Polygonal Wheel and Outrigger-based Balanced Indoor Obstacle Terrain Overcoming Mechanism in Mobile Manipulators

Abstract Wheel-based mobile manipulators are attracting growing interest for manufacturing and factory-floor indoor applications due to their energy efficiency and maneuverability. However, traversing step-shaped discontinuities such as floor joints, cable covers, and pallet lips remains challenging, especially for inverted-pendulum platforms that must maintain balance during terrain transitions. This paper presents a balanced obstacle-climbing mechanism that integrates a front polygonal wheel module based on a triangular omni-wheel arrangement, a linear-actuated balancing module for pitch regulation, and deployable rear outriggers to support larger discontinuities in modular manufacturing layouts. The process is formulated as a mode-based control policy using a finite state machine (FSM) for state-dependent switching among wheel actuation, balancing control, and outrigger deployment. A proportional–integral–derivative (PID) controller regulates trunk pitch using IMU feedback for lightweight real-time stabilization. We evaluate the system on an indoor testbed with 35–70 mm steps under three scenarios: flat-ground self-balancing, obstacle climbing without outriggers, and obstacle climbing with outriggers. The robot maintains pitch within ± 2° during straight driving and within ± 5° during in-place front-wheel rotation (1 rpm). It overcomes steps up to 35 mm without outriggers and up to 70 mm with outriggers, with transient pitch excursions up to 13° and 15°, respectively. These results demonstrate the feasibility of improving robust mobility and task accessibility for manufacturing-oriented indoor environments with small step discontinuities.