CALIBRATION METHOD OF AN INSTRUMENT FOR ANALYZING THE DIRECTION OF WOOD FIBERS IN A PIECE OF WOOD AND THE RELATED CALIBRATION SAMPLE

Description

M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM DESCRIPTION attached to a patent application for an industrial invention entitled: CALIBRATION METHOD OF A WATER ANALYSIS INSTRUMENT DIRECTION OF THE WOOD FIBERS OF A PIECE OF WOOD AND 5 RELEVANT CALIBRATION SAMPLE On behalf of: Microtec Srl resident in: Bressanone (BZ) - Via Julius Durst 98 Designated Inventor: Luca Silvestri Agent: Eng. Simone Ponchiroli c / o Ruffini Ponchiroli and 10 Associates Srl * * * DESCRIPTION The present invention relates to a method of calibration of a tool for analyzing the direction of the wood fibers of a piece of wood and 15 a calibration sample usable in the calibration method. In the wood industry there is often a need to identify the direction of the fibres of a piece of wood (for example, of a board) in order to to identify knots or other defects, or in general to evaluate the progress of the fibers along the piece of wood, which determines the quality of the piece of wood 20 linked to its structural characteristics and, consequently, its value economic. To meet this need, it is known to employ analysis tools that measure the direction of the wood fibers at the surface of the piece of wood by exploiting a phenomenon of light diffusion known in 25 sector as scattering. These analysis tools work by irradiating the surface of the piece of wood with one or more rays of structured light – moving or fixed – and acquiring images of the surface thus illuminated. Each ray illuminates an area generally circular surface with a diameter of a few tenths of 30 millimeter, so as to irradiate a limited number of wood fibers whose M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM direction can be considered substantially constant; in corresponding to the illuminated area, the light beam generates reflected light and possibly – in the case of fibres more or less coplanar to the surface – light emitted by the piece of wood and diffused mainly along the direction of 5 extension of the fibers corresponding to the illuminated area (the light emitted It normally illuminates fibers for lengths of about 2 mm). Through the detection of reflected light and any light emitted following scattering (relating therefore to an anisotropic diffusion of light by the wood), these analysis tools allow to detect the direction of the fibres 10 illuminated; by carrying out this type of detection in multiple points of the surface, These tools allow you to detect the direction of the fibres along the piece of wood and to identify any local variations in the direction of the fibres attributable to defects in the wood (such as knots). For each of these instruments it is standard practice to periodically carry out a 15 calibration of the analysis instrument to ensure the accuracy of the measurements carried out with it. Calibration verifies the capacity of the instrument for making measurements compliant with performance specifications desired, detecting any deviations from the predefined tolerance limits and determining the quality of the analysis tool's performance with respect to 20 to the specifications; with the calibration it is also possible to determine any instrument corrections. Calibration can also include a adjustment of the analysis tool, or a setting of it (for example in the case of a newly manufactured instrument). For these instruments it is also it is possible to foresee the possibility of carrying out a calibration intended as self-calibration (or 25 normalization) before normal use by a user. In the context of the present invention, the term calibration is intended to include all these possibilities. To calibrate the analysis instrument in accordance with the above, the calibration methods known to date involve carrying out – with the 30 instrument to be calibrated – a series of measurements on a calibration sample M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM consisting of a piece of wood which, at least in correspondence with one work surface prepared for measurement, has known characteristics: in particular, this calibration sample shows a trend of the fibres of surface wood which is known and which is used in the calibration method 5 (the known trend of the fibers is typically attested before implementing the calibration method by measuring the direction of the fibres with a different instrument of known accuracy). These calibration methods provide for detect, using the analysis instrument to be calibrated, the trend of the fibres in a plurality of points on the working surface of the calibration sample, and 10 subsequently to process the detected trend of the fibres to identify any deviations from the tolerance limits defined by the specifications performance. However, the technique known to date has some drawbacks. In the known technique, a piece of wood is used as a calibration sample, the 15 which is susceptible to modifications – such as for example loading due to to environmental conditions (variations in humidity and / or temperature) or abrasions of the work surface – which over time can lead to the direction of the fibres at the working surface to differ from the originally known trend of the fibres, and which can therefore lead 20 to an incorrect calibration of the analysis instrument: the processing the trend detected in the fibres could in fact highlight a incorrect measurement by the instrument even where the instrument is analysis was able to correctly measure the direction of the fibers. it is therefore necessary to carry out an optimal calibration of the analysis instrument 25 certify the trend of the fibres – for example with a measuring instrument known accuracy – at the same time as each execution of the method calibration; however, this is not always possible, and in any case complicated. The use of calibration samples according to the known technique also presents critical issues – intrinsic to the natural origin of the wood and its variability – from 30 point of view of the reproducibility of the calibration for different specimens of one M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM same model of analysis tool used in different locations (it would be desirable to ensure the same quality of calibration for all instruments). The known technique therefore has some drawbacks, and the technical task at hand The basis of the present invention is to at least partially remedy this. 5 The technical task is essentially achieved by a calibration method in agreement with what is defined in independent claim 1. The present invention also includes a sample of calibration usable in the calibration method, in accordance with what is indicated in claim 5, a use of the calibration standard in accordance with what 10 referred to in claim 19, and a method of producing the sample of calibration in accordance with the provisions of claim 20. Forms of Particular embodiments of the present invention are defined in the corresponding dependent claims. Further features and advantages of the present invention will appear. 15 more evident from the detailed description of some forms of preferred, but not exclusive, implementation of the calibration method, of the calibration sample and the method of production of the calibration sample. Reference will be made to the drawings in the attached tables, where: - figure 1 shows, schematically and in axonometric view, a phase 20 of detection of the calibration method of the present invention with a calibration sample placed in a first position; - figure 2 shows detail II of figure 1; - figure 3 shows, schematically and in axonometric view, a phase of detection of the calibration method with the calibration sample placed in a 25 different position compared to figure 1; - figure 4 shows detail IV of figure 3; - figure 5 shows, schematically and in axonometric view, a phase of detection of the calibration method performed with a different sample of calibration; 30 - figure 6 shows detail VI of figure 5; M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM - figure 7 shows, schematically and in axonometric view, a form production of the calibration sample; - figure 8 shows detail VIII of figure 7; - figure 9 shows, in axonometric view, an embodiment of the 5 production method in three different subsequent moments; - figure 10 shows, in axonometric view, a different form of implementation of the production method in four different subsequent moments. In the following, the calibration method will be described first in accordance with the present invention, while secondly and thirdly will be described 10 respectively the calibration sample and the production method of the calibration sample. As described for the calibration method in relation the calibration sample must be considered valid, where applicable, also for the calibration sample which is the object of the present invention and vice versa. The calibration method is a method for calibrating an analysis instrument 1 of the 15 direction of the wood fibers of a piece of wood operating by detection of structured light scattering. In the calibration method according to the present invention, a calibration sample 3 having a working surface 5 consisting of a composite material 13. This composite material 13 comprises a matrix 20 15 (advantageously continuous) and 17 fibers, which are dispersed in the matrix 15. At least part of the fibers 17 is illuminable with structured light in corresponding to the work surface 5 and, preferably, is located in correspondence of the work surface 5. In the context of this invention, they are considered to be illuminable with structured light in correspondence 25 of the working surface 5, fibers 17 which are illuminable with structured light with which the analysis tool 1 operates. This implies that the fibres 17 can also be covered by the material that constitutes the matrix 15, provided that it thickness and transmittance of this material allow structured light with which the work surface 5 is illuminated, to reach them and to come out 30 again from the work surface 5 after being reflected and / or scattered M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM from fibers 17. Based on the analysis instrument 1 to be calibrated, the structured light it can – for example – be light in the visible light band, or light in the near-infrared band. At the working surface 5, the fibres 17 have a pattern 5 note of the fibers: at each point of the working surface 5 it is possible identify a limited number of fibres 17 whose direction can be considered constant (more details regarding this direction can be found in the paragraphs subsequent), and this direction is known point by point in correspondence of the entire working surface 5 (its trend is known). 10 The known trend of the fibres can be uniform or variable: in the first case, the direction of the fibers 17 is constant along the entire working surface 5, while in the second case the direction of the fibres 17 is different at a plurality of distinct points on the surface of job 5. 15 Preferably, a calibration standard 3 is used in the method in which the work surface 5 is substantially flat and in which the known trend of the fibers are parallel to the working surface 5, i.e. where the direction of the fibers 17 is parallel to the working surface 5 throughout the entire extension of the surface of work 5 (this does not affect the possibility that the known trend of the fibers 20 whether uniform or variable). Composite material 13 is an anisotropic light scattering material: by “anisotropic light scattering material” it is meant that the material composite 13, when irradiated with a beam of structured light 11 - generally of laser light – at the working surface 5, 25 scatters light in one direction more than in others directions, similar to what can be observed during irradiation of the fibers of wood of a piece of wood with a ray of structured light 11. Using this calibration sample 13, in the calibration method we perform a detection phase and a processing phase. M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM In the detection phase, carried out with analysis tool 1, a detected trend of the fibres at a plurality of points 6 of the work surface 5. Specifically, the trend detected is noted fibers detecting a plurality of directions detected in the plurality of points 6: in 5 corresponding to each point 6, they light up with a ray of light structure 11 of the illuminated fibers – part of the fibers 17 – and one is detected respective direction detected. Each detected direction is a direction identified by the instrument. analysis 1 with respect to a reference system of the instrument: it can, for example 10 example, be identified with respect to a support plane 9 on which place the calibration sample 3, or with respect to a direction of reference of the analysis tool 1 (such as a direction of transport of pieces of wood). In some embodiments, the detection phase is a phase in which each 15 detected direction is measured with respect to this reference system. In the processing phase, taking into account the known trend of the fibres, processes the detected trend of the fibres to calibrate the analysis instrument 1. The The type of processing of the detected fiber trend may vary depending on of the implementing form of the method. 20 In some embodiments such as those in which the known course of the fibres is uniform (in which the direction of the fibres 17 remains constant in correspondence of the entire working surface 5), in the processing phase is for example it is possible to verify that the detected directions (of the trend detected fibers) are identical to each other, or in any case differ between 25 of them within certain limits of tolerance. In some implementations, in the detection phase the calibration sample 3 is located in a position that is known – or that can in any case be determined – with respect to the reference system of the analysis tool 1: in such forms For example, it is possible, in the development phase, to compare implementations 30 the detected trend of the fibers with the known trend of the fibers verifying, M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM for each point 6 where the survey is carried out, the correspondence between the detected direction and the direction of the fibers 17 at that point 6. Figure 1 schematically illustrates the detection phase of the method. calibration: an emission device 19 of the instrument is illustrated 5 analysis 1, a calibration sample 3 placed on a support surface 9, three rays of structured light 11 fixed emitted by the emitting device 19 and incident (in this case perpendicularly) on three points 6 of the work surface 5 of the calibration sample 3, and a detection device 21 (e.g. a camera or video camera) to detect the reflected light and any 10 light emitted following scattering. The detection device 21 detects light in the frequency band of light used for structured light rays 11: for example, if the structured light rays 11 are infrared light rays, the detection device 21 is a camera – or a video camera – infrared. A detail of the calibration sample 3 used is shown in 15 figure 2 (for clarity, fibres 17 of calibration sample 3 are not are illustrated). In some embodiments of the calibration method, a plurality of measurement phases with the calibration sample 3 placed, in each phase of detection, in a respective different (known) position with respect to the instrument 20 of analysis 1: in each phase of detection, the trend detected is recorded fibers at a respective different plurality of points 6 of the work surface 5 and, for each detection phase, the phase of processing. Advantageously, in the embodiments where the known course of the fibres is 25 uniform, you can test the ability of the analysis tool 1 of correctly measure different directions using the same calibration sample 3. In one possible embodiment, for example, performs a first detection phase with calibration sample 3 in a first position (figures 1 and 2); subsequently, a second phase is performed 30 of detection with the calibration sample 3 in a second position obtained, M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM starting from the first position, by rotating the calibration sample 3 on the support plane 9 of the analysis instrument 1 (figures 3 and 4, in which the Calibration sample 3 is rotated 90° with respect to figures 1 and 2). In some embodiments of the calibration method, a plurality of 5 calibration samples 3 and for each calibration sample 3, the detection phase and the processing phase (possibly a plurality of times with each calibration sample 3 as indicated above). Advantageously, the 3 calibration samples all have the same shape but a different known trend of the fibers. 10 In one possible embodiment, two calibration samples 3 are used having the same parallelepiped shape and a rectangular upper face or square as working surface 5: the first sample 3 has the fibers 17 with known course of the fibers which is parallel to the working surface 5 and which is uniform along a direction parallel to two edges 23 of the surface of 15 work 5 (and perpendicular to two other edges 23); the second sample 3 has the fibers 17 with known fiber pattern that is parallel to the working surface 5 and which is uniform according to an oblique direction to the four edges 23 of the work surface 5. Refer, for example, to figures 1 and 2 for the detection phase in which the first sample 3 is used, and in figures 5 and 6 20 for the detection phase in which the second sample 3 is used: placing the two calibration samples 3 in the same position relative to the instrument analysis 1, the direction of the fibres 17 of a sample 3 differs by 45° from to the direction of the fibres 17 of the other sample 3. We now move on to describe in more detail the calibration sample 3 object 25 of the present invention usable in the calibration method just described. The calibration sample 3 according to the present invention has a surface area of work 5 consisting of a composite material 13, which is a material anisotropic light scattering and comprising a matrix 15 and fibers 17 which are dispersed in the matrix 15; at least part of the fibers 17 are illuminable M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM with structured light at the work surface 5 and, preferably, it is located in correspondence with the work surface. The matrix 15 may be of a material that is transparent, translucent or also opaque to the structured light with which the analysis tool 1 operates 5 (at least in the case of an opaque material, the 17 fibres emerge advantageously on the work surface 5). Advantageously, the matrix 15 is made of a material with better resistance performance than wood, in particular better performance in terms of resistance to chemical agents and atmospheric. 10 In preferred embodiments, the matrix 15 is a polymeric material, or plastic. Preferably, the polymeric (or plastic) material is made using one or more intrinsically inert polymers (e.g., polymers which are hydrophobic in nature and do not absorb moisture), and / or using additives which, when added to the polymer, give greater 15 resistance (e.g. stabilizing additives and antioxidant additives). In other embodiments, the matrix 15 is instead a ceramic material, or metallic. In some preferred forms, the matrix 15 of the composite material 13 is a PLA base (polymer known as polylactic acid, or polylactate). The matrix 20 15 can in other cases be based on ABS (acrylonitrile-butadiene-styrene), HDPE (high density polyethylene), polycarbonate, or other polymers thermoplastics. In some embodiments, the matrix 15 is based on a polymer thermosetting, while in other forms it is based on a polymer 25 elastomeric. Preferably, the matrix 15 is continuous: that is, any point inside the matrix 15 can be reached from any other point inside the matrix 15 without leaving matrix 15. M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM As for the fibers 17, these are dispersed in the matrix 15 and, at least at the work surface 5 are preferably dispersed as evenly as possible. In embodiments where the matrix 15 is a polymeric material (or 5 plastic), the weight percentage of fibers 17 in the composite material 13 is advantageously between 5% and 40%, preferably between 20% and 30%. Fibers 17 have a known fiber pattern, which is parallel to the work surface 5 (work surface 5 is, advantageously, 10 substantially flat): at each point of the working surface 5 is it is possible to identify a limited number of fibres 17 whose direction can be considered constant; this direction of the fibers 17 is known point by point in correspondence of the entire working surface 5 (its trend is known) and is substantially parallel to the work surface 5 at each point. The 15 direction of the fibers 17 is intended as an indicative direction of the overall orientation of the limited number of fibers 17 in correspondence of that point. This direction is understood according to the meaning common in the materials industry, particularly in the wood industry. Referring to each fibre 17 to a respective direction of 20 extension parallel to the length of the fiber 17, preferably intended that the direction of the fibers 17 at that point is a direction with respect to which the directions of extension of at least 90% of the fibres 17 at such points are parallel, or in any case inclined by an angle less than 15°, preferably less than 10° and even more preferably less than 5° 25 (the direction of the fibers 17 at that point is in this case an average direction of the main extension directions of the fibers 17 in correspondence with that point). Preferably, all fibers 17 at the entire work surfaces 5 are parallel to each other: in this case, the known trend of the fibers is uniform in a single direction (see for example the 30 calibration sample 3 illustrated in figures 7 and 8). M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM In the context of the present invention, the direction of the fibers 17, as well as the directions of extension of the fibers 17, and the directions detected are intended as not necessarily having a direction of travel (in the manner of a straight line). 5 In some embodiments, the fibers 17 of the calibration sample 3 are short fibers. In the present invention, short fibers are understood to mean fibers 17 having a maximum length to diameter ratio of one hundred. Preferably, furthermore, the short fibers according to the present invention have a minimum length-to-diameter ratio of three. 10 In other embodiments, the fibers 17 of the calibration sample 3 have instead larger ratios between length and diameter. Preferably, all fibers 17 have similar diameters and similar lengths (as illustrated in figures 7 and 8). As for the materials, the 17 fibers can be of inorganic type 15 (e.g. glass fibres) or organic type (e.g. polymer fibres), preferably of the same material. In some embodiments, the fibers 17 are wood fibers, preferably from wood flour and preferably all of the same plant variety. In some embodiments, the composite material 13 is a material 20 extruded. In some embodiments, the composite material 13 has a structure layered, comprising a plurality of layers 25, and the working surface 5 which is transversal to the plurality of layers 25 (see for example the forms obtainable with the production method described below and 25 subject of the present invention). In this layered structure, the fibers 17 are divided into a plurality of layers 25: between one layer 25 and the other there are interface zones 27 where there are no fibers 17 passing from one layer 25 to the other. The interface zones 27, in some cases, present discontinuities premises of matrix 15. M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM In some embodiments, each layer 25 has a relative thickness 29 which has an order of magnitude equal to or less than the order of magnitude of the average fiber length 17. In some embodiments, each layer 25 has a relative thickness 5 29 which is equal to or less than 0.2 mm, even more preferably equal to or less to 0.1 mm. In some embodiments, each layer 25 has a relative thickness 29 which is substantially constant; the thickness 29 of a layer 25 can however differ from the thickness 29 of a different layer 25. In such forms 10 realizations, the layers 25 are parallel to each other and the known trend of the fibers is uniform across the entire work surface 5. The samples of calibration 3 illustrated in the figures have a plurality of layers 25 all having one same thickness 29 constant. In some embodiments of the calibration standard 3, the known trend 15 of the fibers at the working surface 5 is, as mentioned above, variable along the development of the working surface 5. In some of these forms of construction, the composite material 13 has the layered structure and one or most of the layers 25 have a relative thickness 29 which is variable (in the case of more layers 25, even differently from one layer 25 to another) along the development 20 of the relevant layer (25). The relative thickness 29 of each layer 25 is intended in one direction perpendicular to the interface zones 27 between one layer 25 and the other in correspondence of the working surface 5; if the layers 25 develop each in a plane perpendicular to the work surface 5 (case in which 25 each layer 25 has a relative constant thickness 29), this direction is parallel to the work surface 5. In any case, the relative thickness 29 of each layer 25 is greater than 0.01 mm. M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM In some embodiments, the calibration sample 3 consists of only composite material 13 (throughout its thickness perpendicular to the work surface 5). In other embodiments, however, the calibration sample 3 may comprise 5 a first part made of composite material 13 (which defines the work surface 5) and a second part made of a material different, which is fixed to the first part and supports it. In some embodiments, the calibration sample 3 comprises a frame which supports one or more panels which are each made of the material 10 composite 13 and which define the working surface 5 of the sample of calibration 3. In some embodiments, the panels are placed side by side others in correspondence with the same side of the calibration sample 3 defining the working surface 5 on this side, while in other embodiments such panels are distributed along different sides of the sample 15 calibration 3 (for example of an upper side, of a lower side, of one or more lateral sides of the calibration sample 3). In some embodiments, the panels differ from each other due to a different known trend of the fibres. Although developed for the calibration of a direction analysis instrument 1 of wood fibers operating by light scattering detection 20 structured, the calibration sample 3 object of the present invention can be used to calibrate other wood analysis instruments 1 which perform optical analyses. Advantageously, the calibration sample 3 It can also be used to calibrate wood analysis instruments 1 which they carry out different types of analyses. 25 Finally, we move on to describing the production method of the calibration sample. 3 described above in accordance with the present invention. In the production method, the composite material 13 is made by performing an extrusion phase and a deposition phase – performed simultaneously at the extrusion stage – according to a manufacturing method of the type 30 fused deposition modeling (also known as Fused Deposition Modeling) M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM Filament Fabrication, with the acronym FFF, or with the English term Fused Deposition Modeling, with acronym FDM). In the extrusion phase, an extruded material 31 is extruded which comprises a continuous phase and the 17 fibers, which are dispersed in the continuous phase. The 5 extruded material 31 can be extruded, for example, from a filament, from a rod, or from granules of an extrudable material; the fibers 17 can be already previously dispersed inside the filament, of the bar, or starting granules (before carrying out the extrusion phase), or be dispersed in the continuous phase during extrusion to obtain the 10 extruded material 31. The extruded material 31 is extruded along a direction of extrusion which, advantageously, is vertical. The direction of extrusion considered can be understood as the axis 32 of the nozzle of a head extrusion 33 used for the extrusion phase. In the deposition phase, the extruded material 31 is deposited – exiting along 15 the extrusion direction – along a deposition path forming a plurality of extruded segments 35 superimposed on each other in a plurality of layers 25, which extend transversely to the working surface 5 of the calibration sample 3 to be produced (figure 7); in particular, each one is formed extruded segment 35 along a respective deposition direction (part of the 20 deposition path) which is transverse to the extrusion direction. The deposition direction of each extruded segment 35 corresponds to the direction along which the extruded segment 35 extends in length, and corresponds to the direction of the fibres 17 of the calibration sample 3 from produce along this extruded segment 35. 25 Advantageously, a solidification phase is also performed in which, whenever the extruded material 31 is deposited forming a segment extruded 35, this extruded segment 35 is solidified (or allowed to solidify) before depositing a different extruded segment 35 (of the plurality of extruded segments 35). M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM In some embodiments, in the deposition phase each extruded segment 35 such that each layer 25 has a relative thickness 29 with order of magnitude equal to or less than the order of magnitude of the average length of the fibres 17 to favour their orientation along the 5 direction of deposition. In some embodiments, in the deposition phase, each extruded segment 35 such that each layer 25 has a relative thickness 29 equal to or less than 0.2 mm, even more preferably equal to or less than 0.1 mm. 10 In some embodiments, in the deposition phase, each extruded segment 35 such that each layer 25 has a respective thickness 29 which is constant along an entire length of the extruded segment 35. In any case, each extruded segment 35 is formed in such a way that 15 each layer 25 has a respective height greater than 0.01 mm. Figure 9 shows a possible implementation of the method. production in three different successive moments (from top to bottom): they are visible in figure 9 respectively a first extruded horizontal segment 35 just formed, the formation of a second extruded segment 35 to the 20 above the first extruded segment 35 (solidified), and the composite material 13 made following the formation of the last extruded segment 35; in the embodiment of figure 9, the composite material 13 is made with each layer 25 formed by a single extruded segment 35 with thickness 29 constant. 25 In figure 9 (and similarly in figure 10, described below) are represented with dashed arrows of the possible movements of the extrusion head 33 during the formation of the extruded segment 35. In other embodiments, such as the one illustrated for example in figure 10 (illustrated in four different successive moments – from top to bottom), 30 each layer 25 is instead formed by several extruded segments 35 (in the case M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM illustrated, three) which are placed side by side in a transversal direction to the deposition direction and extrusion direction (each segment extruded 35 still extends parallel to the direction of deposition). For each layer 25, only one extruded segment 35 5 helps define the work surface 5. Similarly, in other implementing forms, a structure similar to that of figure 10 can be obtained by making the extruded segments 35 (composed of the extruded material 31) only at the working surface 5 and making the remaining part of the sample always with the same method 10 of fused deposition modeling type manufacturing but with a material different. Preferably, the extruded material 31 is deposited for each layer 25 forming, in correspondence with the working surface 5, a single segment extruded 35 without interrupting the deposition of the extruded material 31. In 15 some cases the entire plurality of extruded segments 35 can be formed without interrupt the deposition of extruded material 31, for example by depositing the extruded material 31 along a serpentine deposition path (as in the embodiment of figure 9), or by interrupting the deposition of extruded material 31 at the ends of each extruded segment 35 (as 20 in the implementing form of figure 10). The production method of calibration sample 3 may include further phases: for example, it may include a cutting phase of the composite material 13 to change the shape and / or size of the work surface 5 (for example example, to obtain a calibration sample 3 with known trend of the 25 uniform fibers in an oblique direction with respect to the edges 23 of the work surface 5). The present invention has allowed us to obtain significant advantages. Through the present invention it has in fact been possible to create a method of calibration, a calibration sample and a production method that M520-12IT93 Eng. Simone Ponchiroli AB / SP Register Prot. n. 1070BM they allow to circumvent the critical issues related to the alterability of the wooden pieces used to date as calibration standards. The invention thus conceived is susceptible to numerous modifications and variations, all falling within the scope of the inventive concept as defined by the 5 independent claims. All details are replaceable by other technically equivalent ones and the materials used, as well as the shapes and sizes of the various components, they can be any depending on the needs. 10 THE AGENCY Eng. Simone Ponchiroli (Register Prot. n. 1070BM)

Claims

CLAIMS 1. Method of calibrating an instrument (1) for analyzing the direction of wood fibers in a piece of wood by means of structured light scattering detection, wherein a calibration sample (3) having a working surface (5) and comprising fibers (17) at least partly illuminable with structured light at the working surface (5) is used, and wherein the following steps are performed: a detection step, performed with the analysis instrument (1), wherein a detected trend of the fibers is detected at a plurality of points (6) of the working surface (5); and a processing step, wherein said detected trend of the fibers is processed to calibrate the analysis instrument (1);and wherein furthermore the calibration sample (3) used has the working surface (5) made of a composite material (13), the composite material (13) being an anisotropic light scattering material and comprising a matrix (15) and said fibres (17), which are dispersed in the matrix (15) and which have a known fibre pattern in correspondence with the working surface (5).; 2. Calibration method according to claim 1, characterised in that a calibration sample (3) is used in which the known direction of the fibres is parallel to the working surface (5).

3. Calibration method according to claim 1 or 2, characterised in that: a plurality of said detection phase is carried out with the calibration sample (3) placed, in each detection phase, in a different position with respect to the analysis instrument (1); in each detection phase, the detected trend of the fibres is detected in correspondence with a different plurality of points (6) of the working surface (5); and for each detection phase, the processing phase is carried out.

4. Calibration method according to any of claims 1 to 3, characterised in that a plurality of calibration samples (3) is used and, for each calibration sample (3), the detection phase and the processing phase are carried out, the calibration samples (3) of the plurality of calibration samples (3) used differing from each other for a different known trend of the fibres.

5. Calibration sample (3) usable in the method according to any of claims 1 to 4, characterised in that: the calibration sample (3) has a working surface (5) made of a composite material (13); the composite material (13) is an anisotropic light scattering material and comprises a matrix (15) and fibres (17); and the fibres (17) are dispersed in the matrix (15), have a known fibre pattern which is parallel to the working surface (5) and are at least partly illuminable with structured light at the working surface (5).

6. Calibration method according to any of claims 1 to 4, or calibration sample (3) according to claim 5, characterised in that the matrix (15) of the composite material (13) is a polymeric material.

7. Calibration method or calibration sample (3) according to claim 6, characterised in that the matrix (15) of the composite material (13) is based on PLA.

8. Calibration method or calibration sample (3) according to claim 6 or 7, characterised in that the weight percentage of the fibres (17) in the composite material (13) is between 5% and 40%, preferably between 20% and 30%.

9. Calibration method according to any of claims 1 to 4 or 6 to 8, or calibration sample (3) according to any of claims 5 to 8, characterised in that the fibres (17) of the calibration sample (3) are wood fibres.

10. Calibration method according to any of claims 1 to 4 or 6 to 9, or calibration sample (3) according to any of claims 5 to 9, characterised in that the fibres (17) of the calibration sample (3) are short fibres.

11. Calibration method according to any of claims 1 to 4 or 6 to 10, or calibration sample (3) according to any of claims 5 to 10, characterised in that the composite material (13) has a layered structure comprising a plurality of layers (25), the fibres (17) being divided into the plurality of layers (25) and the working surface (5) being transversal to the plurality of layers (25).

12. Calibration method or calibration standard (3) according to claim 11, characterised in that each layer (25) has a relative thickness (29) which has an order of magnitude equal to or less than the order of magnitude of an average length of the fibres (17).

13. Calibration method or calibration standard (3) according to claim 11 or 12, characterised in that each layer (25) has a relative thickness (29) equal to or less than 0.2 mm, preferably equal to or less than 0.1 mm. M520-12IT93 AB / SP Ing. Simone Ponchiroli Albo Prot. η. 1070BM 14. Calibration method or calibration sample (3) according to any of claims 11 to 13, characterised in that each layer (25) has a relative thickness (29) which is substantially constant, the known trend of the fibres being uniform across the entire working surface (5).

15. Calibration method according to any of claims 1 to 4 or 6 to 13, or calibration sample (3) according to any of claims 5 to 13, characterised in that the known fibre pattern at the working surface (5) is different at a plurality of distinct points on the working surface (5).

16. Calibration method or calibration standard (3) according to claim 15 when it depends on claim 11, characterised in that one or more layers (25) of the plurality of layers (25) have a relative thickness (29) which, at least in correspondence with the working surface (5), varies along the development of said one or more layers (25).

17. Calibration method according to any of claims 1 to 4 or 6 to 16, or calibration sample (3) according to any of claims 5 to 16, characterised in that the calibration sample (3) comprises a frame supporting one or more panels defining the working surface (5) of the calibration sample (3), each panel being made of the composite material (13).

18. Calibration method according to any of claims 1 to 4 or 6 to 17, or calibration sample (3) according to any of claims 5 to 17, characterised in that the composite material (13) is an extruded material. M520-12IT93 AB / SP Ing. Simone Ponchiroli Albo Prot. η. 1070BM 19. Use of the calibration sample (3) according to any of claims 5 to 18 to perform a calibration of an optical wood analysis instrument.

20. A method of producing the calibration sample (3) according to claim 18 when dependent on claim 11, wherein the composite material (13) is made by performing, in a fused deposition modelling type manufacturing method, the following steps: an extrusion step, wherein an extruded material (31) is extruded along an extrusion direction, the extruded material (31) comprising a continuous phase and fibres (17) which are dispersed in the continuous phase; and a deposition step, performed concurrently with the extrusion step, wherein the extruded material (31) is deposited along a deposition path; and wherein, during the deposition step: the extruded material (31) is deposited forming a plurality of extruded segments (35) which are superimposed on each other in a plurality of layers (25) which extend transversely with respect to the working surface (5) of the calibration sample (3) to be produced;and each extruded segment (35) is formed along a respective deposition direction that is transverse to the extrusion direction.; 21. Production method according to claim 20 when dependent on claim 12 wherein, during the deposition step, each extruded segment (35) is formed in such a way that each layer (25) has a respective thickness with an order of magnitude equal to or less than the order of magnitude of an average fiber length (17).

22. Production method according to claim 20 or 21 when depending on claim 13 wherein, in the deposition step, each extruded segment (35) is formed in such a way that each layer (25) has a respective thickness equal to or less than 0.2 mm, preferably equal to or less than 0.1 mm.

23. A production method according to any of claims 20 to 5 22 when dependent on claim 14 wherein, in the deposition step, each extruded segment (35) is formed such that each layer (25) has a respective thickness that is constant along an entire length of the extruded segment (35).