Abstract: An electromagnetic drive system includes a motor having a first motor section movable relative to a second motor section along a motion axis. The second motor section has three excitation coils. The first motor section includes a magnetic circuit generating a magnetic field in the excitation coils. The first motor section also includes a short-circuit winding for only high-frequency induction currents. This short-circuit winding is magnetically coupled to the excitation coils. The degree of electromagnetic coupling of at least one excitation coil depends on the position of the first motor section relative to the second motor section. The short-circuit winding provides a position-dependent electromagnetic coupling between the center excitation coil and the two outer excitation coils.

Abstract: An electro-optical device is able to follow the information structure (2) of a moving information carrier (3) with a radiation spot 17 in two directions, of which one extends in a plane perpendicular to the other. A lens system (5) is fixed in a lens mounting (9) which relative to a frame (4) may perform pivotal movements about a pivotal axis (10) parallel to the optical axis (6) of the lens system and translational movements along the pivotal axis (10) by means of electromagnetic actuator means (14, 13) which are symmetrically located with respect to the pivotal axis. The lens mounting (9) is of elongate form and its parts which are situated on opposite sides of the pivotal axis (11) have substantially the same mass and mass distribution.

Abstract: A disc-record player includes a pressure apparatus for pressing a disc onto a turntable. A mandril which is coaxial with the turntable engages the edge of a center hole in the disc. The pressure apparatus comprises rollers which can deflect elastically in a radial direction relative to the axis of rotation of the turntable and which are carried by a pressure member. The pressure member is axially movable relative to the mandril and acts on the disc at a radial distance from the center hole. The mandril comprises a conical guide wall whose diameter decreases towards the turntable and which cooperates with the rollers when downward pressing action occurs.

Abstract: An optical focusing-error detection device comprises a beam splitter arranged in the path of a radiation beam originating from a plane on which is to be focused, and a radiation-sensitive detection system comprising a plurality of detectors separated by narrow strips, a first strip being associated with a first one and a second strip with the second one of two subbeams formed by the beam splitter. By arranging the two separating strips at an acute angle relative to each other it is possible to ensure that the centers of the radiation spots formed in the detector plane by the subbeams are disposed on the separating strips when focusing is correct.

Abstract: An optical scanning unit for scanning recording tracks of a record carrier with a radiation beam. The beam is emitted by a radiation source arranged at one end of a tubular member and is concentrated to a radiation spot by a lens system arranged at the other end of the tubular member. A double prism disposed between the source and lens system splits-off a reflected secondary radiation beam and directs it laterally towards an electronic output device through a lateral aperture in the tubular member. The output device converts the modulated reflected radiation into an electrical signal. The radiation source and the double prism are radially and axially aligned within the required tolerances on a metal prism support which, within an adjustment range, can be moved axially relative to the tubular member and which can be rotated to a limited extent.

Abstract: A semiconductor laser device includes a support having a substantially annular assembly block of a metal having a good thermal conductivity, which assembly block includes positioning means on its outer circumference for accurately locating the optical axis of said laser element and a sector-shaped supporting part which extends towards the center line of the block and which has a connection and mounting face for a laser element extending through the center line and accurately located with respect to the positioning means. A base includes mutually-insulated electrical conductors and a photodiode which is secured on the side of the assembly block remote from the supporting part, and a cap having a light-transmitting window is secured to the assembly block so as to form a hermetic envelope.

Abstract: An apparatus for reading a disk-shaped record carrier, the radial scanning position being controlled with the aid of a first servo control loop, which controls a positioning member for the read element depending on a control signal which is read from the record carrier. If this control is disturbed a second servo control loop is rendered operative. This second servo control loop comprises a position indicator for supplying a position signal which is representative of the radial position of the positioning member, a memory circuit for storing the value of this position signal at the instant of failure of the first servo control loop, and a differential amplifier for applying a control signal to the positioning member, which signal corresponds to the difference between the instantaneous and the stored value of said position signal. Furthermore, there is provided a control circuit for changing-over between the first and the second servo control loop and vice versa depending on a built-in criterion.

Abstract: In an apparatus for reading a record carrier on which information is stored in an optically readable structure, the radiation which is supplied by the radiation source is split into a read beam and an auxiliary beam for determining the focussing of the read beam on the record carrier. Said auxiliary beam is intercepted by two radiation-sensitive detectors. By disposing a radiation-absorbing knife between the radiation source and the Wollaston prism a part of the auxiliary beam is blocked. Thus, an accurate indication can be obtained of the magnitude and the direction of a focussing error.

Abstract: An optical scanning device scans recording tracks on a record carrier with the aid of a beam of radiation, while an objective, which concentrates the beam of radiation to a scanning spot, performs automatic electrically controlled movements in a direction perpendicular to the plane of the record carrier with the aid of a focussing bearing arrangement, so as to ensure a continuous focussing of the scanning spot on the recording tracks. Moreover, in order to follow the oscillations of the recording track, the objective also performs electrically controlled movements which are such that the scanning spot moves at least substantially parallel to the plane of the record carrier.