Actuator-based vibration control using position feedback

There are many applications, such as instrument platforms, which make use of linear actuators for active vibration isolation. However, the control algorithms are typically based upon measurements of the accelerations of the isolated platform or upon measurements of the input and output forces at the actuators. As a result, the dynamics of the isolated structure couple into the control algorithm, increasing its complexity, Indeed, if not accounted for in the controller, these dynamics can result in the controlled system becoming unstable. To address this, we have developed a control strategy based entirely on the relative position of the armature and body. Additionally, we have developed an actuator which has the necessary features to take advantage of this approach. This strategy provides a modular approach to vibration isolation because it acts independently of the dynamics of any attached structures. While the system is unable to match the peak performance of adaptive multiple-input multiple-output controllers, it provides significant broadband isolation with a simple, local controller. Further, this control can be implemented within the actuator, providing more sophisticated controllers with an actuator that has less force transmission than conventional devices. This offers the potential of additional gains in isolation performance. We present the analytical model of such an actuator and control algorithm, and investigate practical limits on the general problem of position-based control for vibration isolation of structures. Within these limits, we propose a method for controlling an actual system which provides good broadband isolation with a simple control architecture. Finally, we prove the approach by demonstrating it experimentally.