WO2020229780A1

WO2020229780A1 - Method and system for optically inspecting an object

Info

Publication number: WO2020229780A1
Application number: PCT/FR2020/050804
Authority: WO
Inventors: Frédéric MEUNIER; Romain Roux
Original assignee: Vit
Priority date: 2019-05-15
Filing date: 2020-05-14
Publication date: 2020-11-19
Also published as: FR3096126A1; FR3096126B1

Abstract

The present description relates to a method for optically inspecting an object, employing at least one profilometer comprising a projector configured to project a luminous pattern onto the object and at least first and second image sensors (C1, C2), the method comprising moving the object with respect to the profilometer along a path and controlling, with a processing module, first and second image sensors in order to acquire images of the object in at least first and second successive phases: in one of the first and second phases, the first and second image sensors are controlled alternately to acquire images of the object, and, in the other of the first and second phases, the first and second image sensors are controlled simultaneously to acquire images of the object.

Description

DESCRIPTION

METHOD AND SYSTEM FOR OPTICAL INSPECTION OF AN OBJECT

The present patent application claims the priority of the French patent application FR19 / 05065 which will be considered as forming an integral part of the present description.

Technical area

[0001] The present description relates generally to optical inspection methods and, more particularly, to methods for determining three-dimensional images intended for the online analysis of objects, in particular of electronic circuits.

Prior art

[0002] Optical inspection systems are generally used to check the good condition of an object before it is placed on the market. They make it possible in particular to determine a three-dimensional image, also called a 3D image, of the object which can be analyzed to look for any defects. In the case of an electronic circuit comprising for example a printed circuit equipped with electronic components, the three-dimensional image of the electronic circuit can be used in particular to inspect the good condition of the welds of the electronic components on the printed circuit.

[0003] The 3D image of the object can be determined from the acquisition of two-dimensional images, also called 2D images, of the object by at least one camera while the object is scanned by a light profile , for example a laser beam. A scanning operation corresponds to the set of 2D images of the object to be acquired to allow the determination of a 3D image of the object. The limiting factor for the duration of a scanning operation is generally the speed of image acquisition. 2D by the camera to obtain the desired resolution of the 2D images acquired by the camera.

[0004] It would be desirable to be able to reduce the duration of an operation for scanning an object without degrading the resolution of the 2D images acquired.

Summary of the invention

[0005] An object of an embodiment is to at least partially overcome the drawbacks of the optical inspection methods and systems described above.

Another object of an embodiment is to reduce the duration of a scanning operation of an object, in particular for determining a 3D image of the object.

Another object of an embodiment is not to degrade the resolution of the 2D images acquired of an object for determining the 3D image of the object.

[0008] Thus, one embodiment provides for an optical inspection method for an object comprising at least one profilometer comprising a projector configured to project a light pattern on the object and at least first and second image sensors, the method comprising the movement of the object relative to the profilometer along a path and the control by a processing module of the first and second image sensors for the acquisition of images of the object according to at least first and second successive phases, in one of the first or second phases, the first and second image sensors being alternately controlled to acquire images of the object, and, in the other of the first or second phases, the first and second image sensors being controlled simultaneously for the acquisition of images of the object.

[0009] An embodiment also provides for an optical inspection system of an object comprising at least one profilometer comprising a projector configured to project a light pattern onto the object and at least first and second image sensors and a processing module configured to control the movement of the object relative to the profilometer along a path and to control the first and second image sensors for acquiring images of the object according to at least first and second successive phases, in one of the first or second phases, the first and second image sensors being alternately controlled for the acquisition of images of the object, and, in the other of the first or second phases, the first and second image sensors being controlled simultaneously for the acquisition of images of the object.

[0010] According to one embodiment, the images are used for determining a three-dimensional image of the object.

[0011] According to one embodiment, the method comprises the determination by the processing module of at least a first zone of the object for which a minimum resolution at a first value is sought and of at least a second zone of the object for which a minimum resolution at a second value is sought, the first minimum resolution value being strictly less than the second minimum resolution value.

[0012] According to one embodiment, the method comprises determining by the processing module, from the positions of the first and second image sensors relative to the object along said path when the first and second sensors of images are alternately ordered for the acquisition of images of the object, of at least a third area of the object for which a maximum resolution at a first value is achievable and of at least a fourth area of the object for which a resolution maximum to a second value is attainable, the first maximum resolution value being strictly greater than the second maximum resolution value.

According to one embodiment, on the path, the first and second image sensors are alternately controlled for the acquisition of images of the object in the case where at least part of the object seen by the image sensors correspond to both one of the first zones and one of the third zones and the first and second image sensors are controlled simultaneously for the acquisition of images of the object in the case where the part of the object seen by the image sensors corresponds both to one of the second zones and to one of the fourth zones.

According to one embodiment, the method comprises the movement of the object by a conveyor in a conveying direction and further comprises the movement of the profilometer relative to the conveyor in a direction of movement not parallel to the direction of conveying .

[0015] According to one embodiment, the direction of movement is perpendicular to the direction of conveying.

[0016] According to one embodiment, the object comprises a printed circuit.

[0017] According to one embodiment, the projector is configured to project a light beam onto the object, the thickness of which is less than 200 μm.

[0018] According to one embodiment, the projector comprises a laser source.

Brief description of the drawings

These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the accompanying figures, among which: [0020] FIG. 1 is a perspective view, partial and schematic, of an embodiment of an optical inspection system;

[0021] Figure 2 is a side view, partial and schematic, of the optical inspection system shown in Figure 1;

[0022] Figure 3 is a top view, partial and schematic, of the optical inspection system shown in Figure 1;

[0023] FIG. 4 illustrates the operation of an example of a laser profilometer;

Figure 5 is a block diagram of a standard mode of controlling cameras during an object scanning operation;

FIG. 6 is a block diagram of an alternate control mode of cameras during an operation of scanning an object;

FIG. 7 is a top view image of an electronic circuit used by computer aided design software;

FIG. 8 is a top view image, partial and schematic, of an electronic circuit illustrating different levels of minimum resolution required for optical inspection;

FIG. 9 is a top view image, used by computer-aided design software, of an electronic circuit illustrating areas not seen by a camera located to the left of the electronic circuit during an operation of sweeping;

[0029] Figure 10 is a top view image, used by computer aided design software, of a electronic circuit illustrating the areas not seen by a camera situated to the right of the electronic circuit during a scanning operation;

FIG. 11 is a top view image, partial and schematic, of an electronic circuit illustrating the levels of resolution attainable when the alternate control mode of the cameras is used; and

FIG. 12 represents top view images, partial and schematic, of an electronic circuit illustrating an embodiment of a method for determining the phases of application of the alternating and standard control modes of the cameras during of a sweep operation.

Description of embodiments

The same elements have been designated by the same references in the various figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been shown and are detailed. In particular, the means for conveying the electronic circuit and the means for moving the cameras and projectors of the optical inspection system described below are within the abilities of those skilled in the art and are not described in detail. In addition, the optical inspection processes have not been detailed, the method for determining three-dimensional images being compatible with any optical inspection system and, more generally, with any imaging system. In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "rear", "top", "bottom", "left", "right", etc., or relative, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc. ., Reference is made unless otherwise specified to the orientation of the figures or to an optical inspection system in a normal position of use.

Unless otherwise specified, the expressions "approximately", "approximately", "substantially", and "of the order of" mean within 10%, preferably within 5%.

In the remainder of the description, embodiments will be described in the case of optical inspection of electronic circuits. However, these embodiments can be applied to the determination of three-dimensional images of all types of objects, in particular for the optical inspection of mechanical parts. Two perpendicular directions, for example horizontal, are called X and Y hereinafter.

Figures 1, 2 and 3 are respectively a perspective view, a front view and a top view, partial and schematic, of an embodiment of an optical inspection system 10 of a circuit electronic 12. The term “electronic circuit” is understood to mean either a set of electronic components interconnected by means of a support, the support alone used to achieve this interconnection without the electronic components or the support without the electronic components but provided with fixing means for the electronic components. electronic components. For example, the support is a printed circuit board and the electronic components are fixed to the printed circuit board by solder joints obtained by heating blocks of paste. welding. In this case, by electronic circuit is meant indifferently the printed circuit board alone (without electronic components or solder paste blocks), the printed circuit board provided with solder paste blocks and without electronic components, the circuit board printed circuit board fitted with solder paste blocks and electronic components before the heating operation or the printed circuit board fitted with electronic components attached to the printed circuit board by solder joints.

The electronic circuit 12 is placed on a conveyor 14, for example a flat conveyor. The conveyor 14 is configured to move the circuit 12 parallel to the direction X. By way of example, the conveyor 14 can comprise a set of belts and rollers driven by a rotating electric motor 16, shown only in FIG. alternatively, the conveyor 14 may comprise a linear motor moving a cart on which the electronic circuit 12 rests. The circuit 12 corresponds, for example, to a rectangular card having a length and a width varying from 50 mm to 550 mm. The conveyor 14 is configured to move the circuit 12 in the X direction from a position of introduction of the circuit 12 to an inspection position, at which the circuit 12 is stopped, and from the position of inspection to a circuit 12 recovery position.

The optical inspection system 10 further comprises a device 20 for determining a 3D image of a scene, corresponding in this embodiment to the electronic circuit 12. The device 20 may include a projector P of a thin beam of light. The projector P can include a laser source or a projector adapted to project an image containing only one line. The wavelength of the laser is for example between 400 nm and 700 nm. The projector P is connected to a computer system 22 for controlling, acquiring and processing images, also called processing module 22 hereafter. The device 20 further comprises an image acquisition device comprising at least two cameras, for example digital cameras, two cameras C1 and C2 being shown in Figures 1 to 3. Each camera C1, C2 is connected to the device. processing module 22.

The processing module 22 may include a computer or a microcontroller comprising a processor and a non-volatile memory in which are stored sequences of instructions whose execution by the processor allows the processing module 22 to perform the desired functions. . As a variant, the processing module 22 can correspond to a dedicated electronic circuit. The electric motor 16 can furthermore be controlled by the processing module 22. The processing module 22 can furthermore comprise a man-machine interface, comprising for example a display screen for displaying information and a keyboard and mouse for data entry by an operator.

The cameras C1, C2 can be arranged in pairs on either side of the projector P, parallel to the direction X. According to one embodiment, the direction X is parallel to a preferred direction of the cameras C1, C2 and / or of the projector P. By way of example, the direction X can be parallel to the line passing through the optical centers of the cameras C1, C2. In the remainder of the description, a two-dimensional image, or 2D image, is called a digital image acquired by one of the cameras C1, C2 and corresponding to a matrix of pixels. In the remainder of the description, unless otherwise indicated, the term “image” refers to a 2D image. In the remainder of the description, we call resolution of each camera C1, C2 the total number of pixels of the camera. By way of example, the resolution of each camera C1, C2 is between 500,000 pixels and 3 million pixels.

In the remainder of the description, the assembly comprising the projector P and the cameras C1, C2 is called the optical profilometer 24. The profilometer 24 can correspond to a laser profilometer. According to one embodiment, the optical inspection system 10 comprises a support device 26, shown schematically only in Figures 2 and 3, of the profilometer 24, suitable for simultaneously moving the projector P and the cameras C1, C2, in particular in translation in the X direction and in the Y direction. The support device 26 can be controlled by the processing module 22. By way of example, FIG. 3 is represented by a dotted line 26 ', the profilometer support in another position in the X and Y directions.

The means for controlling the conveyor 14, the support device 26, the cameras C1, C2 and the projector P of the optical inspection system 10 described above are within the reach of those skilled in the art and are not not described in more detail.

Z is called the direction perpendicular to the X and Y directions. The X, Y and Z directions and an origin O constitute a three-dimensional space reference RREF (OX, OY, OZ) fixed with respect to the frame, no shown, of the optical inspection system 10. FIG. 2 is seen in the Y direction and FIG. 3 is seen in the Z direction. The device 20 is suitable for determining a three-dimensional image, also called a 3D image or height map, of the circuit 12. A 3D image of the circuit 12 corresponds to a cloud of points, for example several million points, of at least part of the external surface of the circuit 12 in which each point of the surface is identified by its coordinates (x, y, z) determined with respect to the reference RREF (OX, OY, OZ).

FIG. 4 illustrates the operation of the device for determining a 3D image for a laser profilometer 24, only the camera C1 of the profilometer 24 being shown. The projector P is configured to project a fine light beam which substantially follows a light surface S. According to one embodiment, the light beam corresponds to a substantially cylindrical laser beam and the projector P comprises a mechanism configured to move the laser beam and it scanning the surface S. According to another embodiment, the projector P is configured to emit the light beam directly along the surface S. This is for example a projector P comprising a laser source and a diffraction device or a Powell lens. In the remainder of the description, the light surface S is called the surface defined by the light beam projected by the projector P regardless of whether the light beam extends directly from the projector P along the surface S or whether the light beam sweeps this surface S. According to one embodiment, the thickness of the light beam in the X direction is less than 200 μm. Preferably, the luminous surface S is as flat as possible, for example along a plane parallel to the plane (OYZ), with a scanning of the electronic circuit 12 by the luminous surface S in the direction X during the relative movement of the projector P with respect to to circuit 12 in the X direction. However, especially when the surface S is obtained by diffraction or by means of a Powell lens, it may be difficult to perfectly control the surface S so that the surface S may not be perfectly plane. The light beam is reflected by the electronic circuit 12 and each camera C1, C2 acquires an image I of the scene Sc. The intersection between the light beam delimiting the light surface S and the scene Sc corresponds substantially to a light line L which appears in the form of a line L 'on the image I acquired by each camera C1, C2.

A scanning operation of the circuit 12 corresponds to a phase of acquisition of 2D images of the circuit 12 by the cameras C1, C2 for determining a 3D image of the circuit 12. During a scanning operation, a relative displacement is carried out between the circuit 12 and the profilometer 24, for example in the X direction, and images are acquired by each camera C1, C2, for example at regular intervals in space. The relative movement between the circuit 12 and the profilometer 24 can be temporarily interrupted for the acquisition of each image I by each camera C1, C2 or the acquisition of each image I can be carried out on the fly during the relative movement between the camera. circuit 12 and profilometer 24. There is thus available, for each camera C1, C2, a set of images each comprising a line L 'of different shape from one image to another. As a variant, the projector P can be adapted to project two fine light beams extending in two different directions.

FIG. 5 is a block diagram illustrating a mode of controlling the cameras C1, C2, called standard control mode, during a scanning operation of the circuit 12.

In step 30, the processing module 22 determines the control signals for the acquisitions of 2D images from the cameras C1, C2 as a function of the time for the scanning operation to be performed. FIG. 5 schematically represents a timing diagram of IMP pulses, each pulse IMP corresponding to the command for acquiring a 2D image by a camera.

In step 32, the processing module 22 supplies each camera C1, C2 with the acquisition control signals 2D images. For this purpose, the processing module 22 may include a routing card configured to transmit a series of IMPI pulses to the first camera C1 and a series of pulses IMP2 to the second camera C2 from the series of IMP pulses. . In the standard control mode, the IMPI pulse series is the same as the IMP pulse series and the IMP2 pulse series is the same as the IMP pulse series.

In step 34, the first camera C1 acquires 2D images under the control of the control signals IMPI and in step 36 the second camera C2 acquires 2D images under the control control signals IMP2. As the pulses IMPI and IMP2 are simultaneous, the acquisition of each image by the camera C1 is carried out simultaneously with the acquisition of an image by the camera C2. The images acquired by the cameras C1, C2 are transmitted to the processing module 22.

In step 38, the processing module 22 determines the 3D image of the circuit 12 from the 2D images supplied by the cameras C1, C2. A single camera could in theory be used to acquire the 2D images of an object from which a 3D image of the object is determined. However, in general, at least two cameras are used to increase the viewing angles and minimize hidden areas due to the highest elements in the scene. In fact, the greater the number of cameras, the greater the risk that a zone is not visible on all the images acquired simultaneously by the cameras is reduced. As a result, when the scene is seen by the two cameras, the processing module can use the two 2D images acquired simultaneously from the scene to determine the 3D image. In particular, the processing module 22 can produce a new 2D image from the two 2D images, corresponding for example to a "fusion" of the two images, for the determination of the 3D image. When a part of the scene is seen only by one of the two cameras, the processing module uses only the 2D image on which this part of the scene appears for determining the 3D image.

According to one embodiment, the cameras are controlled during a scanning operation according to a single phase or a succession of at least two phases during each of which the cameras are controlled according to one or the other of the first and second camera control modes, the control modes of two consecutive phases being different. The first mode corresponds to the standard control mode described previously in relation to FIG. 5 according to which the cameras C1, C2 make simultaneous acquisitions of the 2D images. The second control mode, called alternate control mode hereinafter, comprises the alternation of image acquisitions by the cameras C1, C2. According to another embodiment, the cameras are controlled to perform at least first and second scanning operations of the same scene to be inspected, one of the first or second scanning operations being performed by controlling the cameras according to the mode of operation. standard control and the other of the first or second scanning operations being performed by controlling the cameras in the alternate control mode.

FIG. 6 is a block diagram illustrating the alternate control mode of the cameras C1, C2 during a scanning operation of the circuit 12. The alternate control mode comprises all of the steps of the standard control mode described previously in relation to FIG. 5 with the difference that step 32, described previously, is replaced by step 42, and that step 38, described previously, is replaced by step 48. In step 42, the processing module 22 supplies each camera C1, C2 with the 2D image acquisition control signals as has been described above for step 32, by transmitting a series of pulses IMPI at the first camera C1 and a series of pulses IMP2 at the second camera C2, with the difference that the series of pulses IMPI comprises every other pulse of the series of pulses IMP and that the series of pulses IMP2 comprises the other pulses of the series of pulses IMP. As a result, during a phase in which the alternate control mode is implemented, the 2D image acquisitions by the first camera C1 are carried out at different times from the 2D image acquisitions by the second camera C2.

In step 48, the processing module 22 determines the 3D image from the 2D images, taking into account the fact that a single 2D image is available at each moment of acquisition.

The duration of the scanning operation during the application of the alternating control mode is less than the duration of the scanning operation during the application of the standard control mode, since, in the control mode alternately, the cameras take turns acquiring images. Advantageously, the duration of the scanning operation when applying the alternating control mode is less than at least 90%, preferably at least 85%, of the duration of the scanning operation during the application. application of standard command mode. This makes it possible to reduce the total time of the scanning operation.

The determination of the start and end times of each phase of a scanning operation is carried out beforehand by an analysis of the electronic circuit 12 to be inspected. For this purpose, the electronic circuit to be inspected is modeled in computer aided design software or CAD software.

FIG. 7 is an image in top view of a modeling of an electronic circuit as it can be displayed on a display screen by CAD software. In Figure 7, there is shown an electronic circuit 50 comprising a printed circuit board 52 on which are attached electronic components 54 by solder pads, not shown in Figure 7, the components 54 may include connection pins 56, solder pads, not shown, being in practice located at the ends of the connection pins 56.

It is determined from an analysis of the CAD modeling of the electronic circuit 50 of the zones as a function of the necessary resolution of the 2D images acquired for the implementation of the optical inspection method on the 3D image obtained at from 2D images, in particular to inspect the good condition of the welds of the electronic components of the electronic circuit.

FIG. 8 is an image in top view of the electronic circuit 50 in which are indicated three zones, the first zones 60 for which a low resolution of the 2D images acquired is sufficient for the optical inspection, of the second zones 62 for which an average resolution, greater than the low resolution, of the acquired 2D images is sufficient for the optical inspection and of the third areas 64 for which a high resolution, greater than the average resolution, of the acquired 2D images is required for the optical inspection . The average resolution can be twice the low resolution. High resolution can be twice the medium resolution. The determination of zones 60, 62, 64 can be carried out by an operator and / or can be carried out automatically by computer. An operator can transmit instructions to the processing module 22 by means of a man / machine interface, not shown, comprising for example a keyboard, a screen, in particular a touch screen, a mouse, a microphone and / or control buttons. .

During a scanning operation, a relative movement between the circuit 12 and the profilometer 24 is carried out at least between the acquisitions of two successive 2D images by the cameras C1, C2. The relative displacement between the circuit 12 and the profilometer 24 is defined by the processing module 22 beforehand, in particular from an analysis of the modeling of the electronic circuit 50. From the relative displacement between the circuit 12 and the profilometer 24 , the processing module 22 is adapted to determine the parts of the circuit 12 which will remain invisible to each camera C1, C2 during a scanning operation. According to one embodiment, these parts are determined by a theoretical calculation from the data supplied by the CAD software and from the geometry of the cameras C1, C2. According to another embodiment, these parts are determined by measurements carried out beforehand from acquisitions of images of the circuit 12. According to another embodiment, these parts are determined by combining measurements carried out beforehand from 'acquisitions of images from circuit 12 and a theoretical calculation carried out from the data supplied by the CAD software and from the geometry of the cameras C1, C2.

Figures 9 and 10 are top view images of the electronic circuit 50 on which the black areas 70 correspond to the parts of the electronic circuit 50 which are invisible during a scanning operation respectively for the first camera C1 ( figure 9) and for the second camera C2 (figure 10), the outline of the components electronics 54 being indicated in dotted lines in the figures.

From the areas not visible 70 by the cameras C1 and C2 during a scanning operation, the processing module 22 determines the maximum resolution that can be obtained in the case where the entire scan is performed by putting in operates the alternate camera control mode. Indeed, for the parts of the electronic circuit 50 which are visible simultaneously by the two cameras C1, C2, the high resolution can be obtained while, for the parts of the electronic circuit 50 which are visible simultaneously only by one of the cameras C1, C2, the maximum resolution which can be obtained is the average resolution since only one 2D image out of two is then usable.

FIG. 11 is a top view image of the electronic circuit 50 in which are indicated first areas 80 for which a high resolution can be obtained and second areas 82 for which an average resolution can at best be obtained when ' an alternating control mode is implemented throughout the scanning operation.

FIG. 12 illustrates an embodiment of a method for determining the start and end instants of each phase for a scanning operation by the processing module 22. The images of the figures have been reproduced in FIG. 12. 8 and 11 described above. There is also shown in Figure 12, between the images of Figures 8 and 11, a top view image of the electronic circuit 50 illustrating the maximum resolution that can be obtained when a standard control mode is implemented throughout the scanning operation, that is, high resolution. According to one embodiment, the processing module compares between the instant t0 of the start of the scanning operation and the instant t3 of the end of the scanning operation if, at each point on the part of the circuit 50 being in the angle of view of cameras C1 and C2, the maximum resolution possible for this point according to the alternating control mode, obtained from the image of FIG. 11, is compatible with the minimum resolution desired for this point obtained from the image of FIG. 8. If the maximum possible resolution for this point according to the alternate control mode is greater than or equal to the minimum resolution desired for this point, the alternate control mode is applied. If the maximum possible resolution for this point according to the alternating control method is strictly lower than the minimum resolution desired for this point, the standard control mode is applied.

With the images of Figures 8 and 11 of the electronic circuit 50, it follows that the alternate control mode A is applied from time t0 to time tl and from time t2 to time t3 and that the standard control mode S is applied between times t1 and t2.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these various embodiments and variants could be combined, and other variants will be apparent to those skilled in the art. In particular, although embodiments have been described for a profilometer whose projector emits a fine light beam, it is clear that the embodiments described above can be implemented with any type of optical profilometer comprising a projector and at least. at least two cameras, in particular an optical profilometer in which the projector is adapted to project several structured images on the object, that is that is to say images comprising patterns, for example light fringes shifted from one image to another. Finally, the practical implementation of the embodiments and variants described is within the abilities of those skilled in the art based on the functional indications given above.

Claims

1. Method for optical inspection of an object (12) comprising at least one profilometer (24) comprising a projector (P) configured to project a light pattern on the object and at least first and second image sensors ( C1, C2), the method comprising the movement of the object relative to the profilometer along a path and the control by a processing module (22) of the first and second image sensors for the acquisition of images of the object according to at least first and second successive phases, in one of the first or second phases, the first and second image sensors being alternately controlled for the acquisition of images of the object, and, in the other first or second phases, the first and second image sensors being controlled simultaneously for the acquisition of images of the object.

2. System for optical inspection of an object (12) comprising at least one profilometer (24) comprising a projector (P) configured to project a light pattern on the object and at least first and second image sensors ( C1, C2) and a processing module (22) configured to control the movement of the object relative to the profilometer along a path and to control the first and second image sensors for acquiring images of the object according to at least first and second successive phases, in one of the first or second phases, the first and second image sensors being alternately controlled for the acquisition of images of the object, and, in the other of first or second phases, the first and second image sensors being controlled simultaneously for the acquisition of images of the object.

3. Method or system according to claim 1 or 2, wherein the images are used for determining a three-dimensional image of the object (12).

4. Method or system according to any one of claims 1 to 3, comprising the determination by the processing module (22) of at least a first zone (60) of the object (12) for which a minimum resolution at a first value is sought and at least a second area (62, 64) of the object for which a minimum resolution at a second value is sought, the first minimum resolution value being strictly less than the second minimum resolution value .

5. Method or system according to any one of claims 1 to 3, comprising the determination by the processing module (22), from the positions of the first and second image sensors (C1, C2) with respect to the. object (12) along said path when the first and second image sensors are alternately commanded to acquire images of the object, of at least a third area (80) of the object (12) for wherein a maximum resolution at a first value is attainable and at least a fourth area (82) of the object for which a maximum resolution at a second value is achievable, the first value of maximum resolution being strictly greater than the second value maximum resolution.

6. Method or system according to claims 4 and 5, wherein, on the path, the first and second image sensors (C1, C2) are alternately controlled for the acquisition of images of the object in the case where at least a part of the object seen by the image sensors corresponds both to one of the first zones (60) and to one of the third zones (80) and the first and second image sensors are controlled simultaneously for the acquisition of images of the object in the case where the part of the object seen by the image sensors corresponds to both one of the second zones (62, 64) and one of the fourth zones (82).

7. Method or system according to any one of claims 1 to 6, comprising moving the object (12) by a conveyor (14) in a conveying direction (X) and further comprising moving the profilometer (24). ) relative to the conveyor (14) in a direction of movement (Y) not parallel to the direction of conveying (X)

8. Method or system according to claim 7, wherein the direction of movement (Y) is perpendicular to the direction of conveying (X).

9. A method or system according to any one of claims 1 to 8, wherein the object (12) comprises a printed circuit.

10. Method or system according to any one of claims 1 to 9, wherein the projector (P) is configured to project on the object a light beam whose thickness is less than 200 µm.

11. Method or system according to any one of claims 1 to 10, wherein the projector (P) comprises a laser source.