Computed Torque Control

I have been reading the book from K.S. Fu, on the computed torque control, from what I can gather from my shallow understanding of the matter is that it is calculating the servo voltage which is required to produce the necessary torque in order to correct the error in the position and the velocity of the joints. Basically it uses the laplace transform in order to generate the transfer function which relates the voltage of the servo motor and also the joint rotation or torque. In any control system to gauge the performance we normally have 3 critieria which determines the success and the so call performance of the controller. Those criteria are
1) Fast time response
2) small steady state error
3) fast settling time..

This is some of the things that I have dwell inside the book in order to expand the understanding that I have on the PID controller, ohh I wish I have been paying more attention during my class in the university last time..or maybe this is the effect caused by the long working period that causes me to leave my engineering books for a long..long time :)