On the limitations of force tracking control for hydraulic active suspensions

This paper presents analysis of a particular force tracking control problem for rectilinear hydraulic actuators governed by a servovalve. It presents no new theory, but rather uses a revealing model reduction insight coupled with classical analysis to explain a physical phenomenon. As such, this work is an attempt to explain why a seemingly innocuous problem is more subtle than initially believed. A motivation for this problem is given along with prior attempts at a simple solution. The solution method evaluated is a common proportional-integral-derivative type of controller. It is shown that the simple PID is quite adequate for other types of control objectives such as force regulation or position tracking. However, this simple solution method is shown to be inadequate for force tracking due to fundamental limitations of the problem formulation. Therefore, more advanced control algorithms are shown to be a necessity rather than a luxury.