Differential measurements using two Laser Rotational Vibrometers: dynamic backlash

The Laser Rotational Vibrometer is well suited to non-contact measurement of angular vibration on rotating targets, particularly by virtue of inherent insensitivity to target shape and translational motion. A differential measurement is proposed using two Vibrometers to allow a calculation of dynamic backlash between spur gears from relative tangential displacements. It is known that target motions, such as rotation, produce changes in the speckle pattern on the photodetector which add noise to the Vibrometer output. The significance of noise is always increased when differential measurements are required. The noise produced by the speckle pattern is apparent but the data reveals that it is possible to make the dynamic backlash measurement in this way. The dynamic backlash measurement is verified against equivalent high speed video footage, confirming the suitability of Laser Vibrometry in this application.