U.S. patent number 3,686,675 [Application Number 05/021,218] was granted by the patent office on 1972-08-22 for apparatus and method for drawing with a spot of radiant energy.
This patent grant is currently assigned to Faul-Coradi, Inc.. Invention is credited to Thomas L. Faul, Richard G. Young.
United States Patent |
3,686,675 |
Faul , et al. |
August 22, 1972 |
APPARATUS AND METHOD FOR DRAWING WITH A SPOT OF RADIANT ENERGY
Abstract
A line is traced on a photosensitive surface by a moving spot of
light which has a uniform and constant intensity, and variable
outside dimensions to change the width of a line produced thereby.
Within the spot, there is a darkened area which changes in size
according to the velocity of the spot over the photosensitive
surface in order to expose the photosensitive surface uniformly
along the length of the line. A cathode ray tube presents a picture
which is projected on the photosensitive surface to create the spot
of light.
Inventors: |
Faul; Thomas L. (Skaneateles,
NY), Young; Richard G. (Fairfax, VA) |
Assignee: |
Faul-Coradi, Inc.
(N/A)
|
Family
ID: |
21803020 |
Appl.
No.: |
05/021,218 |
Filed: |
March 19, 1970 |
Current U.S.
Class: |
347/226; 355/1;
396/548; 346/100; 346/107.1 |
Current CPC
Class: |
G06K
15/225 (20130101) |
Current International
Class: |
G06K
15/22 (20060101); G03b 027/00 () |
Field of
Search: |
;346/110,108,1 ;95/12
;178/6.7R,6.7A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hartary; Joseph W.
Claims
I claim:
1. A method of drawing on a sensitive surface with a spot of
radiant energy directed thereagainst comprising the steps of
projecting on the sensitive surface a spot of radiant energy having
constant outside dimensions and a given intensity,
said spot surrounding a centrally located void area which has a
lesser intensity than said given intensity,
moving the spot relative to the sensitive surface to irradiate a
line on the sensitive surface,
changing the dimensions of the void area in response to changes in
the velocity of the spot across the sensitive surface, with the
size of the void area decreasing with increases in the velocity of
the spot so that the spot will produce a line which has a constant
density along its length.
2. Apparatus for drawing on a photosensitive surface with a spot of
radiant energy comprising,
a base member for supporting a sheet of sensitive material which
undergoes chemical or physical changes upon exposure to the radiant
energy,
a housing supported for movement along coordinate axes which lie
substantially parallel to a sheet of sensitive material on said
base member, means for projecting a spot of radiant energy which
moves with the housing and is of constant intensity on the
sensitive sheet,
means for moving the housing along said coordinate axes so that the
spot will follow a path to produce a line on the sensitive
sheet,
means for automatically changing the spot dimension which lies
parallel to the spot path in response to changes in the spot
velocity without changing the maximum dimension across the spot in
a direction perpendicular to the spot path, with the magnitude of
the dimension which lies parallel to the spot path increasing with
increases in the velocity of the spot.
3. Apparatus according to claim 2 wherein the spot has a circular
periphery and the changes in the spot dimension are produced by
changing the radial dimensions of the spot while holding its
outside diameter constant.
4. Apparatus according to claim 2 wherein the spot is annular.
5. Apparatus according to claim 2 wherein the spot is
rectangular.
6. Apparatus according to claim 2 wherein the spot is in the shape
of a square which surrounds a darkened interior area.
7. Apparatus according to claim 2 having
means for generating a first signal indicative of the amount of
radiant energy in an area corresponding to an area of the spot
bounded on its sides by a pair of lines which lie substantially
parallel to the path of the spot,
means for generating a second signal indicative of the velocity of
the spot across the sensitive surface,
means for comparing said first and second signals and generating an
error signal indicative of the comparison,
said means for changing the dimension of the spot which lies
parallel to the spot path being responsive to the error signal.
8. Apparatus according to claim 2 including display means providing
a picture having the shape and proportions desired in the spot,
said means for projecting the spot being located and constructed to
receive light from the display means and to direct it on the sheet
of sensitive material.
9. Apparatus according to claim 8 wherein the display means is a
cathode ray tube.
Description
This invention relates to apparatus for drawing with a beam of
light or other radiant energy on a surface which is sensitive to
the particular form of radiant energy presented by the beam.
In order to obtain uniform width and density of lines which are
traced on a sensitive surface by a moving spot, it is important
that the sensitive surface receive a substantially constant amount
of radiation along the length of the lines. Prior to this
invention, others have obtained uniform exposure to radiation by
changing the intensity of the irradiated spot in accordance with
its velocity, with the intensity being equal throughout the extent
of the spot. Changes in the width of a line may be effected either
by maintaining a constant dimension measured along its path,
changing its width and turning the spot so it remains at a constant
orientation with respect to its path across the photosensitive
surface or by varying its simensions in all directions while
changing its intensity. It is also known to utilize a flashing
light source, with its frequency controlled in accordance with the
speed and size of the spot.
This invention, rather than changing the intensity of the spot of
light involves a spot which has a constant intensity and undergoes
dimensional changes to provide for proper exposure of the line. In
order uniformly to expose a sensitive surface as a spot moves
thereacross, the spot dimension measured perpendicular to the spot
path are held constant and the dimensions measured parallel to the
spot path are varied either internally or externally in accordance
with the velocity of the spot. The spot may be in the shape of an
annulus with its inside diameter varied in accordance with the spot
velocity, and its outside diameter varied in order to change the
width of the lines drawn.
We have also provided for the continuous analysis of a portion of
the light beam which creates the spot. A signal indicative of the
spot velocity is compared to a signal generated by a portion of the
light beam being analyzed, and this comparison creates an error
signal which produces changes in the dimensions of the darkened
area.
Another concept utilized in the disclosed apparatus involves the
use of a display means such as a cathode ray tube for presenting a
picture in the form of the desired spot.
A further understanding of the invention is facilitated by
reference to the following description and the accompanying
drawings wherein.
FIG. 1 is a diagrammatic view showing a spot projecting head which
moves relative to a photosensitive surface.
FIG. 2 shows one manner of constructing an apparatus for drawing on
a photosensitive surface according to the invention.
FIGS. 3a 3b are views of spots having different outside diameters
in order to illustrate the principle of controlling the
configuration of the spot with a photoelectric light analyzing
element.
FIGS. 4-7 show various configurations of light spots which may be
used in accordance with the invention.
FIGS. 8 and 9 show signals which may be used to create annular and
square spots, respectively, on the face of a cathode ray tube.
FIGS. 10 and 11 show modified embodiments of the invention.
In FIG. 1, a light projecting head 2 is movable along perpendicular
axes in directions indicated by the arrows 4 and 6. The light head
includes a projecting lens system 8 which emits a beam of light
focused on a photosensitive sheet 10. The light is preferably but
not essentially in the visible light range. The spot 12 created by
the beam from the light head is moved along either of its
coordinate axes. Movement of the spot along the path indicated by
the broken line 14 is preferably initiated in a known manner by
signals generated by a computer having storage or memory components
which contain the desired data for programming the light head
movement will create an exposed line having a width w on the
photosensitive surface 10.
If the spot 12 is directed on the photosensitive surface 10 as the
velocity of the spot along the line 14 varies, there must be some
compensation in the spot 12 to prevent different amounts of
exposure along the line created by the moving spot. As previously
mentioned, others have provided this uniform exposure by changing
the intensity of the light spot or by rapidly flashing the spot at
frequencies which vary according to the velocity of the light
head.
In contrast to these prior practices, the spot 12 in the practice
of this invention has a uniform intensity and it undergoes
dimensional variations. The spot of FIG. 1 is annular so that it
surrounds a centrally located void area of a lesser intensity which
suitably is dark so that its intensity is zero.
The outside dimensions of the spot 12 govern the width w the line,
and the dimensions of the darkened area 16 change in order to
control the amount of exposure of the photosensitive surface 10.
When the velocity of the light head 2 parallel to the path 14 is
low as when the light head is under-going its initial acceleration,
the size of the darkened area 16 is relatively large and the
"thickness" t of the spot is small; however, with an increase in
the velocity of the light head, the darkened area 16 decreases in
diameter in order to provide a uniform exposure along the length of
the line 14.
The control of the outside dimensions of the spot 12 and the
dimensions of its darkened area 16 may be produced using various
electronic, optical or mechanical elements associated with the
light head. One system is shown in FIG. 2 where a stationary
cathode ray tube 18 provides a picture having the desired
proportions of the spot.
The picture on the cathode ray tube 18 may be created in various
manners. In the disclosed embodiment, television cameras having
conventional photomultiplier tubes are used. Other suitable
apparatus may utilize signal generators which do not rely upon the
use of a television camera.
The face plate or screen of the cathode ray tube 18 lies in the
object plane of a projection lens system 20. The beam of light from
the projection lens system passes through a plane which is
selectively obstructed by a shutter 28 and then is reflected by a
partially reflective mirror 26 before coming into focus on one end
of a fiber optic member 24.
The image of the face of the cathode ray tube 18 is then
transmitted by the fiber optic member 24 to the photosensitive
surface 38, where the light spot created thereby is moved along the
path established by movement of the light head 30. The end of the
fiber optic member 24 which confronts the photosensitive surface 38
may ride extremely close to the photosensitive surface by means of
air bearings or it may be associated with a projection lens system
on the light head 30.
The light head 30 is supported on a conventional beam and trammel
arrangement where the beam 32 moves in the direction of the X-axis
along the trackways 34 and 36. The carriage 30 moves on beam 32 in
the Y-axis direction. Preferably, movement of the light head 30 is
produced by electric motors which rotate lead screws in a known
manner to move the carriage 30 in the Y-axis direction and the beam
32 in the X-axis direction.
In FIG. 2, two television cameras 40 and 48 are used to generate
the signal which is displayed on the screen of the cathode ray tube
18. The first of these cameras 40 has a zoom lens 42 and is
directed toward a picture which has a light spot 44 on a dark
background 46. Changes in the setting of the zoom lens 42 will of
course change the outside diameter of the spot-creating image 44 as
it appears on the face of the cathode ray tube 18. An operator or a
computer may change the setting of the zoom lens 42 in order to
change the width of the line projected on the photosensitive
surface 38.
The second television camera 48 has zoom lens 50 which focuses on a
picture having a dark spot 52 on a light background 54. Changes in
the setting of the zoom lens 50 will produce changes in the inside
dimensions of the spot image 44 on the cathode ray tube 18. When
the image of spot 52 seen by the television camera 48 is greater
than the size of the light spot 44 seen by the television camera
40, the face of the cathode ray tube will be darkened. Reduction in
the size of the image of the dark spot 52 will result in an annular
spot-creating image such as the one shown in FIG. 2.
In order to provide a distinctive definition between light and dark
areas, the signals from the television cameras 40 and 48 pass
through discriminators 56 and 58 which may be of the pulse height
type to eliminate any background noise or interference in the
signals. The signals from both of the television cameras are added
at 60, preferably in exact time coincidence, and the combined
signals are carried to the cathode ray tube by the conductor 62.
The cathode ray tube may utilize phosphors which provide a very
bright picture.
As mentioned previously, the setting of zoom lens 42 establishes
the outside diameter of the picture of light spot appearing on the
face of cathode ray tube 18 in order to produce a line of a desired
width w on the photosensitive surface 38. The appropriate internal
dimension of the spot on the face of the cathode ray tube 18 is
dependent both upon the outside diameter of the picture of the spot
on cathode ray tube 18 and the velocity of the light head 30 with
respect to the photosensitive surface 38.
One method of controlling the size of the darkened interior portion
of a spot is shown in FIG. 2 and is based upon the principle that
the thickness of the illuminated area through the center thereof
will be the same for any given velocity regardless of the outside
dimensions of the light spot. This principle may be understood by
referring to FIGS. 3a and 3b which show spots having different
outside dimensions. Although their sizes are greatly exagerated, it
will be assumed for purposes of this explanation that they are
shown in the dimensions which are projected on the photosensitive
surface.
As a starting point, it will be assumed that the spot shown in FIG.
3a is moving in any direction at a given velocity which is
conveniently referred to as v.sub.1. It also will be assumed that
for this velocity, the photosensitive surface is properly exposed
by using a spot with the thickness .sub.1. If the velocity of the
spot doubled to become v.sub.2, then the thickness of the spot,
i.e. the difference between the outside and inside radii of the
spot must increase to become t.sub.2.
Since the amount of light striking any area on the photosensitive
surface is dependent upon both the velocity of the spot and its
dimensions measured along its path of movement, it will be
appreciated that the spot shown in FIG. 3b, even though it has a
smaller outside diameter, must also have the thickness t.sub.1 when
the velocity is v.sub.1 and the thickness t.sub.2 when the velocity
is v.sub.2.
Since the areas of the illuminated portions of these spots in FIGS.
3a and 3b are dependent in part upon the outside diameter of the
spot, the light of the entire spot does not provide an accurate
analysis of the amount of light striking the photosensitive surface
as the spot moves along its path. However, if only that portion of
the illuminated spot within the zone lying between the parallel
broken lines 64 and 65 is analyzed, the effect of the differing
diameters of the spots is avoided. The lines 64 and 65 extend
through the darkened void area. The area which is illuminated
between the lines 64 and 65 in FIG. 3a to provide proper exposure
for one suitable spot velocity is equal in size to the area which
should be illuminated between the lines 64 and 65 in FIG. 3b for
that same velocity.
The principles discussed in connection with FIGS. 3a and 3b are
employed in the apparatus of FIG. 2. A portion of the light from
the projection lens system 20 passes through the partially
reflective mirror 26 and strikes an opaque baffle 68 which has an
area 70 which is transparent to the radiant energy. This area lies
on the center of the light beam passing through the mirror 26 and
it permits the passage of light in the area which corresponds to
the zone between lines 64 and 65 in FIGS. 3a and 3b. The light
passing through the baffle 68 strikes a photosensitive element 72
which may be a photoelectric cell or a photoresistive cell. This
cell forms at least a portion of a light measuring circuit 74 which
generates a signal indicative of the amount of light passing
through the transparent areas 70 of the baffle 68.
The speed of the spot with respect to the photosensitive surface 38
may be ascertained in any of several ways such as by electronically
resolving the signals from the motors which drive the light head 30
along the X and Y axes. Such a circuit is shown in block form at 76
and it generates a signal indicative of the spot speed. For any
given spot velocity, the amount of light striking the
photosensitive element 72 should be the same regardless of the
outside dimensions of the spot. Therefore, the signal from the
light measuring circuit and the spot velocity circuit 76 are
balanced in a comparison circuit 78 which may be a conventional
bridge circuit. An error signal indicative of the difference
between the signals from the circuits 74 and 76 is carried by a
conductor 80 to the zoom lens control 82 which automatically
positions the zoom lens 50 to vary the thickness of the
spot-creating image on the face of cathode ray tube 18.
The operation of the circuitry shown in FIG. 2 is easily explained
by first assuming that the spot is moving at a velocity of v.sub.1
to produce an output signal of a certain value from the spot
velocity circuit 76. At a given instant, if the light striking the
photosensitive elements 72 is insufficient because the darkened
area within the spot is too large, then the signal from the light
measuring circuit 74 will be less than the signal from the spot
velocity circuit 76. This will create an error signal which is
carried by the conductor 80 to the zoom lens control in order to
decrease the area of darkened area 52 on the face of cathode ray
tube 18. This will increase the signal from the light measuring
circuit 74 until it becomes balanced with the signal from the spot
velocity circuit 76. When the spot velocity increases to v.sub.2,
then again the signal from the light measuring circuit 74 is
insufficient and will result in an error signal from comparison
circuit 78 to reposition the zoom lens 50. When the velocity of the
spot is reduced to zero, the darkened interior area will enlarge
until it obstructs the entire area which previously was
illuminated. As precautionary measure, the shutter 28 may also be
closed at this point.
Several advantages accrue from the use of a cathode ray tube to
create the picture which is to be projected onto the photosensitive
surface. One advantage is that it provides a relatively cool light
source, both in terms of heat generated during operation and the
wave-length of light striking the photosensitive surface. A cathode
ray tube easily provides light spots of varying configuration.
Movable spots for drawing lines may be of various other shapes
selected according to the type of work being done. For example,
when pronounced corners are desired where a line turns abruptly, a
spot having a square periphery may be used.
A cathode ray tube also permits the display of alphanumeric
characters and other symbols which may be projected onto the
photosensitive surface when the light head is stationary. In this
fashion, the apparatus may be used to write words or place symbols
on the photosensitive surface. The symbols may be created on a
conventional cathode ray tube by viewing pictures thereof with a
television camera or by using known wave shaping circuits which
generate voltages to approximate the component lines of each
symbol. Alternatively, it is possible to use known special-purpose
cathode ray tubes which employ an internal matrix plate which
shapes the electron beam into the form of selected symbols. Such
tubes are described on pages 5-36 and 5-37 of the Handbook of
Automation Computation and Control, 1959, published by John Wiley
& Sons, Inc.; on pages 142 and 143 of Digital Computer Basics,
1968, Navpers 10088, published by the U.S. Government Printing
Office; and, on pages 109 and 110 of The Encylopedia of
Electronics, 1962, published by Reinhold Publishing Corporation,
all of which are incorporated herein by reference.
Another advantage of using a cathode ray tube for creating an image
of the spot is that, through proper electrical circuitry, it can
provide a great variety in spot shapes, sizes and orientations.
Properly selected and controlled spots can provide uniform exposure
along the length of a line and also across its thickness. For
example, the spot may be of a rectangular shape which is
continuously reoriented so that it has a longitudinal axis which
always extends along or is tangent to the path of the spot.
Reorientation of the spot is preferably performed electronically,
but it may also be accomplished by mechanically rotating the
cathode ray tube or only its deflection coils or plates. This
longitudinal axis is usually also an axis of symmetry of the spot.
Such a spot is shown at 130 in FIG. 4. With this arrangement, the
width w of the spot i.e. the dimension measured transverse to the
spot path 132, remains constant when drawing a line of a given
width; however, the length l of the spot which is its dimension
measured parallel to the path of movement varies in dependence upon
the speed of the light head over the photosensitive surface.
The type of spot described in the preceeding paragraph has certain
drawbacks when the spot has a substantial longitudinal dimension as
it is moving along a curve path since the leading and trailing
corners of the spot which lie toward the outside of the arcuate
path will project a distance greater than one-half the desired line
width beyond the center of the spot's path. This will cause some
fuzziness on the edges of the line. To avoid this difficulty, it is
proposed to provide a spot with convex side edges which, in effect,
will eliminate the leading and trailing right-angle corners of the
spot. This may be done, for example, by a spot of the type shown in
FIG. 5 which may be described as a truncated circular spot having
its side edges 134 and 136 arcuate with their centers of curvature
located at the center 138 of the spot. The leading and trailing
edges 140 and 142 of the spot are defined by straight lines which
lie substantially perpendicular to the path 144 of the spot. Of
course, as a spot such as this moves along its programmed path 144,
its longitudinal axis of symmetry is continuously reoriented in
order to lie parallel or tangential to the desired path. The same
desirable effects attributable to the spot of FIG. 5 may also be
achieved by oval, polygonal or elliptical spots which are provided
with convex side edges.
The velocity-dependent changes in the longitudinal dimensions of
the spots of FIG. 4 and 5 may also be made without changing their
maximum longitudinal dimensions. For example, the spots may be
formed of series of longitudinally spaced-apart bands which extend
transversely to the path of the spot. As velocity changes occur,
the width or number of bands may change to change the longitudinal
dimension of the spot (the total length of the illuminated
segments) while the distance between the forward and rearward edges
of the spot remains constant.
Various other spot shapes may be utilized to produce satisfactory
results.
For example, in FIG. 6, the light spot is in the shape of a
bullseye target with a circular central portion 146 and one or more
annular portions 148 concentric therewith. In this particular type
of spot, the velocity-responsive changes are accomplished by
varying the radial dimensions of the darkened interior area 150,
either by reducing the inside diameter of the annular area 148 or
increasing the outside diameter of the circular area 46.
A square spot 152 which surrounds a darkened interior area is shown
in FIG. 7 and it has the capability of producing a square corner
when the path of the light head shifts from exclusive movement in
X-axis direction to exclusive movement in the Y-axis direction. The
interior dimensions of the spot are varied in response to changes
in the spot velocity in order to provide proper exposure along the
length of a line.
The scanning of the face of the cathode ray tube by the electron
beam may be produced by conventional horizontal and vertical sweep
circuits which produce a scanning raster as in ordinary television
sets. In lieu of this, it is possible to produce images on the face
of a cathode ray tube simple by imposing certain signals on the
horizontal and vertical deflection plates or coils associated with
the cathode ray tube. It is well known, for example, that the
electron beam will form a circular image on the face of a cathode
ray tube if the mutually perpendicular pairs of deflection plates
or coils are subjected to sine wave voltages which are 90.degree.
out of phase with each other. A further refinement of this concept
as shown in FIG. 8 where the voltage V.sub.x on one pair of the
deflection plates or coils follows a degenerating sine wave, i.e. a
sine wave with a progressively decreasing amplitude for each cycle.
The other pair of deflection plates or coils receives the voltage
V.sub.y which identical to but 90.degree. out of phase with
V.sub.x. The effect of this voltage pattern is to cause the
electron beam to move in a substantially circular path which has a
decreasing radius. This may also be described as a very tight
spiral. The maximum amplitude will determine the outside diameter
of the annular image on the cathode ray tube, and the minimum
amplitude will determine the inside diameter of the annular image.
Appropriate circuitry may generate a repetitive signal of this type
in order to maintain the annular image on the face of the cathode
ray tube.
The signals shown in FIG. 9 operate much in the same way as those
of FIG. 8, except that they will have the effect of producing a
square picture of the type shown in FIG. 7. The pairs of deflection
plates or coils will lie at the opposite corners of the image shown
in FIG. 7.
The apparatus of FIG. 2 is shown for illustrative purposes, but it
is susceptable to many modifications within the spirit of the
inventive concepts disclosed in this specification. In some
situations, the cathode ray tube may be mounted directly on the
light-projecting head for concurrent movement with the light spot
created thereby. Light spots may also be created by apparatus which
does not employ cathode ray tubes, as will be seen from an
inspection of the modified embodiments shown diagrammatically in
FIGS. 10 and 11.
In FIG. 10, there is a light source 84 in the form of an
incandescent filament associated with a reflective mirror 86 which
directs light into a condenser or collimating lens 88. The light
emanating from the lens 88 is directed on the upper surface of a
baffle 90 which has a central aperture 92, the diameter of which
establishes the width of a line drawn by this apparatus. The light
from the lens system 88 is a beam which is in an unfocused or
confused state in the plane of the baffle 90 in order to illuminate
the baffle 90 uniformly.
Located centrally within the aperture 92, there is a flexible and
hollow body 94 which is inflated by a liquid or gaseous fluid in
order to vary the difference between the inside and outside radii
of the annular light-transmitting area established by the baffle 90
and the body 94. The size of the body 94 is varied according to the
speed of the light head by a motor 96 connected to the rod of a
piston and cylinder arrangement 98 which, in turn, moves fluid
through the conduit 100 to expand and contract the body 94. A
projection lens system 102 has its object plane coincident with the
plane of the baffle 90, and it is focused so that its image plane
is coincidental with the photosensitive surface 104.
Of course, the apparatus of FIG. 10 may be modified to provide some
of the advantages of the system shown in FIG. 2. For example, the
outside diameter of the light spot may be varied either by
replacing the baffle 90 with a conventional iris diaphragm or by
using a zoom lens system in place of the fixed focused projection
lens system 102. Automatic control of the thickness of the spot may
be provided by control means of the type shown in FIG. 2.
In FIG. 11, there is a light source 106, a reflector 108 and a lens
system 110 which are identical to their counterparts in the FIG. 10
embodiment. Light from the lens system 110 is in a convergent beam
which strikes a baffle 112 having an aperture 114. An internal
baffle 116 is used to create and vary the internal dimensions of a
light spot. Variations in such dimensions is produced by motor 118
which moves the baffle-supporting arm 120 about a pivot pin 122 so
that upward movement of the baffle 116 will increase the thickness
of the light spot. A projection lens system 124 projects the image
established by the baffles 112 and 116 onto the photosensitive
surface 126.
Numerous other forms of apparatus may be devised to employ the
principles utilized in the disclosed embodiments. Accordingly, the
breadth of our invention is not intended to be limited only to the
embodiments shown, but is intended to encompass other methods and
apparatus falling within the scope and spirit of the claims which
follow.
* * * * *