978-1-4673-1975-1/12/$31.00 ©2012 IEEE ICIAfS’12 Localization of a Mobile Robot Using ZigBee Based Optimization Techniques S. Palipana, C. Kapukotuwe, U. Malasinghe, P. Wijenayaka, and S. R. Munasinghe Department of Electronic & Telecommunication Engineering, University of Moratuwa, Katubedda, Moratuwa 10400, Sri Lanka. Email: chiranthakak@gmail.com Abstract — this paper introduces techniques for designing and implementing remotely controllable outdoor robots with the ability to localize itself while traversing in hazardous environments. The robot platform designed is a semi- autonomous tiller modified as required by the application. Localization based on wireless sensor network which has been a research interest of is addressed here with the use of Zigbee protocol. A Kalman filter was applied for the initial gathering of training data. For the improvement of the accuracy of position estimation, a fuzzy inference system is introduced. An extended Kalman filter is applied at the end in order to fuse the encoder data with the filtered RSS data. Results prove that a metric accuracy varying from 2m to 10m is achievable depending on the location of the robot with respect to the sensor nodes. I. INTRODUCTION Outdoor robots should possess the ability to be maneuvered in unstructured terrains. Designing such a robot requires some serious attention to its platform since it should be able to traverse in outdoors carrying all the required equipment onboard. The usage of an IC engine to power the robots movements was essential in our case when the amount of power level required and the way we are going to achieve it is considered. The most possible option we had in this regard was to use a walk behind tractor as the platform and modify it to suit our requirements. The eight horsepower diesel engine of the tractor we used, gave more than enough torque to reach the outdoor locations we needed. Going with this approach a walk behind tractor was modified to have separate disk brakes for each wheel which can be controlled by a linear actuator. Another linear actuator was used to control the clutches associated with the tractors turning mechanism. These two linear actuators were controlled by a motor driving board which takes control signals from the onboard microprocessor. Each time a command is given to either steer the tractor to a certain direction or drive it forward, the linear actuators will change their shaft positions to either pull or release the cables connected with the two clutches and the brakes. Robot localization in a wireless sensor network requires estimation of the position of the robot with respect to several sensor nodes. Each time the user commands the robot to localize itself; it will communicate with the surrounding beacons using ZigBee [1] technology to acquire RSSI values of the most recent communication done between them. The low power consumption of ZigBee and high data rate were the main reasons for us to use ZigBee as our main communication medium. The complexity and the discrepancy of the environment the robot has to navigate determine the overall accuracy of its position estimation. A generic model that describes the position of a robot under various environmental conditions is a difficult task to achieve with the constraints in hardware, software and time limitations of real time localization since acquiring RSS values from a beacon takes a considerable amount of time which will affect the overall time taken for the localization process. Many different methodologies exist currently on the implementation of localization in outdoor environments; wireless network based localization [2], GPS based localization, Sensor based localization (Inertial, Pressure, Induction and RFID) are to name a few. These techniques occupy advantages and disadvantages in their deployment depending on the environment and the platform II.PROCEDURE A. Robot Platform Fig. 1. The Robot Platform Since the robot was an outdoor robot and it should have the capability to handle unstructured terrains, the usage of an IC engine was a must in order to deliver the amount of power needed. After considering the possible outdoor robot platforms we can have in our robot the final and the most suitable option was to utilize a modified power tiller as the robots platform with custom modifications to increase its maneuverability. The tiller consists of two linear actuators which control the two clutches used in turning and the two disk brakes externally fixed to the two wheels. The need of fixing two external disk brakes to each wheel was to reduce the turning radius while the clutches are disengaged since,