Precision Agriculture, 2, 281᎐291, 2000
ᮊ 2001 Kluwer Academic Publishers. Manufactured in The Netherlands.
Guidance of a Forage Harvester with GPS
ALBERT STOLL AND HEINZ DIETER KUTZBACH firstname.lastname@example.org
Institute for Agricultural Engineering, Hohenheim Uni
ersity, 70599 Stuttgartr Germany
Abstract. Precision agriculture requires automatic control of agricultural machinery in order to cope
with the large amount of information which has to be applied during site specific field work. The driver
is occupied with operating and supervising the controlled and non-controlled implements as well as with
vehicle guidance. Steering, in particular, is monotonous and tiring. This can result in reduced operation
quality. This was the motivation to develop a concept of a guidance system for agricultural vehicles. A
self-propelled forage harvester was the test vehicle for this research. The harvester was equipped with
an automatic steering system. Real Time Kinematic Global Positioning System RTK-GPS was used as
the only positioning sensor due to high absolute accuracy within the field and its high reliability. The
system performance was investigated under various test conditions. Additionally a guidance-path-plan-
ning for swath harvesting operations was developed. Both the automatically steered forage harvester
and the path planner could be examined under real field conditions. The standard deviation of the
driving performance was better than 100 mm under all conditions. The swaths could be collected
reliably with the automatically steered forage harvester.
Keywords: automatic steering, GPS, swath guidance
For site specific applications, a large amount of information has to be processed
on-line; therefore, it is mandatory that agricultural vehicles can be managed
efficiently with automated function cycles. Beside operating and supervising the
implements, the guidance of the vehicle demands a high level of concentration
from the driver. In particular, steering is tiring and monotonous in large fields. A
frequent problem is missing or overlap between two adjacent tracks with broad
implements. Glare or darkness can cause additional deterioration of working
conditions. Automatic steering supports the operator so that he can direct his
attention to the main functions of the machinery. Due to this reason, automatic
control of agricultural vehicles is gaining more importance, especially automation
of vehicle guidance.
In general, automatic vehicle controls can be divided into positioning sensor,
vehicle controller and the vehicle with actuators for steering and speed. The error
variable is determined with the help of the positioning sensor by comparing the
desired value with the actual value of position, travel direction and speed of the
vehicle. The desired value is given by the guidance path.
Different kinds of positioning sensors were investigated in former research.
Ž. Ž. Ž.
Tillet 1991 , Sevila and Baylou 1991 and Jahns 2000 reported different concepts
of position sensing and vehicle controlling. The Global Positioning System GPS
has become an important means of positioning in the last decade. Conventional