Case Study: Packaging Line Stretch Wrappers
A large, packaged food manufacturer requested the construction of a conveyor line in their plant. Referred to internally as a greenfield project, it entailed the installation of new shrink wrappers and palletizing equipment. The existing configuration in the plant had four stretch wrappers and four palletizers being shared by 15 packaging lines and the company wanted a dedicated stretch wrapper and palletizer for each packaging line. ECS was responsible for the controls on the entire system, as well as establishing communications with the stretch wrappers and the palletizers. The bulk of the work was the transfer of the pallets either down the line, or into the line and onto two different areas where they could be picked up by trucks. Phase 1 of the two-phase project had eight pickup stations and the additional four stations were installed in Phase 2. This required 73 conveyor sections- each section being about if a pallet and each section, as well as the turntables in the system were driven by an Allen-Bradley ArmorStart VFD (variable frequency drive). In total there were 84 ArmorStart VFD’s on the whole system.
The ArmorStart is a VFD that hangs on the conveyor itself and is not enclosed in a panel box. This reduces the amount of wiring required as well as avoiding the space necessary to accommodate panel boxes. Further, it avoids the need for air conditioning to cool the VFD as it operates. But the arrangement does present additional challenges and demands different safety requirements. For example, the power distribution to the VFD’s was a concern. Even though the power could be provided by way of a series of daisy chains, 15 different 480 VAC circuits were required to provide the amount of current involved.
The operator interface for the project was designated as an Inductive Automation Ignition application utilizing the Perspective Module which was new technology to everyone. An advantage with Perspective is that it can be run on tablets and possibly on a phone if wanted. So, tablets were added to the fork trucks, allowing the operators to communicate with the system. ECS Engineers developed the programming for the tablets, as well as that required for stationary monitors.
The ECS engineers did not experience any roadblocks that could not be worked around, but did face several challenges. For example, the conveyor was split to create an aisle through the middle of the warehouse. Both foot traffic and for truck traffic were allowed to use the new aisle. A transfer conveyor is incorporated into the system to link Phase 1 and Phase 2, allowing Phase 2 pallets to be transferred across the aisle to Phase 1. ECS engineers determined how to provide the power safely and incorporated (at the company’s request) a traffic gate to prevent passage when the transfer conveyor was operating. For this SICK laser sensors were used to scan the area and to shut equipment down if personnel were detected. The SICK laser scanner is about the size of a coffee pot, with a laser fitted inside that can scan the area. ECS arranged for two of these scanners to be mounted on the transfer cart and programmed to operate when the cart was moving.
A further challenge in this project was to provide the safety required, and when designing safety, it was important to consider the consequences of a power loss amidst operations. Another challenge was to communicate with the new palletizers and stretch wrappers (24 individual pieces of OEM equipment), each having a PLC. Each piece of OEM equipment sent data to the Ignition application for reporting and display purposes.
From the company’s viewpoint, the completion of the project resulted in the fork truck traffic being significantly improved. Pick up occurs at one or two locations with convenient access to those areas. Also, the introduction of the tablets allows easy access to data, to allow the identification of bottlenecks in production and the need for preventive maintenance. Data may also be collected on the conveyor system itself and on the OEM work cells to determine the performance of the individual cells.