Extruder assembly and method for forming a three-dimensional building object

Abstract

Extruder assembly (108) for a system for printing three-dimensional objects, comprising: an extruder body (160) having an extrusion slot (168) to enable a continuous filament of material to be extruded through the extrusion slot (168); at least one closure body (264) having a central opening (268); an actuator (272) operatively connected to the at least one closure body (264), the actuator (272) being configured to rotate the at least one closure body (264) to reduce a width of the filament extruded through the extrusion slot (168); and at least one actuator (120) operatively connected to the extruder assembly (108), wherein the at least one actuator (120) is configured to translate the extruder body (160) in a horizontal plane and to rotate the extruder body (160) about a rotational axis (140).

Description

Digital three-dimensional fabrication, also known as digital additive manufacturing, is a process for creating a three-dimensional solid object in virtually any shape from a digital model. Printing three-dimensional objects is an additive process in which one or more extruder or ejector arrangements successively form layers of material on a substrate in various shapes. In some conventional three-dimensional object printers, the extruders are similar to printheads in document printers because they include an array of extruders that deliver a continuous stream of material to form layers, rather than an array of ejectors that eject drops of material to form layers.In other known printers for three-dimensional objects, the extruder arrangement comprises a single die configured to extrude the material to form layers for producing a printed object. The nozzle is generally shaped as a small circular hole that dispenses a continuous filament of build material. The filaments are laid down in layers to form the three-dimensional part. In such an extruder arrangement, the printed object should be quickly and accurately provided. The diameter of the nozzle determines both the minimum resolution of the part and the speed at which the object can be formed. For example, a larger diameter nozzle may form the object more quickly, but has reduced resolution, while a smaller diameter nozzle may form smaller details, but the manufacture of the product requires more time. Thus, in conventional three-dimensional object printers, the size of the nozzle represents a compromise between build speed and build resolution.Accordingly, improvements in systems and methods for forming three-dimensional objects would be advantageous with printers that include extruder assemblies so that the objects have more details with reduced manufacturing time.CN 104 097 327 A discloses a structure for adjusting the nozzle cross section of a 3D printer and a method for controlling the speed and the precision.US 2004 / 164436 A1 discloses a multiple nozzle arrangement for the extrusion of walls for a 3D printer.DE 10 2015 016 823 A1 discloses a 3D large-format full-color printer with a throughput- and shape-variable nozzle.FR 2 684 590 A1 discloses an apparatus for producing three-dimensional solid articles by superimposing successive layers.US 6 030 199 A discloses an improved apparatus and method for forming a three-dimensional object. The apparatus comprises containers for receiving molten molding materials, mechanical piston or screw elements in the containers for pressurizing the molten molding materials in each of the containers, and an adjustable planar nozzle mechanism connected to the containers through which the pressurized molten molding materials flow to form planar jets of variable width.In one embodiment, a three-dimensional object extruder assembly includes an extrusion slot to enable more rapid printing of three-dimensional objects with higher precision. The printing system includes an extruder body having an extrusion slot to allow a continuous filament of material to be extruded through the extrusion slot, and at least one actuator operatively connected to the extruder body. The at least one actuator is configured to displace or move the extruder body translationally in a horizontal plane and to rotate the extruder body about an axis of rotation. Further, the printing system includes at least one closure body having a central opening, an actuator operatively connected to the at least one closure body, the actuator configured to rotate the at least one closure body to reduce a width of the filament extruded through the extrusion slotIn another embodiment, a method of forming a three-dimensional construction object enables more rapid printing of three-dimensional objects with higher precision. The method includes extruding a build material through an extrusion slot of an extruder body of an extruder assembly, translationally moving the extruder body in a horizontal plane with the at least one actuator while extruding build material to form a continuous ribbon of build material, and rotating the extruder body about an axis of rotation with the at least one actuator while extruding the build material. The method further includes moving at least one shutter body over a portion of the extrusion slot by actuating a shutter actuator to close a first portion of the extrusion slot and reduce a width of the filament extruded through the extrusion slot.In yet another embodiment according to the disclosure, an extruder assembly for a three-dimensional object printing system has an extrusion slot and a closure body that enables the extrusion area of the extrusion slot to be adjusted for better accuracy in three-dimensional object printing and faster build times. The printing system comprises an extruder body, at least one first actuator, at least one closure body and a second actuator, wherein the at least one closure body is arranged at an angle with respect to a vertical axis which is parallel to a rotational axis, and the at least one closure body is obliquely in contact with a surface of the first wedge-shaped collet chuck. The extruder arrangement further has a wedge-shaped collet chuck. The extruder body has an extrusion slot to allow a continuous filament of material to be extruded through the extrusion slot. The at least one first actuator is operatively connected to the extruder and configured to translate the extruder body in a horizontal plane. The second actuator is operatively connected to the wedge-shaped collet and configured to selectively vertically move the wedge-shaped collet to selectively horizontally move the at least one closure body across the extrusion slot to close a first portion of the extrusion slot and reduce a width of the filament extruded through the extrusion slot.The foregoing aspects and other features of an extruder printer and a method of operating an extruder printer are discussed in the following description taken in conjunction with the accompanying drawings. Figure 1 is a schematic illustration of a three-dimensional object printer having an extruder assembly with an extrusion slot. FIG. 2 illustrates a partial top sectional view of a shutter system for the 3D object printer of FIG. 1 having a linearly moving shutter body configured to close at least a portion of the extrusion slot. FIG. 3 illustrates a partial top sectional view of a shutter system for the 3D object printer of FIG. 1 having two linearly moving shutter bodies, each configured to close a portion of the extrusion slot. FIG. 4 illustrates a partial cross-sectional side view of an extruder body for the 3D object printer of FIG. 1 with a closure system having flexible, linearly moving closure bodies configured to close a portion of the extrusion slot. FIG. 5 illustrates a partial top sectional view of a shutter system for the 3D object printer of FIG. 1 having a shutter body rotatable about a pivot axis to close a portion of the extrusion slot with the shutter body in an open position. FIG. 6 illustrates a partial top sectional view of the closure system of FIG. 5 with the closure body in a closed position. FIG. 7 illustrates a partial top sectional view of a shutter system for the 3D object printer of FIG. 1 having two shutter bodies each moved by a collet member to close a portion of the extrusion slot. FIG. 8 illustrates a partial cross-sectional side view of the closure system of FIG. 7 with closure bodies not blocking the extrusion slot. FIG. 9 illustrates a partial cross-sectional side view of the closure system of FIG. 8, wherein the closure bodies each block a portion of the extrusion slot. FIG. 10 illustrates a method of operating the 3D object printer of FIG. 1 to produce a build object. FIG. 11 illustrates a top view of a first layer produced by the 3D object printer of FIG. 1 according to the method of FIG. 10. FIG. 12 illustrates a top view of the first layer of FIG. 11 and a second layer produced by the 3D object printer of FIG. 1 according to the method of FIG. 10. FIG. 13 illustrates a partial schematic top view of the extruder body of FIG. 1 translating and rotating simultaneously to form a curved feature. FIG. 14 illustrates a graph of an extrusion factor versus radius to extrusion width ratio for the production of curved features using the extrusion slot of FIG. 1. FIG. 15 illustrates a partial schematic top view of the extruder body of FIG. 1 moving with the long edge of the slot perpendicular to the travel direction. Figure 16 illustrates a partial schematic top view of the extruder body of Figure 1 moving with the long edge of the slot at an angle of 45 degrees with respect to the direction of travel. FIG. 17 illustrates a partial schematic plan view of the extruder body of FIG. 1 moving with the long edge of the slot parallel to the travel direction. Figure 18 is a schematic illustration of a three-dimensional object printer having an extruder assembly with an extrusion slot and including a separate actuator configured to move the extruder body in each of the x, y, z and rotational directions. Figure 19 illustrates a schematic view of a three-dimensional object printer having an extruder assembly comprising a first extruder body having an extrusion slot and a second extruder body having an extrusion die.For a general understanding of the environment for the system and method disclosed herein, as well as the details for the system and method, reference is made to the drawings. Throughout the drawings, like reference numerals have been used to designate like elements.FIG. 1 illustrates a three-dimensional object printer 100. The three-dimensional object printer 100 includes an actuator assembly 104, an extruder assembly 108, a platen 112, and a controller 116. The actuator assembly 104 includes at least one actuator 120 and a pair of rails 124 mounted on a support frame (not shown). The rails 124 are configured to support the actuator 120 and the extruder assembly 108 to allow the actuator 120 to translate the extruder assembly 108 along an x-axis 128, a y-axis 132, and a z-axis 136, and to rotate the extruder assembly 108 about an axis of rotation 140 that is parallel to the z-axis 136 in the illustrated embodiment.In the embodiment of FIG. 1, the actuator assembly 104 includes a single actuator 120 configured to translate the extruder assembly 108 in the x, y, and z axes 128, 132, and 136, respectively, and to rotate the actuator about the axis of rotation 140. In another embodiment, the actuator assembly 104 includes a first actuator configured to move the extruder assembly 108 in the x, y, and z axes 128, 132, 136, and a second actuator configured to rotate the extruder assembly 108 about the axis of rotation 140. In yet another embodiment illustrated in FIG. 18, actuator assembly 104A includes a first actuator 120X configured to move extruder body 160 in x-direction 128, a second actuator 120Y configured to move extruder body 160 in y-direction 132, a third actuator 120Z configured to move extruder body 160 in z-direction 136, and a fourth actuator 120R configured to rotate extruder body 160 about axis of rotation 140.Referring back to FIG. 1, the extruder assembly 108 includes an extruder body 160 and a reservoir 164 configured to store a quantity of build material. An extrusion slot 168 (not drawn to scale in the view of FIG. 1) is defined on the underside of the extruder body 160. The extrusion slot 168 is operatively connected to the reservoir 164 and is configured to extrude build material received from the reservoir 164 to form a build object 180 on the panel 112. In one embodiment, the length of the extrusion slot 168 is between approximately 0.75 mm and approximately 6.4 mm, and the width of the extrusion slot is between approximately 0.2 mm and approximately 0.5 mm. In another specific embodiment, the length of the extrusion slot 168 is approximately 1.2 mm and the width of the extrusion slot is approximately 0.3 mm. In some embodiments, the extrusion slot 168 is configured to be parallel to the plane of the surface of the plate 112, and rotation about the axis 140 maintains the slot in parallel alignment with the surface of the plate. The rotation is adjusted in some cases with reference to the direction of travel of the extruder based on the desired size of the extruded ribbon.In some embodiments, the extruder body 160 includes a closure system for closing the extrusion slot or portion thereof. Various closure systems 200, 220, 240, 260, 280 for use in the extruder body 160 are illustrated in Figures 2-9. FIG. 2 illustrates a closure system 200 having a flat closure body 204. The flat closure body 204 is operatively connected to an actuator 208 configured to linearly slide the flat closure body 204 over the slot 168 to close a portion of the slot. The actuator 208 is operatively connected to the controller 116, which, as discussed in detail below, is configured to actuate the actuator 208 to adjust the position of the flat closure body 204 based on the desired size of the extruded ribbon.Another embodiment of a closure system 220 is illustrated in FIG. 3. The embodiment of FIG. 3 is similar to the embodiment of FIG. 2, except that the closure system 220 includes two flat closure bodies 224, 228, each operatively connected to the actuator 232. The actuator 232 is operatively connected to the controller 116, which is configured to actuate the actuator 232 to adjust the position of each flat closure body 224, 228. In one embodiment, the actuator 232 is configured to move each closure body 224, 228 independently of one another to close different portions of the slot 168 on each side of the slot 168. In another embodiment, the actuator 232 is configured to move the closure bodies together but in opposite directions to close the same portion of the slot 168 on each side of the slot 268.FIG. 4 illustrates another embodiment of a closure system 240 for use in the extruder body 160 of FIG. 1. the closure system 240 includes a flexible closure body 244 operatively connected to an actuator 248. The flexible closure body 244 generally corresponds to the bottom and side walls of the extruder body 160. The actuator 248 is operatively connected to the controller 116, which is configured to actuate the actuator 248 to move the shutter body 244 along the side and bottom walls of the extruder body 160 to cover a portion of the slot 168.The embodiment illustrated in FIG. 4 shows a closure body 244 on one side of the slot. However, the reader should appreciate that in some embodiments, the closure system 240 includes a second closure body operatively connected to the actuator 248 on the opposite side of the slot 168 to close a portion of the opposite side of the slot 168 in a similar manner to the embodiment of FIG. 3.FIGS. 5 and 6 illustrate another closure system 260 for use in the extruder body 160 of FIG. 1. the closure system 260 includes a round closure body 264 defining a central opening 268. In the illustrated embodiment, the central opening 268 is oval-shaped, although other desired shapes, for example, rectangular, trapezoidal, or triangular, may be utilized in other embodiments. The closure body 264 is operatively connected to an actuator 272 configured to rotate the closure body. The actuator 272 is operatively connected to the controller 116, and the controller 116 is configured to actuate the actuator 272 to rotate the closure body 264 about a pivot axis 276 to block at least a portion of the slot 168 with the closure body 264 as illustrated in FIG. 6.FIGS. 7-9 illustrate another embodiment of a closure system 280 for use in the extruder body 160 of FIG. 1. the closure system 280 includes two closure bodies 282, 284 and two wedge shaped collet members 286, 288. Each wedge-shaped collet component is operatively connected to an actuator 292. As can be seen in the vertical cross-sectional views of FIGS. 8 and 9, the closure bodies 282, 284 are pins that lie on an inclined surface of the collet members 286, 288.The actuator 292 is operatively connected to the controller 116, which actuates the actuator 292 to vertically move the collet members 286, 288. The upward and downward movement of the collet members 286, 288 causes the inclined surfaces of the collet members 286, 288 to cooperate with the corresponding shutter bodies 282, 284 to horizontally move the shutter bodies 282, 284. Accordingly, as the collet members 286, 288 move upwardly, shown in FIG. 9, the closure bodies 282, 284 move toward each other, closing a portion of the slot 168. In the illustrated embodiment, the actuator 292 is operatively connected to both collet members 286, 288. However, in another embodiment, the actuator 292 is connected to only one of the collet members 286, 288, and the collet members 286, 288 are connected to each other so as to vertically move together.FIG. 10 illustrates a process 400 used to operate the three-dimensional object printer 100 to extrude build material to create a build object 180. Statements that the process is executing a certain task or function relate to a controller or general-purpose processor executing programmed instructions stored on non-transitory computer-readable storage media operatively connected to the controller or processor to manipulate data and actuate one or more components in the system to execute the task or function. The controller 116 of the three-dimensional object printer 100 mentioned above may be configured with components and programmed instructions to provide a controller or processor executing the process 400. Alternatively, the controller may be implemented with more than one processor and associated circuits and components, each configured to perform one or more tasks or functions described herein.Referring to FIGS. 10-12, the process 400 begins with the controller 116 actuating the actuator 120 to rotate the extruder body 160 to align the width of the slot with the travel direction for the first layer 440 (FIG. 11 ) (block 404). For example, in the embodiment illustrated in FIG. 11, the first direction is in the y-direction. In some embodiments, the controller 116 determines the desired direction of travel based on the digital model of the construction object. The controller 116 then actuates the actuator 120 to translate the extruder body 160 in the travel direction as material is extruded from the slot 168 to extrude strips 442, 444, 446, 448, 450 of build material to form the first layer 440 (block 408). In a particular embodiment, the actuator 120 moves the extruder body 160 at a speed between approximately 5000 mm / min and 8000 mm / min during the extrusion processes. In another particular embodiment, the actuator moves the extruder body 160 at a speed of approximately 6000 mm / min during the extrusion processes.In some embodiments of the three-dimensional object printer, the controller 116 is configured to actuate the actuator 120 and the extruder assembly 108 to produce the strips 442- 450 by first forming the center strip 442 and then forming the adjacent strips 444, 446 and finally forming the outer strips 448, 450 to improve adhesion between the strips 442- 450 and thus improve the structural strength of the layer. In other embodiments, the layers 442- 450 are formed from left to right or right to left to increase a speed of the layer formation. In some embodiments, the strips 442- 450 have different widths from one another. For example, the outer strips 448, 450 may have a width that is half the width of the inner strips 442, 444, 446.Once the first layer 440 is completed, the controller 116 actuates the actuator 120 to rotate the extruder body 160 to align with the second direction (block 412). In the illustrated embodiment, the second direction is oriented toward the x direction orthogonal to the first direction. However, the reader should appreciate that the angle between the first and second directions may form other desired angles depending on the characteristics of the construction object. The controller 116 then actuates the actuator 120 to translate the extruder body 160 as material is extruded from the slot 168 to extrude strips 462, 464, 466, 468, 470 of build material forming the second layer (block 416).If additional layers are to be printed, the controller 116 may actuate the actuator 120 to rotate the extruder body 160 to align with a third direction and form another layer in the third direction, or the controller 116 may actuate the actuator 120 to repeat the processing of block 400 to produce additional layers in the first and second directions.While FIGS. 11 and 12 illustrate the strips 442- 450, 462- 470 as being separated from each other to clearly show the strips 442- 450, 462- 470 of the different layers 440 and 460, respectively, the reader should recognize that the strips 442- 450, 462- 470 are typically formed adjacent to each other to form a continuous layer of material.Typically, the build object consists of irregular layers, not the simple rectangular layers illustrated in Figures 11-12. These irregular layers typically include features that cannot be formed with the strips illustrated above. Consequently, detail formation is required for those details which cannot be formed in the stripes. Detailing is typically performed immediately before, immediately after, or in some cases during the extrusion of the strips forming the bulk of the layer (blocks 408 and 416).An example of details that cannot be formed with the stripes are curved shapes. To form curved details, the controller 116 is configured to actuate the actuator 120, or in embodiments with separate translational and rotational actuators, both the translational and rotational actuators to rotate and translate the extruder body 160 at the same time (FIG. 13 ). As the extruder body 160 and slot 168 rotate and translate, the outer edge of slot 168 defines the outer edge of the curve, while the inner edge of slot 168 defines the inner edge of the curve. Because the outer edge of the extrusion slot 168 traverses a greater distance than the inner edge of the slot 168, adaptation to the extrusion is required to account for the various travel distances of the inner and outer edges. In particular, if the radius of the curve is relatively small compared to the width of the slot 168, the amount of extruded build material must be adjusted. As an example, extruding a small circle having a radius equal to the width of the slot (r) extrudes an area equal to πr 2, while the outer edge traverses a linear distance of 2πr. Thus, the extrusion rate should be proportional to πr 2 / (2 πr) or r / 2. On the other hand, for a very large radius circle (R), the difference between the distances traversed by the inner and outer edges of the extrusion slot 168 is minimal, and the extrusion rate is proportional to the printed area (2πrR) divided by the path length (2πR), which is equal to r, or in this example the slot width. Figure 14 illustrates a curve of extrusion factor plotted against the ratio of radius to extrusion width or slot width.In some embodiments, certain details are formed by the controller 116 that actuates the actuator 120 to rotate the extruder body 160 to an angle relative to the travel direction, which reduces the effective width 480 of the extruded filament in the travel direction, as illustrated in FIGS. 14-16. For example, as illustrated in Figure 16, the width 480 of the extruded belt perpendicular to the direction of travel is slightly reduced because the extruder body 160 is rotated 45 degrees. When the extruder body 160 is rotated so that the long dimension of the slit 168 is parallel to the traveling direction, the extrusion width 480 is reduced to the minimum dimension of the slit 168, as illustrated in FIG. 17.In embodiments of the three-dimensional object printing system having a closure system 200, 220, 240, 260, 280 described above, the controller 116 is configured to actuate the actuator 208, 232, 248, 272, 292 to reduce the width of the belt to form certain details. The controller 116 actuates the actuator 208, 232, 248, 272, 292 to move the associated closure member or members such that the closure members cover a portion of the slot 168 and reduce the width of the ribbon or filament of extruded build material. With the reduced extrusion width, the controller 116 actuates the actuator 120 to translate, rotate, or both translate and rotate the extruder body 160 to form details of the build item that are less than the size of the slot 168. In some embodiments, at the same time, the controller 116 actuates both the translation / rotational actuator 120 and the shutter actuator 208, 232, 248, 272, 292 to form details to form, for example, a triangular or trapezoidal detail. In further embodiments, the controller 116 is configured to actuate the associated actuator 208, 232, 248, 272, 292 to cover the entire slot 168, thereby stopping extrusion and reducing unwanted extrusion as the extruder body 160 is moved, known as "sweeping.".These techniques enabled by the embodiments of the three-dimensional printing system 100 allow the layers of construction object to be formed quickly by aligning the slot 168 with the travel direction and extruding wide bands of construction material. In addition, layers adjacent in the z-direction may be formed at mutually different angles to the traveling direction, thereby enhancing the overall structural strength of the construction object. Moreover, while extrusion through the slot 168 allows for faster formation of a build object than through a conventional die, the closure system 200, 220, 240, 260, 280 and rotation of the extruder body 160 allow the three-dimensional object printing system 100 to form curves and small details that cannot be produced with known three-dimensional object printers using a slotted extruder.FIG. 19 illustrates another embodiment of a three-dimensional object printer 600 similar to the embodiment of FIG. 1 described above. For simplicity, only the differences between the three-dimensional object printer 600 of FIG. 19 and the three-dimensional object printer 100 of FIG. 1 are illustrated herein. In the three-dimensional object printer 600, the extruder assembly 608 includes a second extruder body 672 in addition to the extruder body 160 described above. The second extruder body 672 is operatively connected to the reservoir 164 and is configured to receive the same build material from the reservoir 164 as the first extruder body 160. The second extruder body defines an extrusion die 676 having a diameter less than the extrusion slot 168 of the extruder body 160.The second extruder body 672 is operatively connected to the controller 116, which is configured to operate the first extruder body 160 to produce large objects on the build object 180 by extruding build material through the extrusion slot 168. The controller 116 is configured to operate the second extruder body 672 to extrude a small filament through the die 676 to produce details and smaller objects on the build object 180. Thus, the 3D object printer 600 can quickly produce larger objects, but maintains the ability to produce small details on the build object 180.

Claims

An extruder assembly (108) for a system for printing three-dimensional objects, comprising: an extruder body (160) having an extrusion slot (168) to allow a continuous filament of material to be extruded through the extrusion slot (168); at least one closure body (264) having a central opening (268); an actuator (272) operatively connected to the at least one closure body (264), the actuator (272) configured to rotate the at least one closure body (264) to reduce a width of the filament extruded through the extrusion slot (168); and at least one actuator (120) operatively connected to the extruder assembly (108), wherein the at least one actuator (120) is configured to translate the extruder body (160) in a horizontal plane and to rotate the extruder body (160) about an axis of rotation (140).The extruder assembly (108) of claim 1, wherein the at least one actuator (120) further comprises: a first actuator configured to rotate the extruder body (160); and a second actuator configured to translate the extruder body (160).The extruder assembly (108) of claim 1, wherein the at least one actuator (120) is a single actuator configured to both rotate and translate the extruder body (160).A method of forming a three-dimensional construction object, comprising: extruding a construction material through an extrusion slot (168) of an extruder body (160) of an extruder assembly (108); translationally moving the extruder body (160) in a horizontal plane with the at least one actuator (120) as construction material is extruded to form a continuous ribbon of construction material; rotating the extruder body (160) about an axis of rotation with the at least one actuator as the construction material is extruded; and moving at least one closure body (204, 224, 228) over a portion of the extrusion slot (168) by actuating a closure actuator (208, 232) to close a first portion of the extrusion slot (168) and reduce a width of the filament extruded through the extrusion slot (168).The method of claim 4, wherein positioning the at least one closure body (204, 224, 228) includes actuating the closure actuator (208, 232) to linearly move the closure body (204, 224, 228) across the extrusion slot (168).An extruder assembly (108) for a system for printing three-dimensional objects, comprising: an extruder body (160) having an extrusion slot (168) to allow a continuous filament of material to be extruded through the extrusion slot (168); at least one first actuator (120) operatively connected to the extruder assembly (108), the at least one first actuator (120) configured to translate the extruder body (160) in a horizontal plane; a wedge shaped collet (286, 288); at least one closure body (224, 228, 282, 284), the at least one closure body (282, 284) being disposed at an angle with respect to a vertical axis that is parallel to a rotational axis (140), and the at least one closure body (282, 284) obliquely contacting a surface of the first wedge shaped collet (286, 288); and a second actuator (232, 292) operatively connected to the wedge shaped collet (286, 288) (286, 288), the second actuator (292) configured to selectively vertically move the wedge shaped collet (286, 288) to selectively horizontally move the at least one closure body across the extrusion slot (168) to close a first portion of the extrusion slot (168) and reduce a width of the filament extruded through the extrusion slot.The extruder assembly (108) of claim 6, wherein the at least one closure body further comprises: a first closure body (224); and a second closure body (228), wherein the first closure body (224) and the second closure body (228) are operatively connected to the second actuator (232); wherein the second actuator (232) is further configured to move the first closure body across the extrusion slot (168) to close the first portion of the extrusion slot (168) and to move the second closure body (228) across the extrusion slot (168) to close a second portion of the extrusion slot (168).

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