Abstract:
The invention relates to a drive system comprising a control unit ( 1 ), which is connected to drive units ( 3   a,    3   b,    3   c,    3   d,    3   e,    3   f,    3   g ) via a data bus ( 2 ) for the exchange of data. According to the invention, one drive unit ( 3   a,    3   b ) is connected to the drive motor ( 7   a,    7   b ) in order to control the latter ( 7   a,    7   b ) and an additional drive unit ( 3   c,    3   d,    3   e,    3   f,    3   g ) is connected to a magnetic bearing ( 11   c,    11   d,    11   e,    11   f   , 11   g ) of a magnetic spindle bearing arrangement ( 23 ) in order to control said bearing ( 11   c,    11   d,    11   e,    11   f,    11   g ). The invention thus provides a drive system, in which a magnetic spindle bearing arrangement ( 23 ) is integrated.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a drive system. 
   The invention also relates to a machine tool, production machine or a robot having the abovementioned drive system. 
   According to customary practice, machines, such as, for example, machine tools, production machines or robots, have a multiplicity of “machine axes”, the movements and positions of which are controlled by a controller, in particular a numerical control. An important factor in this case is, inter alia, exact guidance of the relative movement and the relative position between a spindle of the machine and the workpiece to be machined. Machining of the workpiece by the tool produces the desired contour on the workpiece. In the process, the drives of the individual machine axes must perform very exact traverse and rotary movements. In addition to rapid and precise axis drives, the productivity, for example of a machine tool, depends on a high spindle speed. The spindle has a spindle drive motor which normally forms a unit with a spindle rotor. The spindle drive motor sets the spindle rotor in rotation. Virtually all the spindles used at present have a mechanical bearing arrangement, e.g. in the form of a rolling element bearing arrangement. The disadvantages of the mechanical bearings at high speeds are generally known. In this regard, high wear of the mechanical bearings occurs at high speeds. Since the lubricant supply to the bearings is complicated, the disturbances frequently occurring in the lubricant supply lead to an often premature failure of the bearing. A further problem constitutes the residual unbalance of the spindle rotor. This occurs in interaction with the machine structure and causes pronounced vibrations and noise at certain speeds. 
   Wear and vibration behavior can be considerably improved through the use of a magnetically mounted spindle. In many cases, magnetic spindle bearing arrangements are used according to the prior art. The magnetic spindle bearing arrangement is a contactless system in which magnetic forces controllable via magnetic bearings assume the role of the rolling elements. The position of the spindle rotor is in this case measured continuously and the magnetic forces are always dynamically readjusted in such a way that the spindle rotor keeps the desired position in the bearing center even during loading. 
   Shown in  FIG. 1  in a schematic illustration is a magnetic spindle bearing arrangement  23 . It comprises a spindle rotor  10 , which is mounted by means of magnetic bearings  11   c ,  11   d ,  11   e ,  11   f  and  11   g  (only shown schematically for the sake of clarity), and a performance module  16 . Each magnetic bearing  11   c ,  11   d ,  11   e ,  11   f  and  11   g  essentially comprises an electromagnetic yoke which is fitted with coils and acts on the passive spindle rotor  10 . In this case, the magnetic bearings  11   e  and  11   f  carry out the guidance in the X direction, the magnetic bearings  11   d  and  11   g  carry out the guidance in the Y direction and the magnetic bearing  11   c  carries out the guidance in the Z direction. Assigned to the magnetic bearings  11   c ,  11   d ,  11   e ,  11   f  and  11   g  are respectively associated distance sensors  12   c ,  12   d ,  12   e ,  12   f  and  12   g  which measure the distance from the spindle rotor  10  and feed respectively associated analog actual position signals  15   c ,  15   d ,  15   e ,  15   f  and  15   g  as input variables to a performance module  16 . The performance module  16  comprises control devices  18   c ,  18   d ,  18   e ,  18   f  and  18   g  which act on the respectively associated magnetic bearings  11   c ,  11   d ,  11   e ,  11   f  and  11   g  via respectively associated power converters  17   c ,  17   d ,  17   e ,  17   f  and  17   g  and via respectively associated lines  8   c ,  8   d ,  8   e ,  8   f  and  8   g . In this case, the control devices  18   c ,  18   d ,  18   e ,  18   f  and  18   g  and the power converters  17   c ,  17   d ,  17   e ,  17   f  and  17   g  need not necessarily be an integral part of the performance module  16 , but may also be present as individual components. The control devices  18   c ,  18   d ,  18   e ,  18   f  and  18   g  are connected to the respectively associated power converters  17   c ,  17   d ,  17   e ,  17   f  and  17   g  for the exchange of data, which is indicated by double arrows in  FIG. 1 . The performance module  16  and the magnetic bearings  11   c ,  11   d ,  11   e ,  11   f  and  11   g  form a control loop which keeps the spindle rotor  10  floating. 
   Furthermore, a commercially available drive system of a machine, such as, for example, a machine tool, a production machine or a robot, is shown in  FIG. 1 . Via a data bus  2 , of a two-axis machine in the example, a controller  1  is connected to a drive device  3   a  and  3   b  for activating the drive motors  7   a  and  7   b  and in particular to a control device  4   a  and  4   b . The data communicated via the data bus  2  are, for example, speed, acceleration and position data of the individual drives. The control device  4   a  and  4   b  activates a respectively associated power converter  5   a  and  5   b  via a respectively associated connection  6   a  and  6   b . The power converters  5   a  and  5   b  activate respectively associated drive motors  7   a  and  7   b  via respectively associated 3-phase lines  8   a  and  8   b . In this case, each drive motor  7   a  and  7   b  activates a respective machine axis of the machine. A respective actual position encoder  12   a  and  12   b  is assigned to each drive motor  7   a  and  7   b , an actual position signal  15   a  being fed as input variable to the control device  4   a  by the actual position encoder  12   a  and an actual position signal  15   b  being fed as input variable to the control device  4   b  by the actual position encoder  12   b . In this case, each drive device comprises a control device and a power converter, although the control device and the power converter need not necessarily be accommodated in a common housing. The control device and power converter may also quite easily be in the form of separate components. The controller  1 , for example, inputs position setpoints into the control device  4   a  and  4   b  via the data bus  2 . The actual position values  15   a  and  15   b  are then controlled in accordance with the position setpoints input by the controller  1  and the machine axes are moved in this way. 
   As shown in  FIG. 1 , a commercially available drive system of a machine has no connection to the magnetic spindle bearing arrangement  23 . The power converters  5   a  and  5   b  for activating the drive motors  7   a  and  7   b  are, as shown in  FIG. 1 , three-phase, whereas the power converters  17   c ,  17   d ,  17   e ,  17   f  and  17   g  of the magnetic spindle bearing arrangement  23  are only two-phase. For this reason, the drive devices, in particular the power converters  5   a  and  5   b  which serve to activate the drive motors  7   a  and  7   b  and the power converters of the spindle bearing arrangement, have hitherto not been regarded as being interchangeable. This results in considerable disadvantages with regard to maintenance of machines and the stockkeeping of spare parts for machines having a magnetic spindle bearing arrangement. 
   Furthermore, the actual position encoders  12   a  and  12   b , according to customary practice, always deliver incremental actual position signals  15   a  and  15   b , whereas the actual position encoders  12   c ,  12   d ,  12   e ,  12   f  and  12   g  of the magnetic spindle bearing arrangement  23  deliver analog actual position signals  15   c ,  15   d ,  15   e ,  15   f  and  15   g . For this reason, the control devices  4   a  and  4   b  have hitherto not been regarded as being interchangeable with, for example, the control devices  18   c  and  18   d  of the performance module  16  for the magnetic spindle bearing arrangement. As with the power converters, this likewise has considerable disadvantages with regard to maintenance and stockkeeping of spare parts. In addition, due to the separation of the drive system and the magnetic spindle bearing arrangement  23 , two different procedures for the drive devices  3   a  and  3   b  on the one hand and for the magnetic spindle bearing arrangement  23  on the other hand are to be taken into account during start-up. 
   As a result, the labor cost for start-up and maintenance is considerably increased. Since the control devices  18   c ,  18   d ,  18   e ,  18   f  and  18   g  of the magnetic spindle bearing arrangement  23  have no communication with the controller  1 , the magnetic spindle bearing arrangement  23  also cannot be integrated in the motion guidance of the machine axes, e.g. for vibration damping. 
   Furthermore, a modern controller of a machine, in particular a numerical control, contains diverse diagnostic possibilities, extending right through to remote diagnosis via the Internet. However, since the magnetic spindle bearing arrangement  23 , according to customary practice, does not communicate with the controller  1  via the data bus  2 , it also cannot be included in the diagnostic possibilities already existing. 
   SUMMARY OF THE INVENTION 
   The object of the invention is therefore to integrate a magnetic spindle bearing arrangement in a drive system. 
   This object is achieved by a drive system comprising a controller which is connected to drive devices via a data bus for the exchange of data, one drive device for activating a drive motor being connected to the drive motor and a further drive device for activating a magnetic bearing of a magnetic spindle bearing arrangement being connected to the magnetic bearing. 
   Advantageous configurations of the invention follow from the subclaims. 
   A first advantageous design of the invention is characterized in that the drive devices each have a control device and a power converter. According to customary practice, drive devices have a control device and a power converter. 
   Furthermore, it proves to be advantageous if the drive device and the further drive device have identical hardware. This measure standardizes the hardware and increases the reliability and availability of the drive system according to the invention. Furthermore, the costs for the control devices and the power converters for the magnetic spindle bearing arrangement are reduced. 
   Furthermore, it proves to be advantageous that the drive devices are connected to a common grid power supply device for the electrical power supply. This makes it possible to standardize the hardware and reduce the costs for the hardware. 
   Furthermore, it proves to be advantageous that the power converter of the further drive device is designed as a 3-phase power converter. This makes it possible to standardize the hardware, a factor which has a positive effect on the reliability and availability of the drive system and at the same time reduces the costs for the drive system. 
   In this connection, it proves to be advantageous if the control device of the further drive device is set in such a way that two current-carrying phases of a power converter have a current of identical magnitude but opposite sign. This provides a simple and elegant means of operating a 3-phase power converter like a 2-phase power converter. 
   Furthermore, it proves to be advantageous if a signal converter for converting an analog actual position signal from the magnetic spindle bearing arrangement to an incremental actual position signal is provided. This enables control devices which require an incremental actual position signal as input variables to also be used for control devices of the magnetic spindle bearing arrangement. 
   The drive system according to the invention is especially suitable for use as a drive system in a machine tool, a production machine or a robot, as magnetic spindle bearing arrangements are used in these technical fields. However, the drive system according to the invention can of course also be used in other technical fields. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     An exemplary embodiment of the invention is shown in the drawing and explained in more detail below. In the drawing: 
       FIG. 1  shows a drive system and a magnetic spindle bearing arrangement according to the prior art, 
       FIG. 2  shows a drive system according to the invention, and 
       FIG. 3  shows a machine tool. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   A drive system according to the invention is shown in the form of an exemplary embodiment in the block diagram according to  FIG. 2 . Compared with the embodiment according to  FIG. 1  known from the prior art, a magnetic spindle bearing arrangement  23  in integrated in the drive system according to the invention. Just as in the embodiment according to  FIG. 1 , a controller  1  in the embodiment according to  FIG. 2  is connected via a data bus for the exchange of data to the two drive devices  3   a  and  3   b  for activating the drive motors  7   a  and  7   b  and in particular to the control devices  4   a  and  4   b  for the exchange of data. 
   The control device  4   a  and  4   b  activates a respectively associated power converter  5   a  and  5   b  via a respectively associated connection  6   a  and  6   b . The power converters  5   a  and  5   b  activate respectively associated drive motors  7   a  and  7   b  via respectively associated 3-phase lines  8   a  and  8   b . In this case, each drive motor  7   a  and  7   b  activates a respective machine axis of the machine. A respective actual position encoder  12   a  and  12   b  is assigned to each drive motor  7   a  and  7   b , an actual position signal  15   a  being fed as input variable to the control device  4   a  by the actual position encoder  12   a  and an actual position signal  15   b  being fed as input variable to the control device  4   b  by the actual position encoder  12   b . In this case, each drive device comprises a control device and a power converter, although the control device and the power converter need not necessarily be accommodated in a common housing. The control device and power converter may also quite easily be in the form of separate components. The controller  1 , for example, inputs position setpoints into the control device  4   a  and  4   b  via the data bus  2 . The actual position values  15   a  and  15   b  are then controlled in accordance with the position setpoints input by the controller  1  and the machine axes are moved in this way. 
   To this extent, the embodiment according to  FIG. 2  corresponds to the embodiment according to  FIG. 1 . In contrast to the embodiment according to  FIG. 1 , however, the magnetic spindle bearing arrangement  23  in the drive system according to the invention according to  FIG. 2  is integrated in the drive system. For each magnetic bearing  11   c ,  11   d ,  11   e ,  11   f  and  11   g , a respectively associated further drive device  3   c ,  3   d ,  3   e ,  3   f  and  3   g  for activating a respectively associated bearing  11   c ,  11   d ,  11   e ,  11   f  and  11   g  is provided. In an analogous manner to the drive devices  3   a  and  3   b , each of these five further drive devices  3   c ,  3   d ,  3   e ,  3   f  and  3   g  has a respectively associated control device  4   c ,  4   d ,  4   e ,  4   f  and  4   g  and a respectively associated power converter  5   c ,  5   d ,  5   e ,  5   f  and  5   g . The control devices and the power converters in this case need not necessarily be accommodated in a common housing, but may also be realized in the form of separate subassemblies. Just as in the case of the drive devices  3   a  and  3   b , the further drive devices  3   c ,  3   d ,  3   e ,  3   f  and  3   g , in particular the control devices  4   c ,  4   d ,  4   e ,  4   f  and  4   g , are connected to the controller  1  via a data bus  2  for the exchange of data. The control devices  4   c ,  4   d ,  4   e ,  4   f  and  4   g  are connected to the respectively associated power converters  5   c ,  5   d ,  5   e ,  5   f  and  5   g  for the exchange of data, which is indicated by double arrows  6   c ,  6   d ,  6   e ,  6   f  and  6   g . The control devices  4   c ,  4   d ,  4   e ,  4   f  and  4   g  activate the respectively associated power converters  5   c ,  5   d ,  5   e ,  5   f  and  5   g , which in turn activate the respectively associated magnetic bearings  11   c ,  11   d ,  11   e ,  11   f  and  11   g.    
   In the embodiment according to  FIG. 2 , the further drive devices  3   c ,  3   d ,  3   e ,  3   f  and  3   g  which serve to activate the magnetic bearings  11   c ,  11   d ,  11   e ,  11   f  and  11   g  have hardware identical to that of the drive devices  3   a  and  3   b  which serve for the activation of the drive motors  7   a  and  7   b  for moving the machine axes of the machine. This standardized hardware results in greater reliability and availability of the drive system according to the invention compared with conventional drive systems. At the same time, the costs for procuring the drive devices are reduced. The integrated, uniform control structure reduces the labor cost during start-up and maintenance. 
   Commercially available power converters for activating drive motors are of 3-phase design as a rule. However, the magnetic bearings of the magnetic spindle bearing arrangement  23  according to  FIG. 2  are of electrical 2-phase design. The power converters  5   c ,  5   d ,  5   e ,  5   f  and  5   g  are connected to the respectively associated magnetic bearings  11   c ,  11   d ,  11   e ,  11   f  and  11   g  via 2-phase lines  8   c ,  8   d ,  8   e ,  8   f  and  8   g . The third phase not used is indicated by a respective stroke in  FIG. 2  at the power converters  5   c ,  5   d ,  5   e ,  5   f  and  5   g . The control devices  4   c ,  4   d ,  4   e ,  4   f  and  4   g  are in this case set in such a way that the two respective current-carrying phases of the power converters  5   c ,  5   d ,  5   e ,  5   f  and  5   g  have a current of identical magnitude but opposite sign. The power converters  5   c ,  5   d ,  5   e ,  5   f  and  5   g  may then be regarded as controllable power sources, to which the magnetic bearings  11   c ,  11   d ,  11   e ,  11   f  and  11   g  of the magnetic spindle bearing arrangement  23  are connected. With this procedure, the existing hardware of the third de-energized phase is certainly not used, but it has the great advantage that standard drive devices, in particular standard power converters, can be used, which are very cost-effective due to their large scale manufacture. 
   If the control devices  4   c ,  4   d ,  4   e ,  4   f  and  4   g  are designed as control devices which normally serve to control motors, then the requirement that two respective current-carrying phases of a power converter are to have a current of identical magnitude but opposite sign can be achieved especially simply by virtue of the fact that, for example, the commutation angle, required for the control device, for controlling a normally connected motor is set to a fixed, only slightly variable value inside the control device, the fixed commutation angle in the process being selected in such a way that the current only flows in two phases of the power converter and the third phase is de-energized. 
   If, as in the exemplary embodiment according to  FIG. 2 , commercially available drive motors are used, as are normally used for activating the drive motors for the machine axis of the machines, their control devices in particular can often process only incremental encoder signals. Since the actual position encoders  12   c ,  12   d ,  12   e ,  12   f  and  12   g  which measure the position of the rotor spindle  10  output respectively associated analog actual position signals  15   c ,  15   d ,  15   e ,  15   f  and  15   g , said signals must be converted into incremental actual position signals  24   c ,  24   d ,  24   e ,  24   f  and  24   g  before they can be fed to the respectively associated control devices  4   c ,  4   d ,  4   e ,  4   f  and  4   g . To this end, the analog actual position signals  15   c ,  15   d ,  15   e ,  15   f  and  15   g  are fed from the respectively associated actual position encoders  12   c ,  12   d ,  12   e ,  12   f  and  12   g  to a signal converter  14 , which converts the analog actual position signals  15   c ,  15   d ,  15   e ,  15   f  and  15   g  into incremental actual position signals  24   c ,  24   d ,  24   e ,  24   f  and  24   g  and feeds them to the respectively associated control devices  4   c ,  4   d ,  4   e ,  4   f  and  4   g  as input variables. 
   Owing to the fact that, in the drive system according to the invention, all the drive devices can communicate with the controller  1 , the geometric manipulating range of the magnetic spindle bearing arrangement  23  can be actively included in the motion guidance of the machine axes. This is especially appropriate, for example, when actively vibration-damping measures are to be realized, for example for stabilizing a tool. Furthermore, due to this measure, the state of the magnetic spindle bearing arrangement  23  can be diagnosed to the full extent by the controller  1 . This enables very meaningful information from the magnetic spindle bearing arrangement  23  to be included in processes, for example for monitoring for tool fracture, at no extra cost. 
   The interconnected control structure reduces the labor cost during start-up and maintenance. The standardized hardware of the drive devices permits an increase in the reliability and availability of the drive system according to the invention, with at the same time a reduction in the costs for procuring the control devices and power converters for the magnetic spindle bearing arrangement. 
   In the exemplary embodiment according to  FIG. 2 , all the drive devices, in particular all the power converters, are connected to a common grid power supply device  19  via a supply line  20  for the electrical power supply. In conventional drive systems, in which the magnetic spindle bearing arrangement is not integrated in the drive system, separate grid power supply devices are often used for the power supply for the drive devices  3   a  and  3   b  for activating the drive motors  7   a  and  7   b  and for the performance module  16  according to  FIG. 1 , which has an adverse effect with regard to desired standardized hardware. 
   A machine tool  21  in which the drive system  22  according to the invention is integrated is shown in  FIG. 3  in the form of a block diagram. Instead of the machine tool  21 , however, a production machine or a robot could also be formed with the drive system  22  according to the invention.