Filament feeding device having a capacitive filament displacement sensor for use in additive manufacturing system

Patent metadata

Field	Value
Publication number	US-2017136707-A1
Application number	US-201615355441-A
Country	US
Kind code	A1
Filing date	Nov 18, 2016
Priority date	Nov 18, 2015
Publication date	May 18, 2017
Grant date	—

Abstract

A filament feeding device includes a drive mechanism and a displacement sensor. The drive mechanism is configured to feed a filament along a feed path. The displacement sensor is positioned adjacent the feed path and is configured to determine a velocity and direction in which the filament is fed along the feed path based on at least two capacitance measurements that vary in response to movement of the filament along the feed path.

First claim

1 . A filament feeding device for use in feeding a filament into a liquefier assembly of an extrusion-based digital manufacturing system, the filament feeding assembly comprising:
a drive mechanism configured to feed a filament along a feed path; and a displacement sensor adjacent the feed path and configured to determine a velocity and direction in which the filament is fed along the feed path based on at least two capacitance measurements that vary in response to movement of the filament along the feed path.

2 . The filament feeding device according to claim 1 , wherein the displacement sensor comprises:
a first parallel-plate capacitor adjacent the feed path and configured to sense a first capacitance; and a second parallel-plate capacitor adjacent the feed path and separated from the first parallel-plate capacitor along the feed path, the second parallel-plate capacitor configured to sense a second capacitance; and wherein the first and second capacitors are configured to send signals to a processing unit comprising a processor configured to determine the velocity and the direction in which the filament is fed along the feed path based on the signals correlating to the first and second sensed capacitances.

3 . The filament feeding device according to claim 2 , wherein:
the displacement sensor comprises at least one excitation electrode; and the first parallel-plate capacitor includes a first sense electrode and one of the at least one excitation electrode; and the second parallel-plate capacitor includes a second sense electrode and one of the at least one excitation electrode.

4 . The filament feeding device according to claim 3 , wherein the first and second sensed capacitances are spaced a first distance apart that is different from a second periodic distance between a repeating surface pattern on the filament such that velocity of the filament can be determined through quadrature analysis.

5 . The filament feeding device according to claim 4 , wherein the first and second sensed capacitances vary in response to movement of the surface pattern on the filament along the feed path relative to the first and second sense electrodes.

6 . The filament feeding device according to claim 5 , wherein the surface pattern of the filament comprises a series of detents in the surface of the filament having the periodic distance.

7 . The filament feeding device according to claim 6 , wherein the drive mechanism comprises a filament drive having a textured engagement surface that engages the filament and creates the surface pattern in the filament having the periodic distance.

8 . The filament feeding device according to claim 7 , wherein the filament drive comprises a drive wheel having teeth that engage the filament and create the pattern in the surface of the filament, and the drive mechanism comprises a motor configured to drive rotation of the drive wheel.

9 . The filament feeding device according to claim 4 , wherein the first distance is different than a whole number of the second periodic distance.

10 . The filament feeding device according to claim 9 , wherein:
the surface pattern comprises a series of valleys in the surface of the filament that are displaced from each other along the longitudinal axis of the filament; and the first and second sense electrodes are displaced along the longitudinal axis such that when the first sense electrode is positioned at a location along the longitudinal axis corresponding to one of the valleys, the second sense electrode is positioned at a location along the longitudinal axis corresponding to a position in the pattern that is displaced from the valleys.

11 . The filament feeding device according to claim 10 , wherein the first sense electrode is positioned at a location along the longitudinal axis corresponding to one of the valleys of the pattern when the second sense electrode is positioned at a location along the longitudinal axis between two adjacent valleys.

12 . The filament feeding device according to claim 3 , wherein:
the feed path extends through a housing; and the first and second sense electrodes are suspended over openings in the housing.

13 . The filament feeding device according to claim 12 , wherein the housing comprises a liquefier tube of the liquefier assembly.

14 . A method of sensing a velocity and direction in which a filament is fed into a liquefier assembly of an extrusion-based digital manufacturing system, the method comprising:
feeding the filament along a feed path using a drive mechanism; sensing a first capacitance using a first sense electrode positioned adjacent the feed path; sensing a second capacitance using a second sense electrode positioned adjacent the feed path; and determining the velocity and direction in which the filament is being fed along the feed path using a processor of a processing unit based on the first and second sensed capacitances.

15 . The method according to claim 14 , wherein:
the filament comprises a pattern in a surface of the filament that is periodic along a longitudinal axis of the filament that is oriented with the feed path; and the first and second sensed capacitances vary in response to movement of the pattern past the first and second sense electrodes.

16 . The method according to claim 15 , wherein the first capacitance corresponds to a section of the pattern that is different from a section of the pattern corresponding to the second capacitance.

17 . The method according to claim 15 , wherein:
feeding the filament along the feed path using the drive mechanism comprises feeding the filament using a filament drive having a textured engagement surface; and the method comprises forming the pattern in the surface of the filament in response to feeding the filament using the filament drive while engaging the surface of the filament with the textured engagement surface.

18 . The method according to claim 17 , wherein:
the filament drive comprises a drive wheel having teeth; the drive mechanism includes a motor; feeding the filament along the feed path comprises driving rotation of the drive wheel using the motor; and forming the pattern in the surface of the filament comprises engaging the surface of the filament with the teeth.

19 . The method according to claim 14 , wherein:
feeding the filament comprises feeding the filament through a housing; sensing the first capacitance comprises sensing the first capacitance at a first opening in the housing that exposes a portion of the filament using the first sense electrode; and sensing the second capacitance comprises sensing the second capacitance at a second opening in the housing that exposes a portion of the filament using the second sense electrode.

20 . A 3D printer comprising:
a liquefier assembly comprising:
a liquefier tub having an inlet end and a nozzle for extruding a filament feedstock; and
a heating element configured to heat the feedstock to a molten state within the liquefier tube;
a filament feeding device for use in feeding a filament into a liquefier assembly of an extrusion-based digital manufacturing system, the filament feeding assembly comprising:
a drive mechanism configured to feed the filament feedstock along a feed path; and
a displacement sensor adjacent the feed path and configured to determine a velocity and direction in which the filament feedstock is fed along the feed path based on at least two capacitance measurements that vary in response to movement of the filament al

Assignees

• Stratasys Inc

Inventors

• Batchelder J Samuel
• Swanson William J

Classifications

• B29C64/209

  Heads; Nozzles · CPC title

• B29C64/40

  Structures for supporting 3D objects during manufacture and intended to be sacrificed after completion thereof · CPC title

• B29C64/393

  for controlling or regulating additive manufacturing processes · CPC title

• B29C64/118

  using filamentary material being melted, e.g. fused deposition modelling [FDM] · CPC title

• B33Y30/00

  Apparatus for additive manufacturing; Details thereof or accessories therefor · CPC title