LASER: Level-Based Asynchronous Scheduling and Execution Regime for Spatiotemporally Constrained Multi-Robot Timber Manufacturing

2026-03-20

AI Summary

This work addresses the tightly coupled spatiotemporal constraints—such as collision avoidance and coordination within process time windows—in multi-robot wood manufacturing systems by proposing the LASER framework. LASER structures tasks into hierarchical levels with spatiotemporal mutual exclusion, enabling asynchronous parallel execution within layers and synchronized barrier coordination across layers. By integrating synchronization barriers into constraint-based planning and scheduling, the approach ensures collision-free operation and enhances robustness against temporal uncertainties. The method employs constraint programming, an iterative time-relaxation algorithm for handling heterogeneous task sequences, and a two-level decomposition strategy to balance workload among homogeneous tasks. Validated on a full-scale 2.4m × 6m wooden panel assembly involving 108 subroutines and 352 screw insertions by two robots, the framework successfully operated within adhesive curing time windows and demonstrated significantly superior computational performance over monolithic approaches.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Intelligent Robots: Multi-Robot Systems
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications
• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Economics, Online Markets and Human Computation: Cost models of using LLMs in production systems

Abstract

Automating large-scale manufacturing in domains like timber construction requires multi-robot systems to manage tightly coupled spatiotemporal constraints, such as collision avoidance and process-driven deadlines. This paper introduces LASER (Level-based Asynchronous Scheduling and Execution Regime), a complete framework for scheduling and executing complex assembly tasks, demonstrated on a screw-press gluing application for timber slab manufacturing. Our central contribution is to integrate a barrier-based mechanism into a constraint programming (CP) scheduling formulation that partitions tasks into spatiotemporally disjoint sets, which we define as levels. This structure enables robots to execute tasks in parallel and asynchronously within a level, synchronizing only at level barriers, which guarantees collision-free operation by construction and provides robustness to timing uncertainties. To solve this formulation for large problems, we propose two specialized algorithms: an iterative temporal-relaxation approach for heterogeneous task sequences and a bi-level decomposition for homogeneous tasks that balances workload. We validate the LASER framework by fabricating a full-scale 2.4m x 6m timber slab with a two-robot system mounted on parallel linear tracks, successfully coordinating 108 subroutines and 352 screws under tight adhesive time windows. Computational studies show our method scales steadily with size compared to a monolithic approach.

Problem

• multi-robot systems
• spatiotemporal constraints
• collision avoidance
• process-driven deadlines
• timber manufacturing

Innovation

• Level-based scheduling
• Barrier-based synchronization
• Constraint programming
• Multi-robot coordination
• Spatiotemporal decomposition