Abstract:
The present invention provides a  3 D printer comprising a base, a build platform, an adjustable support assembly (e.g., including a resilient support point having a spring and a post) coupling the build platform to the base, and a locking mechanism that secures a position of the build platform relative to the base. The locking mechanism can include a releasable clamp positioned between the base and the post. The present invention also provides a method of tramming a build platform on a  3 D printer. The method comprises resiliently supporting the platform on a base at a first support point, pushing on a build surface of the platform at the first support point to move the platform relative to the base, and locking a position of the platform relative to the base at the first support point after the pushing step. Preferably, pushing includes contacting a print head with the build surface.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to three-dimensional (“3D”) printing, and more particularly to an apparatus and method for establishing the proper geometric relationship between a build surface of a 3D printer and the constrained motion axes of a deposition nozzle. 
         [0002]    BACKGROUND 
         [0003]    3D printing, also called additive manufacturing, involves using a computerized model to make a three-dimensional object in layers using an additive process. As used herein, 3D printing can include any additive process, including selective laser melting (SLM), direct metal laser sintering (DMLS), selective laser sintering (SLS), fused deposition modeling (FDM), and stereolithography (SLA). Fused Deposition Modeling (or Fused Filament Fabrication) is 3D printing process in which a heated head and nozzle system is used to extrude a filament of thermoplastic or similar material, creating a single-layer pattern under numeric control. Subsequent layers are added in sequence and thermally fuse to the underlying layer. By defining and controlling the shape of each layer and the total number of layers, a complete 3D structure can be created or printed. 
         [0004]    The 3D printing space is typically defined via the Cartesian coordinate system, with the X and Y axes being horizontal and the Z axis being vertical. The first layer is deposited on a horizontal, planar build surface and subsequent layers are deposited by indexing along the Z axis. The numerically controlled layer pattern is generated in the XY plane by moving the deposition nozzle along that plane relative to the build surface. In practice, this can be done by moving the deposition nozzle in both the X and Y directions, moving the nozzle in one of the X and Y directions and moving the build surface along the other of the X and Y directions, or moving the build surface in both the X and Y directions. Similarly, layers are generated by moving the nozzle along the Z axis relative to the build surface. This can be accomplished by moving the nozzle or the build surface in the Z direction. 
         [0005]    In order to properly deposit a first uniform layer and ensure that it mechanically bonds to the build surface, a number of conditions must exist. The build surface must be planar with a high degree of mechanical flatness. Also, the planar build surface must be parallel to the XY motion plane described and defined by the relative motion between the extrusion nozzle and build surface in the X and Y directions. Surface deviations (e.g., warping) along the Z axis or a lack of XY plane parallelism can negatively affect thickness uniformity of the first deposited layer or, in extreme cases, can cause the extruded filament to lose contact with the build surface during first layer generation. First layer pattern generation and build surface adhesion will typically fail if contact is lost. 
         [0006]    Tramming is the process of establishing parallelism between the XY motion plane of the nozzle and the build surface. Conventional tramming requires manually and mechanically adjusting the planar attitude of the build surface with multi-point tramming mechanisms, such as jacking screws, cams, and the like. Z-axis measurements are made between the extrusion surface of the nozzle and the build surface as the nozzle is moved within its XY plane. Incremental and sequential mechanical adjustments are made to the tramming mechanisms until the distance along the Z-axis or gap between the build surface and the nozzle is uniform along the XY plane, thus creating the desired parallelism. This process is laborious and time-consuming, requiring precise measurement and adjustment. 
       SUMMARY 
       [0007]    The present invention provides a 3D printer comprising a base, a build platform supported by the base, an adjustable support assembly coupling the build platform to the base, and a locking mechanism that secures a position of the build platform relative to the base. The adjustable support assembly can include a resilient support point (e.g., three resilient support points) between the base and the platform. For example, the resilient support point can include a compressible resilient member supporting the platform on the base and a post extending between the platform and the base. Preferably, the post includes a pivot to facilitate limited angular movement of the post relative to the platform or the base 
         [0008]    In one embodiment, the locking mechanism includes a releasable clamp operatively positioned between the base and the post. For example, the locking mechanism can be movable from an unlocked position, where the platform is movable relative to the base at the support point, and a locked position, where the platform in substantially inhibited from moving relative to the base at the support point. 
         [0009]    The present invention also provides a method of tramming a build platform on a 3D printer. The method comprises resiliently supporting the platform on a base at a first support point, pushing on a build surface of the platform substantially at the first support point to move the platform relative to the base, and locking a position of the platform relative to the base at the first support point after the pushing step. Preferably, pushing down includes contacting a print head with the build surface. In this embodiment, the locking step can occur with the print head in contact with the build surface. 
         [0010]    In one embodiment of the method, after the recited resiliently supporting, pushing, and locking steps associated with the first support point, these steps are repeated at a second support point while maintaining the locked position of the platform relative to the base at the first support point. The method preferably continues by performing the recited resiliently supporting, pushing and locking steps at a third support point while maintaining the locked position of the platform relative to the base at the first and second support points. 
         [0011]    Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  illustrates a 3D printer on which features of the present invention can be applied. 
           [0013]      FIG. 2  is a perspective view of a platform assembly for use in a 3D printer. 
           [0014]      FIG. 3  is a partially exploded view of the platform assembly of  FIG. 2 . 
           [0015]      FIG. 4  is a cross-sectional perspective view taken along line  4 - 4  in  FIG. 2 . 
           [0016]      FIG. 5  is a bottom perspective view of the platform assembly of  FIG. 2 . 
           [0017]      FIG. 6  is a perspective view of a portion of the platform assembly of  FIG. 2 . 
           [0018]      FIG. 7  is a schematic cross-sectional view of the platform assembly of  FIG. 2  during an automatic tramming operation. 
       
    
    
       [0019]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
       DETAILED DESCRIPTION 
       [0020]      FIG. 1  illustrates a 3D printer  10  including a base  12 , a housing  14 , a print head  16 , a control panel  18 , and a platform assembly  100  embodying aspects of the invention. The platform assembly  100  is usable with a variety of different numerically-controlled manufacturing systems, such as the 3D printing systems disclosed in Skubic et al., U.S. Patent Application Publication No. 2010/0100222; and Calderon et al., U.S. Pat. No. 6,629,011, the entire contents of each of which are incorporated herein by reference. Alternatively, the platform assembly  100  may be used with any other type of numerically-controlled manufacturing system, such as a metal injection molding (MIM) system, a computer numerical control (CNC) machining system, and the like. 
         [0021]    With reference to  FIGS. 2 and 3 , the platform assembly  100  includes a base  104  and a build platform  108  having a planar build surface  112  on which layers of material can be deposited during a 3D printing operation. The build platform  108  is supported on the base  104  at three points—A, B, and C—by an adjustable support assembly  116 . In the illustrated embodiment, the three support points A, B, C are located proximate the outer periphery of the build platform  108  for increased stability; however, the three points A, B, C may be located at other locations on the build platform  108 . As described in further detail below, the adjustable support assembly  116  includes automatic tramming functionality that allows the build platform  108  to be leveled relative to the XY motion plane of a deposition nozzle  120  ( FIG. 7 ). 
         [0022]    Referring to  FIG. 3 , the adjustable support assembly includes a spring  124  disposed between the build platform  108  and the base  104  at each of the support points A, B, C such that the build platform  108  can “float” on the springs  124  above the base  104 . In the illustrated embodiment, the springs  124  are coil springs having a relatively low spring rate. Alternatively, the springs  124  can be elastomeric washers, Belleville springs, or other compliant structures. When the springs  124  are in their neutral or relatively uncompressed state (i.e., compressed only by the weight of the build platform  108 ), the build platform  108  floats above the base  104  at a height where the build surface  112  is located above a desired height Z′ of the first layer deposition ( FIG. 7 ). In other words, if Z′=0, the build surface  112  has a positive Z-axis coordinate when the springs  124  are in their neutral state. 
         [0023]    Referring to  FIG. 4 , the adjustable support assembly  116  further includes a rigid pin  128  extending from the build platform  108  and through an opening in the base  104  at each of the support points A, B, C. An upper end  132  of each pin  128  is received in a corresponding boss  136  on the bottom of the build platform  108  to couple the pins  128  to the build platform  108 . In some embodiments, the bosses  136  and the pins  128  have pivot, gimbal, or ball-and-socket capability, allowing for angular deflection of the pins  128  relative to the build platform  108  while still maintaining the relative spacing between the pins  128 . 
         [0024]    With reference to  FIGS. 4-6 , the platform assembly  100  further includes a locking mechanism  140  for selectively locking each of the respective pins  128  relative to the base  104 , thereby locking the build platform  108  at a desired height and orientation relative to the base  104 . In the illustrated embodiment, the locking mechanism  140  includes an electric motor  144 , a cam wheel  148 , and three clamps  152 , each engageable with one of the respective pins  128 . The cam wheel  148  is configured as a worm gear and includes a plurality of teeth  156  that engage a worm  160  on an output shaft  164  of the motor  144 . Thus, when the motor  144  is energized, the cam wheel  148  rotates relative to the base  104 . In some embodiments, the motor  144  may be replaced by a manual crank or other means suitable for rotating the cam wheel  148 . 
         [0025]    Referring to  FIG. 6 , the cam wheel  148  includes a circumferential cam surface  168  that engages cam followers  172  on each of the clamps  152  to impart rotation to the clamps  152  ( FIG. 6 ). When the clamps  152  are rotated in a first direction (counter-clockwise in the orientation of  FIG. 6 ), the clamps  152  tighten on to the pins  128  to lock the pins  128  relative to the base  104 . When the clamps  152  are rotated in a second, opposite direction (clockwise in the orientation of  FIG. 6 ), the clamps  152  release the pins  128 , allowing the pins  128  to freely slide relative to the base  104  in the Z-direction. The clamps  152  can be biased in the second direction by one or more torsion bars, springs, or any other suitable arrangement (not shown). 
         [0026]    In the illustrated embodiment, the cam surface  168  is profiled so that the individual clamps  152  can be tightened or loosened sequentially as the cam wheel  148  rotates. Alternatively, the locking mechanism  140  may include solenoids, servo motors, pneumatic or hydraulic cylinders, or any other actuators suitable for clamping and releasing the respective pins  128 . 
         [0027]    The support assembly  116  is operable to provide automatic tramming functionality for the build platform  108  to level the build surface  112  relative to the XY motion plane of the deposition nozzle  120 . The steps described below can be fully automated and executed by a controller of the 3D printing system as an initialization routine prior to any new 3D printing operation. Alternatively any or all of the steps can be performed or controlled manually by a user of the 3D printing system. 
         [0028]    With reference to  FIGS. 4 ,  6 , and  7 , in order to perform the tramming operation for the illustrated and described embodiment, the deposition nozzle  120  is positioned directly above the build platform  108  at one of the support points (e.g., the first support point A). The clamp  152  at the first support point A is loosened (e.g., by energizing the motor  144  to rotate the cam wheel  148 ) allowing the pin  128  to slide freely relative to the base  104  such that the build platform  108  rests or floats on the spring  124  ( FIGS. 4 and 6 ). The clamps  152  at the remaining two support points (e.g., support points B and C) may be either loose or clamped without affecting the tramming operation at the first support point A. Next, the nozzle  120  is lowered (i.e. moved in the negative Z-direction) until it contacts the build surface  112  ( FIG. 7 ). The nozzle  120  continues to move downward, bearing against the build surface  112  to move the build platform  108  toward the base  104  against the biasing force of the spring  124 . The nozzle  120  stops when it reaches Z′ (e.g., Z=0), corresponding with the desired first deposition layer elevation. The clamp  152  at the first support point A is then tightened (e.g., by energizing the motor  144  to rotate the cam wheel  148 ), locking the pin  128  in place. This fixes the elevation of the build surface  112  to Z′ at the first support point A. 
         [0029]    Once the elevation of the build surface  112  is set to Z′ at the first support point A, the nozzle  120  moves away from the build surface  112  in the Z direction a sufficient distance so as to be completely clear of the build surface  112  in the XY plane. The nozzle  120  then moves into position direction above the build platform  108  at one of the remaining support points (e.g., the second support point B). The clamp  152  at the second support point B is loosened (e.g., by energizing the motor  144  to rotate the cam wheel  148 ) allowing the pin  128  to slide freely relative to the base  104  such that the build platform  108  rests or floats on the spring  124 . The clamp  152  at the first support point A remains clamped to maintain the set elevation of the build surface  112  at the first support point A. The nozzle  120  is then lowered (i.e. moved in the negative Z-direction) until it contacts the build surface  112  above the second support point B. The nozzle  120  continues to move downward, bearing against the build surface  112  to move the build platform  108  toward the base  104  against the biasing force of the spring  124 . The nozzle  120  stops when it reaches Z′, and the clamp  152  at the second support point B is tightened (e.g., by energizing the motor  144  to rotate the cam wheel  148 ), locking the pin  128  in place. This fixes the elevation of the build surface  112  to Z′ at the second support point B. 
         [0030]    Once the elevation of the build surface  112  is set to Z′ at the first and second support points A, B, the nozzle  120  moves away from the build surface  112  in the Z direction a sufficient distance so as to be completely clear of the build surface  112  in the XY plane. The nozzle  120  then moves into position directly above the build platform  108  at the third and final support point C. The clamp  152  at the third support point C is loosened (e.g., by energizing the motor  144  to rotate the cam wheel  148 ) allowing the pin  128  to slide freely relative to the base  104  such that the build platform  108  rests or floats on the spring  124 . The clamps  152  at the first and second support points A, B remain clamped to maintain the set elevation of the build surface  112  at Z′ at the first and second support points A, B. The nozzle  120  is then lowered (i.e. moved in the negative Z-direction) until it contacts the build surface  112  above the third support point C. The nozzle  120  continues to move downward, bearing against the build surface  112  to move the build platform  108  toward the base  104  against the biasing force of the spring  124 . The nozzle  120  stops when it reaches Z′, and the clamp  152  at the third support point C is tightened (e.g., by energizing the motor  144  to rotate the cam wheel  148 ), locking the pin  128  in place. This fixes the elevation of the build surface  112  to Z′ at the third support point. 
         [0031]    At the completion of this procedure, all of the support points A, B, C have been locked, fixing the build surface  112  at a known Z axis position (Z′). Because three points fully define a plane, fixing the build surface  112  at Z′ at each of the three support points A, B, C levels the build surface  112  relative to the XY motion plane of the nozzle  120 . In addition, the elevation of the build surface  112  is equal to the contact point between the build surface  112  and the nozzle. All layering operations during a subsequent 3D printing process can now be performed with reference to this known build surface elevation Z′. 
         [0032]    Thus, the invention provides an automated and efficient method for accurately leveling the build surface  112  relative to the XY movement plane of the deposition nozzle  120  and for establishing the build surface  112  as a known datum plane. The invention may be implemented on both new and existing 3D printing systems. Existing 3D printing systems may be modified simply by replacing the platform assembly with the platform assembly described above and by making minor alterations to the control subsystem. 
         [0033]    Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described. For example, although it is believed that the tramming operation is best performed with the nozzle directly above three support points, it is possible to perform the operation with the nozzle misaligned with the support points, and a different number of support points could be used. In addition, instead of tramming the build surface to be horizontal, the concepts of the present invention could also be used to establish a non-horizontal build surface. 
         [0034]    Various features of the invention are set forth in the following claims.