Description

The present invention relates to a printhead for a 3D printing device, which printhead delivers a printable material during use of the 3D printing device for printing a three-dimensional object therewith.

The invention also relates to a 3D printing device comprising such a printhead and to a method for printing a three-dimensional object by means of such a 3D printing device.

CN 104669623 discloses a 3D printhead, wherein a nozzle part comprising a nozzle is provided, which nozzle part has a space into which a filament consisting of a filamentary solid material is fed, which material is melted. Using a pressure sensor, a fluid pressure of the molten material is measured. The feed rate of the filament is controlled by means of a signal from this sensor. Said known printhead has various drawbacks. The pressure is measured at the hottest part of the printhead, as a result of which the measurement is undesirably affected by the temperature. If the solution that is schematically shown in CN 104669623 were to be implemented in practice, the construction with the pressure sensor would be very difficult to realise. In practice, the diameter of the filament is in the order of a few millimetres. As a result there is virtually no space for realising a correct measurement of the pressure. Furthermore, it is not possible to carry out measurements near the outlet opening, or this is at least highly undesirable, because by connecting a component at that location a path for heat leakage is created. The measurement is furthermore inaccurate because the state of the material in the nozzle part is not constant. While the material flows through the nozzle part, it passes from a solid state to a liquid state. In addition, this process is dependent on the material being used at that moment. Thus a pressure is measured at a position where there is no stable situation. This renders the measurement on only inaccurate but also unreliable.

US2015/0097308 discloses a 3D printhead wherein a nozzle part is provided which comprises a liquefier tube in which material to be printed, which is fed thereto as a filament, is melted. Using a sensor, a fluid pressure of the molten material is measured. The feed rate of the filament is controlled by means of a signal from said sensor. The sensor is a strain gauge that measures material expansion of the liquefier tube. This known printhead also has various drawbacks. The pressure is measured at the hottest part of the printhead, so that the measurement is undesirably affected by the temperature. Furthermore, the measurement is inaccurate, because the state of the material in the nozzle part is not constant. Whilst the material flows through the nozzle part, it passes from a solid-state to a liquid state. In addition, this process depends on the material being used at that moment. A pressure is therefore measured at a position where there is no stable situation. This renders the measurement not only inaccurate but also unreliable. Furthermore, the measurement is unreliable because the pressure is determined indirectly via a material expansion measurement, or extension measurement, of material of the liquefier tube itself. Because of this, the printhead is also costly, since high demands are to be made on the material and the geometry of the liquefier tube.

Accordingly it is an object of the invention to provide a printhead for a 3D printing device, by means of which a process parameter, such as the feed rate of printable material to be printed, such as a filament, can be regulated in a simple and precise manner during use of the printing device fitted with the printhead.

The above object is achieved with the printhead according to the invention as defined in claim 1 for a 3D printing device, wherein the printhead delivers a printable material during use of the 3D printing device for printing a three- dimensional object therewith, the printhead comprising

- a base part provided with a connecting element for connection of the base part to a supply source of the printable material,

- a nozzle part comprising a nozzle which, in use, delivers the printable material for printing the object,

- coupling means that couple the nozzle part and the base part such that the nozzle part is movable in a direction of movement relative to the base part, wherein the printhead is configured for supplying the printable material to be printed to the nozzle part via the base part,

wherein the printhead comprises detection means which, in use, detect movement of the nozzle part in the direction of movement relative to the base part resulting from a force exerted in the direction of movement on the nozzle part by the printable material to be printed and generate a signal related to said movement. Advantages of the printhead according to the invention include the fact that by enabling the base part and the nozzle part to move relative to each other via the coupling means, a possibility is created to provide the detection means separately from the nozzle part. As a result, the nozzle part itself can be produced in a very cost-effective manner, for example, so that it will be quite suitable for single use, for example in the 3D printing of food products. In general, the nozzle part is also liable to wear. Because movement of the nozzle part is detected, any wear that may occur will not affect the detection. If the nozzle part is heated, for example in the case of printable material in the form of a filament, the effect of temperature on the detection can be eliminated, or at least be strongly reduced, in a simple manner by detecting the relative movement at a location spaced from the nozzle part. In addition, the manner of detection, i.e. measuring the force exerted on the nozzle part by the material via the relative movements, is a reliable and accurate detection while there is no need to make high demands on the nozzle part. The signal that is generated can be usefully utilised by the printing device to which the printhead is connected for controlling a process parameter such as a feed rate of the printable material to the printhead. If an increasing force on the nozzle part is detected via the detection means, the feed rate of the printable material can for example be reduced so as to thus realise more complete melting of the filament being supplied whilst the heat output of the nozzle part remains unchanged, so that the force on the nozzle part will decrease and possible obstruction of the nozzle part by unmelted filament is effectively prevented.

It is noted that within the scope of the present invention the term "three-dimensional object" is understood to mean an object made up of a single layer of printed material as well as an object made up of several layers of material printed one on top of the other.

In a constructionally simple embodiment, the base part comprises a channel for the passage of the printable material to be printed, i.e. the printable material from the supply source, and the nozzle part comprises a further channel for the passage of the printable material to be printed, which further channel is in line with the downstream end of the channel in the base part at an upstream end thereof and which merges into a nozzle of reduced diameter relative to the further channel at an opposite, downstream end thereof. The base part preferably comprises connecting means for connecting the printhead to the printing device.

The coupling means are preferably made of a thermally insulating material, such as, preferably, stainless steel.

It is advantageous if the coupling means are configured for pivotally connecting the nozzle part to the base part. A pivoting movement is easy to realise.

It is advantageous in that case if the coupling means comprise a pivot element, to which the nozzle part is connected and which is connected to the base part for pivoting about a pivot axis line, wherein the detection means are operative between the pivot element and the base part.

Alternatively, the coupling means may be configured for connecting the nozzle part to the base part for linear translation therebetween, for example by means of a telescopic guide.

The detection means preferably comprise a force sensor. The force sensor preferably comprises a flexible bending element, i.e. an elastically resilient element. The force sensor is preferably made up of a flexible bending element with a strain gauge attached thereto, wherein the bending element is operative between the base part and the nozzle part. Bending of the bending element caused by relative movement between the base part and the nozzle part results in an output signal from the strain gauge that depends on said movement. Determination of the force exerted on the nozzle part by the printable material from said movement is a very advantageous input that makes it possible to control a process parameter, such as the aforesaid feed rate, on the basis thereof. In an embodiment, the force sensor is made up of a ceramic force sensor or a piezo sensor. In an embodiment, the detection means comprise a force sensor, which is configured as a torsion element, at the location of the aforesaid pivot axis line.

In an alternative embodiment, the force sensor is formed by a Hall sensor that is configured to detect a change in a spacing between the bending element and the base part or between the pivot arm and the base part.

It is advantageous if the detection means is at least substantially thermally insulated. Thermal insulation is advantageous for preventing, or at least strongly reducing, heat loss from the nozzle part via the detection means. If use is made of a bending element as mentioned above, such as a bending beam, said bending element is preferably made of a thermally insulating material. It is further advantageous if the channel and the further channel are straight and in line with each other in the direction of extension, at least at the location of a transition from the channel to the further channel, wherein the pivot element extends in a transverse direction substantially transversely to the direction of extension, wherein the pivot axis line is spaced from the channel, extending transversely to the aforesaid direction of extension and the transverse direction. The direction of the movement of the nozzle part thus allowed can in that case at least substantially be the direction of extension. It is noted in this regard that if use is made of a bending element as mentioned before, the movement of the nozzle part will be very small, preferably less than 1 mm, furthermore preferably less than 0.2 mm. For the sake of completeness it is noted in this regard that a movement of 0 mm, or at least near 0 mm, can take place if the resulting force on the nozzle part is near zero.

It is advantageous in that connection if the bending element extends in the transverse direction, wherein the pivot element is connected to the bending element between a location where the pivot axis line is located and a location where the nozzle part is connected to the pivot element, wherein the bending element is rigidly connected to the base part. In this way a reliable detection can be realised, at a location spaced from the nozzle part.

It is further advantageous if the nozzle part is detachably provided in the printhead.

In an advantageous preferred embodiment, the nozzle part of the printhead is configured for use with printable material in a solid state, for example in the form of a filament, the printhead comprising a heating element for heating the nozzle part, such that the material to be printed will pass from the solid state to a liquid state in use, for delivering the material to be printed in the liquid state via the nozzle. In an embodiment, the heating element is an integral part of the pivot element. In an embodiment, the heating element is provided directly upstream of the nozzle around the further channel. In an embodiment, the heating element is a resistance heating element. I n an embodiment, the nozzle part may comprise cooling elements, such as cooling fins, which are provided between the heating element and the base part and which are configured for thermally insulating the base part and the part of the nozzle part directly near the nozzle from each other. Such cooling elements are in particular advantageous if use is made of printable materials having a relatively high melting temperature, for example in excess of 70 degrees Celsius. Such thermal insulation contributes to a high detecting precision of the detection means.

In an embodiment, the nozzle part is built up of at least two parts which are connected for joint movement, or in other words, which are rigidly interconnected, wherein a first one of the two parts comprises the nozzle and a second one of the two parts is movably connected to the base part. These two parts are preferably interconnected via a third part, which is configured to eliminate or at least greatly reduce the transfer of heat between the first and the second part. This third part may be of a thermally insulating material and/or comprise cooling elements such as cooling fins.

In particular if a printable material is used, it will be advantageous if the base part and the nozzle part are separate from each other, wherein the channel and the further channel define a (narrow) gap between their respective facing ends. The gap height preferably ranges between 0 and 1 mm in use, furthermore preferably between 0 and 0.2 mm. For the sake of completeness it is noted in this regard that the gap height may be 0 mm, or at least near 0 mm, if the resulting force on the nozzle part is zero.

Alternatively it is advantageous if the base part, or at least a portion thereof at the location of the passage for printable material, and the nozzle part form part of an integral part, the integral part also comprising a flexible element between the nozzle part and the base part, which flexible element is configured to allow relative movement between the nozzle part and the base part in the direction of movement. Preferably, the flexible element is further configured for, with respect to the printable material, sealingly connecting the base part and the nozzle part, wherein the flexible element is preferably configured as a bellows. The bellows is preferably co-axial with the channel and the further channel.

The invention also relates to a printing device as defined in claim 13 for 3D printing of three-dimensional objects, comprising a frame, a printhead according to the invention, which printhead is connected to the frame, supply means for supplying printable material to be printed from a source of the printable material to the printhead, wherein the printing device has control means comprising input means and output means, wherein the detection means are connected, quite preferably electrically, to the input means of the control means, and wherein the supply means is connected, quite preferably electrically, to the output means of the control means, wherein the control means are configured to control the supply means in dependence on the signal from the detection means.

It is advantageous in that regard if the supply means is configured for supplying the material to the printhead at a feed rate, wherein the control means are configured to set a parameter regarding the supply of the material, preferably the feed rate, in dependence on the signal from the detection means.

The printing device is preferably configured for supplying the printable material in a solid-state to the nozzle part.

The invention further relates to a method according to claim 16 for

3D printing of a three-dimensional object, using a printing device according to the invention, comprising the steps of:

- supplying the printable material to the printhead via the supply means,

- printing the object by delivering the printable material from the nozzle,

- detecting a movement of the nozzle part relative to the base part via the detection means while the printable material is being delivered,

- controlling a feed rate at which the supply means supplies the printable material to the printhead via the control means in dependence on the signal from the detection means.

Advantages of the printing device and of the method according to the invention are analogous to the aforesaid advantages of the printhead according to the invention.

The present invention will be explained in more detail hereinafter by means of a description of preferred exemplary embodiments of 3D printheads and a 3D printing device according to the present invention, in which reference is made to the following schematic figures, in which:

Figure 1 a is a three-dimensional view of an exemplary embodiment of a printhead according to the invention;

Figure 1 b is a vertical sectional view along the line 1 B-1 B in figure

1 a;

Figure 2a is a three-dimensional view of another exemplary embodiment of a printhead according to the invention; Figure 2b is a vertical sectional view along the line I IB-I I B in figure

2a;

Figure 3 is a three-dimensional, highly schematic view of an exemplary embodiment of a 3D printing device according to the invention comprising the printhead of figure 1 a.

Figures 1 a and 1 b very schematically show a printhead 1 intended for use in a 3D printing device. In use of the 3D printing device, a printable material can be delivered by means of the printhead 1 for printing a three-dimensional object therewith. The printhead 1 is made up of a base part 2 and a nozzle part 3 comprising a nozzle 13. The nozzle part, or at least the lower portion thereof comprising the nozzle, is also referred to as the nozzle. The base part 2 has a connecting element 9, to which a supply element can be connected, for example via a Bowden cable. In the present exemplary embodiment, the printable material is more specifically a filament 7. The filament 7 can be regarded as the "ink" of the 3D printing device 100 and is usually made of a thermoplastic. Examples of materials are ABS, PLA, PC and HDPE. Within the scope of the invention it is also conceivable for the filament 7 to consist of a food product such as chocolate, for example. The printing device 100 has a supply means 202 for supplying the material to the printhead 1 via a Bowden cable as mentioned before or, alternatively, via a rigid channel. The supply means 102 may comprise friction wheels which are driven by a stepping motor or a servo motor, for example, in which case the friction wheels will be in engagement with the filament 7 so as to thus move the filament ahead at an adjustable feed rate from a source of printable material.

The nozzle part 3 is mounted in a pivot arm 4 which forms part of coupling means for coupling the nozzle part 3 and the base part 2 such that the nozzle part 3 will be movable in a direction of movement relative to the base part 2. In the present example, this direction of movement is a rotation of the pivot arm about the pivot axis line 8. Because only a minimal movement is made, as will be explained yet hereinafter, and because the nozzle part 3 is horizontally spaced from the pivot axis line 8, the direction of movement of the nozzle part 3 substantially corresponds to a vertical direction of movement, or at least a direction of movement in line with the direction in which material to be printed is delivered by the nozzle 13. In figures 1 b and 2b this direction of movement is indicated at 10. It is noted that a movement different from the vertical direction of movement of the nozzle part relative to the base part in the printing device, such as a pivoting movement as takes place in the present example, can be corrected, for example by means of a correction via software in control means of the printing device. Furthermore, the movement of the nozzle part and the base part relative to each other can be taken into account in the control of the positioning of the nozzle of the printhead relative to the object to be printed.

The printhead 1 is configured for supplying the filament 7 to be printed to the nozzle part 3 via the base part 2. The base part 2 is to that end provided with a channel 7 for the passage of the filament 7, and the nozzle part 3 is provided with a further channel 12, which is in line with the channel 1 1 . At a lower, downstream end, the channel 12 merges into a nozzle 13 which is narrower than the further channel 12. A typical diameter of the channel 12 is a few millimetres.

The printhead 1 has detection means in the form of a force sensor formed by a bending beam 5 with a strain gauge 14 attached thereto. The bending beam 5 is rigidly connected to the base part 2 at the left-hand (at least in the figures) end 15. At that location the printhead 1 can also be connected to the printing device 100.

The detection means in the form of the flexible bending beam 5 are operative between the base part 2 and the pivot arm 4. This is realised in that the pivot arm 4, which extends substantially underneath the base part 2, whilst the bending beam 5 extends above the base part 2, has a vertical pin 16 which extends upward through an opening in the base part 2 into the right-hand (at least in the figures) end 18 of the bending beam 5. The pin 6 is fixedly mounted in the bending beam 5 at that location. Since the pivot arm 4 is capable of making a pivoting movement about the pivot axis line 8 that is located on one side of the pin 16, whilst the nozzle part 3 is located on the other side of the pin 16, the bending beam 5 will tend to bend downward when a downward force is exerted on the pivot arm 4. This bending of the bending beam 5 is detected by the strain gauge 14, and in this way the bending beam 5 with the strain gauge 14 eventually provides a force detection, via a movement of the nozzle part 3 in the direction of movement 10, and a signal generated in dependence thereon. This movement, or at least the tendency thereto, is caused by the downward force of the filament 7 on the nozzle part 3 at the location of the nozzle 13. Consequently, the combination of the bending beam 5 and the strain gauge 14 forms a force sensor, wherein the bending beam 5 extends in a transverse direction 20 and wherein the pivot arm 4 is connected to the bending beam 5 between a location where the pivot axis line 8 is located and a location where the nozzle part 3 is connected to the pivot arm, wherein the bending beam 5 is rigidly connected to the base part 2.

Since the filament 7 is supplied to the printhead 1 in a solid state, the printhead 1 comprises a heating element 6, more specifically a resistance heating element. The nozzle part 3 has a downwardly extending tubular part 21 , through which the further channel 12 extends up to the nozzle 13. The heating element 6 is arranged around this tubular part 21 , so that the filament 7 can be heated in a very effective manner upon entering this tubular part 21 , causing it to change from the solid state into the liquid state. I n the liquid state, it can flow out via the nozzle 13 for thus printing a three-dimensional object at least to be printed.

Figures 2a and 2b show an alternative embodiment of a printhead 101 , which printhead 101 is intended for use with printable material that is already present in a liquid state in a channel 1 1 1 of the base part 102. Think in this regard of liquids having a relatively high viscosity, such as marzipan, chocolate. The printhead

101 is essentially analogous to the printhead 1 , at least as regards the general operation thereof. Parts having an analogous or comparable function are indicated by the same numerals increased by 100.

The nozzle part 103 has a further channel 1 12, which opens into a nozzle 1 13 with a lower end thereof. The nozzle part 103 is mounted in the pivot arm 104. At the location where the printable material passes through, the base part 102 comprises a sleeve 30, which defines the channel 1 1 1 through the base part 102. The nozzle part 103 and the sleeve 30 form part of an integral part which also comprises a flexible, bellows-shaped element 31 which is provided in the base part

102 between the nozzle part 103 and the sleeve 30. The bellows 31 is configured to allow the above-described relative movement in the direction of movement 10. The bellows 31 is further configured for sealingly (at least to the material to be printed) connecting the base part 102, or at least the sleeve 30 therein, and the nozzle part

103 in connection with the aforesaid use with the liquid printable material.

The printing device 100 shown in figure 3 for 3D printing of objects has a frame 204 and a printhead 1 as described above provided with the above- described detection means. The base part 2 of the printhead 1 is connected to the frame 204. This connection can be effected via a movable robot arm (not shown) to allow manipulation of the printhead 1 in all directions. Alternatively, a movable carrier may be provided for printing the object thereon, in combination with a printhead 1 that is immovably connected to the frame 204. According to another alternative, both the carrier and the printhead can be moved in a coordinated manner. A supply means 202 is provided for supplying material to be printed, for example in the form of a filament 7, to the printhead 1. The printing device 100 is further provided with control means 206, input means 210 and output means 208, wherein the detection means are electrically connected to the control means 206 via the input means 210. The supply means 202 is electrically connected to the output means 208, wherein the control means 206 are configured to control the supply means 202 in dependence on the signal from the detection means.

Using the printing device 100, a 3D object 300 can be printed from a filament 7 in the following manner. The supply means 202 supplies filament 7 to the printhead 1 . The filament 7 being supplied is melted in the printhead 1 and delivered from the nozzle 13. During the delivery from the nozzle 13, movement of the nozzle part 3 relative to the base part 2 is detected by the detection means. The printhead will generate a signal in dependence on the movement of the nozzle part 3 relative to the base part 2 as detected by the detection means, on the basis of which signal the rate at which the filament 7 is supplied to the printhead 1 by the supply means 202 is changed by the control means 206, if necessary.