Abstract:
A fused filament fabrication printer has a fixed extrusion module having multiple printheads having print tips. The fixed arrangement of the printing heads allows the close spacing of multiple print tips in a printhead unit, and the simple routing of multiple plastic or metal filaments to the individual printing heads. The closely spaced print tips in the printhead unit share common components. An exemplary printhead unit has four printing heads which share a common heating block and heating block temperature sensor. The heating block incorporates a group of four print tips evenly spaced along a line. Each printing head has a separate filament which is controlled and driven by its own stepper motor through the heating block to one of the print tips. Printing of a part is by control of individual stepper motors which drive filaments through the heating block and through one of the printing tips.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. application Ser. No. 13/750,731 filed on Jan. 25, 2013 which is incorporated herein by reference. 
     STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to extrusion-based 3-D printers, termed fused deposition modeling or fused filament fabrication printers, in general and more particularly to printers using a printhead which applies layers of thermoplastic (e.g. ABS, HDPE, PLA, PVA) a metal or metal containing carrier, or polymers and composites that are doped with a variety of secondary materials such as wood and carbon nano-tubes to create models, prototypes, patterns, and production parts. 
     Fused filament fabrication works on an “additive” principle by laying down material in layers. This technique was initially developed by S. Scott Crump in 1989 and is described in U.S. Pat. No. 5,121,329. Initially such printers were extremely expensive, purchasable only by large companies, or accessible by outsourcing a 3-D model file to a fused filament fabrication printer or a competing technology, such as stereolithography as described in U.S. Pat. No. 4,575,330. Recent interest in fused filament fabrication has been increased by the development of consumer models of such printers of much lower cost. The development of low cost alternatives has been fueled by the expiration of U.S. Pat. No. 5,121,329 and the decreasing cost of high precision and reliable motors, motor controllers, and other key components required by fused filament fabrication printers. 
     A US patent application entitled Three-Dimensional Printing System Using Dual Rotating Axes, to Thomas Mackey, Nathan Patterson, Benjamin Cox, Nathan Schumacher, and George Petry, filed in 2012 (Mackey et al.) shows a rotating build platform and rotary mounted printheads. 
     Fused filament fabrication, i.e. three-dimensional printing, in addition to providing three-dimensional models or parts for conceptual design studies also allows the manufacturing of functional items or tooling. Patterns for various metal and plastic casting technologies can also be formed. Typically, a plastic filament or metal wire is unwound from a coil and supplies material to an extrusion nozzle that can start and stop material flow. The nozzle is heated to melt the material and can be moved in both horizontal and vertical directions by a numerically controlled mechanism which is often directly controlled by a computer-aided manufacturing (CAM) software package. The model or part is produced by extruding small amounts of thermoplastic or other material to form layers as the material hardens immediately after extrusion from the nozzle. Tools for thermoforming and injection molding can be made, as well as fixtures which assist the manufacturing operation. In addition to providing for very low run manufacturing operations, art objects and display objects can be readily manufactured. Improvements of fused filament fabrication printers requires an increase in printing speed, printing with multiple materials, and lower printer costs. 
     SUMMARY OF THE INVENTION 
     The fused filament fabrication printer of this invention employs an arrangement where the printing head(s) are fixed during printing and the build platform on which parts are made is moved in three dimensions or directions. This arrangement allows optimization of the printheads for greater speed and less cost. In the co-pending U.S. patent application Ser. No. 13/750,731, filed on Jan. 25, 2013, the build platform is formed of a circular disk mounted for rotation about a z-axis, and mounted for linear motion along a radial y-axis direction perpendicular to the z-axis, and for linear motion along the z-axis between successive print planes. But any arrangement where the printheads are fixed and only the build platform moves can be used. Because the printing heads are fixed, multiple printing heads can be affixed with respect to the build platform without causing interference of the printheads with each other and without increasing the complexity of controlling movements of multiple printheads. The fixed arrangement of the printing heads allows the close spacing of multiple printheads in a printhead unit and the simple routing of multiple plastic filaments to the individual printheads. The closely spaced printheads in the printhead unit allow the printheads to share common components. An exemplary printhead unit has four printheads which share a common heating block and heating block temperature sensor(s). The heating block incorporates a group of four print tips evenly spaced along a line. Each printhead has a separate plastic filament which is controlled and driven by its own stepper motor through the heating block to one of the print tip. The spacing of the drives which supply the multiple plastic filaments is independent of the nozzle spacing. This allows much closer together nozzles while maintaining consistent flow paths for the filament. Printing of a plastic part is effected by control of the individual stepper motors which drive each of the plastic filaments through the heating block and through one of the printing tips. Printing heads using the same material enable material deposition to be increased resulting in increased printing speed, while heads using different materials provides increased printing speed and permit the simultaneous deposition of different materials, e.g., different colors, onto the part on the build platform. When multiple colors are used all colors can be used to fill the interior of the part, while particular colors are used to color the exterior surface of the part. 
     In an alternative embodiment, a printhead unit incorporating an array of printheads can be used to replace a conventional printhead in a fused filament fabrication printer with a moving printhead. 
     It is an object of the present invention to provide a fused filament fabrication printer of reduced cost and increased speed. 
     It is another object of the present invention to provide a fused filament fabrication printer which facilitates the use of multiple printheads which are simultaneously active. 
     It is another object of the present invention to provide a fused filament fabrication printer which facilitates the use of multiple printheads to apply different materials. 
     It is a further object of the present invention to provide a fused filament fabrication printer with the printhead unit incorporating an array of printheads to create the printed part. 
     Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front axonometric view of the fused filament fabrication printer of this invention. 
         FIG. 2  is a fragmentary front axonometric view of two printhead units each having four printheads. 
         FIG. 3  is an enlarged fragmentary front elevational view of one of the printhead units of  FIG. 2 . 
         FIG. 4  is an exploded isometric view one of the printhead units of  FIG. 2 . 
         FIG. 5  is a bottom plan view of the top plate of the printer of  FIG. 1 . 
         FIG. 6  is a bottom plan view of an alternative embodiment top plate of a printer of this invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring more particularly to exemplar  FIGS. 1-6 , wherein like numbers refer to similar parts, a fused filament fabrication stereo lithographic printer  20  is shown in  FIG. 1 . The printer  20  has a frame  21  which for clarity is shown without lead screws and drive motors (such as shown in U.S. application Ser. No. 13/750,731). The printer  20  provides movement of a printer build platform  24  along three degrees of freedom to position various portions  22  of the printer build platform beneath a plurality of fixed printheads  26  as shown in  FIG. 2 . The printheads  26  have tips  34  through which thermoplastic polymers or metals are extruded. The three degrees of freedom include a first degree of freedom of rotation of the build platform  24  about a z-axis  28  as shown in  FIG. 1 . The build platform  24  defines a start-print plane or surface  32 . A second degree of freedom is provided by linear motion on a cross slide along a radius along a y-axis  36  perpendicular to a z-axis  28 . A third degree of freedom is provided by linear motion of the printer platform in a Z-direction along the z-axis  28  on the vertical carriage  66 . The build platform  24  is moved in the Z-direction so the surface  32  occupies a series of stacked parallel planes, each parallel to a plane defined by the tips  34  of the printheads  26 . The printed part or model  31  is generated by the indexing of the build platform  24  in the horizontal direction along the y-axis  36 , indexing the build platform in the Z direction  28 , and rotating the build platform either continuously or by a series of steps while controlling the turning on and off of the extrusion process in the printheads. 
     As shown in  FIG. 1 , the printer  20  has a T-shaped base plate  42  and an mirror image upper T-shaped plate  54  which is spaced from the base plate by six vertical supports  40 . The printer  20  is mechanically similar to the one disclosed in U.S. application Ser. No. 13/750,731, where machine screws (not shown) and stepper motors (not shown) drive the vertical movement of the vertical carriage  66 , the cross slide  68 , and the rotation of the build platform  24 . The T-shaped base plate  42  has an extension  53  which provides for mounting a computer and power supply (not shown) above which are mounted scanning cameras (not shown). The mirror image extension  53  of the upper T-shaped plate  54  provides a place for mounting spools of plastic filament or wire (not shown) which sit on rods (not shown) which are mounted to the back or bottom  55  of the T of the upper T-shaped plate  54 . From this position filaments  61  shown in  FIG. 2  can be conveniently fed through openings  57  in the upper T-shaped plate. 
     As shown in  FIGS. 2 and 4 , a fixed fused filament fabrication printhead unit  120  has a fixture  122  composed of two identical rectangular plates arranged in mirror image relation as a first motor mount plate  123  and second motor mount plate  124 . Stepping motors  126  can be mounted in an evenly spaced linear array to the backs  128 ,  129  of the motor mount plates  123 , 124  as shown in  FIG. 4 . Two stepping motors  126  are mounted to the first motor mount plate  123  and two additional stepping motors  126  are mounted to the second motor mount plate  124 . Each stepping motor  126  has a drive shaft  130  to which is mounted a drive gear  132 . The drive shaft and the drive gear extend through one of a plurality of openings  134  formed in the motor mount plates  123 ,  124 . The stepping motors  126  are mounted by screws  136  to the motor mount plates. The fixture  122  forms a plurality of filament guide paths  138  which are milled into the front face  140  of the motor mount plate  123  and into the opposed face  141  of the second motor mount plate  124 . The opposed face  141  engages the front face  140  of the motor mount plate  123 . The filament guide paths  138  are partially interrupted by the openings  135  through which the stepping motor drive gears  132  extend such that the filaments  61 , best shown in  FIG. 2 , are driven along the guide paths by rotation of the drive gears. The guide paths  138  are arranged so the drive gears  132  engage the filaments  61  without significantly deforming the filaments but such that the drive gears pull the filaments in to the printhead units  120 ,  182  with considerable force, e.g., more than 5-10 pounds force, such that no additional parts such as additional bearing, spring, or adjustable pressure points on the opposing side of the filament are needed to feed the filaments. The guide paths are cylindrical results in 180 degrees of supporting surface which prevents a single pinch point, and the force on the filament is on the entire back side of the filament pressing it into a drive gear  132 . Conventionally using flat supporting surfaces there is only 20-30 degrees of support. The drive gears  132  also drive the filaments  61  into an extrusion module  144 . The guide paths  138  are arranged to converge towards the extrusion module  144  mounted to the lower edge  146  of the fixture  122  which is comprised of the lower edges of the motor mount plates  123 ,  124 . 
     The extrusion module  144 , best shown in  FIG. 3 , has insulating standoffs  148  constructed of a low thermal conductivity material i.e. less than about 5 W/(m·K) such as PEEK (polyetheretherketone) with a thermal conductivity around 0.25 W/(m·K). 
     Each of the motor mount plates  123 ,  124  has a milled opening  145  along the lower edge  146 . The insulating standoffs  148  are clamped between the motor mount plates  123 ,  124 , with one end engaged within the milled openings  145 . 
     The insulating standoffs  148  have external circumferential grooves  147  which are captured by portions of the milled openings  146  as shown in  FIG. 3 . The insulating standoffs  148  support a thermally conductive i.e., greater than about 25 W/(m·K), heater bock  149  made of 6061 aluminum having a thermal conductivity of 154-180 W/(m·K). The insulating standoffs  148  support the heater block  149  by two screws  151 . The heater block  149 , as best shown in  FIG. 4 , has portions forming a groove  150  which surrounds a plurality of openings  152  leading to nozzle openings  154 , shown in  FIG. 2 , which lead to the print tips  34 . The filaments  61  are melted within the openings  152  by the heater block  149  which is heated by an electric ceramic heating element  156  as shown in  FIG. 4 . The heating element  156  may be a conductive ceramic or a wire such as an alloy of nickel, chromium and iron containing less than thirty percent iron sold under the trademark Nichrome®, which is placed in the U-shaped groove and ceramic is cast around the wire. The heating element  156  has two leads  158  through which a regulated current is applied. The regulated current is controlled based on the output of a thermal sensor  160 , shown in  FIG. 3 , mounted to the heater block  149  so that the heater block is maintained at a constant temperature sufficient to liquefy the filaments  61 . Alternatively, the ceramic heating element  156  can be used as the thermal sensor  160  by monitoring the resistance of the heating element which varies with temperature. The filaments  61  are driven by the gears  132  of the stepper motors  126  along the filament guide paths  138  and through rigid thermally insulating filament guides  162 . The insulating filament guides  162  are clamped between the milled openings  145  shown in  FIG. 4  and spot faces  164  around the openings  152 . The insulating outer filament guides  162  are lined with nonstick high temperature inner filament guides  166  constructed of, for example, Polytetrafluoroethylene (PTFE), sold under the trademark Teflon®. 
     The printhead unit  120  is mounted to the upper T-shaped plate  54  in a milled groove (not shown) similar to the nonfunctional milled groove  168  shown for illustrative purposes in the base  42 . Bolts  172  extend through support holes formed by the motor mount plate opposed grooves  174 . The bolts  172  extend upwardly through support holes  170  in the upper T-shaped plate  54  and extend above the upper surface  59 . The printhead unit support holes  170  are positioned on either side of the filament holes  57 . 
     The motor mount plates  123 ,  124  are joined together by screws  175  passing through holes  178  so that the grooves  174  define support holes. The plates  123 ,  124  are supported on the bolts  172  by nuts  176  as shown in  FIG. 4 . 
     An alternative embodiment printhead unit  182  is shown in  FIG. 2 , where one half of the printhead unit  182  is shown. The printhead unit  182  is essentially identical to the printhead unit  120  shown in  FIGS. 3 and 4 , except that the first motor mount plate  184  incorporates two extrusion modules  144 , and supports eight stepper motors  126  which drive eight filaments  61  along eight filament guide paths  138 , supplying four filaments through each of the two extrusion modules  144 . By doubling the number of print tips  34  the rate of material deposition can be approximately doubled depending on the scale of the object being printed. 
     Multiple printhead units  120  or  182  can be arranged on either side of the z-axis  28  to the full radius of the printer platform  24 . Increasing the number of print tips  34  will proportionately increase the speed of printing a print layer, assuming the model  31  is of such size that all print tips can simultaneously print on portions of the model. Using more print tips  34  also reduces the necessary motion of the printer platform  24  along the y-axis  36 . With a sufficient number and optimum arrangement of printheads the maximum movement of the cross slide  68  can be limited to only a maximum spacing between print tips  34  which is the spacing as shown in  FIG. 2  between the adjacent print tips  186  and  188 . Mounting of the printhead units  182  or  120  on either side of the z-axis  28  allows an entire print layer to be printed with only a rotation of 180° or π radians. Without any increase in the deposition rate of plastic or metal through the print tips  34 , the angular velocity of the print platform, or the radial velocity of the print platform along the y-axis  36 , the print speed can be increased proportionally by adding additional print tips  34 . 
     Additional printhead units  182  or  120  with their additional print tips  34  can be arranged radially about a z-axis  28  as shown in  FIG. 5 , where four or eight lines of print tips  34  within print units  182  or  120  can, depending on geometry and size of the print object  31 , double or quadruple the speed of deposition of a print layer. Additional printhead units  182  or  120  can also be arranged in a Cartesian grid as shown in  FIG. 6 . In both the Cartesian grid arrangement of  FIG. 6  or the radial arrangement of  FIG. 5 , the print tips  34  of the additional printhead units  182  or  120  can be arranged to be at the same radial distance from the z-axis  28  when the printer platform is centered below the printhead units. Multiple print tips  34  at the same radius will reduce the angular rotation of the printer platform  22  between the radial direction movement steps along the y-axis  36  to print a complete layer. If the print tips  34  are arranged at different radial distances from the z-axis this will reduce the size of the of the total radial direction movement necessary to complete a print layer. The additional printhead units  182  or  120  are easily accommodated by simply milling additional grooves  168  on the underside of the top T-shaped plate  59 . For maximum flexibility, both radial and Cartesian grooves can be superimposed so that the printhead units  182  or  120  can be rearranged between the radial and Cartesian arrangement. 
     The fused filament fabrication printer  20  printhead units  120  can be arranged such that the printheads completely span the radial width of the part  31  to be formed. For example in forming a 10 cm part with an array of printheads  26  with a spacing between printhead tips  34  of one centimeter, an array of six printheads extending from the center of the part  31  to the edge of the part allows printing a layer of the part with a one centimeter movement of the cross slide. Thus the printer  20  can employ an array of printheads over the entire radius of the print platform of, for example, 25 to 50 cm with 25 to 50 printheads. In setting up to print a particular part, filaments can be run to every printhead, or if the number of filaments  61  is limited for practical reasons, only every other or every third or fourth printhead can be supplied with the filament depending on the radius of the part  31  to be formed. In this way the total movement of the cross slide would be limited to 1, 2, 3, or 4 cm centimeters. 
     Control of the printing of a part layer involves determining the maximum extent of the print object  31  and using an optimization algorithm or a Monte Carlo simulation to determine the optimal radial start point and movement of the cross slide  68 . Control of the print layer by the turning on and off of extrusion of plastic or metal under control of the stepper motors  126  employs a coordinate transform from the model coordinates to the instantaneous path of the print tips  34  and printing where the model indicates material is to be added. 
     If multiple print tips are available, different colored plastic filaments can be used to produce color models. To maximize print speed, all colors are used to fill solid parts of the model with a particular selected color for portions of the visible surfaces of the model. By printing with three or four colors RGB (red green blue) or CMYK (cyan, magenta, yellow and black) the possibility of creating a broad range of color hues is offered. 
     It should be understood that the fused filament can be a low melting point metal, for example solder with a melting point of 90 to 180-190° C. or even up to 450° C. If solder is employed, the heater block  149  may be made of stainless steel or other material compatible with liquid metal with a thermal conductivity of even less than 25 W/(m·K) and the insulating standoffs  148  may also be made of stainless steel or other material compatible with liquid metal. The standoffs  148 , particularly in the case of a filament of solder, may be of a relatively high conductive material (i.e., greater than 5 W/(m·K)) like stainless steel where an insulating effect is created by the design geometry, for example using thin materials such as thin walled metal tubes for the filament guides  162 . The inner filament guides  166  of polytetrafluoroethylene (PTFE) can still be used since PTFE may be used up to a maximum use temperature of 260° C./500° F. 
     In at least some circumstances the print head units  120 ,  180  can be simplified by fabricating the motor mount plate  123 ,  124 , or  184 , the standoffs  148 , the filament guides  162 , and the heater block  149  as one unitary part of the same material such as stainless steel or a similar material. 
     It should be understood that where a filament is described or claimed the filament may be any printing material in a form factor which can be used as a filament which function in the disclosed printhead. If the filament is plastic any functional material can be used e.g., ABS, HDPE, PLA, PVA or can be of made of a plastic filled with other material, for example nano particles (between 1 and 100 nanometers in size) of carbon or metal. Such filled plastic filaments could be sintered to form, for example, metal parts. 
     It should also be understood that the filaments  61  can be of a wide range of plastic materials such as acrylonitrile butadiene styrene (ABS), high-density polyethylene (HDPE), polylactic acid (PLA), and polyvinyl alcohol (PVA), waxes, and other thermoplastics. 
     It should be understood that a stepper motor is defined to include any motor with or without feedback which can be controlled to rotate in discrete steps. 
     It should be understood that where thermoconductivity of a material is described or claimed it is in reference to a temperature of between about 20° C. and 350° C. 
     It should be understood that the insulating standoff  148  can be constructed of low thermal conductivity materials, i.e. less than about 5 W/(m·K) such as certain stainless steel alloys, Hastelloy C, ceramics such as Steatite (soap stone) or fused silica could be used. 
     It should be understood that there can be more than one extrusion module mounted to the fixture in filament receiving relation to at least one of the filament guide paths such that several or only one filament is supplied to each of a plurality nozzle block, each block having a heating element, a thermal sensor, a heated guide path, and a filament guide connects a filament guide path to the heated guide path and from there to a portion of the nozzle block forming a print tip. 
     It should be understood that thermally conductive materials of greater than about 25 W/(m·K) can be used to form the heater bock  149  for example, aluminum, copper, silver or their alloys having thermal conductivity of 25, 50, 100, 200 or 350 or greater. It may be of particular advantage to have a greater conductivity when the filaments have a greater diameter. 
     It should be understood that the plurality of drive gears  132  used in the printhead units  120 ,  182  can be of different configuration or sizes, for example where the filaments used are of different materials, shapes or sizes. 
     It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces all such modified forms thereof as come within the scope of the following claims.