Abstract:
A process for working a contour on at least one workpiece using a robot includes positioning the workpiece relative to the robot; acquiring an actual position of the workpiece; acquiring a real course of the contour on the workpiece at predefined points using at least one sensor; and actuating the robot according to individual vectors so as to correct a robot motion during the working of the contour.

Description:
[0001]    This application is a U.S. National Phase Application under 35 U.S.C. §371 of International Application No. PCT/EP2008/004799, filed on Jun. 14, 2008 and claims benefit to German Application No. DE 10 2007 033 309.0, filed on Jul. 18, 2007. The International Application was published in German on Jan. 22, 2009 as WO 2009/010137 under PCT Article 21 (2). 
     
    
     BACKGROUND 
       [0002]    For the purpose of producing, for example, automobile bodies, body parts are so positioned in relation to one another in a receiving device that locations to be worked, for example edges to be welded to one another, are located in the working range of the robot arm. The robot arms moves with the tool, in this case a welding tip, along the line at which the two workpieces are to be welded to one another. Frequently, these lines are not rectilinear, but are curved according to the form of the body, such that a robot control system programmed thereto the robot tip can follow this curved line. 
         [0003]    It is to be noted in connection therewith that no body part is identical to another, because of the existence of tolerances, deformations and the like. 
         [0004]    For this purpose, for the working of body parts an ideal body is first produced, which body is so worked and processed that tolerances are brought almost to zero. This highly precisely produced ideal body, which is also referred to as a measurement body or measurement body-shell, serves the purpose of programming the robot motion. 
         [0005]    When a real body is to be worked, this real body is assigned to the robot, or positioned, and image recordings, for example of the contours to be welded together, are produced by means of a plurality of cameras, as a result of which the misalignment can be identified. There is produced therefrom a mean positional vector, which corresponds to an average displacement or twist of the actual contour in relation to the contour of the ideal body, and which is input to the control system of the robot. 
         [0006]    Accordingly, the robot tip is moved according to the mean positional vector. This can have the consequence that the robot tip does not travel exactly along the contour, it being the case that the deviations of the motion of the robot tip from the the contour are not to be too great. 
       SUMMARY OF THE INVENTION 
       [0007]    An aspect of the invention is to create a process by means of which improved working, for example a body, can be effected. 
         [0008]    Thus, according to the invention, the process for working a contour on at least one workpiece, particularly for welding or sealing a seam between two workpieces, particularly between two body parts, by means of a robot, is characterized by the following process steps: 
         [0009]    positioning in relation to the robot the workpiece that is to be worked, and/or acquiring the actual position of the workpiece, 
         [0010]    acquiring the real course of the contour on the workpiece, at predefined points, by means of at least one sensor, and determining the displacement vectors at the predefined points, 
         [0011]    actuating the robot according to the displacement vectors for the purpose of correcting the motion of the robot during the working of the contour. 
         [0012]    If the contour of a real workpiece that is subject to tolerances is to be worked, the process is additionally characterized by the following steps: 
         [0013]    positioning in relation to the robot an ideally produced workpiece, as a reference workpiece, 
         [0014]    determining the ideal course of the contour in that the robot, by means of at least one sensor, acquires the course of the contour on the reference workpiece, at predefined points, 
         [0015]    positioning in relation to the robot the real workpiece that is subject to tolerances, and/or acquiring the actual position of the real workpiece, 
         [0000]    acquiring the real course of the contour on the workpiece, at the predefined or other points, by means of at least one sensor, and thereby acquiring the deviation of the real course from the ideal course at the predefined points, 
         [0016]    calculating displacement vectors corresponding to the deviations, and 
         [0017]    actuating the robot according to the displacement vectors for the purpose of correcting the motion of the robot during the working of the contour. 
         [0018]    These displacement vectors correspond to the tolerances that occur in the case of the real workpiece, compared with the so-termed ideal workpiece. By means of the displacement vectors, the motion of the tool at the robot tip is matched to the real course of the contour to be worked. In comparison with the known process, in which a mean displacement vector or positional vector is calculated, a displacement vector is assigned to each individual predefined point, such that, overall, the working becomes more accurate. 
         [0019]    In the case of an automobile body, the process is performed in such a way that each contour of the ideal body is defined at particular measurement points, in that the measurement point is acquired by means of a camera or a plurality of cameras; in the case of the real body, the corresponding measurement points are likewise acquired in the same manner and are provided with their respectively own individual or displacement vector, or are calculated, such that the component tolerances and fitting tolerances of the entire body can be compensated. 
         [0020]    A particularly advantageous development of the invention can be achieved, in the case of the working of an invisible, covered contour course, for example an invisible seam on an automobile body, close to a visible contour, in that visible points of the visible contour are first acquired and measured, and the position of the invisible seam is calculated therefrom. 
         [0021]    In this case, expediently, the visible contour of the real workpiece can be divided into a plurality of sectors and a partial measurement of certain points can be performed in each sector, as a result of which correction values are determined for each sector, such that workpiece and positional tolerances are determined and the course of the robot motion is calculated. 
         [0022]    The measuring of the visible points is effected by means of a laser camera, and is operated on and mathematically processed by means of a triangulation measurement process that is known per se. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The invention, further advantageous developments and improvements, as well as further advantages, are explained more fully and described with reference to the drawing, wherein some exemplary embodiments of the invention are represented and wherein: 
           [0024]      FIG. 1  shows a top view of an ideal workpiece, 
           [0025]      FIG. 2  shows a top view of a real workpiece that is to be worked, with positional vectors represented, 
           [0026]      FIG. 3  shows the workpiece according to  FIG. 2 , with the actual guide path of the robot tool, 
           [0027]      FIG. 4  shows a side view of an automobile door, and 
           [0028]      FIG. 5  shows a sectional view according to the section line V-V of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    A workpiece  10 , which may be, for example, an automobile body or the like, is represented here as a rectangular, flat component that is to be welded, at a longitudinal edge  11 , to the longitudinal edge  12  of a further workpiece  13 . The two workpieces  10  and  13  have straight, linear edges  11  and  12 , and, accordingly, they can also be referred to as so-termed ideal workpiece parts. 
         [0030]    A robot arm, not represented here, travels with a sensor, which may be, for example, a camera, along the lines  11  and  12  and, starting from the start point  14 , makes images at predefined locations  15 ,  16 ,  17 ,  18  and  19 , the signals of which images are stored in a memory. 
         [0031]    A real workpiece  20  differs from the ideal workpiece  10  in that the edge  21  corresponding to the edge  11  has been altered in comparison with the ideal edge  11 ′, insofar as the real edge  21  has an S shape, which intersects the ideal edge  11 ′ at certain points  11 ″ and  11 ′″. 
         [0032]    The robot, with the sensor, travels along the curve  11 ′, and images are recorded at the same points  14 ′,  15 ′,  16 ′,  17 ′,  18 ′ and  19 ′ by means of the camera, the signals belonging to the images likewise being stored in a memory. The actual contour  21  deviates from the ideal contour, this being calculated by comparison of the so-termed ideal signals with the real signals, as a result of which there are calculated positional vectors  22 ,  23 ,  24 ,  25  and  26 , by which the contour to be traveled by the robot is displaced from the ideal points to the real points. There is thereby obtained a motional path  30 , as shown by  FIG. 3 , the motional path constituting, between the individual measurement points in each case, a straight line that is approximated to the real curve or real contour  21 . A better approximation of the motional path of the robot to the actual contour can be achieved by increasing the number of measurement points. The motional path of the robot according to  FIG. 1  can also be referred to as a training pass; the next step according to  FIG. 2  is a measuring pass, in which the real workpiece contour is measured, and the motional path  30  according to  FIG. 3  is the corrected path  30 , along which the robot travels in the case of application. 
         [0033]    The mode of operation of the invention has been described above with reference to a very simple workpiece part. It is represented in  FIG. 1  that the two edges of the workpiece parts are close to one another; in reality, the edges overlap one another, such that spot-welding work can be performed at the corresponding locations and the corresponding contours. 
         [0034]    A particular case is the sealing of a so-termed concealed seam. For this, reference is to be made to  FIGS. 4 and 5 .  FIG. 4  shows a top view of a door  40  within a body  41 , a gap  44 , which is to be realized to be as narrow as possible, being constituted between the peripheral edge  42  of the door and the inner edge  43  of the body  41 , which inner edge is matched to the outer contour of the door  40 . A sectional view according to the section line V-V is represented in  FIG. 5 . The door  40  in this case has an outer plate  45 , which is bent over inwards in an L shape at the end edges  42 , so as to form a U shape  46  having a free limb  47  extending parallelwise in relation to the door surface. The outer plate  45  is complemented to form the door in that there is provided an inner plate  48 , which engages in the U shape  46 , such that the limb  47  overlaps a partial region of the inner plate  48 . The limb  47  may, if necessary, be connected to the inner plate  48  by adhesive bonding or by a spot-welding process. A narrow gap  49  is formed in this case, through which moisture might be able to enter the inner space between the outer plate  45  and the inner plate  48 . For this purpose, it will be necessary to seal the gap  49 , or also the seam  49 , this being effected here by means of an L-shaped tool  45 , provided on the L-shaped limb  51  of which there is a slot, not shown in greater detail, through which sealing material  52 , indicated by arrows, can emerge and cover the seam  49 . 
         [0035]    The seam  49  in this case is a so-termed concealed seam, which cannot be detected by a sensor. 
         [0036]    In this case, the contour  42  of the door is detected and acquired at certain measurement points, which are indicated by crosses in  FIG. 5 . The start of the acquisition of the contour  42  is the start point  53 , and a certain number of measurement points, the number of which depends on the course of the contour  42 , is acquired by means of a sensor, according to the curved contour  42 , which is opposite the hinge-points  54  and  55  of the door  40 . After the individual measurement points, of which only the measurement points  56 ,  57  and the end measurement point  58  are denoted by way of example, have been acquired and the signals, determined by the sensor, have been stored in a memory, the measurement points are displaced computationally in consideration of the positional vectors, see  FIG. 2 , that have been acquired in this region, and the motion of the tool  55  is thereby calculated. The tool is then appropriately passed into the gap  44  and arranged as represented in  FIG. 5 , such that the limb  51  extends parallelwise in relation to the limb  47 , and the tool  50 , in the gap  44 , travels along the contour  42  according to the newly calculated, real contour, the sealing material  52  being brought to the gap from behind. Clearly, the same is also effected for the contour  42   a  in the upper region of the door  40  and for the contour  42   b  in the lower region of same. 
       LIST OF REFERENCES 
       [0000]    
       
           10  workpiece 
           11  longitudinal edge/lines 
           11 ′ ideal edge 
           12  longitudinal edge/lines 
           13  further workpiece 
           14  start point 
           15  predefined location 
           16  predefined location 
           17  predefined location 
           18  predefined location 
           19  predefined location 
           20  real workpiece 
           21  real edge 
           22  positional vector 
           23  positional vector 
           24  positional vector 
           25  positional vector 
           26  positional vector 
           30  motional path 
           40  door 
           41  body 
           42  end edge 
           42   a  contour in the upper region of the door 
           42   b  contour in the lower region of the door 
           43  inner edge 
           44  gap 
           45  outer plate 
           46  U shape 
           47  limb 
           48  inner plate 
           49  gap/seam 
           50  tool 
           51  L-shaped limb 
           52  sealing material 
           53  start point 
           54  hinge-point 
           55  hinge-point 
           56  measurement point 
           57  measurement point 
           58  end measurement point