Ausarbeitung/experiment1.tex

   1 \chapter{Experiment 1: Original Movement Behaviour}
   2 \label{sec:exp1}
   3 In the first experiment, the Roomba's original movement behaviour is
   4 measured to get an overview of the errors that occur while moving, and to
   5 establish a pool of data for correction approaches to work on later.
   6 There was no error correction involved (apart from any possible error
   7 correction the Roomba itself implements in its underlying logic, and which is
   8 not known to anyone except iRobot). To achieve this, the Wiselib Roomba Control
   9 is used to access the Roomba over the \ac{ROI}\index{Roomba Open Interface}.
  10
  11 \section{Setup}
  12 \label{sec:exp1:setup}
  13 \begin{figure}[htbp]
  14  \centering
  15  \includegraphics[width=0.45\textwidth]{./images/IMAGE_00079.jpg}
  16  \caption{Roomba with netbook\label{fig:roombasetup}}
  17 \end{figure}
  18 \begin{figure}[htbp]
  19  \centering
  20  \includegraphics[width=0.6\textwidth]{./images/IMAGE_00148.jpg}
  21  \caption{Measuring turn angles with laser pointer\label{fig:laserpointer}}
  22 \end{figure}
  23
  24 The test equipment consisted of a small x86 \index{netbook} netbook which was
  25 mounted on an iRobot Roomba~530\index{Roomba} robot, as seen in
  26 Figure~\ref{fig:roombasetup}. The netbook controlled the Roomba over a
  27 \acs{USB}-to-serial converter plugged into the \ac{ROI}\index{Roomba
  28 Open Interface} port on the Roomba, and hosted as the environment for
  29 executing the Wiselib \index{Wiselib} code.
  30
  31 In this experiment, the Roomba started right off with the full velocity the
  32 movement was executed with; so there was no control to adhere a constant
  33 acceleration when starting or stopping the movement. As mentioned before, due to
  34 limitations in the \ac{ROI}\index{Roomba Open Interface} it is only possible to
  35 explicitly start and stop the Roomba's movements at different times, so the
  36 Wiselib's implementation of the Roomba control code first starts the Roomba's
  37 movement, keeps track of the turned angle and dcovered distance, and then stops
  38 the Roomba if these values exceed the target values.
  39
  40 The tests were done in two atomic drive modes: letting the Roomba walk a
  41 specific straight distance with a specific velocity in its viewing direction and
  42 letting it turn on the spot with a specific velocity about a specific angle.
  43 Each of the two modes was carried out on two different floor types\index{floor
  44 type}, a laminated floor and a carpet floor, to see if the movement behaviour
  45 significantly depended on the floor type. The side brush was removed, since the
  46 Roomba tends to turn slightly towards the left when driving straight on a
  47 carpet floor. Without the side brush, this was not the case.
  48
  49 The actual travelled distance of the straight drive tests were determined using
  50 a measuring tape with an accuracy of 1~mm. Only the distance in the Roomba's
  51 original viewing direction was considered, as it turned out that the offset
  52 perpendicular to the viewing direction and a possible shift in orientation were
  53 too small to be measured precisely.
  54
  55 The actual turn angles of the turn tests were determined using a
  56 \acs{ISO}/\acs{DIN}~A0 sheet of paper with a printed polar coordinate system in
  57 which a circular hole was cut in the center to let the Roomba's wheels touch the
  58 floor. The sheet was fixed on the floor, and the Roomba was aligned in the
  59 center of the paper. A laser pointer\index{laser pointer} attached to the Roomba
  60 pointed to the current orientation on the paper, as shown in
  61 Fig.~\ref{fig:laserpointer}. The accuracy for these tests was 1~degree.
  62
  63 After the initial setup, the application \prog{roomba\_test} (see
  64 section~\ref{sec:impl:measuring}) was started on the netbook for half-automatic
  65 testing. It used a predefined array of nominal distances, angles and velocities
  66 and for each pair of distance (for straight drive tests) or angle (for turn
  67 tests) and velocity it used the Wiselib implementation to move the Roomba. Then
  68 it asked the user to input the measured distance or angle the Roomba had moved
  69 and repeated the process until each combination of distance/angle and velocity
  70 was used. The nominal and input values were written to a log file, as well as
  71 the floor type, the Roomba ID, the \ac{SVN} revision the program was built
  72 from, the battery status\index{battery status}, and other internal
  73 implementation-specific values.
  74
  75 For the straight drive tests, the arrays with predefined values were:\\
  76 \begin{tabular}{@{}ll@{}}
  77 Distances: & 20, 50, 100, 200, 500, 1000, 2000, and 4000~mm \\
  78 Velocities: & 20, 50, 70, 100, 150, 200, 300, and 400~mm/s
  79 \end{tabular}
  80
  81 For the turn tests, the arrays with predefined values were: \\
  82 \begin{tabular}{@{}ll@{}}
  83 Turn angles: & 5, 15, 30, 45, 90, 120, 180, 360, 530, and 720~degree \\
  84 Velocities: & 20, 50, 70, 100, 150, 200, 300, and 400~mm/s
  85 \end{tabular}
  86
  87 According to the implementation of the Wiselib Roomba control, the velocities
  88 were given in mm/sec and referred to the distance the wheels travelled when the
  89 Roomba turned on the spot, which was a circle of 230~mm in diameter.
  90
  91 \section{Results}
  92 \label{exp1:results}
  93 The following graphs show the difference from the measured value to the input
  94 value for driving or turning with different velocities. Positive values mean
  95 that the Roomba had turned too much or travelled more than the target value,
  96 negative values mean that the Roomba had turned or travelled too less. The
  97 plots show multiple test runs; given are the minimum, the maximum and the
  98 arithmetic mean\index{arithmetic mean} of all results for a data point.
  99
 100 \todo{clearpage, cleardoublepage?}
 101 \begin{figure}[p!]
 102  \centering
 103  \includegraphics[width=\textwidth]{images/iz250flur_drive_data.pdf}
 104  \caption{Original behaviour on laminated floor, straight drive movements
 105   \label{fig:orig:lam:drive}}
 106 \end{figure}
 107 \begin{figure}[p!]
 108  \centering
 109  \includegraphics[width=\textwidth]{images/iz250flur_turn_data.pdf}
 110  \caption{Original behaviour on laminated floor, turn movements
 111   \label{fig:orig:lam:turn}}
 112 \end{figure}
 113 \begin{figure}[p!]
 114  \centering
 115  \includegraphics[width=\textwidth]{images/seminarraum_drive_data.pdf}
 116  \caption{Original behaviour on carpet floor, straight drive movements
 117   \label{fig:orig:carpet:drive}}
 118 \end{figure}
 119 \begin{figure}[p!]
 120  \centering
 121  \includegraphics[width=\textwidth]{images/seminarraum_turn_data.pdf}
 122  \caption{Original behaviour on carpet floor, turn movements
 123   \label{fig:orig:carpet:turn}}
 124 \end{figure}
 125
 126 Figure~\ref{fig:orig:lam:drive} shows that the error becomes greater with
 127 increasing input distance when driving straight on the laminated floor, however,
 128 in Figure~\ref{fig:orig:carpet:drive} we see the opposite effect on the carpet
 129 floor, the error decreases with greater input distance. This could happen due to
 130 imprecise measurement of distances in either the Roomba's sensors or the Wiselib
 131 implementation that controls the Roomba, or both, adding up over the time the
 132 movement continues. Also slippage of the wheels on the laminated floor could be
 133 possible, as well as slowdown through the carpet floor, explaining why the error
 134 increases on the laminated floor, but decreases into negative values on the
 135 carpet floor when the distance grows.
 136
 137 On the other hand, rising the velocity always seems to cause the
 138 error to increase.
 139
 140 The same effects also apply for turn tests. Additionally, there could be errors
 141 resulting from false assumptions about the Roomba's wheel base\index{wheel base}
 142 diameter, resulting in false calculations of the circle the Roomba's wheels
 143 describe while turning, and therefore leading to false results.