By Michael Bertuleit, PE, and Dan Walser
A long-held assumption in the paper-converting business
is that safety protocols
negatively impact production rates. In the past, this was often
true because, as extensive guarding and other safety mechanisms
were added, operators were increasingly separated from their machines.
This reduced safety risks, but also reduced operator access to
key machine elements when errors occurred and resulted in increased
downtime and recovery time. In addition, mechanical line shaft
systems enabled maintenance personnel to devise last-minute workarounds
that fixed problems in the short-term but often increased safety
risks and reduced overall production line efficiency in the long-term.
Could there be a way to both reduce safety risks
while increasing production rates? Applied Motion Systems (AMS)
believes the answer lies in a sectionalized converting approach
with co-ordinated digital drives deployed on a distributed safety
network.
We recently worked with a paper mill customer who
is in the process of implementing a comprehensive and stringent
safety program. This program sought to adhere to and improve upon
all regulatory controls and best safety practices. The customer
required us to keep production rates the same after we deployed
the new safety system on one of the mill's continuous rewinders,
but we sensed that management believed production rates would
drop. Our goal was to improve production rates while reducing
safety risks.
We first showed the customer how a sectionalized
and digital winding solution could deliver more system flexibility
and performance while simultaneously reducing downtime and safety
incidents. We wanted to avoid the common pitfall of putting up
so many guards that operators have less access to the machine,
thereby making it difficult to perform their duties.
Furthermore, by replacing the outdated mechanical
line shaft systems with sectionalized digital drives, we would
enable operators to address problems in a sectionalized manner.
If a problem occurred in one section, the operator could safely
enter that section while maintaining web tension in all the other
sections, thus substantially reducing recovery time and the likelihood
of product waste.
The upgraded system features improved diagnostic
capabilities that rely on automated alarming and self-correcting
functionality for consistent, repeatable operation instead of
hard-wired safety systems. Graphical alarming diagrams on the
HMI enable operators to quickly identify and respond to problems
that must be solved by an operator, such as open guard doors,
web breaks, or misaligned components. This is accomplished by
using a distributed network safety solution to minimize system
wiring and enhance diagnostic capabilities. Because each safety
device is wired individually to the safety I/O, troubleshooting
time is virtually eliminated. Additionally, the drive system is
able to automatically realign critical machine components and
thereby speed up recovery time and resumption of production.
New hardware (main drive motor, new drives system-wide,
and extensive safety controls) and software algorithms have increased
production throughput by about 35%. All machine settings are available
from the HMI and flexible safety PLC control. Mechanical adjustments
are no longer required in many cases because the system is digitally
configured by simply loading a new recipe. Drive-integrated safety
features allow Category III electronic isolation (Secure Disable)
instead of using isolation contactors. By electrically modifying
the existing pneumatic speed trim adjustment system, operators
can now safely make accurate dancer responsiveness adjustments
on the fly from outside the safety guarding without having to
deal with tricky jam-nut adjustments or be exposed to the rotating
machinery.
Automatic line balancing has been enhanced so that
excessive accumulation is minimized at downstream conveyors and
packaging equipment by automatically slowing the rewinder when
these downstream problems occur. This allows operators time to
address issues, resulting in reducing the number of start cycles
on the rewinder and fewer culled logs.
The bottom line is that this rewinder upgrade increased
production rates
to 135% of pre-retrofit rates while significantly reducing safety
risks for the operators. The improved line productivity combined
with reduced safety risks also improved morale and led the operators
and management team to further embrace and "own" the
new company-wide safety
initiatives that benefitted all. TW
