Electrographic writing apparatus for a metallized strip recording medium using grounded electrodes between writing electrodes

Abstract

The electrodes of a burnout type electrographic apparatus are grounded during their idle period in order to clear any possible short circuit to an active electrode by the accumulation of metal particles or oxide whiskers which would otherwise cause more than one electrode to be simultaneously activated. An auxiliary grounding electrode is interposed between each pair of adjacent writing electrodes.

Description

This invention relates to an apparatus writing upon a recording medium, particularly recording medium having a metal layer subject to electrical burnout on a carrier such as a paper or synthetic resin tape. The apparatus writing upon the tape has a multiplicity of writing electrodes insulated from each other and disposed in simultaneous contact with the metal layer of the tape. The application of a voltage sufficient to produce an arc causes a burnout at the metal layer, which is to say that an area of the metal layer in the neighborhood of the contact is removed. During writing the recording medium is moved past the electrodes, usually at uniform speed.

In apparatus of the kind just described, the recording medium carrier tape is almost always moved in the same direction, so that the burnout residues and the metal particles loosened from the metal layer by the writing electrodes moving in contact with the layer can stick to the writing electrode points and form an oxide whisker. Such an oxide whisker, which is electrically conductive, can cause a short circuit between two adjacent writing electrodes, with results that are troublesome both for a visible text writing operation and for a writing operation of the perferation code type producing coded indications similar to the holes in a punched tape or a card. In either of the cases just mentioned, the metal layer lying under both of the electrodes thus connected is burned out whenever a burnout signal is provided to only one of the electrodes, producing a false writing result.

It is an object of the present invention to make such short circuit bridging between the writing electrodes quite harmless by some means without undue complication.

SUBJECT MATTER OF THE PRESENT INVENTION

Briefly, means are provided for grounding the electrodes not connected in the writing circuit, so that as soon as an electrode is disconnected from the writing circuit, a ground is applied thereto until the next writing period for that electrode. A continuously grounded electrode is interposed between every two adjacent writing electrodes.

The invention is further described by way of example with reference to the accompanying drawing, in which:

FIG. 1 is a perspective view of the writing head of a visible text writing apparatus, with a symbolic diagram of a writing and grounding circuit connected thereto;

FIG. 2 is a similar view of the writing head of a coded spot writing apparatus having auxiliary grounded electrodes arranged between the writing electrodes, and

FIG. 3 is a simplified circuit diagram of the circuit to which the writing head of FIG. 1 is connected.

FIG. 1 shows the writing head part of a visible text writing apparatus having a number of writing electrodes, 21 arranged one next to the other in a row and insulated from each other by a thin mica sheet. A tape 22 of recording medium of metallized paper is passed underneath the writing electrodes in contact with them in the direction shown by the arrow. The metallized layer of the recording medium, which is in contact with electrodes, is grounded by a broad electrode 23 that extends across the width of the layer as it passes beneath the electrode.

By grounding it is meant, of course, that a connection is made to a fixed potential useful as a return potential because it is subject to little or no fluctuation, such as actual ground potential, chassis potential of an equipment, or the like.

The tape 22 runs over a support body 24 by which it is provided with the necessary pressure against the end of the grounding electrode and of the writing electrodes. In order to make harmless any bridging that might result from the connection of electrically conducting residue particles between adjacent writing electrodes 21, these writing electrodes are connected in an electronic circuit 25 by which all are grounded during the pauses between their writing periods. The circuit 25 is shown in more detail in FIG. 3.

When an electrically conducting bridge 28 is formed between two neighboring writing electrodes 21, the application of a burnout pulse to one of the two electrodes (such as, for example, an electronegative voltage of about 15 volts) produces a current flowing through the other of the electrodes, which is not supposed to be writing and is accordingly grounded. The short circuit current that immediately flows through the circuit 25 to ground is limited by the resistance in the circuit so that it burns away the bridge 28 without then maintaining the arc between the two writing electrodes 21. In order that the writing electrodes may not be short circuited by accumulation of dust or other particles of larger cross-section, all but the bottom of the front surfaces of the writing electrodes are covered with an insulating layer of 27 of mica and only a narrow cross-section of the electrodes remain uncovered.

If the spacing between writing electrodes is greater than 0.5 mm, it is convenient to introduce a continuously grounded auxiliary electrode between adjacent writing electrodes. An arrangement is shown in FIG. 2, which shows a writing head for a coded spot writer having 9 writing electrodes 31. The auxiliary electrodes 32 are located between adjacent writing electrodes 31 and are insulated from them by mica sheets. All of the auxiliary electrodes 32 are connected electrically together and grounded.

A metallized paper tape 34, with the metallized layer on its top surface, passes first under a grounding electrode 35, then over a support body 36 and finally under the writing electrodes 31 of the writing head 30, which are connected to an electronic circuit 37 of such a kind that a writing voltage is applied to them with respect to the metallized layer in periods in which they are respectively to write on the recording medium by producing a burnout 38 in the metal layer of the recording tape 30, the burnout pulses being provided in accordance with some suitable information code to record intelligence on the tape.

As already mentioned, there are electrodes 32 located between each pair of adjacent writing electrodes 31. If now an electrically conducting bridge 39 is formed between a writing electrode and an auxiliary electrode, it is burned away by a short circuit arc. It is useful in the arrangement of FIG. 2 also to ground the writing electrodes 31 when they are not connected in the writing circuit, although that is not necessary when the electrodes 32 are provided in the writing head. Accordingly in the symbolic representation of the circuit of FIG. 2 a single throw switch 40 indicates only connection to and disconnection from a writing potential.

The grounding of the writing electrodes when disconnected from the writing circuit in accordance with the invention is symbolized in FIG. 1 by a double-throw switch 31.

FIG. 3 shows in more detail the circuit 25 of FIG. 1.

Signals for controlling where the burnout marks should occur are provided from the terminal 50, which is connected to a suitable transmission line or signal generating apparatus and provides signals controlling the relay 54 which intermittently connects a source of negative writing potential 52 through contacts of one of the relays 71, 72, 73 . . . to one of the representative writing electrodes 21a, 21b, 21c . . . The circuit for the writing current is completed through the metal layer 22 and the collective ground electrode 23. The relays 71, 72, 73 . . . are activated sequentially by a rotating switch 56 driven by the motor M, which may be a stepping motor synchronized with the incoming signals by a connection symbollically shown by the dashed line 51. The synchronizing signals may of course be furnished by a conductor separate from that which furnished the signals controlling the relay 52. The respective relays 71, 72, 73 . . . are provided with back contacts such as the contact 58 of the relay 71, for grounding the corresponding electrode when the relay is not actuated through a contact of the switch 56, the contact arm of each unoperated relay being pressed against the back contact in the usual way by a restoring spring (not shown).

It is to be understood, of course, that instead of electromagnetic relays, a semiconductor switching circuit may be used to provide the same switching functions and that the rotary switch 56 and the motor M may likewise be replaced by a semiconductor counting chain and associated circuits in the well-known way. Electromagnetic circuits are shown in FIG. 3 for simplicity of illustration.

The current limiting the resistor 53 is of a magnitude such as to permit current to be passed between one of the electrode 21 and the metal layer 22 sufficient to produce a burnout. When a short circuit occurs between an activated electrode and a grounded electrode the current limiting effect of the resistor 53 is sufficient to prevent an arc from being formed which would spread the burnout, but if an additional resistance is desired, to assure clearing the short circuit without formation of a side arc, a resistance may be interposed in the conductor 59.

The invention has been described in detail with reference to particular embodiments, but of course modifications may be made within the inventive concept.

Claims

I claim:

1. Apparatus for writing on a recording medium having a metallic layer subject to electrical burnout marking on a carrier web, which apparatus comprises:

a plurality of writing electrodes (21,31) insulated from each other arranged for simultaneous contact with the metallic layer of said recording medium,

circuit means (25,37) for applying a burnout voltage during writing periods and a grounding potential during a non-writing period to the respective writing electrodes (21,31) and for applying a grounding potential continuously to the metallic layer along a line substantially equally spaced from said writing electrodes, and

a plurality of continuously grounded electrodes (32) respectively located between each adjacent pair of writing electrodes and arranged to make contact with said metallic layer, whereby distortion of the record through inter-electrode short-circuits is prevented.