EP3244067B1 - Vacuum pump and method for reducing a residual imbalance in a vacuum pump - Google Patents

Description

The present invention relates to a vacuum pump, in particular a turbomolecular pump, with a rotor shaft rotatable about an axis of rotation and an electric motor which comprises a stator fixed to a housing of the vacuum pump and a rotor coupled to the rotor shaft, the stator and the rotor for rotatingly driving the rotor shaft are provided. The present invention also relates to a method for reducing a residual unbalance of a rotor shaft of a vacuum pump that can be rotated about an axis of rotation, in particular a turbomolecular pump.

A vacuum pump of the type mentioned is known in principle. In such a vacuum pump, the rotor shaft is normally balanced before the vacuum pump is put into operation, in particular in order to reduce the risk of damage to the rotor shaft and to the bearings of the rotor shaft. Normally there remains a so-called residual unbalance after balancing the rotor shaft, which according to DIN ISO 1925: 2001 is an unbalance of any kind that remains after balancing. The initial balancing of the rotor shaft, which according to the standard mentioned is an unbalance of any kind that is present in the rotor before balancing, can thus be reduced to a remaining residual unbalance by the balancing process. With the residual unbalance, the vacuum pump can normally be started up without any problems. The residual unbalance is based in particular on a mass defect on the rotor shaft, which can be described as a punctiform mass m at a distance r from the axis of rotation of the rotor shaft. The residual unbalance causes a force F _RU = m * r * ω ² , where ω is the angular velocity with which the rotor shaft rotates. Due to the residual unbalance Therefore, during operation of the vacuum pump at the angular velocity ω, the force F _{RU is} generated on the rotor shaft, which rotates synchronously with the rotor shaft and is directed radially outwards in relation to the axis of rotation of the rotor shaft.

A vacuum pump according to the preamble of claim 1 and a method for balancing a rotor of a vacuum pump are in the EP 2 881 591 A2 and in the EP 2 520 807 A2 disclosed.

It may be desirable to further reduce the residual unbalance in a vacuum pump, for example to extend the life of the rotor shaft and / or its bearings. A method for improving the concentricity of a rotor of a vacuum pump is shown in WO 02/07289 A2 disclosed.

The object of the present invention is therefore to reduce a residual unbalance of a rotor shaft of a vacuum pump.

The object is achieved by a vacuum pump with the features of claim 1 or by a method with the features of claim 8. Preferred developments and embodiments of the invention are specified in the dependent claims.

A vacuum pump according to the invention comprises a rotor shaft rotatable about an axis of rotation and an electric motor with a stator fixed to a housing of the vacuum pump and a rotor coupled to the rotor shaft, the stator and the rotor being provided for rotatingly driving the rotor shaft, the electric motor, to be precise whose stator is designed in such a way that it causes a force which rotates synchronously with the rotor shaft, in particular acts in the radial direction, on the rotor shaft, in particular on the rotor coupled to the rotor shaft, a force being generated by the force residual imbalance of the rotor shaft rotating synchronously can be at least approximately compensated for.

In the vacuum pump according to the invention, during operation of the vacuum pump by means of the electric motor, the residual unbalance still present after balancing or the force F _RU caused by the residual unbalance and rotating synchronously with the rotor shaft can be at least approximately compensated for by the force generated by the electric motor. As a result, the rotor shaft runs even less unbalanced, which can increase the service life of the rotor shaft and its bearings.

Since the electric motor generates the force to compensate for the residual unbalance, this force can be adapted to changing conditions in the vacuum pump by correspondingly controlling the electric motor. A vacuum pump according to the invention thus has essentially the same properties over a relatively long operating period as far as the unbalance condition is concerned, for example because an increase in the residual unbalance, for example caused by wear in the bearing, at least to a certain extent by that of the electric motor generated force can be compensated. In addition, it can be achieved that each vacuum pump according to the invention has at least approximately the same state of balance and thus the same state in terms of vibration.

The rotor of an electric motor is also referred to as an armature or a rotor of the electric motor. A so-called PM synchronous motor is preferably used as the electric motor, where PM stands for permanent magnet. With such an electric motor, permanent magnets are arranged in the rotor, which form the rotor or rotor-side magnetic poles of the electric motor. On the stator side, the magnetic poles are realized using current conductor windings. PM synchronous motors are known from the prior art.

The vacuum pump preferably has at least one sensor, in particular an acceleration sensor, for measuring the residual unbalance of the rotor shaft. The residual unbalance can thus be measured during operation of the vacuum pump and the measured value obtained can be used, for example, to control the electric motor.

The at least one sensor can be arranged in a plane which runs through the stator of the electric motor and at least substantially perpendicular to the rotor shaft. The residual unbalance can thus be detected in a balancing plane running through the stator of the electric motor and at least approximately compensated for.

The sensor is preferably arranged on the rotor of the electric motor. The sensor can alternatively be arranged somewhat above or below the rotor on the rotor shaft. The residual unbalance can therefore be detected in the area of the electric motor.

The at least one sensor can also be arranged in the region of a bearing that serves to support the rotor shaft. The detection of the residual unbalance in the area of the bearing has the advantage that this residual unbalance can be at least approximately compensated for by the electric motor. Damage to the bearing due to the residual unbalance can thereby be avoided particularly effectively.

According to the invention, at least one operating parameter of the electric motor for adjusting the force according to the amount and / or phase position and / or for adjusting the rotational speed of the force about the axis of rotation can be adjusted by means of a control. By correctly setting the at least one operating parameter of the electric motor, the force can thus be generated in such a way that it rotates around the axis of rotation synchronously with the rotational speed of the rotor shaft and thus with the residual unbalance, and thereby the residual unbalance is at least approximately compensated. The term "phase position" here refers to the direction of the force in relation to the angular position of the rotor shaft. To compensate for the residual unbalance, the phase position of the force is preferably set so that the force of the residual unbalance is directed in the opposite direction.

For example, at least one alternating current, which is fed into the electric motor, can be set by means of the control so that the magnetic field generated between the stator and the rotor of the electric motor causes a resulting magnetic force on the rotor, which is synchronous with the rotational speed of the rotor shaft and thus revolves with the residual unbalance around the axis of rotation and thereby at least approximately compensates for the residual unbalance, that is to say at least approximately has the amount of the residual unbalance and is counter-directed. The setting of the alternating current can include: setting the amplitude, setting the frequency and / or setting the phase of the alternating current. The electric motor and / or a control for the electric motor can be equipped with appropriate means for adjusting the amplitude, frequency and phase.

The controller can be designed to iteratively adjust the at least one operating parameter of the electric motor as a function of a residual unbalance of the rotor shaft, in particular until the residual unbalance fulfills a predetermined criterion, in particular assumes a minimum value or falls below a predetermined threshold value. Thus, for example using an iterative method, the at least one operating parameter of the electric motor and thus the force generated by the electric motor can be adjusted until the simultaneously measured residual unbalance fulfills the criterion.

The stator has, as seen in the circumferential direction of the stator, staggered auxiliary windings, and the controller can use each of the auxiliary windings to generate a magnetic field with an electrical Supply current, in particular an alternating current, in order to generate the force at least essentially through the interaction of the magnetic fields generated by the auxiliary windings with the magnetic field of the rotor of the electric motor. A number of auxiliary windings which can be energized are thus provided on the stator, with which respective magnetic fields can be generated which interact with the magnetic field on the rotor side. The desired force on the rotor or on the rotor shaft, which compensates for the residual unbalance, can thus be brought about by suitably setting the currents, in particular their respective amplitude, phase and frequency.

For this purpose, it is provided according to the invention that the stator has four auxiliary windings which are arranged offset from one another by at least approximately 90 degrees in the circumferential direction. By means of such a configuration, the desired force for synchronizing the residual unbalance, which rotates synchronously with the residual unbalance, can be generated with relatively little effort.

Each auxiliary winding can be arranged on a pole piece provided on the stator. The pole pieces can serve in particular as carriers for the auxiliary windings.

The controller is preferably designed to adjust the currents through the auxiliary windings, in particular as a function of the respective angular position of the rotor shaft and / or as a function of a measured residual unbalance, in order to generate the force for at least approximately compensating for the residual unbalance.

The vacuum pump can have at least one sensor for measuring the angular position of the rotor shaft. This means that the angular position of the rotor shaft can be permanently recorded during pump operation.

The vacuum pump is preferably a turbomolecular pump. Since the rotor shaft of a turbomolecular pump is normally operated at a very high speed, for example at a speed of a few tens of thousands of revolutions per minute, the at least approximately compensated residual unbalance contributes, for example, to an extension of the service life of the vacuum pump.

The invention also relates to a method for reducing a residual imbalance of a rotor shaft of a vacuum pump which can be rotated about an axis of rotation.

Fig. 1

eine perspektivische Ansicht einer Turbomolekularpumpe,

Fig. 2

eine Ansicht der Unterseite der Turbomolekularpumpe von Fig. 1,

Fig. 3

einen Querschnitt der Turbomolekularpumpe längs der in Fig. 2 gezeigten Schnittlinie A-A,

Fig. 4

eine Querschnittsansicht der Turbomolekularpumpe längs der in Fig. 2 gezeigten Schnittlinie B-B,

Fig. 5

eine Querschnittsansicht der Turbomolekularpumpe längs der in Fig. 2 gezeigten Schnittlinie C-C,

Fig. 6

eine Querschnittsansicht der Turbomolekularpumpe von Fig. 1 in einer durch den Elektromotor verlaufenden Schnittebene, und

Fig. 7

ein Blockdiagramm einer erfindungsgemäßen Vakuumpumpe.

The invention is described below by way of example using advantageous embodiments with reference to the attached figures. Each shows schematically:

Fig. 1

a perspective view of a turbomolecular pump,

Fig. 2

a bottom view of the turbomolecular pump of FIG Fig. 1 ,

Fig. 3

a cross section of the turbomolecular pump along the in Fig. 2 shown section line AA,

Fig. 4

a cross-sectional view of the turbomolecular pump along the in Fig. 2 shown section line BB,

Fig. 5

a cross-sectional view of the turbomolecular pump along the in Fig. 2 shown section line CC,

Fig. 6

a cross-sectional view of the turbomolecular pump of Fig. 1 in a cutting plane running through the electric motor, and

Fig. 7

a block diagram of a vacuum pump according to the invention.

In the Fig. 1 The turbomolecular pump 111 shown comprises a pump inlet 115 surrounded by an inlet flange 113, to which a recipient (not shown) can be connected in a manner known per se. The gas from the recipient can be sucked out of the recipient via the pump inlet 115 and conveyed through the pump to a pump outlet 117 to which a backing pump, such as a rotary vane pump, can be connected.

The inlet flange 113 forms in accordance with the orientation of the vacuum pump Fig. 1 the upper end of the housing 119 of the vacuum pump 111. The housing 119 comprises a lower part 121, on which an electronics housing 123 is arranged on the side. Electrical and / or electronic components of the vacuum pump 111 are accommodated in the electronics housing 123, for example for operating an electric motor 125 arranged in the vacuum pump. Several connections 127 for accessories are provided on the electronics housing 123. Also are a data interface 129, for example in accordance with the RS485 standard, and a power supply connection 131 are arranged on the electronics housing 123.

A flood inlet 133, in particular in the form of a flood valve, is provided on the housing 119 of the turbomolecular pump 111, via which the vacuum pump 111 can be flooded. In the area of the lower part 121 there is also a sealing gas connection 135, which is also referred to as a purge gas connection, via which purge gas to protect the electric motor 125 (see, for example, FIG Fig. 3 ) can be brought into the engine compartment 137, in which the electric motor 125 is housed in the vacuum pump 111, before the gas conveyed by the pump. Furthermore, two coolant connections 139 are arranged in the lower part 121, one of the coolant connections being provided as an inlet and the other coolant connection being provided as an outlet for coolant, which can be guided into the vacuum pump for cooling purposes.

The lower side 141 of the vacuum pump can serve as a standing surface, so that the vacuum pump 111 can be operated standing on the underside 141. However, the vacuum pump 111 can also be fastened to a recipient via the inlet flange 113 and can thus be operated in a manner of hanging. In addition, the vacuum pump 111 can be designed so that it can also be operated if it is aligned in a different way than in FIG Fig. 1 is shown. Embodiments of the vacuum pump can also be realized, in which the underside 141 cannot be arranged facing downwards, but turned to the side or directed upwards.

At the bottom 141, which in Fig. 2 is shown, various screws 143 are also arranged, by means of which components of the vacuum pump, which are not further specified here, are fastened to one another. For example, a bearing cover 145 is attached to the underside 141.

Fastening bores 147 are also arranged on the underside 141, via which the pump 111 can be fastened, for example, to a support surface.

In the Figures 2 to 5 A coolant line 148 is shown, in which the coolant introduced and discharged via the coolant connections 139 can circulate.

Like the sectional views of the Figures 3 to 5 show, the vacuum pump comprises a plurality of process gas pump stages for conveying the process gas present at the pump inlet 115 to the pump outlet 117.

A rotor 149 is arranged in the housing 119 and has a rotor shaft 153 rotatable about an axis of rotation 151.

The turbomolecular pump 111 comprises a plurality of turbomolecular pump stages connected in series with one another with effective pumping, with a plurality of radial rotor disks 155 fastened to the rotor shaft 153 and stator disks 157 arranged between the rotor disks 155 and fixed in the housing 119. A rotor disk 155 and an adjacent stator disk 157 each form a turbomolecular one Pump stage. The stator disks 157 are held at a desired axial distance from one another by spacer rings 159.

The vacuum pump also comprises Holweck pump stages which are arranged one inside the other in the radial direction and have a pumping effect and are connected in series with one another. The rotor of the Holweck pump stages comprises a rotor hub 161 arranged on the rotor shaft 153 and two cylindrical jacket-shaped Holweck rotor sleeves 163, 165 fastened to and supported by the rotor hub 161, which are oriented coaxially to the axis of rotation 151 and nested one inside the other in the radial direction. Furthermore, two cylindrical jacket-shaped Holweck stator sleeves 167, 169 are provided, which are also oriented coaxially to the axis of rotation 151 and are nested one inside the other in the radial direction.

The pump-active surfaces of the Holweck pump stages are formed by the lateral surfaces, that is to say by the radial inner and / or outer surfaces, of the Holweck rotor sleeves 163, 165 and of the Holweck stator sleeves 167, 169. The radial inner surface of the outer Holweck stator sleeve 167 lies opposite the radial outer surface of the outer Holweck rotor sleeve 163, forming a radial Holweck gap 171 and forms the first Holweck pumping stage following the turbomolecular pumps. The radial inner surface of the outer Holweck rotor sleeve 163 faces the radial outer surface of the inner Holweck stator sleeve 169 with the formation of a radial Holweck gap 173 and forms a second Holweck pump stage with the latter. The radial inner surface of the inner Holweck stator sleeve 169 lies opposite the radial outer surface of the inner Holweck rotor sleeve 165, forming a radial Holweck gap 175, and forms the third Holweck pump stage with the latter.

At the lower end of the Holweck rotor sleeve 163, a radially extending channel can be provided, via which the radially outer Holweck gap 171 is connected to the central Holweck gap 173. In addition, a radially extending channel can be provided at the upper end of the inner Holweck stator sleeve 169, via which the central Holweck gap 173 is connected to the radially inner Holweck gap 175. As a result, the nested Holweck pump stages are connected in series. At the lower end of the radially inner Holweck rotor sleeve 165, a connection channel 179 to the outlet 117 can also be provided.

The aforementioned pump-active surfaces of the Holweck stator sleeves 163, 165 each have a plurality of Holweck grooves running spirally around the axis of rotation 151 in the axial direction, while the opposite ones The lateral surfaces of the Holweck rotor sleeves 163, 165 are smooth and drive the gas to operate the vacuum pump 111 in the Holweck grooves.

A roller bearing 181 in the area of the pump outlet 117 and a permanent magnet bearing 183 in the area of the pump inlet 115 are provided for the rotatable mounting of the rotor shaft 153.

In the area of the roller bearing 181, a conical injection nut 185 is provided on the rotor shaft 153 with an outer diameter increasing toward the roller bearing 181. The spray nut 185 is in sliding contact with at least one scraper of an operating fluid reservoir. The operating medium storage comprises a plurality of absorbent disks 187 stacked one on top of the other, which are provided with an operating medium for the rolling bearing 181, e.g. are soaked with a lubricant.

During the operation of the vacuum pump 111, the operating medium is transferred by capillary action from the operating medium storage via the wiper to the rotating spray nut 185 and, as a result of the centrifugal force along the spray nut 185, is conveyed in the direction of the increasing outer diameter of the spray nut 185 to the roller bearing 181, where it e.g. fulfills a lubricating function. The roller bearing 181 and the operating fluid reservoir are enclosed in the vacuum pump by a trough-shaped insert 189 and the bearing cover 145.

The permanent magnet bearing 183 comprises a bearing half 191 on the rotor side and a bearing half 193 on the stator side, each of which comprises an annular stack of a plurality of permanent magnetic rings 195, 197 stacked on one another in the axial direction. The ring magnets 195, 197 lie opposite one another to form a radial bearing gap 199, the rotor-side ring magnets 195 being arranged radially on the outside and the stator-side ring magnets 197 being arranged radially on the inside. The magnetic field present in the bearing gap 199 causes magnetic repulsive forces between the ring magnets 195, 197, which are radial Mount the rotor shaft 153. The rotor-side ring magnets 195 are carried by a carrier section 201 of the rotor shaft 153 which surrounds the ring magnets 195 radially on the outside. The stator-side ring magnets 197 are carried by a stator-side support section 203 which extends through the ring magnets 197 and is suspended from radial struts 205 of the housing 119. Parallel to the axis of rotation 151, the rotor-side ring magnets 195 are fixed by a cover element 207 coupled to the carrier section 203. The stator-side ring magnets 197 are fixed parallel to the axis of rotation 151 in one direction by a fastening ring 209 connected to the carrier section 203 and a fastening ring 211 connected to the carrier section 203. A plate spring 213 can also be provided between the fastening ring 211 and the ring magnet 197.

An emergency or catch bearing 215 is provided within the magnetic bearing, which runs empty without contact during normal operation of the vacuum pump 111 and only comes into engagement with an excessive radial deflection of the rotor 149 relative to the stator in order to provide a radial stop for the rotor 149 to form, since a collision of the rotor-side structures with the stator-side structures is prevented. The catch bearing 215 is designed as an unlubricated roller bearing and forms a radial gap with the rotor 149 and / or the stator, which causes the catch bearing 215 to be disengaged in normal pumping operation. The radial deflection at which the catch bearing 215 engages is dimensioned large enough that the catch bearing 215 does not engage during normal operation of the vacuum pump, and at the same time is small enough so that the rotor-side structures collide with the stator-side structures under all circumstances is prevented.

The vacuum pump 111 comprises the electric motor 125 for rotatingly driving the rotor 149. The armature of the electric motor 125 is formed by the rotor 149, whose rotor shaft 153 extends through the motor stator 217. A permanent magnet arrangement can be arranged radially on the outside or embedded on the section of the rotor shaft 153 which extends through the motor stator 217. Between the motor stator 217 and the section of the rotor 149 which extends through the motor stator 217 there is an intermediate space 219 which comprises a radial motor gap, via which the motor stator 217 and the permanent magnet arrangement for transmitting the drive torque can magnetically influence one another.

The motor stator 217 is fixed in the housing within the motor space 137 provided for the electric motor 125. A sealing gas, which is also referred to as a purge gas and which can be, for example, air or nitrogen, can enter the engine compartment 137 via the sealing gas connection 135. The electric motor 125 can be used before the process gas, e.g. protected against corrosive parts of the process gas. The engine compartment 137 can also be evacuated via the pump outlet 117, i.e. in the engine compartment 137 there is at least approximately the vacuum pressure caused by the backing pump connected to the pump outlet 117.

A so-called labyrinth seal 223, which is known per se, can also be provided between the rotor hub 161 and a wall 221 delimiting the engine compartment 137, in particular in order to achieve a better seal of the engine compartment 217 with respect to the radially outside Holweck pump stages.

Fig. 6 shows a cross-sectional view in a sectional plane running through the electric motor 125, which also runs perpendicular to the rotor shaft 153. The rotor shaft 153 extends through the electric motor 125. As already mentioned above, the armature or rotor of the electric motor 125 is formed by the rotor shaft 153. The section of the rotor shaft 153, which extends through the stator 217 of the electric motor 125, points radially on the outside or embedded permanent magnets, which form the rotor-side magnetic poles of the electric motor 125, which in Fig. 6 is shown by the indicated north pole N and the indicated south pole P. Normally, the magnetic poles on the rotor side do not consist of a single pair of north and south poles, but of several pole pairs.

On the motor stator 217 side, four auxiliary windings 11 are arranged on pole pieces 13 provided on the stator 217. The auxiliary windings 11 are arranged in the circumferential direction U of the stator 217 offset by 90 degrees to one another. Like the block diagram of the Fig. 7 shows, the turbomolecular pump also includes a controller 15 for actuating the electric motor 125, which is shown, for example, in FIG Fig. 1 shown electronics housing 123 is housed.

The controller 15 can supply each of the auxiliary windings 11 with an alternating current, the amplitude, phase and / or frequency of which can be set by the controller 15. If a respective alternating current flows through the auxiliary windings 11, a magnetic field is generated from each auxiliary winding 11 in a manner known per se, which magnetic field interacts with the rotor-side magnetic field of the permanent magnets. Each magnetic field generated by an auxiliary winding 11 is dependent on the current flowing through the respective auxiliary winding 11 and can thus be changed by changing the amplitude, phase and / or frequency of the current. The interaction between the magnetic fields generated by the auxiliary windings 11 and the rotor-side magnetic field can generate a force on the rotor or on the rotor shaft 153. The force generated depends on the amount and direction as well as its rotational speed depending on the magnetic fields generated by the auxiliary windings 11. The force generated is therefore also dependent on the respective currents through the auxiliary windings 11.

The controller 15 is now designed such that it adjusts the electrical currents through the auxiliary windings 11 as a function of a residual unbalance of the rotor shaft 153, which is measured by means of at least one sensor 17, such that the force generated is synchronous with the rotor shaft 153 and thus synchronously circulates with the residual unbalance and at least approximately compensates for the residual unbalance. The residual unbalance can thus be reduced by means of the electric motor 125 or, ideally, eliminated.

An iterative method is used to adjust the currents through the auxiliary windings 11. In a preferred embodiment of this method, the rotational speed of the rotor shaft 153 and thus the residual unbalance is determined, for example by means of a sensor (not shown) fitted in the vacuum pump 111. The frequency of the alternating currents through the auxiliary windings 11 is then set such that, according to the invention, the force generated revolves around the axis of rotation 151 at the rotational speed. Furthermore, the residual unbalance is determined by means of the at least one sensor 17, preferably as a function of the angular position of the rotor shaft 153, which is measured, for example, by means of an angular position sensor, also not shown. A starting value of the amplitude and a starting value of the phase are set individually for each current through the auxiliary windings 11 such that the force generated approximately compensates for the residual unbalance. The starting values can be determined from empirically obtained data. The start values are then changed iteratively, preferably until the measured residual unbalance fulfills a predefined criterion, for example lies below a predefined threshold value or assumes a minimum.

Reference list

11

Auxiliary winding

13

Pole piece

15

control

17th

sensor

111

Turbomolecular pump

113

Inlet flange

115

Pump inlet

117

Pump outlet

119

casing

121

Lower part

123

Electronics housing

125

Electric motor

127

Accessory connection

129

Data interface

131

Power connector

133

Flood inlet

135

Sealing gas connection

137

Engine compartment

139

Coolant connection

141

bottom

143

screw

145

Bearing cover

147

Mounting hole

148

Coolant line

149

rotor

151

Axis of rotation

153

Rotor shaft

155

Rotor disc

157

Stator disc

159

Spacer ring

161

Rotor hub

163

Holweck rotor sleeve

165

Holweck rotor sleeve

167

Holweck stator sleeve

169

Holweck stator sleeve

171

Holweck gap

173

Holweck gap

175

Holweck gap

179

Connecting channel

181

roller bearing

183

Permanent magnet bearings

185

Spray nut

187

disc

189

commitment

191

half of the bearing on the rotor side

193

stator side bearing half

195

Ring magnet

197

Ring magnet

199

Bearing gap

201

Beam section

203

Beam section

205

radial strut

207

Cover element

209

Support ring

211

Mounting ring

213

Disc spring

215

Emergency or catch camp

217

Motor stator

219

Space

221

Wall

223

Labyrinth seal

N

Norpol

S

South Pole

U

Circumferential direction

Claims (10)

1. A vacuum pump, in particular a turbomolecular pump, comprising a rotor shaft (153) rotatable about an axis of rotation (151); and
   an electric motor (125) having a stator (217) fixed to a housing (119) of the vacuum pump (111) and having a rotor coupled to the rotor shaft (153),
   wherein the stator (217) and the rotor are provided for a rotating driving of the rotor shaft (153),
   characterized in that
   the electric motor (125), and indeed its stator (217), is configured such that it brings about a force on the rotor shaft (153), in particular on the rotor coupled to the rotor shaft (153), said force revolving synchronously with the rotor shaft (153) and in particular acting in the radial direction, with a residual imbalance of the rotor shaft (153) which likewise revolves synchronously being able to be at least approximately compensated by means of the force, and with at least one operating parameter of the electric motor (125) for setting the force by magnitude and/or phasing and/or for setting the revolution speed of the force about the axis of rotation (151) being adjustable by means of a control (15), with the stator having auxiliary windings (11) arranged offset from one another, viewed in the peripheral direction (U) of the stator (217), with the control (15) being able to supply each of the auxiliary windings (11) with an electric current to produce a magnetic field in order to produce the force at least substantially through an interaction of the magnetic fields produced by the auxiliary windings (11) with the magnetic field of the rotor of the electric motor (125), and with the stator (217) having four auxiliary windings (11) which are arranged offset from one another by at least approximately 90 degrees in the peripheral direction (U).
2. A vacuum pump in accordance with claim 1,
   characterized in that
   it has at least one sensor (17), in particular an acceleration sensor, for measuring the residual imbalance of the rotor shaft (153).
3. A vacuum pump in accordance with claim 2,
   characterized in that
   the sensor (17) is arranged in a plane which extends through the stator (217) of the electric motor (125) and at least substantially perpendicular to the rotor shaft (153), with, preferably, the sensor (17) being arranged at the rotor of the electric motor (125).
4. A vacuum pump in accordance with at least one of the preceding claims,
   characterized in that
   the control (15) is configured to iteratively adjust the at least one operating parameter in dependence on a residual imbalance of the rotor shaft (153), in particular for so long until the residual imbalance satisfies a specific criterion, in particular adopts a minimum value or falls below a predefined threshold value.
5. A vacuum pump in accordance with at least one of the preceding claims,
   
   characterized in that
   each auxiliary winding (11) is arranged on a pole shoe (13) provided at the stator (217).
6. A vacuum pump in accordance with at least one of the preceding claims,
   characterized in that
   the control (15) is configured to set the electric currents through the auxiliary windings (11), in particular in dependence on the respective angular position of the rotor shaft (153) and/or in dependence on a measured residual imbalance, in order to produce the force for an at least approximate compensation of the residual imbalance.
7. A vacuum pump in accordance with at least one of the preceding claims,
   characterized in that
   it has a sensor for measuring the angular position of the rotor shaft (153).
8. A method of reducing a residual imbalance of a rotor shaft (153), rotatable about an axis of rotation (151), of a vacuum pump (111), in particular of a turbomolecular pump, in particular in accordance with any one of the preceding claims,
   wherein the vacuum pump (111) has an electric motor (125) having a stator (217) fixed to a housing (119) of the vacuum pump (111) and having a rotor coupled to the rotor shaft (153) for driving the rotor shaft (153); and wherein, in the method,

   the rotor shaft (153) is driven such that it rotates at least substantially at a constant speed of rotation;

   a residual imbalance of the rotor shaft (153) is measured; and

   the electric motor (125), and indeed its stator (217), is driven such that it produces a force on the rotor shaft (153), in particular on the rotor coupled to the rotor shaft (153), said force revolving synchronously with the rotor shaft (153), in particular acting in the radial direction and at least approximately compensating the residual imbalance which likewise revolves synchronously;

   wherein the stator (217) has auxiliary windings (11) which are arranged offset from one another, viewed in the peripheral direction (U) of the stator (217), and which are supplied with an electric current to produce a respective magnetic field in order to produce the force at least substantially through the interaction of the magnetic fields produced by the auxiliary windings (11) with the magnetic field of the rotor of the electric motor (125); and

   wherein the electric current through each of the auxiliary windings (11) is set such that the force produced revolves synchronously with the rotor shaft (153) and at least approximately compensates the residual imbalance which likewise revolves synchronously and the setting of at least one electric current takes place iteratively.
9. A method in accordance with claim 8,
   characterized in that
   the residual imbalance is measured in a plane which extends through the stator (217) of the electric motor (125) and which extends perpendicular to the axis of rotation (151).
10. A method in accordance with claim 8 or claim 9,
    characterized in that,
    by adjusting at least one operating parameter of the electric motor (125), the force is adjusted, in particular iteratively adjusted, with respect to its magnitude and/or its phasing for so long until the residual imbalance satisfies a specific criterion, in particular adopts a minimum or falls below a predefined threshold value.

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