Susan C. Schneider

Analysis of algorithms for velocity estimation from discrete position versus time data

Algorithms for constructing velocity approximations from discrete position versus time data are investigated. The study is limited to algorithms suitable to provide velocity information in discrete-time feedback control systems such as microprocessor-based systems with a discrete position encoder. Velocity estimators based on lines per period, reciprocal-time, Taylor series expansion, backward difference expansions, and least-square curve fits are presented. Based on computer simulations, comparisons of relative accuracies of the different algorithms are made. The least-squares velocity estimators filtered the effect of imperfect measurements best, whereas the Taylor series expansions and backward difference equation estimators respond better to velocity transients. >

AC-impedance-based chemical sensors for organic solvent vapors

Abstract A type of chemical sensor based on impedance spectroscopy (IS) measurements utilizing an interdigital transducer structure on a glass substrate is investigated for the detection of organic solvent molecules, such as chloronated hydrocarbons, in the gas phase. The IDT structures were coated with sensitive material such as soluble tetrakis-t-butyl phthalocyaninatonickel(II), ethylcellulose, poly(ethyl acrylate), and poly(etherurethane). The target organic solvent molecules are dichloromethane, chloroform, trichloroethene, tetrachloroethene, toluene, and ethanol. The sensor responses were monitored by measuring changes in the transducer/coating composite properties upon exposure to the organic solvent molecules. The sensor parameters of interest include the electrostatic capacitance, the resistance of the composite and the relaxation time, which will lead to the implementation of a multi-information sensor. Results are presented and compared for selected samples with completely reversible sensor signals at room temperature. Based on the measurements, use of metal complexes can improve sensitivity and increase the signal-to-noise ratio.

Velocity Observations From Discrete Position Encoders

A discrete position encoder is an inexpensive means for sensing the angular position of a rotating device. Often a system with higher performance can be achieved if the angular velocity is known in addition to the position. Typically, the output of a discrete position encoder is two square wave signals in quadrature. This paper investigates various methods for processing these signals to observe the velocity in real time. High performance observers based on Taylor series expansions, backward difference expansions, and least square curve fits are developed. The accuracy of the different observers are analyzed by simulations for systems with time measurement truncation and imperfect encoders. The least square curve fit based observers are the most tolerant observers investigated due to the inherent low pass filtering.

Suspended and localized single nanostructure growth across a nanogap by an electric field.

Direct growth of a suspended single nanostructure (SSN) at a specific location is presented. The SSN is grown across a metallic nanoscale gap by migration in air at room temperature. The nanogap is fabricated by industrial standard optical lithography and anisotropic wet chemical silicon etching. A DC current bias, 1 nA, is applied across the metallic gap to induce nanoscale migration of Zn or ZnO. The history of the voltage drop across the gap as a function of time clearly indicates the moment when migration begins. The shape of SSNs grown across the nanogap by the migration is asymmetric at each electrode due to the asymmetric electric field distribution within the nanogap. An SSN can be used as the platform for two-terminal active or passive nanoscale electronics in optoelectronics, radio frequency (RF) resonators, and chemical/biological sensors.

Discrete-time resilient controller design with general criteria for a class of uncertain nonlinear systems

A discrete-time resilient state feedback control scheme is presented to control nonlinear systems with locally conic type of nonlinearities and driven by finite energy disturbances. The resilience property is achieved in the presence of bounded perturbations in the feedback gain. The controller design is also robust as the design process addresses system models containing a higher degree of uncertainty by allowing perturbations in both the system parameters as well as the center and the boundaries of the cone in which the nonlinearity resides. Results are presented for various performance criteria in a unified framework using linear matrix inequalities (LMIs). Illustrative examples are included to demonstrate the efficiency of the proposed approach.

H2−H∞ control of continuous-time nonlinear systems using the state-dependent Riccati equation approach

ABSTRACT This paper presents a novel state-dependent Riccati equation (SDRE) control approach with the purpose of providing a more effective control design framework for continuous-time nonlinear systems to achieve a mixed nonlinear quadratic regulator and H∞ control performance criteria. By solving the generalized SDRE, the optimal control solution is found to achieve mixed performance objectives guaranteeing nonlinear quadratic optimality with inherent stability property in combination with H∞ type of disturbance reduction. An efficient computational algorithm is given to find the solution to the SDRE. The efficacy of the proposed technique is used to design the control system for inverted pendulum, an under-actuated nonlinear mechanical system.

Robust controller design with general criteria for uncertain conic nonlinear systems with disturbances

A robust state feedback scheme is proposed to control a large class of continuous-time uncertain nonlinear systems with locally conic type nonlinearities and driven by finite energy disturbances. It is assumed that there is also uncertainty regarding the center and the boundary of the cone in which the nonlinearity resides in order to allow the robust control of systems whose models contain a higher degree of uncertainty. Results are presented for various performance criteria using linear matrix inequalities. Illustrative examples are included to demonstrate the efficiency of the proposed approach.

Analysis of the Detection of Organophosphate Pesticides in Aqueous Solutions Using Hydrogen-Bond Acidic Coating on SH-SAW Devices

The work presented in this paper focuses on the synthesis and characterization of a hybrid organic/inorganic chemically sensitive layer for rapid detection and analysis of OPs in aqueous solutions using SH-SAW devices. Coated SH-SAW devices on 36° YX-LiTaO and 42.75° YX-Quartz (ST-90° X Quartz), are used to determine the optimum operating conditions for achieving rapid sensor responses with high sensitivity. Three analytes (parathion-methyl, parathion, and paraoxon), having similar molecular mass and volume, are used to evaluate the performance of the hybrid organic/inorganic coating in terms of sensor properties of interest including sensitivity, selectivity, reproducibility. It is shown that the coating has a high degree of partial selectivity and sensitivity towards the analytes. With the present non-optimized chemical sensor, a limit of detection of 60 (ppb), 20 (ppb) and 100 (ppb) is estimated for parathion-methyl, parathion, and paraoxon, respectively, when using a 0.5 -thick BPA-HMTS sensing layer. Concentrations as low as 500 (ppb) parathion have been measured. This concentration is significantly much lower than the typical concentrations found on agricultural produce (≥10 ppm).

Performance analysis of resilient dynamic feedback H 2 controllers for discrete-time systems

In this work, a procedure is presented for performance analysis intended to evaluate the resilience and H2 norm bound of discrete-time systems controlled by full-order dynamic feedback compensators. Acceptable performance is specified by disks in the complex plane within which the eigenvalues of the controller and the observer remain in the presence of perturbations in the controller and observer gains. Maximum gain perturbation bounds can be obtained based on the designers choices of controller and observer eigenvalue regions and the resulting H2-norm bound is calculated. The linear matrix inequality technique is used throughout the analysis process. Illustrative examples are included to demonstrate the effectiveness of the proposed methodology.

H2-H∞ Control of Discrete Time Nonlinear Systems Using the SDRE Approach

A novel H2 –H∞ State Dependent Riccati Equation control approach is presented for providing a generalized control framework to discrete time nonlinear system. By solving a generalized Riccati Equation at each time step, the nonlinear state feedback control solution is found to satisfy mixed performance criteria guaranteeing quadratic optimality with inherent stability property in combination with H∞ type of disturbance attenuation. Two numerical techniques to compute the solution of the resulting Riccati equation are presented: The first one is based on finding the steady state solution of the difference equation at every step and the second one is based on finding the minimum solution of a linear matrix inequality. The effectiveness of the proposed techniques is demonstrated by simulations involving the control of an inverted pendulum on a cart, a benchmark mechanical system.Copyright