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  • SPACECRAFT PROPULSION AND POWER  (30)
  • CYBERNETICS  (23)
  • 2020-2023
  • 1990-1994  (53)
  • 1
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    Developments of new force reflecting control schemes and an application to a teleoperation training simulator (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Two schemes of force reflecting control, position-error based force reflection and low-pass-filtered force reflection, both combined with shared compliance control, were developed for dissimilar master-slave arms. These schemes enabled high force reflection gains, which were not possible with a conventional scheme when the slave arm was much stiffer than the master arm. The experimental results with a peg-in-hole task indicated that the newly force reflecting control schemes combined with compliance control resulted in best task performances. As a related application, a simulated force reflection/shared compliance control teleoperation trainer was developed that provided the operator with the feel of kinesthetic force virtual reality.
    Keywords: CYBERNETICS
    Type: In: 1992 IEEE International Conference on Robotics and Automation, 8th, Nice, France, May 12-14, 1992, Proceedings. Vol. 2 (A93-35501 13-63); p. 1412-1419.
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  • 2
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    Numerical study of low-current steady arcs (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The development of a high-efficiency CW YLF laser doped with Er,Tm,Ho: and featuring a strongly focusing resonator that collects a high density of pump power on the active crystal is described. The emission is investigated at 2.06 microns and a tuning range both at liquid-nitrogen (77 K) and at dry-ice (210 K) temperature. The noise characteristics and the long-term power stability of the laser is studied with an eye to employing this source for high-resolution spectroscopy in the 2-micron wavelength region. The detection of several absorption lines of NH3 at low pressure is described. The output power of the laser as a function of the power impinging on the crystal for different transmission of the output mirror is illustrated. The best result obtained is 1.46 W output for 3.2 W of argon pump. The minimum threshold achieved is 3.5 mW with a 1-percent transmission mirror. It is concluded that it is possible to develop a highly efficient Ho:YLF laser featuring low noise and sufficient tunability for high-resolution spectroscopy in the 2-micron region.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 8; 5, Se; 1012-101
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  • 3
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    On optimal infinite impulse response edge detection filters (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The authors outline the design of an optimal, computationally efficient, infinite impulse response edge detection filter. The optimal filter is computed based on Canny's high signal to noise ratio, good localization criteria, and a criterion on the spurious response of the filter to noise. An expression for the width of the filter, which is appropriate for infinite-length filters, is incorporated directly in the expression for spurious responses. The three criteria are maximized using the variational method and nonlinear constrained optimization. The optimal filter parameters are tabulated for various values of the filter performance criteria. A complete methodology for implementing the optimal filter using approximating recursive digital filtering is presented. The approximating recursive digital filter is separable into two linear filters operating in two orthogonal directions. The implementation is very simple and computationally efficient, has a constant time of execution for different sizes of the operator, and is readily amenable to real-time hardware implementation.
    Keywords: CYBERNETICS
    Type: IEEE Transactions on Pattern Analysis and Machine Intelligence (ISSN 0162-8828); 13; 1154-117
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  • 4
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    Dynamic coordination of a self-reconfigurable manipulator system (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The authors present the dynamic coordination of a self-reconfigurable manipulator system capable of changing its mechanical structure according to given task requirements. The self-reconfiguration is achieved by reconfiguring the topology of a dual-arm system through serial, parallel, and bracing structures. Particular emphasis is placed on the dynamic coordination of two arms having three different dual-arm topologies. The authors develop the Cartesian space dynamic models of a dual-arm system of three dual-arm topologies and derive the kinematic and dynamic constraints imposed on two arms in cooperation. Dual-arm dynamic manipulabilities are defined to quantify the dynamic performance of three dual-arm topologies in terms of the efficiency of generating Cartesian accelerations. A methodology of selecting serial, parallel, and bracing structures based on dual-arm dynamic manipulabilities is provided.
    Keywords: CYBERNETICS
    Type: In: IEEE Conference on Decision and Control, 30th, Brighton, United Kingdom, Dec. 11-13, 1991, Proceedings. Vol. 3 (A93-13001 02-63); p. 2404-2409.
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  • 5
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    A self-reconfigurable manipulator system with dextrous bracing structure (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The authors present a dextrous bracing structure of a dual-arm system as a means of implementing a self-reconfigurable manipulator system. The dextrous bracing structure allows a dual-arm system to relocate the bracing point between two arms, select the type of contact as the bracing point, and lock or release the joints of individual arms. The self-reconfigurable dual-arm system is now capable of reconfiguring its topology through serial, parallel and bracing structures, supporting general types of contact, rigid or sliding, as well as locking or releasing some of its joints as needed. The focus is on an analysis of the effects of the dextrous bracing on the performance of a dual-arm system in terms of dual-arm manipulabilities and resistivities. The analysis shows that a self-reconfigurable dual-arm system with a dextrous bracing structure gives continuously varying performance characteristics ranging from serial to parallel structures.
    Keywords: CYBERNETICS
    Type: In: IEEE Conference on Decision and Control, 30th, Brighton, United Kingdom, Dec. 11-13, 1991, Proceedings. Vol. 1 (A93-13001 02-63); p. 1033-1038.
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  • 6
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    The phantom robot - Predictive displays for teleoperation with time delay (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An enhanced teleoperation technique for time-delayed bilateral teleoperator control is discussed. The control technique selected for time delay is based on the use of a high-fidelity graphics phantom robot that is being controlled in real time (without time delay) against the static task image. Thus, the motion of the phantom robot image on the monitor predicts the motion of the real robot. The real robot's motion will follow the phantom robot's motion on the monitor with the communication time delay implied in the task. Real-time high-fidelity graphics simulation of a PUMA arm is generated and overlaid on the actual camera view of the arm. A simple camera calibration technique is used for calibrated graphics overlay. A preliminary experiment is performed with the predictive display by using a very simple tapping task. The results with this simple task indicate that predictive display enhances the human operator's telemanipulation task performance significantly during free motion when there is a long time delay. It appears, however, that either two-view or stereoscopic predictive displays are necessary for general three-dimensional tasks.
    Keywords: CYBERNETICS
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  • 7
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    Low Earth orbital atomic oxygen micrometeoroid, and debris interactions with photovoltaic arrays (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Polyimide Kapton solar array blankets can be protected from atomic oxygen in low earth orbit if SiO sub x thin film coatings are applied to their surfaces. The useful lifetime of a blanket protected in this manner strongly depends on the number and size of defects in the protective coatings. Atomic oxygen degradation is dominated by undercutting at defects in protective coatings caused by substrate roughness and processing rather than micrometeoroid or debris impacts. Recent findings from the Long Duration Exposure Facility (LDEF) and ground based studies show that interactions between atomic oxygen and silicones may cause grazing and contamination problems which may lead to solar array degradation.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: Space Photovoltaic Research and Technology Conference; 10 p
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  • 8
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    GaAs (AlGaAs)/CuInSe2 tandem solar cells. Technology status and future directions (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Mechanically stacked, high efficiency, lightweight, and radiation resistant photovoltaic cells based on a GaAs thin film top and CuInSe2 thin film bottom cells were developed, and are considered one of the most promising devices for planar solar array applications. The highest efficiency demonstrated so far using the 4 sq cm design is 23.1 pct. AM0, one sun efficiency when measured in four-terminal configuration. The current status of the GaAs(AlGaAs)/CuInSe2 tandem cell program is presented and future directions that will lead to cell efficiencies higher than 26 pct. Air Mass Zero (AM0). A new 8 sq cm cell design developed for a two terminal and voltage matched configuration to minimize wiring complexity is discussed. Optimization of the GaAs structure for a higher end-of-life performance and further improvement of tandem cells by utilizing AlGaAs as an top absorber are described. Results of environmental tests conducted with these thin film GaAs/CuInSe2 tandem cells are also summarized.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: NASA. Lewis Research Center, Space Photovoltiac Research and Technology Conference; 10 p
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  • 9
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    STME Hydrogen Mixer Study (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The hydrogen mixer for the Space Transportation Main Engine is used to mix cold hydrogen bypass flow with warm hydrogen coolant chamber gas, which is then fed to the injectors. It is very important to have a uniform fuel temperature at the injectors in order to minimize mixture ratio problems due to the fuel density variations. In addition, the fuel at the injector has certain total pressure requirements. In order to achieve these objectives, the hydrogen mixer must provide a thoroughly mixed fluid with a minimum pressure loss. The AEROVISC computational fluid dynamics (CFD) code was used to analyze the STME hydrogen mixer, and proved to be an effective tool in optimizing the mixer design. AEROVISC, which solves the Reynolds Stress-Averaged Navier-Stokes equations in primitive variable form, was used to assess the effectiveness of different mixer designs. Through a parametric study of mixer design variables, an optimal design was selected which minimized mixed fuel temperature variation and fuel mixer pressure loss. The use of CFD in the design process of the STME hydrogen mixer was effective in achieving an optimal mixer design while reducing the amount of hardware testing.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: NASA. Goddard Space Flight Center, Tenth Workshop for Computational Fluid Dynamic Applications in Rocket Propulsion, Part 2; p 1093-1116
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  • 10
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    Performance experiments with alternative advanced teleoperator control modes for a simulated solar maximum satellite repair (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Experiments are described which were conducted at the JPL Advanced Teleoperator Lab to demonstrate and evaluate the effectiveness of various teleoperator control modes in the performance of a simulated Solar Max Satellite Repair (SMSR) task. THe SMSR was selected as a test because it is very rich in performance capability requirements and it actually has been performed by two EVA astronauts in the Space Shuttle Bay in 1984. The main subtasks are: thermal blanket removal; installation of a hinge attachment for electrical panel opening; opening of electrical panel; removal of electrical connectors; relining of cable bundles; replacement of electrical panel; securing parts and cables; re-mate electrical connectors; closing of electrical panel; and reinstating thermal blanket. The current performance experiments are limited to thermal blanket cutting, electrical panel unbolting and handling electrical bundles and connectors. In one formal experiment even different control modes were applied to the unbolting and reinsertion of electrical panel screws subtasks. The seven control modes are alternative combinations of manual position and rate control with force feedback and remote compliance referenced to force-torque sensor information. Force-torque sensor and end effector position data and task completion times were recorded for analysis and quantification of operator performance.
    Keywords: CYBERNETICS
    Type: NASA. Lyndon B. Johnson Space Center, Fifth Annual Workshop on Space Operations Applications and Research (SOAR 1991), Volume 1; p 294-301
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