Decoration method and machine for surface decoration of ceramic articles

Abstract

Decoration method and machine (1) for surface decoration of ceramic articles (T); the decorating machine (1) comprises: a conveyor device (5) having a metal support structure (7) and a belt (8) for supporting and transporting ceramic articles (T) through a printing station (6) of at least about 2 meters long; comprising a plurality of digital printing devices (10); a detection unit (11) for detecting a quantity related to the speed of movement of the conveying means (5), the detection unit comprising a reference (12) integral with the belt (8), a detector (13) for detecting each passage of the reference (12), and processing means for calculating the time interval between successive signals from the detector (13); and a control unit (CU) for adjusting the mutual operation of the different digital printing devices (10) in order to apply a defined pattern on the surface (3) to be decorated of the ceramic article (T), depending on the amount dependent on the speed of movement of the conveying device (5).

Description

[0001] Cross - reference to related applications

[0002] This patent application claims the priority of Italian Patent Application No. 102022000018333, filed on September 8, 2022, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] The present invention relates to a decoration method and a machine for surface decoration of ceramic articles. The present invention also relates to a method and an apparatus for manufacturing ceramic products, in particular ceramic slabs and tiles. Background art

[0004] In the field of production of ceramic products, there is an increasing need to manufacture ceramic articles, such as ceramic slabs and tiles, having a surface decoration on the visible surface suitable for reproducing the appearance of natural materials, such as wood or natural stone, such as marble, granite, etc.

[0005] Generally, in order to produce such a surface decoration, a decoration machine is used. Such a decoration machine is adapted to apply a defined pattern on the surface to be decorated of a ceramic article (usually already dried, thus hot but still raw) by using a specific ink, which ink is capable of penetrating into the surface of each dried ceramic article by printing the desired decoration and at the same time is capable of withstanding even higher temperatures that the article itself will undergo during subsequent firing without deteriorating or impairing the resolution of the decoration itself.

[0006] This type of decoration machine generally includes a belt conveyor device, which in turn includes a metal support structure around which a belt defining a conveying plane is assembled. The belt conveyor device moves the ceramic article along a given path in a moving direction through a printing station, at which the aforementioned pattern (i.e., the aforementioned graphic) is applied by means of a printing assembly provided with a plurality of inkjet printing devices (also called print heads). Generally, in the ceramic field, in order to obtain good resolution and maintain this resolution even after the firing step at high temperature, a printing assembly is used, which is provided with a plurality of inkjet printing devices (in the most common cases, at least six inkjet printing devices; in the most modern systems, up to twelve inkjet printing devices), which inkjet printing devices are arranged one after another along the moving direction of the conveyor device and are operated by a control unit to each apply at least a part of the defined pattern when the ceramic article moves along the given path through the printing station, so that the printing station has an extension of at least about 2 meters along the moving direction of the ceramic article.

[0007] For example, a known type of decoration method and device is described in patent document EP2213462B1, which is adapted to form a pattern on at least a part of an object that is at least partially provided with a three-dimensional structure.

[0008] Although known types of decoration methods and machines generally guarantee excellent performance, they have some drawbacks, among which we mention the following.

[0009] One of the main drawbacks is related to the thermal variations that a decoration machine may undergo during its service life, which vary with the thermal variations of the environment in which the decoration machine is placed and / or the temperature variations of the ceramic articles that the machine is intended to process. This can cause subsequent deformations of the components of the decoration machine itself. This problem is particularly evident when the decoration machine is intended to receive and decorate dried ceramic articles just out of the dryer, which are hot, especially having an average temperature of at least about 35 °C (over their entire extent). Thus, they tend to transfer part of their heat to the belt conveyor device (especially to both the belt and the metal support structure), which will undergo significant temperature variations during its service life. Obviously, these temperature variations (which can be about 20 - 30 °C within a few minutes) cause subsequent deformations of the belt conveyor device, especially of the metal support structure, and the components of the metal support structure will tend to expand or contract as the temperature rises or falls.

[0010] These dimensional variations of the components of the metal structure of the belt conveyor device, especially of the drive and return rollers around which the belt conveyor is assembled, cause subsequent variations in the tension of the belt and thus in the moving speed of the dried ceramic articles. It should be understood that the more significant these variations are, the higher the temperature at which the dried ceramic articles appear in the area of the decoration machine, the longer the printing station, and / or the greater the thermal variations of the working environment in which the decoration machine operates.

[0011] For this reason, it is necessary to increase the deformations or, in any case, the dimensional variations that the belt conveyor device (especially the metal support structure) undergoes during variations in the time and number of work cycles and variations in the weight and dimensions of the various ceramic articles to be transported (in which case this can also cause deformations of the components of the metal structure).

[0012] All these variations (those caused by temperature variations and those more related to the phenomenon of mechanical drift) mean that, assuming the decorating machine is used under optimal conditions and thus the conveying device is used (therefore at room temperature and with the metal structure undeformed), the dried ceramic articles reach the various printing devices (printing heads) of the printing assembly before or after the expected moment by moving along the above - given path on the conveying plane. In other words, such dimensional variations cause misalignment of the dried ceramic articles relative to the different printing devices, thus leading to errors and / or phase shifts in the application of the decoration by the different printing devices of the printing assembly.

[0013] This results in defects in the defined pattern applied by the decorating machine (see in particular Figure 5 the pattern rows at the top in Summary of the Invention

[0014] The aim of the present invention is to provide a decorating method and machine for the surface decoration of ceramic articles, which allows at least partially overcoming the limitations of the prior art.

[0015] According to the present invention, there is provided a decorating method and machine for the surface decoration of ceramic articles as claimed in the appended independent claims and preferably in any claim directly or indirectly subordinate to the independent claims.

[0016] The claims describe the preferred embodiments of the present invention. Description of the Drawings

[0017] The present invention will now be described with reference to the drawings, which show some non - limiting examples of embodiments of the present invention, in which:

[0018] - Figure 1 shows a schematic side view of a part of the equipment for manufacturing ceramic products;

[0019] - Figure 2 shows a schematic side view of a decorating machine for the surface decoration of ceramic articles according to a first embodiment of the present invention;

[0020] - Figure 3 shows a schematic side view of a decorating machine for the surface decoration of ceramic articles according to a second embodiment of the present invention;

[0021] - Figure 4 shows a schematic side view of a decorating machine for the surface decoration of ceramic articles according to a third embodiment of the present invention; and

[0022] - Figure 5Shows a comparison between the patterns printed by a conventional decorating machine (the top four patterns) and the patterns produced with the decorating machine according to the present invention (the bottom four patterns). Detailed Description

[0023] According to a first aspect of the present invention, in the figures, 1 globally represents a decorating machine for the surface decoration of ceramic articles T, in particular articles comprising (raw) ceramic material. Advantageously but not restrictively, in the present discussion, the expression "ceramic article T" is intended to mean an article comprising (raw) ceramic material, which may but does not have to undergo a drying heat treatment; even more specifically (advantageously but not restrictively), the expression "ceramic article T" is intended to mean a raw article, or a raw ceramic article that has been dried and thus has undergone drying but not yet firing.

[0024] Advantageously but not restrictively, the ceramic article T comprises a powdered ceramic material CP (in particular, formed starting from the powdered ceramic material CP), which comprises clay, sand, feldspar and other minerals, and the powdered ceramic material CP is compacted to obtain the ceramic article, which may subsequently be dried but not yet fired. According to some advantageous but not restrictive embodiments, the ceramic article T is a dried ceramic article and comprises (in particular, is) a ceramic article having an average temperature (over its entire extent) of at least about 35 °C, more particularly at least about 40 °C. Even more specifically, advantageously but not restrictively, the ceramic article T is a ceramic article that has undergone a drying heat treatment no more than about 3 minutes (in particular, no more than 4 minutes) before entering the decorating machine 1, and the ceramic article is thus heated in a dryer 2 at a temperature of at least about 80 °C, in particular at least about 100 °C, which will be better explained below.

[0025] The ceramic article T also has at least one surface 3 to be decorated (in use, oriented upwards) and at least one further surface 4, which is parallel and opposite to the surface 3 to be decorated (in use, facing downwards).

[0026] Typically but not necessarily, the ceramic article T has a substantially quadrilateral shape (in plan view). More precisely, the ceramic article T has a substantially parallelepiped shape. In some particular but non-restrictive cases, the ceramic article T has a substantially rectangular shape (in plan view).

[0027] With particular reference to Figures 2 to 4, Advantageously, the decorating machine 1 comprises: a conveying device 5 configured to convey the ceramic article T along a given path P in the moving direction A through a printing station 6, the conveying device 5 further comprising a metal support structure 7 and a belt 8 mounted on the metal support structure 7, the belt 8 defining with its branches a conveying plane for supporting and conveying the ceramic article T during its movement; and a printing assembly 9 arranged at the printing station 6, the printing assembly 9 being configured to apply a defined pattern (i.e., a defined graphic) on the surface 3 to be decorated of the ceramic article T and comprising a plurality of digital printing devices 10 arranged one after another along the moving direction A; and a control unit CU configured to operate each of the printing digital printing devices 10 of the printing assembly 9. According to some non-limiting embodiments (such as Figures 2 to 4 those shown in), the printing assembly 9 comprises (in particular, is) a digital inkjet printer, and the digital printing device 10 is an inkjet print head. Advantageously but not necessarily, the printing assembly 9 comprises at least six (in particular, at least eight; even more particularly, between eight and twenty; more particularly, between four and twelve) digital inkjet printing devices 10 arranged one after another along the moving direction A. In particular, advantageously but non-limitingly, the printing assembly 9 comprises at least one first printing device 10' arranged at the starting position of the printing station 6, and at least three other printing devices (in particular, at least seven other digital printing devices 10; even more particularly, at least eleven other digital printing devices 10) arranged one after another downstream of the first digital printing device 10' along the moving direction A at the aforesaid printing station 6. Even more advantageously but non-limitingly, the digital printing devices 10 of the printing assembly 9 are arranged at a given distance from each other. In particular, the mutual distance between successive digital printing devices 10 among the plurality of digital printing devices 10 is at least about 10 cm between them; in particular, it ranges from about 10 cm to about 2 m.

[0028] Specifically, in the Figures 2 to 4 advantageous but non-limiting embodiment shown, the printing assembly 9 comprises twelve digital printing devices 10, which are subdivided into two printing modules, the first printing module having eight printing devices 10 and the second printing module having the other four digital printing devices 10, these printing devices 10 being arranged at a certain distance from each other and one after another along the moving direction A. The large number of digital printing devices 10 advantageously allows to produce a more precise pattern or graphic, which has a good resolution and can maintain this resolution even after firing and drying the ceramic article T.

[0029] Advantageously but not restrictively, the printing station 6 extends along the moving direction A for a length of at least about 2 meters; in particular, for a length of at least about 4 meters; even more particularly for a length equal to at least about 6 meters.

[0030] Advantageously, the decorating machine 1 further comprises a detection unit 11 which is configured to advantageously but not necessarily continuously detect a quantity related to the moving speed of the conveying device 5 (in particular, the moving speed of the conveying plane defined by the belt 8), and the aforementioned control unit CU is configured to advantageously but not restrictively retroactively adjust the mutual operation of the different digital printing devices 10 of the printing assembly 9 based on the quantity related to the moving speed of the conveying device 5 (detected by the detection unit 11) so as to apply the aforementioned defined pattern on the surface 3 to be decorated of the ceramic article T; in particular, so that when the actual moving speed of the conveying device 5 changes, the aforementioned defined pattern is also accurately applied on the surface 3 to be decorated, that is, independently of different factors that may affect the speed of the conveying device 5 (such as the temperature and the actual tension of the belt 8). This allows any change in the moving speed of the conveying device 5 to be taken into account in real time when the temperature of the metal structure 7 and / or the tension of the belt 8 change (for example, due to environmental factors (such as temperature) and / or mechanical factors causing deformation), without compromising the quality of the defined pattern applied on the surface 3 to be decorated of the ceramic article T.

[0031] Advantageously but not restrictively, the conveying device 5 (which is known per se), in particular the metal structure 7, comprises a pair of driving rollers 70 (schematically shown in Figures 2 to 4 ), which pair of driving rollers 70 are arranged parallel to each other at a given distance from each other along the moving direction A, the given distance being in the range from about 2.5 meters to about 12 meters (in particular, from about 3 meters to about 10 meters; even more particularly, equal to about 4 meters), and the belt 8 is mounted on the pair of driving rollers 70 so as to be stretched and operated by the rotation of the driving rollers 70 during its movement. According to some advantageous but non-restrictive embodiments, the belt 8 (which is known per se) comprises a double aromatic polyamide fiber weft coated with polyurethane (in particular, is made of a double aromatic polyamide fiber weft coated with polyurethane).

[0032] According to some advantageous but non-restrictive embodiments (such as Figure 2 and Figure 4In the illustrated embodiment), the detection unit 11 includes: a reference 12 integral with the belt 7; at least one detector 13 configured to detect each passage of the reference 12 at a first given position P1 and emit a corresponding detection signal; and a processing device (not visible in the drawings) connected to the detector 13 to receive each detection signal and estimate the quantity related to the movement speed of the conveying device 5 (in particular, the belt 8 of the conveying device 5; more particularly, the aforementioned conveying plane) based on the (temporal) variation of a quantity related to the distance covered by the reference 12 between two successive emissions of detection signals by the detector 13 (in particular, during the elapsed time) (more particularly, between two successive passages of the reference 12 at the aforementioned first given position P1).

[0033] Specifically, advantageously but not restrictively, the processing device is configured to estimate a quantity related (in particular, consistent) to the distance covered by the reference 12 between two successive passages at the aforementioned first given position P1, and cyclically compare the latest estimated value of this quantity with the previous one in order to evaluate the aforementioned quantity related to the movement speed of the conveying device 5 (in particular, the belt 8 of the conveying device 5; more particularly, the aforementioned conveying plane) based on the variation over time of the estimated value of the quantity related to the distance covered by the reference 12 between two successive emissions of detection signals by the detector 13 (in particular, between two successive passages of the reference 12 at the aforementioned first given position P1).

[0034] Alternatively or in combination, according to some advantageous but non - restrictive embodiments, the processing device is configured to estimate the quantity related to the movement speed of the conveying device 5 (in particular, the belt 8 of the conveying device 5; more particularly, the aforementioned conveying plane) based on the time interval elapsed between two successive emissions of detection signals by the detector 13. According to some advantageous but non - restrictive embodiments (e.g., Figures 2 to 4 the embodiment schematically illustrated), it includes a processing device which is in particular consistent with the control unit CU of the decorating machine 1.

[0035] According to some advantageous but non - restrictive embodiments (e.g., Figure 2 and Figure 4 those shown), the reference numeral 12 is a metal plate fixed (e.g., hardened) to the belt 8. It should be understood that according to other embodiments not shown, the reference 12 can be of any other type, such as a hole or notch made in the belt, another type of indicator (other than the metal plate) inserted into the structure of the belt itself, etc.

[0036] Advantageously but not restrictively, the reference 12 is arranged at the lateral end region of the belt 7 itself; in particular, in a region which, in use (i.e., when the ceramic article T is on the conveying plane defined by the belt 8), is not affected (covered) by the passage of the ceramic article T on the belt 8 itself. It should be understood that, according to other non-restrictive embodiments not shown, the reference 12 may be arranged in any other position, provided that it can be detected by the detector 13.

[0037] According to some advantageous but non-restrictive embodiments (such as Figure 2 and Figure 4 those shown), the detection unit 11 further comprises an additional detector 13', which is advantageously of the same type as the detector 13 and is configured to detect each passage of the reference 12 at a second given position P2 arranged downstream of the first given position P1 along a given path P, and to emit a corresponding detection signal at each passage of the reference 12 at the second given position P2. In this case, advantageously but not restrictively, the aforementioned processing device is configured to also estimate a quantity related to the moving speed of the conveying device 5 (in particular, the belt 8 of the conveying device 5) as a function of the variation over time of a quantity related (in particular, consistent) to the distance covered between the emission of the detection signal by the detector 13 and the emission of the detection signal by the detector 13' (in particular, between the passage of the reference 12 at the aforementioned first given position P1 and the passage at the aforementioned second given position P2).

[0038] Also in this case, it should be understood that, according to alternative non-restrictive embodiments, the aforementioned processing device may be configured to also estimate the aforementioned quantity related to the moving speed of the conveying device 5 (in particular, the belt 8 of the conveying device 5) as a function of the time interval elapsed between the emission of the detection signal by the detector 13 and the emission of the detection signal by the detector 13'.

[0039] The presence of the additional detector 13' allows the accuracy of the estimation of the quantity related to the moving speed to be increased, and thus the robustness of the detection unit 11 to be improved.

[0040] According to some advantageous but non-restrictive embodiments, (in particular, each) detector 13, 13' comprises (in particular, is) a detector of inductive type, a photocell of known type.

[0041] According to some advantageous but non - limiting embodiments, the detection unit 11 further includes a rotation counter 14 which is configured to count the rotations of at least one drive roller 70 during use (i.e., when the conveying device 5 is in use), and to reset the count whenever the detector 13 emits a detection signal, so as to record the number of rotation cycles between the emissions of two successive detection signals emitted by the detector 13. Advantageously but non - limitingly, the number of rotation cycles is proportional to the aforementioned quantity related to the distance covered by the reference 12 between the emissions of two successive detection signals of the detector 13.

[0042] The number of rotation cycles is also proportional to the time interval elapsed between the emissions of two successive detection signals of the photodetector 13.

[0043] Advantageously but non - limitingly, the counter 14 is connected to a processing device to transmit at least the number of rotation cycles between the emissions of two successive detection signals emitted by the detector 13 to the processing device. The processing device is configured to evaluate the aforementioned quantity related to the distance (specifically, advantageously but non - limitingly, the elapsed time interval) covered by the reference 12 between the emissions of two successive detection signals of the detector 13 based on the number of rotation cycles, and thus to estimate the quantity related to the moving speed based on this data.

[0044] According to some advantageous but non - limiting embodiments, the rotation counter 14 includes (specifically, is) an incremental encoder known per se (and schematically shown in Figure 2 、 Figure 3 and Figure 4 ); even more advantageously but non - limitingly, the incremental encoder is arranged on one of the two drive rollers 70. More specifically, advantageously but non - limitingly, the encoder 14 is configured to detect the rotation and the rotation speed of the drive roller 70 to which it is fixed based on the counting of the number of pulses per revolution. The processing device is configured to evaluate the quantity related to the moving speed of the conveying device 5 by comparing the number of pulses between two corresponding detection signals emitted by the detector 13 and / or by the detector 13' (as will be better explained below), and to compare the number of pulses with the previous number of pulses (i.e., the number of pulses between two previous detection signals emitted by the detector 13 and / or by the detector 13') and / or with the theoretical number of pulses, and then to record an increase or decrease in the quantity related to the moving speed of the conveying device 5, and the control unit CU adjusts (i.e., advances or delays) the operation of different digital printing devices 10 based on this increase or decrease, which will be explained below.

[0045] According to some advantageous but non-exclusive embodiments, when an additional photodetector 13' is also provided, the rotation counter 14 is configured to reset the count to zero whenever the processing device receives a detection signal from the additional detector 13', and to restart the count whenever the processing device receives a detection signal from the detector 13, so as to record the number of rotation cycles (and thus the distance covered by the reference 12, i.e., the elapsed time) required for the reference 12 to reach the second given position P2 from the first given position P1. According to other embodiments, even when an additional detector 13' is provided, the rotation counter 14 is configured to reset the count to zero whenever the processing device receives a detection signal from the photodetector 13, and to store the count (i.e., the number of rotation cycles) corresponding to the moment when the processing device receives a detection signal from the additional detector 13', so as to also record the number of rotation cycles (and thus the distance covered by the reference 12, i.e., the elapsed time) required for the reference 12 to reach the second given position P2 from the first given position P1.

[0046] Alternatively or in combination, according to some embodiments such as those described in Figure 3 and Figure 4 the detection unit 11 includes a temperature detector 15 which is configured to advantageously but non-limitingly continuously detect the temperature of the belt 8 of the conveying device 5. In this case, the control unit CU is configured to estimate a quantity related to the moving speed based on the temperature detected by the temperature detector 15.

[0047] Advantageously but non-limitingly, the temperature sensor 15 is arranged to be in contact with the belt 8 below the conveying plane.

[0048] According to some advantageous but non-limiting embodiments, the control unit CU is configured to operate the above-mentioned first digital printing device 10' at a first given moment, and to operate each of the remaining printing devices 10 arranged downstream of the first digital printing device 10' along the moving direction A after a relevant given time interval starting from the first moment, and to adjust the duration of each of the relevant given time intervals according to a quantity related to the moving speed of the conveying device 5 estimated by the detection unit 11 (according to any of the above embodiments).

[0049] In particular, advantageously but non-limitingly, the control unit CU is configured to change the operation of each digital printing device 10 after the first digital printing device with respect to the first digital printing device 10', so as to delay or advance such operation correspondingly as the quantity related to the moving speed increases or decreases.

[0050] In other words, the control unit CU is configured to increase or decrease each of such relevant time intervals correspondingly as the quantity related to the moving speed decreases or increases.

[0051] Advantageously but not limited thereto, the control unit CU is configured to operate each digital printing device 10 of the printing assembly 9 such that each of them applies at least a predetermined portion of a defined pattern on the surface 3 to be decorated of the ceramic article T and to move the aforesaid predetermined portion of the defined pattern forward or backward along the moving direction A based on a quantity related to the speed of the conveying device 5. In other words, the control unit CU is configured to deform and / or move the said predetermined portion of the defined pattern applied by each digital printing device 10 relative to the actual moving speed of the conveying device 5 and thus relative to the actual moving speed of the ceramic article T, so as to ensure that the above-defined pattern is also correctly applied when external conditions such as temperature and / or all those conditions that cause a change in the moving speed of the conveying device 5 vary (see the Figure 5 following patterns made by the decorating machine 1, and in particular compare the following patterns made by the decorating machine 1 with the above patterns made by traditional decorating machines).

[0052] Alternatively or additionally, the control unit CU is configured to vary the length of the said predetermined portion of the defined pattern made by each printing device 10 on the surface 3 to be decorated of the ceramic article T according to the above quantity related to the moving speed.

[0053] According to some non-limiting embodiments, the control unit CU is connected to the detection unit and the printing assembly 9, in particular to each printing device 10 (as schematically shown in Figures 2 to 4 ), in particular to receive data from the detection unit 11 and transmit them to the printing assembly 9. In some non-limiting cases, the control unit CU is provided with processing means that are directly part of the detection unit 11. Alternatively, the control unit CU is a centralized system external to the detection unit and / or the printing assembly 9. According to other variants, the control unit CU is directly part of the printing assembly 9.

[0054] According to another aspect of the present invention, an apparatus 100 for manufacturing ceramic products (not visible in the drawings, such as ceramic plates and tiles) is proposed.

[0055] The apparatus 100 comprises: at least one feeding device 16 for feeding a powdered ceramic material CP at a feeding station 17; a shaping unit 18 of a known type arranged at a shaping station 19, the shaping unit 18 being configured to form at least one ceramic article T; and a conveying assembly 20 for transporting the powdered ceramic material CP from the feeding station 17 along a path PP in the moving direction A to the shaping station 19 and for transporting the ceramic article T from the shaping station 19 to a drying station 21.

[0056] Advantageously but not limitatively, the shaping unit 18 includes a compaction device 23 and a cutting assembly 24. The compaction device 23 is known per se and will not be described in detail herein. The compaction device 23 is configured to compact the powdered ceramic material CP to form a layer of compacted ceramic powder KP. The cutting assembly 24 is configured to cut the layer of compacted ceramic powder KP at least transversely to the moving direction A to form a plurality of ceramic articles T.

[0057] Advantageously, the apparatus 100 further includes: a decoration machine 1 advantageously implemented according to any one of the above-described embodiments, the decoration machine 1 being arranged at the printing station 6 and configured to apply a defined pattern on the surface 3 to be decorated of the ceramic article T as described above; and a firing kiln 22 for sintering the ceramic article T, thereby obtaining a finished ceramic product, and thus obtaining a ceramic slab or tile.

[0058] Advantageously but not limitatively, the apparatus 100 further includes a dryer 2. The dryer 2 is arranged at the drying station 21 along the path PP and is configured to subject the ceramic article T to a temperature of at least about 80°C (in particular, up to about 100°C) to obtain a dried ceramic article T.

[0059] Advantageously but not limitatively, the conveying assembly 20 is configured to feed the ceramic article T (advantageously but not limitatively, dried) from the drying station 21 to the printing station 6 described above with reference to the decoration machine 1. The printing station 6 advantageously but not limitatively extends downstream of the drying station 21 and is at a distance of at most about 130 meters from the drying station 21 (in particular, the distance is in the range of about 45 meters to about 130 meters).

[0060] With particular reference to Figure 1 , advantageously but not limitatively, the path PP includes the aforementioned given path P. In other words, the given path P is a section of the path PP that extends at the aforementioned printing station 6.

[0061] According to a third aspect of the present invention, a method for surface decoration of a ceramic article T is proposed.

[0062] Advantageously, the method includes: a transporting step during which a conveying device 5 (advantageously of the above type) transports the ceramic article T along the given path P in the moving direction A through the printing station 6; a printing step (at least partially) simultaneous with the transporting step during which a printing assembly 9 arranged at the printing station 6 and provided with a plurality of digital printing devices 10 (advantageously of the above type) arranged one after another in the moving direction A applies a defined pattern on the surface 3 to be decorated of the ceramic article T. The ceramic article T advantageously but not limitatively has undergone a drying heat treatment at a temperature of at least about 80°C (in particular, at least about 100°C) no more than 3 minutes (in particular, no more than 4 minutes) before the printing step.

[0063] Advantageously, the method further comprises: a detection step (at least partially) simultaneous with the conveying step, during which a detection unit 11 (advantageously of the type described above with reference to the decoration machine 1) advantageously but not restrictively continuously detects a quantity related to the moving speed of the conveying device 5; and a control step at least partially after the detection step, during which a control unit CU advantageously but non-restrictively retroactively adjusts the mutual operation of the different digital printing devices 10 of the printing assembly 9 based on the quantity related to the moving speed of the conveying device 5 (detected during said detection step), so as to apply a defined pattern (i.e., independent of the actual moving speed of the conveying device 5) also on the surface 3 to be decorated of the ceramic article T when the actual moving speed of the conveying device 5 changes, i.e., independent of different factors (such as, for example, the temperature and the actual tension of the belt 8) that may affect the speed of the above-mentioned conveying device 5.

[0064] Advantageously but not restrictively, also in this case, the conveying device 5 of the above-mentioned conveying step further comprises a metal support structure 7, which advantageously but not restrictively further comprises a pair of parallel drive rollers 70 spaced apart from each other by a given distance along the moving direction A (schematically shown in Figures 2 to 4 ), and a belt 8 mounted on the metal support structure 7 (in particular, mounted on the pair of rollers 70), the belt 8 defining, with its branches, a conveying plane for supporting and conveying the ceramic article T during its movement. Advantageously but not restrictively, the given distance between the drive rollers 70 is in the range from about 2.5 m to about 12 m (in particular, from about 3 m to about 10 m; even more particularly, equal to about 4 m).

[0065] Advantageously but not restrictively, the control step further comprises: a first operating sub-step, during which the control unit operates a first digital printing device 10' among the plurality of digital printing devices 10 of the printing assembly 9 at a first given moment; at least a second operating sub-step, during which the control unit CU operates each of the remaining digital printing devices 10 arranged downstream of the first digital printing device 10' along the moving direction A after a relevant given time interval starting from the first moment; and an adjustment sub-step (at least partially) simultaneous with the second operating step, during which the control unit CU adjusts the duration of each relevant given time interval based on the quantity related to the moving speed of the conveying device 5.

[0066] According to some advantageous but non-exclusive embodiments of the present invention, the detecting step further includes: a reading sub-step, during which at least one detector 13 (which is advantageously part of the detecting unit 11, as described above with respect to the decorating machine 1) detects each passage of the reference 12 (which is also part of the detecting unit 11 and fixed to the belt 8 of the conveying device 5, as described above) at a first given position P1 and emits a detection signal; and a sub-processing step, during which the processing device (which is part of the detecting unit 11, as mentioned above with respect to the decorating machine 1) receives the detection signal emitted by the detector 13 and estimates a quantity related to the moving speed of the conveying device 5 based on the variation over time of a quantity related (in particular, consistent) to the distance covered by the reference 12 between the emissions of two consecutive detection signals.

[0067] Furthermore, according to some advantageous but non-limiting embodiments, during the above-mentioned processing step, a rotation counter 14 (advantageously, of the type described above with respect to the decorating machine 1) counts the number of rotation cycles of at least one drive roller 70 of the metal structure 7 in the interval elapsed between the emissions of two first detection signals, and the processing device also estimates a quantity related to the moving speed of the conveying device 5 based on the number of rotation cycles counted by the rotation counter 14.

[0068] Additionally or alternatively, according to some advantageous but non-limiting embodiments, the detecting step further includes a temperature detection sub-step, during which a temperature detector 15, which is advantageously but not necessarily part of the detecting unit 11, continuously detects the temperature of the belt 8 of the conveying device 5. According to some advantageous but non-limiting embodiments, as already explained with respect to the machine 1, the quantity related to the moving speed varies with temperature; in particular, it is proportional to the detected temperature.

[0069] Advantageously but not necessarily, the method for surface decoration of the ceramic article T is implemented by the above-mentioned decorating machine 1 (according to the second aspect of the present invention).

[0070] According to a further aspect of the present invention, there is provided a method for manufacturing ceramic products, in particular ceramic slabs or tiles; the method comprising the following steps: a feeding step of feeding a powdered ceramic material CP at a feeding station 17; a shaping step during which a shaping unit 18 arranged at a shaping station 19 forms at least one ceramic article T. Advantageously but not restrictively, the shaping step comprises: a compaction sub-step during which the powdered ceramic material CP is compacted, advantageously but not restrictively by means of the compaction device 23 mentioned above with reference to the apparatus 100, so as to form a layer of compacted ceramic powder KP; and a cutting sub-step during which the layer of compacted ceramic powder KP is cut, advantageously by means of the above-mentioned cutting unit 24, at least transversely to the direction of movement A, so as to form a plurality of ceramic articles T.

[0071] Advantageously but not restrictively, the method also provides a decoration step during which the ceramic article T is decorated by implementing the above-mentioned decoration method (according to the second aspect of the present invention). Even more advantageously but not restrictively, the decoration step is implemented by means of the decoration machine 1 according to the first aspect of the present invention.

[0072] According to some advantageous but non-restrictive embodiments, the manufacturing method also comprises a drying step (at least partially) after the shaping step and (at least partially) before the decoration step, during which the ceramic article T is dried by being subjected to a temperature of at least about 80 °C (in particular, at least about 100 °C) in a dryer 2.

[0073] Advantageously but not restrictively, the decoration step and the drying step are spaced apart from each other by at most about 3 minutes, in particular at most about 4 minutes.

[0074] Advantageously but not necessarily, the method for manufacturing ceramic products is implemented by means of the above-mentioned apparatus 100 (according to the second aspect of the present invention). In this case, when the apparatus 100 provides a dryer 2 arranged upstream of the printing station 6 along the path PP, the dryer 2 is advantageously but not restrictively configured such that the printing station 6 extends at a distance of at most about 130 m (in particular, in the range from about 45 m to about 130 m) from the drying station 21.

[0075] The decoration method and machine 1 for the surface decoration of the ceramic article T of the present invention have many advantages, among which we mention the following.

[0076] Due to the detection of the quantity related to the moving speed of the conveying device 5 and the subsequent retroactive adjustment of the (mutual) operation of the different digital printing devices 10 of the printing assembly 9, the decoration machine 1 and method for the surface decoration of the ceramic article T according to the present invention allow the application of the above-defined pattern on the surface 3 to be decorated of the ceramic article T with high precision, thereby compensating for defects or phase shifts of the defined pattern, which, in the absence of such retroactive adjustment, would be caused by dimensional variations of the conveying device 5, which cause a consequent change in the moving speed of the ceramic article T. In other words, thanks to the solution proposed by the present invention, it is possible to improve the aesthetic appearance of the finished ceramic product while guaranteeing a very high resolution and correct synchronization of the operation of the individual digital printing devices 10 of the printing assembly 9, independently of the expansion and / or contraction and / or deformation phenomena that the conveying device 5 (in particular the metal support structure 7 of the conveying device 5) undergoes during its service life, which can be seen by comparing Figure 5 the top and bottom figures in

Claims

1. A decorating machine (1) for the surface decoration of a ceramic article (T), said decorating machine (1) comprising: A conveying device (5) configured to convey the ceramic article (T) along a given path (P) in a moving direction (A) through a printing station (6), the conveying device (5) further comprising a metal support structure (7) and a belt (8) mounted on the metal support structure (7), the belt (8) defining a conveying plane for supporting and conveying the ceramic article (T); the printing station (6) extends along the moving direction (A) for a length of at least about 2 meters; A printing assembly (9) arranged at the printing station (6), configured to apply a defined pattern on a surface (3) to be decorated of the ceramic article (T), and comprising a plurality of digital printing devices (10) arranged continuously along the moving direction (A); A control unit (CU) configured to operate each of the digital printing devices (10) of the printing assembly (9); And A detection unit (11) configured to detect a quantity related to the moving speed of the conveying device (5), and comprising: a reference (12) integral with the belt (8); at least one detector (13) configured to detect each passage of the reference (12) at a first given position (P1) and emit a corresponding first detection signal; and processing means connected to the detector (13) to receive each first detection signal and estimate the quantity related to the moving speed of the conveying device (5) based on a change in a quantity related (in particular, consistent) to the distance covered by the reference (12) between the emissions of two successive first detection signals; The control unit (CU) is configured to adjust the mutual operation of the different digital printing devices (10) of the printing assembly (9) according to the quantity related to the moving speed of the conveying device (5) so as to apply the defined pattern on the surface (3) to be decorated of the ceramic article (T).

2. The decorating machine (1) according to claim 1, wherein: The control unit (CU) is configured to operate a first digital printing device (10') among the plurality of digital printing devices (10) of the printing assembly (9) at a first given moment, operate each of the remaining digital printing devices (10) of the printing assembly (9) arranged downstream of the first digital printing device (10') along the moving direction (A) after a relevant given time interval starting from the first moment, and adjust the duration of each of the relevant given time intervals according to the quantity related to the moving speed of the conveying device (5).

3. The decorating machine (1) according to claim 1 or 2, wherein the control unit (CU) is configured to operate each of the digital printing devices (10) of the printing assembly (9) such that each of them applies at least a predetermined portion of the defined pattern on the surface (3) of the ceramic article (T) to be decorated, and to move the predetermined portion of the defined pattern forward or backward along the moving direction (A) based on the quantity related to the moving speed of the conveying device.

4. The decorating machine (1) according to any one of the preceding claims, wherein: The metal support structure comprises a pair of parallel drive rollers (70) spaced apart by a given distance along the moving direction (A), and the belt (8) is mounted on the pair of drive rollers (70) so as to be stretched and operated by the rotation of the drive rollers (70) during its movement; and The detection unit (11) includes a rotation counter (14) which is connected to the processing device and is configured to count the rotation of at least one of the pair of drive rollers (70), and to zero the count whenever the at least one detector (13) emits a first detection signal, so as to record the number of rotation cycles between the emissions of two successive first detection signals; the number of rotation cycles between the emissions of two successive first detection signals is proportional to a quantity related to the distance covered by the reference (12) between the emissions of two successive first detection signals.

5. The decorating machine (1) according to any one of the preceding claims, wherein the detection unit comprises an additional detector (13’), the additional detector (13’) being configured to detect each passage of the reference (12) at a second given position (P2) and to emit a corresponding second detection signal; along the given path (P), the second given position (P2) is arranged downstream of the first given position (P1); and the processing device is configured to also estimate the quantity related to the moving speed of the conveying device based on a change in the quantity related (in particular, consistent) to the distance covered by the reference (12) between the emission of the first detection signal and the emission of the second detection signal.

6. The decorating machine (1) for a ceramic article according to any one of the preceding claims, wherein the detection unit (11) comprises a temperature detector (15), the temperature detector being configured to detect the temperature of the belt (8) of the conveying device (5); the quantity related to the moving speed varies with the temperature.

7. The decorating machine (1) according to any one of the preceding claims, wherein the printing assembly comprises at least six (in particular, at least eight; even more particularly, between eight and twenty) inkjet printing devices (10) arranged continuously along the moving direction (A).

8. An apparatus (100) for manufacturing a ceramic product (M), in particular a ceramic plate or tile, the apparatus (100) comprising: A feeding device (16) for feeding the powdered ceramic material (CP) at a feeding station (17); A forming unit (18) arranged at a forming station (19) and configured to form at least one ceramic article (T); A conveying assembly (20) for conveying the powdered ceramic material (CP) from the feeding station (17) along a path (PP) in a moving direction (A) to the forming station (19), and for conveying the at least one ceramic article (T) from the forming station (19) to a printing station (6); A decorating machine (1) according to any one of the preceding claims arranged at the printing station (6), the decorating machine (1) being configured to apply the defined pattern on the surface (3) to be decorated of the ceramic article (T); and At least one firing kiln (22) for sintering the ceramic article (T) to obtain a ceramic product (M).

9. The apparatus (100) for manufacturing a ceramic product (M) according to claim 8, comprising a dryer (2), the dryer (2) being arranged at a drying station (21) upstream of the printing station (6) along the path (PP), and being configured to subject the ceramic article (T) to a temperature of at least about 80°C (in particular, up to about 100°C) to obtain a dried ceramic article (T); The conveying assembly (20) is configured to feed the dried ceramic article (T) from the drying station (21) to the printing station (6), the printing station (6) extending downstream of the drying station (21) along the path (PP) (in particular, along the given path (P), the given path (P) being a section of the path (PP)), at a distance of at most about 130 meters from the drying station (21).

10. A method for surface decoration of a ceramic article (T), the method comprising: A conveying step during which the conveying device (5) conveys the ceramic article (T) in the moving direction (A) along a given path (P) through the printing station (6); A printing step at least partially simultaneous with the conveying step during which a printing assembly (9) arranged at the printing station (6) and provided with a plurality of digital printing devices (10) arranged in succession in the moving direction (A) applies a defined pattern on the surface (3) to be decorated of the ceramic article (T); A detection step at least partially simultaneous with the conveying step during which the detection unit (11) detects a quantity related to the moving speed of the conveying device (5); and A control step at least partially after the detection step during which the control unit (CU) adjusts the mutual operation of the different digital printing devices (10) of the printing assembly (9) according to the quantity related to the moving speed of the conveying device (5) detected during the detection step, so as to apply the defined pattern on the surface (3) to be decorated of the ceramic article (T); The conveying device (5) includes a metal support structure (7) and a belt (8) assembled on the metal support structure (7), the belt (8) defining a conveying plane for supporting the ceramic article (T); The detection unit (11) includes a reference (12) integral with the belt (8); and The detection step further includes a reading sub-step and a processing sub-step. During the reading sub-step, at least one detector (13) detects each passage of the reference object (12) at a first given position (P1) and emits a detection signal. During the processing sub-step, the processing device receives the detection signal emitted by the at least one detector (13) and estimates the quantity related to the moving speed of the conveying device (5) based on the distance between the emissions of two consecutive detection signals.

11. The method for surface decoration of a ceramic article (T) according to claim 10, wherein the control step further comprises: A first operating sub-step, during which the control unit (CU) operates a first digital printing device (10') among the plurality of digital printing devices (10) of the printing assembly (9) at a first given moment. At least a second operating sub-step, during which the control unit (CU) operates each of the remaining digital printing devices (10) of the printing assembly (9) arranged downstream of the first digital printing device (10') along the moving direction (A) after a relevant given time interval starting from the first moment; and An adjustment sub-step at least partially simultaneous with the second operating step, during which the control unit (CU) adjusts the duration of each relevant given time interval based on the quantity related to the moving speed of the conveying device (5).

12. The method for surface decoration of a ceramic article (T) according to claim 10 or 11, wherein: The metal support structure (7) includes a pair of parallel drive rollers (70) spaced apart by a given distance along the moving direction (A), the given distance being in the range from about 2.5 meters to about 12 meters (in particular, from about 3 meters to about 10 meters; even more particularly, equal to about 4 meters), and the belt (8) is assembled on the pair of drive rollers (70) so as to be stretched and operated by the rotation of the drive rollers (70) during its movement; and During the processing sub-step, a rotation counter (14) counts the number of rotation turns of at least one of the drive rollers (70) in the interval elapsed between the emissions of two consecutive first detection signals, and the processing device also estimates the quantity related to the moving speed of the conveying device (5) based on the number of rotation turns counted by the rotation counter (14).

13. A method for surface decoration of a ceramic article (T) according to any one of claims 10 to 12, wherein: The detection step further includes a temperature detection sub-step, during which a temperature detector (15) detects the temperature of the belt (8) of the conveying device (5); the quantity related to the moving speed varies with the temperature.

14. A method for surface decoration of a ceramic article (T) according to any one of claims 10 to 13, the method being carried out using a decoration machine (1) according to any one of claims 1 to 7.

15. A method for manufacturing a ceramic product (M), in particular a ceramic plate or tile, the method comprising the following steps: A feeding step of feeding a powdered ceramic material (CP) at a feeding station (17); A shaping step, during which a shaping unit (18) arranged at a shaping station (19) forms at least one ceramic article (T); And A decoration step implemented according to the decoration method according to any one of claims 10 to 14.

16. A method for manufacturing a ceramic product (M) according to claim 15, comprising a drying step at least partially after the shaping step, during which the ceramic article (T) is dried by being subjected to a temperature of at least about 80 °C (in particular, at least about 100 °C) in a dryer; The decoration step and the drying step are separated from each other by at most 3 minutes (in particular, at most 4 minutes).

Images