Adaptive friction compensations for mechanical systems with measurement delay
Date
2021Source Title
Transactions of the Institute of Measurement and Control
Print ISSN
0142-3312
Publisher
SAGE Publications
Volume
43
Issue
8
Pages
1745 - 1759
Language
English
Type
ArticleItem Usage Stats
80
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162
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Abstract
Application performance of mechanical positioning systems might not coincide with the theory, mainly due to nonlinearities or imperfections of system models. Although it is sometimes possible to ignore these mismatches, systems generally suffer from performance degradation or even instability eventually. Especially, friction force and time delay are two major factors of these undesired effects. Hence, in this paper, Smith predictor-based controllers and an adaptive Coulomb friction observer are designed to enhance position tracking performance of a mechanical system including time delay. In fact, implemented hierarchical control scheme provides two-degree of freedom to control both velocity and position separately. The proposed observer structure is mainly motivated by the Friedland-Park observer but could be considered as an extension of it which characterizes a general class of nonlinear functions for friction estimation. To assure its functionality with delayed measurements, different velocity predictor schemes are designed and their performances are compared. As a guideline for observer design, some conditions for exponential stability and robustness analysis are presented. Simulation results demonstrate that the proposed control system enhances the tracking performance even when the actual friction is a compound of various static and dynamic terms.
Keywords
Friction observerTime delay
Smith predictor
Controller parametrization
Hierarchical position control
Adaptive control