Acquisition method and system configured for implementing such a method

Abstract

Acquisition method and system configured for implementing such a method The invention relates to a method for acquiring, by an acquisition device (1), the light image originating from an object (2) to be controlled by phase-shift deflectometry after a series of light images having sinusoidal fringes, characterized in that the method comprises: adjusting an optical mechanism (11) according to a depth of field (4) whose sharpness distance is less than the thickness of the object (2), positioning a first portion of the object (2) in this depth of field (4), acquiring a first image in reflection or transmission originating from the first portion of the object (2), moving a second portion of the object (2) in this depth of field (4), acquiring a second image originating from a second portion of the object (2),the construction of a light image by combining images acquired from different portions of the object (2). Figure to be published with the abstract: Fig. 1,

Description

Title of the invention: Acquisition method and system configured for implementing such a method

[0001] The present invention relates to the field of systems for controlling transparent components or object surfaces and more particularly to the field of developing such control systems within the framework of a process for acquiring images of these transparent components or object surfaces.

[0002] In the context of the production of components requiring high quality standards, it is imperative to carry out a rigorous control of each of the manufactured parts. For transparent components, this control operation is conventionally carried out by a verification of technical properties relating in particular to the quality of the transmission of a light signal which passes through this component so as to ensure the absence of defects in the thickness of the component likely to be the cause of optical aberrations in the context of this transmission. For similar purposes, this control operation is also likely to be intended to ensure the quality of the reflection properties of one or more of the surfaces of the object examined.For the purpose of efficiency, this control operation is based on the principle of phase-shift deflectometry associated with a mechanism for acquiring the light image likely to be reflected or transmitted by the object or component to be examined. This control by deflectometry is based in particular on the acquisition and analysis of phenomena of deviation of one or more light signals by the controlled element during their reflections and / or their transmissions by comparison with perfect or theoretically predictable modifications of these light signals.

[0003] The precision of the analysis and identification of technical specificities of an object or component by phase shift deflectometry is based in particular on the quality of the characterization of the phenomena of deviation of the light image likely to be reflected or transmitted by the object or component examined. The accuracy of the acquisition of the phenomena of deviation of the light image in the context of phase shift deflectometry thus conditions the quality of the analysis of the object or component examined. The precision of the adjustment allowing the visualization of the alterations of the light signals by the object or component examined is therefore a necessary, if not essential, prerequisite for the acquisition operation so as to ensure sufficient definition on the whole of the object being checked despite its shape, depth and volume.Indeed, the identification of technical specificities of an object or a component by offset deflectometry. phase is likely to be implemented for the control and characterization of defects for objects presenting large surfaces and / or significant transparent thicknesses.

[0004] The technical solution currently implemented to guarantee this sharpness requirement consists of adjusting the acquisition mechanism so that it has a depth of field that is sufficiently wide so that the entire structure of the object or component to be examined is present. However, if such a solution makes it possible to overcome the constraints of shape and volume imposed by the object to be examined, the increase in the depth of field used also requires restricting the level of definition of the light image reflected or transmitted by the object examined during acquisition. The sharpness of the light image reflected or transmitted by the object or component examined is then limited by the volume and shape of this object so that the maximum conceivable degree of precision of analysis and quality of control of the object is capped.

[0005] The present invention aims to overcome these drawbacks by proposing a solution which makes it possible, in the context of a characterization by phase-shift deflectometry of technical features of an object or a component, to carry out the acquisition of the light image coming from the object to be checked with a level of definition and detail sufficiently high to allow a detailed analysis of possible defects in the thickness or on the surface of the checked object, while freeing itself from the constraints which the volume and / or the shape of this object usually imposes on the prior adjustments which this acquisition requires.

[0006] The invention thus relates to a method of acquisition by an acquisition device, through an optical mechanism comprising at least one lens and a diaphragm, of the light image coming from an object to be controlled by phase-shift deflectometry, in reflection or in transmission, the part of the object to be controlled corresponding to a volume arranged between two planes parallel to each other and perpendicular to the acquisition axis, characterized in that the method comprises: - a step of carrying out an adjustment of the optical mechanism according to a depth of field whose sharpness distance is less than the distance separating, along the acquisition axis, the two parallel planes of the volume of the part of the object to be controlled, - a step of positioning the object so that a first portion of the object is positioned in the depth of field of the optical mechanism, - a step of projecting onto or through the object at least one series of at least two light images emitted by at least one projection device and corresponding to at least one succession of light and dark sinusoidal fringes, each image of the series having identical sinusoidal fringes with a phase shift compared to the other images in the series, this shift being less than the phase of the sinusoids, - a step of acquiring a first image originating from the first portion of the object and corresponding to the reflection or transmission by the object of an image originating from at least one series of at least two light images emitted by at least one projection device, - a step of moving the object relative to the assembly combining the acquisition device with the optical mechanism, so that at least a second portion of the object is positioned in the depth of field of the optical mechanism, - a step of projecting onto or through the object at least one series of at least two light images by the at least one projection device, - a step of acquiring at least one second image originating from the at least one second portion of the object and corresponding to the reflection or transmission by the object of the same image originating from the at least one series of at least two light images emitted by at least one projection device during the step of acquiring the first image originating from the first portion of the object, - a step of constructing the light image coming from a part of the object to be controlled by combining the portion of the first image coming from the first portion of the object with the portion of the at least one second image coming from the at least one second portion of the object.

[0007] The invention also relates to a system configured for implementing an acquisition method according to the invention, characterized in that the system comprises: - a means of supporting an object to be controlled, - a device for projecting light against at least one surface of the object to be checked, - an acquisition device associated with an optical mechanism comprising at least one lens and a diaphragm, - a device for processing at least two images acquired by the acquisition device for the construction of at least one light image of a part of the object to be controlled.

[0008] The invention will be better understood from the following description, which relates to the preferred embodiments, given as non-limiting examples, and explained with reference to the appended schematic drawings, in which: - [Fig.l] is a schematic illustration of an example of positioning an acquisition device relative to an object to be controlled during a step of acquiring a first image coming from the first portion of the object within the framework of an acquisition method according to the invention, - [Fig.2] is a schematic illustration of an example of positioning an acquisition device relative to an object to be controlled during a step of acquiring a second image coming from the second portion of the object within the framework of an acquisition method according to the invention.

[0009] The invention thus relates to a method of acquisition by an acquisition device 1, through an optical mechanism 11 comprising at least one lens and one diaphragm, of the light image coming from an object 2 to be controlled by phase-shift deflectometry, in reflection or in transmission, the part of the object 2 to be controlled corresponding to a volume arranged between two planes 31, 32 parallel to each other and perpendicular to the acquisition axis 33, characterized in that the method comprises: - a step of carrying out an adjustment of the optical mechanism 11 according to a depth of field 4 whose sharpness distance is less than the distance separating, along the acquisition axis 33, the two parallel planes 31, 32 of the volume of the part of the object 2 to be controlled, - a step of positioning the object 2 so that a first portion of the object 2 is positioned in the depth of field 4 of the optical mechanism 11, - a step of projection onto or through the object 2 of at least one series of at least two light images emitted by at least one projection device and corresponding to at least one succession of light and dark sinusoidal fringes, each image of the series having identical sinusoidal fringes with a phase shift relative to the other images of the series, this shift being less than the phase of the sinusoids, - a step of acquiring a first image originating from the first portion of the object 2 and corresponding to the reflection or transmission by the object 2 of an image originating from at least one series of at least two light images emitted by at least one projection device, - a step of moving the object 2 relative to the assembly combining the acquisition device 1 with the optical mechanism 11, so that at least a second portion of the object 2 is positioned in the depth of field 4 of the optical mechanism 11, - a step of projecting onto or through the object 2 at least one series of at least two light images by the at least one projection device, - a step of acquiring at least one second image originating from the at least one second portion of the object 2 and corresponding to the reflection or transmission by the object 2 of the same image originating from the at least one series of at least two light images emitted by at least one projection device during the step of acquiring the first image originating from the first portion of the object 2, - a step of constructing the light image coming from a part of the object 2 to be controlled by combining the portion of the first image coming from the first portion of the object 2 with the portion of the at least one second image coming from the at least one second portion of the object 2.

[0010] Phase shift deflectometry involves a successive projection of specific light images onto the surface of an object 2 or an element to be analyzed, so that the transmission or reflection of these light images causes deviations of the light signal. Also, by comparing these measured effective divergences of the light signal with the theoretical deformations envisaged or conceivable of the signal for a perfect surface of the object 2 or for an irreproachable quality of transparency of the material of the object 2, the defects of the surface or of the material of the object 2 are able to be characterized.The projected light images correspond to series of images which essentially relate to a succession of light and dark sinusoidal fringes so that each image of the same series has identical sinusoidal fringes with a phase shift relative to the other images of the series, this shift being less than the phase of the sinusoids. These sinusoidal fringes are preferentially oriented along the same axis of the image. In the context of phase shift deflectometry, different and complementary measurements involving several different series of images are also likely to be carried out so that, between two different groups of measurements, the series of images differ, for example, by the amplitude of their phase shift or with a difference in the axis of the sinusoidal fringes.

[0011] In the context of the method of the invention, the same series of light images is successively projected onto or through different portions of surfaces of the object 2 or of the element to be analyzed, so that the light images successively transmitted or reflected by the object 2 or the part of the object 2 analyzed are recorded to be combined with each other so as to obtain images having a quality definition respectively covering all of the different portions of surfaces of the object 2 or the element analyzed. Each of the reconstructed images thus obtained then makes it possible to characterize the different deviations of the light signals transmitted or reflected by the object 2 or the part of the object 2 analyzed during the projection of the series of images onto or through the object 2 by the at least one projection device.

[0012] The method of the invention thus consists in multiplying the number of acquisitions of the object 2 to be controlled by taking several shots of the same light signal deflected by the object 2 so that each of these acquisitions, from the same point of view, is specifically adapted to the production of an optimal shot of a different respective surface of the object 2. Also, in order to ensure optimized sharpness of each of these acquisitions and more particularly finesse in the characterization of the distortions brought by the object 2 to the light signal, each of the acquisitions is carried out with a reduced depth of field 4, that is to say a depth of field 4 which does not allow an optimal shot to be taken on all the surfaces of the object 2 analyzed, but only a shot of ideal quality at the level of a selected portion of the surfaces of the object 2 analyzed.However, acquisition with a reduced depth of field 4 allows an increase in the fineness of the image and its details at the level of a specific surface or portion of the surface of the object 2 to be controlled without requiring too much closure of the diaphragm. The greater opening of the diaphragm in the context of a reduced depth of field 4 compared to an acquisition carried out in the context of a shot with a wider depth of field 4 also allows an increase in the received brightness so that the quality of the image obtained is improved.

[0013] In the context of the implementation of the acquisition method according to the invention, the reduction of the depth of field 4 to improve the fineness and the quality of each of the acquisitions requires increasing the number of acquisitions of depths of field 4 of identical width so that the respective depths of field 4 of these different acquisitions cover, along the acquisition axis 33, the entire distance which separates two parallel planes 31, 32 forming a volume comprising the part of the object 2 to be controlled. In the context of these different acquisitions, the depths of field 4 of identical width are selected and / or arranged to be juxtaposed and / or partially superimposed on the entire surface, thickness or depth of the object 2 to be controlled, along the acquisition axis 33.

[0014] It should be noted that, in the context of the method according to the invention, during the step of moving the object 2 relative to the assembly combining the acquisition device 1 with the optical mechanism 11, the object 2 preferably remains fixed with the at least one projection device. The conservation of the position of the object 2 relative to the projection device thus makes it possible to confer a strictly identical projection of the at least one series of light images onto or through the surface of the object 2 to be analyzed regardless of the position of the object 2 relative to the assembly combining the acquisition device 1 with the optical mechanism 11. Also, the operation of reconstructing the images is carried out from the light images impacting in a strictly identical manner the surface of the object 2 to be analyzed.

[0015] According to an example relating to an alternative implementation of the acquisition method according to the invention, this method is characterized in that, when the light image comes in transmission from the object 2 to be controlled, the adjustment of the optical mechanism 11 is carried out according to a depth of field 4 whose sharpness distance is greater than or equal to the thickness of at least one portion of the object 2 to be controlled reported on the acquisition axis 33. According to this alternative implementation, the depth of field 4 of the adjustment of the mechanism is determined according to the desired acquisition fineness and the unit amplitude of depth of field 4 desired for each acquisition step.Thus, the sharpness distance which corresponds to the distance reported on the acquisition axis 33 along which the acquisition presents a sufficient level of image quality, covers a depth of field amplitude 4 which defines the unit amplitude used in the context of the implementation of the method. In the context of the implementation variant of the method, this identical, or even similar, unit amplitude for each of the acquisitions is selected to be the largest. In this case, this unit amplitude corresponds at least to the length or depth of the portion of the object 2, along the acquisition axis 33, for which a single acquisition is sought. Thus, this unit amplitude corresponds at most to the distance, depth or thickness at which an analysis of the object 2 or of the portion of the object 2 is sought.When the total distance, depth or thickness of the object 2 or of the portion of the object 2 for which an analysis is desired is greater than the unit amplitude that a single acquisition allows, several acquisition steps are then carried out by moving the position of the depth of field 4 along the acquisition axis 33 so that, along this acquisition axis 33, the depths of field 4 of the different acquisitions successively carried out correspond to juxtaposed or partially superimposed segments so that the cumulative length of these segments covers the length, thickness or depth of the object 2 or of the portion of the object 2 along this axis.

[0016] According to an example relating to another variant of implementation of the acquisition method according to the invention and capable of being implemented according to one or other of the variants detailed previously, this method is characterized in that, when the light image comes in transmission from the object 2 to be controlled, the adjustment of the optical mechanism 11 is produced according to a depth of field 4 whose sharpness distance is of the same order of magnitude as the thickness of at least a portion of the object 2 to be controlled reported on the acquisition axis 33. The implementation of the method of the invention with such an adjustment of the depth of field 4 thus makes it possible to carry out, along the acquisition axis 33, an acquisition of the entire length, thickness or depth of the object 2 or portion of the object 2 without the number of successive displacement and acquisition steps necessary to cover the entire length, thickness or depth of the object 2 or portion of the object 2 along this acquisition axis 33 being too large, or even disproportionate.

[0017] According to an example relating to another variant of implementation of the acquisition method according to the invention and capable of being implemented according to one or other of the previously detailed variants, this method is characterized in that the displacement of the object 2 relative to the assembly combining the acquisition device 1 with the optical mechanism 11 is carried out according to a stroke oriented along the acquisition axis 33. This stroke is capable of corresponding to a translation. The displacement of the object 2 along such an acquisition axis 33 makes it possible to carry out different acquisitions at different levels of depth of the object 2 or distance of the object 2 relative to the acquisition device 1. Such a displacement thus makes it possible to carry out acquisitions, juxtaposed or partially superimposed, in a manner adapted to prominent projecting or raised portions of the object 2, this prominence being oriented in the direction of the acquisition device 1.

[0018] According to an example relating to another variant of implementation of the acquisition method according to the invention and capable of being implemented according to one or other of the previously detailed variants, the acquisition method is characterized in that the movement of the object 2 relative to the assembly combining the acquisition device 1 with the optical mechanism 11 is carried out according to a stroke substantially parallel to a surface of the object 2 and / or substantially perpendicular to the acquisition axis 33. This stroke is capable of corresponding to a translation. The movement of the object 2 along such an acquisition axis 33 makes it possible to carry out different acquisitions at a substantially constant depth distance of the object 2 relative to the acquisition device 1.Such a movement thus makes it possible to carry out acquisitions, juxtaposed or partially superimposed, in a manner adapted to objects 2 or surfaces of objects 2 whose width is too great to be correctly positioned within the field of the optical mechanism 11 associated with the acquisition device 1.

[0019] As an example of implementation, the displacement step is likely to involve the displacement of only the object 2 or the displacement of only the set combining the acquisition device 1 and the optical mechanism 11 or the synchronized movement of each of the two groups which are, on the one hand, the object 2 and, on the other hand, the assembly combining the acquisition device 1 and the optical mechanism 11, these different movements being carried out in relation to a fixed point of a frame taken as a reference. It should be noted that, preferably, this translation concerns the movement of a first assembly which brings together the object 2 and the light projection device in relation to a second assembly which combines the acquisition device 1 with the optical mechanism 11.The object 2 and the light projection device are then kept fixed to each other despite the movement of the object 2 relative to the acquisition device 1 associated with the optical mechanism 11, so as to carry out a strictly identical projection of the at least one series of light images onto the surface or through the surface of the object 2 to be analyzed regardless of the position of the object 2 relative to the assembly combining the acquisition device 1 with the optical mechanism 11. In this way, the position of the object 2 relative to the acquisition device 1 remains constant and the operation of reconstructing the images is then simpler to carry out.

[0020] The invention also relates to a system configured for implementing an acquisition method according to the invention, characterized in that the system comprises: - a means of supporting an object 2 to be controlled, - a device for projecting light from at least one image against at least one surface of the object 2 to be controlled, - an acquisition device 1 associated with an optical mechanism 11 comprising at least one lens and one diaphragm, - a device for processing at least two images acquired by the acquisition device 1 for the construction of at least one light image of a part of the object 2 to be controlled.

[0021] The light projection device is preferably formed by a screen or a display capable of projecting at least one image which corresponds to at least one succession of light and dark sinusoidal fringes so that each image of the series has identical sinusoidal fringes with a phase shift relative to the other images of the series, this shift being less than the phase of the sinusoids, so as to allow the implementation of the principle of phase shift deflectometry.

[0022] According to an example relating to a construction variant of the system of the invention, the system integrates a mechanism for moving the position of the object 2 to be controlled relative to the acquisition device 1 associated with its optical mechanism 11. Preferably, this mechanism for moving the position of the object 2 is configured to keep the position of the object 2 constant relative to the light projection device. The mechanism for moving the position of the object 2 to be controlled relative to the acquisition device 1 is preferably configured to allow translational movement to be carried out, for example along the acquisition axis 33 and / or along an axis perpendicular to this acquisition axis 33.

[0023] According to an example relating to a construction variant of the system of the invention, the system also integrates at least one memory means for recording, on the one hand, the different image acquisitions of different portions of the object 2 carried out prior to their processing within the framework of the reconstruction of a light image from several of the acquired images and, on the other hand, the different reconstructed light images.

[0024] According to an example relating to a construction variant of the system of the invention and capable of being implemented according to one or other of the previously detailed variants, the minimum unit of definition of the image acquired by the acquisition device 1 is less than the size of an optical aberration capable of being generated by the object 2 to be controlled. In the context of the implementation of the method of the invention, the level of definition of the acquisition conditions the quality of the analysis by deflectometry and therefore of the characterization of the optical aberrations generated in transmission or in reflection by the object 2 to be analyzed.Also, by adopting a minimum unit of definition of the image acquired by the acquisition device 1 such as a pixel of a size smaller than the sizes of the optical aberrations likely to be encountered, the acquisition device 1 in combination with the optical mechanism 11 makes it possible to facilitate the identification of an optical aberration generated by the object 2 to be analyzed. Any distortion of the image transmitted or reflected by the object 2 is thus able to be identified.

[0025] Of course, the invention is not limited to the embodiments described and shown in the attached drawings. Modifications remain possible, in particular from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.

Claims

1. Claims Method of acquisition by an acquisition device (1), through an optical mechanism (11) comprising at least one lens and one diaphragm, of the light image coming from an object (2) to be controlled by phase-shift deflectometry, in reflection or in transmission, the part of the object (2) to be controlled corresponding to a volume arranged between two planes (31, 32) parallel to each other and perpendicular to the acquisition axis (33), characterized in that the method comprises: - a step of carrying out an adjustment of the optical mechanism (11) according to a depth of field (4) whose sharpness distance is less than the distance separating, along the acquisition axis (33), the two parallel planes (31, 32) of the volume of the part of the object (2) to be controlled, - a step of positioning the object (2) so that a first portion of the object (2) is positioned in the depth of field (4) of the optical mechanism (11), - a step of projecting onto or through the object (2) at least one series of at least two light images emitted by at least one projection device and corresponding to at least one succession of light and dark sinusoidal fringes, each image of the series having identical sinusoidal fringes with a phase shift relative to the other images of the series, this shift being less than the phase of the sinusoids, - a step of acquiring a first image originating from the first portion of the object (2) and corresponding to the reflection or transmission by the object (2) of an image originating from at least one series of at least two light images emitted by at least one projection device, - a step of moving the object (2) relative to the assembly combining the acquisition device (1) with the optical mechanism (11), so that at least a second portion of the object (2) is positioned in the depth of field (4) of the optical mechanism (11), - a step of projecting onto or through the object (2) the same at least one series of at least two light images by the at least one projection device, - a step of acquiring at least one second image originating from the at least one second portion of the object (2) and corresponding to the reflection or transmission by the object (2) of the same image originating from the at least one series of at least two light images emitted by at least one projection device during the step of acquiring the first image originating from the first portion of the object (2), - a step of constructing the light image originating from a portion of the object (2) to be controlled by combining the portion of the first image originating from the first portion of the object (2) with the portion of the at least one second image originating from the at least one second portion of the object (2).

2. Acquisition method according to claim 1, characterized in that, when the light image comes in transmission from the object (2) to be controlled, the adjustment of the optical mechanism (11) is carried out according to a depth of field (4) whose sharpness distance is greater than or equal to the thickness of at least a portion of the object (2) to be controlled reported on the acquisition axis (33).

3. Acquisition method according to one of the preceding claims, characterized in that, the light image coming in transmission from an object (2) to be controlled, the adjustment of the optical mechanism (11) is carried out according to a depth of field (4) whose sharpness distance is of the same order of magnitude as the thickness of at least a portion of the object (2) to be controlled reported on the acquisition axis (33).

4. Acquisition method according to one of the preceding claims, characterized in that the movement of the object (2) relative to the assembly combining the acquisition device (1) with the optical mechanism (11) is carried out according to a stroke oriented along the acquisition axis (33).

5. Acquisition method according to one of the preceding claims, characterized in that the movement of the object (2) relative

6.

7. the assembly combining the acquisition device (1) with the optical mechanism (11) is produced along a path substantially parallel to a surface of the object (2) and / or substantially perpendicular to the acquisition axis (33). System configured for implementing an acquisition method according to one of claims 1 to 5, characterized in that the system comprises: - a means of supporting an object (2) to be controlled, - a device for projecting light from at least one image against at least one surface of the object (2) to be controlled, - an acquisition device (1) associated with an optical mechanism (11) comprising at least one lens and one diaphragm, - a device for processing at least two images acquired by the acquisition device (1) for the construction of at least one light image of a part of the object (2) to be controlled. System according to claim 6 configured for the implementation of an acquisition method, characterized in that the minimum unit of definition of the image acquired by the acquisition device (1) is less than the size of an optical aberration likely to be generated by the object (2) to be controlled.

Images