Jamming-free multi-robot assembly system for sequential locating pin insertion in non-coaxial dual-hole

Accurate alignment of large-scale components in manufacturing systems is often achieved by inserting locating pins into mating faces. In such operations, each locating pin must sequentially pass through two non-coaxial holes with a clearance of less than 50 μm, a requirement that exceeds the intrinsic positioning capability of standard industrial robots. This challenge necessitates a dedicated robotic assembly system that integrates compliance, force regulation, and fine multi-directional motion adjustment to ensure reliable insertion. The locating pin insertion process consists of two phases: peg-in-hole and hole-over-peg. In our previous work, the peg-in-hole phase was realized using a 3-DOF force-controlled parallel end-effector. However, the hole-over-peg phase introduces significantly greater challenges at the system level, due to constrained contact conditions, coupled position–force interactions, and continuous pose correction under non-coaxial geometric constraints. This study presents a jamming-free multi-robot assembly system for sequential locating pin insertion in non-coaxial dual-hole configurations, with a particular focus on the hole-over-peg phase. The overall system architecture, multi-robot coordination workflow, and jamming-free insertion models embedded within the system framework are described in detail and validated through experiments. Experimental results show that the proposed assembly system can achieve sequential locating pin insertion in a non-coaxial dual-hole configuration through force-feedback-based jamming suppression. In the representative large arm-joint application, a clearance fit of 22 μm was accommodated within 70.2 s, with a maximum contact force of 8.96 N. Repeated cases under the representative application condition achieved a success rate of 87.5%, and the successful cases yielded an average assembly time of 76.34 ± 13.74 s and an average maximum contact force of 7.99 ± 1.49 N. These results verify the applicability and repeatability of the proposed multi-robot assembly system for high-precision locating pin insertion under non-coaxial geometric constraints and extremely small assembly clearances.