METHOD FOR POSITIONING A PUNCH RIVET SETTING TOOL USING A ROBOT

Description

[0001] The present invention relates to a method and system for positioning a punch rivet setting tool by means of a robot and to a computer program or computer program product for carrying out the method.

[0002] DE 10 2008 039 872 A1 relates to a device and a method for its operation and to a tool holder which is operated by the device, wherein the device is designed in such a way that at least partially elastic deformation of the tool holder, in particular the bending of the tool holder, can be determined according to a first deformation description means, wherein the deformation description means describes the deformation properties of the tool holder taking into account the operating force at least partially.

[0003] The object of the present invention is to improve robot-assisted punch riveting.

[0004] This problem is solved by a method with the features of claim 1. Claims 8 and 9 protect a system, computer program, or computer program product for carrying out a method described herein. The dependent claims relate to advantageous embodiments.

[0005] According to one embodiment of the present invention, a method for robot-assisted punch riveting comprises the following steps: Commanding a robot to position a self-piercing riveting tool into a riveting pose on at least two workpieces to be joined; and commanding the self-piercing riveting tool to set a (self-piercing) rivet for joining the at least two workpieces by means of self-piercing rivets; wherein during this punch riveting process the robot is commanded to change the pose of the punch rivet setting tool, in particular starting from or relative to the riveting pose, in such a way or with the stipulation that by this change a punch riveting-induced elastic deformation of the punch rivet setting tool, in particular at least one die-side leg of the punch rivet setting tool, is at least partially compensated, in particular at least partially corrected.

[0006] Punch riveting often requires the application of high process forces, frequently in the range of, sometimes significantly, over 20 kN. This can lead to elastic deformations, even with robust punch riveting tools, which impair the results of the punch riveting process.

[0007] On the other hand, such riveting tools should often be designed to be as light as possible in order to reduce the payload of the robot, and / or legs that carry the rivet punch and die should be long in order to be able to set the rivets far from a component edge.

[0008] By appropriately adjusting the pose of the self-piercing riveting tool during the robotic riveting process, one version allows the use of tools that are lighter and / or have longer legs. Additionally or alternatively, another version can improve the riveting result.

[0009] Thus, in one embodiment, a compensating movement of the riveting tool is commanded or carried out using the robot during the riveting process, thereby at least partially compensating or correcting a riveting-induced elastic deformation of the riveting tool, in particular at least one die-side leg of the riveting tool, or, in particular, this compensating movement is programmed in such a way.

[0010] In one embodiment, changing the pose of the self-piercing rivet setting tool to at least partially compensate for a self-piercing rivet-induced elastic deformation of the self-piercing rivet setting tool comprises a displacement and / or rotation of the self-piercing rivet setting tool such that this displacement and / or rotation of the self-piercing rivet setting tool fully or partially compensates for a bending of the self-piercing rivet setting tool (which in one embodiment is C-shaped) and / or a displacement and / or rotation of a die and / or axis of the self-piercing rivet setting tool resulting from a self-piercing rivet-induced elastic deformation of the self-piercing rivet setting tool, in particular at least one die-side leg of the self-piercing rivet setting tool. In another embodiment, this bending of the self-piercing rivet setting tool or displacement and / or rotation of the die and / or axis is in the same or opposite direction.In one embodiment, an amount of displacement of the die of the self-piercing riveting tool due to changing the pose of the self-piercing riveting tool for at least partial compensation corresponds to at least 25% and / or at most 200% of an amount of (uncompensated) displacement of the die due to a self-piercing rivet-induced elastic deformation of the self-piercing riveting tool, in particular of the die-side leg, and / or an amount of rotation of the die of the self-piercing riveting tool due to changing the pose of the self-piercing riveting tool for at least partial compensation corresponds to at least 25% and / or at most 200% of an amount of (uncompensated) rotation of the die due to a self-piercing rivet-induced elastic deformation of the self-piercing riveting tool, in particular of the die-side leg, or is or is The changing of the pose is commanded in this manner or with this stipulation, in particular specified.The same applies analogously in one embodiment to at least partially compensating for elastic deformation of the self-piercing riveting tool due to a reduction in the force applied by the tool. In one embodiment, the change in the pose of the self-piercing riveting tool is commanded for at least partial compensation in such a way that the position and / or orientation of the die of the self-piercing riveting tool deviates less from the pose of the die or axis in the riveting position during the riveting process than without compensation or change in the pose of the self-piercing riveting tool.

[0011] In one embodiment, the robot is commanded during the punch riveting process based on a deformation model of the punch rivet setting tool, which is stored in a robot controller, in particular a mathematical or numerical model.

[0012] In one embodiment, the deformation model includes a direct or indirect assignment between process values ​​of the punch riveting process, in particular forces, in particular force profiles, stroke paths, in particular stroke path profiles, or the like, and poses (changes) of the setting tool for at least partial compensation, for example in tabular or functional form or the like.

[0013] By using such a (deformation) model-based command of the pose change of the punch rivet setting tool during punch riveting, a punch rivet-induced elastic deformation of the punch rivet setting tool can be compensated at least partially in one embodiment, particularly more precisely and / or with greater process reliability, and thereby the result of punch riveting can be (further) improved in one embodiment.

[0014] In one embodiment, in particular, the deformation model is calibrated based on the punch rivet setting tool type or the individual punch rivet setting tool, preferably in the manner explained below.

[0015] In this way, the precision of the compensation can be (further) improved by using an individual or rivet-setting tool-specific (calibrated) deformation model in one version, while the calibration effort can be reduced by using a type-specific (calibrated) deformation model in one version.

[0016] Additionally or alternatively, in particular, the deformation model is parameterized in one version, preferably after calibration, based on the punch riveting to be carried out and / or on the basis of the workpieces to be joined.

[0017] By using an application-specific (parameterized) deformation model, the precision of the compensation can be (further) improved and / or the calibration effort reduced in one implementation.

[0018] An implementation of such a procedure, which in one version comprises at least two stages, including calibration and subsequent parameterization, can be illustrated by the simplified example of a deformation model that models the die or the die-side leg of the setting tool as a simple spring. First, the spring stiffness c = F / s can be determined using the riveting force F and the die deflection s, and the deformation model can be calibrated accordingly. Then, in a second step, a force profile F = F(t) over the displacement or time t can be specified or determined for a workpiece-specific self-piercing riveting operation. Using this profile, a corresponding change in the position of the self-piercing riveting tool, for example Δ(t) = δ·F(t) / c with a correction factor δ ≠ 0 or the like, can then be determined, and the deformation model can be parameterized accordingly.

[0019] In one embodiment, after the punch riveting process, the robot is commanded to further change the pose of the punch rivet setting tool, preferably based on the stored deformation model and / or in the opposite direction to the changes during the punch riveting process, such that this further change causes an elastic reshaping of the punch rivet setting tool, preferably at least one die-side leg of the punch rivet setting tool, which is at least partially compensated, in particular at least partially corrected, by a reduction of a force applied by the punch rivet setting tool (during or for punch riveting).

[0020] This allows the riveting tool and / or the joined workpieces to be protected in one version.

[0021] In one embodiment, changing the pose of the self-piercing riveting tool during self-piercing riveting and / or changing the pose of the self-piercing riveting tool after joining the at least two workpieces comprises at least one (translational) displacement, preferably at least one displacement in or against an axial direction, in particular the main axial direction, of a TCP ("Tool Center Point") or end effector coordinate system for controlling, in particular programming, the robot and / or in or against a closing, in particular closing force direction of the self-piercing riveting tool and / or transverse to the closing (force) direction, in particular in a longitudinal direction of a leg of the self-piercing riveting tool, in particular on the die side.In particular, a displacement in the closing (force) direction during punch riveting and a displacement against the closing (force) direction after joining, or vice versa, a displacement against the closing (force) direction during punch riveting and a displacement in the closing (force) direction after joining can be commanded.

[0022] Additionally or alternatively, changing the pose of the punch rivet setting tool during punch riveting and / or after joining the at least two workpieces in one embodiment comprises at least one (rotational) rotation, preferably at least one rotation about an axis, in particular a main axis, of a TCP ("Tool Center Point") or end effector coordinate system for controlling, in particular programming, the robot and / or transversely to the closing, in particular closing force direction of the punch rivet setting tool and / or transversely to a longitudinal direction of a leg of the punch rivet setting tool, in particular on the die side.

[0023] In one embodiment, shifts and rotations in, against, or around the TCP axis (direction) can simplify commanding and / or improve precision. In another embodiment, shifts in, against, or around the closing (force) direction and rotation about an axis transverse to this and to the longitudinal direction of the leg can compensate for significant portions of the deformation, thereby (further) improving precision. In one embodiment, shifts can easily compensate for deformation, thereby (further) improving precision; in another embodiment, rotations can particularly well compensate for bending deformations, thereby (further) improving the result of the self-piercing rivet.

[0024] In one iteration, the procedure described here includes the following steps: Commanding the robot to position the self-piercing riveting tool into another riveting pose; and commanding the self-piercing riveting tool to set another rivet to join the at least two workpieces or at least two further workpieces by means of further self-piercing riveting; wherein, during this further punch riveting, the robot is commanded, based on the stored deformation model of the punch rivet setting tool, to change the pose of the punch rivet setting tool, in particular starting from or relative to the further riveting pose, in order to at least partially compensate for an elastic deformation of the punch rivet setting tool caused by the further punch riveting, wherein the deformation model is reparameterized based on this further punch riveting to be carried out and / or the workpieces to be joined in the process.

[0025] This allows for improved precision in a single execution, thereby enhancing the results of both riveting operations. An implementation of such a process, comprising at least two, and in particular at least three, stages, with parameterization of the deformation model for one riveting operation and subsequent reparameterization of the deformation model for the next riveting operation, as well as optional initial calibration, can be illustrated using the simplified example explained above. In a third step, a different force profile F = F'(t) over the displacement or time t is specified or determined for a further riveting operation, and a corresponding change in pose, for example Δ(t) = δ·F'(t) / c, is then determined, or the deformation model is (re)parameterized accordingly.

[0026] According to one embodiment of the present invention, a method for positioning a punch rivet setting tool using a robot comprises the following steps: Commanding the robot to position the self-piercing riveting tool into a riveting pose, in one embodiment on a test element, in a further development on a test coupon; commanding a self-piercing riveting movement of the self-piercing riveting tool, in particular on the test element, without or particularly preferably with setting a rivet; and manually or sensorially, in one embodiment automated, detecting a change in the pose of the test element as a result of, in particular during, the self-piercing riveting movement or a change in the pose of a die of the self-piercing riveting tool as a result of, in particular during, the self-piercing riveting movement.

[0027] In one embodiment, sensory detection is achieved using one or more optoelectronic sensors and / or position sensors, in particular optoelectronic position sensors. This allows for improved precision in one embodiment. According to one embodiment of the present invention, a deformation model is calibrated based on the detected change in pose, and in a further development, after this calibration, a robot-assisted punch riveting method described herein is carried out with this (such) calibrated deformation model and this or an identical punch rivet setting tool and this or another robot.

[0028] In one version, precision can be improved by sensory, especially automated, detection of a change in the pose of the test element or the die; in another version, the apparatus setup can be simplified by manual detection.

[0029] In one embodiment, the acquisition for calibration of the deformation model and the robot-assisted punch riveting based on the calibrated deformation model are performed at different locations. This allows for improved calibration precision, preferably the use of a stationary measurement setup for sensory, particularly automated, acquisition, and / or improved robot-assisted punch riveting, particularly enabling it to be performed without a dedicated measurement station for calibration.

[0030] In addition to or as an alternative to calibrating a deformation model, according to one embodiment of the present invention, the self-piercing riveting tool can be tested based on the detected pose change, and in a further development, long-term effects such as wear or the like can be detected and, in particular, monitored. For this purpose, in one embodiment, the command to position the self-piercing riveting tool into a riveting pose, the command to initiate a self-piercing riveting movement of the self-piercing riveting tool, and the detection of a pose change of the (respective) test element or die as a result of the (respective) self-piercing riveting movement are repeated several times, preferably cyclically. This can again be illustrated by the simplified example explained above: if, for example, the detected pose change increases over several cycles, a change in the setting tool can be detected.

[0031] In one implementation, sensor-detected pose changes are transmitted to a robot controller for robot control and / or calibration of the deformation model. This allows for improved control and / or calibration in this implementation.

[0032] According to one embodiment of the present invention, a system for positioning a punch rivet setting tool by means of a robot, in particular for robot-assisted punch riveting, is set up in a hardware and / or software, in particular programmatic, embodiment for carrying out a method described herein.

[0033] According to one embodiment of the present invention, a system for robot-assisted punch riveting comprises: Means for commanding a robot to position a self-piercing riveting tool into a riveting pose on at least two workpieces to be joined together; means for commanding the self-piercing riveting tool to set a rivet for joining the at least two workpieces by means of self-piercing rivets; and means for commanding the robot to change the pose of the self-piercing riveting tool to at least partially compensate for a self-piercing riveting-induced elastic deformation of the self-piercing riveting tool during this riveting process.

[0034] According to one embodiment of the present invention, a system for positioning a punch rivet setting tool using a robot comprises: Means for commanding the robot to position the self-piercing riveting tool in a riveting pose, in particular on a test element; means for commanding a self-piercing riveting movement of the self-piercing riveting tool, in particular on the test element, with or without setting a rivet; and means for manually or sensorially, in particular automatically, detecting a change in the pose of the test element or a die of the self-piercing riveting tool as a result of the self-piercing riveting movement.

[0035] According to one embodiment of the present invention, this system has: Means for checking the punch rivet setting tool based on the recorded pose change.

[0036] Additionally or alternatively, according to one embodiment of the present invention, this system has: Means for calibrating a deformation model, in particular the deformation model used in a robot-assisted punch riveting system described herein.

[0037] In one version, one of the above-mentioned systems or its means has: Means for commanding the robot during self-piercing riveting based on a stored deformation model of the self-piercing riveting tool; in a further development, means for calibrating the deformation model based on the self-piercing riveting tool type or the individual self-piercing riveting tool and / or for parameterizing it based on the self-piercing riveting to be performed and / or the workpieces to be joined; and / or means for commanding the robot to further change the pose of the self-piercing riveting tool to at least partially compensate for an elastic reshaping of the self-piercing riveting tool as a result of a reduction of a force applied by the self-piercing riveting tool after self-piercing riveting, in particular based on the stored deformation model;and / or means for commanding the robot to position the self-piercing riveting tool into a further riveting pose and commanding the self-piercing riveting tool to set a further rivet for joining the at least two workpieces or at least two further workpieces by means of further self-piercing riveting, wherein, even during this further self-piercing riveting, the robot is commanded, based on the stored deformation model of the self-piercing riveting tool, to change the pose of the self-piercing riveting tool in order to at least partially compensate for a self-piercing riveting-induced elastic deformation of the self-piercing riveting tool, wherein the deformation model is reparameterized based on this further self-piercing riveting to be carried out and / or the workpieces to be joined thereby; and / or means for transmitting measured values ​​of the sensorially detected pose change to control the robot and / or calibrating the deformation model to a robot controller.

[0038] A system and / or means according to the present invention can be configured as hardware and / or software, in particular comprising at least one processing unit, preferably a microprocessor unit (CPU), graphics processing unit (GPU), or the like, preferably connected to a storage and / or bus system via data or signals, and / or comprising one or more programs or program modules. The processing unit can be configured to execute instructions implemented as a program stored in a storage system, to acquire input signals from a data bus, and / or to output signals to a data bus. A storage system can comprise one or more, in particular different, storage media, in particular optical, magnetic, solid-state, and / or other non-volatile media. The program can be configured to embody the methods described herein.is capable of executing such procedures, enabling the processing unit to perform the steps of such processes and thereby, in particular, to control the robot and / or the riveting tool. A computer program product may, in one embodiment, include a storage medium, in particular a computer-readable and / or non-volatile medium, for storing a program or instructions, or with a program or instructions stored thereon. In one embodiment, the execution of this program or these instructions by a system or a controller, in particular a computer or an arrangement of several computers, causes the system or the controller, in particular the computer(s), to execute a procedure described herein or one or more of its steps, or the program or instructions are configured for this purpose.

[0039] In one implementation, one or more, in particular all, steps of the procedure are carried out fully or partially automatically, in particular by the system or its means.

[0040] In one version, the system includes the robot and / or the punch rivet setting tool and / or a robot controller.

[0041] Further advantages and features will become apparent from the dependent claims and the exemplary embodiments. These are shown, in part schematically: Fig. 1: a system for positioning a self-piercing riveting tool using a robot according to a method of an embodiment of the present invention; Fig. 2: the system in a further step of the method; Fig. 3: the system for robot-assisted self-piercing riveting according to a method of an embodiment of the present invention; Fig. 4: the system in a further step of this self-piercing riveting; Fig. 5: a method according to an embodiment of the present invention; and Fig. 6: a method according to a further embodiment of the present invention.

[0042] Fig. 1 shows a system or a process step according to an embodiment of the present invention.

[0043] The system includes a robot 10 which guides a punch rivet setting tool 20 with a leg with a die 23 ("die-side leg") 21 and a leg with a movable rivet punch 22 for setting punch rivets.

[0044] A robot controller 11 commands the robot to insert the punch rivet setting tool 20 into a Fig. 1 The rivet pose shown is positioned on a test coupon 30 ( Fig. 5 : Step S10).

[0045] Afterward ( Fig. 1 → Fig. 2 ) the robot control 11 commands a punch riveting movement of the punch rivet setting tool 20 on the test coupon 30 ( Fig. 5 : Step S20).

[0046] As a result of this punch riveting movement, the punch rivet setting tool 20 deforms, in particular its die-side leg 21, and the pose of the test coupon 30 changes accordingly (cf. Fig. 2 ).

[0047] This change in pose of the test coupon 30 is detected by means of a stationary measuring device with sensors 31 and transmitted to the robot control 11 ( Fig. 5 : Step S30).

[0048] Alternatively, the pose change can also be recorded manually and entered into the robot control 11.

[0049] Based on this recorded change in pose, the punch rivet setting tool 20 is tested in one version ( Fig. 5 : Step S40). For example, the process described above can be repeated cyclically: if the change in pose increases, a change in the punch rivet setting tool 20 can be detected (from this).

[0050] Fig. 6 shows a method according to a further embodiment of the present invention. Steps S10-S30 correspond to those above with reference to Fig. 5 described.

[0051] In this procedure, a deformation model is calibrated based on the pose change recorded in step S30 ( Fig. 6 : Step S100), for example, an assignment between process forces, in particular closing forces and corresponding displacements and / or rotations of the test coupon 30 or displacements and / or rotations of the punch rivet setting tool 20 that at least partially compensate for these, is determined or ascertained.

[0052] Subsequently, when the self-piercing riveting tool 20 is put into operation at a location different from the stationary measuring device, for example in a production line or the like, the stored deformation model calibrated on the basis of the self-piercing riveting tool 20 is parameterized on the basis of a self-piercing riveting operation to be carried out and / or workpieces to be joined in the process ( Fig. 6 (Step S110). For example, if in step S100 corresponding displacements or rotations for compensation were determined for different closing forces or the like and the deformation model was calibrated in this way, a course of displacements or rotations for compensation during this punch riveting can now also be determined with a given closing force curve and the calibrated deformation model can be parameterized in this way.

[0053] Now the robot controller 11 commands the robot to insert the punch rivet setting tool 20 into a Fig. 3 The rivet position shown is positioned on at least two workpieces 40, 41 to be joined together ( Fig. 6 : Step S120).

[0054] Then ( Fig. 3 → Fig. 4 ) the robot control 11 commands the self-piercing riveting tool to set a rivet 3 for joining the at least two workpieces 40, 41 by means of self-piercing rivets ( Fig. 6 : Step S130).

[0055] During this punch riveting process, the robot control 11, based on the stored, calibrated and parameterized deformation model, commands the robot 10 to change the pose of the punch rivet setting tool 20 during the punch riveting process in such a way that a punch rivet-induced elastic deformation of the punch rivet setting tool 20 is at least partially compensated.

[0056] This can be seen in the comparison of the Fig. 2 , 4 To illustrate in a simplified way: in Fig. 2 A displacement and rotation of the test coupon 30 as a result of the punch rivet-induced deformation of the punch rivet setting tool 20, in particular its die-side leg 21, is indicated, in Fig. 4 a corresponding change in the pose of the self-piercing riveting tool 20 by the robot 10. By way of example, in one embodiment, during or with increasing build-up of a riveting or closing force of the self-piercing riveting tool 20, the self-piercing riveting tool 20 is moved against a bending direction of the leg 21 or in Fig. 4 The rivet is rotated counterclockwise and thereby shifted in the axial direction of the rivet punch and / or transversely thereto, in order to at least partially compensate for any bending of the leg 21. For the sake of simplicity, only a bending of the die-side leg 21 is shown or considered, although alternatively or additionally a bending of the remaining self-piercing riveting tool 20 or an upward bending in the axial direction of the rivet punch can also be taken into account.

[0057] After the punch riveting process, the robot controller 11, based on the stored, calibrated and parameterized deformation model, commands the robot 10 to change the pose of the punch rivet setting tool 20 during the (re)dissipation of a force applied by the punch rivet setting tool in such a way that an elastic reshaping of the punch rivet setting tool 20 caused by this force reduction is at least partially compensated ( Fig. 6 : Step S140).

[0058] If other workpieces are to be joined later by means of further punch riveting (S150: "Y"), the above-mentioned steps S120 - S140 are repeated accordingly, whereby the saved deformation model is reparameterized beforehand based on this further punch riveting to be carried out and / or the workpieces to be joined in the process ( Fig. 6 : Step S160).

[0059] If further self-piercing rivets are to be placed on workpieces 40 and 41, the deformation model can also be reparameterized for this purpose, if the process parameters of this additional self-piercing rivet require it. Likewise, the deformation model parameterized in step S110 can also be reused if necessary. Both of these options, as well as terminating the process in Fig. 6 simplified together by step S170.

[0060] Although exemplary versions were explained in the preceding description, it should be noted that a large number of variations are possible.

[0061] In particular, instead of the sensory, automated measurement of the pose change of the test coupon, the pose change of the die of the punch rivet setting tool can also be recorded or used manually.

[0062] Furthermore, it should be noted that the exemplary embodiments are merely examples and are not intended to restrict the scope of protection, applications, or structure in any way. Rather, the preceding description provides the skilled person with a guideline for implementing at least one exemplary embodiment, whereby various modifications, particularly with regard to the function and arrangement of the described components, can be made without departing from the scope of protection as defined in the claims. Bezugszeichenliste

[0063] 10 Robot 11 Robot controller 20 Rivet setting tool 21 Die-side leg 22 Rivet punch 23 Die 3 Rivet 30 Test coupon (test element) 31 Sensor 40, 41 Workpiece

Claims

1. A method of positioning a self piercing rivet setting tool (20) by means of a robot (10), the method comprising the steps of: - commanding (S10) the robot to position the self piercing rivet setting tool in a riveting pose, in particular on a test element (30); - commanding (S20) a self piercing riveting movement of the self piercing rivet setting tool, in particular on the test element, with or without setting a rivet; characterised by: - manually or with the aid of a sensor, in particular automatically, detecting (S30) a change in pose of a die (23) of the self piercing rivet setting tool or of the test element, as a consequence of the self piercing riveting movement; wherein, on the basis of the detected change in pose, a) the self piercing rivet setting tool is checked (S40); and / or b) a deformation model is calibrated (S100).

2. The method according to claim 1, characterised in that measured values of the change in pose detected with the aid of a sensor are transmitted to a control facility of the robot for controlling the robot and / or for calibrating the deformation model, and / or the detecting for the purpose of calibrating the deformation model and the robot-assisted self piercing riveting on the basis of the calibrated deformation model take place at different locations.

3. The method according to any one of the preceding claims, wherein, after the calibrating of the deformation model, a robot-assisted self piercing riveting is carried out with this calibrated deformation model and this self piercing rivet setting tool or a self piercing rivet setting tool of the same type, and with this robot or a different robot, the method comprising the steps of: - commanding (S120) the robot (10) used for the self piercing riveting to position the self piercing rivet setting tool (20) used for the self piercing riveting in a riveting pose on at least two workpieces (40, 41) which are to be joined together; and - commanding (S130) the self piercing riveting tool used for the self piercing riveting to set a rivet (3) for joining the at least two workpieces by means of self piercing riveting; wherein, during this self piercing riveting, the robot used for the self piercing riveting is commanded to change the pose of the self piercing rivet setting tool used for the self piercing riveting in order to at least partially compensate for an elastic deformation of the self piercing rivet setting tool used for the self piercing riveting, which elastic deformation is caused by the self piercing riveting, wherein the robot used for the self piercing riveting is commanded during the self piercing riveting on the basis of the stored deformation model.

4. The method according to claim 3, characterised in that the deformation model is parameterised on the basis of the self piercing riveting to be carried out and / or on the basis of the workpieces to be joined.

5. The method according to any one of the preceding claims 3 to 4, characterised in that, after the self piercing riveting, the robot used for the self piercing riveting is commanded (S140) to further change the pose of the self piercing rivet setting tool used for the self piercing riveting, in order to at least partially compensate for an elastic reverse deformation of the self piercing rivet setting tool used for the self piercing riveting as a result of a reduction in a force applied by the self piercing rivet setting tool used for the self piercing riveting, in particular on the basis of the stored deformation model.

6. The method according to any one of the preceding claims 3 to 5, characterised in that the change in the pose of the self piercing rivet setting tool used for the self piercing riveting comprises, during the self piercing riveting and / or after joining the at least two workpieces, at least one displacement, in particular in or against a closing direction of the self piercing rivet setting tool used for the self piercing riveting and / or transversely thereto and / or in and / or against an axial direction of a TCP of the robot used for the self piercing riveting, and / or at least one rotation, in particular about an axis transverse to the closing direction of the self piercing rivet setting tool used for the self piercing riveting and / or transverse to a longitudinal direction of a leg of the self piercing rivet setting tool used for the self piercing riveting and / or about an axis of a TCP of the robot used for the self piercing riveting.

7. The method according to any one of the preceding claims 3 to 6, comprising the steps of: - commanding the robot used for the self piercing riveting to position the self piercing rivet setting tool used for the self piercing riveting in a further riveting pose; - commanding the self piercing rivet setting tool used for the self piercing riveting to set a further rivet for joining the at least two workpieces or at least two further workpieces by means of further self piercing riveting; wherein, also during this further self piercing riveting, the robot used for the self piercing riveting is commanded on the basis of the stored deformation model to change the pose of the self piercing rivet setting tool used for the self piercing riveting in order to at least partially compensate for an elastic deformation of the self piercing rivet setting tool used for the self piercing riveting, which elastic deformation is caused by the self piercing riveting, wherein the deformation model is re-parameterised on the basis of this further self piercing riveting to be carried out and / or on the basis of the workpieces to be joined in this process.

8. A system for positioning a self piercing rivet setting tool (20) by means of a robot (10), which is arranged to carry out a method according to any one of the preceding claims and / or which comprises: - means for commanding the robot to position the self piercing rivet setting tool in a riveting pose, in particular on a test element (30); - means for commanding a self piercing riveting movement of the self piercing rivet setting tool, in particular on the test element, with or without setting a rivet; and - means for manually, or with the aid of a sensor, in particular automatically, detecting a change in pose of a die (23) of the self piercing rivet setting tool or of the test element as a result of the self piercing riveting movement; as well as: a) means for testing the self piercing rivet setting tool on the basis of the detected change in pose; and / or b) means for calibrating a deformation model.

9. A computer program or a computer program product, wherein the computer program or the computer program product contains instructions, in particular instructions which are stored on a computer-readable and / or non-volatile storage medium, which instructions, when executed by one or more computers or a system according to claim 8, cause the computer or computers or the system to carry out a method according to any one of claims 1 to 7.