Printer unit for a 3D-printing apparatus and method

Abstract

A printer unit (100) for a 3D-printing apparatus. The printer unit comprises a printer head (105) comprising a nozzle (110) arranged to deposit printing material from the printer unit, a pressure sensor (120) configured to sense a pressure exerted on the printer head from the printing material, and a control unit (130) coupled to the pressure sensor. The control unit is configured to control the speed of the printer head based on a transfer function from the pressure sensed by the pressure sensor to a desired speed of the printer head, in order to maintain a constant deposition of the amount of printing material per length unit of deposited printing material.

Claims

1. A printer unit for a 3D-printing apparatus, comprising a printer head comprising a nozzle arranged to deposit printing material from the printer unit onto an underlying material, wherein during deposition of the printing material, said printer head moves with a movement speed S relative to the underlying material a pressure sensor configured to sense a pressure P.sub.s exerted on the printer head from the printing material, and a control unit coupled to the pressure sensor, wherein the control unit is configured to control the movement speed S of the printer head based on an increasing transfer function f from the pressure sensed P.sub.s by the pressure sensor to a desired movement speed S.sub.d of the printer head, in order to maintain a relatively constant deposition of the amount of printing material per length unit of deposited printing material.

2. The printer unit according to claim 1, further comprising a feeding unit configured to feed printing material, wherein the pressure sensor is coupled to the feeding unit and configured to sense a pressure exerted on the feeding unit from the printing material.

3. The printer unit according to claim 1, wherein the pressure sensor is coupled to the nozzle and configured to sense a pressure exerted on the nozzle from the printing material.

4. The printer unit according to claim 1, wherein the transfer function comprises at least one filter function between the pressure sensed P.sub.s by the pressure sensor and the desired movement speed S.sub.d of the printer head.

5. The printer unit according to claim 4, wherein the at least one filter function is selected from a list comprising a delay function, an averaging function, a scaling function, and a non-linear function.

6. The printer unit according to claim 1, wherein the transfer function is determined based on at least one parameter selected from a list comprising a movement speed of the printer head, a temperature of the nozzle, a feeding rate of the printing material, and an amount of printing material deposited per length unit of deposited printing material.

7. The printer unit according to claim 6, further comprising a measuring device configured to measure at least one parameter selected from a list comprising a movement speed of the printer head, a temperature of the nozzle, a feeding rate of the printing material, and an amount of printing material deposited per length unit of deposited printing material.

8. The printer unit according to claim 1, wherein the transfer function is predefined.

9. The printer unit according to claim 1, wherein the control unit is configured to interrupt an operation of the printer unit in case the movement speed of the printer head is outside a predetermined interval.

10. A method for 3D-printing an object by a printer unit comprising a printer head comprising a nozzle arranged to deposit printing material from the printer unit onto an underlying material, wherein during deposition of the printing material, said printer head moves with a movement speed S relative to the underlying material; said method comprising the steps of: sensing a pressure exerted on the printer head from the printing material, and controlling the movement speed S of the printer head based on an increasing transfer function from the pressure sensed by the pressure sensor to a desired movement speed of the printer head, in order to maintain a relatively constant deposition of the amount of printing material per length unit of deposited printing material.

11. The method according to claim 10, wherein the printer unit further comprises a feeding unit configured to feed printing material, and wherein the method further comprises the step of sensing a pressure exerted on the feeding unit from the printing material.

12. The method according to claim 10, further comprising the step of sensing a pressure exerted on the nozzle from the printing material.

13. The method according to claim 10, further comprising interrupting an operation of the printer unit in case the movement speed of the printer head is outside a predetermined interval.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

(2) FIG. 1a shows a schematic view of a 3D-printed object which has been printed by a 3D-printing apparatus according to the prior art,

(3) FIG. 1b is a schematic view of a printer unit for a 3D-printing apparatus according to an exemplifying embodiment of the present invention,

(4) FIG. 2 is a schematic view of a transfer function according to an exemplifying embodiment of the present invention,

(5) FIGS. 3a-b are schematic illustrations of transfer functions according to exemplifying embodiments of the present invention,

(6) FIG. 4 is a schematic view of a 3D-printing arrangement according to an embodiment of the present invention, and

(7) FIG. 5 is a schematic view of a method according to an exemplifying embodiment of the present invention.

DETAILED DESCRIPTION

(8) FIG. 1a shows a schematic view of a 3D-printed object 10 which has been printed by a 3D-printing apparatus according to the prior art. It will be appreciated that the surface of the object 10 discloses significant roughnesses, undulations and irregularities, and these defects or deficiencies are due to variations of the pressure of the molten material inside the printing nozzle of the 3D-printing apparatus. According to the prior art, there is suggested a method to measure the nozzle pressure and trying to control the feeding rate of the printing material to try to keep a relatively constant pressure which the printing material exerts on the nozzle. However, alternative solutions are of interest, which are able to provide an even higher printing quality of a 3D-printed object.

(9) FIG. 1b shows a schematic view of a printer unit 100 for a 3D-printing apparatus. It will be appreciated that the printer unit 100 may comprise additional elements, features, etc. However, these are omitted in FIG. 1b for an increased understanding. The printer unit 100 comprises a printer head 105 which in turn comprises a nozzle 110 and a feeding unit 107. The nozzle 110 is arranged to deposit printing material supplied to the nozzle 110 by the feeding unit 107. During operation of the printer unit 100, the printer head 105 moves with a speed S (indicated to the right in FIG. 1b) during deposition of printing material.

(10) In this example, the nozzle 110 is arranged to deposit printing material in the form of a filament 115 in a vertical direction and on an underlying material 135. The underlying material 135 is exemplified as a slightly undulated build-plate, but may alternatively constitute at least one layer of (previously deposited) printing material. The printing material is extruded from the bottom portion of the tapered nozzle 110. To be able to create a relatively smooth surface of layer(s) of printing material, the first layer of printing material is normally printed with a relatively small layer thickness of 0.1-0.2 mm.

(11) The printer unit 100 comprises a pressure sensor 120, which is schematically indicated in FIG. 1b. The pressure sensor 120 of the printer unit 100 is configured to sense a pressure exerted on the printer head 105 from the printing material, e.g. as described in the following. The pressure sensor 120 may be configured to sense a pressure resulting from a force F exerted on the feeding unit 107 of the printer head 105 from the printing material, which may be explained by the following: during an operation of a 3D-printing apparatus comprising a printer unit 100 according to the depicted example of the invention, printing material deposited upon the underlying material 135 from the printer unit nozzle 110 may push printing material backwards (i.e. in the z-direction) within the printer unit 100 against the printing material feed direction (i.e. the negative z-direction). Consequently, the printing material imparts an (upwards) force F in the z-direction on the feeding unit 107 which pushes the feeding unit 107 away from the nozzle 110. The pressure exerted on the feeding unit 107 from the printing material, resulting from the force F, may hereby be measured by the pressure sensor 120. Alternatively, the pressure sensor 120 may be coupled to the nozzle 110 and configured to sense a pressure exerted on the nozzle 110 from the printing material.

(12) The printer unit 100 further comprises a control unit 130 which is schematically indicated in FIG. 1b. The printer unit 100 is coupled to the pressure sensor 120, wherein the control unit 130 is configured to control the speed S of the printer head 105. The speed S is based on a transfer function f from a pressure P.sub.s sensed by the pressure sensor 120 to a desired speed S.sub.d of the printer head 105, with the purpose of maintaining a constant deposition of the amount of printing material per length unit of deposited printing material.

(13) FIG. 2 is a schematic illustration of a transfer function f according to an embodiment of the present invention. The transfer function f may be interpreted as a transfer or mapping function f from the pressure P.sub.s sensed by the pressure sensor 120 to the desired speed S.sub.d of the printer head 105, i.e. f(P.sub.s)=S.sub.d.

(14) FIGS. 3a-b are schematic illustrations of increasing transfer functions according to exemplifying embodiments of the present invention. It should be noted that the figures are not drawn to scale, and are merely shown as examples. In FIG. 3a, the transfer function f may correspond to a linear function which sets or determines the desired speed S.sub.d of the printer head linearly to the sensed pressure P.sub.s. For example, in case of a linear transfer function f, a change in the pressure P.sub.s from P.sub.s1 to P.sub.s2 as indicated in FIG. 3a may results in a change of the desired speed S.sub.d from S.sub.d1 to S.sub.a2. For example, the function f may be expressed as S.sub.d=f(P.sub.s)=k*P.sub.s+m, wherein k is a scaling factor. For example, the scaling factor k may be selected to be 0.5<k<1. Alternatively, the transfer function may comprise at least one filter function between the pressure P.sub.s sensed by the pressure sensor and the desired speed S.sub.d of the printer head. In FIG. 3b, the filter function f comprises a delay function such that S.sub.d remains unchanged even though the pressure P.sub.s changes from P.sub.s1 to P.sub.s2. Then, if there is an increase of the pressure P.sub.s from P.sub.s2 to P.sub.s3, the desired speed S.sub.d changes from S.sub.d1 to S.sub.d2. It will be appreciated that the transfer function f may comprise other functions which are not exemplified in the figures. For example, the filter function may further comprise an averaging function, whereby data of the pressure P.sub.s is filtered and/or averaged over several measurements. This may be beneficial for a removal of short and/or long-term pressure effects. As yet another alternative, the filter function may further comprise one or more non-linear functions (e.g. comprising one or more offsets, exponential terms, logarithmic functions, etc.)

(15) Moreover, the transfer function may be determined based on other parameters. For example, the speed of the printer head, the temperature of the nozzle, the feeding rate of printing material, the amount of printing material deposited per length unit, etc. may influence the transfer function. For example, the transfer function may generate a higher desired speed S.sub.d in case the feeding rate of printing material increases and/or the temperature of the nozzle increases.

(16) FIG. 4 is a schematic diagram of a desired speed S.sub.d of the printer head as a function of time t during an operation of the printer unit. The control unit of the printer unit may be configured to set or provide a predetermined interval I of the desired speed S.sub.d, wherein the interval I is defined between a lower boundary S.sub.0 and an upper boundary S.sub.1, i.e. S.sub.0≤S.sub.d≤S.sub.1. During a first period of the operation of the printer unit, at a left hand side of the diagram in FIG. 4, the desired speed S.sub.d is found within the predetermined interval I. During this condition of the operation of the printer unit, the printer unit may be configured to maintain its printing operation. However, the printer unit may be configured to interrupt its operation in case the desired speed S.sub.d is outside the predetermined interval I. This is exemplified in FIG. 4 at time t.sub.1, wherein the desired speed S.sub.d is outside the predetermined interval I (i.e. S.sub.d>S.sub.1). It should be noted that FIG. 4 is not drawn to scale, and that S.sub.d is shown only as an example. Furthermore, the predetermined interval I is also provided as an example, and may be defined differently. For example, the predetermined interval I may be wider or more narrow than that indicated.

(17) FIG. 5 is a method 500 for 3D-printing an object by a printer unit comprising a printer head arranged to deposit printing material from the printer unit. The method 500 comprises the step of sensing 510 a pressure exerted on the printer head from the printing material. Furthermore, the method 500 comprises the step of controlling 520 the speed of the printer head based on a transfer function from the pressure sensed by the pressure sensor to a desired speed of the printer head, in order to maintain a constant deposition of the amount of printing material per length unit of deposited printing material.

(18) In case the printer unit further comprises a feeding unit configured to feed printing material, according to a previously described embodiment, the method 500 may optionally comprise the further step of sensing 530 a pressure exerted on the feeding unit from the printing material. Alternatively, the method 500 may comprise the step of sensing 540 a pressure exerted on the nozzle from the printing material.

(19) The method 500 may optionally comprise the further step of interrupting 550 an operation of the printer unit in case the speed of the printer head is outside a predetermined interval.

(20) The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, it will be appreciated that the figures are merely schematic views of printer units according to embodiments of the present invention. Hence, any elements/components of the printer unit 100 such as the printer head 105, the nozzle 110, the feeding unit 107, etc., may have different dimensions, shapes and/or sizes than those depicted and/or described. For example, the printer head 105, the nozzle 110 and/or the feeding unit 107 may be larger or smaller than what is exemplified in the figures.