Abstract:
A device for increasing the uniformity of solids within a solids fabrication system, such as a direct light fabrication (DLF) system in which gas entrained powders are passed through the focal point of a moving high-power light which fuses the particles in the powder to a surface being built up in layers. The invention provides a feed through interface wherein gas entrained powders input from stationary input lines are coupled to a rotating head of the fabrication system. The invention eliminates the need to provide additional slack in the feed lines to accommodate head rotation, and therefore reduces feed line bending movements which induce non-uniform feeding of gas entrained powder to a rotating head.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. provisional application Ser. No. 60/131,995 filed on Apr. 29, 1999. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with Government support under Contact No. W-7405-ENG-36, awarded by the Department of Energy. The Government has certain rights in this invention. 
    
    
     REFERENCE TO A MICROFICHE APPENDIX 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains generally to solids fabrication processes, and more particularly to a feedthrough device for distributing gas entrained materials to a rotating head assembly, such as found within a solids fabrication system. 
     2. Description of the Background Art 
     Fabrication of three-dimensional solids is being performed within fabrication systems that build up a solid by layered fusing bits of material carried in a gas. One such system is a directed light fabrication (DLF) system. In a DLF system powders are injected into a moving beam of high power light, generally a laser light beam. The powders are typically metallic particles, however plastics and other fusible materials can be used. The powders are carried by a stream of gas, commonly argon, to the focal point of the laser beam wherein fusing of the material to the previous layer of material occurs. The gas provides a non-reactive carrier for the particles of the powder which are to be fused into a solid. In practice, the powder often gets injected non-uniformly about the beam resulting in a build-up of the fused powder material that is also of non-uniform structure. The flow of powder in the input feed lines may be adjusted to suit conditions required at the head, yet non-uniform injection may still occur. One contributing factor to the non-uniform injection of powders arises when the laser head and nozzles within a DLF system rotate. Conventionally, in order to accommodate head rotation, the input lines have been provided with an amount of slack in them. During rotational movements, the input lines are thereby subjected to a variety of movements which alter the distribution of gas entrained powder flow being emitted at the nozzles. 
     To achieve a uniform finished structure, therefore, it is important to reduce the disruptive gyrations of powder feed lines whereby increased uniformity of powder injection may occur. The rotary powder feed through apparatus in accordance with the present invention provides a coupling which satisfies the need to minimize feed line movements to the head, and overcomes additional deficiencies in current techniques for the coupling of gas entrained powder to a rotating head assembly. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a feed through coupling between a stationary set of input lines and a set of output lines which are rotating with the head within a solids fabrication system, such as a directed light fabrication (DLF) system. The feed through system thereby eliminates the need for slack supply lines, and the motions thereof, to accommodate the rotation. The gas entrained powder feed through of the invention can employ input and output lines that remain relatively fixed, the lines do not gyrate and flop about in response to head rotations, as they do not contain the slack in the tubing (hoses) which was required previously. Eliminating the gyrations of the feed tubes by the inventive system provides for improvement in the uniformity of the powder flow rate. 
     An object of the invention is to provide a rotational interface between a set of fixed input lines and a rotating nozzle head being fed with gas entrained powder. 
     Another object of the invention is to maintain even distribution of gas entrained powder through the rotary powder feed through. 
     Another object of the invention is to minimize flow restriction introduced by the rotary powder feed through according to the invention. 
     Another object of the invention is to provide a feed through mechanism that can be implemented to accommodate various numbers of feed lines. 
     Another object of the invention is to provide for free rotational movement of the fabrication head without interference from the interactions between feed lines. 
     Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only: 
     FIG. 1 is a cross section of an eight line rotary powder feed through apparatus according to the invention. 
     FIG. 2 is a plan view of the stationary base member portion of the apparatus shown in FIG.  1 . 
     FIG. 3 is a plan view of the rotating base member portion of the apparatus shown in FIG.  1 . 
     FIG. 4 is a plan view of the interior of the rotating base member shown in FIG.  3 . 
     FIG. 5 is a cross section view of the stationary base member shown in FIG. 2 taking though line  5 — 5 . 
     FIG. 6 is a cross section view of the rotating base member shown in FIG. 3 taken through line  6 — 6 . 
     FIG. 7 is a side view of an aperture chamber shape employed within the rotatable base member. 
     FIG. 8 is an end view of the aperture chamber shape of FIG.  7 . 
     FIG. 9 is a top view of the aperture chamber shape of FIG.  7 . 
     FIG. 10 is a cross section of an alternate embodiment of the rotary powder feed apparatus according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring more specifically to the drawings for illustrative purposes, the present invention is embodied in the apparatus generally shown in FIG.  1  through FIG.  10 . It will be appreciated that the apparatus may vary as to configuration and as to details of the parts, and that the method may vary as to the specific steps and sequence, without departing from the basic concepts as disclosed herein. 
     Referring first to FIG. 1, a rotary powder feed through apparatus  10  according to the invention is shown in cross section. The rotary powder feed through apparatus generally comprises an input member and an output member. In the embodiment of rotary powder feed through  10  shown, the input member is provided by a stationary plate assembly  12 , while the output member is provided by a rotatable disk assembly  14 . The stationary plate assembly  12  is retained in position by a mounting bracket  16 . The stationary plate assembly  12  comprises a stationary base member  18  which is attached to the mounting bracket  16 . The stationary base member  18  is configured with six mounting holes  20   a-f  which line up with corresponding mounting holes  22   a- f on the mounting bracket  16  through which bolts  24   a-f  are inserted and retained by nuts  26   a- f. Referring also to FIG. 2, the six mounting holes  20   a-f  on the stationary base member  18  can be seen along with an array of eight input connection cavities  30   a-h.  The stationary base member  18  can be seen as a cutaway view in FIG. 5 wherein a single pair of fluid communication channels can be seen. The input connection cavities  30   a,    30   e  preferably lead into conical, “V-shaped”, input chambers  32   a,    32   e,  respectively. 
     Referring again to FIG. 1, a circular array of eight input feed tubes  28   a-h  are shown for receiving gas entrained powder. The input feed tubes  28   a-h  are insertably held within input connection cavities  30   a-h,  the friction fit within the cavity may be augmented with adhesives or any of various retention fasteners. Alternatively, connectors (not shown) may be used to attach the tubes to the input connection cavities  30   a-h.  The input connection cavities  30   a-h  open up into input chambers  32   a-h  within the stationary base member  18  and terminate at a planar face  34 . 
     Retained in proximal contact with the stationary plate assembly  12  is a rotatable disk assembly  14  which rotates within a bearing  38  held annularly disposed by retainer  40  peripherally about a rotatable base member  36  with axis of rotation  42 . Planar face  44  is thereby retained in proximal surface contact with planar face  34  of the stationary plate assembly  12 . Referring also to FIG. 3, the output side of the rotatable base member  36  is shown with output connections  50   a-h  around a threaded cavity  54 . 
     The opposing planar faces in FIG.  1 . are shown are sealed to one another by seal  46  to prevent excess leakage of gas. It will be appreciated that seal  46  may comprise an o-ring or other sealing mechanism. The embodiment is shown with the rotatable disk assembly  14  retaining bearing  38  in a surrounding recess by means of a retainer  40 . The bearing  38  containing the rotatable disk assembly  14  is held in place between the stationary base member  18  and the mounting bracket  16 . Alternatively the bearing may be used to attach the rotatable disk assembly  14  to the stationary plate assembly  12 , wherein the combination is then attached to a mounting bracket, or other member, for positioning the rotary powder feed-through. 
     Referring also to FIG. 4, eight output chambers  48   a-h  are disposed on the planar face  44  of the rotatable base member  36  to collect gas entrained powder for the output connection cavities  50   a-h.  Chambers  48   a-h  are shown as adjacent arcuate sections on the planar face  44 , the collection of arcuate sections forming a ring  56  which align with the outputs from the stationary base member for collecting the gas entrained material passing therethrough. The corners of the pyramids forming the chambers  48   a-h  are shown extending inwardly as they narrow down toward the output connection cavities  50   a-h.  FIG. 6 shows a cross-section of the rotational base member  36  with chambers  48   a,    48   e,  and output connection cavities  50   a,    50   e.  The shape of a chamber  48  is shown in detail in FIG. 7 as hidden lines connecting with the connection cavity  50 . A detailed view looking into a chamber  48  is shown in FIG. 8. A chamber  48  is shown in FIG. 9 as viewed from the axis of rotation  42  of FIG.  1 . 
     Referring again to FIG. 1, output feed tubes  52   a-h  are retained within the connection cavities  50   a-h  to carry gas entrained powder to the nozzle head. A recessed threaded cavity  54  allows the connection of a rotational driving mechanism along with additional equipment in-line with the rotational axis of the rotary powder feed through. 
     In use, the gas entrained powder enters the array of input feed tubes  28   a-h  into the connection cavities  30   a-h  and expands in the conical chambers  32   a-h.  Each gas entrained powder stream flowing from an input chamber is collected by one or more output chambers  48   a-h.  Therefore, it will be appreciated that an input connection may be in fluid communication with any output connection as determined by the extent of rotation between the input and output members. The output chambers are preferably aligned adjacent to one another such that only a narrow planar divider separates each chamber at the planar face  44  of the rotatable base member  36 ; therefore the gas from the inputs are generally commutated across a pair of output chambers under angular movement of the rotatable disk assembly  14 . It will be appreciated that this configuration of adjacent output chambers separated by a narrow planar divider provides for gas intrained powder collection that induces relatively constant backpressure in view of the minimal flow resistance offered at the planar interface between the input and output chambers. If other chamber configurations or shapes are used, the width of the divider between the could be measured in degrees of arc, and preferably less than one or two degrees. For example, if the arc were as much as five degrees, then for an eight output rotary powder feed through, a forty degree portion (e.g., 10% or more depending on chamber shape) of the rotatable disk portion might be unable to communicate the gas intrained powder from the stationary base member. Therefore with the input chamber described, a separation arc exceeding about five degrees is expected to create fluctuations, in material flow since over a tenth of the area of the chambered ring would be unable to communicate gas entrained powder. 
     The output chambers  48   a-h  are held in closely spaced proximity with the input chambers for communicating gas entrained powder, which can best be seen in FIG.  4 . When the disk assembly  14  is rotating, each input connector is put into fluid communication with one, or more often two, output connectors. The splitting of the flow of gas entrained powder across multiple chambers reduces the specific flow distribution of the input lines by averaging each across two adjacent chambers. If the chambers are alternatively configured to partially overlap one another, leaving no complete dividing space between chambers, the resultant leakage between chambers can have the undesired effect of completely changing the flow distribution from the inputs to the head. 
     FIG. 10 shows a rotary powder feed through apparatus  60  that employs a different rotational mechanism. A stationary base member  62  is attached to a rotational base member  64 , and the assembly is in turn attached to a mounting bracket  66 . The input and output connection arrangement is the same as used for FIG.  1 . However, within this embodiment, a shaft  68  is used in conjunction with a lower bearing  70  and an upper bearing  72  and retained to the shaft with a retainer  74 . As can be seen, the axial arrangement of this embodiment is similar to the manner of retaining the front wheels on many automobiles. In large DLF systems, which could employ large feed lines, this embodiment can eliminate the need for large diameter bearings. 
     The described embodiment is preferably machined from a metal material whose wear resistance to the flow of the gas entrained particulates provides sufficient longevity. Elements of the invention may be materially hardened, or be provided with inserted materials to augment the hardness and thereby further increase longevity of the feedthrough device. 
     It will be appreciated that variations of the described embodiments may be implemented by anyone with ordinary skill in the art. For example, the number and arrangement of the input feed lines can be changed, and even multiple circular arrays of connectors can be supported. Two methods of attaching the rotatable disk assembly to the stationary plate assembly have been shown, whereas a number of alternative connection methods can be configured by one of ordinary skill in the art. A preferred shape for the input and output chambers has been shown, however these chambers can be shaped in a variety of forms. As can be seen, the output chambers are preferably shaped to collect the gas entrained particles over a large area to provide for a constant backpressure. It should be apparent to one of ordinary skill in the art, however, if the input nozzles were configured to uniformly spread the particles over a wide area, then large input chambers could be used with a smaller area of output chambers to collect the gas entrained particles. 
     It should be recognized that the inventive principles are generally applicable to other situations that require material feedthrough while maintaining somewhat fixed levels of flow distribution in lines. Furthermore for applications in which a rotating set of input lines is to be coupled to a fixed set of output lines, the roles of stationary and rotating can be reversed wherein the input member would rotate and the output member would remain stationary. 
     Accordingly, it will be seen that the invention of a rotary powder feed through provides a simple and rugged device for providing uniform flow of gas entrained powder to a rotating head that eliminates the numerous drawbacks associated with the use of long feed tubes wherein the slack of the tubes is used to compensate for the rotation of the head. 
     Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of this invention should be determined by the appended claims and their legal equivalents.