Additive manufacturing method and apparatus

An apparatus for forming a three-dimensional article through successive fusion of parts of a powder bed, which parts corresponds to successive cross sections of the three-dimensional article, said apparatus comprising:

• means for providing a predetermined amount of powder for forming a first powder layer on a surface,
• a powder distributor for distributing said predetermined amount of powder for forming said first powder layer,
• means for directing an energy beam over said first powder layer causing said first powder layer to fuse in selected locations according to a model to form a first cross section of said three-dimensional article,
• a camera for capturing at least one image of a shape of at least one portion of said predetermined amount of powder that has yet to be initially distribute, said at least one image being captured at least one time during said initial distribution of another portion of said predetermined amount of powder to said surface, said at least one image being captured prior to distribution of an entirety of all portions of said predetermined amount of powder over said surface and prior to removal of any portions of said predetermined amount of powder from said surface, and
• means for comparing at least one value of at least one parameter in said image detected by said camera with a corresponding reference parameter value,
• wherein the at least one parameter is associated with said shape of said at least one portion of said predetermined amount of powder that has yet to be initially distributed.