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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Efficient control with an order (n) recursive inversion of the Jacobian for an n-link serial manipulator

A method is presented to order (n) recursively invert the Jacobian matrix for a serial n-link manipulator. By realizing that the Jacobian relationship involving accelerations is a special case for the forward dynamics problem, it is possible to obtain the Jacobian inverse by directly applying Rodriguez's (1987) recursive forward dynamics algorithm. In this technique, the n-link robot equation is formulated as a spatially recursive algorithm in the form of a filtering and smoothing problem. To compute the Jacobian inverse via this algorithm, the n-link manipulator is modeled with only a unit end-point mass and zero applied torques.

Meldrum, D. R.↗
NASA NTRS1992

Task-based configuration control of redundant manipulators

This article establishes new goals for redundancy resolution based on manipulator dynamics and end-effector characteristics. These goals can be accomplished by employing the recently developed configuration control approach. Redundancy resolution is achieved by controlling the joint inertia matrix or the end-effector mass matrix that affect the inertial torques or by reducing the joint torques due to gravity loading and payload. The manipulator mechanical advantages and velocity ratio are also used as performance measurements to be improved by proper utilization of redundancy. Furthermore, end-effector compliance, sensitivity, and impulsive force at impact are introduced as redundancy-resolution criteria. The new goals for redundancy resolution presented in this article allow a more efficient utilization of the redundant joints based on the desired task requirements. Simple case studies using computer simulations are described for illustration.

Seraji, Homayoun↗
NASA NTRS1992

Natural transition from rate to force control of a manipulator

A method for teleoperator control which offers advantages over previous techniques is demonstrated. In the new method, a fundamental variable exchanged between the master and slave is the rate of change in position and force. An inherent capability of the control scheme is demonstrated for transition between control methods based on environmental constraints in a manner natural to the operator. Specifically, rate control of a manipulator makes the transition to force-force control when a force-reflecting hand controller is used with a local force accommodation algorithm running on the remote manipulator. The transition from rate to force occurs when contact is made with the environment.

Harrison, F. W.↗
NASA NTRS1990

Advances in dynamics and control of flexible spacecraft and space-based manipulations; Proceedings of the Symposium, ASME Winter Annual Meeting, Dallas, TX, Nov. 25-30, 1990

Consideration is given to control formulations for vibration suppression of an active structure in slewing motions, the use if distributed sensing in control of large flexible spacecraft, an improved shooting method for solving minimum-time maneuver problems, and nonlinear slew maneuver dynamics of large flexible spacecrafts. Attention is also given to initial experiments in trusterless locomotion control of a free-flying robot, dynamic analysis to evaluate viscoelastic passive damping augmentation for the Space Shuttle Remote Manipulator System, initial experiments in cooperative manipulation from a moving platform, and intelligent pipelined control architecture for remote robotic applications.

Joshi, Suresh M.↗
NASA NTRS1993

Recursive Linearization Of Dynamical Models Of Manipulators

Report shows how spatial-operator algebra developed by authors used to derive linearized mathematical models of dynamics of robotic manipulators. Aspects of spatial-operator algebra also described in "Robot Control Based On Spatial-Operator Algebra" (NPO-17918), "Unified Formulation Of Dynamics Of Robot Arms" (NPO-18040), and "Spatial-Operator Algebra For Robotic Manipulators" (NPO-17770).

Jain, Abhinandan↗
NASA NTRS1992

Self mobile space manipulator project

A relatively simple, modular, low mass, low cost robot is being developed for space EVA that is large enough to be independently mobile on a space station or platform exterior, yet versatile enough to accomplish many vital tasks. The robot comprises two long flexible links connected by a rotary joint, with 2-DOF 'wrist' joints and grippers at each end. It walks by gripping pre-positioned attachment points, such as trusswork nodes, and alternately shifting its base of support from one foot (gripper) to the other. The robot can perform useful tasks such as visual inspection, material transport, and light assembly by manipulating objects with one gripper, while stabilizing itself with the other. At SOAR '90, we reported development of 1/3 scale robot hardware, modular trusswork to serve as a locomotion substrate, and a gravity compensation system to allow laboratory tests of locomotion strategies on the horizontal face of the trusswork. In this paper, we report on project progress including the development of: (1) adaptive control for automatic adjustment to loads; (2) enhanced manipulation capabilities; (3) machine vision, including the use of neural nets, to guide autonomous locomotion; (4) locomotion between orthogonal trusswork faces; and (5) improved facilities for gravity compensation and telerobotic control.

Brown, H. Ben↗
NASA NTRS1991

A vision-based end-point control for a two-link flexible manipulator

The measurement and control of the end-effector position of a large two-link flexible manipulator are investigated. The system implementation is described and an initial algorithm for static end-point positioning is discussed. Most existing robots are controlled through independent joint controllers, while the end-effector position is estimated from the joint positions using a kinematic relation. End-point position feedback can be used to compensate for uncertainty and structural deflections. Such feedback is especially important for flexible robots. Computer vision is utilized to obtain end-point position measurements. A look-and-move control structure alleviates the disadvantages of the slow and variable computer vision sampling frequency. This control structure consists of an inner joint-based loop and an outer vision-based loop. A static positioning algorithm was implemented and experimentally verified. This algorithm utilizes the manipulator Jacobian to transform a tip position error to a joint error. The joint error is then used to give a new reference input to the joint controller. The convergence of the algorithm is demonstrated experimentally under payload variation. A Landmark Tracking System (Dickerson, et al 1990) is used for vision-based end-point measurements. This system was modified and tested. A real-time control system was implemented on a PC and interfaced with the vision system and the robot.

Obergfell, Klaus↗
NASA NTRS1993

On the design of fault-tolerant robotic manipulator systems

Robotic systems are finding increasing use in space applications. Many of these devices are going to be operational on board the Space Station Freedom. Fault tolerance has been deemed necessary because of the criticality of the tasks and the inaccessibility of the systems to maintenance and repair. Design for fault tolerance in manipulator systems is an area within robotics that is without precedence in the literature. In this paper, we will attempt to lay down the foundations for such a technology. Design for fault tolerance demands new and special approaches to design, often at considerable variance from established design practices. These design aspects, together with reliability evaluation and modeling tools, are presented. Mechanical architectures that employ protective redundancies at many levels and have a modular architecture are then studied in detail. Once a mechanical architecture for fault tolerance has been derived, the chronological stages of operational fault tolerance are investigated. Failure detection, isolation, and estimation methods are surveyed, and such methods for robot sensors and actuators are derived. Failure recovery methods are also presented for each of the protective layers of redundancy. Failure recovery tactics often span all of the layers of a control hierarchy. Thus, a unified framework for decision-making and control, which orchestrates both the nominal redundancy management tasks and the failure management tasks, has been derived. The well-developed field of fault-tolerant computers is studied next, and some design principles relevant to the design of fault-tolerant robot controllers are abstracted. Conclusions are drawn, and a road map for the design of fault-tolerant manipulator systems is laid out with recommendations for a 10 DOF arm with dual actuators at each joint.

Tesar, Delbert↗
NASA NTRS1991

A self-reconfigurable manipulator system with dextrous bracing structure

The authors present a dextrous bracing structure of a dual-arm system as a means of implementing a self-reconfigurable manipulator system. The dextrous bracing structure allows a dual-arm system to relocate the bracing point between two arms, select the type of contact as the bracing point, and lock or release the joints of individual arms. The self-reconfigurable dual-arm system is now capable of reconfiguring its topology through serial, parallel and bracing structures, supporting general types of contact, rigid or sliding, as well as locking or releasing some of its joints as needed. The focus is on an analysis of the effects of the dextrous bracing on the performance of a dual-arm system in terms of dual-arm manipulabilities and resistivities. The analysis shows that a self-reconfigurable dual-arm system with a dextrous bracing structure gives continuously varying performance characteristics ranging from serial to parallel structures.

Lee, Sukhan↗
NASA NTRS1991

Direct adaptive impedance control of manipulators

An adaptive scheme for controlling the end-effector impedance of robot manipulators is presented. The proposed control system consists of three subsystems: a simple filter which characterizes the desired dynamic relationship between the end-effector position error and the end-effector/environment contact force, an adaptive controller which produces the Cartesian-space control input required to provide this desired dynamic relationship, and an algorithm for mapping the Cartesian-space control input to a physically realizable joint-space control torque. The controller does not require knowledge of either the structure or the parameter values of the robot dynamics, and it is implemented without calculation of the robot inverse kinematic transformation. As a result, the scheme represents a very general and computationally efficient approach to controlling the impedance of both nonredundant and redundant manipulators. Furthermore, the method can be applied directly to trajectory tracking in free-space motion by removing the impedance filter.

Colbaugh, R.↗
NASA NTRS1993

Joint-space Lyapunov-based direct adaptive control of a kinematically redundant telerobot manipulator

This paper presents the design of a joint-space adaptive control scheme for controlling the slave arm motion of a dual-arm telerobot system developed at Goddard Space Flight Center (GSFC) to study telerobotic operations in space. Each slave arm of the dual-arm system is a kinematically redundant manipulator with seven degrees of freedom (DOF). Using the concept of model reference adaptive control (MRAC) and Liupunov direct method, we derive an adaptation algorithm that adjusts the PD controller gains of the control scheme. The development of the adaptive control scheme assumes that the slave arm motion is non-compliant and slowly varying. The implementation of the derived control scheme does not require the computation of manipulator dynamics which makes the control scheme sufficiently fast for real-time applications. Computer simulation study performed for the 7-DOF slave arm shows that the developed control scheme can efficiently adapt to sudden change in payload while tracking various test trajectories such as ramp or sinusoids with negligible position errors.

Nguyen, Charles C.↗
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 NTRS1993

A theoretical and experimental investigation of impact control for manipulators

This article describes a simple control strategy for stable hardon-hard contact of a manipulator with the environment. The strategy is motivated by recognition of the equivalence of proportional gain explicit force control and impedance control. It is shown that negative proportional force gains, or impedance mass ratios less than unity, can equivalently provide excellent impact response without bouncing. This result is indicated by an analysis performed with an experimentally determined arm/sensor/environment model. The results are corroborated by experimental data from implementation of the control algorithms on the CMU DD Arm II system. The results confirm that manipulator impact against a stiff environment without bouncing can be readily handled by this novel control strategy.

Volpe, Richard↗
NASA NTRS1994

Dynamic Coordination Of A Two-Arm Robotic Manipulator

Report presents study of dynamical and kinematical considerations guiding selection of configuration of self-reconfigurable, two-arm robotic manipulator. Two multiple-link arms cooperate in manipulating single object, reconfiguring their mutual, cooperative structure according to changing task requirements.

Lee, Sukhan↗
NASA NTRS1994

Self-Reconfigurable Two-Arm Manipulator With Bracing

Proposed two-arm robotic manipulator capable of changing its mechanical structure to fit given task. No reassembly or replacement in conventional sense: instead, arms commanded during operation to assume any of number of alternative configurations, described briefly in "Dynamic Coordination of a Two-Arm Robotic Manipulator" (NPO-18816), NASA Tech Briefs.

Lee, Sukhan↗
NASA NTRS1994

Adaptive Impedance Control Of Redundant Manipulators

Improved method of controlling mechanical impedance of end effector of redundant robotic manipulator based on adaptive-control theory. Consists of two subsystems: adaptive impedance controller generating force-control inputs in Cartesian space of end effector to provide desired end-effector-impedance characteristics, and subsystem implementing algorithm that maps force-control inputs into torques applied to joints of manipulator. Accurate control of end effector and effective utilization of redundancy achieved simultaneously by use of method. Potential use to improve performance of such typical impedance-control tasks as deburring edges and accommodating transitions between unconstrained and constrained motions of end effectors.

Seraji, Homayoun↗
NASA NTRS1994

Efficient Kinematic Computations For 7-DOF Manipulators

Efficient algorithms for forward kinematic mappings of seven-degree-of-freedom (7-DOF) robotic manipulator having revolute joints developed on basis of representation of redundant DOF in terms of parameter called "arm angle." Continuing effort to exploit redundancy in manipulator according to concept of basic and additional tasks. Concept also discussed in "Configuration-Control Scheme Copes With Singularities" (NPO-18556) and "Increasing the Dexterity of Redundant Robots" (NPO-17801).

Seraji, Homayoun↗
NASA NTRS1994

Optimized Resolved-Rate Control Of Telerobotic Manipulator

Laboratory Telerobotic Manipulator (LTM) is seven-degree-of-freedom robot arm built for evaluation in ground-based research to assess role of redundant-degree-of-freedom arms in outerspace operations. Each arm has three pitch/yaw joints: one at shoulder, another at elbow, and third at wrist. Seventh degree of freedom provided by wrist-roll joint. Offers advantages of more efficient use of workspaces and ability to reach around obstacles, redundant manipulators used in mobile robots and teleoperators for hazardous environments, automotive assembly, welding, and spray painting.

Barker, L. Keith↗