CALIBRATING A SCANNER DEVICE

Abstract

The present disclosure relates to calibrating scanner devices for positioning laser beams in a processing field, and includes, e.g.: arranging a retroreflector in the processing field of the scanner device, the processing field being formed in a processing chamber for irradiating powder layers; detecting laser radiation reflected back into the scanner device when the laser beam passes over the retroreflector; determining an actual position of the laser beam in the processing field using the detected laser radiation; and calibrating the scanner device by correcting a laser beam target position specified for the scanner device in the processing field using the determined actual position of the laser beam in the processing field.

Claims

1. A method for calibrating a scanner device for positioning a laser beam in a processing field, the method comprising: arranging at least one retroreflector in or above the processing field of the scanner device, wherein the field is formed in a powder layer processing chamber; detecting laser radiation that is reflected back into the scanner device as the laser beam passes over the at least one retroreflector; determining an actual position of the laser beam in the processing field based on the detected laser radiation; and calibrating the scanner device by correcting a target position of the laser beam specified for the scanner device in the processing field on the basis of the determined actual position of the laser beam in the processing field.

2. The method of claim 1, wherein the at least one retroreflector is arranged in or above the processing field of the scanner device in an automated manner.

3. The method of claim 2, wherein the at least one retroreflector is attached to a movable device that is configured to deposit powder layers in the processing field of the scanner device.

4. The method of claim 1, wherein the at least one retroreflector is a ball transparent to a wavelength of the laser beam, and determining the actual position of the laser beam in the processing field is based on an intensity distribution of the reflected laser radiation that is detected.

5. The method of claim 1, wherein the at least one retroreflector is in the form of a retroreflective foil.

6. The method of claim 5, wherein the foil comprises at least one non-retroreflective surface region that adjoins the retroreflective surface region.

7. The method of claim 6, wherein determining the actual position of the laser beam in the processing field is based on a difference in an intensity of the detected laser radiation between the retroreflective surface region and the non-retroreflective surface region.

8. The method of claim 1, wherein the laser beam comprises a pilot laser beam, wherein the pilot laser beam is provided at a lower power than a processing laser beam used to irradiate power layers in the powder layer processing chamber.

9. The method of claim 1, further comprising: directing an additional laser beam at an additional processing field formed in the processing chamber; detecting additional laser radiation that is reflected back into an additional scanner device as the additional laser beam passes over the at least one retroreflector; determining an actual position of the additional laser beam in the additional processing field based on the additional laser radiation detected; and calibrating the additional scanner device by correcting a target position specified for the additional scanner device based on the actual position of the additional laser beam in the additional processing field.

10. The method of claim 9, wherein the actual position of the laser beam and the actual position of the additional laser beam are determined simultaneously.

11. A machining device for producing three-dimensional components by irradiating powder layers, the machining device comprising: an irradiation device comprising a laser source and a scanner device configured to direct a laser beam from the laser source toward a processing field; a processing chamber in which the processing field is located wherein the processing chamber comprises a powder layer support surface on which the powder layers are applied and wherein the processing chamber comprises at least one retroreflector arranged in or above the processing field of the scanner device; a detector arranged to detect laser radiation reflected back into the scanner device from the at least one retroreflector as the laser beam passes over the at least one retroreflector; a computing unit coupled with non-transitory computer-readable medium encoding instructions that cause the computing unit to determine an actual position of the laser beam in the processing field based on the detected laser radiation; and a controller configured to specify a target position of the laser beam in the processing field, wherein the controller is configured to correct the specified target position based on the determined actual position.

12. The machining device of claim 11, further comprising: an arm configured to move the at least one retroreflector into the processing field of the scanner device.

13. The machining device of claim 12, wherein the arm also is configured to deposit powder layers in the processing chamber.

14. The machining device of claim 11, wherein the at least one retroreflector is a transparent ball or is a retroreflective surface region of a foil.

15. The machining device of claim 11, wherein the detector is a diode.

16. A machining device of claim 11, further comprising: an additional scanner device configured to direct an additional laser beam in an additional processing field of the processing chamber; an additional detector arranged to detect additional laser radiation reflected back into the additional scanner device by the at least one retroreflector as the additional laser beam passes over the at least one retroreflector; an additional evaluation device configured to determine an actual position of the additional laser beam in the additional processing field based on the additional laser radiation detected; and an additional controller configured to specify a target position of the additional laser beam in the additional processing field, wherein the additional controller is further configured to correct the specified target position based on the determined actual position of the additional laser beam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 is a schematic view of an exemplary machining device for producing three-dimensional components in which the machining device includes a retroreflector for calibrating a scanner device; and

[0036] FIG. 2 is a schematic view of an exemplary machining device for producing three-dimensional components, in which the machining device includes retroreflectors for calibrating two scanner devices.

DETAILED DESCRIPTION

[0037] FIG. 1 is a schematic view of an exemplary construction of a machining device 1 for producing a three-dimensional component 2 by irradiating powder layers 3. In the example shown in FIG. 1, the powder layers 3 are positioned one on top of the other and form a powder bed in which the three-dimensional component 2 is embedded. The machining device 1 has an irradiation device 4, which has a laser source 5 in the form of a fiber laser for generating a laser beam 6, which is guided to a deflection mirror 9 through a fiber optic cable 7 and a collimation device 8. In the example shown, the laser beam 6 is a pilot laser beam used for the calibration (see below). To irradiate or locally fuse the powder layers 3, a higher-power processing laser beam is used, which is also generated by the laser source 5 in the form of a fiber laser. In the example shown, the pilot laser beam 6 has a wavelength that differs from the wavelength of the processing laser beam. In the example shown in FIG. 1, the deflection mirror 9 has a dielectric coating having a reflectance of more than approximately 99.9% for the wavelength of the processing laser beam, and a reflectance of approximately 30% to 80% for the wavelength of the pilot laser beam 6, and so a predominant proportion of the intensity of the pilot laser beam 6 is deflected towards a focusing device 10 at the deflection mirror 9.

[0038] Downstream of the focusing device 10, the laser beam 6 passes through a scanner device 11 having two scanner mirrors 12a, 12b in the form of galvanometer mirrors. The scanner device 10 is used to position the laser beam 6 in a processing field 13 of the scanner device 10; in the example shown in FIG. 1, said field substantially corresponds to the lateral extension of the powder bed or powder layers 3. The focusing device 10 focuses the laser beam in the processing field 13, which is approximately planar and corresponds to an XY plane of an XYZ coordinate system in which the uppermost powder layer 3 or the top of the powder bed is located.

[0039] As can also be seen in FIG. 1, the powder layers 3 are applied onto a support 14 in the form of a base plate that can be displaced in the Z-direction. The support 14 is arranged in a processing chamber 15, which has a window 16 through which the laser beam 6 is radiated into the processing chamber 15. Since the processing field 13 of the scanner device 11 in which the powder material is fused remains at a constant distance from the scanner device 11 during production of the three-dimensional component 2, the support 14 is lowered by the thickness of a powder layer 3 in order to deposit a new powder layer 3.

[0040] New powder material is taken from a powder reservoir 18, which is also arranged in the processing chamber 15, by a device 17 for depositing (new) powder layers 3. In the example shown in FIG. 1, the device 17 for depositing new powder layers 3 is configured in the form of a displaceable arm, to the underside of which a slider 17a is attached so as to bring powder material from the powder reservoir 18 into the region of the powder layers 3 or to the top of the powder bed located above the support 14 in the build cylinder surrounding said support.

[0041] In the example shown in FIG. 1, a retroreflector 19 in the form of a three-dimensional object, more specifically a transparent ball made of quartz glass, is attached to a slightly tilted surface on the top of the device 17 (powder slider) configured as the displaceable arm for depositing the powder layers 3, said arm extending in the Y-direction, e.g., perpendicularly to the plane of the drawing, in the example shown. The retroreflector 19 can also be fastened to a different position on the arm. In the example shown, the retroreflector 19 in the form of the ball has a diameter of approximately 4 mm and reflects laser radiation 20 that represents a proportion of, for example, more than 5% of the intensity of the laser beam 6 back into the scanner device 11, and specifically substantially independently of the angle of incidence at which the laser beam 6 impinges on the retroreflector 19. The diameter of the retroreflector 19 in the form of the ball can also be smaller than 1 mm, for example, approximately 100 m or less. For handling reasons, however, it may be advantageous for the retroreflector 19 to have a diameter of approximately 1 mm or more. In the example shown in FIG. 1, the laser beam 6 impinges on the retroreflector 19 substantially perpendicularly to the XY plane in which each powder layer 3 also extends; however, it goes without saying that a significant radiation proportion of the laser beam 6 of typically more than approximately 5% is reflected back to the scanner device 11 on the retroreflector 19 even when the direction of incidence of the laser beam 6 deviates from the perpendicular incidence.

[0042] The reflected laser radiation 20 passes through the scanner device 11 and the focusing device 10 in the opposite direction from the laser beam 6 and impinges on the deflection mirror 9. At the deflection mirror 9, a small proportion of the reflected laser radiation 20 is transmitted and is imaged or focused on a detector 22 in the form of a photodiode by an imaging device 21, which is configured as a lens in the example shown in FIG. 1. The detector 22 or photodiode is arranged coaxially with the beam path of the laser beam 6 and substantially detects laser radiation 20 that emanates from an actual position X.sub.P, Y.sub.P of the laser beam 6 in the processing field 13 at which the retroreflector 19 is arranged in the example shown in FIG. 1, and is reflected back to the scanner device 11.

[0043] Due to imaging errors, for example, the actual position X.sub.P, Y.sub.P of the laser beam 6 can deviate from a target position X.sub.T, Y.sub.T specified for the scanner device 11 by a controller 23, and this may lead to deviations when projecting a pattern that corresponds to the two-dimensional geometry of a plane of the three-dimensional component onto the processing field 13. To transmit a pattern of this kind into the processing field 13 as precisely as possible, the scanner device 13 may be calibrated, during which, the target position X.sub.T, Y.sub.T specified for the scanner device 11 is corrected such that it corresponds to the actual position X.sub.P, Y.sub.P in the processing field 13. For this purpose, the projection errors of the scanner device, e.g., the deviation between the target position X.sub.T, Y.sub.T and the actual position X.sub.P, Y.sub.P, may be identified as precisely as possible.

[0044] To do so, the exemplary process described below can be followed: the retroreflector 19 is arranged at a specified reflector position in or above the processing field 13, and a target position X.sub.T, Y.sub.T that notionally corresponds to the specified reflector position in the processing field 13 is specified for the scanner device 11. The scanner device 11 scans a region of the processing field 13 around the notional reflector position, during which the laser radiation 20 reflected back in each case is detected, e.g., the laser beam 6 passes over the retroreflector 19 multiple times in a scanning movement. The actual position X.sub.P, Y.sub.P of the laser beam 6 is determined in an evaluation device in the form of a measurement computer 24 (e.g., a first computing unit coupled with non-transitory computer-readable medium encoding instructions that cause the first computing unit to determine the actual laser beam position X.sub.P, Y.sub.P) on the basis of the intensity distribution I(X, Y) of the detected laser radiation 20. The actual position X.sub.P, Y.sub.P can be determined, for example, in the manner described below:

[0045] First, the evaluation device 24 records the two-dimensional intensity distribution I(X, Y) (e.g., bitmap image) of the laser radiation 20 detected as the retroreflector 19 is passed over multiple times. By way of example, FIG. 1 shows the one-dimensional intensity distribution I(X) that is recorded as the retroreflector 19 is scanned and which extends through the center of the two-dimensional intensity distribution I(X, Y). Using image analysis, an intensity centroid of the intensity distribution I(X, Y) is identified; in the example shown in FIG. 1, in which the laser beam 6 has a rotationally symmetrical intensity distribution I(X, Y), said centroid corresponds to the intensity maximum in the X-direction and in the Y-direction. The centroid of the intensity distribution I(X, Y) of the detected laser radiation 20 forms the retroreflector position, e.g., the actual position X.sub.P, Y.sub.P of the laser beam 6 that should actually coincide with the target position X.sub.T, Y.sub.T originally specified for the scanner device 11 by the controller 23 (e.g. the first or a further computing unit coupled with non-transitory computer-readable medium encoding instructions that cause the first or the further computing unit to specify the laser beam target positions X.sub.T, Y.sub.T, and to correct the specified target positions X.sub.T, Y.sub.T, based on the determined actual positions X.sub.P, Y.sub.P,).

[0046] In the case described above, there is a deviation between the actual position X.sub.P, Y.sub.P of the laser beam 6, or the reflector position, and the target position X.sub.T, Y.sub.T originally specified for the scanner device 11 by the controller 23. This deviation is corrected, for example, by determining the difference between the target position X.sub.T, Y.sub.T and the actual position X.sub.P, Y.sub.P and adjusting the target position X.sub.T, Y.sub.T accordingly in the controller 23 such that the actual position X.sub.P, Y.sub.P and the target position X.sub.T, Y.sub.T coincide. For this purpose, the evaluation device 24 sends the determined actual position X.sub.P, Y.sub.P to the controller 23.

[0047] In the example shown in FIG. 1, multiple retroreflectors 19 in the form of three-dimensional objects, e.g., in the form of transparent balls, are arranged along the device 17 for depositing the powder layers 3 in order to calibrate the scanner device 11 at multiple actual positions X.sub.P, Y.sub.P of the processing field 13. In particular, multiple retroreflectors 19 can be arranged next to one another in the Y-direction so as to calibrate the scanner device 11 for multiple actual positions X.sub.P, Y.sub.P of the laser beam 6 in the Y-direction. This may be particularly advantageous since, in the example shown in FIG. 1, the movement axis of the device 17 for transporting powder material from the powder reservoir 18 to the region of the powder layers 3 extends in the X-direction, and so the device 17 may not be able to move in the Y-direction. However, to calibrate the scanner device 11 at different actual positions X.sub.P, Y.sub.P of the laser beam 6 in the processing field 13 in the X-direction, it may be sufficient to displace the device 17 in the X-direction.

[0048] FIG. 2 shows a machining device 1 that differs from the machining device 1 shown in FIG. 1 in that it has an additional irradiation device 4a, which is constructed identically to the irradiation device 4 shown in FIG. 1. For example, the additional irradiation device 4a comprises an additional scanner device 11a for positioning an additional laser beam 6a in an additional processing field 13a, which partly overlaps the processing field 13 of the scanner device 11. The two irradiation devices 4, 4a are used to produce the same three-dimensional component, which is generated, similarly to FIG. 1, by locally fusing powder layers (not shown in FIG. 2) that are applied onto a support 14 surrounded by a build cylinder.

[0049] In the example shown in FIG. 2, a calibration element in the form of a calibration plate 25 is arranged in the processing chamber 15, said plate being introduced into the respective processing fields 13, 13a of the two scanner devices 11, 11a by a device 17 (not shown in FIG. 2) for depositing powder layers 3. In the example shown, the calibration plate 25 has been placed directly on the support 14.

[0050] In the example shown in FIG. 2, the calibration plate 25 has multiple retroreflectors 19a-f in the form of retroreflective surface regions, between which multiple non-retroreflective surface regions 26a-e are arranged. The non-retroreflective surface regions 26a-e can include, e.g., surface regions that absorb the laser beam 6. In the example shown in FIG. 2, the retroreflectors 19a-e in the form of the retroreflective surface regions are formed on a retroreflector foil in which microbeads are embedded so as to produce the retroreflective properties. Unlike as shown in FIG. 2, the absorbent surface regions 26a-e may be applied to the retroreflector foil in the form of a precision mask, e.g., the retroreflector foil may be covered by absorbent surfaces in the corresponding surface regions 26a-e. The retroreflector foil is applied to a substrate (not shown in FIG. 2). Alternatively or additionally to some of surface regions 26a-e being absorbent, some of surface regions 26a-e of the calibration plate 25 can be scattering or reflective (but not retroreflective) surface regions.

[0051] The scanner devices 13, 13a are calibrated by the calibration plate 25 similar to the method described in relation to FIG. 1. The calibration differs on account of the determination of the actual position X.sub.P, Y.sub.P of the laser beam 6 in the processing field 13. In the calibration plate 25, the positions of the absorbent surface regions 26a-e are precisely known since they have been measured beforehand by means of a suitable measurement method.

[0052] To calibrate the scanner device 11, the laser beam 6 is moved in the processing field 13 along a movement path in which at least one border between a retroreflective surface region 19a-e and an adjacent absorbent surface region 26a-e is passed over. By way of example, the intensity I measured by the detector 22, which can be in the form of the photodiode, as the laser beam 6 moves in the X-direction exhibits a jump or a significant intensity difference I at the transition between the retroreflective surface region 19b and the adjacent absorbent surface region 26b. This difference I in the intensity I of the detected laser radiation 20 is recognized by the evaluation device 24 and assigned to an actual position X.sub.P, Y.sub.P of the laser beam 6 in the processing field 13 The calibration can be carried out for multiple positions in the processing field 13 that are formed at the border between a retroreflective surface region 19a-f and an absorbent surface region 26a-e if a target path at which the laser beam 6 passes over a plurality of such borders has been specified for the scanner device 11.

[0053] The additional scanner device 13a is calibrated in a similar manner, e.g., the additional laser radiation 20a that is reflected back into the additional scanner device 13a by the calibration plate 25 and reaches an additional detector 22a through an additional focusing device 10a, an additional deflection mirror 9a and an additional imaging device 21a is evaluated by an additional evaluation device in the form of a measurement computer 24a (e.g., the first computing unit or an additional computing unit coupled with non-transitory computer-readable medium encoding instructions that cause the computing unit to determine actual laser beam position values X.sub.Pa, Y.sub.Pa). The evaluation result is provided to an additional controller 23a (e.g. the first computing unit or an additional computing unit coupled with non-transitory computer-readable medium encoding instructions that cause the first or the additional computing unit to specify the laser beam target positions X.sub.Ta, Y.sub.Ta, and to correct the specified target positions X.sub.Ta, Y.sub.Ta, based on the determined actual positions X.sub.Pa, Y.sub.Pa) in order to adapt the target values X.sub.Ta, Y.sub.Ta to the actual values X.sub.Pa, Y.sub.Pa determined by the additional evaluation device 24a. By using retroreflectors 19a-e at which a significant proportion of the intensity I of the laser beam 6 is reflected back into the scanner device 11 and a significant proportion of the intensity I of the additional laser beam 6a is reflected back into the additional scanner device 11a, the two scanner devices 11, 11a can be calibrated simultaneously without significant measurement errors, e.g., the actual position X.sub.P, Y.sub.P of the laser beam 6 and the actual position X.sub.Pa, Y.sub.Pa of the laser beam 6a can be determined concurrently.