Civil Engineering Reference
In-Depth Information
the system module is an integrated part of the system, taking a monitoring and
supervising role during run time, allowing for hot swaps of modules, changing of
modes, etc. CK can be implemented in a modular way. A full implementation re-
quires roughly 5.5 K flash and 100 K RAM.
4.5.1
Background
In the early 1980s, the Swedish company Rovac developed an advanced factory au-
tomation system based on distributed embedded controllers. The whole factory was
seen as one big application that included robots, material supply, mould positioning,
heat control, etc. This application was broken down into as small pieces as possible
and each piece was executed in a separate micro-controller, physically integrated
into the device it controlled or monitored. As an example, a robot was constructed
of a set of actuators connected by structural parts, tubes and swivels. In this way,
special robots could be easily designed using standard parts. The micro-controllers
were grouped according to their functions and the members of each group were con-
nected to each other and to a central computer by a serial communication bus. The
central computer coordinated and supervised the groups to act in concert in a safe
manner. The concept, designated 'Trainet', turned out to be very flexible and effi-
cient, but the bit rate of the communication, 9,600 bps, limited the update frequency
to 25 Hz, i.e. any feedback control loop had to be executed locally.
When CAN became available in 1988, high-speed bus communication was avail-
able at a reasonable cost. As the concept of CAN is to minimize the need for run-
time bandwidth by defining as much as possible off-line, it was a perfect match with
the Rovac ideas. The combination of Trainet features and CAN resulted in CK, first
published in 1990 by the company Kvaser. It was developed further and version 3 was
made available at CiA 1992 and reached a broader audience. CK v. 3 formed the basis
for the US DoD CDA 101 project for a common CAN-based protocol for different
types of airborne and seaborne targets. During the development period of CDA 101,
from 1996 until 2001, CK was further improved to meet the high requirements for any
aspect of an embedded CAN, such as adding improved support for hard real-time and
synchronization, composability, membership verification, safety, troubleshooting, etc.
Being a meta-HLP, CK is used as a base for proprietary HLPs, e.g. the Mercury
“SmartCraft” for pleasure boats and the Sauer-Danfoss “Plus+1” for off-highway
machines.
4.5.2
The Concept Behind CK
A cornerstone of the concept is the notion of a system: An electro-mechanical sys-
tem is constructed of a number of modules, each with an ECU that is connected to a
serial communication of some kind. Each module has a specific role in the system,
e.g. a steering wheel or joystick, a gearbox, a motor, an actuator, a sensor, etc. They
