EP2691241B1

EP2691241B1 - Device and method for printing cylindrical bodies

Info

Publication number: EP2691241B1
Application number: EP12722498.8A
Authority: EP
Inventors: Sergio FAIPO'; Roberto Celona
Original assignee: Martinenghi Srl
Current assignee: Martinenghi Srl
Priority date: 2011-03-31
Filing date: 2012-03-29
Publication date: 2016-09-14
Anticipated expiration: 2032-03-29
Also published as: EP2691241A2; WO2012131478A2; CN103596768A; ITMI20110537A1; ES2617033T3; WO2012131478A3

Description

FIELD OF THE INVENTION

The present invention relates to a device and a method for printing on cylindrical bodies. More specifically the present invention relates to a device and a method for painting or coating, or decorating the side surface of substantially cylindrical bodies, such as for example tubes or bottles made of metal or plastic material, used for example for the storage of food, industrial, hygienic or pharmaceutical past or fluid products, and the like.

KNOWN PREVIOUS ART

Here and in the following it has to be noted that with the term "side surface" of the substantially cylindrical body, although preferably it is referred to the surface comprised between the bases of the cylindrical body, all of the body surfaces are meant, comprising the base surfaces.
Machines for coating cylindrical objects are known in the art, such as, for example, metal cans for beverages, that are provided with a plurality of print heads by which the outer surface of the cylindrical objects is painted and decorated with images, the brand of the product, symbols, characters, etc.
There are different techniques for painting cylindrical bodies, and specifically metal cans for beverages, such as the "offset" printing wherein the image intended to be printed is formed on the surface of a plurality of rolls, next transferred on a rubber plate and then on the body of the can.
The greatest drawback of this kind of printing is that in order to modify the image intended to be printed the replacement of the preformed surface of the rollers, wherein initially the ink is transferred, is needed, with the evident problems that the machine results poorly adaptable and that slowing down of the printing process due to the time needed for such a replacement is caused.
For this reason, printing techniques have been developed, known as digital printing (not requiring the use of an intermediate surface for creating the image), wherein the ink is directly applied on the surface of the cylindrical body intended to be treated.
Among the different methods for transferring the ink on the body surface, one of the most used techniques is the digital ink-jet printing technique.
The Patent US 6.769.357 describes a method and a machine for decorating cans of two pieces type, by means of a plurality of ink-jet print heads.
The cans are moved by a circular rotating plate on which are constrained one or more spindles, on which, in turn, the cans are loaded.
By doing so, each can could be displaced at the relevant print heads, that are arranged on a support having the shape of an arc of a circle placed outside of the rotating circular plate.
Further, every single spindle allows the rotation of the can around its own longitudinal symmetry axis, such that each print head can reach the whole outer surface of the can.
Of course, the machine is provided with means for loading and unloading the cans from every single spindle and with a painting station positioned downstream of the print heads.
EP 2 283 932 A1 shows an inkjet printer for printing on a three-dimensional shape.
Moreover, in a further possible embodiment, the decorating device is provided with a further row of print heads arranged in opposite position one to each other.
This kind of machine suffers from problems due to the shape of the transport means on which the cans are moved. Specifically, the use of a circular plate on which the spindles are constrained makes the machine structure very complicated, thereby resulting very expensive and difficult to realize, besides obviously being of considerable bulk.
In fact, the circular structure of the plate and the consequent displacement of cans along a circular path make necessary to provide the machine with wiping contacts in order to ensure the electrical connection needed for the power supply of the spindles and the control thereof.
This causes a high complexity of the machine for printing the cans, that causes a greater likelihood of running into failures over time.
In addition, it has to be noted that this kind of machines is generally provided with spindles retaining the cans thereon by means of air suction, therefore the realization and the management of the connections of pneumatic conduits for every single spindle put in rotation on the transport plate is very complicated and burdensome.
Further, it has to be noted that the specific arrangement of the print heads along an arc of a circle can determine problems to the correct delivery of the ink besides to the undesired build up or outflow thereof. Specifically, in the embodiment wherein two rows of print heads are present and they are arranged in opposite position one to each other on two arcs of a circle, these problems get worse.
As a matter of fact, in the print heads aligned one to each other along a straight vertical line, the bottom print head will undergo frequent problems of building up of ink and sediments coming from the top print head or from the piece under processing.
For the above mentioned reasons, this kind of machines requires frequent services and the need of as much frequent replacement of parts thereof.
The object of the present invention is to provide a device, with a corresponding activation method, for printing on the side surface of cylindrical bodies which is able to solve the problems of the known art, and specifically which is easy and cost effective to realize, of small bulk and able to reduce the complexity of means adapted to the displacement of the cylindrical bodies during processing.
In particular, the object of the present invention is to make less complex the realization and the management of the transport of cylindrical bodies under processing as well as provide transport means for the cylindrical bodies which are easy to control and could be accommodated in a limited space.
Also, it is a further object of the present invention to reduce the possibility of failures and the need of frequent services of the printing device.

SUMMARY OF THE INVENTION

These and other objects are achieved by a device and a method for printing on a side surface of substantially cylindrical bodies according to the independent claims 1 and 11.
Present invention concerns a device for printing on a side surface of at least one substantially cylindrical body, according to appended claim 1
As mentioned, the term "side surface" is herein and hereinafter used to mean all of the surfaces of the cylindrical body, comprising the base surfaces.
Further, with "central axis" the symmetry axis of the surface of the body intended to be treated is meant, specifically in case wherein printing on the side surface of a metal tube having cylindrical shape is intended, the central axis of such a surface corresponds to the longitudinal symmetry axis of the cylinder passing through the center of the two base surfaces.
It has be noted that the moving of the cylindrical bodies under processing along a straight vertical path with its central axis substantially orthogonal to such a vertical path allows to notably limit the bulks of the print device, to simultaneously process different cylindrical bodies without the need of using kinematic systems providing curved paths to these cylindrical bodies, to simplify the activations of the print head and to readily move the cylindrical bodies themselves, mainly during the coming in and out from the device.
According to a preferred embodiment, the printing device comprises at least a couple of ink-jet print heads, arranged in opposite position one to each other, such that the straight path along which the transport means move the cylindrical body/ bodies is comprised in the space between the two print heads of each couple of print heads.
The means for putting in rotation the cylindrical bodies preferably comprise one or more spindles supporting and putting in rotation the cylindrical body around its own longitudinal symmetry axis. The spindles are preferably arranged so that they put in rotation the cylindrical bodies with their central axis substantially perpendicular to the straight vertical path along which the cylindrical bodies are moved.
The transport means of the device according to the present invention, comprise at least one support, which can be shifted along a straight rail, on which one or more spindles are constrained.
The movement of the support/s for the spindles is controlled by means of a linear actuator.
According to a preferred embodiment, each print head delivers ink of one color and due to this reason the device comprises at least four print heads, or couples of print heads, delivering one of the three primary colors and the black, respectively.
By doing so, the cylindrical bodies can be transported in succession in front of the print heads reaching the position wherein the side surface intended to be treated is facing to the print head, or to one or more couples thereof.
The presence of the transport means of the cylindrical bodies allowing their displacement along a straight path, with its central axis substantially perpendicular to the latter, allows to obtain a compact machine easy to realize and control.
In fact, with the movement of the cylindrical bodies along a straight path and with their central axis orthogonal to such a path it is possible to simplify the electrical and/or pneumatic connections needed for the power supply and control of the individual spindles, while allowing to reduce the rate of possible failures and malfunctions complained about the machines known in the art.
These advantages are specifically appreciable since the straight path of movement is vertical.
In particular, these advantages become more evident when relating to the conventional machines for the decoration, such as the machine described in US 6.769.357 , provided with rotating drums for the transportation of the cylindrical bodies, wherein electric wiping contacts are needed to carry out the control of each individual spindle.
It has to be noted that the displacement of the spindles, and therefore of the cylindrical bodies, along the straight path by means of linear actuators allows to obtain high performances in terms of speed and accuracy of the positioning.
Moreover, means for moving one or more print heads are provided at least along a straight direction for at least part of the straight path along which the transport means move the cylindrical bodies.
More in detail, the cylindrical bodies must not be stopped during their movement along the straight path at the print heads to carry out the decoration of their surface. In fact, the device is provided with means for moving the print head too which, because of shifting along a straight direction for at least part of the path followed by the cylindrical bodies transported by the spindles, allow to carry out the moving delivery of the ink.
By doing so, the time required for the processing of the cylindrical bodies can be reduced and specifically the positioning mistakes due to the need of repeatedly stopping the motion of the spindles along the straight path at the print heads, or couples of print heads, with the possibility of running into misalignment errors of the surface of the cylindrical body relatively to the print head, can be limited.
The appended claim 11 discloses a method for printing on the side surface of substantially cylindrical bodies by means of a printing device according to the above described type.
It has to be noted that, in a possible embodiment, the cylindrical bodies can be put in rotation simultaneously with the activation of at least one print head.
Since the printing device is provided with means for moving at least one print head along a straight direction is employed, the method comprises a step wherein the print head is moved to follow the transport movement of at least one cylindrical body for at least one portion of the displacement of the latter along the straight path.
As previously mentioned, by means of these features the printing on the surface of the cylindrical bodies without stopping the movement of the latter, along the straight path, is possible.

BRIEF DESCRIPTION OF THE FIGURES

These and other advantages of the present invention will be evident from the following description and drawings herein enclosed for illustrative and not limitative purposes, wherein:

▪ Figure 1 shows a perspective view of the device for printing on the surface of cylindrical bodies according to the present invention;
▪ Figure 2 shows a front view of the device for printing on the surface of cylindrical bodies according to the present invention;
▪ Figure 3 shows a side view of the device for printing on the surface of cylindrical bodies according to the present invention;
▪ Figure 4 shows a plant view of the device for printing on the surface of cylindrical bodies according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION

Referring to figure 1, the device for printing on a side surface of substantially cylindrical bodies 2, herein illustrated in a perspective view, comprises a plurality of print heads 3a - 3d and 4a - 4d, transport means 5 and 6 for moving the cylindrical bodies along a straight path Z (visible in figure 2) with its own side surface facing to the print head/s, and means 7 for putting in rotation the cylindrical bodies around the central axis of the side surface. As can be seen in figures 1 - 3, the straight path Z for moving the cylindrical body 2 is vertical.
As previously said, with the term substantially cylindrical bodies is meant for example metal or plastic tubes employed for example for the storage of food, pharmaceutical or industrial products, either fluid or paste-like, or also cans for beverages or spray bottles, etc.
Further, it has to be mentioned that with "central axis" the symmetry axis of the surface of the body intended to be treated is meant, specifically in case wherein printing on the side surface of a metal tube, a can, having cylindrical shape is intended, the central axis of such a surface corresponds to the longitudinal symmetry axis X of the cylinder passing through the center of the two base surfaces. As shown in figures, advantageously, such a longitudinal symmetry axis (central axis) X of the cylindrical bodies 2 under processing is substantially orthogonal to the straight vertical path Z along which the same cylindrical bodies 2 are moved.
The printing device according to the present invention comprises a vertical support structure 10 (figure 1), formed by two supporting columns 11 and 12 on which the transport means 5, 6 of the cylindrical bodies 2 are moved.
As represented in the front view of figure 2, the transport means 5, 6 allow the moving of the cylindrical bodies 2 from a loading/unloading station A wherein the cylindrical bodies are loaded/eliminated on/from the printing device, and in succession they are transported into a printing station B, a controlling station C, ad at last, into a transit station D for the retum to the loading/unloading station A.
The displacement of the cylindrical bodies 2 through the device stations A - D, as shown in the attached figures, takes place along the straight vertical path Z.
It has to be noted that the device can be provided with other stations, for example for drying, labeling, assembling of a capsule in the case of tubes, or in general with stations for completing the working process of the cylindrical bodies. Further, although the device stations A - D hereinafter described provide for a movement in succession of the cylindrical bodies from bottom to top (see figure 2 specifically), in other possible embodiments the movement of the cylindrical bodies along the vertical path in subsequent stations from top to bottom can be provided.
As it will be better described in the following, the means 7 for putting in rotation the cylindrical bodies are constrained to the transport means 5 and 6.
The means used for loading and unloading the cylindrical bodies 2 on/from the transport means 5 and 6, and specifically on/from the means 7 for putting in rotation the cylindrical bodies, are not represented in the attached figures and they may comprise systems for moving objects of known type for such an use, such as for example robotic arms, and similar means.
The print heads 3a - 3d and 4a - 4d are preferably heads for digitally printing of the ink-jet type, although, as it will be evident for a person skilled of the art, other kinds of print heads can be used as long as they allow the ink delivery without requiring the contact with the surface of the cylindrical bodies intended to be decorated.
According to a preferred embodiment, the device according to the present invention is provided with four couples of print heads arranged in opposite and corresponding position to each other at the sides of the straight path Z along which the cylindrical bodies 2 under processing are moved (see specifically figure 2).
Of course, the print heads of each couple can be arranged in such a way to appear aligned or offset one to each other although being substantially facing to the sides of the linear path Z.
Alternatively, the print heads of the device can be arranged side by side one to each other, and specifically, in case wherein one or more couples of print heads facing one to each other are provided, each couple can be also formed by two or more print heads that are placed side by side.
As shown in figure 1 and in side view of figure 3, the print heads 3a - 3d and 4a - 4d are constrained apart relatively to the columns 11 and 12 of the device structure thanks to known means, not shown, in such a way to not prevent the passage of the transport means 5 and 6 of the cylindrical bodies 2.
More in detail, looking at the perspective view of the device of figure 1, the print heads 3a-3d are arranged on a support 15 placed on the left relatively to the straight path Z, whereas the print heads 4a - 4d, are arranged on a support 16 placed on the right of the straight path Z.
By doing so, the print heads are arranged in a position opposite to the sides of the straight path Z, specifically the print head 3a is opposed to (facing) the head 4a, the 3b to the 4b and so on to form the four or more couples of print heads through which the cylindrical bodies 2 moved by the transport means 5, 6 pass in succession to be decorated.
Preferably, each couple of print heads is designed to deliver the ink of a single color, so to aid the cleaning and maintaining operations thereof and avoid problems related to the feed of more colors to the print head, for example with connections to more receptacles of different color inks.
Further, it has to be noted that the presence of two or more print heads facing one to each other for each couple, allows to halve the time required for printing the surface of the cylindrical body under processing.
It also has to be noted that, to carry out the printing onto long cylindrical bodies, print heads facing one to each other but in offset position can be used.
As it will be better described in the following, the transport means 5 and 6 allow the alignment of each cylindrical body 2 transported with each couple of print heads, by temporarily stopping the movement along the straight path Z in a controlled way.
Before the surface of the body intended to be decorated is faced to the print head, or heads of a couple, it is put in rotation around its own longitudinal axis X by means of suitable means 7. As shown in the attached figures, the central axis X, that is the longitudinal axis X around which the cylindrical bodies 2 are put in rotation, is substantially perpendicular to the straight vertical path Z.
In case, the rotation motion of the cylindrical bodies 2 around their own longitudinal axis X can be forced when the body that is intended to decorate reaches the position in which it is facing to the print head, or heads of a couple and these are activated.
In the herein illustrated embodiment, the print heads 3a - 3d and 4a - 4d are fixed, in other words the supports 15 and 16 on which they are arranged are constrained apart from the columns 11 and 12 of the vertical structure of the device, but they cannot move relatively to them.
Nevertheless, although not shown in figures, the printing device according to the present invention comprises means for moving one or more print heads, or couple of print heads, along a straight path for at least part of the straight path Z along which the transport means 5, 6 displace the cylindrical bodies 2.
By doing so it is possible to print on the surface of the cylindrical bodies without stopping the movement of the latter, along the straight path Z.
Obviously, the ink delivery from the print heads 3a - 3d and 4a - 4d is controlled based on the image to be obtained on the surface relating also to the position detection of the cylindrical body and its rotation around its own central axis.
The number of couples of print heads can be changed according to the needs, for example relating to the image to be printed and based on colors needed for its complete realization.
In the embodiment shown in the figures, the device is provided with four couples of print heads, each couple delivering a single color, specifically the three primary colors and the black are delivered.
The transport means 5, 6 of the printing device may comprise a metal support 5 sliding along a straight rail 6 which, is its turn, is constrained to the columns 11 and 12 of the device structure.
The means 7 for supporting and putting in rotation the cylindrical bodies 2 consist of a plurality of spindles 7 constrained on the supports 5.
Each spindle 7 supports and puts in rotation, along its own longitudinal symmetry axis X, a cylindrical body 2 to be decorated along its side surface. As shown in figures, the cylindrical bodies are put in rotation around the X axis which is substantially perpendicular to the straight vertical path Z.
The rotation motion is imparted to the spindle 7 by one or more engines, not shown in the figures.
It has to be noted that the spindles 7 are moved independently, or alternatively they can be controlled simultaneously, for example by means of a single engine and a connecting belt transmitting the rotation motion to the spindles, in order to further limit the machine complexity.
In the embodiment shown in figures, the spindles 7 are grouped in three groups, of which each one is formed by four spindles. Each spindle belonging to a group is constrained by its own support 5 to a rail 6.
It has to be noted that each spindle group 7 can be moved on a rail 6 different from the spindles belonging to another group.
Linear actuators, or similar means known for such an use, not shown in figures, allow the controlled sliding of the supports 5 in each rail 6.
Advantageously, the use of linear actuators for the displacement of the supports 5 and thus of the spindles 7 allows to obtain precision and accuracy in the positioning and high speeds.
As better visible in the front view of the device of figure 2, the sliding of the supports 5 in the corresponding straight rail 6 allows to determine the displacement of the spindles 7 and thus of the cylindrical bodies 2 along the straight path Z.
By doing so each cylindrical body 2 passes through each couple of print heads arranged in a position opposite one to each other sideways of the straight path Z.
In other words, the print heads are arranged in opposite position and aligned one to each other, or in case they are offset one to another along a straight and not vertical line, preferably horizontal, thus avoiding problems of building up of the ink belonging to the machines known in the art.
It also has to be noted that the spindles 7 are movable relatively to the support 5 on which they are constrained in such a way that once the transit station D of the device is reached. They can be rearranged at the loading/ unloading station A.
More in detail, the spindles 7 are movable relatively to the supports 5 from an operating position to a rest position and vice versa.
The operating position is the position illustrated in figures, wherein the spindles 7 allow the passage of the cylindrical bodies 2 along the straight path Z between the print heads 3a - 3d and 4a - 4d.
In the rest position, instead, not shown in figures, the spindles 7 go outside of the print heads 3a - 3d and 4a - 4d following a path different from the path followed in the operating position.
Specifically, the spindles 7 of the group represented in figures at the station C of the device (top), can be shifted relatively to the supports 5 in the orthogonal direction relatively to the path Z, as pointed in figures 1, 2 and 4 with the arrow F. When the spindles are shifted to the right along the respective support 5, they reach the rest position in which they slide along the rail 6 passing outside (on the right) of the print heads 4a - 4d.
Similarly, the spindles 7 of the group represented in figures at the station C of the device (bottom), can be shifted relatively to the supports 5 in the orthogonal direction relatively to the path Z, as pointed in figures 1, 2 and 4 with the arrow G. When the spindles are shifted to the left along the respective support 5, they reach the rest position in which they slide along the rail 6 passing outside (on the left) of the print heads 3a - 3d.
The spindles 7 of the third group, represented in figures at the printing station B of the device, are movable on the corresponding supports 5 in the orthogonal direction relatively to the straight path Z, according to a direction parallel to the rotation axis X of the cylindrical bodies, as pointed in figures 1, 3 and 4 by the arrow H.
By doing so the spindles 7 reach the rest position wherein they cover the path Z by passing behind the print heads 3a - 3d and 4a - 4d.
It has to be noted that, according to the known art, the spindles 7 are provided with known means for retaining the cylindrical bodies 2, such as for example suction devices, suction caps, mobile wedges, retaining springs, etc.
It has to be noted as well that the printing device according to the present invention is provided with a control unit, not shown in the attached figures, by which the activation of the print heads and transport means and means for rotating the cylindrical bodies can be coordinated, so that to ensure high easiness of execution of the whole printing process and also to ensure the possibility of printing different images rapidly and without the need of long process stops.
In particular, the device may be provided with means for detecting the position of the cylindrical body relatively to the print heads, not shown in the figures, both relating to the position and the angular speed and therefore the rotation around the central axis of the surface on which the print is intended, and relating to its position along the straight path Z.
Further, as said, the device according to the present invention comprises a control station C in which suitable means check the presence of cylindrical bodies on the corresponding spindles and check their integrity, the conditions of the outer surface and of the carried out print. As said, other stations can be provided wherein the cylindrical bodies undergo other processing such as for example drying, labeling, assembling of a capsule, and further more processing in the same station can be carried out.
Further, although the print on cylindrical bodies has been referred to, the device and the method according to the present invention can be used for overprinting already processed cylindrical bodies.
The steps of a digital printing method on the side surface of cylindrical bodies according to the present invention by a device of the above described type will be now described.
Although reference will be made to the moving steps of a group formed by four spindles 7 along the same rail 6 of the device, it is clear that the number of groups and spindles for each group can change according to needs, and that in a further possible embodiment the spindles can be moved independently and not necessarily grouped.
At first the cylindrical bodies 2 are loaded on the spindles 7 in the loading/unloading station A of the device.
Next, by the activation of the linear actuator, not shown, the group of spindles 7 is moved along the straight rail 6 by the sliding thereon of the supports 5 on which the spindles are constrained.
By doing so the spindles 7 and therefore the cylindrical bodies 2 arranged thereon are transported along the straight rail 6 to the next stations A - D of the device. As already said, although having described and represented the stations A - D of the device in succession from bottom to top, the movement of the cylindrical bodies to be treated can be realized along stations arranged from top to bottom of the straight path along which they are moved.
Therefore, each cylindrical body 2 undergoes at first the printing in the station B and next it is verified in the control station C.
In fact, when the spindle 7 reaches the first couple of print heads 3a-4a the shift movement along the straight path Z is stopped and the cylindrical body reaches the position in which the side surface is facing to the couple of print heads.
Preferably, the cylindrical body 2 is put in rotation around its own central axis X by means of a servomotor activating the spindle 7 before the cylindrical body reaches the position in which its own side surface is facing the couple of print heads. Alternatively, the rotation motion can be imposed to the cylindrical bodies when the cylindrical body reaches the position in which the side surface is facing the couple of print heads and these are activated.
The print heads are activated and the ink, delivered in a controlled way by the print heads, can reach its outer surface.
Then, the cylindrical body 2 is displaced at the next couple of print heads which, in the same way as previously described, proceeds to the delivery of a second color.
By doing so, once the cylindrical body has undergone to the action of the couples of print heads of which the device is provided with, it has the desired image or decoration on its outer surface.
Evidently, as already said, the number of print heads and specifically of couples thereof can change according to needs.
At this point the group of spindles 7 first reaches the transit station D and then the loading/unloading station A in which the so decorated cylindrical bodies are removed by means known for such an use, not shown in the attached figures, to go on to the next processing steps and new cylindrical bodies to be decorated are loaded on the spindles.
In order to allow the displacement of the spindles from the transit station D to the loading/unloading station A, they are arranged in the rest position by the shift with respect to the support 5 they are constrained to, as previously described.
It has to be noted that the spindles, or the group of spindles, are sequentially moved so that a spindle, or a group thereof, is always available in the loading/unloading station A, thus avoiding stops in the printing process.
As already said, the printing device is provided with means for moving at least one print head along a straight direction and the method comprises a step wherein the print head is moved to follow the transport movement of one or more cylindrical bodies for at least part of the displacement thereof along the straight path Z.
By doing so, the printing on the surface of the cylindrical bodies can be carried out without stopping the movement of the latter along the straight path.

Claims

Device for printing on a side surface of at least one substantially cylindrical body (2) of the type comprising at least one print head (3a - 3d, 4a - 4d), transport means (5, 6) for displacing said at least one cylindrical body with its own side surface facing to said at least one print head, as well as means (7) for rotating said at least one cylindrical body around the central axis (X) of said side surface, wherein said transport means (5, 6) move said at least one cylindrical body along a straight vertical path (Z), said central axis (X) of said at least one cylindrical body being substantially perpendicular to said straight vertical path (Z), the device being characterized in that it comprises means for moving said at least one print head at least along a straight direction for at least part of said straight path followed by such transport means for said at least one cylindrical body, said means for moving said at least one print head following the transport movement of said at least one cylindrical body for at least part of the displacement of the latter along said straight path.
Device according to claim 1, characterized by comprising at least a couple of print heads (3a - 3d, 4a - 4d) arranged in an opposed position one to each other, said straight path (Z) along which such transport means (5, 6) move said at least one substantially cylindrical body (2) being comprised in the space between the two print heads of said at least one couple of print heads.
Device according to claim 2, wherein the print heads (3a - 3d, 4a - 4d) belonging to said at least one couple of print heads are disposed in an aligned position while substantially being opposed one to each other along a straight, not vertical, line.
Device according to claim 1 or 2, wherein said rotation means comprise at least one spindle (7) adapted to support and rotate said at least one substantially cylindrical body (2) around its own central axis (X).
Device according to claim 4, wherein said transport means comprise at least one support (5) on which one or more spindles (7) are constrained, said at least one support (5) being shiftable along a straight rail (6).
Device according to claim 5, wherein said displacement of said at least one support (5) for said at least one spindle (7) is controlled by at least one linear actuator.
Device according to claim 6, wherein said at least one spindle (7) is constrained on said at least one support (5) so that it is movable, relatively to said support, between an operating position and a rest position.
Device according to any one of the preceding claims, wherein said at least one print head (3a - 3d, 4a - 4d) is of the ink jet type, said at least one print head (3a - 3d, 4a - 4d) delivering ink of only one color.
Device according to claim 8, characterized by comprising at least four print heads, respectively delivering one of the three primary colors and black.
Device according to any one of the preceding claims, characterized by comprising means for detecting the position of at least one substantially cylindrical body (2) relatively to said at least one print head (3a - 3d, 4a - 4d).
Method for printing on a side surface of at least one substantially cylindrical body (2) by a printing device according to any one of the claims from 1 to 10, comprising the steps of:
• loading at least one of said cylindrical bodies (2) on said transport means (5, 6) of said device at a loading station (A);

• carrying along a straight vertical path (Z) at least one of said cylindrical bodies (2) by said transport means (5, 6);

• rotating, by said rotation means (7), said cylindrical body (2) around the central axis (X) of said side surface; said central axis (X) being substantially perpendicular to said straight vertical path (Z);

• facing said side surface of said at least one cylindrical body (2) to said at least one print head (3a - 3d, 4a - 4d);

• activating said at least one print head (3a - 3d, 4a - 4d) for printing on said side surface;

• displacing, during said step of activating said at least one print head for printing on said side surface, said at least one print head (3a - 3d, 4a - 4d) for following the transport movement of said at least one cylindrical body for at least part of the displacement of the latter along said straight path;

• displacing said at least one cylindrical body (2) by said transport means (5, 6) in an unloading station (A) for removing said at least one cylindrical body from said device.
Method according to claim 11, characterized in that the step of rotating, by said rotation means (7), said substantially cylindrical body (2) around the central axis (X) of said side surface is carried out simultaneously with that step of activating said at least one print head (3a - 3d, 4a - 4d) for printing on said side surface.
Method according to claim 11 or 12, characterized by comprising the further step of stopping, along said straight path, said at least one substantially cylindrical body with its side surface facing to said at least one print head, before said step of activating said at least one print head.