Adaptive Motion Control of a Terrain-Adaptive Self-Balancing Leg-Wheeled Mobile Robot over Rough Terrain

This paper proposes an adaptive motion control approach that incorporates the backstepping sliding-mode motion control, side tilting control and impedance control method to steer a terrain-adaptive self-balancing leg-wheeled mobile robot over rough and uneven terrain. The proposed robot improves a hybrid design of bipedal walking and wheel-driven modes by adding a new locomotion mechanism. Different from ordinary two-wheeled self-balancing robots, the improved mobile robot has two extra knee joints to keep the body balancing when encountering rough terrain. Because of knee joints, the robot's center of gravity also changes when the robot's posture changes, so motion control of the robot is decomposed into three parts: self-balancing for front tilting, trajectory tracking control, side tilting, and center of gravity (COG), and knees joint's impedance control. In particular, two nonlinear backstepping sliding-mode controllers are proposed to achieve self-balancing, speed tracking and orientation control for the robot moving over flat terrain. The robot's mechatronic design uses a low-level controller with an OpenCR control board and Dynamixel motors, where the OpenCR control board is programmed via Arduino. Simulations and experimental results of the mobile platform traveling around its workspace demonstrate the feasibility and effectiveness of the proposed control strategy.