EP4384380A1

EP4384380A1 - Improving the positional accuracy of the supply of energy in an additive manufacturing device

Info

Publication number: EP4384380A1
Application number: EP22753665.3A
Authority: EP
Inventors: Alois LOHR; Uwe STARR; Thomas Mattes; Alexander Prillwitz; Michael GÖTH
Original assignee: EOS GmbH
Current assignee: EOS GmbH
Priority date: 2021-08-13
Filing date: 2022-07-18
Publication date: 2024-06-19
Also published as: CN117881527A; WO2023016759A1; DE102021208911A1

Abstract

The invention relates to a calibration method of a device for layered additive manufacturing of items, which device comprises: a control device for controlling the layered additive manufacturing process; a layer deposition device which is designed to provide a layer of a construction material; and an energy supply device which is designed to solidify points of the layer by supplying electromagnetic radiation; wherein the energy supply device is designed to be moved over the construction region and a predefined target direction (X) is specified to the energy supply device for this movement; and wherein the energy supply device comprises a number of radiation emitters which are arranged along an arrangement direction (Y) transversely to the predefined target direction (X); and, depending on the points, the control device specifies to the radiation emitters the emission locations at which radiation should be emitted over the construction region; in which calibration method it is determined whether the movement of the energy supply device leads to a deviation of the movement direction (B) from the predefined target direction (X) and the control device is prompted to specify other emission locations to the radiation emitters on the basis of a determined deviation.

Description

Improving the positional accuracy of the power supply in an additive manufacturing device

The present invention relates to a calibration method of a device for the layer-by-layer additive manufacturing of three-dimensional objects and to a device that can be calibrated by such a calibration method for the layer-by-layer additive manufacturing of a number of three-dimensional objects.

Additive manufacturing devices and associated methods to which the invention relates are generally characterized in that they manufacture objects by solidifying a formless building material (e.g., a metal or plastic powder) layer by layer. The solidification can be brought about, for example, by supplying thermal energy to the building material by means of irradiating it with electromagnetic radiation or particle radiation (e.g. laser sintering (SLS or DMLS) or laser melting or electron beam melting). For example, in laser sintering or laser melting, a laser beam is moved over those points of a layer of the construction material that correspond to the object cross section of the object to be produced in this layer, so that the construction material is solidified at these points. After the building material has been melted or sintered at one point by the supply of thermal energy, the building material is no longer in a shapeless state after cooling, but is present as a solid body. After all points of an object cross-section to be solidified have been scanned, a new layer of the building material is applied and also solidified at the points corresponding to the cross-section of the object in this layer.

The selective irradiation of the applied powder layer can be done, for example, in that a laser beam through a deflection device formed, for example, from galvanometer mirrors, is deflected in such a way that its point of impingement on the powder surface is moved over the points to be solidified.

Alternatively, WO 2015/091485 A1 discloses an irradiation device (sometimes also called an exposure device) that contains a plurality of laser arrays. Each of these laser arrays is made up of a number of individual VCSELs (vertical cavity surface-emitting lasers), which are switched on or off together. The laser arrays are imaged onto the powder surface using an optical element. By selectively switching the laser arrays on and off and moving the exposure device parallel to the powder surface, the entire powder layer can be exposed selectively. With such a system, which can also be referred to as a line exposer, a selective irradiation process can take place more quickly, since different areas of the powder layer can be irradiated approximately at the same time or at least with a large temporal overlap.

However, the inventors of the present application found that when using a line exposer, new problems can also arise with regard to the positional accuracy with which the radiation is supplied to the areas of the powder layer to be solidified. When using galvanometer mirrors to direct the radiation onto the powder layer, the positional accuracy with regard to the position of the impact point on the powder surface depends, among other things, on how quickly the mechanics can convert the commands given by the controller into angular movements. In contrast, when using a line exposer, the situation is quite different. In contrast to the conventional use of galvanometer mirrors, a significantly larger mass, namely the entire imagesetter, is moved here.

It is therefore an object of the present invention to provide a method and a device by means of which a high positional accuracy can be achieved when the radiation is supplied to a building material layer when using an additive manufacturing device with a line exposer. The object is achieved by a calibration method according to claim 1 and a device according to claim 10. Further developments of the invention are claimed in the dependent claims. In particular, a device according to the invention can also be further developed by features of the method according to the invention that are set out below or in the dependent claims, and vice versa. Furthermore, the features described in connection with a device according to the invention can also be used to develop another device according to the invention, even if this is not explicitly stated.

In a calibration method according to the invention of a device for the layer-by-layer additive manufacturing of a number of objects, the device having: a control device for controlling the layer-by-layer additive manufacturing process, a layer application device which is designed to apply a layer of an amorphous building material on a building base or an already manufactured layer within of a construction field, and an energy supply device, which is designed to solidify defined locations of the provided layer, which are associated with the cross sections of the number of objects in this layer, by supplying electromagnetic radiation, wherein the energy supply device is designed for supplying electromagnetic radiation to be moved to the specified points on the construction field and the energy supply device for this movement a predefined target direction (X) is specified and wherein the energy supply device e has a number of radiation emitters, which are arranged along an arrangement direction (Y) transversely to the predefined target direction (X), and radiation emitters, depending on the specified locations, the control device specifies at which emission locations over the construction field radiation is to be emitted, is determined whether the direction of movement (B) of the energy supply device deviates from the predefined target direction (X) during the movement of the energy supply device, and causes the control device to in Depending on a determined deviation radiation emitters specify other emission locations.

The present invention relates to the calibration of layer-by-layer additive manufacturing devices in which energy as electromagnetic radiation is selectively applied to a layer of build material. The working level (also referred to as the construction level) is a level in which the upper side of the layer lies to which the energy is supplied, usually the uppermost layer of the layer stack resulting from the layer-by-layer production. The construction area is the area of the working level in which objects can be produced in layers.

In particular, the invention relates to laser sintering or laser melting, with heat being supplied to the building material by radiation, so that it at least partially melts and, after cooling, is in a solid, no longer shapeless state, ie is solidified. Since the transitions between partial (ie superficial in the case of powder grains) melting (sintering) and complete melting (melting) are fluid, the terms sintering and melting are used synonymously in the present application and no distinction is made between sintering and melting.

It should also be noted that the methods and devices to which the present invention relates concern the production of three-dimensional objects, in other words it does not relate to the formation of layers on carrier materials (coatings). Nevertheless, the use of fuselage components should also be included, in which a partial volume of the complete component is supplemented by means of the additive manufacturing process.

The shapeless building material can be a powdery or a paste-like material. It is preferably a polymer-containing building material. It should also be noted at this point that, by means of an additive manufacturing device according to the invention, not only one object but also several objects can be manufactured at the same time. If the production of an object is discussed in the present application, then it goes without saying that the respective description can also be applied in the same way to additive production methods and devices in which several objects are produced simultaneously. Furthermore, the term “number” is always used in the sense of “one or more” in the present application. Furthermore, it should be noted that an object in an additive manufacturing process can also be just a component or a portion of the actual object representing the end product.

In order to supply the electromagnetic radiation to the building material, the energy supply device is moved in a plane above the building field, which is parallel to the building plane. If, in practice, unintentional minor deviations from the parallelism of the planes should occur, these can be corrected independently of the procedure described here or in the course of the procedure described here. A predefined target direction (X) is specified for the movement of the energy supply device. This means the motion is constructively constrained to linear motion in one dimension in the plane. The term target direction (X) should not necessarily imply that the movement can only take place in one direction in the plane. Rather, movement in the opposite direction (so to speak -X) will usually also be possible, although the energy supply device normally always moves in the same direction (i.e. not back and forth) for the solidification of the total number of specified locations in a layer.

With any linear motion control in a desired direction, it cannot be ruled out that the direction of motion B will deviate from the desired direction, even with careful design of the components that guide the movement. According to the present procedure, it is therefore checked whether such a deviation from the direction of movement occurs and the radiation supply for the selective solidification of the building material is corrected accordingly. The deviation can result in a linear movement in a direction other than the target direction or in express different directions. Furthermore, alternatively or additionally, the deviation can also be caused by a rotary movement. In all of the cases mentioned, the deviation can only be temporary, ie it can only occur at certain positions in the desired direction, or at almost all points in the desired direction from the first occurrence of a deviation during movement in the desired direction. The last case relates in particular to a cumulative increase in the deviation of the direction of movement from the target direction.

The deviation can only be determined at a predetermined maximum number of positions of the energy supply device in the target direction, or it is determined at as many positions as possible whether a deviation occurs. This depends entirely on the accuracy requirements in the layer-by-layer additive manufacturing of three-dimensional objects. In the latter case, the number of positions at which a deviation is determined can be linked to the spatial resolution of the linear guide in the desired direction (e.g. when using a stepping motor).

If several radiation emitters are arranged in an arrangement direction (Y) transversely to the desired direction (X), preferably next to one another, then the electromagnetic radiation can be supplied to several points of the building material layer to be solidified at the same time or at least with a temporal overlap, so that the solidification step for one layer can take place in a shorter time compared to, for example, a laser scanner. Although the direction of arrangement is preferably essentially perpendicular, preferably exactly perpendicular to the desired direction, embodiments are also possible in which the desired direction and the direction of arrangement enclose an angle that differs from 90°. Irrespective of this, it is possible for the radiation emitters to be offset relative to one another in a direction perpendicular to the arrangement direction. Furthermore, it is also conceivable that the radiation emitters are not arranged next to one another without gaps in the arrangement direction. Rather, what is decisive is that the electromagnetic radiation can be fed in without gaps in the arrangement direction, although there can also be exceptions to this, for example if no electromagnetic radiation is deliberately fed to a strip of the construction field extending in the desired direction should. Each radiation emitter preferably consists of a number of diode lasers, eg VCSELs or VECSELs.

The control device, via which the individual components of the device for layer-by-layer additive manufacturing are controlled in a coordinated manner for carrying out the layer-by-layer additive construction process, can also be arranged partially or entirely outside of the additive manufacturing device. The control device preferably contains a CPU, the operation of which is controlled by a computer program (software). The computer program can be stored separately from the additive manufacturing device in a memory device from where it can be loaded (e.g. via a network) into the controller.

In particular, the control device specifies to the individual radiation emitters at which locations in the plane parallel to the construction plane the individual radiation emitters should emit radiation during the movement of the radiation supply device over the construction field. These emission locations of the radiation emitters correspond to defined locations of the layer provided, at which building material is to be solidified.

In the calibration method described, the control device or its software is prompted to automatically assign at least some of the radiation emitters other emission locations than those which would have been assigned to these radiation emitters had there not been a deviation. In other words, since the position of the radiation emitters in the plane parallel to the building plane changes as a result of the deviation, the control device automatically changes the locations at which radiation emitters should emit radiation, so that the emission locations correctly correlate with the specified locations of the building material layer to be solidified . It is therefore understood that other emission locations are not necessarily assigned to all of the radiation emitters contained in the energy supply device, but often only to some of them Radiation emitters are assigned other emission sites. The number of radiation emitters to which other emission locations are assigned often depends on the extent of the deviation determined.

It should also be noted that, in addition to changing the emission locations, the radiation power emitted by the radiation emitters can optionally also be changed. This procedure relates to the case in which the radiation emitters can not only be switched on and off, but the radiation power emitted by radiation emitters can also be modified.

In the calibration method for determining the deviation, the angle (ctj) between the predefined target direction (X) and the direction of movement (B) is preferably determined and a decision is made that there is a deviation if this angle (ctj) exceeds a specified tolerance angle (ctref).

Depending on the accuracy requirements in the additive manufacturing of objects, it can sometimes be tolerated that the emission locations of the radiation emitters are slightly shifted as a result of the deviation of the direction of movement from the desired direction. The tolerance for minor deviations can be taken into account by specifying the tolerance angle. A modification or adaptation of the emission locations then only takes place in those cases in which the displacement of the emission locations in relation to the locations of the building material layer which are to be solidified can no longer be tolerated. If the deviation falls below the tolerance angle, the shift in the emission locations resulting from the deviation is tolerated. In principle, any small tolerance angle (0°) can be specified. However, a lower limit automatically results from the measurement accuracy with which the tolerance angle can be determined.

For the determination of deviations, the energy supply device is preferably moved with or without the supply of electromagnetic radiation to the defined points over the construction field. With this procedure, it is possible to determine deviations in the direction of movement from the desired direction that occur during a movement of the energy supply device across the construction field, independently of a manufacturing process running in the device for layer-by-layer additive manufacturing. To determine deviations, the energy supply device is moved over the construction area, preferably the entire construction area, and it is checked at individual positions in the desired direction whether there is a deviation between the direction of movement and the desired direction. Based on the result, the control device can then be modified in such a way that in subsequent manufacturing processes it takes into account the deviations that have occurred at the corresponding positions of the energy supply device in the desired direction by specifying other emission locations at these positions. In particular, deviations can be determined before the device for layer-by-layer additive manufacturing is put into operation for the first time or after a long period of downtime, after conversions or changes in the environmental conditions, e.g. B. Changes in the ambient temperature at the installation site or transition to the production of other objects. Apart from that, the deviations can also be determined continuously during the production process, for example in order to counteract gradual changes.

More preferably, information about positions (XJ) in the target direction (X) at which a deviation was determined is stored in a storage device and the information stored in the storage device is accessed for specifying the other emission locations of the radiation emitters.

With this procedure, the control device can then obtain the positions in the desired direction at which a deviation occurred by accessing the memory device. The memory device can be any type of volatile or non-volatile memory. A storage device present in the control device itself, for example a RAM, EPROM, etc., or a storage medium to which the control device can have read access, for example a CD-ROM or DVD, would be grateful Storage device arranged in a completely different location than the layer-by-layer additive manufacturing apparatus, the storage device being accessed via a LAN, in particular the Internet. In particular, a cloud-based implementation of the memory device could also be considered, which then also includes storage on a number of different memory devices.

More preferably, the device for layer-by-layer additive manufacturing has an interface for receiving control data for controlling the sequence of a layer-by-layer additive manufacturing process, the control data having at least one data model of the number of objects to be manufactured, in which radiation emitters it is specified at which emission locations above the Construction field radiation is to be emitted for supplying electromagnetic radiation to specified locations of a provided layer, which are assigned to the cross sections of the number of objects in this layer, the control device specifying other emission locations for radiation emitters by making changes in an accepted data model.

The control data can contain instructions for applying layers of the building material one after the other and for applying radiation to regions of the respective layers which correspond to the cross section of an object to be produced in order to solidify the building material there.

In detail, the control data have a data model that is derived from a computer-based model of the object or objects to be produced, preferably a CAD model of the same. In detail, the control data for each build-up material layer specifies at which emission locations radiation emitters should emit radiation when the energy supply device is moved over the build field in order to solidify locations of the build-up material layer. These emission locations are derived from a computer-based model of the object or objects to be produced, preferably a CAD model of the same. The interface for receiving control data can in particular be an interface known in the prior art for receiving digital data, such as a PCI bus, AGP, SCSI, USB or FireWire interface, the list is not exhaustive.

The use of a device for layer-by-layer additive manufacturing with such an interface allows users of the device to provide the device with the control data with a data model for the production of the objects desired by the users. In such a case, the control device modified by the calibration method can automatically modify the received data model at the positions of the energy supply device in the target direction at which a deviation was determined. In other words, the data model specified by a user for the number of objects to be produced is predistorted before the start of the production process or before the start of the irradiation process of a layer and the production process is carried out on the basis of the predistorted data model.

The control device is preferably caused to specify other emission locations for radiation emitters during an additive manufacturing process, preferably during a movement of the energy supply device over the construction field.

With this embodiment of the calibration method, deviations between the direction of movement and the target direction are determined during a movement of the energy supply device over the construction site for supplying the radiation to the construction material. In this case, the presence of a deviation can be determined at each new position in the target direction that the energy supply device reaches. If there is an anomaly, the controller automatically specifies different emission locations for radiation emitters than those which would have been specified had there not been an anomaly. The control device of the additive manufacturing device is therefore designed in such a way that it either initiates the determination of deviations itself or can at least receive the information about the existence of a deviation, in order in both cases, if a deviation exists to automatically specify other places of emission. Preferably, the angle between the direction of movement and the target direction is also determined or communicated to the control device, so that the control device can then use this information to change emission locations.

A deviation is preferably determined only at a predetermined number of positions (XJ) in the desired direction (X).

The positions in the target direction at which a deviation is determined can be specified, for example, where there is already a suspicion in advance that there may be a deviation from the linear movement. Such a suspicion can, for example, stem from a calibration process that has already taken place in the past or be justified by the knowledge that particularly high temperatures or particularly large temperature differences occur in certain areas of the construction site during the additive manufacturing process. Such a procedure can reduce the effort involved in calibrating.

The associated deviations between the specified positions are calculated on the basis of the deviations determined at the positions (interpolation). It is also possible to specify a maximum number of positions so that, if the boundary conditions permit, a deviation can also be determined at a smaller number of positions in the target direction.

A deviation is preferably determined at positions (XJ) in the desired direction (X) which are at a predetermined distance (Ax) from one another.

With this procedure, on the one hand, the outlay for the calibration is limited by the fact that the presence of a deviation is only determined at certain positions. On the other hand, by specifying the constant distance between the positions, deviations are determined as uniformly as possible along the target direction. Optionally, a maximum distance between the positions in the target direction can also be specified, which must not be exceeded.

In the calibration method, it is preferably also determined whether the movement of the energy supply device results in a change in the distance between the radiation emitters and the construction area and, if this is the case, causes the control device to change the focal position of the radiation emitted by the radiation emitters.

A change in the distance from radiation emitters to the construction area can be caused by the fact that the movement of the energy supply device across the construction area does not run completely in one plane, i.e. the energy supply device as a whole is offset in a direction perpendicular to the plane in which the desired direction runs. In this case, the distance between all radiation emitters changes.

On the other hand, however, the plane in which the energy supply device is moved across the construction area cannot be completely parallel to the construction plane in which the construction area lies. In this case, a different distance from the construction area can result for different radiation emitters, so that the distance of only some of the radiation emitters changes beyond a tolerable extent.

Even if the deviations from plane parallelism are usually negligibly small, this effect can also be taken into account in high-precision applications by checking (e.g. using an (IR) camera arranged above the construction area) whether there are fluctuations in the beam focus . If this is the case, the focus position can be corrected by changing the distance between the energy supply device and the construction level and/or by introducing or changing an inclination of the energy supply device relative to the level of the construction field (the working or construction level) and/or by adjusting the focus become.

A device according to the invention for the layer-by-layer additive manufacturing of a number of objects, which can be calibrated using a calibration method according to the invention, has: a control device for controlling the layer-by-layer additive manufacturing process, a layer application device that is designed to provide a layer of an amorphous building material on a building base or a layer that has already been produced within a building field, an energy supply device that is designed to provide specified points on the layer provided that correspond to the cross sections assigned to the number of objects in this layer, to be solidified by supplying electromagnetic radiation, wherein the energy supply device is designed to be moved over the construction field for supplying electromagnetic radiation to the specified locations and the energy supply device has a predefined target direction (X ) is specified, wherein the energy supply device has a number of radiation emitters, which are arranged along an arrangement direction (Y) transversely to the predefined desired direction (X), and radiation emitters in dependence The control device specifies the emission locations at which radiation is to be emitted above the construction site, and the control device is designed at positions (XJ) in the target direction (X) at which a deviation is determined in the course of the calibration method , Radiation emitters specify other emission sites.

A device according to the invention is set up in such a way that, in the event of deviations in the direction of movement of the energy supply device from the desired direction, it automatically changes the locations at which the radiation emitters are intended to emit radiation. In other words, the control device of the device is designed in such a way that it can either take into account the information about deviations determined before a production process during the production process or else automatically determine the information during the production process and take it into account immediately.

The device is thus designed in such a way that a calibration method according to the invention can be carried out for this device. In particular This can eliminate the need for a user of the device to calibrate the device before use or from time to time. Deviations in the direction of movement from the target direction can in particular also be determined by the manufacturer of the device or the device can do this automatically during the course of a hardening process of a layer of building material.

The device preferably has a linear guide, through which the energy supply device is guided as it moves across the construction site.

There are a multitude of possibilities for the design of the linear guide. In the first place, the linear guide can be implemented by means of a number of rails, in particular one or two rails, which serve to guide the movement of the energy supply device in a straight line. The energy supply device is connected to the rail(s) by means of a coupling device (e.g. carriage or carriage).

The linear guide also preferably has two parallel rails spaced apart from one another, on which the movement of the energy supply device is guided by means of two carriages.

Such a configuration of the linear guide has the advantage that it can be used to ensure a particularly linear movement.

More preferably, the energy supply device is arranged between rails arranged on two sides of the construction area.

Such a configuration of the linear guide has the advantage that it ensures a particularly stable construction, in which the energy supply device mounted on the two rails then spans like a bridge over the construction site. The device according to the invention for the layer-by-layer additive manufacturing of a number of objects preferably also has a position detector which is designed to determine whether the movement of the energy supply device deviates from the predefined target direction (X) in the direction of movement (B) of the energy supply device.

A position detector determines, for example, the angle between the direction of movement of the energy supply unit and the target direction. For example, a camera can be used for this purpose, which is preferably arranged above the energy supply unit and the construction area. Furthermore, the position detector can have a linear measuring system (e.g. a glass scale, an inductive displacement sensor, an interferometer or a combination of linear measuring system and angle measuring system (glass scale and autocollimator).

The device according to the invention for the layered additive manufacturing of a number of objects, in which the linear guide has two parallel rails spaced apart from one another, preferably also has a position detector which is designed to determine whether the movement of the energy supply device has resulted in a deviation in the direction of movement (B ) of the energy supply device comes from the predefined desired direction (X), the position detector comprising two position measuring units, each of which is attached to one of the two rails and is suitable for determining the position of the respective carriage on the rail.

In this configuration, the position of the coupling devices (e.g. the carriages) determined at a given point in time, with which the energy supply units are coupled to the rails, is determined and a deviation between the direction of movement and the desired direction is determined from this, for example via the distance between the position measuring units, and the calculated positions of the angle between the direction of movement of the energy supply unit and the target direction. Linear measuring systems (eg inductive position sensors, interferometers) can be used as position measuring units. More preferably, the position detector is designed to determine an angle (ctj) between the predefined desired direction (X) and the direction of movement (B).

By determining the angle between the direction of movement and the target direction, the information about the deviation that has occurred can be taken into account in a simple manner when redefining emission locations, particularly if the arrangement of the radiation emitters on the energy supply device follows a complex pattern.

More preferably, the position detector is a camera arranged above the energy supply device.

The camera can either be an optical camera, which then takes pictures of the energy supply device and its linear guide in particular, or an infrared camera, which takes pictures of the irradiated layer of building material, which can be used to draw conclusions about a deviation between the direction of movement and the desired direction. Due to the energy supply, the irradiated areas of the building material layer have a higher temperature than the surrounding building material, which is reflected in the IR image. Deviations can then be determined by determining geometric deviations from the associated object cross section (or part thereof) specified in the input data of the additive manufacturing device.

More preferably, the device according to the invention for the layer-by-layer additive manufacturing of a number of objects also has a checking unit that is designed to determine the presence of a deviation if the angle (ctj) determined by the position detector exceeds a predetermined tolerance angle (ctref).

In this case, the test unit can be implemented in particular by means of software, in particular also by means of a program processed by a CPU contained in the control device. The tolerance angle is preferably adjustable and, for example, dependent on the accuracy requirements for the objects to be produced. This means either the manufacturer of the additive manufacturing device can through Specification of the tolerance angle determine the accuracy of the additive manufacturing device or a user of the device can adapt the device to his requirements by changing the tolerance angle.

A method according to the invention for the layer-by-layer additive manufacturing of a number of objects comprises a calibration method according to the invention.

The accuracy of the manufactured objects can be improved in a simple manner by means of such a layer-by-layer additive manufacturing method.

Further features and advantages of the invention result from the description of exemplary embodiments with reference to the attached figures.

1 shows a schematic, partially sectioned view of an exemplary apparatus for additively manufacturing a three-dimensional object in accordance with the invention.

FIG. 2 shows a schematic plan view of a construction field with a line exposer to which the present invention can be applied.

Figure 3 schematically illustrates the problem solved by the invention.

4 serves to explain a procedure according to the invention.

FIG. 5a is a schematic bottom view of an imagesetter included in the apparatus shown in FIG. 1. FIG.

Figure 5b is a schematic view of a laser module included in the imagesetter shown in Figure 5a.

FIG. 5c is a schematic view of a laser array included in the laser module shown in FIG. 5b. 6 illustrates the course of a calibration method according to a first embodiment,

7 schematically shows details of the structure of a control device of an additive manufacturing device according to a first specific embodiment.

8 illustrates the course of a calibration method according to a second embodiment,

9 schematically shows details of the structure of a control device of an additive manufacturing device according to a second specific embodiment.

An exemplary device 1 which is calibrated according to the two embodiments of the present invention is first described below with reference to FIG. 1 . The device shown in FIG. 1 is a laser sintering or laser melting device 1 . For building an object 2, it contains a process chamber 3 with a chamber wall 4.

A container 5 which is open at the top and has a container wall 6 is arranged in the process chamber 3 . A working plane 7 is defined by the upper opening of the container 5 , the area of the working plane 7 lying within the opening, which can be used for constructing the object 2 , being referred to as the construction field 8 .

Arranged in the container 5 is a carrier 10 that can be moved in a vertical direction V and to which a base plate 11 is attached, which closes off the container 5 at the bottom and thus forms its bottom. The base plate 11 may be a plate formed separately from the bracket 10 and fixed to the bracket 10, or may be formed integrally with the bracket 10. Depending on the powder and process used, a construction platform 12 can also be attached to the base plate 11 as a construction base, on which the object 2 is built. However, the object 2 can also be built directly on the base plate 11, which then serves as a building base. In 1 shows the object 2 to be formed in the container 5 on the construction platform 12 below the working plane 7 in an intermediate state with several solidified layers, surrounded by construction material 13 that has remained unsolidified.

The laser sintering device 1 also contains a reservoir 14 for a powdery or pasty construction material 15 that can be solidified by electromagnetic radiation and a coater 16 that can be moved in a horizontal direction H for applying the construction material 15 within the construction area 8. The coater 16 preferably extends transversely to its direction of movement the entire area to be coated.

Optionally, a radiant heater 17 is arranged in the process chamber 3, which is used to heat the build-up material 15 applied. An infrared radiator, for example, can be provided as the radiant heater 17 .

The laser sintering device 1 also contains, as an energy supply device for supplying electromagnetic radiation to the building material, an exposure unit 18 which can also be moved in a horizontal direction and which generates a laser radiation 19 which is focused on the working plane 7 . The exposer 18 is designed as a line exposer that is able to expose an area that extends transversely, in particular perpendicularly, to its direction of movement, which is also referred to as a line and extends over the entire area to be exposed.

FIG. 2 shows a schematic plan view of the construction field 8, which shows the line exposer 18 to be moved in the desired direction X. This has an exposure arm 31 with a longitudinal axis which extends perpendicularly to the desired direction X. To guide the movement of the line exposer 18, the exposure arm 31 is rigidly connected to a coupling device 30, which is arranged in the extension of its longitudinal axis. Two carriages 30a and 30b are attached to the coupling device 30 and can each be slidably moved along one of the two parallel rails 28a and 28b. To register the position of each carriage along the direction of extension (trajectory) of its rail is at each attached to the two carriages is a position measuring unit 32a or 32b. The motor for moving the imagesetter 18 (for example a stepper motor) is not shown in the figures for reasons of clarity.

In this example, the line exposure unit 18 has a plurality of independently controllable exposure units (i.e. radiation emitters) 80 which are arranged next to one another perpendicularly to the direction of movement of the line exposure unit (referred to as the Y direction in Figure 2) and each independently of one another apply laser radiation to the under the line exposure unit 18 lying work level 7 can direct. In this example, it is assumed that n exposure units 801, 802, . . . 80n are present, where n is a natural number and has the value 184, for example. It is assumed in the further course of the description that the exposure unit 801 is at the shortest distance from the rail 28a and the exposure unit 80n is at the greatest distance.

Referring again to FIG. 1, the laser sintering device 1 contains a control device 20, via which the individual components of the device 1 (e.g. the motor for moving the imagesetter 18) are controlled in a coordinated manner for carrying out the building process. Alternatively, the control device can also be arranged partially or entirely outside of the device. The controller may include a CPU whose operation is controlled by a computer program (software). The computer program can be stored on a storage medium from which it can be loaded into the device, in particular into the control device. In the present application, the term "controller" includes any computer-based controller capable of controlling or regulating the operation of an additive manufacturing device or at least one of the components thereof. The connection between the control device and the controlled components does not necessarily have to be cable-based, but can also be implemented by radio, in that the control device has appropriate radio receivers and transmitters.

In the additive manufacturing device just described as an example, a manufacturing process takes place in such a way that the control device 20 generates a control data record processed, which is read by the control device. For each layer of construction material 15 applied by the coater 16, the control data record specifies at which points within the construction field 8 laser radiation is to be directed onto the working plane 7 (and thus onto the construction material 15). This means that the control data record specifies which exposure units 801 . . . The specification of the respective exposure unit 80i in the control data record corresponds to the position of the location to be irradiated in a direction perpendicular to the target direction X. In other words, locations above the construction area are specified in the control data record by specifying data triplets (Xj, 80i, Pij). , at which radiation with the power P is to be emitted. For the sake of simplicity it is assumed here that either radiation is emitted or not, in other words either the power P is supplied or no power is supplied at all, ie Pij is a binary parameter. When no power is supplied, P is zero.

For each layer in the layered production of an object, the control device 20 causes the coater 16 to apply a layer of the construction material 15 in order to then move the line exposer 18 by means of a linear guide in the desired direction X over the construction field 8 and in accordance with the specifications in the control data record for to drive the selective exposure of the build material.

According to the invention, deviations in the direction in which the linear guide moves the imagesetter 18 over the construction field 8 from the desired direction X are determined and the additive manufacturing device is calibrated such that such deviations are automatically taken into account during additive manufacturing processes of objects.

Figure 3 schematically illustrates the problem solved by the invention. Like FIG. 2, FIG. 3 also shows a schematic top view of the construction field 8 with the line exposer 18 to be moved in the desired direction X. In FIG. 3, features that are identical to those in FIG. 2 are provided with the same reference symbols . The straightness of the movement of the imagesetter 18 depends on the straightness of the rails 28a and 28b serving as linear guides. Just one Rail length/construction area length in the range of approx. 50 cm cannot be ruled out that manufacturing tolerances lead to deviations from straightness. In FIG. 3, a deviation in the straightness of the rails is shown oversized for reasons of illustration. As can be seen, the curvature of the rails means that when the imagesetter 18 moves in the desired direction X, an additional rotational movement by the angle β is added. As a result, the exposure units do not occupy a position Xj specified in the control data set in the target direction. In particular, the offset of the exposure units in the X-direction is also dependent on the distance of an exposure unit from the rails, which is illustrated in FIG. 3 using exposure units 80j and 80m. For the exposure units 80j and 80m, the dashed line shows the position at the point Xj that the exposure units 80j and 80m would assume for an exactly straight-line movement of the imagesetter 18 in the desired direction. The consequence of the misalignment of the exposure units is that exposure units emit laser radiation at positions other than those assigned to them, thereby causing assembly errors. It should be noted that if the power P supplied to the material is not specified in binary form, but in more than two stages, construction errors also result from the fact that the wrong power is supplied to the construction material at individual locations in the working plane 7.

It should also be noted that the configuration just described and the mode of operation of the control device 20 just described apply not only to the following first embodiment, but also to the control device 200 of the second embodiment described further below.

First embodiment

In the first embodiment, deviations in the direction in which the linear guide moves the exposure device 18 over the construction field 8 from the target direction X are determined before the start of a manufacturing process, and the additive manufacturing device is calibrated in such a way that it automatically takes such deviations into account during additive manufacturing processes of objects. In order to carry out the calibration method, it is necessary for a control device 20 of the additive manufacturing device to be designed in a special way. The course of the calibration method is described below with reference to FIG. 6 , with FIG. 7 illustrating relevant details of the structure of the control device 20 .

In step S1 shown in FIG. 6, before the start of the production process of an object, the exposer 18 is moved along the rails 28a and 28b over the entire construction field 8. The values supplied by the position measuring units 32a and 32b are compared with one another at selected positions Xj in the desired direction X. If at a position Xj the difference δj of the values supplied by the position measuring units 32a or 32b exceeds a tolerance value, this difference δj is converted into an angle ctj. The angle ctj is arctan (öj/L1), where L1 is the distance between the rails perpendicular to the direction of the rails. The angle ctj is then stored in a deviation table together with the associated position Xj.

The selected positions Xj are preferably selected in such a way that they cover the entire length of the construction field 8 in the target direction X as far as possible. The closer the positions Xj are to one another, in other words the greater the number of selected positions, the more accurately deviations from the straight line can be detected. In this case, a smaller number of positions Xj will suffice for a high tolerance value than for a low tolerance value. It should be noted that a tolerance angle corresponding to the relationship tolerance angle=arctan (tolerance value/L1) corresponds to the tolerance value set in advance.

In step S2 shown in FIG. 6, correction data are calculated from the pairs of values stored in the deviation table and stored in a correction data table. This contains correction data triples (Xj, 80i, Aij), in which, for each of the positions Xj of each of the exposure units 80i (1 < i < n), a position error Aij is assigned, which represents the difference in the X direction between the actual position of the exposure unit 80i and indicates the position Xj. Referring to FIG. 4, it is explained below how the position error Aij is determined for an exemplary exposure unit 80i. In contrast to FIG. 3, those features which are not necessary for the explanation are omitted in FIG. Otherwise, features identical to those in Figure 3 are given the same reference numerals. 4 shows the position of the exposure unit 80i in the direction of the longitudinal axis of the exposure arm 31, where Li denotes the distance of the exposure unit 80i from the rail 28b. It is assumed here that the longitudinal axis of the exposure arm runs perpendicularly to the rail 28b. It can be seen that the position error Aij can be calculated as Aij=Li•sinctj.

As shown in Fig. 7, the control device 20 contains, among other things, a control data access unit 101, a correction data storage unit 102, a control data correction unit 103 and an exposure control unit 104. In step S3 shown in Fig. 6, the correction data table previously generated in step S2 is stored in the correction data storage unit 102 of the control device 20 is stored. As can be seen in FIG. 7, the control data correction unit 103 is connected between the control data access unit 101 and the imagesetter control unit 104 . As a result, after reading in a control data record with the control data for the production of a number of cross sections of an object, optionally also for the entire object, which is done by the control data access unit 101, the control data correction unit 103 can carry out the following steps (i) to (ii) so that the imagesetter control unit 104 does not automatically carry out an irradiation based on the read-in control data triples.

In step i), for each of the control data triples (Xj, 80i, Pij) specified in the control data record, it is checked whether a correction data triple (Xj, 80i, Aij) is stored for the position Xj in the control data triple in the correction data storage unit 102. Step ii) is carried out for the control data triples where this is the case.

In step ii) the corresponding control data triple is modified to (Xj, θi, Pi(Xj+Aij)). In other words, the value of Pij originally specified for an exposure unit 80i located at position Xj becomes one value is set which was originally specified for an exposure unit 80i located at position Xj+Aij.

The control data set modified in this way can now (possibly after intermediate storage) be used as a basis by the exposure control unit 104 for the control of the exposure device 18 . In this case, during a manufacturing process in the additive manufacturing device, a modified control data record is initially generated before the start of construction. Alternatively, it is also possible to first change the control data relating to this layer before irradiating a layer (e.g. during layer application).

Second embodiment

In the second embodiment, deviations in the direction in which the linear guide moves the exposer 18 over the construction field 8 from the desired direction X are determined during a production process. The additive manufacturing device thus calibrates itself during additive manufacturing processes of objects by determining such deviations during additive manufacturing processes and automatically taking them into account during the irradiation of a building material layer. The additive manufacturing device has a control device 200 for this purpose.

The course of the calibration method is described below with reference to FIG. 8, with FIG. 9 illustrating relevant details of the structure of the control device 200, which is designed for a corresponding calibration.

In step S1 shown in FIG. 8, a control data record is first read in by the control data access unit 201 shown in FIG. 9, which contains the control data for the production of a number of cross sections of an object, optionally also for the entire object. In step S2, the coater 16 is then prompted to apply a layer of the construction material 15 in order to then move the line exposer 18 in the desired direction X over the construction field 8 and to control it according to the specifications in the control data record for the selective exposure of the construction material. The components required for this Control devices 200 are known in the prior art and are therefore not shown explicitly in FIG. 9 .

Step S2 also contains a sub-step that is not known in the prior art. During the movement of the imagesetter 18, the deviation determination unit 202 shown in FIG. 9 reads out the values supplied by the position measuring units 32a and 32b and compares them with one another. If at a position Xj the difference δj of the values supplied by the position measuring units 32a or 32b exceeds a tolerance value, then the values specified in the control data for this position Xj for the exposure unit 80i are modified by a control data correction unit 203 shown in FIG. The procedure is explained with reference to FIG. 4 for an exemplary exposure unit 80i.

As in the first embodiment, a position error Aij is determined for each position Xj of the line exposer 18 during the movement in the desired direction X, which indicates the difference in the X direction between the actual position of the exposure unit 80i and the position Xj. For this purpose, as in the first embodiment, the difference δj can be converted into an angle ctj and from this Aij can be determined as Aij=Li·sin ctj. Alternatively, however, Aij can also be determined directly as Aij=L/L1•öj, which is also possible in the first embodiment. Here, use is made of the fact that the deviations from straightness are so minimal that, as a good approximation, the difference öj supplied by the position measuring units 32a and 32b, which relates to different positions along the trajectories of the rails 28a and 28b, is equal to Difference of these positions in the target direction X is.

If it is determined at a position Xj that the difference öj of the values supplied by the position measuring units 32a or 32b exceeds a tolerance value, then the control data triples, which define the actuation of the imagesetter units 80i at position Xj, are modified in that the Control data triples (Xj, 80i, Pij) (1<i<n) are replaced by data triples (Xj, 80i, Pi(Xj+Aij)). The modified data triples (Xj, 80i, Pi(Xj+Aij) (1<i<n) now become the Exposure control unit 204 is provided for the selective irradiation of the building material at the exposure position Xj.

If the above-mentioned comparison of the values supplied by the position measuring units 32a and 32b, which is carried out by the deviation determination unit 202, does not result in the tolerance value being exceeded, the read-in control data triples (Xj, 80i, Pij) (1<i<n), which relate to obtain an exposure position Xj in the target direction, forwarded directly from the deviation determination unit 202 to the exposure control unit 204 without involving the control data correction unit 203.

In this way, when the line exposer 18 moves over a layer of the construction material at each position Xj, the position measuring units 32a or 32b are first checked before the line exposer 18 supplies radiation to the construction material at the position Xj.

Modification of the embodiments

It has been shown that the procedure described in the two embodiments is particularly advantageous when a line exposer is used in which exposure units 80 are arranged next to one another not only transversely to the desired direction X but also in the desired direction X. An example of such an imagesetter is described below:

FIGS. 5a to 5c schematically show a view of the imagesetter 18 from below. The direction of movement of the imagesetter over the construction area is indicated by an arrow X. 5a shows how a plurality of laser modules 30 are arranged in mutually offset rows on the underside of the exposer 18. FIG. FIG. 5 b shows how each laser module 30 is formed from a plurality of laser arrays 31 which represent the exposure units or radiation emitters 80 . FIG. 5c shows how each laser array 31 is formed from a plurality of individual lasers 32. FIG. The individual lasers 32 are in the form of semiconductor diode lasers of the VCSEL (vertical cavity surface-emitting laser) or VECSEL (vertical external cavity surface-emitting laser) type. These laser sources have an emission direction perpendicular to the main extension (wafer plane) and a circularly symmetrical beam divergence and are particularly well suited for arrangement in two-dimensional arrays. In the laser array 31 shown in FIG. 5c, the individual lasers 32 are arranged hexagonally, but any other arrangement is possible. All lasers 32 of a laser array 31 are preferably driven simultaneously. The smallest individually controllable exposure unit 80 of the exposer 18 is then the laser array 31 . This has the advantage that if a single laser fails, a complete exposure unit does not fail, but the drop in performance can be compensated for by the other lasers in the laser array.

Several laser arrays 31 are combined to form a laser module 30. Also provided for each laser module 30 is an optical element (not shown in the figure), with which the laser arrays 31 are imaged onto the working plane 7 . Each laser array 31 is imaged onto a picture element (pixel) in the working plane 7 . Each laser module 30 is aimed at a specific area in the working plane 7 . When the imagesetter 18 is moved in the target direction X, the pixels of the switched-on laser arrays 31 form a track.

In the laser module 30 shown in FIG. 5b, the individual laser arrays 31 are arranged in two staggered rows in such a way that the tracks of their image points in the working plane adjoin one another when the laser module 30 moves in the desired direction X. If, for example, the laser arrays 31 have a width of 0.1 mm transversely to the desired direction X (i.e. transversely to the intended direction of movement of the imagesetter) and the optical element has a reducing image scale of 1:5, then the adjacent tracks of the laser arrays 31 have a width of 0.02mm In other words, the imagesetter 18 has a resolution of 0.02 mm in a direction transverse to its intended direction of movement.

In order to utilize the entire width of the exposer 18, a plurality of laser modules 30 are arranged in a row in the direction transverse to the desired direction X. Because of the optical reduction of the laser modules 30 by the optical element, the total width of a track formed when a laser module 30 moves in the desired direction from the pixels of all laser arrays 31 of the laser module 30 is narrower than the laser module 30 itself by the reduction scale. However, the grid dimension of the tracks of all laser modules in a row, i.e. the center distance between the tracks, corresponds to the (unreduced) grid dimension of the laser modules 30. A non-imageable area thus remains between the tracks that can be exposed by a single row of laser modules 30.

In order to enable continuous exposure of the working plane in the direction transverse to the desired direction X, a number of rows of laser modules 30 are therefore arranged in an offset manner with respect to one another. In other words, individual cascades are formed from laser modules 30, which lie one behind the other in the desired direction X, but are offset from one another in the direction transverse to the desired direction X. In FIG. 5a, for example, the leftmost laser modules 30 of the five rows form a cascade. Several such cascades are then arranged next to one another in the direction transverse to the desired direction X. Within each cascade, the laser modules 30 are offset from one another to such an extent that the tracks of the pixels of their laser arrays 31 adjoin one another.

For example, a linesetter just described may contain 108 laser modules, each laser module may contain 32 laser arrays (exposure units), and each laser array may contain 282 VCSELs. In this case, the imagesetter has 3456 individually controllable exposure units (laser arrays).

It should also be mentioned that an angle between the direction of movement of the energy supply unit and the desired direction can also be determined using an autocollimator, which emits a measuring beam parallel to the construction level.

Finally, it should be mentioned that if the direction of movement of the energy supply unit deviates from the target direction, the exposure units will not only be offset in the X direction, but also in the Y direction (i.e. in a plane parallel to the building plane perpendicular to the X direction ) comes, but perishes is at least a factor of 10 less than the offset in the X direction and is therefore usually negligible. However, should the offset in the Y-direction be in the order of magnitude of the distance between the exposure units in the Y-direction, the values of Pij can be offset in the Y-direction for correction, i.e. the value Pij originally assigned to an exposure unit changes in the Y-direction Be assigned direction adjacent exposure unit.

Finally, it should be mentioned that in addition to the described software

Compensation of deviations, compensation by means of hardware is also possible. For this purpose z. B. (especially when correcting an offset in the Y-direction) the position of the optical element can be changed. It would also be conceivable to design the optical element as an array of spatial light modulators, the properties of which could be adjusted accordingly.

Claims

32 patent claims

1 . Calibration method of a device for the layer-by-layer additive manufacturing of a number of objects, the device having: a control device for controlling the layer-by-layer additive manufacturing process, a layer application device that is designed to provide a layer of an amorphous building material on a building base or an already manufactured layer within a building field , and an energy delivery device adapted to solidify specified locations of the provided layer, which are associated with the cross sections of the number of objects in this layer, by delivery of electromagnetic radiation, wherein the energy delivery device is designed to supply electromagnetic radiation to the specified Places to be moved over the construction field and the energy supply device for this movement a predefined target direction (X) is specified and the energy supply device has a number of radiation emitters ern, which are arranged along an arrangement direction (Y) transversely to the predefined target direction (X), and radiation emitters, depending on the specified locations, the control device specifies at which emission locations above the construction field radiation is to be emitted, with the calibration method determining whether the direction of movement (B) of the energy supply device deviates from the predefined target direction (X) during the movement of the energy supply device, and the control device is prompted to specify other emission locations for radiation emitters as a function of a deviation determined.

2. Calibration method according to claim 1, wherein to determine the deviation of the angle (ctj) between the predefined target direction (X) and the direction of movement 33

(B) is determined and it is decided that there is a deviation when this angle (ctj) exceeds a predetermined tolerance angle (ctref).

3. Calibration method according to claim 1 or 2, wherein for the determination of deviations the energy supply device is moved with or without the supply of electromagnetic radiation to the defined points over the construction field.

4. Calibration method according to claim 3, wherein information about positions (XJ) in the target direction (X) at which a deviation was determined is stored in a memory device and for specifying the other emission locations of the radiation emitters based on the information stored in the memory device is accessed.

5. Calibration method according to claim 4, in which the device for layer-by-layer additive manufacturing has an interface for receiving control data for controlling the course of a layer-by-layer additive manufacturing process, the control data having at least one data model of the number of objects to be manufactured, in which radiation emitters are specified, at which emission locations above the construction field radiation is to be emitted for supplying electromagnetic radiation to specified locations of a provided layer, which are assigned to the cross sections of the number of objects in this layer, the control device specifying other emission locations for radiation emitters by making changes in an accepted data model become.

6. The calibration method as claimed in claim 1 or 2, in which the control device is prompted to specify other emission locations for radiation emitters during an additive manufacturing process, preferably during a movement of the energy supply device over the construction field.

7. Calibration method according to one of the preceding claims, in which a deviation is determined only at a predetermined number of positions (XJ) in the desired direction (X).

8. Calibration method according to one of Claims 1 to 6, in which a deviation is determined at positions (XJ) in the desired direction (X) which are at a predetermined distance (Ax) from one another.

9. Calibration method according to one of the preceding claims, wherein it is additionally determined whether the movement of the energy supply device results in a change in the distance between the radiation emitters and the construction area, and if this is the case, the control device is prompted to change the focal position of the radiation emitters emitted change radiation.

10. Device for the layer-by-layer additive manufacturing of a number of objects, which can be calibrated according to a calibration method according to one of claims 1 to 9, wherein the device comprises: a control device for controlling the layer-by-layer additive manufacturing process, a layer application device that is designed to apply a layer of a to provide amorphous construction material on a construction base or an already produced layer within a construction field, an energy supply device which is designed to solidify fixed points of the provided layer, which are assigned to the cross sections of the number of objects in this layer, by supplying electromagnetic radiation, wherein the energy supply device is designed to be moved over the construction field in order to supply electromagnetic radiation to the defined points and a predefined target direction (X) is specified for the energy supply device for this movement, with di e energy supply device comprises a number of radiation emitters arranged along an array direction (Y) transverse to the predefined target direction (X), and radiation emitters depending on the specified ones The control device specifies the emission locations at which radiation is to be emitted above the construction site, and the control device is designed to emit radiation at other emission locations at positions (XJ) in the target direction (X) at which a deviation is determined in the course of the calibration method to pretend

11 . Device according to claim 10 with a linear guide, by which the energy supply device is guided during its movement over the building site.

12. The device as claimed in claim 11, in which the linear guide has two parallel rails which are spaced apart from one another and on which the movement of the energy supply device is guided by means of two carriages.

13. Device according to claim 12, in which the energy supply device is arranged between rails arranged on two sides of the construction field.

14. The device as claimed in claim 10 or 11, further comprising: a position detector which is designed to determine whether the movement of the energy supply device deviates from the predefined target direction (X) in the movement direction (B) of the energy supply device.

15. The device according to claim 12 or 13, further comprising: a position detector, which is designed to determine whether the movement of the energy supply device causes a deviation in the direction of movement (B) of the energy supply device from the predefined target direction (X), the position detector comprises two position measuring units, each of which is attached to one of the two rails and is suitable for determining the position of the respective carriage on the rail.

16. The device as claimed in claim 14 or 15, in which the position detector is designed to determine an angle (ctj) between the predefined desired direction (X) and the direction of movement (B). 36

17. The apparatus of claim 14 or 16, wherein the position detector is a camera located above the power supply device.

18. Device according to one of claims 14 to 17, further comprising: a checking unit which is designed to determine the presence of a deviation if the angle (ctj) determined by the position detector exceeds a predetermined tolerance angle (ctref).

19. Method for the layer-by-layer additive manufacturing of a number of objects, which comprises a calibration method according to one of claims 1 to 9.