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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Microprocessors for real time displays and control of space teleoperators

This paper describes the use of microprocessors for smart displays in a space teleoperator project at the Jet Propulsion Laboratory. The application of microprocessor systems to demonstrate the utility of smart displays for a wrist mounted force/torque sensor and end-effector mounted proximity sensors are discussed as are the laboratory hardware and software configurations. These displays assist the operator in making critical real time decisions. Avenues for future development of these concepts are also presented.

Paine, G.↗
NASA NTRS1984

Initial experiments on the end-point control of a flexible one-link robot

The present investigation is concerned with initial experiments regarding a specific unsolved control problem which appeared to be central to advances in the art of robotics. This problem involves the control of a flexible member (one link of a robot system). The position of the end-effector, called the end point or tip, is controlled by measuring that position and using the measurement as a basis for applying control torque to the other end of the flexible member, as for instance, the robot's elbow joint. A description is presented of the features of the first experimental arm which has been made, and an outline is provided of the general strategy for controlling it using its tip sensor and shoulder torquer.

Cannon, R. H., Jr.↗
NASA NTRS1983

Robot arm geometric link parameter estimation

A general method for estimating serial link manipulator geometric parameter errors is proposed in this paper. The positioning accuracy of the end-effector may be increased significantly by updating the nominal link parameters in the control software to represent the physical system more accurately. The proposed method is applicable for serial link manipulators with any combination of revolute or prismatic joints, and is not limited to a specific measurement technique.

Hayati, S. A.↗
NASA NTRS1986

Interchangeable Tools for Remote Manipulators

Report presents concepts and specifications for set of interchangeable end-effector tools used on remotely operated manipulator to work on satellites in orbit. Tools make urgent repairs, do routine maintenance, transfer fluids, construct and assemble satellites, and deploy and retract appendages. With modifications, tool concepts and systematic approach to tool design applicable to such terrestrial uses as industrial robots, manually operated tools, and safety equipment. Report discusses concept for tool-storage system that holds tools securely when not used but kept accessible to manipulator.

Cody, J. C.↗
NASA NTRS1987

Robot-Arm Dynamic Control by Computer

Feedforward and feedback schemes linearize responses to control inputs. Method for control of robot arm based on computed nonlinear feedback and state tranformations to linearize system and decouple robot end-effector motions along each of cartesian axes augmented with optimal scheme for correction of errors in workspace. Major new feature of control method is: optimal error-correction loop directly operates on task level and not on joint-servocontrol level.

Bejczy, Antal K.↗
NASA NTRS1987

Linearization of Robot Manipulators

Four nonlinear control schemes equivalent. Report discusses theory of nonlinear feedback control of robot manipulator, emphasis on control schemes making manipulator input and output behave like decoupled linear system. Approach, called "exact external linearization," contributes efforts to control end-effector trajectories, positions, and orientations.

Kreutz, Kenneth↗
NASA NTRS1987

An approach to multivariable control of manipulators

The paper presents simple schemes for multivariable control of multiple-joint robot manipulators in joint and Cartesian coordinates. The joint control scheme consists of two independent multivariable feedforward and feedback controllers. The feedforward controller is the minimal inverse of the linearized model of robot dynamics and contains only proportional-double-derivative (PD2) terms - implying feedforward from the desired position, velocity and acceleration. This controller ensures that the manipulator joint angles track any reference trajectories. The feedback controller is of proportional-integral-derivative (PID) type and is designed to achieve pole placement. This controller reduces any initial tracking error to zero as desired and also ensures that robust steady-state tracking of step-plus-exponential trajectories is achieved by the joint angles. Simple and explicit expressions of computation of the feedforward and feedback gains are obtained based on the linearized model of robot dynamics. This leads to computationally efficient schemes for either on-line gain computation or off-line gain scheduling to account for variations in the linearized robot model due to changes in the operating point. The joint control scheme is extended to direct control of the end-effector motion in Cartesian space. Simulation results are given for illustration.

Seraji, H.↗
NASA NTRS1986

Hybrid position/force control of multi-arm cooperating robots

This paper extends the theory of hybrid position/force control to the case of multi-arm cooperating robots. Cooperation between n robot arms is achieved by controlling each arm such that the burden of actuation is shared between the arms in a nonconflicting way as they control the position of and force on a designated point on an object. The object, which may or may not be in contact with a rigid environment, is assumed to be held rigidly by n robot end-effectors. Natural and artificial position and force constraints are defined for a point on the object and two selection matrices are obtained to control the arms. The position control loops are designed based on each manipulator's Cartesian space dynamic equations. In the position control subspace, a feature is provided which allows the robot arms to exert additional forces/torques to achieve compression, tension, or torsion in the object without affecting the execution of the motion trajectories. In the force control subspace, a method is introduced to minimize the total force/torque magnitude square while realizing the net desired force/torque on the environment.

Hayati, Samad↗
NASA NTRS1988

Handheld Controller For Robotic End Effector

Controller provides both position and force feedback. Hand grip houses controller. End-effector force and position fed back to operator's hand through rotation of trigger and rocking of trigger guard.

Jau, Bruno M.↗
NASA NTRS1987

Telerobotic research at NASA Langley Research Center

An overview of Automation Technology Branch facilities and research is presented. Manipulator research includes dual-arm coordination studies, space manipulator dynamics, end-effector controller development, automatic space structure assembly, and the development of a dual-arm master-slave telerobotic manipulator system. Sensor research includes gravity-compensated force control, real-time monovision techniques, and laser ranging. Artificial intelligence techniques are being explored for supervisory task control, collision avoidance, and connectionist system architectures. A high-fidelity dynamic simulation of robotic systems, ROBSIM, is being supported and extended. Cooperative efforts with Oak Ridge National Laboratory have verified the ability of teleoperators to perform complex structural assembly tasks, and have resulted in the definition of a new dual-arm master-slave telerobotic manipulator. A bibliography of research results and a list of technical contacts are included.

Sliwa, Nancy E.↗
NASA NTRS1988

Base reaction optimization of manipulators with redundant kinematics

A trajectory generation method for space manipulators is introduced. The approach developed employs a manipulator with redundant kinematics. The method is implemented in two steps. First, the end-effector trajectory is developed to satisfy motion requirements. Next, the joint trajectories are developed to minimize base reactions. The analytical development of this method is described and an example illustrating the method is presented.

Chung, C. L.↗
NASA NTRS1987

An adaptive Cartesian control scheme for manipulators

A adaptive control scheme for direct control of manipulator end-effectors to achieve trajectory tracking in Cartesian space is developed. The control structure is obtained from linear multivariable theory and is composed of simple feedforward and feedback controllers and an auxiliary input. The direct adaptation laws are derived from model reference adaptive control theory and are not based on parameter estimation of the robot model. The utilization of feedforward control and the inclusion of auxiliary input are novel features of the present scheme and result in improved dynamic performance over existing adaptive control schemes. The adaptive controller does not require the complex mathematical model of the robot dynamics or any knowledge of the robot parameters or the payload, and is computationally fast for online implementation with high sampling rates.

Seraji, H.↗
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

The use of the articulated total body model as a robot dynamics simulation tool

The Articulated Total Body (ATB) model is a computer sumulation program which was originally developed for the study of aircrew member dynamics during ejection from high-speed aircraft. This model is totally three-dimensional and is based on the rigid body dynamics of coupled systems which use Euler's equations of motion with constraint relations of the type employed in the Lagrange method. In this paper the use of the ATB model as a robot dynamics simulation tool is discussed and various simulations are demonstrated. For this purpose the ATB model has been modified to allow for the application of torques at the joints as functions of state variables of the system. Specifically, the motion of a robotic arm with six revolute articulations with joint torques prescribed as functions of angular displacement and angular velocity are demonstrated. The simulation procedures developed in this work may serve as valuable tools for analyzing robotic mechanisms, dynamic effects, joint load transmissions, feed-back control algorithms employed in the actuator control and end-effector trajectories.

Obergfell, Louise A.↗
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

Adaptive force-position control for teleoperated manipulators

An adaptive controller with self-tuning can be designed for teleoperated robotic manipulators by determining a time-series model for the function of the teleoperator. Specifically, the position and force exerted by the operator are modelled for determining the derived values for the trajectory of the end-effector of the manipulator. Thus, the adaptive controller can be designed by following the steps which have previously been presented for the controller design of the gross motion.

Koivo, A. J.↗
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

Adaptive hybrid position/force control of robotic manipulators

The problem of position and force control for the compliant motion of the manipulators is considered. The external force and the position of the end-effector are related by a second order impedance function. The force control problem is then translated into a position control problem. For that, an adaptive controller is designed to achieve the compliant motion. The design uses the Liapunov's direct method to derive the adaptation law. The stability of the process is guaranteed from the Liapunov's stability theory. The controller does not require the knowledge of the system parameters for the implementation, and hence is easy for applications.

Pourboghrat, F.↗