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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Large planar maneuvers for articulated flexible manipulators

An articulated flexible manipulator carried on a translational cart is maneuvered by an active controller to perform certain position control tasks. The nonlinear dynamics of the articulated flexible manipulator are derived and a transformation matrix is formulated to localize the nonlinearities within the inertia matrix. Then a feedback linearization scheme is introduced to linearize the dynamic equations for controller design. Through a pole placement technique, a robust controller design is obtained by properly assigning a set of closed-loop desired eigenvalues to meet performance requirements. Numerical simulations for the articulated flexible manipulators are given to demonstrate the feasibility and effectiveness of the proposed position control algorithms.

Huang, Jen-Kuang↗
NASA NTRS1987

Telerobotic control of a dextrous manipulator using master and six-DOF hand-controllers for space assembly and servicing tasks

Two studies were conducted evaluating methods of controlling a telerobot; bilateral force reflecting master controllers and proportional rate six degrees of freedom (DOF) hand controllers. The first study compared the controllers on performance of single manipulator arm tasks, a peg-in-the-hole task, and simulated satellite orbital replacement unit changeout. The second study, a Space Station truss assembly task, required simultaneous operation of both manipulator arms (all 12 DOFs) and complex multiaxis slave arm movements. Task times were significantly longer and fewer errors were committed with the hand controllers. The hand controllers were also rated significantly higher in cognitive and manual control workload on the two-arm task. The master controllers were rated significantly higher in physical workload. There were no significant differences in ratings of manipulator control quality.

O'Hara, John M.↗
NASA NTRS1987

Symbolic modeling of flexible manipulators

An algorithm is presented to symbolically derive the full nonlinear dynamic equations of motion of multilink flexible manipulators. Lagrange's assumed modes method is the basis of new algorithm and adapted in a way suitable for symbolic manipulation by digital computers. It is applied to model a two-link flexible arm by means of a commercially available symbolic manipulation program. The advantages of the algorithm and simulation results are discussed.

Cetinkunt, Sabri↗
NASA NTRS1988

Large planar maneuvers for articulated flexible manipulators

An articulated flexible manipulator carried on a translational cart is maneuvered by an active controller to perform certain position control tasks. The nonlinear dynamics of the articulated flexible manipulator are derived and a transformation matrix is formulated to localize the nonlinearities in the inertia matrix. Then a feeback linearization scheme is introduced to linearize the dynamic equations for controller design. Through a pole placement technique, a robust controller design is obtained by properly assigning a set of closed-loop desired eigenvalues to meet performance requirements. Numerical simulations for the articulated flexible manipulators are given to demonstrate the feasibility and effectiveness of the proposed position control algorithms.

Huang, Jen-Kuang↗
NASA NTRS1988

Redundant manipulators for momentum compensation in a micro-gravity environment

This paper is concerned with the implementation and assessment of joint motion management strategies for kinematically redundant robotic manipulators operating in the micro-gravity environment of Space Station. These robots must be capable of conducting experiments and manufacturing processes without disturbing the micro-gravity environment through base reactions/motions. The redundant degrees of freedom of the manipulator permit the inverse kinematic problem to be solved simultaneously with the minimization of a cost function. The cost function in this case is the weighted sum of the squares of the base forces and moments and is minimized over discrete time segments. The Generalized Inverse Method and Rayleigh Ritz technique are used to solve the combined optimization/inverse kinematics problem. Numerical examples include various robotic configurations and degrees of manipulator redundancy.

Quinn, R. D.↗
NASA NTRS1987

Collision-free trajectory planning algorthm for manipulators

Collision-free trajectory planning for robotic manipulators is investigated. The task of the manipulator is to move its end-effector from one point to another point in an environment with polyhedral obstacles. An on-line algorithm is developed based on finding the required joint angles of the manipulator, according to goals with different priorities. The highest priority is to avoid collisions, the second priority is to plan the shortest path for the end effector, and the lowest priority is to minimize the joint velocity for smooth motion. The pseudo-inverse of the Jacobian matrix is applied for inverse kinematics. When a possible collision is detected, a constrained inverse kinematic problem is solved such that the collision is avoided. This algorithm can also be applied to a time-variant environment.

Pourboghrat, F.↗
NASA NTRS1987

Dynamics and control of coordinated multiple manipulators

A technique is presented for controlling multiple manipulators which are holding a single object and therefore form a closed kinematic chain. The object, which may or may not be in contact with a rigid environment, is assumed to be held rigidly by robot end-effectors. The derivation is based on setting up constraint equations which reduce the 6 x n degrees of freedom of a manipulators each having six joints. Additional constraint equations are considered when one or more of the degrees of freedom of the object is reduced due to external constraints. Utilizing the operational space dynamics equations, a decoupling controller is designed to control both the position and the interaction forces of the object with the environment. Finally, simulation results for the control of a pair of two-link manipulators are presented.

Hayati, S. A.↗
NASA NTRS1987

Manipulator control by exact linearization

Comments on the application to rigid link manipulators of geometric control theory, resolved acceleration control, operational space control, and nonlinear decoupling theory are given, and the essential unity of these techniques for externally linearizing and decoupling end effector dynamics is discussed. Exploiting the fact that the mass matrix of a rigid link manipulator is positive definite, a consequence of rigid link manipulators belonging to the class of natural physical systems, it is shown that a necessary and sufficient condition for a locally externally linearizing and output decoupling feedback law to exist is that the end effector Jacobian matrix be nonsingular. Furthermore, this linearizing feedback is easy to produce.

Kruetz, K.↗
NASA NTRS1987

Concept development of a tendon arm manipulator and anthropomorphic robotic hand

AMETEK/ORED inhouse research and development efforts leading toward a next-generation robotic manipulator arm and end-effector technology is summarized. Manipulator arm development has been directed toward a multiple-degree-of-freedom, flexible, tendon-driven concept referred to here as a Tendon Arm Manipulator (TAM). End-effector development has been directed toward a three-fingered, dextrous, tendon-driven, anthropomorphic configuration which is referred to as an Anthropomorphic Robotic Hand (ARH). Key technology issues are identified for both concepts.

Tolman, C. T.↗
NASA NTRS1988

Kinematic calibration of manipulators with closed loop actuated joints

A method for performing forward kinematic calibration of manipulators having one or more closed-loop-actuated joints is presented. The technique is an extension of algorithms designed for open-loop jointed manipulators. The calibration is equivalent to minimizing an objective function subject to constraints. The objective function is taken as the integral of end-effector position and orientation error. The constraints arise from the closed-loop mechanisms present in the manipulator.

Everett, Louis J.↗
NASA NTRS1989

Distribution of dynamic loads for multiple cooperating robot manipulators

For the situation of multiple cooperating manipulators handling a single object, a formulation is presented which allows load distribution of the combined system to be made while taking manipulator dynamics into account. First, object dynamics are used to transform the motion task. An integrated procedure for modeling arm dynamics are used to transform the motion task. An integrated procedure for modeling arm dynamics is detailed. Then, a method is introduced which transforms the object load to the joint level. At this level, various methods of load distribution that allow subtask performance are proposed. These methods allow desired object motion while selecting loads desirable to alleviate manipulator dynamic loads.

Walker, Ian D.↗
NASA NTRS1989

Decentralized adaptive control of manipulators - Theory, simulation, and experimentation

The author presents a simple decentralized adaptive-control scheme for multijoint robot manipulators based on the independent joint control concept. The control objective is to achieve accurate tracking of desired joint trajectories. The proposed control scheme does not use the complex manipulator dynamic model, and each joint is controlled simply by a PID (proportional-integral-derivative) feedback controller and a position-velocity-acceleration feedforward controller, both with adjustable gains. Simulation results are given for a two-link direct-drive manipulator under adaptive independent joint control. The results illustrate trajectory tracking under coupled dynamics and varying payload. The proposed scheme is implemented on a MicroVAX II computer for motion control of the three major joints of a PUMA 560 arm. Experimental results are presented to demonstrate that trajectory tracking is achieved despite coupled nonlinear joint dynamics.

Seraji, Homayoun↗
NASA NTRS1989

Note on hand use in the manipulation of joysticks by rhesus monkeys (Macaca mulatta) and chimpanzees (Pan troglodytes)

MacNeilage et al. (1987) have proposed that nonhuman primate handedness may be contingent on the specific task requirements, with visual-spatial tasks yielding left-hand preferences and fine-motor tasks producing right-hand preferences. This study reports hand preferences in the manipulation of joysticks by 2 rhesus monkeys and 3 chimpanzees. Reach data were also collected for comparison with preference data for manipulation of the joystick. The data indicated that all 5 subjects demonstrated significant right-hand preferences in manipulating the joystick. In contrast, no significant hand preferences were found for the reach data. Reaction-time data also indicated that the right hand could perform a perceptual-motor task better than the left hand in all 5 subjects. Overall, the data indicate that reach tasks may not be sensitive enough measures to produce reliable hand preferences, whereas tasks that assess fine-motor control produce significant hand preferences.

Hopkins, William D.↗
NASA NTRS1989

Forward calibration of closed-loop jointed manipulators

A method for performing forward kinematic calibration of manipulators with one or more closed-loop actuated joints is presented. The technique is an extension of algorithms designed for open-loop jointed manipulators and is equivalent to minimizing a constrained objective function. The constraints arise from the closed-loop mechanisms in the manipulator. The objective function is taken as the integral of end effector position and orientation error and is optimized using the method of Lagrange multipliers.

Everett, Louis J.↗
NASA NTRS1989

Configuration control of redundant manipulators - Theory and implementation

A simple approach for controlling the manipulator configuration over the entire motion is presented, based on augmentation of the manipulator forward kinematics. User-defined kinematic functions and the end-effector Cartesian coordinates are combined to form a set of task-related configuration variables as generalized coordinates for the manipulator. A task-based adaptive scheme is then utilized to control the configuration variables and achieve tracking of the desired reference trajectories. This achieves the desired end-effector motion while utilizing redundancy to achieve any additional task. Simulation results for a direct-drive two-link arm are given to illustrate the proposed control scheme. The scheme has also been implemented for real-time control of three links of a PUMA 560 industrial robot. The simulation and experimental results validate the configuration control scheme and demonstrate its capabilities for performing various realistic tasks.

Seraji, Homayoun↗
NASA NTRS1989

A spatial operator algebra for manipulator modeling and control

A spatial operator algebra for modeling the control and trajectory design of manipulation is discussed, with emphasis on its analytical formulation and implementation in the Ada programming language. The elements of this algebra are linear operators whose domain and range spaces consist of forces, moments, velocities, and accelerations. The effect of these operators is equivalent to a spatial recursion along the span of the manipulator. Inversion is obtained using techniques of recursive filtering and smoothing. The operator alegbra provides a high-level framework for describing the dynamic and kinematic behavior of a manipulator and control and trajectory design algorithms. Implementable recursive algorithms can be immediately derived from the abstract operator expressions by inspection, thus greatly simplifying the transition from an abstract problem formulation and solution to the detailed mechanization of a specific algorithm.

Rodriguez, G.↗
NASA NTRS1990

Simplified Dynamic Control Of Redundant Manipulators

Simplified scheme proposed for dynamic control of robotic manipulator having redundant joints; that is, extra degrees of freedom beyond needed to perform task, to position and orient end effector at specified position and/or move it along specified trajectory. Extra degrees of freedom used to perform simultaneous subtask. Scheme adaptive and based on observed performance of manipulator. Involves neither complicated mathematical model of dynamics of manipulator nor time-consuming inverse kinematic transformation.

Seraji, Homayoun↗
NASA NTRS1990

Robust, High-Performance Control For Robotic Manipulators

Improved control scheme for robotic manipulators results from alternative approach to use of both model-based and performance-based control techniques. Includes feedforward controller and separate feedback controller. Feedforward controller model-based and contains any known part of dynamics of manipulator used to produce nominal control signal. Feedback controller performance-based; compensates for any unknown dynamics and uncertainties or variations in parameters of manipulator and/or payload.

Seraji, Homayoun↗