JP2016181807A - Photoelectric sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photoelectric sensor capable of adjusting a time used for determination of presence or absence of a detection object, in a state where a signal obtained by light reception is in a saturation state.SOLUTION: A first comparator 11 compares an output signal from a light receiving unit 2 with a first threshold. A second comparator 12 compares the output signal from the light receiving unit 2 with a second threshold. An AND circuit 15 outputs a logical product of an output signal from the first comparator 11, and an output signal from an inverted output terminal QN of a DFF 13, to a determination unit 4. At the falling of the output signal of the second comparator 12 resulting from that the output signal from the light receiving unit 2 becomes lower than the second threshold, an inverted signal of the output signal of the first comparator 11 is outputted from the inverted output terminal QN of the DFF 13, and a level of an output signal of the AND circuit 15 is changed. Thereby, in a case where the output signal from the light receiving unit 2 is larger than the second threshold, a signal that indicates a time from when the output signal becomes larger than the first threshold to when the output signal becomes lower than the second threshold is outputted to a controller 4.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a photoelectric sensor that detects a detection object using a change in the amount of received light.

  The photoelectric sensor includes a light projecting unit and a light receiving unit, and for example, as described in Patent Document 1, pulsed light having a constant period is output from the light projecting unit. The light receiving unit receives this pulsed light, performs photoelectric conversion, and outputs a voltage signal. The signal level of the voltage signal output from the light receiving unit is compared with a threshold value. In the case of a photoelectric sensor of the type that performs the presence / absence of the detection target, that is, ON / OFF determination using the fact that the detection target blocks the pulsed light when there is a detection target, the signal level from the light receiving unit is below the threshold value If so, the determination is ON. At this time, there are the following two determination methods.

One is a method of detecting that the signal level is equal to or lower than a threshold at a predetermined timing. When the signal level is equal to or lower than the threshold, an ON determination is made. This is a useful method when the light projection timing of the pulsed light is known in advance on the light receiving unit side.
The other is a method that is useful when the predetermined timing is not known as described above. Based on a preset time width, only a signal output by the light receiving unit during the time width is used as a target. Is to be compared. When the signal level from the light receiving unit output during the time width is equal to or less than the threshold value, the determination is ON. The time width is calculated and set to correspond to the pulse width of the pulsed light.

JP 2014-207466 A

In the above-described method in which the determination is made based on the signal from the light receiving unit during the set time width, it is necessary to set the time width first. For example, the time width detected as exceeding the threshold when there is no detection target is set. At this time, the time width detected as exceeding the threshold ranges from the signal level near the threshold to the signal output range sufficiently higher than the threshold when the threshold is fixed.
When excessive light enters the light receiving unit, the signal output from the light receiving unit reaches a saturation level. The saturation level is given by limiting the signal amplitude inside the light receiving unit. In this saturation state, the amplitude of the output signal of the light receiving unit is limited, but the time width detected as the signal level is greater than or equal to the threshold is the amount of light that has entered the light receiving unit even when the amplitude is saturated. Will change.
For example, as shown in FIG. 6, when there is a signal return or the like in a part of the light receiving unit, the time width S <b> 61 detected as being greater than or equal to the threshold value increases due to the influence.

  For the above situation, it is conceivable to set the time width S61 as a time width used for ON / OFF determination. However, when multiple photoelectric sensors are used at the same time, other photoelectric sensors may malfunction if they set different time widths in advance and make ON / OFF determinations. It is desirable to set the time width as a time width used for ON / OFF determination.

  The present invention has been made in order to solve the above-described problems. When a signal obtained by light reception is in a saturated state, a photoelectric which can adjust the time used for determining the presence / absence of a detection target is provided. The purpose is to obtain a sensor.

  The photoelectric sensor according to the present invention compares a light receiving unit that outputs a signal according to the amount of received light with a second threshold that determines a signal saturation state that is greater than the first threshold and the first threshold, If the signal does not exceed the second threshold between the time when the signal exceeds the first threshold and falls below the first threshold, the time after the signal exceeds the first threshold and falls below the first threshold If the signal exceeds the second threshold between the time when the signal exceeds the first threshold and falls below the first threshold, the signal exceeds the first threshold before the second threshold. A control unit that outputs a time until the time is less than the value, and a determination unit that determines the presence or absence of the detection target based on the time output by the control unit.

  According to this invention, when the signal obtained by light reception is in a saturated state, it is possible to adjust the time used for determining the presence or absence of the detection target.

It is a block diagram of the photoelectric sensor which concerns on Embodiment 1 of this invention. It is a figure which shows the structural example of the control part of the photoelectric sensor which concerns on Embodiment 1 of this invention. It is a timing chart which shows the process of the control part of the photoelectric sensor which concerns on Embodiment 1 of this invention. It is a figure which shows the structural example of the control part of the photoelectric sensor which concerns on Embodiment 2 of this invention. It is a timing chart which shows the process of the control part of the photoelectric sensor which concerns on Embodiment 2 of this invention. It is a figure explaining the influence of the signal return.

Embodiment 1 FIG.
FIG. 1 shows a configuration diagram of a photoelectric sensor according to Embodiment 1 of the present invention. Here, the object is detected using the fact that the detection object passes between the light projecting unit 1 and the light receiving unit 2, and the light traveling from the light projecting unit 1 to the light receiving unit 2 is shielded by the passage of the detection object. A so-called transmissive photoelectric sensor that performs the above will be described as an example.
The photoelectric sensor includes a light projecting unit 1, a light receiving unit 2, a control unit 3, and a determination unit 4.
The light projecting unit 1 projects pulsed light having a constant period. The light projecting unit 1 is composed of, for example, a light emitting diode and a lens.
The light receiving unit 2 receives the pulsed light projected by the light projecting unit 1 and outputs a signal corresponding to the amount of received light by photoelectric conversion. This signal is, for example, a voltage signal. The light receiving unit 2 is configured by, for example, a photodiode, a lens, or the like.

Using the output signal from the light receiving unit 2 and a plurality of preset threshold values, the control unit 3 obtains and outputs the time used when the determination unit 4 determines the presence or absence of the detection target.
The determination unit 4 determines the presence or absence of the detection target based on the time output by the control unit 3.

FIG. 2 is a configuration diagram when the control unit 3 is realized by a logic circuit.
The first comparator 11 compares the output signal from the light receiving unit 2 with the first threshold value, and outputs an H level signal when the output signal from the light receiving unit 2 exceeds the first threshold value. When the output signal from the light receiving unit 2 falls below the first threshold, an L level signal is output.
The second comparator 12 compares the output signal from the light receiving unit 2 with a second threshold value, and outputs an H level signal when the output signal from the light receiving unit 2 exceeds the second threshold value. When the output signal from the light receiving unit 2 falls below the second threshold, an L level signal is output.

The first threshold is a value that can determine the presence or absence of a detection target. For example, it is conceivable that an output signal from the light receiving unit 2 is measured in advance when there is an object to be detected and when there is no detection target, and an intermediate value between the two output signals is used as the first threshold value.
The second threshold value is a value that can determine whether the output signal from the light receiving unit 2 is in a saturated state. For example, a value lower than the output signal in the saturated state by a set ratio can be considered as the second threshold value. In any case, the second threshold value is set to a value larger than the first threshold value and capable of detecting an output signal when the saturation state is close to the saturation state. Therefore, the time width when the output signal of the second comparator 12 is H level is shorter than the time width when the output signal of the first comparator 11 is H level.

A DFF (Delay Flip-Flop) 13 receives an output signal from the first comparator 11 at an input terminal D. Further, the output signal from the second comparator 12 is input to the clock input terminal via the inverter circuit 14. The inverting output terminal QN is connected to the AND circuit 15. By connecting the DFF 13 in this way, when the second comparator 12 detects the saturation state of the output signal from the light receiving unit 2 and outputs an H level output signal, at the fall of the output signal, The DFF 13 gives the output signal from the first comparator 11 connected to the input terminal D to the output terminal Q, and the inverted signal of the output terminal Q is output from the inverted output terminal QN to the AND circuit 15.
Further, the DFF 13 is connected to the AND circuit 16. An output signal from the first comparator 11 and an output signal from the reset control circuit 17 are input to the AND circuit 16. An H level output signal is input from the reset control circuit 17, and when the output signal from the first comparator 11 becomes L level, the output signal of the output terminal Q of the DFF 13 is reset to L level.

  The AND circuit 15 receives the output signal from the first comparator 11 and the output signal from the inverted output terminal QN of the DFF 13. The AND circuit 15 takes the logical product of these two signals and outputs it to the determination unit 4.

FIG. 3 is a timing chart showing processing of the control unit 3. Three patterns with different output signals from the light receiving unit 2 are shown in FIGS.
First, the case of the pattern shown in FIG.
When the output signal from the light receiving unit 2 exceeds the first threshold at the timing T1, the output signal of the first comparator 11 becomes H level. At this time, due to the reset process before the timing T1, the output signal of the output terminal Q is at the L level, and the output signal of the inverted output terminal QN is at the H level. Therefore, the output signal of the AND circuit 15 becomes H level.

Subsequently, when the output signal from the light receiving unit 2 exceeds the second threshold at the timing T2, the output signal of the second comparator 12 becomes H level.
Subsequently, when the output signal from the light receiving unit 2 falls below the second threshold value at timing T3, the output signal of the second comparator 12 becomes L level. At the fall of the output signal of the second comparator 12, the output terminal Q of the DFF 13 becomes the same H level as the output signal from the first comparator 11, and the output signal of the inverting output terminal QN becomes the L level. At this time, since the output signal of the first comparator 11 is at the H level, the output signal of the AND circuit 15 is at the L level.

  Subsequently, when the output signal from the light receiving unit 2 falls below the first threshold at timing T4, the output signal of the first comparator 11 becomes L level. Then, the output signal of the output terminal Q of the DFF 13 is reset to L level by the AND circuit 16, and the output signal of the inverted output terminal QN becomes H level.

  As described above, when it is determined that the output signal from the light receiving unit 2 is in a saturated state between the time when the output signal from the light receiving unit 2 exceeds the first threshold and falls below the first threshold, During the period from the fall of the output signal of the second comparator 12 to the fall of the output signal of the first comparator 11, the output signal of the inverting output terminal QN of the DFF 13 becomes L level. Then, by ANDing the output signal of the first comparator 11 and the output signal of the inverting output terminal QN in the AND circuit 15, the time width S1 in which the output signal of the AND circuit 15 is at the H level is the first width. The output signal of the comparator 11 is shorter than the time width S2 in which the output signal is at the H level. Specifically, the time width S1 indicates the time from when the output signal from the light receiving unit 2 exceeds the first threshold value until it falls below the second threshold value.

  The determination unit 4 uses the output signal of the AND circuit 15 to set a time width used for determining the presence / absence of the detection target. That is, the time width S1 in which the output signal of the AND circuit 15 indicates the H level is set as a preset time width, and thereafter, a signal input from the AND circuit 15 is used during the preset time width. The presence or absence of a detection target is determined. When setting the time width used for the determination, if the output signal from the light receiving unit 2 is in the saturated state, the time width S1 is shorter than the time width S2, that is, the influence of the signal reversion or the like due to the saturated state is reduced. Therefore, the presence / absence of the detection target can be accurately determined within a more appropriate time width.

  In the pattern shown in FIG. 3B, the output signal from the light receiving unit 2 exceeds the first threshold value at the timing T11, the output signal exceeds the second threshold value at the timing T12, and the output signal exceeds the second threshold value at the timing T13. 2 and falls below the first threshold at timing T14. In this case as well, as described with reference to FIG. 3A, the time width S11 in which the output signal of the AND circuit 15 used for the determination in the determination unit 4 is at the H level is the first comparator 11. The output signal is adjusted to be shorter than the time width S12 in which the output signal is at the H level.

  In the pattern shown in FIG. 3C, the output signal from the light receiving unit 2 exceeds the first threshold at timing T21, and the output signal falls below the first threshold at timing T22. That is, FIG. 3C illustrates a case where the output signal from the light receiving unit 2 does not become saturated between the time when the output signal from the light receiving unit 2 exceeds the first threshold and falls below the first threshold. It is a timing chart. In this case, the time width S21 in which the output signal of the AND circuit 15 used in the determination unit 4 is at the H level is not particularly adjusted, and is the same as the time width S22 in which the output signal of the first comparator 11 is at the H level. Become.

  Note that FIG. 3 shows the first threshold value and the second threshold value set in consideration of the hysteresis width. That is, the threshold value when the output signal from the light receiving unit 2 changes from the large side to the small side is set smaller than the threshold value when the output signal from the light receiving unit 2 changes from the small side to the large side. This hysteresis is provided to prevent chattering and is not related to the essence of the present invention.

  As described above, according to the photoelectric sensor according to the first embodiment of the present invention, when the output signal from the light receiving unit 2 is in a saturated state, the output signal exceeds the time width over which the first threshold value is exceeded. The time indicated by the shortly adjusted time width is used by the determination unit 4 for the presence / absence determination of the detection target. Accordingly, even if the output signal from the light receiving unit 2 is turned back due to the saturation state, the presence or absence of the detection target can be accurately determined within a more appropriate time width.

Embodiment 2. FIG.
In the first embodiment, the processing for obtaining the time used for determining the presence / absence of the detection target by comparing the output signal from the light receiving unit 2 with two threshold values in the control unit 3 has been described. In the second embodiment, a case will be described where three threshold values including a third threshold value are used in addition to the first threshold value and the second threshold value described above.
The configuration of the photoelectric sensor according to Embodiment 2 is the same as that in FIG. 1, and FIG. FIG. 4 is a configuration diagram when the control unit 3 of the photoelectric sensor according to the second embodiment is realized by a logic circuit. In FIG. 4, the same or corresponding parts as in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

The third comparator 18 compares the output signal from the light receiving unit 2 with the third threshold value, and outputs an H level signal when the output signal from the light receiving unit 2 exceeds the third threshold value. When the output signal from the light receiving unit 2 falls below the third threshold, an L level signal is output.
The third threshold value is set to a value larger than the first threshold value and smaller than the second threshold value. Therefore, the time width when the output signal of the third comparator 18 is H level is shorter than the time width when the output signal of the first comparator 11 is H level, and the output signal of the second comparator 12 is H level. Longer than the time span of the level. Note that the third threshold value is set to a value that does not have an influence such as signal reversion.

The DFF 19 receives the output signal from the first comparator 11 at the input terminal D. Further, the output signal from the second comparator 12 is input to the clock input terminal via the inverter circuit 14. The output terminal Q is connected to the switch. This switch switches the input to the AND circuit 20 described later between the power supply voltage and the output signal from the third comparator 18 based on the output signal from the output terminal Q. The power supply voltage corresponds to the H level. By connecting the DFF 19 in this way, when the second comparator 12 detects the saturation state of the output signal from the light receiving unit 2 and outputs an H level output signal, at the falling edge of the output signal, The DFF 19 outputs an output signal from the first comparator 11 connected to the input terminal D from the output terminal Q.
Further, the DFF 19 is connected to the AND circuit 16, and when the output signal from the first comparator 11 becomes L level, the output signal of the output terminal Q of the DFF 19 is reset to L level.

  The AND circuit 20 receives the output signal from the first comparator 11 and the output signal or power supply voltage from the third comparator 18. By the function of the switch described above, the output signal from the third comparator 18 is input when the output signal of the output terminal Q of the DFF 19 is H level, and the power supply voltage is changed when the output signal of the output terminal Q is L level. Entered. The AND circuit 20 calculates the logical product of the two input signals and outputs the logical product to the determination unit 4.

FIG. 5 is a timing chart showing processing of the control unit 3 of the photoelectric sensor according to the second embodiment. Three patterns having different output signals from the light receiving unit 2 are shown in FIGS.
First, the case of the pattern shown in FIG.
When the output signal from the light receiving unit 2 exceeds the first threshold at timing T31, the output signal of the first comparator 11 becomes H level. At this time, the output signal at the output terminal Q is at the L level due to the reset process before the timing T31, and the input to the AND circuit 20 is the output signal from the first comparator 11 and the H level power supply. It is a voltage. Accordingly, the output signal of the AND circuit 20 at this time becomes H level.

Subsequently, when the output signal from the light receiving unit 2 exceeds the third threshold value at the timing T32, the output signal of the third comparator 18 becomes H level.
Subsequently, when the output signal from the light receiving unit 2 exceeds the second threshold at timing T33, the output signal of the second comparator 12 becomes H level.

  Subsequently, when the output signal from the light receiving unit 2 falls below the second threshold at timing T34, the output signal of the second comparator 12 becomes L level. At the falling edge of the output signal of the second comparator 12, the output terminal Q of the DFF 19 becomes the same H level as the output signal from the first comparator 11. Thus, the input to the AND circuit 20 is an H level output signal from the first comparator 11 and an H level output signal from the third comparator 18 switched from the power supply voltage. Therefore, the output of the AND circuit 20 remains at the H level.

Subsequently, when the output signal from the light receiving unit 2 falls below the third threshold value at the timing T35, the output of the third comparator 18 becomes L level. Therefore, the output of the AND circuit 20 becomes L level.
Subsequently, when the output signal from the light receiving unit 2 falls below the first threshold value at timing T36, the output signal of the first comparator 11 becomes L level. Then, the output signal of the output terminal Q of the DFF 19 is reset by the AND circuit 16 and becomes L level. As a result, the input to the AND circuit 20 is the H level power supply voltage switched from the third comparator 18 and the L level output signal from the first comparator 11. Therefore, the output of the AND circuit 20 becomes L level.

  As described above, when it is determined that the output signal from the light receiving unit 2 is in a saturated state between the time when the output signal from the light receiving unit 2 exceeds the first threshold and falls below the first threshold, The output terminal Q of the DFF 19 is at the H level from the fall of the output signal of the second comparator 12 to the fall of the output signal of the first comparator 11. The AND circuit 20 calculates the logical product of the output signal from the first comparator 11 and the output signal from the third comparator 18 or the power supply voltage. When the output terminal Q is at the H level, the third comparison is performed. The output signal from the device 18 is selected. For this reason, the output signals of the first comparator 11 and the third comparator 18 are output from the falling edge of the output signal of the second comparator 12 to the falling edge of the output signal of the first comparator 11. The time width S31 in which the logical product is obtained and the output signal of the AND circuit 20 is at the H level is shorter than the time width S32 in which the output signal of the first comparator 11 is at the H level. Specifically, the time width S31 indicates the time from when the output signal from the light receiving unit 2 exceeds the first threshold value to below the third threshold value.

  The determination unit 4 uses the output signal of the AND circuit 20 to set a time width used for determining the presence / absence of the detection target. That is, the time width S31 in which the output signal of the AND circuit 20 indicates the H level is set as a preset time width, and thereafter, a signal input from the AND circuit 20 is used during the preset time width. The presence or absence of a detection target is determined. When setting the time width used for the determination, if the output signal from the light receiving unit 2 is in the saturated state, the time width S31 is shorter than the time width S32, that is, the direction in which the influence of signal reversion or the like due to the saturated state is reduced. Therefore, the presence / absence of the detection target can be accurately determined within a more appropriate time width. Since the time width S31 depends on the third threshold value, the degree of adjustment of the time width S31 can be changed by setting the third threshold value between the first threshold value and the second threshold value in various ways. Is possible.

  In the case of the pattern shown in FIG. 5B, the output signal from the light receiving unit 2 exceeds the first threshold at timing T41, the output signal exceeds the third threshold at timing T42, and the output signal at timing T43. Exceeds the second threshold, the output signal falls below the second threshold at timing T44, the output signal falls below the third threshold at timing T45, and the output signal falls below the first threshold at timing T46. In this case as well, as described with reference to FIG. 5A, the time width S41 in which the output signal of the AND circuit 20 used for determination in the determination unit 4 is at the H level is the first comparator 11. The output signal is adjusted to be shorter than the time width S42 in which the output signal is at the H level.

  In the pattern shown in FIG. 5C, the output signal from the light receiving unit 2 exceeds the first threshold at timing T51, the output signal exceeds the third threshold at timing T52, and the output signal at timing T53. Falls below the third threshold, and the output signal falls below the first threshold at timing T54. That is, FIG. 5C shows a case where the output signal from the light receiving unit 2 does not become saturated between the time when the output signal from the light receiving unit 2 exceeds the first threshold and falls below the first threshold. It is a timing chart. In this case, the time width S51 in which the output signal of the AND circuit 20 used in the determination unit 4 is at the H level is not particularly adjusted, and is the same as the time width S52 in which the output signal of the first comparator 11 is at the H level. Become.

As described above, according to the photoelectric sensor according to the second embodiment of the present invention, the same effect as in the first embodiment can be obtained.
In addition, by using the third threshold value, it is possible to change the degree of adjustment of time used for the presence / absence determination of the detection target in the determination unit 4.

In the above description, the case where the control unit 3 is realized by a logic circuit as shown in FIGS. 2 and 4 has been described as an example. However, the control unit 3 may be realized by a processor executing a program describing the processing content described above. That is, the control unit 3 can be realized by hardware such as a logic circuit or by using software such as a program.
Further, when the control unit 3 is realized by a logic circuit, the circuit configuration is not limited to the illustrated one. In short, any circuit configuration capable of performing the above-described processing of the control unit 3 may be used.

  In the above description, an example has been described in which a comparator is provided for each of the first threshold value, the second threshold value, and the third threshold value. However, the comparator may be shared and the comparison may be performed while switching each threshold value. In this case, each threshold value is switched at high speed using a sufficiently fast clock.

  In the above description, the transmission type photoelectric sensor has been described as an example. However, other types such as a reflection type photoelectric sensor and a reflector type photoelectric sensor may be used.

  Further, within the scope of the present invention, the invention of the present application can be freely combined with each embodiment, modified with any component in each embodiment, or omitted with any component in each embodiment. .

DESCRIPTION OF SYMBOLS 1 Light projection part 2 Light reception part 3 Control part 4 Judgment part 11 1st comparator 12 2nd comparator 13 DFF
14 Inverter circuit 15 AND circuit 16 AND circuit 17 Reset control circuit 18 Third comparator 19 DFF
20 AND circuit

Claims (2)

A light receiving unit that outputs a signal corresponding to the amount of light received;
Comparing the signal to a first threshold and a second threshold that determines a saturation state of the signal that is greater than the first threshold;
If the signal does not exceed the second threshold between the time when the signal exceeds the first threshold and falls below the first threshold, the signal exceeds the first threshold before the signal exceeds the first threshold. Output the time until it falls below the first threshold,
If the signal exceeds the second threshold between the time when the signal exceeds the first threshold and falls below the first threshold, the signal exceeds the first threshold before the second. A control unit that outputs a time until the threshold value of 2 is exceeded;
A photoelectric sensor comprising: a determination unit that determines the presence or absence of a detection target based on the time output by the control unit. A light receiving unit that outputs a signal corresponding to the amount of light received;
A first threshold value; a second threshold value that determines a saturation state of the signal greater than the first threshold value; and a third threshold value that is greater than the first threshold value and smaller than the second threshold value. Compare and
If the signal does not exceed the second threshold between the time when the signal exceeds the first threshold and falls below the first threshold, the signal exceeds the first threshold before the signal exceeds the first threshold. Output the time until it falls below the first threshold,
If the signal exceeds the second threshold between the time when the signal exceeds the first threshold and falls below the first threshold, the signal exceeds the first threshold before the second. A control unit that outputs a time until it falls below a threshold value of 3,
A photoelectric sensor comprising: a determination unit that determines the presence or absence of a detection target based on the time output by the control unit.

Images