Printing – Rolling contact machines – Rotary
Reexamination Certificate
2000-10-13
2004-04-20
Nolan, Jr., Charles H. (Department: 2854)
Printing
Rolling contact machines
Rotary
C101S232000, C101S246000, C101S408000, C101S409000, C271S082000, C271S204000, C271S206000, C271S277000
Reexamination Certificate
active
06722276
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a device for turning sheets in a sheet-fed rotary printing machine in which the device has a storage drum for handling sheets and a turning drum disposed downstream of the storage drum for turning the sheets.
German Patent DE 44 24 968 C2 discloses a turning device of the type discussed above which has a storage drum, on the outer lateral surface of which a plurality of sheets are held. In a direction of movement of the sheets, a turning drum, which has a holding device for engaging a rear edge of the sheet to be turned, is disposed downstream of the storage drum. The configuration of the storage drum and the turning drum is selected such that their lateral surfaces virtually touch one another at a tangent point. The storage drum has a first blowing device, with the aid of which a stream of blast air can be applied to the sheet which has already been taken hold of by the holding device, in order to press the sheet off the storage drum, assisting with the operation of turning the sheet. Moreover, to assist with the turning operation, a second blowing device is provided above the tangent point, with the aid of which air can be blown into the tangent point in order to press the sheet to be turned downward and thus to assist with detaching the sheet from the storage drum.
By detaching the sheet to be turned from the circumference of the storage drum and conveying it onward with the aid of the turning drum, air situated in the turning area is entrained by the sheet, resulting in a local pressure reduction which acts on the next sheet, which is held on the circumferential surface of the storage drum with the aid of the holding device and as a result may be at least partially lifted off the storage drum. Consequently, an in-register transfer of the sheets from the storage drum to the turning drum cannot be ensured in all cases. This occurs because, when turning the rear edge of sheets, to ensure an in-register transfer of the sheet stored on the storage drum, in particular in the case of face-side printing and perfecting, it is necessary to produce precise conditions for the entire path of the stored sheet. For this purpose, the sheet is usually clamped on the storage drum surface at the rear edge by clamping suckers, so that all the sheets come to rest in exactly the same position during the storage operation. In the case of half-turn storage drums, the uniformity of the two halves of the storage drum is ensured by an accurately ground surface. However, perfect transfer of the sheet stored in this way is only ensured if the sheet can be held in this state or position by the clamping suckers. However, this is not the case with a high printing capacity, which may, for example, amount to 15,000 sheets per hour.
With a printing capacity which is as high as this, with only approximately 0.1 second between the instant at which the leading sheet is detached and that at which the next sheet enters the reduced-pressure zone, it is impossible for sufficient air to flow into the reduced-pressure zone which is formed between the turning drum and the storage drum in the space between the turning drum and the storage drum. The blast streams from the first and second blowing devices of the known turning device, which serve to assist with the turning operation, cannot sufficiently reduce the pressure reduction which is active in the turning area, since the blast-air stream of the second blowing device disposed above the tangent point, owing to the very small space between the storage drum and the turning drum, can only reach the turning area lying beneath the tangent point in a weakened form, if at all. The first blowing device disposed in the storage drum is only active for a very short time in order to lift the sheet resting on the storage drum at its rear-edge area. Also, the pressure differences that are customary with blast air and the outlet cross sections of the blowing nozzles are too small to compensate for the pressure reduction that is generated.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide devices for turning sheets in a sheet-fed rotary printing machine which overcome the above-mentioned disadvantages of the prior art devices of this general type, in which an in-register transfer of the sheet stored on the circumferential surface of the storage drum can be ensured even at a high press speed.
With the foregoing and other objects in view there is provided, in accordance with the invention, a sheet turning device for a sheet-fed rotary printing machine. The sheet turning device is formed of a storage drum for handling at least two sheets and has at least one holding device for each of the sheets; and a turning drum disposed downstream of the storage drum and has at least one holding device for engaging a rear edge of a sheet of the sheets to be turned. An operation of detaching the sheet to be turned from the storage drum and carrying it along by the turning drum leads to a formation of a pressure reduction in a reduced-pressure area formed between the sheet to be turned, the storage drum and the turning drum. The turning drum has a lateral surface with at least one channel formed therein in which air can be at least one of sucked from and blown into the reduced-pressure area.
The device is distinguished by the fact that at least one channel and/or at least one passage orifice is connected to an inner chamber of the turning drum, via which channel and/or passage orifice air can be sucked and/or blown into the reduced-pressure area. A free cross section of flow of the channel running, for example, in the circumferential direction of the turning drum and, if appropriate, that of the passage orifice are sufficiently large for a pressure reduction which is formed in the area between the storage drum. The turning drum and the sheet to be turned as a result of the sheet to be turned being detached from the storage drum and as a result of the turning operation to be able to suck in at least enough air through the channel and/or the passage orifice for it to be possible to prevent the next sheet, which is resting on the outer circumferential surface of the storage drum, from being lifted off. In this variant, it is possible to dispense with blowing devices which supply blast air and/or compressed air to the reduced-pressure area, a fact which simplifies the structure of the turning device. In another variant, at least one blast-air/compressed-air supply device is provided, which, by way of example, supplies the inner chamber of the turning drum with blast air or compressed air which passes via the passage orifice in the turning-drum lateral surface, into the reduced-pressure area. The at least one passage orifice is disposed downstream—as seen in the direction of rotation of the turning drum—of the holding device which holds the rear edge of the sheet to be turned and is provided on the turning drum. As an alternative or in addition, it is also possible for a blast-air/compressed-air stream to be introduced into the reduced-pressure area via the channel. A common feature of all these exemplary embodiments is that the incoming flow of air via the channel and/or the passage orifice into the reduced-pressure area is at least assisted by the pressure reduction acting in that area.
According to a refinement of the invention, at least one wall of the channel is formed at least in part by a flattened section made in the lateral surface of the turning drum. In connection with the present invention, the term “flattened section” is understood as meaning a planar or substantially planar area on a circular or curved surface. In an advantageous embodiment, the turning drum, in the region of the flattened section, has for the most part a substantially round cross section, the channel wall having a different, preferably smaller radius of curvature, at least in its area disposed upstream of the flattened section—as seen in the direction of flow of the air—from the turning drum.
In accordance with an a
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Locher Ralph E.
Nolan, Jr. Charles H.
Stemer Werner H.
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