Data processing: measuring – calibrating – or testing – Measurement system – Dimensional determination
Reexamination Certificate
1999-10-28
2002-05-21
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Dimensional determination
C342S118000, C367S099000, C702S079000
Reexamination Certificate
active
06393377
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a distance measurement apparatus using an electromagnetic wave.
2. Description of the Related Art
There is a prior-art distance measurement apparatus mounted on an automotive vehicle which measures the distance between the present vehicle and a preceding target object such as a preceding vehicle. The prior-art apparatus emits a beam of an electromagnetic wave in a forward direction with respect to the body of the present vehicle. The prior-art apparatus receives an echo beam caused by reflection of the forward electromagnetic-wave beam at a preceding target object. Detection is made about the time interval between the moment of the emission of the forward beam and the moment of the reception of the echo beam. The prior-art apparatus measures the distance between the present vehicle and the preceding target object on the basis of the detected time interval.
In the case where a group of raindrops, a fog, or a spray of water occurs between the present vehicle and a preceding target object, the prior-art apparatus tends to inaccurately measure the distance between the present vehicle and the preceding target object for the reason as follows. A group of raindrops, a fog, and a spray of water reflects the forward electromagnetic-wave beam. The reflection of the forward beam thereat causes a scattered wave beam or an undesired echo beam. The prior-art apparatus responds to the undesired echo beam (the scattered wave beam), and hence fails to accurately measure the distance between the present vehicle and the preceding target object.
A first known way of removing such a problem is to disable a receiver in a distance measurement apparatus for a predetermined time interval after the moment of the emission of a forward electromagnetic-wave beam. The predetermined time interval is chosen to cover a time range during which an undesired echo beam (a scattered wave beam) is expected to reach the receiver. A second known way is to gradually increase the gain of a receiver in a distance measurement apparatus in accordance with the lapse of time from the moment of the emission of a forward electromagnetic-wave beam.
Japanese published unexamined patent application 5-312950 discloses a distance measurement apparatus which emits a leaser beam as a forward beam modulated in accordance with a maximum length code. The apparatus of Japanese application 5-312950 receives an echo beam caused by reflection of the forward beam at an object. The received echo beam is demodulated into a received signal. Detection is made about the phase error between the maximum length code related to the forward beam and a maximum length code represented by the received signal. The distance between the apparatus and the object is calculated from the detected phase error. The apparatus of Japanese application 5-312950 adjusts the gain of a transmitter or the gain of a receiver in response to the magnitude of the received signal. The adjustment-resultant gain is used for a next forward beam or a next echo beam.
The apparatus of Japanese application 5-312950 tends to inaccurately measure the distance between the apparatus and the object in the case where a group of raindrops, a fog, or a spray of water occurs therebetween. A group of raindrops, a fog, and a spray of water reflect the forward beam. The reflection of the forward beam thereat causes a scattered wave beam or an undesired echo beam. When the undesired echo beam (the scattered wave beam) is stronger than a desired echo beam caused by reflection of the forward beam at the object, the apparatus of Japanese application 5-312950 responds to the undesired echo beam and hence fails to accurately measure the distance between the apparatus and the object.
Japanese published unexamined patent application 9-159765 discloses a radar apparatus for a vehicle. The radar apparatus of Japanese application 9-159765 emits a forward light beam, and receives an echo light beam caused by reflection of the forward light beam at a preceding target object. The echo light beam is converted into measurement data. The distance between the present vehicle and the preceding target object is detected on the basis of the measurement data. In the radar apparatus of Japanese application 9-159765, a determination is made about whether or not the measurement data actually has a component corresponding to the echo light beam caused by reflection of the forward light beam at the preceding target object. Reference data is set on the basis of the measurement data which does not have a desired-echo-related component. The reference data represents undesired echo light beams (scattered light beams) caused by reflection of the forward light beam at waterdrops and snow grains. In the radar apparatus of Japanese application 9-159765, current measurement data is corrected in response to the reference data to prevent the undesired echo light beams from causing an error of distance measurement.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a distance measurement apparatus which is less adversely affected by a group of raindrops, a fog, and a spray of water.
A first aspect of this invention provides a distance measurement apparatus comprising transmitting means for transmitting a forward electromagnetic wave; receiving means for receiving an echo wave caused by reflection of the forward electromagnetic wave at an object, and converting the received echo wave into a first received signal; scattered-wave detecting means for detecting a scattered wave reaching the receiving means and caused by reflection of the forward electromagnetic wave at an obstacle such as a group of raindrops or a fog which occurs prior to the reflection of the forward electromagnetic wave at the object; cancel-signal generating means for generating a cancel signal to cancel a scattered-wave-corresponding component of the first received signal generated by the receiving means in response to the scattered wave detected by the scattered-wave detecting means; scattered-wave canceling means for removing the scattered-wave-corresponding component from the first received signal in response to the cancel signal generated by the cancel-signal generating means to change the first received signal to a second received signal; and distance calculating means responsive to the second received signal for measuring a time interval between a moment of the transmission of the forward electromagnetic wave by the transmitting means and a moment of the reception of the echo wave by the receiving means, and calculating a distance to the object on the basis of the measured time interval.
A second aspect of this invention is based on the first aspect thereof, and provides a distance measurement apparatus wherein the scattered-wave detecting means comprises means for measuring a strength of the scattered-wave-corresponding component of the first received signal, and means for measuring a delay time between the moment of the transmission of the forward electromagnetic wave by the transmitting means and a moment of the reception of the scattered wave by the receiving means, and wherein the cancel-signal generating means comprises means for generating the cancel signal on the basis of the strength and the delay time measured by the scattered-wave detecting means and at a timing corresponding to the moment of the reception of the scattered wave by the receiving means.
A third aspect of this invention is based on the first aspect thereof, and provides a distance measurement apparatus wherein the transmitting means comprises pseudo-random-noise-code generating means for a pseudo random noise code having a predetermined bit length, means for modulating an electromagnetic wave into a modulated electromagnetic wave in response to the pseudo random noise code, and means for transmitting the modulated electromagnetic wave as the forward electromagnetic wave, and wherein the distance calculating means comprises demodulating means for demodulating the second received signal i
Hoashi Yoshiaki
Matsui Takeshi
Shirai Noriaki
Harness Dickey & Pierce PLC
Hoff Marc S.
Kim Paul
LandOfFree
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