Patent Publication Number: US-2021178689-A1

Title: Dispensing powder

Description:
BACKGROUND 
     Additive manufacturing machines, sometimes called  3 D printers, produce objects by building up layers of material. Digital data may be processed into slices each defining that part of a layer or layers of build material to be formed into the object. In some additive manufacturing machines, the object slices are formed in a powdered build material spread in layers over the work area. Powder in each of the successive layers is fused in the desired pattern to form a solid object. 
    
    
     
       DRAWINGS 
         FIG. 1  is an isometric view illustrating one example of a device to dispense powder. 
         FIG. 2  is an isometric partial section view of the example device shown in  FIG. 1 . 
         FIGS. 3-5  present a sequence of section views illustrating an example dispensing operation for the device of  FIG. 1 . 
         FIG. 6  is an isometric view illustrating another example of a device to dispense powder. 
         FIGS. 7-9  present a sequence of section views illustrating an example dispensing operation for the device in  FIG. 6 . 
         FIG. 10  is a flow diagram illustrating one example of a method to dispense powder from a supply of powder. 
     
    
    
     The same part numbers designate the same or similar parts throughout the figures. The figures are not necessarily to scale. 
     DESCRIPTION 
     Some additive manufacturing machines are capable of using a variety of build material powders. It may be cost effective for the supply hoppers and dispensing mechanisms to accommodate the full range of powders used in such machines. Some build material powders tend to arch or rathole in the hopper, impeding the desired flow of powder at the outlet, particularly at the intermittent low flows associated with dispensing the small volumes of powder characteristic of additive manufacturing. 
     A new technique has been developed to help prevent unwanted arching or ratholing in powdered build material dispensers. In one example, the dispensing device includes an agitator that is movable at the outlet from the hopper intermittently at the urging of the dispenser during a dispensing operation. In one specific example, the agitator is implemented as a flexible flap that extends into the outlet of the hopper and overlaps the dispenser so that, during a dispensing operation, the dispenser pushes the flap across the outlet before releasing the flat to flex back toward the side of the outlet. 
     Actuating a flap or other agitator directly with the dispenser avoids the need for a discrete external drive mechanism while still breaking up powder in or near the outlet where it might otherwise more acutely impede accurately dispensing a small volume of powder. In addition, the intermittent agitation inherent in the dispenser as actuator can be effective for a variety of different powdered build materials, and helps avoid the further blockages that can be caused in some powders by vibrating agitators. 
     While examples implementing the new technique were developed to handle powdered build materials for additive manufacturing, examples are not limited to additive manufacturing. The examples described herein and shown in the figures illustrate but do not limit the scope of the patent, which is defined in the Claims following this Description. 
     As used in this document: “and/or” means one or more of the connected things; a “closer” means a dispenser configured to dispense a fixed volume of material from bulk material inside the hopper; and a “flap” means a flat flexible piece of material fixed along one part and extending to another part that is free to flex back and forth. 
       FIG. 1  is an isometric view illustrating one example of a device  10  to dispense a powder  12 .  FIG. 2  is an isometric partial section view of device  10  from  FIG. 1 .  FIGS. 3-5  are section views with a supply of powder  12  in device  10 . Referring to  FIGS. 1-5 , dispensing device  10  includes a hopper  14  to hold a supply  16  of powder  12 , an outlet  18 , and a dispenser  20  at outlet  18 . A dispenser  20  may be attached to hopper  14  at outlet  18 , for example as shown in  FIGS. 1-5 , or a dispenser  20  may be integrated into outlet  18  (for example as shown in  FIGS. 6-9 ). In the example shown in  FIGS. 1-5 , dispenser  20  is implemented as a doser to dispense a fixed volume of powder  12  from bulk supply  16 . In this example, doser  20  includes a cylindrical shaft  22  seated in a body  24 . Two grooves  26 A,  26 B are formed in shaft  22  opposite one another to hold a dose of powder  12 . Shaft  22  is turned 180° in body  24 , for example with a motor  28  and drive train  30 , to dispense powder  12  alternately from each groove  26 A,  26 B. 
     Dispensing device  10  also includes an agitator  32  that moves in outlet  18  intermittently at the urging of doser  20  to break up powder  12  in supply  16  at the bottom of hopper  14 . In this example, agitator  32  is implemented as a flexible flap that extends from a first part  34  affixed to one sidewall  36  of hopper  14  to a second part  38  in outlet  18  overlapping doser  20 . Also in this example, flap  32  is detachable, clamped to hopper  14  with clamps  40 . As best seen in  FIGS. 3 and 5 , agitator flap  32  is positioned inside hopper  14  so that second part  38  rests against one side  42  of outlet  18  and extends into doser recess  26 A ( FIG. 3 ) or  26 B ( FIG. 5 ). If desired, flap  32  may be positioned inside hopper  14  so that the flex in the flap biases second part  38  against the side  42  of outlet  18 , for example to increase a return force. 
     During a dispensing operation, doser shaft  22  is rotated counter-clockwise to dispense powder  12  from one recess  26 A and refill the other recess  26 B, as shown in the sequence of  FIGS. 3-5 . The rotating shaft  22  moves the second part  38  of agitator flap  32  across outlet  18 , as shown in  FIG. 4 , until flap  32  is released at recess  26 B and flexes back toward the side of outlet  18 , as shown in  FIG. 5 . Flap  32  may be moved part way across outlet  18 , as shown in  FIG. 4 , or fully across outlet  18 . Flap  32  may be moved partially or fully across outlet  18 , as desired, by varying the geometrical relationship of the parts at outlet  18 . For example, extending the second part  38  of agitator flap  32  deeper into recess  26 A,  26 B will allow flap  32  to move further across the width of the outlet  18  during a dispensing operation. Also, flap  32  may be located toward the interior of hopper  14  rather than at the side of hopper  14 . For example, it may be desirable in some implementations to locate flap  32  at the center of hopper  14  to accommodate a doser shaft  22  that rotates bidirectionally (clockwise and counterclockwise) for dispensing. 
       FIG. 6  is an isometric view illustrating another example of a device  10  to dispense powder  12 .  FIGS. 7-9  are section views with a supply of powder  12  in device  10 . In the example shown in  FIGS. 6-9 , device  10  includes a conical hopper  14  with a dispenser  20  implemented as a valve that opens and closes outlet  18  to dispense powder  12  from bulk supply  16 . Also in this example of dispensing device  10 , agitator  32  is implemented as a plate that pivots back and forth on a shaft or other suitable pivot  44 . Agitator plate  32  includes a first part  34  attached to pivot  44  and a second part  38  that extends in to outlet  18  and overlaps valve  20 . During a dispensing operation, valve  20  is rotated 90° clockwise to open outlet  18 , as shown in  FIGS. 7 and 8 . As valve  20  is rotated clockwise from the open position shown in  FIG. 8  toward the closed position (shown in  FIG. 7 ), the rotating valve  20  moves the second part  38  of agitator plate  32  across outlet  18 , as shown in  FIG. 9 , until plate  20  is released and pivots back toward the center of outlet  18  at the urging of a return spring  46 . 
     The extent of travel of agitator plate  32  back and forth across outlet  18  may be varied by changing the geometrical relationship of the parts at outlet  18 . For example, the extent of travel may be lengthened from that shown by biasing plate  32  toward the left side of outlet  18  so that valve  20  engages and moves plate  32  across outlet  18  when opening as well as when closing. Also, opposing torsion springs  46  or other suitable biasing devices may be used to provide a return force in both directions, thus accommodating valve  20  opening and closing clockwise and/or counter-clockwise. 
       FIG. 10  is a flow diagram illustrating one example of a method  100  to dispense powder from a supply of powder, such as might be executed with a dispensing device  10  shown in  FIGS. 1-5 . Part numbers in the description of method  100  are made with reference to the example device  10  shown in  FIGS. 1-5 . However, method  100  may be executed with other dispensing devices. Referring to  FIG. 10 , powder  12  is intermittently dispensed from a supply  16  (block  102 ) and, simultaneously with each dispensing, something is flapped within the powder supply  16  (block  104 ). For example, the flapping may be executed by a doser  20  moving an agitator flap  32  one way and the flap flexing back the other way as shown in  FIGS. 4 and 5 . Intermittently flapping something within the powder supply simultaneously with each dispensing operation helps keep the powder loose for dispensing without constant agitation. 
     As noted above, the examples shown in the figures and described herein illustrate but do not limit the patent, which is defined in the following Claims. 
     “A”, “an” and “the” used in the claims means one or more. For example, “a flap” means one or more flaps and “the flap” means the one or more flaps.