674 research outputs found
Optimal control design for robust fuzzy friction compensation in a robot joint
This paper presents a methodology for the compensation of nonlinear friction in a robot joint structure based on a fuzzy local modeling technique. To enhance the tracking performance of the robot joint, a dynamic model is derived from the local physical properties of friction. The model is the basis of a precompensator taking into account the dynamics of the overall corrected system by means of a minor loop. The proposed structure does not claim to faithfully reproduce complex phenomena driven by friction. However, the linearity of the local models simplifies the design and implementation of the observer, and its estimation capabilities are improved by the nonlinear integral gain. The controller can then be robustly synthesized using linear matrix inequalities to cancel the effects of inexact friction compensation. Experimental tests conducted on a robot joint with a high level of friction demonstrate the effectiveness of the proposed fuzzy observer-based control strategy for tracking system trajectories when operating in zero-velocity regions and during motion reversals
Index to NASA Tech Briefs, 1975
This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs
Solvent fluctuations induce non-Markovian kinetics in hydrophobic pocket-ligand binding
We investigate the impact of water fluctuations on the key-lock association
kinetics of a hydrophobic ligand (key) binding to a hydrophobic pocket (lock)
by means of a minimalistic stochastic model system. It describes the collective
hydration behavior of the pocket by bimodal fluctuations of a water-pocket
interface that dynamically couples to the diffusive motion of the approaching
ligand via the hydrophobic interaction. This leads to a set of overdamped
Langevin equations in 2D-coordinate-space, that is Markovian in each dimension.
Numerical simulations demonstrate locally increased friction of the ligand,
decelerated binding kinetics, and local non-Markovian (memory) effects in the
ligand's reaction coordinate as found previously in explicit-water molecular
dynamics studies of model hydrophobic pocket-ligand binding [1,2]. Our
minimalistic model elucidates the origin of effectively enhanced friction in
the process that can be traced back to long-time decays in the
force-autocorrelation function induced by the effective, spatially fluctuating
pocket-ligand interaction. Furthermore, we construct a generalized 1D-Langevin
description including a spatially local memory function that enables further
interpretation and a semi-analytical quantification of the results of the
coupled 2D-system
Recent Advances in Sustainable Winter Road Operations – A Book Proposal
Investing in winter transportation operations is essential and beneficial to the public and the economy. The U.S. economy cannot afford the cost of shutting down highways, airports, etc., during winter weather. In the northern U.S. and other cold-climate areas, winter maintenance operations are essential to ensure the safety, mobility, and productivity of transportation systems. Agencies are continually challenged to provide a high level of service and improve safety and mobility in a fiscally and environmentally responsible manner. To this end, it is desirable to use the most recent advances in the application of materials, practices, equipment, and other technologies. Such best practices are expected to improve the effectiveness and efficiency of winter operations, to optimize material usage, and to reduce associated annual spending, corrosion, and environmental impacts. Currently, no professional societies, scientific journals, or textbooks are dedicated solely to sustainable winter road operations, and key information is scattered across a variety of disciplines. The objective of the proposed book is to summarize the best practices and recent advances in sustainable winter road operations for the purposes of education and workforce development. This book is now in press and can be cited as follows: Shi, X., Fu, L. (2017). Sustainable Winter Road Operations (Eds.). ISBN: 978-1-119-18506-2. Wiley-Blackwell
Temperature and friction fluctuations inside a harmonic potential
In this article we study the trapped motion of a molecule undergoing diffusivity fluctuations inside a harmonic potential. For the same diffusing-diffusivity process, we investigate two possible interpretations. Depending on whether diffusivity fluctuations are interpreted as temperature or friction fluctuations, we show that they display drastically different statistical properties inside the harmonic potential. We compute the characteristic function of the process under both types of interpretations and analyze their limit behavior. Based on the integral representations of the processes we compute the mean-squared displacement and the normalized excess kurtosis. In the long-time limit, we show for friction fluctuations that the probability density function (PDF) always converges to a Gaussian whereas in the case of temperature fluctuations the stationary PDF can display either Gaussian distribution or generalized Laplace (Bessel) distribution depending on the ratio between diffusivity and positional correlation times
Full- & Reduced-Order State-Space Modeling of Wind Turbine Systems with Permanent-Magnet Synchronous Generator
Wind energy is an integral part of nowadays energy supply and one of the
fastest growing sources of electricity in the world today. Accurate models for
wind energy conversion systems (WECSs) are of key interest for the analysis and
control design of present and future energy systems. Existing control-oriented
WECSs models are subject to unstructured simplifications, which have not been
discussed in literature so far. Thus, this technical note presents are thorough
derivation of a physical state-space model for permanent magnet synchronous
generator WECSs. The physical model considers all dynamic effects that
significantly influence the system's power output, including the switching of
the power electronics. Alternatively, the model is formulated in the -
and -reference frame. Secondly, a complete control and operation
management system for the wind regimes II and III and the transition between
the regimes is presented. The control takes practical effects such as input
saturation and integral windup into account. Thirdly, by a structured model
reduction procedure, two state-space models of WECS with reduced complexity are
derived: a non-switching model and a non-switching reduced-order model. The
validity of the models is illustrated and compared through a numerical
simulation study.Comment: 23 pages, 11 figure
Mapping the energy landscape of biomolecules using single molecule force correlation spectroscopy (FCS): Theory and applications
In the current AFM experiments the distribution of unfolding times, P(t), is
measured by applying a constant stretching force f_s from which the apparent
unfolding rate is obtained. To describe the complexity of the underlying energy
landscape requires additional probes that can incorporate the dynamics of
tension propagation and relaxation of the polypeptide chain upon force quench.
We introduce a theory of force correlation spectroscopy (FCS) to map the
parameters of the energy landscape of proteins. In the FCS the joint
distribution, P(T,t) of folding and unfolding times is constructed by repeated
application of cycles of stretching at constant fs, separated by release
periods T during which the force is quenched to f_q<f_s. During the release
period, the protein can collapse to a manifold of compact states or refold. We
show that P(T,t) can be used to resolve the kinetics of unfolding as well as
formation of native contacts and to extract the parameters of the energy
landscape using chain extension as the reaction coordinate and P(T,t). We
illustrate the utility of the proposed formalism by analyzing simulations of
unfolding-refolding trajectories of a coarse-grained protein S1 with beta-sheet
architecture for several values of f_s, T and f_q=0. The simulations of
stretch-relax trajectories are used to map many of the parameters that
characterize the energy landscape of S1.Comment: 23 pages, 9 figures; accepted to Biophysical Journa
NON-LINEAR MODEL IN REGION OF VERY LOW SPEEDS FOR A PERMANENT MAGNET DIRECT CURRENT MOTOR
Thematic is in mechatronics and automation branches, applicable in the mobile robotics. Permanent Magnet DC collector motors, are widely used in small mobile robots due to their low-cost. Automated control systems of mobile robots, which operate under different conditions and require accuracy of operation, raise the need for the nonlinearities to be taken into account. In this article, a complex non-linear model of a PMDC motor with brushes is synthesized. The aim is to determine of suitable way of motor behaviour simulating in the region of very small speeds. The tribology aspects at different friction regimes are of great importance for a model at low speeds. The parameters and constants of the model are separately defined through referring to their physical equivalents. Besides the theoretical modelling, a simple mathematical way to determine the constants for this detailed model is deduced. Then the synthesized model is simulated and results are graphically represented and then compared with another similar model, proposed by another authors. As a conclusion, the advantages of this non-linear approach are revealed. This research is applicable as a study of direct-current motor and its simulation model or as facilitating example in lectures of robotics or control systems.
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