Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2000-03-06
2002-10-01
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S339100, C324S643000
Reexamination Certificate
active
06459083
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an arrangement for detecting the condition of a road surface.
RELATED TECHNOLOGY
Arrangements for detecting the condition of a road surface may be an important element of vehicle traffic safety. A road surface condition that reduces vehicle tire friction on the road surface can be extremely hazardous. An urgent need therefore exists for a reliable arrangement to detect the condition of the road surface.
A surface monitoring system which can also be used to detect the condition of a road surface and which includes a microwave transceiver system with one or more operating frequencies is known from U.S. Pat. No. 5,497,100. The variable reflectivity of dry, wet, and icy road surfaces is evaluated to distinguish between different road surface conditions.
Other known systems use transceiver equipment with infrared radiation, preferably using multiple wave bands and evaluating the variable reflectivity of different road surface conditions. In German Patent Document No. 40 08 280 A1, for example, information about the road surface condition is obtained by forming the ratio of received signals detected on various wave bands. In Hydrological Processes, Vol. 5, pages 321-327,describes the use of the infrared absorption capacity of water to determine ground moisture by measuring the reflectivity of soil for different IR wavelengths.
Combining a microwave system and an infrared system is particularly advantageous, since both of these systems complement each other advantageously in terms of their ability to distinguish between different road surface conditions. German Patent Document No. 40 40 842 A1, for example describes an infrared microwave sensor system for detecting the condition of a road surface, which applies broadband IR radiation to a surface, detects backscattered light that has been separated into multiple wave bands, and also measures surface reflectivity for microwaves. A decision about the road surface condition is obtained by performing a logic operation on the different measurement signals or signals derived from them in a logic gate arrangement. A similar system is described in German Patent Document No. 196 03 557 A1 in which a first wave band with one water absorption band and a second wave band with a lower absorption by water are selected for the infrared system.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus for detecting the condition of a road surface which provides reliable information about the road surface condition, while maintaining a simple and economical design and, in particular, is suitable for use in road vehicles.
The present invention provides an apparatus for detecting a condition of a road surface. The apparatus includes an infrared transmitter for emitting infrared radiation in at least a first and a second wave band so as to illuminate the road surface, the transmitter varying an intensity of the emitted radiation over time in at least the first wave band. The apparatus also includes an infrared receiver for detecting and evaluating an intensity of backscattered infrared radiation from the road surface in the first and second wave bands so as to obtain information about the condition of the road surface, the receiver correlating at least a portion of the backscattered radiation with the variation over time of the intensity of the emitted radiation in at least the first band.
By improving the distinction between the relevant signal components in the infrared receiver, the present invention provides a more precise assessment of the reflection and absorption properties of the monitored surface segment, thus supplying more accurate and more reliable information about the condition of this surface segment. Advantageously, at least on one of the different wave bands used, the intensity (transmitted power) of the IR radiation emitted on this wave band is varied over time, and a correlation of the radiated power received by the receiver, using knowledge of the variation over time of the emitted radiation intensity, improves the ability to separate the different radiation components. The variation over time of the emitted radiated power and the correlation of the received signal makes it possible, in particular, to effectively eliminate the influence of ambient light. Such devices can be achieved at little expense and also considerably improve the separate evaluation of the individual signal components. The individual means used to vary the intensity of the emitted radiation over time, which can be carried out alone or in different combinations. The design and/or circuitry needed to achieve these devices are basically known to those skilled in the art. Some of these devices have been used in different applications so that experience from other fields can be used for implementation.
The variation over time can apply to the radiation on one wave band alone, or the variation of the emitted radiation intensity can apply to both wave bands. The indication of two wave bands is not intended to exclude the possibility of using and evaluating more than two different wave bands. To provide a simple and cost-effective arrangement, however, a design with two different infrared wave bands is preferred. It has been shown that a good assessment of the condition of a road surface can be obtained with two different wave bands, in particular one wave band with a low absorption in water, for example around 950 nm, and a second wave band with a higher absorption by water (water absorption band), for example 1350 nm.
According to a first advantageous embodiment, the variation over time of the emitted radiation intensity is achieved by clocking the radiated power, in particular by switching between a turn-on power level and an emitter status with no IR power emission. Both wave bands are advantageously operated in a clock mode of this type, with the power being emitted on the two different wave bands by time-division multiplexing, and with emission pauses also being advantageously provided. Time-division multiplex clocking also makes it possible to define receiving intervals in which only the radiation of one wave band is expected as the information signal component. This makes it especially easy to separate the signal components of the different wave bands. A very long switching interval should advantageously be selected, compared to the runtime of the radiation emitted by the emitter over the illuminated surface in the receiver, making it unnecessary to additionally account for a phase shift in the clock signals. Providing emission pauses makes it possible to advantageously determine the ambient radiation component on the two useful wave bands in the receiver at such intervals and to account for this component in the illumination intervals, for example by subtracting a corresponding interference signal component and/or by influencing the working point of one or more receiving elements.
A further advantageous embodiment for achieving the variation over time of the emitted IR radiation intensity involves periodically modulating the radiated power. The intensities on both wave bands are preferably modulated at different modulation frequencies, and the signal components in the receiver separated from each other and from an interference signal component by frequency-discriminating demodulation, for example by synchronous rectification or bandpass filtration. A high-frequency modulation is preferably carried out, for example, in the 10-100 kHz range. Modulating the intensities on both wave bands, using different modulation frequencies, makes it possible to emit, receive, and evaluate signals on both wave bands simultaneously so that equal time segments, and thus backscattering from the same surface segments, can be processed and evaluated through comparison.
Another advantageous means for varying the intensity over time is the pulsed emission of IR radiation, advantageously selecting the length, sequencing time and similar quantities of the on and off pulses according to a pulse code patt
Finkele Rolf
Kippenberg Tobias
Schreck Andreas
Wanielik Gerd
Daimler-Chrysler AG
Hannaher Constantine
Israel Andrew
Kenyon & Kenyon
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