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At least 415 records · Page 23

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NASA NTRS1992

NASA aerospace pyrotechnically actuated systems: Program plan

The NASA Aerospace Pyrotechnically Actuated Systems (PAS) Program, a focused technology program, is being initiated to enhance the reliability, safety, and performance of pyrotechnically actuated systems. In broad terms, this Program Plan presents the approach that helps to resolve concerns raised by the NASA/DOD/DOE Aerospace Pyrotechnic Steering Committee. This Plan reflects key efforts needed in PAS technology. The resources committed to implement the Program will be identified in the Program Implementation Plan (PIP). A top level schedule is included along with major Program milestones and products. Responsibilities are defined in the PIP. The Plan identifies the goals and detailed objectives which define how those goals are to be accomplished. The Program will improve NASA's capabilities to design, develop, manufacture, and test pyrotechnically actuated systems for NASA's programs. Program benefits include the following: advanced pyrotechnic systems technology developed for NASA programs; hands-on pyrotechnic systems expertise; quick response capability to investigate and resolve pyrotechnic problems; enhanced communications and intercenter support among the technical staff; and government-industry PAS technical interchange. The PAS Program produces useful products that are of a broad-based technology nature rather than activities intended to meet specific technology objectives for individual programs. Serious problems have occurred with pyrotechnic devices although near perfect performance is demanded by users. The lack of a program to address those problems in the past is considered a serious omission. The nature of problems experienced as revealed by a survey are discussed and the origin of the program is explained.

Schulze, Norman R.↗

NASA NTRS1991

Implementation of a model based fault detection and diagnosis technique for actuation faults of the SSME

In a previous study, Guo, Merrill and Duyar, 1990, reported a conceptual development of a fault detection and diagnosis system for actuation faults of the Space Shuttle main engine. This study, which is a continuation of the previous work, implements the developed fault detection and diagnosis scheme for the real time actuation fault diagnosis of the Space Shuttle Main Engine. The scheme will be used as an integral part of an intelligent control system demonstration experiment at NASA Lewis. The diagnosis system utilizes a model based method with real time identification and hypothesis testing for actuation, sensor, and performance degradation faults.

Duyar, A.↗

NASA NTRS1993

Actuator tuning for nonlinear truss structures - A neural network approach

The optimal actuator placement problem encompasses finding their best locations and best gains. The latter is referred to as tuning the actuators. This paper deals with tuning a given set of actuators in presence of known structural nonlinearities arising from gaps at some joints. For this purpose, an efficient neural network-based algorithm is proposed and illustrated using numerical simulations.

Toomarian, N.↗

NASA NTRS1993

Actuated forebody strake controls for the F-18 high alpha research vehicle

A series of ground-based studies have been conducted to develop actuated forebody strake controls for flight test evaluations using the NASA F-18 High-Alpha Research Vehicle. The actuated forebody strake concept has been designed to provide increased levels of yaw control at high angles of attack where conventional rudders become ineffective. Results are presented from tests conducted with the flight-test strake design, including static and dynamic wind-tunnel tests, transonic wind-tunnel tests, full-scale wind-tunnel tests, pressure surveys, and flow visualization tests. Results from these studies show that a pair of conformal actuated forebody strakes applied to the F-18 HARV can provide a powerful and precise yaw control device at high angles of attack. The preparations for flight testing are described, including the fabrication of flight hardware and the development of aircraft flight control laws. The primary objectives of the flight tests are to provide flight validation of the groundbased studies and to evaluate the use of this type of control to enhance fighter aircraft maneuverability.

Murri, Daniel G.↗

NASA NTRS1993

Piezoelectric actuator models for active sound and vibration control of cylinders

Analytical models for piezoelectric actuators, adapted from flat plate concepts, are developed for noise and vibration control applications associated with vibrating circular cylinders. The loadings applied to the cylinder by the piezoelectric actuators for the bending and in-plane force models are approximated by line moment and line force distributions, respectively, acting on the perimeter of the actuator patch area. Coupling between the cylinder and interior acoustic cavity is examined by studying the modal spectra, particularly for the low-order cylinder modes that couple efficiently with the cavity at low frequencies. Within the scope of this study, the in-plane force model produced a more favorable distribution of low-order modes, necessary for efficient interior noise control, than did the bending model.

Lester, Harold C.↗

NASA NTRS1993

Modal grammian approach to actuator and sensor placement for flexible structures

The problem of selecting optimal locations of actuators and sensors for the control of flexible structures is addressed. Novel geometrical and physical interpretations are given for both controllability and observability grammians which enhances the intuitive aspects of the actuator and sensor placement problem. The explicit form of controllability and observability grammians for flexible structures is used to define modal grammian coefficients, which provides the basis for an actuator and sensor placement technique. The relationship of the proposed metric to three different existing criteria are given. The method is demonstrated on a model of an experimental large flexible structure.

Lim, K. B.↗

NASA NTRS1994

Actuator Exerts Tensile Or Compressive Axial Load

Compact, manually operated mechanical actuator applies controlled, limited tensile or compressive axial force. Designed to apply loads to bearings during wear tests in clean room. Intended to replace hydraulic actuator. Actuator rests on stand and imparts axial force to part attached to clevis inside or below stand. Technician turns control screw at one end of lever. Depending on direction of rotation of control screw, its end of lever driven downward (for compression) or upward (for tension). Lever pivots about clevis pin at end opposite of control screw; motion drives downward or upward link attached via shearpin at middle of lever. Link drives coupling and, through it, clevis attached to part loaded.

Nozzi, John↗

NASA NTRS1994

Control strategies for systems with limited actuators

This work investigates the effects of actuator saturation in multi-input, multi-output (MIMO) control systems. The adverse system behavior introduced by the saturation nonlinearity is viewed here as resulting from two mechanisms: controller windup - a problem caused by the discrepancy between the limited actuator commands and the corresponding control signals, and directionality - the problem of how to use nonlimited actuators when a limited condition exists. The tracking mode and Hanus methods are two common strategies for dealing with the windup problem. It is seen that while these methods alleviate windup, performance problems remain due to plant directionality. Though high gain conventional antiwindup as well as more general linear methods have the potential to address both windup and directionality, no systematic design method for these schemes has emerged; most approaches used in practice are application driven. An alternative method of addressing the directionality problem is presented which involves the introduction of a control direction preserving nonlinearity to the Hanus antiwindup system. A nonlinearity is subsequently proposed which reduces the conservation inherent in the former direction-preserving approach, improving performance. The concept of multivariable sensitivity is seen to play a key role in the success of the new method.

Marcopoli, Vincent R.↗

NASA NTRS1994

Preparations for flight research to evaluate actuated forebody strakes on the F-18 high-alpha research vehicle

As part of the NASA High-Angle-of-Attack Technology Program (HATP), flight tests are currently being conducted with a multi-axis thrust vectoring system applied to the NASA F-18 High Alpha Research Vehicle (HARV). A follow-on series of flight tests with the NASA F-18 HARV will be focusing on the application of actuated forebody strake controls. These controls are designed to provide increased levels of yaw control at high angles of attack where conventional aerodynamic controls become ineffective. The series of flight tests are collectively referred to as the Actuated Nose Strakes for Enhanced Rolling (ANSER) Flight Experiment. The development of actuated forebody strake controls for the F-18 HARV is discussed and a summary of the ground tests conducted in support of the flight experiment is provided. A summary of the preparations for the flight tests is also provided.

Murri, Daniel G.↗

NASA NTRS1994

Two-Dimensional Scramjet Inlet Unstart Model: Wind-Tunnel Blockage and Actuation Systems Test

This supplement to NASA TM 109152 shows the Schlieren video (10 min. 52 sec., color, Beta and VHS) of the external flow field and a portion of the internal flow field of a two-dimensional scramjet inlet model in the NASA Langley 20-Inch Mach 6 Tunnel. The intent of the overall test program is to study (both experimentally and computationally) the dynamics of the inlet unstart; this (phase I) effort examines potential wind-tunnel blockage issues related to model sizing and the adequacy of the actuation systems in accomplishing the start and unstart. The model is equipped with both a moveable cowl and aft plug. Windows in the inlet sidewalls allow limited optical access to the internal shock structure. In the video, flow is from right to left, and the inlet is oriented inverted with respect to flight, i.e., with the cowl on top. The plug motion is obvious because the plug is visible in the aft window. The cowl motion, however, is not as obvious because the cowl is hidden from view by the inlet sidewall. The end of the cowl actuator arm, however, becomes visible above the inlet sidewalls between the windows when the cowl is up (see figure 1b of the primary document). The model is injected into the tunnel and observed though several actuation sequences with two plug configurations over a range of unit freestream Reynolds number at a nominal freestream Mach number of 6. The framing rate and shutter speed of the camera were too slow to fully capture the dynamics of the unstart but did prove sufficient to identify inlet start and unstart. This series of tests indicated that the model was appropriately sized for this facility and identified operability limits required first to allow the inlet to start and second to force the unstart.

Holland, Scott D.↗

NASA NTRS1994

Strategic avionics technology definition studies. Subtask 3-1A3: Electrical Actuation (ELA) Systems Test Facility

Future aerospace vehicles will require use of the Electrical Actuator systems for flight control elements. This report presents a proposed ELA Test Facility for dynamic evaluation of high power linear Electrical Actuators with primary emphasis on Thrust Vector Control actuators. Details of the mechanical design, power and control systems, and data acquisition capability of the test facility are presented. A test procedure for evaluating the performance of the ELA Test Facility is also included.

Rogers, J. P.↗

NASA NTRS1995

Rotary actuator

Rotary actuators and other mechanical devices incorporating shape memory alloys are provided herein. Shape memory alloys are a group of metals which when deformed at temperatures below their martensite temperatures, resume the shapes which they had prior to the deformation if they are heated to temperatures above their austensite temperatures. Actuators in which shape memory alloys are employed include bias spring types, in which springs deform the shape memory alloy (SMA), and differential actuators, which use two SMA members mechanically connected in series. Another type uses concentric cylindrical members. One member is in the form of a sleeve surrounding a cylinder, both being constructed of shape memory alloys. Herein two capstans are mounted on a shaft which is supported in a framework. Each capstan is capable of rotating the shaft. Shape memory wire, as two separate lengths of wire, is wrapped around each capstan to form a winding around that capstan. The winding on one capstan is so wrapped that the wire is in a prestretched state. The winding on the other capstan is so wrapped that the wire is in a taut, but not a prestretched, state. Heating one performs work in one direction, thus deforming the other one. When the other SMA is heated the action is reversed.

Brudnicki, Myron↗

NASA NTRS1992

Fabrication of silicon-based shape memory alloy micro-actuators

Thin film shape memory alloy has been integrated with silicon in a new actuation mechanism for microelectromechanical systems. This paper compares nickel-titanium film with other actuators, describes recent results of chemical milling processes developed to fabricate shape memory alloy microactuators in silicon, and describes simple actuation mechanisms which have been fabricated and tested.

Johnson, A. David↗

NASA NTRS1995

Piezoelectric Actuators On A Cold Finger

Developmental system for active suppression of vibrations of cold finger includes three piezoelectric actuators bonded to outer surface. Actuators used to suppress longitudinal and lateral vibrations of upper end of cold finger by applying opposing vibrations. Cold finger in question is part of a cryogenic system associated with an infrared imaging detector. When fully developed, system would be feedback sensor/control/actuator system automatically adapting to changing vibrational environment and suppresses pressure-induced vibrations by imposing compensatory vibrations via actuators.

Kuo, Chin-Po↗

NASA NTRS1995

Linear Proof-Mass Actuator

Linear proof-mass actuator (LPMA) is friction-driven linear mass actuator capable of applying controlled force to structure in outer space to damp out oscillations. Capable of high accelerations and provides smooth, bidirectional travel of mass. Design eliminates gears and belts. LPMA strong enough to be used terrestrially where linear actuators needed to excite or damp out oscillations. High flexibility designed into LPMA by varying size of motors, mass, and length of stroke, and by modifying control software.

Holloway, Sidney E., III↗

NASA NTRS1996

Aircraft Interior Noise Control Using Distributed Piezoelectric Actuators

Developing a control system that can reduce the noise and structural vibration at the same time is an important task. This talk presents one possible technical approach for accomplishing this task. The target application of the research is for aircraft interior noise control. The emphasis of the present approach is not on control strategies, but rather on the design of actuators for the control system. In the talk, a theory of distributed piezoelectric actuators is introduced. A uniform cylindrical shell is taken as a simplified model of fuselage structures to illustrate the effectiveness of the design theory. The actuators developed are such that they can reduce the tonal structural vibration and interior noise in a wide range of frequencies. Extensive computer simulations have been done to study various aspects of the design theory. Experiments have also been conducted and the test results strongly support the theoretical development.

Sun, Jian Q.↗

NASA NTRS1997

Updating Gimbal Actuators for the Long Journey to Saturn

The Cassini mission requires extraordinary life and reliability from the linear servo-actuators which position the spacecraft's redundant rocket engines. Both commercial actuators and existing in-house actuator designs were studied for this application. Ultimately a device inherited from JPL's Mariner and Viking missions to Mars was selected because of its close match to functional requirements and its flight pedigree. However, several design improvements were necessary to meet life and reliability goals. Special attention was focused on reliability testing of the motor and mechanism at all stages of procurement and assembly because a brush type of DC motor was retained from the old design. These improvements and, in particular, efforts to develop new component sources are discussed in this paper.

Iskenderian, Theodore↗

NASA NTRS1997

Modeling Piezoelectric Stack Actuators for Control of Micromanipulation

A nonlinear lumped-parameter model of a piezoelectric stack actuator has been developed to describe actuator behavior for purposes of control system analysis and design, and, in particular, for microrobotic applications requiring accurate position and/or force control. In formulating this model, the authors propose a generalized Maxwell resistive capacitor as a lumped-parameter causal representation of rate-independent hysteresis. Model formulation is validated by comparing results of numerical simulations to experimental data. Validation is followed by a discussion of model implications for purposes of actuator control.

Goldfarb, Michael↗