Eggshell crack detection based on acoustic resonance frequency analysis

The human, visual inspection is the main quality control procedure in egg grading. Eggshells are inspected for cracks and dirtiness on the shell and for internal egg abnormalities, such as blood and meatspots. With the development of high-speed electronic grading machines (>10 000 eggs/h per lane), this human candling operation has become a significant bottleneck. Recent researchinto the automation of the detection of eggshell cracks is focused both on optical and mechanical detection principles. In this research, eggshell crack detection is based on the analysis of the acoustically measured frequency response of an egg excited with a light mechanical impact on different locations on the eggshell equator. The optimal configuration of the egg support, the location and design of the impactor and the response sensor are explored by means of an experimental modal analysis study of an intact egg. An egg with an intact eggshell responds by a characteristic frequency pattern that is highly repetitive when impacting on different places around the equator; the response signals' of cracked eggs are heterogeneous and not repetitive. This method allows a crack detection level of 90% and a false reject level of less than 0.5%. (C) 2000 Silsoe Research Institute.