Sercos turns 'soft' PLC into a flexible motion controller
As the popularity of 'soft' PLCs continues to grow, Rockwell adds a
Sercos networking card to its established SoftLogix platform, and shows
how this PC based system can enjoy a high level of determinism without
compromising the openness of its Windows operating system
Rockwell Automation has introduced a Sercos version of its SoftLogix 5800
control software, a 'soft' PLC now providing additional motion control
functionality. Essentially a PC based version of its Kinetix hardware
motion control platform, which was launched last year (see DPA September
2002 page 46), the SoftLogix 5800 with Sercos is aimed at medium to
complex cartesian robot applications such as those found in packaging,
sheet materials cutting and printing operations. Up to 64 axes of control
are available from one PC based application.
The system runs under standard Windows operating systems without real
time extensions, to ensure compatibility with a wide range of third party
applications and future software upgrades. In order to make the system
deterministic, while remaining 'open' for future software revision,
Rockwell has devised a method whereby the motion commands and profiles
execute directly on the native PC processor, not on the PCI card, which
would be treated as a peripheral device by the operating system. In this
way, the motion instructions are placed at highest priority, receiving
frequent (2ms) uninterrupted updates. Such an implementation has only
been made possible thanks to the power of modern processors.
Achieving this level of determinism without compromising rates motion
control the standard Windows operating system opens up the applications
potential of SoftLogix, to include those requiring integration with other
Windows-based packages. A good example is data warehousing in an
automated pharmaceutical compound cross-checking system, which is heavily
reliant on accurate and repeatable motion control. Users may wish to
integrate custom written routines using Visual C or C++ and Visual Basic,
with control applications written in ladder logic. With SoftLogix, these
custom programs are able to run without having to rewrite proprietary
instructions in function block or ladder logic.
It is its Sercos capability, however, which enables the SoftLogix 5800 to
deliver up to 16 axes of motion control per card, seamlessly into a wide
range of applications. The interface replaces the large number of
conductors previously required to connect the controller to the servo
drive (up to 20 per axis) with a single fibre optic cable. In a typical
four-axis system, for example, the number of interconnecting wires is
reduced from 160 to just nine.
Applications that will benefit most from SoftLogix 5800 include those
with large amounts of data, with DDE links to other software, with high
processing power and integral diagnostics. Applications that are HMI
intensive will also benefit as the PC screen acts as the HMI and a
separate unit connected via a network, is not required.