US3345639A

US3345639A - Evacuatable chamber seal for electron beam recorder

Info

Publication number: US3345639A
Application number: US521318A
Authority: US
Inventors: Richard F Dubbe
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1966-01-18
Filing date: 1966-01-18
Publication date: 1967-10-03
Anticipated expiration: 1984-10-03
Also published as: FR1513613A; GB1171972A; DE1614115A1

Description

Oct. 3, 1967 R. F. DUBBE 3,345,639

EVACUATABLE CHAMBER SEAL FOR ELECTRON BEAM RECORDER Filed Jan. 18, 1966 2 Sheets-Sheet 1 INVENTOR -14 ram/E2 5 United States Patent Oflice 3,345,639 EVACUATABLE CHAMBER SEAL FOR ELECTRON BEAM RECORDER Richard F. Dubbe, Richfield, Minn, assiguor to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware Filed Jan. 18, I966, Ser. No. 521,318 18 Claims. (Cl. 346-410 The film transport enclosure has a film transport system which operates to position photo-graphic film relative to a modulated electron beam. The gun enclosure and the film transport enclosure were both pumped to a high vacuum. Thus a seal between the gun chamber and the film transport enclosure was unnecessary to maintain a' high vacuum in the cathode ray tube. In operation of these recorders, when a sufiiciently high vacuum was obtained in the tube and enclosure, the photographic film was bombarded and an image formed on the film by a modulated electron beam. The recorders utilized an aperture mask and a pressure shoe for positioning the film relative to the aperture mask after each successive film frame was advanced. In such systems, a spring-loaded pressure shoe urged the film against an aperture mask during bombardment and exposure of the film. Since such recorder-s required equal pressures in the tube and enclosure, no attempt was made to form any type of a seal between the two. These recorders have not been completely satisfactory since long pumping times were required to bring the enclosure, housing the entire roll of film, to a low vacuum. Thereafter, when the film is unwound, gas trapped between the convolutions of the film or in the films previously unexposed surfaces escapes, reducing the vacuum. The reduced vacuum causes the pressure in the tube and enclosure to increase, seriously shortens the life of the electron gun and otherwise adversely aifects performance of the electron gun.

In other known recorders, an electron gun assembly was located within a chamber having a high vacuum and a photographic film was located outside of the high vacuum chamber at atmosphere. The photographic film was introduced into the high vacuum chamber by passing said film either through narrow slits or through stages of progressively higher vacuum. The narrow slits and stages of progressively higher vacuum provided a somewhat operative but clumsy seal and a bulky recorder.

The present invention provides apparatus for forming a seal between one wall of an evacuatable gun chamber which wall forms an aperture plate having an aperture therethrough, and an ambient pressure external to the' chamber. One surface of a flexible, elongated strip memher is passed across the aperture and exposed to the high vacuum within the evacuatable chamber. The aperture plate has aperture rails and aperture lips which form a border around the aperture across which a strip member may be passed. A pressure shoe mating the aperture plate is positioned in opposed relation to the plate and has pres- 3,345,639 Patented Get. 3, 1967 and the aperture rails toward each other. Thus a strip member disposed between the plate and the shoe is pressed at all times during operation into engagement with the aperture rails and consequently urged toward the aperture lips, covering the aperture and forming a seal between the evacuatable chamber and the ambient pressure surgounding the surface of the plate adjacent the strip mem- In the apparatus of the present invention, a low vacuum chamber encloses a film transport system and a high vacuum chamber encloses an electron gun. The low vacuum chamber is connected to the high vacuum chamber on one wall thereof. The one wall has an aperture communioating with both chambers. The electron gun generates and directs an electron beam through the aperture to impinge directly on the film. The film transport system cooperates with means for forming a seal on the one wall such that as the film is advanced across the aperture the evacuated condition in the high vacuum chamber is not impaired as a seal is formed and maintained during film advancement and exposure. In such apparatus, the film located in the low vacuum chamber is subject to continual outgassintg, and by continually pumping the low vacuum chamber and providing a seal between the high vacuum chamber and the low vacuum chamber the high vacuum in the high vacuum chamber remains relatively stable since the film frames exposed to the high vacuum have been previously adequately degassed. The elfect of outg-assing from a small film area being exposed to the high vacuum chamber does not reduce the vacuum therein to an unacceptable operating level.

An advantage of the present invention is the provision of a structure to form a seal such that one surface of a flexible elongated strip member, such as film, can be exposed in the presence of an evacuated atmosphere and moved relative to the evacuated atmosphere while maintaining the evacuated atmosphere.

Another advantage of the present invention is to provide a seal for maintaining a stable pressure in an evacuated chamber having an aperture across which a strip member may be advanced and treated while passing said aperture.

Yet another advantage of the present invention is to provide a means for maintaining a vacuum in the evacuatable chamber when a strip member is being replaced.

A further advantage is to provide a sealing structure for an evacuated chamber housing an electron gun while preventing build up of electrostatic charges on a nonconductive, electron sensitive photographic film while the film is being directly imaged by an electron beam generated by the electron gun.

The above and further advantages of the present invenaccompanying drawings wherein:

FIGURE 1 is a diagrammatic view of a recorder incorporating the present invention;

FIGURE 2 is a fragmentary sectional view of the recorder of FIGURE 1;

FIGURE 3 is a detail-view taken along line 33 of FIGURE 2;

FIGURE 4 is a detail-view taken along the line 44 of FIGURE 2;

FIGURE 5 is a sectional view taken along the line 55 of FIGURE 2;

FIGURE 6 is a sectional view taken along the line 66 of FIGURE 2; and

FIGURE 7 is a diagrammatic sectional view of an electron gun as employed in the recorder of FIGURE 1.

FIGURE 1 illustrates an electron beam recorder employing the evacuatable chamber seal of the present invention. The recorder comprises a high vacuum section 8 and a low vacuum section 9 enclosing a film chamber 12. The film chamber 12 encloses transport means for an electron beam sensitive media, such as an electron sensitive photographic film 14, which includes a supply reel 16, rotatably mounted by a spindle 17 Within the film chamber 12, and a take-up reel 18 also rotatably mounted on a driven spindle 19 supported within the chamber 12. A sprocket film drive capstan 28 operates to form buffer tape loops in the vicinity of a film gate 22. The supply reel 16, the take-up reel 18 and the sprocket film drive capstan 20 may be driven from a suitable motor or independent motors (not shown). The path forv the film 14 directs the same past a recording aperture 60 (illustrated in FIGURE 2). The detail of the film gate 22 and recording aperture 60 are described hereinafter.

In FIGURE 1, a mechanical fore pump 32 is connected to chamber 12 through a vacuum line 34 and a film chamber valve 36. Additionally, the fore pump 32 is connected to a diffusion pump 38 through a vacuum valve 40 and a vacuum line 42. The diffusion pump 38 is directly connected to the electron gun chamber 10. A flap valve 74 (illustrated in FIGURE 2) is located within the high vacuum gun chamber 10 at the end thereof adjacent the aperture 60. By operation of the

valves

36, 40 and 74 in proper sequence, the electron gun chamber 18 can be kept at high vacuum during loading, exhaust, recording and unloading operations taking place in the chamber 12. By using such a vacuum system, the high vacuum within the electron gun chamber can be maintained, for example, at about 10 to 10- millimeters (mm.) of mercury (Hg). Additionally, the lower vacuum in film chamber 12 can be maintained during operation at vacuum lower than that of the high vacuum, for example, at about .02 mm. of Hg. It is apparent that other combinations of pumps and valves could be used to provide the necessary vacuum in each vacuum chamber. Similarly, the vacuums of each chamber could be varied widely from these given depending on type of operation or application being carried out.

Referring now to FIGURE 2, the high vaccum section 8 includes the high vacuum chamber enclosing an electron gun assembly (illustrated in FIGURE 7). The high vacuum chamber 10 has a terminal end member 44 connected at one side to the cylindrical portion of the chamber 10 by a suitable hermetic seal. The other side of end member 44 is joined in sealing engagement to the chamber 12. The end member 44 encloses an aperture housing 58 which is tubular and rectangular in section and which forms a part of said end member. One plate 62 of end member 44 which forms the common end wall of the

chambers

10 and 12 has the aperture 60 formed therein communicating between the two chambers. One face of the plate 62 is constructed to form the aperture plate member of the film gate generally designated as 22 and enclosed within the chamber 12 along with a film transport means generally designated as 54.

The film gate 22 comprises the aperture plate 62 having the aperture 60, a pressure shoe 66 for urging the film .14 against means defining a border surrounding the aperture 60, and shoe support means 68. A vacuum seal is formed between one side 70 of film 14 and the border around the aperture 60 in the aperture plate 62. A claw 72, driven by suitable cam means (not shown), advances the film 14 incrementally through the film gate 22.

The side of end member 44 joined to chamber 10 has an opening 64 formed therein aligned with the axis of cylindrical chamber 10, which opening 64 is also aligned with aperture 60. The flap valve 74, having an O-ring 76 disposed on its face, is mounted by means of a shaft 78 and crank arm 79 for movement between an open (solid-line position) and closed (broken-line position) position in relation to the opening 64. In closed position the valve 74 and O-ring 76 form a seal around the sides H of opening 64. When reloading the film transport 54with a new film 14, the vacuum seal occurring between the one side 70 of film 14 and the sides of the aperture 60 is disabled. Thus, when chamber 12 is opened, for example during reloading of film 14, flap valve 74 can be closed to maintain the high vacuum in chamber 10 and reduce the time required to place the recorder back in operation.

FIGURE 3 illustrates the face of aperture plate 62 and the border surrounding the aperture as viewed from the low vacuum film chamber side. A pair of parallel raised

aperture rails

80 and 82 are disposed in parallel transversely spaced relationship along the aperture plate and adjacent each of two sides of the aperture 60. The aperture rails 88 and 82 are disposed so as to contact the elongated flexible strip member or film 14 along its longitudinal edges. The aperture rails 80 and 82 extend in a forward and trailing direction beyond the aperture relative to the direction of film movement.

Aperture lips 84 and 86 are positioned one on each of the other two sides of the aperture 60 and extend transversely between the aperture rails 88 and 82. The lips 84 and 86 have narrow planar upper surfaces joined by rounded smooth edges. The lips 84 and 86 and the

rails

80 and 82 form a raised border around the aperture 60. The upper surfaces of the aperture rails 80 and 82 and aperture lips 84 and 86 are preferably flush or planar to contact the sensitized surface 70 of film 14 around the aperture or the lips may be slightly depressed to avoid positive contact. A claw opening 88 isdisposed in the rail 80, in spaced relation to the aperture 60 to permit claw 72 to project therethrough to engage perforations in the film 14 and advance the film 14.

The aperture plate 62 is also formed with means for guiding the film 14. In the illustrated embodiment the guide means engages the longitudinal edges of the film 14 and is illustrated as transversely spaced

side portions

89 and 90 which project above the plane of the rails 8t) and 82 and lips 84 and 86, as best seen in FIGURES 5 and 6, to form a channel to guide the film along the

rails

80 and 82 over the aperture 60.

FIGURE 4 illustrates the face of pressure shoe 66 which is positioned parallel to the aperture plate 62 to engage the back side of the strip member or film 14 within the low vacuum film chamber 12. The pressure shoe 66 has a pair of pressure rails 92 and 94 formed on the face thereof which project away from the surface of the shoe between said rails. Pressure rails 92 and 94 are transversely spaced and extend along the parallel edges of the shoe 66. The

rails

92 and 94 contact the strip member or film 14 adjacent the longitudinal edges and are aligned with the aperture rails 80 and 82 of the aperture plate 62. The pressure shoe has a slotted opening 96 to permit claw 72 to project therethrough as it advances film 14.

Referring now to FIGURES 5 and 6, the pressure shoe 66 is supported by the pressure shoe support 68 to align

rails

92 and 94 thereof with the aperture rails 80 and 82. The support 68 is pivotally mounted on the aperture plate 62 by pins 69 (one of which is shown) allowing the support and pressure shoe 66 to be moved to an out-of-theway position for threading the film 14. A suitable catch 71 secures the support 68 in the operative position as shown in FIGURES 5 and 6. The pressure shoe 66 is mounted by two guide rods 98 to the support 68. The guide rods 98 have one end solidly connected to the pressure shoe 66 with the other end thereof slidably fitted through openings in the pressure shoe support 68, and terminating with collars or heads 100. Springs 182 are disposed around. the periphery of the guide rods 98 between the pressure shoe 66 and the pressure shoe support 68. The springs 102 urge the pressure shoe 66 away from the pressure shoe support 68 such that the pressure rails 92 and 94 are urged toward contacting position with the aperture rails 80 and 82 to afford uniform pressure between the pressure shoe rails 92 and 94 and the apert-

ure rails

80 and 82. When the film 14 is placed between the aperture plate and pressure shoe it is pressed into engagement with the aperture rails 80 and 82 and, when the aperture lips are flush with the aperture rails, into contact with aperture lips 84 and 86 to seal the aperture 60. -When the lips are slightly recessed, the film is still pressed against the aperture rails and into proximity with the aperture lips such that the aperture 60 is effectively sealed.

FIGURE 7 diagrammatically illustrates a simple triode type electron gun 110 housed in the high vacuum electron gun chamber 10. The gun 110 produces and directs an electron beam 112 along a predetermined path through the aperture 60 to bombard the portion of film 14 in register therewith to impart information thereto in the form of images, etc. A triode type electron gun designed in accordance with the parameters set forth in a book entitled, Electron Optics by O. Klem'perer published in 195 3, is illustrative of an electron gun suitable for use in this invention.

The triode gun illustrated herein employs a sharp hairpin tungsten filament cathode 114 to produce an electron beam. A grid 116 is interposed between an anode 118 and the filament cathode 114. The filament cathode 114 and the grid 116 may be operated at about 18,000 volts negative potential. The anode 118, the film chamber 12 and the film 14 are maintained at ground potential. The electrons from filament cathode 114, which is at a high negative potential, are accelerated by anode 118 to bombard surface 70 of the film 14 which is at ground potential. An aperture disk 120 having an aperture 122 there in, with a diameter in the order of .010 inch (0.25 mm.),

is located after the anode 118. The aperture disk 120 limits the cross-sectional spot size of the electron beam to reduce spherical aberration and directs said beam along a predetermined path to impinge on the film.

The electron beam 112 can be modulated by applying a varying video signal to the grid 116. The electron beam 112 is focused to a small size beam spot by an electromagnetic focusing lens 124 and said beam is deflected in a scan pattern by a deflecting yoke 126.

In addition to the conventional elements associated with the triode electron gun 110, several other components have been added to the electron gun assembly. The first component is a Faraday cage 128 which is positioned adjacent the path followed by the modulated electron beam 112. Interposed between the Faraday cage 128 and the aperture disk 120 is a pair of deflecting plates 130 and 132. In the preferred embodiment, deflection plate 132 is connected to ground potential and plate 130, when conditioned by a negative potential of about 250 volts, will deflect the modulated electron beam 112 into the Faraday cage 128 completely removing said beam from the film 14. By removing the electron beam 112 from the film 14, said beam is considered blanked relative to said film.

A stigmator assembly 136 coupled to an oscillator (not shown) is used'to mask each horizontal scan line such that each scan line appears to be composed of a plurality of regularly spaced dots rather than of a continuous trace.

A secondary emission pickup ring 138, for collecting secondary emission in the vicinity of the film 14, is positioned along the path followed by the electron beam 112 and between the deflection yoke 126 and the film aperture 60.

The recording media used with this recorder may be a silver halide emulsion photographic film, for example Ferrania positive type 15 film, and such film has a high resistivity of about ohms per square or greater. When the electron beam from the electron gun assembly located "within the high vacuum chamber 10 is generated and directed along a path to bombard such film, the film acts as a capacitor and becomes charged. The voltage or charge on the film 14 builds up as a function of the capacitance between the film 14, the aperture plate 62 and the pressure shoe 66. To obtain high resolution, it is necessary to dissipate this charge accumulating on the film.

When a voltage or charge accumulates on the film 14, three problems result: (1) the charge Q builds up on the film as the electron beam scans each scan line and tends to deflect the electron beam in subsequent scan lines; (2) the charge on the film tends to cause a physical attraction between the film and the plate or shoe, which attraction tends to increase the force required by the claw 72 to advance the film; and (3) as the charged film is moving out of the film gate after bombardment, the capacitance between the film and the nearest grounded surface of the film gate decreases (due to the increasing distance between the film and grounded surface) whereupon the voltage potential t-herebetween increases to a discharge level causing a sufficiently large discharge to occur which fogs the film.

This undesirable charging effect can be reduced by either employing a film having a conductive layer or by placing a separate ground plane as closely as possible to a surface of the film in the recording area. If the film contains a conductive layer, the layer provides a large and substantially constant capacitance between the film and the conductive layer during bombardment of the film by the electron beam and advancement of the charged film from the film gate. The charge accumulation on the film is subsequently dissipated to the conductive layer as a function of the resistivity of the film.

Similarly, if a ground plane separate from the film media is employed, the ground plane is placed as close as possible to the back surface of the film. The ground plane must be disposed adjacent the film after bombardment for a period of time sufficient to permit the charge, accumulated on the film during bombardment, to dissipate to at least a level sufficient to prevent -a subsequent discharge which would fog the film.

In this instance the pressure rails 92 and 94 should not project above the plane of the pressure shoe 66 more than about ten thousandths of an inch (0.25 mm.) and the pressure shoe should be formed of an electrically conductive material or a conductive plate should be disposed between the rails and recessed from the surface of said rails. In either case, the capacitance between the film and the conductive surface is large and substantially constant to minimize the voltage potential between the charged film and ground plane.

Alternatively, the above charging effect problem could be reduced by utilizing an electron sensitive recording media having a composition which is internally conductive.

In the illustrated apparatus the

rails

80, 82, 92 and 94 are approximately 3 inches (7.60 centimeters) in length and they project above the plane of the aperture plate 52 and pressure shoe 66, respectively, between the rails by an amount not less than about two thousandths of an inch (.05 millimeter) and not greater than about ten thousandths of an inch (.25 millimeter). When the lips 84 and 86 are not planar with the rails and 82, the height of the rails should be at the lower value. Thus on each side of the film a shallow channel exists between the rails restricting movement of gases with the film toward the area of the aperture 60. The aperture 60 is of a size corresponding generally to the size of an image frame on a film such as a frame on 16 millimeter film.

While the invention has been described with reference to a recording apparatus it is to be understod that the invention may be utilized wherever it is desirable to treat one surface of a strip member in the presence of a high vacuum. Further, it is to be understood that various modifications may be made in the illustrated device, such as mounting the aperture plate in sealed relation to the high vacuum chamber but removable relative to a fixed shoe, without departing from the spirit or scope of the present invention.

What is claimed is:

1. In combination:

an evacuatable chamber having at one end an apertured member joined thereto, said apertured member having a single aperture formed therein, spaced aperture rails formed on one surface of said member and disposed adjacent opposite edges of said aperture, and aperture lips extending transversely be tween said aperture rails and disposed adjacent opposite edges of said aperture, said aperture lips having outer surfaces disposed substantially in the plane of the surfaces of said aperture rails such that said rails and said lips form a border around said aperture across which a strip material may be advanced,

a pressure shoe mating with said member and positioned in opposed relation to said member, said shoe having spaced pressure rails formed on one surface thereof and positioned in opposed relation to said aperture rails, and

means for urging said pressure rails and said aperture rails toward each other, whereby a strip material disposed between said member and said shoe is pressed between said pressure rails and aperture rails and into proximity with said aperture lips of said member to form a seal between a said evacuatable chamber and the ambient atmosphere surrounding said one surface of said member as a said strip material is advanced across said aperture.

2. The combination of claim it including transport means for advancing a said strip material between said apertured member and said pressure shoe to position successive areas of said strip material in register with said aperture.

3. The combination of claim 2 including guide means positioned in relationship to said aperture for guiding said strip material in a path to maintain the strip material in position over the aperture rails during advancement of the strip material.

4. The combination of claim 1 wherein said aperture rails are disposed in parallel transversely spaced relationship and the opposed surfaces of said aperture rails and said pressure rails are parallel.

5. The combination of claim 4 wherein said aperture rails extend in a forward and trailing direction beyond the aperture relative to the direction a said strip material will be advanced across the aperture.

6. The combination of claim 5 wherein said means for urging said pressure shoe includes a pressure shoe support and spring means, said pressure shoe support being pivotally mounted to said apertured member and said spring means affords uniform pressure of said pressure shoe rails against said aperture rails.

7. In a recording apparatus for imparting information directly on a media by an electron beam, which apparatus includes a first evacuatable chamber having means for rotatably supporting a supply and take-up reel for said media and a media transport means, a second evacuatable .chamber connected to said first evacuatable chamber on one wall thereof, said one wall being formed with an aperature communicating with both said chambers, said second evacuatable chamber enclosing means for generating and directing an electron beam through said aperture to imping directly on said media, the improvement comprising:

means defining a raised border surrounding said aperture on the side of said wall dispose-d in said first evacuatable chamber,

a pressure shoe positioned in said first evacuatable chamber in opposed relation with respect to said border and formed with a pair of transversely spaced rails positioned in opposed relation to said border and extending longitudinally in relation to the direction of movement of the media across said aperture,

means for supporting and biasing said shoe toward said border to press a media disposed between said shoe and said border into contacting engagement with said border, whereby a media disposed between said shoe and said Wall as the same is moved from a said supply reel toward a said take-up reel will form a' seal for said second evacuatable chamber at said aperture.

8. The recording apparatus of claim 7 wherein guide means are positioned relative to said means defining a border for engaging the edge of a media to maintain said media in position over said border and said aperture during advancement of said media.

9. The recording apparatus of claim 8 wherein a portion of said pressure shoe between said pressure rails is electrically conductive and closely spaced to the surface of the rails to be closely adjacent to the back side of said media to function as a ground plane for preventing excessive electrostatic charges produced by a said beam from accumulating within said media and abruptly discharging to an adjacent surface when said media transport means positions successive areas of said media in register with said aperture.

10. An apparatus for recording information on a strip of electron sensitive media by directly impinging said media with an electron beam, said apparatus comprising means defining a first evacuatable chamber having a hollow tubular housing disposed on one end of said chamber, said housing having one wall with an outer surface which wall is formed with an aperture communicating between said outer surface and said chamber,

means disposed relative to said first chamber for generating an electron beam in said first chamber and for directing said beam toward said one wall and through said aperture,

a second evacuatable chamber joined to the outer surface of said one wall and surrounding said aperture,

means within said second chamber for supporting a supply and take-up reel,

means for advancing a said media from a said supply reel to a said take-up reel and across said aperture,

means for at least partially evacuating said first and second chambers,

said outer surface of said one wall having aperture rails formed on and disposed in transversely spaced relation along opposite edges of said aperture, and having aperature lips extending generally transversely between said rails and positioned on opposite edges of said aperature to define together with said aperture rails a border having an outer generally planar surface around said aperture,

a movable pressure shoe positioned in opposed relationship to said outer wall surface and having pressure rails formed on one side thereof in transversely spaced opposed relationship to said aperture rails, and

means for supporting and urging said pressure shoe and said pressure rails toward said wall and said aperture rails whereby a media disposed between said shoe and said outer wall surface as the same is moved from a said supply reel toward a said take-up reel will seal said aperture to maintain said evacuated condition in said evacuatable chamber.

11. The apparatus of claim 10 wherein said housing has a partition therein spaced from said one wall and positioned between said one wall and said first evacuatable chamber, said partition having an opening extending therethrough,

a flap valve located between said one wall and said partition and mounted to said housing for movement from a retracted out-of-the-way position into contacting sealing engagement with the partition over said opening to seal at said opening when a said media is out of sealing engagement with said aperture.

12. The apparatus of claim 10 wherein said outer Wall has guide means thereon positioned parallel to each aperture rail to engage the edges of said media for maintaining said media during advancement thereof in alignment with said aperture rails.

13. The apparatus of claim 10 wherein said means for supporting and urging said pressure shoe includes a pressure shoe support and spring means, said pressure shoe support being pivotally mounted to said one wall and said spring means being positioned between said support and said pressure shoe to urge said pressure shoe rails toward said aperture rails.

14. The apparatus of claim 10 wherein said means for evacuating said chambers includes means for evacuating said first chamber to a pressure in the range of about 10 to 10 millimeters of mercury and said second chamber to a pressure of about .02 millimeter of mercury during operation of said apparatus.

15. The apparatus of claim 10 wherein an electron sensitive media having a conductive layer is positioned between said pressure shoe and said one wall.

16. The apparatus of claim 12 wherein said aperture rails are parallel and extend in a forward and trailing direction beyond the aperture relative to the direction a said media will be advanced across the aperture.

17. The apparatus of claim 13 wherein a portion of said pressure shoe between said pressure rails is electrically conductive and closely spaced to the surface of the rails to be closely adjacent to the back side of a said media for conducting electrostatic charges, produced during bombardment of a said media by a said beam, away from the media to prevent accumulation of any significant charge on the media.

18. The apparatus of claim 17 wherein a non-conducting electron sensitive media is positioned between said pressure shoe and said one wall.

References Cited UNITED STATES PATENTS 2,716,048 8/1955 Young 346-74 3,205,301 9/1965 Etcheverry 178-66 3,222,678 12/1965 Jones 346-l RICHARD B. WILKINSON, Primary Examiner. I. W. HARTARY, Assistant Examiner.

Claims

1. IN COMBINATION: AN EVACUATABLE CHAMBER HAVING AT ONE END AN APERTURED MEMBER JOINED THERETO, SAID APERTURED MEMBER HAVING A SINGLE APERTURS FORMED THEREIN, SPACED APERTUES RAILS FORMED ON ONE SURFACE OF SAID MEMBER AND DISPOSED ADJACENT OPPOSITE EDGES OF SAID APERTUES, AND APERTURE LIPS EXTENDING TRANSVERSELY BETWEEN SAID APERTURE RAILS AND DISPOSED ADJACENT OPPOSITE EDGES OF SAID APERTURE, SAID APERTURE LIPS HAVING OUTER SURFACES DISPOSED SUBSTANTIALLY IN THE PLANE OF THE SURFACES OF SAID APERTURE RAILS SUCH THAT SAID RAILS AND SAID LIPS FORM A BORDER AROUND SAID APERTURE ACROSS WHICH A STRIP MATERIAL MAY BE ADVANCED, A PRESSURE SHOE MATING WITH SAID MEMBER AND POSITIONED IN OPPOSED RELATION TO SAID MEMBER, SAID SHOE HAVING SPACED PRESSURE RAILS FORMED ON ONE SURFACE THEREOF AND POSITIONED IN OPPOSED RELATION TO SAID APERTURE RAILS, AND MEANS FOR URGING SAID PRESSURE RAILS AND SAID APERTURE RAILS TOWARD EACH OTHER, WHEREBY A STRIP MATERIAL DISPOSED BETWEEN SAID MEMBER AND SAID SHOE IS PRESSED BETWEEN SAID PRESSURE RAILS AND APERTURE RAILS AND INTO PROXIMITY WITH SAID APERTURE LIPS OF SAID MEMBER TO FORM A SEAL BETWEEN A SAID EVACUATABLE CHAMBER AND THE AMBIENT ATMOSPHERE SURROUNDING SAID ONE SURFACE OF SAID MEMBER AS A SAID STRIP MATERIAL IS ADVANCED ACROSS SAID APERTURE.