WO2018127444A1

WO2018127444A1 - Platform unit for a 3d-printing apparatus

Info

Publication number: WO2018127444A1
Application number: PCT/EP2017/084658
Authority: WO
Inventors: Vincent Stefan David Gielen
Original assignee: Philips Lighting Holding B.V.
Priority date: 2017-01-05
Filing date: 2017-12-27
Publication date: 2018-07-12

Abstract

A platform unit (100) for a 3D-printing apparatus, comprising a platform (110) upon which the 3D-printing apparatus is arranged to deposit a printing material in order to create at least one object, and at least one frequency actuator (120, 121, 122) coupled to the platform and configured to excite at least one natural frequency of the platform.

Description

PLATFORM UNIT FOR A 3D-PRINTING APPARATUS

FIELD OF THE INVENTION

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

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, the article or object may be built in three dimensions in a number of printing steps that are usually 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. The 3D-printing apparatus may deposit successive layers of an extrudable material from a dispenser, and the layers may be cured or otherwise hardened after deposition, e.g. using a laser to induce the curing process. An example of such a 3D-printing apparatus is disclosed in US 2010/0327479 Al.

After the printing process, the part(s) and/or object(s) printed need to be detached from the building plate of the 3D-printing apparatus. However, it is relatively well known that printed parts and/or objects tend to stick (i.e. adhere) to the building plate of the 3D-printing apparatus during printing. Actually, detaching a printed part or object from a building plate may be a relatively labour-intensive operation, and may occasionally lead to damaged part(s)/object(s) and/or building plates. Notably, the deposition of a material comprising polyethylene terephthalate (PET) on a building plate comprising glass may lead to a problematic detachment of the material (e.g. in the form of an object) from the building plate.

It will be appreciated that specific tools and/or substances may be suggested to facilitate a removal (detachment) of one or more objects from a building plate of a 3D- printing apparatus. However, a significant drawback of these methods is that they require one or more extra processing steps. Furthermore, the application of a tool and/or substance on the object and/or building plate may still damage (or at least negatively influence the appearance of) the object and/or building plate.

US-2016/0288420 discloses an imaging device that includes an ejector head configured to eject a material, a platen having a first surface configured to receive material ejected by the ejector head and support an object formed with the ejected material, a vibrator configured to vibrate, and a controller operatively connected to the vibrator. The controller is configured to operate the vibrator to vibrate and loosen material adhering to the first surface of the platen to enable the object to be removed from the platen.

Alternative solutions are of interest, which are able to efficiently and conveniently eliminate or reduce any cumbersome, circumstantial and/or problematic detachments of objects printed on a building plate of a 3D-printing apparatus.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a platform unit for a 3D- printing apparatus wherein objects produced may be easily detached from a platform of the 3D-printing apparatus.

This and other objects are achieved by providing a platform unit and a 3D- printing apparatus comprising the platform unit.

Hence, according to a first aspect of the present invention, there is provided a platform unit for a 3D-printing apparatus. The platform unit comprises a platform upon which the 3D-printing apparatus is arranged to deposit a printing material in order to create at least one object. The platform unit also comprises at least one frequency actuator coupled to the platform and configured to excite at least one natural frequency of the platform. The platform unit further comprises a frequency measuring element coupled to the platform, wherein the frequency measuring element is configured to measure at least one natural frequency of the platform.

A method for detaching an object created by a 3D-printing apparatus from a platform of the 3D-printing apparatus comprises the steps of coupling, to the platform, a frequency measuring element configured to measure at least one natural frequency of the platform. The method also comprises the step of coupling, to the platform, at least one frequency actuator configured to excite the at least one natural frequency of the platform. The method further comprises the step of, by operation of the at least one actuator, exciting the at least one natural frequency of the platform, wherein the platform is configured to have at least one natural frequency which is higher than at least one natural frequency of the at least one object.

Thus, the present invention is based on the idea of providing a platform unit for a 3D-printing apparatus, wherein one or more frequency actuators are configured to excite at least one natural frequency of the platform of the platform unit. Hence, the frequency actuator(s) may be configured to induce or introduce one or more standing wave(s) into the platform material, leading to an oscillation, rotation and/or other movement of the platform material. It will be appreciated that the natural frequency or frequencies of the platform, as excited by the frequency actuator(s), may be relatively high, whereas an object produced by the 3D-printing apparatus upon the platform may have a relatively low natural frequency or frequencies. Hence, the natural frequency(ies) of the platform may be above, or even largely above, the natural frequency(ies) of the object produced by the 3D-printing apparatus. In other words, the platform may have different resonant frequency(ies) than the object produced by the 3D-printing apparatus. During the excitation of one of more natural frequencies of the platform, the object may be unable to follow the wave pattern of the platform, leading to a detachment of the object from the platform.

The present invention is advantageous in that the frequency actuators of the platform unit are configured to excite the natural frequency(ies) of the platform such that an object produced on the platform may be easily and conveniently detached. The present invention may hereby avoid any additional processing step related to a removal (detachment) of an object attached to the platform of the 3D-printing apparatus. Hence, the present invention may lead to a relatively time- and/or cost-efficient operation for detachment of one or more objects from a platform compared to related operations of the prior art.

The present invention is further advantageous in that one or more objects may be detached from the platform without the use and/or application of any specific tools and/or substances for that purpose. As tools and/or substances for this purpose may be associated with extra costs, it will be appreciated that the present invention is relatively efficient in terms of cost regarding the detachment of one or more objects from the platform.

Furthermore, it will be appreciated that the frequency actuators of the platform unit are configured to detach one or more objects from the platform by exciting the natural frequency(ies) of the platform, i.e. without any (additional) interaction with the objects produced. Consequently, the present invention may avoid any use of tools, substances, or the like, for detaching the object from the platform. Hence, the present invention is further advantageous in that it may avoid, or at least minimize, any damage of the object and/or building plate which otherwise may occur during the detachment of the object(s) from the platform by applying a tool and/or a substance.

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

The platform unit of the present invention comprises a platform upon which the 3D-printing apparatus is arranged to deposit a printing material in order to create at least one object. By the term "platform", it is here meant a (base) plate, building plate, or the like, arranged to receive a printing material, e.g. in form of one or more filaments, from a 3D- printing apparatus. The platform unit of the present invention further comprises at least one frequency actuator coupled to the platform and configured to excite the at least one natural frequency of the platform. By the term "frequency actuator", it is here meant substantially any element configured to generate, initiate, excite, induce, introduce and/or actuate a frequency of an object to which the frequency actuator is coupled. For example, the frequency actuator may comprise and/or constitute an (ultrasonic) transducer, an

electrostrictive element, a piezoelectric element, etc.

By the term "configured to excite the at least one natural frequency of the platform", it is here meant that the frequency actuator(s) is (are) configured and/or arranged to generate, initiate, excite, induce, introduce and/or actuate one or more of the platform's natural frequencies. Moreover, by the term "at least one natural frequency", it is here meant the at least one eigenfrequency of the platform, i.e. the frequency(ies) at which the platform (material) tends to oscillate in the absence of any driving or damping force.

The platform unit according to the invention comprises a frequency measuring element coupled to the platform and configured to measure at least one natural frequency of the platform. The frequency measuring element may detect a detachment of one or more objects attached to the platform during and/or after the excitation of natural frequency(ies) of the platform. For example, the frequency measuring element may be configured to detect higher natural frequencies of a platform to which one or more objects are attached compared to the natural frequencies of a platform from which one or more objects have been detached.

According to an embodiment of the present invention, the platform is configured to have at least one natural frequency which is higher than at least one of the at least one natural frequency of the at least one object created by the 3D-printing

apparatus. For example, the platform may be relatively stiff (i.e. have a relatively high elastic modulus) and/or have a relatively low mass compared to the at least one object which may have a relatively low stiffness (i.e. have a relatively low elastic modulus) and/or have a relatively high mass. Consequently, the natural frequency(ies) of the platform as excited by the frequency actuator(s) may relatively high compared to the natural frequency(ies) of the object produced by the 3D-printing apparatus. The present embodiment is hereby

advantageous in that the platform unit may be configured to conveniently and efficiently detach object(s) attached or adhered thereto by introducing an oscillation, rotation and/or wave pattern into the platform material. As the object(s) may be unable to follow these movements of the platform material, as induced by the frequency actuator(s), the object(s) may be detached from the platform.

According to an embodiment of the present invention, the platform is arranged in a horizontal plane, and at least one of the at least one frequency actuator is configured to excite at least one natural frequency of the platform in the horizontal plane. In other words, the platform may be arranged horizontally, e.g. in an x-y-plane by Cartesian coordinates, and the frequency actuator(s) may be configured to actuate, introduce and/or excite a wave pattern in the platform in the horizontal plane in which the platform is arranged. The frequency actuator(s) of the platform unit may hereby be configured to create at least one longitudinal wave (i.e. compression wave) in the horizontally arranged platform, wherein the waves displace the platform material in the same direction as, or the opposite direction to, the direction of travel of the wave. Alternatively, the frequency actuator(s) of the platform unit may be configured to create a rotational movement of the platform material, e.g. by exciting at least one natural frequency in the x-direction and at least one natural frequency of the y- direction of the platform. The present embodiment is advantageous in that the excitation of natural frequency(ies) of the platform in the horizontal plane may utilize the maximal stiffness of the platform. In other words, the frequency actuator(s) may be configured to utilize the maximum spring constant of the platform, such that the difference in natural frequency between the platform and the object is maximal. The present embodiment may hereby facilitate the detachment of the object from the platform even further.

According to an embodiment of the present invention, at least one of the at least one frequency actuator is configured to excite at least one natural frequency of the platform along at least one of a first axis (x), a second axis (y), and a third axis (z), wherein the first, second and third axes are perpendicular to each other. In other words, the frequency actuator(s) may be configured to actuate, introduce and/or excite a wave pattern along one, two or three dimensions in the platform. The present embodiment is hereby advantageous in that the platform unit may hereby conveniently and efficiently detach object(s) attached or adhered thereto to an even higher extent by introducing an oscillating and/or rotating wave pattern in the platform material.

According to an embodiment of the present invention, at least one of the at least one frequency actuator is configured to excite at least one natural frequency of the platform along at least two of a first axis (x), a second axis (y), and a third axis (z), wherein the at least two axes, along which the at least one frequency actuator is configured to excite at least one natural frequency of the platform, are not perpendicular to each other. It will be appreciated that the present embodiment may hereby induce a relatively complex wave pattern into the platform material, which may facilitate a removal of an object from the platform even further.

According to an embodiment of the present invention, the platform unit may comprise at least one first frequency actuator being configured to excite at least one natural frequency of the platform along a first axis, and at least one second frequency actuator being configured to excite at least one natural frequency of the platform along a second axis, wherein the at least one natural frequency along the first axis and the at least one natural frequency along the second axis is the same, and wherein the phase shift between the at least one natural frequency along the first axis and the at least one natural frequency along the second axis is zero. The present embodiment hereby implies a symmetric wave pattern in the platform in at least two dimensions of the platform unit, and is advantageous in that the platform unit may even more efficiently detach object(s) attached or adhered thereto.

According to an embodiment of the present invention, the platform unit may comprise at least one first frequency actuator being configured to excite at least one natural frequency of the platform along a first axis, and at least one second frequency actuator being configured to excite at least one natural frequency of the platform along a second axis, wherein at least one of the conditions of the at least one natural frequency along the first axis and the at least one natural frequency along the second axis being different, and the phase shift between the at least one natural frequency along the first axis and the at least one natural frequency along the second axis is non-zero, is fulfilled. In the present embodiment, the platform unit may induce an asymmetric wave pattern in the platform in at least two dimensions of the platform unit, which may facilitate a removal of an object from the platform to an even further extent.

According to an embodiment of the present invention, at least one of the at least one frequency actuator is connected to at least one portion of at least one edge of the platform. For example, in case of a rectangular platform arranged horizontally in an xy-plane, at least one frequency actuator may be connected to a first edge of the platform, and at least one frequency actuator may be connected to a second edge of the platform, perpendicular to the first edge. The present embodiment is advantageous in that the platform unit may create a longitudinal wave in the plane of the platform in a convenient and efficient way.

According to an embodiment of the present invention, at least one of the at least one frequency actuator is connected to at least one portion of an underside of the platform. It will be appreciated that the frequency actuator(s) may hereby be configured to excite one or more natural frequencies along a vertical axis (z-axis) of the platform.

Consequently, the frequency actuator(s) may induce a transverse wave of the platform. It will be appreciated that a standing wave may be generated by the at least one frequency actuator. The present embodiment is advantageous in that the platform unit hereby provides a relatively convenient arrangement for inducing a transverse wave for detaching an object from the platform. Furthermore, one or more frequency actuators may be arranged at off- center positions (i.e. at non-central positions) of the platform for inducing dynamic wave patterns. This may be beneficial in the case there is a wish to compensate for a platform which may be asymmetric.

According to an embodiment of the present invention, at least one of the at least one frequency actuator is configured to excite at least one natural frequency of the platform along an axis passing through the shear center of the platform. By the term "shear center", it is here meant a point of the platform where a force may be applied without causing any rotation of the platform. It will be appreciated that the shear center coincides with the center of gravity in case of a symmetric platform. The present embodiment is advantageous in that the frequency actuator(s) may generate (only) longitudinal waves in the platform.

According to an embodiment of the present invention, at least one of the at least one frequency actuator is configured to excite at least one natural frequency of the platform along an axis which does not pass through the shear center of the platform. The present embodiment is advantageous in that the frequency actuator(s) may hereby generate a rotational movement of the platform.

According to an embodiment of the present invention, at least one of the at least one frequency actuator comprises at least one piezoelectric element. The present embodiment is advantageous in that the use of one or more piezoelectric elements in the frequency actuator(s) may contribute to an even more precise frequency actuation.

According to an embodiment of the present invention, the platform comprises at least one material of a group comprising glass, ceramics and metals. It will be appreciated that a platform comprising or consisting of glass, ceramics and/or metal exhibits a relatively high stiffness, leading to (a) relatively high natural frequency(ies) of the material. Hence, the present embodiment is advantageous in that the platform unit may be able to conveniently detach an object, e.g. of plastics, attached to the platform, as the object may have relatively low natural frequencies.

According to a second aspect of the present invention, there is provided a 3D- printing apparatus comprising a platform unit according to the first aspect of the invention.

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. 1 is a schematic view of a 3D-printing apparatus comprising a platform unit according to an exemplifying embodiment of the present invention,

Fig. 2 is a schematic view of a platform unit according to an exemplifying embodiment of the present invention, and

Figs. 3-5 are schematic views of wave patterns in a platform of a platform unit according to exemplifying embodiments of the present invention.

DETAILED DESCRIPTION

Fig. 1 is a schematic view of a 3D-printing apparatus 200 comprising a platform unit 100 according to an embodiment of the present invention. The 3D-printing apparatus 200 may comprise an extruder 210 for extrusion of a printing material in form of a filament 220 and a nozzle 230 for deposition of the (melted) printing material. The 3D- printing apparatus 200 is arranged to deposit the printing material in order to create at least one (three-dimensional) object 240. It will be appreciated that the basic concept of a 3D- printing apparatus 200 is known to the skilled man, and details regarding the apparatus 200 are therefore omitted.

The platform unit 100 comprises a platform 110 upon which the 3D-printing apparatus 200 is arranged to deposit the printing material for the creation of the object(s) 240. Here, the platform 110 is exemplified as a platform or plate having a rectangular shape, with a surface 112 and an edge 114. A frequency actuator 120, which is configured to excite at least one natural frequency of the platform 110, is connected to a center portion of the edge 114 on a short end of the platform 110. Analogously, a frequency actuator 121 may be connected to a center portion of the edge 114 on a long side of the platform 110, and a frequency actuator 122 may be connected to a center portion of an underside of the platform 110. Although the platform unit 100 as exemplified comprises three frequency actuators 120, 121, 122 arranged on portions of the edge 114 and the underside of the platform 110, respectively, it should be noted that the platform unit 100 alternatively may be provided with one or more frequency actuators 120, 121 on the edge 114 and/or one or more frequency actuators 122 on the underside of the platform 110. For example, it will be appreciated that although only one frequency operator 120 is provided on the edge 114 of the short side of the platform 110, it is feasible to couple a plurality of frequency operators 120 to the edge 114 of the platform 110. Furthermore, the platform unit 100 in Fig. 1 may comprise a frequency measuring element (not shown). The frequency measuring element may be coupled to the platform and be configured to measure at least one natural frequency of the platform.

In Fig. 1, the one or more frequency operators 120, 121, 122 of the platform unit 100 are configured to excite one or more natural frequencies of the platform 110 such that an object 240, attached to the platform 110 after creation of the object 240 by the 3D- printing apparatus, may be detached. During the excitation of one of more natural frequencies of the platform 110 by the frequency operator(s) 120, 121, 122, the material of the platform 110 at the points and/or surfaces of contact with the object 240 may thereby be subjected to a movement as a result of the wave pattern which the object 240 may be unable to follow. For example, if the frequency operator 120 is configured to excite a longitudinal wave in the platform 110, the material of the platform 110 at the points and/or surfaces of contact with the object 240 may be subjected to a force parallel to the surface of the platform 110. If this force is greater than the friction force between the platform 110 and the object 240 at the points and/or surfaces of contact, the object 240 may detach from the platform 110.

Fig. 2 is a schematic view of an exemplifying embodiment of the platform unit 100 shown in Fig. 1. Here, the frequency actuator 120 is connected to a center portion of the edge 114 on a short end of the platform 110, wherein the short end is parallel to a y-axis of a Cartesian coordinate system. The frequency actuator 120 is configured to excite at least one natural frequency of the platform 110, wherein the wave induced by the frequency actuator 120 propagates in a direction parallel to the x-axis. Analogously, a frequency actuator 121 is connected to a center portion of the edge 114 on a long side of the platform 110, wherein the long side is parallel to the x-axis of the Cartesian coordinate system. The frequency actuator 121 is configured to excite at least one natural frequency of the platform 110, wherein the wave induced by the frequency actuator 121 propagates in a direction parallel to the y-axis. In conformance with the description of Fig. 1 , it should be noted that the platform unit 100 may comprise one or more frequency actuators. For example, the platform unit 100 may comprise any one, or all of, the frequency actuators 120, 121, 122 (the latter not shown in Fig. 2).

Fig. 3 is a schematic view of an exemplifying embodiment of the platform unit 100 comprising a frequency actuator 120 which is configured to excite at least one natural frequency of the platform 110. The wave induced in the platform 110 by the frequency actuator 120 propagates in the platform 110 in a direction parallel to the x-axis as a longitudinal wave. The longitudinal wave is visualized in Fig. 3 by a compression of the material of the platform 110 in region 125, and by an expansion of the material of the platform 110 in region 126. It will be appreciated that the frequency actuator 120 may induce a standing wave in the platform 110. Furthermore, it should be noted that the frequency induced and/or the compression and expansion of the material in Fig. 3 is merely shown schematically.

Fig. 4 is a schematic view of an exemplifying embodiment of the platform unit 100. The platform unit 100 comprises a frequency actuator 120 which is configured to excite at least one natural frequency of the platform 110 propagating in the x-direction and a frequency actuator 121 which is configured to excite at least one natural frequency of the platform 110 propagating in the y-direction. The two frequency actuators 120, 121 of the platform unit 100 may hereby induce natural frequencies in the (horizontal) xy-plane of the platform 110. The resulting wave pattern is schematically shown in Fig. 4 comprising material compression in region(s) 125 and material expansion in region(s) 126. It should be noted, however, that the wave pattern indicated in Fig. 4 is merely shown schematically. In other words, the frequency, the compression and expansion of the material, etc., may be different than that shown.

Fig. 5 is a schematic view of an exemplifying embodiment of the platform unit

100. In accordance with Fig. 4, the platform unit 100 comprises frequency actuators (not shown) configured to excite one or more natural frequencies of the platform 110 in the (horizontal) xy-plane of the platform 110. Hence, a longitudinal wave pattern is induced in the platform 110, leading to material compression in region(s) 125 and material expansion in region(s) 126. Furthermore, one or more frequency actuators (not shown), e.g. connected to at least one portion of an underside of the platform 110, may generate a transverse wave of the platform 110 oscillating in the z-direction 128. It will be appreciated that the platform 110 may be supported at its ends, whereby the ends thereof constitute nodes of the transverse wave. Alternatively, the platform 110 may be supported at its center, whereby a node of the transverse wave may be created at the center. Furthermore, it should be noted that the amplitude of the transverse wave in the z-direction 128 is largely exaggerated for an increased understanding on the figure, and analogously, of the concept of the present embodiment.

It will be appreciated that numerous alternative arrangements and/or configurations of the platform unit 100 may be feasible to those already described. For example, in one embodiment, one or more of the frequency actuators 120, 121, 122 may be configured to excite at least one natural frequency of the platform along an axis passing through the shear center and/or gravity center of the platform 110. Alternatively, the frequency actuators 120, 121, 122 may be configured to excite at least one natural frequency of the platform along an axis which does not pass through the shear center or the gravity center of the platform 110, whereby a rotational movement of the platform 110 can be created. Moreover, the platform unit 100 may be configured to generate a relatively complex wave pattern of and/or in the platform 110 by the arrangement of one or more frequency actuators 120, 121, 122 off-center with respect to the center of gravity of the platform 110.

Furthermore, a rotational movement of the platform 110 may be created, e.g. by coupling two or more frequency actuators 120, 121, 122 to the platform 110 and arranging them in an angle to each other, wherein the excitation wave shape and phase correspond to the desired movement of the platform 110.

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 a platform unit 100 according to embodiments of the present invention. Hence, any elements/components of the platform unit 100 such as the platform 110 and/or the one or more frequency actuators 120, 121, 122 may have different dimensions, shapes and/or sizes than those depicted and/or described.

Claims

CLAIMS:

1. A platform unit (100) for a 3D-printing apparatus, comprising

a platform (110) upon which the 3D-printing apparatus is arranged to deposit a printing material in order to create at least one object, and

at least one frequency actuator (120, 121, 122) coupled to the platform (110) and configured to excite at least one natural frequency of the platform (110),

wherein the platform unit (100) further comprises a frequency measuring element coupled to the platform (110), the frequency measuring element being configured to measure at least one natural frequency of the platform (110).

2. The platform unit according to claim 1, wherein said platform is configured to have at least one natural frequency which is higher than at least one natural frequency of the at least one object created by the 3D-printing apparatus.

3. The platform unit according to claim 1 or 2, wherein said platform is arranged in a horizontal plane, and at least one of said at least one frequency actuator is configured to excite at least one natural frequency of said platform in said horizontal plane.

4. The platform unit according to any one of the preceding claims, wherein at least one of said at least one frequency actuator is configured to excite at least one natural frequency of said platform along at least one of a first axis (x), a second axis (y), and a third axis (z), wherein the first, second and third axes are perpendicular to each other.

5. The platform unit according to claim 4, comprising at least one first frequency actuator being configured to excite at least one natural frequency of said platform along a first axis, and at least one second frequency actuator being configured to excite at least one natural frequency of said platform along a second axis, wherein

the at least one natural frequency along said first axis and the at least one natural frequency along said second axis is the same, and wherein the phase shift between the at least one natural frequency along said first axis and the at least one natural frequency along said second axis is zero.

6. The platform unit according to claim 4, comprising at least one first frequency actuator being configured to excite at least one natural frequency of said platform along a first axis, and at least one second frequency actuator being configured to excite at least one natural frequency of said platform along a second axis, wherein at least one of the conditions of

the at least one natural frequency along said first axis and the at least one natural frequency along said second axis being different, and

the phase shift between the at least one natural frequency along said first axis and the at least one natural frequency along said second axis is non-zero,

is fulfilled.

7. The platform unit according to any one of the preceding claims, wherein at least one of said at least one frequency actuator is connected to at least one portion of at least one edge (114) of said platform.

8. The platform unit according to any one of the preceding claims, wherein at least one of said at least one frequency actuator is connected to at least one portion of an underside of said platform.

9. The platform unit according to any one of the preceding claims, wherein at least one of said at least one frequency actuator is configured to excite at least one natural frequency of said platform along an axis passing through the shear center of said platform.

10. The platform unit according to any one of the preceding claims, wherein at least one of said at least one frequency actuator is configured to excite at least one natural frequency of said platform along an axis which does not pass through the shear center of said platform.

11. The platform unit according to any one of the preceding claims, wherein at least one of said at least one frequency actuator comprises at least one piezoelectric element.

12. The platform unit according to any one of the preceding claims, wherein said platform comprises at least one material of a group comprising glass, ceramics and metals.

13. A 3D-printing apparatus (200), comprising a platform unit according to any one of the preceding claims.