OPTO-ELEKTRONISCHE INRICHTING VOOR HET MET EEN STRALINGSBUNDEL INSCHRIJVEN EN/OF UITLEZEN VAN REGISTRATIESPOREN.

摘要

The apparatus comprises an objective (12) mounted in an objective holder (11) which is movable in accordance with a number of desired degrees of freedom by means of a bearing arrangement and comprises electromagnetic actuator means (83-64) for driving the objective holder in accordance with the desired directions of movement. The bearing arrangement of the objective holder on the frame comprises electromagnetic bearing means (53-64) for counteracting movements in accordance with at least one undesired degree of freedom and comprises an objective-position measuring device (43-50) for supplying a positional-error signal which represents the deviation of the objective holder in accordance with the undesired degree of freedom relative to the frame (10) and which is utilized by a levitation control circuit which counter-acts movements of the objective holder relative to the frame in accordance with the undesired degree of freedom by means of electromagnetic levitation forces.