Inversion-based feedforward-feedback control: theory and implementation to high-speed atomic force microscope imaging

In this dissertation, a suite of inversion-based feedforward-feedback control techniques are developed and applied to achieve high speed AFM imaging. In the last decade, great efforts have been made in developing the inversion-based feedforward control as an effective approach for precision output tracking. Such efforts are facilitated by the fruitful results obtained in the stable-inversion theory, including, mainly, the bounded inverse of nonminimum-phase systems, the preview-based inversion method that quantified the effect of the future desired trajectory on the inverse input, the consideration of the model uncertainties in the system inverse, and the integration of inversion with feedback and iterative control. However, challenges still exist in those inversion-based approaches. For example, although it has been shown that the inversion-based iterative control (IIC) technique can effectively compensate for the vibrational dynamics during the output tracking in the repetitive applications, however, compensating for both the hysteresis effect and the dynamics effect simultaneously using the IIC approach has not been established yet. Moreover, the current design of the inversion-based feedforward feedback two-degree-of-freedom (2DOF) controller is ad-hoc, and the minimization of the model uncertainty effects on the feedforward control has not been addressed. Furthermore, although it is possible to combine system inversion with both iterative learning and feedback control in the so-called current cycle feedback iterative learning control (CCF-ILC) approach, the current controller design is limited to be casual and the use of such CCF-ILC approach for rejecting slowly varying periodic disturbance has not been explored. These challenges, as magnified in applications such as high-speed AFM imaging, motivate the research of this dissertation. Particularly, it is shown that the IIC approach can effectively compensate for both the hysteresis and vibrational dynamics effects of smart actuators. The convergence of the IIC algorithm is investigated by capturing the input-output behavior of piezo actuators with a cascade model consisting of a rate-independent hysteresis at the input followed by the dynamics part of the system. The size of the hysteresis and the vibrational dynamics variations that can be compensated for (by using the IIC method) has been quantified. Secondly, a novel robust-inversion has been developed for single-input-single-output (SISO) LTI systems, which minimized the dynamics uncertainty effect and obtained a guaranteed tracking performance for bounded dynamics uncertainties. Based on the robust-inversion approach, a systematic design of inversion-based two-degree-of-freedom (2DOF)-control was developed. Finally, the robust inversion- based current cycle feedback iterative learning control approach was developed for the rejection of slow varying periodic disturbances. The proposed CCF-ILC controller design utilizes the recently-developed robust-inversion technique to minimize the model uncertainty effect on the feedforward control, as well as to remove the causality constraints in other CCFILC approaches. It is shown that the iterative law converges, and attains a bounded tracking error upon noise and disturbances. In this dissertation, these techniques have been successfully implemented to achieve high-speed AFM imaging of large-size samples. Specifically, it is shown that precision positioning of the probe in the AFM lateral (x-y) scanning can be successfully achieved by using the inversion-based iterative-control (IIC) techniques and robust-inversion based 2DOF control design approach. The AFM imaging speed as well as the sample estimation can be substantially improved by using the CCF-ILC approach for the precision positioning of the probe in the vertical direction

Micromanipulation-force feedback pushing

In micromanipulation applications, it is often desirable to position and orient polygonal micro-objects lying on a planar surface. Pushing micro-objects using point contact provides more flexibility and less complexity compared to pick and place operation. Due to the fact that in micro-world surface forces are much more dominant than inertial forces and these forces are distributed unevenly, pushing through the center of mass of the micro-object will not yield a pure translational motion. In order to translate a micro-object, the line of pushing should pass through the center of friction. Moreover, due to unexpected nature of the frictional forces between the micro-object and substrate, the maximum force applied to the micro-object needs to be limited to prevent any damage either to the probe or micro-object. In this dissertation, a semi-autonomous manipulation scheme is proposed to push microobjects with human assistance using a custom built tele-micromanipulation setup to achieve pure translational motion. The pushing operation can be divided into two concurrent processes: In one process human operator who acts as an impedance controller to switch between force-position controllers and alters the velocity of the pusher while in contact with the micro-object through scaled bilateral teleoperation with force feedback. In the other process, the desired line of pushing for the micro-object is determined continuously so that it always passes through the varying center of friction. Visual feedback procedures are adopted to align the resultant velocity vector at the contact point to pass through the center of friction in order to achieve pure translational motion of the micro-object. Experimental results are demonstrated to prove the effectiveness of the proposed controller along with nanometer scale position control, nano-Newton range force sensing, scaled bilateral teleoperation with force feedback

Advanced atomic force microscopy for low-dimenxional systems

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 21-04-2017Esta tesis tiene embargado el acceso al texto completo hasta el 21-10-201

Modeling and Control of Piezoelectric Actuators

Piezoelectric actuators (PEAs) utilize the inverse piezoelectric effect to generate fine displacement with a resolution down to sub-nanometers and as such, they have been widely used in various micro- and nanopositioning applications. However, the modeling and control of PEAs have proven to be challenging tasks. The main difficulties lie in the existence of various nonlinear or difficult-to-model effects in PEAs, such as hysteresis, creep, and distributive vibration dynamics. Such effects can seriously degrade the PEA tracking control performances or even lead to instability. This raises a great need to model and control PEAs for improved performance. This research is aimed at developing novel models for PEAs and on this basis, developing model-based control schemes for the PEA tracking control taking into account the aforementioned nonlinear effects. In the first part of this research, a model of a PEA for the effects of hysteresis, creep, and vibration dynamics was developed. Notably, the widely-used Preisach hysteresis model cannot represent the one-sided hysteresis of PEAs. To overcome this shortcoming, a rate-independent hysteresis model based on a novel hysteresis operator modified from the Preisach hysteresis operator was developed, which was then integrated with the models of creep and vibration dynamics to form a comprehensive model for PEAs. For its validation, experiments were carried out on a commercially-available PEA and the results obtained agreed with those from model simulations. By taking into account the linear dynamics and hysteretic behavior of the PEA as well as the presliding friction between the moveable platform and the end-effector, a model of the piezoelectric-driven stick-slip (PDSS) actuator was also developed in the first part of the research. The effectiveness of the developed model was illustrated by the experiments on the PDSS actuator prototyped in the author's lab. In the second part of the research, control schemes were developed based on the aforementioned PEA models for tracking control of PEAs. Firstly, a novel PID-based sliding mode (PIDSM) controller was developed. The rational behind the use of a sliding mode (SM) control is that the SM control can effectively suppress the effects of matched uncertainties, while the PEA hysteresis, creep, and external load can be represented by a lumped matched uncertainty based on the developed model. To solve the chattering and steady-state problems, associated with the ideal SM control and the SM control with boundary layer (SMCBL), the novel PIDSM control developed in the present study replaces the switching control term in the ideal SM control schemes with a PID regulator. Experiments were carried out on a commercially-available PEA and the results obtained illustrate the effectiveness of the PIDSM controller, and its superiorities over other schemes of PID control, ideal SM control, and the SMCBL in terms of steady state error elimination, chattering suppression, and tracking error suppression. Secondly, a PIDSM observer was also developed based on the model of PEAs to provide the PIDSM controller with state estimates of the PEA. And the PIDSM controller and the PIDSM observer were combined to form an integrated control scheme (PIDSM observer-controller or PIDSMOC) for PEAs. The effectiveness of the PIDSM observer and the PIDSMOC were also validated experimentally. The superiority of the PIDSMOC over the PIDSM controller with σ-β filter control scheme was also analyzed and demonstrated experimentally. The significance of this research lies in the development of novel models for PEAs and PDSS actuators, which can be of great help in the design and control of such actuators. Also, the development of the PIDSM controller, the PIDSM observer, and their integrated form, i.e., PIDSMOC, enables the improved performance of tracking control of PEAs with the presence of various nonlinear or difficult-to-model effects

Nanofracture mechanics : scanning force microscopy for the investigation of adhesion and corrosion at solid-solid interfaces

Fracture processes are crucially determined by structural features on the molecular/nanometer scale (cavities, occlusions, cracks, etc.) as well as on the atomic scale (e.g. interstitial, substitutional and vacancy defects). In this work, fracture mechanics experiments were performed with fabricated nanostructures, so-called nanopillars. Furthermore, material interfaces had been introduced into these nanopillars as weak links in order to act as well-defined breaking points. By exerting calibrated forces onto these nanostructures, the threshold force for fracture incidents can be determined and hence the adhesion strengths of the interfaces involved can be studied. All such experiments were performed using a Scanning Force Microscope (SFM). Here, force and topography investigations, using a cantilever tip as a tool, reveal information about the fracture behavior of a particular interface as well as information regarding the mechanical strength. The SFM was used in the tapping (intermitted) or in the contact mode to fracture single nanopillars or an ensemble of them. For statistical examinations, an area of nanopillars was scanned with increased normal forces. Therefore, interfaces manufactured for microelectronic applications or micro-electro-mechanical systems (MEMS) can be studied by low forces applied to nanopillars exhibiting realistic interface dimensions. Due to the small dimensions of the manufactured nanopillars, slow processes, such as the weakening of the interface by fatigue (also including heat cycling in devices) or by physico-chemical processes (e.g. by tribochemical processes or corrosion which may occur in a liquid environment) can be monitored on considerably shorter time scales and under easier to control conditions than with macroscopic specimens. Additionally, such fracture experiments performed with nanopillars designed to mimic macroscopic fracture experiments, in medium (characteristic cross section ~cm2) to large scale (> ~m2) engineering, are often less cost intensive compared to large, real-world samples in time consuming (~ many load/unload heat/cool cycles, extended exposure to ambient or corrosive fluids etc.) conventional fracture experiments. Another important application comprises the study of a soft metal/polyimide interface, which is important for flexible microelectronic devices and flexible interconnect circuitry. Here, interface problems, specifically failure incidents after exposure to temperature cycling and/or mechanical load/unload cycles, have been associated with the occurrence of interfacial contamination, e.g. with residual water originating from the polyimide curing process. Hence, in a well-chosen model experiment under ultra-high vacuum (UHV) conditions, a precise amount of water was deposited on an in-situ produced polyimide sample which then was coated by a metal. Afterwards, the nanopillar structures were generated by Focused Ion Beam (FIB) milling. This work established a radically new approach to perform fracture mechanics experiments down to the few nanometers, which provides a route towards a better understanding of fracture processes down to an atomic/molecular scale

Bilaterally controlled micromanipulation by pushing in 1-D with nano-Newton scale force feedback

In this thesis the focus is on mechanical micromanipulation which means manipulation of micro objects using mechanical tools. Pushing is a type of motion of the micro parts and pushing ability on micro scale is inevitable for many applications such as micro assembly of systems or characterization of tribological properties of micro scale things. The aim of the work in this thesis was to obtain an improved performance in 1-D pushing of micrometer scaled objects in the sense of giving more control to human operator where it allows human intervention via bilateral control with force feedback in nano-Newton scale. For this purpose a system which can practice 1-D pushing of micrometer scaled objects by human operator is built. A bilateral architecture which is composed of master and slave sides has been used in the system. The micrometer scaled object is pushed by the piezoactuator which constitutes the slave side and the master side is a DC motor where the shaft is turned by the human operator via a rectangular prism rod. This system can be considered as an improved system comparing with the ones in literature, since it has a number of different advantages together. One of them is the ability to calibrate the relation between the movement of the slave system and the cycle that is made by the DC motor shaft which is controlled by the operator. This gives the availability to decide how sensitive will the slave side motion be to the master side motion. Moreover, thanks to the nano-Newton scale force sensing ability of the system user has the chance to use this as a force feedback within the bilateral structure, where by the way the operator will understand when the piezoresistive cantilever beam touched the object that is going to be pushed by it. The operator also understands when there is an obstacle or opposite force that keeps the object from continuing on its track

Characterization of Bending Magnetostriction in Iron-Gallium Alloys for Nanowire Sensor Applications

This research explores the possibility of using electrochemically deposited nanowires of magnetostrictive iron-gallium (Galfenol) to mimic the sensing capabilities of biological cilia. Sensor design calls for incorporating Galfenol nanowires cantilevered from a membrane and attached to a conventional magnetic field sensor. As the wires deflect in response to acoustic, airflow, or tactile excitation, the resultant bending stresses induce changes in magnetization that due to the scale of the nanowires offer the potential for excellent spatial resolution and frequency bandwidth. In order to determine the suitability for using Galfenol nanowires in this role, the first task was experimentally characterizing magnetostrictive transduction in bending beam structures, as this means of operation has been unattainable in previous materials research due to low tensile strengths in conventional alloys such as Terfenol-D. Results show that there is an appreciable sensing response from cantilevered Galfenol beams and that this phenomenon can be accurately modeled with an energy based formulation. For progressing experiments to the nanowire scale, a nanomanipulation instrument was designed and constructed that interfaces within a scanning electron microscope and allows for real time characterization of individual wires with diameters near 100 nm. The results of mechanical tensile testing and dynamic resonance identification reveal that the Galfenol nanowires behave similarly to the bulk material with the exception of a large increase in ultimate tensile strength. The magnetic domain structure of the nanowires was theoretically predicted and verified with magnetic force microscopy. An experimental methodology was developed to observe the coupling between bending stress and magnetization that is critical for accurate sensing, and the key results indicate that specific structural modifications need to be made to reduce the anisotropy in the nanowires in order to improve the transduction capabilities. A solution to this problem is presented and final experiments are performed

Cutting Edge Nanotechnology

The main purpose of this book is to describe important issues in various types of devices ranging from conventional transistors (opening chapters of the book) to molecular electronic devices whose fabrication and operation is discussed in the last few chapters of the book. As such, this book can serve as a guide for identifications of important areas of research in micro, nano and molecular electronics. We deeply acknowledge valuable contributions that each of the authors made in writing these excellent chapters