FIELD

[0001] The present application relates to a calibration method in the field of added manufacturing. In particular, the present application relates to a calibration method for a 3D-printer.

BACKGROUND

[0002] In the field of additive manufacturing an additive manufacturing apparatus is also called a 3D-printer. In 3D-printing parts or workpieces are built/created/generated by subsequent depositing layers of build material onto each other. Each layer comprises at least one individual bead or strand of said build material). This build material may be any thermoplastic material, e.g. plastic material. Further the depositing process may be the FDM or FFF or FLM process or any other polymer melt dispensing process. The build material supplied to the 3D-printer may be -but not limited to- filament or granulated thermoplastic material. However, the present application is not limited to the aforementioned deposition processes but is applicable where technically feasible.

[0003] The 3D-printer usually comprises at least one printhead that moves in three directions along a printing trajectory or tool path. Also, there are 3D-printers that comprise a printhead that moves in two directions (commonly the X- and Y-direction or axis) and a printbed (the surface or structure on/to which the workpiece(s) are created) that moves in the third direction (commonly the Z-direction or axis). Further, there are printers where the printhead and the printbed move in at least one of X, Y and Z. Further, there are 3D-printers having at least one printhead attached to a robotic arm as they are known form industrial applications.

[0004] When beginning producing a workpiece, the 3D-printer generally needs to be calibrated in order to ensure a high quality of the printed workpiece. However, cali- bration procedures may be included during a print as well in order to compare the actual shape (e.g. height or dimension in the Z direction) with the shape/height the workpiece should have according to the programming. Document US 7,680,555 discloses a calibration method for a 3D-printer.

[0005] There is also the problem that the printbed (e.g. often made from steel, large in sized and heated) may be deformed due to e.g. inconsistent material properties which in turn further may lead to deformed workpieces and a lower quality thereof.

[0006] Also, when printing flexible build materials, strongly warping parts or printing into or onto an already existing structures it is desirable to calibrate the 3D-printer before starting the respective print in order to obtain information regarding an actual height profile. With flexible and or swelling build materials it can be difficult to precisely predict the swelling (e.g. with build materials whose expansion is depending on the temperature in the hotend).

SUMMARY

[0007] It is the object of the present application to overcome the aforementioned disadvantages. This object is attained by the appended independent claim. Selected embodiments are comprised in the dependent claims. Each of which, alone or in any combination with the other dependent claims, can represent an embodiment of the present application.

[0008] According to an aspect of the present application a calibration method for a 3D-printer comprises the steps of printing at least one first structure on a printbed with a first printhead, obtaining a height profile of the at least one first structure and at least partially of the printbed surrounding the at least one first structure, determining at least one maximum ("real height") of the at least one first structure from the height profile, comparing the at least one maximum with at least one predetermined value, control the 3D-printer based on the result of the comparison. The maximum may also be the result of a calculation of multiple measurements, as the maximum or "real hight" might vary as seen along the printed (first) structure. [0009] Obtaining the height profile may be carried out by means of contact sensor (e.g. a touch probe) or contactless (e.g. by means of a vision system). The obtained height profile comprises not only the at least one first structure itself but also a portion of the printbed that surrounds the at least one first structure. Determining the at least one maximum from the obtained height profile may be carried out in the control unit of the 3D-printer. Also, the comparison may be carried out in the control unit of the 3D-printer.

[0010] The predetermined value may be an expected height and or width of the at least one first structure e.g. depending on the programmed data. The dimensions of e.g. a printed bead of build material (first structure) is dependent of multiple factors, e.g. the feed rate of the build material, a nozzle diameter, the distance of said nozzle from the print bed, the speed the nozzle or the print head is moved, etc. Each of the aforementioned factors can be adjusted to achieve various changes regarding the properties of the printed bead of build material. For example, if one would like to influence the width of the printed bead of build material an increase of the feed rate, reduction of the distance between the nozzle and the printbed and decreasing the speed the nozzle (the printhead) is moving with respect to the printbed. Of course, the aforementioned factors are not concluding and only with respect to the example of FFF and a width of a deposited bead of build material. Of course, changing the aforementioned factors may also have influence on other dimensions of the deposited bead of build material like its height.

[0011] The method above may have the advantage that not only the maximum of the at least one first structure is obtained, but also a profile of the printbed surrounding the at least one first structure. This information can be used to adjust relevant parameters of the printing process by comparing the obtained results to expected results based on the programming of the 3D-printer.

[0012] According to an aspect of the present application the step of printing the at least one first structure comprises printing a bead of material that changes direction and comprises the at least one first structure. This may have the advantage that the accuracy of the method can be increased. [0013] According to an aspect of the present application the step of obtaining a height profile comprises a height detection along at least two different detection trajectories that intersect with the at least one first structure. The height detection may be discrete in arbitrary intervals or continuous. This may have the advantage that the accuracy of the method can be increased as the obtained data increases. Also, if the at least one first structure comprises a bead of material that changes direction the at least two different detection trajectories may be oriented such that at least one detection trajectories intersects with the differently oriented bead of material that changes direction. In other words, if the at least one first structure is an angled bead of material (e.g. having two arms angled by 90°) than at least one detection trajectory intersects with one arm and at least one detection trajectory intersects with the other arm.

[0014] According to an aspect of the present application the direction of the at least two detection trajectories differs by 90 degrees. This may have the advantage that the accuracy of the method can be increased.

[0015] According to an aspect of the present application the step of printing at least one first structure further comprises simultaneously printing at least one second structure in a different location from the at least one first structure in the vicinity of the at least one first structure with a second printhead. This may for example be two angled beads of material. This may have the advantage that the accuracy of the method can be increased.

[0016] According to an aspect of the present application each of the at least two detection trajectories intersects with the at least one first structure and the at least one second structure. This may have the advantage of reducing calibration time.

[0017] According to an aspect of the present application the method further comprises a step of taking multiple height measurements of the printbed prior to printing the at least one first structure. This may have the advantage that the accuracy of the method can be increased. [0018] According to an aspect of the present application the maximum comprises at least one maximum height of the structure and/or at least one maximum width of the structure. This may have the advantage that the accuracy of the method can be increased.

[0019] According to an aspect of the present application a calibration method for a 3D-printer comprises the steps of printing at least a first structure on a printbed, moving a detection head and obtaining a first height profile along a detection trajectory, wherein the detection trajectory intersects with at least one first structure, moving the detection head in the opposite direction of the detection trajectory and obtaining a second height profile, comparing the first and the second height profile, controlling the 3D-printer based on the result of the comparison. With this calibration method it is possible to detect/calculate the so called backlash. If for example the gantry system to which a printhead is mounted moves in one direction and then in the opposite direction, then there is a certain backlash due to play in the mechanical system. Said backlash needs to be detected and further compensated as it has a negative influence on the quality of a work piece. The method according to this aspect may have the advantage that a quality of a work piece can be increased.

[0020] According to an aspect of the present application a calibration method for a 3D-printer comprises printing at least a first structure on a printbed, moving a detection head along a detection trajectory and obtaining a first height profile. The detection trajectory at least partially corresponds to the shape at least one first structure and/or intersects with the at least one first structure. In other words, the detection head follows the shape or last layer of a previously printed structure on essentially a printing trajectory that a printhead took to build said last or uppermost layer. Alternatively or additionally, it is also possible to establish a detection trajectory that intersects (also in multiple points) with the at least one first structure. The detection trajectory might for example be a grid pattern that intersects with the at least one first structure.

[0021] The calibration method further comprises the step of comparing the first height profile with a predetermined height profile. The predetermined height profile may be the data that is available from the programming of the at least one first structure. According to the programming to print the at least one first structure said structure has an expected height or height profile.

[0022] The calibration method further comprises the step of controlling the 3D- printer based on the comparison. For example, the deviation of the obtained height profile from the predetermined height profile can be used to increase the part quality.

[0023] According to an aspect of the present application further comprises printing a second structure simultaneously with the first structure and the detection trajectory also comprises the second structure. This may have the advantage that the calibration time can be reduced.

[0024] According to an aspect of the present application the at least one first structure and/or the at least one second structure comprise(s) a bead of material having the shape of a curved line, of at least a partial cercle, of at least an angled bead of material. This may have the advantage that the accuracy of the method can be increased.

[0025] Each of the above aspects is to be considered an invention on its own. The aspects may be freely combined with each other and each feature not described as being dependent on another feature may also be freely combined with each other. The height detection can be accomplished in different ways or with different sensors. Preferably, it is carried out by a contact sensor, physically contacting the printed structures.

BRIEF DESCRIPTION OF THE FIGURES

[0026] Further advantages and features of the present disclosure will be apparent from the appended figure. The figure is of merely informing purpose and not of limiting character. The figure schematically describes an embodiment of the present application. Hence, the appended figures cannot be considered limiting for e.g. the dimensions of the present disclosure. [0027] Fig. 1 depicts examples of different first and second structures and detection trajectories.

[0028] Fig. 2 depicts an example of measurement points and a first and second structure and detection trajectories.

[0029] Fig. 3 a flow chart of a first embodiment of the present application.

[0030] Fig. 4 depicts a flow chart of another embodiment of the present application.

[0031 ] Fig. 5 depicts an example of a height profile.

[0032] Fig. 6 depicts another example of a height profile.

[0033] Fig. 7 depicts a flow chart of another embodiment of the present application.

[0034] Fig. 8 depicts a flow chart of another embodiment of the present application.

[0035] It is to be noted that in the different embodiments described herein same parts/elements are numbered with same reference signs, however, the disclosure in the detailed description may be applied to all parts/elements having the regarding reference signs. Also, the directional terms I position indicating terms chosen in this description like up, upper, down, lower downwards, lateral, sideward are referring to the directly described figure and may correspondingly be applied to the new position after a change in position or another depicted position in another figure. All figures are not to scale and no indication of proportions should be taken. Also is the placement of the first and second structures for explanation purposes only. The number of structures can be chosen at will.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] Initially referring to fig. 1 a schematic printbed 10 with different examples of first 20 and second 30 structures. In figs. 1 and 2 the orientation of a coordinate system is indicated with the x-axis parallel to the left-right-direction in the figs. And the y- axis parallel to the up-down-direction in the figs. The z-axis is perpendicular to a plane spanned by the x and y axes. The first and second structures 20, 30 are printed parallel to the x and y axes. In the top right corner of the printbed 10 two first structures 20 are depicted with a first detection trajectory DT 1 and a second detection trajectory DT2 as well as a third detection trajectory DT3 that are also parallel to the x and y axes, respectively. Hence, the detection trajectories DT1 , DT2 and DT3 intersect each with the structures in an angle of preferably 90°. For this disclosure first structures are printed with a first printhead and second structures are printed with a second printhead.

[0037] Each of the detection trajectories comprises a section on the printbed 10 surrounding the first (and second) structure 20 (and 30), respectively. The arrows in fig. 1 indicate the movement of e.g. a detection head or sensor for obtaining a height profile HP. Here, the sensor moves as indicated in one direction and then returns in the opposite direction. Each time a height profile is obtained and then both height profiles are superimposed. Such example of a height profile is depicted in fig. 6. Essentially, the width of the first structure 20 is obtained (corresponding to fig. 5) by interpretation of the height profile HP. In moving the sensor (sensing device of whose data the height profile is created) in opposite direction on the same detection trajectory the height profile HP depicted in fig. 5 is obtained. The indicated difference D corresponds to the backlash in this detection trajectory. Preferably, the detection trajectories or structures are chosen to be parallel to the axes of e.g. a gantry system. With the axial backlash D a compensation can be provided in order to control the 3D- printer accordingly. This procedure can be applied to the entire disclosure.

[0038] In the top left corner of fig. 1 there is an example of angled first and second structure 20 and 30. Here, they are angled by an angle of 90° and the respective legs are printed parallelly to the x and y axis. On the bottom there are two examples of curved first and second structures 20 and 30. Here, they are in the shape of a quarter circle, however, they can have any curved shape.

[0039] Fig. 7 discloses the above described method. In a step 1000 a detection head or sensor is moved along a detection trajectory DT. Thereby a first height pro- file is obtained. The detection trajectory DT intersects with the at least one first structure 20.

[0040] In step 2000 the detection head is moved in the opposite direction on the same the detection trajectory DT1 and a second height profile is obtained.

[0041] In step 3000 the first and second height profiles are compared, for example superimposed and the difference D can be determined and thus the backlash D.

[0042] In step 4000 the 3D-printer can be controlled based on the result of the comparison. In other words the 3D-printer can be controlled such that the backlash D is compensated.

[0043] In the aforementioned example, the first structure 20 (tip right in fig. 1 ) is not a continuous structure, but printed segments parallel to the x-y-axes. In the top left corner of fig. 1 there are a first 20 and second 30 structure depicted, that change direction by an angle of 90° and are also printed parallel to the x-y-axes. Also, there are three detection trajectories DT1 , DT2 and DT3 that are also parallel to the x-y- axes. In this case the first and second structures 20 and 30 can be printed simultaneously with two printheads.

[0044] Fig. 5 depicts a height profile HP that could be obtained with such an arrangement. The first elevation (seen from the left) is the elevation caused by the first structure 20 having a maximum height M1 and a maximum width W1. The second elevation is caused by the second structure 30 having a maximum height M2 and a maximum width W2. In the examples of figs. 5 and 6 the flat line between the respective elevations is the height of the printbed 10 with is here perfectly even as there are no elevations or depressions in the height profile in the regarding section. However, this could be different in reality and the deviations from the area very close to the structures can also be taken into account in order to compensate for a possible deformation of the printbed 10.

[0045] From known data and the data of the programming of the 3D-printer it is known what the maximum height M and the maximum width W of the printed struc- ture should be. The actual data obtained from the height profile can be used to calibrate the 3D-printer such that the actual data (e.g. maximum height and maximum width) match the expected data from the programming of the 3D-printer.

[0046] Finally, the two curves depicted in fig.1 are examples of first 20 and second 30 structures that comprise curved beads of build material. Essentially, such curved beads of build material can have any shape. Here, they have the shape of quarter circles. However, they could be any curved shape, for example a free formed shape. With the depicted curves, the detection trajectories DT 1 , DT2 and DT3 intersect preferably in an angle of 90° and are parallel to the x-y-axes.

[0047] Fig. 3 depicts with a flow chart an embodiment of a calibration method. In step 100 at least one first structure 20 is printed with a first printhead on a printbed 10.

[0048] In step 200 a height profile HP of the at least one first structure 20 and at least partially of the printbed 10 surrounding the at least one first structure 20 is obtained, e.g. by means of a sensor or detection head.

[0049] In step 300 a maximum (e.g. maximum height and/or maximum width) is determined from the height profile HP.

[0050] In step 400 the at least one maximum is compared with at least one predetermined value as described above.

[0051] In step 500 the 3D-printer is controlled based on the result of the comparison as described above.

[0052] Fig. 4 depicts with a flow chart another embodiment of a calibration method similar to the method of fig. 3. In step 10 multiple height measurements of the printbed 10 are taken. Fig. 2 is an exemplary visualisation of the method depicted in fig.

4. The multiple measuring points 40 for the height measurements are depicted in an evenly spread patten across the printbed 10. However, the number of measurement points as well as their arrangement can be freely chosen. A pattern of first 20 and second 30 structures with the detection trajectories DT 1 and DT2 are placed on the printbed 10 corresponding to the regarding disclosure of fig. 1.

[0053] In a step 100 at least one first structure 20 is printed on a printbed 10 with a first printhead. Simultaneously, at least one second structure 30 is printed on a printbed 10 with a second printhead.

[0054] In a step 200 a respective height profile HP1 , HP2 of the at least one first and second structures 20, 30 and at least partially of the printbed 10 surrounding the at least one first and second structures is obtained, as this is disclosed with regard to fig. 5 above.

[0055] In step 300 at least one respective maximum M, W of the at least one first and second structures 20, 30 from the height profiles HP1 , HP2 is obtained, as this is disclosed with regard to fig. 5 above.

[0056] In step 400 the at least one maximum M, W with at least one predetermined value is carried out, as described above.

[0057] In step 500 the 3D-printer is controlled based on the result of the comparison as described above.

[0058] Fig. 8 depicts with a flow chart another embodiment of a calibration method. In step 600 a detection head is moved along a detection trajectory DT and a first height profile HP is thereby obtained. The detection trajectory DT corresponds at least partially to the shape of at least one first structure 20 and/or intersects with the at least one first structure 20. Taking fig. 1 as an example here, the detection head could follow the shape of the at least one first structure 20 and thus move in at least partially a circle. Of course the first height profile could include the second structure 30 as well. Additionally or alternatively, the probe head could move an a detection trajectory that includes multiple passes of the at least one first structure 20. These can be for example a pattern comprising parallel passes like a comb. [0059] In step 610 the first height profile HP is compared with a predetermined height profile. The predetermined height profile can be for example an expected height profile base on the data that were used to print the at least first structure 20.

[0060] In step 620 the 3D-printer is controlled based on the result of the comparison. This could be that differences between the first height profile and the predetermined height profile can be used to provide for compensation.

[0061] In all figures like reference signs are used for like or similar parts/elements as in the other figures. Thus, a detailed explanation of such part/element will only be given one for the sake of brevity. Reference numbers like first and second, as in first detection trajectory and second detection trajectory are meant for distinguishing purposes only, as the order may be changed voluntarily. In the above methods depicted in figs. 7 and 8 at least a first structure 20 is printed on the printbed 10 prior to the respective first step.

[0062] The embodiments depict possible variations of carrying out the subject matter of the application, however, it is to be noted that the subject matter of the application is not limited to the depicted embodiments/variations but numerous combinations of the here described embodiments/variations are possible and these combinations lie in the field of the skills of the person skilled in the art being motivated by this description.

[0063] The scope of protection is determined by the appended claims. The description and drawings, however, are to be considered when interpreting the claims. Single features or feature combinations of the described and/or depicted features may represent independent inventive solutions. The object of the independent solutions may be found in the description. If an 3D-printer comprises more than two printheads then more structures being parallel to each other can be printed. Essentially each printhead prints its structure parallel to the structures of the other printheads.

[0064] It is further to be noted that for a better understanding parts/elements are depicted to some extend not to scale and/or enlarged and/or down scaled. List of reference signs

10 printbed

20 first structure

30 second structure

40 measuring point

HP height profile

M maximum height

W maximum width

DT detection trajectory

DT1 first detection trajectory

DT2 second detection trajectory

DT3 third detection trajectory

D axial backlash