EFS-Web
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`PATENTS
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`MBOT-0048-POl
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`QUICK-RELEASE EXTRUDER
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`CROSS-REFERENCE TO RELATED APPLICATIONS
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`[0001] This application claims the benefit of US. Provisional Application No.
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`61/719,874 filed on October 29, 2012, the entire content of which is hereby incorporated by
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`reference.
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`FIELD OF THE INVENTION
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`[0002] The invention generally relates to an extruder assembly, and more specifically an
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`extruder assembly including a quick-release extruder for a device and system for three-
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`dimensional fabrication.
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`BACKGROUND
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`[0003] Three-dimensional printing is a process for making a three-dimensional solid
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`object of virtually any shape from a digital model. Three-dimensional printing is achieved using
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`an additive process, where successive layers of build material are laid down in different shapes.
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`The build material may be in the form of a filament, and may include, for example, acrylonitrile
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`butadiene styrene (ABS), high-density polyethylene (HDPL), polylactic acid (PLA), or any other
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`suitable plastic, thermoplastic, or other material that can usefillly be extruded to form a three-
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`dimensional object. The filament may be extruded using an extruder, which may include a
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`chamber, an opening at an extruder tip, and a motor to push the filament into the chamber and
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`through the opening in the extruder tip.
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`[0004] Access to extruders is typically fairly limited. In most three-dimensional printing
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`systems, a user must remove the entire extruder to perform maintenance. To remove the extruder
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`typically requires specific tools and can be a time-consuming process. Also, loading, unloading,
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`and replacement of the filament are difficult and time-consuming because of the lack of easy
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`access to the components of the extruder assembly.
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`[0005] There is a need for a quick-release extruder that can allow a user access to the
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`components of the extruder assembly for, e. g., maintenance, loading, unloading, and replacement
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`of the filament.
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`SUMMARY
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`PATENTS
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`MBOT-OO48-P01
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`[0006] A bearing that provides contact force to engage a filament with a drive gear has a
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`movable axis that can be controllably moved toward and away from the drive gear in order to
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`engage and disengage the filament. A bearing is spring-biased toward the drive gear, and a
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`bistable lever mechanism is provided with a first stable position in which the bearing is engaged
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`with a filament and a second stable position in which the bearing is disengaged from the
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`filament. By providing a mechanism that locks in both positions, loading and unloading of
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`filament can be facilitated.
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`[0007] In one aspect there is disclosed herein an extruder assembly including a drive gear
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`shaped and sized to drive a filament; a bearing having a freely rotating contact surface, the
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`bearing positioned to support the filament against the drive gear with the freely rotating contact
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`surface, where an axis of the bearing is substantially parallel to an axis of the drive gear and
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`where the axis of the bearing is movable toward and away from the axis of the drive gear; a
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`spring configured to bias a position of the axis of the bearing relative to the axis of the drive
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`gear; and a lever positioned to apply a counterforce to the bias of the spring, thereby securing the
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`bearing in a position to apply a constant contact force to the filament by the bearing and the drive
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`gear.
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`[0008] The extruder assembly may include an extruder as described herein, which may
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`include an input opening aligned to a feedpath. The build material, which may be in the form of a
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`filament, may travel through the opening and thus into the feedpath, which continues into a
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`chamber of the extruder that is shaped and sized to pass the filament along the feedpath. The
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`filament may then travel through an orifice of the extruder, which may discharge the build
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`material during an extrusion.
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`[0009] The filament may be driven by a drive gear, which may include a number of teeth.
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`The teeth of the drive gear may be positioned to engage the filament before the input opening in
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`the feedpath. Specifically, the filament may be driven into the teeth of the drive gear with enough
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`force to deform the build material, and thus the teeth of the drive gear may grip the filament in
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`this manner. The spring or biasing member may provide the force required to deform the build
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`material into the teeth of the drive gear. The drive gear may then rotate (or otherwise provide
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`movement) such that the teeth drive the filament along the feed path, into the input opening of
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`PATENTS
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`MBOT-OO48-POl
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`the extruder, through the chamber, and out of the orifice. It will be apparent that the drive gear
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`may engage the build material in an alternate manner such that the drive gear is configured to
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`drive the build material through the extruder. The drive gear may include a motor that may be
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`integral with the drive gear or coupled to the drive gear such that the motor rotates (or otherwise
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`drives) the drive gear, which may then drive the filament.
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`[0010] A bearing may be positioned opposite the drive gear, and it may be located along
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`the feedpath. The bearing may be biased by the spring toward the drive gear with a spring force
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`such that the bearing presses the filament against the drive gear. The spring may be coupled to
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`the bearing. The bearing may include a freely rotating contact surface that is able to provide a
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`force against the drive gear and freely rotate with the drive gear without disengaging (when a
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`force maintains the bearing in a position engaged with the drive gear). The spring may maintain
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`a substantially constant contact force of the bearing against a length of the filament between the
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`bearing and the drive gear in the absence of external forces. The bearing may include a smooth
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`surface, and the bearing may be a low friction bearing. The axis of the bearing may be
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`substantially parallel to the axis of the drive gear.
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`[0011] The extruder assembly may further include a lever that may extend from the
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`extruder assembly. The lever may be configured to manually move the bearing (e. g., against the
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`biasing force of the spring) away from the drive gear and/or away from the feedpath. Thus, the
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`lever may be coupled to the bearing. Alternatively, the lever may be coupled to another
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`mechanical element (or series of elements) and then coupled to the bearing, or the lever may be
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`coupled to the drive gear. The lever may move the axis of the bearing away from the axis of the
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`drive gear. The lever may include a pivot (or several pivots), and the spring may be coupled to
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`the lever away from the pivot. The spring may provide a substantially constant force urging the
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`lever into a first position or a second position. The extruder assembly may also include a locking
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`mechanism to secure the lever in a position (which may be the first position, the second position,
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`or another position) with the bearing moved away from and out of the feedpath and/or drive gear.
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`The locking mechanism may also secure the lever in a position with the bearing moved toward
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`and into the feedpath and/or drive gear. The locking mechanism may include a latch, a clamp, an
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`electrical locking mechanism, a clip, a coupling, a dock, a hook, a pin, a snap, or the like.
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`[0012] The spring may include a coil spring, a compression spring, a leaf spring, or the
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`like.
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`[0013] The extruder assembly may further include a heating element to liquefy a length
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`of build material in the chamber of the extruder.
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`[0014] An extruder assembly may include a manual control extending from the extruder
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`assembly to manually move the bearing against the spring force away from the feedpath. The
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`manual control may include a lever, a knob, a slider, a plunger, a push button, a toggle, an
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`actuator, a screw, a piston, and the like.
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`[0015] The lever may also be controlled electronically, and may be activated by a user
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`utilizing a control system, or it may be automatically activated by a control system.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`[0016] The foregoing and other objects, features and advantages of the invention will be
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`apparent from the following description of particular embodiments thereof, as illustrated in the
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`accompanying drawings. The drawings are not necessarily to scale, emphasis instead being
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`placed upon illustrating the principles of the invention.
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`[0017] Fig. l is a block diagram of a three-dimensional printer.
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`[0018] Fig. 2 is an exploded view of an extruder assembly.
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`[0019] Fig. 3 is a perspective view of an extruder assembly.
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`[0020] Fig. 4 is a left side view of an extruder assembly.
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`[0021] Fig. 5 is a front view of an extruder assembly.
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`[0022] Fig. 6 is a right side view of an extruder assembly.
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`[0023] Fig. 7 is a top view of an extruder assembly.
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`DETAILED DESCRIPTION
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`[0024] The embodiments will now be described more fully hereinafter with reference to
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`the accompanying figures, in which preferred embodiments are shown. This invention may,
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`however, be embodied in many different forms and should not be construed as limited to the
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`illustrated embodiments set forth herein. Rather, these illustrated embodiments are provided so
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`that this disclosure will convey the scope of the invention to those skilled in the art.
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`[0025] All documents mentioned herein are hereby incorporated in their entirety by
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`reference. References to items in the singular should be understood to include items in the plural,
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`and vice versa, unless explicitly stated otherwise or clear from the text. Grammatical
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`conjunctions are intended to express any and all disjunctive and conjunctive combinations of
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`conjoined clauses, sentences, words, and the like, unless otherwise stated or clear from the
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`context. Thus, the term “or” should generally be understood to mean “and/or” and so forth.
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`[0026] Recitation of ranges of values herein are not intended to be limiting, referring
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`instead individually to any and all values falling within the range, unless otherwise indicated
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`herein, and each separate value within such a range is incorporated into the specification as if it
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`were individually recited herein. The word “about,” when accompanying a numerical value, is to
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`be construed as indicating a deviation as would be appreciated by one of ordinary skill in the art
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`to operate satisfactorily for an intended purpose. Ranges of values and/or numeric values are
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`provided herein as examples only, and do not constitute a limitation on the scope of the
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`3, “
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`described embodiments. The use of any and all examples, or exemplary language (“e.g.,
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`such
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`as,” or the like) provided herein, is intended merely to better illuminate the embodiments and
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`does not pose a limitation on the scope of the embodiments. No language in the specification
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`should be construed as indicating any unclaimed element as essential to the practice of the
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`embodiments.
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`[0027] In the following description, it is understood that terms such as “first,
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`second,”
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`3, CC
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`“above,” “below” and the like, are words of convenience and are not to be construed as limiting
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`terms.
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`[0028] Described herein are devices, systems, and methods for using an extruder
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`assembly including a quick-release extruder for a three-dimensional printer. It will be understood
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`that while the exemplary embodiments herein emphasize an extruder assembly for a three-
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`dimensional printer, the principles of the invention may be adapted to other fabrication
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`processes. All such variations that can be adapted to use an extruder assembly as described
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`herein are intended to fall within the scope of this disclosure.
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`[0029] Fig. 1 is a block diagram of a three-dimensional printer. In general, the printer
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`100 may include a build platform 102, a conveyor 104, an extruder 106, an x-y-z positioning
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`assembly 108, and a controller 110 that cooperate to fabricate an object 112 within a working
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`volume 114 of the printer 100.
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`[0030] The build platform 102 may include a surface 116 that is rigid and substantially
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`planar. The surface 116 may support the conveyer 104 in order to provide a fixed, dimensionally
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`and positionally stable platform on which to build the object 112.
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`[0031] The build platform 102 may include a thermal element 130 that controls the
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`temperature of the build platform 102 through one or more active devices 132 such as resistive
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`elements that convert electrical current into heat, Peltier effect devices that can create a heating
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`or cooling affect, or any other thermoelectric heating and/or cooling devices. Thus the thermal
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`element 130 may be a heating element that provides active heating to the build platform 102, a
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`cooling element that provides active cooling to the build platform 102, or a combination of these.
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`The heating element 130 may be coupled in a communicating relationship with the controller
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`110 in order for the controller 110 to controllably impart heat to or remove heat from the surface
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`116 of the build platform 102. Thus, the thermal element 130 may include an active cooling
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`element positioned within or adjacent to the build platform 102 to controllably cool the build
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`platform 102.
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`[0032] It will be understood that a variety of other techniques may be employed to
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`control a temperature of the build platform 102. For example, the build platform 102 may use a
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`gas cooling or gas heating device such as a vacuum chamber or the like in an interior thereof,
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`which may be quickly pressurized to heat the build platform 102 or vacated to cool the build
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`platform 102 as desired. As another example, a stream of heated or cooled gas may be applied
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`directly to the build platform 102 before, during, and/or after a build process. Any device or
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`combination of devices suitable for controlling a temperature of the build platform 102 may be
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`adapted to use as the thermal element 130 described herein.
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`[0033] The conveyer 104 may be formed of a sheet 118 of material that moves in a path
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`120 through the working volume 114. Within the working volume 114, the path 120 may pass
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`proximal to the surface 116 of the build platform 102—that is, resting directly on or otherwise
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`supported by the surface 116—in order to provide a rigid, positionally stable working surface for
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`a build. It will be understood that while the path 120 is depicted as a unidirectional arrow, the
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`path 120 may be bidirectional, such that the conveyer 104 can move in either of two opposing
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`directions through the working volume 114. It will also be understood that the path 120 may
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`curve in any of a variety of ways, such as by looping underneath and around the build platform
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`102, over and/or under rollers, or around delivery and take up spools for the sheet 118 of
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`material. Thus, while the path 120 may be generally (but not necessarily) uniform through the
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`working volume 114, the conveyer 104 may move in any direction suitable for moving
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`completed items from the working volume 114. The conveyor may include a motor or other
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`similar drive mechanism (not shown) coupled to the controller 110 to control movement of the
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`sheet 118 of material along the path 120. Various drive mechanisms are described in filrther
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`detail below.
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`[0034] In general, the sheet 118 may be formed of a flexible material such as a mesh
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`material, a polyamide, a polyethylene terephthalate (commercially available in bi-axial form as
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`MYLAR), a polyimide film (commercially available as KAPTON), or any other suitably strong
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`polymer or other material. The sheet 118 may have a thickness of about three to about seven
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`thousandths of an inch, or any other thickness that permits the sheet 118 to follow the path 120
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`of the conveyer 104. For example, with sufficiently strong material, the sheet 118 may have a
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`thickness of about one to about three thousandths of an inch. The sheet 118 may instead be
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`formed of sections of rigid material joined by flexible links.
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`[0035] A working surface of the sheet 118 (e. g., an area on the top surface of the sheet
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`118 within the working volume 114) may be treated in a variety of manners to assist with
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`adhesion of build material to the surface 118 and/or removal of completed objects from the
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`surface 118. For example, the working surface may be abraded or otherwise textured (e. g., with
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`grooves, protrusions, and the like) to improve adhesion between the working surface and the
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`build material.
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`[0036] A variety of chemical treatments may be used on the working surface of the sheet
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`118 of material to further facilitate build processes as described herein. For example, the
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`chemical treatment may include a deposition of material that can be chemically removed from
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`the conveyer 104 by use of water, solvents, or the like. This may facilitate separation of a
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`completed object from the conveyer by dissolving the layer of chemical treatment between the
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`object 112 and the conveyor 104. The chemical treatments may include deposition of a material
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`that easily separates from the conveyer such as a wax, mild adhesive, or the like. The chemical
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`treatment may include a detachable surface such as an adhesive that is sprayed on to the
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`conveyer 104 prior to fabrication of the object 112.
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`[0037] In one aspect, the conveyer 104 may be formed of a sheet of disposable, one-use
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`material that is fed from a dispenser and consumed with each successive build.
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`[0038] In one aspect, the conveyer 104 may include a number of different working areas
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`with different surface treatments adapted for different build materials or processes. For example,
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`different areas may have different textures (smooth, abraded, grooved, etc.). Different areas may
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`be formed of different materials. Different areas may also have or receive different chemical
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`treatments. Thus a single conveyer 104 may be used in a variety of different build processes by
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`selecting the various working areas as needed or desired.
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`[0039] The extruder 106 may include a chamber 122 in an interior thereof to receive a
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`build material. The build material may, for example, include acrylonitrile butadiene styrene
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`(“ABS”), high-density polyethylene (“HDPL”), polylactic acid, or any other suitable plastic,
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`thermoplastic, or other material that can usefully be extruded to form a three-dimensional object.
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`The extruder 106 may include an extrusion tip 124 or other opening that includes an exit port
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`with a circular, oval, slotted or other cross-sectional profile that extrudes build material in a
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`desired cross-sectional shape.
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`[0040] The extruder 106 may include a heater 126 to melt thermoplastic or other
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`meltable build materials within the chamber 122 for extrusion through an extrusion tip 124 in
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`liquid form. While illustrated in block form, it will be understood that the heater 124 may
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`include, e.g., coils of resistive wire wrapped about the extruder 106, one or more heating blocks
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`with resistive elements to heat the extruder 106 with applied current, an inductive heater, or any
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`other arrangement of heating elements suitable for creating heat within the chamber 122 to melt
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`the build material for extrusion. The extruder 106 may also or instead include a motor 128 or the
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`like to push the build material into the chamber 122 and/or through the extrusion tip 126.
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`[0041] In general operation (and by way of example rather than limitation), a build
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`material such as ABS plastic in filament form may be fed into the chamber 122 from a spool or
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`the like by the motor 128, melted by the heater 126, and extruded from the extrusion tip 124. By
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`controlling a rate of the motor 128, the temperature of the heater 126, and/or other process
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`parameters, the build material may be extruded at a controlled volumetric rate. It will be
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`understood that a variety of techniques may also or instead be employed to deliver build material
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`at a controlled volumetric rate, which may depend upon the type of build material, the
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`volumetric rate desired, and any other factors. All such techniques that might be suitably adapted
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`to delivery of build material for fabrication of a three-dimensional object are intended to fall
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`within the scope of this disclosure. Other techniques may be employed for three-dimensional
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`printing, including extrusion-based techniques using a build material that is curable and/or a
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`build material of sufficient viscosity to retain shape after extrusion.
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`MBOT-0048-P01
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`[0042] The x-y-z positioning assembly 108 may generally be adapted to three-
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`dimensionally position the extruder 106 and the extrusion tip 124 within the working volume
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`114. Thus by controlling the volumetric rate of delivery for the build material and the x, y, z
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`position of the extrusion tip 124, the object 112 may be fabricated in three dimensions by
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`depositing successive layers of material in two-dimensional patterns derived, for example, from
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`cross-sections of a computer model or other computerized representation of the object 112. A
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`variety of arrangements and techniques are known in the art to achieve controlled linear
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`movement along one or more axes. The x-y-z positioning assembly 108 may, for example,
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`include a number of stepper motors 109 to independently control a position of the extruder
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`within the working volume along each of an x-axis, a y-axis, and a z-axis. More generally, the x-
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`y-z positioning assembly 108 may include without limitation various combinations of stepper
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`motors, encoded DC motors, gears, belts, pulleys, worm gears, threads, and the like. Any such
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`arrangement suitable for controllably positioning the extruder 106 within the working volume
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`114 may be adapted to use with the printer 100 described herein.
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`[0043] By way of example and not limitation, the conveyor 104 may be affixed to a bed
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`that provides x-y positioning within the plane of the conveyor 104, while the extruder 106 can be
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`independently moved along a z-axis. As another example, the extruder 106 may be stationary
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`while the conveyor 104 is x, y, and z positionable. As another example, the extruder 106 may be
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`x, y, and z positionable while the conveyer 104 remains fixed (relative to the working volume
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`114). In yet another example, the conveyer 104 may, by movement of the sheet 118 of material,
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`control movement in one axis (e. g., the y-axis), while the extruder 106 moves in the z-axis as
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`well as one axis in the plane of the sheet 118. Thus in one aspect, the conveyor 104 may be
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`attached to and move with at least one of an x-axis stage (that controls movement along the x-
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`axis), a y-axis stage (that controls movement along a y-axis), and a z-axis stage (that controls
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`movement along a z-axis) of the x-y-z positioning assembly 108. More generally, any
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`arrangement of motors and other hardware controllable by the controller 110 may serve as the x-
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`y-z positioning assembly 108 in the printer 100 described herein. Still more generally, while an
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`x, y, z coordinate system serves as a convenient basis for positioning within three dimensions,
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`any other coordinate system or combination of coordinate systems may also or instead be
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`employed, such as a positional controller and assembly that operates according to cylindrical or
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`spherical coordinates.
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`[0044] The controller 110 may be electrically coupled in a communicating relationship
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`with the build platform 102, the conveyer 104, the x-y-z positioning assembly 108, and the other
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`various components of the printer 100. In general, the controller 110 is operable to control the
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`components of the printer 100, such as the build platform 102, the conveyer 104, the x-y-z
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`positioning assembly 108, and any other components of the printer 100 described herein to
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`fabricate the object 112 from the build material. The controller 110 may include any combination
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`of software and/or processing circuitry suitable for controlling the various components of the
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`printer 100 described herein including without limitation microprocessors, microcontrollers,
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`application-specific integrated circuits, programmable gate arrays, and any other digital and/or
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`analog components, as well as combinations of the foregoing, along with inputs and outputs for
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`transceiving control signals, drive signals, power signals, sensor signals, and the like. In one
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`aspect, the controller 110 may include a microprocessor or other processing circuitry with
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`sufficient computational power to provide related functions such as executing an operating
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`system, providing a graphical user interface (e.g., to a display coupled to the controller 110 or
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`printer 100), convert three-dimensional models into tool instructions, and operate a web server or
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`otherwise host remote users and/or activity through the network interface 136 described below.
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`[0045] A variety of additional sensors may be usefully incorporated into the printer 100
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`described above. These are generically depicted as sensor 134 in Fig. 1, for which the positioning
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`and mechanical/electrical interconnections with other elements of the printer 100 will depend
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`upon the type and purpose of the sensor 134 and will be readily understood and appreciated by
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`one of ordinary skill in the art. The sensor 134 may include a temperature sensor positioned to
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`sense a temperature of the surface of the build platform 102. This may, for example, include a
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`thermistor or the like embedded within or attached below the surface of the build platform 102.
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`This may also or instead include an infrared detector or the like directed at the surface 116 of the
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`build platform 102 or the sheet 118 of material of the conveyer 104. Other sensors that may be
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`usefully incorporated into the printer 100 as the sensor 134 include a heat sensor, a volume flow
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`rate sensor, a weight sensor, a sound sensor, and a light sensor. Certain more specific examples
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`are provided below by way of example and not of limitation.
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`[0046] The sensor 134 may include a sensor to detect a presence (or absence) of the
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`object 112 at a predetermined location on the conveyer 104. This may include an optical detector
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`arranged in a beam-breaking configuration to sense the presence of the object 112 at a location
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`such as an end of the conveyer 104. This may also or instead include an imaging device and
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`image processing circuitry to capture an image of the working volume 114 and analyze the
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`image to evaluate a position of the object 112. This sensor 134 may be used for example to
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`ensure that the object 112 is removed from the conveyor 104 prior to beginning a new build at
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`that location on the working surface such as the surface 116 of the build platform 102. Thus the
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`sensor 134 may be used to determine whether an object is present that should not be, or to detect
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`when an object is absent. The feedback from this sensor 134 may be used by the controller 110
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`to issue processing interrupts or otherwise control operation of the printer 100.
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`[0047] The sensor 134 may include a sensor that detects a position of the conveyer 104
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`along the path. This information may be obtained from an encoder in a motor that drives the
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`conveyer 104, or using any other suitable technique such as a visual sensor and corresponding
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`f1ducials (e. g., visible patterns, holes, or areas with opaque, specular, transparent, or otherwise
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`detectable marking) on the sheet 118.
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`[0048] The sensor 134 may include a heater (instead of or in addition to the thermal
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`element 130) to heat the working volume 114 such as a radiant heater or forced hot air to
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`maintain the object 112 at a fixed, elevated temperature throughout a build. The sensor 134 may
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`also or instead include a cooling element to maintain the object 112 at a predetermined sub-
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`ambient temperature throughout a build.
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`[0049] The sensor 134 may also or instead include at least one video camera. The video
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`camera may generally capture images of the working volume 114, the object 112, or any other
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`hardware associated with the printer 100. The video camera may provide a remote video feed
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`through the network interface 136, which feed may be available to remote users through a user
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`interface maintained by, e. g., remote hardware, or within a web page provided by a web server
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`hosted by the three-dimensional printer 100. Thus, in one aspect there is a user interface adapted
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`to present a video feed from at least one video camera of a three-dimensional printer to a remote
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`user through a user interface.
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`[0050] The sensor 134 may include may also include more complex sensing and
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`processing systems or subsystems, such as a three-dimensional scanner using optical techniques
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`(e. g., stereoscopic imaging, or shape from motion imaging), structured light techniques, or any
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`other suitable sensing and processing hardware that might extract three-dimensional information
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`from the working volume 114. In another aspect, the sensor 134 may include a machine vision
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`system that captures images and analyzes image content to obtain information about the status of
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`a job, working volume 114, or an object 112 therein. The machine vision system may support a
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`variety of imaging-based automatic inspection, process control, and/or robotic guidance
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`functions for the three-dimensional printer 100 including without limitation pass/fail decisions,
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`error detection (and corresponding audible or visual alerts), shape detection, position detection,
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`orientation detection, collision avoidance, and the like.
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`[0051] Other components, generically depicted as other hardware 135, may also be
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`included, such as input devices including a keyboard, touchpad, mouse, switches, dials, buttons,
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`motion sensors, and the like, as well as output devices such as a display, a speaker or other audio
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`transducer, light emitting diodes, and the like. Other hardware 135 may also or instead include a
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`variety of cable connections and/or hardware adapters for connecting to, e.g., external
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`computers, external hardware, external instrumentation or data acquisition systems, and the like.
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`[0052] The printer 100 may include, or be connected in a communicating relationship
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`with, a network interface 136. The network interface 136 may include any combination of
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`hardware and software suitable for coupling the controller 110 and other components of the
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`printer 100 to a remote computer in a communicating relationship through a data network. By
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`way of example and not limitation, this may include electronics for a wired or wireless Ethernet
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`connection operating according to the IEEE 802.11 standard (or any variation thereof), or any
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`other short or long range wireless networking components or the like. This may include
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`hardware for short range data communications such as BlueTooth or an infrared transceiver,
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`which may be used to couple into a local area network or the like that is in turn coupled to a data
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`network such as the Internet. This may also or instead include hardware/software for a WiMax
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`connection or a cellular network connection (using, e.g., CDMA, GSM, LTE, or any other
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`suitable protocol or combination of protocols). Consistently, the controller 110 may be
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`configured to control participation by the printer 100 in any network to which the network
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`interface 136 is connected, such as by autonomously connecting to the network to retrieve
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`printable content, or responding to a remote request for status or availability.
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`[0053] An extruder assembly including a quick-release extruder will now be described.
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`[0054] The extruder assembly with a quick-release extruder may include any of the
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`features described herein including the features described in US. Provisional Application No.
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`61/719,874, which is hereby incorporated by reference in its entirety.
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`[0055] In a three-dimensional printer, a filament of build material may be supported by
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`and in contact with a drive gear. Also, a filament of build material may be in contact with a drive
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`gear via a bearing, which may be a spring-loaded bearing or the like. The bearing may provide a
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`substantially constant contact force against the filament and toward the drive gear. The bearing
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`may include a quick-release lever or the like to move the bearing away from the drive gear for,
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`e. g., access to and maintenance of an extruder assembly. This arrangement may also permit
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`quick loading, unloading, and r