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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 289 records · Page 16

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NASA NTRS1978

The proto-type wrist joint assembly TACPAW (Triple Axis Common Pivot Arm Wrist), phase 2

A wrist joint assembly is described for use with a mechanical manipulator arm for finely positioning an end-effector carried by the wrist joint on the terminal end of the manipulator arm. The wrist joint assembly is pivotable about a first axis to produce a yaw motion, a second axis to produce a pitch motion, and a third axis to produce a roll motion. The performance of the wrist configuration is indicative of the capability to produce the 15 ft lb torque in either one of the three motions and the smoothness of operation is notable.

Kersten, L.↗

NASA NTRS1980

Triple-axis common-pivot arm wrist device for manipulative applications

A concept in manipulator development to overcome the 'weak wrist syndrome', a triple-axis common-pivot arm wrist (TACPAW), is presented. It contains torque motors for actuation, tachometers for measuring rate, and resolvers for position measurements. Furthermore, it provides three degrees of freedom, i.e., pitch, yaw, and roll, in a single manipulator joint. The advantages of this development are increased strength, compactness, and simplification of controls. Designed to be compatible with the protoflight manipulator arm, the joints of TACPAW are back-driveable with + or - 45 deg rotation in pitch, + or - 45 deg in yaw and continuous roll in either direction while delivering 20.5 N-m (15 ft-lb) torque in each of the three movements.

Kersten, L.↗

NASA NTRS1980

Control of a flexible robot arm

Exact equations of motion of an arm with known parameters were developed and analyzed preparatory to designing control systems for robotic manipulators. The design of an experimental one-link arm for testing control designs is presented.

Schmitz, E.↗

NASA NTRS1981

Surface photometry of spiral galaxies. I - Theoretical color variation and surface brightness across spiral arms

A method for the construction of color variations and surface brightness across a galactic spiral arm, using the concepts and results of the density-wave theory, is developed. The color variation measured by the index Q varies with the ratio of the light of young stars to that of the old stars, the initial mass function, and the pattern speed. The fact that the variation of brightness and color across a spiral arm is relatively smooth and symmetrical and not sharp as in the galactic shock picture is due to the smearing-out effects of star formation inside a cloud in the regions behind the galactic shock, and the tendency of new stars to fall back to small galactocentric distances after their formation because of their lower angular velocity at birth. Both effects arise naturally in the context of the density-wave theory.

Yuan, C.↗

NASA NTRS1981

Cloud fluid compression and softening in spiral arms and the formation of giant molecular cloud complexes

With regard to the galactodynamics of the cloudy interstellar medium, the paper considers the response of such a gas to a forcing potential in the tight-winding density wave theory. The cloud fluid is treated in the hydrodynamic limit with an equation of state which softens at high densities. It is shown that in the inner regions of the galaxy, cooling of the cloud fluid in the arms can result in gravitational instability and the formation of large bound complexes of clouds which are identified with the giant molecular clouds (GMCs). Masses, dimensions, distributions, and scale heights of the GMCs are predicted by the theory. It is suggested that the interstellar gas density in the disk is regulated by the gravitational instability mechanism in the arms which siphons material into star formation. Implications for the evolution of individual GMCs and for galactic morphology are discussed.

Cowie, L. L.↗

NASA NTRS1981

Vertical extensions of galactic spiral arms

The vertical structure of the large scale galactic shock along spiral arms is studied in order to understand the extended features or the wings of spiral arms observed by Kepner (1970) and recently checked by Soukup (1979). Numerical calculations of two-dimensional gas flow were performed for two models of the gas. The results show that the shock front, standing perfectly perpendicular to the galactic plane, extends impressively above the scale height of the interstellar gas. In the extreme case of isothermal gas, the shock solution exists at any distance from the plane. In a realistic model in which the kinetic temperature of the gas is stratified, increasing with height, the shock can extend up to 700 pc. For both models, although the velocity component perpendicular to the galactic plane is small, the solutions corresponding to layered one-dimensional flow contain no shocks at such heights. In order to study the geometry of the shock front and the flow pattern near it, a simplified model is adopted, in which the Coriolis force is neglected. However, estimates show that including it will enhance the shock strength. The compression at the shock front makes the gas observable at high latitudes.

Soukup, J. E.↗

NASA NTRS1982

Computer coordination of limb motion for locomotion of a multiple-armed robot for space assembly

Consideration is given to a possible robotic system for the construction of large space structures, which may be described as a multiple general purpose arm manipulator vehicle that can walk over the structure under construction to a given site for further work. A description is presented of the locomotion of such a vehicle, modeling its arms in terms of a currently available industrial manipulator. It is noted that for whatever maximum speed of operation is chosen, rapid changes in robot velocity create situations in which already-selected handholds are no longer practical. A step is added to the 'free gait' walking algorithm in order to solve this problem.

Klein, C. A.↗

NASA NTRS1982

Controller design for flexible, distributed parameter mechanical arms via combined state space and frequency domain techniques

The potential benefits of the ability to control more flexible mechanical arms are discussed. A justification is made in terms of speed of movement. A new controller design procedure is then developed to provide this capability. It uses both a frequency domain representation and a state variable representation of the arm model. The frequency domain model is used to update the modal state variable model to insure decoupled states. The technique is applied to a simple example with encouraging results.

Book, W. J.↗

NASA NTRS1985

Force Sensor for Large Robot Arms

Modified Maltese-cross force sensor larger and more sensitive than earlier designs. Measures inertial forces and torques exerted on large robot arms during free movement as well as those exerted by claw on manipulated objects. Large central hole of sensor allows claw drive mounted inside arm instead of perpendicular to its axis, eliminating potentially hazardous projection. Originally developed for Space Shuttle, sensor finds applications in large industrial robots.

Bejczy, A. K.↗

NASA NTRS1986

Computational Simplification of Robot-Arm Dynamics

Report presents two general methods for reducing mathematical complexities of state equations of robot-arm dynamics. Robot arms contain both rotary and linear joints. Both methods start with homogenous coordinates and Lagrangian formulation of mechanics briefly summarized in report. First method uses matrix-analysis techniques; second, vector-analysis techniques. Vector-analysis method includes new differential-vector representation of centripetal and Coriolis forces.

Bejczy, A. K.↗

NASA NTRS1985

External Tank GH2 Vent Arm

Because the venting of free hydrogen gas to the atmosphere presents an extremely hazardous situation, it was necessary to devise a means for safe, controlled venting of the shuttle external tank gaseous hydrogen during and after liquid hydrogen tank loading. Several design concepts that were considered initially were discarded as unfeasible because of vehicle weight restrictions, high cost, and because the proposed structure was itself deemed a hazard due to the vehicle's nonvertical launch trajectory. These design concepts are discussed. A design employing a support structure/access arm attached to the fixed service structure was finally selected. The various design problems resolved included vent arm disconnect/drop interference, minimizing refurbishment due to launch damage, disconnect reliability, vehicle movement tracking, minimizing vent line pressure drop, and the presence of other vehicle services at the same centralized supply area. Six launches have proven the system to be reliable, efficient, and of nearly zero refurbishment cost.

Reichle, G. E.↗

NASA NTRS1984

Generalized bilateral control of robot arms

This paper summarizes the theory of a new form of bilateral or force-reflecting manual control of remote robot (slave) arms. The mathematics of workspace representation, command structure, kinematic and dynamic control coordination required for implementing the new form of generalized bilateral control through computer programs is presented. The paper concludes with a brief description of implementation organization of the new system using a six-degree-of-freedom backdrivable hand controller, a PUMA 560 robot arm and a distributed net of microcomputers organized in two groups: one at the remote work site and one at the control station.

Bejczy, A. K.↗

NASA NTRS1985

Parameter identification for a robotic manipulator arm

The development is described of a nonlinear dynamic model for large oscillations of a robotic manipulator arm about a single joint. Optimization routines are formulated and implemented for the identification of electrical and physical parameters from dynamic data taken from an industrial robot arm. Special attention is given to the role of sensitivity in the formulation of robust models of this motion. The importance of actuator effects in the reduction of sensitivity is established and used to develop an electromechanical model of the manipulator system.

Brewer, D. W.↗

NASA NTRS1985

On the gravitational stability of the interstellar medium in spiral arms

The dynamics of self-gravitating gaseous density perturbations in the tightly wound spiral-arm model of the forcing potential (Brown 1969) is investigated. The cloud ensemble of the cold phase of the interstellar medium is regarded as a collisional gas whose 'molecules' are the clouds themselves, and the dynamical evolution of density perturbations is calculated assuming this gas obeys a polytropic pressure-density law. It is suggested that the formation of extreme Population I objects found predominantly along the arms of Sb/Sc systems is regulated by an overall energy balance in the cloud fluid. A single parameter is found which appears to characterize the flow's gravitational response to perturbations; this spiral parameter, Q-sub-sp, differs from the Toomre Q parameter by a factor of the square root of the density enhancement at the shock. It is necessary but not sufficient that Q-sub-sp be less than unity for significant growth to occur.

Balbus, S. A.↗

NASA NTRS1985

Robust torque control of an elastic robotic arm based on invertibility and feedback stabilization

An approach to the control of elastic robotic systems for space applications using inversion, servocompensation, and feedback stabilization is presented. For simplicity, a robot arm (PUMA-type) with three rotational joints is considered. The third link is assumed to be elastic. Using an inversion algorithm, a nonlinear decoupling control law, u sub d, is derived such that in the closed loop system, independent control of joint angles by the three joint torquers is accomplished. For the stabilization of elastic oscillations, a linear feedback torquer control law, u sub s, is obtained applying linear quadratic optimization to the linearized arm model augmented with a servocompensator about the terminal state. Simulation results show that, in spite of uncertainties in the payload and vehicle angular velocity, good joint angle control and damping of elastic oscillations are obtained with the torquer control law u = u sub d + u sub s.

Singh, S. N.↗

NASA NTRS1987

Large scale dissociation of molecular gas in the sprial arms of M51

The distribution of the atomic and ionized hydrogen along the inner spiral arms of M51 are compared. As is the case in M83, the location of both these phases of the interstellar medium with respect to the major dust lanes suggests that molecular hydrogen is dissociated on kpc scales in active star-forming regions, and that this dissociation process may strongly affect the observed morphology of atomic hydrogen in spiral arms.

Tilanus, R. P. J.↗

NASA NTRS1987

Goal driven kinematic simulation of flexible arm robot for space station missions

Flexible arms offer a great degree of flexibility in maneuvering in the space environment. The problem of transporting an astronaut for extra-vehicular activity using a space station based flexible arm robot was studied. Inverse kinematic solutions of the multilink structure were developed. The technique is goal driven and can support decision making for configuration selection as required for stability and obstacle avoidance. Details of this technique and results are given.

Janssen, P.↗

NASA NTRS1987

Solid modelling for the manipulative robot arm (power) and adaptive vision control for space station missions

The structure of a flexible arm derived from concatenation of the Stewart-Table-based links were studied. Solid modeling provides not only a realistic simulation, but is also essential for studying vision algorithms. These algorithms could be used for the adaptive control of the arm, using the well-known algorithms such as shape from shading, edge detection, orientation, etc. Details of solid modeling and its relation to vision based adaptive control are discussed.

Harrand, V.↗