Search NASA⌕ Search

SEARCH · Search NASA

Results for “Manipulator control”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Adaptive control of space-based robot manipulators

A control method is presented that achieves globally stable trajectory tracking in the presence of uncertainties in the inertial parameters of the system. The 15-DOF system dynamics are divided into two components: a 9-DOF invertible portion and 6-DOF noninvertible portion. A controller is then designed to achieve trajectory tracking of the invertible portion of the system, which consists of the manipulator-joint positions and the orientation of the base. The motion of the noninvertible portion is bounded but otherwise unspecified. This portion of the system consists of the position of the robot's base and the position of the reaction wheels. A simulation is presented to demonstrate the effectiveness of the controller. A quadratic polynomial is used to generate the desired trajectory to illustrate the trajectory-tracking capability of the controller.

Walker, Michael W.↗
NASA NTRS1974

Study of design and control of remote manipulators. Modeling manipulator arms with distributed flexibility for design and control

The interactions of control system and distributed flexible structural dynamics is explored for mechanical arms. A modeling process using 4 x 4 transfer matrices is described which permits the closed loop response of many current arm configurations to be evaluated. Root locus, frequency response, modal shapes, and time impulse response have all been obtained from the digital computer implementation of this model, which is oriented to arm design and allows for easy variation of the arm configuration through data cards. The model corresponds with experimentally observed natural frequencies with an average error of less than 5% in the first three flexible modes in the seven cases considered. The model was used to explore the limits imposed by structural flexibility on a nondimensionalized two link arm with one and two joints for planar motion.

Book, W. J.↗
NASA NTRS1990

Multiple task point control of a redundant manipulator

The kinematic control of a redundant arm based on multiple tasks assigned to different locations of the manipulator is presented. This is equivalent to decomposing a redundant arm into two (or more) nonredundant local arms, the basearm and the forearm, at an intermediate arm location or task point called the elbow. A redundant arm is transformed into a serially cooperating dual-arm system, with the cooperation between the local arms being carried out at the elbow. Then, a manipulator end-effector motion specified by a given task is decomposed into motions of individual local arms as well as an end-effector free motion based on achieving maximum efficiency in task execution. To consider global optimization, elbow control is applied to reshaping and reorientation of a manipulability ellipsoid at the end effector during task execution. The resolved rate control of elbow in the end-effector null and free motion space is used to maximize arm homogeneity and to match the forearm motion space with the task space. Simulation results are shown.

Lee, Sukhan↗
NASA NTRS1988

Adaptive control of a manipulator with a flexible link

An adaptive controller for a manipulator with one rigid link and one flexible link is presented. The performance and robustness of the controller are demonstrated by numerical simulation results. In the simulations, the manipulator moves in a gravitational field and a finite element model represents the flexible link.

Yang, Y. P.↗
NASA NTRS1980

Asynchronous interactive control systems

A class of interactive control systems is derived by generalizing interactive manipulator control systems. The general structural properties of such systems are discussed and an appropriate general software implementation is proposed. This is based on the fact that tasks of interactive control systems can be represented as a network of a finite set of actions which have specific operational characteristics and specific resource requirements, and which are of limited duration. This has enabled the decomposition of the overall control algorithm into a set of subalgorithms, called subcontrollers, which can operate simultaneously and asynchronously. Coordinate transformations of sensor feedback data and actuator set-points have enabled the further simplification of the subcontrollers and have reduced their conflicting resource requirements. The modules of the decomposed control system are implemented as parallel processes with disjoint memory space communicating only by I/O. The synchronization mechanisms for dynamic resource allocation among subcontrollers and other synchronization mechanisms are also discussed in this paper. Such a software organization is suitable for the general form of multiprocessing using computer networks with distributed storage.

Vuskovic, M. I.↗
NASA NTRS1992

Object impedance control for cooperative manipulation - Theory and experimental results

This paper presents the dynamic control module of the Dynamic and Strategic Control of Cooperating Manipulators (DASCCOM) project at Stanford University's Aerospace Robotics Laboratory. First, the cooperative manipulation problem is analyzed from a systems perspective, and the desirable features of a control system for cooperative manipulation are discussed. Next, a control policy is developed that enforces a controlled impedance not of the individual arm endpoints, but of the manipulated object itself. A parallel implementation for a multiprocessor system is presented. The controller fully compensates for the system dynamics and directly controls the object internal forces. Most importantly, it presents a simple, powerful, intuitive interface to higher level strategic control modules. Experimental results from a dual two-link-arm robotic system are used to compare the object impedance controller with other strategies, both for free-motion slews and environmental contact.

Schneider, Stanley A.↗
NASA NTRS1985

Direct model reference adaptive control of a flexible robotic manipulator

Quick, precise control of a flexible manipulator in a space environment is essential for future Space Station repair and satellite servicing. Numerous control algorithms have proven successful in controlling rigid manipulators wih colocated sensors and actuators; however, few have been tested on a flexible manipulator with noncolocated sensors and actuators. In this thesis, a model reference adaptive control (MRAC) scheme based on command generator tracker theory is designed for a flexible manipulator. Quicker, more precise tracking results are expected over nonadaptive control laws for this MRAC approach. Equations of motion in modal coordinates are derived for a single-link, flexible manipulator with an actuator at the pinned-end and a sensor at the free end. An MRAC is designed with the objective of controlling the torquing actuator so that the tip position follows a trajectory that is prescribed by the reference model. An appealing feature of this direct MRAC law is that it allows the reference model to have fewer states than the plant itself. Direct adaptive control also adjusts the controller parameters directly with knowledge of only the plant output and input signals.

Meldrum, D. R.↗
NASA NTRS1991

Dynamics modeling and adaptive control of flexible manipulators

An application of Model Reference Adaptive Control (MRAC) to the position and force control of flexible manipulators and robots is presented. A single-link flexible manipulator is analyzed. The problem was to develop a mathematical model of a flexible robot that is accurate. The objective is to show that the adaptive control works better than 'conventional' systems and is suitable for flexible structure control.

Sasiadek, J. Z.↗
NASA NTRS1974

Autonomous manipulation on a robot: Summary of manipulator software functions

A six degree-of-freedom computer-controlled manipulator is examined, and the relationships between the arm's joint variables and 3-space are derived. Arm trajectories using sequences of third-degree polynomials to describe the time history of each joint variable are presented and two approaches to the avoidance of obstacles are given. The equations of motion for the arm are derived and then decomposed into time-dependent factors and time-independent coefficients. Several new and simplifying relationships among the coefficients are proven. Two sample trajectories are analyzed in detail for purposes of determining the most important contributions to total force in order that relatively simple approximations to the equations of motion can be used.

Lewis, R. A.↗
NASA NTRS1993

Experimental object-level strategic control with cooperating manipulators

This article presents the high-level control module and user interface of the Dynamic and Strategic Control of Cooperating Manipulators (DASCCOM) project at Stanford University's Aerospace Robotics Laboratory. In addition to cooperative dynamic control, DASCCOM incorporates real-time vision-ased feedback, a novel strategic programming technique, and an iconic 'object-only' graphical user interface. By focusing on the vertical integration problem, we are examining not only these subsystems, but also their interfaces and interactions. The control system implements a multilevel hierarchical structure interconnected via a real-time network. At the highest level, a mouse-driven graphical user interface allows an operator to direct the activities of the system conceptually. Strategic command is provided by an event-driven finite state machine. This methodology provides a powerful yet flexible technique for managing concurrent system interactions. The dynamic controller implements object impedance control - an extension of Neville Hogan's impedance control concept to cooperative multiple-arm manipulation of a single object. This article concentrates on user interfacing techniques and strategic programming capabilities. These modules allow the user to directly specify conceptual object relationships. Experimental results are presented, showing the system locating and identifying a moving object, 'catching' it, and performing a simple cooperative assembly. Each of these operations is executed autonomously, with only object-level task-specification direction from a remote operator.

Schneider, Stanley A.↗
NASA NTRS1989

Control of free-flying space robot manipulator systems

Control techniques for self-contained, autonomous free-flying space robots are being tested and developed. Free-flying space robots are envisioned as a key element of any successful long term presence in space. These robots must be capable of performing the assembly, maintenance, and inspection, and repair tasks that currently require astronaut extra-vehicular activity (EVA). Use of robots will provide economic savings as well as improved astronaut safety by reducing and in many cases, eliminating the need for human EVA. The focus of the work is to develop and carry out a set of research projects using laboratory models of satellite robots. These devices use air-cushion-vehicle (ACV) technology to simulate in two dimensions the drag-free, zero-g conditions of space. Current work is divided into six major projects or research areas. Fixed-base cooperative manipulation work represents our initial entry into multiple arm cooperation and high-level control with a sophisticated user interface. The floating-base cooperative manipulation project strives to transfer some of the technologies developed in the fixed-base work onto a floating base. The global control and navigation experiment seeks to demonstrate simultaneous control of the robot manipulators and the robot base position so that tasks can be accomplished while the base is undergoing a controlled motion. The multiple-vehicle cooperation project's goal is to demonstrate multiple free-floating robots working in teams to carry out tasks too difficult or complex for a single robot to perform. The Location Enhancement Arm Push-off (LEAP) activity's goal is to provide a viable alternative to expendable gas thrusters for vehicle propulsion wherein the robot uses its manipulators to throw itself from place to place. Because the successful execution of the LEAP technique requires an accurate model of the robot and payload mass properties, it was deemed an attractive testbed for adaptive control technology.

Cannon, Robert H., Jr.↗
NASA NTRS1991

Control strategy for cooperating disparate manipulators: Non-colocated control of disturbances of a flexible arm

The long term objectives for this research are to use a small robot arm to compliment a large robot arm. Disturbances generated by robot tasks were studied. Available equipment made it convenient to study disturbances generated by an abrasive cut off saw mounted on the tip of a large armed robot, and used to cut through rods and pipes in the range of 0.5 in. to 1.5 in. The abrasive process was modeled as a friction operation. The operation of the cut off saw was performed autonomously and under teleoperated control. The behavior was stable in both cases for a P-D joint control algorithm. It was found that broad band excitation during the cutting operation is capable of exciting arm natural frequencies to above the third natural frequency of the arm. The direction of cut changed the modes excited due to the change in coupling coefficients.

Lew, Jae Y.↗
NASA NTRS1974

Tradeoffs in manipulator structure and control. Part 1: Summary

The study of various aspects of manipulator design and control is summarized, focusing on the interaction of the structure's flexible dynamics and the dynamics of the joint control system, including specific information on modeling and design, modal analysis and control, and the flexible manipulator analysis computer program, FMAP.

Whitney, D. E.↗
NASA NTRS1994

Control of parallel manipulators using force feedback

Two control schemes are compared for parallel robotic mechanisms actuated by hydraulic cylinders. One scheme, the 'rate based scheme', uses the position and rate information only for feedback. The second scheme, the 'force based scheme' feeds back the force information also. The force control scheme is shown to improve the response over the rate control one. It is a simple constant gain control scheme better suited to parallel mechanisms. The force control scheme can be easily modified for the dynamic forces on the end effector. This paper presents the results of a computer simulation of both the rate and force control schemes. The gains in the force based scheme can be individually adjusted in all three directions, whereas the adjustment in just one direction of the rate based scheme directly affects the other two directions.

Nanua, Prabjot↗
NASA NTRS1994

Force override rate control for robotic manipulators

The work reported deals with the problem of operating a robot manipulator under a rate control mode while the end effector is not in contact with the external environment, and then switching to a force control mode when contact is made. The paper details how the modal changeover may be accomplished in a manner transparent to the operator, and will allow operator applied forces to be reflected at the robot end effector. A one degree of freedom demonstration system is used to illustrate the concept, which is then applied to a PUMA manipulator. Sample code for the implementation of the control is provided, experimental results show that the optimum setting for the gain is a function of the compliance of the end effector, and the compliance of the external constraint.

Driels, Morris↗
NASA NTRS1981

Robots in modern industry

A survey is presented of robotic device types and capabilities, and an assessment is made of the relative benefits they confer in present and planned numbers on such industrial countries as Japan, the U.S., and West Germany. Attention is also given to possible social impacts of large-scale implementation, and the need for close consultation between management and labor is stressed. It is reported that, while the hourly cost of robot labor remained at between $4.00 and $4.60 over the period 1960-present, human hourly labor costs (including fringe benefits) have risen from less than $4.00 to nearly $17.00. Among the types of devices described are: (1) remotely controlled manipulator vehicles; (2) undersea robotic craft; (3) servo-controlled robots; and (4) articulated robots. Also covered are robot programming languages derived from such standard languages as ALGOL, FORTRAN, and BASIC.

Heer, E.↗