Shane C. Woody

Development of a virtual probe tip with an application to high aspect ratio microscale features

Nondestructive measurement of microscale features remains a challenging metrology problem. For example, to assess a high aspect ratio small hole it is currently common to cut a cross section and measure the features of interest using an atomic force microscope, scanning probe microscope, or scanning electron microscope. Typically, these metrology tools may be suitable for surface finish measurement but often lack the capability for dimensional metrology. The aim of this article is to discuss the development of a high aspect-ratio microscale probe for measurement of microscale features. A 700:1 high aspect ratio probe shank is fabricated with a 7μm diameter, and attached at one end to an oscillator. The oscillator produces a standing wave in the oscillating probe shank as opposed to conventional probes that use a microscale sphere on the end of a comparatively rigid shank. As a result of the standing wave formed in steady state vibration, the free end of the shank generates an amplitude of oscillation grea...

Performance of single-crystal Pb(Mg1∕3Nb2∕3)-32%PbTiO3 stacked actuators with application to adaptive structures

This article presents the performance of ultra-high-strain single-crystal piezoelectric stacked actuators using the composition Pb(Mg1∕3Nb2∕3)-32%PbTiO3 (PMN-32%PT)for adaptive structures (in particular for space-based applications). Generally, dimensionally adaptive or smart structures often utilize piezoelectric actuators [in particular lead zirconate titanate (PZT) elements] to provide high-frequency response motion. However, most commercial stacks are limited in range (often <0.1% strain) and the motion is further reduced at low or cryogenic temperatures for satellite-based and many other applications. Comparatively, single-crystal actuators such as the ultra-high-strain PMN-32%PT provide greater than a factor of 4 displacement, factor of 2 strain energy density, and cryogenic displacements are comparable to room-temperature conditions for PZT actuators. Nonetheless, there are some technological and fundamental limitations, such as plate thickness, which is generally greater than 0.5mm, low elastic mo...

Performance comparison and modeling of PZN, PMN, and PZT stacked actuators in a levered flexure mechanism

This article presents a theoretical and experimental assessment of a translation stage design based on a piezoelectric actuator and levering mechanism. This mechanism incorporates stacked piezoelectric actuators of dimensions 5×5×5 mm3 with each stack made from ten plates of 0.5 mm thickness pushing against a symmetric lever design with an ideal amplification of 6.05:1. Three different stacks made from PZN, PMN, and PZT were tested in a nominally similar mechanism to produce displacements of 101, 104, and 33 μm, respectively. Because of their different elastic moduli, the fundamental resonances with each respective device were 670, 729, and 759 Hz. Lagrange analysis of a lumped model of the mechanism is used to estimate the fundamental mode natural frequency of the system while a model for “lost motion” is also presented. This system has been assembled and evaluated experimentally to assess the validity of the models. In general, these models are shown to provide a reasonable estimate of the mechanism performance in terms of lost motion while predicting higher values for the fundamental frequency. The deviations from the model are consistent with the uncertainties associated with rigid body assumptions and the unknown compliances of assembly interfaces and suggest directions for future research in the modeling of such systems.

Compact fiber-coupled three degree-of-freedom displacement interferometry for nanopositioning stage calibration

Heterodyne displacement interferometry is a widely accepted methodology capable of measuring displacements with sub-nanometer resolution in many applications. We present a compact heterodyne system capable of simultaneously measuring Z-displacement along with changes in pitch and yaw using a single measurement beam incident on a plane mirror target. The interferometers measurement detector utilizes differential wavefront sensing to decouple and measure these three degrees of freedom. Reliable rotational measurements typically require calibration; however, two analytical models are discussed which predict the readout of rotational scaling factors.

Development of a compact, fiber-coupled, six degree-of-freedom measurement system for precision linear stage metrology

A compact, fiber-coupled, six degree-of-freedom measurement system which enables fast, accurate calibration, and error mapping of precision linear stages is presented. The novel design has the advantages of simplicity, compactness, and relatively low cost. This proposed sensor can simultaneously measure displacement, two straightness errors, and changes in pitch, yaw, and roll using a single optical beam traveling between the measurement system and a small target. The optical configuration of the system and the working principle for all degrees-of-freedom are presented along with the influence and compensation of crosstalk motions in roll and straightness measurements. Several comparison experiments are conducted to investigate the feasibility and performance of the proposed system in each degree-of-freedom independently. Comparison experiments to a commercial interferometer demonstrate error standard deviations of 0.33 μm in straightness, 0.14 μrad in pitch, 0.44 μradin yaw, and 45.8 μrad in roll.

Standing wave probes for microassembly

A single standing wave sensor was investigated and experiments demonstrated release capability of glass microscale objects. It is shown that this micrometer scale fiber may be employed as miniaturized tweezers able to pick up specimens and routinely release them when the standing wave is energized. Furthermore, it is demonstrated that the standing wave probe has sensing capability. Both phase and magnitude indicate when the specimen releases, and also provide postrelease information such as mass of sphere and its rotation about its own axis or, surprisingly, about the probe fiber. The current experiments investigated only the release forces acting normal to the sphere/fiber contact interface. Some work was performed by changing the virtual tip from a normally applied force to a tangential applied force. In this condition, the specimen was observed to release differently.

Steering mirror design and dynamic controls for a dual- actuation platform using high-strain actuators

†This manuscript discusses several novel design approaches to enhance dynamic precision of electro-mechanical positioning systems. In particular, a detailed development program for fast steering mirrors is addressed and various unique metrology and motion control strategies are presented. In general, material developments are continually advancing lightweight mirror structures such as the implementation of silicon carbide (SIC) materials to provide higher mechanical bandwidth response. Additionally, electro-mechanical actuators must continue to advance in conjunction with the mirror technologies in order meet stringent performance specifications (i.e. power requirements, weight, and precision dynamic response). The technologies developed through this development effort include; ultra-high strain piezoelectric actuators for enhanced motion control performance, a novel mechanism design employing a dual actuation platform to provide high bandwidth response and long-range, high-precision capability, innovative controller methodologies for the series coarse/fine system and active attenuation of dynamic reaction forces, integration of energy absorbing foams to enhance dynamic control, and real-time precision digital controllers.

VORTEX MACHINING: LOCALIZED SURFACE MODIFICATION USING AN OSCILLATING FIBER PROBE

This paper demonstrates for the first time a method for surface modification of a substrate material based on the generation of localized vortices of abrasive slurry using slender oscillating fibers. In experiments presented in this paper, the abrasive slurry is a water based suspension of 1 µm alumina particles. This is pumped onto, and flows across, the specimen surface. A fiber (typically 7 µm in diameter and between 3.5 to 5 mm long) is immersed into this flowing slurry and oscillated at frequencies around 30–40 kHz to produce a small rotational flow (vortex) that results in the locally accelerated particles. Using such a system, it has been possible, over machining times of 6–24 hours, to produced localized depressions in the surface of a silicon substrate with typical depths of around 60–700 nm and widths of around 10–300 µm. Based on these initial studies the material removal rate is estimated to be approximately 40 nm per hour. Using white light interferometry and stylus profilometry the surface deviations (roughness) of these features have a root mean square variation in the region 1–2 nm, which is comparable to that of the surface remote from the machined feature.