JP4009951B2 - Photoelectric sensor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical state in an optical path formed between the light projector and the light receiver from a change in a light receiving level of the light emitted from the light projector by the light receiver, specifically an object intrusion into the light path, etc. The present invention relates to a photoelectric sensor device that detects the above.
[0002]
[Related background]
Photoelectric sensor devices including a projector and a light receiver include a transmission type and a reflection type. A transmissive photoelectric sensor device basically has a light projector (light projecting unit) and a light receiver (light receiving unit) facing each other with a predetermined distance, and an optical path formed between the light projecting device and the light receiving device. When an object enters the inside, the object detection is performed by utilizing the change in the light reception level (light reception amount) of the light emitted from the projector by the light receiver.
[0003]
In addition, the reflective photoelectric sensor device is provided with a light projector (light projecting unit) and a light receiver (light receiving unit) aligned in the optical axis direction, and the light reflected from the object emitted from the light projector is detected by the light receiver. Thus, object detection is performed. That is, this reflective photoelectric sensor has no reflected light from the object when there is no object on the optical axis, and when there is an object on the optical axis, the intensity (the amount of received light) depends on the distance to the object. ) Is received to receive the reflected light (see, for example, Patent Documents 1 and 2).
[0004]
A photoelectric sensor device that detects the optical state in the optical path formed between the projector and the light receiver as a change in the amount of light received by the light receiver (light reception level) is used for various types of object detection, object determination, and the like. It is used for The optical state in the optical path means not only the reflectance and transmittance of light in the detection target, but also its shape, as well as the amount of light transmission (propagation rate) that depends on the distance to the detection target. Point to.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-308268 [Patent Document 2]
JP-A-9-116411 [0006]
[Problems to be solved by the invention]
By the way, in this type of photoelectric sensor device, for example, due to the deterioration of the characteristics of the projector and the receiver over time, the change in the optical characteristics due to the contamination of the detection object, the brightness of the background, etc. It cannot be denied that the level gradually decreases. Such a phenomenon is generally referred to as a decrease in sensitivity of the photoelectric sensor. Therefore, conventionally, as disclosed in Patent Documents 1 and 2, calibration of the light receiving sensitivity of the photoelectric sensor under a predetermined condition has been performed. Specifically, the calibration of the light reception sensitivity is performed by adjusting a determination threshold (threshold) of the light reception level that changes depending on whether or not an object exists in accordance with the light reception level at that time. The light receiving sensitivity may be adjusted by adjusting the gain (gain) of the sensing amplifier or adjusting the amount of light emitted from the projector.
[0007]
Incidentally, in a conventional photoelectric sensor device, a control signal for sensitivity adjustment (calibration) is given remotely from the outside exclusively as referred to as remote tuning. And in order to realize such remote tuning, in addition to a pair of power supply lines for supplying the operating power to the photoelectric sensor device and an output line for outputting an object detection signal, a control line for remote control is used. A four-core cable is connected.
[0008]
However, when a large number of photoelectric sensor devices are provided at various sites such as factories, even if the number of connections per photoelectric sensor device is as small as four, it is necessary to perform a large number of connections overall. Therefore, it cannot be denied that the connection work takes a lot of time and effort. Further, it is necessary to individually give an auto-tuning command (control signal) at an appropriate timing while grasping the operation state of each photoelectric sensor device. Moreover, there is a problem that it is very troublesome to grasp the operation state of each photoelectric sensor device.
[0009]
The present invention has been made in view of such circumstances, and its purpose is to simplify the wiring work and automatically adjust the light receiving sensitivity according to the deterioration of the characteristics of the projector and the receiver over time. It is an object of the present invention to provide a photoelectric sensor device with excellent handling properties that can eliminate the necessity of grasping the operation status and commanding sensitivity adjustment by appropriately setting.
[0010]
[Means for Solving the Problems]
In order to achieve the above-described object, a photoelectric sensor device according to the present invention includes a projector and a light receiver that form a predetermined optical path, and receives light emitted from the light projector or reflected light thereof by the light receiver. Detecting the optical state in the optical path from the level, specifically the intrusion of an object into the optical path,
A comparator that compares the light reception level of the light receiver with a predetermined threshold value and outputs a signal indicating the presence or absence of the object;
Calibration means for calibrating the threshold according to the light reception level of the light receiver at a timing at which a predetermined change of the signal output from the comparator is exhibited, for example, at a timing when a predetermined time has elapsed from the rise and / or fall timing. It is characterized by having.
[0011]
That is, the photoelectric sensor device according to the present invention includes a comparator that outputs a signal indicating the presence / absence of the object by comparing a light reception level of the light receiver with a predetermined threshold, and a rise of an output signal of the comparator and At the timing when a certain time has elapsed from the falling timing, attention is paid to the fact that the light receiving level by the light receiver is stable,
A light reception level by the light receiver is detected at a timing when a predetermined time has elapsed from the rise and / or fall timing of the output signal of the comparator, and a threshold value (detection sensitivity) given to the comparator is automatically set according to the light reception level. It is characterized in that it is calibrated automatically. Specifically, the rising and / or falling timing of the output signal of the comparator is delayed by a predetermined time, and the threshold value (detection sensitivity) resetting process based on the light reception level by the light receiver is executed at the delayed timing. It is characterized by that.
[0012]
According to the photoelectric sensor device configured as described above, it is not necessary to externally grasp the operation state of the photoelectric sensor device, and it is not necessary to give a sensitivity adjustment command from the outside. Since there is no need to give a sensitivity adjustment command from the outside, the number of core wires to be connected to the photoelectric sensor device is, for example, three pairs of a power supply line for supplying operating power and an output line for outputting an object detection signal. Therefore, it is possible to reduce the burden of wiring work. If the detection signal is output by changing the impedance between the pair of power supply lines, and the power supply line is also used as the signal output line, the number of core wires is further reduced and the burden of the wiring work is reduced. Can be further reduced.
[0013]
It is preferable that a calibration control means for determining a stable state of the light receiving level by the light receiver and for prohibiting the threshold value calibration processing when the light receiving level is unstable is incorporated in the calibration means. If the light reception level is unstable, calibration (readjustment) of the threshold value is stopped, and the object detection (light reception level determination) process may be performed using the already set threshold value as it is.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a photoelectric sensor device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of the main part of a photoelectric sensor device according to this embodiment. 1 is a projector made of a light emitting diode (LED) that emits laser light having a wavelength of 660 nm, for example, 2 is the laser light, or It is a light receiver composed of a photodiode (PD) that receives the reflected light. The light projector 1 and the light receiver 2 may constitute a reflection type photoelectric sensor, or may constitute a transmission type photoelectric sensor.
[0015]
Here, it is assumed that light is directly projected from the light projector 1 to a predetermined object detection target area, and that the light receiver 2 directly receives light from the object detection target area. It is also possible to project light onto a predetermined object detection target area via a light and receive light from the object detection target area via an optical fiber (not shown).
[0016]
The light receiver 2 outputs a signal having a level corresponding to the intensity (amount of received light) of the received light. The output signal (light reception level) is a preamplifier circuit (head) including a frequency selection filter (not shown). After being amplified via an amplifier), it is digitally converted via an AD converter 3 and taken into a signal processing circuit 4 comprising a microcomputer or the like, for example, every 200 μSec. The signal processing circuit 4 basically compares the determination threshold T set in the memory 5 with the light reception level R of the light receiver 2 provided from the AD converter 3 to compare the object in the object detection target region. And a level determination unit (comparator) 6 that outputs a determination signal indicating the presence or absence of the signal. A determination signal from the level determination unit (comparator) 6 is output to the outside as a detection signal from the photoelectric sensor device. The setting means 9 plays a role of setting operation conditions in the photoelectric sensor device such as a delay time Td described later and a time for determining the stability of the light reception level R.
[0017]
Incidentally, the level determiner (comparator) 6 outputs a signal of [L] level, for example, when the light reception level R exceeds the determination threshold T, and when the light reception level R is lower than the determination threshold T, the level determination unit (comparator) 6 A function for outputting a signal is provided. When importance is attached to the stability of the light reception level R, the level determination device (comparator) 6 outputs a signal of [L] level when the light reception level R exceeds the determination threshold T for a predetermined time, When the light reception level R falls below the determination threshold T for a predetermined time, it may be configured to output a [H] level signal. Conversely, when the light reception level R exceeds the determination threshold value T, a [H] level signal is output, and when the light reception level R is lower than the determination threshold value T, a level determination is performed so that an [L] level signal is output. It is of course possible to configure the comparator (comparator) 6.
[0018]
In the photoelectric sensor device having such a basic function, the present invention (embodiment) is characterized in that the rising timing or falling timing of the output of the level judging device (comparator) 6 is set to a predetermined time Td. The delay circuit 7 is provided with a delay circuit 7, and a calibration circuit 8 for resetting (calibrating) the determination threshold T by inputting the delay output is provided. The delay circuit 7 may be the one that delays the output of the level determiner (comparator) 6 as it is over a predetermined time Td in terms of hardware. However, in terms of software, for example, a level determiner ( Any comparator may be used as long as it detects a rising edge and / or a falling edge of the output of the comparator 6 and gives a trigger pulse to the calibration circuit 8 after a predetermined time Td from the edge detection timing.
[0019]
On the other hand, when the above-described trigger pulse is given, the calibration circuit 8 determines, for example, 75% of the level according to the light reception level (output value of the AD converter 3) R by the light receiver 2 at that time, as a determination threshold T. And registering this in the memory 5 serves to update the determination threshold T. Then, the determination threshold T is automatically calibrated so that the updated determination threshold T is used for the subsequent determination of the received light level R (auto calibration).
[0020]
Specifically, as illustrated in FIG. 2, when the rising of the light reception level is detected, the calibration circuit 8 is triggered at a timing delayed by a predetermined time Td to calibrate the determination threshold T. Yes. At a timing when a predetermined time Td has elapsed from the rising timing of the light receiving level R, the light receiving level R rises sufficiently and the level is stable. In other words, the delay time Td is set in anticipation of the time until the light receiving level R rises and becomes sufficiently stable. The calibration circuit 8 detects the light reception level R in a stable state, and calibrates the determination threshold T according to the light reception level R. The calibration process of the determination threshold T is repeatedly executed every time the rising of the light reception level is detected. Accordingly, when the light reception level R gradually decreases with time, the determination threshold T is gradually reduced and corrected as the light reception level R decreases.
[0021]
However, if the light receiving level R changes across the determination threshold T before the delay time Td elapses, the delay circuit 7 that measures the delay time Td does not trigger the calibration circuit 8. Reset. As a result, the delay circuit 7 returns to the time-waiting state and waits until the next timing when the light reception level R exceeds the determination threshold value T.
[0022]
When it is necessary to set the determination threshold value T in consideration of the light reception level R when the amount of light received by the light receiver 2 is low, for example, the timing at which the detection timing of the fall of the light reception level is delayed by a certain time Td. The light reception level Rlow detected in step 1 is stored, and then the detection threshold value is detected according to the light reception level Rhigh and Rlow when the light reception level Rhigh is detected at a timing delayed from the detection timing of the rise of the light reception level by a predetermined time Td. T may be set.
[0023]
Thus, according to the photoelectric sensor device equipped with such an automatic calibration function of the determination threshold T, the determination threshold T is automatically set according to the received light level obtained at that time by using the output timing of the detection signal indicating the presence or absence of the object. Therefore, it is not necessary to give a control signal for calibration of the determination threshold value from the outside. Accordingly, since it is not necessary to connect a control line for supplying a control signal to the photoelectric sensor device from the outside, the number of core wires to be connected to the photoelectric sensor device can be reduced by the amount that the control line is not required. . Therefore, it is possible to reduce the wiring load on the photoelectric sensor device.
[0024]
In addition, since the automatic calibration function of the determination threshold value T described above is provided, the operation state of the photoelectric sensor device is monitored externally, and sensitivity adjustment (calibration of the determination threshold value) is performed on the photoelectric sensor device according to the operation state. There is no need to provide the control signal. Therefore, the monitoring burden on the photoelectric sensor device can be eliminated, and the work load of giving the control signal to the photoelectric sensor device at an appropriate timing is eliminated each time. It becomes possible. Especially in the field of factories and the like, this type of photoelectric sensor device is often installed, for example, over 100 units, so the wiring work burden of the automatic calibration function described above in such a use environment is reduced. The effect of etc. is great. The photoelectric sensor device having the above-described automatic calibration function is extremely useful particularly when the detection target is a plurality of products having the same shape that are arranged and transported at regular intervals on a belt conveyor that moves at a constant speed. .
[0025]
By the way, for example, when the detection period of the light reception level by the light receiver 2 is sufficiently short compared to the period of entry of the object into the optical path formed by the projector 1 and the light receiver 2, the calibration circuit 8 receives the light. You may make it monitor the fluctuation | variation of this light reception level over the fixed period after progress of predetermined time from the detection timing of the rise and / or fall of a level. Then, as shown in FIG. 3, the fluctuation amount of the received light level is determined (step S1). When the fluctuation amount is large, the above-described calibration processing of the determination threshold value T is prohibited (step S2). It is preferable to provide calibration control means for permitting execution of the calibration process for T (step S3).
[0026]
By the way, for the detection of the fluctuation amount of the light reception level described above, for example, the peak value and the bottom value of the light reception level at a predetermined time after the detection timing of the rise and / or fall of the light reception level are detected, respectively. What is necessary is just to determine whether the difference of these detected values is large. Alternatively, the average value of the received light level in the predetermined period is obtained, and it is determined whether the difference between the average value and the peak value or the bottom value of the received light level in the fixed period is large. May be. Specifically, for example, when the light reception level R by the light receiver 2 is sequentially detected at a short sampling period of about 200 μSec, the average value of the light reception level R and its fluctuation over a period of about 10 to 20 mSec. The stability of the received light level may be determined by obtaining the amount.
[0027]
If the control means is provided to execute the calibration processing of the determination threshold T in this way, when the light reception level R by the light receiver 2 is in an unstable state, the determination threshold T is set based on the unstable light reception level R. Problems such as calibration can be avoided. Therefore, the reliability of the determination threshold value T, which is essential for object detection, is not impaired, and it is possible to always perform object detection with high reliability.
[0028]
The present invention is not limited to the embodiment described above. For example, as the light used for object detection, visible light or infrared light emitted from a lamp as well as the above-described LED light can be used. Further, here, the light reception level by the light receiver 2 is converted into a digital signal and processed, but it is of course possible to process the signal as it is with an analog signal level. Further, the delay time Td from the rising or falling timing of the light receiving level may be determined in accordance with the detection and use of the object, and it is sufficient that the photoelectric sensor device can be preset. is there. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.
[0029]
【The invention's effect】
As described above, according to the photoelectric sensor device of the present invention, the timing at which a predetermined change in the light reception level is exhibited, specifically, the timing delayed by a predetermined time with reference to the rise and / or fall timing of the light reception level. Therefore, the detection threshold value for the object detection is automatically calibrated by detecting the light reception level at that time, that is, the detection sensitivity is automatically calibrated. Therefore, stable object detection can always be performed. Moreover, since it is not necessary to provide a control signal for adjusting detection sensitivity from the outside, it is not only necessary to monitor the operation state of the photoelectric sensor device, but also the number of core wires to be connected to the photoelectric sensor device can be reduced. In addition, a great effect in practice, such as being able to significantly reduce the wiring work burden, is achieved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a main part of a photoelectric sensor device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating calibration timing of a determination threshold value in the photoelectric sensor device illustrated in FIG.
FIG. 3 is a diagram showing a form of threshold value calibration process execution / prohibition control according to the amount of fluctuation in received light level according to the present invention.
[Explanation of symbols]
1 Light Emitter 2 Light Receiver 3 AD Converter 4 Signal Processing Circuit (Microcomputer)
5 memory (judgment threshold)
6 Level judging device (comparator)
7 Delay circuit 8 Calibration circuit 9 Setting means

Claims (2)

A photoelectric sensor device that includes a projector and a light receiver that form a predetermined optical path, and receives light emitted from the projector or reflected light by the light receiver and detects an optical state in the optical path from the received light level. There,
A comparator that compares the light reception level of the light receiver with a predetermined threshold value and outputs a signal indicating the presence or absence of the object;
A photoelectric sensor device comprising: calibration means for calibrating the threshold according to a light reception level by the light receiver at a timing when a predetermined time has elapsed from a timing at which a predetermined change in a signal output from the comparator is exhibited. . The photoelectric sensor device according to claim 1, wherein the calibration unit includes a calibration control unit that determines a stable state of a light reception level by the light receiver and prohibits the threshold value calibration process when the light reception level is unstable.

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