An Examination of the Effect of Seat Free-Play on Modal Analysis Results 2003-01-1598

With the amount of adjustability present in today's automotive seat, it is a given that some form of looseness and free-play will exist in the structure. The automotive seat community is commonly faced with free-play issues; this is a significant issue where modal analysis is concerned. Free-play creates a non-linear situation, causing a violation of the linear mathematics that modal analysis is based on. Obviously, this situation is not the ideal circumstances under which to perform modal testing and analysis, but 99.9% of the time, the receipt of better samples (reduced free-play) is not a likely option, and the test must still go on. Ideally, you would want to test this structure using random excitation with a shaker to minimize the nonlinearities and provide a repeatable input force. In reality, the Product Engineer has specified an impact test because it is faster and cheaper and the Test Engineer needs to produce the best results possible while being bound to the requested test method. This paper aims to experimentally document the findings and experiences of impact modal tests on seat structures that feature significant free-play in order to provide insight and reference for those who experience similar situations. Case studies will be presented that show the influence of free-play in the seat structure and general observations will be made about the systems.