An active type magnetic bearing for controllably supporting a rotatable shaft made of a magnetic material is constructed such that a stator made of an annular formed laminated iron core is provided around the rotatable shaft, a number of slots are formed along an internal surface of the iron core, stator windings of a number of phases are wound so as to be settled in the slots, thin sheet-like permanent magnets magnetized radially to provide a number of poles are secured onto the internal surface of the annular formed iron core with a predetermined air gap maintained between the permanent magnets and the rotatable shaft, and the stator windings of each phase are so wound that upon energization, a magnetic field thereby produced enhances a magnetic field produced by one of the permanent magnets while it reduces a magnetic field produced by another permanent magnet provided at a position 180.degree. spaced apart from that one of the permanent magnets.
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of a copending application Ser. No. 810,065, filed Dec. 17, 1985, now abandoned.
A radial magnetic bearing system for use in turbomachinery, machine tools and so forth is disclosed. A rotary yoke made of a magnetic material is rigidly secured to a rotary shaft, and an electromagnet stator is rigidly secured to a casing. The stator is arranged to generate magnetic attraction forces radially at equi-angular spacings of 120.degree. within a plane perpendicular to the axis of the rotary shaft. Three displacement sensors are arranged such that each sensor measures displacement of the rotary shaft with respect to the casing in the direction of one of the three magnetic attraction forces, thus controlling the level of each magnetic attraction force.
According to the method of machining on ultra-precise surface of revolution (240) on a workpiece (204) held in position by means of a workpiece-carrier spindle assembly (1) whose spindle is mounted on a spindle slide (202) by means of active magnetic bearings, the natural frequencies of the bearing servo-control are adjusted to values which are less than about 80 Hz, and the speed of spindle rotation is adjusted to a value of about 20 Hz to about 75 Hz, the radial and axial positions of the spindle are selectively modified about a nominal position by applying variable reference voltages to the circuits controlling the magnetic bearings, said voltages being varied as a function of control signals which are delivered as a function of the position of the tool (207), and displacement of the spindle slide (202) is inhibited so long as the control signals are less than predetermined values lying within the dynamic range of the magnetic bearings. The invention is particularly suitable for machining atypical surfaces of revolution by copying a master template.
A radial, active magnetic bearing apparatus comprising at least three electromagnets which are distributedly arranged is excited by a three-phase rotary current controller.
The invention relates to an apparatus for the contact-free journalling of a rotor by rotary field machine stators. The rotary field machine stators are magnetically coupled, on the one hand, via the rotor of ferromagnetic material and, on the other hand, via a flux conduction ring of a ferromagnetic material and/or a housing of a ferromagnetic material. The radial magnetic bearing forces in the rotary field machine stators are produced in that means are present in the arrangement which produce magnetic unipolar fluxes flowing through the rotary field machine stators. Two-pole control fluxes are superimposed on the unipolar fluxes in the rotary field machine stators, and the control fluxes are controlled by the currents in two-pole rotary field windings. The position of the rotor is measured by position sensors. A control apparatus calculates the required phase currents as a result of the position signals and feeds the rotary field windings in such a manner that the rotor is held in suspension.
On the stationary side of a radial bearing constructed of a plurality of magnetic poles, the magnetic poles are formed into a shape such that the magnetic flux density distribution formed between the inner surfaces of these magnetic poles and a rotor located on the rotating side of the radial bearing has a distribution inclined from the magnetic pole end portion to the magnetic pole center portion. With this arrangement, the rate of change in magnetic flux density during the shift of the rotor from a magnetic pole to the adjacent magnetic pole is reduced, thereby reducing the eddy current loss and heat generation.
