ADDITIVE MANUFACTURING SYSTEMS AND PROCESS AUTOMATION

An additive manufacturing system includes a hopper for containing a feedstock, at least one helical drive positioned downstream from the hopper for receiving the feedstock therefrom, a heat source positioned proximate at least a portion of the at least one helical drive, and an outlet. The at least one helical drive is configured to advance the feedstock toward the outlet, the heat source is configured to at least partially liquefy the feedstock advanced by the at least one helical drive, and the outlet is configured to dispense the at least partially liquefied feedstock based on a desired toolpath. The at least one helical drive may include at least one of a screw, a bolt, an auger, or an Archimedean screw.

FIELD OF THE INVENTION

The present invention relates generally to additive manufacturing systems and methods and, more particularly, to additive manufacturing systems including a helical drive or screw extruder for advancing feedstock to a heat zone to at least partially liquefy the feedstock.

BACKGROUND OF THE INVENTION

With reference now toFIG. 1, a common prior art extrusion method for filament or rod-based additive manufacturing systems is shown. The system10depicted inFIG. 1is mechanically similar to a rack and pinion where the filament or rod12behaves as the rack and the gear or hobbed gear14used to drive the filament12behaves as the pinion. When extrusion additive manufacturing systems utilizing a filament or rod drive system similar toFIG. 1operate correctly, the gear or hobbed gear14applies enough downward pressure to the filament or rod12to drive the filament12into the heat zone of the extruder (not shown) and to overcome the pressure drop that occurs at the nozzle. Extrusion additive manufacturing systems utilizing a filament or rod drive system similar toFIG. 1rely on the mechanical integrity of the filament-hobbed gear interaction, filament-gear interaction, rod-hobbed gear interaction, or rod-gear interaction to drive and control the accuracy of the extrudate. Typically, extrusion additive manufacturing systems that utilize a filament or rod drive system similar toFIG. 1suffer from several common failure modes that limit the ultimate accuracy of the system. These failure modes include, but are not limited to, slipping between the filament12and drive gear or hobbed gear14, shearing of the filament or rod12by the gear or hobbed gear14which may cause the gear or hobbed gear14to freely spin in the cavity that was previously filament or rod, snapping of the filament or rod12, buckling of the filament or rod12, necking of the filament or rod12, or plastic deformation of the filament or rod12. Filaments and rods12are commonly made from polymer materials. It is understood that many new composite materials are being used such as bound metal filaments, bound metal rods, bound ceramic filaments, bound ceramic rods, bound glass filaments, bound glass rods, bound rock filaments, bound rock rods, bound carbon fiber filaments, bound carbon fiber rods. It is also assumed that new filaments and rods may be developed which will continue to rely on the fundamental filament or rod drive system10depicted inFIG. 1and which may include but are not limited to graphite, wood, bamboo, basalt, and cermets.

With reference now toFIG. 2, a common prior art configuration of bound filament or bound rod raw materials for extrusion additive manufacturing systems is shown. These bound filaments or rods12may contain metal, ceramic, and/or a carbon allotrope20, and/or a polymer22in addition to a binding agent, lubricant, and/or surfactant24. It is commonly understood that these filaments or rods12may contain any one of the materials listed above or any combination thereof. When a part is additively manufactured using a bound filament or rod12, for example a metal filament or rod12, the 3D part is then subjected to subsequent debind and sintering steps in the process to ensure a high-density, high-purity metal part is manufactured.

When bound filaments or rods12are manufactured, they can come with many common defects that make the resulting filament or rod12difficult to feed through an extruding system10similar to that ofFIG. 1. Bound filaments and rods12can contain defects that make it difficult to use in an extrusion additive manufacturing system10. These defects include, but are not limited to, slipping between the filament12and drive gear or hobbed gear14caused by imperfections in the diameter of the filament or rod12, shearing of the filament or rod12by the gear or hobbed gear14which may cause the gear or hobbed gear14to freely spin in the cavity that was previously filament or rod12, snapping of the filament or rod12commonly caused by over packing of bound powders within the filament or rod12, buckling of the filament or rod12, necking of the filament or rod12, or plastic deformation of the filament or rod12. Filaments and rods12are commonly made from polymer materials. It is understood that many new composite materials are being used such as bound metal filaments, bound metal rods, bound ceramic filaments, bound ceramic rods, bound glass filaments, bound glass rods, bound rock filaments, bound rock rods, bound carbon fiber filaments, bound carbon fiber rods. For example, these filaments or rods12are typically 40%-80% bound metal powder by volume with the remainder of the volume of the filament12occupied by a binder or lubricant. Another difficulty with making high-density filaments or rods12is the brittle nature of the resulting filament or rod12. When the percentage of bound material (e.g. metal, ceramic, rock etc.) exceeds 30%, the resulting filament or rod12becomes substantially more brittle than an equivalent geometry 100% polymer filament or rod12. The impact of increased brittleness is that extruding systems10similar to the configuration shown inFIG. 1are significantly more susceptible to jamming or failure causing a disruption to the additive manufacturing process. In order to manufacture and handle high-density bound filaments or rods12the manufacturer must ensure that the material is strong enough and not brittle so as to be fed through the filament or rod drive system10, typically resulting in the use of non-optimal binding agents, lubricants, or surfactants24for the debinding and sintering phases.

Thus, it would be desirable to provide an improved additive manufacturing system.

SUMMARY

In one embodiment, an additive manufacturing system includes a hopper for containing a feedstock, at least one helical drive positioned downstream from the hopper for receiving the feedstock therefrom, a heat source positioned proximate at least a portion of the at least one helical drive, and an outlet. The at least one helical drive is configured to advance the feedstock toward the outlet, the heat source is configured to at least partially liquefy the feedstock advanced by the at least one helical drive, and the outlet is configured to dispense the at least partially liquefied feedstock based on a desired toolpath. The at least one helical drive may include at least one of a screw, a bolt, an auger, or an Archimedean screw. In addition or alternatively, the additive manufacturing system may further include a mixing subsystem positioned upstream from the at least one helical drive for mixing at least one of the feedstock, a lubricant, or a binder. For example, the mixing subsystem may include at least one of a vibrator, a rotating shaft, a magnet, a paddle, a brush, a stirrer, a single sigma mixer, a dual sigma mixer, a fluid flow, a liquid flow, or a gas flow. In one embodiment, the at least one helical drive and the mixing subsystem are driven in unison with each other. In another embodiment, the at least one helical drive and the mixing subsystem are driven independently of each other.

In one embodiment, the hopper includes at least one protrusion for controlling flow of the feedstock from the hopper. For example, the at least one protrusion may be at least one of stationary, rotatable, linearly movable, extendable in length and/or retractable in length. In addition or alternatively, the at least one helical drive may be linearly movable relative to the outlet. For example, linear movement of the at least one helical drive relative to the outlet may be controllable. In addition or alternatively, the additive manufacturing system may further comprise an actuator for driving the at least one helical drive, wherein the actuator is operatively coupled to the at least one helical drive by a coupler constructed of at least one thermally resistive material. For example, the coupler may be constructed of at least one of a polymer, a ceramic, a metal, or a carbon allotrope.

In one embodiment, the additive manufacturing system further includes a flexible tube positioned between the at least one helical drive and the outlet. For example, the flexible tube may be actively heated. In addition or alternatively, the additive manufacturing system may further include a feedstock comprising a non-filament material, wherein the feedstock is contained in the hopper. For example, the feedstock may be selected from the group consisting of polymer pellets, polymer granules, polymer powders, polymer gels, polymer suspensions, polymer micro pellets, metal pellets, metal granules, metal powders, metal gels, metal suspensions, metal micro pellets, graphite pellets, graphite granules, graphite powders, graphite gels, graphite suspensions, graphite micro pellets, ceramic pellets, ceramic granules, ceramic powders, ceramic gels, ceramic suspensions, ceramic micro pellets, and/or combinations or composites thereof.

In another embodiment, an additive manufacturing system includes a tank for containing a feedstock, a pump positioned downstream from the tank for receiving the feedstock therefrom, a heat source positioned proximate the pump, and an outlet, wherein the pump is configured to advance the feedstock toward the outlet, wherein the heat source is configured to at least partially liquefy the feedstock advanced by the pump, and wherein the outlet is configured to dispense the at least partially liquefied feedstock based on a desired toolpath. The additive manufacturing system may further include a flexible tube positioned between the helical drive and the outlet. For example, the flexible tube may be actively heated.

In yet another embodiment, a method of manufacturing includes feeding a feedstock into a hopper, advancing the feedstock from the hopper through a heat zone via a helical drive, at least partially liquefying the feedstock in the heat zone, and dispensing the at least partially liquefied feedstock based on a desired toolpath.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure provides methods for using and controlling the flow of commodity pellet, powder, and gel feedstock for extrusion additive manufacturing systems that may solve one or more of the cost, quality, and/or mechanical disadvantages of filament feedstocks (spooled and rod among others) discussed above in conjunction with the prior art. The present disclosure also provides structures and methods that provide rapid and precise extrusion capability using non-filament feedstocks in extrusion additive manufacturing systems at a much lower cost. These non-filament feedstocks include but are not limited to polymer pellets, polymer granules, polymer powders, polymer gels, polymer suspensions, metal pellets, metal granules, metal powders, metal gels, metal suspensions, graphite pellets, graphite granules, graphite powders, graphite gels, graphite suspensions, and composites thereof.

With reference now toFIG. 3, an exemplary additive manufacturing system30includes a hopper32containing any one or combination of feedstock34, a mixing subsystem36at least partially defining a mixing zone Z1, a helical drive38, a heat source40at least partially defining a heat zone Z2, and an outlet nozzle42at least partially defining an extrusion zone Z3. While the heat zone Z2is shown as extending along substantially the entire length of the helical drive38, it will be appreciated that the heat zone Z2may extend along only a portion of the helical drive38, such as, for example, near one end of the helical drive38and/or near a central portion of the helical drive38. The helical drive38may include any helical method or mechanism such as, for example, a screw, bolt, auger, or Archimedean screw. The hopper32may include any device or container for containing feedstock34such as, for example, a box, cartridge, tube, tub, jar, cylinder, receptacle, vessel, canister, repository or any such device for containing feedstock34.

As shown inFIG. 3A, the hopper32may have a single or series of protrusions44at or near the interface between the hopper32and the helical drive38and/or the interface between the hopper32and the mixing zone Z1for the purpose of controlling or influencing the flow of feedstock34from the hopper32into the helical drive38or mixing zone Z1. The protrusion(s)44may be one or a combination of stationary, rotatable, linearly movable, and/or extendable or retractable in length. The protrusion(s)44may be made of magnetic material. The protrusion(s)44may have the ability to conduct electricity or emit an electromagnetic field for the purposes of affecting the path of feedstock34. The protrusion(s)44may be uniform about a central axis. The protrusion(s)44may serve as a filter or be filter shaped (e.g., screen shaped). The protrusions44may naturally vibrate or be forced to vibrate at or near the natural frequency of the protrusion(s)44.

As shown, feedstock34is fed into the helical drive38from the hopper32. An actuator (not shown) controls the rotation of the helical drive38. The force from the helical drive38applied to the feedstock34causes the feedstock34to traverse the helical drive38into the heat zone Z2. Once the feedstock34enters the heat zone Z2, the feedstock34is wholly or partially liquefied from the heat. The wholly or partially liquefied feedstock34′ continues past the heat zone Z2into the outlet nozzle42. Once the wholly or partially liquefied feedstock34′ material passes through the outlet nozzle42, the material is deposited by the 3D printer or additive manufacturing system30based upon the desired toolpath. Pellet sizes, independent of material type, may generally fall in the range of 10 micrometers to 10 millimeters in length, width, thickness or diameter. Powder sizes, independent of material type, may generally fall in the range of 100 nanometers to 500 micrometers. When 3D printing with metal powder, ceramic powder, or other powder typically, but not always, a lubricant or binder is used. The powder, by volume, may occupy anywhere from 20% to 90% of the volume while the remainder of the volume may be approximately occupied by the lubricant or binder used.

The helical drive38may be of any suitable diameter. For example, the helical drive38may have a diameter between 2 millimeters and 200 millimeters. In one embodiment, the helical drive38may not comprise a perfect helix. For example, a tapered helical drive may be used for certain materials. In one embodiment, the changes in helical drive geometry may be defined by a compression ratio ranging from 1:1 to 1:10. In addition or alternatively, the relative length of the helical drive to the diameter of the helical drive (i.e., the L/D ratio) may range from 1:1 to 40:1n embodiments wherein metal injection molding feedstock is used or ceramic injection molding feedstock is used, the overall pellet sizes may range from 10 micrometers to 10 millimeters while the powder bound within the pellet may range from 100 nanometers to 500 micrometers. For example, the pellet sizes may range from 100 micrometers to 10 millimeters and/or the powder sizes may range from 500 nanometers to 100 micrometers. Many different methods may be used to directly rotate the helical drive38or indirectly cause the helical drive38to rotate. These methods may include but are not limited to direct drive via an insulative motor coupling, direct drive via a non-insulative motor coupling, a timing belt, a gearbox interface, a chain and sprocket interface or any other device to convert electromechanical kinetic energy into mechanical rotational energy. It is well understood to those skilled in the art that feedstock raw materials may include undesired material, impurities, or flaws. In on embodiment, the system30may include a screen, mesh screen, filter, magnet, or other means to separate impurities from the bulk of the feedstock34between the helical drive38and the outlet nozzle42.

Referring now toFIG. 4, another exemplary additive manufacturing system50includes one or more feedstock source(s)52, a helical drive54, a mixing or agitating device56at least partially defining the mixing zone Z1, a heat sink58and a heat source60together at least partially defining the heat zone Z2, and an outlet nozzle62at least partially defining the extrusion zone Z3. Feedstock34is fed from the one or more feedstock sources52into the mixing or agitating zone Z1. Once in the mixing or agitating zone Z1the feedstock material34is either controllably or randomly mixed. The mixing or agitation may be actively controlled and actuated via vibration, rotation, magnetism, paddles, brushes, stirring, a single sigma mixer, a dual sigma mixer, fluid flow, liquid flow, or gas flow. The mixing or agitation may be passively controlled and actuated via vibration, rotation, magnetism, paddles, brushes, stirring, a single sigma mixer, a dual sigma mixer, fluid flow, liquid flow, or gas flow. Once the feedstock34passes through the agitation zone Z1, the feedstock34is controlled through the helical drive54. An actuator (not shown) controls the rotation of the helical drive54. The force from the helical drive54applied to the feedstock34causes the feedstock34to traverse the helical drive54, passing the heat sink58and further passing into the heat zone Z2. Once the feedstock34enters the heat zone Z2, the feedstock34is wholly or partially liquefied from the heat. The wholly or partially liquefied feedstock34′ continues past the heat zone Z2into the outlet nozzle62. Once the wholly or partially liquefied feedstock material34′ passes through the outlet nozzle62, the material34′ is deposited by the 3D printer or additive manufacturing system50based upon the desired toolpath. In one embodiment, a flow controller (not shown) may use the feedback received from one or more pressure or flow sensors (not shown) in order to calculate a desired outlet nozzle pressure and control the rotational speed of the lead edge of the auger or helical drive54relative to the inner surface of the outlet nozzle62. In addition or alternatively, a gear pump may be positioned between the helical drive54and the outlet nozzle62, in conjunction with or separately from a feedback control system or flow controller, in order to regulate the flow of liquified or semi-liquified feedstock34′.

Referring now toFIG. 5, another exemplary additive manufacturing system70includes one or more material source(s)72a,72b, an auger or helical drive74, a mixing or agitating shaft76having mixing paddles78and at least partially defining the mixing zone Z1, a heat source80at least partially defining the heat zone Z2, and an outlet nozzle82at least partially defining the extrusion zone Z3. Feedstock (not shown) is fed from one or more feedstock sources72a,72binto a mixing or agitating zone Z1. Once in the mixing or agitating zone Z1the feedstock material is either controllably or randomly mixed. The mixing or agitation can be actively controlled and actuated via rotation of the mixing shaft76. The exterior surface of the mixing shaft76has one or more protrusions78. These protrusions78may be made of metal, polymer, composite, bristles, spikes, mesh, pegs, and/or rods. The mixing shaft76is hollow and contains the auger drive shaft or helical drive shaft84. In one embodiment, the mixing shaft76and auger drive shaft or helical drive shaft84may be controlled using a common actuator and control system. In another embodiment, the mixing shaft76and auger drive shaft or helical drive shaft84may be controlled using separate and distinct actuators and control systems. In any event, the mixing shaft76and helical drive shaft or auger drive shaft84have first ends76a,84a, respectively, near the heat zone Z2and second ends76b,84b, respectively, near the material sources72a,72b. The second ends76b,84bmay each be rotated mechanically, such as via a toothed ring86, gearbox, direct drive, pneumatics, belt, pulley, and/or chain, or electromechanically. Once the feedstock passes through the agitation zone Z1, the feedstock is controlled through the helical drive74. An actuator (not shown) controls the rotation of the helical drive74. The force from the helical drive74applied to the feedstock causes the feedstock to traverse the helical drive74into the heat zone Z2. Once the feedstock enters the heat zone Z2, the feedstock is wholly or partially liquefied from the heat. The wholly or partially liquefied feedstock continues past the heat zone Z2into the outlet nozzle82. Once the wholly or partially liquefied feedstock material passes through the outlet nozzle82, the material is deposited by the 3D printer or additive manufacturing system70based upon the desired toolpath.

With reference now toFIG. 6, in one embodiment, the system70may allow for controlled movement of the auger or helical drive74with respect to the hollow body90of the system70to control the distance and angle between the lead edge of the auger or helical drive74and the inner surface of the outlet nozzle82. The system70may also include a pressure sensor (not shown) configured to measure the pressure of the wholly or partially liquefied feedstock in the hollow body90, such as within the extrusion zone Z3. In addition or alternatively, the system70may include a flow controller (not shown) which uses the feedback received from one or more pressure or flow sensors in order to calculate a desired outlet nozzle pressure and control the distance between the lead edge of the auger or helical drive74and the inner surface of the outlet nozzle82. The distance between the inner surface of the outlet nozzle82and the auger or helical drive74may be changed by using rails, slides, rods, rack and pinion, pulleys, pneumatics, and/or hydraulics. In one embodiment of the invention the outlet nozzle82may be fixed and the auger or helical drive74may be controlled to move in order to change the separation distance. In another embodiment of the invention the auger or helical drive74may be fixed and the outlet nozzle82may be controlled to move in order to change the separation distance. In the embodiment shown, the gap size G between the helical drive74and the hollow body90decreases as the auger or helical drive74moves toward the outlet nozzle82. The gap size G is inversely related to mixture pressure, such that changing the gap size G provides control over extrusion pressure as a print parameter.

As shown inFIG. 7, the auger or helical drive shaft84of the auger or helical drive74described above may be coupled to an actuator92via a coupler94. The coupler94has first and second ends96,98with the first end96connected to the auger or helical drive shaft84and the second end98connected to the actuator92, where the actuator92may interface via the rotor of a DC motor, the rotor of an AC motor, the rotor of a stepper motor, the drive shaft of a gear box connected to a DC motor, the drive shaft of a gear box connected to an AC motor, or the drive shaft of a gear box connected to a stepper motor. In one embodiment, the coupler94may be constructed of a thermally resistive material or materials. For example, the coupler94may be polymeric, ceramic, metallic, or a carbon allotrope.

With reference now toFIG. 8, another exemplary additive manufacturing system100includes a helical drive or auger drive102separated physically and thermally from an outlet nozzle104by a flexible tube106. The flexible tube106may be insulated. The flexible tube106may be actively heated. The flexible tube106may be constrained to move in the plane of the 3D printer gantry. The flexible tube106may be allowed to move freely. The flexible tube106may be permanently connected to one or both of the helical drive102and the outlet nozzle104. The flexible tube106may be connected via latch, pipestrap, ziptie, glue, screw, thread, or clip to one or both of the helical drive102and the outlet nozzle104. While not shown, other components of the system100may be generally similar to those components in the various mixing, heat, and/or extrusion zones Z1, Z2, Z3described above.

Referring now toFIG. 9, another exemplary additive manufacturing system110includes an actuator112located remotely from but mechanically coupled to the helical drive114, such as via a flexible shaft116. In one embodiment, the actuator or motor112may be mounted in a fixed position while the helical drive114and outlet nozzle118are controlled to move by the 3D printer gantry or additive manufacturing system110. While not shown, other components of the system110may be generally similar to those components in the various mixing, heat, and/or extrusion zones Z1, Z2, Z3described above.

Referring now toFIG. 10, another exemplary additive manufacturing system120includes at least one tank122to hold one or more types of feedstock124, a pump126, a flexible low-friction tube128, one or more heat sources130a,130b, and an outlet nozzle132. The feedstock124can be of any suitable type, such as a liquid resin or gel or gel composite. The pump126may include one or more of a rotary pump, a screw drive pump, a pneumatic pump, or other suitable types of pumps.

Referring now toFIG. 11, another exemplary additive manufacturing system140may include multiple helical drive extruders142a,142bwhich may be mechanically movable relative to a build surface144in one, two, three, or more axes. The helical drive extruders142a,142bmay be synchronized with each other or may each have at least some degree of independent control. While not shown, other components of the system140may be generally similar to those components in the various mixing, heat, and/or extrusion zones Z1, Z2, Z3described above.

Referring now toFIG. 12, any extrusion screw, helical drive or drive shaft referenced herein may be made in a modular or interlocking way. For example, a male spline profile150aand female spline profile150bsuitable to transmit the required torque may be used. Splines150a,150bmay be tapered and/or spring loaded to facilitate and secure while allowing simple disassembly. Screws with many multifunctional zones in either single or multi-screw configurations may be used. These multifunctional zones may include but are not limited to feed zone, mixing zone, feedstock transition, and flow rate metering.

Referring now toFIG. 13, any helical drive extruder referenced herein may include more than one helical drive, auger, or screw. For example, the illustrated helical drive extruder160includes two screws162a,162bwhich may be operated together or independently via corresponding gears164a,164bwhich may be movable in and out of engagement with each other and which may either co-rotate or counter-rotate relative to each other. In one embodiment, moving the multiple screws162a,162brelative to each other may provide gap size control and/or pressure control, in a manner generally similar to that described above with respect toFIG. 6. Moving the screws162a,162brelative to each other may be particularly useful when applied in tapered extruder geometries, and may include relative axial movement (e.g., vertical movement in the drawing) as well as relative radial movement (e.g., horizontal movement in the drawing). For example, relative axial and radial movement of the screws162a,162bmay be used to change the intermesh geometry. Subsequently, axial movement of the screws162a,162bin unison may be used to provide gap size control and/or pressure control, in a manner generally similar to that described above with respect toFIG. 6.

With reference now toFIG. 14, an end to end automated 3D printing workflow200is illustrated. For the purposes of this embodiment of the invention atmospheric shall be defined to include forming gas, forming environment, inert gas (such as, but not limited to, argon), inert environment, reducing gas, reducing environment, standard atmospheric gas (such as, but not limited to, a mix of nitrogen, oxygen, and other gases), and standard atmospheric environment. At the highest level this embodiment of the invention contains a 3D printing station202including a 3D printer204which manufactures a desired part either in a vacuum, inert, or atmospheric environment. After the part is produced, the part is subsequently manually or automatically removed from the 3D printer204and may enter into a washing station206. The washing station206, also commonly referred to as a debind station206, may be one or a combination of a solvent debind station208, catalytic debind station210, thermal debind station212, or another type of debinding station. The washing station206may have an actively or passively controlled vacuum environment, inert environment, or atmospheric environment. If the washing station206is included and once the washing is complete, the part is manually or automatically introduced to a heat treating station214. If the washing station206is not included, the 3D printed part is either manually or automatically introduced to the heat treating station214directly from the 3D printing station202. The heat treating station214may operate in a vacuum, inert, or atmospheric environment. The heat treating station214may be one or a combination of a sintering furnace216, sintering—hot isostatic pressing furnace218, or hot isostatic pressing furnace (not shown). Once the 3D printed part has completed the desired heat treating, the 3D printed part manually or automatically enters into a finishing station220. The finishing station220may contain one or a combination of pickling222or polishing224. For the purposes of this embodiment of the invention, actively or passively controlling the environment of each of these steps may contain one or a combination of thermal sensors, pressure sensors, chemical sensors, oxygen sensors, humidity sensors, and means for regulating and controlling the temperature, pressure, chemistry, oxygen, and humidity within each of the substations of the workflow200.

While the present invention has been illustrated by the description of various embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Thus, the various features discussed herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The present invention in its broader aspects is therefore not limited to the specific details and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.