Turning machine
BACKGROUND OF THE INVENTION 
     The invention relates to a turning machine having a multiple track bed, a spindle head with a drive device for a work mount, and a rest, preferably designed as a compound slide or machining turret, for mounting tools or driveable machining units. 
     The turning machines previously comprising a two-track machine bed having a spindle head for work mounting, a tailstock as a counterstay, and also a rest as a tool-holder have now been further developed into high-production turning machines or high-production machining centers. The two-track bed has been further developed into a three-track bed or a four-track bed for independently moving the rest relative to the other parts of the turning machine. In particular, the rest has been extensively developed further as a machining center or a universal tool holder having separate drive devices for tool mounting or complete machining units. Apart from fixed turning tools, driven machining units for grinding, milling and boring are therefore fixed on the rest (DE-A No. 1-34 10 276). 
     In these known machining centers, the rest, apart from executing the known motion (X 1  -axis) transversely to the longitudinal axis of the machine bed by means of a compound slide on a separate carriage (four-track bed), also executes a separate longitudinal motion (Z-axis) parallel to the longitudinal axis of the machine bed. In addition to this cross motion in a horizontal plane, the rest can execute a motion in a vertical axis (Y-axis) and also a rotary motion about this vertical axis (B-axis). With a numerically controlled drive, turning machines of this type can be used as universal metal-cutting machines. 
     In these known metal-cutting machines, the spindle head is essentially used for mounting the workpiece, with the spindle executing the rotary motion (C-axis) about the longitudinal axis of the workpiece. In this connection, it is known to carry out the rotary motion of the spindle of the spindle head in preset angular steps. 
     The known universal turning machines have the disadvantage that on the one hand all possibilities of optimally machining a workpiece are hereby not yet exhausted. On the other hand, it is disadvantageous that the rest assumes spatial motion sequences for which it is not necessarily suitable. If, for example, it is desired to produce a tapered circumference on the workpiece, the rest can only achieve this by moving outward gradually in the transverse direction (X-axis). During this procedure, it is not always guaranteed that the cutting tool is always perpendicular to the cutting surface, i.e. the angle of contact does not correspond to the surface normals. 
     In the known universal machining centers, it can also be of disadvantage that the rest described, which is of complicated construction, as a machining turret has to be of very elaborate design so that the requisite spatial motion sequences can be executed, not least also in combination with a very complicated numerical control system. Because of the guides for the drive units of the rest, which guides are arranged in the most restricted construction space, the machining accuracy can only be produced by maximum precision of the components, with the rigidity and stability of the system of the rest leaving something to be desired. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to remove the abovementioned disadvantages and in particular to develop a turning machine which can execute further suitable motion sequences for the spatial machining of workpieces. 
     Based on a turning machine according to the generic term, this object is achieved by providing a turning machine on which the spindle head is swivelably or rotatably mounted on a separate spindle head machine bed for executing a longitudinal motion in the direction of the longitudinal axis of the spindle head machine bed and in a horizontal plane about a vertical swivel or rotation axis. 
     The invention is based upon the knowledge that the previous relative immobility of the spindle head, with merely the rotary motion of the spindle about the C-axis, is of disadvantage. 
     According to the invention, therefore, the motion sequences typical of the rest are partly or completely transmitted to the spindle head itself. Of particular importance in this connection is the practicable longitudinal motion of the spindle head in the direction of the longitudinal axis of the machine bed (W-axis). According to the invention, a transverse motion is superimposed on this longitudinal motion in the same horizontal plane, with it being possible for the transverse motion to be executed on a straight line (X 2  -axis), for example by means of a compound slide, or on a curve (B 1  -axis). 
     A number of advantages in the machining of workpieces are connected with the combined longitudinal motion (W-axis) and swivel motion (B 1  -axis) of the spindle head in a horizontal plane. If, for example, it is desired to produce a tapered circumferential surface, the spindle head need only be swivelled through the angle which the tapered circumferential surface encloses with the rotational axis of the workpiece. In this way, the tapered circumferential surface to be machined is positioned parallel to the longitudinal axis of the main machine bed, so that the rest need only execute a longitudinal motion in the Z-axis, i.e. parallel to the longitudinal axis of the machine bed, but not an infeed motion in the X-axis or rotary motion in the B 2  -axis. The rest can therefore be of exceptionally simple construction for this machining, with a control system for the rest for producing the tapered circumferential surface being dispensed with completely. 
     Moreover, an advantage here is that the setting angle of the cutting tool to the workpiece surface, even in the case of these curved surfaces, can always be kept constant. This is especially important in the case of tools with line contact, such as, for example, profiled cutting tools, grinding wheels, roller-burnishing devices, milling cutters, etc., or when using measuring sensors. 
     However, as a result of the inventive swivel device of the spindle head, the rest can also be made substantially more robust as a tool holder, for example for boring rods, grinding spindles, etc., since the workpiece opening available, for example in machining internal contours, can be better utilized as a result of the constant angle of contact between the workpiece and the tool. 
     Compared with turning machines with turntables on the rest (B 2  -axis), the present invention has the further advantage that the machining accuracy is substantially increased, since considerably more construction space is available for guides, a drive and measuring systems. In this way, substantially greater rigidity can also be achieved. 
     Moreover, it is advantageous that the drive of the guideways and also the measuring systems, for executing the motion of the spindle head, are located outside the chip area and are therefore protected. 
     Since in the continuous machining of complicated surfaces, constant adjustment of the rest by numerical control can be dispensed with if necessary, the rigidity of the entire machine in the clamped condition of the swivel axis is not impaired. Internal and external tapers can therefore be produced exceptionally accurately in single-axis operation, since no interpolation errors occur outside by simultaneous traversing of two axes as in the conventional system. In this way, the machining units, such as grinding units, boring equipment, etc., can also be made more robust, since they are no longer impaired by the space requirement of a swivel axis on the rest. 
     Depending on the application, the rest can therefore be of very simple design even for producing very complicated parts, with a simple control unit being sufficient. However, the rest can of course also be designed in complicated embodiments as a universal tool holder with mounting fixtures for detachably fixing tools or driveable machining units having a numerical control system. 
     For producing complicated shapes, such as parabolic surfaces, hyperbolic surfaces and the like, the swivel motion and also the longitudinal and/or transverse motions of the spindle head can likewise be executed in numerically controlled manner. For this purpose, the requisite curve functions are transmitted to the infeed motion of the individual axes of the spindle head. This enables, for example, highly accurate parabolic bodies of ceramics, glass, plastic or high-strength steels to be ground, with a setting angle which is always constant of the cutting tool relative to the workpiece being ensured. 
     Moreover, the invention has the advantage that a greater dynamic range of the rest can be achieved provided that swivel drive is not arranged on the rest and therefore need not be accelerated or decelerated along with the rest. 
     It is also advantageous that existing alignment errors between the spindle head and the tailstock can easily be corrected by software so that no mechanical synchronizing work is necessary. 
     The turning machine according to the invention is preferably used as a universal turning machine with a rest as a machining center, with milling stations, internal and external grinding stations and boring stations being provided in addition to machining by turning. Moreover, diverse measuring stations for workpiece measurement can also be attached in an advantageous manner. 
     The swivel device of the spindle head can be designed in various ways. 
     As a first swivelling means, the swivel motion of the entire spindle head is considered about a vertical swivel axis which is preferably at a clear distance from the center of gravity S of the spindle head. In large metal-cutting machines this distance can be between one meter and three meters. This results in a large lever arm with a swivel drive adjustability which can be set correspondingly accurately. However, this distance can also be small. 
     Alternatively or in addition hereto, the swivel motion of the spindle head can be designed as a rotary motion and can be effected in such a way that the vertical rotation axis leads through the center of gravity of the spindle head or is located in the area of this center of gravity. This rotary motion is possible, for example, by means of a rotary table beneath the spindle head. This corresponds, for example, to a transmission of the known motion sequences in the rest to the spindle head, but not with surprising results connected therewith. 
     In the most complicated embodiment, the spindle head can accordingly execute motion sequences in the direction of the longitudinal axis of the machine head (W-axis) and transversely hereto (X 2  -axis) by means of a compound slide and also a rotary motion (B 1  &#39;-axis) by means of a rotary table arranged on the compound table. Moreover, a swivel motion with a large swivel radius and therefore a large swivel angle can be effected (B 1  -axis) via the additional swivel axis at a distance from the center of gravity of the spindle head. 
     Further advantages follow from the advantageous developments of the inventive turning machine according to the sub-claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are explained in greater detail in the description, with further advantages specified, and are shown in the drawing, in which: 
     FIG. 1 shows a perspective representation of a turning machine according to the invention, indicating as many practicable functions as possible for representing the principle, 
     FIG. 2 shows a plan view of a simplified embodiment of a turning machine having a two-track bed according to the inventive principle, and 
     FIG. 3, in plan view, shows a universal turning machine according to the inventive principle, having a four-track bed and a universal machining rest; 
     FIG. 4 schematically illustrates numerical control of movements of the spindle head and the rest. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The turning machine (10) shown in FIGS. 1 to 3 is designed as a universal metal-cutting machine having a known four-track bed (11). The main machine bed (12) shown in FIGS. 2 and 3 in plan view is used for mounting the tailstock (13) or, in a simplified embodiment in FIG. 2, for mounting the rest (14) in the two-track bed. In the four-track bed, the auxiliary machine bed (15) is used for mounting the rest (14) which can be moved independently of the main machine bed. 
     In a first alternative embodiment, the special feature according to the invention is that the entire spindle head (16) is released relative to the main machine bed (12) and is made such that it can be swivelled (B 1  -axis) relative to the longitudinal axis (17) of the latter and transverse longitudinally (W-axis) in the direction of its own longitudinal axis (23). This alternative solution is shown in FIGS. 1 to 3. According to this first alternative, the swivel motion is executed through the angle α about a vertical rotation axis (18) which is located at a distance L 1  &gt;&gt; zero from the center of gravity S of the spindle head (16) or of the headstock (19). Depending on the type of machine, this distance L 1  is in the order of magnitude of one meter to three meters. Accordingly, the entire spindle head (16) is swivelled outward relative to the longitudinal axis (17) of the main machine bed. The rack-and-pinion drive (20) with guides (21) is used for this purpose. So that the spindle head (16) can be swivelled relative to the main machine bed (12), the entire spindle head must therefore be released from the main machine bed (12), as can be particularly plainly seen from FIGS. 2 and 3. The spindle head (16) has a separate spindle-head machine bed (22) on which the headstock (19) is traversable in the direction of the longitudinal axis (W-axis) of the spindle head. Only if α=zero is the longitudinal axis (23) of the spindle head in alignment with the longitudinal axis (17) of the main machine bed, as shown in FIG. 3. 
     The displacement of the spindle head (16) relative to the zero position (in which the tracks 15 and 22 are parallel), when swivelled about the vertical rotation axis (18), is α˜-10° to +90° and preferably α˜-5° to +30°. Preferably the spindle head (16), in the representation according to FIG. 1, can be swivelled out of the zero position clockwise through about 30° and anti-clockwise through about 5°, with the zero position being identified by aligned longitudinal axes (17 and 23) of the main machine bed and of the spindle head. This swivel motion is schematically shown in the figures as α.sub.(+) and α.sub.(-). The swivel motion about the vertical axis (18) is identified as movement along the B 1  -axis. An especially accurate spindle guidance which is free from play can be achieved by the long lever arm L 2  between the swivel axis (18) and the swivel drive (20) (See FIG. 3). This horizontal swivel motion of the spindle head is effected by means of a pretensioned gear drive which is known per se and has automatic backlash compensation which acts on the rack-and-pinion drive (20). As is common practice, such structure allows the relative movement of the parts to be relatively free from play by means of a toothbar rack. This technology is known, for example, from the Siemens Literature &#34;Elektrische Vorschubantriebe fur Werkzeugmaschinen&#34; (Electric Feed Drives for Machine Tools), Verlag Siemens AG 1981, page 236 ff. 
     The embodiment described above is shown in principle in FIG. 1 and in alternative embodiments in FIGS. 2 and 3, with FIG. 2 showing a two-track bed and FIG. 3 showing a three-track bed. Basically, in both designs, the spindle head (16), about the vertical axis (18), is mounted such that it can swivel along the so-called B 1  -axis and can be longitudinally traversed along the W-axis. FIG. 2 shows the spindle head (16) in a position displaced to one side through the angle α.sub.(+) relative to the aligned longitudinal axis (17) of the main machine bed (12) or the zero position of the spindle head. 
     In a considerably simplified embodiment of the invention, the axial independent motion of the spindle head (16) (along the W-axis) can be dispensed with in special cases; i.e. only the inventive swivel motion of the spindle head (16) is executed, while the rest (14) on the main machine bed (12) executes the longitudinal motion (along the Z-axis) and also the transverse motion or feed motion (along the X 1  -axis). 
     In FIGS. 2 and 3, the same construction of the spindle head (16) is shown in principle, i.e. the swivel motion is effected about the vertical axis (18) (along the B 1  -axis), and the longitudinal motion on the spindle-head machine bed (22) made separate from the main machine bed (12) is effected along the W-axis. Also shown are the rack-and-pinion drive (20), at a distance L 2  from the rotation axis (18), and a guide (21). 
     Apart from the main machine bed (12), the embodiment according to FIG. 3, just as in FIG. 1, contains an auxiliary machine bed (15) for the rest (14). In FIG. 3, this rest is designed as a universal machining turret, with mounting fixtures for detachably fixing tools or driveable machining units. A grinding unit is shown as an example of a machining unit (24). The direction of motion of the rest is shown by the Z-axis parallel to the longitudinal axis (17) of the main machine bed (12), and the direction transversely hereto is shown by the X 1  -axis. In addition, the rest can also execute a rotary motion about a vertical rotation axis (26), which is identified as motion along the B 2  -axis. The vertical adjustability in the direction of the vertical rotation axis (26) is designated as &#34;Y-axis&#34;. These directions of motion and degrees of freedom are also reproduced in FIG. 1 in the corresponding representation of the rest. A compound slide (27) or tool slide which runs on a cross slide (28) or the machine bed (15) assumes the motion in the horizontal plane (Z-axis and X 1  -axis). A rotary table (29) assumes the rotary motion along the B 2  -axis, while a lifting device (30), in a manner known per se, assumes the motion along the Y-axis, i.e. in the direction of the vertical rotation axis (26). 
     A simplified rest (14) with a grinding unit (24) and a numerical control unit (25) is shown in FIG. 2. 
     As an alternative embodiment or as a supplementary embodiment to the embodiments shown hitherto, in particular the embodiments according to FIGS. 2 and 3, a possibility is shown in FIG. 1 of producing the rotary motion of the spindle head (16) via a separate rotary table (31), with the rotation center axis (32) being guided through the center of gravity S or in the area of this center of gravity S of the headstock. In this way, the headstock (19) can execute a similar rotary motion (along the circular axis B 1  &#39;) as is executed by the rest as a result of the rotary table (29). In particular applications, this rotary motion can be a very suitable addition to the swivel motion about the rotation axis (18). In a particular embodiment of the device according to the invention, it can even be available on its own. The advantages mentioned at the beginning can likewise be partly achieved with this rotary device. 
     The invention according to the representation according to FIG. 1, in addition to providing the longitudinal motion in the direction of the W-axis, also provides for the possibility of a motion of the spindle head transverse thereto (X 2  -axis). This is achieved by a separate compound table (33) which imparts a mobility to the spindle head as known per se hitherto only from the rest. 
     In FIGS. 1 to 3, the rotary motion of the spindle is shown with the C-axis. In this connection, the rotary motion can be executed in steps by an indexing control (dividing axis drive, not shown) with the setting of any angle or angular ranges of rotation of the spindle about the axis 23. 
     The embodiment of the invention according to FIG. 1 represents in total and in principle the plurality of the possibilities according to the invention. Moreover, a determining factor is that, apart from the known mobility of the rest as a universal machining center with the motion axes X 1 , Z, B 2  and Y, the spindle head can also execute a completely independent motion in the direction of the axes W and X 2  and of the swivel motion B 1  and B 1  &#39;. In addition there is the rotary motion of the spindle (34) itself, i.e. motion along the C-axis. Control of these motions by a numerical control means 35 is schematically illustrated in FIG. 4. 
     Depending on the application, all these motions can be present to a more or less considerable extent. 
     In particular, only the swivel device for rotation about the rotation axis (18) or the swivel device for rotation about the rotation axis 32 by means of the rotary table (31), will generally be available. This is indicated by the representation of the rotary table (31) shown in a broken line. A determining factor for the mobility of the spindle head is principally the swivel motion about the B 1  -axis and also the longitudinal motion along the W-axis along the machine bed (22) of the spindle head. The further motion transversely to the W-axis along the X 2  -axis and also, alternatively or in addition, the rotary motion about the B 1  &#39;-axis can be added. 
     It should be additionally noted that the main spindle of the spindle head is mounted hydrostatically or aerostatically. Separate drives are mainly used here for each motion sequence in order to dispense with resulting inaccuracies during gear shifts.