Engineering:Building maintenance unit

Workers clean the façade of a hospital from the building maintenance unit

A building maintenance unit (BMU) is an automatic, remote-controlled, or mechanical device, usually suspended from the roof, which moves systematically over some surface of a structure while carrying human window washers or mechanical robots to maintain or clean the covered surfaces. BMUs are almost always positioned over the exterior of a structure, but can also be used on interior surfaces such as large ceilings (e.g. in stadiums or train stations) or atrium walls.