Development of a laser-based automated mechanical mobility measurement system for one-dimensional experimental modal analysis

A laser-based automated mechanical mobility measurement system has been developed that can obtain a very high spatial resolution of frequency response functions (FRFs) for experimental modal analysis where one-dimensional structural motion predominates. With this system FRFs are measured and recorded in a format that is readily imported into a popular modal analysis software. A scanning laser Doppler velocimeter is coupled to a multi-channel FFf analyzer system for efficient data collection and management of spatially distributed FRFs. The objectives in designing this measurement system is to take advantage of the laser's non-contacting nature, its high spatial resolution, and its fast point-to-point movement. By using the scanning capabilities of the laser, experimental mobility FRF data can be collected in those structures that have dominant response in one direction at up to 16,000,000 positions. Moreover, the laser does not mass load the structure thus making the structure time invariant unlike "roving" accelerometers. The design and implementation of this automated mechanical mobility measurement system is presented. Instrumentation interfacing and control issues as well as software development issues are addressed in this thesis. Procedures required to implement the laser-based measurement system are presented. The performance of the laser-based system is presented along with an illustrative example of its use on a free-free rectangular plate where the vibration response is primarily in one direction.