Analysis of damage thresholds in apple-to-apple impacts using an instrumented sphere

Abstract

Fruit-to-fruit impacts on commercial packing lines were simulated in the laboratory for pairs of fresh ‘Gala’, ‘Splendour’, ‘Fuji’, ‘Braebum’, and ‘Granny Smith’ apples by dropping (Hie apple onto the other from a range of heights. Bruising was generally more severe on one of the two apples, and it was quite common for only one apple to be damaged. Contact areas above 1 cm2 were closely related to bruise areas. Below this level bruising rarely occurred. Some bruises produced in apple-to-apple impacts were not visible unless the apple skin was removed. ‘Braebum’ apples required a greater drop height to produce a significant bruise than other varieties. An Instrumented Sphere (IS), 89 mm in diameter with a mass of 0.336 kg, which recorded acceleration magnitudes above an adjustable pre-programmed threshold, was used to characterise impacts onto fruit. When the results of apple-to-apple and IS-to-apple impacts were compared, it was found that the area of the larger of the two bruises produced in fruit-to-fruit impacts was directly related to the peak acceleration recorded by the IS when it was dropped onto a fruit from the same height. Using this comparison, damage thresholds resulting from fruit-to-fruit impacts were determined by analysing IS output. The implications of these results to the techniques to interpret IS output during field trials on handling systems are discussed. It was concluded that the IS can be used to identify apple-to-apple impacts likely to cause bruising in commercial packing operations, providing care is taken with interpretation of the data. © 1992 The Royal Society of New Zealand.