ES2310433A1 - Scanning procedure in three dimensions for revolution parts and devices used. (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Scanning procedure in three dimensions for pieces of revolution and devices used. The invention contemplates a method and a three-dimensional scanning device for parts of revolution, using a camera (11) and laser emitters (12, 12 ") mounted on a fastening element (13), which is connected by a one rotational axis (14) and on the other to a motor (15) with encoder, the axis of rotation (14) being able to be positioned substantially in parallel with respect to the axis of revolution of the part (30), having been made previously a previous calibration to correct the real deviations between axes. The motor (15) rotates the fastening element (13) and, therefore, the assembly of chamber (11) and laser emitters (12, 12 "), at a certain distance with respect to said piece (30), the camera (11) at a distance and an angle determined with respect to the laser emitters (12, 12 "). Another aspect of the invention relates to a device for the required calibration before performing the rotary scan. (Machine-translation by Google Translate, not legally binding)

Description

Three-dimensional scanning procedure for revolution parts and devices used.

Object of the invention

The present invention is framed within the field of optical surface scanning and measurement techniques of bodies in three dimensions, applicable to the sector dedicated to general to the manufacture and / or assembly of parts with geometry of revolution, such as metal pipes, especially bushings with double beveling, for example, for the pipe industry of seamless steel.

The main object of the invention is to allow three-dimensional scanning of revolution parts with precision, eliminating the capture of shadow areas by the vision camera artificial that records images of a piece configured as body of revolution, thanks to a rotating sweep that takes place by means of one or more laser emitters that rotate together with said camera at a certain distance and around the piece.

Background of the invention

At present, the Artificial Vision techniques, which are used to obtain information of a captured image, using a digital camera with its optics, a computer, an image capture card and a Custom software for the required application. The Main areas of usefulness of the Artificial Vision are:

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Measurement: Measure the dimensions of a piece, diameters, etc. and determine the flatness of the surfaces Of the piece.

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Guided: Guide robots to locate or assemble parts, from the roll of paper rolls, fabric, paperboard.

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Identification: Identify pieces or products by their profile, shape or color, and realization of pattern recognition

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Inspection: Determine the Presence-absence of parts in assembly, Orientation of parts, locate surface defects.

From its functionalities, it follows that the Vision Artificial by computer has application in most industrial sectors, proving especially useful in any series production system, for example:

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Automotive and auxiliaries.

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Packaging, packaging and plastics.

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Electrical components and electronic

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Metallurgy and derivatives.

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Pharmacy and medical equipment.

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Textile and footwear manufacturing.

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Industrial machining

In particular, for carrying out measures Dimensional in production parts, control requirements they are increasingly high, so the controls do not Three-dimensional cease to be enough.

Today, these types of high measures precision are carried out by means of manual probes or comparator clocks With these methods, there are difficulties to access some areas, since the quality of the measure depends on contact quality It is very difficult to obtain resolutions high, because the smallest roughness or lack of rectification in the element to study implies the loss of hundredths, tenths and even millimeters.

On the other hand, in the particular case of the measurement of dimensions of a tube or bushing, which can have an external and internal bevel, in the attempt to control with enough accuracy both the measurements of the cap itself like those of the bevels, the appreciation of the bevel zones external and internal with these methods is not possible in a way automatic and an estimate by an operator is necessary skilled. The possibility of placing a probe or clock comparator to control, in particular, the inner bezel (also for the rest of the variables) it is reduced, since it is required locate the tube carefully and very precisely, factors that in a automated manufacturing process at a certain speed is very complicated.

With a view to saving these difficulties, for the bevel measurement projection methods are used profiles The profile projector is a device that projects the element profile observing its dimensions with a strong amplification, allowing controlled movement and focus to Your best inspection. The problem with this system is that at each moment you can only carry out the projection of a profile, that is to say, of a diameter of the tube, with what its location and measurement takes a long time, unthinkable for Inspect all production. For bevel measurement interiors would be necessary as a destructive test consisting in the cut of the tube in two halves before proceeding to the measurement of the bezel. In addition, these measurements correspond exclusively to a profile, instead of the entire cap, that is, it You can judge the goodness or not of the cap through a single point. Therefore, several measures would be needed to study the cutting trend (by means of averages, seeing trends in all the diameters), so it is not an operating method for continuous inspection

Measurement procedures by vision conventional, using the appropriate camera and lighting, are only suitable for flat measurements, that is, in two dimensions (2D). Thus, it is possible to control the dimensions of diameters, thicknesses via 2D vision, ..., but it is not possible to capture the third dimension, that is, for example, the inner or outer bevel of the cap, since the bevel could not be perceived when its projected dimension on the previous plane, constituting the outer diameter of the tube.

Therefore, for these cases you have to resort to the three-dimensional (3D) vision offered by the techniques of Artificial Vision. There are various techniques to obtain 3D information by optical procedures, among which stereovision, optical triangulation and projection of patterns.

Stereovision is based on the way that human beings and other living beings obtain information three-dimensional, from the differences of image of the same target element experienced by n (2 or more) sensors located in known and constant positions respectively. Even when it is a conceptually intuitive technique, it presents serious inconvenience due to the difficulty of identifying such objects common (corners, objects, etc.) in general scenarios. Is by This means that its use is limited to controlled environments.

Optical triangulation is a method of Obtaining contactless 3D information, based on methods optical, that is to say using lighting sources and sensors Optical It is a non-intrusive method with objects in study (NDT: "Non-Destructive Testing"). Is one of the most widespread techniques for three-dimensional inspection and it is based on the variation that the reflection of light pattern depending on the layout of the set illumination-observer and the distance to the object to observe. It is commonly used in reverse engineering, although It also serves in process simulation, quality control and manufacturing measure. It is based on the use of information obtained from the position variation (ratio of angles and lengths) experiencing the reflection of a light beam in set layout function laser-observer and the distance to the object to observe.

As samples of the application of the method of optical triangulation, it is worth mentioning the inventions included in the Spanish Patent Applications ES 9601994 and Patent US 2005/0111009. Document ES 9601994 refers to a scanner that has one or more laser emitters and two micro cameras, located at a distance from each other such that errors they are averaged by acting simultaneously, while when one of the cameras is in "shadow" to visualize an area of the piece to be inspected, the other chamber remains operational to provide all the information to a computer. In the application US 2005/0111009, a method is described based on laser triangulation applied to the measure three-dimensional cylindrical piece of aluminum or the caliber of train tracks, through real-time calculation with a FPGA card of the XY coordinates of certain points of the line of light reflected on the surface of the object to be examined and captured by a group or array of photodetectors. Another example is the assembly to generate 3D images contemplated by the US Patent  United US 4645348, consisting of an array of optical sensors acting in collaboration with a light source, all mounted the components in a single housing that allows calibration internal of these components.

Another technique that can also be used in three-dimensional inspection of parts consists of the use of scanners linear scanning laser, but linear scanners have the inconvenience of presenting "shadow" areas of measurement depending on the geometry of the object of study. In addition, the Profile extraction algorithm varies depending on the area of inspection. In this regard, the patent application deserves mention PCT International WO 93/08448, which describes a system that uses two cameras placed in different but known positions that capture a linear scan of the laser on the object inspected, without the need to move the positioning system, to increase the speed of the process while reducing the data sent to the computer that carries the CAD program.

However, none of the known techniques for three-dimensional inspection it is completely accurate for the scanning of parts with revolution geometry, without present the inevitable "shadow" areas in the sweep optical or scanning of some geometries, which would be solved performing a rotating sweep, instead of linear.

Description of the invention

The present invention is resolved in a manner effective the problem described above, in each and every one of the different aspects commented, constituting a solution advantageous against the background that allows the scanning of pieces of revolution for its measurements in three dimensions, based on optical triangulation but performing with a source multiple laser, preferably double, a rotating sweep that adjusts to the geometry of the piece.

The solution proposed here is designed especially to solve the scanning of geometric pieces complex, taking as an example a tube with double bevel, internal and external While a linear scan scan would generate as sections seen by the scanner, each with its conditions of reflection and shadows, the strings of the periphery of the tube, in a three-dimensional scanning with rotating scan like the one advocates, the sections of the scanner are pseudo-diameters instead of ropes of a circle. In the ideal case that the axis of sweeping turn that is performed according to this invention matches exactly with the axis of revolution of the scanned piece, the sections obtained are proper diameters of the piece. When he sweeping rotation is done on a slightly offset axis with respect to to the mentioned axis of said piece, as in practice, the sections given by the rotary scan scanner are not strictly diameters of the circumference of the piece but pseudo-diameters, but all sections have conditions Similar reflection and shadows. This peculiar characteristic of the sections resulting from a rotating sweep represent a key advantage over a linear scan, in its application to tubular pieces with respective bevels in their corresponding external and internal edges, where the first sections of the sweep laser linearly cut only and tangentially the outer bezel of the tube, the central sections cut perpendicularly its two walls and the last sections return to tangentially cut the outer bezel but also with shadow.

An aspect of the invention is thus a three-dimensional scanning procedure for pieces of revolution, based on laser optical triangulation, using an artificial vision camera that defines a plane of camera and at least one laser emitter that defines a laser plane, characterized in that it comprises a rotating sweeping phase that determines profiles (pseudo-diameters) of the piece of revolution by cutting the laser plane with said piece, which performs with a three-dimensional rotary scan scanner like the which will be described later.

After the rotating sweep phase, the proposed scanning procedure determines a few points of projection of the cut in the camera plane, defined in pixels, between the laser plane and the edge of the revolution piece. After, said projection points in pixels are converted to points of laser plane projection defined in length measurements (mm), through the relationship between the laser plane and the plane of camera that is established in a previous calibration phase. TO then a geometric correction of the laser plane is performed with respect to the axis of rotation of the scan, since it is practically impossible to match this axis with the real axis of rotation of the system, so the laser plane does not make trajectories This phase is therefore necessary to determine the Actual position of the laser plane in space. Finally, the scanning procedure determines the actual position of the points projection defined in length measurements (millimeters) in a three-dimensional system of absolute coordinates, from which can generate a three-dimensional image of the piece scanned and then make measurements on it convenient, processable by a conventional computer system through a computer program (software) specifically developed for the application.

Before the rotating sweep phase, a calibration of the devices used in the described procedure is performed to be able to relate the real space, where the three-dimensional system of absolute coordinates taken as a reference is established, with the space captured by the artificial vision camera . The calibration process comprises a first phase, which we call two-dimensional calibration, where an adapted calibration device is used, as explained below in another aspect of the invention, for this function and to achieve a three-dimensional coordinate system in the plane laser that serves as a reference. The two-dimensional calibration converts a three-dimensional coordinate system in the camera plane, established as a reference in the space covered by the camera, to a reference system in the laser plane, compensating for possible perspective and aberration effects that the camera itself can introduce. Next, a calibration of the laser plane is performed that relates the reference system obtained in the laser plane according to the previous phase with the absolute coordinate system defined in real space. To perform this second calibration, a piece of standard revolution is used, which is an object with a geometry similar to that of the pieces that are really going to be scarce in the subsequent phases and
described.

Another aspect of the invention is a device Calibration for three-dimensional scanning of parts with revolution geometry, which is expressly conceived to be used in the two-dimensional calibration phase previously described. Said calibration device consists of a body of revolution with a conical head endowed with a plurality of concentric staggered, mounted on a trihedral support of precise positioning, progressively advancing a certain distance along an axis of the trihedral support arranged in concordance with the laser plane. From the derived measures of this scan on the calibration device, you can perform a conversion of the projection points of the cut between the laser plane and camera plane defined in pixels to a system of reference in the laser plane, with which the defined points in length measurements (millimeters).

A final aspect of the invention but not less important is a three-dimensional scanning device for parts of revolution, with which the explained procedure is implemented. The scanning device comprises means for capturing images, preferably an artificial vision camera, mounted in a balanced mechanical clamping element and together with some lighting sources, preferably one or more laser emitters to better illuminate all areas of the piece to be scanned. The essential property of such a scanning device is that it incorporates a rotation axis connected to the clamping element of the assembly laser camera on one end and on the other at a servo motor, the axis of rotation being able to position itself substantially parallel to the axis of revolution of the piece, although both axes do not necessarily have to coincide. He servomotor, preferably composed of a stepper motor, a movement transmission mechanism, an encoder electro-opto-mechanical or encoder and a electronic controller rotates the clamping element to certain distance from the piece of revolution. In said clamping element the imaging media are mounted at a certain distance and angle with respect to the lighting sources (principle of optical triangulation), being turn the set focused on the piece of revolution to turn a certain distance (different from the separation distance between the means of capturing images and the sources of lighting) with respect to said piece, thus producing the rotating sweep.

Description of the drawings

To complement the description that is being performing and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical realization of it, is accompanied as part member of this description, a set of figures where with illustrative and non-limiting nature, what has been represented next:

Figure 1.- Shows a perspective view of the scanning device, according to an aspect of the invention and a preferred embodiment

Figure 2.- Shows a graphic representation of the performance of the scanning device, according to the embodiment presented in the previous figure, when performing the swivel sweep according to the object of the invention.

Figure 3.- Shows a representation schematic of the planes defined respectively by the camera and the laser of the scanning device, illustrating the respective three-dimensional systems of reference in space.

Figure 4.- Shows a perspective view of the calibration device, according to a preferred embodiment of Another aspect of the invention.

Figure 5.- Shows a block diagram of the scanning procedure according to the purpose of the invention.

Preferred Embodiment of the Invention

In view of Figure 1, it can be described as one of the possible embodiments of the invention, a three-dimensional scanning device (10) for parts revolution (30) comprising:

- Lighting sources that guarantee a reflection of the sufficient beam of light even in the inclined areas present in the geometry of the piece (30), to avoid errors of measured by occlusion zones. Therefore, it is desirable to have a double light source consisting of a pair of laser emitters (12, 12 '), which are arranged, at a certain distance and with the convenient orientation towards said part (30), in a support balanced or clamping element (13).

- Some means of capturing images, which concreted in an artificial vision camera (11), with a high resolution, for example, 1536x512 pixels, with the possibility of 1/10 sub-pixel division on the Z axis of coordinates.

- An axis of rotation (14) connected by one end to the clamping element (13) of the chamber assembly (11) plus emitters laser (12, 12 '), while at the other end it is associated with a servomotor, with which said assembly can rotate so rectified and permanently with a deviation of less than 0.005 mm .:

- The servomotor, which in turn consists of a stepper motor (15), a transmission mechanism (9) of the movement, an encoder sensor that quantifies displacement angular and the speed of rotation, to move the motor (15) and connected to the axis of rotation (14) transmitting the output pulses from the encoder directly to the camera (11). In addition, the servomotor controls the movement of the motor (15) through cards electronic data acquisition. The encoder and the cards input / output are not represented in Figure 1.

All components of the scanning device  Three-dimensional (10) are conveniently powered and connected  each other by wiring an electrical cabinet designed to effect. The design of the mechanical assembly that constitutes this three-dimensional scanning device (10) has been made taking into count all the necessary degrees of freedom to obtain a high mechanical precision, optimally adjusting the components to achieve a high resolution of at least 0.01 mm at the same time which allows precise control of the angle of rotation, the alignment and focus of the laser emitters (12, 12 ').

According to Figure 2, the three-dimensional scanning device (10) performs a scan rotating around the revolution piece (30) to be inspected, caused by the action of the servomotor by causing the rotation of the clamping element (13) and, therefore, of the entire chamber assembly (11) and laser emitters (12, 12 '), with respect to said part (30), obtaining as many profiles of the piece (30) as desired without further that turning gold passed the motor (15) that moves the axis of rotation (14). Thus, the laser emitters (12, 12 ') that define a laser plane (16) rotate, producing the cutting of the laser plane (16) with the various areas of the piece (30), giving rise to the different profiles, captured from the perspective of the camera (11), displaced a certain distance and with a certain angle with respect to the plane laser (16), which in turn defines a camera plane (17) where the profiles of the piece (30) seen from that chamber are framed (eleven). Three-dimensional measurements are made using the triangulation of the points cut by the laser plane (16) and captured in the camera plane (17).

During the rotary scanning process, causing a controlled rotation of the laser plane (16), it is obtained the position in three-dimensional space of all points of the piece (30), by proper modeling of this turn, knowing the real position of this laser plane (16). To do this, it is a previous calibration of the same is necessary, because, in the practical, the laser plane (16) is not coincident with the axis of rotation (14) of the camera assembly (11) - laser emitters (12, 12 ').

First, a calibration is performed two-dimensional, where the projection points of the cut between the laser plane (16) with the part (30) collected in the camera plane (17), therefore, defined in pixels according to a system three-dimensional camera coordinates (18) set of reference, they become points in a three-dimensional system of laser coordinates (19), as illustrated in Figure 3. This  three-dimensional coordinate system calibration in the plane laser (19) to measure the cut points in millimeters is performed by means of a three-dimensional calibration device (20) illustrated in Figure 4.

The three-dimensional calibration device (20) serves as a universal positioning system to relate both coordinate systems (18, 19), at the same time as compensates for the effects of perspective and aberration caused by the camera (11). Said three-dimensional calibration device (20) is a body of revolution with a conical head (21) provided with a plurality of concentric steps (22), mounted on a support Trihedral precise positioning. Advancing through one of the axes of the trihedron belonging to the laser plane (16) progressively, every 2 + -0.005 mm, more than 500 pairs of relationships are obtained between points of the camera coordinate system (18) with the points of the coordinate system in the laser plane (19).

After the two-dimensional calibration phase made with the three-dimensional calibration device (20), it knows the position of the points of the piece (30) defined in the coordinate system in the laser plane (19), but to determine the actual position of these points in a three-dimensional system of XYZ absolute coordinates, previously you have to know the position and orientation of the laser plane (16) at each turn, that is, at each turn encoder pulse that gives the three-dimensional scanning device (10) For this, a piece of standard revolution is used, similar to the piece (30), with which the three-dimensional system of absolute coordinates defined in space in relation to the system three-dimensional coordinates in the laser plane (19).

In the ideal assumption that the axis of rotation of the laser plane (16) coincided with the axis of revolution of the piece (30), the position equations of the laser plane (16), assuming N encoder pulses per lap would be:

Absolute Coordinates = f (Coordinates: PlaneLaser, \ Pulse Encoder)

quad

X_ {Absolute} = X_ {laser} \ cdot cos (2 \ cdot \ pi \ cdot n / N)

quad

Y_ {Absolute} = Y_ {laser} \ cdot sin (2 \ cdot \ pi \ cdot n / N)

quad

Z_ {Absolute} = Z_ {laser}

However, the laser plane (16) really performs movements with respect to an unknown axis of rotation, due to the mechanical clearances of the motor shaft (15), so it is complex to know the situation of the laser plane (16) with respect to the axis of rotation (14) in each moment. To generally model the position of the laser plane relative to the axis of rotation are calculated about parameters (X0, Y0, Alpha, Beta, Gamma) that make up the equation of step between the laser coordinate system (19) and the system of absolute reference.

Absolute Coordinates = f (Coordinates: PlaneLaser, \ Pulse Encoder, \ X_ {0}, Y_ {0}, \ alpha, \ beta, γ)

Once the position of each point in the space following these calibration processes, it is related the real space with the one detected by the camera's focal point and already the scanning procedure can be completed in three dimensions that are summarized in Figure 5, gathering all the phases as follows:

(1) prior calibration, first with the calibration device (20) and then with one piece Pattern;

(2) determination of the profiles of the piece of revolution (30) that are required by rotating sweeping with the scanning device (10);

(3) extraction of the projection points of the camera plane cut (17), defined in pixels, corresponding to the edge of the piece (30);

(4) conversion of points in pixels to points of projection in the laser plane (16) defined in measurements of length, usually millimeters;

(5) calculation of the actual position of the laser plane (16) in the space and establishment of points of interest in the three-dimensional absolute coordinate system;

(6) three-dimensional image generation corresponding to the piece (30);

(7) point filtering and adjustment to circumferences, in the case of pieces (30) of circular section, to extract measures such as radii, circularity, concentricity, minimum thickness, maximum thickness, angle of bezel,...

Indeed, from the image three-dimensional obtained from the piece of revolution (30), by means of software specifically developed for the application, subsequent operations can be performed: Point filtering is refers to the elimination of noise or spurious points away from the average of the measurements obtained, once the points have been determined of a cylindrical part (30) in the absolute coordinate system. With this, you can proceed to obtain the equation three-dimensional circumference associated with the periphery of the piece (30). From such circumference equations perfect, making numerous cuts with the laser by planes perpendicular to the circumferences according to different angles, of 0 at 180, the cut points of said planes are obtained with each one of the circumferences and data on the desired dimensions of the piece (30).

Claims (8)

1. Three-dimensional scanning device for revolution parts, comprising image capture means and lighting sources mounted together in a balanced mechanical clamping element (13), is characterized in that it additionally comprises a rotation axis (4) connected to the element for securing (13) at one end and at the other to a servomotor, the axis of rotation (14) being able to be positioned substantially in parallel with respect to the axis of revolution of a piece (30) and rotating the clamping element ( 13) at a certain distance from said part (30), by the action of the servomotor, so that the image collection means are kept at a certain distance and angle with respect to the lighting sources oriented towards the revolution piece . 2. Scanning device according to claim 1, characterized in that the image collection means consist of at least one artificial vision camera (11). 3. Device according to any of the preceding claims, characterized in that the lighting sources consist of at least one laser emitter (12, 12 '). 4. Calibration device for three-dimensional scanning of parts with revolution geometry, where using an artificial vision camera (11) that defines a camera plane (17) and at least one laser emitter (12, 12 ') that defines a laser plane (16), projection points of the cut between the laser plane (16) and camera plane (17) defined in pixels are determined, characterized in that it consists of a body of revolution with a conical head (21) provided with a plurality of concentric steps (22), mounted on a tripod support of precise positioning, on which a scan is carried out progressively advancing a certain distance along an axis of the trihedral support arranged in accordance with the laser plane (16) and by which The projection points defined in length measurements are determined. 5. Three-dimensional scanning procedure for revolution parts, based on laser optical triangulation, using an artificial vision camera (11) that defines a camera plane (17) and at least one laser emitter (12, 12 ' ) that defines a laser plane (16), characterized in that it comprises the following phases: - determine profiles of a piece of revolution (30) by means of laser plane cuts (16) with said piece (30) produced by a rotating sweep with a device scan (10) as described in claims 1 to 3, by rotating the camera (11) together with the laser emitter (12, 12 ') to certain distance from the piece of revolution (30) and from so that the camera (11) is kept at a distance and an angle determined with respect to the laser emitter (12, 12 '); - determine cut projection points in the camera plane (17), defined in pixels, between the plane laser (16) and the edge of the revolution piece (30); - convert projection points to pixels to projection points on the laser plane (16) defined in measurements in length, through the relationship between the laser plane (16) and the camera plane (17); - determine the actual position of the laser plane (16) with the calculation of the geometric correction between the axis of rotation (14) of the camera assembly (11) - laser transmitter (12, 12 ') and the laser plane (16); - determine the actual position of the points of projection defined in length measurements in a system three-dimensional absolute coordinates. 6. Scanning method according to claim 5 characterized in that it additionally comprises, before the phase of determining the profiles of the revolution piece by means of the rotary scanning, the following phases: - calibrate a three-dimensional system of coordinates in the laser plane in relation to a system three-dimensional coordinates in the established camera plane as a reference, using a calibration device (20) according to is described in claim 4; - calibrate the three-dimensional system of absolute coordinates in space relative to the system three-dimensional coordinate in the laser plane (16), using A piece of pattern revolution. 7. Scanning method according to any of claims 5 or 6, characterized in that it additionally comprises, after the phase of determining the actual position of the projection points, a phase of generating the three-dimensional image of said piece of revolution (30 ). 8. Scanning method according to any one of claims 5, 6 or 7, characterized in that it additionally comprises, after the phase of determining the actual position of the projection points, a filtering phase of said points to extract measurements from the part of revolution (30).