Abstract:
A workpiece clamping systems for a measuring machine includes a rotary table disposed in a workpiece rotation axis and includes a chuck for the concentric accommodation of a workpiece, a rotary drive for the rotary table, an upper centering tip mountable or mounted on the measuring machine in the workpiece rotation axis vertically opposed to the rotary table and a lower centering tip mountable or mounted on the rotary table in addition to the chuck for accommodating a workpiece between the centering tips instead of in the chuck, wherein the lower centering tip is provided and formed to be concentrically clamped in the chuck instead of a workpiece, and in that the workpiece clamping system is provided with a conveying device for vertically or vertically and chuck.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a workpiece clamping system for a measuring machine comprising a rotary table disposed in a workpiece rotation axis and comprising a chuck for the concentric accommodation of a workpiece, a rotary drive for the rotary table, an upper centering tip mountable or mounted on the measuring machine in the workpiece rotation axis vertically opposed to the rotary table and a lower centering tip for accommodating a workpiece between the centering tips instead of in the chuck mountable or mounted on the rotary table in addition to the chuck. 
         [0003]    2. Discussion of the Related Art 
         [0004]    A measuring machine in which a workpiece clamping system of the abovementioned type is used can be found, for example, in the company&#39;s catalogue “KLINGELNBERG P26/P40 Präzisionsmesszentren” comprising the publication information “DE 05/2013”. A measuring machine as shown in the appended drawings in  FIG. 13  as the state of the art is, according to the description on page 4 of the company&#39;s catalogue, a precision measurement centre in which the measuring machine comprises a precision heavy-duty rotary table. It is embodied as a measuring axis (C axis) and concentrically accommodates workpieces to be examined in a workpiece rotation axis designated by  17  in the appended  FIG. 13 . In combination with three linear measuring axes, tangential (X-axis), radial (Y-axis), and vertical (Z-axis), illustrated in the figure on page 4 of the company&#39;s catalogue the measuring machine scans functional surfaces of indentations and generally driving components in the manufacturer mode and examines them with the highest measuring and reproduction precision. 
         [0005]    In the Applicant&#39;s current P production series which is among the precision measurement centres P26 and P40 according to the abovementioned company catalogue, there are the options of clamping between tips (illustrated in the company&#39;s catalogue on page 4), the accommodation in the chuck (illustrated in the company&#39;s catalogue on page 12, image on the left in the second last row of images) or the direct placement of the workpiece on the rotary table (which is of no relevance here) for accommodating the workpieces. In a measuring machine as partly visible in the abovementioned left image on page 12 of the company&#39;s catalogue no upper centering tip is provided as a backing device so that clamping between the tips is inapplicable with this machine. In the machine according to page 12 of the company&#39;s catalogue, it is therefore envisaged that the workpieces to be measured are accommodated in a clamping system comprising a multi-jaw chuck. 
         [0006]    In the illustration in the appended  FIG. 13  corresponding to the illustration on page  4  of the company&#39;s catalogue an additional chuck  11 ′ in which short, symmetric workpieces are clamped is mounted on a rotary table  13 . A lower centering tip  40 ′ indicated by dotted lines in  FIG. 13  may also be concentrically mounted on the rotary table  13  in a column  19  concentrically mounted on the rotary table  13  and supporting the chuck  11 ′. If a workpiece is to be clamped between the upper centering tip  30  and the lower centering tip  40 ′ instead of in the chuck  11 ′ the measuring machine has to be converted in advance which consumes time. The conversion includes the removal of the chuck  11 ′ and the column  20  supporting the chuck  11 ′ so that the lower centering tip  40 ′ is made accessible or can be fixed on the rotary table  13 . The latter case corresponds to the alternative that the lower centering tip  40 ′ is not accommodated in the column  19  but kept separately and only mounted on the rotary table  13  after the removal of the chuck  11 ′ and the column  19 . In this case the conversion will cost even more time. 
         [0007]    Such measuring machines are generally used in assembly lines as employed in automobile and utility vehicle industry as well as in aircraft industry. If different parts are to be produced in an assembly line the conversion of the measuring machine should be possible and automatable with less time expenditure. In addition, the solution comprising a lower centering tip disposed in a column under a chuck  11 ′ and to be made accessible only by the removal of the column and the chuck is not flexible. 
       SUMMARY OF THE INVENTION 
       [0008]    It is the object the invention to make switching between two clamping types in a workpiece clamping system of the above-mentioned type more flexible and less time-consuming. 
         [0009]    Proceeding from a workpiece clamping system the above-mentioned type, said object is, according to the invention, solved by the lower centering tip being provided and designed to be concentrically clamped in the chuck instead of a workpiece and by the workpiece clamping system being provided with a conveying device for vertically or vertically and horizontally conveying the lower centering tip into its and from its clamping position in the chuck. The workpiece clamping system according to the invention particularly provides for the advantage that the measuring machine can be readily switched between clamping in the chuck and clamping between tips. This is achieved by leaving the chuck on the measuring machine and by conveying the lower centering tip into the chuck by means of a conveying device so that it is clamped there, or by conveying the lower centering tip previously clamped in the chuck out of the chuck. In contrast to converting a machine by removing the chuck and the column supporting the chuck, or by installing the chuck and the column supporting the chuck the workpiece clamping system according to the invention which can be simply changed over to another clamping type without being retrofit is well suited for a time-saving automation of a clamping type change in a measuring machine used in an assembly line. 
         [0010]    The chuck used for the workpiece clamping system according to the invention may be a multi-jaw chuck as known, for example, from the Applicant&#39;s utility model DE 20 2014 004 713 U1. There, the multi-jaw chuck is part of a clamping system for a workpiece on a measuring machine. To ensure a simplified handling of such a clamping system and to cover a wider bandwidth of clamping situations no manually operable multi-jaw chuck is used in this known clamping system. Rather, the clamping system is motor-driven, namely by the electric rotary drive of the multi-jaw chuck. The use of such a multi-jaw chuck which is motor-operated, namely by the electric rotary drive of the multi-jaw chuck, reduces the time expenditure required for clamping the workpiece to be measured and increases the flexibility of the measuring machine of the workpiece clamping system according to the present invention. This in turn enables a simple automation of a clamping type change in the workpiece clamping system according to the invention. In the known clamping system a part of the clamping system is fixed with the aid of a coupling during a clamping or release process so that the rotary drive of the multi-jaw chuck assumes the function of the clamping jaw adjustment. The torque of the C-axis rotary drive can be controlled with high precision. Through this torque control a force control of the workpiece clamp is possible. The direct coupling of the C-axis rotary drive to the C-axis is maintained during the deployment of this known clamping system and is also an economically attractive solution for the present invention. 
         [0011]    In one embodiment of the workpiece clamping system according to the invention the rotary table and/or the rotary drive of the rotary table comprise(s) at least one segment of a hollow shaft in which the lower centering tip is vertically conveyable along the workpiece rotation axis by means of the conveying device. In this way, converting the workpiece clamping system according to the invention from one clamping type to the other clamping type is substantially facilitated. Namely, the lower centering tip only has to be conveyed out of the hollow shaft into the chuck so that it can be clamped therein, or, if the workpiece clamping system is to be used for clamping a workpiece in the chuck, simply be fed from the chuck into the hollow shaft. 
         [0012]    In a further embodiment of the workpiece clamping system according to the invention the conveying device comprises a rod which is disposed in the hollow shaft and can be moved up and down between an non-operating position and the clamping position of the lower centering tip inside the hollow shaft for vertically conveying the lower centering tip along the workpiece rotation axis. This is a particularly simple and useful possibility for conveying the lower centering tip into and out of the chuck. 
         [0013]    In a further embodiment of the workpiece clamping system according to the invention the rod can be reciprocated along the workpiece rotation axis with the aid of an actuator. This embodiment is particularly suitable if no drive suitable for conveying the lower centering tip along the workpiece rotation axis exists under the chuck. When switching the clamping type, this embodiment gives rise to a further facilitation if, in combination with the chuck, clamping in the chuck or between centering tips depending on the component to be accommodated (workpiece or lower centering tip) is to be realised without converting the measuring machine. 
         [0014]    In a further embodiment of the workpiece clamping system according to the invention the rod is a rack which can be reciprocated by means of a pinion drivable by the actuator. The drive for the conveying device could also be implemented in another way, for example, by means of a threaded spindle or a linear motor or with the aid of an electric, pneumatic or hydraulic cylinder. The latter options, however, require more expenditure since in these cases the required energy has to be specifically supplied or generated. 
         [0015]    In a further embodiment of the workpiece clamping system according to the invention the conveying device comprises conveying equipment for conveying the lower centering tip transversely relative to the workpiece rotation axis and along the workpiece rotation axis. This embodiment is particularly advantageous if a robot can be used as the conveying equipment within the scope of an assembly line. Conveying will then be effected transversely relative to the workpiece rotation axis, and then along the workpiece rotation axis, or vice versa. 
         [0016]    In a further embodiment of the workpiece clamping system according to the invention the chuck is formed as a multi-jaw chuck. It was already mentioned above that for this purpose a motor-operated multi-jaw chuck as known from the Applicant&#39;s utility model DE 20 2014 004 713 U1 can be used. 
     
    
     
       DESCRIPTION OF THE INVENTION 
         [0017]    In the following, embodiments of the invention will be described in detail with reference to the drawings in which: 
           [0018]      FIG. 1  to  FIG. 6  respectively show a partial longitudinal sectional view of a first embodiment of a workpiece clamping system according to the invention in which conveying a lower centering tip into a multi-jaw chuck and clamping the lower centering tip in the multi-jaw chuck are illustrated in different phases of the conveying and clamping process, 
           [0019]      FIG. 7  to  FIG. 12  respectively show a partial longitudinal sectional view of a second embodiment of the workpiece clamping system according to the invention in which a lower centering tip can not only be conveyed vertically along a workpiece rotation axis but also horizontally or transversely relative the workpiece rotation axis, wherein again different phases of the conveying and clamping process of the lower centering tip are illustrated, and 
           [0020]      FIG. 13  shows a perspective view of a conventional measuring machine comprising a conventional workpiece clamping system on which a workpiece can be clamped between tips or in a multi-jaw chuck. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    A first embodiment of a workpiece clamping system according to the invention is generally denoted by  10 , wherein conveying a lower centering tip  40  into a chuck  11  and clamping the lower centering tip  40  in the chuck  11  are illustrated in various phases of the conveying and clamping process. In this first embodiment the chuck  11  is a multi- or three-jaw chuck provided with an electric rotary drive  12  rotating the three-jaw chuck. The rotary drive  12  comprises a stator  12   a  and a rotor  12   b.  Furthermore, the chuck  11  comprises a chuck body  14 . The chuck body  14  is not fixedly connected to the rotor  12   b  on the inside as in a conventional multi-jaw chuck but rotatable relative to the rotor  12   b.  Jaws  16   a,    16   b  and  16   c  (the latter is not shown in  FIGS. 1 to 6 ) are guided within the chuck body  14  so as to be radially shiftable for clamping a workpiece (not illustrated) or, as here in the embodiment, a lower centering tip  40  in the chuck  11  or to release it from the chuck  11 . 
         [0022]    A scroll  18  on which the chuck body  14  is rotatably supported is fixedly connected to the rotor  12   b  on the inside, or, according to the illustration in  FIGS. 1 to 6 , integrally formed with the rotor  12   b  but still rotatable relative to the chuck body  14 . The scroll  18  is in a positive engagement with the jaws  16   a,    16   b  and  16   c.  The clamping jaws  16   a,    16   b  and  16   c  are radially shifted by a rotation of the scroll  18  relative to the chuck body  14  induced with the aid of the electric rotary drive  12 . The rotation of the scroll  18  is not induced manually like with the conventional chuck  11  according to  FIG. 13  but motor-driven with the aid of the electric rotary drive  12  which is the rotary drive of a measuring machine, for example, the conventional measuring machine shown in  FIG. 13  in the C-axis of which the chuck  11  including a workpiece  12  (not illustrated) is disposed. The measurements on a workpiece and the measurement setup are analogous to those of a conventional measuring machine as shown in  FIG. 13 . A rotary table  13  of the measuring machine carries a column  19  which in turn carries the chuck  11  on its upper end. The lower centering tip  40  is disposed inside of the column  19  in  FIG. 13  and therefore drawn in dotted lines. If a workpiece is to be clamped between the centering tips  30  and  40  the measuring machine according to  FIG. 13  first has to be converted by removing the column  19  comprising the chuck  11  as already described in the introduction. 
         [0023]    In the clamping system according to the Applicant&#39;s abovementioned utility model an outer collar is formed on, i.e. integrally formed with the chuck body  14 . On its outer circumference, the outer collar doesn&#39;t have a knurling or the like for facilitating a manual operation of the outer collar, but an indentation which is part of a coupling which, like the outer collar in  FIGS. 1 to 6 and 7 to 12 , is not illustrated. With the aid of this coupling a part of the workpiece clamping system  10  is fixable during a clamping or releasing process so that the electric rotary drive of the measuring machine illustrated by the stator  12   a  and the rotor  12   b  here assumes the function of the clamping jaw adjustment. A comprehensive description of the function of the outer ring and the coupling  30  can be found in the Applicant&#39;s abovementioned utility model to which reference is made to avoid repetitions. It should only be mentioned here that, with the aid of the coupling, the outer collar and with it the chuck body  14  can be fixed on the stator  12   a  so that the electric rotary drive  12  assumes the function of the clamping jaw adjustment by rotating the scroll  18  relative to the chuck body  14 . Since the chuck body  14  can be mechanically coupled via the coupling comprising the stator  12   a  the chuck body  14  will not rotate along while the rotor  12   b  rotates the scroll  18 . While the coupling is not activated and the workpiece is clamped by the clamping jaws  16   a,    16   b  and  16   c  the electric rotary drive  12 , as conventionally, serves to rotate the entire chuck  11  including the workpiece clamped therein. 
         [0024]    In the illustration of the workpiece clamping system  10  of  FIGS. 1 to 6  also a partial sectional view of the scroll  18  is shown in addition to the chuck body  14 . The fixed connection of the scroll  18  to the rotor  12   b  can be established by a positive or bonded connection (both not illustrated in  FIGS. 1 to 6 ). 
         [0025]    The lower centering tip  40  is provided and formed to be concentrically clamped in the chuck  11  instead of a workpiece. A central bore of the chuck body  14 , a central bore the scroll  18 , a central bore of the rotor  12   b  and a central bore of the rotary table  13  are hollow shaft sections  20   a,    20   b,    20   c  or  20   d  which together form a hollow shaft generally designated by  20 . The workpiece clamping system  10  serving as a clamping system for the lower centering tip  40  according to the invention is provided with a conveying device for the lower centering tip  40  generally designated by  50 . The conveying device  50  serves to vertically convey the lower centering tip  40 , i.e. to move it up and down within the hollow shaft  20  into and from its clamping position in the chuck  11 . The clamping position of the lower centering tip  40  in the chuck  11  is shown in  FIG. 5 . The initial or non-operative position of the lower centering tip  40  is shown in  FIG. 1 . The rod  52  can be reciprocated along the workpiece rotation axis  17  with the aid of an actuator  54 . In the embodiment shown, the rod  52  is a rack which can be reciprocated by a pinion  56  drivable by the actuator  54 . 
         [0026]    Conveying the lower centering tip  40  into the chuck  11  and clamping the lower centering tip  40  in the chuck  11  are shown in various phases of the conveying and clamping process in  FIGS. 1 to 6  to which reference is made again now. If the lower centering tip  40  is in an initial or non-operational position the chuck  11  can be used to clamp a workpiece which is not shown here. In the illustration in  FIG. 2  the lower centering tip  40  has been moved upwards into a position in which it can be clamped by the chuck  11  by means of the conveying device  50 .  FIGS. 3 and 4  show phases of the movement the clamping jaws in the direction of the clamping position, the clamping jaw  16   c  which is above the plane of projection in the Figures not being shown. In  FIGS. 2 to 5  the lower centering tip  40  is clamped in the chuck  11  by the clamping jaws on a lateral surface  40   a  having a larger diameter of a cylindrical section and on a lateral surface  40   b  having a smaller diameter of another cylindrical section. It is also possible to only clamp the lower centering tip  40  on the lateral surface  40   b  of the cylindrical section having a smaller diameter. In any case the rod  52  below the lower centering tip  40  is also clamped by the chuck  11  in the clamping position together with the lower centering tip  40  as shown in  FIGS. 2 to 5 . When the lower centering tip  40  is in the clamping position according to  FIG. 5  a workpiece to be measured is clamped between the lower centering tip  40  and the upper centering tip  30 . For this clamping process, the upper centering tip  30  ( FIG. 13 ) is vertically shiftable. The clamping of the lower centering tip  40  in the chuck  11  is performed by radially shifting the clamping jaws  16   a,    16   b  and  16   c.  This radial shift of the clamping jaws can be accomplished like in the clamping system according to the Applicant&#39;s aforementioned utility model, or manually, or by a separate drive (not shown) which is independent of the rotary drive of the chuck  11 . 
         [0027]      FIGS. 7 to 12  show a second embodiment of the workpiece clamping system  10  according to the invention in which a lower centering tip  40  is not only vertically conveyable along the workpiece rotation axis  17  but also transversely relative to the workpiece rotation axis  17 , wherein in turn various phases of the conveying and clamping process of the lower centering tip  40  are illustrated. The difference between the first embodiment according to  FIGS. 1 to 6  and the second embodiment according to  FIGS. 7 to 12  resides in that the conveying device  50  conveying the lower centering tip  40  only vertically is replaced by a conveying device  50 ′ which conveys the lower centering tip both vertically and horizontally, i.e. transversely relative to the workpiece rotation axis  17  and along the workpiece rotation axis  17 . To this end, the conveying device  50 ′ comprises horizontally shiftable conveying equipment  58 . The conveying equipment  58  comprises a pliers-like claw  59  gripping and clamping the lower centering tip  40  at the lateral surface  40   a.  The conveying device  50 ′ may be a robot as typically used in assembly lines, for example, in automobile industry. 
         [0028]      FIG. 7  shows the conveying device  50 ′ in a phase in which it has already moved the lower centering tip  40 , particularly horizontally, into a position above the chuck  11 . In  FIG. 8 , the conveying device  50 ′ has moved the lower centering tip  40  further, horizontally, into a position in which a central axis of the lower centering tip  40  is located in the workpiece rotation axis  17 . In  FIG. 9 , the positioning device  50 ′ has moved the lower centering tip  40  vertically downwards into a position between the clamping jaws  16   a - 16   c.  In  FIG. 10 , the clamping jaws  16   a - 16   c  are already almost closed around the lateral surfaces  40   a  and  40   b  of the lower centering tip  40 . In  FIG. 11 , the claw  59  does no longer retain the lower centering tip  40  but already begins to open to release the lower centering tip  40  in its clamping position in the chuck  11 . In  FIG. 12 , the conveying device  50 ′ has already moved the conveying equipment  58  and the claw  59  away from the lower centering tip  40 . The lower centering tip  40  is now operational. 
         [0029]    The release of the lower centering tip  40  from the chuck  11  would be performed in the reverse order. That means that the claw  59  would be returned from position shown in  FIG. 12  to the position according to  FIG. 11  and clamp the lower centering tip  40  in the position according to  FIG. 10 . Then the chuck  11  would be opened in the Position according to  FIG. 9  while the lower centering tip  40  would be retained in its position by the conveying device  50 ′. Finally. the conveying device  50 ′ would lift the lower centering tip  40  vertically upwards into the workpiece rotation axis  17  to convey it into the position according to  FIG. 8 , and eventually into the position according to  FIG. 7 . 
         [0030]    A hollow shaft also exists in the embodiment according to the  FIGS. 7 to 12 , however, it is not required there. 
       LIST OF NUMERALS 
       [0000]    
       
           10  workpiece clamping system 
           11  chuck 
           11 ′ chuck 
           12  rotary drive 
           12   a  stator 
           12   b  rotor 
           13  rotary table 
           14  chuck body 
           16   a  clamping jaw 
           16   b  clamping jaw 
           16   c  clamping jaw 
           17  workpiece rotation axis 
           18  scroll 
           19  column 
           20  hollow shaft 
           20   a  hollow shaft section 
           20   b  hollow shaft section 
           20   c  hollow shaft section 
           20   d  hollow shaft section 
           30  upper centering tip 
           40  lower centering tip 
           40 ′ lower centering tip 
           40   a  lateral surface 
           40   b  lateral surface 
           50  conveying device (vertically) 
           50 ′ conveying device (vertically and horizontal) 
           52  rod 
           54  actuator 
           56  pinion 
           58  conveying equipment 
           59  claw