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Motion System Design

Load cells speed bottle filling

Digital load cells with high-speed dynamic weighing capabilities make it possible to fill baby bottles with formula at a rate of 10,000/hr, about three per second.

The baby bottler is manufactured by Krones AG, Moline, Ill. It incorporates 16 load cells in a single carousel for weighing. Empty bottles move into the rotating carousel, fill, get check-weighed, and move out. Load cell transducers sample bottle weight during filling at a rate of 100 measurements/sec until the system detects the target weight.

One problem with this setup is vibration during filling. Either electronics must filter or adjust for the vibration, or vibrations must settle out before the weighing operation. Settling times are difficult to accommodate in the high-speed operations needed to hit production goals.

The weighing system is from HBM in Marlboro, Mass. FIT (Fast Intelligent Transducer) electronics let users download settings and adjustments to the weighing processes via an RS-485 serial bus. Up to 32 load cells connect to a single bus system, and all parameters store in EEPROM to guard against power failures.

The bottling machines use a type PW2/H3R4/10kg load cell, which can make up to 100 measurements/sec. Each load cell sits in a stainless steel housing, hermetically encapsulated to handle the harsh environment of food manufacturing plants. The load cells don't need a trigger signal to initiate a measurement. The devices themselves offer a 2 kg tare load, a 300 g to 2 kg life load, and a standard deviation of 0.5 to 0.7 g.

Krones uses a similar weighing system on a soybean oil operation. Each of these filling machines has 72 FIT load cells per carousel. The machine can fill as many as 38,000 bottles/hr. The machine runs for 22 hours daily and needs only two hours for cleaning. This particular operation took advantage of the software program supplied with the load cells. The program was used to analyze the behavior of the filling procedure over time, which helped engineers in optimizing the mechanical system.

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