Experimental Implementation of a Nonlinear Feedback Controller for a Stroke Limited Inertial Actuator

This research consists of theoretical and experimental studies of a stroke limited inertial, or proof mass, actuator used in active vibration control. Traditionally, inertial actuators are used with velocity feedback controllers to reduce structural vibrations. However, physical limits, such as stroke saturation, can affect the behaviour and the stability of the control system. In fact, stroke saturation results in impulse like excitations, which are transmitted to the structure that is liable to damage. Moreover, the shocks produced by the impacts are in phase with the velocity of the structure. This produces an input force, which reduces the overall damping and eventually leads to limit cycle oscillations and the instability of the system. This paper examines the experimental implementation of a nonlinear feedback controller to avoid collisions of the proof mass with the actuator’s end stops, hence preventing the instability of the system due to stroke saturation. Firstly, the nonlinear behaviour of the stroke limited inertial actuator is reported. This allows identifying the stroke length of the proof mass. Secondly, the nonlinear feedback controller is presented, which acts as a second loop alongside the velocity feedback control loop. The main purpose of the nonlinear feedback controller is to increase the damping of the actuator when the poof mass gets close to the end stops. Finally, the experimental implementation of the nonlinear controller is investigated and a comparison in terms of performance and stability of the control system is made when both the feedback loops or only the velocity feedback loop are present.