Method for calibrating an apparatus for producing an object by means of additive manufacturing, and apparatus for the method

1. A method for calibrating an apparatus for producing an object by means of additive manufacturing, wherein the apparatus comprises:

a process chamber for receiving a bath of material configured to be solidified by exposure to electromagnetic radiation;

a support for positioning the object in relation to the surface level of the bath of material; and

a solidifying device for solidifying a selective layer-part of the material on the surface level by means of electromagnetic radiation;

wherein the method comprises the step of providing, on or near the support, a calibration marker that faces the solidifying device, and the step of providing a calibration system with an imaging device configured to be directed to the support, wherein the apparatus further comprises a deflector unit, and wherein the imaging device and the solidifying device are aligned and operate via the deflector unit such that an optical path of the imaging device, in use of the apparatus, coincides with an optical path of the electromagnetic radiation of the solidifying device; and

wherein the method comprises the further steps of:

a) determining, with the imaging device, a measure for the position of the calibration marker;

b) controlling the solidifying device for making a solidifying marker that relates to the calibration marker;

c) determining, with the imaging device via the deflector unit, a measure for the position of the solidifying marker; and

d) determining, with the calibration system, at least a correction vector based on the positions of both the calibration marker and the solidifying marker related to this calibration marker.

2. The method according to claim 1 , wherein the step of determining a measure for the position of the calibration marker comprises:

determining an expected position of the calibration marker; and

controlling, based on the expected position, the apparatus and determining a resulting set position.

3. The method according to claim 2 , further comprising the step of determining a calibration marker difference vector, defined as the difference between the expected position of the calibration marker and the resulting set position.

4. The method according to claim 1 , wherein the step of determining the measure for the position of the solidifying marker comprises:

determining an expected position of the calibration marker; and

controlling, based on the expected position, the apparatus and determining a resulting set position.

5. The method according to claim 4 , wherein the method further comprises the step of determining a solidifying marker difference vector, defined as the difference between the solidifying marker and the resulting set position.

6. The method according to claim 1 , wherein the apparatus for producing an object by means of additive manufacturing comprises a further solidifying device, and wherein the method comprises the further steps of:

controlling the further solidifying device for making a further solidifying marker that relates to the calibration marker;

determining, with the calibration system, a measure for the position of the further solidifying marker; and

determining, with the calibration system, at least a further correction vector based on the positions of both the calibration marker and the further solidifying marker related to this calibration marker.

7. The method according to claim 6 , wherein the calibration system comprises at least a further imaging device, wherein the further imaging device is used for obtaining an image of the calibration marker and/or of the further solidifying marker.

8. The method according to claim 7 , wherein the further imaging device is arranged such that an optical path of the further imaging device, in use of the apparatus, coincides, at least partly, with an optical path of the electromagnetic radiation of the further solidifying device.

9. The method according to claim 1 , wherein at least a further calibration marker is provided, and at least part of the method is repeated at least once for the at least one further calibration marker.

10. The method according to claim 1 , wherein the solidifying device and the imaging device are not required to be operated at the same time.

11. An apparatus for producing an object by means of additive manufacturing, comprising:

a process chamber for receiving a bath of material configured to be solidified by exposure to electromagnetic radiation;

a support for positioning the object in relation to the surface level of the bath of material;

a solidifying device for solidifying a selective layer-part of the material on the surface level by means of electromagnetic radiation; and

a calibration system having an imaging device configured to be directed to the support, wherein the apparatus further includes a deflector unit and the solidifying device and the imaging device operate via the deflector unit such that an optical path of the imaging device, in use of the apparatus, coincides with an optical path of the electromagnetic radiation of the solidifying device,

wherein the calibration system is adapted and arranged for:

a) determining, with the imaging device, a measure for the position of a calibration marker that is directed towards the solidifying device;

b) controlling the solidifying device for making a solidifying marker that relates to the calibration marker;

c) determining, with the imaging device via the deflector unit, a measure for the position of the solidifying marker; and

d) determining at least a correction vector based on the positions of both the calibration marker and the solidifying marker related to this calibration marker.

12. The apparatus according to claim 11 , wherein the apparatus comprises a thermal conditioning arrangement for thermally conditioning the imaging device.

13. The apparatus according to claim 12 , wherein the apparatus comprises the deflector unit for deflecting the electromagnetic radiation, wherein the thermal conditioning arrangement is further arranged for thermally condition the deflector unit and for thermally conditioning a part of the apparatus connecting the imaging device to the deflector unit.

14. The apparatus according to claim 11 , wherein the apparatus comprises a further solidifying device, and the calibration system is adapted and arranged for:

controlling the further solidifying device for making a further solidifying marker that relates to the calibration marker;

determining, with the calibration system, a measure for the position of the further solidifying marker; and

determining at least a further correction vector based on the positions of both the calibration marker and the further solidifying marker related to this calibration marker.

15. The apparatus according to claim 14 , wherein the calibration system comprises at least one further imaging device for obtaining an image of the calibration marker and/or of the further solidifying marker.

16. The apparatus according to claim 15 , wherein the deflector unit is arranged in such a way that an optical path of the further imaging device, in use of the apparatus, coincides with an optical path of the electromagnetic radiation of the further solidifying device.

17. The apparatus according to claim 11 , wherein the solidifying device and the imaging device are not required to be operated at the same time.