Abstract:
Dynamically stable two-wheeled mobile robots are the main theme of this thesis. Like everything, the environment we are living in is not constant but dynamic, which makes us adaptive to these changes. In dynamic environment, uncertain perturbations highly exist and collision are likely to happen. Robots expected to work alongside human are also required to be robust and adaptive against disturbance, collisions, and etc. Dynamic stability, compliance, and redundancy some of the key concepts providing higher adaptivity and flexility in this kind of environment. This thesis are concentrated on the dynamically stabilized two-wheeled manipulator and two-wheeled wheelchair systems. Chapter 1 covers the background information and related works about the dynamic stability, underactuated, redundancy and backstepping. Chapter 2 explains the basic information about disturbance observer based acceleration control. Disturbance observer provides a robustness and simply structure to deal with nonlinear coupling terms in multi-degrees of freedom easily. Chapter 3 describes the key features of dynamically stabilized two-wheel mobile systems and the related works addressed before. High center of gravity, small footprints, fast response, compliant behavior are some the features of these two-wheeled systems. The dynamically stable two-wheeled mobile manipulator is simply the combination of a two-wheeled mobile base and a manipulator, which makes it possess properties of both types of robots. Although casters in wheelchairs provide the static stability, they also limits the mobility of the wheelchair sidewalk curbs, and small steps. Unlike the ordinary wheelchairs, two-wheeled wheelchair system does not possess front casters, which makes it easy to deal with these kinds of obstacles. Whereas these systems are inherently unstable, they are generally lighter, more flexible, agile and capable of turning with zero radiuses. Chapter 4 introduces the robust motion control structure for the two-wheeled mobile manipulator. This system has highly nonlinear and complex dynamics due to the underactuated and high degrees of freedom structure. To reduce the complexity, simplified virtual models are utilized. The robust motion control is applied to stabilize passive joint. Chapter 5 focuses on the compliant CoG compensation for the two-wheel wheelchair system. In two-wheeled electrical wheelchair system, rider can sit the seat and control the motion this system by leaning his/her body. The CoG position of the upper body is mainly determined by the position of the rider. Thus, the CoG position may not overlap with the wheel axis. In that case, sensor information cannot be used to measure the exact position of the CoG, which affects the stability negatively. As a result, compensation of the unknown CoG position for two-wheeled wheelchair is considered to increase the flexibility and improve the overall stability. Chapter 6 addresses the multi-task issue for the two-wheeled mobile manipulator system. It is important to ensure the issues such as safety and reliability during human-robot interaction. This structure also provides redundancy to perform the main task with different configurations or additional tasks at the same In redundant systems, conflict or conflicts between tasks may occur when dealing with multiple objectives at the same time. Task priority strategy is introduced for two-wheeled mobile manipulator to perform multiple tasks simultaneously through a hierarchical order between the tasks so that lower-priority tasks do not affect the high-priority ones. Thereby, conflicts between tasks can be avoided by assigning an order of priority to the given tasks.