This master thesis contains modeling and nonlinear automatic control of an autonomous lawn mower. The vehicle shall be able to follow a magnetic field loop buried in the lawn on an arbitrary distance, including straddling. A unicycle model of the lawn mower has been derived based on previous work. The model holds for the assumption of non slip environment. Two diff erent control strategies have been implemented and evaluated in this thesis. One is based on feedback linearization  and with the feedback gain estimated using an LQ-controller. The other strategy is based on linearization at an equilibrium point  and also with the use of an LQ-controller. The only state that can be measured is the distance to the magnetic loop. In order to estimate the other states, an observer has been implemented using the linearized in an equilibrium point  model and a Kalman filter. The navigation of the autonomous lawn mower is performed using a magnetic loop buried in the lawn. The non-linearity of the magnetic field causes diffi culties when estimating the distance to the loop. One magnetic field strength corresponds to two distances to the magnetic loop. The nature of the magnetic field and the measurement noise causes the precision of the controller to be limited. The conclusion of this master thesis is that it is possible to navigate and follow the magnetic loop at a distance greater than 0.3 [m], but with overshoots during sharp turns. If the reference distance is smaller than that, the behavior of the robot will be oscillating when following the loop. The limitations of the controller performance is due to the lack of information which can be extracted from the measurements of the magnetic field.

SammanfattningExamensarbetet har syftat till att undersöka möjligheten att utrusta Husqvarnas autonomagräsklippare med avståndssensorer. Dessa ska hindra gräsklipparen från att kollidera med hinder i sinomgivning. Gräsklipparen arbetar i en miljö där väder, temperatur, ljusförhållanden och underlagvarierar kraftigt. Detta innebär att kravet på sensorerna är högt.Av de sensorer som undersökts har det visat sig att ultraljud och ”structured light” är de system sombäst skulle kunna uppfylla all dessa krav till ett rimligt pris.I examensarbetet undersöks därför ultraljudssensorer från företaget Maxbotix närmare ochimplementeras i en prototyp. Fyra stycken sensorer placeras på gräsklipparens kaross. Dessakommunicera med en mikrokontroller som i sin tur förmedlar mätdata till en dator. På datorn körsen sökalgoritm som tolkar och sammanfogar sensorernas mätdata.Efter ett antal tester visar det sig att de sensorer som valts inte uppfyller de krav som ställts. Dockbör den metod och algoritm som används kunna uppfylla kraven om en annan typ av sensor används. / AbstractThis master thesis is aiming to investigate the possibility of adding distance sensors to Husqvarna’sautonomic lawnmower. The goal is to prevent the lawnmower from colliding with obstacles in itssurroundings. The environment where the lawnmower is working is very dynamic in sense ofweather, temperature, ambient lightning and terrain. This gives high requirements on the sensors.Of all the sensors that were examined, ultrasonic and structured lightning came out as the ones bestfit to fill these requirements to a reasonable cost.In this thesis ultrasonic sensors from Maxbotix were implemented on a prototype. Four sensors wereplaced on the lawnmower body and connected to a microcontroller. The microcontroller then passesalong the sensor data to a computer that is running a search algorithm. The algorithm is used tointerpret the data and merge the different measurements.After certain amount of testing it was shown that the chosen sensor did not meet all therequirements. However the method and the chosen algorithm should suffice with another type ofsensor.

Husqvarna AB is one of the leading producers of outdoor products such as autonomous lawn mowers. One important feature of these products is the ability toquickly respond to environmental factors such as slippy areas. A reliable slip detector is needed for this mission and many different technologies exists for detectingslip events. A common technique is to check the wheel motor current, which clearlydeviates when the lawn mower is subjected to slipping. The on-board sensors opensup for an alternative solution which utilizes the loop sensors as the main slip detector. This thesis covers the construction of a slip detection prototype which is basedon the loop sensors. In the end, Husqvarna AB was provided with a new alternativesolution, which was successfully compared to the exiting solution. It proved to bea reliable slip detector for manually induced slipping indoors, outdoor performancewere not investigated. Ultimately, the implemented prototype outperformed the existing solution in the intended environment of indoor testing.

Purpose:The purpose of this thesis was to identify a useful solution to find the location of a broken boundary wire. By useful we mean that the solution should be inexpensive, user friendly and accurate. However, this thesis will only investigate the accuracy of the method where the hypothesis is that an investigated method is applicable for all underground wires. Method:This study conducted a literature research in order to investigate what methods that are used in other industries to locate faults in underground, low-voltage electrical wires. After the research, the most commonly used fault locating methods were described and the one that seemed most useful was chosen as a possible solution.For the solution to be useful the accuracy was investigated. The method used to conduct an experiment and gather data to validate the solution was Design Science Research. Result:Three methods were investigated as possible solutions:Time Domain Reflectometry (TDR), Frequency Domain Reflectometry (FDR) and Murray bridge where experiments were conducted using TDR.TDR proved to be unapplicable in locating faults in boundary wires, although it was confirmed to be a valid solution to locate faults in coaxial cables with <1% error margin.What makes TDR and other reflectometry methods unsuitable methods within the autonomous lawn mower industry is the lack of characteristic impedance in the used boundary wires. The hypothesis that an investigated method is applicable for all underground wires is thereby refuted. Limitations:Experiments were conducted in laboratory environment with a signal generator and an oscilloscope. One experiment was conducted on a boundary wire in the ground which provided no reflected signal.