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36                                     Introduction to Control Theory




                                                                       (2.3.8)


            where U(k) and c are defined similarly to those given in equation (2.3.4).

            EXAMPLE 2.3–3: Logistics Equation
            Consider the scalar system





            which leads to the state-space representation









            We will not emphasize the study of discrete nonlinear systems since robots
            are described by differential equations. However, as discussed in Chapter 4,
            robot controllers are usually implemented using digital controllers. It will
            therefore be advantageous to be able to translate between continuous-and
            discrete-time description of nonlinear dynamical systems as discussed in
            [åAström and Wittenmark 1995], [Franklin et al. 1997].



            2.4 Nonlinear Systems and Equilibrium Points

            In this section, we concentrate on systems described by (2.2.15) with the
            additional requirement that u(t) is specified as a function of the state x(t),
            i.e.


                                                                       (2.4.1)


              This will allow us to concentrate on the Analysis problem. We require a
            few definitions which we shall now introduce.







            Copyright © 2004 by Marcel Dekker, Inc.
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