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Utilizing arrays of sequentially-excited piezoelectric elements to provide motion in a nonmagnetic motor provide built-in redundancy and long life required for deployment or actuation of devices on spacecraft. Linear-motion motor devices can also be fabricated.
Bimorph strip composed of two layers of poled piezoelectric ceramic material closes and opens valve. Strip performs like capacitator, allowing initial inrush of current when valve is energized and then only small leakage current flows as valve remains energized.
A surface shear force transducer for use in impulse type hypersonic tunnels is described. Sensors are constructed of lead zirconate titanate composition piezoelectric ceramic materials. The diameter of the sensing diaphragm is 0.75 inches and overall transducer dimensions are 1.0 inch diameter and 0.625 inch height. Analysis of the tranducer is made to help design criteria and fabrication techniques. Discussions on design and fabrication techniques are presented as well as performance of transducers delivered.
An oriented piezoelectric film has been incorporated in the insulator region of a silicon insulated-gate field-effect transistor to provide a sensitive high-frequency strain transducer. With this device, strains as low as 10 to the -8th power have been detected, and gauge factors of roughly 7000 have been attained for applied ac strains at 5.6 MHz.
After discussing the principal calibration methods for piezoelectric accelerometers, an experimental setup for accelerometer calibration by the reciprocity method is described It is shown how the use of a lock-in voltmeter eliminates errors due to viscous damping and electrical loading.
The paper presents the results of an experimental evaluation of a new type of piezoelectric ceramic device designed for use as a laser mirror tuner. Thin plates made from various materials were assembled into a circular bimorph configuration and tested for linearity of movement, maximum travel, and resonant frequency for varying conditions of clamping torque and mirror loading values. Most of the devices tested could accept mirror diameters up to approximately 1.3 cm and maintain a resonant frequency above 2 kHz. Typical mirror translation without measurable tilt was plus or minus 20 micrometers or greater for applied voltages of less than plus or minus 300 V.
Special housing couples piezoelectric transducers to nonporous surfaces for ultrasonic or acoustic-emission testing. Device, while providing sound isolation on flat or nonflat surfaces, can be attached and detached quickly. Vacuum sealing mechanism eliminates need for permanent or semipermanent bonds, viscous coupling liquids, weights, magnets, tape, or springs ordinarily used.
Expressions for piezoelectric and pyroelectric coefficients for a crystal of polarizable point dipoles are derived. The effect of crystal structure on the local electric field acting to polarize the molecules is included via the Lorentz-factor formalism. The derived expressions for the piezo- and pyroelectric coefficients are found to contain terms dependent on derivatives of the Lorentz factors. These terms reflect the changing of molecular dipole moments in response to the changing local electric field in the strained crystal. Inclusion of this effect results in predictions of coefficients substantially different from those obtained using the Lorentz field approximation.
When a pointing system is attached to a large flexible body that is subject to continuous excitation, a mechanical isolator becomes a key element in achieving high performance. An active softmount based on the piezoelectric polymer poly (vinylidene fluoride) is considered here for use in a precision pointing system for Space Station. A finite element model of the softmount is developed and added to simple Space Station and payload models for performance analysis. Both linear frequency domain and nonlinear time domain simulations are carried out in order to demonstrate the wideband disturbance rejection capabilities of the design. Nonlinear geometric effects of large nodal deflections are also considered.
This paper describes recent research advances made in the development of radiation-hardened piezoelectric quartz oscillators, hydrogen masers, and superconducting oscillators, with emphasis placed on the principles involved in the operation of these oscillators and the factors affecting the operation. Particular attention is given to the radiation-susceptibility studies of quartz-crystal resonators, the hydrogen-maser relaxation process and noise sources, and low-phase-noise superconducting oscillators. Diagrams of these devices and performance graphs are included.
The development of a particulate mass-sensing instrument based on a quartz-crystal microbalance and enhanced with the new surface acoustic-wave (SAW) technology is reported. Mass sensitivity comparisons of a 158-MHz SAW piezoelectric microbalance and a conventional 10-MHz quartz-crystal microbalance show that the SAW crystal is 266 times more sensitive, in good agreement with the theoretical value of 250. The frequency stability of a single SAW resonator is 6 parts in 10 to the 8th over 1 min. The response to temperature changes is found to be very linear over the range +30 to -30 C. A strong response to 15 ppm SO2 has been demonstrated on a chemically coated SAW crystal.
Vibration-suppressing control systems including piezoelectric actuators undergoing development. Small, lightweight, and rugged. Requires simpler electronic control subsystems and does not require large electromagnet coils. Continues to provide support and some passive damping even when electronic control subsystems or power supplies fail. Intended primarily to enhance safety and prevent damage in rotating machinery by sensing and counteracting vibrations. Useful in suppressing unpredictable vibrations caused by changes in loads, losses of rotating components and consequent imbalances in rotors, and ingestion of foreign objects into turbines.
In many spacecraft applications, mechanisms are required to perform precision pointing operations or to sometimes dither about or track a moving object. These mechanisms perform in a predictable and repeatable manner in benign temperature environments. Severe thermal gradients experienced in actual space applications however, cause assemblies to expand and contract around their bearings. This results in unpredictable changes in bearing preload, and hence bearing friction. This becomes a limitation for servos controlling pointing accuracy. Likewise, uncontrollable vibrations may couple into fixed preload (hence, fixed stiffness) mechanisms and limit pointing accuracy. Consequently, a complex problem faced today is how to design mechanisms that remain insensitive to changing thermal and vibrational spacecraft environments. Research presented involves the simplified modeling and test results of an actuator module that used piezoelectrically preload controlled bearings. The feasibility of actively controlling bearing preload was demonstrated. Because bearing friction is related to preload, a thermally active system designed with aluminum components and a 440 C bearing, was friction tested at temperatures ranging from 0 to 70 C (32 to 158 F). Effectiveness of the translators were demonstrated by mapping a controllable friction range throughout tested temperatures. It was learned that constant preload for this system could be maintained over an approximate 44 C (79 F) temperature span. From testing, it was also discovered that at the more deviate temperatures, expansions were so large that radial clearances were taken up and the duplex bearing became radially preloaded. Thus, active control of bearing preload is feasible but may be limited by inherent geometry constraints and materials used in the system.
A laboratory investigation was conducted to characterize two piezoelectric-film sensor configurations, a rigidly mounted sensor and a sensor mounted over an air cavity. The sensors are evaluated for sensitivity and frequency response, and methods to optimize data are presented. The cavity-mounted sensor exhibited a superior frequency response and was more sensitive to normal pressure fluctuations and less sensitive to vibrations through the structure. Both configurations were sensitive to large-scale structural vibrations. Flight-test data are shown for cavity-mounted sensors, illustrating practical aspects to consider when designing sensors for application in such harsh environments. The relation of the data to skin friction and maximum shear stress, transition detection, and turbulent viscous layers is derived through analysis of the flight data.
The design and development of a zero stiction active member containing piezoelectric and electrostrictive actuator motors is presented. The active member is intended for use in submicron control of structures. Experimental results are shown which illustrate actuator and device characteristics relevant to precision control applications.
The application of piezoelectric actuators for active vibration control (AVC) of rotating machinery is examined. Theory is derived and the resulting predictions are shown to agree closely with results of tests performed on an air turbine driven-overhung rotor. The test results show significant reduction in unbalance, transient and sub-synchronous responses. Results from a 30-hour endurance test support the AVD system reliability. Various aspects of the electro-mechanical stability of the control system are also discussed and illustrated. Finally, application of the AVC system to an actual jet engine is discussed.
Experimental flutter results obtained from wind tunnel tests of a two degree of freedom wind tunnel model are presented for the open and closed loop systems. The wind tunnel model is a two degree of freedom system which is actuated by piezoelectric plates configured as bimorphs. The model design was based on finite element structural analyses and flutter analyses. A control law was designed based on a discrete system model; gain feedback of strain measurements was utilized in the control task. The results show a 21 pct. increase in the flutter speed.
A method is presented for simulating the coupled 'electromechanical' system to predict rotordynamic stability and unbalance response along with control system stability. The piezoelectric actuators and their amplifiers are represented as equivalent linear electrical circuits. The electromechanical system modeling approach is utilized to correlate test results from a double overhung rotor rig. The test results also show the effectiveness of the control system for suppressing the unbalance response of two modes using active stiffness and active damping.