Measuring Vibration of Cylindrical Surfaces using a Continuous-Scan LDV

摘要

Measurement of vibration "operating deflection shapes" (ODSs) on cylindrical or conical surfaces is difficult with optical techniques, because of the restricted angle of view. Point measurement transducers such as accelerometers, on the other hand, can provide extensive coverage, but with poor spatial resolution. This paper proposes two techniques using a continuous-scan LDV which can be used to give full area coverage on such components. In the first technique, the structure is mounted on a stand which is oscillated, typically, at 0.3 Hz, over +-180°, to provide a scan in the circumferential direction, with a straight line scan parallel to the axis of rotation. Analysis is identical to that for a rectangular scan, and gives the ODS as a 2D polynomial series. The second technique uses a fixed-point LDV with a continuously-rotating 45° mirror to provide a circumferential scan, the mirror being simultaneously translated, sinusoidally, along the axis to give a scan on the inside of the structure. Analysis is the same as that for a spiral, circular scan on a vibrating disc, and gives the ODS as a Fourier series in the circumferential direction and a polynomial in the axial direction.