Parallel Self-assembly for Modular USVs with Diverse Docking Mechanism Layouts

TL;DR

This work tackles self-assembly of heterogeneous multi-USV systems by introducing CuBoat, a modular omnidirectional USV with configurable docking on four sides. It proposes a generalized parallel SAP pipeline that combines tabu-search target dispatch, assembly-tree generation, target extension, and distributed navigation, supported by LESO-ADRC control for robust motion. The approach is validated through extensive simulations across maps and two docking scenarios, plus real-world experiments in a pool showing successful parallel assembly with reduced docking requirements compared to homogeneous systems. The results demonstrate improved synchronization, connectivity guarantees, and practical viability for on-water self-assembly and reconfigurable floating platforms.

Abstract

Self-assembly enables multi-robot systems to merge diverse capabilities and accomplish tasks beyond the reach of individual robots. Incorporating varied docking mechanisms layouts (DMLs) can enhance robot versatility or reduce costs. However, assembling multiple heterogeneous robots with diverse DMLs is still a research gap. This paper addresses this problem by introducing CuBoat, an omnidirectional unmanned surface vehicle (USV). CuBoat can be equipped with or without docking systems on its four sides to emulate heterogeneous robots. We implement a multi-robot system based on multiple CuBoats. To enhance maneuverability, a linear active disturbance rejection control (LADRC) scheme is proposed. Additionally, we present a generalized parallel self-assembly planning algorithm for efficient assembly among CuBoats with different DMLs. Validation is conducted through simulation within 2 scenarios across 4 distinct maps, demonstrating the performance of the self-assembly planning algorithm. Moreover, trajectory tracking tests confirm the effectiveness of the LADRC controller. Self-assembly experiments on 5 maps with different target structures affirm the algorithm's feasibility and generality. This study advances robotic self-assembly, enabling multi-robot systems to collaboratively tackle complex tasks beyond the capabilities of individual robots.

Figures (13)

• Figure 1: A heterogeneous multi-USV system consists of four types of USVs designed for diverse applications, including transportation and river cleaning. These USVs, featuring distinct docking mechanism layouts, can seamlessly assemble into on-demand dynamic platforms.
• Figure 2: System overview of the CuBoat.
• Figure 3: (a) The undocked state of the docking subsystem. The docked state of (b) the genderless pattern and (c) the gendered pattern. The contact detection mechanism is presented.
• Figure 4: Coordinate system for the movement of the CuBoat: the inertial coordinate $O \text{-} X Y Z$, the body coordinate $O_b \text{-} X_b Y_b Z_b$ and the target coordinate $O_d \text{-} X_d Y_d Z_d$. Red arrows represent positive propulsion forces, while pink arrows indicate negative forces.
• Figure 5: Overview of the SAP algorithm. A seven-robot self-assembly process illustrates the four stages vividly. Homogeneous docking systems are indicated by the bold red borders of robot points. For stages II and IV, subplots in the panels depict the recording and tracing processes of the landmark points, respectively.