Measurement of Shaft Orbits with Photographic Images and Sub-Sampling Technique

Vibration measurement in rotating machines is an important procedure in the identification of malfunctions and in the prevention of failure. In this case, due to difficulties in mounting sensors on rotating parts, non-contacting measurement methods are usually employed (interferometry, vibrometry, proximity sensing, photogrammetry). This work focuses on the development of a low cost image acquisition system capable of measuring the dynamic behavior of a rotor shaft (lateral vibration) using photographic images (full field measurement). The proposed method is based on sub-sampling techniques (reconstruction of the vibration signal by measuring long acquisition periods), and it is suitable for structures or machines whose vibrating frequencies are known (e.g. rotating machines). After image acquisition, the vibration at specific points of interest in the shaft is obtained by adopting a suitable image processing technique. Experimental tests are performed in a rotating system with flexible shaft, driven by an electric motor controlled by a frequency inverter in the frequency range of 300 rpm (5 Hz) to 990 rpm (16.5 Hz). Shaft vibration measurements are compared to measurements obtained with proximity sensors, and good agreement is observed even for small vibration amplitudes (130 μm).