Second Generation Impact Force Response Fruit Firmness Sorter

Abstract

A probe-type sensor was developed to measure the impact response of fruit conveyed on a packing line and predict firmness. The impact probe consisted of a machined aluminum mass connected to an air cylinder, with the fruit struck on the side from a fixed distance. Peak acceleration of the mass during impact was used to predict flesh firmness measured by penetrometer. Static tests on commercially grown Bartlett pears gave a correlation between peak acceleration and penetrometer firmness of 0.83. The prototype handling system consisted of a feed belt for singulation, an inclined chute for alignment, a sensor belt for spacing and lateral stabilization prior to impact, and a pneumatically activated gate to separate the fruit into two firmness classes. Dynamic tests on pears loaded singly onto the feed belt showed a correlation of 0.84 between peak acceleration and penetrometer firmness. Handling performance with pears continuously loaded onto the feed belt showed that 97% of the fruit were properly aligned at the time of sensing, 86% of the fruit were singly spaced, and 98% were properly handled by the segregation system after sensing. Firmness classification errors for removing soft fruit were 14% on soft fruit and 37% on firm and hard fruit. Similar tests for removing hard fruit gave errors of 13% on soft and firm fruit and 51% on hard fruit.