Abstract:
In order to improve a lathe includes a machine frame, a workpiece spindle unit arranged on the machine frame and having a workpiece spindle housing and a workpiece spindle rotatingly drivable about a workpiece spindle axis in the workpiece spindle housing. A supporting unit which is arranged on the machine frame and in which a workpiece receptacle rotatable about the workpiece spindle axis can be supported on the machine frame radially to the workpiece spindle axis, in such a manner that rotary machining operations other than longitudinal turning are possible in a simple manner. It is suggested that the supporting unit have a bearing member receptacle, in which a guide bushing for longitudinal turning can be supported in the area of its workpiece receptacle in a longitudinal turning version of the lathe and the workpiece spindle unit can be supported in the area of its workpiece receptacle radially to the workpiece spindle axis in a short turning version of the lathe.

Description:
This application is a continuation of international application number PCT/EP2009/062746 filed on Oct. 1, 2009. 
     This patent application claims the benefit of International application No. PCT/EP2009/062746 of Oct. 1, 2009 and German application No. 10 2008 051 611.2 of Oct. 7, 2008, the teachings and disclosure of which are hereby incorporated in their entirety by reference thereto. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a lathe comprising a machine frame, a workpiece spindle unit which is arranged on the machine frame and has a workpiece spindle housing and a workpiece spindle which can be rotatingly driven about a workpiece spindle axis in the workpiece spindle housing, a supporting unit which is arranged on the machine frame and in which a workpiece receptacle, which is rotatable about the workpiece spindle axis, can be supported on the machine frame radially to the workpiece spindle axis. 
     Lathes of this type are known as so-called longitudinal turning lathes, with which the workpiece receptacle is comprised by a guide bushing for longitudinal turning which, for its part, is held on the supporting unit and, therefore, is itself supported directly on the machine frame, wherein such a stationary guide bushing for longitudinal turning serves the purpose of guiding the workpiece, in particular a bar of stock, radially to the workpiece spindle axis in a stable manner as close as possible to a spot to be machined. With such a longitudinal turning lathe, the workpiece spindle, for its part, serves the purpose only of displacing the workpiece, in particular the bar of stock, in a Z direction relative to the guide bushing for longitudinal turning and of driving it rotatingly for the rotary machining. 
     Only a limited number of workpieces can be machined inexpensively and advantageously with such a longitudinal turning lathe. 
     The object underlying the invention is, therefore, to improve such a lathe in such a manner that rotary machining operations other than longitudinal turning are possible in a simple manner. 
     SUMMARY OF THE INVENTION 
     This object is accomplished in accordance with the invention, in a lathe of the type described at the outset, in that the supporting unit has a bearing member receptacle, in which a guide bushing for longitudinal turning can be supported in the area of its workpiece receptacle in a longitudinal turning version of the lathe and the workpiece spindle unit can be supported in the area of its workpiece receptacle radially to the workpiece spindle axis in a short turning version of the lathe. 
     The advantage of the solution according to the invention is, therefore, to be seen in the fact that it offers the possibility of converting a lathe in a longitudinal turning version into a short turning version with little resources and, therefore, of being able to exploit, on the one hand, the possibilities of a short turning version of a lathe and, on the other hand, the possibilities of a longitudinal turning version with the same machine in an optimum manner with little resources required for conversion. 
     It is possible, in particular, with this solution to be able to convert the longitudinal turning version into the short turning version or vice versa quickly without essential parts of the lathe which determine its exactness, such as the workpiece spindle unit or the supporting unit, needing to be removed or modified. 
     The alternating support of the guide bushing for longitudinal turning or the workpiece spindle unit in the bearing member receptacle may be realized in a particularly simple and inexpensive manner in that a bearing member supporting the guide bushing for longitudinal turning or a bearing member supporting the workpiece spindle unit may be releasably inserted into the bearing member receptacle. 
     With such bearing members which support either the guide bushing for longitudinal turning or the workpiece spindle unit and can each be releasably inserted into the bearing member receptacle, a conversion may be realized in a simple manner without great resources for the conversion being necessary. 
     It is particularly favorable when the bearing member can be accommodated in the bearing member receptacle in a clearance-free, clamped manner as a result of forces acting radially to the workpiece spindle axis in order to be able to arrange the bearing member precisely and exactly in relation to the supporting unit in both cases, i.e. in the longitudinal turning version and in the short turning version. 
     In this respect, it is particularly favorable when, in the case of the support for the guide bushing for longitudinal turning, a bearing member of a housing sleeve thereof can be supported in the bearing member receptacle such that the guide bushing for longitudinal turning experiences a support directly on the supporting unit with its housing sleeve. 
     Alternatively thereto, it is provided for the workpiece spindle unit to be supported in the bearing member receptacle in a forward area of the workpiece spindle housing with a bearing member of a supporting unit. 
     In this respect, it is particularly expedient, in order to be able to likewise utilize the Z axis movement of the workpiece spindle unit, when the supporting unit is a supporting sleeve accommodating the forward area of the workpiece spindle housing for displacement in the direction of the workpiece spindle axis. 
     Alternatively or in addition to the solution described above, a precise support for the workpiece receptacle is possible in one advantageous embodiment of a lathe in that the supporting unit has a bearing member receptacle, in which a bearing member which supports the workpiece receptacle radially to the workpiece spindle axis can be releasably inserted and a radial support of the bearing member in the bearing member receptacle is brought about via supporting members which are elastic on account of their cross-sectional shape. 
     The provision of such elastic supporting members for supporting the bearing members relative to the bearing member receptacle has the great advantage that, as a result, a rigid and very stable fixing of the bearing member in the bearing member receptacle is possible, on the one hand, and, on the other hand, however, the necessary elasticity can also be provided in order to subject the bearing member constantly to forces acting radially to the workpiece spindle axis and to position it, as a result, free from clearance and in a clamped manner in the bearing member receptacle. 
     The supporting members are preferably provided with a cross-sectional surface or with two cross-sectional surfaces which allow the necessary elasticity to be ensured simply on account of their variation in shape in a supporting direction, wherein the supporting members are normally likewise formed from the same material as the bearing member receptacle and the bearing members, i.e. are normally of steel, in order to obtain the necessary strength and rigidity for the support of the bearing member. 
     In this respect, the supporting members can be supported on supporting surfaces of different designs. 
     One advantageous solution provides, for example, for the supporting members to be supported on supporting surfaces of the bearing member receptacle which extend at an acute angle in relation to the workpiece spindle axis. 
     It is particularly favorable when the supporting surfaces of the bearing member receptacle extend conically in relation to the workpiece spindle axis so that spheres can, in particular, be used as supporting members, as a result. 
     Another advantageous solution provides for the supporting members to be supported on supporting surfaces of the bearing member which extend at an acute angle in relation to the workpiece spindle axis. 
     In this respect, the supporting surfaces of the bearing member are preferably designed such that they extend conically in relation to the workpiece spindle axis. 
     With receptacle supporting surfaces and bearing member supporting surfaces designed in this manner an elastic deformation of the supporting members arranged between the supporting surfaces of the receptacle and supporting surfaces of the bearing member may be brought about in a simple manner during the insertion of the bearing member into the bearing member receptacle with an insertion direction parallel to the workpiece spindle axis. 
     For example, the supporting members can be designed as rollers which can be deformed elastically on account of their circular cross section. 
     It is particularly advantageous when the supporting members are designed as spheres since spheres of this type, as known in conjunction with ball bearings, can be deformed elastically as a result of being acted upon with pressure. 
     In the case of such receptacle supporting surfaces and bearing member supporting surfaces which extend at an acute angle in relation to the workpiece spindle axis, the position of the bearing member is undefined in the direction of the workpiece spindle axis. 
     For this reason, it is preferably provided for the bearing member to be supported relative to a receptacle counter surface with a bearing member contact surface in the direction of the workpiece spindle axis. 
     In this case, as well, it would be conceivable to provide supporting members between the bearing member contact surface and the receptacle counter surface which are elastic on account of their cross-sectional shape, allow a compensation of tolerance on account of their elastic deformation and, in addition, enable a clearance-free tensioning in the direction of the workpiece spindle axis, as well. 
     For reasons of simplicity, it is, however, provided in one embodiment for the bearing member to abut directly on the receptacle counter surface with the bearing member contact surface. 
     With respect to carrying out machining of a workpiece in the longitudinal turning version and in the short turning version, no further details have so far been given. In the longitudinal turning version, it is known for the workpiece spindle unit to be able to travel in the direction of a Z axis for the machining of the workpiece. In the short turning version, a movement in the direction of the Z axis by a tool carrier could take place for the machining of the workpiece without any movement of the workpiece spindle unit being required or possible. 
     In one embodiment according to the invention, it is, however, provided for the workpiece spindle unit to be able to travel in the direction of a Z axis in a controlled manner for the machining of the workpiece not only in the longitudinal turning version but also in the short turning version. 
     Additional features and advantages of the invention are the subject matter of the following description as well as the drawings illustrating several embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a first embodiment of a lathe according to the invention in a longitudinal turning version with a longitudinal section through a workpiece spindle unit and a guide bushing for longitudinal turning; 
         FIG. 2  shows an enlarged section of  FIG. 1  in the area of the guide bushing for longitudinal turning and a supporting unit; 
         FIG. 3  shows a side view with a longitudinal section similar to  FIG. 1  of a second embodiment of a lathe according to the invention in a short turning version and 
         FIG. 4  shows a section similar to  FIG. 2  of a forward area of the workpiece spindle unit and the supporting unit. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment of a lathe according to the invention, which is designed as a longitudinal turning version and illustrated in  FIG. 1 , comprises a machine frame which is designated as a whole as  10  and has guides  12  which extend in the direction of a Z axis and on which a Z slide  14 , which can be moved in the Z direction, is guided for displacement with guide members  16  and  18 . 
     Furthermore, the Z slide  14  can be moved, driven by a Z axis drive  20 , wherein the Z axis drive  20  comprises a drive motor  22 , a threaded spindle  24  driven by it and a spindle nut  26  rigidly connected to the Z slide so that the spindle nut  26  can be displaced in the Z direction together with the Z slide  14  when the threaded spindle  14  is driven by the drive motor  22 . 
     A workpiece spindle unit designated as a whole as  30  is seated on the Z slide  14  and has a workpiece spindle housing which is designated as a whole as  32  and in which a workpiece spindle designated as  34  is mounted for rotation about a workpiece spindle axis  36 . 
     The workpiece spindle housing  32  comprises, for its part, a housing member  40  which is seated directly on the Z slide and in which a stator  42  of a spindle motor designated as  44  is arranged which has, in addition, a rotor  46  which is seated on the workpiece spindle  34  in the area of the stator  42  and co-rotates with it. 
     The workpiece spindle housing  32  comprises, in addition, a bearing tube  50  which extends from the housing member  40  in the direction of the workpiece spindle axis  36 , extends in a freely projecting manner relative to the housing member  40  and the Z slide and in which a first spindle bearing  52  and a second spindle bearing  54  are arranged, wherein the first spindle bearing  52  is arranged to adjoin the spindle motor  44  and the second spindle bearing  54  on a side of the first spindle bearing  52  facing away from the spindle motor  44 . 
     The first spindle bearing  52  and the second spindle bearing  54  serve the purpose of the defined guidance and rotatable mounting of the workpiece spindle  34  in the bearing tube  50  of the workpiece spindle housing  32 , wherein the second spindle bearing  54  mounts the workpiece spindle  34  in the area of a forward end  56  of the bearing tube  50  and in the area of a clamping device  58  of the workpiece spindle  34 . In addition, the workpiece spindle  34  is mounted on the housing member  40  on a side of the spindle motor  44  facing away from the spindle bearing  52  with a rearward spindle bearing  55 . 
     The clamping device  58  serves to fix a workpiece in place, preferably a bar of stock W, namely for fixing the bar of stock against any movement in the direction of the workpiece spindle axis  36  and for the rotary drive of the bar of stock W. 
     The embodiment of the lathe according to the invention, illustrated in  FIG. 1 , is designed as a so-called longitudinal turning lathe, with which the workpiece, in this case the bar of stock W, is guided during the machining by a guide bushing for longitudinal turning which is designated as a whole as  60  and is supported, for its part, directly on the machine frame  10  by means of a supporting unit  62 . 
     The guide bushing  60  for longitudinal turning comprises a housing sleeve  64  which bears a bearing member  66  which, for its part, can be releasably inserted into a bearing member receptacle  68  of the supporting unit  62 . 
     A rotatable workpiece receptacle  70  is provided in the housing sleeve  64  and comprises a receptacle bushing  76  which is rotatably mounted in the housing sleeve  64  with two rotary bearings  72  and  74  and, for its part, is provided with clamping elements  78  for the clearance-free accommodation and precise, radial guidance of the bar of stock W for sliding displacement in the direction of the Z axis. 
     The workpiece receptacle  70  is preferably coupled non-rotatably to the workpiece spindle  34 , namely by a telescopic tube  80  which extends between a holding flange  82  connected to the workpiece receptacle  70  and a front end  84  of the workpiece spindle  34  facing the guide bushing  60  for longitudinal turning and is thereby coupled non-rotatably to the workpiece spindle  34 . 
     Furthermore, a tool carrier designated as a whole as  90  is provided on the machine frame  10 , is designed, for example, as a tool turret and has a turret housing  92  which bears a rotatable turret head  94  which is located in a working space  88  arranged on a side of the supporting unit  62  located opposite the workpiece spindle unit  30 , wherein individual machining tools WZ, with which machining of the bar of stock W can be carried out in the working space  88 , are arranged on the turret head  94 . 
     In a longitudinal turning lathe, the precise guidance of the bar of stock W during machining by the tools  96  is brought about by means of the guide bushing  60  for longitudinal turning and so the guide bushing  60  for longitudinal turning is, for its part, to be arranged and guided precisely relative to the machine frame  10 . 
     This means that the guide bushing  60  for longitudinal turning must be positioned precisely in the supporting unit  62 . 
     For this purpose, the supporting unit  62  comprises in the area of the bearing member receptacle  68 , as illustrated on an enlarged scale in  FIG. 2 , a receptacle supporting surface  96  which extends conically in relation to the workpiece spindle axis  36 , a receptacle counter surface  98  which extends at right angles in relation to the workpiece spindle axis  36  and faces, for example, the working space  88 , as well as an opening  100  which adjoins the receptacle supporting surface  96  and passes through the supporting unit  62  in the direction of the workpiece spindle unit  30  and through which the telescopic tube  80  extends. 
     Furthermore, the bearing member  66  of the guide bushing  60  for longitudinal turning comprises, for its part, a bearing member supporting surface  102  which extends conically in relation to the workpiece spindle axis  36  as well as a bearing member contact surface  104  which extends at right angles in relation to the workpiece spindle axis  36 . 
     In order to keep the bearing member  66  aligned as exactly and clearance-free as possible in the bearing member receptacle  68 , supporting members  106  are provided between the receptacle supporting surface  96  and the bearing member supporting surface  102  and are designed as rollers, preferably as spheres, and, on account of their cross-sectional shape, display an elastic behavior when acted upon with a force which makes it possible for an elastic force extending transversely to the receptacle supporting surface  96  and the bearing member supporting surface  102  to be active between them, this force having the tendency to act on the receptacle supporting surface  96  and the bearing member supporting surface  102  in the sense of increasing the distance between them and, therefore, of acting on the bearing member  66  in the area of its bearing member supporting surface  102  with a force component KR which extends radially to the workpiece spindle axis  36  and keeps the bearing member  66  centered in the bearing member receptacle  68  in a clearance-free manner. 
     The axial positioning of the bearing member  66  relative to the supporting unit  62  with the bearing member receptacle  68  is brought about by way of a direct abutment of the bearing member contact surface  104  on the receptacle counter surface  98  without any elastic bodies arranged between them in order to achieve an exact positioning of the bearing member  66  in the direction of the workpiece spindle axis  36 . 
     For the purpose of the relative fixing of the supporting members  106  between the receptacle supporting surface  96  and the bearing member supporting surface  102 , they are arranged in a supporting member cage  108  which, for its part, can be fixed in place on the supporting unit  62 . 
     The supporting members  106  are preferably steel spheres, in the same way as those used for ball bearings. 
     In this respect, the supporting members  106  can be arranged so as to be evenly distributed in circumferential direction over the receptacle supporting surface  96  and the bearing member supporting surface  102  or the bearing members  106  are arranged at certain angular distances from one another in circumferential direction, for example at angular distances of between 30° and 120°. 
     The machine tool according to the first embodiment, illustrated in  FIGS. 1 and 2 , can, as illustrated in  FIGS. 3 and 4 , be converted as a short turning version into a machine tool according to a second embodiment, wherein in this second embodiment the guide bushing  60  for longitudinal turning is removed and the workpiece spindle unit  30  is moved in the direction of the supporting unit to such an extent that the bearing tube  62  of the workpiece spindle housing  32  passes through the opening  100  of the supporting unit  62  and projects with its forward area  56  into the working space  88  on a side of the supporting unit  62  located opposite the housing  40  in order to thus suitably position the workpiece or the bar of stock W for machining with one of the tools WZ. 
     In this respect, the workpiece or the bar of stock W is fixed and positioned relative to the machine frame  10  by means of the clamping device  58  of the workpiece spindle  34 . 
     In order to bring about, in particular, a positionally stable support for the workpiece spindle  34  relative to the machine frame  10 , the bearing tube  50  is, so as to be displaceable in the direction of the Z axis, accommodated in a bearing tube sleeve  114  which is provided with a bearing member  116  which, for its part, has a bearing member supporting surface  122  and a bearing member contact surface  124 , in the same way as the bearing member  66 , wherein the supporting members  106  already described are arranged between the bearing member supporting surface  102  and the receptacle supporting surface  96  in the supporting member cage  108  and alternatingly support them as well as allow a clearance-free accommodation of the bearing member  116  in the bearing member receptacle  68 . 
     The precise guidance of the bearing tube  50  in the bearing tube sleeve  114  for displacement in the direction of the Z axis is brought about by an inner surface  126  of the bearing tube sleeve  114  which is machined to fit exactly as well as an outer surface  128  of the bearing tube  50  which is likewise machined to fit exactly, these surfaces being preferably ground and guided exactly relative to one another either hydrostatically or hydrodynamically by lubricant penetrating between them. 
     Furthermore, the bearing member  116  abuts with its bearing member contact surface  124  on the receptacle counter surface  98  so that the bearing member  116  is, therefore, positioned exactly in the direction of the workpiece spindle axis  36 . 
     As a result, it is possible to realize a so-called short turning lathe from a lathe designed according to  FIGS. 1 and 2  as a longitudinal turning lathe merely by removing the guide bushing  60  for longitudinal turning from the supporting unit  62 , wherein, in this case, the exact alignment of the workpiece or the bar of stock W relative to the tools WZ is likewise brought about in that the bearing tube of the workpiece spindle  34  is supported on the supporting unit  62 . 
     As a result, the same alignment of the workpiece or the bar of stock W relative to the tools WZ is ensured when operating the lathe as a short turning lathe. 
     It is possible not only in the longitudinal turning version illustrated in  FIGS. 1 and 2  as well as in the short turning version illustrated in  FIGS. 3 and 4 , to realize the movement of the workpiece or the bar of stock W in the direction of the Z axis relative to the tools WZ by way of a controlled displacement of the workpiece spindle unit in a Z direction, for example with a computer numerical control, so that in both versions there is no necessity for the tools WZ to be moved in the direction of the Z axis and so, in the minimal case, a movement of the tools WZ in a so-called X direction transversely to the workpiece spindle axis  36  is sufficient. 
     This movability of the tools WZ in the X direction can be improved further by an additional movability of the tools WZ in a Y direction which extends transversely to the X direction and to the spindle axis  36 , which is advantageous, in particular, when rotatingly driven tools WZ are used in order to be able to carry out a complete machining of the workpiece or the bar of stock W with these tools in addition to the normal tools for rotary machining.