PROCESS AND INSTALLATION OF ONLINE DIMENSIONAL CONTROL OF MANUFACTURED OBJECTS

The invention relates to the field of dimensional control by X-rays, manufactured objects of identical nature forming a series of objects.

The object of the invention aims more particularly to obtain the measurement by X-rays, of linear dimensions, that is to say of the lengths taken on manufactured objects in the general sense such as for example on containers, molded parts or machined, mechanical parts, packaging, bodywork components,

The prior art knows various techniques for checking the dimensions of objects by X-rays. Baggage inspection systems are also known, which do not aim to measure the dimensions of known objects but to detect prohibited objects or quantities. of prohibited materials in virtually random arrangements, shapes and quantities.

Axial rotation systems are thus known, including computer-assisted tomography or CT (“computed tomography”). This classic method is described in the article of “Computed tomography for dimensional metrology” by JPKruth (l) & ail, in CIRPAnnals

Volume 60, Issue 2, 2011, Pages 821-842 and implementation for example, by tomography devices marketed by the companies Werth Messtechnik or General Electric. This method consists in positioning between an X-ray generator tube and a matrix or linear X-ray image sensor, an object on a turntable around a vertical axis. A very large number (at least 100 and often more than 600) 2D x-ray images of the objects are acquired during the rotation. If the image sensor is matrix, the beam is conical. If the image sensor is linear, the beam is advantageously confined as a fan ("fan beam") in a plane orthogonal to the axis of rotation and the rotation is accompanied by a translation along the vertical axis of the rotation. , for a full helical-type sweep. This technique can provide high precision three-dimensional measurements. However, the acquisition time requires at least

one minute for the fastest systems, plus the time to load and unload objects so that a maximum of 10 to 30 objects are inspected per hour.

Another so-called rotating gantry solution is proposed, for example, by the device known under the trade name “speed / scan CT 64” from the General Electric Company. Like some 3D scanners for luggage, this concept of solution is similar to medical imaging tomographs in terms of relative movements between source, object and image sensor. In fact, manufactured objects or luggage, placed on a conveyor, are in translation in the device. They cross a projection plane orthogonal to the direction of movement In a circular gantry containing said plane, an X-ray source and a generally curved image sensor, opposite the source, are rotated around the central axis of movement. , to obtain, slice by slice or by helical scan, the projections necessary for the 3D reconstruction by an algorithm implementing, for example, the “filtered rear projection” method or the ART method. The objective of these devices is to allow the acquisition of a very large number of projections at each turn of the gantry, for example 100, or even 700 to 1000 images per slice. The 3D reconstruction of the objects is made for example slice by slice. Having in fact determined the attenuation at any point of the slice, by concatenating the slices obtained during the movement of the object, an attenuation value is obtained at any volume element of the object The objective of these devices is to enable the acquisition of a very large number of projections at each turn of the gantry, for example 100, or even 700 to 1000 images per slice. The 3D reconstruction of the objects is made for example slice by slice. Having in fact determined the attenuation at any point of the slice, by concatenating the slices obtained during the movement of the object, an attenuation value is obtained at any element of the object's volume The objective of these devices is to allow the acquisition of a very large number of projections at each turn of the gantry, for example 100, or even 700 to 1000 images per slice. The 3D reconstruction of the objects is made for example slice by slice. Having in fact determined the attenuation at any point of the slice, by concatenating the slices obtained during the movement of the object, an attenuation value is obtained at any volume element of the object

If these devices with vertical axis rotation or rotating gantry are very precise thanks to the large number of images provided, these devices are expensive and slow and are in practice reserved for off-line control because they are not suitable for dimensional control in line for speeds up to and exceeding 600 articles per minute with runs of lm / s.

Patent application DE 10 2014 103137 describes a method for determining geometric characteristics on a workpiece using a system of tomodensitometric detectors, consisting of an X-ray source, a plane detector and a mechanical axis to rotate the part or to rotate the x-ray source and the detector.

The method acquires x-ray images upon rotation and provides a representation of the surface using a model of the surface. Such a method avoids the implementation of steps for reconstructing the volume data to reduce the calculation time. Such a technique does not make it possible to measure parts manufactured at high speed because it requires loading the parts on a turntable followed by a rotation of at least 180 ° then its unloading for checking another part.

To overcome the drawbacks of the tube and image sensor on board a rotating gantry, US Pat. No. 8,971,484 describes a baggage inspection system in which the rotating system is replaced by an array of stationary multi-beam X-ray sources actuated successively. to create a virtual displacement of the X-ray sources to provide a large number of radiographic images with different angles of projection. Compared to physical rotation systems limited to 4 revolutions per second, the number of "virtual rotations" is increased to 40 revolutions per second. This technique, which is implemented by the device known under the trade name Rapiscan RTT from the company Rapiscan Systems, is capable of checking 1,200 bags per hour, carrying out tens of thousands of

This technique is very expensive because of the high price for multisource X-rays and the computing power required to process a very large volume of data. In addition, the control rates are still limited and are not suitable for on-line control.

US Patents 7,319,737 and US 7,221,732 propose checking baggage by a technique called digital laminography or tomosynthesis. The baggage passes through a succession of conical projection planes called "fan beam" and each containing a pair of linear image sensors arranged in an L. These techniques aim to search for weapons or explosives in the baggage which contains shaped objects and very diverse materials, by visualizing their 3D positions in the luggage and by evaluating for example the volume of suspect product. It is common to use multispectral technology to also determine the atomic number of matter. These systems therefore seek to determine an attenuation value at any point of a piece of luggage. On the other hand,

Patent application JP S60 260807 proposes measuring the thickness of the walls of a tube moving in translation along the axis of the tube, using X-ray measurements from one or more foci at each of which sensors are associated. The foci and the sensors are positioned to produce radiographic projections in a plane orthogonal to the direction of movement of the tube. The radiographic projections are therefore coplanar in a projection plane which is orthogonal to the axis of symmetry of the tube. The direction of these radiographic projections makes a right angle (90 °) to the direction of travel. This technique does not allow complete knowledge of the internal and external surfaces of the tube. The method described by this patent application makes it possible to measure only the

Likewise, US Pat. No. 5,864,600 describes a method for determining the filling level of a container using an X-ray source and a sensor arranged transversely on either side of the transport conveyor. containers. This system does not make it possible to carry out measurements for a non-transversely oriented surface because this document does not provide for three-dimensional modeling of the containers.

Patent application US 2009/0262891 describes a system for detecting, by X-ray, objects placed in baggage moved in translation by a conveyor. This system comprises pulsed generator tubes or a sensor having a large dimension parallel to the direction of travel. This document provides a method of reconstructing the object which is not satisfactory because the absence of projections in the direction of displacement does not allow the measurement of dimensions in the direction orthogonal to the direction of displacement. The lack of radiographic projections in an angular sector does not make it possible to produce a digital model suitable for ensuring precise measurements.

Patent application DE 197 56 697 describes a device exhibiting the same drawbacks as patent application US 2009/0262891.

Patent application WO 2010/092368 describes a device for viewing an object moving in translation by X-rays using a radiation source and three linear sensors.

Patent application US 2010/220910 describes a method for detecting anomalies in an object by producing a reference 3D model representing an ideal object. The method then aims to compare a 2D image acquired of a real object with the 2D image corresponding to the reference model in order to deduce an anomaly therefrom. This method does not make it possible to take precise measurements of an object and only makes it possible to control an object in the 2D images produced, therefore only the directions orthogonal to the directions of projection.

The object of the invention aims to remedy the drawbacks of the prior art by proposing a process that is inexpensive to implement and allowing precise dimensional control by X-rays of manufactured objects moving in translation at high speed.

It is known in tomography, that the absence of radiographic projections around a given direction prevents the reconstruction of surfaces parallel to this direction, creating the phenomenon of "missing border", which prevents for a dimensional control, the measurement of dimensions. orthogonal to the missing radiographic projections.

Another object of the invention therefore aims to propose a method making it possible to carry out precise measurements on objects moved in translation, by building a precise and complete three-dimensional digital model while the radiographic projections are in limited number and cannot be acquired. around the direction of conveying the objects.

According to the invention, the method for automatically measuring linear dimensions of manufactured objects in a series consists of:

- choose a series of manufactured objects in which each of said objects is made of a material with a constant attenuation coefficient at any point of the object;

- choose at least one region to inspect objects in which at least one linear dimension is to be measured;

- Transporting, by means of a transport device, the moving objects in a direction of movement along a substantially rectilinear path in a conveying plane, these objects generating a conveying volume during their movement;

- positioning, outside the conveying volume, at least one focus of an X-ray generator tube and image sensors exposed and each sensitive to X-rays from an associated focus, these X-rays having passed through at least the region in inspecting producing on each image sensor a radiographic projection in the direction of projection;

- acquire using image sensors, for each object during its movement, at least three radiographic images of the region to be inspected, obtained from at least three radiographic projections of the region to be inspected, including the directions of projection are different from each other;

- analyze the at least three radiographic images, using a computer system;

- make available to the computer system, an a priori geometric model of the region to be inspected for the series of objects;

- determine using the computer system by considering a constant attenuation coefficient and from the a priori geometric model and at least three radiographic images of the region to be inspected, a digital geometric model of the region to be inspected consisting of 'at least two three-dimensional points each belonging to a boundary surface of the region to be inspected and situated in a plane not orthogonal to a direction of projection;

- determine from the digital geometric model of the region to be inspected, at least one linear dimension measure of the region to be inspected for each object in the series, as being the distance between at least two three-dimensional points each belonging to a boundary surface of the region to be inspected and located in a plane not orthogonal to a direction of projection.

In addition, the method according to the invention may further comprise in combination at least one and / or the other of the following additional characteristics;

- to determine a digital geometric model made up of:

• at least two three-dimensional points in space each belonging to a boundary surface of the region to be inspected and located in a plane not orthogonal to a direction of projection and not parallel to the direction of displacement;

· And / or at least one three-dimensional surface of the region to be inspected containing points not belonging to a plane orthogonal to a direction of projection, and not belonging to a plane parallel to the direction of displacement;

• and / or at least one section of the region to be inspected, along a plane different from a plane orthogonal to a direction of projection and different from a plane parallel to the direction of displacement;

- making the value of the constant attenuation coefficient available to the computer system;

- to make available to the computer system, the a priori geometric model of the region to be inspected for the series, obtained by:

“The digital computer design model of the objects in the series;

• or the geometric digital model obtained from the measurement of one or more objects of the same series by a measuring device;

»Or the geometric digital model generated by the computer system from values ​​entered and / or drawings produced and / or shapes selected by an operator on a man-machine interface of the computer system;

- Positioning a focus from which comes a divergent X-ray beam with an aperture greater than or equal to 120 ° or at least two foci from which originate divergent X-ray beams the sum of the openings of which is greater than or equal to 120 °;

- to have at least one hearth in the conveying plane;

- To have on one side of a secant plane of the conveying volume, orthogonal to the conveying plane, a focus from which a divergent X-ray beam emanates, so that its beam crosses the secant plane and the region to be inspected;

- Arranging on the opposite side with respect to the secant plane, at least one image sensor associated with said focus to receive the X-rays coming from said focus;

- To have on one side of the conveying plane, a focus from which a divergent X-ray beam emerges, so that its beam passes through the conveying plane;

- Arranging on the opposite side with respect to the conveying plane, at least one image sensor associated with said focus to receive the X-rays coming from said focus;

- to acquire using the image sensors, for each object in the series during its movement, at least two radiographic images of the inspected region corresponding to projection directions defining a useful angle greater than or equal to 45 ° and less than or equal to 90 ° and, advantageously greater than or equal to 60 ° and less than or equal to 90 °;

- to acquire using the image sensors, for each object of the series during its movement at least one radiographic image of the inspected region corresponding to a direction of projection having an opening angle with the direction of displacement between 10 ° and 60 °;

- making and acquiring radiographic projections of the inspected region of an object so that the X-rays coming from the focal point (s) and reaching the image sensors do not pass through another object;

- to acquire using the image sensors, for each object of the series during its movement, radiographic images from between three and forty, and preferably between four and fifteen radiographic projections of the region to be inspected from different directions;

the image sensors are of linear type each comprising a linear array of elements sensitive to X-rays, distributed along a support line defining with the associated focus, a projection plane containing the direction of projection, these image sensors being arranged so that:

• at least m sensitive elements of each of these image sensors receive the radiographic projection of the region to be inspected by the X-ray beam coming from the associated focus;

• the projection planes for the different sensors are distinct from one another and not parallel to the conveying plane;

• using each of the at least three linear image sensors is acquired, at each incremental displacement of each container along the trajectory, radiographic linear images of the region to be inspected according to a number chosen so that for each object, l the entire region to be inspected is shown completely in the set of linear radiographic images;

• the at least three sets of radiographic linear images of the region to be inspected are analyzed for each object.

Another object of the invention is to provide an installation for automatic measurement of linear dimensions of at least one region to be inspected of manufactured objects of a series, the installation comprising:

a device for transporting objects in a direction materialized by a displacement vector, along a substantially rectilinear path in a conveying plane, the objects traveling through a conveying volume extended in the direction;

at least one focal point of an X-ray generator tube located outside the volume crossed, and creating a divergent beam of X-rays directed to pass through at least one region of the object to be inspected;

- at least three image sensors, located outside the conveying voiume, so as to receive X-rays from an associated focus, the focus (s) and the image sensors being arranged so that each sensor of images receive the radiographic projection of the region to be inspected by the rays coming from the focus when the object crosses these rays, the directions of projection of these radiographic projections being different from one another;

an acquisition system connected to the image sensors, so as to acquire for each object during its movement, at least three radiographic projections of the region to be inspected with all different directions of projection;

a device for making available for a computer system, an a priori geometric model of the region to be inspected for the series of objects; the computer system:

"Determining a digital geometric model for each object in the series consisting of at least two three-dimensional points each belonging to a boundary surface of the region to be inspected and located in a plane not orthogonal to a direction of projection, considering a coefficient of constant attenuation of the material for the objects, from the a priori geometric model and at least three radiographic projections of the region to be inspected;

Determining for each object in the series, from the digital geometric model of the region to be inspected, at least one linear measure of the region to be inspected as being for each object in the series! A distance between at least two three-dimensional points each belonging to at a boundary surface of Its region to be inspected and located in a plane not orthogonal to a direction of projection.

In addition, the installation according to the invention may further include in combination at least one and / or the other of the following additional characteristics;

a device for making the material attenuation coefficient of the objects in a series available to the computer system;

the device for making an a priori geometric model of the region to be inspected available to the computer system is a mass memory, a wired or wireless computer network or a man-machine interface;

a device for making available to the computer system, values ​​and / or tolerances for the required linear dimensions, and / or at least one geometric reference model;

- at least two X-ray production foci, positioned separately in two distinct positions and at least three image sensors, sensitive to X-rays and positioned so that:

• each focus emits its beam through at least the region to be inspected to reach at least one associated sensor;

• each sensor is associated with a focal point and receives the X-rays from said focal point after passing through the region to be inspected;

at least one focal point from which a divergent X-ray beam emanates with an opening greater than or equal to 120 ° or at least two focal points from which emanate beams of divergent X-rays the sum of the apertures of which is greater than or equal to 120 °;

- at least one hearth arranged in the conveying plane;

on one side of a plane secant to the conveying volume and orthogonal to the conveying plane, a focus from which a divergent X-ray beam emerges, so that its beam crosses the secant plane and the region to be inspected;

- on the opposite side with respect to the secant plane, at least one image sensor associated with said focus to receive the X-rays coming from said focus; - on one side of the conveying plane, a focus from which a divergent X-ray beam emanates, so that its beam crosses the conveying plane;

- on the opposite side with respect to the conveying plan, at least one image sensor associated with said focus to receive the X-rays coming from said focus;

- at least one focus and two image sensors are arranged so that the directions of projection of the inspected region that they receive have between them a useful angle greater than or equal to 45 ° and less than or equal to 90 ° and, advantageously greater than or equal to 60 ° and less than or equal to 90 °;

- at least one focus and one image sensor are arranged so that, when an object passes through the field of the sensors, the direction of projection of the region inspected on the image sensor makes an opening angle with the direction of displacement between 10 ° and 60 °;

the image sensors and the focal points are arranged so that the X-rays coming from the focal point (s) and reaching the image sensors and passing through the region of an object do not pass through another object at the same time;

- between one and four foci, resulting from one or more tubes generating X-rays;

- the number and arrangement of the image sensors and the associated foci are such that for each object in the series during its movement, the radiographic projections of the region to be inspected on the image sensors present between three and forty , and preferably between four and fifteen different directions of projection;

the image sensors are of the linear type and each comprise a linear network of elements sensitive to X-rays, distributed along a support line defining with the associated focus, a projection plane containing the direction of projection, these sensors of images being arranged so that:

at least m sensitive elements of each of these image sensors receive the radiographic projection of the region to be inspected by the X-ray beam coming from the associated focus;

- the projection planes for the different sensors are distinct from one another and not parallel to the conveying plane;

- at least three linear image sensors have their support lines parallel to each other;

- at least three linear image sensors have their support lines orthogonal to the conveying plane;

- a focus is positioned on one side of the conveying plane, and according to the invention at least one associated linear image sensor is positioned on the side opposite the focus with respect to the conveying plane and so that its straight support is parallel to the conveyor plane.

Various other characteristics emerge from the description given below with reference to the appended drawings which show, by way of non-limiting examples, embodiments of the object of the invention.

Figure 1 is a schematic top view showing an installation for measuring by X-rays, dimensions on objects scrolling in line.

Figure 2 is a schematic side perspective view showing part of the installation for measuring by X-rays, dimensions on an object.

Figure 3 is a schematic perspective view showing the volume traversed or generated by the objects during their linear displacement.

Figure 4 is a schematic top view showing an embodiment of an installation according to the invention comprising three focal points generating X-rays.

Figure 5 is a schematic cross-sectional elevation view of the installation illustrated in Fig. 4.

Figure 6 is a schematic side elevational view of the installation illustrated in Fig. 4.

Figures 7 and 8 are schematic views explaining the definition of the useful angle between two directions of projection.

Figures 9 and 10 are schematic perspective views showing the positioning of image sensors with respect to the movement of the objects to be inspected.

Figure 11 is a view of an exemplary embodiment of an installation according to the invention implementing matrix image sensors.

FIG. 12 is a view of a matrix of elements sensitive to X-rays on which appears two distinct zones corresponding to two sensors of matrix images.

As a preliminary, some definitions of the terms used in the context of the invention are given below.

A focus Fj of an X-ray generator tube is a point X-ray source, preferably a “micro focus”, with a diameter for example between 0.01 mm and 1 mm, creating a divergent beam of X-rays. It is possible to d '' use any type of point or near point X-ray source.

A sensitive element is an element sensitive to X-rays, in other words an elementary surface, of dimension for example 0.2 x 0.2 mm or 0.02 x 0.02 mm, converting the X-rays that it receives into a signal electric. Typically, a scintillator converts x-rays into visible light and then a photoelectric sensor converts visible light into an electrical signal. Techniques for the direct conversion of X-rays into an electrical signal also exist. A pixel designates an elementary value of a point of a sampled image, characterized by its gray level between 0 and a maximum value. For example, for a 12-bit digital image, a pixel takes digital values ​​between 0 and 4095.

A system for reading or acquiring radiographic images comprises one or more surfaces sensitive to X-rays, that is to say surfaces comprising sensitive elements converting the X-rays into an electrical signal to be transmitted to an X-ray system. analysis conventionally implemented by a computer and referred to as a computer system in the remainder of the description. The signals originating from a set of sensitive elements belonging to the same sensitive surface zone, acquired by the acquisition device and transmitted together to the computer system, constitute a radiographic image. To be analyzed by the computer system, the radiographic images are preferably converted into digital radiographic images either as close as possible to the sensitive surface,

The X-ray beams coming from a focal point Fj pass through at least one inspected region, and form on a sensitive surface, the radiographic projection of the inspected region, which is sometimes called the radiant image and which contains the information of X-ray attenuation by the material passed through.

An X-ray sensitive surface area which receives the X-ray projection of the inspected region is referred to as image sensor Cj1. An image sensor Cji is exposed to X-rays from an associated focus Fj. The image sensor converts this X-ray projection into an X-ray image of the inspected region. When the sensitive surface area contains a line of photosensitive elements, the transmitted radiographic image is linear, composed of a line of pixels forming an array of one-dimensional values. When the sensitive surface area contains a matrix of photosensitive elements, the transmitted radiographic image is a matrix, composed of a matrix of pixels forming an array of two-dimensional values.

The direction of projection Dji is the oriented direction or the vector, starting from the focus Fj to pass through the center of the image sensor Cji, that is to say through the center of an X-ray sensitive area which receives the radiographic projection of the region inspected at the time of acquisition during movement of the object between the focal point and the image sensor. For an associated image sensor-focus pair, the projection direction is the vector from the focus reaching the middle of the image sensor. The positioning of the image sensors is such that the sensitive surface is not parallel to the direction of projection. It may be advantageous in certain cases for the sensitive surface of the image sensor to be orthogonal to the direction of projection defined with the associated focus. But this is not

The directions of projection Dji of radiographic projections are different if the directions of projection Dji taken in pairs form a minimum angle of at least 5 ° between them.

A sensitive surface area containing a single line of sensitive elements constitutes a linear image sensor, which comprises a linear array of sensitive elements, distributed along a line segment of support. According to this definition, a column or a row belonging to a sensitive matrix surface, acquired and transmitted separately by the acquisition device is considered to be a linear image sensor. Several sensitive surface areas of the same surface and each containing a single row of different pixels therefore constitute several linear image sensors. The direction of projection associated with the linear radiographic image obtained is therefore the direction starting from the focus and passing through the middle of the support line segment at the instant of acquisition of the

A sensitive surface area which contains an array of sensitive elements constitutes a matrix image sensor, which comprises a matrix array of x-ray sensitive elements, distributed in a matrix. As shown in Fig. 11, according to this definition, an area of ​​matrix sensitive surface C11, C12, which belongs to a larger sensitive surface Ss, and which is acquired and transmitted separately by the acquisition device, is a matrix image sensor. Several matrix sensitive surface areas C11, C12 of the same surface, acquired and transmitted separately by the acquisition device therefore constitute several matrix image sensors providing different radiographic images, Mil, M12, respectively (FIG. 12). The DU direction, Projection D12 associated with the matrix radiographic image respectively Mil, M12 is the direction starting from the focus F1 and passing through the middle of the zone C11, C12 of the matrix sensitive surface, at the instant of acquisition of the image. It is therefore possible that the image sensors C11, C12 are non-disjoint regions activated successively in time.

Of course, a person skilled in the art can use a matrix sensor technology based on an image intensifier or else a “screen capture camera” in which a scintillator plate receives the radiant image, converts it into visible light, the image visible at the rear of the scintillator being photographed by a visible camera fitted, if necessary, with an objective.

The invention applies to series of manufactured objects composed of a material, such as objects obtained by machining, molding, blow molding, sintering, injection, extrusion, of which the attenuation coefficient μ is unique, that is, that is to say having the same value at all points of a region to be inspected of the object and preferably constant over time and identical for the objects of the series. For example mechanical parts of steel or aluminum foundry, glass bottles, plastic packaging. These are generally so-called mono-material objects. However, the invention can be implemented for multi-material objects, provided that the attenuation coefficient is constant, in the sense of uniform over the whole of the inspected region.

It should be noted that the attenuation coefficient μ of a material is strictly speaking a spectral property μ (λ) depending on the wavelength λ or the energy of the X-rays. This characteristic is not necessarily taken into account. account insofar as the X-ray source having its own emitted spectral composition, it is possible to consider that the attenuation μ is a characteristic of the material for the spectrum of the chosen source. Those skilled in the art will also know how to carry out the invention by using any method of taking into account the spectral attenuation or the hardening of the beams.

Of course, local and / or temporal variations of the attenuation coefficient μ of low amplitude do not prevent the implementation of the method, but could possibly, depending on their amplitude, cause

slight or significant losses of precision in the measurements carried out by the installation. It is therefore considered that such small variations due for example to variations in the composition of the objects, variations in parameters of the manufacturing process, modifications of the environmental conditions, or even changes in the operation of the X-ray sources, are possible. while considering the uniqueness and constancy of the attenuation of the material as verified.

The air attenuation can be considered negligible compared to the material. In this case, the attenuation of an X-ray beam passing through the object will depend only, on the one hand, on said constant attenuation for the emitted X-ray spectrum, and on the other hand, on the cumulative thickness of feedthrough material. Alternatively, it is considered that the thickness of the air passed through is large and uniform for all the beams, therefore it can be considered to be known. The attenuation due to air can be subtracted from the total measured attenuation. Thus, the gray level in each X-ray image, possibly corrected, depends solely and directly on the total cumulative thickness of material traversed.

The digital analysis of the radiographic images of each object makes it possible to construct a three-dimensional digital geometric model of each object, referred to as a digital geometric model in the following description. Optionally, this digital geometric model can simply be a stack of two-dimensional digital geometric models. The making of a digital geometric model is the way - in mathematical, graphical and data structure terms - three-dimensional objects are represented and manipulated in digital form in a memory of a computer system. It should be considered that the object of the invention aims to determine as many three-dimensional digital geometric models as there are radiographed objects.

The modelization can be voluminal. The mono-material object can therefore be represented by voxels whose value represents a quantity of material. The voxel can be full, partially full or empty of material (in this case it is air). The solid geometric model can be analyzed to locate object boundaries and then to measure linear dimensions such as lengths or thicknesses. It can also be transformed into a surface model, that is to say in which the boundary surfaces of the object are modeled.

It is possible to obtain a surface model directly from the radiographic images, that is to say without going through the calculation of a volume model.

In surface models, an object is defined by at least one three-dimensional surface. A three-dimensional surface corresponds to the border between the material of the object and the external environment (generally the air), which makes it possible to understand the notions of interior and exterior of the object. Generally, three-dimensional surfaces are modeled in several ways such as by polygonal modeling, by curves or parametric surfaces (cylinders, cones, spheres, splines, ...) or by subdivision of surfaces. Using a mesh of polyhedra, for example triangles, the three-dimensional surfaces of objects are represented by sets of plane facets connected by their edges.

A section of a three-dimensional object is its intersection with a plane, The section of three-dimensional surfaces are two-dimensional curves in the section plane. Knowledge of these two-dimensional curves in a succession of section planes allows reconstruction of three-dimensional surfaces.

In order to carry out length measurements, there are several approaches.

In a first volume method, it is possible to travel a volume model along a straight line or a bundle of straight lines and determine the material / air boundary voxels.

In a second surface method, it is possible to calculate a segment whose ends are the intersections of a line with the material / air boundary surface of a surface model. Algorithms solve topological problems quite well. The points of intersection are unique. Finally, a mixed method consists in transforming the solid model into a surface model, then in applying the second method.

A third method consists in determining, in a section plane, the distance between two points of one or two two-dimensional curves, any curve being a border between matter and air.

A three-dimensional point is a point whose coordinates are known in three-dimensional space, in any frame of reference.

These three previous methods are examples of determining a distance between two three-dimensional points, to determine a measure of linear dimension.

L'objectif de l'invention est de réaliser des mesures plus complètes que celles rendues possibles par de simples images radiographiques bidimensionnelles. En effet, il est aisé à l'aide d'un capteur d'images matricielles d'obtenir une image radiographique bidimensionnelle correspondant à une projection de la région inspectée et de mesurer des dimensions dans un plan orthogonal à la direction de projection dit « plan projeté ». De même, il est aisé à l'aide d'un capteur d'images linéaires d'obtenir une image radiographique bidimensionnelle correspondant à une projection en éventail (plans parallèles) de la région inspectée obtenue par juxtaposition des lignes d'image successives acquises durant le déplacement dans la direction de déplacement, et de mesurer des dimensions dans un plan projeté, qui est parallèle à la direction de déplacement. En revanche, selon l'invention, on peut mesurer des dimensions linéaires selon des directions qui ne sont ni contenues dans les plans projetés, ni parallèles aux plans projetés. Le procédé selon l'invention consiste en effet lors du traitement d'une combinaison des images radiographiques selon au moins trois directions de projection différentes, à reconstruire et mesurer des dimensions selon pratiquement toutes les directions. Ceci est possible par toute méthode permettant la détermination de points tridimensionnels dans l'espace appartenant à une surface frontière incluse dans la région à inspecter de l'objet. La reconstruction d'un modèle tridimensionnel de la région à inspecter, de type surfacique ou volumique ou à base de plans de coupe, est une méthode possible. En effet, selon l'invention on peut soit indirectement à partir d'un modèle surfacique ou voiumique ou de plans de coupes, soit directement, déterminer au moins deux points tridimensionnels, voire de préférence des nuages de points tridimensionnels, répartis selon des directions non mesurables uniquement dans les images radiographiques bidimensionnelles.

The digital geometric model is therefore made up of geometric elements such as points, segments, surfaces, elementary volumes, calculated from radiographic projections, considering to calculate each element, the attenuation of at least some X-rays that have passed through this point on the real object, with the aim that the digital geometric model is a faithful representation of the geometry of the real object, including deformations with respect to an ideal object. In other words, the coordinates of the geometric elements are determined by considering that said coordinates have modified the radiographic projections, even when these geometric elements are not distinguishable in any of the 2D radiographic projections.

Consequently, an advantage of the method according to the invention is that it consists in determining, for each object, a digital geometric model consisting of at least two three-dimensional points each belonging to a border surface of the region to be inspected and located in a plane not orthogonal to a direction of projection Djî, and not parallel to the direction of displacement.

Of course, the interest of the method is not only to provide measurements in a plane not orthogonal to a direction of projection Djî, but also to provide a large number of measurements distributed in the inspected region, therefore dimensions in many directions. , between multiple pairs of points. Preferably, the digital geometric model consists of:

at least two three-dimensional points in space each belonging to a border surface of the region to be inspected and located in a plane not orthogonal to a direction of projection Djî, and not parallel to the direction T of displacement;

at least one three-dimensional surface of the region to be inspected, containing points not belonging to a plane orthogonal to a direction of projection Dji, and not belonging to a plane parallel to the direction T of displacement;

- And / or at least one section of the region to be inspected, along a plane different from a plane orthogonal to a direction of projection Dji and different from a plane parallel to the direction of displacement.

The a priori geometric model is a geometric digital model of the series of objects, serving as an initialization for reconstruction software in order to build the digital geometric model of the object. Its role is mainly to provide the computer system with information on the shape, geometry and dimensions of the object to be modeled by calculation.

Thanks to this information it becomes possible:

- not to model, from the radiographic images, the attenuation in regions of the image space empty of material a priori because the attenuation is considered there as zero;

and or

- from the radiographic images only model the surfaces on which the measurements of dimensions are to be made, possibly directly without going through the determination of voxels; and or

- to determine only the differences between the surfaces modeled from the radiographic images and the theoretical ideal surfaces.

In the case of mono-material objects, knowledge of the a priori geometric model also makes it possible not to determine from the radiographic images, attenuation values ​​in regions of the space of the image containing material according to the model a priori because it is known as that of the material of manufacture of the object.

However, it should be understood that according to the invention, no measurement of an object is deduced from a measurement on the a priori geometric model, since this model is known independently of said object and represents a non-real theoretical ideal.

As emerges from the drawings and more specifically from Figs. 1 and 2, the object of the invention relates to an installation 1 allowing the implementation of a method for automatically performing linear dimensional measurements on manufactured objects 2 moving in scrolling at high speed. The invention relates to so-called “on-line” control of a series of manufactured objects, after a processing or manufacturing step, in order to control the quality of the objects or of the transformation or manufacturing process.

The method operates for a scrolling rate of a stream of objects 2. Ideally, the installation 1 is capable of processing production at the production rate, for example 600 objects per minute.

However, the calculation time can exceed the interval between two objects. Likewise, the exposure times of the image and reading sensors may be too long. If the fastest flow cannot be processed by a single installation according to the invention, then several installations can be implemented in parallel, each controlling a part of the production. Thus it is possible to divide the production flow into two or three parallel flows inspected by two or three installations according to the invention. Obviously, the economic interest of the invention is achieved if the number of flows and therefore of installations according to the invention remains low.

The invention provides a considerable improvement thanks to the measurement of moving objects, by avoiding the helical scanning and the scanning on a plate which are not adapted to the production rates because these two methods imply a relative rotation of the objects with respect to the foci. and / or the sensors create a “break in scrolling” or a very slow movement of objects within the installation.

The method according to the invention ensures the measurement on each object 2, of at least one and generally of several linear dimensions.

that is, lengths. A length is a measurement expressed in units of length e.g. inch or meter and covers all measurements of linear dimensions such as e.g. diameter, thickness, height, length, width, depth, distance, coordinate, perimeter of manufactured objects. At least one linear measure of the inspected region is the distance between at least two three-dimensional points each belonging to a border surface of the region to be inspected and situated in a plane not orthogonal to a direction of projection Dji.

According to the invention, the objects 2 are identical objects except for the dimensional variations, forming a series of objects. In other words, a series is composed of theoretically identical objects when they are in conformity. Dimensional control consists of measuring actual dimensions and comparing them to the required dimensions. A priori, any object in a series is close to an ideal reference object having the required dimensions but deviates from them by dimensional variations.

According to an advantageous embodiment characteristic, at least one region of the object 2 is chosen to be inspected so as to be able to carry out measurements of dimensions in this region of the object, corresponding to a dimensional characteristic of the region to be inspected. At least the region of the object in which the linear dimension (s) are to be measured is inspected by X-rays. Thus, the inspected region can correspond to the whole of the object or to one or more regions of this object.

As indicated, all the objects 2 in a series are made up of a material having a constant attenuation coefficient at all points of each object.

According to an advantageous variant of the invention, this coefficient is known by the computer system. The method therefore consists in providing a means for making available for the computer system the value of the attenuation coefficient of the material. This value can be spectral, non-spectral, or even made dependent on the settings of the X-ray sources. The provision is possible by various capture, communication and ^ devices.

memory. For example, the device for making the value of the material's attenuation coefficient available to the computer system is a mass memory, a wired or wireless computer network or a man / machine interface.

The installation 1 also comprises a device 5 for transporting the objects 2 in a conveying plane Pc, that is to say along a plane path, with a direction materialized by a displacement vector T. Preferably, the path is substantially rectilinear, but a curve or an arc is possible. Conventionally, the transport device 5 is a conveyor belt or chain conveyor ensuring linear translation of the objects 2 which are deposited therein. Thus, the objects 2 of the same series are essentially in translational movement in a conveying plane. As emerges more precisely from the Fïg. 1 and 2, the direction of movement of the objects 2 is established along a horizontal axis X with a reference X, Y, Z comprising a vertical axis Z perpendicular to the

The position of the objects considered in a mobile frame orthonormal in translation in the direction T is fixed during their displacement and the acquisition of the radiographic images. For example, the objects are placed on the conveyor belt, resting stable, possibly on a clean laying surface such as the bottom of a container or the legs of a seat.

In a variant of the invention, it is possible to provide a support for its objects 2. In this case, this support is fixed in the orthonormal mobile frame, in translation in the direction T, and it also keeps the object fixed in the mobile frame orthonormal in translation in the direction T. So that the support does not influence the measurements, according to a first variant it is excluded from the inspected region so as not to appear in superposition of the inspected region in the projections. According to a second variant, its attenuation coefficient is negligible relative to that of the objects and can be likened to air or to zero attenuation. According to a third less advantageous variant, the geometry of the support, as well as its position in the movable frame,

The position of the objects being stable (during scrolling and acquisition of the radiographs), it remains preferable that this position in the orthonormal mobile frame in translation in the direction T, is also the same for each object in a series of objects. .

If this is not the case, it is then possible according to a variant of the invention, to implement a means for determining the position of each object in the orthonormal mobile frame in translation in the direction T with respect to a common reference mark of the installation, this position being taken into account by the means for calculating the digital geometric model of the region to be inspected. This preliminary step consists in determining the position of each object, then in putting in correspondence in a virtual reference mark, the a priori geometric model and the images. That amounts in all cases to calculating the 3D model of the objects in the orthonormal mobile coordinate system in translation according to the direction T.

As emerges more precisely from FIG. 3, during their translational movement, the objects 2 generate or pass through a so-called conveying volume Vt. The plane Ps is the secant plane of the conveying volume Vt, orthogonal to the conveying plane Pc and parallel to the direction of movement T. For example, a median plane separates the volume into two equal sub-volumes. The plane Ps is a vertical plane insofar as the conveying plane is generally horizontal.

The installation 1 also comprises, as illustrated in FIGS. 1 and 2, at least one focus Fj (with j varying from 1 to k) of an X-ray generator tube 7 creating a divergent beam of X-rays directed to pass through the conveying volume Vt and more precisely to cross at least the region to be inspected from object 2. Installation 1 also has at least three ^

Cji image sensors (with i varying from 1 to N and N greater than or equal to 3) sensitive to X-rays and located so as to be exposed to X-rays coming from an associated focus Fj and having passed through the conveying volume Vt and more precisely, at least the region to be inspected of the object 2. Of course, the tube 7 and the image sensors Cji are located outside the conveying volume Vt to allow the free movement of the objects in this volume. Conventionally, the X-ray generator tubes 7 and the Cji image sensors are placed in an X-ray sealed enclosure.

The X-ray beams coming from a focus Fj associated with said image sensor Cji, pass through at least the inspected region, and form on the image sensor, the radiographic projection of the inspected region, according to a projection direction Dji ( Fig. 1 and 2). The direction of projection Dji is the oriented direction of the vector starting from the focus Fj to pass through the center Mji of the image sensor Cji. The focal point (s) Fj and the image sensors Cji are arranged so that each image sensor receives the radiographic projection of the region to be inspected in a direction of projection of the region to be inspected.

The installation 1 also comprises an acquisition system connected to the image sensors Cji, so as to acquire for each object 2 during its movement, at least three radiographic projections of the region to be inspected having different directions between them. It is recalled that the direction of projection associated with the radiographic image obtained is its direction starting from the focus and passing through the middle of the zone of the sensitive surface of the sensor, at the time of acquisition of the image. Thus, the at least three radiographic projections have directions of projections which form two by two, an angle between them.

The acquisition system is connected to a computer system, not shown, but of all types known per se. According to an advantageous embodiment characteristic, the computer system records with the aid of image sensors Cji, for each object of the series during its movement, radiographic images originating from a determined number of radiographic projections of the region to be inspect from different projection directions. Typically, the number of different projection directions Dji is between three and forty, and preferably between four and fifteen. According to an advantageous variant embodiment, the installation 1 comprises between three and forty Cji image sensors. According to a preferred variant embodiment, the installation 1 comprises between four and fifteen image sensors.

Comme cela sera expliqué en détail dans la suite de la description, le système informatique est programmé pour analyser, pour chaque objet, les au moins trois images radiographiques issues des au moins trois projections radiographiques de directions différentes de manière à construire un modèle géométrique numérique de chaque objet. Ce modèle géométrique numérique peut être réalisé de toute manière appropriée. Ainsi, le modèle géométrique numérique peut être constitué par au moins deux points tridimensionnels chacun appartenant à une surface frontière de la région à inspecter de l'objet et situés dans un plan non orthogonal à une direction de projection Djî, et non parallèle à la direction de déplacement T. Les au moins deux points peuvent appartenir à deux surfaces frontières différentes, par exemple pour mesurer une épaisseur ou un entrefer.

The digital geometric model can also consist of a section of the region to be inspected along a plane different from a plane orthogonal to a direction of projection Djî, and different from a pian parallel to the direction T of displacement. Furthermore, the digital geometric model can be constituted by at least one three-dimensional surface of the region to be inspected, different from a plane orthogonal to a direction of projection Djî and different from a plane parallel to the direction of displacement T.

Of course, the invention makes it possible to construct a digital geometric model with a large number of three-dimensional points, three-dimensional point clouds or complex three-dimensional surfaces.

According to the invention, the digital geometric model is constructed by using the material attenuation coefficient of the objects of the series and an a priori geometric model of the region to be inspected for the series of objects. In other words, the computer system uses to construct the digital geometric model of each object, on the one hand, the attenuation coefficient of the material of the objects and on the other hand, an a priori geometric model of the region to be inspected. for the series of objects.

Thus, the computer system takes into account the attenuation coefficient of the material of the objects being inspected for this calculation operation. Advantageously, the installation 1 comprises a device for making the material attenuation coefficient of the objects of a series available to the computer system.

This provision device can be produced by a mass memory, a man-machine interface or by a wireless or wireless computer network,

Likewise, the computer system has a so-called a priori geometric model of the region to be inspected in order to perform this calculation operation. Thus, the installation 1 comprises a device for making available to the computer system an a priori geometric model of the region to be inspected for the series of objects.

The device for making available to the computer system an a priori geometric model of the region to be inspected is a mass memory, a wired or wireless computer network or a man-machine interface.

As indicated in the definition part, the a priori geometric model is a digital model of the series of objects, serving as an initialization for the reconstruction software.

In the absence of knowledge of the a priori geometric model and of the single material property of the inspected objects, the reconstruction is extremely costly in terms of calculation, because for each point in 3D space its attenuation must be calculated. The present invention thus makes it possible to carry out measurements of linear dimensions on objects, with good precision, in a very short time and at low cost.

According to a first variant of the invention, the a priori geometric model is obtained by the digital computer design model of the objects of the series, produced during the design (3D CAD) of the objects. In this case, it is made available to the computer system by various possible means, such as a connection through a computer network, to a database containing several CAD models corresponding to the various series of objects capable of being measured in production, selection by the operator from a database internal to the installation, etc. .

According to a second variant of the invention, the a priori geometric model is obtained from a geometric digital model constructed from the measurement of one or more objects of the same series by a measuring device, for example by a machine to be measured by a feeler or an axial tomography device, the slowness of which compared to the invention is recalled. The a priori geometric model can be built by a fusion of measurements of several manufactured objects of the same series.

According to a third variant of the invention, the a priori geometric model is a geometric digital model generated by the computer system from values ​​entered and / or drawings made and / or shapes selected by an operator on the human interface. system machine.

For example, to provide the a priori geometric model in the case of a standard type M 13 external hexagon nut, with a threaded hole, the following is sufficient. The operator enters on a keypad the number and height of the flats, the diameter and the thread pitch, the system being configured to inspect metric nuts. No additional precise dimension is indicated. In another example, for the inspection of a polyethylene container, the operator gives only as information that the object is a closed cylinder at the bottom, surmounted by a cone, two diameters, two heights and one thickness are sufficient for that the computer system knows an a priori geometric model of the object to be inspected. According to another example, the computer system can through its interfaces receive technical descriptions of the a priori model such as a number, diameters, depths and positions of various bores present in a surface which would be part of the region to be inspected of a larger object. The description can be geometric for example if the computer system receives the number and general shape of the surfaces making it possible to describe it, the number of cavities, the number of faces or sides of a polyhedron. In summary, it should be understood that the a priori geometric model must at least contain sufficient technical, geometric, topological and / or numerical information, to inform the computer system about the 3D structure of the object,

The computer system determines for each object of the series, from the digital geometric model of the region to be inspected corresponding to said object of the series, at least one linear measurement of the region to be inspected in a direction contained in a plane not orthogonal to a direction of projection.

According to the invention, one and generally several dimensions are checked on the objects 2. The objective is generally to compare the measurements obtained on the objects with required values, for example defined by a quality service. These dimension measurements or the deviations of these measurements from the required values ​​can be displayed, recorded, etc. They can also be used to make object compliance decisions that can be sorted automatically.

The measurements can be taken from the measurements of the digital geometric model of the inspected region established for each object. For example, the inspected region may have a bore. In the digital geometric model, it is possible to determine measurements of diameter or depth of the bore, by calculating on the digital geometric model the distances between diametrically opposed surface elements. The object being mono-material, the determination of the position of the surface elements is precise.

Another way to determine bore diameter or depth measurements is by comparing the digital geometric model of the inspected region with a reference or theoretical geometric model.

The geometric reference model is an ideal model from the series of inspected objects. To realize a control dimensionnei f one can compare the digital geometric model of the region inspected with the geometric model of reference, by an algorithm comprising the mapping model, and then measuring the differences between the models. The geometric reference model can be obtained from CAD.

It is thus possible to carry out a matching operation of the digital geometric model of the inspected region with the reference geometric model, then to determine dimensional deviations by measuring distances between surface elements belonging to the reference model and surface elements belonging to the digital geometric model. In the example of the measurement of the bore, it is possible to virtually position a cylinder of maximum diameter that fits into the modeled internal surface of the bore, and likewise a cylinder of minimum diameter containing said surface. internal modeled, and to consider as measurements of the diameter of the bore in the inspected region, the diameter of one and / or the other of the registered and excribed cylinders.

According to a variant of the invention, the geometric reference model and the a priori geometric model are the same geometric model.

According to another variant of the invention, the a priori geometric model is less precise, less complete and / or is different from the reference geometric model.

In order to carry out such measurements, the installation advantageously comprises a device for making available to the computer system, values ​​of linear dimensions, and / or tolerances on these dimensions, and / or geometric reference models.

According to an advantageous embodiment characteristic, the computer system is connected to a device for displaying the linear measurement values ​​of the region to be inspected and / or dimensional deviations from reference values, and / or deviations between the model digital geometry of the inspected region and a reference geometric model.

For example, for a nut are displayed measurements such as a thread depth, an average thread pitch, an average thread root radius, a height, a minimum or maximum internal diameter, a flatness of one or more of its external faces. For a plastic container, the system will display the total height and for example the minimum diameter and the maximum diameter of the cylindrical part at a height predefined by the setting of the dimensions to be checked. The ribs can be displayed with different colors depending on their conformity or not.

According to an advantageous embodiment characteristic, the computer system is connected to a device for sorting objects according to the linear measurement of the region to be inspected. Thus, this sorting device can eject from the transport device, the objects considered to be defective in consideration of the measured linear dimensions.

According to an advantageous embodiment characteristic, the computer system is connected to a device for marking objects as a function of the linear measurement of the region to be inspected. This marking device can register, for example, the measured linear dimensions or the compliant or defective state of the object.

The relative positions of the foci Fj and the sensors Cji in a fixed reference frame Χ, Υ, Ζ of the installation are known to the computer system. This position can be obtained by hypothesis or by calibration. Calibration consists, for example, of placing or conveying a precision machined gauge into the installation.

Of course, the relative positions of the foci Fj and the image sensors Cji are various, it being remembered that the foci Fj and the image sensors Cji are positioned outside the conveying volume Vt.

According to an alternative embodiment, the installation 1 comprises a single hearth Fj = Fl arranged along one side of the conveying volume Vt and a series of image sensors Cji = Cli = Cil, C12, C13, ... arranged according to the opposite side of the conveying volume Vt to receive the rays coming from the focus Fl and having crossed the region to be inspected. In this example, the focus has an opening Of which is measured in at least one plane

arbitrary, as for example the plane X, Y in FIG. 1, which is greater than or equal to 120 °. This opening Of is considered at the outlet of the focal point, in the case where the installation comprises between the focal point and the volume Vt, or between the volume Vt and the image sensors, screens limiting the beams to only useful beams, in the goal of reducing the broadcast.

According to another variant embodiment, at least two X-ray production focal points Fj (F1 and F2) are positioned separately in two distinct positions and at least three image sensors Cji, sensitive to X-rays are placed so that each focal point is associated with at least one Cji image sensor, and each Cji image sensor is associated with a focal point and receives the X-rays coming from said focal point and passing through the region to be inspected. In this example, each focus has an opening greater than or equal to 60 ° so that the sum of the openings of the two homes is greater than or equal to 120 °.

In the exemplary embodiment illustrated in FIGS. 4 to 6, the installation 1 comprises three foci Fl, F2, F3 each associated with a separate generator tube 7 Installation 1 also includes five image sensors Cil, C12, C13, C14 and C15 each sensitive to X-rays coming from of the first associated focus F1, five image sensors C21, C22, C23, C24 and C25 each sensitive to X-rays coming from the second associated focus F2 and three image sensors C31, C32, C33 each sensitive to X-rays coming from the third associated home F3.

According to this exemplary embodiment, it should be noted that at least one focus (F1 and F2 in the example) from which a diverging X-ray beam emerges is positioned on one side of the intersecting plane Ps so that its beam passes through the intersecting plane Ps and the region to be inspected, while at least one image sensor Cji associated with said focus Fj to receive the X-rays coming from said focus Fj is arranged on the opposite side with respect to the secant plane Ps. (In the example, these are the five image sensors Cil, C12, C13, C14 and C15 each sensitive to X-rays from the associated focus Fl and the five image sensors C21, C22, C23, C24 and C25 each sensitive to X-rays from the associated outbreak F2).

According to an advantageous variant embodiment which is illustrated in FIGS. 4 to 6, a focus Fj from which a divergent X-ray beam emanates is arranged on one side of the conveying plane Pc so that its beam crosses the conveying plane Pc, while at least one image sensor Cji associated with said focus Fj to receive the X-rays from said focus is positioned on the opposite side with respect to the conveying plane Pc. In the example illustrated, a hearth F3 is placed above the conveying plane Pc while three image sensors C31, C32, C33 are positioned below the conveying plane Pc. Of course, the position between the focus and the image sensors can be reversed relative to the conveying plane.

According to an advantageous variant embodiment, at least one of the foci Fj is placed in the conveying plane Pc. Preferably, these foci cooperate with associated image sensors located at their opposite relative to the intersecting plane Ps. Thus, in the case of transporting objects arranged on a flat conveyor, this arrangement allows that in the radiographic images, the projections of objects are not superimposed on the projection of the conveyor. Thus, in the digital geometric model of objects, the part of the object in contact with the conveyor can be precisely determined.

According to an advantageous embodiment characteristic, the arrangement of the image sensors Cji and of the focal points is such that the X-rays coming from the focal point (s) Fj and reaching the image sensors Cji only pass through one region to be inspected at a time. In other words, X-rays only pass through one object at a time. It should be noted that the installation may include a system for controlling the spacing between successive scrolling objects.

An object of the invention is to obtain a method which is not only rapid, but also inexpensive, capable of calculating with the precision necessary for a dimensional check. The invention aims to reduce the number of images necessary for reconstruction to the minimum number making it possible to achieve the desired dimensional precision. For example, the invention allows, with nine projections and a limited number of images of the inspected region, to measure the internal diameter of a cylinder at +/- 0.05 mm. Advantageously, the installation according to the invention comprises between one and four focal points Fj and preferably one or two focal points Fj and preferably between four and fifteen image sensors Cji.

Selon l'invention, ii convient de disposer les capteurs d'images et ie ou les foyers afin que la combinaison des au moins trois directions de projections optimise la détermination du modèle géométrique numérique de la région inspectée, en considérant qu'il faut laisser le volume traversé Vt libre pour la circulation des objets. Les régies ci-après sont avantageusement mises en œuvre dans le cadre de l'invention, ces règles étant valables pour des capteurs d'images linéaires ou matricielles.

In the following, an angle is an absolute value. Figs. 7 and 8 illustrate two directions of projection Dji and D'jï which are also vectors. These Figures show the angle r between these two directions of projection, ie r = (Dïj D'ij) and s the angle complementary to the angle r, or s = 180 ° -r. By definition, the useful angle a between two different directions of projection Dji and D'ji, is the smallest of the angles r and s, that is to say a = Min (r, s). Thus, the useful angle a is the smallest of the angles formed by the two straight lines bearing the directions of projection Dji, D'ji and brought back to any point of the inspected region.

According to an advantageous variant of the invention, at least two images from two radiographic projections in two different directions Dji and D'ji are acquired for each object, forming between them a useful angle a greater than or equal to 45 ° and less than or equal at 90 °. According to an advantageous variant embodiment, at least two images from two radiographic projections in two different directions forming between them a useful angle a greater than or equal to 60 ° and less than or equal to 90 ° are acquired for each object.

To do this, the installation 1 according to the invention comprises at least one focus and two image sensors arranged so that the directions of projection of the inspected region which they receive have between them a useful angle greater than or equal to 45 ° and less than or equal to 90 ° and, advantageously greater than or equal to 60 ° and less than or equal to 90 °.

For example, as illustrated in Fig, 4, the useful angle a between the directions D15 and DU, and between the directions D13 and D25 are greater than 45 °. Obviously it must be understood that at least one useful angle is greater than or equal to 45 ° and less than or equal to 90 ° and advantageously that at least one useful angle is greater than or equal to 60 ° and less than or equal to 90 ° and the other useful angles between two directions Dji, D'ji are arbitrary. Those skilled in the art from this rule will know how to look for an arrangement which offers the most complete possible distribution of the directions of projections of the inspected region.

According to another advantageous characteristic, for each object, the computer system acquires at least one radiographic image of the inspected region corresponding to a direction of projection forming an opening angle β determined with the direction of displacement T.

As illustrated in Figs. 9 and 10, the angle p between a direction of projection (vector Dji) and the trajectory of the objects (vector T) is considered, i.e. the angle p = (Dji, T) that is to say p = (DU, T) and p = (D12, T) in the example illustrated in Fig. 9 and p = (D22, T) and p = (DU, T) in the example illustrated in FIG. 10. The angle q complementary to the angle p is such that q = 180 ° -p. By definition, the opening angle β between a direction of projection Dji and the trajectory T is the smallest of the angles p and q, namely β = Min (p, q). Thus, the opening angle β is the smallest of the angles formed by the two straight lines, one carrying the direction of projection Dji and the other the trajectory T, brought back to any point of the inspected region.

According to another advantageous characteristic, for each object, the computer system acquires at least one radiographic image of the inspected region corresponding to a projection direction Dji having with the direction of displacement T, an opening angle β between 10 ° and 60 °. In other words, the installation according to the invention comprises at least one focus and an image sensor Cji arranged so that, when an object crosses the field of the image sensors, the projection direction Dji of the region inspected on the image sensor Cjî makes an opening angle β with the direction of movement T of between 10 ° and 60 °.

In other words, the configuration of the installation 1 is optimized to reduce its size in the direction of movement while maintaining a traversed volume Vt suitable for the objects and good reconstruction quality.

Due to the volume Vt traversed, the installation does not produce a projection around the direction of displacement T. The volume traversed Vt imposes a minimum beta angle. According to the invention β min = 10 °. There is no sensor arranged so as to provide a projection with an angle β less than 10 °.

It must be deduced from the above that the distribution of the angles of projections for each object is not uniform according to the invention.

As shown in Fig. 9, the distribution of the angles of projection presents a gap, which one calls a blind spot region, of twice 2 x 10 ° or 20 °, instead of having a complete coverage over 180 °.

For example as illustrated in FIG. 9, an installation according to the invention comprises at least one focus Fl and two image sensors Cil, C12 whose projection directions DU, D12 define with the direction of movement T, an opening angle β between 10 ° and 60 ° corresponding respectively to the angles p and q. In the example illustrated in Fig. 10, the installation comprises at least one image sensor Cil, associated with a focus F1 and an image sensor C22 associated with a focus F2. The directions of projections DU, D22 define the opening angle β between 10 ° and 60 ° and corresponding to the angles p. Likewise, the installation illustrated in FIG. 4, comprises an Cil image sensor associated with the focus Fl and the direction of projection D22 of which makes an angle β between 10 ° and 60 °,

Cji image sensors are of the matrix or linear type.

According to a preferred variant embodiment, the installation 1 comprises linear image sensors. According to this preferred variant, each image sensor Cji comprises a linear array of elements sensitive to X-rays, distributed along a support line Ljî defining with the associated focus Fj, a projection plane Pji containing the direction of projection Dji (Fîg . 2). These image sensors Cji are arranged so that at least m sensitive elements of each of these image sensors receive the radiographic projection of the region to be inspected by the X-ray beam coming from the associated focus Fj, with the planes of projection Pji for the various sensors which are distinct from one another and not parallel to the conveying plane Pc. The number m of sensitive elements of each sensor of linear images is greater than 128, preferably greater than 512. The distance between neighboring sensitive elements (called “pitch” or “pitch”) and / or the dimension of the sensitive elements is preferably less than 800 μm. The reading frequency of the image lines is preferably greater than 100 Hz, advantageously greater than 1 kHz. Of course, these parameters are adapted according to the size of the objects, the required precision and the scrolling speed.

According to an advantageous embodiment characteristic, at least three linear image sensors Cji have their support lines Ljî parallel to each other.

According to another advantageous embodiment characteristic, at least three linear image sensors Cji have their support lines Ljî orthogonal to the conveying plane Pc,

According to a variant, a focus Fj is positioned so that its beam passes through the inspected region and then the conveying plane Pc. In addition, at least one associated linear image sensor Cji is positioned opposite the focus Fj relative to the conveying plane Pc and so that its straight support Ljî is parallel to the conveying plane Pc.

According to these variant embodiments with linear image sensors, the acquisition system acquires using each of the at least three image sensors Cji, at each incremental displacement of each object on the trajectory, linear images radiographs of the region to be inspected according to a number chosen so that for each object, the whole of the region to be inspected is completely represented in the set of linear radiographic images. Thus, during the movement of an object, each image sensor is able to acquire linear radiographic images so that the whole of the region to be inspected of the object is completely represented in the set of linear radiographic images. obtained from said image sensor. Thus, for each object, at least three sets of radiographic linear images of the region to be inspected are obtained which are then analyzed. It is possible to build up matrix radiographic images of the inspected region by juxtaposing sets of linear radiographic images. But the reconstruction of the geometric model and the measurement do not necessarily impose it

Il est à noter que compte tenu du volume traversé Vt, aucune projection radiographique n'est acquise dans la région d'angle mort (β < ± 10°) située de part et d'autre de la direction de déplacement T. Le procédé selon l'invention permet, malgré l'absence de projections radiographiques dans cet intervalle d'angles, de reconstruire, grâce au modèle géométrique a priori, un modèle géométrique numérique précis et complet de l'objet mono-matériau. Il est ainsi possible de réaliser des mesures de dimension linéaire sur tout le modèle géométrique numérique et en particulier selon des directions non orthogonales aux directions de projection possibles, y compris des mesures de dimension linéaire selon des directions de mesure orthogonales aux directions de projections manquantes correspondant à la région d'angle mort située de part et d'autre de îa direction de déplacement T. En effet, sans le procédé selon l'invention, par exemple avec les méthodes destinées à la tomographie axiale « complètes » traditionnelles, dans le cas où aucune projection radiographique n'est acquise selon les directions d'un angle mort, alors le modèle reconstruit présente également dans un secteur angulaire orthogonal à l'angle mort, des erreurs de reconstruction rendant impossible de déterminer une surface précisément et donc rendant impossible tout mesure de dimension linéaire d'un objet mono-matériau.

Thus, as illustrated in Figs. 11 and 12, according to the invention, no projection is possible in a dead angle of for example 20 ° (β min = 10 °). According to the prior art, no precise measurement could be made in the direction A, which is not orthogonal to any of the directions of projection, The direction A is not close to the orthogonal of any of the directions of projection to at minus 10 ° near. According to the invention, thanks to the reconstruction from a priori models of the series of objects and of the constant and uniform attenuation, the measurement of the internal diameter in direction A (distance al) and the measurement of the distance between the two exterior sides perpendicular to direction A (distance a2) are correct and precise.

Of course, the number of focal points, the number of image sensors associated with each focal point, and their relative arrangements are chosen in any suitable manner as a function of the degree of measurement precision desired, the shape of the objects and their spacing on them. the conveyor.

It should be noted that in industrial mass production, it is possible that several series are present at the same time on the same production or control line. In this case, the installation comprises a system for indicating to the computer system the series to which each of the objects belongs in order to implement the method of the invention for all the objects of the same series. In fact, the installation according to the invention can be used to inspect a flow of manufactured objects composed of several series of different objects, for example a first series and a second series. The series can differ by the shape of the mono-material objects or by the specific attenuation coefficient or both. In this case, the installation must be fitted wit
CLAIMS

1 - Method of automatic measurement of linear dimensions of manufactured objects (2) of a series consisting of:

- choose a series of manufactured objects (2) in which each of said objects is made of a material with a constant attenuation coefficient at any point of the object;

- choose at least one region to inspect objects in which at least one linear dimension is to be measured;

- transport, by means of a transport device, the moving objects in a direction (T) of movement seion a substantially rectilinear path in a conveying plane (Pc), these objects generating a conveying volume (Vt) during of their displacement;

- positioning, outside the conveying volume (Vt), at least one focus (Fj) of an X-ray generator tube and image sensors (Cjî) each exposed and sensitive to X-rays from an associated focus ( Fj), these X-rays having passed through at least the region to be inspected, producing on each image sensor a radiographic projection in the direction of projection (Dji);

- acquire using image sensors (Cji), for each object during its movement, at least three radiographic images of the region to be inspected, obtained from at least three radiographic projections of the region to be inspected, of which the directions of projection (Dji) are different from each other;

- analyze the at least three radiographic images, using a computer system;

- make available to the computer system, an a priori geometric model of the region to be inspected for the series of objects;

- determine using the computer system by considering a constant attenuation coefficient and from the a priori geometric model and at least three radiographic images of the region to be inspected, a digital geometric model of the region to be inspected for each object of the series consisting of at least two three-dimensional points each

belonging to a border surface of the region to be inspected and situated in a plane not orthogonal to a direction of projection Dji;

- for each object in the series, determine from the digital geometric model of the region to be inspected, at least one linear dimension measure of the region to be inspected as being the distance between at least two three-dimensional points each belonging to a boundary surface of ia region to be inspected and located in a plane not orthogonal to a direction of projection (Dji).

2 - Method according to claim 1, characterized in that it consists in determining a digital geometric model consisting of:

- at least two three-dimensional points in space each belonging to a border surface of the region to be inspected and located in a plane not orthogonal to a direction of projection (Dji), and not parallel to the direction (T) of displacement;

- and / or at least one three-dimensional surface of the region to be inspected containing points not belonging to a plane orthogonal to a direction of projection (Dji), and not belonging to a plane parallel to the direction (T) of displacement;

- And / or at least one section of the region to be inspected, according to a plan different from a plane orthogonal to a direction of projection (Dji) and different from a plane parallel to the direction (T) of displacement.

3 - Method according to one of the preceding claims, characterized in that it consists in making the value of the constant attenuation coefficient available to the computer system.

4 - Method according to one of the preceding claims, characterized in that it consists in making available to the computer system, the a priori geometric model of the region to be inspected of the series, obtained by:

- the digital computer design model of the objects in the series;

- or the geometric digital model obtained from the measurement of one or more objects of the same series by a measuring device; - Or! e geometric digital model generated by the computer system from values ​​entered and / or drawings made and / or shapes selected by an operator on a man-machine interface of the computer system.

5 - Method according to one of the preceding claims, characterized in that a focal point from which emanates a diverging X-ray beam with an opening greater than or equal to 120 ° or at least two focal points from which emanate from the beams. X divergent with a sum of the openings greater than or equal to 120 °.

6 - Method according to one of the preceding claims, characterized in that it consists in having at least one focus in the conveying plane (Pc).

7 - Method according to one of the preceding claims, characterized in that it consists in:

- have on one side of a secant plane (Ps) of the conveying volume (Vt), orthogonal to the conveying plane (Pc), a focus (Fj) from which a diverging X-ray beam emerges, so that its beam crosses the secant plane (Ps) and the region to be inspected;

- Having on the opposite side with respect to the secant plane (Ps), at least one image sensor (Cji) associated with said focus (Fj) to receive the X-rays coming from said focus (Fj).

8 - Method according to one of the preceding claims, characterized in that it consists in:

- Have on one side of the conveying plane (Pc), a focus (Fj) from which a divergent X-ray beam emanates, so that its beam passes through the conveying plane (Pc);

- Having on the opposite side with respect to the conveying plane (Pc), at least one image sensor (Cji) associated with said focal point (Fj) to receive the X-rays coming from said focal point (Fj).

9 - Method according to one of the preceding claims, characterized in that it consists in acquiring using image sensors (Cji), for each object of the series during its movement, at least two images

radiographic images of the inspected region corresponding to projection directions (Dji) defining a useful angle (a) greater than or equal to 45 ° and less than or equal to 90 ° and, advantageously greater than or equal to 60 ° and less than or equal to 90 ° ,

10 - Method according to one of the preceding claims, characterized in that it consists in acquiring using image sensors (Cjï), for each object of the series during its movement at least one radiographic image of the inspected region corresponding to a direction of projection (Dji) having an opening angle (β) with the direction of displacement (T) of between 10 ° and 60 °.

11 - Method according to one of the preceding claims, characterized in that it consists in acquiring with the aid of the image sensors (Cjï), for each object of the series during its movement, no radiographic image of the inspected region corresponding to a direction of projection (Dji) having an opening angle (β) with the direction of displacement (T) of less than 10 °.

12 - Method according to one of the preceding claims, characterized in that it consists in making and acquiring radiographic projections of the inspected region of an object so that the X-rays coming from the focus (s) and reaching the image sensors (Cji) do not cross other object.

13 - Method according to one of the preceding claims, characterized in that it consists in acquiring using the image sensors (Cji), for each object of the series during its movement, radiographic images from between three and forty, radiographic projections of the area to be inspected from different directions.

14 - Method according to one of the preceding claims, characterized in that it consists in acquiring with the aid of image sensors (Cji), for each object of the series during its movement, radiographic images from between four and fifteen radiographic projections of the region to be inspected from different directions.

15 - Method according to one of the preceding claims, characterized in that:

- the image sensors (Cji) are of the linear type each comprising a linear network of elements sensitive to X-rays, distributed along a support line (Ljï) defining with the associated focus (Fj), a projection plan (Pji ) containing the direction of projection (Dji), these image sensors being arranged so that:

- at least m sensitive elements of each of these image sensors receive the radiographic projection of the region to be inspected by the X-ray beam coming from the associated focus (Fj);

- the projection planes (Pji) for the different sensors are distinct from one another and not parallel to the conveying plane (Pc);

- using each of the at least three linear image sensors (Cji) is acquired, at each incremental displacement of each container along the trajectory (T), radiographic linear images of the region to be inspected according to a number chosen in order to that for each object, the whole of the region to be inspected is represented completely in the set of linear radiographic images;

the at least three sets of radiographic linear images of the region to be inspected are analyzed for each object.

16 - Installation for automatic measurement of linear dimensions of at least one region to be inspected of manufactured objects of a series, the installation comprising:

- a device for transporting objects in a direction materialized by a displacement vector (T), along a substantially rectilinear path in a conveying plane (Pc), the objects traveling through a conveying volume (Vt) extended in the direction (T) );

- at least one focus (Fj) of an X-ray generator tube located outside the traversed volume (Vt), and creating a diverging X-ray beam directed to pass through at least one region to be inspected of the object;

- at least three image sensors (Cji), located outside the conveying volume (Vt), so as to receive X-rays from a

associated focus (Fj), the focus (s) (Fj) and image sensors (Cji) being arranged so that each image sensor receives the radiographic projection of the region to be inspected by the rays coming from the focus (Fj) when the object crosses these rays, the directions of projection of these radiographic projections being different from one another;

an acquisition system connected to the image sensors (Cji), so as to acquire for each object during its movement, at least three radiographic projections of the region to be inspected with all different directions of projection (Dij);

a device for making available for a computer system, an a priori geometric model of the region to be inspected for the series of objects; the computer system:

• determining a digital geometric model for each object in the series consisting of at least two three-dimensional points each belonging to a boundary surface of the region to be inspected and located in a plane not orthogonal to a direction of projection (Dji), considering a constant attenuation coefficient of the material for the objects, from the a priori geometric model and at least three radiographic projections of the region to be inspected;

"Determining for each object in the series, from the digital geometric model of the region to be inspected, at least one linear measure of the region to be inspected as being the distance between at least two three-dimensional points each belonging to a boundary surface of the region to be inspected and located in a non-orthogonal projection plane (Dji).

17 - Installation according to claim 16, characterized in that it comprises a device for making available to the computer system, the attenuation coefficient of the material of the objects in a series.

18 ~ Installation according to claim 17, characterized in that the device for making available to the computer system, an a priori geometric model of the region to be inspected is a mass memory, a wireless or wireless computer network or an interface man machine.

19 - Installation according to one of claims 16 to 18, characterized in that it comprises a device for making available for the computer system, values ​​and / or tolerances for the required linear dimensions, and / or at minus one geometric reference model.

20 - Installation according to one of claims 16 to 19, characterized in that it comprises at least two foci (Fl, F2) for producing X-rays, positioned separately in two distinct positions and at least three image sensors ( Cji), sensitive to X-rays and positioned so that;

- Each focus emits its beam through at least the region to be inspected to reach at least one associated sensor (Cji);

- Each sensor (Cji) is associated with a focus and receives the X-rays from said focus after passing through the region to be inspected.

21 - Installation according to one of claims 16 to 19, characterized in that it comprises at least one focal point from which a divergent X-ray beam emerges with an opening greater than or equal to 120 ° or at least two focal points of which are from diverging X-ray beams with a sum of the apertures greater than or equal to 120 °.

22 - Installation according to one of claims 16 to 21, characterized in that it comprises at least one hearth disposed in the conveying plane (Pc).

23 - Installation according to one of claims 16 to 22, characterized in that it comprises:

- on one side of a plane secant (Ps) to the conveying volume and orthogonal to the conveying plane (Pc), a focus (Fj) from which a divergent X-ray beam emerges, so that its beam crosses the plane secant (Ps) and the region to be inspected;

- on the opposite side with respect to the secant plane (Ps), at least one image sensor (Cji) associated with said focus (Fj) to receive the X-rays coming from said focus (Fj).

24 - Installation according to one of claims 16 to 23, characterized in that it comprises:

- on one side of the conveying plane (Pc), a focus (Fj) from which a diverging X-ray beam emerges, so that its beam passes through the conveying plane (Pc);

- on the opposite side with respect to the conveying plane (Pc), at least one image sensor (Cji) associated with said focus (Fj) for receiving the X-rays coming from said focus (Fj).

25 - Installation according to one of claims 16 to 24, characterized in that at least one focus and two image sensors are arranged so that the directions of projection of the inspected region they receive have an angle between them useful (a) greater than or equal to 45 ° and less than or equal to 90 ° and, advantageously greater than or equal to 60 ° and less than or equal to 90 °.

26 - Installation according to one of claims 16 to 25, characterized in that at least one focus and one image sensor (Cji) are arranged so that, when an object passes through the field of the sensors, the direction of projection (Dji) of the inspected region on the image sensor (Cji) makes an opening angle (β) with the direction of displacement (T) of between 10 ° and 60 °.

27 - Installation according to one of claims 16 to 26, characterized in that, no focus (Fj) of an X-ray generator tube being located in the volume traversed (Vt), no image sensors (Cji ), not being located in the conveying volume (Vt), when an object crosses the field of the sensors, the direction of projection (Dji) of the region inspected on the image sensor (Cji) never makes an angle opening (β) with the direction of movement (T) less than 10 °.

28 - Installation according to one of claims 16 to 27, characterized in that the image sensors (Cji) and the foci (Fj) are arranged so that the X-rays coming from the foci and reaching the sensors of images (Cji) and crossing the region of one object do not cross another object at the same time.

29 - Installation according to one of claims 16 to 28, characterized in that it comprises between one and four foci (Fj), from one or more tubes generating X-rays.

30 - installation according to one of claims 16 to 29, characterized in that the number and arrangement of image sensors (Cji) and associated foci, are such that for each object of the series during its movement, the X-ray projections of the region to be inspected on the image sensors have between three and forty different projection directions.

31 - Installation according to one of claims 16 to 30, characterized in that the number and arrangement of image sensors (Cji) and associated foci, are such that for each object of the series during its movement, the X-ray projections of the region to be inspected on the image sensors have between four and fifteen different projection directions.

32 - Installation according to one of claims 16 to 31, characterized in that:

- the image sensors (Cji) are of the linear type and each comprise a linear network of elements sensitive to X-rays, distributed along a support line (Lji) defining with the associated focus (Fj), a projection plane ( Pji) containing the direction of projection (Dji), these image sensors being arranged so that:

• at least m sensitive elements of each of these image sensors receive the radiographic projection of the region to be inspected by the X-ray beam coming from the associated focus (Fj);

β the projection planes (Pji) for the different sensors are distinct from one another and not parallel to the conveying plane (Pc).

33 - Installation according to claim 32, characterized in that at least three linear image sensors (Cji) have their support lines (Lji) parallel to each other.

34 - Installation according to one of claims 32 and 33, characterized in that at least three linear image sensors (Cji) have their support lines (Ljî) orthogonal to the conveying plane (Pc).

35 - Installation according to one of claims 32 to 34, characterized in that a focus (Fj) is positioned on one side of the conveying plane (Pc), and in that at least one image sensor (Cji) linear associated, is positioned on the side opposite the hearth (Fj) relative to the conveying plane (Pc) and so that its straight support (Lji) is parallel to the conveying plane (Pc).