ROBOTIZED HAMMERING METHOD AND ROBOTIZED SYSTEM FOR IMPLEMENTING THE METHOD

Abstract

A robotised hammering method for hammering a weld seam (C) made on a base surface (S) of a metal workpiece (V) using a robotised system (32), comprising the following steps:controlling the robotised system (32) provided with an effector (35; 38) carrying a scanning tool (30) in such a way as to follow, with the scanning tool (30), an initial path along the weld seam (C), said initial path having been determined from the digital model of the workpiece or from the actual workpiece,acquiring, by means of the scanning tool (30), along the initial path, local data concerning the elevation and position of the weld seam and of the area or areas of the base surface close to the weld seam,calculating, from the elevation and position data acquired in this way and from the initial path, a corrected path, andcontrolling the robotised system (32) provided with an effector (40; 38) carrying a hammering tool (41) to hammer the weld seam along this corrected path.

Claims

1. A method for robotized peening of a weld bead produced on a base surface of a metal workpiece using a robotized system, comprising: controlling the robotized system provided with an effector bearing a scanning tool to follow, with the scanning tool, an initial trajectory along the weld bead, this initial trajectory having been determined from the numerical model of the piece or of the real workpiece; acquiring, using the scanning tool, along the initial trajectory, local data on the relief and position of the weld bead and on the zone or zones of the base surface in proximity to the weld bead; calculating, from the relief and position data thus acquired and from the initial trajectory, a corrected trajectory; and controlling the robotized system provided with an effector bearing a peening tool for peening the weld bead along this corrected trajectory.

2. The method as claimed in claim 1, wherein the local data on the relief and position of the weld bead comprise, for any point of the weld bead, the spatial coordinates of the root of the weld bead and the angle formed at the root between the weld bead and the base surface of the workpiece.

3. The method as claimed in claim 1, further comprising a step of monitoring the corrected trajectory consisting in: controlling the robotized system provided with the effector bearing the scanning tool to follow, with the scanning tool, the corrected trajectory, acquiring, using the scanning tool, along the corrected trajectory, local data on the relief and position of the weld bead, and comparing the new scanned trajectory and the corrected trajectory.

4. The method as claimed in claim 2, further comprising: the step of monitoring the corrected trajectory comprising the taking of geometrical measurements of the surface to be peened.

5. The method as claimed in claim 1, further comprising, after the peening step a quality control step consisting in controlling the robotized system provided with the effector bearing the scanning tool to acquire local data on the relief and position of the peened weld bead, in order to monitor and quantify the quality thereof.

6. The method as claimed in claim 4, further comprising, after the peening step a quality control step consisting in controlling the robotized system provided with the effector bearing the scanning tool to acquire local data on the relief and position of the peened weld bead, in order to monitor and quantify the quality thereof, the quality control step comprising the taking of geometrical measurements of the peened surface, and the comparison with the taking of geometrical measurements of the surface to be peened, in order to conclude on the quality of the peening.

7. The method as claimed in claim 6, further comprising, if the quality of the peening is deemed insufficient, a subsequent step of peening of all or part of the peened surface by control of the robotized system provided with the effector bearing the peening tool along the corrected trajectory.

8. The method as claimed in claim 1, further comprising a step of control of the robotized system provided with an effector bearing a grinding or milling tool along the corrected trajectory in order to perform a finishing of the peened surface.

9. The method as claimed in claim 1, further comprising at least one step of changing of effector, the robotized system being provided either with an effector bearing the peening tool capable of performing the peening step or steps, or an effector bearing the scanning tool capable of performing the step or steps of acquisition of local data on the relief and position of the weld bead.

10. The method as claimed in claim 1, wherein no step of changing of effector is provided, the robotized system being provided with an effector bearing both at least the scanning tool and the peening tool, and the grinding or milling tool.

11. A robotized system for implementing the method as claimed in claim 1, comprising at least one effector comprising at least: a scanning tool configured to acquire local data on the relief and the position of the weld bead, and a peening tool configured to perform a peening treatment of said weld bead.

12. The robotized system as claimed in claim 11, the robotized system being provided alternatively with an effector bearing said at least one scanning tool and an effector bearing the peening tool, the effectors bearing the scanning tool and the peening tool being configured such that the reference point of the tool is identical for the effector bearing the peening tool and the effector bearing the scanning tool.

13. The robotized system as claimed in claim 12, the robotized system being provided with a single effector bearing said at least one scanning tool and said at least one peening tool.

14. The robotized system as claimed in claim 11, comprising a compliance provided to maintain the contact between the peening tool and the weld bead during the peening and to monitor the contact force, the compliance being situated in a detection axis resulting from the spatial position of the root of the weld bead and of the bisector, the compliance comprising a passive or active damping means, the calibrated contact force at rest lying between 1N and 500N.

15. The robotized system as claimed in claim 11, further comprising an angular compliance, arranged to deflect, if necessary, the peening tool toward the root of the weld bead to be treated in a plane substantially orthogonal to the bead, the angular compliance allowing an angular play of the peening tool lying between 0 and 30.

16. The robotized system as claimed in claim 11, further comprising an effector bearing a grinding or milling tool or the effector bearing a grinding or milling tool.

17. The robotized system as claimed in claim 11, wherein the scanning tool is chosen from the group composed of the contact-based systems for acquiring relief and position data and the contactless systems for acquiring relief and position data.

18. The robotized system as claimed in claim 11, wherein the peening technology of the peening tool is chosen from the group composed of ultrasound, pneumatic, linear mechanical and linear electric motor peening.

19. The robotized system as claimed in claim 11, further comprising a counterweight system configured to compensate the weight of the peening tool whatever the orientation thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0059] The invention will be able to be better understood on reading the following description, of nonlimiting exemplary implementations thereof, and on studying the attached drawing, in which:

[0060] FIG. 1 represents, in the form of a functional diagram, different steps of the method according to an exemplary implementation of the invention,

[0061] FIG. 2 schematically represents, partially and in perspective, a scanner of a part of weld bead,

[0062] FIG. 3A represents, in schematic transverse cross section, the weld bead of FIG. 2, before peening,

[0063] FIG. 3B partially represents, in transverse cross section and schematically, the weld bead of FIG. 2 after peening,

[0064] FIG. 4 represents, schematically and in perspective, an effector bearing a scanning tool used in the implementation of the method of FIG. 1,

[0065] FIG. 5 represents, schematically and in perspective, an effector bearing a peening tool used in the implementation of the method of FIG. 1,

[0066] FIG. 6 illustrates, by a functional diagram, another exemplary implementation of the method according to the invention,

[0067] FIG. 7 schematically represents, partially and in perspective, an example of an effector bearing the peening tool and the scanning tool or tools for the implementation of the method illustrated in FIG. 6,

[0068] FIG. 8 is a schematic and perspective bottom view of the effector of FIG. 7,

[0069] FIG. 9 illustrates, partially, schematically and in a perspective view, a production line with robots each provided with a robotized system according to an example of the invention,

[0070] FIGS. 10 and 11 schematically represent the trajectories, respectively real and initial after scan, and real and corrected after correction,

[0071] FIG. 12 represents, schematically and in perspective, a weld bead after peening,

[0072] FIG. 13 schematically and partially represents, in cross section, a weld bead root after peening,

[0073] FIG. 14 represents the weld bead root of FIG. 13 after grinding,

[0074] FIGS. 15 and 16 schematically represent, in perspective, two examples of tools that may be used for the grinding or milling step,

[0075] FIG. 17 is a schematic view of a graph of fatigue behavior in relation to the effort of pressure of a weld peened and/or ground or not,

[0076] FIGS. 18 and 19 respectively schematically represent the effector bearing the scanning tool and the effector bearing the peening tool linked to the robotized system and having the same TCP,

[0077] FIGS. 20 and 21 represent, schematically in plan view, different examples of weld beads treated by peening using the method according to the invention,

[0078] FIG. 22 is a schematic diagram illustrating the robotized system comprising a counterweight system, and

[0079] FIG. 23 is an enlarged view of a detail of FIG. 22.

DETAILED DESCRIPTION OF EMBODIMENTS

[0080] FIG. 1 shows the different steps of the method for robotized peening of a weld bead performed on a base surface of a metal workpiece, using a robotized system, according to an exemplary implementation of the invention.

[0081] In this example, the method comprises a step 1 consisting in defining the initial trajectory of the part or parts of the weld bead which will be treated by peening. The initial trajectory is the trajectory of a peening tool used in the subsequent peening operation. This initial trajectory, which is theoretical, is determined from the numerical model of the workpiece and using, for example, offline programming tools (PHL), or else from the real workpiece by manual learning.

[0082] In a step 2, an effector bearing a scanning tool is fixed removably onto a robotized system so as to be able, in a step 3, to control the robotized system provided with the effector bearing the scanning tool so as to scan the weld bead to be treated by following the initial trajectory which was defined in the step 1. The scanner of the weld bead will make it possible to acquire, by virtue of the scanning tool, local data on the relief and position of the weld bead and on the zones of the base surface of the workpiece which are adjacent thereto. A schematic example of curve illustrating the deviation between the plots of the real trajectory and of the initial trajectory has been illustrated in FIG. 10. In this figure, the plot of the initial trajectory has been represented at the bottom and that of the real trajectory at the top. These plots are not fully overlaid, with a deviation illustrated by the larger or smaller double-headed arrows between the two plots. Obviously, FIG. 10 shows only the trajectories in two dimensions but the acquisition of local data on the relief and position of the weld bead make it possible to access the spatial coordinates in three dimensions of the weld bead and of its near environment, in particular over the weld bead root and of the angle formed between the weld and the surface of the workpiece, at the root.

[0083] FIG. 2 very schematically illustrates the scan using the scanning tool 30 composed of a system for acquiring relief and position data performing a scan 31 of the weld bead C, more particularly of the root P consisting of the zone extending to the join between the weld bead C and the base surface S of the metal workpiece on which the weld has been produced.

[0084] When the scan of the weld bead is performed, the aim is to obtain, as illustrated in FIG. 3A, local data on the relief and position of the weld bead and its near environment, in particular the positioning in three dimensions of the weld bead root, at any point P.sub.i of the weld to be peened, and also the angle 2*a formed between the weld and the workpiece, at the root, in order to determine the coordinates in three dimensions of the bisector, at any point P.sub.i of this root, consisting of the half-line passing through the root with equiangle a between the surface S and the weld bead C at the root P. Thus, through this scan, it is possible to know the three-dimensional coordinates of the point P.sub.i and also those of the straight line A, forming the detection axis, of orientation coinciding with that of the bisector passing through P.sub.i.

[0085] To perform the scan, the effector bears a scanning tool 30 which may be a contact-based relief and position data acquisition system, for example comprising mechanical feelers, or a contactless relief and position data acquisition system, such as optical sensors, in particular laser or cameras, inductive sensors or capacitive sensors, or another contact-based or contactless location system. In the example illustrated, the effector 35 illustrated in FIG. 4 comprises a scanning tool 30 composed of an optical sensor 36 consisting of a laser ray and a camera.

[0086] In a step 4, a post-processing of the acquired data is performed to locate the root P of the weld bead C.

[0087] In a step 5 illustrated in FIG. 1, and based on the acquired data on the relief and position of the weld bead C and on the post-processing, the difference is calculated between the result of the scan, that is to say the real trajectory, and the initial trajectory. The result of this differential calculation is a correction of the initial trajectory, in a step 6, which will make it possible to obtain a corrected initial trajectory, the plot of which is illustrated schematically in FIG. 11 as being superimposed on that of the real trajectory modulo the accuracy achieved by the installation as a whole.

[0088] In a step 7, the scanning tool is used again to scan by following the corrected trajectory in order to check, in a step 8 of FIG. 1, that the correction is correct. If the latter is not correct, indicated NOK in FIG. 1, there is a return to the step 3 as illustrated and the steps 3, 4, 5, 6 and 7 are implemented again until the correction is acceptable, indicated OK in FIG. 1, in which case the implementation of the method may be continued.

[0089] Moreover, this step 7 may make it possible to obtain output data illustrated in the box 9 of FIG. 1, namely geometrical measurements of the zone or surface to be peened, before treatment.

[0090] When the correction checked in the step 8 is correct, there is a transition to the step 10 of changing of effector so as to fix an effector bearing a peening tool onto the robotized system.

[0091] An example of effector 40 bearing a peening tool 41 has been illustrated in FIG. 5. It should be noted that the high-frequency peening technology may consist of an ultrasound, pneumatic, linear mechanical or linear electric motor peening, preferably ultrasound peening.

[0092] In the example illustrated, the peening technology is ultrasound-based with a vibration amplitude lying between 5 and 200 m peak-to-peak (p/p). In the example illustrated, as may be seen in particular in FIGS. 7 and 8, the peening tool 41 comprises a single needle or impactor 43 in the peening head 42. The vibration frequency lies between 10 kHz and 60 kHz.

[0093] In a step 11, the robotized system is controlled to perform a peening using the peening tool 41 by following the corrected trajectory then the effector is changed again in a step 12 so as to place the effector 35 bearing the scanner tool 30 on the robot.

[0094] In a step 13, a new monitoring scan is performed on the peened zone in order, in the step 14, to check the quality of the treatment of the peened zone. If the latter is not correct at least at certain points, denoted NOK in FIG. 1, then, in the step 16, the specific zones to be peened are determined, the effector is changed for the robot to be provided with the effector 40 bearing the peening tool 41 in a step 17 and a new peening of the weld bead C or only of one or more defective zones is performed in the step 18.

[0095] During this monitoring scan of the peened zone, it is also possible to perform a measurement of the geometry of the peened zone, noted in the box 19, and the latter is compared to the measurement of the geometry of the zone before peening 2 of box 9. This comparison may make it possible, if appropriate, in particular if the peening is not satisfactory, to also perform a new peening of all or part of the weld bead by following the steps 16, 17 and 18.

[0096] On the other hand, if this comparison and the check culminate in a satisfactory conclusion concerning the peening performed, called OK, after repeat peening or not, it is possible to reposition the robotized system to perform a new peening treatment of a weld bead as illustrated in the step 20.

[0097] The geometrical measurements taken after peening may comprise data making it possible, by comparison with the geometrical measurements of the box 9, taken before peening, to obtain, as illustrated in FIG. 3B: the maximum depth b1 of peening of the weld bead C, the maximum depth b2 of peening of the base surface S, and width w of peening, the radius r of the peened zone Z.

[0098] As already indicated, the robotized system 32, illustrated partially in FIGS. 4 and 5, according to the invention, used for the implementation of the method illustrated in FIG. 1, comprises a mounting interface 45 with a coupler on the robot side 46. The robotized system 32 also comprises an effector 35 bearing a mechanical interface 49 forming a fixing plate that may be equipped if appropriate with a spatial positioning adjustment system, a coupler on the effector 48 side and a scanning tool 30 configured to register, digitize the spatial position in three dimensions of the weld bead root at any point thereof and the angle formed between the base surface S of the workpiece on which the weld has been produced and the weld bead C so as to be able to find the bisector and detection axis A. The robotized system 32 also comprises an effector 40 bearing at least one peening tool 41. It should be noted that, in this example, the mounting interface 45 makes it possible alternatively to mount on the robotized system 32 the effector 35, as illustrated in FIG. 4, and the effector 40, as illustrated in FIG. 5.

[0099] As illustrated in FIGS. 18 and 19, the TCP, that is the tool reference point or Tool Center Point, is, in this example, identical for the effector 40 and the effector 35. That makes it possible to ensure a repeatablility of the movement of the robot and to use this repeatability as a basis for reliabilizing the trajectory monitoring and the peening trajectory.

[0100] The robotized system 32 also comprises, on the effector 40, a compliance 47 provided to maintain the contact between the peening tool 41 and the weld bead C and monitor the contact force. The axis of mobility of the compliance 47 is positioned parallel to the detection axis A resulting from the spatial position of the root and of the bisector. The compliance 47 comprises a passive or active damping means. The calibrated contact force at rest that it seeks to ensure lies between 1N and 500N, better between 2N and 200N and preferentially between 70N and 100N.

[0101] In a way that cannot be seen in the drawing in the interests of clarity because it is arranged inside, the robotized system 32 also comprises, in this example, an angular compliance arranged to deflect, if necessary, the peening tool 41 toward the weld bead root to be treated in a plane substantially orthogonal to the bead. The angular compliance in fact allows an angular play of the peening tool 41 lying between 0 and 30, better between 0 and 5.

[0102] FIG. 6 represents another example of implementation of the method according to the invention. In the implementation of this method, the robotized system 32, illustrated in FIGS. 7 and 8, differs essentially from that illustrated in FIGS. 4 and 5 in that the effector comprises at least one scanning tool 30 and at least peening tool 40 and borne by the robotized system, not requiring a changing of effector in the implementation of the method. In this example, as may be seen, the effector 38, called combined effector, bears both a first scanning tool 30 allowing the acquisition of relief and position data arranged upstream in the direction of the trajectory on the robot, the peening tool 41 and a second scanning tool 30 allowing the acquisition of relief and position data downstream in the direction of the trajectory.

[0103] In this case, there is at the same time a monitoring and a peening that are almost simultaneous and point-by-point of the weld bead root qualified as virtually real-time correction.

[0104] The method whose steps are illustrated in FIG. 6 proceeds as follows. In a step 21, the initial trajectory of the weld bead is defined, in the same way as for the method illustrated in FIG. 1. The robotized system 32 of FIGS. 7 and 8 is used, for each point of the weld bead root, to perform the step 22 of scanning by following the initial trajectory, the step 23 of correction of the theoretical trajectory as a function of a differential calculation, the step 24 of scanning by following the corrected theoretical trajectory with a step 25 of checking of the correction of the trajectory and the step 26 of measurement of the geometry of the zone to be peened, these steps being performed using the first scanning tool 30, and the step 27 of peening by following the corrected trajectory using the peening tool 41 and the step 28 of monitoring scan of the peened zone and the step 29 of measurement of the geometry of the peened zone using the second scanning tool 30. As may be seen, the steps are substantially the same as illustrated in FIG. 1, apart from the fact that there is no changing of effector and that, instead of performing a complete scan of the part of the weld bead to be treated or of the parts of weld bead to be treated, there are performed the steps of scanning of a set of points with the first scanning tool 30 just before they are peened with the peening tool 41 then of monitoring them with the second scanning tool 30 while performing a scan of other points just before they are peened and then of monitoring them. This embodiment is called virtual real-time correction.

[0105] If necessary, as illustrated in FIG. 6, a second run is performed after having performed all of the scanning, peening and monitoring steps, to monitor and/or peen at least certain zones once again.

[0106] As may be seen in FIG. 9, it is possible to have a production line with a robotized cell in a workshop and the workpiece V, in this example a motor vehicle, is treated by a set of fixed robots R each bearing the robotized system 32 in the form of robotized arm.

[0107] As a variant, in a manner that is not illustrated, the robot or robotized system 32 may be displaced to the zone of the workpiece which is immobile in order to treat certain zones. Finally, as a variant, the robot may be stuck to the immobile piece, being fixed to the latter to treat certain parts thereof.

[0108] The peening may consist in treating only certain parts E of a single weld bead C as illustrated in FIG. 20 or several parts E of different weld beads, as illustrated in FIG. 21.

[0109] In this case, the system previously described may treat a single part E or several parts E of one and the same weld bead or of different weld beads. An entire weld bead may also be treated.

[0110] The peening produces, from a succession of impacts, a furrow, also called undercut, which is generally quite smooth. FIG. 12 illustrates, in an exaggerated manner, the result of the peening of a weld bead C on which may be seen, enlarged and schematically, the impacts I obtained on the weld bead root P, at least in the area surrounding this weld bead root P. The impacts I may, as illustrated in FIG. 13, create material folds U. The method may comprise the finishing step consisting in grinding these folds U as illustrated in FIG. 14 so as to obtain a smoother peened surface. The grinding makes it possible to crop the U-shape folds forming peening defects. In this case, the method may comprise a step of changing of effector to arrange an effector bearing a grinding or milling tool and a grinding or milling step. The grinder may, as a variant, be incorporated in the peening robot.

[0111] Examples of cutting or abrasive grinding or milling tools 50 that may be used for the grinding effector have been illustrated in FIGS. 15 and 16. In the example illustrated in FIG. 15, the tool 50 is a ball milling cutter with spherical end 51. The radius of curvature of the ball milling cutter is approximately equal to the radius of the undercut, that is to say of the zone formed around the root P by peening. In the example of FIG. 16, the tool 50 is a disk-grinder with rounded edge. The rounded edge has a radius of curvature substantially equal to the radius of the undercut.

[0112] As illustrated in FIG. 17, the fatigue behavior of a weld, whatever the force exerted, offers better performance when the weld has been peened. This peened weld offers even better performance if the peening has been followed by a controlled grinding again as illustrated in this FIG. 17.

[0113] FIGS. 22 and 23 represent the possibility for the robotized system 32 to be provided with a counterweight system 60 comprising an effort-opposing transfer link rod 61, capable of pivoting about the central axis X, and a counterweight 62. The link rod 61 is, as may be seen, fixed at a point 64 to the peening tool 41 bearing the peening head 42 and the impactor 43 and, at a point 65, opposite in relation to the central axis X, to the counterweight 62. The counterweight system 60 also comprises two translation guiding axes 66 and 67. The peening tool 41 is mounted to slide on the guiding axis 66 so as to be able to be translationally displaced along the latter. The counterweight 62, for its part, is mounted to slide on the guiding axis 67 so as to be able to be translationally displaced along the latter. As illustrated in FIG. 23, a distance d.sub.1 separates the central axis X from the point 64 and a distance d.sub.2 separates the central axis X from the opposite point 65, on the link rod 61.

[0114] The weights P.sub.t of the peening tool 41 and P.sub.e of the counterweight 62 are linked by the relationship: P.sub.e=d.sub.i/d.sub.2*P.sub.t. If d.sub.1=d.sub.2, then P.sub.c=P.sub.1.

[0115] The counterweight system 60 is configured to compensate the weight of the peening tool 41, whatever its orientation, inclined or straight. The presence of the counterweight system 60 makes it possible to more easily ensure that the peening head applies an effort that is constant during the peening.