Mobile hybrid robots with adaptive morphology for advanced locomotion and object manipulation

Abstract

Mobile robots have demonstrated exceptional capabilities in traversing diverse environments, while manipulators excel at precise object interaction. However, combining these functionalities within a single compact system remains challenging, particularly for applications requiring navigation through confined spaces while maintaining object handling capabilities. This thesis introduces a novel solution: a hybrid mobile robot with adaptive stiffness and morphology that can transition between functioning as an efficient mobile platform and a versatile manipulator. The proposed system features a dual locomotion unit architecture connected by a variable stiffness bridge incorporating low melting point alloy. This design enables controlled transitions between rigid and flexible states, providing stability during locomotion and adaptability during manipulation. The robot's modular construction significantly reduces stiffness transition time while maintaining optimal mechanical properties throughout operation. Each locomotion unit functions autonomously while collectively facilitating coordinated bridge deformation during flexible states, enabling precise morphological adaptations for object manipulation. This dissertation presents the complete development process from design conceptualization to experimental validation. A comprehensive hybrid kinematic model characterizes the robot's behavior across both rigid and flexible states, identifying four distinct locomotion modes emerging from its variable stiffness capabilities. The hierarchical control framework integrates stiffness management with motion planning through model predictive control schemes that optimize performance across operational modes. For navigation, two complementary approaches are implemented: a hybrid RRT*-APF algorithm for environments with sparse obstacles, and a sophisticated Voronoi-based optimization method for highly cluttered environments requiring morphological adaptations. Experimental results demonstrate the robot's capacity for efficient omnidirectional mobility, rapid stiffness transitions, and effective full-body grasping of objects with diverse geometries. The system successfully navigates through confined spaces by leveraging its variable morphology to adapt to environmental constraints. Performance metrics validate significant advantages over conventional single-function systems in terms of versatility, adaptability, and operational effectiveness across multiple domains. This research establishes fundamental design principles and control methodologies for a new generation of multifunctional robots with adaptive properties. The contributions advance the field of robotics by bridging the gap between conventional rigid systems and soft robots, creating versatile platforms capable of addressing complex challenges in exploration, inspection, and search and rescue operations where both mobility and manipulation capabilities are essential within strict size constraints.