On the design of approximate non‐linear parametric controllers

This paper focuses on the design of non‐linear parametric controllers, around a nominal input/output trajectory of a discrete‐time non‐linear system. The main result provided herein is a relationship between the tracking performance of the closed‐loop control system in the neighbourhood of a nominal trajectory, and some local features (the first‐order linear approximations about the nominal trajectory) of the non‐linear mappings which characterize the plant and the feedback controller. Such a result can be used to predict the dynamic behaviour of the control system, and to reduce the computational complexity of the optimization task associated with the tuning of the parametric feedback controller. Copyright © 2000 John Wiley & Sons, Ltd.     

Position Control of a Wheeled Mobile Robot Including Tire Behavior

Advanced driver assistance systems are increasingly available on road vehicles. These systems require a thorough development procedure, an important part of which consists of hardware-in-the-loop experiments in a controlled environment. To this end, a facility called vehicle hardware-in-the-loop (VeHIL) is operated, aiming at testing the entire road vehicle in an artificial environment. In VeHIL, the test vehicle is placed on a roller bench, whereas other traffic participants, i.e., vehicles in the direct neighborhood of the test vehicle, are simulated using wheeled mobile robots (WMRs). To achieve a high degree of experiment reproducibility, focus is put on the design of an accurate position control system for the robots. Due to the required types of maneuvers, these robots have independently driven and steered wheels. Consequently, the robot is overactuated. Furthermore, since the robot is capable of high-dynamic maneuvers, slip effects caused by the tires can play an important role. A position controller based on feedback linearization is presented, using the so-called multicycle approach, which regards the robot as a set of identical unicycles. As a result, the WMR is position controlled, whereas each unicycle is controlled, taking weight transfer and longitudinal and lateral tire slip into account.     

Organic field-effect transistors as new paradigm for large-area molecular junctions

Self-Assembly Monolayers (SAMs) are considered a promising route for solving technological hindrances (such as bias-stress, contact resistance, charge trapping) affecting the electrical performances of the Organic Field-Effect Transistors (OFETs). Here we use an OFET based on pentacene thin film to investigate the charge transport across conjugated SAMs at the Au/pentacene interface. We synthesized a homolog series of π-conjugated molecules, termed Tn-C8-SH, consisting of a n-unit oligothienyl Tn (n = 1…4) bound to an octane-1-thiol (C8-SH) chain that self-assembles on the Au electrodes. The multi-parametric response of such devices yields an exponential behavior of the field-effect mobility (μ), current density (J), and total resistivity (R), due to the SAM at the charge injection interface (i.e. Au-SAM-pentacene). The surface treatment of the OFETs induces a clear stabilization of different parameters, like sub-threshold slope and threshold voltage, thanks to standardized steps in the fabrication process.     

Nonsmooth stabilizability and feedback linearization of discrete-time nonlinear systems

We consider the problem of stabilizing a discrete-time nonlinear system using a feedback which is not necessarily smooth. A sufficient condition for global dynamical stabilizability of single-input triangular systems is given. We obtain conditions expressed in terms of distributions for the nonsmooth feedback triangularization and linearization of discrete-time systems. Relations between stabilization and linearization of discrete-time systems are given.     

Mechanical reliability of Ce0.8Gd0.2O2−δ-FeCo2O4 dual phase membranes synthesized by one-step solid-state reaction

Ce_0.8Gd_0.2O_2−δ-FeCo₂O₄ composites are attractive candidate materials for high-purity oxygen generation providing robust chemical stability. Aiming for future industrial applications, a feasible solid-state reaction process with one thermal processing step was used to synthesize 50 wt% Ce_0.8Gd_0.2O_2−δ:50 wt% FeCo₂O₄ and 85 wt% Ce_0.8Gd_0.2O_2−δ:15 wt% FeCo₂O₄ composites. Mechanical reliabilities of the sintered membranes were assessed based on the characterized mechanical properties and subcritical crack growth behavior. In general, the fracture strengths of as-sintered membranes were reduced by tensile residual stresses and microcracks. In particular, the enhanced subcritical crack growth behavior, which leads to limited stress tolerance and high failure probability after a 10-year operation, was evaluated in more detail. Further materials and processing improvements are needed to eliminate the tensile stress and microcracks to warrant a long-term reliable operation of the composites.     

Controlled invariance for nonlinear systems: Two worked examples

In this note, we present two worked examples of disturbance decoupling for nonlinear systems, using the concept of controlled invariance, which was recently generalized to nonlinear systems. In the first example, we explicitly construct a feedback which decouples a disturbance from the vertical components of the axes of a rotating rigid body, while the second example deals with a particle in a potential field subject to a disturbance.     

Dynamic input-output decoupling of nonlinear control systems

The problem of dynamic input-output decoupling of nonlinear control systems is studied. Based on an analytic algorithm the authors obtain necessary and sufficient conditions for the solvability of this problem. The solution of the problem is constructed by applying a series of simple precompensations and linking maps. Some interesting connections with other approaches in nonlinear control theory are discussed. The authors also give a few (simple) examples to illustrate the methods used     

Simulation of optical fiber growth in three dimensions

We have carried out 3-dimensional molecular dynamics simulations of a crystal growth technique known as laser heated pedestal growth. Previously, we simulated this technique in 2 dimensions and our current work is an attempt to extend those simulations to the more realistic 3D case. We demonstrate that such 3D simulations are feasible in a study of the influence of the growth speed and the influence of the laser heating on various aspects of the fiber growth. Although much more realistic than the 2D study, the moderate system sizes used in this study and other crude representations of the experimental process still prevent us from making quantitative comparisons with the latter.