Abstract: In a disk player/recorder apparatus, a radial access mechanism is disclosed in which a first guide rod is positioned on a mounting plate accurately with respect to the information storage medium. A head assembly engages the first guide rod through bushings which provide stringent tolerance requirements. The position of the head assembly is accurately controlled by the position of the first guide rod and the tolerances on the bushings. A second guide rod coupled to the mounting plate and a single bushing also supports and guides the head assembly, however, the tolerances on the components associated with the second guide rod are less stringent. Coupled to each of the guide rods is a bracket with a permanent magnet coupled thereto. The permanent magnets interact with the coils of linear motors coupled to the head assembly. The linear motors are arranged to minimize torque on the head assembly. The brackets and the guide rods form magnetic circuits for the associated permanent magnets and linear motors.

Abstract: Focusing apparatus is described for a lens holder for an actuator of a read/write head in a optical information storage system which provides a fine adjustment for focussing an optical beam on the storage medium. A lens holder unit is coupled to a base unit by springs, the springs establishing an equilibrium position relative to a base unit. The base unit includes a plurality of coils through which current can flow. The lens holder unit includes a permanent magnet. When current flows through the plurality of coils, a force is exerted on the permanent magnet and, consequently, on the lens holder unit. The position of the lens holder unit relative to the base unit is determined by the magnitude of the current applied to the coils. The springs are arranged to maintain an orientation of the lens assembly unit in space. For small displacements of the lens assembly unit from an equilibrium position, the lens remains proximate the optic axis.

Abstract: An array of alternatingly polarized permanent magnets of equal pole strength, disposed in side by side relationship, provides a monotonically decreasing, spatially varying magnetic transfer field for a master and slave tape wrapping a rotatable capstan. Alternating flux-exiting and flux-returning pole faces of the magnets are disposed along a curvilinear plane adjacent to, but deviating from the tape wrap at the circumferential surface of the capstan in the direction of media movement. This arrangement subjects the slave tape to multiple cycles of an alternating transfer field of gradually diminishing strength as the tapes move through the transfer field.

Abstract: In a shift-correcting code which represents (d,k)-constrained run-length-limited (RLL) channel data as symbols drawn from GF(p.sup.m), the encoding process produces a set of redundant parity ternary GF(p.sup.m) symbols representing three shift error conditions: forward shift, backward shift and no shift, for p=3 and m=1 for example. The encoder of the invention transforms the parity symbols into (d,k)-constrained RLL channel bits to produce a binary data sequence that can be inserted in the RLL channel data stream without a large number of linking bits to maintain compliance with the (d,k) RLL constraints. A shift error in the RLL channel data representing parity symbols affects no more than one decoded parity symbol.

Abstract: A thermal printer is disclosed in which a receiver is driven back and forth relative to a printing head by a driving roller. The receiver is driven at a nip formed between the driving roller and a pinch roller. The pinch roller is adapted to contact only the receiver during the movement of the receiver. The receiver is thereby permitted to move at the surface speed of the driving roller with reduced shear forces being introduced by the pinch roller. Consequently, a pinch roller with a high length to diameter ratio is usable and images can be produced on wide receivers with narrow image-free borders. The images are produced with precise registration and image artifacts are reduced.

Abstract: A thin film magnetometer includes first and second thin film magnetoresistive elements and first and second thin film laminated flux collectors. The first magnetoresistive element is located in a gap formed by the flux collectors, and the second magnetoresistive element is subtantially magnetically shielded by the flux collectors, and acts as a thermistor. The magnetoresistive elements are connected in a bridge circuit whereby any signal component due to thermal effects on the magnetoresistive elements is removed from the signal produced by the first magnetoresistive element.

Abstract: In the read/write head of an optical storage system, a bi-direction grating coupler is used to replace optical components normally found in the read/write head. The use of the bi-directional grating coupler reduces the bulk and weight of the read/write head. The two channels of the bi-directional grating coupler can be used to separate a radiation component that can used to provide a tracking control signal from a radiation component that can be used to provide a focus control signal. One of the channels is also used to provide the radiation component from which the data on the storage medium can be identified. The bi-directional coupler can be implemented by two grating couplers, each grating coupler having a thin film associated therewith and each grating coupler diverting a selected radiation portion into the associated thin film.

Abstract: A dual diffraction grating useful in optical disk heads comprises first and second light diffracting surfaces of identical pitch and depth, wherein the diffraction grooves of the first and second diffraction surfaces are angularly oriented with respect to one another. Incident light beams are diffracted into first and second components with the first components being TM polarized components and the second components being TE polarized components. Upon emerging from the dual diffraction grating, the first and second components diverge with respect to one another because the first component is substantially transmitted through the diffraction grating without diffraction while the second component is diffracted. The initial diffraction by the first grating causes the TE component to diverge away from the TM component while the second diffraction grating diffracts the TE component back toward the TM component so as to diverge therefrom by only a slight angle of, for example, about 0.1.degree. to 3.0.degree..

Abstract: A power efficient amplifier uses two stages, a low voltage stage and a high voltage stage. The low voltage stage supplies a nominal operating current to a load from a low voltage low power output when the requirements are small, and the high voltage stage supplies a desired output current to the load exceeding the nominal operating current when the load requires such. Switching to the high voltage output stage in response to sensing current to the load exceeding the nominal operating current conserves energy and increases operational efficiency. The amplifier circuitry produces a power efficient voltage-to-current transformation. The circuitry includes an operational amplifier that receives a signal proportional to the current flowing to the load and, an input signal which represents the desired load current. When the output increases above a certain level, it turns off the low voltage stage and turns on the high voltage stage causing the available output power to increase.

Abstract: A method for coding/decoding ternary symbols to d,k-constrained binary runs in a way that (i) associates (codes) a number of ternary symbols with a lesser number of d,k-constrained binary runs and (ii) provides that an individual single-shift error in any of the received binary runs that constitute a binary data codeword will cause at most one ternary symbol to be in error in the associated (decoded) ternary symbol codeword. This method allows shift-correction codeword parity checks to be transmitted (i.e., transformed to a d,k-constrained channel data sequence) with increased efficiency, so that the required number of channel bits needed to represent the parity checks is decreased.

Abstract: Process for magnetographic printing and apparatus for carrying out said process, said process being characterized in that:a) a first information is recordedb) part of the information recorded at step (a) is erasedc) a second information is recorded, at least one part of said second information is recorded in the area erased during step (b).Apparatus comprising at least three magnetic heads with at least one erasing head and two recording heads, characterized in that said erasing head is arranged so as to erase the writing area (14) common to at least two recording heads.Application to continuous printing of information of the bar code type.

Abstract: An optical head is disclosed in which a beam from a diode laser is directed onto an optical disc, and a beam reflected from the optical disc is passed through an optical device which forms a plurality of discrete beams of different orders. The beams from the optical device are focussed onto photodetectors, and signals from the photodetectors are used for error detection, tracking, and signal detection. The optical device comprises two diffraction gratings which are supported on a substrate and are separated from each other by a thin film. In order to obtain the advantages of a doubly-periodic structure, the thickness of the thin film between the two gratings is very accurately controlled to be on the order of the wavelength of the incident beam of radiation.

Abstract: A thin film magnetic record/playback head having suitably thin layers of soft, high permeability magnetic material, such as permalloy, electrically insulated from each other by very thin layers of a magnetic material having suitably high resistivity, such as NiZn ferrite. The improved magnetic record/playback head is capable of reading and writing much higher bit densities (up to about 100 kfci) and at much higher frequencies (100 MHz or higher) than prior art devices while remaining fully compatible with existing electronic circuitry.

Abstract: A method and apparatus for recovering information prerecorded in a vertically magnetized magneto-optic recording element wherein a laser is operated in a state of polarization instability (i.e., its TE and TM losses are equal). The linearly polarized (TE and TM) output of the laser is converted to circularly polarized (left-handed and right-handed) polarized radiation, and the latter is used to scan irradiate the recording element. Upon being reflected by the recording element, the circularly polarized radiation is reconverted to linear polarization and fed back to the laser cavity. Depending on which polarization mode (TE or TM) experiences the lesser loss as a result of the MCD effect, the laser operates in either its TE or TM mode. Means are provided for detecting the instantaneous polarization mode of the laser which, in turn, is indicative of the orientation (up/down) of the magnetic domains scanned by the laser radiation.

Abstract: A data processing system is disclosed in which a plurality of central processing units have access to all the system resources, i.e., have a peer relationship. During initialization of the data processing system, all the system resources are allocated to the individual central processing units according to a preselected distribution procedure, the identification of available resources thereafter being stored in the files of the individual central processing units. During the operation of the data processing system, the resources can be reallocated by a predetermined procedure. The central processing units entering such a relationship are required to include apparatus and/or software procedures that prevent access to system resources not assigned thereto. A mail box procedure, using locations in the main memory unit permit communication between the central processing units and are used in the dynamic allocation of resources.

Abstract: A multitrack head assembly has a plurality of magnetic heads arranged side-by-side along a transducing gap line extending across an upwardly facing tape-engaging surface which includes a series of elongated coplanar ribs alternating with low-pressure channels on both sides of and orthogonal to the gap line. For continuous in-contact recording, each rib is aligned with a particular one of the magnetic heads and has a width that is greater than the width of the transducing gap of the head with which it is aligned; furthermore, each rib has a gently curved tape-engaging surface with a radius of curvature R.sub.1 in a direction orthogonal to the gap line and a radius of curvature R.sub.2 in a direction substantially parallel with the gap line, where R.sub.1 and R.sub.2 are not necessarily the same.

Abstract: A magnetic field bushing has a movable member and stationary rod. The stationary rod has high permeability strips of magnetic material forming a portion of the surface. The stationary rod further includes at least two sets of coils, the magnetic field resulting from application of a current to each coil being coupled to a strip. The movable member is configured to encircle substantially the stationary rod. The movable member has regions of high permeability magnetic material which are positioned on the movable member to complete a magnetic circuit with related magnetic strips. The magnetic circuits are completed through air gaps between the movable member regions and the stationary rod strips. The magnetic field in the air gaps results in a force between the movable member regions and the stationary rod strips. Forces are generated between the movable member and the stationary rod, the forces being selected to prevent contact between the movable member and the stationary rod.

Abstract: A composite read-while-write magnetic head assembly includes a substrate having first and second opposing planar surfaces. An inductive record head of the thin film type is situated on the first planar surface, and a playback head of the magnetoresistive (MR) type is located on the second planar surface, in alignment with the record head. With an MR playback head and a thin film record head, the alignment between the two heads is limited by the precision of a photolithographic process, which is very accurate relative to the width of even the most narrow record track. Furthermore, the substrate is selected to be of sufficient thickness to isolate the MR playback head from the effects of fields created by the inductive record head, thereby eliminating crosstalk between the two heads.

Abstract: Apparatus for reading out information magneto-optically recorded in a magnetic layer comprises a single, polarization-preserving optical guide (e.g., an optical fiber or two-dimensional waveguide) for transmitting plane-polarized read-out radiation to the recording layer, as well as for transmitting such radiation, upon being reflected by the recording layer, toward a photodetector. Either the TE or TM axis of the optical guide is initially aligned with the plane of polarization of the readout source. A polarization rotator, such as a Faraday rotator, is positioned between the output end of the optical guide and the recording medium. The Faraday rotator serves to rotate the plane of polarization of the readout radiation by a total of 45 degrees, whereby the optical guide transmits reflected light in both TE and TM modes equally. A pair of photodiodes cooperate with a polarizing beam splitter to differentially detect the Kerr rotation angles (.+-..THETA..sub.

Abstract: Apparatus, for duplicating magnetically recorded information by contact transfer from a master medium in the form of a magnetic rotatable drum to a slave medium in the form of a magnetic tape, includes a magnetic head, for initially recording the information to be duplicated on the magnetic drum, having a media-contact surface the curvature of which conforms to the curvature of the drum. The magnetic head is mounted with its media-contact surface essentially parallel with the surface of revolution of the drum, thereby enhancing signal-to-noise performance by suppressing spacing losses.