Automated sorting of pistachio nuts with closed shells.

An automated machine vision system was developed to identify and remove pistachio nuts with closed shells from processing streams. The system includes a novel material handling system to feed nuts to linescan cameras without tumbling. The camera output signals are input to digital signal processing boards which extract image features characteristic of closed and open shell pistachios. The classification accuracy of this machine vision system for separating open shell from closed shell nuts is approximately 95%. The system has a throughput rate of approximately 40 nuts per second and cost of about $15,000 per channel. This throughput and cost is comparable to color sorters used to remove other pistachio defects. Currently, closed shell pistachio nuts are removed by mechanical devices. These devices also have a classification accuracy of about 95% but damage kernels in open shell pistachios by “pricking” them with a needle. The needle hole can give the appearance of an insect tunnel and cause rejection by the consumer. The newly developed machine vision system is a non-invasive inspection method.