US3335994A - Vacuum holder - Google Patents

Description

Aug. 15, 1967 .1. M. COCITO 3,335,994

VACUUM HOLDER Filed April 27, 1965 Fig.6

INVENTOR JOE MICHAEL COCITO ATTORNEYS United States Patent 3,335,994 VACUUM HOLDER Joe Michael Cocito, 11008 Nicholas Drive, Wheaten, Md. 20902 Filed Apr. 27, 1965, Ser. No. 451,212 14 Claims. (Cl. 248-363) This invention relates to vacuum holders for thin sheets or films of the type having a large number of suction holes distributed over the surface of a supporting plate, and more particularly relates to improved structure for filtering, controllingand distributing the flow of air into the plural vacuum holes, and for back-lighting sheets of material supported by the vacuum holder while photographing them.

It is a principal object of this invention to provide a holder of the above type in which novel and improved automatic valve means are provided at each suction hole to virtually close the bore extending from the front face of the plate into a vacuum manifold located behind the plate whenever no film or sheet overlies and closes the bore, and said valve means automatically opening when a film is laid thereover.

It is another principal object of the invention to provide a holder of the above type having a novel foraminous covering over the front face of the supporting plate wherein the pores or openings through the covering are small enough to effectively filter dust out of the air entering the suction holes to protect the automatic valve means from contamination.

Another major object of this invention is to provide novel. barriers by filling the pores in the foraminous covering along rows and columns in the pattern of a grid of rectangular coordinates to isolate each hole from its neighboring holes to prevent one hole from drawing air from a zone which should be under the control of an adjacent hole.

I am aware that there are a number of prior-art patents showing structures which operate in this same general way, for instance Patents 2,910,265, 2,753,181, 2,782,574, 2,594,337, 2,425,921 and 2,198,765, but the present structure is an improvement from the point of view of efliciency and economy of manufacture, and from the point of view of being less subject to dust clogging. One of the most serious problems encountered in connection with valved vacuum-board structures results from their tendency to collect dust in the bores of the suction holes with the result that the valves become jammed or the bores clogged, or both.

This invention teaches simplified valve means which by virtue of improved structure have less tendency to become jammed. The present valve means takes the form of a ball which is a loose fit in a larger hemispherical bore having an offset smaller bore through its inner end and communicating with a vacuum manifold therebehind. The parts of the valve means are shaped so that when the vacuum pulls the ball against the hemispherical blind end of-the larger bore, the ball cannot possibly seat tightly enough to fully block the smaller bore, thereby leaving a small leakage space. This structure provides the desired valving action, without however, completely closing the bore to the flow of air. Such leakage assures that when the outer end of the larger bore is closed by a film laid thereover, the air within the larger bore and between the ball and the film will leak into the manifold by passing through the imperfect seat where the ball attempts to close the smaller bore and thus release the air pressure holding the ball thereagainst to fully open the valve. The smaller bore is so located through the blind hemispherical end of the larger bore that the vacuum holder can be sup- 3,335,994 Patented Aug. 15, 1967 ported at any angle within a large range of angles, exceeding and the valve ball will still operate properly to virtually close the smaller bore when the vacuum pulls the ball thereagainst or to roll away from the smaller bore under the influence of gravity when the vacuum is released so as to provide a larger and unrestricted opening sufficient to freely pass any collected dust or lint into the manifold.

The present disclosure shows the improved valve means coupled with an advantageous manifold structure located behind the pattern of suction holes and communicating with the bores therethrough. The present structure comprises a continuous manifold including a lengthy channel which is folded in a serpentine manner and communicates with all of the suction points sequentially. A vacuum is drawn upon the channel at one end, and the channel is of such small cross-sectional area that when the system is first turned on, the evacuating effort will be applied initially to a relatively few valve means near the beginning of the serpentine channel. When these valve means have closed, the vacuum gradient will move along the channel causing each valve means which it approaches to close in a sequential manner. Therefore, the vacuum pump need not be capable of closing substantially all of the ball valves simultaneously, but rather the pump need be capable only of closing a few of the valve means at any one time.

Another object of this invention is to provide a rela tively simple and easily machined structure which can be economically manufactured using inexpensive materials. In one illustrated embodiment the balls are held in the larger bores by press-fit washer means located in recesses at the film supporting end of the bores. These washers may be knurled or otherwise roughened on their outer surfaces so that when a film is laid over the washer, the vacuum from the air hole therethrough can spread outwardly through the grooves provided in the front face of the washers by the surface knurling, but these grooves are so small and shallow as compared with the diameter of the air hole through the washer that in the event that the film overlies only a portion of the washer including the hole therethrough,the holding effect of the vacuum upon the film will not be lost by escape through those knurled areas of the washer which are not covered by the film. The air hole through the washer can be placed olfcenter to cause the air to swirl in the larger bore to improve the cleaning action tending to flush out dust particles.

Another major object of this invention is to provide a foraminous covering having the capability of glowing under the stimulation of an external source of energy. For example, the covering can be a tight-woven cloth of fibers or wires coated or impregnated with a fluorescent material which glows when stimulated by an ultraviolet lamp. Another possible embodiment would include an electroluminescent covering, caused to glow by the application of a voltage across spaced locations of the foraminous covering, which may be made up of laminated perforate sheets including electroluminescent materials. In this way, the foraminous covering itself can be made to serve as the source of light to illuminate the sheet or film which is being supported by the vacuum holder.

Other objects and advantages of the present invention will become apparent during the following discussion of the drawings, wherein:

' FIG. 1 is a broken elevation view of a vacuum film holder according to the present invention connected with an external vacuum pump and illuminated by an energy source to cause fluorescence of the front covering, a por tion of the front of the holder being cut away to show the air-hole plate and the manifold construction therebehind;

FIG. 2 is an enlarged sectional view taken along line 22 of FIG. 1, this figure showing the upper ball valve in open position and the lower ball valve in closed position;

FIG. 3 is a sectional view similar to FIG. 2 and showing the same valve structure lying down in a horizontal position with the left ball valve in open position and the right ball valve in closed position;

FIG. 4 is an enlarged view of the air-hole plate and rear cover plate and showing in detail a preferred structure for the larger and the smaller bores meeting at a hemispherical surface;

FIG. 5 is a view looking into the larger bore and showing a preferred location of the smaller bore; and

FIG. 6 is a view similar to the upper half of FIG. 2, but showing modified means for holding the ball in the larger bore.

Referring now to the drawings, FIGURES 1 through 5 show preferred embodiments of the invention which include front and rear panel members. The front panel member 1 has a large number of holes arranged in a closely proximate pattern, and passing all the way through it. Each of the holes comprises a larger bore 2 meeting a smaller bore 3 at a hemispherical blind end surface 4, these bores extending from the front surface 1a of the panel 1 through the rear surface 11) thereof.

The rear surface has a series of serpentine channels 5 therein which are separated by ribs 1c and which form a continuous passage commencing in the center of FIG. 1 and winding around the figure and eventually opening into an evacuation outlet 5a which connects to a suitable vacuum pump P through a suitable conduit C. The rear surfaces of the ribs 10 mate with a rear closure panel member 10, and the front and rear panels are held together by any suitable means such as screws 10a as shown in FIGS. 2, 3, and 5.

The manner in which the present board is intended to operate is basically similar to the functioning of numerous other vacuum holders such as the ones illustrated in the patents mentioned above in which valve means are provided to automatically close any of the bores which have not been covered by film sheets F or other relatively non-porous webs overlying the front face 1a of the panel 1. In the present disclosure the valve means by which the closing of the uncovered bores is accomplished includes a ball 6, located in each of the larger bores 2 and fitting it loosely to provide some clearance. The ball 6 is kept in the bore 2 by a foraminous covering 8, or in FIG. 6,

by a retainer washer 7 having a hole 7a therethrough and having a knurled front face 7b. This washer is a press-fit in a bore 11b in the front face 11a of a panel 11, having bores 12 and 13 corresponding with bores 2 and 3 in FIG. 2. The roughening of the front face at 7b is unnecessary'if the washer 7 and front face 11a are then covered by a foraminous sheet 8, as will be more fully described below. However the ball 6 is retained in the bore 2, it tends to roll away from the mouth of the smaller bore 3 under the influence of gravity, since the intersection of the two bores 2 and 3 is part-way up the hemispherical surface 4, or 14, regardless of whether the panel 1 is upright as shown in FIG. 2 or horizontal as shown in FIG. 3. There are a large number of other angles at which the panel 1 can be disposed relative to horizontal and still have the ball tend to roll away from and uncover the bore 3.

- However, the ball 6 can never seat perfectly against the opening 3a in the hemispherical surface 4, or 14, where the bore 3 enters the bore 2, because this opening 3a, FIG. 5, is egg-shaped due to the fact that the axis A, FIG. 5, of the hole 3 does not pass through the center point K of the hemisphere 4. In the practical embodiment of the invention the balls 6 are steel and in diameter. The bore 2 is A inch in diameter and the bore 3 is inch in diameter. Its axis A makes an angle 0 of 2.2 degrees with respect to the axis H of the bore 2. The pump P comprises an ordinary domestic vacuum cleaner which provides enough suction to attract the balls 6 to cover the openings of the bores 3 at 3a, but the balls can seat only imperfectly at the egg-shaped openings 3a. When a vacuum is drawn upon the bore 2 through the manifold 5 and the bore 3, the ball 6 moves toward the latter and tries to seat against the opening 3a at the inner end of the bore 2, as shown at the lower position in FIG. 2. However, when a film F covers and closes the outer end of the bore 2, the air between the ball 6 and the film F bleeds off through the imperfect seating at 3a and thus releases the ball to fall away from the opening 3a under the influence of gravity, except for the case where the bore is at an angle where the opening 3a is at the bottom of the bore 2. The holder is still operative in this position, but its automatic dust flushing action is impaired by failure of the balls to roll around in the bores 2 as the vacuum is turned on and off, or as the front face of the holder is covered or uncovered by films F. If the opening 3a-is offset from both the vertical and the horizontal axes of the vacuum holder in the position shown in FIG. 5, the ball 6 will probably never lie directly on the opening 3a due solely to the influence of gravity thereon during normal use of the vacuum holder.

For the purpose of increasing the area of influence of each hole 2, a forairninous covering 8 is secured by cementing or bonding in some suitable way to the front face 1a of the panel 1. This covering is then divided into noncommunicating square zones Z by filling spaced rows and columns of its pores with a suitable plastic material 9 which can be squeezed into the pores from a nozzle (not shown). The pores in the covering 8 are so small that the vacuum within any zone Z will tend not to become dissipated even if the film F only partly covers the zone. This is of course a matter of degree, but the film tends to be attracted against the covering in a zone provided the film covers most of the area of the bore 2 lying within that zone.

The forarninous covering 8 can be woven mesh such as metal or plastic screening, and where the fluorescent effect is desired, a very tight weave, such as a Dutch weave, is especially useful since none of the holes or pores extends straight through the covering 8, but air can pass therethrough only via circuitous routes. As a result, if the wires or plastic filaments are provided with fluorescent properties or coatings which glow when excited by the ultraviolet light L, the whole surface of the vacuum holder will glow with a substantially homogeneous light distribution. It is also desirable to add fluorescent materials to the cement or plastic substance 9 forming the partitions between zones Z of the covering 8.

Operation The reasons for the novel structures of the present disclosure will become apparent during the following explanation of operation. As is recognized in the prior art, if unlimited vacuum pump facilities are available, it is not necessary to virtually close the exposed bore holes through the front panel member in locations not overlapped by the film F, but since it is desirable to use only a relatively small vacuum pump P in a practical installation, the closure valves shown in the bores become necessary in order to conserve the vacuum, especially when only a small proportion of the bores 2 through the front panel member are covered by a film -F.

In practical working embodiments of the present invention, the channels 5 are milled into or built up upon one of the panel members 1 or 10 only to a depth of about A; inch, and the width of each channel is about five inches. Since the channels are of relatively small cross-sectional area, they exhibit considerable impedance to the flow of air therethrough with the result that when the vacuum pump -P is first started, the end of the channel nearest the conduit C drops in pressure considerably ahead of the time that the pressure begins dropping in the more reto first evacuate the entire manifold to do so. Hence, when the pump P is started, the valves close first in the outer channels, andthen successively close in a sequence winding around the panels and approaching the center of the panel members.

Referring now to FIGS. 2', 3, and 6, these figures illustrate novel valve structures having very practical features. Experience has shown that the presence of dust in most valve structures is highly damaging to their operation, and eventually renders the device inoperative. A major advantage of the present structure is that the valve has only one moving part, a smooth ball, which does not tend to entrap or hold dust. The ball 6 has considerable clearance with respect to the bore 2, there-by encouraging air jetting past the ball to flush out the clearance space. However, when the ball is in closed position as shown in the lower half of FIG. 2, the air which seeks to pass leftwardly through the suction hole is further restricted by the smallness of the gap between the ball 6 and the egg-shaped opening 3a through which the escaping air must travel to reach the manifold 5. On the other hand when the vacuum is released and the ball rolls to the right to a more open position, the dust can easily escape through the bore 3 or 13, which is then opened Wider. The escape tends to occur on a subsequent cycle of the valving action, the dust being swept along by the air jetting through the clearance between the ball and the end of the bore 3 as the ball is sucked up toward the hemispherical end 4. This structure therefore provides a small leaky seal when the valve is in closed position, but a much larger opening when the valve is in open position.

The outer surface 7b of each of the washers 7 of the FIG. 5 embodiment is knurled so that minute grooves will be provided on the outer surface of each washer 7 permitting a vacuum to be drawn on the film F over as much of the surface area of the washer 7 as is covered thereby, and not merely over the relatively small area of the hole 711. Some prior art patents have shown other types of roughening of the outer surface in the vicinity of each suction hole, but many of these structures require expensive concentric-groove machining of the front plate itself. The present invention is believed to constitute an improvement by requiring only inexpensive knurling of the washers themselves before they are installed in the bores 11b of the front panel, and where no foraminous covering is placed over the washers 7.

The present invention is not to be limited to the exact form shown in the drawings, for obviously changes may be made therein. For example, the shapes of the bores 2 and the valving members 6 can be varied to take cylindrical, or conical forms, and the desired imperfect valving action can be obtained by drilling the smaller bore 3 so that its opening into the bore 2 is a shape which cannot be perfectly sealed by the selected moving valving member. These and other modifications fall within the scope of the following claims.

I claim:

1. A vacuum holder for supporting sheets in a plane, comprising:

(a) a panel member having plural suction holes therethrough, each including a larger bore having a first axis and extending from the front face of said member thereinto toward the rear and ending at an inner surface, and including a smaller bore having a second axis and extending from the rear of the panel member through said inner surface at a location spaced from the side wall of the larger bore;

(b) vacuum manifold means on the rear of the panel member and communicating with said bores;

(c) vacuum-operated valve means in each larger bore and shaped to roll about its center therein and to overlie and restrict the entrance to the smaller bore at the .6 inner surface when sucked therea'gainst by the manifold means, the axis of the smaller bore being skewed with respect to that of the larger bore and with respect to the center of the valve means to form an entrance of distorted shape against which the valve means can seat only imperfectly; and

((1) means near the front-face for retaining the valve means in the bores.

2. In a holder as set forth in claim 1, said retaining means comprising a sheet of fibrous cloth secured to said front face of the panel member.

3. In a holder as set forth in claim 2, said material including fluorescent material; and means for exciting said fluorescent material to glow.

4. A vacuum holder for supporting sheets in a plane, comprising:

(a) a panel member having plural suction holes therethrough, each including a larger bore extending from the front face of said member thereinto toward the rear and ending at a hemispherical surface, and including a smaller bore offset from the center of the larger bore and extending from the rear of the panel member through said hemispherical surface;

(b) vacuum manifold means on the rear of the panel member and communicating with said bores;

(c) vacuum-operated valve means in each suction hole and comprising a ball of diameter smaller than the diameter of the hemispherical surface but larger than the diameter of said smaller bore;

((1) the smaller bore having an axis disposed to exclude the center of said hemispherical surface; and

(e) means near the front-face for retaining the valve means in the bores.

5. In a holder as set forth in claim 4, said retaining means comprising a sheet of fibrous cloth secured to said front face of the panel member.

6. In a holder as set forth in claim 5, said material including fluorescent material; and means for exciting said fluorescent material to glow.

7. In a holder as set forth in claim 4, said larger bore having an enlargement where it meets the front face of the panel member, and said retaining means comprising a washer pressed into said enlargement and having a hole therethrough offset from the center of said larger bore and disposed to pass air toward said hemispheric-a1 surface.

8. In a holder as set forth in claim 4, said smaller bore intersecting said hemispherical surface within one quadrant thereof and offset from planes passing through its center point parallel to the edges of the holder panel and normal to its front face.

9. In a holder as set forth in claim 4, the axis of the smaller bore making an acute angle with the axis of the larger bore and crossing the latter in the plane of the front face of the panel member.

10. In a holder as set forth in claim 4, said smaller bore intersecting the hemispherical surface in a non-planar peripheral contour against which said ball cannot be perfectly seated.

11. A vacuum holder for supporting sheets in a plane, comprising:

(a) a panel member having plural suction holes ex tending therethrough;

(b) vacuum manifold means on the rear of the panel member and communicating with said suction holes;

(c) a porous covering over the front of the panel member and secured to the surface thereof between suction holes, the size of the pores in the covering being very small as compared with the size of a suction hole; and

(d) sealing means filling the pores in narrow strips disposed between adjacent suction holes to divide the covering into adjacent non-communicating zones each surrounding a suction hole and of greater area than the area of a hole.

12. In a holder as set forth in claim 11, said covering comprising a woven cloth.

13. In a holder as set forth in claim 11, said covering comprising a cloth woven of filaments including fluorescent material.

14. In a holder as set forth in claim 11, said covering comprising a for-aminous web including fluorescent material; and means for exciting said fluorescent material to glow.

References Cited UNITED STATES PATENTS ROY D. FRAZIER, Primary Examiner.

I F. FOSS, Assistant Examiner.

Claims (1)

1. A VACUUM HOLDER FOR SUPPORTING SHEETS IN A PLANE, COMPRISING: (A) A PANEL MEMBER HAVING A PLURAL SUCTION HOLES THERETHROUGH, EACH INCLUDING A LARGER BORE HAVING A FIRST AXIS AND EXTENDING FROM THE FRONT FACE OF SAID MEMBER THEREINTO TOWARD THE REAR AND ENDING AT AN INNER SURFACE, AND INCLUDING A SMALLER BORE HAVING A SECOND AXIS AND EXTENDING FROM THE REAR OF THE PANEL MEMBER THROUGH SAID INNER SURFACE AT A LOCATION SPACED FROM THE SIDE WALL OF THE LARGER BORE; (B) VACUUM MANIFOLD MEANS ON THE REAR OF THE PANEL MEMBER AND COMMUNICATING WITH SAID BORES; (C) VACUUM-OPERATED VALVE MEANS IN EACH LARGER BORE AND SHAPED TO ROLL ABOUT ITS CENTER THEREIN AND TO OVERLIE AND RESTRICT THE ENTRANCE TO THE SMALLER BORE AT THE INNER SURFACE WHEN SUCKED THEREAGAINST BY THE MANIFOLD MEANS, THE AXIS OF THE SMALLER BORE BEING SKEWED WITH RESPECT TO THAT OF THE LARGER BORE AND WITH RESPECT TO THE CENTER OF THE VALVE MEANS TO FORM AN ENTRANCE OF DISTORTED SHAPE AGAINST WHICH THE VALVE MEANS CAN SEAT ONLY IMPERFECTLY; AND (D) MEANS NEAR THE FRONT-FACE FOR RETAINING THE VALVE MEANS IN THE BORES.

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