of both worlds – combining the advantages of decentralized
Switch I/O architecture with application centralized engineering
for industrial control systems widely differ depending on their
respective task definitions. Accordingly different control concepts and
architectures emerged for the diverse industries and applications. Due
to this trend, vendors of control systems nowadays offer their customers
differentiated product ranges. Starting from the elementary distinction
between centralized and decentralized control architectures, the product
ranges are diversified up to a very detailed level of granularity. Apart
from purely technical characteristics of the control equipment (e.g.
maximum reaction time), customers increasingly consider the efficiency
of the control system’s programming, configuration and commissioning.
An ideal control solution hence fulfils all the necessary technical
requirements and additionally enables the user to perform an efficient
and intuitive engineering according to the respective industry
important step in this regard is the usage of prefabricated and
self-contained modules during the creation of control programs and
configurations. This is evident in the increasing employment of function
blocks in PLC programming languages according to IEC 61131-3. Another
step to decrease engineering time is the application of
vendor-independent standardized software modules for the implementation
of frequently occurring tasks in control programs. Especially in the
areas of manufacturing automation and motion control function blocks
according to the PLCopen standard have proven to be useful. PLCOpen
defines function blocks for single- and multi-axis movements as well as
a state model for transitions between different motion types and error
handling. The basic functionalities are extended by several function
blocks for e.g. torque control and cam switches.
to the consistent structure and the flexibility of the PLCopen standard,
users can create control programs in a very fast and concise manner. The
widespread adaption of PLCOpen by vendors of industrial control systems
allows users to use control systems of several vendors without
prohibitive effort for programmer and commissioner training.
Accordingly, the user’s dependency on single vendors decreases.
frequently used application type in the area of manufacturing
engineering is the electronic cam switch. Electronic cam switches
consist of an arbitrary number of electronic cams that activate or
deactivate digital outputs according to a rotary encoder’s measurement
value and their configured respective turn-on and turn-off angles.
tracks are created analogous to their mechanical counterparts by
assigning several cams to a shared digital output.
cam switches are advantageous to mechanical solutions due to the
possibility of very simple changes and extension to the cam
configuration as well as significantly reduced maintenance effort.
Common application examples of electronic cam switches can be found in
all areas of machine building industries where actions have to be
triggered high dynamically and synchronous to rotating mechanical
components (e.g. a rotary disc). Such applications can e.g. be found in
the packaging, printing, manufacturing and plastics processing
order to support their customers with these types of applications, ABB
STOTZ-KONTAKT created a new generation of bus modules (CI 511 und CI
512) for their PLC platform AC500. These novel bus modules are based on
fast real-time capable Ethernet protocols and hence allow realizing
extremely fast decentralized cam switches. EtherCAT was chosen as bus
protocol due to its high bandwidth, on-the-fly-processing and
slave-to-slave-communication. These capabilities offer the best
prerequisites for highly dynamic cam switches.
that put their focus on the support of complex and flexible fieldbus
topologies and do not depend on the bus couplers’ optimization for
highly dynamic switching operations can gainfully employ equivalent bus
couplers that support PROFINET IO communication (CI 501 and CI 502).
These bus couplers additionally implement parallel standard Ethernet
as already mentioned above, decentralized electronic cam switches rely
on very high requirements concerning the bus-couplers reaction time.
Accordingly, the EtherCAT bus modules CI 511 and CI 512 are the
preferred options for implementing decentralized electronic cam
switches. The topology of a typical decentralized electronic cam switch
is depicted in figure 1.
: Topology of a decentralized electronic cam switch
EtherCAT bus master is implemented as a communication module of the
AC500. The first node on the fieldbus is a rotary encoder with an
EtherCAT interface that transmits the absolute angle value of a rotating
machinery component. This node is succeeded by up to 254 bus modules.
The bus modules comprise either only digital input or output terminals
or alternatively also analog inputs and output terminals that can be
configured for all prevailing analog signal types. Each bus module can
employ up to 16 cam tracks and up to 32 cams.
constraints of traditional electronic (or even mechanical) cam switches
are resolved by the decentralized system topology which allows distances
of up to 100m between the individual bus modules. Hence spatially
decentralized applications can be realized in straightforward manner. An
additional advantage of the decentralized solution lies in the
cost-effective setup that contains only one AC500 and multiple
inexpensive bus modules. Nevertheless the cam switch network achieves
very low reaction times. For instance, a cam switch network consisting
of 40 bus modules can still switch its cams with an accuracy of ±200μs.
This enables the cam switch’s usage in highly accurate and dynamic
applications (e.g. the production of PET bottles).
the possibility of a large number of bus modules, the parameterization
of the cams can be conducted centrally in a simple and concise manner.
The engineering of the entire cam switch network occurs in a single
place – the AC500 PLC’s programming environment. In the IEC 61131
conforming programming environment PLCOpen function blocks of type
MC_CamSwitch are created and parameterized (c.f. figure 2). Hereby, the
cams are assigned to specific bus modules and provided with all relevant
switching information. This information comprises the cam’s switch-on
and switch-off angles (in 0.01°) as well as dead-time compensation.
grouping of multiple cams to form a cam track is conducted in a
graphical editor that is also used for the bus modules’
the decentralized cam switch network is configured in a central place
and hence combines the high accuracy and dynamic of a decentralized
system with a centralized system’s efficient engineering.
3:a highly dynamic rotating laser control
system as exemplary application.