As global pressures squeeze manufacturers, many
feel the urgency to optimize equipment in their
plants. Existing controls are being tossed out
and replaced with modern programmable
automation controllers (PACs) that deliver
more processing capabilities and more
network connectivity.
PACs have been gaining acceptance for
years, giving engineers a single platform to
address a broad range of needs. These platforms
include software, which eradicates the
need for a range of tools to do programming.
PACs also leverage technologies developed for
the PC world, assuring industrial users they’ll see
steady advances in performance and compatibility
with front office equipment, among other benefits.
The versatility of PACs has prompted many
plant managers to replace their programmable logic
controllers (PLCs). However, this changeover isn’t
expected to mean the end of the line for PLCs. Product
developers and plant managers are clearly focusing on
PACs, but PLCs are also adopting faster processors and
adding networking capabilities. They’re now seeing use
in jobs that don’t change often and don’t require lots of
computing power.
“There are still a lot of applications that don’t need
the flexibility of a PAC. A PLC is ideal for customers
who can use ladder logic for simple discrete control,”
says Bill Black, controllers product manager at GE
Fanuc.
In some instances, PLCs have become one of the many
modules that fit into PAC architectures. For example, Mitsubishi
Electric Automation’s iQ automation architecture
blends a PLC, motion control, computer numerical control
(CNC), and robotic control in a single platform (Fig. 1). Many
of the modules that work in this architecture are small, which
is helping developers create complex systems without taking
up a lot of space.
“From a physical standpoint, it has a very small footprint.
The CPU measures only 4 by 1 inches and it’s 4 inches deep,”
explains Scott Rohlfs, director of product marketing for Mitsubishi.
By shrinking size while increasing performance, equipment
and system designers can continue to combine operations
that were once the domain of dedicated controllers. As these
systems boost performance and handle more jobs, the control
modules also manage more complex tasks.
Five-axis control was an advanced feature a few years ago,
but now it’s becoming fairly routine for PACs to manage more
motion. Rockwell Automation’s recently introduced Allen-
Bradley CompactLogix L45 PAC expands motion capability
to handle eight-axis applications (Fig. 2).
THE ROLE OF BACKPLANES
The controllers are only part of the equation. Backplanes
play a critical role, linking the modules so they act as a single
system. These backplanes also employ ruggedized PC architectures
for industrial environments. They offer enough bandwidth
to make motion control just another element in a closely
coupled system.
“Motion controllers and PACs are being tightly integrated
using high-speed backplanes that assure the best of both
worlds. You don’t have to do a lot of handshaking, which is
good because motion is very compute-intensive,” says Paul
Derstine, motion products manager at GE Fanuc (Fig. 3).
Communication between the cards in these backplanes
makes it possible to run complex motion tasks while other
operations are running. The basic PCI architecture used by
many systems routinely moves data at 27 MHz, which is fast
enough for many operations, says Derstine.
Users who want more speed can move to the ruggedized
PXI and PXI Express. They give users a ruggedized bus that’s
compatible with PCI. PXI Express has bandwidth up to 2
Gbytes/s per slot along with timing and synchronization capabilities.
National Instruments heavily endorses PXI Express,
rolling out a number of products based on the architecture.
These releases include the CompactRIO
and CompactFieldPoint families,
which extensively employ FPGAs.
These products
add even greater versatility, allowing
engineers to alter hardware
when operations change. This
hardware programmability can
help plant managers configure
systems that meet their specific
needs without the additional
cost of customized equipment.
FPGAs were once avoided
because of the difficulties in
programming and reconfiguring
them. But the advent of graphical
programming techniques has
helped eliminate those problems.
Thus, plant managers can more
easily exploit the flexibility provided
by programmable logic
devices.
“Users don’t have to learn
the abstract commands usually
needed to program an FPGA.
They can use LabVIEW and control their real-time systems,” says
Arun Veeramani, product manager at National Instruments.
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