Abstract:
A method of constructing an object includes depositing a first material in a predetermined arrangement to form a structure. The method further includes depositing a second material within the structure. The second material may have electrical properties and the method also includes providing electrical access to the second material to enable observation of the one or more electrical properties.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of the following Patent Applications, the contents of which are hereby incorporated by reference in their entirety: U.S. Provisional Patent Application Ser. No. 61/638,576, filed Apr. 26, 2012 and U.S. Provisional Patent Application Ser. No. 61/804,440, filed Mar. 22, 2013. 
     
    
     BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    This invention generally relates to methods and systems of Additive Manufacturing. More particularly, the invention relates to a motorized hardware extruder that can inject or extrude a conductive material (for example, a piezoresistive elastomer) into parts as they are being fabricated by a 3D printer or other Additive Manufacturing system. 
         [0004]    2. Description of Related Art 
         [0005]    An object with complex freeform three-dimensional (3D) contours can be very challenging and very costly to prototype &amp; manufacture with traditional fabrication methods. Additive Manufacturing (AM), also known as “3D Printing,” “Layered Fabrication,” “Rapid Prototyping,” “Additive Fabrication,” or “Layered Manufacturing,” is a fabrication methodology which provides the ability to readily fabricate these previously impossible features in a fast, accurate, and cost-effective way. Subtractive machining practices like milling and turning remove waste material until only the part features remain. AM is a maskless process that fabricates a three-dimensional object from the base up by adding thin consecutive cross-sectional profiles of the object which bind together for a complete 3D shape. This is fixtureless fabrication since no new tooling is required and although there are many different fabrication materials, machines, and procedures worldwide, the nature of these technologies remain similar. 
         [0006]    The unique capabilities of Additive Manufacturing have benefitted the engineering design process in reduced development time &amp; cost, greater variety in a family designs, and prototypes more accurate to functional testing of the final device. The normally long time periods between design iterations for form and fit evaluation can be significantly reduced with AM, so depending on part size it may take only a few hours to go from digital design to physical part. These factors make the technology excellent for custom parts produced to order in small quantities. Virtually all layered processes can deposit material in the horizontal plane much more rapidly than they can build up thickness. Consequently parts are typically built lying down so that their shortest overall dimension is oriented along the z-axis to optimize for build time. Parts are also frequently nested within the build chamber to maximize parts per build cycle. 
         [0007]      FIG. 1  (available at http://www.custompartnet.com/wu/images/rapid-prototyping/fdm-small.png) shows main elements of Fused Deposition Modeling (FDM) system, which is a type of additive manufacturing system. A heated extrusion head receives materials in filaments and uses heat to liquefy the material, e.g., plastics, and deposit them in a layer on a build platform. When the system finishes printing one layer, the system lowers the platform, where the printed object is located, and prints another layer. This figure shows an extrusion head  101  that moves in the X-Y plane and a heated build platform  102  that moves in the Z plane. The extrusion head  101  includes one nozzle  103  for support material, one nozzle  104  for build material. The build material is typically thermoplastic modeling material that enters the system from spools  104  and  105  and feeds into the temperature controlled FDM extrusion head  101 . The thermoplastic modeling material is pulled by drive wheels  106  and passed into liquefiers  107  that heat the material. The heated material is extruded on to the build platform  102  by extrusion nozzles  103  and  104 . After each layer of material has been deposited, the build platform  102  is moved down and the next layer of material is deposited. A motor system (not shown) provides force to drive wheels  106 . Additional motors control the X-Y-Z location of the extrusion head  101  and heated build platform  102 . 
         [0008]    Current Additive Manufacturing processes do not support the direct fabrication of objects that contain embedded electronics or sensors. Methods have been suggested which allow the user to pause the build cycle of the machine and pick and place off-the-shelf mechanical or electrical components into pre-designed cavities. For standard components this is labor-intensive but functional, however for fabricating custom or non-planar sensors inside the structure of the produced part this not feasible. For components which are non-planar and need to be routed/connected in all three axes (for example such as wires with curved trajectories, cylindrical &amp; helical features such as induction coils, or measuring strain across several planes like within an airfoil, turbine blade, or device which superficially interfaces with anatomical features) a manually-intensive two-step process used. 
         [0009]    First the object must be completely fabricated with a series of specifically designed channels (or voids). Next, a conductive material is manually injected using a syringe into the channels (or voids) of the object and allowed to cure. This requires that the part be designed and fabricated with injection ports on the outside of each of the conductive channels which lock into the syringe to provide an adequate seal. Programming and 3D printing of the object occurs entirely before the conductive material is added. As the conductive material is pushed along the pathways the reliability of complete filling is questionable from sharp bends and bifurcations in the channels. Therefore, the spaces need to be as open as possible, the interior diameter large as possible, and any turns under 100 degrees be avoided. Additionally, after the injection of the conductive material, the injection locks need to be broken away and the residual surfaces need to be polished. This accomplishes the goal of embedding electronics in the components but with significant limitations and uncertainties. 
         [0010]    This method of manufacturing has many limitations. It can be difficult to force the silicone all the way through a complicated channel without breaking the path of the silicone at any point, or causing irregularities and uneven areas. The likelihood of breaks in the circuit increases with more complicated cavities (this includes paths that take multiple turns, bends 100 degrees or smaller, or interior diameters which are under 1 mm diameter). Multiple entries and exits in a cavity cause differences in pressure for each pathway, further increasing the likelihood of an incomplete fill of the cavity. This process is also messy. Manual injection can be inefficient and unreliable. The reliability is affected because the conductive material must be injected completely through the cavities to conduct a signal, which can be difficult to achieve. When trying to inject along an internal channel, the high shear friction along the walls can cause a material to stop moving, yielding an cavity that has not been completely filled. 
         [0011]      FIG. 4A  shows a cross sectional view of a fabricated object with channels (or voids) to illustrate the injection process of conductive material. The fabricated object has material  403  and voids  404 . The layout of voids  404  creates a channel for a conductive material to be added. Extrusion head  401  uses injection lock  405  to inject the conductive material  402  through an entrance of voids  404 . A close up of the injection lock feature is shown in  FIG. 4B . To reduce spillage when injecting a conductive material into a channel, an extrusion head is attached to a Luer Lock  405  with a tube  407 . Typically, a Luer Lock is attached to a syringe using a threaded element  406 . The material is injected through the tube  407  into the interior channels of a fabricated object. 
         [0012]      FIG. 5A  is a picture of an object where the conductive material has been injected into interior channels and allowed to cure.  FIG. 5B  shows the exterior of an object where extra conductive material is present at the injection points. This spillage occurs in the absence of a proper seal between the extrusion head and the entrance to the interior channels in the object. 
         [0013]      FIG. 6A  shows a fabricated object with plastic materials of two colors that have similar material properties. Unlike using materials with similar properties, fabricating an object with different material properties, is difficult to achieve. For example, the deposition method for ABS plastic is very different from the deposition method for a conductive silicone solvent-based suspensions. In addition the solid/liquid material flow properties and required curing conditions for ABS plastic are very different from those of a conductive silicone solvent-based suspension.  FIG. 6B  shows a fabricated object using two material (plastic and conductive silicone) that have different material properties. In this example the conductive silicone is incompletely cured or solidified. During deposition of the conductive silicone a balance is required such that material cures quickly (to improve the fabrication time), but also slowly enough that the material does not cure while before being fully deposited into the deposition channel. 
       BRIEF SUMMARY 
       [0014]    In one aspect, the invention is a system for fabricating a three-dimensional object with electrical properties where the system includes a build chamber, a build platform disposed within the build chamber, and a deposition head disposed within the build chamber configured to deposit a first material onto the build platform and further configured to deposit a second material with electric properties onto the build platform. The system may also include a memory for receiving data representing a three dimensional object and a controller for forming a layer of material, adjacent to any last formed layer of material, accordance to the data representing the three dimensional object, where the controller is operable to selectively control the deposition of the first and second material within the layer. 
         [0015]    In one aspect, the invention further includes a reservoir capable of containing a material with electrical properties, at least one motor assembly configured to impart a force on an actuator, a controller configured to control the motor assembly, a deposition nozzle in fluid contact with the interior of the reservoir, where the actuator imparts a force on the material; and where at least some portion of the material is expelled from the reservoir. 
         [0016]    In one aspect, the invention includes a motor that drives a lead screw and nut assembly. In one aspect, the invention includes a motor that drives a pinion of a rack and pinion system. In one aspect, the invention includes a motor that drives an auger. 
         [0017]    In one aspect, the invention includes a reservoir that is directly mounted on the deposition head of a 3D printer. In one aspect, the invention includes a reservoir that is mounted on the exterior of a 3D printer. In one aspect, the invention includes a reservoir that is mounted on a mechanically grounded frame above the 3D printer. 
         [0018]    In one aspect, the invention is attached as a tool head on a numerically controlled or computer numerically controlled system. In one aspect, the invention is attached as a tool head on a drill press. 
         [0019]    In one aspect, the invention includes a nozzle design that reduces the force required to expell high viscosity material from the reservoir. In one aspect, the environmental conditions, including temperature or pressure, of the nozzle can be controlled by the controller. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]    The foregoing and other objects of this invention, the various features thereof, as well as the invention itself, may be more fully understood from the following description, when read together with the accompanying drawings in which: 
           [0021]      FIG. 1  illustrates the main elements of a Fused Deposition Modeling (FDM) system. 
           [0022]      FIG. 2A  illustrates the Makerbot Replicator 1 3D printer. 
           [0023]      FIG. 2B  illustrates the RepRap Prusa Open Source 3D printer. 
           [0024]      FIG. 3  illustrates the Cubify 3D printer. 
           [0025]      FIG. 4A  illustrates the process of injecting conductive material into an object fabricated with channels (or voids). 
           [0026]      FIG. 4B  illustrates an injection lock used during the injection of conductive material. 
           [0027]      FIG. 5A  is a picture of an object where the conductive material has been injected into interior channels and allowed to cure. 
           [0028]      FIG. 5B  is a picture of an object where extra conductive material is present at the injection points. 
           [0029]      FIG. 6A  shows an object fabricated with plastic materials of two colors that have similar material properties. 
           [0030]      FIG. 6B  shows an object fabricated with two material that have different material properties. 
           [0031]      FIG. 7A  is a process flow diagram for using a 3D printer to create an object with embedded electrical connections. 
           [0032]      FIG. 7B  is a process flow diagram for using the Embedded Electronics by Layered Assembly (EELA) system to create an object with embedded electrical connection. 
           [0033]      FIG. 8A  is a side view showing the deposition of conductive material. 
           [0034]      FIG. 8B  is a side view showing the deposition of non-conductive material. 
           [0035]      FIG. 9A  is an isometric view of the Embedded Electronics by Layered Assembly (EELA) system integrated with a 3D printer. 
           [0036]      FIG. 9B  is an exploded view of the Embedded Electronics by Layered Assembly (EELA) system integrated with a 3D printer. 
           [0037]      FIG. 10  shows one embodiment of the Embedded Electronics by Layered Assembly (EELA) system. 
           [0038]      FIG. 11  shows the operation of the Embedded Electronics by Layered Assembly (EELA) system. 
           [0039]      FIG. 12  is a cross section view of connection between a material reservoir and an impermeable transfer tube. 
           [0040]      FIG. 13  is the feedback loop for the Embedded Electronics by Layered Assembly (EELA) controller. 
           [0041]      FIG. 14  illustrates a slider and nut assembly. 
           [0042]      FIG. 15  illustrates a plunger reinforcement slug. 
           [0043]      FIG. 16  illustrates a syringe reinforcement housing. 
           [0044]      FIG. 17  illustrates a plunger reinforcement fitting. 
           [0045]      FIG. 18  is an isometric view of one embodiment of an Embedded Electronics by Layered Assembly (EELA) system integrated with a 3D printer. 
           [0046]      FIG. 19  is an isometric view of one embodiment of an Embedded Electronics by Layered Assembly (EELA) system integrated with a 3D printer. 
           [0047]      FIG. 20A  is a side view of a miniature motorized syringe design. 
           [0048]      FIG. 20B  is a cross section view of a miniatures motorized syringe design. 
           [0049]      FIG. 21  illustrates an internal helical plunger mechanism. 
           [0050]      FIG. 22  is a cross section view of a conductive material reservoir. 
           [0051]      FIG. 23  is an isometric view of one embodiment of an Embedded Electronics by Layered Assembly (EELA) system integrated with a drill press. 
           [0052]      FIG. 24  is an isometric view of one embodiment of an Embedded Electronics by Layered Assembly (EELA) system integrated with a mill. 
       
    
    
     DETAILED DESCRIPTION 
       [0053]    The Embedded Electronics by Layered Assembly (EELA) system is a motorized extruder that can be used to extrude a piezoresistive elastomer, such as a conductive silicone compound, into channels built during the additive manufacturing process on a 3D printer. The EELA system enables the building of conductive circuitry directly into an object while the object is being printed, rather than requiring the injection of the conductive material after the 3D printing is completed. The EELA system is capable of more fine-tuned and precise movements than a person can make with a syringe, and since printing and extrusion occur together, the EELA system may easily reach all areas of the conductive path in the object since it has access to the cross section of each layer during the build. This eliminates the potential problems described above and requires less overall work during manufacturing. Additionally, this can help to standardize the process of embedding conductive materials. 
         [0054]      FIG. 7  is a process flow diagram for using the Embedded Electronics by Layered Assembly (EELA) system to create an object with embedded electrical connection. When the Embedded Electronics by Layered Assembly (EELA) system is integrated with a 3D printer the number of steps to fabricate an object is reduced. The injection of the conductive silicone is no longer performed by hand. Instead the conductive silicone is extruded during the fabrication process itself. 
         [0055]    In one embodiment, the first step in fabricating an object is to define the object in a computer aided design file. This file defines the 3D geometry of the object to be fabricated. One well known file format is the STL (STereoLithography) file format; however, any file type that can contain geometry information, such as .svg, .dxf, .cmp, .sol, .plc, .sts, .stc, .gtl and *.jpg, may potentially be used. One geometry file is used for the non-conductive (thermoplastic) features. A second geometry file is used for the conductive material. The two geometry files are then integrated and converted into a set of commands to move the extrusion head, move the build platform, and actuated the mechanism to deposit the thermoplastic/silicone material. One well known converter is ReplicatorG which will take the input geometry file and generate GCode commands. GCode is a well known numerical control programming language, that allows for the control of the position of the extrusion heads, the speed at which the heads move, and the temperature of the nozzles and build platform. The GCode is then executed. The thermoplastic will be extruded leaving gaps or troughs for the conductive silicone. The silicone is then deposited into the gaps. This process continues layer by layer until the object is completely fabricated. 
         [0056]    In one embodiment, the Embedded Electronics by Layered Assembly (EELA) system is integrated into the 3D printing system electronically and mechanically, and is software-compatible.  FIG. 7B  is a process flow diagram where the Embedded Electronics by Layered Assembly (EELA) system fully integrated with the 3D printing system. The controller  701  uses the GCode commands to control the position of the non-conductive extrusion head  702 , the position of the non-conductive extrusion head  703 , the position of the build platform, as well as the deposition rate of the thermoplastic and conductive material. After the thermoplastic and conductive materials have been deposited, the finished object can be removed from the build chamber. Position and pressure feedback loops allow the controller to precisely deposit the conductive silicone at the required locations within the build chamber. 
         [0057]      FIGS. 8A and 8B  show side profile views of the conductive deposition system  803  moving along the XY build plane and depositing non-conductive material and uncured conductive material  802 . A non-conductive deposition system  808  uses a heated nozzle  807  to deposit non-conductive material. Then the conductive deposition system  803  will become active and place conductive material  802  in any open layer spaces  804  (i.e., spaces where no non-conductive material is deposited) that have been formed in the current layer. This uncured conductive material  802  will cure when exposed to air and form the conductive material layer  801 . The thickness of uncured conductive material  802  deposited is equal to or similar to the layer thickness of the open layer spaces  804 . The non-conductive deposition system  805  and conductive deposition system  803  are contained in the same extrusion head and thus move together, but only one of the conductive and non-conductive deposition systems extrudes its material at any one point in time. Alternatively, the two deposition systems can be placed in two separate extrusion heads for independent operations. In this example, the conductive deposition system can concurrently extrude a conductive material as the non-conductive deposition system deposits its material. Once one layer has been completely deposited, the next layer will be formed. The process repeats until the object is fully formed. 
         [0058]      FIG. 9A  shows one embodiment of the EELA system  901  attached to a 3D printer  902 . The 3D printer has an on-board non-conductive material storage  903 , internal build chamber  904 , motorized deposition system  905 , and heated build platform  906 . The EELA system  901  integrates with the 3D printer  902  to control the motorized deposition system  905  so that components with embedded electronics can be fabricated within the internal build chamber  904 .  FIG. 9B  shows the EELA extrusion mechanism  907  connected to flexible tubing  909  that allows the conductive material to be deposited within the internal build chamber  904 . Similarly, The non-conductive material  911  is guided to the motorized deposition system  912  via its own flexible guide  910 . The location of deposition of the conductive material is controlled by the EELA system  901  sending signals to the motorized deposition system  905  of the 3D printer  902 . The temperature on the motorized deposition system  905  is regulated by a fan and thermal sensor  912 . 
         [0059]    3D Printing System 
         [0060]    In one embodiment the 3D printing system uses Fused Deposition Modeling (FDM) to create layers of material by extruding beads of molten thermoplastic, which bond as they contact the part surface and immediately cool. FDM can utilize many compositions of plastic—the most common being ABS, Polycarbonate, Polylactide, or a combination. 
         [0061]    In one embodiment, the 3D printing system  102  is a MakerBot Replicator, but the EELA system can be used with a variety of 3D printer hardware configurations. Example 3D printing systems are listed in Table 1. Each of the 3D printers listed extrude only non-conductive materials and can be used in conjunction with the EELA system to extrude conductive silicone for internal electronic circuits in the fabricated object. 
         [0000]    
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                 Manufacturer 
                 Model 
                 Price 
                 Materials 
                 Strengths 
                 Weaknesses 
               
               
                   
               
             
             
               
                 MakerBot 
                 Replicator 
                 $1,749/$2000  
                 PLA, ABS 
                 Low cost; high 
                 Slow process 
               
               
                   
                 (single or 
                   
                 plastic 
                 adaptability; 
               
               
                   
                 dual 
                   
                   
                 open source; can 
               
               
                   
                 extrusion) 
                   
                   
                 extrude 2 colors 
               
               
                   
                 (Commercial/ 
                   
                   
                 or materials 
               
               
                   
                 Open Source) 
                   
                   
                 simultaneously 
               
               
                 MakerBot 
                 Thing-O- 
                  $2500 
                 PLA, ABS 
                 Low cost; high 
                 Slow 
               
               
                   
                 Matic 
                   
                 plastic 
                 adaptability; 
                 process; low 
               
               
                   
                 (Commercial/ 
                   
                   
                 heated build 
                 resolution 
               
               
                   
                 Open Source) 
                   
                   
                 platform; open- 
               
               
                   
                   
                   
                   
                 source 
               
               
                 Reprap 
                 Mendel 
                 $520 (kit) 
                 PLA, 
                 Lowest cost; 
                 Slow 
               
               
                   
                 (Open 
                   
                 HDPE, 
                 high adaptability 
                 process; not 
               
               
                   
                 Source/ 
                   
                 ABS 
                   
                 user- 
               
               
                   
                 Hobbyist) 
                   
                 plastic 
                   
                 friendly; low 
               
               
                   
                   
                   
                   
                   
                 resolution 
               
               
                   
                   
                   
                   
                   
                 finish 
               
               
                 BotMill 
                 Glider 
                 $1,395 
                 PLA, ABS 
                 Low cost; user- 
                 Slow process 
               
               
                   
                   
                   
                 plastic 
                 friendly 
               
               
                 MakerGear 
                 M2 
                 $1,299 
                 PLA, ABS 
                 Low-cost; 
                 Slow 
               
               
                   
                   
                   
                 plastic 
                 compact size; 
                 process; low 
               
               
                   
                   
                   
                   
                 low maintenance 
                 resolution 
               
               
                 MakerGear 
                 Prusa Mendel 
                   $825 
                 PLA, ABS 
                 Low-cost; 
                 Slow 
               
               
                   
                   
                   
                 plastic 
                 compact size; 
                 process; low 
               
               
                   
                   
                   
                   
                 low maintenance 
                 resolution 
               
               
                 Fab @ 
                 Model 1 &amp; 2 
                 $2400/$1600 
                 silicone 
                 Low cost; 
                 Limited 
               
               
                 Home 
                 (Open 
                   
                 rubber 
                 compact size; 
                 workspace; 
               
               
                   
                 Source/ 
                   
                 caulk; 
                 many material 
                 accuracy 
               
               
                   
                 Hobbyist) 
                   
                 epoxy; 
                 options 
                 depends on 
               
               
                   
                   
                   
                 many 
                   
                 material 
               
               
                   
                   
                   
                 household 
               
               
                   
                   
                   
                 materials 
               
               
                 3D Systems 
                 Rapman 3.2 
                 $1,390 
                 Plastic 
                 Low-cost; 
                 Slow process 
               
               
                   
                   
                   
                 polymer 
                 compact size; 
               
               
                   
                   
                   
                   
                 user-friendly 
               
               
                 3D Systems 
                 Cube 
                 $1,299 
                 Recyclable 
                 Able to make very 
                 Single 
               
               
                   
                   
                   
                 plastic 
                 complicated 
                 material/color 
               
               
                   
                   
                   
                   
                 structures; can 
                 printing at a 
               
               
                   
                   
                   
                   
                 print from Wi-Fi; 
                 time 
               
               
                   
                   
                   
                   
                 easy to load new 
               
               
                   
                   
                   
                   
                 color cartridges 
               
               
                 Stratasys 
                 uPrint ™ SE 
                 $13,900/$18,900 
                 ABS plastic 
                 Strong, durable 
                 Slow process; 
               
               
                   
                 and Plus SE 
                   
                 with soluble 
                 parts; 
                 relatively 
               
               
                   
                 (Commercial) 
                   
                 supports 
                 FDM reliability; 
                 expensive 
               
               
                   
                   
                   
                   
                 quiet and clean 
                 material 
               
               
                 Hewlett 
                 DesignJet 3D 
                 $17,000/$22,000 
                 ABS plastic 
                 Strong, durable 
                 Slow process; 
               
               
                 Packard 
                 Printer 
                   
                 with soluble 
                 parts; 
                 relatively 
               
               
                   
                 (Color option 
                   
                 supports 
                 FDM reliability; 
                 expensive 
               
               
                   
                 available) 
                   
                   
                 quiet and clean 
                 material 
               
               
                   
                 (Commercial) 
               
               
                   
               
             
          
         
       
     
         [0062]      FIGS. 2A ,  2 B and  3  show examples of commercial 3D printers that can be used with the EELA system.  FIG. 2A  is the Makerbot Replicator 1 available from the Makerbot Store and additional details are available at http://store.makerbot.com/replicator.html.  FIG. 2B  is the RepRap Prusa Open-Source System and additional details are available at the RepRap Mendel Design Wiki ad http://reprap.org/wiki/Prusa_Mendel_(iteration — 2).  FIG. 3  shows a 3D touch system sold by by Cubify 3D systems and additional details are available at http://cubify.com. 
         [0063]    Embedded Electronics by Layered Assembly (EELA) System 
         [0064]      FIG. 10  shows one embodiment of the EELA extrusion mechanism  907 . The EELA extrusion mechanism  907  is actuated by stepper motor  1005  that drives threaded rod  1009 . The threaded rod  1009  is supported by motor stop  1005  and slider stop  1013 . A pair of guide rails  1010 , mounted parallel to the threaded rod  1009 , is also supported by motor stop  1005  and slider stop  1013 . A nut (not shown) is embedded in slider  1006  and is held in place by syringe guide block  1007 . 
         [0065]    One end of syringe feed shaft  1008  is mounted in syringe guide block  1007 . The other end of syringe feed shaft  1008  is attached to one end of syringe  1011 . The other end of syringe  1011  is mounted in syringe support  1013 . The syringe support  1013  is held in place by slider stop  1013 . An impermeable tube (not shown) connects the syringe  1011  to extrusion head (not shown). A fluid impermeable seal, such as a friction fit Luer Lock Barb, is used to connect the material reservoir in the syringe  1011  to the flexible tube channel with a tight seal. 
         [0066]      FIG. 14  shows one slider  1401  and nut  1403  mounted together. Nut  1403  is held in place in slider  1401  by grooves (not shown) and cannot rotate with respect to slider  1401 . Nut  1403  is prevented from sliding out of the grooves by syringe guide block  1404 . Slider  1401  also includes a series of bushings  1402  which allow slider  1401  to move along the guide rails  1010 . A pressure sensor  1405  is mounted on the syringe guide block  1404 . The pressure sensor measures the pressure applied to the syringe  1011  via syringe feed shaft  1008  and the pressure measurement is used to precisely control force applied to the syringe. 
         [0067]      FIG. 12  shows the details of the connection between the end of the reservoir end  1201  of the syringe and the impermeable tube  1203 . In one embodiment a friction fit Luer Lock Barb  1202  is used to connect the reservoir end  1201  of the syringe and the interior of the impermeable tube  1203 . The Luer Lock Barb  1202  provides a fluid impermeable seal which prevents the silicone in the reservoir and impermeable tube  1203  from being exposed to air and curing inside the EELA system. In one embodiment the impermeable tube  1303  would contain a valve-nozzle combination. The valve portion of the valve nozzle would seal the nozzle when the system was not in use. An alternative option is to use a small threaded plug  1204  that can be manually screwed onto the tip of the impermeable tube  1203  to seal off the silicone path when the 3D printer is not in use. Another alternative option is to direct the extruder to clean nozzle of any material left in it from the last print prior to starting the build of a new object. This will ensure that no cured or crusted silicone inside the nozzle interferes with the build of a new object. 
         [0068]      FIGS. 15 ,  16 , and  17  shows the details of the syringe, plunger, and plunger plug. To use the syringe ( FIG. 16 ) for the injection of silicone, the plunger on the end of the plunger ( FIG. 17 ) is replaced with a smaller plunger reinforcement slug that screws over the end of the plunger rod.  FIG. 15  shows the plunger plug. In one embodiment, the plug is part is slightly longer than half an inch, with a diameter of 0.43″ at its thicker end. The slug bottlenecks before flattening into a plunger end that fits inside the syringe passageway, with a diameter of 0.35″. The exact size of this piece is very important; if it is slightly too small, silicone may leak out the back of the syringe, flowing around the rubber reinforcement that is placed over the end of the plunger. 
         [0069]    Referring again to  FIG. 10 , slider  1006 , and therefore nut  1403 , cannot rotate with respect to stepper motor  1005  that drives threaded rod  1009  because of guide rails  1010 . When stepper motor  1005  drives threaded rod  1009 , nut  1403 , and therefore slider  1006 , will move longitudinally along threaded rod  1009 . As slider  1006  moves along threaded rod  1009 , the syringe feed shaft  1008  will depress the plunger in syringe  1011  forcing the material in the syringe through the impermeable tube (not shown) and into the extrusion head. 
         [0070]      FIGS. 11A ,  11 B, and  11 C shows the slider moving longitudinally along threaded rod  1104 . In  FIG. 11A  the slider is retracted and located at the end of the threaded rod  1004  near the stepper motor. The syringe can then be inserted into the assembly.  FIG. 11B  shows the syringe in the assembly. The pressure sensor  1102  is mounted on the syringe guide block and measures the longitudinal pressure applied to the syringe.  FIG. 11C  shows the stepper motor rotating the threaded rod  1104 . This causes the slider to move along the treaded rod  1104  applying force to the syringe feed shaft. The contents of the syringe is extruded through the syringe outlet  1105 . Any mechanism that creates a linear force could be used as an alternative to the stepper motor, threaded rod, nut, and slider. Alternative examples include a rack and pinion, a crank and rocker, or a rack and pinion. 
         [0071]      FIG. 13  shows the details of the controller for the conductive deposition system. In order to control the deposition rate of the conductive material, the controller must be able to control the stepper motor that provides the linear force on the syringe. Position and pressure feedback loops, shown in  FIG. 13 , allow the controller to precisely deposit the conductive silicone at the required locations within the build chamber. The controller sends commands to the actuator to extrude the conductive material, while using a pressure sensor to monitor the pressure in the system. In addition the controller monitors the position of the syringe plunger according the number of rotations of the stepper motor via encoder or potentiometer. It monitors the backpressure on the syringe using a force sensor (such as thin film force sensor) and stops the motor turning if the pressure passes a set thread hold. The set thread hold is indicative of a clog in the syringe and stops the motor to avoid damaging the syringe seal. 
         [0072]    The conductive material can be a conductive silicone compound or any other piezoresistive elastomer, silver ink, platinum ink, iron filings compound, conductive rubber, copper, graphite/nickel suspension, or tin particle suspension that does not require vulcanizing conditions with high pressures and temperatures above the creep values for thermoplastics used to build the object. In one embodiment the conductive compound is a silicone room-temperature-vulcanizing (RTV) material containing conductive particles of nickel-coated graphite, for example MMS-020 available from Moreau Marketing &amp; Sales, Lexington NC. This material is representative of a group of Room Temperature Vulcanizing (RTV) materials which cure by degassing a solvent reaction inhibitor. Common single part solvent-based epoxies include cyanoacrylite instant adhesive “Crazy Glue” and DWP-24 Wood Adhesive “Liquid Nails.” When in the sealed environment of the syringe, the material remains in a liquid state because the trapped solvent inhibits the curing process. But when applied to a surface, the solvent inside the liquid escapes into the surrounding atmosphere and the epoxy molecules cross-knit and pull together to form chains. When conductive graphite is suspended inside this material the end state is that these particles are close enough together to allow electrons to jump from one to the next when fitted into a circuit with a voltage differential. Combining this silicone with graphite adds the piezoresistive response when the particles are strained apart. Silicone is a good elastomer for the suspension because it is abundant, inexpensive, and thermally stable. 
         [0073]      FIG. 18A  shows one embodiment of the EELA system attached to a 3D printing system. The EELA system is mounted on a frame  1802  above the build chamber  1801  of the 3D printing system. A reservoir  1804  contains the conductive material and is in fluid connection with an auger chamber  1803 . The conductive material flows from the reservoir  1804  through the auger chamber  1803  and into the to the extrusion head in the build chamber  1801 . A stepper motor is attached to the reservoir  1804 . The stepper motor  1805 , the reservoir  1804 , and the auger chamber  1803  are attached to the frame  1802  by joint  1806 . The joint  1806  may be a ball and socket, universal joint, or any other joint type that allows stepper motor  1805 , the reservoir  1804 , and the auger chamber  1803  to move in the X-Y direction during the fabrication process. 
         [0074]      FIG. 18B  shows a cross section view of the EELA system mounted on a frame above the build platform  1807  of the 3D printing system. The interior of reservoir  1811  contains an auger  1810  that is driven by stepper motor  1812 . Auger  1810  is used to control the flow rate of the conductive material through the tapered extrusion point  1808  in the conductive deposition extrusion head  1809 . This design allows for a large reservoir of conductive material to be located close to the extrusion head  1809 . Because the weight of the reservoir is not supported by the extrusion head  1809  the inertia of the extrusion head  1809  does not change and no changes to the standard control logic for the extrusion head  1809  are required. In this figure the extrusion head  1809  has been moved to the far right of the build platform  1807 . 
         [0075]      FIG. 18C  shows a cross section view of the EELA system mounted on a frame above the build platform  1807  of the 3D printing system, where the extrusion head has been moved to the far left of the build platform  1807 . This figure also shows the non conductive extrusion head  1815  that heats the thermoplastic modeling material to a semi-liquid state. The thermoplastic modeling material is then expelled from the extrusion head and deposited on the object on the build platform within the build chamber. The build chamber is a heated space, maintained at a temperature just below the material&#39;s melting point. Within the build chamber when one layer of liquid plastic contacts the semi-molten layer beneath it they will harden together as the two layers bind. After the extruder has completed the cross-section of the object in the X-Y plane, the build platform drops one layer thickness for the next profile. 
         [0076]      FIG. 19A  shows one embodiment of the EELA system attached to a 3D printing system. In this embodiment the entire EELA system is mounted on the moveable extrusion head in the 3D printing system.  FIG. 19B  shows the details of this embodiment of the EELA system. A rack  1901  and pinion  1902  provides a linear force that is applied to the reservoir that contains the conductive material. The pinion  1902  is a circular gear with teeth that engage the teeth on the rack  1901 . When the pinion rotates the rack  1901  moves, thereby translating the rotational motion of the pinion  1902  into linear motion of the rack  1901 . The stepper motor  1904  is connected to pinion  1902  via a pulley  1905  and pulley belt (not shown). Fan  1906  is used to control the temperature of the conductive material as it is extruded.  FIG. 11C  shows a exploded view of the EELA system mounted on extrusion head, including pulley  1910  and pinion  1909 . 
         [0077]      FIG. 20A  is a side view of one embodiment of the EELA system.  FIG. 20B  is an interior cross section view of one embodiment of the EELA system.  FIGS. 20A and 20B  show a miniature motorized syringe design where a rack and pinion  2004  interfaces with the syringe plunger  2003  to extrude material. An on-board stepper motor  2005  drives the rack and pinion  2004  to move the syringe plunger  2003 . The opposite side the syringe plunger  2003  is held in place by an idler pulley  2001  for alignment. Within the syringe plunger  2003  there is an O-ring  2006  to create a pressure seal during extrusion. 
         [0078]      FIG. 21  shows the internal helical plunger mechanism which consists of a static assembly  2101  and a moving assembly  2102 . This mechanism has a threaded housing  2103  which holds the syringe  2108 , plunger  2107 , rotating nut  2106 , and fixed lock  2104 , and drive shaft  2105 . A rotational force  2109  is applied to the drive shaft  2105  to actuate the mechanism. The rotating nut  2111  moves along the interior of the threaded housing  2104  to apply force to extrude through the syringe  2112 . The fixed lock  2110  interlocks with the threaded housing to prevent it from turning but not from supporting. As the rotating nut  2113  moves down along the threaded housing  2103 , conductive material is extruded out of the syringe  2114 .  FIG. 21C  shows the plunger fully retracted.  FIG. 21D  shows the plunger fully extended. 
         [0079]      FIG. 22A  shows a cross-section view of the conductive material reservoir  2201  for extruding conductive suspensions of low viscosity. The shallow taper contour  2202  is a straight chamfer. For extruding higher-viscosity materials, the shallow taper contour  2202  may alternatively be a deep tapered contour  2203 , as shown in  FIG. 22B . The deep tapered contour edge height  2204  indicates the boundary of the deep tapered contour  2203 . For extruding higher-viscosity materials, the shallow taper contour  2202  may alternatively be a elliptical contour  2206 , as shown in  FIG. 22C . The elliptical contour edge height  2206  indicates the boundary of the elliptical contour  2206 . 
         [0080]    The conductive deposition unit can be used with systems other than traditional 3D printers.  FIG. 23  shows the EELA conductive deposition system  2303  mounted to the exterior of a drill press  2301 . The extrusion site  2304  is able to add conductive material to components which are placed on the drill press platform  2302 . The height of the EELA conductive deposition system  2303  above the drill press platform  2302  is adjusted according to the type of part (not shown) which will receive the conductive injection.  FIG. 24  shows the EELA conductive deposition system  2403  mounted to the exterior of a mill  2401 . The extrusion site  2404  is able to add conductive material to components which are placed on the mill bed  2402 . The height of the EELA conductive deposition system  2403  above the mill bed  2402  is adjusted according to the type of part (not shown) which will receive the conductive injection.