AU2014200252A1

AU2014200252A1 - Worm gear driven filament feed mechanism for 3d printer head extruders.

Info

Publication number: AU2014200252A1
Application number: AU2014200252A
Authority: AU
Inventors: Zbigniew Mioduszewski
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-01-16
Filing date: 2014-01-15
Publication date: 2014-07-31

Abstract

The invention presented in this application relates to a feed mechanism for driving of a filament, whereby the gearing is obtained via a worm gear pair, enabling very high ratios in a compact volume and allowing the use of smaller and lighter motors. This mechanism allows for compensation of filament size without compromising the gear engagement distance, which is achieved by allowing the drive shaft to move parallel with the axis of the worm screw. The tangential force applied to the worm gear on the drive shaft is allowed to be transmitted into the filament. The presented invention also allows the use of multiple drive shafts to simultaneously drive a single filament, increasing the extrusion force while still compensating for filament size changes. rI I 105 Fig 1A. Fig lB.

Description

1 Title of invention Worm gear driven filament feed mechanism for 3d printer head extruders. Technical Field The present invention relates to apparatus for driving a filament, with the practical application of a feed mechanism for the extrusion print head of a filament extrusion based 3 dimensional printer. Background In filament fed rapid prototyping 3d printers, a filament (often made of low melting point polymers or metal alloys) is forced into a heated block which heats and softens the material, prior to it being extruded through a narrowed channel. This 3d print head extruder is then moved along by a 3 axis machine to lay down this extruded material in programmed paths, thereby generating a 3 dimensional object. In these applications, the reliability and rate of the feed is very important so that a consistent amount of material is deposited. Minimization of the weight of the extruder allows for higher speed and reduced printing times as less force is required to accelerate the print head. Furthermore, accuracy is also improved as less force is transmitted to the chassis of the printer. Additionally, the physical size of the extruder limits the maximum available printing area, particularly when printing with multiple materials or colours, which requires multiple extruders to be mounted side by side. In this case the total size of the extruder as well as the separation distance between the extruder outlets limits the maximum available print volume. One method used to implement the drive mechanism of these extruders is to directly drive the filament with a motor, requiring a large amount of 2 torque, which leads to large motors and poor control at low feed rates. Another common method to implement the filament feed for extruders is use a drive shaft which is driven through a spur, helical or herringbone gear arrangement, with the filament is pressed against the drive shaft by the use of a fixed or spring loaded plate, often with an idler bearing attached. Existing filament drive mechanisms cannot adequately compensate for damage to, or changes in the size of, the filament effectively which can lead to the filament feed stopping or being uneven when the filament slips or allowing the drive shaft to grind away the filament material to a point where it cannot be forced into the extrusion head. Furthermore, existing mechanisms have no mechanisms for providing a varying amount of force on the filament depending on the printing speed, resulting in unnecessary load being applied to the motor at slow speeds, and too low force being applied at high speeds, resulting in an increased risk of slipping of the filament. Summary of Invention The invention presented in this application relates to a feed mechanism for driving of a filament, whereby the gearing is obtained via a worm gear pair, enabling very high ratios in a compact volume and allowing the use of smaller and lighter motors. This mechanism allows for compensation of filament size without compromising the gear engagement distance, which is achieved by allowing the drive shaft to move parallel with the axis of the worm screw. The arrangement of the gears and constriction of movement in the presented invention is such that the tangential force applied to the worm gear on the drive shaft is allowed to be transmitted into the filament, resulting in an increased force being applied onto the filament relative to 3 the torque applied. A spring loading mechanism can also be added, which allows for increasing the nominal amount of load placed on the filament by the drive shaft. The presented invention also allows the use of multiple drive shafts to simultaneously drive a single filament, increasing the extrusion force while still compensating for filament size changes. This arrangement further limits the chances of slipping of the filament, as both drive shafts would have to slip simultaneously to result in an interruption of filament feeding. Furthermore, each drive shaft applies the tangential load from the worm gear onto the filament, hence also increasing the pinch load onto the filament. Additionally, the presented invention allows multiple filaments to be driven individually with a compact arrangement. This is achieved by the first drive shaft pressing onto the first filament with the second drive shaft acting as an idler, and vice versa. This further reduces the size and weight of a multi material extruder by sharing common components, and allowing a closer arrangement of components. Brief description of drawings Fig 1A and Fig 1B show a plan view and side view of the drive mechanism in a single motor, single filament configuration. Fig 2A and Fig 2B show a plan view and side view of the drive mechanism (filament hidden for clarity in Fig 2B) in a dual motor, dual filament configuration. Fig 3 shows the drive mechanism with filament shown, demonstrating the forces and direction of movement in normal forward operation. Fig 4 shows a plan view of the drive mechanism in single filament dual drive orientation. Fig 5 shows a possible implementation of how to add additional load onto the drive shafts with the use of springs.

4 Detailed Description [0001] In the following detailed description, detail is given in order to provide an understanding of the invention. It should be pointed out that the invention may be implemented with variations to these details, such as the removal of specific details or addition of other well known components, mechanisms etc. [0002] The presented invention is a mechanism for use in feeding of filament, which can be of circular, square or any other cross sectional shape, and comprised of polymers, metals or their alloys, or any other material. The application of this filament drive mechanism can be applied to several fields; with a specific example given going forward of driving a filament for a filament extrusion based 3 dimensional print head extruder. [0003] The simplest implementation of this invention is shown in Fig 1A. This implementation involves a single power input driving a single filament. In this drawing, input power is supplied by motor (100), which could be a stepper motor, DC or AC motor, or other remote power which is transmitted via mechanical means, with the preferred implementation of a stepper motor. The torque is transmitted to worm screw (101), which is meshed and transmitted to the worm gear (102) with a ratio between the gear pair of at least 1:8 and up to 1:200, with a preferred range of 1:12 to 1:80, and a preferred value of 1:20. [0004] Worm gear (102) then transmits the torque and tangential load to the drive shaft (104), which is then transmitted to the filament (103). The filament is held against the drive shaft through either a low friction fixed hard stop consisting of a solid body, 5 adjustable block, screw or other fixed means or pressed against a bearing or similar element which can be fixed or loaded against the filament. The preferred implementation is to use a bearing (105) that is aligned with the drive portion of the drive shaft. [0005] The drive shaft (104) consists of a straight, stepped or otherwise shaped portion for mounting the gears, and support bearings (105), as well as a drive portion that presses on the filament (103). This drive portion of the drive shaft may consist of a specific section of the shaft that may or may not have friction enhancing coatings or modifications applied, additional hardware mounted to the drive shaft or involve the use of the worm gear's (102) teeth directly. The preferred implementation of the drive portion is a larger diameter section which has had a grooved pattern cut into its surface that acts to increase the friction between the drive shaft and the filament. The drive portion is pressed against the filament to improve grip and reduce the chance of slippage. The drive shaft (104) is supported by several bearings (105). [0006] The movement of the components allowed is demonstrated in Fig 1B. The drive shaft (104) and associated hardware is constrained such that it is able to move only in a direction parallel to that of the central axis of the worm screw (101). This is demonstrated by the arrow (109). Movement in a perpendicular direction is limited, so that the gear meshing distance between the worm screw (101) and worm gear (102) is maintained. This allowed movement of the drive shaft means that the width allowed for the filament allows a range of different sizes of filament to be driven, as well as compensating for filament which has a varying cross sectional size or shape along its length. The preferred method of constraining this movement is to use a chassis with channels cut on 6 the internal faces, which the outer bearings (105) are able to travel along. [0007] Another possible implementation of the invention is shown in Fig 2A and Fig 2B, which demonstrates the use of multiple versions of the mechanism described previously to enable multiple filaments to be driven independently. This can be achieved by adding components to one or more drive shafts (104) or to the chassis such that that each filament is pressed between a drive shaft and idling mechanism. The preferred implementation is a bearing mounted to each drive shaft. [0008] Another possible implementation of the invention is shown in Fig 4, where a filament (103) is able to be driven by more than 1 drive shaft (104) simultaneously. Fig 4 demonstrates the configuration for 2 drive shafts, with more being possible by adding additional of the presented mechanisms along the length of the filament. In addition, the invention can be implemented by the use of two or more worm screws of opposite thread direction mounted to a single torque input such as a stepper motor. This means that a single torque input is able to rotate two or more drive shafts in opposite directions, reducing the number of motors required to implement the invention. [0009] Fig 3 demonstrates the forces and torques which are relevant to this invention. Other forces are generated however are not discussed or shown so as not to take the focus from the functionality of the invention. Fig 3 shows the implementation of this invention whereby the filament is driven by more than one drive shaft. This figure demonstrates the torque transmitted to the worm gear, demonstrated by the curved arrow (107), which is 7 further transmitted to the drive shaft and hence to the filament, which is driven in the direction shown by the arrow (108). An additional tangential force is generated by the interaction of the worm gear and the worm screw. This force is normally a nuisance load and is transmitted to the chassis through the bearings. In the case of the presented invention however, the tangential load (shown by arrow 110) is transmitted to the drive shaft and onto the filament. This assists in increasing the friction force between the drive shaft and the filament. The magnitude of the tangential force varies in accordance to the torque applied, and hence varies with the required extrusion drive force. This means that the friction between the drive shaft and the filament will increase during high extrusion drive force requirements (for example, high speed sections of the print), reducing the chance of the drive shaft slipping against the filament. During low extrusion drive force requirements (for example, during slow speed sections of the print), the friction between the drive shaft and filament is minimized, reducing any excessive load placed on the motor and increasing the efficiency of extrusion. [0010] Where the force applied between the drive shaft and filament is still not sufficient for increasing the friction force, additional loading can be applied to the drive shafts. This can be achieved through the use of springs or other flexible components. The preferred implementation is with the use of springs (106), as shown in Fig 5. The force generated by the spring can be adjusted via a screw which is set into the chassis (not shown for clarity). [0011] A problem faced with existing filament feed mechanisms is the linear width and height of the extrusion head, which is largely driven by the size of the filament feed mechanism. This size influences the maximum printing envelope available in a 3 8 dimensional printer, due to interference of the extrusion head and the chassis. This problem is resolved with this invention by the use of a worm gear pair, which enables a large gear ratio with a very small volume. The high gear ratio also means that a smaller motor can be selected that operates at a higher speed, minimizing the width and height of the mechanism. [0012] Another problem affecting maximum print size is extruder tip separation on a 3d printer capable of printing with multiple materials, as the separation between the extruder tips affects the maximum reach of the positioning mechanism to print with both materials. This separation distance is largely driven by the maximum packing of discrete filament feed mechanisms. The presented invention allows minimization of the extruder tip separation by arranging multiple drive shafts in an orientation where more than one filament may be driven individually by applying force between the drive shaft and an adjacent drive shaft with an idler bearing attached. This is demonstrated in Fig 2, where each drive shaft (104) can drive a filament (103) against an idler bearing (105) of an adjacent drive shaft. This means that the separation between filaments is minimized compared to existing implementations with discrete filament feed mechanisms. Furthermore, several of such mechanisms may be stacked side by side to achieve a higher number of filament drive mechanisms with minimal filament separation. [0013] Another problem facing filament based extruders is the weight of the payload on the print head, which consists of a heated extrusion die and filament feed mechanism. The payload weight limits the maximum acceleration which can be applied to the extruder for a given motor size, and the amount of force placed on the chassis which can influence vibration or flexing of the 3d printer 9 chassis. The presented invention minimizes the weight of the filament feed mechanism by the use of smaller gears which can achieve a large ratio. As mentioned previously this large ratio allows for use of smaller motors which further limits the total weight of the mechanism. Furthermore by combining multiple mechanisms as demonstrated in Fig 2A and Fig 2B, the weight of common components such as the chassis can be distributed amongst several filament feed mechanisms, reducing the weight per number of filaments driven. The additional tangential force loading applied to the filament by the arrangement of components as presented in this invention reduces complexity and weight further, by reducing the amount of hardware required to apply this force. [0014] An additional problem faced with existing filament feed mechanisms is slipping of the filament on the drive shafts, which can result in an intermittent feed into the extrusion head. This slipping can be caused by changes in filament size, a lack of compensation for filament size, or a limited range of movement for filament size compensation. The presented invention solves this problem by allowing the drive shafts to move along the entire length of the worm, varying the distance between two sets of drive shafts or the drive shaft and idler bearing, without compromising on the engagement distance between the worm screw and worm gear. This is demonstrated in Fig 1B, where the drive shafts (104) are constrained to move in only the directions indicated by the direction arrow (109). This gives an increased range of filament size compensation. Additionally, the tangential load generated when torque is applied is not affected by the filament size, hence allowing an even load to be applied to the filament even with large changes to filament size.

10 [0015] Slipping of the filament can also be caused by a high force requirement for extrusion due to the viscosity of the heated material, or because of a low friction coefficient of the filament either due to its composition or hardness. These factors can cause slippage due to insufficient friction between the drive shaft and the filament. This invention allows for an additional adjustable amount of amount of force being transmitted from the drive shaft to the filament by the use of springs (106) as demonstrated in Fig 5. The force applied can be adjusted using existing methods to vary the force placed on the filament. This invention also presented the use of multiple drive shafts to allow an increased extrusion force, as demonstrated in Fig 4. The torque indicated with the direction arrow (107) can be applied to multiple drive shafts simultaneously and applied to a single filament (103), resulting in a larger linear drive force (108) being applied to the filament, as seen in Fig 3. Reversal of the torque also allows retraction of the filament. Slippage is reduced as all of the drive shafts would simultaneously have to slip to prevent the movement of the filament, and grinding through the material is reduced as the other drive shafts continue to push the filament. Fig 4 demonstrates the preferred layout to achieve this, which involves swapping the location of the drive mechanism and idler bearing. A symmetrical design allows for the shaft to simply be flipped so that either functionality can be selected as desired. [0016] Slippage of the filament can also be caused due to a variation in the speed of the filament feed. This is because the force applied to the filament by the drive shaft is often optimised for a small range of possible feed rates. A change in this feed rate can result in filament slippage at higher feed rates due to insufficient force applied from the drive shaft, or excessive loads which must be overcome at low feed rates. The presented invention solves this problem by arranging the gears in such a way that the tangential 11 reaction load applied by the worm gear pair meshing is transmitted into the drive shaft and onto the filament. This is demonstrated in Fig 3, where the tangential force is applied as indicated by the arrows (110). The layout proposed in Fig 3 means that the higher the filament drive force (108) is required, the higher the tangential load applied between the drive shaft and filament. This force is reduced when the torque is low (for example during slow feed rates), and is increased when torque is high (for example during higher feed rates), expanding the range of usable feed rates. Reversal of torque 107 results in a reduced amount of force being applied to the filament, as a high force is not required during retraction, allowing for lower motor load during filament retractions. The reduction in force when reversing also allows for the filament to be removed manually without requiring the filament drive to retract the entire length of unextruded filament.

Claims

1. A drive mechanism for feeding filament comprising of a. One or more devices for providing input rotational power, for example, an electric stepper motor; and b. One or more drive shafts; and c. One or more worm screw and worm gear pairs for transferring input power to the drive shaft, where, a. The worm gears are arranged such that when torque is applied from the worm onto the worm gear, the resulting tangential force is applied to the drive shaft and hence between the drive shaft and the filament, and b. The drive shafts are constrained such that they are able to move parallel to the axis of the worm screw, but not in a direction perpendicular to the axis of the worm screw.

2. A drive mechanism as set forth in claim 1 where the drive shafts are arranged such that multiple filaments may be driven with each filament being able to be driven by at least one drive shaft, independently or simultaneously to the other filaments.

3. A drive mechanism as set forth in claim 2 where some or all of the drive shafts have an external force applied, which is then applied to the filament, for example, a spring pressing onto a bearing on the drive shaft increasing the force between the drive shaft and the filament.

4. A drive mechanism as set forth in claim 1 where the drive shafts are arranged such that two or more drive shafts can simultaneously drive a filament. 13

5. A drive mechanism as set forth in claim 4 where some or all of the drive shafts have an external force applied, which is then applied to the filament, for example, a spring pressing onto a bearing on the drive shaft increasing the force between the drive shaft and the filament.

6. A drive mechanism as set forth in claim 4 where a single motor is used which has both a left and right handed worm screw attached or has a rotational reversing device, and is hence capable of turning the 2 drive shafts in opposite directions with only a single motor.

7. A drive mechanism as set forth in claim 1 where the motors are able to move in the same direction as the drive shafts, pressing the entire motor, gear and drive shaft assembly against the filament.

8. A drive mechanism as set forth in claim 1 which is coupled to a heating element capable of melting polymer or metallic materials wherein the mechanism forces the polymer or metallic material into the heating element and out of an extrusion nozzle on the output.

9. A system comprising of the extruder subsystem detailed in claim 6 which is coupled to a 2 or 3 dimensional positioning mechanism, capable of synchronously positioning and extruding material to build a 3 dimensional object.