US2777745A - Electrostatic recording apparatus - Google Patents

ELECTROSTATIC RECORDING APPARATUS Filed Oct. 4, 1952 3 Sheets-Sheet 1 2 V- souzcz or

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ELECTROSTATIC RECORDING APPARATUS Filed Oct. 4, 1952 3 Sheets-

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3 INVENTOR: J05 e Jh T Mc Naney United States Patent 6 l 2,777,745 ELECTROSTATIC RECORDING APPARATUS Joseph T. McNaney, San Diego, Calif... assignor, by mesne assignments, to General Dynamics Corporation, a corporation of Delaware Application October 4, 1952, Serial No. 313,167 9 Claims. (Cl. 346-74) This invention relates to recording apparatus and particularly to apparatus for recording intelligence projected on the screen of a cathode-ray tube.

The recording arrangement shown in Fig. 1 is a simplified illustration of the principles of the invention. A cathode-

ray tube

12 serves to convert the intelligence to be recorded from electrical impulses into suitable form to provide a permanent and readable record. The tube of Fig. l is of a conventional type except that it is provided at one end with a screen or

target area

13 which is substantially flat so as to accommodate a

flat recording medium

26 in contact with or nearly in contact with its outer surface. Preferably an

intensifier anode

14 of a conventional type is employed in the tube.

A

conventional source

16 of high voltage and a

voltage divider

18 provide suitable focusing and accelerating potentials of the electron beam of the tube.

The intensity of the beam of electrons in the cathoderay tube and its position on the screen or

target area

13 is controlled by a

source

20 of control signals which may be of any desired type.

An electrically

capacitative plate member

22 is disposed in juxtaposition to and slightly spaced from the outer surface of the target area or

screen

13 and is substantially parallel thereto.

Fig. 2 is a cross-section of the

tube

12 looking toward the target area illustrating a construction in which the inner surface of the target area or

screen

13 is coated with a secondary-emissive substance, such as aluminum oxide, in such a manner that the particles of the second ary-emissive materials are separated and insulated from each other to form a mosaic structure, each serving as an individual electrocapacitative cell. Since the material is of a secondary-emissive character, the electrostatic charges in each particle do not accumulate but are only energized during the time the electron beam of the gun is impinged against them. Preferably the glass forming the

target area

13 of the

tube

12 is thin with respect to the thickness of the walls of the tube in order to minimize the fringing efiect of the electrical fields passing through it.

Fig. 3 illustrates another form of

suitable screen

13 in which the target area comprises a plurality of closely spaced

conductors

30 Which are electrically insulated from each other and extend from the inner surface of the glass forming the

screen

13 of the tube to its outer surface, as shown in detail in Fig. 4, thus providing a mosaic of elements serving to conduct electrical energy from within the evacuated tube to the outer surface of its screen. This embodiment of the

screen

13 has the advantage that the conductive path from the negative terminal of the

source

24 is extended to the outer surface of the target area of the

tube

12, thereby minimizing the effect of stray electrostatic fields in passing through the glass wall of the tube.

The invention contemplates the use of a

recording medium

26 adapted to be disposed between the outer surface of the

target area

13 and the

plate member

22, to provide a permanent record of the intensity, movement, and shape of the electron beam Within the

tube

12.

The

recording medium

26 is preferably thin, flexible, and has high insulating properties. It will be noted that the system comprising the

target area

13 of the

tube

12, the

plate member

22, and the

recording member

26 forms a condenser, with the latter element serving as the dielectric.

A potential developed between the

plate member

22 through the

source

24, to the

cathode

25 and any portion of the

target area

13 energized by the resulting electron beam will polarize or create an electrostatic stress on the

recording medium

26 when interposed therebetween thus providing an electrostatic recordcorresponding to the intensity, and shape of the electron beam'and to the location of its impingement against the target area. Those portions of the

recording medium

26 that are,not exposed between the

plate member

26 and the energized portion of the

target area

13, remain unpolarized and form a field" for the images produced by the polarized regions.

The definition of the polarized images produced in the above manner from the unpolarized field requires a minimization of the air gaps on either side of the

recording medium

26 between the

plate'member

22 and the face of the

tube

12, and therefore the

plate member

22 is preferably spaced from the tube only as much as practically necessary to permit the interposition and movement of the

recording medium

26.

When intelligence is to be recorded electrostatically by the arrangement of Fig. 1, it ispreferable that the

member

26 be electrostatically polarized before it is positioned between the

plate member

22 and the target area of the

tube

12. The initial charge on the

recording member

26 should be opposite in polarity to that of the images which are electrostatically developed so that the polarization of the areas of the

member

26 in which the images are recorded is reversed from the field by the charge applied through the beam of the cathode-

ray tube

12.

In the embodiment of the invention utilizing a tube having a

target area

13 of the type shown in Figs. 3 and 4, the

recording medium

26 may be a current-sensitive paper which changes in color when an electrical current ispassed through it. In this case, the potential built up from the

source

24 between the

plate member

22 and the energized portion of the

target area

13 is sufficient to break down the

dielectric recording member

26, and

produce a visible image by its discoloration, of the same shape as that of the electron beam and corresponding to its location on the

target area

13.

Thus, when a screen of the type shown in Figs. 3 and 4 is employed, the

recording medium

26 may be either a current-sensitive paper which provides a direct record of the images which are projected on the target area of the tube, or it may bean electrostatically polarizable member which provides an electrostatic record of the images. In the latter case and in the case in which a target area of the type described in connection with Fig. 2 is employed, the electrostatic record may be converted to a visible record by a suitable electrostatically charged powder over the surface of the'recording

member

26. The powder should be of a contrasting-color to the

recording member

26. The powder is preferably charged so that it will adhere to the electrostatically charged image areas and it will fall 01f or be repelled from the uncharged field areas.

By properly proportioning the electrostatic charges on the

member

26 and the charge on the electroscopic powder, an indication of the relative intensity of the images which are projected on the screen of the tube may be obtained.

The cathode-

ray tube

32 is provided with means for shaping the cross-section of the electron beam in the form of alphabetic or numeric characters which are to be printed. The tube is of the general type disclosed in my U. S. Patents Nos. 2,275,017 and 2,283,383, and in my co-pending applications Serial No. 297,480, filed July 7, 1952 and Serial No. 298,603, filed July 12, 1952. The target area or

screen

33 of the

tube

32 may be any of the types described above with reference to Fig. 1, and it is preferably curved so as to conform to recording arrangement mounted on a rotatable drum 4.0.

The

tube

32 is provided with a

thin matrix

34 disposed perpendicularly with respect to the path of the electron beam of the tube. The

matrix

34 is a solid member provided with apertures shaped like the characters to be printed. Openings shaped in the form of the numbers one to nine are shown in Fig. 5 in order to illustrate the invention. The letters of the alphabet and some punctuation marks may also be provided.

A set of

selection plates

36 is'provided for selectively directing the electron beam of the tube through the apertures in the

matrix

34, and a set of

deflection plates

38 is provided for positioning the electron beam after it traverses the matrix. Thus, the

selection plates

36 serve to select the respectivecharacters which are to be printed, and the

deflection plates

38 serve to cont'rolthe position or orientation of the characters on the screen or

target area

33 of the

tube

32.

A

source

39 of control signals serves to provide the signals required for gating and positioning the electron beam of the tube. By way of example, the

source

39 of control signals may be a circuit for converting binary code signals to suitable potentials for controlling the electron beam of the tube. One such arrangement is disclosed in my co-pending application Serial No. 340,240, filed March 4, 1953.

The electrostatic recording apparatus comprises a conductive drum 4 0 which is provided with a thin coating of electrostatically polarizable. material 42-, say polystyrene, on its outer surface. The drum A) may be rotated continuously or in steps if desired. Preferably the movement of the drum is synchronized with the control signals which are provided by the

source

39 so that information may be recorded along straight lines. The shaft of the

drum

49 is connected to the conductive portion of the

drum

40 and through a

brush

44 to ground.

As shown in Fig. 5, the

drum

40 is intended for clockwise rotation. An

electrode

46 extends across the

drum

40 adjacent the outer polarizable coating 2 on the portion of the drum advancing towards the position of the

tube

32, and is connected to one side of a

source

48 of high potential, serving to apply an electrostatic charge to the polarizable

outer surface

42 of the

drum

40.

In the arrangement of-Fig. 5, the

tube

32 functions identically to the

tube

12 of the arrangement shown in Fig. l, and is provided with the

equivalent elements

14, 16, 18 and 24,. In the present instance, the source of high potential 24 is electrically connected to the portion of the

drum

40 juxtaposed to the

target area

33 of the

tube

32 through ground and the

brush

44, so that the latter serves' as the electrically

capacitative plate member

22 of the'arrangement of Fig. 1.

As the polarized

outer surface

42 is moved into position opposite the

target area

33, electrostatic images are produced on its outer surface in correspondence with the intensity, shape, and location of the electron beam of the

tube

32, the polarity of the image portions being opposite in sign to that of. the

polarized surface

42 forming the field or background.

A

receptacle

49 and

agitators

50 serve to cause particles of suitably charged

electroscopic powder

51 to impinge upon the

member

42 as the drum rotates. The powder may be charged so that it is attractedand adheres to the image areas and is repelled by the oppositely charged background areas or vice versa. Thus, the electroscopic powder produces a visible record of the images which are electrostatically recorded on the

member

42. i i

'The images formed by the electroscopic powder are transferred to paper 52 which ism'oved in synchronism with the drum 4%. An

electrode

54, which is connected to a

source

56 of high voltage, serves to apply an electrostatic charge to the paper 52. The charge is of opposite polarity to that of the powder onthe image areas of the

member

42 and of sufficient intensity so that the powder is attracted and the images are transferred from the

member

42 to the paper.

The

electroscopic powder

51 is fusible or thermoadhesive and a

heater

58 is provided for causing the powder images to be aifixed to the paper so as to provide a permanent printed record of the images. One suitable powder for the purpose is formed of carnauba wax with .a coloring material. In the alternative, the paper may be provided with a thermo-adhesive coating so that sub stantially any powder will adhere to it when it is heated.

A cleaning

brush

60 is provided for removing surplus powder from the drum after each transfer operation.

In operation, the

drum

40 is moved in synchronism with the intelligence which is projected onto the

screen

33 of the

tube

32 so that the images are recorded at predetermined positions along the drum. The images to be printed are recorded electrostatically on the

polarizable material

42 by the charge which is applied from the

source

24 of high voltage through the shaded electron beam of the cathode-

ray tube

32.

As the electrostatically recorded images pass the

receptacle

49, the

electroscopic powder

51 adheres to the charged image areas, and as thepowder images pass the

electrode

54 they are transferred to the recording paper 52 which provides a permanent record of the information.

The arrangement shown in Fig. 6 is similar to that shown and described in connection with Fig. 5, but in this embodiment, the electrostatic images are developed directly on the recording media which is then processed to form a permanent record. For this purpose, the polarizable outer covering of the

drum

40 is replaced with a thin, flexible, recording media 64 which is preferably continuously fed over the drum 4% and between the target area of the

tube

32 from a roll and by a suitable feed mechanism. The recording media 64, by way of example, may be a paper impregnated with polystyrene resin, or wax to produce a high dielectric constant.

Electrostatic images are produced on the continuously moving media 64 from the target area of the cathoderay tube as the media is moved by it, and the exposed media is then passed over the

receptacle

49 so as to produce visible images of the electrostatically recorded images by the adherence of the electroscopic powder. The media 64 is then passed over the

heater

58 which causes the powder images to fuse into or adhere to the paper and form a permanent record of the intelligence.

The arrangement shown in Fig. 7 employs a

currentsensitive material

70 for permanently recording the images which are produced on the target area of the cathode-

ray tube

32. The material 70 employed in this embodiment of the invention is of a type which changes in color when an electric current is passed through it. It is necessary to provide a target area of the type shown and described in connection with Figs. 3 and 4 for the cathode-

ray tube

32 in order to provide a conductive path through the envelope of the

tube

32 and permit a breakdown of the dielectric represented by the

material

70 and a passage of high voltage current between the target area of the

tube

32 and the drum 4t). If desired, the conductive wires forming the target area may be extended from the face of the screen so as to make positive electrical contact with the paper '70.

Since the intelligence which is produced on the screen of the cathode-

ray tube

32 is recorded directly on the paper '70 by the current which flows from the

source

24 to the

conductive drum

40, no further processing of the paper is required.

Fig. 8 illustrates a recording arrangement for providing a visible record of intelligence which is projected onto the screen of a cathode-ray tube in a radar receiver. In this embodiment of the invention the cathode-

ray tube

74 is a type which is suitable for projecting radar displays on the target area of the tube. The target area, however, is constructed in accordance with arrangement heretofore described in connection with Figs. 1 and 2.

A rotatable magnetic deflection coil 76 and a radar receiver '78 for controlling the electron beam of the tube are shown in block diagrammatic form. The magnetic deflection coil '76 and the

radar receiver

78 may be conventional types for providing PPI type displays on the target area of the

tube

74.

As in the case of Fig. 1 arrangement, an electrically

capacitative plate

22 is located in juxtaposition with and slightly spaced from the outer surface of the target area of the

tube

74.

It is preferable that the screen of the cathode-

ray tube

74 be substantially flat so that a

recording medium

7 8 can be passed between the face of the

tube

74 and the

plate member

22.

In this embodiment of the invention a thin, flexible polarizable

member

78 in the form of a continuous belt is employed to provide an electrostatic record of the intelligence which is produced on the target area of the

cathoderay tube

74. The belt '78 should be composed of a transparent or translucent material. A crank 80 is shown for moving the

belt

78, representing means for continuously feeding the belt 73 across the face of the

tube

74 and through the succeeding apparatus.

A portion of the belt '78 is initially polarized by means of a

source

48 of high voltage and a pair of spaced

electrodes

46, 82. Then the polarized portion of the belt '73 is positioned between the target area of the cathode-

ray tube

74 and the

plate member

22. A

switch

34 is closed to cause the beam of the cathode-ray tube to reverse the charge in the

belt

78 as heretofore described, and in accordance with the intelligence which is produced on the screen of the tube during the period while the switch is closed. The switch 84 is then opened and the portion of the belt on which the electrostatic images are recorded is passed over the

receptacle

49 where properly charged

electroscopie powder

51 is deposited on the image areas. The portion of the belt which carries the powder images is then positioned over a

ground glass screen

88 which is illuminated by a lamp 99. The images thus can be visually observed while the belt is in this position, and thereafter the information may be transferred to a printed record by moving the belt '78 between the

electrodes

54 and 92 which causes the electroscopic powder to be transferred to the paper 52. The continuously-fed paper 52, which is synchronously moved with the

belt

7 8'by suitable drive means, is then passed over a heater 53 which fuses the

powder

51 and forms a permanent record as heretofore described. A

cleaning wheel

60 is provided for removing any surplus powder from the belt. It will be apparent that the paper recording arrangement of Fig. 8 may be omitted if a permanent record of the electrostatically recorded information is not required.

9. Recording apparatus in accordance with

claim

7 wherein said polarizable member is a continuous belt polarizable member.