Abstract:
In order to improve a machine tool for machining a workpiece by a relative movement between the workpiece and a tool, comprising a first receiving device for the workpiece or the tool, a compound slide system with a second receiving device for the tool or the workpiece and comprising a drive device for moving the second receiving device in relation to the first receiving device, which drive device acts at least two spaced-apart points of application by at least three drive struts extending parallel to at least two different directions and each with a pivot joint, and with which drive device the at least two points of application can be positioned by means of the at least three drive struts, in such a way that exact positioning of the second slide element can be achieved by structural measures, it is proposed that four drive struts of invariant length, each with a pivot joint, act on the slide element, each of which struts is pivotally connected to a guiding slide, which is guided in a linearly movable manner transversely in relation to the longitudinal direction of the respective drive struts, and a maximum of two of which drive struts run parallel to one another.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
   This patent application is a continuation of U.S. patent application Ser. No. 11/508,573, now U.S. Pat. No.7,334,304 filed Aug. 23, 2006, and claims the benefit of German Application No. 10 2005 041 496.6, filed Sep. 1, 2005, the teachings and disclosure of which are hereby incorporated in its entirety by reference thereto. 

   BACKGROUND OF THE INVENTION 
   The invention relates to a machine tool for machining a workpiece by a relative movement between the workpiece and a tool, comprising a machine frame, a carrier disposed on the machine frame and having a first receiving means for the workpiece or tool, a compound slide system disposed on the machine frame and having a slide element which carries a second receiving means for the tool or the workpiece and can be moved by the compound slide system in relation to the first receiving means in a fixed movement zone of a compound slide movement area in the direction of two compound slide movement axes running transversely in relation to one another and comprising a drive device for moving the slide element that is movable in relation to the first receiving means, which drive device acts on the slide element at least two spaced-apart points of application by at least three drive struts extending parallel to at least two different directions and each with a pivot joint, and with which drive device the at least two points of application can be positioned by means of the at least three drive struts. 
   Machine tools of this type are already known from the prior art, for example from DE 100 19 788 A1. 
   In the case of a machine tool of this type, it has been found that the required precision in the positioning of the second slide element requires complex measuring systems. 
   It is therefore an object of the invention to achieve exact positioning of the second slide element by structural measures. 
   SUMMARY OF THE INVENTION 
   This object is achieved according to the invention in the case of a machine tool of the type described at the beginning by four drive struts of invariant length, each with a pivot joint, acting on the slide element, each of which struts is pivotally connected to a guiding slide, which is guided in a linearly movable manner transversely in relation to the longitudinal direction of the respective drive struts, and a maximum of two of which struts run parallel to one another. 
   The advantage of the solution according to the invention is to be seen in the fact that the precision of the positioning of the second slide element is distinctly improved by the four drive struts, in particular by an improvement of the torsional stiffness about axes of rotation running perpendicularly in relation to the compound slide movement area, in particular about a so-called B axis. 
   The second slide element can be positioned particularly advantageously if the four drive struts form two drive groups, each with two non-parallel drive struts, so that the two drive groups can uniquely fix the position of the movable slide element. 
   A particularly suitable solution provides here that a position of the slide element can be fixed with the first drive group apart from a first still possible form of movement. 
   A further advantageous solution provides that a position of the slide element can be fixed with the second drive group apart from a second still possible form of movement. 
   Since, however, the first drive group and the second drive group do not act at identical points of the movable slide element, a unique positioning of the movable slide element is thereby obtained, since the first still possible form of movement as a result of the first drive group is blocked by the second drive group and the second still possible form of movement due to the second drive group is blocked by the first drive group. 
   In principle, the drive struts of each drive group act on the movable slide element with a point of application of their own, so that four drive struts may be provided altogether, each acting on the slide element with their own points of application. 
   To improve the stability of the positioning, however, it has proven to be advantageous if the drive struts of one of the drive groups act on the movable slide element at a common point of application. 
   In this case, the respective still possible form of movement of the slide element represents a pivoting movement about the common point of application. 
   However, it is even more advantageous for the precision of the positioning of the slide element if the drive struts of each of the drive groups respectively act on the slide element at one of two spaced-apart points of application. 
   In this case, consequently, only two points of application are provided on the slide element, each of which is uniquely and stably defined by the respective drive group apart from the still free possible form of movement in the form of a pivoting movement. 
   With regard to the path followed by the guiding directions of the guiding slides, nothing has been stated in connection with the description so far of the solution according to the invention. For example, it is conceivable for two guiding slides to be movably disposed in each case, parallel to the same guiding direction. This could be, for example, the guiding slides respectively of one drive group, in which case the guiding directions of the two drive groups could still differ from one another. 
   However, in order to minimize the space required for the drive device, it is advantageous if in each case two of the guiding slides are guided on a common guideway. 
   In this case, there is the possibility of for example allowing the guiding slides of each drive group to run on a common guideway. 
   A further advantageous solution provides that the guiding slides of the drive struts are guided in guiding directions running parallel to one another. 
   There is consequently the possibility in principle of guiding each of the guiding slides along a guiding direction of its own, which directions however all run parallel to one another. 
   It is particularly advantageous, however, if a first guiding slide of the first drive group and a first guiding slide of the second drive group are movable along the same guiding direction. 
   Such a solution is still more space-saving if the first guiding slides of the first and second drive groups are guided on a common guideway. 
   Furthermore, an advantageous exemplary embodiment provides that a second guiding slide of the first drive group and a second guiding slide of the second drive group are movable along the same guiding direction. 
   Furthermore, it is advantageous if a second guiding slide of the first drive group and a second guiding slide of the second drive group are guided on a common guideway. 
   In order to simplify the drive of the guiding slides, a particularly advantageous solution provides that the first guiding slides of the first and second drive groups are rigidly coupled to one another, that is to say that the first guiding slides of the first and second drive groups are only movable together with one another. 
   A rigid coupling of the first guiding slides to one another in this way may take place for example by a rigid coupling of the drives of the first two guiding slides taking place via the control. 
   The rigid coupling can be realized particularly easily if the first guiding slides of the first and second drive groups are rigidly coupled to one another mechanically. 
   As an alternative to this, however, it is also conceivable to combine the first guiding slides of the first and second drive groups to form a common guiding slide. 
   Furthermore, it is provided in a similar way that the second guiding slides of the first and second drive groups are rigidly coupled to one another, so that they can also be driven in a simple manner. 
   In this case it would likewise be conceivable to provide a rigid coupling of the second guiding slides via a control for the drives of the two second guiding slides, it being easier for the rigid coupling to be realized if the second guiding slides of the first and second drive groups are rigidly coupled to one another mechanically. 
   A solution that is spatially particularly advantageous and of a small construction provides that all the guiding slides are disposed on a common guideway. 
   When all the guiding slides are provided on a common guideway, the guiding slides are preferably disposed one following the other on it. 
   It is particularly advantageous in this case if the guiding slides of each drive group are disposed one directly following the other, this directly successive sequence in which the guiding slides are disposed providing within the scope of the solution according to the invention a controllable variable spacing between the guiding slides in addition to the controllable variable position along the guiding direction. 
   A mechanical coupling of the first guiding slides of the drive groups and the second guiding slides of the drive groups can be realized particularly advantageously when all the guiding slides are provided on a common guideway, if the mechanically rigid connection between the first guiding slides runs on a different side of the guideway than the mechanically rigid connection between the second guiding slides. 
   The kinematics of the drive device according to the invention can be realized particularly easily if two of the drive struts respectively run parallel to one another. 
   It is preferably provided in this case that the drive struts articulated on the first guiding slides of the drive groups run parallel to one another and the drive struts articulated on the second guiding slides of the drive groups run parallel to one another. 
   Furthermore, the kinematics according to the invention can be controlled particularly easily if two of the four drive struts respectively are of the same length. 
   The drive struts are preferably designed in such a way that all four drive struts are of the same length. 
   With regard to the drive of the guiding slides, it would be conceivable in principle to drive each of the guiding slides separately. 
   In particular in the case where the first guiding slides of the drive groups and the second guiding slides of the drive groups, respectively, are rigidly coupled to one another, it is adequate if a linear drive is associated with the respectively mechanically coupled guiding slides. 
   The linear drive could be, for example, a linear motor. However, it is mechanically simpler if the linear drive is a spindle drive. 
   With regard to the disposition of the guideways for the guiding slides, so far nothing more specific has been stated. So a structurally particularly advantageous solution provides that all the guideways for all the guiding slides are disposed on the same side of the points of application, in order to make the drive device according to the invention as compact as possible. 
   In order to allow the relative position, and consequently in particular the position in the X direction, to be easily detected, a measuring system which directly detects a relative position of the first guiding slides in relation to the second guiding slides is provided. 
   Position detection of this kind can be realized particularly advantageously if the measuring system is disposed on connecting struts of the first guiding slides and of the second guiding slides. 
   As an alternative or in addition to the solution described so far, a further solution provides that drive struts of invariant length act on the slide element, each of which struts is pivotally connected to a guiding slide, which is guided in a linearly movable manner transversely in relation to the longitudinal direction of the drive struts, and that guideways for at least two of the guiding slides are disposed on a side of the points of application facing the spindle axis. 
   The advantage of this solution can be seen in that the drive struts consequently extend from a region of the machine tool which undergoes minor thermal displacements with respect to the spindle axis, and consequently also the position of the movable slide elements that is predetermined by the drive device undergoes only minor thermal displacements. 
   Furthermore, it is advantageous in the case of this solution that, on account of their invariance of length, no heat directly enters the drive struts as a result of a length adjustment of the same, so that the thermal displacement in the region of the drive struts can also be kept low. 
   In the case of this solution, it is particularly advantageous if the guideways for the guiding slides are disposed near a reference plane which runs through the spindle axis and perpendicularly in relation to the X direction of the machine tool. 
   This solution has the great advantage that the base for the drive struts of the drive device consequently already lies near the spindle axis, and consequently substantially only thermal displacements in the region of the drive struts have any effect on the position of the movable slide element, while all other thermal displacements, in particular in the machine bed body, have substantially no effect on the position of the movable slide element in relation to the spindle axis. 
   It is particularly advantageous if the guideways for all the guiding slides are disposed on the side of the points of application facing the spindle axis, so that all the drive struts have an effect on the positioning accuracy in the same direction in the event of a thermally induced change in their length. 
   Otherwise, further advantageous embodiments have the same features as described above. 
   Further features and advantages of the invention are the subject of the description which follows and of the graphic representation of an exemplary embodiment of a solution according to the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a perspective schematic representation of an exemplary embodiment of a machine tool looking toward a front side, but without showing a slide element on the machine bed side for an upper movable slide element; 
       FIG. 2  shows a perspective representation of the machine tool looking at the rear side; 
       FIG. 3  shows a perspective representation of the drive device as used in the exemplary embodiment represented of the machine tool, and 
       FIG. 4  shows a section along line  4 - 4  in  FIG. 3 . 
       FIG. 5  shows a view similar to that of  FIG. 3 , but with the points of application  82 ,  84  schematically shown affixed to a slide element including receiving means for receiving a workpiece instead of a tool, in an embodiment wherein this slide element moves the workpiece relative to receiving means for receiving a tool. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An exemplary embodiment of a machine tool according to the invention, represented in  FIG. 1 , comprises a machine frame, which is designated as a whole by  10 , can be placed with a foot  12  on a base area and comprises a machine bed body, which is designated as a whole by  20  and is preferably formed in a way similar to a plate. 
   On this machine bed body  20  there are, for example, two headstocks  22 ,  24 , in which workpiece spindles  30 ,  32  are disposed coaxially in relation to a spindle axis  26 , lie opposite each other and are provided with workpiece receiving means  34 ,  36  for workpieces WS, which represent first receiving means and are disposed facing one another. 
   In this case, the machine tool represents a lathe. 
   However, instead of workpiece spindles  30 ,  32 , it would also be conceivable to provide tool spindles with tool receiving means. 
   In the case of this exemplary embodiment of the machine tool according to the invention, the headstock  22  is disposed on the machine bed body  20  in a stationary manner, while the headstock  24  can for example be made to move in the direction of the spindle axis  26 . 
   However, it would also be conceivable to arrange for both headstocks  22 ,  24  to be movable in relation to the machine bed body  20 . 
   For machining the workpieces WS disposed in the workpiece receiving means  34 ,  36 , a tool carrier  38 , which can only be made to move transversely in relation to the spindle axis  26  and is associated with the workpiece spindle  32 , and also tool carriers  40 ,  42 , which are associated with the workpiece spindles  30 ,  32 , are provided, each of which comprises a multiplicity of tool receiving means  44 ,  46  for tools WZ, representing second receiving means. 
   In order to allow the tool carriers  40 ,  42 , and consequently the tool receiving means  44 ,  46 , to be moved in relation to the workpiece receiving means  34 ,  36 , the tool carriers  40 ,  42  are disposed on for example identically constructed compound slide systems  50 ,  52 , each of which comprises a first slide element  60  on the machine bed side, which is formed for example as a plate  62  with an aperture  64  in a central region of the same and has around the aperture  64  surfaces  66 ,  68  running substantially parallel to one another, the surfaces  66  being front surfaces and the surfaces  68  being rear surfaces of the plate  62 . 
   As an alternative to this, instead of the plate  62 , it is also conceivable to provide on both sides of the aperture  64  guiding strips, which lie with their two surfaces  66 ,  68  respectively in the same plane. 
   On this first slide element  60  on the machine bed side, a second slide element  70  on the tool carrier side is movably guided, to be precise by the latter sliding with guiding bodies  72 ,  74  on the surfaces  66 ,  68 . 
   Consequently, the surfaces  66 ,  68  of the first slide element  60  running parallel to one another define a compound slide movement area, parallel to which the respective second slide element  70  is movable in relation to the machine bed body  20 , both in the X direction, that is to say transversely in relation to the spindle axis  26 , and in the Z direction, that is to say parallel to the spindle axis  26 . 
   Further details and embodiments of compound slide systems  50 ,  52  of this type, in which the respective second slide element  70  is movable in the direction of both compound slide movement axes X, Z, are described in German Patent Application DE 100 19 788 A1, to which reference is made with regard to the embodiments of the various compound slide systems. 
   The tool carriers  40 ,  42  are preferably also in each case rotatable with respect to the corresponding second slide element  70  about a B axis, which is perpendicular to the X/Z plane. 
   For moving the respective second slide element  70  in relation to the respective first slide element  60 , as represented in  FIG. 2 , associated with each compound slide system  50 ,  52  is a drive device  80 , which acts on the respective slide element  70  at two spaced-apart points of application  82 ,  84 , in order to position the respective second slide element  70  in relation to the first slide element  60  in the X and Z directions in the respective compound slide movement plane. 
   As shown enlarged in  FIGS. 3 and 4 , the drive device  80  comprises altogether four drive struts  90 ,  92 ,  94 ,  96 , the drive struts  90  and  92  acting by means of pivot joints  100 ,  102  at the point of application  82 , formed by a bearing pin  86 , and the drive struts  94  and  96  acting by means of pivot joints  104  and  106  on a bearing pin  88  defining the point of application  84 . 
   Furthermore, each of the drive struts  90 ,  92 ,  94 ,  96  is pivotally connected by means of a pivot joint  110 ,  112 ,  114 ,  116  to in each case a guiding slide  120 ,  122 ,  124 ,  126 , the guiding slides  120 ,  122 ,  124 ,  126  being guided along a guideway  132 , which fixes a common guiding direction  130  and is formed for example by a guiding rail  134 . 
   The guiding rail  134  is preferably disposed on a rear side  136  of the machine bed body  20  and is held by the machine bed body  20 . 
   Disposed in this way, the drive struts  90 ,  92 ,  94 ,  96  always extend with their longitudinal directions  140 ,  142 ,  144 ,  146  transversely, in particular obliquely, in relation to the guiding direction  130 , irrespective of the position of the guiding slides  120  to  126  along the guideway  132 , and the longitudinal directions  140 ,  142 ,  144  and  146  run parallel to a central plane  154 . 
   Furthermore, in the case of the exemplary embodiment represented, the drive struts  90 ,  92 ,  94 ,  96  are formed in such a way that their length between the respective pivot joints  100  and  110 ,  102  and  112 ,  104  and  114  and also  106  and  116  is of the same size. 
   In addition, the guiding slides  120  and  122  and also  124  and  126  are positioned in relation to one another in such a way that the longitudinal directions  140  and  144  of the drive struts  90  and  94  and also the longitudinal directions  142  and  146  of the drive struts  92  and  96  run parallel to one another. 
   This can be achieved in particular by the guiding slides  120  and  124  being rigidly coupled to one another by connecting struts  150  and  152 , the connecting struts  150  and  152  running between the guiding slides  120  and  124 , for example on both sides of the central plane  154  of the drive device  80 , to be precise at such a spacing from the guiding slide  122  that the latter can move freely between the connecting struts  150  and  152  and also along the guideway  132  between the guiding slides  120  and  124 . 
   The connecting struts  150  and  152  in this case preferably lie in such a way that they act on side faces  156  and  158  of the guiding slides  120  and  124 , the side faces  156  and  158  being side faces of the guiding slides  120  and  124  that run for example approximately parallel or obliquely in relation to the central plane  154 . 
   Furthermore, the guiding slides  122  and  126  are likewise rigidly coupled to one another by connecting struts  160  and  162 , the connecting struts  162  and  164  acting on the guiding slides  122  and  126  in the region of upper sides  166  and  168  running transversely in relation to the central plane  154 , and consequently running in a collision-free manner in relation to the connecting struts  150  and  152 , and the connecting struts  160  and  162  being disposed with such a spacing from one another that a pivot joint flange  174  of the guiding slide  124  is freely movable between the connecting struts  160  and  162 . 
   Otherwise, all the pivot joint flanges  170 ,  172 ,  174  and  176  supporting the pivot joints  110 ,  112 ,  114  and  116  are formed in such a way that the pivot joints  110 ,  112 ,  114  and  116  can be moved at the same spacing from the guiding rail  134  and parallel to the guiding direction  130  by moving the guiding slides  120 ,  122 ,  124  and  126 . 
   The parallel alignment of the longitudinal directions  140  and  144  of the drive struts  90  and  94  and also of the longitudinal directions  142  and  146  of the drive struts  92  and  96  is ensured in every relative position of the guiding slides  120  and  124  with respect to the guiding slides  122  and  126  by the rigid connection of the guiding slides  120  and  124  and also  122  and  126  by means of the connecting struts  150  and  152  or  160  and  162 , respectively. 
   Consequently, the drive struts  90  and  92 , the pivot joints  110  and  112  of which are always spaced apart from one another while the pivot joints  100  and  102  of which act on the same bearing pin  86 , form the sides of an isosceles triangle, which on the one hand uniquely fixes the position of the point of application  82  in the guiding direction  130 , which preferably runs parallel to the Z direction of the machine tool, and on the other hand also uniquely fixes its spacing from the guideway  132 , which corresponds to the X direction whenever—as provided in the case of the exemplary embodiment represented—the central plane  154  of the drive device  80  runs parallel to the compound slide movement plane, and consequently parallel to the surfaces  66  and  68  of the first slide element  60 . 
   Consequently, the Z position of the point of application  82  on the slide element  70  can be uniquely fixed by the absolute position of the guiding slides  120  and  122  in the guiding direction  130 , and the X position of the point of application  82  on the slide element  70  can be uniquely fixed by the relative position of the guiding slides  120  and  122 . 
   The single degree of freedom of the movement of the slide element  70  when the point of application  82  is fixed in such a way consists in the slide element  70  having the possibility of turning about the point of application  82  on account of the pivot joints  100  and  102 , and the bearing pins  86  that are consequently rotatable in relation to the latter. 
   Altogether, the drive struts  90  and  92 , the longitudinal directions  140  and  142  of which run transversely in relation to one another, preferably in a V-shaped manner with respect to the point of application  82 , consequently form a drive group  180 , which fixes the X and Z positions of the point of application  82  of the slide element  70 . 
   In the same way, the drive struts  94  and  96  form a drive group  182 , since these drive struts  94  and  96  also form the sides of an isosceles triangle and, on the basis of the spaced-apart pivot joints  114  and  116  and the pivot joints  104  and  106 , acting together on the bearing pin  88 , uniquely define the point of application  84  in relation to the Z direction and in relation to the X direction of the machine tool for the same reasons as described in connection with the first drive group  180 , so that the slide element  70  would only be left with the possibility of rotating about the point of application  84 . 
   However, the position of the slide element  70  with regard to its position in the X direction and the Z direction is likewise uniquely fixed by the unique fixing of both points of application  82  and  84 , and furthermore this drive device  80  only allows the slide element  70  to be displaced in positions in which the slide element  70  always maintains the same alignment in relation to the Z direction and the X direction, which is evident from the fact that a connecting line  184  between the points of application  82  and  84  always remains aligned parallel to the guiding direction  130 , irrespective of the position of the guiding slides  122  and  126  in relation to the guiding slides  120  and  124 , since the drive struts  90  and  94  and also  92  and  96  also always remain aligned parallel to one another on account of the rigid mechanical coupling of the guiding slides  120  and  124  and also  122  and  126 , and consequently there is double parallel guidance for the slide element  70 . 
   As represented in  FIG. 2 , the movement of the guiding slides  120  and  124  takes place by means of a first linear drive  190 , which could be formed for example as an electric linear motor, but is preferably a spindle drive, and comprises an adjusting spindle  192 , on which there is a spindle nut  194 , which is for example fixedly connected to the bearing flange  170  of the first guiding slide  120 . 
   The adjusting spindle  192  is for its part mounted in a bearing support  196  fixedly connected to the machine bed body  20  in such a way that it is non-displaceable in the direction of its longitudinal axis  198  but rotatable, so that turning of the adjusting spindle  192  leads to a displacement of the spindle nut  194  in the direction of the longitudinal axis  198 . 
   Furthermore, the adjusting spindle  192  can be driven in a rotating manner about the longitudinal axis  198  by a drive  200 . 
   Consequently, the guiding slides  120  and  124  can be moved together in the guiding direction  130  by the linear drive  190 . 
   In the same way, a second linear drive  210  is provided for moving the guiding slides  122  and  126 , which drive comprises an adjusting spindle  212 , a spindle nut  214  and a bearing support  216 , the adjusting spindle  212  being accommodated in the bearing support  216  in such a way that it is immovable in the direction of its longitudinal axis  218  but rotatable. 
   Since it is also provided in the case of the second linear drive  210  that the spindle nut  214  is fixedly connected to one of the guiding slides, in this case the guiding slide  126 , both the guiding slide  126  and the guiding slide  122  can be displaced in the guiding direction  130  by turning the adjusting spindle  212 , for example driven by a drive  220 . 
   Depending on the absolute position of the guiding slides  120  and  124  or  122  and  126 , and depending on the relative position of the guiding slides  120  and  124  or  122  and  126 , the position of the second slide element  70  can consequently be fixed with the required rigidity both in the Z direction and in the X direction. 
   The absolute position of the guiding slides  120  and  124  or  122  and  126  can be detected in this case by rotary encoders which are associated with the linear drives  190  and  210  and detect the rotational positions of the adjusting spindles  192  and  212 . 
   Furthermore, as already represented in  FIG. 3 , the relative position of the guiding slides  120  and  124  or  122  and  126  that are connected to one another can be detected by a measuring system  230 , which comprises a first element  232 , disposed for example on the connecting strut  150 , and a second element  234 , disposed on the connecting strut  160 , so that the two elements  232  and  234  are displaceable with respect to one another, one of the elements carrying a glass scale, with which the relative position of the guiding slides  120  and  124  and also  122  and  126  that are coupled to one another can be detected, this relative position representing a measure of the position of the second slide element  70  in the X direction of the machine tool. 
   In order to minimize the effects of thermal displacements on the position of the slide elements  70   1  and  70   2 , the guiding rails  134  of the drive devices  80  are preferably disposed in such a way that they lie on a side of the points of application  82 ,  84  that is facing the spindle axis  26 , in particular near a reference plane  240  of the machine tool which runs through the spindle axis  26  and perpendicularly in relation to the X direction, that is to say parallel to the Y direction. Consequently, the thermal displacements caused by the drive devices  80  according to the invention are minimal, in particular since the drive struts  90 ,  92 ,  94 ,  96  do not have their own heat-dissipating drives, but instead the heat-dissipating drives, namely the drives  200  and  220 , can be disposed at a sufficient distance from the drive device  80 , so that heat only enters the drive devices  80   1  and  80   2  according to the invention indirectly via the drives  200 ,  220 , and consequently the resultant thermal displacements are likewise minimal. 
   Furthermore, the guiding rail  134  associated with the respective drive device  80   1  and  80   2  is fixedly connected directly to the machine bed body  20  near the reference plane  240 , so that thermal displacements of the reference plane  240  itself, for example caused by heating of the machine bed body  20 , do not have any effect on the positional accuracy of the respective second slide element  70   1  or  70   2 , since its position relates substantially to the relative position in relation to the reference plane  240 , the absolute position of which is immaterial. 
   The drives  200 ,  220  of each of the drive devices  80   1  and  80   2  can be controlled by means of a control which is designated as a whole by  250 , positions the respective slide element  70  in the X direction by synchronous displacement of the guiding slides  120  and  124  or  122  and  126  that are coupled to one another and converts the desired position of the slide element  70  in the X direction into a relative position between the slide elements  120  and  124  or  122  and  126  that are coupled to one another.