WO2015196237A1

WO2015196237A1 - Delivering material

Info

Publication number: WO2015196237A1
Application number: PCT/AU2015/000350
Authority: WO
Inventors: Josh MILLAR
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-06-25
Filing date: 2015-06-15
Publication date: 2015-12-30
Anticipated expiration: 2016-12-25

Abstract

A system (1), for delivering material, including a vessel (10), an elongate member (20) and a drive system (30). The vessel has an inlet (14) for material to enter the vessel, and an outlet (15) for the material to leave the vessel. The elongate member is within the vessel and mounted to rotate, about an axis, relative to the vessel. The drive system is for rotating, about the axis, the elongate member relative to the vessel. The vessel and the elongate member are shaped such that said relative rotation drives the material toward the outlet. The elongate member is mounted to move along the axis relative to the vessel. The system includes an arrangement (40) by which the elongate member is urged, relative to the vessel and along the axis, towards the outlet.

Description

DELIVERING MATERIAL

FIELD

The invention relates to delivering material.

Preferred forms of the invention may be implemented in the context of extrusion or injection moulding, and the invention will be described in the context of extrusion, although the invention may be embodied in other contexts such as auger systems for conveying bulk material.

The invention is not limited to the described context. Rather, the invention is defined by the claims. BACKGROUND

Certain existing extrusion devices include a vessel system, in the form of a barrel system, for delivering material to and driving material through an extrusion die.

The barrel system includes a barrel and an elongate member in the form of a screw concentrically mounted within the barrel. The extrusion die defines an outlet from the barrel. A drive system, such as an electric motor, drives the screw to rotate about its axis. Pelletised thermoplastic is received into the barrel via an inlet. Helical flutes of the screw act on the received material, as the screw is rotated, to drive the material along the barrel towards the extrusion die. The barrel is heated to melt the thermoplastic. The inventor has recognised that the production of a quality extruded product requires the provision of melt at a consistent temperature and pressure to the extrusion die. On the other hand, the inventor has also recognised that the material input rate has a large influence on melt pressure: a drop in the rate at which material is fed into the barrel results in lower melt pressure.

In various existing extruders, the input feed rate can be increased by increasing the rotational speed of the screw, but this has the unfortunate consequence of also increasing the shear stresses in, and in turn the temperature of, the melt. Some existing extruders are configured to rotate the screw at a constant speed and include complex screw and barrel geometries that promote consistent input feed rates and melt pressures.

The inventor has also recognised a need for a small, domestic-scale extruder and that the foregoing design considerations are an impediment to the provision of such an extruder. A domestic-scale extruder is a useful adjunct to certain existing 3D printing machines. These 3D printing machines consume a filament of thermoplastic typically having a diameter of either 1 .75 mm or 3 mm which is melted as it passes through a printing head. At the time of writing, a spool of thermoplastic filament costs about 15 times the price of an equivalent weight of pelletised thermoplastic.

It is not admitted that any of the information in this patent specification is common general knowledge, or that the person skilled in the art could be reasonably expected to ascertain or understand it, regard it as relevant or combine it in any way at the priority date. SUMMARY

One aspect of the invention provides a system, for delivering material, including a vessel having an inlet for material to enter the vessel, and an outlet for the material to leave the vessel; an elongate member within the vessel and mounted to rotate, about an axis, relative to the vessel; and a drive system for rotating, about the axis, the elongate member relative to the vessel; the vessel and the elongate member being shaped such that said relative rotation drives the material toward the outlet; the elongate member being mounted to move along the axis relative to the vessel; and the system including an arrangement by which the elongate member is urged, relative to the vessel and along the axis, towards the outlet.

The arrangement by which the elongate member is urged is preferably configured to provide a substantially invariable axial force to the elongate member at least over a working range of movement of the elongate member. Indeed the arrangement by which the elongate member is urged may include a mechanical energy storage device, for storing energy to move the elongate member towards the outlet, having force-displacement characteristics; and a mechanical transmission for transmitting force from the mechanical energy storage device to the elongate member; the transmission including a force multiplication device configured to multiply the transmitted force by an amount that varies to complement the force-displacement characteristics of the mechanical energy storage device. Regardless of whether the axial force is invariable, the arrangement by which the elongate member is urged may include a mechanical energy storage device for storing energy to move the elongate member towards the outlet. By way of example the mechanical energy storage device may be a spring. Preferably the system includes a control arrangement configured to maintain a relative axial position of the elongate member by controlling the relative rotational speed of the elongate member.

The system may include a material feeder configured to feed material to the elongate member at a rate variable relative to a rotational speed of the elongate member. If so the system preferably includes a control arrangement configured to control an axial position of the elongate member by controlling the rate at which material is fed to the elongate member.

Another aspect of the invention provides a system, for delivering material, including a vessel having an inlet for material to enter the vessel, and an outlet for the material to leave the vessel; an elongate member within the vessel and mounted to rotate, about an axis, relative to the vessel; a drive system for rotating, about the axis, the elongate member relative to the vessel; and a material feeder; the vessel and the elongate member being shaped such that said relative rotation drives the material toward the outlet; the material feeder being configured to feed material to the elongate member at a rate variable relative to a rotational speed of the elongate member.

Preferably the feeder includes another elongate member within the vessel and rotatable relative to the elongate member and to the vessel; another drive system for rotating the other elongate member relative to the vessel; the vessel and the other elongate member being shaped such that said rotation of the other elongate member relative to the vessel drives the material toward the outlet.

A heating arrangement for heating the material as it moves through the vessel may be provided, in which case the system preferably includes a control arrangement configured to control the heating arrangement in response to drive system.

The system preferably includes a control arrangement configured to control one or more operating parameters of the system in response to data, the data being from the drive system and indicative of, or sufficient to infer, drive torque and rotational speed.

Another aspect of the invention provides a system, for delivering material, including a vessel having an inlet for material to enter the vessel, and an outlet for the material to leave the vessel; an elongate member within the vessel and mounted to rotate, about an axis, relative to the vessel; a drive system for rotating, about the axis, the elongate member relative to the vessel; and a control arrangement; the vessel and the elongate member being shaped such that said relative rotation drives the material toward the outlet; the control arrangement being configured to control one or more operating parameters of the system in response to data; and the data being from the drive system and indicative of, or sufficient to infer, drive torque and rotational speed.

The system preferably includes a heating arrangement for heating the material as it moves through the vessel, and most preferably an output of the heating arrangement is one of the controlled parameter(s). In variants of the system having heating arrangements preferably the heating arrangement is associated with a higher temperature zone of the vessel; and the system includes an air-cooled spacing portion spacing a lower temperature zone of the vessel from the higher temperature zone.

Another aspect of the invention provides a system, for delivering material, including a vessel having an inlet for material to enter the vessel, and an outlet for the material to leave the vessel; an elongate member within the vessel and mounted to rotate, about an axis, relative to the vessel; and a drive system for rotating, about the axis, the elongate member relative to the vessel; a heating arrangement, for heating the material as it moves through the vessel, associated with a higher temperature zone of the vessel; and an air-cooled spacing portion spacing a lower temperature zone of the vessel from the higher temperature zone; the vessel and the elongate member being shaped such that said relative rotation drives the material toward the outlet.

Systems including the spacing portion preferably include an air-driver arranged to move air over the spacing portion.

The elongate member may be a screw. The system preferably includes an additive feeder configured to feed additive(s) to the vessel, in which case the system preferably includes a mechanical transmission via which the drive system drives the additive feeder. The mechanical transmission via which the drive system drives the additive feeder may be a Geneva drive.

Another aspect of the invention provides an extruder including a material delivery system including an air driver; an extrusion die through which the material flows; the air-driver being arranged to move air past, to cool downstream of the extrusion die, the material.

Another aspect of the invention provides an extruder including a material delivery system; and an extrusion die through which the material flows. The extruder is preferably configured to produce a filament, having a diameter of about one of 1.75 mm and 3 mm, to suit 3D printing.

Another aspect of the invention provides an injection moulding machine including a material delivery system. Another aspect of the invention provides a system, for delivering material, including elongate members each of which is rotationally driven to drive material along its axis; and a Geneva drive by which drive is transmitted from one of the elongate members to the other of the elongate members. Another aspect of the invention provides a method, of delivering material, including rotating, about an axis and relative to a vessel, an elongate member in the vessel and movable along the axis relative to the vessel, to drive the material toward an outlet of the vessel; urging the elongate member relatively along the axis toward the outlet. Preferably the urging is applying a substantially invariable force. The method may include storing energy, for axially moving the elongate member, in a mechanical energy storage device having force-displacement characteristics; transmitting force, from the mechanical energy storage device to the elongate member via a mechanical transmission, to so urge the elongate member; and multiplying, in the mechanical transmission, the transmitted force by an amount that varies to complement the force-displacement characteristics of the mechanical energy storage device.

Another aspect of the invention provides a method, of delivering material, including rotating, about an axis and relative to a vessel, an elongate member in the vessel, to drive the material toward an outlet of the vessel; feeding the material to the elongate member at a rate variable relative to a rotational speed of the elongate member relative to the vessel.

Another aspect of the invention provides a method, of delivering material, including rotating, about an axis and relative to a vessel, an elongate member in the vessel, to drive the material toward an outlet of the vessel; and varying one or more parameters of the method in response to data indicative of, or sufficient to infer, drive torque and relative rotational speed of the rotating.

Another aspect of the invention provides a method, of delivering material, including rotating, about an axis and relative to a vessel, an elongate member in the vessel, to drive the material toward an outlet of the vessel; heating a higher temperature zone of the vessel separated from a lower temperature zone of the vessel by a spacing portion, to heat the material as it moves through the vessel; and moving air over the spacing portion.

Preferably the method is a method of moving material in an extruder including an extrusion die; the moving air being operating an air-driver arranged to move air past, to cool downstream of the extrusion die, the material.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the apparatus will now be described by way of example only with reference to the accompanying drawings in which:

• Figure 1 is an axial vertical cross-section view of an extruder;

• Figure 2 is a side view of selected components of the extruder of Figure 1 ;

• Figure 3 is a front perspective view of the components of Figure 2;

• Figure 4 is a schematic side view of an extruder; · Figure 5 is a schematic side view of another extruder;

• Figure 6 is a schematic side view of yet another extruder; and

• Figure 7 is an axial vertical cross-section view of yet another extruder. DESCRIPTION OF EMBODIMENTS

The extruder 1 includes a barrel 10, a screw 20, a drive system 30 and an arrangement 40.

The barrel 10 includes a forward barrel portion 1 1 in the form of a horizontal hollow cylinder, a ring-shaped heat insulating spacer 12 fitted to the rear of the barrel portion 1 1 , and a rear barrel portion 13 which also has a hollow horizontal cylindrical form. These components 11 , 12, 13 are coaxially arranged to define a substantially continuous cylindrical interior of the barrel 10. An elongate inlet port 14 runs along and opens upwardly through the wall of the barrel portion 13. The forward end of the barrel 10 is capped by an extrusion die 15.

The screw 20 is concentrically mounted within the barrel 10 so that its long axis is coincident with the long axis of the barrel's cylindrical interior. The screw includes a shaft 21 and a helical flute 22 encircling the shaft 21 . In this example the shaft 21 is conical and orientated so that it grows in diameter in the forward direction. Alternatively the shaft may be a straight shaft such as the shaft 21 ' of Figure 7.

Rotation of the screw 20 in a predetermined direction drives the material in the forward direction along the barrel 10 from the inlet port 14 to and through the extrusion die 15. Optionally a puller may be located downstream of the extrusion die 15 to draw material through the extrusion die by pulling on the solidified extruded material. It is also possible that a breaker plate and screen pack may be fitted between the screw 20 and the die 15.

The described screw and barrel geometry is only one example of how the barrel 10 and screw 20 might be shaped such that relative rotation therebetween drives material along the barrel. Other geometries are possible. By way of example, the screw 20 might be replaced by an elongate member having axial spline-like formations and the barrel 10 replaced by a tubular body having internal helical flutes. It is also contemplated that the screw 20 could be fixed whilst the barrel 10 is mounted to move along and rotate about the screw 20. The drive system 30 is mounted to slide in the fore-aft direction along slot 51 of a chassis 50 and includes an output shaft by which it rotationally drives the screw 20. The ends of the slot 51 constitute stops defining an axial range of motion of the components 20, 30.

The arrangement 40 is a spiral pulley with linear extension spring-type constant force mechanism. It urges the screw 20 forward and includes an energy storage device in the form of tension spring 41 , a force multiplication device 42 and cord 43. The force multiplication device 42, cord 43 and drive system 30 together constitute a transmission for transmitting force from the spring 41 to the screw 20.

The force multiplication device includes a horizontal axle 42a running perpendicularly to and below the screw 20. The axle 42a is pivotally carried by the chassis 50. The axle 42a carries a lobe 42b and on each side of the screw 20 a respective lobe 42c. The axle 42a, lobe 42b and lobes 42c are all fixed relative to each other to move as a single unitary body. The spring 41 is a tension spring acting between a force application point 52 of the chassis 50 and a force application point 42b' of the lobe 42b.

The lobes 42c are partly circular in profile, i.e. a portion of the profile of each lobe 42c is a smooth, continuous curve concentric to the axle 42a. Each of the two ends of the cord 43 is fixed to a respective one of the lobes 42c at a respective force application point 42c'. On each side of the screw 20, the cord 43 wraps around the concentric exterior portion of one of the lobes 42c. A central portion of the cord 43 loops around and engages a rear of the drive system 30 so that, whilst the cord 43 remains taut, tension in the cord urges forward the drive system 30, and in turn the screw 20.

There is a linear relationship between the axial position of the axially movable portions 20, 30 and the angular position of the lobes 42c. There is also a direct correspondence between the force with which the movable portions 20, 30 are urged in the forward direction and the tension in the cord 43, and also between those forces and the resultant torque about the axle 42a, because the cord co-operates with the portion of the lobe 42c concentric to the axle 42a.

The lobe 42b has a more complex geometry. It is shaped such that the effective lever arm distance through which the spring acts varies, as parts 42a, 42b, 42c rotate through their range of motion, to complement the varying force from the spring 41. US patent 6,434,851 describes this complex geometry in more detail. A typical tension spring will have an invariable spring constant such that its force is proportional to the degree of extension, although different springs having different force deflection characteristics are contemplated. Indeed, other mechanical energy storage devices are possible. For example, the spring 41 may be replaced by a gas-filled cylinder.

The changing lever arm length is carefully selected so that the resultant urging of the screw in the forward direction is constant.

The arrangement 40 is but one example of possible urging arrangements. Other variants are possible. By way of example, spring 41 could be eliminated by attaching an end of the cord 43 to a mass (instead of connecting it to the force application point 42c' of the lobe 42c), so that the weight of the mass is redirected by the lobe 42c to urge the screw in the forward direction, and energy for this urging is stored in the form of potential energy.

Indeed, one arrangement for urging the screw in the forward direction would be to downwardly orient, e.g. orient substantially vertically, the screw and barrel. By this arrangement, the screw 20 would be urged forward by its own weight and by the weight of the drive system 30 (or at least a portion thereof, depending on the angle of inclination).

A heating arrangement 60 in the form of a resistive electrical element 60 underlies the forward barrel portion 1 1. The forward barrel portion 11 thus defines a high temperature zone of the barrel 10. The heater 60 is controlled to maintain the melt at an optimum temperature which of course varies from application to application. A temperature range of 100°C to 250°C is preferred to suit domestic 3D printing applications.

In preferred forms of extruder 1 , this temperature is maintained without a thermocouple, or any other form of direct temperature measurement, by monitoring the drive system 30. A control arrangement 70 takes the form of a microcontroller. The drive system 30 includes an electric motor and a suitable arrangement of thrust bearings to rotationally drive and axially urge the screw 20. By monitoring the motor torque and motor speed, the melt temperature can be inferred because the melt viscosity varies as a function of melt temperature.

The melt viscosity, and in turn the melt temperature, can be inferred from any two of output power, torque and rotational speed of the motor. Of course, these parameters can be inferred from a wide variety of differing data signals, depending on the drive system configuration. By way of example, if the drive system includes a simple induction motor that has a known relationship between speed and current, and a known relationship between torque and current, then knowing the current is sufficient to infer output torque and speed. In yet another example, the inputs to a brushless DC motor may be monitored in a manner often referred to as 'sensorless motor control'. To emphasise, drive systems without electric motors are also contemplated. Also to emphasise, operating parameters other than the rate of heating might be controlled based on inferences drawn from the drive, e.g. the rate at which material is drawn from the die 15 and/or the rate at which material is fed to the screw 20 might be varied.

A feed mechanism 80 is mounted atop a rearward portion of the barrel 10 to supply pelletised thermoplastic material and additive (such as colourant) to the barrel 10 via the inlet port 14.

The mechanism 80 includes an upwardly open main hopper 81 and an upwardly open additive hopper 82. The inclined walls of the main hopper 81 funnel pelletised material downwardly towards an outlet port 81 a at the base of the hopper 81. The outlet port 81 a is dimensioned to match and sits in register with the inlet port 14 so that pelletised material can fall freely from the hopper 81 into the barrel 10 as fast as the material can be driven along the barrel by the screw 20. Thus the rotational speed of the screw 20 determines the rate at which the pelletised material is fed into the barrel 10.

The additive hopper 82 is smaller than the main hopper 81 but likewise includes inclined walls by which pelletised material is funneled downwardly to an opening. The additive hopper 82 sits at the rear of the hopper 81. An auger mechanism 83 runs in the fore-aft direction through the feed mechanism 80. The auger 83 includes a screw 83a carried within a cylindrical housing and which is driven to rotate via a Geneva drive 83b. The Geneva drive 83b transforms the continuous motion of the screw 20 to periodic motion and connects the screw 83a to the screw 20 so that the screw 83a rotates a sixth of a turn for each turn of the screw 20. The screw 83a drives the additive forwardly along the screw's tubular housing to an outlet port 81 b which opens downwardly through a wall of the cylindrical housing to drop the additive into the barrel 10. Thus, in the example of Figure 1 , the rate at which additive is supplied to the barrel 10 ultimately depends on the rotational speed of the screw 20.

The Geneva drive 83b is a preferred form of transmission for transmitting drive from the screw 20 to the screw 83a because it allows for a significant reduction ratio and for those two screws to be more closely spaced than would be possible with a simple pair of meshing gears, bearing in mind that strength and other design requirements would impose a practical minimum on the size of any gear profile fixed to rotate with the screw 20.

The insulating spacer 12 is a single member that spaces the differing temperature zones of the barrel 10. This member may be either integral or made up of two or more pieces. It is but one example of possible spacing portions. For example, the spacing portion 1 could be a band of a single integral tube making up the barrel 10.

The insulating spacer 12 is formed of a suitable thermally insulating material, such as polytetrafluoroethylene (PTFE), to reduce the conduction of heat from the higher temperature zone at the front of the barrel to the lower temperature zone at the rear of the barrel. The chassis 50 of the device 1 is configured to define a void 12a that separates the exterior of the higher temperature zone from the exterior of the lower temperature zone. The void 12a surrounds the spacer 12 so that the spacer 12 is cooled by the air in the void 12a. In this example, this cooling is enhanced by moving air through the void 12a. As suggested in Figure 1 by arrows A, an air-driver in the form of fan 12b is configured to drive air through the void 12a. As such, the spacer 12 is bathed in cooling air flowing upwardly through the void 12a. Indeed, in this example the spacer's entire cylindrical exterior is bathed in cooling air. Air-cooling is more cost-effective than water-cooling. Other forms of air-driver are possible.

The void 12a is partly defined by the rearward extent of a plenum 53 of the chassis 50. The plenum 53 guides air from the fan 12b, as suggested by arrow B, forwards and upwards to cool extruded material emerging from the extrusion die 15. For this purpose, the plenum 53 includes a short horizontal tubular section 53a that extends in the fore-aft direction and is aligned with the extrusion die 15 to receive the extruded material via opening 53b formed in the wall of the plenum. The extension 53a is one example of a cooling chamber in which the cooling air turbulently moves about the extruded product. The plenum 53 is but one example of an air-guide. Other forms of guide are possible. By way of example, the extruder 1' of Figure 7 includes a guide 53' including an outlet 53a' that directs the cooling air toward the emerging extrusion.

The chassis 50 includes an integral moulding defining the plenum 53. In this example, the fan 12b is bolted to the rear of this moulding. Thus a simple, cost-efficient arrangement is disclosed wherein a single air-driver in the form of fan 12b is employed to mutually insulate the different temperature zones of the barrel 10 and also to cool the extruded product. To emphasise, Figure 1 shows but one example of this concept. Other examples are possible. By way of example, the fan 12b might be mounted further to the left (as drawn) so as to downwardly draw air through the space 12a as in the extruder V of Figure 7. It is also contemplated that the direction of air flow through the fan 12b might be reversed. It is contemplated that the device 1 might directly supply filament from the extrusion head 15 to the printing head of a 3D printing device. Indeed, it is also contemplated that variants of the invention may supply a 3D printing head with melt, instead of filament, to negate the need for re-melting through the printing head. That said, the described variant 1 includes a spool system 90 about which filament from the extrusion head 15 is wrapped. Of course other extrusion storage arrangements are possible. The spool system 90 includes a motor-driven hub 91 and a control system by which the speed of the hub is regulated to provide a consistent wind on rate. For this purpose, the spool system 90 includes device 92 pivotally connected to the chassis 50 at pivot mount 92a to pivot relative to the chassis 50.

The device 92 includes a pair of arms that extend away from the pivot axis 92 and are resiliently biased towards each other. During set up of the extruder, filament emerging from the extruder die 15 may be looped around, and at a distance from, the spool 90 along a spiral shaped path to approach the free end of the device 92 from rearward of and above the pivot axes 92a. Still during set up, the filament is drawn through the device 92 and engaged with the hub 91 .

During operation, the arms under their own resilience grip the filament whilst the spool

90 is rotated to draw the filament through that grip. At the same time, the spiral portion of the filament from the extrusion die 15 to the device 92 remains loose. Thus the tension in the filament between the device 92 and the spool 90 depends on the gripping force of the arms of the device 92 and the wind-on speed, and the device 92 pivots about its axis to always point to the wind-on point. In this example the device 92 rotates counterclockwise (as drawn) as filament accumulates on the spool 90 and in turn the wind-on point moves outwardly. As convolutions of extruded material accumulate about the hub 91 of the spool system 90, the effective hub diameter grows and the control system reduces the speed of hub

91 in response to the angular position of the device 92 to maintain a constant wind-on speed. Figure 1 , 2 and 3 illustrate the axially movable components 20, 30 in their forwardmost position. It will be observed that the rear of the barrel 10 is open. As the volume of melt in the barrel 10 increases, the movable components 20, 30 are driven backwards (in reaction to the screw's force on the melt) such that the screw 20 partly projects rearwardly from the barrel 10. As the components 20, 30 so rearwardly move, the substantially inextensible cord 43 acts on the force multiplication device 42, causing it to rotate about its axle 42a, which in turn extends the tension spring 41. Whilst the components 20, 30 so rearwardly move, energy is stored in the spring 41 for a subsequent return stroke, and yet there is no resultant increase in pressure of the melt at the outlet end of the barrel. Also, during this movement the screw continues to rotate at its fixed speed, such that the rate at which material enters the barrel 10 from the feed system 80 is substantially unaffected. Thus, two previously interrelated variables, melt pressure and feed rate, have been decoupled and made independent.

Screw speed and melt pressure are decoupled by adding a new variable: the axial position of the screw. This additional variable means that surging can be reduced or eliminated. Variations in input or output flow rates are absorbed by axial displacement of the screw. At least in preferred forms of the extruder 1 , the only variations in melt pressure are relatively minor variations resultant from the rate of axial movement of the screw being limited by inertia and/or viscous damping. Also, this can be achieved with screw and barrel geometries simpler and more cost-efficient than the geometries of various existing extruders.

Also, whilst the screw 20 is rearward from the extrusion die 15, the melt immediately adjacent that die is not exposed to the shear stresses caused by the screw.

Preferred forms of the system incorporate a control system via which the rotational speed of the screw 20 is adjusted to maintain the axial position of the screw. In this example, the axial position of the screw 20 is determined by an angular position sensor associated with the force multiplication device 42 and the microcontroller 70. In response to the screw 20 approaching the front of the barrel 10, the microcontroller 70 controls the drive system 30 to increase the rotational speed of the screw. Likewise, as the screw 20 moves towards the rearward end of its axial range of motion, the microcontroller slows the screw 20. Thus, a feedback loop that adjusts the input rate whilst the output rate remains constant is disclosed. By adjusting the parameters of this feedback loop, a system that quickly reaches a stable dynamic equilibrium between input and output can be reached, so that the screw 20 does not move when the output rate is continuous.

Preferred forms of the device 1 include a trio of rotary potentiometers: one to measure the position of the axle 42a, one to measure the position of the device 92, and a third by which a user may manually trim the spool wind-on speed.

Figure 4 schematically illustrates the operation of the extruder 1. The constant force mechanism 40' urges the screw 20' forward within the barrel 10 towards the outlet 15'. Figure 5 schematically illustrates another variant in which the constant force device is moved to the front of the barrel. The constant force device 40" urges the screw 20" forward within the barrel 10" and towards the outlet 15" by pulling it forward from the front rather than pushing forward from the rear.

Figure 6 shows another example similar to the example of Figure 4 but for the inclusion of an additional solids-conveying screw 80"'. The solids-conveying screw 80"' is mounted coaxially within the barrel 10"' but is able to rotate independently of the screw 20"'. The solids-conveying screw 80"' forms part of a feeder mechanism. Its rate of rotation can be controlled to control the rate at which material is fed into the barrel 10"'. As such, the rate at which material is so fed is made independent of the rotational speed of the screw 20"'. The screws 20"' and 80"' are mounted to axially move together whilst allowing free relative rotation. This arrangement allows for even better control over the quality of the melt in that the rotational speed of the screw 20"' can be set to optimise the shear stresses in the melt, whilst the screw 80"' is rotated so as to control the axial position of the movable components 20"', 80"' by controlling the rate at which material is fed into the barrel 10"'.

To emphasise, the invention is not limited to the described examples or to the described context. Rather the invention is defined by the claims. By way of example, whilst a vessel in the form of a tubular barrel is disclosed, the vessel might take the form of an open trough in which case, end portions of the trough's open top might define an inlet and an outlet through material enters and exits the trough.

Claims

1 . A system, for delivering material, including a vessel having an inlet for material to enter the vessel, and an outlet for the material to leave the vessel; an elongate member within the vessel and mounted to rotate, about an axis, relative to the vessel; and a drive system for rotating, about the axis, the elongate member relative to the vessel; the vessel and the elongate member being shaped such that said relative rotation drives the material toward the outlet; the elongate member being mounted to move along the axis relative to the vessel; and the system including an arrangement by which the elongate member is urged, relative to the vessel and along the axis, towards the outlet.

2. The system of claim 1 wherein the arrangement by which the elongate member is urged is configured to provide a substantially invariable axial force to the elongate member at least over a working range of movement of the elongate member.

3. The system of claim 2 wherein the arrangement by which the elongate member is urged includes a mechanical energy storage device, for storing energy to move the elongate member towards the outlet, having force-displacement characteristics; and a mechanical transmission for transmitting force from the mechanical energy storage device to the elongate member; the transmission including a force multiplication device configured to multiply the transmitted force by an amount that varies to complement the force-displacement characteristics of the mechanical energy storage device.

4. The system of claim 1 or 2 wherein the arrangement by which the elongate member is urged includes a mechanical energy storage device for storing energy to move the elongate member towards the outlet.

5. The system of claim 3 or 4 wherein the mechanical energy storage device is a spring.

6. The system of any one of claims 1 to 5 including a control arrangement configured to maintain a relative axial position of the elongate member by controlling the relative rotational speed of the elongate member.

7. The system of anyone of claims 1 to 5 including a material feeder configured to feed material to the elongate member at a rate variable relative to a rotational speed of the elongate member.

8. The system of claim 7 including a control arrangement configured to control an axial position of the elongate member by controlling the rate at which material is fed to the elongate member.

9. A system, for delivering material, including a vessel having an inlet for material to enter the vessel, and an outlet for the material to leave the vessel; an elongate member within the vessel and mounted to rotate, about an axis, relative to the vessel; a drive system for rotating, about the axis, the elongate member relative to the vessel; and a material feeder; the vessel and the elongate member being shaped such that said relative rotation drives the material toward the outlet; the material feeder being configured to feed material to the elongate member at a rate variable relative to a rotational speed of the elongate member.

10. The system of claim 7, 8 or 9 wherein the feeder includes another elongate member within the vessel and rotatable relative to the elongate member and to the vessel; and another drive system for rotating the other elongate member relative to the vessel; the vessel and the other elongate member being shaped such that said rotation of the other elongate member relative to the vessel drives the material toward the outlet.

1 1 . The system of any one of claims 1 to 10 including a heating arrangement for heating the material as it moves through the vessel.

12. The system of claim 11 including a control arrangement configured to control the heating arrangement in response to drive system.

13. The system of any one of claims 1 to 10 including a control arrangement configured to control one or more operating parameters of the system in response to data, the data being from the drive system and indicative of, or sufficient to infer, drive torque and rotational speed.

14. A system, for delivering material, including a vessel having an inlet for material to enter the vessel, and an outlet for the material to leave the vessel; an elongate member within the vessel and mounted to rotate, about an axis, relative to the vessel; a drive system for rotating, about the axis, the elongate member relative to the vessel; and a control arrangement; the vessel and the elongate member being shaped such that said relative rotation drives the material toward the outlet; the control arrangement being configured to control one or more operating parameters of the system in response to data; and the data being from the drive system and indicative of, or sufficient to infer, drive torque and rotational speed.

15. The system claim 13 or 14 including a heating arrangement for heating the material as it moves through the vessel.

16. The system of claim 15 wherein an output of the heating arrangement is one of the controlled parameter(s).

17. The system of any one of claims 1 1 , 12, 15 and 16 wherein the heating arrangement is associated with a higher temperature zone of the vessel; and the system includes an air-cooled spacing portion spacing a lower temperature zone of the vessel from the higher temperature zone.

18. A system, for delivering material, including a vessel having an inlet for material to enter the vessel, and an outlet for the material to leave the vessel; an elongate member within the vessel and mounted to rotate, about an axis, relative to the vessel; and a drive system for rotating, about the axis, the elongate member relative to the vessel; a heating arrangement, for heating the material as it moves through the vessel, associated with a higher temperature zone of the vessel; and an air-cooled spacing portion spacing a lower temperature zone of the vessel from the higher temperature zone; the vessel and the elongate member being shaped such that said relative rotation drives the material toward the outlet.

19. The system of claim 17 or 18 wherein the spacing portion includes a spacing member.

20. The system of claim 17, 18 or 19 including an air-driver arranged to move air over the spacing portion.

21 . The system of any one of claims 1 to 20 wherein the elongate member is a screw.

22. The system of any one of claims 1 to 21 including an additive feeder configured to feed additive(s) to the vessel.

23. The system of claim 22 including a mechanical transmission via which the drive system drives the additive feeder.

24. The system of claim 23 wherein the mechanical transmission via which the drive system drives the additive feeder is a Geneva drive.

25. An extruder including the system of claim 20; and an extrusion die through which the material flows; the air-driver being arranged to move air past, to cool downstream of the extrusion die, the material.

26. An extruder including the system of any one of claim 1 to 24; and an extrusion die through which the material flows.

27. The extruder of claim 25 or 26 configured to produce a filament, having a diameter of about one of 1.75 mm and 3 mm, to suit 3D printing.

28. An injection moulding machine including the system of any one of claims 1 to 24.

29. A method, of delivering material, including rotating, about an axis and relative to a vessel, an elongate member in the vessel and movable along the axis relative to the vessel, to drive the material toward an outlet of the vessel; urging the elongate member relatively along the axis toward the outlet.

30. The method of claim 29 wherein the urging is applying a substantially invariable force.

31 . The method of claim 30 including storing energy, for axially moving the elongate member, in a mechanical energy storage device having force-displacement characteristics; transmitting force, from the mechanical energy storage device to the elongate member via a mechanical transmission, to so urge the elongate member; and multiplying, in the mechanical transmission, the transmitted force by an amount that varies to complement the force-displacement characteristics of the mechanical energy storage device.

32. The method of claim 29 or 30 including storing energy, for moving the elongate member, in a mechanical energy storage device.

33. The method of claim 31 or 32 wherein the mechanical energy storage device is a spring.

34. The method of any one of claims 29 to 33 including controlling a relative axial position of the elongate member by controlling a rate at which the elongate member is rotated relative to the vessel.

35. The method of any one of claims 29 to 33 including feeding the material to the elongate member at a rate variable relative to a rotational speed of the elongate member relative to the vessel.

36. The method of claims 35 including controlling an axial position of the elongate member by controlling the rate at which material is fed to the elongate member.

37. A method, of delivering material, including rotating, about an axis and relative to a vessel, an elongate member in the vessel, to drive the material toward an outlet of the vessel; feeding the material to the elongate member at a rate variable relative to a rotational speed of the elongate member relative to the vessel.

38. The method of claim 37 wherein the feeding includes rotating, relative to the vessel and to the elongate member, another elongate member within the vessel.

39. The method of any one of claims 29 to 38 including heating the material as it moves through the vessel.

40. The method of claim 39 including varying the heating in response to the driving.

41 . The method of any one of claims 29 to 40 including varying one or more

parameters of the method in response to data; the data being indicative of, or sufficient to infer, drive torque and relative rotational speed of the rotating elongate member.

42. A method, of delivering material, including rotating, about an axis and relative to a vessel, an elongate member in the vessel, to drive the material toward an outlet of the vessel; and varying one or more parameters of the method in response to data indicative of, or sufficient to infer, drive torque and relative rotational speed of the rotating.

43. The method claim 41 or 42 including heating the material as it moves through the vessel.

44. The method of claim 43 wherein at least one of the controlled parameter(s) is a rate of the heating.

45. The method of any one of claims 40, 41 , 43 and 44 wherein the heating is heating a higher temperature zone of the vessel separated from a lower temperature zone of the vessel by a spacing portion; and the method includes moving air over the spacing portion.

46. A method, of delivering material, including rotating, about an axis and relative to a vessel, an elongate member in the vessel, to drive the material toward an outlet of the vessel; heating a higher temperature zone of the vessel separated from a lower temperature zone of the vessel by a spacing portion, to heat the material as it moves through the vessel; and moving air over the spacing portion.

47. The method of claim 45 or 46 being a method of moving material in an extruder including an extrusion die; the moving air being operating an air-driver arranged to move air past, to cool downstream of the extrusion die, the material.