Distance detecting apparatus

A distance detecting apparatus in which an operator is able to readily and accurately see to which one of a plurality of objects the distance is detected. The apparatus is able to concurrently detect the distances to a plurality of objects which exist within the field of view of the subject vehicle. To this end, the apparatus includes: a pair of first and second image sensors including a pair of optical systems for optically sensing a plurality of objects; a first memory for storing the pictures of the objects sensed by the first image sensor as first image signals; a second memory for storing the pictures of the objects sensed by the second image sensor as second image signals; a window defining device for defining a plurality of windows at specific areas of the first or second image signals; and a calculator for making image signals within the respective windows defined by the window defining device as reference signals. The calculator is operable to make a comparison between those of the first and second image signals which correspond to the reference signals, to individually calculate the distance to each object in each window. Preferably, the first and second image sensors are disposed in a vertically spaced apart relation.

BACKGROUND OF THE INVENTION 
The present invention relates to a distance detecting apparatus for 
optically measuring the distance from a vehicle to an object such as an 
obstacle, a preceding vehicle, etc., lying ahead thereof. 
Some typical examples of such a distance detecting apparatus are disclosed 
in Japanese Patent Publication Nos. 63-38085 and 63-46363. The apparatuses 
disclosed therein commonly have a pair of first and second parallel 
optical systems having two convex lenses 101, 102 disposed in a 
horizontally aligned relation at a prescribed distance L away from each 
other, as shown in FIG. 5. A pair of separate image sensors 103, 104 are 
horizontally disposed at focal points of the lenses 101, 102 apart their 
focal distance f from the locations of corresponding lenses 101, 102, 
respectively, for generating respective image signals to a common signal 
processor 120. The signal processor 120 successively shifts the image 
signals from the image sensors 103, 104 and electrically superposes them 
one over the other, so that the perpendicular distance R from the lenses 
101, 102 to an object 121 is calculated based on the principle of 
triangulation using the following formula: 
EQU R=(f.times.L)/d 
where d is a shift distance by which the image signals are moved to obtain 
the best match. 
With the above-described conventional distance detecting apparatus as 
constructed above, however, if there are many objects within the field of 
view of the image sensors 103, 104, it is unclear to which object the 
distance from the subject vehicle is being detected. In particular, let us 
assume that the distance to an object in the form of a preceding vehicle 
is detected by the above-described distance detecting apparatus mounted on 
the subject vehicle during the travel thereof. In this, case, if another 
vehicle travelling on a lane of a road adjacent the one on which the 
subject vehicle is travelling comes into the field of view of the subject 
vehicle, it is not clear at all or the driver cannot tell to which vehicle 
(i.e., travelling on the same lane or on an adjacent lane) the distance is 
detected. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention is intended to overcome the 
above-mentioned problem encountered with the conventional distance 
detecting apparatus. 
An object of the present invention is to provide a novel and improved 
distance detecting apparatus in which an operator is able to readily and 
accurately see to which one of a plurality of objects the distance is 
detected. 
Another object of the present invention is to provide a novel and improved 
distance detecting apparatus which is able to concurrently detect the 
distances to a plurality of objects which exist within the field of view 
of the subject vehicle. 
In order to achieve the above objects, according to present invention, 
there is provided a distance detecting apparatus comprising: 
a pair of first and second image sensors including a pair of optical 
systems for optically sensing a plurality of objects; 
a first memory for storing the pictures of the objects sensed by the first 
image sensor as first image signals; 
a second memory for storing the pictures of the objects sensed by the 
second image sensor as second image signals; 
window defining means for defining a plurality of windows at specific areas 
of the first or second image signals; 
a calculator for making image signals within the respective windows defined 
by the window defining means as reference signals, the calculator being 
operable to make a comparison between those of the first and second image 
signals which correspond to the reference signals, to individually 
calculate the distance to each object in each window. 
Preferably, the first and second image sensors are disposed in a vertically 
spaced apart relation. 
A display having a screen may be provided on which the windows defined by 
the window defining means are displayed. Preferably, the window defining 
means defines the plurality of windows in such a manner that the windows 
are displayed on the screen of the display in a horizontally separate 
relation. 
The above and other objects, features and advantages of the invention will 
become more readily apparent from the following detailed description of a 
preferred embodiment thereof taken in conjunction with the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of the present invention will now be described in 
detail with reference to the accompanying drawings. 
FIG. 1 illustrates, in a block diagram, the schematic arrangement of a 
distance detecting apparatus which is constructed according to the 
principles of the invention and which is mounted on a vehicle for 
detecting the distances to preceding vehicles running ahead (in front) of 
the subject (driving) vehicle. 
The apparatus illustrated includes a pair of first and second parallel 
optical systems having two convex lenses 1, 2 disposed in a vertically 
aligned relation at a prescribed distance L away from each other, and a 
pair of separate first and second (e.g., upper and lower) image sensors 3, 
4 which are vertically or otherwise disposed at focal points of the lenses 
1, 2, respectively, at a distance f from the locations of the 
corresponding lenses 1, 2 for generating first and second image signals 
each in the form of an analog signal representative of a two-dimensional 
image, which are input to a pair of corresponding first and second 
analog-to-digital (A/D) converters 6, 7. The outputs of the A/D converters 
6, 7 are input to a pair of corresponding first and second memories 8, 9 
and stored therein. A calculator 10 in the form of a microcomputer 
performs data transfer with the memories 8, 9 as well as various 
calculations and determinations based on the data stored in the memories 
8, 9. A display 11 having a screen is connected to the first and second 
memories 8, 9 and the microcomputer 10 for displaying a picture sensed by 
the first or second image sensor 8, 9 on the screen. The operation of the 
display 11 is controlled by the microcomputer 10. A window defining means 
12 is connected to the microcomputer 10 for defining on the screen of the 
display 11 a plurality of windows which can be utilized for designating a 
plurality of objects for distance measurements. More specifically, as 
shown in FIG. 2, the driver of a vehicle can manipulate the window 
defining means 12 to define a plurality (e.g., five in the illustrated 
embodiment) of windows 13 through 17 on the screen of the display 11 at 
horizontally spaced or separate predetermined specific locations thereof 
while looking at the screen. 
The operation of the above-described apparatus will be described below 
while referring to FIGS. 2, 3 and 4(a) and 4(b). First, assume that the 
picture of an object in the form of a preceding vehicle 5a ahead of the 
subject vehicle is sensed by the second or upper image sensor 4 and 
digitized by the second A/D converter 7 and then displayed on the screen 
of the display 11 within the images stored in the second memory 9, as 
shown in FIG. 3. In this case, the microcomputer 10 reads out from the 
second memory 9 picture element signals within the window 15 that catches 
the preceding vehicle 5a, to make them as reference image signals, which 
are used as a basis for calculating the distance to the vehicle 5a. Then, 
the microcomputer 10 selects a specific area corresponding to the window 
15 from the first memory 8, which stores image signals of pictures sensed 
by the first or lower image sensor 3. Then, the microcomputer 10 
calculates a total sum of the absolute values of the differences between 
the corresponding image signals for the first and second picture elements 
stored in the first and second memories 8, 9 while vertically shifting the 
image signals from the first memory 8 relative to the above defined 
reference picture signals in a stepwise manner one picture element by one 
picture element. In other words, by sequentially shifting the first memory 
image signals one picture element by one picture element, the best 
position of the imaged picture of the object 5a in the first memory 8 is 
determined in which the imaged picture in the first memory 8 best matches 
the reference picture. Thus, the amount of shift or shift distance of the 
first memory picture relative to the reference picture is calculated which 
minimizes the total sum of the absolute values of the differences. 
In this connection, it is to be noted that the area in the first memory 8 
relating to the above calculation is a vertically extending band area 20, 
as shown in FIG. 4(b), which corresponds to the position of the window 15 
in which the reference picture exists, as shown in FIG. 4(b). 
With the use of the amount of shift n in terms of the number of picture 
elements as calculated above, the distance R to the preceding vehicle 5a 
is calculated as follows: 
EQU R=(f.times.L)/nP (1) 
where f is the focal distance of the first and second lenses 1, 2; L is the 
distance between the centers of the first and second lenses 1, 2; n is the 
amount of shift represented by the number of picture elements for 
minimizing the total sum of the absolute values of the differences between 
the first and second picture elements in the first and second memories 8, 
9; and P is the vertical pitch between adjacent picture elements in a 
vertical array. 
In this manner, the distance R to the object 5 imaged in the window 15 can 
be measured. Likewise, if another vehicle 23 running on an adjacent lane 
of the road ahead of the subject vehicle comes into the fields of view of 
the image sensors 3, 4 and if it is caught by the image sensors 3, 4 and 
displayed on the screen of the display 11 inside the window 17, as 
illustrated in FIG. 3, the microcomputer 10 makes the image signals inside 
the window 17 as reference picture signals as shown in FIG. 4(a), selects 
an image area 22 in the first memory 8 corresponding to the image signals 
of the second memory 9 inside the window 17, and determines the position 
of the imaged picture in the first memory 8 which provides a best match 
with the picture inside the window 17. Then, using equation (1) above, the 
distance to the other preceding vehicle 23 is calculated in the same 
manner. 
In this manner, even in cases where there are a plurality of preceding 
vehicles running ahead of the subject vehicle, it is possible to 
concurrently detect the distances to the respective preceding vehicles. 
As can be seen from the foregoing, the objects caught by the plurality of 
windows 13 through 17 defined on the screen of the display 11, as shown in 
FIG. 4(a), are compared with the imaged pictures thereof in the 
calculation areas of the memory 8 corresponding to the windows 13 through 
17, respectively, as shown in FIG. 4(b), whereby the distances to the 
respective objects can substantially and concurrently be measured using 
the individual windows 13 through 17. 
Although in the above description, five windows 13 through 17 are 
exemplarily set and shown, the number of windows can arbitrarily be varied 
in accordance with the size or dimensions of objects within the fields of 
view of the image sensors as well as the number of objects to which 
distance measurements are required. 
In addition, the size and shape of each window can also be varied 
optionally depending on the objects to be measured, and hence the 
invention is not limited to those which are described and shown in 
relation to the above embodiment.