US2997953A - Flat-bed cylinder printing presses - Google Patents

Description

Aug. 29, 1961 P. PAPA ETAL FLAT-BED CYLINDER PRINTING PRESSES 2 Sheets-Sheet 1 Filed March 25, 1954 1iillllIIIIIIIIIIILEUHH!""" P. PAPA ET AL 2,997,953

Aug. 29, 1961 FLAT-BED CYLINDER PRINTING PRESSES 2 Sheets-Sheet 2 Filed March 25. 1954 f/vws/vroks:

United States Patent 2,997,953 FLAT-BED CYLINDER PRINTING PRESSES Paolo Papa and Federico Capetti, Turin, Italy, assignors to Nebiolo Societir per Azioni, Turin, Italy Filed Mar. 25, 1954, Ser. No. 418,589 Claims priority, application Italy Mar. 25, 1953 2 Claims. (Cl. 101-275) This invention relates to flat-bed cylinder printing presses, known as stop-cylinder presses, in which the cylinder rolls over a carriage carrying the printing form during the working or impression stroke and remains stationary during the return stroke of the carriage.

In order to achieve this, the mechanism of the press comprises a drive which transmits a rectilinear reciprocating movement to the carriage and the latter carries a rack which engages with a toothed ring on the cylinder only during the greater part of the working stroke of the carriage, while during the remaining portion of the working stroke and during all the return stroke, the cylinder is disengaged from the carriage and is connected to a separate drive intended to cause the stopping and re-st-arting of the cylinder.

In the known constructions, this drive comprises a rod actuated by cams and articulated to a fork which, in the neighbourhood of the dead points in the impression stroke of the carriage, engages with a pivot carried by the cylinder and transmits to the latter a movement substantially equal to that of the carriage. Consequently, the arcs traversed by one point of the periphery of the cylinder, in the intervals when the latter is disengaged from the carriage, respectively after the beginning and before the end of the impression stroke, correspond almost exactly to the rectilinear lines traversed simultaneously by one point of the carriage.

It follows that the circumference of the cylinder has to be substantially equal to the stroke of the carriage.

At the same time it is known to be advisable to give the impression cylinder the largest possible dimensions for various reasons. For example, there is a known procedure, currently adopted by printers, of varying the theoretical value of the thickness of the covering of the cylinder in order to obtain the desired printing pressure, but thus causing an alteration in the dimensions of the printed impression in relation to the form (shortening and lengthening for cover thicknesses respectively lower and higher than the theoretical value). Now, given the same alteration in the thickness of the covering, and the same development of the impression, the said deformations are less noticeable for greater diameters of the cylinder.

In addition, a cylinder of greater diameter gives rise to a more robust construction, makes it easier to house the various members, etc. However, in the present machines the diameter of the cylinder cannot exceed certain limits determined by the consequent increase in the length of the stroke of the carriage, which gives rise to various disadvantages.

According to the present invention, the diameter of the cylinder is made independent of the stroke of the carriage, thus permitting the cylinder diameter to be increased without it being necessary to extend the stroke of the carriage, in that, between the end of one impression stroke and the beginning of the succeeding impression stroke, the drive to which the cylinder is connected, apart from ensuring the desired period of rest, transmits to the cylinder the angular movement required to bring it into position to be re-engaged by the carriage for direct drive. In this manner, the beginning and the end of the movement of the cylinder can be more gradual than in known constructions while reducing the acceleration of the cylinder in relation to the corresponding acceleration of the carriage, in view of the fact that the initial and final stages of the ice cylinder movement can take place over a fairly long period extending beyond the dead points of the impression stroke of the carriage.

Moreover, since the impression cylinder, and consequently the reversing cylinder, covers a greater peripheral course before stopping, the known disadvantage of the foot of the printed sheet touching the printing form during the halt of the sheet after the printing operation is avoided.

An embodiment of a printing press according to the invention is hereinafter described, by way of example, with reference to the accompanying drawings which are limited to show only the parts of the press necessary to the understanding of the invention and in which:

FIGURE 1 is a partial side elevation of the press;

FIGURE 2 is a partial plan view of the press;

FIGURES 3 and 4 are partial views in elevation showing different operating positions of members of the press mechanism;

FIGURES 5 and 6 are speed and acceleration diagrams for the carriage and the cylinder of a press as a function of the angles of the crank turning at a uniform speed, as obtained respectively in known presses and the press according to the invention;

FIGURE 7 shows a modified form of members of the press mechanism in side elevation.

In FIGURES 1 and 2, 1 represents the frame of the printing press in which is mounted an impression cylinder 2, rotating on pivots 3, and a bed or carriage 4, which can slide on its guides and which is actuated, by means of a lower toothed rack 5, by a toothed wheel 6 which engages with a fixed rack 7 and is moved backwards and forwards by a connecting rod 8 articulated to a crank 9 of the driving shaft 10 of the press.

The cylinder 2 has a circumference appreciably greater than the length of the stroke transmitted to the carriage 4 which carries a rack 11 on top, while the cylinder 2 bears on its periphery, a partially toothed ring 12, the toothed portion of which has a development substantially equal to the length of the rack 11, leaving a smooth stretch the extent of which depends on the length by which the circumference of the cylinder 2 exceeds the length of the stroke of the carriage 4.

The ring 12 is mounted in such a position as to permit it to engage with the rack 1 1 of the carriage 4.

The cylinder 2 is provided with a toothed sector 13 in a different plane from that of the ring 12, while a toothed sector 15 which engages with the sector 13 is pivoted at 14 in the frame 1 of the press. A connecting rod 17, articulated at 16 to the sector 15 is mounted to slide, by means of an aperture 18, on a guide-block 19 rotating freely on the driving shaft 10.

Two cams 20 and 21, the kinematic pro-files of which are complementary, that is to say are such that diametrically opposed points on the two profiles are situated at aconstant distance apart, are fixed on the shaft 10'. Two rollers, 22 and 23, carried by the connecting rod 17, cooperate respectively with the earns 20 and 21, which are arranged on either side of the rod 17, the axes of rotation of said rollers being arranged in such a manner that there is never any play between the rollers and the cam profiles, the latter being traced with lines of constant curvature and variable curvature in such a manner that, as a result of the rotation of the shaft 10, the sector 15 performs an alternating movement with an intermediate period of rest in one of the two strokes. These cam systems are well known.

The toothed arc of the two sectors 13 and 15 should also be of such an extent that, during the rotation of the cylinder 2, said sectors inter-engage at the moment when the ring 12 is about to leave the rack 11 of the carriage and disengage at the moment when said rack is about to engage with the ring 12.

These moments of engagement and disengagement between the sectors 13 and 115; willnaturally be selected in such a manner-asto facilitate the passage from one-transmission to the othenof movement to the cylinder 2. The engagement should take place shortly before me carriage '4 reaches the dead point corresponding to-theend of the impression stroke, in such a manner as to compel the cylinder to slow down and stop after the carriage 4,

. having'reached its dead point, has already initiated its return stroke.

The disengagement should, take place shortly after the carriage 4 has reached its, left-"hand dead point and has 'begunits working or impression stroke.

Thesepositions are illustrated in FIGURES 3 and 4, FIGURE 3 showing the carriage 4 at its right-hand dead point and the cylinder 2 in its resting stage, while FIG- and'the sector 15 is set in oscillation with periods of rest by the cams and 21, the following stages occur:

1) Gradual starting of the cylinder 2 through the action of the sector 15 on the sector 13 to bring the end of the toothed section of the ring 12 into mesh with the rack 11 of the carriage, while the carriage finishes its return stroke (towards the left) and begins the working stroke (towards the right) (FIGURE 4).

(2) Actuation of the cylinder 2 at the same speed as the carriage 4- by the action of the rack 11 on the ring 12 (impression stroke), while. the sector 15, disengaged from the sector 13, completes the return idle.

(3)"Disengagement' of the toothed ring 12 from the rack 11 of the carriage 4 and engagement of the sector 13 with the sector 15; the cylinder gradually stops while the carriage completes its working stroke and begins the return stroke; (4) The cylinder is stationary (the sectors 13 and 15 being still in mesh with one another), while the carriage is in the course of completing the major part of its return stroke. Then stage 1 begins again.

Under the action of the sector 15 driven by the cams 20 and 21, the cylinder 2 is thus kept stationary during a considerable portion of the return stroke of the carriage from the right to the left, while before and after the rest there are two driving periods, which may be more or less progressive, for the gradual passage from the speed to rest, and vice versa.

In FIGURES 5 and 6, where the full-line curves represent speeds and the broken line curves represent accelerations, a comparison is made between the operation of the known presses with a cylinder having a circum ference equal to the stroke of the carriage (FIGURE 5) on the one hand, and the operation of a press according to the invention (FIGURE 6) on the other.

Whereas in the known presses, in which the'circumference of the cylinder ispractically equal to the stroke of the carriage, the speeds and the accelerations. of the cylinder coincide with those of the carriage (FIGURE 5 in the press according to the invention, as seen in FIG- URE 6, the stages of rest and of restarting the cylinder extend considerably beyond the period of time in which the impression stroke of the carriage takes place and which is included between the moments corresponding to the left-hand and right-hand dead points (0 and 180), and during these phases the speed of the cylinder diifers from that of the carriage (lines A B and A 3 in the speed-curve), and ,it can be given any desiredvalue by suitable profiling of the cams 20 and 2.1.

V The average or pitch-circle radii of the sectors 13 and 15 may be equal to or different from one another, constant or variable, for example forming arcs of ellipses,

"parabolas, etc. to obtain the desired transmission ratio.

One example of such. amodification is shown in FIG- URE.7, in which the two toothed sectors 13 and 15 have pitch lines constituted by arcs having variable radii.

The driving members of the cylinder, that is to say the toothed sectors, the toothed ring and the rack of the carriage, may be on one side of the press only or on both sides. The mechanism comprising the toothed sectors 13 and 15, the crankarm 17, and the earns 20 and 21, may be inside or outside the frame of the press.

Finally, the mechanism, 13, 15-, 17, 19, 20, 2.1 may be replaced by any mechanism permitting the succession of movements and rests, necessary for the operation described, tobe transmitted to the sector 15.

Thus it would be possible to use cams acting directly on the sector 15 itself, or eccentrics, tie-rods, push-rods with return springs, etc;

With the press described, it is possible to achieve all the advantages of a large impression cylinder diameter without having to increase thelength of the stroke of thecarriage and at the same time it is possible to ensure a maximum progressiveness and smoothness in the passage from the direct drive of the cylinder to its stopping, and from rest to the succeeding direct drive.

What we claim is:

1. In a stop cylinder printing press, a frame, a main shaft, a reciprocating carriage carrying the printing form and driven by the main shaft, an impression cylinder arranged to make less than a complete revolution during the printing stroke of said carriage and consequently having a circumference substantially greater than the full stroke length of said carriage, driving means on said carriage for driving directly said cylinder during the greater part of the working or printing stroke of said carriage, and a drive for said cylinder comprising a toothed sector on said cylinder, atoothed sector pivoted in said; frame and periodically in engagement with said toothed sector on the cylinder, the two inter-engaging sectors being shaped to insure the required transmission ratio, and a driving member on said main shaft acting on said pivoted sector in a variable manner to produce at' the required moment the deviations in the opposite dimotions and the period of rest, said drive constructed and arranged to engage said cylinder before the end of the working stroke of said carriage, to slow down and to stop said cylinder after the beginning of the return stroke of said carriage, to maintain said cylinder stationary for the period of rest and then to restart said cylinder before the end of the return stroke of said 'carriage, bringing it gradually up to the speed of the direct drive anddisengaging saidcylinder after the beginning of the impression stroke of said carriage, whereby the cylinder makes exactly one turn from the moment it starts rotation to the moment it stops in order to constantly reach the same sheet-gripping position, and where- ReferencesCited in thefile of this patent- UNITED STATES PATENTS 293,678 Scott Feb. 19, 1884 300,370' 'Huber June 17,1884

344,496 Potter June 29, 1886 344,507 Tucker June 291;; 1886 681,253

North Aug. 27-, .1901

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