The Control of Transmitted Power in an Active Isolation System

The isolation of vibration through a system with multiple active mounts is discussed, in which each of the mounts can transmit vibration in several degrees of freedom. Theoretical models of the various parts of this system have been developed which include a flexible receiving structure and distributed active mounts, and these models can be connected together to produce an overall theoretical description of a realistic active isolation system.

Total transmitted power has been found to be an excellent criterion to quantify the effect of various control strategies in this model in which the contributions to the transmitted power in the various degrees of freedom can be clearly understood. It has also been found, however, that an active control system which minimises a practical estimate of transmitted power, calculated from the product of the axial forces and velocities under the mounts, can give a very poor performance in terms of reducing the total transmitted power, and can even increase it under some circumstances.

Such a control system was also found to be very sensitive to measurement errors and the presence of flanking paths, which give rise to the phenomena of 'power circulation'. A more practical control strategy appears to be to minimise the weighted sum of squared forces and velocities below the mounts, which gives near-optimal performance in simulations.

These theoretical results are supported by experiments with a real-time control system. The actuator and sensor requirements of such an active vibration control system are also discussed.