US2986598A

US2986598A - Machine for producing printing plates with variable reproduction scale

Info

Publication number: US2986598A
Application number: US733971A
Authority: US
Inventors: Hell Rudolf
Original assignee: RUDOLF HELL KOMMANDITGESELLSCH
Current assignee: Dr-Ing Rudolf Hell KG; RUDOLF HELL KOMMANDITGESELLSCH
Priority date: 1957-06-04
Filing date: 1958-05-08
Publication date: 1961-05-30
Anticipated expiration: 1978-05-30
Also published as: CH357975A; FR1196434A; DE1057877B; NL110812C; NL228318A; GB845156A

Description

May 30, 1961 HELL MACHINE FOR PRODUCING PRINTING PLATES WITH VARIABLE REPRODUCTION SCALE Filed May 8, 1958 United States Patent MACHINE FOR PRODUCING PRINTHWG PLATES WITH VARIABLE REPRODUCTION SCALE Rudolf Hell, Kiel, Germany, assignor to Dr.-Ing. Rudolf Hell Kommanditgesellschaft, Kiel-Dietrichsdorf, Germany, a German company Filed May 8, 1958, Ser. No. 733,971

Claims priority, application Germany June 4, 1957 6 Claims. (Cl. 178-6.6)

This invention is concerned with a machine of the twotable type for electromechanically producing printing plates with continuously variable reproduction scale.

Systems are known for electromechanically producing printing plates, whereby the reproduction scale, that is, the ratio between dimensions on the printing plates and on the copies to be reproduced, can be selectively and adjustably changed. Thus, there are methods and devices known in which the copy and the printing plate blank are respectively mounted each upon a rotating drum, whereby both drums are advanced axially, with the scanning and engraving elements in fixed positions, or else wherein the two drums are in fixed position, while the scanning and engraving elements are advanced with respect to the circumference of one of the drums. The scanning and engraving is efiected either along equidistant circles or along helical lines. The enlargement or reduction of the scale on the printing plate, as compared with the scale of the copy to be reproduced, is obtained either by the use of drums of difierent diameter, to be selectively used for one of the drums, and operating both drums at identical speed of rotation, or by using drums of identical diameter but rotating them at diflerent speeds. The ratio of the advance steps per drum revolution and advance speeds of the scanning and engraving elements, corresponding respectively to the enlargement and reduction and the selected screen, is produced by corresponding step-up and step-down gear means.

There are also systems known, comprising horizontally extending tables adapted to reciprocate in parallel planes, one table carrying the copy to be reproduced, which is scanned by a scanning element point for point in successive lines, the other table carrying the printing plate blank to be processed which is simultaneously engraved, by a suitable tool, point for point along successive lines. Upon conclusion of the scanning and engraving of each line, the scanning and engraving elements each execute a stepwise line advance motion, perpendicular to the scanning and engraving directions, by the distance of two scanning lines and engraving lines, respectively, such spacing corresponding respectively to the screening applied and to the reproduction scale desired. The enlargement or reduction of the scale on the printing plate, as compared with the copy to be reproduced, is thereby effected by step-up and step-down gears or by lever mechanisms respectively interposed between the drives of the two tables and the drives for the line shifting or advance of the scanning and engraving elements.

It is further known to impart either to the scanning or to the engraving element or to both auxiliary motions in the scanning and engraving directions, respectively relative to drums of identical diameter rotating with identical speed of rotation or relative to tables reciprocating with identical speed, and employing suitable step-up and stepdown gears for the purpose of producing the desired ratio of line advance or shifting motion of the scanning and engraving elements.

"ice

Another known system uses, instead of two separate tables respectively for the copy to be reproduced and for the printing plate blank which is to be engraved according to variable reproduction scale, a single reciprocating table carrying upon one side the copy to be reproduced and upon the other side thereof the printing plate blank which is to be engraved. In such known system, either the scanning element or the engraving element executes relative to the reciprocating table in auxiliary motion in the respective scanning and engraving direction or else, both elements execute such auxiliary motions.

A further known system is of the hybrid table-drum type, in which a flexible printing plate foil is wrapped about a rotating drum, an engraving head being moved with respect thereto parallel to the drum axis, such head carrying a heated tool for engraving the foil along a helical line by burning out the screen elements. The copy to be reproduced is carried by a horizontally disposed table which executes a translatory motion parallel to the drum axis. The copy to be reproduced is scanned by an optical scanning device swinging forth and back about a fixed axis, in a plane perpendicular to such axis, along successive lines transverse to the drum axis. The reproduction scale is changed by alteration of the ratio between the swinging amplitude of the scanning system and the constant speed of rotation of the drum, and by corresponding alteration of the ratio between the speed of translatory motion of the table carrying the copy and the invariable translatory speed of the scanning head along the drum.

Other known systems project by optical means including a picturing objective, an enlarged or reduced picture image of the copy to be reproduced onto a frosted plate or screen, and such projected picture is photoelectrically scanned point by point along successive lines, thereby producing fluctuating photoelectric currents for controlling the depth of penetration of an engraving tool which engraves a printing plate of a size corresponding to the optically projected picture, point by point in successive lines.

Further systems have become known in which the enlargement or reduction of scale on the printing plate as compared with the scale of the copy to be reproduced, is likewise carried out by means of a picturing objective, without, however, Projecting the copy to be reproduced in its entirety, as in the system noted in the preceding paragraph, but instead scanning the original copy by a dot of light whose diameter and path correspond to the optically enlarged or reduced image of the diameter and path of a punctiform light source, such source being fixedly connected with the engraving system which engraves a printing plate blank simultaneously with the scanning of the copy, the depth of penetration of the engraving tool being controlled by means of a plurality of photocells fixedly disposed in the neighborhood of the objective and ascertaining the relative brightness of the picture point which is being scanned upon the copy.

Finally, a system has become known in which the alteration of the reproduction scale on the printing plate, as compared with the scale on the copy to be reproduced is effected by optical picturing of the copy with electrical means. The alteration of the reproduction scale is thereby obtained by picturing the copy to be reproduced, by means of a picturing optics with variable picturing scale, always in the identical size upon the photo cathode of a picture chopping tube, scanning the optical picture upon the photo cathode line for line by an electron beam, controlling the depth of penetration of the engraving tool in the printing plate blank by the picture currents produced by the tube, controlling the deflection of the electron beam in one coordinate direction by the relative motion of the engraving table with respect to the engraving system in the engraving direction while controlling the deflection of the electron beam in the coordinate direction perpendicular to the first direction by the relative line advance or shift motion of the engraving system with respect to the engraving table perpendicular to the engraving direction, such, that one deflection volt age for the electron beam is proportional to the table stroke while the other deflection voltage is proportional to the line advance or shift path of the engraving system with respect to the engraving table.

Due to recent advances which have made it possible to engrave metallic printing plates electromechanically, demands for such engraving have arisen with increasing frequency. Systems employing rotating drums cannot satisfy the requirements for the electromechanical engraving of metal plates on account of the relative rigidity of such plates. Systems employing tables or drums in which the screen elements are burned out from printing plate blanks made of foils of synthetic material, by means of heated engraving tools are likewise unsuitable for the processing of metallic printing plates. Systems employing tables, in which the variable reproduction scale is produced mechanically by means of step-up and stepdown gears have the drawback of permitting setting of the reproduction scale only in fixed increments or stages but not continuously. One of the oldest two-table machines for making printing plates, employing for continuous variation of the reproduction scale a lever mechanism resembling a parallelogram, has the serious drawback that there is no linear relation between the motions of the two tables but a complicated non-linear relation,

so that the image on the printing plate will not agree in smallest details with the copy to be reproduced, thus furnishing a printing plate carrying an engraved image which is distorted as compared with the picture copy.

The invention proposes a two-table machine employing lever mechanisms for the continuous setting of the reproduction scale and for the coupling of the similarity motion of both tables.

The invention avoids the previously noted drawbacks by coupling the two table motions which are in identical sense in the engraving direction and also the two oppositely directed line advance or shift motions of the scanning and engraving heads perpendicular to the table motions, by two continuously adjustable similar swing-lever mechanisms, in such a manner, that the ratios between the two table strokes and the two line advance or shift strokes as well as the ratios between the two table speeds and the two line advance or shift speeds are, independent of the selected screening and at a selected reproduction scale, constant and equal to the reproduction ratio.

The machine according to the invention comprises a reciprocable copy table carrying the picture copy to be reproduced, a similarly reciprocable engraving table swing levers disposed for motion, forth and back, in iden- Y tical direction within a vertical plane, means for rotatably journalling the lower ends of said swing levers at structural parts of the machine, means for rotatably journalling the upper ends of said swing levers at said engraving table and the copy table, respectively, a slide for interconnecting said swing levers, said slide extending in a plane perpendicular to the planes of said tables and parallel to the planes of said swing levers, means for positively guiding said slide for forth and back motion corresponding to the reciprocating motion of said tables,

selectively adjusting the respective pivot means longitudinally of the corresponding swing levers in accordance with the desired reproduction scale, a double-armed horizontally extending lever for interconnecting said engraving head and said scanning head for the purpose of coupling said heads for the line advance motion thereof, means for rotatably journalling one end of said doublearmed lever at the engraving head and the other end thereof at the scanning head at respectively vertically extending axes, vertically disposed pivot means extending from a structural part of the machine for rotatably journalling said double-armed lever intermediate the opposite ends thereof, and means for selectively adjusting the position of said last named pivot means with respect to the opposite ends of said double-armed lever in ac cordance with the desired reproduction scale.

The invention will now be explained with reference to the accompanying drawing, wherein- Fig. 1 shows in schematic manner essential parts of a machine according to the invention; and

Fig. 2 is a diagram to aid in explaining the kinematic operation of the swing-lever mechanisms.

In Fig. 1, numeral 1 indicates a rectangular horizon tally disposed engraving table guided in rails 2 and 3 for reciprocating motion, numeral 4 indicating the printing plate blank mounted on the table 1 which is to be engraved in accordance with parallel or diagonal engraving cutting. Numeral 5 indicates a cylinder mounted on structural parts of the machine, containing a piston 6 connected with the piston rod 7 which is fastened to cars 8 extending from the engraving table 1. The cylinder 5 is provided with two

orifices

9 and 10 formed therein to which are connected

hydraulic pressure lines

11 and 12 terminating in a hydraulic control device 13 for governing the feed and return of hydraulic fluid so as to eifect reciprocation of the piston 6 and therewith reciprocation of the engraving table 1. The drive of the engraving table 1 may also be effected by means of a rotating spindle threadedly guided within a nut carried by the engraving table, with suitable reversing gear means for reversing the direction of rotation at the conclusion of engraving of each line. The reversal of the table motion is effected by suitable control means, always when the engraving tool reaches an edge of the printing plate blank.

Numeral 14 in Fig. 1 indicates the rectangularly shaped horizontally disposed copy table which is guided in rails 15 and 16 for reciprocating motion in the same direction as the engraving table 1. The two tables may be positioned in the same plane or in difierent parallel planes or levels. The latter arrangement of the tables in dilierent planes or levels is advantageous for reasons of saving space; the two tables may overlap incident to their mot-ions, resulting in a shortening of the machine dimensions. The copy table 14 carries the copy or picture 17 which is to be reproduced.

There are provided two swing-

levers

18 and 19 which are respectively rotatably journalled upon axes 20 and pendicular to the, plane of the tables. At the upper ends of the levers are formed longitudinal slots respectively indicated at 22 and 23', stub shafts or pins indicated at 24 and 25, extending respectively from the engraving table and the copy table and entering the respective slots. Incident to reciprocation of the tables, the swing levers 18 and 19 will be displaced with the corresponding slots gliding along the

respective stub shafts

24 and 25. The copy table 14 is in the illustrated example at a lower level than the engraving table 1, and the svw'ng-lever 19 is, accordingly, shorter than the swing-lever 18, by the level diiference. The swing-lever 18 is alsopro vided with a longitudinal slot 26 and the swing-lever 19 is provided with a similar longitudinal slot Z7.

The coupling of the swing-

levers

18 and 19 and therewith the coupling of the. tables 1 and 14 is efiected by a slide 28 which is disposed in a vertical plane extending in parallel to the plane of the swing levers.

Bearings

29 and 30 provide positive guidance for the slide 28 in its horizontal displacement, the slide, accordingly, executing a reciprocating motion in parallel with the reciprocating motion of the tables 1 and 14. Vertically extending

slots

31, 32 are formed in the slide 28 respectively in line with the two

lever pivots

20, 21, which are respectively engaged by

pivots

33 and 34.

Numerals

35, 36 indicate means for fixing the pivots 3'3, 34 in any adjusted position with respect to the

respective slots

31, 32. The positions of the

pivots

33, 34, are, accordingly, adjustable on the slide 28. The two

pivots

33, 34 extend respectively through the

slots

26, 27 formed in the

swing levers

18, 19, these slots permitting sliding of the levers along the pivots incident to angular displacement of the levers and resulting reciprocation of the slide 28, the swing-levers coincidently rotating about the pivots 3-3, 34. Scales 37, 38 are provided, respectively carried by the

swing levers

18, 19, upon which may be set the distance of the pivots 3-3, 34 from the

axes

20, 21, in the vertical zero position of the two swing-levers, by means of the

pointers

39, 40, respectively associated with the

pivots

33, 34. The coupling of the two swing levers 18, 19, by means of the slide 28, etfects a linear similarity motion of the two tables 1 and 14, such, that the ratios of the table strokes and speeds are at any instant constant and in accordance with the adjusted reproduction ratio. It is possible, by alteration of the adjustment of the two

pivots

33, 34 with respect to the

slots

31, 32 in the slide 28, to set the machine in accordance with reproduction ratio which is within certain limits steadily variable as desired.

Considered kinematically, the slide 28 with its

pivots

33, 34 which are

adjustable slots

31, 32, constitutes a rod of variable length. Incident to reciprocating motion of the two tables, this rod always remains parallel to itself, and the vertical distances of its rotation and gliding

pivots

33, 34, from the connecting line ofthe two lever axes 20', 21, remain during the reciprocation constant. The horizontal paths ofthe two pivots 3-3, 34, considered from the vertical zero position of the two swing-levers, are always equal one to the other. However, the angles of the two swing-levers, measured from the vertical zero position about which they are displaced incident to the table motion, are generally speaking different. They will be equal to one another only when the connecting line of the two pivots 33', 34 is parallel to the connecting line between the

axes

20, 21. However, the reproduction ratio is in this case not 1 to 1 since the tables 1 and 14 have different constant vertical distances from the lever axes 20, 21. Moreover, the reproduction ratio is not determined by the absolute amounts of the vertical spacings of the pivot 33 from the axis 20 and of the pivot 34 from the lever axis 21, but by their ratio, thus making the level setting of one of the two

pivots

33, 34, for obtaining a desired reproduction ratio, arbitrary. However, in order to produce for facilitating operation unambiguous conditions, the absolute amounts of the spacing of the pivots from the respectively associated lower lever axis is in connection with the reproduction ratio 1 to l fixed by the scale marking l and 1 upon the scales 37 and 38.

In connection with all enlargements to appear on the printing plate as compared with the picture copy, the pivot 34 is invariably set on the right hand scale to the scale mark 1 and the pivot 33 is set on the left hand scale underneath the scale mark 1 the greatest enlargement being efiected when the pivot 33 is set to the scale mark 4. In connection with all reductions to appear on the printing plate as compared with the picture copy, the pivot 33 is set invariably on the mark 1 of the scale 37, and the pivot 34 is set to a mark underneath 1, the greatest possible reduction resulting when the pivot 34 is set opposite the scale mark 0.33. The

scales 37v and 38 are not provided with linear subdivisions.

The kinematic conditions incident to similarity of motion of the two tables are represented in Fig. 2 in abstract manner. The constant vertical distance of the guide axis 24 from the lower iever axis 20* is assumed to be c, and the constant vertical distance of the guide axis 25 from.- the lower lever axis 211 is assumed to be d. It is further assumed that c d, that is, that the engraving table 1 moves in a level extending above the level of the copy table 14. The adjustable spacing of the pivot 33 from the lever axis 20' shall be assumed to be a, and the adjustable spacing of the pivot 34- from the lever axis 21 shall be assumed to be b. It shall further be assumed that a b, that is, that the machine is set for enlargement of the image on the printing plate as compared with the picture copy, as contrasted with the conditions illustrated in Fig. 1 in which it is assumed that reduction of the image on the printing plate as compared with the picture copy, is to be efiected. The angle of swing of the lever 18 from its vertical position shall be assumed to be on and the angle of swing of the lever 19' shall be assumed to be 3. The slide 28 so far as its kinematic effect is. concerned may be considered to be substituted by a rod 28 which interconnects the

pivots

33 and 34, thereby holding the spacing therebetween, at an adjusted reproduction ratio, constant. Due to the positive horizontai guiding of the

pivots

33 and 34, upon angular displacement of the

levers

18 and 19, the pivot 33 will be shifted by an amount alga, reaching the position 33', and the pivot 34 will be shifted by an amount h1g5, moving into the position 34'. The shifting of the

pivots

33, 34 are, due to the rigid interconnection therebetween, by means of the rod 28', equal to one another, that is and the rod 28 is in the shifted position 28 in parallel with its initial position. The stroke of the engraving table 1 is x=c.tgot

and the stroke of the copy table is y= fi Upon considering this relation, there will result for the ratios of the two table strokes x and y, that is, for the Since it was assumed that c d, therefore, k l. Accordingly, there will result an enlargement v 1 on the printing plate as compared with the picture copy, when k.b/a l; a reproduction scale 1 to 1, that is, v=1, when k.b/a=l; and reduction of the printing plate image as compared with picture copy v l, when k.b/a 1.

The foregoing considerations show that it does not depend upon the absolute values of a and b but upon the ratios thereof. They also show that there is a strictly linear similarity motion of the tables since the reproduction scale xzy is at fixediy set values a and b constant, that is, independent of x and y.

There are several possibilities for the longitudinal equalization of the two

levers

18, 19 incident to their swinging motion. Instead of elfecting the longitudinal equalization by means of the slots 22, 2.6 and 23, 27, as shown in Fig. l, the swing-levers, to produce the same eifect, may be journalled at 24, 25 rotatably but not shiftable, and the slots for the longitudinal equalization or compensation may be provided at the lower ends of the levers, so that the levers glide up and down with respect to the

axesv

20, 21. The second longitudinal compensation between the lower ends. must also be maintained in such embodiment by the provision of the

slots

26, 27. A third possibility for the compensation in length resides in providing slots in the opposite ends of the

levers

18, 19 for sliding cooperation with the shafts or

axes

24, 20 and 25, 21 incident to the swinging motion of the levers. However, in such a case, the lever 18 and the lever 19 must be arranged merely rotatable about the

pivots

33 and 34, respectively, but not movable relative to the

intermediate lever slots

26, 27, contrary to the arrangement illustrated in Fig. 1, wherein the longitudinal compensation or equalization must be effected along the

slots

26, 27 due to the fixed journalling of the lower lever ends at 20, 21, so that the

pivots

36, 34 can slide relative to the

intermediate slots

26, 27, and therewith also relative to the scales 37 and 38. This applies, of course, only in case the two levers are fixedly journalled at their upper ends, the longitudinal compensation being effected by slots formed in the lower ends thereof.

The guide shaft extending from the copy table 14 is connected with a bushing 41 which may be clamped to the rail 43 in any adjusted position, by means of member 42. This coupling-uncoupling device makes it possible to place the copy table 14 in the scanning direction in desired initial position with respect to the en graving table 1 as well as with respect to the scanning head 50 which will be presently described. The couplinguncoupling device is very important, making it possible to place the scanning head prior to engraving at desired points of the picture copy so as to ascertain the brightest and the darkest points for the adjustment of the whiteblack level and, further, in order to make it possible to scan a picture copy section lying at any desired area of the picture copy. The coupling-uncoupling device may be also provided in connection with the engraving table 1 to obtain similar efiects.

Numeral 44 indicates the engraving head containing a known electromagnetic drive system for actuating the engraving tool or stylus 45, such stylus executing during the engraving up and down motions controlled in accordance with the brightness of the picture copy. The engraving head 44 is fastened to the carrier 46 which is pivoted on the nut 48 at 47, whereby the engraving head may be lifted with respect to the engraving table 1. The not 48 is either split midway thereof in the line shift or advance direction or is formed in the manner of a segment so as to make it possible to separate the engraving head 44 from the threaded spindle 49 for the purpose of placing it in the advance direction in alignment with a desired point on the printing plate blank 4. The threaded spindle 49- is intermittently rotated so as to move the engraving head upon conclusion of the engraving of each line in a stepwise line shift or advance motion perpendicular to the engraving direction. This intermittent rotation of the threaded spindle 49 may be effected by means of a rotary ball wedge clutch device generally known from free-Wheeling drives used, for example, in connection with bicycles. The advantage ofsuch a clutch drive is that it permits steadily alterable adjustment of the angle of rotation of the line advance or shift spindle 49. The release of the stepwise advance motion is controlled by the reversal of the table motions,

that is, a control element, for example, a contact is in known manner actuated at the conclusion of the engraving of a line, efiFecting known and suitable control means for reversing the table motion, and also effecting actuation of the clutch device so as to advance the engraving head 44 and the scanning head 50 in a direction perpendicular to the line engraving motion and line scanning motion, respectively, in position for respectively scanning and engraving the next line.

In-case only a small number of fixed advance or shift steps is required, corresponding to a small number of fixed screen'elements, the above described clutch device for'the (invent the line shift or advance spindle may be were replaced by a plurality of known gears with difi'erent numbers of teeth controlled by resilient stop pawls.

The scanning head 50, containing a known optical and photoelectric scanning device, serves for the line by line scanning of the picture copy 17.

A horizontally extending two-armed swing-lever 51 is provided for the coupling of the line advance or line shift motions of the engraving head 44 and the scanning head 50. The lever 51 has at the end facing the scanning head 50' a longitudinal slot 52 formed therein, a vertically disposed pin 53 extending from the scanning head 50 entering the slot 52. Incident to line advance motion of the scanning head 50, the lever 51 will be angular-1y displaced by the action of the pin 53 in the slot 52. The opposite end of the lever 51, facing the engraving head 44, is journalled for rotation about trunnion 54 which may be clamped, by member 55, in position at any desired place along the dovetailed bar 56, such bar being disposed on the nut 48 in parallel to the line advance motion controlled by the spindle 49. The corresponding coupling device comprising the members 54, 55, 56 permits placing of the scanning head in the line advance direction in any desired position with respect to the engraving head. The adjustment made possible by this coupling device is of value in connection with making enlargements or reductions of sections of a picture copy. The coupling device may be provided in connection with the scanning head 50 instead of with engraving head 44 to obtain similar efl ects.

The lever 51 has a longitudinal slot 57 formed therein intermediate its opposite ends for accommodating a stub shaft 58 in sliding cooperation therewith. The stub shaft 58 may be clamped to a stationary bar 60 which is connected with a structural part of the machine and extends in parallel to the engraving direction, in any desired position with respect to such bar, by clamping means 59, a pointer 62 extending from the stub shaft 58 cooperating with a scale 61 on the bar 60 to set and to indicate the desired reproduction ratio for the line advance motion, such ratio being generally equal to the reproduction ratio in the engraving and scanning direction. The lever 51 will be rotated about the stub shaft 58, incident to the line advance motion, the stub shaft sliding within the slot 57 and constituting the changeable or adjustable pivot for the lever 51. Enlargement of the image on the printing plate as compared with the picture copy will result when the pointer 62 extending from the stub shaft 58 is placed at the right of the scale mark "1 since the left (changeable) arm of the lever will be longer than the right (changeable) arm thereof. Reduction of the image on the printing plate will be eifected when the pointer 62 extending from the stub shaft 58 is placed to the left of the scale mark "1 because the lengths of the respective arms of the lever 51 will differ in opposite sense. The lengths of the two lever arms change steadily incident to the line advance motions, but the ratio remains at any instant constant and equal to the adjusted reproduction scale which is given by the ratio of the distance of the trunnion 54 from the stub shaft 58 and the distance of the pin 53 from the stub shaft 58. The reproduction scale is set with the lever 51 in zero position, that is, when the lever extends in parallel to the engraving direction.

The lever 51, instead of having its left end journalled at a fixed point and having its right end slotted, as shown in Fig. 1, may have its right end journalled at a fixed point and its left end slotted. The operative effect will be the same, namely, the stub shaft 58 which is fixedly clamped to the rail 60, by means of member 59, will be slidable within the slot 57 in the lever 51. The lever 51 may also be disposed rotatable about the stub shaft 58 but not shiftable with respect thereto, and the stub shaft and claw 63 may be slidable on the rail 60. The adjustment or setting of the reproduction scale is efiected as de 9 scribed before, with the lever 51 in its zero position, that is, disposed parallel to the engraving and scanning direction.

The lever 51 may also be provided with slots formed therein at both ends thereof and may be rotatable about the stub shaft 58 but not displaceable relative thereto, and the shaft 58 may be fixedly connected with the rail 60 by means of the claw 63. The reproduction scale may in such case be set on the scale 61 in any desired position of the lever 51.

The line shift motions of the engraving head 44 and of the scanning head 50 are due to the two-armed lever 51 in opposite sense; the result is, that the printing plate blank will be engraved in mirror-picture image of the picture copy, as it must be to obtain side correct reproduction.

Generally speaking, the same reproduction scale must be set on the scale 61 as on the scales 37 and 38 to obtain a printing plate image which corresponds geometrically to that on the picture copy. However, it is possible to set a reproduction ratio for the tables, on the scales 37 and 38, different from that for the line advance or shift motions set for the lever 51 on the scale 61. This is important in connection with making a printing plate from a picture copy bearing an image which is dilferently distorted in two directions perpendicular to one another and when such distortions are to be corrected. The reproduction scale, in such a case, must be different in the two directions extending perpendicular one to the other. Such distortion correction may, however, be considered an exceptional case. The requirement for producing a printing plate bearing a distorted image of a picture copy may arise, for example, when it is desired to produce distortions for the sake of creating amusing or cartoon-like effects.

In the production of screen printing plates, the line advance or line shift motion of the engraving head is regardless of the reproduction scale, solely dependent upon the selected number of screening lines. The total number of scanning lines upon the picture copy is equal to the total number of engraving lines upon the printing plate. However, the density of the scanning lines, that is, the number of scanning lines per unit of length, will depend upon the selected number of screening lines as well as upon the reproduction scale.

Changes may be made within the scope and spirit of the appended claims.

I claim:

1. In a machine for producing printing plates having a reciprocable copy table carrying the picture copy to be reproduced, a similarly reciprocable engraving table carrying a printing plate blank, a scanning head for scanning the picture copy, an engraving head for engraving the printing plate blank in accordance with the scanning of said scanning head, means for advancing said scanning head and said engraving head in a direction perpendicular to the direction of reciprocating motion of said copy table and said engraving table, the combination for efiecting variable reproduction scale in the production of printing plates, comprising a pair of single-arm swing levers disposed for motion, forth and back, in identical direction within a vertical plane, means for rotatably journalling the lower ends of said swing levers at structural parts of the machine, means for rotatably journalling the upper ends of said swing levers at said engraving table and said copy table, respectively, a slide for inter-connecting said pair of swing levers, said slide extending in a plane perpendicular to the planes of said tables and parallel to the planes of said swing levers, means for positively guiding said slide for forth and back motion corresponding to the reciprocating motion of said tables, pivot means for rotatably journalling said pair of swing levers on said slide intermediate the ends of said levers, means for selectively adjusting the respective pivot means longitudinally of the corresponding swing levers in accordance with the desired reproduction scale, means associated with the repective single-arm swing levers for effecting compensation of the length of the latter, incident to displacement thereof, a double-armed horizontally extending lever for interconnecting said engraving head and said scanning head for the purpose of coupling said heads for the advance motion thereof, means for rotatably journalling one end of said double-armed lever at the engraving head and the other end thereof at the scanning head at respectively vertically extending axes, vertically disposed pivot means extending from a structural part of the machine for rotatably journalling said double-armed lever intermediate the opposite ends thereof, means for selectively adjusting the position of said last named pivot means with respect to the opposite ends of said double-armed lever in accordance with the desired reproduction scale, and means associated with said double-armed lever for effecting compensation of the length of the latter incident to displacement thereof.

2. A structure according to claim -1, comprising means cooperatively associated with said first and said second named pivot means for visually indicating the reproduction scale respectively adjusted thereby.

3. A structure according to claim 1, wherein the means for compensation of length of said single-arm swing levers incident to displacement thereof is positioned at said pivot means and at the upper ends thereof which are respectively journalled at said engraving table and at said copy table.

4. A structure according to claim 1, wherein the means for compensation of length of said double-armed lever incident to displacement thereof is positioned at said last named pivot means and at one of the ends of said lever.

5. A structure according to claim 1, wherein said tables are reciprocated along mutually parallel and partially overlapping planes.

6. A structure according to cairn 1, comprising journal means for journalling the upper end of one of said singlearm swing levers at said copy table, and means for selectively adjusting the position of said journal means with respect to such table.

References Cited in the file of this patent UNITED STATES PATENTS 2,086,798 Greenberg July 13, 1937 2,092,764 Losier Sept. 14, 1937 ,092,765 Losier Sept. 14, 1937 2,225,915 Losier Dec. 24, 1940 2,512,918 Chamberlin June 27, 1950 2,733,510 Darago Feb. 7, 1956 2,899,493 Levine Aug. 11, 1959 2,909,598 Lifierth Oct. 20, 1959