Progressive directional evacuation of vacuum copy frames

The present invention provides an improved vacuum frame having upper and lower frame members of rectangular shape, the upper one of which supports a plate of glass. Connected to the lower frame is a flexible sheet such as a rubber sheet with a backing member connected to its lower surfae. Resilient members such as springs urge one edge of the sealing sheet upwardly toward the glass plate and the other edge downwardly away from the glass plate to produce a wedge shaped vacuum chamber which upon being evacuated becomes progressively smaller as air is progressively and directionally removed proceeding from one edge of the glass plate to the other.

FIELD OF THE INVENTION 
The invention relates to copy systems and processes and more particularly 
to vacuum frames that are used for holding superimposed sheets in close 
contact during exposure. 
BACKGROUND OF THE INVENTION 
Vacuum frames employed for supporting a superimposed original and copy 
sheet have long been used for maintaining the sheets in close contact 
during exposure to light in order to achieve the best possible contact 
copy. Vacuum frames of this kind consist of a base that supports a backing 
or blanket upon which the copies are placed and an upper frame member 
including a glass plate to permit exposure of the sheets to light. While 
vacuum frames of this kind have been widely used, as air is removed, the 
backing or blanket tends to rise toward the glass in an unpredictable 
pattern. This causes air pockets to become trapped between the sheets or 
between the glass and the superimposed sheets. Several minutes may be 
required before these trapped air pockets or air bubbles finally work 
their way out of the system so that the exposure can be made. Moreover, it 
has been common for exposures to be wasted due to the presence of trapped 
air pockets. Because both setup time and materials are costly, previous 
vacuum frame systems have been wasteful and unnecessarily expensive to 
operate. Previous efforts to eliminate these problems have been 
unsuccessful. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a vacuum frame apparatus is 
provided for supporting superimposed sheet material which includes an 
original and a copy sheet in close contact. The apparatus includes a glass 
plate customarily located above the sheet material. Directions such as 
"above," "below," "front" and "rear" herein are for relative orientation 
only and are not recited by way of limitation. On the opposite side of the 
sheet material from the glass plate (normally below the glass plate) is a 
sealing membrane which supports the sheets. The glass plate is usually 
rectangular and includes front, rear and side edges. A vacuum exhaust port 
is provided adjacent the rear edge of the glass plate. Means if provided 
for sealing the membrane against the glass plate to thereby form a vacuum 
chamber between the membrane and the plate to hold a superimposed sheet 
material. A backing means is operatively associated with the membrane to 
preferentially facilitate contact of a portion of the sealing membrane 
adjacent the front edge of the plate opposite the location of the vacuum 
exhaust port whereby evacuation of the chamber will produce progressive 
air removal proceeding in a direction toward the vacuum port so that the 
membrane will progressively contact the glass along an increasing area 
having as one edge a transverse line of contact which moves from the front 
edge to the rear edge as air is removed from the chamber through the 
vacuum port.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the figures and particularly FIGS. 1-6, which illustrate a 
vacuum frame apparatus indicated generally by the numeral 10 for exposing 
copy sheets to light with a provision for progressive directional 
evacuation of air to maintain the sheets in close contact. The apparatus 
includes upper and lower open generally rectangular superimposed frame 
members 12 and 14, the upper one of which supports a plate of glass 16. At 
the front edge of the upper frame member 12 is a handle 18. The rear edge 
of the frame 12 and the corresponding edge of the glass plate 16 is 
connected to the lower frame member 14 by means of hinges 20 (FIGS. 7 and 
10). When the upper frame member is elevated as shown in FIG. 1 for the 
insertion of superimposed sheets 24 (FIG. 3), it is held in the open 
position by means of one or more gas spring supports 25 (FIG. 2). The 
upper frame member 12 is held during operation in the down position during 
exposure of the sheets to light from a suitable source such as the lamp 22 
by means of a suitable latch 19 (FIG. 10). Latch 19 when locked is engaged 
over pin 14a which itself is supported on the frame 14. Supported at its 
edges upon the upper surface of the lower frame member 14 around the 
entire periphery thereof by means of retaining clips 28 is a flexible 
sealing sheet 26. Sheet 26 thus extends across and entirely covers the 
open center 14' of the lower frame member 14. The flexible sheet material 
may have various compositions but one suitable sheet material is a sheet 
of 1/4" closed cell neoprene foam to which is bonded synthetic cloth such 
as nylon on at least one surface. A suitable sheet material of this kind 
can be obtained from Rubatex, Inc. of Bedford, Va. 24523. 
A rubber strip 30 encircles the entire edge of the sheet 26 just inside the 
retaining clips 28 to form a seal between the plate 16 and the sheet 26. 
The strip 30 can be secured to the sheet 26 by means of an adhesive 
bonding it to the upper surface thereof. 
Positioned beneath the flexible rubber sheet 26 and preferably bonded to it 
is a foam rubber or plastic sheet 40 that is preferably relatively thick 
at its center but tapers downwardly toward the side edges 42 and 44. The 
relatively thick center section between the intersection lines L may be 
for example about an inch thick. Side edges 42 and 44 may be about 5/8" 
thick. This will apply greater pressure at the center of the vacuum frame 
than at the edges. The variation in pressure on different parts of the 
copy sheet produced by the differences in thickness of the sheet 40 is 
also very beneficial in facilitating the removal of the nitrogen gas 
produced when a diazo dye is exposed to ultraviolet light. If allowed to 
collect in pockets, this gas can adversely affect the resulting copy. 
However, the greater pressure at the center facilitates transfer of the 
gas laterally and this cooperates with a greater pressure along the front 
edge of frames to prevent gas accumulation. 
The foam sheet 40 is supported upon a backing plate 46 having opposed side 
edges 48 and 52 connected together by front and rear edges 50 and 54. The 
backing plate 46 is supported along its front edge 50 by means of a pair 
of compression springs 60a and 60b each mounted between a bracket 64 and a 
support plate 66 connected to the backing plate 46. The compression 
springs 60a and 60b each fit loosely over a mounting pin 67 the upper end 
of which is connected to the mounting plate 66 upon a spherical ball 
bushing 69 so that its lower end will be free to articulate. The lower 
ends of the mounting pins 67 pass through openings at the lower end of the 
brackets 64. Over the end of each is mounted a spacer 68 that is secured 
in place by means of any suitable retaining means such as a screw and 
washer assembly 70 so that the comression of the springs 60a and 60b 
yieldably bias the forward edge of the mounting plate and corresponding 
overlying portion of the sealing sheet 26 upwardly to touch or almost 
touch the glass plate 16. In this way one edge of the sealing sheet 26 
acts somewhat as a hinge held in contact or closely adjacent to the 
corresponding edge of the glass plate, viz. the left end as seen in FIGS. 
3-6 and 10. 
The right (rear) edge of the support plate 46 and corresponding portion of 
the sealing sheet 26 is initially supported in spaced relationship from 
the glass plate and frame by the provision of a special mounting means 
including bracket 72 connected to the lower frame member 14. Corresponding 
portions of the plate 46 are provided with mounting plates 74. Support 
pins 76 are supported at their upper ends from plates 74 and extend 
downwardly through openings in brackets 72. If desired, optional helical 
compression springs 62a and 62b can be mounted loosely over the pins 76 
below bracket 72 and if used each is held in place by means of a screw and 
washer assembly 78. When under compression, they force the pins 76 and the 
corresponding edge of plate 46 at the right in FIGS. 3-6 and 10 away from 
plate 16 prior to evacuation. Thus, whether the springs 62a and 62b are 
present or not, a wedge shaped chamber 27 is formed as can be clearly seen 
between the glass plate 16 and the sheet 26. The right edge of the sealing 
sheet hangs downwardly and its left edge is in close proximity, in this 
case in contact with the glass plate 16. Air is removed from the wedge 
shaped chamber 17 into which the sheets 24 are placed through exhaust 
ports 32 and 34 that are connected through an exhaust pipe 36 to a vacuum 
pump 38 (FIGS. 1 and 9). In operation with the upper frame raised as shown 
in FIG. 1, the original and copy sheets 24 are inserted between the 
flexible sealing sheet 26 and the glass plate 16 as shown in FIG. 3. The 
upper frame 12 is then lowered to the position of FIGS. 2, 4-6 and 10 and 
is retained in place by means of the latch 19. 
When this has been done, the pump 38 is started causing air to be evacuated 
from the wedge shaped chamber 27. As this occurs, air will be 
progressively and directionally evacuated as shown sequentially in FIGS. 
2-6 as well as from the top in FIGS. 7 and 8. Contact between the sealing 
sheet 26 and the plate 16 initially occurs at the right and moves quickly 
toward the left in FIGS. 3-6 (from the bottom to the top in FIGS. 7 and 
8). In this way, the air is progressively, directionally evacuated as the 
wedge shaped chamber 27 diminishes in size by an action which can be 
thought of as similar to that of a squeegee traveling from one edge of the 
plate 16 to the other. The backing 46 is thus operatively associated with 
the sealing sheet to preferentially urge it into contact with the forward 
edge of the glass plate thereby facilitating contact between them in one 
area prior to evacuation of the chamber whereby evacuation of the wedge 
shaped chamber 27 will produce a progressive evacuation away from an edge 
first and toward an opposite edge so that the membrane progressively and 
directionally contacts the glass over an area expanding along a transverse 
moving line of contact advancing toward one edge of the chamber. 
The squeegee-like action on the wedge shaped vacuum chamber 27 as it 
diminishes in size was found to be surprisingly effective in reducing the 
draw down time of the vacuum frame without the formation of air pockets 
from a period of up to 1.5 minutes in an ordinary vacuum frame not using 
the invention to about 3-6 seconds. Moreover, the invention promotes 
better contact between the sheets 24 since no trapped air pockets form. 
Moreover, the squeegee or wiping motion from the front to the back of the 
vacuum frame maintains perfect registration between the sheets. When upper 
frame 12 is moved to the closed position, the wedge shaped vacuum chamber 
27 which is initially formed gradually diminishes in size and finally 
disappears as shown in FIG. 6 after an elapsed time of about 5 seconds at 
which time the sheets 24 are maintained in close registration without air 
pockets either between them or between the sheets and the glass. In this 
way, when the lamp 22 is operated, exposures of excellent quality are 
reliably obtained. It can be seen that the principle of operation allows 
the backing 46 and correspondingly the sealing sheet 26 to, in effect, 
pivot upwardly about the left end thereof as seen in FIGS. 1-6 and 10. The 
invention can be thought of as providing a single pivot point for the 
sealing sheet 26 and backing 46 so that at least one air port adjacent an 
edge opposite the pivot point communicates with the wedge shaped chamber 
between the port and the pivot. 
During the evacuation process, the foam pressure pad 40 cooperates with the 
angular mounting of the backing 46 to assist in the directional removal of 
air through the air ports 32, 34 by applying somewhat more pressure at the 
center than at the edges. In this way, the prevention of trapped air 
pockets is even more reliably assured. 
The invention has several advantages over the prior art. One advantage of 
the invention is particularly evident when a registration device is used 
as may be done, for example, for aligning a separation negative with a 
printing plate. In such a case, one or more registration pins or a pin bar 
(not shown) aligns the negative and a printing plate placed between the 
negative and blanket 26. The registration pin or bar is placed at the 
front of the frame. The wiping action of the invention toward the rear and 
toward the sides as shown in FIG. 7 automatically tends to straighten the 
superimposed original and copy sheet (the printing plate) by drawing them 
away from the registration pins thereby maximizing the effectiveness of 
the pins and maintaining good registration throughout all portions of the 
copy sheet. In this way, the microscopic dots of color that make up 
halftone photographs can be reliably maintained in their proper locations 
without wiping the sheets by hand prior to exposure as used to be done. 
The cushion sheet 40 also helps by conforming to the contour of the 
registration pins thereby accommodating them regardless of their size or 
location. 
Many variations of the present invention within the scope of the appended 
claims will be apparent to those skilled in the art once the principles 
described above are understood.