Method for acquiring the position and orientation of at least one user reference frame in a universal installation reference frame.

Abstract

The invention relates to a method for acquiring the position and orientation of at least one user reference frame in a universal installation reference frame, the universal installation reference frame being linked to a device for moving a receiving support of a work tool, a tool reference frame being linked to the receiving support, the moving device allowing the receiving support to be moved relative to a workstation, the method comprises: - mounting a camera on the receiving support, a camera reference frame being linked to this camera, - affixing a materialization element of a user reference frame to the workstation, - pre-positioning the camera relative to the workstation so that the materialization element is located in the camera's field of vision.- to move the camera into several distinct positions relative to the materialization element so as to allow the camera to capture several images of the materialization element from several different positions, these different images allowing the camera to determine the position and orientation of the user coordinate system in the camera coordinate system, and - to determine the position and orientation of the user coordinate system in the universal installation coordinate system from the information transmitted by said camera. Figure in the abstract: none.

Description

Title of the invention: Method for acquiring the position and orientation of at least one user reference frame in a universal installation reference frame.

[0001] The present invention relates to the learning and control of the position of a work tool moved relative to a workstation.

[0002] In many industrial installations, a work tool must be moved precisely in relation to one or more workstations.

[0003] For example, in tire manufacturing, a gripping tool mounted at the end of a robotic arm is used to transport a finished or semi-finished product from one workstation to another. For example, these different workstations are part of the same manufacturing installation.

[0004] To avoid production hazards, it is necessary that the movements of the gripping tool be precise and that they remain precise from one production cycle to another.

[0005] In order to control the movements of the work tool in relation to one or more workstations, it is known to associate local reference frames with the different devices of the manufacturing installation and to acquire, by physical measurements and different calculations, the matrices of change of reference frames between these different local reference frames and the universal installation reference frame linked to this manufacturing installation.

[0006] In the case of a gripping tool mounted at the end of a robotic arm, the universal installation marker is associated with the robotic arm, and more specifically with the fixed base of this robotic arm, and local markers are associated with the gripping tool and each workstation. For example, a tool marker is associated with the gripping tool, and a user marker is associated with each workstation.

[0007] The present invention relates more specifically to the control of the position and orientation of the tool reference frame in the universal installation reference frame of the robotic arm, and therefore the acquisition of the reference frame change matrix between the universal installation reference frame and the tool reference frame.

[0008] Indeed, even if this coordinate system change matrix between the universal installation coordinate system and the tool coordinate system can be precisely determined during an initial commissioning stage of the manufacturing installation, it may happen that the robotic arm is subjected to shocks or impacts that alter the position of the gripping tool relative to the robotic arm, resulting in a non-conformity of the initially determined coordinate system change matrix with the current state of the installation, and more specifically of the robotic arm. In such a case, it is therefore necessary to perform a new step of acquiring the position and orientation of the tool reference frame in the universal installation reference frame of the robotic arm to correct the reference frame change matrix.

[0009] A known method for acquiring the datum change matrix between the universal installation datum and the tool datum at a given workstation consists of using a calibration template positioned precisely on said workstation and representing a user datum on that workstation. This calibration template generally includes three reference points represented by probes. The method involves equipping the gripping tool with a probing tool such as a probe and probing the different reference points of the calibration template with this probing tool.

[0010] In this known method, the movements of the probing tool are performed manually by an operator, for example via a human-machine interface such as Teach Pendant®. Therefore, the accuracy obtained depends on the attention and care given by the operator to this probing operation.

[0011] In addition, measurement discrepancies were observed when two different operators performed this probing operation of the three reference points of the template, or when the same operator performed this probing operation twice in a row.

[0012] Therefore, this known method does not offer sufficient precision, for example down to the millimeter, nor the repeatability desired for an industrial application.

[0013] Finally, the calibration jig is often a bulky object that must be handled carefully despite its significant mass. Therefore, this jig is impractical to use and requires time during the commissioning of the manufacturing installation, or subsequently to verify or correct the datum change matrix between the universal installation datum and the tool datum.

[0014] Document WO2022150800 proposes a method for creating a 3-dimensional tool frame comprising identifying a reference point positioned on, or near, a reference component, creating a user frame originating from the reference point, and creating a 3-dimensional tool frame at a known position relative to the reference component.

[0015] The method described in this document WO2022150800 also provides that the 3-dimensional tool frame has coordinates substantially identical to the coordinates of the user frame in a universal installation frame, and it provides for positioning a robotic vision system so that the reference component is located in the field of vision of the robotic vision system, this reference component being a calibration grid, and for identifying the coordinates of the reference point in a universal installation frame with the robotic vision system.

[0016] The method described in this document WO2022150800 is more automated than the method using a calibration template. However, for certain industrial applications, there is a need for a method of acquiring the position and orientation of at least one user datum in a universal installation datum that offers greater accuracy.

[0017] The present invention aims to overcome the drawbacks of prior art methods.

[0018] To this end, the invention relates to a method for acquiring the position and orientation of at least one user reference frame in a universal installation reference frame, the universal installation reference frame being linked to a device for moving a support for receiving a work tool, a tool reference frame being linked to the support for receiving a work tool, and the moving device allowing the support for receiving a work tool to be moved relative to a work station.

[0019] According to the invention, the acquisition method provides: - to mount a camera on the receiving bracket of a work tool, with a camera marker linked to this camera, - to affix a user-friendly marker to the workstation, - to pre-position the camera relative to the workstation so that the user-friendly marker is within the camera's field of vision, - to move the camera into several distinct positions relative to the materialization element of a user reference frame so as to allow the camera to capture several images of the materialization element of a user reference frame from several different positions, these different images allowing the camera to determine the position and orientation of the user reference frame in the camera reference frame, - to determine the position and orientation of the user reference frame in the universal installation reference frame from the information relating to the position and orientation of the user reference frame in the camera reference frame transmitted by said camera, the position and orientation of the camera reference frame in the universal installation reference frame having been determined prior to the implementation of the acquisition method, and the position and orientation of the tool reference frame in the universal installation reference frame being known by the movement device.

[0020] Advantageously, but not necessarily, the invention may also provide that: - the camera is moved to at least three distinct positions relative to the user-referenced marker element so as to allow the camera to capture at least three images of the user-referenced marker element from at least three different positions, these different images allowing the The camera determines the position and orientation of the user's coordinate system within the camera's coordinate system. - The camera is moved by rotation between distinct positions in which the camera captures different images of the user-defined marker's materialization element from different positions. - the camera axis is always inclined relative to a vertical direction when this camera captures the different images of a material element used to determine the location and orientation of the user coordinate system in the camera coordinate system, - The element used to materialize a user reference takes the form of a patch comprising a plurality of patterns arranged in a matrix, - The patterns of the materialization element are circular and arranged on a background of a different color, the color of the patterns being lighter than the color of the background on which the patterns are arranged, - the patterns are white and arranged on a black background.

[0021] When the moving device allows the receiving support of a work tool to be moved from one workstation to another, the acquisition method provides: - to apply a user marker to each workstation, each user marker affixed to each workstation being different from the user markers affixed to the other workstations, - to successively preposition the camera in relation to each workstation so that each element representing a user reference point is successively located within the camera's field of vision, - to move the camera into several distinct positions relative to each element of a user reference frame so as to allow the camera to capture several images of each element of a user reference frame from several different positions in order to determine the position and orientation of each user reference frame in the camera frame, - to determine by calculations the position and orientation of each user reference frame in the universal installation reference frame from the information relating to the position and orientation of each user reference frame in the camera reference frame transmitted by said camera.

[0022] Advantageously, but not necessarily, the invention may also provide that: - The position and orientation of the camera reference frame within the universal installation reference frame are determined during a camera calibration step performed before the implementation of the acquisition process. - The camera calibration step is performed with a calibration target placed near the moving device and comprising a plurality of patterns arranged in a matrix, - The camera captures different images of said calibration target from different positions relative to this target to determine the position and orientation of the camera reference frame in the universal installation reference frame, - The acquisition method is implemented during the commissioning of the moving device in a manufacturing installation comprising at least one workstation on which a user reference mark is affixed; - The acquisition method is implemented again during the use of the moving device in the manufacturing installation in order to verify the position and orientation of the tool reference mark in the universal installation reference mark, for example following an impact sustained by the moving device or after a certain period of use of the moving device in the manufacturing installation; - The acquisition method is implemented again during the use of the moving device in the manufacturing installation in order to verify the position and orientation of the user reference mark of a workstation in the universal installation reference mark.for example, following an impact to the workstation.

[0023] Other features and advantages of the invention will become apparent from the following description. This description, given by way of example and not limitation, refers to the accompanying drawings in which: - [Fig. 1] represents a manufacturing installation in which the acquisition process according to the invention can be implemented, - [Fig.2] represents a materialization element of a user reference point used in the acquisition process according to the invention, and - [Fig.3] represents the capture of different images of a materialization element of a user reference carried out in the acquisition process according to the invention.

[0024] The invention relates to a method for acquiring the position and orientation of at least one user reference frame in a universal installation reference frame of a manufacturing installation such as that schematically illustrated in [Fig.1].

[0025] This manufacturing installation 10 includes a movement device 12 for a receiving support 14 of a work tool (not shown) relative to at least one workstation. For example, the movement device 12 is a robotic arm mounted on a base 16 fixed to the floor of the workshop in which the manufacturing installation is located. This robotic arm is, for example, of the 6-axis type, that is to say, comprising 6 joints and therefore 6 different axes of rotational mobility between its base 16 and the receiving support 14. The receiving support 14 takes, for example, the form of a flange on which various equipment and / or work tools can be mounted.

[0026] The manufacturing installation 10 comprises at least one workstation PI, and for example, several workstations P1, P2, P3. In the case where the installation comprises several workstations P1, P2, P3, the moving device 12 allows the receiving support of a work tool to be moved from one workstation to another. For example, the work tool mounted on the receiving support 14 is a gripping tool for transporting a finished or semi-finished product (not shown) from one workstation to another. For example, the manufacturing installation 10 is located in a tire manufacturing workshop, and the finished or semi-finished product transported by the moving device 12 is a tire blank or a component made of rubber material intended for the assembly of a tire blank.

[0027] For its implementation, the acquisition method according to the invention provides that a camera 18 is mounted on the receiving support 14 of a work tool. The mounting of this camera 18 on the receiving support 14 may be temporary or permanent. The term "camera" refers to any type of device capable of capturing an image of an object within its field of vision. Preferably, the camera 18 is capable of capturing multiple images. Also preferably, the camera 18 includes means for processing and analyzing the images it has captured. For example, the camera 18 is a camera marketed by the company SENSOPART®.

[0028] For the implementation of the method according to the invention, different reference frames are associated with the different components of the manufacturing installation 10. Thus, a universal installation reference frame Riu is linked to the movement device 12, a tool reference frame Ro is linked to the receiving support 14 of a working tool, and a camera reference frame Rc is linked to the camera 18. By reference frame, a three-dimensional Cartesian and orthonormal reference frame is preferably designated. Such a reference frame comprises an origin point and a basis of three unit vectors that are orthogonal to each other. For example, the universal installation reference frame Riu, like each of the other reference frames used in the acquisition method according to the invention, comprises its own origin point O and three orthogonal unit vectors ε, U, εt.

[0029] In order to associate a user reference frame with a workstation, the acquisition method according to the invention provides for affixing a materialization element 20 of a user reference frame Ru onto a workstation. In the case where the manufacturing installation comprises several workstations P1, P2, P3, the acquisition method provides for applying a materialization element 20 of a user reference frame to each workstation. In order to allow a control unit UC, such as a PLC, of ​​the movement device 12 to differentiate the user reference frame Ru1, Ru2, Ru3 from each workstation P1, P2, P3, each materialization element 20 a user marker affixed to each workstation is different from the materialization elements 20 of a user marker affixed to other workstations.

[0030] According to the invention, and as illustrated in [Fig. 2], a materialization element 20 of a user marker takes the form of a patch comprising a plurality of patterns M, for example, one hundred or more, arranged in a matrix. Preferably, to facilitate the precise localization of the user marker, the patterns M of the materialization element are circular and arranged on a background of a different color, the color of the patterns M being lighter than the color of the background on which the patterns are arranged. For example, the patterns M are white and arranged on a black background. For example, a materialization element 20 is a dark-colored square several centimeters on each side, and the patterns M are lighter-colored circles several millimeters on each side.Different materialization elements 20 affixed to different workstations are distinguished from one another by a different number of patterns M and / or by a different arrangement of these patterns M in the rows and / or in the columns of the pattern matrix M. For example, the materialization elements 20 are target marks marketed by the company SENSOPART®.

[0031] Once a materialization element 20 has been affixed to a workstation, the acquisition process provides for: - to pre-position the camera 18 in relation to the workstation so that the materialization element 20 of a user reference Ru is located in the field of vision of the camera 18, - to move the camera 18 into several distinct positions relative to the materialization element 20 of a user frame Ru so as to allow the camera 18 to capture several images of the materialization element 20 of a user frame Ru from several different positions.

[0032] When the manufacturing installation 10 comprises different workstations P1, P2, P3, and a materialization element 20 of a user reference Rui, Ru2, Ru3 has been affixed to each of these workstations, the working method involves: - successively pre-positioning the camera 18 relative to each workstation P1, P2, P3 so that each materialization element 20 of a user reference Rui, Ru2, Ru3 is successively located in the field of vision of the camera 18, - moving the camera 18 to several distinct positions relative to each materialization element 20 of a user reference Rui, Ru2, Ru3 so as to allow the camera 18 to capture several images of each materialization element 20 of a user reference Rui, Ru2, Ru3 from several different positions in order to determine the position and orientation of each user reference Rui, Ru2, Ru3 in the camera reference Rc.

[0033] Advantageously, since the camera 18 has its own image processing and analysis means and its own camera frame Rc, the various images of the materialization element 20 captured by the camera allow it to determine the position and orientation of the user frame Ru in the camera frame Rc. The plurality of patterns M arranged in a matrix on the materialization element 20 makes it possible to obtain a precise localization of the user frame Ru in the camera frame Rc via the image processing performed by the camera. For example, the camera 18 analyzes the deformations of the different patterns M to determine the position and orientation of the user frame Ru in the camera frame Rc.Advantageously, the different positions taken by the camera relative to the materialization element 20 and the different images of the materialization element 20 captured by the camera in these different positions make it possible to improve the accuracy of the localization of the user frame Ru in the camera frame Rc obtained by image processing and to make this localization more reliable and more representative of reality.

[0034] For example, the pre-positioning of the camera 18 relative to the workstation, enabling the placement of the materialization element 20 of a user reference point Ru within the camera 18's field of vision, is achieved through human intervention. For example, an operator directs the movements of the displacement device 12 via a human-machine interface until the materialization element 20 of a user reference point Ru is positioned within the camera's field of vision.

[0035] Following this pre-positioning of the camera 18, the movements of the camera 18 in several distinct positions relative to the materialization element 20 allowing to capture several images of the materialization element 20 are operated automatically by the movement device 12. For example, the control unit UC, like an automaton, of the movement device 12 operates these movements of the camera 18 in these different positions.

[0036] For example, the camera 18 is moved to two distinct positions relative to the materialization element 20 of a user frame so as to allow the camera 18 to capture two different images of the materialization element 20 of a user frame Ru from two different positions. Thus, two different images of the materialization element 20 are used by the camera 18 to determine the position and orientation of the user frame Ru in the camera frame Rc. As shown in [Fig. 3], the camera 18 is, for example, moved by rotation R1, R2 between two distinct positions in which the camera 18 captures different images of the materialization element 20 of a user frame Ru from different positions. For example, two distinct camera positions 18 relative to the materialization element 20 are obtained from a central position of the camera 18 and two lateral positions obtained by rotating the camera. For example, one of these lateral camera positions is obtained by a clockwise rotation R2 from the central position, while the other lateral position is obtained by a counterclockwise rotation RI from the central position. For example, these camera rotations R1, R2 have the same amplitude. For example, the amplitudes of these camera rotations R1, R2 are between 10 and 30 degrees. For example, these camera rotations R1, R2 are performed around different axes.

[0037] Preferably, to obtain optimal localization accuracy and reliability, the camera 18 is moved to at least three distinct positions relative to the user frame 20 so as to allow the camera 18 to capture at least three images of the user frame 20 from at least three different positions. Thus, at least three different images are used by the camera 18 to determine the position and orientation of the user frame Ru in the camera frame Rc. For example, three distinct positions of the camera 18 relative to the user frame 20 are obtained from a central position of the camera 18 and three lateral positions obtained by rotating the camera.For example, one of these lateral camera positions is obtained by a clockwise rotation from the central position, while the other two lateral positions are obtained by two counterclockwise rotations of different amplitudes from the central position. For example, the amplitude of these three camera rotations is between 10 and 30 degrees.

[0038] For example, after its pre-positioning relative to the materialization element 20 and before being moved into the different image capture positions of the materialization element 20, the movement device 12 realigns the camera 18 relative to the materialization element 20. This realignment preferably aims to position the camera 18 vertically above the materialization element 20. During this realignment, the movement device 12 also readjusts the distance between the camera 18 and the materialization element 20. For example, the camera 18 is positioned at a distance of between 45 and 80 cm from the materialization element 20.Advantageously, since the camera 18 is connected to the control unit UC of the displacement device 12, this realignment and readjustment of the distance of the camera relative to the materialization element 20 is obtained by means of a first image of the materialization element 20 captured and analyzed by the camera 18 from its pre-positioning position relative to the materialization element 20. For example, when two or three distinct positions of the camera 18 relative to the materialization element 20 are obtained from. from a central position of the camera 18 and from two or three lateral positions obtained by rotating the camera, the central position of the camera 18 corresponds to the position obtained after this realignment and readjustment of the distance of the camera with respect to the materialization element 20.

[0039] Preferably, in the acquisition method according to the invention, the axis of the camera 18 is always inclined with respect to a vertical direction when this camera captures the different images of a materialization element 20 used to determine the location and orientation of the user frame Ru in the camera frame Rc.

[0040] When the camera 18 uses different images of a materialization element 20 to determine the position and orientation of a user frame Ru in the camera frame Rc, each coordinate of the user frame Ru in the camera frame Rc retained by the camera and transmitted to the control unit UC of the displacement device is, for example, an average of the different values ​​of this same coordinate of the user frame Ru in the camera frame Rc determined by the camera for each of these different images.

[0041] Once the position and orientation of a user frame Ru in the camera frame Rc have been determined by the camera 18, the acquisition method provides for determining, in particular by means of various calculations and change-of-frame matrices, the position and orientation of this user frame Ru in the universal installation frame Riu of the displacement device 12 from the information relating to the position and orientation of the user frame Ru in the camera frame Rc transmitted by said camera.

[0042] When the manufacturing installation 10 comprises different workstations P1,P2,P3 and the position and orientation of each user reference Rui,Ru2,Ru3 in the camera reference Rc have been determined by the camera 18, the acquisition method provides for determining, in particular by means of different calculations and coordinate change matrices, the position and orientation of each user reference Rui,Ru2,Ru3 in the universal installation reference Riu from the information relating to the position and orientation of each user reference Rui,Ru2,Ru3 in the camera reference Rc transmitted by said camera.

[0043] The camera 18 being for example connected to the control unit UC of the movement device 12, the determination, in particular with the help of different calculations and coordinate system change matrices, of the position and orientation of one or more user reference frames in the Riu universal installation reference frame of the movement device 12 is carried out by this control unit UC, from the information transmitted by this camera 18.

[0044] In order to determine the position and orientation of one or more user reference frames in the Riu universal installation reference frame of the movement device 12 from the information transmitted by the camera 18, it is necessary, for example for the control unit UC, to know the position and orientation of the camera reference frame Rc in the Riu universal installation reference frame and the position and orientation of the tool reference frame Ro in the Riu universal installation reference frame. Indeed, the different reference frame change matrices of a manufacturing installation 10 according to the invention are related by the following equation:

[0045] M Riu -Ro = M Riu -Ru

[0046] with: M Riu _Ro = Matrix of coordinate system change between the universal installation coordinate system Riu of the movement device 12 and the tool coordinate system Ro of the receiving support 14, M Riu -Ru = Matrix of coordinate system change between the universal installation coordinate system Riudu of the movement device 12 and the user coordinate system Ru of a materialization element 20 affixed to a workstation, M Ru- Rc = Matrix of coordinate system change between the user coordinate system Ru of a materialization element 20 affixed to a workstation and the camera coordinate system Rc of camera 18, and M Rc -RO = Change of reference matrix between the camera reference Rc of camera 18 and the tool reference Ro of the receiving support 14.

[0047] As an alternative or complement to coordinate transformation calculations performed using matrices, the acquisition method may also provide that the control unit CU performs some of these coordinate transformation calculations with vectors. For example, these calculations may be performed with Cartesian coordinates and / or spherical coordinates.

[0048] For example, the position and orientation of the camera reference frame Rc in the universal mounting frame Riu are determined prior to the implementation of the acquisition method according to the invention, and the position and orientation of the tool reference frame Ro in the universal mounting frame Riu are known by the displacement device 12, and more particularly by its control unit UC. For example, the position and orientation of the tool reference frame Ro in the universal mounting frame Riu are determined at the factory by the manufacturer of the displacement device 12 and stored in the control unit UC of this displacement device 12.

[0049] Since the displacement device 12 is not equipped with the camera 18 by its manufacturer, this camera 18 is subsequently mounted on the receiving support 14, for example, for the implementation of the acquisition method. Also, the acquisition method according to the invention provides that the position and orientation of the camera reference frame Rc in the frame Riu universal installation are determined during a camera calibration step performed before the implementation of the acquisition process.

[0050] For example, the calibration step of the camera 18 is carried out with a calibration target (not shown) positioned near the movement device 12 and comprising a plurality of patterns, for example more than one hundred, arranged in a matrix. For example, a calibration target comprises light-colored circular patterns arranged in a matrix on a dark-colored background. For example, the patterns of the calibration target are white circles arranged in a matrix on a black background. This calibration target is, for example, positioned near the movement device 12 and the workstation(s) P1, P2, P3 by an operator.

[0051] In order to determine the position and orientation of the camera reference frame Rc in the Riu universal installation coordinate system, the camera captures different images of the calibration target from different positions relative to that target. For example, the camera captures approximately ten images of the calibration target from approximately ten different positions. The displacement device 12 moves the camera 18 between these different calibration positions. Even if the calibration target is positioned arbitrarily relative to the displacement device 12, since the position of this calibration target remains the same throughout the calibration step, it constitutes a fixed reference point that allows the control unit UC to deduce the position and location of this camera 18 relative to the displacement device 12, and therefore the position and location of the camera reference frame Rc in the Riu universal installation coordinate system.

[0052] As previously stated, the position and orientation of the tool reference Ro of the receiving support 14 in the universal installation reference Riu of the moving device 12 are determined by the manufacturer of the moving device 12 and stored in the control unit UC of this moving device 12. Also, the acquisition method according to the invention provides for a first implementation during the commissioning of the moving device 12 in a manufacturing installation 10 comprising at least one workstation on which is affixed a materialization element 20 of a user reference.Advantageously, during this first implementation of the acquisition process, the displacement device 12 and the receiving support 14 of a work tool have not yet been used in manufacturing and have therefore not yet been subjected to shocks likely to modify the position and orientation of the tool reference Ro in the universal installation reference Riu determined by the manufacturer of the displacement device 12 and recorded in its control unit UC. .

[0053] Once the displacement device 12 has been put into service and the initial implementation of the acquisition method according to the invention has been carried out, the device The movement device is used to perform various tasks within the manufacturing installation. During the execution of these tasks, the movement device, and more specifically one of its articulated arms, may be subjected to one or more impacts. These impacts can alter the position and orientation of the receiving support, and therefore of the tool reference Ro and the universal installation reference Riu, making the movements of the movement device 12, and consequently those of the work tool mounted on the receiving support 14, imprecise. This can lead to failures in the execution of certain tasks or to dangerous situations.

[0054] Moreover, over time, and simply due to the wear of certain mechanical parts of the displacement device 12 and the large number of repeated movements by the displacement device, it may happen that the position and orientation of the receiving support, and therefore of the tool reference Ro, in the universal installation reference Riu are modified little by little.

[0055] Also, the acquisition method according to the invention provides for other implementations during the use of the displacement device 12 in the manufacturing installation 10 in order to verify the position and orientation of the tool reference Ro, in the universal installation reference Riu, for example following a shock suffered by the displacement device 12 or after a certain period of use of the displacement device 12 in the manufacturing installation 10.

[0056] Like the displacement device 12, a workstation P1, P2, P3 can be subjected to shocks during its use in the manufacturing installation. Therefore, the acquisition method according to the invention can be implemented during the use of the displacement device 12 in the manufacturing installation 10 in order to verify the position and orientation of the user reference frame Ru of a workstation in the universal installation reference frame Riu, for example following a shock to the workstation.

Claims

Demands

1. A method for acquiring the position and orientation of at least one user reference frame in a universal installation reference frame, the universal installation reference frame being linked to a device for moving a work tool receiving support, a tool reference frame being linked to the work tool receiving support, the moving device allowing the work tool receiving support to be moved relative to a workstation, the acquisition method being characterized in that it provides for: - mounting a camera on the work tool receiving support, a camera reference frame being linked to this camera, - affixing a materialization element of a user reference frame to the workstation, - pre-positioning the camera relative to the workstation so that the materialization element of a user reference frame is located in the camera's field of vision,- to move the camera into several distinct positions relative to the materialization element of a user reference frame so as to allow the camera to capture several images of the materialization element of a user reference frame from several different positions, these different images allowing the camera to determine the position and orientation of the user reference frame in the camera reference frame, and - to determine the position and orientation of the user reference frame in the universal installation reference frame from the information relating to the position and orientation of the user reference frame in the camera reference frame transmitted by said camera, the position and orientation of the camera reference frame in the universal installation reference frame having been determined prior to the implementation of the acquisition method, and the position and orientation of the tool reference frame in the universal installation reference frame being known by the movement device.

2. An acquisition method according to claim 1, wherein the camera is moved to at least three distinct positions relative to the materialization element of a user landmark so as to allow the camera to capture at least three images of the materialization element of a user landmark from at least three different positions, these different images allow the camera to determine the position and orientation of the user frame in the camera frame.

3. Acquisition method according to claim 1 or 2, wherein the camera is moved by rotation between distinct positions in which the camera captures different images of the materialization element of a user reference point from different positions.

4. An acquisition method according to any one of the preceding claims, wherein the camera axis is always inclined with respect to a vertical direction when this camera captures the different images of a materialization element used to determine the location and orientation of the user frame in the camera frame.

5. Acquisition method according to any one of the preceding claims, wherein the materialization element of a user marker takes the form of a patch comprising a plurality of patterns arranged in a matrix.

6. Acquisition method according to claim 5, wherein the patterns of the materialization element are circular and arranged on a background of different color, the color of the patterns being lighter than the color of the background on which the patterns are arranged.

7. Acquisition method according to claim 6, wherein the patterns are white and arranged on a black background.

8. An acquisition method according to any one of the preceding claims, wherein, - the displacement device for moving the receiving support of a work tool from one workstation to another workstation, the acquisition method comprises: - applying a user reference point materialization element to each workstation, each user reference point materialization element affixed to each workstation being different from the user reference point materialization elements affixed to the other workstations, - successively pre-positioning the camera relative to each workstation so that each user reference point materialization element is successively located within the camera's field of vision, - to move the camera into several distinct positions relative to each materialization element of a user reference frame so as to allow the camera to capture several images of each materialization element of a user reference frame from several different positions in order to determine the position and orientation of each user reference frame in the camera reference frame, - to determine by calculations the position and orientation of each user reference frame in the universal installation reference frame from the information relating to the position and orientation of each user reference frame in the camera reference frame transmitted by said camera.

9. Acquisition method according to any one of the preceding claims, wherein the position and orientation of the camera reference frame in the universal installation reference frame are determined during a camera calibration step carried out before the implementation of the acquisition method.

10. Acquisition method according to claim 9, wherein the camera calibration step is carried out with a calibration target disposed near the displacement device and comprising a plurality of patterns arranged in a matrix.

11. Acquisition method according to any one of claims 9 or 10, wherein the camera captures different images of said calibration target from different positions relative to that target to determine the position and orientation of the camera reference frame in the universal installation reference frame.

12. Acquisition method according to any one of the preceding claims, the acquisition method being implemented during the commissioning of the displacement device in a manufacturing installation comprising at least one workstation on which is affixed a materialization element of a user reference point.

13. Acquisition method according to claim 12, the acquisition method being again implemented during the use of the displacement device in the manufacturing installation in order to verify the position and orientation of the tool reference in the universal installation reference, for example following a shock suffered by the displacement device or after a certain period of use of the displacement device in the manufacturing installation.

14. Acquisition method according to claim 12 or 13, the acquisition method being again implemented during of the use of the displacement device in the manufacturing installation in order to check the position and orientation of the user reference of a workstation in the universal installation reference, for example following a shock suffered by the workstation.

Images