Abstract:
A printing system for forming three-dimensional objects includes two laterally spaced rails, each of the rails have an internal cavity extending through the rail along a longitudinal axis. The printing system further includes two heating devices, one heating device is connected to the internal cavity of one of the two laterally spaced rails and the other heating device is connected to the internal cavity of the other of the two laterally spaced rails to enable each heating device to heat a surface of the rail in which the heating device is positioned. The printing system further includes a platform configured to move along the laterally spaced rails. The printing system also includes at least one of a pair of scrapers, wiper pads, and wiper blades mounted to the cart.

Description:
TECHNICAL FIELD 
       [0001]    The system and method disclosed in this document relate to printers that produce three-dimensional objects and, more particularly, to the maintenance of cart drive mechanisms in such printers. 
       BACKGROUND 
       [0002]    Digital three-dimensional manufacturing, also known as digital additive manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital model. Three-dimensional printing is an additive process in which one or more ejector heads eject successive layers of material on a substrate in different shapes. Typically, ejector heads, which are similar to printheads in document printers, include an array of ejectors that are coupled to a supply of material. Ejectors within a single ejector head can be coupled to different sources of material or each ejector head can be coupled to different sources of material to enable all of the ejectors in an ejector head to eject drops of the same material. Materials that become part of the object being produced are called build materials, while materials that are used to provide structural support for object formation, but are later removed from the object are known as support materials. Three-dimensional printing is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling. 
         [0003]    A previously known three-dimensional object printing system  10  is shown in  FIG. 8 . In the view depicted in that figure, the cart  14  ( FIG. 8 ) moves in a process direction P on precision rails  38  underneath the printing station  26 . Precision rails  38  are cylindrical rail sections that are manufactured within tight tolerances to help ensure accurate placement and maneuvering of the cart  14  beneath the ejector heads  30 . Linear electrical motors are provided within housing  42  to interact with a magnet inside housing  46  ( FIG. 7 ) connected to the lower surface of the cart  14 , as described below, to propel the cart  14  along the track rails  22  between printing stations  26 . Once the cart  14  reaches the rails  38 , the bearings  34  transition to the precision rails  38 . As the cart  14  passes beneath the printing station  26 , the ejection of material occurs. Electrical motors (not shown) are configured to move the ejector heads  30  in an X-Y plane that is parallel to the process direction P as layers of material are printed on the cart  14 . Additional motors (not shown) move the printing station  26  vertically with respect to the cart  14  as layers of material accumulate to form an object. Alternatively, a mechanism can be provided to move an upper surface of the cart  14  on which the object is being formed vertically and horizontally with respect to rails  38  as the layers of the object are formed. Once the printing to be performed by a printing station is finished, the cart  14  moves to a position that enables the bearings  34  to contact rails  22  so the cart can slide along the rails  22  to another printing station for further part formation, layer curing or other processing. 
         [0004]    An end view of the prior art system  10  is shown in  FIG. 7 . That view depicts in more detail the relationship between the cart  14  and the track rails  22  as well as the precision rails  38 . In the area underneath a printing station  26 , bearings  34  of the cart  14  are positioned on the precision rails  38  in an arrangement that facilitates accurate positioning of the build platen on the cart  14 . Specifically, bearings  34  are positioned at a right angle to one another on one of the rails  38  to remove 4 degrees of freedom of the cart  14 , while the other bearing  34  is perpendicular to the other rail  38  to remove one more degree of freedom. Linear motors within the housing  42  generate electromagnetic fields that interact with the magnet in housing  46 , which has a bottom surface  50 , to move the cart  14  along the precision rails. Gravity and magnetic attraction between the stationary motor segment and the magnet within housing  46  hold the bearings  34  in contact with the rails  38 . Extensions from the rails  22  fit in the slots  52  of the cart  14  to enable the cart to slide along the extensions between printing stations  26  as the linear motors propel the cart. 
         [0005]    When a cart is not present underneath the ejector heads  30 , errant drips of materials can fall from the ejector heads and produce undesired debris and contamination on an area  54  that can include the precision rails  34 , the track rails  22 , and the housing  42 . In order to produce three-dimensional objects with acceptable quality, the motion of the cart  14  beneath the ejector heads  30  needs to be precise. If materials from the ejector heads collect where the bearings  34  interface with the precision rails, the linear velocity of the cart is disrupted and the quality of the printed object is affected. Additionally, the collection of material drops on top of the housing  42  may affect the dissipation of heat from the motors and impact the performance and reliability of the motors. Therefore, improvements in three-dimensional printing systems that help eliminate the contamination on the precision rails and motor housing that affects the accuracy of the placement and movement of the cart would be beneficial. 
         [0006]    Devices have been produced that enable clearing of undesirable material from tracks. Metal flaps and plows positioned in front of wheels on a railroad engine have been used to clear materials such as ice and snow from railroad tracks. Wiping cloths or cleaning tissues affixed to an underside of model trains have also been used to wipe undesired materials from model railroad tracks. However, such techniques are not optimized for use in removing materials used in three-dimensional printing, which may solidify or cure after being ejected. Such techniques are also not adapted to cleaning curved surfaces. Hand-tools having a curved edge adapted to scrape a curved surface have been produced, but such hand-tools are not optimized for cleaning materials used in three-dimensional printing or for cleaning along a continuous track. 
       SUMMARY 
       [0007]    An improved cart helps clean materials from rails in a three-dimensional object printing system. The cart includes two laterally spaced rails, each of the rails having an internal cavity extending through the rail along a longitudinal axis, two heating devices, one heating device connected to the internal cavity of one of the two laterally spaced rails and the other heating device connected to the internal cavity of the other of the two laterally spaced rails to enable each heating device to heat a surface of the rail to which the heating device is connected, a platform configured to move along the two laterally spaced rails, and a pair of scrapers mounted to the platform, one scraper being positioned to engage one of the two laterally spaced rails and the other scraper being positioned to engage the other of the two laterally spaced rails to enable the two scrapers to remove contaminant from the heated surfaces of the laterally spaced rails as the platform moves along the two laterally spaced rails. 
         [0008]    A three-dimensional object printing system that incorporates improved the carts includes two laterally spaced rails, each of the rails having an internal cavity extending through the rail along a longitudinal axis, two heating devices, one heating device connected to the internal cavity of one of the two laterally spaced rails and the other heating device connected to the internal cavity of the other of the two laterally spaced rails to enable each heating device to heat a surface of the rail to which the heating device is connected, a platform configured to support a three-dimensional object being formed by the three-dimensional object printing system, a plurality of bearings mounted to the platform to enable the platform to be supported on the two laterally spaced rails, and a pair of scrapers mounted to the platform, one scraper being positioned to engage one of the two laterally spaced rails and the other scraper being positioned to engage the other of the two laterally spaced rails to enable the two scrapers to remove contaminant from the heated surfaces of the laterally spaced rails as the platform moves along the two laterally spaced rails. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The foregoing aspects and other features of a cart that removes accumulated material and other debris from the precision surfaces within the printing system are explained in the following description, taken in connection with the accompanying drawings. 
           [0010]      FIG. 1A  and  FIG. 1B  illustrate an exemplary embodiment of the cart that is configured to remove the contaminants from the printing system. 
           [0011]      FIG. 2A  illustrates an exemplary embodiment of the scrapers configured to remove contamination from the printing system. 
           [0012]      FIG. 2B  illustrates an exemplary cross-section of the scrapers depicted in  FIG. 2A . 
           [0013]      FIG. 3  illustrates an exemplary embodiment of wiper pads that are configured to remove the contaminants from the printing system. 
           [0014]      FIG. 4  illustrates an exemplary cross-section of an internally heated precision rails that enable contamination to be removed from the printing system. 
           [0015]      FIG. 5  illustrates an exemplary embodiment of an externally heated precision rails. 
           [0016]      FIG. 6A ,  FIG. 6B ,  FIG. 6C , and  FIG. 6D  illustrate an exemplary process of removing contamination from the printing system. 
           [0017]      FIG. 7  illustrates an end view of an exemplary prior art embodiment of a cart for a printing system. 
           [0018]      FIG. 8  illustrates an isometric view of the exemplary prior art embodiment of a cart for a printing system depicted in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    For a general understanding of the environment for the system and method disclosed herein as well as the details for the system and method, reference is made to the drawings. In the drawings, like reference numerals designate like elements 
         [0020]      FIG. 1A  and  FIG. 1B  illustrate an exemplary embodiment of the cart  104  that is configured to remove the contaminants from rails of the printing system on which the cart moves. The cart  104  includes bearings  108  on which a platform  112  is mounted. The bearings  108  allow the cart  104  to roll along the precision rails  116 . The cart  104  also includes scrapers  120  that are mounted on the platform of the cart  104  to scrape and remove contamination from the surface of the precision rails  116  as the cart  104  moves along the precision rails  116 . The scrapers  120  can be in the shape of the perimeter of the precision rails  116 , such as circular, and be mounted to a support member affixed to the front of the cart  104 . In one example, the scrapers  120  can be semi-circular to engage with an upper portion of the surface of the precision rails  116 . In another example, the scrapers  120  are shaped into circular segments having a central angle that is less than 180 degrees, such as about 160 degrees. The cart  104  also includes a wiper blade  124  that extends beneath the cart  104  to wipe contamination from the housing  128  for the linear motors. The wiper blade  124  can be angled to direct the contamination towards one side of the housing  128  of the motors away from equipment such as pucks that are mounted beneath the cart  104 . The reader should also understand that the scrapers  120  and the wiper blade  124  can be positioned either in front of the cart  104  as illustrated in  FIG. 1A  and  FIG. 1B  or in another position with respect to the cart  104 . 
         [0021]      FIG. 2A  illustrates an exemplary embodiment of the scrapers  120  configured to remove contamination from the printing system. In this exemplary embodiment, the scrapers  120  are circular in shape to allow the scrapers  120  to roll along the surface of the precision rails  116  and scrape contamination from the surface of the precision rails  116 .  FIG. 2B  illustrates an exemplary cross-section of the scrapers  120 . The scrapers  120  include a lip  208  that extends from the scraper  120  at an angle, such as an acute angle, towards the surface of the precision rails  116  to scrape off contamination from the precision rails  116 . The lip  208  can be positioned in a shell  204  on one side of the scraper  120 . The shell  204  consists of a metal such as steel. In one example, the lip  208  engages less than one-half of the circumference of the rail engaged by the scraper  120 . The lip  208  can consist of a material such as a metal or the like. In one example, the lip  208  essentially consists of spring brass. The scraper  120  also includes a wiper  212  that is enclosed within the scraper  120 . The wiper  212  can consist of acrylonitrile-butadiene rubber (NBR). The wiper  212  is configured to remove contaminants that were loosened from the precision rail  116  by the lip  208 . As the cart transitions onto the precision rails  116 , the lip  208  and the wiper  212  are in contact with the precision rails but are not constrained to the diameter of the precision rails  116 . In one example, while the bearings are rigidly mounted to and fully support the cart  104  on the precision rails  116 , the scrapers  120  rest on the circumference and translate along the precision rails  116  as the cart  104  rolls on the precision rails  116  in a process direction. Positioning the scrapers  120  in this manner can avoid over-constraining the cart  104  due to mechanical tolerances. The wiper  212  and the lip  208  enable the scraper  120  to scrape contamination such as dirt, foreign particles, or moisture from the surface of the precision rails  116 . The reader should understand that parameters related to the scraper, precision rails, and cart, examples of which include, but are not limited to, the geometry of the scraper, the precision rails, and the cart and the velocity of the cart can vary to accommodate the geometries and dimensions of other printing systems. 
         [0022]      FIG. 3  illustrates another exemplary embodiment of the cart  104  that is configured to remove the contaminants from the printing system. The cart  104  includes wiper pads  304  that are mounted to the front of the cart  104  at a position that enables the wiper pads to remove contaminants away from the precision rails  116  of the printing system. In one example, the wiper pads  304  extend towards the center of the precision rails to direct debris and contamination falling from the precision rails to either side of the pucks mounted underneath the cart  104 . 
         [0023]      FIG. 4  illustrates an exemplary cross-section of the precision rails  116  that enable contamination to be removed from the rails of the printing system. The precision rails  116  consist of a heating device  404  connected to the internal cavity of a rail  116  to heat the precision rails  116 . In one embodiment, the heating device  404  is positioned either inside or outside a cylindrical shell  408  of the precision rails  116  in order to heat the exterior  408  of the precision rails  116  to a predetermined temperature. The exterior  408  can essentially consist of metal, ceramic, or the like. In one example, the heating device  404  can be positioned along the entire length of the precision rails  116 . 
         [0024]      FIG. 5  illustrates an exemplary embodiment of the precision rails  116 . The heating device  404  can be flexible to conform to the shape of the rails  116  and provide heat to the precision rails  116 . In one example, the heating device  404  is mounted along a lower surface of a rail  116  to provide controlled heating in the required areas of the precision rails  116 . In another example, the heating device  404  is positioned either inside the rail  116  or outside the rail  116 . Examples of the heating device  404  include, but are not limited to, a heat pad, a heat sheet, or the like. The reader should understand that parameters commonly associated with heating devices, such as watt density, control voltage and temperature set points can vary to accommodate the geometries and dimensions of the precisions rails being heated by the heating devices. 
         [0025]      FIG. 6A ,  FIG. 6B ,  FIG. 6C , and  FIG. 6D  illustrate an exemplary process of removing contamination  604  from the printing system. As illustrated in  FIG. 6A , as the cart  104  transitions from the standard track rails  22  ( FIG. 8 ) onto the precision rails  116  in a process direction, the scrapers  120  engage with the outer diameter of the precision rails  116 . A heating device  404  is mounted to the rails  116  to heat the precision rails  116 . As illustrated in  FIG. 6B , the precision rails  116  are heated to a temperature that causes the contaminants  604  to melt or loosen from the surface of the precision rails  116 . The thermal energy needed to heat the precision rails  116  is provided by the heating device  404 . As illustrated in  FIG. 6C , the contaminants  604  melt and drip from the surface of precision rails  116  after being melted. As illustrated in  FIG. 6D , the scraper  120  scrapes and removes the residual contaminants  604  that remain on the surface of the precision rails  116  as the cart  104  and the scraper  120  move along a process direction. In one example, the scrapers  120  are located ahead of the cart  104  and the bearings  108  to scrape, wipe, and prevent any contaminants coming in contact with the cart  104 , such as the bearings  108 . The reader should understand that while the scrapers  120  and the wiper pads  304  in these examples are positioned in front of the cart  104 , other embodiments locate the scrapers  120  and the wiper pads  304  in other positions that can vary with respect to the cart  104 . 
         [0026]    It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.