Liquifier pump control in an extrusion apparatus

• US 6,814,907 B1
• Filed: 12/18/2001
• Issued: 11/09/2004
• Est. Priority Date: 12/18/2001
• Status: Active Grant

• Current Assignee: Stratasys Incorporated
• Original Assignee: Stratasys Incorporated
• Inventors: Comb, James W.
• Primary Examiner(s): Lechert, Jr., Stephen J.
• Application Number:
  US10/025,207
• Time in Patent Office: 1,057 Days
• Field of Search: 264/40.7, 264/40.1, 264/308, 425/135, 425/145
• US Class Current: 264/40.7
• CPC Class Codes: B29C 2948/92514 Pressure
• CPC Class Codes: B29C 2948/9258 Velocity
• CPC Class Codes: B29C 2948/926 Flow or feed rate
• CPC Class Codes: B29C 2948/92866 Inlet shaft or slot, e.g. passive hopper; Injector, e.g. injector nozzle on barrel
• CPC Class Codes: B29C 2948/92904 Die; Nozzle zone
• CPC Class Codes: B29C 2948/92952 Drive section, e.g. gearbox, motor or drive fluids
• CPC Class Codes: B29C 41/36 Feeding the material on to the mould, core or other substrate
• CPC Class Codes: B29C 41/52 Measuring, controlling or regulating
• CPC Class Codes: B29C 48/02 Small extruding apparatus, e.g. handheld, toy or laboratory extruders
• CPC Class Codes: B29C 48/05 Filamentary, e.g. strands
• CPC Class Codes: B29C 48/155 Partial coating thereof
• CPC Class Codes: B29C 48/2888 in band or in strip form, e.g. rubber strips
• CPC Class Codes: B29C 48/92 Measuring, controlling or regulating
• CPC Class Codes: B29C 64/106 using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material
• CPC Class Codes: B29C 64/118 using filamentary material being melted, e.g. fused deposition modelling [FDM]
• CPC Class Codes: B29C 64/40 Structures for supporting 3D objects during manufacture and intended to be sacrificed after completion thereof
• CPC Class Codes: B33Y 50/02 for controlling or regulating additive manufacturing processes
• CPC Class Codes: G05B 19/4099 Surface or curve machining, making 3D objects, e.g. desktop manufacturing
• CPC Class Codes: G05B 19/416 characterised by control of velocity, acceleration or deceleration G05B19/19 takes precedence

Abstract

An extrusion apparatus employs a method for controlling the output flow rate of a liquifier. The apparatus includes an extrusion head which moves along a predetermined tool path at an extrusion head velocity. The extrusion head carries a liquifier. The liquifier receives a solid element of a modeling material, heats the modeling material, and outputs a flow of the modeling material at an output flow rate. A material advance mechanism is employed to supply the solid element of modeling material to the liquifier at an input rate which controls the output flow rate. In order to control the output flow rate, an extrusion head velocity profile is determined based on the tool path. The input rate of modeling material to the liquifier is then controlled to produce an output flow rate of modeling material from the liquifier that is proportional to a current extrusion head velocity corresponding to the extrusion head velocity profile.

Claims

1. In an extrusion apparatus having an extrusion head including a liquifier which receives a solid element of a modeling material, heats the modeling material, and outputs a flow of the modeling material at an output flow rate while the extrusion head moves along a predetermined tool path at an extrusion head velocity, the apparatus using a material advance mechanism to supply the solid element of modeling material to the liquifier at an input rate which controls the output flow rate, a method for controlling the output flow rate comprising:

determining an extrusion head velocity profile based on the tool path; and

controlling the input rate of modeling material to the liquifier to produce an output flow rate of modeling material from the liquifier that is proportional to a current extrusion head velocity corresponding to the extrusion head velocity profile.

2. The method of claim 1, wherein determining the extrusion head velocity profile comprises:

determining maximum extrusion head velocities for portions of the tool path based on shapes of the portions of the tool path; and

determining extrusion head accelerations and decelerations that are continuous.

3. The method of claim 2, wherein the extrusion head accelerations and decelerations have constant finite jerk terms.

4. The method of claim 2, wherein the extrusion head accelerations and decelerations have jerk terms with an absolute value below a predetermined threshold based on a capacitance of the liquifier.

5. The method of claim 1, wherein the extrusion head velocity profile is an S-profile.

6. In an extrusion apparatus having an extrusion head including a liquifier which receives a solid element of a modeling material, heats the modeling material, and outputs a flow of the modeling material at an output flow rate while the extrusion head moves along a predetermined tool path at an extrusion head velocity, the apparatus using a material advance mechanism to supply the solid element of modeling material to the liquifier at an input rate which controls the output flow rate, a method of controlling the output flow rate comprising:

determining an extrusion head velocity profile and an extrusion head acceleration profile based on the tool path;

calculating the input rate of modeling material to the liquifier required to achieve an output flow rate of modeling material from the liquifier that is proportional to a current extrusion head velocity corresponding to the extrusion head velocity profile, the input rate being calculated based on the extrusion head velocity profile, the extrusion head acceleration profile and a time constant; and

controlling the input rate of modeling material to equal the calculated input rate.

7. The method of claim 6, wherein calculating the input rate of modeling material to the liquifier comprises solving a differential equation that governs the performance of the liquifier.

8. The method of claim 7, wherein the differential equation is:

9. The method of claim 6, wherein determining the extrusion head velocity profile comprises:

determining maximum extrusion head velocities for portions of the tool path based on shapes of the portions of the tool path; and

determining extrusion head accelerations and decelerations that are continuous.

10. The method of claim 9, wherein the extrusion head accelerations and decelerations have constant finite jerk terms.

11. The method of claim 9, wherein the extrusion head accelerations and decelerations have jerk terms with an absolute value below a predetermined threshold based on a capacitance of the liquifier.

12. The method of claim 6, wherein the extrusion head velocity profile is an S-profile.

13. An extrusion apparatus comprising:

an extrusion head movable along a predetermined tool path at an extrusion head velocity;

a liquifier carried by the extrusion head which receives a solid element of a modeling material, heats the modeling material, and outputs a flow of the modeling material at an output flow rate;

a material advance mechanism which supplies the solid element of modeling material to the liquifier at an input rate that controls the output flow rate;

a modeling system for determining an extrusion head velocity profile based on the tool path; and

a control system for providing control signals to the material advance mechanism, the control signals commanding operation of the material advance mechanism to have an input rate of modeling material to the liquifier that produces an output flow rate of modeling material from the liquifier that is proportional to a current extrusion head velocity corresponding to the extrusion head velocity profile.

14. The apparatus of claim 13, wherein the modeling system is operable to determine maximum extrusion head velocities for portions of the tool path based on shapes of the portions of the tool path, and to determine extrusion head accelerations and decelerations that are continuous.

15. The apparatus of claim 14, wherein the extrusion head accelerations and decelerations have constant finite jerk terms.

16. The apparatus of claim 14, wherein the extrusion head accelerations and decelerations have jerk terms with an absolute value below a predetermined threshold based on a capacitance of the liquifier.

17. The apparatus of claim 13, wherein the modeling system is operable to determine an S-profile for the extrusion head velocity profile.

18. The apparatus of claim 13, wherein the control system is operable to calculate the input rate of modeling material to the liquefier required to achieve the output flow rate of modeling material from the liquifier that is proportional to a current extrusion head velocity corresponding to the extrusion head velocity profile based on the current extrusion head velocity, a current extrusion head acceleration and a time constant.

19. The apparatus of claim 18, wherein the input rate of modeling material to the liquifier is calculated by the control system by solving a differential equation that governs the performance of the liquifier.

20. The apparatus of claim 19, wherein the differential equation is:

21. In an extrusion apparatus having an extrusion head including a liquifier which receives a solid element of a modeling material, heats the modeling material, and outputs a flow of the modeling material at an output flow rate while the extrusion head moves along a predetermined tool path at an extrusion head velocity, the apparatus using a material advance mechanism to supply the solid element of modeling material to the liquifier at an input rate which controls the output flow rate, a method for controlling the output flow rate comprising:

receiving a predetermined extrusion head velocity profile based on the tool path; and

controlling the input rate of modeling material to the liquifier to produce an output flow rate of modeling material from the liquifier that is proportional to a current extrusion head velocity corresponding to the extrusion head velocity profile.

22. The method of claim 21, wherein the extrusion head velocity profile has accelerations and decelerations that are continuous.

23. The method of claim 22, wherein the extrusion head velocity profile is an S-profile.

24. An extrusion apparatus comprising:

an extrusion head movable along a predetermined tool path at an extrusion head velocity;

a liquifier carried by the extrusion head which receives a solid element of a modeling material, heats the modeling material, and outputs a flow of the modeling material at an output flow rate;

a material advance mechanism which supplies the solid element of modeling material to the liquifier at an input rate that controls the output flow rate; and

a control system for providing control signals to the material advance mechanism, the control signals commanding operation of the material advance mechanism to have an input rate of modeling material to the liquifier that produces an output flow rate of modeling material from the liquifier that is proportional to a current extrusion head velocity corresponding to an extrusion head velocity profile based on the tool path.

25. The apparatus of claim 24, wherein the extrusion head velocity profile has accelerations and decelerations that are continuous.

26. The apparatus of claim 25, wherein the extrusion head velocity profile is an S-profile.

27. The apparatus of claim 24, wherein the control system is operable to calculate the input rate of modeling material to the liquifier required to achieve the output flow rate of modeling material from the liquifier that is proportional to a current extrusion head velocity corresponding to the extrusion head velocity profile based on the current extrusion head velocity, a current extrusion head acceleration and a time constant.

28. The apparatus of claim 27, wherein the input rate of modeling material to the liquifier is calculated by the control system by solving a differential equation that governs the performance of the liquifier.

29. The apparatus of claim 28, wherein the differential equation is: