Electricity: motive power systems – Automatic and/or with time-delay means – Radiant energy
Patent
1998-06-12
2000-03-21
Nappi, Robert E.
Electricity: motive power systems
Automatic and/or with time-delay means
Radiant energy
15250001, G05B 500
Patent
active
060406690
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a control device for an optical sensor.
BACKGROUND INFORMATION
A control device for optical rain sensors for use in vehicle windshield wiper systems is described in (U.S. Pat. No. 4,859,867), which includes a compensation circuit for ambient light, temperature and other system variables. To compensate for the ambient light, the optical transmitter (emitter device) of the rain sensor is operated with high-frequency pulsing. A receiver detects the high-frequency radiation output by the transmitter and supplies modulated signals to a microcontroller, which separates the alternating component (cyclical portion) of the signals from the direct component (non-cyclical portion) of the false signals (such as of ambient light, etc.). The frequency currently used for driving the transmitter, in this case a light-emitting diode (LED), is 1000 Hz. The preferred pulse width is 15 microseconds. The signals analyzed in the microcontroller control the wiper motor. As a secondary effect, the service life of the LED is prolonged as compared to continuous operation.
The service life is not sufficiently prolonged, however, when this high pulse frequency is used.
When the frequency is reduced and the turn-on time of the optical transmitter is kept the same to maximally prolong the service life, it becomes more and more difficult, however, to isolate the alternating component from the direct component. Moreover, the sensor's reaction time to the occurrence of moisture is adversely affected.
SUMMARY OF THE INVENTION
One of the advantages of the control device according to the present invention is that the service life of the transmitter is increased by reducing the transmitter power, without degrading the responsivity of the rain sensor. Thus, the service life of the transmitter is made to conform with the service life of the other electronic components, prolonging the service life of the entire sensor.
One advantage of the control device according to the present invention is that the control device of the optical sensor makes the distinction between dryness and moisture. In response to dryness, the transmitter is operated with reduced power and, in response to moisture, with full power.
A further advantage lies in the fact that the reduction in transmitter power is likewise achieved through a pulsed operation of the rain sensor.
What is particularly advantageous in this case is that the upper limiting value of the period duration (cycle) is matched to the reaction time of the human eye, making any delay imperceptible. On the other hand, there is no need to take external events, such as rain drops falling on a pane, into consideration, since such events transpire clearly at a slower rate than the reaction time.
Another advantage is that the degree of reduction in power can be varied by other (e.g., predetermined) parameters, such as day or night, and thus be optimally adjusted to the different needs of the motor vehicle driver. It may also be adventageous if the reduced transmitter power is pulsed with a frequency of less than 1000 Hz.
One advantage of pulsed operation is that the sensor also retains its responsivity under conditions dryness, and senses even little moisture.
One advantage of reducing the transmitter power in a nonpulsed operation is that the sensor detects a greater level of moisture without delay.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a block diagram for a pulsed operation of a transmitter.
FIG. 2 shows a diagram of quotients of voltages dropping across the transmitter plotted over time, in response to a presence of moisture or dryness on a pane when working with a pulsed operation of the transmitter.
FIG. 3 shows a block diagram of the transmitter that is switchable between a reduced power and a full power.
FIG. 4 shows a diagram of the quotients of the voltages dropping across the transmitter plotted over time, in response to the presence of moisture or dryness on the pane when working with the transmitter that is switchable between the
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patent: 5059877 (1991-10-01), Teder
patent: 5560245 (1996-10-01), Zettler et al.
patent: 5568027 (1996-10-01), Teder
Duda Rina I.
Nappi Robert E.
Robert & Bosch GmbH
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