METHOD FOR CALIBRATING AN APPARATUS FOR ADDITIVELY MANUFACTURING THREE-DIMENSIONAL OBJECTS

Abstract

Method for calibrating an apparatus (1) for additively manufacturing three-dimensional objects by means of successive layerwise selective irradiation and consolidation of layers of a build material which can be consolidated by means of an energy beam (3), comprising the steps: providing at least one calibration source (8, 9, 10) in a calibration plane (16) imaging the calibration source (8, 9, 10) to an actual position (18) in a determination plane (15) comprising at least two determination regions (19-27), preferably with given coordinates, in particular arranged in a grid-like pattern moving the image (28) of the calibration source (8, 9, 10) from the actual position (18) in at least one direction (29, 32, 34, 35) across the determination plane (15) until the image (28) passes from the actual determination region (19-27) into another determination region (19-27) determining a distance information indicating a defined distance (30, 33, 36, 37) the image (28) is moved determining the actual position (18) of the image (28) based on the determined distance information.

Claims

1. Method for calibrating an apparatus (1) for additively manufacturing three-dimensional objects by means of successive layerwise selective irradiation and consolidation of layers of a build material which can be consolidated by means of an energy beam (3), characterized by providing at least one calibration source (8, 9, 10) in a calibration plane (16) imaging the calibration source (8, 9, 10) to an actual position (18) in a determination plane (15) comprising at least two determination regions (19-27), preferably with given coordinates, in particular arranged in a grid-like pattern moving the image (28) of the calibration source (8, 9, 10) from the actual position (18) in at least one direction (29, 32, 34, 35) across the determination plane (15) until the image (28) passes from the actual determination region (19-27) into another determination region (19-27) determining a distance information indicating a defined distance (30, 33, 36, 37) the image (28) is moved determining the actual position (18) of the image (28) based on the determined distance information.

2. Method according to claim 1, characterized in that the image (28) is incident on a first determination region (19-27), in particular matching a first pixel of the determination plane (15), wherein the image (28) is moved for the defined distance (30, 33, 36, 37) in a first direction (29, 32, 34, 35) until the image (28) is incident on a second determination region (19-27), in particular a second pixel, adjacent to the first pixel in moving direction (29, 32, 34, 35).

3. Method according to claim 2, characterized in that the image (28) is moved continuously or step-wise via a beam guiding unit (13) of the apparatus (1), wherein a minimum moving distance is below a size of the determination regions (19-27), in particular the pixel size of the pixels, in the determination plane (15).

4. Method according to claim 3, characterized in that the determination process is performed for at least two, preferably four, directions (29, 32, 34, 35).

5. Method according to claim 3, characterized in that the determination process is performed for at least two different energy beams (3).

6. Method according to claim 1, characterized in that a nominal position (38) of the image (28) is compared with the actual position (18), wherein if a difference between the nominal position (38) and the actual position (18) is determined, the beam guiding unit (13) is adjusted.

7. Apparatus (1) for additively manufacturing three-dimensional objects by means of successive layerwise selective irradiation and consolidation of layers of a build material which can be consolidated by means of an energy beam (3), which apparatus (1) comprises an irradiation device that is adapted to generate and guide the energy beam (3) across a build plane (5), characterized by at least one calibration unit (6) that is arrangeable or arranged inside a process chamber (7) of the apparatus (1), wherein the calibration unit (6) comprises at least one calibration source (8, 9, 10), wherein the apparatus (1) comprises a beam guiding unit (13) that is adapted to image the calibration source (8, 9, 10) to an actual position (18) on a determination plane (15) of a determination unit (14), wherein the determination plane (15) comprises at least two determination regions (19-27), wherein the beam guiding unit (13) is adapted to move the image (28) of the calibration source (8, 9, 10) in at least one direction (29, 32, 34, 35) across the determination plane (15) for a defined distance (30, 33, 36, 37), wherein a distance information indicating the defined distance (30, 33, 36, 37) is determined, wherein the defined distance (30, 33, 36, 37) depends on a changeover criterion, wherein the determination unit (14) is adapted to determine an actual position (18) of the image (28) of the calibration source (8, 9, 10) before the movement based on the distance information.

8. Apparatus according to claim 7, characterized in that the changeover criterion defines a changeover in at least one illuminated determination region (19-27), in particular the image (28) passing from the actual determination region (19-27) into another determination region (19-27).

9. Apparatus according to claim 7, characterized in that the beam guiding unit (13) comprises at least one beam guiding element, in particular a scanning mirror, wherein the beam guiding element is adapted to position the image (28) of the calibration source (8, 9, 10) on the determination plane (15) with a defined positioning accuracy.

10. Apparatus according to claim 9, characterized in that the defined positioning accuracy is less or equal the size of the determination region (19-27), in particular the pixel size.

11. Apparatus according to claim 7, characterized in that the calibration unit (6) comprises a plurality of calibration sources (8, 9, 10) that are arranged in a defined pattern, in particular a grid-like pattern, preferably 11 times 11 calibration sources (8, 9, 10).

12. Apparatus according to claim 7, characterized in that the calibration unit (6) comprises a calibration base body with at least one recess in which the at least one calibration source (8, 9, 10) is received.

13. Apparatus according to claim 7, characterized in that the at least one calibration source (8, 9, 10) is built as light source, in particular as light emitting diode, or as fiber coupled with a light source or as surface element adapted to emit radiation upon irradiation with an energy beam (3).

14. Apparatus according to claim 7, characterized by at least one receiving means arranged in the process chamber (7) of the apparatus (1), which is adapted to receive the calibration unit (6).

15. Apparatus according to claim 7, characterized in that the calibration unit (6) is adapted to compare a nominal position (38) of the image (28) with an actual position (18), wherein the beam guiding unit (13) is adjusted dependent on a difference between the nominal position (38) and the actual position (18).

Description

[0034] Exemplary embodiments of the invention are described with reference to the Fig. The Fig. are schematic diagrams, wherein

[0035] FIG. 1 shows an inventive apparatus; and

[0036] FIG. 2 shows a top view on a determination plane of the inventive apparatus from FIG. 1.

[0037] FIG. 1 shows an apparatus 1 for additively manufacturing three-dimensional objects by means of successive layerwise selective irradiation and consolidation of layers of a build material. The apparatus 1 comprises an irradiation device 2 that is adapted to generate an energy beam 3 via a beam source 4, for example a laser source adapted to generate a laser beam. The irradiation device 2 is further adapted to guide the energy beam the 3 to a build plane 5, i.e. a plane in which build material can be arranged to be irradiated in a regular mode of operation of the apparatus 1.

[0038] The apparatus 1 comprises a calibration unit 6 arranged inside a process chamber 7 of the apparatus 1. The process chamber 7 is the chamber in which the additive manufacturing process is performed during a regular mode of operation, in particular during an additive manufacturing process performed on the apparatus 1. The calibration unit 6 according to this exemplary embodiment comprises multiple calibration sources 8, 9, 10, wherein the amount of calibration sources 8, 9, 10 can be chosen arbitrarily and it is sufficient for the inventive method to provide only one calibration source 8, 9, 10, as will be described in below.

[0039] In this exemplary embodiment the calibration source 8 is built as active calibration source, for example as light source, such as a light emitting diode that is adapted to emit radiation 11. The calibration source 9, 10 are adapted to passively emit radiation 12, for example upon irradiation with the energy beam 3. The calibration source 9 can for example be a body of metal that can be heated up via the energy beam 3 and emit thermal radiation. The calibration source 10 may reflect at least one part of the energy beam 3. In other words, the calibration sources 8, 9 and 10 can either be active calibration sources that are actively adapted to emit radiation or the calibration sources can be generated via the energy beam 3. An arbitrary combination or selection of calibration sources 8, 9, 10 can be made.

[0040] Independent of the mode of generation of the calibration source 8, 9, 10 the irradiation device 2 comprises a beam guiding unit 13 that is adapted to image the calibration source 8, 9, 10 to a determination unit 14, in particular onto a determination plane 15 of the determination unit 14. The determination unit 14 is for example built as a camera comprising a CCD-chip providing the determination plane 15. In other words, the energy beam 3 may be guided onto the calibration unit 6 to generate calibration sources 9, 10, i.e. an irradiation pattern generated in a calibration plane 16, for example the top surface of the calibration unit 6, for example arranged in the build plane 5. It is also possible that the calibration unit 6 is built as calibration base body, for example a metal plate with recesses in which the calibration sources 8, for example light emitting diode, is received. The calibration source 8 may also be imaged to the determination plane 15, as described before.

[0041] The beam guiding unit 13 is further adapted to move the images of the calibration sources 8, 9, 10 across the determination plane 15, as indicated via arrows 17. Hence, images of the calibration sources 8, 9, 10 are generated in the determination plane 15, as the calibration sources 8, 9, 10 are imaged via the beam guiding unit 13, for example comprising a beam guiding element, such as a movable mirror, to the determination plane 15. The image of the calibration sources 8, 9, 10 are incident in an initial position 18 in the determination plane 15, as can be derived from FIG. 2 which shows a top view onto the determination plane 15, for example the detection surface of the determination element of the determination unit 14, in particular a CCD-chip of a camera.

[0042] The determination plane 15 comprises multiple determination regions 19-27 that are arranged in a grid-like pattern, for example a pixel grid. Although, only nine pixels are depicted in the determination plane 15 according to this exemplary embodiment, it is to be understood that any arbitrary number of determination regions 19-27 (pixels) can be provided. As an example, an image 28 of the calibration source 9, for example a spot of the energy beam 3 in the calibration plane 16, is imaged to the determination region 23, for example the center pixel of the determination plane 15 (optional). Hence, the image 28 is incident on the determination region 23 in the actual position 18 which can also be referred to as initial position. The determination unit 14 is adapted to generate a signal indicating that the determination region 23 is illuminated, e.g. that the image 28 is incident on the determination region 23.

[0043] The image 28 is moved in a first direction 29 which can also be referred to as x-direction for a defined distance 30 which can also be referred to as x. The image 28 is moved via the beam guiding unit 13 dependent on a change criterion, in particular until the image 28 passes from the determination region 23 to the adjacent determination region 24, wherein the change of the illuminated determination region 23, 24 can be determined via the determination unit 14, for example via the change of the illuminated pixel of the determination region 15, as the image 28 passes an edge 31 between the determination regions 23, 24. Accordingly, dependent on the distance the beam guiding unit 13 moved the image 28, the defined distance 30 can be determined. Of course, it is also possible to determine any other distance information relating to the defined distance 30, such as the time required to move the image 28 and conclude on the defined distance 30.

[0044] Subsequently, the image 28 may be moved from the initial position 18 according to this exemplary embodiment (or from the end position of the first movement, e.g. after the change criterion was met) in a second direction 32 which can also be referred to as y-direction also for a defined distance 33 which can also be referred to as y. As the determination regions 19-27 can be arranged in defined spatial positions, for example comprising given coordinates in a coordinate systems, it is possible to determine the actual position 18 dependent on the defined distances 30, 33 or any other distance information, such as the moving time of the beam guiding unit 13 or the like.

[0045] It is also possible to further perform two more determination processes, in the directions 34 and 35, which can also be referred to as x and y for corresponding distances 36, 37. After the actual position 18 of the image 28 of the calibration source 8-10 has been determined, the actual position 18 can be compared with a nominal position 38 in which the image 28 would be incident on the determination plane 15, if the apparatus 1 was properly calibrated. Hence, the determination unit 14 may determine the difference between the nominal position 38 and the actual position 18 and may therefore, generate calibration information. It is also possible to calibrate the apparatus 1 dependent on the calibration information, in particular to adjust the beam guiding unit 13 in that the nominal position 38 is met, wherein the beam guiding unit 13 is adjusted to ensure that the image 28 is incident in the nominal position 38.

[0046] Of course, the determination and calibration process can be performed for multiple calibration sources 8, 9, 10, for example for a plurality of calibration sources 8, 9, 10, in particular 11 times 11 calibration sources 8, 9, 10. Self-evidently, it is also possible to generate the calibration sources 9, 10 directly on a build plate 39 or any other arbitrary structure of the apparatus 1 instead of inserting a calibration base body into the process chamber 7. Thus, it is possible to perform a calibration of the apparatus 1 in advance to, during or after an additive manufacturing process without the need for inserting a test specimen into the process chamber 7. Of course, the inventive method may be performed on the apparatus 1.