Sheet-conveying drum for skew register correction

A sheet-conveying drum for skew register correction in multicolor printing that does not affect the drive in sheet-fed rotary presses. The sheet-conveying drum comprises gripper bars and support or carrying webs that are disposed on a drum shaft. The web disposed nearest the drive input has on its flange an arcuate bearing surface around which the drum body can be skewed relatively to the drum shaft. The web disposed opposite the drive input is coupled to an adjusting eccentric bushing by way of a flange to cause the drum to skew. The movements of drum skewing do not adversely affect the drive and, therefore, the transmission ratios of the sheet-guiding cylinders relative to one another.

FIELD OF INVENTION 
The invention relates generally to printing presses, and more specifically 
to drums for conveying sheets through such presses. 
BACKGROUND OF THE INVENTION 
In the printing of multicolor images on printed sheets, care must be taken 
to ensure that the subimages register accurately with one another. 
Orientation lengthwise and laterally of the image can be provided by means 
of conventional peripheral and lateral register devices on sheet-fed 
presses. However, the skew of the image cannot readily be corrected by 
these means. Consequently, transfer devices have been developed that 
permit skewing of the printed sheets as they are conveyed through the 
press so that the sheets are properly oriented for accurate subimage 
registration. 
A device of this kind is disclosed in DE-OS 3 400 652. The aim of the 
sheet-fed press disclosed therein is to enable a correcting cylinder to be 
adjusted at its control side or end relative to its set-value or reference 
position. Therefore, the axis of the correcting cylinder is skewed as a 
whole relative to the adjacent cylinders. Placement of the skew adjuster 
on the control side permits better control and reduces assembly costs. 
The disadvantage of the device disclosed in DE-0S 3 400 652 is that the 
skewing affects the transmission of drive mechanisms. Displacing the 
cylinder always causes a skewing, and, in the worst case, even a 
displacement of a gear in the drive train relative to the adjacent gears. 
This is true whether the cylinder is displaced directly on the 
transmission side or on the opposite side, although the position in this 
connection is not known. Thus, although the device improves sheet 
transfer, it likewise increases problems in the drive train. 
DE-C1 37 04 314 discloses an arrangement for adjusting tooth backlash 
between the drive gears of sheet-conveying rollers and drums of sheet-fed 
rotary presses wherein eccentric bushings are provided at both ends for 
the mounting of each drum. The bushings provide parallel displacement of 
the drums to adjust the backlash during operation. The arrangement does 
not provide for skewing the drums and skewing cannot be effected without 
upsetting drive ratios. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of the invention to provide a skewable sheet-conveying drum 
for conveying sheets through a press which does not affect drive gear 
engagement by the additional skewing action on sheet register adjustment. 
It is a more specific object of the invention to provide, a device for 
conveying sheets through a press which obviates any change in drive ratios 
as a result of skewing of a sheet-conveying drum. 
In accordance with the invention, the drive shaft of a sheet-conveying drum 
is non-displaceably mounted at one end within a bearing on the input side 
of the drum. The drum is mounted for translational movement such that the 
drum body is pivotable about the axis of the input bearing. This isolation 
of the pivoted parts of the drum from the input gear permits skew 
correction by drum or cylinder skewing in a broad range of applications. 
More particularly, the invention simplifies the procedure for correction 
of skew. Moreover, the invention has a significant effect on bearing 
loading and drive ratio accuracy. The invention permits the input gear and 
the bearing of the input journal to remain in their respective positions 
during skewing. Indeed, in one embodiment of the invention, the entire 
drum mounting can remain in its original position. Therefore, the drum 
does not require expensive bearings and means for guiding the same during 
displacements. 
Various embodiments of the invention which isolate the skewing movement in 
a sheet-conveying drum from the drum input bearing or drum input gear are 
discussed below, however, the invention is not intended to be limited to 
those embodiments. In one embodiment, the drum shaft has elements that 
move one end radially in relation to the axis of the input bearing, which 
is radially and peripherally immobile. In another embodiment, a skewable, 
but generally rigid drum body is disposed on a rigid drum shaft. 
These and other features and advantages of the invention will be more 
readily apparent upon reading the following description of a preferred 
exemplified embodiment of the invention and upon reference to the 
accompanying drawings wherein:

While the invention will be described and disclosed in connection with 
certain preferred embodiments and procedures, it is not intended to limit 
the invention to those specific embodiments. Rather it is intended to 
cover all such alternative embodiments and modifications as fall within 
the spirit and scope of the invention. 
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention will be described by way of example hereinafter with 
reference to illustrations. The alteration in the position of the drum 
body and the axis thereof is shown in dotted lines in the respective 
FIGURES. 
FIG. 1 shows a sheet-conveying drum 1 according to the invention. The drum 
1 comprises an input journal 2 and an output journal 3, and support webs 
4, 5, which are flanged on to the journals 2, 3, respectively. Gripper 
bars 6, 7, which convey the sheets, are provided between the webs 4 and 5. 
The journals 2, 3 are mounted in bearings 8, 9, respectively, in frame 
elements, or the press wall 10. An input or drive gear 11 is secured to 
input journal 2. At the opposite end an adjusting eccentric bushing 12 is 
also provided on the bearing 9 to enable the drum shaft to be pivoted. 
Rotation of the eccentric bushing 12 by means of a drive (not shown) skews 
the position of the drum shaft through a pivoting angle at point S from 
its normal position, as indicated by a dotted line in FIG. 1. The point S 
is disposed on the drum shaft at the inner edge of the input journal 2. In 
order to prevent the input gear 11 from tilting as the drum shaft tilts, a 
coupler having a lower resistance to radial movement than the input 
journal 2 is provided at the junction between the input-end web 4 and the 
journal 2. The coupler permits the web 4 to tilt relative to the journal 
2, however, the coupler does not permit relative rotary and radial 
movement of the web 4 and the journal 2. 
FIG. 2 shows the construction of the junction in the connection between the 
web 4 and the input journal 2. It will be appreciated that the input 
journal 2 carries the input gear 11 and is guided in the bearing 8. The 
web 4 is disposed at the inner end of the journal 2 and is connected 
thereto by way of an annular coupling diaphragm 13. The diaphragm is 
connected to the inner end face of the input journal 2 and to the inner 
periphery of the web 4 by means of uniformly distributed sets of 
connecting screws 14. The web 4 and the input journal 2, therefore, remain 
flush with one another, axial movements being substantially obviated. 
However, the diaphragm 13 permits bending around the connection. 
Referring to FIG. 3, there is shown an enlarged, fragmentary view of the 
diaphragm 13 and the junction between the web 4 and the input journal 2. 
The inner peripheral surface 26 of the web 4, which is disposed opposite 
the outer peripheral surface 15 of the input journal 2, is arcuate in 
cross-section--i.e., axially of the drum 1. In this way, the web 4 
contacts the input journal 2 in a substantially linear manner along its 
peripheral surface 15. When the eccentric bushing 12 is adjusted, the drum 
body and, therefore, the web 4 are skewed relatively to the input journal 
2. The skewing occurs in a fixed plane determined by the eccentric bushing 
12 and lies substantially perpendicularly to the plane connecting the axes 
of sheet-guiding cylinders, such as impression cylinders of a sheet-fed 
offset press, cooperating with the drum As seen radially, therefore, the 
diaphragm 13 experiences axial resilient deformation in its central zone, 
the web 4 rocking or "rolling" by way of its arcuate inner peripheral 
surface 26 on the outer peripheral surface 15 of the input journal 2. 
Since the pivoting plane is static, the deflection at the junction between 
the input journal 2 and the web 4 rotates relatively to the drum 1 in 
accordance with the rotational movement. However, the total movement is 
minimal. For an eccentricity of, for example, 5 mm at the eccentric 
bushing 12, a pivoting distance of approximately 5/100 mm is likely at the 
interface of the diaphragm 13 and the web 4 and can readily be taken up by 
the diaphragm 13. The actual pivoting distances are much smaller since the 
adjustments are in the region of 1/10 mm. The pivoting of the web 4 and 
the flexing of the diaphragm 13 are shown in dotted lines in the enlarged 
fragmentary view shown in FIG. 3. 
FIG. 4 shows an alternate embodiment of the invention in which the drum 
body is skewed on a continuous drum shaft 16. To this end the drum body is 
mounted by way of webs 17, 18 at two places on the drum shaft 16, the webs 
17, 18 being connected to the drum shaft 16 in peripherally rigid manner. 
At the end remote from the input gear 11, adjusting eccentric bushing 19 
is provided between the web 18 and the shaft 16. The adjusting eccentric 
bushing 19 enables the drum member to be skewed relatively to the drum 
shaft 16. To obviate bending of the shaft 16 due to the skewing of the web 
17, the web 17 has an arcuate bearing surface 20 associated with the shaft 
16. By displacing the web 18 and shifting its center, the web 17 rolls at 
the input end on its arcuate bearing surface 20. Thus, the drum skews 
sheet transfer without bending of the drum shaft 16. The webs 17, 18 are 
secured by way of flange 21, 22 to the shaft 16 and rigidly connected 
peripherally thereto by pins 23, 24. An appropriate adjusting drive can be 
disposed either to rotate on the web 18 or to be stationary on press frame 
25 with a coupling transmission extending through the shaft 16. 
In yet another embodiment of the invention, a groove 27 is provided in the 
shaft in the transition between the journal and the drum body, as 
indicated by dotted lines in FIG. 5. The groove 27 permits flexing of the 
shaft at this place to skew the drum body without flexing the bearing and 
the input gear.