  The experience gained with numerous successful applications permits to
revisit some points of model-free control. The numerical differentiation of
noisy signals may be replaced by a real time parameter identification which is
much simpler. The strange ubiquity of classic PIDs is explained as well as the
almost universal utilization of ultra-local models of order 1. We show that
even with a partially known model the utilization of an intelligent PI
controller remains profitable. Two examples, an inverted pendulum and a heat
exchanger, seem to confirm the superiority of model-free control with respect
to sliding modes control and techniques stemming from infinite-dimensional
systems, such as delays or partial differential equations. Our paper is
illustrated by several computer simulations.
