EP2922704A1

EP2922704A1 - Method and system for marking a surface by laser treatment

Info

Publication number: EP2922704A1
Application number: EP13803176.0A
Authority: EP
Inventors: Stéphane MOREL
Original assignee: Akeo Plus
Current assignee: Akeo Plus
Priority date: 2012-11-26
Filing date: 2013-11-26
Publication date: 2015-09-30
Also published as: WO2014080149A1; US20150298260A1; FR2998505A1; FR2998505B1

Abstract

The invention concerns a method for marking a surface (S) by laser treatment, consisting of etching a plurality of patterns (M(0), M(1)) onto the surface by means of a laser source (2), said patterns being distributed across the surface according to a predefined tessellation of adjacent patterns, which involves: -etching each pattern from a corresponding virtual image generated in an image plane (20) of the laser source and physically reproduced by laser etching on the surface, in which each virtual image defines a frame physically reproduced on an area of the surface such that the corresponding etched pattern has an etched frame covering said area, the etched frames of adjacent patterns covering adjacent areas; and -the laser source is controlled in position between each etching of a pattern by means of a three-dimensional surface mapping system (3) coupled to the laser source; the method being remarkable in that it involves resetting the laser source, before etching each pattern, by matching up hook elements and target elements between adjacent patterns. The present invention is applicable in the field of etching items made from a material suitable for laser marking.

Description

METHOD AND SYSTEM FOR MARKING A SURFACE BY

LASER TREATMENT

The present invention relates to a method of marking a surface by laser treatment, comprising engraving on the surface a plurality of patterns by means of a laser source, said patterns being distributed on the surface according to a predefined tiling of adjacent patterns .

The invention finds application in the field of marking parts made of material suitable for laser marking, in other words of any type that can be etched by a laser treatment.

In a specific but non-limiting application, the invention is applicable for the marking of large parts, such as for example dashboards or door trim of a motor vehicle, trim parts or trim in the aeronautical field , hood parts, cover or protection of electronic, medical, etc.

Currently, there is a search for marked geometric patterns on parts increasingly complex and thin, mainly for aesthetic reasons, requiring the implementation of digital techniques to control the laser source that will perform the desired etching.

It is thus known to implement marking methods in which:

each pattern is etched from a corresponding virtual image generated in an image plane of the laser source and physically reproduced by laser etching on the surface, where each virtual image defines a frame reproduced physically on an area of the surface so that the corresponding engraved pattern has an engraved frame covering said area, the engraved frames of the adjacent patterns covering adjacent areas; and

the laser source is driven in position between each etching of a pattern by means of a three-dimensional mapping system of the surface coupled to the laser source.

The difficulty of such a method lies in the necessary precision to be applied to each etching of a pattern, the laser source being moved between each etched pattern. Indeed, it is essential that the patterns are glued to each other, otherwise we see appear holes and / or discontinuities and / or overlaps between the frames of the different patterns, detrimental to the overall aesthetic appearance of the surface marking. We generally speak of local defects of concordance between the patterns.

Such local defects have their origins essentially within the limits of the three-dimensional mapping system and within the limits of the automaton (usually a five or six-axis robot) which ensures the displacement and orientation of the substrate, which induce uncertainties of relative positioning between the patterns.

It is also common to seek accuracies of the order of 2 to 5 micrometers, depending on the quality of the laser source. However, achieving such a level of accuracy proves extremely difficult when the marking covers several thousand patterns to be engraved, over lengths of the order of one meter or even several meters, and with a controller that controls the movement and the orientation of the laser source with a precision generally of the order of

0.2 to 0.5 millimeters. Indeed, the inaccuracy of the automaton inevitably induces problems of continuity between the etched patterns as marking progresses, especially over long lengths where it is found that the error accumulates and becomes prohibitive at the end of marking.

To these difficulties are also added the errors generated by computer-aided manufacturing calculation which brings its share of inaccuracy, and the defects of shape of the surface to be treated which is generally different from the theoretical three-dimensional model which serves as a basis for calculations. the route of the laser source.

The object of the present invention is to propose a method of marking a surface by laser treatment which makes it possible to readjust the laser source, and more specifically to optically readjust the image plane of the laser source, before each etching of a pattern, for in the end ensure good agreement between the grounds.

For this purpose, it proposes a method for marking a surface by laser treatment, consisting in engraving on the surface a plurality of patterns by means of a laser source, said patterns being distributed on the surface according to a predefined tiling of adjacent patterns , in which :

each pattern is etched from a corresponding virtual image generated in an image plane of the laser source and physically reproduced by laser etching on the surface, where each virtual image defines a virtual frame reproduced physically on an area of the surface so that that the engraved pattern corresponding has an engraved frame covering said area, the etched frames of adjacent patterns covering adjacent areas; and

the laser source is driven in position between each etching of a pattern by means of a three-dimensional mapping system of the surface coupled to the laser source;

said method being remarkable in that it comprises the following steps: a) a prior theoretical modeling of the paving of the patterns on the surface is carried out from a three-dimensional model of the surface, said modeling consisting in calculating the shapes and the positions a plurality of virtual images providing the tiling of this three-dimensional model by adjacent virtual images, and a given sequence in the physical reproduction of the virtual images, each virtual image defining:

a virtual frame,

virtual elements said to be hooked inside said virtual frame, and

said target virtual elements located outside said virtual frame, where the positions of the virtual target elements and the hooked virtual elements relative to the corresponding virtual frames are calculated so that the set of virtual target elements d a virtual image coincide on the three-dimensional model with virtual elements of hanging adjacent virtual images, and so that the set of virtual elements of hook of a virtual image coincide on the three-dimensional model with virtual elements of target of adjacent virtual images;

b) calculating, for each virtual image, an orientation and a position of the laser source relative to the surface to allow the implementation of the etching of the patterns in accordance with the prior theoretical modeling;

c) a basic pattern of starting, from a virtual image, an orientation and a position of the laser source said starting from the calculations of steps a) and b) is engraved, the starting reason having an engraved frame covering a so-called area of departure from the surface, etched target elements located outside the engraved frame of the starting pattern and therefore outside said starting zone;

d) preparing the etching of a new pattern on a new area adjacent to said start area, generating a new virtual image and moving and orienting the laser source according to the calculations of steps a) and b), some of the target elements of the starting pattern being etched on said new area;

e) identifying with the three-dimensional mapping system the positions of the target elements of the starting pattern etched on said new area;

f) calculating the projections, in the image plane of the laser source, of the target elements of the starting pattern etched on the new zone;

g) we apply, in the image plane, a geometrical transformation on the new virtual image to make coincide:

said projections of the target elements of the starting pattern, with

the virtual hook elements of the new virtual image that were initially calculated, during step a), to coincide with virtual elements of target of the starting virtual image;

h) the new pattern is etched from the new virtual image transformed in step g), so that the new pattern has an engraved frame covering the new area, engraved hanging elements which coincide with the elements of target of the start pattern etched on said new area, and etched target elements located outside the new area;

j) repeating steps d) to h) for the following patterns to pave the surface of adjacent etched patterns.

Thus, the method according to the invention comprises preliminary calculation steps a) and b) (pre-ca lcu l or preprocessing stages) which essentially consist in virtually modeling the tiling (definition of the shapes and positions of the images virtual, definition of the sequence or the order of etching between the patterns, definition of the positions and orientations of the laser source at each etching). However, if we implement this modeling directly, without taking into account the reality of the etching and the position of the laser source before etching, we risk creating local defects, hence the need to optically recalibrate the image plane of the laser source before each etching.

For this purpose, the invention proposes defining virtual hook elements and virtual target elements that will be used to re-align the image plane of the laser source, by implementing a transformation (in other words a correction) on the new virtual image. (step g)) to finally ensure that the hooked elements and the target elements concerned coincide, which makes it possible to catch the errors of position and orientation of the laser source, the actual defects on the surface not provided for in the model three-dimensional surface, etc. ; such a registration being ultimately independent of the length or size of the surface to be marked.

According to one characteristic, during the calculations of step a), each virtual image is calculated so that its virtual elements of hanging are located on virtual elements of texture of its virtual frame, said virtual elements of texture defining the drawing of the virtual frame, so that, in step h), the target elements of the start pattern engraved on the new area are etched on texture elements of the engraved frame of the new pattern.

In this way, the target elements and the hung elements are etched on texture elements, and they are thus hidden by these texture elements and perfectly integrated into the final texture of the marking, without detracting from the aesthetic appearance. These target and hook elements will have been used to make the registration, and they disappear in the texture.

According to another characteristic, the method further comprises, prior to step c), two calibration steps:

- a first calibration of the three-dimensional mapping system to determine the position in space of a point of the surface,

a second step of calibrating the laser source with respect to the three-dimensional mapping system so as to be able to project, in the image plane of the laser source, a point of the surface detected by the three-dimensional mapping system.

These calibration steps make it possible to determine the mathematical calculation tools necessary for the implementation of step f) which, as a reminder, consists in projecting the target elements of the starting pattern (real engraved elements in a three-dimensional space) in the image plane of the laser source (in other words in a two-dimensional space in which we find the new virtual image).

In a particular embodiment, the second calibration step consists in using the three-dimensional mapping system coupled to the laser source as follows:

a plurality of calibration patterns are engraved on a flat surface, situated at a first height, from a virtual image composed of a plurality of virtual calibration patterns distributed according to a given conformation, and then the position of the calibration patterns engraved on said flat surface is determined with the three-dimensional mapping system;

the preceding step is repeated on flat surfaces situated at different heights with respect to said first height.

In this way, a calibration is performed at different heights

(Z calibration) using calibration patterns ordered according to a predefined geometric conformation (calibration in x and y) and which are preferably easily recognizable by the mapping system. We thus establish the correspondences between the three-dimensional space (in x, y and z) and the image plane of the laser source, to finally calculate a set of matrices of projection (or change of reference) between the observed three-dimensional space by the three-dimensional mapping system and the image plane in which the virtual images are generated before etching.

In a particular embodiment, the method uses, as a three-dimensional mapping system, at least one stereoscopic vision system comprising at least two cameras coupled to the laser source.

Such a stereoscopic vision system is particularly advantageous for accurately mapping the surface.

Advantageously, the first calibration step of the stereoscopic vision system implements an intrinsic calibration and an extrinsic calibration of the two cameras, or a stereoscopic calibration to determine the relative position and orientation of the cameras.

Thus, one can know the position and the relative orientation of the cameras and the laser source in an absolute coordinate of Cartesian work, and one can determine by triangulation techniques the position of a point in three-dimensional space in different ways known.

According to a possibility of the invention, the method uses, as a three-dimensional mapping system, at least one system included in the following list: depth sensor, measurement system by projection of structured light fringes, measurement system by projection of fringes laser, 3D camera.

Preferably, this or these systems are complementary to the stereoscopic vision system, to enhance the detection of the points of the surface in the three-dimensional space. It is also conceivable to use specific lighting means (eg UV, IR, visible) to improve the contrast on the surface to be treated and thus increase the accuracy of the three-dimensional mapping.

According to another possibility of the invention, during calculations of step a), at least one virtual image comprises a so-called composite virtual frame which is composed of a plurality of pavement sub-elements grouped against each other.

This technique, called clustering or "patch", has the advantage of maximizing the area etched at each etching, and thus reduce the time of the marking operation; the sub-elements of paving being shaped and oriented in particular according to the morphology of the area on which they are intended for engraving. The target and hung elements are then calculated respectively outside and inside the grouping of the sub-elements of paving.

Advantageously, the composite virtual frame is based on the grouping of several polygonal pavement sub-elements of planar shape, said sub-elements of paving being preferably grouped to fill to the maximum the area of the image plane of the laser source.

This grouping consists in generating a polygonal model, based on polygonal tessellation sub-elements, from a surface model to maximize the surface of the frame at each etching as a function of the morphology of the area of the surface to be treated. .

Preferably, the polygonal pavement sub-elements are grouped according to a triangulation model using a so-called cordial error criterion.

The string error determines the number of polygonal tiling sub-elements of the polygon triangulation model. The smaller the chordal error, the more consistent and accurate the polygon model is, but the greater the number of polygonal tiling sub-elements. It is therefore necessary to arbitrate between the number of sub-elements of polygonal paving and the geometric fineness.

The invention also relates to a system for marking a surface by laser treatment, suitable for implementing a marking method according to the invention, said system comprising:

a laser source provided with an image plane;

a three-dimensional mapping system coupled to the laser source; a system for generating a virtual image in the image plane of the laser source, adapted to generate a virtual image;

an actuation system ensuring the displacement and orientation of the laser source and the three-dimensional mapping system;

a calculation system designed to perform calculation steps a), b) and f), and to apply the geometric transformation of step g) to the new virtual image.

Other characteristics and advantages of the present invention will appear on reading the following detailed description of an example of non-imitative implementation, made with reference to the appended figures in which:

- Figures 1 and 2 are schematic perspective views of a marking system according to the invention;

FIGS. 3a to 3d schematically illustrate the steps of etching a starting pattern on a starting area of the surface, where:

FIG. 3a is a schematic view of the three image planes (image plane of the first camera, image plane of the laser source, image plane of the second camera) during the generation of the initial virtual image, before etching;

FIG. 3b is a diagrammatic view of the marking system occupying a position and a starting orientation, and carrying out the etching of the starting pattern from the initial virtual image;

FIG. 3c is a partial diagrammatic view of the surface on which the starting pattern is engraved;

FIG. 3d is a schematic view of the three image planes after the etching of the starting pattern;

FIGS. 4a to 4h schematically illustrate the steps of etching a new pattern on the surface, contiguous to the initial pattern, where:

FIG. 4a is a diagrammatic view of the marking system occupying a new position and a new orientation for preparing the etching of the new pattern on a new zone adjacent to the starting zone;

- Figure 4b is a schematic view of the surface on which is engraved the starting pattern and is shown in broken lines the new area; FIG. 4c is a schematic view of the three image planes during the generation of the new virtual image;

FIG. 4d is a diagrammatic view of the three image planes after the at least partial projection of the starting pattern in the image plane of the laser source, to make it possible to perform the registration of the laser source;

FIG. 4e is a schematic view of the three image planes after the transformation of the new virtual image for the registration of the laser source;

FIG. 4f is a schematic view of the marking system embossing the new pattern from the transformed new virtual image;

- Figure 4g is a schematic view of the surface on which is engraved the starting pattern and the new pattern;

FIG. 4h is a schematic view of the three image planes after the etching of the new pattern;

FIGS. 5a to 5d schematically illustrate steps of construction of a virtual image by the regulation of polygonal pavement sub-elements according to a triangulation model;

FIG. 6 is a schematic view of the marking system during the second calibration step of the laser source with respect to the three-dimensional mapping system.

With reference to FIGS. 1 and 2, a marking system 1 according to the invention of a surface S comprises:

a laser souce 2, otherwise called a laser scanner, adapted to physically reproduce on the surface S by laser etching a virtual image generated in a so-called laser image plane 20;

a three-dimensional mapping system 3 coupled to the laser source 2 and adapted to scan in three dimensions the surface S, the laser source 2 and the three-dimensional mapping system 3 being integrally coupled and thus integral in rotation and displacement;

a generation system (not shown, because integrated to the laser source 2) of a virtual image in the image plane of the laser source;

an actuation system (not illustrated) ensuring the displacement and the orientation of the welder 2 and the three-dimensional mapping system 3, in particular of the five or six-axis robot type; a calculation system (not shown), of the control unit type, adapted to perform the calculations detailed below, and to control the laser source, the three-dimensional mapping system 3, the generation system and the control system.

As illustrated in FIGS. 1 and 2, the three-dimensional mapping system 3 comprises a stereoscopic vision system comprising:

at least two cameras 31, 32 each designed to record at least one image of the surface S in a corresponding image plane 310, 320, each camera 31, 32 being associated with at least one coordinate making it possible to deduce the relative position of the cameras 31 , 32; and

calculation means connected to the cameras 31, 32 and designed to reconstitute a three-dimensional representation of the surface S by means of stereovision evaluation of the images from the cameras 31, 32 and from the relative position of the cameras.

In addition to or replacement of the stereoscopic vision system 3, it is conceivable to provide at least one three-dimensional mapping system included in the following list: depth sensor, measurement system by projection of structured light fringes, projection projection system of laser fringes, 3D camera.

According to the invention, the marking method using such a marking system 1, consists in etching on the surface S a plurality of patterns M (i) by means of the marking system 1, with patterns M (i) distributed over the surface S according to a predefined tiling of adjacent patterns.

More precisely, each pattern M (i) is etched from a corresponding virtual image IV (i) generated in the laser image plane 20 of the laser source 2, where each virtual image IV (i) defines a virtual TV frame ( i) physically reproduced on a zone Z (i) of the surface S so that the corresponding pattern M (i) has an engraved field TG (i) covering said zone Z (i), the etched frames TG (i) of the adjacent M (i) patterns covering adjacent Z (i) zones.

In a first step, the marking method implements preliminary calculation steps (so-called pre-calculation or "preprocessing" steps).

In a first step a) of pre-calculation, a prior theoretical modeling of the tiling of the patterns M (i) on the surface S to from a three-dimensional model of the surface (theoretical surface), said modeling consisting in calculating the shapes and positions of a plurality of virtual images IV (i) providing the tiling of this three-dimensional model by virtual images IV (i ), as well as a given sequence in the physical reproduction of the virtual images IV (i).

The objective of this step a) is to calculate in advance all the parameters of the virtual images IV (i) (shape, location, order in the sequence) to pave the three-dimensional model of the surface, these virtual images IV (i ) are then reproduced by etching on the actual surface S in the form of a patterning pattern M (i). However, between the theoretical modeling and the reality, distortions and errors appear which necessitate recalibration of the laser source between each etching of a pattern M (i).

Each virtual image IV (i) defines:

a virtual TV frame (i) which presents virtual elements of texture EVT (i), such as straight lines, curves, etc. which define the drawing of the virtual image IV (i);

virtual elements called hooked EVA (i) located inside the virtual frame TV (i); and

virtual elements called EVC target (i) located outside the virtual frame TV (i).

The virtual image TV (i) is physically reproduced by laser etching on a zone Z (i) of the surface S, in the form of a pattern M (i) which presents:

an engraved T (i) frame which has ET (i) texture elements, such as straight lines, curves, etc. that define the pattern design

M (i);

- Hook elements EA (i) etched and located inside the frame T (i) and therefore the zone Z (i); and

EC (i) target elements etched and located outside the frame T (i) and therefore outside the zone Z (i), that is to say at the periphery of the zone Z (i) on zones Z (j) directly adjacent to or contiguous to zone Z (i).

For the remainder of the description, and as illustrated in the figures, the so-called virtual EVA hook elements (i) and the so-called EVC virtual target elements (i) are made in the form of dots, respectively called virtual dots. hooked EVA (i) and EVC target virtual points (i); which is physically reflected by elements of hooked EA (i) and target elements EC (i) engraved in the form of dots, respectively called hooked points EA (i) and target points EC (i). Of course, the virtual elements of hooked EVA (i) and the virtual elements of target EVC (i) can present other shapes (cross, circle, ellipse, triangle, etc.), so that the elements of hooked EA (i) and corresponding EC (i) target elements may have other forms.

Preferably, in order to hide in the engraved texture (or frame) the points of hanging EA (i) and the target points EC (i) of the patterns M (i), the virtual points of hanging EVA (i) are located on the virtual texture elements EVT (i) of the corresponding virtual frame TV (i).

With virtual TV frames (i) of polygonal shape delimited by successive sides, it is advantageous to have at least two EVC (i) virtual target points per side, which corresponds to at least two virtual points of hanging. EVA (i) per side.

The positions of the virtual target points EVC (i) and the virtual points of hooked EVA (i) relative to their corresponding virtual frames TV (i) are calculated so that:

the set of virtual target points EVC (i) of a virtual image IV (i) coincide on the three-dimensional model with virtual points of hanging EVA (j) virtual images IV (j) adjacent to said virtual image IV (i), and

the set of virtual points of hooked EVA (i) of a virtual image IV (i) coincide on the three-dimensional model with virtual target points EVC (j) virtual images IV (j) adjacent to said virtual image IV (i).

Thus, the principle is to engrave, for each pattern M (i), target points EC (i) on the zones Z (j) adjacent to the corresponding zone Z (i); these target points EC (i) serving as a reference for optically resetting the laser source 2 during the etching of the adjacent M (j) patterns.

In a second pre-calculation step b), for each virtual image IV (i), an orientation and a position of the laser source 2 relative to the surface S are calculated to enable the etching of the M units to be performed. (i) in accordance with the theoretical modeling previously calculated in step a).

Thus, at the end of steps a) and b) of pre-calculation, it is possible to start the etching, the etching of each pattern M (i) being defined essentially by: shape and position of the virtual image IV (i) , order in the engraving sequence, orientation and position of the laser source 2. With reference to FIGS. 3 and 4, the remainder of the description relates to the etching itself, with the intermediate steps of optical registration of the laser source 2.

With reference to FIGS. 3a to 3d, the method comprises a step c) of etching a starting pattern M (0) from a starting virtual image IV (0), in which:

in the laser image plane 20, the initial virtual image IV (0) (see FIG. 3a) resulting from the pre-calculation step a) is generated, this initial virtual image IV (0) presenting a frame virtual TV (0) inscribed in a rectangle and defined by EVT virtual text elements (0) composed of parallel virtual lines, and virtual EVC target points (0) arranged outside the virtual TV frame (0) ) (the hooked virtual dots are here absent, because the hanging dots are useless for the starting reason);

the laser source 2 is positioned and oriented in accordance with the pre-calculation step b), to enable etching on a starting zone Z (0) of the surface

(see Figure 3b);

the starting pattern M (0) is engraved on the starting zone Z (0), (see FIGS. 3b and 3c), the starting pattern M (0) having an engraved frame T (0) covering the starting zone Z (0) rectangular, with ET (0) texture elements composed of parallel lines, and engraved EC (0) target points located outside the engraved T (0) frame and thus outside the starting zone Z (0).

Thus, the target points EC (0) of the starting pattern M (0) are etched on zones Z (1), Z (2), Z (3), Z (4) adjacent to the departure zone Z ( 0), new patterns M (1), M (2), M (3), M (4) being provided to be etched thereafter on these zones Z (1), Z (2), Z (3), Z (4) adjacent.

FIG. 3d illustrates the IM (1) and IM (2) images of the first 31 and second 32 cameras, taken in their respective image planes 310, 320, after the etching of the M (0) starting pattern.

FIGS. 4a to 4h illustrate the etching of a new pattern M (1) on the zone Z (1) adjacent to the departure zone Z (0).

For this, the method comprises a step d) of preparing the etching of the new pattern M (0) on this new zone Z (1) adjacent to the starting zone Z (0), which consists in:

positioning and orienting the laser source 2 in accordance with the precalculation step b), to enable etching on this new zone Z (1) (see FIG. 4a), some of the target points EC (0) of the starting pattern M (0) being etched on this new zone Z (1) (see Figure 4b);

a new virtual image IV (1) is generated in accordance with the calculations of step a) (see FIG. 4c).

This new virtual image IV (1) presents:

a TV virtual frame (1) inscribed in a rectangle and defined by EVT virtual texture elements (1) composed of parallel virtual lines;

EVC target virtual points (1) arranged outside the virtual TV frame (1), except on the departure zone Z (0) side, and

- EVA hooked virtual points (1) arranged inside the virtual TV frame (1) and theoretically provided to coincide, after etching, with the target points EC (0) of the starting pattern M (0) engraved on the new zone Z (1).

Then, a step e) is carried out, with the cameras 31, 32 of the stereoscopic vision system 3, of the positions of the target points EC (0) of the starting pattern M (0) etched on the new zone Z (1). ) (see images IM (1) and IM (2) in FIGS. 4c and 4d).

Then, a step f) for calculating the projections PC (0), in the laser image plane 20 of the laser source 2, target points EC (0) of the starting pattern M (0) etched on the new zone Z (1) (see Figure 4d). In other words, a transformation of the three-dimensional space (the EC (0) target points etched on a three-dimensional S surface) is performed to a two-dimensional space (the projections P (0) in the laser image plane 20); noting that the three-dimensional location of the EC (0) target points is obtained by stereoscopic reconstruction from the IM (1), IM (2) images from the cameras 31, 32.

In general terms, a projection P (0) of the elements etched on the surface is calculated from the images IM (1), IM (2) from the cameras 31, 32, and from these elem ents g ravés fig u find interesting EC (0) target points. In other words, we recover the positions in the space of the elements engraved on the surface S in the vicinity of the new zone Z (1), from the images IM (1), IM (2), then we project in the plane laser image 20 these engraved elements visualized by the cameras 31, 32, thus forming a projection P (0) in this laser image plane 20; this projection P (0) comprising the projections PC (0) of the target points EC (0) in the new zone Z (1).

If there were no distortion or inaccuracy, we would have had the PC (0) projections of the EC (0) target points coincident with the points virtual hooked EVA (1). In the example of FIG. 4d, it is not noted that the projections PC (0) do not coincide with the virtual points of hanging EVA (1), so that a registration of the laser source 2 is to be carried out.

This step g) of resetting consists of applying, in the laser image plane 20, a geometrical transformation (rotation, translation, deformation) on the new virtual image IV (1) (see FIG. 4e) to make it coincide:

the projections PC (0) of the target points EC (0) of the starting pattern M (0) etched on the new zone Z (1), with

- the virtual points of hanging EVA (1) of the new virtual image IV (1).

In the example of FIGS. 4d and 4e, only a translation of the new virtual picture IV (1) was necessary to make the projections PC (0) coincide with the virtual points of hanging EVA (1). ).

Once this registration has been completed, it is possible to carry out step h) of etching the new pattern M (1) from the new virtual image IV (1) transformed or corrected during step g) (see FIGS. 4f and 4g). ), so that the new motif M (1) presents:

an engraved T (1) frame covering the new zone Z (1);

- etched EA points (1) which coincide with the target points EC (0) of the starting pattern M (0) etched on the new zone Z (1); and

- engraved EC (1) target elements located outside the new zone

Z (1), except on the starting zone Z (0).

As a reminder, the hooked points EA (1) are localized on the texture elements ET (1) of the frame T (1), so that the target points

EC (0) are concealed in the texture of the new M (1) pattern (in Figures 3 and 4, the target and hung points are oversized with respect to the texture lines to facilitate understanding of the figures).

Steps d) to h) are repeated for the following patterns M (2), ... M (N) in order to pave the surface of adjacent etched patterns, considering each etched pattern as a starting pattern potential for etching. a new motive; it being specified that the last pattern M (N) to be engraved does not have target points.

Prior to the etching step c), the method also provides:

a first step of calibrating the stereoscopic vision system 3, with an intrinsic calibration and an extrinsic calibration of the two cameras 31, 32 with a stereoscopic calibration, in order to be able to determine the position in the space of a point of the surface S; and a second step of calibrating the laser source 2 with respect to the stereoscopic vision system 3 in order to be able to establish the projection, in the image plane 20 of the laser source 2, of a point of the surface detected by the stereoscopic vision system 3.

The second calibration step aims to allow the step f) of projecting, in the laser image plane 20, the points engraved on the surface S, and in particular the target points EC (i).

With reference to FIG. 6, this second calibration step consists in carrying out the following steps:

on a flat surface S1, located at a first height H1, a plurality of calibration patterns MC (eg a succession of points distributed in line and in column) is engraved on the basis of a virtual calibration image IVC composed of a plurality of virtual calibration patterns distributed in a given geometrical conformation, then determining with the stereoscopic vision system 3 the position of the calibration patterns MC engraved on the flat surface S1;

the previous step is repeated on flat surfaces S2, S3, etc. located at different heights H2, H3, etc. with respect to said first height H1.

In this way, we can establish the correspondences between the real points engraved on the surfaces S, S1, S2, etc. and the points on the three image planes 20, 310, 320. By performing these steps at different heights (or depths), the laser source 2 is strongly calibrated with respect to the stereoscopic vision system 3. The result of this second step The calibration method results in a set of marker change matrices (in other words projection) between the three-dimensional space (measured by the cameras 31, 32) and the laser image plane 20.

In addition and with reference to FIGS. 5a to 5d, it is conceivable to provide, during step a) of pre-calculation, that at least one or each virtual image IV (i) is calculated according to a so-called grouping technique. , wherein the virtual image IV (i) has a so-called composite virtual frame which is composed of a plurality of pavement sub-elements SP (k, i) grouped against each other.

Working from predefined pavement sub-elements SP (k, i), the virtual TV frame (i) is constructed by grouping several pavement sub-elements SP (k, i), taking into account the three-dimensional morphology of the zone Z (i) to be processed, and the virtual points are positioned hooked EVA (i) and EVC target virtual points (i) once clustering completed.

As can be seen in FIGS. 5a to 5d, it is conceivable to work with planar polygonal pavement sub-elements SP (k, i), said pavement sub-elements SP (k, i) being preferably grouped together to fill maximum the area of the image plane of the laser source. We then speak of a conversion of a surface model (here the three-dimensional model of the surface) into a polygonal model.

To implement such a conversion, the use of a triangulation model using a cord error criterion is favored, which corresponds in known manner to the maximum distance allowed between the plane of each sub-element of paving. polygonal and three-dimensional model of the surface. In this case, it is conceivable to work on the normal vectors VN (k, i) to the respective paving sub-elements SP (k, i) (see FIG. 5b) and the pavement sub-elements SP (k, i) by comparison of the normal vectors close according to the fixed criterion retained (the cordial error).

Of course the implementation example mentioned above is not limiting and further improvements and details can be made to the method according to the invention without departing from the scope of the invention where other forms can for example be made for the reasons.

Claims

1. A method of marking a surface (S) by laser treatment, comprising engraving on the surface (S) a plurality of patterns (M (i)) by means of a laser source (2), said patterns (M (i) )) being distributed on the surface (S) according to a predefined tiling of adjacent patterns (M (i)), in which:

each motif (M (i)) is etched from a corresponding virtual image (IV (i)) generated in an image plane (20) of the laser source (2) and physically reproduced by laser etching on the surface ( S), wherein each virtual image (IV (i)) defines a virtual frame (TV (i)) physically reproduced on an area (Z (i)) of the surface (S) so that the pattern (M (i)) ) corresponding engraved has a frame (T (i)) etched covering the ite zone (Z (i)), the frames (T (i)) etched adjacent patterns (M (i)) covering areas (Z (i)) ) adjacent; and

the laser source (2) is driven in position between each etching of a pattern (M (i)) by means of a three-dimensional mapping system (3) of the surface (S) coupled to the laser source (2) ;

said method being characterized in that it comprises the following steps: a) a prior theoretical modeling of the tiling of the patterns (M (i)) on the surface (S) is carried out from a three-dimensional model of the surface (S ), said modeling of calculating the shapes and positions of a plurality of virtual images (IV (i)) paving this three-dimensional model with adjacent virtual images (IV (i)) and a sequence given in the physical reproduction of the virtual images (IV (i)), each virtual image (IV (i)) defining:

a virtual frame (TV (i)),

virtual elements known as hooked elements (EVA (i)) located inside said virtual frame (TV (i)), and

virtual so-called target elements (EVC (i)) located outside said virtual frame (TV (i)),

where the positions of the virtual target elements (EVC (i)) and the virtual hook elements (EVA (i)) relative to the corresponding virtual frames (TV (i)) are calculated so that the set of virtual elements of target (EVC (i)) of a virtual image (IV (i)) coincide on the three-dimensional model with virtual elements of hooked (EVA (j)) adjacent virtual images (IV (j)), and that the set of virtual elements hooked (EVA (i)) of a virtual image (IV (i)) coincide on the three-dimensional model with virtual target elements (EVC (j)) adjacent virtual images (IV (j));

b) calculating, for each virtual image (IV (i)), an orientation and a position of the laser source (2) relative to the surface (S) to enable the etching of the patterns (M (i )) in accordance with the prior theoretical modeling;

c) a basic pattern of departure (M (0)), from a virtual image (IV (0)), of an orientation and a position of the laser source (2) referred to as starting from the calculations of steps a) and b), the starting pattern (M (0)) having an engraved field (T (0)) covering a so-called start zone (Z (0)) of the surface (S), etched target elements (EC (0)) located outside the frame (T (0)) etched from the start pattern (M (0)) and thus outside said start area (Z ( 0));

d) preparing the etching of a new pattern (M (1)) on a new area (Z (1)) adjacent to said start area (Z (0)), by generating a new virtual image (IV (1) )) and moving and orienting the laser source (2) according to the calculations of steps a) and b), some of the target elements (EC (0)) of the starting pattern (M (0)) being etched on said new zone (Z (1));

e) identifying with the three-dimensional mapping system (3) the positions of the target elements (EC (0)) of the starting pattern (M (0)) etched on said new area (Z (1));

f) the projections (PC (0)), in the image plane (20) of the laser source (2), of the target elements (EC (0)) of the starting pattern (M (0)) etched on the new zone (Z (1));

g) applying, in the image plane (20), a geometrical transformation on the new virtual image (IV (1)) to coincide:

said projections (PC (0)) of the target elements (EC (0)) of the starting pattern (M (0)), with

the virtual hook elements (EVA (1)) of the new virtual image (IV (1)) that have been calculated, during step a), to coincide with virtual elements of target (EVC (0) )) of the starting virtual image (IV (0)); h) the new pattern (M (1)) is written from the new virtual image (IV (1)) transformed in step g), so that the new pattern (M (1)) has a frame Engraved (T (1)) covering the new zone (Z (1)), engraved hook elements (EA (1)) which coincide with the target elements (EC (0)) of the starting pattern (M (0)) etched on said new area (Z (1)), and elements of engraved target (EC (1)) located outside the new zone (Z (1));

j) repeating steps d) to h) for the following patterns (M (i)) to pave the surface (S) of adjacent engraved patterns (M (i)).

The method according to claim 1, wherein, in the calculations of step a), each virtual image (IV (i)) is computed so that its virtual hook elements (EVA (i)) are located on virtual texture elements (EVT (i)) of its virtual frame (TV (i)), said virtual texture elements (EVT (i)) defining the drawing of the virtual frame (TV (i)), so that, in step h), the target elements (EC (0)) of the starting pattern (M (0)) etched on the new area (Z (1)) are etched on texture elements (ET (1) )) of the frame (T (1)) engraved with the new pattern (M (1)).

3. Method according to any one of the preceding claims, further comprising, prior to step c), two calibration steps:

- a p re m e r a d ca l i b b e of the three-dimensional mapping system (3) to be able to determine the position in space of a point on the surface (S),

a second step of calibrating the laser source (2) with respect to the imitation tridimensional mapping system (3) in order to be able to establish the projection, in the image plane (20) of the laser source (2), of a point of the area (S) detected by the three-dimensional mapping system (3).

The method of claim 3, wherein the second calibration step comprises using the three-dimensional mapping system (3) coupled to the laser source (2) as follows:

- on a flat surface (S1), located at a first height (H1), a plurality of calibration patterns (MC) are processed from a virtual image (IVC) composed of a plurality of distributed virtual calibration patterns. according to a given conformation, and then determining with the three-dimensional mapping system (3) the position of the calibration patterns (MC) etched on said plane surface (S1); - The previous step is repeated on flat surfaces (S2, S3) located at different heights (H2, H3) relative to said first height (H1).

5. Method according to any one of the preceding claims, in leq uel the method, such as three-dimensional mapping system (3), at least one stereoscopic vision system comprising at least two cameras (31, 32). coupled to the laser source (2).

6. Method according to claims 3 and 5, wherein the first step of calibration of the stereoscopic vision system implements an intrinsic calibration and an extrinsic calibration of the at least two cameras (31, 32), then a stereoscopic calibration to determine the relative position and orientation of the cameras (31, 32).

7. A method according to any one of the preceding claims, in which the method, such as a three-dimensional mapping system (3), comprises at least one system included in the following list: depth sensor, measuring system by projection of structured fringes of light, measurement system by projection of laser fringes, 3D camera.

The method as claimed in any one of the preceding claims, wherein, during calculations of step a), at least one virtual image (IV (i)) comprises a so-called composite virtual frame (TV (i)) which is composed of a plurality of pavement sub-elements (SP (k, i)) grouped against each other.

9. The method of claim 8, wherein the composite virtual frame (TV (i)) is based on the grouping of several planar polygonal pavement sub-elements (SP (k, i)), said sub-elements of paving (SP (k, i)) being preferably grouped to fill to the maximum the area of the image plane (20) of the laser source (2).

10. The method of claim 9, wherein the polygonal pavement sub-elements (SP (k, i)) are grouped according to a triangulation model using a so-called cordial error criterion.

1 1. A system for marking a surface (S) by laser treatment, adapted for the implementation of a marking method according to any one of the preceding claims, said system comprising:

a laser source (2) provided with an image plane;

a three-dimensional mapping system (3) coupled to the laser source (2);

a system for generating a virtual image (IV (i)) in the image plane of the laser source (2), adapted to generate a virtual image (IV (i));

an actuation system ensuring the displacement and orientation of the laser source (2) and the three-dimensional mapping system (3);

a calculation system designed to perform calculation steps a), b) and f), and to apply the geometric transformation of step g) to the new virtual image (IV (i)).