Attitude and Steering Control of the Long Articulated Body Mobile Robot KORYU

Abstract

The authors have designed and actually built a mechanical prototype of a class of articulated body mobile robots, 3.3m long, and mass of more than 400kg, called KR-II. Attitude control and steering control has been successfully implemented, and the robot can move stably in the outdoors, even on uneven terrain. The presented steering control method is based on parameter representation for describing trajectories in an inertial reference frame, with travelled distance as a parameter. In doing so, the position of each element (in the case of the articulated body mobile robot KR-II, segment center positions) on the trajectory can be tracked by simple and effective numerical searching algorithms. For the real robot KR-II, the introduced method demonstrated good energy efficiency and trajectory tracking performance as well as real-time control feasibility. This method was successfully extended for use in the "W-Shaped Configuration", and it can be considered the best steering control scheme for articulated body mobile robots with long intersegment lengths, such as the KR-II. The presented attitude control scheme is based in optimal force distribution using quadratic programming, which minimizes joint energy consumption. Similarities with force distribution for multifingered hands, multiple coordinated manipulators and legged walking robots were demonstrated. The attitude control scheme to maintain the vertical posture of the robot was introduced inside this force distribution problem. The validity and effectiveness of proposed methods were verified by computer simulations and also experimentally using the actual mechanical model. Moreover, the introduced attitude control and steering control can be used not only for control of big "snake-like" robots, but even for walking machines at some extent. Some negative points for developing such big robots, is the complexity in the mechanical design and also the high cost to build it, which makes the advance in this area of research a little bit slow, compared to other mobile robot systems. Nonetheless, sometime passed since the last prototype has been built (1990-2000), and we experienced many advances in actuators, computers, materials technology, so a much better design should be possible now. The authors hope the mechanical concept and practical results presented in this Chapter, could give enough insights for new developments in the area.