Remote monitoring and control of a three-dimensional object in a fabrication apparatus

FIELD

p-0002Embodiments of the invention relate to three-dimensional object fabrication techniques. More specifically, embodiments of the invention relate to rapid fabrication of arbitrary three-dimensional objects.

BACKGROUND

p-0003The state of the art in fabrication of arbitrary three-dimensional objects is fused deposition modeling (FDM) in which tiny deposits of plastic analogous to a pixel in a three-dimensional model are deposited individually to build a desired object from the ground up. Among the problems facing FDM are speed and cost. Because each subsequent deposit fuses to the underlying previously deposited plastic, the size of the deposit and the temperature control required to effect the fusing is strictly limited. As a result, very small amounts of plastic are deposited with each deposition and if the temperature is not precisely controlled, failure along corresponding knit line is manifestly likely. Moreover, because of the small amount of each deposit, the other constraints of controlling the system during fabrication, the time required to produce even a relatively simple object is measured in hours.

p-0004Among the additional problems includes the need to insure desiccation of the plastic supply as moisture in the supply further causes the risk of failure of proper knit during fusing. Also, because of the small amount of plastic deposited any overhang cantilevered portion of the object must be supported by a sacrificial material that is laid down during the fabrication process and then dissolved away post-fabrication. The sacrificial material requirement increases the cost and time required to fabricate any particular object. Typically, both the sacrificial material and the build plastic are provided as a spool often costing hundreds of dollars for a relatively small volume of plastic. Moreover, if there is insufficient plastic remaining on the spool to complete a desired build, the spool must be removed and replaced and it is difficult to change spools mid-process or reuse a partially consumed spool. This further increases the cost associated with FDM.

p-0005A faster lower cost system with higher reliability is desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

p-0006The embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” embodiment of the invention in this disclosure are not necessarily to the same embodiment, and they mean at least one.

p-0007<figref idrefs="DRAWINGS">FIG. 1</figref> is a diagram of an external view of a fabricator of one embodiment of the invention.

p-0008<figref idrefs="DRAWINGS">FIG. 2</figref> is an internal view of the fabricator of one embodiment of the invention.

p-0009<figref idrefs="DRAWINGS">FIG. 3</figref> is a center vertical sectional view of a fabricator of one embodiment of the invention.

p-0010<figref idrefs="DRAWINGS">FIG. 4</figref> is a view of the melt impeller of one embodiment of the invention.

p-0011<figref idrefs="DRAWINGS">FIG. 5</figref> is a cross-sectional view in which the build surface and extrusion nozzle can be seen.

p-0012<figref idrefs="DRAWINGS">FIGS. 6A-C</figref> are internal views showing the addition of a sub-element to a partially constructed object.

p-0013<figref idrefs="DRAWINGS">FIG. 7</figref> is a schematic representation of the welding process of one embodiment of the invention.

p-0014<figref idrefs="DRAWINGS">FIG. 8</figref> is an internal view of one embodiment of the invention with a mill arm extended.

p-0015<figref idrefs="DRAWINGS">FIG. 9</figref> is a schematic diagram of one embodiment of the invention.

p-0016<figref idrefs="DRAWINGS">FIG. 10</figref> is a schematic diagram of an embodiment of the invention permitting modular expansion.

p-0017<figref idrefs="DRAWINGS">FIG. 11</figref> is a flow diagram of operation of one embodiment of the invention.

DETAILED DESCRIPTION

p-0018<figref idrefs="DRAWINGS">FIG. 1</figref> is a diagram of an external view of a fabricator of one embodiment of the invention. Housing <b>110</b> has a portal <b>114</b> in its top surface <b>118</b>. Portal <b>114</b> may be accessed through sliding door <b>116</b> to load a material supply into the fabricator and also to retrieve a fabricated object there from. In some alternate embodiments, separate portals are provided for loading the material supply and retrieving the fabricated object. In some embodiments, the portal <b>114</b> represents less than 50% of the area of the top surface. Interface unit <b>112</b> may provide USB ports, wireless antenna, an Ethernet port, or other suitable media ports that facilitate the passage into the unit of three-dimensional data representing at least a portion of the geometry of a substantially arbitrary object to be fabricated.

p-0019<figref idrefs="DRAWINGS">FIG. 2</figref> is an internal view of the fabricator of one embodiment of the invention. Internally, there is an assembly zone <b>200</b> and a fabrication zone <b>202</b>. Sub-elements of the ultimate three-dimensional object to be created are fabricated within fabrication zone <b>202</b> and then put together (assembled) in assembly zone <b>200</b>. To a large degree, the maximum size of the object to be fabricated is constrained by the size of the assembly zone <b>200</b>. To a lesser degree, the size of the fabrication zone affects the ultimate size of the object. In many cases, the sub-element fabricated in fabrication zone <b>202</b> will be an entire layer of the object. It should be understood that sub-elements may be a portion of a layer or other portion of the object consistent with the geometry that is the source of the build instructions. It should be further understood that to be “consistent with the geometry”, the sub-element must have a size greater than a single voxel/pixel as a single voxel cannot be deemed to correspond to any distinct region with the geometry.

p-0020Within assembly zone <b>200</b> resides a build platform <b>234</b> including a turntable having a build surface <b>208</b> on which the object to be fabricated is assembled. Build surface <b>208</b> is provided with a rotational axis and a vertical axis. A driver within build platform <b>234</b> raises and lowers the build surface <b>208</b> along leadscrew shaft <b>232</b> to provide the vertical axis. An additional driver within build platform <b>234</b> rotates build surface <b>208</b> so that the object being fabricated can have any rotational orientation desired. In an alternative embodiment, the build platform may have x and y drives instead of a rotational drive, but such embodiment requires a larger assembly zone for the same size object.

p-0021When build surface <b>208</b> is driven to the top of its vertical range, it is exposed through the portal (<b>114</b> of <figref idrefs="DRAWINGS">FIG. 1</figref>), which permits easy access to a fabricated object.

p-0022In one embodiment, a material supply for fabrication is a monolithic helically-threaded plastic ingot <b>220</b>. The helical thread acts as part of the drive that advances the material supply, and may be consumed and eliminated as the material is used. In alternative embodiments, the thread may be replaced with gear teeth, and index step, a flange or series of flanges or the like, all features that may form part of the drive system to advance the material.

p-0023Build platform <b>234</b> is driven to its maximum height to be exposed through the portal. Any time the build platform <b>234</b> is at its maximum height, to protect the vertical axis from misalignment, one or more shear pins engage the platform so that vertical or lateral forces applied by a user are not applied to the drive servo or the vertical axis. An ingot is then loaded thereon and build platform <b>234</b> is then driven to its minimum height along shaft <b>232</b>. Plastic slide <b>230</b> then engages the plastic ingot <b>220</b> from build surface <b>208</b> and transports it laterally to be accessed by the fabrication zone <b>202</b>. Extrusion collar <b>224</b> is lowered over the ingot <b>220</b> and a peripheral helical ball screw drive therein engages the helical threading of the ingot <b>220</b> to allow the extrusion collar <b>224</b> to draw the ingot <b>220</b> upward. While other ways of lifting the material supply are possible such as a jack type lifter etc., the collar drive reduces the vertical space requirements over those alternatives. A bent leaf spring <b>226</b> automatically engages an index slot <b>228</b> that runs the length of the cylindrical ingot <b>220</b> to prevent the ingot <b>220</b> from turning while the collar drive is attempting to raise it. An internal drive <b>228</b> within the fabrication zone <b>202</b> then draws the ingot into the extrusion collar <b>224</b> so that it may provide source material for molder <b>204</b>.

p-0024<figref idrefs="DRAWINGS">FIG. 3</figref> is a center vertical sectional view of a fabricator of one embodiment of the invention. A processor <b>360</b> receives geometry for an object to be fabricated via one or more of the interfaces (<b>112</b> from <figref idrefs="DRAWINGS">FIG. 1</figref>). Processor <b>360</b> then controls the drivers to control the fabrication and assembly of sub-elements described below.

p-0025As can be seen, fabrication zone <b>202</b> includes a molder <b>204</b> having a compressor <b>328</b> that receives plastic from ingot <b>220</b>. Extrusion collar <b>224</b> draws the ingot <b>220</b> up into contact with melt impeller <b>326</b>, which melts and shaves the plastic and routes the resulting molten plastic via compressor <b>328</b> to an extrusion nozzle <b>330</b>. Compressor <b>328</b> provides a reservoir to allow a relatively large instantaneous supply of plastic without requiring high pressure or rapid acceleration of the entire material supply. Extrusion nozzle <b>330</b> is maintained in linear relationship with the compressor and does not translate within the fabrication zone. This linear relationship and lack of translation of the nozzle and supply source allows the material supply melting to occur at lower pressure, while the smaller material reservoir in the compressor <b>328</b> can operate at high pressure and therefore draw at greater speed. However, nozzle <b>330</b> may rotate and may be narrowed or widened, as is discussed more fully below.

p-0026When the ingot <b>220</b> is mostly consumed, e.g., 90%, in one embodiment a new ingot can be added to follow on behind the mostly consumed ingot reducing or eliminating waste. The level of consumption required before addition of an additional ingot is, to some degree, dependent on the length of the extrusion collar as the consumed ingot should be sufficiently inside the collar such that the collar can engage the helical threading of the additional ingot. A sensor may be included to measure material supply usage and report the supply level via the processor. It is desirable to report not only a “supply low” condition, but also the volume of supply remaining so that a user can know if sufficient material exists to complete and intended build.

p-0027Extrusion nozzle <b>330</b> is flush with a temperature-controlled plate <b>340</b> and draws a desired sub-element on a temperature-controlled receiving plate <b>342</b>. Plates <b>340</b> and <b>342</b> are retained in parallel relation. Receiving plate <b>342</b> may be slightly textured to allow improved grip by the molded plastic. The slight texture or surface pitting allows the plastic molded thereon to grip or, in other words, sustain a greater lateral force than is sustainable by plate <b>340</b>. Plate <b>340</b> has a smooth surface to allow the molded, cooled layer or sub-element to glide over the surface and not stick thereto. For simplicity of discussion, we shall refer to sub-elements as “layers”. However, one should understand that the discussion is equally pertinent to sub-elements generally.

p-0028By controlling the temperature of both receiving plate <b>342</b> and plate <b>340</b>, efficient cooling of the molded material can be assured. In one embodiment, heat absorbed buy one or both plates in cooling the molded plastic is recycled and returned to the melt heater via a heat pump to improve the energy efficiency of the system.

p-0029The space <b>344</b> between plate <b>342</b> and <b>340</b> defines the thickness of the layer. Thus, by varying the distance between the two plates, different thickness layers of the ultimate object may be achieved. In one embodiment, receiving plate <b>342</b> is driven by a driver to control the distance between plates <b>340</b> and <b>342</b>. The desirable thickness of a layer may depend on the variability of the edges of the object being fabricated. For example, where the edge is uniformly vertical over a distance a thicker layer up to that distance may be used. But where the edge is very irregular thinner layers to accommodate that irregularity or slope may be desirable. Notably, the thickness of the layer is not tied to voxel dimension. As explained below with reference to <figref idrefs="DRAWINGS">FIG. 8</figref>, minor irregularities can be addressed with an integral subtractive tool existing in some embodiments of the invention.

p-0030Additional drivers move receiving plate <b>342</b> relative to nozzle <b>330</b> to permit the arbitrary layer to be drawn. Because the aperture of nozzle <b>330</b> is variable width and can rotate, thicker or thinner walls may be drawn. In some embodiments the angular orientation or the extrusion may be controlled by for example air jets or water jets adjacent to the nozzle <b>330</b>. In other embodiments the nozzle <b>330</b> may pitch to mold an angled wall. In still other embodiments, a mechanical roller or wiper may be use to profile the side walls of the layer before or after they have hardened.

p-0031As with all molders, instances will occur when the molder needs to be purged to eliminate degraded build material, etc. In one embodiment, to minimize waste and the space required for its containment, the purged material may be drawn as a disk of a desired diameter on the receiving plate <b>342</b>. A waste tube having a minimally greater diameter may be provided near the fabrication zone. The receiving plate <b>342</b> may then be driven over to align the purge disk with the tube, lower the purge disk into the tube and translate away, thereby scraping the purge disk off into the tube. Subsequent purges will stack in the tube like quarters in a roll and reduce the waste storage requirements.

p-0032In one embodiment, ingot <b>220</b> formed having the helical threading also has a hydrophobic coating <b>320</b> which repels moisture but is also consumed as the ingot is melted. Beneath the hydrophilic coating is a core <b>322</b> of, for example, ABS or other suitable thermoplastic which forms the primary material of fabrication. Wax-based compounds may also be used as the thermally formable material for some applications (such as lost-wax casting mandrels). Typically the core <b>322</b> will exceed 70% by volume of the ingot and more commonly will exceed 95% by volume of the ingot <b>220</b>. This provides a very high density of material supply in a single piece form factor. Such an ingot is effectively self packaged reducing waste and production costs. In some embodiments the core <b>322</b> can be formed unitarily as a whole. In other embodiments, the core <b>322</b> is formed by first molding a shell and then filling the shell with additional material.

p-0033Within the assembly zone, the driver <b>334</b> to drive the vertical and rotational components of build surface <b>208</b> is shown. Build surface <b>208</b> is part of a turntable that rotates on bearings <b>338</b> when driven by driver <b>334</b>. The turntable includes a plurality of part-off rings <b>336</b> which are flush with build surface <b>208</b> during assembly. Once assembly is complete, rings <b>336</b> can be driven to elevate above surface <b>208</b> to separate the fabricated object from the build surface <b>208</b>. This avoids a prior art problem that the object must be split off of a build platen by hand.

p-0034<figref idrefs="DRAWINGS">FIG. 4</figref> is a view of the melt impeller of one embodiment of the invention. Melt impeller <b>326</b> resides within extrusion collar <b>224</b>. As extrusion collar <b>224</b> draws the plastic supply up into contact with melt impeller <b>326</b>, the melt impeller is heated to melt the surface of the plastic. Additionally, melt impeller <b>326</b> rotates and the channels <b>402</b> of melt impeller <b>326</b> channel the molten plastic towards the center portal <b>406</b> and into the extrusion compressor. Melt impeller has a relatively large surface area in contact with the surface of the ingot to increase the melting efficiency. The edges <b>404</b> of the channels <b>402</b> also serve to shave off small pieces of the plastic, further facilitating melting and allowing a relatively large volume of plastic to be delivered in a short time without excessive pressure.

p-0035<figref idrefs="DRAWINGS">FIG. 5</figref> is a cross-sectional view in which the build surface and extrusion nozzle can be seen. In this view, build surface <b>208</b> and part-off rings <b>336</b> are visible. Additionally, the surface of temperature control plate <b>340</b> and extrusion nozzle <b>330</b> are shown. Extrusion nozzle <b>330</b>, in this embodiment, is a slot. The length and orientation of this slot may be varied to change the profile and orientation of the molded plastic. In one embodiment, the slot with is under servo control as is the rotational orientation.

p-0036<figref idrefs="DRAWINGS">FIGS. 6A-C</figref> are internal views showing the addition of a sub-element to a partially constructed product. In <figref idrefs="DRAWINGS">FIG. 6A</figref> receiving plate <b>342</b> having layer <b>604</b> adhered thereto translates along track drive <b>608</b> into assembly area <b>200</b>. This clears a path for hot box <b>602</b> to shift downward to reside within the extrusion zone below track drive <b>608</b>. Hot box <b>602</b> is a thermally insulated storage box with one or more ohmic heaters therein. Hot box <b>602</b> retains welding iron <b>620</b> (shown in <figref idrefs="DRAWINGS">FIGS. 6B and 6C</figref>). Receiving plate <b>342</b> then translates back over hot box <b>602</b> along track drive <b>608</b>. The partially assembled object <b>606</b> is aligned with the layer <b>604</b> by the turntable under the control of the processor as mentioned above.

p-0037As shown in <figref idrefs="DRAWINGS">FIG. 6B</figref>, receiving plate <b>342</b> then hooks or otherwise engages iron <b>620</b> and translates back into assembly zone <b>200</b> bringing iron <b>620</b> with it. Iron <b>620</b> will be maintained at a temperature to melt the surface of the plastic used in fabrication to a degree that permits adhesion between two such heated layers of plastic. To that end, a temperature sensor may be coupled thereto to ensure that the ohmic heaters in the hot box <b>602</b> are engaged when the iron <b>620</b> falls below a lower threshold temperature and disengaged when the iron <b>620</b> rises above an upper threshold temperature. The iron <b>620</b> is desirably sized to be slightly larger than the largest possible object to be assembled as this reduces the precision with which the iron must be controlled. It is also desirable that the iron <b>620</b> is selected to have a significant thermal mass as the ability to retain sufficient heat to conduct welds in fairly rapid succession reduces the wattage of the ohmic heaters required to heat the iron. Typically, iron <b>620</b> will be Teflon coated or otherwise non-stick to prevent the heated plastic from adhering thereto. It is also desirable that the material selected for the iron <b>620</b> have a high heat transfer coefficient relative to the material to be welded. A heat transfer coefficient at least twice that of the weld constituent is desirable and often it will be an order of magnitude or more higher.

p-0038<figref idrefs="DRAWINGS">FIG. 6C</figref> shows the iron pressed between two elements to be connected. Once receiving plate <b>328</b> has drawn iron <b>620</b> fully from the hot box, the layer <b>604</b> is brought together with the object <b>606</b> having the iron there between. The pressure between the layer <b>604</b> and iron <b>620</b> causes surface melting on both the object <b>606</b> and the layer <b>604</b>. Typically, the entire expected contact area between the layer <b>604</b> and the expected contact surface of the object <b>606</b>. The layer <b>604</b> and object <b>606</b> are then separated to release the iron <b>620</b>. Preferably, the iron <b>620</b> is returned to the hot box <b>602</b> by, for example, stored mechanical force such as a spring. This results in a rapid return of the iron <b>620</b> and allows the surface molten layer <b>604</b> and object <b>606</b> to be pressed together creating a weld between them such that the resulting bond yields an object having substantially isotropic material properties. Because such a bond is relatively strong, it has no difficulty breaking adhesion between the receiving plate <b>328</b> and the layer <b>604</b>. Meanwhile, the hot box <b>602</b> with the iron <b>620</b> are returned to the position above the molder as shown in <figref idrefs="DRAWINGS">FIG. 6A</figref>.

p-0039Layer <b>604</b> has now been added to the object <b>606</b> and a further layer may be molded and added subsequently. Because a layer has its own lateral strength, it is unnecessary to build a sacrificial layer to support it. Rather, the layers can be cantilevered or otherwise extend over a space below without an underlying supporting substrate. In the case of the first layer, its lower surface would be melted by the iron <b>620</b> and it would be adhered to the build surface. Once the object <b>606</b> is completed, the build platform <b>234</b> is driven to its full height to automatically expose the object <b>606</b> through the portal in the top of the unit. Again at this point the shear pins engage to protect the vertical access. Then, as mentioned above, elevation of the part-off rings <b>336</b> separates the object <b>606</b> from the build surface. The part-off rings also help to protect from unintentional misalignment of the vertical axis because they reduce lateral force that would be required if the user were to manually break the object off the build surface.

p-0040In some embodiments, once exposed through the portal, the turntable may rotate 360 degrees to provide a rotational display of the completed object.

p-0041<figref idrefs="DRAWINGS">FIG. 7</figref> is a schematic representation of the welding process of one embodiment of the invention. At <b>702</b>, the two elements to be welded are aligned. At <b>704</b>, the iron is introduced between the two elements in aligned fashion. Alternatively, as previously disclosed, the alignment and the introduction of the iron may occur concurrently. In <b>706</b>, the elements are pressed against the iron to cause surface melting of both elements. At <b>708</b>, the elements are separated. At <b>710</b>, the iron is removed from between the elements. At block <b>712</b>, the slightly molten surfaces are pressed together and at stage <b>714</b> a new partial object including both sub-elements then exists. In other embodiments, the probe between the elements may introduce a glue or adhesive or additional molten plastic resin to cause the adhesion between the elements instead of heating the element to melt them.

p-0042<figref idrefs="DRAWINGS">FIG. 8</figref> is an internal view of one embodiment of the invention with a mill arm extended. A mill arm <b>802</b> is shown extended to allow it to detail a partially assembled object within the assembly zone <b>200</b>. Mill arm <b>802</b> can typically be driven in arc to provide access to the entire object under assembly. Mill arm <b>802</b> also includes a drive to adjust the incidence angle of the mill head <b>804</b>. Typically, provided that mill head <b>804</b> can reach the center of the turntable that provides build surface <b>208</b>, mill bit <b>804</b> can be used to detail any portion of the object simply by appropriately rotating the build surface <b>208</b>. In one embodiment, mill arm is provided with a suction head to collect waste particles that result from the milling. In another embodiment, an air jet is provided to clear the particles from the assembly area into a collection tray below. This avoids the risk of particles from the milling causing defects in subsequent welds.

p-0043While layers are being added within the assembly zone, typically mill arm <b>802</b> will be retracted. However, milling may be performed while extrusion is occurring within the fabrication zone. Thus, layer-by-layer access to the object can be provided to mill head <b>804</b> such that portions of the object that might be obscured when completed can be correctly detailed during the assembly of the object. The mill is driven by the motor <b>806</b> and controlled by the internal processor (not shown). In this way, minor defects in the extrusion fabrication may be corrected by subtractive detailing with mill head <b>804</b>. Additionally, edge detail may be provided to permit a thicker layer to be molded than would be possible if the extrusion needed to provide all the edge detail directly. Thus, the extrusion of a layer can be used to “get close” and the mill head <b>804</b> can be use to provide added precision.

p-0044<figref idrefs="DRAWINGS">FIG. 9</figref> is a schematic diagram of one embodiment of the invention. In one embodiment, plural fabrication zones <b>902</b> and <b>904</b> are associated with one assembly zone <b>900</b>. Layers or sub-elements may be manufactured and assembled in an interleaved manner to improve the speed of overall fabrication. In some embodiments, a camera <b>910</b> may exist within the assembly zone. The camera may be linked to a wide area network (WAN) <b>914</b> such as the Internet by link <b>912</b>. Link <b>912</b> could be a wired or wireless link and may be direct or through a host processor. A remote node <b>916</b> may the access the camera feed in substantially real time to monitor the assembly process. Remote node <b>916</b> could be a desktop computer, a smart phone, a tablet computer, a laptop, or any suitable WAN connected device. Some embodiments may include cameras in the fabrication zone(s) to permit similar remote monitoring of the fabrication process in addition to or instead of the assembly process.

p-0045Remote node <b>916</b> may also provide an interface that permits a user to send control signals back to the fabricator to control its operation, including for example starting or stopping the process, adjustment of system calibration, etc. In one embodiment, the interface is a web page served to the remote node <b>916</b>. In some embodiments, no control panel exists on the fabricator itself and all control of the operation is performed though the interface on remote node <b>916</b>. It is also within the scope and contemplation of the invention to have plural assembly zones in addition to plural fabrication zones. In some embodiments, one or more layers may be assembled in a first assembly zone and then added to other layers that have been previously assembled in the second assembly zone. By increasing the parallelism of layer production and assembly, output speeds can be increased.

p-0046<figref idrefs="DRAWINGS">FIG. 10</figref> is a schematic diagram of an embodiment of the invention permitting modular expansion. An array of additive fabrication cells <b>1002</b>, which may be each similar to the fabrication zone described with reference to <figref idrefs="DRAWINGS">FIGS. 1-5</figref> above, may be modularly added. In other words, a user may initially constitute the system with fewer than the 4×4 array of additive cells <b>1002</b> and then expand the system as demand requires to, in this example, achieve a maximum of 16 additive cells <b>1002</b>. Similarly, each additive cell <b>1002</b> may have a corresponding subtractive cell <b>1004</b>, such that a layer fabricated in an additive cell <b>1002</b> is transported to the adjacent subtractive cell for detailing, for example, with a mill head, before being transported by lateral transport <b>1006</b> to elevator <b>1008</b>.

p-0047Elevator <b>1008</b> raises the individual platen <b>1010</b> and places it in its intended order within the platen hopper stack <b>1012</b> residing in hopper <b>1014</b>. The bottom platen in the platen stack <b>1012</b> is transported into assembly zone <b>1018</b> and aligned with build object <b>1016</b>. Proper alignment of the platens can be assured by registration holes and pins that guarantee a known orientation. The weld layer <b>1020</b> is then welded within the assembly zone <b>1018</b> in a manner similar as described above in connection with <figref idrefs="DRAWINGS">FIGS. 6A-C</figref>. Specifically, a suitable hot plate heats the surface of both build object <b>1016</b> and weld layer <b>1020</b>. The hot plate is then removed and the layers are pressed together. In this manner, because no post-weld detailing is required, the object can be assembled layer by layer as quickly as the welding can occur.

p-0048Once the layer is removed from its platen, the platen itself can be transported back laterally to the elevator shaft which will return it to a lateral transport <b>1006</b>, which will return it to a waiting additive cell for extrusion of a subsequent layer. While in the shown embodiment a 4×4 array of additive and subtractive cells is shown, it is envisioned that other embodiments of the invention may permit either larger or smaller arrays of cells. Moreover, it is also envisioned that an additional elevator hopper and assembly zone may be added, for example, to the opposite end of the fabrication array such that two objects may be built concurrently. Notably, because the creation of layers in the additive cells, the detailing of layers in the subtractive cells and the addition of layers in the assembly zone can all occur in parallel, higher speed object creation is rendered possible.

p-0049In some embodiments, assembly zone <b>1018</b> is sufficient to accommodate the build of an object that has layers larger than any of the additive cells <b>1002</b> can draw at one time. This will generally imply that edges of layer sub-element should be welded together. However, by appropriately selecting the sub-elements of subsequent layers such that vertically pressed lamination occurs, the need for a side pressure process can be eliminated. For example, presume a cylindrical object for which an additive cell <b>1002</b> can only produce a third of the cylinder. If the three pieces forming each layer are shifted ten degrees on each subsequent layer, the weak joint between the sub-elements of any single layer does not cause systemic weakness in the finished object.

p-0050<figref idrefs="DRAWINGS">FIG. 11</figref> is a flow diagram of operation of one embodiment of the invention. At block <b>1102</b>, material from which a three-dimensional object is to be built is loaded into a fabricator. At block <b>1104</b>, geometric data corresponding to the object to be built is received in the fabricator. Geometric data may have been processed prior to loading to expressly indicate the sub-elements in order of build, or they may be processed internally within the apparatus from a simple three-dimensional model. At block <b>1106</b>, a layer of the object to be built is molded onto a receiving plate in a fabrication zone of the apparatus. That layer is then transported and bonded to the object being formed at block <b>1108</b>. In the case of the first layer, it is bonded to a build surface and forms the substrate for subsequent additional layers to be bonded. A determination is made at decision block <b>1110</b> whether subtractive detailing is required. If subtractive detailing is required, the object is milled to subtractively detail the layer at block <b>1112</b>. The determination is made at block <b>1114</b> whether the object is complete. If the object is complete, the object is ejected from the fabricator at block <b>1116</b>. Otherwise, a next layer is molded and bonded and the process continues. It should be understood that, while this is shown as a linear flowchart, many of these operation can occur in parallel. In particular, it may be possible to mill one layer while extruding another or, depending on the number of extrusion zones and the parallelism permitted, extruding and bonding may occur concurrently. These levels of parallelism are intended to be within the scope and contemplation of the invention.

p-0051While embodiments of the invention are discussed above in the context of flow diagrams reflecting a particular linear order, this is for convenience only. In some cases, various operations may be performed in a different order than shown or various operations may occur in parallel. It should also be recognized that some operations described with respect to one embodiment may be advantageously incorporated into another embodiment. Such incorporation is expressly contemplated.

p-0052It should be appreciated that reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Therefore, it is emphasized and should be appreciated that two or more references to “an embodiment” or “one embodiment” or “an alternative embodiment” in various portions of this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined as suitable in one or more embodiments of the invention.

p-0053In the foregoing specification, the invention has been described with reference to the specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.