System and method for calibrating a rotating profilometer

Abstract

SYSTEM AND METHOD FOR CALIBRATING A ROTATINGLY DRIVED PROFILOMETER Calibration system (100) of a profilometer (11) based on a laser triangulation sensor, said TLS, said system comprising an optical head (10) provided with a rotation plate (12) intended to receive the profilometer to impart to it a rotational movement around an arbitrary 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 a maximized coverage of a measurement area of ​​said profilometer. Figure for the summary: Figure 2

Description

Title of the invention: System and method for calibrating a rotating profilometer technical field

[0001] The present invention relates to the field of three-dimensional (3D) laser triangulation profilometers, known as TLS (Triangulation Laser Sensor). It relates in particular to calibration techniques for these profilometers, and more specifically to a calibration system for 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 three-dimensional geometric controls of industrial surfaces (manufactured parts and the like). State of the art

[0004] Nowadays, industrial manufacturing processes are increasingly demanding in order 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, their flexibility for integration into various manufacturing equipment (machine tools, coordinate measuring machines, robotic arms, etc.), and their reasonable cost. This has led to the widespread use of these profilometers.

[0006] For example, document DE10130937C1 describes the use of a TLS profilometer in a method and device for determining the spatial geometry of a bent extruded profile. The sensor, based on the laser triangulation technique, comprises a camera unit and two light sources designed as linear lasers. Using suitable optics, this sensor projects a line from each light source onto the surface of the tube, 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 calibration checks, particularly in sectors where Manufacturing requirements are high (aerospace, automotive, rail, renewable energy, etc.), necessitating rapid and precise measurements. However, it has been observed that no verification is required in practice, and profilometers are used with their initial (factory) calibration without revision.

[0008] Moreover, other non-contact measuring instruments have been implemented in industry, such as photogrammetry, interferometry, etc., however, TLS profilometers offer 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] Kinematic calibration techniques, called extrinsic, are known, which consist of finding the rigid transformation that 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 by Xie Zeixiao et al., the authors propose a 5-axis measurement system composed of a coordinate measuring machine (CMM) offering three degrees of motion (XYZ), a 2-axis rotary head coupled to the latter, and a profilometer. They propose to characterize, firstly, the misalignment of the profilometer with respect to the rotary head using a transformation matrix and, secondly, the misalignment of the rotary head with respect to the CMM using another transformation matrix.

[0013] Chenggang Che et al. propose, for their part, 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, as described in US patent US6967726, which uses a target positioned on a platform that can be used within the sensor's measuring range. The platform is translated in the vertical direction. For example, the platform may include a sliding mechanism attached to a highly accurate, stable, and repeatable calibration measuring device used to determine a very precise 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. Furthermore, these techniques do not do not appear particularly suited to profilometers driven in rotation around any axis of rotation, especially horizontal, which can generate significant inertial stresses and therefore an uncontrolled deviation. Summary of the invention

[0016] The present invention aims to overcome all or part of the disadvantages of the prior art described above by proposing a solution 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 classical degrees of freedom of said profilometer.

[0017] To this end, the present invention relates to a calibration system for a profilometer based on a laser triangulation sensor, referred to as a TLS. This system comprises an optical head equipped with a rotating platform for receiving the profilometer and imparting to it a rotational movement around any axis of rotation, in particular a non-vertical one, and a frame on which the optical head is slidably mounted. This calibration system is notable in that it further comprises a calibration frame positioned around the TLS sensor and comprising at least four shims, two horizontal and two vertical, each having a specific geometric shape and relative positioning within the calibration frame. The shapes and positions of said shims are configured such that traces of a laser beam from the profilometer on the calibration frame allow for maximized coverage of a measurement area of ​​said profilometer.

[0018] Maximizing the coverage of the profilometer's measurement area thus increases the calibration quality. This maximization of the measurement area is achieved through the shapes and locations of the shims, which are specifically determined by numerical simulation.

[0019] It should be noted that in the prior 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 makes it possible to overcome this difficulty. More specifically, the four shims make it possible to determine all the degrees of freedom and to decouple 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 facing horizontal sides and two facing vertical sides on which are the wedges arranged in.

[0023] More specifically, each horizontal side has a wedge and each vertical side has a wedge.

[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 wedges have dimensional and angular variations from one wedge to another, so as to maximize the coverage of the profilometer's measurement area.

[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 straight segments in the profiles measured by the profilometer; • a step of calculating the traces of the laser beam on the wedges in a frame of reference of the profilometer, and matching them 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 of the measured points to the traces; • an optimization step using a gradient descent algorithm; • a step involving the implementation of multiple levels of quality control; and • a quality control step on the implemented quality levels.

[0028] Advantageously, in the calibration process, the axis of rotation of the profilometer can 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 microprocessor-readable medium and / or executable by a microprocessor, comprising program code instructions for the execution of such a calibration process, as well as a terminal-readable and non-transient storage medium, storing a computer program comprising a set of instructions executable by a computer or a processor to implement said process.

[0030] The fundamental concepts of the invention having been set forth above in their most elementary form, other details and features will become clearer upon reading the following description and with reference to the accompanying drawings, which give, by way of non-limiting example, an embodiment of a system and a method for calibrating a rotating profilometer, in accordance with the principles of the invention. Presentation of the drawings

[0031] The figures are given for illustrative purposes only to facilitate 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 are identified by the same numerical reference.

[0032] It is thus illustrated in: [Fig.1]: a perspective view of a calibration system (test bench) according to an embodiment of the invention; [Fig.2]: a partial perspective view from another angle of the calibration system, showing the measuring laser beam of the rotating profilometer; [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 reference points shown; [Fig.5]: Views at successive times showing the rotation of the profilometer in the calibration frame, from (a) to (d); [Fig.6]: the profilometer measurement area, as well as the traces of the measurements on the wedges 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 measured point cloud obtained on the calibration frame with the shims of [Fig.7]; [Fig.9]: a synoptic view of the main steps of a calibration process according to the invention; [Fig. 10]: an intrinsic distortion vector field by isodistortion curves. Detailed description of implementation methods

[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 calibration system for a rotating profilometer, said profilometer being primarily intended for the geometric control (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 to calibrate profilometers operating on the same principle but intended for other industrial applications such as measuring gaps between surfaces (clearances and flushness), measuring volumes, recognizing molded shapes, etc.

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

[0036] Figure 1 shows 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 includes a profilometer 11, a rotating plate 12 on which the profilometer is fixed, and an interface piece 13 for fixing the profilometer to said plate. The calibration frame 20 is provided with shims 21 for precise and robust calibration of the profilometer 11, according to the invention.

[0037] The calibration system 100 is thus similar to a test bench allowing the profilometer 11 to be calibrated before the latter is used to measure, or "scan", the condition of a surface for example.

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

[0039] The optical head 10, according to the illustrated example, is a mechanical assembly having an elongated shape with the rotation plate 12 which extends to a support (or base) 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 axis of rotation of the rotation plate 12 and, by the same token, of the profilometer 11.

[0041] Axis A is substantially horizontal, in a direction usually 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 measuring certain mechanical parts is insufficient to determine it precisely. The present invention makes it possible to overcome this difficulty and calibrate the profilometer despite this uncertainty regarding 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 rotating 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 Anglo-Saxon acronym TLS (Trian 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 thus generates a trace that is detected in pixel form by a digital laser sensor and which allows, through triangulation, the calculation of 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 wedges 21, of the calibration frame 20.

[0047] In the following description, the laser beam L will be referred to as the "brush" and will designate the measurement area of ​​the profilometer 11.

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

[0049] The rotating plate 12 supports the profilometer 11 via the interface piece 13.

[0050] The interface piece 13 is, according to the illustrated example, a bias wedge and has a geometry directly related 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 move in a rectilinear translational motion in the frame linked to the frame 30. For this purpose, the optical head 10 is mounted to slide 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 positioning of the profilometer 11 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 includes four calibration wedges 21, called staircases in view of their shape which will be described below.

[0055] The calibration frame 20 is considered to be non-deformable and pre-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 former receiving the right and left shims 21 and the latter receiving the high and low shims 21. This configuration is visible in [Fig.1].

[0058] The wedges 21 perform two main functions: blocking the degrees of freedom of the profilometer 11 and covering the brush of the latter.

[0059] Each wedge 21, whose planes are previously measured in the 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 shape of a profile as instantly represented in [Fig. 2].

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

[0062] Therefore, rotating the profilometer 11 around axis A produces a point cloud. More precisely, the point cloud is obtained by merging the measured profiles and exhibits a high point density due to the large number of profiles measured.

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

[0064] Mathematically, the merging of the measured profiles necessarily involves the accumulation of a certain number of changes in reference points.

[0065] A base reference frame R0 is linked to the frame 30; three other reference frames 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 frame R3 is linked to the calibration frame 20.

[0066] The reference points R0 and R3 are coincident when the calibration frame 20 is embedded in the frame 30 as is the case in the illustrated embodiment example.

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

[0068] The frame R0 linked to the frame 30 is a direct orthogonal frame defined by an origin O and two axes (OY) and (OZ): the origin O is for example coincided with the position 0 of the mirror 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 wedges 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 with respect 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 rotating plate is designed to work conventionally with a vertical axis of rotation, so that the functional clearances allow the position of the axis of rotation to be well 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 mass carried on it 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 frame of the profilometer 11 within 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 indeed be defined by a point and a vector. The 100 calibration system advantageously allows the determination of 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 process which implements the calibration system 100 according to the present invention, as will be described later. To achieve this, the four 21 wedges have geometric shapes specifically designed to determine all degrees of freedom and decouple 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 chosen are those that allow, through 360° measurements, as represented 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 allows the measurements of Fig. 8 to be obtained by triangulation.

[0082] Figure 6 shows the brush, with its trapezoidal outline, representing the measurement area of ​​the profilometer sensor, as well as the measurement traces on the shims after a complete rotation (360°) of the profilometer. Each shade of gray corresponds to a given shim.

[0083] These measurements allow, by triangulation, to obtain the cloud of [Fig.8].

[0084] Thus, given the good coverage of the measurement area, 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] Figure 7 shows the four wedges according to a particular embodiment. These wedges 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 represented in (a), shim 21b is the right shim represented in (b), shim 21c is the left shim represented in (c), and shim 21d is the upper shim represented in (d).

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

[0089] Conversely, the wedges 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 wedges 21 all have a stepped shape when arranged on their widest rear face as in [Fig.7],

[0091] The geometric definition of each wedge 21 simply consists, for each functional plane of the wedge, in defining the coordinates of an approximate center of gravity and a normal to 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 approximately 45°, the measurement accuracy of the profilometer decreasing with the angle of 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 forms in [Fig. 7] are not exhaustive, and other forms can be considered by a person skilled in the art provided that good coverage of the profilometer's measurement area is obtained.

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

[0095] By making these profiles obtained public, it is possible to carry out the calibration process described below and thus verify its validity.

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

[0097] The change of reference frames 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 frame 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 (shown as a dashed line in [Fig.4]).

[0099] Indeed, a rotation matrix of a change of reference frame can always be represented by an axis and an angle (here the angle of the rotation plate 12). Therefore, 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 rotation angles around the axes (OX) and (OZ) respectively.

[0100] Figure 9 illustrates the main steps of a calibration process 500 implementing the calibration system 100, said process comprising: • a step 510 of detection and identification of straight segments in the profiles measured by the profilometer; • a step 520 of calculating the traces of the brush on the wedges in the R2 frame of the profilometer, and matching with said segments; • a step 530 balancing the measurements between the different planes of the wedges, with a cost function corresponding to the distance of the laser points to the traces; • a step 540 of optimization of said cost function by a gradient descent algorithm; • a step 550 of implementation of two levels of quality control: an internal level (to optimization) and an external level (to optimization); • an internal quality control step 560 with the determination of: • global estimators of the 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 corners from a model of straight segments; • a step 572 of 3D modeling of the shim edges in the RO coordinate system linked to the calibration frame; and • a step 573 of comparison of 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 relies 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 shim planes.

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

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

[0104] The calibration process 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 step, reduction of the resampling of the profile points), so as to reach a very large number of observations (typically on the order of a million) and to have a very high density of points measured on the measurement area.

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

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

[0107] The [Fig. 10] represents a distortion vector field by isodistortion curves.

[0108] Within the framework of this hyper-calibration, all 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 inaccuracies related to local anomalies specific to each profilometer.

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

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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