Method for calibrating irradiation device of device for producing three-dimensional workpieces

Abstract

A method for calibrating an irradiation device of an apparatus for producing a three-dimensional workpiece is provided. The method includes applying a first powder layer onto a carrier or onto a previously applied powder layer; irradiating the first powder layer with an irradiation beam along at least one first irradiation portion; defining a first correction direction having an angle in the range of 70 DEG to 110 DEG with respect to the at least one first irradiation portion; acquiring a first image of process radiation at a location where the irradiation beam impinges on the first powder layer during irradiation along the at least one first irradiation portion; and determining a correction value in the first correction direction for calibrating the irradiation device based on the first image. Furthermore, an apparatus and a computer program product for producing a three-dimensional workpiece are provided.

Description

Technical Field

[0001] The present invention generally relates to calibration of an irradiation device. In particular, the present invention relates to a technique for calibrating an irradiation device of an apparatus for producing a three-dimensional workpiece. The apparatus for producing a three-dimensional workpiece may be, but is not limited to, an apparatus for additive manufacturing, and more precisely an apparatus for powder bed fusion, such as selective laser sintering and / or selective laser melting. Background Art

[0002] Powder bed fusion is an additive layering process by which powdered, in particular polymer, metal and / or ceramic raw materials can be processed into three-dimensional workpieces with complex shapes. To this end, layers of raw powder are applied to a carrier and, depending on the desired geometry of the workpiece to be produced, are subjected to radiation (e.g. laser or particle radiation) in a position-selective manner. The radiation penetrating into the powder layer causes heating and thus melting or sintering of the raw powder particles. Further layers of raw powder are then applied sequentially to the layer on the carrier that has been subjected to the radiation treatment until the workpiece has the desired shape and size. Powder bed fusion can be employed in order to produce prototypes, tools, replacement parts, high-value components or medical prostheses, such as dental or orthopedic prostheses, based on CAD data. Examples of powder bed fusion techniques include selective laser melting and selective laser sintering.

[0003] Devices for producing one or more workpieces according to the above-mentioned techniques are known. For example, EP2961549A1 and EP2878402A1 respectively describe devices for manufacturing three-dimensional workpieces according to the selective laser melting technique. The general principles described in these documents can also be applied to the technology of the present disclosure.

[0004] In order to direct and focus the irradiation beam onto a specific predetermined point within the uppermost powder layer, the apparatus for manufacturing a three-dimensional workpiece generally comprises an irradiation device. To this end, the irradiation device may comprise an irradiation source (such as a laser source or a particle source), a focusing optical device (for performing focusing along a beam direction that is substantially in the z-direction), and / or a scanning optical device for moving the irradiation beam in an xy plane (corresponding to the plane of the powder layer).

[0005] In the event that more than one irradiation spot needs to be irradiated (in particular simultaneously), more than one irradiation device can be provided.

[0006] Current illumination devices (also called scan heads) include high-precision optical components and are therefore very expensive. Cheaper illumination devices may not achieve the required accuracy (e.g., with respect to long-term drift and / or thermal drift in the xy plane and / or z direction, respectively).

[0007] Furthermore, in order to eliminate or at least mitigate the effects of inaccurate positioning and in particular drift, it is known to calibrate the illumination device. For example, a reference plate with reference marks can be placed in the process chamber, the position of the laser beam relative to the reference marks can be determined, and calibration can be performed based on this determination. This calibration can be performed, for example, at the beginning of each building process. Furthermore, it is known to burn a calibration pattern into a calibration film and observe the generated pattern, for example with a camera.

[0008] However, known calibration techniques are not accurate enough, are too complex and / or do not allow calibration that can handle strong drift phenomena in the context of low-cost irradiation devices. Furthermore, known calibration techniques often have the disadvantage of requiring time, during which no melting process can take place. As a result, the productivity of the device may be reduced. Summary of the invention

[0009] It is therefore an object of the present invention to provide a technique that solves at least one of the above problems and / or other related problems. In particular, but not limited to, there is a need for an improved calibration technique for an illumination device of an apparatus for producing three-dimensional workpieces.

[0010] This object is achieved by the subject matter of the independent claims. Advantageous embodiments are indicated in the dependent claims.

[0011] According to a first aspect, a method for calibrating an irradiation device of an apparatus for producing a three-dimensional workpiece is provided. The method comprises: applying a first powder layer onto a carrier or onto a previously applied powder layer; irradiating the first powder layer with an irradiation beam along at least one first irradiation portion; defining a first correction direction, the first correction direction having an angle in the range of 70° to 110° relative to the at least one first irradiation portion; acquiring a first image of process radiation at a position where the irradiation beam strikes the first powder layer during irradiation along the at least one first irradiation portion; and determining a correction value along the first correction direction for calibrating the irradiation device based on the first image.

[0012] One or more of the following features of the method aspect may also be applied to the device of the device aspect described below.

[0013] The method may be performed by an apparatus for producing a three-dimensional workpiece (hereinafter referred to as an apparatus). The apparatus may be an additive manufacturing apparatus, for example, an apparatus for powder bed fusion (such as for selective laser melting or selective laser sintering). In this regard, the apparatus may exhibit the features discussed in the introduction above. The techniques of selective laser melting and selective laser sintering are well known to those skilled in the art and are only briefly described in this disclosure.

[0014] In particular, the building process performed by the device may involve depositing a first layer of raw powder onto a carrier of the device. The first layer (and subsequent layers) may have a predetermined layer thickness, wherein the layer thickness may be adjusted layer by layer or may be fixed. The powder layers may be deposited by any suitable technique, wherein a plurality of methods and devices for generating raw powder layers are known in the art. After depositing the first raw powder layer, a predetermined area of ​​the powder is irradiated by an irradiation beam (e.g., a laser or electron beam), for example, according to a CAD file. In this way, the first layer of the workpiece to be generated can be irradiated and thereby cured. In a subsequent step, a second layer of raw powder is deposited, and a predetermined area of ​​the second layer is irradiated and cured. In this way, the workpiece is generated layer by layer.

[0015] The method of the first aspect may be performed on one or more layers of a workpiece to be produced. For example, the method may be performed on the bottom layer of a workpiece to be generated, or the method may be performed on every M layers of a workpiece, where M is one or more layers.

[0016] When expressions such as "first" and "second" are used in the present disclosure, they are only used to distinguish the respective features in language. For example, the "first" powder layer is not necessarily the first powder layer applied to the carrier (because other previous powder layers may have been applied before).

[0017] The carrier may be a carrier of an apparatus, which is movable or stationary relative to the z-direction (perpendicular to the surface of the carrier in the xy plane). When a first powder layer is applied onto a previously applied powder layer, the previously applied powder layer may be part of a stack of powder layers applied onto the carrier. However, hybrid manufacturing situations are also included, in which the component to be repaired or completed by powder bed fusion is embedded in a powder bed below a previously applied powder layer. The previously applied powder layer may include a solidified portion.

[0018] Irradiating the first powder layer along at least one first irradiation portion may include irradiating with an irradiation beam (e.g., a laser beam or a particle beam, such as an electron beam). Specifically, a beam source for generating the irradiation beam may be provided, such as a laser source or a particle source (such as an electron source). When irradiating with a laser beam is discussed below, it should be understood that irradiating with a different irradiation beam (such as an electron beam) is also possible and included in the present disclosure.

[0019] Irradiating the first powder layer along at least one first irradiation portion may comprise: sintering or melting the powder at a position corresponding to the first irradiation portion. In other words, the energy of the irradiation beam used for the irradiation step may be suitable for solidifying the irradiated powder at a position corresponding to the first irradiation portion. The irradiation portion may be an irradiation vector (in particular of a workpiece layer). The irradiation step may be part of a manufacturing process of a three-dimensional workpiece. The irradiation vector may be, for example, part of a cross-sectional pattern (hatch pattern) of the interior (core) of the workpiece to be generated. However, the irradiation portion may also be part of a contour of the workpiece to be generated.

[0020] In the case where the irradiated portion is an irradiation vector, the irradiation vector is a straight line vector along a predetermined direction (i.e., along a straight line in the xy plane). The irradiation vector has a start point and an end point, wherein the irradiation beam scans from the start point to the end point during the irradiation step. The first correction direction may be perpendicular to at least one first irradiated portion. The first correction direction is located in the xy plane (i.e., in the plane of the first powder layer). The first correction direction having an angle in the range of 70° to 110° relative to at least one first irradiated portion may mean that the first correction direction is almost perpendicular or perpendicular to the first irradiated portion. For example, the angle between the first correction direction and the first irradiated portion may be in the range of 80° to 100°, or in the range of 85° to 95°. The angle may be 90°, so that the first correction direction is perpendicular to the first irradiated portion.

[0021] In the present disclosure, when it is mentioned that the correction direction is "perpendicular to" the illumination portion, the illumination vector or the tangent direction of the illumination portion, this means that the angle between the two elements can actually be 90°, or at least in the range of 70° to 110°. Therefore, even if it is not explicitly stated below, the indicated angle of two "perpendicular" elements can also be 90°, or at least in the range of 70° to 110°.

[0022] The first image may be a digital image and may therefore be represented by digital image data. In particular, the first image may be obtained by a digital camera. The exposure time of the first image may be such that the direction of the first irradiated portion can be derived from the first image. In other words, the first image may include a portion of the first irradiated portion that is not just an irradiated light spot, but an irradiated line. In particular, the first image may include the entire first irradiated portion, for example, the entire first irradiated vector (i.e., from its starting point to its end point). In other words, the exposure time of the first image may be at least the time required to scan the first irradiated vector from the starting point of the first irradiated vector to the end point of the first irradiated vector. However, the first image may include a portion of the first irradiated portion from which the direction of the first irradiated portion cannot be derived, wherein, in particular, since it only shows the irradiated light spot, the direction of the first irradiated portion cannot be derived from it. This may be because the exposure time is very short and / or the scanning speed of the laser along the first irradiated portion is very slow. In this case, the direction of the first irradiated portion may be determined based on control data provided by a control unit of the device to a scanning unit such as the device. In other words, the direction of the first irradiated portion may be derived by the control unit of the device based on an irradiation pattern and / or a scanning strategy stored in the control unit and / or provided to the scanning unit, for determining a correction value along the correction direction.

[0023] The process radiation (captured in the first image) may correspond to scattered laser radiation (i.e., the wavelength of the laser beam used for irradiation) or melt pool radiation (thermal radiation, e.g., in the visible or infrared wavelength region), or a combination of both. Specifically, a filter may be provided to block the laser radiation and to let the melt pool radiation pass, so that the image includes only the melt pool radiation.

[0024] In order to determine the correction value, the position of the first illumination portion within the acquired image (particularly relative to the first correction direction) may be determined. The acquired position of the first illumination portion may be compared with an expected position of the first illumination portion, particularly relative to the first correction direction. The expected position may be an expected position, for example, a position expected based on a previous calibration.

[0025] The correction value along the first correction direction may be a value that can be applied to the input data of the irradiation device to correct the irradiation position along the first correction direction. More precisely, the correction value may be applied to scanner data for controlling a scanning unit of the irradiation device. The correction value may include a lateral shift value representing a length (e.g., in mm), or may include a linear correction factor or a nonlinear correction value.

[0026] The method may further include performing a calibration of the illumination device along the first correction direction based on the first correction value. Calibration techniques are well known and will not be discussed in detail in this disclosure. The calibration may configure the illumination device so that the actual illumination position corresponds to the desired illumination position. The correction value may represent a deviation of the actual illumination position from the desired illumination position. After the calibration process, the deviation should be zero or at least minimized.

[0027] Calibration can be absolute or relative to another irradiation device. Absolute calibration refers to calibration relative to the position of the powder bed. Specifically, relative to the position of at least one reference mark arranged on the carrier or in the process chamber (for example, on the process chamber floor). Thus, absolute calibration can mean that a specific desired position of the powder bed can be irradiated accurately. Relative calibration (relative to another irradiation device) means that the position of the irradiation beam of an irradiation device relative to the irradiation beam of another irradiation device is known. In this way, for example, two irradiation devices can irradiate the same irradiation light spot accurately.

[0028] In order to achieve an absolute calibration, the camera (optical detection device) used to acquire the image can be used to perform an image field correction. For this purpose, a correction plate with reference marks can be used, which is placed in the field of view of the camera, for example, before the construction process begins.

[0029] The method may further include: applying a second powder layer onto the first powder layer or onto a powder layer that has been applied after the first powder layer; irradiating the second powder layer with an irradiation beam along at least one second irradiation portion, the second irradiation portion being not parallel to the first irradiation portion; defining a second correction direction having an angle in the range of 70° to 110° relative to the at least one second irradiation portion; acquiring a second image of process radiation at a position where the irradiation beam strikes the second powder layer during irradiation along the at least one second irradiation portion; and determining a correction value along the second correction direction for calibrating the irradiation device based on the second image.

[0030] For irradiating the second powder layer along at least one second irradiation portion, the same details and / or features as discussed above with respect to irradiating the first powder layer along at least one first irradiation portion may apply. In particular, during irradiation along the second irradiation portion, the irradiated portion of the second powder layer may melt or sinter and may thus solidify. Furthermore, the second irradiation portion may be an irradiation vector or a portion of an irradiation vector for producing a three-dimensional workpiece, for example, a portion of a cross-sectional pattern of an inner region (core) of a workpiece. However, the second irradiation portion may also be a portion of a contour of the workpiece.

[0031] Furthermore, for acquiring the second image, the same or corresponding details and / or features as discussed above with respect to acquiring the first image may apply.The first image and the second image may be acquired with the same optical detection device, in particular, a camera.

[0032] For the second correction value along the second correction direction the same details and / or features as discussed above with respect to the first correction value along the first correction direction may apply accordingly.

[0033] The method may further comprise performing a calibration of the illumination device along a second correction direction based on the second correction value.

[0034] Here, it should be noted that calibration with respect to the first correction direction can be performed after the first powder layer and before irradiating another powder layer. More specifically, calibration with respect to the first correction direction can be performed before applying the second powder layer. Therefore, calibration with respect to the second correction direction can be performed after calibration with respect to the first correction direction has been performed. However, optionally, a combined calibration can be performed based on the first correction value and the second correction value. In this way, calibration is performed not only in one direction (i.e., the first correction direction) but relative to the xy plane.

[0035] Therefore, the method may further comprise performing a (combined) calibration of the illumination device in the first correction direction and in the second correction direction based on both the first correction value and the second correction value.

[0036] The second correction direction may be perpendicular to the first correction direction. It should be noted that, even in the case where the second correction direction is not perpendicular to the first correction direction, it is sufficient that the angle between the two directions is greater than zero (in particular, greater than 10° or greater than 20° or greater than 45°), so that, for example, the x-component and the y-component used for calibration can be derived.

[0037] The first illumination portion may be a linear illumination vector. The second illumination portion may be a linear illumination vector.

[0038] However, the first illumination section and / or the second illumination section may also be a curved section, i.e. a curve. In this case, the direction of the first correction direction and / or the second correction direction is determined according to a tangent direction of the first illumination section and / or the second illumination section. The tangent direction may be determined at a specific point of the section, in particular, a point considered for calibration.

[0039] The first illumination portion may be a first illumination vector that is part of a first cross-sectional pattern of a first layer of a three-dimensional workpiece to be produced. The second illumination portion may be a second illumination vector that is part of a second cross-sectional pattern of a second layer of a three-dimensional workpiece to be produced.

[0040] The first cross-sectional pattern and the second cross-sectional pattern may each include a plurality of parallel illumination vectors.

[0041] The first cross-sectional pattern and / or the second cross-sectional pattern may be used as a filling structure for an inner region (core) of a workpiece to be produced. The direction of the irradiation vector of the first cross-sectional pattern and the direction of the irradiation vector of the subsequent cross-sectional pattern may be rotated by about a predetermined angle (e.g., 45° or 90°), for example, for each layer or every N layers (where N is 2 or more).

[0042] As described above, since the first irradiation vector and / or the second irradiation vector can be part of the corresponding cross-sectional pattern, irradiation of the corresponding (first and / or second) irradiation vector can cause melting (or sintering) and solidification of the irradiated portion of the corresponding powder layer. In other words, the calibration method can be performed in situ (i.e., during the construction process of the three-dimensional workpiece).

[0043] In this way, the calibration of the illumination device (or devices) of the device can be maintained at all times during the build process. Furthermore, time and effort can be saved, since a calibration process does not need to be performed before the build process begins. In this way, cheaper illumination devices can be used, which can drift significantly during the build process.

[0044] The at least one first illumination vector and the at least one second illumination vector may form an angle greater than 10°, greater than 15°, or greater than 20°.

[0045] For example, the angle may be 45° or 90°.

[0046] The first image may include a start point and an end point of the first illumination vector.

[0047] In particular, this may be true in both time and space. More specifically, the field of view of the camera acquiring the first image may be large enough so that the entire first illumination vector is within the field of view. Furthermore, the exposure time of the camera may be long enough so that illumination of the entire first illumination vector occurs during the exposure time. The first image may also include one or more additional illumination vectors or one or more parts thereof.

[0048] The first irradiated portion may be a contour portion which is a part of the contour of a three-dimensional workpiece to be produced.

[0049] For example, calibration with respect to the x-direction and the y-direction can be performed based on one powder layer. To this end, different parts of the contour of the workpiece can be considered, wherein the different parts extend to different directions in the xy plane. In addition, an irradiated part, i.e., an irradiation vector of the profile pattern, can be considered, and another irradiated part, i.e., a contour part of the workpiece can also be considered, wherein the irradiated part and the other irradiated part are not parallel to each other. In addition, a second correction value obtained for a second powder layer can also be considered.

[0050] Using more than two correction values ​​can increase the accuracy of the calibration. The contour portion is a contour portion of a workpiece to be generated. Therefore, during irradiation of the contour portion, the powder is melted (or sintered).

[0051] The contour portion may be a straight contour portion. In other words, the contour portion may be a portion of the workpiece contour that is a straight line. In this case, the first correction direction is defined as being perpendicular to the straight contour portion. However, the contour portion may also be a curved contour portion. In this case, the first correction direction is defined as being perpendicular to the tangent direction of the contour portion at a specific point that is part of the first image. Since the contour of the workpiece is generally a closed line, it changes its direction during irradiation of the contour, so that full calibration can be performed in the xy plane, that is, full calibration is performed not only along one first direction, but also along a plurality of non-parallel first directions.

[0052] The optical detection device configured as a device for acquiring an image can be controlled so that the contour of the workpiece is captured without gaps or almost without gaps. In other words, the optical detection device can be controlled so that it continuously acquires images. This can also be applied to the irradiation of the profile vector and the determination of the correction value for the profile vector. Therefore, the optical detection device can be controlled so that it continuously acquires images during the irradiation of the profile pattern including the first irradiation vector and / or during the irradiation of the contour of the three-dimensional workpiece.

[0053] The apparatus may include an irradiation device for emitting an irradiation beam and another irradiation device for emitting another irradiation beam. The method may include selectively irradiating the other irradiation beam onto the first powder layer. The irradiation device may be configured to scan the irradiation beam over a first scanning field, and the other irradiation device may be configured to scan the other irradiation beam over a second scanning field, the second scanning field at least partially overlapping the first scanning field in an overlapping region. The optical detection device that acquires the first image may be oriented or orientable such that the field of view of the optical detection device includes at least a portion of the overlapping region.

[0054] By providing at least two scanning fields that at least partially overlap, a three-dimensional workpiece with a larger coverage area can be generated in a short time, since at least two irradiation beams can be irradiated simultaneously in their corresponding scanning fields. The optical detection device can be a camera. When the field of view of the optical detection device includes at least part of the overlapping area, the optical detection device can be used, for example, for: a) absolute calibration of the irradiation device and the other irradiation device (i.e., calibration relative to the powder bed), and / or b) relative calibration of the irradiation device and the other irradiation device relative to each other. For the absolute calibration case a), the camera must be calibrated relative to the powder bed, i.e., it must be known which position in the image acquired by the camera corresponds to which position on the powder bed. This can be done with the aid of reference marks on a calibration plate, for example.

[0055] The irradiation device and the other irradiation device can irradiate simultaneously in the overlapping area, and can be imaged simultaneously by the optical detection device. Alternatively, the irradiation device and the other irradiation device can irradiate sequentially in the overlapping area, and can be imaged sequentially by the optical detection device.

[0056] The direction of the illumination portion produced by an illumination device may be different from the direction of the illumination portion produced by another illumination device. In this case, the corresponding correction directions for the illumination device and the other illumination device may be different. Thus, the illumination device may be calibrated in a different direction than the other illumination device. Typically, the calibration of the other illumination device may be performed in a manner similar to the calibration of the illumination device.

[0057] According to a second aspect, a device for producing a three-dimensional workpiece is provided. The device includes: a powder application device configured to apply at least one powder layer to a carrier or a previously applied powder layer; an irradiation device for selectively irradiating an irradiation beam to an irradiation plane corresponding to the applied powder layer; an optical detection device for optically detecting at least a portion of the irradiation plane; and a control unit. The control unit is configured to: instruct the powder application device to apply a first powder layer to the carrier or a previously applied powder layer; instruct the irradiation device to irradiate the first powder layer along at least one first irradiation portion; define a first correction direction having an angle in the range of 70° to 110° relative to at least one first irradiation portion; instruct the optical detection device to acquire a first image of process radiation at a position where the irradiation beam hits the first powder layer during irradiation along at least one first irradiation portion; and determine a correction value along the first correction direction for calibrating the irradiation device based on the first image.

[0058] All details described in the context of the method of the first aspect above can be applied to the device of the second aspect accordingly. In other words, the device of the second aspect can be configured to perform each method of the first aspect above.

[0059] The control unit can be configured to: instruct the powder application device to apply a second powder layer onto the first powder layer or onto a powder layer that has been applied after the first powder layer; instruct the irradiation device to irradiate the second powder layer along at least one second irradiation portion, the second irradiation portion being not parallel to the first irradiation portion; define a second correction direction having an angle in the range of 70° to 110° relative to the at least one second irradiation portion; instruct the optical detection device to acquire a second image of process radiation at a position where the irradiation beam hits the second powder layer during irradiation along at least one second irradiation portion; and determine a correction value along the second correction direction for calibrating the irradiation device based on the second image.

[0060] The first illumination portion may be a rectilinear illumination vector.

[0061] The first illumination portion may be a first illumination vector that is part of a first cross-sectional pattern of a first layer of a three-dimensional workpiece to be produced. The second illumination portion may be a second illumination vector that is part of a second cross-sectional pattern of a second layer of a three-dimensional workpiece to be produced. The first cross-sectional pattern and the second cross-sectional pattern each include a plurality of parallel illumination vectors.

[0062] According to a third aspect, there is provided a computer program product which, when executed by an apparatus for producing a three-dimensional workpiece, instructs the apparatus to perform the method of the first aspect.

[0063] The device for producing a three-dimensional workpiece may be the device of the second aspect. Specifically, the computer program product may be executed by a control device or a control unit of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Preferred embodiments of the present invention are described in more detail below with reference to the accompanying drawings, in which:

[0065] Figure 1 A schematic diagram showing an apparatus for producing a three-dimensional workpiece by additive manufacturing according to the present disclosure is shown;

[0066] Figure 2 A schematic diagram of an apparatus for producing a three-dimensional workpiece by additive manufacturing, comprising two irradiation devices according to the present disclosure, is shown;

[0067] Figure 3 A flow chart showing a method for calibrating an irradiation device of an apparatus for producing a three-dimensional workpiece according to the present disclosure;

[0068] Figure 4 A schematic diagram showing a control unit of an apparatus for producing a three-dimensional workpiece by additive manufacturing according to the present disclosure is shown;

[0069] Figure 5a) shows a top view of a first layer of a workpiece illuminated with two illumination beams, wherein this layer of the workpiece is filled with a cross-sectional pattern in a first direction; and

[0070] Figure 5 b) shows Figure 5 a) a top view of a second layer of the workpiece, wherein the layer of the workpiece is filled with a cross-sectional pattern in a second direction different from the first direction. DETAILED DESCRIPTION

[0071] Figure 1 A schematic diagram of an apparatus 10 for producing a three-dimensional workpiece 12 is shown. The apparatus 10 is known to a person skilled in the art, except for the calibration method which is usually programmed into the control unit 40 of the apparatus 10. The apparatus 10 may be, for example, a typical additive manufacturing apparatus, wherein the method for calibrating the irradiation device 24 according to the present disclosure is programmed into the control unit 40 of the apparatus 10.

[0072] The principle of the apparatus 10 is well known to those skilled in the art of additive manufacturing and will only be briefly described. For example, such an apparatus 10 may be a selective laser melting apparatus or a selective laser sintering apparatus, wherein one or more laser beams 14 may be used to selectively irradiate and solidify subsequent layers of raw material powder.

[0073] The apparatus 10 for performing the selective laser melting process described below can be used as an example. The typical characteristics of powder bed fusion are that the raw material powder is applied in layers and each layer is selectively irradiated and cured to generate a layer of the workpiece 12 to be produced. After removing the excess powder and after optional subsequent processing steps (for example, removing one or more support structures), the final workpiece 12 is obtained.

[0074] Figure 1 An apparatus 10 for producing a three-dimensional workpiece 12 by selective laser melting is shown. The apparatus 10 comprises a process chamber 16. The process chamber 16 is sealable relative to the surrounding atmosphere (i.e. relative to the environment around the process chamber 16). A powder application device 18 arranged in the process chamber 16 is used to apply raw material powder to a carrier 20. A vertical movement unit 22 is provided so that the carrier 20 can be moved in a vertical direction, so that when the workpiece 12 is layered from the raw material powder on the carrier 20, the carrier 20 can be moved downward in the vertical direction as the build height of the workpiece 12 increases.

[0075] Since the movability of the carrier 20 by the vertical movement unit 22 is well known in the field of selective laser melting, it will not be described in detail here. As an alternative to a movable carrier 20, the carrier 20 can be configured as a stable (or fixed) carrier (particularly in the vertical z-direction), wherein the irradiation device 24 (described below) and the processing chamber 16 are configured to move upwards during the building process (i.e., as the building height of the workpiece 12 increases). In addition, both the carrier 20 and the irradiation device 24 can be moved independently in the z-direction.

[0076] The carrier surface of the carrier 20 defines a horizontal plane (xy plane), wherein the direction perpendicular to the plane is defined as the vertical direction or the build direction (z direction). Therefore, each uppermost layer of the raw material powder and each layer of the workpiece 12 extends in a plane parallel to the above-mentioned horizontal plane (xy plane).

[0077] The apparatus 10 also includes a gas inlet 26 for supplying an inert gas (e.g., argon) into the process chamber 16. A gas outlet (not shown) may be provided so that a continuous gas flow through the process chamber 16 may be created by implementing a gas loop. In a preferred embodiment, a unidirectional laminar flow is created over the uppermost raw material powder layer.

[0078] Furthermore, a camera 28 is arranged in the processing chamber 16 for observing the laser beam 14 emitted by the irradiation device 24 towards the powder bed during operation, and / or for observing the irradiated area during and / or after irradiation with the laser beam 14. Furthermore, by blocking the wavelength of the laser beam 14 with a corresponding filter, only the thermal radiation of the generated molten pool (also called molten pool radiation) can be observed. The camera 28 can be part of the molten pool observation device. The field of view of the camera 28 includes the entire uppermost powder layer or part of the uppermost powder layer.

[0079] The apparatus 10 further comprises an irradiation device 24 (also referred to as an irradiation unit or optical unit) for selectively irradiating the laser beam 14 onto the uppermost layer of raw material powder applied to the carrier 20. By means of the irradiation device 24, the raw material powder applied to the carrier 20 can be laser irradiated in a position-selective manner according to the desired geometry of the workpiece 12 to be produced.

[0080] The irradiation device 24 includes a scanning unit 30, which is configured to selectively irradiate the laser beam 14 onto the raw material powder applied to the carrier 20. The scanning unit 30 is controlled by a control unit 40 of the device 10. The scanning unit 30 may include a mirror that is tiltable relative to two vertical axes. Optionally, the scanning unit 30 may include two tiltable mirrors, each tiltable mirror being configured to tilt relative to a corresponding axis. The tiltable mirror may be, for example, a galvanometer mirror.

[0081] Laser radiation is supplied from a laser beam source 32 to the irradiation device 24. Figure 1 As shown, the laser beam source 32 can be arranged inside the irradiation device 24 or outside the irradiation device 24. In the first case, the laser beam source 32 can be considered as a part of the irradiation device 24. In the latter case, the laser beam is generated by the laser beam source 32 and guided into the irradiation device 24 via the optical fiber 34. Alternatively, the laser beam can be guided into the irradiation device 24 through air or by vacuum, for example by using one or more mirrors to guide the laser beam into the irradiation device 24.

[0082] The laser beam is directed from a laser beam source 32 to the scanning unit 30. The laser beam source 32 may include, for example, a diode pumped Ytterbium fiber laser emitting laser light having a wavelength of about 1070 nm to 1080 nm (ie, in the infrared wavelength range).

[0083] The irradiation device 24 also includes two lenses 36 and 38, which are configured to focus the laser beam 14 to a desired focus position along the z-axis. Figure 1 In the embodiment shown, both lenses 36 and 38 have positive refractive power. Lens 38 further upstream in the beam path is configured to collimate the laser light emitted by optical fiber 34 so as to produce a collimated or substantially collimated laser beam. Lens 36 further downstream in the beam path is configured to focus the collimated (or substantially collimated) laser beam to a desired z position.

[0084] In addition, Figure 1 4. Reference marks 42 are shown in FIG. Reference marks 42 are arranged in the bottom region of process chamber 16, adjacent to the uppermost layer of raw material powder. At least one of reference marks 42 is within the field of view of camera 28. As described below, reference marks 42 can be used for absolute calibration of irradiation device 24. However, reference marks 42 are not necessary, for example, for situations where irradiation device 24 should only be calibrated relative to another irradiation device (relative calibration). Therefore, reference marks are considered optional.

[0085] The control unit 40 comprises a processor and a memory, wherein instructions are stored on the memory for controlling the various components of the apparatus 10. For example, the control unit 40 may be configured to control one or more of the following: the camera 28, the vertical movement unit 22, the powder application device 18, the gas flow provided by the gas inlet 26, and the irradiation device 24. User input and output interfaces may be provided and connected or connectable to the control unit 40. Furthermore, the control unit 40 has an interface for receiving workpiece data representing the three-dimensional shape of the workpiece 12 to be produced.

[0086] Similar to Figure 1The device 10 of an embodiment, Figure 2 Different embodiments of the device 10 are shown. As the only difference between the two devices 10, Figure 2 The device 10 comprises two irradiation devices 24a and 24b instead of Figure 1 The device 10 has an irradiation device 24. However, Figure 2 The remainder of the device 10 has the same Figure 1 The same components and functions as those discussed above are omitted from repetition of the description. In addition, the reference numerals of the components of the irradiation devices 24a, 24b are the same as those of the irradiation devices 24a, 24b. Figure 2 However, the suffixes "a" and "b" are used to distinguish between the components of the illumination device 24a (suffix a) and the components of the other illumination device 24b (suffix b). The functions of the various components within the illumination devices 24a and 24b are the same as those discussed above with respect to the illumination device 24.

[0087] Hereinafter, unless otherwise explicitly stated, reference numerals without a suffix (a or b) are used to refer also to corresponding elements with the suffixes a and b. For example, when "scanning unit 30" is mentioned, scanning units 30a and 30b are also referred to.

[0088] Figure 2 The device 10 is configured so that the irradiation device 24a is configured to scan a first predetermined area (i.e., a first scanning field) of the uppermost powder layer. Similarly, another irradiation device 24b is configured to scan a second predetermined area (i.e., a second scanning field) of the uppermost powder layer. The first scanning field and the second scanning field overlap each other in the overlapping area. In other words, there is an area (i.e., an overlapping area) in the uppermost powder layer that can be reached and selectively irradiated by the two laser beams 14a and 14b. The first scanning field and the second scanning field can be rectangular or circular, respectively, and the size and / or shape of the corresponding scanning field can be predefined by the movement range of the corresponding scanning units 30a and 30b of the irradiation devices 24a and 24b, respectively.

[0089] In order to produce a three-dimensional workpiece 12, two laser beams 14a and 14b can simultaneously irradiate different portions of the same powder layer, wherein each laser beam 14a and 14b irradiates a portion of the workpiece 12 in its corresponding scanning field. In this way, compared with the case of using only one laser beam 14 (see, for example, Figure 1 ) compared to the previous example, artifact 12 can be built faster.

[0090] However, in order to achieve a high quality of the generated workpiece 12, it is important that the two lasers 14a and 14b are calibrated relative to each other. In other words, it is important that the relative position of the first laser beam 14a with respect to the second laser beam 14b is known. For example, when the two laser beams 14a and 14b are to illuminate the same point (or one laser beam is to continue illuminating a line started by the other laser beam), proper relative calibration is required.

[0091] Furthermore, for only one irradiation device 24 (see Figure 1 ) and for more than one irradiation device 24a, 24b (see Figure 2 ), it is also important to provide an absolute calibration (i.e. a calibration according to the position of the uppermost powder layer). This may be important for situations such as hybrid manufacturing, where the object to be repaired is embedded in a powder bed below the uppermost powder layer in order to hit a specific predetermined position within the uppermost powder layer to continue building the object to be repaired.

[0092] As described above, the technology of the present disclosure provides absolute and / or relative calibration of one or more irradiation devices. Providing calibration (especially constant calibration or calibration at short time intervals) is particularly important in the case of using an irradiation device 24 that does not have the same stability as a high-cost, high-precision irradiation device. Cheaper irradiation devices 24 may include cheaper components that have significant drift (e.g., long-term drift or short-term drift), such as thermal drift during heating of various components of the irradiation device 24 (e.g., lenses) during the build process. Specifically, the drift may include a drift of the position of the laser beam 14 in the xy plane relative to a fixed position of the topmost powder layer. In other words, although the corresponding irradiation device 24 is instructed (e.g., by a corresponding command) to irradiate a specific position of the topmost powder layer, the actual irradiated position varies over time and thus "drifts."

[0093] Furthermore, the method described herein is also very useful for high-cost and / or high-precision illumination devices, since these (expensive) illumination devices may also drift in the xy plane. In this case, the proposed method can be used to further improve the accuracy of the multi-laser alignment and the accuracy of the resulting workpiece.

[0094] By providing calibration as described in the present disclosure, the above-mentioned drift phenomenon can be avoided.

[0095] Figure 3 A flow chart of a method for calibrating an illumination device 24 of an apparatus 10 for producing a three-dimensional workpiece 12 according to the present disclosure is shown.

[0096] The method uses, for example, the above-mentioned Figure 1 or Figure 2 The method is performed by one of the devices 10.

[0097] The method starts with step 50, in which a first powder layer is applied onto a carrier or onto a previously applied powder layer. The application is performed using a powder application device 18 and under the control of a control unit 40. The first powder layer extends in the xy plane and has a predetermined thickness. The first powder layer may be the actual first (i.e., initial) powder layer of the building process, or the first powder layer may be a powder layer applied during the course of the building process after a previous powder layer has been applied.

[0098] In step 52, the first powder layer is irradiated along at least one first irradiation portion. The irradiation is performed by the irradiation device 24 or 24a. The irradiation is performed using an irradiation beam, in particular using Figure 1 The laser beam 14 of the device 10 or the use Figure 2 The laser beam 14a of the device 10 is irradiated. The first irradiated portion may be a straight portion and may have a start point and an end point, wherein the irradiation beam scans from the start point to the end point. During irradiation, the powder melts or sinters in the area irradiated by the irradiation beam. More precisely, a molten pool is formed by molten fluid powder material, which then cools and thereby solidifies. This leaves a line of solidified powder material along the irradiated portion after irradiation.

[0099] In step 54, a first correction direction is defined, which has an angle in the range of 70° to 110° relative to at least one first irradiation vector. The angle may be 90°. The definition of the first correction direction is performed by the control unit 40 of the device 10. More precisely, the control unit 40 has information about the scanning direction of the first irradiation portion, and therefore, the first correction direction can be defined based on this information. For example, in the case where the first irradiation portion is scanned along the x-direction (1, 0), the first correction direction can be defined along the y-direction (0, 1). The first irradiation portion and the first correction direction are in the plane of the uppermost powder layer (i.e., in the xy plane).

[0100] In step 56, during the irradiation along at least one first irradiation portion, a first image of the process radiation at the location where the irradiation beam impinges on the first powder layer is acquired (56). The acquisition is performed by the camera 28 and under the control of the control unit 40. The corresponding image data can be stored and / or processed by the control unit 40.

[0101] In step 58, correction values ​​along the first correction direction are determined for calibration of the irradiation device based on the first image. This step is performed by the control unit 40. The correction values ​​are suitable for calculating the actual irradiation position along the correction direction based on the position data as input into the scanning unit 30 of the irradiation device 24. The correction values ​​may represent an offset along the first correction direction or may represent a linear correction factor along the first correction direction. Furthermore, one or more non-linear correction factors may be considered.

[0102] Based on the correction values ​​along the first correction direction, a calibration of the irradiation device 24 can be performed along the first correction direction. The calibration can be performed directly after steps 50 to 58 or after steps 50 to 58 have been repeated for a different (second) powder layer and therefore for a different (second) correction direction. In the first case, the calibration is performed only along the first correction direction. In the latter case, since the first correction direction and the second correction direction are not parallel to each other, a full xy calibration can be performed.

[0103] Figure 4 Shows Figure 1 or Figure 2 Schematic diagram of a control unit 40 of one of the devices 10. The control unit 40 includes a plurality of modules 60 to 68, each of which can be represented in the form of hardware and / or software. In one example, the control unit 40 includes a processor and a memory. The memory stores instructions that cause the processor to execute Figure 3 To this end, the software stored on the memory may be considered to include Figure 4 Modules 60 to 68 shown in FIG.

[0104] Specifically, these modules are:

[0105] The first instruction module 60 is used to instruct the powder applying device to apply a first powder layer onto the carrier or onto a previously applied powder layer.

[0106] The second instruction module 62 is used to instruct the irradiation device to irradiate the first powder layer with an irradiation beam along at least one first irradiation portion.

[0107] A defining module 64 is used to define a first correction direction having an angle in the range of 70° to 110° with respect to the at least one first illumination portion.

[0108] The third instruction module 66 is used to instruct the optical detection device to acquire a first image of the process radiation at a position where the illumination beam hits the first powder layer during illumination along at least one first illumination portion.

[0109] The determination module 68 is configured to determine a correction value along a first correction direction for calibration of the illumination device based on the first image.

[0110] The details discussed herein with respect to the individual method steps may also be applied to the corresponding modules 60 to 68 of the control unit 40. In other words, the control unit 40 is configured to perform the above Figure 3 wherein the details of the method discussed herein apply accordingly to the software of the control unit 40 and / or Figure 4 The corresponding modules and / or additional modules shown in .

[0111] Figure 5 The construction process of one or more three-dimensional workpieces 12 using two laser beams 14a and 14b is shown. Figure 5 Description of the first layer ( Figure 5 a)) and the second layer ( Figure 5 It is not important whether the two corresponding illuminated portions 70a / 70b and 72a / 72b of b)) are part of the same workpiece 12 or two different workpieces 12. Both cases are included in the following description, which will generally be referred to as "workpiece 12" (singular).

[0112] for Figure 5 The build process shown can be used Figure 2 The device 10 (having two irradiation devices 24a and 24b) can also be used. In addition, any other suitable additive manufacturing device capable of emitting at least two irradiation beams can be used. Figure 5 The construction process.

[0113] Figure 5 a) shows the irradiation of a first layer of the workpiece 12 , which first layer may be an initial layer (ie the actual first layer on the carrier 20 ) or another arbitrary layer during the building process of the workpiece 12 . Figure 5 b) shows the irradiation of a second layer of the workpiece 12 , wherein the second layer may be directly after the first layer, or may be any layer of the same workpiece 12 that is irradiated at some point after the irradiation of the first layer.

[0114] and Figure 2 Similarly as discussed, the area of ​​the carrier 20 defining the total footprint of the workpiece 12 to be generated is divided into two scanning fields 74a and 74b. The first scanning field 74a defines the area of ​​the uppermost powder layer that can be irradiated by the first laser beam 14a, while the second scanning field 74b defines the area of ​​the uppermost powder layer that can be irradiated by the second laser beam 14b. In other words, each of the laser beams 14a and 14b can be scanned to each position within their respective scanning fields 74a and 74b by means of the scanning units 30a, 30b of their respective irradiation devices 24a, 24b.

[0115] The two scanning fields 74a and 74b define an overlapping region 76 in which the two scanning fields 74a and 74b overlap. Both laser beams 14a and 14b can reach the overlapping region 76. Irradiation in each scanning field 74a and 74b (and in the overlapping region 76) can be performed simultaneously or sequentially.

[0116] exist Figure 5 , the field of view 78 of the camera 28 is also shown. The field of view 78 is defined as the area of ​​the uppermost powder layer imaged by the camera 28 when the image is acquired by the camera 28. Figure 5 As shown, the field of view 78 covers at least a portion of the overlap region 78. Figure 5 In the embodiment of FIG. 7 , the field of view 78 also covers portions of the first scanning field 74 a and the second scanning field 74 b that are not part of the overlap region 76 .

[0117] The first layer of the workpiece 12 includes a first portion 70a and a second portion 70b. The first portion 70a is irradiated with the first laser beam 14a and the second portion 70b is irradiated with the second laser beam 14b according to an irradiation strategy stored and / or defined in the control unit 40. The same applies to portions 72a and 72b of the second layer, which may or may not have the same shape as portions 70a and 70b.

[0118] In the first layer, the scanning strategy includes a cross-sectional pattern defining a plurality of parallel illumination vectors 80. Although only one illumination vector 80 in the first portion 70a and the second portion 70b has a reference number, it is understood that a plurality of illumination vectors 80 are defined in each of the first portion 70a and the second portion 70b. The cross-sectional pattern defines a plurality of parallel illumination vectors 80, which serve to fill the interior (also referred to as the core) of the workpiece 12. In addition to the hatched interior, a contour 82 is provided along which the contour of the workpiece 12 is solidified. The contour 82 may be irradiated with the same laser beam 14a, 14b as the corresponding cross-sectional pattern (vector 80) or with a different laser beam (or with the same laser beam but with different illumination parameters, such as illumination power).

[0119] Figure 5 The arrow in a) indicates a direction perpendicular to the direction of the individual illumination vector 80. As described below, this direction (according to the arrow) corresponds to a first correction direction.

[0120] exist Figure 5b), the scanning strategy also includes a cross-sectional pattern defining a plurality of parallel illumination vectors 84. Although only one illumination vector 84 in the first portion 72a and the second portion 72 has a reference numeral, it is understood that a plurality of illumination vectors 84 are defined in each of the first portion 72a and the second portion 72. The cross-sectional pattern defines a plurality of parallel illumination vectors 84, which serve as a fill of the interior (also referred to as the core) of the workpiece 12. In addition to the filled interior, a contour 86 is provided along which the contour of the workpiece 12 is solidified. The contour 86 may be irradiated with the same laser beam 14a, 14b as the corresponding cross-sectional pattern (vector 84) or with a different laser beam (or with the same laser beam but with different illumination parameters, such as illumination power).

[0121] Figure 5 The arrow in b) indicates a direction perpendicular to the direction of the individual illumination vector 84. This direction (according to the arrow) corresponds to the second correction direction, as described below.

[0122] like Figure 5 As shown, the directions of the illumination vectors 80 and 84 are different. In other words, the directions in which the illumination vectors 80 and 84 extend are rotated between the first layer and the second layer. For example, the scanning strategy may involve a rotation of the illumination vector for each layer, for example about 45° or 90°. The rotation of the direction of the illumination vector in the xy plane may be performed, for example, for each layer or for each N layers (where N is 2 or more). For the present embodiment discussed, it is only important that the (first) illumination vector 80 of the first layer and the (second) illumination vector 84 of the second layer are not parallel to each other.

[0123] In the following, it will be explained how the illumination of illumination vectors 80 and 84 performed for producing a three-dimensional workpiece 12 can be used to calibrate the respective illumination devices 24a and 24b. In the following, the calibration of the first illumination device 24a is described, wherein the calibration of the second illumination device 24b is performed in a similar manner.

[0124] The illumination of the illumination vector 80 is performed based on a scan strategy stored in the control unit 40. Thus, the direction of the illumination vector 80 is predefined by the scan data stored in the control unit 40.

[0125] Based on the scanning strategy and / or the scanning data, the control unit 40 defines a first correction direction perpendicular to the first illumination vector 80 .

[0126] The camera 28 acquires a first image (covering the field of view 78) of at least a portion of one of the illumination vectors 80. In other words, the camera 28 is operated with a predetermined exposure time, which covers at least a portion of one of the illumination vectors 80. According to one embodiment, the direction of the illumination vector 80 can be derived from the acquired image. Thus, the image does not only show a single one-dimensional illumination spot. In an example considered in this embodiment, the exposure time of the camera 28 is selected so that a complete illumination vector 80 is part of the image. Each illumination vector 80 has a start point and an end point, wherein the laser beams 14a and 14b are used to scan the corresponding illumination vector 80 from the start point to the end point. In the example discussed, the exposure time is selected so that the exposure time at least covers the scan from the start point to the end point. Thus, the direction of the illumination vector 80 can be derived from the image.

[0127] However, according to another embodiment, the exposure time is so short that the image shows only a single one-dimensional illumination spot. In this case, the direction of the first illumination vector 80 is known since it can be derived from the scanning strategy and / or the scanning data.

[0128] In the present example using two laser beams 14a and 14b, the image includes one illumination vector illuminated by the first laser beam 14a and one illumination vector illuminated by the second laser beam 14b. Of course, the image may include additional illumination vectors (or portions of illumination vectors) illuminated, for example, before or after the illumination vector 80 under consideration.

[0129] The control unit 40 analyses the first image and, in particular, determines the position of the first illumination vector 80 relative to the first correction direction. In the control unit 40, the expected position of the first illumination vector 80 is stored so that the deviation of the acquired position relative to the expected position can be calculated. For example, an offset value (e.g. in mm) can be calculated, defining the offset of the expected position from the actual position within the image. The offset value is also referred to as the first correction value. Other possibilities for the first correction value are correction factors (for linear multiplication) or parameters applied in a non-linear correction function.

[0130] In a subsequent calibration step performed by the control unit 40, calibration of the irradiation device 24a is performed based on the first correction value. Calibration is performed along a first correction direction using the first correction value. For example, calibration may be performed such that the first correction value is applied by the control unit 40 to the position data transmitted to the irradiation device 24a, and more precisely, to the position data transmitted to the corresponding scanning unit 30a. As described above, calibration of the second irradiation device 24b is performed in the same manner as explained above with respect to the first irradiation device 24a.

[0131] Furthermore, the calibration of the illumination devices 24a, 24b may be absolute or relative to each other.

[0132] Absolute calibration means calibration relative to a fixed position of the carrier 20 (and thus the powder bed). To this end, the camera 28 must be calibrated beforehand, for example by using, for example, reference marks 42 (such as Figure 1 and Figure 2 4 (shown) to pre-calibrate the camera 28. More precisely, the image field correction can be performed by using a plurality of reference marks 42. As an alternative to using reference marks 42 in the side areas close to the powder bed, a calibration carrier can be used, which is placed at a fixed position in the process chamber 16 relative to the carrier 20. In each case, the camera 28 records an image of the calibration mark, and the control unit 40 is used to map the position in the recorded image to the actual position on the carrier 20.

[0133] Relative calibration means that the first laser beam 14a is calibrated relative to the second laser beam 14b so that the relative position of the laser beams 14a and 14b is known and can be controlled. For example, in the case where the two scanning units 30a and 30b are instructed to illuminate the same light spot within the overlap area 76, the two laser beams can be directed to the same light spot. However, without an absolute calibration, the position of the light spot within the uppermost powder layer may not be known with certainty.

[0134] for Figure 5 b) as described above with respect to the second layer Figure 5 However, the direction of the second illumination vector 84 is different from the direction of the first illumination vector 80, so that in combination with the calibration after the first layer and the calibration after the second layer, a full calibration can be performed for the x-direction and the y-direction (i.e., in the xy plane).

[0135] In an alternative method, after irradiating the first layer, a first correction value is obtained, and after irradiating the second layer, a second correction value is obtained. In a subsequent calibration step, calibration can be performed based on the first correction value and the second correction value. Thus, calibration is performed with respect to both the x-direction and the y-direction.

[0136] Calibration according to the present technology can also be described as follows. Evaluation software is stored in the control unit 40. The evaluation software includes an interface to a scanner controller device for controlling the position and / or deflection of the scanning unit 30. The interface is used to obtain the current position of the scanning unit 30 (especially the scanning mirror of the scanning unit 30) in a timely and synchronous manner. The software automatically evaluates the image to obtain the actual position of the laser beam 14a. Optionally, interpolation can be performed between pixels to obtain higher resolution. In addition, in particular for the scan vector list sent to the scanner controller device or even for each coordinate sent to the scanning unit 30, the detected deviation between the actual position and the expected position of the laser light spot is corrected.

[0137] In the following, we discuss the above Figure 5 Alternative or modified methods of the embodiments of. If applicable, the following alternatives can be performed in combination with the techniques discussed above.

[0138] According to a first alternative, for a device 10 having only one irradiation device 24 (e.g. Figure 1 The method is the same as discussed above, wherein only the first parts 70a and 70b are considered.

[0139] According to a second alternative, the direction of the first illumination vector 80 of the first portion 70a is different from the direction of the first illumination vector 80 of the second portion 70b. In general, the direction of the illumination vector of the first illumination device 24a may be different from the direction of the illumination vector of the second illumination device 24b. However, the calibration method is the same as discussed above. In this case, the first correction direction of the first illumination device 24a is different from the correction direction of the second illumination device 24. The same applies to the second layer.

[0140] The above technique may be performed such that in the step of determining the correction value along the first correction direction, no correction values ​​along a different, perpendicular correction direction are obtained. Thus, in the first correction step performed after irradiating the first layer, calibration is performed only for the first correction direction (and not for another correction direction). In other words, the calibration performed after irradiating the first layer may be one-dimensional. Similarly, the calibration after irradiating the second layer may be one-dimensional.

[0141] However, according to a third alternative, the start and / or end point of the first illumination vector may be considered and used to perform a calibration with respect to a direction perpendicular to the first correction direction. Similarly, the start and / or end point of the second illumination vector may be considered and used to perform a calibration with respect to a direction perpendicular to the second correction direction. However, these "perpendicular" calibrations may not be as accurate as the corresponding calibrations with respect to the first and second correction directions.

[0142] According to a fourth alternative, more than one camera 28 may be used and, for calibration, the combined field of view of the cameras may be taken into account.

[0143] Furthermore, according to a fifth alternative, a movable camera 28 can be used, which can move its field of view on the carrier 20 to provide a larger field of view. Furthermore, as the camera 28, a camera of a process observation system of a laser optical device can also be used.

[0144] According to a sixth alternative, a contour portion of the contour 82 of the first layer and / or a contour portion of the contour 86 of the second layer is considered for determining the correction value. The contour portion may be a straight line (e.g. Figure 5 ), or it may be a curved line (such as Figure 5 ) as shown in the corner portions of the roughly rectangular shape of the illumination pattern.

[0145] In addition to the illumination vectors 80, 84 for calibrating the respective illumination device 24, contour portions of the contours 82, 86 may also be considered. The contour portions are processed similarly to the illumination vectors 80 and 84 discussed above. Therefore, the correction direction is defined as being perpendicular to the contour portion and the corresponding correction values ​​are calculated.

[0146] In the case where the contour portion is a straight contour portion (e.g., Figure 5 In the case of a straight line of the profile shown in ), in this case, the correction direction is defined as being perpendicular to the straight profile portion. However, the profile portion considered may also be a curved profile portion (e.g. Figure 5 In this case, the correction direction is defined as the direction perpendicular to the tangent of the contour portion at the point under consideration.

[0147] One or more embodiments of the present technology may have at least one of the following advantages. Since calibration can be performed during the actual building process, there is no need to perform time-consuming calibration in advance. More specifically, the embodiments described herein may have the following advantages: calibration information is obtained without interfering with the regular ongoing building process simply by observing the building process. In addition, since calibration is performed for each layer or every N layers during the building process, it is possible to ensure that the irradiation device is constantly calibrated during the building process and that drift is compensated at any time. In this way, a cheaper irradiation device with significant drift can be used while ensuring the accuracy of the irradiation position.

Claims

1. A method for calibrating an irradiation device (24; 24a, 24b) of a device (10) for producing a three-dimensional workpiece (12), the method comprising: applying (50) a first powder layer onto the carrier (20) or onto a previously applied powder layer; irradiating (52) the first powder layer along at least one first irradiation portion (80) with an irradiation beam (14; 14a, 14b); defining (54) a first correction direction having an angle in the range of 70° to 110° relative to the at least one first illumination portion (80); acquiring (56) a first image of process radiation at a location where the illumination beam (14; 14a, 14b) impinges on the first powder layer during illumination along the at least one first illumination portion (80); Based on the first image, correction values ​​for calibrating the illumination device (24; 24a, 24b) along the first correction direction are determined (58).

2. The method according to claim 1, further comprising: applying a second powder layer onto the first powder layer or onto a powder layer that has been applied after the first powder layer; irradiating the second powder layer with the irradiation beam (14; 14a, 14b) along at least one second irradiation portion (84), the second irradiation portion (84) being non-parallel to the first irradiation portion (80); defining (54) a second correction direction having an angle in the range of 70° to 110° relative to the at least one second illumination portion (84); acquiring, during irradiation along the at least one second irradiation portion (84), a second image of the process radiation at a location where the irradiation beam (14; 14a, 14b) impinges on the second powder layer; and Based on the second image, correction values ​​for calibrating the illumination device (24; 24a, 24b) along the second correction direction are determined (58).

3. The method according to claim 1 or 2, wherein: The first illumination portion (80) is a straight illumination vector (80).

4. The method according to claim 3, wherein: The first illumination portion (80) is a first illumination vector that is part of a first cross-sectional pattern of a first layer of the three-dimensional workpiece (12) to be produced, and The second illumination portion (84) is a second illumination vector that is part of a second cross-sectional pattern of a second layer of the three-dimensional workpiece (12) to be produced.

5. The method according to claim 4, wherein: The first cross-sectional pattern and the second cross-sectional pattern each include a plurality of parallel illumination vectors (80, 84).

6. The method according to claim 4, wherein: The at least one first illumination vector (80) and the at least one second illumination vector (84) form an angle greater than 10°, greater than 15°, or greater than 20°.

7. The method according to any one of claims 3 to 6, wherein: The first image includes a start point and an end point of the first illumination vector (80).

8. The method according to claim 1 or 2, wherein: The first irradiated portion is a contour portion that is a part of a contour (82, 86) of the three-dimensional workpiece (12) to be produced.

9. The method according to any one of claims 1 to 8, wherein: The device (10) comprises an irradiation device (24a) for irradiating the irradiation beam (14a) and another irradiation device (24b) for irradiating another irradiation beam (14b), the method comprising: The further irradiation beam (14b) is selectively irradiated onto the first powder layer, wherein: The illumination device (24a) is configured to scan the illumination beam (14a) over a first scanning field (74a), and the further illumination device (24b) is configured to scan the further illumination beam (14b) over a second scanning field (74b), the second scanning field (74b) at least partially overlapping the first scanning field (74a) in an overlap region (76), and wherein The optical detection device (28) acquiring the first image is oriented or can be oriented such that a field of view (78) of the optical detection device (28) includes at least a portion of the overlap region (76).

10. The method according to claim 9, in, The irradiation device (24a) and the further irradiation device (24b) irradiate simultaneously in the overlapping area (76) and are imaged simultaneously by the optical detection device (28), or The irradiation device (24a) and the further irradiation device (24b) irradiate sequentially in the overlapping area (76) and are imaged sequentially by the optical detection device (28).

11. An apparatus (10) for producing a three-dimensional workpiece (12), comprising: a powder application device (18) configured to apply at least one powder layer onto the carrier (20) or onto a previously applied powder layer; an irradiation device (24; 24a, 24b) for selectively irradiating an irradiation beam (14; 14a, 14b) onto an irradiation plane corresponding to the applied powder layer; optical detection means (28) for optically detecting at least a portion of the illumination plane; and The control unit (40) is configured to: instructing the powder application device (18) to apply a first powder layer onto the carrier (20) or onto the previously applied powder layer; instructing the irradiation device (24; 24a, 24b) to irradiate the first powder layer along at least one first irradiation portion (80); defining a first correction direction having an angle in the range of 70° to 110° relative to the at least one first illumination portion (80); instructing the optical detection device (28) to acquire (28) a first image of process radiation at a location where the illumination beam (14; 14a, 14b) impinges on the first powder layer during illumination along the at least one first illumination portion (80); and Based on the first image, correction values ​​for calibrating the illumination device (24; 24a, 24b) along the first correction direction are determined.

12. The device (10) according to claim 11, wherein The control unit is configured to: instructing the powder applying device (18) to apply a second powder layer onto the first powder layer or onto a powder layer that has been applied after the first powder layer; instructing the irradiation device (24; 24a, 24b) to irradiate the second powder layer with the irradiation beam (14; 14a, 14b) along at least one second irradiation portion (84), the second irradiation portion (84) being non-parallel to the first irradiation portion (80); defining (54) a second correction direction having an angle in the range of 70° to 110° relative to the at least one second illumination portion (84); instructing the optical detection device (28) to acquire (28) a second image of process radiation at a location where the illumination beam (14; 14a, 14b) impinges on the second powder layer during illumination along the at least one second illumination portion (84); and Based on the second image, correction values ​​for calibrating the illumination device (24; 24a, 24b) along the second correction direction are determined (58).

13. The device (10) according to claim 11 or 12, wherein: The first illumination portion (80) is a straight illumination vector (80).

14. The device (10) according to claim 13, wherein: The first illumination portion (80) is a first illumination vector that is part of a first cross-sectional pattern of a first layer of the three-dimensional workpiece (12) to be produced, and The second illumination portion (84) is a second illumination vector, the second illumination vector being part of a second cross-sectional pattern of a second layer of the three-dimensional workpiece (12) to be produced; and optionally, wherein, The first cross-sectional pattern and the second cross-sectional pattern each include a plurality of parallel illumination vectors (80, 84).

15. A computer program product which, when executed by a device (10) for producing a three-dimensional workpiece (12), instructs the device (10) to perform the method according to any one of claims 1 to 10.

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