System for Inline Detection of Cherry Depitting

In typical industrial cherry depitting machinery approximately 100-150 cherries are depitted simultaneously with a cycle time of 1-2 seconds.

© Photo FhG IIS

Signal of the acceleration sensor according to an axis of the impact of a stone.

© Photo FhG IIS

Signal upon impact of pulp and juice on the spring steel.

Depitting is not always successful though, so  it is possible for a part of a pit to remain inside the cherry. Eating a cherry with a partial pit remaining in the fruit can result in personal injury of the consumer. To minimize this risk, the depitting process can be monitored, and not successfully depitted cherries removed from the product stream.

Solution

Pits in cherries can not be detected with conventional non-destructive testing techniques like e.g. X-rays. Instead, an alternative solution was chosen by monitoring the depitting process itself directly, and determining whether or not the whole pit has been ejected from the cherry. The depitting is performed by a piston ejecting the pit while holding back the cherry with e.g. a rubber ring.

The impact of the ejected pit on a target is measured using an acceleration sensor and a detection unit. Each detected pit is reported to the machine control supervising the depitting process. If the pit is not detected on the target, the respective cherry is removed from the product stream.

A study was performed depitting cherries and detecting the pit impacting an acceleration sensor mounted on a spring loaded steel target. Successfully depitted cherries cause a specific deceleration curve when impacting the target with significantly different curves for whole pits, partial pits and pulp.