Method of determining the orientation of a three-dimensional model for additive manufacturing

Abstract

A method of determining the orientation of a 3D Model to be generated by an additive manufacturing apparatus having a vat for holding photocurable material; and a platform for holding the 3D object corresponding to the 3D model. The platform is relatively movable with respect to the vat and the method includes a step of defining the surface geometry of the 3D model and the surface geometry includes surface segments s.sub.i.

Claims

1. A method of determining the orientation of a 3D Model to be generated by an additive manufacturing apparatus having: a vat for holding photocurable material; and a platform for holding the 3D object corresponding to the 3D model wherein the platform is relatively movable with respect to the vat, the method comprising: a step of defining the surface geometry of the 3D model, wherein the surface geometry includes a plurality of surface segments s.sub.i, wherein i denotes an integer, and A.sub.i denotes the surface area of the i.sup.th surface segment s.sub.i; the method further comprising: a step of assigning, either manually by the user or automatically by a computer program, one or more weighing factors i to the surface segments si respectively, wherein the weighing factor i is indicative of a degree of sensitivity of each of the surface segments s.sub.i against effects arising from mechanical removal of any support structure thereon, wherein the weighing factor i is larger than 1 for surface segments s.sub.i which are considered as being sensitive against effects mi sing from mechanical removal of any support structure, and for all other surface segments s.sub.i, i is equal to 1; a step of defining an evaluation function $R\left(,\right)=-\frac{{.Math.}_i{f}_i{p}_{\mathrm{supp},i}}{{.Math.}_i{A}_i}$ wherein and respectively denote the polar and, the azimuth angles of the 3D object relative to the building direction, p.sub.supp,i denotes a probability indicative of the need of the individual surface segments s.sub.i to be supported through a support structure, and, the summations denoted with extend over all surface segments s.sub.i and a step of determining the orientation of the 3D model relative to the building direction based on the evaluation function R through optimization with respect to the polar and the azimuth angles and , respectively, to avoid or reduce as a need of support structures in sensitive surface segments of the 3D model; wherein in the evaluation function
p.sub.supp,i=A.sub.i{right arrow over (n)}.sub.i(,).Math.{right arrow over (e)}.sub.z n.sub.i(,) denotes the normal vector of the i.sup.th surface segment s.sub.i, .sub.z denotes the unit vector in the vertical direction perpendicular to the platform and pointing in the building direction, and denotes the scalar product; wherein the evaluation function R directly controls support structure placement by the additive manufacturing apparatus during the layer-by-layer printing process; a step of automatically controlling the additive manufacturing apparatus based on the determined orientation to physically position the 3D object on the platform according to the optimized polar and azimuth angles and ; and a step of automatically generating, by the additive manufacturing apparatus, support structures at locations determined by the optimized orientation, wherein the support structures are positioned to avoid attachment to surface segments s.sub.i having weighing factors i>1.

2. The method according to claim 1, wherein the surface geometry of the 3D model is represented by triangulation, where the i.sup.th surface segment s.sub.i is a triangle with the surface area A.sub.i.

3. The method according claim 1, wherein the assigning step is performed manually by the user through marking, on a display of the 3D model, one or more surface segments s.sub.i respectively with weighing factors .sub.i.

4. The method according to claim 1, wherein the assigning step is performed through a computer program which comprises a neural network which has been trained for classifying regions of the 3D models based on its local surface geometry and assigns weighing factors .sub.i to the surface segments based on the region classification.

5. A non-transitory computer-readable storage medium which stores the computer-program according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the subsequent description, further aspects and advantageous effects of the present invention will be described in more detail by using exemplary embodiments and by referring to the drawings, wherein

(2) FIG. 1is a schematic vertical cross-sectional view of a hemisphere as a 3D model according to an embodiment, wherein the curved surface indicated with the bold section has been assigned a weighing factor >1 which is considered as being sensitive against post-processing;

(3) FIG. 2is a schematic vertical cross-sectional view of a hemisphere as a 3D model according to an alternative embodiment wherein the flat surface indicated with the bold section has been assigned a weighing factor >1 which is considered as being sensitive against post-processing.

DETAILED DESCRIPTION OF THE INVENTION

(4) The reference numbers shown in the drawings denote the elements as listed below and will be referred to in the subsequent description of the exemplary embodiments:

(5) 1. 3D Model

(6) i: Integer s: Surface segment s.sub.i: i.sup.th surface segment : Weighing factor, .sub.i: Weighing factor assigned to the i.sup.th surface segment A.sub.i: Surface area of the i.sup.th surface segment R(,): Evaluation function : Polar angle : Azimuth angle {right arrow over (n)}.sub.i (,): Normal vector of the i.sup.th surface segment {right arrow over (e)}.sub.z: Unit vector in the vertical direction

(7) FIG. 1 is a schematic vertical cross-sectional view of a hemisphere as a 3D model (1) whose orientation has been determined through the method according to an embodiment of the present invention.

(8) In a defining step of the method, the surface geometry of the 3D model (1) is initially defined. The surface geometry includes a plurality of surface segments s.sub.i, where i is an integer. The surface geometry of the 3D model (1) is preferably represented by triangulation, where the i.sup.th surface segment is a triangle (not shown) with the surface area A.sub.i. In a further defining step an evaluation function R is defined such that

(9) $R=-\frac{{.Math.}_i{f}_i{p}_{\mathrm{supp},i}}{{.Math.}_i{A}_i}$

(10) The evaluation function R depends on weighing factors .sub.i which indicate a degree of sensitivity of the surface segments s.sub.i respectively against effects from removal of any support structure and on p.sub.supp,i which denotes the probability that a surface segment s.sub.i will need to be supported through a support structure. The summations denoted with extend over all surface segments s.sub.i.

(11) A shown in FIG. 1, the entire curved surface indicated with the bold section has been assigned a weighing factor >1 which is considered as being sensitive against post-processing. The flat surface has been assigned a weighing factor =1. In a determining step, the orientation of the 3D model (1) is determined relative to the building direction based on the evaluation function R with the assigned weighing factors . In FIG. 1 the hemisphere i.e., the 3D model (1) is oriented in the optimized direction for which R is maximum. The 3D model (1) can be generated by an additive manufacturing apparatus (not shown). The additive manufacturing apparatus has a vat for holding a photocurable material, and a platform for holding the 3D object corresponding to the 3D model (1). The platform is relatively movable with respect to the vat. When generating the 3D model (1) with an additive manufacturing apparatus all support structure will be located on the flat surface, and thus the curved surface will be protected from effects arising from mechanical removal of the support structures.

(12) FIG. 2 is a schematic vertical cross-sectional view of a hemisphere as a 3D model (1) according to an alternative embodiment. In this alternative embodiment, the curved surface indicated with the bold section has been assigned a weighing factor =1. The flat surface has been assigned a weighing factor >1 which is considered as being sensitive against effects arising from mechanical removal of the support structures. In FIG. 2, the hemisphere i.e., the 3D model (1) is oriented in the optimized direction for which R is maximum. When generating the 3D model (1) with an additive manufacturing apparatus all support structure will be located on the curved surface, and thus the flat surface will be protected from mechanical post-processing.

(13) The above two exemplary embodiments in FIG. 1 and FIG. 2 have been chosen to demonstrate the invention by using a relatively simple 3D model (1). Of course, the method can be easily applied to more complex geometries like dental restorations and the like.