Patent Description:
A rotary printing press having a calibration unit of this type has been disclosed in <CIT>.

The calibration unit is used for adjusting the longitudinal register and side register of each printing cylinder by aligning the position mark with the sensor on the sensor arm. For example, the position mark may be formed by a magnet, and the sensor is a magnetic field sensor outputting an electronic signal that indicates an offset of the magnet relative to the sensor. During the process of a setting the longitudinal and side register, the sensor arm must be held in a position in which the radial direction of the sensor arm coincides with the radial direction from the axis of rotation of the CI (central impression cylinder) and the point of contact between the periphery of the CI and the periphery of the printing cylinder.

In a typical printing press, the printing cylinder in each colour deck is guided for linear motion relative to the CI, so that it can be set against the CI and lifted off from the periphery of the CI. In a typical printing press of this type, the direction of the linear motion of the printing cylinder of at least some of the colour decks forms an angle with the radial direction of the CI. This has the consequence that the point of contact between the printing cylinder and the CI is dependent upon the diameter of the printing cylinder and, accordingly, shifts when the printing cylinder is replaced by a printing cylinder with a different diameter so as to print images with a different repeat. Consequently, the angular position of the sensor arm must be changed in accordance with changes of the diameter of the printing cylinders.

In the known printing press, the arrangement of the colour decks relative to the CI has a <NUM>° symmetry, so that pairs of printing cylinders are disposed diametrically opposite to one another. The calibration unit has two sensor arms that are rigidly connected to one another and extend in opposite directions from the axis of rotation of the CI, so that the register of the two opposite printing cylinders can be adjusted simultaneously. When the register of another pair of printing cylinders is to be adjusted, the sensor arms are rotated into a position in which the sensors are aligned with the points of contact of these printing cylinders.

It is an object of the invention to provide a calibration unit that is suitable for a more efficient register adjustment process.

In order to achieve this object, a calibration unit according to the invention as defined in claim <NUM> is provided, wherein at least two of the sensor arms are interconnected by a drive mechanism configured for controlling a symmetric pivotal movement of the sensor arms with respect to a reference axis which, when the unit is mounted to the frame, is aligned with said axis of symmetry.

In this design, only a single drive mechanism is needed for simultaneously moving two sensor arms which form an angle of less than <NUM>° with one another to their respective target positions. Thus, the calibration unit is suitable for simultaneous register adjustment of two printing cylinders that are not diametrically opposite to one another, and it has the further advantage that the two sensor arms can be moved into the required positions simultaneously. The invention takes advantage of the fact that, in a typical printing press, the arrangement of the colour decks is also mirror-symmetric with respect to at least one axis of symmetry. Consequently, whatever the diameter of the printing cylinders may be, the points of contact of these two printing cylinders will be mirror-symmetric, so that the sensor arms can be adjusted to these positions by a symmetric pivotal movement.

More specific optional features of the invention are indicated in the dependent claims.

The drive mechanism configured for controlling the symmetric pivotal movement of the sensor arms may be constituted for example by a rack-and-pinion drive with two parallel racks meshing with the pinion such that they move in opposite directions when the pinion is rotated. In another embodiment, the drive mechanism comprises two links connected to one another and to each of the two sensor arms by articulated joints, and a linear drive arranged for linear displacement of the joint that interconnects the two links. As in the known calibration unit, pairs of sensor arms that extend in opposite directions from the axis of the CI may be rigidly connected to one another, so that as many as four sensors can be moved into their target positions in a single operation and with only a single drive mechanism.

More generally, if a printing press has a number 2n of colour decks with n being even, only n/<NUM> drive mechanisms are needed for positioning the sensor arms for all colour decks. If the arrangement of the colour decks relative to the CI has more than one axis of symmetry, the drive mechanisms may have different reference axes. For example, the reference axis of one drive mechanism may be horizontal and the reference axis of another drive mechanism may be vertical.

If a printing press has 2n of colour decks with n being odd, it is common practise to arrange the colour decks such that there are two diametrically opposite colour decks in which the direction of linear movement of the printing cylinders is a radial direction of the CI, so that the points of contact are independent from the diameter of the printing cylinders. In this case, the calibration unit may comprise a pair of sensors that are rigidly mounted to the frame for aligning the position marks of the printing cylinders of these two colour decks. The sensor arms for the remaining 2n-<NUM> colour decks may then be arranged in the same manner as described above.

Embodiment examples will now be described in conjunction with the drawings, wherein:.

<FIG> schematically shows essential parts of a rotary printing press, e.g. a flexographic printing press, comprising a central impression cylinder (CI) <NUM> and eight colour decks 12a - <NUM> symmetrically disposed around the periphery of the CI. Each colour deck comprises a printing cylinder <NUM> and an inking cylinder <NUM> (anilox roller). In this specification, the term "printing cylinder" is to designate not only a one-piece printing cylinder but also a coaxial arrangement of one or more sleeves on a mandrel. The peripheral surface of the printing cylinder <NUM>, which carries a printing form, engages the peripheral surface of the CI <NUM> at a point of contact P.

The printing cylinder <NUM> and the inking roller <NUM> of each colour deck are guided for linear movement relative to the CI <NUM> in a direction (horizontal in this example) that forms an angle with the radius from the central axis of the CI to the point of contact P. As a consequence, if the printing cylinders <NUM> are replaced by printing cylinders <NUM>' that have a different diameter, then the point of contact P shifts in circumferential direction of the CI, and this amount of shift is different for different colour decks. For example, in case of the colour deck 12a, the amount of shift is larger than in case of the colour deck 12b, and in case of the colour decks 12c and 12d the point of contact shifts in opposite direction.

In the example shown, the arrangement of the colour decks 12a-<NUM> around the periphery of a CI <NUM> is symmetric with respect to a vertical axis of symmetry V and with respect to a horizontal axis of symmetry H. As a consequence, the positions of the points of contact P are also symmetric under a <NUM>° rotation about the central axis of the CI <NUM>.

The CI <NUM> has a shaft <NUM> that has been shown in cross-section in <FIG> and is supported with its opposite ends in side frames <NUM> of the printing press. These side frames have not been shown in <FIG>, but one of them is visible in a sectional view in <FIG>.

As is well known in the art, the printing cylinders <NUM> of the various colour decks 12a-<NUM> serve for printing superposed images in different colours onto a web that is trained around the periphery of the CI <NUM>. In order for these images to be perfectly aligned with one another, the rotary position of each printing cylinder <NUM> (longitudinal register) and the axial position (side register) of each printing cylinder have to be properly adjusted. For that purpose, a position mark <NUM> (see colour deck 12d in <FIG>) is embedded in the printing cylinder in an end portion that projects beyond the end of the CI <NUM>, and a calibration unit <NUM> is provided for detecting the positions of the position marks <NUM> of all printing cylinders.

As is shown in <FIG>, the calibration unit <NUM> has a star-shaped configuration with four bar-shaped sub-units <NUM> that are rotatably supported on the shaft <NUM> via nested hubs <NUM>. Each sub-unit <NUM> constitutes two sensor arms 30a, 30e; 30b, 30f; 30c, <NUM> and 30d; <NUM>, respectively, that project radially from the hubs <NUM> in opposite directions. Each sensor arm carries at its free end a sensor <NUM> for detecting the magnetic field of the position mark <NUM> of the printing cylinder of an associated colour deck. Each sensor <NUM> points towards the point of contact of the associated printing cylinder and is configured to output an electronic signal indicating the axial and circumferential deviation of the position mark <NUM> from the position of the sensor <NUM>. Thus, the position mark <NUM> can be aligned with the sensor <NUM> by rotating the printing cylinder about it axis and shifting it in axial direction in a process of adjusting the longitudinal register and the side register of the printing cylinder. Since a separate sensor arm 30a-<NUM> is associated with each of the colour decks 12a-<NUM>, the adjustment operations can be performed simultaneously for all colour decks, which has the advantage that the time needed for preparing the printing press for a new print run is greatly reduced, in particular, if the adjustment process is automated.

If the printing cylinders are exchanged by cylinders with a different diameter, the angular positions of the sub units <NUM> have to be shifted in accordance with the shift of the points of contact P.

In view of the symmetry with respect to the vertical axis V, the sub units having the sensor arms 30a, 30e and 30d, <NUM>, respectively, have to be shifted symmetrically, i.e. by the same amount but in opposite directions. This shift is achieved by means of a drive mechanism <NUM> the function of which will be described below with reference to <FIG>. Similarly, in view of the symmetry with respect to the horizontal axis H, another drive mechanism <NUM> is provided for inducing a symmetric shift of the sub-units that comprise the sensor arms 30b, 30f and 30c, <NUM>, respectively.

<FIG> shows the calibration unit <NUM> in the same condition as in <FIG>, with the sub-units aligned with the points of contact P of the printing cylinders <NUM>.

<FIG> shows the calibration unit in a state adapted for the printing cylinders <NUM>' having a smaller diameter. The points of contact have shifted to positions P', and the sub-units of the calibration unit <NUM> have been shifted accordingly.

In order to effect the shift of the sensor arms 30a, 30e, 30d, <NUM>, the drive mechanism <NUM> comprises two links <NUM> connected etween the sensor arms 30d and 30e via articulated joints. The joint that interconnects the two links <NUM> is driven for linear movement in radial direction of the CI by a linear drive having a stationary part <NUM> and a movable part <NUM>. The stationary part <NUM> has a reference axis that defines the direction of movement of the moveable part <NUM>, and it is attached to the frame <NUM> of the printing press (<FIG>) in a position in which the reference axis is aligned with the vertical axis of symmetry V. For example, the movable part <NUM> may comprise a spindle, and the stationary part <NUM> may comprise a nut that is in engagement with the spindle and is driven for rotation by a motor. When, in the situation shown in <FIG>, the movable part <NUM> is withdrawn in a downward movement, the links <NUM> push the sensor arms 30d and 30e apart symmetrically, so that the angle between these sensor arms becomes larger. Since the sensor arm 30d is rigidly connected to the sensor arm <NUM> and the sensor arm 30e is rigidly connected to the sensor arm 30a, the angle between the sensor arms 30a and <NUM> is increased by the same amount. In this way, the angular positions of the sub-units <NUM> can be adjusted to the respectively desired positions with high accuracy. When the diameter of the printing cylinders <NUM>, <NUM>' is known, the positions of the points P, P' of contact and, accordingly, the target positions of the sub-units <NUM> can be calculated and the sub-units can be adjusted to these positions with high accuracy.

The drive mechanism <NUM> for the sensor arms 30b, 30c, 30f and <NUM> has the same design as the drive mechanism <NUM>, with the only difference that the stationary part <NUM> is aligned with the horizontal axis of symmetry H.

<FIG> is a view of an end portion of the CI <NUM> and a portion of the shaft <NUM> supported in the side frame <NUM> of the printing press on the drive-side, i.e. the side where a drive motor (not shown) is arranged for driving the shaft <NUM>. The calibration unit <NUM> is accommodated in a narrow space between the side frame <NUM> and the end of the CI. The sub-units <NUM> on the nested hubs <NUM> are offset from one another in axial direction of the CI, but the sensor arms are configured such that all sensors <NUM> are aligned in a common plane. The sensor arms 30a and 30e are shown in a side view in <FIG>, whereas the sensor arms <NUM>, <NUM> and 30f are shown in slanting views. The other sensor arms 30b, 30c and 30d are shown in sectional views. Also shown in sectional views are the movable part <NUM> and the links <NUM> of the drive mechanism that drives the sensor arms 30d and 30e. A part of the link <NUM> that connects the movable part <NUM> to the sensor arm 30e is also shown in a slanting view.

Near its free end and on the side facing the side frame <NUM>, each sensor arm has a locking member <NUM> that can cooperate with a locking device <NUM> on the side of the frame <NUM> for tightly locking the sensor arm to the frame without altering the angular position of the sensor arm. This assures that the sensors <NUM> can be held stably in position during the register adjustment process.

Thus, the process of adjusting the longitudinal register and side register of all printing cylinders may be performed as follows. When a new set of printing cylinders is to be inserted into the colour decks, the angular positions of the sensor arms 30a-<NUM> are calculated and adjusted on the basis of the known diameter of the printing cylinders. Then, the locking mechanisms <NUM> are actuated to firmly lock or clamp the sensor arms to the side frame <NUM> in the correct angular positions. Once the printing cylinders have been inserted, they are moved linearly against the CI until they engage the CI at their respective point of contact P. Then, the printing cylinders are withdrawn by a small amount, just enough to avoid friction between the printing cylinders and the CI, so that the printing cylinders can be rotated freely. Then, the longitudinal register and the side register of the printing cylinders are adjusted by rotating the printing cylinders about their respective axis and moving them in axial direction until the position mark <NUM> of each printing cylinder is perfectly aligned with the corresponding sensor <NUM>. These processes can be performed in parallel for all printing cylinders, so that the printing press will be ready for starting a print run within short time.

When the printing press has to be prepared for a print run with a different repeat, the locking mechanisms <NUM> will be released and the sensor arms will be adjusted to the new points of contact.

<FIG> shows an example of a calibration unit <NUM>' for a ten-colour printing press, i.e. a printing press wherein the number of colour decks divided by two is an odd number (<NUM>).

Claim 1:
A calibration unit (<NUM>; <NUM>') configured for calibrating a rotary printing press having a central impression cylinder (<NUM>) and a number of colour decks (12a - <NUM>) disposed around the periphery of the central impression cylinder, each colour deck comprising a rotatable printing cylinder (<NUM>; <NUM>') which carries a position mark (<NUM>) and is adapted to be set against the periphery of the central impression cylinder, the arrangement of the colour decks being symmetric with respect to at least one axis of symmetry (V, H), the calibration unit (<NUM>; <NUM>') having a number of sensor arms (30a-<NUM>) each carrying a sensor (<NUM>) for detecting the position mark (<NUM>) of one of the printing cylinders, the calibration unit being adapted to be mounted on a frame (<NUM>) of the printing press such that the sensor arms project radially from the axis of rotation of the central impression cylinder (<NUM>) and are pivotable about that axis independently of the central impression cylinder, characterized in that at least two of the sensor arms (30a-<NUM>; 30b, 30c) are interconnected by a drive mechanism (<NUM>; <NUM>) configured for controlling a symmetric pivotal movement of the sensor arms (30d, 30e; 30b, 30c) with respect to a reference axis which, when the unit is mounted to the frame (<NUM>) is aligned with said axis of symmetry (V; H).