Rca Inc.

Research, Incorporated

USA As Represented by Secretary of the Navy

William E Barnette

Kyriacos Costa Nicolaou

Ronald L Magolda

Robert W Jebens

Fred W Spong

Edward Coley Fox

William G McGuffin

Joseph A Zenel

Zenon Lysenko

A focus servo system for optical disc record/playback apparatus includes three current drivers for maintaining the distance between an objective lens and an information surface of the disc substantially constant. One driver is a DC to low frequency amplifier which can drive the transducer over its full range to the mechanical stops. The second current driver is a DC to high frequency amplifier whose output at DC is limited to drive the transducer approximately twice the expected disc runout. At higher frequencies, the output is such that the displacement of the transducer does not exceed the displacement corresponding to DC value. In operation, the low frequency driver adjusts the DC operating point of the high frequency driver so that its output averages to approximately zero, thus decreasing the drive requirements of the high frequency driver. The third driver is a DC current source which sets the static operating point of the transducer.

Lens positioning controller for optical playback apparatus

In a capacitance distance sensor apparatus in a focus servo loop for an optical disc playback and record system, stable high servo loop gain and small closed-loop error correction signals are achieved despite surface variations of the disc by compensating for the periodic error command signals generated by the surface variations. A comb filter is provided in the loop tuned to major error component frequencies. The comb filter is formed of a plurality of parallel, bandpass filters that are tuned to frequencies substantially corresponding to the disc rotation frequency and several harmonics thereof. In the distance sensor servo focus control loop, the loop gain can be maintained at a high value to achieve proper beam focus within 0.5 micron (0.5.times.10.sup.-6 meters) for disc surface amplitude variation of three mils (0.0075 centimeters) peak-to-peak.

Compensation apparatus for a servo system with periodic command signals

Stable biologically active 6,9 .alpha.-thiaprostacyclin derivatives having the formula ##STR1## wherein X represents &gt;S, &gt;SO or &gt;SO.sub.2 ;

Pharmaceutically active 6,9-thiaprostacyclin analogs and derivatives

Unsaturated alcohols, thiols and thioesters are cyclized by a phenyl selenenyl halide; wherein the conformation flexibility of the unsaturated alcohol, thiol or thioester is selected such that the hydroxy group, thiol group or thioester group is capable of internal addition to at least one unsaturated bond in said alcohol, thiol or thioester; and wherein the ratio of the phenyl selenenyl halide to said unsaturated alcohol, thiol or thioester is 0.9-1.5 to 1. In a preferred embodiment, oxygen isomers and sulfur analogs of prostacyclin of the formula ##STR1## wherein X= ##STR2## Y=(E)- and (Z)- &gt;C.dbd.CH--CH.sub.2 CH.sub.2 CH.sub.2 COOR; (E)- &gt;CH--CH.dbd.CH--CH.sub.2 CH.sub.2 COOR; and

Method for preparing cyclic ethers and thioethers including oxygen

Stable biologically active aromatic prostacyclin analogues of the formula ##STR1## wherein X represents ##STR2## and R represents hydrogen, a pharmaceutically acceptable cation or a pharmaceutically acceptable lower alkyl group, are useful in the treatment of blood platelet aggregation and vascular constriction.

Pyridoza prostacyclin analogues and N-oxides thereof

A non-contact type, capacitance distance sensing probe having one or two electrodes disposed about one end of an objective lens system in an optical video disc system is used with a focus control servo loop to maintain focus of a light beam on the surface of a reflective disc record despite undesirable axial displacements of the surface when the record is rotated. The two electrode probe is balanced to provide immunity to variations in the impedance of the external circuit which grounds the disc.

Capacitance distance sensor apparatus for video disc player/recorder

A counterwound, magnetic core for a towed-cable, helically wound, ELF anta comprising a cylindrical, plastic, center insert, with or without a center conductor, with two strips or sets of strips of magnetic material counterwound about it so that a plurality of good-mechanical-contact, strip, crossover points are formed distributed around the circumference of the insert and down its length. An insulating material is then wrapped around these counterwound strips and a conductor helically wound around that. This design, by providing alternate flux paths down the core via the crossover points provides a lower, core reluctance and, when the core is under stress, provides a flux path that avoids the high-stress regions of the core thus reducing the amount of flux that is stress-modulated. Thus a substantial magnetostrictive noise reduction is obtained.

Growing community of inventors

Levittown, PA, United States of America

William E Barnette