53 lines
2.8 KiB
TeX
53 lines
2.8 KiB
TeX
\section{Goal Alignment}
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\label{p sec goal align}
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After the approach, described in the section \ref{p sec approach}, is finished,
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the robot is facing the ball, and the ball is at a short distance. In the stage
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of goal alignment, the task is to ensure that from the robot's point of view
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the ball lies between the goalposts. This means, that when the robot is
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centered at the ball, the goalposts should lie on either side of the center of
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the camera image. So the robot will first detect the goal and determine if that
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is the case. If that is not the case, the robot will go around the ball in a
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circle in the appropriate direction, until the ball is indeed between the
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goalposts.
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The walk in circle was implemented in the following way: the robot will step
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several steps sideways, then will turn to ball, as described in the section
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\ref{j sec turning to ball}, and finally will adjust the distance to the ball
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by stepping forwards or backwards, so that the ball is neither too close nor
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too far. The distance to the ball, similarly to the stage of the direct
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approach, is not measured explicitly, but is approximated through the position
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of the ball image in the camera frame. After performing these steps, the check
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is performed, if the goal alignment is completed. Otherwise, the steps will be
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repeated until alignment is achieved. The figure \ref{p figure goal-alignment}
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depicts the successful completion of this stage.
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\begin{figure}[ht]
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\includegraphics[width=\textwidth]{\fig goal-alignment}
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\caption{Successful goal alignment}
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\label{p figure goal-alignment}
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\end{figure}
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\section{Ball Alignment}
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Now that the ball and the goal are aligned, the robot has to move into a
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position, from which the kick can be performed. Depending on the situation, it
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may be feasible to select the foot, with which the kick should be performed,
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but due to time constraints we programmed the robot to kick with the left foot
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only. So, the task now is to place the ball in front of the left foot. We
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realized, that when the ball is in the correct position, then its image in the
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lower camera should be within a certain region. We experimentally determined
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the extents of this region, which is schematically presented in figure \ref{p
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figure ball-alignment}. The algorithm therefore is for the robot to gradually
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adjust its position in small steps, until the ball image reaches the target,
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after which the robot will proceed with the kick. Our tests have shown, that
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this method while being relatively simple, works sufficiently robust, which
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means that we didn't have the situations, when the robot missed the ball after
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alignment or even hit the ball with an edge of the foot.
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\begin{figure}[ht]
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\includegraphics[width=\textwidth]{\fig ball-align}
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\caption{Ball alignment}
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\label{p figure ball-alignment}
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\end{figure}
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