Motion Control and Stability Improvement of Autonomous Mobile Robots with Suspended Wheels

Mobile manipulators have been given extensive attention in recent years since they have many applications such as materials transport and service for disabled persons. A mobile modular manipulator is normally composed of an m-wheeled mobile platform and an n-degree-of-freedom (DOF) onboard modular manipulator. This combination extends the workspace of the entire robot dramatically. Building up the dynamic model for such kind of robots is a challenging task due to the interactive motions between the manipulator and the mobile platform. Also the vibration control is an important research topic in mobile robots, especially when robots move through rough terrain. As for a mobile manipulator, the trajectory tracking task becomes even more complex and difficult to achieve since the platform and the manipulator move simultaneously. Furthermore, stability is another concerning issue since the probability of tip-over increases due to this kind of mechanical structure. To ensure steady movement of robots on rough terrain, usually suspension systems are installed between the wheels and the platform to absorb the vibration induced by road. Typically, Figs. 1 and 2 show a suspended wheeled robot called Seekur and a suspended manipulator, respectively. Seekur is a large, all-weather robot that can traverse rugged terrain. The suspended mobile manipulator can achieve tasks in the field so that more and more researchers have been devoted to the researches involving this kind of robot. This study focuses on the suspended wheeled mobile robot and deal with the following problems: Firstly, mobile robots with suspension system can absorb vibration induced by rough roads, but due to center-of-gravity (CG) shift and the dynamic of manipulator, the suspended platform is subject to vibration when the robot moves with acceleration. Secondly, trajectory tracking of a mobile platform and a manipulator simultaneously is a challenging work because of its complex nonlinearity and dynamic interaction between the platform and manipulator. Thirdly, when robots move through rough terrain, it is necessary to improve their stability to eliminate external interference that degrades the performance of vision systems. Finally, although teleoperation has been a benefit to remote control, how to generate an intuitive user interface for teleoperation is still a troublesome problem. Fig. 1 Seekur robot.