Cool automation: cold storage system tracks product from order to delivery

Dairy Foods, June, 1999 by Jack Mans

Cold storage system tracks product from order to delivery

Nine year ago, grocery chain Giant Food in stalled one of the dairy industry's most automated cold storage systems at its Landover, Md., milk plant. Costing $15 million and including a 15,000-sq-ft building, the system handles 24,000 gal of milk per hour, all in plastic dairy cases, utilizing 20-case shipping dollies.

A year later, Giant added a state-of-the art production automation system that ties into the warehouse computer. In total, it tracks product from milk receiving through processing and filling to package delivery into the warehouse.

With this system, orders from each store are tabulated and the production and packaging schedules for each day are established. The system also tells the warehouse computer what products to pick for each store and how they are to be assembled for delivery.

Computer controls production

Each truckload of milk is assigned a code number, and that milk is tracked all the way through the warehouse and onto the truck delivering product to Giant stores. When a truckload of raw milk is received, the operator takes a sample to the lab, which must release it before it can be pumped out of the truck.

The operator then assigns a silo and the computer checks to make sure there is room in that silo for the full load. Otherwise it will not allow the milk to be pumped into the silo. If milk is assigned to an empty silo, the computer checks to ensure that the silo has been washed or, again, it will not allow the milk to be pumped to that silo.

Truck discharge pumps, which have a maximum output of 350 gal per min, are equipped with variable speed drives. The pumps start pumping at minimum output and ramp up to full speed. However, if the pump starts cavitating, the speed will be reduced until the cavitation stops.

The plant has two HTST pasteurizers. When the operator selects a raw silo for one of these, the computer sets the valves throughout the system and also checks to see that the swing connections are set properly. The computer monitors the pasteurized silos and will only allow product to be pumped from the raw silos through the HTST and into only clean silos.

Landover has seven fillers. To start a run, the operator sets the pasteurized silo, the product to be run and the package size, if it is a line with more than one package size. The computer checks to ensure that the silo contains the product selected and then sets the valves in the line and sets the filler speed in accord with the product and package size.

"The computer is set to maintain a 15-psi pressure in the line to the filler, so it adjusts the speed of the discharge pump to maintain that pressure," says Chief Eng. Pete Carrino. In practice, the pump is not required until the level in the silo drops to about 40 ft, and then the pump will come on and slowly speed up as the level drops. The computer will also slow the filler if the level in the bowl drops below the set point and will ultimately stop the filler if the level in the bowl can't be maintained. Containers from each filler are conveyed to a dedicated case loader that places containers into plastic dairy cases. This is followed by a machine that automatically assembles the cases into five-high stacks. These stacks are merged onto two conveyors feeding the cooler. A third conveyor carries stacks of products not made at Landover into the cooler.

Automated warehouse

The automated cooler handles product on four-wheeled dollies that hold four of the five-high stacks. Each of the three conveyors carrying stacks of cases into the cooler has an automatic dolly loader that places four stacks on a dolly. The computer keeps track of the stacks of dairy cases from each filler and assembles four stacks of a given product at a time to place on a dolly.

The cooler includes automated storage and retrieval cranes, high rise storage racks and computer controls as well as dolly equipment, conveyors and other material handling components. The system has an operating rate of 60,000 cases on dollies in 16 hours for a total storage capacity of 330,000 gallons.

Two computers operate simultaneously to provide redundant memory and control in case one should malfunction. The system also includes an unloader and washer for empty dollies and cases.

When the automated cooler was first installed, a worker entered the product on each dolly into the computer. The new automation system eliminated this manual entry and the computer keeps track of all product by remembering the location of each dolly at every step of the operation.

"We also replaced the PLCs with faster models that reduced response time from 2.5 to 0.03 microseconds. This reduced mechanical errors and increased throughput by 20%," says Carrino. "Next we're going to replace the VAX computer that runs the warehouse with a Compaq computer running Windows NT."

The computer accounts for products in dolly loads and caseloads. However, only dolly loads enter the system initially. Caseloads are broken down inside the system from fully loaded dollies at a rate of 1,300 cases per hour.