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MULTIPLE PAPER ROLLS on COMMON INVERTER



MULTIPLE PAPER ROLLS
on COMMON INVERTER


Criteria

General

Many web processing systems incorporate large numbers of paper carrying rolls (Paper Rolls) to effectively
transport the web (sheet) from one processing point to the next, and to effect the appro priate entrance and exit web
path geometry for the various web processes.

In many such applications, it is important to provide a method for driving most or all of these paper carrying rolls
(Paper Rolls), for two(2) primary reasons:

To relieve the web being processed from providing the surface force (strip tension) otherwise necessary to drive
these rolls. This would be particularly important with webs requiring relatively low tension levels.
To reduce the roll-surface to web-surface slippage and potentially consequential web-product scratch marking.

AC drives can provide a very effective solution for optimizing the trade-offs between effectively satisfying the above
two (2) considerations while reducing the number of drives required - thereby also reducing the costs and long term
operational issues associated with supporting each Paper Roll with a dedicated drive control.

AC motors will inherently operate at motor shaft speeds synchronous with the frequency of their applied voltage,
within the slip speed characteristic of the respective motor. As such, there are a number of web transport zones
which can be effectively driven with one (1) inverter control powering multiple Paper Rolls.

The following are the established criteria for configuring multiple Paper Rolls powered by common inverters.

The AC drive inverter product must be a Scalar / Volts-per-Hertz control, as opposed to a Vector or Flux Oriented
product. This is because Vector and Flux Oriented AC drive products will only be effective on multiple-motor
applications if the respective motor shafts are mechanically linked.
All of the grouped Paper Rolls must be contiguous relative to their sequence of contacting the web. That is, there
can be no other transport or processing equipment influencing the web between the first and last inclusive Paper
Rolls. See point 6 below relative to Spreader Rolls.
All of the grouped Paper Rolls must be of the same nominal outside diameter (OD).
Only one (1) of the grouped Paper Rolls should realize significant web wrap angle. This is a relatively subjective
criteria, and will vary depending on the web and process. The point is that wrap angles should have some degree
of consideration.
If a Tension-Transducing Roll is a candidate for inclusion in a multiple-roll group it should at either end of the group
and not inside the group. Per item 4 above, when a Tension-Transducing Roll is included, it would normally
delineate one paper-roll group from another.
The Paper Roll with the greatest wrap angle of the group should have its speed regulated via an encoder-based
closed-loop speed regulator, responsible for the final frequency output of the inverter.
Cross-Machine Spreader Rolls of any type must be excluded from any Paper Roll grouping and supported with
dedicated drive controls, even if their ODs are common to the grouped Paper Rolls. Also, a Spreader Roll within a
series of Paper Rolls would interrupt the contiguous criteria per point 2 above.


MULTIPLE PAPER ROLLS on COMMON INVERTER
.
The following are the potential benefits of this multiple -Paper-Roll-per-inverter approach:

Costs of purchasing and installing the otherwise required dedicated drive controls.
Reduced drive system equipment real-estate.
Reduced drive system start-up time and costs.
Increase in Mean-Time-Between-Failure - due to fewer inverters.
Lower burden on the drive system communications network.
Lower probability of operators introducing unnecessary and often confusing Paper Roll speed adjustments. This of
course is assuming that the above six (6) configuration criteria are maintained.

For web transport processes which require rapid acceleration and deceleration rates, there is one potential negative
consideration when controlling multiple paper rolls with a common inverter supply.

Because of the need to use a Scalar Volts / Hertz drive with multiple unlinked motors, there is no effective capability
of introducing the per-motor torque -step inertia compensation - commonly used to reduce the speed following error
during acceleration and deceleration.


Copyright © 2002 Rockwell Automation, Inc. All rights reserved. Printed in USA.