Additive manufacturing of building and other structures

Abstract

Freeform, additive manufacturing equipment, processes and products, including residential, commercial and other buildings. A movable extruder places extrudate that solidifies in open space to create scaffolding or skeletons of buildings and other products. Elongated extrudate elements are fused to each other or connected by other means to form a cellular structure. Filler material such as polymeric insulating foam may simultaneously or thereafter be placed within the cellular structure to contribute desired strength, rigidity, insulative, barrier or other properties. Finish materials may also be applied.

Claims

1. An object comprising: a. a three dimensional cellular matrix structure comprising a framework of a plurality of extrudate members intersecting at joints, wherein at least three of the plurality of extrudate members extend along three different extrudate pathways, the framework further defining interstitial spaces; b. filler in at least some of the interstitial spaces; and c. wherein the framework of extrudate members of the cellular matrix defines an arrangement of individual cells, each cell defining a cell geometry, wherein the cell geometries of the individual cells are not all uniform with one another.

2. The object of claim 1, further comprising a different filler in at least some of the other of the interstitial spaces.

3. The object of claim 1, wherein the object comprises a component of a building.

4. The object of claim 3, wherein the framework of the plurality of extrudate members comprises at least one of a thermoplastic or thermoset plastic material.

5. The object of claim 4, wherein the filler comprises insulating foam.

6. The object of claim 3, wherein the filler comprises concrete.

7. The object of claim 3, wherein the filler contributes at least one of structural integrity, thermal insulation, rigidity, strength and a fluid barrier.

8. The object of claim 3, wherein the cellular matrix structure has at least two sides and further comprising a finish material applied to at least one of the cellular matrix structure sides.

9. The object of claim 8, further comprising a different finish material applied to at least another of the cellular matrix structure sides.

10. The object of claim 3, wherein the plurality of extrudate members are reinforced by fibers incorporated in the extrudate members.

11. The object of claim 10, wherein the fibers comprise at least one of fiberglass, carbon, ceramic and polymer.

12. The object of claim 3, wherein the object is an internal wall structure of an air liner.

13. The object of claim 1, wherein at least some of the joints are located in an interior area of the cellular matrix structure.

14. The object of claim 13, wherein at least some of the joints in the interior area are at an intersection of at least three extrudate members.

15. The object of claim 13, wherein at least some of the joints in the interior area are at an intersection of at least four extrudate members.

16. The object of claim 1, wherein the cellular matrix structure defines at least one repeating pattern of cells.

17. The object of claim 1, wherein the cellular matrix structure comprises a scaffold for the filler.

18. The object of claim 1, wherein at least some of the plurality of extrudate members include a plurality of arms in cross-section.

19. The object of claim 1, wherein the cellular matrix includes a first region and a second region, wherein cells in the first region have a different geometry than cells in the second region.

20. The object of claim 19, wherein the first region of the cellular matrix is configured for a higher stress on the cellular matrix than the second region.

21. The object of claim 19, wherein the cellular matrix and the filler comprise a composite structure.

22. The object of claim 1, wherein the filler comprises a first type of filler in a first portion of the cellular matrix and a second type of filler in a second portion of the cellular matrix.

23. An object comprising: a three dimensional cellular matrix structure comprising a framework of a plurality of extrudate members intersecting at joints, wherein at least three of the plurality of extrudate members are in a non-planar arrangement and extend along three different extrudate pathways, wherein at least some of the extrudate members have a cross-sectional shape defining a plurality of arms, the framework further defining interstitial spaces; wherein the framework of extrudate members of the cellular matrix defines an arrangement of individual cells, wherein at least some of the cells have a hexahedron geometry.

24. The object of claim 23, wherein the framework of extrudate members is a three dimensional truss.

25. The object of claim 23, wherein the object comprises a curved component of a structure.

26. The object of claim 25, wherein the object comprises a curved wall component for a building.

27. The object of claim 23, wherein at least one side of the hexahedron cell geometry includes an extrudate member extending diagonally between two non-adjacent vertices of the side of the hexahedron.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Illustrative embodiments of the present invention are described in detail below with reference to the following drawing figures:

(2) FIG. 1 is a perspective view of one embodiment of this invention.

(3) FIG. 2 is axonometric view of an exemplary extruder mechanism of this invention.

(4) FIG. 3 is an exploded axonometric of the extruder mechanism shown in FIG. 2.

(5) FIG. 4 is a section through the long axis of the extruder shown in FIG. 2.

(6) FIG. 5 is a view of one side of the extruder-shown in FIG. 2.

(7) FIG. 6 is a view of the front of the extruder shown in FIG. 2.

(8) FIG. 7 is a top view of the extruder shown in FIG. 2.

(9) FIG. 8 is a bottom view of the extruder shown in FIG. 2.

(10) FIGS. 9-12 depict nozzle heat transfer variations.

(11) FIG. 13 depicts alternative extrudate shapes.

(12) FIG. 14 depicts a nozzle with multiple orifices.

(13) FIG. 15 depicts a nozzle with multiple material sources.

(14) FIG. 16 depicts a nozzle with multiple orifices supplied from multiple materials sources.

(15) FIG. 17 depicts an exemplary nozzle showing feedstock in filament form.

(16) FIG. 18 depict a nozzle that extrudes materials together with a fiber.

(17) FIG. 19 is an exemplary isometric view of segments in accordance with this invention.

(18) FIG. 20 is an isometric view of exemplary robot movement.

(19) FIG. 21 is an isometric view of an exemplary wall illustrating programming ranges of patterns within a wall.

(20) FIG. 22 is a perspective view of an object being constructed with a movement mechanism capable of multiple degrees of motion.

(21) FIG. 23 depicts a mobile platform for manipulating an extruder.

(22) FIG. 24 depicts a hand-held embodiment of an extruder of this invention.

(23) FIGS. 25-30 are schematic depictions of exemplary cellular structures of various embodiments of this invention.

(24) FIG. 31 is a schematic perspective view of a structure of an embodiment of this invention.

(25) FIG. 32 is an isometric view is a mobile platform in use in accordance with an embodiment of this invention forming a wall structure.

(26) FIG. 33 depicts steps of an exemplary method of this invention.

DETAILED DESCRIPTION

(27) The subject matter of embodiments of the present invention is described here with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described.

(28) Extruder

(29) In one embodiment of this invention, depicted in FIG. 1, an extruder assembly 101 is manipulated by a robotic armature system 102 to fabricate a structure 103. The nozzle end 104 of extruder assembly 101 is moved along a pathway 105 while material is dispensed from the orifice 106 of the nozzle 104 at a controlled rate. Once the material exits the orifice 106 it is rapidly cooled by air jets that harden the extrudate to a solid that can be formed without support for a given segment length. As the extruder 101 dispenses material, the motion of the extruder through space at a controlled speed is coordinated with the extrusion rate such that material is dispensed along a pathway in a controlled manner. The rate of deposition may be faster or slower than the induced motion to create varying effects. The motion is programmed or controlled via computer 108 that is coupled to a controller 109 that controls the motion of the robot 102. Temperature is controlled by a thermostatic temperature controller 110 attached to the heating elements of the extruder 101. Air pressure and air movement are supplied by an air compressor 111 fed to the extruder via a hose 112. Material is fed to the extruder mechanism 101 from a supply source 113 via a material feed system 114.

(30) As illustrated in FIGS. 2-8, an exemplary extruder 101 holds material 201 in pellet form temporarily in a hopper 202 that feeds the material into the barrel 203 of the extruder through an opening 204. Within the barrel 203 a screw 205 rotates to pulverize, partially melt, and dispense the material. The screw is preferably designed for the particular extrusion process in use. The rotation of the screw is driven by a motor assembly 206 that may include a gear assembly 207 to control the motor speed and a motor controller 208 to regulate the speed of the motor 206.

(31) The motor 206 may be mounted to the thrust bearing assembly 209 with the motor drive shaft 210 connected to the screw by a coupling 211. The thrust bearing assembly contains means to resist the thrust of the screw with a rotational thrust bearing 212.

(32) As the material is pushed along by the extrusion screw, heat is applied to facilitate the melting process by various means, such as resistance heater bands 213 mounted around the extruder at various locations. Other methods to add heat may include other resistance heat methods such as cartridge heaters, or coil heaters. Other methods such as heated air, heated fluids, vibratory, ultrasonic, infrared, direct current interaction or lasers may be used. Temperature may be monitored by thermocouples 214 and controlled thermostatically at each heater band 213.

(33) A breaker plate 215 with holes in a variety of patterns may be used to generate back pressure in the barrel and ensure a consistent mixture in the extrudate. A shutoff valve 216 may be employed that controls the flow of the extrudate. Valve 216 may work in coordination with the pressures induced by the rotation of the screw 205 to open and close a spring loaded opening mechanism, or it may be controlled in other manners, such as pneumatically.

(34) An extruder may be monitored as to location, temperature, flow rate and otherwise with great precision, enabling manipulation of the extruder and control of the extrudate it produces with similarly great precision. For instance, a pressure transducer may be used to monitor internal pressure within the barrel. Temperature sensors within the barrel and or within the melt may be used to precisely control the temperature of the material.

(35) Nozzle

(36) The nozzle 217 (sometimes called a die) forms the shape of the material and dispenses it from an orifice 218. The heat may be removed from the material by means of air flow 219 cooling through and out of the nozzle 217 through opening 220 so that the air flows around extrudate 221. The air may also be used to remove heat within the nozzle without flowing onto the extrudate 221.

(37) FIGS. 9-12 depict structures that use other fluids that may also recirculate out of the nozzles and that may include supplementary heating and cooling systems. These fluid passageways may be internal or external to the nozzles.

(38) FIG. 9 illustrates a system where a fluid 901 is introduced into the nozzle 217 that circulates around the material 201 while it is moving through the nozzle 217. This fluid then exits nozzle 217 and flows over the extrudate 221. The fluid may either be a liquid or a gas.

(39) FIG. 10 employs a similar fluid as FIG. 9 except the fluid 901 re-circulates and does not flow over the extrudate 221. FIG. 11 illustrates a similar approach as FIGS. 9 and 10 but the fluid 901 exits the nozzle and does not flow directly onto the extrudate 221. FIG. 12 illustrates a similar approach as FIG. 9 except that the fluid 901 circulates external to the nozzle and does not flow within the nozzle proper. The fluid 901 may circulate around the nozzle and flow onto the extrudate 221.

(40) Motor speed, valve operation, temperature control, and heat removal may all be controlled and operated in coordination with each other or may be controlled separately.

(41) The shape of the extrudate 221 may be adjusted by various methods, either by changing nozzles, dynamically adjusting the shape of the extrudate 221, or changing the rate of motion causing the material to accumulate or stretch as shown in FIG. 13. The shape of the extrudate may be modulated to be thicker 1301 or thinner 1302 in certain areas or the cross section may be changed from one shape 1303 to another shape 1304 or 1305.

(42) FIGS. 14, 15 and 16 depict nozzle variations, including nozzles that dispenses extrudate from multiple holes simultaneously, nozzles that dispenses extrudate from two components and or at different times in a connected or disconnected manner. FIG. 14 illustrates a nozzle 217 with multiple orifices 218 extruding from one material source 201. FIG. 15 illustrates a nozzle 217 with one orifice 218 combining multiple material sources 201a and 201b that may be mixed prior to exit from orifice 218 or extrude in a laminated format. FIG. 16 illustrates a nozzle 217 with multiple orifices 218a and 218b that are supplied from multiple materials sources 201a and 201b that may be controlled together or separately.

(43) Filament

(44) FIG. 17 depicts an alternative extruder assembly 1700 that operates similarly to a common 3D printer whereby filament 1701 is fed into a heating chamber 1702, is melted, and extruded from the nozzle 1703. The nozzle 1703 would work similarly to the description of nozzles in FIGS. 9-12, except that the material from which the extrudate is formed is initially in filament form rather than pellet form.

(45) Materials

(46) Among many other existing and yet-to-be-developed materials, ABS plastic resin becomes fluid within a range of temperatures but in a controlled manner depending on the desired result. ABS with a fibrous or other additive may be used to change certain properties of the extrudate. Various other thermoplastics may be utilized to achieve similar results.

(47) Any other materials may be used that can be extruded through an orifice and then rapidly solidify. Some of these may be thermoplastic, thermoset, epoxies, wax, polymer, metallic, foam, organic, cementitious, ceramic, biological, or other existing and later-developed materials. Some such materials are fluids above certain temperatures and rapidly solidify when their temperature drops.

(48) Other usable materials may solidify as a result of chemical processes such as two-part materials, like some epoxies that crosslink and solidify after the two parts are combined, or other materials that crosslink after introduction of a catalyst, or exposure to moisture or ultraviolet light. Some such materials bond to themselves, at least when contact occurs above certain temperatures or before chain linking or other chemical reactions have fully occurred. Other materials systems may utilize a structural extrudate and a separately supplied bonding material or agent dispensed at the points of contact of the structural extrudate, such as a cyanoacrylate or other fast-acting adhesive.

(49) One method of reinforcing the extrudate is through the addition of a continuous or broken strand(s) of fiber reinforcing. Common materials used for this may include glass fiber, ceramic fiber, metallic wire, or carbon fiber strands. As depicted in FIG. 18, the fiber 1801 is incorporated into the melt 1802 such that the melt may encapsulate the fiber 1801 strand to reinforce each segment of the cellular matrix fabricated from the fiber 1801 and melt 1802 extrudate 1803.

(50) Other existing and future extrusion techniques may also be employed to combine materials or enhance extrusion, including use of a mandrel or air or other fluid or by, for instance, utilization of bladed sheet flow or blown film extrusion techniques.

(51) Motion

(52) Extruder nozzle motion may be accomplished in any way that places the nozzle where it needs to be at a particular time. In one embodiment, as generally depicted in FIG. 1, extruder and nozzle movement is provided by a multiple axis industrial robot 102. The extruder 101 is attached to the robot 102 by means of a bracket assembly 222 shown in FIGS. 2, 3, 4 and 6 that which mounts to the end of the armature 223 shown in FIGS. 4 and 6.

(53) The robot 102 is programmatically controlled by a computer 108 to execute the motion necessary to create the desired cellular matrix pathways. One method for producing this motion is by drawing the cellular matrix in a CAD program that is then translated into a sequential motion process. to control the robot 102. This motion is programmed to include information that coordinates the extrusion speed, temperature control, cooling mechanism and other parameters for extrusion.

(54) Such a basic motion control program allows the movement mechanism to move from one point to another point along a prescribed path at a certain speed as shown by reference to exemplary three dimensional shapes in FIGS. 19 and 20. While the robot 102 is executing such movement of the extruder 101 and attached nozzle 217, the extruder motor 208 may also be activated at a prescribed speed, a material shutoff valve 216 may be opened, temperature of various portions of the apparatus and the material may be monitored and heating or cooling mechanism(s) may be turned on or off as appropriate. The motion of the robot may pause to create (as shown in FIG. 20) a node 2001 or joint 2002 built up with the extrudate 2003. The cooling or heating systems may turn off or on to modulate solidity in the extrudate 2003 viscosity or other flow characteristics. Motor 206 speed may also be changed to increase or decrease the extrudate flow out of the extruder 101. The rate of extrusion, rate of motion, heat transfer, cooling, heating and fusing are coordinated to produce a solid filament of desired shape and size along the prescribed pathway bonded to other filaments or other structures where desired.

(55) Sequence

(56) As shown in FIGS. 19 and 20 the program sequence and resulting nozzle movement allows material to be added that connects to previously deposited material at joints without passing back through previously applied material. This programming determines the overall shape of the final structure along with all the interconnected sequential segments forming a part of it.

(57) Segments

(58) Each of these segments such as segments 2004 and 2005 in FIG. 20 may be derived by breaking down the cellular matrix into pathways such as the path 2-3 and the joint 1, 5. Each pathway is assigned characteristics such as speed of extrusion, speed of motion, temperature, and cooling. These characteristics determine how elements such as segments 2004 and 2005 and the resulting structure comprised by those elements will be built up. Once a region of the cellular matrix (like the cells depicted in FIGS. 19 and 20) is complete, additional material is added to build up the structure in a horizontal and/or vertical manner by the addition of more cells.

(59) Range Programming

(60) Another method of building up the cellular matrix in lieu of discreet pathway programming is illustrated in FIG. 21. In this technique, certain patterns of material deposition 2101, 2102, or 2103 are applied to similarly structured volumes of space. The program may dictate the application of a certain cellular pattern over a particular range without having to program each discreet motion step. In this manner, a structure may be divided into ranges that would inform the pattern formation by the robot and the motion programming may be substantially simplified.

(61) The example wall illustrated in FIG. 21 has certain physical characteristics and internal stresses as a result of its design. The application of the cellular matrix and resulting motion control programming may be algorithmically automated to respond to the geometry and stresses within the wall by allocating certain patterns of formation 2201, 2202, or 2203 to certain ranges within the wall. In an area of higher stress, geometry 2101 may be applied to range A1, but in an area of lower stress, geometry 2102 may be applied to range B2. This method of algorithmically responding to the necessary requirements of a given wall area may significantly simplify the programming and reduce material use by optimizing the internal structure for the stresses needed to be resisted.

(62) Feedback Sensors

(63) To ensure accuracy in the built structure, feedback and adjustment mechanisms may be employed that sense the actual conditions of the joints and other previously applied materials, as distinguished from the ideal designed conditions of the joints and previously applied material. Since deflection, material creep, wind, temperature, and other real world conditions will affect the previously extruded areas, methods to dynamically adjust the motion and extrusion parameters to accommodate these factors may be employed to increase the accuracy of the end result. Some of the methods may include range finding, optical feedback, motion sensing, photogrammetry, motion capture, sonar, lidar, among other feedback mechanisms.

(64) Motion Methods

(65) As shown in the drawings, alternative methods for moving the extruder may be employed. These may include, without limitation, a gantry system, CNC system, or traditional 3D printers with additional axes of control as illustrated in FIG. 22, hydraulic equipment as depicted in FIG. 23, or handheld versions of the extruder as shown in FIG. 24.

(66) The explained above, purpose for the extruder and the movement mechanism is to connect points to create a pathway along which material is deposited. Each pathway is added to others to finally create the cellular matrix which makes up the internal structure of the final building or object.

(67) Cellular Matrix

(68) The cellular matrix is created by a applying a given cellular pattern to the internal volume of a solid as illustrated with the examples of FIGS. 25-30. The cellular pattern may be self-repeating or may be different from one cell or group of cells to another. Idealized versions of the structures of molecules, plant, animal, or human cells, minerals, foams, naturally occurring patterns, mathematical formulae, polyhedral, space frames, trusses or other patterns may be used to modularize the internal volume of the overall structure. The purpose of the cellular matrix is to create a balance between material used, space occupied, and strength derived from a certain pattern. The material, diameter, shape, and length of each extruded segment will determine the density of the cellular matrix. As with natural cellular constructions, various qualities may be modulated to achieve various results but may include structures to add strength, separation, flexibility, openness, rigidity, and specificity of function among other beneficial qualities.

(69) In addition to the above-described and illustrated methods of construction of the cellular matrix, there are other methods of fabricating the cellular matrix that do not include extrusion, but may produce substantially similar end results. For instance, crystallizing foam, growing organic structures, the drying process within a medium, modular bricks, connected faces of a panelized structure or using conventional additive manufacturing to make the structures specified in this patent.

(70) Added Materials

(71) The strength and durability of a structure may be a function of the extruded material alone, but additional benefits may be realized by utilizing the cellular matrix as a scaffold onto which other materials are applied to fill the voids between the individual segments. Similar to a living cellular structure, the cell walls alone provide some strength, but in most cases without the internal volume filling material, the structure would not hold up. Like the water pressure in human bodies, calcification in bones, or turgor pressure in plants, the material filling the cells provides additional strength for structural support. In one aspect of the present invention, a similar method of construction utilizes material filling the cellular matrix to additionally strengthen the overall structure.

(72) Other methods to combine materials with the cellular matrix may be used such as attachment of materials to the exterior faces or that grow into the voids of the structure.

(73) Walls & Buildings

(74) In a structure used as a building, one method for filling the cellular matrix may be described with reference to FIG. 31, where the internal structure 3101 of a wall 3100 includes a septum layer 3102 that separates one area of the wall from the other areas. Multiple septums 3102 may be utilized, but in this example one septum layer 3102 is used. Spray foam insulation is applied from the interior side 3112 of the wall and is stopped by the septum layer 3102 from penetrating further into the wall assembly. The spray foam 3103 fills a depth determined by reference to the R-value desired from the wall assembly 3100.

(75) The next step is the application of concrete 3104 from the exterior side 3113 by means of a shotcrete, pumping or other appropriate application mechanism or technique. Concrete 3104 may be applied so that the entire matrix 3101 is filled with concrete 3104 and then finished or the concrete 3104 may be applied in a thickness that leaves the exterior face grid 3105 partially exposed. A stucco finish 3106 may then be applied using the outer face 3105 of the cellular matrix as lathe to which the stucco is secured. Other exterior finishes may also be utilized that are attached to the concrete 3104 and grid 3105 utilizing existing or yet to be developed construction practices and products. Once the concrete 3104 cures, it may serve as a significant structural element of the building, as is common in thin shell concrete construction. In this case, however, the cellular matrix 3101 is acting as both a form and part of the tensile reinforcement of the concrete. After sufficient curing of the concrete 3104, spray applied gypsum 3107 may be applied to the interior face 3112 of the structure, struck off with a tool, sanded smooth, and finished as is common with other interior wall finishes. Numerous other interior surface finishes may also be used.

(76) Certain areas or portions 3108 of the cellular matrix may be extruded in a solid fashion to create decorative trim elements 3108, joints, or to help integrate other fixtures or equipment into the wall assembly. Conduit, raceways, wiring, airways, and pipes may be either printed in situ or integrated after the concrete cures. If completed after the concrete cures, spaces may be routed out in the foam 3103, and normal conduit/piping may be placed in the routed voids and then reinsulated, if desired, prior to the application of the interior finish.

(77) One optional method to increase the strength of the structure is to apply a sprayed reinforcing material that coats the outer surfaces of the extrudate and begins to build up at joints to round out and reinforce the cellular matrix. The sprayed reinforcing material may provide a rigid sheath around the extrudate, adding strength without adding substantial weight. This reinforcement technique could be analogized to the calcification method that certain microscopic sea creatures use to build their skeletons.

(78) The addition of materials to the cellular matrix may be accomplished with conventional normal manual processes, may be automated by utilizing the movement mechanisms described here or by any other techniques that accomplish the desired addition of materials to the matrix.

(79) Scale and Utilization

(80) The building construction examples described here are merely exemplary; myriad other uses are possible, including, without limitation, use in the fields of building construction, manufacturing, agriculture, automotive, aerospace, fashion, three-dimensional printing, furniture, and medicine among many others. The scale in the construction industry may be between to 6 or greater per segment. Smaller scale segments may be as small as those produced by skipping layers on a 3D printer on the order of 0.002. Larger scale structures may incorporate volumes and spans as great as several feet or more. The spans possible and desirable depend on material properties, extrudate section properties, and segment shape.

(81) A small device may be built with the techniques described here. For instance, an object with hollow interior voids may be fabricated and the exterior coated with porcelain enamel to form a coffee cup. A larger scale example might be the internal wall structure of an airliner where the exterior skin is fitted over a cellular matrix with an internal space made up of insulation, an airtight pressure vessel membrane, and interior finishes.

(82) With the robotic armature or other motion mechanisms, additional scale and motion flexibility may be gained by mounting the mechanism on a rail system that allows for a greater degree of motion. A more flexible method may be enabled by mounting a robotic arm on a mobile platform to produce a robotically controlled platform 3200 that has infinite range of motion as shown in FIG. 32.

(83) Logic Flow

(84) FIG. 33 is a logic flow diagram. This is a basic, exemplary overview of steps that may be taken to produce a given structure. Numerous substitutions, alterations, modifications, omissions and the like may be possible and desirable depending on the nature of the structure being fabricated and the materials being used. In the method of FIG. 33:

(85) An object or structure is conceived and documented preferably with a CAD program in step 3300.

(86) This design's volume is filled with a cellular matrix having desirable properties for the final structure in step 3301.

(87) A sequential pathway tracing each segment of the matrix is derived in step 3302.

(88) The movement mechanism is programmed with this sequential motion pathway in step 3303. Additional information relating to speeds, temperatures, stop/start, flow, and other properties may be input with the programming.

(89) The program is executed, inducing motion and extrusion to create the structure in step 3304.

(90) Once portions or the whole is complete, other materials may be added to the structure in step 3305.

(91) Different arrangements of the components and activities depicted in the drawings or described above, as well as components and steps not shown or described are possible. Similarly, some features and subcombinations are useful and may be employed without reference to other features and subcombinations. Embodiments of the invention have been described for illustrative and not restrictive purposes, and alternative embodiments will become apparent to readers of this patent. Accordingly, the present invention is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications can be made without departing from the scope of the claims below.