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Title:
PRINT HEAD FOR 3D PRINTERS
Document Type and Number:
WIPO Patent Application WO/2017/090032
Kind Code:
A1
Abstract:
A print head (110, 1100) for use in a 3D printing system, comprising one or more nozzles (140, 1110, 1310, 1400, 1500, 1600, 1700), wherein said print head has an elongate cross-sectional extrusion shape having first and second pairs of opposing sides, wherein the length of the sides of one of said pairs is greater than the length of the sides of the other pair. Also a 3D printing system comprising a print head as defined above.

Inventors:
GILBOA PINHAS (IL)
Application Number:
PCT/IL2016/051250
Publication Date:
June 01, 2017
Filing Date:
November 22, 2016
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
GILBOA PINHAS (IL)
International Classes:
B29C67/00; B33Y30/00; B33Y40/00
Domestic Patent References:
WO2013064826A12013-05-10
WO2016049640A12016-03-31
Foreign References:
JPH02130132A1990-05-18
US6578596B12003-06-17
US4094492A1978-06-13
US20140048969A12014-02-20
Attorney, Agent or Firm:
RUTMAN, Avraham (P.O. Box 1417, 00 Meitar, IL)
Download PDF:
Claims:
CLAIMS:

1. A print head for use in a 3D printing system, comprising one or more nozzles, wherein said print head is characterized by a cross-sectional extrusion shape having first and second pairs of opposing sides, wherein the length of the sides of one of said pairs is greater than the length of the sides of the other pair.

2. The print head according to claim 1, wherein the ratio between the length of the long sides and the length of the short sides of the cross-sectional extrusion shape is 2: 1 or greater.

3. The print head according to claim 2, wherein the ratio between the length of the long sides and the length of the short sides of the cross-sectional extrusion shape is 3: 1 or greater.

4. The print head according to claim 1, comprising a single rectangular, slit-shaped or elongated nozzle.

5. The print head according to claim 4, wherein the ratio between the length of the long sides and the length of the short sides of the nozzle is 2:1 or greater.

6. The print head according to claim 4, wherein the ratio between the length of the long sides and the length of the short sides of the nozzle is 3:1 or greater.

7. The print head according to claim 1, comprising a series of two or more individual circular nozzle apertures.

8. The print head according to clam 7, comprising a series of three or more nozzle apertures arranged along in a straight line.

9. The print head according to claim 1, comprising a distal portion fitted with a single small diameter circular nozzle aperture, a proximal portion, and a flexible joint connecting said portions, such that said circular nozzle aperture is configured to be moved in a back-and- forth manner along an imaginary straight line, thereby causing said print head to have a cross- sectional extrusion shape as defined in claim 1.

10. The print head according to any one of the previous claims, configured to be rotatable, such that the angular position of said print head in relation to the x and y coordinates of the object being printed.

11. A 3D printing system comprising a print head according to any one of the previous claims.

12. The 3D printing system according to claim 11 , further comprising an actuator for causing rotation of the print head.

13. The 3D printing system according to claim 11, wherein the print head comprises a distal portion fitted with a single small diameter circular nozzle aperture, a proximal portion, a flexible joint connecting said portions, such that said circular nozzle aperture is configured to be moved in an oscillatory manner along an imaginary straight line, and one or more actuators for causing said oscillatory motion of said distal portion.

14. The 3D printing system according to claim 13, comprising two orthogonally-arranged actuators for causing the oscillatory motion of the distal portion of the print head.

15. The 3D printing system according to claim 14, wherein the actuator is selected from the group consisting of an electromechanical actuator, electric actuator, electromagnetic actuator, electrohydraulic actuator and electroacoustic actuator.

Description:
Print head for 3D printers

Field of the invention

The present invention relates to a novel print head for three-dimensional (3D) printers which is suitable for use in high speed, high resolution 3D printing.

Background of the invention

Additive manufacturing, known also as 3D printing, is a technology for producing volumetric objects. In its original form, it has an extruder, to inject thin wire of molten polymer - usually having a diameter of 0.3-0.4mm - and a moving bed. The manufacturing process is implemented stepwise, layer by layer. Each layer is typically 0.2mm thick. In each layer, the head and bed are moved to lay a molten strip of material within the boundaries of the object being constructed.

The process may involve three different types of building structure. The first one is known as 'solid layer', in which strips of material are laid side by side, covering the entire area inside the boundaries. These are the outer surfaces at the bottom and at the top of the built object. Usually, outer surfaces are built from three consecutive layers to achieve good coverage and the required thickness. The second type of building structure is known as Outer perimeter', this is the outer surface on the side of the object. To achieve a smooth surface, it is made in multiple (usually three) continues adjacent paths. The third type of building structure is a crisscross of thin lines known as 'infill', which fills part of the volume inside the built object. After completion, it is not seen from the outside. It serves two purposes: one is to strengthen the body; and the other, and more important, is to give support to the upper solid layer while printed. When layers are accumulated, the 'infill' acts as a grid structure of vertical honeycomb tunnels. The additive manufacturing process is, by its nature, a very slow process. "Printing" the strips of material require physically moving the head and the printing bed, and that, because of the mass involved, essentially limits the extrusion speed. Since layers are produced by laying down thin strips of material side by side, one could consider hastening the process by using thicker strips. Indeed, using an extruder having a bigger orifice does reduce the building time in direct proportion to the orifice diameter. However, increasing the orifice size is also associated with a serious disadvantage, namely reducing the resolution of the printing process, and thus the ability to achieve sharp corners in the object being constructed.

A key purpose of the invention described herein, is to shorten the time required for printing 3D objects, without reducing the resolution, in comparison with the resolution achieved by prior art printers.

Summary of the invention

The present invention is primarily directed to a print head for use in a 3D printer (also commonly referred to in the art as an "additive printer") wherein said print head comprises one or more nozzles, and wherein said print head is configured such that the extruded material exiting therefrom has a cross-sectional shape that is not circular. Preferably, the cross-section of the extruded material is generally rectangular. The cross-sectional geometry of the extruded material exiting the print head is sometimes referred to herein as the "extrusion profile", for the sake of brevity.

The term "print head" (also commonly referred to in the art as a "nozzle head" or "printing head") refers to the element or module in a 3D printer comprising the nozzles or exits, through which the material used to construct the product (also referred to herein as a "model" or "object) is extruded. The term "generally rectangular", as used herein to define the cross-sectional geometry of the extruded material, refers to a cross-sectional shape which may be characterized by having first and second pairs of opposing sides, wherein the length of the sides of one of said pairs is greater than the length of the sides of the other pair. It is to be noted that angle between each of the longer sides and its adjacent shorter side (i.e. the corners of the cross-section profile) need not be exactly 90 degrees, and that in some cases, said corners may be slightly rounded (i.e. arcuate). However, as will be seen from the detailed description hereinbelow, print heads of the present invention having extrusion cross-sectional profiles with rounded corners of this type may be used for the rapid production of objects characterized by sharp corners, such as gear wheels, and the like. The novel cross-sectional geometry of the extruded material exiting the print head of the present invention has been found by the present inventor to significantly reduce the time needed to print a 3D object without adversely affecting the resolution of said printed object, when compared with the print time and resolution achieved using print heads having standard sized circular nozzles. Thus, the print head of the present invention may advantageously be used for the commercial production of 3D objects having complex shapes such as gear wheels and objects having rounded corners. The use of the print head of the present invention in the high-speed manufacture of such objects will be described in more detail hereinbelow, in conjunction with the accompanying drawings. Thus, in a first aspect, the present invention is directed to a print head characterized by non- circular extrusion profile.

In one preferred embodiment, the shape of said no-circular extrusion profile is generally rectangular (as defined hereinabove).

In one particularly preferred embodiment, the ratio between the length of the long sides and the length of the short sides of the generally rectangular extrusion profile is 2:1 or greater. In another preferred embodiment, this ratio is equal to or larger than 3: 1.

In one embodiment, the print head of the present invention may comprise a single elongated, rectangular or slit-shaped nozzle, through which the extruded material of generally rectangular profile may exit said print head. In one particularly preferred embodiment, the ratio between the length of the long sides and the length of the short sides of the generally rectangular nozzle is 2: 1 or greater. In another preferred embodiment, this ratio is equal to or larger than 3: 1.

In another embodiment, the print head of the present invention may comprise a series of 2 or more individual nozzle apertures each having a circular, elliptical, oval or other cross- sectional shape. In one preferred embodiment, the print head comprises a series of 3 or more such nozzle apertures, wherein said apertures are arranged along the length of an imaginary straight line, and wherein the spacing between each adjacent nozzle is such that the material extruded from each of said individual nozzles combines to form a single extrusion profile of generally elongated outline. It may be appreciated that one key difference between the print head fitted with a rectangular nozzle and the print head fitted with a plurality of circular (or other shaped) nozzle apertures is that in the former case, the shape and size of the extrusion profile is determined by a single nozzle aperture, while in the latter case, the extrusion profile is created as a combination of the individual output of each of the individual apertures that are arranged in a linear series.

The second of the above-disclosed nozzle arrangements (i.e. the linear series of small circular nozzle apertures) is associated with some specific advantages. Firstly, the use of a plurality of apertures provides the possibility of selectively using either all of said apertures or only some of them. In this way, the overall length of the generally rectangular extrusion profile may be chosen according to the needs of any particular manufacturing protocol. Several different mechanisms may be used to control the number of nozzle apertures being used at any given time. All of these various mechanisms fall within the scope of the present invention; several examples thereof are provided hereinbelow. Secondly, in many instances it may be easier and less expensive to manufacture print heads with this nozzle arrangement than to manufacture print heads containing a single elongated nozzle.

In another preferred embodiment, the rectangular (or other elongate shaped extrusion profile) is achieved by means of having the print head comprise a single small diameter circular nozzle aperture, as well as means for swinging or vibrating said nozzle, such that it is caused to swing in a back-and-forth oscillatory manner along a line perpendicular to the build direction. In this way, a small circular aperture maybe used to create a rectangular extrusion profile. In one preferred implementation of this embodiment, the print head comprises a distal portion containing the nozzle aperture and a proximal portion, said portions being mutually connected by a flexible joint, such that said distal portion is adapted for moving in a back-and-forth manner along an imaginary straight line. In this way, a small diameter circular nozzle may be used to create an elongate extrusion profile.

In embodiments of the type of print head described in the previous paragraph, the 3D printing system in which said print head is incorporated further comprise one or more actuators for causing the swinging motion of the distal portion said print head. In one embodiment, the actuator is an electromechanical activator. In another embodiment, the actuator is an electromagnetic actuator. Other types of actuator are listed hereinbelow. In many of the print head embodiments disclosed hereinabove, it is advantageous to be able to rotate said print head, such that the angular disposition of the long and short axes of the rectangular extrusion profile in relation to the x and y planes or coordinates (i.e. the length and width) of the object being produced may be changed. This may be done, for example, in order to increase the height or depth of the extruded material being deposited in the object, by means of rotating the print head by, for example, 90 degrees. Also, rotation is used to alter the relative direction of movement between the print head and the moving base of the 3D printer that contains the object being built, such that there is dynamic vectorial control over the build direct - as opposed to a pre-determined raster movement. Thus, in some preferred embodiments, the print head of the present invention is configured to be rotated.

In another aspect, the present invention is directed to a 3D printing system comprising a print head according to any of the embodiments disclosed hereinabove.

In embodiments in which the print head is configured to be rotated, the 3D printing system further comprises an actuator for causing rotation of said print head. In one implementation, said actuator is an electromechanical actuator. Other types of actuator may also be used.

In embodiments in which the print head comprises a flexible joint between its distal and proximal portions, in order to facilitate a swinging or oscillatory motion of said distal portion, the 3D printing system further comprises one or more actuators for causing said swinging motion. Said actuator is preferably selected from the group consisting of an electromechanical actuator, electric actuator, electromagnetic actuator, electrohydraulic actuator and electroacoustic actuator.

In one particularly preferred implementation of this aspect of the invention, the 3D printing system comprises two orthogonally-arranged actuators for causing the oscillatory motion of the distal portion of the print head.

Brief description of the drawings

Figure 1 is a general perspective view of a 3D additive printer of the prior-art. Figures 2a and 2b illustrate prior art methods used to build solid surfaces. Figure 3 illustrates a prior-art method for manufacturing a 3D object.

Figure 4 depicts the orientation definition of the extrusion cross-section.

Figure 5 depicts the process of building an outer perimeter of an object having a sharp corner.

Figure 6 illustrates the construction of an arcuate outer perimeter of an object. Figure 7 provides an illustrative example of a gear wheel being created using the print head of the present invention.

Figure 8 illustrates the process of building a solid layer.

Figure 9 depicts the manner in which a thicker layer may be built.

Figures 10a, 10b and 10c illustrates various types of extrusion orifice that are suitable for use in the present invention.

Figure 11 provides a perspective view of a printing head having a rotation mechanism.

Figure 12 provides a vertical section of the printing head illustrated in figure 11.

Figures 13a and 13b provides a general depiction of a printing head fitted with a vibrating nozzle. Figure 14 illustrates a printing nozzle having an electro mechanical actuating mechanism.

Figure 15 depicts a printing nozzle having an electromagnetic actuating mechanism.

Figures 16a and 16b illustrates a first example of an implementation aimed at reducing the extrusion cross-section in the context of the first embodiment of the present invention.

Figure 17 illustrates a second example of an implementation used to reduce the extrusion cross-section in the context of the first embodiment of the present invention.

Detailed description of the invention

Figure 1 shows the general components of an additive manufacturing printer. Frame 100 holds extrusion head 110, said head being conformed to move horizontally along slider 111. A bed 120, on which the product (also referred to herein as the "model") is built, moves horizontally on slider 122. Slider 122 is oriented in a direction perpendicular to that of slider 111. The bed is also able to move vertically along slider 123. The combined movements of the extrusion head and the bed, allows the printing head to be placed anywhere in the 3D volume above the bed. Spool 130 contains thermoplastic filament 131 and feeds it to the extrusion head through a feed mechanism embedded in the extrusion head itself (not shown). The extrusion head heats the filament beyond its melting temperature. Nozzle 140, has a circular aperture (made by drilling), through which the molten material is extruded, selectively adding it to the built model. The movements of the bed and the head, the rate of material injection and the temperature of the system components are all controlled by a micro-computer located in base 150. The model is built by layers. Each layer is a cross- section of the model cut parallel to the bed at increments of height, each filled with vectors of molten strips of polymer material, along the cross-section, only at the solid parts of the model. In common practice, the width of each of the strips is around 0.35mm and height of each layer is 0.2mm.

The data for the printed object is usually coded in STL (Stereo Lithography) format, or in the newer format, AMF (Additive Manufacturing File Format). The software for preparing the printing, called Sheer, reads the STL data and slices the object into separate layers. For each layer, the solid parts of the cross-section of the object are transformed into vectors grouped in separate types of structure: outer perimeter vectors, the inner infill vectors, supporting vectors and so on. If the Sheer is running on a different machine than the printer, the sliced data needs to be sent to the printer, and this is done using a common standard format called G-code.

Figure 2 and figure 3 describe the prior-art method for 3D printing of an object. Figures 2a, 2b together with figure 1 describe the process of building a solid layer. While the bed 120 and head 110 move the nozzle 140 along the extrusion vector, the building material is injected, laying adjacent strips of building material one after the other, filling the entire surface inside the layer's perimeter. The direction of the extruded strips in one layer - strips 210 and 220 of figure 2a - are perpendicular to that of the following layer (strips 230 and 240 in figure 2b). Usually, at least two but preferably more layers, are required for achieving a sufficiently strong surface. Figure 3 shows an example of the prior-art method for building a non-solid layer 300, of an object. The outer perimeter of the object is printed by continuous adjacent strips 310, 320 and 330. Usually the inner volume is not left empty, but filled with an infill supporting structure, as shown by lines 340 and 350, when accumulated vertically along the build layers, it forms hollow square tubes. Other supporting shapes, such as honeycomb, for example, may also be used.

After each layer is finished, the bed is lowered incrementally and the next layer is printed. The increments by which the bed is lowered defines the vertical resolution. Usually the build is finished with three solid layers at the top of the model.

The invention described herein, aims to combine the advantage of using large diameter strips for hastening the building process, while still taking the advantage of using thin strips in achieving high resolution building. Now referring to Figure 4, which describes the orientation definition with respect to the first preferred embodiment of the invention that aims to maximize the printing speed. The 'x' axis 406 and the 'y' axis 408 are orthogonal vectors oriented parallel to the build planes. Material is added perpendicularly to the built plane. At each moment in time, vector 'x' is pointing in the direction of the advancing head, as it is adding material to strip 410. At the point of the extrusion, the shape of the cross section of the flow of material is a narrow rectangle 400, where its length dimension 402 is directed along the 'x' axis, and its width dimension 404 is directed along the 'y' axis. If the length of narrow rectangle 400 (i.e. the rectangular cross section of the flow material) is greater than its width (for example: 1mm and 0.3mm respectively), the print time is shortened proportionately. In straight lines, the result is identical to that achieved using a single circular aperture of extremely large diameter (1mm in the above example). However, the benefit of using an extrusion cross section having a narrow shape perpendicular to the advancing head (shown as 404 in figure 4) is readily understood from the following examples.

Figure 5 illustrates the manner in which an outer perimeter sharp corner is built according to the present invention. Material is added through a moving slit, moves along strip 500, entering the corner at location 510 in a first direction 501, and exiting the corner at location 520 in a second direction 502. It is essential that the corner will be built at a sharp angle 504, which is the difference between direction 501 and direction 502. If the extrusion cross section would simply be rotated between location 510 and location 520, it would result in a radial or arcuate corner, as shown by dashed line 530. To maintain a sharp corner, it is necessary to move the outer edge of the extrusion cross section along the outer perimeter of the body, starting from point 511 at cross section location 510, and proceeding to point 541 at cross section mid corner location 540. Then, it is moved towards point 521 at cross section location 520 at a 90-degree angle. Thus, during the course of this movement, the orientation of the extrusion cross section changes progressively from direction 501 to direction 502, where at mid-location 540 the orientation is 503. Of course, other variants of this approach may also be used in order to orient the narrower side of the extrusion cross section to achieve high resolution sharp changes in the contour of the outer perimeter, and all such variants are within the scope of the present invention as claimed.,

Figure 6, describes the way in which the outer perimeter of an arc may be constructed using the print head of the present invention. Additive manufacturing uses straight vectors to build objects, and thus an arc is built up from a series of small straight lines. In the case of a simple arc with a known center point, the extrusion cross section is oriented in the direction of the normal to the arc, that is, along the local direction of the radius. However, the STL standard does not usually provide that information. Therefore, for each of the joint lines of the arc, the local radius direction may be determined by the direction of the vectors of the lines as follows: normal 632 of line 630 is determined; normal 642 of line 640 is determined; the local direction 631 of the radius is the sum of vectors 632 and 642. in the same fashion, the local radii directions 611 and 621 between lines 610, 620 and 630 are determined. During the building of the arc, the extrusion cross section is moving along lines 610, 620, 630 to 640, and changes its direction consecutively from direction 611 to 621 to 631.

The method described above is suitable for manufacturing various different object shapes, for example, the manufacture of a toothed gear as shown in Figure 7. The outer perimeter of a gear segment is defined by a series of lines shown in this example as 710, 720 and 730, oriented with a sharp angle between each pair of adjacent lines. The lines are arranged around a common centre 700. At each cross point, the radius direction is determined, as in the previous example, by the vectorial sum of the normal of each of the joint lines, direction 711 from lines 710 and 720; direction 721 from lines 720 and 730 and so on. During the building of the gear, the print head is moved along lines 710, 720, 730 and continuously change the orientation of the extrusion cross section from direction 711, to 721 and so forth.

Solid layers are built according to the same principles, as shown in Figure 8. A Solid layer is made by extruding adjacent strips of material. To achieve faster production speed, the length of the extrusion cross section needs to be oriented perpendicularly to the head movement direction, for instance as shown at point 810. At the ends of the extruding strip, the orientation of the extrusion cross section needs to be aligned with the direction of the boundary, as in point 820. The means for determining and changing the cross-sectional orientation is the same as used in the methods described above.

When thin extruded strips are required, the orientation of the extrusion cross section, as described in Figure 4, can be rotated by 90 degrees, so that the width dimension (the narrow side) of the extrusion cross section is directed towards axis 'x', the direction in which material is added. The rate of addition should also be reduced.

Increase in the production speed can also be achieved by increasing the layer height. In the prior-art printers, in which circular aperture nozzles are used, layer thickness is limited by the diameter of the extruder orifice. For example, if the diameter of the orifice is 0.3 mm, then the maximum achievable height is 0.3 mm as well.

In building the infill criss-cross thin lines, rotating the extrusion cross section at a 90-degree angle can help to achieve thicker layers as shown in figure 9. The extrusion cross section 900 is oriented so that its length 920 (the large size of the extrusion cross-section) is parallel to the direction of movement 910. The maximum building height 930 is equal to the length of the extrusion cross section 900. If the dimensions of the cross section are 0.3mm by 1mm, then the maximum achievable height is 1mm, which is more than 3 times thicker than obtainable with prior- art systems and the infill printing time may be shortened by the same factor.

There are several ways in which the invention may be implemented. In the first implementation, described in figure 10a, instead of using an orifice of a circular aperture for the extrusion nozzles as in the prior-art, an orifice 1012, in the shape of rectangular slit, is placed at the center of nozzle 1010. The length of the slit is at least twice, or more preferably three times, bigger than its width. Characteristic size values are length of 1mm, and width of 0.3mm. Producing a very thin slit with high accuracy and quality is an expensive process. The nozzle shown in figure 10b, however, is easier to produce, while achieving similar extrusion results. Three circular apertures, 1012, 1013 and 1014 are drilled along a straight line at the center of nozzle 1020. For the simplification of the mathematical calculations used to calculate the location of the orifices along the perimeter, it may be of some benefit to place the extrusion orifice off-center, as shown in figure 10c. Aperture 1032 is placed at the center of the nozzle 1030, and the two more apertures, 1034 and 1036 placed along a straight line, non-symmetrically off the center of the nozzle. In addition, the nozzle is combined with a mechanism that rotates it around its center.

Figure 11 provides a perspective view of a printing head of the present invention comprising a rotation mechanism, to rotate the nozzle, as required by this implementation of the invention. A printing head 1100 is comprised of filament driver mechanism 1140, heating unit 1120, nozzle 1110, rotating gear 1132 and 1134 and gear actuator 1130. The heating unit melts the polymer squeezed into it by the filament driver. It is heated by heater 1124, and temperature controlled by thermistor 1122. The temperature required to melt ABS, for example, is 240 degrees Celsius. The polymer is forced through the nozzle, as shown in figures lOa-lOc. The direction of the nozzle is controlled by actuator 1130.

A vertical section view of the printing head of figure 11 is shown in figure 12. Tubule 1114, which passes through the heating unit 1120, feeds melted polymer to the extrusion nozzle. Bearing 1112 attaches the nozzle to the heater body, allowing it to rotate with little friction, while maintaining efficient heat transfer between the heating unit and the nozzle, heat isolation between the head and the surroundings, and good sealing. In order to meet these requirements a combination of materials such as stainless steel and bronze for low friction and heat transfer, and PEEK polymer for high heat resistance and isolation are used. Printing head 1100 is intended to replace printing head 110 of the prior art printer, described in figure 1. It may be required at some stages of the printing process, to use a smaller extrusion cross- section. Solutions to narrow orifice size can be found in the prior art and adapted for use in the context of the present invention. Thus, US 4,094,492 to Beeman et al. teaches how to implement a variable orifice using an iris shutter. A different method is shown in US 2014/0048969 to Swanson et. al., in which a nozzle having circumference grooves around the extrusion orifice is used. By means of forcing extra material through the orifice, the accumulated material trapped between the nozzle and the built body, is forced to spread out, resulting with a larger extruding spot. The function of the grooves is to control the size of the spot by limit the expanding material up to the boundary of the groove. However, this method cannot be used when the built body under the nozzle, is not fully leveled, as happen when, for instance, a built perimeter line is spread in or out in relative the perimeter line bellow, or when a solid layer is built on top of an infill layer, which is partially hollow. The use of separate orifices in making the nozzle, according to the invention described herein, allows control of the size of the extrusion strips more efficiently than the methods of the prior art. Figures 16a and 16b show an exemplary mechanism for reducing the orifice size. A nozzle 1600 has three orifices, a center orifice 1622, and two adjacent orifices, 1620 and 1624. The orifices are drilled such that they are continuous with an internal cavity 1602, from which the extruding material is fed to said orifices. Cavity 1602 receives the extruding material through tubule 1610. The tubule may move along cavity 1602. When the tubule is withdrawn from cavity end 1614, all orifices are open, as shown in figure 16a, and the material may flow out from all three orifices. When tubule 1610 is pushed against cavity end 1614, as shown in figure 16b, orifices 1620 and 1624 are blocked, leaving only orifice 1622 free to be fed material to the extrusion process, hence, narrowing extrusion cross-section.

A different approach is shown in figure 17. In this approach, flow resistance is used to control the width of the extruded strip. Nozzle 1700 has an internal cavity 1740, through which material is fed to three orifices, a center orifice 1710, and two peripheral orifices 1720 and 1730. The center orifice 1710 receives material through large cavity 1750 and short thin tunnel 1752. The two adjacent orifices 1720 and 1730 receive material through long, thin tunnels 1760 and 1762, respectively. Since the length of tunnel 1752 is significantly shorter than tunnels 1760 and 1762, the flow resistance of the material brought to orifice 1710 is significantly smaller than that brought to orifices 1720 and 1730. Consequently, when the material is applied at low pressure, material is extruded mainly from the center orifice 1710. When the pressure is increased, the amount of material that is extruded through 1760 and 1762 become more significant, thereby increasing the width of the extruded strip. Other methods to force different resistance along the channels lead material to the orifices, such as using tunnels of different diameters, may also be used to implement the present invention. An entirely different approach for obtaining a rectangular extrusion cross section is described in figures 13a and 13b. According to this approach, a nozzle 1310, having a small aperture (for example, diameter of 0.3mm), is connected to the printing head by a flexible joint 1311, such that it swings at a high frequency harmonic vibration. The direction of the vibrating swing is perpendicular to the movement of the head while in the process of building a strip of material. Nozzle 1310 replaces nozzle 140 of the prior art printer described in figure 1. As shown in Figure 13b the amplitude of the swing movement of nozzle 1310 and its direction, are synchronized with the movement of the extrusion head in relation to the built object. The nozzle end may swing in any direction, and may be vibrational at two orthogonal axes, axis 1320 and axis 1330. Since the axes are orthogonal, the frequencies, phase and amplitudes are independent of each other. Hence, it is possible to build the swing of the nozzle at any desirable direction, as a superposition of two independent signals, one along axis 1320 and the other along 1330.

Figure 13a describes how a large strip, 1300 in this example, may be built by a vibrating nozzle 1310. The strip is built by swinging the nozzle at high frequency perpendicularly to the strip build direction. For instance, between 1301 and 1302 at the building direction 1303, and between 1305 and 1306 at the building direction 1307. When the building direction changes, the vibration directions also need to be changed consecutively as well, as shown at location 1308.

Locally, the extrusion width is in the magnitude of the diameter of the extrusion aperture- in one example about 0.3mm. During the constant movement of the extrusion head, it takes one full swing - one cycle of back and forth movements- to cover 0.9mm in length, if the two movements are synchronized. Thus, at least 1/0.9 cycles are required in order to cover 1mm strip length. A commonly-used printing speed is 4800 mm min, which is equal to 80mm/sec.

Thus, in order to cover 1mm length of the built strip, it is needed to swing the nozzle at least at 1/0.9 (cycles/mm) multiplied by 80 (mm/sec). Hence, good coverage may be achieved at vibrations equal to 89 Hz. However, in practice, for the above printing speed, it has been found that it is better to vibrate the nozzle at frequency of 200 Hz or more. Generally, the amplitude of the swing motion of the nozzle is in the order of 1 mm.

In this implementation, it is necessary to use a mechanism that produces vibration with minimal addition of moving mass. It should be emphasized that robotic mechanisms, such as described in WO 2016/049640 to Batchelder, for example, is highly ineffective in the implementation of this invention. Moving and stopping the nozzle at high speed and acceleration, requires actuators which can develop high forces. Increasing the actuation force necessarily leads to increasing the mass of the actuator, further increasing the power of the actuator, which in turn leads to increasing the actuator size and mass, and so forth. Instead, it is much preferable to use a mechanical harmonic oscillator, with the nozzle acting as its moving mass. When vibrating at self -resonance frequency, the power required to move the nozzle is only that which is required to compensate for energy lost due to friction and due to adhesion of the molten material. Hence, a very small and effective mechanism may be constructed.

Various harmonic oscillation mechanisms may be used to actuate nozzle vibrations. Figures 14 and 15 are examples of actuators suitable for use in the context of the present invention. In the embodiment shown in figure 14, vibration is forced by linear electromechanical actuators. Nozzle 1400 is connected to the printing head (not shown) via a flexible joint 1402, allowing the tip of the nozzle to swing freely at any horizontal direction. A spring, embedded in the flexible joint 1402 (not shown), forces nozzle 1400 to a "zero" position. Cam 1432 is joined to actuator 1430, and applies energy to the tip, forcing it to vibrate in direction 1410. Cam 1442 is connected to actuator 1440, forcing vibration of the tip in direction 1420, orthogonally to direction 1410. The actuators fed by sinusoidal signals, which cause them to vibrate in alternating movements. The sum of movements of cam 1432 in direction 1410, and cam 1442 in direction of 1420, makes the tip move at the vectorial sum of said movements. Said signals should be synchronized with the movements of tip 1400 to achieve harmonic vibration. Controlling, the frequency, phase and amplitude of the signals fed to the actuators, during the process of three-dimensional model building, allows the varying of the directions, and, to a certain limit, also the frequencies and amplitudes of the nozzle tip, according the required direction and cover.

One drawback of the implementation described immediately hereinabove and illustrated in figure 14 is that the mass of cams 1432 and 1442, affect or influence the movements of the mass of tip 1400.

A further (and in some ways, preferable solution) is illustrated in figure 15. This implementation uses a similar arrangement as described in figure 14, however, without adding extra mass to that of the nozzle. Thus, electromagnetic actuators 1520 and 1530 are arranged perpendicularly to each other and to the shaft of nozzle 1500. Nozzle 1500 is free to swing around a flexible joint, connecting it to the printing head (not shown). Springs embedded in the flexible joint force nozzle 1500 to a "zero" position. There are no direct contacts between the actuators and the nozzle. Instead, the tip of the nozzle 1510 is comprised of magnetized metal, that is drawn and repelled by the magnetic forces. As in the case of the embodiment of figure 14, by feeding alternating currents of the proper frequency and phase to the electro-magnets, the nozzle will vibrate at its resonant frequency. When no signal is fed to the electromagnets, tip 1500 is held at its center of movement, allowing the addition of a thin strip of material to the model. Using the proper signals, the direction and amplitude of the nozzle's vibration swings can be controlled and used to mold strips of material, according to the methods described hereinabove. The material exerted from nozzle 1500 is in the form of a continuous molten wire. The extrusion rate is calculated to fill the width of the built strip without gaps but also without spillover.

The term 'flexible joint' used above, refers to any joint that allows the nozzle swing above the building plan, including, but not limited to: spring joint, cardan joint or other arrangement of multiple rotatable joint.

The vibrating nozzle can also be combined with a rotation mechanism, where, instead of using a slit-like orifice, a vibrating nozzle is used to achieve the same effect.

There are additional applicable methods, technologies and techniques that may be used for laying down wider strips of material during the movement of the extrusion head in the building of a three-dimensional model. These may be implemented either by extending the extrusion cross section or by fast periodical motion of the point of material adding. The periodical motion of the application point can be actuated by the use of one or more of the following forces: electrical, magnetic, electro-magnetic, acoustical, pneumatic, thermic and mechanical. Said forces can be applied to either move or rotate a nozzle, or to move, pull, push or rotate directly the stream of the added material. The added material can be hot or at room temperature. The curing of the material can be achieved by drawing energy from the added material or by adding energy to it.

The signals fed to actuate the actuators in the examples described above are: the signals fed to actuators 1130 and 1150 in figure 11; signals fed to actuators 1430 and 1440 in figure 14; and the electrical currents activate electro-magnets 1520 and 1530 of figure 15, fed from drivers controlled by the same computer which controls the mechanism of the printer described in figure 1. Any skilled artisan in this field, will be capable of designing and building drivers and actuators, according to the requirements described in this patent.

The data required for proper functioning of the devices described herein is determined by software that is either part of the Slicer, or by an additional separate package of software. Some additions are needed to the G-code, to allow the data to be sent to the printer. The operating software that run on the micro-controller that operate the printer need to be rewritten in purpose to control the orientation and size of the extrusion cross-section, as will readily be appreciated by any skilled artisan in this field.

The specific embodiments disclosed and described hereinabove are given by way of example only. Other embodiments included within the scope of the present invention include all those implementations in which the print head produces a cross-sectional extrusion shape that is generally elongate or rectangular, and whose direction in relation to the direction in which the strips are being laid down in the object under construction may be controlled, thereby enabling increased print speed, without any loss of resolution.