Motion Planning And Control For Nonholonomic Wheeled Mobile Robots

With recent advances in technology, the fields of human research have been furtherexpanded through the use of mobile robot in a complex environment. People can explore thehuman thinking mode and discuss the generation of complex agent behaviors by taking themobile robot as an experimental platform. The motion planning and motion control issues of themobile robot are related to cognitive science, pattern recognition, nonlinear control, and otherfields. The resulting outcomes will also promote the development of military, transportation andindustrial robot system applications. In this dissertation, the motion planning and control forwheeled mobile robots is considered. Major researches and innovations are summarized asfollows:1. The trajectory tracking problem of nonholonomic wheeled mobile robots is considered.Unlike the path following problem, the trajectory tracking problem not only have the spatialposition requirements, but also have time requirements, i.e., to control the mobile robot reachesa specific location at a specific time. A novel trajectory tracking control method based on thedynamic model of a wheeled mobile robot is proposed. Tracking errors between the referenceand the real postures are calculated in the robot body coordinate system. Then the guidanceangle is designed by analyzing the relationship between lateral and angular errors. Thekinematics tracking controller is developed with the backstepping approach by taking theguidance angle as a virtual input. Parameter selection criterion for the controller is alsoinvestigated. By taking the external disturbances into account, a torque controller based on thedynamic model is derived. Simulation results verify the effectiveness of the proposed method.2. The problem of path following of nonholonomic wheeled mobile robots is considered.The goal of path following is to control the mobile robot to follow a geometric curve withoutany time requirements. A control scheme is proposed for the following of parametric curves. Tracking errors between the actual and desired postures are first calculated in the pathcoordinate system. The origin of the path frame is fixed to the desired poison on the referencepath. The guidance angle is assigned by analyzing the relationship between lateral and angularerror in the path frame. The path following controller and the update law of the path parameterare designed by using the Lyapunov direct method and backstepping technique. Simulationresults following a Bezier curve path demonstrate the effectiveness of the method.3. The control problem of wheeled mobile robots with model uncertainties is considered.Since the actual physical parameters of the mobile robot are difficult to determine accurately, itis first assumed that the physical parameters of the robot were assumed to be unknown exceptthe wheel radius and the distance between the two driving wheels. The problem is solved byusing the nonlinear approximation capacity of the fuzzy system. And by taking the trajectorytracking problem as an example, an integrated controller based on the dynamics model of themobile and the update law of fuzzy weight matrix are designed. Then it is further assumed thatall the physical parameters of the mobile robot are unknown. The control law is designed byusing the adaptive backstepping and the fuzzy approach. The adaptive law of unknownparameters and fuzzy weight matrix are also given.. The effectiveness of the proposed method isverified by simulation results.4. Proposed an improved method for mobile robot motion planning without violatingacceleration limits. When a mobile robot tracking a trajectory planned in advance, willinevitably produce tracking errors. One of the causes of the tracking error is that the curvature ofthe planned path is not continuous. Another reason for the generation of tracking error is theslippage of the driving wheels. When the acceleration limits are exceeded, slippage occursbetween the tire and the ground, resulting in tracking error. The acceleration limits aredetermined by the friction between the wheels and the ground. The tangential acceleration isresponsible for the change in the robot’s velocity. The radical acceleration is due to the curvatureof the path. Given the terminal posture sand velocities, the cubic Bezier curve is employed forpath planning. Then the maximum allowable velocity profile can be calculated according to theacceleration limits while the acceleration limits can be determined by the surface frictionbetween the wheels and the ground. Simulation results show the effectiveness and quickness ofthe proposed algorithm.