Weighcheckers are the Electronic Inspectors conceived to measure the weight of packs, clusters and cartons into Food and Beverage Packaging Lines. They exist in several types but we’ll consider in the following just a particularly simple version based on:
- constant speed motor;
- no one encoder;
- one trigger;
- four load cells;
- open pack safety.
Refer to the figure on side showing one of these devices. It does not uses Shifting-Register principles: only one pack has to exist on top of the (green colour) conveyor). This implies that a prior, (here not shown) Conveyor always has to exists before the measurement area shown in the picture on side, before its trigger. Purpose of this faster additional Conveyor being the separation of the incoming packs, so to assure only one of them shall infeed following inspection area.
Any of the simplest, economic and efficient designs for a Weigh Checker (FT-System srl). The model shown on side has a constant speed motor, no Encoder and 4 load cells, whose independent measurements are combined and evaluated to derive the pack weight
Four independent weight measurements are executed, by 4 load cells interposed in between the (green-colour) conveyor and the base plate, after a delay time counted after a pack starts to obscure the trigger photocell. Results averaged to derive a single value representing pack’s weight. An additional photocell, over the trigger one, acts as “open pack safety”, forcing the reject of the pack if encountered too high, i.e. due to non closed sides. Rejectors are mono-cylinder type, on a conveyor immediately following the Weighchecker, controlled by a 24 VDC output.
For a model like the one shown above, the standard deviation of the measurement results around 3 grams, when referred to packs weighing 7000 grams whose speed is 800 mm/s. Then, precision results so high that a pack (3 x 4) of 12 containers 500 ml each, where only one is semi-filled (lost product), can be safely identified and rejected.
These inspectors are not second checks for fill level or content: their main purpose is to verify:
- completeness of the pack, after a Carton Packer machine;
- liquid content of the pack, considering that a container can be always damaged after the
last fill level inspection and before the ending phases of the Packaging Line.
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