[Show abstract][Hide abstract] ABSTRACT: A new hybrid tracking controller for neuromuscular electrical stimulation is
proposed. The control scheme uses sampled measurements and is designed by
utilizing a numerical prediction of the state variables. The tracking error of
the closed-loop system converges exponentially to zero and robustness to
perturbations of the sampling schedule is exhibited. One of the novelties of
our approach is the ability to satisfy a state constraint imposed by the
International Journal of Robust and Nonlinear Control 10/2013; · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fluid-film bearings can suffer from flow-induced instabilities known as ‘whirl’ and ‘whip,’ especially when supporting lightly-loaded shafts. This phenomenon can lead to large rotor (self-excited) vibrations, which eventually result in rotor-bearing failure. In this paper, we introduce a new active hydrodynamic bearing to mitigate such vibrations in lightly loaded rotating machines. The system contains a rotating bushing, actuated by a motor, that serves as the control input. This input is used to control the mean flow velocity in the bearing and thereby the journal vibration. A simple feedback control law is proposed for the bushing velocity, and numerical simulations are presented to evaluate the active bearing.
Journal of Vibration and Control 10/2013; 19(14):2211-2222. · 4.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Acetyl-CoA carboxylase catalyses the first committed step in fatty acid synthesis in all organisms. The chemistry is accomplished in two half-reactions: activation of biotin via carboxylation by biotin carboxylase, followed by the carboxyltransferase-catalysed transfer of the carboxyl moiety from carboxybiotin to acetyl-CoA to generate malonyl-CoA. The Escherichia coli form of the carboxyltransferase subunit was recently found to regulate its own activity and expression by binding its own mRNA. By binding acetyl-CoA or the mRNA encoding its own subunits, carboxyltransferase is able to sense the metabolic state of the cell and attenuate its own translation and enzymatic activity using a negative feedback mechanism. Here, the network of these interactions is modelled mathematically with a set of non-linear differential equations. Numerical simulations of the model show that it qualitatively and quantitatively agrees with the experimental results for both inhibition of carboxyltransferase by mRNA and attenuation of translation. The modelling of the autoregulatory function of carboxyltransferase confirms that it is more than isolated interactions, but functions as a single dynamic system.
IET Systems Biology 05/2011; 5(3):220-8. · 1.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The enzyme biotin carboxylase (BC) uses adenosine triphosphate (ATP) to carboxylate biotin and is involved in fatty acid synthesis. Structural evidence suggests that the B domain of BC undergoes a large hinge motion of ∼45° when binding and releasing substrates. Escherichia coli BC can function as a natural homodimer and as a mutant monomer. Using molecular dynamics simulations, we evaluate the free energy profile along a closure angle of the B domain of E. coli BC for three cases: a monomer without bound Mg(2)ATP, a monomer with bound Mg(2)ATP, and a homodimer with bound Mg(2)ATP in one subunit. The simulation results show that a closed state is the most probable for the monomer with or without bound Mg(2)ATP. For the dimer with Mg(2)ATP in one of its subunits, communication between the two subunits was observed. Specifically, in the dimer, the opening of the subunit without Mg(2)ATP caused the other subunit to open, and hysteresis was observed upon reclosing it. The most stable state of the dimer is one in which the B domain of both subunits is closed; however, the open state for the B domain without Mg(2)ATP is only approximately 2k(B)T higher in free energy than the closed state. A simple diffusion model indicates that the mean times for opening and closing of the B domain in the monomer with and without Mg(2)ATP are much smaller than the overall reaction time, which is on the order of seconds.
Proteins Structure Function and Bioinformatics 02/2011; 79(2):622-32. · 3.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study a recently-proposed nonlinear model for human heart rate response that describes the central and peripheral local responses during and after treadmill exercise. The treadmill speed is the control input, and the control objective is to make the heart rate track a prescribed reference trajectory. Using a strict Lyapunov function analysis, we design new state and output feedback tracking controllers that render the error dynamics globally exponentially stable to the origin. This allows us to show that the feedback stabilized error dynamics enjoys input-to-state stable performance under actuator errors. This robustness condition quantifies the effects of deviations of the treadmill speed from the controller values. We illustrate our control design through simulations.
Decision and Control (CDC), 2010 49th IEEE Conference on; 01/2011
[Show abstract][Hide abstract] ABSTRACT: We study adaptive tracking problems for nonlinear systems with unknown control gains. We construct controllers that yield uniform global asymptotic stability for the error dynamics, and hence tracking and parameter estimation for the original systems. Our result is based on a new explicit, global, strict Lyapunov function construction. We illustrate our work using a brushless DC motor turning a mechanical load. We quantify the effects of time-varying uncertainties on the motor electric parameters.
Fuel and Energy Abstracts 01/2011; 74(4):1132-1145.
[Show abstract][Hide abstract] ABSTRACT: We study adaptive tracking control problems for nonlinear systems in feedback form with multiple inputs and unknown high-frequency control gains. We design controllers that yield uniform global asymptotic stability for the error dynamics, which implies parameter estimation and tracking for the original systems. Our proof relies on a new global strict Lyapunov function construction. We apply our result to a brushless DC motor turning a mechanical load. We use integral input-to-state stability to quantify the effects of time-varying uncertainties on the motor electric parameters.
[Show abstract][Hide abstract] ABSTRACT: Biotin carboxylase (BC) is a homodimer which catalyzes biotin
carboxylation. A reaction is thought to occur in one monomer at a time
(half-sites reactivity). BC can also function as a monomer. Evidence has
shown that the B domain moves with hinge motion of 45 between an
unliganded form and one with bound ATP, suggesting that some of the
energy from ATP hydrolysis might be harnessed to do useful work. The
free energy along a closure angle for the B domain was calculated using
MD simulations for a monomer and dimer with and without one bound ATP.
We found that the monomer favors a closed state with or without ATP with
mean times for opening much smaller than the reaction time, and the most
stable structure for the dimer without ATP was with both monomers open.
For the dimer with ATP, opening the B domain without ATP caused the
other B domain to open, but hysteresis was observed when closing it,
preventing an accurate calculation. The data suggest that the most
stable state has both sides closed, supporting the idea of half-sites
[Show abstract][Hide abstract] ABSTRACT: This article introduces a new type of active fluid film bearing and its feedback control. In particular, the active adjustment of the angular velocity of the pads of a tilting-pad bearing in response to changes in the operating conditions of the rotating machine is proposed. This is motivated by the observation that there is more control authority in the pad tilting motion than in its radial translation. To this end, a dynamic model for the bearing system is first developed, inclusive of the nonlinear hydrodynamic force for the infinitely short bearing case. A model-based controller is then constructed, based on measurements of the journal position and velocity and pad tilting angles, to ensure that the journal is asymptotically regulated to the bearing center. Numerical simulations illustrate the performance of the active bearing under the proposed control in comparison with the bearing's standard passive mode of operation.
[Show abstract][Hide abstract] ABSTRACT: Biotin carboxylase is a homodimer that utilizes ATP to carboxylate biotin. Studies of the enzyme using X-ray crystallography revealed a prominent conformational change upon binding ATP. To determine the importance of this closing motion, the potential of mean force with the closure angle as a reaction coordinate was calculated using molecular dynamics simulations and umbrella sampling for a monomer of Escherichia coli biotin carboxylase in water with restraints to simulate attachment to a surface. The result suggests that the most stable state for the enzyme is a closed state different from both the ATP-bound and open state X-ray crystallography structures. There is also a significant motion of a region near the dimer interface not predicted by considering only open and closed configurations, which may have implications for the dynamics and activity of the dimer.
The Journal of Physical Chemistry B 08/2009; 113(30):10097-103. · 3.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We give a new explicit, global, strict Lyapunov function construction for the error dynamics for adaptive tracking control problems, under an appropriate persistency of excitation condition. We then allow time-varying uncertainty in the unknown parameters. In this case, we construct input-to-state stable Lyapunov functions under suitable bounds on the uncertainty, provided the regressor also satisfies an affine growth condition. This lets us quantify the effects of uncertainties on both the tracking and the parameter estimation. We illustrate our results using Rossler systems.
IEEE Transactions on Automatic Control 06/2009; · 2.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This note presents a new method for identifying the unknown unbalance parameters of a rotor. The active feedback method asymptotically learns the unbalance-induced disturbance forces. From the resulting disturbance estimates, we show how to identify the unbalance parameters. Simulation results illustrate the proposed identification method.
Journal of Vibration and Control 01/2009; 15(9):1365-1374. · 4.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We announce a new class of tracking controllers, applicable to both electrostatic and electromagnetic microelectromechanical (MEM) relays, that yield arbitrarily fast local exponential convergence of the tracking error to zero and uniform global asymptotic stability of the error dynamics. Our stability analysis is based on an explicit, strict, global Lyapunov function construction. Our Lyapunov approach also leads to an input-to-state stability based quantification of the effects of parametric uncertainty on the tracking performance. The MEM dynamics contain a quadratic nonlinearity that leads to constraints on the class of reference trajectories that can be tracked. We illustrate how to craft a reference trajectory that is compatible with these constraints and with a typical opening and closing relay operation. Our simulation indicates the good tracking performance of our controllers.
[Show abstract][Hide abstract] ABSTRACT: For original paper see Y. Su. ibid., vol.52, no.7, p.1340-5, (2007). This article presents a comment on the paper ldquoa simple nonlinear observer for a class of uncertain mechanical systemsrdquo.
IEEE Transactions on Automatic Control 05/2008; · 2.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper reports a new robust adaptive tracking controller for multi-input/multi-output nonlinear parametric strict-feedback systems in the presence of parametric uncertainty and any unknown continuous bounded additive disturbance. The proposed solution uses a new projection-like adaptation that allows the application of the standard tuning function approach, thereby avoiding over parametrization and the need for extra nonlinear damping-type terms in the control. The robust adaptive control is shown to guarantee practical tracking in the presence of the disturbance and asymptotic tracking when the disturbance disappears.
Decision and Control, 2007 46th IEEE Conference on; 01/2008
[Show abstract][Hide abstract] ABSTRACT: A promising mechanical bearing candidate for an active operation is the tilting-pad bearing. The proposed active tilting-pad bearing has linear actuators that radially translate each pad/pivot pair. The use of feedback control in determining the actuator forces allows for the automatic, continuous adjustment of the pad position during the operation of the rotating machine. In this paper, we develop a nonlinear dynamic model of the active bearing system. The hydrodynamic force produced by the fluid film is modeled as a nonlinear, squeeze-film damper plus repellent spring. A model-based nonlinear controller is then designed to exponentially regulate the rotor position to the origin. A proof-of-concept experiment shows that the active strategy improves the bearing performance relative to its traditional passive operation. Further, the experiment demonstrates that the model-based nonlinear control regulates the rotor comparably to a linear proportional integral derivative (PID) control, but requires significantly less control energy.
IEEE/ASME Transactions on Mechatronics 01/2008; · 3.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we address the problem of controlling a magnetic levitation system with reduced electric power losses. A general control/biasing strategy is proposed which introduces a bias flux in the nonlinear control law, function of the mechanical states. The bias flux ensures the power losses converge to zero as the mechanical states converge to zero and a singularity-free control, without affecting the closed-loop stability. General conditions on the functional form of the bias are provided along with a design example of the control/biasing strategy. An experimental study illustrates that the proposed time-varying-bias controller yields a stabilization performance comparable to the constant-bias version of the controller, but with significantly less ohmic power losses.
IEEE Transactions on Control Systems Technology 12/2007; · 2.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we show that voltage-controlled, electrostatic and electromagnetic micro-relays have a common dynamic structure. As a result, both types of microelectro-mechanical (MEM) relays are subject to the nonlinear phenomenon known as pull-in, which is usually associated with the electrostatic case. We show that open-loop control of MEM relays naturally leads to pull-in during the relay closing. Two control schemes - a Lyapunov design and a feedback linearization design - are presented with the objectives of avoiding pull- in during the micro-relay closing and improving the transient response during the micro-relay opening. Simulations illustrate the performance of the two control schemes in comparison to the typical open-loop operation of the MEM relay.
American Control Conference, 2007. ACC '07; 08/2007
[Show abstract][Hide abstract] ABSTRACT: Biotin carboxylase catalyzes the ATP-dependent carboxylation of biotin and is one component of the multienzyme complex acetyl-CoA carboxylase that catalyzes the first committed step in fatty acid synthesis in all organisms. In Escherichia coli, biotin carboxylase exists as a homodimer where each subunit contains a complete active site. In a previous study (Janiyani, K., Bordelon, T., Waldrop, G.L., Cronan Jr., J.E., 2001. J. Biol. Chem. 276, 29864-29870), hybrid dimers were constructed where one subunit was wild-type and the other contained an active site mutation that reduced activity at least 100-fold. The activity of the hybrid dimers was only slightly greater than the activity of the mutant homodimers and far less than the expected 50% activity for completely independent active sites. Thus, there is communication between the two subunits of biotin carboxylase. The dominant negative effect of the mutations on the wild-type active site was interpreted as alternating catalytic cycles of the active sites in the homodimer. In order to test the hypothesis of oscillating catalytic cycles, mathematical modeling and numerical simulations of the kinetics of wild-type, hybrid dimers, and mutant homodimers of biotin carboxylase were performed. Numerical simulations of biotin carboxylase kinetics were the most similar to the experimental data when an oscillating active site model was used. In contrast, alternative models where the active sites were independent did not agree with the experimental data. Thus, the numerical simulations of the proposed kinetic model support the hypothesis that the two active sites of biotin carboxylase alternate their catalytic cycles.
Journal of Theoretical Biology 06/2007; 246(1):167-75. · 2.35 Impact Factor