RESUMO
Additive manufacturing methods1-4 using static and mobile robots are being developed for both on-site construction5-8 and off-site prefabrication9,10. Here we introduce a method of additive manufacturing, referred to as aerial additive manufacturing (Aerial-AM), that utilizes a team of aerial robots inspired by natural builders11 such as wasps who use collective building methods12,13. We present a scalable multi-robot three-dimensional (3D) printing and path-planning framework that enables robot tasks and population size to be adapted to variations in print geometry throughout a building mission. The multi-robot manufacturing framework allows for autonomous three-dimensional printing under human supervision, real-time assessment of printed geometry and robot behavioural adaptation. To validate autonomous Aerial-AM based on the framework, we develop BuilDrones for depositing materials during flight and ScanDrones for measuring the print quality, and integrate a generic real-time model-predictive-control scheme with the Aerial-AM robots. In addition, we integrate a dynamically self-aligning delta manipulator with the BuilDrone to further improve the manufacturing accuracy to five millimetres for printing geometry with precise trajectory requirements, and develop four cementitious-polymeric composite mixtures suitable for continuous material deposition. We demonstrate proof-of-concept prints including a cylinder 2.05 metres high consisting of 72 layers of a rapid-curing insulation foam material and a cylinder 0.18 metres high consisting of 28 layers of structural pseudoplastic cementitious material, a light-trail virtual print of a dome-like geometry, and multi-robot simulations. Aerial-AM allows manufacturing in-flight and offers future possibilities for building in unbounded, at-height or hard-to-access locations.
RESUMO
Friction and wear decrease the efficiency and lifetimes of mechanical devices. Solving this problem will potentially lead to a significant reduction in global energy consumption. We show that multilayer polyethylenimine/graphene oxide thin films, prepared via a highly scalable layer-by-layer (LbL) deposition technique, can be used as solid lubricants. The tribological properties are investigated in air, under vacuum, in hydrogen, and in nitrogen gas environments. In all cases the coefficient of friction (COF) significantly decreased after application of the coating, and the wear life was enhanced by increasing the film thickness. The COF was lower in dry environments than in more humid environments, in contrast to traditional graphite and diamond-like carbon films. Superlubricity (COF < 0.01) was achieved for the thickest films in dry N2. Microstructural analysis of the wear debris revealed that carbon nanoparticles were formed exclusively in dry conditions (i.e., N2, vacuum), and it is postulated that these act as rolling asperities, decreasing the contact area and the COF. Density functional theory (DFT) simulations were performed on graphene oxide sheets under pressure, showing that strong hydrogen bonding occurs in the presence of intercalated water molecules compared with weak repulsion in the absence of water. It is suggested that this mechanism prevents the separation graphene oxide layers and subsequent formation of nanostructures in humid conditions.
