Development of a novel mechatronic system for mechanical weed ...
Development of a novel mechatronic system for mechanical weed ...
Development of a novel mechatronic system for mechanical weed ...
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State <strong>of</strong> the art<br />
26<br />
2.2 Detection <strong>of</strong> the plants<br />
Generally, two concepts <strong>of</strong> the data collection can be defined in site specific<br />
<strong>weed</strong> control:<br />
� the <strong>weed</strong> mapping concept and<br />
� the real-time concept.<br />
In the <strong>weed</strong> mapping concept, the in<strong>for</strong>mation about the <strong>weed</strong>s (location,<br />
species, density etc.) needs to be collected be<strong>for</strong>e the <strong>weed</strong>ing, as a separate<br />
operation. In the real-time concept, the <strong>weed</strong> detection is carried out during the<br />
<strong>weed</strong>ing (Nordbo et al. 1994).<br />
In the <strong>weed</strong> mapping concept data about the <strong>weed</strong>s are associated with GPS<br />
coordinates, which refers to a possible built-in error in the accuracy <strong>of</strong> the<br />
<strong>system</strong>. For site specific spraying <strong>system</strong>s such an error is irrelevant, but <strong>for</strong><br />
robotic <strong>system</strong>s which are oriented on a single plant treatment, such an error<br />
can cause significant decrease in efficiency. The error can first occur after the<br />
plant or <strong>weed</strong> has been detected and the combined data about the plant and<br />
position stored to the map. During the <strong>weed</strong>ing operation the <strong>system</strong> reads data<br />
from the map and combines them with the GPS coordinates <strong>of</strong> the vehicle. That<br />
could be a point when the error appears <strong>for</strong> the second time. The most recent<br />
GPS <strong>system</strong>s have real time kinematic signal correction (RTK) which provides<br />
+/– 1 inch (~2.5 cm) accuracy (Buick 2007). In the worst case, according to the<br />
mapping concept, the error can reach twice the accuracy value, which is<br />
approximately 5 cm. Concerning the intra-row distances in row crops, (e. g.<br />
sugar beet 17 to 20 cm) the positioning error <strong>of</strong> the intra-row <strong>weed</strong>ing<br />
equipment can reach 33%. Also, the plants can theoretically emerge up to 2 cm<br />
from the position where the seed was originally planted, reducing the positional<br />
accuracy <strong>of</strong> the map even more. Because <strong>of</strong> the possibility that such an error<br />
can occur, the <strong>weed</strong>/plant mapping concept has not been taken into<br />
consideration in this research.<br />
Taking into account the real-time concept, two major principles have typically<br />
been used <strong>for</strong> plant/<strong>weed</strong> distinction (Thompson et al. 1990): either the