Development of the Rough Terrain Hybrid Mobile Robot (RHyMo) with Low Posture Variation Index and High Terrainability

Abstract

This thesis presents a new mobile robotic platform (RHyMo) which can reduce unexpected variations in height and pitch angle of its main body while traversing rough terrains and also has high terrainability to overcome an obstacle. A new performance metric for a mobile platform called as a posture variation index (PVI) was suggested to evaluate the smoothness of its movement on rugged terrain, which may play an important factor to predict undesired oscillations of a mobile platform while traveling on rugged terrain. The proposed PVI is defined as a combination of height and pitch angle variations of center of mass (CM) of a mobile platform. By using this proposed PVI, the movements of various mobile platforms are exhaustively analyzed. A new linkage mechanism which has low posture variation was suggested by adopting the inverse four-bar mechanism. Height variation and pitch angle variation of main body of the new linkage mechanism were measured, and the resulting PVI is much smaller than those of other mobile platforms. The new linkage mechanism was optimized by kinematic analysis and the resulting PVI value was significantly reduced by 17.9 % compared to Rocker-Bogie mechanism which showed the smallest PVI value previously. In order to ensure smooth movement as well as excellent terrainability, a new mobile platform (RHyMo) is proposed based on the kinematic and inverse dynamic analysis results. The extensive experiments are carried out by using Rocker-Bogie and RHyMo on artificial rugged terrain, which validate that in comparison with the Rocker-Bogie, the average and maximum height variations of RHyMo are reduced by 12.72 % and 5.96 %, respectively. Moreover, the average and maximum pitch angle variations of RHyMo are significantly reduced by 65.87 % and 60.53 %, respectively. The terrainability of RHyMo against a step and stairs of high slope is proved to be compatible to those of obstacle climbing mobile platforms with the help of the track mechanism installed at the front linkage