System and method for calibrating a rotationally driven profilometer

Abstract

SYSTEM AND METHOD FOR CALIBRATING A ROTATIONALLY DRIVEN PROFILOMETER Calibration system (100) for a profilometer (11) based on a laser triangulation sensor, called TLS, said system comprising an optical head (10) provided with a rotation plate (12) intended to receive the profilometer to communicate to it a rotational movement around any axis of rotation (A), and a frame (30) on which the optical head is slidably mounted, said system further comprising a calibration frame (20) positioned around the TLS sensor and comprising four shims (21) each having a determined geometric shape and relative positioning in the calibration frame, the shapes and positions of said shims being configured so that the traces (T) of the laser beam (L) of the profilometer on the calibration frame (20) allow maximized coverage of a measurement area of ​​said profilometer. Figure for abstract: Figure 2

Description

Title of the invention: System and method for calibrating a rotationally driven profilometer Technical field

[0001] The present invention belongs to the field of three-dimensional (3D) laser triangulation profilometers, known as TLS (Triangulation Laser Sensor). It relates in particular to the techniques for calibrating these profilometers, and more particularly relates to a system for calibrating a rotating profilometer and a calibration method implementing such a system.

[0002] The invention relates more particularly to profilometers driven in rotation around any axis, which is not necessarily vertical.

[0003] The invention finds a direct, but not exclusive, application in the geometric three-dimensional controls of industrial surfaces (manufactured parts and the like). State of the art

[0004] Nowadays, industrial manufacturing processes are increasingly demanding to remain competitive in a globalized market, where the survival of industries depends on the production of high-quality, high-value-added products without increasing manufacturing costs. One of the essential keys lies in the measurement process (metrology).

[0005] In this context, TLS profilometers offer an advantage as non-contact measuring instruments due to their high measurement accuracy, flexibility of integration into various manufacturing equipment (machine tools, coordinate measuring machines, robotic arms, etc.), and reasonable costs. This has made the use of these profilometers very widespread.

[0006] For example, document DE10130937C1 describes the use of a TLS profilometer in a method and a device for determining the spatial geometry of a curved extruded profile. The sensor, based on the laser triangulation technique, comprises a camera unit and two light sources designed as line lasers. Using suitable optics, this sensor projects one line per light source onto the tube surface each time, and this line is detected by the camera unit. 3D points on the tube surface are detected along the light lines using the light section sensor and are used to determine the central axis of the cylinder by cylindrical approximation.

[0007] During their use and in order to improve their performance, profilometers require regular verification of their calibration, particularly in sectors where Manufacturing requirements are high (aerospace, automotive, rail, renewable energy, etc.), requiring fast and accurate measurements. However, it is found that no verification is required in practice, and profilometers are used with their initial (factory) calibration without revision.

[0008] Furthermore, other non-contact measuring instruments have been implemented in the industry, such as photogrammetry, interferometry, etc., however, TLS profilometers have a more favorable performance and versatility to cost ratio.

[0009] The equipment or machines used to ensure the movement of the profilometer are generally three-dimensional measuring machines, industrial robots or other mechanical systems for translational and / or rotational movement. One of the key processes for achieving good coupling between the profilometer and its actuation system is calibration.

[0010] We know kinematic calibration techniques, called extrinsic, which consist of finding the rigid transformation which exists between the coordinates of the profilometer and the coordinates of the equipment with which it is coupled.

[0011] Many authors have dealt with the calibration of complex kinematic systems, always focusing on the integration of the profilometer into the measuring machine, or robotic arms.

[0012] In the research of Xie Zeixiao et al., the authors propose a 5-axis measuring system consisting of a three-dimensional measuring machine that offers three degrees of movement (XYZ), a 2-axis rotating head and, coupled to the latter, a profilometer. They propose to characterize, on the one hand, the misalignment of the profilometer with respect to the rotating head using a transformation matrix and, on the other hand, the misalignment of the rotating head with respect to the three-dimensional measuring machine using another transformation matrix.

[0013] Chenggang Che et al. propose a method for the extrinsic calibration of a laser scratch sensor integrated into a multi-axis CNC machining center.

[0014] A suitable calibration technique for a TLS sensor is also known, described in US patent US6967726, which uses a target positioned on a platform, which can be used within the measuring range of the sensor. The platform is translated in the vertical direction. For example, the platform may comprise a sliding mechanism which is attached to a highly accurate, stable and reproducible calibration measuring device which is used to determine a highly accurate indication of the displacement step during the calibration process.

[0015] All these solutions have limitations in terms of extrinsic calibration accuracy and require third-party measurement means. In addition, these techniques do not do not seem particularly suited to profilometers driven in rotation around any axis of rotation, particularly horizontal, which can generate significant inertial constraints and therefore uncontrolled deviation. Summary of the invention

[0016] The present invention aims to overcome all or part of the drawbacks of the prior art set out above by proposing a solution making it possible to overcome the limited movements of the test bench to determine four degrees of freedom characterizing a horizontal axis of rotation of the profilometer, in addition to the six conventional degrees of freedom of said profilometer.

[0017] To this end, the present invention relates to a system for calibrating a profilometer based on a laser triangulation sensor, called TLS, said system comprising an optical head provided with a rotation plate intended to receive the profilometer to communicate to it a rotational movement around any axis of rotation, in particular non-vertical, and a frame on which the optical head is slidably mounted. This calibration system is remarkable in that it further comprises a calibration frame positioned around the TLS sensor and comprising at least four shims, two of which are horizontal and two of which are vertical, each having a determined geometric shape and relative positioning in the calibration frame, the shapes and positions of said shims being configured so that traces of a laser beam from the profilometer on the calibration frame allow maximized coverage of a measurement area of ​​said profilometer.

[0018] Maximized coverage of the profilometer's measurement area thus makes it possible to increase the quality of the calibration. This maximization of the measurement area is achieved via the shapes and locations of the shims, which are specifically obtained by numerical simulation.

[0019] It should be noted that in the state of the art of TLS sensors on measuring arms or robotic arms, the TLS sensor has six degrees of freedom for 6 unknowns to be determined.

[0020] In the present invention, there are 6+4 unknowns for only 2 possible movements: a rotation of the profilometer around its axis and possibly a translation along this axis.

[0021] It is the calibration frame (working standard) that overcomes this difficulty. More specifically, the four shims make it possible to determine all the degrees of freedom and to decorrelate some of them. In other words, the shims make it possible to overcome the limited movements of the profilometer.

[0022] According to one embodiment, the calibration frame is polygonal in shape and has two horizontal sides facing each other and two vertical sides facing each other on in which the wedges are arranged.

[0023] More particularly, each horizontal side has a shim and each vertical side has a shim.

[0024] According to a particular embodiment, the calibration frame is octagonal and arranged vertically.

[0025] According to a particularly advantageous aspect of the invention, each wedge has a stepped shape defining two parallel planes, horizontal or vertical depending on the positioning of said wedge, and an inclined plane between these two parallel planes.

[0026] Advantageously, the shims have dimensional and angular variations from one shim to another, so as to maximize the coverage of the profilometer's measurement zone.

[0027] The present invention also relates to a method for calibrating a profilometer implementing a calibration system as presented, said method comprising: • a step of detecting and identifying rectilinear segments in the profiles measured by the profilometer; • a step of calculating the traces of the laser beam on the shims in a profilometer reference frame, and matching with the previous segments; • a step of balancing the measurements between the different planes of the wedges, with a cost function corresponding to a distance from the measured points to the traces; • an optimization step using a gradient descent algorithm; • a step of implementing several levels of quality control; and • a quality control step on the implemented quality levels.

[0028] Advantageously, in the calibration method, the axis of rotation of the profilometer may be horizontal and, where appropriate, characterized by four additional degrees of freedom, said degrees of freedom being determined in addition to six degrees of freedom of said profilometer.

[0029] The present invention also relates to: a computer program product downloadable from a communication network and / or stored on a medium readable by a microprocessor and / or executable by a microprocessor, comprising program code instructions for the execution of such a calibration method, as well as a storage medium readable by a terminal and non-transitory, storing a computer program comprising a set of instructions executable by a computer or a processor to implement said method.

[0030] The fundamental concepts of the invention having just been set out above in their most elementary form, other details and characteristics will emerge more clearly on reading the description which follows and with reference to the appended drawings, giving by way of non-limiting example an embodiment of a system and a method of calibrating a rotationally driven profilometer, in accordance with the principles of the invention. Presentation of the drawings

[0031] The figures are given purely for illustrative purposes for a better understanding of the invention without limiting its scope. The various elements may be represented schematically and are not necessarily to scale. Throughout the figures, identical or equivalent elements bear the same numerical reference.

[0032] It is thus illustrated in: [Fig.l]: a perspective view of a calibration system (test bench) according to one embodiment of the invention; [Fig.2]: a partial perspective view from another angle of the calibration system, showing the profilometer's measuring laser beam driven in rotation; [Fig.3]: examples of digital profiles obtained from 3D surfaces by a profilometer calibrated according to the invention; [Fig.4]: a perspective view of the calibration system with the different markers represented; [Fig.5]: views at successive times showing the rotation of the profilometer in the calibration frame, from (a) to (d); [Fig.6]: the measuring area of ​​the profilometer, as well as the traces of the measurements on the shims after a complete turn (360°) of the profilometer; [Fig.7]: the different shapes of the four wedges: low in (a), right in (b), left in (c) and high in (d); [Fig.8]: the cloud of measured points obtained on the calibration frame with the shims of [Fig.7]; [Fig.9]: a synopsis of the main steps of a calibration method according to the invention; [Fig. 10]: a field of intrinsic distortion vectors by iso-distortion curves. Detailed description of embodiments

[0033] It should be noted that certain technical elements well known to those skilled in the art are recalled here to avoid any insufficiency or ambiguity in the understanding of the present invention.

[0034] In the embodiment described below, reference is made to a system for calibrating a profilometer driven in rotation, said profilometer being mainly intended for geometric controls (shapes and positions) of surfaces of manufactured parts. This non-limiting example is given for a better understanding of the invention and does not exclude the use of the system for calibrating profilometers operating on the same principle but intended for other industrial applications such as the measurement of gaps between surfaces (clearances and flushness), the measurement of volumes, the recognition of molded shapes, etc.

[0035] In the present description, the term “profilometer” designates a metrological instrument for measuring profiles using a non-contact technique, in particular by laser, generally used in industrial production lines.

[0036] [Fig.l] represents a calibration system 100 comprising an optical head 10, a calibration frame 20 and a frame 30 on which the optical head is slidably mounted. The optical head 10 comprises a profilometer 11, a rotation plate 12 on which the profilometer is fixed, and an interface part 13 allowing the profilometer to be fixed on said plate. The calibration frame 20 is, for its part, provided with shims 21 allowing precise and robust calibration of the profilometer 11, according to the invention.

[0037] The calibration system 100 is thus similar to a test bench for calibrating the profilometer 11, before using the latter to measure, or “scan”, the state of a surface for example.

[0038] Indeed, the calibration system 100 has been specially designed to calibrate the profilometer 11 whose axis of rotation is not necessarily vertical and can be any, as explained below.

[0039] The optical head 10, according to the example illustrated, is a mechanical assembly having a lengthwise shape with the rotation plate 12 which extends to a support (or sole) located at an anchoring end on the frame 30, opposite its free end supporting the profilometer 11.

[0040] The optical head 10 thus has a longitudinal axis A which corresponds to the proper axis of rotation of the rotation plate 12 and, therefore, of the profilometer 11.

[0041] The axis A is substantially horizontal, in a usual direction given by an observer in a normal implementation of the calibration system 100.

[0042] The axis of rotation A is not known a priori and the measurement of certain mechanical parts is not sufficient to determine it precisely. The present invention makes it possible to overcome this difficulty and to calibrate the profilometer despite this uncertainty about the position of said axis.

[0043] The rotation of the optical head 10 can be manual or automated, and its angular positioning is ensured by means of an external incremental encoder whose axis is centered via a coupler with the bore of the rotation plate 12.

[0044] Alternatively, the rotation plate can be coupled to a motor which also allows its angular position to be controlled.

[0045] The profilometer 11 operates by laser triangulation and for this purpose includes a laser triangulation sensor, better known by its English acronym TLS (Trian gulation Laser Sensor). This sensor is based on the use of a laser, whose trace is a plane, and a camera. The laser plane intercepts a surface and therefore generates a trace which is detected in a pixelated manner by a digital laser sensor and which allows, by triangulation, to calculate the three-dimensional (3D) coordinates of said trace.

[0046] [Fig.2] represents the calibration system 100 with the profilometer 11 emitting a laser beam L whose trace T intersects the surfaces, in particular the shims 21, of the calibration frame 20.

[0047] In the remainder of the description, the laser beam L will be called a “brush” and will designate the measurement zone of the profilometer 11.

[0048] The profilometer 11 thus sweeps the surfaces of the calibration frame with the brush, in a circular manner, thanks to the rotation plate 12, and carries out measurements synchronized with the rotation of said plate.

[0049] The rotation plate 12 supports the profilometer 11 via the interface part 13.

[0050] The interface part 13 is, according to the example illustrated, a biased wedge and has a geometry directly linked to the six degrees of freedom of the profilometer 11 determined by calibration.

[0051] In addition to its own rotation around the horizontal axis A, the optical head 10 can be animated by a rectilinear translation movement in the reference frame linked to the frame 30. The optical head 10 is, for this purpose, slidably mounted on a translation plate 31 of the frame 30, provided with sliding rails.

[0052] According to another alternative embodiment, the position of the optical head can be determined by means of a laser tracker associated with a set of prisms placed both on the optical head 10 and on the calibration frame 20, or by any other suitable measuring instrument.

[0053] The translation plate of the frame 30 thus allows the profilometer 11 to be positioned relative to the calibration frame 20 in order to carry out the calibration.

[0054] The calibration frame 20 is integral with the frame 30 and comprises four calibration wedges 21, called stairs in view of their shape which will be described below.

[0055] The calibration frame 20 is considered to be non-deformable and previously calibrated.

[0056] The calibration frame 20 has a geometric shape and dimensions completed, in order to serve as a working standard during the calibration operation.

[0057] According to the illustrated embodiment, the calibration frame 20 has an octagonal shape with two vertical sides and two horizontal sides, the first receiving the right and left shims 21 and the second receiving the upper and lower shims 21. This configuration is visible in [Fig.l].

[0058] The shims 21 provide two main functions: blocking the degrees of freedom of the profilometer 11 and covering the latter's brush.

[0059] Each shim 21, the planes of which are previously measured in the reference frame linked to the frame 20, has three functional planes intended to be measured by the profilometer 11 to obtain a reference geometry.

[0060] Indeed, upon reaching a wedge 21, the laser beam of the profilometer 11 (or brush) defines a trace T which corresponds to its intersection with the shape of said wedge. The camera of the profilometer 11 then allows the acquisition of this trace in the form of a profile as represented instantly in [Fig.2].

[0061] The profilometer 11 thus makes it possible to obtain the 3D coordinates of a profile.

[0062] As a result, the rotation of the profilometer 11 around the axis A makes it possible to obtain a point cloud. More precisely, the point cloud is obtained by merging the measured profiles and has a high density of points due to the large number of measured profiles.

[0063] [Fig.3] shows examples of profiles measured from footprints of mussels, a leaf in (a) and an insect wing in (b), with very small details requiring a high resolution of the order of 50pm.

[0064] Mathematically, the merging of the measured profiles is necessarily accompanied by the accumulation of a certain number of changes of reference points.

[0065] A base reference mark R0 is linked to the frame 30; three other reference marks RI, RI' and R2 are linked to the moving parts of the calibration system 100, namely the optical head 10, the rotation plate 12 and the profilometer 11 respectively; and a reference mark R3 linked to the calibration frame 20.

[0066] The references R0 and R3 are merged when the calibration frame 20 is embedded in the frame 30 as is the case in the illustrated embodiment.

[0067] [Fig.4] schematically represents these different reference points on the system of calibration 100.

[0068] The reference frame R0 linked to the frame 30 is a direct orthogonal reference frame defined by an origin O and two axes (OY) and (OZ): the origin O is for example coincident with the position 0 of the first in the illustrated example; the axis (OY) passes through the centers of the bore of the rotation plate 12 at different positions of the optical head 10 along the translation plate; and finally the axis (OZ) is substantially perpendicular to the plane of the rails of said translation plate.

[0069] According to the present invention, and in order to redundantly fix the degrees of freedom of the profilometer 11, the four shims 21 of the profiling frame 20 are necessary.

[0070] The table below shows the role of each wedge 21 (left, right, top and bottom), via their functional planes, in determining the degrees of freedom of the profilometer (the notation T or R / axis simply designates the translation or rotation relative to the axis):

[0071] [table]

[0072] Wedge Plan T / OXT / OYT / OZ R / OX R / OY R / OZ left 2 vertical * * * 1 inclined * * * * * right 2 vertical * * * 1 inclined * * * * * high 2 horizontal * * * 1 inclined * * * * * low 2 horizontal * * * 1 inclined * * * * *

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079]

[0080] It should be remembered that a rotation stage is designed to operate conventionally with a vertical rotation axis, so that the functional clearances allow the position of the rotation axis to be clearly characterized. In the case of the present invention, the axis of rotation is horizontal. This implies that the moments experienced by the rotation plate 12 due to the on-board mass can be significant and induce an uncontrolled deviation of the axis of rotation relative to the translation plate of the frame 30. Therefore, in addition to the six degrees of freedom characterizing the position of the R2 reference frame of the profilometer 11 in that of the rotation plate 12, there are also four degrees of freedom to characterize the horizontal axis of rotation. The axis of rotation can in fact be defined by a point and a vector. The calibration system 100 advantageously makes it possible to determine 6+4 degrees of freedom, i.e. 10 unknowns to be determined from two possible movements: the translation of the optical head and the rotation of the profilometer. This constitutes the purpose of the calibration method which implements the calibration system 100 according to the present invention, as will be described later. To do this, the four shims 21 have geometric shapes specifically designed to determine all the degrees of freedom and decorrelate some of them. Indeed, some of the 4 degrees of freedom of the horizontal rotation axis are correlated with other degrees belonging to the 6 degrees of freedom of the profilometer. The precise geometric shapes of the 21 wedges were obtained iteratively by numerical simulation using computer-aided design (CAD). The geometries selected are those which allow, by measurements over 360° as shown in [Fig.5], to obtain the best coverage of the measurement area shown in [Fig.6].

[0081] [Fig.5] represents successive positions, from (a) to (d), of the brush during the rotation of the profilometer 11. This scanning makes it possible to obtain by triangulation the measurements of [Fig.8].

[0082] [Fig.6] shows the brush, trapezoidal outline, i.e. the measuring area of ​​the profilometer sensor, as well as traces of the measurements on the shims after a complete rotation (360°) of the profilometer. Each shade of gray corresponds to a given shim.

[0083] These measurements allow us to obtain the cloud in [Fig.8] by triangulation.

[0084] Thus, taking into account the good coverage of the measurement zone, the chosen geometry of the shims 21 and their relative positioning make it possible to obtain a quality calibration.

[0085] Overall, each shim 21 has two horizontal or vertical planes, depending on its positioning on the calibration frame 20, and an inclined plane. Each plane has the function of fixing certain degrees of freedom as indicated in the table above.

[0086] [Fig.7] shows the four shims according to a particular embodiment. These shims all have different shapes and dimensions.

[0087] In order to better distinguish these shims according to their positions in the calibration frame, the letters a to d are added to their numerical references. Thus, shim 21a is the lower shim shown in (a), shim 21b is the right shim shown in (b), shim 21c is the left shim shown in (c), and shim 21d is the upper shim shown in (d).

[0088] The shims 21a and 21d are therefore horizontal on the calibration frame and have two horizontal planes H connected by an inclined plane.

[0089] Conversely, the shims 21b and 21c are vertical on the calibration frame and have two vertical planes V connected by an inclined plane.

[0090] Despite their dimensional differences, the shims 21 all have a stepped shape when they are arranged on their widest rear face as in [Fig.7],

[0091] The geometric definition of each wedge 21 consists simply, for each functional plane of the wedge, in defining the coordinates of an approximate center of gravity and a normal of this plane.

[0092] There is a strong constraint on the slope of the inclined planes of each wedge 21, because the slope measured by the profilometer 11 must not exceed an angle of the order of 45°, the measurement accuracy of the profilometer decreasing with the incidence. Consequently, the horizontal planes H of the wedges 21 occupy different positions on the brush, as shown in [Fig.6].

[0093] Of course, the shapes of [Fig.7] are not limiting, and other shapes can be considered by those skilled in the art provided that good coverage of the profilometer measurement area is obtained.

[0094] [Fig.8] represents a cloud of points measured on the shims 21 of [Fig.7] fixed on the calibration frame 20.

[0095] By noise-reducing these obtained profiles, it is possible to execute the calibration process described below and thus verify its validity.

[0096] With reference to [Fig.4] which shows the different reference points, it appears that the change of reference point between the reference point of the optical head RI, the reference point of the rotation plate RI' and the reference point of the profilometer R2 must take into account, in addition to the rotation angle, the four additional degrees of freedom which characterize the position of the rotation axis A.

[0097] The change of reference points is obtained by the following formula: [math] IX\ ■ ■ , / (Kv;DXyz)|- i / («) , / (6 DOF) Y - ■ - 0 ZU Lo ■■ ÆO ■ 1 *-0 " .0 ■■ ■ l-ljRT / ÆS El /

[0098] The change of reference Rl / Rl' only shows the rotation angle above; in reality, f(a) must be replaced by f(a,4DOF). These 4 degrees of freedom (DOF) describe the effective position of the rotation axis of the profilometer (in broken line in [Fig.4]).

[0099] Indeed, a rotation matrix of a change of reference can always be represented by an axis and an angle (here the angle of the rotation plate 12). Consequently, the 4 additional degrees of freedom are: the X and Z coordinates of the intersection of the rotation axis A with the plane (OXZ), and two angles of rotation around the axes (OX) and (OZ) respectively.

[0100] [Fig.9] represents the main steps of a calibration method 500 implementing the calibration system 100, said method comprising: • a step 510 of detecting and identifying rectilinear segments in the profiles measured by the profilometer; • a step 520 of calculating the traces of the brush on the shims in the R2 reference frame of the profilometer, and of matching with said segments; • a step 530 of balancing the measurements between the different planes of the shims, with a cost function corresponding to the distance from the laser points to the traces; • a step 540 of optimizing said cost function by a gradient descent algorithm; • a step 550 of implementing two levels of quality control: an internal level (for optimization) and an external level (for optimization); • an internal quality control step 560 with the determination of: • global estimators of optimization (by the robust least squares method); • local estimators for each plane of each wedge to highlight areas of greater inaccuracy in the measurement area (brush); and • an external quality control step 570 comprising the following sub-steps: • a step 571 of extracting the corners from a modeling of the rectilinear segments; • a step 572 of 3D modeling of the edges of the shims in the RO reference frame linked to the calibration frame; and • a step 573 of comparing the modeled edges with the previously calibrated geometry of the calibration frame with criteria of straightness, parallelism and concentricity.

[0101] The processing carried out according to this method is based on a differentiation between the optimization function (gradient descent) and the external quality control validating the calibration. Thus, the equations of the optimization function use only the distance of the measured points to the trace of the planes of the shims.

[0102] After the analysis of the global estimators, the analysis of the local estimators and the external quality control 570 will allow us to zoom in on very local disorders.

[0103] Indeed, the external quality control 570 consists of starting from the corners detected by intersection between the traces of the different planes of each profile, of modeling the edge in 3D and of analyzing the parallelism and concentricity defects with respect to the calibrated geometry of the calibration frame. Level 2 is only validated if the dimensional deviations linked to the comparison criteria are lower than threshold values.

[0104] The calibration method can thus be implemented by measuring a large number of profiles over the entire surface of the brush (several axial positions, reduction of the angular pitch, reduction of the resampling of the profile points), so as to achieve a very large number of observations (typically of the order of a million) and have a very high density of measured points on the measurement zone.

[0105] This calibration is called hyper calibration and therefore consists of determining a grid of distortions from all the observations, which is characterized by a step between two nodes of the grid (approach by a finite element method). At each node of the grid a 2D distortion vector is calculated, the set of these vectors forming a vector field.

[0106] All the calibration observations are therefore used. The mathematical function of the optimization is a bilinear interpolation of a point located between four knots.

[0107] [Fig. 10] represents a field of distortion vectors by iso-distortion curves.

[0108] As part of this hyper calibration, all the distortion vectors can be saved in a calibration file, and constitute a corrective filter to be applied to any new point measured by the profilometer. Thus, the 10 degrees of freedom determined by calibration (following disassembly for example) will not be affected by an inaccuracy linked to local disorders specific to each profilometer.

[0109] It is apparent from the present description that certain non-essential elements of the system and / or the calibration method may be modified, replaced or deleted without departing from the scope of the invention defined by the claims below.

Claims

Claims

1. Calibration system (100) of a profilometer (11) based on a laser triangulation sensor, called TLS, said system comprising an optical head (10) provided with a rotation plate (12) intended to receive the profilometer to communicate to it a rotational movement around any axis of rotation (A), and a frame (30) on which the optical head is slidably mounted, said system being characterized in that it further comprises a calibration frame (20) positioned around the TLS sensor and comprising at least four shims (21), two of which are horizontal and two vertical, each having a determined geometric shape and relative positioning in the calibration frame, the shapes and positions of said shims being configured so that traces (T) of a laser beam (L) of the profilometer on the calibration frame (20) allow maximized coverage of a measurement area of ​​said profilometer.

2. Calibration system according to claim 1, wherein the calibration frame (20) is polygonal in shape and has two facing horizontal sides and two facing vertical sides on which the shims (21) are arranged.

3. A calibration system according to claim 2, wherein each horizontal side comprises a shim (21) and each vertical side comprises a shim (21).

4. A calibration system according to any preceding claim, wherein the calibration frame (20) is octagonal and arranged vertically.

5. Calibration system according to any one of the preceding claims, in which each shim (21) has a stepped shape defining two parallel planes, horizontal or vertical depending on the positioning of said shim, and an inclined plane between these two parallel planes.

6. Calibration system according to claim 5, in which the shims (21) have dimensional and angular variations, from one shim to another, so as to maximize the coverage of the measurement zone of the profilometer (11).

7. Method for calibrating (500) a profilometer (11) implementing a calibration system (100) according to one of the preceding claims, characterized in that it comprises: • a step (510) of detecting and identifying rectilinear segments in the profiles measured by the profilometer (11); • a step (520) of calculating the traces (T) of the laser beam (L) on the shims (21) in a reference frame (R2) of the profilometer, and of matching with said segments; • a step (530) of balancing the measurements between the different planes of the shims (21), with a cost function corresponding to a distance from the measured points to the traces (T); • a step (540) of optimization by a gradient descent algorithm; • a step (550) of implementing several levels of quality control; and • a step (560) of quality control on the implemented quality levels.

8. Calibration method according to claim 7, wherein the axis of rotation (A) of the profilometer (11) is horizontal and characterized by four additional degrees of freedom, said degrees of freedom being determined in addition to six degrees of freedom of said profilometer.

9. Computer program product downloadable from a communication network and / or stored on a microprocessor-readable medium and executable by a microprocessor, characterized in that it comprises program code instructions for executing a calibration method (500) according to claim 7 or 8.

10. A terminal-readable, non-transitory storage medium storing a computer program comprising a set of instructions executable by a computer or processor to implement a calibration method (500) according to claim 7 or 8.

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