US2076220A - Method of and means for producing printing plates - Google Patents

Description

April 6, 1937. J. A. BENNETT METHOD OF AND MEANS FOR PRODUCING PRINTING PLATES 3 Sheets-Sheet 1 Filed Feb. 3, 1934 wmmmwi wbi el anon-W1 J. A. BENNETT April 6, 1937.

METHOD OF AND MEANS FOR PRODUCING PRINTING PLATES Filed Feb. 5, 1934 3 Sheets-Sheet 2 abbot/1 3 W 9.130% U Q m bbqm Q. 3

J/Z Benneil April 1937- J. A. BENNETT 2,076,220

METHOD OF AND MEANS FOR PRODUCING PRINTING PLATES Filed Feb. 3, 1954 3 Sheets-Sheet 3 Patented Apr. 6, 1937 UNITED STATES PATENT OFFICE METHOD OF AND MEANS FOR PRODUCING PRINTING PLATES 8 Claims.

This invention relates to a method and apparatus for producing printing plates to be used for surface printing and producing these printin plates as exact copies of either negatives or posi- 5 tives of pictures and particularly to a method and means for etching a plate in correspondence with variations of a light responsive element affected by variations of light passing through a negative or reflected from a positive.

The general object of the invention is to provide an improvement in the method and apparatuswhich is shown and described in my application for patent, Serial No. 696,096 filed on October 31, 1932, on Mechanisms for producing printing 15 plates by electric arc, in which application an electric arc is used, controlled by the light responsive element, the intensity of the arc varying with the tonal variations of the negative or other picture to be reproduced and the are forming pits 20 in the plate, the size of the pits depending upon the intensity of the arc, the completed plate being capable when printed of giving an extremely close imitation or simulation of a photo-engraved half-tone plate.

One of the particular objects of the present invention is to provide a means for controlling the action of the stylus, which means is capable of very fine and delicate modulations corresponding to the fine and delicate modulations of light passing through or reflected from a picture, this means providing, therefore, for very delicately modulating the intensity of the arc and thus the depth and the diameter of the pits formed by the arc in the surface of the metal, thus securing like 35 fine and delicate modulations or variations in the tonal values of the print made from the engraved plate.

The apparatus used includes 'a ram which is reciprocated to thereby reciprocate the picture in relation to a scanning light and correspondingly reciprocate the tool or stylus with relation to the plate to be engraved. In the mechanism which is illustrated in my application before referred to and which is illustrated in the present application, the ram is reciprocated by means of a crank or the equivalent thereof. The consequence is that the reciprocation of the ram is not uniform throughout the entire stroke but the movement of the ram is accelerated toward the ends of the stroke. The arc forming stylus is continually reciprocated into and out of contact with the face of the plate. As a consequence of this,

if the stroke of the ram is accelerated toward the end of the stroke, the spaces between the pits formed by the are are further apart than they are at the middle portion of the stroke and one of the objects of the present invention is to provide means for so controlling the reciprocations of the stylus toward and from the plate that notwithstanding the acceleration or deceleration of the ram in its stroke, the pits formed by successive arcs will be spaced from each other a uniform distance.

Other objects will appear in the course of the following description.

My invention is illustrated in the accompanying drawings, wherein:-

Figure 1 is a side elevation of an apparatus for producing a printing plate, the electrical connections being shown diagrammatically;

Figure 2 is a top plan view of a reciprocation controlling strip for the stylus;

Figure 3 is a fragmentary section on the line 3-3 of Figure 1;

Figure 4 is a diagrammatic elevation of another form of modulator;

Figure 5 is a diagrammatic view of another form of amplifying system applied to my apparatus;

Figure 6 is a side elevation of a clutch controlling structure used in connection with the apparatus shown in Figure 8;

Figure 7 is a fragmentary diagrammatic top plan view of the supporting frame for the plate or picture with a portion of the ram and its guide and showing the means for properly registering the plate at the beginning of the scanning operation;

Figure Bis a diagrammatic view of the scanning and printing plate producing means at two stations and the remote control therefor, the electrical connections being shown diagrammatically.

In the accompanying drawings, I have illustrated a mechanism which is in many respects the same mechanism as is illustrated in my application for patent filed on the 25th day of June, 1932, Serial No. 619,716 and which is also shown in my application Serial No. 696,096 previously referred to and which embodies generally a mechanism for reciprocating the negative and the tool. or arc forming pencil or stylus comprising a ram or longitudinally shift-able rod designated i0 sliding within guides ll carried by a supporting frame. Disposed either above or below the supporting frame and mounted thereon is a gear wheel 12 which is driven by an intermediate gear wheel l3 which, in turn, is driven by a driving pinion it connected to a motor designated M,

nuously operating while the enis being done. Preferably, this motor electric motor. The shaft iii upon. J is mounted carries upon grooved wheel it, the groove l 7 and pivotally mounted upon the p ition Zia of the frame is a swinging arm which is longitudinally slotted. Engaging in slot is the pivot which is connected to a block which is adiustably mounted within the ove so that it may be adjusted nearer to ,..irther from the center it to thus secure a. readily adjustable stroke for the arm lhe e end of the arm ii? is pivotally connected to a in turn pivotally connected to ears 2. niounted upon the rain. Thus as the wheel iii rotates, the ram will be given a reciprocating overnent to an extent dependent upon the adent of the bloclr 59 within the slot essary to give transverse traverse age, which carriage includes the the it and the parts sup mount the guides ,ansverse traclrs Eta and provide a I screw mounted in the ends of the screw engagin the frame to shift it. non one end of the traversingscrew screw shaft may be rotated hand he carriage to its initial position. ounter. upon the shaft is an oscillating ing tl double pawls and :39 coby means or? a linlr. enng a plug adjustably slo of a gear whe E3 1 driven As t.e wheel 35 rotates, the arm l he oscillated and will give a step by step sin' movement to the guide carriage traverse or" the carriage occurs upon ove ent of the rain iii to its initial tion a er a rull stroke in one direction.

The picture supporting means is shown as a table which has on it a rotatable plate 36 formed vfith an opening or recess within which a picture in y be disposed, the rotatable plate 36 being so arranged that the plate may be rotated through a quarter of a circle. Inasmuch as this o0 is an obvious construction and fully shown in my prior applications, there is no necessity for delling the particular construction of the negative ippor means. Furthermore, it is to be dis tinctly understood that while I have illustrated a E gative supporting means and a source of light acsing through the negative, a positive may be p: orted upon the table and light may be recte the face of this positive. liiiounted upon the ram it at the end of the ram Josite the support for the negative is an arc ring stylus This is mounted upon one i J. a of resilient support such as a leaf spring ich spring is operatively mounted upon point stereoplate or suitable material stylus is a permanent magnet ill with an arms. ture disposed between the poles thereof, this armature being pivoted at its center as lli. Around this armature is coil which may connected to a source of oscillatory culrent or may be connected to any other means whereby current may be intermittently broken through the coil id. The current through the coil, of course, sets up a reaction against the field set up by the permanent magnet. The armature is connected by a link 46 to the spring 39. With this construction, the stylus 38 is continually vibrated or oscillated into and out of contact with the metal plate ll. The stylus and the metal plate ii are connected in circuit with a source of heavy D. 0. current which in turn is modulated by light variations acting upon a lightsensitive element and through a radio-amplifying system to an inductive modulator.

[is illustrated in Figure l, the light-sensitive element is preferably a caesium cell, though I do not wish to be limited to this as any of the various ligl'lt-sensitive cells such a sodium cell. or a potassium cell may be used. 'vlhile these are types of cells which have to be excited, yet it will be understood that a photo-tron may also to used as the light-affected element.

The light-affected cell is designated generally it. This is supported on the frame of the machine above the picture or negative to be copied by engraving and below this negative (if the picture used is a negative) is disposed a tungsten filament volt lamp which acts as an excite]? lamp and which is designated 16, this being connected to a transformer in turn connected to a source of 110 volt alternating current. The light passing through the lamp ill passes through a lens thence through a negative and thence to the light-sensitive element ll. The light from this lamp is focused to a fine point on the negative by means of the lens il and then strikes the sensitized su ace in the photo-electric cell ll. Thus as the picture carrier or plate reciprocates, the light spot traverses the negative and a beam of light enters the cell, the intensity of this beam at any given instant being proportional to the density of the negative at the portion through which the light is passing or if a positive is being used and light thrown down upon this positive and reflected by this positive up into the photoelectric cell, then the light which enters this cell is proportional to the tonal value of the picture at the point from which the light is being reflected. This constantly varying light changes the electrical conductivity of the cell and this impresses a varying voltage on the screen grid tube in]. This positive voltage bucks out to a greater or less amount the normal negative voltage which is applied to the grid by the amplifier system. This tube fill is disposed in an audio frequency amplifying system which requires no particular description but which includes the two tubes 5i and 52 disposed in parallel and a resistor The tubes 5i and used in this system are pentodes. Because of the changes in bias voltage, corresponding variations talze place in the plate or out-put current of the tube Elli and the resis tor tlrese changes being accompanied by simi lar changes in the voltage drop across the resistor It will be seen that the resistor is common to the plate circuit of the tube 58 and to the grid circuits of the tubes and which, as before stated, are in parallel and thus a varying voltage IliBSSEd on the grids of tubes iii and which Ill) in turn variably influence the plate current of these out-put tubes. Thus it will be'seen that the current in the out-put circuit varies in accordance with the amount of light passing through the negative (or from a positive) and into the photo-electric cell. Furthermore, it is to be particularly noted that this out-put current does not depend on a pulsating or alternating input current but that for any given amount of light entering the cell 41, the output current will assume a definite and steady value which may be maintained for any length of time. This output current from the amplifying system in turn iniluences a modulator which I have designated generally 54 which in turn causes the variations in the intensity of the are which etches or burns out the metal plate H in an exact reproduction of the scanned negative or positive.

It will also be appreciated that by varying the resistor 55 which is provided with a variable resistance, the normal or static bias on the tube 50 may be varied bringing about a change in the static level of the out-put circuit from the tubes 5| and 52, this out-put circuit including the wires 56 and 51.

The modulator 54 includes a soft iron core 58 having a central leg and two lateral legs and constituting a transformer, the primary of which is designated 59. This coil 59 is connected at one terminal to a source of heavy D. C. current while the other terminal of the coil 59 is connected by a conductor Bil to the plate 4|. There is, therefore, a constant current of uniform value flowing through the circuit which includes the source of current, the stylus 38, plate 4| and the coil 59. Surrounding the lateral legs are the secondary coils 8|, these coils being in aiding relation and electrically connected to each other. One end of one coil is electrically connected to the terminal 56 of the amplifying system and the other coil is connected to the terminal 51 of such system. This modulator depends for its operation upon the fact that an iron chokemay have its inductance varied by a change inthe magnetic condition of the core upon which it is wound and the coils are so arranged that the device also acts as a transformer. At the instant the stylus 38 breaks contact with the metal plate 4!, a voltage will be induced in the winding 59. As the coils Bl are connected to the output of the amplifying system, they will induce voltage within the modulator which will increase the plate current of the tubes 5| and 52 bringing about an increase in current through the stylus or etching point 38. This increase will be in addition to that caused by the change in inductance in the heavy current wlnding. Thus a certain amount of current will pass from the source of D. C. current through the coil 59 to the plate, stylus and the spring 39 but the variations in light falling upon the light-sensitive element 41 will, through the amplifying means, cause additional current to pass through the plate and etching point as the stylus is lifted, thus varying the are formed upon a lifting of the stylus in complete correspondence with the variations in the light falling upon the light-sensitive element. It is to be understood, of course, that the stylus is reciprocating toward and from the plate a predetermined number of times per minute and that the plate is moving forward at a predetermined speed. As the point is lifted from the plate, an arc is formed, the metal of the plate is oxidized and passes upward from the plate toward the point as it moves away,-thus carrying the metal of the plate upward and outward and forming a pit in the plate. The stylus 38 again drops upon the plate at a point spaced from the pit last formed, an arc is again formed as the point moves away from the plate and a pit is again formed. The depth and diameter of the pit so formed depends entirely upon the voltage of the current passing from the plate to the point and this in turn depends entirely upon the intensity of the light received on the cell 41. If the pits are sufficiently close together and are sufliciently wide, the entire surface of the metal will be cut away or etched away so that it will not receive any ink at all. If on the other hand, some light or very strong light passes through to the photoelectric cell, as where the negative is very thin, no pits or very slight pits will be formed and ink will be fully retained or almost fully retained upon the surface of the plate. The result is a plate which is varyingly pitted over its entire surface with pits varying in depth and diameter and verging from pits so shallow as to have little or no effect to deep and wide pits and a print taken from this plate has an extremely close similitude to a half -tone print.

It will be seen from the drawings that while the disk l6 acts to reciprocate the ram 10, it reciprocates this ram at an unequal speed. The ram moves slowly forward while the crank pin is moving downward, then moves rapidly forward while the crank pin is moving in the same direction as the ram, and then again slows downward as the crank pin moves upward, the reverse stroke of the ram being very rapid. The consequence of this is that if the stylus 38 is reciprocated toward and from the plate 41 by oscillatory cur" rent or by an ordinary interrupter or any like means, where the plate is moving rapidly, the space between the pits on plate will be greater than where the plate is moving slowly so that the pits would be closer together at the middle of the plate than at the ends of the plate or if the ram starts to move forward with the arm ill in the position shown in Figure 1, then the pits would be closer together at one end of the plate and middle and further apart at the other end of the plate. To compensate for this, I have illustrated the ram as being provided with a longitudinally extending support designated 62, which supports a more or less transparent strip 63 which is ruled with lines 64 extending transversely to the strip or the strip might be provided with pin holes and the strip made opaque. These lines or pin holes are uniformly spaced throughout the entire length of the strip. These lines or the spaces between the pin holes, if pin holes are used, act to intermittently interrupt the passage of light through the strip from a lamp 63 condensed by a lens 66 upon the strip 63, this beam of light being directed in a very fine pencil to a photo-cell 61. From this cell, conductors lead toany amplifying system, not shown in detail, but designated generally as 68 and from thence to the coil 45.

It will thus be seen that as the ram speeds up toward the end of its stroke, that the oscillations the armature &3 become more rapid pondence with the increased speed of increased speed and causing the pits to be evenly spaced over the entire face of the plate. Of

course, these strips 63 are interchangeable so that the interrupter strips may be used having their .lines or pin hoies nearer to or further apart depending upon the fineness or coarseness of the work to he done corresponding, of course, to the or and. stylus, thus compensating for this fineness or coarseness of screens through which photo-engravings are produced.

In Figure 4, I have shown another form of modulator 5411 which may be used. This modulator depends on the fact that an iron core choke may have its inductance varied as before stated. The core has three legs and is similar to that of a shell type transformer. On the middle leg is placed the low current winding 6|a which is fed from the output of the tubes 5| and 52. On the lateral legs are placed the heavy current windings 51a and so connected that they have no magnetic effect on the central leg. One terminal of the winding 57a is connected to a source of heavy D. C. current, the other terminal being connected to the metal plate 4|. By this arrangement a varying current in the central winding will produce a varying magnetic density in the two outer core legs. Hence, there will be a change in the inductance of these two outer windings. Since these outer windings are disposed in series with each other, with the stylus 38 and with the plate 4| and D. C. voltage source, any change in their inductance will cause a variation i in the current through this series at the instant when the stylus breaks connection with the plate and moves away from it. This varying current in turn causes a variation in the intensity of the arc and, therefore, in the amount of metal oxidized by the stylus.

In Figure 5, I have illustrated a modification or alternative system of radio amplification. The scanning and amplification is identical with the system shown in Figure 1 up to the grid or output terminals of the tubes 5i and 52. In Figure 1, these tubes, as heretofore stated, are pentodes while the tubes Ski and 52a in Figure 5 are tried tubes and are not supplied with plate voltage from a power pack as is shown in the system disclosed in Figure 1.

In the method shown in Figure 5, a modulator 5c is used of the same character as heretofore stated but advantage is taken merely of its transformer action. The amount of light reaching the 7 photo-electric cell determines the grid bias voltage on tubes bid and 52a. These tubes have no plate voltage supplied to them other than the induced voltage from the secondary coils of the modulator 54. This voltage is present due to the fact that the stylus 38 is being constantly vibrated and constantly breaks and makes the circuit from the D. C. source through this modulator. Since the amount of plate current which these tubes can draw depends on the bias voltage, the amount of current delivered by the secondary of the out-put device and consequently the amount drawn by the primary will depend on the bias voltage also and since the arc current depends on the current drawn through the primary and through the vibrating stylus 38, it will be obvious that the etching effect of the arc will be in accordance with the output-tube platecurrent and, therefore, proportional to the current passing through the photo-electric cell or affecting this cell.

The advantage of the systems of amplification which I have described over amplification by any other system known to me is that when the light energy of the exciter lamp is transformed into electrical energy by the photo-cell, the electrical current starts to flow in a smooth line. Any changes in the density of the negative (or the tonal value of the positive) set up varying current in the system and tend to cause the ampliher to pass and build up this current in the ampliher in direct proportion to the amount of light that gets to the cell. There is a smooth and constant flow, there is no lag or intermittent building up of current and the output is in direct proportion to the light energy input. In these systems, one advantage is that the smallest amount of energy is passed as well as the largest amount of energy and low frequencies are not lost in the resulting reproduction.

The specific action that takes place in the actual etching, as it may be called, of the surface of the plate, that is, the pitting of the surface of the plate, is a physiochemical reaction. As the stylus leaves the surface of the plate, an arc is formed, the intensity of which depends on the value of the light or shade in the'subiect. The are flows from the plate 4| to the stylus. The molecular construction of this area is affected and an ionization of the molecules takes place and they flow to the stylus. The metal of the plate 4! at this point is thus oxidized and deposits on the stylus in the form of an oxide which is dissipated by the heat of the stylus. It is thus seen that metal is bitten out in the same sense that it is bitten out by acid in the process of etching and that just as the uncovered metal of an etching plate becomes chemically combined with the etching acid and is carried away from the plate itself, so the metal on the surface of the plate 4| is oxidized and carried away.

In my prior application I referred to this as an engraving process. It will be seen that, as a matter of fact, it is really an etching process because in engraving, a tool cuts out more or less cleanly the metal of a line and this thread so cut out must be cleared away. If the engraving tool does not cut out this thread but in rorming a groove merely crowds the metal laterally or forms a burr on each side of the line, the plate will not print properly. There is no difficulty of this sort in the apparatus described in my pending application wherein an electric arc is used or in the present application because the metal of the pit is carried away by the arc and entirely dissipated.

It will be obvious that not only may my mechanism be used for forming a printing plate at one end of the ram |0 while the other end of the ram is scanning a negative over a light, but that the mechanism may be also used to control a second engraving machine at a distance from the controlling machine. Such an arrangement is illustrated in Figure 8 where two engraving machines are illustrated diagrammatically each of exactly the same construction as the engraving machine shown in Figure l and each capable of forming a printing plate from a negative carried by the ram on the individual machine. Inasmuch as the sameparts are used that have been heretofore described, the same reference numerals have been applied to Figure 8 as in Figure 1. The output wires from the amplifying system, which in Figure 8 is supposed to be within the case C, connect in this instance to a doublethrow switch 69 whereby these out-put wires may be connected to the wires leading to the plate and the stylus 38 as heretofore described. The switch is capable, however, of being thrown to line wires 70 and H which lead to the amplifying system of the second machine. This in Figure 8 is diagrammatically illustrated as being within a casing C, the output wires of which, as previously described lead to the plate 4| and to the stylus. When the switch 65 is thrown to connect the wires 79 and 1|, variations in the amount Figure 6 bearing against the face of of light beam thrown upon the photo-electric cell will be transmitted through the amplifying systems to the plate and stylus of the second machine, the photo-electric cell of the second machine being thrown out of circuit by means of the switch 12.

In order that both rams may be operated at the same time, however, that is, synchronously, means must be provided whereby each ram may be operatively connected to its corresponding motor at the same instance. The shaft I5 is formed in two sections He and I5!) as shown in detail in Figure 6, each of these sections carrying upon it a clutch member, the clutch member 13 being fast upon the section l5b while the clutch member 14 is shiftable into or out of engagement with the clutch member 13 and is normally held in yielding engagement therewith by the spring IS. The clutch member 14 is provided with an annular collar or shoulder 16 which is beveled upon one face or rounded. Coacting with this ring 16 is a latch I1 pivoted at 18, one end of this latch being adapted to bear against the rounded corner of the ring 16, the other end of this latch being formed with an armature 19 coacting with an electro-magnet 80. The latch 11 is urged in a direction away from the electromagnet by means of a spring 8|. When the magnet 80 is de-energized, the spring urges the outer end of the latch into the position shown in the ring 16 and holding the clutch member 14 out of engagement with clutch member 13. When the magnet 80 is energized, however, the latch moves to the dotted lined position in Figure 6 and releases the clutch member 14 which immediately clutches the motor to the shaft section I5?) and to the operating mechanism for the ram. These electro-magnets 80 on the two machines are disposed in series with each other in a circuit including the amplifier of the controlling machine or any other source of D. C. current and passage through this circuit is controlled by the switch 82. Initially a signal is sent from the sending office to the receiving office which may be of any suitable character indicating that the sending office is about to send a. picture to the receiving office.

Any suitable signaling mechanism may be used for this purpose.

The two otlices adjust the rams of the two machines at a starting point which may be indicated by the registering marks 82 on the ram and on the guide therefor. At the same time, the guide or carriage wil be shifted over to its starting position indicated by a point 83, both machines thus being placed in readiness to transmit and receive impulses, the motors are started up both at a certain agreed upon speed and after a predetermined period suflicient for both motors to have reached the agreed upon speed and to warm up the lamps and tubes of the amplifying systems, the switch 69, of course, having been previously closed, the sender closes switch 82 which immediately releases the clutches of both ma chines and immediately that this is done, the picture in the sending machine is scanned by being reciprocated between the lamp and the photoelectric cell of that machine and the stylus of the receiving machine traverses the plate 40 in the manner heretofore described and the plate 40 on the receiving machine will be bitten or pitted as heretofore described to form a duplicate of the picture being sent from the sending machine.

Preferably, whether the picture being repro the plate 40 of one duced is being reproduced on machine or on the plate ll! of a distant machine, the picture and the plate will be turned to an angle of 45, that is, 45 with the top margin or side margin of the picture so that the stylus will traverse diagonally across the face of the picture. By traversing the stylus in this manner, there is no necessity of traversing the stylus in one direction across the face of the picture and then, in the other direction as was necessary with the cutting or engraving tool shown in my application for patent, Serial No. 619,716 where it was necessary to cut lines in one direction and then cut lines at an angle to the first named linesin order to form dots.

It will be understood that within the construction shown in Figure 8, the amplifier C amplifies the product of the lamp 4'! while the amplifier C where the two machines at distant stations are used together, acts to compensate for any line loss or lag in the line.

It is to be understood that as designed, the stylus operates to form pits in the face of the plate 4| when the ram is moving in one direction and that it is traversed as the ram moves in the other direction. Upon a reverse movement of the ram and of the stylus, the current to the stylus is automatically cut off so that no arcs are formed upon the reverse movement of the stylus. Any switch mechanism may be used for this purpose, but I have illustrated in Figure l a commutator 84 meshing with the gear wheel 34, though it may be driven from any suitable portion of the apparatus, this commutator 84 having thereon the commutator segment 85 of insulating material. One of the wires 60 which carries current to the spring 39 and the chuck 40 extends from the source of direct curent to a commutator brush 86, the other brush 8'! being electrically connected to the spring 39. The commutator is so arranged that upon the rearward stroke of the ram, no current passes to the stylus 38 and the plate 4| but just as the ram is about to move forward, that is, in the direction of the arrow in Figure 1, circuit through the source of direct current is completed through the stylus and plate 4 I. It is while the ram is moving rearward, that is in the reverse direction to that of the arrow in Figure 1, that the lateral traverse is performed.

It is to be understood that in order to get a uniform pitting of the plate and to secure the same traverse separation for the pits as the longitudinal separation, the amount of traverse is equal to the distance between the longitudinal series of pits. The traverse separation and the longitudinal separation must be the same in order to produce a proper geometrical design and half-tone dot formation.

While I have heretofore referred in this specification to the use of this machine for the purpose of producing half-tones and while it is capable particularly of producing similitudes of half tones, yet it is to be understood that the machine is equally capable of producing similitudes of line drawings, that is, producing a plate which is capable of printing the similitude of a line drawing. In this case, the current can be readily varied to produce a deeper etch than ordinarily necessary for the production of half tones and in this case, the potential from the amplifier completely bucks out the potential of the stylus circuit so that those parts of the plate which are intended to print solid black would not be pitted in any way as at these portions of the plate, the

current in the stylus would be completely bucked out. i

It will be seen that by this machine and the process described, printing plates are made which have the same qualities as plates made by the ordinary photo-engraving processes. These plates are made, however, much more quickly and are made directly from either a photograph or a negative Without the use of screens. As a matter of practice, a picture of ordinary size such as commonly used in newspapers may be transl lated to an etched plate in about three minutes.

It is also to be understood that these plates are not intaglio plates but are surface printing plates.

With this machine and method, there is no engraving tool properly so called which has to plow through the metal of the plate but there is a true etching process in that the metal is eaten away by a physio-chemical action, the tool which performs the work of biting the metal away is not subjected to strains such as is the case where the tool engraves and plows through the metal, there is no resistance offered to the free movement of the tool or stylus and consequently the power applied to move the ram may be relatively light. There is no tendency with this mechanism and method to form a burr upon the face of the plate, nor to crowd the metal laterally on each side of the line, and a similitude of a half-tone plate is formed without the necessity of traversing the plate first at one angle and then at another as the tool moves diagonally across the plate with reference to its corners.

The half-tone effect produced is much finer than can be produced by an engraving tool cutting a series of lines in one direction and then cutting a series of lines at an angle to the first named series of lines to form a series of diamond-shaped minute printing surfaces.

While I have used in this specification the word engraving as applied to the work done by the .stylus 38 and by my mechanism, yet it is reiterated that this is not an engraving machine properly so called and the plate is not engraved,

- but that the work performed by the stylus is a biting or etching away of the face of the plate and not a cutting or engraving cf the plate.

It is to be understood that the word stylus as used in this specification and throughout the claims is designed to include any electrically conductive element which may be carried upon the spring Eli and confront the plate 4i and which will, when it is lifted from the plate, cause an arc to be formed between the plate and the ele merit.

I claimz- 1. In a mechanism for producing printing plates, a suitable subject, means for scanning the subject, a photo-electric cell of the exoiter type,

a stylus, means for traversing the stylus across the face of the printing plate, means for rapidly reciprocating the stylus to and from the face of the plate at uniform spaced intervals, an amplifying system amplifying the voltage produced by the photo-cell and including a screen grid tube having a grid connected to the photo-cell and having its screen connected to a power pack, and means for impressing the positive and varying voltage of the photo-cell on the control grid thereof, a pair of screen grid tubes disposed in parallel and having their grid circuits connected to the plate circuit of the first named tube, a resistor common to the plate circuit of the first named tube and the grid circuits of the second named tubes, a circuit including the plate and stylus and connected to 8.

source of direct current having a constant mam imum value during each period of contact of the stylus and plate,'"a modulator having a core formed with a central leg and a coil surrounding the central leg and connected to the plate, stylus and said source of direct current, the core having lateral legs, and coils surrounding the lateral legs and coupled in aiding relation, and means for supplying voltage to the last named pair of tubes by said coils.

2. In a mechanism for producing printing plates, a suitable subject, means for scanning the subject including a longitudinally reciprocatable ram, crank means for reciprocating said ram, the linear speeds of the ram varying at difierent portions of the stroke, and including a crank pin operatively connected to the ram, a stylus, means for constantly reciprocating the stylus to and from the printing plate, a light affected element, means for varying the light discharged upon said element in accordance with variations in the light and shade of the subject, means for connecting the stylus and plate in circuit with a source of current, means controlled by the light affected element for modulating this current to thus vary the arcs formed between the stylus and the plate, the means for reciprocating the stylus including a photo-electric cell, a light source therefor, and means for co-ordinating the reciprocations of the stylus in accordance with the varying speeds of the ram comprising a strip of material carried by the ram and interposed between the source of light and the last named cell and having alternate opaque and transparent places thereon by which the light may be intermittently cut off or allowed to pass.

3. In a mechanism for producing printing plates, a suitable subject, a stylus, means for intermittently reciprocating the stylus to and from the printing plate, means for passing current through the stylus, means for scanning the subject including a light affected element through which light is passed to the cell, and means for modulating the current passing through the stylus and plate by variations in the output of said cell, the scanning means including a reciprocating ram, a crank operatively connected to the ram to reciprocate it, and means for varying the reciproc-ations of the stylus to correspond with the acceleration or deceleration of said ram.

4-. A method of forming a metal printing plate which includes traversing a stylus across the face of the metal plate while intermittently lifting the stylus from the face of the plate and simultaneously passing current thru a circuit including a source of current having a. definite voltage, the plate and stylus, efiecting the modulation of the voltage in a circuit having an independent source by and in accordance with the light and shade of a pattern, and employing the modulations in the last circuit for producing corresponding modulations in the circuit which ineludes the plate and the stylus.

5. In a mechanism for producing metallic printing plates, 2. suitable subject, means for scanning the subject, a photo-electric cell, an amplifying system modulated by the light and shade of the subject impressed on the cell and having an out-put circuit, a stylus, means for traversing the stylus relative to the plate, means for constantly reciprocating the stylus to and from the plate to be produced, means connecting the stylus and plate in circuit with source of current having a constant maximum value during each period of contact of the stylus and plate to form a series of arcs between the plate and stylus, a transformer having a central core and parallel flanking cores, an induction coil en circling the central core and connected in the circuit with the stylus and plate, and a pair of induction coils connected in series in said output circuit and each encircling a flanking core and each being in aiding relation with the other.

6. In a mechanism for producing metallic in printing plates, a suitable subject, means for scanning the subject, a photo-electric cell of the exciter type, a stylus, means for rapidly reciprocating the stylus to and from the face of the printing plate, a circuit connected to a source of current having a uniform intial voltage and including the stylus and the plate, said circuit current having a constant maximum value during each period of contact of the stylus and plate, means for amplifying the current produced by the photo-cell, and producing a non-pulsating current in the out-put circuit of the amplifying means varying with the in-put of the photo-cell, a transformer having a central core and parallel flanking cores, an induction coil encircling the central core and connected in the circuit with the stylus and plate, and a pair of induction coils connected in series in said output circuit and each encircling a flanking core and each being in aiding relation with the other.

'7. In a -mechanism printing plates, a suitable subject, means for scanning the subject, a photo-electric cell of the exciter type, a stylus, means for rapidly reciprocating the stylus to and from the face of the 35 printing plate, a circuit including a source of current having a uniform initial voltage and including the stylus and plate, said circuit current having a constant maximum value during each period of contact of the stylus and plate, an 40 audio-amplifying system having an out-put circuit, the amplifying system producing a non-pulfor producing metallic I sating current in said out-put circuit varying with the in-put of the photo-cell, and means for inductively coupling the out-put circuit of the amplifier to the stylus and plate circuit, said means including a modulator having a core, a winding on the core connected with the source of current having a definite and uniform voltage and a winding of the core connected in the out-put circuit of the amplifying system.

8. In a mechanism for producing metallic printing plates, a suitable subject, means for scanning the subject, a photo-electric cell of the exciter type and receiving light from the subject, a stylus, means for traversing the stylus over the face of the plate, means for rapidly reciprocating the stylus to and from the face of the plate at uniform spaced intervals, an amplifying system including a screen grid tube having its screen connected to a power pack and having means for impressing the positive and varying voltage of the photo=cell on the control grid of the tube, a pair of screen grid tubes disposed in parallel and having their grid circuits connected to the plate circuit of the first-named tube, a. resistor common to the plate circuit of the first-named tube, a resistor common to the plate circuit of the first-named tube and the grid circuits of the second-named tubes, an out-put circuit including the second-named tubes, a second circuit including the plate and the stylus and connected to ascurce of direct current having a constant maximum-value during each period of contact of the stylus and plate, and means for inductively coupling the plate and stylus circuit with the out-put circuit of the amplifying system, whereby the current flow through the plate and stylus circuit-is modulated during the period of arcing between'the stylus and plate when the stylus is lifted, by the modulated and amplified picture currents.

JOSEPH A. BENNETT.

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