Tabletop Object Rearrangement: Structure, Complexity, and Efficient Combinatorial Search-Based Solutions

TL;DR

This paper analyzes the complexity of tabletop object rearrangement with overhand grasps and introduces efficient algorithms for planning and buffer management in cluttered environments, advancing robotic manipulation capabilities.

Contribution

It provides a theoretical and algorithmic framework for buffer space requirements and introduces lazy buffer verification for complex rearrangement tasks.

Findings

Minimum buffer space requirements are characterized for free-space scenarios.

Lazy buffer verification improves efficiency in multi-arm and mobile manipulators.

Exact algorithms for buffer planning are developed and analyzed.

Abstract

This thesis provides an in-depth structural analysis and efficient algorithmic solutions for tabletop object rearrangement with overhand grasps (TORO), a foundational task in advancing intelligent robotic manipulation. Rearranging multiple objects in a confined workspace presents two primary challenges: sequencing actions to minimize pick-and-place operations - an NP-hard problem in TORO - and determining temporary object placements ("buffer poses") within a cluttered environment, which is essential yet highly complex. For TORO with available external free space, this work investigates the minimum buffer space, or "running buffer size," required for temporary relocations, presenting both theoretical insights and exact algorithms. For TORO without external free space, the concept of lazy buffer verification is introduced, with its efficiency evaluated across various manipulator configurations, including single-arm, dual-arm, and mobile manipulators.