Method and device for replacing the printing roller of a printing unit of a printing machine

The present invention relates to a device for replacing the printing roller in a printing unit, in particular for in line rotary flexographic machines.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 of PCT/IB2015/053085, filed Apr. 28, 2015, which claims the benefit of Italian Patent Application No. MI2014A000784, filed Apr. 29, 2014.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device for replacing the printing roller in a printing unit, in particular for in-line rotary flexographic machines.

BACKGROUND OF THE INVENTION

At present, in the printing sector, and in particular in the sector of printing labels and flexible wrappings, there exists a very urgent need to increase the general efficiency of the printing processes, on the one hand reducing the printing time and on the other hand limiting the wastage of material, such as the printing medium.

In particular, the step of changing the printing rollers is one of the most critical steps in the entire printing process since the so-called “job change-over” times constitute downtime, during which the printing process is substantially interrupted. Moreover, the change-over between two different printing jobs generally results in a huge amount of wasted material.

Some solutions for automatically changing the printing rollers are known. For example reference is made to international publication WO2009/144016. This describes a printing machine associated with a device which performs replacement of the printing roller with a new one. This device comprises gripping means displaceable on a guide for gripping the used printing roller, depositing it in a suitable store, gripping a new printing roller and then arranging it in the working position. This device is constructionally complex and bulky. Moreover, replacement of the printing roller is relatively slow because it requires successive and consequent movements of the same gripping element.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a device for replacing the printing rollers of a printing unit, in particular for in-line rotary flexographic machines, which solves the technical problems described above, allowing an increase in the efficiency and the productivity of the printing processes.

In connection with this task, one object of the present invention is to provide a device for replacing the printing rollers of a printing unit which is able to achieve a reduction in the “job change-over” time and the amount of wasted material associated with this “job change-over” operation.

A further object of the invention consists in providing a device for replacing the printing rollers of a printing unit which is able to provide greater guarantees as regards reliability and safety during use.

Another object of the invention consists in providing a device for replacing the printing rollers of a printing unit which is easy to produce and competitive from a cost point of view when compared with the prior art.

Yet another object of the present invention is to provide a device which performs replacement of the printing roller quickly and which at the same time is constructionally simple and has compact dimensions.

These results are achieved by the device for replacing the printing roller in a printing unit, in particular for in-line rotary flexographic machines according to the present invention, the essential characteristic features of which are described, respectively, in the independent claim1and in the independent method claim12. Further important characteristic features are also described in the dependent claims.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the aforementioned figures, the device for replacing the printing roller of a printing unit is denoted overall by the reference number1, while the printing unit is denoted overall by the reference number2and comprises at least one anilox roll8and one counter-roll6.

According to the invention, the device1comprises a work station5for a first working printing roller130associated with a first support spindle13, a holding station3,7for a second holding printing roller110associated with a second support spindle11, a removal station7,3for removing a printing roller110,130to from a support spindle11,13, and displacement means9for displacing the first support spindle13from the work station5to the removal station7,3and for displacing the second support spindle11from the holding station3,7to the work station5.

The work station is arranged in a substantially intermediate position between the removal station7,3and the holding station3,7, as can be seen from the figures.

In the figures, the holding station is indicated by the reference number3and is occupied by the support spindle11which supports a held printing roller110, while the removal station is indicated by the reference number7and is not temporarily occupied by any spindle since it is waiting to receive the support spindle13which supports the printing roller130currently in operation in the work station5, when this printing roller130must be replaced. However, the station indicated by the reference number3may be a removal station, and the station indicated by the reference number7may be a holding station, namely the holding and removal stations may reverse their functions depending on the station which momentarily is not occupied.

In greater detail, each spindle has two ends, a first end13a,11aof which is connected to the displacement means, as will be described in detail below, and a second end13b,11bof which is designed to be connected to the means for performing locking in the working position, as will become clear further below. A first section of the spindle13c,11c, adjacent to the first end, is free, while the second section13d,11d, adjacent to the second end, is occupied by the printing roller.

Considering again the displacement means9, these comprise advantageously a pair of guides90, each of which extends between the work station and the removal station7and the holding station3, respectively.

Each guide is defined by a rail90′ which has, slidably associated with it, a carriage91with which, in turn, the first support spindle13, or the second support spindle11, or a first end of said spindles, is rigidly associated.

In a preferred constructional version, each guide is defined by a pair of rails90′ and90″ parallel with each other and having two carriages91slidably associated therewith. Each spindle, or the first end thereof, is rigidly associated with the carriages. The presence of a double system of rails90′,90″ and carriages91for each support spindle11,13ensures greater stability for the displacements of said spindles between the work station5and the holding station3or removal station5and vice versa.

The displacement means9comprise, both for the holding station3and for the removal station7, actuating means93configured to perform the displacement of each support spindle11,13along the rails, owing to the sliding action allowed by the carriages91. The actuating means93may be hydraulic or pneumatic pistons.

The displacement means9comprise advantageously, for the holding station3and the removal station7, a pivoting plate94with which the guides90and the actuating means93are associated. Each pivoting plate94is hinged in the vicinity of the holding station3or removal station7. In particular, this pivoting plate94is hinged, by means of a pivot pin97, with a flat support structure96which supports the displacement means9. The pivoting plate94has a top end located opposite the holding station3or removal station7and a bottom end located opposite the work station5. Hinging of the support structure96by means of the pivot pin97is performed at the top end of the pivoting plate94.

The support structure96takes the form of a flat plate in which two straight through-incisions960are formed.

The guides90are located on a first side96aof the flat plate96, while the first printing roller130and the second printing roller110project from an opposite side96b. As a result the ends of the spindles are located on the opposite sides of the plate, and therefore the free section11c,13cof each spindle is arranged so as to straddle and pass through the respective incision. The guides90are arranged substantially along the respective incision and in particular along a bottom edge960′ thereof owing to the engagement of the spindle inside the incision and the aforementioned hinging arrangement.

In the preferred constructional solution the incisions are arranged symmetrically inclined with respect to a vertical axis X (FIG. 3), defining a substantially V-shaped configuration (obviously the apex of the V corresponds to the working position). Consequently, the guides are also arranged in the form of a V relative to each other. This configuration is particularly advantageous because the device as a whole is compact and has a small volume.

However, it is also quite possible, in constructional variants, for the incisions, and to consequently the guides, to be arranged horizontally, extending in opposite directions from the work station in a symmetrical manner.

Furthermore, it is also possible for the incisions, and consequently the guides, to extend in opposite directions from the work station, but not symmetrically, with different inclinations.

The device1comprise finally thrusting means95,950which are configured to press, along the axis X, the printing roller in the work station5against the anilox roll8and/or against the counter-roll6which form part of the printing unit2, in order to define the maximum printing pressure. In the constructional solution shown in the figures, the thrusting means take the form of two actuators (of the pneumatic or oil-hydraulic type) which each act on one end of the spindle.

The method for replacing printing rollers of a printing unit2, in particular for in-line rotary flexographic machines, according to the invention, comprises the steps of:

providing a first working printing roller130in a work station5, associated with a first support spindle13;

providing a second held printing roller110in a holding station3,7, associated with a second support spindle11;

displacing, by means of the displacement means9, the first support spindle13from the work station5to the removal station7,3and displacing, again by means of the displacement means9, the second support spindle11, from the holding station3,7to the work station5;

removing the first printing roller130from the first support spindle13, when the spindle13and the roller130are in the removal station7,3.

Moreover, the step of displacing the first support spindle13and the second support spindle11is advantageously performed without stopping the printing process and may also be advantageously performed at any stage of the printing process.

The operating principle of the device is clear and evident from the description provided above.

In particular, the device1allows a new printing roller110to be positioned on the printing spindle11, in the holding station3, while the working printing roller13in the work station5is completing the printing cycle. At the end of the printing step, the displacement means9cause displacement, along the guides90, of the support spindle13, the printing roller130of which was in operation, bringing it into the removal station7, and at the same allow the displacement, along the guides90, of the new printing roller110associated with the support spindle11, which was on holding in the holding station3, into the work station5, in order to resume operation. During displacement, the spindle travels in contact along the bottom edge of the incision960′ until the printing roller supported by the spindle reaches the work position, namely at a tangent to the anilox cylinder and counter-roll. As a result, depending on the diameter of the printing roller, the displacement of the spindle stops in a position more or less advanced along the guide90. In order to be properly seated in the working position the printing roller must engage inside the support cradles (not shown but known in the configuration of flexographic printing machines). This positioning arrangement may require an adjustment in the position of the printing roller also along the vertical axis X. The movement is therefore permitted by the fact that the guide may vary slightly its inclination with respect to said axis X, owing to the hinged arrangement.

As regards the pistons93, in a preferred constructional solution, these push the carriage until the roller comes into contact with the cradle. In this maximum stroke position of the carriage, the piston has not yet reached its fully extended stroke. In general, during the entire stroke movement of the carriage along the guide, the piston does not reach the fully extended stroke. Obviously solutions may also be envisaged where stoppage of the piston is performed automatically.

Once the printing roller is in the working position the thrusting means95,950are operated.

The above comments are also applicable, in an analogous manner, to the step of removal of the printing roller from the working position, namely during movement of the printing roller from the work position to the removal position. Obviously, before removal of the printing roller from the working position the thrusting means must be deactivated.

Once the worn printing roller has been removed from the spindle in the removal station it is possible to replace it with a new one, such that the removal station becomes in fact a holding station for the next working step of the device.

In the case where the device1is applied to all the printing units2of the printing machine, both selective and sequential changing of the printing rollers is permitted.

In the case of selective changing, if it is required to change only one printing roller (for example, in order to obtain a new text, a new language, etc.), the change may be performed instantaneously without any wastage of material due to machine stoppage and consequent loss of the printing register. The machine does not stop, the device1performs the change-over on the selected printing station, without losses or wastage of any type, immediately and perfectly in register.

In the case of sequential changing, instead, during the job change-over changing of the printing rollers is performed starting from a first printing unit, in which the “new” cylinder replaces the “old” cylinder, and starts to print the “new” job. The “old” job continues its path as far as a second printing unit and, when the “new” job arrives from the first printing unit, the “new” printing cylinder of the second unit takes over from the old cylinder, printing the second colour of the “new” job, perfectly in register with the first colour of the preceding job, without any wastage between “old” and “new” jobs. The “old” job thus continues its path as far as a third printing unit and, when the “new” printed job arrives from the first and second printing units, the “new” printing roller of the third unit takes over from the old roller, printing the third colour of the “new” job, perfectly in register with the first and second colours of the “new” job, without any wastage between “old” and “new” jobs. And so on, for all the successive printing units, the procedure continues with a sequential replacement of the “old” job with the “new” job without leaving wastage of material between the two jobs.

It has been established in practice how the device and the method for replacing a printing roller of a printing unit, according to the present invention, fulfil the task and achieve the predefined objects since they allow the efficiency of the printing process to be increased, reducing the job change-over time and reducing the amount of wasted material. In fact, changing of the printing rollers may be performed at a low speed, without stopping the flexographic machine. This allows the job change-overs to be performed without disturbing the tension of the printing medium, which continues to be driven, and therefore without loss of register, both in the “old” printed job and in the “new” printed job.

The device therefore achieves a series of not insignificant advantages, namely it increases the efficiency and the productivity of the printing process, while being constructionally simple and compact. Moreover, it provides ample guarantees as regards reliability and safety during use.

Also, the device is easy to produce and competitive from a cost point of view when compared to the prior art. Furthermore, in the particularly preferred constructional solution, it has compact overall dimensions. It is also suitable for installation on machines which are already in use.

The present invention has been described up to here with reference to its preferred embodiments. It should be understood that each of the technical solutions implemented in the preferred embodiments described here as an example can advantageously be combined differently with each other, to create other embodiments, which derive from the same inventive core, in any case within the scope of protection of the attached claims.