back into the actuators, which then drive the mechanical system through the
required task, thereby closing the loop. The problem of robot control has received
extensive attention in the literature, and will not be pursued here. The
interested reader is referred to the excellent works on the subject, e.g., those of
Samson, Le Borgne, and Espiau (1991); Khalil and Dombre (2002); and Spong,
Hutchinson and Vidyasagar (2006). Of special relevance to robot control is the
subject of nonlinear control at large, a pioneer here being Isidori (1989).