Apparatus for producing a three-dimensional workpiece, comprising: a carrier adapted to receive material for producing the workpiece; at least one mobile production unit , comprising: - a solidification device adapted to produce solidified material layers on the carrier in order to produce the workpiece by an additive layer construction method; - a gas supply system adapted to supply, along an uppermost material layer on top of the carrier , a shielding gas to an area that is to be irradiated; the apparatus further comprising: a moving unit that is adapted to move the mobile production unit relative to the carrier so as to position the mobile production unit oppositely to different sections of the carrier ; a sensing unit that is adapted to generate sensor signals relating to a relative arrangement of the mobile production unit and the carrier ; and a control unit that is configured to, in addition to the positioning of the mobile production unit via the moving unit , provide at least one fine positioning function to compensate for an offset from a desired relative arrangement of the mobile production unit and the carrier based on the sensor signals generated by the sensing unit. a carrier adapted to receive material for producing the workpiece; at least one mobile production unit , comprising: - a solidification device adapted to produce solidified material layers on the carrier in order to produce the workpiece by an additive layer construction method; - a gas supply system adapted to supply, along an uppermost material layer on top of the carrier , a shielding gas to an area that is to be irradiated; the apparatus further comprising: a moving unit that is adapted to move the mobile production unit relative to the carrier so as to position the mobile production unit oppositely to different sections of the carrier ; a sensing unit that is adapted to generate sensor signals relating to a relative arrangement of the mobile production unit and the carrier ; and a control unit that is configured to, in addition to the positioning of the mobile production unit via the moving unit , provide at least one fine positioning function to compensate for an offset from a desired relative arrangement of the mobile production unit and the carrier based on the sensor signals generated by the sensing unit. - a solidification device adapted to produce solidified material layers on the carrier in order to produce the workpiece by an additive layer construction method; - a gas supply system adapted to supply, along an uppermost material layer on top of the carrier , a shielding gas to an area that is to be irradiated; a moving unit that is adapted to move the mobile production unit relative to the carrier so as to position the mobile production unit oppositely to different sections of the carrier ; a sensing unit that is adapted to generate sensor signals relating to a relative arrangement of the mobile production unit and the carrier ; and a control unit that is configured to, in addition to the positioning of the mobile production unit via the moving unit , provide at least one fine positioning function to compensate for an offset from a desired relative arrangement of the mobile production unit and the carrier based on the sensor signals generated by the sensing unit. <EOS>