Method for determining the thickness of layers added to a 3D model for manufacturing

Abstract

The present invention relates to a method for determining the layer thickness (t) of a three-dimensional model (1) produced by an additive manufacturing device, the method comprising: a step of determining the layer thickness (t) according to an adaptive slicing algorithm, in which the thickness of the layer (2) is calculated based on the relationship of the inclination of the normal vector (n) of the surface element (s) of the 3D model (1), and the surface element (s) of the 3D model (1) at least partially encloses the layer (2) from the horizontal direction (x; y); the method is characterized by further comprising: a step of selectively applying, on at least one surface element (s) of the 3D model (1), a precision requirement selected from one or more selectable different precision requirements, and the one or more selectable different precision requirements respectively differently change the relationship of the inclination with respect to the normal vector (n) of the at least one surface element in the determining step, which allows, by the changed relationship, the layer thickness (t) to obtain a value smaller or larger than the layer thickness (t) determined by the unchanged relationship.

Description

Technical Field

[0001] The present invention relates to an additive manufacturing system having an additive manufacturing device. The present invention more particularly relates to a method for determining the layer thickness of a three-dimensional model to be produced by an additive manufacturing device. Background Art

[0002] In additive manufacturing, a three-dimensional model is printed layer by layer by light-based curing of a liquid printing medium, i.e., a liquid photocurable resin, which selectively cures under the influence of ultraviolet radiation. In known variants of additive manufacturing such as SL (stereolithography) or DLP (digital light processing), the 3D object is preferably pulled downwards from the liquid printing medium by a platform. The duration of the printing process depends on factors such as the number of layers to be printed. Thus, printing a 3D model in many thin layers takes longer than printing in a few thick layers. The layer thickness of the printed 3D model defines the resolution of the printing process in the printing direction (hereinafter referred to as the z-direction). For detailed printing and high resolution in the z-direction, it is therefore necessary to select thin layers at the expense of the printing speed. However, depending on the geometry of the 3D model to be printed and its orientation in the printing volume, not every z-position requires the same resolution, i.e., layer thickness. Surface elements with a normal vector perpendicular to the z-axis deviate less from the desired geometry than surface elements with a normal vector parallel to the z-axis, even at large layer thicknesses. For comparison, this is shown in Figure 1 and Figure 2 by using the example of a sphere. The "staircase effect" and thus the deviation of the printed 3D model from the desired geometry are more pronounced at the top and bottom of the sphere (where the surface normals are equivalent to being parallel to the z-axis) than in the middle (where the surface normals are equivalent to being perpendicular to the z-axis). At the top and bottom, thin layers are necessary to accurately reproduce the desired geometry, while in the middle, the desired geometry can be well reproduced even with thick layers.

[0003] With the so-called "adaptive slicing" method, the local layer thickness is calculated based on the geometry of the 3D model to be printed, such that the maximum value of the layer thickness is set to the required reproduction accuracy (hereinafter referred to as the standard or reference accuracy requirement), and thus the duration of the printing process is minimized. This selection of layer thickness is shown in Figure 3 and the staircase effect is the same regardless of the z-position, as shown in Figure 3As shown. In the adaptive slicing method, the layer thickness is determined according to an adaptive slicing algorithm, wherein the layer thickness is calculated based on the relationship of the inclination of the normal vector of the surface elements of the 3D model, and the surface elements of the 3D model at least partially enclose the layer in the horizontal direction. When the normal vector of such a surface element has the minimum inclination and is perpendicular to (or parallel to) the z-axis, the calculated layer thickness has the maximum (or minimum) value. For a rotationally asymmetric model, for a given z interval, the surface element with the smallest angle between its normal and the z-axis always determines the corresponding layer thickness. In addition, the calculated layer thickness is limited by a minimum value and a maximum value. Using this well-known adaptive slicing method, a constant printing accuracy, such as a standard accuracy requirement, can be achieved for the entire 3D model.

[0004] In the journal Computer-Aided Design, Volume 107 (2019), pages 89-101, an adaptive slicing based on efficient contour analysis was disclosed by H. Mao et al.

[0005] Using the adaptive slicing method cannot further reduce the number of layers and thus further reduce the printing duration. Therefore, this printing duration must be accepted, otherwise, a lower printing quality must be accepted.

[0006] In many dental 3D objects, the same printing accuracy is not required for each surface element of the 3D object. An example of such a 3D object is a drilling template. At the top of the drilling template, no special accuracy is required compared to those parts where the template rests on the tooth or the drill bit is guided. However, the adaptive slicing method cannot be flexibly applied to such dental 3D models to allow further reduction of the printing time without reducing the overall printing quality.

[0007] US2014 / 0203463 A1 discloses a drilling guide that uses multi-layer materials with different mechanical properties to achieve the common goals of rigidity, assembly, and retention. For example, a rigid outer shell and a soft interior are used together to firmly and precisely assemble the drilling guide to the surgical site. SUMMARY OF THE INVENTION

[0008] An object of the present invention is to overcome the disadvantages of the prior art in a flexible manner and provide a method for determining the layer thickness of a three-dimensional model produced by an additive manufacturing device.

[0009] The present invention provides a method for determining the layer thickness of a three-dimensional model produced by an additive manufacturing device (hereinafter referred to as the modified adaptive slicing method). The method includes: a step of determining the layer thickness according to an adaptive slicing algorithm, wherein the thickness of the layer is calculated based on the relationship of the inclination of the normal vector of the surface elements of the 3D model, and the surface elements of the 3D model at least partially enclose the layer from the horizontal direction. The method is characterized in that it further includes: a step of selectively applying, on at least one surface element of the 3D model, one accuracy requirement selected from one or more selectable different accuracy requirements, and the one or more selectable different accuracy requirements respectively differently change the relationship of the inclination with respect to the normal vector of the at least one surface element in the determination step.

[0010] The main advantageous effect of the present invention is that the existing method in 3D printing, namely the above-mentioned adaptive slicing method, is further modified to achieve an improvement in the printing process with respect to the printing duration by further allowing the selective application of accuracy requirements to surface elements. Thus, surface elements with high accuracy requirements can be printed relatively finely, while surface elements with low accuracy requirements can be printed relatively coarsely. Therefore, for example, low accuracy requirements for certain surface elements can be used to save additional layers in the modified adaptive slicing method, and thus the printing process can be further accelerated. In addition, high accuracy requirements for certain surface elements can be used to print additional layers, so the printing accuracy can be further improved locally without relatively extending the printing process.

[0011] According to the present invention, the selectable different accuracy requirements may include at least one of a high accuracy requirement and a low accuracy requirement. Through the changed relationship, the high accuracy requirement allows the layer thickness to obtain a value smaller than the layer thickness determined by the unchanged relationship corresponding to the reference accuracy requirement. Thus, compared with applying a high accuracy requirement to the entire 3D model in the well-known adaptive slicing method, the printing accuracy can be improved locally, and thus the extension of the printing duration can be relatively reduced. Through the changed relationship, the low accuracy requirement allows the layer thickness to obtain a value larger than the layer thickness determined by the unchanged relationship corresponding to the reference accuracy requirement. Thus, the printing accuracy can be locally reduced, and thus the printing duration can be further shortened. The reference accuracy requirement is between the low accuracy requirement and the high accuracy requirement.

[0012] According to the present invention, the accuracy requirement with the highest printing accuracy can determine the layer thickness, such that among the layer thicknesses calculated for the surface elements corresponding to the same layer, the minimum value applied through the relationship and through one or more different changed relationships is determined as the layer thickness.

[0013] According to the present invention, the selective application step can be automatically performed by a software algorithm based on the characteristic features of the 3D model to be manufactured and / or the characteristics of the manufacturing process. For example, if the 3D model is a drilling template, then at the top of the drilling template, compared to the parts where the template rests on the tooth or the drill bit is guided, a lower precision requirement may be applied. At the parts where the template rests on the tooth or the drill bit is guided, a higher precision requirement may be applied. The drilling template is preferably printed as a single piece using the same photocurable resin during the layer-by-layer printing process. Alternatively, the software algorithm can allow the selective application step to be performed manually. In the manual selective application step, the user can selectively mark on the display of the 3D model the surface elements to which a precision requirement selected from one or more selectable different precision requirements will be applied. The marking can be performed by an input device such as a keyboard or a mouse, etc.

[0014] According to the present invention, the selective application of the precision requirements in the selective application step can be further restricted in various alternative ways, for example, to prevent an undesired extension of the printing accuracy or the printing duration. In a first alternative, one or more surface elements of the 3D model can be selected, on which one or more precision requirements can be selectively applied. Alternatively, one or more surface elements of the 3D model can be selected, on which one or more precision requirements must not be applied.

[0015] According to the present invention, the determined layer thickness is constrained by a maximum value and a minimum value. The maximum value and the minimum value can be preset in the software algorithm or manually set by the user according to standard or reference precision requirements. Different pairs of maximum and minimum values can be selectively set by the user.

[0016] The present invention also provides a computer program having code, namely a software algorithm for causing a computer-based system to perform the above method. The computer program can be stored on a computer-readable storage device independent of or provided together with the computer-based system. The computer-based system can have a display for displaying the 3D model to the user, and an input device for allowing the user to selectively mark surface elements on the display of the 3D model or input other relevant information such as setting information related to the software algorithm. The computer-based system can be provided as a computer-based additive manufacturing system or device for performing the above method and generating a 3D object corresponding to the 3D model. The computer-based system can also be provided with a post-processing device for post-processing (washing, drying, curing) the 3D object generated using the computer-based additive manufacturing device. Description of the Drawings

[0017] In the following description, other aspects and advantageous effects of the present invention will be described in more detail by using exemplary embodiments and referring to the drawings, wherein

[0018] Figure 1 is a three-dimensional spherical model having a thin layer according to a comparative example;

[0019] Figure 2 is another three-dimensional spherical model having a thick layer according to another comparative example;

[0020] Figure 3 is another three-dimensional spherical model having layers determined only by an adaptive slicing algorithm known in the prior art;

[0021] Figure 4 is another three-dimensional spherical model according to an embodiment of the present invention, having layers determined by a modified adaptive slicing algorithm;

[0022] Figure 5 is another three-dimensional spherical model according to another embodiment of the present invention, having layers determined by a modified adaptive slicing algorithm.

[0023] The reference numerals shown in the drawings denote the elements listed below and will be referred to in the subsequent description of the exemplary embodiments:

[0024] 1. 3D model (object)

[0025] 2. Layer

[0026] t: layer thickness

[0027] n: normal vector

[0028] s: surface element

[0029] x, y: horizontal direction

[0030] L: low precision requirement

[0031] R: reference precision requirement DETAILED DESCRIPTION

[0032] The present invention provides a method for determining the layer thickness (t) of a three-dimensional model (1) produced by an additive manufacturing device. The method includes: a step of determining the layer thickness (t) according to an adaptive slicing algorithm, wherein the thickness of the layer (2) is calculated based on the relationship of the inclination of the normal vector (n) of the surface element (s) of the 3D model (1), and the surface element (s) of the 3D model (1) at least partially encloses the layer (2) from the horizontal direction (x; y). Figure 3 A sphere is shown as a comparative example of the 3D model (1), and its layer thickness (t) has been determined according to the adaptive slicing algorithm known in the prior art.

[0033] The method of the present invention further includes the step of selectively applying, to at least one surface element of the 3D model (1), a precision requirement selected from one or more selectable different precision requirements, where the one or more selectable different precision requirements respectively differently change the relationship of the inclination of the normal vector (n) of the at least one surface element (s) in the determination step. Figure 4 Shows a sphere as an example of the 3D model (1), the layer thickness (t) of which has been determined according to an embodiment of the present invention. In this embodiment, the one or more selectable different precision requirements include at least one low-precision requirement (L), and this low-precision requirement allows the layer thickness (t) to obtain a value greater than the layer thickness (t) determined by the unchanged relationship through the changed relationship. As Figure 4 shown, the low-precision requirement (L) is selected and applied to the entire upper hemisphere, marked with a thick arc. In this simplest embodiment, in the determination of the layer thickness (t), the surface elements (s) with the low-precision requirement (L) are regarded as if their normal vectors (n) are all perpendicular to the z-axis. Therefore, in the determination step, the relationship of the inclination with respect to the normal vector (n) of the surface elements (s) is changed. Thus, these surface elements (s) do not result in the same layer thickness (t), as Figure 3 shown and calculated according to the unchanged relationship based on the true geometry by the adaptive slicing algorithm. As Figure 4 shown, in the upper hemisphere with the low-precision requirement (L) marked with a thick arc, the maximum value obtained for all layer thicknesses (t) is greater than Figure 3 the maximum value of the corresponding layer (2) in the comparative example of the 3D sphere in , while in the lower hemisphere, the adaptive slicing algorithm applies as usual, that is, with the reference precision requirement (R).

[0034] Figure 5 Shows another sphere as an example of the 3D model (1), the layer thickness (t) of which has been determined according to an embodiment of the present invention. As Figure 5 shown, the low-precision requirement (L) is selected and applied only to the entire upper left half hemisphere marked with a thick arc, and is thus controlled by the upper right half hemisphere that does not have the low-precision requirement (L) but has a higher reference precision requirement (R). In this embodiment, among the layer thicknesses (t) calculated for the surface elements (s) corresponding to the same layer (2) through the relationship and applied through one or more different changed relationships, the minimum value is determined as the layer thickness (t). Therefore, although the low-precision requirement (L) is applied to the upper left half hemisphere, these surface elements (s) result in the same layer thickness (t), as Figure 3 shown. Thus, the adaptive slicing algorithm applies as usual, that is, with the reference precision requirement (R).

[0035] The present invention is not limited to a low precision requirement (L). In another embodiment (not shown), one or more alternative different precision requirements include at least one high precision requirement, which allows, through a modified relationship, a layer thickness (t) to obtain a value less than the layer thickness (t) determined by the unmodified relationship corresponding to a reference precision requirement (R).

[0036] The reference precision requirement (R) lies between the low precision requirement (L) and the high precision requirement.

[0037] In another embodiment, the method includes the step of displaying a 3D model (1) to a user on a display; and the step of allowing the user to selectively mark surface elements (s) on the display of the 3D model (1), for which surface elements (s), a precision requirement selected from one or more alternative different precision requirements is imposed.

[0038] In another embodiment, the method includes the step of selecting one or more surface elements (s) of the 3D model (1) on which one or more precision requirements can be selectively imposed. In an alternative embodiment, the method includes the step of selecting one or more surface elements (s) of the 3D model (1) on which one or more precision requirements shall not be imposed. By any of the alternative embodiments in the alternative embodiment, the selective imposition of precision requirements can be restricted.

[0039] In another embodiment, the determined layer thickness (t) is constrained by a maximum value and a minimum value preset or adjustable by the user.

[0040] Comparative examples of 3D spheres shown respectively in Figures 1 to 3 can also be obtained by the method of the present invention. For example, Figure 1 the 3D sphere in Figure 3 can be obtained by imposing a high precision requirement on the entire surface, i.e., on all surface elements (s). Thus, all surface elements with a high precision requirement are considered to have their normal vectors (n) parallel to the z-axis, and thus the minimum value obtained for all layer thicknesses (t) is equal to or less than

[0041] For example, Figure 2 the 3D sphere in Figure 3 can be obtained by imposing a low precision requirement (L) on the entire surface, i.e., on all surface elements (s). Thus, all surface elements (s) with a low precision requirement (L) are considered to have their normal vectors (n) perpendicular to the z-axis, and thus the maximum value obtained for all layer thicknesses (t) is equal to or greater than

[0042] For example,Figure 3 The 3D sphere in Figure 3 can be obtained by not imposing either different high / low precision requirements on the entire surface. Thus, all surface elements (s) are processed according to the true geometry, and therefore the adaptive slicing algorithm applies as usual, i.e., with the reference precision requirement (R).

Claims

1. A method for determining the layer thickness (t) of a three-dimensional model (1), the three-dimensional model (1) being for generating a corresponding three-dimensional object by an additive manufacturing device, the method comprising: A step of determining the layer thickness (t) according to an adaptive slicing algorithm, wherein the thickness of the layer (2) is calculated by defining a reference accuracy requirement (R) and based on the relationship of the inclination of the normal vector (n) of the surface element (s) that at least partially encloses the layer (2) from the horizontal direction (x; y) of the three-dimensional model (1); The method is characterized in that it further comprises: A step of selectively applying, on at least one surface element (s) of the three-dimensional model (1), an accuracy requirement selected from one or more selectable different accuracy requirements, wherein the one or more selectable different accuracy requirements respectively differently change the relationship of the inclination of the normal vector (n) with respect to the at least one surface element (s) in the determining step, wherein the one or more selectable different accuracy requirements include at least one of a high accuracy requirement and a low accuracy requirement (L), and the high accuracy requirement allows the layer thickness (t) to obtain a value smaller than the layer thickness (t) determined by the unchanged relationship through the changed relationship; and The low accuracy requirement allows the layer thickness (t) to obtain a layer thickness (t) value greater than the layer thickness (t) determined by the unchanged relationship through the changed relationship, wherein the reference accuracy requirement (R) is between the low accuracy requirement (L) and the high accuracy requirement, wherein, among the layer thicknesses (t) calculated by the relationship for the surface elements (s) corresponding to the same layer (2) and applied through one or more differently changed relationships, the minimum value is determined as the layer thickness (t).

2. The method according to claim 1, characterized in that, It further comprises: A step of selecting one or more surface elements (s) of the three-dimensional model (1) on which one or more accuracy requirements can be selectively applied.

3. The method according to claim 1 or 2, characterized in that, It further comprises: A step of selecting one or more surface elements (s) of the three-dimensional model (1) on which one or more accuracy requirements shall not be applied.

4. The method according to claim 1 or 2, characterized in that It further comprises: A step of displaying the three-dimensional model (1) to the user on a display; and A step of allowing the user to selectively mark the surface elements (s) on the display of the three-dimensional model (1), and an accuracy requirement selected from one or more selectable different accuracy requirements will be applied to the surface elements (s).

5. The method according to claim 1 or 2, characterized in that, The determined layer thickness (t) is constrained by a maximum value and a minimum value.

6. The method according to claim 1 or 2, characterized in that, The selective application step is also based on the characteristic features of the three-dimensional model (1) to be manufactured and / or the characteristics of the additive manufacturing process.

7. A three-dimensional object corresponding to the three-dimensional model (1) determined by the method according to any one of claims 1 to 6, characterized in that, The three-dimensional object is a one-piece dental drilling template, wherein, compared with those parts where the template rests on the tooth or guides the drill bit, the accuracy requirement applied at the top of the drilling template is a low accuracy requirement (L), while at those parts where the template rests on the tooth or guides the drill bit, the applied accuracy requirement is a high accuracy requirement.

8. A computer program product comprising code for causing a computer-based system to perform the method according to any one of claims 1 to 6.

9. A computer-readable storage device comprising the computer program product according to claim 8.

10. A computer-based system adapted to perform the steps of the method according to any one of claims 1 to 6.

11. The computer-based system according to claim 10, further comprising: a display for displaying the three-dimensional model (1) to a user; and an input device for allowing a user to selectively mark the surface element(s) on the display of the three-dimensional model (1).

12. The computer-based system according to claim 10 or 11, wherein, The computer-based system further comprises an additive manufacturing device for generating the three-dimensional object.

13. The computer-based system according to claim 12, wherein The computer-based system further comprises a post-processing device for post-processing the three-dimensional object generated by the additive manufacturing device.

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