Fast passing over stairs by a biped leg-wheeled robot

Most robots put to practical use are industrial robots that work in factories. Most of them are manipulators mounted on fixed bases. This is partly due to the great demand for robots in factories and partly due to the immature technologies for stable, safe and autonomous mobile robots. These technologies include the basic technology of moving on rough surfaces stably and fast There are several types of locomotion such as by wheel, leg, and crawler. Recently, by combining the mechanisms of two or more types of locomotion, mobile robots with the merits of those types have been developed. Among these robots, a typical class is leg-wheeled robots that can negotiate obstacles using legged locomotion and can travel fast on flat surfaces using wheeled locomotion. In order to allow a leg-wheeled robot to efficiently and speedily negotiate steps and stairs which are typical indoor obstacles, we are studying new mechanisms and their control schemes. Our new types of leg-wheeled robot will travel by driving the wheels with static stability on a flat surface and can negotiate steps and stairs with dynamic stability by balancing its body on those actively controlled wheels that contact the ground. This type of robot with dynamic stability has a simple structure, because its mechanism does not necessitate static stability. We previously developed a wheeled robot called a Variable structure type four-wheeled robot' capable of passing over a single step, but it cannot negotiate the stairs whose tread is short compared with the wheelbase of the robot In this paper, in order to realize the fast negotiation of stairs, we propose a 'biped leg-wheeled robot' which has ability to pass over stairs with short treads. We also propose two dynamic trajectory planning methods and investigate the possibility to realize the fast and stable negotiation of stairs. Moreover, we investigate the robustness about some trajectory control methods on the computer simulation. Lastly, we investigate a control method to connect the dynamic trajectory control motion in statically unstable state and the structure changing motion in statically stable state. As the result, we realize the fast going up and down stairs by this robot successfully and confirm the effectiveness of our proposed methods.