Extruder feed system.

(54) Title: EXTRUDER FEED SYSTEM.

(54) Title: EXTRUDER FEED SYSTEM.

(57) Summary

An extruder feed system is described. The system includes a pair of internally and opposingly threaded separate rotating members (20, 22, 34, 36) to receive and couple a plastic filament material (10). An electric motor (38) rotates the rotating elements (20, 22, 34, 36) in opposite directions, thereby driving the filament (10) in a liquefaction chamber for subsequent discharge through a nozzle. The system provides very precise layer-by-layer construction.

(57) Abstract

Extruder feed system. The system includes a pair of spaced-apart, internally and oppositely threaded rotatable elements (20, 22, 34, 36) for receiving and engaging a plastic filament material (10). An electric motor (38) rotates the rotatable elements (20, 22, 34, 36) in opposite directions thereby to drive the filament (10) into a liquefier chamber for subsequent discharge through a nozzle. The system provides very accurate layer-by-layer build up.

EXTRUDER FEED SYSTEM

Cross reference to related request

This application claims priority to the utility application serial number 14 / 448,364 filed on July 31, 2014 and the provisional application serial number 61 / 863,110 filed on August 7, 2013, the content of which is incorporated in this document. by reference.

Field of the Invention

This invention relates to an extruder, and more particularly, to an extruder used in an additive manufacturing device employing a drive screw.

Background of the Invention

Additive manufacturing devices like 3-D printers build an object layer by layer by extruding a filament material onto a support surface. The quality of the produced object largely depends on tight control of the flow of the filament material through the extruder in conjunction with controlling the XY position of the extruder head as it crosses an area to build a layer.

A state-of-the-art extrusion system is shown schematically in Figure 1. The filament material 10 passes through a pressure roll feed system that conducts the filament material 10 down into a liquefaction chamber 14 Subsequently, the filament material is discharged through a nozzle 16 in a support 18. The pressure roller system 12 engages with the filament material 10 on each side as it conducts the filament material in the liquefaction chamber 14. The driving force that can be achieved with the arrangement in Figure 1 is limited . Furthermore, the arrangement shown in Figure 1 is not as accurate as desired due to progressive pitch limitations in motorized systems that drive pressure rollers.

The use of an internally threaded nut to drive a filament into a liquefaction chamber is also known. In this case, the filament passes through an internally threaded nut which, after turning, drives the filament material linearly. However, twisting the nut causes unwanted torque on the filament, causing it to distort when linearly driven.

An object of the present invention is a spindle drive that employs opposing rotating elements to substantially eliminate unwanted torque while driving the filament into the extruder.

Brief description of the invention

The extruder feed system according to the invention includes a pair of internally and opposite threaded separate rotating elements for receiving and coupling a plastic filament material. An electric motor is provided to rotate the rotating elements in opposite directions whereby the filament is driven into a liquefaction chamber for subsequent discharge through a nozzle. In a preferred embodiment, the system includes a motor-driven gear train to rotate the rotating elements in opposite directions. A suitable motor is a stepper motor or a direct current motor.

In a preferred embodiment, the gear train includes motor driven bevel gears.

In yet another embodiment, the system of the invention further includes a control loop for controlling motor power, thereby controlling the extrusion rate of the filament material.

Brief description of the drawings

Figure 1 is a cross-sectional view of an additive manufacturing extruder system of the state of the art.

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<td>nuts</td><td>hexagonal</td><td>of</td><td colspan="2">reverse turn for drive</td><td>of</td><td>a</td>

<td>material</td><td>filament.</td><td></td><td></td><td></td><td></td><td></td>

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An embodiment of the invention described herein using a motor, a flow controller, and the bevel gears that drive the reverse turn gears.

Detailed description of the invention

Referring to Figure 2, it is noted that the filament material 10 passes through the interior of the first and second hex nuts 20 and 22. Hex nut 20 is internally threaded in, for example, a threaded pattern to the right. Similarly, hex nut 22 is internally threaded to have the opposite direction for threads, as a left hand threaded pattern. It is preferred that the diameter of the filament 10 be slightly oversized with respect to the threaded hole through the hex nuts 20 and 22. As can be seen from the figure, the hex nut 20 is rotated in a counterclockwise direction and the hex nut 22 is rotated in a clockwise direction. Because the threads of the reverse turn hex nuts 20 and 22 are opposite, the filament material 10 is driven down in Figure 2.

It is important that because the hex nuts 20 and 22 are rotated oppositely, the distortion of the material resulting from the torque between the two hex nuts is substantially eliminated while the reverse torque nuts balance the effects of the torque.

An embodiment of the present invention is shown in Figure 3. A frame 30 supports rotating bevel gears 32, 34, and 36. A motor 38 under the control of a flow controller 40 rotates bevel gear 32. Bevel gear 32 operably engages bevel gears 34 and 36 that drive these bevel gears in opposite rotating directions. As will be appreciated, the interior of bevel gear 34 is threaded in a first direction, as to the right, and bevel gear 36 is internally screwed in the opposite direction as to the left. When the motor 38 is driven under the control of the flow controller 40, the filament 10 will be driven in a liquefaction chamber as shown in Figure 1. The motor 38 can be a stepper motor or a direct current motor. . The arrangement of the motor 38 shown in Figure 3 ensures that the flow of the filament material 10 through the system can be precisely controlled.

Those of skill in the art will recognize that the separate motors could be used to drive the rotating elements, if desired. It is also noted that the gap between the bevel gears 34 and 36 should be small to minimize distortion of the filament passing through the reverse turning bevel gears. The hole in Figure 3 is enlarged for clarity.

The inventors herein have determined that driving bevel gears 34 and 36 at the same speed in opposite directions is not sufficient to ensure a constant extrusion speed due to variability in filament diameter 10 and other physical inconsistencies. The inventors have analytically determined that there is a direct relationship between extrusion speed and electrical input power to motor 38 by driving the spindle of the invention. In particular, the inventors have determined that the extrusion rate is Q = klV. That is, the flow velocity of filament Q is linearly proportional to the power (IV) in motor 38. As an example, if you want to have a constant flow rate, the electrical power in motor 38 is kept constant (i.e., for example, the product of motor current (I) and motor voltage (V) remains constant). To increase or decrease the flow rate, the motor voltage 38 is controlled through a PWM control on the motor voltage 38. Therefore, the flow rate of the filament is controlled by controlling the power in the motor. 38. Flow controller 40 may include a conventional control loop that employs, for example, PID control.

It is recognized that modifications and variations of the present invention will be apparent to those skilled in the art, and all such modifications and variations are intended to be included within the scope of the appended claims.