JP4908975B2 - Displacement sensor and photoelectric sensor - Google Patents

Description

  The present invention relates to a displacement sensor and a photoelectric sensor that detect an object to be detected without contact.

  In the photoelectric sensor, a light projecting element for projecting light toward the object to be detected, an image sensor for receiving reflected light reflected by the object to be detected, and a light receiving amount of the image sensor are periodically detected. There is a displacement sensor provided with a control circuit for detecting the position (distance) of the detected object based on the detection of the peak position corresponding to the reflected light from the detected object in the received light distribution obtained on the image sensor.

By the way, since the intensity of the reflected light incident on the image sensor differs depending on the reflectance of the reflecting surface of the object to be detected, for example, the displacement sensor shown in Patent Document 1 has a certain level of light reception by the image sensor. A duty cycle control circuit for controlling the light projection time is provided. The duty cycle control circuit projects the light projection time of the light projecting element in the next detection period so that the peak position corresponding to the reflected light from the detected object can be accurately detected based on the amount of light received by the image sensor in the detection period. Set.
JP-A-10-267648

  By the way, the amount of light received by the light receiving element in the detection period is determined by the light projecting time of the light projecting element and the light projecting intensity (light projecting amount per unit time, illuminance). Therefore, a light receiving element for adjusting the amount of light received by setting the light projecting time is provided with a monitor light receiving element that directly receives irradiation light, and the light receiving intensity of the light projecting element is detected by the monitor light receiving element. It has become. However, if the light projecting time of the light projecting element in the detection period is shortened, before the light projecting intensity of the light projecting element reaches the threshold that can be detected by the light receiving element for monitoring (light projecting intensity detectable by the light receiving element for monitoring). Therefore, the light projection intensity of the light projecting element cannot be detected. That is, in order to appropriately control the amount of light received by the light receiving element, the light projecting element is projected for the time required until the light projecting intensity of the light projecting element becomes equal to or greater than the threshold that can be detected by the monitor light receiving element. It is necessary to let Therefore, the lower limit value of the light projection time in the detection period is limited by the rise time of the light projecting element and the threshold value of the light receiving element for monitoring, which hinders speeding up of the detection process.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a displacement sensor and a photoelectric sensor that control the light projecting time of the light projecting means to make the amount of light received by the light receiving means in the detection period constant. The present invention provides a displacement sensor and a photoelectric sensor capable of setting the light projection time in the detection period as short as possible.

In order to solve the above-mentioned problem, the invention described in claim 1 includes a light projecting means for projecting light toward the object to be detected and a plurality of pixels, and reflected light reflected by the object to be detected. An image sensor that receives light to obtain a light reception distribution from each light reception amount of the plurality of pixels, a detection unit that detects a displacement of the detection object based on the light reception distribution in the image sensor, and the detection unit A detection period setting unit that switches between a detection period that enables detection of an object to be detected and a non-detection period that disables the detection, and a monitor that is arranged so as to be able to directly receive irradiation light from the light projecting unit Light receiving means, light projection intensity setting means for setting the light projection intensity of the light projecting means to a predetermined intensity based on the light received by the monitor light receiving means, and the detected light received by the image sensor The light projection time of the light projection means In the displacement sensor comprising Gosuru a light projection time control means, said light projection time control means, even during the non-detection period in the detecting means is projecting said light projecting means, the projection light intensity setting means The light projection intensity of the light projecting means is set to a predetermined intensity based on the amount of light received by the light receiving means for monitoring by light projection in the non-detection period and the detection period by the light projecting means .

  According to this configuration, since the light projecting time control means projects the light projecting means during the non-detection period, the amount of light received by the monitor light receiving means is ensured regardless of the light projecting time of the light projecting means during the detection period. can do. Therefore, it is possible to set the light projection time of the light projection means in the detection period as short as possible without being limited by the rise time of the light projection means or the threshold value of the monitor light reception means, which contributes to speeding up the detection process. Can do.

  According to a second aspect of the present invention, in the displacement sensor according to the first aspect, the light projecting time control unit includes a light projecting time of the light projecting unit in the non-detection period. The light projecting means is projected so as to be continuous with the light projecting time.

  According to the same configuration, the light projecting time control unit lights the projecting unit so that the projecting time of the projecting unit in the non-detection period is continuous with the projecting time of the projecting unit in the detection period. In addition, it is possible to reduce unnecessary consumption of the light projecting means due to repeated turning off and lighting. Further, compared with the case where the light projection time of the light projecting means in the non-detection period is not made to be continuous with the light projection time of the light projecting means in the detection period, the light projection time of the light projecting means in the detection period is equal to that in the non-detection period. It is possible to shorten the light projecting time of the light projecting means. Therefore, this also makes it possible to reduce wasteful consumption of the light projecting means.

  According to a third aspect of the present invention, in the displacement sensor according to the second aspect of the invention, the light projection time control means is configured such that the light projection time of the light projection means in the non-detection period is the light projection time in the detection period. The light projecting means is caused to project before the light projecting time.

  According to the same configuration, the light projecting time control unit projects the light projecting unit so that the light projecting time of the light projecting unit in the non-detection period is before the light projecting time of the light projecting unit in the detection period. The projection of the light projecting means at the initial stage of unstable light projection is difficult to be received by the image sensor. Therefore, it is possible to stabilize the detected light reception amount received by the image sensor per unit time during the detection period, and the change in the light projection time of the light projecting means during the detection period is the change in the detected light reception amount of the image sensor during the detection period. Can be suitably reflected.

According to a fourth aspect of the present invention, in the displacement sensor according to any one of the first to third aspects, the light receiving means for monitoring is constituted by a photodiode.
According to this configuration, the monitor light-receiving means is composed of an inexpensive photodiode, so that an increase in manufacturing cost can be suppressed.

According to a fifth aspect of the present invention, there is provided a light projecting means for projecting light toward the object to be detected, a light receiving means for detection for receiving reflected light reflected by the object to be detected, and a light receiving means for detection. Detecting means for detecting the detected object based on the detected amount of received light, a detection period for enabling the detecting means to detect the detected object, and a non-detecting period for disabling the detection Detection period setting means for switching to, light receiving means for monitoring arranged so as to be able to directly receive the irradiation light from the light projecting means, and the light projection intensity of the light projecting means based on the light received by the light receiving means for monitoring In a photoelectric sensor comprising: a light projection intensity setting means for setting to a predetermined intensity; and a light projection time control means for controlling a light projection time of the light projection means in accordance with a detected light reception amount received by the light receiving means for detection. the light projection time control means is, said detection means That the even during the non-detection period is projected the light projecting means, the projection light intensity setting means, by projecting light in the said detection period and the non-detection period by the light projecting means, in the monitoring light-receiving means Based on the amount of received light, the light projection intensity of the light projecting means is set to a predetermined intensity .

  According to this configuration, since the light projecting time control means projects the light projecting means during the non-detection period, the amount of light received by the monitor light receiving means is ensured regardless of the light projecting time of the light projecting means during the detection period. can do. Therefore, it is possible to set the light projection time of the light projection means in the detection period as short as possible without being limited by the rise time of the light projection means or the threshold value of the monitor light reception means, which contributes to speeding up the detection process. Can do.

  According to the present invention, in the displacement sensor and the photoelectric sensor that control the light projecting time of the light projecting unit to make the amount of light received by the light receiving device in the detection period constant, the light projecting time in the detection period is set as short as possible. It is possible to provide a displacement sensor and a photoelectric sensor.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
FIG. 1 shows a displacement sensor (photoelectric sensor) 1 of the present embodiment. The displacement sensor 1 includes a light projecting element driving circuit (light projecting means) 3 having a light projecting element 2 made of a red semiconductor laser diode or the like, and a light receiving element having a light receiving element 4 made of a CCD image sensor, a CMOS image sensor or the like. A drive circuit (detection light receiving means) 5 and a detection circuit (monitor light reception means) 7 including a monitor light receiving element 6 made of a photodiode or the like are provided. The displacement sensor 1 also includes a control circuit 8 that outputs various control signals and controls the circuits 3, 5, and 7 as detection means, detection period setting means, light projection intensity setting means, and light projection time control means. ing.

  As shown in FIG. 2, the light projecting element drive circuit 3 supplies a drive current to the light projecting element 2 based on the H level drive pulses S01 to S03 from the control circuit 8, and supplies the light projecting element 2 with a predetermined time ( The light projecting time for detection t01 to t03), the object W is irradiated (projected) with light. The light receiving element 4 receives the light irradiated from the light projecting element 2 toward the detection target W and reflected by the detection target W. The light receiving element driving circuit 5 receives the light received by each pixel of the light receiving element 4 for a predetermined time (detection period) based on the light receiving control signal output from the control circuit 8 simultaneously with the driving pulses S01 to S03. The charge corresponding to is accumulated, and the detected amount of received light (incident) received by the light receiving element 4 during that period (detection period) is detected. Then, the light receiving element driving circuit 5 prohibits the accumulation of electric signals in each pixel of the light receiving element 4 for a time (non-detection period) required to output the electric signals accumulated in all the pixels of the light receiving element 4, During this period (non-detection period), the amount of light received (incident) by the light receiving element 4 is not detected. The light receiving element driving circuit 5 amplifies the electrical signal accumulated in each pixel of the light receiving element 4 and outputs the amplified signal to the control circuit 8.

  In addition, a monitor light receiving element 6 is disposed in the vicinity of the light projecting element 2 so as to be able to directly receive the irradiation light from the light projecting element 2. The monitor light receiving element 6 outputs an analog light reception signal S11 corresponding to the light projection intensity (light projection amount per unit time, illuminance) of the light projecting element 2 to the detection circuit 7. The detection circuit 7 outputs an H level monitoring light reception signal S21 while the analog light reception signal S11, that is, the light projection intensity of the light projecting element 2 is equal to or higher than a predetermined threshold value TH. The detection circuit 7 also outputs a signal corresponding to the light projection intensity of the light projecting element 2 together with the monitor light reception signal S21 of H level.

  The control circuit 8 detects the detected amount of received light received by the light receiving element 4 based on the electrical signal output from the light receiving element driving circuit 5 and acquires the light reception distribution on the light receiving element 4. When the amount of light received by each pixel of the light receiving element 4 is within a range that can be accumulated by each pixel of the light receiving element 4, a light reception peak occurs in the light reception distribution at a position corresponding to the reflected light from the detection object W. Then, the control circuit 8 detects (measures) the position of the detected object W based on the position of the received light peak. The control circuit 8 outputs the drive pulses S01 to S03 and the light reception control signal at a predetermined cycle (measurement cycles T1 to T3), and repeats the detection of the position of the detection target W.

  In addition, the control circuit 8 projects the light intensity of the light projecting element 2 so that the detected light reception amount becomes a predetermined level that is not saturated, that is, the light projecting intensity and the light projecting time of the light projecting element 2 in the detection period (detection light projecting time t01). To t03).

  More specifically, based on the H level monitoring light reception signal S21 output from the detection circuit 7, the control circuit 8 makes the light projection intensity of the light projecting element 2 constant at a predetermined intensity in the detection period of the current measurement cycle T1. The value (magnitude) of the drive current supplied to the light projecting element 2 is set so that In addition, the control circuit 8 acquires the amount of light received by the light receiving element 4 (detected amount of received light) in the detection period of the current measurement cycle T1. At this time, if the amount of light received by the light receiving element 4 (detected amount of received light) in the detection period of the current measurement cycle T1 is larger than the optimum value, the control circuit 8 projects the light for detection in the detection period of the current measurement cycle T1. A detection light projection time t02 shorter than the time t01 is set. Then, at the start of the next measurement cycle T2, the detection light projection time t02 and the drive pulse S02 for projecting the light projecting element 2 are output at the set drive current value (predetermined light projection intensity). Incidentally, when the received light amount (detected received light amount) of the light receiving element 4 in the detection period of the current measurement cycle T1 is smaller than the optimum value, the control circuit 8 detects the light projection time for detection in the detection period of the current measurement cycle T1. A light projection time t02 for detection longer than t01 is set. Then, at the start of the next measurement cycle T2, the detection light projection time t02 and the drive pulse S02 for projecting the light projecting element 2 are output at the set drive current value (predetermined light projection intensity) ( (Not shown). That is, the control circuit 8 changes the light projecting time (detection light projecting times t01 to t03) of the light projecting element 2 in the detection period so that the detected light reception amount of the light receiving element 4 becomes a predetermined level that is not saturated.

  In the present embodiment, the light projecting element drive circuit 3 supplies a drive current to the light projecting element 2 based on the monitor drive pulse S31 from the control circuit 8, and the light projecting element 2 is supplied during the non-detection period. Light up. At that time, as shown in FIG. 2, the control circuit 8 detects the light projection time t02 of the light projecting element 2 in the detection period when the light projection time of the light projecting element 2 in the non-detection period (monitoring light projection time t21). The monitor drive pulse S31 is output so as to be continuous with the signal. Further, the control circuit 8 projects the light so that the light projecting time of the light projecting element 2 in the non-detection period (monitoring light projecting time t21) is before the light projecting time t02 for detecting the light projecting element 2 in the detection period. The monitor drive pulse S31 is output from the element 2 before the start time of the detection period of the next measurement cycle T2, that is, during the non-detection period of the current measurement cycle T1. The monitor light projecting time t21 is a rise time t11 required from when the light projecting element 2 starts to project until the monitor light receiving amount of the monitor light receiving element 6 becomes equal to or greater than the predetermined threshold value TH in the detection circuit 7. Is set longer than. This is to solve the problem that has occurred in the conventional displacement sensor.

  That is, in the conventional displacement sensor, as shown in FIG. 4, for detecting the light projecting element 2 in the detection period of the next measurement period T2 in accordance with the detected amount of light received by the light receiving element 4 in the detection period of the previous measurement period T1. When the light projection time t02 is set shorter than the rise time t11, the analog light reception signal S41 output from the monitor light receiving element 6 rises slowly, and thus the H level monitor light reception signal S51 is not output. Therefore, based on the light projection intensity (illuminance) of the light projecting element 2 in the detection period of the current measurement period T1, the value of the drive current supplied to the light projecting element 2 in the detection period of the next measurement period T2 is set to a predetermined light project. It becomes impossible to set the light intensity so that the amount of light received by the light receiving element 4 cannot be appropriately controlled.

  On the other hand, according to the displacement sensor 1 of the present embodiment, as described above, the light projecting element drive circuit 3 is based on the monitor drive pulse S31 from the control circuit 8 during the non-detection period. Light up. For this reason, the detection light projection time t02 of the light projecting element 2 in the detection period of the next measurement period T2 set based on the light reception amount (detected light reception amount) of the light receiving element 4 in the detection period of the previous measurement period T1 rises. Even if it is set shorter than the time t11, the amount of light received by the monitor light receiving element 6 is secured. Therefore, the monitoring light reception signal S21 of H level is output during the next measurement cycle T2, and the control circuit 8 outputs the light projection intensity of the light projecting element 2 and the amount of light received by the light receiving element 4 (in the detection period of the measurement cycle T2). Detection light amount), and further, the value of the drive current supplied to the light projecting element 2 and the drive current supply time (light projection time (detection light projection time t03)) in the detection period of the next measurement cycle T3. Further, at the start time of the next measurement cycle T3, the control circuit 8 uses the newly set drive current value for the detection light projecting time t03 and the drive pulse for projecting the light projecting element 2. In other words, S03 is output, that is, the optimal light projection intensity of the light projecting element 2 and the light projecting time t03 for detection are set according to the detected amount of light received by the light receiving element 4. The light is projected during the non-detection period. Detected light is not received by the light receiving element 4 It will not span affect the amount of light received by the light receiving element 4 between.

  At that time, the control circuit 8 monitors so that the light projecting time of the light projecting element 2 in the non-detection period (monitoring light receiving time t21) is continuous with the light projecting time t02 for detecting the light projecting element 2 in the detection period. Drive pulse S31 is output. Therefore, the light is continuously projected from the light projecting element 2 for the total time of the light projection times (the detection light projection time t02 and the monitor light projection time t21) in the detection period and the non-detection period.

  Further, the control circuit 8 projects the light projecting element so that the light projecting time (monitoring light receiving time t21) of the light projecting element 2 in the non-detection period is before the light projecting time t02 for detecting the light projecting element 2 in the detection period. 2 is output before the start time of the next measurement period T2 (detection period), that is, during the non-detection period of the current measurement period T1. Therefore, the light projection amount of the light projecting element 2 increases to a level that is sufficiently stable in the non-detection period of the current measurement cycle T1, and the light projection element in the initial stage of light projection that is relatively unstable in the detection period of the next measurement cycle T2. 2 is less likely to be received by the light receiving element 4.

Next, the operational effects of the above embodiment will be described below.
(1) Since the control circuit 8 projects the light projecting element 2 during the non-detection period, the control circuit 8 is used for monitoring regardless of the light projecting time of the light projecting element 2 during the detection period (detection light projecting times t01 to t03). The amount of light received by the light receiving element 6 can be ensured. Therefore, the light projecting time of the light projecting element 2 (detection light projecting time t01 to t03) in the detection period is set as short as possible without being limited by the rise time of the light projecting element 2 or the threshold value of the monitor light receiving element 6. Can contribute to speeding up the detection process. Further, since the light projecting time (detection light projecting time t01 to t03) of the light projecting element 2 in the detection period can be set shorter, for example, the detected object W is arranged closer and the amount of light incident on the light receiving element As the incident light amount increases, the light projection amount of the light projecting element 2 can be reduced as the incident light amount increases, and the detection target W arranged at a closer position can be detected.

  (2) In the control circuit 8, the light projecting time of the light projecting element 2 in the non-detection period (monitoring light projecting time t21) is continuous with the light projecting time of the light projecting element 2 in the detection period (detecting light projecting time t02). Thus, since the light projecting element 2 is projected, wasteful consumption of the light projecting element 2 due to repeated lighting and extinction can be reduced. In this embodiment, the monitor light projection time t21 is set longer than the rise time t11. However, since the monitor light projection time t21 is continuous with the detection light projection times t01 to t03, The monitor light projection time t21 may be set so that the light projection time obtained by combining the light projection time t21 and the detection light projection times t01 to t03 is longer than the rise time t11. That is, as compared with the case where the monitoring light projecting time t21 is not continued from the detection light projecting time t01 to t03, the light projecting time of the light projecting element 2 (detection light projecting time t01 to t03) in the detection period, It is possible to shorten the light projecting time (monitoring light projecting time t21) of the light projecting element 2 in the non-detection period. Therefore, this also makes it possible to reduce wasteful consumption of the light projecting element 2.

  (3) In the control circuit 8, the light projecting time of the light projecting element 2 in the non-detection period (monitoring light projecting time t21) is before the light projecting time of the light projecting element 2 in the detection period (light projecting time t02 for detection). Since the light projecting element 2 is projected so that the light projecting element 2 is relatively unstable, it is difficult for the light receiving element 4 to receive the light from the light projecting element 2 at the initial stage of light projection. Therefore, it is possible to stabilize the amount of detected light received by the light receiving element 4 per unit time during the detection period, and to detect the change in the light projecting time (detection light projecting time t01 to t03). It is possible to favorably reflect the change in. In the present embodiment, since the monitor light projection time t21 is set longer than the rise time t11, the light projection amount (illuminance) of the light projecting element 2 in the detection period of the next measurement cycle T2 is more stable. To do.

(4) Since the monitor light receiving element 6 is composed of an inexpensive photodiode, an increase in manufacturing cost can be suppressed.
In addition, you may change embodiment of this invention as follows.

  In the above embodiment, the control circuit 8 uses the light projection time of the light projecting element 2 in the non-detection period (monitor light projection time t21) as the light projection time of the light projecting element 2 in the detection period of the next measurement cycle T2. It is assumed that the monitor drive pulse S31 is output continuously at (detection light projection time t02). However, as shown in FIG. 3, for example, the control circuit 8 uses the light projecting time of the light projecting element 2 in the non-detection period (monitoring light projecting time t21) of the light projecting element 2 in the detection period of the next measurement cycle T2. The monitor drive pulse S61 that is not continued to the projection time (detection projection time t02) may be output.

  In the above embodiment, the displacement sensor 1 (photoelectric sensor) for detecting the position of the detection object W is shown. However, for example, the detection object W is detected by using a light receiving element (detection light receiving means) made of a photodiode. You may apply to the photoelectric sensor etc. which detect the presence or absence.

  In the above embodiment, the control circuit 8 sets the drive current value so that the light projecting intensity of the light projecting element 2 is constant at a predetermined intensity, and the detected light reception amount of the light receiving element 4 becomes a predetermined level that does not saturate. As described above, the detection light projection times t01 to t03 of the light projecting element 2 are changed. However, the control circuit 8 is configured to change the light projection intensity of the light projecting element 2 and the light projecting times t01 to t03 for detection of the light projecting element 2 so that the detected light reception amount of the light receiving element 4 becomes a predetermined level that is not saturated. Also good. In the above embodiment, the value of the drive current supplied to the light projecting element 2 by the control circuit 8 is set. However, an APC (Automatic Power Control) circuit is provided as the light intensity setting means, and the control circuit 8 May be configured to set only the drive current supply time (detection light projection times t01 to t03).

  In the above embodiment, the photodiode is used as the monitor light receiving element 6, but other elements such as a phototransistor may be used.

The block diagram which shows schematic structure of the displacement sensor of this Embodiment. 4 is a timing chart showing the output timing of the monitor light reception signal according to the present embodiment. The timing chart which shows the output timing of the light reception signal for a monitor of another example. The timing chart which shows the output timing of the conventional light reception signal for a monitor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Displacement sensor (photoelectric sensor), 2 ... Light projection element which comprises light projection means, 3 ... Light projection element drive circuit which comprises light projection means, 4 ... Light reception element which comprises light reception means for detection, 5 ... Detection Light receiving element drive circuit constituting light receiving means for monitoring, 6... Light receiving element for monitoring constituting light receiving means for monitoring, 7... Detection circuit as light receiving means for monitoring, 8. Control circuit as means and light projection time control means, W ... detected object, t01 to t03 ... detection light projection time, t21 ... monitor light projection time.

Claims (5)

A light projecting means for projecting light toward the object to be detected;
An image sensor comprising a plurality of pixels, receiving reflected light reflected by the object to be detected, and obtaining a light reception distribution from each light reception amount of the plurality of pixels;
Detecting means for detecting a displacement of the detected object based on the received light distribution in the image sensor;
A detection period setting unit that switches between a detection period that enables detection of the detection object by the detection unit and a non-detection period that disables the detection;
A light receiving means for monitoring disposed so as to be able to directly receive the irradiation light from the light projecting means;
Projection intensity setting means for setting the projection intensity of the projection means to a predetermined intensity based on light received by the monitor light receiving means;
In a displacement sensor comprising: a light projecting time control unit that controls a light projecting time of the light projecting unit according to a detected light reception amount received by the image sensor;
The light projection time control means, said even during the non-detection period is projected the light projecting means in the detecting means,
The light projecting intensity setting means determines the light projecting intensity of the light projecting means based on the amount of light received by the light receiving means for monitoring by light projection in the non-detection period and the detection period by the light projecting means. A displacement sensor characterized by being set to a predetermined strength . The displacement sensor according to claim 1,
The light projecting time control means causes the light projecting means to project so that the light projecting time of the light projecting means in the non-detection period is continuous with the light projecting time of the light projecting means in the detection period. Displacement sensor. The displacement sensor according to claim 2, wherein
The light projection time control unit causes the light projection unit to project light so that the light projection time of the light projection unit in the non-detection period is before the light projection time of the light projection unit in the detection period. Displacement sensor. The displacement sensor according to any one of claims 1 to 3,
A displacement sensor according to claim 1, wherein the light receiving means for monitoring comprises a photodiode. A light projecting means for projecting light toward the object to be detected;
A light receiving means for detection that receives reflected light reflected by the object to be detected;
Detecting means for detecting the object to be detected based on the amount of received light detected by the light receiving means for detection;
A detection period setting unit that switches between a detection period that enables detection of the detection object by the detection unit and a non-detection period that disables the detection;
A light receiving means for monitoring disposed so as to be able to directly receive the irradiation light from the light projecting means;
Projection intensity setting means for setting the projection intensity of the projection means to a predetermined intensity based on light received by the monitor light receiving means;
In a photoelectric sensor comprising: a light projecting time control unit that controls a light projecting time of the light projecting unit according to a detected light reception amount received by the light receiving unit for detection;
The light projection time control means, said even during the non-detection period is projected the light projecting means in the detecting means,
The light projecting intensity setting means determines the light projecting intensity of the light projecting means based on the amount of light received by the light receiving means for monitoring by light projection in the non-detection period and the detection period by the light projecting means. A photoelectric sensor characterized by being set to a predetermined intensity .

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