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BACKGROUND OF THE INVENTION
From U.S. Pat. No. 4,202,612 it is known how to sense the geometric
characteristics of an object or surface by sensing the location of points
thereon. In sensing such points on a surface, however, false data may be
obtained from the sensor systems, resulting in an incorrect representation
of the surface being investigated.
The present invention relates to techniques from which it is possible to
determine whether data on any points that are reported by a
three-dimensional optical sensor are erroneous. By identifying erroneous
data points, the information is available for eliminating such erroneous
points. These erroneous points may be caused by light directed into the
optical sensor or detector, which is not related to the primary projector
light beam reflections. Thus, such erroneous points can be caused by
secondary light reflections from a projector beam, or from another light
source.
Accordingly, it is an object of the present invention to provide an
arrangement for eliminating all points reported by a sensor, which are not
true data points from the projector's primary light beam.
Another object of the present invention is to provide an arrangement of the
foregoing character which is substantially simple in construction and may
be economically produced.
A further object of the present invention is to provide an arrangement, as
described, which has a substantially long operating life and may be
readily maintained in service.
SUMMARY OF THE INVENTION
According to the present invention, the surface location of points is
measured with two different sensors, and false data reports are detected
and eliminated by cross-correlating the data obtained from two different
optical detector locations. The true reports from each sensor location
will compare favorably and can be designated as true reports. False
reports will not compare identically, as will the true reports, and as a
result such non-identical comparisons can be used to efficiently eliminate
the false report. With such elimination of these false reports, only the
true data is left, as desired.
To obtain the data reports, a point on a surface being investigated is
illuminated by a projector, and the light directed onto the surface at
that point is reflected and directed onto a detector, from which the
location of the point is computed by, for example, triangulation methods.
The light applied to the surface at the point being investigated is also
reflected in a different direction onto another detector, for example,
which uses the detected reflected light to compute the position of that
point on the surface. The two computations are then compared to determine
whether the results are identical or not. If the computational results are
identical, then the point detected on the surface can be designated as a
true point. If, on the other hand, the computational results are not
identical, then it may be concluded that the point which has been detected
is not a true point on the surface.
The novel features which are considered as characteristic for the invention
are set forth in particular in the appended claims. The invention itself,
however, both as to its construction and its method of operation, together
with additional objects and advantages thereof, will be best understood
from the following description of specific embodiments when read in
connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic plan view and shows the relationship between the
surface being investigated, a projector and a detector for sensing the
location of a point on the surface, according to the present invention;
FIG. 2 is a schematic view and shows an embodiment in which two detectors
cooperate with one projector for determining true and erroneous data
points;
FIG. 3 is a schematic view of an embodiment in which two sensors, each
equipped with a camera and a projector, are used to determine true and
erroneous data points;
FIG. 4 is a schematic view of a further embodiment in which a single
detector is used in combination with a single projector to eliminate
erroneous data points;
FIG. 5 is a schematic view and shows a method for detecting erroneous data
points by computational techniques.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, FIG. 1 shows the essential elements for
determining the depth location of a point on a surface. Projector 10
projects a narrow beam of light onto the surface 12 at point T, which is
reflected and focused on the detector 14 at point T' on the image plane 16
of this detector 14. By knowing the locations and orientations in space of
the projector 10 and detector 14, together with the projected beam 18 and
reflected beam 20, the three-dimensional location of point T can be
calculated.
If a spurious or falsely illuminated point F on the surface occurs within
the field of view of detector 14, the location of point F is calculated as
being at point G, along the projector beam 18.
With only these two data points, no reliable method or technique exists for
determining if either or both points are false data.
In FIG. 2, a second detector 22 is used to report the locations of points T
and F in a similar manner as carried out above. However, point F is
reported or calculated to be located on the projector axis 18, at point H.
When data from detectors 14 and 22 are compared in the comparator 26, the
data for the true point T will be found the same by both detectors, and
the comparator will find the two sets of data to agree, whereby the output
from the comparator 26 may be interpreted as point T being a true point.
The reflections of points T and F impinge on the detector 22, on its image
plane 24 at points T "and S", respectively.
When, on the other hand, the data outputs from detectors 14 and 22 are
found not to be identical by the comparator 26, the output of this
comparator may be interpreted that the point F is a false point.
As may be observed from FIG. 2, the technique for eliminating false points
used two detectors and one projector. The same results, however, can also
be obtained by the arrangement of FIG. 3 in which two sensing systems are
provided, each having a projector.
Thus, the arrangement in FIG. 3 uses two independent sensors, each equipped
with its own detector and projector. Accordingly, detector 14 cooperates
with its own projector 10 whereas detector 22 is provided with its own
projector 38. With these two detector locations, it is possible to
determine the erroneously reported data, similar to what was described in
relation to FIG. 2. The arrangement of FIG. 3, however, requires more
equipment than FIG. 2, and is slower than this arrangement of FIG. 2.
FIG. 4 is another embodiment in which only one projector 10 and one
detector 14 is used to provide the desired results. In this arrangement of
FIG. 4, the detector 14 is moved to the second position 14', shown by
dashed lines, to obtain a second set of data for comparison purposes by
the comparator 26. The second position of the detector 14 and its beam
axis 20 is represented in FIG. 4 by dashed elements 14' and 20'
respectively.
FIG. 5 shows a still further embodiment in which a false point F is
identified from computational data associated with a number of neighboring
points J lying on the surface. Thus, after determining the locations of
the various neighboring points J, and the false point F, and a surface is
passed through the points J, the point F is found not to lie on that
surface, and therefore may be identified as a spurious point. This
technique of excluding such spurious points F from other points found to
lie on a surface, is commonly known as curve fitting or surface fitting.
As may be seen, this technique requires considerable computations which
are complex and require substantial processing time and/or processing
equipment. The technique is generally feasible for relatively simple
surfaces.
For purposes of computing the three-dimensional location of the true and
false points that are detected at the different locations of the
detectors, a computer 34 is provided. This computer calculates the
three-dimensional locations of the points by using conventional
triangulation calculations based on data obtained from the detectors, as
well as the relative locations of the detectors and projectors. The
computer 34 applies the computed results to the comparator 26 for
comparison purposes. Thus, for example, the data obtained by the detector
14 is applied to the comparator 26 at the input 30 thereof, whereas the
data from detector 22 is applied to the comparator through its input 32.
After comparing the computed results obtained from the two different
locations of the detectors, the comparator applies its output signal
through its output terminal 28 which may, in turn, be connected to an
indicator, for example.
Without further analysis, the foregoing will so fully reveal the gist of
the present invention that others can, by applying current knowledge,
readily adapt it for various applications without omitting features that,
from the standpoint of prior art, fairly constitute essential
characteristics of the generic or specific aspects of this invention, and
therefore, such adaptations should and are intended to be comprehended
within the meaning and range of equivalence of the following claims.
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