The application of high-speed TV-holography to time-resolved vibration measurements

We describe an electronic speckle pattern interferometer (ESPI) system that has enabled non-harmonic vibrations to be measured with us temporal resolu tion. The short exposure period and high framing rate of a high-speed camer a at up to 40,500 frames per second allow low-power CW laser illumination a nd fibre-optic beam delivery to be used, rather than the high peak power pu lsed lasers normally used in ESPI for transient measurement. The technique has been demonstrated in the laboratory and tested in preliminary industria l trials. The ability to measure vibration with high spatial and temporal r esolution, which is not provided by techniques such as scanning laser vibro metry, has many applications in manufacturing design, and in an illustrativ e application described here revealed previously unmeasured "rocking" vibra tions of a car door. It has been possible to make the measurement on the do or as part of a complete vehicle standing on its own tyres, wheels and susp ension, and where the excitation was generated by the running of the vehicl e's own engine. (C) 2000 Elsevier Science Ltd. All rights reserved.