Flexible locomotion control of a self-contained biped leg-wheeled system

Combination of wheels and legs has the potential to realize efficient locomotion on a flat surface and also negotiation of artificial irregularity such as stairs or steps. We have been studying on biped leg-wheeled system to realize flexible locomotion in our daily life environment. This paper describes the design concept of the self-contained biped leg-wheeled system and its locomotion concept. The system has three locomotive modes-4-wheeled locomotive mode, 2-wheeled locomotive mode, stair negotiation mode. In the first mode, it can travel quickly and steer like a car with its four wheels contacting the ground. In the second mode, it can travel and steer like a wheeled inverted pendulum with two wheels contacting the ground. In the stair negotiation mode, it can negotiate the stairs with front and rear wheels continuously in contact with the horizontal and vertical surfaces of stairs. In this mode torque control of both wheels while maintaining the posture of the system is the key to successful negotiation. The control scheme and method for stair negotiation, which can be applied generally to a leg-wheeled system, are introduced. The effectiveness of the system is demonstrated by a successful experiment of the lift-up motion of the wheel using a biped leg-wheeled system developed in the authors' previous research.