Active Control for Vibration Suppression in a Flexible Beam Using a Modal Domain Optical Fiber Sensor

In this paper we discuss the use of a modal domain optical fiber sensor (MD sensor) as a component in an active control system to suppress vibrations in a flexible beam. An MD sensor consists, roughly, of a laser source, an optical fiber, and detection electronics. The basic operating principles of this sensor are reviewed and a model of this sensor is derived. It is shown that the output of an MD sensor is proportional to the integral of the axial strain along the optical fiber. Since we use a significant length of fiber for sensing, this sensor is called a distributed-effect sensor. When an MD sensor is attached to, or embedded in, a flexible structure, it will sense the strain in the structure along its gage length. Here we integrate the sensor model into the model for a flexible structure. Based on this system model, a control system with a dynamic compensator is designed to add damping to the low order modes of the flexible structure. To verify the modeling procedure an experiment was conducted. The experimental setup consisted of a cantilevered beam with a piezoelectric actuator and an MD sensor. A simulation of the experiment was developed based on the component models. It is shown that experimental responses closely match simulated responses for both open loop and closed loop tests. The experiment also incorporated several recent advances for practical MD sensor implementation including lead-in/lead-out insensitive fibers and elliptical core sensing fiber.