New Slitter Positioning System Uses Linear Sensor to Shave Setup Time

Pulp & Paper, Oct 2004 by Edeal, David, Turcotte, Jeffrey

Linear position sensor helps a 2,000-tpd Arkansas mill improve productivity on its 18-year-old winder through reduction of overall roll size change time by 45-50%

The paper industry faces increasing demands for highquality products at low cost. To meet these demands, many paper mills must respond with a fast turnaround, which results in more frequent roll size changes.

At a 2,000-tpd paper mill in Arkansas, a key winder needed a faster and more reliable positioning system to shave off as much positioning time as possible. The existing slitter positioning system failed almost 50% of the time due to multiple factors causing it to error out during its routine. The main culprit was a photo eye feedback system, but the station positioning was also unreliable because it worked off of belt-driven encoders in conjunction with software. When the belt that these units clamped onto slipped (which happened frequently), the setup would be out of tolerance. The paper mill needed a complete controls redesign, gravitating away from the original Siemens/Electronic system to the mill standard GE 90/70 PLC.

Positioning Errors/Support Issues Drive Upgrade

The Wartsilla winder was installed 18 years ago, and its positioning system utilized technology from the 1980s that was difficult to support. The software and PLC control was difficult to troubleshoot because of its proprietary nature, and the stations used encoders polled one at a time to provide the position feedback.

In addition, these stations were belt driven, making them susceptible to slippage, and due to the control design, there was nothing to compensate for this slippage. The slitters had separate positioning solenoids for each of their elements but only one sensing device. This sensing device was a photo eye that correlated the slitter to a position on a magnetic tape measure via software. This type of design does not support rugged applications and resulted in positioning errors due to the harsh environment and paper dust.

Problems with the original positioning systems resulted in costly production time losses for the facility, and a new system was desperately needed. The basic setup time took at least 15 minutes if there were no major problems. The mill was hoping to cut down its entire setup time to somewhere near five minutes.

Orders in today's market are based on quick turnaround, and the mill routinely performed as many as eight size changes per shift. Unrelated to the positioning system, but equally important, the mill lost time unloading each new set of rolls due to the nature of the sequence.

The mill knew the importance of accurate feedback to position its slitters and stations. It also recognized that repeatable, reliable, and durable components improve mill efficiency. Some problems, such as mechanical limitations brought on by wear and tear, are hard for mills running 24/7 to address without excessive downtime. To resolve these issues, the paper mill needed dependable feedback devices that could withstand operation in harsh mechanical and environmental conditions. New position sensors from MTS, coupled with a new software design incorporating diagnostics to assist in troubleshooting, proved to be the most cost-effective upgrade.

Linear Sensors Boost Productivity for Older Winders

The Arkansas mill selected PLC Concepts/JNE Engineering, a controls integration/service specializing in providing positioning and control systems, to design the upgraded controls system. The control integrator's primary designs are based on Rockwell solutions, and many of these systems are related to upgrades on existing production equipment in the paper industry. In this case, a Cimplicity HMI and GE 90/70 solution was proposed because that is the mill's standard.

The controls integrator chose a MTS R-Series position sensor to provide position feedback within the new system. This was the only sensor that passed the extensive field testing required for the job. For newer and retrofit slitter positioning designs, manufacturers prefer the use of sensors that can provide multiple simultaneous slitter cartridge position measurements. This saves the cost of having to use multiple position sensors.

Also, position sensors that utilize magnetostrictive feedback are the only such devices that can provide up to 30 simultaneous position outputs. This is ideal for slitters, some of which might use up to 60 slitter cartridges on a single machine and require sensors with stroke ranges greater than 180 in. and up to 600 in. Further, there are more than a dozen manufacturers that have been using this technology for paper and other materials for the past five years.

The upgraded paper winder is designed to operate with increased efficiency and with less wasted time-generating more paper, more quickly. The Arkansas mill wanted to reduce the setup and unloading time, and this is a difficult task on an existing piece of equipment. The winder typically runs at the same speed, so the target is to increase how often the mill is able to run the paper. The primary goal of the new system was to increase production by approximately a 1-2% margin.