JP2006119032A - Optical raindrop sensor drift correction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical raindrop sensor in which a drift effect after power-on is eliminated.
A light emitting element 4 and a light receiving element 5 and an optical system for controlling the light path of light emission and light reception are in close contact with glass through a light-transmitting sheet, and light emission is performed in order to keep the light reception signal level constant. An optical raindrop sensor drift correction method for controlling the drive current of the element 4, wherein the received light signal level is corrected with respect to drift after power-on with a map coefficient preset by the drive current of the light emitting element 4. A drift correction method for an optical raindrop sensor, characterized in that it is configured as described above.
[Selection] Figure 1

Description

  The present invention relates to a drift correction method for an optical raindrop sensor capable of appropriately sensing raindrops attached to an automobile windshield or the like.

  Conventionally, a raindrop detection device that can detect raindrops attached to this type of windshield is known (for example, Patent Document 1).

  Further, an optical raindrop sensor as shown in FIG. 4 is known. That is, the lens 3 is attached to the glass 1 via the optical sheet 2, and the light from the light emitting element 4 such as an infrared light emitting diode is condensed through the lens 3 and reflected from the optical sheet 2 on the surface of the glass 1. The lens 3 is again passed through the optical sheet 2, condensed on the light receiving element 5 of the photodiode at the open position, and the amount of raindrops attached to the surface of the glass 1 is converted into an electrical value by converting the change in light into an electrical value. A wiping device such as a wiper was activated.

  However, in this type of raindrop sensor, the amount of light incident on the light receiving element 5 changes due to contamination and deterioration of the glass 1, the optical sheet 2, and the lens 3, so that a microcomputer 9a shown in FIG. Is controlled so as to be constant.

  That is, the microcomputer 9a automatically corrects the light reception signal so that the light reception signal level is constant by changing the gain of the light reception signal and the light emission power.

In the figure, 6 is a constant current circuit, 7 is a current setting circuit, and 8 is an amplifier circuit.
JP 2001-147278 A

  By the way, in the conventional example shown in FIGS. 4 and 5, when the light reception signal is changed, the S / N ratio may be lowered. Usually, the light emission power is changed to make the light reception signal level constant.

  Further, when the light emission power of the LED is increased, self-heating is generated, and the amount of light with respect to the drive current decreases as the temperature increases.

  Further, although this type of conventional sensor emits light with a pulse, although it generates a small amount of heat, it is not negligible compared to the detection level, and there is a problem of erroneous detection due to drift characteristics after power-on.

  The present invention has been made paying attention to the above points, and in order to eliminate the influence of drift after power-on, a change characteristic map of light emission current over time is collected for each light emission current to light emitting elements such as LEDs. Another object of the present invention is to provide a drift correction method for an optical raindrop sensor that is mapped and stored in a CPU, ROM, or the like such as a microcomputer.

  This invention can solve the said subject by providing the following structures.

  (1) A light emitting element and a light receiving element, and an optical system for controlling the light path of the light emission and light reception are provided in close contact with glass through a light-transmitting sheet, and the light emitting element is driven in order to keep the light reception signal level constant. A method for correcting the drift of an optical raindrop sensor that controls current, wherein the light reception signal level is corrected for drift after power-on with a coefficient of a map set in advance by the drive current of the light emitting element. A drift correction method for an optical raindrop sensor.

  (2) The temperature sensing element is installed on the same substrate as the light emitting element, and the received light signal can be corrected using a map selected by the temperature detected by the temperature sensing element and the driving current of the light emitting element. (1) The drift correction method for the optical raindrop sensor according to (1).

  According to the present invention, since the optimum drift correction can be performed by the light emission current of the light emitting element, malfunction due to drift can be prevented without reducing the detection sensitivity.

  In addition, since drift correction detects the ambient temperature and selects a map, it can perform correction with high accuracy.

  Furthermore, the present invention has an effect that the cost of the product is not increased due to the response by the program.

  In the following, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows an automobile window provided with a raindrop sensor of the present invention showing a light emitting element for irradiating a windshield surface, a light receiving element for receiving reflected light reflected by the windshield surface, and an electronic circuit connecting the two. An example of the case is shown.

  FIG. 2 is a graph showing a difference between a light reception signal to a light receiving element that receives reflected light reflected from a window surface by light emitted from the light emitting element and an initial level that changes with time according to a temperature change. The graph which shows the relationship between a received light signal and a raindrop detection level is shown.

  The overall circuit configuration shown in FIG. 1 includes a light emitting element 4 corresponding to an infrared light emitting diode and a light receiving element 5 corresponding to a photodiode as in the conventional example shown in FIGS. 4 and 5, and a constant current circuit. 6. A current setting circuit 7 and an amplifying circuit 8 are provided, but a temperature sensitive element T provided in the substrate is provided, and light is emitted over time for each light emitting current of the light emitting element 4 of the LED in order to eliminate the influence of drift. There is a significant structural feature in that the microcomputer 9 is provided with a ROM or the like that collects and maps current change characteristic data.

  That is, when the power is turned on, the light reception signal drifts due to self-heating of the light emission current of the LED as shown in FIG. Since the current of the light emitting element 4 of the LED is controlled in order to make the light reception signal constant, the current of the light emitting element 4 of the LED is increased as the light incident on the light receiving element 5 of the photodiode becomes weaker. Increase. That is, the current increases from i1 to in.

  In order to eliminate the influence of the drift in FIG. 1, the light emission current change characteristic data for each light emission current of the LED light emitting element 4 is collected, mapped, and stored in the ROM or the like of the microcomputer 9.

  In the map, the initial value (immediately after turning on the current) is set to a ratio k, and the subsequent calculation is performed using the value kr multiplied by the value r of the received light signal as time passes (FIG. 2).

  In addition, since the drift characteristics vary depending on the ambient temperature (substrate temperature), the ambient temperature is measured with the temperature sensing element T housed in the same substrate, and the drift characteristics are as follows depending on the drive current and ambient temperature of the light emitting element 4. You can create and use a more accurate map than shown.

  As a result, it is possible to appropriately detect water droplets attached to the glass surface, particularly the windshield surface of an automobile, and to properly automatically control the wiper operation.

Explanatory drawing which shows an example at the time of giving the drift correction method of the optical raindrop sensor which concerns on this invention to the glass of a motor vehicle window A graph showing a state that changes over time according to a temperature change between a light reception signal of a light receiving element and an initial level Graph showing the relationship between the light reception signal of the light receiving element and the raindrop detection level Explanatory drawing which shows the optical raindrop sensor of a prior art example Explanatory drawing of the automatic correction method in the optical raindrop sensor of the conventional example

Explanation of symbols

4 Light emitting element such as LED 5 Light receiving element such as photodiode 9 Microcomputer T Temperature sensing element

Claims (2)

  Light-emitting element and light-receiving element, and an optical system that controls the light-emitting and light-receiving optical paths are in close contact with the glass via a light-transmitting sheet, and the drive current of the light-emitting element is controlled to keep the light-receiving signal level constant. An optical raindrop sensor drift correction method, characterized in that a received light signal level is corrected with respect to a drift after power-on with a coefficient of a map set in advance by a driving current of a light emitting element. Optical raindrop drift correction method.   The temperature sensing element is installed on the same substrate as the light emitting element, and the received light signal can be corrected using a map selected by the temperature detected by the temperature sensing element and the driving current of the light emitting element. Drift correction method for optical raindrop sensors.

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