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284                            Robust Control of Robotic Manipulators



                                                                          (3)

            Then all the stabilizing controllers are given by


                                                                          (4)


            where Q(s) is a stable rational function which is otherwise arbitrary. One
            choice, of course, is to let Q(s)=0, which leads to the “central solution”
            [Vidyasagar 1985]


                                                                          (5)



            One can also choose Q(s) to satisfy the required performance. In particular,
            the following choice of  Q(s) is presented in [Spong and Vidyasagar
            1987]:


                                                                          (6)



            which leads to the following controller:




            where










            and


                                                                          (7)


            As k increases, the disturbance rejection property of the controller is enhanced
            at the expense of higher gains as seen from the expression of C(s). A simulation


            Copyright © 2004 by Marcel Dekker, Inc.
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