- July 01, 1996, Mykytiuk, Andrew
A new MagneTek AC drive gives Kanzaki Specialty Papers the chance to evaluate it against DC units, and the results make AC look good.
Kanzaki Specialty Papers, Ware, MA, recently completed the installation of a coating and laminating line incorporating one of the first full-scale all-vector drive systems in the converting industry, supplied by MagneTek.
The Worldwide Process Technologies pressure-sensitive line was installed and commissioned in May 1995 and is now in full production, providing rollstock for label converters. The new line includes a proprietary coating head design and an Advanced Systems flotation dryer with an exceptionally long dryer section for high-speed processing of p-s adhesives. It utilizes a distributive-controlled system of 16 MagneTek VCD 723 vector control drives applied to individual sections of the coating and laminating line and linked by a coaxial ARCNET LAN.
KSP ordered the most advanced AC drive technology available for this high-performance application requiring precise control of motor speed and torque. The VCD 723 provides Kanzaki with a method to utilize AC technology in a traditionally DC application without giving up LAN communication and control capabilities.
These drives allow Kanzaki to take advantage of the cost and maintenance benefits of AC motors and drives, as well as power efficiencies and utility rebates, while meeting the rigorous demands of a tension-controlled production process. Such precise control previously was thought to be available only from DC drives and motors.
Because Kanzaki utilizes both DC and AC drives at its Ware facility, chief electrical engineer Chad Sherwood is in a unique position to compare the two drive systems. He has noted a considerable maintenance cost benefit with the vector drive compared to the DC drives and motors on comparable machines. "With no brush maintenance for the vector drive, thousands of dollars per year will be saved without sacrificing precision control," says Sherwood.
"Our maintenance program is very labor-intensive, and we actually contract some of this work out," says Sherwood. "I have monthly maintenance billings of $600 for each DC machine." He also notes that the brushes on DC machines must be seated right, and the springs that hold the brush in place must be checked for proper tension. "All that is eliminated with the AC vector drive, because there are no brushes. This is a major benefit."
Accuracy from Matched Drive and Motor
Kanzaki's precise control is accomplished in a number of ways, reports Sherwood. First, the vector drives and motor combinations are matched. Motors are energy-efficient MagneTek Spartan VCM motors with high-pulse-count digital encoders for extremely accurate speed control through feedback to the motor model stored in the drive's onboard microprocessor.
Accuracy is said to be further enhanced by thermistor temperature feedback, used to calculate motor slip for improved low-speed torque performance. Precise control of low-speed torque enables Kanzaki to accurately control line speeds during low-speed thread-up operation, full roll-to-roll splicing on the unwinds, and automatic roll-to-roll transfer on the winder.
"Previously, DC drives were required on machines such as this because of torque requirements at lower speeds, and, with older AC, the variable-frequency technology used to have poor torque performance at low speeds," says Sherwood. "We realize comparable or better low-speed and low-torque control with MagneTek's AC vector control technology."
Regeneration, demanded on this type of exacting, tension-trimmed process line, was heretofore assumed to be only in the domain of regenerative DC drives. The solution to the regeneration problem was provided by a single, main AC-to-DC converter installed to handle incoming 460VAC power and supply DC to all the vector drives via a common DC buss.
This allows "regeneration" and braking for the running tension control scheme. While load cells measure the actual web process tension, each sending a trim signal back to its drive, regulation accuracy is enhanced over standard braking modules and/or resistors.
Additionally, braking modules and resistor banks were supplied to handle normal and emergency stop load simulations. This scheme provided for tension regulation equivalent to that achieved from a regenerative DC drive system.
"With a mechanical braking system on the unwinds, what you do with all that energy necessary to maintain the required tension is turn it into heat and release it into the atmosphere," says Sherwood. "With the MagneTek system, we now have 50-horsepower motors on our unwind spindles, and we're taking that previously lost braking energy and reintroducing it back into our other line drives. I was trying to gauge what kind of power consumption the AC drive would have, and I would say the regenerative AC drive uses 25 percent less electric power, just because we're using the 50-horsepower motors as generators. It's a world of difference as far as efficiency goes."
LAN Communication: PAC Software
MagneTek's VCD 723 utilizes the same operational platform as the company's digital DC system drives, the MicroTrac LAN. This local, distributive regulator takes the standard vector and provides local distributive control for each section. Drive functionality is accomplished through MagneTek's PAC (Programmable Application Control) software.
As a Microsoft Windows-compatible software package, PAC software is extremely user-friendly and easy to understand, says Sherwood. "The software includes a supervisory control package. We set up the machine, adjust all the parameters, and then upload the parameters and save them. The next time we run the same job, instead of going through and resetting 50 parameters for drying, speeds, tensions, and so on, we can press one button to download our saved parameters from the database into the PLC, and the machine is ready to ran." Drive-to-drive, drive-to-PLC, drive-to-operator control panels communication is all handled over the ARCNET LAN-based network.
Interconnection between nodes is through a single coaxial cable, which eliminates hundreds of wires. Sherwood points out that elimination of the wires, connections, and accompanying problems significantly reduced installation time, simplified the startup and troubleshooting, and will help in minimizing long-term maintenance.
The drives allow operator interface from the machine via touch screen operator panels, through pick and Panelviews. The drive appears as a "remote rack" through the Gateway interface. This allows reliable, fast communication right on the input/output substructures for real-time, instantaneous response for machine operation.
Kanzaki engineers and technicians underwent intensive training at MagneTek's in-factory schools at New Berlin, WI. This training was reinforced during startup at the Ware facility. "MagneTek provided training at their facility before the machine was ready for startup so we'd have a good idea of what the equipment consisted of," explains Sherwood. "They had simulation at their facility for training, so our engineers and technicians were able to program the drives and help us get familiar with the equipment. We were given the opportunity to experiment and try some things you really wouldn't want to do on a production machine. As a result, we had no trouble with startup or operation."
Sums up Russell E. Granquist, Kanzaki president, "This highly sophisticated all-vector drive system is anticipated to give a high degree of accuracy, control, and runnability in the production of variable information processing and product-identification, pressure-sensitive products."
MagneTek, New Berlin, WI; ph: 414/782-0200; fax: 414/782-1283. Worldwide Process Technologies, Allendale, NJ; ph: 201/327-5690; fax: 201/327-5970. Advanced Systems Inc., Green Bay, WI; ph: 414/4685477; fax: 414/468-0931.
Charles E. Lincoln, MagneTek application engineer, contributed information to the development of this article.