METHODS FOR CALIBRATING A PROCESSING MACHINE, AND PROCESSING MACHINES

Abstract

The disclosure provides methods for calibrating processing machines for the production of 3D components by irradiation of powder layers, wherein the processing machine includes a scanner device for positioning a laser beam in a processing field in which a height-adjustable construction platform for the application of the powder layers by sweeping at least two, e.g., three markings, e.g., in the form of spherical retroreflectors, which are applied on the construction platform and/or on a preform , by the laser beam, detecting laser radiation reflected back from the markings into the scanner device , determining actual positions of the markings , determining deviations of the actual positions of the markings from setpoint positions of the markings, and calibrating the processing machine by correcting the positioning of the laser beam and/or the position of the construction platform using the determined deviations. The disclosure also relates to associated processing machines.

Claims

1. A method for calibrating a processing machine for the production of three-dimensional components by irradiation of powder layers, wherein the processing machine comprises a scanner device for positioning a laser beam in a processing field in which a height-adjustable construction platform for the application of the powder layers is positioned, the method comprising: sweeping the laser beam over at least two markings that are applied on either one or both of the construction platform and a preform fixed to the construction platform; detecting laser radiation reflected back from the markings into the scanner device during the sweeping of the at least two markings;, determining actual positions of the markings using the detected laser radiation; determining deviations of the actual positions of the markings from setpoint positions of the markings; and using the determined deviations to calibrate the processing machine by (i) correcting the positioning of the laser beam in the processing field, (ii) correcting the position of the construction platform in the processing machine, or (iii) correcting both the positioning of the laser beam in the processing field and the position of the construction platform in the processing machine.

2. The method of claim 1, wherein either one or both of a lateral offset and a rotation of either one or both of the construction platform, and the preform in a processing plane of the processing machine are corrected using the determined deviations.

3. The method of claim 1, wherein a tilt of either one or both of the construction platform and the preform relative to a processing plane of the processing machine is determined using a distance measurement, and then correcting the determined tilt of either one or both of the construction platform and the preform relative to the processing plane.

4. The method of claim 1, wherein deviations between a respective setpoint distance and a respective actual distance are determined, and then correcting a tilt of either or both of the construction platform and the preform relative to a processing plane of the processing machine using the determined deviations.

5. The method of claim 1, further comprising measuring either one or both of the construction platform and the preform to determine the setpoint positions of the markings.

6. The method of claim 1, wherein the markings comprise retroreflectors.

7. The method of claim 6, wherein the retroreflectors are spheres, wherein the laser beam is reflected from the retroreflector spheres back into the scanner device, and wherein the actual position of the retroreflector is determined using an intensity distribution of the detected back-reflected laser radiation.

8. The method of claim 7, wherein the sphere is held in a frame that is fixed to the construction platform or to the preform before the calibration.

9. The method of claim 1, wherein the markings are arranged in or in the vicinity of a processing plane of the processing machine by moving the height-adjustable construction platform to carry out the calibration.

10. The method of claim 1, further comprising determining a distance in a height direction between at least one of the markings and the scanner device, by triangulation to align the laser beam at an angle with the at least one the markings.

11. The method of claim 10, wherein, the distance is determined by displacing the height-adjustable construction platform in the height direction and the distance is determined by triangulation using a travel distance of the construction platform in the height direction between a first height position and a second height position.

12. The method of claim 11, further using an angle at which the laser beam is aligned with the at least one marking at a respective height position to determine the distance.

13. The method of claim 11, wherein the distance is determined by aligning a further laser beam of a further scanner device with the at least one marking and the distance is determined by triangulation using a separation of the scanner device from the further scanner device from a point of rotation of the further scanner device, and using a respective angle at which the laser beam and the further laser beam are aligned with the at least one marking.

14. The method of claim 1, wherein a pilot laser beam is used as the laser beam for the calibration of the processing machine.

15. The method of claim 1, further comprising detecting at least one retroreflector in the processing field by scanning at least one search region, predetermined with the aid of the setpoint position of the retroreflector, in the processing field by the laser beam.

16. The method of claim 1, wherein there are at least three markings.

17. The method of claim 16, wherein there are three markings arranged in a triangle.

18. A processing machine for the production of three-dimensional components by irradiation of powder layers, comprising: an irradiation device having a scanner device and arranged to position a laser beam in a processing field; a processing chamber, in which the processing field is formed and which comprises a construction platform for the application of the powder layers; at least two markings, which are applied on either one or both of the construction platform and a preform fixed to the construction platform; a detector arranged to receive laser radiation reflected from the markings back into the scanner device during the sweeping of the markings with the laser beam; an evaluation device for determining actual positions of the markings using the detected laser radiation ; and a control device arranged to determine deviations of the actual positions of the markings from setpoint positions of the markings and to correct either or both of the position of the laser beam in the processing field and the position of the construction platform in the processing machine using the determined deviations.

19. The processing machine of claim 18, wherein the two or more markings comprise retroreflectors.

20. The processing machine of claim 18, wherein the control device is configured to correct either or both of a lateral offset and a rotation of either one or both of the construction platform and the preform in the processing plane using the determined deviations.

21. The processing machine of claim 18, further comprising: a distance measuring device configured to determine a tilt of either one or both of the construction platform and the preform relative to the processing plane of the processing machine, wherein the control device is configured to correct the tilt, determined by the distance measuring device, of either one or both of the construction platform and the preform relative to the processing plane.

22. The processing machine of claim 21, wherein the distance measuring device comprises a triangulation laser.

23. The processing machine of claim 18, wherein the control device is configured to determine deviations between a respective setpoint distance and a respective actual distance, of two of at least three markings, and wherein the control device is configured to correct a tilt of either one or both of the construction platform and the preform relative to the processing plane using the determined deviations.

24. The processing machine of claim 19, wherein the retroreflectors comprise spheres.

25. The processing machine of claim 24, wherein the spheres are formed from quartz glass or sapphire and have a diameter of less than 5 mm.

26. The processing machine of claim 24, wherein the spheres are held in a frame comprising a screw thread for fixing in a threaded bore of either one or both of the construction platform and the preform.

27. The processing machine of claim 26, wherein the frame comprises at least one opening for a portion of the laser beam to emerge.

28. The processing machine of claim 18, wherein the control device is configured to determine by triangulation a distance in the height direction between at least one of the markings and the scanner device to align the laser beam at an angle with the at least one marking.

29. The processing machine of claim 28, wherein the control device is configured to determine the distance by displacing the height-adjustable construction platform between a first height position and a second height position in the height direction and to determine the distance by triangulation using a travel distance of the construction platform in the height direction between the first and second height positions.

30. The processing machine of claim 28, further comprising: a further scanner device arranged to align a further laser beam with a further processing field, which is formed in the processing chamber, wherein either one or both of the control device and a further control device are configured, to determine the distance, to align the further laser beam of the further scanner device with at least one marking and to determine the distance by triangulation using a separation of the scanner device from the further scanner device, and using a respective angle at which the laser beam and the further laser beam are aligned with the at least one marking.

31. The processing machine of claim 18, wherein the detector is configured as a diode.

Description

DESCRIPTION OF DRAWINGS

[0060] Further advantages of the invention are found in the description and the drawing. Likewise, the features mentioned above and those referred to below can be used independently, or several of them can be used in any desired combinations. The embodiments shown and described are not to be interpreted as an exhaustive list, but rather have an exemplary nature for description of the invention.

[0061] FIGS. 1A and 1B show schematic representations of a processing machine for the production of three-dimensional components, which includes a construction platform with a preform, on which two retroreflectors are applied.

[0062] FIG. 2 shows a representation of the upper side of a construction platform, on which three markings in the form of retroreflectors, which form the vertices of a triangle, are applied.

[0063] FIG. 3 shows a side view representation of the variation of an actual position of the first retroreflector of FIG. 2 in the event of a tilt of the construction platform out of a processing plane.

[0064] FIG. 4 shows a partial sectional representation of a retroreflector in the form of a transparent sphere, which is held in a frame.

[0065] FIGS. 5A-5C show schematic representations of a plurality of triangles for the determination by triangulation of a distance in the height direction between two markings and a point of rotation of a scanner device.

DETAILED DESCRIPTION

[0066] In the following description of the drawings, identical reference signs are used for components which are the same or functionally equivalent.

[0067] FIG. 1A shows an example of a structure of a processing machine 1 for the production of a three-dimensional component (not graphically represented). The processing machine 1 includes a height-adjustable construction platform 2, on which powder layers can be applied in order to construct the three-dimensional component layerwise. In the example shown, a preform 3, which forms a lower part of the component to be produced, is fixed to the construction platform 2. The generally metallic material of the preform 3 is selected in such a way that it bonds to the generally likewise metallic powder material during the local irradiation and local fusion of the powder layers. The fixing of the preform 3 to the construction platform 2 is carried out by a clamp connection (not represented in detail).

[0068] For the irradiation of the powder layers, the processing machine 1 includes an irradiation device 4, which includes a laser source 5 in the form of a fiber laser for generating a laser beam 6, which is guided by a fiber optic cable 7 and a collimation device 8 onto a deflection mirror 9. In the example shown, the laser beam 6 is a pilot laser beam, which is used for the calibration (see below). For the irradiation or the local fusion of the powder layers, a processing laser beam with a higher power is used, which is likewise generated by the laser source 5 in the form of the 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. 1A, the deflection mirror 9 comprises a dielectric coating with a reflectivity of more than about 99.9% for the wavelength of the processing laser beam and a reflectivity of from about 30% to about 80% for the wavelength of the pilot laser beam 6, so that a significant proportion of the intensity of the pilot laser beam 6 is deflected at the deflection mirror 9 toward a focusing device 10.

[0069] After the focusing device 10, the laser beam 6 passes through a scanner device 11, which comprises two scanner mirrors 12a, 12b in the form of galvanometer mirrors. The scanner device 11 is used for positioning the laser beam 6 in a processing field 13 of the scanner device 11, which is delimited by a maximum angle deflection of the scanner mirrors 12a, 12b and, in the example shown in FIG. 1A, corresponds substantially to the lateral extent of the powder bed, or of the construction platform 2. The focusing device 10 focuses the laser beam 6 in a processing plane 14, which corresponds to an XY plane of an XYZ coordinate system, in which the uppermost of the powder layers, or the upper side of the powder bed which is fused by the laser beam 6, or the processing laser beam, is located during the production of the three-dimensional component.

[0070] As may likewise be seen in FIG. 1A, the construction platform 2 is displaceable, or height-adjustable, in the Z direction by means of a drive (not graphically represented). The construction platform 2 is arranged in a processing chamber 15 having a window 16, through which the laser beam 6 is radiated into the processing chamber 15. Since the processing plane 14, or the focal plane of the scanner device 11, in which the powder material is fused, remains at a constant distance from the scanner device 11 during the production of the three-dimensional component, the construction platform 2 is lowered by the thickness of one powder layer to apply a new powder layer. New powder material 17 is taken with the aid of a slide arm (not graphically represented) from a powder reservoir 18 likewise arranged in the processing chamber 15 and brought into the region of a powder bed, which is located above the construction platform 2 in a construction cylinder surrounding the construction platform 2 during the production of the three-dimensional component. In the representation shown in FIG. 1A, the processing machine 1 is shown in a state before the production of the three-dimensional component, in which there is still no powder material 17 on the construction platform 2, which makes it possible to calibrate the processing machine 1.

[0071] To this end, in the example shown in FIG. 1A, two retroreflectors 19a, 19b in the form of a three-dimensional object, e.g., in the form of transparent spheres made of sapphire (Al.sub.2O.sub.3), are applied on the preform 3. The two retroreflectors 19a, 19b are respectively applied next to the outer edge of the substantially plate-shaped preform 3, on diametrically opposite sides of the preform 3. The preform 3, or more precisely the upper side 3a of the preform 3, is arranged approximately at the height of the processing plane 14 for the calibration. It is to be understood that the retroreflectors 19a,b may also be fastened to other locations on the preform 3.

[0072] In the example shown, the retroreflectors 19a,b in the form of spheres have a diameter of about 4 mm and reflect laser radiation 20 that constitutes a proportion of, for example, more than 5% of the intensity of the laser beam 6, back into the scanner device 11. The diameter of a respective retroreflector 19a,b in the form of the sphere may also be less than 1 mm, for example about 100 m or less. For handling reasons, it is however advantageous for the retroreflectors 19a,b to have a diameter of about 1 mm or more.

[0073] In the example shown in FIG. 1A, the laser beam 6 strikes the first retroreflector 19a substantially perpendicularly to the processing plane 14 in which the respective powder layers also extend, although it is to be understood that even with an incidence direction of the laser beam 6 differing from normal incidence, a significant radiation portion of the laser beam 6, typically more than about 5%, optionally more than about 90%, is reflected at the first retroreflector 19a back to the scanner device 11.

[0074] The laser radiation 20 reflected back passes through the scanner device 11 and the focusing device 10 in the opposite direction to the laser beam 6, and strikes the deflection mirror 9. At the deflection mirror 9, a small proportion of the laser radiation 20 reflected back is transmitted and imaged, or focused, with the aid of an imaging device 21, which in the example shown in FIG. 1A is configured as a lens, onto a detector 22 in the form of a photodiode. The detector 22, or the photodiode, is arranged coaxially with the beam path of the laser beam 6 and essentially detects laser radiation 20 that comes from an actual position X.sub.P1, Y.sub.P1 of the laser beam 6 in the processing field 13, at which the first retroreflector 19a is arranged in the example shown in FIG. 1A, and is reflected back by the latter to the scanner device 11, i.e. the actual position X.sub.P1, Y.sub.P1 of the laser beam 6 coincides with the actual position X.sub.P1, Y.sub.P1 of the first retroreflector 19a.

[0075] The actual position X.sub.P1, Y.sub.P1 of the first retroreflector 19a may differ from a setpoint position X.sub.S1, Y.sub.S1, which is specified to the scanner device 11 by a control device 23, if the preform 3 deviates from a setpoint position and/or from a setpoint alignment in the processing machine 1. In the setpoint alignment, the preform 3, or more precisely its upper side 3a, is aligned parallel with the processing plane 14. In the setpoint position, the preform 3 is in a predetermined lateral position relative to the fixed coordinate system of the processing machine 1 and has a predetermined orientation relative to the fixed coordinate system.

[0076] To allow maximally precise connection of the three-dimensional component during the construction of the preform 3, i.e., to join the contour of the component section constructed on the preform 3 as precisely as possible to a contour predetermined by the preform 3, it is necessary to know the location or the positioning of the preform 3 relative to the coordinate system of the scanner device 11, or relative to the fixed coordinate system of the processing machine 1, and to carry out calibration during which deviations from the setpoint position and the setpoint alignment of the preform 3 may be corrected. For the correction, for example, the positions or the component coordinates of the three-dimensional component, which is intended to be constructed on the preform 3, can be adapted to the coordinate system that is predetermined by the preform 3, i.e., the respective setpoint positions that are specified to the laser beam 6 to produce the three-dimensional component can be corrected accordingly. To this end, calibration is necessary, i.e., it is necessary to determine the location of the preform 3 in space as precisely as possible.

[0077] To achieve this, the procedure described below can be used. A setpoint position X.sub.S1, Y.sub.S1 at which the first retroreflector 19a is arranged nominally, i.e., when the preform 3 has the desired arrangement in space, is specified to the scanner device 11. Using the laser beam 6, a predetermined search region 24 around the setpoint position X.sub.S1, Y.sub.S1 of the first retroreflector 19a is scanned coarsely, i.e., with a relatively low resolution. In the example shown in FIG. 1A, the search region 24 is squarely shaped, and the setpoint position X.sub.S1, Y.sub.S1 of the first retroreflector 19a is at the center, although a search region 24 with a different geometry, for example, a rectangular or circular search region 24, can also be used.

[0078] If the retroreflector 19a is detected, for example, because the measured intensity I of the laser radiation 20 reflected back lies above a threshold value, the scanner device 11 scans a smaller region of the processing field 13 around the setpoint position X.sub.S1, Y.sub.S1 of the first retroreflector 19a with the laser beam 6 with a higher resolution, and the laser radiation 20 reflected back is respectively being detected, i.e., the laser beam 6 sweeps the first retroreflector 19a several times in a scanning movement and is then detected. The actual position X.sub.P1, Y.sub.P1 of the first retroreflector 19a is determined in an evaluation device 25 with the aid of the intensity distribution I(X, Y) of the detected laser radiation 20. As is the case with the control device described herein, the evaluation device is a programmable device, including a processor for executing a computer program that can be used to determine the actual position XP1, YP1, e.g., by performing the method steps described herein. The programmable device may be a computer with a suitable software, a programmable logic device, having reconfigurable digital circuits, or a combination of both. The determination of the actual position X.sub.P1, Y.sub.P1 of the first retroreflector 19a, for example, can be carried out in the manner described below.

[0079] First, the two-dimensional intensity distribution I(X,Y) (bitmap) of the laser radiation 20 detected during the repeated sweeping of the first retroreflector 19a is recorded by the evaluation device 25. FIG. 1A represents, by way of example, the one-dimensional intensity distribution I(X) recorded during the scanning of the first retroreflector 19a, this distribution extending through the center of the two-dimensional intensity distribution I(X,Y). With the aid of an image evaluation algorithm, an intensity centroid of the intensity distribution I(X,Y) is determined, which in the example shown in FIG. 1A, in which the laser beam 6 has a rotationally symmetrical intensity distribution I(X,Y), 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 actual position X.sub.P1, Y.sub.P1 of the first retroreflector 19a. The actual position X.sub.P2, Y.sub.P2 of the second retroreflector 19b may also be determined correspondingly. The evaluation device 25 transmits the actual positions X.sub.P1, Y.sub.P1; X.sub.P2, Y.sub.P2 of the two retroreflectors 19a,b to the control device 23.

[0080] In the control device 23, deviations of the actual positions X.sub.P1, Y.sub.P1; X.sub.P2, Y.sub.P2 of the two retroreflectors 19a,b from the setpoint positions X.sub.PS, Y.sub.S1; X.sub.S2, Y.sub.S2, specified to the control device 23, of the two retroreflectors 19a,b are determined. For example, to this end an actual difference vector (X.sub.P1X.sub.P2, Y.sub.P1Y.sub.P2) between the actual positions X.sub.P1, Y.sub.P1; X.sub.P2, Y.sub.P2 of the two retroreflectors 19a,b and a setpoint difference vector (X.sub.S1X.sub.S2, Y.sub.S1Y.sub.S2) between the setpoint positions X.sub.S1, Y.sub.S1; X.sub.S2, Y.sub.S2 of the two retroreflectors 19a,b may be determined. The angle between the actual difference vector and the setpoint difference vector corresponds in this case to the rotation of the preform 3 out of the setpoint alignment in the processing plane 14.

[0081] A lateral offset of the preform 3 relative to a setpoint position can also be determined, for example, by determining a first difference vector (X.sub.P1X.sub.S1, Y.sub.P1Y.sub.S1) between an actual position X.sub.P1, Y.sub.P1 and a setpoint position X.sub.S1, Y.sub.S1 of the first retroreflector 19a and a second difference vector (X.sub.P2X.sub.S2, Y.sub.P2Y.sub.S2) between an actual position X.sub.P2, Y.sub.P2 and a setpoint position X.sub.S2, Y.sub.S2 of the second retroreflector 19b. The lateral offset corresponds to the vector sum of the first difference vector (X.sub.P1X.sub.S1, Y.sub.P1Y.sub.S1) and the second difference vector (X.sub.P2X.sub.S2, Y.sub.P2Y.sub.S2) divided by the number of vectors (here: two). In the example described here, the calibration may be carried out by suitably correcting the positions, or the position coordinates, which are specified to the control device 23 for the production of the three-dimensional component, for example, by adapting the coordinate system of the scanner device 11 to the coordinate system, rotated and/or displaced relative to the setpoint location, of the preform 3, i.e., to the actual positions X.sub.P1, Y.sub.P1; X.sub.P2, Y.sub.P2 of the two retroreflectors 19a,b.

[0082] Error-free calibration or correction of the positioning of the laser beam 6 in the manner described above is possible only when the preform 3 has been leveled, i.e., when the preform 3 is not tilted in relation to the processing plane 14 or when the tilt of the preform 3 with respect to the processing plane 14 is corrected. For the leveling, the processing machine 1 shown in FIG. 1A includes a distance measuring device in the form of a triangulation laser 26, which aligns a triangulation laser beam with the processing field 13. To this end, the triangulation laser 26 uses a structural evaluation of the structures produced, for example in the form of lines, during the projection of the triangulation laser beam in the processing field, and thereby measures a respective distance between the preform 3 and the triangulation laser 26, or the irradiation device 4. In this way, it is possible to determine a tilt of the preform 3 relative to the processing plane 14, or relative to an XY plane extending parallel thereto. The tilt of the preform 3 can be determined according to the above-described determination of the deviations in the X and Y coordinates of the actual positions X.sub.P1, Y.sub.P1; X.sub.P2, Y.sub.P2 from the setpoint positions X.sub.S1, Y.sub.S1; X.sub.S2, Y.sub.S2 of the two retroreflectors 19a,b, to adapt the correction of the positioning of the laser beam 6 suitably, although in general the determination of the tilt of the preform 3 out of the processing plane 14 generally takes place before the determination of the deviations of the X and Y coordinates of the two retroreflectors 19a,b in the processing plane 14.

[0083] The leveling can, for example, be used to modify the setpoint positions X.sub.S1, Y.sub.S1; X.sub.S2, Y.sub.S2 of the two retroreflectors 19a,b suitably in the control device 23, and specifically in such a way as if the retroreflectors 19a,b were arranged in the processing plane 14 and not offset relative thereto in the Z direction. As an alternative or in addition, it is possible to correct the tilt of the construction platform 2 relative to the processing plane 14 by the control device 23 acting on suitable adjustment device(s) (not graphically represented), for example in the form of adjustment screws, which are applied on the construction platform 2 or in the vicinity of the construction platform. The control device is implemented as a programmable device, e.g. a computer or the like, e.g., including a processor that can execute a computer program. The computer program can generate control commands for the adjustment device(s) via suitable control signals. In some embodiments, the evaluation device and the control device are implemented in the same hardware and/or software. For the case in which the preform 3 and the construction platform 2 are not tilted relative to one another, not only the construction platform 2, but also the preform 3 can be aligned in parallel with the processing plane 14 in this way.

[0084] For the case in which the preform 3 has a relatively large height, or possibly an unfavorable geometry, which shadows the triangulation laser beam, the tilt cannot readily be determined by triangulation. In the example shown in FIG. 2, the tilt of the construction platform 2 relative to the processing plane 14 is therefore determined with the aid of three retroreflectors 19a-c. As can be seen in FIG. 2, the three retroreflectors 19a-c are applied in the vicinity of the outer edge of the circular upper side 2a of the construction platform 2, and specifically on an (imaginary) circle 27, and the three retroreflectors 19a-c form the three vertices of an equilateral triangle. In the simplified example shown in FIG. 2, all three retroreflectors 19a-c lie at their setpoint positions X.sub.S1, Y.sub.S1, X.sub.S2, Y.sub.S2, X.sub.S3, Y.sub.S3 in the processing plane 14, i.e., the construction platform 2 shown in FIG. 2 is arranged exactly at its setpoint location and is correctly aligned.

[0085] In this case, the setpoint distance A.sub.AB,S between the first and the second retroreflector 19a,b corresponds precisely to the actual distance A.sub.AB,I between the first and the second retroreflector 19a,b. The same applies for the setpoint distances A.sub.BC,S, A.sub.AC,S and the actual distances A.sub.BC,I, A.sub.AC,I between the second and the third retroreflector 19b, 19c and the first and the third retroreflector 19a, 19c.

[0086] FIG. 3 shows a detail of FIG. 2 in the vicinity of the first retroreflector 19a, and specifically along the connecting line between the first retroreflector 19a and the second retroreflector 19b. A solid line in FIG. 3 shows the alignment, represented in FIG. 2, of the construction platform 2, in which the construction platform 2 lies in the processing plane 14 (XY plane). Broken lines in FIG. 3 represent two cases in which the construction platform 2 is tilted in the region of the first retroreflector 19a by a small tilt angle + upward and by a small tilt angle downward from the processing plane 14, respectively.

[0087] As can be seen in FIG. 3, in the event of a tilt of the construction platform 2 in the region of the first retroreflector 19a upward, i.e., in the positive Z direction (+z), the actual position X.sub.P1, Y.sub.P1 of the first retroreflector 19a is displaced in the direction of the actual or setpoint position X.sub.P2, Y.sub.P2 of the second retroreflector 19b, i.e., the distance A.sub.AB,I determined between the actual positions X.sub.P1, Y.sub.P1, X.sub.P2, Y.sub.P2 of the two retroreflectors 19a,b is increased. This is identified by the scanner device 11 by the deflection angle that the laser beam 6 has at the actual position X.sub.P1, Y.sub.P1 of the first retroreflector 19a likewise being increased compared with the case in which the construction platform 2 is arranged in the processing plane 14.

[0088] Correspondingly, by a tilt of the construction platform 2 in the region of the first retroreflector 19a downward, i.e., in the negative Z direction (z), the determined actual position X.sub.P1, Y.sub.P1 of the first retroreflector 19a is moved toward the actual or setpoint position X.sub.P2, Y.sub.P2 of the second retroreflector 19b, so that the deflection angle of the laser beam 6 at the actual position X.sub.P1, Y.sub.P1 of the first retroreflector 19a, and therefore the actual distance A.sub.AB,I determined between the two retroreflectors 19a,b, is decreased.

[0089] If it is assumed that the tilt axis 28 (cf. FIG. 2) in the case of the tilt of the construction platform 2 runs through the second retroreflector 19b and extends in the Y direction, i.e., parallel to the connecting line between the two retroreflectors 19a, 19b, the tilt of the construction platform 2, or the tilt angle +/ of the construction platform 2 in the XZ plane, may be determined directly from the difference between the actual distance A.sub.AB,I and the setpoint distance A.sub.AB,S of the first and the second retroreflector 19a,b.

[0090] It is to be understood that, in general, the location of the tilt axis 28 about which the construction platform 2 is tilted out of the processing plane 14 is generally not known.

[0091] With the aid of the known setpoint distances A.sub.AB,S, A.sub.BC,S, A.sub.AC,S of the three retroreflectors 19a-c and the determined actual distances A.sub.AB,I, A.sub.BC,I, A.sub.AC,I of the three retroreflectors 19a-c, the tilt of the construction platform 2, i.e., both the tilt angle and the location and the alignment of the tilt axis 28 can, however, also be determined in this case. The correction of the positioning of the laser beam 6 to take the tilt into account can also be carried out in this case in the manner described above in connection with the triangulation laser 26.

[0092] The setpoint positions X.sub.S1, Y.sub.S1, X.sub.S2, Y.sub.S2, X.sub.S3, Y.sub.S3 of the three retroreflectors 19a-c, which are specified to the control device 23, depend of course not only on the setpoint position and the setpoint alignment of the construction platform 2, but also on their (fixed) positions relative to the construction platform 2. These positions are typically known, or, if necessary, can be determined before the calibration, for example, by measuring the construction platform 2 with the aid of a coordinate measuring machine before it is introduced into the processing machine 1. It is to be understood that the construction platform 2 need not be configured in one piece as represented above, but may optionally be configured in several pieces. In particular, the construction platform 2 may form a plate-shaped component that is fixed, for example screwed, on a height-adjustable piston.

[0093] FIG. 4 shows a retroreflector 19a in the form of a transparent sphere made of sapphire, which is held in a frame 30. The frame 30 comprises a screw thread 31 that can be used to fix the frame 30 in a threaded bore 32, represented in FIG. 1A, of the preform 2, or to screw the frame 30 firmly in the threaded bore 32. The frame 30 includes a precision fitting collar 33 to increase the accuracy of the lateral positioning of the sphere 19a or the frame 30 in the threaded bore 32 of the preform 3. The frame 30 also includes an axial end stop 34, on the lower side of the fitting collar 33, relative to which the center of the sphere 19a is positioned at a predetermined height h. The threaded bore 32 is a blind bore with a shoulder, which likewise has a predetermined distance from the upper side 3a of the preform 3. In this way, the upper side of the sphere 19a can be positioned at a distance of a few tenths of a millimeter from the upper side 3a of the preform 3. As may likewise be seen in FIG. 4, the sphere 19a in this case protrudes slightly upward beyond the frame 30 to allow the laser beam 6 to enter from different directions.

[0094] As can likewise be seen in FIG. 4, the frame 30 includes openings 35 distributed along its circumference for radiation components of the laser beam 6 to emerge, to minimize absorption of the laser beam 6 in the frame 30 and heating associated therewith as much as possible. In the example shown, the transparent sphere 19a is gripped in the frame 30 by thermally induced tension. To this end, the frame 30 is heated to about 80 C. when inserting the sphere 19a. In order not to lose the tension of the frame 30 during operation of the processing machine 1, in the example shown the frame 30 can be formed from KOVAR (a nickel-cobalt ferrous alloy), which has an almost identical linear thermal expansion coefficient to sapphire.

[0095] It is to be understood that the spheres 19a-c can be applied in a similar way on the construction platform 2. For the application of the retroreflectors 19a-c, for example, in the form of spheres, in a fixed position, it is however also possible to select a different type ofreleasable or non-releasablefastening that allows precise positioning of the retroreflectors 19a-c. Instead of transparent spheres, it is optionally also possible to use spheres made of a material that is not transparent for the laser beam, if the (retro)reflection takes place on the upper/outer side of the sphere. Instead of retroreflectors 19a-c, it is also possible to use different types of markings, which do not necessarily have retroreflective properties. For example, the markings may be surface regions in the form of a coating, which are applied onto a substrate that is applied on the construction platform 2 or on the preform 3. The markings in the form of the surface regions are detected with the aid of at least one different property of an adjacent surface region, which may for example be a section of the substrate.

[0096] For the calibration of the processing machine 1, it is necessary to determine a reference height position (zero point) of the construction platform 2 in a height direction Z (hereafter: Z direction) absolutely, i.e., in relation to a predetermined height reference of the processing machine 1. To this end, the markings in the form of the retroreflectors 19a-c can likewise be used, and specifically by determining a distance h of one or more of the retroreflectors 19a-c in relation to the predetermined height reference, which can, for example, be a point of rotation D1 of the scanner device 11, the height position of which in relation to the processing machine 1, or its machine frame, is known. It is to be understood that the determination of the distance h from the point of rotation D1 is equivalent to the determination of the distance from a different height reference, the height position of which in the processing machine 1 is known.

[0097] The determination of the distance h between two of the retroreflectors 19a, 19b, which are arranged in a common plane parallel to the processing plane 14, and the point of rotation D1 of the scanner device 11 will subsequently be described with the aid of FIGS. 5A-5C with the aid of a two-dimensional case to simplify the representation. For simplification, it is assumed that the two retroreflectors 19a, 19b and the point of rotation D1 lie in the XZ plane. In this simplified example, the laser beam 6 is rotated by one of the scanner mirrors 12a about an axis of rotation extending in the Y direction and containing the point of rotation D1, to align it with the processing field 13.

[0098] For the determination of the distance h in the Z direction, the first scanner mirror 12a is initially rotated about the point of rotation D1 of the scanner device 11 until the laser beam 6 is aligned at an angle , at which the laser beam 6 strikes the first retroreflector 19a. The alignment of the laser beam 6 with the first retroreflector 19a is recognized as described above by detecting laser radiation 20 reflected back into the scanner device 11.

[0099] In a subsequent step, the first scanner mirror 12a is rotated about the point of rotation D1 until the laser beam 6 is aligned at a second (viewing) angle , at which the laser beam 6 strikes the second retroreflector 19b. As shown by the representation in FIG. 5A, the distance h in the Z direction can be determined by conventional triangulation while taking into account the distance A.sub.AB between the two markings 19a, 19b, which extends perpendicularly to the height direction, according to the following formula:

h=A.sub.AB/(tan()+tan()) (1)

[0100] During the determination of the distance h in the Z direction in the manner described in FIG. 5A, however, the problem can arise that the distance A.sub.AB between the two retroreflectors 19a, 19b cannot be determined precisely, since as described above the retroreflectors 19a, 19b have been configured in the form of spheres and are introduced into a respective frame 30, these being fixed by means of a screw thread 31 in a threaded bore 32 of the preform 3, or of the construction platform 2. The distance A.sub.AB between the two retroreflectors 19a, 19b is therefore affected by a relatively large measurement inaccuracy. To eliminate this measurement inaccuracy, the measurement can be carried out in the manner described below in connection with FIGS. 5B and 5C, in which, for the determination of the distance h in the Z direction, a different length quantity for the triangulation, which is affected by a smaller measurement inaccuracy, is used instead of the distance A.sub.AB between the two retroreflectors 19a, 19b. To this end, it is possible to use the fact that the processing machine 1 includes actuators that allow movement of component parts of the processing machine 1 with a very high accuracy.

[0101] In the example shown in FIG. 5B, a travel distance A of the height-adjustable construction platform 2 is used instead of the distance A.sub.AB for the triangulation. The travel A is covered when the construction platform 2 is displaced by means of an actuator (not denoted in detail) between a first height position H.sub.1 and a second height position H.sub.2 for the determination of the distance h. The distance h in the Z direction can be determined with the aid of an angle , at which the laser beam 6 is aligned with the first retroreflector 19a in the first height position H.sub.1, and with the aid of an angle , at which the laser beam 6 is aligned with the first retroreflector 19a in the second height position H.sub.2, as well as with the aid of the travel distance , according to the following formula:

h=tan()/(tan()tan())(2a)

[0102] Correspondingly, the distance h in the Z direction between the point of rotation D1 and the second retroreflector 19b can be determined with the aid of the travel distance and the two angles , , at which the laser beam 6 must be aligned in the two height positions H.sub.1, H.sub.2 to strike the second retroreflector 19b, according to the following formula:

h=tan()/(tan()tan())(2b)

[0103] The distance h from the point of rotation D1 is determined, or measured, in both cases from the first height position H.sub.1. It is, however, to be understood that the distance h can be determined similarly starting from the second height position H.sub.2. The travel distance of the construction platform 2 can typically be determined with a higher precision than the distance A.sub.AB between the two retroreflectors 19a, 19b, so that the distance h in the Z direction can be determined with a higher accuracy in the manner described in connection with FIG. 5B than in FIG. 5A.

[0104] A further possibility for accurate determination of the distance h between the retroreflectors 19a, 19b and the scanner device 11 can be carried out in the processing machine 1 represented in FIG. 1B. The processing machine 1 represented in FIG. 1B differs from the processing machine 1 represented in FIG. 1A essentially in that it includes a further irradiation device 4a, which is constructed identically to the irradiation device 4 shown in FIG. 1, i.e., it includes a further scanner device 11a for positioning a further laser beam 6a in a further processing field 13a, which overlaps partially with the processing field 13 of the scanner device 11. The other component parts of the further irradiation device 4a likewise have the same design as the component parts of the irradiation device 4, and have correspondingly been denoted by references 6a to 11a, 21a to 24a. Both the radiation devices 4, 4a are used for the production of the same three-dimensional component, which in a similar way to FIG. 1A is produced by local fusion of powder layers (not shown in FIG. 1B) that are applied onto the construction platform 2, or onto the preform 3.

[0105] With the aid of the further scanner device 11a, the distance h in the Z direction can be determined by a respective angle , at which the further laser beam 6a of the further scanner device 11a, which comes from a further point of rotation D2 of the further scanner device 11a, is aligned with the first and second retroreflector 19a, 19b, respectively, also being used for the triangulation in addition to the respective angle , at which the laser beam 6, which comes from the first point of rotation D1, is aligned with the first and second retroreflector 19a, 19b, respectively. In the example represented in FIG. 5C, the distance h is obtained from the angle , at which the laser beam 6 is aligned with respect to the Z direction when it strikes the first retroreflector 19a, and from the angle , at which the further laser beam 6a is aligned with respect to the Z direction when it strikes the first retroreflector 19a, as well as from the separation A.sub.D1D2 between the two points of rotation D1, D2, according to the following formula:

h=A.sub.D1D2/(tan()tan()) (3a)

[0106] Correspondingly, the distance h is obtained from the angle , at which the laser beam 6 is aligned with respect to the Z direction when it strikes the second retroreflector 19b, and from the angle 6, at which the further laser beam 6a is aligned with respect to the Z direction when it strikes the second retroreflector 19b, as well as from the separation A.sub.D1D2 between the two points of rotation D1, D2, according to the following formula:

h=A.sub.D1D2/(tan()tan()) (3b)

[0107] The separation A.sub.D1D2 in the horizontal direction between the two points of rotation D1, D2 of the scanner device 11 and of the further scanner device 11a is determined with a high accuracy beforehand by calibration of the two scanner devices 11, 11a relative to one another, i.e., the measurement inaccuracy during the determination of the separation A.sub.D1D2 is less than during the determination of the distance A.sub.AB between the two retroreflectors 19a, 19b.

[0108] To increase the accuracy during the determination of the distance h between the retroreflectors 19a, 19b and the scanner device 11, or the point of rotation D1, the two methods described in connection with FIG. 5B and FIG. 5C can be combined: for example, the distance h can be determined as an (optionally weighted) average value from the two distances h determined according to the above formulae (2a) and (3a), and respectively (2b) and (3b). Both in the procedure described in connection with FIG. 5B and in the procedure described in connection with FIG. 5C, the accuracy during the determination of the distance h can be further increased by carrying out more than two angle measurements.

[0109] For example, in the procedure described in connection with FIG. 5B, the construction platform 2 can be displaced in the Z direction to three or more different height positions H.sub.1, H.sub.2, . . . , in which case the distance h in the Z direction can be measured several times with the aid of a respective travel distance respectively between two of the height positions and the corresponding angles, and an (optionally weighted) average value can be formed. Correspondingly, in the procedure described in connection with FIG. 5C, the accuracy during the determination of the distance h can be increased further with the aid of further (third, fourth, . . . ) scanner devices of the processing machine 1. In this case, the same retroreflector 19a-c, for example, can be observed from more than two (viewing) angles, and the distance h can be determined respectively for two of the (viewing) angles. In this case as well, the measurement or detection accuracy can be increased further by (optionally weighted) averaging of the values respectively determined for the distance h.

[0110] It is to be understood that although the procedure described above in connection with FIGS. 5A-5C has been described with the aid of retroreflectors 19a-c, it can, in principle, also be carried out with different types of markings. The generalization of the two-dimensional case described in FIGS. 5A-5C to the three-dimensional case is also clear and does not affect the basic procedure.

Other Embodiments

[0111] It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.