GB2236097A - Sheet handling devices - Google Patents

Abstract

A sheet handling device includes a rotatable suction feeder 2 which cyclically accelerates sheets to a run-on registration drum 5 as described in GB 2166419. Sheets are then fed to at least one dual cylinder 6 with printing nip 8. Delivery system comprises belts 12 with sucker bars 13 supplying stock 15. in the embodiment of Figure 2, 3 dual cylinders are arranged. In the embodiment of Figure 3 sheets are accelerated in two stages by feeders (20, 21), and thence fed to head and side registration drums (22, 23). <IMAGE>

Description

"Sheet Handling Devices The invention relates to an apparatus and a process for handling individual sheets of thin material, for example paper, which is brought to a machine in the form of a single sheet or a stack of sheets and which the machine may form or re-form into a stack after processing. In particular but not exclusively it relates to machines, e.g., printing presses, in which the process performed requires highly accurate positioning involving, typically, the printing of successive images superimposed in a precise relationship to each other.

The invention has special relevance to offset litho presses in which an image is transferred from a moistened and inked plate to an intermediate surface (known as a blanket) and from there to the sheet being printed. In such presses, the plate and blanket are fixed to the circumferential surfaces of revolving cylinders which roll upon each other. The paper passes between the blanket surface and a third surface, the counter-pressure surface, which squeezes the sheet with considerable force against the blanket in order that the image will be completely transferred.

Hitherto, with one exception, such presses have comprised three separate cylinders for the plate, blanket and counter-pressure functions. The cylinders have been mounted between side frames, the whole being constructed strongly to minimize the deflection caused by the high forces between the cylinders. As a consequence, the cylinders have always been relatively inaccessible for inspection and servicing, and actual replacement of a cylinder has been a long and arduous task.

Also, the operating speed of such presses has been severely limited by the delicacy of the registration process and by the intermittent motions of the mechanisms involved. Because of this the maximum speed of sheet-fed presses is limited relative to that of web-fed presses.

Another problem with present-day sheet fed presses is the complexity and potential unreliability of the feeder which separates the sheets from the feed stack and advances them one by one into the machine. This arises from the fact that with systems where high precision is necessary each sheet, after feeding, is brought to a halt and then released into the machine at a precise time.

This means that at high feed rates (say over 10,000 sheets per hour) the sheets must be made to overlap before arriving at the registration mechanism, otherwise they could not be accurately, satisfactorily and consistently halted because the speed of a single sheet would be too high. The desired overlapping is achieved by the precise timing of the sheet pick-up mechanism, but the resulting overlap leaves only the rear part of the sheet exposed, so the feeder must engage the sheet at its rear end only and push it forwards, in most cases assisted by air jets. With such an arrangement, there is always the danger of the sheet's buckling because the leading part fails to move forward with the rear part.

A further drawback of present-day multicolour or perfector machines is the complex mechanism required to transfer the sheet from one printing module (i.e. plate, counter pressure and blanket cylinders with associated inking devices) to another while preserving register.

This mechanism normally comprises three transfer cylinders, each with cam operated grippers elaborately contrived to allow the sheet to be reversed, if desired, so that the second module prints on the reverse side of the sheet.

The object of the present invention is to reduce or eliminate disadvantages associated with traditional machines, while allowing sheets to be processed at a considerably higher speed.

According to one aspect of the invention, there is provided a sheet handling, especially printing, apparatus comprising a rotatable sheet feeder that in operation acts upon the leading edge of a first sheet in an array of sheets and accelerates the sheet to a first speed, the speed being sufficiently great that the distance between the leading edge of one sheet and the trailing edge of the preceding sheet is greater than the sheet length, and a registration device for effecting headlay and sidelay registration on the sheet while transporting the sheet from the feeder to a further handling stage, and, optionally, a combined plate and counter-pressure cylinder ("dual cylinder").

Such cylinders are more fully described in British Patent Specification No. 541,215 (Davidson), to which the reader is referred for more detailed information.

As used in this specification, the term "dual cylinder" includes any printing cylinder in which the image surface occupies less than half the circumference and a portion of the remainder provides a counterpressure surface.

The invention also comprises a sheet handling process using such apparatus.

Advantageously, the sheet feeder comprises at least one set, and preferably at least two sets, of pick up means, for example suckers, arranged to rotate so as to start substantially from rest in a first position where the leading edge region of a sheet is taken up, to accelerate it to reach a first speed at a second position, where the sheet is released, and eventually to return to the first position. In the preferred embodiment, two sets of such means, the term suckers being used herein for ease of reference, are mounted in diametrically opposed locations on a shaft, and the takeup position and the release position are separated by less than 180", preferably by about 90", so that the feeder accelerates from rest to maximum speed and slows down to rest every half turn.

In one embodiment of the invention, there is provided a two stage feeder, in which a feeder as described above transfers the sheets to a second rotating feeder, advantageously provided with a single set of suckers, and operating, if required, at a speed of rotation and having a diameter such that transfer of a sheet from each of the two sets of suckers on the first feeder is effected to the single set of suckers on the second feeder. If desired, the second feeder may accelerate the sheet to a second speed.

In other, presently preferred, embodiments, the first feeder transfers the sheets directly to a registration device. The registration device is advantageously one which effects both sidelay and frontlay, preferably simultaneously, and preferably without stopping the sheet, while transferring the sheet to the dual cylinder.

Advantageously, the device is one constructed in accordance with the description of British Patent Specification No. 2166419, but other devices, e.g. a belt system as described in more detail with reference to Fig.

4 below, are also suitable.

According to the invention, a sheet feeder separates the top sheet of the infeed stack (by known means) and immediately accelerates it to a very high speed corresponding to the surface speed of the printing cylinders. This speed is so high that the gap between successive sheets is greater than the sheet length. The sheet is then registered at full speed by a device according to British Patent No. 2166419 or similar means. The high speed brings three benefits: (a) the sheet is cleared from the stack so quickly that a "front feeder", which pulls the sheet, may be used.

(b) the sheet may be passed 360 round a cylinder (for registration or other purposes) without interference from the succeeding sheet.

(c) a combined plate and counter-pressure cylinder may be used.

This combined cylinder, known as a dual cylinder, has a circumference more than twice the sheet length.

The inked image is transferred from the plate surface to an adjacent blanket cylinder (whose circumference is half that of the dual cylinder) and on to the paper which is passed between the blanket cylinder and counter pressure section of the dual cylinder.

While the dual cylinder concept is not new, according to the present invention it is used in novel combinations of one or more dual cylinders and/or with other known or novel devices.

The first of these is in combination with an on the run registration system as described above. The second is a combination with another dual cylinder to provide direct transfer for printing on both sides of the sheet ("perfecting") and, if desired, to repeat the sequence with any number of cylinders. Perfecting is very inconvenient with conventional cylinder configurations unless special transfer drums are provided. It may, however, be done easily and elegantly with dual cylinders as proposed here. It is also possible for a single impression/colour machine to be converted to a perfector quickly and on the customer's premises by adding the second module.

The present invention accordingly also provides a printing assembly comprising at least two dual cylinders each provided with a blanket cylinder and an inking device, which may include moistening means.

Advantageously, the dual cylinders are supported on a single frame, preferably at one end of each cylinder only. The cylinders may be arranged so that, in operation, they or, where there are three or more, adjacent cylinders, are in contact and are capable of transferring a sheet direct from one cylinder to the other, or to the next cylinder.

In other embodiments, transfer cylinders are provided to transfer a sheet from one dual cylinder to the next. The third novel use of the dual cylinder is to create a geometry in which the point of transfer of the image on the paper is well separated from the point of subsequent transfer of the paper off the counter surface.

This allows the image to be almost completely printed before the sheet begins to be transferred, and this has two advantages: (a) it prevents the formation of "stripoff marks" caused by the sheet starting to be transferred while it is still being printed, and (b) greatly reduces the force required to be exerted by the stripping grippers and thus allows the stripping and delivery mechanism to be of a lighter construction incorporating toothed belts, thereby avoiding the need for chains, which are noisy, greasy and dirty.

Accordingly, the present invention further provides a printing apparatus comprising a dual cylinder, a blanket cylinder, and a take-off device, the take-off device being so arranged that its point of take-off is located at a point on the dual cylinder at least 1000 from the location of the blanket roller, preferably at least 120 , measured around the circumference of the dual cylinder.

The invention also provides a printing process which comprises printing an image from a blanket cylinder onto a sheet positioned on a dual cylinder, and stripping the printed sheet from the dual cylinder in such a manner that the sheet remains on the dual cylinder until it has travelled at least 100 , advantageously at least 120", from the nip of the cylinders.

A fourth novel application of the dual cylinder exploits its relatively large periphery and the fact that only two cylinders are required for offset printing.

This enables the printing machine to be constructed sothat working parts are not hung between frames but are cantilevered from a single frame, giving major advantages in ease and accuracy of construction, visibility and accessibility for operation and maintenance. It is particularly suited to the "long format" presentation and gives a better view of the printed sheet from the operating side of the machine. The cantilever approach allows the machine user to perform all observations, operations, and adjustments, including loading and unloading, from one side of the machine. Because of the resulting accessibility, a greater degree of automation is possible, for example it becomes practical for all adjustments required for a sheet size change to be motorized and activated at a single command.In addition, the parts requiring adjustment, including inking and damping systems, may be mounted in such a way that one adjustment does not influence another. The outer ends of the cantilevered cylinders may if desired or required be supported by small removable structures capable of withstanding the high forces applied to certain cylinders.

Several forms of apparatus constructed in accordance with the invention will now be described in greater detail, by way of example only, with reference to the accompanying drawings in which: Fig. 1 illustrates a printing machine with a sheet feeder, in-line registry, dual cylinder, and take-off device; Fig. 2 illustrates a machine similar to that of Fig.

1, with three dual cylinders; Fig. 3 illustrates a machine similar to that of Fig.

1, but with a second sheet feeder device; and Fig. 4 illustrates a machine similar to that of Fig. 3 but with a different registration device and with two dual cylinders.

Referring now to the drawings, in which the circles mainly represent rotatable cylinders or the pitch circles of driving gears, and more especially to Fig. 1, there is shown an offset litho press, capable of printing a single colour, which is provided with sheets of paper from a stack 1 by a feeder indicated generally by the reference numeral 2. The feeder 2 comprises sets of conventional "search suckers'1 4 and 4', timed by conventional means and adapted to move in a circular path coincident with the edge of disks 52 which are mounted on a rotating shaft 3 for assistance in guiding the sheet to a register drum 5. This shaft is provided with a means (such as an epicyclic linkage, a Geneva motion or a programmed servo motor) such that it comes to rest in the position shown, i.e., with one set of suckers in contact with the first sheet in the stack 1, is smoothly accelerated to a maximum speed in approximately one quarter of a turn, then decelerated and brought to rest again after a total rotation of half a turn. This half turn coincides with one cycle of the press, and the maximum peripheral speed attained is equal to the peripheral speed of a dual cylinder 6. The two sets of suckers 4 and 4' alternately engage the topmost sheet of the stack and accelerate it to meet the register drum 5.

The radius created by the sucker mounted on the sucker leg may have any value up to two thirds of the maximum sheet length to be used. The radius should be as long as conveniently possible, thereby reducing the acceleration applied to the sheet. After the accelerating quarter turn, the sheet is drawn away by the register drum at a constant speed while the sucker decelerates to rest in its second quarter turn. For a given sucker path radius, the acceleration may be chosen to match the sheet speed required, i.e., such that the gap between sheets is slightly greater than the sheet length. As an alternative embodiment, intermittent or timed suction may be used to assist or effect the required timing and positioning.

On reaching drum 5, the sheet is engaged and registered by the means described in British Patent No.

2166419 in the course of which the leading edge of the sheet traces one and a half revolutions. On its arrival against the dual cylinder 6, it coincides with grippers 7 mounted on the latter, which engage the leading 5 mm of the sheet and cause it to be drawn over the counterpressure surface of the dual cylinder and through the printing "nip" 8 between it and blanket cylinder 9. If it is of maximum length the sheet covers about 3/8ths of the peripheral surface of the dual cylinder 6 and consequently has been almost completely printed before the leading edge reaches the point 10 where a delivery system indicated generally by the reference numeral 11 takes the sheet from the dual cylinder 6. The system 11 comprises toothed belts 12 carrying two or more sucker bars 13.Because they do not have to accelerate the sheet, these suckers can be much smaller than suckers 4 and 4'. They are arranged as a row of small holes which engage the 5mm gripper margin at the leading edge of the sheet, drawing it away to position 15. Here the suction is released and the sheet is delivered to the top of the delivery stack 16, striking plate 17 as it falls.

Figure 2 shows how two further dual cylinders 18 and 19 may be interposed between the dual cylinder 6 and the delivery system 11, allowing a single colour machine to be upgraded to a capability of three printed images (including if required up to three different colours) in one pass, one image being on the reverse side of the sheet. The user can of course instantly choose a 2colour mode (either one side only or "perfect") by disengaging the printing mode of any one of the three dual cylinders.

Figure 3 shows an alternative configuration for the feeding and registration systems which may be convenient in certain cases. The acceleration is performed in two successive stages by the suckers 20, 20', and the suckers 21, whose drives are geared together so that suckers 21 perform a complete revolution during the half revolution of suckers 20, 20'. The sheet reaches maximum speed as its leading edge arrives at the drum 22. Drums 22 and 23 perform the sidelay and headlay functions respectively, according to the same principles as the single drum in British Patent No. 2166419.

Figure 4 shows an alternative configuration which would have advantages in certain applications. The sheet passes from a 2-stage feeder 20, 20', 21 to a system of propulsion belts 24 passing over a curved guide 25. The curvature causes the sheet to be gripped at every point along the belts, which are slightly inclined so as to urge the sheet sideways and register it against a fixed surface or another belt moving at the same speed but in a true path, i.e. perpendicular to the axis of the main cylinder.

The effect is to register the sheet sideways, substantially in the manner described in British Patent No. 2166419. The sheet then passes between belts 26 and a drum 27, upon which headlay register is established, again substantially as described in the above Patent specification. The sheet then passes between a cylinder 28 and a blanket cylinder 29, afterwards being delivered, in a similar manner to that described above, by the suitably located belt and sucker system 30.

This configuration more nearly resembles a conventional chain delivery system. It also allows convenient simultaneous inspection of the plate and blanket, and a sample tray 31 may be arranged to receive a single sheet by early release of the dual cylinder grippers.

Figure 4 also shows how two printing modules of this type may be combined to provide an option for either 2 colour or "perfect". For 2-colour printing, transfer drums 32 are employed. For perfecting, second dual cylinder 33 and the delivery system 30 are driven in the opposite direction and the paper is transferred by drums 35.

All configurations described above can be adapted for direct litho operation by the use of an undercut counter pressure segment on the dual cylinder.

Claims (5)

What we claim is:

1. A sheet handling apparatus comprising a rotatable sheet feeder that in operation acts upon the leading edge of a first sheet in an array of sheets and accelerates the sheet to a first speed, the speed being sufficiently great that the distance between the leading edge of one sheet and the trailing edge of the preceding sheet is greater than the sheet length, and a registration device for effecting headlay and side lay registration of the sheet on the run while transporting the sheet from the feeder to a further handling stage, and, a combined image and counter-pressure cylinder.

2. A printing assembly comprising at least two dual cylinders directly juxtaposed each provided with a blanket cylinder and an inking device, supported on a common frame.

3. A printing apparatus comprising a dual cylinder, a blanket cylinder, and a take-off device, the take-off device being so arranged that its point of takeoff is located at a point on the dual cylinder at least 100 from the nip between the blanket cylinder and the counter pressure cylinder.

4. A sheet-fed printing apparatus comprising sheet feeding means, sheet registering means, at least one dual cylinder, and sheet receiving means, the dual cylinder or cylinders being cantilevered from a frame and supported thereby substantially at one end only of the cylinder or cylinders.

5. Any new feature hereinbefore described or any new combination of hereinbefore described features.