Tractor drivers soon
may say,
"Look, Ma! No hands!"
BY DAVID F. SALISBURY
Future farmers of America
may never have to learn to drive a tractor.
A Stanford research team
has equipped a John Deere tractor with a satellite-based
automatic control system that can guide the 20,000-pound
farm vehicle more precisely than the best human drivers.
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Information:
Doctoral students Gabriel
H. Elkaim and Michael O'Connor report that their team has
perfected the system to the point that it can control the
tractor at all speeds while pulling a variety of
implements, with centimeter-level precision.
The team, which is
supervised by Bradford Parkinson, the Edward C. Wells
Professor of Aeronautics and Astronautics, previously had
reported obtaining this level of precision at specific
speeds and loads following both straight-line and closed
loop paths . The students presented the new findings
Sept. 19 at the Institute of Navigation's GPS-97
conference in Kansas City.
"These guys have done
an amazing job in controlling the tractor. They've taken
it beyond anything we expected," said Gary K.
Hendrickson, manager of product test and reliability for
John Deere, who has been working with the Stanford team.
The research group
achieved this unprecedented level of control by using the
Global Positioning System (GPS), a constellation of 24
satellites operated by the U.S. Department of Defense.
The satellites circle the Earth every 12 hours. The
system originally was designed and constructed primarily
for military purposes, but it has been made available for
civilian use.
Normal civilian GPS
receivers have a precision of about 100 yards; a system
called differential GPS, which requires a local base
station, can provide meter-level accuracy. At these
accuracy levels the technology has found widespread use
in the nation's farmland, as part of a movement called
precision agriculture.
In the days before
agriculture was industrialized, farmers were familiar
with the characteristics of their fields yard by yard,
and successful farmers adapted their practices, such as
seeding, cultivating and irrigation, to these variations.
The advent of industrialization, however, forced farmers
to prepare entire fields in the same way, regardless of
the variations in soil conditions and other factors.
By mapping their fields
with GPS, innovative farmers now have begun to adapt
their seeding and fertilization practices to take these
small-scale variations into account once again. Using
these electronic maps, for example, farmers have begun
varying the amount of seed they plant and the fertilizer
they apply. In some cases, they are doing these tasks
manually, guided by an inexpensive handheld GPS receiver.
In others, they are using GPS-guided systems that
automatically vary the application rates.
Although these efforts
remain experimental, proponents argue that precision
agriculture will improve farm productivity while reducing
applications of fertilizers, herbicides and pesticides.
Not only would this save farmers money, it also could
reduce the adverse environmental impact of their
operations. Some proponents even are calling these
developments the "third agricultural
revolution."
Until now, however, the
degree of precision available from GPS has been
inadequate for control of farm vehicles. To achieve this
control, the Stanford researchers adapted a method that
they had developed for an automatic aircraft landing
system in 1994. The system employs an additional ground
station, called a pseudolite, that puts out GPS-like
signals. When combined with differential GPS, the system
provides information on the tractor's position and
attitude with centimeter-level precision.
Automatic control of
ground vehicles has been a research objective for many
years. Such control has many potential applications,
including development of smart roads that automatically
pilot vehicles to the destinations their users select;
control of construction vehicles that build roads
automatically; and control of vehicles operating in
hazardous environments.
"We think that farm
vehicles will be the first major application," said
graduate student O'Connor, citing several reasons: Solid
objects such as mountains and tall buildings block the
satellites' signals, so a large expanse of sky must be
available for the GPS system to work properly, which is
normally the case in agricultural fields. Farmers and
farm equipment manufacturers already are embracing GPS
technology, O'Connor said, and the potential economic
benefits to farmers are large enough to provide a real
incentive for its adoption.
Although the ultimate
application of this technology would be an autonomous
tractor that a farmer can command and monitor from the
office, there also are potential advantages to adding
such a control system to tractors with drivers. Bedding,
seeding, disking, fertilizing and similar procedures are
among the most monotonous and time-consuming tasks that
farmers face. Many farmers tell stories about falling
asleep on the tractor and taking out a couple of rows of
crops.
"This kind of control
system, which does the basic driving, frees the operator
to make higher-level decisions," O'Connor said. It
also could allow less experienced operators to plow more
precisely than veterans. The accuracy of the best human
tractor drivers that the Stanford researchers have been
able to measure is about 10 centimeters. That compares to
a 2-centimeter error with the satellite controller.
Such high level of
precision is not required for all field preparation, but
it is necessary for some applications. In growing melons,
for instance, farmers use buried hoses, called tapes, to
water the crops. Once a field has grown up, however, it
is difficult for farmers to locate the buried tapes.
Typically, they dig up each end of the row to locate the
end of the tapes and then mark them with flags. The
tractor operator is expected to drive the entire length
of the field and avoid the tapes by sighting on the
distant flags. Despite their best efforts, the tractor
operators do thousands of dollars' damage to the tapes
annually. With the GPS control system, by contrast, the
exact location of the tapes could be recorded at the time
they are installed and the tractors programmed to avoid
them.
Such a system also would
allow farmers to operate during the night, through heavy
dust or fog. This capability could potentially minimize
losses at times when crops must be harvested as quickly
as possible.
Satellite-based
controllers also might allow farmers to do things that
are impossible or impractical manually, such as enabling
a single driver to operate a convoy of several tractors
at the same time. Or it could allow farmers to plow their
fields in a spiral pattern, rather than in parallel rows.
A spiral pattern would allow a farmer to plow a large
field continuously, without wasting time making U-turns
at the end of each set of rows, but it is very difficult
for drivers to do.
The Stanford project began
four years ago when O'Connor asked Parkinson if he could
try to develop a control system for an electric golf
cart. In a year, O'Connor and two other students had a
working system. At that point, the Stanford researchers
approached the John Deere Co. for support. The company
supplied an older, mid-sized tractor model, the 7800,
which weighs about 20,000 pounds, has a 140 horsepower
engine and can travel at speeds up to 22 mph.
Since then, the team has
grown to seven students. In addition to O'Connor and
Elkaim, doctoral students Tom Bell, Andy Rekow and Ajit
Chaudhari work on various aspects of the system. Two
undergraduates, Arti Garg and Seebany Datta-Barua, work
on related topics.
O'Connor, who will
graduate in a few months, said he hopes to get a job
building a commercial prototype of the tractor control
system.
The research has been
supported by Deere and Company. It is a spin-off of
previous Stanford research that was sponsored by the
Federal Aviation Administration and the National
Aeronautics and Space Administration. Trimble Navigation
provided the GPS receivers used in the project.
For more information, see
the GPS Laboratory home page under research projects,
land vehicles. The URL is
http://www.stanford.edu/group/GPS/.
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