Vehicle collision avoidance system

A collision avoidance system for a vehicle has a vehicle steering sensor for sensing a direction in which the vehicle is being steered, a source of radiation, an articulated reflector for directing radiation from the source in a desired direction, an articulation mechanism for effecting articulation of the articulate reflector, and a close loop control circuit responsive to the vehicle steering sensor for controlling the articulation mechanism so as to cause the articulated reflector to direct radiation in a direction which is generally the same as that direction in which the vehicle is turning.

FIELD OF THE INVENTION 
The present invention relates generally to radar systems and more 
particularly to a collision avoidance system for a vehicle, the system 
using a mechanically steered radar antenna to facilitate side-looking as 
the vehicle travels along a curve. 
BACKGROUND OF THE INVENTION 
Vehicle collision avoidance systems for preventing a moving vehicle from 
colliding with an obstacle are well known. It is also known to utilize 
radar and the like to determine the bearing and range of such obstacles, 
such that the vehicle may evade the obstacles by turning and or braking. 
Such vehicle collision avoidance systems require that the radar beam be 
swept or steered from side to side, so as to determine the bearing of an 
obstacle. However, as those skilled in the art will appreciate, such 
contemporary means for effecting steering of the radar beam are complex 
and costly. Three examples of mechanisms for steering radar beams are 
provided in U.S. Pat. No. 3,745,582 issued on Jul. 10, 1973 to Karikomi et 
al. and entitled DUAL REFLECTOR ANTENNA CAPABLE OF STEERING RADIATED 
BEAMS; U.S. Pat. No. 5,025,262 issued on Jun. 18, 1991 to Avdelrazik et 
al. and entitled AIRBORNE ANTENNA AND A SYSTEM FOR MECHANICALLY STEERING 
AN AIRBORNE ANTENNA; and U.S. Pat. No. 5,432,524 issued on Jul. 11, 1995 
to Sydor and entitled DRIVE ARRANGEMENT FOR MECHANICALLY-STEERED ANTENNAS. 
It is clear that the techniques for steering a radar antenna, which are 
disclosed in the patents, have evolved directly from those commonplace in 
aerospace, where cost is much less of a concern than it is in the consumer 
marketplace. Thus, as will be appreciated from a review of U.S. Pat. Nos. 
3,745,582, 5,025,262 and 5,432,524, such contemporary radar beam steering 
mechanisms are very complex and consequently too expensive for use in 
privately owned vehicles. 
In view of the foregoing, it would be beneficial to provide a mechanically 
steered radar antenna for use in vehicle collision avoidance systems which 
is much less complex than contemporary steered radar antennas, and which 
is consequently much less expensive to manufacture. 
SUMMARY OF THE INVENTION 
The present invention specifically addresses and alleviates the 
above-mentioned deficiencies associated with the prior art. More 
particularly, the present invention comprises a collision avoidance system 
for a vehicle, the system having a vehicle steering sensor for sensing a 
direction in which the vehicle is being steered; a source of radiation; an 
articulated reflector for directing radiation from the source in a desired 
direction; an articulation mechanism for effecting articulation of the 
articulate reflector; and a closed loop control circuit responsive to the 
vehicle steering sensor for controlling the articulation mechanism so as 
to cause the articulated reflector to direct radiation in a direction 
which is generally the same as that direction in which the vehicle is 
turning. 
The source of radiation comprises both a feed horn and a fixed reflector 
receiving radiation from the feed horn and directing the radiation onto 
the articulated reflector. The radiation preferably comprises microwave 
radiation, i.e., radar. The articulated reflector is preferably configured 
as a section of a paraboloid, with an elliptic outline. 
The articulation mechanism is configured to effect rotation of the 
articulated reflector about a generally vertical axis and or to effect 
translation of the articulated reflector along a transverse axis of the 
vehicle. In any instance, movement (rotation and or translation) of the 
articulated reflector is such that it is capable of causing the microwave 
beam to be swept from right to left and back. 
The vehicle steering sensor senses a direction in which a steering wheel 
has been turned. The closed loop control circuit comprises a 
microprocessor for controlling the direction in which the radiation is 
directed from the articulated reflector. In this manner, the radiation is 
accurately and reliably directed in the same direction that the car is 
being turned. 
Thus, the vehicle collision avoidance system of the present invention 
prevents collision of a vehicle by sensing a direction in which the 
vehicle is being steered and directing radiation upon an articulated 
reflector which directs the radiation therefrom using position feedback to 
control the direction in which the radiation is directed therefrom, the 
direction being generally the same as the sensed direction in which the 
vehicle is being steered. 
These, as well as other advantages of the present invention will be more 
apparent from the following description and drawings. It is understood 
that changes in the specific structure shown and described may be made 
within the scope of the claims without departing from the spirit of the 
invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The detailed description set forth below in connection with the appended 
drawings is intended as description of the presently preferred embodiment 
of the invention and is not intended to represent the only form in which 
the present invention may be constructed or utilized. The description sets 
forth the functions and the sequence of steps for constructing and 
operating the invention in connection with the illustrated embodiment. It 
is to be understood, however, that the same or equivalent functions and 
sequences may be accomplished by different embodiments that are also 
intended to be encompassed within the spirit and scope of the invention. 
The collision avoidance system of the present invention is illustrated in 
FIGS. 1-3 which depict a presently preferred embodiment of the invention. 
Referring now to FIG. 1, the collision avoidance system generally 
comprises a feedhorn 10 for generating radiation to be utilized in the 
detection of obstacles. According to the preferred embodiment of the 
present invention, the feedhorn 10 transmits microwave radiation, thereby 
defining the preferred embodiment of the present invention as a radar 
collision avoidance system. However, as those skilled in the art will 
appreciate, various different types of radiation, e.g., acoustic, light, 
etc., may likewise be utilized. 
Thus, according to the present invention, microwave radiation from the 
feedhorn 10 is transmitted along path D to fixed reflector 12, from which 
it is focused toward articulated reflector 14, along path C. As those 
skilled in the art will appreciate, the sum of the lengths of paths C and 
D is approximately equal to the focal length of the parabolic articulated 
reflector 14, so as to facilitate effective transmission and reception of 
the radar signals. 
As discussed in further detail below, articulated reflector 14 moves so as 
to effect steering of the radar beam reflected therefrom, generally such 
that the transmitted radar beam 15 is directed in the same direction that 
the vehicle is travelling. Dimension A (FIG. 1) is the clearance necessary 
between the articulated reflector 14 and the fixed reflector 12 to assure 
that the fixed reflector 12 does not interfere with the microwave 
radiation from articulated reflector 14. 
The signal to be transmitted is generated via transmitter 20 and travels 
through transmitter receiver combiner 16 which facilitates the 
simultaneous transmission and reception of radar signals according to well 
known principles. From the transmitter receiver combiner 16, the radar 
signal travels through wave guide transition 18 to the feedhorn 10. 
Received radar signals, i.e., those reflected from obstacles, are reflected 
by the articulated reflector 14 to the fixed reflector 12 and into the 
feedhorn 10. From the feedhorn 10, such received radar signals travel 
through wave guide transition 18 to transmitter receiver combiner 16, from 
which they are directed to receiver 22. From the receiver 22, a signal 
representative of the size and bearing of the obstacle is transmitted to 
CPU 24 which is then utilized to effect the evasive control, i.e., 
steering and/or braking, of the vehicle, according to well known 
principles. 
The CPU 24 also receives an output from the vehicle steering transducer 26, 
so as to effect control of the articulated reflector 14. The articulated 
reflector 14 is moved so as to steer the transmitted radar signal 15 such 
that the transmitted radar signal 15 is generally directed in the 
direction in which the vehicle is travelling. For example, if the vehicle 
is turning left, then the articulated reflector 14 will direct the 
transmitted radar signal 15 to the left, so as to facilitate the 
identification of any obstacles which may be encountered by the vehicle in 
that direction. The sharper the vehicle is turned to the left, for 
example, the sharper the articulated reflector 14 directs the transmitted 
radar beam 15 to the left. In this manner, the likelihood of detecting 
obstacles in the path of the moving vehicle is enhanced. 
The CPU 24 utilizes the vehicle steering transducers 26 output so as to 
generate a signal in response thereto for causing the motor drive 28 to 
drive the motor 30, via linkage 32, in a manner which causes the 
articulated reflector 14 to direct the transmitted radar beam 15 in the 
desired direction. 
Thus, according to the present invention, the transmitted radar beam 15 is 
directed in generally the same direction as the vehicle travels, even when 
the vehicle is making a turn. 
As discussed in detail below, the articulated reflector 14 may either be 
rotated or translated, so as to effect such desirable directing of the 
transmitted radar beam 15. 
Referring now to FIG. 2, rotation of the articulated radar reflector 14 is 
illustrated. According to one configuration of the present invention, the 
articulated reflector 14 rotates about a generally vertical axis 17, such 
as that generally at the center thereof, so as to effect steering of the 
transmitted radar beam 15. 
As those skilled in the art will appreciate, a given rotation of the 
articulated reflector 14 results in twice that much deflection of the 
transmitted radar beam 15, e.g., a 1.degree. rotation of the articulated 
reflector results in a 2.degree. deflection of the transmitted radar beam 
15. 
In this manner, the transmitted radar beam 15 may be directed to the left 
(a counter-clockwise rotation), or to the right (a clockwise rotation, as 
shown), such that it generally corresponds to the direction of travel, 
even when the vehicle is turning. 
Alternatively, the transmitted radar beam 15 may be caused to sweep 
continuously back and forth, from left to right and back again, so as to 
constantly provide an indication of the presence of obstacles both ahead 
and to the sides. 
Such rotation of the articulated antenna 14 may be accomplished via either 
a linear motor or actuator or via a conventional rotary motor, as well as 
the appropriate linkage, according to well known principles. 
Referring now to FIG. 3, the articulated reflector 14 may alternatively be 
translated, i.e., moved in a generally linear fashion from left to right 
or right to left, so as to effect such steering of the transmitted radar 
beam 15. As those skilled in the art will appreciate, translation of the 
articulated antenna 14 results in the displacement of the feed horn 10 
from the axis of the articulated reflector 14, causing the beam to change 
direction. For example, if the articulated reflector 14 is moved to the 
right as shown, then the transmitted radar beam 15 is directed to the 
right. 
As those skilled in the art will appreciate, the articulated reflector 14 
may thus be moved either via rotation, translation, or a combination 
thereof, so as to effect the desired steering of the transmitted radar 
beam 15. 
Thus, according to the present invention, radar or the like is provided 
with a mechanically steered antenna so as to facilitate collision 
avoidance and intelligent cruise control for ground based vehicles such as 
cars, trucks, motorcycles, and the like. According to the present 
invention, the antenna facilitates the detection of obstacles both 
straight ahead and to the sides of the vehicle, particularly as the 
vehicle is executing a turn. 
The articulated reflector is preferably configured as an elliptic 
paraboloid according to the formula: 
EQU z=f((x/b).sup.2 +(y/b).sup.2).ltoreq.c where f=focal length, b=radius, 
c=height. 
The size of the articulated reflector 14 is reduced somewhat, so as to make 
it compatible with use in ground base vehicles, by removing a portion of 
the paraboloid. This is accomplished by removing that portion of the 
paraboloid which is bounded by the elliptical cylinder: 
EQU (x/d).sup.2 +((y-e)/d).sup.2 =1 
where d=radius of the selection, e=offset from center. 
The gain of the resulting antenna is determined by the formula: 
EQU G=4.pi.a/.lambda..sup.2 where a=.pi.d.sup.2 area, .lambda.=wavelength. 
As mentioned above, Dimension A is a mechanical clearance between the 
articulated reflector 14 and the fixed reflector 12. Dimension A provides 
clearance between the articulated reflector 14 and the fixed reflector 12, 
so as to prevent mechanical interference during movement of the 
articulated reflector 14 and also so as to provide a clear field of view 
during transmission and reception of radar signals by the articulated 
reflector 14. The requirement that Dimension A be greater than 0 
necessitates that the articulated reflector define a partial section of a 
parabolic dish. 
The fixed reflector 12 is preferably defined by a section of a hyperboloid. 
It is positioned and configured so as to assure that dimension A is 
greater than 0 and is disposed within the paraboloid articulated 
reflectors 14 focal length according to the formula: 
EQU (z'/f).sup.2 -(x'/g).sup.2 -(y'/g).sup.2 =1 
The prime notation indicates new coordinates, f and g are constants. 
The feedhorn 10 is the input output element for the radar subsystem. The 
antenna pointing angle is 0.degree. when the feedhorn 10 is located at the 
focus of the main reflector. The feedhorn 10 and the fixed reflector 12 
cooperate to define a folded, or Cassegrain style feed for the articulated 
reflector 14. The articulated reflectors 14 axis is the line from the 
center of the feedhorn to the fixed reflector 12 and then to the 
articulated reflector 14. 
According to the present invention, the transmitter/receiver combiner 16 
facilitates the sharing of a single antenna system, i.e., the feedhorn 10, 
the fixed reflector 12 and the articulated reflector 14, for both 
reception and transmission of the radar beam, thereby reducing the cost 
and providing for a more efficient packaging of the collision avoidance 
system of the present invention. 
The wave guide transition 18 between the feedhorn 10 and the 
transmitter/receiver combiner 16 provides efficient signal transfer from 
the coaxial cable, microstrip transmission line, or co-planar transmission 
line in the transmitter/receiver combiner to the wave guide of the 
feedhorn 10. Of course, this transition is bidirectional. 
The motor subsystem consists of the CPU 24, the motor drive 28, motor 30, 
mechanical linkage 32 to the articulating reflector 14, and vehicle 
steering transducer 26. The steering signal originates from one or more 
sensors associated with the vehicle's steering linkage. Such sensor(s) 
sense the orientation of the steering wheel or wheels of the vehicle, so 
as to provide an indication of the direction in which the vehicle is 
heading, i.e., straight ahead or turning. The CPU 24 receives the steering 
signal from the vehicle's steering transducer 26 and the output from the 
radar receiver 22 and calculates the pointing angle therefrom. The output 
from the CPU 24 is applied to the motor drive 28 which converts the 
digital signal from the CPU 24 into an analog signal suitable for driving 
the motor 30. The analog drive signal is applied to the motor 30 so as to 
effect desired movement of the articulated reflector 14. 
As those skilled in the art will appreciate, either stepping or continuous 
motors may be utilized to effect either rotational translation of the 
articulated reflector. The motor is preferably reversible. 
As the vertex of the articulated reflector 14 is rotated .theta., the 
resulting antenna angle is varied by .DELTA.=2.theta.. As the articulated 
reflector 14 is moved along a line perpendicular to the vertex by a 
distance B, the resulting change in antenna angle .DELTA. is approximately 
equal to arcsin (D/F), where F is the focal length of the articulated 
antenna 14. Maximum gain and minimum sidelobes are obtained for .DELTA.=0. 
As those skilled in the art will appreciate, when the reflector is moved 
from the focal point, the performance degrades. It has been found that the 
performance of the present invention is acceptable for 
.DELTA..ltoreq..+-.3 beamwidths in the vehicle application (beamwidth is 
-3 dB of antenna boresight). 
The position of the articulated reflector 14 is sensed by position 
transducer 34, which provides an output to the CPU, so as to facilitate 
closed loop feedback control of the position of the articulated reflector 
14, thereby enhancing the accuracy with which such directional control is 
provided. The position transducer 34 preferably converts position to a 
voltage applies this voltage to the CPU, which then converts the voltage 
to a digital form and then calculates an error correction signal which is 
then fed back to the articulated reflector 14 via the motor drive 28, 
motor 30 and linking, according to well known principles. 
Thus, according to the present invention, the path from the CPU 24 to the 
position transducer 34 is a closed loop feedback circuit. 
Alternatively, the CPU 24 may point the articulated antenna 14 based upon 
information provided in the return radar signal, such as when angle scan 
is based upon signal power, according to well known principles. 
According to the preferred embodiment of the present invention, the 
transmitter 20 provides a carrier frequency of 77 gHz. The main reflector 
is approximately 10 cm across its longest dimension and the subreflector 
is approximately 2 cm in diameter. Distance A is approximately 1 cm, so as 
to provide the desired clearance between the fixed reflector 12 and the 
articulated reflector 14. 
It is understood that the exemplary method for collision avoidance system 
described herein and shown in the drawings represents only a presently 
preferred embodiment of the invention. Indeed, various modifications and 
additions may be made to such embodiment without departing from the spirit 
and scope of the invention. For example, the shape and or configuration of 
the articulated reflector 14 may be varied, so as to accommodate desired 
packaging within a particular vehicle. Thus, portions of the periphery of 
the paraboloid thereof may be omitted or cut away, so as to obtain desired 
clearance to facilitate the necessary motion thereof for directing the 
radar beam. In this manner, the shape of the articulated reflector 14 may 
be varied so as to prevent it from contacting nearby vehicle components as 
it moves. Additionally, as mentioned above, various types of radiation, 
acoustic, laser, etc., may be utilized according to the present invention. 
Thus, these and other modifications and additions may be obvious to those 
skilled in the art and may be implemented to adapt the present invention 
for use in a variety of different applications.