Abstract: A cartridge case for containing a disk-shaped recording medium has a shutter attached slidably thereon. The shutter is U-shaped sectionally and the edge sections where the shutter contacts the surface of the cartridge case are rounded so that friction therebetween is reduced when the shutter slides on the surface of the cartridge case. The cartridge case is provided with a notch and an indentation on at least one of its side surfaces corresponding to protruding pieces in the device into which the cartridge case is inserted such that a sensor in the device can be activated only when a cartridge case compatible with the device is inserted and these protruding pieces properly engage with the notch and the indentation on the cartridge case.

Abstract: A disc clamping device comprises a disc base on which to set a disc and which has a spindle for rotating the disc, and a disc holding member movable in the axial direction of the spindle. The disc holding member comprises a portion for pressing a disc with a centering hub and a portion to be engaged with the center hole of a disc with no centering hub.

Abstract: An extra magnetic field positioning apparatus includes a motor which does not have stable points for defining the extra magnetic field. An encoder is provided which is rotated with the motor and individually has the information which indicates rotating displacement and the information which indicates rotating position. Further, a sensor detects the information indicating the rotating position recorded on the encoder, and another sensor detects the information indicating the rotating displacement recorded on the encoder.

Abstract: A linear motor for magneto-optical disk drive or the like, including a movable member, a guide for guiding the movable member, a driving yoke provided at a central portion of the guide, an actuating member provided at the movabole member and a coil wound around the actuating member such that the actuating member is axially movably fitted around the guide. In the linear motor, a height of a line of action of a driving force produced by electromagnetic action between the coil and the driving yoke is so set as to coincide with a height of a centerline of the guide.

Abstract: An optical memory disc includes a glass substrate on which a plurality of concentric circular guide grooves (or a spiral groove) are formed for tracking purposes. A centering plate is secured to the glass substrate in a manner that the center of a circular opening formed in the centering plate is exactly adjusted to the center of the plurality of concentric circular guide grooves (spiral groove). The circular opening formed in the centering plate is utilized to drive the optical memory disc on a turntable. Since the circular opening is not formed directly in the glass substrate, the center adjustment is easily conducted, and there is no possibility that the glass substrate is damaged when the circular opening is formed.

Abstract: Concentric guide grooves are formed on a glass substrate, and recording medium is disposed on the glass substrate having the concentric grooves. A centering device is secured to the glass substrate in a manner that the center of the centering device is positioned at the center of the concentric guide grooves. In a preferred form, photopolymer is disposed between the centering device and the glass substrate as adhesive. The centering device is provided with an aperture through which ultraviolet rays are applyed to the photo-polymer to cure it.