For the control of a dynamic mobile robot, the attitude in the gravity space is an important state of the robot. Usually, the attitude is difficult to detect by simply using the signals from sensors. For example an external sensor contacting the ground gets disturbances from the roughness of the ground; the integration of a gyroscope signal has the problem of drift; the inclination sensor does not indicate the direction of gravity when acceleration exists. To solve these problems, the authors propose a control method in which the attitude of a mobile robot is estimated by an observer considering the robot dynamics and using only the information obtained by internal sensors.
The authors applied this method to a wheeled inverted pendulum as an example of a dynamic mobile robot. The estimation of the attitude was made with good accuracy using the signals from the rate gyroscope and the motor encoder, and the control of stable running of the pendulum on a flat level plane worked successfully. The authors also realized the running control of the pendulum on an unknown rough road using the estimation of the slope gradient by the observer. Thus, the effectiveness of the proposed method was demonstrated experimentally.