FIELD OF THE INVENTION

The present invention generally relates to the field of 3D printing. More specifically, the present invention relates to a printer unit for a 3D printing apparatus, and a printing method.

BACKGROUND OF THE INVENTION

Additive manufacturing, sometimes also referred to as 3D printing, refers to processes used to synthesize a three-dimensional object. 3D printing is rapidly gaining popularity because of its ability to perform rapid prototyping without the need for assembly or molding techniques to form the desired article.

By using a 3D-printing apparatus, an article or object may be built in three dimensions in a number of printing steps that often are controlled by a computer model. For example, a sliced 3D model of the object may be provided in which each slice is recreated by the 3D-printing apparatus in a discrete printing step.

One of the most widely used 3D-printing processes is Fused Filament Fabrication (FFF). FFF printers often use a thermoplastic filament which in its molten state is ejected from a nozzle of the printer. The material is then placed layer by layer, to create a three-dimensional object. FFF printers are relatively fast and can be used for printing objects of various kinds, even those having relatively complex structures.

During 3D-printing, it is desirable to provide an adequate adherence of the printing material to the underlying material, and that the deposited layer of printing material has a predictable layer thickness and layer width. It will be appreciated that these factor contribute to the print quality and/or surface finish of the 3D-printed objects.

The print quality and/or surface finish of 3D-printed objects are often determined by a visual inspection of an operator and/or by inspecting the output from a camera or a 3D-scanner. The 3D-printed object may thereafter be compared to a predefined, ("ideal") model, wherein the amount of deviation of the 3D-printed object with the predefined model may be used to determine if the quality of the 3D-printed object is acceptable or not. However, it should be noted that quality checks of this kind occur after the printing of the object has finished. If it is decided to reject the product, it may be realized that the process is relatively time- and/or cost efficient, in particular when considering that time for printing the object may have been lost.

Hence, alternative solutions are of interest, which are able to provide a more time- and/or cost-efficient manner for monitoring the printing quality of a 3D-printed object.

WO-2009/134300 discloses a liquefier assembly for use in an extrusion-based digital manufacturing system. The liquefier assembly has a filament tube with an inlet opening to receive a filament strand, and an outlet opening. The filament tube also has a sidewall with a port disposed through it at a location between the inlet and outlet openings. This port is configured to provide access for a filament drive mechanism to engage with the filament strand. The filament tube further has a strain gauge that is secured to the sidewall adjacent to the port. This strain gauge is configured to compensate for variations in extrusion rates due to back pressure that may be generated the filament tube during operation. Such back pressure may be generated due to a reduction in cross-sectional diameter at an extrusion tip carried by an extrusion head of the manufacturing system. As a result of the back pressure, the sidewall of the filament tube is axially stretched, and the amount of stretching is monitored by the strain gauge. The strain gauge is capable of communicating with a computer-operated controller of the manufacturing system.

SUMMARY OF THE INVENTION

It is an object of the present invention to mitigate the above problems and to provide a printer unit and a method which are able to provide a time- and/or cost-efficient manner for monitoring the printing quality of a 3D-printed object.

This and other objects are achieved by providing a printer unit and a method having the features in the independent claims. Preferred embodiments are defined in the dependent claims.

Hence, according to a first aspect of the present invention, there is provided a printer unit for a 3D-printing apparatus. The printer unit comprises a feeding unit and a nozzle. The feeding unit is arranged to feed a printing material to the nozzle, and the nozzle is arranged to deposit the printing material from the printer unit. The printer unit further comprises a force sensor coupled to the feeding unit and configured to sense a force exerted on the feeding unit from the printing material. The printer unit further comprises a registration means coupled to the force sensor. The registration means, based on a transfer function from the force sensed by the force sensor to an estimated pressure exerted on the nozzle from the printing material, is configured to register data of the estimated pressure as a function of the force sensed by the force sensor during an operation of the printer unit.

According to a second aspect of the present invention, there is provided a method for a printer unit of a 3D-printing apparatus, wherein the printer unit comprises a feeding unit and a nozzle. The method comprises the step of feeding a printing material from the feeding unit to the nozzle, wherein the nozzle is arranged to deposit the printing material. The method further comprises the step of sensing a force exerted on the feeding unit from the printing material. The method further comprises the step of, based on a transfer function from the sensed force to an estimated pressure exerted on the nozzle from the printing material, estimating the pressure exerted on the nozzle from the printing material as a function of the sensed force. The method further comprises the step of registering data of the estimated pressure during an operation of the printer unit.

Thus, the present invention is based on the idea of providing a printer unit for a 3D-printing apparatus which is configured to monitor the printing quality of the 3D-printed object in real time during printing. More specifically, it will be appreciated that pressure variations from the printer material inside the nozzle during printing are directly related to the outflow of printing material from the printer unit, wherein pressure deviations of this kind may lead to irregularities and/or defects of the 3D-printed object.

It will be appreciated that during an operation of a 3D-printing apparatus, printing material deposited upon an underlying material from the printer unit nozzle may push printing material backwards within the printer unit against the printing material feed direction. Consequently, the printing material may impart a force on the feeding unit, wherein this force may be sensed by the force sensor.

The force sensed by the force sensor of the printer unit is indicative of pressure variations inside the nozzle that are directly related to the material outflow from the nozzle. These pressure variations may be caused by a variety of parameters, such as the nozzle temperature, the flow rate of the printing material, variations in filament diameter (in case the printing material is supplied in the form of a filament), the viscosity of the printing material, the thickness of the deposited layers, the presence of previously deposited layers, and any nozzle blockage. By estimating the pressure exerted on the nozzle from the printing material via a sensed force exerted on the feeding unit from the printing material, and registering data of the estimated pressure during an operation of the printer unit, the printing quality of the 3D-printed object may be monitored in a convenient manner. The present invention is advantageous in that the printer unit hereby may be configured to stop, abort and/or interrupt a printing operation of a 3D-printing apparatus based on the deviations of the pressure as determined in the nozzle. By aborting a 3D- printing process during printing instead of waiting for the process to finish, unnecessary, cost- and/or time-wasting printing may be minimized.

The present invention is further advantageous in that the printer unit may save material by stopping, aborting and/or interrupting a printing operation of a 3D-printing apparatus based on the estimated pressure.

Furthermore, by aborting a 3D-printing process in case of (relatively large) pressure deviations, damage and/or wear on the components of the printer unit and/or 3D- printing apparatus may be avoided. Consequently, the service life of the printer unit and/or 3D-printing apparatus may be prolonged, hereby contributing to a saving of time and/or costs.

The present invention is further advantageous in that the printer unit may be able to determine the quality of 3D-printed objects without any additional inspection (human and/or automatic), such that additional time and/or costs related to the inspection may be saved.

It will be appreciated that the force sensor is configured to register data of an estimated pressure exerted on the nozzle from the printing material as a function of the force sensed by the force sensor during an operation of the printer unit. Hence, by the present invention, a direct measurement of the pressure in or near the nozzle may be avoided. This is highly beneficial, as such a measurement may be circumstantial, complex and/or

inconvenient, especially when considering that the nozzle may be relatively hot.

It will be appreciated that the mentioned advantages of the printer unit of the first aspect of the present invention also hold for the method according to the second aspect of the present invention.

The printer unit of the present invention comprises a feeding unit and a nozzle. The feeding unit is arranged to feed printing material to the nozzle, and the nozzle is arranged to deposit the printing material from the printer unit. By "printing material", it is usually meant a plastic, provided as a filament. By "deposit", it is hereby meant that the nozzle is configured to eject, provide or extrude (a filament of a) printing material supplied to the nozzle, whereby the depositing of the nozzle is commonly made in a vertical direction and on an underlying material. The printer unit further comprises a force sensor coupled to the feeding unit. By the term "force sensor", it is here meant substantially any device for measuring a load, force and/or pressure, wherein such a device is known to the skilled man. For example, the force sensor may comprise a piezo-electric element, wherein the force is determined based on an electric signal. Alternatively, the force sensor may comprise a resilient element. The force sensor may hereby be configured to measure the force or pressure of the printing material on the feeding unit as a function of the compression (contraction) or elongation of the resilient element.

The force sensor is configured to sense a force exerted on the feeding unit from the printing material. Hence, the feeding material may apply a force and/or pressure on the feeding unit, and the force sensor is arranged to sense and measure the force and/or the pressure associated with the force sensor.

The printer unit further comprises a registration means coupled to the force sensor. By the term "registration means", it is here meant substantially any unit, device or arrangement for registering or saving data, wherein such a means is known to the skilled man.

By the phrasing "transfer function from the force sensed by the force sensor to an estimated pressure exerted on the nozzle from the printing material", it is here meant a (mapping) function which is able to determine or estimate a pressure exerted on the nozzle from the printing material based on the force sensed by the force sensor. The transfer function may alternatively be explained mathematically as f(F)=P _n , wherein f is the transfer function, F is the force sensed by the force sensor, and P _n is the estimated pressure exerted on the nozzle from the printing material.

By the phrasing "data of the estimated pressure", it may hereby be meant substantially any data associated with the estimated pressure. For example, the data may comprise the estimated pressure, the estimated pressure as a function of time and/or space, etc.

According to an embodiment of the present invention, the data of the estimated pressure comprises an estimated pressure as a function of time. Hence, during an operation of the printer unit, the registration means may be configured to register the estimated pressure as a function of time.

According to an embodiment of the present invention, the printer unit further comprises a control unit coupled to the registration means. The control unit is configured to interrupt an operation of the printer unit in case at least one characteristics of the data of the estimated pressure registered by the registration means is outside a predetermined interval of the at least one characteristics of the data of the estimated pressure. By the term

"characteristics", it is here meant a feature, a pattern, or the like, of the data of the estimated pressure registered by the registration means. The present embodiment is advantageous in that the control unit may interrupt an operation of the printer unit in case an undesired characteristics of the data of the estimated pressure is registered by the registration means, thereby saving time and/or costs. For example, in case the feeding unit of the printer unit feeds a relatively thick filament of printing material to the nozzle, there may be an increased flow of material from the nozzle. As a consequence, defects in the deposited material (e.g. protrusions) may occur which may decrease the quality of the surface of the 3D-printed object. Analogously, in case the feeding unit of the printer unit feeds a relatively thin filament of printing material to the nozzle, there may be a decreased flow of material from the nozzle. This may result in defects in the deposited material (e.g. dimples), and the quality of the surface of the 3D-printed object may be decreased. Furthermore, in case the filament runs out and/or if the nozzle is blocked (e.g. caused by debris, particles, etc.), the printer unit operation will continue without any deposition of printing material, leading to a waste of (valuable) printing capacity. As yet another example, in case the 3D-object has collapsed and/or if the deposited printing material falls off the previously deposited layer, the result may be a defect object and/or there may be a waste of printing material. It will be appreciated that these previously mentioned examples may influence or impact the data of the estimated pressure registered by the registration means, e.g. by relatively large increases or decreases (drops) in the estimated pressure. The control unit of the present embodiment may be configured to react to these characteristics of the data of the estimated pressure, and efficiently and conveniently interrupt the operation of the printer unit accordingly.

According to an embodiment of the present invention, the control unit is configured to interrupt the operation of the printer unit in case an estimated pressure is outside a predetermined interval of the data of the estimated pressure. In other words, the control unit may interrupt an operation of the printer unit in case the estimated pressure is too high or too low with respect to the predetermined pressure interval. As nozzle pressure deviations may lead to irregularities and/or defects of the 3D-printed object, the present embodiment is advantageous in that the control unit may save time and/or costs by interrupting an operation of the printer unit in case of such pressure deviations.

According to an embodiment of the present invention, the control unit is configured to evaluate a pressure gradient as a function of the data of the estimated pressure. The control unit is further configured to interrupt the operation of the printer unit in case the evaluated gradient of the estimated pressure is outside a predetermined interval of the evaluated gradient of the estimated pressure. For example, the control unit may be configured to interrupt the operation of the printer unit in case the evaluated gradient of the estimated pressure is relatively high, e.g. due to a relatively large increase or relatively large decrease in the estimated pressure. The present embodiment is advantageous in that the control unit may save time and/or costs by interrupting an operation of the printer unit in case of an undesired increase or decrease in the estimated pressure, as fluctuations of these kind may result in an inferior quality of the 3D-printed object.

According to an embodiment of the present invention, the printer unit comprises an alarm unit coupled to the registration means. The alarm unit is configured to generate an alarm in case at least one characteristics of the data of the estimated pressure registered by the registration means is outside a predetermined interval of the at least one characteristics of the data of the estimated pressure. For example, if the estimated pressure and/or gradient of the estimated pressure is outside a respective predetermined interval, the alarm unit may generate an alarm to notify an operator.

According to an embodiment of the present invention, the registration means is configured to register a position of the nozzle as a function of time. For example, the registration means may register both an estimated pressure exerted on the nozzle from the printing material and a position of the nozzle as a function of time. This is advantageous in that a surface profile of the 3D-printed object may be determined (or at least estimated) based on the information of the position of the nozzle and the estimated pressure as a function of time.

According to an embodiment of the second aspect of the present invention, the data of the estimated pressure comprises an estimated pressure as a function of time.

According to an embodiment of the invention, the method further comprises the step of interrupting an operation of the printer unit in case at least one characteristics of the data of the estimated pressure registered by the registration means is outside a predetermined interval of the at least one characteristics of the data of the estimated pressure.

According to an embodiment of the invention, the method further comprises the step of interrupting an operation of the printer unit in case the estimated pressure is outside a predetermined interval of the data of the estimated pressure.

According to an embodiment of the invention, the method further comprises the step of evaluating a pressure gradient as a function of the data of the estimated pressure. Furthermore, the method comprises the step of interrupting the operation of the printer unit in case the evaluated gradient of the estimated pressure is outside a predetermined interval of the evaluated gradient of the estimated pressure.

According to an embodiment of the invention, the method further comprises the step of generating an alarm in case at least one characteristics of the data of the estimated pressure registered by the registration means is outside a predetermined interval of the at least one characteristics of the data of the estimated pressure.

According to an embodiment of the invention, there is provided a method for registering at least one 3D-printed object. The method comprises the step of 3D-printing at least one object by the method according to any one of the previously described

embodiments. The method further comprises the step of associating the at least one object with the respective registered data of the estimated pressure. Furthermore, the method comprises the step of registering the associated at least one object with the respective registered data of the estimated pressure into a register.

According to an embodiment of the invention, there is provided a method for identifying a 3D-printed object. The method comprises the step of determining a surface profile of a 3D-printed object based on measuring at least a portion of a surface of the 3D- printed object. The method further comprises the step of performing the method of the previous embodiment and predicting a surface profile of a 3D-printed object based on the registered data of the estimated pressure. The method further comprises the step of determining if the surface profile corresponds to the predicted surface profile.

Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art will realize that different features of the present invention can be combined to create embodiments other than those described in the following.

BRIEF DESCRIPTION OF THE DRAWINGS

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.

Fig. 0 shows a schematic view of a 3D-printed object 10 which has been printed by a 3D-printing apparatus according to the prior art,

Fig. 1 is a schematic view of a printer unit for a 3D-printing apparatus according to an exemplifying embodiment of the present invention, Fig. 2 is a schematic view of a mapping function f according to an

exemplifying embodiment of the present invention,

Fig. 3 is a schematic diagram of an estimated pressure P _n according to an exemplifying embodiment of the present invention,

Fig. 4 is a schematic diagram of a surface profile and a predicted surface profile of a 3D-printed object according to an exemplifying embodiment of the present invention,

Fig. 5 is a schematic view of a method for a printer unit of a 3D-printing apparatus according to an exemplifying embodiment of the present invention,

Fig. 6 is a schematic view of a method 600 for registering at least one 3D- printed object according to an exemplifying embodiment of the present invention, and

Fig. 7 is a schematic view of a method 700 for identifying a 3D-printed object according to an exemplifying embodiment of the present invention. DETAILED DESCRIPTION

Fig. 0 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, quality inspection takes place after the printing of the object has finished. If it is decided to reject the product, it may be realized that time and/or costs has been lost in the process. Hence, alternative solutions are of interest, which are able to provide a more time- and/or cost-efficient manner for monitoring the printing quality of a 3D-printed object.

Fig. 1 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. 1 for an increased understanding. The printer unit 100 comprises a nozzle 110 which is arranged to deposit printing material supplied to the nozzle 110 by a feeding unit 107. In this example, the nozzle 110 is arranged to deposit printing material in the form of a filament 1 15 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 1 10. 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.

In the exemplifying embodiment of Fig. 1, the nozzle 1 10 is fixed to an element 125 (e.g. a carriage) of the printer unit 100. Hence, the nozzle 110 is hereby fixed in a vertical direction.

The printer unit 100 is configured to sense a force F exerted on the feeding unit 107 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 force F exerted on the feeding unit 107 from the printing material is measured by the printer unit 100, and the feeding rate of the printing material may be controlled as a function of this force.

The sensing and/or measurement of the force F as described above may be performed by a force sensor 120 of the printer unit 100, wherein the force sensor 120 is coupled to the feeding unit 107.

The printer unit 100 further comprises a registration means 140, which is schematically indicated in Fig. 1. The registration means 140 is coupled to the force sensor 120, wherein the coupling may be by wire or be a wireless connection.

During operation of the printer unit 100, the registration means 140 is configured to register data of an estimated pressure P _n exerted on the nozzle 110 from the printing material. More specifically, the registration means 140 is configured to register the data of the estimated pressure P _n as a function of a force F sensed by the force sensor 120, i.e. f(F)=P _n . The function f may be interpreted as a transfer or mapping function f from the force F sensed by the force sensor 120 to the estimated pressure P _n . This is schematically indicated in Fig. 2, wherein the force F sensed by the force sensor 120 is provided as input to the registration means 140, and wherein the output is the estimated pressure P _n .

Fig. 3 is a schematic diagram of an estimated pressure P _n exerted on the nozzle from the printing material as a function of time t during an operation of the printer unit, wherein the estimated pressure P _n is registered by the registration means. The printer unit may be configured to set or provide a predetermined interval I of the estimated pressure P _n , wherein the interval I is defined between a lower boundary Po and an upper boundary Pi, i.e. Po≤ Pn≤ Pi. It should be noted that Fig. 3 is not drawn to scale, and that the estimated pressure P _n 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 and/or comprise other features related to the behavior or pattern of the estimated pressure P _n .

Analogously, the printer unit may be configured to evaluate a pressure gradient P _n '=dP _n /dt as a function of the data of the estimated pressure P _n , and be configured to set or provide a predetermined interval Γ of the estimated pressure P _n ' wherein the interval Γ is defined between a lower boundary Po' and an upper boundary Pi ', i.e. Po' < P _n '≤ Pi' (it should be note that neither the pressure gradient P _n ', nor its related interval Γ, is shown in Fig. 2).

During a first period of the operation of the printer unit, at a left hand side of the diagram in Fig. 3, the estimated pressure P _n is found within the predetermined interval I. In other words, the deviations of the estimated pressure P _n is relatively small, which may indicate a relatively high printing quality of the 3D-printed object. Furthermore, also the estimated pressure gradient P _n ' is relatively small, which also may indicate a relatively high printing quality. During one or more of these conditions of the operation of the printer unit, e.g. when the estimated and/or P _n ' is within a predetermined pressure interval I and/or Γ, 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 estimated pressure P _n is outside the predetermined interval I. This is exemplified in Fig. 3 at time ti, wherein the estimated pressure P _n is outside the predetermined interval I (i.e. P _n > Pi). Furthermore, between time to and ti in Fig. 3, it will be appreciated that the example shows a relatively sharp increase in the estimated pressure P _n . The printer unit may find that the pressure gradient is outside a predetermined interval of the evaluated gradient P' of the estimated pressure P _n (e.g. P _n '=dP _n /(ti-to) > Pi'), and interrupt its operation accordingly.

It will be appreciated that the control unit may be configured to interrupt an operation of the printer unit in case of one or more scenarios. For example, in case the feeding unit of the printer unit feeds a relatively thick filament of printing material to the nozzle, there may be an increased flow of material from the nozzle and an increase of the (estimated) nozzle pressure. Consequently, the estimated pressure P _n may be outside the predetermined interval I, and the control unit may be configured to interrupt the printer unit operation. Analogously, in case the feeding unit of the printer unit feeds a relatively thin filament of printing material to the nozzle, the estimated pressure P _n may be relatively low, and the control unit may be configured to interrupt the printer unit operation.

The printer unit 100 may further comprise an alarm unit (not shown) coupled to the registration means, wherein the coupling may be by wire or be a wireless connection. The alarm unit is configured to generate an alarm in case at least one characteristics (e.g. P _n and/or P _n ') of the data of the estimated pressure P _n registered by the registration means is outside a predetermined interval (e.g. I and or Γ) of the at least one characteristics of the data of the estimated pressure n.

The printer unit 100 may further comprise a control unit 130 coupled to the registration means 140, wherein the coupling may be by wire or be a wireless connection. The control unit 130 may be configured to interrupt the operation of the printer unit 100 according to the above-mentioned examples. Hence, the control unit 130 may be configured to interrupt an operation of the printer unit 100 in case at least one characteristics of the data of the estimated pressure is outside a predetermined interval.

Fig. 4 is a schematic diagram of a surface profile 210 of a 3D-printed object and a predicted surface profile 220 of the 3D-printed object. It will be appreciated that the quantities of the axes are arbitrary, as Fig. 4 is merely provided for exemplifying reasons. For example, the x-axis may denote time and/or space whereas the y-axis may denote pressure and/or length. The surface profile 210 of the 3D-printed object may be provided by measurements, e.g. by performing a scanning along the side-wall of the 3D-printed object. The layered structure is visible as a small periodic signal, whereas the larger peaks/valleys indicate surface roughness. The predicted surface profile 220 of the 3D-printed object may be obtained by the estimated pressure P _n as previously described. For example, a transfer function from the data of the estimated pressure P _n to the predicted surface profile 220 may be provided. It will be appreciated that the example in Fig. 4 shows a relatively strong correlation between the predicted surface profile 220 and the (real, measured) surface profile 210 of the 3 D-printed obj ect. Hence, the printer unit may be configured to accurately predict the surface profile of a 3 D-printed object.

Fig. 5 is a schematic view of a method 500 for a printer unit of a 3D-printing apparatus, wherein the printer unit comprises a feeding unit and a nozzle. The method 500 comprises the step of feeding 510 a printing material from the feeding unit to the nozzle, wherein the nozzle is arranged to deposit the printing material from the printer unit. The method 500 further comprises the step of sensing 520 a force exerted on the feeding unit from the printing material. The method 500 further comprises the step of estimating 530 a pressure exerted on the nozzle from the printing material as a function of the sensed force based on a transfer function from the sensed force to an estimated pressure exerted on the nozzle from the printing material. The method 500 further comprises the step of registering 540 data of the estimated pressure during an operation of the printer unit.

Optionally, the data of the estimated pressure may comprise an estimated pressure as a function of time.

The method 500 may optionally comprise the further step of interrupting 550 an operation of the printer unit in case at least one characteristics of the data of the estimated pressure registered by the registration means is outside a predetermined interval of the at least one characteristics of the data of the estimated pressure. Furthermore, the method 500 may comprise the step of interrupting 560 an operation of the printer unit in case the estimated pressure is outside a predetermined interval of the data of the estimated pressure.

The method 500 may optionally comprise the further steps of evaluating 570 a pressure gradient as a function of the data of the estimated pressure, and interrupting 580 the operation of the printer unit in case the evaluated gradient of the estimated pressure is outside a predetermined interval of the evaluated gradient of the estimated pressure.

The method 500 may optionally comprise the further steps of generating 590 an alarm in case at least one characteristics of the data of the estimated pressure registered by the registration means is outside a predetermined interval of the at least one characteristics of the data of the estimated pressure.

Fig. 6 is a schematic view of a method 600 for registering at least one 3D- printed object. The method 600 comprises the step of 3D-printing 610 at least one object by the method according to any one of the previously described embodiments. The method 600 further comprises the step of associating 620 the at least one object with the respective registered data of the estimated pressure. Furthermore, the method comprises the step of registering 630 the associated at least one object with the respective registered data of the estimated pressure into a register.

Fig. 7 is a schematic view of a method 700 for identifying a 3D-printed object. The method 700 comprises the steps of providing 710 a 3D-printed object, and associating 720 the 3D-printed object with a pressure function. The method further comprises the steps of providing 730 a register and determining 740 if the pressure function corresponds to a registered data of an estimated pressure in the register.

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 nozzle 1 10, the feeding unit 107, etc., may have different dimensions, shapes and/or sizes than those depicted and/or described. For example, the nozzle 110 and/or the feeding unit 107 may be larger or smaller than what is exemplified in the figures.