US2846947A - Gripper control for sheet printing machines - Google Patents

Description

1.958 A. RODENHAUSEN 2,846,947

GRIPPER CONTROL FOR SHEET PRINTING MACHINES Filed April 19, 1955 Br M 191 r'oRNEF GRIPPER CONTROL FOR SHEET PRINTING MACHINES Andreas Rodenhausen, Ofienbach am Main, Germany, assignor to Faber & Schleicher Akfiengesellschaft, Offenbach am Main, Germany, a German body corporate Application April 19, 1955, Serial No. 502,299

Claims priority, application Germany May 5, 1954 2 Claims. (Cl. 101-409) Grippers such as are used in sheet printing machines serve the purpose of transferring each sheet in complete registry with the printing mechanism through the machine in order either to deposit it onto the delivery stack or to pass it correctly on to a subsequent printing machine. One condition for the proper transfer of the sheet rests in that each gripper must hold the sheet indisplaceably fast or, in other words, the clamping force exerted by the gripper on the sheet must be larger, even under adverse conditions, than all other forces acting on the sheet during its transfer, and it is a known fact that these forces vary considerably in their magnitudes. For instance, during the passage of the front edge of the sheet from the feeding table to the printing zone, these forces are constituted practically only by the, mass of the sheet acting in opposition to its being accelerated to the circumferential velocity of the cylinder and by some slight amounts of friction. This condition, however, becomes fundamentally different after the front edge of the sheet has passed through the printing zone, when it has to be pulled away from the printing form, or from the rubber :blanket in the case of an offset printing machine for example. The pulling forces to Which the sheet is then objected, are considerable, particularly when tacky colors and high printing speeds are used, in which case there is always a tendency of the sheets adhering to the form, or blanket, and to be pulled out of the bite of the grippers. These pulling forces are strongest when the front edge of the sheet is just about leaving the printing zone, and they become smaller the farther the front edge of the sheet moves away from the printing zone, since with an increasing enwrapping angle the friction of the sheet on the cylinder grows accordingly and thereby enhances the action of the grippers.

It has been tried to counteract this undesirable effect by strengthening the gripper closing springs so that, especially in the case of individually spring-controlled grippers, all of the grippers would securely hold the sheets under even the most unfavorable conditions and incorrect adjustment. This exigency, however, has another undesirable effect which consists in that the whole gripper arrangement gets overstrained and the machine begins to run irregular, which in many cases is well apt to mar the prints or to exert other unfavorable influences on the operation of the machine.-

Other gripper arrangements have been known, in which individually spring-controlled grippers are moved positively into their closed position by cam-controlled means. In these ca es one spring only had tobe relied on for opening all grippers in common. This spring acted in opposition to the gripper closing device and thus caused the control cam to be considerably overstrained.

Now, in view of the aforesaid disadvantages, the main object of the invention is the provision of a gripper control for sheet printing machines in which these disadvantages are eliminated and in which means are provided for temporarily varying the effective pressure on ates, Patent F 2,846,947 Patented Aug. 12, 1958 ICC the closed grippers during a complete working cycle of the machine in accordance with the requirements.

Another and more specific object of the invention rests in the provision of means by which the pressure of the gripper on the sheet will always be suited to the varying tensile strains which act on the sheet in the course of a working cycle.

A further object of the invention is the provision of means for enabling a quiet, regular operation of the control cams by extending the application of the turning moment in the direction of gripper closing over a considerably larger portion of the cylinder revolution than heretofore.

A still further object of the invention rests in the arrangement of the aforementioned means so that they will serve for both the cylinder grippers and for the chain grippers in a sheet printing machine.

With these and other objects in view the invention substantially consists in the provision of appropriate means for so intensifying the gripper pressure during the passage of the sheet from the feed table to the printing zone of the machine as to enable the front edge of the sheet to be held sufficiently fast after the sheet has left the printing zone. With increasing distance of the said front edge from the printing zone the pressure on the gripper may be allowed to become less again.

In one embodiment of the invention the aforesaid variation in the pressure on the gripper in the course of a working cycle of the machine can beobtained in connection with individually spring-controlled grippers which, in a manner known per se, are supported on a rocking shaft which is turned in gripper closing direction by spring means, as by the gripper shaft being given an additional turn, or twist, by means of a positively acting gear at always the correct time interval when the grippers are in their closed position. In this way a relatively weak gripper closing spring has been found sufiicient for the actuation of the gripper shaft, and a quiet, even run of the machine is ensured.

In a modification of the aforementioned embodiment of the invention and in connection also with individually spring-controlled grippers mounted in known manner on a shaft which is yieldingly oscillated as by means of a spring, the force of this spring is periodically varied so as would correspond in each case to the requirements of gripper pressure. If a higher pressure is required, the force exerted by the spring is increased, as for instance by further compressing the spring if a compression spring is used. Reversedly, when in the opening period of the gripper, the gripper shaft is under the influence of the gripper opening cam, it can be obtained by suitably shaping the control cam of the spring power changing gear, so that the force exerted by the spring remains constant or becomes even less. This eliminates a further disadvantage which is felt in some of the known gripper arrangements and which consistsv in that the turning moment acting on the gripper shaft in its gripper closing direction is smallest when the grippers are closed, while it rises wholly unnecessarily when the grippers begin to open.

The accompanying drawings illustrate by way of example the application of the invention to the controlling arrangement of the cylinder grippers of a printing ma chine in a more diagrammatic way. It is to be understood, that the same or a similar arrangement would also apply to the chain grippers which are used for carrying a sheet from one printing machine to another. In these draw- 1ngs,

Fig. 1 represents a front view, partly in section, of the new gripper control, and

Fig. 2 a cross section on line AA of Fig. 1.

In the embodiment of the invention which is shown in Figs. 1 and 2 the numeral 1 designates an end wall of the impression or printing cylinder of a sheet printing machine, in which is journaled the gripper shaft 2 upon which the individually spring-controlled grippers 4 are freely turnable. In Fig. 1 they are shown to rest with their free ends upon the gripper bars 3. A two-arm lever 5 is keyed to the shaft 2 and, with one of its arms, is placed under the action of a compression spring 6 which tends to turn the shaft in clockwise direction and.

thereby to turn also a clamping member 7 so that a spring 8, which is interposed between the eye 26 of the loosely turnable gripper and the hook 27 on the fast clamping member 7, holds the gripper firmly down to the gripper bar 3.

The spring 6 is carried on a rod 9 and with its free end rests against a lug 10 which is pivoted to the end face of the cylinder ll, while the head of the rod is pivoted by a bolt 11 to the outwardly extending arm of lever 5. Turnable at the free end of the other arm of lever 5 on a pin 12 is a roller 13 which cooperates in known manner with a cam piece 15 on the side wall 14 of the machine in such a manner as to turn the gripper shaft 2 in counterclockwise direction and to thereby open the gripper when the sheetis to be released.

In accordance with the invention, a second control cam 16 is provided which is also fixed to the side wall of the machine and which is so shaped as to act at a predetermined interval on the roller 13 so as to positively impart to the shaft 2 an additional turning moment in gripper closing direction. This movement causes the spring 8, which is subjected to tension, to extend and to thus increase the pressure of the grippers 4 on the gripper bar 3. This second cam 16 extends preferably all around the cylinder, except at the place of the cam 15, and it thus ensures a firm gripping action of the grippers on the gripper bar 3.

Although in the foregoing specification a circumferential cam has been described to control the variations in the gripper pressure, it is to be understood that other means, such as a gear for example or a different kind of cam, may be used for the same purpose without thereby departing from the spirit of the invention as described and as will now be pointed out in the following claims.

What I claim is:

1. In a machine for printing on sheets having a rotary printing cylinder and spring-actuated grippers associated with said printing cylinder for gripping the sheets and transferring them through the machine, a rocking shaft for the said grippers on which they are loosely mounted, a clamp on said rocking shaft, a spring acting on the said rocking shaft over, the said clamp to move said grippers into closing position, cam means in fixed relation on the printing machine for opening the grippers against the action of said spring, other springs for exerting an additional turning moment in gripper closing direction on the said grippers, a stationary control cam on the printing machine for varying-the tension of said other springs,

and a cam follower lever connected to the said springs for transmitting the pressure of said control cam to the said other springs and to thereby increase the pressure on the grippers while the said grippers are closed.

2. In a machine for printing on sheets having a rotary printing cylinder and individually springactuated grippers associated with the said printing cylinder for seizing the sheets and transferring them through the machine, a rocking shaft for loosely mounting the said grippers, a clamp on the said rocking shaft, a gripper spring acting on the said rocking shaft and the said clamp tending to move the said grippers into closing position, a cam stationary on the frame of the printing machine for opening said grippers against the action of the said gripper spring, other springs for exerting a turning movement in gripper closing direction on the said grippers, another stationary cam on the frame of the printing machine substantially conforming to the circumference of the circumference of the printing cylinder for varying the tension of said other springs, and a cam follower lever connected to the said other springs for transmitting the movement initiated by the said second cam to the grippers so as temporarily to increase the closing pressure on the grippers during the closing period of the latter.

References Cited in the file of this patent UNITED STATES PATENTS

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