Patent Description:
Additive manufacturing, including three dimensional printing, has constituted a very significant advance in the development of not only printing technologies, but also of product research and development capabilities, prototyping capabilities, and experimental capabilities, by way of example. Of available additive manufacturing (collectively "3D printing") technologies, fused deposition of material ("FDM") printing is one of the most significant types of 3D printing that has been developed.

FDM is an additive manufacturing technology that allows for the creation of 3D elements on a layer-by-layer basis, starting with the base, or bottom, layer of a printed element and printing to the top, or last, layer via the use of, for example, heating and extruding thermoplastic filaments into the successive layers. Simplistically stated, an FDM system includes a print head which feeds the print material filament through a heated nozzle to print, an X-Y planar control for moving the print head in the X-Y plane, and a print platform upon which the base is printed and which moves in the Z-axis as successive layers are printed.

More particularly, the FDM printer nozzle heats the thermoplastic print filament received to a semi-liquid state, and deposits the semi-liquid thermoplastic in variably sized beads along the X-Y planar extrusion path plan provided for the building of each successive layer of the element. The printed bead/trace size may vary based on the part, or aspect of the part, then-being printed. Further, if structural support for an aspect of a part is needed, the trace printed by the FDM printer may include removable material to act as a sort of scaffolding to support the aspect of the part for which support is needed. Accordingly, FDM may be used to build simple or complex geometries for experimental or functional parts, such as for use in prototyping, low volume production, manufacturing aids, and the like.

However, the use of FDM in broader applications, such as medium to high volume production, is severely limited due to a number of factors affecting FDM, and in particular affecting the printing speed, quality, and efficiency for the FDM process. As referenced, in FDM printing it is typical that a thermoplastic is extruded, and is heated and pushed outwardly from a heating nozzle, under the control of the X-Y and/or Z driver of a print head, onto either a print plate/platform or a previous layer of the part being produced. More specifically, the nozzle is moved about by the robotic X-Y planar adjustment of the print head in accordance with a pre-entered geometry, such as may be entered into a processor as a print plan to control the robotic movements to form the part desired.

Thus, current limitations on the cost, efficiency, and performance of additive manufacturing often occur due to the nature of known print heads, such as those print heads typically provided in FDM printing. In short, in a typical known print head, print material is fed from a spool through, for example, two print hobs that serve to extrude the print material toward the "hot end" of the printer. In known embodiments, a stepper motor drives one of the hobs to press the filament against, and thereby cause to rotate, the other of the hobs in order to feed the print material from the spool to the hot end. However, the available forces that are typically applied by current print material feeds may score or warp the filament, if excessive, or may further subjects the print material filament to various undesirable effects, such as compression, crimping, friction, and lag if excessive or insufficient. Lagging of the print material, which may occur when high feed rate is needed by the print plan, but insufficient feed force is provided, may be particularly detrimental, at least in that the print material may curl or otherwise re-spool at the output from or input to the hobs, thereby jamming the printer.

Therefore, the need exists for a print head providing enhanced filament forces in additive manufacturing.

Conventional print heads for additive manufacturing are disclosed in <CIT> and <CIT>.

Thus, the disclosed embodiments provide an apparatus, system, and method for an apparatus, system and method for enhanced drive force in an additive manufacturing print head.

The disclosed non-limiting embodiments are discussed in relation to the drawings appended hereto and forming part hereof, wherein like numerals indicate like elements, and in which:.

The figures and descriptions provided herein may have been simplified to illustrate aspects that are relevant for a clear understanding of the herein described apparatuses, systems, and methods, while eliminating, for the purpose of clarity, other aspects that may be found in typical similar devices, systems, and methods. Those of ordinary skill may thus recognize that other elements and/or operations may be desirable and/or necessary to implement the devices, systems, and methods described herein. But because such elements and operations are known in the art, and because they do not facilitate a better understanding of the present disclosure, for the sake of brevity a discussion of such elements and operations may not be provided herein. However, the present disclosure is deemed to nevertheless include all such elements, variations, and modifications to the described aspects that would be known to those of ordinary skill in the art.

Embodiments are provided throughout so that this disclosure is sufficiently thorough and fully conveys the scope of the disclosed embodiments to those who are skilled in the art. Numerous specific details are set forth, such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. Nevertheless, it will be apparent to those skilled in the art that certain specific disclosed details need not be employed, and that embodiments may be embodied in different forms. As such, the embodiments should not be construed to limit the scope of the disclosure. As referenced above, in some embodiments, well-known processes, well-known device structures, and well-known technologies may not be described in detail.

For example, as used herein, the singular forms "a", "an" and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The steps, processes, and operations described herein are not to be construed as necessarily requiring their respective performance in the particular order discussed or illustrated, unless specifically identified as a preferred or required order of performance. It is also to be understood that additional or alternative steps may be employed, in place of or in conjunction with the disclosed aspects.

When an element or layer is referred to as being "on", "engaged to", "connected to" or "coupled to" another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present, unless clearly indicated otherwise. Further, as used herein the term "and/or" includes any and all combinations of one or more of the associated listed items.

Yet further, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the embodiments.

As discussed herein, improved print head embodiments are sought: in which print head speed and feed force may be improved without the referenced detrimental effects, such as lagging or jamming; in which printing precision may be improved; and in which printing responsiveness is improved. Print head speed may be improved in the disclosed embodiments and their equivalents to, for example, <NUM><NUM> or more per second; precision may be improved, such as to <NUM><NUM> or better per count, such as with a <NUM> micrometer trace length resolution at a <NUM> micrometer wide and <NUM> micrometer thick trace; and responsiveness may be improved, such as to a <NUM> system or better response with a <NUM> microsecond slam stop.

<FIG> is a block diagram illustrating an exemplary filament-based printer <NUM> with a print head that is not according to the claimed invention. In the illustration, the printer includes an X-Y axis driver <NUM> suitable to move the print head <NUM>, and thus the print nozzle <NUM> on the print head <NUM>, in a two dimensional plane, i.e., along the X and Y axes. Further included in the printer <NUM> for additive manufacturing are the aforementioned print head <NUM>, including print nozzle <NUM>. As is evident from <FIG>, printing may occur upon the flow of heated print material outwardly from the nozzle <NUM> along a Z axis with respect to the X-Y planar movement of the X-Y driver <NUM>. Thereby, layers of printed material <NUM> may be provided from the nozzle <NUM> onto the build plate <NUM> along a path dictated by the X-Y driver <NUM>.

More particularly, filament-based 3D printers include an extruding print head <NUM> that uses the hobs <NUM> to move the filament <NUM> into the heated nozzle <NUM> with great precision and at a highly controlled feed rate tied to the controller <NUM> executing the print plan algorithm <NUM> via the X-Y-Z axis driver <NUM>. A motor <NUM> is generally used to drive a driven one of the hobs <NUM> against an undriven one of the hobs <NUM>. The driven hob <NUM> may be, as discussed herein, a knurled, recessed, and/or toothed wheel. The undriven hob may comprise, by way of non-limiting example, a pinching roller. The friction between the hobs <NUM> applies force to the filament <NUM> to impart the feed motion to the filament material <NUM> when the hobs rotate. Typical extruder forces in the known art vary from <NUM>,<NUM> to <NUM>,<NUM> (<NUM> to <NUM> lbs) of force.

The embodiments herein may provide an extruder capable of <NUM>,<NUM> (<NUM> lbs) of peak force, such as using a <NUM> filament. The embodiments may even provide a peak drive force of <NUM>,<NUM> (<NUM> lbs) or more of force with larger filament sizes, and thus also provide operational force well in excess of the known art.

<FIG> illustrates with greater particularity a print head <NUM>, that is not according to the claimed invention, having nozzle <NUM> for an exemplary additive manufacturing device, such as a <NUM>-D printer, such as a FDM printer. As illustrated, the print material <NUM> is extruded via hobs <NUM> of the head <NUM> from a spool of print material 110a into and through the heated nozzle <NUM>. As the nozzle <NUM> heats the print material <NUM>, the print material is at least partially liquefied for output from an end port 106a of the nozzle at a point along the nozzle distal from the print head <NUM>. Thereby, the extruded material is "printed" outwardly from the port 106a via the Z axis along a X-Y planar path determined by the X-Y driver (see <FIG>) connectively associated with the print head <NUM>.

The embodiments may provide the foregoing improvements to the print head <NUM> by, among other things, providing improved hobs <NUM> to grip the print material filament <NUM> from the print material spool 110a. <FIG> illustrate the "engagement length" 304a of a hob with the print material filament <NUM>, as those terms are used herein. In the current art, this engagement length 304a typically results from hobs having diameters in the range of <NUM> to <NUM> or <NUM>.

The gripping of the print material <NUM> by hobs <NUM> having smaller diameters of <NUM> to <NUM>, and hence smaller engagement lengths 304a, is illustrated with respect to <FIG>. Certain of the embodiments improve the engagement length <NUM> by increasing the engagement surface, that is, by increasing the diameter of the hobs <NUM> to enhance the engagement length 304b with the printed material filament <NUM>, as illustrated in <FIG>. Such increased diameter hobs <NUM> may, for example, have a diameter in the <NUM>-<NUM> range. The larger hob diameter in the illustrated embodiments enables significantly enhanced hob feed force, as discussed throughout.

According to the claimed invention and as illustrated in the exemplary embodiments of <FIG>, a series of teeth 402a, 402b is provided on each half hob 103a, 103b. The teeth <NUM> may, by way of non-limiting example, have sharpened surfaces, such as in order to enhance grip on filament <NUM>.

According to the claimed invention, the teeth <NUM> of the hob <NUM> are offset with respect to the matched set of teeth 402a, 402b on each hob half 103a, 103b by a predetermined offset amount, such as <NUM> degrees. More particularly, such misalignment may be between <NUM> degrees and <NUM> degrees, and may occur by sheer random association of the two hob halves. Moreover, the two hob halves may be provided with a shim therebetween, such that the shim <NUM> may be selected based on the desired grip level to be provided by the hob once the two halves are joined.

Of note, overly sharpened teeth <NUM> may bite undesirably significantly into the print material filament <NUM>, thereby increasing drag, and as such teeth <NUM> may be sandblasted, plated, or offset but with non-sharpened surfaces (such as square or spherical filament grip surfaces), or offset but with varying teeth shapes (such as varying between triangular, square, and spherical grip surfaces), and so on.

Of course, hob halves 103a, 103b may be consistently manufactured in the same manner, and thus the teeth 402a, 402b may be offset only upon interconnection of the hob halves 103a, 103b. Therefore, adjustability, such as an adjustable shim <NUM>, may be provided between hob halves 103a, 103b in order to adjust the grip level of the hobs <NUM> onto the printed material filament <NUM>. Increased grip provided by the hobs <NUM> may allow for a correspondent decrease in the diameter of the hobs <NUM> over that referenced above in relation to <FIG>, due, in part, to the decreased necessity of an increase in engagement length <NUM> in light of the enhanced grip. Additionally and alternatively, the number of teeth <NUM> in a hob <NUM> may be reduced, but with the teeth <NUM> still staggered, so long as an engagement length <NUM> along the printed material filament <NUM> maintains a predetermined level of friction in order to meet the characteristics discussed throughout.

In accordance with the foregoing, very high levels of grip on filament <NUM> with very low loss (i.e., drag/friction) is thus provided. Moreover, hob diameter is adjusted over the known art to vary across print environments to provide only the necessary level of torque, such as for a given print material <NUM> or a given printing technique. The foregoing may also lead to decreased costs, such as due to the ready replaceability of the hobs <NUM>, which may also improve the time needed to clean and service a print head <NUM>.

<FIG> illustrates an exemplary assembly for hobs <NUM> according to to the claimed invention.

The control of feed force and resolution is enhanced with both hobs <NUM>-<NUM> and <NUM>-<NUM> being driven. Driving both hobs <NUM>-<NUM>, <NUM>-<NUM> via motors <NUM> allows for the contacting of the filament <NUM> on two sides thereof, to better drive the filament. This approximate equivalency of the applied force to the filament on both sides thereof, and along a great length thereof corresponded to the enhanced hob size discussed herein, better avoids the damage to the filament geometry that is caused in the known art by the affirmative application of force to only one side of the filament.

More particularly, multi-positional extrusion forces from multiple driven hobs <NUM>-<NUM>, <NUM>-<NUM> also decreases stress forces on the filament <NUM> at least in that, for a given force, dual driven-hobs <NUM> allow the force load to be applied, and thus distributed, to multiple areas of the filament, thus greatly reducing the point-force and single side-force loads that would otherwise be applied to single aspects of the filament <NUM>. This multi-point force distribution thereby avoids the deformation in filament geometry and filament melt and flow impedance of the known art.

Dual driven hobs may further enhance the feed force and resolution via other means. For example, servo-motor feedback from each hob drive motor <NUM> may enable more intelligent motion of hobs <NUM>-<NUM>, <NUM>-<NUM>, both with regard to filament <NUM>, heating <NUM> (see above), and each other <NUM>-<NUM>, <NUM>-<NUM>. This may occur, by way of example, by the passing of feedback <NUM> from each motor <NUM> to controller <NUM>, and decisions on motor control from controller <NUM> based on application of algorithm <NUM> to motor(s) <NUM>. This feedback may be provided directly, such as by reading motor current, and/or by one or more sensors <NUM> and/or motor encoders <NUM> provided to generate data indicate of print and motor performance. Correspondingly, all of the foregoing forces, i.e., between the hobs <NUM>, as applied to filament <NUM>, that dictates feed speed to nozzle <NUM>, and so on, may be fully programmable to algorithm <NUM> in the embodiments.

The improvements to the extruding print head provided in the embodiments enable acceleration and deceleration of the filament at a much higher rates than in the known art. That is, the X-Y stage driver may accelerate and decelerate more quickly than in the known art, and the extruder nevertheless maintains proper material flow. Of note, improved deceleration also enhances retraction of the filament, which avoids dripping, thereby improving both nozzle performance the nozzle tip cleaning process.

Increased extruder force and control additionally allows for the filament to be better pushed through the inlet plugs that may arise if the filament heating and feed force is mismatched, as discussed herein. Further, improved extruder force and adjustable control enables changes in the filament drag between the material spool and the print head to be readily overcome. Yet further, the improved rotation rate and rate-tolerance in the embodiments also leads to more repeatable and precise bead size at the print nozzle.

Yet further, there occurs a pressure decay in the nozzle when print speed is dramatically changed. In order to address this pressure decay, substantial performance out of the extruder is required, which includes both the force and the acceleration rate of the filament. That is, the quicker the acceleration, the more force that is generated. This high force allows the system to have the capability to drive very high acceleration and deceleration rates without slipping. For example, for purposes of a corner print, the control system <NUM> may perform a suck back before and during a slow down to address lead, such as slowing to zero at the corner. Thereafter, a pre-pump may be performed as the corner is exited, driving to the desired speed, thus addressing lag.

Impulse is the change of momentum of an object when the object is acted upon by a force for an interval of time. That is, Impulse = Force * time = force * Delta t. As such, an impulse calculation by the control system <NUM> may be suitable to indicate the variations in filament driving for particular aspects of the print plan, such as are discussed in the example immediately above.

<FIG> depicts an exemplary computing system <NUM> for use as the controller <NUM> in association with the herein described systems and methods. Computing system <NUM> is capable of executing software, such as an operating system (OS) and/or one or more computing applications/algorithms <NUM>, such as applications applying the print plan and control algorithms discussed herein, and may execute such applications, such as to control one or more hob motors by sending data from, and by using data, such as sensor data, such as in the form of feedback <NUM>, received at, the I/O port.

The operation of exemplary computing system <NUM> is controlled primarily by computer readable instructions, such as instructions stored in a computer readable storage medium, such as hard disk drive (HDD) <NUM>, optical disk (not shown) such as a CD or DVD, solid state drive (not shown) such as a USB "thumb drive," or the like. Such instructions may be executed within central processing unit (CPU) <NUM> to cause computing system <NUM> to perform the operations discussed throughout. In many known computer servers, workstations, personal computers, and the like, CPU <NUM> is implemented in an integrated circuit called a processor.

It is appreciated that, although exemplary computing system <NUM> is shown to comprise a single CPU <NUM>, such description is merely illustrative, as computing system <NUM> may comprise a plurality of CPUs <NUM>. Additionally, computing system <NUM> may exploit the resources of remote CPUs (not shown), for example, through communications network <NUM> or some other data communications means.

In operation, CPU <NUM> fetches, decodes, and executes instructions from a computer readable storage medium, such as HDD <NUM>. Such instructions may be included in software such as an operating system (OS), executable programs, and the like. Information, such as computer instructions and other computer readable data, is transferred between components of computing system <NUM> via the system's main data-transfer path. The main data-transfer path may use a system bus architecture <NUM>, although other computer architectures (not shown) can be used, such as architectures using serializers and deserializers and crossbar switches to communicate data between devices over serial communication paths. System bus <NUM> may include data lines for sending data, address lines for sending addresses, and control lines for sending interrupts and for operating the system bus. Some busses provide bus arbitration that regulates access to the bus by extension cards, controllers, and CPU <NUM>.

Memory devices coupled to system bus <NUM> may include random access memory (RAM) <NUM> and/or read only memory (ROM) <NUM>. Such memories include circuitry that allows information to be stored and retrieved. ROMs <NUM> generally contain stored data that cannot be modified. Data stored in RAM <NUM> can be read or changed by CPU <NUM> or other hardware devices. Access to RAM <NUM> and/or ROM <NUM> may be controlled by memory controller <NUM>. Memory controller <NUM> may provide an address translation function that translates virtual addresses into physical addresses as instructions are executed. Memory controller <NUM> may also provide a memory protection function that isolates processes within the system and isolates system processes from user processes. Thus, a program running in user mode may normally access only memory mapped by its own process virtual address space; in such instances, the program cannot access memory within another process' virtual address space unless memory sharing between the processes has been set up.

In addition, computing system <NUM> may contain peripheral communications bus <NUM>, which is responsible for communicating instructions from CPU <NUM> to, and/or receiving data from, peripherals, such as peripherals <NUM>, <NUM>, and <NUM>, which may include printers, keyboards, and/or the sensors, encoders, and the like discussed herein throughout. An example of a peripheral bus is the Peripheral Component Interconnect (PCI) bus.

Display <NUM>, which is controlled by display controller <NUM>, may be used to display visual output and/or presentation generated by or at the request of computing system <NUM>, responsive to operation of the aforementioned computing program. Such visual output may include text, graphics, animated graphics, and/or video, for example. Display <NUM> may be implemented with a CRT-based video display, an LCD or LED-based display, a gas plasma-based flat-panel display, a touch-panel display, or the like. Display controller <NUM> includes electronic components required to generate a video signal that is sent to display <NUM>.

Further, computing system <NUM> may contain network adapter <NUM> which may be used to couple computing system <NUM> to external communication network <NUM>, which may include or provide access to the Internet, an intranet, an extranet, or the like. Communications network <NUM> may provide user access for computing system <NUM> with means of communicating and transferring software and information electronically. Additionally, communications network <NUM> may provide for distributed processing, which involves several computers and the sharing of workloads or cooperative efforts in performing a task. It is appreciated that the network connections shown are exemplary and other means of establishing communications links between computing system <NUM> and remote users may be used.

Network adaptor <NUM> may communicate to and from network <NUM> using any available wired or wireless technologies. Such technologies may include, by way of non-limiting example, cellular, Wi-Fi, Bluetooth, infrared, or the like.

It is appreciated that exemplary computing system <NUM> is merely illustrative of a computing environment in which the herein described systems and methods may operate, and does not limit the implementation of the herein described systems and methods in computing environments having differing components and configurations. That is to say, the concepts described herein may be implemented in various computing environments using various components and configurations.

In the foregoing detailed description, it may be that various features are grouped together in individual embodiments for the purpose of brevity in the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that any subsequently claimed embodiments require more features than are expressly recited.

Claim 1:
A print head (<NUM>) for additive manufacturing, comprising:
two proximate hobs (<NUM>) configured to receive and extrude therebetween a print material filament (<NUM>) for the additive manufacturing, each of the two hobs (<NUM>) comprising a diameter of greater than <NUM>;
two motors (<NUM>) each configured to impart a rotation to a respective one of the two hobs (<NUM>), wherein an extrusion results from the rotation; and
an interface to a liquefier configured to output the extruded print material filament (<NUM>) after at least partial liquefication by at least one nozzle heater (<NUM>) to perform the additive manufacturing,
wherein each hob (<NUM>) comprises two halves (103a, 103b);
wherein a series of teeth (402a, 402b) are provided on each hob half (103a, 103b) and the teeth (402a) of a first hob half (103a) are offset with respect to the matched set of teeth (402b) on a second hob half (103a, 103b).