Note: Descriptions are shown in the official language in which they were submitted.
j Background and Summa y_of the Invention
~` This inven~ion pertains to electro-optical distance~
measuring apparatus, and more particularly, to a unique positional
and attitudinal arrangement of components in such apparatus which
promotes a high degree of accurate performance over a relatively
wide dynamic range of distances.
There are many ~nstances, such as for example in a
plywood mill, where it is desired to make an accurate
measurement of the distance between a known location and a
particular object, so as to locate the object (or more particularly,
the object's near surface) as precisely as possible in space. A
preferred embodiment of the present invention is described herein
in conjunction with a block centering operation, wherein it is
important to be able to position a log in a closely controlled
position relative to a veneer peeler blade.
According to this preferred embodiment a small-diameter
laser beam is projected along one axis toward what might be
thought of as a viewing zone, in which logs are expected to appear
prior to a block centering operation. "~ooking", so-to-speak,
along another and intersecting axis is an optically sensitive
viewer which looks for light from this beam which is reflected
from a log's surface.
It is known, and expected, that logs appearing within
this zone will have different diameters. For example, it miyht
be typical to expect logs having diameters in the range of about
8-inches to about 48-inches. Obviously, the distance-measuring
system of the invention must be capable of monitoring logs within
such a diameter range. ~s will be more fully explained below,
the angle between the beam-projection axis and the viewing axis
is selected both to accommodate the "dynamic ranye" of expected
log-diameter differences, and to maximize the resolution accuracy
of viewed reflected light, so that such accuracy does not vary,
1.
s~
in any appreciable sense, over the entire selected dynamic
range.
Employed in the "viewing" portion of the apparatus are
a lens and a linear (straight-line) photodetector array. I~hen
the laser beam strikes the surface of a log, the lens focuses
onto the array an image of the reflected light. The position of
such image J along the length of the array, is directly inter-
pretable to indicate the distance to the impinged log surface~
Throughout the dynamic range of the apparatus, and as logs of
different diameters are observed, imaged reflected light will
strike the photodetector array at different specific points along
its length.
A unique and important feature of the present invention
is the discovery that the angular positioning of the photodetector
array is critical to assuring that, throughout the dynamic range
which is contemplated, a reflected image on the array will always
be in sharp focus thereon. In other words, with proper attention
to such angular positioning, the focus of the image is indepen-
dent of log-surface distance. If attention is not paid to this
important angular positioning of the array, the focus of a re-
flected image thereon will change throughout the dynamic range,
and will thus cause significant resolution accuracy differences.
These and various other objects and advantages which
are attained by the invention ~ill become more fully apparent as
the description which now follows is read in conjunctîon with
the accompanying drawing.
Description of the Drawing
The single drawing figure illustrates, in schematic
form, a preferred embodiment of the distance-measuring apparatus
of the invention. The drawing is not prepared to scale.
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; Detailed Descript~`on of the Inventîon
Turning now to the drawing, what is shown herein is a
side schematic view illustrating the components o~ the distance-
measuring apparatus contemplated herein, and of the special
positional and attitudinal arrangement of such components. The
parts are not drawn to scale. Included within the apparatus are
a laser 10, aLso referred to as a beam-projecting means, a lens
12, also referred to as a gathering means) and a linear photo-
de~ector array 14, which i5 also referred to as a radiation-
-~ sensing means. Each of these components is conventional in
construction, and commercially available.
Indicated generally at 16 is what might be thought of
as a viewing zone in which the apparatus is intended to monitor
the positions of the near sides of logs. A log within this zone
is shown at 18.
Laser 10 is positioned and oriented to project a
small-diameter beam (typically about 1.5-millimeters in diameter)
along a projection axis shown at 20. Axis 20 extends into zone
16, and occupies the plane of the drawing.
Lens 12 is positioned and oriented to view zone 16
generally along a central vie~ing a~is shown at 22. Axis 22
intersects axis 20 J and also lies in the plane Qf the drawing.
Lens 12 herein is a circular, double-convex lens which lies in a
plane 24 that is normal both to ~he plane of the drawing, and to
axis 22.
As was mentioned briefly earlier, the apparatus of the
invention is designed to offer a pr~selected dynamic vie~Ing
range suited to the particular setting in which it is employed.
In the 5pecific example now being described, the apparatus of the
invention is used to locate t~e near surfaces of logs whose
diameters lie within the range of about 8-inches to abbut 48-
inches. Logs presented in viewing zone 16 will, through conven-
tional log-handling apparatus which is in no way involved with
the present invention, normally be placed in zone 16 with their
approximate central axes always closely aligned with a predeter-
mined axis that extends (~at a known location) through the viewing
zone Csubstantially normal to the plane of the drawing~. Thus,
with logs hàving such a range of expected diameters, the required
dynamic range for the illustrated system is about 20-inches.
Referring to the left side of the drawing, circular
line 26 represents one "end" of the selected dynamic range, and
line 28 represents the other "end". More specifically, a log
having a diameter o~ about 48-inches would, as viewed in the
drawing, have its outside generally coincident with line 26. On
the other hand, an 8-inch diameter log similarly viewed would
have its outside generally coincident with line 28. Line 30
represents a log having a diameter o~ about 24-inches. Log 18
has a diameter of about 38-inches.
Still with reference to the left side of the drawing,
it can be seen ~hat axis 20 intersects line 26 at a point 32,
intersects the near surface of log 18 at a point 34, in~.ersects
line 30 at a point 36, and intersects line 28 at a point 38.
These points are, of course, merely representative of the infinite
number of points, between points 32, 38, where the beam from
laser 10 could intersect, or impinge, the side of a log in zone
16.
With respect to the four particular points just men-
tioned, and considering the operation of lens 12, t~e`lens, onits right side, images a beam-impingement occurring at poin~ 32
along a line~40, images an impingement at point 34 with log 18
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along a line 42, images an impingement at point 36 along a line
44, and images an impingement at point 38 along a line 46. Lines
40, 42, 44, 46 all lie in the plane of the drawing.
The exact angle ~hich i5 used between axe~ 20, 22
is a matter of choice, and depends upon the specific application
in which the apparatus is to be used. Generally speaking, and
considering the use of a photodetector array having a particular
length, the greater this angle, the smaller the dynamic range and
the greater the optical resolution. Conversely, the smaller the
angle, the greater the dynamic range and the poorer the optical
resolution. In the particular application now being described,
wherein the dynamic range is a~out 20-inches, the angle between
these axes is about 14.5.
Another factor which is a matter of choice, and which
depends upon the particular application for the apparatus, is the
distance of the apparatus from the viewing zone. In the parti-
cular apparatus illustrated herein, :Lens 12 is located about 60-
inches from previously mentioned point 38.
Turning attention now to a key aspect of the invention,
in order to maximize the resolution accuracy of the apparatus, it
; is important th~t, throughout the selected dynamic range, reflec-
tion images produced by len~ 12 on array 14 all be in sharp focus
where they impinge the array. For example, an image reflection
from point 32 which strikes the surface of the array where the
same is intersected by a line 4Q should be as sharply in focus as
an imaged reflection derived from any other point of intersection
between the beam of the`laser and the surface of a log in zone
16. ~ith specific reference to the several illustrated points,
the imaged reflection from impingement point 34 ~ith log 18
strikes the photodetector ~here the same is intersected b~ line
42; one derived from point 36 strikes the`photodetector where it
is intersected by line`44; and one`derived from point 38 strikes
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the photodetector where it is intersected by line 46.
To achieve the kind of consistant, dynamic-range, sharp
focusing now being discussed, it is critical that the surface of
array 14 which faces lens 12 lie along a line which intersects
axis 20 at the same point where axis 20 is intersected by the
plane containing lens 12. Such a line for the array is repre-
sented by line 48, and can be seen to intersect axis 20 and plane
24 at a point 50. Tl~e photodetector array may occupy different
angular orientations which may be a matter of choice, but will
only perform with the accuracy praposed by the present invention
if the "point 50" intersection geometry just descrîbed is observed.
Further, while line 48 may be disposed at a slight angle extending
either toward or away from the plane of the dra~ing, according to
a preferred embodiment of the apparatus, line 48 also lies in the
plane of the drawing.
So long as the above geometrical arrangement is observed,
for any selected dynamic range for the apparatus, all reflected
images directed onto the photodetector array throughout the range
will be in sharp conslstant focus thereon. Thus, information
derived from the apparatus will exhibit uniform and consistant
accuracy.
Completing a description of what is shown in the
drawing, indicated ~enerally iTl block form at 52 is a convention-
al scan control and signal processing unit. This unit repetîtive-
ly scans the light-receiving condition of array 14, and produces,
on an output conductor 54, a signal directly reflective of the
position along the array at ~hich an image appears. The present
invention is not concerned ~ith the details of unit 52. ~ommer-
cially available units, like unit 52, are readily available to
perform the functions just des;cribed.
It is thus now beIieved to be obvious ho~ appa~atus in
accordance with the`present invention ma~ be constructed, arranged
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and used to produce extremely accurate dîstance measurements.
Obviously, îf it îs desirable`to look, for example, at multiple
different points along the length of a long obj.ect such as a log,
a plurality pf apparatus units., such as t~e one shown in the
drawing, may be used which are distributed in such a fashion to
take views at predetermined interYals along the object~ Further,
it will be`obvious that the inventîon is useable in an extremely
; wide variety of applications involving industries other than the
wood products industry~
10While a preferred embodiment of the invention has been
described herein, it is appreciated that variations and modifica-
tions, some of which have been suggested above, may be made
without departing from the spirit of the invention~
