  "Model-free control" and the corresponding "intelligent" PID controllers
(iPIDs), which already had many successful concrete applications, are presented
here for the first time in an unified manner, where the new advances are taken
into account. The basics of model-free control is now employing some old
functional analysis and some elementary differential algebra. The estimation
techniques become quite straightforward via a recent online parameter
identification approach. The importance of iPIs and especially of iPs is
deduced from the presence of friction. The strange industrial ubiquity of
classic PID's and the great difficulty for tuning them in complex situations is
deduced, via an elementary sampling, from their connections with iPIDs. Several
numerical simulations are presented which include some infinite-dimensional
systems. They demonstrate not only the power of our intelligent controllers but
also the great simplicity for tuning them.
