LASER: Level-Based Asynchronous Scheduling and Execution Regime for Spatiotemporally Constrained Multi-Robot Timber Manufacturing
Zhenxiang Huang, Lior Skoury, Tim Stark, Aaron Wagner, Hans-Jakob Wagner, Thomas Wortmann, Achim Menges
AI summary
Problem
Automating large-scale timber assembly requires multi-robot systems to simultaneously satisfy tight spatial collision constraints and process-driven adhesive time windows, which typically causes computational intractability and execution fragility.
Approach
The framework partitions tasks into spatiotemporally disjoint levels that robots execute asynchronously, synchronizing only at level barriers to guarantee collision-free operation by construction while minimizing makespan.
Key results
- Barrier-based constraint programming formulation embedding spatial and temporal constraints
- Specialized algorithms for heterogeneous bottom sessions and homogeneous top sessions
- Physical validation on a full-scale 2.4×6 m slab coordinating 108 subroutines and 352 screws
- Computational scalability study demonstrating steady performance scaling across eight design variants
Why it matters
Provides a scalable, robust scheduling paradigm for automating large-scale, low-carbon timber construction with multi-robot teams.
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 glu- ing 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 2.4 m × 6 m timber slab (Fig. 1) 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.