Turbomolecular Pump with a Flexible Mount

Abstract

The flexibly-mounted turbomolecular pump comprises a leaktight casing mounted on a structure via a mechanical damper, a vertical support driven by an electric motor, radial magnetic bearings, an axial magnetic bearing, radial detectors, an axial detector, an emergency mechanical bearing, and a control module comprising power supply circuits and servo-control circuits for the axial and radial magnetic bearings. The servo-control circuits present low stiffness and include filter circuits for defining a limited passband. The control module comprises a comparator unit for detecting abnormally large movements of the rotor from signals delivered by the axial and radial detectors, which movements are greater than predetermined thresholds. The servo-control circuits include a restabilization network and a unit for selectively activating the restabilization network during a predetermined duration after a time at which the crossing of at least one of the predetermined thresholds is detected during a movement of the rotor.

1 . A flexibly-mounted turbomolecular pump comprising a leaktight casing designed in such a manner as to be capable of being mounted on a structure via a mechanical damper, a vertical support secured to the casing and located therein for supporting a hollow rotor fitted with fins and driven in rotation by an electric motor, at least first and second radial magnetic bearings mounted on the support,
 at least one axial magnetic bearing mounted on the support, radial detectors for detecting the radial position of the rotor, at least one axial detector for detecting the axial position of the rotor, at least one emergency mechanical bearing, and a control module including at least circuits for powering the electric motor and the axial and radial magnetic bearings, and servo-control circuits for servo-controlling the axial and radial magnetic bearings suitable for correcting any movement of the rotor in translation along three axes xyz in an orthonormal frame of reference and any tilting relative to two tilt axes;   wherein the servo-control circuits present low stiffness and include filter means for filtering the signals received by said servo-control circuits to define a limited passband, in that the control module includes a comparator unit for detecting abnormally large movements of the rotor from the signals delivered by the axial and radial detectors, said movements being greater than predetermined thresholds Sxd, Syd, Szd, Sxb, Syb relative to said three axes xyz of an orthonormal frame of reference and relative to said two tilt axes, and wherein the servo-control circuits include a restabilization network and activation means for selectively activating the restabilization network to activate said stabilization network for a predetermined duration Δt after a time t 1  at which the crossing of at least one of said predetermined thresholds was detected during a movement of the rotor.   
     
     
         2 . The pump according to  claim 1 , wherein said predetermined duration Δt for selective activation of the restabilization network is settable. 
     
     
         3 . The pump according to  claim 1 , wherein said predetermined duration Δt of selective activation of the restabilization network lies in the range 0.5 s to 5 s. 
     
     
         4 . The pump according to  claim 1 , wherein said predetermined duration Δt for selective activation of the restabilization network is fixed. 
     
     
         5 . The pump according to  claim 1 , wherein the predetermined thresholds Sxd, Syd, Szd, Sxb, Syb relative to said three axes xyz of an orthonormal frame of reference and relative to said two tilt axes are settable. 
     
     
         6 . The pump according to  claim 1 , wherein the predetermined thresholds Sxd, Syd, Szd, Sxb, Syb relative to said three axes xyz of an orthonormal frame of reference and relative to said two tilt axes lie in the range 25% to 40% of the maximum possible movement of the rotor in the emergency mechanical bearing. 
     
     
         7 . The pump according to  claim 1 , wherein said comparator unit and said means for selectively activating the restabilization network are included in a digital signal processor DSP of the pump.