Rain responsive windshield wiper control
DCFirst Claim
1. In a vehicle of the type incorporating a windshield and at least one motor for operating a device on said vehicle, a control circuit for said motor for automatically activating same upon detection of moisture droplets on the exterior surface of said windshield, comprising:
- (a) a housing secured to the inside surface of said windshield, said housing having means for mounting an array of radiant energy sources and an array of radiant energy sensors such that radiant energy emitted by said sources are directed to the plane of the exterior surface of said windshield and normally are directed back to said array of sensors when no moisture droplets are present on the portion of said windshield occupied by said housing;
(b) driver means for periodically energizing said radiant energy sources with pulses of a predetermined duty cycle, the interval when said radiant energy sources are "on" defining a rain sense interval and the interval when said radiant energy sources are "off" defining an ambient light sense interval;
(c) first means for sampling and holding the output of said radiant energy sensors during said rain-sense interval;
(d) second means for sampling and holding the output of said radiant energy sensors during said ambient light sense interval, the sampling by said first and second means occurring successively within a time interval which is significantly less than the time required for changes in ambient light impinging on said windshield;
(e) means for linearly rejecting signal components in said sensor output due to ambient light disturbances in successive samples taken by said first and second means to leave only a signal component due to sensing of moisture droplets on said windshield; and
(f) activating means responsive to said signal component due to sensing of moisture droplets for activating said motor.
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Abstract
A control circuit for a windshield wiper motor is disclosed in which the wiper motor is made automatically responsive to the presence of moisture droplets on the windshield causing the wiper blades to sweep back and forth at a rate dependent upon the level of precipitation encountered. By using a set of sample-and-hold circuits, bandpass filtering and a differential amplifier under microprocessor control, disturbances to the system due to changes in ambient light are linearly rejected and the system becomes immune to such disturbances. The system utilizes an intentional-retrigger algorithm enabling the system to detect water droplets that miss the sensor yet fall within the area of the windshield which is swept by the wiper blades. The system automatically adapts to windshields of differing transmittance and is not falsely set into action by electromagnetic disturbances.
461 Citations
15 Claims
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1. In a vehicle of the type incorporating a windshield and at least one motor for operating a device on said vehicle, a control circuit for said motor for automatically activating same upon detection of moisture droplets on the exterior surface of said windshield, comprising:
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(a) a housing secured to the inside surface of said windshield, said housing having means for mounting an array of radiant energy sources and an array of radiant energy sensors such that radiant energy emitted by said sources are directed to the plane of the exterior surface of said windshield and normally are directed back to said array of sensors when no moisture droplets are present on the portion of said windshield occupied by said housing; (b) driver means for periodically energizing said radiant energy sources with pulses of a predetermined duty cycle, the interval when said radiant energy sources are "on" defining a rain sense interval and the interval when said radiant energy sources are "off" defining an ambient light sense interval; (c) first means for sampling and holding the output of said radiant energy sensors during said rain-sense interval; (d) second means for sampling and holding the output of said radiant energy sensors during said ambient light sense interval, the sampling by said first and second means occurring successively within a time interval which is significantly less than the time required for changes in ambient light impinging on said windshield; (e) means for linearly rejecting signal components in said sensor output due to ambient light disturbances in successive samples taken by said first and second means to leave only a signal component due to sensing of moisture droplets on said windshield; and (f) activating means responsive to said signal component due to sensing of moisture droplets for activating said motor. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A control circuit comprising in combination:
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(a) an optical sensor means for detecting the accumulation of moisture droplets on a transparent surface and producing a composite electrical signal having a component due to the presence of moisture and a component due to changes in ambient light reaching said sensor means, and producing an output signal having a component due to changes in ambient light; (b) means for sampling said composite electrical signal in a first interval when both components are present; (c) means for sampling the output signal from said optical sensor in a second interval when only said component due to changes in ambient light is present, said first and second intervals being taken close to one another in time; (d) differential amplifier means for forming a linear differential summation of said signals obtained during said first and second intervals; and (e) means for determining whether the output of said differential amplifier means exceeds a predetermined threshold.
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9. In a motor vehicle of the type incorporating a windshield and a motor-driven windshield wiper, an improved windshield wiper motor controller for automatically activating the motor of said motor-driven windshield wiper upon detection of moisture droplets on the exterior surface of said windshield, comprising:
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(a) an opaque housing secured to the inside surface of said windshield, said housing having a first and a second plurality of bores whose longitudinal axes intersect at points at the exterior surface of said windshield and at an acute angle to the plane of the windshield, said first plurality of bores including individual radiant energy sources and said second plurality of bores including individual radiant energy sensors, individual ones of said sources being associated with individual ones of said sensors; (b) driver means for periodically energizing said radiant energy sources with pulses of a predetermined duty cycle, the interval when said radiant energy sources are "on" defining a rain-sense interval and the interval when said radiant energy sources are "off" defining an ambient light sense interval; (c) first means for sampling and holding the voltage output of said radiant energy sensors during said rain-sense interval; (d) second means for sampling and holding the voltage output of said radiant energy sensors during said light-sense interval; (e) differential summing means coupled to receive the outputs from said first and second means for sampling and holding, said differential summing means providing an output voltage, Vdiff, proportional to the difference between said voltage outputs sampled and held by said first and second means; (f) first window comparator means coupled to receive said voltage, Vdiff, for signaling when the amplitude of said Vdiff voltage falls outside of a predetermined range of amplitudes; and (g) rain-control oscillator means coupled to receive the signal output from said first window comparator means for driving said windshield wiper motor at a rate proportional to the frequency with which said Vdiff voltage falls outside of said range of amplitudes during successive rain-sense intervals. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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Specification