			Home About us Contact

Time System (time + system)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

The Liapunov's second method for continuous time difference equations

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 15 2003
P. PepeArticle first published online: 10 OCT 200
Abstract Among many other cases such as economic and lossless propagation models, continuous time difference equations are encountered as the internal dynamics in a class of non-linear time delay systems, when controlled by a suitable state feedback which drives the output exponentially to zero. The Liapunov's second method for these infinite dimensional systems has not been extensively investigated in the literature. This paper has the aim of filling this gap. Liapunov's second method theorems for checking the stability and the asymptotic stability of this class of infinite dimensional systems are built up, in both a finite and an infinite dimensional setting. In the finite dimensional setting, the Liapunov function is defined on finite dimensional sets. The conditions for stability are given as inequalities on continuous time. No derivatives are involved, as in the dynamics of the studied systems. In the infinite dimensional setting, the continuous time difference equation is transformed into a discrete time system evolving on an infinite dimensional space, and then the classical Liapunov theorem for the system in the new form is written. In this paper the very general case is considered, that is non-linear continuous time difference equations with multiple non commensurate delays are considered, and moreover the functions involved in the dynamics are allowed to be discontinuous, as well as the initial state. In order to study the stability of the internal dynamics in non-linear time delay feedback systems, an exogenous disturbance is added, which goes to zero exponentially as the time goes to infinity. An example is considered, from non-linear time delay feedback theory. While the results available in the literature are inconclusive as far as the stability of that example is concerned, such stability is proved to hold by the theorems developed in this paper, and is validated by simulation results. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Real Time Foot Drop Correction using Machine Learning and Natural Sensors

NEUROMODULATION, Issue 1 2002
Morten Hansen MScEE
Abstract The objective of this study was to investigate and test a real time system implemented for Functional Electrical Stimulation (FES) assisted foot drop correction, deriving control timing from signals recorded from a peripheral sensory nerve. A hemiplegic participant was attached with a cuff electrode on the sural nerve connected to a telemetry controlled implanted neural amplifier, and a stimulation cuff electrode on the peroneal nerve connected to an implanted stimulator. An input domain was derived from the recorded electroneurogram (ENG) and fed to a detection algorithm based on an Adaptive Logic Network (ALN) for controlling the timing of the peroneal stimulation. The detection system was tested in real time over a period of 392 days, covering a variety of walking tasks. The detection system's ability to detect heel strike and foot lift without errors and to detect the difference between walking and standing proved to be stable for the duration of the study. We conclude that using ALNs and natural sensors provide a stable and accurate control signal for FES foot drop correction. [source]

International competition and pay, working time and employment: exploring the processes of adjustment

INDUSTRIAL RELATIONS JOURNAL, Issue 2 2001
James Arrowsmith
The internationalisation of markets, competition and regulation is increasingly recognised. So far, however, debate about the effects has been largely speculative. This article examines the UK engineering industry. Survey evidence suggests that international comparisons are relatively unimportant, little benchmarking is going on and that stability characterises pay and working time arrangements. Further interview evidence explains that this is because pay and working time are set with employee expectations in mind, whereas it is the treatment of unit costs that reflects international pressures. As a consequence there has been substantial reductions in employment as well as some important changes in work organisation, even if there has been little change in pay or working time systems. In effect, it suggests that there is a form of ,implicit contract' taking place. A wider implication is that the main impetus for the ,Europeanisation' of industrial relations is likely to come from the growing convergence of costs rather than pressures for wage parity. [source]

Robust adaptive tracking control of uncertain discrete time systems

INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 9 2005
Shengping Li
Abstract In this paper, the problem of robust adaptive tracking for uncertain discrete-time systems is considered from the slowly varying systems point of view. The class of uncertain discrete-time systems considered is subjected to both ,,, to ,,, bounded unstructured uncertainty and external additive bounded disturbances. A priori knowledge of the dynamic model of the reference signal to be tracked is not completely known. For such problem, an indirect adaptive tracking controller is obtained by frozen-time controllers that at each time optimally robustly stabilize the estimated models of the plant and minimize the worst-case steady-state absolute value of the tracking error of the estimated model over the model uncertainty. Based on ,,, to ,,, stability and performance of slowly varying system found in the literature, the proposed adaptive tracking scheme is shown to have good robust stability. Moreover, a computable upper bound on the size of the unstructured uncertainty permitted by the adaptive system and a computable tight upper bound on asymptotic robust steady-state tracking performance are provided. Copyright © 2005 John Wiley & Sons, Ltd. [source]