Dynamic trajectory control of a variable structure type four-wheeled robot to pass over steps

Abstract

We have developed a robot called a 'variable structure type four-wheeled robot' which, with a simple structure, has ability to pass over a step. Though this robot has only one degree of freedom to change the body's structure, it can run on four wheels (4-wheeled mode) or on two wheels like a wheeled inverted pendulum (2-wheeled mode). For the realization of stepping up and down, we already proposed a method by combining the transfer from 4- to 2-wheeled mode and the transfer from 2- to 4-wheeled mode and realized an experiment of passing over a step whose height is larger than the radius of the wheel successfully. In this paper, we propose two dynamic trajectory control methods to make the passing over a step speedy. First, we have divided the whole sequence of stepping up or down into two sequences and extended the planning of soft-landing trajectory which we already proposed in the transfer from 2-to 4-wheeled mode to cover each sequence. As a result, we have successfully realized an experiment of stepping up or down of this robot in about 15 seconds. Second, using the same trajectory planning method to cover the exchange of the contacting wheel from rear to front, we have planned a continuous trajectory throughout stepping up or down. As the result we have successfully realized an experiment of the stepping up or down of this robot in only 2.4 seconds.