Abstract: An optical recording medium for use with a recording apparatus of the type that focuses onto the medium, as the medium is moved in a prescribed fashion, a beam of light that is modulated in intensity in accordance with a data signal to be recorded. The recording medium includes a substrate having a smooth, planar upper surface, with a thin light-absorbing coating overlaying the surface, such coating including an explosive material such as nitrocellulose, and a light-absorbing dye. As the medium is moved with respect to the intensity-modulated beam, the explosive coating is selectively energized by the beam to induce spaced explosions threin, whereby corresponding optically readable irregularities, representative of the data signal, are formed in the outer surface of the coating.

Abstract: An improved process for making video discs, which enables the molding of replicas having substantially higher signal-to-noise ratios during playback. One aspect of the invention extends the duration of a photoresist development process to yield developed recording masters having spaced information-bearing pits with unexpectedly steeper sidewalls. Another aspect of the invention forms metallic stampers using an initial vapor deposition step carried out in an extremely low pressure of about 1.times.10.sup.-6 torr, to reduce oxidation and thereby improve conformity between the photoresist geometry and the stamper geometry.

Abstract: A lens assembly is positionally adjusted for precisely focusing a light beam upon a video information disc in a video recorder-playback machine. The lens assembly includes a focusing lens supported on an air bearing within an assembly housing for movement toward and away from the disc. A current conducting coil is movable with the focusing lens and is adapted to receive an electrical current indicative of instantaneous focusing error of the light beam upon the disc. A fixed magnetic field formed by a permanent magnet mounted on the housing between opposite pole pieces comprising portions of the housing is magnetically coupled with the coil whereby variations in the current result in adjustment of the position of the focusing lens with respect to the disc to correct the focusing error.

Abstract: A control system for use in controllably adjusting a prescribed characteristic of a beam scanning a record medium. In the preferred embodiments, the control system is embodied in a tracking apparatus for use in a playback system for recovering information from a selected recording track on an optical record medium such as a video disc. The tracking apparatus produces a tracking error signal representative of the deviation of a scanning reading beam from the centerline of the selected track, and couples this error signal to a movable tracking mirror to form a servo for controllably positioning the beam in alignment with the track. The tracking apparatus further includes a dimple compensation circuit for monitoring the tracking error signal and producing a tracking loop disable signal whenever it determines that the reading beam is scanning a video disc defect, such as a dimple.

Abstract: A method and apparatus for detecting a property such as a defect in a surface to be scanned. A focusing, or objective lens is provided together with a subsystem for maintaining a substantially fixed distance between the focusing lens and the scanned surface. Scanning is effected by providing lateral movement between the lens and the surface. An off-axis light beam source is provided having a beam of light which is directed to pass through the lens to the scanned surface. A light beam sensing element is positioned so as to detect that portion of the light beam reflected off of the surface and transmitted back through the lens.

Abstract: A method and apparatus for selectably retrieving information from any of a plurality of spirally-formed information tracks formed in a video disc by means of controlling a carriage for translating the video disc in a forward or a reverse direction relative to radiant beam information recovery means in a video disc player. Each information track is identified by a unique address and means are provided for selecting the address of a particular track to be retrieved. A prescribed sequence of drive signals is applied to a carriage motor dependent on the distance to be traveled by the carriage to retrieve the selected information, the drive signals being successively stepped downward to intermittently redetermine carriage motor speed as predetermined location thresholds are reached during carriage translation.

Abstract: An injection molding apparatus for use in producing centrally-apertured video disc records. The apparatus includes first and second mold halves reciprocally movable with respect to each other between a closed position, wherein the two mold halves are in proximity to each other and molten plastic material is injected into a planar, annular cavity defined therebetween to form the record disc, and an open position, wherein the two mold halves are spaced apart from each other and the molded record disc can be removed. The molding apparatus further includes first and second annular rings carried by the respective first and second mold halves and defining the outer perimeter of the cavity.

Abstract: A system for recovering information from a movable information storage medium by scanning with a beam of radiation, the system including a movable lens for focusing the beam of radiation. The movable information storage medium includes a plurality of substantially parallel information tracks containing a pilot signal having a phase angle aligned with the phase angle of the pilot signal recorded on adjacent tracks. The movement of the lens to acquire focus of the beam is controlled such that the lens is retracted until the pilot signal is no longer detected. When detection of the pilot signal ceases, the retraction of the lens also ceases. The lens is subsequently advanced until focus is achieved. Defining the limits of retraction of the lens based on the limits of detection of the pilot signal minimize the range over which the lens must be moved for initial acquisition of focus.

Abstract: A hot sprue valve assembly is provided for controlling flow of molten material through a hot sprue bushing of an injection molding machine. The valve assembly is particularly designed for use with an injection molding machine for molding centrally apertured record discs, such as video information discs, and the valve assembly includes means for forming the central aperture in the disc. In one embodiment, the aperture-forming means comprises a sleeve valve for molding the aperture in the disc prior to solidification of the disc-forming melt, whereas in another embodiment the aperture-forming means comprises a punch for punching the aperture subsequent to solidification of the disc-forming melt.

Abstract: A video disc player is described for use with a video disc having frequency modulated video information recorded thereon in the form of a plurality of concentric circles or a single spiral. The information track comprises successively positioned light reflective and light non-reflective regions. A focused light beam is caused to be positioned over the center of an information track and the light reflected from the information track is gathered by an objective lens for application to electronic circuitry for recovering the recorded frequency modulated video signals. Radial tracking means are described for maintaining the focused light spot to impinge upon the center of an information track. Lens focusing means are described for positioning the objective lens at the optimum focused position above the information track for gathering the maximum amount of reflected light from the information track.

Abstract: A video disc player is described for use with a video disc having frequency modulated video information recorded thereon in the form of a plurality of concentric circles or a single spiral. The information track comprises successively positioned light reflective and light non-reflective regions. A focused light beam is caused to be positioned over the center of an information track and the light reflected from the information track is gathered by an objective lens for application to electronic circuitry for recovering the recorded frequency modulated video signals. Radial tracking means are described for maintaining the focused light spot to impinge upon the center of an information track. Lens focusing means are described for positioning the objective lens at the optimum focused position above the information track for gathering the maximum amount of reflected light from the information track.

Abstract: An objective lens comprising five lens elements and intended for use in an optical recording system wherein a laser beam is focused onto a recording surface located beneath a plastic layer over the disc. The disclosed lens has a relatively large numeric aperture of 0.75, but has a relatively large working distance between the lens and the disc and a relatively low total mass, to facilitate rapid movement of the lens. In addition, the lens is color corrected to accommodate a range of spectral frequencies present in the laser beam.

Abstract: A video disc player assembly is described employing a fixed base member with a pair of fixed rails, and a movable carriage member employing a pair of linear bearing assemblies in engagement with said rails. A capstan and pulley assembly provides a means for moving the carriage member over the rails in the base member. A motor and spindle are mounted on the carriage for rotary driving of the video disc, a centering means is provided to accurately center the disc about the spindle, and a stabilization plate is provided adjacent and parallel to the rotating disc.

Abstract: A control system for maintaining proper focus of a radiant recording or writing beam, such as a laser beam, with respect to a recording surface, by measurement of the duty cycle of an oscillatory information-carrying signal recorded from the recording surface immediately after recording. The system includes a photodetector for detecting a reading beam used to recover the recorded information, a focusing lens movable with respect to the recording surface to focus the writing and reading beams, a dither oscillator to generate a dither signal employed to move the focusing lens in an oscillatory manner, a duty cycle detector to provide a signal indicative of the duty cycle of the information-carrying signal recovered by the reading beam, and a multiplier for comparing the phases of the duty cycle signal and the dither oscillator signal, and thereby providing a correction signal indicative of the magnitude and polarity focus error.

Abstract: A player for video discs includes an improved rotating turntable to provide a fluid cushion bearing to support a thin, flexible video disc. The turntable includes apertures which direct an air flow between the disc and the turntable surface and the flow of air acts as a hydrodynamic bearing.

Abstract: A video disc player is described for use with a video disc having frequency modulated video information recorded thereon in the form of a plurality of concentric circles or a single spiral. The information track comprises successively positioned light reflective and light non-reflective regions. A focused light beam is caused to be positioned over the center of an information track and the light reflected from the information track is gathered by an objective lens for application to electronic circuitry for recovering the recorded frequency modulated video signals. Radial tracking means are described for maintaining the focused light spot to impinge upon the center of an information track. Lens focusing means are described for positioning the objective lens at the optimum focused position above the information track for gathering the maximum amount of reflected light from the information track.

Abstract: Electro-optical focus detection apparatus for providing a signal indicative of the magnitude and polarity of focus error in a light beam impinging on a surface, such as a recording surface in a recording or playback system. The detector includes a beam splitter for dividing the beam reflected from the recording surface into two reflected beams of equal power, and includes an aperture placed in the path of the two reflected beams. The first reflected beam converges at a focal point before encountering the aperture and the second reflected beam converges at a focal point after encountering the aperture, both beams thereafter impinging upon separate photodetector elements. The aperture reduces the light incident on the photodetectors from both reflected beams, and the apparatus is so configured that the powers of the reflected beams incident on the photodetector elements are identical when the original beam is in focus on the recording surface.

Abstract: A direct-read-after-write optical recording disc having a pair of transparent, disc-shaped members, each being formed with integral inner and outer ring-shaped bosses on one of its sides. A thin recording layer of a light-sensitive material is coated on each disc-shaped member, in a shallow annular recess formed between its two ring-shaped bosses, and the two members are disposed in a coaxial relationship, with their respective bosses in abutment with each other, whereby the two recording layers are located within a sealed, annular chamber.

Abstract: Method and apparatus for recovering information from an information storage medium, such as a disc-shaped record carrier, and for correcting time base variations in the recovered information. The disc includes a plurality of substantially parallel information tracks arranged in a spiral or in concentric circles, and information recorded thereon includes a pilot signal having a predetermined frequency. The apparatus includes means for comparing the phase angle of the recovered pilot signal with the phase angle of a locally generated reference signal, to produce an error signal for controlling a variable delay for correcting time base variations of the recovered information.