JP7194354B2 - photoelectric sensor - Google Patents

Description

The present invention relates to photoelectric sensors.

2. Description of the Related Art Conventionally, in a photoelectric sensor, there is a method of detecting a failure or the like of a light projecting element by monitoring the amount of pulsed light projected from the light projecting element (for example, Patent Document 1, etc.). In the method described above, for example, the light receiving element for monitoring directly receives the pulsed light projected from the light projecting element to monitor the amount of projected light. The photoelectric sensor amplifies the light-receiving signal of the light-receiving element for monitoring with an amplifier, and then acquires it with an analog-digital converter (hereinafter referred to as "ADC") incorporated in the CPU. The photoelectric sensor detects a failure by determining whether or not the light projecting element is abnormal with a determination circuit that determines an abnormality of the light projecting element based on the acquired received light signal.

JP 2006-238185 A

In the photoelectric sensor as described above, the pulse width of the pulsed light projected from the light projecting element has become shorter as the detection principle has evolved and the detection speed has improved. For example, there are cases where the pulse width is shortened on the order of about 1/1000 times the conventional one. Then, the light receiving signal of the light receiving element for monitoring which monitors the pulsed light having a pulse width which is very short as compared with the conventional one likewise also has a very short pulse width. For this reason, in the photoelectric sensor as described above, it is necessary to increase the speed of components such as the determination circuit for processing a light reception signal with a very short pulse width. Such speeding up of components also leads to higher costs.

In view of the above, the present invention provides a photoelectric sensor capable of detecting a failure of a light projecting element without increasing the speed of a determination circuit for determining an abnormality of the light projecting element even if the pulse width of the pulsed light projected from the light projecting element is shortened. The object is to provide a sensor.

A photoelectric sensor according to an aspect of the present invention includes a light projecting element that projects pulsed light onto a detection area, a light projecting unit that generates a monitor signal according to the amount of light projected by the light projecting element, and a pulse light from the detection area. a light-receiving unit that receives light; a comparison circuit that compares the monitor signal with a predetermined threshold; a storage circuit that temporarily stores the comparison result of the comparison circuit; It has a detection circuit that detects at a predetermined clock cycle longer than the pulse width, and a determination circuit that determines abnormality of the light emitting element based on the comparison result detected by the detection circuit.

According to this aspect, by temporarily storing the monitor signal corresponding to the amount of light projected by the light projecting element of the photoelectric sensor in the memory circuit, the comparison result is detected at a clock cycle longer than the pulse width, and the abnormality of the light projecting element is detected. can be determined. Therefore, failure of the light projecting element can be detected without increasing the speed of components such as the determination circuit.

In the above aspect, there is provided a reference voltage circuit that generates a reference voltage corresponding to a predetermined threshold value from the reference voltage control signal output from the determination circuit, and the comparison circuit compares the voltage of the monitor signal and the reference voltage to perform the comparison. As a result, it may be configured by a comparator that outputs a pulse signal representing the magnitude relationship between the voltage of the monitor signal and the reference voltage.

According to this aspect, the comparator can output the comparison result as a pulse signal, that is, a binary value (High or Low). Abnormality can be determined by

In the above aspect, the reference voltage corresponds to the lower limit of the voltage of the monitor signal, the comparator compares the voltage of the monitor signal and the reference voltage while the light emitting element projects the pulsed light, and the determination circuit compares the voltage of the monitor signal with the reference voltage. It is also possible to count non-detection of a signal and determine that the light projecting element is abnormal when the counted number of non-detections is equal to or greater than a predetermined number.

According to this aspect, the determination circuit can determine whether or not the amount of light projected by the light projecting element is abnormally small. Further, according to this aspect, the determination circuit can determine an abnormality with a certain degree of accuracy by determining an abnormality when the comparison result pulse signal is not detected a predetermined number of times or more.

In the above aspect, the reference voltage corresponds to the lower limit of the voltage of the monitor signal, the comparator compares the voltage of the monitor signal and the reference voltage while the light emitting element is not emitting pulsed light, and the determination circuit compares the voltage of the monitor signal with the reference voltage. The number of signal detections may be counted, and if the counted number of detections is equal to or greater than a predetermined number of times, it may be determined that the light projecting element is abnormal.

According to this aspect, the determination circuit can determine whether or not the light projection amount is abnormally large at the timing when the light projection amount of the light projecting element should be zero. Further, according to this aspect, the determination circuit can determine an abnormality with a certain degree of accuracy by determining an abnormality when the comparison result pulse signal is detected a predetermined number of times or more.

In the above aspect, the comparator may alternately compare the voltage of the monitor signal and the lower limit of the voltage of the monitor signal while the light is being projected and while the light is not being projected.

According to this aspect, the determination circuit compares the voltage of the monitor signal and the reference voltage corresponding to the lower limit of the voltage of the monitor signal alternately during light emission and non-light emission, thereby determining the intensity of the emitted pulsed light. It can be determined whether the pulse width is abnormally long.

In the above aspect, the reference voltage corresponds to the upper limit of the voltage of the monitor signal, the comparator compares the voltage of the monitor signal and the reference voltage while the light emitting element projects the pulsed light, and the determination circuit compares the voltage of the monitor signal with the reference voltage. The number of signal detections may be counted, and if the counted number of detections is equal to or greater than a predetermined number of times, it may be determined that the light projecting element is abnormal.

According to this aspect, the determination circuit can determine whether or not the amount of light projected by the light projecting element is abnormally large. Further, according to this aspect, the determination circuit can determine an abnormality with a certain degree of accuracy by determining an abnormality when the comparison result pulse signal is detected a predetermined number of times or more.

In the above aspect, the comparison circuit, storage circuit, detection circuit, and determination circuit may be implemented on a single FPGA.

According to this aspect, it is possible to implement circuits related to fault detection, such as the comparison circuit, the storage circuit, the detection circuit, and the determination circuit, on a single circuit. Therefore, according to this aspect, a circuit for fault detection can be mounted with a simple configuration.

In the above aspect, the memory circuit may be configured by a latch circuit mounted on an FPGA.

According to this aspect, the comparison result input by the latch circuit can be internally recorded to fix the output. Therefore, the comparison result can be temporarily stored with a simple configuration.

In the above aspect, the comparator may consist of a differential signal receiver implemented on an FPGA.

According to this aspect, it is possible to efficiently use resources and reduce the cost of the photoelectric sensor by configuring the comparator with a differential signal receiver generally mounted on an FPGA for communication.

In the above aspect, the light projecting unit may have a light receiving element that generates a light reception signal corresponding to the amount of light projected by the light projecting element, and the monitor signal may be the light reception signal.

According to this aspect, the photoelectric sensor can generate a monitor signal for detecting an abnormality of the light projecting element by using the light receiving element that generates a light receiving signal corresponding to the amount of light projected by the light projecting element.

In the above aspect, the monitor signal may be a signal generated according to the driving current of the light projecting element.

According to this aspect, the photoelectric sensor can detect an abnormality in the light projecting element using the signal generated according to the driving current of the light projecting element.

According to the present invention, even if the pulse width of the pulsed light projected from the light projecting element is shortened, the photoelectric sensor can detect the failure of the light projecting element without increasing the speed of the judgment circuit for determining the abnormality of the light projecting element. can be provided.

1 is a schematic block diagram of a photoelectric sensor according to an embodiment; FIG. 4 is a schematic waveform diagram for explaining the relationship between the pulse width of pulsed light and the clock cycle of the detection circuit according to the embodiment; FIG. FIG. 4 is a schematic waveform diagram for explaining a pattern of abnormality of a light projecting element determined by a determination circuit according to the embodiment; 4 is a schematic configuration diagram of a failure detection portion of the photoelectric sensor according to the embodiment; FIG. 5 is a time chart showing an example of an abnormality determination operation in the determination circuit according to the embodiment; Fig. 5b is a schematic diagram of a fault detection part according to the time chart of Fig. 5a; It is a schematic diagram showing a pulse count of the failure detection portion and an abnormality determination method according to the embodiment. FIG. 4 is a flow chart showing an example of failure detection operation of the photoelectric sensor according to the embodiment; FIG. 8 is a flowchart showing an example of operations after connector A in FIG. 7;

A preferred embodiment of the present invention (hereinafter referred to as "this embodiment") will be described with reference to the accompanying drawings. It should be noted that, in each figure, the same reference numerals have the same or similar configurations.

<1. Configuration example>
A configuration example of a photoelectric sensor 1 according to the present embodiment will be described with reference to FIGS. 1 to 6. FIG.

FIG. 1 is a schematic block diagram of a photoelectric sensor 1 according to an embodiment. A portion surrounded by a long two-dot chain line indicates the photoelectric sensor 1 . The photoelectric sensor 1 according to the present embodiment is a reflective photoelectric sensor for detecting the existence of an object, etc., but is not limited to this. The photoelectric sensor 1 may be, for example, a transmissive photoelectric sensor. Further, the photoelectric sensor 1 may be a sensor such as a TOF (Time Of Flight) sensor that projects light pulses having a very short pulse width of about 3 to 10 nsec.

The photoelectric sensor 1 includes a light projecting unit 10 , a light receiving unit 20 and a control circuit 30 . The photoelectric sensor 1 projects pulsed light from the light projecting unit 10 toward the detection area, and receives reflected light from the detection area with the light receiving unit 20 . A portion surrounded by a dashed line in the photoelectric sensor 1 indicates a portion for detecting a failure of the light projecting element 11 (hereinafter referred to as a "failure detection portion 5").

The light projecting unit 10 has a light projecting element 11 and a light receiving element 12 . The light projecting unit 10 generates a monitor signal corresponding to the amount of light projected by the light projecting element 11 . The light projecting unit 10 also has a light projecting circuit for driving the light projecting element 11, although not shown for the sake of simplicity. The light projection circuit outputs a driving signal for driving the light projection element 11 to the light projection element 11 based on the light projection command signal from the control circuit 30 . The light projecting element 11 is an element that projects pulsed light onto the detection area. The light projecting element 11 may be, for example, an LD (laser diode), but may also be composed of an element such as a light emitting diode. The light-receiving element 12 is an element that generates a light-receiving signal according to the amount of light projected by the light-projecting element 11 . The light receiving element 12 receives part of the pulsed light projected from the light projecting element 11 in order to monitor an abnormality of the light projecting element 11 . The light-receiving element 12 generates a light-receiving signal as the monitor signal based on the light quantity of the received pulsed light, and outputs the light-receiving signal to the control circuit 30 . Hereinafter, this light receiving signal generated and output by the light receiving element 12 is referred to as a "monitor light receiving signal" or an "MPD (Monitor Photo Diode) light receiving signal". In this example, monitor received light output is used to monitor the abnormality of the light projecting element 11. However, the driving of the light projecting element 11 is output from the light projecting circuit approximately proportional to the amount of light projected by the light projecting element 11. The current may be monitored to generate a monitor signal corresponding to the drive current. The photoelectric sensor 10 determines abnormality of the light projecting element 11 based on the generated monitor signal.

The light receiving unit 20 is a unit that receives pulsed light from the detection area. The light-receiving unit 20 receives, for example, the reflected light of the pulsed light projected from the light-projecting unit 10 reflected from the object to be detected or the reflector, and outputs a light-receiving signal corresponding to the amount of received light to the control circuit 30 .

The control circuit 30 has a comparison circuit 31 , a memory circuit 32 , a detection circuit 33 and a determination circuit 34 . The control circuit 30 is composed of, for example, a microcomputer including a CPU and memory, an FPGA, and the like.

The comparison circuit 31 is a circuit that compares the monitor received light signal with a predetermined threshold value. Here, the "predetermined threshold value" is a value for determining whether or not the voltage of the monitor received light signal is a normal value.

The storage circuit 32 is a circuit that temporarily stores the comparison result of the comparison circuit 31 . The configuration for temporarily storing the comparison result in the storage circuit 32 is a configuration for detecting the comparison result in a detection circuit 33 described later at a clock cycle longer than the pulse width of the pulse light projected from the light projecting element 11. be.

The detection circuit 33 detects the comparison result stored in the storage circuit 32 at a clock cycle longer than the pulse width of the pulsed light projected from the light projecting element 11 . Here, the relationship between the pulse width of the pulsed light from the light projecting element 11 and the clock cycle of the detection circuit 33 will be described with reference to FIG. As shown in FIG. 2, (a) the operation clock of the detection circuit 33 can read the pulse signal of the pulsed light at the clock periods T1, T2 and T3 with respect to the pulse width of the monitor light receiving signal in the conventional pulsed light. can. Specifically, the pulse width of the monitor light reception signal in the conventional pulsed light is, for example, about 10 μsec, and the operation clock of the detection circuit 33 operates at a clock cycle of about 0.1 to 0.01 μsec, for example. Therefore, the detection circuit 33 can detect the comparison result.

On the other hand, (b) the operation clock of the detection circuit 33 is set to the pulse width of the monitor light receiving signal in the pulse light which is shorter than the conventional pulse light projected by the light projecting element 11 according to the present embodiment. longer than wide. Specifically, the pulse width of the monitor light receiving signal in the pulsed light projected by the light projecting element 11 according to this embodiment is, for example, about 3 to 10 nsec. As above. For this reason, the operation clock of the detection circuit 33 cannot read the pulse signal of the pulse light in any clock cycle with the configuration as it is. Therefore, the photoelectric sensor 1 according to the present embodiment temporarily stores the comparison result in the storage circuit 32 to compensate for the timing difference between the pulse width of the monitor light receiving signal and the clock period in the short pulse light, and the detection circuit. Synchronize with 33. As a result, the photoelectric sensor 1 can determine an abnormality without increasing the speed of subsequent components such as the determination circuit 34 .

The determination circuit 34 determines whether the light projecting element 11 is abnormal based on the comparison result detected by the detection circuit 33 . Here, with reference to FIG. 3, the abnormality pattern of the light projecting element 11 determined by the determination circuit 34 will be described. The determination circuit 34 determines an abnormality from the viewpoint of whether or not the monitor received light signal deviates from a preset threshold value. The determination circuit 34 uses, for example, a predetermined threshold value set based on the waveform of the drive pulse for the light emitting element 11 from the control circuit 30 in FIG. The determination is made by comparing the upper and lower limits of the amplitude of the signal and the pulse width.

Specifically, the determination circuit 34 determines whether the light projecting element 11 is abnormal, as shown in FIGS. The determination circuit 34 determines whether or not the amplitude and pulse width of the monitor light receiving signal in (b) above exceed preset upper threshold values. Also, the determination circuit 34 determines whether the pulse width can be detected at the lower limit threshold of the monitor light receiving signal in (b) above, that is, whether the voltage of the light receiving signal corresponding to the amount of light emitted by the light projecting element 11 can be detected. to judge.

FIG. 3(a) shows a state in which the light projecting element 11 has not failed. The amplitude and pulse width of the monitor light reception signal in FIG. 3(a) are determined to be normal because both the amplitude and pulse width do not exceed the threshold values. 3(a) to 3(d) all show a state in which the light projecting element 11 has a failure. As shown in FIGS. 3A to 3D, there are three types of abnormal patterns determined by the determination circuit 34. FIG. Since the amplitude of the monitor received light signal of (b) exceeds the upper limit threshold value of the amplitude, it is determined to be abnormal as the peak power exceeds the upper limit. Since the pulse width of the monitor light receiving signal (c) exceeds the upper limit threshold of the pulse width, it is determined to be abnormal. The pulse of (d) is determined to be abnormal because the pulse width is not detected at the lower limit threshold value of the amplitude. When determining any of the abnormal patterns (a) to (d), the determination circuit 34 determines that the light projecting element 11 is abnormal.

The determination circuit 34 also outputs to the I/O 35 a reference voltage control signal for controlling a reference voltage generated by a reference voltage circuit 40 which will be described later.

The I/O 35 receives the reference voltage control signal output by the determination circuit 34 and outputs an analog signal obtained by D/A converting the reference voltage control signal for input to the reference voltage circuit 40 .

The reference voltage circuit 40 generates a reference voltage corresponding to a predetermined threshold from the analog signal of the reference voltage control signal output from the I/O 35 . A reference voltage circuit 40 is indicated by a portion surrounded by a dashed line. The reference voltage circuit 40 may be configured with an LPF (Low Pass Filter), and by configuring it with an LPF, it is possible to block noise and generate a stable reference voltage. The reference voltage circuit 40 inputs the generated reference voltage to the comparison circuit 31 .

The reference voltage may correspond to, for example, the upper limit of the voltage of the monitor received light signal (hereinafter also referred to as "upper limit threshold"). Also, the reference voltage may correspond to, for example, the lower limit of the voltage of the monitor received light signal (hereinafter also referred to as "lower limit threshold"). Switching between the upper limit and the lower limit of the reference voltage is switched by a reference voltage control signal.

FIG. 4 is a schematic configuration diagram of the failure detection portion 5 of the photoelectric sensor 1. As shown in FIG. The control circuit 30 may be composed of a single FPGA 301, for example. In other words, the comparison circuit 31, the storage circuit 32, the detection circuit 33, and the determination circuit 34 may be mounted on a single FPGA301. According to such a configuration, circuits related to failure detection such as the comparison circuit 31, the storage circuit 32, the detection circuit 33, and the determination circuit 34 can be implemented on a single circuit. Therefore, according to this aspect, a circuit for fault detection can be mounted with a simple configuration. Also, the FPGA 301 may operate a synchronous flip-flop 331, a determination circuit 34, and a DAC converter 351, which will be described later, at a clock cycle of 64 MHz, for example.

The comparison circuit 31 compares, for example, the voltage of the monitor received light signal with a reference voltage, and as a result of the comparison, a comparator 311 that outputs a pulse signal (hereinafter simply referred to as a “pulse signal”) representing the magnitude relationship with respect to the reference voltage. may consist of With such a configuration, the comparator 311 can output the comparison result as a pulse signal, that is, binary (High or Low). Abnormality can be determined by the determination circuit 34 of the configuration.

Comparator 311 may comprise, for example, a differential signal receiver implemented on FPGA 301 . In this way, by constructing a comparator with a differential signal receiver generally mounted on an FPGA for communication, resources can be used efficiently and the cost of the photoelectric sensor can be reduced.

The comparator 311 may, for example, compare the voltage of the monitor received light signal with the lower limit threshold while the pulsed light is projected by the light projecting element 11 (hereinafter also referred to as “during light projection”). Further, the comparator 311 may compare the voltage of the monitor received light signal with the lower limit threshold while the pulsed light is not projected by the light projecting element 11 (hereinafter also referred to as “non-projection time”). Further, the comparator 311 may compare the voltage of the monitor received light signal and the upper limit threshold while the light projecting element 11 projects the pulsed light. With such a configuration, the comparator 311 can binarize the comparison result between the voltage of the monitor light receiving signal and the upper and lower limits of the voltage.

The storage circuit 32 may be composed of a latch circuit 321 mounted on the FPGA 301, for example. The latch circuit 321 sets the data of the input D to "1", and when the Gate signal output from the determination circuit 34 rises from Low ("0") to High ("1"), the Gate signal and the logical product The pulse signal output from the comparator 311 is stored. In the latch circuit 321, the stored pulse signal is reset when read by a synchronous flip-flop (hereinafter referred to as "synchronous FF") 331, which will be described later. According to such a configuration, the latch circuit 321 can internally record the input comparison result and fix the output. Therefore, the comparison result can be temporarily stored with a simple configuration.

The detection circuit 33 may be composed of, for example, a synchronous flip-flop 331 mounted on an FPGA. The synchronous FF 331 receives the pulse signal stored in the latch circuit 321 and outputs the pulse signal to the determination circuit 34 in synchronization with the clock cycle of the synchronous FF when the clock pulse rises.

The determination circuit 34 may count non-detection or detection of pulse signals as a pulse counting function. Further, the determination circuit 34 may output a Gate signal to the logic element 322 for the latch circuit 321 as a timing control function to control the timing at which the latch circuit 321 stores the comparison result.

The determination circuit 34 counts, for example, non-detection of the pulse signal, which is the result of comparison between the voltage of the monitor light receiving signal and the lower limit threshold when light is emitted from the light emitting element 11, and the counted number of non-detections reaches a predetermined number. If it is equal to or greater than the number of times, it may be determined that the light projecting element 11 is abnormal. Here, the "predetermined number of times" is the number of times of non-detection of the pulse signal or the threshold of the number of times of detection for determining whether or not the light projecting element 11 is abnormal.

According to the above configuration, the determination circuit 34 can determine whether or not the amount of light projected by the light projecting element is abnormally small. Further, according to the above configuration, the determination circuit 34 can determine an abnormality with a certain degree of accuracy by determining an abnormality when the pulse signal of the comparison result is not detected a predetermined number of times or more. .

For example, the determination circuit 34 counts the detection of the pulse signal, which is the result of comparing the voltage of the monitor received light signal and the lower limit threshold when the light emitting element 11 is not emitting light, and determines that the number of counted detections is a predetermined number. In the above cases, it may be determined that the light projecting element 11 is abnormal. With such a configuration, the determination circuit 34 can determine whether or not the amount of light projected is abnormally large at the timing when the amount of light projected by the light projecting element should be zero. Further, according to such a configuration, the determination circuit 34 can determine an abnormality with a certain degree of accuracy by determining an abnormality when the pulse signal of the comparison result is detected a predetermined number of times or more. .

For example, the determination circuit 34 counts the detection of the pulse signal, which is the result of comparison between the voltage of the monitor light receiving signal and the upper limit threshold when light is projected by the light projecting element 11, and the counted number of detections is equal to or greater than a predetermined number. In the case of , it may be determined that the light projecting element 11 is abnormal. With such a configuration, the determination circuit 34 can determine whether or not the amount of light projected by the light projecting element is abnormally large. Further, according to such a configuration, it is possible to determine an abnormality with a certain degree of certainty by determining an abnormality when the pulse signal of the comparison result is detected a predetermined number of times or more.

As a DAC control function, the determination circuit 34 generates a DAC control signal (DAC value (8 bits)) as a reference voltage control signal for use in controlling the reference voltage circuit 40, and converts the generated DAC control signal into a D/A signal. The conversion unit 351 may output. The D/A converter 351 inputs a DAC control signal, performs DA conversion on the input DAC control signal, and supplies current determined based on the DAC control signal to the reference voltage circuit 40 . The reference voltage circuit 40 generates a reference voltage (MPD_CMP) based on the supplied current.

FIG. 5a is a timing chart showing the relationships of the main signals in the fault detection part 5. FIG. FIG. 5b is a schematic diagram showing the relationship between each signal in the timing chart of FIG. 5a and the comparison circuit and storage circuit.

As shown in FIG. 5A, this timing chart includes a monitor received light signal (A) corresponding to the light projecting pulse of the light projecting element 11, and a ΔΣ modulated DAC analog signal output from the D/A converter 351 of the FPGA 301. (B), a reference voltage (C) indicating upper and lower thresholds, a Gate signal (D) for controlling the storage timing of the comparison result of the latch circuit 321, and detection or non-detection of a pulse signal in the determination circuit 34. It shows the change over time of the waveform with the counter clear signal (E) for clearing the number of detection counts. The hatched portion of the reference voltage (C) indicates a period during which pulse width detection is effective.

As shown in FIG. 5b, the comparator 311 compares the monitor light reception signal (A) with the reference voltage (C) and outputs the comparison result (High or Low). When the Gate signal (D) rises from Low to High while the comparison result is High, or when the Gate signal is High and the comparison result changes from Low to High, the latch circuit 321 performs the comparison. store the result of

In the analog signal (B), the signal corresponding to the upper limit of the monitor light receiving signal is "MPD_DAC_A", and the signal corresponding to the lower limit of the monitor light receiving signal is "MPD_DAC_B". These signals are signals for switching the upper and lower thresholds.

The judging circuit 34 judges three abnormalities of the light projecting element 11, namely, (1) judging that the amount of projected light is insufficient, (2) judging that the pulse width is excessive, and (3) judging that the amount of projected light is excessive. The determination circuit 34 has independent counters for each of the determinations (1) to (3), and counts the number of times the pulse signal is detected or not detected.

In the above (1) judging whether the amount of projected light is too small, in sampling during light projection of the light projecting element 11 in MPD_DAC_B, the comparison result is High when the light projecting element 11 is normal when compared with the lower limit threshold. In the above (2) determination of excess pulse width, when the light projecting element 11 is sampled in MPD_DAC_B when the light projecting element 11 is not projecting light, the comparison result is Low when the light projecting element 11 is normal compared with the lower limit threshold. In the determination of (3) excess light amount, when the light projecting element 11 is sampled in MPD_DAC_A at the time of light projection, the comparison result is Low when the light projecting element 11 is normal when compared with the upper limit threshold. Further, the determination circuit 34 resets the counter value while the counter clear signal (E) is High.

Specifically, first, the delta-sigma modulation DAC analog signal (B) output from the D/A conversion unit 351 is switched from MPD_DAC_A to MPD_DAC_B. During the period in which the D/A converter 351 outputs MPD_DAC_B, which is a signal corresponding to the lower limit of the monitor received light signal, the above (1) light emission amount is alternately set while the light emitting element 11 is emitting the pulsed light and not emitting the pulsed light. Determination of insufficient pulse width and (2) Determination of excessive pulse width determines whether the light projecting element 11 is abnormal. With such a configuration, the determination circuit 34 alternately compares the voltage of the light-receiving signal with the reference voltage corresponding to the lower limit of the voltage of the light-receiving signal at the time of light emission and non-light emission, thereby determining the projected pulsed light. can be determined whether the pulse width of is abnormally long.

As input parameters, t1 is set as the MPD_DAC output pattern switching period, and t6 is set as the counter clear time in the counter clear signal (E). As input parameters, timings for controlling the Gate signal output from the determination circuit 34 are set to t2 to t5.

Specifically, t2 is the timing for invalidating the sampling for (1) determination of insufficient light emission amount and (3) determination of excessive light emission amount of the Gate signal. t4 is the timing for validating the sampling for determination of excessive pulse width; and (3) the timing of validating the sampling for the determination of the excess amount of projected light.

In the above (1) judging whether the amount of projected light is too small, the judgment circuit 34 specifically determines whether the monitor light is The signal (A) is compared with a reference voltage (C) corresponding to the lower limit of the voltage of the received light signal (A). When the light projecting element 11 is normal in the above (1) determination of insufficient amount of projected light, the result of the comparison becomes High. detected by Therefore, the determination circuit 34 counts the non-detection of the pulse signal, and determines that the light projecting element 11 is abnormal when the counted number of non-detection is equal to or greater than a predetermined number.

In the above (2) determination of excess pulse width, the determination circuit 34 specifically monitors when the light emitting element 11 is not emitting light and while the comparator 311 is High in (PT2) of the Gate signal (D). The light receiving signal (A) is compared with a reference voltage (C) corresponding to the lower limit of the voltage of the monitor light receiving signal (A). If the light projecting element 11 is normal in the above (2) determination of excess pulse width, the result of the comparison is Low, and the pulse signal representing High is not detected by the synchronous FF 331 . Therefore, the determination circuit 34 counts the detections of the pulse signal, and determines that the light projecting element 11 is abnormal when the counted number of detections is equal to or greater than a predetermined number of times. The determination of (2) excessive pulse width is performed alternately with the determination of (1) insufficient amount of light emission. Abnormalities exceeding the upper limit can be detected.

When t1 has passed since the switching of the D/A conversion unit 351, the determination circuit 34 next switches the analog signal (B) of the delta-sigma modulation DAC output from the D/A conversion unit 351 from MPD_DAC_B to MPD_DAC_A. During the period when the D/A converter 351 outputs MPD_DAC_A, which is the signal corresponding to the upper limit of the monitor received light signal, the determination circuit 34 detects the above (3) excess light intensity while the light projecting element 11 projects the pulsed light. Abnormality of the light projecting element 11 is determined in the determination.

In the determination of (3) the amount of light emitted is excessive, the determination circuit 34 specifically determines whether the monitor light is received while the light emitting element 11 is emitting light and while the comparator 311 is High (PT3) of the Gate signal (D). The signal (A) is compared with a reference voltage (C) corresponding to the upper limit of the voltage of the monitor received light signal (A). If the light projecting element 11 is normal in the above (3) judgment of the amount of light projected excessively, the result of the comparison is Low. Therefore, the determination circuit 34 counts the detection of the pulse signal, and determines that the light projecting element 11 is abnormal when the counted number of detections is equal to or greater than a predetermined number of times. In the above (3) determination of excessive light emission amount, an abnormality exceeding the peak power upper limit as shown in FIG. be able to.

Using FIG. 6, the counting of pulse signal non-detection or detection in the determination circuit 34 and the abnormality determination method based on the counting will be described. As shown in FIG. 6, in the determinations (1) to (3) above, the determination circuit 34 independently counts the number of times the pulse signal is not detected or detected. In these judgments, the judgment circuit 34 detects a failure of the light projecting element 11 and outputs a single failure detection result in the light projecting element 11 when any one of them reaches a predetermined number of times (nCnt) or more. do. In the judgments (1) to (3) above, the judgment circuit 34 clears the number of times counted independently by the counter clear signal. It should be noted that, in the above (1) judging whether the amount of projected light is insufficient, if the setting is such that the light projecting element 11 is not turned on, in order not to monitor for abnormality in the judgment, the count-up when the pulse signal is not detected is not counted up. A pulse non-detection counter counts the result of ANDing the trigger generation Enable (S1) for .

<2. Operation example>
An operation example of failure detection of the light projecting element 11 of the photoelectric sensor 1 according to the present embodiment will be described with reference to FIGS. 7 and 8. FIG. The flow charts shown in FIGS. 7 and 8 are interconnected by connectors indicated by the same reference numerals.

As shown in FIG. 7, the determination circuit 34 switches the reference voltage generated by the reference voltage circuit 40 to the lower limit threshold (S10). When the light projecting element 11 is emitting light (Yes in S11), the comparator 311 detects the voltage of the monitor received light signal while the light projecting element 11 is projecting the pulse light and It compares with the lower limit threshold, and outputs a pulse signal as a result of the comparison (S12). The storage circuit 32 temporarily stores the result of the comparison (S13). The detection circuit 33 detects the comparison result stored in the storage circuit 32 at a clock cycle longer than the pulse width of the pulse light (S14). The determination circuit 34 counts the non-detection of the pulse signal, which is the comparison result.

When the light projecting element 11 is not projecting light (No in S11), the comparator 311 detects the voltage of the monitor received light signal while the light projecting element 11 is projecting the pulsed light as the above (2) determination of excessive pulse width. is compared with the lower limit threshold, and a pulse signal is output as a result of the comparison (S16). The storage circuit 32 temporarily stores the result of the comparison (S17). The detection circuit 33 detects the comparison result stored in the storage circuit 32 at a clock cycle longer than the pulse width of the pulse light (S18). The determination circuit 34 counts the detection of the pulse signal, which is the comparison result (S19).

The determination circuit 34 determines when it is time to switch between the upper threshold value and the lower threshold value indicated by the reference voltage (Yes in S20), and when the counted pulse signal non-detection and detection counts are not equal to or greater than a predetermined recovery (S21 No), the counted number of undetected and detected pulse signals is cleared (S22). Through the connector A, the process proceeds to the flow chart of (3) judging the excess amount of projected light in FIG.

If it is not the time to switch between the upper threshold value and the lower threshold value (No in S20), the photoelectric sensor 1 returns to step S11 and again performs (1) determination of insufficient amount of projected light and (2) determination of excessive pulse width. Abnormality monitoring such as comparison of the voltage of the received light signal with the lower limit threshold when the light projecting element 11 projects or does not project light.

If the switching timing of the upper limit threshold value and the lower limit threshold value indicated by the reference voltage is reached (Yes in S20), and if one of the counted pulse signal non-detection and detection counts is equal to or greater than a predetermined recovery, the determination circuit 34 (Yes in S21), the determination circuit 34 determines that the light projecting element 11 is abnormal (S23). When the determination circuit 34 determines that the light projecting element 11 is abnormal, the photoelectric sensor 1 terminates the failure detection operation of the light projecting element 11 .

8 via the connector A, the decision circuit 34 switches the reference voltage generated by the reference voltage circuit 40 from the lower limit threshold to the upper limit threshold (S24). . The comparator 311 compares the voltage of the monitor received light signal with the upper limit threshold value while the pulse light is projected by the light projecting element 11, and outputs a pulse signal as a result of the comparison (S25). The storage circuit 32 temporarily stores the comparison result (S26). The detection circuit 33 detects the comparison result stored in the storage circuit 32 at a clock cycle longer than the pulse width of the pulsed light (S27). The determination circuit 34 counts the detection of the pulse signal, which is the comparison result. (S28)

When it is time to switch between the upper threshold and the lower threshold indicated by the reference voltage (Yes in S29), and when the counted number of pulse signal detections is not equal to or greater than a predetermined recovery (No in S30), the determination circuit 34 The counted number of pulse signal detections is cleared (S22). Via the connector B, the flow returns to before step S10 in the flow chart of (1) judging whether the amount of projected light is insufficient and (2) judging whether the pulse width is excessive in FIG.

If it is not the time to switch between the upper threshold value and the lower threshold value (No in S29), the photoelectric sensor 1 returns to step S25 and repeats the above (3) when the light emitting element 11 emits excess light. Abnormality monitoring such as comparison between the voltage of the received light signal and the upper limit threshold is performed.

When it is time to switch between the upper threshold value and the lower threshold value indicated by the reference voltage (Yes in S29), and when the counted number of pulse signal detections is equal to or greater than a predetermined recovery (Yes in S30), the determination circuit 34 determines The circuit 34 determines that the light projecting element 11 is abnormal (S32). When the determination circuit 34 determines that the light projecting element 11 is abnormal, the photoelectric sensor 1 terminates the failure detection operation of the light projecting element 11 .

The embodiments described above are for facilitating the understanding of the present invention, and are not intended to limit and interpret the present invention. Each element included in the embodiment and its arrangement, materials, conditions, shape, size, etc. are not limited to those illustrated and can be changed as appropriate. Also, it is possible to partially replace or combine the configurations shown in different embodiments.

A part or all of this embodiment may be described in the following appendices, but is not limited to the following.

[Appendix]
a light projecting unit (10) having a light projecting element (11) for projecting pulsed light onto a detection area and generating a monitor signal according to the amount of light projected by the light projecting element;
a light receiving unit (20) for receiving the pulsed light from the detection area;
a comparison circuit (31) for comparing the monitor signal with a predetermined threshold;
a storage circuit (32) for temporarily storing the result of comparison by the comparison circuit (31);
a detection circuit (33) for detecting the comparison result stored in the storage circuit (32) at a clock cycle longer than the pulse width of the pulsed light;
a determination circuit (34) that determines an abnormality of the light projecting element (11) based on the comparison result detected by the detection circuit (33);
Photoelectric sensor (1).

DESCRIPTION OF SYMBOLS 1... Photoelectric sensor 5... Failure detection part 10... Light emitting unit 11... Light emitting element 12... Light receiving element 20... Light receiving unit 30... Control circuit 31... Comparison circuit 311... Comparator 32... Memory Circuits 321 Latch circuit 322 Logic element 33 Detection circuit 331 Synchronous FF 34 Judgment circuit 35 I/O section 351 DAC conversion section 40 Reference voltage circuit

Claims (11)

a light projecting unit having a light projecting element for projecting pulsed light onto a detection area and generating a monitor signal according to the amount of light projected by the light projecting element;
a light receiving unit that receives the pulsed light from the detection area;
a comparison circuit that compares at least one of the amplitude and pulse width of the monitor signal with a predetermined threshold set for each of the amplitude and the pulse width;
a storage circuit that temporarily stores the result of comparison by the comparison circuit;
a detection circuit that detects the comparison result stored in the storage circuit at a clock cycle longer than the pulse width of the pulsed light;
If at least one of the amplitude and pulse width of the monitor signal deviates from the predetermined threshold based on the comparison result detected by the detection circuit, the light emitting element is determined to be abnormal. having a circuit and
The comparison circuit compares the voltage value of the monitor signal with the predetermined threshold value, and outputs a pulse signal representing a magnitude relationship with respect to the predetermined threshold value as a result of the comparison,
The detection circuit detects the pulse signal stored in the storage circuit in synchronization with the clock cycle, and resets the pulse signal stored in the storage circuit upon detection.
Photoelectric sensor. a reference voltage circuit that generates a reference voltage corresponding to the predetermined threshold from the reference voltage control signal output from the determination circuit;
The comparator circuit compares the voltage of the monitor signal with the reference voltage, and outputs a pulse signal representing a magnitude relationship with respect to the reference voltage as a result of the comparison.
The photoelectric sensor according to claim 1. the reference voltage corresponds to a lower limit of the voltage of the monitor signal;
The comparator compares the voltage of the monitor signal and the reference voltage while the light projecting element projects the pulsed light,
The determination circuit counts the non-detection of the pulse signal, and determines that the light emitting element is abnormal when the counted number of non-detections is equal to or greater than a predetermined number of times.
The photoelectric sensor according to claim 2. the reference voltage corresponds to a lower limit of the voltage of the monitor signal;
The comparator compares the voltage of the monitor signal and the reference voltage while the light emitting element is not emitting pulsed light,
The determination circuit counts the detections of the pulse signal, and determines that the light projecting element is abnormal when the counted number of detections is equal to or greater than the predetermined number of times.
The photoelectric sensor according to claim 3. The comparator alternately compares the voltage of the monitor signal and the lower limit of the voltage of the monitor signal while the light is being projected and while the light is not being projected.
The photoelectric sensor according to claim 4. the reference voltage corresponds to an upper limit of the voltage of the monitor signal;
The comparator compares the voltage of the monitor signal and the reference voltage while the light projecting element projects the pulsed light,
The determination circuit counts the detections of the pulse signal, and determines that the light projecting element is abnormal when the counted number of detections is equal to or greater than a predetermined number of times.
A photoelectric sensor according to any one of claims 2 to 5. The comparison circuit, the storage circuit, the detection circuit, and the determination circuit are mounted on a single FPGA,
Photoelectric sensor according to any one of claims 2 to 6. The storage circuit is composed of a latch circuit mounted on the FPGA,
The photoelectric sensor according to claim 7. wherein the comparator consists of a differential signal receiver implemented on the FPGA;
The photoelectric sensor according to claim 8. The light projecting unit has a light receiving element that generates a light receiving signal corresponding to the amount of light projected by the light projecting element,
The monitor signal is the received light signal,
Photoelectric sensor according to any one of claims 1 to 9. The monitor signal is a signal generated according to the driving current of the light projecting element.
Photoelectric sensor according to any one of claims 1 to 9.

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