Calibration of equipment for selective powder melting.

Abstract

The present invention particularly relates to a method for calibrating an installation (10) for producing objects from a material powder by selective powder fusion, the installation (10) comprising: a build chamber (22) provided for accommodating the powder to be melted and the object to be produced; a build plate holder (24) provided in the build chamber (22) so as to be height adjustable, the build plate holder (24) provided for supporting a build plate together with the object to be produced; and a controllable optical unit (20) including a laser source (18), a plurality of lenses (16), and a mirror assembly with a plurality of adjustably arranged mirrors (14), the controllable optical unit (20) being configured to selectively direct a laser beam (L) emitted from the laser source (18) to a point (S) in the build chamber where the material powder is to be melted. In this case, the method includes the steps of placing a scan field plate (26) on a build plate holder (24) in a build chamber (22), creating a plurality of optical reference points at predefined positions on the scan field plate (26) using a controllable optical unit (20), creating a measurement pattern (M) on the scan field plate (26) using the controllable optical unit (20) by correspondingly adjusting the mirrors (14) of the mirror assembly based on a calibration data set, and determining the relative positioning between the optical reference points and the measurement pattern.

Description

[Technical Field]

[0001] The present invention relates to a method for calibrating an installation for manufacturing objects from a material powder by selective powder fusion, the installation comprising: a build chamber provided for accommodating the powder to be melted and the object to be manufactured, a build plate holder provided in the build chamber so as to be height adjustable, the build plate holder provided for supporting a build plate together with the object to be manufactured, and a controllable optical unit including a laser source, a plurality of lenses, and a mirror assembly with a plurality of adjustably arranged mirrors, the controllable optical unit being configured to selectively direct a laser beam emitted from the laser source to a point in the build chamber where the material powder is to be melted. Furthermore, the present invention relates to an installation in which a control unit is configured to control the controllable optical unit to perform such a method, and to a system formed from such an installation and a reading device.

[0002] For the prior art in the field of selective powder fusion, reference is made, purely by way of example, to DE 19905067 A1, DE 10112591 A1, WO 98 / 24574 A1, DE 102009038165 A1, DE 102012221641 A1, EP 2052845 A1, DE 102005014483 A1 and WO 2017 / 084781 A1.

[0003] It is known that selective powder fusion can be used to produce molded bodies, such as machine parts, tools, prosthetics, decorative objects, and the like, by layer-by-layer application of metallic or ceramic material powder in accordance with the geometrical shape description of the corresponding molded body. In the manufacturing process, several successive powder layers are applied one above the other, and each powder layer is heated by a focused laser beam in a predetermined area corresponding to a selected cross-sectional area of ​​the molded body model before the application of the next powder layer. This causes the material powder to melt in the irradiated areas, forming a series of hardened sections.

[0004] Due to various external and internal influences exerted by the individual components on the controllable optical unit of the equipment for carrying out such a method, for example mechanical errors or misalignments between or within the components due to thermal expansion, positional deviations occur in the melting plane between the target position to be controlled by the mirror of the mirror assembly and the actual position that actually exists.

[0005] In conventional laser beam methods, to check and possibly correct this actual position, a measurement pattern is written on a medium, often called a scan field plate, based on calibration data. Then, using a measuring device provided for the measurement, the measurement pattern, which represents the actual coordinates on the scan field plate, is measured. Based on the measured values ​​thus determined, corrections are made to the calibration data for controlling the components of the controllable optical unit and appropriately stored in the device's control unit. By repeatedly performing this process, the actual coordinates can be iteratively brought closer to their target values, thereby achieving even small deviations between the actual and target coordinates after the final iteration, even when system disturbances affect the actual coordinates. However, in the case of dynamic disturbances, it must be assumed that, due to lack of convergence of the iteration sequence, more iterations must be performed or the process must be completely individualized and started anew.

[0006] In fact, it has been found that the calibration process described above has drawbacks in many different respects, and the object of the present invention is to advantageously improve the methods known from the prior art for calibrating such equipment.

[0007] In particular, it has been found that the main dynamic disturbance influence in the above-mentioned method is given by the relative position or positioning accuracy between the optical system and the mechanical system of the facility.For the calibration process, the scan field plate must be mechanically positioned in the facility so that it can be illuminated by the controllable optical unit.As a result, in addition to the degree of freedom of the controllable optical unit, such as the relative positioning of the individual components of the optical unit with each other, that is, in particular the relative positioning of the adjustably arranged multiple mirrors and the laser source, another degree of freedom is added for the positioning and locking of the scan field plate relative to this.These additional degrees of freedom cause the above-mentioned dynamic disturbance influence or at least cause additional errors in all spatial and rotational degrees of freedom.

[0008] To solve this problem, according to a first aspect of the present invention, a method according to the present invention includes the steps of placing a scan field plate on a build plate holder in a build chamber, creating a plurality of optical reference points at predefined positions on the scan field plate using a controllable optical unit, creating a measurement pattern on the scan field plate using the controllable optical unit by adjusting the mirrors of the mirror assembly accordingly based on a calibration data set, and determining the relative positioning between the optical reference points and the measurement pattern.

[0009] According to the present invention, since a mechanical reference, i.e., a geometrically absolute reference, for the measurement pattern is no longer formed on the scan field plate used, but rather optical reference points are set at predefined positions on the scan field plate, independent of the mechanical coupling of the scan field plate in the installation, the uncertainty due to mechanical degrees of freedom can be completely eliminated, thereby significantly improving the accuracy and convergence of the method according to the present invention compared to known methods based on the prior art. In particular, it should be noted that the optical reference points are generated independently of the calibration data used to generate the measurement pattern, and thus form a static reference independent of the actual calibration process.

[0010] The method according to the invention can further comprise a step of adapting the calibration data set based on the determination of the relative positioning, so that disturbance effects can be directly corrected in a subsequent manufacturing method for the object in order to be able to obtain an improved accuracy of the object. Naturally, however, the method according to the invention may also be used only to qualify such equipment by checking whether the calibration data set used allows a sufficient accuracy of the manufacturing process based on the determined relative positioning between the optical reference points and the measurement pattern.

[0011] In particular, when adapting the calibration data set based on the determination of the relative positioning, it is possible to carry out an iterative implementation of the method according to the invention, for example, until the determined relative positioning satisfies one or more predetermined conditions, which may be considered as the maximum deviation in one or more spatial dimensions and / or the maximum deviation with respect to the rotational degrees of freedom, or a more complex combination of parameters may be used, which may for example include the above-mentioned deviations with different weightings.

[0012] To be able to eliminate or reduce further uncertainties in the method according to the invention, at least one of the optical reference points can correspond to an extreme position or another characterized position of at least one of the mirrors of the mirror assembly and / or at least one of the reference points can correspond to a beam path of the laser beam that is perpendicularly incident on the scan field plate, thereby reducing or completely eliminating the above-mentioned mechanical uncertainties in the orientation of the mirror to create the reference points and / or optical imaging errors due to refraction of the laser beam at certain angles relative to optical components in the beam path.

[0013] The method according to the invention can theoretically already be carried out with one or two optical reference points, but preferably three or more optical reference points are provided, which are in particular not collinear, thereby eliminating all rotational degrees of freedom between the quantity of reference points and the measurement pattern.

[0014] While the measurement pattern can in principle take any form as long as it allows information to be derived about the relationship between the respective target positions and the actual positions, it has been found that the measurement pattern may comprise a plurality of crosses formed by intersecting line segments, the line segments preferably intersecting at right angles to one another. These intersections, on the one hand, provide geometric data points that can be measured with great precision, and, on the other hand, are relatively easy to detect and read by pattern recognition in an automated process.

[0015] In this connection, the method according to the invention may further be carried out in an automated manner, in which the determination of the relative positioning and optionally the fitting of the calibration data set is carried out using a reading device configured to determine the relative positioning with the aid of pattern recognition, thus enabling the method according to the invention to be carried out in an automated manner, which may further improve the efficiency and accuracy of the method according to the invention.

[0016] A further drawback of known methods for calibrating equipment for selective powder fusion arises from the need to uniquely identify the used scan field plate in order to be able to track the adjustments and individual iteration steps in the data set. In particular, information such as the equipment serial number, the current iteration number, the last used correction data, etc., must be reliably transferred together with the scan field plate from the equipment to the measuring device used, and vice versa. In previously known methods, this information transfer must be performed manually by the operator of the corresponding equipment and the equipment, i.e., the scan field plate is characterized by the affixing of a label or the like, which creates another source of error. Experience has shown that such manually performed activities can lead to confusion or confusion, which, in the worst case scenario, can lead to the waste of all the iterations previously performed.

[0017] In order to eliminate this problem, according to a second aspect of the present invention, which can be provided alternatively or additionally to the first aspect of the present invention in the method of the present invention, it is proposed that after placing the scan field plate on a build plate holder in the build chamber, the mirrors of the mirror assembly are correspondingly adjusted based on the calibration data set, and before, during or after creating a measurement pattern on the scan field plate using a controllable optical unit, a unique identification element is further created on the scan field plate, and optionally, according to the first aspect of the present invention, a plurality of optical reference points can also be created at predefined positions on the scan field plate using the controllable optical unit, and the relative positioning between the optical reference points and the measurement pattern can be determined.

[0018] By creating unique identification elements directly on the scan field plate during the implementation of the calibration method according to the first aspect of the invention, or in connection with known calibration methods in which the creation of optical reference points is omitted, for example due to known mechanical positioning data according to the prior art, the user of the equipment is relieved of the responsibility of uniquely identifying the scan field plate used by himself, thus reliably eliminating operator errors in this regard.

[0019] In particular, unique identification elements may include a QR code, a one-dimensional code, a barcode and / or an alphanumeric code encoding the equipment serial number, the instantaneous repeat number, the calibration data set used and / or a key value for database access. Of course, any other conceivable identification element may also be provided, for example metadata such as timestamps, the identification of the equipment operator during the calibration process and the like may also be encoded.

[0020] The method further comprises storing data relating to the method performed for the calibration and the identification element in a database, thereby reducing the information to be coded in the identification element itself, since only a unique identification of the corresponding calibration step needs to be coded, and all relevant data can then be stored in the database, with access to the corresponding data being possible via the unique identification as a key value.

[0021] According to another aspect, the present invention relates to an installation for producing an object from a material powder by selective powder fusion, comprising: a build chamber provided for accommodating the powder to be melted and the object to be produced; a build plate holder provided in the build chamber so as to be height adjustable, the build plate holder provided for supporting a build plate together with the object to be produced; a controllable optical unit comprising a laser source, a plurality of lenses, and a mirror assembly comprising a plurality of adjustably arranged mirrors, the controllable optical unit being configured to selectively direct a laser beam emitted from the laser source to a point in the build chamber where the material powder is to be melted; and a control unit configured to control the controllable optical unit to perform the method according to the first and / or second aspect of the present invention.

[0022] In this system according to the invention, the controllable optical unit comprises a hermetically closed housing in which at least some of the adjustably arranged mirrors and at least some of the lenses are arranged, and the housing may comprise a transparent disk that allows the laser beam to enter the build chamber from the housing. Such a closed housing is often referred to as an "optics box" and is provided as a single modular component for the system.

[0023] Furthermore, the present invention relates to a system formed from the above-mentioned arrangement and a reading device configured to determine the relative positioning between the optical reference points and the measurement pattern and / or to read the unique identification elements on the scan field plate, the optical reference points / measurement patterns / unique identification elements being provided on the scan field plate according to the first and / or second aspects of the invention.

[0024] In particular, the reading device may further be configured to automatically adapt the calibration data set based on the determination of the relative positioning and / or to store data relating to the unique identification element in a database and / or to read it from the database and / or to display it to the user. Any known display device may be provided to display this information, which may be integrated into the installation or which may obtain the data to be displayed via any data connection.

[0025] Further features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention, when viewed in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0026] [Figure 1] 1 shows a schematic diagram of an installation according to the invention; [Figure 2] 2 shows a schematic diagram of a scan field plate used in the installation shown in FIG. 1 in the method according to the invention;

[0027] FIG. 1 first shows, in purely schematic cross section, an installation for producing objects from material powders by selective powder fusion, which installation is designated by the reference numeral 10 .

[0028] The installation 10 comprises optical and mechanical components, which, according to the technical conventions, form an optical system and a mechanical system. The main optical components are housed in a so-called optics box 12, which houses, among other things, adjustably arranged mirrors 14 and a lens system 16. For clarity, only one mirror 14 is shown here, and the lens system 16 is also shown only diagrammatically. Overall, the mirrors 14, the lens system 16, and an externally arranged laser source 18, which directs a laser beam into the optics box 12, form a controllable optical unit 20. By appropriately controlling the components of the optical unit 20 by a control unit (not shown), the laser beam L can be directed from the optical box 12 through the transparent disk 12a at a predetermined angle into the build chamber 22 after passing through the lens system 16 and reflecting off the mirror 14, so that the laser beam L impinges on the target position S in the plane of incidence where the material powder is to be selectively melted during normal operation of the equipment 10.

[0029] However, for this calibration step, neither the build plate nor the material powder is placed on the build plate holder 24, which is height-adjustable in the build chamber 22, but instead a scan field plate 26 is placed on the build plate holder 24. This scan field plate 26 is made of a material on which a mark can be written by the incidence of the laser beam L. For this purpose, an anodized aluminum plate is used, for example, but other suitable materials that can be written by the laser beam typically used to melt the material powder in such equipment are also conceivable.

[0030] 1, however, the laser beam L does not strike the scan field plate 26 at the target position S, but at the actual position P due to various possible disturbances. The deviation between the target position S and the actual position P of the laser beam L incident on the scan field plate 26 can be reduced by appropriate calibration of the control of the controllable optical unit 20. First, disturbances in the coordinate system K1 of the controllable optical unit 20 can cause deviations between the target position S and the actual position P. Therefore, if, as is conventional in the prior art, the absolute position of the mark generated at the actual position P by the laser beam L incident on the scan field plate 26 is taken as a measure for the deviation between these two positions, disturbances in the coordinate system K2 of the mechanical system must also be taken into account. This is because the positional and rotational position of the scan field plate 26 relative to the build plate holder 24 and further degrees of freedom, such as the relative positioning of the optics box 12 with respect to the build chamber 22, constitute other sources of disturbances or errors. Because such mechanical disturbance sources may vary from measurement to measurement, they are imperfections in the dynamic system that cause the identified iterative method to not converge or not converge significantly quickly.

[0031] In contrast to this method known from the prior art, according to the present invention, the illumination of the scan field plate 26 is carried out in such a way that the pattern shown in Fig. 2 is generated on the scan field plate 26. First, an optical coordinate system consisting of three optical reference points O1 to O3 is generated on the scan field plate 26, and these three reference points O1 to O3 are always generated at precisely defined points that are not subject to calibration, preferably when at least one of the mirrors 14 of the optical unit 20 is in an end position or another characterized position, and / or when the beam path of the laser beam L passing through the disk 12a and thus the irradiation of the scan field plate 26 is vertical, thereby eliminating imaging errors.

[0032] Relative to an optical coordinate system formed from the reference points O1 to O3, a plurality of cross marks M1 to M4 are written by the laser beam L on the scan field plate 26 by means of a calibration data set. By using the calibration data set, which should also be used during normal operation of the installation 10, by the control unit of the installation 10 to create the marks M1 to M4 forming the measurement pattern M, the deviation between the expected target positions and the actual actual positions of the marks M1 to M4 can be calculated in a subsequent step of determining their relative positioning, independent of the mechanical system.

[0033] Based on this calculation, a corrected calibration data set can then be created, whereby the iterative approximation of the actual position to the target position can be achieved in multiple steps. The reading of the marks M1-M4 on the scan field plate 26 and the subsequent creation of a new calibration data set can be performed in a dedicated external reading device.

[0034] Furthermore, just to be clear, an identification element ID is further written on the scan field plate 26 using a laser beam L, and in the embodiment shown in Figure 2, a barcode, a QR code and an alphanumeric code are shown as examples, but in practice, usually only one of these codes is used.

[0035] This identification element can encode, for example, the instantaneous repeat, the serial number of the equipment 10 and other relevant data, which can then be read in an automated manner as well, eliminating operator errors when marking and handling the scan field plate 26 with successive repeats or different equipment.

Claims

1. 1. A method for calibrating an installation (10) for manufacturing objects from material powders by selective powder fusion, comprising: The equipment (10) a building chamber (22) provided to accommodate the powder to be melted and the object to be produced; a build plate holder (24) provided in the build chamber (22) in a height-adjustable manner, the build plate holder (24) being provided to support a build plate together with the object to be manufactured; a controllable optical unit (20) including a laser source (18), a plurality of lenses (16), and a mirror assembly including a plurality of adjustably arranged mirrors (14), the controllable optical unit (20) being configured to selectively direct a laser beam (L) emitted from the laser source (18) to a point (S) within the building chamber where the material powder is to be melted; Equipped with The method comprises: placing a scan field plate (26) on the build plate holder (24) in the build chamber (22); creating a plurality of optical reference points (O1-O3) at predefined positions on the scan field plate (26) using the controllable optical unit (20); generating a measurement pattern (M) on the scan field plate (26) using the controllable optical unit (20) by correspondingly adjusting the mirrors (14) of the mirror assembly based on a calibration data set; determining the relative positioning between the optical reference points (O1-O3) and the measurement pattern (M); Including, A method in which three or more optical reference points (O1 to O3) that are not located on a straight line are provided, and at least three of the reference points (O1 to O3) correspond to beam paths of the laser beam (L) that are perpendicularly incident on the scan field plate (26).

2. The method of claim 1 , further comprising adapting the calibration data set based on the determination of the relative positioning.

3. The method of claim 2 , wherein the method is performed iteratively until the determined relative positioning satisfies one or more predetermined conditions.

4. 4. The method according to claim 1, wherein at least one of the optical reference points (O1-O3) corresponds to an extreme position or another characterized position of at least one of the mirrors (14) of the mirror assembly.

5. 5. The method according to claim 1, wherein the measurement pattern (M) comprises a plurality of crosses (M1-M4) formed by intersecting line segments, the line segments intersecting each other at right angles.

6. 6. The method according to claim 1, wherein the determination of the relative positioning and optionally the adaptation of the calibration data set is performed in an automated manner using a reading device configured to determine the relative positioning using pattern recognition.

7. 1. A method for calibrating an installation (10) for manufacturing objects from material powders by selective powder fusion, comprising: The equipment (10) a building chamber (22) provided to accommodate the powder to be melted and the object to be produced; a build plate holder (24) provided in the build chamber (22) in a height-adjustable manner, the build plate holder (24) being provided to support a build plate together with the object to be manufactured; a controllable optical unit (20) including a laser source (18), a plurality of lenses (16), and a mirror assembly including a plurality of adjustably arranged mirrors (14), the controllable optical unit (20) being configured to selectively direct a laser beam (L) emitted from the laser source (18) to a point (S) in the building chamber (22) where the material powder is to be melted; Equipped with The method comprises: placing a scan field plate (26) on the build plate holder (24) in the build chamber (22); generating a measurement pattern (M) on the scan field plate (26) using the controllable optical unit (20) by correspondingly adjusting the mirrors (14) of the mirror assembly based on a calibration data set; creating a unique identification element (ID) on the scan field plate (26); Optionally, the method further includes the step of creating a plurality of optical reference points (O1 to O3) at predefined positions on the scan field plate (26) using the controllable optical unit (20), and determining relative positioning between the optical reference points (O1 to O3) and the measurement pattern (M). Including, The method, wherein three or more of the optical reference points (O1 to O3) are provided.

8. 8. The method according to claim 7, wherein the unique identification element (ID) comprises a QR code, a one-dimensional code, a bar code and / or an alphanumeric code encoding the serial number of the equipment (10), an instantaneous repeat number, the calibration data set used and / or a key value for database access.

9. 9. The method of claim 7 or 8, further comprising the step of storing data relating to the method and the identification element performed for the calibration in a database.

10. An installation (10) for producing an object from a material powder by selective powder fusion, comprising: a building chamber (22) provided to accommodate the powder to be melted and the object to be produced; a build plate holder (24) provided in the build chamber (22) in a height-adjustable manner, the build plate holder (24) being provided to support a build plate together with the object to be manufactured; a controllable optical unit (20) including a laser source (18), a plurality of lenses (16), and a mirror assembly including a plurality of adjustably arranged mirrors (14), the controllable optical unit (20) being configured to selectively direct a laser beam (L) emitted from the laser source (18) to a point (S) in the building chamber (22) where the material powder is to be melted; a control unit configured to control the controllable optical unit (20) to perform the method according to any one of claims 1 to 9; The facility (10) comprises:

11. 11. The equipment (10) of claim 10, wherein the controllable optical unit (20) comprises a hermetically closed housing (12) in which at least some of the adjustably arranged mirrors (14) and at least some of the lenses (16) are arranged, and the housing (12) comprises a transparent disk (12a) that allows the laser beam (L) to enter the building chamber (22) from the housing (12).

12. An installation (10) according to claim 10 or 11, a reading device configured to determine the relative positioning between the optical reference points (O1-O3) and the measurement pattern (M) and / or to read a unique identification element (ID) on the scan field plate (26); A system formed from

13. The system of claim 12 , wherein the reader is further configured to automatically adapt a calibration data set based on the determination of the relative positioning.

14. 14. The system according to claim 12 or 13, wherein the reader is further configured to store data relating to the unique identification element (ID) in a database and / or read it from the database and / or display it to a user.

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