Extraction system for apparatus for the layer-by-layer formation of three-dimensional objects, and associated methods and controller

A method for extracting gas from the working space of an apparatus for layer-by-layer formation of three-dimensional objects, wherein the working space comprises a ceiling and a floor and wherein the floor comprises a build bed surface, the method comprising:

• (a) extracting gas from the working space via a first secondary conduit comprising a first secondary inlet and a first secondary outlet, and a second secondary conduit comprising a second secondary inlet and a second secondary outlet, wherein the first and second secondary inlets are arranged in the ceiling above and to either side of the build bed surface, the first and second secondary inlets each spanning the width of the build bed surface and receiving gas from the working space;
• (b) moving the gas from the first and second secondary conduits either (i) directly into a primary conduit via the first and second secondary outlets to a first interfacing inlet and a second interfacing inlet of the primary conduit or (ii) indirectly into the primary conduit by flowing gas from the second secondary conduit into the first secondary conduit at an intermediate section of the first secondary conduit so that a combined flow of gas from the first and second secondary conduits flows from the intermediate section of the first secondary conduit into the primary conduit, wherein gas from the working space is only received by the primary conduit from the first and second secondary conduits;
• (c) extracting the gas from a primary outlet of the primary conduit by operating an external extraction source connected to the primary outlet;
• (d) suctioning, by operating the external extraction source, a flow of gas from an environment external to the working space into the primary conduit via a primary inlet of the primary conduit that is open to the environment external to the working space, such that the gas extracted from the primary conduit in step (c) is a mixture of gas extracted from the working space via the first and second interfacing inlets, or via the first interfacing inlet and gas suctioned from the external environment to the working space via the primary inlet;
• and
• (e) operating a first internal flow control device located in the first secondary conduit and a second internal flow control device located in the second secondary conduit, or an internal flow control device located in the intermediate section, to control the flow of gas through the first secondary conduit and/or the second secondary conduit, and
• (f) determining one of a temperature, a flow speed or a flow direction of the gas flow at the primary inlet;
• and
• (g) generating, based on determining that, for a predetermined duration, at least one of:
• the detected temperature is above a normal operating range, the detected flow speed is below a normal operating range, or the detected flow direction is out of the primary conduit, a failure signal to indicate insufficient extraction at (d) for normal operation of the apparatus.