摘要：
A method for dimensional compensation of a 3D object to be formed by an apparatus for the layerwise manufacture of objects from build material comprises receiving an object model to form a corresponding object in an apparatus for the manufacture of objects, positioning the model in a virtual build volume representing an actual build volume of the apparatus in which the object is to be formed, and determining a reference point for the object model, such as a centre of mass/gravity, to determine a location within the volume. A scaling factor corresponding to the model location is selected from a scaling factor map 30 comprising a plurality of predetermined scaling factors 40 corresponding to a plurality of location within the volume, and the factor is then applied to the object model. This allows for compensation for differential shrinkage within a build volume during additive manufacturing, such as powder bed fusion.
权利要求：
CLAIMS
1. A method for dimensional compensation of a 3D object to be formed by an apparatus for the layerwise manufacture of 3D objects from build material, the method comprising: - receiving an object model to form a corresponding object in an apparatus for the layerwise manufacture of objects;
- positioning the object model in a virtual build volume representing an actual build volume of the apparatus in which the object is to be formed;
- determining a reference point for the object model, the reference point determining a location within the virtual build volume;
- selecting, from a scaling factor map comprising a plurality of predetermined scaling factors, a scaling factor corresponding to the object model location, each scaling factor corresponding to one or more of a plurality of locations within the virtual build volume; and - applying the scaling factor to the object model.
2. The method of claim 1, comprising determining the reference point for the object model based on the volume and/or shape of the object model.
3. The method of claim 2, wherein the reference point is the centre of gravity or the centre of mass of the object model.
4. The method of claim any preceding claim, wherein the scaling factor map is a 2D map defining a predetermined scaling factor for each of a plurality of vertical zones extending upwards through the virtual build volume.
5. The method of claim 4, wherein the two or more vertical zones correspond to substantially the same scaling factor.
6. The method of claim 4 or claim 5, wherein the scaling factor selected for a reference point within a vertical zone at or near the centre of the virtual build volume is larger than the scaling factor selected for a reference point within a vertical zone at or near a vertical boundary of the virtual build volume.
7. The method of any one of claims 1 to 3, wherein the virtual build volume comprises a plurality of vertical zones extending upwards through the virtual build volume, and wherein each vertical zone comprises a plurality of vertically stacked sub zones, each sub zone
corresponding to a respective predetermined scaling factor, such that the scaling factor map is a 3D scaling factor map.
8. The method of claim 7, wherein the scaling factor selected for a reference point within a sub zone located at or near the top of the virtual build volume is larger than a scaling factor selected for a reference point within a sub zone located at or near the floor of the virtual build volume.
9. The method of any preceding claim, wherein the virtual build volume is a reduced virtual build volume smaller in at least one dimension than the actual build volume; the method comprising:
- positioning the one or more object models in the reduced virtual build volume; - expanding the reduced virtual build volume comprising the one or more object models to the dimensions of the actual build volume by an expansion transformation, wherein the expanded virtual build volume comprises the one or more object models expanded within the expanded virtual build volume;
- determining the reference point for each expanded object model; and
- applying the selected scaling factor to the expanded object model.
10. The method of any preceding claim, wherein each scaling factor is predetermined for one or more coordinates within each zone, or sub zone, wherein, for a reference point falling outside the one or more coordinates of a zone, an interpolated scaling factor is determined based on the scaling factor of that zone or sub zone and at least one further scaling factor of an adjacent zone or sub zone.
11. The method of any preceding claim, further comprising, after applying the scaling factor, generating slices by dividing the virtual build volume into a stack of parallel planar slices stacked in the vertical direction, the vertical direction corresponding to the layering direction of the layers in the actual build volume; wherein each slice comprises voxels defining a cross section of the one or more object models, and wherein a plurality of voxels correspond to each zone or sub zone.
12. The method of claim 11, wherein generating the slices comprises dividing the virtual build volume into groups of slices, wherein each group comprises one or more slices of the same slice thickness, and wherein the slice thickness is progressively increased from one
group to the next, such that the slice thickness of an upper group is greater than the slice thickness of a lower group with respect to the vertical direction.
13. The method of claim 12, wherein the slice thickness is increased non-linearly in the layering direction.
14. The method of claim 12 or claim 13, wherein the slice thickness of the upper group is larger than an intended layer thickness to be formed in the actual build volume, and wherein the intended layer thickness is constant for all layers.
15. The method of claim 11, wherein the slices are evenly spaced, the method further comprising, forming the one or more objects based on the generated slice data, and controlling a platform supporting the layers to create a recess in a work surface over which build material is spread, whereby the recess is filled with particulate material to form a layer, wherein controlling the platform comprises lowering the platform by a predefined distance for each layer, wherein the predefined distance decreases over the number of layers generated to form the one or more objects, such that the formed layer thickness remains substantially the same.
16. The method of claim 15, wherein the predefined distance decreases non-linearly over the number of layers generated.
17. The method of any preceding claim, comprising positioning each of said object models such that a distance between each said object model and a further said object model is equal to or greater than a predefined minimum object model separation; and/or a distance between each said object model and a boundary of the virtual build volume is equal to or greater than a predefined minimum boundary distance.
18. The method of claim 17, comprising, after scaling the object model, verifying that the distance between each scaled object model and a further scaled object model is equal to or greater than the predefined minimum object model separation; and/or the distance between each said object model and a boundary of the virtual build volume is equal to or greater than the predefined minimum boundary distance; and if one or both of said distances are smaller than the corresponding predefined minimum object model separation and predefined minimum boundary distance, generating an alert that the one or more objects models are to be repositioned.
19. The method of any preceding claim, comprising applying the selected scaling factor to the object model, or to the expanded object model, from a predefined origin of the object model or the expanded object model.
20. The method of claim 19, wherein the predefined origin is the reference point. 21. A controller configured to provide slice data to one or more additive manufacturing apparatus for the layerwise formation of 3D objects from particulate build material, and a data storage device storing one or more scaling factor maps, each scaling factor map predetermined from test objects formed by the one or more additive manufacturing apparatus for a particular build material; wherein the controller is configured to carry out the method according to any one of claims 1 to 20 and to access the data storage device to select the said scaling factor.
22. The controller of claim 21, wherein the data storage device is a remote data storage device accessible by the controller via a network, and wherein each scaling factor map is identifiable as corresponding to one or more of a plurality of additive manufacturing apparatuses, and wherein the controller is configured to access a respective scaling factor map by identifying it as corresponding to the apparatus for which the slice data is to be generated.
23. The controller of claim 22, wherein the data storage device comprises a plurality of respective data storage devices, each located within one of the plurality of additive manufacturing apparatuses and accessible by the controller via a network to provide slice data for said additive manufacturing apparatus.
24. The controller of any one of claims 21 to 22, configured to determine an interpolated scaling factor from the determined scaling factor based on the determined reference point and one or more further scaling factors from respective adjacent zones.
25. The controller of any one of claims 21 to 24, wherein the reference point is selectable from one of the centre of mass, the shape, the volume, and an origin of a virtual envelope of the object model or the expanded object model, wherein the controller is further configured to select one of the defined reference points for each respective object model or expanded object model.