Model-Based Pitch Angle Compensation for Center of Gravity Variation in Underactuated System with an Arm

Abstract

Two-wheeled robots are expected to be used at sites where humans work together. The subject of this paper is a two-wheeled robot with an arm, which can take out loads from shelves in the same manner as a human. When the center of gravity (CoG) of the two-wheeled robot shifts back and forth due to placing a load on the arm, the wheel position control performance deteriorates. A possible method to compensate for the shift in the CoG is to use repulsive compliance control (RCC). However, RCC has the disadvantages that the parameters must be adjusted experimentally and the CoG compensation is slow because the pitch angle is determined dynamically. To address these disadvantages, this paper proposes a method that uses model-based CoG compensation and position control for pitch angle. The model-based controller design simplifies parameter setting and achieves fast CoG compensation by statically determining the desired pitch angle. The validity of the proposed method is confirmed through experiments. The obtained results show that the performance of wheel position control is improved when the load is placed on the arm.