Satellite based guidance technology is a very challenging principle for future automation of
agricultural machinery. The first generation types of systems are primarily self-contained
solutions and added to the existing system set-up of the tractor. As being an important step
towards robotics in agricultural machines, a better integration of this technology into the
mechanical, hydraulic and especially the electronic architecture is a major issue.
In principle, there are two main strategies for the integration. One is a concept based on a
proprietary, manufacturer specific approach. The other one is to map as many functions as
possible into the just state of the art becoming open and standardized ISOBUS. Within this
paper, the capabilities of ISOBUS to be used for X-by-Wire applications are discussed from
different point of views. In consequence, ISOBUS can only be used to create X-by-Wire
applications with mechanical or hydraulic backup. Basic real-time capability with a reaction time
of 100 ms seems to be achievable. However, some features of time-triggered protocols like
determinism should be integrated by simulation on application layer level. Such concepts are the
introduction of a heartbeat mechanism to serve as a coarse time synchronization and timeout
reference. Additionally, the lack of unique and hard-wired addressing within ISOBUS demands
new concepts like encryption algorithms.
Based upon these theoretical considerations, a first proposal for a Steer-by-Wire approach via
ISOBUS has been derived and implemented. First results are very promising, but further
investigations like fault injection trials and extended network set-ups with pre-defined bus load
scenarios are necessary.