| 摘要 |
The invention relates to an optical scanning unit for controlling and directing a radiation beam towards recording tracks of a surface to be scanned on an information carrier. The scanning unit comprises an objective, a translational-position and angular-position detection system for detecting the positions of the objective and an electromagnetic actuating means for correcting the position of the objective relative to the information carrier in response to the electrical error signals supplied by said position detection system. The actuating means comprises a movable objective holder with an axially magnetized magnet whose axial ends are provided with magnetic poles and at least three sets of coils situated in the magnetic field of the magnet. The coils are arranged adjacent each other viewed in the circumferential direction of the magnet and cooperate magnetically with the magnet via an air-gap. The sets of coils each comprise two peripheral coils situated substantially in the magnetic field near one of the axial ends of the magnet, and at least one central coil arranged between the two peripheral coils. The coils are each electrically connected to a matrix circuit via only two amplifiers.
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