| 摘要 |
A turbo molecular pump including a magnetic bearing system which comprises a rotor consisting of an impeller connected to a shaft (1a) and a motor; a stator (2) positioned between the shaft (1a) and the impeller (1); radial magnetic bearings (21, 22, 23, 24), an active axial magnetic bearing (25, 26) and emergency bearings (10, 11) each provided between said rotor and said stator (2) is disclosed. The radial magnetic bearings (21, 22, 23, 24) comprise passive magnetic bearings provided on the rotor and the stator (2) respectively. The axial magnet bearing (25, 26) is disposed in the vicinity where the impeller (1) is connected to the shaft (1a). The emergency bearings (10, 11) are disposed on a low vacuum side with one (10) emergency bearing being positioned near the axial magnetic bearing (25, 26), and a diameter of the shaft (1a) is made smaller than an inside diameter of the emergency bearing (10) near the axial magnetic bearing (25, 26). By this arrangement, the number of control axis for controlling the position of the rotor is made only one, disassembling of the shaft and impeller is made easy and a contamination of the high vacuum side can be prevented. <IMAGE>
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