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BACKGROUND OF THE INVENTION
This invention relates generally to a borescope or endoscope for providing
a full color video image of a generally inaccessible object, and more
particularly to a system for measuring the size of objects viewed on the
video image display of the borescope.
Various devices have been provided in the prior art for realizing a full
color video picture of a target situated within a remote cavity. These
devices have been gradually improved over time to where today most devices
of this type employ an external light source conveyed to the image head by
fiber optic bundles together with a solid state image sensor and lens
system positioned in the distal end of the insertion tube of the
borescope/endoscope connected to an external video display. A particularly
compact head including a light source and solid state image sensor lens
system of this type is shown in U.S. Pat. No. 4,491,865 to Danna et al.
which patent is owned by a common assignee of the present applicant.
Generally, in systems of this type, the fiber optic illumination bundle and
the image sensor and optical system are disposed side by side in the end
of a small insertion tube adapted to be inserted in cavities for viewing
objects therein. The light provided by the fiber optic bundle has a field
of view slightly displaced from the optical field of view of the image
sensor, but generally overlapping sufficiently to provide an effective
field of vision for the device. The image detected by the image sensor is
displayed on a video screen and will vary in magnification, apparent size,
and detail, depending upon how close the end of the insertion tube
carrying the lens system is from the object being viewed. Generally
speaking, devices of this type have a depth of field from an eighth of an
inch to something over one inch. The real close images, of course, have
the greatest magnification and the more distant images the least.
Heretofore, all attempts to measure the image on the video display to
determine the size of the object being viewed have had to rely on either
the placing of a known scale adjacent to the image to be measured for a
comparison measurement, or the provision of a physical standoff over the
lens on the end of the borescope insertion tube at which point the
magnification is known and then actually adjusting the end of the
borescope until it just touches the object to be viewed at the standoff.
With this known magnification, the image can be measured on the screen and
the precise size determined.
OBJECTS AND SUMMARY OF THE INVENTION
Obviously, this method of measurement has been somewhat awkward and time
consuming and it is therefore an object of the present invention to
provide a system for measuring objects viewed with a borescope video
sensor and lens system that allows measurement without the necessity of
placing scales adjacent the object to be measured or use of physical
standoffs to determine the object distance from the lens system.
It is another object of the present invention to provide an object
measuring system that is self-contained and integral with the illumination
and sensor systems of a borescope.
It is a further object of the present invention to provide an object
measuring system for a borescope or the like that can be operated entirely
externally of the cavity into which the borescope insertion tube is
placed.
It is a further object of the present invention to provide an object
measuring system for measuring the size of an object directly off the
video display screen of a borescope.
It is a further object of the present invention to provide an illumination
system for a full color video image device that additionally provides a
measuring indicator for determining object distance from the lens assembly
of the video imaging device.
It is further object of the present invention to provide an illumination
system including a shadow creating means for automatically indicating the
object distance on a video display screen.
It is a further object of the present invention to provide an illuminating
system for use in a video imaging device that includes projecting an image
of known size and shape through the viewing field of the imager device so
that the image size on the video display screen will indicate the object
distance from the lens system.
It is a further object of the present invention to provide an illumination
system for general illumination of the object to be viewed and for special
measurement illumination of a known pattern that will indicate
magnification, and thus object distance from the lens assembly.
It is a still further object of the present invention to provide an object
measuring system for electronically measuring the size of an object being
viewed with a borescope
It is yet a further object of the present invention to provide an
illumination system for a video imaging device in which a constant size
ring image is projected on the object to be measured so as to indicate
object distance from the lens system.
BRIEF DESCRIPTION OF THE DRAWING
These and other and further objects of the invention, together with
additional features and advantages accruing therefrom will be apparent
from the following description of a preferred embodiment shown in the
accompanying drawings in which like reference numerals indicate
corresponding parts throughout wherein:
FIG. 1 is a partial sectional view of the imager head of a borescope
according to the present invention showing in diagrammatic form the
principles of the present invention;
FIG. 2 is an enlarged end view of the imager head of the borescope of FIG.
1 in accordance with the present invention;
FIG. 3 is an elevation of a display screen and calibrated scale for
particular imaging system showing the relationship between magnification
and object distance from the image detecting lens system;
FIG. 4 is a display screen similar to FIG. 3 with an object to be measured
showing electronic cursors for measurement of the object to be measured;
FIG. 5 is a schematic and diagrammatic representation of another embodiment
of the present invention;
FIG. 6 is an enlarged end view of the imager head of a borescope in
accordance with the invention of the embodiment of FIG. 5; and
FIG. 7 is a display screen showing the use of the embodiment of FIGS. 5 and
6 for measuring objects on the display screen.
FIGS. 8A and 8B are diagrammatic showings of the shadow means of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1 there is shown a borescope imager head 10 having a
fiber optic illumination source 12 and a video image sensor channel 14
with associated lens system 16 positioned in the end of the insertion tube
of a borescope. As described in the prior art, the optical fiber source 12
provides a general illumination which may be single or full color and
which illuminates an area shown diagramatically as arc 18 emanating from
the face of the fiber optic source. The field of view of the imaging
device is determined by the lens system and its juxtaposition with the
solid state sensor device, and is represented by arc 22 in FIG. 1. In the
particular embodiment of the present invention, the fiber optic source is
configured in a thin strip 19 shown in FIG. 2 extending across the fiber
optic channel in a planar fashion. This configuration provides enough
general illumination in as fully an effective manner as the more
conventional circular fiber bundles. Positioned a spaced distance in front
of the termination of the fiber optic thin strip 19 is an opaque index
element or bar 20 which extends the full width of strip 19 and casts a
shadow image from the illumination emanating from the fiber optic strip
onto the objects being viewed. The standard lens system generally is shown
directly below the illumination system in FIG. 2.
The shadow cast by index bar 20 will fall on objects within the field of
view of the imager channel 14 depending upon how far the object is from
the imager lens. An object near the lens such as at line 24 will have the
shadow 21 from bar 20 close to the edge which, in FIG. 3 is translated to
the left edge of the screen. An object farther away from the lens such as
at line 26 will have the shadow from bar 20 falling further down in FIG. 1
or to the right in FIG. 3 and when the image of the object is projected on
the display screen, the shadow will be displaced to the right such as
shadow 23 in FIG. 3. Shadow 27 represents the limit of the measurement
range of the borescope.
An object located at line 24 will appear on the video display as a
relatively large object, while the same object at line 26 will appear
quite small on the display. The shadow 23 will actually be wider in the
line 26 display than the shadow 21 in the line 24 display because of the
divergence of the light from fiber optic strip 19. The shadow will appear
to remain substantially the same width as it traverses across the display.
Referring now to FIG. 3 there is shown a video display screen for the
imager system of the borescope head. Shown in an overlay on the screen is
a magnification and object distance scale 29 calibrated for the particular
display screen based on the geometry of the particular borescope head,
illumination source, imager lens, and detector system. The particular
calibration shown is for a thirteen inch video display screen and a
borescope head illumination pickup system wherein when the imager head is
placed approximately an eighth of an inch from the screen, the
magnification of that image is something on the order of twenty-five times
actual size when displayed on the video display screen. Conversely, when
the imager head is about half an inch from the object being viewed, the
magnification will be reduced to a factor of about nine. The maximum depth
of vision for borescopes of this type is something in the neighborhood of
one inch which, in this configuration, yields a magnification of about
five.
Referring again to FIG. 1, it will be seen that the shadow bar 20 is
positioned off-center of the illumination field so that it will cast a
shadow across the field of view of the lens system at different positions
from left to right on the display screen of FIG. 3 and as represented in
FIG. 1, from top to bottom. Thus, as shown diagramatically in FIG. 1, the
shadow 21 when looking at an object placed at the position of line 24,
will just touch the edge of the field of view and it will appear on the
left side of the display screen of FIG. 3. If the above lens system for
picking up the image is spaced only 0.1 inches or so from the object
itself, the image will be highly magnified on the display screen of FIG.
3. The shadow created by shadow bar 20 will be all the way to the left of
the presentation in FIG. 3, indicating that the image pickup lens system
is approximately 0.140 of an inch from the object being viewed in this
system. The scale in FIG. 1 has been exaggerated for clarity of
presentation, but the actual numbers for a particular borescope and
display screen are as indicated on the overlay in FIG. 3.
Looking again at FIG. 1, it will be seen that as the field of view of the
image device and lens system expands, as you go further from the face of
the lens, the shadow created by the shadow bar 20 from the light source 12
will appear to move to the right on the display screen or to the bottom of
FIG. 1. The distance that this shadow moves from top to bottom in FIG. 1
or left to right in FIG. 3 is proportional to the distance the object
being viewed is from the face of the lens system. This geometric distance
has been related, for the specific embodiment of the present invention as
shown in FIGS. 1 and 3, to the overlay on the screen which shows in scale
form the magnification and object distance for this system from the very
closest visualization to the most distant, for this particular light
source and lens system. It is thus possible to determine the distance from
the object being viewed to the lens face by noting where the shadow falls
on the calibrated scale. This will translate into inches, and at the same
time it will indicate the magnification of the object at the particular
location of the shadow.
The system described can be used in a variety of ways to make measurements
of objects being viewed. To make a measurement in the plane of the image
of an object i.e., a plane at right angles to the axis of the lens system,
the first step would be to note the area where the shadow falls on the
image of the object being measured. If for instance the shadow falls at
the location on the display screen at ten magnification, which means that
the lens system is 0.475 inches from the object being viewed and that the
object is magnified ten times larger than it actually is, then by
measuring the image of the object on the display screen with vernier
calipers or similar measuring device and dividing by ten, the actual size
of the object being viewed by the borescope will be obtained.
Similarly, if the object being measured is a hole or a scratch 25 or other
depression in the surface, there will be found a "blip" 28 in the shadow
line, and instead of being a straight line as shown at 24, it will be a
notched or displaced line, as shown at 28 in FIG. 3. The difference
between the main portion of the shadow 26 and the displaced blip 28, when
measured on the calibrated scale of distance, will show the depth of the
indentation. If the actual surface dimensions of the depression are
desired, they can be physically measured on the display screen with a
vernier caliper or other scale and then divided by the magnifications
indicated at the location of the shadow on the scale to obtain the actual
physical surface size of the depression.
In another embodiment of the present invention, instead of physically
measuring the size of the image on the display screen, one may
electronically measure the object by use of one or more cursors that may
be set at each edge of the object. Thus, as may be seen in FIG. 4, if the
object 30 is to be measured, a first cursor 32 is positioned at the left
edge and a second cursor 34 is positioned at the right edge. The pixels
between cursors 32 and 34 are then electronically counted, translated into
inches or other suitable measurement, and displayed on the viewing screen
or recorded as the case may be. The size translation is accomplished by
noting the position of the shadow and the magnification which is used to
convert the pixels to physical dimensions. Electronically this can be done
by a first step of positioning cursor 32 at the shadow and electronically
counting pixels from the left edge of the screen to the cursor 32. While
the foregoing examples have been shown with the shadow created by shadow
bar 20 moving from left to right in FIG. 3 or top to bottom in FIG. 1, the
system could be set up so that the shadow would move from top to bottom in
FIG. 3 or any other convenient arrangement.
Referring now to FIGS. 5, 6, and 7, there is shown another embodiment of
the present invention. This embodiment involves the projection of a
constant diameter ring image of a known diameter out of the head of the
borescope and into the viewing field of imager channel 14' so as to
impinge on the object to be viewed at whatever distance it may be from the
borescope head. By projecting a constant diameter ring, the apparent size
of the ring will change at the video display as the borescope head is
moved from very closely adjacent the object to the maximum distance the
image can be seen. However, as shown in FIG. 7, we will now have a center
which is the zero point and the extremities which are the maximum
magnification.
By noting the apparent size of the ring as projected on the display screen,
one can determine the magnification, and by measuring the size of the
object on a display screen and dividing by the magnification, the actual
dimension of the object being measured can be determined. The concept is
similar to that shown in FIGS. 1-3, namely by noting the change in
diameter on the display screen of the ring instead of the displacement of
the shadow from left to right, the distance to the object from the lens
system is known and directly related through the geometry of the system to
the magnification of the object being viewed and thus, the actual physical
size of the object being viewed.
In this embodiment, shown in FIG. 5, there is provided a general
illumination source 40 which is fed through a lens system 42 to circular
fiber optic bundle 44 (FIG. 6) extending through the insertion tube 46 to
the image head of the borescope. This source 40 provides general
illumination throughout the field of view of the borescope as shown by the
dotted lines 48 in FIG. 5. The video imager field of view is indicated by
lines 50.
Superimposed upon this general illumination is a source 52 of coherent
laser-like light which is projected via mirror 54 through the fiber optic
cable 46 to the borescope head. The laser light emerges from the head in a
coherent circular beam 56 of light the diameter of which remains
essentially constant throughout the depth of field of the borescope. The
general source of illumination is emitted from the circular fiber optic
termination so that it provides a broad cone of illumination for the
target area of the objects to be viewed. The laser light, which is colored
for easy detection, is superimposed on the general illumination, and
appears on top of the general image of the object being viewed at the
video display.
As can be seen in FIG. 5, as this ring is projected upon the image of the
object being viewed at the display screen, it will appear at image
distance 58 to be a large percentage of the field of view represented by
rectangle 59 and at image distance 60 a smaller percentage of its field of
view represented by rectangle 61. By noting the difference in circle size
on a precalibrated overlay 62, shown in FIG. 7, one can readily determine
the object distance from the lens which gives the magnification, and thus
the actual physical dimension of the object being measured can be
determined from physical measurement of the video screen image.
Thus, in FIG. 7 the defect 64 physically measures 1.5 inches across and the
ring 66 indicates a magnification of 18. Therefore, the defect actually is
0.083 inches across in the 20 object being viewed. If the dotted line ring
66' were used, a magnification of ten would be shown, resulting in an
actual size of 0.150 inches. Similarly in FIG. 4 the defect 30 measures
1.5 inches on the display screen and the shadow 26' indicates a
magnification of six so the actual size of defect 30 in the object being
viewed is 0.245 inches.
In FIG. 4 this can also be determined directly from the overlay by noting
the object distance at each end of the defect and subtracting one from the
other. This, of course, assumes that the object is in a plane essentially
perpendicular to the axis of the video imager channel 14 optical lens
system.
Again, the size of the ring can be measured electronically by counting
pixels in a manner similar to that for the embodiment of FIGS. 1-3, and
with cursors such as in FIG. 4 the size of the object can be determined
automatically and displayed on the video screen.
The embodiment of FIGS. 5-7 has a further advantage in that it allows the
construction of an extremely small diameter borescope insertion tube. For
instance, in one preferred embodiment the video imager lens system has a
diameter of approximately five millimeters. The optical fibers and the
physical encapsulation of the fibers add about one more millimeter so that
the total diameter of the borescope insertion tube becomes approximately
six millimeters. This is considerably smaller in diameter than the system
of FIG. 1 or other known systems today.
In the embodiment of FIGS. 1-3, the shadow bar 20 preferably is of a size
slightly thicker than the thickness of the fiber optic strip 19 so that
the shadow 70 cast on the screen will be a solid black shadow regardless
of the distance from the image head within the depth of field of the
borescope image system. (FIG. 8A). If the shadow strip 20 is narrower than
the light source strip, it is possible that the shadow would be lost at a
more distant object location. (See FIG. 8B).
Obviously the more dense and crisp the edge of the shadow is when projected
on the object and on the display screen, the more accurately one can
measure the objects under consideration. This relative size limitation is
not encountered in FIGS. 5-7.
While this invention has been explained with reference to the structure
disclosed herein, it is not confined to the details as set forth and this
application is intended to cover any modifications and changes as may come
within the scope of the following claims.
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