Nonholonomic Mobile Robot Motion Planning Algorithm Research

Motion planning for mobile robot is the problem of how to design an appropriate control-input to make the system move from the starting point to the goal point safely and collision-freely. Nonholonomic constraints are widely present in the mobile robot system, like wheeled robots, space robots and so on. For this kind of robot, the limited range of motion caused by nonholonomic constraints should be taken into account in addition to the need of considering the configure-space constraints caused by obstacles. Therefore nonholonomic constraints have brought great challenges to the mobile robot motion planning problem.This paper is focused on solving motion planning problem for mobile robot under nonholonomic constraints. The main contribution of this work is:1. Elaborated on the definition of nonholonomic constraints and how to establish the kinematic model for non-complete system. Several typical models of mobile robots under nonholonomic constraints are given for the research of motion planning algorithm follow-up.2. Analyzed the Rapidly-exploring Random Trees (RRT) algorithm and proposed four improvements to this algorithm. In order to reduce unnecessary costs caused by uniformly random searching, the idea of goal bias is introduced in this paper; A new distance parameter of low computational complexity is selected to advance the calculation speed; An preprocessing stage is proposed to provide the estimate index on the workspace’s free volumes which can lead the tree to explore free space tendentiously and improve the extensibility; Selection mechanism of control-input is improved to advance the exploring speed. The improved RRT algorithm is valid and efficient even when other planners get into scrapes in some complex environment.3. Combined the improved RRT algorithm and the rolling windows method to solve motion planning in globally unknown environment. A simplified sub-goal determination strategy is proposed to improve the efficiency of the algorithm. The idea of critical state is used to solve the problem that the rolling window method might cause oscillations sometimes.Compared the improved algorithm to some traditional methods; the simulation results verified the validity and advantage of the proposed algorithm.