OPTICAL EFFECTS OF 3D PRINTED ITEMS

Abstract

The invention provides a method for producing a 3D item (1) by means of fused deposition modelling, the method comprising a 3D printing stage comprising layer-wise depositing an extrudate (321) from 3D printable material (201), to provide the 3D item (1) comprising 3D printed material (202), wherein the 3D item (1) comprises a plurality of layers (322) of 3D printed material (202), wherein each layer (322) has a layer height (H) and a layer width (W), wherein the 3D printing stage comprises generating a stack (1322) of the layers (322) of the 3D printed material (202), wherein at a fixed first x,y-position the layer height (H) is varied layer by layer for a subset of a total number of layers (322), wherein either (i) the layer height (H) increases for consecutive layers (322) and then the layer height (H) decreases for consecutive layers (322), or (ii) the layer height (H) decreases for consecutive layers and then the layer height (H) increases for consecutive layers (322); and wherein at least part of the 3D printable material (201) comprises light transmissive polymeric thermoplastic material (401).

Claims

1. A method for producing a 3D item by means of fused deposition modelling using a 3D printer, the method comprising a 3D printing stage during which a stack of layers of a 3D printed material is generated by layer-wise depositing an extrudate from 3D printable material, at least part of the 3D printable material comprising a light transmissive polymeric thermoplastic material, wherein each layer of the stack has a non-constant layer height (H), wherein at a fixed first x,y-position: (i) the layer height (H) increases for consecutive layers and then the layer height (H) decreases for consecutive layers, or (ii) the layer height (H) decreases for consecutive layers and then the layer height (H) increases for consecutive layers, wherein the stack has a first stack height (H11) at the fixed first x,y position, and wherein the method comprises generating at a fixed second x,y-position the stack with layers having a layer height (H), thereby providing the stack with a second stack height (H12) at the fixed second x,y position, wherein 0.9≤H12/H11≤1.1.

2. (canceled)

3. The method according to claim 1, wherein a layer from the stack has a maximum overall height (H.sub.L1), wherein the method comprises generating the same layer with a minimum overall height (H.sub.L2) of that layer in the stack, wherein |H.sub.L1−H.sub.L2|/L*≤1, where L* is a distance between these two points measured parallel to an x,y-plane.

4. The method according to claim 3, comprising 3D printing a plurality of maximum overall heights (H.sub.L1) and minimum overall heights (H.sub.L2) in the stack, where the maximum overall heights (H.sub.L1) and minimum overall heights (H.sub.L2) of each layer follow a spiral on a surface of the 3D item, and wherein the method comprises printing a concave 3D item.

5. The method according to claim 1, wherein the method comprises printing the layers for the subset of a total number of layers at the fixed first x,y position with a constant layer width (W).

6. The method according to claim 1, wherein the method comprises printing the layers for the subset of a total number of layers at the fixed first x,y-position with layer heights (H) that vary according to a mathematical function selected from the group consisting of sinusoidally, triangularly, saw tooth, and square, or a combination of two or more of these.

7. The method according to claim 1, wherein the light transmissive polymeric thermoplastic material is transparent for visible light having a one or more wavelengths selected from the range of 450-650 nm.

8. The method according to claim 1, wherein the 3D printable material and the 3D printed material comprise one or more of polycarbonate (PC), polyethylene (PE), polypropylene (PP), polyethylene naphthalate (PEN), styrene-acrylonitrile resin (SAN), polysulfone (PSU), polyphenylene sulfide (PPS), polytethylene terephthalate (PET), poly(methyl methacrylate) (PMMA), polystyrene (PS), styrene acrylic copolymers (SMMA), and polyurethane (PU).

9. A 3D item comprising a stack of layers of a 3D printed material, at least part of the 3D printed material comprising a light transmissive polymeric thermoplastic material, wherein each layer of the stack has a non-constant layer height (H), wherein at a fixed first x,y-position: (i) the layer height (H) increases for consecutive layers and then the layer height (H) decreases for consecutive layers, or (ii) the layer height (H) decreases for consecutive layers and then the layer height (H) increases for consecutive layers, wherein the stack has a first stack height (H11) at the fixed first x,y position, and wherein at a fixed second x,y-position the layers of the stack have a constant layer height (H), wherein the stack has a second stack height (H12) at the fixed second x,y position, wherein 0.1≤H12/H11≤10.

10. (canceled)

11. The 3D item (1) according to claim 8, wherein 0.9≤H12/H11≤1.1; and wherein the layers for the subset of a total number of layers at the fixed first x,y position have a constant layer width (W).

12. The 3D item according to claim 9, wherein for the subset of a total number of layers at the fixed first x,y-position the layer heights (H) vary sinusoidally or vary triangularly; wherein the 3D item is a concave 3D item; wherein the stack is a single wall stack.

13. The 3D item (1) according to claim 10, wherein the 3D printed material comprise one or more of polycarbonate (PC), polyethylene (PE), polypropylene (PP), polyethylene naphthalate (PEN), styrene-acrylonitrile resin (SAN), polysulfone (PSU), polyphenylene sulfide (PPS), polytethylene terephthalate (PET), poly(methyl methacrylate) (PMMA), polystyrene (PS), styrene acrylic copolymers (SMMA), and polyurethane (PU), wherein the 3D printed material comprises light transmissive polymeric thermoplastic material.

14. A lighting device comprising the 3D item according to claim 9, wherein the 3D item (1) is configured as one or more of (i) at least part of a lighting device housing, (ii) at least part of a wall of a lighting chamber, and (iii) an optical element.

15. A computer program product comprising instructions which, when the computer program product is executed by a computer which is functionally coupled to or comprised by a fused deposition modelling 3D printer, causes the fused deposition modelling 3D printer to carry out the method as described in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0089] FIGS. 1a-1c schematically depict some general aspects of the 3D printer and of an embodiment of 3D printed material;

[0090] FIGS. 2a-2d schematically depict some embodiments;

[0091] FIGS. 3a-3c schematically depict some further embodiments and aspects;

[0092] FIG. 4 schematically depicts an application; and

[0093] FIGS. 5a-5c show some examples. The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0094] FIG. 1a schematically depicts some aspects of the 3D printer. Reference 500 indicates a 3D printer. Reference 530 indicates the functional unit configured to 3D print, especially FDM 3D printing; this reference may also indicate the 3D printing stage unit. Here, only the printer head for providing 3D printed material, such as an FDM 3D printer head is schematically depicted. Reference 501 indicates the printer head. The 3D printer of the present invention may especially include a plurality of printer heads (see below). Reference 502 indicates a printer nozzle. The 3D printer of the present invention may especially include a plurality of printer nozzles, though other embodiments are also possible. Reference 320 indicates a filament of printable 3D printable material (such as indicated above). For the sake of clarity, not all features of the 3D printer have been depicted, only those that are of especial relevance for the present invention (see further also below). Reference 321 indicates extrudate (of 3D printable material 201).

[0095] The 3D printer 500 is configured to generate a 3D item 1 by layer-wise depositing on a receiver item 550, which may in embodiments at least temporarily be cooled, a plurality of layers 322 wherein each layers 322 comprises 3D printable material 201, such as having a melting point T.sub.m. The 3D printable material 201 may be deposited on a substrate 1550 (during the printing stage). By deposition, the 3D printable material 201 has become 3D printed material 202. 3D printable material 201 escaping from the nozzle 502 is also indicated as extrudate 321. Reference 401 indicates thermoplastic material.

[0096] The 3D printer 500 may be configured to heat the filament 320 material upstream of the printer nozzle 502. This may e.g. be done with a device comprising one or more of an extrusion and/or heating function. Such device is indicated with reference 573, and is arranged upstream from the printer nozzle 502 (i.e. in time before the filament material leaves the printer nozzle 502). The printer head 501 may (thus) include a liquefier or heater. Reference 201 indicates printable material. When deposited, this material is indicated as (3D) printed material, which is indicated with reference 202.

[0097] Reference 572 indicates a spool or roller with material, especially in the form of a wire, which may be indicated as filament 320. The 3D printer 500 transforms this in an extrudate 321 downstream of the printer nozzle which becomes a layer 322 on the receiver item or on already deposited printed material. In general, the diameter of the extrudate 321 downstream of the nozzle 502 is reduced relative to the diameter of the filament 322 upstream of the printer head 501. Hence, the printer nozzle is sometimes (also) indicated as extruder nozzle. Arranging layer 322 by layer 322 and/or layer 322t on layer 322, a 3D item 1 may be formed. Reference 575 indicates the filament providing device, which here amongst others include the spool or roller and the driver wheels, indicated with reference 576.

[0098] Reference A indicates a longitudinal axis or filament axis.

[0099] Reference C schematically depicts a control system, such as especially a temperature control system configured to control the temperature of the receiver item 550. The control system C may include a heater which is able to heat the receiver item 550 to at least a temperature of 50° C., but especially up to a range of about 350° C., such as at least 200° C.

[0100] Alternatively or additionally, in embodiments the receiver plate may also be moveable in one or two directions in the x-y plane (horizontal plane). Further, alternatively or additionally, in embodiments the receiver plate may also be rotatable about z axis (vertical). Hence, the control system may move the receiver plate in one or more of the x-direction, y-direction, and z-direction.

[0101] Alternatively, the printer can have a head can also rotate during printing. Such a printer has an advantage that the printed material cannot rotate during printing.

[0102] Layers are indicated with reference 322, and have a layer height H and a layer width W.

[0103] Note that the 3D printable material is not necessarily provided as filament 320 to the printer head. Further, the filament 320 may also be produced in the 3D printer 500 from pieces of 3D printable material.

[0104] Reference D indicates the diameter of the nozzle (through which the 3D printable material 201 is forced).

[0105] FIG. 1b schematically depicts in 3D in more detail the printing of the 3D item 1 under construction. Here, in this schematic drawing the ends of the filaments 321 in a single plane are not interconnected, though in reality this may in embodiments be the case. Reference H indicates the height of a layer. Layers are indicated with reference 203. Here, the layers have an essentially circular cross-section. Often, however, they may be flattened, such as having an outer shape resembling a flat oval tube or flat oval duct (i.e. a circular shaped bar having a diameter that is compressed to have a smaller height than width, wherein the sides (defining the width) are (still) rounded).

[0106] Hence, FIGS. 1a-1b schematically depict some aspects of a fused deposition modeling 3D printer 500, comprising (a) a first printer head 501 comprising a printer nozzle 502, (b) a filament providing device 575 configured to provide a filament 321 comprising 3D printable material 201 to the first printer head 501, and optionally (c) a receiver item 550. In FIGS. 1a-1b, the first or second printable material or the first or second printed material are indicated with the general indications printable material 201 and printed material 202, respectively. Directly downstream of the nozzle 502, the filament 321 with 3D printable material becomes, when deposited, layer 322 with 3D printed material 202.

[0107] FIG. 1c schematically depicts a stack of 3D printed layers 322, each having a layer height H and a layer width W. Note that in embodiments the layer width and/or layer height may differ for two or more layers 322. Reference 252 in FIG. 1c indicates the item surface of the 3D item (schematically depicted in FIG. 1c).

[0108] Referring to FIGS. 1a-1c, the filament of 3D printable material that is deposited leads to a layer having a height H (and width W). Depositing layer 322 after layer 322, the 3D item 1 is generated. FIG. 1c very schematically depicts a single-walled 3D item 1.

[0109] It is interesting to have light sources luminaires and lamp shades having decorative and/or optical effects such as angular dependent light scattering, light absorption and light transmission. It is (thus) also interesting to have visual effects in decorative luminaires such as enhanced light reflection. In the case of transparent luminaires, it may be interesting to create (decorative) optical effects. It may also be interesting to have (decorative) wavy features at e.g. the edges of lamp shade (skirt) instead of it being straight.

[0110] For this purpose, we suggest amongst others using fused deposition modelling where the height of the deposited layer can be changed during printing. For example, layer height during the printing of each layer can change about a sinus function. When multiple layers are printed where the relative heights change increases, a wavy edge of the print is realized which can be very decorative. When printing continues and relative heights change during printing is decreased to reach a level that during printing no height change takes place structures showing lens working can be realized. It is also possible to use other functions such as saw tooth and other functions. In this way it is also possible to produce lamp shades with edges according to the function used such as wavy, saw teeth or triangular. Printed object does not to have straight surfaces, but their surface can be conical, spherical or have bent. It goes without saying that it is also possible to use height variation only in certain parts of the print while the rest of the object is printed using a constant layer height. In this way various optical effects such as lensing but also spatially varying diffraction effects can be realized.

[0111] During printing the printer head moves in XY plane to deposit a layer subsequently the platform moves down, and the following layer is printed. In this way of printing the layer height stays constant during the whole printing process. Amongst others, herein we suggest changing the layer height during printing by enabling the movement of the printing platform along the z axis as schematically shown in FIG. 2a. FIG. 2a is a schematically representation of a side view of e.g. a possible wall. Hence, in embodiments we suggest using fused deposition modelling where the height of the deposited layer can be changed during printing. For example, layer height during the printing of each layer can change about a sinus function. When multiple layers are printed where the relative height change increases, a wavy edge of the print is realized which can—amongst others—be very decorative. This is shown in FIG. 2a. Such shape may also have specific (optical) functionalities.

[0112] When printing continues and relative height change during printing more layers is decreased to reach a level that during printing no height change takes place structures showing light refraction based effects such as lens working can be realized. It is also possible to use other functions such as saw tooth and other functions. In this way it is also possible to produce lamp shades with edges according to the function used such as wavy, saw teeth or triangular. Printed object does not to have straight surfaces, but their surface can be conical, spherical or have bent. It goes without saying that it is also possible to use height variation only in certain parts of the print while the rest of the object is printed using a constant layer height.

[0113] FIG. 2a schematically depicts an embodiment wherein the height variations are not (fully) compensated, leading to variation in the total height (see the lower height at reference H12 and the higher height at reference H11). FIG. 2b, however, shows schematically an embodiment wherein the height variation is compensated. Hence, the total height is essentially constant. The lower height at reference H12 and the higher height at reference H11 may in embodiments refer to the height of the stack, or a part of the stack 1322.

[0114] Referring to FIGS. 2a-2b and also FIGS. 1a-1c, amongst others the invention provides a method for producing a 3D item 1 by means of fused deposition modelling. Such method may comprise a 3D printing stage comprising layer-wise depositing an extrudate from 3D printable material, to provide the 3D item 1 comprising 3D printed material 202 (on a receiver item 550). The 3D item 1 comprises a plurality of layers 322 of 3D printed material 202. Each layer 322 has a layer height H and a layer width W, of which one or more may vary along the layer. Hence, in embodiments the 3D printing stage may comprise generating a stack 1322 of the layers 322 of the 3D printed material 202, wherein at a fixed first x,y-position the layer height H is varied layer by layer for a subset of a total number of layers 322. In embodiments, the stack 1322 may be a single wall stack. This first x,y position is indicated with x1,y1 in FIG. 2b. The layer height H may increase for consecutive layers 322 and/or the layer height H may decrease for consecutive layers 322. Hence, in specific embodiments either (i) the layer height H increases for consecutive layers 322 and then the layer height H decreases for consecutive layers 322 (see at x1y1), or (ii) the layer height H decreases for consecutive layers and then the layer height H increases for consecutive layers 322 (effectively left and right of the first x,y position).

[0115] Referring to FIG. 2a, the stack 1322 has a first stack height H11 at the fixed first x,y position. The method may comprises generating at a fixed second x,y-position the stack 1322 with layers 322 having a layer height H, thereby providing the stack 1322 with a second stack height H12 at the fixed second x,y position, wherein 0.1≤H12/H11≤10, such as 0.1≤H12/H11≤5, like 0.2≤H12/H11≤5, with in embodiments at least 0.1≤H12/H11≤1.5. Referring to FIG. 2b, however, the stack 1322 has a first stack height H11 at the fixed first x,y position, wherein the method comprises generating at a fixed second x,y-position the stack 1322 with layers 322 having an essentially constant layer height H, thereby providing the stack 1322 with a second stack height H12 at the fixed second x,y position, wherein e.g. 0.9≤H12/H11≤1.1.

[0116] Referring to FIGS. 2a and 2b, the stack 1322 may especially share the same layers 322. Hence, a lowest layer and a highest layer of the stack will define the stack height. This stack height may vary over the stack (length) (see FIG. 2a), thought this stack height may also be essentially constant over the stack length (see FIG. 2b).

[0117] Further, referring to FIGS. 2a-2b a layer from the stack 1322 has a maximum overall height (H.sub.L1) of the layer in the stack, wherein the method comprises generating (adjacently) the same layer with a minimum overall height (H.sub.L2) of the layer in the stack, wherein |H.sub.L1−H.sub.L2|/L*≤1, where L* is a distance between these two points measured along a surface of the 3D item, especially parallel to the layers 322, such as especially parallel to an x,y plane. Further, in specific embodiments, stacks may be provided wherein values between minima and (adjacent) maxima are achieved selected from the range of 0.1≤|H.sub.L1−H.sub.L2|/L*≤1, such as 0.25|≤H.sub.L1−H.sub.L2|/L*≤0.8. Here, the minimum and maximum overall heights are defined relative to a lowest layer or a planar layer, that may be available on or may have been available on a receiver item. By way of example, for a specific layer, here the minimum mi and the maximum are indicated. For that layer, the height difference between the minimum mi and the maximum is largest.

[0118] Referring to FIG. 2a. the stack 1322 comprises two essentially the same stack parts 1322′.

[0119] The layer height changes over the height of the segment may vary in different ways (see also below). In embodiments, the (waveform) amplitudes are aligned along the printing direction or along a line that extends at an angle to the printing direction. This is schematically depicted in FIG. 2c. The amplitudes are either aligned along the printing direction (i.e. they are directly on top of each other, see I) or they are shifted along the printing direction (see II).

[0120] Depth perception can be divided into monocular and binocular cues, where the former has the benefit that the observer's position and orientation does not depend so much on the depth perceived and therefor does not require extensive addressing. The monocular cues that are described in this proposal are based on texture gradient and contrast. Conventional 3d printing may create surfaces using regular spaced layer height. In case layer heights are varied during the print process then this may be applied for different print sections. Amongst others, a printing method in vase (aka spiral) mode is proposed that creates layer height variations in both z and circumferential direction that in turn results in an omnidirectional depth perception in reflection for an otherwise perfectly plane surface illuminated by ambient lighting, while it also can have impact the perception of how the active illumination from the inside when turned on.

[0121] In FIG. 2d the depth perception is explained using texture gradient that results from the brightness variations related to the elliptical shape of the print tracks. Here the layer height is varied in the z direction only. The variation in layer height result in variation in brightness: small layer heights, indicated with A, yield a rapidly alternation between high and low brightness surface areas that effectively results in a nearly uniform surface brightness: One is unable to identify the individual dark and bright contributions. Large layer heights, indicated with B, yield a low frequency alternation between high and low brightness such that one can clearly distinguish to individual components to the surface brightness when looking close to the texture. Light that impinges on the item 1 is indicated with reference 11. This may e.g. be light source light (see FIG. 4), but this may also be daylight.

[0122] To obtain texture variation in circumferential direction one may need to vary the layer height within the layer. In order to create a uniform luminaire wall thickness without cavities, i.e. constant track width, one may require compensating both the extrusion and the z coordinate during printing. As in such configuration the z-coordinate also depends on the layer heights below the predefined position, one may need to consider these previous layer heights directly beneath that position. This is in distinct contrast with conventional 3d printing where during printing of a single revolution the z coordinate may be confined to either a constant position or in case of spiral mode within one-layer height.

[0123] Different items were made. The high frequency texture appears much brighter than the low frequency one: the layers in the high frequency texture are thinner and therefore the low brightness surface area within these layers contributed less to the average brightness in that region. In the low frequency texture, the low brightness areas constitute much more to the average brightness and as a result they appear darker. Also embodiments were created wherein one can immediately identify that the low frequency texture is in fact more transparent as opposed to the high frequency texture that is more Lambertian scattering. Clearly the modulation in transmissivity closely depends on the optical properties of the filament choice of material. Embodiments where made wherein even the layer height variations (and hence the variation in texture) are not directly visible from the distance where the picture was taken, it is the difference in reflectivity of the ambient light that gives the depth impression.

[0124] As can be seen in FIG. 2e the positions of maxima (indicted with ma) and minima (indicated with mi) and in layers can follow a curve which is in the form of a spiral on the surface such as a helix creating decorative effects.

[0125] Referring to e.g. FIGS. 2c and 2e, the increase of the layer height may be essentially parallel to the z-direction. In yet other embodiments, the increase may be under an angle (smaller than 90°, such as equal to or smaller than 45°) to the z-direction. Likewise, in embodiments the decrease may be essentially parallel to the z-direction. In yet other embodiments, the decrease may be under an angle (smaller than 90°, such as equal to or smaller than 45°) to the z-direction.

[0126] FIG. 3a schematically depict two possible cross-sectional views. In both embodiments, the layer height H varies over the height. In the left embodiment, indicated with I, the layer width W is essentially kept constant. In the right embodiment, indicated with II, the layer width also varies. Hence, in embodiments the layers 322 for the subset of a total number of layers 322 at the fixed first x,y position may have an essentially constant layer width W. However, in other embodiments the subset of a total number of layers 322 at the fixed first x,y position may have a cross-sectional area of the layers 322 that is constant.

[0127] As indicated above, in embodiments the method comprises printing the layers 322 for the subset of a total number of layers 322 at the fixed first x,y-position with layer heights H that vary sinusoidally or triangularly. Alternatively, in embodiments the method may comprise printing the layers 322 for the subset of a total number of layers 322 at the fixed first x,y-position with layer heights H that vary like a sawtooth. For instance, in embodiments the method may comprise printing the layers 322 for the subset of a total number of layers 322 at the fixed first x,y-position with stack heights that vary along the surface of the object gradually according to a mathematical function such as sinusoidally or triangularly. FIG. 3b schematically depicts in the upper graph some possibilities for the layer height, such as sinusoidal (I), saw tooth (II), and step wise (III). Note that in the latter embodiments, it is also taken into account that not each next layer should have a different layer height H. On the x-axis, the layers are indicated. In the lower graph of FIG. 3b, possible layer widths are schematically depicted. The sinusoidal layer height may in embodiments be compensated with an inverse sinusoidal layer width (I). However, in embodiments the layer width may also be chosen constant (IV)(see also FIG. 3a, embodiment I). Curve II in the top and bottom figure of FIG. 3b are also used as embodiment to show that layer height and layer width may be controlled such, that essentially the cross-sectional area stays constant. However, as indicated with curve IV, the width may also be kept constant, or partly be used to compensate for the increased or decreased layer height. These drawings are very schematically.

[0128] Hence, especially at least part of the 3D printable material 201 comprises light transmissive polymeric thermoplastic material 401. In embodiments, the 3D printable material 201 and the 3D printed material 202 comprise one or more of polycarbonate PC, polyethylene PE, polypropylene PP, polyethylene naphthalate PEN, styrene-acrylonitrile resin SAN, polysulfone PSU, polyphenylene sulfide PPS, polytethylene terephthalate PET, polymethyl methacrylate PMMA, polystyrene PS, and styrene acrylic copolymers SMMA polyurethane (PU).

[0129] As schematically depicted in FIG. 3c in embodiments the light transmissive polymeric thermoplastic material 401 comprises particulate reflective material 410 embedded therein.

[0130] FIG. 4 schematically depicts an embodiment of a lamp or luminaire, indicated with reference 2, which comprises a light source 10 for generating light 11. The lamp may comprise a housing or shade or another element, which may comprise or be the 3D printed item 1. Here, the half sphere (in cross-sectional view) schematically indicates a housing or shade. The lamp or luminaire may be or may comprise a lighting device 1000 (which comprises the light source 10). Hence, in specific embodiments the lighting device 1000 comprises the 3D item 1. The 3D item 1 may be configured as one or more of (i) at least part of a lighting device housing, (ii) at least part of a wall of a lighting chamber, and (iii) an optical element. Hence, the 3D item may in embodiments be reflective for light source light 11 and/or transmissive for light source light 11. Here, the 3D item may e.g. be a housing or shade. The housing or shade comprises the item part 400. For possible embodiments of the item part 400, see also above.

[0131] FIGS. 5a-5b depict pictures of possible luminaire housings. A depth impression is obtained using layer height variation in both the z and the circumferential direction. Note that the overall contour is only smoothly varying and is essentially constant. In specific embodiments, the method may comprise printing a concave 3D item 1. FIG. 5c shows a picture of a 3D item obtainable by e.g. varying the layer height during the printing of each layer can change about a sinus function. When multiple layers are printed where the relative height change increases, a wavy edge of the print may be realized. FIGS. 5a-5c also schematically depict that a stack 1322 may also comprise a plurality of (smaller) stacks. Referring to FIG. 5c. the stack 1322 comprises a plurality of essentially the same stack parts 1322′. Hence, a stack may comprise multiple smaller stacks which may in embodiments be configured in a regular pattern.

[0132] The term “plurality” refers to two or more.

[0133] The terms “substantially” or “essentially” herein, and similar terms, will be understood by the person skilled in the art. The terms “substantially” or “essentially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially or essentially may also be removed. Where applicable, the term “substantially” or the term “essentially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%.

[0134] The term “comprise” includes also embodiments wherein the term “comprises” means “consists of”.

[0135] The term “and/or” especially relates to one or more of the items mentioned before and after “and/or”. For instance, a phrase “item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term “comprising” may in an embodiment refer to “consisting of” but may in another embodiment also refer to “containing at least the defined species and optionally one or more other species”.

[0136] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0137] The devices, apparatus, or systems may herein amongst others be described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation, or devices, apparatus, or systems in operation.

[0138] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

[0139] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

[0140] Use of the verb “to comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

[0141] The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.

[0142] The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim, or an apparatus claim, or a system claim, enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0143] The invention also provides a control system that may control the device, apparatus, or system, or that may execute the herein described method or process. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the device, apparatus, or system, controls one or more controllable elements of such device, apparatus, or system.

[0144] The invention further applies to a device, apparatus, or system comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

[0145] The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.

[0146] It goes without saying that one or more of the first (printable or printed) material and second (printable or printed) material may contain fillers such as glass and fibers which do not have (to have) influence on the on T.sub.g or T.sub.m of the material(s).