EP1537010A2

EP1537010A2 - Method and device for the positionally precise mounting of a hinged flap on a part

Info

Publication number: EP1537010A2
Application number: EP03773621A
Authority: EP
Inventors: Volker Brose; Helmut Kraus; Enrico Philipp; Michael Riestenpatt Genannt Richter; Bernd Schuler
Original assignee: DaimlerChrysler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2002-09-13
Filing date: 2003-09-06
Publication date: 2005-06-08
Also published as: JP2006514588A; EP1537008A2; EP1537008B1; WO2004026672A3; EP1537009A2; WO2004026669A3; JP2005537939A; EP1537011A2; JP2005537990A; US20060015211A1; WO2004026672A2; WO2004026673A3; WO2004026670A2; US20060107508A1; WO2004026670A3; JP2005537988A; WO2004026673A2; EP1539562B1; WO2004026537A3; US20070017081A1

Abstract

The invention relates to a method for the positionally precise mounting of a hinged flap (3) on a production part (1), particularly for mounting a vehicle door on a vehicle body. To this end a robot-guided gripping tool (5) is used that comprises a fixing device (14) for holding the hinged flap (3) and comprises a sensor system (18), which is connected in a fixed manner to the gripping tool (5). Within the scope of a positioning phase (A-2), the gripping tool (5) is, in a first step, moved from a proximity position (37), which is independent of the position of the production part (1) in the working area (27) of the robot (7), and into a mounting position (29), in which the flap (3) held in the fixing device (14) of the gripping tool (5) is aligned in a positionally precise manner with regard to the production part (1). In order to approach the mounting position (29), an iterative control process is run through over the course of which an (actual) measured value of the sensor system (18) is firstly generated that is compared to a (set) measured value generated within the scope of a setting-up phase. A displacement vector of the gripping tool (5) is calculated based on the difference between the (actual) measured value and (set) measured value while using a Jacobian matrix that is calculated within the scope of the setting-up phase, and the gripping tool (5) is displaced by this displacement vector. The flap is subsequently attached to the production part (1) with the aid of fastening elements (9). A metric calibration of the sensor system (18) of the gripping tool (5) can be forgone in order to perform this positioning task.

Description

Method and device for the precise mounting of a flap on a component

The invention relates to a method for assembling a flap on a workpiece, the flap being positioned precisely in relation to a reference area on the workpiece, according to the preamble of claim 1, as is known, for example, from EP 470 939 AI. The invention further relates to a device for performing this method.

In the course of assembly, flaps are attached to vehicle bodies at different locations inside and outside. The term "flap" is intended to refer generally to a pivotable attachment which is fastened to another component - in the present case the body - with the aid of a hinge, a swivel joint or the like. Examples of such flaps in vehicle construction are driver and rear doors, bonnets , Trunk lid, fuel cap, etc. In the interest of a high-quality appearance of the body, it is necessary to align these flaps with high precision in relation to adjacent areas on the body or in relation to other (neighboring) attachments and built-in parts and to position them so that a predetermined transition between the The flap and the adjoining areas of the bodywork are guaranteed by aligning the flap in relation to the bodywork and fastening it to the bodywork using the connecting elements (hinges, joints, screws, ...).

For example, the driver's door and the rear door must be fitted into the door cutout of the body in such a way that gap dimensions that are as uniform as possible Transitions and depth dimensions to the adjacent areas of the body, in particular with respect to the A or C pillar, the B pillar and the roof area can be achieved. Each of these two doors is attached to the body using two hinges. In order to ensure a highly precise alignment of the driver and rear doors with respect to the adjacent body areas, the doors must first be fitted in the optimum position in the door cut-out in question and then attached to the hinges in this position.

In the EP _. 470 939 _. AI, an assembly method is proposed, with the help of which a precise alignment and fastening of a vehicle door in the door cutout of a body is to be achieved. Here, a robot-guided gripping tool is used, which takes the door to be inserted from a load carrier and inserts it into the door cutout. In the method of EP 407 939 AI, the unequipped gripping tool is first moved into a (fixed) reference position with respect to the door cutout, in which images of the door cutout of the body are recorded with the aid of cameras which are firmly mounted on the gripping tool; From this (first) set of images, the position of the door section relative to the reference position of the gripping tool is calculated. Then a door is removed from the load carrier with the gripping tool and the equipped gripping tool is moved back to the reference position, in which another (second) set of images is taken with the cameras mounted on the gripping tool, from which the position of the door held in the gripping tool is calculated. By comparing the image data sets, a displacement vector is determined by which the gripping tool has to be displaced in order to achieve the desired alignment of the door with respect to the door cutout. The gripping tool is offset by this displacement vector, and in the position of the gripping tool relative to the door cutout now assumed, the hinges provided on the door are connected to the body (using welding robots). The method known from EP 470 939 A1 is based on two image data sets of the door cutout or the door, both of which are recorded in a (fixed) reference position of the gripping tool. The method is therefore based on a detection of the absolute positions of the body and of the door relative to the reference position in the working space of the robot, on the arm of which the gripping tool is attached. Several boundary conditions must be met in order to use this method successfully:

- First of all, each camera used for the position determination must be able to determine individual measured values metrically in relation to their internal reference coordinate system ("internal metric calibration of the cameras").

- Furthermore, the position of the cameras in the working area of the gripping tool robot must be known ("external metric calibration of the cameras").

- Finally, the individual measurements of the cameras have to be combined and compressed in such a way that the exact position of the door cutout or the door can be calculated consistently and reliably in relation to the robot's workspace.

To calibrate the sensors, a calibration device (not described in more detail) is provided in EP 470 939 AI, which has to be started in every cycle of the robot. Experience has shown, however, that the setup and calibration effort required for the cameras and the overall system to meet the above-mentioned boundary conditions is very high and can only be achieved by experts. In addition, high accuracy and reproducibility of the measured values can only be achieved with high-quality (and therefore expensive) sensors.

Another problem of the method proposed in EP 470 939 AI is that the image data acquisition of the body-door cutout on the one hand and the door on the other hand take place in different, staggered process steps. Even slight movements of the body rie during the positioning process therefore lead to large errors and must be excluded.

The invention is therefore based on the object of proposing a method for accurately fitting a flap on a workpiece, in particular on a vehicle body, which is associated with a significantly reduced calibration effort and which - even when using inexpensive sensors - an increase in accuracy compared to conventional methods allowed. The invention is also based on the object of proposing a device which is suitable for carrying out the method.

The object is achieved by the features of claims 1 and 8.

A robot-guided gripping tool is used to position and attach the flap to the body, which includes a fixing device for the flap and a sensor system that is firmly connected to the gripping tool. The fixation device of the gripping tool is equipped with a flap and is first brought into a proximity position with respect to the body (controlled by the robot, regardless of the current position of the body in the work area of the robot). The gripping tool is then brought into an assembly position by means of a control process, in which the flap held in the fixing device is aligned in the desired “optimal” installation position relative to the adjacent areas on the body. In this control process, the gripping tool is moved from the approach position into transferred to the assembly position, the sensor system generates (actual) measured values from selected reference areas on the body and on the flap, which (actual) measured values are compared with (target) measured values generated in a previous set-up phase shifted by a displacement vector (including linear displacements and / or rotations), which using a so-called “Jacobi matrix” (or “sensitivity matrix”) is calculated from the difference between the (actual) and (target) measured values. Both the (target) measured values and the Jacobian matrix are determined in the course of a set-up phase - upstream of the actual positioning and assembly process - in which the gripping tool is taught in for the specific assembly task. This setup phase is carried out once in the course of setting a new combination of tool, sensor system, body type and type and installation position of the flap to be used.

If the control process described above is complete and the flap held in the gripping tool is thus in the desired assembly position with respect to the body, the next process step begins, in the course of which the flap is mounted on the body. Here, a predefined assembly program is run in a robot-controlled manner, in which - in addition to the gripping tool - other robot-guided tools (such as welding robots, screwing robots, feeding devices for fastening elements, ...) are also involved. What is essential here is that when the assembly program is being processed, the assembly position found in the course of the positioning process and arranged precisely in relation to the body is used as a reference position for all other tools and work steps involved in the assembly.

The controlled positioning process, in which the flap held in the gripping tool is moved from the (robot-controlled) approach position to the (position-oriented to the body) assembly position, differs fundamentally from the positioning process known from EP 470 939 AI: In the EP method 470 939 AI, the absolute position of the body (or the door cutout) in the robot's workspace is determined during the positioning process, which then forms the basis for the alignment of the gripping tool. In contrast to this, the method according to the invention is based on relative measurements conditions, within the framework of which (in the set-up phase) information - corresponding to a set of (target) measured values of the sensor system - is restored via the control process.

This leads to two major simplifications compared to the prior art:

- On the one hand, no internal metric calibration of the sensors is necessary, because the sensors used no longer "measure", but only react to a monotonous incremental movement of the robot with a monotonous change in their sensor signal. This means, for example, that when using a television - or CCD camera as a sensor, the camera-internal lens distortions do not have to be compensated for or that the exact metric calculation of distance values is omitted when using a triangulation sensor.

- Furthermore, an external metric calibration of the sensors is no longer necessary: In contrast to the prior art, the position of the sensors no longer has to be determined metrically in relation to the working space of the robot or the coordinate system of the robot hand in order to be able to calculate suitable correction movements. The sensors only have to be attached to the gripping tool in such a way that they can record suitable measurement data of the reference areas on the body and the flap in their capture area.

The metric measuring function, which can generally only be determined at great expense, and the calibration device shown in EP 470 939 A1 can thus be completely dispensed with when using the method according to the invention. Therefore, metrically uncalibrated sensors can be used, which are much simpler and therefore cheaper than calibrated sensors. Both the instrumental structure as well as the establishment and operation of the overall system is therefore very cost-effective when using the method according to the invention. affordable to implement. Furthermore, when using the method according to the invention, the initial setup and maintenance of the assembly system is drastically simplified and can also be carried out by trained personnel.

The result of the flap positioning in relation to the body is still independent of the absolute positioning accuracy of the robot used, since any robot inaccuracies are corrected when the assembly position is approached. Due to the resulting short error chains, a very high repeatability in the positioning result can be achieved if required. Robot positioning inaccuracies due to temperature fluctuations, incorrect measurement of the robot, etc. are settled.

The number of degrees of position freedom that can be compensated for in the positioning phase with the method according to the invention can be freely selected and depends only on the configuration of the sensor system. The number of sensors used can also be freely selected. The number of (scalar) sensor information provided need only be equal to or greater than the number of degrees of freedom to be controlled. In particular, a larger number of sensors can be provided, and the redundant sensor information can be used, for example in order to be able to better detect shape errors in the body area under consideration and / or the flap to be fitted, or to improve the accuracy of the positioning process. Finally, sensor information from different non-contact and / or tactile sources can be used (eg a combination of CCD cameras, optical gap sensors and tactile distance sensors). Thus, by using suitable sensors, the measurement results of different quality-relevant sizes (gap dimensions, transition dimensions, depth dimensions) can be taken into account during the fitting process of the flap. The method according to the invention can be very easily adapted to new problems, since only the sensor data acquisition and processing, but not the regulating system core, has to be adapted. It is not necessary to use model knowledge about the body and the flap to be inserted during the positioning process.

In comparison to the method of EP 470 939 AI, the invention allows a much faster compensation of residual uncertainties that can occur when the flap is positioned in relation to the body cutout; Such residual uncertainties can arise due to conveyor-related position errors of the body in the working area of the robot, by positional deviations of the flap in the gripping tool and / or by shape errors of the flap or body to be inserted, which are caused by component tolerances. Due to this quick position control of the gripping tool relative to the body, the body does not have to be clamped stationary during the positioning process, but can be moved (for example on an assembly line or other suitable conveyor technology) relative to the robot. This enables a high degree of flexibility of the method according to the invention, which can thus be used for a wide variety of applications of flap assembly on stationary and moving workpieces.

The controlled approach to the assembly position can be done in a single control loop; However, an iterative method is advantageously used in which threshold values are specified as termination criteria: the iteration process is terminated when the deviation between the (target) measured value and the (actual) measured value lies below a predetermined threshold value; the iteration process is also terminated when the reduction in the deviation between the (target) measured value and (actual) measured value which can be achieved in successive iteration steps is below a further predetermined threshold value. The fastening elements (hinges, joints, ...), by means of which the flap is connected to the body, can be part of the flap to be assembled, so that these fastening elements - after completion of the positioning of the flap in the body cutout described above - only in this Assembly position need to be connected to the workpiece. In many cases, however, hinges are used to link flaps to bodies, which are first attached to the vehicle body before the flap is hinged to the hinges. In this case, it is advantageous to carry out the assembly of the hinges on the body in the same step as the flap assembly. In this case, the assembly process advantageously comprises the following process steps:

A The gripping tool is equipped with a flap to be installed and is moved - according to the iterative control process described above - from the (approached) approach position to the assembly position opposite the body, in which the flap is precisely aligned with the body cutout; B the gripping tool is moved robot-controlled from the assembly position by a fixed predetermined offset into an evasive position in order to make room in the assembly area for a robot-guided hinge assembly system; C the hinge mounting system, for example a screwing tool equipped with hinges, fixes the hinges in a predetermined fastening area of the body in a robot-controlled manner and then withdraws from the working area; D the gripping tool is robot-controlled and moved by the predefined offset from the avoidance position back to the assembly position (and the flap is thus positioned precisely in the assembly area); E the flap is attached to the hinges using a robot-controlled assembly tool (e.g. a screwdriver attached to the gripping tool); F The gripping tool is moved to a retracted position in a robot-controlled manner, in which - without the risk of the gripping tool colliding with the body - the body can be removed from the robot's work area and a new body can be added.

Process step B corresponds to a "swap" of the flap, which is reversed in process step D. What is essential here is that process steps B, D and E are robot-controlled as relative movements to the assembly position found in process step A, so that the The assembly position found in the control process of process step A is used as a reference position for the other tools involved in these process steps.

In order to achieve particularly high accuracy, it is advantageous to also couple the hinge assembly (process step C) to the assembly position found in process step A as a reference position. In this case, the hinge assembly (process step C) comprises the following work steps: Cl The hinge assembly system is equipped with hinges and is moved in an iterative control process - analogous to the control process described above for fitting the flap - into a working position in relation to the gripping tool, in which the Hinge mounting system is positioned precisely in relation to the hinge screwing surface of the door or is aligned with an auxiliary surface of the gripping tool (in the evasive position); the hinge mounting system is connected to the mounting position of the flap (found in process step A) by this control process; C-2, starting from the working position, the hinge assembly system runs robot-controlled through a predetermined machining program in which the hinges are fastened to the body cutout, for example with the aid of screwdrivers from the hinge assembly system; C-3 the hinge assembly system is moved out of the machining area under robot control so that the gripping tool can be moved back into the assembly position with the flap without the risk of collision.

In the process sequence described here - with the exception of steps A and C-1 - all process steps are robot-controlled, i.e. by processing specified machining programs or path shifts of the robots and tools involved. Steps A and C-l correspond to iterative control procedures, in the course of which the flap to be used is positioned in the body cutout (step A) or the hinge mounting system is aligned with the flap or gripping tool (step C-l).

Further advantageous embodiments of the invention can be found in the subclaims. The invention is explained in more detail below on the basis of an exemplary embodiment illustrated in the drawings; show:

1 is a schematic view of a vehicle body with a mounting system for installing a rear door,

2a shows a schematic plan view of the rear door held in a gripping tool;

2b shows a schematic sectional view of the rear door which is held in an assembly position with respect to the body by means of the gripping tool;

3 shows a schematic plan view of a hinge assembly tool with hinges held therein;

Figure 4 is a schematic representation of the trajectories of the gripping tool and the hinge assembly tool carrying robot hands when processing the door assembly.

5 shows a schematic view of the vehicle body with the gripping tool located in the evasive position and the hinge mounting tool located in the working position. 1 shows a section of a vehicle body 1 with a rear door cutout 2 into which a rear door 3 is inserted and a front door cutout 2 "into which a driver's door (not shown in FIG. 1) is to be mounted. This body 1 is an example of a workpiece 1 with a cutout 2, in which a pivotable flap 3 (adapted to the shape of the cutout) is to be inserted.

The assembly of the rear door 3 in the body 1 is carried out with the aid of an automatic assembly system 4 (shown schematically in FIG. 1) with a work space 27. The assembly system 4 comprises a gripping tool 5 guided by an industrial robot 7, which feeds the rear door 3 and is located precisely opposite the Body 1 positioned. Furthermore, the mounting system 4 comprises a hinge mounting system 6 guided by an industrial robot 8, which feeds the hinges 9 to the body 1, aligns them with the body 1 and the precisely positioned door, and fastens them to a hinge joining area 39 in the door cutout 2. A control system 10 is provided for position and movement control of the robots 7, 8 and thus of the tools 5, 6.

Analogous to the assembly system 4 of FIG. 1 for the assembly of the left rear door 3 (on the opposite side of the body 1) there is a further assembly system for the right rear door, the structure and mode of operation of which correspond to that of the assembly system 4 (mirror image). The driver's doors are installed using appropriately adapted additional mounting systems analogous to the rear door assembly.

To assemble the rear door 3 in the door cutout 2, the hinges 9 are first fastened in the hinge joining areas 39 of the door cutout 2; then the rear door 3 is attached to the hinges 9 in a defined position. The position in which the hinges 9 are fastened in the door cutout 2 determines the position of the fully assembled rear door 3 in the door cut-out 2. In order to ensure a high-quality visual impression of the body 1, the rear door 3 must be positioned precisely (in terms of position and angular position) relative to the areas 11 of the body adjacent to the door cut-out 2 1 can be installed; these surrounding areas 11 thus form a so-called reference area for aligning the rear door 3 with respect to the body 1.

The gripping tool 5, which is used to position the rear door 3 in the door cutout 2 and the subsequent assembly, is shown schematically in FIG. 2a. This gripping tool 5, which is fastened to the hand 12 of the industrial robot 7, comprises a frame 13, to which a fixing device 14 is fastened, by means of which the rear door 3 can be picked up in a well-defined position. The rear door 3 is advantageously received by the fixing device 14 on the inside 15 of the rear door 3 in the immediate vicinity of the hinge receiving surfaces 16, to which the fastening hinges 9 are screwed in the course of the door assembly. This choice of the points of application of the fixing device 14 on the rear door 3 ensures that the shape distortion that occurs when the door is installed is minimal. Settling phenomena of door 3 are thus taken into account. This ensures that the fixing device 14 is designed such that the area of the hinge receiving surfaces 16 on the inside of the door 15 is freely accessible, so that the hinges 9 can be mounted while the door 3 is in the fixing device 14. The design of the fixing device 14 shown in FIG. 2a further ensures that the door 3 can be positioned on the body 1 by the gripping tool 5 in the installed position (ie in the closed state). The fixing device 14 is arranged such that it can be rotated and / or swiveled relative to the frame 13 of the gripping tool 5, so that after installation through the window cutout 17 of the assembled and closed door 3 can be removed. Alternatively, the door 3 can also be gripped on the outer paneling.

To measure the position and orientation of the rear door 3 fixed in the gripping tool 5 relative to the body 1, the gripping tool 5 is provided with a sensor system 18 with a plurality (five in the schematic illustration of FIG. 2a) of sensors 19 which are rigid with the frame 13 of the gripping tool 5 are connected; they thus form a structural unit with the gripping tool 5. These sensors 19 are used to determine joint, gap and depth dimensions between edge areas 20 of the rear door 3 and the adjacent areas 11 of the door cutout 2 on the body 1. With the aid of this sensor system 18, the gripping tool 5 is held in place as described below Rear door 3 aligned in an iterative control process with respect to the door cutout 2 of the body 1.

The hinge mounting system 6 is fastened to the hand 21 of the second industrial robot 8 and comprises two hinge clamps 22, in which the two hinges 9, which are necessary for fastening the door 3 in the door cutout 2, are accommodated in a defined orientation in terms of position and angle (see figure 3). Furthermore, the hinge mounting system 6 (not shown in FIG. 3) comprises robot-controlled torque screwdrivers for fastening the hinges 9 in the door cutout 2 of the body 1. The hinge clamps 22 are designed in such a way and arranged opposite the screwdrivers that the screw surfaces 23, which the hinges 9 are connected to the body 1, for the screwdriver are accessible. The hinges 9 are inserted (automatically or manually) into the receptacles 22, it being possible for the fastening screws (not shown in FIG. 3) with which the hinges 9 are fastened to the body 1 to be inserted together with the hinges 9 or to be automatically fed in later , The hinge mounting system 6 is further provided with a sensor system 24, which comprises a plurality (two in the schematic illustration of FIG. 3) of sensors 25, which form a structural unit with the hinge mounting system 6. As will be described later, these sensors 25 serve to position the hinge mounting system 6 relative to the gripping tool 5.

If the assembly system 4 is to be set for a new machining task - for example, for the rear door assembly in a new vehicle type or for the driver's door assembly - a so-called setup phase must first be carried out in which the gripping tool 5 and the hinge assembly system 6 are configured. A fixing device 14 adapted to the door 3 to be assembled, a suitably designed frame 13 and the sensor system 18 with the corresponding sensors 19 are selected and configured together to form a gripping tool 5. Subsequently, the sensor system 18 of the gripping tool 5 is “taught in” by — as described below under I. — (target) measurement values of the sensor system 18 on a “master” body 1 ′ and a “master” door 3 ′ are recorded and the controlled path sections of the trajectory of the robot 7 are programmed in. In addition, the hinge mounting system 6 is configured according to the assembly task, provided with sensors 25 and "taught" by also for this tool - as described below under II -) Measured values of the sensors 25 are recorded in a reference area 26 of the gripping tool 5 and the path sections of the path of the robot 8 to be traversed to be controlled are programmed. After completion of this set-up phase, the assembly system 4 configured and measured in this way is now ready for series use, in which a so-called work phase is carried out for each body 1 supplied to the work space 27 of the robot 7, 8, in which - as in the following under III. described - an associated door 3 is positioned on the door cutout 2 and fastened. I. Set-up phase of the gripping tool 5:

To solve a new assembly task, in a first step a sensor system 18 adapted to the assembly task is selected for the gripping tool 5 and fastened to the frame 13 together with the fixing device 14. The gripping tool 5 thus assembled is attached to the robot hand 12. The fixing device 14 is then fitted with a (“master” -) rear door 3 'and ^' (.manually or "interactively) aligned in such a way with respect to a (" master ") body 1 'in the working space 27 of the robot 7, that there is an “optimal” alignment of the (“master”) rear door 3 'with respect to the (“master”) body 1' (see FIG. 2b). Such an “optimal” alignment can be defined, for example, by the fact that a gap 28 between the (“master” -) rear door 3 'and (“master” -) body 1' is as uniform as possible, or by the gap 28 determining certain regions The relative position of the gripping tool 5 in relation to the (“master”) body 1 'is referred to below as the assembly position 29.

The number and the position of the sensors 19 on the frame 13 are selected such that the sensors 19 are directed to suitable areas 30 'on the (“master”) body 1 ′ or areas 31 that are particularly important for the “optimal” alignment 2a. Five sensors 19 are used in the exemplary embodiment in FIG. 2a, which are directed to the areas 30, 31 shown in FIG. 1, so that three sensors 19 point to the gap 28 in the Area of the B-pillar 32 are directed, while the other two sensors 19) carry out gap measurements in the rear area of the rear door 3. Experience has shown that these areas 30, 31 are particularly important for the position and orientation of the rear door 3 in the door cutout 2. The number of Individual sensors 19 and the surrounding Exercises 30, 31 to which they are aimed are selected in such a way that they allow the best possible characterization of the quality features relevant to the respective application. In addition to the gap measurement sensors 19, further sensors can be provided which, for example, measure a (depth) distance and / or a transition between the body 1 and the rear door 3.

The gripping tool 5 with the sensor system 18 and with the ("master" -) rear door 3 'held in the fixing device 14 is now moved with the help of the robot 7 to the position (set by manual or interactive alignment, shown in FIG. 2b) ) Assembly position 29 with respect to the (“master”) body 1 ′ “taught in.” First, measured values of all sensors 19 are recorded in assembly position 29 and stored as “setpoint measurement values” in an evaluation unit 33 of the sensor system 18; this sensor evaluation unit 33 is expediently integrated into the control system 10. Then - starting from the assembly position 29 - with the help of the robot 7, the position of the gripping tool 5 and the ("master" -) rear door 3 'held therein with respect to the ("master" -) body 1' along known travel paths - as in FIG 2b indicated by arrows 34 - systematically changed; as a rule, these are incremental movements of the robot 7 in its degrees of freedom. The changes in the measured values of the sensors 19 that occur are recorded (completely or in parts). From this sensor information, a so-called Jacobi matrix (sensitivity matrix) is calculated in a known manner, which describes the relationship between the incremental movements of the robot 7 and the changes in the sensor measured values that occur in the process. The method for determining the Jacobian matrix is described, for example, in "A tutorial on Visual servo control" by S. Hutchinson, G. Hager and P. Corke, IEEE Transactions on Robotics and Automation 12 (5), October 1996, pages 651— 670. This article also describes the requirements for the travel paths and the measurement environments (continuous speed, monotony, ...) that must be fulfilled in order to obtain a valid Jacobi matrix. The incremental movements are selected in such a way that no collisions of the gripping tool 5 or the (“master”) rear door 3 ′ with the (“master”) body 1 ′ can occur during this setting-up process.

The Jacobian matrix generated in the set-up phase is stored together with the “target measured values” in the evaluation unit 33 of the sensor system 18 and form the basis for the later positioning control process A-2 in the working phase (see below under III.).

Furthermore, a trajectory 35 of the robot hand 12 (and thus of the gripping tool 5) is generated in the set-up phase, which trajectory III. is controlled. This trajectory 35 is shown schematically in FIG. 4. The starting point of the trajectory 35 is a so-called “retreat position” 36, which is selected such that a new body 1 can be introduced into the working space 27 of the robot 7 without the body 1 colliding with the gripping tool 5 or the rear door held therein 3. This retraction position 36 can correspond, for example, to an assembly station (not shown in the figures) in which the gripping tool 5 is (manually) equipped with a rear door 3 to be built in. Alternatively, the retraction position 36 can correspond to a removal station in which the Gripping tool 5 removes a rear door 3 to be installed from a load carrier, starting from this retreat position 36, the travel path 35 comprises the following separate sections:

Al The gripping tool 5 with an inserted (“master”) rear door 3 ′ is brought from a retracted position 36 into a “proximity position” 37 on a path A1 to be passed through in a controlled manner, which is selected such that all the individual sensors 19 of the sensor system 18 have valid measurements - values of the respective area 30, 31 of the (“master” -) rear door 3 'and / or of the (“master”) body 1', while at the same time ensuring that no collisions of the gripping tool 5 or the rear door 3 with the Body 1 can occur.

A-2 The gripping tool 5 with an inserted (“master”) rear door 3 ′ is moved on a path A-2 to be controlled in a controlled manner from the approach position 37 into the (taught-in “position” as described above), in which the gripping position Tool (5) held ("master" -) rear door 3 'is aligned precisely and angularly with respect to the door cutout 2' of the ("master") body 1 '. What happens in detail during this regulated process step is described below (in III. Work phase).

B. The gripping tool 5 with an inserted (“master”) rear door 3 'is moved on a path B to be passed through in a controlled manner from the assembly position 29 into an evasive position 38, in which the (“master”) rear door 3 ′ covers the joining area 39 of the Hinges 9 in the door cutout 2 'are not impaired. The gripping tool 5 thus deviates in a defined manner in order to make room for the installation of the hinges 9.

D. The gripping tool 5 with an inserted (“master”) rear door 3 'is transported back on a path D to be controlled in a controlled manner from the evasive position 39 to the (taught-in ”position 29 described above) in which the (held in the gripping tool 5) "Master" -) rear door 3 'is aligned precisely and angularly with respect to the door cutout 2' of the ("Master" -) body 1 '. This path D can in particular be the “reversal” of path B.

F. The gripping tool 5 is moved back into the withdrawal position 36 in a robot-controlled manner.

The path 35 of the gripping tool 5 generated during the set-up phase thus consists of four controlled to be current sections Al, B, D and F as well as a section A-2 to be followed in a regulated manner. Steps A1, B, D and F can be entered interactively during the learning phase of the gripping tool 5, or they can be stored in the control system 10 in the form of a (offline generated) CNC program.

II. Set-up phase of the hinge mounting system 6:

In a next step, the travel path 40 of the hinge mounting system 6 (provided with a plurality of sensors 25 and fastened to the robot hand 21 of the hinge robot 21) is taught:

Analogous to teaching the assembly position 29 of the gripping tool 5 as described above, the so-called “working position” 41 of the hinge mounting system 6 is first taught in here. For this purpose, the gripping tool 5 is in the avoidance position 28 (end position of the track section B) relative to the (“master”) body 1 'positioned. The hinge assembly system 6 is then equipped with two hinges 9 and (manually or interactively) aligned with the door cutout 2 ′ of the (“master”) body 1 ′ in such a way that the hinges 9 in the joining area 39 of the door cutout 2 ′ in FIG an "optimal" orientation and mounting position are positioned. The relative position of the hinge mounting system 6 in relation to the ("master") body 1 'is referred to below as the "working position" 41 of the hinge mounting system 6.

The sensors 25 are attached to the hinge mounting system 6 in such a way that they are directed to a selected reference area 26 on the gripping tool 5, in the present exemplary embodiment to an auxiliary surface 42 of the gripping tool 5. In the present case, the “auxiliary surface” 42 is a flat surface, the surface normal 43 of which is approximate. runs approximately parallel to the vehicle longitudinal direction 44 when the gripping tool 5 is in the avoidance position 38 (shown in FIG. 5). The sensors 25 are (optical) distance sensors, which measure (for example using the triangulation principle) the distance to the auxiliary surface 42. The distance of the hinge mounting system 6 in the vehicle longitudinal direction 44 from the auxiliary surface 42 can be determined by evaluating the measured values of the sensors 25; Furthermore, the angular position of the hinge mounting system 6 relative to the auxiliary surface 42 (and thus relative to the avoidance position 38 of the gripping tool 5) can be calculated.

The hinge mounting system 6 with the sensors 25 is now "taught" with the help of the hinge robot 8 to the (manually or interactively set) working position 41 opposite the auxiliary surface 42 of the gripping tool 5. This iterative teaching takes place analogously to the teaching process of the gripping tool described under I 5, in which the gripping tool 5 has been taught in the mounting position 29 opposite the (“master”) body 1 ': first, while the hinge mounting system 6 is in the working position 41, measured values of the auxiliary surface 42 are measured using the sensors 25 recorded and stored as “target measured values” in an evaluation unit 45 belonging to the sensor system 24, which is integrated into the control system 10. Then, starting from this working position 41, the position of the hinge mounting system 6 relative to the auxiliary surface 42 of the Gripping tool 5 systematically changed along known trajectories The Jacobi matrix (sensitivity matrix) of the hinge mounting system 6 is calculated from the changes in the measured values of the sensors 25, which describes the relationship between the incremental movements of the hinge robot 8 and the changes in the measured values of the sensors 25 that occur in the process. The incremental movements are selected in such a way that no collisions of the hinge assembly system 6 with the (“master”) body 1 ′ can occur during this set-up process. The Jacobi matrix generated is stored together with the “target measured values” in the evaluation unit 45 of the sensor system 24 and forms the basis for the subsequent control process in the positioning phase of the hinge mounting system 6 (see below under Cl).

In addition to teaching in the working position 41, a path 46 of the hinge robot hand 21 is generated in the set-up phase of the hinge mounting system 6, which - together with the path 35 of the robot hand 12 of the. Gripping tool 5- cal ^' matically shown in Figure' 4 ^' . The starting point of the trajectory 46 of the hinge mounting system 6 is a so-called “hinge mounting position” 47, which is selected such that a new body 1 can be inserted into the working space 27 of the robot 8 without the body 1 colliding with the hinge mounting system 6. In this hinge mounting position 47, the hinge clamps 22 (manually or automatically) can be fitted with hinges 9 to be installed. Starting from this hinge mounting position 47, the travel path 46 of the hinge mounting system 6 comprises the following separate sections:

C-0 The hinge mounting system 6 with inserted hinges 9 is brought on a path C-0 to be passed through in a controlled manner from the hinge receiving position 47 into a so-called proximity position 48, which is selected such that the sensors 25 have valid measured values of the auxiliary surface 42 of the (in the evasive position 38) gripping tool 5.

C1 The hinge mounting system 6 with inserted hinges 9 is moved from the approach position 48 to the (learned position) (as described above) on a path C1 to be run through in a controlled manner, in which the hinge mounting system 6 is accurate in terms of angle and distance from the auxiliary surface 42 of the gripping tool 5 is aligned. C-3 The hinge mounting system 6 is moved back into the hinge mounting position 47 by robot control.

The travel path 46 of the hinge mounting system 6 generated in the course of this set-up phase thus consists of two sections C-0 and C-3 to be controlled and one section C-1 to be controlled.

III. working phase

In the working phase, bodies 1 are sequentially fed and clamped to the working space 27 of the assembly system 4, and for each body 1, the gripping tool 5 and the hinge mounting system 6 traverse the trajectories 35, 46 generated in the set-up phases.

Track section A-l:

While the new body 1 is being fed, the gripping tool 5 is in the retracted position 36 and is or is being fitted with a rear door 3 to be fitted; the hinge mounting system 6 is in the hinge receiving position 47, in which the hinge clamps 22 are fitted with hinges 9. As soon as the new body 1 has been moved into the working space 27 and fixed there, the gripping tool 5 with the inserted rear door 3 is moved into the approach position 37 in a controlled manner.

Track section A-2 (positioning phase of gripping tool 5):

Starting from the approach position 37, a positioning phase of the tool (path section A-2 in FIG. 4) is run through, in the context of which the rear door held in the gripping tool 5 3 is brought into the assembly position 29 (learned during the learning phase) with respect to the body 1 and is aligned precisely with respect to the door cutout 2 of the body 1. For this purpose, sensors 19 of the sensor system 18 record measured values in selected areas 30, 31 of the rear door 3 and the body 1. With the help of these measured values and the Jacobian matrix determined in the setup phase, a movement increment (displacement vector) is calculated, which reduces the difference between the current (actual) sensor measured values and the (target) sensor measured values. The rear door 3 held in the gripping tool 5 is then moved and / or pivoted by this movement increment with the aid of the robot 7, and new (actual) sensor measured values are recorded during the ongoing movement.

This iterative measuring and shifting process is repeated in a control loop until the difference between the current (actual) and the desired (target) sensor measured values falls below a predetermined error level, or until this difference no longer exceeds one in advance set threshold changes. The rear door 3 is now (within the accuracy specified by the error measure or threshold value) in the assembly position 29 (shown in FIG. 3) relative to the body 1.

The iterative minimization carried out in this positioning phase A-2 eliminates inaccuracies of the body 1 with regard to its position and orientation in the working space 27 of the robot 7 as well as any shape errors of the body 1 (ie deviations from the ("master") body 1 Simultaneously, inaccuracies of the rear door 3 with regard to their position and orientation in the gripping tool 5 and any existing shape errors of the rear door 3 are compensated for (ie deviations from the (“master”) rear door 3 '). The rear door 3 is thus in the course of this iterative control process - regardless of shape and position inaccuracies - in the "optimal" manner in the door cutout 2 of the body 1 fitted. For separate detection and evaluation of shape errors of the rear door 3 and the body 1, additional sensors can be provided on the gripping tool 5, the measured values of which are used exclusively or partially to record the shape errors. Furthermore, the measured values of the individual sensors 19 can be provided with different weighting factors in order to bring about a weighted position optimization of the rear door 3 in relation to the door cutout 2 of the body 1.

The positional and angular displacement of the rear door 3 held in the gripping tool 5 (corresponding to the displacement between the approach position 37 and the assembly position 29) that occurred during the control process of this positioning phase A-2 can be passed on to the control system 10 of the robot 7 in the form of a so-called zero point correction , The control system 10 of the robot 7 thus “knows” the starting position (corresponding to the mounting position 29), which corresponds to the optimal fit of the rear door 3 in the door cutout 2. An important property of this positioning phase is its independence from the robot accuracy: since the positioning process is based on an iterative comparison based on the (actual) measured values with (target) measured values, any positional inaccuracy of the robot 7 is immediately compensated for by the iterative control process.

Track sections B and C-0 (avoidance phase of the gripping tool 5 and preparation of the hinge mounting system 6):

Starting from the assembly position 29, the gripping tool 5 with the rear door 3 held therein is now transported by the robot 7 into the avoidance position 38 in a controlled manner. In this way, space is created in the joining area 39 of the door cutout 2 for the hinge mounting system 6 equipped with hinges 9, which subsequently or simultaneously with the evasion phase B of the gripping Tool 5 is brought into the approach position 48 controlled.

Track section C-l (positioning phase of hinge assembly system 6):

Starting from the approach position 48, the hinge mounting system 6 is now brought into the working position 41 (learned during the teach-in phase) relative to the gripping tool 5 located in the avoidance position 38. This positioning phase is analogous to the positioning phase of section A-2, in the course of which the gripping tool 5 was positioned relative to the body 1: With the help of the sensors 25 of the hinge mounting system 6, measured values of the auxiliary surface 42 are recorded on the gripping tool 5, and these measured values are used with the help of the Jacobian matrix determined in the set-up phase, a movement increment is calculated by which the hinge assembly system 6 is moved with the aid of the robot 8. This measuring and shifting process is repeated iteratively until the difference between the current (actual) and the desired (target) sensor measured values falls below a predetermined error level, or until this difference no longer exceeds a threshold value set in advance changes. The hinge mounting system 6 is then in the working position 41 (shown in FIG. 5) with respect to the gripping tool 5 and with respect to the body 1. The spatial position of the robot hand 21 corresponding to this working position 41 is stored in the control system 10. Sensors 49 on the auxiliary surface 42 measure the position of the hinges 9 and also save the result as a target data record in the control system 10.

Since the hinge mounting system 6 is aligned with the gripping tool 5 on the basis of distance measurements from the flat surface 42, which is oriented approximately perpendicular to the longitudinal direction 44 of the vehicle, this enables Although the hinge assembly tool 6 is positioned in the longitudinal direction 44 of the vehicle, it is not perpendicular to it. In this case, the movement of the hinge assembly tool 6 in the vehicle transverse direction is carried out in a controlled manner (in contrast to the movement in the vehicle longitudinal direction, which takes place in a controlled manner), so that the hinge assembly system 6 is moved towards the joining area 39 in the door cutout 2 in a controlled manner perpendicular to the vehicle direction 44, and the hinges 9 are moved with it Can be pressed onto the joining area 39 with the aid of springs or suitable pneumatics.

Work step C-2 (fastening of the hinges 9 in the door cutout 2)

In the working position 41 of the hinge mounting system 6, in which the hinges 9 are positioned and pressed at the desired location in the joining area 39 of the door cutout 2 and, the hinges 9 are now mounted in the door cutout 2. For this purpose, for example, screwdrivers can be used are provided on the hinge mounting system 6 (but are not shown in the figures) and engage the fastening screws of the hinges 9 for this step. Alternatively, other screwdrivers can be used that are attached to additional robots or handling systems.

After assembly of the hinges 9, the hinge clamps 22 are opened and the hinges 9 are released. With the help of the sensors 49 on the auxiliary surface 42, the position of the screwed-on hinges 9 is measured with the hinge position (stored as a target data set in the control computer 10) in the unscrewed state. In the event of deviations, the hinges 9 are again fixed in the hinge clamps 22 and moved robotically by the measured offset. This process is repeated until the position of the screwed hinges 9 with the position of the unscrewed Hinges matches. In this way, the elastic and plastic influences of the screwing process can be compensated and a particularly high positional accuracy of the hinges 9 in the joining area 39 can be achieved.

If the hinges are fastened in the desired (target) position in the joining area 39 of the door cutout 2, the hinge clamps 22 are opened and the hinges 9 are released.

Track sections C-3 and D (retraction of the hinge mounting system 6 and approach of the gripping tool 5):

Subsequently, the hinge mounting system 6 (without the hinges 9) is withdrawn from the working position 41 into the hinge receiving position 47 in a robot-controlled manner. As a result, the space around the joining area 39 is cleared again, and the gripping tool 5 with the rear door 3 can be moved back from the evasive position 38 into the assembly position 29 in a robot-controlled manner. The high-precision alignment of the hinge assembly tool 6 relative to the gripping tool 5 (achieved in the previous process section C1) ensures that the hinge receiving surfaces 16 of the rear door 3 come to lie on the hinges 9 in a highly precisely aligned manner, while the alignment (carried out in section A-2) of the gripping tool 5 relative to the body 1 ensures that the rear door 3 is optimally aligned with the door cutout 2.

Work step E (fastening the rear door 3 to the hinges 9)

In the now reassembled assembly position 29 of the gripping tool 5, in which the rear door 3 is optimal in relation to the door cutout 2 is positioned, the rear door 3 is now attached to the hinges 9 in the door cutout 2. Screwdrivers (not shown in the figures) can be used for this purpose, which are mounted, for example, on the gripping tool 6 and for this step on the hinges 9 or on fastening screws. Alternatively, additional screwdrivers can be used that are attached to other robots or handling systems.

After mounting the vehicle door 3, the fixing device 14 of the gripping tool 5 is released, so that the door 3 hangs freely on the body 1. In this position, control measurements of the joint dimensions, gaps and depth dimensions are carried out in the regions 30, 31 (with the aid of the sensors 14). If deviations from the nominal dimensions are found, the operator of the system is sent defined information for rework.

Track section F (retraction of gripping tool 5):

If the rear door 3 is fastened in the correct position in the door cutout 2, the fixing device 14 of the gripping tool 5 is pivoted out of the engagement position in such a way that the gripping tool 5 can be moved back from the assembly position 29 into the retracting position 36 in a robot-controlled manner. The body 1 is relaxed, lifted and conveyed, and at the same time the tools 5, 6 are equipped with a new door 3, hinges 9 and screws, and a new body 1 is fed to the work space 4.

For data communication between the different system components (evaluation units 33, 45 of the sensor systems 18, 24 and the controls of the robots 7, 8 in the control system 10), one is advantageously used in the present exemplary embodiment TCP / lP interface used, which enables a high data rate. Such a high data rate is necessary in order to manage regulation of the overall system (sensor systems / robots) with the large number of individual sensors 19, 25 in the interpolation cycle of the robots 7,8 (typically 12 milliseconds) during the positioning phases A-2 and Cl to be carried out in a controlled manner can. For control problems of lower complexity - ie with lower requirements for accuracy and longer control times - the control can also be implemented via a conventional serial interface.

In the previous description, the special case of mounting a rear door 3 in a body 1 was described. Of course, the method can also be applied to the assembly of driver's doors in bodies 1, with the rear door and driver's door advantageously being positioned and assembled sequentially rather than simultaneously, for reasons of better accessibility for the associated tools 5, 6.

In addition to the door assembly, the method can also be transferred to the assembly of any other flaps (tank flap, bonnet, tailgate, etc.) which have to be mounted on the body 1 in the correct position. Finally, the method is not limited to the scope of assembly on bodies 1 but can basically be applied to any assembly problems in which a flap is to be mounted on a workpiece with the aid of robot-guided tools 5, 6. In the context of the present application, “robot-guided” tools are to be understood quite generally as tools that are mounted on a multi-axis manipulator, in particular a six-axis industrial robot 7, 8.

In addition to the gap sensors described so far, any optical sensors can be used as sensors 19 for detecting the actual position of the flap 3 relative to the reference area 11 on the workpiece 1. For example, area-measuring CCD cameras can be used as sensors 19, with the help of which (in combination with suitable image evaluation algorithms) the spatial positions and the mutual offset of edges as well as spatial distances etc. can be generated as measured variables. The same applies to the sensors 25 which are used for the alignment of the hinge mounting system 6 with respect to the auxiliary surface 42 on the gripping tool 5. Furthermore, any tactile and / or non-contact measuring system can be used, the selection of the suitable sensors being strongly dependent on the respective application.

In the exemplary embodiment in FIG. 5, in which the reference area on the gripping tool 5 is designed as a flat surface 42 perpendicular to the vehicle longitudinal direction 44 and the sensors 25 are distance sensors, the auxiliary surface 42 permits position measurement and alignment of the hinge assembly tool 6 only in the vehicle longitudinal direction; In this case, the positioning in the transverse direction of the vehicle is controlled, as described above. In very general terms, the reference surface 26 can be any surface that enables the hinge mounting system 6 to be spatially aligned with respect to the gripping tool 5 in all three spatial directions. In particular, the hinge assembly tool 6 can be aligned with the hinge screw surface 16 of the door 3.

Furthermore, the hinges 9 can be assembled manually in the door cutout 2 of the body 1: in this case, process steps C-0 to C-2 of the automatic preparation, positioning and assembly of the hinges 9 are omitted and are instead replaced by a manual hinge assembly process.

In the exemplary embodiment in FIGS. 1 to 5, a (first) sensor system 18 is provided on the gripping tool 5, which serves to position the gripping tool 5 relative to the body 1, while a (second) sensor system 24 is provided on the hinge mounting system 6, which is used for positioning tion of the hinge mounting system 6 relative to the gripping tool 5 is used. Instead of these double sensor systems 18, 24, the positioning of the hinge mounting system 6 with respect to the gripping tool 5 can also take place with the aid of additional sensors on the gripping tool 5; in this case, the auxiliary surface 42 is not provided on the gripping tool 5, but on the hinge mounting system 26. In this way, only a single sensor system 24 can be used, which is attached to the gripping tool and contains both sensors 19 for aligning the gripping tool 5 with respect to the body and sensors 25 for aligning the hinge mounting system 6 with the gripping tool 5.

Furthermore, the position control of the gripping tool 5 with respect to the body cannot be limited to the positioning phase A-2, but the gripping tool 5 can monitor the body 1 with the aid of selected (additional) sensors during the entire assembly process. In such a case, the body algorithms need not be clamped stationary during the positioning and assembly process due to the fast algorithms for position control, but they can be moved (for example on an assembly line or other suitable conveyor technology) relative to the robots 7, 8. This enables a high degree of flexibility of the method according to the invention, which can thus be used for a wide variety of applications of flap assembly on stationary and moving workpieces.

.oOo.

Claims

claims

Method for mounting a flap (3) on a workpiece (1), in particular on a vehicle body (1), the flap (3) being positioned precisely on the workpiece (1) with respect to a reference area (11, 30),

- In which method a gripping tool (5) guided by means of a robot (7) is used, which has a fixing device (14) for receiving the flap (3) and a sensor system (18) with at least one sensor which is firmly connected to the gripping tool (5) (19) includes

- The gripping tool (5) initially in the context of a positioning phase (A-2) starting from a proximity position (37), which is independent of the position of the workpiece (1) in the working space (27) of the robot (7), in a mounting position (29) is moved, in which the flap (3) held in the gripping tool (5) is aligned precisely in relation to the reference area (11, 30) of the workpiece (1)

- And the flap (3) then this mounting position

(29) of the gripping tool (5) is connected to the workpiece (1), so that an iterative control process is carried out to move to the assembly position (29), in the course of which

an (actual) measured value of the at least one sensor (19) is generated,

this (actual) measured value is compared with a (target) measured value generated in the course of a set-up phase,

- from the difference between the (actual) measured value and the (target) measured value using a set-up phase calculated Jacobi matrix a displacement vector of the gripping tool (5) is calculated,

- The gripping tool (5) is moved by this displacement vector.

2. The method according to claim 1, and that the iterative control process is terminated when

- either the deviation between the (target) measured value and (actual) measured value lies below a predetermined threshold value, or

- The reduction of this deviation to be achieved in successive iteration steps lies below a predetermined threshold.

3. The method according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t,

- That the gripping tool (5) is moved in a controlled manner into an evasion position (38) after the controlled approach to the assembly position (29),

that fastening elements (9) are fastened to the workpiece (1) using a robot-guided hinge mounting system (6),

- That the gripping tool (5) is moved back from the avoidance position (38) into the assembly position (29) and

- That the flap (3) held in the gripping tool (5) is fastened to the fastening elements (9).

4. The method of claim 3 d a d u r c h g e k e n n z e i c h n e t that for fastening the fasteners (9) on

Workpiece (1)

- The hinge assembly system (6) is first brought under robot control into an approach position (48), which is independent of the position of the workpiece (1) in the working space (27) of the robot (8), - The hinge mounting system (6) is then moved in an iterative control process into a working position (41) in which the hinge mounting system (6) is aligned with the gripping tool (5),

- and then a robot-controlled machining process (C-2) is carried out, in the course of which the fastening elements (9) supplied in the hinge mounting system (6) are connected to the workpiece (1).

5. Method according to one of the claims 1 to 4, that the fastening elements (9) are hinges which are screwed to the workpiece (1) and the flap (3).

6. The method according to any one of the preceding claims, characterized in that a TCP / IP interface is used for communication between the control system (10) of the robot (7, 8) and the evaluation unit (33, 45) of the sensor system (18, 24) ,

7. Use of the method according to one of claims 1 to 6, so that the method is used for assembling a vehicle door (3) on a vehicle body (1).

8. Device for mounting a flap (3) on a workpiece (1), in particular for mounting a vehicle door on a vehicle body

- with a gripping tool (5) guided with the aid of a robot (7),

- With a sensor system (18) which is firmly connected to the gripping tool (5) and comprises at least one sensor (19), - With a control system (10) for controlling the robot

(7) and the gripping tool (5),

- And with an evaluation unit (33) for evaluating the measured values of the sensor system (18) so that at least one of the sensors (19) is a metrically uncalibrated sensor.

9. The device as claimed in claim 8, so that the at least one sensor (19) is an optical gap measurement sensor.