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 (35, 37) 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 (35, 37) 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 (35, 37) 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.