Distance measuring apparatus

Details Distance measuring apparatus Distance measuring apparatus

2003-02-05

2004-11-16

Gregory, Bernarr E. (Department: 3662)

Optics: measuring and testing

Range or remote distance finding

With photodetection

C356S141100, C180S169000

Reexamination Certificate

active

06819407

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a distance measuring apparatus of the type which may be set on an automobile and uses electromagnetic waves such as laser light to detect the presence of a car in front and to obtain data on its position.
Development of radars (or distance measuring apparatus) to be on an automobile for monitoring the conditions in front has been continuing, including the use of laser light. These apparatus are adapted to transmit electromagnetic waves and to measure the distance to an object in front from the delay time which elapses until reflected waves are received, or to scan an area in front to determine the direction at which a target object of detection is located. If the detection sensitivity of such an apparatus for reflected waves is constant, however, the apparatus may fail to detect an object within its detection area when it is snowing or the weather condition is otherwise adverse, or depending on the surface condition of the target object of detection, such that the intensity of the reflected waves is weakened.
In view of this problem, Japanese Patent Publication Tokkai 10-197635 has disclosed an apparatus comprising means for detecting an adverse weather condition such as rain and snow and adapted to change the transmission condition of laser light such as the speed of its scanning and the frequency of light transmission to adjust the detection time (that is, the duration of time over which received signals are integrated) depending on the weather condition detected by this means such that the detection sensitivity can be improved. As another example, Japanese Patent Publication Tokkai 2000-275340 has disclosed a laser radar adapted to calculate a rate of atmospheric attenuation of reflected waves from a standard target object and to integrate the received signals for a number of times corresponding to this rate of attenuation. Both are adapted to increase the quantity of received signals to be cumulatively added by integration as the weather condition deteriorates and to thereby suppress the noise effect and to improve the sensitivity to maintain the detection capability of the radar under adverse weather conditions.
With these prior art apparatus, either a detector of weather conditions is required or the rate of atmospheric attenuation must be obtained. Thus, the physical structure of the apparatus and the control process become complicated and hence these prior art apparatus are disadvantageous from the points of view of both the cost and the space for installation. An additional disadvantage of these prior art apparatus is that they cannot be adjusted against the surface condition of the target object of detection such as when the surface is stained or dirty. Apparatus disclosed in aforementioned Japanese Patent Publication Tokkai 2000-275340 are particularly disadvantageous because they cannot be used effectively if there is no suitable standard object. In the case of radar device set on an automobile, in particular, the weather conditions are likely to change from one moment to another and a standard object is usually very difficult to set.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a distance measuring apparatus with a simple structure capable of preventing its sensitivity from becoming lowered due to deteriorated weather conditions or the surface condition of the target object of detection without the necessity of detecting the weather conditions.
A distant measuring apparatus embodying this invention may be characterized as comprising what are herein referred to as light-transmitting means, light-receiving means, memory means, area-combining means and judging means. The light-transmitting means is for transmitting electromagnetic waves to scan in a specified scan direction a specified detection area which is partitioned into a plurality of standard areas of a fixed width. The light-receiving means is for receiving reflection of the electromagnetic waves transmitted from the light-transmitting means and reflected by a target object which may be in the detection area. The memory means is for storing signals from the light-receiving means corresponding to individual standard areas. The area-combining means is for carrying out cumulative addition of the signals stored in the memory means corresponding to a set of those standard areas which are mutually adjacent in the scan direction. The result of the cumulative addition is defined as a combined signal associated with a single combined area which is defined as consisting of the set of standard areas if the signals corresponding to these standard areas do not exceed a specified threshold value. Those of the standard areas, the signal from which is not cumulatively added, are each defined as one combined area, the signal therefrom being defined as the combined signal associated with it. The judging means is for judging presence/absence, as well as the position, of a target object based on the combined signals from the combined areas as defined above and obtained by the area-combining means.
In the above, what is referred to as the signal to be stored in the memory means is the data that are received corresponding to each of the standard areas as a result of transmitting and receiving electromagnetic waves once or more times, such as waveform data showing the variations in intensity with time. If transmission and reception take place more than once corresponding to each standard area, the result of the cumulative addition of these more than one signals received within the corresponding standard area is the “signal to be stored.” The area-combining and judging means may be comprised of a microcomputer.
If a signal exceeding the threshold value cannot be obtained in a plurality of mutually adjacent standard areas, signals corresponding to them are cumulatively added by the area-combining means according to this invention and these standard areas are combined together to form a single one of what are herein referred to as the combined areas having the result of this cumulative addition as its corresponding signal. Presence or absence of a target object for detection and its position are judged on the basis of these combined areas and their corresponding signals. Thus, in a situation where reflected waves do exist from a target object and the received signals would normally exceed the target value but fail to do so because of the weather condition such as snow or rain and/or the reflecting surface condition of the target object, the aforementioned cumulative addition will be repeated and the signal intensity will increase and the actual detection sensitivity will be improved although the resolving power of detection will diminish accordingly. As a result, deterioration of detection capability of the apparatus due to weather and surface conditions can be prevented. Since environmental conditions such as the rate of atmospheric attenuation need not be separately measured, the apparatus does not become bulky or complex. If the standard areas are made sufficiently narrow, the resolving power can be improved and such an apparatus installed on an automobile may be able to detect the traffic lane in which the car in front is traveling or even the type of such a car in front.
According to a preferred embodiment of the invention, the area-combining means will operate such that, if neither the result of cumulative addition of signals corresponding to a set of mutually adjacent standard areas nor the signal from the next one of the standard areas after this set of standard areas in the scan direction exceeds the threshold value, cumulative addition will be repeated by including the signal from the next standard area and the next standard area will be included together in the single combined area corresponding to the set of standard areas. In this manner, the number of standard areas combined in a single combined area may be sequentially increased.
For example, if the signal corresponding to one standard area exceeds the threshold value, this signal

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