Large amplitude point-vibration measurement with optical-fiber moiré-based technique

We describe a technique that is used for the real-time measurement of the vibration of an object point. The technique can be used when the vibration is characterized by a large amplitude, i.e. several millimeters. The technique has additional advantages that it requires no special surface treatment and is insensitive to object in-plane displacements that are small. In this technique an object point is illuminated by a small diameter beam (at an angle) that is structured with straight parallel fringes. The illuminated object point is then imaged onto a Ronchi ruling. The total light transmitted through the Ronchi ruling is then used to recover the vibration of the object point, in real time, by using well-known servo techniques.