Abstract: In a disk drive unit, a top cover, a front cover and a loading base attached with a body module cooperatively form a substantially closed receiving space for an optical disk. The front cover is provided with a dustproof shutter which closes the foregoing receiving space except upon insertion or ejection of an optical disk cartridge including therein the optical disk. Further, a dustproof cap is attached to the body module so as to cover the underside of the body module where a circuit board is disposed for processing signals relative to an optical head. A hermetically closed space is formed between the underside of the body module and the dustproof cap, in which the circuit board is accommodated.

Abstract: A disk cartridge driving apparatus contains a loading mechanism for loading a cartridge or cassette case inserted through an opening and a spindle motor, optical head, optical head driving mechanism for recording and reproducing data from a disk in the cartridge or cassette case. The spindle motor, optical head and optical head driving mechanism are flexibly sealed to prevent the entry of dust even when a disk cartridge is being loaded into the apparatus.

Abstract: An optical disk apparatus for an optical disk enclosed in a disk cartridge comprises a casing for accommodating the cartridge through a cassette insertion aperture formed therein. A disk drive motor for rotating the optical disk, a loading assembly for detachably loading the cartridge on the disk drive motor, and an optical pickup device for recording data on and/or reproducing data from the optical disk are provided in the casing. Deflecting member provided for sealing the periphery of the optical pickup device against the flow of outside air introduced in the casing. A specific air-seal or door structure is provided for preventing introduction of air from the cassette insertion aperture into the casing.

Abstract: An optical pick-up device suitable for use in an optical disk memory system includes a semiconductor laser unit which emits a laser light beam which, in turn, passes through a beam splitter, a quarter-wave plate, and an objective lens to impinge on an optical disc thereby forming a light spot thereon. The light is then reflected from the disc and this reflected light passes through the objective lens and the quarter-wave plate and its direction of advancement is altered by the beam splitter to move into a convergent lens. Then, as the reflected light further advances, it is partly blocked by a tracking error detecting sensor and the remaining non-blocked portion of the reflected light impinges upon a focusing error detecting sensor. The objective and convergent lenses have f.sub.0 and f.sub.1 as their focal distances, respectively, and, preferably, ratio f.sub.0 /f.sub.1 is set equal to or larger than approximately 10.

Abstract: A knife edge type focus detection method for optics associated with an optical pickup is disclosed. A light intercepting member is interposed between an object lens and a light receiving element for focus detection in order to cut 60-95% of a reflected flux for focus detection before the flux reaches the light receiving element. The intercepted part of the flux includes a light ray which propagates through the optical axis of the optics.

Abstract: An optical pickup for detecting a distance to an optical disk on which information is optically stored includes a tracking error detecting device for detecting a tracking error by receiving a part of the light reflected from the disk and a focusing error detecting device for detecting the remaining part of the light reflected from the disk, structured such that the tracking error detecting device receives 60% or more of the reflected light.

Abstract: Three primary color toner images are transferred successively onto a copy sheet from three photoconductive drums. The copy sheet is successively moved into engagement with the drums in register with the toner images by an endless belt. Various transfer charging means are provided to electrostatically adhere the copy sheet to the belt and counteract an adverse accumulation of charge on the copy sheet caused by accumulation of toner substance thereon during the three successive transfer operations.