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At least 163 records · Page 9

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NASA NTRS1991

Sensing Temperatures Via Prostheses And Manipulators

Proposed temperature-sensing system applies heat to (or removes heat from) human user's skin according to temperature of remote object. Used in artificial limbs and in telerobotic manipulators. In prosthetic arm and hand, sensors on tips of artificial fingers send signals to electronic control network that drives small, lightweight thermoelectric heat pump worn on back of user's shoulder. Heat pump heats or cools skin according to signals from sensors. Heat pump and control network worn like article of clothing. In manual control of remote robot, sensors placed in fingers of remote manipulator. Sensors drive, via similar electronic control network, thermoelectric heat pumps in fingers of glove worn by operator, who then has benefit of information about temperatures on manipulated object.

Zerkus, Mike↗

NASA NTRS1990

Local sensory control of a dexterous end effector

A numerical scheme was developed to solve the inverse kinematics for a user-defined manipulator. The scheme was based on a nonlinear least-squares technique which determines the joint variables by minimizing the difference between the target end effector pose and the actual end effector pose. The scheme was adapted to a dexterous hand in which the joints are either prismatic or revolute and the fingers are considered open kinematic chains. Feasible solutions were obtained using a three-fingered dexterous hand. An algorithm to estimate the position and orientation of a pre-grasped object was also developed. The algorithm was based on triangulation using an ideal sensor and a spherical object model. By choosing the object to be a sphere, only the position of the object frame was important. Based on these simplifications, a minimum of three sensors are needed to find the position of a sphere. A two dimensional example to determine the position of a circle coordinate frame using a two-fingered dexterous hand was presented.

Pinto, Victor H.↗

NASA NTRS1991

Overcenter collet space station truss fastener

A quick-connect fastener is arranged with a tubular body that is arranged to be engaged against the exterior surface of a hollow attachment fitting and coincidentally aligned with an opening in the fitting. A collet having normally-contracted fingers with outwardly-enlarged ends is operatively arranged in the body to be moved forwardly by an expander member mounted in the tubular body for advancing the collet fingers through the opening in the attachment fitting. Biasing means are arranged between the expander member and a toggle linkage in the tubular body which is selectively operated to urge the expander member forwardly into engagement with the collet fingers with an initial biasing force to advance their forward portions through the body opening and then expand them outwardly. The biasing means also provide a subsequent biasing force for retaining the collet members in their expanded positions once their enlarged forward end portions are on the opposite side of the body.

Sheridan, Philip L.↗

NASA NTRS1991

A prototype power assist EVA glove

The most recent generation of space suit EVA gloves has addressed the problem of loose fit and stiffness in the fingers, but it remains difficult to build a glove assembly with low metacarpophalangeal joint stiffness. Fatigue due to constantly displacing the glove from a neutral position has been reported as the limiting factor in some EVA activities. This paper outlines an actuation system that uses gas filled bladders attached to the back of the EVA glove to provide the necessary force to bend the glove at the metacarpal joint, thus providing greater endurance during finger grasping tasks. A simple on-off controller senses hand movement through small pressure sensors between the finger and the glove restraint. The controller then fills or exhausts the bladders on the back of the glove to effectively move the neutral position of the glove as the hand inside moves.

Main, John A.↗

NASA NTRS1992

Numerical simulation of plasma transport driven by the Io torus

The Rice convection model (RCM) has been modified to a form suitable for Jupiter (RCM-J) to study plasma interchange motion in and near the Io plasma torus. The net result of the interchange is that flux tubes, heavily loaded with torus plasma, are transported outward, to be replaced by tubes containing little low-energy (less than 1 keV) plasma. The process is numerically simulated in terms of time evolution from an initial torus that is longitudinally asymmetric and with gradually decreasing density outward from Io's orbit. In the simulations, the nonlinear stage of the instability characteristically exhibits outreaching fingers of heavily-loaded flux tubes that lengthen at an accelerating rate. The principal finding is that the primary geometrical form of outward transport of torus plasma in Jupiter's magnetosphere is through long, outward-moving fingers of plasma. In the simulations, the fingers mainly form in the active sector of the Io torus (the heavier side of the asymmetric torus), and they are spaced longitudinally roughly 20 deg apart.

Yang, Y. S.↗

NASA NTRS1993

Bladder operated robotic joint

This invention is a robotic joint which is operated by inflatable bladders and which can be used in applications where it is desired to move or hold an object. A support block supports an elongated plate to which is pivotally attached a finger. A tension strip passes over a lever attached to the finger and is attached at its ends to the support block on opposite sides of the plate. Bladders positioned between the plate and the tension strip on opposite sides of the plate can be inflated by pumps to pivot the finger, with one of the bladders being inflated while the other is being deflated.

Robertson, Glen A.↗

NASA NTRS1994

Thermal feedback in virtual reality and telerobotic systems

A new concept has been developed that allows temperature to be part of the virtual world. The Displaced Temperature Sensing System (DTSS) can 'display' temperature in a virtual reality system.The DTSS can also serve as a feedback device for telerobotics. For virtual reality applications the virtual world software would be required to have a temperature map of its world. By whatever means (magnetic tracker, ultrasound tracker, etc.) the hand and fingers, which have been instrumented with thermodes, would be tracked. The temperature associated with the current position would be transmitted to the DRSS via a serial data link. The DTSS would provide that temperature to the fingers. For telerobotic operation the function of the DTSS is to transmit a temperature from a remote location to the fingers where the temperature can be felt.

Zerkus, Mike↗

NASA NTRS1995

KAO observations of SN1987A

Explosion calculations of SN1987A generate pictures of Rayleigh-Taylor fingers of radioactive Ni-56 (Ni-56 yields Co-56 yields Fe-56) which are boosted to velocities of several thousand km/s. From the KAO observations of the mid-IR iron lines, a picture of the iron in the ejecta emerges which is consistent with the 'frothy iron fingers' having expanded to fill about 50% of the metal-rich volume of the ejecta (nu(sub m) less than or equal to 2500 km/s). The ratio of the nickel line intensities I(sub (Ni I)7.5 micron)/I(sub (Ni II)6.6 microns) yields a high ionization fraction of x(sub Ni) greater than or equal to 0.9 in the volume associated with the iron-group elements at day 415, before dust condenses in the ejecta. From the KAO observations of the dust's thermal emission (2 microns to 100 microns), it is deduced that when the grains condense, their infrared radiation is trapped, their apparent opacity is gray, and they have a surface area filling factor of about 50%. The dust emission from SN1987A is featureless: no 9.7 micron silicate feature, nor PAH features, nor dust emission features of any kind are seen at any time. The total dust opacity increases with time even though the surface area filling factor and the dust/gas ratio remain constant. This suggests that the dust forms along coherent structures which can maintain their radial line-of-sight opacities, i.e., along fat fingers. The coincidence of the filling factor of the dust and the filling factor of the iron strongly suggests that the dust condenses within the iron, and therefore the dust is iron-rich. It only takes approximately 10(exp -4) solar mass of dust for the ejecta to be optically thick out to approximately 100 microns; a lower limit of 4 x 10(exp -4) solar mass of condensed grains exists in the metal-rich volume, but much more dust could be present. The episode of dust formation started at about 539 days and proceeded rapidly, so that by 600 days 45% of the bolometric luminosity was being emitted in the IR; by 775 days, 86% of the bolometric luminosity was being reradiated by the dust. Measurements of the bolometric luminosity of SN1987A from 1000 to 2300 days are based on 10 micron and 20 micron photometry and rely on the suppositions that the IR emission is a graybody (proven to be true by the KAO observations at 615 and 775 days) and that the dust temperature drops to and remainsat 150 K. The late-time bolometric luminosity is stronger than that expected from the radioactive decay of Co-56, Co-57, Ti-44, and Na-22 and the late-time dust temperatures are consistent with the presence of a compact object.

Wooden, Diane H.↗

NASA NTRS1993

Multicomponent Convection Induced by Fronts in the Chlorate-Sulfite Reaction

An application of a new method is presented for the measurement of the temperature profiles of chemical waves propagating through a solution. Using solutions of thermocolor materials, the temperature distribution caused by the heat released in the propagating chlorate oxidation of sulfite was visualized and recorded using digital image processing methods. After calibration, the temperature gradient was calculated from the gray scale value in a digitized image. Extensive multicomponent convection ('fingering') was induced by descending fronts. Only ascending fingers were observed because of the large thermal gradient that suppressed descending ones. The characteristics of the temperature profile were determined as a function of initial sulfite and chlorate concentration, and tube diameter. Unusual behavior was observed when the fronts propagated under conditions of continuously changing diameter in a conical vessel. Fingering occurred periodically in a front descending in a flask with an increasing diameter. However, when a front propagated down in flask whose diameter decreased, no multicomponent convection was observed.

Nagy, Istvan P.↗

NASA NTRS1997

Applying Space Technology to Enhance Control of an Artificial Arm

At the present time, myoelectric prostheses perform only one function of the hand: open and close with the thumb, index and middle finger coming together to grasp various shaped objects. To better understand the limitations of the current single-function prostheses and the needs of the individuals who use them, The Institute for Rehabilitation and Research (TIRR), sponsored by the National Institutes of Health (August 1992 - November 1994), surveyed approximately 2500 individuals with upper limb loss. When asked to identify specific features of their current electric prosthesis that needed improvement, the survey respondents overwhelmingly identified the lack of wrist and finger movement as well as poor control capability. Simply building a mechanism with individual finger and wrist motion is not enough. Individuals with upper limb loss tend to reject prostheses that require continuous visual monitoring and concentration to control. Robotics researchers at NASA's Johnson Space Center (JSC) and Rice University have made substantial progress in myoelectric teleoperation. A myoelectric teleoperation system translates signals generated by an able-bodied robot operator's muscles during hand motions into commands that drive a robot's hand through identical motions. Farry's early work in myoelectric teleoperation used variations over time in the myoelectric spectrum as inputs to neural networks to discriminate grasp types and thumb motions. The resulting schemes yielded up to 93% correct classification on thumb motions. More recently, Fernandez achieved 100% correct non-realtime classification of thumb abduction, extension, and flexion on the same myoelectric data. Fernandez used genetic programming to develop functions that discriminate between thumb motions using myoelectric signal parameters. Genetic programming (GP) is an evolutionary programming method where the computer can modify the discriminating functions' form to improve its performance, not just adjust numerical coefficients or weights. Although the function development may require much computational time and many training cases, the resulting discrimination functions can run in realtime on modest computers. These results suggest that myoelectric signals might be a feasible teleoperation medium, allowing an operator to use his or her own hand and arm as a master to intuitively control an anthropomorphic robot in a remote location such as outer space.

Atkins, Diane↗

NASA NTRS1998

Radiative Ignition and Transition to Spread Investigation (RITSI)

A total of 25 experiments was conducted in the Glovebox Facility on the Third United States Microgravity payload (USMP3) mission to study the behavior of both flaming and smoldering ignition events, the transition from ignition to the flame/smoldering spread, and the flame/smoldering growth pattern in air. Twenty one of the 25 experiments were flaming experiments and the remainder were smoldering experiments. Ignition was initiated by a heated wire across a thermally thin filter paper in the middle of the sample for the two-dimensional configuration and by a focused beam from a halogen/tungsten lamp at the center of the sample for the three-dimensional configuration. The external air flow velocity was varied from 0 cm/s to 6.5 cm/s. The ignition and subsequent flame spread events were recorded by a video camera, a 35 mm camera, and 6 thermocouples (2 in the gas phase and 4 in the sample). The results indicate that non-piloted radiative ignition of the paper by external thermal radiation tends to occur more easily than in normal gravity. In the two-dimensional configuration, the transition from ignition to downstream flame spread never occurred; only the transition to upstream spread took place. In the three-dimensional configuration, a char growth pattern emerged in the shape of a fan, with the ignited area as the center of the fan and the fan spreading in the upstream direction. The internal angle of the fan increased with an increase in external flow velocity (higher flow velocity gave a more opened fan pattern). At an external flow velocity of 5 cm/s, the flame was horseshoe-shaped and the char pattern became an elongated semicircle toward upstream. It appears that the peak upstream flame spread rate was reached at a higher external velocity than for the two-dimensional flame front. Flame spread much faster along open edges of the sample paper than along the sample face, presumably due to there being larger supply of oxygen and energy feedback at the open edges than at the surface. These results indicate the possible importance of the effect of the flame front shape such as the curvature of the flame front on spread rate and flame strength. A complex, unexpected finger-shaped char growth pattern was observed during the smoldering experiment. Higher external flow velocity increased the number of localized smoldering fronts, of the char fingers they left behind, and frequency of bifurcations from the fingers. At present, it is not clear what caused such a complex char growth pattern.

Kashiwagi, Takashi↗

NASA NTRS1998

Burner Rig Hot Corrosion of a Single Crystal Ni-48Al-Ti-Hf-Ga Alloy

The hot corrosion resistance of a single crystal Ni-48Al-1Ti-0.5Hf-0.2Ga alloy was examined in a Mach 0.3 burner rig at 900 C for 300 hours. The combustion chamber was doped with 2 ppmw synthetic sea salt. The hot corrosion attack produced a random mound morphology on the surface. Microstructurally, the hot corrosion attack appeared to initiate with oxide-filled pits which were often broad and shallow. At an intermediate stage, the pits increased in size to incorporate unoxidized Ni islands in the corrosion product. The rampant attack stage, which was observed only at sharp sample corners, was characterized by rapid inward growth of alumina in finger-like protrusions incorporating significant amounts of Al-depleted Ni islands. Aluminum consumption in the oxide fingers resulted in the growth of a gamma' layer ahead of the advancing oxide fingers.

Nesbitt, James A.↗

NASA NTRS2000

The Dynamics of Miscible Interfaces: A Space Flight Experiment

Experiments as well as accompanying simulations are described that serve in preparation of a space flight experiment to study the dynamics of miscible interfaces. The investigation specifically addresses the importance of both nonsolenoidal effects as well as nonconventional Korteweg stresses in flows that give rise to steep but finite concentration gradients. The investigation focuses on the flow in which a less viscous fluid displaces one of higher viscosity and different density within a narrow capillary tube. The fluids are miscible in all proportions. An intruding finger forms that occupies a fraction of the total tube diameter. Depending on the flow conditions, as expressed by the Peclet number, a dimensionless viscosity ratio, and a gravity parameter, this fraction can vary between approximately 0.9 and 0.2. For large Pe values, a quasi-steady finger forms, which persists for a time of O(Pe) before it starts to decay, and Poiseuille flow and Taylor dispersion are approached asymptotically. Depending on the specific flow conditions, we observe a variety of topologically different streamline patterns, among them some that leak fluid from the finger tip. For small Pe values, the flow decays from the start and asymptotically reaches Taylor dispersion after a time of O(Pe). Comparisons between experiments and numerical simulations based on the 'conventional' assumption of solenoidal velocity fields and without Korteweg stresses yield poor agreement as far as the Pe value is concerned that distinguishes these two regimes. As one possibility, we attribute this lack of agreement to the disregard of these terms. An attempt is made to use scaling arguments in order to evaluate the importance of the Korteweg stresses and of the assumption of solenoidality. While these effects should be strongest in absolute terms when steep concentration fronts exist, i.e., at large Pe, they may be relatively most important at lower values of Pe. We subsequently compare these conventional simulations to more complete simulations that account for nonvanishing divergence as well as Korteweg stresses. While the exact value of the relevant stress coefficients are not known, ballpark numbers do exist, and their use in the simulations indicates that these stresses may indeed be important. We plan to evaluate these issues in detail by means of comparing a space experiment with corresponding simulations, in order to extract more accurate Korteweg stress coefficients, and to confirm or deny the importance of such stresses.

Maxworthy, Tony↗

NASA NTRS2001

Multiple Radially Aligned Plasmaspheric Structures as Evidence of Standing Hydromagnetic Waves: IMAGE EUV Observations and Forward Modeling

The IMAGE EUV imager has observed several instances where the outer plasmasphere is populated by multiple radially aligned structures resembling "plasmaspheric fingers". The observation of these plasmaspheric structures suggests the presence of an azimuthal standing hydromagnetic wave mode. Eiganmodes appear to explain finger-like. nearly radial density structures that sometimes divide into two structures with increasing radial distance. The implication is of boundaries at fixed local times, which results in a widening "box" in which standing waves are developed. The structures also suggest a single driving frequency for the source of the waves. We present EUV observations of plasmaspheric fingers observed on August 2000 as well as plasmaspheric modeling of azimuthal wave modes in an effort to quantify the origin of these observed structures

Gallagher, D. L.↗

NASA NTRS1994

Explosion Calculations of SN1087

Explosion calculations of SNT1987A generate pictures of Rayleigh-Taylor fingers of radioactive Ni-56 which are boosted to velocities of several thousand km/s. From the KAO observations of the mid-IR iron lines, a picture of the iron in the ejecta emerges which is consistent with the "frothy iron fingers" having expanded to fill about 50% of the metal-rich volume of the ejecta. The ratio of the nickel line intensities yields a high ionization fraction of greater than or equal to 0.9 in the volume associated with the iron-group elements at day 415, before dust condenses in the ejecta. From the KAO observations of the dust's thermal emission, it is deduced that when the grains condense their infrared radiation is trapped, their apparent opacity is gray, and they have a surface area filling factor of about 50%. The dust emission from SN1987A is featureless: no 9.7 micrometer silicate feature, nor PAH features, nor dust emission features of any kind are seen at any time. The total dust opacity increases with time even though the surface area filling factor and the dust/gas ratio remain constant. This suggests that the dust forms along coherent structures which can maintain their radial line-of-sight opacities, i.e., along fat fingers. The coincidence of the filling factor of the dust and the filling factor of the iron strongly suggests that the dust condenses within the iron, and therefore the dust is iron-rich. It only takes approximately 4 x 10(exp -4) solar mass of dust for the ejecta to be optically thick out to approximately 100 micrometers; a lower limit of 4 x 10(exp -4) solar mass of condensed grains exists in the metal-rich volume, but much more dust could be present. The episode of dust formation started at about 530 days and proceeded rapidly, so that by 600 days 45% of the bolometric luminosity was being emitted in the IR; by 775 days, 86% of the bolometric luminosity was being reradiated by the dust. Measurements of the bolometric luminosity of SN1987A from 1000 - 1800 days are based on 10 micrometers and 20 micrometers photometry and rely on the suppositions that the IR emission is a greybody (proven to be true by the KAO observations at 615 and 775 days) and that the dust temperature drops to and remains at 150 K. The late time bolometric luminosity is stronger than that expected from the radioactive decay of Co-56, Co-57, Ti-44, and Na-22 and the possibility of an embedded compact object will be discussed.

Wooden, Diane H.↗

NASA NTRS2002

Splashing Droplets

Current data on droplet breakup is scarce for the sizes and velocities typical of practical applications such as in spray combustion processes and coating processes. While much more representative of practical applications, the small spatial scales and rapid time-scales prevent detailed measurement of the internal fluid dynamics and liquid property gradients produced by impinging upon surfaces. Realized through the extended spatial and temporal scales afforded by a microgravity environment, an improved understanding of drop breakup dynamics is sought to understand and ultimately control the impingement dynamics of droplets upon surfaces in practical situations. The primary objective of this research will be to mark the onset of different 'splashing modes' and to determine their temperature, pressure and angle dependence for impinging droplets representative of practical fluids. In addition, we are modeling the evolution of droplets that do not initially splash but rather undergo a 'fingering' evolution observed on the spreading fluid front and the transformation of these fingers into splashed products. An example of our experimental data is presented below. These images are of Isopar V impacting a mirror-polished surface. They were acquired using a high-speed camera at 1000 frames per second. They show the spreading of a single droplet after impact and ensuing finger instabilities. Normal gravity experimental data such as this will guide low gravity measurements in the 2.2 second drop tower and KC-135 aircraft as available. Presently we are in the process of comparing the experimental data of droplet shape evolution to numerical models, which can also capture the internal fluid dynamics and liquid property gradients such as produced by impingement upon a heated surface. To-date isothermal numerical data has been modeled using direct numerical simulations of representative splashing droplets. The data obtained so far indicates that the present model describes well the droplet wall interactions to a point in time just before splash. Additional information is included in the original extended abstract.

VanderWal, Randall L.↗

NASA NTRS1998

NICMOS Narrow-band Images of OMC-1

We present images of a 90in. x 90in. field centered on BN in OMC-1, taken with the Near-Infrared Camera and MultiObject Spectrograph (NICMOS) aboard the Hubble Space Telescope. The observed lines are H2 1-0 S(l), Pa, [FeII] 1.64 pm, and the adjacent continua. The region is rich in interesting structures. The most remarkable are the streamers or "fingers" of H2 emission which extend from 15in. to 50in. from IRc2, seen here in unprecedented detail. Unlike the northern H2 fingers, the inner fingers do not exhibit significant [FeII] emission at theirdips, which we suggest is due to lower excitation. These observations also show that the general morphology of the Pa and [FeII] emission (both imaged for the first time in this region) bears a striking resemblance to that of the Ha and [SII] emission previously observed with WFPC2. This implies that these IR and optical lines are produced by radiative excitation on the surface of the molecular cloud. The Pa morphology of HH 202 is also very similar to its H a and [OIII] emission, again suggesting that the Pa in this object is photo-excited by the Trapezium, as has been suggested for the optical emission. We find evidence of shock-excited [FeII] in HH 208, where it again closely follows the morphology of [SII]. There is also H2 coincident with the [SII] and [FeII] emission, which may be associated with HH 208. Finally, we note some interesting continuum features: diffuse "tails" trailing from IRc3 and IRc4, more extensive observations of the "crescent" found by Stolovy, et al. (1998), and new observations of a similar oval object nearby. We also find a "V"-shaped region which may be the boundary of a cavity being cleared by IRc2.

Schultz, Angela S. B.↗

NASA NTRS2002

Skin microvascular flow during hypobaric exposure with and without a mechanical counter-pressure space suit glove

INTRODUCTION: Current space suits are rigid, gas-pressurized shells that protect astronauts from the vacuum of space. A tight elastic garment or mechanical-counter-pressure (MCP) suit generates pressure by compression and may have several advantages over current space suit technology. In this study, we investigated local microcirculatory effects produced with and without a prototype MCP glove. METHODS: The right hand of eight normal volunteers was studied at normal ambient pressure and during exposure to -50, -100 and -150 mm Hg with and without the MCP glove. Measurements included the pressure against the hand, skin microvascular flow, temperature on the dorsum of the hand, and middle finger girth. RESULTS: Without the glove, skin microvascular flow and finger girth significantly increased with negative pressure, and the skin temperature decreased compared with the control condition. The MCP glove generated approximately 200 mm Hg at the skin surface; all measured values remained at control levels during exposure to negative pressure. DISCUSSION: Without the glove, skin microvascular flow and finger girth increased with negative pressure, probably due to a blood shift toward the hand. The elastic compression of the material of the MCP glove generated pressure on the hand similar to that in current gas-pressurized space suit gloves. The MCP glove prevented the apparent blood shift and thus maintained baseline values of the measured variables despite exposure of the hand to negative pressure.

NASA Discipline Cardiopulmonary↗