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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Modification in drag of turbulent boundary layers resulting from manipulation of large-scale structures

The effects of placing a parallel-plate turbulence manipulator in a boundary layer are documented through flow visualization and hot wire measurements. The boundary layer manipulator was designed to manage the large scale structures of turbulence leading to a reduction in surface drag. The differences in the turbulent structure of the boundary layer are summarized to demonstrate differences in various flow properties. The manipulator inhibited the intermittent large scale structure of the turbulent boundary layer for at least 70 boundary layer thicknesses downstream. With the removal of the large scale, the streamwise turbulence intensity levels near the wall were reduced. The downstream distribution of the skin friction was also altered by the introduction of the manipulator.

Corke, T. C.↗
NASA NTRS1980

Modification in drag of turbulent boundary layers resulting from manipulation of large-scale structures

The effects of placing a parallel-plate turbulence manipulator in a boundary layer are investigated by means of flow visualization and hot-wire measurements. The manipulator was found to be effective in inhibiting the intermittent large scale structure of the boundary layer, and the effect persists for at least 70 boundary-layer thicknesses downstream of the manipulator. With the removal of the large scale, there was an observed reduction in the streamwise turbulence intensity levels near the wall. The downstream distribution of the skin friction coefficient, determined from the stream wise change in fluid momentum, was also altered by the introduction of the manipulator. The data from both the visualization and hot wire studies are provided.

Corke, T. C.↗
NASA NTRS1986

Automatic Guidance for Remote Manipulator

Position sensor and mirror guides manipulator toward object. Grasping becomes automatic when sensor begins to receive signal from reflector on object to be manipulated. Light-emitting diodes on manipulator produce light signals for reflector, which is composite of plane and corner reflectors. Proposed scheme especially useful when manipulator arm tends to flex or when object is moving. Sensor and microprocessor designed to compensate for manipulatorarm oscillation.

Johnston, A. R.↗
NASA NTRS1986

Mobile Remote Manipulator

Turret, roll arm, and trolley enhance manipulator dexterity. Remote manipulator moves on trolley base along structure. Roll-axis arm positions manipulator arm so it can extend end effector under structure. Yaw-axis rotation gives added reach to arm above structure. Designed for handling, inspecting, and maintaining modules of space station. Manipulators having such capabilities useful on Earth; robots in manufacturing, erection of large structures, or performing complicated tasks in hazardous locations.

Coryell, S.↗
NASA NTRS1986

Skin friction and Reynolds stress measurements for a turbulent boundary layer following manipulation using flat plates

Research has been undertaken to experimentally study the alterations in turbulent boundary-layer properties due to turbulence manipulation using thin flat plates. Plate geometry and placement within the boundary layer were selected to coincide with recent studies. Direct, local measurements of skin friction and Reynolds stresses were made within the boundary layer downstream of the manipulator devices for cases with an approach momentum thickness Reynolds number of 3700. A strong tendency for recovery of the Reynolds stresses was observed, accompanied by local skin-friction reductions of up to 15 percent. The mean velocity profile in the manipulated flow displayed the same similarity shape in the logarithmic region as a natural boundary layer, but had an enhanced wake component. The results indicate that the plate wake plays an important role in the boundary layer response to this sort of manipulation.

Westphal, R. V.↗
NASA NTRS1985

Time optimal robotic manipulator motions and work places for point to point tasks

High productivity requires that manipulators perform complex tasks quickly. Recently, optimal control algorithms have been developed which enable manipulators to move quickly, but only for simple motions. A method is presented here which combines simple time optimal motions in an optimal manner to yield the minimum time motions for an important class of complex manipulator tasks composed of point to point moves, such as assembly, electronic component insertion and spot welding. This method can also be used to design manipulator actions and work places so that tasks can be completd in minimum time. The method has been implemented in a CAD software package. Examples are presented which show the methods effectiveness.

Dubowsky, S.↗
NASA NTRS1987

An optimal resolved rate law for kinematically redundant manipulators

The resolved rate law for a manipulator provides the instantaneous joint rates required to satisfy a given instantaneous hand motion. When the joint space has more degrees of freedom than the task space, the manipulator is kinematically redundant and the kinematic rate equations are underdetermined. These equations can be locally optimized, but the resulting pseudo-inverse solution has been found to cause large joint rates in some cases. A weighting matrix in the locally optimized (pseudo-inverse) solution is dynamically adjusted to control the joint motion as desired. Joint reach limit avoidance is demonstrated in a kinematically redundant planar arm model. The treatment is applicable to redundant manipulators with any number of revolute joints and to non-planar manipulators.

Bourgeois, B. J.↗
NASA NTRS1987

Manipulator arm design for the Extravehicular Teleoperator Assist Robot (ETAR): Applications on the space station

The preliminary conceptual design of a new teleoperator robot manipulator system for space station maintenance missions has been completed. The system consists of a unique pair of arms that is part of a master-slave, force-reflecting servomanipulator. This design allows greater dexterity and greater volume coverage than that available in current designs and concepts. The teleoperator manipulator is specifically designed for space applications and is a valuable extension of the current state-of-the-art earthbound manipulators marketed today. The manipulator and its potential application on the space station are described.

Clarke, Margaret M.↗
NASA NTRS1988

The dynamic control of robotic manipulators in space

Described briefly is the work done during the first half year of a three-year study on dynamic control of robotic manipulators in space. The research focused on issues for advanced control of space manipulators including practical issues and new applications for the Virtual Manipulator. In addition, the development of simulations and graphics software for space manipulators, begun during the first NASA proposal in the area, has continued. The fabrication of the Vehicle Emulator System (VES) is completed and control algorithms are in process of development.

Dubowsky, S.↗
NASA NTRS1988

Next-generation space manipulator

In 1977, the Protoflight Manipulator Arm (PFMA) was designed and built. It is one of two space qualified manipulators. A new conceptual design for the next generation manipulator of space applications is presented. The next generation manipulator and the PFMA are described in detail. Their differences could have a major influence on the construction, testing, and performance of a space arm. Assessed in detail are these technologies and their effect on the design. Servicing is an important goal of robotics in space. Parameters such as environment, type of task, time sequence, and dexterity will affect the arm and its ability to accomplish its mission. Requirements such as these are important considerations in the design of the next generation space arm.

Brunson, P.↗
NASA NTRS1987

A new approach to adaptive control of manipulators

An approach in which the manipulator inverse is used as a feedforward controller is employed in the adaptive control of manipulators in order to achieve trajectory tracking by the joint angles. The desired trajectory is applied as an input to the feedforward controller, and the controller output is used as the driving torque for the manipulator. An adaptive algorithm obtained from MRAC theory is used to update the controller gains to cope with variations in the manipulator inverse due to changes of the operating point. An adaptive feedback controller and an auxiliary signal enhance closed-loop stability and achieve faster adaptation. Simulation results demonstrate the effectiveness of the proposed control scheme for different reference trajectories, and despite large variations in the payload.

Seraji, H.↗
NASA NTRS1987

A comparison of position and rate control for telemanipulations with consideration of manipulator system dynamics

Position and rate control are the two common manual control modes in teleoperations. Human operator performance using the two modes is evaluated and compared. Simulated three-axis pick-and-place operations are used as the primary task for evaluation. First, ideal position and rate control are compared by considering several factors, such as joystick gain, joystick type, display mode, task, and manipulator work space size. Then the effects of the manipulator system dynamics are investigated by varying the natural frequency and speed limit. Experimental results show that ideal position control is superior to ideal rate control, regardless of joystick type or display mode, when the manipulation work space is small or comparable to the human operator's control space. Results also show that when the manipulator system is slow, the superiority of position control disappears. Position control is recommended for small-work-space telemanipulation tasks, while rate control is recommended for slow wide-work-space telemanipulation tasks.

Kim, Won S.↗
NASA NTRS1987

Time optimal paths and acceleration lines of robotic manipulators

The concept of acceleration lines and their correlation with time-optimal paths of robotic manipulators is presented. The acceleration lines represent the directions of maximum tip acceleration from a point in the manipulator work-space, starting at a zero velocity. These lines can suggest the number and shapes of time-optimal paths for a class of manipulators. It is shown that nonsingular time-optimal paths are tangent to one of the acceleration lines near the end-points. A procedure for obtaining near-optimal paths, utilizing the acceleration lines, is developed. These paths are obtained by connecting the end-points with B splines tangent to the acceleration lines. The near-minimum paths are shown to yield better traveling times than the straight-line path between the same end-points. The near-minimum paths can be used as initial conditions in existing optimization methods to speed-up convergence and computation time. This method can be used for online robot path planning and for interactive designs of robotic-cell layouts. Examples of time-optimal paths of a two-link manipulator, obtained by other optimization procedures and their acceleration lines, are shown.

Shiller, Zvi↗
NASA NTRS1988

Minimum-time pointing control of a two-link manipulator

Minimum-time pointing control for the end-effector of a planar, two-link manipulator is developed. Minimum-time pointing control is a new area of research for multilink manipulators, which can be applied to rapid retargeting control of a multibody spacecraft. The minimum-time control problem of aligning the second link of the two-link manipulator with a given target point is considered. A numerical method called the minimizing-boundary-condition method is used to determine optimal solutions for the two-point boundary-value problem associated with first-order necessary conditions. Minimum-time solutions for different models of pointing systems are compared. The results of the comparison show that a two-link manipulator with two degree-of-freedom performs better than a conventional one-link system for minimum-time pointing.

Wie, Bong↗
NASA NTRS1988

Performance of lightweight manipulators under joint variable feedback control - Analytical study of limitations

The performance limitations of joint-variable-feedback-controlled manipulators due to manipulator flexibility are studied in fine and gross motions. A finite-dimensional time-domain manipulator model is used in the study. Fine-motion analysis results agree very well with the previously reported results of infinite-dimensional frequency-domain models. The limitations of a class of adaptive controllers in high-speed gross motion control are studied. Manipulation speeds are quantified as low, medium, or high with reference to the arm flexibility and dynamic nonlinearities.

Cetinkunt, Sabri↗
NASA NTRS1989

Improving A Remote Manipulator

Set of three reports describes work on Protoflight Manipulator Assembly (PFMA). "Performance Characteristics of Protoflight Manipulator Assembly" presents parameters of PFMA after refurbishment of operating components. "End Effector and Task Board Development for the Protoflight Manipulator Assembly" describes special tools and adaptations allowing PFMA to be used for servicing equipment. "Modular Software Development for the Protoflight Manipulator Assembly" documents interface and control software for PFMA.

Haslam, John W., Jr.↗
NASA NTRS1987

An optimal resolved rate law for kindematically redundant manipulators

The resolved rate law for a manipulator provides the instantaneous joint rates required to satisfy a given instantaneous hand motion. When the joint space has more degrees of freedom than the task space, the manipulator is kinematically redundant and the kinematic rate equations are underdetermined. These equations can be locally optimized, but the resulting pseudo-inverse solution was found to cause large joint rates in some case. A weighting matrix in the locally optimized (pseudo-inverse) solution is dynamically adjusted to control the joint motion as desired. Joint reach limit avoidance is demonstrated in a kinematically redundant planar arm model. The treatment is applicable to redundant manipulators with any number of revolute joints and to nonplanar manipulators.

Bourgeois, B. J.↗
NASA NTRS1988

Local position control: A new concept for control of manipulators

Resolved motion rate control is currently one of the most frequently used methods of manipulator control. It is currently used in the Space Shuttle remote manipulator system (RMS) and in prosthetic devices. Position control is predominately used in locating the end-effector of an industrial manipulator along a path with prescribed timing. In industrial applications, resolved motion rate control is inappropriate since position error accumulates. This is due to velocity being the control variable. In some applications this property is an advantage rather than a disadvantage. It may be more important for motion to end as soon as the input command is removed rather than reduce the position error to zero. Local position control is a new concept for manipulator control which retains the important properties of resolved motion rate control, but reduces the drift. Local position control can be considered to be a generalization of resolved position and resolved rate control. It places both control schemes on a common mathematical basis.

Kelly, Frederick A.↗