Field of the Invention

[0001] The present invention relates to a stereolithography system and, in particular, to a stereolithography system including a tank with a wettable material at an optically transparent bottom wall of the tank.

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.

[0003] PCT Application Publication Number WO 2016/172805 to Castanon, the full disclosure of which is incorporated herein by reference, discloses a stereolithography system comprising an emitting device and a tank disposed above the emitting device. The tank has an optically transparent bottom wall. There is a linear stage that extends away from the tank and a carrier platform is moveable along the linear stage away from the tank. There is also a wettable material at the optically transparent bottom wall of the tank within the tank. The wettable material results in a gap at an interface between the wettable material and resin in the tank. This allows an object to be formed continuously because the object is not formed directly on the optically transparent bottom wall of the tank, thereby doing away with the need for the object to be peeled or pulled away from the bottom wall during the formation of sequential cross-sections of the object being formed. SUMMARY OF THE INVENTION

[0004] It is an object of the present invention to provide an improved stereolithography system.

[0005] There is accordingly provided a stereolithography system comprising an emitting device and a tank disposed above the emitting device. The tank has an optically transparent bottom wall. There is a linear stage that extends away from the tank and a carrier platform is moveable along the linear stage away from the tank. There is also a wettable material at the optically transparent bottom wall of the tank within the tank. The wettable material includes a hydrogel including a polysaccharide, ions and a sugar alcohol. The polysaccharide may be an agar substitute. The agar substitute may be a Gellan gum. The agar substitute may be a Phytagel™. The ions may include calcium chloride ions. The ions may include zinc sulfate ions. The sugar alcohol may be sorbitol. The hydrogel may further include a polyacrylamide. The hydrogel may further include sodium alginate. The hydrogel may further include collagen. The hydrogel may be coated on the optically transparent bottom wall of the tank. The hydrogel may be a membrane which overlays the optically transparent bottom wall of the tank.

[0006] There is also provided a stereolithography system comprising an emitting device and a tank disposed above the emitting device. The tank has an optically transparent bottom wall. There is a linear stage that extends away from the tank and a carrier platform is moveable along the linear stage away from the tank. There is also a wettable material at the optically transparent bottom wall of the tank within the tank. The wettable material includes silica gel. The silica gel may be coated on the optically transparent bottom wall of the tank. The silica gel may be a membrane which overlays the optically transparent bottom wall of the tank.

[0007] There is further provided a stereolithography system comprising an emitting device and a tank disposed above the emitting device. The tank has an optically transparent bottom wall. There is a linear stage that extends away from the tank and a carrier platform is moveable along the linear stage away from the tank. There is also a wettable material at the optically transparent bottom wall of the tank within the tank. The wettable material includes a polyurethane. The polyurethane may be coated on the optically transparent bottom wall of the tank. The polyurethane may be a membrane which overlays the optically transparent bottom wall of the tank. BRIEF DESCRIPTIONS OF DRAWINGS

[0008] 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: [0009] Figure 1 is a perspective view of an improved stereolithography system with doors thereof in a closed position;

[0010] Figure 2 is another perspective view of the stereolithography system with doors thereof in an open position;

[0011] Figure 3 is a partially sectional, perspective view of a frame of the stereolithography system; [0012] Figure 4 is a perspective, sectional view of a tank of the stereolithography system;

[0013] Figure 5 is a perspective, sectional view of the tank of the stereolithography system showing a gap between a wettable material at a bottom wall of the tank and an object being formed by the stereolithography system;

[0014] Figure 6 is an elevation view of the frame of the stereolithography system showing an object starting to be formed by the stereolithography system;

[0015] Figure 7 is an elevation view of the frame of the stereolithography system showing the object partially formed by the stereolithography system; and [0016] Figure 8 is an elevation view of the frame of the stereolithography system showing the object fully formed by the stereolithography system.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS [0017] Referring to the drawings and first to Figures 1 and 2, an improved stereolithography system 10 is shown. The stereolithography system 10 comprises a housing 12 which, in this example, is substantially cylindrical. The housing 12 has an upper door 14 provided with a handle 16 and a lock 18 to allow and restrict access to an interior of the housing 12. The upper door 14 is a curved, optically transparent door in this example. When the upper door 14 is moved between a closed position, shown in Figure 1, and an open position, shown in Figure 2, the upper door 14 generally travels along a curvature of an inner wall 20 of the housing 12. This minimizes the footprint of the stereolithography system 10 when the upper door is opened. The upper door 14 of the housing 12, when closed, may seal an upper portion of the housing 12 to allow the upper portion of the housing 12 to be pressurized. [0018] The housing 12 also has a lower door 22 provided with a handle 24 and a lock 26 to allow and restrict access to an interior of the housing 12. The lower door 22 is a curved door in this example. When the lower door 22 is moved between a closed position, shown in Figure 1 , and an open position, shown in Figure 2, the lower door 22 generally travels along the curvature of the inner wall 20 of the housing 12. This minimizes the footprint of the stereolithography system 10 when the upper door is opened. The housing 12 further has a vent 28 to allow air to circulate in the lower portion of the housing to help keep the lower portion of the housing 12 cool.

[0019] Referring now to Figure 3, a frame 30 of the stereolithography system 10 is shown. The frame 30 of the stereolithography system 10 has a base 32 and a wall 34 that extends vertically from the base 32. There is a tank 36 mounted on the wall 34 and a light-emitting device 38 is mounted on the base 32. The tank 36 is mounted on the wall 34 above the light-emitting device 38. The light-emitting device may be any suitable light-emitting device which may be used to cure a polymerizable resin. However, in this example, the light-emitting device 38 includes an LED array 40 mounted on a heat sink 42. There is an opening 44 on the light-emitting device 38 through which light is emitted. There is a linear stage 46 that extends vertically away from the tank 36 and a carrier platform 48 is moveable along the linear stage 46. The stereolithography system 10, as thus far described, is a stereolithography system used in a "top down" three-dimensional printing technique in which new cross-sections of an object being formed are formed at a bottom of the object being formed.

[0020] However, as best shown in Figure 4, the tank 36 of the stereolithography system 10 has a bottom wall 50 which is optically transparent and there is a plurality of side walls, for example, side walls 52, 54, 56 which extend from the bottom wall 50 of the tank 36. There is a wettable material 58 at the bottom wall 50 of the tank 36 within the tank 36. The wettable material 58 may be coated on the bottom wall 50 of the tank 36 or the wettable material 58 may overlay the bottom wall 50 of the tank 36. The wettable material 58 may have a thickness of between 1 millimeter and 4 millimeters. The wettable material 58 may be any material that is capable of being wetted, i.e. retaining water.

[0021] In this example, the wettable material 58 is in the form of a membrane and overlays the bottom wall 50 of the tank 36. The wettable material 58 may be adhered to the bottom wall 50 of the tank 36 by an optically transparent adhesive such as an adhesive primer or a cyanoacrylate adhesive applied in a grid pattern with intersecting lines 60 and 62. This allows the wettable material 58 to flex only within defined areas. However, in other examples, the wettable material 58 may be coated or formed on the bottom wall 50 of the tank 36. The wettable material 58 may be coated on the bottom wall 50 of the tank 36 by using a mould to cast the wettable material 58 in liquid form over the bottom wall 50 of the tank 36 then curing the wettable material 58 to affix the wettable material 58 to the bottom wall 50 of the tank 36.

[0022] The wettable material 58 may be a hydrogel, for example, a hydrogel prepared by mixing a polysaccharide with water/hydrogen peroxide and other components in different proportions. The method of preparation may vary according to the polysaccharide employed. The hydrogel may include a mix of two or more polysaccharides to develop variations in the mechanical properties of the hydrogel. The polysaccharide may be an agar substitute such as Gellan gum or Phytagel™ which is composed of glucuronic acid, rhamnose, and glucose. The hydrogel may include ions, for example, calcium chloride ions or zinc sulfate ions for cross-linking the agar substitute. The hydrogel may include sodium alginate for cross-linking the agar substitute. The hydrogel may include a sugar alcohol, for example, sorbitol. Hydrogels including ions and sugar alcohols have been found to withstand the stereolithography (three-dimensional printing) process. An example of a formulation of a hydrogel comprising a polysaccharide is a hydrogel comprising Gellan gum at about 0.75% by weight, polyacrylamide at about 0.5% by weight, sorbitol at about 35% by weight, distilled water at about 63.75% by weight and calcium chloride (CaCb) at about 0.065 pph. Another example of a formulation of a hydrogel comprising a polysaccharide is a hydrogel comprising Phytagel™ at about 1.5% by weight, sorbitol at about 35% by weight, distilled water at about 63.5% by weight and calcium chloride (CaCb) at about 0.01 pph. The hydrogels may include collagen for increased relative strength and elasticity. The hydrogel can be wetted with a suitable liquid including, but not limited to, hydrogen peroxide, sorbitol, glycerin, and water. [0023] The wettable material 58 may include a silica glass or a silica gel which can be wetted with a suitable liquid including, but not limited to, hydrogen peroxide, sorbitol, glycerin, and water. The wettable material 58 may include an optically transparent polyurethane which can be wetted with a suitable liquid including, but not limited to, hydrogen peroxide, sorbitol, glycerin, and water. Alternatively, the wettable material may be a silica glass or a silica gel membrane or an optically transparent polyurethane membrane. It will however be understood by a person skilled in the art that the wettable material may be any material capable of being wetted including a wet piece of optically transparent paper or other suitable optically transparent film or membrane. The bottom wall 50 of the tank 36 may alternatively be formed of silica glass. [0024] Referring now to Figure 5, the wettable material 58 results in a gap 64 at an interface between the wettable material 58 and resin 66 in the tank 36. The gap 64 may be a result of intermolecular forces of repulsion between the wettable material 58 and the resin 66 in the tank 36 and/or the gap 64 may be the result of a layer of water which separates the wettable material 58 and the resin 66 because the resin and water are immiscible. Figure 5 shows the gap 64 between the wettable material 58 at the bottom wall 50 of the tank 36 and an object 68 being formed from the resin 66 in the tank 36. The gap 64 allows the object 68 to be formed continuously because the object 68 is not formed directly on the bottom wall 50 of the tank 36 thereby doing away with the need for the object 68 to be peeled or pulled away from the bottom wall 50 of the tank 36. It will be understood by a person skilled in the art that the resin is cured or polymerized by irradiation to form the object 68.

[0025] Figure 6 shows the object 68 starting to be formed using the stereolithography system 10. The carrier platform 48 is disposed within the tank 36 as the light-emitting device 38 emits a substantially continuous blast or emission of light 70 as the object 68 starts to be formed on the carrier platform 48. The carrier platform 48 then moves continuously and upwardly away from the tank 36 as the light-emitting device 38 emits the blast or emission of light 70 and the object 68 is formed continuously as shown in Figure 7. This process continues until the object 68 is fully formed as shown in Figure 8. The gap 64, shown in Figure 5, between the bottom wall 50 of the tank 36 and resin 66 in the tank 36 allows the object 68 to be formed continuously because the object 68 is not formed directly on the bottom wall 50 of the tank 36, thereby doing away with the need for the object 68 to be peeled or pulled away from the bottom wall 50 of the tank 36. [0026] A controller 72 may be used to control the duration and the intensity of the blast or emission of light depending on the object being formed or part of the object being formed. The object 68 being formed in Figures 6 to 8 has solid parts, for example, a solid part 74, and hollow parts, for example, a hollow part 76, which are shown in Figure 7. The controller 72 will increase the duration of the blast or emission of light 70 and lower the intensity of the blast or emission of light 70 during the formation of the solid part 74. Conversely, the controller 72 will decrease the duration of the blast or emission of light 70 and increase the intensity of the blast or emission of light 70 during the formation of the hollow part 76. The duration of the blast or emission of light 70 is increased during the formation of the solid part 74 because additional time is required for the resin to cure or polymerize due to the larger surface area being cured. The intensity of the blast or emission of light 70 is lowered during the formation of the solid part 74 to minimize excess heat which may dry the wettable material 58. The duration of the blast or emission of light 70 is decreased during the formation of the hollow part 76 because less time is required for the resin to cure or polymerize due to the smaller surface area being cured. However, the intensity of the blast or emission of light 70 is increased during the formation of the hollow part 76 to accelerate the dimensional printing process.

[0027] 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.

[0028] 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.