Experimental Modal Analysis on Chicken Eggs

摘要

We report as first an experimental modal technique to control egg quality. Egg quality is an important factor in the different stages of the production and marketing process. A multitude of measurement techniques has been reported which may be used as indicators for egg quality. The cost, time, skillness of the operator and the accuracy required to make the assessments varies widely. We use the dynamic behaviour of a chicken egg as indicator for internal and external egg quality. In order to understand the dynamic behaviour of an chicken egg, a total modal analysis is performed. The natural frequencies of the modes are situated between 2000 Hz and 7000 Hz. Some mode shapes are similar to theoretical shapes of homogeneous, elastic spheres. Once the dynamic behaviour is known, a test protocol is developed based on the frequency-responses, the location of nodes and anti-nodes and the variance of the measurement results in one measurement point. In a first orientating experiment, the frequency spectrum is measured during conservation of eggs under room conditions. The natural frequencies of two selected modes arised during conservation. In another experiment, 120 eggs are compressed between two parallel steelplates. The non-destructive, quasi-static deformation under a certain load is a measure for the stiffness of the eggshell. A correlation of 68 % is found between the stiffness measured in the classic test and the dynamic stiffness measured as a simple mass-spring model. Measurements of the natural frequencies offer the possibility of simple, non-destructive and rapid characterization of the external and internal egg.