Patent Application
20180169971
The present disclosure relates generally to fused filament fabrication (FFF) machines and methods of operation.
Fused filament fabrication is a 3D printing process that uses a continuous filament of a thermoplastic material fed through a moving, heated head assembly to form a workpiece. The media is heated to a molten state and forced out of a dispenser and deposited on the growing workpiece. The head assembly is moved, under a computer control build sequence, to define the printed shape of the workpiece. The workpiece includes the desired part and a sacrificial tower for the part. Usually the head assembly moves to deposit one horizontal layer at a time, moving in two dimensions to form the workpiece, before moving upwards or having the build platform holding the workpiece move downwards to begin a new layer.
However, known FFF machines are not without disadvantages. For instance, media and/or debris build-up on the dispenser tip needs to be periodically removed. Conventional FFF machines provide a tip wipe assembly used to clean the dispenser tip and the machine causes the head assembly to move to the tip wipe assembly at predetermined times. However, during the time that the head assembly is moving to the tip wipe assembly and back to the workpiece, the deposited material in the workpiece is cooled and the media in the dispenser, which is not moving through the dispenser, can be heated above the normal deposition temperature. Such material may be detrimentally affected by the excess heating. For example, the initial slug of media that is dispensed after the tip wipe may be more viscous and thus more easily dispensed, which may lead to a thinner filament at the location of the initial dispensing. When the material is deposited after the tip wipe process, the material in the workpiece and the material in the head assembly are at different temperatures and can yield a weaker bond at the interface between the materials. The media may be weakened or chemically altered due to the excess and/or prolonged heating in the head assembly leading to changes and possible local reduction in the properties of the material, such as the strength of the material. The filament on the workpiece at the break area may be physically altered, such as being partially set up, prior to the re-dispensing of the new media, forming a line of weakness at the interface between the old material and the new material. The final part may be subject to faults, property variability or other problems at the breaks in the corresponding layer(s) caused by the tip wipe process leading to lower average tensile strength characteristics for the parts. As such, the parts cannot be certified or need to be overdesigned, leading to higher cost, higher weight, and the like.
In accordance with one embodiment, a fused filament fabrication (FFF) machine is provided including a cabinet defining a build chamber for building a part and a sacrificial tower for the part at a build location. A head assembly is provided in the cabinet for dispensing media at the build location during a build process. The head assembly has a filament dispenser for dispensing the media through a liquefier tip of the filament dispenser. A tip wipe assembly is provided in the cabinet remote from the build location. A controller is operably coupled to the head assembly to control the position of the head assembly and dispensing of the media during the build process. The controller periodically moves the head assembly away from the build location to the tip wipe assembly to clean the liquefier tip at the tip wipe assembly during a tip wipe process. The controller moves the head assembly from the tip wipe assembly to the build location to resume the build process at the sacrificial tower such that the media dispensed immediately after the tip wipe process is used to build the sacrificial tower.
In another embodiment, a method of operating a fused filament fabrication (FFF) machine having a head assembly with a filament dispenser for dispensing media through a liquefier tip is provided including fabricating a part in layers using the filament dispenser during a part fabricating process and fabricating a sacrificial tower for the part in layers using the filament dispenser during a sacrificial tower fabricating process. The method also includes cleaning the liquefier tip at a tip wipe assembly during a tip wipe process. The sacrificial tower fabricating process is performed prior to the part fabricating process after the tip wipe process.
In a further embodiment, a controller for a fused filament fabrication (FFF) machine having a head assembly with a filament dispenser for dispensing media through a liquefier tip is provided including a positioning unit for controlling a position of the head assembly, a build unit storing a program for controlling a build sequence for building a part in layers and a sacrificial tower for the part in layers, and a tip wipe unit for initiating a tip wipe process to clean the liquefier tip at a tip wipe assembly. The tip wipe unit periodically causes the positioning unit to move the head assembly to the tip wipe assembly to perform the tip wipe process. The build unit causes the positioning unit to move the head assembly to the sacrificial tower to reinitiate dispensing of the media at the sacrificial tower after the tip wipe process prior to moving the head assembly to the part such that the media dispensed immediately after the tip wipe process is used to build the sacrificial tower.
The features and functions that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.
The following detailed description of certain embodiments will be better understood when read in conjunction with the appended drawings. It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings.
Various embodiments will be better understood when read in conjunction with the appended drawings. To the extent that the figures illustrate diagrams of the functional blocks of various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry. Thus, for example, one or more of the functional blocks (e.g., processors, controllers or memories) may be implemented in a single piece of hardware (e.g., a general purpose signal processor or random access memory, hard disk, or the like) or multiple pieces of hardware. Similarly, any programs may be stand-alone programs, may be incorporated as subroutines in an operating system, may be functions in an installed software package, and the like. It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings.
As used herein, the terms “system,” “unit,” or “module” may include a hardware and/or software system that operates to perform one or more functions. For example, a module, unit, or system may include a computer processor, controller, or other logic-based device that performs operations based on instructions stored on a tangible and non-transitory computer readable storage medium, such as a computer memory. Alternatively, a module, unit, or system may include a hard-wired device that performs operations based on hard-wired logic of the device. The modules or units shown in the attached figures may represent the hardware that operates based on software or hardwired instructions, the software that directs hardware to perform the operations, or a combination thereof. The hardware may include electronic circuits that include and/or are connected to one or more logic-based devices, such as microprocessors, processors, controllers, or the like. These devices may be off-the-shelf devices that are appropriately programmed or instructed to perform operations described herein from the instructions described above. Additionally or alternatively, one or more of these devices may be hard-wired with logic circuits to perform these operations.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.
It should be noted that the particular arrangement of components (e.g., the number, types, placement, or the like) of the illustrated embodiments may be modified in various alternate embodiments. For example, in various embodiments, different numbers of a given module or unit may be employed, a different type or types of a given module or unit may be employed, a number of modules or units (or aspects thereof) may be combined, a given module or unit may be divided into plural modules (or sub-modules) or units (or sub-units), one or more aspects of one or more modules may be shared between modules, a given module or unit may be added, or a given module or unit may be omitted.
As used herein, a structure, limitation, or element that is “configured to” perform a task or operation is particularly structurally formed, constructed, or adapted in a manner corresponding to the task or operation. For purposes of clarity and the avoidance of doubt, an object that is merely capable of being modified to perform the task or operation is not “configured to” perform the task or operation as used herein. Instead, the use of “configured to” as used herein denotes structural adaptations or signals, and denotes structural requirements of any structure, limitation, or element that is described as being “configured to” perform the task or operation. For example, a processing unit, processor, or computer that is “configured to” perform a task or operation may be understood as being particularly structured to perform the task or operation (e.g., having one or more programs or instructions stored thereon or used in conjunction therewith tailored or intended to perform the task or operation, and/or having an arrangement of processing circuitry tailored or intended to perform the task or operation). For the purposes of clarity and the avoidance of doubt, a general purpose computer (which may become “configured to” perform the task or operation if appropriately programmed) is not “configured to” perform a task or operation unless or until specifically programmed or structurally modified to perform the task or operation.
The FFF machine 100 includes a cabinet 110 defining a build chamber 112 for building the workpiece 104 at a build location 114 in the build chamber 112. In an exemplary embodiment, the FFF machine 100 includes a build platform 116, which is movable up and down in the build chamber 112. The build platform 116 supports a build sheet 118 that defines the build location 114. The build sheet 118 may be removably coupled to the build platform 116 and replaced, such as after completion of the build or when building a different type of part 106. The workpiece 104 is built on the top surface of the build sheet 118.
In an exemplary embodiment, the FFF machine 100 includes a tip wipe assembly 120 in the build chamber 112. The tip wipe assembly 120 cleans the dispensing tip used to dispense the material used to build the workpiece 104. The tip wipe assembly 120 may be fixed at a location in the build chamber 112, such as to a frame in the cabinet 110. Alternatively, the tip wipe assembly 120 may be mounted to the build platform 116 and movable with the build platform 116. In an exemplary embodiment, the tip wipe assembly 120 includes a scraper 122 and a brush 124. The scraper 122 and/or the brush 124 may remove debris, such as material buildup, from the dispenser during a tip wipe process.
Optionally, the FFF machine 100 includes a purge canister 130 that accepts material purge from the dispenser. In various embodiments, the purge canister 130 is positioned adjacent the tip wipe assembly 120. The purge canister 130 may be fixed at a location in the build chamber 112, such as to a frame in the cabinet 110. Alternatively, the purge canister 130 may be mounted to the build platform 116 and movable with the build platform 116. The purge canister 130 may be positioned near the tip wipe assembly 120 or near the build location 114.
The FFF machine 100 includes a door 132 opening and closing access to the build chamber 112. The door 132 may be handedly coupled to the cabinet 110. The door 132 may be sealed against the cabinet 110 in the closed position.
The FFF machine holds one or more filament canisters 140 each having a length of filament 102 therein. For example, the filament 102 may be arranged on a reel or spool in the filament canister 140. The filament 102 is continuously fed from the filament canister 140 during the build process.
The FFF machine 100 includes a head assembly 150 in the cabinet 110 for dispensing media at the build location 114 during the build process. The filament 102 is routed from the filament canister 140 to the head assembly 150, such as through tubing arranged in the cabinet 110. The head assembly 150 includes a positioning system 152 for positioning the head assembly 150 within the build chamber 112, such as relative to the build location 114, the tip wipe assembly 120, and the purge canister 130. The positioning system 152 may move the head assembly 150 in two dimensions (for example, horizontally) or in three dimensions (for example, horizontally and vertically). The positioning system 152 may be a belt driven, screw driven or otherwise movable, such as to slide the head assembly 150 along rails. Alternatively, the positioning system 152 may be a robotic arm positioning system movable in two or three dimensions. The FFF machine 100 includes a controller 180 operably coupled to the head assembly 150 to control the position of the head assembly 150 and dispensing of the media during the build process.
The head assembly 150 includes a filament feed device 156 for each filament dispenser 154. The filament feed device 156 feeds the corresponding filament 102 to the filament dispenser 154. For example, the filament feed device 156 may be a feed wheel operated in one direction to advance the filament 102 and operated in the opposite direction to retract the filament 102. The filament feed device 156 may pull the filament 102 from the filament canister 140 (shown in
The head assembly 150 includes a heater 158 for each filament dispenser 154, such as a thermocouple. The heater 158 heats the corresponding filament 102 for dispensing from the filament dispenser 154. For example, the filament 102 may be made molten or liquefied as the filament 102 passes through the heater. The temperature of the heater 158 may be controlled based on the feed rate of the filament 102. For example, the heater 158 may increase in temperature as the filament 102 is fed more quickly through the head assembly 150. In other various embodiments, the heater 158 has a static temperature while in use and may be off when not in use.
The head assembly 150 includes guide elements 160 to guide the filament 102 through the head assembly 150. Various guide elements 160 are fixed in place, such as rings. Other various guide elements 160 are flexible, such as guide tubes, and may be routed between the head assembly 150 and other components, such as the filament canister 140. The guide tubes are used to protect and direct the filament 102 through the machine. Optionally, dry air may be pumped through the tubes to limit moisture exposure of the filament 102.
In various embodiments, the part 106 may be an interior part, such as for an interior of an aircraft. For example, the part may be used for ducting, clips, brackets, filler blocks, and the like. The part 106 may have any desired shape. The sacrificial tower 108 has a complementary shape as the part 106 to lend support to the part 106 as the workpiece 104 is built up. The workpiece 102 may be made from any type of material, such as thermoplastic material, polycarbonate material, polyetherimide material, metal materials, and the like. The material may be selected for desired characteristics, such as strength, smoothness, flame and smoke tolerance, chemical resistance, toxicity requirements, and the like.
The workpiece 104 is built up in layers 200 the filament dispenser 154 (shown in
In an exemplary embodiment, after the tip wipe process, the build process resumes at the sacrificial tower 108, rather than the part 106, such that the sacrificial slug of media dispensed immediately after the tip wipe process is used to build the sacrificial tower 108 and is not used to build the part 106. For example, because the media in the filament dispenser 154 for the extended time of the tip wipe process may be compromised or inferior, such media is dispensed in the sacrificial tower 108 and does not form any portion of the finished part 106. The sacrificial tower 108 may be the supporting tower or may be a separate sacrificial tower 108 that is built separate on the build platform 116 such that the workpiece is fabricated in different pieces, some of which are sacrificial and intended to be discarded. In other various embodiments, rather than first dispensing into the sacrificial tower 108, the initial slug of material dispensed after the tip wipe process may be discarded into the purge canister 130 before resuming dispensing into the workpiece 104. In such embodiments, the workpiece 104 may be built without the sacrificial tower 108.
Optionally, multiple layers 200 may be fabricated between tip wipe processes. In an exemplary embodiment, the head assembly 150 completes building an entire layer 200 prior to initiating the tip wipe process, rather than initiating the tip wipe process in the middle of building one of the layers 200. In various embodiments, if the tip wipe process is initiated in the middle of building one of the layers 200, the build sequence ensures that the breakpoint when the head assembly 150 leaves the workpiece 104 is during dispensing of the sacrificial tower 108 rather than the part 106.
Returning to
In an exemplary embodiment, the media dispensed immediately after the tip wipe process is not used to build the part. For example, substantially all of the media in the liquefier tip 170 and the feed tube 174, during the tip wipe process, is dispensed prior to building the part 108. In various embodiments, substantially all of the media in the liquefier tip 170 and the feed tube 174 heated by the heater during the tip wipe process is dispensed in the sacrificial tower 108. In other various embodiments, substantially all of the media in the liquefier tip 170 and the feed tube 174 heated by the heater during the tip wipe process is dispensed in the purge canister 130 remote from the part 106 and from the sacrificial tower 108.
In various embodiments, the controller 180 includes a microprocessor 182 for controlling one or more aspects of the FFF machine 100. The controller 180 includes a memory 184 for receiving and/or storing programs or other data for controlling one or more aspects of the FFF machine 100. For example, the memory 184 may store build sequences for the build process. The controller 180 includes a user interface 186 for receiving input from a user for controlling one or more aspects of the FFF machine 100.
In an exemplary embodiment, the controller 180 receives inputs from the head assembly 150. For example, the head assembly 150 may include one or more sensors sending signals to the controller 180. In various embodiments, the head assembly 150 includes a position sensor 252 identifying a position of the head assembly 150, such as of the filament dispenser 154. The positions sensor 252 may be a linear sensor, an angular sensor, a multi-axis sensor, a GPS sensor, a proximity sensor, a displacement sensor, a visual sensor, and the like. In various embodiments, the head assembly 150 includes a camera 254 for providing visual feedback for vision guidance of the head assembly 150 by the controller 180. In various embodiments, the head assembly 150 includes a temperature sensor 258 identifying a temperature of the heater, of the liquefier tip 170 and/or of the media. Other types of sensors may be coupled to the controller 180 for providing data to the controller 180 for operating the FFF machine 100.
The controller 180 includes one or more control modules 280 having one or more units for performing various tasks for operating the FFF machine 100. It should be noted that the various embodiments may be implemented in hardware, software or a combination thereof. The various embodiments and/or components of the controller, for example, the modules, or units and components therein, also may be implemented as part of one or more computers or processors. The computer(s) or processor(s) of the controller may include a computing device, an input device, a display unit and an interface, for example, for accessing the Internet. The computer or processor may include a microprocessor. The microprocessor may be connected to a communication bus. The computer or processor may also include a memory. The memory may include Random Access Memory (RAM) and Read Only Memory (ROM). The computer or processor further may include a storage device, which may be a hard disk drive or a removable storage drive such as a solid state drive, optic drive, and the like. The storage device may also be other similar means for loading computer programs or other instructions into the computer or processor.
As used herein, the term “computer,” “controller,” and “module” may each include any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set computers (RISC), application specific integrated circuits (ASICs), logic circuits, GPUs, FPGAs, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term “module” or “computer”.
The computer, module, or processor executes a set of instructions that are stored in one or more storage elements, in order to process input data. The storage elements may also store data or other information as desired or needed. The storage element may be in the form of an information source or a physical memory element within a processing machine.
The set of instructions may include various commands that instruct the computer, module, or processor as a processing machine to perform specific operations such as the methods and processes of the various embodiments described and/or illustrated herein. The set of instructions may be in the form of a software program. The software may be in various forms such as system software or application software and which may be embodied as a tangible and non-transitory computer readable medium. Further, the software may be in the form of a collection of separate programs or modules, a program module within a larger program or a portion of a program module. The software also may include modular programming in the form of object-oriented programming. The processing of input data by the processing machine may be in response to operator commands, or in response to results of previous processing, or in response to a request made by another processing machine.
As used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by a computer, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program. The individual components of the various embodiments may be virtualized and hosted by a cloud type computational environment, for example to allow for dynamic allocation of computational power, without requiring the user concerning the location, configuration, and/or specific hardware of the computer system.
In various embodiments, the controller 180 includes a positioning unit 282 having one or more programs for controlling a position of the head assembly 150. The controller 180 includes a build unit 284 having one or more programs for generating, storing or otherwise controlling a build sequence for building the part 106 and the sacrificial tower 108 in the various layers 200. The controller 180 includes a tip wipe unit 286 having one or more programs for generating, storing or otherwise controlling the tip wipe process. The tip wipe unit 286 provides a control sequence (for example, for control of the positioning unit 282 during the tip wipe processes) for the positioning unit 282. The build unit 284 provides a control sequence (for example, for control of the positioning unit 282, during the build processes) for the positioning unit 282. The control sequence provided by the tip wipe unit 286 periodically interrupts the control sequence provided by the build unit 284 to cause the positioning unit 282 to move the head assembly 150 to the tip wipe assembly 120 to perform the tip wipe process and then move the head assembly 150 back to the build location 114. The build unit 284 causes the positioning unit 282 to move the head assembly 150 to the sacrificial tower 108 to reinitiate dispensing of the media at the sacrificial tower 108 after the tip wipe process prior to moving the head assembly 150 to the part 106 such that the media dispensed immediately after the tip wipe process is used to build the sacrificial tower 108.
The tip wipe sequence may be part of the build sequence in various embodiments. The build sequence identifies the position of the head assembly 150 as well as controlling feeding of the filament and heating of the filament for building the workpiece 104. The build sequence controls building of the part 106 as well as the sacrificial tower 108, including the timing of building the part 106 compared to the sacrificial tower 108 for the given layers 200. The build sequence controls the shape, thickness and width of the contour 202 and the raster 204.
In an exemplary embodiment, the build sequence identifies predetermined breaks for performing the tip wipe processes. The breaks may occur after a predetermined time, such as requiring that the break occurs within an M second interval after N seconds after initiating the current build process. For example, the build sequence may require that the break occur within 60 seconds after 1800 seconds after the current build process (for example, after the last tip wipe process); however other times are possible in alternative embodiments, such as more or less flexible time and/or more or less time between tip wipe processes. In an exemplary embodiment, the predetermined breaks for the tip wipe process occurring during building of the sacrificial tower 108 rather than during building of the part 106. In various embodiments, the build sequence may ensure that the breaks between build processes for tip wiping occur at the end of building a layer 200. As such, the next build process resumes at the start of a new layer 200, rather than in the middle of building a layer 200.
Beginning at 302, the FFF machine runs a build process for building a part in a sacrificial tower for the part in a plurality of layers. The build process is performed in accordance with a build sequence which may be stored or generated by a controller of the FFF machine. For example, the build sequence may be downloaded or uploaded to the FFF machine and stored in memory, such as from a CAD file. In other various embodiments, the build sequence may be generated by the controller by a build unit of the controller. For example, the build unit may generate the build sequence based on the size and shape of the desired part.
At 304, the FFF machine fabricates one or more layers of a sacrificial tower for the part during a sacrificial tower fabrication process. The FFF machine fabricates the layers of the sacrificial tower by dispensing a bead or filament of media from a filament dispenser of a head assembly. The controller controls the position of the head assembly as the media is dispensed to build each layer of the sacrificial tower.
At 306, the FFF machine fabricates one or more layers of a part during a part fabrication process. The FFF machine fabricates the layers of the part by dispensing a bead or filament of media from a filament dispenser of a head assembly. The controller controls the position of the head assembly as the media is dispensed to build each layer of the part. In an exemplary embodiment, the FFF machine alternates between the sacrificial tower fabrication process and the part fabrication process within or between each of the layers. For example, the head assembly may dispense the media to build some or all of one of the layers of the sacrificial tower before continuing to dispense the media to build some or the entire corresponding layer of the part. In other various embodiments, the head assembly may dispense media to build some or all of one of the layers of the part before continuing to dispense the media to build some or the entire corresponding layer of the sacrificial tower. During the build process, any number of layers of the workpiece may be built before the filament dispenser 154 needs to be cleaned by a tip wipe process.
At 308, the FFF machine determines an elapsed period since the start of the current build process or since the previous tip wipe process. The elapsed period may be an elapsed time (for example, xxx seconds), a number of layers built (for example, xxx layers), an amount of material consumed (for example, xxx meters of material dispensed), or another metric. At 310, the FFF machine compares the elapsed period to a tip wipe trigger. If the elapsed period is less than the tip wipe trigger, then the FFF machine continues to run the build process by proceeding along 312. However, if the elapsed period is greater than the tip wipe trigger, then the FFF machine may begin to initiate the tip wipe process at 314. In various embodiments, when the tip wipe process is initiated, the FFF machine may continue to run the build process until the current layer of the workpiece is complete.
At 316, the FFF machine determines if the build process is in the part fabrication process. If the build process is not in the part fabrication process, but rather is in the sacrificial tower fabrication process or is transitioning between the part fabrication process and the sacrificial tower fabrication process, the FFF machine runs a tip wipe process at 318 cleaning a liquefier tip at a tip wipe assembly. However, if the build process is in the part fabrication process, the FFF machine continues to run the build process until the build process is in the sacrificial tower fabrication process at 320. The FFF machine determines if the build process is in the sacrificial tower fabrication process at 322. If not, then the FFF machine continues to run the build process at 320. However, when the FFF machine determines that the build process is in the sacrificial tower fabrication process, the FFF machine runs the tip wipe process at 318.
After the tip wipe process, at 324, the FFF machine determines if the build process is complete. If the build process is complete, the processes ended at 326. However, if the build process is not complete, the FFF machine may optionally initiate a purge at 328 and/or return to running the build process by fabricating the sacrificial tower at 304. The sacrificial tower fabricating process is performed prior to the part fabricating process after the tip wipe process such that the media dispensed immediately after the tip wipe process is used to build the sacrificial tower rather than building the part.
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the various embodiments without departing from the scope thereof. Dimensions, types of materials, orientations of the various components, and the number and positions of the various components described herein are intended to define parameters of certain embodiments, and are by no means limiting and are merely exemplary embodiments. Many other embodiments and modifications within the spirit and scope of the claims will be apparent to those of skill in the art upon reviewing the above description. The scope of the various embodiments should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112(f), unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.
This application claims the benefit of U.S. Provisional Application No. 62/437,114 filed Dec. 21, 2016, the subject matter of which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62437114 | Dec 2016 | US |
