Control system retrofit extends old labeling machine life, improving throughput 25%
By Michael Gurney
The situation was a familiar one: A manufacturer was reaching production capacity and facing the possibility of either adding an additional shift or purchasing new equipment.
Before making a commitment, manufacturers must determine if they can meet their needs using existing equipment with a simple, more cost-effective control system upgrade. Most modern manufacturing lines are mechanically sound, but they can suffer from the lightning-speed evolution of technology; their control systems become outdated in a matter of years.
In the aforementioned case, a labeling machine used to put shrink-wrap labels on plastic containers for frozen drinks was only five years old; however, it was based on a ten-year-old design. The control system used outdated hardware and software, with replacement parts and software support already becoming scarce.
The labeling machine is part of a complex production line, where the plastic containers were made on the extrusion/molding line, conveyed, labeled, palletized, packed, and shipped nationwide. The labeling process requires tight synchronization between the container and the label, as each container is individually wrapped as it is conveyed through the system.
Faced with a capacity constraint, the package manufacturer, which owns the machine designs and manufactures customized blow-molded plastic containers, could have purchased a new labeling machine. Instead, Concept Systems, Inc., analyzed the system and determined that the required performance could be achieved at a significantly lower cost by upgrading only the control system.
Multiple vendors adds to costs
At the heart of the machine's production issues was downtime associated with maintenance and changeovers. The old system used control components from multiple vendors that resulted in higher maintenance costs and burdened maintenance staff from a training perspective, as well as from a spare parts and support perspective. This meant that when the machine went down, it could lead to extended downtime. For the retrofit project, a single control system vendor was selected.
The new system consists of components from one vendor, including a programmable logic control (PLC), a servo motion controller, five servo drives and motors (for five different axes of motion), and a touchscreen PC with human-machine interface (HMI) software and diagnostic tools. The system uses fiber optics interconnections between the motion components and the PLC, and Ethernet between the HMI and the PLC. The system also uses a data highway plus (DH+) network to interface with the existing subcontrollers. This common platform allows maintenance personnel to better deal with issues as they arise.
On-the-fly tuning cuts waste
The new, closed-loop control system performs an "electronic gearing" between the system's high-speed servo motors. In electronic gearing, the motion of one axis is directly related to the motion of another axis. Motors that feed the labels are kept in lockstep with the motor that feeds the containers into the machine and spins the containers. When a command is given to increase or decrease the speed, all motor speeds are adjusted automatically to maintain the correct relationships, with electronic feedback maintaining the proper relationships.
The label must be affixed precisely the same on each container. With the old machine, when parts were replaced or if the operator needed to adjust the process, the system had to be retuned by hand. It would take several minutes to adjust setpoints using a trial-and-error process, which resulted in wasted containers, in order to re-establish proper operation. Since the older system did not display meaningful process parameters, the operator sometimes did not know which way to move a parameter to correct the process. Each machine restart wasted several plastic containers used to "prime" the machine.
The new system displays setpoint information in familiar terms (e.g., degrees of rotation), enabling easy adjustment. When changes are necessary, the system quickly adjusts the position of the label with respect to the can during the small time window between labels on the tape. The dynamic, "on-the-fly" tuning capability cuts the amount of product spoilage dramatically. Our engineer designed the new touchscreen controls to mimic those of the old system. For example, start/stop controls were displayed in the same colors used on the old panel.
Our main design challenge was dealing with the lack of detailed documentation of how the old system was designed to support the labeler functionality. The electrical part of retrofit was simplified by the use of Ethernet and fiber optics to connect the modules. The new networks made installing and troubleshooting the new system relatively straightforward: One day to dismantle the old system, and a second day to install and connect the new system.
More productivity, less waste
Although improved ease of use and decreased maintenance costs were benefits of the control systems upgrade, the most impressive advance was an increase in productivity. The package manufacturer estimates that the upgraded system provides 25 percent higher throughput, while decreasing the number of wasted containers by approximately 80 percent - numbers that met the performance specifications of a new machine.
ABOUT THE AUTHOR
Michael Gurney is co-CEO and vice president of sales and marketing at Concept Systems Inc., a certified member of the Control System Integrators Association (CSIA). For more information about CSIA and CSIA Certification, visit www.controlsys.org.