Measurement of dynamic deformation using a superimposed grating

Abstract

Mechanical devices are normally used under conditions of dynamic motion. Due to resonance effects, this condition produces undesired modes of vibration, which are necessary to be measured for satisfactory design. This paper describes a method to measure the temporal development of the vibrational modes in mechanical objects subjected to external vibration, by a double exposure fringe technique. A grating placed directly on the object under study serves as a carrier frequency, which enables automatic phase calculation. This grating, which is imaged by a commercial digital camera, used in conjunction with a spatial carrier fringe method for phase evaluation, allows determining the vibration deformation. This technique is suitable for the analysis of rapid transient events since no movable parts are required in the system. The obtained range of deformation by the proposed method goes from a few tenths of micrometers to millimetres.