3D kinematic modeling of a self-reconfigurable wheeled mobile robot for enhancing multimode motion capability

Self-reconfigurable wheeled mobile robots (SRWMRs) are capable of achieving multiple motion modes and subsequent switching between them through the coordinated sequential movements of multiple rocker–bogie joints, leading to overcoming dynamic obstacles posed by different terrains. However, real-time coordination of internal joints for executing reconfiguration actions while maintaining strong adhesion between the wheels and terrain remains challenging, particularly during action transitions. To enhance multimode motion capability by using a unified model, this work develops an inverse kinematics control (IKC) method, including 3D kinematic modeling of an SRWMR with actively and passively articulated suspensions, and additional motion-constraint inequalities for multi-joints in the wheel-suspension system. Specifically, the 3D model is built to achieve horizontal movements and vertical lifting of the robot chassis and its wheels. To further stabilize body posture and reduce wheel slippage during multimode motion, motion constraints are proposed to regulate the relative velocities among multiple joints and the displacement of the robot’s center of mass. According to the results of physical experiments with the HIT-MRII robot, Wheel Rolling, Wheel Crabbing, Wheel Lifting, Robot Chassis Lifting, Robot Creeping modes, and parts of their hybrid modes are achieved steadily and safely by the developed IKC method. The maximum motion performance of each mode is achieved by the proposed motion constraints. The enhanced mobility of the robot is demonstrated by comparing various traversal modes on soil terrain and presenting the corresponding control strategies.