I. Introduction
Mobile robots have been widely used in many fields, such as space exploration and rescue in hostile environments. Among many technologies related with mobile robots, path planning is a key problem for successful navigation, whose aim is to generate a collision-free path in an environment while satisfying some optimal criteria [1]. A good strategy of robot path planning can guarantee a robot to safely and effectively fulfill a desired task. Therefore, the issue of robot path planning has been extensively studied in recent years.