Abstract: An image projection method for projecting laser beams and an image projector that projects laser beams are adapted to shut down the laser beams instantaneously when an obstacle intruding into the projection area of the laser beams is detected. A detection wave is projected onto a display screen along with the laser beams for displaying an image. The reflection wave of the detection wave reflected from the display screen is detected so as to find out whether the obstacle, if any, is intruding into the projection area of the laser beams.

Abstract: The recording area of a recording medium is separated into a first region and a second region. The basic information among plural channels is recorded in the first region and the remaining subsidiary information is recorded in the second region. As the basic information, digital audio signals of at least the left, center, right, surround left, surround right and sub-woofer channels are recorded. As the subsidiary information, digital audio signals of at least the left center channel, right center channel, delayed center channel, mixed left channel and mixed right channel are recorded. If the information recorded in one of the regions is lost, it is reproduced using the information of the other region during subsequent reproduction.

Abstract: An image projection method and an image projector are adapted to shut down the laser beams instantaneously when an obstacle intruding into the projection area of the laser beams is detected. A detection wave is projected onto a display screen 3 along with laser beams for displaying an image and detect the reflection wave of the detection wave reflected from the display screen 3 to find out the obstacle, if any, intruding into the projection area of the laser beams. The laser beams are shut down when the intrusion of the obstacle is detected.

Abstract: An optical disc includes a disc base plate of a light-transmitting synthetic material having a recess for mounting a magnetic plate, and a holding part, integral with the disc base plate, for loosely holding the magnetic plate mounted in the recess with respect to the disc base plate. It is possible with the present optical disc to prevent distortion of the disc base plate otherwise caused by the difference in thermal expansion coefficients of the two components to inhibit double refraction of the disc base plate otherwise caused by such distortion to maintain good recording/reproducing characteristics.

Abstract: A plate made of a magnetic material is secured to an optical disk so that it closes a central hole formed in a disk substrate. An optical disk chucking mechanism for chucking the optical disk to a disk table attracts the magnetic plate by the magnet to cause a platen to abut to the disk substrate and a tapered portion to abut to the inner side of the central hole so that the optical disk is restricted in position and is held. The optical disk and optical disk chucking mechanism restrict the loading position of the optical disk on the disk table independently of the mounting position of the magnetic plate on the disk substrate.

Abstract: An optical disc, and a disc recorder and a disc reproducer therefor, wherein in a lead-in region of the disc table of contents data indicating the record position on the disc of main data, e.g. musical numbers or the like, are recorded as subcodes and display data of, e.g. the titles of the musical numbers, the performers, etc., are also recorded as main data and wherein in a data region on the disc are recorded play data for the musical numbers as well as display data of the titles, performers, etc. of the musical numbers.

Abstract: An optical disc, and a disc recorder and a disc reproducer therefor, wherein in a lead-in region of the disc table of contents data indicating the record position on the disc of main data, e.g. musical numbers or the like, are recorded as subcodes and display data of, e.g. the titles of the musical numbers, the performers, etc., are also recorded as main data and wherein in a data region on the disc are recorded play data for the musical numbers as well as display data of the titles, performers, etc. of the musical numbers.

Abstract: A disc cleaning device for cleaning a disc on which information signals are pre-recorded or are to be recorded and which is housed within a disc cartridge, is disclosed. The disc cleaning device includes a cartridge holder in which a disc cartridge is loaded. The disc cartridge is the disc accommodated in a cartridge main body. The disc cleaning device also includes a shutter opening unit for moving a shutter member for opening an aperture in the disc cartridge loaded on the cartridge holder, which aperture has been closed by the shutter member. The disc cleaning device also includes a disc rotating and driving unit for rotating the disc housed within the disc cartridge, and a cleaning unit having a cleaning member adapted for being caused to bear on an information recording surface of the disc via the aperture in the disc cartridge.

Abstract: An optical disc recording apparatus in which audio data obtained by digitizing analog audio signals and time base compressing the resulting digital audio signals are read from a buffer memory on the cluster-by-cluster basis so as to be recorded on a recording track of a first optical disc and then a second optical disc. During the time interval when a cluster audio data unit next to the last cluster audio data unit written on the first optical disc by a first optical disc driver 14 is read from a memory 14, a second optical disc driver is captured into synchronization for continuously recording audio signals on the first and the second optical discs under the control of a system controller.

Abstract: A disc-shaped recording medium and a recording/reproducing apparatus employing the disc-shaped recording medium as a recording medium, are disclosed. The recording medium has a diameter of not more than 80 mm, and a recording track is formed on the recording medium with a track pitch of approximately 1.6 .mu.m. Information in excess of 130 Mbytes is recorded in a data compressed state on the recording track and the recording medium is rotationally driven at a constant linear velocity for recording and optically reproducing the information.

Abstract: A disc protecting cover for preventing a disc used as an information recording medium from being damaged or wounded while the disc is not in use, which comprises a flat portion (11;11A) having a diameter smaller than that of a disc which is provided with a center hole and a signal reading surface portion formed on a part of the surface thereof extending around the center hole, and an engaging portion (12) projecting from a central part of the flat portion (11'11A) and adapted to be inserted into the center hole of the disc to engage with the same. The flat portion (11;11A) covers the signal reading surface portion of the disc when the engaging portion (12) is inserted into the center hole of the disc to engage with the same. The disc protecting cover is attached to the disc to be detachable therefrom and can reliably protect the signal reading surface portion of the disc against damage or wound without covering portions of the disc which are not required to be covered therewith.

Abstract: A disc-shaped recording medium for storing compressed audio data which have been recorded thereon by an optical recording apparatus. The inner diameter of a data recording region of the disc-shaped recording medium is in the range from 28 mm to 50 mm. The outer diameter of the data recording region is in the range from 58 mm to 62 mm for an inner diameter of 28 mm, and is in the range from 71 mm to 73 mm for an inner diameter of 50 mm. The disc-shaped recording medium may be used with a small-sized portable disc recording and reproducing apparatus, and can record compressed audio data for playback with a playback time substantially as long as that of a standard compact disc having 12 cm diameter.

Abstract: The present invention relates to a recording method and a recording apparatus for use with a disc having a data area in which data has been recorded and an area for recording control information (i.e., Table of Contents information) for accessing a head to the data area. The recording apparatus comprises means for inhibiting the fetching of a disc if the control information has not been recorded in a predetermined area of the disc. Further, by providing a memory for storing the control information, the invention permits the accessing of a head to the data area in accordance with the content of the memory. Thus, information recorded on the disc before the control information is recorded onto a predetermined area on the disc can be reproduced.

Abstract: An optical disc player comprises a rotating member for rotating the optical disc, an optical pickup member for reproducing a digital audio signal including an error correcting code such as the Reed-Solomon Code from the disc, an error correcting decoder for decoding the error correcting code so as to produce a corrected or interpolated digital audio signal and condition flag data indicating the correction of the digital audio signal, and a display for indicating the condition flag data as a stain or contamination condition of the disc.

Abstract: In an optical disc player or other apparatus in which a light beam is directed through an objective lens to be focused thereby at a record medium surface for optically reading information recorded in a track on such surface; the objective lens has its central axis offset in respect to the longitudinal axis of a cylindrical body forming part of a movable assembly and through which the light beam passes axially, and such cylindrical body is both angularly displaceable about its longitudinal axis and axially displaceable relative to a guide bearing forming part of a fixed assembly to correct for tracking errors and for focusing errors, respectively. The fixed assembly further includes a magnetic circuit generating a magnetic field which intersects coils included in the movable assembly to receive focusing error and tracking error signals, respectively.

Abstract: In an optical disc player or other apparatus in which a light beam is directed through an objective lens to be focused thereby at a record medium surface for optically reading information recorded in a track on such surface; the objective lens is mounted eccentrically in a circular end wall of a body member having a cylindrical side wall depending from the periphery of the end wall, a bearing sleeve extends axially from the center of the end wall and is slidable on a shaft extending upwardly from a base member so that the body member is both angularly displaceable about the shaft axis and axially displaceable relative to the base member to correct for tracking and focusing errors, respectively, inner and outer yokes extend upwardly from the base member at the inside and outside, respectively, of the cylindrical side wall and have respective radially aligned gaps, a magnet is associated with the yokes for generating magnetic flux through the side wall of the body member between the inner and outer yokes, and t

Abstract: A bias circuit particularly adapted for use with a field effect transistor whereby the drain bias current of the field effect transistor is maintained constant in the event of fluctuations in the operating voltage applied to the field effect transistor by a power supply. The bias circuit changes the gate bias voltage applied to the FET as a function of the fluctuations in the operating voltage to thereby restore the drain bias current to a constant value. A variable impedance is included in the bias circuit, the variable impedance being voltage dependent such that its impedance varies as the voltage applied thereto varies in accordance with a hyperbolic relation. The voltage applied to the variable impedance is derived from, and thus includes the fluctuations in, the operating voltage. The hyperbolic relation between the impedance and the voltage applied to the variable impedance effectively matches the relation between the pinch-off voltage V.sub.P and the amplification constant .mu. of the FET.

Abstract: A muting circuit which includes an amplifier having input and output terminals and a bi-directional transistor connectd between the output terminal and a circuit point of low reference potential. The transistor has emitter base and collector regions, the emitter region having a low impurity concentration substantially the same as that of the collector region and a potential barrier being provided opposite to the junction of the emitter and base regions at a distance which is smaller than the diffusion length of minority carriers of the base region. A control signal generating means including time constant means for turning on the bi-directional transistor is provided. The time constant means assures that the bi-directional transistor will be on for only a brief interval of time to bypass the output signal of the amplifier to the low reference potential circuit point and thereby avoid the presence of a pop noise at the speaker.

Abstract: A field effect transistor amplifier comprising one or more depletion-type field effect transistors, preferably with triode characteristics, and having an operating voltage applied across its drain and source electrodes through a load, while an input signal to be amplified is applied to its gate electrode and a predetermined DC gate bias voltage is applied between the gate and source electrodes; is provided with a protective circuit for preventing damage to the field effect transistor by an excessive input signal that is, by over-drive, and which includes a source resistor connected in series with the source electrode and a constant voltage element, for example, constituted by one or more diodes, connected between the gate electrode and the side of the source resistor remote from the respective source electrode.

Abstract: An oscillator circuit is provided which employs a single active element. In particular, the circuit utilizes a novel four-terminal semiconductor device which is able to act as a transistor with three of its terminals and, in case of use as the transistor, has the emitter-grounded current amplification factor h.sub.FE controllable with a voltage at its fourth terminal. When the novel four-terminal semiconductor device is connected so as to operate as an emitter-grounded transistor, voltage changes at its output terminal, which corresponds to the collector of the transistor, is the same in phase as voltage changes at its fourth terminal. This fact is utilized in the present invention to cause oscillation by the generative feedback from the output terminal to the fourth terminal.