MEASURING SYSTEM FOR A DEVICE FOR THE GENERATIVE MANUFACTURING OF A THREE-DIMENSIONAL OBJECT

Abstract

A measuring system (40) serves for equipping or retrofitting a device (1) for manufacturing a three-dimensional object (2) by selective layerwise solidification of a building material (15). The device (1) includes an irradiator (18) for selectively irradiating a layer of the building material (15) applied in a working plane (7) of the device (1) at locations corresponding to a cross-section of the object (2) to be manufactured for solidifying the irradiated locations. The irradiator (18) comprises at least two irradiation units (31), preferably laser arrays, and each irradiation unit (31) can be projected onto a pixel in the working plane (7) and can be at least switched on and off. The measuring system (40) includes at least one camera (41) for determining and evaluating the radiation (19) emitted by the irradiator (18) and/or the position and/or orientation of the irradiation unit(s) (31) in absolute and/or relative to one another, and at least one distance sensor (42) for detecting an extension in a direction (z) perpendicular to the working plane (7).

Claims

1. Measuring system for equipping or retrofitting a device for manufacturing a three-dimensional object by selective layerwise solidification of a building material, wherein the device includes an irradiator for selectively irradiating a layer of the building material applied in a working plane of the device at locations corresponding to a cross-section of the object to be manufactured, for solidifying the irradiated locations, the irradiator comprises at least two irradiation units, and each irradiation unit can be projected onto a pixel in the working plane and is at least switchable on and off, and said measuring system includes: at least one camera for determining and evaluating the radiation emitted by the irradiator and/or the position and/or orientation of the irradiation unit(s) in absolute and/or relative to one another, and at least one distance sensor for detecting an extension in a direction perpendicular to the working plane.

2. Measuring system according to claim 1, further comprising at least one power measuring device for determining a radiation power of the irradiator and/or of at least one irradiation unit.

3. Measuring system according to claim 1, comprising at least one switch which is designed to avoid a collision of the irradiator and/or a recoater, further included in the device with the measuring system.

4. Measuring system according to claim 1, wherein the camera comprises a CMOS sensor and/or a CCD sensor, and/or the power measuring device comprises a photodiode and/or a photo resistor.

5. Device for manufacturing a three-dimensional object by selective layerwise solidification of a building material, wherein the device comprises: an irradiator for selectively solidifying a layer of the building material applied in a working plane of the device at locations corresponding to a cross-section of the object to be manufactured, the irradiator comprising at least two irradiation units, each irradiation unit being projectable onto a pixel in the working plane and being at least switchable on and off, the device being adapted and/or controlled to repeat the steps of applying and selectively solidifying until the object is completed, and wherein the device further comprises a measuring system according to claim 1.

6. Device according to claim 5, wherein the irradiation units are arranged in modules, and/or the modules are arranged in cascades and/or the irradiation units are formed as laser arrays.

7. Device according to claim 5, wherein a holding device is arranged in the device such that it can be moved in the moving direction of the irradiator and in a direction perpendicular to the working plane, and wherein the measuring system is arranged on the holding device so as to be movable in a direction perpendicular to these two directions.

8. Device according to claim 5, wherein the measuring system and/or the holding device is removable from the device.

9. Method for using a measuring system according to claim 1, wherein a recoater of the device and/or the irradiator and/or the measuring system are aligned with each other and/or with respect to a reference plane of the device.

10. Method according to claim 9, wherein at least one reference plane of the recoater and/or of the irradiator and/or of the measuring system and/or of the device is determined.

11. Method according to claim 9, wherein an alignment of the irradiator and/or a determination of the mean focal plane of the irradiator is carried out on the basis of determined sharpness values of the projection of individual irradiation units in different image planes lying perpendicular to the vertical z-axis and of their position in an x/y plane.

12. Method according to claim 9, wherein the recoater and/or the irradiator is aligned on the basis of absolute z positions and/or angular positions about an x and/or y direction of the associated reference plane(s).

13. Method according to claim 9, wherein first a coarse alignment and then a fine alignment of the recoater and/or of the irradiator and/or of the measuring system is carried out.

14. Method for using a measuring system according to claim 1, wherein, by means of the power measuring device, failed lasers or irradiation units are detected and/or power levels of individual irradiation units are detected.

15. Method according to claim 9, wherein a intended operating state of the device is established before the use of the measuring system.

16. Measuring system according to claim 1, wherein the at least two irradiation units are laser arrays.

17. Measuring system according to claim 1, wherein the at least one camera and the at least one distance sensor are integrated in a single measuring device.

18. Measuring system according to claim 4, wherein the photodiode and/or the photo resistor of the power measuring device are integrated in an Ulbricht sphere.

19. Device according to claim 5, wherein the at least two irradiation units are laser arrays.

20. Device according to claim 6, wherein the lasers of the laser array are VCSELs or VECSELs.

21. Method according to claim 10, wherein a reference plane of the recoater is a recoating plane and/or a reference plane of the irradiator is a mean focal plane of the irradiation units.

Description

[0024] Further features and functionalities of the invention can be derived from the description of implementation examples on the basis of the attached drawings.

[0025] FIG. 1 is a schematic view shown partially in section of an embodiment of a device for the layerwise manufacturing of a three-dimensional object to which the present invention is applicable.

[0026] FIG. 2a is a schematic view of an irradiator included in the device shown in FIG. 1 from below.

[0027] FIG. 2b is a schematic view of a laser module included in the irradiator shown in FIG. 2a.

[0028] FIG. 2c is a schematic view of a laser array included in the laser module shown in FIG. 2b.

[0029] FIG. 3 is a schematic perspective view of a portion of the device shown in FIG. 1 with a measuring system according to an embodiment of the present invention.

[0030] In the following, an embodiment of a device which is suitable for carrying out the present invention will be described with reference to FIG. 1. The device illustrated in FIG. 1 is a laser sintering or laser melting device 1. For building the object 2, it includes a processing chamber 3 having a chamber wall 4.

[0031] A container 5, which is open at the top and which has a container wall 6, is arranged in the processing chamber 3. By the upper opening of the container 5, a working plane 7 is defined, wherein the portion of the working plane 7 lying within the opening that can be used for building the object 2 is referred to as a build area 8.

[0032] In the container 5, a support 10 is disposed which is movable in a vertical direction V and onto which a base plate 11 is attached which closes the container 5 towards the bottom and thus forms the base of the latter. The base plate 11 may be a plate which is formed separately from the support 10 and which is attached to the support 10, or it may be formed so as to be integral with the support 10. Depending on the powder and process used, a building platform 12 may also be attached to the base plate 11 as a building base on which the object 2 is build. However, the object 2 may also be built on the base plate 11 which then itself serves as the building base.

[0033] In FIG. 1 the object 2 which is to be formed in the container 5 on the building platform 12 is illustrated below the working plane 7 in an intermediate state, having a plurality of solidified layers and being surrounded by remaining non-solidified building material 13.

[0034] The laser sintering device 1 further comprises a storage container 14 for a pulverulent building material 15 which can be solidified by electromagnetic radiation, and a recoater 16 which is movable in a horizontal direction H for applying the building material 15 within the build area 8. Preferably, the recoater 16 extends across the entire area to be applied in a direction traverse to its moving direction.

[0035] Optionally, a radiation heater 17 for heating the applied building material 15 is arranged in the processing chamber 3. An infrared lamp may for example be provided as a radiation heater.

[0036] The laser sintering device 1 further comprises an irradiator 18 which is also movable in a horizontal direction H and generates a laser beam 19 which is focused onto the working plane 7. The irradiator 15 is preferably designed as a line irradiator which is capable of irradiating a line which extends transversely to its moving direction and which extends over the entire area to be irradiated.

[0037] The laser sintering device 1 further comprises a control unit 20 by way of which the individual component parts of the device are controlled in a coordinated manner for carrying out the building process. As an alternative, the control unit may partially or entirely be arranged outside of the device. The control unit may include a CPU, the operation of which is controlled by a computer program (software). The computer program may be stored on a storage medium separate from the device, from where it may be loaded into the device, especially into the control unit.

[0038] For applying a powder layer during the operation, the support 10 first is lowered by a height corresponding to the desired layer thickness. The recoater 16 is first moved to the storage container 14 and receives from it an amount of building material 15 which is sufficient for applying a layer. Then, it moves across the build area 8 where it applies a thin layer of the pulverulent building material 15 onto the building base or a previously applied powder layer. The application is carried out at least across the entire cross-section of the object 2 to be produced, preferably across the entire build area 8, i.e. the area delimited by the container wall 6. Optionally, the pulverulent building material 15 is heated by means of the radiation heater 17 to a working temperature.

[0039] The irradiator 18 then moves across the applied and preheated powder layer and solidifies the powdery building material 15 at the locations corresponding to the cross-section of the object 2 to be produced by selectively irradiating these locations with the laser beam 19. The powder grains at these locations are partially or completely melted by the energy introduced by the radiation so that after cooling, they are agglutinated to each other to form a solid body. These steps are repeated until the object 2 is completed and can be removed from the process chamber 3.

[0040] The irradiation of the locations to be solidified is preferably carried out in such a way that the irradiator travels in one direction across the build area and irradiates all the locations of the powder layer to be solidified that lie below the current position of the irradiator simultaneously. For this purpose, the irradiator has to be equipped to generate different irradiation profiles in the direction transverse to the irradiation direction. In the present embodiment, this is achieved by a number of independently controllable irradiation units.

[0041] FIG. 2 schematically shows a view of the irradiator 18 from below. The moving direction of the irradiator across the build area here is indicated by an arrow B. FIG. 2a shows how a number of laser modules 30 are arranged in rows offset from each other on the underside of the irradiator 18. FIG. 2b shows how each laser module 30 is formed from a plurality of laser arrays 31. FIG. 2c shows how each laser array 31 is formed from a plurality of individual lasers 32.

[0042] The individual lasers 32 are configured as semiconductor diode lasers of the type VCSEL (vertical cavity surface-emitting laser) or VECSEL (Vertical External Cavity Surface Emitting Laser). These laser sources have a beam direction perpendicular to the main extension (wafer plane) and a circular symmetric beam divergence and they are particularly suitable for the arrangement in two-dimensional arrays. In the laser array 31 shown in FIG. 2c, the individual lasers 32 are arranged in a hexagonal manner, but any other arrangement is possible. All the lasers 32 of a laser array 31 are preferably controlled simultaneously. The smallest individually controllable irradiation unit of the irradiator 18 is the laser array 31. This has the advantage that in the case of a failure of a single laser, it is not one complete irradiation unit that immediately fails, but the power drop can be compensated by the other lasers of the laser array.

[0043] Multiple laser arrays 31 are combined to a laser module 30. For each laser module 30, an optical element (not shown in the figure) is also provided for projecting the laser arrays 31 onto the working plane 7. Each laser array 31 is mapped onto a pixel in the working plane 7. Each laser module 30 is directed to a specific area in working plane 7. If the irradiator is moved in its moving direction B, the pixels of the switched-on laser arrays 31 form a track.

[0044] In the laser module 30 shown in FIG. 2b, the individual laser arrays 31 are arranged in two staggered rows in such a way that the tracks of their pixels in the working plane are adjacent to each other when the laser module 30 is moved in the moving direction B. If, for example, the laser arrays 31 have a width of 0.1 mm transverse to the direction of movement and the optical component has a reducing scale of 1:5, the adjoining tracks of the laser arrays 31 have a width of 0.02 mm. In other words, the irradiator 18 has a resolution of 0.02 mm in a direction transversal to its moving direction B.

[0045] To utilize the entire width of the irradiator 18, multiple laser modules 30 are arranged in a row in the direction transversal to the moving direction B. Due to the optical reduction of the laser modules 30 by the optical element, the sum of the widths of a track formed from the pixels of all laser arrays 31 of the laser module 30 during a movement of a laser module 30 in the moving direction B is narrower by the reduction scale than the laser module 30 itself. However, the pitch of the tracks of all laser modules in a row, i.e. the center distance of the tracks to each other, corresponds to the (undiminished) pitch of the laser modules 30. Thus a non-irradiable area remains between the tracks which can be irradiated by a single row of laser modules 30.

[0046] In order to enable a continuous irradiation of the working plane in the direction transverse to the direction of movement B, several rows of laser modules 30 are arranged offset to each other. In other words, individual cascades of laser modules 30 are formed which lie behind each other in the moving direction F, but are offset from each other in the direction transverse to the moving direction. In FIG. 2a, for example, the laser modules 30 of the five rows located furthest to the left form a cascade. Several such cascades are then arranged next to each other in the direction transverse to the moving direction. Within each cascade, the laser modules 30 are arranged offset to each other to such an extent that the tracks of the pixels of their laser arrays 31 are adjacent to each other.

[0047] In an exemplary implementation form the irradiator contains 108 laser modules, each laser module contains 32 laser arrays, and each laser array contains 282 VCSELs. This results in 3456 individually controllable irradiation units (laser arrays). If, for example, these are to be controllable in 61 power levels (from 0=off to 60=maximum power), over 200,000 measurements are required for a complete calibration or adjustment.

[0048] Such measurements may be necessary, for example, in the context of production-accompanying calibration/adjustment, production-accompanying quality assurance or periodic quality assurance by customers or service personnel. The measurements have to be carried out automatically, accurately and quickly, so that a measurement of an irradiator can be carried out with acceptable processing times and acceptable effort.

[0049] FIG. 3 shows a simplified perspectival view of a measuring device 40 which is suitable for equipping or retrofitting the laser sintering device 1. Parts of the laser sintering device 1 which are not necessary for describing the measuring device 40 and its use are omitted for the sake of clarity.

[0050] As shown in FIG. 3, a three-dimensional coordinate system of the device is defined as follows: [0051] The x-direction is the direction in the working plane in which the recoater 16 and the irradiator 18 move across the working plane 7 of the device 1. [0052] The y-direction is the direction in the working plane 7 which is perpendicular to the x-direction. In this direction, the longitudinal directions of recoater 16 and irradiator 18 extend. [0053] The z-direction is the height direction in which the carrier 10 is moved. A movement in this direction changes the vertical distance to the recoater or irradiator.

[0054] The measuring device 40 comprises a camera 41, a distance sensor 42 and a power measuring device 43. These three components of the measuring device 40 are mounted in a fixed position relative to each other on a measuring head holder 44.

[0055] Preferably the three components are arranged side by side in the x-direction with a minimum expansion in the y-direction.

[0056] The measuring head holder 44 is mounted movable in the y-direction on a y-positioning unit 45 which is attached to a (not shown) holding device arranged in the device 1 so that it can move in the x-direction and in the z-direction. Since the device 1 already contains drives for the movement of the recoater 16 and the irradiator 18 in the x-direction and for the movement of the carrier 10 in the z-direction, no separate drives are required for that purpose.

[0057] The holding device is arranged in the device 1 so that it can be removed from the device 1. Preferably, the measuring head holder 44 is also attached to the y-positioning unit 45 so that it can be removed from device 1. The holding device may for example be attached to the carrier 10 with magnets.

[0058] The measuring device 40 is aligned with the coordinate system of the machine by means of elements and methods known per se, such as levelling with respect to the working plane by means of three adjusting screws. A displacement measuring system is provided for all three directions so that the position of the measuring device can be determined and reproducibly adjusted.

[0059] The camera 41 serves for the acquisition of an optical image of the irradiator 18 from below, in particular of the laser arrays 31 and laser modules 30 in the light-emitting state. For this purpose, a camera lens 41 can be set in such a way that, for example, the laser array 31 to be observed is projected directly onto the image acquisition chip of the camera. However, a frosted glass pane can also be inserted in the plane in which the optical element of a laser module 30 images the laser array 31, and the resulting image can be imaged by the camera lens onto the image acquisition chip, or this real image can be mapped onto the image acquisition chip without the interposition of a frosted glass pane.

[0060] A CCD sensor or a CMOS sensor, for example, is used as an image acquisition chip. The sensor converts the received image into electrical signals, which can then be digitized, stored and processed.

[0061] The camera may also include holders for filters, for example for attenuating the laser power to a value suitable for the image acquisition chip.

[0062] The distance sensor 42 serves for determining the vertical distance (in the z-direction, i.e. perpendicular to the working plane) to an element located above the sensor. The measuring principle of the distance sensor may be formed mechanically by means of a button or contactless, for example inductive, capacitive or optical.

[0063] Typically, the distance sensor has a measuring range of a few mm. The resolution is preferably in the μm range, ideally 1 μm or better.

[0064] The power measuring device 43 is used to determine the radiation power emitted by one or more laser arrays 31. For this purpose, it contains a sensor that is capable of converting an optical power into an electrical signal that can then be digitized, stored and processed. For this purpose, the power measuring device 43 contains a photoelectric sensor, for example a photo resistor, a photodiode, or an OLPC sensor (Online Laser Power Control). This sensor is preferably integrated into an Ulbricht sphere which serves to collect the radiation emitted by the laser array.

[0065] Optionally, further elements are provided, such as limit switches, which preferably operate without contact and avoid a collision of the measuring device 40 with the recoater 16, the irradiator 18 or other components of device 1.

[0066] In the following, methods for the measurement, calibration and adjustment of the device 1 are described, in which the measuring device 40 is used.

[0067] After the installation of device 1, the relative position of the recoater 16 and the irradiator 18 is only insufficiently determined and known due to long mechanical tolerance chains. Therefore, it is necessary to align them relative to each other and to the device 1 before starting-up.

[0068] For this purpose, reference planes of the device 1, the recoater 16 and/or the irradiator 18 are preferably determined and brought into coincidence with each other or are at least aligned parallel to each other. As a reference plane of the device 1 the x/y plane at a constant z-position or the upper edge of the container 5 is used, for example. As a reference plane of the recoater 16, for example, a recoating plane is used which is determined by the extension of a lower edge of a recoating element of the recoater 16, e.g. a blade or a roller, in the y-direction and its displacement in the x-direction. As a reference plane of the irradiator 18, for example, a lower surface of an irradiation window terminating the irradiator downwards or a mean focal plane of the individual laser arrays 31 is used. The mean focal plane is taken into account because the focal planes of the individual laser arrays 31 may deviate slightly from each other due to tolerances.

[0069] Since the measuring device 40 in each case can only determine positions of the reference planes relative to each other, one plane has to be mechanically adjusted in advance. This may, for example, be the moving plane of the measuring device 40 itself or the reference plane of the recoater 16. This is done, for example, by aligning the recoater using feeler gauges parallel to the upper edge of the container 5.

[0070] The alignment of the reference planes to each other is carried out using absolute z positions and/or angular positions around an x and/or y direction of the individual reference planes.

[0071] The relative orientation between the reference planes of the measuring device 40 and the recoater 16 is determined by measuring the lower edge of the recoating element (or of the recoating elements, shown in FIG. 3 are two recoating rollers) at two positions as far apart as possible in the y-direction by means of the distance sensor 42. From these measured values a tilting of the two planes relative to each other about the x-axis can be determined and corrected if necessary. Tilting about the y-axis can be determined and corrected if the recoater 16 and the measuring device 40 are sufficiently moved in the x-direction and the measurement is repeated. If, however, the recoater 16 and the measuring device 40 are moved in the x-direction by the same drive, they automatically run in parallel and such a measurement is not required.

[0072] The adjustment of the irradiator 18 is preferably done in two steps. For a coarse alignment, at least three positions of the irradiation window that are as far apart as possible are measured by means of the distance sensor 42. From these measured values a tilting of the plane of the irradiation window can be determined and corrected if necessary.

[0073] For a fine adjustment, the mean focal plane of the irradiator 18 is used as a reference plane. This mean focal plane is determined on the basis of determined sharpness values of the imaging of individual irradiation units in different image planes perpendicular to the vertical z-axis and their position in an x/y plane. The measuring device 40 moves in the x and y direction to different positions below the irradiator 18. One (or more) laser arrays 31 are switched on, their imaging is evaluated with the camera 41 and the position of maximum sharpness is determined by moving the measuring device 40 in the z direction via the path measuring system of the z axis. From the differences of the z-positions a tilting of the mean focal plane can be determined and corrected if necessary. The same can be done for different positions of the irradiator 18 in the y-direction.

[0074] By moving the measuring device 40 in the x and y direction below the laser arrays 31 to be measured and determining the position of the image of the laser array 31 on the image acquisition sensor of the camera, deviations in the position of the laser arrays 31 can also be detected and corrected. Such deviations occur, for example, when the irradiator 18 is rotated around the z-axis.

[0075] In addition to the position and focal plane of each laser array 31, the failure of individual lasers 32 can also be determined from the image of the laser array 31.

[0076] Furthermore, the measuring device 40 can also determine the power output of the individual laser arrays 31. For this purpose, the power measuring device is placed below the laser array 31 to be measured and the laser array 31 is controlled by means of a pulse-width-modulated signal (PWM signal) in different power levels from off-state (PWM signal continuously off) to continuous operation (PWM signal continuously on). The dependency of the emitted light intensity on the PWM control can be recognized from the measurement results and corrected if necessary. Deviations result, for example, from a different efficiency of individual laser arrays, from non-linearities or from the failure of individual lasers of a module. In extreme cases, a laser array may have failed completely, which is then detected by the measuring device.

[0077] Such a measurement of the individual laser arrays 31 is not only useful during the start-up, but may also be carried out repeatedly during the operating time of device 1, preferably at predetermined time intervals or depending on the use of the device.

[0078] Before the measuring device 40 is used, an intended operating state of the device can be established, which corresponds, for example, to the irradiation case during the manufacturing of a three-dimensional object.

[0079] Instead of a movement of the irradiator in one moving direction and an extension of the irradiator in the transverse direction to the moving direction across the entire width of the build area to be irradiated, an irradiator with smaller dimensions may also be used, which is led across the build area in two dimensions. With the described measuring device a positioning accuracy of the irradiator in y-direction can then be determined and corrected if necessary.

[0080] Since the camera 41, the distance sensor 42 and the power measuring device 43 are mounted in a fixed positional relation to each other in the device, it is possible to carry out combined measurements of two of these measuring devices or of all the three measuring devices. Complex alignments of the measuring devices during the measuring process are no longer required, and the measuring results of the three measuring devices can be set in relation to each other accurately and reproducibly. This allows a fast, highly automated and customer-friendly measurement of all relevant performance data of the irradiator in a simple way and can be used for calibration, adjustment, documentation and maintenance purposes.

[0081] The measuring device 40 may be implemented as a measuring system with components provided separately from each other, but the components may also be integrated in a single measuring device.

[0082] Even if the present invention has been described using a laser sintering or laser melting device, it is not limited to laser sintering or laser melting. It can be applied to any method for the generative manufacturing of a three-dimensional object by layerwise application and selective solidification of a building material, in which the energy required for the solidification of the building material is introduced into the building material in the form of radiation. In general, any device can be used as an irradiator by which energy in the form of wave or particle radiation can be selectively applied to a layer of the building material.

[0083] Various materials can be used as building materials, preferably powders, in particular metal powders, plastic powders, ceramic powders, sand, filled or mixed powders.