Abstract:
A pivot bearing device, particularly for a rotating circular table of a machine tool is provided, and includes a first device part, which is to be connected to an element that is to be rotatably mounted, particularly to the circular table, and a second fixed device part. The device parts are connected via at least one antifriction bearing upon which an axial force acts. A magnet device ( 21 ), which acts between the first and second device parts ( 2, 3 ), is provided for generating a compensating force (F k ) oriented in essentially the opposite direction to the axial force (F a ).

Description:
BACKGROUND 
       [0001]    The invention relates to a pivot bearing device, particularly for a rotating circular table of a machine tool, comprising a first device part, which is to be connected to an element, which is to be rotatably mounted, particularly to the circular table, and comprising a second fixed device part, wherein these device parts are connected using at least one anti-friction bearing, on which an axial force acts. 
         [0002]    Pivot bearing devices are typically used to support a first element so that it can rotate relative to a fixed second element. An embodiment to be named is a machine tool with a circular table, which is moved, for example, in a clocked way, and which is held so that it can rotate relative to the machine frame or the like using the pivot bearing device. Known pivot bearing devices comprise a first device part, which is coupled with the element to be supported rotatably, for example, the circular table, and a second fixed device part, which is connected, for example, to the machine frame or the like. The two device parts are connected rotatably to each other by at least one anti-friction bearing. 
         [0003]    In a typical horizontal arrangement of the pivot bearing device, an axial force resulting essentially from the weight of the first device part, from the similarly constant own weight of the coupled element, for example, the table, and also a variable weight portion from a workpiece to be processed and the clamping means arranged, for example, on the circular table, for attaching the workpiece, etc., acts on the one or more anti-friction bearings. Furthermore, for example, from the processing of the workpiece or the like and also from any unbalanced masses, radial forces, such as possible tilting moments resulting from unbalanced masses and processing forces, also act on the one or more anti-friction bearings. 
         [0004]    The static axial forces are the primary factor deciding the service life of the bearing. To avoid any difficulties resulting from this, the anti-friction bearing that is used is dimensioned accordingly. This is cost intensive, sometimes structural difficulties are also produced, and furthermore, the maximum rotational speed is limited. 
       SUMMARY 
       [0005]    The invention is based on the objective of providing a pivot bearing device, in which the problems resulting from the axial force acting on the one or more anti-friction bearings can be at least partially compensated. 
         [0006]    To meet this objective, it is provided according to the invention that, for a pivot bearing device of the type noted above, a magnetic device acting between the first and the second device parts for generating a compensating force directed essentially opposite the axial force is provided. 
         [0007]    The pivot bearing device according to the invention is distinguished by the use of a magnetic device, by which a compensating force can be generated, which necessarily acts on the one or more anti-friction bearings because the magnetic device is arranged between the two device parts or acts between these and which is directed opposite the axial force. A permanent force of attraction, which is directed opposite the own weight-related axial force and which compensates this axial force, acts between both device parts through the magnetic device. The resulting force actually acting on the one or more anti-friction bearings can thus be compensated to a large degree according to the layout of the magnetic device. Thus it is also possible to use relatively small anti-friction bearings with a simultaneously sufficiently long service life, which can also operate at high continuous rotational speeds. Advantageously, hydrostatic bearings or the like can be eliminated. 
         [0008]    The magnetic device itself preferably comprises several permanent magnet elements, which are arranged on the first or on the second device part and which interact with the other, opposing device part. Each opposing device part is obviously metallic, so that the permanent magnet elements and the opposite device part necessarily attract each other. Here, it is not significant whether the permanent magnets are now arranged on the first device part, which is turned actively by a drive motor, or on the second, fixed device part. 
         [0009]    As an alternative to the arrangement of the permanent magnet elements on only one device part, it is obviously also conceivable to arrange the several permanent magnet elements on the first and on the second device parts opposite each other, wherein the permanent magnet elements are naturally aligned with their poles accordingly, so that they attract each other. 
         [0010]    According to an especially preferred construction of the invention, in which the permanent magnet elements are arranged at least on the first device part, which rotates, it is especially advantageous that the first device part with the permanent magnets simultaneously forms or comprises the rotor of a motor driving the first device part and the second device part forms the stator of the motor. The motor is preferably constructed as a disk-shaped torque motor. In this embodiment, the motor is integrated on the device side and forms a part of the pivot bearing device. Such a torque motor preferably allows a direct drive. The permanent magnets are arranged on the disk-shaped rotor, which is formed by the first device part or which is part of this first device part, for the torque motor constructed here as a disk armature. Lying above these parts at a distance in the axial direction is the second device part, which forms or comprises the stator and which obviously provides all of the electrotechnical or electromagnetic components necessary for forming a torque motor. This construction is especially advantageous since both an integrated direct drive and also the magnetic load compensation according to the invention are achieved through the construction of the torque motor as a horizontally arranged disk armature. 
         [0011]    As an alternative to the use of a disk-shaped torque motor, the permanent magnet elements can also interact as purely passive elements with the metallic or magnetic counterpart. The first device part can be coupled or is coupled in this part with the rotary drive of a motor, especially an electric motor with a worm gear. The permanent magnets are also arranged here for generating the axial compensating force preferably on a disk, which lies horizontally in the installed position and which is coupled with the rotary drive and which forms a part of the first device part and which interacts with the second device part lying opposite and spaced apart in the axial direction, wherein this second device part also forms somewhat of a stator. 
         [0012]    Preferably a combined radial-axial bearing, especially in the form of a cylinder anti-friction bearing, is used as the anti-friction bearing. Alternatively, two or more rows of angular contact ball bearings can also be provided. 
         [0013]    In addition to the pivot bearing device, the invention further relates to a machine tool comprising a rotating circular table, which provides a pivot bearing device according to one of the described embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Additional advantages, features, and details of the invention emerge from the following description of an embodiment. Shown herein are: 
           [0015]      FIG. 1  a section view of a block diagram of a pivot bearing device according to the invention with an attached circular table, and 
           [0016]      FIG. 2  an enlarged detail view of the pivot bearing device from  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]      FIG. 1  shows a pivot bearing device  1  according to the invention comprising a first device part  2  that can rotate in the mounted state and a second device part  3  that is fixed in the installed position. In the shown embodiment according to  FIG. 1 , a circular table  4 , on which, for example, various clamping devices can be placed for holding a workpiece or the like, is arranged on the first device part. The first device part  2  and the second device part  3  are joined in rotation to each other by a combined two-part pivot bearing  5 , wherein the pivot bearing  5  comprises a radial bearing  6  and also two axial bearings  7 . It involves, for example, a combined radial-axial cylinder anti-friction bearing. 
         [0018]    As  FIG. 2  further shows, on one hand, the circular bearing table  4  is fixed to the inner annular bearing part  8  by screw connections  9  and, on the other hand, a motor disk  11 , which is fixed to the intermediate piece  10  by screw connections  22 , is arranged above an intermediate piece  10 . The intermediate piece  10  and also the motor disk  11  form part of the first device part. The motor disk  11  forms the rotor  12  of a torque motor  13  constructed here as a disk armature, which will be discussed in more detail below. 
         [0019]    The bearing housing  16 , which is locked in rotation, for example, with the machine frame, by attachment means guided by corresponding attachment boreholes  17 , is arranged on a second bearing part  14  by screw connections  15 . A stator  19 , which forms the torque motor  13  together with the rotor  12 , is further connected to the bearing housing  16  by additional screw connections  18 . The bearing housing  16  and also the stator  19  are part of the second, fixed device part. 
         [0020]    A plurality of permanent magnets  20  are arranged, preferably distributed over the entire disk plane, on the side directed toward the stator  19  on the motor disk  11  forming the rotor  12 . In the stator itself are the electromagnetic components, such as exciter coils, etc., necessary for implementing the torque motor  13 , not shown in more detail. These components do not need to be discussed in more detail. In principle, a torque motor involves a multiple-pole, permanently excited synchronous motor, wherein, in a known way the permanent magnets are arranged on the rotor, while on the stator the individually wound coils are arranged at a high packing density, by which high magnetic forces can be generated when the coils are energized. Typically, the individual coils or the winding heads are arranged between the stator sheets. Because almost no friction is generated in such torque motors, these motors are essentially maintenance free. The basic construction of a torque motor has long been known to those skilled in the art, so that it does not need to be discussed in more detail. The central elements also must be provided in the torque motor designed here as a disk armature. 
         [0021]    A static axial force F a  in the axial direction, which results, on one hand, from the own weight of the first device part  2 , here, the bearing part  8 , the intermediate piece  10 , as well as the motor disk  11 , and the additional attachment elements or other components, which form the first device part  2 , acts continuously on the anti-friction bearing  5 . Added to this are also the force components resulting from the weight of the circular table  4  itself, any clamping elements, as well as workpieces to be processed, etc., on the table. 
         [0022]    This axial force F a  can be compensated to a certain degree or to a large extent by a compensating force acting in the opposite direction. This compensating force F k  is generated by the magnetic device  21  provided between the first and the second device part  2 ,  3 , here formed by the permanent magnets  20  in connection with the stator  19 , between which a magnetic coupling acts outward from the housing. Permanent forces of attraction act between the permanent magnets  20  and the stator  19  such that the rotor  12  generates a compensating force F k  directed opposite the axial force F a  via the connection piece  10 . This compensating force F k  is also generated during the operation of the torque motor  13 , because the permanent magnets  20  and the stator  19 , which are separated from each other by the air gap d, also continuously attract each other. The generated compensating force depends on how strong the force of attraction of the magnetic device  21  is, which can be set in the end by the magnetic field strength that can be generated by the permanent magnets  20 . 
         [0023]    For the embodiment described in  FIGS. 1 and 2 , an integrated torque motor  13  is provided as described. This means that no additional drive element must be provided. A double function is given to the torque motor, namely, on one hand, the rotational driving of the circular table  13  and, on the other hand, the function of load compensation, that is, the function of generating the compensating force F k . 
         [0024]    Alternatively, however, the construction can be such that instead of an integrated torque motor, the first device part  2  is coupled with a separate drive, for example, a conventional electric motor with a worm gear. This drive is flanged, for example, to the motor disk  11 . In this case, as is shown in  FIG. 2 , the permanent magnets  20  distributed over the disk plane are located on the motor disk  11 . Because the rotary drive is external to the pivot device, a stator no longer has to be provided. That is, instead of the stator  19  shown in  FIG. 2 , a simple metallic element, just a correspondingly dimensioned metal ring, can be integrated, which interacts with the permanent magnet  20 . It is also naturally conceivable to use a suitable sheet-metal package arrangement for generating the magnetic forces or for interacting with the permanent magnets  20 , wherein the arrangement is selected so that when the table rotates, eddy currents, which could be induced due to the rotation, are largely prevented. In this embodiment, the two first and second device parts  2 ,  3  would also attract each other, which would also result in the generation of the compensating force F k  for the use of an external drive. Here, there is naturally the possibility of arranging not only corresponding permanent magnet elements  20  on the motor disk  11 , but also on the opposing part of the second device part, so that the magnetic coupling could be reinforced. 
       LIST OF REFERENCE NUMBERS 
       [0000]    
       
           1  Pivot bearing device 
           2  Rotating device part 
           3  Fixed device part 
           4  Circular table 
           5  Anti-friction bearing 
           6  Radial bearing 
           7  Axial bearing 
           8  Bearing part 
           9  Screw connections 
           10  Intermediate piece 
           11  Motor disk 
           12  Screw connections 
           13  Torque motor 
           14  Bearing part 
           15  Screw connections 
           16  Bearing housing 
           17  Attachment boreholes 
           18  Screw connections 
           19  Stator 
           20  Permanent magnets 
           21  Magnetic device 
           22  Screw connections 
         F a  Axial force 
         F k  Compensating force 
         d Air gap