Manufacturers produce microbore tubing in a broad range of sizes for different medical purposes. Whatever the size, microbore tubing requires a rigorously precise and consistent production process. One particularly delicate step occurs at the end, when long sections of newly extruded tubing are wound around spools. By carefully aligning layers around a hard core – just as thread is wound on a sewing spool – manufacturers maintain the tubing’s proper shape until it is unwound to make medical products.
Tension is a major quality-control issue in the spooling process. If the tubing is too taut, the plastic can stretch; if it’s too loose, it can warp. Either effect can ruin the product.
Challenge
With the need for optimal tension control and several other features firmly in mind, an unidentified medical-device company tapped CKC Engineering to design and develop a custom microbore tubing spooler machine for a new extrusion plant. Based in San Francisco, CKC provides custom equipment solutions for clients in the pharmaceutical, medical-device and drug-delivery industries.
“Often, device makers will approach us to provide automated equipment for a new production line, and usually the client is looking to enhance the level of automation on the new line,” said Carl DiPietro, vice president and controls engineering manager at CKC Engineering. “In this case, the client stressed the need for a closed-loop electronic control system to govern its tube-spooling process.”
The application required multi-axis coordinated motion, and closed-loop control of the tubing tension by a proportional-integral-derivative (PID) feedback mechanism. Closed-loop control provides far greater accuracy and repeatability than a manual open-loop system, which depends on the operator’s judgment and intuition about how much to adjust the output on a tensioning device.
“The main goal was to create a system that would operate at an extremely low tension set point, while automatically handling tubing coming in at varying speeds and tensions,” DiPietro explained. “A complicating factor was that the client also wanted two spools in the system, so that the tubing could be quickly switched to an empty spool on the fly.”
Versatility was another requirement. The machine needed to handle more than 100 different extrusions and their specific recipe parameters. It also needed to fi t and accurately fill different-sized spools. All these capabilities needed to come in a machine approximately the size of a small refrigerator. That way, operators could move the spooler between extrusion lines and out of the way when they were not using it.
CKC choose the CompactLogix 5370 controller, along with three Kinetix 350 EtherNet/IP servo drives, as the control platform for the new tubing spooler machine.
“By coupling the Logix controller with the Kinetix 350 drives, we got the high-performance, integrated-motion package we needed in a small footprint,” said DiPietro. “The new products using EtherNet/IP also offer a significant cost savings over the SERCOS platform, which previously was our preferred platform for coordinated motion.”
The machine operates via closed-loop tension control using a high-accuracy tension sensor to ensure the tubing is not stretched or flattened during the spooling process. A traverse axis is electronically geared to the operating spool, such that it travels at the correct speed to smoothly lay the tubing, even as the spool speeds up and slows down to maintain the optimal tension. Optical sensors enable the traverse system to detect the edge of the spool and reverse direction – allowing multiple spool sizes to be used interchangeably.
“The Rockwell Automation technology provided the tight integration and communication our application required,” DiPietro explained. “The combination is unique, because the drive uses the same programming code as the controller. That single programming platform, Rockwell Software RSLogix 5000, dramatically decreases development and commissioning time.”
The RSLogix 5000 design and configuration software helped the CKC team develop the motion-control code in a modular fashion, so that they could reuse the code in future projects to drastically reduce development time.
EtherNet/IP provides even more simplicity. “The ease of integrating the HMI, PAC and motion components on the single EtherNet/IP network reduced design time and simplified debug,” DiPietro said.
Results
The new custom-built tubing spooler accommodates over 100 different extrusions, and enhances the quality and repeatability of the process by accurately controlling the tension.
DiPietro believes the new Rockwell Automation products decreased programming and commissioning time by 25 percent. In addition, the component cost was reduced by 25 percent compared to the SERCOS platform.
“The CompactLogix controller, paired with the Kinetix servo drives, gave us all the capabilities the application required,” DiPietro said. “Going forward, this combination gives CKC Engineering a standard platform for any motion control application.”
