WO2019239351A1

WO2019239351A1 - Method and machine for the surface decoration of a base article of the ceramic processing industry

Info

Publication number: WO2019239351A1
Application number: PCT/IB2019/054920
Authority: WO
Inventors: Matias BALLARDINI; Daniele Cortecchia; Sanzio Caroli
Original assignee: Sacmi Cooperativa Meccanici Imola Societa' Cooperativa
Priority date: 2018-06-12
Filing date: 2019-06-12
Publication date: 2019-12-19
Also published as: IT201800006225A1

Abstract

A method and a machine for the surface decoration of a ceramic article (2); the article (2) is conveyed along a given path (P) through a detection station (10), at which two matrix video cameras (13, 14) detect the position of two front corners (7, 8) of the article (2), and through a printing station (11), at which a manipulated drawing (19) is applied on an upper surface (3) of the article (2); the manipulated drawing (19) is obtained by rotating and/or translating a predetermined drawing (18) as a function of the detected positions of the corners (7, 8).

Description

"METHOD AND MACHINE FOR THE SURFACE DECORATION OF A BASE ARTICLE OF THE CERAMIC PROCESSING INDUSTRY"

CROSS-REFERENCE TO RELATED APPLICATIONS

This Patent Application claims priority from Italian Patent Application No. 102018000006225 filed on June 12, 2018, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method and a machine for the surface decoration of a base article of the ceramic processing industry, in particular an article comprising ceramic material. The present invention furthermore relates to a method and a plant for the production of ceramic articles.

BACKGROUND OF THE INVENTION

In the field of the production of ceramic articles (in particular, flagstones; more in particular, tiles) machines for the surface decoration of a base article are known.

In particular, machines are known that comprise a printing device adapted to apply a drawing (graphics) on a base article so as to decorate it and create an effect that allows simulation of a natural object, for example a slab of marble or wood.

These types of machine comprise a belt conveyor, which feeds the base article through a printing station, at which the said drawing is applied, and one or more fixed guides, which keep the base article correctly orientated while it is being fed to the printing station.

Typically, the base article is not (yet) fired and is therefore delicate. In view of this and the fact that it is relatively large and heavy, the base article can be easily damaged and, in some cases, has to be subsequently discarded. Alternatively or additionally to what is described above, often, in order to avoid areas of the article not being covered by the drawing, a drawing with dimensions larger than the article is used. Obviously, in these cases more ink is consumed than what is really necessary and the excess ink badly dirties the machines and neighbouring areas .

To remedy the above-mentioned problems, machines without guides for orientating the base article, but provided with a scanner arranged upstream of the printing station to estimate the orientation of the base article, have been described. In use, the drawing is printed after being rotated to take account of the estimated orientation of the base article.

These machines have several drawbacks, including the inability to operate in a simple, quick and accurate manner. In other words, acquisition of the data on which to estimate the orientation of the article is slow and inaccurate and the processing of said data is complex and approximate.

The object of the present invention is to provide a method and a machine for the decoration of a base article, and a method and a plant for the production of ceramic articles, which allow the drawbacks of the known art to be overcome, at least partially, and at the same time are easy and inexpensive to produce .

SUMMARY

According to the present invention, a method and a machine are provided for the surface decoration of a base article as claimed in the following independent claims and, preferably, in any one of the claims depending directly or indirectly on the independent claims .

BRIEF DESCRIPTION OF THE FIGURES

The invention is described below with reference to the attached drawings, which illustrate some non-limiting embodiment examples thereof, in which:

- figure 1 is a schematic plan view of a machine according to the present invention;

- figure 2 illustrates schematically a step of the method according to the present invention;

- figure 3 is a schematic plan view of the machine of figure 1 in a different operating step;

- figure 4 is a side view of details of the machine of figure i;

- figure 5 is a schematic plan view of the machine of figure 1 in a further operating step; and

- figure 6 is a schematic plan view of a portion of the machine of figure 1 in a different operating step.

DETAILED DISCLOSURE

In accordance with a first aspect of the present invention, in figure 1 the number 1 indicates overall a machine for the surface decoration of a base article 2 of the ceramic processing industry. The article 2 has at least one surface 3 (orientated upwards) and at least three edges 4, 5 and 6, which are joined together so as to define two corners 7 and 8.

In particular, the base article 2 is not (yet) fired.

More precisely but not necessarily, the corner 7 is arranged between the edges 4 and 5 and the corner 8 is arranged between the edges 5 and 6.

Typically, but not necessarily, the article 2 substantially has the shape (in plan view) of a quadrilateral. More precisely, the article 2 substantially has the shape of a parallelepiped. In some specific and non-limiting cases, the article 2 substantially has a rectangular shape (in plan view) .

Advantageously but not necessarily, at least one of the edges 4, 5 and 6 (in particular, the edges 4 and 6) have a length of at least 1 metre, in particular of at least 1.3 metres.

In particular, the base article 2 comprises (is made of) ceramic material .

The machine 2 comprises a conveyor device 9 to convey the base article 2 along a given path P, in a feeding direction A, through a detection station 10 and a printing station 11 arranged downstream of the detection station 10; and a detection device 12, which is arranged at the detection station 10 and, in particular, comprises at least two video cameras 13 and 14 (more in particular matrix video cameras), which are configured to capture one (single) image 15 of the corner 7 and one (single) image 16 of the corner 8, respectively. Advantageously but not necessarily, the conveyor device 9 is configured to feed the article 2 along the path P with a substantially continuous (not stepper) motion.

The machine 2 further comprises a control system 17, which is configured to move (in particular, rotate) a predetermined drawing 18 (figure 2) based on the images captured by the matrix video cameras 13 and 14 so as to obtain a manipulated drawing 19 (which adapts to the position/estimated orientation of the article 2); and a printing device 20, which is configured to apply the manipulated drawing 19 on the surface 3 of the base article 2.

In particular (figure 1), the control system 17 is configured to estimate (only) one position 21 of the corner 7 and one position 22 of the corner 8 of the images 15 and 16.

More in particular, the control system 17 is configured to estimate the inclination (orientation) of the base article 2 relative to the feeding direction A as a function of the positions 21 and 22 so as to obtain an estimated inclination (orientation) , and is configured to rotate a predetermined drawing 18 to be reproduced on said surface as a function of the estimated inclination (orientation) to obtain the manipulated drawing 19.

According to some non-limiting embodiments, the control system 17 is configured to estimate an inclination angle Q of the base article 2 (more precisely, of the edge 6) relative to the feeding direction A, in particular as a function of the position 21 and the position 22. More in particular, the control system 17 is adapted to estimate the inclination angle Q relative to a theoretical reference article 2 (arranged with its longitudinal extension in the direction A) . More precisely, the article 2 has two edges substantially parallel to the direction A (and at least one edge - in particular, two edges - substantially perpendicular to the direction A) . The article 2 defines a nominal reference position.

In particular, the control system 17 is adapted to move (rotate and/or translate; more precisely, rotate) the predetermined drawing 18 as a function of the positions 21 and 22.

More in particular, the control system 17 is adapted to rotate a predetermined drawing 18 as a function of the estimated inclination (orientation) to obtain the manipulated drawing 19. In some specific and non-limiting cases, the control system 17 is adapted to rotate the predetermined drawing 18 by the inclination angle Q.

According to some non-limiting embodiments, the inclination (the orientation or, more precisely, the inclination angle Q) is estimated by interpolating the positions 21 and 22 and (knowing the form of the article 2) by determining the angle between the interpolating curve (straight line) and the direction A. Additionally or alternatively, the inclination (the orientation or, more precisely, the inclination angle Q) is estimated (knowing the form of the article 2) based on the differences between the coordinates X and Y of the positions 21 and 22.

The coordinates X and Y of a point (or of a position) are the coordinates on a plane parallel to or coinciding with the one on which (the printing surface of) the article 2 lies while, in use, it is fed along the path P. In particular, the Y axis (namely the axis of the coordinate Y) is substantially parallel to the direction A (and the X axis - namely the axis of the coordinate X - is substantially perpendicular to the direction A) the plane of the coordinates X and Y is the plane of the surface 3.

More precisely, the plane on which the article 2 lies is an upper supporting plane of the conveyor device 9, more precisely a movement plane 23 (plane of a movement element 23' - for example belt, chain and roller unit), configured to support at the bottom the article 2 and to move along the (at least part of the) path P (in particular, the plane of movement 23 extends along - at least part of the - path P) .

In particular, the control system 17 is adapted to determine the coordinates X and Y based on the information detected by the video cameras 13 and 14. More in particular, the control system 17 is adapted to determine the coordinates X and Y in a reference system of the detection device 12 (of the video cameras 13 and 14) . Even more in particular, said reference system is a reference system in pixels (as unit of measurement) .

According to some non-limiting embodiments, the control system 17 is adapted to convert the (coordinates of the) positions 21 and 22 acquired in the reference system of the detection device 12 (in pixels) into positions according to a reference system of the printing device 20 (in millimetres) .

According to some non-limiting embodiments (like the one illustrated in figure 1), the control system 17 is connected to the detection device 12 and to the printing device 20, in particular to receive data from the detection device 12 and transmit them to the printing device 20. In some non-limiting cases, the control system 17 is provided with a unit directly part of the detection device 12 (in particular, of the video cameras 13 and 14) and, according to some variations, with a unit directly part of the printing device 20. Alternatively, the control system 17 is a centralized system external to the detection device 12 and/or to the printing device 20.

According to some non-limiting embodiments, the video cameras 13 and 14 are able to identify the edges (4, 5 and 6) and therefore the corners (7 and 8) of the article 2. In particular, to identify the edges, edge based matching image processing techniques are used. Alternatively or additionally, the corners (7 and 8) can be determined by intersecting the edges (4, 5 and 6) and/or using corner detector image processing techniques.

The edge based matching image processing techniques are described, for example, in one of the following documents: Steger, C, Occlusion, clutter, and illumination invariant object recognition. In Kalliany, R., Leberl, F., eds . : International Archives of Photogrammetry, Remote Sensing, and Spatial Information Sciences. Volume XXXIV, part 3A., Graz (2002); Hofhauser, C. Steger, N. Navab, Edge-based Template Matching and Tracking for Perspectively Distorted Planar Objects, Proc. 4th International Symposium on Advances in Visual Computing ISVC '08, 2008; Borgefors, G., 1988. Hierarchical chamfer matching: A parametric edge matching algorithm. IEEE Transactions on Pattern Analysis and Machine Intelligence 10(6), pp . 849-865; Steger, C., 1998. An unbiased detector of curvilinear structures. IEEE Transactions on Pattern Analysis and Machine Intelligence 20(2), pp . 113-125; and the patent US7016539B1.

The detector image processing techniques known as corner detector" are described, for example, in A Combined Corner And Edge Detector, by Chris Harris & Mike Stephens Plessey Research Roke Manor, United Kingdom © The Plessey Company pic. 1988, Proceedings of the 4th Alvey Vision Conference, pp . 147-151 (http : //www . bmva . org/bmvc/ 1988/avc-88-023. pdf) .

In some specific and non-limiting cases, the video cameras are devices that comprise on-board processing and are known as smart cameras (video cameras, known per se, which in addition to capturing images can also process them to obtain information at a higher level) .

Advantageously but not necessarily, the control system 17 is adapted to estimate at least the position 21 (and/or 22) based on the image 15 (and/or 16), and is adapted to translate the predetermined drawing 18 to obtain the manipulated drawing 19 as a function of the position 21 (or 22) . In particular, the control system 17 is adapted to translate the predetermined drawing 18 transversally (in particular, perpendicularly; more in particular, in a direction parallel to the X axis) to the feeding direction A as a function of the position 21 (and/or 22) .

More in particular, the control system 17 is adapted to estimate at least the position 21 (and/or 22) along the X axis based on the image 15 (and/or 16) . More precisely, the control system 17 is adapted to estimate the distance x of the position 21 (and/or 22) along the X axis relative to a reference position 21' (and/or 22'). For example, said reference position 21' (and/or 22') is the position of a corner 7' (and/or 8') of the above-mentioned theoretical reference article 2' . In particular, the control system 17 is adapted to translate the predetermined drawing 18 by the distance x.

According to some non-limiting embodiments, the control system 17 is adapted first to estimate the distance x according to the reference system of the detection device 12 and then convert the distance x into the reference system of the printing device 20. Alternatively or additionally, the control system 17 is adapted first to estimate the inclination angle Q according to the reference system of the detection device 12 and then convert the inclination angle Q into the reference system of the printing device 20.

Advantageously but not necessarily, the detection device 12 comprises a sensor 24 which is configured to detect the presence of the article 2 in (a correct position) at the detection station 12. More precisely, the sensor 24 is configured to detect the presence of the article 2 in a correct position in the direction A (along the Y axis) . In particular, in use, when the sensor 24 detects that the article 2 (which moves along the path P in the direction A) has reached the detection station 10 it enables operation of the video cameras 13 and 14 to capture the images 15 and 16. More in particular, when the sensor 24 detects that the article 2 (which moves along the path P in the direction A) has reached (the correct position in) the detection station 10, the sensor 24 emits a signal for activation of the video cameras

13 and 14 (or for capturing - by the control system 17) of the images 15 and 16.

Advantageously but not necessarily (figure 4), the detection device 12 further comprises at least one lighting device 25 (preferably, several lighting devices 25 are provided) orientated towards the given path P and configured to emit a lighting towards the base article 2. The video cameras 13 and

14 and the lighting device 25 are orientated towards the given path P so that the video cameras 13 and 14 do not receive the lighting (directly) reflected by the base article 2 (and/or by the conveyor device 9; more precisely, by the movement plane 23, on which the article 2 rests) . In particular, the lighting device 25 is not orientated perpendicular to the surface 3 of the base article 2 arranged at the detection station 10. Advantageously but not necessarily, the video cameras 13 and 14 are orientated towards the path P substantially perpendicular to the direction A and, in particular, to the article 2 (and/or to the conveyor device 9; more precisely, to the plane of movement 23, on which the article 2 rests) .

According to some non-limiting embodiments (figure 1), the printing device 20 comprises a digital printer (in particular, an inkjet digital printer; alternatively, a laser digital printer) .

Advantageously but not necessarily, the machine 1 is without guides or other elements arranged at the path to impose on the article 2 a given position/orientation (on the movement element) .

Advantageously but not necessarily, the movement plane 23 has a different colour from the base article 2. In this way, the operations of the video cameras 13 and 14 and, more precisely, of the control system 17 to identify the edges (4, 5 and 6) of the article 2 and, in particular, the corners (7 and 8) of the article 2 are facilitated.

According to some non-limiting embodiments, the movement plane 23 is dark (black) . Typically, the article 2 is light (white- light grey) .

In accordance with a second aspect of the present invention (figure 5), a plant 26 is provided for producing a ceramic product 27. In particular, the ceramic product 27 is a flagstone (more precisely, a tile) .

The plant 26 comprises the machine 1 for decoration. According to some embodiments, the plant 26 further comprises a compacting machine 28 for compacting a powder material CP comprising ceramic powder so as to obtain a layer of compacted powder KP; and a conveyor assembly 29 (in particular, comprising the conveyor device 9) , which is configured to feed (in a substantially continuous manner) the powder material CP along a path PP (of which the path P is a section) from an inlet station 30 to the compacting machine 28 and the layer of compacted powder KP (again along the path PP) from the compacting machine 28 to the machine 1 for decoration (and to an outlet station 31) . In particular, the compacting machine 28 and the machine 1 are arranged along the path PP between the inlet station 30 and an outlet station 31. More in particular, the machine 1 is arranged downstream of the compacting machine 28.

In particular, the base article 2 comprises (at least) a portion of the layer of compacted powder KP .

According to some non-limiting embodiments, the plant 26 comprises at least a cutting assembly 32 for transversally cutting the layer of compacted powder KP so as to obtain the base article 2, which has a portion of the layer of compacted powder KP . In particular, the cutting assembly 32 is arranged along the path PP (more in particular, downstream of the compacting machine 28 and upstream of the machine 1) . Advantageously but not necessarily, the conveyor assembly 29 is configured to feed the layer of compacted powder KP to the cutting assembly 32 and transport the base article 2 downstream of the cutting assembly 32 (through the machine 1) .

According to some non-limiting embodiments, the plant 26 further comprises a dryer 33 arranged along the path PP downstream of the compacting machine 28 (more precisely, downstream of the cutting assembly 32) and upstream of the machine 1.

According to some non-limiting embodiments, the plant 26 also comprises at least one firing kiln 34 for sintering (the layer of compacted powder KP of) the base article 2 so as to obtain the ceramic product 27. In particular, the firing kiln 34 is arranged along the path P downstream of the machine 1.

According to some non-limiting embodiments not illustrated, the plant 26 does not comprise the compacting machine 28 and the cutting assembly 32 but comprises a traditional pressing machine (of known type) for tiles. Typically, said pressing machine is provided with a vertical axis oleodynamic pressing device configured to press ceramic material in powder so as to directly obtain single flagstones (which do not require cutting) of pressed material.

In accordance with a third aspect of the present invention a method is provided for the surface decoration of a base article 2 (figure 1), in particular an article 2 as defined above (in relation to the first aspect of the present invention) . Advantageously but not necessarily, the method is implemented by a machine 1 in accordance with the first aspect of the present invention .

The method comprises a first conveying step during which the base article 2 is conveyed along a given path P, in a feeding direction A, through a detection station 10 and a printing station 11 arranged downstream of the detection station 10; a detection step, during which at least one image of the corner 7 and of the corner 8 (more precisely, at least one image 15 of the corner 7 and at least one image 16 of the corner 8) is captured at the detection station 10; and a first processing step, during which a position 21 of the corner 7 and a position 22 of the corner 8 are detected (estimated) as a function of the image captured (more precisely of the images 15 and 16, respectively) , and the position (in particular, the orientation) of the base article 2 relative to the feeding direction A is estimated as a function of the positions 21 and 22.

According to some non-limiting embodiments, during the first processing step, the edges (4, 5 and 6) (and therefore the corners 7 and 8 of the article 2) are identified. In particular, edge based matching image processing techniques are used to identify the edges. Alternatively or additionally, the corners (7 and 8) are determined by intersecting the edges (4, 5 and 6) and/or using corner detector image processing techniques.

In some specific and non-limiting cases, the video cameras are devices that comprise on-board processing and are known as smart cameras .

The method further comprises a second processing step during which a predetermined drawing 18 is moved (in particular, rotated) as a function of (the information detected during the detection step and) the information obtained during the first processing step (in other words, as a function of the positions 21 and 22) so as to obtain a manipulated drawing 19 (coordinated with the estimated orientation/position of the article 2); and a printing step, during which the manipulated drawing 19 is applied on the surface 3 of the base article 2.

Advantageously but not necessarily, a matrix video camera 13 captures the image 15 and a matrix video camera 14 captures the image 16.

In particular (figure 1), the position 21 of the corner 7 and the position 22 of the corner 8 are estimated based on the images 15 and 16.

According to some non-limiting embodiments, during the first processing step, an inclination angle Q of the base article 2 (more precisely, of the edge 6) relative to the feeding direction A is estimated, in particular as a function of the position 21 and the position 22. More in particular, the inclination angle Q is estimated relative to a theoretical reference article 2 (arranged and orientated as hypothetically correct along the path P - in particular, with its longitudinal extension parallel to the direction A) . More precisely, the article 2 has edges 4' and 6 substantially parallel to the direction A (and the edge 5' substantially perpendicular to the direction A) .

In particular, during the second processing step, the predetermined drawing 18 is rotated as a function of the estimated inclination (orientation) to obtain the manipulated drawing 19.

In some specific and non-limiting cases, during the second processing step, the predetermined drawing 18 is rotated by the inclination angle Q.

In particular, the control system 17 is adapted to determine the coordinates X and Y based on the information detected by the video cameras 13 and 14. More in particular, the coordinates X and Y are determined in a reference system of the video cameras 13 and 14. Even more in particular, said reference system is a reference system in pixels (as units of measurement) .

According to some non-limiting embodiments, during the first processing step the (coordinates of the) positions 21 and 22, captured in the reference system of the video cameras 13 and 14 (in pixels), are converted into positions according to a reference system used for the printing step (in millimetres) . Typically, this conversion is performed by means of a function, in particular a matrix function (more in particular, with coefficients determined during a calibration step - described in greater detail below - and knowing the thickness of the article 2 ) .

According to some non-limiting embodiments, during the first processing step, at least the position 21 (and/or the position 22) is estimated in a transverse direction, in particular orthogonal to the feeding direction A. According to some non limiting embodiments, during the second processing step, the predetermined drawing 18 is translated (moved) as a function of the position 21 (and/or of the position 22) .

In particular, during the second processing step, the predetermined drawing 18 is translated transversally (in particular, perpendicularly; more in particular, in a direction parallel to the X axis) to the feeding direction A as a function of the position 21 (and/or the position 22) .

More in particular, during the first processing step, at least the position 21 (and/or the position 22) along the X axis is estimated on the basis of the image 15 (or 16) . More precisely, during the first processing step, the distance x of the position 21 (and/or of the position 22) along the X axis is estimated relative to a reference position 21' (and/or 22') . For example, said reference position 21' (and/or 22') is the position of a corner 7' (and/or 8') of the above-mentioned theoretical reference article 2' . In particular, during the second processing step, the predetermined drawing 18 is translated by the distance x.

According to some non-limiting embodiments, during the first processing step, first the distance x according to the reference system of the video cameras 13 and 14 (in pixels) is estimated and then the distance x is converted into the reference system used during the printing step (in mm) . Alternatively or additionally, the inclination angle Q according to the reference system of the video cameras is first estimated and then converted into the system used during the printing step.

Typically, this conversion is performed by means of a function, in particular a matrix function (more in particular, with coefficients determined during a calibration step and knowing the thickness of the article 2) .

Advantageously but not necessarily, during the conveying step, the base article 2 is conveyed with a substantially continuous (not stepper) motion.

Advantageously but not necessarily, the detection step, and the first and the second processing step are performed in less than 10 seconds, in particular in less than 6 seconds (more precisely, from 1 to 10 seconds; even more precisely, from 3 to 6 seconds) . Considering that the distance between the detection station 10 and the printing station 11 is typically approximately 1 metre and that the article 2 is conveyed along the path P at a speed of approximately 10-20 metres per minute, in this way it is possible to apply the manipulated drawing 19 on the article 2 without stopping said article 2.

Preferably but not necessarily, the above-mentioned control system 17 is able to carry out its activities (first and second processing step) within the times indicated above. In said context, advantageously, the control system 17 comprises a suitable graphics card.

According to some non-limiting embodiments, the method comprises a first calibration step, which is prior to the detection step and during which at least one reference drawing 35 is printed (by the printing device 20) on a surface of a control substrate at the printing station 11 (in particular, by means of the printing device 20) so as to obtain a printed substrate 36. In particular, while the reference drawing 35 is printed, the control substrate is fed along the path P (through the printing station 11) and kept in a predetermined position and orientation by means of guide elements (e.g. abutment - not illustrated) .

Advantageously but not necessarily, the control substrate has dimensions (width and length) greater (preferably, greater) than the base article 2.

During the first calibration step, furthermore, the video cameras 13 and 14 detect the reference drawing 35 present on the printed substrate 36; a function (in particular, a matrix function) is created for correspondence between a reference system used while the reference drawing is printed (by the printing device 20) and a reference system used while the reference drawing 35 is detected (by the video cameras 13 and 14) based on the information detected by the video cameras 13 and 14 during the calibration step and data relative to the reference drawing 35 (more precisely, the data used during printing of the reference drawing 35) . In particular, the function of correspondence between the two cited reference systems is obtained by using calibration algorithms of known type (for example described in Tsai R Y. A versatile camera calibration technique for high-accuracy 3D machine vision metrology using off-the-shelf TV cameras and lenses. IEEE Journal of Robotics and Automation, 1987, 3(4) : 323—344; Zhang Zhengyou; Flexible camera calibration by viewing a plane from unknown orientations lllnternational Conference on Computer Visbn(lCCV) . Proceedings Seventh International Conference on Computer Vision. Liege, Belgium : Elsevier Science Publishers, 1999 : 666-674; Chen Shengyong, Liu Sheng. Implementation of

Computer Vision Technology Based on OpenCV. Beijing: Science Press, May, 2008); Jean-Yves Bouguet . Camera calibration toolbox for Matlab [OBIOL] . 2012. http:

caltech . edu/jtsouguet )/calib....doc; David A.

Forsyth, Jean Ponce. Computer Vision: A Modern Approach. Person

Education, Inc.2004).

According to some non-limiting embodiments, during the first calibration step, the printed substrate 36 is conveyed (by a conveyor device 9) along the given path P in the feeding direction A through the detection station 10 (at which the video cameras 13 and 14 are arranged and the reference drawing 35 is detected) . Advantageously but not necessarily, at least one guide 37 (e.g. an abutment) maintains the substrate 36 in a predetermined position and orientation as it passes through the detection station 12 (and the video cameras 13 and 14 detect the reference drawing 35 present on the printed substrate 36) .

According to some embodiments not illustrated, at least one guide (or an abutment) allows the control substrate to be maintained in a predetermined position and orientation as it passes through the (is arranged at the) printing station 20 (and the reference drawing 35 is printed, in particular by the printing device 20) .

Advantageously but not necessarily, during the first calibration step, the following are detected: the position of at least one point 38 at a first zone of the reference drawing 35 (in particular, close to the corner 7), the position of at least one point 39 of the reference drawing at a second zone (in particular, close to the corner 8) . In other words, the point 38, which is approximately in the position in which the corner 7 should be during the detection step, and the point 39, which is approximately in the position in which the corner 8 should be during the detection step, are detected.

In particular, in these cases, the positions (the coordinates) of the points 38 and 39 are used to relate (as better explained above) the reference system used while the reference drawing is printed (by the printing device 20) to the reference system used while the reference drawing is detected (by the video cameras 13 and 14) .

According to specific non-limiting embodiments, the reference drawing 35 comprises at least one checkerboard (more precisely, two checkerboards) . The checkerboard (which is printed by the printing device 20) allows the video cameras to be calibrated with the known methods. Furthermore, points 38 and 39 allow a correspondence to be established between the reference systems of the video cameras 13 and 14 (for example as described in Zhang Ling, Yin Muyi, Li Weil, Liu Hailin, 2014; Applied Mechanics and Materials Implementation of Camera Calibration Method Based on OpenCV; Applied Mechanics and Materials; ISSN: 1662-7482, Vols. 602-605, pp 3796-3799; doi : 10.4028 /www . scientific . net/AMM .602-605.3796) .

Advantageously but not necessarily, the method comprises a second calibration step, which in turn comprises a conveying sub-step, during which a control substrate 40 (different from or equal to the one previously cited) is conveyed along the given path P, in the feeding direction A, with an own front edge 41 arranged at least partially at the front in the feeding direction A relative to the other edges of the control substrate 40, and through the printing station 11, at which a printing device 20 is arranged.

The second calibration step also comprises an operating step during which, while the control substrate 40 passes through the printing station 11, the printing device 20 is operated so as to apply at least one reference mark 42 on the control substrate 40 as a function of an indication of the position of the control substrate 40 along the path P so as to obtain a marked substrate 43.

For example, the printing device 11 is operated as a function of the presumed position of the control substrate 40 given by the feeding of the conveyor device 9. Alternatively or additionally, a sensor (e.g. a photocell) is provided at the inlet to the printing station 11 to detect the passage of objects (more precisely, of the control substrate 40); the printing device 11 is operated based on the information detected by said sensor (in other words, the information detected by the sensor acts as an indication of the position of the control substrate 40 along the path P) .

The second calibration stage further comprises a measurement sub-step, during which the distance between the mark 42 and the front edge 41 is measured and a comparison is made with a reference distance (at which the mark 42 should have been printed relative to the front edge 41); and an adjustment sub-step during which the function that connects operation of the printing device 20 to indication of the position of the control substrate 40 along the path P is modified based on the cited comparison.

In particular, if the mark 42 is too far from the front edge 41, operation of the printing device 20 is anticipated; on the other hand, when the mark 42 is too near the front edge 41, operation of the printing device 20 is postponed.

According to some non-limiting embodiments, the method also comprises a pre-calibration step which is, in particular, prior to the calibration step. During the pre-calibration step, the intrinsic parameters for each video camera 13 and 14 (separately) are determined with known procedures. More precisely, each video camera 13 and 14 is made to capture an image of known dimensions.

In short, the pre-calibration step allows each video camera 13 and 14 to be calibrated individually; the first calibration step allows cumulative calibration of the detection device 12 (the video cameras 13 and 14) together with the printing device 20, in particular as regards the position along the X axis and the inclination angle Q; and the second calibration step allows operation of the printing device 20 to be calibrated and therefore printing of the manipulated drawing along the Y axis.

In accordance with a further aspect of the present invention, a method is provided for the production of a ceramic product 27. Said method comprises a method for surface decoration according to the third aspect of the present invention and comprises a firing step, which is subsequent to the printing step and during which (the layer of compacted powder KP of) the base article 2 is sintered so as to obtain the ceramic product 27.

According to some non-limiting embodiments, the method also comprises a compacting step, which is prior to the printing step and during which a powder material CP comprising ceramic powder is compacted so as to obtain a layer of compacted powder KP .

Advantageously but not necessarily, the method for the production of the ceramic product 27 is implemented by the plant 26 described above (in accordance with the second aspect of the present invention) .

Unless explicitly indicated otherwise, the content of the references (articles, books, patent applications etc.) cited in this text is referred to here in full. In particular, the mentioned references are herein incorporated by reference.

Claims

1.— A machine for the surface decoration of a base article (2) of the ceramic processing industry having at least one surface (3), a first, a second and at least a third edge (4, 5, 6), which are joined together so as to define a first and at least a second corner (7, 8); in particular, the base article (2) comprises ceramic material; in particular, the first and the second edges (4, 5) are joined so as to define the first corner

(7), the second and the third edge (5, 6) are joined so as to define the second corner (8);

the machine (1) comprises a conveyor device (9) for conveying the base article (2) along a given path (P) , in a feeding direction (A), through a detection station (10) and a printing station (11) arranged downstream of the detection station (10); the machine (1) being characterized in that it comprises:

a detection device (12), which is arranged at the detection station (10) and is configured to capture a first image (15) of the first corner (7) and a second image (16) of the second corner

(8) ;

a control system (17), which is configured to move a predetermined drawing (18) based on the first image (15) and on the second image (16) so as to obtain a manipulated drawing (19) ;

a printing device (20), which is configured to apply the manipulated drawing (19) onto the surface (3) of the base article (2) ;

the control system (17) is configured to estimate a first position (21) of the first corner (7) and a second position (22) of the second corner (8) based on the first and the second image (15, 16), and to move the predetermined drawing (18) as a function of the first position (21) and the second position (22) in order to obtain the manipulated drawing (19) .

2 .— The machine according to claim 1, wherein the detection device (12) comprises a first and a second video camera (13, 14) (more in particular, a matrix video camera) , which are configured to capture the first image (15) of the first corner (7) and the second image (16) of the second corner (8), respectively; in particular, the control system (17) is adapted to move said predetermined drawing (18) based on the first image (15) and the second image (16) captured by the first and the second cameras (13, 14) so as to obtain the predetermined drawing (19) .

3.— The machine according to claim 1 or 2, wherein the control system (17) is configured to estimate the orientation of the base article (2) relative to the feeding direction (A) as a function of the first and the second positions (21, 22) so as to obtain an estimated orientation, and is configured to rotate the predetermined drawing (18) to be reproduced on said surface (3) as a function of the estimated orientation in order to obtain the manipulated drawing (19) .

4.— The machine according to any one of the preceding claims, wherein the control system (17) is configured to estimate an inclination angle (Q) of the base article (2) relative to the feeding direction (A) , in particular as a function of the first and the second positions (21, 22) .

5.— The machine according to any one of the preceding claims, wherein the control system (17) is configured to estimate a first position (21) of at least the first corner (7) based on the first image (15), and is configured to translate the predetermined drawing (18) transversely (in particular, perpendicularly) to the feeding direction (A) as a function of the first position (21) in order to obtain the manipulated drawing (19) .

6.— The machine according to any one of the preceding claims, wherein detection device (12) comprises a lighting device (25) orientated towards the given path (P) and configured to emit a lighting towards the base article (2); the first and the second video camera (13, 14) being orientated towards the given path

(P) so as not to receive the lighting reflected by the base article (2); in particular, the lighting device (25) not being orientated perpendicularly to said surface (3) of the base article (2) arranged at the detection station (11); in particular, the base article (2) is not fired.

7 .— The machine according to any one of the preceding claims, wherein the printing device (20) comprises a digital printer.

8.— A method for the surface decoration of a base article (2) of the ceramic processing industry having at least one surface (3), a first, a second and at least a third edge (4, 5, 6), which are joined together so as to define a first and at least a second corner (7, 8); in particular, the base article (2) comprises ceramic material; in particular, the first and the second edge (4, 5) are joined so as to define the first corner

(7), and the second and the third edges (5, 6) are joined so as to define the second corner (8);

the method comprises a first conveying step, during which the base article (2) is conveyed along a given path (P) , in a feeding direction (A), through a detection station (10) and a printing station (11) arranged downstream of the detection station (10); the method being characterized in that it comprises :

a detection step, during which at least a first image (15) of the first corner (7) and at least a second image (16) of the second corner (8) are captured at the detection station (10); a first processing step, during which a first position (21) of the first corner (7) and a second position (22) of the second corner (8) are estimated as a function of the first and the second images (15, 16), respectively;

a second processing step, during which a predetermined drawing (18), to be reproduced on said surface (3) of the base article (2), is moved as a function of said first position (21) and said second position (22) in order to obtain a manipulated drawing (19) ; and

a printing step, during which the manipulated drawing (19) is applied onto the surface (3) of the base article (2) .

9.— The method according to claim 8 wherein, during the detection step, a first video camera (13) (in particular, a matrix video camera) captures the first image (15) of the first corner (7) and a second video camera (14) (in particular, a matrix video camera) acquires the second image (16) of the second corner (7) .

10.— The method according to claim 8 or 9, wherein, during the first processing step, the orientation of the base article (2) relative to the feeding direction (A) is estimated as a function of the first position (21) and of the second position (22); during the second processing step, the predetermined drawing is rotated as a function of the estimated orientation.

11.— The method according to any one of the claims from 8 to 10 wherein, during the first processing step, the first position (21) of the first corner (7) is estimated in at least a direction that is transverse, in particular orthogonal, to the feeding direction (A) ; during the second processing step, the predetermined drawing (18) is moved, in particular translated, as a function of the first position (21) .

12.— The method according to any one of the claims from 8 to 11 wherein, during the first processing step, an inclination angle (Q) of the base article (2) relative to the feeding direction (A) is estimated (in particular, as a function of the first and the second position) ; in particular, the inclination angle (Q) is estimated relative to an orientation of a reference article (2), in particular orientated in the feeding direction (A); during the second processing step, the predetermined drawing (18) is rotated by the estimated inclination angle (Q) .

13.— The method according to any one of the claims from 8 to 12 and comprising a first calibration step, which is prior to the detection step and during which at least a reference drawing (35) is printed on a surface of a control substrate at the printing station (11); said first video camera (13) and second video camera (14) detect the reference drawing (35) present on the printed substrate (36); a correspondence function is created between a reference system used while the reference drawing is printed and a reference system used while the reference drawing is detected based on the information detected by the first video camera (13) and by the second video camera (14) and on the data concerning the reference drawing (35) .

14.— The method according to claim 13 wherein, during the first calibration step, the following parameters are detected: the position of at least a first point (38) at a first zone of the reference drawing (35) close to the first corner (7), the position of at least a second point (39) of the reference drawing (35) at a second zone of the reference drawing (35) close to the second corner (8) .

15.— The method according to claim 14, wherein a first video camera (13) (in particular a matrix video camera) detects the position of the first point (38) and a second matrix video camera (14) (in particular a matrix video camera) detects the position of the second point (39) .

16.— The method according to any one of the claims from 8 to 15 and comprising a second calibration step which, in turn, comprises a conveying sub-step, during which a control substrate (40) is conveyed along the given path (P) , in the feeding direction (A), with a front edge (41) thereof arranged at least partially at the front in the feeding direction (A) relative to the other edges of the control substrate (40), and through the printing station (11), where a printing device (20) is arranged; an operating sub-step during which, while the control substrate (40) goes through the printing station (11), the printing device (20) is operated so as to apply at least one reference mark (42) onto the control substrate as a function of an indication of the position of the control substrate (40) along the path (P) and so as to obtain a marked substrate (43) ; a measuring sub-step, during which the distance between the mark (42) and the front edge (41) is measured and compared with a reference distance; an adjusting sub-step, during which the function connecting the operation of the printing device (20) to the indication of the position of the control substrate (40) along the given path (P) is changed based on said comparison.

17.— The method according to any one of the claims from 8 to 16 wherein, during the printing step, a digital printer (in particular, an inkjet printer) applies the manipulated drawing (19) on the surface (3) of the base article (2) .

18.— The method according to any one of the claims from 8 to 17, wherein the base article (2) is not fired.

19.— The method according to any one of the claims from 8 to 18 and implemented by a machine (1) for the surface decoration of a base article (2) according to one of the claims from 1 to 7.

20.— A plant for the production of a ceramic product (27); the plant (26) comprises the machine (1) according to any one of the claims from 1 to 7 and at least one firing kiln (34) for sintering the base article (2) in order to obtain the ceramic product (27); in particular, the firing kiln (34) is arranged along the path (P) downstream of the machine (1) .