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For several years, U of I agricultural
engineers have been mounting cameras on tractors and using them to
observe the terrain and help steer the machine -- without anyone
behind the wheel. Their first automatically guided tractors used
monocular cameras (cameras with only one lens) to help steer, but
now they have taken machine vision to a new level. Their
automatically guided tractor is equipped with a stereo-vision camera
mounted in front.
You might say that this camera has two
eyes, or lenses.
Much like the human eye, an automatic
guidance system for a tractor needs two eyes, or a stereo camera, to
see depth, said Qin Zhang, U of I agricultural engineer. With a
monocular camera, the field appears two-dimensional to the automatic
guidance system, but a stereo-vision camera brings the field image
into the three-dimensional world.
Also, a monocular camera is much more
sensitive to light changes, said Zhang. When the light changes,
contrast is lost, making it difficult for the tractor's camera to
distinguish between the crop rows and the background soil. But the
stereo camera is not as sensitive to light changes, making it
significantly more accurate.
Zhang and his fellow engineers tested
the new system in 2003 on a John Deere 7700 tractor with great
success.
"With curved rows and straight rows, we
successfully achieved a speed of 8 mph without any problem," said
Zhang. The tractor stayed on track. But at higher speeds, he added,
the tractor starts to bounce, making it difficult for the camera to
study the terrain and guide the tractor.
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However, Zhang believes that in the
near future they will develop a stronger mounting frame, preventing
camera bouncing and making the system accurate even up to 12 mph.
The camera is only one part of the
tractor's automatic guidance system, Zhang noted. A global
positioning system sensor determines the tractor's precise position
in the field, while other sensors provide information about the
tractor's motion and calculate its path. The "sensor fusion" system
combines all of the information from the cameras and sensors and
decides when to tell the electro-hydraulic steering valve to turn
the wheel.
But exactly how safe is it for a
tractor to be driving itself?
The stereo camera deals with this issue
with a new safety feature, Zhang pointed out. When an object is far
away, it appears white, while the background is black. But when the
tractor gets close to something in its path, the object will turn
black and the background will become white. This signals the tractor
to automatically stop.
Some farmers may not be willing to
completely give up the steering wheel to a machine, but Zhang said
it is possible that in the future there will be a combination of
traditional and nontraditional equipment. For example, one
possibility is that the farmer's tractor could be accompanied by a
fleet of smaller, cheaper, self-guided equipment, moving through the
field together and getting the work done much faster.
Zhang is optimistic. As he put it,
"We're hoping to make farming more enjoyable by reducing tedious or
intense work levels."
[University
of Illinois news release]
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