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| Opening
up Opportunities
As control
components move away from proprietary architectures, engineers
welcome the benefits of flexibility and buying power.
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Bill
Southard, DST Controls
Keywords:
Ethernet
Semiconductor
Programmable logic
controllers
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The secret is out: engineers like to shop. At
least, when it comes to components. And, while the retail industry may
still overlook engineers, control manufacturers are listening and
responding to their urge to scour catalogs, talk to sales people, and
contemplate multiple purchasing decisions. The result -- which permits
engineers to buy devices from any vendor’s line and create a control
system -- is called open architecture, and it has changed the way we
design and engineer.
Opening more than windows
Because the concept of open architecture has
evolved over two decades, manufacturers and engineers have varying
definitions of "open." In the 1980s, an open system involved
practical network connectivity issues. Designers selected components from
within proprietary product lines and searched for an open answer to
communication at the host-computer level. The connotation of open
eventually expanded to include operating systems. Unix was considered open
because essential elements were in the public domain. Additionally,
platform vendors -- such as IBM and Hewlett-Packard -- supported the
environment.
Today, most people have an even broader
definition of open architecture. This definition was steered by the
automotive industry and reflects the mid-1990s white paper,
"Requirements of Open, Modular Architecture Controllers for
Applications in the Automotive Industry." An open system now means
that an engineer can select components from multiple vendors and construct
a seamless system. This definition encompasses every level of control
components. Theoretically, a system could include an open PLC from one
manufacturer, stepper modules from another, HMI from a third source, and
so on.
Multiple-vendor component integration gives
engineers the flexibility and buying power that they lacked when locked
into proprietary product lines. Because devices integrate, designs should
include only the best-in-class products that the market has to offer for
particular applications. Additionally, engineers can choose one
comfortable control philosophy and integrate components that work best
with their scheme.
For example, Alvey Systems, Inc., a Pinnacle
Automation company, wanted a smart distributed system as the basis for
conveyor and palletizing applications. All other components are designed
around the intelligent I/O concept. Alvey integrated GE Fanuc Series
90™-30 PLCs into the design because these open devices provide
enhanced features that support the selected I/O, the Honeywell Smart
Distributed System (SDS). The PLCs fully integrate with the SDS, despite
the difference in manufacturers. This combination of GE Fanuc’s SDS
interface and Honeywell’s I/O offers the solution of choice for Alvey.
In addition to acquiring the best technology
at the beginning of a design, engineers can substitute new components from
any vendor into existing machines. In the past, these upgrades had to wait
for developments within proprietary product lines. With open architecture,
control systems can grow with industry technology -- rather than growing
with an individual vendor.
And, buying power doesn’t just buy
components. It also helps engineers acquire the best technical assistance
and training. Because one manufacturer’s products can substitute for
another, competition within the control industry remains fierce.
Value-added services in the form of systems support can make all the
difference in final selection. Engineers can avoid companies that resort
to problem finger-pointing and search for those that offer real
assistance. Thus, manufacturers are not only trying to design the best
open systems but also improving training, service -- and sometimes -- even
prices.
Can we talk?
The heart of open architecture is
communication -- whether between devices or as a connectivity issue. On
the connectivity side, open systems have facilitated communication within
control processes. More types of devices can be added to a network and
controlled seamlessly as one system. The technology also supports remote
monitoring and control. Engineers can access systems through a modem or
over the Internet from any location. In many applications, Ethernet is
emerging as the network of choice.
Open architecture is particularly important
when connectivity requirements vary from one machine to the next. DST
Controls recently designed a system for Air Liquide -- whose customers
want connectivity ranging from Ethernet to a simple serial port. To meet
their requirements, DST developed the controls for a hazardous gas
distribution system that includes Series
90-30 PLCs. These PLCs offer expanded communication protocol
capabilities that allow Air Liquide’s customers to achieve their
individual level of connectivity.
Open architecture also facilitates
communication between process and business management. Analysts can review
production processes online and manipulate data in spreadsheets and
reports. With this more accurate and timely information, business
management has the ability to refine strategies and logistics -- as well
as speed response to crisis situations.
Keeping options open
There’s no doubt that open systems offer
benefits and that motion control -- driven by the automotive industry --
is moving in this direction. While manufacturers have responded to this
trend, some would say the response has been too quick. Just about every
manufacturer now claims to have some open products. With the varying
definitions of openness, it’s difficult for engineers to assess whether
these claims are valid, which can lead to major integration problems.
The validity of these claims recently added
three frustrating weeks to a DST Controls design. The system involved
compliance with MMS. DST selected devices from GE Fanuc and another
manufacturer, which both claimed full compliance. However, only GE Fanuc
had implemented the full version while the other company had implemented
the draft. DST could not integrate the devices until first identifying the
problem and then correcting to accommodate the draft-version protocol.
In addition to invalid claims, the many
levels of component openness complicate control engineering and design.
Table 1 shows just some of the standards and protocols that dictate
openness. Individual components vary with type of device as well as
manufacturer. In the case of field buses, there is no recognized industry
standard, and engineers must wade through a conflicting and competitive
jungle. Plus, the protocols change frequently as new trends enter the
motion control industry, which increases the complexity of system design
and upgrade.
To reduce this complexity, engineers need to
assess the openness of products. The only way to do this -- after reading
product literature and manuals -- is through testing under application
specifications. Tests allow control engineers to evaluate products,
attempt full integration, and monitor prototype performance.
For the Air Liquide control system, DST
tested all components within the lab before finalizing design. Preliminary
criteria identified by Air Liquide’s wafer fabrication customers guided
the tests. At the top of this list was flexibility, which lends itself to
open architecture. The controller had to be easily configurable to
accommodate a wide range of international end-users’ needs.
Customer-specific "moving targets" included unique
computer/software systems and local area networks, requiring bidirectional,
plug-and-play communication. System security requirements varied from
complex multi-level password access, to key switches, to no restrictions
at all. Testing helped DST select a variety of devices and attempt
integration across manufacturing lines. Full product compliance with
standards -- as implemented by GE Fanuc -- facilitated testing and
verification. The resulting system permits customers to choose specific
devices, including even the PLCs, as options to meet their individual
needs.
Alvey also recommends testing to assess
product openness. For a conveyor application, the company is evaluating
PC-control software from four different vendors, including GE Fanuc’s
CIMPLICITY® PC Control. The tests allow the company to work
with the packages away from customer sites. Alvey engineers first
developed selection criteria, including speed, HMI interfaces, programming
options, and IEC-1113 compliance. They identified and acquired other
devices that would need to work with the software. So far, the tests have
revealed that none of the packages meet all of their requirements.
Additionally, some packages limit the choices of I/O systems and HMI. The
Alvey team is currently evaluating third-party agreements that expand
design options with fully integrated wrap-around products.
Open for business
Third-party partnerships, another trend in
the control industry, involve vendors working with one another to develop
products that expand on each others’ features and integrate seamlessly.
Qualified manufacturers create modules that help customers with a wide
variety of needs take advantage of specific devices.
For example, GE Fanuc opened up its PLC
backplane to accommodate Horner Electric modules as part of its Accompany
Program. These devices plug directly into the Series 90-70 VME backplane
and the Series 90-30 backplane. Now, customers can purchase a GE Fanuc PLC
and acquire seamless integration with a Horner Electric module.
Essentially, these partnerships help
engineers identify which control components integrate easily with another
manufacturers’ products. The components -- and their communication with
one another -- are validated by the manufacturer to save end-users the
time and expense involved with testing. This process consumes about 40
percent of vendor costs to develop new products.
However, even with validation, engineers face
integration challenges. The move toward open architecture is still new
enough that most devices are not validated for communication across
manufacturer lines. Integration may require extensive troubleshooting,
custom cables or boards, or complete redesign. Fortunately, engineers can
ease the process by asking manufacturers for technical assistance -- which
is all part of buying power opening new opportunities.
| Type
of control |
Open
architecture standards and protocols |
| Programmable
logic controller |
•
VME and SDT backplane
• Connectivity: Genius®,
WorldFIP, SDS, LONworks,
DeviceNet, InterBus-S, Profibus-DP
|
| PC-based
control |
•
Windows® NT and 95
• Connectivity: Genius, WorldFIP, SDS,
LONworks,
DeviceNet, InterBus-S, Profibus-DP
|
| I/O |
•
PC, PLC and VME networking
• Connectivity: Genius, WorldFIP, SDS,
LONworks,
DeviceNet, InterBus-S, Profibus-DP
|
| Human
machine interface (HMI) |
•
Drivers to different PLCs and other forms of control
• Advanced DDE, OLE and ODBC
• Windows NT and 95
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| Communications |
•
Ethernet (TCP/IP, IPX, MMS, MAP, etc.)
• Connectivity: Genius, WorldFIP, SDS,
LONworks,
DeviceNet, InterBus-S, Profibus-DP
• Host communication drivers and tool kits
for
third-party products
|
| Application |
•
IEC-1131 programming |
Table 1: An open architecture requires that
products meet a multitude of standards and protocols, which are different
for each type of control component.
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CIMPLICITY and Genius is a registered trademark and
Series 90 is a trademark of GE Fanuc Automation North America, Inc.
Windows is a registered trademark of
Microsoft Corporation.
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Bill
Southard is President of DST Controls, a systems integrator located in
Benicia, Calif.
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651
Stone Road, Benicia, CA 94510