Trajectory Planning Of Wheeled Mobile Robot Based On Differential Flatness

Trajectory planning and generation is one of the most key technologies for the control problem of Wheeled Mobile Robot (WMR), which aim is generating the temporal motion sequences satisfying internal systemic constraints after path planning process, and ultimately finding the smooth motion trajectory which connect the initial state and terminal state. It's an important part of motion planning and also the foundation of trajectory tracking controller later.Wheeled Mobile Robot is a typical nonholonomic system, and the trajectory planning problem of which becomes even harder and complex for the existing nonholonomic constraint has limits on velocity space. But we can solve this problem finely by use of the concept of differential flatness. Because using flatness outputs we can reduce the dimentions of planning problem maximum and at the same time can ensure the planned trajectory satisfy nonholonomic constraints automatically. Furthermore dynamic optimization can be integrated with planning which could ensure the trajectory not only admissible but also optimal in practice.On the basis of summarizing and reviewing previous research works on trajectory planning of WMR, this paper makes some further research work and exploration on the control inputs constraint problem combining the dynamic model of WMR, at the same time we solved the optimization problem like time and enegy objective functions, and finally generated the optimal reference states and front-feedback control inputs for the following tracking controller. The results of simulation verify that the proposed method is reasonable and effective.The main research work in the thesis is as follows:1. First we summarized the background and central control problems of Wheeled Mobile Robot, and explained the basic process of moton planning which contains path planning and trajectory planning.2. Then the most important characters of Wheeled Mobile Robot which is nonholonomy and flatness are deeply analyzed, we showed how they impacting the WMR systems and at the end we introduced the most commen solution techniques classes for dynamic optimization.3. Considenring The significance of models for trajectory planning problem, we set up some kinamic models for the three and four wheeled vehicles which are mostly commen seen. Besides we proposed the basic process for the dynamic modeling using Langrange equation.4. Flatness based method for trajectory generation using dynamic model is proposed, which basic idea rely on flatness output which can transform system dynamic differential equation to algebric equation through interior feedback, therefor the key dynamic transforming problem is solved. Then through parameterizing the flatness output we can generate the trajectory of given paths. Simulation results showed that the mothod is effective. And also we found the conservation about not considering the constraints of control inputs, which caused some results can't be carry out in practice.5. Considenring commenly existed control input constraint in practice and the higher demands on system performance, we improved the trajectory planning method based on differential flatness throuth combining dynamic optimization. Firstly we ensure the trajectory could satisfy the nonholonomic constraints applying differential flatness, secondly dynamic optimization solution is combined to flatness based trajectory planning problem, which ensure the trajectory satisfy the saturation demand on inputs and minimize the objective function about time and energy at the same time, so the trajectory is admissible in practice. Simulation results showed that the mothod is effective.There is also some problem which is not solved in this thesis, such as real time trajectory planning and generation problem and basis function selection problem.