Established in 1880, Bennett Opie is a private, family-owned business based in Sittingbourne, Kent. The company manufactures a wide range of products, including pickled walnuts, cocktail cherries, lemon slices and luxury bottled fruit such as pears and peaches, as well as organic sauces. Most products are packed into vacuum-tight jars with metal lids.

There are three main filling lines at the Sittingbourne plant, which between them run continuously for 10 hours a day, 4 to 5 days per week. Empty jars are fed into each line, where they first pass through a jar cleaning station. Next, the jars are fed to a spice dosing system (if the product requires this) and then through a solids filler, where the jars are filled at high speed with fruits or other solid foods. The jars are filled with a liquid preservative, then transferred to a metal detector system that checks each jar for traces of metal. Towards the end of the line, a metal lid is screwed onto each jar. The final stage involves each jar lid passing through a vacuum integrity check or “dud detector”, which is performed by a ‘vacControl’ non-contact eddy current measurement system supplied by Micro-Epsilon, installed on each of the three filling lines.

 

Vacuum integrity

A key issue with regard to set up times is the vacuum integrity check on each jar lid. This inspection is necessary to ensure that the jar is correctly sealed and that no bacteria have entered the product during production. James Jennings, engineering manager at the plant, explained: “Before installing the first two Micro-Epsilon systems in 2005, we had to use special compressed air blasters to remove water from the jar lids before they could pass through the original dud detection machine. This machine used optical sensors to check the tightness of the jar lids. However, we soon realised that the machine could not measure accurately if the colour of the lid was black. As most of our lids are now black, we needed to look for an alternative measurement solution that could handle up to 200 jars per minute.”

At that time, says Jennnings, manual intervention and inspections were required on each filling line. A batch of jars with defective lids may build up until a stop button was pressed or the jars would be left undetected. There were no automatic stops or alarm systems in place to detect ‘bad’ jars. During the Christmas shutdown period in 2005, Bennett Opie installed two vacControlmeasurementsystems from Micro-Epsilon. A third system was installed in August 2010.

 

Few engineering issues

“We installed the first two dud detector systems from scratch within just three days,” said Jennings. “This work included mounting the vacControl systems on some stainless steel tables that we’d designed and fitting an ejection table for each line. The systems were up and running with few engineering issues. In fact, since installing the first two dud detectors, we’ve only had to re-calibrate the systems twice in five years, which is pretty impressive.”

Micro-Epsilon’s vacControl system uses a non-contact inductive sensor that is unaffected by water or by the colour of the jar lid.

The inductive sensor, which is positioned approximately 3mm from the target (lid), measures the lid deflection caused by the vacuum inside the jar. The sensor scans the lid shape while the individual jars pass the measuring point. The microprocessor unit records the measurement values and uses these to calculate the lid deflection as a function of the internal pressure. The system then compares the values with a pre-set deflection value and decides about the tightness of the jar lid. If the lid deflection is not large enough, an eject pulse of adjustable length is generated. This pulse controls a sorter, which separates the jars into ‘good’ (sealed correctly) and ‘bad’. Bennett Opie no longer requires compressed air blasters to remove water from the jars and so cost savings have already been made.

 

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