FIELD OF THE INVENTION

This invention is related to rotogravure presses, in particular to the inking systems used in the printing units of a rotogravure press.

TECHNICAL BACKGROUND

A common rotogravure printing machine is made of a gravure cylinder or printing cylinder in contact with a second cylinder, which is usually a rubber cylinder, also called the impression roller. The gravure cylinder exhibits a collection of tiny cells on its surface whose distribution defines the image to be printed. These cells are filled with ink which is transferred onto a support by pressuring the support between the gravure and the impression cylinders. Some systems use an inking roller to fill the cells, which partially or completely dips into a pan filled with ink, rolls against the gravure cylinder and provides the necessary pressure to fill the cells completely. During printing, a doctor blade removes the excess of ink from the surface of the gravure cylinder while leaving the ink inside the cells. This remaining ink is transferred to the support and results in the desired image.

A function of the inking roller is to avoid air bubbles inside the cells of the gravure cylinder. Another function of the inking roller is to perform a pre-cleaning of the gravure cylinder surface, in particular removing the dried ink from the gravure cylinder surface. The inking roller is in freewheel in some systems, or is driven by a motor in some other systems; in both cases, the inking roller runs slower than the gravure cylinder to fulfil the functions mentioned above.

A new generation of printing machine allows printing faster than machines of the older generation. This evolution is made possible thanks to new generations of inks that tend to dry faster than older generations of inks. The ink drying phenomenon is critical in this context. On the one hand, the ink should not dry while being transported by the gravure cylinder, on the other hand, when transferred to the support, the ink must be dried before coming in contact with the next cylinder in the printing machine. Today, several inking configurations exist to address the ink transfer problem, but none can address all the aspects of the problem optimally.

US 6 640 703, from Japan management Co, discloses a system that uses an inking roller that freewheels, partially dipped into the ink pan. The gravure cylinder is always kept outside from the ink pan. The invention is meant for water-soluble inks.

DE10 2004 056 539, from W&H, discloses a system with an inking roller with its own ink source, and a second ink pan with its ink in direct contact with the gravure cylinder. It also discloses a protection shield to avoid colour splashes.

US 5,103,723 from Albert Frankenthal AG discloses an inking system where the printing cylinder is always dipped into the ink of the ink pan. The inking cylinder is mounted on two pivoting arms that are inside the ink pan, and whose function is to maintain the pressure with the printing cylinder even if the size of the printing cylinder is changed. The pressure is controlled by a piston at one end of the pivoting arm(s). The ink height of the ink pan can be modified thanks to a vertical gearing system and related motor. Being completely inside the ink pan, the inking roller is in freewheel.

US 5,438,924 from Albert Frankenthal AG, presented as an improvement over the US 5,103,723, discloses a system to regulate the pressure between a freewheel inking cylinder and a printing cylinder. The system can accommodate for a varying printing cylinder diameter. The inking cylinder is dipped from 60% to 80% of its diameter into the ink, while the printing cylinder is always dipped into the ink of the pan. Instead of using a piston, the system uses torsion bars, which result in a more compact and simple system.

As of today, several inking configurations exist, and the ink manufacturer optimise their ink for a given configuration of inking. Inks made by Asian manufacturers tend to use inking systems where the gravure cylinder avoids direct contact with the ink of the ink pan, while European ink manufacturers tend to use configurations where the gravure cylinder is in direct contact with the ink of the ink pan. Neither of the above-mentioned inking systems is able to obtain an optimal print quality with all the existing inks. An aim of the present invention is to provide an inking system which combines the advantages of several existing printing presses into a single device, for obtaining an optimal print quality with any types of ink.

Modern printing presses tend to get faster generation after generation. Thus, the time required for a print job tends to shorten. In parallel, the demand for packaging tends to change faster, generating more jobs with smaller volumes. These two parameters combined make the cost of the time lost in changing the rolls and/or the ink in a press increasingly critical.

Some inks, for example, the basic colour inks (Cyan, Magenta, Yellow, Black), tend to be the same across print jobs. Changing a print cylinder alone is potentially faster than changing the cylinder and the ink. Another aim of the invention is to provide an inking system for cleaning and for changing the gravure cylinder without changing the ink while adapting to print cylinders with different diameters.

Another aim of the invention is to provide a faster solution for changing the inking system. The solution is faster than the traditional way which consists in emptying the ink pan, cleaning it, and filling it with new ink.

Another aim of the invention is to provide a solution where the complexity of the inking system to be changed is kept as low as possible.

Another aim of the invention is to provide a solution to provide an inking system reaching state-of-the-art print quality for a large set of ink types, yet being simpler than existing ones.

SUMMARY OF THE INVENTION

According to the invention, these aims are achieved by an inking system with an ink pan and an inking roller where the ink level can be adjusted. The level can be adjusted by setting the ink pan height in the printing unit and/or by varying the amount of ink in the pan. As a result, the level can be chosen so as to offer two types of configurations of inking: a first configuration type, called the“dipped configuration”, where the gravure cylinder is partially dipped into the ink, and a second configuration type, called the “dry configuration”, where the gravure cylinder is kept out of contact with the ink. When the press is used for a printing job using inks that work better in dipped configuration, the operator sets the press advantageously into a dipped configuration. Conversely, when the press is used for a printing job with a type of ink that works better in a dry configuration, the operator sets the press advantageously into a dry configuration. In both configurations, the inking roller is in contact with the gravure cylinder and is partially dipped into the ink. The inking roller comprises a shaft that is configured to protrude from the ink pan, allowing to control the rotation speed of said inking roller by an external motor for optimal inking of the gravure cylinder.

Advantageously, the ink pan, which holds the ink, is a pan with an open top where the inking roller is partially dipped (into the ink), and where the gravure cylinder can be dipped from above. By open top we mean that there is an air-ink interface in the ink pan; the ink pan could also be closed.

Advantageously, the inking system can be embodied as an inking cartridge with an ink pan configured to store ink and suitable for being positioned in the printing unit below the gravure cylinder and with the inking roller comprising a roof positioned above the inking roller and configured to prevent ink splashes from reaching a printing support when the printing unit is running.

Advantageously, the rotation speed of the inking roller may be controlled. For controlling the rotation speed of the inking roller, the shaft holding the inking roller (which can be made of two shafts on each side of the roller) protrudes from the ink pan, at least from one side of the ink pan, but preferably protrudes from both sides of the ink pan. This allows an external mechanical system to engage with the shaft and rotate the inking roller. In practice, the width of the inking roller including the shaft must be larger than the internal width of the ink pan. The internal width of the ink pan is measured along the rotation axis of the inking roller when the printer is running and is the distance between the internal side walls of the pan.

Advantageously, in both dry and dipped configuration types, the inking roller may be pressed against the gravure cylinder with some means to control the pressure. The pressure can be set at the beginning of a print job using some fixed pressuring device (fixed over time, but not necessarily across printing jobs), or can be set dynamically by a control system. The inking and gravure cylinders are rolling (and sliding) over each other; in other words, their revolution axes are parallel (small angle between axis can also be used to compensate deflections). The inking roller is partially dipped into the ink pan and brings ink onto the gravure cylinder. The pressure is used to prevent air bubbles from appearing in the gravure cylinder cells, to ensure these cells are completely filled with ink. The speed of the inking roller is different than the speed of the gravure cylinder. This difference in speed allows for wiping off some of the ink from the gravure cylinder surface, in particular, the ink that has already dried that is typically found in areas with no cells that form a very thin layer of ink.

In the dry configuration type, the gravure cylinder is kept out of the ink. In practice, a distance margin is kept between the ink level and the bottom surface of gravure cylinder, which we call the“dry margin”. In this configuration, the gravure cylinder is supplied with ink by the sole inking roller.

Advantageously, before the impression on the substrate (and after inking), the gravure cylinder may be wiped off by a doctor blade, which ensures that there is no ink remaining on the surface of the gravure cylinder (i.e. there is ink only in the gravure cylinder cells).

The inking system comprises a device to set the ink level, defined with respect to the bottom surface of gravure cylinder. This device allows to configure the inking system into one of the dry or dipped configuration types. We refer to “configuration types” rather than to “configurations” because, within a configuration type, the dipping depth and the margins might vary, but the dipping (or non-dipping) characteristics of the gravure cylinder is maintained.

Additional advantageous features of the inventions are disclosed in the dependent claims. BRIEF DESCRIPTION OF THE FIGURES

Exemplary embodiments of the present invention are illustrated by way of example in the accompanying drawings.

Figure 1 shows the inking system according to the invention, using a small gravure cylinder in a dipped configuration.

Figure 2 shows the inking system according to the invention, using a small gravure cylinder in a dry configuration.

Figure 3 shows the inking system according to the invention, using a large gravure cylinder in a dipped configuration. Figure 4 shows the inking system according to the invention, using a large gravure cylinder in a dry configuration.

Figure 5 shows a perspective view of an ink cartridge according to the invention.

Figure 6 shows a side view of the inking system according to the invention.

Figure 7 shows the cartridge of Figure 5 from a different perspective. Figure 8 shows a different side view of the inking system of Figure 6.

Figure 9 and 10 show the ink cartridge according to the invention mounted in a press; in Figure 9, the inking roller is engaged with the pressure and speed control mechanisms; in Figure 10 the inking roller is disengaged from these mechanisms.

Figure 11 and 12 show a side view of the inking system with the ink cartridge moved vertically to set the contact between the inking roller and gravure rollers of different diameters, both in a dry configuration.

Figure 13 shows the housing around the gears of the inking roller; the roof is not shown here.

Figure 14 shows the inking roller with its housing engaged by the arms holding the roller.

Figure 15 shows the pivoting axis location of the arms holding the inking roller. DETAILED DESCRIPTION OF THE INVENTION AND OF SOME OF ITS EMBODIMENTS

This section describes in details different ways for implementing the features claimed in the invention followed by specific examples of embodiments. It is structured into paragraphs and, unless stated otherwise, the features disclosed in distinct paragraphs may be used independently from each other. For example, an embodiment comprising a feature disclosed in a paragraph can be used without the feature disclosed in the next paragraph. Nevertheless, the features disclosed in distinct paragraphs may also be used in combination with the features disclosed in other paragraphs. For example, one paragraph (below) discloses a piston to control the pressure of the inking roller on the printing cylinder, while another paragraph discloses a motor to control the speed of the inking roller. The paragraph disclosing the piston does not mention, nor refers to the inking roller speed, while the paragraph disclosing the motor controlling the speed does not mention, nor refers to the inking roller pressure. Thus, according to the structure of this section, an embodiment according to this invention can be build using a piston to control the pressure of the inking cylinder, without using a motor to control its speed. Conversely, another embodiment can be built using a motor to control the speed of the inking roller without using a piston to control its pressure on the printing cylinder. Finally, yet another embodiment can be built using both the piston and the motor to control the speed and the pressure of the inking roller.

The dipped configuration, where the gravure cylinder is dipped into the ink pan, is characterised by having a thicker ink layer (on the gravure cylinder) reaching the doctor blade, compared to the dry configuration in the same conditions. Typically the thickness differs by a factor of 10 to 20. It is unclear, from a physics point of view, why a configuration is better than the other depending on the ink. In practice, the configuration is chosen by trial-and-error, and the ink manufacturer specifies, for each ink, which configuration works the best.

A shaft 38 is holding the inking roller 10 and can be attached by two bearings 34 on both sides of the shaft. The shaft can be manufactured as a single piece protruding on each side of the inking roller 10 or as two pieces protruding on each side of the inking roller 10. The shaft 38 preferably sits above the ink pan top walls to avoid the need for a tight seal between the shaft 38 and the ink pan walls. In other words, the inking roller 10 including the shaft(s) 38 is wider than the ink pan (i.e. wider than the distance separating the two internal sidewalls of the pan), allowing to position it (10,38) on the sidewall of the ink pan, and allowing it (10,38) to be grabbed from the sides of the ink pan by some external arms 36,37. Avoiding the tight seal saves costs in maintenance, as well as manufacturing costs. As a consequence, to prevent the ink from flowing over the ink pan walls, the ink level in the pan has to be kept below the shaft of the inking roller. The ink level is kept below the ink pan top walls within a margin, which we call the“pan overflow margin”. For example, a pan overflow margin of 20mm may be used; another margin— called the“pan-to-shaft margin”— of 5mm may be used between the surface of the shaft and the ink pan top walls.

When the inking roller 10 freewheels, there is a natural difference in speed that occurs between the gravure cylinder surface and the inking roller surface. This difference cannot be controlled and depends also on the pressure applied between the rollers. When using a motor 30 to control the speed of the inking roller, the speed may be set between 5% and 30% of the gravure cylinder speed, for example at 10% of the gravure cylinder speed. Our tests showed that by controlling the speed of the inking roller, the print quality tends to be better. When the press is running, the inking roller is partially dipped into the ink pan.

To control the pressure between the inking roller and the gravure cylinder, a pneumatic piston (not shown) with controllable pressure applies a force on the arms 32 that hold the inking roller. As an alternative, one can use a hydraulic piston, or a linear motor to apply the force. Also, one could use a motor to apply a torque on the arms 32 to control the pressure between the inking roller and the gravure cylinder. A typical pressure used is 0.8 Newton per millimetre of roller width (N/mm). Usually, this pressure ranges between 0.1 N/mm and 2 N/mm.

The rotation speed of the inking roller is advantageously controlled by an electric motor. As an alternative, it could be controlled by a brake whose braking torque is adjustable (the adjustment may be made online or offline), for example, a mechanical or an eddy current brake. It could also be controlled by a hydraulic motor or any other suitable mean.

In the dipped configuration type, the gravure cylinder 1 1 is partially dipped into the ink 20, so is the inking roller 10. Thus, the ink is brought to the gravure cylinder 1 1 by the inking roller 10 and also directly by the ink pan 13. The inking system 1 is set up such that, from the gravure cylinder perspective, the ink is first brought by the inking roller, and then by the drop into the ink pan 13. Finally, it reached the doctor blade 14 where the ink is removed from the surface of the gravure cylinder 1 1 and kept only in the cylinder cells. The important aspect of the dipped configuration type is that there exist a direct contact between the ink 20 and the gravure cylinder 1 1 after the contact between the gravure cylinder 1 1 and the inking roller 10.

Preferably, the ink level is set by moving the ink pan vertically. To be exact, the motion of the ink pan can be arbitrary, but, in this example, it must have a vertical component to modify the distance between the ink top surface 17 and the gravure cylinder (bottom) surface 19. By moving the ink pan, the dipping of the gravure roller into (or out of) the ink can be set while keeping an optimal amount of ink in the pan which reduces ink waste.

In embodiments where the ink pan is moved to set the system into either of a dipped or dry configuration type (or equivalently, where the gravure cylinder is moved vertically), the ink level can be maintained by keeping the ink level to a full state. An overflow occurs at the location of a dam 21 where the ink drips into a recycling/recirculating circuit 223. The ink is added to the ink pan at a rate above the consumption rate of the press to ensure that the ink level remains constant. The ink pan (or the ink cartridge) comprises an ink outlet (222) for conecting the recirculating circuit 223 to the pan. Advantageously, the ink pan (or the ink cartridge) comprises a tilted portion 22 configured to make the ink slide toward the ink outlet 222 (when the ink pan is used while the press is running).

As an alternative to the ink pan motion, we can vary the amount of ink in the pan. By pouring a lot of ink, the ink level reaches the gravure cylinder and sets the press into a dipped configuration to print with ink old generation. When pouring only a little amount of ink, we avoid the contact with the gravure cylinder and set the press into a dry configuration to print with modern ink. The disadvantage of this solution is the large amount of ink needed for the dipped configurations, which potentially generates a big waste. The advantage is a simpler inking system, albeit only for presses where the gravure cylinder diameter cannot change a lot, otherwise, the height of the ink pan must be configurable to adapt to the gravure cylinder diameter.

Preferably, the ink pan is made of a single basin, but it could also be made of two basins, one for the inking roller, and one for the gravure cylinder.

Preferably, the ink level in the ink pan is controlled by an overflow dam 21 and a recirculating circuit 223. The ink is provided in excess, so as to flow over the dam 21 and being recirculated. The excess rate of ink is, for example, of the order of 10 to 100 times the ink consumption rate of the press. The dam extends over at least 80% of the width of the gravure cylinder, preferably over the whole width of the pan or of the gravure cylinder. Please note that, with suitable inks, it is also possible to avoid the use of a dam 21 and an ink overflow (for example by an ink level control system), or to limit the dam 21 to a very small extension (width). The described solution (extended dam and high ink overflow) is the preferred with fast-drying inks, to avoid dried skin on the ink surface. Said extension in conjunction with ink provided in excess pushes the ink on the surface away from the inking cylinder and prevents ink that may have dried (for example when some foam appears) to be grabbed by the inking cylinder and introduced in the printing process. By going through the recirculating circuit, the dried ink has time to be dissolved again. In another embodiment, the ink level in the pan can be set by adjusting the height of the dam in the pan.

To be able to carry out a whole set of printing jobs, a press may advantageously be able to accept gravure cylinders with different diameters (1 1 , 12). Indeed, the circumference of the gravure cylinder defines the size of the print job (or a multiple of its size), i.e. the length or the width, measured on the support 16, of the printed motif. This assumes that we aim at printing with the minimal possible gap between the repeated motifs printed on the support 16 with the cylinder, which makes sense according to economic or environmental considerations. Typical cylinder circumferences range between 550 mm and 700 mm, and in modern presses, said circumferences range between 400 mm and 1020 mm.

Using cylinders of different sizes affects the relative height between the bottom 19 of the gravure cylinder and the bottom 18 of the inking roller (when both are in contact). Let’s call this height difference the“dipping delta” 101 . To keep the cost of the press as low as possible, we do not adapt the inking roller diameter to the gravure cylinder diameter, but we use an inking roller with a fixed diameter instead. In any case, the bottom of the inking roller 10 is kept lower than the bottom of the gravure cylinder 1 1 , 12. Preferably, for every diameter of the gravure cylinder that the press is able to handle, the inking system can adopt both dipped and dry configurations, as illustrated in Figures 1 to 4. The dipping delta may be kept within some bounds to fulfil the margins mentioned earlier in the text (the pan overflow margin, the pan-to-shaft margin and the dry margin). Let’s call the maximum variation of the dipping delta, across all the possible acceptable setups, the“dipping delta variation”.

The dry margin can, for example, be set at 5 mm. The pan overflow margin can be set at 20 mm. An inking roller with a diameter of 135 mm with 25 mm shaft may be used. A typical value for the minimal dipping depth is 10 mm; the dipping depth being defined as the depth below the ink surface at which a cylinder dips into the ink. The values mentioned in this paragraph being independent from each other.

With the values of the former paragraph taken in combination, between a dry and dipped configuration, the ink level must vary by 15 mm (from 5 mm under the gravure cylinder to 10mm above). The maximum dipping depth of the inking roller is then 30mm, it minimal value 10mm. Since the dipping depth variation between dry and dipped configuration is 15 mm, the maximum value of the dipping delta variation is (30-10)-15=5mm. In particular, the dipping delta varies from 15mm to 20mm.

The inking roller shaft 38 is held by two arms 32. These arms have a first end 41 and a second end 42, respectively. The first ends 41 are holding the shaft 38 of the inking roller by both extremities. In other words, the first end 41 of each arm comprises a bearing 34 that holds the shaft of the inking roller (as shown in Figure 10). The arms are positioned at both extremities of the shaft of the inking roller (as shown in Figure 10). The second ends 42 of the arms are configured to rotate about a pivoting axis 43 parallel to the axis of the inking roller. The pivoting allows for setting the inking roller 10 in contact with the gravure cylinder (1 1 ,12) as well as setting the inking roller out of contact with the gravure cylinder. For example, each second end may comprise a shaft that is attached to a bearing connected to the inking system 1 . As an alternative said bearing and a part of the inking system may also be a part of the press frame 100. The pivoting also allows setting the inking roller in contact with gravure rollers of various diameters while keeping the dipping delta variation within acceptable bounds, as illustrated in the example depicted in Figures 1 1 and 12. The arms 32 can be configured to engage with and disengage from the inking roller. As an alternative, they may also be configured to hold the inking roller permanently. The embodiment with the arms 32 attached to a bearing fixed to the press frame and with an engageable inking roller is preferred since it results in an inking system with fewer components; the inking system being removable, and being produced in several copies per printing unit. Preferably, if possible, we want the removable inking system to consist only of the pieces that get dirty (by the ink) during printing.

The inking system 1 according to the present invention comprises an ink cartridge 2. The ink cartridge is removable from the press and replaced by another identical ink cartridge. By using a spare cartridge, the operator of the press can prepare the ink for the next print job while the current print job is still running. This change of cartridge is faster than the direct replacement of the ink because the time to clean the cartridge is not part of the job change over time.

The ink cartridge comprises the ink pan 13, and the inking roller 10. The ink pan comprises two lateral walls 23 to contain the ink. The ink cartridge comprises means to hold the inking roller in a well-defined position. For example, these means can be implemented with a cutout 24 in the lateral walls 23 to hold the shaft 38 of the inking roller. Advantageously, the shaft 38 protrudes from the ink pan wall, to allow a control device, for example, the arms 32, to engage with the shaft. The control device, once engaged, can set the inking roller in contact with the gravure cylinder, and can optionally control the rotation speed of the inking roller. The arms 32 can be engaged and disengaged from the inking roller shaft 38 by a pinching operations: the bearings 34, the arms 32 and the axle 43 are approached toward (or set apart from) both extremities of the shaft 38 by two structures 36 and 37. A motor 30 is connected to the inking roller axis with a gearing system (in the arms 32) for controlling the rotation speed of the inking roller. In a preferred configuration, the arms 32 pivot about the axle 43 which is located at a fixed location on the printing unit frame. The gravure cylinder axis being also (preferably) located at a fixed location on the printing unit frame.

As illustrated in Figure 15, The location of the pivoting axis 43 of the arms 32 is fixed with respect to the location G of the rotation axis of the gravure cylinder 1 1 ,12. It is located preferably at a (vertical) distance V of 320 mm below G and at a (horizontal) distance H of 150 mm to the side of G. The length of the arms 32 is set accordingly to put the inking roller 10 in contact with the gravure cylinder 1 1 ,12 (in our example, it is set to 410 mm measured between the two axes). The distance V ranges from 240 mm to 400 mm, preferably from 280 mm to 360 mm. The distance H ranges from 100 mm to 200 mm, preferably from 125 mm to 175 mm. The position of the pivoting axle 43 within said ranges (defining a rectangular area 90) results in a reasonably small dipping delta variation for typical gravure cylinders 1 1 ,12 (whose circumference ranges from 450mm to 1040mm).

The gearing system that controls the speed of the inking roller is protected from the dust by a housing 45. The inking roller may be kept in a well-defined position, to ease the engagement of a gearing system with the shaft 38 of the inking roller. Also, the housing 45 of the gears may be kept in a well-defined position and orientation on the ink cartridge 2. In a preferred embodiment, the orientation of the housing is controlled by a protrusion 47 attached to the ink pan wall that gets inserted into a corresponding groove in the housing 45. The protrusion 47 is preferably attached to the pan wall through an elastic blade so as to prevent damages when the housing does is not exactly well aligned when putting back by the arms 32 into its rest position onto the inking system. The protrusion 47 can be mounted on any suitable elastic device, for example, a spring, a rubber or an air bubble.

When engaging the inking roller with the arms 32, and to control the orientation of the housing 45 of the inking roller, a pin is provided on the housing 45, and a corresponding protrusion is provided in the arms 32 which engage with the housing while the arms engage with the inking roller (the converse is also possible with the protrusion on the housing; any mean to engage and disengage the housing with the arms can be used). The control of the orientation of the housing is important because the housing comprises a roof 70 with a slidable surface 71 . The roof and the surface extend over (at least) the whole width of the inking roller and prevent ink splashes from being ejected toward the support 16 which runs above the inking roller - gravure cylinder interface. The roof 70 also acts as a protection in case an operator has to manually clean the gravure cylinder in the space between the roof 70 and the support 16. Advantageously, the roof is arranged such that the gap 76 between the roof and the gravure cylinder ranges between 2 and 6mm, over the whole range of possible gravure cylinder diameters. This setting is performed by the engagement of the housing with the arms 32, a proper arm 32 length and proper placement of the arms 32 pivoting point. The 2mm margin allows some wearing of the inking roller over time while still preventing the roof from contacting and ruining the gravure cylinder 1 1 . The upper margin (6mm) is small enough to prevent injuries for the operator. The slidable surface 71 is positioned for each gravure cylinder diameter at the begin of a print job. It is set such that the remaining gap 76 between the slidable surface and the gravure cylinder is set to a small value, for example, 1 to 2 mm.

The housing can be any frame which at least partially surrounds the shaft of the inking roller, at least partially protects the gears 49 used for driving the inking roller and supports the roof. Also, the housing comprises the elements 46 needed for proper positioning and orientation of the housing at the rest position of the inking roller - housing assembly. The roof 70 can be any structure suitable for preventing the ink from splashing the support 16. Advantageously, it can be any frame that, in addition, fulfils the function of protection of the operator by guaranteeing a small space between the roof (non-removable) border and the printing cylinder (the remaining gap 76 between the slidable surface and the printing cylinder does not count for security reasons according to current regulation because the sliding surface can be moved away). Advantageously, the sliding surface is held by two or more screws, and a can be slid toward and away from the gravure cylinder, for example using slotted holes on the surface. A linear motor can be used to automate the positioning of the sliding surface, albeit complexifying the system. Any suitable mean to reduce the gap between the roof and the gravure cylinder can be used as an alternative to the sliding surface.

An alternative to the roof and surface assembly is a rigid roof mounted on the housing with a pivoting axis. Said axis is parallel to the rotation axis of the inking roller so that a rotation around this axis of the rigid roof modifies the gap 76 between the roof and the gravure cylinder. In one embodiment, the rotation can be controlled by a motor for obtaining an automated system. In another embodiment, the rotation can be set by hand using a screwing and unscrewing mechanism. In yet another embodiment, the orientation of the roof can be set as a function of the orientation of the arms 32 through a passive mechanical system, for example, a mechanical cam or a gearing system. This last embodiment can be used to ensure a small gap, for example, 1 or 2 mm, for a cylinder of any diameter (compatible with the press). In this last embodiment, a slidable surface, similar to the one of figure 1 , could optionally be used solely for compensating the wear of the inking cylinder; and thus would need to be set only very rarely.

In a preferred embodiment, a cleaning device is provided with the housing for dropping cleaning liquid in the area of contact of the inking roller with the printing cylinder.

The cleaning device may comprise a spraying nozzle located under the roof 70 and above the contact point between the inking roller and the gravure cylinder. It may also comprise several nozzles distributed along the direction of the rotation axis of the rollers.

In an alternative embodiment, the cleaning device may comprise a cleaning pipe 80, with a hole 81 instead of a nozzle. The hole diameter may advantageously be chosen so as to prevent ink splashes from clogging the hole. A hole of 3 mm to 8mm of diameter may be used, for example, a hole with a diameter of 5 mm. There may be several holes along the whole width of the roof, or there may be a single hole, preferably located in the middle of the printing cylinder width. In the latter example, a pipe with an open end may be used instead of a hole. When cleaning liquid is provided in the middle of the printing cylinder, it will push the ink toward the extremities of the cylinder until the cleaning is completed.

The cleaning device may comprise a set of spraying nozzles, or holes, located above the roof 70 and above the contact point between the inking roller and the gravure cylinder. By setting the spraying nozzles, or holes, above the roof prevents ink from clogging the nozzle (or holes), thanks to the protective function of the roof. This allows for smaller hole diameters compared to the embodiment with the spraying nozzle(s) or hole(s) below the roof, and allows to distribute several nozzles (holes) along the width of the gravure cylinder 1 1 ,12. A more uniform distribution of the solvent delivery along the cylinder width, embodied by the multitude of solvent outlets, permits a faster cleaning of the gravure cylinder 1 1 ,12.

To feed the cleaning device with cleaning liquid, a fluid connector is provided on the housing (connected to the cleaning liquid pipe 80), and a complementary fluid connector is provided on the arms 32. While the arms engage with the housing and the inking roller, the fluid connector engages with its complementary counterpart. Thus, when pressure is released to the cleaning liquid, it gets sprayed or poured above the area of contact of the gravure cylinder with the inking roller. Advantageously, the fluid connector is placed at the opposite extremity of the inking roller from the gearing system used to control the inking roller torque. The inking system 1 can be used to clean the gravure cylinder without changing the ink. The ink pan is lowered to the point where neither the gravure cylinder nor the inking cylinder touches the surface of the ink in the ink pan. Then, a small amount of cleaning liquid is sprayed through the nozzles (or poured through the hole(s)), while the rollers are turning against each other, similarly than during printing. Preferably, the doctor blade is still in place during cleaning. The cleaning liquid and the ink that was on the rollers before the cleaning operation is collected by the ink pan. The total amount of cleaning liquid should not exceed 5%-10% of the total amount of ink in the inking system so that the added solvent has a negligible effect on the print quality of the next print job. Also, the cleaning liquid is chosen as being a compatible solvent for the ink for the printing process. Part of the added amount of ink to the inking system has the time to evaporate before the new printing job is in place. For example, for an inking system containing 10 litres of ink, we deliver a total amount of 1 litre of solvent to clean the system. Once the system is cleaned, the inking roller is moved away from the gravure cylinder, and the gravure cylinder can be exchanged for a new one with a different cliche. The use of the little amount of ink is made possible by the presence of the inking roller that is out of contact with the ink in the pan, which in turn is made possible by the vertical motion of the ink pan. Also, the pressure provided by the inking roller on the gravure cylinder improves the efficiency of the cleaning and lowers the required amount of cleaning liquid. Please note that for water-soluble inks, the solvent or cleaning liquid may be water.

To change the complete ink pan, the preferred method comprises the steps of delivering a small amount of ink toward the gravure cylinder, like in the method mentioned above, while having the gravure cylinder in contact with the inking roller, and both rollers out of contact with the ink in the pan. In this way, there is a cleaning of the rollers, and some of the ink is recycled instead of being lost. The inking roller is placed in its rest position, the arms 32 are disengaged, and the ink pan can be removed from the machine to be replaced by a new one. Optionally, but most of the times, the gravure cylinder is also changed during this process. To get a more thorough cleaning, a two-step process may be used: as before, a small amount of ink is delivered, the printing cylinder cleaned and the cleaning liquid added to the ink. Then, the ink pan is emptied via the recirculating circuit. Then the circuit is switched toward a second reservoir, and a second, larger, amount of cleaning liquid is used to clean better the ink pan (which also results in better cleaning of the printing cylinder, the doctor blade and the inking roller).

To use the press with the inking system according to this invention, the operator may use the following method: While the press is running with a printing job, the operator can prepare an additional print cartridge with ink for the next printing job. Once the former print job is finished and the former ink cartridge removed, the operator can insert the new ink cartridge. Then, the operator engages the inking roller and sets it in contact with the gravure roller, for example with the control means 32. While doing so, the operator sets the height of the ink cartridge (and thus the height of the ink pan), using, for example, the linear actuator 40. Depending on the ink characteristics, which determine whether the gravure roller must be dipped into the ink or not, the operator sets the height to a value where the inking gravure cylinder is kept out of the ink (i.e. in a dry configuration) or to a value where the gravure cylinder is dipped into the ink (i.e. in a dipped configuration). The ink level is then maintained during all the printing operation. The operation of engaging the inking roller, setting the inking roller against the gravure cylinder and setting the height of the ink cartridge can be easily centralised by an automated control system where the operator may just choose the configuration type, the pressure between the inking and gravure cylinders and the speed ratio between them. These settings may be replicated automatically in all the printing units of the press.

The height of the ink cartridge may be set by a linear actuator 40. This setting capability has two functions: it allows to put the inking roller 10 in contact with the gravure cylinder (1 1 ,12) while keeping the inking roller dipped partially into the ink 20. It also allows setting the press into either a dry configuration or a dipped configuration.

The assumptions and the vocabulary used in this disclosure are as follows: A gravure cylinder of a gravure printing unit is always positioned horizontally when the press is running (in other words, the axis of the gravure cylinder is horizontal). By horizontal direction or horizontally we mean perpendicular to the gravitational force. By vertical, we mean parallel to the gravitational force. By “below” or“above” we refer to a lower or higher altitude, respectively.

The“inking roller” may also be called the“furnisher roller”.“Roller” and“cylinder” are used interchangeably, and mean the same thing. The“impression cylinder” may also be called the“counter cylinder”. A“printing machine” or a“printing press” or a“press” refer to the same concept. By“axis of a cylinder” is meant the axis of rotation of the cylinder when the press is running. By“bottom of a cylinder”, we refer to the generatrix of the cylinder (straight line) which is located at the lowest altitude. By“speed of the cylinders”, we mean the speed of the cylinder surface, thus a relative cylinder speed of 100% between two cylinders means that the two cylinders roll on each other without sliding. The“gravure cylinder” may also be called the“printing cylinder”. The“ink level” refers the height of the ink (top surface) compared to the height of the bottom of the gravure roller (i.e. the vertical distance); thus the ink level in a dipped configuration is higher than the ink level in a dry configuration.

When an arm is engaging a roller, we mean that the arm can grab the roller by its shaft to allow the roller to turn around its axis when it is engaged. Depending on the roller configuration, if the roller comprises a gearing system then the gearing will be engaged with some compatible counter gears and connected to some control means like a motor. If the roller system comprises a cleaning liquid pipe, then engaging the roller system means that the cleaning pipe is also connected in the engaging process.

When mentioning the largest acceptable radius or smallest acceptable radius of the printing cylinder, we refer to the specification of the printing unit: Each printing unit is designed for a given range of printing cylinder radii, from the smallest acceptable radius to the largest acceptable radius. This information is usually found in the printing unit specifications from the manufacturer.