U.S. patent number 3,797,934 [Application Number 05/187,171] was granted by the patent office on 1974-03-19 for system and method for making multigraded tv masks.
This patent grant is currently assigned to Buckbee-Mears Company. Invention is credited to Gerald M. Miller, George M. Munter.
United States Patent |
3,797,934 |
Miller , et al. |
March 19, 1974 |
SYSTEM AND METHOD FOR MAKING MULTIGRADED TV MASKS
Abstract
A method for forming a multigraded negative by utilizing an
arcuate shaped light diffuser of uniform thickness.
Inventors: |
Miller; Gerald M. (Sylvania,
OH), Munter; George M. (Roseville, MN) |
Assignee: |
Buckbee-Mears Company (St.
Paul, MN)
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Family
ID: |
22687875 |
Appl.
No.: |
05/187,171 |
Filed: |
October 6, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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838459 |
Jul 2, 1969 |
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Current U.S.
Class: |
355/52; 359/888;
396/563; 355/71 |
Current CPC
Class: |
G03C
5/02 (20130101); G03B 15/00 (20130101); H01J
9/142 (20130101); H01J 2229/0761 (20130101) |
Current International
Class: |
H01J
9/14 (20060101); G03C 5/02 (20060101); G03B
15/00 (20060101); G03b 027/26 () |
Field of
Search: |
;95/1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Horan; John M.
Attorney, Agent or Firm: Jacobson and Johnson
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of our application filed
July 2, 1969, Ser. No. 838,459, now abandoned, and assigned to the
same assignee as the present invention.
Claims
We claim:
1. An apparatus for producing a multigraded image comprising: a
source of light energy located along an optical axis; said source
of light energy including means for rotating the light source about
said axis for at least 360.degree. during exposure of the
photosensitive plate; a diffuser for decreasing the intensity of
the light projectible through the diffuser in a predetermined
direction, said light diffuser having a uniform thickness and an
arcuate shape, said diffuser located along said optical axis; a
master plate having a set of openings and located along said
optical axis on the opposite side of said diffuser from said source
of light; and a photosensitive plate located adjacent said master
plate and on the opposite side from said diffuser so that said
light source exposes the portions of the photosensitive plate that
are not shielded by said master plate in proportion to the
intensity of the light arriving at said plate.
2. The apparatus of claim 1 wherein said master contains a
plurality of parallel elongated openings of uniform width.
3. The apparatus of claim 1 wherein the set of openings in said
master are of uniform width.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention. This invention relates generally to
shadow masks for colored television tubes and, more specifically,
to a method and system of forming shadow masks having differently
graded openings along the horizontal and vertical axis of the
masks.
2. Description of the Prior Art. In a colored picture tube a shadow
mask is located between the electron gun at the rear of the tube
and the phosphor coated face plate at the front or viewing face of
the tube. The electron beam from the electron gun passes through
the openings or apertures in the shadow mask and impinges upon a
suitable color producing phosphor on the face plate. Typically, the
openings in the shadow mask may be circular, hexagonal or
elongated. In a mask having elongated openings, the openings extend
vertically from the bottom of the mask to the top of the mask. In
masks having elongated openings, it is necessary to have the width
of the openings at the center of the mask larger than the width of
the openings at the edges of the mask. In addition, it is necessary
that the width of the openings are smaller at a given vertical
distance from the center of the mask than at the same given
horizontal distance from the center of the mask. This requires
having a predetermined grading of the width of the openings in a
horizontal x axis and a different predetermined grading of the
width of the openings in the vertical y axis.
Briefly, the specific problem is how to produce a mask having a set
of elongated openings that have a predetermined graded orientation
in the x axis and a predetermined different graded orientation in
the mutually perpendicular y axis.
Typically, the openings in the shadow mask can vary from .006 to
.003 inch with the openings spaced about .020 inch apart. With
these small dimensions and the number of graded openings required
for each shadow mask, it is apparent that it would be extremely
costly and difficult to produce a mask that has the proper number
of openings as well as the desired grading through such techniques
as scribing a multigraded pattern on a negative and then using
photoprinting techniques to form a multigraded pattern in
photoresist on the mask. However, once the multigraded pattern had
been printed in photoresist on the mask, the mask could be etched
using well known etching techniques.
The present invention eliminates the costly and difficult
intermediate step of preparing a multigraded negative pattern
through such process as scribing and the like by using optical
techniques that utilize an arcuate or curved diffuser of uniform
thickness that diminishes the intensity of light projected through
a non-graded pattern to produce a multigraded pattern on a plate
located behind the non-graded pattern.
BRIEF SUMMARY OF THE INVENTION
Briefly, the present invention comprises a system having an arcuate
shaped light diffuser of uniform thickness that diffuses light
horizontally and vertically before transmitting the light through a
plurality of non-graded openings onto a photosensitive plate.
Because of the arcuate shaped light diffuser the light diffuses
more in one axis than in the mutually perpendicular axis. This
diffused light, when projected through a set of non-graded
openings, produces a multigraded master image on a photosensitive
plate which is located behind the non-graded image. The multigraded
master image on the photosensitive plate can then be developed and
printed to form a master pattern for photoprinting the multigraded
image in photoresist on the shadow mask. Once the multigraded
pattern has been formed on the mask the mask openings can be etched
through conventional techniques.
BRIEF SUMMARY OF THE DRAWINGS
FIG. 1 is a schematic view showing the components of the system for
producing the multigraded mask; and
FIG. 2 is a view showing the appearance of the mask on the
photosensitive plate after exposure in the present system.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, FIG. 1 shows, in schematic form, a
system for producing a master with multigraded openings. The system
comprises a revolving light source 11, a bowed or arcuate light
diffuser 12 which is the heart of the present system and a camera
20 which holds a focusing lens 13, an aperture 10, a negative
contact of a scribed or ruled master 14 and a photosensitive plate
16 located adjacent master 14. For the purposes of this invention,
adjacent is taken to mean that master 14 is near to plate 16 or at
some small distance from plate 16 but not in contact with plate
16.
Referring to the individual components of the system, light source
11 comprises a conventional frosted bulb that is mounted in a
socket that can be slowly rotated through 360.degree. by a suitable
means (not shown). The purpose of having a rotating light source is
to eliminate the difference in luminous intensity inherent in
filament bulbs which would produce an unevenness in photosensitive
plate 16 in addition to the desired gradient that is introduced
into the pattern on plate 16. Located next to the light source 11
is an arcuate shaped light diffuser 12 of uniform thickness which
comprises the heart of the present invention. Light diffuser 12
comprises a sheet of flexible material such as acrylic resin which
has been bent in an arcuate shape through the application of force
on opposite ends of the sheet. The present invention utilizes a
sheet of acrylic resin which is held in shape by force but it is
apparent that the acrylic resin material could also be preformed in
an arcuate shape so that it would not be necessary to support the
edges in compression. Although acrylic resin is preferred for the
light diffuser material, it is apparent that other types of
material could equally well be used.
This type of light diffuser is not a lens and should not be
confused with a lens. A lens has a varying thickness from the
center to the outside edge whereas light diffuser 12, in contrast,
has a uniform thickness from the center to the outside edge. By
having the diffuser located in front of light source 11, it
diffuses the light causing a variation in the luminous intensity as
it passes through the diffuser. With the bow in the light diffuser
located along the vertical axis, it decreases the luminous
intensity of the light more rapidly along the vertical axis than
along the horizontal axis. Thus the center of photosensitive plate
16 receives the highest luminous intensity with the edges receiving
the lowest luminous intensity.
In the absence of light diffuser 12, the luminous intensity of
photosensitive plate 16 would vary uniformly in a direction
radially outward from the center of photographic plate 16. However,
by placing light diffuser 12 along optic axis 21, it causes the
light to diffuse at a different rate along the vertical axis thus
further diminishing the intensity of the light on the top and
bottom half of photosensitive plate 16.
The amount of light diffusion can be controlled by varying the
choice of the light diffusers, that is, the greater the curve the
greater the diffusion and, consequently, the steeper the grade of
the opening. Also, it will be apparent that the diffusion of the
light can be further varied in the mutually perpendicular axis by
placing a second bowed diffuser along the optical axis in series
with diffuser 12. It is further envisioned that for certain
application diffusers may be made in a hemispherical or oval shape
to produce the desired light diffusion.
In operation of the system, the operator places his non-graded
master 14 which may be formed through a scribed process or the like
in front of a photosensitive plate 16 located at the back of the
camera 20. Next, the operator activates light source 11 and also
starts rotation of light source 11 about optic axis 21. The light
from source 11 projects through diffuser 12, lens 13 and aperture
10 and onto the non-graded master plate 14. A portion of light
passes through the opening in master plate 14 and onto
photosensitive plate 16. The variation of the luminous intensity on
the photosensitive plate 16 causes the pattern of parallel
elongated opening in master 14 to become distorted into the
appearance shown in FIG. 2.
While the present invention is shown and described in conjunction
with a master utilizing a set of elongated openings, it will be
apparent to those skilled in the art that the present invention
could equally well be used to grade round holes, hexagonal holes or
any other type of pattern requiring a multigraded mask.
Also, in the present invention the acrylic resin diffuser 12 is a
translucent white material as opposed to a clear acrylic resin. The
purpose of using a translucent white material is to reduce the
source concentration of light present with a conventional source
such as a light bulb or an elongated tube type lamp. A typical
material having a suitable degree of opacity for use is
manufactured by Rohm Haas Company under the designation Plexiglas
2447. This example is given as being merely illustrative of a
typical material that could be used and no limitation is intended
thereto. Although it is preferred to use an acrylic resin material
with a predetermined degree of opacity that transmits only a
portion of the light, it is apparent that a clear arcuate shaped
acrylic resin diffuser with a suitable light dispensing source
could also be used. In this latter arrangement the suitable light
source could constitute a conventional light bulb located behind a
flat sheet of material having a suitable degree of opacity, such as
the aforementioned acrylic resin. Furthermore, materials other than
acrylic resin could be used but commercially available acrylic
resins have been found to have both the desired degree of opacity
and the uniformity of opacity throughout the sheet.
* * * * *