Paolo Valigi

Adaptive input-output linearizing control of induction motors

A nonlinear adaptive state feedback input-output linearizing control is designed for a fifth-order model of an induction motor which includes both electrical and mechanical dynamics under the assumptions of linear magnetic circuits. The control algorithm contains a nonlinear identification scheme which asymptotically tracks the true values of the load torque and rotor resistance which are assumed to be constant but unknown. Once those parameters are identified, the two control goals of regulating rotor speed and rotor flux amplitude are decoupled, so that power efficiency can be improved without affecting speed regulation. Full state measurements are required. >

Adaptive partial feedback linearization of induction motors

A nonlinear adaptive state feedback input-output linearizing control is designed for a fifth-order model of an induction motor which includes both electrical and mechanical dynamics under the assumptions of linear magnetic circuits. The control algorithm contains a nonlinear identification scheme which asymptotically tracks the true values of the load torque and rotor resistance, which are assumed to be constant but unknown. Once those parameters are identified, the two control goals of regulating rotor speed and rotor flux amplitude are decoupled. Full state measurements are required. Preliminary simulations show that a good performance is maintained when flux signals are provided to the adaptive control algorithm.<<ETX>>

Experimental results in state estimation of industrial robots

A simple asymptotic observer, with linear and decoupled structure, is proposed for the estimation of the generalized velocities of a robotic manipulator. High-gains are used in the attenuation of the nonlinearities characterizing the dynamic behavior of the robot. Lyapunov stability theory is used to prove the convergence of the proposed observer and of the control laws based on such a high-gain observer. The accuracy of the proposed algorithm is verified through some experimental tests.<<ETX>>

Supply Chain Management by H-Infinity Control

In this paper, a H infin control technique is proposed for the management of a supply chain (SC) model linearized about nominal operating conditions. The performance considered is a weighted H infin norm comprising the inventory and the orders placed by each site, hence controlling the bullwhip effect together with local management costs. It is shown how the optimization of local costs at each site is related to the performance of the whole chain and a decentralized control methodology is proposed based on this relation.

Automated defect detection in uniform and structured fabrics using Gabor filters and PCA

This paper describes an algorithm for texture defect detection in uniform and structured fabrics, which has been tested on the TILDA image database. The proposed approach is structured in a feature extraction phase, which relies on a complex symmetric Gabor filter bank and Principal Component Analysis (PCA), and on a defect identification phase, which is based on the Euclidean norm of features and on the comparison with fabric type specific parameters. Our analysis is performed on a patch basis, instead of considering single pixels. The performance has been evaluated with uniformly textured fabrics and fabrics with visible texture and grid-like structures, using as reference defect locations identified by human observers. The results show that our algorithm outperforms previous approaches in most cases, achieving a detection rate of 98.8% and a false alarm rate as low as 0.20-0.37%, whereas for heavily structured yarns misdetection rate can be as low as 5%.

A solution to the generalized problem of nonlinear map inversion

Abstract This paper deals with the generalization of some problems related to map inversion. Solutions of such problems are proposed by means of observers, for which a structure is proposed.

Use of observers for the inversion of nonlinear maps

Abstract In this paper we deal with the problem of the inversion of nonlinear maps. The first contribution of the paper is the definition, in a formal framework, of some problems related to map inversion, which are already present in the literature, for instance in the robotics area and in observer theory. The second and the main contribution consists in the solution of such problems by means of observers, for which some structures are proposed, for the state estimation of a time-varying nonlinear system associated with the given map and reference trajectory.

A decentralized controller for the robust stabilization of a class of MIMO linear systems

This work deals with the problem of the robust stablization of a class of multi-input multi-output (MIMO) dynamical sytems. A simple decentralized controller is proposed, which reduces to the clasical PID controller in case of single-input single-output dynamical systems. Such a controller includes integral actions for the compensation of the entire dynamics of the system. The paper is completed with an application to robotic systems.

Hedging point policies remain optimal under limited backlog and inventory space

In this note, we consider a fluid flow, single part-type, single unreliable machine production system with a bounded backlog/inventory space. We prove that, as in the unbounded case, the problem of minimizing an infinite horizon average demand loss/backlog/surplus cost is solved by a hedging point policy. An implicit equation is given, whose structure easily allows to numerically evaluate the optimal safety stock. The effect of system parameters on the optimal safety stock is analyzed and some numerical examples illustrate the presented results.

Dynamic modelling of a two link flexible robot and experimental validation

The paper discusses the modelling issues for a two link flexible robot arm. The exact dynamic model of the robot arm is derived, and approximate forms suitable for the analysis and control design are proposed. The approach used here to derive an approximate finite dimensional model of the flexible robot arm is based on the Ritz expansion method. Simulations and experimental tests have been carried out to validate the approximate dynamic model of the robot.