US2952796A - Electrostatic printing tube - Google Patents

Description

Sept 13, 1960 R. w. CRI-:ws ET AL 2,952,796

ELECTROSTATIC PRINTING TUBE F'iled May 13, 1957 INVENTORS, ,605527 EEMS BY auf@ ELECTRoSTATIc PRINTING TUBE Robert W. Crews and Casper W. Barnes, Jr., Palo Alto, Calif., assignors to A. B. Dick Company Filed May 13, 19157, Ser. No. 658,797

2 Claims. (Cl. 315-21) This invention relates to electrostatic-printing tubes, and, more particularly, to improvements therein.

In an application for Electrostatic Printing Systems, by lohn L. Tregay, fined May l0, 1957, Serial No. 658,275, and assigned to a common assignee, there is described an improved electrostatic printing tube which has as its target a Wire array consisting of small-diameter, short, closely spaced, parallel and mutually insulated wire segments which have one of their ends extending through the target wall to the outside of the tube. A conductive plane at anode potential, which can thus be termed an external anode, is positioned opposite the Wire ends which are outside the tube, and a dielectric Writing medium is passed between the external anode plane and the wire ends. Means are provided for sweep.- ing the electron beam generated in the tube across the wires and maintaining the beam turned ott, except When it traverses selected ones of the wires. `These Wires then charge up toward the cathode potential. When the potential of any Wire reaches a critical value with respect to the external anode, a discharge takes place between that wire and the plane. If the writing medium is present, it is at anode potenti-a1 and the discharge results in aspot of charge under the Wire and on the dielectric -Wxitrng material. Means are provided for repetitively sweeping the electron beam across the wires as well as controlling its intensity so that, `as the dielectric Writing medium is moved, charges are deposited thereon which, upon subsequent development, produce visible characters corresponding to the ones dictated by the deection land intensity-control signals.

With the target configuration described the wire-to-wire capacity is high, whereas the wire-to-anode capacity is low. As `a result, when the electron beam strikes a given wire and causes it to charge toward cathode potential, the adjacent wire, and to a lesser degree, all succeeding wires, also charge towards cathode potential because of the coupling capacity between them. This eiiect can result in loss of denition.

-An object of this invention is to minimize detrimental wire-to-Wire capacity in an electrostatic writing tube.

Another object of this invention is to provide a novel and improved target arrangement for an electrostatic Writing tube.

Still another object of the present invention is to provide an improved electrostatic printing tube.

Yet vanother object of the present invention is to provide an electrostatic printing tube which has better de-finition than was obtainable heretofore.

These and other objects of the invention are achieved by providing an electrostatic printing tube having a target consisting of `a plurality of insulatingly supported and spaced wires. Each one of these wires has one of its ends extending through the face of the tube in the manner described previously. This affords means whereby external discharges from these wire ends may be obtained as a result of the cathode-ray beam within the tube strikate t ing a selected one of these wires and elevating its potential to the point where such discharge can take place. In order to minimize adjacent wire coupling and thus mitigate any loss in denition, a shielding is provided for each writing wire of the array by connecting all alternate wires together. The common coupling to the shielding wires may thereafter be grounded or, if desired, connected to a source of potential below discharge potential. The resulting shielding effect obtained permits each Wire to be altered electrically by the electron beam without appreciable effect on its neighbors. The wire-to-wire capacity of the writing wires is thus minimized.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as Well as additional t objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

Figure 1 is a cross-sectional View of one -embodiment of the invention;

Figure 2 is a plan view of the target of the electrostatic Writing tube in accordance with this invention; y

Figure 3 shows a view in section of the wire-mounting arrangement employed in Figure 2;

Figures 4A rand 4B are respectively end and side views of another arrangement, which is preferred, for locating the writing and shielding wires; and

Figure 5 shows in section the finished arrangement of the preferred arrangement for the shielding wires.

Reference is now made to Figure l, Where there is shown a cross-sectional View of the improved electrostatic writing tube in accordance with this invention. The electrostatic writing tube is a conventional cathode-ray tube except for its target. Thus, it includes an evacuatedenvelope 10, which has therein a cathode l2, acontrol electrode 14, `an anode or laccelerating electrode 16, a focus coil 1S, and adeiiection'coil 20. Thecathode 12 is connected yto a negative point of potential in the operating-potential supply 22. Signals are applied to the intensity-control grid from asignal source 24. Deflection signals are applied tothe deflection coil from adeflectionsignal source 26. By means of a voltage-droppingresistor 28, the required more-positive operating potential is applied to the anode 16 andtothe centering coil 18.

The target includes ametal faceplate 30, which is at anode potential. Insulatingly supported within a slot in the target is a plurality ofwires 32. Each one of these wires is separated from the other by a material such as glass and is mounted so that one end extends through to the outside face of the tube, which is finished in iiat fashion so that thedielectric writing medium 34, such as paper, may be passed extremely close to the wire points which are arrayed in a column, to receive electrostatic charges. An external plane or conductor 36 is connected to the anode and extends along the column of wire points, and is spaced therefrom.

In operation, the cathode-ray beam which emanates from the cathode is deiiected by the deilection-signal source to sweep across the portions of the wires which are inside the tube. Whether or not a wire is energized is determined by the intensity-control signals received from thesignal source 24 at the time the electron beam is directed upon it. Thus, if the deflection signals and the intensity-control signals are being received from a suitable scanning mechanism, such as a facsimile scanl ner or television camera, and if thewriting paper 34 is moved at a synchronized vertical scanning speed, a pattern of charges will be deposited on the writing paper, which when subsequently developed, using well-known electrostatic developing techniques, will produce a visible nnage of the original copy.

Heretofore, each one of thewires 32 in the target was separated from the adjacent wire by the glass insulating medium within the target. Since the wires are substantially parallel to one another, the -wire-to-wire capacity is high and the Wire-to-ground capacity is low. Accordingly, when the electron beam strikes a given wire and causes it to charge toward cathode potential, which is necessary before the wire can discharge, vto a lesser degree all succeeding wires also charge toward cathode potential because of the coupling capacity between them. In accordance with this invention, a simple method is proposed for shielding each wire of the array from the neighboring wires by connecting all alternate wires together. This is eifectuated by the connectinglead 38, which connects with alternate ones of the Wires 32. The connectinglead 38 is brought out from the tube to aterminal 39. This may be connected either to the anode or, preferably, to theresistor 28 in order to establish these alternate wires at a suitable potential whereby discharges take place to the external anode plane in preference to an adjacent shielding wire. The shielding effect obtained by this arrangement permits each wire to be altered electrically by the electron beam without an appreciable eifect on its neighbors. 'I'he wire-towire capacity of the writing wires is thus made small. The existence of the shield wires in the wire array results in small wire-to-wire coupling of the writing wires, thus restricting the discharge to those wires directly charged by the beam. The net result is an improvement in the resolution of the material written.

Figure 2 is a view along the lines 2-2 of one arrangement of the improved target. It includes themetal plate 30, which is sealed to the end of theenvelope 10, which has a slot in the center within which is mounted the plurality ofwires 32. As shown in section in Figure 3, one way of mounting these wires is wherein eachwire 32 has one of its ends 33 (the one which extends outside of the tube) held clamped between two pieces ofy.glass 40, 42. The wire end extends to theliat printing surface 44. The remainder of the wire is wound over aglass rod 46 and another segment ofglass 48 clamps the other side or end of thewire 32 against thesegment 42 androd 46. An insulatingmember 50 has on the underside thereof printed-circuit conductors 52 which, as shown by the dotted line in Figure 2, are spaced to connect to the alternate ones of thewires 32. Theconductor 38 which connects to all these wires is brought to the terminal 39 on the surface of thetube 10, from whence connection with the external potential source may be made.

Referring now to Figures 4A and 4B, there are shown respectively end and side views of the preliminary steps in placing the writing and shielding wires to obtain the preferred arrangement vfor the target which is shown in section in Figure 5. A rectangular insulating material rod, such as a glass rod 60, has ametal conducting strip 62 extending along one face thereof. Ashield wire 64 is wound with a desired pitch around both the glass rod 60 and the conductingmetal strip 62. A second at insulating material rod which can also be a glass rod orstrip 66 is placed and held against the turns of the Wire' 64, which are over the conducting metal strip to cover these portions of the turns. Over the entire assembly there is wound thewriting wire 68 with a desired pitch and in a manner so that its turns fall between the turns of the shield wire.

Thereafter, the wire is ground away at Itwo sides as shown by the dotted lines leaving the results shown in Figure 5. The shield wires are in the form of a U on its side. The Writing wires are in the form of an upsidedown L. Against Ithe side of the assembly wherein the base of the shield wire U exists, there is 'assembled with sealing compound another rectangular glass rod 70, The

points of the writing wires extend between the two glass rods 60, 70, whose at faces serve as a writing surface. The shield wires in the arrangement shown -shield the adjacent writing wires andare bent away from the writingwire writing tips to lessen the chances of discharge to shield wires instead of lto dielectric medium. The glassrod surfaces at right angles to the writing surfaces are used for holding the assembly inthe metal faceplate.

As a consequence of the quantization of the beam current lacross the focus lbearn spot by the shielded writing wires, only those Wires will discharge which intercept a high-current-density portion of the beam. This has the effect of external concentration of the writing beam, resulting in a much higher resolution of the material written.

Accordingly, there has been shown and described herein a novel, useful, and simple arrangement for improving an electrostaticV writing tube by providing shielding for the writing wires therein. While the connection to the .alternate wires has been shown as being made inside the tube, it is possible to make it outside the tube with the( alternate wire points. However, this is not too desirable -an arrangement.

We claim: p

l. An improved electrostatic writing Vapparatus comprising a tube envelope enclosing a cathode for generating an electron Ibeam, an anode, anda target, said target including =a plurality of spaced insulatingly supported wires, each of which has one end extending through said envelope, means connecting alternate ones of said Wires together, 4an anode plane positioned outside of said tube opposite said one ends of said wires, a source of operating potential, means for applying -a irst potential Vhaving a first value from said source to said cathode, means for applying a second potential having a second value from said source to said anode, and means for applying to said means connecting 'alternate ones of said wires together Y from said sourcea third potential having a value below that of said rst potential.

2.V A target for an electrostatic writing ltube comprising a first insulating material rod,a conducting metal strip extending axially along said first rod and over a portion 0f its circumference, a plurality of Ushaped shield wires spaced :along and wound on said rst rod with one side of said U in contact with said conductive strip, -a second insulating material rod abutting 4and covering -said one side of all said shield wires, a plurality of L-shaped Writing wires wound on said rst rod, each writing wire positioned between -two shield wires and having one lside of said L extending along the base of said -U and beyond said second glass rod, and the other sidel of said L extendf ing along the side lof said U which is not between said rst and second rods, and a third insulating material rod positioned 4adjacent said first and second glass rods to hold said shield and writing wires in place therebetween, said second and third glass rod surfaces which abut said writing wires forming an electrostatic writing 'surface therewith.

References Cited in the le of this patent UNITED STATES PATEN'lS` YGreat Britain Nov..3o,f19ss

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