Patent Publication Number: US-2022227042-A1

Title: Additive manufacturing recoat assemblies including sensors and methods for using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Patent Application 61/851,953 filed May 23, 2019, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Field 
     The present specification generally relates to additive manufacturing systems and, more specifically, to recoat assemblies for additive manufacturing systems and methods for using the same. 
     Technical Background 
     Additive manufacturing systems may be utilized to “build” an object from build material, such as organic or inorganic powders, in a layer-wise manner. Conventional additive manufacturing systems include various “recoat” apparatuses that are configured to sequentially distribute layers of build material, such that a binder material can be deposited and cured to “build” an object. However, conventional recoat apparatuses may inconsistently distribute build material, leading to variation in the objects built by the additive manufacturing system. Furthermore, in the event of breakage of components of conventional recoat apparatuses generally requires that the recoat apparatus be removed for repair, thereby increasing contributing to system downtime and increasing operating costs. Moreover, some conventional recoat apparatuses distribute build material by fluidizing the build material, and airborne build material may be dispersed to other components of the additive manufacturing system, and may interfere with and/or degrade the other components of the additive manufacturing system. 
     Accordingly, a need exists for alternative recoat assemblies for additive manufacturing systems. 
     SUMMARY 
     In one embodiment, a recoat assembly for an additive manufacturing system includes a first roller support, a second roller support, a first roller disposed between and supported by the first roller support and the second roller support, a first rotational actuator operably coupled to the first roller and configured to rotate the first roller about a first rotation axis, and a first sensor mechanically coupled to and in contact with the first roller support, where the first sensor outputs a first output signal indicative of a first force incident upon the first roller. 
     In another embodiment, an additive manufacturing system includes a recoat assembly including a first roller support, a second roller support, a first roller disposed between and supported by the first roller support and the second roller support, a first rotational actuator operably coupled to the first roller and configured to rotate the first roller about a first rotation axis, a first sensor mechanically coupled to and in contact with the first roller support, where the first sensor outputs a first output signal indicative of a first force incident upon the first roller, and an electronic control unit configured to receive the first output signal of the first sensor, determine a first force on the first roller based on the first output signal of the first sensor, and adjust at least one operating parameter of the additive manufacturing system in response to the determined first force. 
     In yet another embodiment, method of adjusting at least one operating parameter of an additive manufacturing system includes distributing a layer of a build material on a build area with a recoat assembly, the recoat assembly including a first roller disposed between and supported by a first roller support and a second roller support, a first rotational actuator operably coupled to the first roller and configured to rotate the first roller about a first rotation axis, and a first sensor mechanically coupled to and in contact with the first roller support, receiving a first output signal from the first sensor as the layer of the build material is distributed on the build platform with the recoat assembly, determining a first force on the first roller based on the first output signal of the first sensor, and adjusting the at least one operating parameter of the additive manufacturing system in response to the determined first force. 
     Additional features and advantages of the additive manufacturing apparatuses described herein, and the components thereof, will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically depicts a conventional additive manufacturing systems; 
         FIG. 2A  schematically depicts an additive manufacturing system, according to one or more embodiments shown and described herein; 
         FIG. 2B  schematically depicts another additive manufacturing system, according to one or more embodiments shown and described herein; 
         FIG. 2C  schematically depicts an enlarged view of build material of an additive manufacturing system according to one or more embodiments shown and described herein; 
         FIG. 3  schematically depicts an embodiment of a recoat assembly of the additive manufacturing system of  FIG. 2A , according to one or more embodiments shown and described herein; 
         FIG. 4  schematically depicts another view of the recoat assembly of  FIG. 3 , according to one or more embodiments shown and described herein; 
         FIG. 5  schematically depicts another view of the recoat assembly of  FIG. 3 , according to one or more embodiments shown and described herein; 
         FIG. 6A  schematically depicts another side view of a recoat assembly, according to one or more embodiments shown and described herein; 
         FIG. 6B  schematically depicts a section view of a recoat assembly, according to one or more embodiments shown and described herein; 
         FIG. 6C  schematically depicts rollers and roller supports of the recoat assembly of  FIG. 6B  shown in isolation, according to one or more embodiments shown and described herein; 
         FIG. 7A  schematically depicts a roller support of  FIG. 6C  in isolation, according to one or more embodiments shown and described herein; 
         FIG. 7B  schematically depicts another view of the roller support of  FIG. 7A , according to one or more embodiments shown and described herein; 
         FIG. 7C  schematically depicts a strain gauge for use with the roller support of  FIG. 7A , according to one or more embodiments shown and described herein; and 
         FIG. 8  schematically depicts another roller support in isolation, according to one or more embodiments shown and described herein; 
         FIG. 9A  schematically depicts another roller support in isolation, according to one or more embodiments shown and described herein; 
         FIG. 9B  schematically depicts another view of the roller support of  FIG. 9A , according to one or more embodiments shown and described herein; 
         FIG. 9C  schematically depicts a section view of the roller support of  FIG. 9A , according to one or more embodiments shown and described herein; 
         FIG. 9D  schematically depicts a load cell for use with the roller support of  FIG. 9A , according to one or more embodiments shown and described herein; 
         FIG. 10  schematically depicts a roller support coupled to a load cell and at least one strain gauge, according to one or more embodiments shown and described herein; 
         FIG. 11A  schematically depicts another section view of the recoat assembly of  FIG. 6B , according to one or more embodiments shown and described herein; 
         FIG. 11B  schematically depicts a perspective view of a recoat assembly, according to one or more embodiments shown and described herein; 
         FIG. 11C  schematically depicts a perspective section view of the recoat assembly of  FIG. 11B , according to one or more embodiments shown and described herein; 
         FIG. 11D  schematically depicts a section view of the recoat assembly of  FIG. 11B , according to one or more embodiments shown and described herein; 
         FIG. 11E  schematically depicts a bottom perspective view of a recoat assembly, according to one or more embodiments shown and described herein; 
         FIG. 12  schematically depicts rollers and energy sources of the recoat assembly of  FIG. 6B , according to one or more embodiments shown and described herein; 
         FIG. 13  schematically depicts one embodiment of a layout of the rollers of the recoat assembly of  FIG. 6B , according to one or more embodiments shown and described herein; 
         FIG. 14  schematically depicts another embodiment of a layout of the rollers of the recoat assembly of  FIG. 6B , according to one or more embodiments shown and described herein; 
         FIG. 15  schematically depicts another embodiment of a layout of the rollers of the recoat assembly of  FIG. 6B , according to one or more embodiments shown and described herein; 
         FIG. 16A  schematically depicts a perspective view of a recoat assembly including a cleaning member, according to one or more embodiments shown and described herein; 
         FIG. 16B  schematically depicts a perspective view of a recoat assembly including a cleaning member, according to one or more embodiments shown and described herein; 
         FIG. 16C  schematically depicts a perspective section view of the recoat assembly of  FIG. 16B , according to one or more embodiments shown and described herein; 
         FIG. 16D  schematically depicts an exploded view of a cleaning position adjustment assembly engaged with the cleaning member of  FIG. 16C , according to one or more embodiments shown and described herein; 
         FIG. 17A  schematically depicts a top view of the cleaning member and the rollers of the recoat assembly of  FIG. 3 , according to one or more embodiments shown and described herein; 
         FIG. 17B  schematically depicts another top view of the rollers of the recoat assembly of  FIG. 3  and the cleaning member, according to one or more embodiments shown and described herein; 
         FIG. 17C  schematically depicts a side view of the rollers of the recoat assembly of  FIG. 3  and the cleaning member, according to one or more embodiments shown and described herein; 
         FIG. 18A  schematically depicts a perspective view of a secondary containment housing and a vacuum of the recoat assembly of  FIG. 3 , according to one or more embodiments shown and described herein; 
         FIG. 18B  schematically depicts a perspective view of a primary containment housing and a vacuum of the recoat assembly of  FIG. 3 , according to one or more embodiments shown and described herein; 
         FIG. 19  schematically depicts a section view of the vacuum and the recoat assembly of  FIG. 3 , according to one or more embodiments shown and described herein; 
         FIG. 20  schematically depicts a perspective view of another recoat assembly, according to one or more embodiments shown and described herein; 
         FIG. 21  schematically depicts another perspective view of the recoat assembly of  FIG. 20 , according to one or more embodiments shown and described herein; 
         FIG. 22  schematically depicts a section view of the recoat assembly of  FIG. 20 , according to one or more embodiments shown and described herein; 
         FIG. 23  schematically depicts another section view of a recoat assembly, according to one or more embodiments shown and described herein; 
         FIG. 24  schematically depicts a control diagram of the additive manufacturing system according to one or more embodiments shown and described herein; 
         FIG. 25  is a flowchart for adjusting an operating parameter of the additive manufacturing system, according to one or more embodiments shown and described herein; 
         FIG. 26  is another flowchart for adjusting an operating parameter of the additive manufacturing system, according to one or more embodiments shown and described herein; 
         FIG. 27  is a flowchart for moving build material to a build area, according to one or more embodiments shown and described herein; 
         FIG. 28  schematically depicts a recoat assembly moving build material to a build area, according to one or more embodiments shown and described herein; 
         FIG. 29A  schematically depicts a recoat assembly moving build material to a build area, according to one or more embodiments shown and described herein; 
         FIG. 29B  schematically depicts a recoat assembly compacting build material within the build area, according to one or more embodiments shown and described herein; 
         FIG. 29C  schematically depicts a recoat assembly moving build material to a build area, according to one or more embodiments shown and described herein; 
         FIG. 29D  schematically depicts a recoat assembly moving in a return direction, according to one or more embodiments shown and described herein; and 
         FIG. 30  is a flowchart of a method for drawing build material out of a recoat assembly, according to one or more embodiments shown and described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of additive manufacturing apparatuses, and components thereof, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. One embodiment of an additive manufacturing system  100  is schematically depicted in  FIG. 2A . The additive manifesting system may generally include recoat assemblies for spreading build material in a build area. In embodiments described herein, recoat assemblies include one or more sensors that detect forces acting on the recoat assembly. By detecting forces acting on the recoat assembly, defects may be identified and one or more parameters related to the operation of the recoat assembly may be adjusted to optimize the performance of the recoat assembly. In some embodiments, recoat assemblies described herein may include multiple redundant components, such as rollers and energy sources, such that the recoat assembly may continue operation in the event of failure of one or more components of the recoat assemblies. In some embodiments, recoat assemblies described herein are in fluid communication with a vacuum that acts to collect and contain airborne build material. These and other embodiments of recoat assemblies for additive manufacturing systems, additive manufacturing systems comprising the recoat assemblies, and methods for using the same are described in further detail herein with specific reference to the appended drawings. 
     Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. 
     Directional terms as used herein—for example up, down, right, left, front, back, top, bottom—are made only with reference to the figures as drawn and are not intended to imply ab solute orientation unless otherwise expressly stated. 
     The phrase “communicatively coupled” is used herein to describe the interconnectivity of various components and means that the components are connected either through wires, optical fibers, or wirelessly such that electrical, optical, and/or electromagnetic signals may be exchanged between the components. 
     Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification. 
     As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise. 
     Embodiments described herein are generally directed to recoat assemblies for additive manufacturing systems. Additive manufacturing systems may generally “build” materials through successive deposition and binding of build material. In conventional additive manufacturing systems, deposition of build material is a difficult, dirty, time-consuming, and error-prone process. Embodiments described herein are directed to recoat assemblies that deposit build material in a consistent and configurable manner. 
     Referring now to  FIG. 1 , a conventional additive manufacturing system  10  is schematically depicted. The conventional additive manufacturing apparatus  10  includes a supply platform  30 , a build platform  20 , a cleaning station  11 , and a build head  15 . The supply platform  30  is coupled to a supply platform actuator  32 . The supply platform actuator  32  is actuatable in the vertical direction (i.e., the +/−Z direction of the coordinate axes depicted in the figure) such that the supply platform  30  may be raised or lowered. The build platform  20  is located adjacent to the supply platform  30  and, like the supply platform  30 , is coupled to an actuator, specifically a build platform actuator  22 . The build platform actuator  22  is actuatable in the vertical direction such that the build platform  20  may be raised or lowered. The cleaning station  11  is located adjacent to the supply platform  30  opposite the build platform  20 . That is, the supply platform  30  is located between the cleaning station  11  and the build platform  20  along the working axis of the conventional additive manufacturing apparatus  10  (i.e., an axis extending parallel to the +/−X axis of the coordinate axes depicted in the figure). The build head  15  may be traversed along the working axis of the conventional additive manufacturing apparatus  10  with an actuator (not depicted) such that the build head  15  passes from a home position  12  co-located with the cleaning station  11  over the supply platform  30 , over the build platform  20 , and back again, ultimately returning to the home position  12 . 
     In operation, build material  31 , such as organic or inorganic powder, is positioned on the supply platform  30 . The supply platform  30  is actuated to present a layer of the build material  31  in the path of the build head  15 . The build head  15  is then actuated along the working axis of the conventional additive manufacturing apparatus  10  from the home position  12  towards the build platform  20  in the direction indicated by arrows  40 . As the build head  15  traverses the working axis over the supply platform  30  towards the build platform  20 , the build head  15  distributes the layer of build material  31  in the path of the build head  15  from the supply platform  30  to the build platform  20 . Thereafter, as the build head  15  continues along the working axis over the build platform  20 , the build head  15  deposits a layer of binder material  50  in a predetermined pattern on the layer of build material  31  that has been distributed on the build platform  20 . Optionally, after the binder material  50  is deposited, an energy source within the build head  15  is utilized to cure the deposited binder material  50 . The build head  15  then returns to the home position  12  where at least a portion of the build head  15  is positioned over the cleaning station  11 . While the build head  15  is in the home position  12 , the build head  15  works in conjunction with the cleaning station  11  to provide cleaning and maintenance operations on the elements of the build head  15  which deposit the binder material  50  to ensure the elements are not fouled or otherwise clogged. This ensures that the build head is capable of depositing the binder material  50  in the desired pattern during a subsequent deposition pass. During this maintenance interval, the supply platform  30  is actuated in an upward vertical direction (i.e., in the +Z direction of the coordinate axes depicted in the figure) as indicated by arrow  43  to present a new layer of build material  31  in the path of the build head  15 . The build platform  20  is actuated in the downward vertical direction (i.e., in the −Z direction of the coordinate axes depicted in the figure) as indicated by arrow  42  to prepare the build platform  20  to receive a new layer of build material  31  from the supply platform  30 . The build head  15  is then actuated along the working axis of the conventional additive manufacturing apparatus  10  again to add another layer of build material  31  and binder material  50  to the build platform  20 . This sequence of steps is repeated multiple times to build an object on the build platform  20  in a layer-wise manner. 
     Referring now to  FIG. 2A , an embodiment of an additive manufacturing system  100  is schematically depicted. The system  100  includes a cleaning station  110 , a build area  124 , a supply platform  130 , and an actuator assembly  102 . The actuator assembly  102  comprises, among other elements, a recoat assembly  200  for distributing build material  31  and a print head  150  for depositing binder material  50 . The actuator assembly  102  is constructed to facilitate traversing the recoat assembly  200  and the print head  150  over the working axis of the system  100  independent of one another. This allows for at least some steps of the additive manufacturing process to be performed simultaneously thereby reducing the overall cycle time of the additive manufacturing process to less than the sum of the cycle time for each individual step. In the embodiments of the system  100  described herein, the working axis  116  of the system  100  is parallel to the +/−X axis of the coordinate axes depicted in the figures. It should be understood that the components of the additive manufacturing apparatus  100  traversing the working axis  116 , such as the recoat head  140 , the print head  150 , or the like, need not be centered on the working axis  116 . However, in the embodiments described herein, at least two of the components of the additive manufacturing apparatus  100  are arranged with respect to the working axis  116  such that, as the components traverse the working axis, the components could occupy the same or an overlapping volume along the working axis if not properly controlled. 
     In the embodiments described herein, the cleaning station  110 , the build platform  120 , and the supply platform  130  are positioned in series along the working axis  116  of the system  100  between a print home position  158  of the print head  150  located proximate an end of the working axis  116  in the −X direction, and a recoat home position  148  of the recoat assembly  200  located proximate an end of the working axis  116  in the +X direction. That is, the print home position  158  and the recoat home position  148  are spaced apart from one another in a horizontal direction that is parallel to the +/−X axis of the coordinate axes depicted in the figures and the cleaning station  110 , the build area  124 , and the supply platform  130  are positioned therebetween. In the embodiments described herein, the build area  124  is positioned between the cleaning station  110  and the supply platform  130  along the working axis  116  of the system  100 . 
     The cleaning station  110  is positioned proximate one end of the working axis  116  of the system  100  and is co-located with the print home position  158  where the print head  150  is located or “parked” before and after depositing binder material  50  on a layer of build material  31  positioned on the build area  124 . The cleaning station  110  may include one or more cleaning sections (not shown) to facilitate cleaning the print head  150  between depositing operations. The cleaning sections may include, for example and without limitation, a soaking station containing a cleaning solution for dissolving excess binder material on the print head  150 , a wiping station for removing excess binder material from the print head  150 , a jetting station for purging binder material and cleaning solution from the print head  150 , a park station for maintaining moisture in the nozzles of the print head  150 , or various combinations thereof. The print head  150  may be transitioned between the cleaning sections by the actuator assembly  102 . 
     While reference is made herein to additive manufacturing systems including a print head  150  that dispenses a binder material  50 , it should be understood that recoat assemblies  200  described herein may be utilized with other suitable additive powder-based additive manufacturing systems. For example, in some embodiments, instead of building objects with a cured binder  50  applied to build material  31 , in some embodiments, a laser or other energy source may be applied to the build material  31  to fuse the build material  31 . 
     In the embodiment depicted in  FIG. 2A , the build area  124  comprises a receptacle including a build platform  120 . The build platform  120  is coupled to a build platform actuator  122  to facilitate raising and lowering the build platform  120  relative to the working axis  116  of the system  100  in a vertical direction (i.e., a direction parallel to the +/−Z directions of the coordinate axes depicted in the figures). The build platform actuator  122  may be, for example and without limitation, a mechanical actuator, an electro-mechanical actuator, a pneumatic actuator, a hydraulic actuator, or any other actuator suitable for imparting linear motion to the build platform  120  in a vertical direction. Suitable actuators may include, without limitation, a worm drive actuator, a ball screw actuator, a pneumatic piston, a hydraulic piston, an electro-mechanical linear actuator, or the like. The build platform  120  and build platform actuator  122  are positioned in a build area  124  located below the working axis  116  (i.e., in the −Z direction of the coordinate axes depicted in the figures) of the system  100 . During operation of the system  100 , the build platform  120  is retracted into the build area  124  by action of the build platform actuator  122  after each layer of binder material  50  is deposited on the build material  31  located on build platform  120 . While the build area  124  described and depicted herein includes a receptacle, it should be understood that the build area  124  may include any suitable structure for supporting build material  31 , and may for example include a mere surface supporting the build material  31 . 
     The supply platform  130  is coupled to a supply platform actuator  132  to facilitate raising and lowering the supply platform  130  relative to the working axis  116  of the system  100  in a vertical direction (i.e., a direction parallel to the +/−Z directions of the coordinate axes depicted in the figures). The supply platform actuator  132  may be, for example and without limitation, a mechanical actuator, an electro-mechanical actuator, a pneumatic actuator, a hydraulic actuator, or any other actuator suitable for imparting linear motion to the supply platform  130  in a vertical direction. Suitable actuators may include, without limitation, a worm drive actuator, a ball screw actuator, a pneumatic piston, a hydraulic piston, an electro-mechanical linear actuator, or the like. The supply platform  130  and supply platform actuator  132  are positioned in a supply receptacle  134  located below the working axis  116  (i.e., in the −Z direction of the coordinate axes depicted in the figures) of the system  100 . During operation of the system  100 , the supply platform  130  is raised relative to the supply receptacle  134  and towards the working axis  116  of the system  100  by action of the supply platform actuator  132  after a layer of build material  31  is distributed from the supply platform  130  to the build platform  120 , as will be described in further detail herein. 
     In embodiments, the actuator assembly  102  generally includes a recoat assembly transverse actuator  144 , a print head actuator  154 , a first guide  182 , and a second guide  184 . The recoat assembly transverse actuator  144  is operably coupled to the recoat assembly  200  and is operable to move the recoat assembly  200  relative to the build platform  120  to dispense build material  31  on the build platform  120 , as described in greater detail herein. The print head actuator  154  is operably coupled to the print head  150  and is operable to move the print head  150  and is operable to move the print head  150  relative to the build platform  120  to dispense the binder material  50  on the build platform  120 . 
     In the embodiments described herein, the first guide  182  and the second guide  184  extend in a horizontal direction (i.e., a direction parallel to the +/−X direction of the coordinate axes depicted in the figures) parallel to the working axis  116  of the system  100  and are spaced apart from one another in the vertical direction. When the actuator assembly  102  is positioned over the cleaning station  110 , the build platform  120 , and the supply platform  130  as depicted in  FIG. 2A , the first guide  182  and the second guide  184  extend in a horizontal direction from at least the cleaning station  110  to beyond the supply platform  130 . 
     In one embodiment, such as the embodiment of the actuator assembly  102  depicted in  FIG. 2A , the first guide  182  and the second guide  184  are opposite sides of a rail  180  that extends in a horizontal direction and is oriented such that the first guide  182  is positioned above and spaced apart from the second guide  184 . For example, in one embodiment, the rail  180  has an “I” configuration in vertical cross section (i.e., a cross section in the Y-Z plane of the coordinate axes depicted in the figures) with the upper and lower flanges of the “I” forming the first guide  182  and the second guide  184 , respectively. However, it should be understood that other embodiments are contemplated and possible. For example and without limitation, the first guide  182  and the second guide  184  may be separate structures, such as separate rails, extending in the horizontal direction and spaced apart from one another in the vertical direction. In some embodiments, the first guide  182  and the second guide  184  may be positioned at the same height and spaced apart from one another on opposite sides of the rail  180 . In embodiments, the first guide  182  and the second guide  184  are positioned in any suitable configuration, and may be collinear. 
     In the embodiments described herein, the recoat assembly transverse actuator  144  is coupled to one of the first guide  182  and the second guide  184  and the print head actuator  154  is coupled to the other of the first guide  182  and the second guide  184  such that the recoat assembly transverse actuator  144  and the print head actuator  154  are arranged in a “stacked” configuration. For example, in the embodiment of the actuator assembly  102  depicted in  FIG. 2A , the recoat assembly transverse actuator  144  is coupled to the second guide  184  and the print head actuator  154  is coupled to the first guide  182 . However, it should be understood that, in other embodiments (not depicted) the recoat assembly transverse actuator  144  may be coupled to the first guide  182  and the print head actuator  154  may be coupled to the second guide  184 . 
     In the embodiments described herein, the recoat assembly transverse actuator  144  is bi-directionally actuatable along a recoat motion axis  146  and the print head actuator  154  is bi-directionally actuatable along a print motion axis  156 . That is, the recoat motion axis  146  and the print motion axis  156  define the axes along which the recoat assembly transverse actuator  144  and the print head actuator  154  are actuatable, respectively. The recoat motion axis  146  and the print motion axis  156  extend in a horizontal direction and are parallel with the working axis  116  of the system  100 . In the embodiments described herein, the recoat motion axis  146  and the print motion axis  156  are parallel with one another and spaced apart from one another in the vertical direction due to the stacked configuration of the recoat assembly transverse actuator  144  and the print head actuator  154 . In some embodiments, such as the embodiment of the actuator assembly  102  depicted in  FIG. 2A , the recoat motion axis  146  and the print motion axis  156  are located in the same vertical plane (i.e., a plane parallel to the X-Z plane of the coordinate axes depicted in the figures). However, it should be understood that other embodiments are contemplated and possible, such as embodiments in which the recoat motion axis  146  and the print motion axis  156  are located in different vertical planes. 
     In the embodiments described herein, the recoat assembly transverse actuator  144  and the print head actuator  154  may be, for example and without limitation, mechanical actuators, electro-mechanical actuators, pneumatic actuators, hydraulic actuators, or any other actuator suitable for providing linear motion. Suitable actuators may include, without limitation, worm drive actuators, ball screw actuators, pneumatic pistons, hydraulic pistons, electro-mechanical linear actuators, or the like. In one particular embodiment, the recoat assembly transverse actuator  144  and the print head actuator  154  are linear actuators manufactured by Aerotech® Inc of Pittsburgh, Pa., such as the PRO225LM Mechanical Bearing, Linear Motor Stage. 
     In embodiments, the recoat head actuator  144  and the print head actuator  154  may each be a cohesive sub-system that is affixed to the rail  180 , such as when the recoat head actuator  144  and the print head actuator  154  are PRO225LM Mechanical Bearing, Linear Motor Stages, for example. However, it should be understood that other embodiments are contemplated and possible, such as embodiments where the recoat head actuator  144  and the print head actuator  154  comprise multiple components that are individually assembled onto the rail  180  to form the recoat head actuator  144  and the print head actuator  154 , respectively. 
     Still referring to  FIG. 2A , the recoat assembly  200  is coupled to the recoat assembly transverse actuator  144  such that the recoat assembly  200  is positioned below (i.e., in the −Z direction of the coordinate axes depicted in the figures) the first guide  182  and the second guide  184 . When the actuator assembly  102  is positioned over the cleaning station  110 , the build platform  120 , and the supply platform  130  as depicted in  FIG. 2A , the recoat assembly  200  is situated on the working axis  116  of the system  100 . Thus, bi-directional actuation of the recoat assembly transverse actuator  144  along the recoat motion axis  146  affects bi-directional motion of the recoat assembly  200  on the working axis  116  of the system  100 . In the embodiment of the actuator assembly  102  depicted in  FIG. 2A , the recoat assembly  200  is coupled to the recoat assembly transverse actuator  144  with support bracket  176  such that the recoat assembly  200  is positioned on the working axis  116  of the system  100  while still providing clearance between rail  180  of the actuator assembly  102  and the build platform  120  and the supply platform  130 . In some embodiments described herein, the recoat assembly  200  may be fixed in directions orthogonal to the recoat motion axis  146  and the working axis  116  (i.e., fixed along the +/−Z axis and/or fixed along the +/−Y axis). 
     Similarly, the print head  150  is coupled to the print head actuator  154  such that the print head  150  is positioned below (i.e., in the −Z direction of the coordinate axes depicted in the figures) the first guide  182  and the second guide  184 . When the actuator assembly  102  is positioned over the cleaning station  110 , the build platform  120 , and the supply platform  130  as depicted in  FIG. 2A , the print head  150  is situated on the working axis  116  of the system  100 . Thus, bi-directional actuation of the print head actuator  154  along the print motion axis  156  affects bi-directional motion of the print head  150  on the working axis  116  of the system  100 . In the embodiment of the actuator assembly  102  depicted in  FIG. 2A , the print head  150  is coupled to the print head actuator  154  with support bracket  174  such that the print head  150  is positioned on the working axis  116  of the system  100  while still providing clearance between rail  180  of the actuator assembly  102  and the build platform  120  and the supply platform  130 . In some embodiments described herein, the print head  150  may be fixed in directions orthogonal to the print motion axis  156  and the working axis  116  (i.e., fixed along the +/−Z axis and/or fixed along the +/−Y axis). 
     While  FIG. 2A  schematically depicts an embodiment of an actuator assembly  102  which comprises a first guide  182  and a second guide  184  with the recoat assembly transverse actuator  144  and the print head actuator  154  mounted thereto, respectively, it should be understood that other embodiments are contemplated and possible, such as embodiments which comprise more than two guides and more than two actuators. It should also be understood that other embodiments are contemplated and possible, such as embodiments which comprise the print head and the recoat assembly  200  on the same actuator. 
     Referring to  FIG. 2B , in some embodiments, the additive manufacturing system  100  comprises a cleaning station  110 , and a build area  124 , as described herein with respect to  FIG. 2A . However, in the embodiment depicted in  FIG. 2B , the additive manufacturing system does not include a supply receptacle. Instead, the system comprises a build material hopper  360  that is used to supply build material  31  to the build area  124 . In this embodiment, the build material hopper  360  is coupled to the recoat assembly transverse actuator  144  such that the build material hopper  360  traverses along the recoat motion axis  146  with the with the recoat assembly  200 . In the embodiment depicted in  FIG. 2B , the build material hopper  360  is coupled to the support bracket  176  with, for example, bracket  361 . However, it should be understood that the build material hopper  360  may be directly coupled to the support bracket  176  without an intermediate bracket. Alternatively, the build material hopper  360  may be coupled to the recoat assembly  200  either directly or with an intermediate bracket. 
     The build material hopper  360  may include an electrically actuated valve (not depicted) to release build material  31  onto the build area  124  as the build material hopper  360  traverses over the build area  124 . In embodiments, the valve may be communicatively coupled to an electronic control unit  300  ( FIG. 24 ) which executes computer readable and executable instructions to open and close the valve based on the location of the build material hopper  360  with respect to the build area. The build material  31  released onto the build area  124  is then distributed over the build area with the recoat assembly  200  as the recoat assembly  200  traverses over the build area  124 . 
     Referring to  FIG. 2C , to form an object layers of build material  31 AA- 31 DD may be sequentially positioned on top of one another. In the example provided in  FIG. 2C , sequential layers of binder  50 AA- 50 CC are positioned on the layers of build material  31 AA- 31 DD. By curing the layers of binder  50 AA- 50 CC, a finished product may be formed. 
     Referring to  FIG. 3 , a perspective view of one embodiment of the recoat assembly  200  is schematically depicted. In embodiments, the recoat assembly  200  may include one or more housings  222 ,  224  that at least partially encapsulate a portion of the recoat assembly  200 . The recoat assembly  200  includes the recoat assembly transverse actuator  144  that moves the recoat assembly  200  in the lateral direction (i.e., in the X-direction as depicted). In some embodiments, the recoat assembly  200  further includes a recoat assembly vertical actuator  160  that moves the recoat assembly  200  in the vertical direction (i.e., in the Z-direction as depicted). 
     In some embodiments, the recoat assembly  200  includes a base member  250 , and the recoat assembly transverse actuator  144  is coupled to the base member  250 , moving the base member  250  in the lateral direction (i.e., in the X-direction as depicted). As referred to herein the base member  250  may include any suitable structure of the recoat assembly  200  coupled to the recoat assembly transverse actuator  144 , and may include a housing, a plate, or the like. In the embodiment depicted in  FIGS. 3 and 4 , the recoat assembly  200  further includes at least one tilt actuator  164  that is operable to tilt the base member  250  of the recoat assembly  200  (e.g., about an axis extending in the X-direction as depicted in  FIG. 4 ). As described in greater detail herein, in embodiments, the tilt actuator  164  may tilt the base member  250  of the recoat assembly  200 . In embodiments, the tilt actuator  164  may also tilt the base member  250  to provide access to an underside of the recoat assembly  200  such that maintenance may be performed on the recoat assembly  200 . 
     Referring to  FIGS. 3 and 5 , in some embodiments, the recoat assembly  200  further includes a base member rotational actuator  162  coupled to the base member  250 . The base member rotational actuator  162  is operable to rotate the base member  250  about an axis extending in the vertical direction (e.g., in the Z-direction as depicted). In embodiments, the base member rotational actuator  162  and the tilt actuator  164  may include any suitable actuators, for example and without limitation, a worm drive actuator, a ball screw actuator, a pneumatic piston, a hydraulic piston, an electro-mechanical linear actuator, or the like. 
     In some embodiments and referring to  FIGS. 4 and 6A , the recoat assembly  200  may include a tilt locking member  161  that is selectively engagable with the base member  250 . For example, the tilt locking member  161  may selectively restrict movement of the base member  250  about the X-axis shown in  FIG. 4 . By selectively restricting movement of the base member  250 , the orientation of the base member  250  can be maintained without the application of force by the tilt actuator  164 . In this way, the base member  250  can be maintained in a tilted position as shown in  FIG. 4  while maintenance is performed on the recoat assembly  200  without requiring the application of energy to the tilt actuator  164 . In some embodiments, the recoat assembly  200  further includes a first rotational locking member  163  and/or a second rotational locking member  165 . The first rotational locking member  163  and/or the second rotational locking member  165  may selectively restrict movement of the base member  250  about the Z-axis depicted in  FIG. 4 . In embodiments, the recoat assembly  200  includes a powder spreading member, such as one or more rollers, that distribute build material  31  ( FIG. 2A ). 
     For example and referring to  FIGS. 6B and 6C , a side view of the recoat assembly  200  and a view of rollers  202 ,  204  of the recoat assembly  200  are depicted, respectively. In embodiments, the recoat assembly  200  includes a first roller support  210 , a second roller support  212 , and a first roller  202  disposed between and supported by the first roller support  210  and the second roller support  212 . In the embodiment depicted in  FIGS. 6B and 6C , the recoat assembly  200  further includes a third roller support  216 , a fourth roller support  218 , and a second roller  204  disposed between and supported by the third roller support  216  and the fourth roller support  218 . In embodiments, the second roller  204  is positioned rearward of the first roller  202  (i.e., in the −X-direction as depicted). In these embodiments, the first roller  202  may generally be referred to as the “front” roller, and the second roller  204  may be referred to as the “rear” roller. 
     In embodiments, the recoat assembly  200  includes a roller vertical actuator  252  that is coupled to the first roller  202  and/or the second roller  204 . The roller vertical actuator  252  is operable to move the first roller  202  and/or the second roller  204  with respect to the base member  250  in the vertical direction (i.e., in the Z-direction as depicted). In some embodiments, the vertical actuator  252  is coupled to the front roller  202  and the rear roller  204  such that the front roller  202  and the rear roller  204  are moveable with respect to the base member  250  independently of one another. In some embodiments, the roller vertical actuator  252  is a first roller vertical actuator  252  coupled to the first roller  202 , and the recoat assembly  200  further includes a second roller vertical actuator  254  coupled to the second roller  204 , such that the front roller  202  and the rear roller  204  are moveable with respect to the base member  250  independently of one another. The first and second roller vertical actuators  252 ,  254  may include any suitable actuators, for example and without limitation, pneumatic actuators, motors, hydraulic actuators, or the like. 
     The recoat assembly  200  further includes a first rotational actuator  206  coupled to the first roller  202  as best shown in  FIG. 11B . In some embodiments, the first rotational actuator  206  is spaced apart from the first roller  202 , and may be coupled to the first roller  202  through a belt, a chain, or the like. In embodiments in which the recoat assembly  200  includes the second roller  204 , the recoat assembly  200  may include a second rotational actuator  208 , best shown in  FIG. 11B , coupled to the second roller  204 . In some embodiments, the second rotational actuator  208  is spaced apart from the second roller  204 , and may be coupled to the second roller  204  through a belt, a chain, or the like. In some embodiments, the recoat assembly  200  may include a single rotational actuator coupled to both the first roller  202  and the second roller  204 . In some embodiments, the first rotational actuator  206  is directly coupled to the first roller  202  and/or the second rotational actuator  208  is directly coupled to the second roller  204 . 
     The first rotational actuator  206  is configured to rotate the rotate the first roller  202  about a first rotation axis  226 . Similarly, the second rotational actuator  208  is configured to rotate the second roller  204  about a second rotation axis  228 . In the embodiment depicted in  FIG. 6C , the first rotation axis  226  and the second rotation axis  228  are generally parallel to one another and are spaced apart from one another in the X-direction as depicted. As described in greater detail herein, the first roller  202  and the second roller  204  may be rotated in a “rotation direction” (e.g., a clockwise direction from the perspective shown in  FIG. 6C ) and/or a “counter-rotation direction” that is the opposite of the rotation direction (e.g., a counter-clockwise direction from the perspective shown in  FIG. 6C ). The first and second roller  202 ,  204  can be rotated in the same direction or may be rotated in opposite directions from one another. The first and second rotational actuators  206 ,  208  may include any suitable actuator for inducing rotation of the first and second rollers  202 ,  204 , such as and without limitation, alternating current (AC) or direct current (DC) brushless motors, linear motors, servo motors, stepper motors, pneumatic actuators, hydraulic actuators, or the like. 
     In embodiments, the recoat assembly  200  includes one or more sensors mechanically coupled to the roller supports  210 ,  212 ,  216 , and/or  218 , the one or more sensors configured to output a signal indicative of forces incident on the roller supports  210 ,  212 ,  216 , and/or  218  via the first roller  202  and/or the second roller  204 . 
     For example and referring to  FIGS. 7A-7C , in embodiments, a strain gauge  240 A is mechanically coupled to the first roller support  210 . In some embodiments, the strain gauge  240 A is a first strain gauge  240 A, and a second strain gauge  240 B is mechanically coupled to the first roller support  210 . While reference is made herein to the strain gauges  240 A,  240 B being mechanically coupled to the first roller support  210 , it should be understood that one or more strain gauges may be coupled to any or all of the first, second, third, and fourth roller supports  210 ,  212 ,  216 ,  218 . 
     In embodiments, the roller supports  210 ,  212 ,  216 , and/or  218  define one or more flexures  214  to which the strain gauges  240 A,  240 B are coupled. The strain gauges  240 A,  240 B are configured to detect elastic deformation of the flexures  214 , which may generally correlate to forces acting on the roller supports  210 ,  212 ,  216 , and/or  218 . In the depicted embodiment, the flexures  214  are walls of a cavity extending through the roller supports  210 ,  212 ,  216 , and/or  218 , however, it should be understood that the flexures  214  may include any suitable portion of the roller supports  210 ,  212 ,  216 , and/or  218  that elastically deform such that strain of the flexures  214  may be determined. 
     In embodiments, the strain gauges  240 A,  240 B are oriented in order to measure a strain. For example, in the embodiment depicted in  FIGS. 7A and 7B , the strain gauges  240 A,  240 B are oriented in the vertical direction (i.e., in the Z-direction as depicted and transverse to the first rotation axis  226 ), and measure a strain in a resultant vector at some angle between the horizontal (X-axis) and the vertical (Z-axis) direction. By measuring strain in the resultant vector direction, normal forces, i.e., forces acting on the roller supports  210 ,  212 ,  216 , and/or  218  in a direction transverse to a coating direction, can be determined. For example, forces normal to the X-direction and Z-direction may be imparted on the roller supports  210 ,  212 ,  216 , and/or  218  by build material  31  ( FIG. 2A ) distributed by the recoat assembly  200 , and/or by cured binder  50  ( FIG. 2A ), as the recoat assembly  200  moves build material  31  over build area  124  to cover the build material  31  ( FIG. 2 ) and/or cured binder  50  with a layer of build material  31 . One or more parameters of the operation of the recoat assembly  200  may be changed to reduce normal forces acting on the roller supports  210 ,  212 ,  216 , and/or  218  to maintain the structural integrity of build material  31  bound by the cured binder  50  ( FIG. 2C ) positioned beneath build material  31 , as described in greater detail herein. 
     Referring to  FIG. 8 , in some embodiments, one or both of the strain gauges  240 A,  240 B are oriented in a horizontal direction (i.e., in the X-direction as depicted and transverse to the first rotation axis  226 ), and may measure a strain in a resultant vector at some angle between the horizontal (X-axis) and the vertical (Z-axis) direction. In some embodiments, the strain gauges  240 A,  240 B may be oriented in the horizontal direction on the first and second roller supports  210 ,  212 , while the strain gauges  240 A,  240 B may be oriented in the vertical direction, as depicted in  FIGS. 7A-7B , on the third and fourth roller supports  216 ,  218 . By measuring strain in the horizontal direction (i.e., in the X-direction as depicted), shear forces, i.e., forces acting on the roller supports  210 ,  212 ,  216 , and/or  218  in a direction corresponding to a coating direction, can be determined. For example, shear forces may be imparted on the roller supports  210 ,  212 ,  216 , and/or  218  by build material  31  ( FIG. 2A ) distributed by the recoat assembly  200 , and/or by build material  31  bound by cured binder  50  ( FIG. 2A ) as the recoat assembly  200  moves to the build area  124  to cover a previous layer the build material  31  bound by cured binder  50  and/or the build material  31  with another layer of build material  31 . One or more parameters of the operation of the recoat assembly  200  may be changed to reduce shear forces acting on the roller supports  210 ,  212 ,  216 , and/or  218  to maintain the structural integrity of the build material  31  bound by cured binder  50  ( FIG. 2A ), as described in greater detail herein. As described in greater detail herein, determined forces can also be utilized in open-loop (i.e., feedforward) control of the recoat assembly  200  and/or closed-loop (i.e., feedback) control of the recoat assembly  200 . For example, in embodiments, determined forces may be compared to a lookup table of desired forces, and one or more parameters of the operation of the recoat assembly  200  may be changed based on the comparison of the determined forces as compared to the desired forces. In embodiments, the forces acting on the roller supports  210 ,  212 ,  216 , and/or  218  may depend on any of a number of factors, including but not limited to, a layer thickness of the build material  31  ( FIG. 2A ), a traverse speed of the recoat assembly  200  ( FIG. 2A ), the direction and rotational speed of the first and/or second roller  202 ,  204  ( FIG. 6C ), on the type/composition of build material  31  ( FIG. 2A ), the particle size of the build material  31  ( FIG. 2A ), the type/composition of the binder  50  ( FIG. 2A ), the volume (or saturation) of binder material  50  ( FIG. 2A ), on if and how the binder is partially or fully cured in situ, on the geometry of the component being built, etc. 
     In some embodiments, information related to a current layer of the object being built and/or a prior layer may be utilized to generate an expected force or pressure curve to be experienced as the recoat assembly  200  traverses the build area  124 . In some embodiments, a geometry of the current layer of the object being built or a geometry of the immediately preceding layer that was built may be used to determine an expected pressure or force profile (e.g., shear forces expected to be experienced as the recoat assembly  200  traverses the build area  124  to distribute material for the current layer, normal forces expected to be experienced as the recoat assembly  200  traverses the build area  124  to distribute material for the current layer and/or any other type of expected force to be experienced as the recoat assembly  200  traverses the build area  124  to distribute material for the current layer), output signals from the one or more sensors coupled to the roller supports (e.g., one or more strain gauges and/or one or more load cells) may be used to calculate a measured force or pressure as the recoat assembly  200  traverses the build area  124  to distribute material for the current layer, a comparison between the expected pressure or measured force profile and the measured force or pressure may be made, and an action may be taken in response to the comparison. In some embodiments, a lookup table containing expected force or pressure information may be previously generated, such as based on calibration force measurements generated under various conditions (e.g., size of build area coated with binder, recoat traverse speed, recoat roller rotation speed, layer thickness, recoat roller geometry coating, and the like). For example, in some embodiments, when an expected pressure or force deviates from a measured pressure or force during spreading of material for a current layer by the recoat assembly  200 , the printing recoat process may be determined to be defective. The extent of force deviation may be used to determine a type of defect (e.g., a powder defect, a recoat roller defect, insufficient binder cure, a jetting defect, or the like). When a deviation beyond a given threshold is determined to have occurred, a corrective action may be taken, such as to adjust a recoat traverse speed for the current layer, adjust a roller rotation speed for the current layer, adjust a recoat traverse speed for one or more subsequent layers, adjust a roller rotation speed for one or more subsequent layers, adjust a height of one or more rollers for the current layer and/or for one or more subsequent layers, etc. Such measurements, comparisons, and control actions may be implemented by the electronic control unit  300  executing one or more instructions stored in its memory component. 
     In some embodiments, the one or more sensors mechanically coupled to the roller supports  210 ,  212 ,  216 , and/or  218  may include a load cell. 
     For example and referring to  FIGS. 9A-9D , in embodiments a load cell  242  is mechanically coupled to the first roller support  210 , and is configured to measure a force in the vertical direction (i.e., in the Z-direction as depicted and transverse to the first rotation axis  226 ). As shown in  FIG. 9C , in some embodiments, a set screw  246  may engage the load cell  242  to calibrate the load cell  242 , for example, by applying a known amount of force to the load cell  242 . 
     Referring to  FIG. 10 , in some embodiments, the first roller support  210  may include both the load cell  242  and the strain gauges  240 A,  240 B. While in the embodiment depicted in  FIG. 10 , the strain gauges  240 A,  240 B are oriented in the horizontal direction, it should be understood that one or both of the strain gauges  240 A,  240 B may be oriented in the vertical direction. 
     In some embodiments, an accelerometer  244  is coupled to the first roller support  210 . While in the embodiment depicted in  FIG. 10 , the load cell  242 , the strain gauges  240 A,  240 B, and the accelerometer  244  are coupled to the first roller support  210 , it should be understood that in some embodiments, only the accelerometer  244  may be mechanically coupled to the first roller support  210 . In some embodiments, the accelerometer  244  is coupled to the first roller support  210  along with any combination of the load cell  242 , the strain gauge  240 A, and/or the strain gauge  240 B. Furthermore, the accelerometer  244  may be coupled to any of the roller supports  210 ,  212 ,  216 , and/or  218 . 
     In some embodiments, a roller support temperature sensor  247  is coupled to the first roller support  210 . The roller support temperature sensor  247  is operable to detect a temperature of the roller support  210 , which may be utilized to calibrate and/or compensate for a load cell reading from the load cell  242 . While in the embodiment depicted in  FIG. 10 , the load cell  242 , the strain gauges  240 A,  240 B, the accelerometer  244 , and the roller support temperature sensor  247  are coupled to the first roller support  210 , it should be understood that in some embodiments, only the roller support temperature sensor  247  may be mechanically coupled to the first roller support  210 . In some embodiments, the roller support temperature sensor  247  is coupled to the first roller support  210  along with any combination of the load cell  242 , the strain gauge  240 A, the strain gauge  240 B, and/or the accelerometer  244 . Furthermore, the roller support temperature sensor  247  may be coupled to any of the roller supports  210 ,  212 ,  216 , and/or  218 . 
     Referring to  FIG. 11A , in some embodiments, the recoat assembly  200  generally includes a front energy source  260  coupled to the base member  250  and positioned forward of the front roller  202  (i.e., in the +X-direction as depicted). The recoat assembly  200 , in the embodiment depicted in  FIG. 11A , further includes a rear energy source  262  coupled to the base member  250  and positioned rearward of the rear roller  204  (i.e., in the −X-direction as depicted). The front energy source  260  generally emits energy forward of the front roller  202 , and the rear energy source  262  emits energy rearward of the rear roller  204 . In embodiments, the front and rear energy sources  260 ,  262  may generally emit electromagnetic radiation, such as infrared radiation, ultraviolet radiation, or the like. In some embodiments, the front and rear energy sources  260 ,  262  may emit energy, which may act to heat build material  31  ( FIG. 2A ) and/or cure binder material  50  ( FIG. 2A ) on the build material  31 , as described in greater detail herein. While in the embodiment depicted in  FIG. 11A , the front energy source  260  is positioned forward of the front roller  202  and the rear energy source  262  is positioned rearward of the rear roller  204 , it should be understood that this is merely an example. For example in some embodiments, the front energy source  260  and the rear energy source  262  may both be positioned forward of the front roller  202 , as shown in  FIG. 6A , or the front energy source  260  and the rear energy source  262  may both be positioned rearward of the front roller  202  and the rear roller  204 . By including multiple energy sources (e.g., the front energy source  260  and the rear energy source  262 ), energy can be applied to build material  31  ( FIG. 1A ) over a comparatively longer period of time as compared to the application of energy via a single energy source. In this way, over-cure of build material  31  bound by cured binder  50  can be minimized. While in the embodiment depicted in  FIG. 11A , a front energy source  262  and a rear energy source  262  are depicted, it should be understood that embodiments described herein can include any suitable number of energy sources positioned in any suitable manner forward and rearward of the front roller  202  and the rear roller  204 . Referring to  FIGS. 11B-11D , in some embodiments, the recoat assembly  200  includes one or more hard stops  410  coupled to the base member  250 . While a single hard stop  410  is shown in the section views depicted in  FIGS. 11C and 11D , it should be understood that each of the hard stops  410  may be identical. Moreover, although in the embodiment depicted in  FIG. 11B  the recoat assembly  200  includes two hard stops  410 , it should be understood that the recoat assembly  200  may include a single hard stop  410  or any suitable number of hard stops  410 . 
     The hard stops  410  may assist in limiting movement of the first roller  202  and/or the second roller  204  about the Y-axis as depicted, for example, as a result of actuation of the roller vertical actuator  252 . For example and referring particularly to  FIGS. 11A, 11C, and 21 , in some embodiments, the roller vertical actuator  252  is coupled to a pivoting portion  249  of the base member  250  that is movable with respect to a stationary portion  251  of the base member  250  about the Y-axis as depicted. The first roller  202  and the second roller  204  may be coupled to the pivoting portion  249 , such that movement of the pivoting portion  249  about the Y-axis results in movement of the first roller  202  and/or the second roller  204  about the Y-axis as depicted. 
     In embodiments, the hard stop  410  includes a coupling portion  414  that is coupled to the pivoting portion  249  of the base member  250 , and a post portion  412  that is movably engaged with the stationary portion  251  of the base member  250 . For example, the post portion  412  of the hard stop  410  may be movable with respect to the stationary portion  251  in a vertical direction (e.g., in the Z-direction as depicted). Movement of the post portion  412  of the hard stop  410  in the vertical direction (e.g., in the Z-direction as depicted) may be restricted. For example, a nut  420  may be adjustably engaged with the post portion  412 , and may restrict movement of the post portion  412  with respect to the stationary portion  251  of the base member  250 . Because the coupling portion  414  of the hard stop  410  is coupled to the pivoting portion  249  of the base member  250 , restriction of the movement of the post portion  412  of the hard stop  410  with respect to the stationary portion  251  thereby restricts movement of the pivoting portion  249  with respect to the stationary portion  251  in the vertical direction (e.g., in the Z-direction as depicted). In some embodiments, the nut  420  is adjustable on the post portion  412  in the Z-direction as depicted. By moving the nut  420  along the post portion  412  in the Z-direction, the freedom of movement of the pivoting portion  249  of the base member  250 , and accordingly the first roller  202  and/or the second roller  204 , with respect to the stationary portion  251  of the base member  250  can be adjusted. Through the hard stop  410 , movement of the pivoting portion  249  of the base member  250 , and accordingly the first roller  202  and/or the second roller  204 , via actuation of the roller vertical actuator  250  can be precisely tuned as desired. While in the embodiment depicted in  FIGS. 11C and 11D  the hard stop  410  includes the nut  420  that limits movement of the hard stop  410 , it should be understood that this is merely an example. For example, in some embodiments, the movement of the hard stop  410  may be limited by a manual micrometer, one or more motors, or the like. For example and as best shown in  FIG. 16B , in some embodiments, the recoat assembly may include multiple hard stops  410  that limit movement of the first roller  202  and the second roller about the Y-axis as depicted. The hard stops  410  may include micrometers for moving a position of the hard stops  410 . In some embodiments, the hard stops  410  may further include a load cell for detecting a position of the hard stop  410 . 
     In some embodiments, the post portion  412  of the hard stop  410  extends through an aperture  253  extending through the stationary portion  251  of the base member  250 . In some embodiments, the recoat assembly  200  includes a dust shield  430  that at least partially encapsulates the aperture  253  and/or at least a portion of the hard stop  410 . For example in the embodiment depicted in  FIGS. 11C and 11D , the dust shield  430  includes an upper portion  432  that at least partially covers an upper opening of the aperture  253  and the post portion  414  of the hard stop  410 , and a lower portion  434  that at least partially covers a lower opening of the aperture  253 . The dust shield  430  may further include a lower biasing member  436  that biases the lower portion  434  of the dust shield  430  into engagement with the aperture  253 . The dust shield  430  may further include an upper biasing member  438  that biases the upper portion  432  of the dust shield  430  into engagement with the aperture  253 . By at least partially enclosing the aperture  253 , the dust shield  430  may assist in preventing build material  31  ( FIG. 1 ) from entering the aperture  253  and interfering with movement of the post portion  412  of the hard stop  410  through the aperture  253 . Further, in embodiments, the lower biasing member  436  and/or the upper biasing member  438  may at least partially offset tension resulting from a connection between the first rotational actuator  206  and the first roller  202  and/or between the second rotational actuator  208  and the second roller  204 . For example, as shown in  FIG. 11B , the first rotational actuator  206  may be coupled to the first roller  202  via a belt. Similarly, the second rotational actuator  208  may be coupled to the second roller  204  via a belt. Tension in the belts may cause movement of the first roller  202  and/or the second roller  204  in the Z-direction as depcited. This movement may be opposed by the lower biasing member  436  and/or the upper biasing member  438 , thereby stabilizing the position of the first roller  202  and/or the second roller  204  in the Z-direction as depicted. 
     Referring to  FIG. 11E , a lower perspective view of the recoat assembly  200  is schematically depicted. In some embodiments, the recoat assembly  200  includes a powder guide  450  pivotally coupled to the base member  250  of the recoat assembly  200  at a pivot point  452 . The powder guide  450  may be pivotable with respect to the base member  250  about the Y-axis as depicted. By pivoting with respect to the base member  250  about the Y-axis, the powder guide  450  may maintain contact with the build platform  20  ( FIG. 1 ) and/or the supply platform  30  ( FIG. 1 ) as the rollers  202 ,  204  move in the Z-direction as depicted. The powder guide  450  may assist in restricting the flow of build material  31  ( FIG. 1 ) in the Y-direction away from recoat assembly  200 . 
     Referring to  FIGS. 11A and 12 , in some embodiments, the front energy source  260  and the rear energy source  262  are each positioned at least partially within an energy source housing  264 . The energy source housings  264  can, in some embodiments, focus energy emitted by the front energy source  260  and the rear energy source  262 , and may include a reflective interior surface or the like. 
     In some embodiments, the recoat assembly  200  includes one or more housing temperature sensors  266 . In the embodiment depicted in  FIG. 12 , the recoat assembly  200  includes a housing temperature sensor  266  coupled to the energy source housing  264  of the front energy source  260 , and a housing temperature sensor  266  coupled to the energy source housing  264  of the front energy source  262 . In embodiments, the housing temperature sensors  266  are configured to detect a temperature of the respective front and rear energy sources  260 ,  262  and/or the energy source housings  264 . The energy emitted by the front and rear energy sources  260 ,  262  may be controlled based at least in part on the detected temperature of the front and rear energy sources  260 ,  262  and/or the energy source housings  264 , so as to prevent damage to the front and rear energy sources  260 ,  262  and/or the energy source housings  264  and/or to ensure that appropriate energy is applied to the build material  31 . 
     In some embodiments, the recoat assembly  200  includes one or more housing engagement members  257  positioned at outboard ends of the recoat assembly  200  and engaged with a housing of the additive manufacturing system  100 . The housing engagement members  257  are generally configured to engage and “plow” or “scrape” build material  31  off of the sides of the additive manufacturing system  100 . In embodiments, the housing engagement members  257  may include any structure suitable, such as brushes, blades, or the like. 
     Referring to  FIG. 12 , a side view of the recoat assembly  200  is schematically depicted. In embodiments, the front roller  202  has a front roller diameter d 1 , and the rear roller  204  has a rear roller diameter d 2 . In some embodiments, the front roller diameter d 1  is different from the rear roller diameter d 2 . For example, in some embodiments, the front roller diameter d 1  is less than the rear roller diameter d 2 . In embodiments, the front roller diameter d 1  is between 20 millimeters and 25 millimeters, inclusive of the endpoints. In some embodiments, the front roller diameter d 1  is between 10 millimeters and 40 millimeters, inclusive of the endpoints. In some embodiments, the front roller diameter d 1  is less than about 22.23 millimeters. As described in greater detail herein, a relatively small diameter may assist the front roller  202  in fluidizing build material  31  to distribute the build material  31 . In embodiments, the rear roller diameter d 2  is between 35 millimeters and 40 millimeters, inclusive of the endpoints. In embodiments, the rear roller diameter d 2  is between 20 millimeters and 60 millimeters, inclusive of the endpoints. In some embodiments, the rear roller diameter d 2  is greater than about 38.1 millimeters. As described in greater detail herein, a relatively large diameter may assist the rear roller  204  in compacting build material  31 . 
     In some embodiments, the recoat assembly  200  includes a powder engaging member  255  coupled to the base member  250  ( FIG. 11A ) and positioned forward of the front roller  202 . In embodiments, the powder engaging member  255  is positioned at a height evaluated in the vertical direction (i.e., in the Z-direction as depicted) that is within a roller window Rw defined by the front roller  202 . The powder engaging member  255  may be a “doctor” blade that generally acts to plow and clear build material  31  forward of the front roller  202 , thereby minimizing a height of build material  31  contacted by the front roller  202 . While in the depicted embodiment, the recoat assembly  200  includes the powder engaging member  255  and the front and rear rollers  202 ,  204 , it should be understood that in some embodiments, the recoat assembly  200  may include only the powder engaging member  255  to spread build material  31 . While in the embodiment depicted in  FIG. 12 , the powder engaging member  255  is positioned forward of the front roller  202 , embodiments described herein may include a single or multiple powder engaging members positioned forward of the front roller  202  and/or rearward of the rear roller  204 . 
     In some embodiments, the recoat assembly  200  includes multiple front rollers  202  and/or multiple rear rollers  204 . 
     For example and referring to  FIG. 13 , a top view of one configuration of front rollers  202 A,  202 B and rear rollers  204 A,  204 B is schematically depicted. In the embodiment depicted in  FIG. 13 , the recoat assembly  200  includes a first front roller  202 A and a second front roller  202 B that is spaced apart from the first front roller  202 A in the lateral direction (i.e., in the Y-direction as depicted). In the embodiment depicted in  FIG. 13 , the recoat assembly  200  further includes a first rear roller  204 A and a second rear roller  204 B spaced apart from the first rear roller  204 A in the lateral direction (i.e., in the Y-direction as depicted). While the embodiment depicted in  FIG. 13  includes the two front rollers  202 A,  202 B and two rear rollers  204 A,  204 B, it should be understood that the recoat assembly  200  may include any suitable number of front rollers spaced apart from one another in the lateral direction (i.e., in the Y-direction as depicted), and any suitable number of rear rollers spaced apart from one another in the lateral direction. In some embodiments, the recoat assembly  200  may include the two front rollers  202 A,  202 B, and a single rear roller, or the two rear rollers  204 A,  204 B with a single front roller. By including multiple front rollers  202 A,  202 B, aligned with one another in the lateral direction (i.e., in the Y-direction as depicted), and/or by including multiple rear rollers  204 A,  204 B aligned with one another in the lateral direction, the recoat assembly  200  may extend a greater distance in the lateral direction, as compared to recoat assemblies including a single front roller and a single rear roller. As an example and without being bound by theory, the longer a roller extends in the lateral direction (i.e., in the Y-direction as depicted), the more susceptible the roller may be to elastic and/or inelastic deformation due to forces acting on the roller. Accordingly, the width of recoat assemblies including a single front roller and a single rear roller may be effectively limited, which may limit the size of objects that may be built by the additive manufacturing system  100 . However, by including multiple front rollers  202 A,  202 B, aligned with one another in the lateral direction (i.e., in the Y-direction as depicted), and/or by including multiple rear rollers  204 A,  204 B aligned with one another in the lateral direction, the recoat assembly  200  may extend a greater distance in the lateral direction. 
     Referring to  FIG. 14 , in some embodiments, the front rollers  202 A,  202 B overlap one another in the lateral direction (i.e., in the Y-direction as depicted). In embodiments in which the recoat assembly  200  includes the two rear rollers  204 A,  204 B, the two rear rollers may similarly overlap one another in the lateral direction (i.e., in the Y-direction as depicted). By overlapping the front rollers  202 A,  202 B and/or the rear rollers  204 A,  204 B in the lateral direction (i.e., in the Y-direction as depicted), the front rollers  202 A,  202 B and/or the rear rollers  204 A,  204 B may prevent build material  31  ( FIG. 12 ) from passing between adjacent front rollers  202 A,  202 B and/or adjacent rear rollers  204 A,  204 B. 
     Referring to  FIG. 15 , in some embodiments, rollers are positioned to extend across gaps defined by adjacent rollers. For example, in the embodiment depicted in  FIG. 15 , the recoat assembly  200  includes three front rollers  202 A,  202 B, and  202 C, wherein adjacent front rollers  202 A,  202 B define a gap G 1  positioned between the rollers  202 A,  202 B in the lateral direction (i.e., in the Y-direction as depicted), and adjacent front rollers  202 B,  202 C define a gap G 2  positioned between the rollers  202 B,  202 C in the lateral direction. The recoat assembly  200  includes a rear roller  204 A extending between the adjacent front rollers  202 A,  202 B, and rear roller  204 B extending between the adjacent front rollers  202 B,  202 C. In particular, the rear roller  204 A extends across the gap G 1  between the adjacent front rollers  202 A,  202 B, and the rear roller  204 B extends across the gap G 2  between the adjacent front rollers  202 B,  202 C. By extending across the gaps G 1 , G 2 , the rear rollers  204 A,  204 B may engage build material  31  ( FIG. 12 ) that passes through the gaps G 1 , G 2 . 
     Referring to  FIG. 16A , in some embodiments, the recoat assembly  200  includes a cleaning member  270 . In embodiments, the cleaning member  270  that is selectively engagable with at least one roller. For example, in the embodiment depicted in  FIG. 16A , the cleaning member  270  is positioned between and engaged with the first roller  202  and the second roller  204 . In the embodiment depicted in  FIG. 16A , the cleaning member  270  generally engages both the first roller  202  and the second roller  204  along the length of the first roller  202  and the second roller  204  evaluated in the lateral direction (i.e., in the Y-direction as depicted) and generally removes build material  31  ( FIG. 12 ) and/or cured binder  50  ( FIG. 12 ) that may remain attached to the first roller  202  and the second roller  204  as the first roller  202  and the second roller  204  rotate. In some embodiments, the cleaning member  270  is a cleaning roller including grooves  272  or brush that is configured to rotate while engaged with the first roller  202  and the second roller  204 . In some embodiments, the cleaning member  270  may include a blade or the like that removes build material  31  ( FIG. 12 ) from the first roller  202  and the second roller  204 . While in the embodiment depicted in  FIG. 16A  the cleaning member  270  is simultaneously engaged with the first roller  202  and the second roller  204 , it should be understood that the cleaning member  270  may in some embodiments be engaged solely with either the first roller  202  or the second roller  204 . Moreover, while the embodiment depicted in  FIG. 16A  depicts a single cleaning member  270 , it should be understood that in embodiments, the recoat assembly  200  may include multiple cleaning members  270 . 
     In some embodiments, the position of the cleaning member  270  can be adjusted with respect to the first roller  202  and/or the second roller  204 . For example and referring to  FIGS. 16B, 16C, and 16D , in some embodiments, the recoat assembly  200  includes a cleaning position adjustment assembly  500 . In some embodiments, the cleaning position adjustment assembly  500  includes a first rotational member  510  and a second rotational member  520 . As best shown in  FIG. 16D , in some embodiments, the first rotational member  510  includes a first notched flange  512  and a first eccentric tube  514 . The second rotational member  520  includes a second notched flange  522  and a second eccentric tube  524 . In embodiments, the first eccentric tube  514  is insertable within the second eccentric tube  524 , as shown in  FIG. 16C . The cleaning position adjustment assembly  500  may further include a bearing  530  that is insertable within the first eccentric tube  514 , and the cleaning member  270  is engaged with the bearing  530 . 
     By rotating the first rotational member  510  and/or the second rotational member  520  with respect to one another, the position of the cleaning member  270  with respect to the base member  250 , and accordingly the first roller  202  and the second roller  204 , may be adjusted. For example, the position of the second rotational member  520  with respect to the base member  250  may be generally fixed. As the first rotational member  510  and the second rotational member  520  rotate with respect to one another, the eccentricity of the first eccentric tube  514  and the second eccentric tube  524  move the cleaning member  270  with respect to the base member  250 , and accordingly with respect to the first roller  202  and the second roller  204 . In this way, a user, such as a technician, can adjust the position of the cleaning member  270  with respect to the first roller  202  and the second roller  204 . In some embodiments, the cleaning position adjustment assembly  500  further includes one or more pins  540  that are insertable into the base member  250  through notches of the first notched flange  512  and the second notched flange  522 . The one or more pins  540  restrict rotational movement of the first rotational member  510  and the second rotational member  520  with respect to one another, and with respect to the base member  250 . The one or more pins  540  may be positioned into the base member  250  through notches of the first notched flange  512  and the second notched flange  522 , for example by a technician, once the cleaning member  270  is positioned as desired. In some embodiments, the first rotational member  510  and/or the second rotational member  520  may be rotated with respect to one another and/or retained in position by an actuator or the like. 
     Referring to  FIGS. 17A-17C , top views and a side view of the cleaning member  270  engaged with the first and second rollers  202 ,  204  are schematically depicted. As shown in  FIG. 17A , in some embodiments, such as embodiments in which the first roller  202  and the second roller  204  are offset from one another in the lateral direction (i.e., in the Y-direction as depicted), the cleaning member  270  may extend along the length of both the first roller  202  and the second roller  204  in the lateral direction. As shown in  FIG. 17B , the cleaning member  270  may similarly extend along the length of both the first roller  202  and the second roller  204  in the lateral direction (i.e., in the Y-direction as depicted) in embodiments in which the first roller  202  and the second roller  204  are aligned with one another. In embodiments, as depicted in  FIG. 17C , the cleaning member  270  is generally positioned above the first roller  202  and the second roller  204  in the vertical direction (i.e., in the Z-direction as depicted). 
     Referring to  FIGS. 11A, 18A, 18B, and 22  in some embodiments, the recoat assembly  200  is in fluid communication with a vacuum  290 . In particular, in embodiments, the vacuum  290  is in fluid communication with at least a portion of the base member  250  of the recoat assembly  200 . The vacuum  290  is generally operable to draw airborne build material  31  ( FIG. 12 ) out of the recoat assembly  200  and/or control the flow of aerosolized build material  31  within the additive manufacturing system  100  ( FIG. 2A ). In particular, as the rollers  202 ,  204  ( FIG. 19 ) fluidize build material  31  ( FIG. 17C ), some build material  31  will become airborne, unless controlled, may foul components of the additive manufacturing system  100 . The vacuum  290 , in embodiments, may include any suitable device for applying a negative and/or a positive pressure to the recoat assembly  200 , such as a pump or the like. As depicted in  FIG. 18A , the base member  250  generally includes a secondary containment housing  278 . In some embodiments, the primary containment housing  276  and/or the secondary containment housing  278  may include one or more adjustable openings  279  that can be adjustably opened and closed to selectively restrict the flow of air and/or build material through the primary containment housing  276  and/or the secondary containment housing  278 . For example and as shown in  FIGS. 11A and 23 , the primary containment housing includes a first adjustable opening  279  and a second adjustable opening  279 ′. The recoat assembly  200  may further include a first movable cover  269  that can selectively cover the first adjustable opening  279 . For example, the first moveable cover  269  may be movable in the Z-direction as depicted to selectively widen or narrow the first adjustable opening  279  (evaluated in the Z-direction as depicted). Similarly, the recoat assembly  200  may include a second movable cover  269 ′ that can selectively cover the second adjustable opening  279 ′. For example, the second moveable cover  269 ′ may be movable in the Z-direction as depicted to selectively widen or narrow the second adjustable opening  279 ′ (evaluated in the Z-direction as depicted) independently of the first adjustable opening  279 . By widening or narrowing the first and/or second adjustable openings  279 ,  279 ′, airflow into the primary containment housing  276  can be tuned as desired to direct flow of airborne build material  31 .  FIG. 18B  shows the base member  250  with the secondary containment housing  278  removed, and depicts a primary containment housing  276  of the base member  250 . 
     Without being bound by theory, airborne build material  31  may include particles that are smaller than the average particle size of the build material  31  that does not become airborne. Accordingly, by drawing airborne build material  31  of smaller size out of the recoat assembly  200 , the mean particle size of the build material  31  in the supply receptacle  134  ( FIG. 2A ) and/or the build area  124  ( FIGS. 2A, 2B ) may increase. Accordingly, in some embodiments, build material  31  including smaller particles, such as the build material  31  drawn from the recoat assembly  200 , may be periodically re-introduced to the supply receptacle  134  ( FIG. 2A ) and/or the build material hopper  360  ( FIG. 2A ) to maintain a relatively consistent particle size of the build material  31 . 
     Referring to  FIG. 19 , a section view of the base member  250  is depicted. In embodiments, the primary containment housing  276  at least partially encapsulates the powder spreading member (e.g., the first and second rollers  202 ,  204  and/or the powder engaging member  255  ( FIG. 12 )). The secondary containment housing  278  is spaced apart from the primary containment housing  276  and at least partially encapsulates the primary containment housing  276 . The primary containment housing  276  and the secondary containment housing  278  generally define an intermediate cavity  277  that is disposed between the primary containment housing  276  and the secondary containment housing  278 . In embodiments, the vacuum  290  is in fluid communication with the intermediate cavity  277 , and is operable to draw airborne build material  31  from the intermediate cavity  277 . In some embodiments, the intermediate cavity  277  is a forward intermediate cavity  277 , and the secondary containment housing  278  and the primary containment housing  276  define a rear intermediate cavity  283  separated from the forward intermediate cavity  277  by a bulkhead  281 . By separating the forward intermediate cavity  277  and the rear intermediate cavity  283 , different vacuum pressures may be applied to the forward intermediate cavity  277  and the rear intermediate cavity  283 . For example, the rear intermediate cavity  283  may pass over generally settled build material  31 , and accordingly, it may be desirable to apply less vacuum pressure at the rear intermediate cavity  283  to avoid disturbing the settled build material  31 . 
     In some embodiments, the recoat assembly  200  further includes an agitation device  284  coupled to the base member  250 . The agitation device  284  is operable to vibrate components of the recoat assembly  200 , such as the base member  250 , the first roller  202 , and/or the second roller  204  to dislodge build material  31  ( FIG. 12 ) that may be attached to the base member  250  and/or the first roller  202  and the second roller  204 . Referring to  FIGS. 20 and 21 , in some embodiments the base member  250  may include only the primary containment housing  276  at least partially enclosing the powder spreading member (e.g., the first roller  202  and/or the second roller  204 ). In these embodiments, the vacuum  290  is in fluid communication with the primary containment housing  276 . 
     Referring to  FIG. 22 , a section view of the base member  250  is schematically depicted. As shown in  FIG. 22 , the vacuum  290  is in fluid communication with the primary containment housing  276 , and generally operates to draw airborne build material  31  ( FIG. 12 ). In some embodiments, the recoat assembly  200  includes a diffuser plate  280  positioned between the vacuum  290  and the powder spreading member (e.g., the first roller  202  and/or the second roller  204 ). The diffuser plate  280  generally includes a plurality of apertures  282  extending therethrough. The diffuser plate  280  may generally assist in distributing the negative pressure applied to the primary containment housing  276  by the vacuum  290 . 
     Referring to  FIG. 23 , in some embodiments, the vacuum  290  is operable to draw airborne build material  31  from the recoat assembly  200 , and is further operable to direct the collected build material  31  beneath the recoat assembly  200  in the vertical direction (i.e., in the Z-direction as depicted). In the embodiment depicted in  FIG. 23 , the vacuum  290  is positioned within the primary containment housing  276  and is positioned between the first roller  202  and the second roller  204 . The vacuum  290  generally acts to draw in and collect airborne build material  31  and subsequently deposit the collected build material  31  below the recoat assembly  200 . In the embodiment depicted in  FIG. 23 , the vacuum  290  is positioned between the first roller  202  and the second roller  204 , and the vacuum  290  deposits the collected build material  31  between the first roller  202  and the second roller  204 . In some embodiments, the vacuum  290  may be positioned outside of the recoat assembly  200  and may redeposit the collected build material  31  at any suitable location beneath the recoat assembly  200 . 
     Referring to  FIG. 24 , a control diagram for the additive manufacturing system  100  is schematically depicted. In embodiments, the strain gauges  240 A,  240 B, the load cell  242 , and the accelerometer  244  are communicatively coupled to an electronic control unit  300 . The first and second rotational actuators  206 ,  208 , the recoat assembly transverse actuator  144 , the recoat assembly vertical actuator  160 , and the print head actuator  154  are communicatively coupled to the electronic control unit  300 , in embodiments. The electronic control unit  300  is also communicatively coupled to the roller vertical actuators  252 ,  254 , the front and rear energy source  260 ,  262 , the agitation device  284 , the one or more housing temperature sensors  266 , and the vacuum  290 . In some embodiments, a temperature sensor  286  and a distance sensor  288 , and the roller support temperature sensor  247  are also communicatively coupled to the electronic control unit  300  as shown in  FIG. 24 . 
     In some embodiments, the electronic control unit  300  includes a current sensor  306 . The current sensor  306  generally senses a current driving the recoat assembly transverse actuator  144 , the first rotational actuator  206 , the second rotational actuator  208 , the vertical actuator  160 , and/or the print head actuator  154 . In embodiments in which the recoat assembly transverse actuator  144 , the first rotational actuator  206 , the second rotational actuator  208 , the vertical actuator  160 , and/or the print head actuator  154  are electrically actuated, the current sensor  306  senses current driving the recoat assembly transverse actuator  144 , the first rotational actuator  206 , the second rotational actuator  208 , the vertical actuator  160 , and/or the print head actuator  154 . While in the embodiment depicted in  FIG. 24 , the current sensor  306  is depicted as being a component of the electronic control unit  300 , it should be understood that the current sensor  306  may be a separate component communicatively coupled to the electronic control unit  300 . Furthermore, while in the embodiment depicted in  FIG. 24 , a single current sensor  306  is depicted, it should be understood that the additive manufacturing system  100  may include any suitable number of current sensors  306  associated with the recoat assembly transverse actuator  144 , the first rotational actuator  206 , the second rotational actuator  208 , the vertical actuator  160 , and/or the print head actuator  154 . 
     In embodiments, the electronic control unit  300  generally includes a processor  302  and a memory component  304 . The memory component  304  may be configured as volatile and/or nonvolatile memory, and as such may include random access memory (including SRAM, DRAM, and/or other types of RAM), flash memory, secure digital (SD) memory, registers, compact discs (CD), digital versatile discs (DVD), bernoulli cartridges, and/or other types of non-transitory computer-readable mediums. The processor  302  may include any processing component operable to receive and execute instructions (such as from the memory component  304 ). In embodiments, the electronic control unit  300  may store one or more operating parameters for operating the additive manufacturing system  100 , as described in greater detail herein. 
     Methods for operating the recoat assembly  200  will now be described with reference to the appended drawings. 
     Referring collectively to  FIGS. 24 and 25 , an example method of operating the recoat assembly  200  is schematically depicted. In a first step  2502 , the electronic control unit  300  receives a first output signal of a first sensor. In embodiments, the first sensor is mechanically coupled to and in contact with the first roller support  210  ( FIG. 6B ), and may include any of the first strain gauge  240 A, the second strain gauge  240 B, the load cell  242 , and/or the accelerometer  244 . The first sensor, in embodiments, outputs the first output signal, which is indicative of a first force incident on the first roller  202  ( FIG. 6B ). In a second step  2504 , the electronic control unit  300  determines the first force on the first roller  202  ( FIG. 6B ) based on the first output signal of the first sensor. At step  2506 , the electronic control unit  300  adjusts at least one operating parameter of the additive manufacturing system  100  ( FIG. 2A ) in response to the determined first force. 
     As noted above, in embodiments, the electronic control unit  300  may include one or more parameters for operating the additive manufacturing system  100  ( FIG. 2A ). By adjusting at least one operating parameter in response to determined forces acting on the first roller  202  ( FIG. 6B ), the electronic control unit  300  may actively adjust operation of the additive manufacturing system  100 . As one example, in embodiments, the at least one parameter of the additive manufacturing system  100  ( FIG. 2A ) includes a speed with which the recoat assembly transverse actuator  144  moves the recoat assembly  200  ( FIG. 2A ) relative to the build area  124  ( FIGS. 2A, 2B ). In embodiments, upon determining a force acting on the first roller  202  below a configurable threshold, the electronic control unit  300  may direct the recoat assembly transverse actuator  144  to increase the speed at which the recoat assembly  200  ( FIG. 2A ) moves relative to the build area  124  ( FIGS. 2A, 2B ). For example, the determination of comparatively low force or forces acting on the first roller  202  may be indicative that the speed at which the recoat assembly  200  ( FIG. 2A ) is moved may be increased without detrimentally affecting the first roller  202 . By contrast, upon detecting a force acting on the first roller  202  exceeding a configurable threshold, the electronic control unit  300  may direct the recoat assembly transverse actuator  144  to decrease the speed at which the recoat assembly  200  ( FIG. 2A ) moves relative to the build area  124  ( FIGS. 2A, 2B ). For example, the determination of comparatively high force or forces acting on the first roller  202  may be indicative that the speed at which the recoat assembly  200  ( FIG. 2A ) should be decreased to reduce the forces acting on the first roller  202 . 
     In some embodiments, the at least one parameter is a height of the first roller  202  ( FIG. 6B ) evaluated in the vertical direction (e.g., in the Z-direction as depicted in  FIG. 6B ). In embodiments, upon determining a force acting on the first roller  202  below a configurable threshold, the electronic control unit  300  may direct the vertical actuator  160  to lower the recoat assembly  200  relative to the build area  124  ( FIGS. 2A, 2B ). For example, the determination of comparatively low force or forces acting on the first roller  202  may be indicative that the height at which the recoat assembly  200  ( FIG. 2A ) may be lowered to engage an additional volume of build material  31  ( FIG. 2A ). By contrast, upon detecting a force acting on the first roller  202  exceeding a configurable threshold, the electronic control unit  300  may direct the vertical actuator  160  to raise the recoat assembly  200  relative to the build area  124  ( FIGS. 2A, 2B ). For example, the determination of comparatively high force or forces acting on the first roller  202  may be indicative that the first roller  202  should be raised so as to engage a reduced volume of build material  31  ( FIG. 2A ). 
     In some embodiments, the at least one parameter of the additive manufacturing system  100  comprises a speed at which the print head actuator  154  moves the print head  150  ( FIG. 2A ). In embodiments, upon determining a force acting on the first roller  202  below a configurable threshold, the electronic control unit  300  may direct the print head actuator  154  to increase the speed at which the print head actuator  154  moves the print head  150  ( FIG. 2A ) relative to the build area  124  ( FIGS. 2A, 2B ). For example, the determination of comparatively low force or forces acting on the first roller  202  may be indicative that the speed at which first roller  202  ( FIG. 2A ) moves with respect to the build area  124  ( FIGS. 2A, 2B ) may be increased, and the speed at which the print head actuator  154  moves the print head  150  may be similarly increased, and/or a volume of binder  50  ( FIG. 1A ) can be increased. By contrast, upon detecting a force acting on the first roller  202  exceeding a configurable threshold, the electronic control unit  300  may direct the print head actuator  154  to decrease the speed at which the print head  150  ( FIG. 2A ) moves with respect to the build area  124  ( FIGS. 2A, 2B ). For example, the determination of comparatively high force or forces acting on the first roller  202  may be indicative that the speed at which first roller  202  ( FIG. 2A ) moves with respect to the build area  124  ( FIGS. 2A, 2B ) should be decreased, and the speed at which the print head actuator  154  moves the print head  150  should similarly be decreased, and/or a volume of binder  50  ( FIG. 1A ) can be decreased. 
     In some embodiments, the electronic control unit  300  is configured to adjust the at least one operating parameter of the additive manufacturing system  100  based on sensed current from the current sensor  306 . For example, in embodiments, the current sensor  306  may detect current from the first rotational actuator  206  and/or the second rotational actuator  208 . Detection of a current below a configurable threshold may be generally indicative of relatively low forces acting on the first roller  202  and/or the second roller  204 . By contrast, detection of a current above a configurable threshold may be generally indicative of relatively high forces acting on the first roller  202  and/or the second roller  204 . In some embodiments, the current sensor  306  may sense a current driving the transverse actuator  144  that moves the recoat assembly  200  relative to the build area  124 . Similar to the first and second rotational actuators  206 ,  208 , detection of a current below a configurable threshold may be generally indicative of relatively low forces acting on the first roller  202  and/or the second roller  204 . By contrast, detection of a current above a configurable threshold may be generally indicative of relatively high forces acting on the first roller  202  and/or the second roller  204 . 
     Referring to  FIGS. 2A, 2B, 24, and 26 , another method for adjusting at least one operating parameter of the additive manufacturing system  100  is depicted. In a first step  2602 , the method comprises distributing a layer of a build material  31  on the build area with the recoat assembly  200 . In a second step  2604 , the method comprises receiving a first output signal from a first sensor as the layer of the build material  31  is distributed on the build area  124  with the recoat assembly  200 . As described above, in embodiments, the first sensor is mechanically coupled to and in contact with the first roller support  210  ( FIG. 6B ), and may include any of the first strain gauge  240 A, the load cell  242 , and/or the accelerometer  244 . The first sensor, in embodiments, outputs the first output signal, which is indicative of a first force incident on the first roller  202  ( FIG. 6B ). 
     At step  2604 , the method comprises determining the first force on the first roller  202  based on the first output signal of the first sensor). In some embodiments, a lookup table containing expected force or pressure information may be previously generated, such as based on calibration force measurements generated under various conditions (e.g., size of build area coated with binder, recoat traverse speed, recoat roller rotation speed, recoat roller direction, layer thickness, recoat roller geometry coating, and the like). In some embodiments, information related to a current layer of the object being built and/or a prior layer may be utilized to generate an expected force or pressure curve to be experienced as the recoat assembly  200  traverses the build area  124 . In some embodiments, a geometry of the current layer of the object being built or a geometry of the immediately preceding layer that was built may be used to determine an expected pressure or force profile (e.g., shear forces expected to be experienced as the recoat assembly  200  traverses the build area  124  to distribute material for the current layer, normal forces expected to be experienced as the recoat assembly  200  traverses the build area  124  to distribute material for the current layer and/or any other type of expected force to be experienced as the recoat assembly  200  traverses the build area  124  to distribute material for the current layer), a comparison between the expected pressure or measured force profile and the measured force or pressure may be made, and an action may be taken in response to the comparison. 
     At step  2608 , the method comprises adjusting the at least one operating parameter of the additive manufacturing system  100  in response to the determined first force. For example, in some embodiments, the at least one operating parameter of the additive manufacturing system  100  is adjusted based on a comparison of an expected force on the first roller  202  to the first force on the first roller  202  determined based on the first output signal of the first sensor. In embodiments, when a deviation beyond a given threshold is determined to have occurred, a corrective action may be taken, such as to adjust a recoat traverse speed for the current layer, adjust a roller rotation speed for the current layer, adjust a recoat traverse speed for one or more subsequent layers, adjust a roller rotation speed for one or more subsequent layers, adjust a height of one or more rollers for the current layer and/or for one or more subsequent layers, etc. 
     In some embodiments, when an expected pressure or force deviates from a measured pressure or force during spreading of material for a current layer by the recoat assembly  200 , the layer recoat process may be determined to be defective. The extent of force deviation may be used to determine a type of defect (e.g., a powder defect, a recoat roller defect, insufficient binder cure, a jetting defect, or the like. 
     In embodiments, each of steps  2602 - 2608  may be performed, for example, by the electronic control unit  300 . As noted above, in embodiments, the electronic control unit  300  may include one or more parameters for operating the additive manufacturing system  100 . By adjusting at least one operating parameter in response to determined forces acting on the first roller  202  ( FIG. 6B ), the electronic control unit  300  may actively adjust operation of the additive manufacturing system  100 . As one example, in embodiments, the at least one parameter of the additive manufacturing system  100  includes a speed with which the recoat assembly transverse actuator  144  moves the recoat assembly  200  relative to the build area  124 , as outlined above. 
     In some embodiments, the at least one parameter is a speed of rotation of the first rotational actuator  206 . In embodiments, upon determining a force acting on the first roller  202  below a configurable threshold, the electronic control unit  300  may direct the first rotational actuator  206  to decrease the speed at which the first rotational actuator  206  rotates the first roller  202 . For example, the determination of comparatively low force or forces acting on the first roller  202  may be indicative that the speed at which the first rotational actuator  206  may be reduced while still being sufficient to fluidize the build material  31 . By contrast, upon detecting a force acting on the first roller  202  exceeding a configurable threshold, the electronic control unit  300  may direct may direct the first rotational actuator  206  to increase the speed at which the first rotational actuator  206  rotates the first roller  202 . For example, the determination of comparatively high force or forces acting on the first roller  202  may be indicative that the speed at which the first rotational actuator  206  is rotating the first roller  202  is insufficient to fluidize the build material  31  as desired. 
     In some embodiments, the at least one parameter is a target thickness of a subsequent layer of build material  31  and/or the layer of build material  31  being distributed. In embodiments, upon determining a force acting on the first roller  202  below a configurable threshold, the electronic control unit  300  may direct the recoat assembly  200  to increase a target thickness of a subsequent layer of build material  31 , for example by changing the height of the recoat assembly  200 . For example, the determination of comparatively low force or forces acting on the first roller  202  may be indicative that the thickness of the layer of build material  31  distributed by the recoat assembly  200  may be increased. By contrast, upon detecting a force acting on the first roller  202  exceeding a configurable threshold, the electronic control unit  300  may direct the recoat assembly  200  to decrease a target thickness of a subsequent layer of build material  31 , for example by changing the height of the recoat assembly  200 . For example, the determination of comparatively high force or forces acting on the first roller  202  may be indicative that the thickness of the layer of build material  31  distributed by the recoat assembly  200  should be decreased. 
     In some embodiments, the method illustrated in  FIG. 26  further comprises determining a type of defect. For example, in some embodiments, a type of defect may be determined based on a comparison of an expected force on the first roller  202  and the first force on the first roller  202 . For example, a defect in the build material  31  may be associated with a particular amount of force applied to the first roller  202 , while a defect in the first roller  202  may be associated with a different amount of force applied to the first roller  202 . Accordingly, the amount of force applied to the first roller  202  may be utilized to determine a type of defect within the additive manufacturing system  100 . 
     In embodiments, the adjustment of the at least one operating parameter of the additive manufacturing system  100  can be implemented at one or more times during a build cycle. For example, in embodiments, the at least one operating parameter may be adjusted while the layer of build material  31  is being distributed by the recoat assembly  200 . In some embodiments, the at least one operating parameter of the additive manufacturing system  100  is adjusted when a next layer of build material  31  is distributed by the recoat assembly  200 . 
     In some embodiments, a wear parameter may be determined based on the determined first force. For example, as the first roller  202  wears, for example through repeated contact with the build material  31 , the diameter of the first roller  202  may generally decrease. The decreased diameter of the first roller  202  may generally lead to lower forces on the first roller  202  as the first roller  202  distributes build material  31 . 
     In some embodiments, wear on other components of the recoat assembly  200  may be determined based on the determined first force. For example, the first roller  202  may be coupled to the base member  250  ( FIG. 3 ) via one or more bearings, or the like. Additionally and as noted above, the first roller  202  may be coupled to the first rotational actuator  206  ( FIG. 3 ) through a belt, a chain, or the like. Wear on the one or more bearings and/or the belt, chain, or the like may generally lead to increased forces on the first roller  202 . In some embodiments, the increased forces on the first roller  202  may be determined by the current sensor  306 . 
     In some embodiments, the method depicted in  FIG. 26  further includes receiving a second output signal from a second sensor mechanically coupled to and in contact with the second roller support  212 . In embodiments, the second sensor may include any of the first strain gauge  240 A, the second strain gauge  240 B, the load cell  242 , and/or the accelerometer  244 . In embodiments, the method further includes receiving the second output signal from the second sensor as the layer of the build material  31  is distributed on the build area  124  with the recoat assembly  200  and determining the first force on the first roller  202  based on the first output signal of the first sensor and the second output signal of the second sensor. 
     In some embodiments, the method depicted in  FIG. 26  further includes receiving a third output signal from a third sensor mechanically coupled to and in contact with the third roller support  216 . In embodiments, the third sensor may include any of the include any of the first strain gauge  240 A, the second strain gauge  240 B, the load cell  242 , and/or the accelerometer  244 . In embodiments, the method further includes receiving the third output signal from the third sensor as the layer of the build material  31  is distributed on the build area  124  with the recoat assembly  200  and determining a second force on the second roller  204  based on the third output signal of the third sensor. In some embodiments, the method further includes adjusting the at least one operating parameter in response to the determined first force and the determined second force. In this way, the at least one operating parameter may be adjusted based on determined forces acting on both the first roller  202  and the second roller  204 . For example a detection of a deceleration of the first roller  202  and/or the second roller  204  above a configurable threshold may be indicative of a collision of the recoat assembly  200  with an object, such as a foreign object within the additive manufacturing system  100 . By detecting a collision, operation of the additive manufacturing system  100  may be halted to prevent further damage to the additive manufacturing system  100 , and/or provide an indication to a user that maintenance is necessary. 
     In some embodiments, the method depicted in  FIG. 26  further includes determining a collision of the recoat assembly  200 . For example, in some embodiments, the method further includes determining a roller collision event based on an output of the at least one accelerometer  244 , an adjusting the at least one operating parameter when the roller collision event is determined to have occurred. 
     Referring to  FIGS. 24, 27, and 28 , a method for forming an object is schematically depicted. In a first step  2702 , the method comprises moving the recoat assembly  200  over the supply receptacle  134  in a coating direction, as indicated by arrow  40 . The supply receptacle  134  comprises build material  31  positioned within the supply receptacle  134 , and the recoat assembly  200  comprises a first roller  202  and a second roller  204  that is spaced apart from the first roller  202  As noted above, in some embodiments, the recoat assembly  200  may include only a single roller. In a second step  2704 , the method comprises rotating the first roller  202  of the recoat assembly  200  in a counter-rotation direction  60 , such that a bottom of the first roller  202  moves in the coating direction  40 . In the embodiment depicted in  FIG. 28 , the counter-rotation direction  60  is shown as the clockwise direction. In a third step  2706 , the method comprises contacting the build material  31  with the first roller  202  of the recoat assembly  200 , thereby fluidizing at least a portion of the build material  31 . At step  2708 , the method comprises irradiating, with the front energy source  260 , an initial layer of build material  31  positioned in the build area  124  spaced apart from the supply receptacle  134 . As noted above, irradiating the initial layer of build material  31  may bind the build material  31  to binder  50  positioned in the build area  124 . Subsequent to step  2708 , at step  2710 , the method comprises moving the fluidized build material  31  from the supply receptacle  134  to the build area  124  with the first roller  202 , thereby depositing a second layer of the build material  31  over the initial layer of build material  31  within the build area  124 . Subsequent to step  2710 , at step  2712 , the method comprises irradiating, with the rear energy source  262 , the second layer of build material  31  within the build area  124 . In some embodiments, steps  2708 - 2712  may occur within a predetermined cycle time. For example, in some embodiments, steps  2708 - 2712  may be performed within a range between 5 seconds and 20 seconds. 
     While the method described above includes moving the recoat assembly  200  over a supply receptacle  134 , it should be understood that in some embodiments a supply receptacle  134  is not provided, and instead build material  31  may be placed on the build area  124  through other devices, such as the build material hopper  360  ( FIG. 2B ). 
     In embodiments, the electronic control unit  300  may direct various components of the additive manufacturing system  100  to perform steps  2702 - 2712 . In embodiments, by irradiating the initial layer of build material  31 , the front energy source  260  may act to cure binder  50  positioned on the build material  31  of the build area  124 . By irradiating the second layer of build material  31 , the rear energy source  262  may generally act to pre-heat the build material  31 , and/or further cure the binder material  50 . 
     By irradiating the build material  31  with a front energy source  260  that is separate from a rear energy source  262 , the intensity of energy emitted by the recoat assembly  200  may be distributed, as compared to recoat assemblies including a single energy source, which may reduce defects in the binder  50  and/or the build material  31 . More particularly, the thermal power density of a single energy source heating system can quickly reach a limit due to space and cost constraints. Excessive power output in a single energy source heating system can be detrimental to the quality of the cure of the binder  50  in each layer of build material  31 , as large spikes in temperature may induce stress and cracks in the relatively weak parts and can cause uncontrolled evaporation of solvents within the binder  50 . By including the front energy source  260  and the rear energy source  262 , the thermal power intensity of the recoat assembly  200  may be distributed. In particular and as noted above, including multiple energy sources (e.g., the front energy source  260  and the rear energy source  262 ), energy can be applied to build material  31  ( FIG. 1A ) over a comparatively longer period of time as compared to the application of energy via a single energy source. In this way, over-cure of build material  31  bound by cured binder  50  can be minimized. 
     Furthermore, because the recoat assembly  200  includes the front energy source  260  and the rear energy source  262 , operation of the recoat assembly  200  may be maintained in the case of failure of the front energy source  260  or the rear energy source  262 . In particular, by providing multiple energy sources (e.g., the front energy source  260  and the rear energy source  262  and/or other additional energy sources), in the case of failure of one of the energy sources, the other energy source may continue to be utilized, so that the recoat assembly  200  may continue to operate, thereby reducing downtime of the recoat assembly  200 . 
     The first roller  204 , in embodiments, is rotated at a rotational speed sufficient to fluidize at least a portion of the build material  31 . In some embodiments, the first roller  204  is rotated at a rotational speed of at least 2.5 meters per second. In some embodiments, the first roller  204  is rotated at a rotational speed of at least 2 meters per second. In some embodiments, the first roller  204  is rotated at a rotational speed of at least 1 meter per second. 
     In some embodiments, the operation of the front energy source  260  and/or the rear energy source  262  may be controlled and modified. In embodiments, the front energy source  260  and/or the rear energy source  262  may be communicatively coupled to the electronic control unit  300  through one or more relays, such as solid state relays, that facilitate control of the front energy source  260  and/or the rear energy source  262 . 
     In some embodiments, the additive manufacturing system  100  may include a temperature sensor  286  communicatively coupled to the electronic control unit  300 . The temperature sensor  286  may include any contact or non-contact sensor suitable for detecting a temperature of the build material  31 , for example and without limitation, one or more infrared thermometers, thermocouples, thermopiles or the like. As shown in  FIG. 6A , one or more temperature sensors  286  may be positioned rearward of the first roller  202  and/or the second roller  204 , however, it should be understood that the one or more temperature sensors  286  may be coupled to the recoat assembly at any suitable position. In embodiments, subsequent to irradiating the initial layer of build material  31  with the front energy source  260  and/or irradiating the second layer of build material  31 , the method further comprises detecting a temperature of the irradiated build material  31  with the temperature sensor  286 . In some embodiments, the output of the front energy source  260  and/or the rear energy source  262  may be adjusted in response to the detected temperature of the build material  31  (e.g., feedback control). In some embodiments, the detected temperature may be stored such that the electronic control unit  300  may develop a model for controlling the front energy source  260  and/or the rear energy source  262  (e.g., feedforward control). For example, in some embodiments, the method further comprises changing at least one parameter of the front energy source  260  or the rear energy source  262  based at least in part on the detected temperature. Further, in some embodiments, at least one of irradiating the initial layer of build material  31  with the front energy source  260  and irradiating the second layer of build material  31  comprises applying a predetermined power to the front energy source  260  or the rear energy source  262 , and the method further comprises changing the predetermined power based at least in part on the detected temperature. 
     In some embodiments, the recoat assembly  200  includes a distance sensor  288  communicatively coupled to the electronic control unit  300 . The distance sensor  288  is generally configured to detect a thickness of a layer of build material  31  positioned below the recoat assembly  200 . In embodiments, the electronic control unit  300  may receive a signal from the distance sensor  288  indicative of the layer or build material  31  moved to the build area  124 . The electronic control unit  300  may change one or more parameters based on the detected thickness of the layer of build material  31  such that the recoat assembly  200  may move build material  31  to the build area  124  as desired. In embodiments, the distance sensor  288  may include any sensor suitable for detecting a thickness of build material  31 , such as and without limitation, a laser sensor, an ultrasonic sensor, or the like. 
     In some embodiments, the second roller  204  may be positioned above the first roller  202  in the vertical direction (i.e., in the Z-direction as depicted). In these embodiments, only the first roller  202  may contact the build material  31 , and the second roller  204  may act as a spare roller that can be utilized in the case of failure or malfunction of the first roller  202 . 
     In some embodiments, the second roller  204  is rotated in a rotation direction  62  that is the opposite of the counter-rotation direction  60  and the second roller  204  contacts the build material  31  within the build area  124 . The second roller  204  may be rotated at a rotational velocity that corresponds to a linear velocity of the recoat assembly  200 . More particularly, by matching the rotational velocity of the second roller  204  to match the linear velocity of the recoat assembly  200 , the second roller  204  may generally act to compact the build material  31 , while causing minimal disruption to the build material  31  as the recoat assembly  200  moves with respect to the build area  124 . In embodiments, the rotational velocity of the first roller  202  is greater than the rotational velocity of the second roller  204 . In some embodiments, as the second roller  204  compacts the build material  31 , the second roller  204  may be positioned lower than the first roller  202  in the vertical direction (i.e., in the Z-direction as depicted). 
     In some embodiments, once the second layer of build material  31  is deposited the first roller  202  is moved upward in the vertical direction (i.e., in the Z-direction as depicted), such that the first roller  202  is spaced apart from the second layer of build material  31 . The recoat assembly  200  is then moved to the supply receptacle  134  in a direction that is opposite of the coating direction  31 . In this way, the recoat assembly  200  may be returned to the recoat home position  148  ( FIG. 2A ). In some embodiments, the recoat assembly  200  is moved to the supply receptacle  134  at a return speed. In embodiments the return speed is greater than a coating speed at which the recoat assembly  200  moves the fluidized build material  31  to the build area  124 . In some embodiments, to avoid damaging cured binder the build material  31 , the coating speed may be limited, and accordingly, by increasing the return speed, the overall cycle time required to deposit build material  31  may be reduced. 
     In some embodiments, the first roller  202  and/or the second roller  204  may compact the build material  31  in the build area  124  as the recoat assembly  200  moves back to the home position  148 . For example and referring to  FIGS. 29A and 29B , the recoat assembly  200  is depicted moving in coating direction  40 , and a direction  42  opposite the coating direction  40 , respectively. In some embodiments, the method further comprises rotating the first roller  202  and/or second roller  204  in the counter-rotation direction  60 . Rotating the first roller  202  and/or the second roller  204  in the counter-rotation direction  60  may comprise rotating the first roller  202  and/or the second roller  204  at a rotational velocity that corresponds to a linear velocity of the recoat assembly  200  moving toward the supply receptacle  134 . 
     In some embodiments, before moving the recoat assembly  200  to the supply receptacle  134 , the method further comprises moving the first roller  202  and/or the second roller  204  upward in the vertical direction (i.e., in the Z-direction as depicted). In some embodiments, the first roller  202  and/or the second roller  204  is moved upward between 8 micrometers and 12 micrometers in the vertical direction, inclusive of the endpoints. In some embodiments, the first roller  202  and/or the second roller  204  is moved upward about 10 micrometers in the vertical direction. In some embodiments, before moving the recoat assembly  200  to the supply receptacle  134 , the method further comprises moving the first roller  202  and/or the second roller  204  upward in the vertical direction (i.e., in the Z-direction as depicted). In some embodiments, the first roller  202  and/or the second roller  204  is moved upward between 5 micrometers and 20 micrometers in the vertical direction, inclusive of the endpoints. By moving first roller  202  and/or the second roller  204  upward in the vertical direction, the first roller  202  and/or the second roller  204  may be positioned to compact the build material  31  in the build area  124 . 
     In some embodiments, as the first roller  202  and/or the second roller  204  contacts the build material  31  in the build area  124  moving back toward the supply receptacle  134 , the first roller  202  and/or the second roller  204  is rotated at a rotational velocity that corresponds to the linear velocity of the recoat assembly  200  moving back toward the supply receptacle  134 . As noted above, by correlating the rotational velocity of the first roller  202  and/or the second roller  204  to the linear velocity of the recoat assembly  200 , the first roller  202  and/or the second roller  204  may compact the build material  31 , with minimal disruption of the build material  31  in the longitudinal direction (i.e., in the X-direction as depicted). 
     While  FIGS. 29A and 29B  include a supply receptacle  134 , it should be understood that in some embodiments a supply receptacle  134  is not provided, and instead build material  31  may be placed on the build area  124  through other devices, such as the build material hopper  360  ( FIG. 2B ). 
     In some embodiments, the first roller  202  and the second roller  204  may be rotated in the counter-rotation direction  60  as the recoat assembly  200  moves in the coating direction  40 , as shown in  FIG. 29C . In some embodiments, the first roller  202  is positioned above the second roller  204  as the recoat assembly  200  moves in the coating direction  40 . The first roller  202  and the second roller  204  may be rotated in the rotation direction  62  as the recoat assembly  200  moves in the return direction  42 , as shown in  FIG. 29D . In some embodiments, the first roller  202  is positioned below the second roller  204  as the recoat assembly  200  moves in the return direction  42 . Further, in some embodiments, the front energy source  260  and/or the rear energy source  262  may irradiate the build material  31  in the build area  124  as the recoat assembly  200  moves in the coating direction  40  ( FIG. 29C ) and/or as the recoat assembly  200  moves in the return direction  42 . 
     Referring to  FIGS. 24 and 30 , an example method for drawing airborne build material  31  out of the recoat assembly  200  is schematically depicted. In a first step  3002 , the method comprises moving the recoat assembly  200  build material  31  in the coating direction  40 . At step  3004 , the method further comprises contacting the build material  31  with the powder spreading member, causing at least a portion of the build material  31  to become airborne. At step  3006 , the method further comprises drawing airborne build material  31  out of the recoat assembly  200  with a vacuum  290  in fluid communication with the recoat assembly  200 . 
     In embodiments, each of steps  3002 - 3006  may be performed, for example, by the electronic control unit  300 . 
     In embodiments, the vacuum  290  may draw the airborne build material  31  out of the recoat assembly  200  at one or more times during a build cycle. For example, in some embodiments, the step of drawing airborne build material  31  out of the recoat assembly  200  is subsequent to or during the step of moving the build material  31 . Put another way, the vacuum  290  draws the build material  31  out of the recoat assembly  200  at the end of a build cycle. In some embodiments, the step of drawing airborne build material  31  out of the recoat assembly  200  is concurrent with the step of moving the build material  31 . Put another way, the airborne build material  31  may be drawn out of the recoat assembly  200  during the build cycle in a continuous or semi-continuous manner. 
     In some embodiments, the vacuum  290  may apply a positive pressure to the recoat assembly  200  to dislodge build material  31  accumulated within the recoat assembly  200 . For example, in some embodiments, subsequent to moving the build material  31 , the vacuum  290  directs a process gas, such as air or the like, to the recoat assembly  200 . In some embodiments, the vacuum  290  may apply positive pressure while the recoat assembly  200  is positioned over a drain that applies a negative pressure to collect the build material  31 . In embodiments, the drain may be positioned proximate to the build area  134  ( FIG. 2A ). 
     Based on the foregoing, it should be understood that embodiments described herein are directed to recoat assemblies for an additive manufacturing system. In embodiments described herein, recoat assemblies include one or more sensors that detect forces acting on the recoat assembly. By detecting forces acting on the recoat assembly, defects may be identified and one or more parameters related to the operation of the recoat assembly may be adjusted to optimize the performance of the recoat assembly. In some embodiments, recoat assemblies described herein may include multiple redundant components, such as rollers and energy sources, such that the recoat assembly may continue operation in the event of failure of one or more components of the recoat assemblies. In some embodiments, recoat assemblies described herein are in fluid communication with a vacuum that acts to collect and contain airborne build material. 
     Further aspects of the embodiments are provided by the subject matter of the following clauses: 
     1. A recoat assembly for an additive manufacturing system, the recoat assembly comprising a first roller support, a second roller support, a first roller disposed between and supported by the first roller support and the second roller support, a first rotational actuator operably coupled to the first roller and configured to rotate the first roller about a first rotation axis, and a first sensor mechanically coupled to and in contact with the first roller support, wherein the first sensor outputs a first output signal indicative of a first force incident upon the first roller. 
     2. The recoat assembly of any preceding clause, wherein the first sensor is a strain gauge mechanically coupled to the first roller support, and wherein the strain gauge is oriented in order to measure a strain in at least one of a vertical direction transverse to the first rotation axis of the first roller or a horizontal direction transverse to the first rotation axis of the first roller. 
     3. The recoat assembly of any preceding clause, wherein the first sensor is a load cell mechanically coupled to the first roller support and configured to measure a force in a vertical direction transverse to the first rotation axis of the first roller. 
     4. The recoat assembly of any preceding clause, wherein the first roller support includes a flexure to which the first sensor is coupled. 
     5. The recoat assembly of any preceding clause, further comprising a second sensor mechanically coupled to and in contact with the second roller support. 
     6. The recoat assembly of any preceding clause, further comprising a third roller support, a fourth roller support, a second roller disposed between and supported by the third roller support and the fourth roller support, a second rotational actuator operably coupled to the second roller and configured to rotate the second roller about a second rotation axis, the second rotation axis being parallel to the first rotation axis, and a third sensor mechanically coupled to and in contact with the third roller support, wherein the third sensor outputs a third output signal indicative of a second force incident upon the second roller. 
     7. The recoat assembly of any preceding clause, further comprising an accelerometer mechanically coupled to the first roller support. 
     8. An additive manufacturing system comprising a recoat assembly comprising a first roller support, a second roller support, a first roller disposed between and supported by the first roller support and the second roller support, a first rotational actuator operably coupled to the first roller and configured to rotate the first roller about a first rotation axis, a first sensor mechanically coupled to and in contact with the first roller support, wherein the first sensor outputs a first output signal indicative of a first force incident upon the first roller, and an electronic control unit configured to receive the first output signal of the first sensor, determine a first force on the first roller based on the first output signal of the first sensor, and adjust at least one operating parameter of the additive manufacturing system in response to the determined first force. 
     9. The additive manufacturing system of any preceding clause, further comprising a build area, a transverse actuator operably coupled to the recoat assembly and operable to move the recoat assembly relative to the build area to spread a build material on the build area, and a current sensor configured to sense a current driving the transverse actuator, wherein the electronic control unit is configured to adjust the at least one operating parameter of the additive manufacturing system based on the sensed current. 
     10. The additive manufacturing system of any preceding clause, wherein the at least one parameter of the additive manufacturing system comprises a speed with which the transverse actuator moves the recoat assembly relative to the build area. 
     11. The additive manufacturing system of any preceding clause, further comprising a build area, and a vertical actuator for moving the first roller in a vertical direction transverse to the rotation axis of the first roller, wherein the at least one parameter of the additive manufacturing system comprises a height of the first roller relative to the build area set by the vertical actuator. 
     12. The additive manufacturing system of any preceding clause, further comprising a build area, a print head for depositing binder material, and a print head actuator operably coupled to the print head and operable to move the print head relative to the build area to deposit binder material on the build area, wherein the at least one parameter of the additive manufacturing system comprises a speed with which the print head actuator moves the print head relative to the build area. 
     13. A method of adjusting at least one operating parameter of an additive manufacturing system, the method comprising distributing a layer of a build material on a build area with a recoat assembly, the recoat assembly comprising a first roller disposed between and supported by a first roller support and a second roller support, a first rotational actuator operably coupled to the first roller and configured to rotate the first roller about a first rotation axis, and a first sensor mechanically coupled to and in contact with the first roller support, receiving a first output signal from the first sensor as the layer of the build material is distributed on the build platform with the recoat assembly, determining a first force on the first roller based on the first output signal of the first sensor, and adjusting the at least one operating parameter of the additive manufacturing system in response to the determined first force. 
     14. The method of any preceding clause, wherein the at least one operating parameter of the additive manufacturing system comprises one or more of (i) a speed with which a transverse actuator moves the recoat assembly relative to the build area, (ii) a speed of rotation of the first rotational actuator, (iii) a target thickness of a subsequent layer of the build material, and (iv) a height of the first roller relative to the build area. 
     15. The method of any preceding clause, wherein the at least one operating parameter of the additive manufacturing system is adjusted based on a comparison of an expected force on the first roller to the first force on the first roller determined based on the first output signal of the first sensor. 
     16. The method of any preceding clause, further comprising determining a type of defect based on the comparison of the expected force on the first roller to the first force on the first roller determined based on the first output signal of the first sensor, and adjusting the at least one operating parameter of the additive manufacturing system based on the type of defect. 
     17. The method of any preceding clause, wherein adjusting the at least one operating parameter of the additive manufacturing system in response to the determined first force comprises one or more of (i) adjusting the at least one operating parameter of the additive manufacturing system while the layer is being distributed by the recoat assembly, and (ii) adjusting the at least one operating parameter of the additive manufacturing system when a next layer is distributed by the recoat assembly. 
     18. The method of any preceding clause, further comprising determining a wear parameter of the first roller based on the determined first force. 
     19. The method of any preceding clause, wherein the recoat assembly further comprises a second sensor mechanically coupled to and in contact with the second roller support, the method further comprising receiving a second output signal from the second sensor as the layer of the build material is distributed on the build area with the recoat assembly, and determining the first force on the first roller based on the first output signal of the first sensor and the second output signal of the second sensor. 
     20. The method of any preceding clause, wherein the recoat assembly further comprises a second roller disposed between a third roller support and a fourth roller support, a second rotational actuator operably coupled to the second roller and configured to rotate the second roller about a second rotation axis, and a third sensor mechanically coupled to and in contact with the third roller support, the method further comprising receiving a third output signal from the third sensor as the layer of the build material is distributed on the build area with the recoat assembly, determining a second force on the second roller based on the third output signal of the third sensor, and adjusting the at least one operating parameter of the additive manufacturing system in response to the determined first force and the determined second force. 
     21. The method of any preceding clause, further comprising sensing a current driving a transverse actuator that moves the recoat assembly relative to the build area, and adjusting the at least one operating parameter of the additive manufacturing system based on the sensed current. 
     22. The method of any preceding clause, further comprising determining a roller collision event based on an output of at least one accelerometer, and adjusting the at least one operating parameter of the additive manufacturing system when the roller collision event is determined to have occurred. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.