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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Intelligent Robotic Systems Study (IRSS), phase 2

Under the Intelligent Robotics System Study (IRSS) contract, a generalized robotic control architecture was developed for use with the ProtoFlight Manipulator Arm (PFMA). The controller built for the PFMA provides localized position based force control, teleoperation and advanced path recording and playback capabilities. Various hand controllers can be used with the system in conjunction with a synthetic time delay capability to provide a realistic test bed for typical satellite servicing tasks. The configuration of the IRSS system is illustrated and discussed. The PFMA has six computer controllable degrees of freedom (DOF) plus a seventh manually indexable DOF, making the manipulator a pseudo 7 DOF mechanism. Because the PFMA was not developed to operate in a gravity field, but rather in space, it is counter balanced at the shoulder, elbow and wrist and a spring counterbalance has been added near the wrist to provide additional support. Built with long slender intra-joint linkages, the PFMA has a workspace nearly 2 meters deep and possesses sufficient dexterity to perform numerous satellite servicing tasks. The manipulator is arranged in a shoulder-yaw, pitch, elbow-pitch, and wrist-pitch, yaw, roll configuration, with an indexable shoulder roll joint. Digital control of the PFMA is implemented using a variety of single board computers developed by Heurikon Corporation and other manufacturers. The IRSS controller is designed to be a multi-rate, multi-tasking system. Independent joint servos run at a 134 Hz rate and position based impedance control functions at 67 Hz. Autonomous path generation and hand controller inputs are processed at a 33 Hz.

Source record↗
NASA NTRS1990

Constrained trajectory optimization for kinematically redundant arms

Two velocity optimization schemes for resolving redundant joint configurations are compared. The Extended Moore-Penrose Technique minimizes the joint velocities and avoids obstacles indirectly by adjoining a cost gradient to the solution. A new method can incorporate inequality constraints directly to avoid obstacles and singularities in the workspace. A four-link arm example is used to illustrate singularity avoidance while tracking desired end-effector paths.

Carignan, Craig R.↗
NASA NTRS1990

FACE computer simulation

A computer simulation of the FACE (Flexible Arm Controls Experiment) was conducted to assess its design for use in the Space Shuttle. The FACE is supposed to be a 14-ft long articulate structure with 4 degrees of freedom, consisting of shoulder pitch and yaw, elbow pitch, and wrist pitch. Kinematics of the FACE was simulated to obtain data on arm operation, function, workspace and interaction. Payload capture ability was modeled. The simulation indicates the capability for detailed kinematic simulation and payload capture ability analysis, and the feasibility of real-time simulation was determined. In addition, the potential for interactive real-time training through integration of the simulation with various interface controllers was revealed. At this stage, the flexibility of the arm was not yet considered.

Sadeh, Willy Z.↗
NASA NTRS1991

Trajectory optimization for kinematically redundant arms

A review of local optimization methods for resolving joint configurations in underconstrained manipulation tasks is conducted. A new approach is developed for observing joint limits and avoiding obstacles during the trajectory planning. The methodology is used in a four-link arm example to avoid a workspace singularity and is compared with results using the extended Moore-Penrose technique. An alternative measure of arm 'manipulability' based directly on the rank of the Jacobian is also introduced.

Carignan, Craig R.↗
NASA NTRS1990

Task decomposition for multilimbed robots to work in the reachable-but-unorientable space

Multilimbed industrial robots that have at least one arm and two or more legs are suggested for enlarging robot workspace in industrial automation. To plan the motion of a multilimbed robot, the arm-leg motion-coordination problem is raised and task decomposition is proposed to solve the problem; that is, a given task described by the destination position and orientation of the end-effector is decomposed into subtasks for arm manipulation and for leg locomotion, respectively. The former is defined as the end-effector position and orientation with respect to the legged main body, and the latter as the main-body position and orientation in the world coordinates. Three approaches are proposed for the task decomposition. The approaches are further evaluated in terms of energy consumption, from which an optimal approach can be selected.

Su, Chao↗
NASA NTRS1990

Adaptive tracking for complex systems using reduced-order models

Reduced-order models are considered in the context of parameter adaptive controllers for tracking workspace trajectories. A dual-arm manipulation task is used to illustrate the methodology and provide simulation results. A parameter adaptive controller is designed to track a payload trajectory using a four-parameter model instead of the full-order, nine-parameter model. Several simulations with different payload-to-arm mass ratios are used to illustrate the capabilities of the reduced-order model in tracking the desired trajectory.

Carnigan, Craig R.↗
NASA NTRS1992

Integrated Scene And Graphics For Multiple-Camera Viewing

Multiple-video-camera viewing system for monitoring telerobot undergoing development. System presents user with variety of information on single video display: picture of robot from any of five movable cameras, graphical depiction of location and orientation of camera producing current picture in middle of video display, graphical depiction of locations and orientations of other cameras, and graphical images of fields of view of cameras and three-dimensional relationship to workspace of telerobot. Display helps user control telerobot quickly and efficiently.

Diner, Daniel B.↗
NASA NTRS1992

Magnetic Location Indicator

Ferrofluidic device indicates point of highest magnetic-flux density in workspace. Consists of bubble of ferrofluid in immiscible liquid carrier in clear plastic case. Used in flat block or tube. Axes of centering circle on flat-block version used to mark location of maximum flux density when bubble in circle. Device used to find point on wall corresponding to known point on opposite side of wall.

Stegman, Thomas W.↗
NASA NTRS1992

Hand/Eye Coordination For Fine Robotic Motion

Fine motions of robotic manipulator controlled with help of visual feedback by new method reducing position errors by order of magnitude. Robotic vision subsystem includes five cameras: three stationary ones providing wide-angle views of workspace and two mounted on wrist of auxiliary robot arm. Stereoscopic cameras on arm give close-up views of object and end effector. Cameras measure errors between commanded and actual positions and/or provide data for mapping between visual and manipulator-joint-angle coordinates.

Lokshin, Anatole M.↗
NASA NTRS1990

Planning and reasoning in the JPL telerobot testbed

The Telerobot Interactive Planning System is developed to serve as the highest autonomous-control level of the Telerobot Testbed. A recent prototype is described which integrates an operator interface for supervisory control, a task planner supporting disassembly and re-assembly operations, and a spatial planner for collision-free manipulator motion through the workspace. Each of these components is described in detail. Descriptions of the technical problem, approach, and lessons learned are included.

Peters, Stephen↗
NASA NTRS1991

Computational modelling of polymers

Polymeric materials and polymer/graphite composites show a very diverse range of material properties, many of which make them attractive candidates for a variety of high performance engineering applications. Their properties are ultimately determined largely by their chemical structure, and the conditions under which they are processed. It is the aim of computational chemistry to be able to simulate candidate polymers on a computer, and determine what their likely material properties will be. A number of commercially available software packages purport to predict the material properties of samples, given the chemical structures of their constituent molecules. One such system, Cerius, has been in use at LaRC. It is comprised of a number of modules, each of which performs a different kind of calculation on a molecule in the programs workspace. Particularly, interest is in evaluating the suitability of this program to aid in the study of microcrystalline polymeric materials. One of the first model systems examined was benzophenone. The results of this investigation are discussed.

Celarier, Edward A.↗
NASA NTRS1991

Visual direction as a metric of virtual space

Two experiments examine the abilities of ten subjects to visualize directions shown on a perspective display. Subjects indicated their perceived directions by adjusting a head-mounted cursor to correspond to the direction depicted on the display. This task is required of telerobotic operators who use map-like pictures of their workspace to determine the direction of objects seen by direct view. Results show significant open loop judgment biases that may be composed of errors arising from misinterpretation of the map geometry and overestimation of gaze direction.

Ellis, Stephen R.↗
NASA NTRS1992

Precise positioning and compliance synthesis for automatic assembly using Lorentz levitation

Many manufacturing assembly tasks require fine compliant motion and fast, accurate positioning. Conventional robots perform poorly in these tasks because of their large mass, friction and backlash in gears, cogging in drive motors and other deleterious effects. Even robots equipped with special control systems enabling compliant operation offer only partial solutions. It is difficult or impossible to automate many product assemblies requiring fine, compliant motion. This problem can be greatly alleviated by dividing the manipulation system into coarse and fine domains. In this scenario, a standard industrial robot can serve as a coarse positioner which in turn carries a six degrees of freedom fine motion wrist. Thus the robot can access a workspace measured in meters at low bandwidth and low resolution while the wrist can move over millimeters at high bandwidth and high resolution during the final phase of the assembly operation. Work indicates that fine motion wrists using Lorentz levitation can greatly augment the accuracy and dexterity of robots because they are frictionless, have high bandwidths and have a single back drivable moving part. Also, since there is no contact between the moving and stationary parts, wear and contamination can be eliminated. The use of six Lorentz force actuators in combination with real time position and orientation sensing offers several important advantages over magnetic bearing approaches.

Hollis, R. L.↗
NASA NTRS1992

Obstacle avoidance for redundant robots using configuration control

A redundant robot control scheme is provided for avoiding obstacles in a workspace during the motion of an end effector along a preselected trajectory by stopping motion of the critical point on the robot closest to the obstacle when the distance between is reduced to a predetermined sphere of influence surrounding the obstacle. Algorithms are provided for conveniently determining the critical point and critical distance.

Seraji, Homayoun↗
NASA NTRS1990

Navigating through large display networks in dynamic control applications

Special display navigation challenges in computer-based display systems for monitoring and controlling dynamic processes are reviewed. Particular attention is given to trends in information technology, workspace design, and paradigmatic cognitive functions related to display navigation.

Woods, David D.↗
NASA NTRS1991

Task decomposition for a multilimbed robot to work in reachable but unorientable space

Robot manipulators installed on legged mobile platforms are suggested for enlarging robot workspace. To plan the motion of such a system, the arm-platform motion coordination problem is raised, and a task decomposition is proposed to solve the problem. A given task described by the destination position and orientation of the end effector is decomposed into subtasks for arm manipulation and for platform configuration, respectively. The former is defined as the end-effector position and orientation with respect to the platform, and the latter as the platform position and orientation in the base coordinates. Three approaches are proposed for the task decomposition. The approaches are also evaluated in terms of the displacements, from which an optimal approach can be selected.

Su, Chau↗
NASA NTRS1991

Experiments in robotic catching

Real-time coordination of visual information with high-speed manipulator control is studied in the context of three-dimensional robotic catching. All path planning for the catch occurs in real-time during the half-second that the targeted object is airborne. A trajectory-matching algorithm is used that combines an observer with a varying-strength filter, an error estimator, and an initial motion algorithm. The results are demonstrated experimentally using a real-time vision system and a four-degree-of-freedom, cable-driven arm with a workspace of 4.2 m3 and speed capabilities of up to 2.0 m/s.

Hove, Barbara↗
NASA NTRS1992

Teleoperator performance in simulated Solar Maximum Satellite repair

An investigation is conducted of the relative benefits of different teleoperator control modes in simulated space servicing. The simulation replicates part of the Solar Maximum EVA Satellite Repair (SMSR) mission of STS-13, in 1974. The formal experimental design and statistical analysis presented demonstrates that position control is superior for small workspace volume management. Quantitative studies demonstrate significant benefits of shared Cartesian control modes for contact tasks; good performance will require the systematic analysis and synthesis of man-machine systems.

Schenker, Paul S.↗