Hardware Implementation of a Robust Control Strategy for Mechanical Systems
by
David I. Rosas Almeida
Facultad de Ingeniería Mexicali, Universidad Autónoma de Baja California
Coauthors: Joaquin Alvarez, Jonatan Peña Scientific Research and Advanced Studies Center of Ensenada Electronics and Telecommunications Department Km. 107 Carr. Tijuana-Ensenada Ensenada, B.C. Mexico. 22860 Email:jqalvar@cicese.mx

Control of mechanical systems has been an important engineering problem since long time ago. A problem that is very common in this kind of systems is the fact that the model is not exact, indeed in several cases is not near to the reality. This is due to there are parametric uncertainties, external disturbances and unmodelled modes (for example friction forces). Then it is necessary to apply robust control techniques in order to solve these problems.

A robust control technique that has been succesful applied due to its robustness properties is the sliding mode control [3], [4] and [5], which displays a very good performance for regulation and tracking objetives in mechanical systems. However, when the state reaches the discontinuity surface, the control input usually displays chattering which may produce harmful effects in the mechanism. There are works that faces solutions to chattering problem [1] and [2].

In this paper we present the performance of a new robust control strategy for a class of mechanical systems (for those which model could be represented by lagrangian equations) is presented. It is called Control Structure with Disturbance Identification (CSDI) and it is based-on a sliding modes observer presented in [6]. This observer not only estimates the state vector, but also allows to identify the disturbance term using equivalent output injection approach [5]. Also state feedback linearization controller is used and chattering is not a matter; the chatttering is not an issue because the control input does not have high frequency components. In order to implemet this control strategy the only required information about the system is the generalized position vector and nominal value of the inertia matrix.

Usually the control algorithms are implemented in software due to this is the easiest way of implement large and complex control laws. In this implementation it is necessary to have a real time interface to read the variables and to send the control law to the mechanism. However, in some cases it is possible, and may be convenient , to realize analog control implementations.

Analog technology provide some adventajes like low power consumption, speed and space requeriments, also this kind of implementation is cheaper than PC-based real time implementation. In analog implementation there is a direct connection between variables and is not necessary to perform A/D and D/A conversions in order to process the control signal.

Nevertheless there are some control strategies that are very complex and then this is not possible to implement them with analog technology. Moreover, as is well-known the accuracy that could be achievable it is limited by factors such as noise, and nonidealities presents in the analog circuits.

In this paper an analog implementation of the CSDI is presented, in order to show that in this case analog implementation have a good and acceptable performance.

References [1] Jian-Xin, X., Ya-Jun P. y Tong-Heng L. 2004. Sliding mode control whith closed-loop filtering architecture for a class of nonlinear systems. IEEE Transactions on Circuits and Systems. Vol. 51, Issue 4, 168-173 pp [2] Rosas, D., Álvarez, J. y Fridman, L. 2006. Robust observation and identification of nDOF Lagrangian systems. International Journal of Robust and Nonlinear Control. 17:842-861 p. [3] Utkin, V., Chang, H. 2002. Sliding mode control on electro-mechanical systems. Mathematical Problems in Engineering, Vol. 8, Issue 4-5, 451-473 p. [4] Utkin, V., Guldner J. and Shi, J. 1999. Sliding Mode Control in Electromechanical Systems, Taylor and Francis Ed., 325 p. [5] Weibing Gao and James C. Hung. 1993. Variable structure control of nonlinear systems: A new approach. IEEE Transactions on Industrial Electronics, Vol. 40, No. 1, 45-55 pp. [6] Sellami, A., Arzelier, D., M'hiri R. and Zrida, J. 2007. A sliding mode control approach for systems subjected to a norm-bounded uncertainty. International Journal of Robust and Nonlinear Control. Vol. 17, Issue 4, 327-346 p.

Date received: March 13, 2008

Copyright © 2008 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cawz-31.