Pressure Feedback in Fluid Power Systems--Active Damping Explained and Exemplified

Fluid power systems are inherently nonlinear and typically suffer from very poor damping. Despite these characteristics, it is not uncommon that traditional linear type controllers are applied. This typically results in conservative adjustment of the controllers, or when more advanced controllers are applied, that they do not benefit from the possibilities for improving the damping by applying (internal) pressure feedback in the systems. In both cases, the result will be degraded performance compared with what may be obtained. Pressure feedback, also referred to as active damping, is not a new method. However, it is an often overlooked method, and when it is applied, it is not adjusted optimally to also account for model uncertainties, unmodeled system dynamics, and parameter variations. The focus of this paper is to explain various types of pressure feedback that may be applied; how these affect a given system, and how to adjust the parameters of the pressure feedback to obtain the best results. This is done for both a traditional symmetric cylinder servo system and a system with a differential cylinder using both pressure and nonpressure compensated proportional valves. Based on the presented models, the analysis yields results for how to properly adjust the parameters.