Optics: measuring and testing – Angle measuring or angular axial alignment – Apex of angle at observing or detecting station
Reexamination Certificate
1999-11-12
2001-11-13
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Angle measuring or angular axial alignment
Apex of angle at observing or detecting station
C356S004010, C356S005010, C180S167000, C180S169000
Reexamination Certificate
active
06317202
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to an automotive radar system designed to emit a beam of light over a frontal scanning area to gather data used in identifying obstacles existing ahead of an automotive vehicle, and more particularly to an automotive radar system for detecting lane marks printed on a road surface and another obstacle present in front of the vehicle.
2. Background Art
In recent years, automotive radar systems are used in anti-collision systems which detect preceding vehicles and other obstacles existing on a road and white lane marks printed on the road surface and alert a vehicle operator when the vehicle is in close proximity to the obstacle or when the vehicle is going to run out of the lane mark or in automatic cruise control systems which keep the distance to the preceding vehicle constant between the right and left lane marks.
In such radar systems, detection of obstacles located at a distance of approximately 100 m requires sweeping a radar beam horizontally within a frontal zone, while detection of lane marks requires sweeping a radar beam downward to scan the road surface.
Japanese Patent First Publication No. 8-248133 discloses an automotive radar system designed to sweep radar beams both horizontally for detecting obstacles in a frontal zone, which will also be referred to as a frontal zone scanning operation below) and downward for detecting lane marks, which will also be referred to as a road surface scanning operation below). The frontal zone scanning operation and the road surface scanning operation are achieved simultaneously by splitting a single beam of light into a plurality of radar beams, directing them to a moving mirror at different vertical angles through respective reflecting mirrors, and sweeping the radar beams horizontally.
Usually, a scan beam emitted from a radar mounted on an automotive, as clearly shown in FIG.
14
(
a
1
), intersects each lane mark printed on one of sides of a road diagonally, so that an area of the lane mark to which the scan beam is irradiated is relatively small. Additionally, the smaller the incident angle &psgr; of the scan beam to the road surface is, as shown in FIG.
14
(
a
2
), the greater will be an area S irradiated by the scan beam, which will cause the density of power of the scan beam on the road surface to be decreased greatly. Further, the reflectivity of lane marks is usually low as compared with reflectors mounted on typical automotive vehicles. It is, therefore, difficult for typical radar systems to detect a return of a scan beam from a distant road surface.
The above problems may be alleviated by emitting a scan beam at a great angle to the road surface so as to decrease the area S for increasing the density of power of the scan beam. This, however, requires emission of the scan beam in the vicinity of the vehicle, thereby resulting in an increase in scan angle for detecting the lane marks accurately. The increase in scan angle without reducing the resolving power of the azimuth angle of a target requires a large number of times beams are generated for each scan, thereby resulting in an increase in load of a scan beam source (e.g., laser diodes), leading to an decrease in lifetime of the scan beam source.
Further, in the above radar system designed to perform both the frontal zone scanning operation and the road surface scanning operation, the increase in angle of a scan of the road surface will also cause the angle of a scan of the frontal zone to be increased, thus resulting in undesirable detection of many safe obstacles on the sides of the road. This leads to complex signal processing for identifying target objects and an increase in operations therefor.
The sensitivity of the radar system to the lane marks may be increased by increasing the power of the scan beam source, but it will cause the lifetime of the scan beam power to be decreased greatly.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide a beam scanning radar system for automotive vehicles capable of detecting lane marks printed on a road surface and another obstacle present in front of the vehicle accurately without decreasing the lifetime of a beam source of the radar system.
According to one aspect of the invention, there is provided a radar apparatus for a vehicle which comprises: (a) a beam source mounted in the vehicle, emitting a beam of light; (b) a first scanning mechanism directing the beam from the beam source forward of the vehicle so as to scan a first scanning area extending horizontally over a first angular range; (c) a second scanning mechanism directing the beam from the beam source forward of the vehicle so as to scan a second scanning area extending on a road surface horizontally over a second angular range which is greater than the first angular range; and (d) a light receiving mechanism receiving a return of the beam of light directed by the first scanning mechanism to detect an object present in the first scanning area and a return of the beam of light directed by the second scanning mechanism to detect a lane mark printed on the road surface to define a traffic lane.
In the preferred mode of the invention, a rotary mirror is further provided which is rotated to change a direction of the beam of light from the beam source so as to scan the first and second scanning areas selectively. The rotary mirror has a plurality of mirror surfaces which are arranged around a periphery of the rotary mirror and which are inclined at different angles to an axis of rotation of the rotary mirror. The second scanning mechanism includes at least one of the mirror surfaces, while the first scanning mechanism includes the other mirror surfaces.
The light receiving mechanism includes a light sensitive surface and an upper mirror. The light sensitive surface is responsive to input of the return of the beam of light to produce a signal indicative thereof. The upper mirror is designed to direct light traveling from a lower side of a traveling direction of the vehicle to the light sensitive surface.
The light receiving mechanism also includes a side mirror which is designed to direct light falling thereon from a lateral direction traversing the traveling direction of the vehicle to the light sensitive surface.
The side mirror is so arranged that a mirror surface faces downward.
According to another aspect of the invention, there is provided a radar apparatus for a vehicle which comprises: (a) a beam source mounted in the vehicle, emitting a beam of light; (b) a first scanning mechanism directing the beam from the beam source forward of the vehicle so as to scan a first scanning area extending horizontally over a first angular range; (c) a second scanning mechanism directing the beam from the beam source forward of the vehicle so as to scan a second scanning area extending on a road surface horizontally over a second angular range; (d) a light receiving mechanism receiving a return of the beam of light directed by the first scanning mechanism to detect an object present in the first scanning area and a return of the beam of light directed by the second scanning mechanism to detect a lane mark printed on the road surface to define a traffic lane; and (e) a light focusing mechanism provided in the second scanning mechanism, the light focusing mechanism focusing the beam of light on a given portion in the second scanning area.
In the preferred mode of the invention, the light focusing mechanism includes a concave mirror which directs the beam emitted from the beam source so as to scan the second scanning area.
The second angular range is greater than the first angular range.
A rotary mirror is further provided which is rotated to change a direction of the beam of light from the beam source so as to scan the first and second scanning areas selectively. The rotary mirror has a plurality of mirror surfaces which are arranged around a
Hosokawa Toshio
Terui Takekazu
Buczinski Stephen C.
Denso Corporation
Pillsbury & Winthrop LLP
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