US3384900A

US3384900A - Electron beam recording system with recording medium and pressure wheel as continuous vacuum seal

Info

Publication number: US3384900A
Application number: US606625A
Authority: US
Inventors: Erwin C Buschmann
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1967-01-03
Filing date: 1967-01-03
Publication date: 1968-05-21
Anticipated expiration: 1985-05-21

Description

May 21, 1968 E. c. BUSCHMANN 3,334,900

ELECTRON BEAM RECORDING SYSTEM WITH RECORDING MEDIUM AND PRESSURE WHEEL AS CONTINUOUS VACUUM SEAL Filed Jan. 6, 1967 2 Sheets-Sheet 1 MOTOR 5 2 r sway 52w /9 4 ow /T I GENERATOR HM veer/cm. I W 7 snwroorfi POWER H WE GENERAWR su pu s 3 Z rem; HOR/Z. p .swvc. .swvc. L /3 2 70 H Z Z 27? r TELEVISION It /1 a wow RECEIVER cmcu/m ll ac DRIVER y 2 5 Paula? :5 /8 SUPPLY fit/57.212 M 97 4 s 2 3 /6 g 5 E 5 M4 24 fiypowm Inventor":

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E. c. BUSCHMANN 3,384,900 ELECTRON BEAM RECORDING SYSTEM WITH RECORDING MED AND PRESSURE WHEEL AS CONTINUOUS VACUUM SEAL 1967 May 21, 1968 g g-.1 Jan. 7,

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United States Patent 3,384,900 ELECTRON BEAM RECORDING SYSTEM WITH RECGRDING MEDIUM AND PRESSURE WHEEL AS CONTINUOUS VACUUM SEAL Erwin C. Busclrmann, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Jan. 3, 1967, Ser. No. 606,625 Claims. (Cl. 346-110) ABSTRACT UP THE DISCLOSURE Background of the invention This invention relates to electron beam recording, and more particularly to a high resolution system for electron beam recording wherein the recording medium is situated outside a vacuum containing the beam and is backed with a pressure wheel to allow the recording medium and the pressure wheel to maintain a continuous gas pressure seal for the system in complementary fashion.

Electron beam recording of information on moving storage media is well-known in the art, as evidenced, for example, by W. E. Glenn, Jr., et al., Patent No. 3,116,962, issued January 7, 1964, assigned to the instant assignee. In systems of this nature, maintenance of a vacuum through which the beam passes is essential in order to avoid dissipation of the electron beam energy due to an unduly large number of electron collisions with gas molecules.

In application Serial No. 606,626 of Sterling P. Newberry, filed concurrently herewith and assigned to the instant assignee, the vacuum necessary for proper operation of electron beam recording apparatus is maintained even though the recording medium is situated outside the vacuum chamber, and no gas impermeable window is situated in the path of the beam. Moreover, the apparatus of the Newberry application operates without requiring differentially-pumped apertures within the vacuum enclosure. This is accomplished by impinging the electron beam on a gas-impermeable recording medium through an open slot in the vacuum enclosure. The recording medium is placed over this beam exit slot and, with sufiicient pressure applied against the recording medium by a pressure pad, the medium itself seals the vacuum. If the recording medium is in the form of a strip, as herein disclosed, it may be continuously moved over the slot without breaking vacuum.

Each time the recording medium is replaced, however, it is necessary to back the pressure pad away from the slot, albeit but a short distance, in order to insert a replacement medium between the pressure pad and the slot. To avoid breaking vacuum at this time, the aforementioned apparatus of Newberry incorporates a valve within the vacuum enclosure which is closed prior to lifting of the pressure pad. This valve seals off the internal volume of the vacuum enclosure. After the recording medium has been replaced, the valve is again opened.

The instant invention obviates any need for a valve in the vacuum chamber by replacing the pressure pad of the Newberry apparatus with a resilient wheel, By backing the recording medium with a resilient pressure wheel, passage of the end of the recording medium strip over the slot still fails to break vacuum, since the resilient pressure wheel bears against the slot so as to maintain a seal therewith. Hence, not only need the vacuum chamber not be opened in order to replace the recording medium, but the chamber is automatically sealed whenever the medium is removed from the exit slot. Therefore, no valve is required for sealing off the internal volume of the vacuum enclosure in order to avoid breaking the vacuum. The ease with which the recording medium may be replaced is thus readily apparent. Moreover, if the pressure wheel is driven by an external motor, or at least can be manually rotated, threading a new strip of recording medium over the slot is greatly facilitated, still without breaking vacuum, since the strip of recording medium is thus pulled by the resilient pressure wheel into the region between the wheel and the exit slot periphery. The wheel is not lifted from the slot until forced upward by the recording medium, at which time the recording medium has supplanted the wheel in sealing the slot in the region where the wheel has been raised. Furthermore, because the wheel rotates with the film, any possibility of scratches occurring on the surface of the film due to relative motion therebetween is eliminated.

Summary of the invention One object of this invention is to provide a simple, high-resolution system for impinging an electron beam upon a medium situated outside a vacuum surrounding the electron beam wherein no valve is required to preserve the vacuum when the recording medium is replaced.

Another object is to provide an electron beam recording system in which the recording medium itself serves as a movable gas-tight seal having but a single sliding surface for an electron beam exit slot of the system.

Another object is to provide an electron beam recording system in which a vacuum is preserved at all times either by the recording medium or, in the absence of a recording medium, by a pressure wheel normally bearing against the recording medium.

Briefly, in accordance with a preferred embodiment of the invention, an improved system for recording data on an information storage medium by impingement of an electron beam thereon is provided. This system comprises a gas-tight chamber having at least one open slot therein. The chamber includes a source of electrons positioned so as to direct the electrons through the slot. Means are provided for evacuating gas from the chamber, and resilient means are bonded to the outer surface of the chamber around the periphery of the slot with capability of forming a hermetic seal around the slot. A rotatable, resilient pressure wheel is provided for applying pressure against the resilient means around the periphery of the slot so as to form a hermetic seal therewith around the slot. When recording, a gas-impermeable recording medium covers the slot in scalable contact with the resilient means, backed by the pressure wheel which forces the recording medium against the resilient means with sufiicient pressure to form a hermetic seal between the recording medium and the resilient means completely around the slot. Brief description of the drawings The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, both as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a schematic diagram of the vacuum chamber showing the relationship among the beam-controlling components therein, along with the pressure wheel and a block diagram of circuitry for achieving control of beam parameters with television signals;

FIGURE 2 is a detailed showing of the top portion of the vacuum chamber containing a slot over which the film passes, and its relationship to the pressure wheel; and

FIGURE 3 is a sectional view along line 33 in FIGURE 1.

Description of the preferred embodiments In FIGURE 1, an electrically conductive electron optical column or tube 10 comprising the vacuum chamber is illustrated in section. A source of electrons 11 is secured by electrically insulated support means 7 at one end of the tube, and an open slot 12 is situated at the opposite end of the tube. The electron source preferably comprises a nonthermionic hollow cathode structure adapted to formation of plasma electron beams, such as described in L. H. Stauffer Patent No. 3,218,431, issued November 16, 1965, and assigned to the instant assignee. The slot at the opposite end of the chamber is typically 0.125 inch wide by 0.300 inch long. Chamber 10 is divided into upper and lower sections 8 and 9, respectively, by a plate 14 containing an aperture 13. Aperture 13 may conveniently be 0.002 inch in diameter.

The upper section of chamber 10 is pumped, preferably by a mechanical pump 15, down to a pressure of approximately 10- to 10- torr, although pressures as high as torr may be utilized if desired. The lower section of chamber 10 is exhausted by pump 15 through aperture 13 to a pressure which varies from 60 to 40 microns of mercury, depending upon beam requirements. A plasma gas, such as nitrogen, is supplied from a gas reservoir 16 maintained at constant pressure by a conventional diaphragm-type regulator (not shown). Gas pressure in the lower section is controlled by a throttle valve 17, so that electron beam current can be adjusted since, as is well-known in the art, the beam current is proportional to plasma gas pressure.

A pair of

magnetic lenses

17 and 18 are positioned about the upper and lower sections of tube 10, respectively, and are energized from power supplies 19 and 20, respectively.

Lenses

17 and 18 serve to focus the beam of electrons to a diameter of approximately 0.004 inch at its arrival at aperture 13 and to a diameter of approximately 0.002 inch at its arrival at slot 12, respectively. A deflection coil 22 is disposed about the upper section of tube 10 between magnetic lens 17 and exit slot 12. This coil is capable of deflecting the beam through a raster over the entire area of exit slot 12. High voltage negative potential is supplied to cathode 11 from a high voltage power supply 23 through a series-connected current limiting resistance 24 and milliammeter 25. The conductive casing of tube 10 is grounded, so as to establish a high anode-to-cathode potential through the entire length of the tube. In addition, a DC. bias is applied to one modulation deflection plate 26 of a pair of electrostatic deflection plates in lower section 9 of tube 10, while a video signal is supplied to the other one 27 of this pair of deflection plates from a video driver circuit or amplifier 28.

Deflection plates

26 and 27 are energized from conductors passed through insulators 48. The DC. bias on plate 26 serves to establish an operating reference point required by the modulating signal.

Exit slot 12 in the upper secti on of tube 10 is sealed by a recording medium 30 which passes over the exit slot in scalable engagement therewith. This medium, which 'may comprise photographic film, is supplied from a pay-out reel 31 to a take-up reel 32 which is driven by a motor 34. This motor preferably drives take-up reel 32 at a controllably variable speed so as to maintain a constant linear speed for photographic film 30 regardless of the amount of film wound upon reel 32. Means for achieving such speed characteristics are well-known in the art. It is to be understood, however, that recording medium 30 may, if desired, comprise a form other than film, such as a disc, for example.

A resilient wheel 33 bears against film 30, preferably under adjustable spring tension, so as to force the film into scalable relationship with exit slot 12. To achieve smooth operation, wheel 33 may be driven at a constant speed by a synchronous motor 21, shown dotted, so as to move in sync'hronism with medium 30. It should be noted that resilient wheel 33 may be made of silicone rubber.

Tube 10 in FIGURE 1 is illustrated in combination with circuitry for reproducing television signals on recording medium 30. This is accomplished by supplying hori zontal and vertical sawtooth signals from a horizontal sawtooth generator 36 and a vertical sawtooth generator 37 through a driver amplifier 38 to deflection coil 22. The horizontal and vertical signals are algebraically added by amplifier 38. Television receiver circuitry, indicated generally at 40, furnishes horizontal sync signals to horizontal sawtooth generator 36 and vertical sync signals to vertical sawtooth generator 37. In addition, the video signal is supplied to video driver 28 for modulating the electron beam. A television monitor 41 may the driven by television receiver circuitry 40 so as to provide visual indication of the signal being recorded on recording medium 30.

In operation, tube 10 is evacuated by pump 15, and plasma gas, preferably nitrogen, is introduced into the lower section 9 of tube 10. A beam of electrons is produced by cathode 11 and focused by magnetic lens 18 to a diameter larger than that of aperture 13, which constitutes the focal point. Assuming a 0.002 inch diameter for aperture 13, the diameter of the focused beam arriving at aperture 13 is preferably about 0.004 inch, with essentially Gaussian distribution. This aperture then acts as though it were a new source of electrons, emitting a beam which is initially 0.002 inch in diameter. The beam emerging from aperture 13 is focused by magnetic lens 17 to a final 0.002 inch diameter at exit slot 12. The sawtooth voltage waveforms supplied to deflection coil 22 cause the beam to scan a television raster pattern at exit slot 12 when the recording medium is at least momentarily at rest. For continuously moving recording media, however, vertical sawtooth generator 37 is deenergized, since only the horizontal sweep of the electron beam is desired in such case.

Modulation of the electron beam may be accomplished by deflecting the beam across the edge of aperture 13 by control of the voltage between

electrostatic deflection plates

26 and 27; that is, the beam emitted by cathode 11, when fully unmodulated, is substantially undeflected by

plates

26 and 27 so as to occupy a position whereby a maximum number of electrons are admitted through aperture '13, while, as modulation is increased, the beam is deflected by

plates

26 and 27 onto plate 14 progressively farther, so as to progressively admit less and less electrons through aperture 13. Hence, as modulation is increased, the beam emerging from aperture 13 becomes increasingly weaker, [and vice-versa.

During recording operation, suflicient pressure is supplied by wheel 33 against recording medium 30 to seal slot 12, thereby preventing loss of vacuum within tube 10. Even when the end of the recording medium has traveled past slot 12, wheel 33 itself bears against the slot with suflicient pressure to maintain the seal. Being preferably comprised of silicone rubber, wheel 33 is gasimpermeable, so that no leakage occurs into the vacuum chamber by passage of outside atmosphere through the wheel.

In FIGURES 2 and 3, details of the seal at exit slot 12 are shown. A resilient surface 43, having :a low coeflicient of friction to promote smooth sliding contact therewith, which is preferably comprised of polytetrafluoroethylene (such as that sold by E. I. du Pont de Nemours and Company, Wilmington, Del., under the trademark Tefl-on), is shown bonded or otherwise adhered to a groove in the upper surface of metallic tube 10. The Teflon is cut at exit slot 12 so as to coincide with the slot. The Teflon is also provided with sidewalls 44 which serve as guides to maintain recording medium 30 in the proper position with respect to slot 12 for suitable recording on medium 30 and sealing of tube 10.

Resilient wheel 33 bears against recording medium 30 with suflicient pressure, as mentioned hereinbefore, to maintain a gas-tight seal at exit slot 12 by sandwiching the recording medium tightly between itself and Teflon surface 43. To accomplish this objective when medium 30 comprises 16 millimeter film for example, and the dimensions of exit slot 12 are 0.125 inch by 0.300 inch, wheel 33 preferably comprises a 6 inch diameter cast silicon rubber pressure wheel with a hardness of 45 durometer. A suitable silicone rubber for this purpose is type RTV-ll, available from General Electric Company, Waterford, N.Y. In order to press the film tightly against Teflon surface 43 under these conditions, the pressure wheel is squeezed substantially flat, as shown in FIGURE 2, for a linear distance of approximately 4 inch. The sides of wheel 33 are preferably tapered, so that when the wheel is compressed against the bottom 43 and sides 44 of the Teflon channel, the wheel bears against the entire Width of surface 43 without bulging against sides 44, thereby preventing external atmosphere from entering the vacuum chamber. To assure a tight seal, the circular sur face of the wheel, when uncompressed, is slightly concave in shape, as shown at 51 in FIGURE 3. This causes the wheel to bear with greater pressure against the edges of recording medium 30' than against the inner area thereof. In this fashion, not only does wheel 33 provide a seal for exit slot 12 when recording medium 30 is not present, but, if wheel 33 is driven in synchronism with recording medium 30, or is merely capable of being manually rotated, threading of medium 30 through the Teflon channel beneath the wheel without breaking vacuum is greatly facilitated, since the film is thereby drawn beneath the wheel through the channel.

FIGURE 3 illustrates the relative positions of wheel 33, exit slot 12 and sides 44 and bottom 43 of the Teflon tnack through which recording medium 30 is slideably passed. In this view, the tapered sides of wheel 33 may be seen at the upper portion of the wheel, and the shape of the compressed lower portion of wheel 33 is also illustrated. The wheel is adhered to a slotted metallic sleeve 45 which may be free to rotate on a shaft 47. Alternatively, the wheel may be driven by shaft 47 by insertion of a key into a slot 46 on shaft 47.

While the Teflon track is shown in FIGURE 3 as being recessed within the upper portion of tube 10, this is for convenience only; it is also feasible to mount the Teflon channel directly upon the upper surface of the top of tube without necessity for a grooved recess to hold the channel. Additionally, a photographic shutter effect can be obtained by substituting a stepper motor for motor 34, or for motor 21 if used. Moreover, recording media other than photographic film may be utilized, such as thermoplastic film for instance. Photographic or thermoplastic discs may alternatively be utilized; in such case, the recording end of tube 10 would preferably be flattened, and a smooth surface of Teflon applied thereover and bonded thereto instead of the Teflon channel.

The foregoing describes a simple, highuesolution system for impinging an electron beam upon a medium situated outside a vacuum surrounding the electron beam source, wherein no valve is required to preserve the vacuum when the recording medium is replaced. The recording medium itself serves as a movable gas-tight seal for the beam exit slot of the system, having but a single sliding surface. Moreover, by bringing a resilient wheel to bear upon the recording medium, it is unnecessary to break vacuum when changing recording media since, in absence of a recording medium, the resilient wheel itself seals the exit slot so as to retain the vacuum.

While only certain preferred features of the invention have been shown by way of illustration, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit and scope of the invention.

I claim:

1. In a system for recording data on an information storage medium by impingement of an electron beam thereon, the combination comprising: a gas-tight chamber having at least one open slot therein, said chamber including a source of electrons positioned so as to direct said electrons through said slot; means communicating with said chamber for evacuating gas therefrom; resilient means having a low coeflicient of friction bonded to the outer surface of said chamber around the periphery of said slot capable of forming a hermetic seal around said slot; and a rotatable, resilient wheel bearing against said resilient means with sufficient pressure to form a hermetic seal around said slot.

2. In a system for recording data on an information storage medium by impingement of an electron beam thereon, the combination comprising: a gas-tight chamber having at least one open slot therein, said chamber including a source of electrons positioned so as to direct said electrons through said slot; means communicating with said chamber for evacuating gas therefrom; resilient means having a low coefficient of friction bonded to the outer surface of said chamber around the periphery of said slot capable of forming a hermetic seal around said slot; a gasimpermeable recording medium covering said slot in sealable contact with said resilient means; and a rotatable, resilient wheel bearing against said recording means with pressure over sufficient area so as to force said recording means tightly against said resilient means around the periphery of said slot.

3. The system of claim 1 wherein said wheel comprises silicone rubber.

4. The system of claim 2 wherein said wheel comprises silicone rubber.

5. The system of claim 2 including transport means for moving said recording medium between said wheel and said resilient means at a substantially constant speed.

6. The system of claim 2 including means coupled to said wheel for driving said wheel to advance said record ing medium between said wheel and said resilient means.

7. The system of claim 1 including a groove in the outer surface of said chamber directed over said slot, said resilient means being bonded to the outer surface of said chamber around the periphery of said slot within said groove, and said Wheel being tapered such that the width of said wheel when undeformed is narrowest at the periphery thereof.

8. The system of claim 2 including a groove in the outer surface of said chamber directed over said slot, said resilient means being bonded to the outer surface of said chamber around the periphery of said slot within said groove, and said wheel being tapered such that the width 7 8 of said wheel when undeformed is narrowest at the References Cited periphery thereof. 7

9. The system of claim 1 wherein the undeformed cir- UNITED STATES PATENTS cular surface of said wheel contains a concave recess 3,341,728 9/1967. Fofland r therein 5 3,34 ,639 10/1967 Dubbe 346-410 10. The system of claim 2 wherein the undeformed circular surface of said wheel contains a concave recess therein. I

RICHARDB. WILKINSON, Primary Examiner. J. W. HARTARY, Assistant Examiner.