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Description  |
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BACKGROUND AND SUMMARY
The present invention relates to apparatus and the process for making
duplicate image-bearing films from a master film on which intelligence is
recorded in the form of relief or deformation images. The way in which
intelligence exists on prerecorded photoplastic film is so different from
that which is found on more traditional microfiche and microfilm as to
render the traditional processes for generating duplicate film unuseable.
In order to simplify the discussion herein, the term "mircofiche" will be
used throughout. Those skilled in the art will understand, however, that
the discussion applies to microfilm as well as to microfiche.
Although photoplastic film is known (see for example, the structures
disclosed in U.S. Pat. Nos. 3,268,361 and 3,592,643) it is still
relatively new. One of its principal advantages is that it is updateable,
i.e. single microfiche frames can be exposed and developed without
affecting other frames and previously recorded frames can be annotated
and/or erased and rerecorded. This updateability feature makes
photoplastic fiche particularly suitable for use in recording and storing
active files. Prior art films, such as silver halide, on the other hand,
were, in most instances, restricted to recording dead or substantially
inactive files. Recording and storing live files on photoplastic
microfiche permits creation of a system whereby the integrity of an
organization's files is improved dramatically. A central file area can be
established where original documents are immediately recorded on
photoplastic microfiche and the hard copy originals permanently stored or
destroyed. Thereafter, requests for files are satisfied by supplying
duplicates produced on conventional microfiche, which duplicates can be
disposed of when no longer needed. The photoplastic masters need never
leave the central filing area.
Traditionally, duplicates have been made by projection through lenses or by
contact duplication. Duplication through use of an optical system is not
preferred, in part, because lenses are expensive and because of the space
normally required to accommodate the light path. Additionally, optical
systems have proven unsatisfactory in producing acceptable quality
duplicates from photoplastic film masters. Contact duplicating from a
photoplastic master also yields duplicates of inferior quality. It has
been found, however, that one can produce duplicates from such a master by
projecting light from the master through a small gap onto the duplicate
film. One such method is disclosed in U.S. Pat. No. 3,809,473, although no
apparatus is disclosed therein for implementing that process.
The primary criteria in evaluating the quality of microfiche recordings are
contrast and resolution. In general, I have discovered that when employing
the gap duplicating process described herein, as gap size is increased,
although contrast is enhanced, resolution deteriorates. Thus, there is an
apparent incompatability between quality duplicating, where both high
resolution and high contrast are required, and use of the gap duplicating
process.
In the gap duplicating process, at least moderately collimated light is
used. I have found, however, that the degree of collimation needed depends
upon the gap size. The smaller the gap, the less the requirement for a
high degree of collimation. Since collimation reduces the energy available
to irradiate the film, for a given required irradiation intensity, the
less the light must be collimated, the lower the source luminance that is
needed. Conversely, the more the light must be collimated, the lower the
irradiance available from a given source.
Since the exposure time required is a function of the intensity of
irradiation, the less the collimation that is needed the better. Stated
another way, for a predetermined exposure time, as collimation demands
increase so too must the intensity of the source.
Thus, as gap size is reduced, resolution improves and the collimation,
power and/or exposure times needed are reduced. However, as gap size is
reduced, so too is contrast and the ability to duplicate low signal
strength intelligence.
"Signal strength" is a parameter which I presently believe is related to
the contour of the deformations in the photoplastic film. Normally, it has
been my experience that high signal strength intelligence does not
duplicate well when a large gap is employed, but low signal strength
intelligence is lost when too small a gap is employed.
I have discovered that to accommodate the abovementioned divergent needs of
the system, the gap between the emulsion face of the master and the
emulsion face of the duplicate must be between about 1 and 3.5 mils.
Preferably it should be between about 2.5 and 3.5 mils. To produce
acceptable duplicates using a gap within these ranges, I found, the
photoplastic master must carry relatively high signal strength
intelligence. In order to record, with suitably high signal strength
intelligence, from a wide range of originals, it has been discovered that
the master fiche must have a relatively thick thermoplastic emulsion
layer. Layers less than about 8.mu. thick do not produce recordings with
sufficiently high signal strength to be used with suitably small gaps. At
the other extreme, the resolution of images recorded on emulsion layers of
greater than about 25.mu. is very poor. The optimum emulsion thickness
appears to be between 14 and 20.mu..
These comparatively thick emulsions are capable of recording high signal
strength images of high contrast and they can be duplicated using gaps
within the above-specified range.
The process and apparatus described herein take advantage of these
discoveries of the interrelationships between gap size, emulsion
thickness, signal strength, contrast and resolution. They are capable of
producing high contrast duplicate microfiche with resolution in excess of
200 line pairs per millimeter from a wide variety of hard copy originals,
and can do so despite normal line voltage fluctuations and light source
deterioration. In addition, duplicates made on the disclosed apparatus
have uniformly exposed frames, each of which includes identification of
the location or address of the corresponding frame on the master fiche.
BRIEF DESCRIPTION OF DRAWINGS
For a thorough understanding of the nature and features of the invention,
reference should be had to the following detailed description taken in
conjunction with the accompanying drawings in which:
FIG. 1 is a schematic drawing of the basic components of one embodiment of
the invention;
FIG. 2 shows the glass platen upon which the master fiche rests during the
duplicating process;
FIG. 3 shows the overlay grid, which intervenes between master and
duplicate, and the grid mount;
FIG. 4 shows one heat absorbing glass which intervenes between one light
source and the master fiche;
FIGS. 5a and 5b is a schematic diagram of the power supply control circuit;
and
FIG. 6 is a right side sectional view of the lid area and parts lying
directly beneath the lid.
In the drawings, like reference numerals have been employed to refer to
like parts throughout.
DETAILED DESCRIPTION
The duplicator, generally referred to by the numeral 10, has an enclosure
12, two light sources 14 and 16, two condensing lenses 18 and 20, and two
heat glasses 22 and 24. A fan 26 is provided at the rear of enclosure 12
for cooling purposes.
As can be seen in the drawing, the embodiment depicted is comprised of two
sections; a left duplicating section and a right duplicating section. The
components in one section are identical with those in the other.
In employing the process of the present invention, high intensity light is
required. Although an arc lamp could be used as a light source, such lamps
are quite expensive, require heavy power supplies and are unreliable in
starting. In order to avoid these and other problems associated with arc
lamps, I have employed two high intensity incandescent bulbs 14 and 16. It
has been found that BCK lamps (e.g. GTE Sylvania -TF 7460-0024) serve
quite well.
In the embodiment of the drawings, the light emitted by lamp 14 passes up
through condenser 18 and then through heat glass 22. After passing through
glass 22 it goes through platen 28, the photoplastic master fiche 30
resting thereon, thence up through the metal spacer grid 32 which covers
and separates the master fiche from the duplicate and finally onto the
duplicate fiche 34. Similarly, in the right section the light from lamp 16
passes through condenser 20, heat glass 24 and thence through platen 28,
master 30, the openings on grid 32 and onto duplicate 34.
When a duplicate is being made, the entire assembly of glass platen 28,
master fiche 30, grid 32 and duplicate film 34 is covered by lid 36. As
can best be seen in FIG. 6, lid 36 is hinged around pivot 38 and grid
mount 33 to which grid 32 is secured is hinged around its own pivot 40.
Lid pivot 38 is located outboard of grid pivot 40 so that when lid 36 is
open in its upright position, grid 32 can be opened without there being
any interference between grid and lid.
Means are also provided for properly locating master fiche 30 and duplicate
fiche 34 relative to one another and relative to platen 28 and grid 32.
The master fiche, which is placed on platen 28 emulsion up, is provided
with locating holes which cooperate with locating pins 42. Grid mount 33
provides a three sided rececess to receive and properly locate the
duplicate fiche, which is placed thereon emulsion down. In the standard
microfiche format the exposure region contains 98 frames arranged in 7
rows and 14 columns. When master 30 is positioned with locating pins 42 in
the locating holes and grid 32 lies on the master, each frame opening 58
in the grid is coincident with one frame on the master and the grid
support strips lie directly over unexposed frame borders.
It is important that a uniform gap between master and duplicate be
maintained across the entire fiche. This is achieved, in part, by emulsion
to emulsion juxtaposition of master and duplicate and by use of a grid
having closely controlled thickness. In order to make sure that the entire
bottom face of the grid is flat against the emulsion face of the master
fiche and that the emulsion face of the duplicate fiche is flat against
the top face of the grid, a thick pad of deformable foam 44 is cemented to
the inside of lid 36. To prevent the duplicate fiche from being forced
into individual open frame areas 58 in the grid, a metal plate 46 is
cemented to the bottom face of foam pad 44. During duplicating, lid 36 is
held closed by a latch consisting of lip 48 at the end of lid 36 which
engages catch 50 on housing 12. When lid 36 is closed and lip 48 engages
catch 50, foam pad 44 is compressed and substantially uniform pressure is
applied by plate 46 against the entire back face of duplicate fiche 34.
Intimate contact between the duplicate fiche and the top face of grid 32
and between the bottom face of grid 32 and master fiche 30 is thereby
assured. Metal plate 46 prevents foam pad 44 from depressing unsupported
regions 58 of duplicate fiche 34 below the plane of the top face of grid
32. In each frame area, therefore, the gap between the emulsion faces is
substantially the same as the thickness of the grid.
In the embodiment shown, the gaps between juxtaposed frames are filled with
air. They may, however, be filled with any transparent medium, for
example, plastic or glass. Illustratively, a continuous clear plastic
sheet could be used as a separator instead of grid 32, or frame areas 58
of grid 32 could be filled with clear plastic. If a medium other than air
intervenes between juxtaposed frames, the gap size must be modified to
take this into account. The gap size may be determined by application of
the following formula:
G.sub.x /G.sub.a = n.sub.x /n.sub.a
where
G.sub.x is the gap distance to be determined
G.sub.a is the gap distance when air intervenes
n.sub.x is the index of refraction of the intervening medium
n.sub.a is the index of refraction of air.
For example, if the ratio of the index of refraction of the plastic to that
of air were 1.6:1, the gap should be between 1.6 and 5.6 mils., and
preferably between 4.0 and 4.8 mils.
If one were to decide upon use of a clear plastic separator, it could be
incorporated as part of the photoplastic fiche envelope and serve as a
protector as well. Alternatively, both duplicate and master fiches could
be placed with their emulsion sides facing in the same direction so that
the support substrate of one or the other would function as the separator.
Although use of a solid separator offers certain advantages, it does so at
some expense. Adding an additional solid separator inevitably introduces
unwanted optical "noise." It also involves making physical contact with
the emulsion face of the photoplastic film in frame areas thereof and
applying pressure thereto to improve optical contact with the film faces.
This tends to distort the photoplastic film deformations and scratch the
film.
While use of the film support substrate as the separator avoids introducing
refracting surfaces and other sources of noise not already present, it
still involves making physical contact with and applying pressure to
photoplastic film frame areas and the disadvantages attendant thereupon.
As pointed out above, two light sources, lamps 14 and 16, are used. Each
lamp irradiates one zone of 49 frames in the exposure region, or one half
of the fiche. By using two or more sources the uniformity of irradiance is
significantly improved over that which would result were only a single
source employed. One lamp, 14, exposes that exposure zone which lies
immediately above chamber 74, and the second lamp, 16, exposes the other
zone, that which lies above chamber 76.
In gap duplicating, it is essential that each given area of the master and
duplicate be irradiated by only one light source (either a single lamp or
several lamps closely clustered). If two or more physically separated
sources were to expose one area of the duplicate, "ghosting," the
recording of multiple, slightly displaced, images, would result. In order
to avoid the "ghosting" effect and ensure relatively uniform intensity
across each microfiche half, the light emitted by one source is isolated
from that emanating from the others. In the embodiment of the drawings,
this isolation is achieved by use of dividing wall 52 which extends from
the bottom of the enclosure up to the underside of glass platen 28 and
separates chamber 74 from chamber 76. Nevertheless, because dividing wall
52 does not meet the underside of duplicate fiche 34, there remains a
small band of light emission overlap. The band of overlap, however, is
very narrow and the apparatus has been designed so the overlap falls under
and entirely within the confines of grid band 80.
As mentioned previously, in order to produce acceptable duplicates on
vesicular or diazo film, substantial amounts of energy in the near
ultraviolet wavelength range must be transmitted through the master fiche
onto the duplicate fiche. Incandescent lamps capable of emitting
sufficient amounts of energy in the form of near ultraviolet rays, also
emit large amounts of infrared radiation. Although light in the infrared
range serves no useful function in duplicating, it carries a substantial
amount of heat energy. Since heat build up is to be avoided, particularly
when using vesicular duplicates which develop upon application of heat,
heat glasses 22 and 24 are designed to absorb infrared radiation. The heat
absorbed by glasses 22 and 24 is dissipated by the flow of air that
results from use of fan 26.
Although at the mouth of each chamber the light source subtends a
relatively small angle, since light intensity vaies approximately as the
fourth power of the cosine of the half-angle subtended, the angle is
sufficiently large so that the light intensity at each edge of a fiche
half is significantly less than that at its center. In order to ameliorate
this lack of uniform illumination and eliminate the hot spot effect at the
center of each fiche half, a thin film of chromium is vacuum deposited on
one face of each heat absorbing glass, thereby forming a low density
filter. Glass 24 has low density filter 55 deposited on it and glass 22
has filter 54 deposited on it. The light reaching the center of each fiche
half must first pass through a filter but the light reaching the perimeter
does not.
Frequently, hard copies will be made, for working purposes, from a single
frame of the duplicate fiche. Thereafter, it may be desireable to locate
the frame on either the master or the duplicate fiche from which the hard
copy came. In order to facilitate locating the proper frame, means are
provided for putting an address on the duplicate fiche and on the hard
copy. As can best be seen in FIG. 2, glass platen 28 is provided with
alpha-numeric addresses located so that when a duplicate is produced, the
address of the fiche frame will appear in the upper left hand corner
thereof. The alpha-numeric figures on platen 28 are of chromium deposited
on the top side of the platen. Since the adddress is on the duplicate
film, when a hard copy is made from it, the address will appear on the
hard copy.
It has been found that the exposure time required to produce an acceptable
duplicate on the disclosed apparatus tends to be very sensitive to
fluctuations in light intensity. Light intensity in turn, is a function of
the voltage applied to the lamps. The required exposure time, therefore,
varies inversely as a function of the voltage. This voltage dependency is
sufficiently sensitive that the normal fluctuations found in line
voltages, if applied to the lamps, all else being held constant, would
have a substantial effect on the quality of the duplicate. In addition, it
has been found that, even with constant voltage applied, the exposure time
required for an optimum duplicate varies as the lamp ages. Moreover, since
incandescent lamps tend to age at different rates, if the same voltage
were always applied to both lamps in the duplicator, the irradiation of
one half of the fiche would frequently differ from the irradiation of the
other half.
To overcome these difficulties, I have provided a control circuit, shown in
FIGS. 5a and 5b which assures uniform light output over the entire fiche
and assures that said light output is maintained at a predetermined level
irrespective of line voltage fluctuations or lamp age and efficiency.
Uniform irradiation of the master fiche is achieved by making the voltage
applied to each lamp responsive to the amount of light emitted by that
lamp. Light chambers 74 and 76 are, therefore, provided with light sensors
62 and 64 respectively. A light shield or hood 66 and 68 is provided for
each sensor so that the sensor is not "fooled" by light reflections from
the surfaces above.
Generally, through the use of transformer 82, the control circuit steps up
the incoming line voltage to about 156 volts. The voltage is then reduced
to the desired level by use of triacs 70 and 72. Each triac is triggered
at a point in the cycle to produce a voltage output to the lamp such that
the lamp emits the predetermined amount of light. The triggering of triac
70 is controlled by sensor 62 and of triac 72 by sensor 64. Once initially
adjusted, within reasonable limits, the circuit of FIG. 5 will maintain a
constant and uniform amount of light across the entire face of the fiche,
irrespective of line voltage fluctuations and lamp efficiency. It has been
found that a typical exposure time, using vesicular film in the disclosed
apparatus, can be kept constant at about 8 seconds.
Although in the embodiment shown herein two light sources have been
employed, the process can be practiced using three or more. The greater
the number of sources, the less need there is for hot-spot filters.
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