US3762323A - Flexographic printing system - Google Patents

Abstract

A wipe roll and an engraved ink transfer roll of a flexographic printing assembly are suspended from a frame to permit movement of the axis of the wipe roll and the ink transfer roll with respect to the axis of the print cylinder. A first force is continuously applied to the transfer roll. A second force is intermittently exerted on the transfer roll and is capable of overriding the first force to urge the surface of the transfer roll into an ink transfer relationship with the print cylinder. The wipe roll can be mounted for movement with the engraved transfer roll to maintain the desired clearance between these two rolls during the movement of the transfer roll away from and towards the print cylinder.

Description

FLEXOGRAPHIC PRINTING SYSTEM [751 Inventors: Theodore J. Hartka. Phoenix;

William C. Stuley, Ruxton, both of Md.

[73 I Assignec: Wm. C. Staley Machinery C0rp.,

Hunt Valley, Md.

[221 Filed: Oct. 6, 1971 21 Appl. No.: 186,978

[52] U.S. Cl. 101/350, 101/352 [51] Int. C1. B411 31/06, B41f 31/36 [58] Field of Search ..10l/349352, 363, 364,

[ 56] I References Cited UNITED STATES PATENTS 1,975,681 10/1934 Brawn l0l/351 2,333,962 11/1943 Terry 4. 101/351 2,614,492 10/1952 Brodie 101/426 X 2,606,520 8/1952 Hoel 101/351 X 3,343,484 9/1967 Dahlgren 101/148 3,404,625 lO/1968 White 101/148 3,417,693 12/1968 Hartka.... 101/364 3,433,155 3/1969 Norton 101/349 3,507,215 4/1970 Shuhmann ,101/351 1 Oct. 2, 1973 3,673,959 7/1972 Jezuit 101/148 FOREIGN PATENTS OR APPLlCATlONS 1,238,046 4/1967 Germany [01/364 741,781 5/1943 Germany 101/351 Primary EXamim'rJ. Reed Fisher A!l0rneyFinnegan, Henderson & Farabow [57] ABSTRACT A wipe roll and an engraved ink transfer roll of a flexographic printing assembly are suspended from a frame to permit movement of the axis of the wipe roll and the ink transfer roll with respect to the axis of the print cylinder A first force is continuously applied to the trans- 4 Claims, 5 Drawing Figures United States Patent 1 111 3,762,323

Hartka et al. 1 Oct. 2, 1973 PATENIED 21973 3.762.323

SHEET 1 UF 5 FIG. 1

INVENTORS THEODORE J HARTKA WlLLIAM C. STALEY T NTE 21975 3.762.323

SHEET 2 [1F 5 INVENTORS THEODORE J. HARTKA WILLIAM C. STALEY SHEET 30F 5 INVENTORS THEODORE J. HARTKA PATENTEDUEI 2 I973 WILLIAM C. STALEY PATENTED flcI 2 197a SHEET l 0F 5 1N VENTORS J H ART KA THEODORE WILLIAM C. STALEY PAIENIED 2W 3.762.323

sum 5 OF 5 mag '39 HEODORE J. HARTKA WILLIAM C. STALEY FLEXOGRAPHIC PRINTING SYSTEM FIELD OF THE INVENTION This invention relates to a method and apparatus useful .in flexographic printing. More particularly, the invention relates to a method of adjusting the position of an engraved ink transfer roll with respect to a print cylinder, and to an improved flexographic printing assembly.

BACKGROUND OF THE INVENTION The flexographic printing process utilizes water base ink which permits easy equipment clean up. Because of the magnitude of the cost savings that result from the ease of clean up, printers have shown considerable interest in converting existing oil-base ink equipment to the flexographic process.

Typically, the conversion of existing oil-base printing equipment to the flexographic process has involved mounting the wipe roll and the engraved ink transfer roll on a mounting frame, and holding these rolls and the mounting frame in a fixed relationship with the print cylinder. This conversion technique has required that exact tolerances be maintained during installation in the fielda difficult operation. Further, the need to maintain precise tolerances has required'the use of a heavy, cumbersome roll support structure. Because the wipe roll and the engraved transfer roll are also heavy, it has been difficult and undesirable to convert larger installations, for example, installations having a printing roll of 184 inches in length, to the flexographic system since such installations are typically situated in buildings that lack overhead crane facilities. The weight problem has also tended to restrict the use of the flexographic process in new installations where a long print cylinder is required.

Also, there has existed a need for an improved method and apparatus for adjusting and maintaining the position of the wipe roll and the ink transfer roll relative to each other and to the print roll during printing operations, and for moving the ink transfer roll from the print roll when printing operations terminate.

BRIEF DESCRIPTION OF THE INVENTION The invention provides a method of adjusting the position of an engraved ink transfer roll with respect to 'a print cylinder. The transfer roll is suspended so that its axis can move in an arcuate path of movement with respect to the print cylinder with the axis of the transfer roll remaining parallel to'the axis of the print cylinder. A first force is continuously exerted on the transferro'll and tends to "move the axis of the transfer roll a'longthe arcuate path and to move the surface of the transfer roll out of contact with the print cylinder. A second force is intermittently applied to the transfer roll that is capable of overriding the first force to urge .thesurface of the transfer roll into ink transfer contact'with the print cylinder, with the release of the second force permitting the firstforc'e to move the transfer'roll out of contact with the print'c.ylinder.

In preferred embodiments, the method "of the invention includes the steps of suspending a wipe roll soithat its axis can move in an arcuate path'ofmovem'ent relative to the print cylinderwith the axis of the 'wipe roll remaining parallel to'the axis of the'ptint cylinder,and holding the distance between the axisof the wipe roll and theaxis of the'transfer roll a predetermined constant distance apart during movement of the transfer roll along its arcuate path.

Also, it is preferred to limit the arcuate movement of the axis of the transfer roll towards the print cylinder by applying a blocking force that acts on the transfer roll when the transfer roll achieves a predetermined position in its travel towards the print cylinder.

In another embodiment, the invention provides a flexographic printing assembly for supplying ink to a print cylinder. The assembly includes a frame held in fixed position with respect to the print cylinder. A pair of spaced pivot arms are pivotally mounted on oppos' ing sides of the frame for pivotal movement about a first axis. An engraved transfer roll is provided having each end rotatably mounted on one of the pivot arms. The axis of the transfer roll is movable in an arcuate path with respect to the print cylinder due to the pivotal mounting of the pivot arms. A pair of spaced wipe arms are pivotally mounted on the frame for movement about a second axis parallel to the first axis. A wipe roll is provided having each end rotatably mounted on one of the wipe arms.

The assembly further includes adjustment means, such as a pair of length-adjustable tie members, for adjusting and maintaining the nip between the wipe roll and the transferroll. Each of the tie members is pivotally mounted on one of the wipe arms and pivotally mounted on one of the pivot arms. Stop means are mounted on the frame for limiting the pivotal movement of the pivot arms and the approach of the transfer roll towards the print cylinder.

The position of the transfer roll and the wipe roll are adjusted and maintained by (a) a force applying means, for example, resilient means such as a compression spring for exerting on the pivot arms a first moment arm that is capable of pivoting the pivot arms to move the transfer roll out of ink transfer relationship with the print cylinder; and (b) releasable actuating .means for exerting a second moment arm on the pivot arms that can overcome the first moment arm and .thus rotate the pivot arms into engagement with the stop means .to

hold the transfer roll in ink transfer relationship with the print cylinder during printing operations, with the release of the actuating means permitting the resilient means to move the transfer roll outof contact with the print cylinder.

Supply means are provided for .feeding ink to the nip formed by the wipe roll and the engraved transfer roll, and drive meansmay be provided to rotate the :transfer roll .and the 'wipe .roll.

The invention provides an assembly which permits easy conversion in the field :of an .o'il-base ink installation to the flexographic process. The conversion .can be effected without the need to establish precise tolerances,b'ecause the apparatus formountingzthe .rollsihas a 'built-in adjustment capability. The assembly 10f the invention isalso desirably incorporatedintoznewz flexographic printing installations such as prlinterfslotters .used in making corrugated iboxes.

The assembly permits conversion of even ;relatively long printing cylinders 10 :the flexographic process, hecause there is a lessened need for .amassive frame to rolls can be removed separately.

The adjustment means preferably includes tieing members which permit the nip adjustment between the wipe roll and the engraved transfer roll to be easily made during assembly. Operating adjustment of the nip is preferably accomplished by suspending the wipe arms from a shaft mounted for eccentric rotation relative to the frame, and by varying the position of the shaft.

The engraved ink trnasfer roll mounting arrangement permits movement of this roll away from the print cylinder during cessation of printing operations, and then movement back into ink-transferring relationship with a minimum of operator adjustment. Further, in preferred embodiments of the invention, the adjustment between the wipe roll and the transfer roll is not disturbed when the transfer roll is moved away from the print cylinder.

The invention consists of the novel methods, parts, constructions, arrangements, combinations, and improvements shown and described. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate certain embodiments and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Of the drawings:

, FIG. I is a schematic perspective view of a flexographic printing assembly;

FIG. 2 is a side elevation view of one embodiment of the flexographic printing assembly of this invention with some elements of the frame not shown for ease of viewing;

FIG. 3 is a vertical section taken along line 33 of FIG. 2 and showing more elements of the frame and drive means than are illustrated in FIG. 2, and omitting the print cylinder for ease of viewing;

FIG. 4 is a vertical section taken along line 44 of FIG. 2 and showing more elements of the frame and drive means than are illustrated in FIG. 2; and

FIG. 5 is a side elevation view of another embodiment of the flexographic printing assembly of this invention with some elements of the frame not shown for ease of viewing.

DETAILED DESCRIPTION OF THE INVENTION FIGS. 1-4 illustrate a flexographic printing assembly constructed in accordance with the invention. FIGS. 1

and 2 show such an assembly installed for use with a print cylinder that is rotatably mounted on a main frame 12 (not shown in FIGS. 1 and 2, but illustrated in FIGS. 3 and 4). The assembly includes as major components a wipe roll 14, an engraved ink transfer roll 16, and a subframe generally 18 (FIG. 2) from which wipe roll 14 and transfer roll 16 are suspended. Subframe 18 is rigidly attached to main frame 12 and is thus held in a fixed position with respect'to print cylinder 10.

In accordance with the invention, a pair of spaced pivot arms are provided which are pivotally mounted on opposing sides of the frame for pivotal movement about a first axis. As here embodied and as illustrated in FIG. 3, a pair of spaced pivot arms 20 are mounted on pivot pins 22 for pivotal motion about the axis of pivot pins. Pivot pins 22 are mounted in a fixed position on subframe 18.

In accordance with the invention, an engraved transfer roll is rotatably mounted between the pivot arms,

and thus is suspended so that its axis can move in an arcuate path into and out of ink transfer contact with the print cylinder.

In the embodiment of FIGS. 2-4, and as best shown in FIG. 3, the ends of engraved ink transfer roll 16 are rotatably mounted in journal boxes 24 mounted on pivot amrs 20. A suitable engraved ink transfer roll is sold under the registered trademark Anilox by the Interchemical Corporation.

Engraved transfer roll 16 is driven by the drive train of the print cylinder so that its surface rotates at the speed of the surface of the print cylinder. As illustrated in FIG. 3, a drive shaft 26 extends from the transfer roll 16 through one pivot arm 20, through an opening 27 in main frame 12, through a journal housing 28, and extends into an overrum clutch 30. Power is transmitted to shaft 26(a) from an idler gear 32, mounted on bracket 34 that is suspended from housing 28, (b) to a transfer roll gear 36 that is driven by idler gear 32, (c) from transfer roll gear 36 to overrun clutch 30, and (d) from clutch 30 to shaft 26. The lower end of bracket 34 is fixed on the frame by a torque nut (not shown).

Idler gear 32 is driven by a second idler gear (not shown) that, in turn, is driven by a gear mounted on the axis of the print cylinder. Overrun clutch 30 prevents shaft 26 from exerting torque on gear 36 during a cessation of printing operations as explained in more detail below.

In accordance with the invention, a pair of spaced wipe arms are pivotally mounted on the frame. The wipe arms suspend a wipe roll so that the wipe roll forms a nip with the ink transfer roll as seen in FIG. 2. Preferably, the wipe arms are mounted and dimensioned to maintain the distance between these two rolls the same even when the transfer roll is moved away from the print cylinder. Thus, readjustment of the clearance between the ink transfer roll and the wipe roll is usually unnecessary even after a shutdown of printing operations and the automatic movement of the ink transfer roll away from the print cylinder.

As illustrated in FIG. 4, a pair of spaced wipe arms 40 are pivotally mounted on a pair of spaced lengths 41 of adjusting shaft 42. Lengths 41 are mounted for eccentric rotation relative to frame 18 as described below. The axis 44 of lengths 41 is offset from the axis 46 of a pair of horizontally aligned eccentric housings 50 and 52. Eccentric housings 50 and 52 are fixed on shaft 42 for rotation therewith and are rotatably mounted relative to frame 18 by bearings 53. Thus, torque exerted on a handwheel 48 will act through a conventional drive train generally 54 including a flexible coupling 56 to adjust the position of axis 44, about which wipe arms 40 pivot, with respect to transfer roll 16. It should be noted that eccentric housing 50 forms one hub of flexible coupling 56.

In accordance with the invention, adjustment means are provided for adjusting and maintaining a nip between said wipe roll and said transfer roll. In the embodiment of FIGS. 2-4, the adjustment means comprise a pair of length-adjustable tie members 58. As illustrated in FIG. 2, each tie member 58 is pivotally mounted on a pin 60 on one wipe arm 40 and pivotally mounted on a pin 62 on an adjacent pivot arm 20. The adjustment means also includes eccentric adjusting shaft 42 on which wipe arms 40 are pivotally mounted as described above. Eccentric adjusting shaft 42 permits making operating adjustments to change the ink film thickness on the engraved roll.

As illustrated in FIG. 2, the distance between the axis of said transfer roll 16 and the axis of pivot pin 22, and the distance between the axis of wipe roll 14 and the axis of shaft 42 are substantially equal, and the distance between (a) the pivot axis 61 of each tie member 58 about the pivot arm 20 on which it is mounted, and the axis of pivot pin 22, and (b) the distance between the pivot axis 63 of each tie member 58 about the wipe arm 40 on which it is mounted and the axis of shaft 42 are substantially equal. Further, the distance between the axis of shaft 42 and the axis of pin 22 and the distance between axes 61 and 63 is substantially equal. The above-described arrangement helps maintain the proper nip relationship between the transfer roll and the wipe roll.

In accordance with the invention, stop means are provided for limiting the pivotal motion of the pivot arms and for thus limiting the approach of the transfer roll towards the print cylinder. In the embodiment illustrated in FIGS. 2-4, and as seen in FIG. 3, the stop means are position adjustable and comprise wear collars 68 concentrically mounted on an adjusting shaft 72 (described in detail below). A bolt 64 is mounted on each pivot arm 20 with bolts 64 engaging wear collars 68, to limit pivotal movement of the pivot arms.

One end of shaft 72 extends through an eccentric coupling hub 74 and the other end extends through an eccentric hub 76 as seen in FIG. 3. Hubs 74 and 76 are aligned and are fixed on shaft72 for rotation therewith. The axis of revolution 78 of the'hubs is spaced from the axis of revolution 80 of shaft 72.

Coupling hub 74 forms part of a flexible coupling generally 82 and is rotatably mounted on frame 18 by bearing 83, with hub 76 being rotatably mounted on frame 18 by bearing 84 as illustrated in FIG. 3. Coupling 82 is rotated by a miter-gear assembly 86 that, in turn, is driven by a handwheel (not shown) for adjustment purposes. Thus, shaft 72 is mounted for eccentric rotation relative to frame 18.

In accordance with the invention, force applying means are provided for exerting on the pivot arms a first moment arm that is capable of pivoting the pivot arms and moving the transfer roll out of ink transfer relationship with the print cylinder; and releasable actuating means are provided'for exerting a second moment arm on the pivot arms. The second moment arm is made capable of overcoming the first moment arm to rotate the pivot arms into engagement with the stop means and thus hold the transfer roll in fixed relationship with the print cylinder during printing operations. The release of the actuating means permits the force applying means to movethe transfer roll out of contact with the print cylinder.

In the embodiment of FIGS. 2-4, the force applying means comprises a resilient means and specifically a pair of compression spring assemblies generally 90, with one assembly 90 interposed between each wipe arm 40 and each pivot arm 20 and seated therebetween as illustrated in FIG. 2. "Spring assembly 90 exerts a force on projection 92 of pivot arm 20 that tends to pivot arm 20 in a clockwise direction about pivot pin 22 and thus tends to move transfer roll 16 out of contact with print cylinder. Spring assembly 90 also exerts a force on wipe arm 40 with this force tending to pivot wipe arm 40 in a clockwise direction about eccentric shaft 42.

In the embodiment of FIGS. 2-4, and as illustrated. in, FIG. 2, the releasable actuating means comprise a pair of air actuators generally 94 including a retractable ram 96 that can be urged into contact with pivot arm 20 to exert a releasable force on the pivot arm. The releasable force exerts a releasable moment arm that rotates pivot arm 20 in a counterclockwise direction into engagement with the stop means, and specifically wear collar 68 (illustrated in FIG. 3). Ram 96 can be retracted to permit spring assembly to rotate pivot arm 20 in a clockwise direction and thus move transfer roll 16 to the left and up, and out of ink transfer contact with print cylinder 10.

In accordance with the invention, ink supply means are provided for feeding ink to the nip formed by the wipe roll and the engraved ink transfer roll. As here embodied and as schematically illustrated in FIG. 1, the ink supply means is conventional and comprises a pump 100, a supply tank 102, an ink feed line 104 for supplying ink to a nozzle 106, collection means 108 for collecting ink that overflows the ends of transfer roll 16 and wipe roll 14, and a return line 110 connecting collection means 108 and pump 100. Ink is constantly circulated to nozzle 106 by pump 100 and recirculated to the pump by gravity flow.

With reference to FIG. 4, it can be seen that drive means are provided for driving wipe roll 14 independently of the drive train of the print cylinder. (The print cylinder drive train drives transfer roll 16 as described above.) Wipe roll 14 is driven by a motor 112 (illustrated in FIG. 1) that is rigidly mounted on frame 18. A conventional drive train 1 14 is provided for transmitting torque from the motor 112 to a flexible coupling 116 mounted on a stub shaft 118 which extends from wipe roll 14. Motor 112 normally drives wipe roll l4v both during printing operations and during short interruption in the rotation of the print cylinder. Thus, wipe roll 14 and transfer roll 16, due to its frictional contact with wipe roll 14, continue to rotate during such an interruption, and are maintained in a state of readiness for the resumption of printing operations.

Overrun clutch 30 prevents rotation of transfer roll 16, due to frictional engagement with wipe roll 14, from driving print cylinder 10 when torque is not being transmitted from the main drive system to print cylinder 10 as illustrated in FIG. 3.

In the embodiment illustrated in FIGS. 2-4, ,a disengage stop means is mounted on the frame for engaging the pivot arms and limiting the pivotal motion of the transfer roll away from the print-cylinder. In practice, the stop means are usually adjustedso the transfer roll clears the print cylinder by about l/8 inch. As illustrated in FIG. 2, the stop means comprises a'threaded bolt 120 that is mounted in a threaded opening of element 122 of frame 18. The position of bolt 120 is thus adjusted by advancing or retracting the threaded bolt in the threaded opening.

FIG. I schematiclaly illustrates the operation of a flexographic printing system. Sheets to, be printed are fed to the nip formed by roll and cylinder '10having a printing die 132 mounted thereon. Ink is transferred to the printing dieby engraved ink transferroll 16 which forms a nip with wipe roll 14, which preferably is a rubber roll.

In the flexographic process, hydraulic pressure on the ink, generated mainly by the dynamic flow of ink along the roll contact area, is compensated by the contact pressure between wipe roll 14 and engraved transfer roll 16 to regulate the ink film thickness on transfer roll 16.

A roll adjusting procedure which can be used in the assembly of the flexographic printing system of FIGS. 2-4 will now be described. As illustrated in FIG. 2, the force of gravity urges transfer roll 16 towards print cylinder by tending to cause pivot arms to rotate in a counterclockwise direction. Similarly, gravity urges transfer arms 40 to pivot in a counterclockwise direction in the absence of other forces. Thus, gravity will tend to align the rolls in the position shown in FIG. 2.

The length of tie members 58 is adjusted with eccentric shaft 42 in a mid position to permit wipe roll 14 and engraved transfer roll 16 to touch. The adjustable stop means, eccentric shaft 72 having wear collars 68 mounted thereon, is positioned to limit the travel of engraved transfer roll 16 toward the surface of print cylinder 10.

Each spring assembly 90 is capable of exerting an adjustable amount of force on the pivot arm 20 and the wipe arm 40 it engages because threaded bolt 124, extending through a threaded opening in wipe arm 40, and seated on plate 126 can advance and retract the plate with respect to projection 92 on pivot arm 20. During the roll adjusting procedure, spring assembly 90 is adjusted to provide a sufficient force to rotate the rolls l4 and 16 and arms 20 and 40 away from print cylinder 10. i

The disengage stop means are adjusted to limit the travel of the rolls l4 and 16 away from print cylinder 10. This is a screw adjustment made by advancing or retracting bolt 120 in the threaded opening in frame element 122.

Operating adjustments of the roll psoitions can be accomplished as described below. The thickness of the film of ink on engraved transfer roll 16 is controlled by rotating adjusting shaft 42 by means of force transmitted by an adjusting handwheel (not shown) that rotates miter gear assembly 86 and flexible coupling 82 which is coupled to shaft 42.

Adjustment of the transfer of ink to the printing die is accomplished by rotating eccentric shaft 72 which changes the clearance tolerance between the printing die mounted on pivot cylinder 10 and transfer roll 16 by stopping the actuator-induced movement of the transfer roll towards print cylinder 10 at the desired position.

In starting up a printing operation, air actuator 94 forces rolls 14 and 16 towards print cylinder 10and into an operating position. In forcing rolls 14 and 16 towards the print cylinder, the moment arm exerted by actuator 94 overcomes the moment arms exerted by spring assembly 90 on rolls l4 and 16.

By releasing air pressure acting on actuator 94, the spring forces exerted by spring assembly 90 pivot arms 20 and 40 and move rolls l4 and 16 until pivot arm 20 engages stop means 120. At this time, the entire assembly has retracted and is spaced clear of the printing die.

The unique mounting arrangement and linkage is arranged so that the relative position and adjustment of wipe roll 14 and engraved transfer roll 16 are not significantly changed by the controlled movement towards or away from the printing die. Thus, these rolls do not need to be reset or readjusted before resumption of printing.

FIG. 5 illustrates another embodiment of the invention in which a wipe roll 14 and an engraved transfer roll 16 are rotatably mounted, respectively, on the lower end of a pair of wipe arms 40 and the lower end of a pair of pivot arms 20. Arms 40 and arms 20 are, respectively, pivotally mounted on pivot pins 124 and 126. Pivot pins 124 and 126 are attached to frame elements (not shown) and are held in a fixed position relative to print cylinder 10. It should be understood that FIG. 5 illustrates the mounting arrangement at one end of rolls 14 and 16, and that the mounting arrangement at the other end of the rolls is identical.

In the embodiment of FIG. 5, the axis of transfer roll 16 is movable in an arcuate path with respect to print cylinder 10 due to the pivotal movement of pivot arms 20. The center of gravity of transfer roll 16 exerts about pivot pin 126 a momentarm, which is passive for reasons discussed below, that tends to move the surface of transfer roll 16 in a clockwise direction towards print cylinder 10. The center of gravity of wipe roll 14 exerts a first moment arm about pivot pin 124 that moves wipe roll 14 in a counterclockwise direction towards transfer roll 16.

Through the mounting arrangement of rolls 14 and 16 on their respective arms 40 and 20, and the relationship of the axes of rolls l4 and 16 with their respective pivot pins 124 and 126, the first moment arm is made capable of overcoming the passive moment arm. When wipe roll 14 is in contact with transfer roll 16, the first moment arm moves transfer roll 16 out of contact with print cylinder 10.

The adjustment means of the embodiment of FIG. 5 include a pair of adjustable spring loaded tie bars 138. Each tie bar 138 is rigidly attached to the upper end of pivot arm 20. A contact plate 140 having an opening therethrough for insertion of tie bar 138 is seated against wipe arm 40 by a spring 142. Tie bar 138 thus exerts a force producing a moment arm acting in a clockwise direction on wipe arm 40 and in opposition to the counterclockwise first moment arm caused by gravity action on wipe roll 14 and wipe arms 40. Tie bar 138 exerts a force producing a moment arm acting in a clockwise direction that tends to turn pivot arm 20 in a clockwise direction about pin 126, and in opposition to the passive moment arm resulting from gravity acting on transfer roll 16 and pivot arms 20. Each tie bar 138 exerts an equal moment arm on wipe arm 40 and pivot arm 20 since it applies an equal force to each arm and the forces are applied at an equal distance from the pivot axis of each arm. The amount of force exerted by tie bar 138 can be adjusted by advancing or retracting a threaded nut 139 along the threaded tie bar to vary the force exerted by spring 142. The adjustment means also includes a wipe arm pivot stop as described below.

Stop means are provided for limiting the pivotal movement of pivot arms 20 in a clockwise direction, and thus limiting the approach of transfer roll 16 towards print cylinder 10. The stop means comprises a pair of position-adjustable brackets 144, each having a cylindrical stop member 148 mounted thereon. Bracket 144 is pivotally mounted on frame 18 by pin 150. An adjusting screw 154 which is rotatably mounted on frame 18 is seated against each bracket 144 to prevent clockwise rotation of the brackets when a pivot arm 20 is rotated in a clockwisedirection intov contactwith a stop member 148.

A pair of wipe arm pivot stops comprise part of the adjustment means of the embodiment of FIG. 5. Each pivot stop is mounted on pivot arm 20 and comprises a bracket 146 that is pivotally mounted on pivot arm 20 by pin 152, and a stop member 148 mounted on each bracket 146 that prevents clockwise rotation of wipe arm 40 past a defined adjustable point. The position of bracket 146 relative to pivot arm 20 can be adjusted by adjusting screw 154 which is rotatably mounted in threaded engagement with a bracket 155 extending from pivot arm 20.

The force applying means of the embodiment of FIG. comprises the mounting-arrangement of transfer roll 16 and pivot arms'20, and'wipe roll 14 and wipe arms 40 in relation to print cylinder 10. As described above, the illustrated mounting arrangement results in a gravity-induced moment arm that acts on pivot arms 20 to urge transfer roll 16 to move in a counterclockwise di' rection and out of contact with print cylinder 10.

A pair of air actuators 156 exert a second moment arm on each pivot arm 20 with the second moment arm urging pivot arms 20 into engagement with stop member 148 to hold transfer roll 16in fixed ink transfer relationship with print cylinder during printing operations. Retraction of ram 158 by release of air pressure to actuator 156 permits the gravity-induced moment arm that constantly acts on pivot arms when transfer roll 16 is in contact with wipe roll 14 to move transfer roll 16 out of ink transfer contact with print cylinder 10.

Disengage stop means comprising a pair of threaded bolts 160 are provided for engaging pivot arms 20 and limiting the movement of transfer roll 16 away from print cylinder 10 upon release of the force applied by actuator 156.

Operatingadjustment of the contact relationship between rolls 14 and 16, and roll 16 and print cylinder 10 in the embodiment of FIG. 5 is provided by eccentric adjusting shafts 162 and 164, respectively.

Eccentric shaft 164 extends between pivot arms 20 and is mounted on the pivot arms for eccentric rotation relative to the pivot arms. It is eccentric shaft 164 that contacts stop member 148 when the pivot arm 20 is pivoted in a clockwise direction. Thus, adjustment of the position of eccentric shaft 164 adjusts the distance between transfer roll 16 and print cylinder 10, and the transfer of ink to the printing die.

Similarly, eccentric shaft 162 extends between wipe arms 40 and is mounted on the wipe arms for eccentric rotation relative to the wipe arms. Eccentric shaft 162 constitutes part of the adjusting means for making operating adjustments on the nip between wipe roll 14 and transfer roll 16. Adjustment of the position of eccentric shaft 162, which contacts stop member 148 attached on arm 20, adjusts the position of wipe roll 14 relative to transfer roll 16.

Preferably, eccentric shafts 162 and 164 can be rotated by operator-controlled hand wheels (not shown in FIG. 5) which operate a drive train similar to that illustrated in FIG. 4.

In the embodiment of FIG. 5, the drive means for wipe roll 14 is a motor that drives wipe roll 14 through a structure similar to that illustrated in FIG. 4 for driving the wipe roll in that embodiment, and the drive means for engraved transfer roll 16 =comprisesa gear and clutch arrangement as illustrated in FIG. 3.

The invention in its broader aspects is not limited to the specific details shownand described. Departures;

pivotally mounted on opposing sides of said frame for pivotal movement about a first axis;

C. an engraved transfer roll having eachend rotat ably mounted on the lower end of one of said pivot arms, theaxis of said transfer roll being movable in an arcuate path with respect to the print cylinder due to the pivotal mounting of saidvpivot arms with the center of gravity of said transfer roll exertinga passive moment arm tending to move saidvtransfer roll towards the print cylinder;

D. a pair of spaced wipe arms pivotally mounted on said frame for movement about a second axis parallel to said first axis;

E. a wipe roll having each end rotatably. mounted on the lower end of one of said wipe arms, the center of gravity of said wipe roll exerting a first moment arm that moves said wipe roll into contact with said transfer roll with said first moment arm capable of overcoming said passive moment arm when said wipe roll and said transfer roll are in contact to thereby move said transfer roll out of contact with said print cylinder;

F. a pair of adjustable spring-loaded tie bars, each of said tie bars connecting the upper end of one of said wipe arms and the upper end of one of said pivot arms for exerting on each of said one wipe arm and said one pivot arm a force creating a moment arm that opposes the gravity-induced moment arm applied to the respective wipe arm and pivot arm;

G. stop means mounted on said frame for engaging said pivot arms to limit the pivotal movement. of said pivot arms and thus limit the approach of said transfer roll towards said print cylinder;

H. releasable actuating means for exerting a releasable second moment arm on said pivot arms that can overcome said first moment arm and thus to,- tate said pivot arms into engagement with said stop means to hold said transfer roll in fixed ink transfer relationship with the print cylinder during printing operations, with the release of said actuating means permitting said first moment arm to move said transfer roll out of contact with the print cylinder; and

I. supply means for feeding ink to the nip formed by the wipe roll and the engraved transfer roll.

2. The printing assembly of claim 1 including an cecentric shaft extending between said pivot arms, and mounted on said pivot arms for eccentric rotation relative to said pivot arms, said eccentric shaft engaging said stop means mounted on said frame, for adjusting the distance between said transfer roll and said print cylinder during printing operations.

4. The printing assembly of claim 1 including a disengage stop means mounted on said frame for engaging said pivot arms and limiting the pivotal motion of said transfer roll away from the print cylinder upon release of said actuating means.

Claims (4)

1. A flexographic printing assembly for supplying ink to a print cylinder comprising: A. a frame held in fixed position with respect to the print cylinder; B. a pair of spaced pivot arms, said pivot arms being pivotally mounted on opposing sides of said frame for pivotal movement about a first axis; C. an engraved transfer roll having each end rotatably mounted on the lower end of one of said pivot arms, the axis of said transfer roll being movable in an arcuate path with respect to the print cylinder due to the pivotal mounting of said pivot arms with the center of gravity of said transfer roll exerting a passive moment arm tending to move said transfer roll towards the print cylinder; D. a pair of spaced wipe arms pivotally mounted on said frame for movement about a second axis parallel to said first axis; E. a wipe roll having each end rotatably mounted on the lower end of one of said wipe arms, the center of gravity of said wipe roll exerting a first moment arm that moves said wipe roll into contact with said transfer roll with said first moment arm capable of overcoming said passive moment arm when said wipe roll and said transfer roll are in contact to thereby move said transfer roll out of contact with said print cylinder; F. a pair of adjustable spring-loaded tie bars, each of said tie bars connecting the upper end of one of said wipe arms and the upper end of one of said pivot arms for exerting on each of said one wipe arm and said one pivot arm a force creating a moment arm that opposes the gravity-induced moment arm applied to the respective wipe arm and pivot arm; G. stop means mounted on said frame for engaging said pivot arms to limit the pivotal movement of said pivot arms and thus limit the approach of said transfer roll towards said print cylinder; H. releasable actuating means for exerting a releasable second moment arm on said pivot arms that can overcome said first moment arm and thus rotate said pivot arms into engagement with said stop means to hold said transfer roll in fixed ink transfer relationship with the print cylinder during printing operations, with the release of said actuating means permitting said first moment arm to move said transfer roll out of contact with the print cylinder; and I. supply means for feeding ink to the nip formed by the wipe roll and the engraved transfer roll.

2. The printing assembly of claim 1 including an eccentric shaft extending between said pivot arms, and mounted on said pivot arms for eccentric rotation relative to said pivot arms, said eccentric shaft engaging said stop means mounted on said frame, for adjusting the distance between said transfer roll and said print cylinder during printing operations.

3. The printing assembly of claim 2 including an eccentric adjusting shaft extending between said wipe arms, and mounted on said wipe arms for eccentric rotation relative to said wipe arms, said eccentric adjusting shaft engaging said stop means on said pivot arms for permitting the operating adjustment of the nip between said transfer roll and said wipe roll.

4. The printing assembly of claim 1 including a disengage stop means mounted on said frame for engaging said pivot arms and limiting the pivotal motion of said transfer roll away from the print cylinder upon release of said actuating means.

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