Field of the Invention

[0001] The present invention relates to a stereolithography system and, in particular, to a stereolithography system that is scaled to allow for the rapid formation of large objects or a plurality of large or small objects.

Description of the Related Art

[0002] PCT Application Publication Number WO 2014/126837 to DiSimone et al, the full disclosure of which is incorporated herein by reference, discloses a method of forming a three-dimensional object. The method comprises providing a carrier and an optically transparent member having a build surface. The carrier and the build surface define a build region therebetween. The build region is filled with a polymerizable liquid and the build region is irradiated through the optically transparent member to form a solid polymer from the polymerizable liquid while concurrently advancing the carrier away from the build surface to form the three-dimensional object from the solid polymer, while also concurrently: (i) continuously maintaining a dead zone of polymerizable liquid in contact with the build surface, and (ii) continuously maintaining a gradient of polymerization zone between the dead zone and the solid polymer and in contact with each thereof, the gradient of polymerization zone comprising the polymerizable liquid in partially cured form. An apparatus for carrying out the method is also disclosed.

SUMMARY OF THE INVENTION

[0003] It is an object of the present invention to provide an improved stereolithography system. [0004] There is accordingly provided a stereolithography system comprising a carrier platform and a plurality of frame members which extend from the carrier platform. A carriage is coupled to and able to reciprocate along the frame members. There is a tank and an emitting device which are each mounted on the carriage such that the tank and the emitting device do not move relative to one another when the carriage reciprocates along the frame members. The tank has an optically transparent bottom wall and the tank is disposed between the carrier platform and the emitting device.

[0005] There may be a wettable material at the optically transparent bottom wall of the tank within the tank. The wettable material may be coated on the optically transparent bottom wall of the tank or the wettable material may overlay the optically transparent bottom wall of the tank. The wettable material may include a hydrogel and, in certain examples, may include a hydrogel and hydrogen peroxide. The wettable material may include a hydrogen donor and an oxygen scavenger. The wettable material may include glycerin. The wettable material may include a UV inhibitor. The wettable material may have a superhydrophobic surface. A nanostructure of the superhydrophobic surface of the wettable material may be a vertically aligned surface or a hierarchically structured surface, or a combination thereof. A nanostructure of the superhydrophobic surface of the wettable material may include a plurality of projections which have a top diameter of between 5 microns and 15 microns and which are spaced less than 10 microns apart. The wettable material may be adhered to the optically transparent bottom wall of the tank using adhesive applied in a pattern having intersecting lines.

[0006] The optically transparent bottom wall of the tank may have a thermal conductivity of greater than 20 W/(m x K) at 300K. The optically transparent bottom wall of the tank may be sapphire glass. The optically transparent bottom wall of the tank may be transparent ceramic spinel. BRIEF DESCRIPTIONS OF DRAWINGS

[0007] The invention will be more readily understood from the following description of the embodiments thereof given, by way of example only, with reference to the accompanying drawings, in which:

[0008] Figure 1 is a perspective view of an improved stereolithography system;

[0009] Figure 2 is a perspective, fragmentary view of the stereolithography system of Figure 1 showing a resin tray and emitting device thereof;

[0010] Figure 3 is a perspective, fragmentary view of the stereolithography system of Figure 1 showing a drive mechanism thereof;

[0011] Figure 4A is a perspective, sectional view of a resin tray of the stereolithography system of Figure 1 ;

[0012] Figure 4B is an enlarged view of a surface area of a wettable material within the tank of the stereolithography system of Figure 1 ; [0013] Figure 5 is a simplified schematic showing a gap between a wettable material on a bottom wall of the resin tray and a three-dimensional object being formed by the stereolithography system of Figure 1 ;

[0014] Figure 6 is a perspective, fragmentary view of the stereolithography system of Figure 1 showing a three-dimensional object starting to be formed by the stereolithography system; [0015] Figure 7 is a perspective, fragmentary view of the stereolithography system of Figure 1 showing a three-dimensional object being formed by the stereolithography system;

[0016] Figure 8 is another perspective, fragmentary view of the stereolithography system of Figure 1 showing a three-dimensional object being formed by the stereolithography system;

[0017] Figure 9 is still another perspective, fragmentary view of the stereolithography system of Figure 1 showing a three-dimensional object being formed by the stereolithography system; [0018] Figure 10 is a perspective view of the stereolithography system of Figure 1 showing a three-dimensional object formed by the stereolithography system;

[0019] Figure 11 is a perspective, fragmentary view of the stereolithography system of Figure 1 showing a plurality of three-dimensional objects being formed by the stereolithography system; [0020] Figure 12 is another perspective, fragmentary view of the stereolithography system of Figure 1 showing a plurality of three-dimensional objects being formed by the stereolithography system;

[0021] Figure 13 is still another perspective, fragmentary view of the stereolithography system of Figure 1 showing a plurality of three-dimensional objects being formed by the stereolithography system;

[0022] Figure 14 is a perspective view of the stereolithography system of Figure 1 showing a plurality of three-dimensional objects being formed by the stereolithography system; [0023] Figure 15 is a perspective view of the stereolithography system of Figure 1 showing a plurality of three-dimensional objects being formed by the stereolithography system with some of the three-dimensional objects harvested; and

[0024] Figure 16 is a perspective view of the stereolithography system of Figure 1 showing a plurality of three-dimensional objects formed by the stereolithography system.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

[0025] Referring to the drawings and first to Figure 1 , an improved stereolithography system 10 is shown. The stereolithography system 10 comprises a plurality of vertical frame members 12, 14, 16 and 18 which together support a top 20. In this example, the top 20 is a planar quadrilateral member and the frame members 12, 14, 16 and 18 are each secured to a respective corner of the top 20. The frame members 12, 14, 16 and 18 are also each provided with a respective foot 22, 24, 26 and 28 which provide stability to the stereolithography system 10. There is a plurality of struts, for example, struts 30 and 32 extending between the frame members 12 and 14 as well as struts 34 and 36 extending between the frame members 16 and 18. The struts provide stability to the stereolithography system 10.

[0026] The frame members 12, 14, 16 and 18 are each further provided with a respective one of tracks 42, 44, 46 and 48 which extends along a length thereof as best shown in Figure 2. There is a carriage 50 which is mounted on the tracks 42, 44, 46 and 48 and is movable along the tracks. Figure 3 shows one of the frame members 12 and a respective one of the tracks 42 in greater detail. The tracks 42, 44, 46 and 48 are racks in this example. Pinions, for example pinion 52, which are mounted on axles, for example axle 54, of the carriage 50 translate linearly along the racks, e.g. track 42. This allows the carriage 50 to reciprocate along a length of the frame members 12, 14, 16 and 18. The carriage 50 is also coupled to each of the frame members by a respective linear guide, for example, Figure 3 shows the carriage 50 coupled to one of the frame members 12 by a respective linear guide 56. It will be understood by a person skilled in the art that the carriage is likewise coupled to the other frame members by linear guides. The linear guides provide stability to the stereolithography system 10.

[0027] Referring now back to Figures 1 and 2, the carriage 50 supports an emitting device 60 and a tank 70. The emitting device 60 and the tank 70 are each securely mounted to the carriage 50 such that the emitting device 60 and the tank 70 do not move relative to one another as the carriage 50 reciprocates along the length of the frame members 12, 14, 16 and 18. The emitting device may be any suitable light-emitting device which may be used to cure a polymerizable resin. The tank 70, as best shown in Figure 4A, has a bottom wall 72 which is optically transparent. The tank 70 also has a plurality of side walls, for example, side walls 74, 76 and 78 which extend from the bottom wall 72 of the tank 70. The tank 70 and, in particular, the bottom wall 72 of the tank 70 may be glass or another optically transparent material with a thermal conductivity of greater than 20 W/(m x K) at 300K.

[0028] There is a wettable material 80 at the bottom wall 72 of the tank 70 within the tank 70. The wettable material 80 may overlay the bottom wall 72 of the tank 70, or the wettable material 80 may be coated on the bottom wall 72 of the tank 70, or the bottom wall 72 of the tank 70 may be formed from a wettable material. The wettable material 80 may be any material that is capable of being wetted, i.e. retaining water. The wettable material 80 may have a thickness of between 1 millimeter and 4 millimeters. [0029] In this example, the wettable material 80 is a membrane that overlays the bottom wall 72 of the tank. An optically transparent adhesive 82 such as an adhesive primer or a cyanoacrylate adhesive may be used to affix the wettable material 80 to the bottom wall 72 of the tank 70. The wettable material 80 may be adhered to the bottom wall 72 of the tank 70 in a grid pattern as shown in Figure 4A. This allows the wettable material 80 to flex only within defined areas. A similar result may be achieved by adhering the wettable material 80 in circular patterns or any other suitable pattern with intersecting lines. The wettable material 80 may alternatively be affixed to the bottom wall 72 of the tank 70 by using a mould to cast the wettable material 80 in liquid form over the bottom wall 72 of the tank 70 then curing the wettable material 80 to affix the wettable material 80 to the bottom wall 72 of the tank 70. Still alternatively, in other examples, the wettable material 80 may be affixed to the bottom wall 72 of the tank 70 by applying a vacuum to a hollow interior of the bottom wall 72 of the tank 70 through a conduit.

[0030] Figure 4B shows the nanostructure of a surface of the wettable material 80. The nanostructure of the surface of the wettable material 80 includes a plurality of projections in the form of truncated cones, for example projections 82a, 82b and 82c, which are spaced apart along the surface of the wettable material 80. In this example, the projections 82a, 82b and 82c have a base diameter of between 10 microns and 20 microns and a top diameter of between 5 microns and 15 microns. The projections 82a, 82b and 82c are spaced at less than 10 microns apart in this example. The nanostructure of the surface of the wettable material 80 renders the surface of the wettable material 80 a superhydrophobic surface and may take alternative suitable forms in other examples. The nanostructure of the surface of the wettable material 80 may be prepared by chemical treatment or laser sculpting or photolithography. The nanostructure of the surface of the wettable material 80 may be a vertically aligned surface, or a hierarchically structured surface, or a combination thereof. It may still alternatively be possible to coat the nanostructure of the surface of the wettable material 80 with Teflon® or another hydrophobic material.

[0031] Referring now to Figure 5, and with reference back to Figure 4A, the wettable material 80 may be a hydrogel, e.g. silicone hydrogel, or any other suitable wettable material which results in a dead zone or a gap 84 at the interface between the wettable material 80 and resin 86 in the tank 70. The gap 84 may be a result of intermolecular forces of repulsion between the wettable material 80 and the resin 86 in the tank 70 and/or the gap 84 may be the result of a layer of water which separates the wettable material 80 and the resin 86 because the resin and water are immiscible. Figure 5 best shows the gap 84 between the wettable material 80 at the bottom wall 72 of the tank 70 and an object 110 being formed from the resin 86 in the tank 70. The gap 84 allows the object 110 to be formed continuously because the object 110 is not formed directly on the bottom wall 72 of the tank 70, thereby doing away with the need for the object 110 to be peeled or pulled away from the bottom wall 72 of the tank 70.

[0032] The separation between the wettable material 80 and the resin 86 may be improved by adding glycerin to the wettable material 80 since glycerin is immiscible with the resin. The separation between the wettable material 80 and the resin 86 may be further improved by adding a UV inhibitor and glycerin to the wettable material 80. Addition of the UV inhibitor and glycerin prevents the curing of a very thin layer of the resin 86 at the interface between the wettable material 80. The wettable material 80 may further include a hydrogen donor and an oxygen scavenger which may be in the form of hydrogen peroxide or perfluorocarbons.

[0033] The concentrations of glycerin and UV inhibitor in the wettable material 80 depend on the type of resin being used. The concentration of glycerin in the wettable material 80 may be as low as 1 % by volume for a hydrogel-based wettable material and as high as 95% by volume for a glycerin gel-based wettable material. The concentration of UV inhibitor in the wettable material 80 may be between 0.5% by volume and 25% by volume. High reactive resins, which contain more photoinitiators, may require more glycerin and more UV inhibitor while low reactive resins, which contain less photoinitiators, may require less glyercine and less UV inhibitor. [0034] Since heat is created as the resin cures, it is desirable to dissipate as much heat as possible, in particular, when the object 110 is being formed continuously. By forming the bottom wall 72 of the tank 70 from a material with high thermal conductivity, the heat can be dissipated more quickly which allows the size of the cross-section and the height of the object 110 to be increased as a result of less heat being accumulated. Furthermore, if the bottom wall 72 of the tank 70 has a high thermal conductivity, then air bubbles are generally not formed in the wettable material 80 and/or resin 86. The formation of air bubbles in the wettable material 80 and/or resin 86 may adversely affect the formation of the object 110. [0035] It is accordingly desirable to form the bottom wall 72 of the tank 70 from an optically transparent material with high thermal conductivity. Sapphire glass, which has a thermal conductivity of 25 W/ (m x K) at 300K, may be used to form the bottom wall 72 of the tank 70. Transparent ceramic spinel, which has a thermal conductivity of 25 W/ (m x K) at 300K, may also be used to form the bottom wall 72 of the tank 70. Low-iron glasses with high thermal conductivity such as Starphire™ glass may also be used However, the bottom wall 72 of the tank 70 may also be formed from acrylic glass, which has a thermal conductivity of 0.20 W/ (m x K) at 25K, or soda-lime glass or soda-lime- silica glass which has a thermal conductivity of 0.95 W/ (m x K) at 25K. [0036] Figure 6 shows the object 110 starting to be formed using the stereolithography system 10. The carriage 50 is disposed near the top 20 of the stereolithography system 10 which functions as a carrier platform. The emitting device 60 emits a substantially continuous emission or blast of light 62 as the object 110 starts to be formed on the top 20 of the stereolithography system 10. In this example, the object 110 is provided with a bore 112 which receives a support shaft 114 as best shown in Figure 7. The support shaft 114 sits on the struts 32 and 36 to support the object 110 and prevent the object 110 from being peeled or pulled off the top 20 of the stereolithography system 10. This allows for large objects and/or heavy objects to be formed. The object 110 may also be supported on the stereolithography system 10 by alternative means in other embodiments, for example, clamps or ties. The tank may be filled with resin manually or by a pump system.

[0037] The carriage 50 then moves continuously and downwardly away from the top 20 of the stereolithography system 10 as the emitting device 60 emits the substantially continuous emission or blast of light 62 and the object 110 is formed continuously as shown in Figure 8 to 9. This process continues until the object 110 is fully formed as shown in Figure 10. The gap 84, shown in Figure 5, between the bottom wall 72 of the tank 70 and the resin 86 in the tank 70 allows the object 110 to be formed continuously because the object 110 is not formed directly on the bottom wall 72 of the tank 70, thereby doing away with the need for the object 110 to be peeled or pulled away from the bottom wall 72 of the tank 70. The stereolithography system 10 disclosed herein may also be scaled to allow for the rapid formation of large objects or a plurality of large objects. For example, in Figures 6 to 10, the object 110 being formed is one of a plurality of blades for a wind turbine. [0038] Figure 11 shows the stereolithography system 10 being used to form an object 120 that may later be broken up into a plurality of small objects, for example small objects 122a and 122b, which are individual soles for running shoes. The object 120 is supported at various points along a length of the stereolithography system 10 by support means extending longitudinally along the frame members 12, 14, 16 and 18. In this example, the object 120 is supported by a support shaft 124 which sits on the struts 32 and 36 to support the object 120 and prevent the object 120 from being peeled or pulled off the top 20 of the stereolithography system 10. The support shaft 124 extends through a bore (not shown) in a support portion 126 of the object 120. The carriage 50 then moves continuously and downwardly away from the top 20 of the stereolithography system 10 as the emitting device 60 emits the substantially continuous emission or blast of light 62 and the plurality of the small objects, for example smaller objects 120a and 120b, are formed in a linked arrangement until the tank 70 is aligned with the struts 30 and 34 as shown in Figure 12. A support portion 128 of the object 120 is then formed. It will be understood by a person skilled in the art that the object 120 may be supported on the stereolithography system 10 by alternative means in other embodiments, for example, clamps or ties.

[0039] The support portion 128 of the object 120 has a bore 130, shown in Figure 12, which receives a support shaft 132 as best shown in Figure 13. The support shaft 132 sits on the struts 30 and 34 to support the object 120. The carriage 50 then moves continuously and downwardly away from the top 20 of the stereolithography system 10 as the emitting device 60 emits the substantially continuous emission or blast of light 62 and the plurality of the small objects, for example smaller objects 120c and 120d, are then formed in a linked arrangement as shown in Figure 14. This continues until earlier formed ones of the smaller objects 120a and 120b are harvested or removed from the stereolithography system 10 as shown in Figure 15. This is possible because the object 120 is supported at various points along a length of the stereolithography system 10 as described above. It is alternatively possible to not harvest or remove the smaller objects from the stereolithography system 10 until the process is completed as shown in Figure 16.

[0040] It will be understood by a person skilled in the art that although the stereolithography systems as disclosed herein are used to continuously form an article that the stereolithography systems as disclosed herein may be used to form an article stepwise.

[0041] It will also be understood by a person skilled in the art that many of the details provided above are by way of example only, and are not intended to limit the scope of the invention which is to be determined with reference to the following claims.