The vibratory response of a typical mirror support/positioning system used at the experimental stations of the advanced photon source (APS) project at Argonne National Laboratory is investigated. Positioning precision and stability are especially critical when the supported mirror directs a high-intensity beam aimed at a distant target. Stability may be compromised by low level, low frequency seismic and facility-originated vibrations traveling through the ground and/or vibrations caused by flow-structure interactions in the mirror cooling system. The example case system has five positioning degrees of freedom through the use of precision actuators and rotary and linear bearings. These linkage devices results in complex, multi-dimensional vibratory behavior that is a function of the range of positioning configurations. A rigorous multibody dynamical approach is used for the development of the system equations. Initial results of the study, including estimates of natural frequencies and mode shapes, as well as limited parametric design studies, are presented. While the results reported here are for a particular system, the developed vibratory analysis approach is applicable to the wide range of high-precision optical positioning systems encountered at the APS and at other comparable facilities.

In recent years there has been an increasing need of ultra precision positioning and scanning systems with nanometer, or even subnanometer, resolution and accuracy. To meet the demand requires the development of new design concepts and techniques. A newly developed x-y stage is introduced in the paper. The stage was mainly designed for applications in SPMs, with subnanometer resolution and equivalent repeatability over a 50 by 50 micrometers scanning range. The yaw, roll and pitch errors of the stage are 2 arcsec., 0.8 arcsec., and 0.8 arcsec., respectively for the whole range. Some design considerations, such as stiffness, settling time and distortion of the frame are discussed. The experimental results are presented and its application in SPM demonstrated.

Capacitance micrometry is a technique for measuring the relative displacement of two surfaces. As the spacing between the two surfaces changes so the capacitance changes. This short paper is a summary of recent measurements made to characterize and understand the linearity and scale factor.

In order to collect as much information as possible from the universe, the latest generation of astronomical telescopes have exceptionally large diameter primary mirrors. This dramatic increase in mirror diameter, and corresponding increase in weight, has placed ever increasing demands on the technical performance of the mirror support system. In this paper the authors discuss the mechanical design, fabrication, and testing of the six servo controlled position-actuators that mechanically link the 6.5 m honeycomb mirror to six rigidly reinforced locations in the multiple mirror telescope conversion mirror cell. During telescope operation, these adjustable length actuators assure that the natural frequency of the mirror does not degrade the optical performance of the telescope. Flexures are provided on each end of the actuators to minimize any moments applied to the attachment of the actuator to the mirror. These actuators provide a precise measurement of the external forces applied to the mirror, such as wind loads, for the control of the pneumatic force system that supports the weight of the mirror. The total length of each actuator can be measured to sub-micron resolution upon request. Each actuator has a reliable fail-safe system that limits the compressive and tensile forces that can be applied to the mirror. The position-actuators meet all of the above technical specifications in both tension and compression.

Over the past decade, the principle focus in the lead magnesium niobate (PMN) family of relaxor ferroelectric ceramics has been on the electrostrictive formulation due mainly to its application in deformable optics. Electrostrictive response of the PMN material is very low in hysteresis, contains near-zero creep, and features subnanometer precision. Temperature dependence is its major drawback. Highly desirable is a material which has the broad temperature response of piezoelectric lead-zirconate- titanate with the stable, accurate response of electrostrictive PMN. In this paper we report the development of novel piezoelectric and composite formulations of PMN which provide temperature stabilized response with moderate hysteresis and enhanced structural response with high authority.

Energy density is the key to higher authority actuators. New generation electroceramics, such as temperature stabilized lead magnesium niobate (PMN), generate large forces which can do work in adaptive structures. Ever increasing induced- strains and energy conversion efficiencies require process advances to handle high applied electric fields which are required to fully utilize the saturation strain of the materials. The PMN-based family of materials provide output energy which exceeds magnetostrictive TERFENOL by a factor of 16 and piezoelectric lead zirconate titanate (PZT) by a factor of 4. By tailoring the formulation, the PMN materials have been temperature stabilized to function from -50 to 150 degrees C. Cofired stacks which are 1 inch n diameter and epoxy bonded stacks which are 2 inches in diameter have been produced and operated to induced-strains as large as 1000 ppm. Key to tapping the energy in electroceramics is a mechanical amplifier or mechanism which can efficiently convert force into displacement. Amplification ratios up to 10:1 have been built and integrated with electroceramic stacks. Electronic amplifiers are also required to handle the highly capacitive loads of high authority actuators. Switching and linear amplifiers are compared in terms of power and efficiency.

Unique as an optical component, the deformable mirror must have a quality optical surface which can be contoured and controlled to a fraction of wavelength of light. The key element is the actuator. The actuator must provide precision motion for nanometer wavefront control and provide a stable structure for high quality optical figure. It must be dimensionally stable in terms of both time and temperature. Being in a dynamic environment, it must also withstand high tensile loads and high cycle fatigue. Despite its mechanical, optical, and electrical functions, it simply must work when the voltage is applied during any season and for any reason.

Multilayer actuators are being used in optical communications, large-scale telescopes, semiconductor processing, medical imaging, and a host of optical instruments which need submicron control. PMN multilayer actuators have hysteresis which is less than 1 percent, linearity which is better than 99 percent, and precision which is accurate to a few nanometers. Fundamental to the electrostrain and strength of the multilayer actuators is the ceramic microstructure. The particle size of the starting powders and the thermal processes used to densify the ceramic are key elements in producing a microstructure which provides reliable response at ever increasing applied electric fields.

Recent advances in material science have lead to the development of new, very low temperature actuators of Terbium and Dysoprosium with hitherto unavailable stroke, energy efficiency and force. The test instrument described here was developed to investigate the performance characteristics of these new materials and the devices based upon them. The instrument, referred to as a cryogenic dilatometer, is designed for measuring linear displacements, at accuracies of 0.1 micron, in a material, actuator or sensor operating at low temperatures including that of liquid helium. The instrument, just completed, maintains the sample at a known temperature between 4.2 and 77 K, subjects the actuator material to a known and variable magnetic field of up to 1,500 gauss, places a specific and variable preload of 750 N maximum against the actuator or sample, and measures the resulting actuator displacement. A secondary capability is to provide a reference measurement for calibrating commercial capacitance, eddy current, linear variable differential transformers and other displacement gages at low temperatures. The primary linear displacement measurement tool is a fringe counting interferometer. A liquid helium cooled probe provides the sample test environment.

This paper describes research in the development of a very high stability Fabry-Perot etalon that is tunable over about three to five interference orders at visible wave lengths. The etalon is intended to support very high resolution spectroscopy by providing stable characteristics that are unachievable by electronic control techniques. The etalon is made possible by the commercial availability of angstrom actuators and their associated technology.

The power provided by individual surface micromachined micro-actuators is often insufficient to drive micro-optical components. Therefore, arrays of polycrystalline silicon thermal micro-actuators have been developed. The coupling of the actuators combines their forces to overcome the friction involved with sliders and hinges. This is demonstrated with the fabrication of a scanning micro-mirror and a lateral scanning micro-mirror. The scanning micro-mirror is connected to the substrate using substrate micro-hinges, thus allowing the plate to rotate off of the substrate surface. The micro-mirror is lifted off the substrate and locked into a support mechanism directly connected to the thermal actuator array. Utilizing the actuators, the angle between the micro-mirror and the substrate surface is modulated. The actuator array is capable of moving the mirror plate through a range of 15 degrees. The lateral scanning micro-mirror is connected to the substrate with flowing substrate hinges mounted to the substrate with a rotating pin joint. The hinge support is directly connected to an actuator array by a thin polysilicon tether. The micro-mirror rotates through 5 degrees about the pin joint by driving the actuator array with an electrical current. These mirrors can be used in a variety of micro-optical systems such as optical scanners, corner cube reflectors, and optical couplers.

As with all motors, linear actuator designers strive for increased force from smaller packages with less weight and power consumption. This paper describes a unique linear electromagnetic actuator configuration based on the Lorenz force that provides significant improvement in force/mass and force/power ratios. The magnets and core pieces have simple rectangular shapes reducing fabrication costs. Coils are located in the gap between two magnets. The magnetic return path is back through the second leg of the coil rather than around the outside of the actuator . This reduces the iron required and increases the portion of the magnetic path used for generation of force. The result is a low-cost actuator for linear or limited angular motion with increased efficiency in terms of force/mass ratio, force/power ratio, or the product of these two figures of merit. Designs of varying sizes are presented along with performance analyses and verification test data. An analytical model for dynamic properties as well as various figures of merit are presented.

Operation of sensitive equipment aboard multi-sensor platforms requires active vibration isolation technology. In response to these needs, the active isolation fitting (AIF) was developed to replace passive mechanical end fittings and joints in truss structures. The AIF combines intrastructural and inertial devices to cancel vibration transmission into a vibration-sensitive subsystem. This paper discusses the AIF principles of operation, details its robust performance characteristics and reviews the extensive experimental results that have been accumulated over the past several years. Test results show 20 to 30 dB of broadband isolation for both single AIF tests and six degree-of-freedom isolation systems demonstrated on two major, government- supplied testbeds.

A high-performance active/passive actuator has been developed for a multi-axis isolation and positioning system. This system will be used for pointing and vibration isolation of an optical spacecraft payload. The complementary active and passive elements are designed to provide passive broadband isolation,with active low- frequency isolation and steering. The active element is a linear, voice coil motor, based on Lorentz's force equation, and designed specifically for this application. The passive element consists of a tuned, three-parameter passive isolator. The governing relationships and methodology used in the active/passive actuator design are discussed along with integration issues. Actuator test data are presented and compared to expected performance demonstrating the actuator's predictability.

This paper describes research on a new mechanism to reduce undesirable cross-track motions in precision mechanisms driven by lead screws and micrometer heads. The discussion includes an analysis of the forces between a driving micrometer tip and a driven carriage, the forces which generate the undesirable cross-track motions of the carriage. Test data from a typical mechanism are presented. A novel machine element is proposed to reduce these forces and their effects. The mechanisms was modified to incorporate the element and laboratory test data are presented corroborating the analysis, showing the anticipated reduction in the cross-track motions in the mechanism.