JP2008218021A - Transparent body detecting sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transparent body detecting sensor capable of getting rid of influence of the lens effect of a transparent body, and stably detecting the transparent body when the received light quantity of a light receiving part fluctuates due to dirt on lenses provided in a light projection part, the light receiving part, and an optical path, and when it is used for a long period of time. <P>SOLUTION: This transparent body detecting sensor 10 functions as a threshold value setting means to set a second threshold value level region for a microcomputer to determine a non-detected state. When the microcomputer 16 sets the second threshold value level region, it is set so that a range of values shifted to plus and minus respectively with respect to the received light quantity level under the non-detected state in the past by a prescribed quantity (that is M %) is used as the second threshold value level region. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transparent body detection sensor having a transparent body as a detection target.

  As a transparent body detection sensor for detecting a transparent body such as a bottle or a plastic bottle, a regression reflection type transparent body detection sensor is known. The retroreflective type transparent body detection sensor reflects the light projected from the light projecting unit by the retroreflecting plate and receives the reflected light by the light receiving unit arranged on the light projecting unit side, and changes the amount of received light. The transparent body passing between the light projecting section (light receiving section) and the retroreflecting plate is detected. The recursive reflecting plate has a large number of corner cubes arranged without gaps, and the incident light is reflected parallel to the optical axis by the pitch of each corner cube and reflected to the light projecting portion side.

  Since the light receiving section detects the light that has passed through the transparent body twice in the recursive reflection plate type transparent body detection sensor by having the above-mentioned regressive reflection board, the light receiving element is disposed at the position where the recursive reflection board is disposed. Since the level of the amount of light received at the light receiving portion is attenuated, the transparent body can be detected more easily than the transparent type transparent body detection sensor.

  By the way, as in the case of bottles and plastic bottles, the transmitted light is condensed toward the light receiving part by the curved surface shape or thickness of the transparent body, and the light intensity of the transmitted light is not attenuated. In spite of the existence of non-detection, non-detection determination may be performed.

In order to solve this problem, a transparent body detection sensor has been proposed in which an optical design that limits the emission range of the light projecting element with a slit so as not to be affected by the lens effect (Patent Document 1).
JP-A-10-255612

  However, according to the optical path design of Patent Document 1, there is a problem that cannot be dealt with when the amount of light received by the light receiving unit varies due to dirt of the light projecting unit, the light receiving unit and the lens provided on the optical path due to long-term use. there were.

  The object of the present invention is to eliminate the influence of the lens effect of the transparent body, and when the amount of light received by the light receiving unit varies due to dirt on the light projecting unit, the light receiving unit and the lens provided on the optical path, or An object of the present invention is to provide a transparent body detection sensor capable of stably detecting a transparent body even after long-term use.

  In order to solve the above problem, the invention according to claim 1 is a light projecting unit, a regressive reflection plate that reflects light from the light projecting unit, and a light receiving device that receives reflected light from the regressive reflection plate. And a transparent body that passes between the light projecting means and the light receiving means and the regressive reflecting plate is detected by determining the magnitude of the first threshold level and the level corresponding to the amount of light received by the light receiving means. When the level corresponding to the amount of received light continues for a predetermined time within a range of a second threshold level region different from the first threshold level, the transparent body is not detected. A transparent body detection sensor comprising: a threshold value setting means for setting a second threshold level region for determining the non-detection state, wherein the threshold value setting means includes the second threshold level setting means. When setting the threshold level area The transparent body detection sensor is characterized in that a range of values shifted respectively by a predetermined amount plus and minus with respect to the received light amount level in the past non-detection state is set as the second threshold level region. It is what.

  According to the first aspect of the present invention, when the second threshold level region is set, the threshold value setting unit newly sets a second range of values each shifted by a predetermined amount plus and minus with respect to the received light amount level in the past non-detection state. Set as threshold level area. As a result, the second threshold level region is updated, so that even when the received light amount level, particularly the non-detected received light amount level, decreases due to long-term use, or adverse effects due to the lens effect of the transparent body are suppressed. And a stable non-detection state can be determined.

  According to a second aspect of the present invention, in the first aspect, when the second threshold level region is set, the threshold value setting unit has a value that is shifted by a predetermined amount plus and minus with respect to the received light amount level in the past non-detection state. The setting is prohibited when a predetermined first limit value on the positive side or a second limit value on the negative side is exceeded.

According to the invention of claim 2, it is possible to prevent excessive setting of the second threshold level region.
According to a third aspect of the present invention, in the first or second aspect, the predetermined amount is a fixed value.

  According to the invention of claim 3, when the threshold value setting means sets the second threshold level region, the predetermined amount which is a fixed value with respect to the light reception amount level in the past non-detection state is shifted to plus and minus respectively. When the predetermined first limit value on the plus side or the second limit value on the minus side is exceeded, the setting is prohibited. This can prevent excessive setting of the second threshold level region. According to a fourth aspect of the present invention, in any one of the first to third aspects, the threshold value setting unit performs the setting of the second threshold level region every time the transparent body non-detection state ends. It is characterized by that.

According to the fourth aspect of the invention, since the setting of the second threshold level region is performed every time, it is possible to cope with the change in the received light amount level.
According to a fifth aspect of the present invention, in any one of the first to third aspects, the threshold value setting means sets the second threshold level region according to an end count at which the transparent body non-detection state ends. This is performed every time the predetermined number of times is reached.

  According to the fifth aspect of the invention, since the setting of the second threshold level region is performed every time the end number of times the non-detection state of the transparent body ends is a predetermined number of times, it is necessary to set the second threshold level region. Compared with the case where the condition is determined and reset, only a simple process of counting the reset timing at a predetermined number of times is required, and the load on the processing circuit for the reset can be reduced. is there.

  A sixth aspect of the present invention provides the method according to any one of the first to third aspects, wherein the threshold value setting unit compares the received light amount level in the past non-detection state with a preset allowable level, The second threshold level region is set when there is a change exceeding the allowable level.

According to the sixth aspect of the present invention, the second threshold level region can be reset when it is really necessary without performing unnecessary resetting.
A seventh aspect of the present invention is the storage medium according to any one of the first to sixth aspects, wherein when the power is shut off, the latest value of the second threshold level region is stored and the power is turned on. The storage means is capable of reading out the latest stored value of the second threshold level region.

  According to the invention of claim 7, when the power is shut off, the latest value of the second threshold level region is stored in the storage means, and when the power is turned on, the stored latest second threshold value is stored. Since the value of the level region can be read, the value of the second threshold level region that is always updated when the power is turned on can be used.

  As described above in detail, according to the inventions of claims 1 to 7, the influence of the lens effect of the transparent body can be eliminated, and the light projecting means (light projecting part) or the light receiving means (light receiving part). In addition, when the amount of light received by the light receiving unit varies due to dirt on the lens provided on the optical path, or even when used for a long time, a stable transparent body can be detected.

Hereinafter, an embodiment embodying the present invention will be described with reference to FIGS.
As shown in FIG. 1, the transparent body detection sensor 10 includes a sensor body 13 including a light projecting element 11, a light receiving element 12, and the like. The light projecting element 11 is composed of, for example, an LED or a laser diode. The light receiving element 12 is composed of, for example, a photodiode or a phototransistor. The light projecting element 11 emits light when a drive current is applied from a light projecting element drive circuit (not shown). The light projecting element 11 corresponds to the light projecting means of the present invention.

  The light projected from the light projecting element 11 is made into a parallel light projecting beam by a lens (not shown), and is incident on the regressive reflection plate 14 disposed away from the light projecting element 11. A large number of corner cubes are densely arranged on the retroreflecting plate 14, and the incident light is shifted in parallel from the optical axis by the pitch of each corner cube and reflected to the light receiving element 12 side. The light receiving element 12 outputs a light reception signal at a level corresponding to the amount of received light (amount of received light). The received light signal is A / D converted by an A / D converter (not shown) and is taken into a buffer (not shown) of the microcomputer 16 as a received light amount. The light receiving element 12 corresponds to the light receiving means of the present invention.

  The microcomputer 16 includes a CPU, a ROM (not shown), an EEPROM 19 including a flash memory which is a nonvolatile memory, and a RAM (not shown), and functions as the detection means 17 and the threshold setting means 18 shown in FIG. Have. A detection program is stored in the ROM. The EEPROM 19 may be composed of other memories as long as it is a nonvolatile memory.

  And the transparent body detection sensor 10 passes the passage route through which the transparent body W as a detected body provided between the sensor main body 13 provided with the light projecting element 11 and the light receiving element 12 and the return reflection plate 14 passes, for example. Opposing to be sandwiched. Examples of the transparent body W include bottles and plastic bottles.

(Function)
Next, the operation of the transparent body detection sensor 10 of the present embodiment will be described with reference to the flowchart of FIG. This flowchart represents processing by a detection program stored in the ROM of the microcomputer 16 and is executed regularly every several msec.

  In S10, the microcomputer 16 reads the received light amount of the light receiving element 12 stored in the buffer, and in S20, compares the received light amount level with the second threshold level region. The second threshold level region has a range of an upper limit value TH2h and a lower limit value TH2l (<TH2h). This range is a value set in advance to detect the amount of light received by the light projecting element 11 in a state where the transparent body W does not pass between the sensor main body 13 and the return reflection plate 14. When this program is started for the first time, the values input by the initial setting are used as the initial values of the upper limit value TH2h and the lower limit value TH2l. In addition, the upper limit value TH2h and the lower limit value TH2l are written in the RAM when the update is performed, and stored and stored in the EEPROM when the transparent body detection sensor 10 is not used. The

Here, the microcomputer 16 corresponds to storage means for storing the updated second threshold level region (that is, the upper limit value TH2h and the lower limit value TH2l).
In S20, if the received light amount level is within the second threshold level region, the process proceeds to S30. In S30, the microcomputer 16 reads whether or not the current received light amount level (hereinafter referred to as current value Ga) is the same level as the previous received light amount level (hereinafter referred to as previous value Go), and the same level continues for a predetermined time. It is determined whether or not. That is, in S30, it is determined whether the received light amount level is stably input. Here, the predetermined time is a time for determining whether the received light amount level is stable, and this time is an interval between the transparent bodies W when a plurality of transparent bodies W are sent, or the transparent body W. Is set according to the feed rate. If the received light amount level is stable, the microcomputer 16 determines that the transparent body W does not pass through the passage between the sensor body 13 and the regressive reflection plate 14 (determines “YES”). If it is not stable, it is determined that the transparent body W is fluctuating because it is passing through the passage route (that is, “NO” is determined).

  If the microcomputer 16 determines “NO” in S30, the process of this detection program is once terminated. If “YES” is determined in S30, the microcomputer 16 resets the detection flag F in S40 (that is, “0”), and the transparent body W does not pass through the passage route, and the non-detection state is detected. And The detection flag F when the detection program is started is reset.

In S20, if the current value Ga is outside the second threshold level region, the process proceeds to S50.
In S50, the microcomputer 16 compares the current value Ga with the first threshold level TH1. When the current value Ga> the first threshold level TH1, the microcomputer 16 once ends the processing of this detection program. If the microcomputer 16 determines that the current value Ga is equal to or lower than the first threshold level TH1, the microcomputer 16 determines whether or not the detection flag F is set to 1 in S60. If the detection flag F is set to 1, the processing of this detection program is temporarily terminated.

  If it is determined in S60 that the detection flag F is not set to 1, the microcomputer 16 sets the detection flag F to 1 in S70. That is, it is assumed that the transparent body W is in a detection state by the transparent body detection sensor 10.

  In subsequent S80, the microcomputer 16 performs a setting process for the second threshold level region. Specifically, the microcomputer 16 reads the latest received light amount level G in the second threshold level region from the buffer at the past received light amount level instead of the current value Ga, and sets M as a predetermined amount to this value. Add or subtract (shift) the% value. That is, the received light amount level G ± M% is calculated, the value of G + M% is set as the upper limit value TH2h of the new second threshold level region, and the value of G−M% is set as the lower limit value TH2l of the new second threshold level region. To do. Then, the updated range of the upper limit value TH2h and the lower limit value TH2l is set as a new second threshold level region that is used at the next and subsequent detection timings. M% is a value obtained from a test value or the like, and is a fixed value.

  When the microcomputer 16 finishes the process of S80, the process of this detection program is once finished. The updated range of the upper limit value TH2h and the lower limit value TH2l (that is, the value of the new second threshold level region) is stored in the EEPROM 19.

  FIG. 2 shows the received light amount level indicating the detection state and non-detection state of the transparent body detection sensor 10 configured as described above, the first threshold level TH1, the second threshold level region (upper limit value TH2h, lower limit value TH2l), and Shows the relationship. In FIG. 2, the horizontal axis represents time t, and the vertical axis represents the received light amount level.

  As shown in FIG. 2, when the detection program is executed at the detection timing of t1, when the detection program is executed from the detection timing t1 until the previous detection timing, the processes of S10, S20, and S50 to S80 are performed. Is called. When the detection program is executed at the next detection timing t2 and the process proceeds to S60 via S10, S20, and S50, the detection flag F is set to “1” at the previous detection timing t1. In S60, “YES” is set, and the detection program is terminated.

  In FIG. 2, the detection timing tm is when the received light amount level is within the second threshold level region due to the lens effect of the transparent body W. In this case, in FIG. 2, when the detection program is executed at the detection timing tm in the detection state, when the process proceeds to S10 and S20, it is determined in S20 that the current value Ga is “in area”. The process proceeds to S30. At this time, as shown in FIG. 2, since the previous value Go is smaller than the current value Ga, it is determined that the level is not the same and “NO” is determined, and the detection program is terminated.

  Thus, even if the received light amount level is increased by the lens effect of the transparent body W and is within the second threshold level region, it is determined in S30 that the previous value Go and the current value Ga are not the same level. Even if the amount of received light increases due to the W lens effect, erroneous detection can be prevented.

  In FIG. 2, the detection timing tn is when the received light amount level exceeds the second threshold level region due to the lens effect of the transparent body W. In this case, in FIG. 2, when the detection program is executed at the detection timing tn in the detection state, when the process proceeds to S10 and S20, it is determined in S20 that the current value Ga is “out of region”. The process proceeds to S50. At this time, as shown in FIG. 2, since the current value Ga is larger than the first threshold level TH1, it is determined as “NO” and the detection program is terminated.

  Thus, even if the received light amount level exceeds the upper limit value TH2h of the second threshold level region due to the lens effect of the transparent body W, it is determined in S30 that the previous value Go and the current value Ga are not the same level. Even if the amount of received light increases due to the W lens effect, erroneous detection can be prevented.

  In FIG. 2, the detection timing to is when the transparent body W passes and the received light amount level is in the second threshold level region. In this case, as shown in FIG. 2, at the detection timing to, the process proceeds to S10 and S20. In S20, it is determined that the current value Ga is “inside the region”, and when the process further proceeds to S30, the current value Ga is If it is the same level as the previous value Go and it is determined “YES”, the process proceeds to S40, the detection flag F is reset to 0, and the detection program is terminated.

  When the power is cut off, the transparent body detection sensor 10 stores the latest updated upper limit value TH2h and lower limit value TH2l in the EEPROM 19 as a storage means (that is, a new second threshold level region). Value) is stored and held. Thereafter, when the power of the transparent body detection sensor 10 is turned on, when the transparent body W detection program is executed, the latest updated upper limit TH2h and lower limit stored in the EEPROM 19 are stored. A range of values TH2l (ie, a new second threshold level region value) is used.

(Operation of the first embodiment)
Now, according to the first embodiment, there are the following features.
(1) The transparent body detection sensor 10 of this embodiment functions as a threshold setting unit that sets a second threshold level region for the microcomputer 16 to determine the non-detection state. When the microcomputer 16 sets the second threshold level region, a range of values obtained by shifting (adding or subtracting) a predetermined amount (that is, M%) plus and minus each with respect to the received light amount level in the past non-detection state. The second threshold level region is set.

  Accordingly, since the second threshold level region is updated, even when the received light amount level, particularly, the undetected received light amount level is lowered by long-term use, or there is an adverse effect due to the lens effect of the transparent body W. It can suppress and can determine the stable non-detection state.

  (2) In the transparent body detection sensor 10 of the present embodiment, the microcomputer 16 sets the second threshold level region as the threshold setting means every time the non-detected state of the transparent body W ends. As a result, according to the invention of claim 4, since the setting of the second threshold level region is performed every time, it is possible to cope with the change in the received light amount level.

  (3) In the transparent body detection sensor 10 of the present embodiment, when the power is shut off, the latest value of the second threshold level region is stored in the EEPROM 19 as the storage means, and when the power is turned on, Since the stored value of the latest second threshold level region can be read, the updated value of the second threshold level region can be used whenever the power is turned on.

(Second Embodiment)
Next, the transparent body detection sensor 10 of 2nd Embodiment is demonstrated with reference to the flowchart of FIG. Since the hardware configuration is the same as that of the first embodiment, the same components are denoted by the same reference numerals, detailed description thereof is omitted, and different software differences will be mainly described.

The second embodiment is different from the steps of the flowchart of FIG. 3 in that S72, S74, and S76 are provided between S70 and S80 as shown in FIG.
That is, when the process of S70 is completed and the process proceeds to S72, the microcomputer 16 increments the counter C by one. Note that the initial value of the counter C when the detection program is started is 0.

  In next S74, the microcomputer 16 determines whether or not the value of the counter C has reached R times. The R times correspond to a predetermined number of times and are set in advance to an arbitrary number of times. If the value of the counter C has not reached R times in S74, the microcomputer 16 ends this detection program. If the value of the counter C has reached R times, the microcomputer 16 resets the counter C to 0 in S76 and performs the process of S80.

Now, according to the second embodiment, there are the following features.
(1) In the transparent body detection sensor 10 of the second embodiment, the microcomputer 16 sets the second threshold level region every predetermined number of times (that is, R times) when the non-detection state of the transparent body W ends. I have to. As a result, in the second embodiment, since the second threshold level region is reset every predetermined number of times (that is, R times) when the non-detection state of the transparent body W is completed, the reset process is less and the resetting is performed. This has the effect of reducing the load on the processing circuit. Furthermore, the transparent body detection sensor 10 of the second embodiment can be suitable for high-speed response.

(Third embodiment)
Next, a third embodiment will be described with reference to the flowchart of FIG. Since the hardware configuration is the same as that of the first embodiment, the same components are denoted by the same reference numerals, detailed description thereof is omitted, and different software differences will be mainly described.

The third embodiment is different from the flowchart of FIG. 3 in that S78 is provided between S70 and S80 as shown in FIG.
That is, when the processing of S70 is completed and the routine proceeds to S78, the microcomputer 16 determines whether or not the received light amount level in the past latest non-detection state is within a preset allowable level range.

  This allowable level range is a value obtained from a test value or the like. If the microcomputer 16 determines that the received light amount level in the latest latest non-detection state is not within the allowable level range (that is, has changed beyond the allowable level range), the microcomputer 16 performs the process of S80. .

Now, according to the third embodiment, there are the following features.
(3) In the transparent body detection sensor 10 of the third embodiment, the microcomputer 16 serves as a threshold value setting means for comparing the received light amount level in the past non-detection state with a preset allowable level. When there is a change exceeding, the second threshold level region is set. As a result, unlike the first embodiment, the third embodiment is not performed every time the non-detected state of the transparent body W is completed, and thus the received light amount level is attenuated and resetting is performed without wasteful resetting. The second threshold level region can be reset when necessary.

In addition, you may change embodiment of this invention as follows.
In each of the above embodiments, the processes of S90 and S100 may be added after the process of S70 as shown in FIG. That is, in S90, the microcomputer 16 determines whether the upper limit value TH2h of the second threshold level region exceeds the first limit value or whether the lower limit value TH2l exceeds the second limit value.

  Here, the first limit value is Q1% (for example, 50%) of the initial value of the upper limit value TH2h of the second threshold level region, and the second limit value is the initial value of the lower limit value TH2l of the second threshold level region. Q2% (for example, 50%). In addition, Q1 shall set Q2 beforehand by a test value etc., and both may be the same value or a different value.

  In S90, the microcomputer 16 detects this detection program when the upper limit value TH2h of the second threshold level region does not exceed the first limit value and the lower limit value TH2l does not exceed the second limit value. Is temporarily terminated.

  In S90, it is determined that the upper limit value TH2h of the second threshold level region exceeds the first limit value or that the lower limit value TH2l exceeds the second limit value. In this case, the microcomputer 16 performs a prohibition process for setting the second threshold level region, that is, an error process, and ends the detection program. In this case, the microcomputer 16 notifies the worker by issuing a warning by a warning means such as a warning lamp or a warning buzzer based on the error processing.

  A forecast warning level value is provided before the upper limit value TH2h reaches the first limit value. When the upper limit value TH2h exceeds the forecast warning level value, a warning lamp for error prediction or The operator may be notified by issuing a warning by a warning means such as a warning buzzer. After that, when the upper limit value TH2h exceeds the first limit value, the second threshold level region setting prohibition process, that is, the error process may be performed.

Similarly, a forecast warning level value is provided before the lower limit value TH2l reaches the second limit value. When the lower limit value TH2l exceeds the forecast warning level value, a warning for error prediction is provided. The operator may be notified by issuing a warning by a warning means such as a lamp or a warning buzzer. After that, when the lower limit value TH2l exceeds the second limit value, the second threshold level region setting prohibition process, that is, the error process may be performed. Note that the error processing in these cases simply notifies that there was an error in the transparent body detection sensor 10. TH
In this way, since the warning is issued in advance by a warning lamp for error prediction or warning means such as a warning buzzer, the transparent body detection sensor 10 can be maintained or replaced before an error occurs. .

  In each of the above embodiments, in S30, whether or not the current value Ga is the same level as the previous value Go is determined based on whether or not the previous value Go and the current value Ga are the same. If it is within the range of the value obtained by adding and subtracting ± α to Go, the same level may be determined. Note that the value of α is set as appropriate within the allowable range that may be determined to be stable. In this way, when the transparent body W is not passing, even if the received light amount level fluctuates for some reason, it can be determined that it is stable.

  In each of the embodiments, in the “second threshold level area setting process” in S80, the microcomputer 16 does not have the current value Ga, but the “latest received light level” in the second threshold level area. Is read from the buffer, and the value of M% is added to or subtracted from this value.

  The past received light amount level is not limited to “latest”, and may be, for example, a “predetermined” received light amount level or “an average value of predetermined received light amount levels”. May be.

  In the first embodiment, a range of values shifted respectively by a predetermined amount (that is, M%) plus and minus with respect to the received light amount level in the past non-detection state is set as the second threshold level region. I did it. In this case, the amounts shifted positively and negatively are the same, but they are not necessarily the same, and the predetermined amounts shifted positively and negatively may be different from each other.

The schematic block diagram of the transparent body detection sensor 10 of 1st Embodiment which actualized this invention. Explanatory drawing which similarly shows the setting timing of the 2nd threshold level area | region of the transparent body detection sensor 10. FIG. The flowchart of a detection program similarly. The flowchart of the detection program of 2nd Embodiment. The flowchart of the detection program of 3rd Embodiment. The principal part flowchart of the detection program of other embodiment.

Explanation of symbols

G: received light level, W: transparent body, TH1: first threshold level,
10 ... transparent detection sensor, 11 ... light projecting element (light projecting means),
12 ... light receiving element (light receiving means), 13 ... sensor body, 14 ... regression reflector,
16 ... Microcomputer, 17 ... Detection means, 18 ... Threshold setting means,
19: EEPROM (storage means).

Claims (7)

Floodlight means;
A return reflector that reflects light from the light projecting means;
A light receiving means for receiving reflected light from the regressive reflection plate;
By determining the level between the level corresponding to the amount of light received by the light receiving means and the first threshold level, the transparent body passing between the light projecting means and the light receiving means and the regressive reflection plate is in a detection state. When the level according to the amount of received light continues for a predetermined time within a range of a second threshold level region different from the first threshold level, the transparent body is not detected and is in a non-detection state. In a transparent body detection sensor comprising a detection means for determining,
Threshold setting means for setting a second threshold level region for determining the non-detection state,
The threshold setting means is
In setting the second threshold level region, a range of values each shifted by a predetermined amount plus and minus with respect to the received light amount level in the past non-detection state is set as the second threshold level region. A transparent body detection sensor. The threshold setting means includes
When setting the second threshold level region, a value shifted by a predetermined amount plus and minus with respect to the received light amount level in the past non-detection state is a predetermined positive first limit value or minus side first value, respectively. 2. The transparent body detection sensor according to claim 1, wherein setting is prohibited when a limit value of 2 is exceeded.   The transparent body detection sensor according to claim 1, wherein the predetermined amount is a fixed value. The threshold setting means includes
4. The transparent body detection sensor according to claim 1, wherein the setting of the second threshold level region is performed every time the non-detection state of the transparent body is finished. 5. The threshold setting means includes
4. The method according to claim 1, wherein the second threshold level region is set every time the end number of times that the non-detection state of the transparent body ends is a predetermined number of times. 5. Transparent body detection sensor. The threshold setting means includes
The second threshold level region is set when the received light amount level in the past non-detection state changes compared with a preset allowable level range exceeding the allowable level. The transparent body detection sensor according to any one of claims 1 to 3.   The storage means stores the latest value of the second threshold level area when the power is cut off and can read out the stored value of the latest second threshold level area when the power is turned on. The transparent body detection sensor according to claim 1, wherein the transparent body detection sensor is a transparent body detection sensor.

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