Autonomous Shape-Variable Crawler: One-Dimensional Displacement Coordination for Constant Upper Frame Posture

Abstract

With technical advances, various locomotion mechanisms for use on bumpy roads have been introduced. Among these locomotion mechanisms, crawler-based platforms are widely employed. However, due to their tilt on uneven terrain, accidents such as overturning and falling loads have been reported. To overcome these situations, this paper proposes a constant balance scheme for crawler-based transportation systems (hereinafter called crawler robots for simplicity). Practically, a variable-shape crawler robot with four foldable legs is designed to maintain a constant upper-frame posture regardless of ground conditions. The four legs by coordinating expand and contract, thereby enabling the robot to adapt to local surface conditions and configure its desired posture while traveling. The coordination-based crawler mechanism is realized by employing rack-and-pinion units for raising and lowering. The effectiveness and performance of the developed crawler robot are demonstrated by verifying its movement under continuous and discontinuous surface conditions with the use of a balanced posture from a tilted state. Specifically, we pose an innovative challenge of information transformation to maintain balance effectively. In detail, three-dimensional state variations (e.g., gradients and inclinations) of the crawler robot depending on ground conditions are transformed into one-dimensional displacements. Unlike previous works, this study presents the novel idea of coordinating the motions of individual legs to configure a variable-shape crawler robot. In other words, the crawler shape is deformed while it maintains the desired balance.