97 research outputs found
Modeling and Control of Piezoactive Micro and Nano Systems
Piezoelectrically-driven (piezoactive) systems such as nanopositioning platforms, scanning probe microscopes, and nanomechanical cantilever probes are advantageous devices enabling molecular-level imaging, manipulation, and characterization in disciplines ranging from materials science to physics and biology. Such emerging applications require precise modeling, control and manipulation of objects, components and subsystems ranging in sizes from few nanometers to micrometers. This dissertation presents a comprehensive modeling and control framework for piezoactive micro and nano systems utilized in various applications. The development of a precise memory-based hysteresis model for feedforward tracking as well as a Lyapunov-based robust-adaptive controller for feedback tracking control of nanopositioning stages are presented first. Although hysteresis is the most degrading factor in feedforward control, it can be effectively compensated through a robust feedback control design. Moreover, an adaptive controller can enhance the performance of closed-loop system that suffers from parametric uncertainties at high-frequency operations. Comparisons with the widely-used PID controller demonstrate the effectiveness of the proposed controller in tracking of high-frequency trajectories. The proposed controller is then implemented in a laser-free Atomic Force Microscopy (AFM) setup for high-speed and low-cost imaging of surfaces with micrometer and nanometer scale variations. It is demonstrated that the developed AFM is able to produce high-quality images at scanning frequencies up to 30 Hz, where a PID controller is unable to present acceptable results. To improve the control performance of piezoactive nanopositioning stages in tracking of time-varying trajectories with frequent stepped discontinuities, which is a common problem in SPM systems, a supervisory switching controller is designed and integrated with the proposed robust adaptive controller. The controller switches between two control modes, one mode tuned for stepped trajectory tracking and the other one tuned for continuous trajectory tracking. Switching conditions and compatibility conditions of the control inputs in switching instances are derived and analyzed. Experimental implementation of the proposed switching controller indicates significant improvements of control performance in tracking of time-varying discontinuous trajectories for which single-mode controllers yield undesirable results. Distributed-parameters modeling and control of rod-type solid-state actuators are then studied to enable accurate tracking control of piezoactive positioning systems in a wide frequency range including several resonant frequencies of system. Using the extended Hamilton\u27s principle, system partial differential equation of motion and its boundary conditions are derived. Standard vibration analysis techniques are utilized to formulate the truncated finite-mode state-space representation of the system. A new state-space controller is then proposed for asymptotic output tracking control of system. Integration of an optimal state-observer and a Lyapunov-based robust controller are presented and discussed to improve the practicability of the proposed framework. Simulation results demonstrate that distributed-parameters modeling and control is inevitable if ultra-high bandwidth tracking is desired. The last part of the dissertation, discusses new developments in modeling and system identification of piezoelectrically-driven Active Probes as advantageous nanomechanical cantilevers in various applications including tapping mode AFM and biomass sensors. Due to the discontinuous cross-section of Active Probes, a general framework is developed and presented for multiple-mode vibration analysis of system. Application in the precise pico-gram scale mass detection is then presented using frequency-shift method. This approach can benefit the characterization of DNA solutions or other biological species for medical applications
Fidelity study in surface measurements in nanometre metrology
The object of this Ph.D work is to evaluate fidelity in surface measurements in nanometric
metrology for both contact and non-contact methods, namely stylus instruments and scanning
tunnelling microscopy. Fidelity is defined, in this thesis, as a measure to which an instrument
system reproduces the surface features and thus the parameters of interest. High fidelity
measurement has two meanings; less distortion in the measured result and less disturbance to the
surface being measured. Interaction at the interface between the probe and the surface is the source
of failure to achieve high fidelity.
No instrument measures surface topography alone: all instruments measure a convolution of
topography and the geometrical and physical interaction of the measured probe and the surface. In
the case of a mechanical stylus, factors extraneous to the topography include (a) the shape and size
of the stylus, (b) mechanical properties of the stylus and the specimen such as elastic moduli and
hardness, (c) frictional force of the sliding pair. and (d) dynamic interaction forces during the
sliding. For the scanning tunnelling microscope, factors which affect measurement in addition to
topography include the geometry of the tip, the electronic properties of the surface and mechanical
deformation due to electrostatic forces and contamination.
'These factors have been investigated in great detail, particularly for the stylus instruments. A
specially designed electro-magnetic force actuator has been developed to give a better control on
loading force during the experiments. Tracking force effects were evaluated by profiling statistical
parameters, and scanning electron microscopy. Friction between a stylus and specimen has been
measured for different loading force, sliding speed, material and surface finish. Improvement on
dynamic characteristics of a stylus system has been achieved by active damping control. An optimal
damping ratio for stylus instruments is found to be within 0.5-0.7. Through the study, the tracking
force and traversing speed are found to be the crucial factors to be tackled so that high fidelity
measurement can be obtained. A similar investigation has been also made on two home-built
scanning tunnelling microscopes to explore the potential applications of STM on nanometric
metrology
Unified Hysteresis and Creep Compensation in AFM Tip Positioning with an Extended PI Model
The nonlinearities such as hysteresis and creep are the major factors inherent in PZT actuation that affect the tip positioning precision and manipulation performance of the AFM system. In this study, an extended PI model is generalized by introducing a creep model to the basic hysteretic operator of the PI model at the inflexion point of the hysteresis loop. Unified compensation for hysteresis and creep can be implemented with the extended PI model. Experiment results demonstrate the validity and effectiveness of the extended PI model and it is implied that the inflexion creep compensation not only improves the tip positioning precision at the inflexion points on the hysteresis loops, but also the localization effectiveness during the whole process of PZT actuation
Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics
This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact
Nonlinear and Rate-Dependent Hysteresis Electro Mechanical Responses of Ferro Electric Materials
This study presents nonlinear and time-dependent analyses of ferroelectric materials and structures. Phenomenological constitutive models are considered for simulating macroscopic responses of materials undergoing various histories of electromechanical inputs. When the electric field inputs are less than the coercive limit (minor loop simulations), there will be no polarization switching and a nonlinear time-dependent electro-mechanical constitutive model based on a single integral form is considered for the piezoelectric materials undergoing small deformation gradients and large electric field. The nonlinearity is accounted for by incorporating higher order terms of the electric field and the effect of loading history is incorporated through the time integrand. When the electric field inputs are above the coercive limit (major loop simulations), the electro-mechanical coupling constants are expressed as functions of a polarization state and it is assumed that in absence of the polarization, the material does not exhibit electro-mechanical coupling response. The polarization state consists of time-dependent reversible and irreversible parts, where the irreversible part is incorporated to account for polarization switching responses. This constitutive model is implemented at each material (Gaussian) point within continuum FEs. A quasi-linear viscoelastic (QLV) model is adopted in order to incorporate the time-dependent effect on the nonlinear electro-mechanical response of piezoelectric ceramics. The recursive integration technique is used to solve for the time-dependent constitutive model at each Gaussian point. Finite element method is then used for analyzing behaviors of several piezoelectric structures and structural components under various boundary conditions. Parametric studies are also conducted to examine the effect of loading rates and coupled electro-mechanical boundary conditions on the overall performance of smart structures. The developed FE model is also used for predicting the overall responses Active Fiber Composite (AFC). A unit cell of AFC, where different responses of the constituents (fiber, matrix, electrode finger, kapton layer) are incorporated, is considered and time dependent and nonlinear responses of AFC are determined. The overall responses of AFCs at different frequencies and electric field amplitude determined from the FE are compared with experiments. Reasonably good predictions are observed. Finally, FE analyses are performed to simulate shape changing in smart truss structures. An electro-active truss FE undergoing large deformations is formulated. Each truss member is modeled as an active element with nonlinear time-dependent electromechanical constitutive model. The desired shape is induced in the overall structure by applying electric field to each truss member. The truss FE model can handle both material and also geometric nonlinearities
Control strategies and motion planning for nanopositioning applications with multi-axis magnetic-levitation instruments
This dissertation is the first attempt to demonstrate the use of magnetic-levitation
(maglev) positioners for commercial applications requiring nanopositioning. The key objectives
of this research were to devise the control strategies and motion planning to overcome the
inherent technical challenges of the maglev systems, and test them on the developed maglev
systems to demonstrate their capabilities as the next-generation nanopositioners. Two maglev
positioners based on novel actuation schemes and capable of generating all the six-axis motions
with a single levitated platen were used in this research. These light-weight single-moving
platens have very simple and compact structures, which give them an edge over most of the
prevailing nanopositioning technologies and allow them to be used as a cluster tool for a variety
of applications. The six-axis motion is generated using minimum number of actuators and
sensors. The two positioners operate with a repeatable position resolution of better than 3 nm at
the control bandwidth of 110 Hz. In particular, the Y-stage has extended travel range of 5 mm ÃÂ 5
mm. They can carry a payload of as much as 0.3 kg and retain the regulated position under
abruptly and continuously varying load conditions. This research comprised analytical design and development, followed by experimental
verification and validation. Preliminary analysis and testing included open-loop stabilization and
rigorous set-point change and load-change testing to demonstrate the precision-positioning and
load-carrying capabilities of the maglev positioners. Decentralized single-input-single-output
(SISO) proportional-integral-derivative (PID) control was designed for this analysis. The effect
of actuator nonlinearities were reduced through actuator characterization and nonlinear feedback
linearization to allow consistent performance over the large travel range. Closed-loop system
identification and order-reduction algorithm were developed in order to analyze and model the
plant behavior accurately, and to reduce the effect of unmodeled plant dynamics and inaccuracies
in the assembly. Coupling among the axes and subsequent undesired motions and crosstalk of
disturbances was reduced by employing multivariable optimal linear-quadratic regulator (LQR).
Finally, application-specific nanoscale path planning strategies and multiscale control were
devised to meet the specified conflicting time-domain performance specifications. All the
developed methodologies and algorithms were implemented, individually as well as collectively,
for experimental verification. Some of these applications included nanoscale lithography,
patterning, fabrication, manipulation, and scanning. With the developed control strategies and
motion planning techniques, the two maglev positioners are ready to be used for the targeted
applications
Contemporary Robotics
This book book is a collection of 18 chapters written by internationally recognized experts and well-known professionals of the field. Chapters contribute to diverse facets of contemporary robotics and autonomous systems. The volume is organized in four thematic parts according to the main subjects, regarding the recent advances in the contemporary robotics. The first thematic topics of the book are devoted to the theoretical issues. This includes development of algorithms for automatic trajectory generation using redudancy resolution scheme, intelligent algorithms for robotic grasping, modelling approach for reactive mode handling of flexible manufacturing and design of an advanced controller for robot manipulators. The second part of the book deals with different aspects of robot calibration and sensing. This includes a geometric and treshold calibration of a multiple robotic line-vision system, robot-based inline 2D/3D quality monitoring using picture-giving and laser triangulation, and a study on prospective polymer composite materials for flexible tactile sensors. The third part addresses issues of mobile robots and multi-agent systems, including SLAM of mobile robots based on fusion of odometry and visual data, configuration of a localization system by a team of mobile robots, development of generic real-time motion controller for differential mobile robots, control of fuel cells of mobile robots, modelling of omni-directional wheeled-based robots, building of hunter- hybrid tracking environment, as well as design of a cooperative control in distributed population-based multi-agent approach. The fourth part presents recent approaches and results in humanoid and bioinspirative robotics. It deals with design of adaptive control of anthropomorphic biped gait, building of dynamic-based simulation for humanoid robot walking, building controller for perceptual motor control dynamics of humans and biomimetic approach to control mechatronic structure using smart materials
Superconductors at the Nanoscale
By covering theory, design, and fabrication of nanostructured superconducting materials, this monograph is an invaluable resource for research and development. Examples are energy saving solutions, healthcare, and communication technologies. Key ingredients are nanopatterned materials which help to improve the superconducting critical parameters and performance of superconducting devices, and lead to novel functionalities. Contents Tutorial on nanostructured superconductors Imaging vortices in superconductors: from the atomic scale to macroscopic distances Probing vortex dynamics on a single vortex level by scanning ac-susceptibility microscopy STM studies of vortex cores in strongly confined nanoscale superconductors Type-1.5 superconductivity Direct visualization of vortex patterns in superconductors with competing vortex-vortex interactions Vortex dynamics in nanofabricated chemical solution deposition high-temperature superconducting films Artificial pinning sites and their applications Vortices at microwave frequencies Physics and operation of superconducting single-photon devices Josephson and charging effect in mesoscopic superconducting devices NanoSQUIDs: Basics & recent advances intrinsic Josephson junction stacks as emitters of terahertz radiation| Interference phenomena in superconductor-ferromagnet hybrids Spin-orbit interactions, spin currents, and magnetization dynamics in superconductor/ferromagnet hybrids Superconductor/ferromagnet hybrid
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