Inkjet digital printing press

Abstract

The present disclosure provides an inkjet digital printing machine (1) configured to detect a run-out profile of a container (5) to be printed and to move a print head (8) according to a per hour regularity uniquely determined by the run-out profile so as to keep constant the distance between the print head (8) and the container to be printed during the rotation of the container (5) itself.

Description

TECHNICAL FIELD

[0001] The present invention relates to an inkjet digital printing machine for printing on containers having a longitudinal axis. BACKGROUND

[0002] Among the solutions existing on the market for printing on cylindrical containers, there are rotary tables provided with support spindles of the cylindrical containers.

[0003] The rotary table rotates to position the spindles at the next printing station, in each of which a dedicated printing head applies an ink of a different colour between one printing station and the other.

[0004] When stopped at the printing station, the spindle itself rotates to expose the entire lateral surface of the cylindrical container to the printing head.

[0005] One of the main problems faced in printing machines of this type is how to ensure the same printing quality as the cylindrical container format changes.

[0006] This problem is further complicated by the fact that it occurs in the presence of some uncertainties in actual production.

[0007] First of all, the diameter tolerance of the containers to be printed, which is determined by the specific production process. This tolerance is quite low for metal products, but it is related to the digital printing process for plastic products.

[0008] Secondly, the gap between the spindle and the cylindrical container, which is necessary for the handling of the cylindrical container itself in the machine. This tolerance is common to both plastic and metal containers. The above technique has solved this problem for metal containers with a clamping system of the workpiece with an expanding clamp as shown in DE 102005052506 B4. When, during the rotation of the cylindrical container itself provided on the spindle, the surface to be printed is ensured equidistant from the nozzles of the printing head, this solution poses a critical problem that can cause damage to the workpiece itself if the material of the container is soft (for example, annealed aluminium) or the internal painting is particularly delicate. SUMMARY

[0009] The technical task of the present invention is therefore to provide an inkjet digital printing machine for printing on containers having a longitudinal axis, which eliminates the above technical drawbacks of the prior art.

[0010] As part of this technical task, one purpose of the present invention is to create an inkjet digital printing machine for printing on containers having a longitudinal axis, which is universal and can be adapted to print in different formats always with the same printing quality, regardless of the construction tolerances of the containers and of the tolerances for coupling the containers to the main shafts.

[0011] Another purpose of the present invention is to create an inkjet digital printing machine for printing on containers having a longitudinal axis, in which printing can be carried out with high quality without damaging the containers.

[0012] Another purpose of the present invention is to provide an inkjet digital printing machine for printing on containers having a longitudinal axis, which are also not cylindrical.

[0013] Another purpose of the present invention is to provide an inkjet digital printing machine for printing on containers having a longitudinal axis, which combines printing quality and production capacity. According to the technical task of the present invention and these and other purposes are all achieved by providing an inkjet digital printing machine for printing on containers having a longitudinal axis, comprising a conveyor table for conveying the at least one container and at least one printing station provided with at least one printing head, wherein the table has a rotation axis and supports at least one support main shaft on which the container can be locked, wherein the at least one main shaft has an axis oriented radially with respect to the rotation axis of the conveyor table, wherein the conveyor table is configured to convey and position the at least one main shaft at the at least one printing station, wherein the at least one main shaft can be activated in a manner rotating around its axis, wherein the axis of the at least one main shaft positioned at the at least one printing station is parallel to the longitudinal axis of the at least one printing head, characterized in that it comprises movement means for moving the at least one printing head, a detection station for detecting the eccentricity profile of the at least one container, comprising distance sensor means of the at least one container locked on the at least one main shaft rotating by itself, and an actuation controller for actuating the movement means, configured to drive the movement means according to a regularity per hour uniquely determined by the detected eccentricity profile, so as to keep the distance of the at least one printing head constant from the at least one container, during the rotation of the at least one main shaft by itself at the at least one printing station.

[0014] With the present invention, the distance between the emitter of the ink drops, i.e. the nozzle of the printing head, and the substrate to be disposed is kept constant, to always ensure the same printing quality.

[0015] In fact, since the drops are emitted at a constant speed, the time of arrival on the substrate is the same for all emitted drops.

[0016] This advantageously allows maintaining the alignment between the different colors and avoiding distortion of the image to be printed.

[0017] According to the application, the eccentricity of the container is compensated during printing in order to ensure the application precision of the drops and a relatively high image quality, without risking a deterioration of the quality of the paint or even of the geometry of the workpiece itself, thus leaving the workpiece itself free to be positioned on the support spindle.

[0018] According to the application, the movement device comprises a servo-assisted motorized device for the bidirectional linear movement (for example, vertically upwards and downwards) of the print head or group of print heads present in the printing station.

[0019] Advantageously, the workpiece can be placed on the spindle without being subjected to any mechanical action or pressure.

[0020] As far as ferromagnetic containers are concerned, the workpiece can be held on the spindle by pneumatic action (suction cup with vacuum) or by magnetic force.

[0021] During the rotation of the workpiece, the distance sensor device detects the eccentricity of the workpiece by measuring the mutual distance, thus obtaining a series of points along the outer peripheral contour of the workpiece.

[0022] The electronic controller obtains the eccentricity profile and constructs the corresponding workpiece eccentricity curve, which is sent to the motorized device driver, which moves the print head or group of print heads of the printing station.

[0023] The motorized device then generates a movement based on the eccentricity curve so that the distance between the print head or group of print heads and the container is constant during the self-rotation of the container in the printing station.

[0024] The detection of the eccentricity profile of the container is performed at a station upstream of the printing station.

[0025] As is often the case, if the printing machine comprises a series of printing stations aligned along the trajectory of the spindles supported by the rotating table, the print head or group of print heads of the subsequent printing station is moved in turn according to the same hourly regularity during the placement of the container.

[0026] In fact, once locked by the spindle, the container maintains its eccentricity position and angular position within the printing machine for the entire duration.

[0027] The synchronous rotation within the printing machine allows the hourly movement regularity to be transmitted to the next printing station in order to apply the next ink color accurately.

[0028] Preferably, the distance sensor device detects the eccentricity distribution at at least two axial dimensions of the container to better and more accurately reconstruct the actual position of the workpiece. If the workpiece is positioned skewed relative to the spindle axis, better control is allowed.

[0029] This invention expands the application of digital printing on non-cylindrical containers but with an axis of symmetry along the generatrix (e.g., tubular fittings or elliptical bottles).

[0030] In this case, through a special printing algorithm, the electronic controller can stretch the image to adapt to the different tangential speeds of the container presented in front of the printhead or printhead assembly.

[0031] Other features of the invention are further defined in the following claims. Attached Figure Description

[0032] Further features and advantages of the invention will become more apparent from the description of a preferred, but non-exclusive, embodiment of an inkjet digital printing press according to the invention for printing on a substrate having a longitudinal axis, illustrated by non-limiting examples in the accompanying drawings, wherein:

[0033] Figure 1 A schematic side front view of the printing press is shown, with only two printing stations shown for clarity;

[0034] Figure 2 A floor plan is shown, viewed from below the printing station.

[0035] Figure 3 This shows a view of the printing station in the radial direction relative to the axis of rotation of the table.

[0036] Figure 4 It shows the relationship with Figure 3 The same view, but in a vertical section, where the axial generatrix of the printed substrate has been added schematically;

[0037] Figure 5 An isometric view of the printing station is shown;

[0038] Figure 6 A plan view is shown, viewed from below the printing press;

[0039] Figure 7 A side front view of the eccentricity distribution detection station is shown;

[0040] Figure 8 The eccentricity distribution of the container locked on the main shaft is shown;

[0041] Figure 9 The hourly movement pattern of the print head or print head assembly at the printing station is shown. Detailed Implementation

[0042] With reference to the figures described, an inkjet digital printer 1 for printing on containers 5 having a longitudinal axis C is shown.

[0043] The substrates 5 can be intended for various purposes, such as food cans or deodorizing spray cans, detergents, etc.

[0044] The machine 1 comprises a printing unit 3, which comprises one or preferably a plurality of longitudinally extending printing stations 4, and a rotating conveyor table 2 for sequentially conveying the containers 5 through the printing stations 4.

[0045] The table 2 has a rotation axis L and supports one or more main shafts 6 for supporting the containers 5.

[0046] The rotation axis L of the table 2 is preferably vertical.

[0047] The main shafts 6 are positioned at a defined angular pitch, in particular constant, around the rotation axis L of the table 2.

[0048] Each main shaft 6 has an axis M radially oriented with respect to the rotation axis L of the table 2 and can be activated in rotation about its axis M by special motor means not shown.

[0049] Each main shaft 6 has an internal suction to lock the containers 5 on the main shaft 6.

[0050] In the case of ferromagnetic containers 5, the containers 5 can also be locked on the main shafts 6 by special magnetic locking elements.

[0051] The printing unit 3 has the printing stations 4 positioned along a circular trajectory of the main shafts 6.

[0052] In the case shown, in which the table 2 has a vertical rotation axis L, the printing stations 4 are positioned above the rotating table 2.

[0053] The printing stations 4 are positioned at a defined angular pitch around the rotation axis L of the table 2, in particular equal to or a multiple of the angular pitch of the main shafts 6. Each printing station 4 is provided with one or preferably a group of printing heads 8 having parallel longitudinal axes P.

[0054] The table 2 can be activated in step-by-step rotation by special motor means not shown for the sequential transfer and stop of the main shafts 6 and the containers 5 at the printing heads 8 of the printing stations 4.

[0055] The axis M of each main shaft 6 is parallel to the longitudinal axis P of the printing heads 8 of the printing station 4 in which it is stopped.

[0056] With reference to the printing heads 8 of substantially parallelepiped shape shown, the main lying plane S corresponds to a central plane parallel to the two lateral longitudinal surfaces.

[0057] In printing heads 8 of this shape, the lower longitudinal surface is equipped with one or more rows of longitudinal ejection nozzles in parallel.

[0058] The axis M of each spindle 6 is equidistant from the printing heads 8 of the printing station 4 on which it stops.

[0059] Advantageously, each printing station 4 comprises special movement means for moving all the printing heads 8 in common.

[0060] In particular, these movement means comprise servo-assisted motor means for bi-directional linear movement of the heads 8 in a direction parallel to the rotation axis L of the table 2.

[0061] Furthermore, advantageously, the printing machine 1 comprises a station 100 for detecting the eccentricity profile of the containers 5.

[0062] The detection station 100 comprises distance sensor means of the containers locked on the respective spindles 6 that rotate by themselves.

[0063] The detection station 100 also comprises an actuation controller for actuating the movement means of each printing station 4.

[0064] The controller is configured to activate the movement means at each printing station 4 with a per hour law s = s(t) uniquely determined by the detected eccentricity profile during the self-rotation of the spindle 6.

[0065] The per hour law s = s(t) is defined starting from the detected eccentricity profile so as to keep the distance of the printing heads 8 from the containers 5 constant at each printing station 4 during the printing process.

[0066] The sensor means 101 comprise one or more non-contact distance sensors, for example optical sensors.

[0067] The distance sensors 101 are installed in a fixed position in the detection station 100 and are oriented orthogonally to the axis M of the spindles 6.

[0068] During a 360° rotation of the spindle 6 by itself, the sensors 101 acquire the eccentricity profile of the container 5 locked on the spindle 6.

[0069] Preferably, in order to more accurately reconstruct the eccentricity of the container 5, at least two optical sensors are included, spaced apart along the axis of the spindle 6.

[0070] During the rotation of the container 5, the sensor means detect the eccentricity of the container by measuring the mutual distance, thus acquiring a series of points along the outer peripheral contour of the container 5.

[0071] In the implementation, the electronic controller acquires the distance measurements and constructs the eccentricity profile of the workpiece, with which it details the hourly law s = s(t). Such a profile is sent to the motorized means driver of the moving print head 8.

[0072] The motorized means generate a movement according to the hourly law s = s(t) so that the distance between the print head 8 and the container 5 is constant during the self-rotation of the container 5 at each printing station 4.

[0073] The detection of the eccentricity profile of the container 5 is performed at a station upstream of the printing station 4.

[0074] The print heads 8 of the subsequent printing stations are then moved in succession according to the same hourly law during the same stop of the container 5.

[0075] In fact, once the container 5 is locked by the main shaft 6, it maintains its eccentricity position and angular position within the printing machine 1 for the entire duration.

[0076] As for containers with a significant eccentricity profile, by means of a special printing algorithm, the electronic controller can stretch the image to be printed so as to adapt it to the different tangential speed with which the container 5 presents itself in front of the print head 8.

[0077] The machine 1 comprises initial setting means for setting the initial distance d between the axis M of the main shaft 6 and the print head 8 of the printing station 4 and the orientation of the main placement plane S of the print head 8.

[0078] The initial setting depends on the format of the container 5 to be printed.

[0079] With this initial setting, the print head 8 is tilted so that the axis M of the main shaft 6 stopped at the printing station 4 belongs to the central plane S of the print head 8.

[0080] The longitudinal size of the printing station 4 must be such as to fit the axial length of the cylindrical printing substrate 5.

[0081] Therefore, although the solution shown by way of example only comprises three print heads 8 per printing station 4, the number of print heads 8 per printing station 4 can be variable.

[0082] If the printing station 4 is designed with multiple print heads 8, these must have an overlapping portion F in the direction of their longitudinal axis P.

[0083] In order to ensure the partial overlap and at the same time the tilt required by their main placement plane S, adjacent print heads 8 have their main placement plane S with an offset angle a with respect to the axis M of the main shaft 6.

[0084] Therefore, two rows of printing heads 8 are delineated, each of which shares a main placement plane S.

[0085] The printing station 4 has frames 30, 36 for supporting the two rows of printing heads 8.

[0086] Each row of printing heads 8 is supported by a respective support structure 13, 23, 31.

[0087] Each support structure 13, 23, 31 comprises a longitudinal plate 13 and corner supports 31a, 31b for each printing head 8, which in turn support a carriage 23 for housing the printing head 8.

[0088] Each corner support 31a, 31b is independently supported by the longitudinal plate 13 in a linearly adjustable position along the longitudinal plate 13 itself.

[0089] Each corner support 31a, 31b in turn supports the carriage 23 and the printing head 8 fixed therein in an angularly adjustable position about a pin 32.

[0090] Each corner support 31a, 31b has a base 31a and a shoulder 31b.

[0091] More precisely, the carriage 23 is fixed to a base 33 which abuts against the base 31a of the corner support 31a, 31b.

[0092] The device for setting the orientation of the printing heads 8 comprises an elbow lever system 9.

[0093] The elbow lever system 9 can be activated to force the two rows of printing heads 8 to rotate in unison about respective pivots 10.

[0094] For each row of printing heads 8, the respective pivot 10 is positioned at the lower end 11 of the printing heads 8 and defines an axis of rotation Q parallel to the axis M of the main shaft 6.

[0095] An end block 36 of the longitudinal plate 13 is engaged on the pivot 10, which is constituted by a pin having a crescent cross-section.

[0096] In particular, the end block 36 has, on its outer peripheral edge, a special engagement seat 36 which is conjugated with the pivot 10.

[0097] The elbow lever system 9 has symmetrical connecting levers 12, the lower end of each of which is hinged on the longitudinal plate 13 of the corresponding support structure 13, 23, 31a, 31b.

[0098] While the upper end of each connecting lever 12 is operatively connected to an engaging nut 15 so as to slide along a screw 16 having a vertical axis V which intersects the axis M of the main shaft 6.

[0099] More precisely, the longitudinal bars 37 have, at opposite ends, articulations connected to the connecting rod 12, which are fixed centrally to the nut 15.

[0100] The lower articulation axis H and the upper articulation axis I of the connecting rod 12 are in turn parallel to the axis M of the main shaft 6.

[0101] The screw 16 is supported in a special housing 19 fixed to the longitudinal bars 36 of the frame 30, 36.

[0102] In the implementation, the screw 16 can rotate by itself without translation, in order to drag the nut 15 upwards and downwards, and thus activate the toggle lever 9.

[0103] Elastic pushing means are provided to keep the two rows of printing heads 8 rotating around their respective pivots 10 when the toggle lever 9 is activated.

[0104] The elastic pushing means comprise symmetrical springs 17 configured and arranged to exert a pushing force in an obliquely downward direction at the lower articulation of the connecting rod 12.

[0105] Each printing station 4 also comprises fine adjustment means for adjusting the mutual position of the printing heads 8.

[0106] The fine adjustment means comprise first fine adjustment means of the overlapping portion F between the printing heads 8.

[0107] For each printing head 8, the first fine adjustment means comprise a micrometer screw 20 resisted by a spring 21, for eliminating the thread play of the micrometer screw 20.

[0108] The micrometer screw 20 is supported in a housing 22 fixed to the longitudinal plate 13 and engages a threaded hole 24 present in a flange 25 fixed to the base 31a of the corner plate 31a, 31b.

[0109] For the adjustment, by activating the micrometer screw 20 the corner plate 31a, 31b and consequently the carriage 23 housing the printing head 8 are moved along the longitudinal plate 13.

[0110] The fine adjustment means also comprise second fine adjustment means for adjusting the mutual alignment between the longitudinal axes P of the printing heads 8.

[0111] Also in this case, for each printing head 8, the second fine adjustment means comprise a micrometer screw 26 resisted by a spring 40, for eliminating the thread play of the micrometer screw 26.

[0112] The micrometer screw 26 is supported in a housing 38 fixed to the base 31a of the corner plate 31a, 31b and engages a threaded hole 39 present in the base 33 of the carriage 23.

[0113] The micrometric screw 26 rotates the carriage 23 about the pin 32, and the rotation of the carriage 23 is opposed by the spring 41, which is supported by the shoulder 31b of the angular support 31a, 31b and abuts against the carriage 23.

[0114] The spring 41 slides on the carriage 23 to allow the rotation thereof, but remains under tension so as to oppose the angle of rotation effected by the carriage 23 after the activation of the micrometric screw 26.

[0115] Each printing station 4 is arranged to dispense ink in a single colour.

[0116] The printing process is carried out as follows.

[0117] Before starting the printing process, initial settings are carried out relating to the format of the containers 5 to be printed.

[0118] If the outer diameter of the batch of containers 5 to be printed is greater than that of the batch of containers just printed, the printing unit 3 must move away from the table 2 to allow the containers 5 to be positioned correctly under the printing heads 8 of each printing station 4, and vice versa if the outer diameter is smaller.

[0119] At this point, the toggle lever 9 is activated at each printing station 4 to re-orient the lying plane S in which the printing heads 8 lie, so that the printing can take place substantially on the condition that the axis of the containers 5 belongs to the main lying plane S of the printing heads 8.

[0120] Before starting the printing process, the printing heads 8 of each printing station 4 are also adjusted by means of the micrometric screws 20, 26, which adjust the overlap F between the printing heads 8 and the alignment of their longitudinal axes P in the direction parallel to the axis M of the main shaft 6, respectively.

[0121] In particular, the overlap F must be set so as to overlap one or more jet nozzles comprised in an adjacent printing head 8.

[0122] Once the preliminary adjustment has been completed, the table 2 is activated, and the containers 5 are supplied to the main shafts 6 of the table by a loader not shown.

[0123] The table 2 is activated in a step-by-step manner, and in each advancement step, the table sequentially positions each first container 5 under the detection station 100 and subsequently under the subsequent printing station 4.

[0124] At each stop of the table 2, the main shafts 6 are rotated about their axis M.

[0125] During the rotation of the containers 5 under the detection stations 100, their eccentricity profile is acquired, which will be processed by the electronic controller to establish the hourly movement law s = s(t) to be executed by the print heads 8 to keep their distance from the containers 5 constant when they will stop here.

[0126] The ink is dispensed at each printing station 4 with a single channel, in which the print heads 8 move according to the hourly movement law s = s(t) in a synchronized manner with the own rotation of the containers 5.

[0127] Each printing station 4 is dedicated to the application of a single ink of a different color from that used in the other printing stations 4.

[0128] The inkjet digital printer for printing on cylindrical substrates as envisaged herein is susceptible to many modifications and variants, all falling within the scope of the inventive concept; moreover, all the details can be replaced by technically equivalent elements.

[0129] In practice, the materials used, as well as the dimensions, can vary according to requirements and the state of the art.

Claims

1. An inkjet digital printing machine (1) for printing at least one container (5) having a longitudinal axis (C), the inkjet digital printing machine comprising: A conveyor table (2) for conveying the at least one container (5) and at least one printing station provided with at least one print head (8), wherein the conveyor table (2) has a rotation axis (L) and supports at least one spindle (6) on which the container (5) can be locked, wherein the at least one spindle (6) has an axis (M) radially oriented relative to the rotation axis (L) of the conveyor table (2), wherein the conveyor table (2) is configured to convey and place the at least one spindle (6) at the at least one printing station, wherein the at least one spindle (6) can be activated to rotate about its axis (M), wherein the axis (M) of the at least one spindle (6) placed at the at least one printing station is parallel to the at least one print head. (8) longitudinal axis (P), characterized in that the inkjet digital printer includes a moving device for moving the at least one printhead (8), a detection station (100) for detecting the eccentricity distribution of the at least one container (5), and an actuation controller for actuating the moving device, the detection station including a distance sensor device (101) of the at least one container (5) locked on the at least one spindle (6) rotating on itself, the actuation controller being configured to drive the moving device according to an hourly pattern uniquely determined by the detected eccentricity distribution during the rotation of the at least one spindle (6) at the at least one printing station, so as to maintain a constant distance between the at least one printhead (8) and the at least one container (5).

2. The inkjet digital printing machine (1) according to claim 1, characterized in that, The moving device includes a servo-assisted motor for bidirectional linear movement of the at least one printing head (8) along the rotation axis (L) parallel to the conveyor table (2).

3. The inkjet digital printing press (1) according to claim 1 or 2, characterized in that, The distance sensor device (101) includes one or more non-contact distance sensors.

4. The inkjet digital printing press (1) according to claim 3, characterized in that, The distance sensor (101) is an optical sensor.

5. The inkjet digital printing press (1) according to claim 4, characterized in that, The optical sensor is installed at a fixed position in the detection station (100) and is oriented in a emission direction orthogonal to the axis (M) of the main shaft (6).

6. The inkjet digital printing press (1) according to claim 5, characterized in that, At least two optical sensors are configured to be spaced apart along the axis of the main shaft (6).

7. The inkjet digital printing press (1) according to claim 1 or 2, characterized in that, The actuation controller is further configured to perform stretching of the image to be printed to adapt the image to different tangential speeds at which the container (5) presents itself to the at least one printhead (8).

8. The inkjet digital printing press (1) according to claim 1 or 2, characterized in that, The conveyor table (2) has a vertical axis of rotation.

9. The inkjet digital printing press (1) according to claim 1 or 2, characterized in that, The at least one printing station (4) includes a set of printing heads (8) having a longitudinal axis (P) parallel to the axis (M) of the main shaft (6) and equidistant from the axis of the main shaft.

10. A printing method using an inkjet digital printer (1), the inkjet digital printer being used to print at least one container (5) having a longitudinal axis (C), wherein the inkjet digital printer (1) comprises: A conveyor table (2) for conveying the at least one container (5) and at least one printing station (4) provided with at least one print head (8), wherein the conveyor table (2) has a rotation axis (L) and supports at least one spindle (6) locked thereon, wherein the at least one spindle (6) has an axis (M) radially oriented relative to the rotation axis (L) of the conveyor table (2), wherein the conveyor table (2) conveys and positions the at least one spindle (6) at the at least one printing station, wherein the at least one spindle (6) is activated by rotation about its axis (M), wherein the at least one print head (8) is positioned at the at least one printing station The axis (M) of the at least one spindle (6) at the printing station is parallel to the longitudinal axis (P) of the at least one print head (8), wherein an eccentricity distribution of the at least one container (5) is detected upstream of the printing station (4), the container (5) is locked on the at least one spindle (6) which is rotating on its own, and wherein during the rotation of the at least one spindle (6) at the at least one printing station (4), the at least one print head (8) moves according to an hourly regularity uniquely determined by the detected eccentricity distribution in order to maintain a constant distance between the at least one print head (8) and the at least one container (5).

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