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At least 1,603 records · Page 89

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NASA NTRS1988

Computer simulations of two-pickup-ion instabilities in a cometary environment

This paper presents a one-dimensional electromagnetic hybrid computer simulation of distant cometary environments, in which protons and oxygen ions are injected continuously at the same time. It is demonstrated that, when, instead of a single component, both protons and oxygen ions are injected, the faster growing shorter-wavelength proton-proton right-hand resonant instability dominates the early time physics, leading to linear temporal growth of the fluctuating magnetic field energy density and pitch angle scattering of the protons (but causing no significant response by the nonresonant oxygen ions). At later times, as the injected oxygen ions accumulate sufficient density, the oxygen-proton right-hand resonant instability emerges, exhibiting exponential temporal growth to a relatively large peak amplitude, phase bunching, and magnetically trapping the oxygen ions. At times after peak amplitude, the oxygen-proton fluctuations stochastically accelerate some of the injected protons.

Gary, S. Peter↗

NASA NTRS1988

Filamentation instability of large-amplitude Alfven waves

An instability that leads to the filamentation of large-amplitude Alfven waves and gives rise to purely growing density and magnetic field fluctuations is studied. The dispersion relation of the instability is derived, from which the threshold conditions and the growth rates of the instability are analyzed quantitatively for applications to the solar wind plasma. Their dependence on the filamentation spectrum, the plasma beta, and the pump frequency and intensity was examined for both right-hand and left-hand circularly polarized Alfven waves. The excitation of filamentation instability for certain cases of interest is discussed and compared with that of the parametric decay and modulation instability. The relevance of the proposed instability to some observations is discussed.

Kuo, S. P.↗

NASA NTRS1989

Pilot Delays For Three Cockpit Controllers

Pilot effective delay increases with system delay. Report compares pilot effective time delays measured in simulations of aircraft-control systems equipped with Space Shuttle rotational hand controller and with two versions of conventional stick-type hand controller. Report of interest to those concerned with design of multiple-axis controllers in aircraft, armored vehicles, industrial machinery, and remote manipulators: operator response or delay critical to stable and accurate operation of such systems.

Privoznik, Cynthia M.↗

NASA NTRS1989

Force-Feedback Cursor Control

Robot controller moves cursor and manipulates images. Use of force-feedback hand-held controller proposed to help computer operators position cursors on computer video displays. To control cursor, hand controller replaces joystick or electronic mouse. Operator presses button on handle to obtain action when cursor reaches desired position indicated by icon or image. Controller has additional degrees of freedom.

Hannaford, Blake↗

NASA NTRS1988

Don/doff support stand for use with rear entry space suits

A don/doff support stand for use with rear entry space suits is disclosed. The support stand is designed for use in one-g environments; however, certain features of the stand can be used on future spacecraft, lunar, or planetary bases. The present invention has a retainer which receives a protrucing lug fixed on the torso section of the space suit. When the lug is locked in the retainer, the space suit is held in a generally upright position. In a one-g environment a portable ladder is positioned adjacent to the rear entry of the space suit supported by the stand. The astronaut climbs up the ladder and grasps a hand bar assembly positioned above the rear entry. The astronaut then slips his legs through the open rear entry and down into the abdominal portion of the suite. The astronaut then lowers himself fully into the suit. The portable ladder is then removed and the astronaut can close the rear entry door. The lug is then disengaged from the retainer and the astronaut is free to engage in training exercises in the suit. When suit use is over, the astronaut returns to the stand and inserts the lug into the retainer. A technician repositions the ladder. The astronaut opens the rear entry door, grasps the hand bar assembly and does a chin-up to extricate himself from the suit. The astronaut climbs down the movable ladder while the suit is supported by the stand.

Kosmo, Joseph J.↗

NASA NTRS1988

The WCSAR telerobotics test bed

Component technologies for use in telerobotic systems for space are being developed. As part of this effort, a test bed was established in which these technologies can be verified and integrated into telerobotic systems. The facility consists of two slave industrial robots, an articulated master arm controller, a cartesian coordinate master arm controller, and a variety of sensors, displays and stimulators for feedback to human operators. The controller of one of the slave robots remains in its commercial state, while the controller of the other robot has been replaced with a new controller that achieves high-performance in telerobotic operating modes. A dexterous slave hand which consists of two fingers and a thumb is being developed, along with a number of force-reflecting and non-force reflecting master hands, wrists and arms. A tactile sensing finger tip based on piezo-film technology has been developed, along with tactile stimulators and CAD-based displays for sensory feedback and sensory substitution. The telerobotics test bed and its component technologies are described, as well as the integration of these component technologies into telerobotic systems, and their performance in conjunction with human operators.

Duffie, N.↗

NASA NTRS1988

Distributed proximity sensor system

The invention relates to sensors embedded on the surface of a robot hand, or other moving member. By distributing proximity sensors capable of detecting distances and angles to points on the surface of an object, information is obtained for achieving noncontacting shape and distance perception, i.e., for automatic determination of the object's shape, direction, and distance, as well as the orientation of the object relative to the robot hand or other moving member.

Lee, Sukhan↗

NASA NTRS1988

Experimental and simulation studies of hard contact in force reflecting teleoperation

Experiments and simulations of a single-axis force-reflecting teleoperation system have been conducted to investigate the problem of contacting a hard environment and maintaining a controlled force in teleoperation in which position is fed forward from the hand controller (master) to the manipulator (slave), and force is fed back to the human operator through motors in the master. The simulations, using an electrical circuit model, reproduce the behavior of the real system, including effects of human operator biomechanics. It is shown that human operator properties, which vary as a result of different types of grasp of the handle, affect the stability of the system in the hard-contact task. The effect of a heavier grasp on the handle is equivalent to increased hand-controller velocity damping in terms of the systems stability in the contact task, but control system damping sufficient to guarantee stable contact results in perceptible sluggishness of the control handle's response in free motion. These results suggest that human operator biomechanics must be taken into account to guarantee stable and ergonomic performance of advanced teleoperators.

Hannaford, Blake↗

NASA NTRS1988

The polarization of escaping terrestrial continuum radiation

The polarization of an escaping terrestrial continuum radiation event that occurred on March 2, 1982, was determined using plasma wave measurements from the DE-1 spacecraft. The source of the radiation was determined to be located near the magnetic equator on the nightside of the earth at a radial distance of about 2.8-3.5 earth radii. Two meridional beams were detected, one directed north at an angle of about 20-30 deg with respect to the magnetic equator, and the other directed south at a comparable angle. Polarization measurements indicated that the radiation is right-hand polarized with respect to an outward directed E plane normal in the Northern Hemisphere and left-hand polarized in the Southern Hemisphere.

Gurnett, D. A.↗

NASA NTRS1989

Control experiments in planar manipulation and grasping

Many algorithms have been proposed in the literature for control of multifingered robot hands. Here, the performance of several of these algorithms is compared, along with that of some extensions of more conventional manipulator control laws, in the case of planar grasping. Based on experiments performed on Styx, the most effective control laws are the simple joint control law and the generalized computed torque law. The computed torque control law is shown to be an attractive alternative for position control of multifingered hands.

Murray, Richard M.↗

NASA NTRS1989

Cooperative control of visual displays for telemanipulation

Two cooperative control schemes for telerobot visual displays are addressed. In the first scheme, on-the-screen visual enhancements such as reference lines indicating the vertical height of the robot hand, a stick figure model of the robot hand, and its projection on the horizontal grid plane are constructed by the interactive cooperation between the human operator and the telerobotic system, and then superimposed on the video screen. Experimental results with a five-degree-of-freedom robot and a frame grabber indicate that superimposition of visual enhancements on the video screen greatly improves telemanipulation task performance. In the second scheme, the position and orientation of an object on video screens are determined interactively; these then assist the telerobotic system in executing the human operator's task-level commands autonomously.

Kim, Won S.↗

NASA NTRS1990

Proximity Sensors Make Robot Dexterous

Control system enables robot hand to grasp objects of varied shapes. Key features of system: reflective proximity sensors furnishing data on position, orientation, and distance of object and software protocol controlling sequence of operations in approaching and grasping objects. Reflected-beam sensing concept applied to simple opposed-jaw industrial grippers as well as to dexterous robot hands.

Hess, Cliff↗

NASA NTRS1990

Simple Regulator For Positive-Pressure Glove Box

Weighted, inflated bag regulates pressure in positive-pressure glove box such as those used to manipulate samples in atmosphere isolated from such contaminations in open air as moisture or oxygen. Weight atop the inflated bag rises and falls as gas flows into and out of bag from glove box. Positive pressure relative to surroundings pushes gloves outward when not being used. To manipulate items in box, technician forces gloves inside. Sensitive materials manipulated in dry or inert atmosphere without danger of overpressure when technician inserts hands in gloves, or of underpressure - and inward leakage of air - when technician draws hands out of gloves. Replaces elaborate system of pressure-activated valves. Quieter, cheaper, and more reliable.

Shlichta, Paul J.↗

NASA NTRS1989

Efficiency and capabilities of multi-body simulations

Simulation efficiency and capability go hand in hand. The more capability you have the lower the efficiency will be. The efficiency and capabilities are discussed. The lesson learned about generic simulation is: Don't rule out any capabilities at the beginning, but keep each one on a switch so it can be bypassed when warranted by a specific application.

Vandervoort, R. J.↗

NASA NTRS1986

Independent Orbiter Assessment (IOA): Analysis of the manned maneuvering unit

Results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) are presented. The IOA approach features a top-down analysis of the hardware to determine failure modes, criticality, and potential critical items (PCIs). To preserve indepedence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. This report documents the independent analysis results corresponding to the Manned Maneuvering Unit (MMU) hardware. The MMU is a propulsive backpack, operated through separate hand controllers that input the pilot's translational and rotational maneuvering commands to the control electronics and then to the thrusters. The IOA analysis process utilized available MMU hardware drawings and schematics for defining hardware subsystems, assemblies, components, and hardware items. Final levels of detail were evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the worst case severity of the effect for each identified failure mode. The IOA analysis of the MMU found that the majority of the PCIs identified are resultant from the loss of either the propulsion or control functions, or are resultant from inability to perform an immediate or future mission. The five most severe criticalities identified are all resultant from failures imposed on the MMU hand controllers which have no redundancy within the MMU.

Bailey, P. S.↗

NASA NTRS1989

Performance evaluation of a six-axis generalized force-reflecting teleoperator

Work in real-time distributed computation and control has culminated in a prototype force-reflecting telemanipulation system having a dissimilar master (cable-driven, force-reflecting hand controller) and a slave (PUMA 560 robot with custom controller), an extremely high sampling rate (1000 Hz), and a low loop computation delay (5 msec). In a series of experiments with this system and five trained test operators covering over 100 hours of teleoperation, performance was measured in a series of generic and application-driven tasks with and without force feedback, and with control shared between teleoperation and local sensor referenced control. Measurements defining task performance included 100-Hz recording of six-axis force/torque information from the slave manipulator wrist, task completion time, and visual observation of predefined task errors. The task consisted of high precision peg-in-hole insertion, electrical connectors, velcro attach-de-attach, and a twist-lock multi-pin connector. Each task was repeated three times under several operating conditions: normal bilateral telemanipulation, forward position control without force feedback, and shared control. In shared control, orientation was locally servo controlled to comply with applied torques, while translation was under operator control. All performance measures improved as capability was added along a spectrum of capabilities ranging from pure position control through force-reflecting teleoperation and shared control. Performance was optimal for the bare-handed operator.

Hannaford, B.↗

NASA NTRS1989

OMV mission simulator

The Orbital Maneuvering Vehicle (OMV) will be remotely piloted during rendezvous, docking, or proximity operations with target spacecraft from a ground control console (GCC). The real-time mission simulator and graphics being used to design a console pilot-machine interface are discussed. A real-time orbital dynamics simulator drives the visual displays. The dynamics simulator includes a J2 oblate earth gravity model and a generalized 1962 rotating atmospheric and drag model. The simulator also provides a variable-length communication delay to represent use of the Tracking and Data Relay Satellite System (TDRSS) and NASA Communications (NASCOM). Input parameter files determine the graphics display. This feature allows rapid prototyping since displays can be easily modified from pilot recommendations. A series of pilot reviews are being held to determine an effective pilot-machine interface. Pilots fly missions with nominal to 3-sigma dispersions in translational or rotational axes. Console dimensions, switch type and layout, hand controllers, and graphic interfaces are evaluated by the pilots and the GCC simulator is modified for subsequent runs. Initial results indicate a pilot preference for analog versus digital displays and for two 3-degree-of-freedom hand controllers.

Cok, Keith E.↗

NASA NTRS1989

Prototype part task trainer: A remote manipulator system simulator

The Part Task Trainer program (PTT) is a kinematic simulation of the Remote Manipulator System (RMS) for the orbiter. The purpose of the PTT is to supply a low cost man-in-the-loop simulator, allowing the student to learn operational procedures which then can be used in the more expensive full scale simulators. PTT will allow the crew members to work on their arm operation skills without the need for other people running the simulation. The controlling algorithms for the arm were coded out of the Functional Subsystem Requirements Document to ensure realistic operation of the simulation. Relying on the hardware of the workstation to provide fast refresh rates for full shaded images allows the simulation to be run on small low cost stand alone work stations, removing the need to be tied into a multi-million dollar computer for the simulation. PTT will allow the student to make errors which in full scale mock up simulators might cause failures or damage hardware. On the screen the user is shown a graphical representation of the RMS control panel in the aft cockpit of the orbiter, along with a main view window and up to six trunion and guide windows. The dials drawn on the panel may be turned to select the desired mode of operation. The inputs controlling the arm are read from a chair with a Translational Hand Controller (THC) and a Rotational Hand Controller (RHC) attached to it.

Shores, David↗