Abstract:
A self-centering clamping device for a blade includes a mount having a root reception orifice which has a contour adapted to a root of the blade. The root reception orifice extends in the vertical direction and has a vertically running groove for receiving at least part of the root of the blade. A rotatable roller is arranged in a lower region of the root reception orifice and forms a stop for the root of the blade, a contact region of the roller for the root lying in an angular range larger than 0° and smaller than 90°, and the angular range being oriented upward and into the root reception orifice.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Stage of International Application No. PCT/EP2011/067367 filed Oct. 5, 2011 and claims benefit thereof, the entire content of which is hereby incorporated herein by reference. The International Application claims priority to the European application No. 10187251.3 EP filed Oct. 12, 2010, the entire contents of which is hereby incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates in general to a self-centering clamping device and a measuring device for a blade. The invention relates particularly to a self-centering clamping device and a measuring device with a blade of a turbine, engine or compressor. 
       BACKGROUND OF INVENTION 
       [0003]    In the measurement of moments or geometric measurements, it is important to fix and center the measurement objects exactly for the purpose of exact measurement. The measurement objects must be capable of being positioned quickly and reliably in a reproducible way. 
         [0004]    Conventionally, blades, such as turbine, engine or compressor blades, are fixed in a grooved block with bracing by an eccentric. Damage to the blade may occur during bracing. 
         [0005]    GB 2 047 897 shows a device for the measurement of turbine blades, with a groove for receiving the blade in a transverse direction of the blade and with a bracing mechanism for bracing the blade in a longitudinal direction of the blade. 
         [0006]    U.S. Pat. No. 5,792,267 discloses a fastening device for a turbine blade for the purpose of coating the blade, with a cylindrical base block, with a groove receiving the root and with a push-on sleeve and a cover for the block in order thereby to secure the blade. 
       SUMMARY OF INVENTION 
       [0007]    The object of the invention is to improve the fixing of blades. 
         [0008]    This object is achieved by the features of the independent claim(s). 
         [0009]    According to a first aspect of the invention, a self-centering clamping device for a blade comprises a mount with a root reception orifice which has a contour adapted to a root of the blade. The root reception orifice extends in the vertical direction and has a vertically running groove for receiving at least part of the root of the blade, and a rotatable roller is arranged in a lower region of the root reception orifice and forms a stop for the root of the blade, a contact region of the roller for the root lying in an angular range larger than 0° and smaller than 90°, and the angular range being oriented upward and into the root reception orifice. 
         [0010]    When the blade is inserted into the reception orifice, the blade is moved by gravity onto the roller functioning as a stop and is thus centered automatically. Reliable positioning without bracing is thus possible. On account of the movability of the roller, wear caused by friction is prevented. Damage to the blade is likewise avoided. The reception orifice is adapted essentially to the set-up of a turbine or compressor wheel disk, thus making it easier to position the blade. The arrangement of the roller make it possible to apply the blade in that quadrant of the roller which assists a downward movement of the blade by rotation. The blade thus slides with low friction into the reception orifice. 
         [0011]    The roller may have, in particular, a rolling bearing. By means of a rolling bearing, for example in the form of a ball, barrel or needle bearing, friction is reduced and reliability and precision are increased. However, plane bearings may basically also be considered as bearings for the roller. 
         [0012]    An axis of rotation of the roller may be at an angle with respect to the horizontal. By means of an inclined roller, the centering of the blade can be further improved, since the blade, as it were, may slip along the inclined circumferential surface of the roller into the reception orifice. 
         [0013]    The mount ( 5 ) may be a grooved block, thus making handling easy. 
         [0014]    The roller may be arranged opposite a vertically running groove orifice. As a result of the arrangement of the roller, the blade is pressed into the groove and is thereby fixed securely. 
         [0015]    A sliding roller may be arranged above the roller and opposite the groove orifice. The sliding roller makes it possible for the blade to be introduced into and removed from the reception orifice without any friction. In this case, in particular, a plurality of sliding rollers may also be arranged one above the other. This reduces the risk that the blade tilts and also, with regard to larger blades, makes it possible to handle the blade in the reception orifice in a simple way. Instead of the sliding roller or sliding rollers, a sliding surface made from a material having low friction may also be present. 
         [0016]    Two rollers may be provided. The distribution of the weight of the blade to two rollers makes it possible to have an even more reliable clamping device. The two rollers may be inclined with respect to one another in such a way that a type of funnel is obtained for the blade. 
         [0017]    Although not necessary, an eccentric for clamping the root may be arranged opposite the groove orifice. In addition, an eccentric may fix the blade if, for example, the clamping device has to be moved together with the inserted blade for the purpose of the workstep. 
         [0018]    The root reception orifice may be in the form of a blade fastening groove, thus making handling easier. 
         [0019]    According to a second aspect of the invention, a measuring device for a blade comprises a self-centering clamping device, as described above. The measuring device likewise has the abovementioned advantages and designs. By means of the measuring device, for example, the blade can be positioned reliably and reproducibly on a moment balance or a measuring apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The invention is described in more detail below by means of the drawings. 
           [0021]      FIG. 1  shows a perspective illustration of a measuring device with self-centering clamping device according to the invention. 
           [0022]      FIG. 2  shows a sectional illustration of the measuring device and of the self-centering clamping device in a side view according to the invention. 
           [0023]      FIG. 3  shows a sectional illustration of the measuring device and of the self-centering clamping device in a top view according to the invention. 
           [0024]      FIG. 4  shows diagrammatically a contact region of the roller according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0025]    The drawings serve merely to explain the invention and do not restrict this. The drawings and the individual parts are not necessarily true to scale. Identical reference symbols designate identical or similar parts. 
         [0026]      FIG. 1  shows a measuring device  1  with a clamping device  2  for a measurement object, such as, for example, a turbine blade or a compressor blade  3  (referred to below as “blade”). The clamping device  2  comprises a baseplate  4 . By means of the baseplate  4 , the measuring device  1  is fastened to a moment balance, not illustrated, or to an intermediate structure for measuring the blade  3 . 
         [0027]    A mount  5  is fastened essentially vertically on the baseplate  4 . Formed in the mount  5  is a reception orifice  6  in which a blade root  7  of the blade  3  is fastened. The mount  5  and reception orifice  6  may be designed, for example, as a grooved block. A plurality of sliding rollers  8  are arranged in the reception orifice  6  and make it easy to insert the blade  3  into the clamping device  2 . By means of an inclined roller  9 , the blade root  7  of the blade  3  is positioned securely and reproducibly in the reception orifice  6 . 
         [0028]      FIG. 2  shows a sectional illustration of the measuring device  1  with the roller  9  serving as a stop. Three sliding rollers  8  are arranged vertically one above the other in the mount  5 . 
         [0029]    Part of the sliding rollers  8  projects into the reception orifice  6 , specifically at a base region of the groove-shaped reception orifice  6 , that is to say opposite a vertically running groove orifice. The sliding rollers  8  consequently assist the insertion and removal of the blade  3 . 
         [0030]    Further sliding rollers  8  may be arranged at the two lateral regions of the reception orifice  6 . Two or only one sliding roller  8  may also be provided. 
         [0031]    Arranged in the lower region of the reception orifice  6 , underneath the sliding rollers  8 , is the roller  9  on which part of the blade root  7  of the blade  3  lies and which consequently serves as a movable stop. 
         [0032]    The roller  9  is mounted rotatably about an axis of rotation  10 . The roller  9  may be designed, for example, as a rolling bearing with an inner fixed inner ring or inner core, with an outer rotatable roller and with rolling bodies, such as, for example, rollers or balls, arranged between them. 
         [0033]    Instead of a roller, a cylinder, ball or similar body which enables the blade  3  to roll may also be used as a stop for the blade  3 . Not the entire circumferential surface is needed for the functions of a stop, and therefore a body which has only part of the circumferential surface of, for example, a roller, cylinder or ball may also be used as a stop. 
         [0034]    With regard to the blade roots  7  shown in the exemplary embodiment, the end faces  12  do not run at right angles (90°) to the side faces  13 , but instead at an angle which may lie between 30° and 90°. In the present exemplary embodiment, therefore, the axis of rotation  10  of the roller  9  is at an angle with respect to the horizontal. The axis of rotation  10  of the roller  9  is consequently not parallel to the axes of rotation of the sliding rollers  8 . Instead, the axis of rotation  10  is oriented parallel to the end face  12  of the blade root  7 . If the end faces  12  run at right angles (90°) to the side faces  13 , it is advantageous if, instead of one roller  9 , two rollers are present, the axes of rotation of which run, in particular, in a v-shaped manner with respect to one another. 
         [0035]    The roller  9  is arranged with respect to the reception orifice  6  in such a way that a contact region  11  of the roller  9  for the blade root  7  lies in an angular range larger than 0° to smaller than 90°, in particular 30° to 60°, for example at an angle of about 45°, to the circumferential surface of the roller  9  (cf.  FIG. 4 ). In this case, the angular range is measured from the horizontal upward, so that the angular range is oriented upward and toward the reception orifice  6 . This ensures that the root  7  does not engage either tangentially, that is to say at a virtual interface of a horizontal with the outer face of the roller  9 , or directly radially, that is to say at a virtual interface of a vertical with the outer face of the roller  9 . The horizontal and vertical in this case run through the center point of the roller  9 . 
         [0036]    With tangential bearing contact, there is the risk that the blade root  7  could move past the roller  9 , while, in the case of directly radial perpendicular contact, the rolling properties of the roller  9  are not brought to bear. Since the blade root  7  impinges in the region between these two end points, the blade root  7  and as it were roll automatically into the end position on account of its weight by means of the roller  9 . 
         [0037]    The roller  9  or part of the roller  9  may be elastically deformable in order to make it possible to adapt the roller  9  to the blade root  7 . The width of the roller  9  may be dimensioned according to the conditions of the blade  3 , although the roller  9  should have a minimum width which keeps the pressure load for the blade  3  and for the roller  9  within tolerable limits. The diameter of the roller  9  and its orientation should be dimensioned in such a way that impingement of the blade  3  in the correct circumferential region and subsequent rolling are possible. 
         [0038]    Alternatively, two rollers may be provided, which are then advantageously inclined with respect to one another and form a funnel or V-shaped stop into which the blade root  7  can slide. 
         [0039]    An optional eccentric for clamping the blade root  7  may be arranged opposite the vertically running groove orifice, that is to say in the region of the sliding rollers  8 . For example, the middle of the three sliding rollers  8  will be replaced by an eccentric which can additionally brace the blade  3 , for example for transport purposes. 
         [0040]      FIG. 3  shows the measuring device  1  in a sectional illustration in a top view. The baseplate  4  can be fastened to a moment balance by means of screws, pins, bolts or similar fastening means. The reception orifice  6  formed in the mount  5  is adapted in its contour to the blade root  7  of the blade  3  in order to ensure secure fixing of the blade  3 . In particular, side regions of the reception orifice  6  taper conically so as to be adapted to the blade root  7 . 
         [0041]    The reception orifice  6  may contain a groove or be designed as a groove, in particular it can be adapted to a blade fastening groove into which the blade  3  is finally mounted. The sliding rollers  8  and the roller  9  are arranged in a rearward part or base region of the reception orifice  6 , said rearward part or base region being arranged opposite a vertically running groove orifice. 
         [0042]    The measuring device  1  is used as described below: first, the measuring device  1  is fastened to a moment balance or a similar measuring instrument. The blade root  7  of the blade  3  is subsequently introduced into the reception orifice  6  of the clamping device  2  until the blade root  7  comes to bear on the roller  9 . In this case, the sliding rollers  8  assist frictional movement of the blade root  7  in the reception orifice  6 . The blade  3  is self-centered by means of the roller  9 . As a result of gravity, the blade  3  slides through the reception orifice  6  until it is fixed to the roller  9 . 
         [0043]    After measurement has taken place, the blade  3  is drawn out of the reception orifice  6  and is in this case assisted again by the sliding rollers  8 .