JP2017146284A - Foreign matter sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make unnecessary advance measurement of a dust-free state and restrain deterioration of foreign matter detecting sensitivity in long-time use.SOLUTION: A dust sensor device (110) is equipped with an LED (1) that emits light, a driver circuit (31) that so drives the LED (1) as to alternately turn on and off light emission, a photodiode (2) that receives reflected light resulting from reflection of light emitted from the LED (1) by a foreign matter (47), a light-on period measuring unit (22) that measures the cumulative light-on period which is the cumulative total of individual light-on periods of the LED (1), and a driving period adjusting unit (21) that so performs control as to restrain deterioration of sensitivity of foreign matter (47) detection according to the cumulative light-on period of the LED (1) as measured by the light-on period measuring unit (22).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a foreign matter sensor that reflects light emitted from a light emitting element to a foreign substance and receives the reflected light by a light receiving element.

  Conventionally, a photoelectric dust sensor device reflects light emitted from an LED (Light Emitting Diode) driven by a microcomputer or the like to a foreign substance such as dust or tobacco smoke particles, and reflects the reflected light. Is captured by the light receiving element. Further, the dust sensor device replaces the reflected light captured by the light receiving element with an electric signal, amplifies the electric signal, and outputs a pulse. Further, the dust sensor device calculates the concentration of the foreign matter by receiving the amplified electric signal and performing information processing with a microcomputer or the like. In a conventional dust sensor device, an LED is driven by a pulse having a predetermined period and a predetermined pulse width, and an output pulse from a light receiving element is read at a predetermined sampling timing to calculate the concentration of foreign matter. It is like that.

  FIG. 5 is a peripheral view of a foreign object detection region in a conventional photoelectric dust sensor device. This dust sensor device includes an LED 1 and a photodiode 2, and an internal region 3 (foreign matter detection region) is provided inside a substantially rectangular parallelepiped case 5.

  The LED 1 has a light emitting surface normal to the surface 5 of the case 5 at a predetermined angle (<90 °), and the light emitting surface faces a substantially central portion of the case 5 (two corners of the case 5). It is arranged in the vicinity of the portion where the surfaces meet.

  In addition, the normal of the light receiving surface of the photodiode 2 forms a predetermined angle (<90 °) that is substantially the same as the predetermined angle with the one surface 12 of the case 5, and the light receiving surface faces the substantially central portion of the case 5. Moreover, it arrange | positions in the corner | angular part opposite to the corner | angular part in which LED1 in case 5 is arrange | positioned.

  In addition, a dust passage hole 10 is formed in the center of each of the two surfaces of the case 5 that are arranged to face each other in the direction perpendicular to the paper surface. Foreign matter from the contamination source of foreign matter can enter the internal region 3 of the case 5 which is a foreign matter detection region through the dust passage hole 10.

  This dust sensor device calculates the concentration of foreign matter in the case 5 based on the amount of light that is emitted from the LED 1 and reflected by the foreign matter floating near the center of the case 5 and incident on the photodiode 2. It is like that.

  Next, FIG. 6 is a diagram showing a circuit configuration of the dust sensor device. As shown in the figure, the dust sensor device includes a microcomputer (hereinafter simply referred to as “microcomputer”) 30, a drive circuit 31, an LED1, a photodiode 2, a first amplifier circuit 37, a second amplifier circuit 39, and A third amplifier circuit 45 and the like are provided.

  The microcomputer 30 includes an A / D converter (analog / digital converter) 24 inside. The microcomputer 30 outputs a pulse signal to the drive circuit 31. The drive circuit 31 receives the pulse signal from the microcomputer 30 and controls the driving and stopping of the LED 1. In addition, the first amplifier circuit 37, the second amplifier circuit 39, and the third amplifier circuit 45, which form a three-stage amplifier circuit configuration, can convert a very small analog signal output from the photodiode 2 into a microcomputer. Amplification is performed until 30 can be read, and the amplified analog signal is output to the microcomputer 30. When the microcomputer 30 receives the amplified analog signal, the A / D converter 24 converts the analog signal into a digital signal, and calculates the concentration of the foreign matter based on the digital signal. Yes.

  In FIG. 6, 46 indicates a storage container, and 47 indicates foreign matter such as dust and tobacco smoke particles. In the figure, reference numeral 42 denotes a resistance, 43 denotes a capacitor, and 40 denotes a variable resistance. The resistor 42 and the capacitor 43 are arranged in series between the ground GND of the microcomputer 30 and the potential Vcc so that the capacitor 43 is on the ground GND side. In addition, each of the terminals at both ends of the capacitor 43 is connected to the drive circuit 31. The resistor 42 and the capacitor 43 have a role of adjusting the voltage applied to the drive circuit 31. The variable resistor 40 is disposed between the second amplifier circuit 39 and the ground GND, and plays a role of adjusting the magnitude of the amplified signal output to the microcomputer 30.

  Next, FIG. 7 is an operation timing chart of the dust sensor device. More specifically, this figure is a timing chart of the LED drive current pulse output from the microcomputer 30 and the output pulse output from the photodiode 2 to the microcomputer 30 via the amplifier corresponding to the LED drive current pulse. is there. In the figure, the horizontal axis indicates time, and the vertical axis indicates current and voltage.

  The waveform indicated by 81 in FIG. 7A is an input current waveform of the LED drive current, and the waveform indicated by 91 is an output voltage waveform output from the photodiode 2 and amplified and output to the microcomputer 30. . As shown in the figure, the LED drive current waveform is a pulse having a constant period T1, a pulse width PW having a constant T2, and a current amplitude A. In this dust sensor device, the LED is driven during the period when the current is in a high state (A in this case), and the LED emits light. On the other hand, the LED is turned off while the voltage is low.

  Further, as shown in FIG. 7B, the voltage waveform of the output signal gradually rises from the moment when the LED drive voltage changes from the low state to the high state and reaches a peak, and then gradually. It has a falling hill-shaped local waveform. In the voltage waveform 91 of the output signal, a hill-shaped local waveform 93 indicates a state in which no foreign object is detected, and a hill-shaped local waveform 94 indicates an example of a state in which a foreign object is detected. As can be seen from the presence of the local waveform 93, there is an output level even when there is no foreign matter such as cigarette smoke or dust, but this is emitted from the LED 1 and reflected by the wall of the case to the photodiode 2. This is due to the unnecessary light that arrives.

  As shown in the figure, the output value of the hill-shaped local waveform 94 when a foreign object is detected is larger than the output value of the hill-shaped local waveform 93 when no foreign object is detected. Foreign matter detection and foreign matter concentration calculation are performed by reading the peak value of the voltage waveform of the output signal. If only the presence / absence of a foreign object is to be detected, a threshold value for the peak value may be determined in advance, and if the threshold value is exceeded, it may be determined that a foreign object has been detected.

  In the dust sensor device having such a sensor structure, a decrease in dust detection sensitivity is a problem due to a decrease in the light emission output of the LED. If the light emission output of the LED decreases, the peak value of the voltage waveform of the output signal also decreases, so that the measurement result differs even if the amount of foreign matter is the same.

  For this reason, in the technique described in Patent Document 1, the voltage of the output signal in the initial state of the LED when there is no dust is stored and compared with the voltage of the output signal of the LED when there is no dust during measurement. By doing so, the reduction of the light emission output of the LED is corrected.

Japanese Patent Laid-Open No. 11-94741 (released on April 9, 1999)

  However, in the conventional sensitivity correction method, it is necessary to measure the dust-free state in advance, and it is difficult to realize the dust-free state in the actual usage state of the dust sensor device. is there.

  The present invention has been made in view of the above-mentioned problems, and its purpose is to make it unnecessary to measure the dust-free state in advance and to suppress a decrease in the detection sensitivity of foreign matter over a long period of use. The object is to realize a foreign matter sensor capable of

  In order to solve the above problems, a foreign matter sensor according to one embodiment of the present invention includes a light-emitting element that emits light, a driving unit that drives the light-emitting element so as to be alternately turned on and off, and the light-emitting element. A light-receiving element that receives reflected light reflected by a foreign object, and a measurement unit that measures a cumulative lighting time that is a cumulative result of each lighting time of the light-emitting element. And a control unit that performs control to suppress a decrease in the detection sensitivity of the foreign matter according to the accumulated lighting time of the light emitting element measured by the measurement unit.

  According to one embodiment of the present invention, there is an effect that it is not necessary to previously measure a dust-free state, and it is possible to suppress a decrease in detection sensitivity of a foreign object in a long-term use.

It is a circuit diagram which shows the electrical structure of the dust sensor apparatus (foreign substance sensor) which concerns on Embodiment 1 of this invention. (A) is a figure which shows an example of the operation test data of the light emitting element in actual use temperature, (b) shows an example of the drive pulse which drives a light emitting element, (c) drives a light emitting element. Another example of the driving pulse to be performed will be described. It is a circuit diagram which shows the electrical structure of the dust sensor apparatus (foreign substance sensor) which concerns on Embodiment 2 of this invention. It is a circuit diagram which shows the electrical structure of the dust sensor apparatus (foreign substance sensor) which concerns on Embodiment 4 and 5 of this invention. It is a periphery figure of the foreign material detection area | region in the conventional dust sensor device of a photoelectric system. It is a circuit diagram which shows the electrical constitution of the said conventional dust sensor apparatus. It is a timing chart regarding operation | movement of the said conventional dust sensor apparatus, (a) is a timing chart of the LED drive current pulse which the microcomputer output, (b) is from a photodiode corresponding to the said LED drive current pulse. It is a timing chart of the output pulse output to the microcomputer via the amplifier.

  The embodiment of the present invention will be described with reference to FIGS. Hereinafter, for convenience of explanation, components having the same functions as those described in the specific embodiment may be denoted by the same reference numerals and description thereof may be omitted.

Embodiment 1
FIG. 1 is a circuit diagram showing an electrical configuration of a dust sensor device (foreign matter sensor) 110 according to Embodiment 1 of the present invention. The dust sensor device 110 (also the dust sensor devices 120 and 130 described later) reflects light emitted from the LED (light emitting element) 1 to a foreign substance 47 such as dust or tobacco smoke particles, and reflects the reflected light. This is a photoelectric device that receives light by a photodiode (light receiving element) 2. Further, the dust sensor device 110 (also the dust sensor devices 120 and 130 described later) can be applied to an air cleaner or the like that automatically operates by detecting dust or tobacco smoke particles.

  Further, the dust sensor device 110 of the present embodiment includes a lighting time measurement unit (measurement unit) 22 and a driving time adjustment unit 21 in the microcomputer 30 as compared with the conventional dust sensor device shown in FIG. Is different.

(Drive circuit 31)
The drive circuit (drive unit) 31 drives the LED 1 in pulses. Specifically, the drive circuit 31 drives the LED 1 so that lighting and extinguishing are repeated alternately.

(Lighting time measuring unit 22)
The lighting time measuring unit 22 measures a lighting cumulative time that is a cumulative result of each lighting time of the LED 1.

(Microcomputer 30)
The microcomputer (control unit) 30 performs control to suppress a decrease in the detection sensitivity of the foreign matter 47 based on the correspondence relationship between the accumulated lighting time of the LED 1 and the luminance decrease rate of the LED 1. In the present embodiment, control for suppressing a decrease in the detection sensitivity of the foreign matter 47 is performed according to the accumulated lighting time of the LED 1 measured by the lighting time measuring unit 22.

(Driving time adjustment unit 21)
The microcomputer 30 includes a drive time adjustment unit 21. The drive time adjustment unit 21 increases the drive time (corresponding to the pulse width) of the LED 1 in one cycle of the pulse signal output from the microcomputer 30 (the LED 1 is turned on at least once). The reduction in the detection sensitivity is suppressed. This driving time is adjusted by the following method.

The operation time of the LED 1 has a correlation with the luminance decrease rate of the LED 1. For example, the light output (P) of the LED 1 decreases exponentially with respect to the operation time (t) and is expressed by the following equation.
P = Po × exp (−βt) (1)
Here, Po is the initial light output, β is the deterioration rate (or luminance reduction rate), t is the operating time of the LED 1, and more strictly, the lighting time of each time of the LED 1. This is the cumulative lighting time that is the cumulative result. FIG. 2A shows an example of LED operation test data at the actual use temperature (35 ° C., 450 mA).

  Since the deterioration rate (β) in the equation (1) differs depending on the material, structure, use conditions, etc. of the element, it is calculated in advance by a test in an assumed environment.

  The operation time (t) is calculated by counting the number of LED drive pulses output from the microcomputer 30 to the drive circuit 31 by the lighting time measuring unit 22. The count result of the number of LED drive pulses is held in a storage unit (not shown).

  If the above degradation rate (β) is set, the degree of degradation of the light output of the LED 1 with respect to the operating time (t) (or the degree of decrease in luminance) can be found from the equation (1). By performing adjustment by increasing the luminance of (decrease), control for suppressing a decrease in detection sensitivity is performed.

  The brightness is adjusted by widening the pulse width of the LED drive pulse and extending the LED drive time (lighting time). For example, the pulse width of the LED driving pulse in the initial state shown in (b) of FIG. 2 is expanded as shown in (c) of FIG.

(Effect of dust sensor device 110)
As described above, the dust sensor device 110 controls the reduction in the detection sensitivity of the foreign matter 47 according to the accumulated lighting time of the LED 1, thereby suppressing the reduction in the detection sensitivity of the foreign matter 47 even in long-term use. be able to. Further, the dust sensor device 110 uses a correlation (characteristics of the LED 1) between the accumulated lighting time of the LED 1 and the luminance reduction rate of the LED 1, so that the technique described in Patent Document 1 described above is used. It is not necessary to measure the dust-free state in advance. As described above, it is not necessary to measure the dust-free state in advance, and a decrease in the detection sensitivity of the foreign matter 47 can be suppressed during long-term use.

[Embodiment 2]
FIG. 3 is a circuit diagram showing an electrical configuration of the dust sensor device (foreign matter sensor) 120 according to the second embodiment of the present invention.

(Variable resistor 44)
The dust sensor device 120 of this embodiment is different from that of the first embodiment in that a variable resistor (control unit) 44 is provided.

  In the present embodiment, the microcomputer 30 and the variable resistor 44 decrease the detection sensitivity by increasing the drive current of the LED 1 driven by the drive circuit 31 according to the accumulated lighting time of the LED 1 measured by the lighting time measuring unit 22. The control which suppresses is performed.

  The drive current of the LED 1 is increased so as to correct the deterioration of the light output of the LED 1 (the degree of decrease in luminance) according to the lighting accumulated time calculated by the lighting time measuring unit 22. Specifically, the resistance value of the variable resistor 44 is made controllable from the microcomputer 30, and the LED drive current is changed so as to perform the above correction.

(Effect of dust sensor device 120)
The dust sensor device 120 increases the luminance of the LED 1 by changing the resistance value of the variable resistor 44 and increasing the drive current of the LED 1 driven by the drive circuit 31 as described above. For this reason, since the fall of the brightness | luminance of LED1 can be supplemented, the fall of the detection sensitivity of the foreign material 47 can be suppressed.

[Embodiment 3]
A functional block of the dust sensor device 110 shown in FIG. 1 can be applied to the dust sensor device (foreign matter sensor) of the present embodiment.

  In the present embodiment, the microcomputer 30 determines whether or not the peak value of the output voltage of the photodiode 2 exceeds a predetermined voltage threshold according to the accumulated lighting time of the LED 1 measured by the lighting time measuring unit 22. By reducing the voltage threshold, control is performed to suppress a decrease in the detection sensitivity of the foreign matter 47. For example, the microcomputer 30 corrects the determination level (predetermined voltage threshold) of the output voltage of the photodiode 2 in the microcomputer 30. More specifically, the peak value of the output voltage of the photodiode 2 corresponding to the deterioration degree of the light output of the LED 1 (brightness reduction rate) calculated from the accumulated lighting time of the LED 1 measured by the lighting time measuring unit 22. If it is programmed in advance that the light falls, it can be automatically corrected by measuring the accumulated lighting time.

[Embodiment 4]
FIG. 4 is a circuit diagram showing an electrical configuration of a dust sensor device (foreign matter sensor) 130 according to Embodiment 4 of the present invention.

  The dust sensor device 130 of the present embodiment is different from the above-described embodiment in that the temperature sensor 26 is provided.

(Temperature sensor 26, microcomputer 30)
The temperature sensor 26 detects the ambient temperature of the LED 1, and the microcomputer 30 corrects the luminance reduction rate of the LED 1 according to the ambient temperature detected by the temperature sensor 26, thereby Control to suppress a decrease in detection sensitivity is performed.

  The deterioration of LED1 (decrease in luminance) is proportional to the accumulated lighting time, but the speed of deterioration differs depending on the ambient temperature of LED1. Generally, the deterioration speed increases as the temperature increases. For this reason, the temperature is measured, the temperature accumulation is recorded, and the deterioration rate β of the above equation (1) is adjusted when a certain accumulation value is reached.

  For example, the deterioration rate β of the above formula (1) is calculated at environmental temperatures of 75 ° C., 80 ° C., 85 ° C., 90 ° C., and 95 ° C., and the respective deterioration rates are β 75, β 80, β 85, β 90, and β 95. deep.

  The microcomputer 30 obtains the average temperature from the accumulated temperature every lighting time 100 h, and uses β75 if the average temperature is 75 ° C. or more and less than 80 ° C., and β80 if the average temperature is 80 ° C. or more and less than 85 ° C. Review (correct) the deterioration rate using. The average temperature is obtained by dividing the accumulated measurement temperature by the measurement time.

  If the average temperature is 85 ° C or more and less than 90 ° C, β85 is used. If the average temperature is 90 ° C or more and less than 95 ° C, β90 is used, and the average temperature is 95 ° C or more and less than 100 ° C. For example, β95 is used and the deterioration rate is reviewed (corrected). As a result, correction (detection sensitivity suppression processing) suitable for the environment in which it is actually used is possible, and correction accuracy (detection sensitivity suppression processing accuracy) is improved.

[Embodiment 5]
FIG. 4 is a circuit diagram showing an electrical configuration of a dust sensor device (foreign matter sensor) 130 according to Embodiment 5 of the present invention.

  The dust sensor device 130 of the present embodiment is different from the above-described embodiment in that it includes a surge current detection circuit (surge current detection unit) 25.

(Surge current detection circuit 25, drive time adjustment unit 21)
The surge current detection circuit 25 detects a strong surge current exceeding a predetermined current threshold value that enters the drive circuit 31, and the drive time adjustment unit 21 of the microcomputer 30 responds to the time when the detected strong surge current flows. The control for suppressing the decrease in the detection sensitivity of the foreign matter 47 is performed by lengthening the cumulative lighting time that is the cumulative result of the lighting time of the LED 1.

  The deterioration of LED 1 (decrease in luminance) is proportional to the accumulated lighting time, but the deterioration progresses due to a surge current that enters the drive circuit 31. For this reason, when a surge current is detected and a surge current with a certain level or more is detected, the lighting accumulated time of the LED 1 is adjusted.

  The surge current detection circuit 25 is a circuit that is activated when a current (or a strong surge current exceeding a predetermined current threshold) flows by a voltage higher than a set voltage that is higher than the circuit power supply of the LED 1. The drive time adjustment unit 21 performs correction for adding B seconds to the accumulated lighting time every time the surge current flows for A seconds. The relationship between the surge current and the additional correction time is calculated in advance by an acceleration test or the like.

[Summary]
The foreign matter sensor according to aspect 1 of the present invention includes a light emitting element (LED1) that emits light, a driving unit (driving circuit 31) that drives the light emitting element so as to be alternately turned on and off, and the light emitting element. A light-receiving element (photodiode 2) that receives the reflected light reflected by the foreign matter, and a foreign matter sensor (dust sensor devices 110 to 130) having a lighting time of each time of the light-emitting element. A measurement unit (lighting time measurement unit 22) that measures the accumulated lighting time as a cumulative result, and a control that suppresses a decrease in the detection sensitivity of the foreign matter according to the accumulated lighting time of the light emitting element measured by the measurement unit. And a control unit (a microcomputer 30 and a variable resistor 44).

  The accumulated lighting time of the light emitting element has a correlation with the luminance reduction rate of the light emitting element. For this reason, as in the above-described configuration, by performing control that suppresses the decrease in foreign matter detection sensitivity according to the accumulated lighting time of the light emitting elements, the decrease in foreign matter detection sensitivity can be suppressed even in long-term use. . In addition, since the above configuration uses the correlation (light emitting element characteristics) between the accumulated lighting time of the light emitting element and the luminance decrease rate of the light emitting element, as in the technique described in Patent Document 1, It is not necessary to measure the dust-free state in advance. As described above, it is not necessary to measure the dust-free state in advance, and it is possible to suppress a decrease in the detection sensitivity of foreign matters in long-term use.

  The foreign matter sensor according to aspect 2 of the present invention is the foreign matter sensor according to aspect 1, wherein the control unit detects the foreign matter sensor based on a correspondence relationship between the accumulated lighting time of the light emitting element and the luminance decrease rate of the light emitting element. It is preferable to perform control that suppresses a decrease in sensitivity. According to the above configuration, it is not necessary to measure the dust-free state in advance, and a decrease in foreign matter detection sensitivity can be suppressed in long-term use.

  The foreign matter sensor according to aspect 3 of the present invention is the above-described aspect 1 or 2, wherein the control unit is configured to control at least one of the light emitting elements by the driving unit in accordance with the accumulated lighting time of the light emitting element measured by the measurement unit. You may perform control which suppresses the fall of the said detection sensitivity by lengthening lighting time of 1 time.

  According to the said structure, the brightness | luminance of a light emitting element can be improved by lengthening at least 1 time of lighting of the said light emitting element by a drive part. For this reason, since the fall of the brightness | luminance of a light emitting element can be supplemented, the fall of the detection sensitivity of a foreign material can be suppressed.

  In the foreign matter sensor according to aspect 4 of the present invention, in the aspect 1 or 2, the control unit is configured to control the light emitting element driven by the driving unit according to the accumulated lighting time of the light emitting element measured by the measuring unit. You may perform control which suppresses the said detection sensitivity fall by enlarging drive current.

  According to the above configuration, the luminance of the light emitting element can be improved by increasing the drive current of the light emitting element driven by the driving unit. For this reason, since the fall of the brightness | luminance of a light emitting element can be supplemented, the fall of the detection sensitivity of a foreign material can be suppressed.

  The foreign matter sensor according to aspect 5 of the present invention is the foreign matter sensor according to aspect 1 or 2, wherein the control unit has a peak value of the output voltage of the light receiving element according to the accumulated lighting time of the light emitting element measured by the measuring unit. You may perform control which suppresses the said detection sensitivity fall by making the said voltage threshold value in the case of determining whether it exceeds a predetermined voltage threshold value small.

  According to the above configuration, a decrease in the detection sensitivity of the light receiving element can be suppressed by reducing the voltage threshold when determining whether or not the peak value of the output voltage of the light receiving element exceeds the predetermined voltage threshold.

  A foreign matter sensor according to aspect 6 of the present invention includes the temperature sensor that detects the ambient temperature of the light emitting element in the aspect 2, and the control unit emits the light according to the ambient temperature detected by the temperature sensor. Control for suppressing the decrease in the detection sensitivity may be performed by correcting the decrease rate of the luminance of the element.

  According to the above configuration, it is possible to perform detection sensitivity suppression processing in accordance with the environment actually used, and it is possible to improve the accuracy of detection sensitivity suppression processing.

  A foreign matter sensor according to aspect 7 of the present invention includes a surge current detection unit that detects a strong surge current that exceeds a predetermined current threshold value that enters the driving unit in any one of the above aspects 1 to 6, and the control unit includes: Depending on the detected time during which the strong surge current flows, control for suppressing a decrease in the detection sensitivity may be performed by lengthening the accumulated lighting time.

  The decrease in luminance of the light emitting element is proportional to the cumulative lighting time, but the decrease in luminance proceeds due to the surge current that enters the drive unit. Therefore, in the above configuration, it is possible to suppress a decrease in detection sensitivity of the foreign matter by lengthening the cumulative lighting time of the light emitting element according to the time when the detected strong surge current flows.

[Another expression of the present invention]
The present invention can also be expressed as follows. That is, the dust sensor according to one aspect of the present invention is a photoelectric dust sensor that reflects light from a light emitting diode to dust or smoke particles and receives the reflected light by a light receiving element. There may be provided means for correcting a detection error with respect to a decrease in luminance of the light emitting diode.

  In addition to the above structure, the dust sensor according to one embodiment of the present invention is configured such that the light emitting diode is lit by pulse driving, the lighting cumulative time is performed by counting the pulses, and the correction is performed by the light emission. It may be performed by adjusting the lighting time of the diode.

  In addition to the above structure, the dust sensor according to one embodiment of the present invention is configured such that the light emitting diode is lit by pulse driving, the lighting cumulative time is performed by counting the pulses, and the correction is performed by the light emission. This may be done by adjusting the drive current of the diode.

  In addition to the above structure, the dust sensor according to one embodiment of the present invention is configured such that the light emitting diode is lit by pulse driving, the lighting cumulative time is performed by counting the pulses, and the correction is performed by the light receiving. It may be performed by adjusting the output voltage of the element.

  A dust sensor according to an aspect of the present invention includes, in addition to the above configuration, a sensor that measures the ambient temperature of the light-emitting diode and a cumulative temperature recording device, and the correction is adjusted by the cumulative recording of the temperature. May be.

[Additional Notes]
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

1 LED (light emitting element)
2 Photodiode (light receiving element)
22 Lighting time measurement unit (measurement unit)
25 Surge current detection circuit (surge current detector)
26 Temperature sensor 30 Microcomputer (control unit)
31 Drive circuit (drive unit)
44 Variable resistance (control unit)
110-130 Dust sensor device (foreign matter sensor)

Claims (7)

A light emitting element that emits light;
A drive unit that drives the light emitting element so that lighting and extinction are alternately repeated;
A light-receiving element that receives the reflected light reflected by the foreign matter, and the light emitted from the light-emitting element,
A measuring unit for measuring a cumulative lighting time that is a cumulative result of each lighting time of the light emitting element;
A foreign matter sensor comprising: a control portion that performs control to suppress a reduction in foreign matter detection sensitivity according to the accumulated lighting time of the light emitting element measured by the measurement portion.   The said control part performs control which suppresses the fall of the detection sensitivity of the said foreign material sensor based on the correspondence of the lighting lighting time of the said light emitting element, and the decreasing rate of the brightness | luminance of the said light emitting element. 1. The foreign matter sensor according to 1.   The control unit suppresses a decrease in the detection sensitivity by extending at least one lighting time of the light emitting element by the driving unit according to the lighting accumulated time of the light emitting element measured by the measuring unit. The foreign matter sensor according to claim 1, wherein control is performed.   The control unit performs control to suppress a decrease in the detection sensitivity by increasing a driving current of the light emitting element driven by the driving unit in accordance with an accumulated lighting time of the light emitting element measured by the measuring unit. The foreign matter sensor according to claim 1, wherein the foreign matter sensor is performed.   The control unit reduces the voltage threshold when determining whether the peak value of the output voltage of the light receiving element exceeds a predetermined voltage threshold according to the accumulated lighting time of the light emitting element measured by the measuring unit. The foreign matter sensor according to claim 1, wherein control for suppressing a decrease in the detection sensitivity is performed. A temperature sensor for detecting the ambient temperature of the light emitting element;
The said control part performs control which suppresses the said detection sensitivity fall by correcting the fall rate of the brightness | luminance of the said light emitting element according to the ambient temperature detected by the said temperature sensor. 2. The foreign matter sensor according to 2. A surge current detection unit that detects a strong surge current exceeding a predetermined current threshold value that enters the drive unit,
The said control part performs control which suppresses the said detection sensitivity fall by lengthening the said lighting accumulation time according to the time when the detected said strong surge current flowed. 6. The foreign matter sensor according to any one of 6 to 6.

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