X-Git-Url: http://git.rohieb.name/bachelor-thesis/written-stuff.git/blobdiff_plain/600380af57fe95132b89fbf21db1ef26258f955b..e1b31bbb160bcdaeef79f2c60f2b69d173876ff1:/Ausarbeitung/preliminaries.tex diff --git a/Ausarbeitung/preliminaries.tex b/Ausarbeitung/preliminaries.tex index a6124b4..1796dcb 100644 --- a/Ausarbeitung/preliminaries.tex +++ b/Ausarbeitung/preliminaries.tex @@ -1,166 +1,8 @@ \chapter{Preliminaries} -This chapter describes the preliminary topics. \todo . +In the following, basic concepts used in this thesis are described. In +particular, there is a description of the iRobot Roomba, its hardware +and software, and an overview of the Wiselib algorithm library that is used to +control the Roomba. -\section{Dead reckoning} -The process of \definition{dead reckoning} describes an inexpensive method for -relative positioning by computing a vehicle's position from an initial -starting position and the covered distance and course it has moved. In the case -of mobile robots, the covered distance can be simply computed in real time from -the revolution of its wheels, or by accelerometers the robot may be equipped -with. However, since the vehicle's current position is based on its previous -position, and the distance measurement may be imprecise, dead reckoning has the -disadvantage that errors in position calculation can cumulate and the error -of the calculated position grows with time. - -Another approach to determine a vehicle's position is absolute positioning, for -example satellite-based, over navigation beacons or by map matching. Still, -these techniques are rather expensive to deploy, cannot (yet) be used in real -time, or are even impreciser than relative approaches\cite{umbmark}, so dead -reckoning can still be useful for the time being. - -\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 drive straight with a velocity of 1000~mm, one would send the -following bytes over the serial interface: -\begin{verbatim} -0x80, // start byte -0x83, // safe mode -0x89, // drive -0x03, 0xe8 // drive: parameter velocity: 0x03e8 == 1000 -0x80, 0x00 // drive: 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 interval the robot needs to -travel that distance, measure the time interval, and stop the robot after that -time interval has passed. - -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. - -\section{Wiselib} -The \definition{Wiselib}\cite{wiselib} is a 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. - -Moreover, the Wiselib includes code to control the iRobot -Roomba\index{Roomba~500} 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} +\input{roomba} +\input{wiselib}