258 research outputs found
Integral Resonant Control for vibration damping and precise tip-positioning of a single-link flexible manipulator
Peer reviewedPostprin
Model-based Control of the Scanning Tunneling Microscope: Enabling New Modes of Imaging, Spectroscopy, and Lithography
The invention of scanning tunneling microscope (STM) dates back to the work
of Binnig and Rohrer in the early 1980s, whose seminal contribution was
rewarded by the 1986 Nobel Prize in Physics for the design of the scanning
tunneling microscope. Forty years later, the STM remains the best existing tool
for studying electronic, chemical, and physical properties of conducting and
semiconducting surfaces with atomic precision. It has opened entirely new
fields of research, enabling scientists to gain invaluable insight into
properties and structure of matter at the atomic scale. Recent breakthroughs in
STM-based automated hydrogen depassivation lithography (HDL) on silicon have
resulted in the STM being considered a viable tool for fabrication of
error-free silicon-based quantum-electronic devices. Despite the STM's unique
ability to interrogate and manipulate matter with atomic precision, it remains
a challenging tool to use. It turns out that many issues can be traced back to
the STM's feedback control system, which has remained essentially unchanged
since its invention about 40 years ago. This article explains the role of
feedback control system of the STM and reviews some of the recent progress made
possible in imaging, spectroscopy, and lithography by making appropriate
changes to the STM's feedback control loop. We believe that the full potential
of the STM is yet to be realized, and the key to new innovations will be the
application of advanced model-based control and estimation techniques to this
system
OlinInfo, September 2009
Newsletter of the Franklin W. Olin Library at Rollins Colleg
Theory of electrostatically induced shape transitions in carbon nanotubes
A mechanically bistable single-walled carbon nanotube can act as a
variable-shaped capacitor with a voltage-controlled transition between
collapsed and inflated states. This external control parameter provides a means
to tune the system so that collapsed and inflated states are degenerate, at
which point the tube's susceptibility to diverse external stimuli--
temperature, voltage, trapped atoms -- diverges following a universal curve,
yielding an exceptionally sensitive sensor or actuator that is characterized by
a vanishing energy scale. For example, the boundary between collapsed and
inflated states can shift hundreds of Angstroms in response to the presence or
absence of a single gas atom in the core of the tube. Several potential
nano-electromechanical devices can be based on this electrically tuned
crossover between near-degenerate collapsed and inflated configurations
Precise tip positioning of a flexible manipulator using resonant control
A single-link flexible manipulator is fabricated to represent a typical flexible robotic arm. This flexible manipulator is modeled as an SIMO system with the motor torque as the input and the hub angle and the tip position as the outputs. The two transfer functions are identified using a frequency-domain system identification method, and the resonant modes are determined. A feedback loop around the hub angle response with a resonant controller is designed to damp the resonant modes. A high-gain integral controller is also implemented to achieve zero steady-state error in the tip position response. Experiments are performed to demonstrate the effectiveness of the proposed control scheme
Two sensor based H-infinity control of a piezoelectric tube scanner
The performance of a feedback-controlled piezoelectric tube scanner is limited by its inherent nonlinear properties such as hysteresis and creep, its mechanical resonance modes and its displacement sensor bandwidth and associated noise properties. Capacitive sensors have emerged as the displacement sensor of choice in piezoelectric tube scanners. Resolution of a capacitive sensor is largely determined by its bandwidth and noise density which is typically in the order of 20 pm/root Hz for a +/-100 micrometer range. Consequently, to achieve sub-nanometer resolution, the sensors bandwidth needs to be made small. Achieving satisfactory tracking performance using a low-bandwidth displacement sensor is a challenging task. To improve the bandwidth, the piezoelectric strain voltage induced in the electrode opposite to the actuating electrode is used as a secondary measurement. A two-sensor-based H-infinity controller is designed and implemented on a prototype piezoelectric tube nanopositioning system. The tube is driven by a charge amplifier to reduce the hysteresis. Experimental results demonstrate a significant increase in the tracking bandwidth due to the use of the additional sensor
Precise tip positioning of a flexible manipulator using resonant control
A single-link flexible manipulator is fabricated to represent a typical flexible robotic arm. This flexible manipulator is modeled as a SIMO system with the motor-torque as the input and the hub angle and the tip position as the outputs. The two transfer functions are identified using a frequency-domain system identification method. A feedback loop around the hub angle response with a resonant controller is designed to damp the resonant modes. A high gain integral controller is also designed to achieve zero steady-state error in the tip position response. Experiments are performed to demonstrate the effectiveness of the proposed control scheme
Negative Imaginary Control Using Hybrid Integrator-Gain Systems: Application to MEMS Nanopositioner
In this paper, we propose a new approach to address the control problem for
negative imaginary (NI) systems by using hybrid integrator-gain systems (HIGS).
We investigate the single HIGS of its original form and its two variations,
including a multi-HIGS and the serial cascade of two HIGS. A single HIGS is
shown to be a nonlinear negative imaginary system, and so is the multi-HIGS and
the cascade of two HIGS. We show that these three types of HIGS can be used as
controllers to asymptotically stabilize linear NI systems. The results of this
paper are then illustrated in a real-world experiment where a 2-DOF
microelectromechanical system nanopositioner is stabilized by a multi-HIGS.Comment: 13 pages, 9 figures. Accepted for publication as a Full Paper in the
IEEE Transactions on Control Systems Technology (TCST
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