Fieldbus modules connect 120 drives in pallet conveyor system

PCA Roboter- und Verpackungstechnik, located in Southern Germany, specialises in customised palletising and packaging conveyor systems. The company primarily serves the food and beverage industry, but also works with other industries such as chemical and pharmaceutical manufacturers, and the consumer goods industry.

In 2010, PCA received an order for its most complex project to date: a major food producer needed a 200m pallet conveyor system with a capacity of up to 80 pallets per hour. Some 90m of this system was going to be located in a cooling tunnel. Along with the conveyor system, PCA supplied both a packaging system and seven palletising lines.

After leaving the palletising system, the pallets containing fresh produce at 10degC reach the cooling tunnel, where cooling units chill the air to -10degC. As the pallets of fresh produce move slowly forward through the tunnel, their temperature is lowered to 2degC. Care is taken to ensure the produce is not frozen during is journey. Upon exiting the cooling tunnel, the pallets are either stored at -24degC in a deep-freeze warehouse or transported to the shipping department.

Conveyor line speed is controlled by means of 120 drives, with the motors controlled via Murrelektronik Cube67 RS232/485 modules that each feature four digital I/O ports connected to light barriers for detecting the position of the pallets.

The target temperature is selected by a preset time. There are two conveyor racks in the cooling tunnel: the left track has two pallets moving as a set while the right track is designed as an 'express track'. Destinations and other data required for the transport are stored in the system's control software.

Benefits of fieldbus technology

In total the system covers a very long distance, so the decision had to be made whether to use conventional technology or choose a bus system. The conventional method meant having a frequency converter in the cabinet and wiring the drives with very long cables routed from the cabinet to the drives. John Price, the UK Sector Manager for Food, Beverage and Packaging, explains: "The decision to install a Profibus solution was made very quickly since a space-saving solution was required for controlling the drives."

Following initial consultations with Murrelektronik's system specialists, PCA was confident that Murrelektronik's fieldbus technology, specifically Cube67 (pictured right), would be the most economic option for a decentralised installation.

John Price explains: "Because of their compact design, Cube 67 modules can be easily protected from damage with simple means, like stable edge protectors. Another prerequisite for the application in the cooling tunnel was being IP66 compliant. Cube67 modules, with their IP67 rating, meet these requirements."

Rapid, faultless wiring

Five months after the project started, PCA was able to set up and test the conveyor system in its own production hall and demonstrate its capabilities to the customer. Four months after the demonstration, the system was shipped, assembled at the food manufacturer's site and put into operation. Dieter Hubner, the managing director of PCA, explains: "The assembly and set-up time took about four weeks, and the complete electrical set-up at the customer's site took one week. Such a short time for such a complex system with a lot of data handling was possible because of Murrelektronik's preliminary work. Thanks to the plug connection technology we were very fast. All we had to do was install the connection cables; everything else was ready. As the drive was pre-wired, we only had to connect the Cube67+ bus node with pre-wired cables to ensure faultless wiring."

Follow the link for more information about the Cube 67 distributed I/O system and other products and services from Murrelektronik.