Contact Force Guidance Assembly towards Unknown-Shaped Dual Peg-in-Hole

The automatic assembly of dual peg-in-hole often relies on the concrete CAD model, either explicitly or implicitly. However, especially in daily life, the shapes of pegs vary, and the robot cannot always obtain an accurate CAD model of the peg before performing the insertion task. Therefore, inspired by the force constraint during contact, we used contact force as the completion indicator of the assembly and proposed a novel two-stage assembly strategy for unknown-shaped dual peg-in-hole. Additionally, a variable remote compliance center method is employed to decouple the contact forces of two pegs and their adjustments. Three types of unidirectional movement modes—exploration, compliance, retention—are utilized to guide the peg to contact with the hole under large initial offsets. The performance of the proposed assembly strategy was evaluated through a series of experiments using various shapes of pegs. The results show that our method effectively completes arbitrary mixed-shaped dual peg-in-hole task under large initial offsets in terms of orientation error (>20°) and position error (>30mm) acorss all test cases.