SEARCH · Engineering Papers

Results for “closed-loop”

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.

SourceResearch connectionFrom yearThrough year

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

At least 667 records · Page 37

All sources NASA NTRS DOE OSTI

NASA NTRS1990

Telefunctioning - An approach to telerobotic manipulations

This study introduces three concepts: telefunctioning, a control method for achieving telefunctioning, and an approach to the analysis of human-robot interaction when telefunctioning governs the system behavior. Telefunctioning facilitates maneuvering of loads by creating a perpetual sense of the load dynamics for the operator. Telefunctioning is defined as a robotic manipulation method in which the dynamic behaviors of the slave robot and the master robot are functions of each other; these functions are the designer's choice and depend on the application. In a subclass of telefunctioning called telepresence, all of the relationships between the master and the slave are specified as unity so that all of the master and slave variables (e.g., position and velocity) are dynamically equal. To create telefunctioning, a minimum number of functions relating the robots' variables is identified. A control architecture which guarantees that the defined functions govern the dynamic behavior of the system is then developed. The stability of the closed-loop system (master robot, slave robot, human, and the load being manipulated) is analyzed, and sufficient conditions for stability are derived.

Kazerooni, H.↗

NASA NTRS1990

Active disturbance rejection in large flexible space structures

The design of an active control law for the rejection of persistent disturbances, in large space structures is presented. The control system design approach is based on a deterministic model of the disturbances and it optimizes the magnitude of the disturbance that the structure can tolerate without violating certain predetermined constraints. In addition to closed-loop stability, the explicit treatment of state, control, and control rate constraints, such as structural displacement and control actuator effort, guarantees that the final design will exhibit desired performance characteristics. The technique is applied to a simple two-bay truss structure, and its response is compared with that obtained using a linear-quadratic-Gaussian/loop-transfer-recovery (LQG/LTR) compensator. Preliminary results indicate that the proposed control system can reject persistent disturbances of greater magnitude by utilizing most of the available control, while limiting the structural displacements to within desired tolerances.

Parlos, Alexander G.↗

NASA NTRS1990

A unified perspective on robot control - The energy Lyapunov function approach

A unified framework for the stability analysis of robot tracking control is presented. By using an energy-motivated Lyapunov function candidate, the closed-loop stability is shown for a large family of control laws sharing a common structure of proportional and derivative feedback and a model-based feedforward. The feedforward can be zero, partial or complete linearized dynamics, partial or complete nonlinear dynamics, or linearized or nonlinear dynamics with parameter adaptation. As result, the dichotomous approaches to the robot control problem based on the open-loop linearization and nonlinear Lyapunov analysis are both included in this treatment. Furthermore, quantitative estimates of the trade-offs between different schemes in terms of the tracking performance, steady state error, domain of convergence, realtime computation load and required a prior model information are derived.

Wen, John T.↗

NASA NTRS1990

Long term life support for space exploration

A general strategy for the development of life-support systems is discussed in terms of present and future requirements for NASA exploration missions. A general life-support strategy is delineated for both intravehicular activity (IVA) and extravehicular activity (EVA) for lunar and Mars transfer vehicles, Mars habitats, and pressurized rovers. The baseline capability presented corresponds to the systems needs for the Space Station Freedom permanently manned capability and the Shuttle Extended Duration Orbiter. Design guidelines and system design goals are given for IVA life support with an emphasis on closed-loop systems, and the design prerogatives for EVA include a minimum time to transition between IVA and EVA, and minimum resitriction for human activity.

Rummel, John D.↗

NASA NTRS1984

Stable direct adaptive control of linear infinite-dimensional systems using a command generator tracker approach

The topics are presented in view graph form and include the following: an adaptive model following control; adaptive control of a distributed parameter system (DPS) with a finite-dimensional controller; a direct adaptive controller; a closed-loop adaptively controlled DPS; Lyapunov stability; the asymptotic stability of the closed loop; and model control of a simply supported beam.

Balas, Mark↗

NASA NTRS1990

Flight control system design factors for applying automated testing techniques

Automated validation of flight-critical embedded systems is being done at ARC Dryden Flight Research Facility. The automated testing techniques are being used to perform closed-loop validation of man-rated flight control systems. The principal design features and operational experiences of the X-29 forward-swept-wing aircraft and F-18 High Alpha Research Vehicle (HARV) automated test systems are discussed. Operationally applying automated testing techniques has accentuated flight control system features that either help or hinder the application of these techniques. The paper also discusses flight control system features which foster the use of automated testing techniques.

Sitz, Joel R.↗

NASA NTRS1990

Commercial applications

Viewgraphs on commercial applications of fuzzy logic in Japan are presented. Topics covered include: suitable application area of fuzzy theory; characteristics of fuzzy control; fuzzy closed-loop controller; Mitsubishi heavy air conditioner; predictive fuzzy control; the Sendai subway system; automatic transmission; fuzzy logic-based command system for antilock braking system; fuzzy feed-forward controller; and fuzzy auto-tuning system.

Togai, Masaki↗

NASA NTRS1988

Requirements for significant problem reporting and trend analysis

This handbook supplements policies, requirements, and procedures of NMI 8070.3 to ensure that NASA management at each organizational level is: fully aware of trends affecting both the level of safety and the potential for mission success established for both NASA manned space programs and its supporting institutions; fully and independently informed of problems that represent significant risk to the safety of all personnel (including the general populace) and to the success of a mission or operation through a program mechanism herein defined as Significant Problem Reporting; and in full agreement with the level of elimination of these problems through the closed-loop accounting of corrective actions. The requirements of this handbook are supportive of the agency's safety, reliability, maintainability, and quality assurance (SRM&QA) program objectives and are applicable to all organizational elements of NASA connected with or supporting developmental or operational manned space program/projects (including associated payloads) and the related institutional facilities.

George A Rodney↗

NASA NTRS1989

Design and implementation of components for a bioregenerative system for growing higher order plants in space

This report summarizes the efforts of the NASA/USRA Advanced Design Program during the 1988-89 scholastic year. The primary goal was to address specific needs in the design of an integrated system to grow higher order plants in space. The initial phase of the design effort concentrated on studying such a system and identifying its needs. Once these needs were defined, emphasis was placed on the design and fabrication of devices to meet them. Specific attention was placed on a hand-held harvester, a nutrient concentration sensor, an air-water separator, and a closed-loop biological system simulation.

Brakman, B.↗

NASA NTRS1990

Optimization of structure-control systems with efficiency constraint

The structure-control system optimization problem is formulated with constraints on the closed-loop eigenvalues and the efficiency of the reduced order system. The feasibility of the approach is illustrated by designing the ACOSS-FOUR structure with a reduced order system and improving the efficiency characteristics of the structures-control system.

Oz, H.↗

NASA NTRS1990

Structural dynamic and control considerations for Space Station transportation node concepts

This paper discusses the results of two studies which investigated the expected low frequency dynamic characteristics of conceptual Mars and lunar transportation nodes. Both concepts are based on evolution of the assembly-complete Space Station Freedom configuration by the addition of keels, booms, and modules. Finite-element models of the concepts were developed and a set of undamped modes and frequencies was computed below 2 Hz for each concept. The modes were used as basis vectors for modal analyses describing the dynamic response of the structures to typical reboost maneuvers. The reboost maneuvers had fairly complex loading characteristics since the reaction control system (RCS) jets used for the maneuvers were off-modulated to control pitch and yaw attitude. Interaction of the dynamic response of the structure with the closed-loop attitude control system is investigated for both concepts. The elastic response in the solar dynamic region is investigated to evaluate the severity of the dynamic environment, since the solar dynamic systems have stringent sunpointing requirements which must be maintained during the reboost maneuver.

Cooper, Paul A.↗

NASA NTRS1981

Flight Simulator Visual-Display Delay Compensation

A piloted aircraft can be viewed as a closed-loop man-machine control system. When a simulator pilot is performing a precision maneuver, a delay in the visual display of aircraft response to pilot-control input decreases the stability of the pilot-aircraft system. The less stable system is more difficult to control precisely. Pilot dynamic response and performance change as the pilot attempts to compensate for the decrease in system stability. The changes in pilot dynamic response and performance bias the simulation results by influencing the pilot's rating of the handling qualities of the simulated aircraft. The study reported here evaluated an approach to visual-display delay compensation. The objective of the compensation was to minimize delay-induced change in pilot performance and workload, The compensation was effective. Because the compensation design approach is based on well-established control-system design principles, prospects are favorable for successful application of the approach in other simulations.

Crane, D. Francis↗

NASA NTRS1961

Analytical Evaluation of a Method of Midcourse Guidance for Rendezvous with Earth Satellites

A digital-computer simulation was made of the midcourse or ascent phase of a rendezvous between a ferry vehicle and a space station. The simulation involved a closed-loop guidance system in which both the relative position and relative velocity between ferry and station are measured (by simulated radar) and the relative-velocity corrections required to null the miss distance are computed and applied. The results are used to study the effectiveness of a particular set of guidance equations and to study the effects of errors in the launch conditions and errors in the navigation data. A number of trajectories were investigated over a variety of initial conditions for cases in which the space station was in a circular orbit and also in an elliptic orbit. Trajectories are described in terms of a rotating coordinate system fixed in the station. As a result of this study the following conclusions are drawn. Successful rendezvous can be achieved even with launch conditions which are substantially less accurate than those obtained with present-day techniques. The average total-velocity correction required during the midcourse phase is directly proportional to the radar accuracy but the miss distance is not. Errors in the time of booster burnout or in the position of the ferry at booster burnout are less important than errors in the ferry velocity at booster burnout. The use of dead bands to account for errors in the navigational (radar) equipment appears to depend upon a compromise between the magnitude of the velocity corrections to be made and the allowable miss distance at the termination of the midcourse phase of the rendezvous. When approximate guidance equations are used, there are limits on their accuracy which are dependent on the angular distance about the earth to the expected point of rendezvous.

Eggleston, John M.↗

NASA NTRS1961

Study of an Active Control System for a Spinning Body

The mission requirements for some satellites require that they spin continuously and at the same time maintain a precise direction of the spin axis. An analog-computer study has been made of an attitude control system which is suitable for such a satellite. The control system provides the necessary attitude control through the use of a spinning wheel, which will provide precession torques, commanded by an automatic closed-loop servomechanism system. The sensors used in the control loop are rate gyroscopes for damping of any wobble motion and a sun seeker for attitude control. The results of the study show that the controller can eliminate the wobble motion of the satellite resulting from a rectangular pulse moment disturbance and then return the spin axis to the reference space axis. The motion is damped to half amplitude in less than one cycle of the wobble motion. The controller can also reduce the motion resulting from a step change in product of inertia both by causing the new principal axis to be steadily alined with the spin vector and by reducing the cone angle generated by the reference body axis. These methods will reduce the motion whether the satellite is a disk, sphere, or rod configuration.

Adams, J. J.↗

NASA NTRS1989

Moving Target Tracking for a Next Generation Space Telescope

The Hubble Space Telescope required a complex method for tracking targets in motion in the solar system, due mostly to atmospheric drag effects. A NGST in high earth orbit, or on the Moon, would not suffer these drag effects, thus mitigating the tracking problem. Many of the HST problems arise from the "open-loop" nature of the tracking method. An NGST would be better off if it could use "closed-loop" tracking of all targets, both fixed and moving. A method to accomplish this is proposed. Methods to reduce the jitter and lower the ambient temperature of the optics via a tethered optical system are proposed.

Skillman, David R.↗

NASA NTRS1986

Integrating Computer Architectures into the Design of High-Performance Controllers

Modern control systems must typically perform real-time identification and control, as well as coordinate a host of other activities related to user interaction, on-line graphics, and file management. This paper discusses five global design considerations that are useful to integrate array processor, multimicroprocessor, and host computer system architecture into versatile, high-speed controllers. Such controllers are capable of very high control throughput, and can maintain constant interaction with the non-real-time or user environment. As an application example, the architecture of a high-speed, closed-loop controller used to actively control helicopter vibration will be briefly discussed. Although this system has been designed for use as the controller for real-time rotorcraft dynamics and control studies in a wind-tunnel environment, the control architecture can generally be applied to a wide range of automatic control applications.

Jacklin, Stephen A.↗

NASA NTRS1990

Dynamic Characteristics of Space Station Freedom Mars and Lunar Evolution Reference Configurations

One concept for a manned mission to Mars uses an evolutionary version of Space Station Freedom (SSF) as a transportation node. The station is modified by the addition of dual keels, an upper and lower boom, additional laboratory and habitation modules, increased power and an assembly platform. With these modifications the station is called the Mars Evolution Reference Configuration (MERC). The mass of the station is 65 percent greater than the mass of SSF and its moments of inertia through the mass center are greater by approximately a factor of four. Over a period of months, several flights from Earth to low-Earth-orbit carry the components of a manned Mars piloted vehicle (MPV) to the MERC where the vehicle is constructed on the assembly platform. After each flight the station is reboosted to an appropriate altitude, such that the orbit decay due to atmospheric drag forces lowers the spacecraft to the proper altitude at the appropriate time for rendezvous with the next assembly flight. When the assembly process is completed, the MPV, which has a mass of approximately 200,000 lbm, is situated on the evolutionary station. The mass increase of the MERC with MPV system over SSF is 112 percent and the moments of inertia about axes through the mass center increase by up to a factor of 12. When the MPV is assembled, inspected and verified, the mission is ready to proceed and the MPV is moved from the station to a staging area and mated with fueled trans-Mars injection stages for the flight to Mars. This presentation describes a finite element model of the MERC formulated to investigate the expected low frequency modes and its variation with the addition of a large payload. A basic reboost procedure using near-continuous firing of reaction control system jets is proposed with off-modulation of the jets used to control flight attitude. The reboost procedure is described with the closed-loop attitude control dictating jet on/off cycling based on feedback signals which contain both the rigid body rotation information and the elastic rotations local to the attitude sensor. The presentation contains a description of the dynamic response at critical points of the station during the reboost and concludes with results of a brief study of the dynamic characteristics of a Lunar transportation node configuration.

Ayers, J. Kirk↗

NASA NTRS1987

Irradiance and spectral distribution control system for controlled environment chambers

This paper describes a closed-loop control system for controlling the irradiance and spectral quality generated by fluorescent lamps in a controlled environment chamber. The 400 to 800 nm irradiance and the ratio of the red waveband (600 to 700 nm) to the far-red waveband (700 to 800 nm) were independently controlled and varied as functions of time. A suggested application is to investigate the possibility of synergistic effects of changing irradiance levels and changing spectral distributions on photoperiodism and photomorphogenesis.

NASA Center KSC↗