SERCOS News - Issue 1 - 2008

4 Sercos-Inside
The Real-Time Ethernet Magazine
Block I/O - easy integration of I/O signals
in SERCOS III
mum cycle times of only 31.25 µs (the
blink of an eye takes approx. 330,000
µs), the fast transfer of the information
is guaranteed. Also, the architecture
enables direct communication between
the executing units (slaves) so as to keep
reaction times down to a minimum. To
optimise the network, SERCOS III does
not require expensive additional network
components, such as switches or
hubs. The integrated network functions
ensure that TCP/IP packets can also be
transmitted next to the real-time data.
The reliability is increased by a robust design,
a ring structure of the lines against
the consequences of a cable break, as
well as the secured data transmission
via a certified safety protocol. The data
is protected automatically, which require
no additional hardware.
Since October 2007, the SERCOS III real
time Ethernet solution has been part
of mandatory IEC standards. The vote
for SERCOS III as the international standard
was unanimous. This reflects the
worldwide importance of the SERCOS
interface. SERCOS II was already standardized
worldwide. In parallel to standardization
of third generation SERCOS,
IEC decided to incorporate the existing
IEC 61491 SERCOS II standard into the
new IEC 61158/ 61784-1 standards series.
The SERCOS drive profile was included
in the new IEC 61800-7 standard. All
three SERCOS generations are now part
of the IEC standards.
2 million SERCOS nodes are currently installed
worldwide, and the IEC decision
is goods news for SERCOS developers
and users. The evolution of SERCOS is
characterized by continuity and a clear
migration path. The common interface
ensures interoperability between
products from different manufacturers
which use the same standardized interfaces,
commands and synchronization
methods. More than 80 different manufacturers
now offer SERCOS-enabled
products.
At the field level, which is where communication
between individual drives,
sensors and controllers takes place,
SERCOS III real time functions guarantee
the required level of precision. Connectivity
to higher level control systems is
extremely simple. Companies gain direct
access to data at the lowest production
level, and every Ethernet-enabled computer
can be connected to a SERCOS III
port without any additional hardware
or software. The computer can link into
corporate TCP/IP communications without
putting production-level runtime
performance at risk.
This works because in addition to real
time communications, SERCOS III has a
channel for non real time information
(NRT). The completely transparent integration
of real time and non real time
data enables users to operate a large
mix of devices on the same network.
In contrast to other Industrial Ethernet
solutions, SERCOS III does not require
additional hubs and switches, and it
does not use any additional protocols.
Connectivity is completely transparent,
because Ethernet systems without a
SERCOS III ID are automatically allocated
to the NRT channel. A 100 Mbit
data rate supports data exchange between
many devices in parallel without
compromising the integrity of real time
communications.
Transparent integration of real time
and non real time data allows companies
to completely rethink their systems
strategies. SERCOS III brings two worlds
Highest precision - with cycle times till 31,25µs
together. All nodes speak the same
language. Different modules can even
share the same cables without compromising
integrity and reliability.
SERCOS III, like previous SERCOS generations,
is based on the field-proven
hardware synchronization solution as it
offers the greatest reliability. Every module
comes with a special logic module
which coordinates the SERCOS nodes
with each other. This eliminates any
need for additional expensive con trol
points in the form of hubs and switches,
and the network coordinates itself automatically.
Synchronization is therefore
one of the basic features of every SERCOS
solution, not a feature which has to be
added on each time with additional
modules or protocols.
At the same time the cycle time of 31.25
μs in real-time mode does not mean
that one individual module would take
up the complete range for itself alone.
Instead, it is possible for up to eight
drives in Motion Control applications
to be supplied with 8 bytes of cyclical
data and for them to send the same
number of diagnoses as well. This is
sufficient for the most demanding tasks
currently conceivable in mechanical
engineering. Even high-precision CNC
machines have minimal cycle times of
500 µs. Thanks to the greater efficiency
of SERCOS techno logy it will not
be long before there will be no applications
which would make it necessary
to have a higher network speed. Moreover,
Fast Ethernet also offers sufficient
reserves for TCP/IP communication in
production – especially because SERCOS
is very efficient in the use of resources.
Flexibility is a success factor in production
and Industrial Ethernet is a protocol
which allows planning and production
to be coordinated with each other with-