Abstract: The workpiece-carrier spindle assembly comprises a stator (10) mounted on a slide (202), a spindle (50) supported by active magnetic bearings and rotated by an external electric motor (2) connected to the stator via a coupling (3) which filters the mechanical disturbances due to the excentricity of the motor, and a chuck (5) fixed to the spindle (50). Additional means for detecting movements of the spindle assembly slide (202) include, in the servo-control plane of each of the radial beraings, two position detectors (216, 218: 215, 217) fixed to the stator (10) and facing two plane reference surfaces (211, 212) disposed parallel to the direction of slide displacement and delivering signals which are applied to means for selectively modifying the electric reference voltages applied to the servo-control loops of the magnetic bearings. The spindle assembly is applicable to machine tools for providing optical-quality machining.

Abstract: 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.