FIG. 7) in consideration of the hysteresis width from the temporary OP threshold value in step ST3. Further, in step ST4, the control unit 11 outputs a set-on signal, maximizes the count value of the up / down counter 9, creates a pseudo light incident state, and makes a determination based on the temporary RP threshold value.

Note that the search method for the OP threshold value and the RP threshold value is not limited to the bisection method shown in FIG. 6, and may be any method. Hereinafter, the sequential method will be described with reference to FIG.
FIG. 8 is a conceptual diagram of the OP threshold and the RP threshold, and the vertical axis represents the light amount. The previous state is a pseudo light incident state when a set-on signal is output or a pseudo light-shielding state when a set-off signal is output, and the subsequent state is a determination result of the light incident state. It is. When the previous state is OFF (light shielding state), the light amount <OP threshold value if the subsequent state is OFF, and the light amount> OP threshold value if the subsequent state is ON (light incident state). On the other hand, if the previous state is ON, the light amount <RP threshold value if the subsequent state is OFF, and the light amount> RP threshold value if the subsequent state is ON.

  The control unit 11 repeatedly determines whether or not the light is in an incident state while gradually changing the temporary RP threshold and the temporary OP threshold from the threshold lower limit side to the threshold upper limit side, as shown in FIG. Search for the RP threshold value at the boundary where A is turned from OFF to ON and the OP threshold value at the boundary where the subsequent state is turned from OFF to ON. Of course, the temporary RP threshold and the temporary OP threshold may be gradually changed from the threshold upper limit side to the threshold lower limit side. Moreover, it is necessary to consider the hysteresis width when setting the temporary RP threshold and the temporary OP threshold.

  As described above, according to the first embodiment, the reflective photoelectric sensor 1 receives the light from the light projecting element 2 that projects light onto the detection region and the light from the light projecting element 2, and receives light at a level corresponding to the amount of light received. , A comparator 6 that discriminates and outputs a light-receiving signal from the light-receiving element 4 with a predetermined threshold (OP or RP), and an up-down that counts up or down the output of the comparator 6 at predetermined intervals The counter 9, the output control circuit 10 that outputs a signal indicating that the light is in the incident state when the count value of the up / down counter 9 is the maximum value, and the light shielding state when the value is the minimum value, and the comparator 6 based on the light reception signal The control unit 11 is configured to reset the count value of the up / down counter 9 to the maximum value or the minimum value when tuning the threshold value. For this reason, when tuning the threshold value of the comparator 6, a set-on signal or a set-off signal is output from the control unit 11 without waiting for the count value of the up / down counter 9 to reach the maximum value or the minimum value. A light incident state or a light shielding state can be created. Therefore, in the reflective photoelectric sensor 1 having a configuration in which the received light amount is converted into an electric signal and the threshold value is determined by the comparator 6, auto-tuning can be performed quickly without increasing the circuit scale.

  Further, according to the first embodiment, the control unit 11 initially sets the maximum value of the range that can be taken by the threshold value of the up / down counter 9 as the threshold upper limit and the minimum value as the threshold lower limit. The threshold value is obtained and set in the comparator 6 via the threshold setting circuit 7 to determine whether the light is in the light incident state or the light shielding state. If it is in the light incident state, the temporary threshold is set as the threshold lower limit. In this case, the provisional threshold is set to the upper limit threshold and the provisional threshold is obtained again, and the provisional threshold after being repeated a predetermined number of times is set in the comparator 6. Therefore, in the reflective photoelectric sensor 1 configured to convert the received light amount into an electrical signal and determine the threshold value by the comparator 6, the OP threshold value and the RP threshold value can be automatically tuned based on the received light amount. There is no need to externally set whether to perform tuning or tuning of the RP threshold. Further, the threshold value can be quickly searched using the bisection method, and the tuning time can be shortened.

  In the above description, the set-on signal and set-off signal are automatically output when auto-tuning (automatic sensitivity adjustment). However, when manual tuning (manual sensitivity adjustment) is performed, button operation, etc. A configuration may be adopted in which a set-on signal and a set-off signal are output in response to an instruction from the outside.

  In the above description, the threshold values (OP and RP) of the received light amount are tuned as sensitivity adjustment of the reflective photoelectric sensor 1, but the present invention is not limited to the threshold values. For example, the threshold value is fixed, and the amplification degree is tuned by repeating the determination of the incident light state while changing the amplification degree (gain) of the amplifier circuit 5 or the incident light quantity from the light projecting element 2 is changed. The sensitivity of the reflective photoelectric sensor 1 may be adjusted by tuning the light projection amount by repeating the determination of the light state. The adjustment of the amplification degree is performed by notifying the amplification degree selection signal from the control unit 11 to the amplification circuit 5, and the adjustment of the light emission amount is performed by notifying the light emission amount selection signal from the control unit 11 to the light projection circuit 3. Just do it.

  Furthermore, the light receiving sensitivity may be adjusted by changing a plurality of threshold values, amplification factors, and light projection amounts. For example, when both the amplification degree (two stages) and the threshold value are changed, the control unit 11 first determines the light incident state when the amplification signal is output in two stages, and the on signal is output. The threshold value is tuned by executing the flowchart of FIG.

  In the above description, the reflective photoelectric sensor 1 is tuned. However, this tuning can also be applied to a transmissive photoelectric sensor. A transmissive photoelectric sensor has a projector and a light receiver placed facing each other with a detection region in between, and when the detection target exists in the detection region, the light emitted from the projector is shielded by the detection target Detect objects using. Therefore, the light receiving signal is small when there is a detection target in the detection region, and the light receiving signal is large when there is no detection target, except that it is different from the reflective photoelectric sensor 1 in the same manner as the reflective photoelectric sensor 1. Tuning can be performed, and the reflective photoelectric sensor 1 can also be used as a transmission type.

  However, in the case of the transmissive type, the projector and the light receiver are installed apart from each other, so that it is difficult to route the signal line for the synchronization signal. Therefore, when used as a transmission type, the pulse detection circuit 8 determines whether the pulse of the comparator 6 is valid without using the synchronization signal. Accordingly, when the reflection type photoelectric sensor 1 is configured to be used as both a reflection type and a transmission type, a detection method signal for switching the pulse detection method of the pulse detection circuit 8 between the reflection type and the transmission type is supplied to the control unit 11. To the pulse detection circuit 8, the pulse detection circuit 8 determines the validity of the pulse by using the synchronization signal when the reflection type is used, and determines the validity of the pulse by a method that does not use the synchronization signal when the transmission type is the transmission type. To do.

  The embodiment of the present invention has been described in detail with reference to the drawings, but the specific configuration is not limited to the configuration of the above-described embodiment, and the design is within the scope not departing from the gist of the present invention. Needless to say, changes and the like are included in the present invention.

DESCRIPTION OF SYMBOLS 1 Reflection type photoelectric sensor 2 Light emitting element 3 Light emitting circuit 4 Light receiving element 5 Amplifying circuit 6 Comparator (discrimination part)
7 Threshold Setting Circuit 8 Pulse Detection Circuit 9 Up / Down Counter 10 Output Control Circuit 11 Control Unit 12 Storage Unit

Claims (12)

A light projecting element that projects light to the detection area;
A light receiving element that receives light from the light projecting element and outputs a light receiving signal at a level corresponding to the amount of light received;
A discrimination unit that discriminates and outputs a light reception signal from the light receiving element at a predetermined threshold;
An up / down counter that counts up or counts down the output of the discriminator at predetermined intervals;
An output control unit that outputs a signal indicating that the up / down counter is in a light incident state when the count value is a maximum value and is in a light shielding state when the count value is a minimum value;
A photoelectric sensor comprising: a control unit that resets the count value of the up / down counter to a maximum value or a minimum value when tuning the threshold value of the discrimination unit based on the light reception signal.   The control unit initially sets a maximum value of a range that can be taken by the threshold value of the discrimination unit as a threshold upper limit and a minimum value as a threshold lower limit, and obtains a temporary threshold from the threshold upper limit and the threshold lower limit and sets the threshold in the discrimination unit In the case of the light incident state, the temporary threshold value is set to the lower threshold value. On the other hand, in the light blocked state, the temporary threshold value is set to the upper threshold value. 2. The photoelectric sensor according to claim 1, wherein setting and recalculating the temporary threshold are repeated, and the temporary threshold after being repeated a predetermined number of times is used as the threshold of the discrimination unit. An amplification unit that amplifies a light reception signal from the light receiving element and inputs the amplified signal to the discrimination unit;
The control unit resets the count value of the up / down counter to a maximum value or a minimum value when tuning the amplification degree of the amplification unit based on a comparison between the light reception signal and a threshold value of the discrimination unit. The photoelectric sensor according to claim 1 or 2, wherein the photoelectric sensor is characterized in that:   The said control part resets the count value of the said up / down counter to the maximum value or the minimum value, when an instruction | indication is received from the outside, The any one of Claims 1-3 characterized by the above-mentioned. Photoelectric sensor. A light projecting element that projects light to the detection area;
A light receiving element that receives light from the light projecting element and outputs a light receiving signal at a level corresponding to the amount of light received;
A discrimination unit that discriminates and outputs a light reception signal from the light receiving element at a predetermined threshold;
An up / down counter that counts up or counts down the output of the discriminator at predetermined intervals;
An output control unit that outputs a signal indicating that the count value of the up / down counter is in an input state when the count value is a maximum value and is in a light shielding state when the count value is a minimum value;
A photoelectric sensor comprising: a control unit that resets the count value of the up / down counter to a maximum value or a minimum value when tuning the amplification degree of the amplification unit based on a comparison between the light reception signal and the threshold value.   The said control part resets the count value of the said up / down counter to the maximum value or the minimum value, when tuning the threshold value of the said discrimination part based on the light reception signal of the said light receiving element. Photoelectric sensor.   The control unit sets the count value of the up / down counter to a maximum value or a minimum value when tuning the light projection amount of the light projection element based on a comparison between a light reception signal of the light reception element and a threshold value of the discrimination unit. 7. The photoelectric sensor according to claim 5, wherein the photoelectric sensor is reset.   The control unit initially sets a maximum value of a range that can be taken by the threshold value of the discrimination unit as a threshold upper limit and a minimum value as a threshold lower limit, and obtains a temporary threshold from the threshold upper limit and the threshold lower limit and sets the threshold in the discrimination unit In the case of the light incident state, the temporary threshold value is set to the lower threshold value. On the other hand, in the light blocked state, the temporary threshold value is set to the upper threshold value. 7. The photoelectric sensor according to claim 6, wherein setting and re-determining the temporary threshold are repeated, and the temporary threshold after being repeated a predetermined number of times is used as the threshold of the discrimination unit.   The said control part resets the count value of the said up / down counter to the maximum value or the minimum value, when an instruction | indication is received from the outside, Any one of Claims 5-8 characterized by the above-mentioned. Photoelectric sensor. A light projecting element that projects light to the detection area;
A light receiving element that receives light from the light projecting element and outputs a light receiving signal at a level corresponding to the amount of light received;
A discrimination unit that discriminates and outputs a light reception signal from the light receiving element at a predetermined threshold;
An up / down counter that counts up or counts down the output of the discriminator at predetermined intervals;
An output control unit that outputs a signal indicating that the up / down counter is in a light incident state when the count value is a maximum value and is in a light shielding state when the count value is a minimum value;
A photoelectric sensor comprising: a control unit that resets the count value of the up / down counter to a maximum value or a minimum value when tuning a light projection amount of the light projecting element based on a comparison between the light reception signal and the threshold value. An amplification unit that amplifies a light reception signal from the light receiving element and inputs the amplified signal to the discrimination unit;
The control unit resets the count value of the up / down counter to a maximum value or a minimum value when tuning the amplification degree of the amplification unit based on a comparison between the light reception signal and a threshold value of the discrimination unit. The photoelectric sensor according to claim 10.   12. The photoelectric sensor according to claim 10, wherein the controller resets the count value of the up / down counter to a maximum value or a minimum value when receiving an instruction from the outside.

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