-\section{iRobot Roomba 500}
-Originally, the \definition{Roomba} is an autonomous vacuum cleaning robot,
-manufactured by the US-based company \definition{iRobot}. The 500 series
-currently represents the third generation of iRobot's cleaning robots, and the
-first generation of robots controllable over an external interface.
-
-\subsection{Hardware design}
-\todo{diagram?}
-\paragraph{Wheels}
-The Roomba lives in a cylindrical case with diameter of about 34~cm and height
-of about 7~cm. It has two main wheels which are positioned slightly behind the
-centerline, so the Roomba leans forward due to gravity, and a small caster on
-the front to prevent it from sliding on the floor. The main wheels can be
-controlled over two independent motors, each one allowing to turn the connected
-wheel with a minimum of 10~mm/s and a maximum of 500~mm/s in each direction.
-One of the main wheel motors consumes about 300~mA in their slowest rotation
-speed, and about 1000~mA when driving with normal speed. Each wheel is also
-equipped with a drop sensor that tells if the respective wheel has dropped into
-a hole or similar, and does not reach the ground anymore. These sensors are
-realized with a spring pushing the wheel towards the ground, with the spring
-force adjusted to the Roomba's weight, and a micro switch which triggers if the
-wheel drops below a specified level. Furthermore, both wheels feature rotating,
-toothed discs, which in conjunction with an LED and a photo-electric resistor
-act as an optical interrupter. This system can be used to measure the wheel's
-current speed by counting the optical interruptions the wheel causes while
-moving.
-
-\paragraph{Brushes}
-In addition to the wheel motors, the Roomba has a motor which operates the
-vacuum brush, and a small motor on the front connected to a side brush, to allow
-cleaning of room corners.
-
-\paragraph{Bumper shield}
-Since the main movement direction in normal operation is forward, the front of
-the Roomba consists of a crecent-shaped bumper shield which contains several
-sensors. This bumper\index{Roomba!bumper} is spring-loaded and on the one
-hand absorbs shock to reduce damage, on the other hand, it allows the Roomba to
-detect obstacles in front of it, both via infrared sensors as well as by
-mechanical means. There are two sensors for mechanical bump detection, located
-30° to the left and to the right of the bumper's center, each implemented as
-photo-electrical interruptors. Additionally, six infrared sensors are unevenly
-distributed over the bumper, facing away from it in a star-like manner. Each one
-of them allows the Roomba to recognize objects in a maxmimum distance of 10~cm.
-Finally, the bumper shield contains four infrared sensors facing downwards,
-acting as cliff sensors \index{Roomba!cliff sensor} to recognize steps or
-similar chasms which could be dangerous for the Roomba to drive towards.
-
-The back part of the Roomba contains the main vacuum brush\index{Roomba!vacuum
-brush}, and the reservoir for holding dirt. Both of them can be removed, though
-the removal of the main brush reduces the Roomba's weight and slightly
-unbalances the Roomba so the springs used for the wheel drop sensors are not in
-balance anymore and push the Roomba upwards, so it tilts more to the front when
-accelerating forwards. There is also a sensor on the underside
-\index{Roomba!dirt sensor} for detecting particularly dirty regions of the
-floor, which is implemented as a capacitive touch sensor.
-
-\paragraph{Battery}
-The battery\index{Roomba!battery} is placed in the front part behind the bumper,
-it is a rechargeable NiMH battery and holds a capacity of 3300~mAh which lasts
-for about 90 to 120 minutes under normal operation. The Roomba can also find its
-home base and charge itself when it has finished cleaning or runs out of energy
-by using a special infrared sensor mounted on top of the Roomba. This sensor can
-see in all directions and is able to detect the home base by looking for a
-special infrared signal the home base\index{Roomba!home base} emits. The same
-principle is used for so-called "`virtual walls"'\index{virtual wall} which can
-be placed by the user in regions the Roomba should not move into.
-
-\subsection{Behaviour}
-\paragraph{Intended Behaviour}
-The Roomba normally follows its own, non-customizable algorithm to detect dirt
-and clean rooms. It is kind of a random walk\index{random walk}, controlled by
-the internal logic, which tries to keep the Roomba away from dangers like
-stairs and walls (by evaluating the cliff and bump sensors), and direct it to
-the more dusty regions of the room (by using the dirt sensor). The random walk
-concept allows a more or less complete coverage of the room, given the time for
-cleaning is large enough, while at the same only needing very little information
-about the environment. Of course, that concept is not very efficient when it
-comes to cleaning rooms, but cleaning time is not neccessarily the constraining
-factor, and the robot still saves the human some time.
-
-\paragraph{Roomba Open Interface}
-However, robots of the Roomba 500 series are also easily controllable over a
-serial port, which provides a two-way communication at 5~V TTL levels over a
-Mini-DIN connector, with a speed of either 19,200 or 115,200 Baud. Over this
-serial port, the Roomba speaks a specified protocol, called the
-\ignoreoutput{\ac{ROI}}\definition{\acl{ROI}} (\acs{ROI})~\cite{irobot-oi},
-which allows the user to interact with the robot's internal logic, reading its
-sensor values, and control its movements and cleaning behaviour.
-
-After starting the communication with the Roomba by sending the \cmd{Start}
-command, the robot is in a state called \definition{Passive mode}. In this mode,
-the user cannot control the robot by himself, but the internal logic defines
-icants behaviour. However, the user is able to read the internal sensors. The
-\ac{ROI} then allows the user to set the Roomba into two different modes:
-\begin{itemize}
- \item In \definition{Safe mode}, the Roomba monitors the wheel drop, cliff
- and internal charger sensors, and reverts into Passive mode if safety
- conditions occur, so the Roomba is not harmed.
- \item In \definition{Full mode}, the user has full control over the Roomba,
- and has to take care not to harm the Roomba by evaluating the wheel drop,
- cliff and internal charger sensors by himself.
-\end{itemize}
-
-In particular, every command is assigned an \ac{opcode} of one byte length,
-followed by a fixed amount of bytes as parameters which depend on the opcode.
-For example, to start the communication with the Roomba, the \cmd{Start}
-command has to be sent, which has the \opcode{0x80} and takes no parameters. The
-\cmd{Safe} command to put the Roomba into safe mode has \opcode{0x83}, and like
-the \cmd{Full} command with \opcode{0x84}, it takes no parameters.
-
-For example, to start the communication with the Roomba and set it into Safe
-mode, one would send the following bytes over the serial interface:
-\begin{verbatim}
-0x80, // Start command
-0x83 // Safe command
-\end{verbatim}
-The, additional commands can be sent over the \ac{ROI}, like actuator commands
-for controlling the Roomba's driving behaviour.
-
-\paragraph{Actuator commands}
-The \ac{ROI} specifies various actuator commands to control the Roomba's wheels,
-brushes and \ac{LED} displays, and let the Roomba play tunes. However, the
-central command needed for the experiments in thie thesis is the \cmd{Drive}
-command, \opcode{0x89}, which takes 4 additional bytes as parameter: the first
-two bytes specify the velocity that the Roomba's centerpoint should travel with
-while driving, and the third and fourth bytes specify the radius of the arc the
-Roomba's centerpoint should describe. The Roomba then calculates the required
-right and left wheel velocities internally without further interference of the
-user.
-
-The velocity is interpreted in mm/s, the value can range from -500~mm/s to
-500~mm/s, with negative values implying backwards movement. The radius is
-interpreted in mm, ranging from -2000~mm to 2000~mm. Negative values make the
-Roomba turn toward the right, whereas positive values make it turn toward the
-left. There are also four special values for the radius: \magicnumber{1} makes
-the Roomba turn on the spot in counter-clockwise direction, \magicnumber{-1}
-makes the Roomba turn on the spot in clockwise direction, and
-\magicnumber{0x7fff} and \magicnumber{0x8000} make him drive straight.
-
-For example, to drive straight with a velocity of 1000~mm, one would send the
-following bytes over the serial interface:
-\begin{verbatim}
-0x89, // Drive command
-0x03, 0xe8 // parameter velocity: 0x03e8 == 1000
-0x80, 0x00 // parameter radius: special value "straight"
-\end{verbatim}
-
-A little disadvantage of the \ac{ROI} \cmd{Drive} command is that the robot is
-modeled as a state machine. In the previous example, the Roomba would keep on
-driving until it runs out of energy, or a safety condition occurs which causes
-the Roomba to revert into Passive mode, or a new \cmd{Drive} command with the
-velocity parameter set to zero is sent. Thus, if the user wants to drive a
-specific distance, he has to calculate the time the robot needs to travel that
-distance, measure the time, and stop the robot after that time interval has
-passed. When using incorrect clocks, or when using inaccurate timers, this can
-lead to errors in movement. Because of that, it is appropriate to monitor the
-Roomba's movement, for example with its internal sensors.
-
-\paragraph{Input commands}
-The Roomba~500 series features a total of 49 different sensor values. Among the
-sensors mentioned above, there are also some internal values concerning battery
-charge, capacity, and temperature, motor currents, and even some more (or less)
-useful variables like the characters read from the infrared remote control, the
-current \ac{ROI} mode or the currently playing song. Nevertheless, there is
-also the possibility to query the travelled distance, the turned angle and the
-internal encoder counts ("`ticks"') for the left and right wheel. Each sensor
-value is 1 or 2 bytes long and is assigned a specific \definition{packet ID}.
-Some packet IDs also describe groups of multiple sensor values sent together.
-
-Sensor values can be retrieved either by explicit polling or by enabling a
-stream of values that is sent every 15~ms. Explicit polling works through the
-\cmd{Sensors} command (\opcode{0x8e}), which takes the packet ID of a single
-sensor as parameter, or through the \cmd{Query List} (\opcode{0x95}) command,
-which takes multiple packet IDs headed by the total number of requested packets
-as parameter. Both of these functions send back the requested values directly.
-
-By using the \cmd{Stream} command (\opcode{0x94}), it is possible to receive
-the requested sensor values every 15~ms. This is very convenient for real-time
-behaviour, when the sensor values have to be evaluated very often. As the
-\cmd{Query List} command, the \cmd{Stream} command takes the total number of
-packet IDs followed by the requested packet IDs as parameter. It sends back the
-sensor values in packets using the following format:\\
-\verb|0x13|, $n, p_1, v(p_1), p_2, v(p_2), \ldots, p_n, v(p_n), c$\\
-where:
-\begin{description}
- \item[$n$] is the number of bytes sent back, excluding $n$ and $c$,
- \item[$p_i$] is a requested packet ID, $i = 1, \ldots, n$
- \item[$v(p_i)$] is the value of the packet with the packet ID $p_i$
- \item[$c$] is a checksum, with
- $\sum_{i=1}^n\left(p_1 + v(p_1)\right) + c + n \equiv 0 \mod 256$
-\end{description}
-
-Example: The following byte sequence requests data from the left cliff
-signal (packet~ID \magicnumber{0x1d}) and virtual wall sensor (packet~ID
-\magicnumber{0x0d}):
-\begin{verbatim}
-0x94, // Stream command
-0x02, // parameter: 2 packets following
-0x1d, 0x0d // parameter: request packets 0x1d and 0x0d
-\end{verbatim}
-
-The Roomba then returns the following bytes every 15~ms:
-\begin{verbatim}
-0x13, // Header byte
-0x05, // 5 bytes following, except checksum
-0x1d, // Packet ID 0x1d following
-0x02, 0x19, // Data for Packet ID 0x1d (2 byte)
-0x0d, // Packet ID 0x1d following
-0x00, // Data for Packet ID 0x0d (1 byte)
-0xb6 // checksum: 0x5 + 0x1d + 0x2 + 0x19 + 0xd + 0x0 + 0xb6 = 256
-\end{verbatim}
-
-In our setup, an iRobot Roomba~530 is used as an instance of an autonomous,
-mobile robot to conduct the experiments described afterwards. For that, the
-Roomba's movements are controlled over a netbook mounted on top of the Roomba
-(cf.~Figure~\ref{fig:roombasetup}), which is running Wiselib code. The Wiselib
-code in turn uses the \ac{ROI} and especially the \cmd{Stream} and
-\cmd{Drive} command to control the Roomba.
-
-\section{Wiselib}
-The \definition{Wiselib}\cite{wiselib} is a C++\index{C++} algorithm library for
-sensor
-networks, containing for example algorithms for routing, localization and time
-synchronization, and is strongly focused on portability and cross-platform
-development. In particular, it allows the user to develop applications that run
-on different hardware platforms without the need to change the code, and it
-strongly uses C++ templates to achieve that feature. Amongst the supported
-platforms are diverse sensor node platforms, like iSense, Contiki and TinyOS,
-but there are as well implementations for the diverse x86-compatible Personal
-Computer platforms, and the Shawn sensor network simulator.
-
-\subsection{Architecture}
-\paragraph{Concepts and Models}
-Wiselib makes strong uses of \definition{concepts} and \definition{models} as
-central design objects. Concepts serve as an informal description of interfaces,
-only existent in documentation, defining expected parameters and types. Models
-however implement these interfaces in C++ code while fulfilling their
-specification. The Wiselib algorithms can in turn rely on the concepts as a
-generic specification, and take models as template parameters to use their
-functionality, so a function call will be immediately resolved to a specific
-model at compile time without the need for an additional function call as it is
-the case with virtual inheritance.
-
-This makes cross-platform development easily possible. For example, to implement
-a routing algorithm, one can rely on the concept of a Radio to send and receive
-data packets, without needing to implement code specific to the used radio
-hardware. The users of that routing algorithm can now choose which radio model
-they want to use, according to their needs and the underlying hardware, provided
-that their radio model also implements the same Radio concept that the routing
-algorithm uses.
-
-\begin{figure}
- \centering
- \includegraphics[width=.8\textwidth]{images/Wiselib-Arch.pdf}
- \caption{Wiselib architecture\label{fig:wiselib-arch}}
-\end{figure}
-Besides algorithms, the Wiselib also consists of two other main parts: the
-internal interface and the external interface (see Figure
-\ref{fig:wiselib-arch}).
-
-\paragraph{}
-
-\subsection{Roomba}
-Moreover, the Wiselib includes code to control the iRobot
-Roomba\index{Roomba} over a
-serial interface, and getting access to its internal sensor data, using the
-iRobot Roomba Open Interface mentioned earlier.
-
-\todo{cite Wisebed book chapter on Roomba code}
-\todo{which roomba sensors were used?}
\ No newline at end of file
projects / bachelor-thesis / written-stuff.git / commitdiff