At 30 years old and approximately 75-ft long, the
Black-Clawson two-station extrusion laminator that dominates the Amgraph
production floor has made the switch from analog drives and drifting system
variables to a modern all-digital system.
As customer requirements surpassed the capabilities of
the existing system, Amgraph faced several choices for supplying flexible
packaging solutions for the food industry. It could spend millions on a new
machine, settle for lower productivity and product diversity, or retrofit the
equipment with modern controls. Amgraph opted to replace its analog control
system with high-efficiency motors, digital drives and updated controls.
As
a result, Amgraph now produces a wider variety of coated plastic and foil
flexible food packages, was able to cut material expenditures and improve
throughput, and boost productivity.
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Tension Control
Circonix, a Siemens
system integrator and solutions partner that specializes in web handling applications, was contracted
by Amgraph to redesign its packaging machine's automation system.
"Initially,
the machine had four different motors with analog drives and controls, each
with their own wiring harness and relay logic, which really made the machines a
challenge to maintain," says Andrew Alaya, vice president of engineering for
Circonix. "Only one of the sections was capable of tension control, which
forced Amgraph to operate the extrusion machine in draw mode. This meant that
the machine could only handle certain types of coatings without breaking the
web and going down. Improving that uptime through better tension control was
the main goal of the project."
Circonix
engineers decided to retrofit the extruder's four existing analog drives with
Siemens motors and Sinamics S120 drives, while adding four load cells inline
and a new Fulton Machinery dancer to the machine's two unwind spindles. Two
Vetaphone treaters were also added inline as part of the retrofit. These
effectively eliminated the need for the primer coater, and served as pull
stations for the machine, also now driven by Siemens motors and drives. These
modifications allowed the machine to work in closed-loop tension control mode.
By
changing values on the HMI and PLC (provided by Wonderware and Rockwell
Automation, respectively), Amgraph can now precisely control the speed and
thickness of the web, turn various systems such as treaters, laminators and
tension control systems on or off, and apply thinner coatings to package
materials without worrying about additional web breaks and downtime, or thicker
coatings to meet special customer needs.
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"Now that we have more control of the system, we're looking at replacing the thicker films that we used to purchase from other vendors with extruded materials we make ourselves, which saves us money," says David Rand, production manager at Amgraph. "Our initial trials have been successful."
The new motors, upgraded digital drives and new controls also increased the extrusion machine's uptime, throughput and productivity. The high bandwidth of the Sinamics S120 digital drives allows for improved speed regulation and faster response, both of which are key to improving tension control. Amgraph set aggressive goals of 95 percent uptime for the retrofitted extrusion machine.
In addition to increasing uptime and the number of products the machine can handle, Rand says the retrofit has increased throughput up to 20 percent, depending on the product line. "We've definitely increased production speeds," he says. "We're happy where we are now, but we still have opportunities to improve throughput."
Addressing Retrofit Concerns
The
primary issues with the original system centered on the analog drive system and
system variables that drifted, so the challenge was moving to an all-digital
system. Sections of the older system used draw control, developed by using the
speed differential from one section to another, rather than direct tension
control on the individual axes.
Load
cells for direct tension control were added to sections that originally used
draw control, and the final configuration provided an ability to use either
draw or tension control. This is important when you have an extensible web,
because it is easier to use draw control and a speed ratio to develop tension
on the material. But if the web doesn't have modulus in it, the resolution of
the speed differential becomes more critical. If the accuracy of the drive,
which provides speed regulation, is not as good, that also complicates the
application.
Induction motors were used for the application, with the
drives providing an ability to run in a servo mode. On several converting
applications (due to torque requirements), many engineers still use
high-performance induction motors. The drive offers a servo mode which
increases dynamic performance to reduce motor current more quickly and provide
optimized performance with a standard NEMA induction motor in the 30 to 40 hp
range.
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Retrofitting large production machinery like the Black-Clawson extrusion laminator machine rarely progress as scheduled, because changing a machine from discrete analog to digital control systems with the latest energy-saving ac induction motors presents significant electronic and mechanical engineering challenges.
Customers also typically want to use specific equipment providers for certain systems. In this case, Amgraph specified a third-party HMI and PLC technology, which meant Circonix needed to interface the Sinamics S120 drives with third-party systems. Using Siemens' Starter drive engineering and commissioning software, and integrating the Sinamics S120 drives using the electronic nameplate capabilities of Drive-Cliq for motor and drive components, the project was able to be delivered to Amgraph on time and within budget.
"We used Profibus to tie the drives together and an SST module in the PLC to talk to the Siemens drives," Alaya explains. "With the Siemens dc bus lineup, all the drives fit in a single cabinet that was smaller than the space of one of the previous motor control systems. We were able to eliminate the wiring mess and relay logic that came with the older analog controls as well, which significantly simplified maintenance and troubleshooting for the customer while improving performance and uptime."