US3001848A - Electron beam recording apparatus - Google Patents

Description

Sept. 26, 1961 1.. E. WALKUP ELECTRON BEAM RECORDING APPARATUS Filed July 15, 1958 5 Sheets-Sheet 1 T-R SWITCH TRANSMITTER TIMER HORIZONTAL SWEEP RECEIVER GATE RECORDER INVENTOR. Lewis E.Walkup F/Gl BY M Ma W A TTORNE Y Sept. 26, 1961 E. WALKUP ELECTRON BEAM RECORDING APPARATUS Filed July 15, 1958 5 Sheets-Sheet 2 FIG. 2

INVENTOR. Lewis E. Walkup Sept. 26, 1961 L.. E. WALKUP ELECTRON BEAM RECORDING APPARATUS Filed July 15, 1958 5 Sheets-Sheet 3 50-, PICKUP WEB as- PICKUP WEB 25-,L PICKUP WEB [IO-p. PICKUP WEB ZERO PICKUP WEB THICKNESS C c c w w w o o 0 m 6 6 4 2 20 60 Air Gap, ,4.

INVENTOR. Lewis E.Walkup ATTORNEY L. E. WALKUP 5 Sheets-Sheet 5 ELECTRON BEAM RECORDING APPARATUS Sept. 26, 1961 Filed July 15, 1958 DEVELOPMENT v35 MECHANISM I 1 I I II," I]

-5a (F) '1 & FUsER BY flu W77 INVENTOR. Lewis E.Walkup United States Patent 3,001,848 a r ELECTRON BEAM RECORDING. APPARATUS Lewis E. Walkup, Columbus, Ohio, assiguor, by mesne assignments, to Xerox Corporation, a corporation of New York J t Filed July 15, 1958, Ser. No. 748,655 '2 Claims. (Cl. 34674) by electrical transmission wherein the image intelligence is carried in the form of.varying characteristics of 'elec trical transmission denotative of the intelligence. At the recording station suitable means are provided for transducing the electrical transmission into a visual form and reducing the same to record, permanent or transitory as the needs dictate. In many environments the sensing of the intelligence to be transmitted and the transmission thereof, particularly when sensed electronically or optically, may be effected with extreme rapidity. However, the transducing and reduction of the intelligence to visual and record form frequently imposes serious time limitations on the overall system due to the inability of the recording station to accept the information at the rate capabilities of the sensing and transmission systems.

Electron beam or cathode ray tubes with phosphor screens, due to their ability to respond essentially instantaneously to electrical intelligence applied thereto, have therefore commonly been resorted to as a means for transducing the electricallyfltransmitted intelligence into visual forms. However, the image on the phosphor screens of such tubes is transitorygand doesnot of itself afford a suitable means for displaying a-large amount '1 of intelligence simultaneously, or amemory of intel ligence for any significant period of time, particularly if the nature of the transmitted intelligence is continuous- 'ly varying. Numerous efiorts have been directed to recording permanently the transitory images from cathode ray tubes by various optical photographic methods. For many purposes such optical photographic recording is not well adapted, because of the time delay between ex} posure and developing of the record, the need for'wet 3,391,848 Patented Sept. 26, 1961 i More particularly, in accordance with the present invention, an electron beam is caused to repetitively traverse a single line of scan at a desired repetition rate. The target scanned by this beam is formed basically from a block of material highly resistive electrically and substantially opaque to (i.e. essentially non-transmissive of) p the impinging electron beam. Embedded within the target along the line of scan is a row of electrically conducting pins, each isolated electrically from the others by the target material. With each traverse of the target, the beam deposits an electron charge on the pins. The

, quantity of charge deposited on each pin may be caused tovary in accordance with variations in the beam current during the traverse, as required by electrical intell gence signals fed to the recording station. While one side of the target is thus repetitively traversed by the electron beam, a web of dielectric sheet material is fed past and in close proximity to the opposite side of the target. Maintaining one side of the web grounded orat a suitable potential difierence from the target, the air dielectric between the target and web is disrupted and ionized, resulting in the positive ions traveling to the target, and the negative ions traveling to the web and establishing a corresponding charge thereon. If the web is properly positioned relative to the target, the resultant charge thus induced on the web will constitute a line of charge, and the quantity of charge along the length of the line will correspond to the quantity of charge and variations thereof created .on the line of pins in the target by the electron beam. Thus, for each traverse of the target by the electron beam, a line of electrostatic charge is-induced on the web corresponding to the intelligence fed to the recording station. The rate of move-.

developing techniques and equipment, and the sensitivity of optical film to cosmic, nuclear, and other radiation; The foregoing drawbacks ofoptical photographic recording systems are particularly apparent in the environment of military radar, where the equipment may be installed in high altitude reconnaissance craft, and where the need response characteristics of such beams. However, rather than utilizing a phosphor screen to convert the intelligence to visual form with the foregoing attendant limitations thereof and disadvantages in the ensuing optical photographic recording of the phosphor image, in accordance with the present invention, the beam is utilized to create an electrostatic image on a moving web, and by xerographic techniques, the electrostatic image may be immediately and continuously developed into a visual image, and, if desired, formed into a permanent record. I P

, means and methods.

ment of the web past the target, and the rate of scan of the target by the electron beam are appropriately correlated to provide on the web a succession of lines of electrostatic charge which taken together denote the image or facsimile intelligence fed to the recording station. This electrostatic image may be continuously developed by xerognaphic means to provide a visual image of the intelligence, and this image may, if desired, be fixed to a permanent record. It is accordingly one object of the present invention to provide for the recording of intelligence presented in electrical form. a 7

Another object of the present invention is to provide for the recording of facsimile or image intelligence.

, A further object of the present invention is to provide for the recording of intelligence presented in electrical form and transduced to record form by use of an electron 'beam.

A still further object of the present invention is to provide for. the reduction of intelligence carried as a modulation of an electron beam into record form.

, .-An additional object of the present invention is to provide for the reduction of intelligence carried as a modulation of an electron beam into record form by Xerographic Other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of one exemplary specific embodiment of the present invention had in conjunction With the accompanying drawings,

wherein:

FIG. 1 is an exemplary presentation ofone embodiment or the present invention, showing a radar system in functional block diagram cooperating with an electron beam recorder illustrated schematically;

FIG. 2 is an enlarged detailed view, partially in section, ofthe electron beam target used in FIG. 1 and the adjacent image receiving web;

accuses Xerographic developing system used in conjunction with the electron beam recorder of the present invention.

As previously indicated, one environment in which it contemplated that the present invention will find important utility is that of recording intelligence derived from a radar scanning system. So far as the Present invention is concerned, the particular radar system, or the particular mode of radar scan, is not material. However, in FIG, 1 there is presented schematically an exemplary embodiment of a recorder embodying the princi'plesof the present invention, in conjunction with a functional block diagram of ageneralized radar system.

h r r e .10 is ShDWH wi hin a dfl hfid ,face 48 and for reasonssubsequently explained is bent line box being fed intelligence from a radar system. The radar system comprises a transmitter 11, feeding an antenna 12. The reflected energy received by the antenna is transmitted through the T-R switch 13 to receiver '14, Whose detected output is fed to the recorder through a gating circuit 15. Timer 16 keyed by the radar transmissions triggers a horizontal sweep circuit '17 for the recorder and the gating circuit to program and synchronize the horizontal sweep sequence of the recorder with the application of the received radar intelligence. The radar received intelligence and horizontal sweep output are applied from circuits 15 and 17 to the res corder 10. The recorder comprises a cathode ray tube 21, whose electron gun and beam control circuits are of conventional design. These include a 'cathodeZ-Z, control grid 23, first and second anodes 24 and 25, electrostatic horizontal deflection plates 26, electrostaticvertical deflection plates 27, and intensifying ring 28, all operated in a conventional manner from a suitable power supply generally indicated as 29. The output of the radar receiver 14 as passed by the gating circuit 15 is appliedto the control grid of the electron gun, and'thus controls the electron beam current. The output of the horizontal sweep circuit 17 is applied across the horizontalbeam d e-. flection plates 26, and thus controls the electron beam scan pattern and sequence across the target of 'the cathode'ra'y tube. It may be mentioned at this time that the vertieal beam deflection plates 27 are adjustably set to aselected bias value. The reason-for-thisig as will become'apparent subsequently, that the present'recorder operates "on 'only onehorizontal'line or vertical position for the electron beam. a

Considering the general operationof the apparatus thus far described, for each scan cycle of the-radar'system, the reflected energy denoting that scan cycle 'is passed by the gate 15 and applied to the control grid 23 of the-electron gun in tube 2.1. Simultaneously and in timed'relation thereto, the electron beam is caused to effect-one scan across the tube target, generally denoted by numeral 31 in tube face 46, the vertical deflection plates of the tube being biased-to this vertical beam angle. The intelligence contained in the reflected radar energy, which may for example be in thetime of receiving the'reflected energyor in the intensity thereof, or both, is utilized to modulate the current in the electron beam of tube 21 through-operation of the control grid 23,, Thus, as determined by the radar intelligence, a varying quantity of charge, or a'varye ing charge pattern, is established along the horizontal scan line of the target 31 for each scan cycle of the elec tron beam. As will be more fully explained subsequently, from this charge pattern applied to the target 31, acon responding line of charge pattern is induced on that portion of the web '32 immediately adjacent the target, Thus, as each successive line of intelligence, so to'speak, is ob tained from-the radar system, it is accordinglytransduced ontosuccessive lines of the web 32 as the latter is advanced past the target from supply roll 33 to take-up roll 84.

At 35 the electrostatic charge pattern thus induced on web 32 is developed by usual xerographic means into a visual image, thereby providing a visual facsimile presentation and record of the information, such as the topography, scanned by the radar system.

The electron beam target per se 31 is shown in FIG'. 3 g as a rectangular block of material havinga high electria cal resistance, and which is substantially impervious to the electrons impinged thereon by the electron beam. The

target may be formed, for example, from polymethyl methaerylate or glass, or otherhigh resistance material.

having a resistivity of at least 10 ohm-cm. Embedded within the target material .31' is a line of pins 44, each extending transversely through the target arid lying in the plane 40 indicated in dotted lines.

I The pins are formed from a conducting material such as tungsten wire.

- One end of each pin 44 is formed flush with the surfac cathode ray tu eam esi d by arrows 41 imp 4-7 of target 3.1, while the other end extendsfrom the sin of the current to the pins, with the result that the pins will become positively charged rather than negatively charged. Certain compounds, generally suitably activated oxides such cesiumozrygen-silver compounds, produce electron yields of from 4m 6. To obtain an effective charge multiplication in the pins utilizing this effect as by coating the portions of the pins receiving the primary electron beam witha cesium-oxygen-silver compound) req nros the control of a number of factorssuch as relatively low primary electron potentials, the angle of incidense of the primary electrons to'the target surface, etc.

As .shQWn in FIG. 2, the target 31 is sealed in the face of cathode my tube 21, with the flush ends of pins 44 on the exterior of the tube, and the bent ends, or tails,"45 on the interior of the tube. Electrons from the ta ls 45 a d a e t collected. on t ep 4: Immediately opposite and exterior of the target 3-1 there isypo ned a mandrel 43 or electrical conducting material whf h may be grounded .as shown, or have a positive potential applied thereto. Web 52 0t dielectric material, such as polyethylene terephthalate aluminized on the surface contacting mandrel 43, is passedover the tip offltlhe mandrel 43 in intimate electrical contact there- W1 ,he electron charges accumulated on the pins 44 set up electrostatic'fields between the pins and the mandrel 43, and-when the potentials of these fields are of suficient magnitude, the air in the space 49 between pins 44 and Web 132 s on ze The p sitive ion a attracted to he pins, while the negative ions are attracted to the web.

spot on-web 3g-is a functionof the charge present on that 7 Pin immediate y opposite he sp on e 32 1 co sideration: S am the-ch r p e t o any pa tiw a ri ie d func io ct e c beam cu n mp n d thereon, and this in turn is a function of the radar intellin s ob aine from h ra a s m iti app re t a o ea h-cycle o c along target 31by beam e t f i e lisen e induc d acro s t e eb. it he a ation o in igenc Within t a i e b i den ed by e va i ti n harge i du e th rec I As pre i us men oned, the p n 44 a e p ide th depen in ta ls 45.: Th purpo e of the tails is to eliminate theinced for critical :adjustmentof the vertical deflec+ tion anglejotiztheeleetronheam, since the beam may aimpinge r-nponianyportion :of -theteils rather than be required to be precisely-adjustedto the'line of the pins.

The foregoing description of the present invention sets where E is the pin potential with respect to ground in volts, Q is accumulated charge on the pin in coulombs, and C is the pin-capacitance to ground in farads.

Since 7 where C; is the capacitance of the area of the pickup sheet adjacent to the pin, in farads, and.

C is the capacitance of the pin to the pickup sheet in farads;

therefore,

This potential, E, from pin to ground consists of two components, one, E is across the air gap from the pin' to the surface of the pickup sheet, and the second is across the pickup web. E can be expressed as:

where E is the potential across the gap in volts.

The potential across the Whole system can therefore be expressed as;

If E is the breakdown potential of air for the air gap thickness used,.then E is that potential which, when applied to the pin, will just initiate electrical breakdown in the air gap and, hence, cause charge induction on the present invention because of poor image quality generally produced. 7

FIG. 6 presents a graph of image width as a function of pin potential and air gap distance for three air gap distances, 6n, l2,u., and 25p, using pins having a diameter of 25 Upper and lower limits of'the measured image widths are presented, as well as the range common to all three air gaps. The values given are those obtained with the mandrel and pickup web adjusted to optimum obtainable-lateralalignment with the line of pins in the tube. From this graph one may observe that a resolution of 10 lines/ mm. is obtainable, and such is considered an important minimum limitation upon good quality facsimile reproduction. Image width increases with increasing pin potential. Image width appears to be independent of air gap in the ranges of 6 1. to 25 11.. For gaps greater than 25 however, image width increases rapidpickup web in response, to pin potential; Thus, this potential: always will be greater than that necessary to break down the air gap alone, and assuming no electrical leakage, will depend on the capacitance of the pins and the pickup web. Equation 5 is approximate, in that spreading of the electric field is neglected. However, experimental results have shown this equation to be quite accurate. Based on Equation 5, FIG. 4 shows graphically the relationship of air gap distance 49* to pin potential required for charge induction on the pickup web, for various thicknesses of polyethylene terephthalate Webs. As a generalization from said graph, it should be noted that for each thickness of pickup web there is a minimum value of charge induction potentialoccurring in the air gap range of from about 10 1. to about 30 In FIG. 5 there is presented the experimentally ascertained relationship of minimum pin potential to air gap for obtaining an induced xerographically developable.

charge on a pickup web of polyethylene terephthalate having athickness of 35;. It may be observed from this graph that air gaps in the range of from 6 to 25 require a pinpotential of from about 600 volts to 800 volts. These ranges represent the preferred operating ranges of the presentinvention. It has been found that air gaps greater-than 5011. are unsuitable for the purposes of the ly' with increased air gap.

The matter of lateral alignment of the mandrel and pickup web with the row of pins in the tube is mentioned above. The tolerance with respect to this parameter has been found to be about p at an air gap of 6p, increasing to a maximum of 200g with a 12;/. air gap, and decreasing again to about 100p. with an air gap of 25 1.. By tolerance herein is meant the lateral range over which image induction is had on the web at the minimum transfer potential as shownin FIG. 5. Although the greatest tolerance in lateral positioning is had with an air gap of about 12 it is preferred to utilize a 25 air gap, which would be less diflicult to maintain than 12 and accept the reduced tolerance in lateral alignment.

Accordingly, it may be summarized that to render the invention herein described suitable for facsimile recording, the following operational characteristics must be met: The air gap between pins and pickup web must be less than 50g, and preferably between 6,14 and 25 1. The pin potential must be at least in the range of from about 600 volts at a 6 air gap to about 900 volts at a 50p. air gap, when using a pickup web having the capacitance of 35 1. thick polyethylene terephthalate (polyethylene terephthalate has a dielectric constant of approximately 3.5), the voltages generally increasing with increasing air gap, and of from about 600 volts to about 800 volts in the preferred air gap range of 6p. to 25 For maximum line resolution, the pin potential should be kept close to the minimum value at which xerographically developable charge induction occurs.

It has been shown that with tungsten pins of 25p. in diameter spaced from each other 50 $0 125, on centers, embedded in a polymethyl methacrylate block, line resolution of better than 10 lines/mm. is obtainable, if the foregoing parameters are adhered to. Of course, the electron beam scanning the target must have a diameter at the target of less than the line resolution sought. Electron beam guns are commercially available with beam diameters substantially less than ,0.1 mm. In order to obtain the pin potentials required, the electron beam gun should also be capable of an acceleration potential of 5 to 10 kv., and an electron beam current of 1 ampere. These requirements together with a beam spot of less than 0.1 mm. are available in a Type 5F electron gun.

With reference to FIGS. 7 and 8, there is presented the principles of, and an exemplary mechanism for, transforming into visual form the electrostatic image of intelligence induced on web 32 by operation of the electron beam. The thin electrically insulating web 3 2 drawn from supply roll 33 may be a plastic film, such as polyethylene terephthalate, polystyrene, cellulose acetate, ethyl cellulose, or like sheet material of good insulating properties, and preferably 'of the order of one or two mils thick; or it may be of paper coated on the working surface with one of theseplastics, or with a wax; or in some instances thoroughly dry paper or cellophane. can be used,v As theweb 32 is drawn from its roll 33, it first passes through a preliminary charging device 51, where the web is broughtto a uniform state .of electrostatic charge. From the preliminary charger, the web is then passed between'the electron beam target of tube 21 adjacentfone surface of the web, and the ground mandrel 43 adjacent the opposite surface, where'an electrostatic charge pattern depicting the intelligence is induced on the web. The web then enters a development mechanism 35, where the electrostatic charge pattern on the web is rendered w'sible by the selective application of a finely di-' vided-material, such as electroscopic powder, 'or a liquid ink, or like material. As the web emerges from the developer, the intelligence carried thereon is visually intelligibleQ Where 'a permanent record of .the intelligence j is de'sire'd, the web i'sthen passed to fuse'r 57, where the powder is Ipermanently fused to the web, "or the ink is dried. As is apparent, if only a transitory presentation of the intelligence is desired, the fuser may be omitted,-

and instead of a fresh web supply roll, the web may be in the form of an endless belt, with means interposed between .the developer 35 and the preliminary charger 51,

on the return side, to clean the intelligence off the web.

potentiometer 55 is center-tapped to ground, and the battery 'ofvoltage source53 is preferably one hundred to several hundred volts. By varying the potentiometer setting, one can thus establish afield of either polarity and of adjustable intensity betweenelectrode 52 and web 32 The alpha or other ionizing particles emitted by the radioactive layer on electrode 52 produce ionization of the air in the chamber 51 into negative and positive ions, and these ions migrate in opposite directions, depending on their polarity, under the influence of the electrostatic field existing between electrode 52 and plate 54. As ions of one polarity deposit their charge on web 32, the field becomes altered by the charge on the web until a state of equilibrium i reached, in which the potential of the web surface is equal to the potential applied to electrode 52 by the potentiometer. Whether a small positive potential' or negative potential is applied to the web, as controlled by the setting of the potentiometer tap, depends on factors subsequently'considered. In some instances the electrode 52 may be held at ground potential, in which case the device merely serves to remove incidentally acquired electrostatic charges from the web in preparation for receiving the electrostatic intelligence charge pattern. Instead of a radioactive source of ionizing particles, the electrostatic charges may be supplied by corona emission as disclosed, for example, in U.S. 2,777,957 to L. E.

Walkup. With the web 32 thus prepared, it is passed be-' tween the electron beam target of tube 21 and mandrel 43 19 receive the intelligence "charge pattern, as aforedescr'ibed. The web 32'carrying the intelligence in electrostatic charge form, passes from intelligence'transducing station into the developer 35, shown schematically in FIG. :5. This device comprises a pair of rollers 60 and 65. 'Roller6tl includes alcentral bearing shaft '64 carrying a pair of axially spaced disks 62 over which the web edge peripheries pass. Flanges 61 confinethe web in place on disks 62. The web and disks 62 thus form a hopper in which a supply of electroscopic powder 63 is contained. It is preferable, although not necessary, that the powder 63 be "charged by triboelectric or other means to carry an "electrostatic charge opposite from that induced on the web at the transducing station. The p'owderadheres in jtlie charged areas to produce a visiblepresentation of the intelligence carried by thewe b. As the powder is tumbled over theweb 32, if the initial preliminary charging of the web at 51 were of apolarity opposite from t at obtained at the tube 21, then this background charge on th'eweb'would be of the same polarity as the charged powder, and would assist in repelling the developer :powder from this background area. After being developed, the Web passes from roller 60 up over roller 65,;and down into fuser 57. In'fuser 57, the web passesabout roller 58 where it, is heated to a temperature suflici'ent-to fuse the developer powder to the web, or, if ink were used as the developer, to dry the ink thereon, thus form; ing a permanent visual and directly readable record of the intelligence transduced at tube 21. The web may then pass between suitable drive rolls such as 8i).

The described method of rendering the pattern of electrostatic charges visible, i.e., developing the image, is known as loop development. This 'syst'ein' isdisclosed in U.S. Patent 2,761,416 to C. F. "Carlson; The method of development is not critical in the 'inst'ahtinvention and other methods for contacting electrostatica-lly charged marking particles with the electrostatic image may be used. Thus a spray of electrostatically charged liquid droplets or dry powder particles, as disclosed in 1 U.S. Patent 2,784,109 to L. E. Walkup may be used or magnetic brush development described in U.S. Patent 2,791,949 to Simmons and .Saul are all operable. -A powder cloud development apparatus particularly 'suited for use as developer 35 in the present system is the ,de-

vice known as.a slot development apparatus'mo'r'e p'articularly described in U.S. 2,815,734 to C. F; Carlson. --Dejvices such as that described in' said U.S. 2,815,734 have been made wherein the development system is limited to A inchythereby making possible almost instantaneous viewing of the developed image. The choice of apartic'ular developing process or apparatus would obviously be=dependent on the combination anddesign limitations imposed in assembling the machine for a particular operation.

Similarly, the means of permanently afiixing the powder image to the backing material is not critical in the instant invention. Thus, if no permanent image is de: sired, after examination of the roll, the loosely adhering powder image may be wiped oif as by swabbing with cotton or a rapidly rotating fur brush and the roll reused.

If a permanent record is desired, the powder particles may be rendered adherent to the backing material by heating, as previously disclosed herein, by contacting the powderbearing sheet with the vapors of a solvent for'the marking particles or for a resin coating on the image receiving member as disclosed for example in U.S. Patent 2,776,907 to C. F. Carlson. Where liquid droplets are used, absorption of the liquid into the capillaries of the backing-mermber or an evaporation of the liquid would serve to 'afiix the imageto the image receiving sheet. Other means of aflixing the powder image, as by the use of pressure, by spraying with a fixative'liquid, etc.,' also may be used if desired. If desired the image may be transferred from dielectric web 32 to an image support member as paper and affixed thereto with web 32 being recycled in the image-forming process. 7

The possibility of using a pin tube for direct electron beam recording has long been obvious to those skilled in the art. Heretofore, however, it has not been possible to obtain dependable operation with high resolution. Thus this manner while using the instant invention 10-15 lines 7 per mm. are easily obtained) it has also been suggested -to space the-image receiving web from the pins, hut-under conditions of voltage and spacing causing poor-resolution or undependable operation, or both, Theinstant -invention for the first time presents the critical interrelationship between potential and spacing required for high resolution and dependable operation.

From the foregoing detailed exemplary description of the present invention, it will be appreciated that there is presented a method and means for recording electrically transmitted intelligence, utilizing an electron beam as the means of transducing the electrical form of intelligence onto record form, in such manner as the record may be rendered visual and permanent, if desired, by usual xerographic techniques. Although the present recording technique has been illustrated in conjunction with a radar system for sensing and presenting the intelligence to be recorded, such is presented only as exemplary of one field of use for the present invention. As will be apparent to those skilled in the art, the present invention may be'utilized generally in the field of recording, and it is not intended that the foregoing description shall be interpreted as limiting the scope of the present invention to radar. Also, other variations, modifications and adaptations of the present invention will be apparent to those skilled in the art, and such as come Within the spirit and scope of the appended claims are considered to be embraced by the present invention.

I claim:

1. A cathode ray device comprising an envelope, an electron gun in said envelope for projecting a beam of electrons, and a target in the face of said envelope to which said beam is directed, said target comprising a block of material essentially non-transmissive of electrons impinged thereon by said beam and having a high electrical resistance, a plurality of electrically conducting pins embedded in said block extending through said block from the interior of said envelope to the exterior thereof and arranged in a line, the ends of said pins extending to the interior of said envelope having portions extending exten'orly of said block and angularly disposed relative to the portions thereof embedded in said block, said angularly disposed portions being substantially parallel to each other, whereby said electron beam may scan said pins by traversing said angularly disposed portions, means to modulate said electron beam and an electrically conductive mandrel adjacent said pins but spaced therefrom and adapted to support a web of electrically insulat- ,ing material in spaced parallel relation to said pins at a distance of from about 6 to about 50 microns, said mandrel being in electrical circuit with said gun whereby a charge established on said pins by scanning thereof by said beam will disrupt the air between said pins and web and thereby induce an electrostatic charge on said web in accordance with the electron charge carried by said pins.

2. A device as set forth in claim 1 wherein said electron beam is modulated by varying the current thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,273,793 Ekstrand Feb. 17, 1942 2,283,148 Bruce May 12, 1942 2,657,377 Gray Oct. 27, 1953 2,829,025 Clemens Apr. 11, 1958 FOREIGN PATENTS 1,077,037 France Nov. 3, 1954

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