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Two clamps hold rod in fixed extension from cylinder even when power is off, converting actuator into stiff structural member. Locked actuator is useful as mechanical support or linkage or as fail-safe device in case of loss of hydraulic pressure. Potential applications include manufacturing processes and specialized handling and holding devices.
The dynamics, attitude, and shape control of a large thin flexible square platform in orbit are studied. Attitude and shape control are assumed to result from actuators placed perpendicular to the main surface and one edge and their effect on the rigid body and elastic modes is modelled to first order. The equations of motion are linearized about three different nominal orientations: (1) the platform following the local vertical with its major surface perpendicular to the orbital plane; (2) the platform following the local horizontal with its major surface normal to the local vertical; and (3) the platform following the local vertical with its major surface perpendicular to the orbit normal. The stability of the uncontrolled system is investigated analytically. Once controllability is established for a set of actuator locations, control law development is based on decoupling, pole placement, and linear optimal control theory. Frequencies and elastic modal shape functions are obtained using a finite element computer algorithm, two different approximate analytical methods, and the results of the three methods compared.
A comprehensive digital model for the analysis of the dynamic-instantaneous performance of a power conditioner fed samarium-cobalt permanent magnet brushless DC motor is presented. The particular power conditioner-machine system at hand, for which this model was developed, is a component of an actual prototype electromechanical actuator built for NASA-JSC as a possible alternative to hydraulic actuators as part of feasibility studies for the shuttle orbiter applications. Excellent correlation between digital simulated and experimentally obtained performance data was achieved for this specific prototype. This is reported on in this paper. Details of one component of the model, its applications and the corresponding results are given in this paper.
A comprehensive digital model for the analysis and possible optimization of the closed loop dynamic (instantaneous) performance of a power conditioner fed, brushless dc motor powered, electromechanical actuator system (EMA) is presented. This model was developed for the simulation of the dynamic performance of an actual prototype EMA built for NASA-JSC as a possible alternative to hydraulic actuators for consideration in Space Shuttle Orbiter applications. Excellent correlation was achieved between numerical model simulation and experimental test results obtained from the actual hardware. These results include: various current and voltage waveforms in the machine-power conditioner (MPC) unit, flap position as well as other control loop variables in response to step commands of change of flap position. These results with consequent conclusions are detailed in the paper.
Miniature 1-ampere, 1-watt pyrotechnic actuator enclosed in flexible metal bellows. Bellows confines outgassing products, and pyrotechnic shock reduction achieved by action of bellows, gas cushion within device, and minimum use of pyrotechnic material. Actuator inexpensive, compact, and lightweight.
Electrically controlled actuator produces predetermined force, torque, or displacement without motors, solenoids, or gears. Using memory-metal elements, actuator responds to digital input without electronic digitalto-analog conversion. To prevent overheating and consequent loss of hotformed shape, each element protected by thermostat turns off current when predetermined temperature is exceeded. Memory metals used to generate fast mechanical response to electric signals.
An electromechanical actuator is applicable to a variety of spaceflight requirements. Characterized by high torque and a small output step angle, the device is comprised of a coaxial, symmetrical arrangement in which a cup type harmonic drive is directly coupled to a pancake configuration drive motor. The motor, with its dual stator driving a common rotor, is one illustration of the concept of selective redundacy. Selective redundancy promotes the idea that redundancy, to be effective, must not compromise inherent design simplicity nor introduce new failure modes. The usefulness of the actuator is exemplified by its selection for a broad range of positioning and driving applications including TDRSS gimbal drives, Space Telescope deployment and latching machanisms, and Space Telescope secondary mirror drive, as well as others.
An analysis and optimization of a mirror-actuator system for large excursion/high-frequency chopping is developed. The results of this analysis, combined with laboratory measurements of a prototype actuator operating at cryogenic temperatures, allow performance predictions to be made for a real system utilizing this technology.
This paper describes the two actuators developed for pointing the remote science instruments from the spinning Galileo spacecraft. Details of the key elements are presented together with their design features and developmental difficulties. Four techniques used for power and signal transfer across the actuators' rotating joints are also discussed.
Actuator stabilizes spacecraft spin by varying length of support struts that hold spacecraft booms. Variation changes spin axis and controls wobble. Linear actuator controls spacecraft wobble applicable in rotating systems on Earth.
Development of the Body Flap Actuation Subsystem for Space Shuttles included alterations from the original design to mechanical stops, planet gears, control valves, and solenoid valves. The mechanical stops were redesigned to absorb stall load and rotating inertia of the hydraulic motors instead of only stall load. The institution of a quill shaft (torsion spring) was a successful solution. The planet gears in the geared rotary actuators developed cracks during testing. This failure was alleviated via modification to the gears. A motor pressurization - brake release timing technique was developed thru analysis and testing. This resulted in a control valve configuration which would not permit freewheeling of the body flap surface. Finally, several solenoid valve configurations were tested to obtain the desired performance. Conceptual redesigns and modifications were weighted against each other to optimize a solution. Tradeoffs were usually made between life, performance, failure tolerance, and reliability versus weight, envelope, and maintainability.
The design and development of a linear thermal actuator (LTA) for space applications is described. The actuator is driven by thermal energy and utilizes the property of thermal expansion to do work. Equations to predict performance are developed and used to optimize the design of the development model LTA. Design details and test results are presented and discussed.
Two types of superconducting electromagnetic actuators linear and angular - for precise control of Fabry-Perot spectrometer etalons at liquid helium temperature were manufactured and tested successfully. The linear displacement unit (45 Newtons/Amp) has maximum travel of + or - 44 microns with off-axis deviation of less than 1.5 arcseconds for 15 microns path. The angular unit has maximum tilt of + or - 8 arcminutes and can maintain parallelism of two etalons to better than 0.3 arcsecond of angle by compensating the differential contraction upon cooling and off-axis deviation of the linear displacement unit. These actuators are proving especially useful in low temperature infrared instrumentation where other choices, such as piezoelectric crystals, fail and where essentially zero power dissipation permits low infrared backgrounds to be maintained along with long cryogenic lifetimes.
The performance of the detection filter in detecting and isolating aircraft control surface and actuator failures is evaluated. The basic detection filter theory assumption of no direct input-output coupling is violated in this application due to the use of acceleration measurements for detecting and isolating failures. With this coupling, residuals produced by control surface failures may only be constrained to a known plane rather than to a single direction. A detection filter design with such planar failure signatures is presented, with the design issues briefly addressed. In addition, a modification to constrain the residual to a single known direction even with direct input-output coupling is also presented. Both the detection filter and the modification are tested using a nonlinear aircraft simulation. While no thresholds were selected, both filters demonstrated an ability to detect control surface and actuator failures. Failure isolation may be a problem if there are several control surfaces which produce similar effects on the aircraft. In addition, the detection filter was sensitive to wind turbulence and modeling errors.
Hydraulic actuator moves several nuclear-reactor control rods in unison. Electromagnetic pump pushes liquid lithium against ends of control rods, forcing them out of or into nuclear reactor. Color arrows show lithium flow for reactor startup and operation. Flow reversed for shutdown. Conceived for use aboard spacecraft, actuator principle applied to terrestrial hydraulic machinery involving motion of ganged rods.
The design and development of a large diameter high pressure quick acting propulsion valve and valve actuator is described. The valve is the heart of a major test facility dedicated to conducting full scale performance tests of aircraft landing systems. The valve opens in less than 300 milliseconds releasing a 46-centimeter- (18-in.-) diameter water jet and closes in 300 milliseconds. The four main components of the valve, i.e., valve body, safety shutter, high speed shutter, and pneumatic-hydraulic actuator, are discussed. This valve is unique and may have other aerospace and industrial applications.
A rotary stepping device includes a rotatable shaft which is driven by means of a coiled spring clutch which is alternately tightened to grip and rotate the shaft and released to return it to a resting position. An actuator formed of a memory metal is used to pull the spring clutch to tighten it and rotate the shaft. The actuator is activated by heating it above its critical temperature and is returned to an elongated configuration by means of the force of the spring cloth.
The applications, design, control and testing of an actuator that provides the precise motion control of a gimbal platform without torquing against the basebody to which it is attached are described. The reactionless actuator described was given the name reactuator.