Communications: electrical – Land vehicle alarms or indicators – Of relative distance from an obstacle
Reexamination Certificate
2001-05-01
2002-04-23
Wu, Daniel J. (Department: 2632)
Communications: electrical
Land vehicle alarms or indicators
Of relative distance from an obstacle
C340S436000, C340S903000, C340S904000, C340S933000, C340S942000, C340S943000, C340S552000, C340S556000, C342S070000
Reexamination Certificate
active
06377167
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to detection systems for detecting the presence of an object in a monitored zone and, more particularly, to an infrared detection system using infrared signals at multiple frequencies to discriminate between light reflected from an object within the monitored zone and other light and having means to selectively vary the boundaries of the monitored zone.
In many known photoelectric synchronous detection systems, a pulsed optical beam signal is transmitted into a volume or zone of space being monitored, typically by using an LED which is activated by a square wave or low duty factor pulse generator/oscillator. An optical photodetector is aimed into the monitored zone with a field of view which includes the pulsed LED beam so that it will receive any reflection of that signal to detect the presence of an object in the monitored zone. Such a system uses triangulation to discriminate between light reflected from objects within the monitored zone and light emanating from beyond the boundaries of the monitored zone, and is shown in U.S. Pat. No. 5,463,384—Juds.
To screen out noise and signals from sources other than a reflection from an object (e.g. other electrical or optical sources), synchronous receivers are used which operate the receiver only when a reflection of the pulsed signal is expected. This blocks any response resulting from detection of light energy from other sources during intervals when no reflected pulsed signal is possible.
To reject possible detection of intrinsic random circuit noise and detector shot noise, a fixed detection threshold is imposed on the system at a level above the expected intrinsic random noise levels seen by the detection circuit. This allows the detection circuit to ignore this noise. The probability of false detection due to noise is a function of the threshold level relative to the actual noise level, the amplitude of which is generally a Gaussian distribution.
Other examples of fixed threshold photoelectric detection systems are found in U.S. Pat. No. 4,356,393—Fayfield, U.S. Pat. No. 4,851,660—Juds, U.S. Pat. No. 4,851,661—Everett, Jr., U.S. Pat. No. 4,990,895—Juds, and U.S. Pat. No. 5,122,796—Beggs et al. Although these fixed threshold synchronous detection systems have been found useful for most photoelectric sensor applications, they are not sufficiently accurate in a situation where high receiver sensitivity is desired in an operating environment where the noise level is highly inconsistent and randomly variable.
In such an environment, detector system performance is handicapped by the necessity of tailoring detection threshold levels to performing in an environment of the worst expected noise conditions to assure a satisfactory level of noise rejection. This situation exists when the detection system is used for vehicle detection in an outdoors operating environment. Such a system used to detect vehicles in a driver's blind spot will encounter a wide variation in noise resulting from ambient light conditions that range from pitch dark nighttime, to 8500 ft-cdls of sunlight reflected from a white surface, to as high as 70,000 ft-cdls of sunlight reflecting from a wet road surface. Also, such systems can be fooled by the presence of atmospheric backscatter caused, for example, by heavy fog or snow, to falsely indicate the presence of a vehicle in the blind spot. Since false detects by such systems renders them unreliable to a vehicle driver, elimination of false detects is an important goal.
In a blind spot detection system, the reflectivity of detected target vehicles will vary wildly, as will ambient lighting conditions. Thus, such a system will be required to detect vehicles that range in reflectivity from black to white, in lighting conditions that vary from pitch-dark nighttime to bright sunlight. Thus detection requirements range from a black vehicle at nighttime to a white vehicle in bright sunlight.
In the dark of night very little DC photocurrent is produced in the detectors, resulting in very little shot noise. However, operation in bright daylight will result in quite significant DC current in the receiver photodiodes, resulting in high shot noise levels. When the receiver views a white target vehicle in bright sunlight, the photocurrent generates shot noise which is many times greater than the intrinsic electronic noise of the receiver amplifier itself. To avoid false detection caused by a high level of shot noise, the required threshold must be quite large in comparison the worst case shot noise. This high threshold results in low system capability of detecting very dark, low reflective targets in all lighting conditions.
There have been several attempts to overcome the operational problems caused by this wide variation in system noise levels. These involve providing the detection system with some form of adaptive adjustment based on a measurement of the noise amplitude characteristics which are then used to set the detection threshold of the receiver. The resulting adaptive threshold receiver optimizes its sensitivity relative to the ambient measured receiver noise to maintain signal reception integrity. Examples of such systems are found in U.S. Pat. No. 3,999,083—Bumgardner, U.S. Pat. No. 4,142,116—Hardy et al, U.S. Pat. No. 4,992,675—Conner et al, and U.S. Pat. No. 5,337,251—Pastor.
Such systems are quite expensive, since they require the addition of circuitry to continually measure noise, to block such measurement and maintain the prior measurement when an actual signal is detected, and to feed measured levels back to the variable gain stage. This circuitry adds components and assembly labor, and increases system size.
Vehicle blind spot detector systems such as disclosed in the above-mentioned patents utilize both driver-side and passenger-side detectors. One system comprises sets of six emitter-detector pairs in a module, the detectors being, pairs of photodiodes of opposite polarity. The effective range of the system is determined by the geometry of these components. These components are quite small and require holding very precise tolerances during manufacturing to maintain their geometry.
It has also been proposed to provide a blind spot detector featuring a synchronous pulse detection system having an adaptive threshold that is inherently controlled by the statistical nature of the receiver noise to optimize sensitivity of the system receiver and maintain an acceptably low false detection rate. A multi-test zero threshold detector checks the combined noise and pulse response of a bandwidth-limited receiver at two or more spaced time points which are timed by pulse emission to correspond with expected maximum and minimum voltage peak and flyback responses from reflections of the emitted pulses. An up/down counter is employed to count up only if the comparator reports the correct polarity of the responses, and counts down for all other responses. The up/down counter is heavily biased to count down until the received signal is large enough relative to the noise to overcome the negative count bias and count up to produce a detect signal. In this system, the false detection rate in the absence of a valid signal decreases exponentially with the length of the counter. Such a system is disclosed in PCT/US97/20637, the disclosure of which is incorporated herein by reference.
This detector system also operates on the geometric arrangement of the emitters and photosensors. Since triangulation is used to discriminate between sensed reflections from objects within the zone and from beyond the monitored zone, precise placement of these elements is critical. Also, since three lenses are required, the unit remains bulky and must be mounted on or within the vehicle body, usually at the taillights.
Systems using triangulation require a second receiver for each emitter to be sufficiently insensitive to reflections from non-uniform objects in the monitored zone. Such double triangulation systems not only bear an added cost burden for the extra circuitry and componen
Juds Scott
Lewis Robert I
Mathews Paul
Auto-Sense LLC
Greenlee David A.
Nguyen Tai T.
Wu Daniel J.
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