Outdoor range finder

Details Outdoor range finder Outdoor range finder

1999-09-23

2001-12-18

Buczinski, Stephen C. (Department: 3662)

Optics: measuring and testing

Range or remote distance finding

Triangulation ranging to a point with one projected beam

C356S005040, C348S031000, C348S135000

Reexamination Certificate

active

06331887

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a range finder for an outdoor use, specifically to a range finder that calculates a distance by the light-section method.
BACKGROUND ART
The range finder has been diversified in these days, where the non-contact measuring method such as the light propagation time measuring method and binocular stereopsis method, etc., has been employed more frequently than the contact measuring method. Specially in terms of the accuracy, the light-section method has been prevailing in the application fields such as the robot handling, etc.
Hereafter, a construction of a general measuring equipment using the light-section method will be explained.
FIG. 4
illustrates a construction of a conventional range finder using the light-section method. A laser beam projector
301
emits a laser beam on an object
302
to be measured. When a CCD camera
303
takes an image of the object
302
, a position of the laser beam spot projected on the CCD camera
303
varies depending on a position of the object
302
(triangulation method). In order to measure the position of the laser beam spot, an analog video signal on the CCD camera
303
is converted into a digital signal by an A/D converter
304
. The digital signal is converted into a binary image data by a binarizing circuit
306
on the basis of a predetermined threshold
305
. A labeling unit
307
applies the labeling processing to this binary image data, and a centroid detection unit
308
detects a centroid of the image data, whereby the position of the laser beam spot on the image can be detected. If the position of the laser beam spot on the image is detected, a distance calculation unit
310
is able to calculate the distance by using optical parameters (focal length, distance between the laser projector
301
and the CCD camera
303
, and angle formed by the two) or a calibration table
309
.
Here, in the conventional construction, it is a premise that the image of the laser beam spot projected on the CCD camera
303
is brighter than those of the other parts on the image; however in the outdoors, in a place where the brightness is influenced by the sunbeam, the output power of the laser is inevitably raised, which leaves a problem in terms of safety. Further, since the intensity of illumination complicatedly varies in the outdoors, the threshold cannot be predetermined.
Accordingly, the inventor proposed an equipment in which the coordinate transformation processing is applied concurrently to the image information obtained from a CCD camera, and thereafter the superposition processing is applied to the image with the coordinate transformed, whereby the surrounding light is removed and only the laser beam is identified (see JP-A 8-94322).
However, still in this proposal, when a moving object comes in, or when a background object swings owing to the wind or the like, the images influenced by the moving objects cannot be removed, and are left as noises.
DISCLOSURE OF THE INVENTION
Therefore, it is an object of the invention to provide an equipment that is able to measure a distance with a low power laser without noises remained, when a moving object comes in, or when a background object swings by the influence of the wind.
To accomplish this object, the invention comprises:
a laser emitting means that emits a pulse laser beam to an object to be measured,
an image reading means that takes in an image of the object synchronously with an emission and stop of the laser beam,
a means that requires a plurality of differential images between the images read by a plurality of emissions and stops of the laser beam,
a means that detects a minimum value of said plurality of differential images,
a means that determines a binary threshold from the minimum value of the differential images, and
a means that makes a binary data from the minimum value of the differential images, and detects a position where the laser beam is received.


REFERENCES:
patent: 3463588 (1969-08-01), Meyerand, Jr. et al.
patent: 4274735 (1981-06-01), Tamura et al.
patent: 6-344144 A (1994-12-01), None
patent: 8-177263 A (1996-07-01), None

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