Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Radar mounted on and controls land vehicle
Reexamination Certificate
2002-11-07
2004-02-10
Sotomayor, John B. (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
Reexamination Certificate
active
06690319
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a scan type radar device, particularly to an on-vehicle scan type radar device for detecting a target by a beat signal obtained by mixing a transmitted signal with a received signal which is a frequency modulation signal of the transmission signal reflected from an objective such as a car or a stationary objective (hereinafter referred to as a target), wherein the target is accurately acquired by forecasting a detected value to be obtained at this time from a detected value obtained at a preceding time even though the target detected at the front of a host vehicle moves in the lateral direction.
2. Description of the Related Art
Recently, car crash accidents are liable to increase due to a distraction of attention caused by long and monotonous driving, on a highway, of a vehicle. Also, there is a requirement for the automatic running of a vehicle not only at a constant speed by means of a constant speed driving device but also while tracking a preceding vehicle running at the front of a host vehicle.
Under such circumstances, an on-vehicle radar device has been put into practice, which always measures a distance from the preceding vehicle and automatically reduces the running speed of the host vehicle or brakes the host vehicle if the degree of reduction of the distance becomes large, to prevent a car crash, or always monitors positions of a plurality of preceding vehicles to enable the host vehicle to carry out automatic driving.
Such an on-vehicle radar device generally includes an FM-CW (frequency-modulated continuous wave) radar or a pulse drive radar. Among them, the FM-CW radar device provides a base band signal whose frequency changes like a sawtooth waveform (a triangular wave) to a transmission voltage controlled oscillator (VCO), then transmitted forward of the host vehicle from an antenna after being frequency-modulated, receives the signal reflected from a target such as the preceding vehicle by the antenna and mixes the transmitted signal and the received signal to result in a beat signal from which the preceding target is detected.
In this case, the transmitted signal is transmitted as a plurality of beams spaced at a predetermined angle by oscillating (scanning) the antenna in a predetermined angular range forward of the host vehicle. When the lateral position of the target at the front of the host vehicle is detected by using this on-vehicle scan type radar device, in general, peaks of the received signal in the respective beams are gathered to obtain groups of peaks and the lateral position of the one or more targets are calculated based on the maximum peak in each group.
However, there are drawbacks in the above-mentioned scan type on-vehicle radar device as follows:
(1) When two targets are at the front of the host vehicle and positioned side by side in the lateral direction or overlapped with a stationary objective such as a guard rail in the lateral direction, a position of the maximum peak may fluctuate largely. It the lateral position of the target fluctuates largely as described above, the identification of the position of the target becomes difficult and the target may be lost.
(2) When the host vehicle carrying the radar changes its position, for, example, by changing a traffic lane, the lateral position of the target fluctuates largely to cause a loss of continuity in a system wherein the continuity is obtained by tracking data of the target obtained at this time from the past data of the target because the reference value for determining the continuity is definite whereby if the fluctuation exceeds this reference value, the continuity is lost.
(3) When the peak representing the target is overlapped with a stationary objective such as a guard rail or the peak fluctuates in the lateral direction by a multiple reflection from a concrete wall or the like, there may be a case in which the lateral position of the target is outside of the guard rail or the concrete wall to lose the position of the preceding vehicle.
(4) When there is a stationary objective widely spread in the lateral direction at the front of the host vehicle, such as an overbridge, data signal of the target is combined by data signal of the overbridge as if the lateral position of the target largely fluctuates, which may cause the target to be lost.
Also, there are the following problems:
(5) In the FM-CW radar device, pairing is carried out by extracting the respective peaks in the up-beat (beat generated by the mixture of the transmitted beam and the reflected beam when the frequency of the transmitted beam is increasing) and down-beat (beat generated by the mixture of the transmitted beam and the reflected beam when the frequency of the transmitted beam is decreasing) corresponding to each other. If there are a lot of peaks in the same angular direction, the pairing may be carried out between invalid peaks to miss the target.
(6) When the detected target is positioned adjacent to a more reflective target in the lateral direction (angular direction), only one group of peaks is formed in the angular direction whereby the actual peak of the preceding vehicle is embedded in a powerful peak of the other large target and the detection of the peak of the preceding vehicle becomes impossible. As result, the continuity of the target cannot be detected.
(7) When the detected target is positioned adjacent to a more reflective target in the distance direction (frequency changing direction of the rador device), only one group of peaks is formed in the frequency changing direction whereby the actual peak of the preceding vehicle is embedded in a powerful peak of the other large target and the detection of the peak of the preceding vehicle becomes impossible to lose the continuity of the target.
(8) when a target to be detected is a less reflective object such as a motor cycle, a peak is lower than a threshold value of detection to lose the target.
(9) while a correspondence is made between the respective peaks of the up-beat and the down-beat in a certain angular range, in some cases, an invalid pairing is made when the peaks of different objects are detected at the same frequency.
SUMMARY OF THE INVENTION
A first object of the present invention is to solve the problems in the above-mentioned on-vehicle radar device in the prior art and provide a scan type radar device capable of assuredly acquiring the preceding target and detecting the lateral position thereof even though the peak representing the lateral position of the target detected by a plurality of beams irregularly fluctuates in the lateral direction.
A second object of the present invention is to solve the problems in the above-mentioned on-vehicle radar device in the prior art and provide a scan type radar device having a lower risk of mis-pairing, wherein regarding a target previously detected, the position of the target at this time is estimated by the position thereof at the preceding time, and a representative peak is calculated by executing the grouping with the forecast position as a center.
The scan type radar device for achieving the first object is defined by the first to ninth aspects described below.
The first aspect is a radar device for detecting a target by receiving a returned signal reflected from the target, having a reference value of the lateral fluctuation of the target for judging the continuity between past-detected target data and that detected at this time, characterized in that means is provided for changing the reference value in accordance with the movement of the detected target.
The second aspect is a modification of the first aspect that the reference value changing means comprises means for detecting the lateral fluctuation of the target between the past-detected target data and that detected at this time and means for changing the reference value if it is judged that the target moves to exceed the reference value.
The third aspect is a modification of the second aspect that the reference value changing means forms the j
Kishida Masayuki
Matsui Sadanori
Ono Daisaku
Shinagawa Tokio
Fujitsu Ten Limited
Ryan Laura A.
Sotomayor John B.
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