1. In a damping unit of an offset printing machine having a support and a plate cylinder, the damping unit including two applicator rollers, a transfer roller in simultaneous rolling engagement with said applicator rollers, a distributor roller in rolling contact with only one of said applicator rollers, said cylinder and said rollers being mounted on said support for rotation about respective axes extending in a common direction, and moving means for moving said applicator rollers between an operative position of rolling engagement with a plate fastened on said cylinder and an inoperative position remote from said cylinder, the improvement which comprises:
2. In a unit as set forth in claim 1, said guide means including two guide members mounted on said support, each guide member being formed with two slots respectively receiving the bearings on corresponding axial ends of said applicator rollers in guiding engagement, said slots defining said paths respectively.
3. In a unit as set forth in claim 2, the path of at least said one applicator member being straight, and said paths converging in a direction away from said cylinder, said hanger member being pivotally mounted on said support.
4. In a unit as set forth in claim 3, said moving means including an arm pivotally mounted on said support and two abutment members mounted on said arm in engagement with respective bearings in said two slots, the abutment members moving the engaged bearings in the associated slots when said arm pivots on said support; and control means for pivoting said arm.
5. In a unit as set forth in claim 4, said control means including a shaft journaled in said support, said arm and another arm being mounted on said shaft and extending radially from the same, said other arm carrying a cam follower, and the control means further including a cam member movably mounted on said support and engaging said cam follower.
6. In a unit as set forth in claim 4, said slots being open in a direction away from said plate cylinder, said hanger means biasing said bearings of the applicator rollers toward said cylinder in the associated slots, and said abutment members engaging said bearings in said two slots in a direction to move the same toward the open ends of the slots against the restraint of said hanger means.
BACKGROUND OF THE INVENTION
This invention relates to offset printing machines and particularly to the positions and movements of the several rollers in the damping unit of such a machine.
It is normal practice to provide a damping unit with two plate dampers or applicator rollers which simultaneously engage circumferentially offset portions of the plate cylinder of the machine, or of a plate fastened on the cylinder. The applicator rollers usually cooperate with the circumferential portion of the plate cylinder which moves mainly upward during normal printing operations, and the invention will be described with reference to such an arrangement.
In early offset printing machines, both applicator rollers are provided with damping fluid from a common distributor roller. Because of the rolling contact between the several rollers mentioned and the plate cylinder in which relative circumferential movement at the point of contact is avoided, it is inherent in such an arrangement that most damping fluid is transferred from the distributor roller to the plate cylinder by the upper applicator roller while the useful functions of the applicator roller are minimal.
To make proper use of both applicator rollers, modern offset printing machines are arranged for rolling contact between the distributor roller and the lower applicator roller only, and a transfer roller simultaneously engaging the two applicator rollers supplies the upper applicator roller with fluid taken from the lower roller after contact of the latter with the plate cylinder. When properly adjusted and maintained, such a unit deposits a much more uniform film of damping fluid on a plate fastened to the plating cylinder than the earlier arrangement, and produces superior printed work. However, the known damping units of this type are quite complex and it is difficult to maintain the necessary uniform contact pressures between the several rollers and the plate cylinder.
A primary object of this invention is the provision of a damping unit of the last-described type which is simple in its structure, yet reliable in its operation. Other objects will become apparent as the disclosure proceeds.
SUMMARY OF THE INVENTION
In the damping unit of the invention, the bearings of the applicator rollers are engaged by guides which guide the axes of rotation of the rollers in respective paths toward and away from the plate cylinder when the bearings are moved relative to the guides by a moving mechanism. The distributor roller is mounted on the supporting structure of the printing machine for rotation about a normally fixed axis which is located in the following manner: A plane is drawn through a point bisecting the path traveled by the axis of the applicator roller directly engaged by the distributor roller between the operative and inoperative positions at an angle of 88° to 92° to that path, and the axis of the distributor roller is located in that plane. The transfer roller is held in rolling contact with both applicator rollers during their movements between the operative and inoperative positions by a suitably biased hanger having a recess in which a bearing of the transfer roller is movably received.
Other features, additional objects, and many of the attendant advantages of this invention will readily become apparent from the following description of a preferred embodiment when considered in connection with the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 shows a damping unit of the invention in side elevational section on the line I-I in FIG. 2;
FIG. 2 illustrates the unit in front-elevational section on the line II-II in FIG. 1; and
FIG. 3 shows the unit in side elevation taken in the direction of the arrow III in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The drawings show as much of an offset printing machine as is necessary for an understanding of the invention and the machine may be entirely convention in its nonillustrated features.
The supporting stationary frame of the machine is represented in the drawings by an upright sidewall 2 on which a bracket 1 is releasably mounted in an adjustable, but normally fixed position. The bracket 1 has two guide slots 3,4 which are vertically spaced. The upper guide slot 3 slidably receives a bearing 5 of an upper applicator roller or plate damper 6 and permits the axis of rotation of the roller to be shifted in a path which is nearly horizontal. The bearing 7 of a lower applicator roller 8 moves in the slot 4 in a more nearly vertical path. The paths of the bearings 5,7 converge at an angle of 45°.
The drawings show only the axial end portions of the rollers 6,8 near the sidewall 2, and it will be understood that the rollers extend over almost the entire width of the machine, and are journaled in another set of bearings symmetrical to the bearings 5,7 and similarly supported. The description of the damping unit will be limited hereinafter to the illustrated side of the machine, and it will be understood that every feature shown and described is duplicated on the nonillustrated side with obvious exceptions.
A distributor roller 9 is rotatably supported in a recess of a bracket 10, and is normally retained in the recess by a screw 11. The bracket 10 is pivotally mounted on a flanged bushing 12 attached to the sidewall 2 by screws 13 passing through the flange of the bushing. The angular position of the bracket 10, and thus the location of the axis of rotation S1 of the distributor roller 9, may be adjusted by means of an abutment 14 threadedly mounted on a bar 15 which projects from the wall 2, but the bracket 10 is fixed in normal operation of the printing machine in such a manner that the cylindrical face of the distributor roller 9 makes rolling contact with the lower applicator roller 8. The distributor roller 9 is driven by gears 35 connected with the main drive shaft of the machine in a conventional manner, not shown.
A shaft 16 is coaxially journaled in the bushing 12. A key 17 secures a radial arm 18 on the shaft 16. Two discs 19 are mounted on the arm 18 and are pressed against the bearings 5,7 respectively by springs 20. Springs 20 secure discs 19 against undesired rotating. When the arm 18 pivots counterclockwise from the position shown in FIG. 2, the bearings 5,7 are pushed by the discs 19 toward the open ends of the guide slots 3,4. The free end of the shaft 16 outside the sidewall 2 is fastened by a pin 21 to another radial arm 22 whose free end carries a pin 23. A cam follower roller 24 is rotatably mounted on the pin 23 and engages a radial cam 25 pivotally mounted on the wall 2 in a nonillustrated manner. The cam 25 is an element of the central control mechanism of the printing machine, not otherwise shown.
The two applicator rollers 6,8 are covered with absorbent cloth as is conventional and not explicitly shown in the drawings, and simultaneously engage an intermediate or transfer roller 26 whose cylindrical face consists of bare metal. The roller 26 floats in the machine, and its bearing 27 is biased toward the applicator rollers 6,8 by a flat hanger 28 pivotally mounted on a pin 29 on the sidewall 2 and having a V-shaped notch 34 whose wall engages the bearing 27. A strong helical tension spring 30 is mounted between a stud 31 on the hanger 28 and another stud 32 on the sidewall 2.
In the position I of the apparatus illustrated in fully drawn lines, both applicator rollers 6,8 engage the partially shown plate cylinder 33 or a printing plate mounted on the cylinder 33. The direction of rotation of the cylinder 33 is clockwise, as viewed in FIG. 2, so that a plate mounted on the cylinder is first engaged by the lower roller 8 and only thereafter by the upper roller 6.
When the control cam 25 is turned from the fully drawn position to that indicated in broken lines, the shaft 16 is pivoted counterclockwise, as viewed in FIG. 2, so that the rollers 6,8 are shifted in the guide slots 3,4 into the inoperative position II in which they are lifted from the plate cylinder 33. The positions I and II of the axis of rotation S2 of the applicator roller 8 are oppositely spaced and equidistant from the intersection between a plane drawn through the axis S1 of the distributor roller 9 and the plane in which the axis S2 moves in the slot 4 during the angular movement of the shaft 16.
Damping fluid is supplied from a nonillustrated fountain tray to the distributor roller 9 by one or more other rollers in a conventional manner, not shown, when the machine is operated and is transmitted from the driven roller 9 to the lower applicator roller 8 as the latter is being rotated by contact with the roller 9. Most of the fluid received by the applicator roller 8 is transferred to a plate on the cylinder 33 in the illustrated position I of the apparatus, the remainder of the fluid being transferred by the intermediate roller 26 to the upper applicator roller 6, and from the latter to the nonillustrated plate on the cylinder 33. The amount of fluid which reaches the plate by way of the upper applicator roller 6 is only a small fraction of the fluid received from the lower roller 8, and it is the primary function of the upper applicator roller to spread the liquid deposited from the lower roller 8 in a film of more uniform thickness.
When printing is interrupted, the cam 25 is turned into the position shown in broken lines, and the resulting angular movement of the shaft 16 causes the bearings 5,7 to be shifted against the restraint of the spring 30 until the applicator rollers 6,8, and the abuttingly engaged transfer roller 26 assume their inoperative position II in which the applicator rollers are radially spaced from the plate cylinder 33 a distance sufficient to prevent contact with a plate on the cylinder.
The contact pressure between the distributor roller 9 and the lower applicator roller 8 is adjusted by means of the threaded abutment 14. The contact pressure between the applicator rollers 6,8 and the plate cylinder 33 in the operative position of the rollers can be adjusted by shifting the discs 19 on the arm 18 by means of the screws holding the discs 19 to the arm. The plane through the axis S1 of the distributor roller 9 which bisects the path of the axis S2 in the slot 4 between the positions I and II intersects that path at an approximately right angle, the magnitude of the angle being preferably limited to the range from 88° to 92°. The planes drawn through the axes S1 and S2 in positions I and II respectively intersect the path of the axis S2 at respective angles of approximately 80° and 100°. The contact pressure between the distributor roller 9 and the applicator roller 8 is therefore identical in positions I and II of the roller 8. Moreover, this contact pressure is not significantly affected when the pressure between the plate cylinder 33 and the applicator rollers is adjusted.
When the hanger 28 is swung away from the applicator rollers 6,8 against the restraint of the spring 30, or after removal of the spring, the intermediate roller 26 drops from the machine, and the plate dampers or applicator rollers 6,8 can be lifted from the slots 3,4, whereby normal maintenance work on the machine is greatly facilitated.
The metallic surface of the intermediate roller 26 tends to collect ink from the absorbent cloth covers of the applicator rollers 6,8 and has been found significantly to increase the useful life of the covers. Because of the equal contact pressure between the distributor roller 9 and the lower applicator roller 8 in the operative position I and in the inoperative position II of the damping unit, the applicator rollers 6,8 can be coated with damping fluid prior to a printing run without removing them from the unit by merely driving the gears 35.