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Johnston, A. R.

Publications and source records attributed to Johnston, A. R..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Proximity sensor technology for manipulator end effectors

Optical proximity sensing devices suitable for hand mounting on a manipulator are described, which use near IR LED light sources operating at 0.94 micron and silicon detectors, with appropriate signal processing so that the data are unaffected by ambient light. Laboratory tests with simple proximity sensors are described. Extension of the same techniques to yield multipoint or digital sensors is also discussed. A cooperative proximity sensor concept is described, which employs a composite mirror attached to the work piece to generate an unambiguous set of position and orientation signals. A very rudimentary experiment in local control of a manipulator with a pair of hand mounted proximity sensors is also described.

Johnston, A. R.↗
NASA NTRS1977

Control techniques for an automated mixed traffic vehicle

The paper describes an automated mixed traffic vehicle (AMTV), a driverless low-speed tram designed to operate in mixed pedestrian and vehicular traffic. The vehicle is a six-passenger electric tram equipped with sensing and control which permit it to function on existing streets in an automatic mode. The design includes established wire-following techniques for steering and near-IR headway sensors. A 7-mph cruise speed is reduced to 2 mph or a complete stop in response to sensor (or passenger) inputs. The AMTV performance is evaluated by operation on a loop route and by simulation. Some necessary improvements involving sensors, sensor pattern, use of an audible signal, and control lag are discussed. It is suggested that appropriate modifications will eliminate collision incidents.

Meisenholder, G. W.↗
NASA NTRS1976

Bit error rate measurement for evaluation of a fiber optic link

Digital fiber-optic data-link terminal modules are being developed in a number of laboratories, and often the modules take the form of black boxes without convenient access to internal signals. This paper discusses types of measurements which can be made using only the digital terminals of the link. Bit-error-rate (BER) vs signal-power data can, of course, provide a means for proving overall link performance, but it can also be used to determine certain internal parameters of the receiver. The theoretical dependence of the BER-vs-light-signal-power curve shape on receiver input-noise equivalent power and comparator slicing level is discussed. BER-vs-light-signal-power measurements obtained with an experimental link are presented and interpreted with the aid of the theoretical curves. The effects of other problems, such as hum or oscillation, on the BER data are mentioned. Sensitivity of the system BER to bit rate is also discussed, with application to determining system operating limits. Since BER measurements are simple to make and can easily be automated, they may prove to be a useful means for either laboratory evaluation or production-line acceptance testing of sealed terminal modules.

Bergman, L. A.↗
NASA NTRS1975

Proximity sensor technology for manipulator end effectors

Optical proximity sensing techniques which could be used to help control the critical grasping phase of a remote manipulation are described. The proximity sensors described use a triangulation geometry to detect a surface located in a pre-determined region. The design of the proximity sensors themselves is discussed, as well as their application to manipulator control with a local control loop, and possibilities for future development are discussed.

Johnston, A. R.↗
NASA NTRS1974

An experiment in manipulator control with proximity sensors

Optical proximity sensors were used in a feedback loop to automatically position a manipulator hand for grasping. The experiment was a simplified one, involving two dimensional motion only. Two proximity sensors were mounted on the hand, and control signals derived from their outputs were used to drive the hand vertically and horizontally. The sensors employ a pulsed gallium arsenide light-emitting diode together with a silicon detector. They indicate, without contact, the approximate distance between the manipulator hand and object in the range from 5 to 12 cm. Positioning within approximately + or - 5 mm was observed. Extension of the technique to general three-dimensional control is briefly discussed.

Johnston, A. R.↗
NASA NTRS1973

Kerr response of nematic liquids.

Description of the results of recent observations of the Kerr effect in nematic liquid crystals in a temperature range just above their nematic-isotropic transition. These results indicate that the intermolecular ordering forces in a nematic substance can enhance the Kerr effect just above the nematic transition in their isotropic state. It is felt that existing theory provides a useful approximation for relating molecular size to response time.

Johnston, A. R.↗
NASA NTRS1973

Light-direction sensor based on birefringency

Optical system consisting of polarizer, analyzer, quarterwave retarder converts incident light beam to one which has an intensity related to the extent the incident beam is off axis.

Johnston, A. R.↗
NASA NTRS1971

Stark-effect modulation of a CO2 laser by NH2D.

Use of the molecular Stark effect in NH2D to modulate the 10.6-micron P(20) line of a CO2 laser, yielding a modulation depth of 40% from a 200-V/cm rms signal applied to a 19.7-cm gas cell external to the laser. NH2D was prepared by mixing ND3 and NH3. The absorption coefficient of the M = 4 Stark-split line was measured as a function of mixing ratio and pressure. The observed pressure-broadening coefficient was 32.5 MHz/torr.

Johnston, A. R.↗
NASA NTRS1970

Optics at the Jet Propulsion Laboratory

Optical equipment development at Jet Propulsion Laboratory, discussing flight TV systems and associated digital image processing laboratory, planetary spectroscopy, spacecraft guidance, etc

Johnston, A. R.↗
NASA NTRS1967

Polarimeter provides transient response in nanosecond range

Conventional polarimeter with a Senarmont compensator improves transient response and eliminates manual manipulation. A sampled photomultiplier output is fed to a low pass filter, resulting in a signal representing the optical state existing at the instant of sampling. With this technique, an unknown transient-induced retardation can be measured.

Johnston, A. R.↗
NASA NTRS1965

Miniature servo accelerometer is force- balanced

Miniature servo accelerometer measures unusually small forces of torques. The pendulous mass of the accelerometer is suspended by fused quartz torsion fibers in an electromagnetically force- balanced environment. It is used in gravity surveys for exploring mineral deposits.

Johnston, A. R.↗