A Spanish customer who has been cultivating potatoes since 1963 required a Nemesis checkweigher to weigh different varieties of potatoes, all packaged in net bags.

The packages weighed between 6 and 8 kg, and the packaging line operated at a maximum speed of 60 packs per minute.

The project required collecting the packaged potatoes coming from several net-bagging machines, conveying them onto the weighing conveyor, weighing them, and rejecting them appropriately whenever they were underweight or overweight.

The first challenge was to develop a suitable spacing system for the potato bags discharged by the net-bagging machines, ensuring accurate dynamic weighing.

As for the rejection of non-compliant packages, the use of a conventional push-type reject device was not feasible due to the high risk of the rejector becoming entangled in the potato netting, which could result in a complete stoppage of the packaging line.

It was therefore necessary to develop an alternative rejection system capable of operating reliably even with a high product flow rate.

Flow Adjustment Photocells

Normally, photoelectric sensors are installed on the infeed and weighing conveyors to monitor and control the product flow through the checkweigher.

In this case, since the potato net bags are bulky and heavy, it is essential that they be properly spaced to ensure accurate weighing and smooth conveyor movement.

This is particularly important when products are fed onto the infeed conveyor from multiple net-bagging machine discharge stations. In such cases, additional photoelectric sensors must be installed at the merging points along the collection conveyor. These sensors are connected to a PLC, which controls a stop-and-go operation of the conveyor, thereby ensuring the correct spacing and timing of the packages before they enter the weighing section.

Special Rejection System for Nets

To reject potato bags that are either overweight or underweight, a trap-door rejection system was adopted. When activated, the trap door opens, causing the non-compliant bags to drop into a reject bin.

Compared with conventional push-type reject systems, this solution enables rapid and reliable rejection while keeping pace with packaging lines operating at speeds of up to 60 packs per minute, without any risk of becoming entangled in the netting. The system has been specifically designed for medium-weight products.

The Nemesis solution integrates easily into existing packaging lines.
Its extremely compact design allows feeding, weighing, and rejection operations to be performed within less than 1.8 meters of total machine length.
The use of robust 300 mm diameter rollers beneath the conveyor belts ensures precise and reliable product handling downstream of the production line.
Thanks to the special trap-door rejection system, net bags are rejected in a firm yet gentle manner. The product itself is not touched, preventing damage and eliminating any risk of entanglement with reject devices. This makes the system particularly suitable for rejecting netted citrus fruits and other soft fruits.
When required, the checkweigher is capable of achieving a weighing accuracy of up to 2 g.

Weight control of food packaged in nets

Product collection from netting machines with anti-entanglement rejection

THE CHALLENGE

Flow Adjustment Photocells

Special Rejection System for Nets

THE BENEFITS

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