In recent years mobile robots have widely developed for various tasks, including building iection, military reconnaissance, and planetary exploration and recently it is used in wheelchair design for assistant disabled people. The aim of this research is design a wheeled mobile robot for climbing stairs and presenting an algorithm based on friction between wheel and terrain, which can move on steps, symmetric obstacles and asymmetric obstacles without any complex sensors and the other equipments that they normally are so expensive and they are used in many robots. Due to light weight, simple controlling algorithm, high energy efficiency and low noise, wheeled mobile robots have attached much attention. Wheeled mobile robot with passive linkage mechanism is capable to adapt with rough terrain and step with appropriates dimension. In the chosen robot, effective parameters such as: links length, distance between robot, central gravity and ground and wheels mass are selected. Optimizing these parameters will result in improvement of stair climbing. Due to low speed of robot, using quasi-static analysis is possible. Using this analysis for some special cases, results in obtaining reaction forces such as: traction and surface reaction force in contact point between robot wheel and the wall of step. In order to enhancing robots capability in passing steps, robots dimensions are optimized. The used optimization method is a multi-objective goal attainment problem. In this method, goal attainment, constraints problem and optimization goals are defined. Using this method will lead our goal functions to suitable values. In the rough terrain, it is important for mobile robots to maintain adequate traction as excessive wheel slip cause the robot to lose mobility or even be trapped. In the end, traction controlling algorithm is implemented based on stick-slip phenomenon on the wheel. In this algorithm, the exerted wheel torque will be between the maximum generated torque due to kinetic and static friction forces on the wheel. Then by calculating wheel angular, effective parameters on control algorithm are obtained. This algorithm is implementing by using ADAMS and MATLAB softwares and the only required information is the wheel angular velocity. Using ADAMS, angular velocity is calculated then using MATLA S-function Simulink traction controller, suitable torque will be applied to wheels by estimation angular acceleration. Simulation results show that, robot can move on smooth surfaces and surfaces with symmetric and asymmetric obstacles and steps with suitable dimensions. Torque, angular velocity and angular acceleration graphs related to each path are derived. In the path with symmetric obstacles similar results are observed. In path with asymmetric obstacles, the graphs are not similar due to robot motion. By using algorithms, robot could up 10cm step in 7seconds. Result shows that torque exerted on wheel in most per iod is between maximum static and dynamic friction. The steep changes in the simulation results are caused by the instantaneous collision between wheel and the wall of the step. Keyword : wheelchair mechanism, rough terrain, ADAMS, multi-objective goal attainment, traction force.
