Development of a novel mechatronic system for mechanical weed ...

Results and discussion
position of the tool is acquired with an incremental encoder the most recent
position of the system can be calculated as the reminder value after dividing the
value acquired from encoder N with the number of pulses corresponding to one
rotation RESsys. To make a decision of whether the hoeing tool needs to be
accelerated or decelerated a simple rule was applied: in cases where the latest
position is between 0° and 180°, the system needs to be decelerated and
between 180° and 360° it needs to be accelerated as defined in Equation 5.20.
⎧ ⎛ N ⎞ R ⎛ sys N ⎞
⎪rest ⎜ ⎟ for ≥ rest ⎜ ⎟ ≥ 0
⎪
⎜ RES ⎟
sys 2 ⎜ RES ⎟
⎝ ⎠ ⎝ sys ⎠
ϕ recent = ⎨
(5.20)
⎪ ⎛ N ⎞ ⎛ N ⎞ RESsys
⎪rest ⎜ − R sys for Rsys > rest >
⎜
⎟ ⎜ ⎟
RES ⎟ ⎜
sys RES ⎟
⎩ ⎝ ⎠ ⎝ sys ⎠ 2
where rest is defined as:
x / y = q * y + rest
(5.21)
The required rotation speed value ωnew can be estimated based on the recent
angular position and the remaining time until the hoeing tool arrives to the
position exactly above the next plant centre position, as follows:
ωnew
ϕ − ϕ
T
desired recent
= (5.22)
The required rotational speed need to be transformed into voltage and sent to
the servo drive as an external control signal. If there is only a small difference
between unew and uold it is better to leave the servo system in the steady state,
achieved after the previous adjustment, than to change the input voltage and
upset the system from the steady state. A size of the difference between unew
and uold which will be considered as small can be defined in the VI and it
depends on the size of the protected area, number of arms, number of cuts
between successive plants and angular adjustment of the arms.
The flow chart of the algorithm for the hoeing tool’s rotational speed control is
illustrated in Figure 5.22.
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