Requirement:

As the machine required by Dew Valley Foods would be dealing with a frozen food product, the machine's reliability was of paramount importance, as was hygiene and hazard control. For Newtech, the machine was the biggest and most challenging it had tackled, requiring not only an innovative design of stacker for 'difficult' products, but also one that would work at high speed. The machine had to be flexible enough to deal with formatting bacon into packs of different sizes, and of course had to meet all the hygiene requirements of the food industry.

Needing an effective control system for an innovative new design of food handling machine, Wisbech-based Newtech turned to Omron for a solution. Working together, the two companies developed and proved a specification that would meet the customer's requirements.

Omron Solutions:

The machine uses a control system built around 14 servo drives - the majority used in the stacking operation - and 22 inverters, all under PLC control.

"The key to the design was the stacker," says Newtech Engineering Manager Phil Thompson. "We had to prove not only that this could work, but that it would cope reliably with the throughput speed of the bacon, with the customer previously relying on a labour intensive manual stacking operation. The bacon slices go through cooking and freezing processes, and are presented to our machine in four lanes. The speed of throughput meant the stacker needed to be able to handle three slices per second."

With frozen bacon being a particularly tricky product to handle, significant design effort also went into ensuring the machine would cope with it reliably. Constant jams or downtime simply would not be acceptable in the handling of a frozen product, which, for hygiene and hazard control reasons, could only be on the line for a fixed period of time. In operation, the frozen bacon is presented to the machine in four lanes. The first operation is to check each slice. Any incomplete slices are immediately rejected. A combination of sensors is also used to detect any slices that are at an awkward orientation that could cause problems for the stacker, and these are separated from the main lines.

With each lane going to a stacker, sensors count the required number of slices onto the stacker, which in turn indexes the formatted slices onto a second conveyor. A flip conveyor then merges the four lines into two.

The combined slices are then indexed to a checkweigher. Here, any underweight combinations are diverted to a separate line, where the weight can be made up manually. Bacon stacks that pass the weighing operation are then indexed to a station where they are made up into packs of the required size, before being sent for packaging in the thermoformer.

HMIs provide the operator interface to the machine, allowing parameters such as pack sizes to be entered for each batch, and communicated to the PLCs. The PLCs can be linked to a PC to provide batch reporting facilities.

The machine was designed in a modular fashion, and assembled in two separate sections either side of the checkweigher, which was sourced from a third party supplier, with the PLCs networked to provide effective synchronization. With available space for control equipment limited, and with the requirement to minimize cabling, extensive use was made of distributed I/O. All components and enclosures are protected to IP65, and the machine is constructed in all stainless steel and designed for easy cleaning.

Newtech chose Omron because:

"This has been our biggest job to date," says Mr Thompson, "and uses some highly innovative design. Working with Omron, and building in their expertise and advanced technologies, we have built a highly capable machine designed to operate reliably for 20 hours a day."