Multi-robot Rigid Formation Navigation via Synchronous Motion and Discrete-time Communication-Control Optimization

TL;DR

This work tackles rigid formation navigation for untethered, nonholonomic multi-robot systems over wireless networks. It introduces a hold-and-hit synchronization framework to align control executions despite delays and packet loss, paired with a Discrete-time Error Minimization (DEM) controller that optimizes intra-cycle error correction under curvilinear paths. The approach is implemented on ROS and validated through simulations and real-world TurtleBot experiments, demonstrating robust formation maintenance with tight position and orientation bounds even under lossy communications. The proposed framework offers a practical, scalable solution for cooperative transportation and other collaborative MRS tasks in realistic wireless environments, with potential extension to broader nonholonomic platforms and larger robot teams.

Abstract

Rigid-formation navigation of multiple robots is essential for applications such as cooperative transportation. This process involves a team of collaborative robots maintaining a predefined geometric configuration, such as a square, while in motion. For untethered collaborative motion, inter-robot communication must be conducted through a wireless network. Notably, few existing works offer a comprehensive solution for multi-robot formation navigation executable on microprocessor platforms via wireless networks, particularly for formations that must traverse complex curvilinear paths. To address this gap, we introduce a novel "hold-and-hit" communication-control framework designed to work seamlessly with the widely-used Robotic Operating System (ROS) platform. The hold-and-hit framework synchronizes robot movements in a manner robust against wireless network delays and packet loss. It operates over discrete-time communication-control cycles, making it suitable for implementation on contemporary microprocessors. Complementary to hold-and-hit, we propose an intra-cycle optimization approach that enables rigid formations to closely follow desired curvilinear paths, even under the nonholonomic movement constraints inherent to most vehicular robots. The combination of hold-and-hit and intra-cycle optimization ensures precise and reliable navigation even in challenging scenarios. Simulations in a virtual environment demonstrate the superiority of our method in maintaining a four-robot square formation along an S-shaped path, outperforming two existing approaches. Furthermore, real-world experiments validate the effectiveness of our framework: the robots maintained an inter-distance error within $\pm 0.069m$ and an inter-angular orientation error within $\pm19.15^{\circ}$ while navigating along an S-shaped path at a fixed linear velocity of $0.1 m/s$.

Figures (15)

• Figure 1: Cooperative transportation with the leader-follower scheme.
• Figure 2: Sequence diagram of the hold-and-hit mechanism.
• Figure 3: Cooperative transportation with four nonholonomic wheeled robots. The blue square represents an object on top of the group. The dashed line is the predefined path towards the target.
• Figure 4: (a) Differential mobile robot with nonholonomic constraints, (b) The master-slave scheme for rigid formation.
• Figure 5: Four TurtleBots were arranged in a square formation. Using a LiDAR sensor, the master measured the relative positions between itself and the slaves, and computed the control inputs $\bar{\mathbf{\textbf{v}}}_{i,\hat{t}}$ for the slaves.