JP2004317209A - Light curtain - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light curtain made preventive from mutual interference with other sensors by making settable appropriate detection sensitivity according to an installation environment. <P>SOLUTION: The light curtain, where a projection sensor head in which a plurality of floodlights are arranged and a light receiving sensor head in which a plurality of light receivers are arranged are arranged opposingly is provided with a sensitivity adjustment means for adjusting detection sensitivity. The adjustment of detection sensitivity is made, for example, by the setting of a detection judgment threshold, that of the amount of projection, or that of light reception signal amplification factors. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light curtain for detecting, for example, intrusion of a human body into a danger area, and more particularly to a light curtain capable of setting an appropriate detection sensitivity according to an installation environment.
[0002]
[Prior art]
In general, a light curtain is configured such that a light projector in which a plurality of light emitting elements are arranged is arranged on one side, and a light receiver in which the same number of light receiving elements are arranged is arranged on the opposite side. When an object enters the detection target area (dangerous area), the detection light from the light emitter is blocked or reflected in front of the light receiver, so that the light reception amount in the light receiver changes partially or entirely (the light reception amount is attenuated). ), Whereby an object intrusion is detected.
[0003]
By the way, in the case of a light curtain, since the light emitting and receiving elements in the light emitting device and the light receiving device are integrated into the main body (light emitting and receiving device) at the time of assembling the product, variations in the light receiving amount for each optical axis are likely to occur. In addition, in order to ensure the longest distance detection, the light emitting element emits light with the maximum light emission amount within the rating, almost irrespective of the actual installation environment, and the light receiving side maximizes the amplification factor of the amplifier. Generally, the detection determination threshold is set to the lowest value that does not cause a malfunction due to noise generated inside the circuit (for example, see Patent Document 1). As for a transmission type sensor including a set of light emitting and receiving elements, there has been proposed a transmission type sensor which automatically sets a detection determination threshold according to an installation environment by performing teaching while the sensor is actually installed. (See Patent Document 2).
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-4664 [Patent Document 2]
Japanese Patent Application Laid-Open No. Hei 9-18318
[Problems to be solved by the invention]
However, in the light curtain, as described above, since there is a problem of variation in the amount of received light for each optical axis and a problem of securing the longest detection distance, the amount of projected light, amplification factor, and threshold are still fixed. Have been. For this reason, the following problems have been pointed out.
(1) Since the amplification factor is large and the threshold value is small, the light is blocked in a situation where detection light from another sensor (for example, an adjacent light curtain) is incident on the light receiving element. Nevertheless, it is easy to cause a erroneous determination of the light incident state.
(2) Since the amount of projected light is large, it easily affects the detection determination of other sensors.
[0006]
The present invention has been made in view of the above-described problems, and an object of the present invention is to enable setting of an appropriate detection sensitivity in accordance with an installation environment, and thereby to prevent mutual interference with other sensors. An object of the present invention is to provide a light curtain for which prevention is possible.
[0007]
Other objects and operational effects of the present invention will be easily understood by those skilled in the art by referring to the description in the following specification.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a light curtain of the present invention is a light curtain in which a light emitting sensor head in which a plurality of light emitters are arranged and a light receiving sensor head in which a plurality of light receivers are arranged are opposed to each other. Accordingly, a sensitivity adjusting means for adjusting the detection sensitivity is provided.
[0009]
Here, "adjust detection sensitivity" means that adjustment of, for example, a detection determination threshold value, a projection light amount, a light receiving signal amplification factor, and the like is enabled.
[0010]
According to the light curtain of the present invention, it is possible to set an appropriate detection sensitivity in accordance with the installation environment, so that it is possible to avoid, for example, mutual interference with another adjacent light curtain or photoelectric sensor. .
[0011]
For example, when the detection sensitivity is adjusted by setting a detection determination threshold, preferably, the detection determination threshold is a light reception signal level at each light receiver obtained by light emission / reception sampling for a series of optical axes. It is configured to be automatically set based on.
[0012]
According to such a configuration, the threshold can be set by so-called "teaching (automatic learning)", so that a troublesome setting operation or the like is not required, and an appropriate threshold according to the installation environment can be set. Can be.
[0013]
Here, it is preferable that the detection determination threshold value is set to a value equal to or lower than the lowest level among the light reception signal levels acquired by the light emission / reception sampling.
[0014]
Although there is a "value lower than the minimum level", in the case where the light emitting and receiving sampling is performed a plurality of times, for example, a value equal to or less than the minimum level of the average value of the minimum light receiving signal level obtained by each light emitting and receiving sampling is used. Is preferably set to １ ／ of the average value of the lowest light receiving signal level.
[0015]
According to such a configuration, it is possible to reliably receive its own light projection. Further, if the value is set to a value close to the lowest level, it is possible to minimize malfunctions due to detection light from other light curtains and photoelectric sensors.
[0016]
Next, when the detection sensitivity is adjusted by setting the amount of projected light, preferably, the amount of projected light is a series of optical axes that are executed as the amount of projected light from each of the plurality of patterns. It is configured such that any one of the plurality of light emission light levels is automatically set based on a light reception signal level in each light receiver obtained by a plurality of target light emission / light reception samplings.
[0017]
According to such a configuration, the amount of projected light can be set by so-called “teaching (automatic learning)”, so that a troublesome setting operation or the like is not required, and an appropriate amount of projected light according to the installation environment can be set. it can.
[0018]
Here, preferably, the light projecting light amount is set to the minimum light emitting light amount level when the light receiving signal level of each light receiver obtained by the light emitting / receiving sampling exceeds a predetermined level.
[0019]
The predetermined level refers to a light receiving signal level that is at least equal to or higher than a light receiving signal level at which a light entering state and a light blocking state can be determined. According to such a configuration, in addition to automatically setting an appropriate amount of projected light according to the installation environment, it is possible to minimize the influence (mutual interference) on other light curtains and photoelectric sensors.
[0020]
Next, when the detection sensitivity is adjusted by setting the light-receiving signal amplification factor, preferably, the light-receiving signal amplification factor is a series of optical axes that are executed with each of the amplification levels of a plurality of patterns as the light-receiving signal amplification level. Is configured to be automatically set to any one of the plurality of amplification levels based on a light reception signal level in each light receiver obtained by a plurality of light emission / sampling samplings for.
[0021]
According to such a configuration, since the light receiving gain can be set by so-called “teaching (automatic learning)”, a troublesome setting operation or the like becomes unnecessary, and an appropriate light receiving gain according to the installation environment can be set. it can.
[0022]
Here, preferably, the light-receiving signal amplification rate is set to the minimum one of the amplification levels when the light-receiving signal level of each light-receiving device obtained by a plurality of light-emitting / light-receiving samplings exceeds a predetermined level. To be configured.
[0023]
According to such a configuration, it is possible to automatically set an appropriate light receiving gain according to an installation environment, and to minimize malfunction due to detection light from other light curtains or photoelectric sensors or internally generated noise. Become.
[0024]
In the light curtain according to the present invention, preferably, the automatically set threshold value, the projected light amount or the received light signal amplification factor is numerically displayed on a display unit of an external setting device electrically connected to the projected light sensor head or the received light sensor head. Means for displaying, and means for changing the automatically set threshold value, light emission amount or light receiving signal amplification rate based on the teaching signal by receiving a teaching signal generated by operating an external setting device. Provided.
[0025]
According to such a configuration, fine adjustment of various set values after the so-called teaching process can be performed through the external setting device.
[0026]
Here, more preferably, the external setting device is further provided with means for displaying the amount of received light at that time, the threshold value, the projected light amount or the amplification factor of the received light signal on the display unit of the external setting device in real time. .
[0027]
According to such a configuration, the detection status can be confirmed in real time, and it is possible to perform appropriate readjustment of the detection sensitivity and the like as necessary.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of a light curtain according to the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are merely examples of the present invention, and the gist of the present invention is, of course, defined only by the appended claims.
[0029]
The configuration of the light curtain 100 of the present embodiment is shown in the external view of FIG. As shown in the figure, the light curtain of the present embodiment is configured by connecting a light projector 1 and a light receiver 2 with a communication cable 101. The external setting device 3 is connected to the communication cable 101 via a connection connector 102. Although not shown, a power supply wiring box and the like are interposed between the connector 102 and the projector 1.
[0030]
The external setting device 3 has an operation unit 3a configured by a push button switch and a display unit 3b configured by a liquid crystal display. In the present embodiment, by operating the external setting device 3, it is possible to appropriately set the amount of light emitted from the light emitting device 1, the light receiving signal amplification factor (light receiving gain) in the light receiving device 2, and the detection determination threshold value. The display unit 3b displays the amount of received light and the threshold value at that time.
[0031]
FIG. 2 shows a circuit configuration of the light curtain of the present embodiment. As shown in FIG. 1, the light projector 1 generates a plurality of light emitting units 11 (111 to 11n) including a light emitting element, a current control circuit, and an optical axis selecting circuit, and generates drive signals and the like for the light emitting units 11. A communication circuit 13 for performing communication with the light receiver 2 and communication with the external setting device 3, and an I / O interface 14 for performing communication with a host device (in this example, a PLC). are doing.
[0032]
The light receiver 2 includes a photoelectric conversion unit including a light receiving element, a preamplifier for amplifying a light receiving signal from the light receiving element, and a light receiving unit 21 (211 to 21 n) including an optical axis selection circuit, a main amplifier, a filter (high-pass filter or A signal processing unit 22 including a comb filter and an A / D converter; a CPU 23 that generates a drive signal for the light receiving unit 21 and performs an operation for detection determination based on a signal from the signal processing unit 22; 1 and a communication circuit 24 for performing communication with the external setting device 3 and an I / O interface 25 for performing communication with a host device (in this example, a PLC).
[0033]
The details of the circuit configuration of the projector 1 are shown in FIG. As shown in FIG. 1, each light projecting unit 1 includes a light projecting element 111 that emits infrared light (or red light), and a driving signal (optical axis selection) from a CPU for driving the light projecting element 111. A signal (input signal) to the base terminal, a current control circuit 113 for adjusting the amount of light emitted from the light emitting element 111 based on a signal from the CPU 12, a CPU 12, and a CPU 12. , And a decoder 120 having three signal input lines and three output lines.
[0034]
As can be understood from the figure, each projector 11 is selectively driven via a transistor by an optical axis selection signal S1 from the CPU 12.
[0035]
Further, the current control circuit 113 includes three FETs (field effect transistors) connected in parallel to the transistor 112 with the main resistor 113a interposed therebetween. Reference numerals 113RA, 113RB, and 113RC are resistors having different resistance values interposed between the main resistor 113a and each FET.
[0036]
A drive signal is input from the decoder 120 to each of the FETs (113TRA, 113TRB, 113TRC). That is, four types (22) of signal inputs (S2) of two bits can be input from the CPU 12 to the decoder indicated by the reference numeral 120 in the figure. Three kinds of signal outputs (S3) for selectively driving are performed. As can be understood from this, in each of the light projectors 11, it is possible to set three types of light emission amounts (light emission current values) via the FETs (113TRA, 113TRB, 113TRC) and the resistors 113RA, 113RB, 113RC. It is possible.
[0037]
The details of the circuit configuration of the light receiver 2 are shown in FIG. As shown in the figure, each light projecting unit 2 includes a light projecting unit 21 including a photoelectric conversion unit 21a, a preamplifier 21b, and an optical axis selection circuit 21c, a main amplifier 22a for amplifying a light receiving signal from the preamplifier 21, and A filter 22b that filters the amplified light receiving signal and a CPU 23 that receives the filtered light receiving signal via the A / D converter 22c and performs a detection determination process based on the light receiving signal are mainly configured.
[0038]
The CPU 23 stores a detection determination threshold value in a predetermined memory, and performs a detection determination process by comparing the threshold value with a light receiving signal (S4) from the signal processing unit 22.
[0039]
In addition, the CPU 23 outputs a 3-bit signal (S5) for defining the light receiving signal amplification factor in the main amplifier 22a. That is, in the present embodiment, eight (23) light receiving gains can be set in the main amplifier 22 based on the 3-bit signal (S5).
[0040]
Also, the CPU 23 outputs an optical axis selection signal (S6) for selectively driving a light receiving element in the photoelectric conversion unit 21 via an optical axis selecting circuit 21c having a transistor (not shown), and the validity of the light receiving signal. And a gate control signal (S7) for instructing the opening (gate opening).
[0041]
Next, an outline of the operation contents of the light curtain of the present embodiment is shown by a general flowchart of FIG.
[0042]
As shown in the flowchart, when the power of the light curtain of the present embodiment is turned on, first, a startup process such as initialization of a memory is executed (step 501). When the start-up process ends, a detection process is then performed. This detection processing includes light emitting / receiving processing (step 502), communication between the light emitter 1, the light receiver 2, and the external setting device 3 or the light receiver 2 and another light curtain (when a light curtain is provided side by side). The communication process (step 503) for performing communication with the photodetector is repeated. In the present embodiment, through communication processing after the end of the communication processing, it is confirmed whether or not to shift to a setting mode for setting a threshold value, a projection light amount, a light receiving gain, and the like (step 504). In this example, when a predetermined setting start signal is input from the external setting device (step 504: YES), the mode shifts to the setting mode (step 505).
[0043]
The details of the light emitting / receiving process shown in step 502 are shown in the flowchart of FIG. It should be noted that the process in the light projector 1 (steps 611 to 614) and the process in the light receiver 2 are shown in parallel in FIG. In the light emitting / receiving process, the light emitting device 1 first reads light emitting current data (light emitting amount setting value) in the CPU 12 (step 611). Thus, the FET drive signal output (S3) from the decoder 120 shown in FIG. 3 is determined. On the other hand, in the light receiver 2, first, the set values of the amplifier gain and the threshold value are read in the CPU 23 (step 621). Thus, the gain specifying signal (S5) from the CPU 23 and the threshold value shown in FIG. 4 are determined.
[0044]
Next, in the light projector 1 and the light receiver 2, synchronous communication for synchronization between the light projector 1 and the light receiver 2 is performed (steps 612 and 622).
[0045]
Next, in the light projector 1, light is emitted (step 614) by sequentially and selectively driving each light emitting unit based on the previously determined light intensity (step 613). This is repeated a predetermined number of times (steps 613 to 614). On the other hand, in the light receiver 2, the light receiving process is executed by sequentially opening the gates of the respective light receiving units (sequentially taking in the light receiving signals from the respective light receiving units) based on the amplifier gain determined previously (step 623). Is performed (step 624). The light receiving signal generated by the light receiving process is A / D converted by the A / D converter 22c (step 625), and is taken into the CPU 23. The CPU 23 performs a detection determination process (determines whether or not an object has entered a predetermined area) by comparing the received light reception signal with the previously determined threshold value (step 626).
[0046]
Details of the communication processing shown in step 503 are shown in the flowchart of FIG. It should be noted that FIG. 3 shows the processing in the light projector 1 (steps 721 to 722), the processing in the light receiver 2 (steps 711 to 714), and the processing in the external setting device 3 in parallel.
[0047]
In the communication processing, first, an inter-connection inquiry is made in the light receiver 2 (step 711). This inter-connection inquiry is for confirming the state of the projector 1 itself, the state of another light curtain, and the like. When the inter-connection inquiry is performed, the projector 1 responds to the inquiry (step 721). This response notifies the light receiver 2 whether the projector 1 is operating normally or not.
[0048]
Next, a connection notification is performed. The connection notification issues a predetermined command to its own light projector 1 according to the state of another light curtain. Specifically, when it is confirmed from the previous inter-connection inquiry (step 711) that the other light curtain has stopped operating or the like (abnormal operation), the light emission from the own projector 1 is performed. A command signal for stopping is generated. This is because, in the present embodiment, when all of the series of light curtains are not normally operating, the other light curtains that are operating normally are temporarily stopped from operating.
[0049]
Next, communication between the light receiver 2 and the external setting device 3 is performed. This communication is for confirming whether or not to shift to a setting mode for setting a threshold value, a light projection amount, a light receiving gain or other parameters (step 731 and step 713). Here, when a predetermined operation for shifting to the setting mode is performed in the external setting device, a setting mode entry confirmation signal (setting start signal) is transmitted from the external setting device 3 to the light receiving device 2 (step). 714 YES), whereby the light receiver 2 shifts to the setting mode (setting processing). If the setting start signal is not transmitted (NO in step 714), the process is temporarily terminated without moving to the setting process.
[0050]
The details of the setting process are shown by the flowcharts of FIGS. FIG. 8 is a flowchart showing the processing for setting the projection light amount, FIG. 9 is a flowchart showing the processing for setting the light receiving gain, and FIG. 10 is a flowchart showing the processing for setting the threshold.
[0051]
In the light curtain of the present embodiment, as shown in FIG. 8, in the setting process, parameter setting for selecting parameters related to basic operations such as dark on / dark off (step 803) and so-called “teaching (automatic learning)” are performed. )) (Steps 804 to 1006) and manual setting (teaching of set values by operating an external setting device) (step 802).
[0052]
Here, first, the contents of the setting processing by teaching which is the main part of the invention will be described.
[0053]
In the teaching process, first, a process for setting the amount of projected light is performed. In the projection light amount setting, each of the three types of projection light amounts described above is set as a projection light amount, and light emission / reception processing (six times loop for all the optical axes for each projection light amount) is performed (step 804). The light reception amount (light reception value) obtained by the light emission / reception processing is temporarily stored in a predetermined memory of the CPU 23 corresponding to each light reception unit 21 (step 805). In the present embodiment, the projected light amount is set to the smallest one among the projected light amounts in which the light receiving amounts of the light receiving units 21 all exceed a predetermined value (step 806). Here, the smallest one is selected, for example, in order to minimize the influence on the adjacent light curtain.
[0054]
Next, a teaching process for setting the light receiving gain shown in FIG. 9 is performed. In the light receiving gain setting, each of the eight light receiving gains described above is set as the gain of the main amplifier 22a, and light emitting / receiving processing (six loops for all the optical axes for each amplification amount) is performed (step 901). ). The light reception amount (light reception value) obtained by the light emission / reception processing is temporarily stored in a predetermined memory of the CPU 23 corresponding to each light receiving unit 21 (step 902). In the present embodiment, the light receiving gain is set to the smallest of the light receiving gains obtained when the light receiving amount of the light receiving unit 21 has all exceeded the predetermined value (step 903). Here, the reason for selecting the smallest one is to minimize noise amplification.
[0055]
Next, a teaching process for setting a threshold value shown in FIG. 10 is performed. In the threshold setting, light emission / reception processing (10 loops for all optical axes) is performed based on the light emission amount and light reception gain set previously (step 1001). When the light receiving amounts of all optical axes are acquired by the light emitting and receiving processes of each time (step 1002), the minimum value of the acquired light receiving amount (light receiving value) is temporarily stored in a predetermined memory of the CPU 23 each time (step 1002). 1003).
[0056]
When the light emission / reception processing of the loop is completed ten times, the average value of the minimum light reception values stored in the memory of the CPU 23 is calculated (step 1004), and then a value of １ ／ of the average value is calculated (step 1005). ). The value of １ ／ of the calculated average value is set as a new threshold value (step 1006). Note that, here, the threshold value is set to half of the average value of the minimum received light values for each optical axis, but theoretically, the threshold value is lower than the minimum received light value, and The threshold value is not limited to the above calculation method, as long as it is equal to or more than the light receiving value at the time of light shielding and 0 or more assuming complete light shielding.
[0057]
As described above, according to the light curtain of the present embodiment, the amount of emitted light, the light receiving gain, and the threshold value are variable, so that it is possible to set an appropriate detection sensitivity according to the installation environment, and to establish a connection with other sensors. Mutual interference can be prevented beforehand.
[0058]
In the above description, the teaching of the light emission amount, the light receiving gain, and the threshold is executed mainly by the CPU 23 of the light receiver 2, but the teaching of the set values is not shown by the CPU 12 of the light emitter 1 or the external setting device 3. You may comprise so that it may perform mainly by CPU.
[0059]
Further, in the above description, the projected light amount, the light receiving gain, and the threshold value are set uniformly for all the optical axis light units, but these set values may be set for each optical axis.
[0060]
Finally, details of the manual setting process shown in step 802 of FIG. 8 will be described. In the present embodiment, in addition to teaching various set values by the above-described teaching, direct teaching of set values by operating the external setting device 3 is also possible.
[0061]
The details of the manual setting process are shown in the flowchart of FIG. In this flowchart, the processing in the light curtain 100 and the processing in the external setting device 3 are shown in parallel.
[0062]
When the user performs an operation for shifting to the setting process by pressing the operation unit 3a of the external setting device 3 or the like, the effect is transmitted from the external setting device 3 to the light curtain (the light receiving device in this example) through the communication cable 101. The second CPU 23) is notified (step 1111).
[0063]
When receiving the notification of the setting process, the CPU 23 of the light receiver 2 reads the set value already set at that time (Step 1121), and notifies the external setter 3 of the read set value (Step 1122). ). As a result, the various setting values set at that time are displayed on the display unit 3b of the external setting device 3 (steps 1112 and 1113). As a result, the CPU 23 of the light receiver 2 and the external setting device 3 enter a temporary standby state (step 1123 NO, step 1124, step 1114 NO, step 1115).
[0064]
In this state, when the user specifies various setting values (light emission amount, light receiving gain, threshold value) by operating the operation unit 3 of the external setting device 3 (step 1114 YES), the specified values are notified to the CPU 23. (Step 1116).
[0065]
The CPU 23 reads the notified designated value (step 1125), and updates and sets the value as a new set value (step 1126).
[0066]
As described above, in the present embodiment, by making a configuration in which the set value can be directly taught from the external setting device 3, fine adjustment of various set values after the teaching process can be performed.
[0067]
【The invention's effect】
As is clear from the above description, according to the light curtain of the present invention, it is possible to set an appropriate detection sensitivity in accordance with the installation environment, thereby preventing mutual interference with other sensors. Possible light curtains can be provided.
[Brief description of the drawings]
FIG. 1 is an external view of a light curtain of the present invention.
FIG. 2 is a diagram showing a circuit configuration of a light curtain of the present invention.
FIG. 3 is a diagram showing details of a circuit configuration of a light projector.
FIG. 4 is a diagram showing details of a circuit configuration of a light receiver.
FIG. 5 is a general flowchart showing an outline of operation contents of the light curtain of the present invention.
FIG. 6 is a flowchart showing details of a light emitting / receiving process.
FIG. 7 is a flowchart illustrating details of a communication process.
FIG. 8 is a flowchart showing the content of a teaching process of a projected light amount.
FIG. 9 is a flowchart illustrating the content of a teaching process of a light receiving signal amplification factor.
FIG. 10 is a flowchart showing the contents of a teaching process of a threshold value.
FIG. 11 is a flowchart illustrating details of a manual setting process.
[Explanation of symbols]
1 Emitter 2 Receiver 3 External setting device 3a Operation unit 3b Display unit 4 PLC
11 Light emitting unit 12 CPU
13 Communication circuit 14 I / O
21 light receiving section 22 signal processing section 23 CPU
24 Communication circuit 25 I / O
Reference Signs List 10 Cable 100 Light curtain 101 Communication cable 102 Communication cable connector 111 Light emitting element 112 Selection circuit 113 Current control circuit 120 Decoder

Claims (9)

A light curtain in which a light emitting sensor head in which a plurality of light emitters are arranged and a light receiving sensor head in which a plurality of light receivers are arranged are arranged to face each other,
A light curtain provided with sensitivity adjustment means for adjusting detection sensitivity. Adjustment of the detection sensitivity is performed by setting a detection judgment threshold value, and the detection judgment threshold value is automatically set based on a light receiving signal level in each light receiver obtained by light emitting and receiving sampling for a series of optical axes. The light curtain according to claim 1, wherein The light curtain according to claim 2, wherein the detection determination threshold value is set to a value equal to or lower than a lowest level among light reception signal levels acquired by light emission / light reception sampling. The adjustment of the detection sensitivity is performed by setting the amount of projected light. 2. The light curtain according to claim 1, wherein the light curtain is automatically set to any one of the plurality of light emission light levels based on a light reception signal level in each light receiver obtained by the light emission and reception sampling. 3. The light projection light amount is set to a minimum light emission light level among light emission light levels when a light reception signal level of each light receiver obtained by light emission / reception sampling exceeds a predetermined level. Light curtain. The detection sensitivity is adjusted by setting the gain of the received light signal, and the gain of the received light signal is adjusted a plurality of times for a series of optical axes, each of which is executed as the gain level of the received signal. 2. The light curtain according to claim 1, wherein the light curtain is automatically set to any one of the plurality of amplification levels based on a light reception signal level in each light receiver acquired by the light emitting / receiving sampling of (a). The light reception signal amplification factor is set to a minimum one of amplification levels when a light reception signal level of each light receiver obtained by a plurality of light emission / reception samplings exceeds a predetermined level. Item 10. A light curtain according to item 9. Means for numerically displaying the automatically set threshold value, light emission amount or light receiving signal amplification rate on a display of an external setting device electrically connected to the light emitting sensor head or the light receiving sensor head, and operating the external setting device And means for changing the automatically set threshold value, projected light amount, or received light signal amplification factor based on the teaching signal by receiving a teaching signal generated by the control unit. The light curtain according to any one of items 4 and 6. 9. The light curtain according to claim 8, further comprising means for displaying the received light amount, the threshold value, the projected light amount, or the received light signal amplification factor in real time on a display unit of the external setting device. .

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