METHOD FOR INSPECTING A WELD

Description

[0001] The invention relates to a method for checking and / or correcting a weld, such as a weld spot, of a test object, such as a motor vehicle, or one or more parts thereof, comprising the method steps: Aligning an ultrasonic probe guided by a robot to the target position of the weld, determining the actual position of the weld using an optical sensor and aligning the ultrasonic probe to the actual position and placing the ultrasonic probe in the normal direction of the weld, measuring the weld.

[0002] DE 101 25 782 A1 describes a method for automated ultrasonic testing of resistance spot welds. This method involves moving to a known target position of the resistance weld to be tested, and interacting with a computer-controlled test signal evaluation in the robot controller, activating motion modules programmed in such a way that a matrix of spatial positions of the ultrasonic probe is gradually processed, which most likely includes an optimal position. The ultrasonic signal is evaluated between each two probe positions until a clear test result based on known criteria is obtained.

[0003] DE 10 2004 044 342 A1 describes an arrangement and method for automated ultrasonic testing of three-dimensional, beam-welded components. A five-axis articulated-arm robot with a probe carrier, in which an ultrasonic probe with an ultrasonic transmitter and receiver are integrated, is used for the testing.

[0004] DE 11 2006 000 360 T5 discloses a method for inspecting weld spots. First, the expected position coordinates of a weld spot are specified to an industrial robot. The industrial robot is then positioned, and the weld spot to be inspected is detected using an optical device. The measuring head is then aligned to the actual position coordinates of the weld spot.

[0005] In order to check weld points, according to DE 10 2017 125 033 A1, an industrial robot has a measuring tool with an optical device for taking an image of a weld to be inspected and a measuring head for checking the weld.

[0006] To measure workpieces, according to EP 2 322 897 A1, a sensor is deployed from a robot arm. This sensor is first moved to a starting position at a first speed and then approached to a measuring point at a second speed.

[0007] A non-destructive inspection of spot welds is described in US 2017 / 0284970 A1. It uses a phased array ultrasonic probe.

[0008] DE 10 2005 043 776 A1 describes a generic method for positioning an ultrasonic test head, which is moved from an estimated position to an ideal test position using a camera.

[0009] JP H02263157 A describes an ultrasonic testing system with an ultrasonic probe that pivots from a mount. Connected to the mount is a spray device that can be used to wet the front surface of the ultrasonic probe.

[0010] The subject of DE 31 22 408 A1 is a method and a device for cleaning and wetting the front surface of an ultrasound lens.

[0011] The present invention is based on the object of developing a method of the type mentioned at the outset in such a way that a weld can be checked quickly and precisely and the results can be used for further welds or welded joints if necessary.

[0012] In terms of the method, the task is essentially solved by providing CAD data of the target position of the weld, aligning the ultrasonic test head to the target position of the weld on the basis of the CAD data of the weld and, after determining the actual position of the weld using the optical sensor, placing the ultrasonic test head on the weld in a force-controlled manner, wherein one or more calibration bodies of known CAD data are assigned to the robot in a stationary manner, the calibration body or bodies together with the test piece or pieces.of the one part or several parts of the test object are measured by means of a camera or a 3D scanner, and that the position of the test object is determined by means of 2D images from the camera or 3D point cloud from the 3D scanner and is transformed into the coordinate system of the robot taking into account CAD data of the test object, and that in order to place the ultrasonic test head in the normal direction of the weld, the normal direction is determined by means of ultrasonic sensors of the ultrasonic test head and / or by determining the direction of the vector of the force acting on the weld by means of at least one force and / or moment sensor.

[0013] According to the invention, in particular, a multi-axis robot is used to which an ultrasonic probe is attached. This is in particular a phased array ultrasonic probe, which can, for example, have a matrix of 10 x 10 to 15 x 15 transmitter / receiver elements. The operating frequency can be 20 MHz. Furthermore, a sensor, in particular an optical sensor, is arranged in a fixed position relative to the ultrasonic probe, by means of which the weld or the weld point is detected. For the inspection, the ultrasonic probe is first aligned to the appropriate positions based on the target data of the weld, specifically using CAD files, in order to then determine the actual weld position using the optical sensor and subsequently align the probe to the weld in order to inspect it. The probe is placed on the weld with adaptive force control.For this purpose, the force-torque sensor system of the robot is used to allow the ultrasonic probe to act on the weld with a force P of, for example, P ≤ 30 N, in particular 5 N ≤ P ≤ 15 N, preferably P approximately 5 N - 10 N, when measuring the weld.

[0014] The test itself is performed by placing a coupling medium, preferably water, between the transmitter and receiver of the ultrasonic test sensor. This coupling medium is located in an encapsulated area of ​​the test head. This area, or a housing containing the coupling medium, is sealed on the test piece side with a cover, such as a membrane or foil, which is previously moistened with a coupling fluid, such as water or oil, for measurement.

[0015] The robot's movement is calibrated in the coordinate system of the test object, taking the CAD data of the test object into account. This means that the position of the test object relative to the robot, and thus to the ultrasonic probe, is determined using the CAD data of the test object.

[0016] Calibration can be performed using one or more 2D images from a camera or 3D point clouds from a 3D scanner. A best fit is performed between the 2D images or 3D point clouds and the CAD model to capture the 6D position of the test object.

[0017] Therefore, the invention provides that one or more calibration bodies of known CAD data are assigned to the robot in a stationary manner, that the calibration body(s) are measured together with the test object or one part or several parts of the test object by means of a camera or a 3D scanner, and that by means of 2D images of the camera or 3D point cloud of the 3D scanner the position of the test object is transformed into the coordinate system of the robot, taking into account CAD data of the test object.

[0018] The alignment of the ultrasonic probe to the target position of the weld is carried out on the basis of CAD data of the weld, since the robot movement has been calibrated into the CAD data of the test object, even though the robot moves in its world coordinate system.

[0019] Aligning the ultrasonic probe to the weld is a rough orientation, meaning that the CAD data is used as the starting position for the measurement. At the same time, the optical sensor, particularly in the form of a camera, is positioned at a defined distance from the surface of the test piece.

[0020] A fine correction to the actual weld point position is then carried out using the optical sensor and image processing.

[0021] The weld, specifically a spot weld, is recorded. Image processing is used to determine the 2D position of the weld. Any necessary corrections are transmitted to the robot controller to align the measuring head centrally over the weld.

[0022] During the measurement itself, the ultrasonic probe should be aligned along the normal of the weld, namely in the center of the weld or the weld point.

[0023] The normal direction is approximately determined from the CAD data of the target weld position. Tolerances between the actual component and the CAD model are corrected by communication with the ultrasonic probe. For this purpose, the position of the area to be measured is recorded based on the time-of-flight measurements from several transmitters / receivers in the ultrasonic probe array. The corresponding information is then transferred to the robot controller to align the probe in the normal direction of the weld spot. In other words, the probe itself evaluates the spatial position of the weld spot and then aligns the probe in the normal direction accordingly. This enables communication between the measuring robot and the ultrasonic testing device.

[0024] Additionally or alternatively, the normal direction can also be determined using the force and / or torque sensor, as this determines the X, Y, and Z components of the force vector. Alignment by determining the force vector is particularly useful when accurate determination using ultrasonic sensors is no longer possible, for example, due to excessive tilt of the ultrasonic probe.

[0025] Between each weld, the ultrasonic testing sensor should be moved at a higher speed than when approaching a weld.

[0026] In particular, the invention provides for a pre-sorting of the welds or weld spots to be inspected to avoid unnecessary robot travel. This way, adjacent weld spots are approached one after the other.

[0027] In other words, it is intended that when several welding points are inspected, a pre-sorting takes place so that after one welding point has been inspected, the welding point closest to the previously inspected one is then inspected.

[0028] In a further development of the invention, it is possible for the welding points to be divided into groups, whereby the welding points of one group are checked first and then the welding points of other groups are checked one after the other.

[0029] The groups should be divided in such a way that the distance between the welding points in each group is smaller than the distance between the groups.

[0030] In particular, it is intended that welding points are determined independently with regard to welding defects, such as spikes, and that measurements of a weld containing a welding defect are omitted.

[0031] It is particularly important to note that the recorded deviations between the target and actual positions of one or more welds are taken into account in subsequent welds on the same or the same test specimen, so that self-regulation takes place so that measurements on welds can be carried out with high precision and at the exact location.

[0032] In ultrasonic testing, the ultrasonic probe, which comprises at least one ultrasonic sensor and an ultrasonic delay line, such as a water delay line, which is preferably enclosed or housed in a tubular housing, must be in contact with the object to be tested. This requires a coupling medium, such as water or oil, to be present between the probe and the object. Therefore, it must be ensured that a sufficient amount of a coupling medium can be provided.

[0033] Further details, advantages, and features of the invention emerge not only from the claims and the features derived therefrom—alone and / or in combination—but also from the following description of preferred embodiments. The features relating to the ultrasonic probe itself are not covered by the patent claims.

[0034] They show: Fig. 1 a section of a robot arm with ultrasonic probe, Fig. 2 a section of a test specimen, Fig. 3 an arrangement for measuring and checking welds, Fig. 4 a first representation of an ultrasonic probe arrangement, Fig. 5 the ultrasonic probe arrangement according to Fig. 4 in a different position, Fig. 6a-c different swivel positions of an ultrasonic probe and Fig. 7 a detailed view of an ultrasonic probe without a camera.

[0035] Ultrasound can be used to inspect welds on a test object, such as a motor vehicle, or parts of one.

[0036] The welds include, for example, spot welds, which are created in particular by resistance welding, which is a widespread technique for firmly joining two or more metal parts, usually sheets or plates made of steel or aluminum. Of particular note is the production of automobile bodies, where resistance welding is an important joining process. However, the inspection of welds or weld spots according to the invention is not limited to this. Other areas of sheet metal processing or the joining of sheet metal, for example in household appliances, are also possible. The metal parts are connected via several smaller circular welds, i.e. weld spots. To ensure the quality of the connections, the corresponding weld spots must be inspected.However, since there is no guarantee that the welds will always be performed at the specified positions, the target positions, inspection at the target positions cannot provide reliable information about the quality of the welds. Instead, inspection must be performed at the actual welding position. This can be performed non-destructively using an ultrasonic testing sensor, which uses the ultrasonic pulse-echo method, i.e., the reflected sound method. This requires a coupling medium, typically water, between the transmitter and receiver. These are explained in principle below.

[0037] To determine the quality of the weld, it is therefore necessary to record the actual position of the weld and then perform an inspection. The basic principles of this process are explained below.

[0038] According to the invention, the weld is inspected using a robot. A test head 14 can be attached to the flange 10 of an arm 12 of a multi-axis robot. This test head has an ultrasonic test head 16 with a water pre-flow path. In the exemplary embodiment, this test head is connected via an adapter 18 to a force-torque sensor 20, which in turn is connected to the flange 10 via fastening elements not further described. An optical sensor in the form of a camera 22 is provided in a fixed position relative to the ultrasonic test head 16. The camera 22, for example, projects from a mount arranged between the adapter 18 and the force sensor 20.

[0039] The probe 16 itself is preferably designed as a phased array ultrasonic probe and has a matrix of transmitters / receivers, for example, a matrix of 10 x 10 to 15 x 15 transmitters / receivers is particularly suitable. The probe 16 is coupled to the test object via a water pre-flow path, preferably using proven bubbler technology.

[0040] Using the optical sensor 22, particularly in the form of a camera, the actual position of a weld can be determined in order to then align the ultrasonic measuring head 16 to the actual position and place it on the weld. A membrane 24, which seals the water flow path in the ultrasonic test head 16 on the test piece side, is placed on the test piece with a force preferably in the range of 5-10 N. Adaptive, force-controlled placement takes place with the aid of the robot's force-torque sensor system. Furthermore, the test head 16 is aligned with the weld in such a way that the test head exerts a force on the weld in its normal direction.

[0041] The normal direction is determined, in particular, through communication between the ultrasonic probe 16 and the robot controller. The position of the area to be measured is determined using time-of-flight measurements from at least some, preferably four, sensors of the phased-array ultrasonic probe. Once the position has been determined, the normal can be determined, and the probe can be aligned accordingly via the robot controller so that its longitudinal axis runs along the normal direction of the weld point. In particular, the longitudinal axis of the probe 14 is aligned with the normal emanating from the center of the weld point.

[0042] The ultrasonic probe 16 is screwed to the adapter 18 (screw connection 17). Furthermore, a silicone layer 19 can be provided on the probe side as collision protection. This ensures, in particular, that the approach to an obstacle is not too harsh, allowing braking or evasive maneuvering without damaging the ultrasonic probe 16.

[0043] In the event of a possible collision of the ultrasonic test head 16 with the test object, such as sheet metal walls, when approaching a welding point, a minimal evasive movement can be introduced so that the test head 16 continues to sit as centrally as possible on the welding point.

[0044] Based on the Fig. 2 The measurement procedure should be explained in principle. Fig. 2 A section 26 of a test specimen is shown, which is, for example, welded to a non-illustrated object. The corresponding welding points are available as CAD data and are shown in the Fig. 2 symbolized by solid circles 28, 30, 32.

[0045] In practice, the position of the actual weld points 34, 36, 38 does not always correspond to the target weld points 28, 30, 32, as is illustrated by the dashed circles 34, 36, 38. However, in order to measure the quality of the weld points 34, 36, 38 with precise positioning and non-destructively, the ultrasonic sensor 16 must be aligned with the actual weld points and then applied to them with the necessary force to perform a proper measurement. The position of the actual weld point 34, 36, 38 is determined using the camera and image processing, and its normal direction is determined using time-of-flight measurements. Alternatively or additionally, the force vector can be determined using the force-torque sensor, and its alignment along the normal can be achieved by adjusting the test head.

[0046] According to the invention, after calibrating the robot to the coordinate system of the test piece, the ultrasonic sensor 16 is first aligned to the target weld points 28, 30, or 32, which are derived, for example, from CAD data. After alignment to the target weld point, the actual weld point is optically detected by the camera 22 and its coordinates are determined. For this purpose, an image processing algorithm can determine the 2D center point of the actual weld point and transfer it to the measuring robot. If there is a deviation between the target and actual value, the robot arm 12 is adjusted accordingly so that the ultrasonic sensor 16 is aligned to the actual weld point 34, 36, or 38 and can measure it.

[0047] The corresponding deviations can also be used to make corrections during subsequent welds on the same or a similar test specimen, in order to achieve a better match between the target and actual weld points. This involves a correction of the position at which the weld is to be performed.

[0048] Alternatively or additionally, measurement results and determined differences between actual and target positions of the welds or weld points can be stored in a customer database and / or in a CAD model that contains the target positions of the welds.

[0049] Based on the Fig. 1 In principle, an ultrasonic probe arrangement has been explained to check welds in the form of welding spots, so the Fig. 3 bis 7 a preferred embodiment of an ultrasonic probe assembly 104 as well as further features characterizing the invention, individually and / or in combination, wherein the ultrasonic probe assembly per se is not covered by the claims.

[0050] Based on the Fig. 3 The calibration of a robot 100 is explained in principle to check welds on a test piece 102 for which CAD data is available. Without limiting the invention, the welds are generally referred to below as spot welds.

[0051] In order to determine the spatial position of the test object 102 in relation to the robot 100 and thus an ultrasonic probe assembly 104 attached to an end flange 106 of the robot, i.e., to calibrate the robot 100, both the test object 102 and calibration bodies 108, 110, 112 are scanned using a 3D scanner 107. The spatial coordinates of the test object 102 can be transformed from the 3D point cloud(s) of the 3D scanner 107 into the coordinate system of the robot 100, while simultaneously incorporating the CAD data of the test object 102 and the calibration bodies 108, 110, 112. The CAD data of the calibration bodies 108, 110, 112 are known. The spatial coordinates in the robot coordinate system are also available.

[0052] The calibration bodies 108, 110, 112 extend from a mount 113, which is part of the ultrasonic probe assembly 104, which is connected to the flange 106 of the robot 100. Thus, the probe assembly 104 can be moved toward the test object 102 based on the CAD data of the test object.

[0053] The holder with the calibration bodies can be removed after calibration has been completed, so that the mass that has to be moved when measuring or checking the weld points using the robot is reduced.

[0054] In order for the working area of ​​the robot 100 to reach all areas of the test object 102 to be tested, the test object 102 is preferably held and fixed by a second robot 118 and can thus be aligned with the first robot 100 in such a way that the measurements can be carried out.

[0055] Furthermore, it is planned that the 3D point cloud data and the CAD data will be fitted using the best-fit method.

[0056] The resulting 3D point cloud is compared with the CAD data and the component position is determined.

[0057] Consequently, the CAD data available in the component position-independent format is converted into absolute robot positions using the 3D scanner.

[0058] Through these measures, the coordinates of the test object and its spatial position relative to the robot 100 are available. The 6D data in the component coordinate system are exported to the robot's world coordinate system and are available there.

[0059] The probe assembly 104 is described in more detail in the Fig. 4 and 5 shown.

[0060] From a base or flange plate 116, which can be connected in a clear spatial relationship to the robot 100 via centering pins 120, extends, on the one hand, the holder 113 for the calibration bodies 108, 110, 112 and, on the other hand, a carrier 122 which is connected to the plate 116 via a force-torque sensor 123.

[0061] The carrier 122 has a holder 124 in its distal region, which in the exemplary embodiment has an L-geometry with a leg 126 extending in the longitudinal axis direction of the carrier 122, which rotatably accommodates an ultrasonic probe 128 with a camera 130. The camera 130 is rigidly connected to the housing 132 of the ultrasonic probe 128, so that a synchronous movement of the ultrasonic probe 128 and the camera 130 takes place, which can be surrounded by a ring illumination on the beam entrance side.

[0062] The calibration bodies 108, 110, 112 with the holder 113 can be connected in a fixed manner to the flange 116, namely via a locking bolt 115, as the drawing clearly shows.

[0063] The ultrasonic probe 128 may be a phased array probe.

[0064] As usual, the probe 128 has a water pre-flow section surrounded by a housing 134. To enable the use of pre-flow sections of different lengths, the housing 134 is detachably connected to the housing 132 of the ultrasonic probe 128, e.g., via a knurled nut 136. Distally, the housing 134 of the pre-flow section has a cover, such as a membrane 140, which is placed over a weld spot when measuring it. The membrane 140 can also be replaced, e.g., using the knurled nut 142.

[0065] A transmission drive is provided to pivot the ultrasonic probe 128 and thus the camera 130. A belt 144 is adjusted via an actuator 146.

[0066] The belt 144 is guided by a guide pulley (not further specified), the axis of which defines the pivot axis 129 of the ultrasonic test head 128.

[0067] Furthermore, a dosing device is integrated into the carrier 122, which has an outlet nozzle 148 through which a wetting fluid can be dispensed to wet the membrane 140. The wetting medium, such as water or oil, is sprayed conically from the nozzle 148, with the longitudinal axis of the cone 150 coinciding with or running parallel to the longitudinal axis of the carrier 122. The pivot or rotation axis 129 of the ultrasonic probe 128 runs perpendicular to this axis, as can be seen from the drawings.

[0068] Furthermore, a shielding plate 154 extends from the transverse leg 152 of the holder 20, which is connected to the carrier 122 and is dimensioned such that when the ultrasonic test head 128 and thus the membrane 140 is aligned with the spray cone 150 of the dosing device with the nozzle 148, the camera 130, ie its entrance optics, is shielded so that it cannot be sprayed.

[0069] The connections leading to the ultrasonic probe 128, the camera 130 and the actuator 146 are accommodated by cable guides 156, 158, which simultaneously provide strain relief.

[0070] Based on the Fig. 6 It should be clarified once again that the ultrasonic probe 128 and, synchronously with it, the camera 130 can be pivoted toward the holder 124 and thus the base plate 116. In illustration a), the pivot angle is 0°, in illustration b) the pivot angle is 90°, and in illustration c) the pivot angle is 180°, in which the membrane 140 is aligned with the spray cone 150 for wetting it.

[0071] At the same time, the separating plate 154 can be seen, which runs between the camera 130 and the spray cone 150, so that wetting of the optics of the camera 130 is excluded.

[0072] Between the Fig. 6 Any of the positions of the ultrasonic probe 128 shown can be assumed, allowing optimal alignment of the ultrasonic probe 128 to a weld point and thus avoiding collisions with the test piece 102. In addition, the robot arm 100 can rotate around the axis of the ultrasonic probe 128 at a fixed pivot angle to avoid collisions. Overall, this results in two angular degrees of freedom for collision-free placement of the ultrasonic probe on a weld point: the pivot angle and the rotation angle around the axis of the ultrasonic probe.

[0073] In order to check a weld spot with the arrangement, the test head 128 is first roughly adjusted on the basis of the CAD data of the weld spots, which have been transformed into the coordinates of the robot 100 in the manner described above.

[0074] From this target position, the test head 128 is adjusted based on the image recorded by the camera 130 and the image processing by means of the software processing this data, ie the member of the robot 100 holding the test head arrangement 104 or its arms, in order to then, after determining the normal emanating from the center of the weld point, place the ultrasonic test head 128 in the normal direction onto the weld point as the actual position.

[0075] In particular, the normal direction is determined using four sensors. If this is not possible, the force-torque sensor 123 is used. Independently of this, both the ultrasonic sensors and the force-torque sensor 123 can be used to determine the normal, thus providing redundancy.

[0076] Furthermore, the force-torque sensor 123 ensures that any collisions are detected immediately and thus the test head 128 can be moved immediately away from the collision area.

[0077] The communication between the ultrasonic probe 128 and the test piece 102 or the weld point ensures that alignment along the normal is ensured during measurement or testing.

[0078] Before measuring, the membrane 140 can be sprayed using the dosing device.

[0079] In order to ensure optimal alignment while simultaneously avoiding collision with areas of the test object, the test head 128 can be pivoted according to the invention.

[0080] The target-actual offset of the welding point can be saved.

[0081] Since the membrane 140 is wetted, there is no need to wet the test specimen.

[0082] Preferably, the membrane 140 is wetted before each measurement.

[0083] Since several weld spots generally need to be inspected, pre-sorting is performed to avoid unnecessary travel. This means that neighboring weld spots are approached one after the other. Pre-sorting can also be performed by dividing weld spots into groups, with the groups being approached one after the other to inspect the weld spots within them.

[0084] Further advantages arise due to camera image processing, as explained below.

[0085] Not only are weld spots detected, but damaging features are also identified.

[0086] In a first step, it can be determined whether a weld spot or only pure test piece material has been recorded.

[0087] If it is determined that a weld point does not exist in reality, but one has been stored in the CAD model, an error message is generated to update the data. Alternatively, a weld point can be created using a robot.

[0088] The 2D positions of several weld spots in the image can be detected to determine the weld spot that is closest to the center of the image.

[0089] The procedure for detecting weld spots is as follows: Several patterns of real weld spots can be stored in the software as training images with corresponding search circles for pattern generation. These search patterns are applied simultaneously in the pattern search. The number of weld spots to be searched for can be freely set.

[0090] It is important to look for more than just one welding point in the image, since in practice several welding points can appear close to one another.

[0091] If a weld spot is detected, it is examined to determine whether a mandrel is present. If this is the case, the weld spot is not approached, as this could damage the membrane of the ultrasonic probe. An error message may be issued.

[0092] If an acceptable weld spot is identified, a final safety check can be performed to determine whether the correction suggestion, i.e. the position change for alignment to the actual weld spot based on image processing, is smaller than an adjustable limit in order to avoid unwanted collisions with implausible correction values.

[0093] Finally, the robot moves to the weld point in a single pass at a safe distance from the surface, ensuring that the ultrasonic probe is centered and aligned at a defined distance from the weld point. The membrane is then placed on the weld point and measured.

[0094] In Fig. 7 In principle, an ultrasonic test head 212 is shown, which has a housing 228 comprising a delay line, a membrane 224 and ultrasonic sensors 229 located in a housing 218 or connected to the housing 218, which are connected to an electronic system via a connection (cable 227) in order to emit ultrasonic pulses and to receive reflected ultrasonic pulses and then to be able to evaluate them.

[0095] Furthermore, a rotation axis 231 is shown purely in principle, which passes through the holder 124 in order to be able to pivot the test head 212 by means of the drive 144, 146 to the extent explained above.

[0096] Essential features of the invention are that the ultrasonic test head and the optical sensor can be pivoted synchronously, whereby an alignment takes place with a dosing device by means of which a coupling medium can be sprayed onto the cover of the ultrasonic test head.

[0097] Also independently inventive is the determination of the spatial position of the test object having the welds to be measured in relation to the robot having the ultrasonic test head, wherein the CAD data of the test object and the welds are transformed into absolute robot positions, in particular using a 3D scanner with which the position in space of both the test object and the calibration bodies assigned to the part of the robot holding the ultrasonic test head arrangement are determined, the CAD data of which are known.

[0098] Also inventive is the rough alignment of the ultrasonic probe to the welds based on the exported CAD data of the welds and subsequent fine alignment using the optical sensor and image processing as well as the placement of the ultrasonic probe to the weld such as the welding point in the normal direction.

[0099] Also worth mentioning is the determination of the normal direction by measuring the time of flight of the ultrasonic measuring field of the ultrasonic probe and / or the alternative or redundant determination of the normal by determining the X, Y, Z components of the force vector with the ultrasonic probe placed on the weld point.

[0100] The pre-sorting of the welds to be inspected and, if necessary, the division of the welds into groups and successive inspection of the welds in the groups are also worth emphasizing.

[0101] Other features worth highlighting are: Placing the ultrasonic probe on the welding point with a defined force, preferably between 5 N and 10 N, identifying welding defects such as spikes that could cause damage to the ultrasonic probe or its cover, performing welds if missing welds are detected.

Claims

1. Method for testing and / or correction of a weld (34, 36, 38), such as a spot weld, of a test object (26, 102), such as a motor vehicle, or of one or more parts thereof, comprising the method steps: - alignment of an ultrasonic probe (16, 128) guided by a robot (100) on a target position (28, 30, 32) of the weld, - determination of the actual position (34, 36, 38) of the weld by means of an optical sensor (22, 130) and alignment of the ultrasonic probe (16) on the actual position, and placing the ultrasonic probe in a normal direction of the weld, - measurement of the weld, charceterized in that CAD data of the target position of the weld (28, 30, 32) is made available, on the basis of the CAD data of the weld the ultrasonic probe (16, 128) is aligned on the target position of the weld, and the ultrasonic probe is placed on the weld with controlled force after determination of the actual position (34, 36, 38) of the weld by means of the optical sensor (22, 130), wherein one or more calibration bodies (108, 110, 112) of known CAD data are assigned stationary to the robot (100), the calibration body / bodies together with the test object (26, 102) or with the one or more parts of the test object are measured by means of a camera or 3D scanner (107), and by means of 2D images of the camera or 3D point cloud of the 3D scanner the position of the test object is determined and transformed into the coordinate system of the robot taking into account CAD data of the test object, and wherein for placing the ultrasonic probe (16, 128) in normal direction of the weld (34, 36, 38) the normal direction is determined by means of ultrasonic sensors of the ultrasonic probe (16, 128) and / or by determining the direction of the vector of the force acting on the weld by means of at least one force sensor and / or torque sensor (20, 123).

2. Method according to claim 1, wherein during measurement of the weld the ultrasonic probe (16, 128) acting on the weld with a force P of P ≤ 30 N, in particular 5 N ≤ P ≤ 15 N, preferably P approximately 5 N - 10N.

3. Method according to claim 1 or 2, wherein during a test of several spot welds, they are pre-sorted for testing to the effect that after testing of one spot weld the one closest to the previously tested spot weld is then tested, and / or the spot welds are divided up into groups, the spacing of the spot welds in the respective group preferably being less than the spacing between the groups, and / or spot welds are determined in respect of welding defects, such as spikes, and measurement of a weld having a welding defect does not take place.

4. Method according to at least one of the preceding claims, wherein the test object (102) is held by a second robot (118) such that the robot (100) guiding the ultrasonic probe (128) reaches an optimum number, if possible all or at least a plurality of the welds to be tested.

5. Method according to at least one of the preceding claims, wherein the ultrasonic probe is designed swivelable relative to the robot, collisions with the test object being avoided by swiveling of the ultrasonic probe.

6. Method according to at least one of the preceding claims, wherein the ultrasonic probe and the optical sensor are swiveled synchronously, and preferably the ultrasonic probe is connected with the optical sensor, such as a camera.