Robotic equilibrium: Scaffold free arch assemblies

Abstract

Compression-only arch structures are structurally highly efficient in force equilibrium. However, the material efficiency is offset by the traditional use of scaffolds to position materials and counter the out-of-equilibrium forces during assembly. We introduce a method of sequentially assembling compression-only structures without a scaffold by robotically maintaining the compression equilibrium in every step. A two-arm collaborative robotic setup was used to maintain force equilibrium throughout arch assembly. The arms took turns first hot-wire cutting and placing blocks then providing a temporary scaffold to support the arch end point. To test the approach, a single catenary arch was generated using form-finding techniques and sequentially built from foam blocks. Moving forward we show the relationship between the joint valence (largest number of joined branches) of a multi-branched structure and the minimum number of robotic arms required for assembly using our initial technique. With only two robotic arms available, the technique was further developed to reduce the required number of arms per arch branch from two to one by attaching caterpillar tracks at the block-supporting end effector. This allows a human to load the next block and the arm to move forward along the arch while maintaining equilibrium. Results show that robotic equilibrium scaffold-free arch assembly is possible and can reduce scaffold waste and maintain the material efficiency of compression-only structures. Future work will explore further applications of assistive robotics in construction, replacing static construction aids with dynamic sensory feedback of equilibrium forces.