Abstract: An optical recording and reproducing head wherein light beams emitted from two light sources are combined and applied to a recording medium and the light beams reflected from the recording medium are drawn out in such a way that they are separated from each other. The wavelengths of the light beams from both light sources are different from each other, i.e., .lambda..sub.1, .lambda..sub.2, and the light beams from the light sources are combined by means of a polarization beam splitter, two quarter wave plates and optical filters, and are then simultaneously focussed by a single focussing lens substantially along the optical axis thereof, thereby allowing microspots of focussed light to be disposed on a disc close to each other. The light beams reflected from the disc are drawn out so as to be completely separated from each other by the polarization beam splitter owing to the difference in polarization direction.

Abstract: An optical data recording and reproducing apparatus for recording digital data in a recording track on an optical recording disc. The apparatus includes a light illuminating unit for condensing an output light beam from a light source and for illuminating the disc, a recording-reproducing unit for recording and reproducing the digital data by a recording light beam and a reproducing light beam from the light illuminating unit, a dropout detecting and inspecting unit, and a recording-prohibited sector detecting unit to produce an output signal identifying a recording-prohibited sector where recording is prohibited responsive to an output signal from the dropout detecting and inspecting unit. The sector address of a recording-prohibited sector is recorded at least until recording of digital data in the recording track on the optical disc is begun. A comparator unit compares the sector address of the recording-prohibited sector with a sector address read continuously from the disc.

Abstract: In an optical disc having a file region and a directory region for carrying various pieces of information or data, one or more designated information can be erased by irradiating a laser light beam on a corresponding region in the file region where the light beam is modulated by a superposing writing signal which may be a d.c. or a predetermined a.c. signal. When it is intended to renew the information, designated information is first read out and stored in an external memory prior to performing superposing writing. Meanwhile, the data is renewed and is then written on an unused region in the file region. The directory of the renewed data region is also written so that the renewed information will be read out by searching the new directory. In another embodiment of the invention, the information in the file region is not erased to renew the same, but its directory is erased by superposing writing.

Abstract: The disclosure is directed to an optical recording and reproducing disc in which each track circumference of guide tracks formed into a concentric or spiral configuration is divided into a plurality of sectors for selective recording and reproduction of information in any desired sectors. Sector separating zones of predetermined configuration are provided at starting portions of the respective sectors, while predetermined sector marks indicating the sector separating zones are formed on an index track provided at an outer or inner periphery of the disc in positions corresponding to the sector separating zones so that, during selection of the sectors at recording and reproduction, reproduction signals by the sector marks are used for selection of the sectors, while starting of the recording and reproduction is effected by the reproduced information of the sector separating zones.

Abstract: A friction material made of a molded cork, a friction surface of which is covered with a liquid or semi-solid lubricant layer including a solid lubricant layer comprising a solid lubricant having a larger particle size and a solid lubricant having a smaller particle size and filling vacant spaces between the larger-sized solid lubricant in dense form, affords a long service life when used in a power controlling apparatus which can transmit power and/or change rotation speed by applying friction and using a friction material.

Abstract: A modulation and demodulation system for an optical data recording and reproducing apparatus is disclosed in which, in an optical disc having an optical guide track and capable of recording and reproducing optically, the guide track is divided into a plurality of data sectors and the recording or reproduction or reading is effected by data sector. The modulation system for the data field for recording the data is different from that for the identification field containing identification data such as a track address and a sector address in such a way that the identification field is reproduced at high reliability and high demodulation speed while at the same time recording data at high density in the data field.

Abstract: A system for driving a semiconductor laser which is especially adapted for use with an optical recording and reproducing device is disclosed. In the write mode the power of laser light emitted from the semiconductor laser is so raised above a threshold or critical level that the laser beam focused on the surface of a recording medium can cause physical, chemical or electromagnetical changes thereof, but in the readout or reproduction mode, the power of laser light is lowered than the threshold or critical level and focused on the recording medium. A laser light power control loop is provided which is enabled or energized only in the readout or reproduction mode, so that the laser light can be maintained at a predetermined level.

Abstract: A track searching system for an optical information recording and reproducing apparatus in which a disc-like information carrier provided with concentric or spiral guide tracks of a channel-like configuration is used as an information recording and storing means and adapted to be scanned by a light beam for recording or retrieval of information. Light flux reflected by the information carrier and presenting variable distribution of light intensity is received by paired photoelectric elements. A difference signal and a sum signal derived from the output signals from the photoelectric elements or a reproduced RF signal representative of reproduced information undergo phase comparison processing, the result of which is utilized for determining the direction and number of guide tracks traversed by the scanning light beam.

Abstract: An optical signal recording and reproduction or retrieval system which records a primary signal on a recording track provided on a recording medium by projecting a laser beam which has been modulated by the primary signal onto the recording track, and further records a secondary signal, by superposition, on the recording track by projecting the laser beam which has been modulated by the secondary signal having a frequency band which is different from that of the primary signal onto the recording track for enabling the deleting of the previously recorded primary signal.

Abstract: An optical information recording and reproducing apparatus for optically recording and reproducing information on and from a disk-shaped information carrier having a guide track is disclosed. A digital track address prerecorded on the guide track is reproduced and the intensity of a recording laser beam is controlled by the reproduced digital track address so that the exposures of the recording laser beam at an inner periphery and an outer periphery of the disk-shaped information carrier rotated at a constant rotation speed are corrected to enable an optimum recording over an entire surface of the disk-shaped information carrier.

Abstract: An optical reproducing device for reproducing still image signals recorded on circular tracks and moving image or audio signals recorded on spiral tracks on a disk. Concentric and spiral tracks may be intermingled on the same disk. The address signals for each concentric track or each coil of a spiral track are previously recorded. When the address signals are reproduced, they are processed so as to detect whether the readout address signals changes with time, thereby detecting whether the accessed track is concentric or spiral. An optical head drive system is controlled in a manner depending on whether the track is circular or spiral, so that an optical head can scan the desired concentric or spiral track.

Abstract: An apparatus for recording, reproducing and erasing for an optical recording disc capable of recording information data with a high density, and capable of recording new information data and simultaneously erasing the previously recorded information data.

Abstract: An optical recording and reproducing disc for recording and/or reproducing information by the application of laser beams having a wavelength .lambda. in the range of 0.7 to 1.0 .mu.m, the disc being constituted by a disc-shaped base having at least one spiral guide track thereon with top surfaces parallel to the surface of the base at a height above the base different from the top surfaces of the portions of the base between the spires of the track, which height is in the range of .lambda./12 to .lambda./6, the guide track having a width approximately equal to the effective diameter of the laser beams; and a uniform thickness coating of a light recording material on the top surface of the guide track and the portions of the base between the spires of the guide track, the light recording material being a material the transmittance and/or the reflectance of which is varied by irradiation by the laser beams.

Abstract: A servo control system includes an error amplifier for deriving an error signal representing the displacement of a focus point of laser beam from different planes of an optical record disc, a differentiator for differentiating the error signal to detect its rate of variation, and a comparator for detecting the maximum peak of the differentiated signal which corresponds to reflections from the plane on which information is recorded. The focus point is moved in a direction toward the disc in an open loop mode until the maximum peak of the differentiated signal is detected, whereupon the focus point is controlled in response to the error signal in a closed loop mode to keep track of the recording plane.

Abstract: In an optical recording device in which the writing laser light beam is focused to a small spot on a disk which is coated with a photosensitive medium and spins at a predetermined velocity so that the data are recorded in terms of variable density or surface irregularities, the forward DC current applied to a semiconductor laser is varied depending upon the radius position of the writing laser beam spot on the disk but the AC current which is superposed on the DC current and rises or drops above or below the DC current level by a predetermined amplitude depending upon the data to be recorded is maintained constant regardless of the radius position of the writing laser beam spot, whereby the duty ratio can be maintained constant regardless of the distance from the center of the disk of a selected recording track.

Abstract: Disclosed is a process for producing a positive electrode for a non-aqueous electrolytic cell. Manganese dioxide is heat-treated at a temperature between 250.degree. and 400.degree. C. The heat-treated manganese dioxide is next mixed with a conducting agent and binder. The binder is suspended in water by means of non-ionic surface active agent, and the mixture is heat-treated at a temperature between 180.degree. and 350.degree. C. and then pressured molded into a positive electrode. This production process allows the provision of a positive electrode for a non-aqueous electrolytic cell of excellent discharge characteristics.

Abstract: An optical system for an optical data recording and reproducing apparatus such as an optical video disc apparatus comprising a diode laser light source, a condenser lens disposed adjacent to the diode laser, a cylindrical lens assembly arranged to exhibit different magnifications to light beams emitted by the diode laser in the direction perpendicular to a junction plane thereof and in the direction parallel to the junction plane, and a concentrating lens for constricting the resulting light beam into a light spot of a small size for projection on a recording medium. Recording of information is attained by the constricted light beam of a substantially circular cross-section with a high recording density at a low energy consumption. When reproducing the recorded information, the constricted beam is laterally enlarged in the transverse direction of the information recording track thereby to assure generation of a signal utilized for tracking control.

Abstract: A process for producing a thermoplastic resin having excellent impact resistance and processability, which comprises: polymerizing an aromatic monovinyl monomer and a vinyl cyanide monomer in the presence of an aqueous elastomeric latex, mixing with agitation the resulting copolymer latex with an aromatic monovinyl monomer and a vinyl cyanide monomer in the presence of a polyalkylene oxide and a coagulant to give a stable suspension phase, and polymerizing the mixture, and said thermoplastic resin thus produced, and a composition comprising said thermoplastic resin and a copolymer produced from an aromatic monovinyl monomer and a vinyl cyanide monomer.

Abstract: A process for producing a thermoplastic resin having excellent impact resistance and processability, which comprises polymerizing an aromatic monovinyl monomer and a vinyl cyanide monomer in the presence of an aqueous elastomeric latex, mixing with agitation the resulting copolymer latex with an aromatic monovinyl monomer and a vinyl cyanide monomer in the presence of a polyalkylene oxide and a coagulant to give a stable suspension phase, and polymerizing the mixture, and said thermoplastic resin thus produced, and a composition comprising said thermoplastic resin and a copolymer produced from an aromatic monovinyl monomer and a vinyl cyanide monomer.