marsrover/document/robot.tex

   1 \section{Robot architecture}
   2 \subsection{Tools}
   3 \emph{LeJOS}\cite{lejos_team_lejos_2015}
   4
   5 \subsection{Design patterns}
   6 \subsubsection{Leader-Follower}
   7 Ultimately we want to only program one robot. The fact that the one robot
   8 contains multiple control bricks is something that needs to be abstracted away
   9 from. As will be discussed in Section~\ref{sec:mapping} the first brick, from
  10 now on \textit{Leader}, has the direct control over all the motors. However the
  11 second brick, from now on \textit{Follower}, controls no motors. Both the
  12 \textit{Leader} and the \textit{Follower} control $4$ sensors. Because of this
  13 configuration the \textit{Follower} only needs to send its sensor data to the
  14 \textit{Leader}. There is no need to communicate anything back since the
  15 \textit{Follower} can not respond in any physical way. An option could be to
  16 distribute the processing power but due to the strength of the bricks and the
  17 limitation of the bluetooth this is very hard or even impossible to achieve.
  18
  19 \subsubsection{Subsumption}
  20 As the higher level architecture we use a slightly adapted version of the
  21 subsumption architecture first described by Brooks\cite{brooks_robust_1986}.
  22 We use the pre-implemented architecture from the \emph{LeJOS} where with the
  23 use of a \texttt{suppressed} flag in every behaviour we can start and interrupt
  24 the behaviour. Our version is a little bit adapted from the original
  25 subsumption behaviour because in our implementation the robot can finish the
  26 designated task even if the behaviour does not want control anymore. For
  27 example when the left light sensor detects that the robot is driving of the
  28 planet a right turn of $90$ degrees may be initiated. This right turn will be
  29 completed even when the left light sensor is not detecting a dangerous value.
  30 The suppressed flag can take three states. \texttt{IDLE}, \texttt{IN\_ACTION}
  31 and \texttt{SUPPRESSED}. By default all behaviours have the \texttt{IDLE}
  32 state. When a behaviour is started the state will change to \texttt{IN\_ACTION}
  33 and when a behaviour finished the state will be reset to \texttt{IDLE}. When a
  34 behaviour needs to be interrupted the state is set to \texttt{SUPPRESSED} and
  35 since the behaviour is always monitoring the state it will shutdown as soon as
  36 possible and reset the state.
  37
  38 \subsection{Mapping of the sensors and actuators}\label{sec:mapping}
  39 The actuators are all plugged into the master brick to achieve the maximum
  40 safety in case the \emph{Bluetooth} connection fails between the master and the
  41 slave and one of the actuators is moving. All the safety-critical sensors for
  42 movement are placed on the master brick too. All other sensors are placed on
  43 the slave brick. Any increased latency on those sensors will not danger the
  44 safety. The final mapping is described in \autoref{tab:mapping}.
  45
  46 \begin{table}[H]
  47         \centering
  48         \begin{tabular}{lll}
  49                 \toprule
  50                         & Master Brick & Slave Brick\\
  51                 \midrule
  52                 \multirow{2}{*}{Actuators} & Left motor\\
  53                         & Right motor & \\
  54                         & Measurement motor\\
  55                 \midrule
  56                 \multirow{4}{*}{Sensors} & Left light sensor & Color sensor\\
  57                         & Right light sensor & Front ultrasone sensor\\
  58                         & Back ultrasone sensor & Left touch sensor\\
  59                         & Gyro sensor & Right touch sensor\\
  60                 \bottomrule
  61         \end{tabular}
  62         \caption{Proposed mapping of the sensors and actuators}\label{tab:mapping}
  63 \end{table}
  64