Abstract:
A device and method for monitoring and correcting the position and orientation of an operating device ( 2 ) with respect to a piece (P). A measuring device ( 5 ) including a plurality of sensors ( 505 ) connected to the operating device is used to measure through contactless technology the distances of the sensors from a surface (π) of the piece along respective directions (l, r, s) having given orientations. The sensor measurements are compared to predetermined desired values and the position of the operating device ( 2 ) is selectively changed to maintain a desired positional relationship between a main operative axis (X 1 ) of the operative device and operation axis (X 2 ) defined by the surface of the piece.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to systems and methods for checking and correcting the position of an operating device with respect to a piece. 
       BACKGROUND OF THE INVENTION 
       [0002]    The expression “operating device” is used in the present description and in the appended claims to indicate any device, implement, or tool that can be used in an industrial plant for carrying out an industrial operation. 
         [0003]    A specific application that is described herein is that of a riveting device carried by a manipulator robot and designed to apply joining rivets on sheet-metal elements, for example in a motor-vehicle assembly line. A further example of application of the invention is that of an electric spot-welding gun carried by a manipulator robot or just simply a welding gun controlled manually by an operator. Yet a further example is constituted by a roller-hemming device carried by a manipulator robot. 
         [0004]    In any application of the type referred to above there exists the problem of positioning and orienting the operating device properly with respect to the workpiece. Specifically, reference is here made to the case where the operating device has a main operative axis, having a predetermined position and orientation with respect to the operating device, and the piece has a surface that defines a preferential axis along which the operation must be performed, here referred to as “operation axis”, having a predetermined position and orientation with respect to the aforesaid surface of the piece. 
         [0005]    In the case, for example, of a riveting device, it is in general necessary for the main operative axis of the device, corresponding to the direction of application of the rivet, to be orthogonal, within a predetermined margin of error, with respect to the surface portion of the piece (for example, an element of sheet metal) on which the operation itself is carried out. Likewise, in the case of a welding gun or in the case of a roller-hemming head, it is necessary for the tool to be correctly oriented with respect to the piece. 
         [0006]    In the specific case of a motor-vehicle assembly line, the problem of proper orientation of an operating device, such as for example a riveting device or a welding gun, or a roller-hemming head, is rendered more complicated by that the sheet-metal constituting the structures to be processed may present a non-uniform quality, so that, even if the operating device is precisely positioned during preliminary set-up of the installation, defects may occur during normal production in the final produced structures. 
       SUMMARY OF THE INVENTION 
       [0007]    The object of the present invention is to provide a checking device of universal use, which can be associated by simple and quick operations to any operating device and which will enable performing in real time, prior to execution of the operation on each single piece (or, if preferred, periodically on a piece of each predetermined batch of pieces), a checking operation on position and orientation of the operating device with respect to the piece and also, if necessary, a correction of the position and/or orientation of the operating device, so as to ensure the necessary quality of the operation. 
         [0008]    With a view to achieving the above object, the subject of the invention is a device for checking and correcting the position of an operating device with respect to a piece, 
         [0009]    wherein the operating device has a main operative axis, having a predetermined position and orientation with respect to the operating device; 
         [0010]    wherein the piece has a surface that defines an operation axis having a predetermined position and orientation with respect to said surface of the piece; and 
         [0011]    wherein an apparatus is provided for positioning the operating device and/or the piece, which is able to modify the position and/or orientation of the operating device with respect to the piece, 
         [0012]    said position checking and correcting device being characterized in that it comprises: 
         [0013]    a measuring device, which can be associated to the operating device and carries one or more sensors at given positions with respect to the operating device, said sensors being adapted to measure, by means of a contactless technology, distances of the sensors from said surface of the piece, along respective directions having given orientations; 
         [0014]    first electronic processing means configured for processing measurement values detected by said contactless sensors so as to obtain a value of at least one angle indicating the orientation of said main operative axis of the operating device with respect to said operation axis defined by the piece; and 
         [0015]    second electronic control means, adapted to use an information coming out from said first electronic processing means for generating, if necessary, a control signal that is used by said positioning apparatus for positioning said operating device according to a desired orientation with respect to the piece. 
         [0016]    In a preferred embodiment, the above mentioned measuring device comprises a supporting structure, which can be associated in a given position to the operating device, and at least three sensors for contactless distance measurement, which are carried in given positions by said supporting structure and are adapted to detect measurement values of respective distances from the surface of the piece, along at least three respective measuring directions. More specifically, in the aforesaid exemplary embodiment, the above supporting structure can be removably associated to the operating device in a position where said sensors are distributed about said main operative axis of the operating device, with the aforesaid three measuring directions that are mutually convergent towards the surface of the piece. 
         [0017]    Once again in the case of the preferred exemplary embodiment, the supporting structure comprises a sensor-carrying portion, having walls for carrying the aforesaid sensors which are adapted to surround at a distance, on two or more sides, the operating device, and an attachment portion, which is adapted to be secured to an element carried by the automated apparatus used for positioning the operating device, said attachment portion supporting said sensor-carrying portion in a cantilever fashion. 
         [0018]    Once again in the case of the preferred exemplary embodiment, the automated positioning apparatus is a manipulator robot carrying the operating device and provided with an electronic controller. 
         [0019]    In this case, preferably the aforesaid first electronic processing means and second electronic control means are both incorporated within the controller of the robot. Not, however, ruled out is a solution in which the first electronic processing means are, instead, incorporated in the aforesaid sensors or in any case in the aforesaid measuring device including the sensors. 
         [0020]    Thanks to the above characteristics, the invention enables the problem of a continuous and effective checking of proper positioning of an operating device during normal production on a production line to be solved in a simple and effective way. 
         [0021]    The device according to the invention is of universal use given that it can be associated in a simple and fast way to any operating device. It enables performing in real time, prior to execution of the operation on each single piece (or if so preferred periodically on a piece of each predetermined batch of pieces), a check on the position and orientation of the operating device with respect to the piece, and moreover makes possible immediate execution, if necessary, of a correction of the position and/or orientation of the operating device, in order to guarantee the necessary quality of operation. 
         [0022]    Positioning of the supporting structure carrying the sensors with respect to the operating device can be carried out also in a non-precise way in so far as the system can be calibrated during a setting-up stage by storing in the memory a “zero” position of the system in which the electronic control means detect proper orientation of the main axis of the operating device. 
         [0023]    Of course, the type of sensors used and the way in which they are prearranged in association with the operating device may vary widely with respect to what has been illustrated herein purely by way of example. 
         [0024]    The subject of the invention is also a method for checking and correcting the position of an operating device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Further characteristics and advantages of the invention will emerge from the following description with reference to the annexed drawings, which are provided purely by way of non-limiting example and in which: 
           [0026]      FIG. 1  is a schematic view of a manipulator robot carrying a riveting device to which a checking and positioning device according to the invention is associated; 
           [0027]      FIG. 2  is a perspective view at an enlarged scale of the riveting device of  FIG. 1 , to which the checking and positioning device according to the invention is associated; 
           [0028]      FIG. 3  is a perspective view at an enlarged scale of the checking and positioning device according to the invention; 
           [0029]      FIG. 4  is a schematic diagram of the device according to the invention; and 
           [0030]      FIG. 5  is a schematic variant of  FIG. 1  that shows application of the invention to a manipulator robot equipped with an electric spot-welding gun. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    With reference to  FIG. 1 , number  1  generally designates a manipulator robot of any known type carrying an exemplary riveting device  2 . According to the conventional art, the manipulator robot  1  comprises a chain of elements mutually articulated about a plurality of axes I, II, III, IV that terminates with a robot wrist articulated about two mutually perpendicular axes V, VI. The proximal element of the chain of elements constituting the manipulator robot  1  is a flange F, connected to which is the attachment flange  3  of a C-shaped frame  4  constituting the supporting structure of the exemplary riveting device  2 . 
         [0032]    According to the conventional art, the various elements constituting the manipulator robot  1  are controlled by electric motors, driving of which is controlled by a robot controller RC so as to displace, position, and orient the riveting device  2  in any desired way. 
         [0033]    In the case of the example illustrated, the riveting device  2  is designed to apply joining rivets to sheet-metal elements constituting the piece P on which the riveting device operates. During execution of the operation, the elements constituting the piece P are clamped in position by any clamping tool B suited for the purpose (illustrated only schematically in  FIG. 1 ). 
         [0034]      FIG. 2  illustrates the exemplary riveting device  2  at an enlarged scale. The details of construction of this device are not described herein, since they can be made in any known way and also in so far as they do not fall, taken in themselves, within the scope of the present invention. In general, the riveting device  2  comprises a cylindrical body  200 , associated to which is a pneumatic actuator  201  that receives in succession the rivets (not shown) to be applied from a rivet reservoir  202  and applies them on the sheet-metal elements constituting the piece P, feeding them in a direction X 1  that defines the main operative axis of the riveting device  2 . 
         [0035]    The rivets are applied on a plane surface portion π of the piece P, which defines a preferential axis X 2  of execution of the operation, here referred to as “operation axis”. In the case of the application illustrated, the operation axis X 2  is typically an axis orthogonal to the surface π. 
         [0036]    In general, proper execution of the riveting operation requires the main operative axis X 1  of the riveting device  2  to have a given position and/or orientation with respect to the operation axis X 2  defined by the surface of the piece. In the specific example illustrated in the annexed drawings, main operative axis X 1  must be substantially coincident with operation axis X 2 . 
         [0037]    According to the illustrated example of the invention, associated to the riveting device  2  is a measuring device  5  which is used for checking and correcting the position of the exemplary riveting device  2 . This device  5  is more clearly visible in  FIG. 3 . With reference to the example illustrated in  FIG. 3 , the device  5  includes a supporting structure  500  that is rigidly connected to the C-shaped frame  4  of the operating device  2 , adjacent to the attachment flange  3 . 
         [0038]    Once again with reference to the specific example illustrated, the supporting structure  500  includes two parallel planar plates  501  spaced apart from each other, with top ends having holes for engagement of screws for attachment to the two sides of the C-shaped frame  4 . The bottom end portions  502  of the plates  501  are rigidly connected together by a front plate  503 . The structure constituted by the aforesaid end portions  502  and by the front plate  503  is set in three mutually orthogonal planes about the main operative axis X 1  of the device. Each of the three planes defined by the end portions  502  of the plates  501  and by the front plate  503  carries a respective sensing unit  504 , each of which includes a distance sensor  505  (illustrated in  FIG. 3 ), which, in the case of the example described herein, is constituted by an optical laser sensor of any known type, operating in reflection. Any other known type of distance sensor operating with contactless technology may also be used. 
         [0039]    As may be seen, the supporting structure  500  therefore comprises a sensor-carrying portion  500 A, constituted by the walls of bottom end portions  502 , and front plate  503  that surround the operating device  2  at a distance, on two or more sides, and an attachment portion  500 B (constituted, in the example illustrated, by the attachment ends of the plates  501 ), which is secured to an element, for example attachment flange  3 , which is selectively connected to the apparatus (in the specific case, the robot  1 ) through, for example flange F, that carries the operating device and which is designed to support the sensor-carrying portion in a cantilever fashion  500 A. 
         [0040]    Thanks to the above described arrangement, the measuring device  5  according to the invention can be easily adapted on any operating device, at most upon modifying the conformation of the supporting structure  500 . 
         [0041]    Referring to  FIG. 4 , each unit  504  includes an electronic card  505   a  designed to receive the signals coming out from the respective sensor  505  and to send them to an electronic processing unit  506  (see  FIG. 4 ) configured for processing the information coming out from the sensors  505 . With reference once again to  FIG. 4 , the three sensors  505  operate in three respective directions l, r, s and are designed to detect the distances of each of the sensors themselves from the plane π, along the respective operating direction. In the example illustrated, the three sensors  505 , arranged about the main operative axis X 1 , are oriented in directions l, r, s slightly convergent in the direction of the piece P. In any case, the theoretical points of intersection of the directions l, r, s with the plane  7 C of the piece P are located along a circumference the radius R of which (see  FIG. 4 ) is less than the minimum distance d that must be maintained between the main operative axis X 1  of the operating device and the edge of the piece P for the riveting operation to be carried out properly. 
         [0042]    The unit  504  associated to the three sensors  505  sends the information regarding the respective measurements to the electronic processing unit  506 . The electronic unit  506  is configured for processing this information in order to obtain an information on the orientation of the main operative axis X 1  of the operating device  2  (the position of the sensors  505  relative thereto being known from a dedicated calibration operation) with respect to the operation axis X 2  defined by the piece P (i.e., in the example illustrated, the operation axis X 2  orthogonal to the plane surface π). The orientation of main operative axis X 1  with respect to operation axis X 2  is defined by one or more angles that the processing unit  506  is able to determine on the basis of the measurements made by the sensors  505 . 
         [0043]    According to the most general arrangement, the information coming out from the processing unit  506  is used in an electronic control unit  507  for generating, if necessary, a signal for controlling the apparatus  1  for positioning the operating device  2  in order to orient this device correctly. 
         [0044]    In the case of the embodiment illustrated, however, both the electronic processing unit  506  (which calculates the angle of inclination of the main operative axis X 1  with respect to the operation axis X 2  on the basis of the measurements made by the sensors  505 ) and the electronic control unit  507  (which carries out correction of the position of the operating device  2 ) are incorporated in the robot controller RC. 
         [0045]    In a variant, the processing unit  506  is, instead, integrated in the unit  504  and/or is associated to the structure  500  for supporting the sensors, whereas the unit  507  is integrated in the robot controller RC. 
         [0046]    According to one example of the invention, immediately prior to operation on each single piece P, or alternately, if so preferred, periodically on one piece P of each predetermined batch of pieces P, the measuring device  5  is activated to enable the electronic unit  506  to receive the measurements made by the sensors  505  and to process them so as to calculate the value of at least one angle of inclination of the main operative axis X 1  of the exemplary riveting device  2  with respect to the operation axis X 2  defined by the piece P. If the retrieved inclination angle does not coincide with the desired value within a predetermined margin of error, the information generated by the electronic processing unit  506  is used by the unit  507  for positioning and orienting the riveting device correctly, through a closed-loop control. As already mentioned, in the embodiment illustrated herein the functions of units  506 ,  507  are all performed by the robot controller RC. 
         [0047]    As emerges clearly from the foregoing description, the device according to the invention may be easily and rapidly applied to the operating device  2  in order to enable it to control itself in real time in order to ensure proper execution of any operation. 
         [0048]    As already mentioned, application to an operating device  2  in the form of a riveting device carried by a manipulator robot  1  is here provided purely by way of example. 
         [0049]      FIG. 5  illustrates an alternative variant in which the measuring device  5 ′ according to the invention is carried by a supporting structure  500 ′ associated to an electric spot-welding gun W, carried by a manipulator robot  1 . In this case, the main operative axis X 1 ′ of the operating device  2  is the axis along which the two electrodes of the gun W press between them two sheet-metal elements constituting the structure of the piece P to be welded. The operation axis X 2 ′ is the axis orthogonal to the two flanges of sheet metal to be welded (as generally illustrated). 
         [0050]    An alternative application similar to that of  FIG. 5  is that of a manipulator robot carrying a roller-hemming head (not shown). 
         [0051]    As likewise already mentioned, the invention may, however, be applied to any other operating device  2 , also in the case where it is controlled manually by an operator. 
         [0052]    Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what has been described and illustrated herein purely by way of example, without thereby departing from the scope of the present invention.