JP2007303887A - Raindrop detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect information on raindrops accurately, even when the ambient light is strong, while suppressing size enlargement or cost increase, in a raindrop detection device for detecting optically information on the raindrops. <P>SOLUTION: An input terminal of an operational amplifier 6 is connected to the input terminal side of an amplifying circuit 7. A transistor 12 is connected to a resistance element 13 in parallel. The output terminal of the operational amplifier 6 is connected to the base terminal of the transistor 12 via a switching element 10. A capacitor 15 for charging the output voltage of the operational amplifier 6 is provided between the switching element 10 and the transistor 12. When a light-reception current is increased, and thereby a voltage inputted into the amplifying circuit 7 becomes higher than the reference voltage generated from a voltage source 14, a part of the light-reception current flows into the transistor 12. When an LED 3 is allowed to emit light, a CPU 9 opens the switching element 10. In the transistor 12, the same current flows, before and after light is made to emit from the LED 3 by the voltage charged in the capacitor 15. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a raindrop detection device that detects information related to raindrops such as whether or not it is raining or the amount of raindrops, which is used, for example, for wiper control of automobiles.

  Conventionally, as a raindrop detection device, for example, a device applied to an automatic wiper control device for an automobile is known (Patent Documents 1 to 4). These raindrop detection devices described in Patent Documents 1 to 4 optically obtain information on raindrops. The figure shown in FIG. 5 has shown the raindrop detection apparatus of patent document 1. FIG. As shown in the figure, the raindrop detection apparatus includes a light emitting element 30 that emits light when an electric current is passed, and a light receiving element 40 that receives light to generate a current. The light emitting element 30 is installed so as to emit light toward the window glass, and the light receiving element 40 is installed at a position where the light emitted from the light emitting element 30 is reflected by the window glass and can receive the reflected light. Yes.

  And when detecting the information regarding raindrops, the drive part 80 is driven based on the instruction signal from CPU70, and an electric current is sent through the light emitting element 30. FIG. Thus, light is emitted from the light emitting element 30 toward the window glass, and the light reflected by the window glass is detected as an electric current by the light receiving element 40 through an optical system including a prism or the like. Since this current is a minute current, it is converted into a voltage by the resistance element 90, and the voltage is amplified by the amplifier circuit 50. Next, an AC amplifier circuit (not shown) removes a voltage corresponding to ambient light, and amplifies only a voltage corresponding to reflected light from the light emitting element 30. Thereafter, the CPU 70 takes in the current value by performing AD conversion.

  Here, when light is emitted from the light emitting element 30, the light receiving current when it rains increases because the ratio of the light emitted from the light emitting element 30 being transmitted by rain at the window interface increases. Smaller than when not. Therefore, it is possible to determine whether or not it is raining by storing in advance the light receiving current when it is not raining. Even when it is raining, the ratio at which the light emitted from the light emitting element 30 is reflected by the window varies depending on the amount of raindrops. Therefore, the current for the light received by the light receiving element 40 varies depending on the amount of raindrops. As a result, the raindrop detection device can also detect the amount of raindrops. Therefore, the wiper automatic control device can automatically drive the wiper when it rains, or can change the intermittent time and speed of the wiper according to the amount of raindrops. In the raindrop detection device of Patent Document 1, an AC amplifier circuit is not shown.

The raindrop detection device described in Patent Document 2 is a special optical filter that suppresses reception of ambient light and transmits only reflected light with respect to light emitted from the light emitting element, and houses the light receiving element.
JP 2002-267598 A JP 2000-28753 A

  As described above, the current corresponding to the light received by the light receiving element 40 must be amplified by the amplifier circuit 50. However, the amplification circuit 50 has an amplifiable range, and when the input voltage becomes equal to or higher than the operation voltage of the amplification circuit, the output voltage is saturated. In this case, the raindrop amount cannot be detected accurately.

  As a means for solving this, it is conceivable to reduce the voltage input to the amplifier circuit 50 by reducing the value of the resistance element 90. However, in this case, since the minute voltage is further reduced, it is necessary to increase the amplification factor of the amplifier circuit 50 and the AC amplifier circuit 60. However, if the amplification factor is increased, it is erroneously detected as information on raindrops due to noise or the like. It may cause

  Further, as in Patent Document 2, a method of housing the light receiving element with a special optical filter is also conceivable. However, the installation of the special optical filter increases the size of the raindrop detection device and increases the cost.

  The present invention has been made in view of the above problems, and provides a raindrop detection device capable of accurately detecting information on raindrops even when ambient light is strong while suppressing an increase in size and cost. For the purpose.

  In order to achieve the above object, a raindrop detection device according to claim 1 is a light emitting element that emits light from the back surface side to the front surface side of a light transmission member on which raindrops adhere to the surface, and instructs the light emitting element to emit light. Of the light emitted from the light emitting instruction unit and the light emitting element, the reflected light reflected from the surface of the light transmitting member toward the back side of the light transmitting member is received, and a current corresponding to the amount of light received is generated. A light receiving element that is connected in series with the light receiving element and generates a voltage corresponding to a current generated by the light receiving element, and an amplifiable voltage is limited to a predetermined voltage. A first amplifying circuit for inputting and amplifying the voltage generated by the first resistance element; and the light transmission of light from the light emitting element among the voltages amplified by the first amplifying circuit. Electricity based on the reception of reflected light on the surface of the member In the raindrop detection apparatus comprising: a second amplification circuit that takes out the voltage and amplifies the voltage; and a raindrop detection means that detects information about raindrops based on the amplification voltage of the second amplification circuit. An output circuit that outputs a voltage signal corresponding to the difference between the input voltage to the amplifier circuit and a predetermined reference voltage, and connected in parallel with the first resistance element, according to the voltage signal output by the output circuit A current control element that limits the input voltage of the first amplifier circuit to a voltage corresponding to the reference voltage by flowing a current so as to bypass the first resistance element; and a voltage output by the output circuit A connection between the output circuit and the holding circuit so that the current control element is driven by a voltage signal held in the holding circuit while the light emitting element emits light; Characterized in that a blocking circuit for disconnection.

  According to this, when the current generated in the light receiving element increases due to the strong ambient light, the current generated in the light receiving element is maintained so that the voltage input to the first amplifier circuit is maintained at the reference voltage. A part of the current flows through the current control element (control at this time is called feedback control). Thereafter, when the light emitting element is used to emit light, the feedback control is stopped by the cutoff circuit. Without this cancellation, the voltage input to the first amplifier circuit does not change before and after the light emitting element emits light, and corresponds to the voltage corresponding to the ambient light and the light emitted from the light emitting element. This is because the voltage cannot be distinguished.

  Even when the feedback control is stopped, the current flowing through the current control element is held at the same value as before the stop by the holding circuit. As a result, as the voltage input to the first amplifier circuit, a voltage obtained by instantaneously adding the voltage controlled before the light emission and the voltage generated by the light emission is input. Therefore, by setting the reference voltage controlled before the light emission to an appropriate value, the added voltage can be within the amplifiable range of the first amplifier circuit. Thereby, even if ambient light is strong, the information regarding raindrops can be detected.

  In addition, since a special optical filter or the like for suppressing ambient light is not used, an increase in size and cost can be suppressed.

  Further, in this raindrop detection device, in order to control the voltage input to the first amplifier circuit, a part of the current generated in the light receiving element is passed through the current control element. That is, the voltage input to the first amplifier circuit is controlled by the current. Thus, even when the light receiving current is large (when the ambient light is strong or when the light emitted from the light emitting element is strong), information on raindrops can be detected without being restricted by the power supply voltage. .

  3. The raindrop detection apparatus according to claim 2, wherein the output circuit has one of a non-inverting input terminal and an inverting input terminal connected to an input terminal of the first amplifier circuit, and the other connected to a voltage source that generates the reference voltage. The output terminal is composed of an operational amplifier connected to the current control element. By using an operational amplifier, an output circuit that operates as claimed in claim 1 can be easily constructed.

  4. The raindrop detection apparatus according to claim 3, wherein the current control element stops bypassing the current when a voltage input to the first amplifier circuit is smaller than the reference voltage. According to this, when the voltage input to the first amplifier circuit is equal to or lower than the reference voltage, no current flows through the current control element. In this case, information on raindrops is detected by a method similar to that of a conventional raindrop detection device.

  5. The raindrop detection apparatus according to claim 4, wherein the current control element is a transistor, and the output circuit and the holding circuit are connected to a base terminal of the transistor. According to this, when the output circuit and the holding circuit are not interrupted, the current flowing through the transistor is controlled by the voltage signal output from the output circuit. On the other hand, when the output circuit and the holding circuit are cut off, although the feedback control is solved, the same current as before the cutoff flows through the transistor by the voltage signal held in the holding circuit. As described above, when the transistor is used, the current control having the functions of the first and third aspects can be easily constructed.

  6. The raindrop detection apparatus according to claim 5, wherein the blocking circuit includes a switching element that conducts / cuts off and a switching instruction unit that instructs the switching element to conduct or block, and the switching element is the output circuit. And the holding circuit. According to this, the said feedback control can be stopped by interrupting | blocking a switching element.

  7. The raindrop detection device according to claim 6, wherein the holding circuit is a capacitor. Thus, the output voltage signal of the output circuit can be held by using the capacitor.

  The raindrop detection apparatus according to claim 7, wherein the interruption circuit receives a second resistance element connected to the current control element and a terminal voltage of the second resistance element to one of two input terminals, On the other hand, the operational amplifier is connected so that the voltage held in the holding circuit is inputted, and the output terminal is connected to a terminal for controlling the current flowing in the current control element, and by the cutoff circuit, When the connection between the output circuit and the holding circuit is cut off, the discharge of the voltage signal held in the holding circuit is made insensitive.

  Thereby, the discharge by a capacitor | condenser can be blunted. As a result, fluctuations in the current value flowing through the current control element before and after light emission can be kept low. The second resistance element is used as a reference voltage for the second operational amplifier. However, the value of the current flowing through the current control element is limited by connecting the second resistance element to the current control element.

  Hereinafter, embodiments of a raindrop detection apparatus according to the present invention will be described in detail with reference to the drawings. The raindrop detection device 100 of this embodiment is used for automatic control of a wiper of an automobile. FIG. 1 is a schematic configuration diagram showing a cross section of the raindrop detection device 100 when the raindrop detection device 100 is installed on the vehicle interior side of the vehicle front window, and FIG. 2 is a schematic configuration diagram showing an electric circuit portion of the raindrop detection device 100.

  As shown in FIG. 1, the raindrop detection device 100 is attached to a portion on the front window shield 2 of the vehicle that does not obstruct the driver's view on the vehicle interior side, for example, using a transparent adhesive that transmits light. . The raindrop detection device 100 can optically detect the state (presence / absence and amount of raindrops) of the raindrop X, and emits incident light according to a drive signal from the CPU 9 (shown in FIG. 2) (hereinafter referred to as a light emitting element 3). A light receiving element 4 (hereinafter simply referred to as a PD (photodiode)) that receives reflected light that is dimmed according to the amount of raindrops X attached thereto and generates a current according to the amount of light received by the reflected light. ), The state of raindrop X (presence / absence) attached to the front window shield 2 which is a raindrop adhesion object by controlling an input / output signal to the optical system including the prism 5 and the like for guiding incident light and reflected light And an electric circuit for determining the amount of raindrops).

  When detecting information related to raindrops, the transistor 11 (shown in FIG. 2) is driven based on an instruction signal from the CPU 9 to cause a current to flow through the light emitting element 3. As a result, light is emitted from the light emitting element 3 toward the window glass, and the light reflected by the window glass is detected as a current by the light receiving element 4 through an optical system including a prism or the like. Since this current is a minute current, it is converted into a voltage by the resistance element 13 (shown in FIG. 2), and the voltage is amplified by the amplifier circuit 7 (shown in FIG. 2). Next, the AC amplifier circuit 8 (shown in FIG. 2) amplifies only the voltage corresponding to the reflected light from the light emitting element 3 except for the voltage corresponding to the ambient light using, for example, a high-pass filter. Thereafter, the CPU 9 (shown in FIG. 2) takes in this current value after AD conversion.

  Here, when light is emitted from the light emitting element 3, the light reception current when it rains increases because the ratio of the light emitted from the light emitting element 3 being transmitted by rain at the window interface increases. Smaller than when not. Therefore, it is possible to determine whether or not it is raining by storing in advance the light receiving current when it is not raining. Even when it is raining, the ratio at which the light emitted from the light emitting element 3 is reflected by the window varies depending on the amount of raindrops. Therefore, the current for the light received by the light receiving element 4 varies depending on the amount of raindrops. As a result, the raindrop detection apparatus 100 can also detect the amount of raindrops.

  Next, the configuration of the electric circuit portion of the raindrop detection device 100 (hereinafter simply referred to as the raindrop detection device) will be described with reference to FIG. A raindrop detection apparatus 100 shown in FIG. 2 includes an LED 3, a PD 4, an operational amplifier 6, an amplification circuit 7, an AC amplification circuit 8, a CPU 9, a switching element 10, transistors 11 and 12, a resistance element 13, a voltage source 14, and a capacitor 15. The

  The CPU 9 sends a drive signal to the base terminal of the transistor 11 to turn on the transistor 11 when the LED 3 emits light by causing a current to flow (hereinafter, this time interval is referred to as a detection interval). Thus, a current flows through the LED 3 due to a voltage from the voltage source Vc (for example, 5 V), and light corresponding to the amount of the current is emitted from the LED 3.

  Further, the CPU 9 opens the switching element 10 or makes it conductive. Specifically, when light is not emitted from the LED 3 (hereinafter, the time interval at this time is referred to as a non-detection interval), a signal instructing conduction is transmitted to the switching element 10 to drive the switching element 10 to be in a conduction state. To. On the other hand, in the detection period, the transmission of the signal transmitted to the switching element 10 is canceled. As a result, the switching element 10 is opened. For example, a bipolar transistor or a field effect transistor can be used as the switching element 10.

  Further, the CPU 9 performs AD conversion on the signal transmitted from the AC amplifier circuit 8 in synchronization with the light emission, and determines the presence / absence of raindrops and calculates the amount of raindrops based on the converted signals. When the CPU 9 determines that there are raindrops and calculates the amount of raindrops, the CPU 9 transmits a signal for instructing wiper drive, intermittent time, and drive speed to a wiper controller (not shown).

  A signal transmitted from the AC amplifier circuit 8 in the absence of raindrops is stored in advance in a storage device (not shown). Thereby, CPU9 can determine the presence or absence of a raindrop with reference to the signal in the state without the raindrop. Further, the correspondence relationship between the magnitude of the signal transmitted from the AC amplifier circuit 8 and the raindrop amount is measured in advance, and the correspondence relationship is stored in a storage device (not shown). Thereby, CPU9 can calculate the amount of raindrops based on the correspondence.

  The PD 4 receives light from the LED 3 and ambient light, and generates a light receiving current corresponding to the amount of light received. Therefore, the stronger the ambient light is, the more light is received and the light receiving current is increased. In the detection section, the PD 4 also receives the light reflected by the window glass as well as the ambient light. On the other hand, in the non-detection section, the PD 4 receives only ambient light.

  The resistance element 13 converts the received light current into a voltage. The voltage is input to the amplifier circuit 7. The amplifier circuit 7 is a circuit that amplifies an input voltage, and for example, a circuit described in Patent Document 1 is used. Since the voltage corresponding to the received light current is very small, this amplifier circuit 7 is used. Further, the amplifier circuit 7 has a characteristic that it cannot be amplified beyond the operating voltage for driving itself, and is saturated. Therefore, when the ambient light becomes strong and the received light current increases, the output voltage of the amplifier circuit 7 may be saturated. Note that a voltage obtained by adding the voltage corresponding to the light emitted from the LED 3 and the voltage corresponding to the ambient light is output to the output terminal of the amplifier circuit 7 in the detection section. Therefore, when the conventional raindrop detection device has a large light receiving current, there is a case where the threshold voltage that can be amplified by the amplifier circuit 7 is exceeded in the detection section. As a result, since a constant saturation voltage is output as the output voltage of the amplifier circuit 7, the voltage corresponding to the light emitted from the original LED 3 cannot be accurately amplified. Therefore, there is a problem that information on raindrops cannot be detected accurately. Needless to say, only the voltage corresponding to the ambient light is amplified and output to the output terminal of the amplifier circuit 7 in the non-detection section.

  The AC amplifier circuit 8 receives the output voltage of the amplifier circuit 7 at its input terminal. Then, the AC amplifier circuit 8 removes the voltage corresponding to the ambient light from the output voltage of the amplifier circuit 7 by, for example, a high-pass filter, amplifies only the voltage corresponding to the light emitted from the LED 3, and the amplified voltage Is output. In the conventional raindrop detection device, for example, the output voltage of the AC amplifier circuit 7 may become zero even though the LED 3 emits light and the reflected light is received by the PD 4. This is because when the ambient light is strong, all the voltages corresponding to the LEDs 3 may reach the saturation voltage when output from the amplifier circuit 6.

  The operational amplifier 6 monitors the voltage input to the amplifier circuit 7 and outputs a voltage corresponding to the voltage. Specifically, the non-inverting input terminal of the operational amplifier 6 is connected to the input terminal of the amplifier circuit 7, and the inverting input terminal is connected to the voltage source 14. The voltage source 14 generates a voltage such that the voltage input to the amplifier circuit 7 is equal to or lower than a threshold voltage that can be amplified by the amplifier circuit 7 in the detection period. The output terminal of the operational amplifier 6 is connected to the switching element 10.

  The capacitor 15 is charged with the output voltage of the operational amplifier 6 when the switching element 10 is conductive. Therefore, the capacitor 15 has a capacity that can charge the output voltage of the operational amplifier 6. If a capacitor 15 having an excessively large capacity is used, charging and discharging cannot be performed quickly in a situation where the amount of ambient light frequently changes, and the output voltage of the operational amplifier 6 cannot be quickly charged.

  The transistor 12 is for flowing a part of the light receiving current in order to lower the voltage input to the amplifier circuit 7 to the reference voltage when the voltage input to the amplifier circuit 7 becomes larger than the reference voltage. is there. The base terminal of the transistor 12 is connected to the output terminal of the operational amplifier 6 through the switching element 10, the collector terminal is connected between the PD 4 and the resistance element 13, and the emitter terminal is connected to the ground line. . The transistor 12 is an NPN bipolar transistor. Therefore, a current flows through the transistor 12 when the base-emitter voltage is positive. Therefore, when the switching element 10 is conductive, the transistor 12 is driven when the output voltage of the operational amplifier 6 is positive, that is, when the voltage input to the amplifier circuit 6 is larger than the reference voltage. As a result, a part of the received light current flows into the transistor 12. When the switching element 10 is open, the transistor 12 is driven by the voltage charged in the capacitor 15. As a result, the same current that flows when the switching element 10 is conducted flows through the transistor 12. That is, the current flowing in the transistor 12 is the same before and after the switching element 10 is turned on and off. However, since the voltage charged in the capacitor 15 is discharged when the transistor 12 is driven by the voltage charged in the capacitor 15, strictly speaking, before and after the conduction and release of the switching element 10. Thus, the current flowing through the transistor 12 cannot be said to be the same. However, since the detection period is usually short, it can be said that the change in the value of the current flowing through the transistor 12 due to the charging of the capacitor 15 is very small.

  Next, the operation of this electric circuit will be described by dividing it into a non-detection section and a detection section using the time chart of FIG. The time chart of FIG. 3 shows the case where there is no ambient light, the case where the ambient light is weak, and the case where the ambient light is strong. For convenience of explanation, the case where there is no ambient light refers to the case where the light receiving current is zero in the non-detection section, and the case where the ambient light is weak refers to the case where the light reception current is less than 3 mA in the non-detection section. The case where the ambient light is strong means a case where the light receiving current is larger than 3 mA in the non-detection section. Further, it is assumed that the voltage source 14 generates a voltage of 3V, the resistance element 13 is 1 kΩ, and the threshold voltage that can be amplified by the amplifier circuit 7 is 4V.

  First, in the non-detection section (light emission current = 0), the magnitude of the light reception current (FIG. 3B) and the potentials of the terminals A to D (FIGS. 3C to 3F) for each ambient light. ), The state of the output voltage (FIG. 3G) of the AC amplifier circuit 8 will be described. FIG. 3A is a time chart showing the state of the light emission current.

  As shown in FIG. 4B, the light receiving current generated in the PD 4 increases as the ambient light increases. Further, as shown in FIG. 5C, in the non-detection period, a positive signal is continuously transmitted to the terminal A (the input terminal of the switching element 10), and as a result, the switching element 10 is in a conductive state. This is because the capacitor 15 is charged with the positive voltage output from the operational amplifier 6 when the voltage input to the amplifier circuit 6 becomes larger than the reference voltage.

  As shown in FIG. 6D, the potential at the terminal B (the output voltage of the operational amplifier 6 or the voltage charged in the capacitor 15) is negative or zero when there is no ambient light and the ambient light is weak. This is because when the light receiving current is smaller than 3 mA, the voltage input to the amplifier circuit 7 becomes smaller than 3 V (because the resistance element 13 is 1 kΩ), and the output voltage of the operational amplifier 6 becomes negative or zero. is there. On the other hand, in the case of strong ambient light, the voltage input to the amplifier circuit 7 is greater than 3V, and the output voltage of the operational amplifier 6 is positive. The transistor 12 may or may not be driven according to the potential of the terminal B.

  Further, as shown in FIG. 5E, the potential at the terminal C increases as the ambient light becomes stronger. However, in the case of strong ambient light (light reception current> 3 mA), since the potential of the terminal B is positive as described above, a part of the light reception current is driven so that the transistor 12 is driven and the terminal C becomes 3V. Flows into the transistor 12. For example, if the light receiving current is 10 mA, 7 mA flows through the transistor 12 (because the resistance element 13 = 1 kΩ). That is, in the case of strong ambient light, the potential of the terminal C is controlled to 3V regardless of the magnitude of the received light current. On the other hand, when the ambient light is weak, the transistor 12 is not driven, so that a voltage obtained by purely converting the received light current by the resistance element 13 is output to the terminal C.

  As a result, as shown in FIG. 5F, the potential of the terminal D (the output voltage of the amplifier circuit 7) also increases as the ambient light becomes stronger. Also in this case, when the ambient light intensity is high (light reception current> 3 mA), the voltage becomes a constant voltage equal to or lower than the output voltage when the amplifier circuit 7 is saturated, regardless of the magnitude of the light reception current.

  In the non-detection section, no light is emitted from the LED 3, so there is no reflected light. Therefore, the output voltage of the AC amplifier circuit 8 is zero as shown in FIG.

  Next, in the detection section (light emission current ≠ 0), the magnitude of the light reception current (FIG. 3B) and the potentials at the terminals A to D (FIGS. 3C to 3F) for each ambient light. The state of the output voltage (FIG. 3G) of the AC amplifier circuit 8 will be described. It is assumed that the magnitude of the received light current immediately before the LED 3 emits light, the potentials at the terminals A to D, and the output voltage of the AC amplifier circuit 8 are in the state shown in FIG.

  As shown in FIG. 5A, when a certain light emission current flows, the light emitted from the LED 3 is reflected by the front window, and the PD 4 receives the reflected light. As a result, as shown in FIG. 5B, the light receiving current is a value obtained by adding the current due to the ambient light and the current corresponding to the light emitted from the LED 3.

  Further, as shown in FIG. 3C, in the detection section, the CPU 9 transmits a negative or zero signal to the terminal A to open the switching element 10. Therefore, the transistor 12 is disconnected from the output terminal of the operational amplifier 6. However, even in this case, the capacitor 15 is charged with the output voltage of the operational amplifier 6 immediately before the switching element 10 is opened. Therefore, the transistor 12 is continuously driven by this charging voltage, and the current flowing in the transistor 12 immediately before the switching element 10 is opened is held. Therefore, as shown in FIG. 4D, the voltage at the terminal B does not change between the detection interval and the non-detection interval. Note that when the ambient light is zero or weak, the voltage is not charged in the capacitor 15, so the transistor 12 is not driven.

  Note that the switching element 10 is opened in the detection section. If the ambient light is strong unless it is opened, the voltage input to the amplifier circuit 7 is controlled to the reference voltage, and the non-detection section and the detection section This is because the voltage input to the amplifier circuit 7 does not change. That is, the voltage corresponding to the LED 3 cannot be detected.

  As shown in FIG. 5E, the potential at the terminal C is a potential obtained by adding the potential corresponding to the LED 3 to the potential in the non-detection section. As described in the description of the non-detection section, when the ambient light intensity is high (light reception current> 3 mA), the voltage is equal to or lower than the threshold voltage that can be amplified by the amplifier circuit 7 regardless of the magnitude of the light reception current. For example, if the light receiving current corresponding to the LED 3 in the state where there is no raindrop is 1 mA, that in the state where there is a raindrop is less than 1 mA. For this reason, the potential of the terminal C with respect to the intensity of ambient light is equal to or lower than the threshold voltage (4 V) that can be amplified by the amplifier circuit 7 (because the resistance element is 1 kΩ).

  Therefore, as shown in FIG. 5F, the potential at the terminal D (the output voltage of the amplifier circuit 6) does not reach the saturation voltage of the amplifier circuit. For this reason, as shown in FIG. 5G, the output terminal of the AC amplifier circuit 8 corresponds to the light emission of the LED 3 even in the case of strong ambient light, as in the case of no ambient light and weak ambient light. Voltage is output. Thus, the CPU 9 can detect the presence / absence of raindrops and the amount of raindrops even in the case of strong ambient light.

  After that, the CPU 9 transmits a signal for instructing a wiper control device (not shown) to drive the wiper, the intermittent time, and the driving speed.

  As described above, when the voltage input to the amplification circuit 7 is smaller than the reference voltage, the raindrop detection apparatus 100 according to the present embodiment converts the received light current into the voltage as it is and amplifies it by the amplification circuit 7. On the other hand, when the ambient light becomes strong and the light receiving current increases and the voltage input to the amplifier circuit 7 becomes higher than the reference voltage, the voltage input to the amplifier circuit 7 becomes the reference voltage. To be controlled. At this time, in order to control the voltage input to the amplifying circuit 7 to the reference voltage, a part of the received light current flows into the transistor 12.

  When detecting information on raindrops, the switching element 10 is opened, and feedback control of the voltage input to the amplifier circuit 7 is released. At this time, due to the voltage charged in the capacitor 15, the current flowing through the transistor 12 becomes the same value before and after opening the switching element 10. As a result, the voltage input to the amplifier circuit 7 is a value obtained by adding the reference voltage and the voltage corresponding to the light emission of the LED 3 when the amplified voltage immediately before the detection period is controlled to the reference voltage. . In the detection period, the reference voltage is set so that the voltage input to the amplifier circuit 7 is equal to or lower than a threshold voltage that can be amplified by the amplifier circuit 7. Thereby, even if ambient light is strong, the information regarding raindrops can be detected without the output of the amplifier circuit 7 being saturated.

  Further, in order to control the voltage input to the amplifier circuit 7 to the reference voltage, a part of the received light current flows into the transistor 12. On the other hand, when the voltage input to the amplifier circuit 7 is controlled by the voltage, the power supply voltage is restricted, and when the received light current becomes large, information regarding raindrops cannot be detected accurately. In other words, by allowing a part of the received light current to flow into the transistor 12 and controlling the voltage input to the amplifier circuit 7 to the reference voltage, the allowable range of the received light current can be increased.

  Moreover, since the special optical filter is not used in order to suppress ambient light like patent document 4, a cost increase and an enlargement can be suppressed.

  In addition, the raindrop detection apparatus according to the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the spirit thereof. For example, in the above embodiment, the switching element 10 is always conducted in the non-detection section. This is because the output voltage of the operational amplifier 6 is charged in the capacitor 15 when the voltage input to the amplifier circuit 7 becomes equal to or higher than the reference voltage. For this reason, the switching element 10 may be turned on for a certain time before detecting information on raindrops. That is, until then, the switching element 10 is opened.

  Further, when the ambient light is small, the switching element 10 may be always opened even in the non-detection section as in the detection section. In this case, the configuration is the same as that of a conventional raindrop detection device.

(Modification)
In the above-described embodiment, when the capacitor 15 is charged with voltage in the detection section, the transistor 12 is driven by the voltage so that the current flowing through the transistor 12 does not change before and after the LED 3 emits light.

  However, if the capacitor 15 is discharged quickly, the current flowing through the transistor 12 may change before and after the LED 3 emits light. Therefore, as shown in FIG. 4, an operational amplifier 16 is inserted between the capacitor 15 and the transistor 12. Specifically, the operational amplifier 16 is connected to the non-inverting input terminal so that the voltage charged in the capacitor 15 is input, and the inverting input terminal is connected to the emitter terminal side of the transistor 12. Further, a resistance element 17 for determining the reference voltage of the operational amplifier 16 is connected to the emitter terminal side of the transistor 12. Thereby, it is considered that the discharge of the capacitor 15 can be blunted. Therefore, the above problem can be prevented.

  However, the value of the current flowing through the transistor 12 is limited by connecting the resistance element 17 to the transistor 12. As a result, the allowable range of the received light current is considered to be smaller than that in the above embodiment.

  In FIG. 4, the same reference numerals as those shown in FIG.

It is the figure which showed the cross section of the raindrop detection apparatus 100, and the state which attached the raindrop detection apparatus 100 to the front window. It is the schematic which shows the whole structure of the raindrop detection apparatus 100 in this embodiment. It is a time chart with respect to the light emission current, the light reception current, the potential of terminals A to D, and the output voltage of the AC amplifier circuit. It is the schematic which shows the whole structure of the raindrop detection apparatus 200 in a modification. It is the schematic which shows the whole structure of the conventional raindrop detection apparatus.

Explanation of symbols

  100, 200 Raindrop detection device, 3 LED, 4 PD, 6 operational amplifier, 7 amplification circuit, 8 AC amplification circuit, 9 CPU, 12 bypass transistor, 13 resistance element, 14 voltage source, 15 capacitor, 16 operational amplifier, 17 resistance element

Claims (7)

A light emitting element that emits light from the back side to the front side of the light transmitting member on which raindrops adhere to the surface;
A light emission instruction unit for instructing the light emitting element to emit light;
A light receiving element that receives reflected light that is reflected toward the back side of the light transmitting member on the surface of the light transmitting member out of the light emitted by the light emitting element, and generates a current according to the amount of light received;
A first resistance element connected in series with the light receiving element and generating a voltage according to a current generated by the light receiving element;
A first amplifying circuit for amplifying a voltage generated by the first resistance element, wherein the amplifiable voltage is limited to a predetermined voltage;
A second amplifying circuit for extracting a voltage based on reception of light reflected from the surface of the light transmitting member of light from the light emitting element among the voltages amplified by the first amplifying circuit; and amplifying the voltage; ,
In a raindrop detection apparatus comprising raindrop detection means for detecting information on raindrops based on the amplified voltage of the second amplifier circuit,
An output circuit that outputs a voltage signal corresponding to a difference between an input voltage to the first amplifier circuit and a predetermined reference voltage;
An input voltage of the first amplifying circuit is connected in parallel with the first resistance element, and a current corresponding to a voltage signal output from the output circuit is caused to flow so as to bypass the first resistance element. Current control elements that limit the voltage to a voltage corresponding to the reference voltage;
A holding circuit for holding a voltage signal output from the output circuit;
A cut-off circuit for cutting off the connection between the output circuit and the holding circuit so that the current control element is driven by the voltage signal held in the holding circuit while the light-emitting element emits light; A raindrop detection device.   The output circuit has one of a non-inverting input terminal and an inverting input terminal connected to the input terminal of the first amplifier circuit, the other connected to a voltage source that generates the reference voltage, and an output terminal connected to the current control element. The raindrop detection apparatus according to claim 1, wherein the raindrop detection apparatus is configured by an operational amplifier connected to the terminal.   3. The raindrop detection device according to claim 1, wherein the current control element stops bypassing the current when a voltage input to the first amplifier circuit is smaller than the reference voltage. 4.   The raindrop detection device according to claim 1, wherein the current control element is a transistor, and the output circuit and the holding circuit are connected to a base terminal of the transistor.   The cutoff circuit includes a switching element that conducts / cuts off and a switching instruction unit that instructs the switching element to conduct or block, and the switching element is connected between the output circuit and the holding circuit. The raindrop detection apparatus according to claim 1, wherein the raindrop detection apparatus is provided.   The raindrop detection device according to claim 1, wherein the holding circuit is a capacitor. The interruption circuit includes a second resistance element connected to the current control element;
A terminal voltage of the second resistance element is input to one of the two input terminals, a voltage held by the holding circuit is connected to the other, and an output terminal is connected to the current control element. An operational amplifier connected to a terminal for controlling the flowing current,
The raindrop detection according to claim 1, wherein when the connection between the output circuit and the holding circuit is cut off by the cutoff circuit, discharge of a voltage signal held in the holding circuit is made insensitive. apparatus.

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