Material Storage, Blending and Batching.

On behalf of a major food additive manufacturer, a leading materials handling company contracted Advanced Control Systems Ltd to provide a system that would control material storage, handling, blending, batching and finished product packaging to food industry standards.

The system design took account of the manufacturers legal obligations. These include due care not to have incorrect formulations of finished product, or contamination by foreign bodies. Ingredient tracking and traceability, coupled with accurate weighing were also important design criteria.

The supervisory computer, bar code labelling PC, production office PC and seven plant floor operator panels are networked using TCP/IP. The operator panels are industrial PCs each with an attached bar code reader.

Control of 42 motors, divertors, slides, weighing and so on is carried out by a Programmable Logic Controller. The PLC has 480 digital and 24 analogue signals attached to it.

Products are formulated from ingredients held in fifteen bulk storage silos and a minimum of 1,000 other ingredients delivered in either bulk form or a variety of cartons or bags. Tankers delivering bulk ingredients for storing in the silos enter the plant over a weighbridge. The nature and quantity of the material is entered into the supervisory computer, initiating an import transaction. The data base is checked for existing stock of the material, and to check that there is sufficient spare capacity to take in the intended delivery quantity. After unloading, the tanker is driven back over the weighbridge and the entry/exit weight difference gives the actual amount of product delivered.

If the ingredients is delivered in either cartons or bags, and if these containers are bar coded, this is scanned and the type, quantity and reference code are stored in the data base. Where larger bags are pre-packed into smaller sacks, the system generates a bar code label giving product type, batch code, use-by date and exact weight. These details are also entered into the data base.

The automation system controls a production facility of seven mixing vessels. Five pneumatic transfer lines feed the bulk ingredients from the silos to each of the seven mixers. Production is forward planned, and the system issues a printout of the bagged ingredients that need to be moved to each of the bag tip stations associated with each mixer, in order to meet the recipes for up to 30 mixer runs.

Each run consists of a number of batches of a certain recipe, containing particular ingredients of given weights. Recipes are loaded into the systems file server through the supervisory computer or over the network from the production managerís office. Production schedules and mixing schedules can be dynamically re-allocated, using the supervisory computer, should operating conditions change or emergencies arise.

Every employee has a certain level of security clearance, ranging from sack tip station operator to super user. The super user is empowered to make system changes via the supervisory computer. Personnel identification and clearance are held on bar coded security badges. Mixer station operators log on to the system using hand held bar code readers attached to each of the plant floor operator panels. The panels display the type, and start time, of the next run.

Silo ingredients are transferred, weighed and loaded under system control. Operators use the hand held bar code readers to identify the correct sack selection to the computer. The system then unlocks the door of the sack tip station, allowing the operator to add the ingredient.

In addition to control of stock levels and stock movement, the system records and reports production data, alarm states and plant utilisation. Preventive maintenance scheduling is then based on this utilisation data.