System and methods for three-dimensional printing

Abstract

A fast and economical system and methods directed to low-fidelity fabrication of three-dimensional (3D) objects using 3D printing. The invention facilitates rapid prototyping by providing a wireframe structure in the form of the underlying design structure of a 3D model, which may be useful for a variety of reasons including to provide a prototype preview that may be used for design validation of a 3D model.

Claims

1. A method for fabricating a wireframe structure of a 3D object on a surface comprising the steps of: providing a processor, the processor operatively connected to a controller and a print head; creating a wireframe mesh pattern of the 3D object; registering parameters of the print head, wherein the parameters include an angle of the print head defined from a horizontal axis and a diameter of the print head; calculating from the angle and the diameter a depth value defined along a vertical axis at which the print head is configured to deposit a material; defining a plane at the angle of the print head at which the print head is configured to deposit the material, the depth value and the plane defining an area for printing the wireframe structure on the surface; moving the print head along a path defined by both the wireframe mesh pattern and the parameters of the print head while extruding material; and solidifying the extruded material of a portion of the wireframe structure before continuing to extrude material of another portion of the wireframe structure of the 3D object.

2. The method according to claim 1, wherein the material is filament material.

3. The method according to claim 2, wherein the filament material is selected from the group consisting of: Acrylonitrile Butadiene Styrene (ABS), Polylactic Acid, Polylactide (PLA), and high-density polyethylene (HDPL).

4. The method according to claim 1, wherein the solidifying step further comprises the step of cooling the extruded material using an air flow from one or more air jets or built-in fans attached to the print head.

5. The method according to claim 4, wherein the solidifying step further comprises the step of pausing the print head for a period of time.

6. The method according to claim 1, wherein the moving step further comprises the step of repeatedly moving vertically the print head.

7. The method according to claim 1, wherein the wireframe mesh pattern is in a format selected from the group consisting of: a stereolithography (STL) format, a polygon file format, and a triangle format (PLY).

8. The method according to claim 1, wherein the wireframe mesh pattern is a zig-zag type pattern.

9. The method according to claim 1, wherein the method is performed up to a factor of 10 compared to traditional layer-by-layer printing.

10. The method according to claim 1, wherein the method is implemented by a 3D printer.

11. The method according to claim 10, wherein the 3D printer is one selected from the group consisting of: a stereolithography (SLA), a fused deposition modeling (FDM), a selective laser sintering (SLS), a selective laser melting (SLM), an electronic beam melting (EBM), a laminated object manufacturing (LOM), and a degree of freedom (DOF) printing device.

12. The method according to claim 10, wherein the 3D printer is one selected from the group consisting of: a delta design printer and a Cartesian-based printer.

13. The method according to claim 1, wherein the method is implemented on a device operatively connected to a 3D printer.

14. The method according to claim 1, wherein the method further comprises the step of fabricating a solid structure of the 3D object using layer-wise printing to form a hybrid structure incorporating both the wireframe structure and the solid structure.

15. The method according to claim 1, wherein the print head deposits the material as an overhang of up to 90.

16. The method according to claim 1, wherein the creating step further comprises the step of specifying each edge of the 3D object at which two mathematically continuous smooth surfaces meet.

17. The method according to claim 1, wherein the creating step further comprises the step of connecting constituent vertices of the 3D object using straight lines or curves.

18. The method according to claim 1, wherein the depth value of the print head is a maximum value to avoid collisions with extruded material defined by:
max depth=(/2)tan wherein is the diameter of the print head and is the angle of the print head.

19. The method according to claim 1, wherein the creating step further comprises the steps of: slicing the 3D object into segments, each segment defined by a first layer positioned from a second layer at a distance equal to the depth value; and defining the wireframe mesh pattern joining the first layer and the second layer, the wireframe mesh pattern including a support edge connected to a downward edge, the downward edge limited by the angle of the print head from the horizontal axis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The preferred embodiments of the invention will be described in conjunction with the appended drawings provided to illustrate and not to limit the invention, where like designations denote like elements, and in which:

(2) FIG. 1 illustrates an exemplary system that may be used to implement the invention.

(3) FIG. 2A illustrates a block diagram of a collision constraint according to the invention.

(4) FIG. 2B illustrates another block diagram of the collision constraint according to the invention.

(5) FIG. 3A illustrates a block diagram of a deformation constraint according to the invention.

(6) FIG. 3B illustrates another block diagram of the deformation constraint according to the invention.

(7) FIG. 4A illustrates a block diagram of a material transition constraint according to the invention.

(8) FIG. 4B illustrates another block diagram of the material transition constraint according to the invention.

(9) FIG. 5 illustrates a flow chart of a method according to one embodiment of the invention.

(10) FIG. 6 illustrates a flow chart of another method according to another embodiment of the invention.

(11) FIG. 7 illustrates a block diagram of a segment according to one embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(12) Unlike traditional 3D printers that stack filament material on filament material, the invention fabricates objects by alternating between (a) printing a contour or layer and (b) printing a mesh pattern on top of the contour.

(13) FIG. 1 illustrates an exemplary 3D printing device 100 according to the invention. 3D printing device 100 is capable of fabricating a 3D object and includes at least a controller 102, a processor 104, and a memory 106. The printing device 100 includes a print head 108 that extrudes filament material onto a support surface 75 such as a platform or plate. The device 100 uses digital data such as a CAD model.

(14) The invention advantageously can be implemented in a 3D printer, for example, as software stored in memory 106. The software may be in the form of a program configured with existing systems either before or after market. The software is processed by the processor 104 such that the controller 102 controls the device 100, i.e., moves the print head along the desired path and controls how much material is extruded at which points in order to fabricate a wireframe structure.

(15) The methods according to the invention can be implemented on any printing device based on the following parameters(1) diameter of the print head and (2) angle of the slanted portion of the print head. These parameters are used to determine the mesh pattern of the wireframe structure such that collisionsbetween filament material and/or filament material and the print headare prevented. The printer parameters may dictate the depth the print head can reach to extrude filament material without colliding with already printed material and the distance the print head can travel to extrude filament with a spacing that avoids collisions with already printed material.

(16) Specifically, the diameter of the print head limits the spacing between two vertical or support edges. As shown in FIG. 2A, two vertical edges need to be spaced at least half the diameter of the print head apart to avoid a collision between the print head and already printed material.

(17) In certain embodiment the angle of the slanted portion of the print head (along with the diameter ) may be used to determine the depth or how far the print head can reach while printing a wireframe structure without the print head colliding with that already printed:

(18) $\max \mathrm{depth}=\left(\frac{}{2}\right)$
tan . However, in certain other embodiments, the depth the print head can be increased beyond the max depth by using an extender element attachable to the print head. In either contemplated embodiment material cannot be extruded at a depth steeper than the slant of angle or the print head itself as shown in FIG. 2B, as steeper edges can cause the slanted tip of the print head to collide with either that already printed or with that currently being printed.

(19) FIG. 3A and FIG. 3B illustrate block diagrams of an edge deformation constraint according to the invention. Edge deformation must be considered resulting when filament material is not yet solidified during fabrication. In order to obtain the intended result in FIG. 3A, it can be seen that the filament material acting as a support edge must be cooled and solidified prior to fabricating any downward edges. This may be done by simply adding a temporal pause or delay at the end of each floating edge allowing filament material to cool and harden.

(20) In addition to compensating for edge deformation, material transition time must be considered. As shown in FIG. 4A and FIG. 4B, the invention anticipates deformation by extending the vertical movement of the print head before beginning the downward stroke to fabricate the downward edge.

(21) The quality of the system and methods of the invention is improved by not only reducing overall speed with which the print head moves, but also allowing filament material to solidify as it is being printed. In one embodiment, this may be achieved by using an air flow to cool the material. For example, one or more air jets controllable by a solenoid valve may be attached to the print head. The additional cooling causes the filament material to solidify faster after extrusion. It is also contemplated that the air flow can be reduced or turned off such as in circumstances in which filament material needs to stick to another part of the model. Alternatively, the invention may make use of a built-in fan or integrate an additional pause to wait for material to solidify before continuing on to print the next feature. It is contemplated that a more aggressive cooling process increases speed of fabrication.

(22) FIG. 5 illustrates a flow chart of a method 200 according to one embodiment of the invention. At step 210, a 3D model is received for processing. According to one embodiment the 3D model is in stereolithography (STL) format, but any format is contemplated such as polygon file format or a triangle format (PLY).

(23) The 3D model is converted to a vector representation at step 230. The vector representation may include one or more points, lines, cures, polygons, etc. The vector representation is used to determine the print order of the object at step 250 as more fully discussed in reference to FIG. 6. At step 270, the vector representation is translated into g-code of a 3D printer representation of the wireframe structure based on the order for printing segments of the vector representation.

(24) At step 290, the printer is instructed to execute the g-code to print the printer representation. At step 300, the wireframe structure is printed as strokes in 3D space. According to one exemplary embodiment, the invention creates segments by moving the print head up and down repeatedly. Specifically, the printing device extrudes filament material from the print head based on the order for printing segments to fabricate the wireframe structure. It should be noted that a larger opening in the extrusion nozzle print head leads to thicker and thus sturdier edges and thus to sturdier objects. On the flipside, thicker edges require more time to cool down, which slows down the printing process. As an example, in one embodiment a 0.7 mm extrusion nozzle provides both sturdy and fast to print results.

(25) FIG. 6 illustrates a flow chart of a method 250 for determining the print order of the object according to one embodiment of the invention. Parameters of the printing device are registered at step 251. The parameters include an angle of the print head defined from a horizontal axis and a diameter of the print head. These parameters dictate the constraints of the mesh pattern used in fabricating the wireframe structure of the 3D model in order to prevent collisions with filament material during printing. More specifically, the printer parameters and may dictate the depth the print head can reach to extrude filament material without colliding with already printed material and the distance the print head can travel to extrude filament material with spacing to avoid collisions with already printed material.

(26) In particular, the parameters are used to calculate a depth at step 253 defined along a vertical axis at which the print head deposits a material and at step 255 to define a plane at the angle of the print head at which the print head deposits the material. The depth and the plane define a portion of space viable for printing the wireframe structure without collisions. As mentioned above, the depth may be increased though use of an extender element attachable to the print head

(27) At step 257, the model is sliced into segments using the depth as the maximum thickness or height of the segment (see FIG. 7). As mentioned above, the depth cannot be steeper than the slant of angle or the print head itself.

(28) The locations of the segments are determined by (1) important features on the model geometry, and (2) the minimum and maximum height of the mesh pattern between two subsequent segments. In one embodiment the invention slices the 3D model into segments along a z-axis forming horizontal slices (width and length of the object's bounding box) at a specific height using a Boolean intersect operation. It is also contemplated the 3D model may be sliced into segments along an x-axis forming one or more vertical slices.

(29) According to a particular embodiment, for each segment the invention extracts the top layer by converting it to a high-resolution bitmap and then applying an algorithm, for example, OPENCV'S FINDCONTOUR. If there are multiple layers on one segment, the relationship to each other is known, i.e. whether they are located next to each other or contained in each other.

(30) At step 259, a mesh pattern is defined. Again, the mesh pattern is determined by the parameters of the print head of the printing device. For example, as described more fully in reference to FIG. 7, the vertical or support edges of an exemplary mesh pattern have a height equal to the depth the print head can reach (also equal to the maximum thickness or height of the segment). The downward edges of the exemplary mesh pattern are limited by the angle or slanted edge of the print head. The mesh pattern is positioned between two consecutive contours or layers.

(31) When generating the mesh pattern, the invention maximizes the object's physical stability by aligning all vertical lines across segments. Simply using the points from the segment below does not work, because subsequent segments might: (1) have a different length, which can lead to insufficient space between two subsequent points (print head collision), and (2) segments might have different heights, which can lead to invalid printing angles. Therefore, a mixed approach is used by first calculating the optimal even spacing of points for each layer and then calculating the minimum distance from a point on the bottom segment to the top segment. The average of both is used to promote good stability and a comparably homogeneous spacing. In the case where two vertical lines are still too close to each other, one is simply ignored. In addition, all geometrical modifications are implemented due to the mechanical properties of the filament material and print head such as removing the last diagonal edge of the mesh pattern from the list of edges to avoid print head collision. In other embodiments where a segment has a single contour and its subsequent segment has two contours (and vice versa), they are printed on top of each other without the intermediate mesh pattern. This particular approach may be used in instances to ensure that any mesh patter of each new segment has filament material printed underneath it.

(32) FIG. 7 illustrates a block diagram of a segment 300 according to one embodiment of the invention. The embodiment as shown in FIG. 7 is in the form of a zig-zag type pattern that is triangle based, however any suitable pattern is contemplated such as one that is not triangle-based (i.e. without a support edge, for example). As shown, each segment 300 includes a first layer or contour 310 positioned from a second layer or contour 320. The distance between the contours 310, 320 is equal to the

(33) $\mathrm{depth}-\left(\frac{}{2}\tan \right)$
or as determined by using an extender element attachable to the print head. The surface 315 between the layers 310, 320 is replaced with the mesh pattern 330. The mesh 330 joins the first layer 310 and the second layer 320 and includes a support edge 332 connected to a downward edge 334, the downward edge 334 limited by the angle of the print head from a horizontal axis shown by .

(34) As mentioned above, the invention translates the vector representation into a printer representation using g-code. Specifically, a list of edges including all contours and mesh patterns are exported for printing. The coordinates for the start point and end point of each edge are used to generate the movement commands for the print head and the length of the edge to determine how much extrusion is required. Additionally, g-code is generated to command any cooling mechanism, i.e., turn the fan on/off to properly cool the wireframe edges.

(35) As mentioned above, the invention may be used in combination with layer-wise printing to obtain a hybrid structure. This is accomplished by generating additional segments between two subsequent segments. The number of additional segments depends on the printing resolution (e.g. if two wireframe segments are 3.5 mm apart and the extrusion nozzle is 0.7 mm, the invention generates 3.5 mm/0.7 mm=5 additional layers). After generating the segments and extracting their contours, the invention analyzes which portion is selected for layer-wise printing in order to cut the contours at the start point and end point of the selected portion, the remaining which is filled with the mesh pattern.

(36) Furthermore, whether a wireframe structure or hybrid structure, the invention prints all detail of the same segment. For example, if a segment contains multiple disconnected contours, the invention prints all contours located on the same segment first before moving up to the next segment.

(37) While the disclosure is susceptible to various modifications and alternative forms, specific exemplary embodiments of the invention have been shown by way of example in the drawings and have been described in detail. It should be understood, however, that there is no intent to limit the disclosure to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure as defined by the appended claims.