APPARATUS FOR FABRICATION OF THREE DIMENSIONAL OBJECTS

Abstract

An apparatus for bottom-up fabrication of three dimensional objects, the apparatus comprising: a vat for a photosensitive polymer, the floor of the vat including a working surface arranged such that, in use, light incident on the working surface interacts with the photosensitive polymer at the working surface to fabricate a portion of the three dimensional object; a build platform capable of being inserted into the vat, the build platform having a planar surface; an elevator mechanism capable of adjusting the separation between the working surface of the vat and the planar surface of the build platform; and a rotation mechanism capable of varying the relative rotational position of the vat relative to the build platform, the relative rotation being about an axis which is normal to the working surface of the vat.

Claims

1.-16. (canceled)

17. A system for printing a three-dimensional (3D) object, comprising: a build head for holding at least a portion of said 3D object; a base for holding a resin; an actuator operatively coupled to said base, wherein said actuator is configured to move said base, to adjust a vertical distance between said base and said build head; an optical source configured to provide a light to said resin that is disposed between said base and said build head, wherein said light is sufficient to cure at least a portion of said resin; and a processor operatively coupled to said optical source and said actuator, wherein said processor is configured to: (a) direct said optical source to provide said light to said resin, to cure said at least said portion of said resin, thereby to print said at least said portion of said 3D object adjacent to a surface of said build head; and (b) subsequent to (a), direct said actuator to move said base, to adjust said vertical distance between said base and said build head.

18. The system of claim 17, wherein said movement of said base increases said vertical distance between said base and said build head.

19. The system of claim 17, wherein said movement of said base decreases said vertical distance between said base and said build head.

20. The system of claim 17, wherein, subsequent to (b), said processor is further configured to (c) direct said actuator to move said base, to further adjust said vertical distance between said base and said build head, to provide an additional resin between said base and said build head for printing an additional portion of said 3D object.

21. The system of claim 17, wherein said optical source is configured to direct said light through of said base and toward said resin.

22. The system of claim 17, wherein said base comprises an optically clear surface.

23. The system of claim 22, wherein said optically clear surface is a polymer.

24. The system of claim 22, wherein said optically clear surface is removable from said base.

25. The system of claim 17, wherein said actuator is a linear actuator.

26. The system of claim 17, wherein said actuator is a stepper motor.

27. A method for printing a three-dimensional (3D) object, comprising: (a) providing a resin adjacent to a base, such that said resin is disposed between said base and a build head, wherein said build head is for holding at least a portion of said 3D object; (b) directing an optical source to provide a light to said resin, to cure at least a portion of said resin, thereby to print said at least said portion of said 3D object adjacent to a surface of said build head; and (c) subsequent to (b), directing an actuator to move said base, to adjust a vertical distance between said base and said build head.

28. The method of claim 27, wherein movement of said base by said actuator increases said vertical distance between said base and said build head.

29. The method of claim 27, wherein movement of said base by said actuator decreases said vertical distance between said base and said build head.

30. The method of claim 27, further comprising, subsequent to (c), directing said actuator to move said base, to further adjust said vertical distance between said base and said build head, to provide an additional resin between said base and said build head for printing an additional portion of said 3D object.

31. The method of claim 27, wherein said optical source directs said light through of said base and toward said resin.

32. The method of claim 27, wherein said base comprises an optically clear surface.

33. The method of claim 32, wherein said optically clear surface is a polymer.

34. The method of claim 32, wherein said optically clear surface is removable from said base.

35. The method of claim 27, wherein said actuator is a linear actuator.

36. The method of claim 27, wherein said actuator is a stepper motor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

[0065] FIG. 1A shows a cross section of (a) a top-down prior art arrangement and FIG. 1B shows a bottom-up prior art arrangement.

[0066] FIG. 2 shows a cross section of an apparatus according to a first embodiment of the present invention.

[0067] FIG. 3A shows a cross section of a first vat and FIG. 3B shows a cross section of a second vat.

[0068] FIGS. 4A, 4B, 4C, and 4D illustrates the apparatus of FIG. 1 at various stages of use.

[0069] FIG. 5 shows a cross section of an apparatus according to a second embodiment of the present invention.

[0070] FIG. 6 shows a cross section of a third embodiment of the present invention.

[0071] FIG. 7 shows a cross section of a fourth embodiment of the present invention.

[0072] FIGS. 8A, 8B, and 8C shows a schematic views taken from above of the apparatus of FIG. 7.

[0073] FIGS. 9A, 9B, and 9C show cross sections of a third vat.

DETAILED DESCRIPTION

[0074] With reference to FIGS. 2, 3 and 4, the apparatus for bottom-up fabrication of three dimensional objects includes a vat 13 for a photosensitive polymer 16, a build platform 17 an elevator mechanism 19 and a rotation mechanism 7.

[0075] The floor of the vat includes a working surface 14 at which light from a light source 21 incident on the working surface interacts with photosensitive polymer 16 at the working surface to fabricate a portion of the three dimensional object.

[0076] The build platform has a planar surface 26, and the elevator mechanism 19 is arranged to hold the build platform above the vat such that when the working surface of the vat is located directly underneath the build platform, the planar surface of the build platform is parallel with the working surface 14.

[0077] The build platform 17 is the part onto which the cured cross-sections are built. The build platform 17 is attached to the elevator mechanism 19 by a quick release mechanism 18. The elevator mechanism 19 is powered by a stepping motor 20 which enables controlled movement of the build platform 17 in the z-axis (i.e. in the vertical direction). The elevator mechanism is therefore capable of adjusting the separation between the working surface 14 of the vat 13 and the planar surface 26 of the build platform 17, the separation being the distance in the vertical direction (i.e. the direction normal to the planar surface and normal to the working surface of the vat).

[0078] The rotation mechanism takes the form of a rotatable plate 7 onto which the vat 13 is mounted. The rotatable plate is circular and is connected to a stepping motor 10. The stepping motor controls the rotation of the circular plate and therefore the rotation of the vat in a controlled manner about an axis which is normal to the working surface at the floor of the vat.

[0079] The vat 13 includes an integral plug 25, and the rotatable plate 7 includes an aperture 24 (i.e. a cut-out) the plug 25 being configured to engage the aperture 24 to secure the vat 13 to the rotatable plate 7. As the plugs 25 are made from liquid silicone rubber they can deform into the apertures 24, thus fastening the vat 13 in place without the use of complex mechanisms. Furthermore, the apertures 24 and plugs 25 allow for quick and easy removal of the vat 13.

[0080] In the embodiment shown in FIG. 2, the axis of rotation about which the relative rotation occurs is the central axis of the rotatable plate 7.

[0081] The vat consists of a floor and surrounding walls, the floor including a first floor portion 14 having a first thickness and a second floor portion 15 having a second floor thickness, the second thickness being less than the first thickness. In this way, when the vat is filled with liquid photosensitive polymer the first floor portion is a raised working surface, and the second floor portion forms a deeper channel of photosensitive polymer.

[0082] The apparatus includes a source of electromagnetic radiation in the form of a digital projector 21. The digital projector 21 consists of a 405 nm LED, a spatial light modulator and a projection lens. The 405 nm LED can be turned on and off independently of turning the spatial light modulator on and off. The preferred spatial light modulator is a DMD however any spatial light modulator such as LCD, LCOS etc. could be used. The digital projector 21 is located such that the projected image fits within the bounds of the apertures 6 and 8 so that the projected image is in focus at the raised working surface 14. The size of the working surface 14 and the build platform 17 are slightly larger than the size of the projected image at the raised working surface 14. The apparatus is controlled by a networked computer 22, which receives the 3D object data over a network and synchronises the output of the stepping motors 10 and 20 and the projector 21 it also providing updates on the progress of the fabrication to other networked computers. Enclosing the top half of the apparatus 1 is a cover 23, which is fabricated from a transparent material that blocks electromagnetic radiation with wavelengths below 450 nm.

[0083] The apparatus 1 includes a frame 2, which has a bottom 3, a top 4, sides 5 and an aperture 6. The rotatable plate 7 is located directly above the top of the frame 5. The rotatable plate 7 includes an aperture 8 made from an optically clear material which allows light from the projector 21 to get to the vat 13. The rotatable plate 7 sits on casters 9 so that the rotatable plate is free to rotate.

[0084] Referring to FIG. 3, the vat 13 is either entirely fabricated from optically clear liquid silicone rubber (FIG. 3A) or the first floor portion 14 is fabricated from optically clear silicone pad and set into the second floor portion 15 that is fabricated from a stiffer non-optically clear liquid silicone rubber (FIG. 3B). The optically clear silicone pad which forms the first floor portion may be replaceable or may be permanently fixed to the second floor portion. Both types of vat are suitable for use with all of the apparatuses described herein.

[0085] It is crucial that the vat 13 is fabricated from a material that inhibits the cure of the liquid photosensitive polymer. The preferred material is generically referred to as liquid silicone rubber (LSR). More specifically, it is an addition cured vinyl terminated —polydimethylsiloxane, where the catalyst is platinum.

[0086] Phenyl resins are preferably added to the vat material to ensure that the optically clear silicones do not yellow under UV light. This is particularly advantageous where light of 405 nm is used. The optical grade of the LSR used is preferably QSIL 216 although QSIL 218 may also be used.

[0087] Where a stiffer non-optically clear liquid silicone rubber is used, due to its high tear strength and elastic modulus, MM 730FG is a suitable grade. In this way, the non-optically clear parts of the vat will be relatively stiff and will not deform easily. This is especially true for a wall thickness of at least 5 mm. MM260 grade may also be used.

[0088] In operation, the cross-sectional data of the 3D model and a configuration file is transferred to the controlling computer 22 by the user over a network. The vat 13 is then filled with liquid photosensitive polymer 16 up to a prescribed level. Once the operator has confirmed that the vat 13 has sufficient photosensitive polymer 16 to fabricate the desired 3D object and that the build platform 17 is clean and securely fastened to the elevator mechanism 19 the fabrication process begins. Checking of the photosensitive polymer 16 level may be done manually by eye or using a liquid depth sensor (not shown).

[0089] At the beginning of each fabrication the following calibration process is carried out. The calibration process ensures that all subsequent cross-sections are of the desire thickness.

[0090] As shown in FIG. 4A, the rotatable plate 7 is rotated to its start position by a first stepper motor 10. The start position is defined as the working surface 14 of the vat being located under build platform 17 and the apertures 6 and 8 being coincident. The start position may be defined by a micro-switch (not shown) located on the elevator mechanism. Thus, when the elevator mechanism reaches the start position, the micro switch is triggered. The elevator mechanism 19 and a second stepper motor 20 (not shown in FIG. 4) then move the build platform 17 to its start position at which the face of the build platform 26 is located beneath the surface of the photosensitive polymer 16 so that a layer of photosensitive polymer 27 less than 1 mm is sandwiched between the planar surface 26 of the build platform 17 and the working surface 14. Again a micro switch may define this start position (not shown).

[0091] The digital projector 21 then projects an image that is the maximum size of the photo mask onto the layer of photosensitive polymer 27 thereby curing it onto the planar surface 26 of the build platform 17. The duration of exposure of this first layer can be in the order of a minute.

[0092] As shown in FIG. 4B, after exposure, due to the oxygen richness of the liquid silicone rubber vat 13, which inhibits the cure of acrylate polymers, a lubricating layer 28 of uncured photosensitive polymer exists between the working surface 14 and the cured photosensitive polymer 29. This means that the cured photosensitive polymer has not formed a bond with the raised working surface 14.

[0093] As shown in FIG. 4C, the circular plate 7 is then rotated 180 degrees positioning the second floor portion (the deeper channel) 15 below the build platform 17. This increases the depth of uncured photosensitive polymer 16 between the cured photosensitive polymer 29 and the vat 13 thus the separation forces decreases and the elevator mechanism 19 can easily move the build platform 17 up by a distance defined by the cross-sectional thickness of the layers of the 3D model.

[0094] As shown in FIG. 4D, the rotatable plate 7 is then rotated a further 180 degrees, resulting in re-positioning of the working surface 14 beneath the build platform 17 and also recoating the working surface 14 with a fresh layer of photosensitive polymer 16. This means that there is a layer of photosensitive polymer 30 between the raised working surface 14 and the face of the build platform 26 that corresponds to the desired thickness of the specific layer or cross section of the 3D model.

[0095] After calibration, the following printing process is carried out:

[0096] 1. The digital projector 21 exposes the layer of photosensitive polymer 30 to the first ‘2D’ cross section as shown in FIG. 2. The exposure time depends on the desired thickness of the cross section.

[0097] 2. After exposure, and as described above, there exists a lubricating layer on uncured photosensitive polymer 28. The circular plate 7 rotates 180 degrees as shown in FIG. 4C positioning the deeper channel under the build platform 17.

[0098] 3. The build platform 17 is raised by the elevator mechanism 19 by desired cross-sectional thickness of the next layer.

[0099] 4. The circular plate 7 rotates back 180 degrees repositioning the working surface 14 under the build platform and re-coating the build platform with fresh photosensitive polymer that is the thickness of the next cross-section 30 as shown in FIG. 4D.

[0100] 5. During steps 2-4 the 405 nm LED is turned off by the controlling computer 22 and the controlling computer 22 prepares the next cross section to be displayed and sends this to the digital projector 21.

[0101] The above process is repeated until the final cross section is completed to create the final material layer of the three dimensional object.

[0102] Once fabrication of the three dimensional object is completed, the elevator mechanism 19 moves to an end position located at the top of the apparatus 1. This allows the easy removal of the build platform 17 using the quick release mechanism 18. The three dimensional object needs to be removed from the build platform 17 and cleaned. Whilst this occurs a second build platform 17 can be attached to the elevator mechanism 19 and the photosensitive polymer 16 level in the vat 13 can be checked to ensure the apparatus 1 is ready to fabricate the next three dimensional object.

[0103] FIG. 5 shows a second embodiment which differs from the first embodiment in that it further comprises a heating element 11, which has an aperture 12 that sits in between the rotation mechanism 7 and the vat 13 such that the apertures 8 and 12 are coincident and beneath the raised working surface 14.

[0104] In operation, the heating element 11 is turned on before calibration in order to heat up the resin 16 to a temperature of 40-90° C., the temperature depending on the formulation of the photosensitive polymer. A controlling computer 22 regulates the temperature of the heating element 11. At the end of fabrication the heating element is turned off and the photosensitive polymer 16 returns to room temperature.

[0105] The temperature of the photosensitive polymer needs to be precisely controlled in order to avoid the production of any vapours, which could be potentially unpleasant; this is achieved by the controlling computer.

[0106] FIG. 6 depicts a third embodiment, where like reference numerals are used to label the same features as the previous embodiments. The third embodiment differs from the first embodiment in that relative rotation of the vat and the build platform is achieved by a rotation mechanism arranged to rotate the build platform 17.

[0107] The rotation mechanism takes the form of a first stepper motor 10 attached to the elevator mechanism 19. The build platform 17 is attached to the first stepper motor 10 by quick release mechanism 18. In this embodiment, the axis of relative rotation is the central axis of the first stepper motor 10. The controlling computer 22 controls the rotation of the build platform about this central axis.

[0108] In this embodiment, there is no need for a rotation mechanism. The frame 3 includes an aperture 124 and the plug 25 is configured to engage the aperture 124.

[0109] A fourth embodiment is shown in FIGS. 7 and 8. This embodiment shares most of the features of the first embodiment but differs from the first embodiment in that a z-axis assembly (including the elevator mechanism 19, the build platform 17, the quick release motor and the second stepper motor 20) is located on top of the rotation mechanism 7 such that the rotation of the first stepper motor 10 has the effect of rotating the z-axis assembly 30. The vat 13 is in a fixed position on the top of the frame 4.

[0110] The operation of the system is similar to that described above, with the exception that it is the z-axis assembly 30 that rotates during the relative rotation and the vat 13 remains in a fixed position. This embodiment is advantageous in that the size of the apparatus 1 is reduced. The torque required by the first stepper motor 10 is also reduced, as is the duration of time taken between the curing of each material layer.

[0111] The operation of this embodiment is shown in FIGS. 8A, 8B, and 8C. The vat 13 is shown in FIG. 8a. with the working surface 14 of the first floor portion fabricated from optically clear liquid silicone rubber and the deeper channel 15 of the second floor portion. As shown in FIG. 8B, after a layer has been cured onto the build platform 17 the z-axis assembly 30 rotates 120 degrees about its central axis. This moves the build platform 17 from the raised working surface 14 into the deeper channel 15. The elevator mechanism 19 then moves the build platform 17 up by the desired thickness. As shown in FIG. 8C, the z-axis assembly then rotates back 120 degrees thereby moving the build platform back over the raised working surface at the new height thereby re-coating the build platform with fresh photosensitive polymer ready for fabrication of the next material layers.

[0112] 120° is the minimum angle of rotation required for the build platform to have moved completely away from the working surface. The angle could range between 120°-360°, but is preferably selected 120° as this leads to the shortest distance and therefore advantageously reduces the duration of time taken between layers for the overall print process.

[0113] Referring to FIGS. 9A, 9B, and 9C, a third type of vat is shown which is suitable for use with any of the apparatuses described herein. The vat of FIGS. 9A, 9B, and 9C is similar to that of FIG. 3B in that it includes a replaceable optically clear silicone pad. However, it differs from the first and second vats shown in FIGS. 3A and 3B in that the vat of FIG. 9A is not made entirely from silicone.

[0114] As shown in FIGS. 9A, 9B, and 9C, the vat comprises a vat body 13 and an optically clear silicone pad 32. The vat body 13 including a recessed section 31, and the optically clear silicone pad configured to be located in the recessed section.

[0115] The optically clear silicone pad 32 forms a first portion 14 of the floor of the vat which corresponds to a raised working surface of the floor of the vat. The remainder of the vat body 13 forms the second portion of the floor of the vat 15 as well as the surrounding walls of the vat. When the optically clear silicone pad is located in the recessed section 31 of the vat body, the raised working surface formed by the optically clear silicone pad is located at least 1 mm above the deeper channel of the second floor portion.

[0116] The recessed section 31 is fabricated from an optically clear material (preferably a thermoplastic) that is positioned such that when the vat 13 is fixed to the apparatus of any of the embodiments described above, the apertures in the frame, rotatable plate and heating element 6,8 and 12 lie are aligned with the recessed section 31.

[0117] The vat body 13 of the vat may be fabricated from any suitable material such as a thermoplastic. A water tight seal can be created between the first floor portion of the optically clear silicone pad and the second floor portion of the vat body 13.

[0118] In a further embodiment (not shown), the apparatus may take the form of any of the previously described embodiments, but the projector 21 is replaced with any directional source of electromagnetic radiation. This may be, for example a scanning laser or an array of LEDs.

[0119] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.