Calibration device and calibration procedure for a device for the layer-by-layer production of an object

Abstract

Calibration device (30; 40) for a device (1) for the layer-by-layer production of a three-dimensional object (2) by layer-by-layer solidification of build-up material (10) at the locations corresponding to the cross-section of the object to be produced in the respective layer by at least two energy beams (14a, 14b), wherein the calibration device comprises: a housing (31; 41) and a sensor (32; 42) arranged in the housing for receiving the at least two energy beams and outputting a signal depending on the intensity of the energy beams, wherein the housing has at least two openings (34a, 34b; 44a, 44b) for allowing the passage of at least two energy beams which are arranged such that their central axes intersect on a surface of the sensor.

Description

[0001] The present invention relates to a calibration device and to a calibration method for a device for layer-by-layer production of a three-dimensional object by layer-by-layer solidification of building material at the locations corresponding to the cross-section of the object to be produced in the respective layer by energy input.

[0002] A device for producing a three-dimensional object by means of a process known as “selective laser sintering” is described in DE 10 2005 024 790 A1.

[0003] DE 198 18 469 A1 discloses a device that contains two separate laser sources and emission devices for solidifying the build-up material. Furthermore, the applicant itself has been marketing laser sintering devices equipped with a dual-head system for years.

[0004] JP 2009 - 006 509 A also describes a method and an apparatus for producing a three-dimensional object in which a metal powder is melted by two or more light beams.

[0005] A method for calibrating a device for producing a three-dimensional object using a calibration plate containing a light-sensitive film is described in DE 199 18 613 A1. The laser exposes alignment crosses onto the light-sensitive film, which are then compared with reference crosses applied to the calibration plate.

[0006] DE 10 2009 016 585 A1 also describes a method and a device for calibrating an irradiation device of a system for the additive manufacturing of a three-dimensional object. Calibration includes the following steps: arranging an image converter plate in or parallel to the working plane of the system, wherein the image converter plate emits detectable light when the irradiation device irradiates predetermined positions of the image converter plate with energy-containing radiation; scanning the image converter plate by the irradiation device; detecting the detectable light by a light detector; determining coordinates of the irradiation device when the detectable light is detected; comparing the determined coordinates with predetermined reference coordinates; and calibrating the irradiation device based on a deviation between the determined coordinates and the reference coordinates.

[0007] Both methods are complex and designed for only one scanner. Furthermore, calibration must be performed before the actual construction process.

[0008] DE 694 11 280 T2 describes a device for laser sintering, comprising a laser device for generating a sintering laser beam and a warming laser beam, wherein the warming laser beam is directed onto a warming zone on the surface of the powder, which is located in the vicinity of the sintering point.

[0009] The subsequently published document DE 10 2013 208 651 A1 describes a method for automatically calibrating a device for the generative production of a three-dimensional object with at least two scanners for irradiating at least two scanning fields in the construction field of the production device.

[0010] The subsequently published document DE 10 2013 103 006 A1 describes a device for the layer-by-layer additive manufacturing of an object from a material with at least two laser beams and respective scanners for each laser beam for scanning the respective laser beam over a planar field, wherein the entire planar field is common to each scanner and at least one scanner is inclined with respect to the planar field and the at least one scanner is provided with a lens arranged to produce a focal plane that is inclined with respect to this scanner.

[0011] The object of the present invention is to provide a calibration device and a calibration method with which an apparatus for producing a three-dimensional object which uses more than one radiation source can be calibrated and thus the manufacturing accuracy of the objects can be improved.

[0012] The object is achieved by a calibration device according to claim 1, a calibration method according to claim 6, a method for producing a three-dimensional object according to claim 8 and a device for producing a three-dimensional object according to claim 10. Further developments of the invention are specified in the respective subclaims.

[0013] The calibration device enables a calibration process in which the positions of the individual laser beams at which the calibration device's sensor delivers the maximum output signal are iteratively determined. By comparing these positions with each other and / or with the corresponding target positions, deviations can be detected and corrected. This calibrates the device and thus improves the manufacturing accuracy of the objects.

[0014] Further features and advantages of the invention will become apparent from the description of embodiments with reference to the accompanying drawings. Fig. 1 is a schematic, partially sectioned view of an embodiment of an apparatus for layer-by-layer manufacturing of a three-dimensional object suitable for carrying out the present invention. Fig. 2 is an enlarged partial sectional view of a Fig. 1, on which a calibration device according to a first embodiment of the present invention is arranged. Fig. 3 is an enlarged partial sectional view of a Fig. 1, on which a calibration device according to a second embodiment of the present invention is arranged.

[0015] In the following, with reference to Fig. 1 describes an embodiment of a device suitable for carrying out the method according to the invention. Fig. The device shown in Figure 1 is a laser sintering or laser melting device 1. For building the object 2, it contains a process chamber 3 with a chamber wall 4.

[0016] In the process chamber 3, an upwardly open container 5 with a vertically (V) movable carrier 6 is arranged, on which the object 2 is built. In Fig. 1, the object 2 to be formed is shown below a working plane 7 in an intermediate state with several solidified layers, surrounded by unsolidified building material 8. Furthermore, a storage container 9 for a powdered building material 10 that can be solidified by electromagnetic radiation and a horizontally (H) movable coater 11 for applying the building material 10 to the working plane 7 are arranged in the process chamber 3.

[0017] The laser sintering device 1 further includes an irradiation device 12 for solidifying the applied powder layer. The irradiation device contains two lasers 13a, 13b, each of which generates a laser beam 14a, 14b, which is deflected by a deflection device 15a, 15b and focused by a focusing device 16a, 16b via a coupling window 17 in the wall of the process chamber 3 onto a predetermined point on the working plane 7.

[0018] Finally, the laser sintering device 1 includes a control unit 18, via which the individual components of the device are controlled in a coordinated manner to carry out the construction process. The control unit may include a CPU whose operation is controlled by a computer program.

[0019] During operation, the carrier 6 is first lowered by the desired layer thickness, then a layer of the powdered build material 10 is applied using the coater 11. Subsequently, the cross-section of the object to be produced is scanned by the two laser beams 14a, 14b, so that the powdered build material 10 is solidified at these points. These steps are repeated until the object 2 is completed and can be removed from the build space. Instead of one object, several objects can also be produced simultaneously. For example, one laser beam can solidify part of the objects and the other laser beam the other part.

[0020] By using two separate laser beams 14a, 14b and deflection devices 15a, 15b, a larger area of ​​the working plane 7 can be irradiated than with a single radiation source. While maintaining the same working area, irradiating two different areas simultaneously can reduce the production time of the object(s) 2.

[0021] The irradiation device 12 can be constructed so that both laser beams 14a, 14b can scan the same area of ​​the working plane 7. Preferably, however, the two laser beams 14a, 14b have different working areas (in Fig. 1 separated from each other by the central plane 19). Preferably, the working areas of the two laser beams 14a, 14b overlap, so that object sections in the overlapping area can be scanned selectively by one or the other laser beam 14a, 14b.

[0022] To ensure that both laser beams are focused on the same point in the working plane when the same target point is entered via the control, the irradiation device 12 must be calibrated.

[0023] Fig. 2 shows a section of the Fig. 1, on whose surface a calibration device 30 according to a first embodiment of the present invention is arranged. Schematically indicated in the carrier are two working areas 20a, 20b, each of which can be scanned by one of the two laser beams 14a, 14b, as well as an overlap area 21, which can be scanned by both laser beams 14a, 14b. In the overlap area 21, the lasers generally impinge on the working plane 7 at an angle.

[0024] The calibration device 30 contains a housing 31, which can be formed in one or more parts, and a sensor 32 arranged in the housing 31. In the present embodiment, the housing is formed from a metal block having a recess, and the sensor is inserted into this recess. The support is adjusted so that the surface 33 of the sensor 32 lies in the working plane 7, in which the laser beams 14a, 14b are focused. The support 6 can be adjusted lower than the working plane 7 by a distance that corresponds to the height of the sensor surface above the base of the calibration device.

[0025] Any sensor sensitive to the laser wavelength can be used, for example, optoelectronic sensors that convert the incident light into an electrical signal. For example, a photodetector in the form of a semiconductor detector made of germanium or silicon can be used. However, a thermopile sensor, preferably an atomic layer thermopile (ALTP), can also be used, which measures the laser power via the heat generated when the laser beam hits the sensor. Very short response times can be achieved with such atomic layer thermopile sensors.

[0026] Two through holes 34a, 34b are formed at an angle in the housing 31 of the calibration device 30. These holes are provided for the passage of the two laser beams 14a, 14b. The angle to the vertical is preferably less than 60°, more preferably less than 45°. The lower section of the through holes 34a, 34b is formed as a very fine pinhole 35a, 35b, while the upper section is formed as a conical section 36a, 36b whose diameter increases toward the top. The holes 35a, 35b are arranged such that their central axes intersect on the surface 33 of the optical sensor 32.

[0027] During operation, this calibration device 30 is placed at a measuring point located within the overlap area 21. The control unit then first directs one of the two laser beams 14a, 14b so that it falls on the measuring point. The laser beam 14a, 14b passes through the corresponding aperture 34a, 34b and strikes the surface 33 of the sensor 32. The sensor detects the incident light and emits a signal corresponding to the measured light intensity.

[0028] The position of the laser beam 14a, 14b is then iteratively adjusted so that the signal delivered by the sensor 32 reaches a maximum. As the laser beam 14a, 14b moves across the pinhole 35a, 35b of the through-opening 34a, 34b, the sensor 32 delivers a signal with a bell-shaped curve. The maximum of this signal corresponds to the maximum passage of the laser beam 14a, 14b through the pinhole 35a, 35b.

[0029] The accuracy of the measurement is determined, among other things, by the diameter of the pinhole. This diameter is preferably selected so that it is approximately equal to the diameter of the laser beam at the measurement point. If the pinhole diameter is too large, the bell-shaped curve will not have a distinct maximum, but rather a broad plateau, which reduces the accuracy of the position determination. If the pinhole diameter is too small, the received laser power decreases, and in this case, too, the bell-shaped curve will not have a distinct maximum, which also reduces the accuracy.

[0030] On the other hand, the conical section 36a, 36b ensures that the laser beam does not have to be incident at a specific angle, but rather that a certain angle range is permissible. It also prevents disruptive reflections in the event of incorrect positioning of the laser beam 14a, 14b. However, it does not focus the laser beam.

[0031] Preferably, the output signal of the sensor 32 is fed to the control device 18, so that the iterative adjustment to the position corresponding to a maximum irradiation of the sensor and thus a maximum output signal of the sensor can be carried out automatically by the control device 18.

[0032] Subsequently, the same process is performed for the second laser beam. The actual positions at which the maximum sensor output signal is achieved are compared with each other and / or with the respective target positions. The actual and target positions refer to the representations of the point of impact of the laser beam on the working plane in the coordinate system of the laser sintering device. A correction value for controlling the laser beams is calculated from the deviations, which is then taken into account during the subsequent production of the three-dimensional object. Preferably, the determination of the deviation and the correction are also performed automatically by the controller 18.

[0033] Since the overlap area of ​​two laser beams is in a Fig. 2 extends in the form of an elongated strip in a direction perpendicular to the plane of the drawing, it is advantageous to perform the calibration at least at two positions at opposite ends of the strip. This can be achieved by performing two consecutive measurements at different locations using the same calibration device, which is offset between the two measurements, or by performing the two measurements in parallel using two calibration devices arranged at different locations in the overlap area. This allows, in addition to a lateral offset, scaling and rotation errors, for example, to be detected and corrected.

[0034] For such a measurement at two different locations within the overlap area, a bar equipped with two sensors can be used, for example. The two sensors are positioned at each end of the bar. The bar is then positioned at a predefined position within the overlap area on the construction site.

[0035] This form of calibration is more accurate and easier to perform than the calibration using a camera described in the prior art.

[0036] Fig. 3 shows a section of the Fig. 1, on the surface of which a calibration device 40 according to a second embodiment of the present invention is arranged.

[0037] The calibration device 40 is constructed similarly to the calibration device 30 and, like the latter, contains a single- or multi-part housing 41 and a sensor 42. The housing 41 contains the two through holes 44a, 44b with the pinhole 45a, 45b and the conical section 46a, 46b. These elements correspond to those of the first embodiment and will not be described again here.

[0038] In addition, the calibration device 40 contains two beam splitters 47a, 47b, each arranged in the center axis of the through holes 44a, 44b, two radiation absorbers 48a, 48b arranged laterally of the beam splitters 47a, 47b, and a partition wall 49.

[0039] The calibration process is carried out in the same way as in the first embodiment. The additional beam splitters 47a, 47b reduce the light intensity incident on the sensor compared to the first embodiment. This prevents the sensor from being overdriven or even destroyed at higher laser powers, without having to specifically reduce the laser power for calibration, which could potentially also change the beam shape.

[0040] The radiation absorbers 48a, 48b absorb the radiation deflected from the optical path by the beam splitters 47a, 47b, and the partition wall 49 prevents radiation from passing from one beam splitter to the other.

[0041] Any laser suitable for solidifying the powdered build-up material can be used, including gas lasers such as CO2 lasers, solid-state lasers such as NdYAG lasers, semiconductor lasers, fiber lasers, etc.

[0042] Although the present invention has been described with reference to a laser sintering or laser melting device, it is not limited to laser sintering or laser melting. For example, instead of a laser, a light-emitting diode (LED), an LED array, or any other energy or radiation source suitable for solidifying the powdered building material can be used.

[0043] In particular, energy input is not limited to visible light, but can also be achieved through invisible infrared light or ultraviolet radiation. The sensor must then be selected according to the energy source used.

[0044] The two energy beams do not have to come from two separate energy sources; they can also be obtained from one energy source by beam splitting and deflected by separate deflection devices.

[0045] The number of energy beams is not limited to two; more than two energy beams can be used. For example, the individual work areas on four-head machines form four adjacent squares that overlap one another. Using the calibration devices described above, a calibration process can be performed in an overlapping area of ​​two energy beams. By providing four through openings in the calibration device, a calibration process can also be performed simultaneously in the overlapping area of ​​all four squares for the four energy beams. Any other number of energy beams and / or through openings in the calibration device are also possible.

[0046] The upper section 36a, 36b of the through-hole 34a, 34b can also be configured in a different way than conical. It can be flared upwards in any desired shape or even be cylindrical with a larger diameter than the pinhole.

[0047] Instead of a sensor that only determines the overall intensity of the radiation, sensors that can determine the location of the incident beam can also be used. For example, using a two- or four-quadrant sensor that detects differential currents between adjacent active areas can provide more precise spatial information because the quadrant separation edge then determines the spatial resolution. This ensures accurate position measurement even if the diameter of the laser beam is smaller than that of the pinhole. Such a differential current measurement is also possible with an atomic layer thermopile sensor.

[0048] The calibration procedure is preferably performed before the start of the build process. However, it can also be repeated during the build process. In this case, the calibration device is not placed directly on the substrate, but on the last solidified layer of the object to be manufactured.

[0049] While the calibration device in the above embodiments is described as a single object that is placed on the carrier or a solidified material layer, the calibration device can also be included in the device for producing a three-dimensional object. It can then, for example, be attached to a movable arm that moves to the desired location for calibration and positions the sensor so that its surface lies in the working plane.

[0050] However, calibration can also be performed if the sensor is not positioned in the work plane. If the offset height is known, the actual values ​​relevant for the work plane can be derived from the measured actual values ​​of the beam position in another plane. This corresponds to a purely geometric conversion. This is particularly relevant when mounting the sensor system on a movable arm or when measuring during the construction process.

Claims

[1] Calibration device (30; 40) for a device (1) for layer-by-layer production of a three-dimensional object (2) by layer-by-layer solidification of building material (10) at the locations corresponding to the cross-section of the object to be produced in the respective layer by means of at least two energy beams (14a, 14b), the calibration device comprising: a housing (31; 41) and a sensor (32; 42) arranged in the housing for receiving the at least two energy beams and outputting an output signal depending on the intensity of the energy beams, wherein the housing has at least two through-openings (34a, 34b; 44a, 44b) for passing the at least two energy beams, which are arranged such that their central axes intersect on a surface of the sensor. [2] Calibration device (30; 40) according to claim 1, wherein each of the at least two through openings (34a, 34b; 44a, 44b) comprises: a lower portion (35a, 35b; 45a, 45b) formed in the shape of a thin bore having a first diameter, and an upper portion (36a, 36b; 46a, 46b) whose diameter is larger than the first diameter. [3] Calibration device (40) according to claim 2, in which the diameter of the upper section (36a, 36b; 46a, 46b) increases upwards, wherein the upper section is preferably conically widened upwards. [4] Calibration device (40) according to one of claims 1 to 3, wherein the calibration device further comprises a beam splitter (47a, 47b) for each of the at least two through openings (44a, 44b) for coupling out a part of the corresponding energy beam (14a, 14b). [5] Calibration device (40) according to claim 4, wherein the calibration device further comprises a radiation absorber (48a, 48b) for each beam splitter (47a, 47b) for absorbing the portions of the energy beam (14a, 14b) coupled out by the beam splitter, and / or wherein the calibration device further includes a partition wall (49) for optically decoupling the beam splitters (47a, 47b). [6] Method for calibrating a device (1) for layer-by-layer production of a three-dimensional object (2) by layer-by-layer solidification of building material (10) at the locations corresponding to the cross-section of the object to be produced in the respective layer by means of at least two energy beams (14a, 14b), the method comprising the steps of: Positioning a calibration device (30; 40) according to one of claims 1 to 5 in the device such that a surface (33, 43) of the sensor (32; 42) lies in an overlap region (21) of the at least two energy beams, iteratively deflecting a first energy beam (14a) and determining a first actual position at which an output signal of the sensor reaches a maximum signal, iteratively deflecting a second energy beam (14b), and determining a second actual position at which the output signal of the sensor reaches a maximum signal, Comparing the first and second actual positions with each other and / or with corresponding target positions and Determine at least one correction value from the comparison. [7] Calibration method according to claim 6, wherein the at least one energy beam is at least one laser beam (14a, 14b). [8] Method for producing a three-dimensional object (2) by layer-by-layer solidification of building material (10) at the locations corresponding to the cross-section of the object to be produced in the respective layer by means of at least two energy beams (14a, 14b), the method comprising the steps of: Calibration by means of a calibration method according to one of claims 6 to 7 and Producing the object using at least one correction value determined during the calibration process, wherein the object is preferably produced by means of laser sintering or laser melting. [9] Device (1) for producing a three-dimensional object (2) by layer-by-layer solidification of building material (10) at the locations corresponding to the cross-section of the object to be produced in the respective layer by energy input with a support (6) on which the object (2) is built, a coater (11) for applying a layer of the building material (10) to the carrier or a previously at least selectively solidified layer of the building material, at least one energy source (13) for generating at least two energy beams (14a, 14b), at least two scanning devices for scanning the locations of the applied layer of the building material (10) corresponding to a cross-section of the object (2) to be produced with the at least two energy beams (14a, 14b) for selectively solidifying the powdered building material (10) and a calibration device according to one of claims 1 to 5. [10] Device (1) for producing a three-dimensional object (2) by layer-by-layer solidification of building material (10) at the locations corresponding to the cross-section of the object to be produced in the respective layer by energy input with a support (6) on which the object (2) is built, a coater (11) for applying a layer of the building material (10) to the carrier or a previously at least selectively solidified layer of the building material, at least one energy source (13) for generating at least two energy beams (14a, 14b), at least two scanning devices for scanning the locations of the applied layer of the building material (10) corresponding to a cross-section of the object (2) to be produced with the at least two energy beams (14a, 14b) for selectively solidifying the powdered building material (10) and a control unit (18) for controlling the operation of the device, characterized by that the control unit is adapted to control the device for carrying out a method according to one of claims 6 to 8.

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