US2079310A - Mechanism for producing printing plates by electric arcs - Google Patents

Description

May 4, 1937. J. A. BENNETT I MECHANISM FOR PRODUCING PRINTING PLATES BY ELECTRIC ARCS Filed 00-1. s1, 1953 2 Sheets-Sheet l M y 1937- J. A. BENNETT 2,079,310

MECHANISM FOR PRODUCING PRINTING PLATES BY ELECTRIC ARCS 7 Filed Oct. 31, 1933 2 Sheets-Sheet 2 Patented May 1937 UNITED STATES PATENT OFFICE MECHANISM ron rnonncmo PRINTING PLATES BY ELECTRIC mos Joseph A. Bennett, Bloomington, Ind., assignor game-half to Joseph W. Pieroy, Bloomington,

Application October 31, 1933, Serial No. 696,096

24 Claims. 178-5) This invention relates'to a method and appa-- ducing pencil being .of the general character ratus for producing printing plates and producshown in my prior application for patent on ing these printing plates as exact copies of either Machines for reproducing printing plates for picnegatives or positives and particularly to means tures, filed June 23, 1932, Serial No. 619,716.

for producing a plate in correspondence with A further object is to provide a mechanism of 5 variations of alight responsive element such as this general character which is capable of rea phototron afiected by radio waves induced producing line cuts and another mechanism from a distance or affected by variations oi light having the same general characteristics but in passing through a negative or reflected from a detail somewhat different from the first named positive. mechanism for the purpose of reproducing half- 10 This invention depends upon the action of an tones.

electric are or rather a plurality of rapidly suc- Other objects will appear in the course of the cessive arcs formed between the plate and a tool following description. which cause the molecular construction of the My invention is illustrated in the accompanyi5 immediate area at which the arc is formed on ing drawings, wherein:- 1'5 the plate to be afiected and cause an ionization Figure 1 is a side elevation 01' my printing of the molcules of the metal of the plate which plate producing mechanism, the amplifier system flow to the stylus or tool, the metal of the plate being shown diagrammatically; becoming oxidized and deposited on the stylus Figure 2 is an enlarged elevation of the tool in the form of an oxide which is dissipated by carrying head, the metallic plate and the support the heat 01' the stylus. The metal is thus bitten therefor being shown in section;

out in the same sense that it is bitten out by Figure 3 is a fragmentary top plan view of the acid in the process of etching and that just as negative support carried upon the ram; the uncovered metal of an etching plate becomes Figure 4.1 a, diagrammatic l ti h w chemically combined with the etching acid and another form of tool head particularly adapted is carried away from the etching plate, itself, for hair tone work. so the metal on the plate H is oxidized and In the accompanying drawings, I hav m carried away at successive points by the succestrated generally a mechanism for reciprocating sive arcs. the negative and the arc-forming pencil or The general object of the present lnventifln S stylus which is illustrated in detail in my before 30 to provide a printing p ate p odu machine of mentioned application and which includes a lonthe character stated which will reproduce upon a itudinally movable bar or ram designated l0 Pr Plate masses of P bl ck, masses 0! operating within guides H carried by a supportpure white and intermediate tones grading by i frame, Disposed above the supporting 3;, fi d s into the P black into p frame and carried thereby is a gear wheel I2 white a p e for this. P p an electric arc which through an intermediate gear wheel I! is actin up n the pla and nt d y t driven by a driving pinion it connected to a mol1s sp n element PhOtOtrOn, the tor or any other source of power, this motor tensity of the arc varying with the light variacontinually ()peraung while t engraving is 40 tions of the negative or picture to be reproduced ing d ne, The shaft l5 upon'which the gear and the are thu f rmin P in the Pl te, the wheel I2 is mounted carries upon it the diametsize of the p s depending p the intensity 0! rically grooved wheel Hi, the groove of which is the a cdesignated l1 and mounted upon the portion A fur bj is to provide a mechanism Ha oi the frame is a swinging arm l8 which is of this cha act in which the Picture to be pivoted intermediate its ends to a block 19 ad- 45 produced is. scanned between a source of light justably t d within the groove IT. The deand a phot'otron or other light-sensitive element pending free d of this arm is connected by a by a rectilinear movement of the negative in one link 20 t upwardly extending ears 2| mounted direction and a step by step traversing moveupon the ram. The arm I8 is longitudinally 50, me o the negative in the other direction, the slotted and the bolt 2| which connects the arm sty us o other element Producing the are being to the block i9 slides in this longitudinally excorrespondingly traversed longitudinally and lattending slot. It will thus be seen that as the erally across the plate to be engraved, the mechwheel l6 rotates, the arm Will be given an oscilanism for producing the longitudinal and translatory movement and the ram will be reciproverse traverse of the negative and the are procated to an extent depending upon the ad ust- 55 ment of the block l9 nearer to orfurther from the shaft I5.

'For' the purpose of-giving a transverse traverse to the carriage, which includes the guides I I and the ram 10 and the parts supported thereon, I provide a traversing screw 23 which is mounted in the ends of the frame and at one end carries upon it the two reversely notchedratchet Wheels.

24 and 25. The shaft also carries upon it the 10 handle 26 whereby the screw shaft may be rotated by hand to retract the carriage to its initial position. 7

Mounted upon the ratchet end of the shaft 23 is an oscillating arm 21 carrying the double pawls 23 and 23, these pawls coacting respecmovement may be, communicated tothe feed screw 36 so that the step 'by step traversing movement of the'arc forming stylus across the I face of the plate will be'very slight or relatively coarse. A single traverse step is made upon the return movement of the ram 10 to its initial position. Thus the are forming stylus moves in one direction along the plate the full length of 30 the stroke for which it is adjusted and is then retracted and or as when it is retracted, it is given a lateral movement of one step and then again moves longitudinally across the face of. the plate.

The negative supporting means may be of any suitable character and is carried by the ram but is shown as a table 35 having thereon a rotatable plate 36 formed with an opening or recess within which the negative 31 may be disposed, this plate being so arranged that the plate may be rotated through a quarter of a circle. Suitable masking means may be provided for this as disclosed in my prior application.

Mounted upon the ram I!) at the end of the ram opposite the support for the negative is a tool controlling head and disposed below'the tool controlling head is a frame or clamp designated generally 33 for supporting the metal plate .to be etched designated 39. This metal plateis entirely insulated from the supporting frame. The metal plate is held rigid from either longitudinal or transverse movement bythe supporting frame and the tool controlling head which is mounted upon the ram I3 reciprocates back and forth over 55 the metal plate to bc etched and-is given a lateral traverse over this metal plate. The tool controlling head in the form 'of my invention illustrated in Figure 2 includes a field magnet having a core ll] of soft iron surrounded by a 50 coil or winding ll. The core 30 extends upward at its center at l-2 and disposed above this end of the field magnet is an armature designated 5 3 which extends down around the central hub -3-2 of the core and includes windings 34.

55 The coil 35 is connected by wires 35 and 55 to a source of field coil. current, as will be later explainect while the core of the float armature 33 is connected wires 5? and 88 to a radio amplifier will be later stated.

' bore and extending downward through supported by a leaf spring 56 carried by a iii projecting from the casing 52 which onc'ioses the field magnet '38 of the armature t3. Supported upon the lower end of {his rod 39 is a The core 53 has a supporting member 53 which at one end is carried upon a leaf spring 54 in turn mounted upon a bracket 55 attached to the casing 52. I member 53 carries at its outer end an electromagnet or solenoid coil 56 having a core 51. Also mountedupon the member 53 and extending longitudinally beneath the coil 56 is a leaf spring5la and carried upon this leaf spring is an upwardly and fo'rwardly extending armature 58 facing the inclined end face of the core .51 and This coacting therewith. This armature carries upon it a clamp59 upon which a metallic arc forming stylus B0 is mounted, this stylus normally engaging against the face of the plate 39.

When the' coil 56 is energized, however, the armature will be raised from the face of the plate carrying with it the stylus 60. An arc is formed between the end'of the stylus 6B and the face of the plate when this occurs. I

The metallic plate 39 to be etched is connected by a wire 6| to a source of direct current. The coil 55 is also connected by a wire. 62 to the source of direct current but through a carbon pile rheostat designated generally 63. This rheostat as usual includes aseries of carbon disks disposed within an outer casing and from the rheostat 63 extends a wire 64 to the source of current, as before stated. When the disks are loosely engaged 'with eachother, the resistance, of this rheostat is increased and when the disks are forced gages the lower disk of the'series in the rheostat.

the inner end of this lever being provided with teeth 61. Attached to the member 53 is a rack 68 having teeth engaging the teeth 61. Thus as the member 53 is raised, the resistance of the rheostat will be increased and as the member 53 is lowered, the resistance of the rheostat will be reduced.

Disposed beneath the negative 31 is a lamp 69 whose rays are focused upon the negative or upon the negative plane and disposed above the negative 31 is a phototron 10 which is electrically' connected through amplifying means to the floating armature 43. Thus variations of light caused by different densities in the negative will cause the photo-electric cell or other light-sensitive element 10 to vary the electric current passing through the coils of the floating armature 43.

Impulses controlled by the scanning device, that is, by the phototron are transmitted and amplified in the radio amplifier shown diagrammatically in Figure 1 and are used to energize this floating armature. The poles of the fixed field magnet 40 and the floating armature have the same polarity and thus any increase in the energy passing through the negative will cause the armature to be repelled by the field coils and this causes the member 53 to rise and lift the stylus 53 from the surface of theplate 39 and at the same time causes the disks of the carbon pile rheostat to be separated which increases the resistance in the electrical circuit which includes the rheostat, the magnet 55, the stylus 60, the plate 39 and the wire 6|. The moment that the current passes into the coil 56, the armature 58 will be attracted to the core 51, lifting the stylus from the face of the metal plate 39 so that the circuit is broken. As it is broken, an arc is made between the stylus 60 and the plate 39 and the difference in the resistance due to the difference in the height that themember 53 is raised, do-

. termines the size of the pit that the arc burns in the plate 39. This arcing is only momentary and as soon as the circuit is broken, the armature 58 is released from the core 51 and the stylus drops and makesanother contact with the plate. As soon asthis occurs, the circuit is again completed, the armature and -the stylus are again raised and again an arc is formed. Thus a series of however.

recesses. or pits will be burned in the face of the plate, the size of these pits depending upon the intensity of the arc.

Whena dark portion of the negative is being scanned, a relative weak current flows through the field coils 4 I, so that the armature 53 and the stylus are drawn upward but a short distance. This increases only slightly the resistance of the rheostat 63 and current passes through the local circuit 64, 63, 62, 56, 51a to the stylus, across the gap of the arc to the plate 39 and back by wire 60, 5!, this circuit being immediately broken,

The passage of relatively slight current through the field coils 44 causes a relatively slight lifting of the stylus and this causes a short but intense arc to be formed which burns a deep and wide crater in the face of the pit, or a series of these craters, which, if the craters overlap, causes this portion of the face of the plate to be entirely burned out, as if routed out and provides a white printing surface. When alight portion of the negative is being scanned, a relatively strong current flows through the field magnet 44 causing a greater lifting of the armature 53, a greater increase in the resistance of rheostat 83 and less current flows through the local circuit of the stylus so that only a relatively small diametered pit or series of pits are formed by a longer arc of less intensity. This provides a nearly black printing surface and if the negative is so thin that the stylus is entirely lifted and held lifted, the printing surface will be unpitted and will provide an absolutely black printing surface.

If the entirely transparent portion or white portion of a negative permits the passage of considerable current to the floating armature. the

armature will be held raised, the stylus will be supported entirely above the face of the plate 39 and this portion of the plate will, therefore, print a solid black. It will thus be seen that my structure provides for engraving the plate so that the plate will reproduce either solid white or solid black or intermediate tones in between the solid white and solid black.

It will be seen that when the stylus leaves the plate, an arc is made the intensity of which is determined by the tone value of the negative. Where the negative is darker, the arc is intense and burns out more of the surface. In the lighter places, a contact is still made but a smaller arc occurs and a smaller pit is burned in the plate. This is due to the action of the floating armature operating the carbon pile rheostat which takes its current from a battery or other power source.

After a line of pits is burned in the plate on one longitudinal stroke of the ram, the traverse feed moves the negative and also moves the tool head with stylus 50 one step laterally and another line of pits is burned and so on until the plate is completed. The mechanism which I have above described is particularly applicable in line cuts, that is, cuts in which pure black and pure white are used but is not adapted to the reproduction of half tones.

In Figure 4, I illustrate a modification of the mechanism previously described which is intended for the reproduction of half-tones or, in other words, photographs. The ram ill in this instance carries upon it a coil H constituting a solenoid and extending through this is a core 12 constituting a stylus or etching element, the lower end of which is pointed. A spring 13 urges this stylus upward. When the coil H is energized, the stylus is forced downward. The coil II is intermittently energized through a circuit, the wires of which are designated generally 14 and which includes within it an interrupter 15 of any suitable character which mechanically interrupts the passage of current to the coil. The circuit which includes the interrupter and the coil is connected to a source of direct current. It will be seen that with this construction, the stylus is continually reciprocating toward and from the plate 31. The stylus or core I3 is connected by a wire 16 to the carbon rheostat H and to a battery 18 or other source of current, the wire from the other pole of this battery being connected to the plate 31. Associated with the rheostat I1 is the control head previously described and including the field magnet 40 and the floating armature 43 supported by the spring 50. A spindle 49 extends from the armature downward through the field magnet and is connected to a resilient arm 53a which is directly connected to a plunger 66a and corresponding to arm 33 and plunger 66. The floating armature has its wires connected to the amplifying circuit and controlled by the photo-cell 10.

In the operation of this mechanism, the interruptor 15 is such as to make a certain number of contacts per inch as the stylus 12 moves across the plate. Thus the stylus is being continuously reciprocated toward and from the plate 31. When the stylus leaves the plate, it makes an arc, the intensity of which is determined by the tone value of the-negative which in turn, of course, controls the floating armature l3 and controls the degree of compression of the carbon in the rheostat l'l. In those places where the negative is the darkest, the arc is intense and burns out more of the surface of the plate. In the light places, a contact is still made but a smaller arc occurs and a smaller pit is, therefore, burned. After a line of pits is burned in the plate on one stroke of the ram, the traverse feed moves the ram with its coil laterally one step and another line of holes is burned and so on until the plate is completed. This construction makes a half tone plate from a photographic negative.

It will, of course. be understood that the tone value of the negative is the reverse or opposite of the tone value of the engraved plate, that is. where the negative is dark or dense, the stylus will be lifted only slightly from the plate, a rela tively large amount of current will flow through the stylus. and a relatively large pit will be formed. Where the negative is thin or light, the arc formed will be very short and have relatively slight intensity because of the slight amount of current flowingso that the plate will print either black at this point or with only a slight tone.

It is also to be understood that the guides H with the supporting frame Ila and allied parts slide laterally upon rails 89 or equivalent devices under the action of the traversing screw 23.

It is to be understood that the means for reciprocating the ram and causing the lateral traverse 0f the ram are not part of the present invention as they are fully disclosed and claimed in my prior application for patent before referred Preferably the stylus will etch the plate only upon a stroke in one direction, the other stroke 5 being idle. As illustrated in Figure 1, the stylus operates to etch the plate upon the backward stroke of the stylus, that is, a stroke toward the right hand in Figure 1 and in order that the stylus may be lifted while the stylus is traveling H) in a reverse direction, I provide a commutator designated generally 93 which may be mounted upon the shaft of gear wheel 34 to turn therewith or maybe rotated by this gear wheel at the same speed as the gear wheel. The commul5 tator has set into it the semi-circular sector of non-conducting material designated 94. Coacting with this commutator are the contact fingers 95 and 96 which are connected by conductors 91 and 98 to the amplifying system as shown in Figure When the two contact fingers 95 and 96 both rest upon the metalof the gear 93 a circuit is completed which causes the stylus to be entirely lifted and held lifted while the ram l0 moves to the right in Figure 1. When one: of the contact fingers 95, for instance, reaches the fibre part 94 of the gear, the circuit is broken and the tool lowered so that it can operate under the control of the negative as before described. Obviously the structure may be readily modified to etch upon the forward stroke of the ram or upon the rearward stroke of the ram as desired. In the construction illustrated, of course, the lateral traverse of the ram and of the etching stylus with the negative is secured upon the travel of the ram to the right in Figure 1.

i As before stated, I electrically connect the phototron T0 with the floating armature 43 through an-amplifying system by the wires 19 and 80 so that the impulses received from the phototron will be amplified when they'aifect the floating armature. Any suitable amplifying system may be used and I have here illustrated a direct coupled amplifying system diagrammatically. I have also 1 Y illustrated the field coils ll as being connected to a source of alternating current through a power transformer designated 90, the alternating current thus produced being rectified by the rectifier 9]. I have also illustrated the radiotrons of the amplifying system as being supplied with current from a source of A. C. through a power transformer 92 having therein a rectifier 93. 11 do not wish to be limited to this, however. The rlheostat 63 may be supplied with current from any suitable source of D. C. current. I

It will be seen in each of the structures shown in Figures 1 and 4, the stylus rests upon metal and that it is intermittently and very rapidly raised and lowered and thus brought intermittently into contact with the metal plate as it travels across the face of the plate, thus making a series of momentary contacts. In each case, as the stylus raises, an arc is formed and the strength of the currentforming the arc is controlled by the rheostat which in'turn is controlled bythe variations in light passing through the photo-cell 69. A series of pits are thus formed in the plate, I

which pits are shallowv and fsina llyinE diameter,

where the current is reducedor and larger across the face of aplate, stylus-and plate being connected to-a source.. of"-current-, interin diameter, where the currentis increased so that if these pits are very large and wide in dlameter, they will overlap each other and the metal will be entirely burned away from that portion. of the plate which is to print white, whereas if a portion of the plate is to print black, the pits will be relatively slight in depth and narrow in diameter. Where the mechanism shown in Figure 4 is being usedfor the purpose of reproducing half-tones, tones between solid black and solid white will be secured by variation in the depth and diameter of the pits produced by the arc.

While I have illustrated certain mechanism which Ihave actually tested and which will produce the results called for, I do not wish to be limited to this mechanism as it may be varied in many ways without departing'from the principle of the invention as claims.

I claim: 1. A method of forming a metal printing plat which consists in traversing a stylus across the face of the plate, in contact therewith, the metal defined in the appended plate and the stylus being in circuit with a source and the stylus being in circuit with a source of 7 current, causing the stylus to rapidly reciprocate against theface of the plate while it is traversing the plate, and varying the current passing into the stylus and across the gap to the plate in accordance withvariations in light passing through a light-sensitive element. a

3. A method of forming a printing plate which consists in traversing a stylus across the face of the plate in contact therewithytheplate and stylus being in circuit with a source of current, rapidly and intermittently lifting the stylus from the face of the plate and as the stylus is lifted, varying the current passing into the stylus and across the gap to the plate in accordance with variations in the light and shade of a pattern.

a 4;A method of forming a metal printingplate which includes traversing a stylus across the face of the plate, passing electric current through the stylus and plate,.lifting the stylus varying distances from the plate at intervals by the action of light affected by the light and shade of a controlling picture to thereby form arcs between the stylus and plate, and varying the current passing through the stylus and across the gap to the coacting plate in accordance with the distance that the stylus is raised from the plate.

5. A method of forming a metal printing plate,

which includes traversing a stylus across the face of 7 the plate, passing an electric current through the stylus and plate, lifting the stylus varying distances from the plate at intervals by and in correspondence with the action of light affected by the light and shade ofa controlling picture to thereby form arcs between the stylus and plate, and reducing the current passing'through the stylus and across the gap to the coacting plate in proportion to the distance that .the stylus is lifted from the plate.

6. A method of forming a metal printing plate I which consists in causing a; stylus to travel mittently lifting the stylusjfr'om the plate to Y form an arc between the plate and the stylus, and varying the strength of said are in. accord ance with variations in the conductivity in a photo-cell.

'7. Means for forming a metallic printing plate including a stylus normally resting upon and disposed in an electric circuit with the plate, means for traversing the stylus over the plate, means for rapidly and intermittently lifting the stylus from the plate while the plate and stylus are strength of the arcs in accordance with a pattern to be reproduced upon the plate including a rheostat and light operated means for controlling the resistance of said rheostat. v

9. Means for forming a metal printing plate including a reciprocatable plate support, means.

for reciprocating the plate support, means for shifting the support laterally after each reciprocation, a stylus connected in an electric circuit 7 with the plate on said support, means for causing the stylus to be intermittently lifted from and lowered into contact with the plate as the stylus is traversed over the face of the plate, and means acting as the stylus is lifted to vary the current in said circuit in accordance with variations in light and shade of a pattern to be reproduced.

10. Means for forming a metal printing plate including a reciprocatable plate support, means for reciprocating the plate support, means for shifting the support laterally after each reciprocation, a stylus connected in an electric circuit with the plate on said support, means for causing the stylus to be intermittently lifted from and lowered into contact with the plate as the stylus is traversed over the face of the plate, and means acting as the stylus is lifted to decrease the current passing through said circuit between the stylus and the plate in proportion to the height to which the stylus is raised and in accordance with variations of light and shade in a pattern.

11. Means for forming a metal printing plate including a plate support and a stylus, means for relatively shifting the support and stylus to carry the'stylus in a plurality of directions over the face of the plate, means electrically connecting the stylus and the plate in circuit with a source of energy, means for intermittently lifting the stylus from the plate and lowering it into contact therewith as the plate and stylus are relatively traversed to form arcs between the stylus and the plate, and means for varying the strength of said arcs by and in accordance with variations in the light and shade of a pattern.

12. Means for forming a metallic printing plate including a plate support, a stylus coacting with the plate, means for causing the stylus and plate to move in a plurality of directions relative to each other to carry the stylus over all portions of the face of the plate to be engraved, means for electrically connecting the stylus and the plate in circuit with a source of energy, means for intermittently lifting the stylus from the plate to form arcs between the stylus and the plate, and means for varying the current in the circuit of the plate and stylus including a carbon rheostat and means controlled by variations in the light and shade of a pattern to be reproduced controlling said rheostat.

13. Means for forming a metallic printing plate including a plate support, a stylus coacting therewith and normally resting upon the plate, means for causing relative movement between the stylus and the plate in a plurality of directions to thereby cause the stylus to traverse over all portions of the face of the plate, means for causing the stylus to be intermittently lifted from and lowered into contact with the plate as the stylus and plate are traversed relative to each other, a carbon rheostat in said circuit, a field magnet, an armature yieldingly supported in coactive relation to the field magnet and having a coil, the armature being operatively connected to the plunger of the rheostat, and means for varying the current passing through the coil of the armature by and in accordance with light and shade in a pattern.

14. Means for forming a metallic printing plate including an insulating support for the plate, a stylus, means for causing the stylus to traverse over and in normal contact with all portions of the plate to be engraved, the stylus being mounted for vertical movement away from the face of the plate but being urged against the plate, an armature carried by the stylus, an electro-magnet associated with the armature, a carbon rheostat, the electro-magnet, the rheostat, the stylus and the plate being connected in circuit with a source of current, a field magnet having a coil connected in circuit with a source of current, an armature for the field magnet and having the same polarity thereas, means yieldingly supporting the armature in spaced relation to the field magnet, means for supporting the stylus and its associated magnet from the armature, and means operatively connected to the floating armature and to the rheostat acting to increase the resistance of the rheostat as the stylus is withdrawn from the surface of the plate.

15. Means for forming a metal printing plate including a stylus resting on the plate and disposed in a circuit with the plate and a source of energy, means for traversing the stylus relative to the surface of the plate, means for intermittently lifting the stylus from the plate while the plate and stylus are relatively moving to form successive arcs between the plate and the stylus,

a light-sensitive element, means for scanning a picture by the light-sensitive element, and means controlled by the light-sensitive element for varying the intensity of successive arcs.

16. Means for forming a metal printing plate including a reciprocatable plate support, means for reciprocating the support, means for shifting the support laterally after each stroke in one direction, a stylus connected in an electric circuit with said plate on said support, means for causing the stylus to be intermittently lifted from and lowered into contact with the plate as the stylus is traversed over the face of the plate, means acting as the stylus is lifted to vary the current in said circuit in accordance with variations in light and shade of a pattern to be reproduced, and means for rendering the stylus inoperative upon a movement of the stylus in the opposite direction.

17. Means for forming a metal printing plate including a reciprocatable plate support, means for reciprocating the plate support, means for shifting the support laterally after each stroke of the plate support in one direction, a stylus connected in an electric circuit with the plate on said support, a s lenoid surrounding said stylus and (ill of which the stylus is the core, means urging the stylus upward, means for intermittently breaking the circuit through said solenoid to thereby cause a vertical reciprocation of the stylus toward and from the plate as the stylus is traversed over the facelof the plate, and means acting as the stylus is lifted to vary the current in said circuit int cluding'the plate and stylus in accordance with uvarlations inthe light and shade of a pattern to be reproduced. V

V 18. A method of forming a metal printing plate which includes traversing a stylus across the face 7 of the plate, passing a current through the stylus A and plate, intermittently lifting the stylus from the plate while the plate is being traversed relative to f the stylusjto thus forma series of suc-' cessivearcs between the plate and the stylus and modulating the current passing between the stylus andplateln accordance with variations of apattem. c 7

19. A method of forming a metal printing plate by pitting the surface of the plate which consists in subjecting the printing plate to the action of rapidly. successive electrical arcs along a twodimensional. scanningpattern, and varying the strength of the arcsin accordancefwith, variations of light and shade in said pattern.

20. Means for forming a metal printing plate by pitting the surface of-ithe plate including a stylus electrically engaging the platef'means for traversing the plate and stylus relatively to each other, means electrically connecting the plate and stylus, means for intermittently forming rapidly successive arcs between the plateand stylus as the plate is moved and means for simultaneously varying the strength of the arc in accordance with a pattern to be reproduced upon theprinting plate. Q

21. A method of forming a design upon the sur- 4 face of a metallic plate which includes traversing a stylus across the face of a plate, passing an electric current through the stylus and plate while intermittently lifting the stylus from the face of the plate, and modulating said current by current from an extraneous source, the voltage of the current from the extraneous source being modulated by and in accordance with the light and shade of a pattern; I V

22.A method of forming a metalprlnting plate which includes pitting the surface of the plate uniformly in accordance with a two-dimensional scanningpattern by a series of electric arcs and modulating the strength of the arcs in accordance with the light and shade of the pattern to thereby form pits of greater or less depth [and correspondingly greater or less diameter 'to vary' current flow-through an electric circuit, amplifying the said current flow, andemploying the said amplified current to effect the intermittent lifting of the stylus from the face of the plate While it is traversing the same.

24. A method of producing a metallic printing plate from a picture including traversing the stylus across tne face of the metal plate while in- 'termittently lifting the stylus from the face of the plate and simultaneously passing. current from a source of definite voltage through the plate, effecting the modification of a beam of light by the variationsin the tonal value of the picture, employing themodifications of said light beam to vary current flow in an electriccircuit,

- amplifying the current variations in said circuit,

and effecting the modulation of the current passing through the plate and stylus by the amplified current of said circuit. 7

I JOSEPH A. BENNETT.

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