Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Radar mounted on and controls land vehicle
Reexamination Certificate
2002-10-15
2004-03-02
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls external device
Radar mounted on and controls land vehicle
C342S071000, C342S072000, C342S118000, C342S158000
Reexamination Certificate
active
06700529
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a radar device to be carried on an automobile for measuring on real time the distance to a front-running vehicle.
The radar device carried on an automobile is a kind of so-called pulsed radar device for transmitting a pulsed beam of electromagnetic waves forward and measuring the distance to an object in front inclusive of a vehicle which may be accelerating, decelerating or even stationary (hereinafter referred to as the front-running vehicle) or its relative speed on the basis of the time it takes to receive its reflection. It now goes without saying that ordinary visible light and x-rays are examples of electromagnetic waves.
FIG. 10A
is a conceptual diagram showing the principle of a prior art radar device
1
carried on an automobile. A pulsed beam
3
of electromagnetic waves transmitted from its signal transmitter (TX)
2
is reflected by a body surface
4
(or any reflective surface such as a back reflector) of a front-running vehicle and received by its signal receiver (RX)
5
. If the time between the transmission of the beam and the reception of the reflected beam is T as shown in
FIG. 10B
, the distance L to the front-running vehicle is given by cT/2 where c is the speed of light. The relative speed between the front-running vehicle and one's own vehicle carrying the radar device
1
can be calculated from the time-rate of change in the distance L between the two vehicles, or as the slope of the curve on the graph of L plotted against the time. If the change in L along the time-axis is zero, for example, this means that the relative speed is zero, or that the front-running vehicle is running at the same speed as one's own vehicle. If L is increasing with time, this means that the front-running vehicle is accelerating with respect to one's own vehicle, and if L is decreasing with time, this means that the front-running vehicle is decelerating with respect to one's own vehicle.
Since the radiative energy of transmitted electromagnetic waves generally decreases inversely proportional to the fourth power of distance, it must be sufficiently large in order to obtain a sufficiently intense reflected beam. Since the capability of the signal transmitter
2
is limited, the beam
3
is generally patterned in a narrowed form, say, with the angle &thgr; of the range of vision equal to about 4°. Such a narrowed pattern is preferred also for the purpose of improving the directional resolution.
FIG. 11A
shows an example of narrowed beam pattern in the horizontal direction.
FIG. 11B
is an example of narrowed beam pattern in the vertical direction.
FIG. 11C
is an example of the cross-sectional shape of such a narrowed beam. Although an example of a narrowed beam with a nearly circular cross-sectional shape is illustrated, the angle &thgr; of the range of vision need not be equal in the horizontal and vertical directions. Such a narrowed beam is generally transmitted at a specified elevation angle (the elevation angle shown in
FIG. 11B
being zero) while scanning in the horizontal direction within a specified range, as shown in FIG.
11
A. The range of the scanning may be determined such that the entire width of an automobile at a sufficiently large distance from one's own vehicle can be covered, that is, about 2.5 m-3 m at 10 m.
With a prior art radar device
1
thus structured, a beam
6
is transmitted from one's own vehicle
7
as shown in FIG.
12
A and if its reflection from the front-running vehicle
8
indicates that the distance between the two vehicles
7
and
8
is sufficiently large, one's own vehicle
7
may be accelerated to reduce the distance. If the distance in between is found to be too small to be safe, such as shown in
FIG. 12B
, one's own vehicle
7
may be braked so as to avoid a collision. In this manner, a so-called stop-and-go system for creeping forward in a traffic jam while maintaining a constant distance from the front-running vehicle may be realized.
With a prior art radar device
1
as described above, a front-running vehicle at a certain distance can be reliably kept visible because a narrowed beam
6
is made used of. There is a problem of suddenly losing sight of the front-running vehicle, however, when the distance between the vehicles is very short.
FIGS. 13A and 13B
show an example of such a situation where one's own vehicle
7
may be a sports car and is relatively low while the front-running vehicle may be a large freight truck having a back reflector attached at a relatively high position. Since the radar beam
6
is usually transmitted with an elevation angle of about zero degree and a range of vision of about 4°, the front-running vehicle
8
is safely visible as long as it is at a sufficiently large distance, as shown in FIG.
13
A. When the distance between the two vehicles
7
and
8
is small as shown in
FIG. 13B
, however, the beam
6
goes under the body of the front-running vehicle
8
without reaching its reflector at the back.
FIGS. 14A and 14B
show another example of such a situation where one's own vehicle
7
may be a large freight truck while the front-running car
8
may be a sports car and is relatively low. When the distance between the two vehicles
7
and
8
is sufficiently large, the front-running vehicle
8
remains within the spreading range of vision of the beam
6
, as shown in FIG.
14
A. When the distance between the two vehicles
7
and
8
is small as shown in
FIG. 14B
, however, the beam
6
may pass above the highest reflective part of the front-running vehicle
8
, thereby inconveniently losing sight of it.
These two examples show that necessary data can be reliably obtained as long as the front-running vehicle
8
is sufficiently far away because its presence can be monitored by the radar device
1
on one's own vehicle
7
but the front-running vehicle
8
may be “lost” if the distance between the vehicles
7
and
8
suddenly decreases, say, because the front-running vehicle
8
has suddenly decelerated. From the point of view of safety requirement on such a device, the aforementioned problem is one that must be solved.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide an improved radar device to be carried on an automobile with which the problem of suddenly losing sight of the front-running vehicle can be solved.
A radar device embodying this invention, with which the above and other objects can be accomplished, may be characterized not only as comprising a transmitter for transmitting forward a beam of electromagnetic waves having a specified vertical angular range of vision at a specified elevation angle (the “specified initial elevation angle”), a receiver for receiving reflected waves of the transmitted beam from a vehicle traveling in front, and a measuring device for measuring a distance to the vehicle in front based on outputs from the receiver, but also as including a command outputting means for outputting a command signal when the distance measured by the measuring device is decreasing and reaches a certain threshold distance below which the measuring device becomes incapable of measuring the distance based on the outputs from the receiver and a beam adjusting means for changing either the elevation angle or the angular range of vision of the transmitted beam in response to this command signal.
In the above, the threshold distance is the distance at which the reflecting portions such as reflectors at the back of the vehicle in front come to be at a dead angle, not reachable by the beam which is directional, usually having a very small angular range of vision. This can happen most frequently where the difference in height between the transmitter of the beam and the reflector on the vehicle in front is great, and this threshold distance can be calculated from this height difference and the angular range of vision of the transmitted beam.
When the distance to the vehicle in front measured by the measuring device is decreasing and reaches this thr
Alsomiri Isam
Omron Corporation
Tarcza Thomas H.
LandOfFree
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