Patent Publication Number: US-2019168436-A1

Title: Fused Deposition Modeling Filament Production Apparatus

Description:
FIELD OF THE INVENTION 
     The invention relates to a fused deposition modeling filament production apparatus. 
     BACKGROUND OF THE INVENTION 
     Fused deposition modelling (FDM) also known as 3D printing is becoming available in both professional and private environments. Various materials can be printed into a wide variety of printed objects. Most objects are modeled by feeding an FDM material into an FDM or 3D printer which fuses the material and the objects are made. The fusing can be a thermal process wherein the FDM material is molten and subsequently fused to previously deposited parts of the object. The previously deposited parts of the object are very often layers of the FDM material. The FDM material in such thermal process is usually a thermoplastic material. The deposition and fusion of the molten material requires a steady flow of material. Thus, the thermoplastic material in a large variety of 3D printers is provided as a filament, an FDM filament. The material however is not limited to thermoplastic. It can also be any other material suitable for FDM or 3D printing provided that it can be cast into a filament. Other examples comprise (glass) fiber reinforced plastics, or plastics with a wood or metal filler, or plastics filled with for example piezo-electric particles or nano circuits. 
     FDM filament is usually efficiently produced off line in factories on a large scale at relatively low cost. Also, relatively high quality can be maintained as the manufacturing equipment can be very well tuned for mass production. The produced filament is subsequently provided on reels which can be loaded into a local FDM or 3D printer for the various purpose and applications. 
     For product developers or scientists exploring new FDM applications standard FDM materials do not meet their needs, as they may want to experiment with various material compositions. Ordering FDM materials adapted for specific purposes may be expensive if possible at all. Moreover, materials used in FDM objects, or other objects may be recycled and re-used in the FDM printing. An example is polyethylene, which is very used in for example soda bottles. This material is very suitable for recycling and re-use in FDM printing. Another example is acrylonitrile butadiene styrene (ABS), which is commonly used in larger plastic objects such as chairs, computers covers and more. 
     Thus a demand is growing for FDM filament production on a small scale allowing a free choice of FDM material compositions and additives such as coloring which can be utilized in homes, offices and laboratories. This enables researchers, students, artists to further develop FDM materials and bring FDM or 3D printing to a new level. 
     Known small scale FDM production units allow raw materials in shredded form to be extruded into FDM filament. Such production units however tend to lack the accuracy required to produce FDM filaments with constant composition and size. Varying FDM filament quality, causes varying quality of the FDM objects made from these materials. 
     SUMMARY OF THE INVENTION 
     It is therefore an object to provide a fused deposition modeling filament production apparatus which is suitable for producing filament on a small scale, while maintaining stable filament cross section with high accuracy of the produced filament diameter. 
     The object is achieved in a fused deposition modeling filament production apparatus comprising an extrusion unit comprising an extruder, feeding means for feeding FDM raw material into the extrusion unit, a filament discharge at an end of the extruder, a filament cooling unit linked to the filament discharge, a filament buffer unit for receiving and storing the filament from the cooling unit. The extrusion unit, the filament cooling unit and the filament buffer unit are accommodated in a frame. The extrusion unit is horizontally accommodated in a top section of the frame, having the feeding means on top of the extrusion unit and extending vertically from the extrusion unit. The filament discharge is arranged for substantially vertically downward discharging the extruded filament from the extrusion unit. The filament cooling unit and filament buffer unit are accommodated in a lower section of the frame below the extrusion unit. 
     The combination of horizontally oriented extruder and vertical discharge opening or nozzle allows optimal use of gravity. The feeding means arranged vertically on top of the horizontal extruder allows the FDM material to be captured and transported by a screw or shaft in the extruder barrel, which is arranged as a horizontally oriented tube. A vertically arranged extruder, and subsequently extruder screw would not have this advantage for FDM material in the form of granulate, and would require additional features to ensure proper feeding of the material in granulate form. For small scale production of FDM filament from shredded, granulate material using the filament production apparatus the orientation of the extruder relative to the feeding means is most advantageous, as it does not require any further feeding and mixing means other than the extruder and extruder screw itself. 
     Moreover, it is most advantageous to have a vertical downward discharge of the filament from the extrusion unit. This allows a cross section of the filament to be maintained in a same circumferential form or profile. For example, in case of a circular discharge opening, the filament will keep a circular cross section while flowing out of the discharge opening. When horizontally discharging the extruded filament and subsequently vertically further processing the filament, the cross section would become ovally or ellipsoidally distorted due to gravity and bending of the filament material while it is still hot and flexible. Thus, the vertically oriented discharge opening or nozzle allows the cross section of the extruded filament, determined by the cross section of the discharge opening at the moment of extrusion, to be maintained after the extrusion, even when the extruded filament may stretch due to gravity. So this cross section is maintained despite the influence of gravity on the hot filament exposed to this gravity. Any deformation due to gravity will be homogeneous in a horizontal direction. Thus, gravity has no adverse effect on the filament cross section after extrusion. 
     As an additional advantage, the vertical discharge opening allows a mutual position of the cooling unit and buffer below the extruder, which enable a compact design of the filament production apparatus with relatively low dimensions in horizontal and vertical direction, and make it particularly suitable for small scale use in for example an artist&#39;s office or studio. 
     In an embodiment, the extruder comprises an extruder barrel, a rotary extrusion shaft arranged within the extruder barrel, and a drive for driving the rotary extrusion shaft. The drive can be connected and controlled by a control unit, which allows the extrusion unit to produce FDM filament at a rate previously set. 
     In an embodiment, the filament discharge opening, when extending horizontally from the extrusion unit can have a right angle bend having its horizontal leg attached to the extrusion unit, i.e. barrel, whereas the filament discharge opening is disposed at the vertical leg end. 
     In a further embodiment, the extruder comprises at least one heating element for heating the extruder barrel. The heating elements can be spaced along the extruder barrel to allow the creation of a temperature profile. Thereby, the extrusion unit can be adaptable for various materials, which may require a specific temperature profile along the extrusion extruder barrel. 
     In an embodiment, the buffer unit comprises a reel holder, a reel holder drive and an access port for introducing a reel into the buffer unit for storing the filament from the cooling unit, and filament guide for evenly winding the filament onto the reel. This allows the FDM filament manufacturing apparatus to produce FDM filament off-line. The filament is stored onto the reel, which reel can be exchanged with an empty reel when filled. 
     In an embodiment, the buffer unit comprises a container wherein the filament from the cooling unit can be stored, and coiling means for coiling up the filament from the cooling unit within the container, and a filament output port for outputting the coiled up filament from the container. 
     This allows the FDM filament manufacturing apparatus to be used online while printing is in progress. In this case the filament can be output from the apparatus and fed into the FDM printer. The buffer ensures that differences in filament production rate of the FDM filament manufacturing apparatus and the FDM printer are accommodated. 
     In a further embodiment, the coiling means comprise a rotator and a rotatable guide mounted on the rotator, wherein the rotatable guide is arranged for feeding the filament through the rotator and for tangentially releasing and coiling the filament in opposite direction relative to the rotational direction of the rotator. 
     In an embodiment, the cooling unit is arranged having a port at a top end for receiving the filament from the filament discharge, and transport means for substantially vertically transporting the filament through the cooling means. The transport means allows the filament to be pulled through the cooling unit. 
     In an embodiment, the cooling means comprise a blower arranged for blowing air onto the filament received from the filament discharge. Using air allows the just extruded filament to cool wherein no contact other than air with the hot filament is required. This advantageous, as this prevents distortion of the just extruded filament. 
     In an embodiment, the apparatus further comprises a control unit, and wherein the transport means comprise filament stretching means and the control unit is arranged for controlling the filament stretching means. By introducing a difference in production rate of the extrusion unit and the transport means, the amount of stretching can be controlled. The stretching allows a filament diameter to be controlled. 
     In an embodiment, the control unit is arranged for controlling the filament stretching means transport rate. The higher the transport rate relative to the production rate, the more stretching is performed, the thinner the filament will be. 
     In an embodiment, the control unit is arranged for controlling the filament stretching means transport rate relative to an extruder production rate. By varying the stretching, i.e. the transport rate of the transport means relative to the production rate, the filament diameter can be controlled and a preset diameter can be obtained. 
     In a further embodiment, the apparatus further comprises a filament diameter sensor connected to the control unit for sending a filament diameter to the control unit, and wherein the control unit is arranged for controlling the filament stretching means transport rate as a function of the filament diameter and a filament diameter set value. This allows to accurately control the filament diameter and obtain high quality filament with a preset diameter value. This preset value may be constant or may vary in time for example continuously or be vary per filament batch to be produced. 
     In an embodiment, the diameter sensor comprises a light source and an optical imaging device for measuring the filament diameter. This allows contactless measurement of the actual filament diameter which is advantageous, since no pressure needs to be exerted on the filament to obtain its diameter, thus no distortion results. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a topology of a fused deposition modelling filament production apparatus according to an embodiment of the invention. 
         FIG. 2  shows a side view of the FDM production apparatus according to an embodiment of the invention. 
         FIG. 3 a    shows a perspective view of the FDM filament production apparatus according to an embodiment of the invention. 
         FIG. 3 b    shows a filament diameter sensor and control unit according to an embodiment of the invention. 
         FIG. 4 a    shows a front view of the FDM filament production apparatus according to an embodiment of the invention. 
         FIG. 4 b    shows a perspective view of the FDM filament production apparatus according to an embodiment of the invention. 
         FIG. 4 c    shows a perspective view of the FDM filament production apparatus according to an embodiment of the invention. 
         FIG. 4 d    shows a detail of the perspective view of  FIG. 4 c    of the FDM filament production apparatus according to an embodiment of the invention. 
         FIG. 4 e    shows a perspective view of the FDM filament production apparatus according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1  a basic topology of the FDM filament production apparatus is shown, having an extrusion unit for extruding FDM filament from raw material supplied to the extrusion unit via hopper  102 . The extrusion unit  101  can be a small scale or lab extruder suitable for the materials supplied via the hopper  102 . The extrusion unit  101  can be provided with heating elements  112  which are placed around the extruder barrel  111  of the extrusion unit  101 . The extruder barrel preferably has a filament discharge  103  having its opening directed vertically downwards. As shown in  FIG. 1 , the filament discharge  103  is formed by a discharge channel having a right angle bend  110 , which is horizontally connected to the extruder barrel  111  and which has its discharge opening directed vertically downward. 
     Filament  105  extruded from the extrusion unit  101  passes downward vertically trough cooling unit  104 . The cooling unit lowers the temperature of the filament  105  such that the filament  105  can be guided buffer unit  106  for storing or buffering. The vertical outflow of the filament  105  from the filament discharge  103  assures that the filament cross section is maintained. Horizontal outflow of the filament  105  would cause bending of the filament  105  as it is still hot when discharged from the extrusion unit  101 . Bending of the filament  105  would cause a distortion of its cross section, which is undesirable in the production of quality filament. 
     A guide  113  can be provided to aid proper buffering of the filament  105  in filament buffer  106 . 
     As a certain length L is required for sufficiently cool down and/or processing of the filament  105 , a space  107  can be created underneath the extrusion unit  101  which advantageously provides room for accommodating the filament buffer unit  106 . The extrusion unit  101  preferably is located in the top section of the FDM filament production apparatus, as its hopper  102  is in that position easily accessible for the user to supply raw material. The extrusion unit  101  has a drive  109  for driving one or more extrusions screws within the extrusion extruder barrel  111 . The frame  108   a - 108   d  provides support for the extrusion unit  101 , with its drive  109 , the cooling unit  104  and the filament buffer unit  106 . 
       FIG. 2  shows a side view of the FDM production apparatus  100 . Centrally on the top section of the apparatus  100  is shown the filament discharge  103  from which filament  105  is discharged vertically downward. The cooling unit  104  is shown arranged at the side panel  108   b  of the frame. The cooling unit  104  comprises blowers  202  positioned oppositely to each other on both sides of the discharged filament  105 . 
     In  FIG. 2 , a filament puller  201  is shown, which is arranged to exert a pulling force to the vertically discharged filament  105 . As the filament  105  after extrusion has an increased temperature causing the filament to be more flexible. The pulling force can be used to adjust a filament diameter to a required size. The more pulling force exerted to the filament, the thinner the filament diameter will result. The filament cross section profile however will not be affected by the pulling force. 
     The puller  201  is shown having puller wheels  203   a ,  203   b  wherein puller wheel  203   b  can be positioned on the extruded filament  105  by means of a lever  204 . This results in the filament  105  to be clamped between the puller wheels  203   a ,  203   b . By driving one or both of the puller wheels  203   a ,  203   b  pulling force is affected on the filament  105 . By properly adjusting the pulling force in relation to an extrusion speed, set by the extruder drive  109 , the filament diameter of the extruded filament  105  can be controlled. The pulling force can be adjusted by controlling the puller transport rate or speed. The higher the puller transport rate or speed, the higher the pulling force. The controlling can be performed by controller  205  which controls  206 ,  207  both the extrusion drive  109  and the puller drive, driving either of the puller wheels  203   a ,  203   b.    
       FIG. 3 a    shows a perspective view of the FDM filament production apparatus  100 , or more specifically the side of the FDM filament production apparatus having the cooling unit  104  and the puller  201 .  FIG. 3 a    shows a filament diameter sensor  301 , which is arranged above the puller  201  for sensing the filament diameter of the filament  105  passing through a slot of the filament diameter sensor  301 .  FIG. 3 b    shows a detailed view of the filament diameter sensor  301 , having two parts  301   a ,  301   b . In a first part  301   a , light source  302  is disposed which is arranged to emit light to a collimator  303 . The collimated light  304  is then passed via an aperture  306  in the side wall of the sensor part  301   a  to the other sensor part  301   b , which holds an imaging sensor  307 . The collimated light  304  crosses the slot  305  through another aperture  306 , in  FIG. 3 b    on the left side of the second element diameter sensor part  301   b . The filament  105  will affect the image formed on the imaging sensor  307  for example by casting a shadow in the incident collimated light  304 . The imaging sensor can for example be an optical line sensor having pixels arranged in one line, or CCD line sensor, which captures a shadow of the filament passing through the collimated light within the slot  305 . This allows a filament diameter of the filament passing through the slot  305  to be estimated, which signal can be passed on to the control unit  205 . By actively comparing the measured filament diameter  308  with a preset value, the control unit  205  can control  206  the extrusion drive  109  and control  207  puller  201  to produce a filament  105  with the desired filament diameter. The controlling of the filament diameter can thus be performed based on a difference between the measured filament diameter and the preset filament diameter value 
     Thus, the filament production apparatus is equipped to produce filament with a controlled diameter. The filament diameter preset value may be constant, but may also vary per batch or period of produced filament, which provides flexibility in use of the filament production apparatus, depending on filament diameter requirements of FDM equipment downstream of the filament production apparatus. No hardware modifications are required for producing various filament diameters, only modification of the preset value is required. 
       FIG. 4 a    shows a front view of the FDM filament production apparatus  100  while wherein the filament buffer unit  106  comprises a drive  401 . The drive  401  which drives a belt  402 , which subsequently drives a spindle  403 . On the spindle  403  a reel  404  can be removably mounted, on which the filament  105  extruded from extrusion unit  101  can be wound. The filament guide  113  can be arranged to evenly distribute the filament over with of the filament reel  404  for example by moving it between ultimate positions corresponding to a reel size. At least one of the spindle drive  401  and the spindle  403  can be provided with a slip clutch to compensate for speed differences between extrusion speed of the extrusion unit  101  and the filament reel  404 . Alternative ways of driving the reel  404  may be provided, such as directly driving the spindle  403 . 
       FIG. 4 b    shows a perspective view of the FDM filament production apparatus  100  wherein the filament buffer unit  106  located in the lower section  107  of the apparatus comprises a puller  406  and rotator  405 . The puller  406  has a drive and drive wheels which clamp the extruded filament and cause the filament to be pushed into a cylindrical container (see reference number  412  in  FIG. 4 c   ). The rotator  405  is driven by a drive in a rotation direction  410 . The rotator  405  can for example be driven by the puller drive or a separate drive. The rotator  405  receives the filament  105  via the puller  406  and by its revolving motion  410  it forms a filament coil  409  into the cylindrical container  412 . Filament  408  can be extracted from the container  412  via an output  407  depending on filament demand from subsequent devices using the filament  408  from the FDM filament production apparatus  100 . This output  407  can optionally comprise a puller. A subsequent device can for example be a fused deposition modeling printer or 3D printer. 
       FIG. 4 c    shows a perspective view of the FDM filament production apparatus  100  wherein the cylindrical filament container  412  is shown, which accommodates the filament coil  409 . The rotator  405  and puller  406  may also be accommodated by the filament container  412 , as shown in  FIG. 4   c.    
       FIG. 4 d    shows a detail from the perspective view of the FDM filament production apparatus  100  of  FIG. 1 , wherein the filament  105  is guided via guide wheels  416  of the filament guide  113  towards the puller  406 . The rotator  405  has a rotatable guide  414  which guides the filament  105  in the rotational motion  410 , causing the formation of the filament coil  409  within the filament container  412 . The rotator  405  can be cup shaped and is rotationally mounted within the lower section  107 . The skilled person will know various alternative solutions for rotationally mounting the rotator within the lower space  107 . It can for example have a bearing mounted between a central hollow axle of the rotator  405  within the cup and a support connected to the lower frame section  108   c . The rotatable guide  414  extends in this example through the axle holding the rotator  405 . The rotator in this example has a serrated rim  413  with teeth cooperating with a gear wheel  411 . The gear wheel  411  can be driven independently, or by the same drive which drives the filament wheels  415  of the puller  406  as shown in  FIG. 4   d.    
       FIG. 4 e    shows another perspective view of the FDM filament production apparatus  100  wherein the filament buffer unit  106  located in the lower section  107  of the apparatus wherein the rotator  405 , having the rotatable guide  414 , is shown together with the filament coil  409 . Filament  408  can be extracted via output  407  depending on filament demand from subsequent devices using the filament  409  from the FDM filament production apparatus  100  as described. The rotatable guide  414  extends through the rotator  405  to receive filament  105  from the puller  406 . The rotatable guide  414  releases the filament tangentially in an opposite direction as to the rotation direction  410  of the rotator  405  into the container  412 . The filament for the filament coil  409  is released near the rotator circumference while rotating the rotator  405  and rotatable guide  414  to make the filament coil  409 , accommodated within the filament container  412 . 
     The above described embodiments are given by way of example only. Variations and modifications of the embodiments can be made without departing from the scope of protection as defined by the claims set out below. 
     REFERENCE NUMERALS 
     
         
           100  FDM filament production apparatus 
           101  extrusion unit 
           102  hopper 
           103  filament discharge 
           104  cooling unit 
           105  filament 
           106  filament buffer unit 
           107  lower section 
           108   a - 108   d  frame 
           109  extrusion drive unit 
           110  right angle bend 
           111  extruder barrel 
           112  heating element 
           113  filament guide 
           201  puller 
           202  fan 
           203   a ,  203   b  puller wheel 
           204  lever 
           205  filament diameter controller 
           301  filament diameter measuring unit 
           302  light source 
           303  collimator 
           304  collimated light 
           305  slot 
           306  aperture 
           307  light sensor 
           308  sensor signal 
           401  spindle drive 
           402  belt 
           403  spindle 
           404  reel 
           405  rotator 
           406  puller 
           407  puller 
           408  filament 
           409  coiled filament 
           410  rotation direction 
           411  rotator gear wheel 
           412  container 
           413  cam 
           414  rotatable guide 
           415  puller wheel 
           416  guide wheel