Patent GB-1257423-A (GB)
IPC: F16C39/06
Filed: 1970-04-11
Abstract: 1257423 Magnetic bearings K BODEN W GROTH and D SCHEFFER 11 April 1970 17295/70 Headings G3 R9D 68 8N 727 74 31X and 4 In an assembly of a rotor journalled in a stator by magnetic bearings for rotation about a substantially vertical axis without mechanical contact between the rotor and the stator, said rotor such as at 11, Fig.1, comprises ferromagnetic portions as at 17, 20 and a carrier magnet as at 21 acting upon at least one of said ferromagnetic portions for supporting said rotor, said carrier magnet producing a constant magnetic field with a vertical component for maintaining the rotor in a stable vertical position, said assembly including a stabilizing device as at 15 disposed on the stator at an upper zone for maintaining the axis of the rotor in a specified position, said stabilizing device comprising at least two contactless sensors as at 28 for measuring low and higher frequency deviations of the position of the rotor from a predetermined position and producing electrical sensor signals in accordance therewith, an electronic control device as at 31 for amplifying and phase displacing the sensor signals for producing for example in electromagnetic means 25 substantially radially directed magnetic fields controlled in accordance with said output signals and influencing at least one of said ferromagnetic portions on the rotor in such a way that a restoring force component is applied to the rotor to restore the rotor to said predetermined position and a damping force component is also applied to the rotor to counteract a lateral deflection brought about by the gyroscopic effect of the rotor and for damping such effect, said assembly further including means as at 14 disposed at a lower zone for at least damping of vibratory movements of the rotor by the use of magnetic fields. The sensors 28 comprise inductive pick-ups preferably responsive to movement of a ring 19 which may or may not be ferromagnetic. Opposed pairs of sensor windings 28 are arranged with two rectifiers in a bridge circuit Fig.4 (not shown) and the sensor signal is demodulated, amplified and phase-shifted (0-90 degrees depending on frequency of sensor signals) in a transistorized circuit illustrated in Fig.5 (not shown). By means of a potentiometer, the position of the axis of rotation of the rotor may be shifted. Alternatively, the sensors may comprise magneto-resistive plates 128 Fig.9 (not shown) in which case no carrier frequency is required. Similarly, magnetic diodes or transistors or Hall probes or other galvanomagnetic semi-conductor elements may be used or capacitive proximity detectors. The ferromagnetic rings may be formed of steel. The rings 20 may be annular laminations of transformer sheets insulated from one another or ferrite material. The ring 18 may be of titanium. The carrier magnet 21 may be a single annular magnet or a stack of such magnets Fig.6 (not shown) or an electromagnet Fig.7 (not shown) or an assembly of magnetic segments or a bar magnet projecting into the hollow rotor end Fig.8 (not shown). The electromagnetic means 25 may comprise four windings with their cores in the form of a cross or may be in the form of a stator of a D.C. motor Figs.7-11 (not shown). The electromagnetic means 25 may provide a rotating field to drive the rotor. In modifications, the sensors 28 may be placed on top of a carrier magnet Fig.6 (not shown) or adjacent larger diameter portions of the rotor 11 Fig.7 (not shown), the magnetic damping at the lower end may be provided Fig.8 (not shown) by a permanent annular magnet 42 and disc 44, identical carrier magnets may be provided top and bottom Fig.9 (not shown), the rotor may comprise an uninterrupted hollow cylinder of ferromagnetic material Fig.10 (not shown), triple bearings or stabilizing devices 25, 28 may be provided Fig.10 (not shown) to avoid bending oscillations in long rotors and the lower bearing may be raised to a position close to the carrier magnet 21 Fig.11 (not shown). The magnetic bearings may support the rotor of an axial vacuum or agressive media pump; various components being encased in gas-tight materials.