U.S. Philips Corporation

Other

Robert N Van Sluys

Gerard E Van Rosmalen

Wilhelmus A Gijzen

Johannes J Schoenmakers

Karl-Hanns Meyer

Leonhard Honds

An optical scanning unit with an objective for the focussing a beam of radiation along an optical axis into a scanning spot on the surface of an information carrier. The scanning unit also has an electromagnetic drive for correcting the position of the objective with respect to the information carrier. The drive has an objective mount supported in an annular, moving magnetic member which is axially magnetized and is arranged coaxially about the optical axis. The drive is further provided with fixed coils which interact with the magnetic member via an air gap. The fixed coils are arranged along at least three radial planes which are normal to the optical axis. Two planes lie in the area of the axial ends of the centrally positioned magnetic member and the third central plane which extends between the two outer radial planes.

Driver for an objective of an optical scanning unit

A pivotal-arm device (15) for a disc scanning unit (13) for recording and/or reading information comprises a deck plate (3A), a pivotal arm (25) carrying the scanning unit, and pivotal-arm bearing means. The pivotal arm bearing means comprise two bearings disposed on opposite sides of the pivotal arm, at least one of the bearings comprising two bearing members (31, 33), a spherical bearing element, which cooperates with these bearing members, and a viscous medium. At least one of the bearing members has a concave bearing surface (33A), between which bearing surface and the bearing element a gap (35) is formed, which gap widens towards the edge of said bearing surface and which contains said viscous medium. A resilient element (39), which is secured to the deck plate, urges the bearings towards one another.

Pivotal-arm device for a disc scanning unit

The disclosed apparatus for recording and/or reading information in or from a track of a radiation-reflecting record carrier by means of a light beam includes an objective system for focusing the light beam so as to form a light spot on the record carrier in dependence on a control signal (S.sub.f). The control signal is generated by a focusing-error detection system having an astigmatic element and four detectors (D.sub.1 to D.sub.4). The output signals S.sub.1 to S.sub.4 of the four detectors are combined in an electric circuit arranged to produce a control signal satisfying the formula: ##EQU1## This control signal drastically reduces the influence on the focusing of offset of the light spot on the four detectors.

Optical recording/playback apparatus having a focusing control system

In an optical device an objective (11) can be moved relative to the frame (1) along its optical axis (13) in parallel guide means (3, 5) by means of an electromagnetic actuating device. The actuating device comprises first actuating means (21) and second actuating means (23) which are connected to the objective (11) and which cooperate with said first actuating means via an air gap (25). The first actuating means (21) are arranged in a mount (27) which is supported by a leaf-spring-shaped element (29) which is secured to the frame (1).

Optical focusing device

A switchable compression-expansion device, in which a first and a second impedance are included in the emitter circuits of two emitter followers. The impedances are also included in two isolated signal circuits which are coupled via a current mirror circuit. A selection means maintains one of the two emitter followers in the non-conducting state. The current which is produced in the associated impedance by the conducting emitter follower is coupled to the other impedance by the current mirror arrangement. In the other condition of the selection circuit the reverse occurs so that two complementary transfer functions are realized.

Device for optionally realizing two mutually complementary functions

Method of encoding quadraphonic signals in four channels, in which for each side the front signal is recorded together with the phase-shifted back signal, and the back signal is recorded together with the supplementarily phase-shifted front signal.

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Eindhoven, Netherlands

Robert N Van Sluys