WO2002086643A1

WO2002086643A1 - Device and method for optical lane recognition

Info

Publication number: WO2002086643A1
Application number: PCT/EP2002/003781
Authority: WO
Inventors: Norbert Amann
Original assignee: Automotive Distance Control Systems Gmbh
Priority date: 2001-04-23
Filing date: 2002-04-05
Publication date: 2002-10-31

Abstract

The invention relates to a lane recognition device and method. The lane recognition device, in general, comprises a radiation source with a number of light sources, which are lined up next to one another and which are provided for illuminating a roadway stripe and comprises a detector device having a number of photodetector elements for detecting, in a location-related manner, the light of the radiation source reflected by the lane. The novel device should be able to be economically realized with a low level of circuit complexity. The novel lane recognition device comprises means for sequentially controlling the light sources and has a photodetector element for detecting the light of the light sources reflected by the lane. The device advantageously comprises a lens device via which the light emitted by light sources is projected in an out-of-focus manner onto scanning sections of the lane whereby partially overlapping two of the scanning sections at a time. This enables a wide lane stripe to be scanned while using few light sources. The local resolution that is dependent on the number of light sources can be improved by interpolating the measurement results. The novel device can be used in motor vehicles in order to realize systems for automatically holding course or sleep warning systems.

Description

description

DEVICE AND METHOD FOR OPTICAL DRIVE DETECTION

The invention relates to a device for lane detection according to the preamble of claim 1 and a method for operating the device.

A generic device is known for example from DE 1 95 07957 C1. This known device comprises a radiation source with a plurality of infrared light-emitting diodes strung together and a detector arrangement with a plurality of photodetector elements designed as a CCD series and an evaluation unit for transit time measurement, contrast detection and contour detection. The radiation source is attached to the side of a motor vehicle and illuminates a lane strip running next to the motor vehicle. The light reflected on the lane is then imaged on the photodetector elements of the CCD series. The lateral lane area of the motor vehicle is thus scanned without contact, the spatial resolution being determined by the CCD series.

From DE 32 1 1 620 C1, a device for lane detection is also known, which has a radiation source designed as a bar light source or row of light-emitting diodes and which has a multiplicity of photodetector elements for detecting the light reflected on the roadway in each case from a scanning section.

The main disadvantage of this device is that it has a high energy consumption and expensive means for detecting the reflected light. The invention is therefore based on the object of specifying a device according to the preamble of patent claim 1 which can be produced inexpensively. The invention is also based on the object of specifying a method for operating this device.

The object is achieved by the features of claim 1 or by the features of claim 3. Advantageous further developments and refinements result from the subclaims.

The device according to the invention comprises a radiation source with a plurality of light sources which are each imaged on a scanning section of the roadway. The light sources are controlled sequentially and thus emit light beams one after the other, the light beams advantageously being pulsed, i. h as a result of individual light pulses. The device further comprises a photodetector element for detecting the portion of the light beams sequentially emitted by the light sources that is reflected on the road in the direction of the photodetector element.

The device advantageously has a lens device by means of which light sources are imaged onto the roadway in such a blurred manner that two of the scanning sections each partially overlap. This means that a wide lane can also be scanned with only a few light sources.

The light sources of the radiation source are preferably controlled in succession, so that the photodetector element successively receives a light beam originating from one of the light sources and generates a corresponding signal. The roadway is thus scanned line by line, with a brightness value being determined as the scanning point (pixel) for each scanning section of a line. The light of the light sources reflected on the roadway is detected by the photodetector element in relation to the light source. H. brightness values assigned to the light sources are determined, each of which corresponds to the reflected portion of the light beam emitted by the respective light source.

The contrast in a line of the roadway scanned by the light sources is advantageously analyzed by evaluating the brightness values and, in the case of a contrast occurring at a specific line position, one of these line positions corresponding distance value is determined as a rough value of the distance between the vehicle and a marking strip of the road.

In an advantageous development of the method, the spatial resolution of the method is refined by identifying neighboring light sources by means of a contrast analysis, which are imaged on a roadway area containing the edge of a marking strip. A fine value is then determined from the brightness values assigned to these light sources in order to correct the distance between the vehicle and the marking strip, which is determined as a rough value.

The main advantage of the invention is that the spatial resolution of the device is determined by the transmission side due to the sequential activation of the light sources and the light source-related detection of the reflected light beams. The result of this is that a small number of small and inexpensive light sources, for example with light-emitting diodes, give a high spatial resolution and high measuring accuracy. The sequential activation of the light sources also results in low energy consumption, low electrical consumption

Stress on the light sources and a low and even distribution of heat. Another advantage is the low circuit complexity, since the device has only a single photodetector element on the receiving side and can therefore only be processed for a detector signal in a downstream signal processing device.

The device according to the invention is ideally suited for implementing automatic lane keeping systems for motor vehicles or for implementing sleep warning systems to warn the driver of an impending departure from the lane.

An embodiment of the invention is described below with reference to figures. Show it:

FIG. 1: a schematic diagram of the device for determining the lane,

FIG. 2: a diagram of the light pulses emitted,

FIG. 3: a signal evaluation device, FIG. 4: a signal generated by the signal evaluation device,

5a, b: a scanned line of a roadway and associated brightness values.

According to FIG. 1, the device according to the invention comprises a radiation source S with a predetermined number of light sources, for example a light-emitting diode array with 16 infrared light-emitting diodes, and a lens device L for imaging the light sources onto a section of the roadway FB. The device is advantageously installed in an exterior mirror SP of a motor vehicle FS in such a way that the light sources radiate downwards through the lens device L and in each case onto a scanning section A1, A2,... AI 6 of an approximately 90 cm long one, next to the vehicle FS of the lane I running perpendicular to the direction of travel. The light sources are imaged onto the respective scanning sections A1, A2,... A1 6 in such a blurred manner that neighboring scanning sections partially overlap, i. h Adjacent light sources are mapped onto overlapping scanning sections. The device also has a photodetector element D, which is designed, for example, as a PIN diode and which detects the light beams of the light sources reflected on the roadway and generates a detector signal corresponding to the detected light.

The vehicle can have its own device for lane detection for the left and right side of the vehicle.

The light sources are controlled during operation in such a way that they emit a light beam in sequence, i. H. they are controlled sequentially like a running light and thus act like a radiation source that scans the roadway line by line with a light beam jumping from one scanning section to the next.

When controlling the light sources, the time required for one

Measurement can be used since interrupted marking strips MS, in particular at high speed, are only visible to the device for a finite time. For example, at a speed of 180 km / h and a strip length of 2.5 m, there is only 50 ms to capture the marking strips MS. In this short time you have to choose between an approach, distance or

A distinction can be made between parallel travel to the MS marking strip. from that it is deduced that at least one multiple scan must take place within the 50 ms.

In order to achieve optimal suppression of extraneous light, in particular sunlight, the light sources (LED1, LED2) are operated in a pulsed manner, as shown in FIG. The light sources thus send the respective light beam as a modulated one

Signal LS off, so that the light beam emitted by a light source is composed of a sequence of n light pulses which are emitted at a predetermined pulse repetition frequency fm (modulation frequency). The predetermined pulse repetition frequency fm is, for example, 455 kHz.

According to FIG. 3, the detector signal DS generated by the photodetector element D is fed to a signal evaluation device, the task of which is to recognize marking strips which are provided for delimiting the lane on the carriageway FB and to determine the distance of the vehicle FS from the recognized marking strips.

In the signal evaluation device, the detector signal DS is initially with a

Input amplifier VO selectively amplified, then rectified with a synchronous rectifier or lock-in demodulator DEM in synchronism with the predetermined pulse repetition frequency fm and then filtered with a low-pass filter LP. The synchronous rectifier DEM has, for example, two operational amplifiers V1, V2, which are activated alternately by a switch SW connected downstream. The

Switch SW is designed as a MOS field effect transistor and it is switched in time with the pulse repetition frequency fm. The synchronous rectification suppresses the influence of extraneous light, since these are not correlated with the pulse repetition frequency fm. This achieves good noise suppression and the detection of the marking strips both at night and at night

Day guaranteed even in extreme sunlight.

The low-pass LP connected downstream of the synchronous rectifier DEM serves to suppress the pulse repetition frequency fm from the signal emitted by the synchronous rectifier DEM. Its cutoff frequency is dimensioned such that a sufficient slope for the pixel scan frequency is still achieved at its output. The

The cutoff frequency is thus, for example, the product of the pixel scan frequency and the number of light sources, at 100 Hz pixel scan frequency and 16 light sources thus equal to 1.6 kHz. The pixel scanning frequency corresponds to the frequency with which the scanning sections are scanned.

The low-pass filter LP is followed by a microprocessor μP for further processing of the signal PD emitted by the low-pass filter LP. The microprocessor μP also controls the light sources LED1, LED2,... LED1 6 of the radiation source S via a driver and modulator device DRV.

FIG. 4 shows the signal PD emitted at the output of the low-pass filter LP. This signal is sampled in order to generate a measurement signal in the microprocessor μP after a settling time, multiple sampling, as shown by arrows in the figure, and averaging being advantageous due to the further noise suppression that can be achieved thereby.

According to FIG. 5, the line-by-line scanning of the roadway gives a brightness value for each light source LED1, LED2, ... and thus for each scanning section A1, A2, ... onto which the respective light source LED1, LED2, ... is mapped (Pixel), which is assigned to the respective light source. The light from the light sources LED1, LED2, ... reflected on the roadway is thus detected and evaluated in relation to the light source. Each light source LED1, LED 2, ... is also assigned a distance value x (1), x (2), ..., which is the distance between the vehicle and the scanning section A1, A2, ... to which the respective Light source is shown corresponds. By assigning the brightness values y (1), y (2), ... to the light sources LED1,

LED2, ... is therefore also assigned to each brightness value y (1), y (2), ... a distance value x (1), x (2), ...

FIG. 5a shows the distance values x (1), x (2), ... and the associated brightness values y (1), y (2), ..., which are obtained when the roadway line shown as an example in FIG. 5b is scanned becomes. According to FIG. 5b, the scanning sections A1, A2,... An-1 lie on an unmarked area of the road and the scanning sections An, An + 1, An + 2 are at least partially on the marking strip MS. This leads to low brightness values y (1), y (2), ... y (n-1) for the scanning sections A1, A2, ... An-1 and, in contrast, higher brightness values y (n), y (n +1), y (n + 2) for the scan sections An, An + 1, An + 2, the brightness values being greater the greater the proportion of the marking strip MS from the corresponding scan section. The brightness values y (1), y (2), y (3), ... generated in the microprocessor μP as a result of the signal evaluation are each a measure of the reflection factor of the scanning section irradiated by the respective light source LED1, LED2, LED3, ... A1, A2, A3, ... of the FB lane. They represent the contrast curve in the scanned lines of the roadway, since a light source which is imaged on a dark scan section, for example on the scan section An, delivers a lower brightness value than a light source which is on a bright scan section, for example on the scan section An + 2, is shown. A high brightness value y (1), y (2), ... is therefore an indication that the light source which has led to this brightness value is imaged on a marking strip MS which is brighter than the rest of the roadway.

If the brightness value y (1) or y (2) or ... assigned to a light source LED1 or LED2 or ... or the brightness values assigned to a plurality of adjacent light sources is higher by a threshold value, that is to say by more than one noise value or are as the other brightness values (in FIG. 5a this applies to the brightness values y (n), y (n + 1) and y (n + 2), this means that this light source or these light sources meet one Marking strips MS of the roadway was or were shown. This light source or these light sources are therefore identified in order to determine the position of the marking strip MS. The distance value assigned to the identified light source or, if several light sources are identified, the smallest of the distance values assigned to the identified light sources (in FIG. 5a this is the distance value x (n)) then corresponds to the gross value of the distance between the vehicle and the Marking strips MS.

When using 1 6 light sources LED1, LED2, ... and mapping these light sources onto a 90 cm long lane, the centers x (1), x (2), ... are

Scanning sections A1, A2, ... on which the light sources are imaged, spaced apart by approximately 6 cm. This means that the distance of the vehicle FS from the marking strip MS is determined with a resolution of 6 cm.

However, the resolution can be refined by interpolation. A sub-pixel resolution is thus obtained. This takes into account the fact that for a

Light source, which is imaged on a scanning section containing the edge of the marking strip MS, a brightness value is determined which is based on the area portion of the marking strip MS from the scanning section of this light source is dependent. Thus, the light source, which is mapped to the scanning section An according to FIG. 5b and thus only to a small extent on the marking strip MS, delivers a lower brightness value y (n) than the neighboring light source which points to the scanning section An + 1 and thus to one higher proportion is shown on the MS marking strips. A fine value d can therefore be calculated from the brightness values y (n) and y (n + 1) assigned to these light sources, which is a measure of the distance of the edge of the marking strip MS from the center x (n) of the scanning section An. With the fine value d, the distance value determined as the rough value x (n) of the distance between the vehicle FS and the marking strip MS is then corrected to the more precise distance value xi.

In the present exemplary embodiment, the contrast ratio K in the scanned line is first determined to determine the fine value d. The contrast ratio K corresponds to the distance between two brightness values, one of which corresponds to the reflection factor of the marking strip MS and the other to the reflection factor of the unmarked roadway. The fine value d is then obtained by determining the intersection of the straight lines g1 and g2, the straight line g1 corresponding to half the contrast ratio K / 2 and the straight line g2 representing the straight line which the two points P (n) = (x (n), y (n)) and P (n + 1) = (x (n + 1), y (n + 1)) connects. Furthermore, it is conceivable to replace the straight line g2 by a curve which is interpolated by the points P (n), P (n + 1) and by further points lying in the vicinity of these points, for example those in the vicinity of the Points P (n-1), P (n), P (n + 1), P (n + 2) lying on the edge of the marking strip MS.

The distance between the vehicle and the MS marking strip can thus also be determined when only 16 light sources are used and when these light sources are imaged on a 90 cm long lane strip with a resolution of approximately 1 cm. Because of the small number of light sources, this high spatial resolution can be achieved with little computing effort and little circuitry.

Claims

claims

1 . Device for lane detection with a radiation source (S) having a plurality of light sources (LED1, LED2, ...), characterized in that means (DRV) are provided for sequentially actuating the light sources (LED1, LED2, ...) and in that a photodetector element (D) is provided for detection of the light of the light sources reflected on the road.

2. Device according to claim 1, characterized in that a Linsenvorrich- device (L) for imaging the light sources (LED1, LED2, ...) is provided on a strip of the roadway (FB), the lens device (L) with respect to Light sources (LED1, LED2, ...) is positioned in such a way that two of the light sources (LED1, LED2, ...) are imaged out of focus on overlapping scanning sections (A1, A2, ...) of the roadway (FB).

3. A method of operating the device according to claim 1 or 2, characterized in that the light sources (LED1, LED2, ...) for scanning the roadway (FB) line by line each emit a light beam that the on the roadway (FB) reflected light rays are detected by the photodetector element (D) and that brightness values (y (1), y (2), ...) are determined from the light rays detected by the photodetector element (D), which reflect the reflected portion of one of the light sources ( LED1, LED2, ...) correspond to the light beam emitted.

4. The method according to claim 3, characterized in that the contrast in a line of the roadway scanned by the light sources (LED1, LED2, ...) by evaluating the brightness values (y (1), y (2), .. .) is analyzed and that with a contrast occurring at a certain line position, a distance value (x (n)) corresponding to this line position is determined as a rough value of the distance between the vehicle (FS) and the marking strip (MS) of the road.

5. The method according to claim 4, characterized in that two of the light sources are identified by evaluating the brightness values (y (1), y (2), ...), which are imaged on a roadway area containing the edge of a marking strip (MS) , and that from the brightness values assigned to these light sources (y (n), y (n + 1)) a fine value (d) for correcting the distance between the vehicle and the marking strip (MS.) determined as a rough value (x (n)) ) is determined.

6. The method according to any one of claims 3 to 5, characterized in that the light beams of the light sources (LED1, LED2, ...) are emitted in a pulsed manner with a predetermined pulse repetition frequency (fm).