Engineering topics

Lindner, D. K.

Publications and source records attributed to Lindner, D. K..

9 records

NASA NTRS1993

Nonlinear effects of a modal domain optical fiber sensor in a vibration suppression control loop for a flexible structure

Recently, a modal domain optical fiber sensor has been demonstrated as a sensor in a control system for vibration suppression of a flexible cantilevered beam. This sensor responds to strain through a mechanical attachment to the structure. Because this sensor is of the interferometric type, the output of the sensor has a sinusoidal nonlinearity. For small levels of strain, the sensor can be operated in its linear region. For large levels of strain, the detection electronics can be configured to count fringes. In both of these configurations, the sensor nonlinearity imposes some restrictions on the performance of the control system. In this paper we investigate the effects of these sensor nonlinearities on the control system, and identify the region of linear operation in terms of the optical fiber sensor parameters.

Lindner, D. K.↗

NASA NTRS1992

Optical distributed sensors for feedback control: Characterization of photorefractive resonator

The aim of the project was to explore, define, and assess the possibilities of optical distributed sensing for feedback control. This type of sensor, which may have some impacts in the dynamic control of deformable structures and the monitoring of small displacements, can be divided into data acquisition, data processing, and control design. Analogue optical techniques, because they are noninvasive and afford massive parallelism may play a significant role in the acquisition and the preprocessing of the data for such a sensor. Assessing these possibilities was the aim of the first stage of this project. The scope of the proposed research was limited to: (1) the characterization of photorefractive resonators and the assessment of their possible use as a distributed optical processing element; and (2) the design of a control system utilizing signals from distributed sensors. The results include a numerical and experimental study of the resonator below threshold, an experimental study of the effect of the resonator's transverse confinement on its dynamics above threshold, a numerical study of the resonator above threshold using a modal expansion approach, and the experimental test of this model. A detailed account of each investigation, including methodology and analysis of the results are also included along with reprints of published and submitted papers.

Indebetouw, Guy↗

NASA NTRS1991

Vibration suppression using a proofmass actuator operating in stroke/force saturation

The design of the control-loop structure for a feedback control system which contains a proofmass actuator for suppressing vibration is discussed. The loop structure is composed of inner control loops, which determine the frequency of the actuator and which are directly related to the actuator and the outer loops which add damping to the structure. When the frequency response of the actuator is matched to the stroke/force saturation curve, the actuator is most effective in the vibration suppression loops, and, since the stroke/force saturation curve is characterized by the stroke length, the mass of the proofmass, and the maximum current delivered by the motor electronics, the size of the actuator can be easily determined. The results of the loop-structure model calculations are verified by examining linear DC motors as proofmass actuators for the Mast in NASA's Control of Flexible Structures program.

Lindner, D. K.↗

NASA NTRS1991

Optical fiber sensors for materials and structures characterization

The final technical report on Optical Fiber Sensors for Materials and Structures Characterization, covering the period August 1990 through August 1991 is presented. Research programs in the following technical areas are described; sapphire optical fiber sensors; vibration analysis using two-mode elliptical core fibers and sensors; extrinsic Fabry-Perot interferometer development; and coatings for fluorescent-based sensor. Research progress in each of these areas was substantial, as evidenced by the technical publications which are included as appendices.

Lindner, D. K.↗

NASA NTRS1991

Active control for vibration suppression in a flexible beam using a modal domain optical fiber sensor

An account is given of the use of a modal-domain (MD) fiber-optic sensor as an active control system component for vibration suppression, whose output is proportional to the integral of the axial strain along the optical fiber. When an MD sensor is attached to, or embedded in, a flexible structure, it senses the strain in the structure along its gage length. On the basis of the present integration of the sensor model into a flexible-structure model, it becomes possible to design a control system with a dynamic compensator which adds damping to the low-order modes of the flexible structure. This modeling procedure has been experimentally validated.

Cox, D. E.↗

NASA NTRS1989

Optical fiber sensors and signal processing for intelligent structure monitoring

Few mode optical fibers have been shown to produce predictable interference patterns when placed under strain. The use is described of a modal domain sensor in a vibration control experiment. An optical fiber is bonded along the length of a flexible beam. Output from the modal domain sensor is used to suppress vibrations induced in the beam. A distributed effect model for the modal domain sensor is developed. This model is combined with the beam and actuator dynamics to produce a system suitable for control design. Computer simulations predict open and closed loop dynamic responses. An experimental apparatus is described and experimental results are presented.

Thomas, Daniel↗

NASA NTRS1988

Optical fiber sensors and signal processing for intelligent structure monitoring

The analytic and experimental performance of optical fiber sensors for the control of vibration of large aerospace and other structures are investigated. In particular, model domain optical fiber sensor systems, are being studied due to their apparent potential as distributed, low mass sensors of vibration over appropriate ranges of both low frequency and low amplitude displacements. Progress during the past three months is outlined. Progress since September is divided into work in the areas of experimental hardware development, analytical analysis, control design and sensor development. During the next six months, tests of a prototype closed-loop control system for a beam are planned which will demonstrate the solution of several optical fiber instrumentation device problems, the performance of the control system theory which incorporates the model of the modal domain sensor, and the potential for distributed control which this sensor approach offers.

Rogowski, Robert↗

NASA NTRS1987

A survey of decentralized control techniques for large space structures

Preliminary results on the design of decentralized controllers for the COFS I Mast are reported. A nine mode finite element model is used along with second order model of the actuators. It is shown that without actuator dynamics, the system is stable with collocated rate feedback and has acceptable performace. However, when actuator dynamics are included, the system is unstable.

Lindner, D. K.↗

NASA NTRS1986

Distributed control for COFS 1

An overview is given of the work being done at NASA LaRC on developing the Control of Flexible Structures (COFS) 1 Flight Experiment Baseline Control Law. This control law currently evolving to a generic control system software package designed to supply many, but not all, guest investigators. A system simulator is also described. It is currently being developed for COFS-1 and will be used to develop the Baseline Control Law and to evaluate guest investigator control schemes. It will be available for use whether or not control schemes fall into the category of the Baseline Control Law. First, the hardware configuration for control experiments is described. This is followed by a description of the simulation software. Open-loop sinusoid excitation time histories are next presented both with and without a local controller for the Linear DC Motor (LDCM) actuators currently planned for the flight. The generic control law follows and algorithm processing requirements are cited for a nominal case of interest. Finally, a closed-loop simulation study is presented, and the state of the work is summarized in the concluding remarks.

Montgomery, R. C.↗