Reduction of vibrations by bang–bang controlled electrorheological dampers

Summary This article is concerned with the application of electrorheological fluids (ERF) to the reduction of vibrations by controlled damping. Many papers deal with mechanical characteristics of ERF, but only a few articles have been published about the technical applications of these fluids, although great expectations have been placed into it some years ago. Vibration reduction by damping control is a difficult task because forces can only be generated when relative velocities exist between both ends of the damper. The design of a control strategy cannot be investigated by the methods of linear control theory. It is a task for the dynamic programming. The main objective of this paper is to present different methods for the investigation of suitable control strategies, and to verify the theoretical results by simulation and experiments. By simulation, it can be shown that the bang–bang control of damping – that means switching between the highest and the lowest possible damping – is an efficient way for the reduction of vibrations in special systems. Nearly no additional power is necessary. This switching can be realised with controlled valves and bypasses or by the ERF. Experiments with the ERF prove the theoretical considerations; still, there are several side effects making it difficult to perform a useful experiment, for example, leakage in the damper or electric isolation problems or the dependence on whether the AC or the DC is used. Received 26 October 1998; accepted for publication 20 October 1999