WO2021145818A1

WO2021145818A1 - 3d printing method and apparatus with a variable-geometry nozzle

Info

Publication number: WO2021145818A1
Application number: PCT/SG2020/050771
Authority: WO
Inventors: Wenxin LAO; Tegoeh TJAHJOWIDODO; Mingyang Li
Original assignee: Nanyang Technological University
Current assignee: Nanyang Technological University
Priority date: 2020-01-17
Filing date: 2020-12-22
Publication date: 2021-07-22
Anticipated expiration: 2022-07-17

Abstract

A 3D printing method and apparatus with a variable-geometry nozzle is disclosed. The method includes slicing a model of an object into a plurality of primary slices, and further slicing each primary slice into a plurality of thinner secondary slices. A target extrudate profile of the selected primary slice is defined. The method includes predicting a target nozzle shape correlated with the target extrudate profile; and adjusting the nozzle shape such that the nozzle shape adaptively conforms with the target nozzle shape as the nozzle travels along a printing path to deposit an extrudate layer.

Description

3D PRINTING METHOD AND APPARATUS WITH A VARIABLE-GEOMETRY

NOZZLE

The present application claims priority from the Singapore patent application no. 10202000465R, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0001] The present disclosure relates to methods and apparatus for additive manufacturing.

BACKGROUND

[0002] Owing to its ability to directly create three-dimensional (3D) products without the need for underlying formwork, 3D printing (also referred to as additive manufacturing) has the potential to reduce total fabrication time and labor cost. Despite the rapid development of 3D printing technology, several challenges remain, including in the area of 3D printing of large objects where the surface finish of the printed product is important, not only for the sake of aesthetics but also because it may have a bearing on the function and performance of the objects. Taking 3D concrete printing (3DCP) as an example, the geometry of the extrudate often does not follow the shape of the nozzle due to the effects of gravity and material rheological properties. Surface roughness is important as a rough surface tends to wear more rapidly than a smooth surface. In addition, stress concentration at the layer interface may reduce the bonding strength between layers of the extrudate. Therefore, there is a need to improve the surface finish quality of 3DCP -printed objects.

SUMMARY

[0003] A 3D printing method and apparatus with a variable-geometry nozzle is disclosed. The method includes slicing a model of an object into a plurality of primary slices, and further slicing each primary slice into a plurality of thinner secondary slices. A target extrudate profile of the selected primary slice is defined. The method includes predicting a target nozzle shape correlated with the target extrudate profile; and adjusting the nozzle shape such that the nozzle shape adaptively conforms with the target nozzle shape as the nozzle travels along a printing path to deposit an extrudate layer.

[0004] A nozzle system operable with a nozzle positioning system to deposit an extrudate to form an object based on a model, the nozzle system including: a nozzle, the nozzle including a variable-geometry section spaced apart from an outlet lip, the nozzle being coupled to the nozzle positioning system such that the nozzle positioning system is configured to move the nozzle along a printing path defined by the nozzle system; an actuating system operably coupled to controllably position a plurality of slidable plates along respective tracks, the plurality of slidable plates being slidably disposed at the variable-geometry section to define a nozzle shape; at least one processor; and a computer- readable memory coupled to the at least one processor, the computer-readable memory embodying instructions executable by the at least one processor to perform a method including: acquiring a target extrudate profile for a primary slice of the model, the target extrudate profile being approximated based on intersections between a plurality of secondary slicing planes and a cross-section of a primary slice of the model; based on the target extrudate profile, predicting a target nozzle shape based on a machine learning model; and positioning the plurality of slidable plates at respective selected positions along the respective tracks such that the nozzle shape corresponds to the target nozzle shape.

[0005] In another aspect, the nozzle includes: a nozzle body having an interior wall, the interior wall extending in a longitudinal direction to define a channel terminating at an outlet lip, the outlet lip being disposed in a first transverse plane substantially parallel to the printing path and substantially perpendicular to the longitudinal direction; a side opening disposed at the nozzle body and longitudinally spaced apart from the first transverse plane; and a plurality of slidable plates in slidable engagement with the side opening, each of the plurality of slidable plates including a first end surface disposed to form a part of the interior wall defining a nozzle shape, wherein each of the plurality of slidable plates is in slidable contact with at least one other of the plurality of slidable plates.

[0006] In yet another aspect, a method includes: slicing a model of the object into a plurality of primary slices, each of the plurality of primary slices having a primary slice thickness corresponding to a thickness of an extrudate layer; slicing a selected primary slice into a plurality of secondary slices according to a plurality of secondary slicing planes, the selected primary slice being selected from the plurality of primary slices; and defining a target extrudate profile of the selected primary slice such that the target extrudate profile corresponds to a cross-section of the extrudate layer, wherein the target extrudate profile is defined by a plurality of intersections between the plurality of secondary slicing planes and a cross-section of the selected primary slice.

[0007] In a further aspect, a method of forming a three-dimensional object can be performed by a processor configured to execute instructions embodied by a computer- readable memory coupled to the processor. The method includes: acquiring a target extrudate profile for a nozzle having a nozzle shape; predicting a target nozzle shape correlated with the target extrudate profile; and adjusting the nozzle shape such that the nozzle shape adaptively conforms with the target nozzle shape as the nozzle travels along a printing path to deposit an extrudate layer.

BRIEF DESCRIPTION OF DRAWINGS

[0008] Fig. 1 is an exploded view of a nozzle system according to an embodiment of the present disclosure;

[0009] Fig. 2 is a partial sectional view of the nozzle system of Fig. 1;

[0010] Fig. 3 A is a cross-section of the nozzle of Fig. 1;

[0011] Fig. 3B is a close-up view of Fig. 3A showing a variable-geometry section of the nozzle;

[0012] Fig. 4 is a partial cross-sectional view of a nozzle system according to another embodiment;

[0013] Fig. 5 is another perspective view of the nozzle system of Fig. 4; [0014] Fig. 6 A schematically illustrates an example of a nozzle shape;

[0015] Fig. 6B shows another example of the nozzle shape;

[0016] Fig. 7 is a process flow chart of a method according to an embodiment of the present disclosure;

[0017] Fig. 8 A to Fig. 8C are schematic representations according to the method of

Fig. 7;

[0018] Fig. 9 is another process flow chart of the method according to an embodiment of the present disclosure;

[0019] Fig. 10 schematically illustrates exemplary extrudate profiles obtained according to the method of Fig. 9;

[0020] Fig. 11 is a schematic representation of a zero-position state nozzle shape and a corresponding extrudate profile;

[0021] Fig. 12 is a schematic block diagram of a nozzle system; and

[0022] Fig. 13 is a workflow diagram according to embodiments of the present disclosure.

DETAILED DESCRIPTION

[0023] It will be readily understood that the components of the embodiments, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations, in addition to the described example embodiments. Thus, the following more detailed description of the example embodiments, as represented in conjunction with the figures, is not intended to limit the scope of the embodiments, as claimed, but is merely representative of example embodiments. [0024] The present disclosure provides a 3D printing method and apparatus with a nozzle (100). The nozzle includes a variable-geometry section (121), and the nozzle is also referred to herein as a variable-geometry nozzle. Embodiments of the nozzle are suitable for use in 3D printing or additive manufacturing in different fields, including but not limited to the fabrication of medical devices, building structures, etc. The nozzle is also not limited to use with any particular type of printing material. Examples of printing materials that may be used with the nozzle include but are not limited to polymers, metals, bio-printing materials, ceramics, concrete, etc. In 3D printing, a three-dimensional object may be formed by depositing one extrudate layer on another earlier deposited extrudate layer until a desired thickness of the object is achieved. Conventionally, a horizontal deposition is favored so as to permit the material to exit the nozzle in a transverse direction, similar to the final orientation of the extrudate layer. A vertical deposition mode or process would involve the material exiting the nozzle in a longitudinal direction, substantially perpendicular to the final orientation of the extrudate layer. It can be appreciated that, in a vertical deposition process, the material at different parts in a cross-section of the extrudate would travel paths of different lengths and different degrees of curvature, after exiting through the outlet lip and before coming to rest. For this and other reasons, vertical deposition is technically more challenging. Nonetheless, embodiments of the present disclosure have been found to enable the use of vertical deposition to obtain surprisingly significantly improved surface quality and shape compliance.

[0025] As a non-limiting example, one embodiment of the nozzle (100) will be described with reference to Fig. 1. Fig. 1 is an exploded view of a nozzle system (300) in which an actuating system (200) is provided to enable variable geometry of the nozzle (100). As shown in the partial sectional views of Fig. 2 and Fig. 3A, the nozzle (100) includes a nozzle body (110) having an interior wall (114) and an exterior wall (115). The interior wall (114) extends in a longitudinal direction (80) to define a channel (112) in the nozzle, such that a material received by the nozzle (100) can be made to flow in the channel (112) until the material exits the nozzle, forming an extrudate. The channel (112) begins at an inlet (117) and extends longitudinally to terminate at an outlet lip (116). The nozzle (100) may be coupled to an adaptor (170) at the inlet to facilitate reception of the material into the channel (112). The outlet lip (116) is disposed in a first transverse plane (60), that is, the nozzle wall (110) terminates at the first transverse plane where an edge of the interior wall (114) defines the outlet lip. The first transverse plane (60) is substantially perpendicular to the longitudinal direction (80). In the non-limiting example shown, the channel (112) nearer the inlet (117) has a circular cross-section which tapers to a narrower rectangular cross-section nearer the outlet lip (116). The interior wall (114) further includes a variable-geometry section (121) longitudinally spaced apart from the first transverse plane (60), that is, from the outlet lip (116). The variable-geometry section (121) may be disposed nearer the outlet lip (116) than the inlet (117). The channel (112) may be configured with different cross-sectional shapes and sizes. The variable-geometry section is a section of the nozzle that is controllably changeable to define various channel cross- sectional profiles. In this disclosure, the cross-sectional profile of the channel (112) at the variable-geometry section is referred to as a nozzle shape (129). The nozzle shape (129) is defined with respect to a transverse plane (62), in which the transverse plane is substantially parallel to the first transverse plane (60). The variable-geometry section is configured such that the material flowing past the variable-geometry section (121) is shaped thereby, even before the material exits through the outlet lip (116). As shown in Fig. 3B, the variable- geometry section extends longitudinally for a length H (162) such that the volume of material as well as the profile of the material is affected or regulated over a longitudinal distance, even before the material reaches the outlet lip (116). The variable-geometry section is coupled with an actuating system (200) configured to change the nozzle shape (129) at the variable-geometry section. The nozzle (100) may further be coupled to a nozzle positioning system (310). The nozzle positioning system (310) is configured to move the nozzle (100) along a printing path (70), such that the material exiting the outlet lip (116) is deposited as an extrudate layer (90) following the printing path.

[0026] Referring also to the embodiment of Fig. 4 and Fig. 5, the variable-geometry section (121) may include a plurality of slidable plates (120) slidably disposed thereat, the variable-geometry section (and hence the plurality of slidable plates) being spaced apart from the outlet lip (116). The slidable plates (120) are configured to be in slidable engagement with the nozzle body (110). A side opening (118), such as an opening, may be disposed at the nozzle body (110) such that the plurality of slidable plates (120) are in slidable engagement with the side opening (118). The side opening (118) is longitudinally spaced apart from the first transverse plane (60) or the outlet lip (116) by a lip thickness (111), such that a dynamic seal (119), such as an O-ring, may be disposed between the side opening (118) and the plurality of slidable plates (120). The dynamic seal (119) is configured to prevent significant leakage of material out of the channel (112) at the side opening. Each of the plurality of slidable plates (120) may be configured with two substantially opposing or parallel major surfaces (123) with a first end surface (122) disposed therebetween. The slidable plates (120) may be arranged as a lateral stack (124) with each of the plurality of slidable plates (120) in slidable contact with at least one other of the plurality of slidable plates (120). Adjacent slidable plates (120) contact one another at the respective major surfaces (123), which are configured to permit relative movement while preventing significant leakage of material between the adjacent slidable plates, for example, through the use of tight tolerances. Each of the plurality of slidable plates (120) may be slidable in respective parallel planes or along a first transverse direction (82) independently of one another. The first end surface (122) of each of the plurality of slidable plates is disposed to form a part of the variable-geometry section (121) of the interior wall (114) to define the nozzle shape (129). As shown in Fig. 6A and Fig. 6B, the plurality of the slidable plates is configured to be positionable at selected positions (125) along respective tracks (84). For example, the slidable plates (120) may be moved relative to the side opening (118) by the actuating system, such that the first end surfaces (122) can be positioned at different displacements or positions (125) relative to the side opening or relative to a fixed part of the inner wall (114). The tracks (84) may be substantially parallel to a first transverse direction (82). A track (84) refers to a path defined by movement of the corresponding slidable plate (120). The first end surfaces (122) of each of the plurality of slidable plates can define a corresponding variable channel width (127) in the first transverse direction, that is, the channel width (127) is measured along the first transverse direction (82). In this manner, the plurality of slidable plates (120) can define a variable nozzle shape (129), at the variable-geometry section (121) of the nozzle body (110). Referring again to Fig. 3B, each of the plurality of slidable plates (120) may be configured with the respective first end surface (122) defining a rectangle having longer edges (162) and shorter edges (163). The plurality of slidable plates (120) may be disposed such that the longer edges (162) are substantially parallel to the longitudinal direction (80), such that the length of the longer edges (162) defines a longitudinal length H of the variable- geometry section (121). Each of the shorter edges (163) has a thickness dimension Wl, configured to allow for a desired number of the slidable plates (120) to be disposed in one side opening, resulting in a corresponding degree of freedom for configuring the nozzle shape (129). Each stack (124) of the slidable plates (120) forms a collective thickness of W2 (164) which contributes towards defining the thickness (95) of the extrudate layer (90). The longer edges (162) of the first end surface (122) allows a longer path during which the material can conform to the nozzle shape (129). The result is a more consistent and predictable extrudate layer. In use, material flowing in the channel (112) is subject to a shaping effect of the variable-geometry section over the longitudinal length of the variable- geometry section, providing a controllable volume of the material as well as a controllable cross-sectional profile to the extrudate layer.

[0027] The nozzle (100) may be operable with various types of actuating systems (for example, pneumatic actuating systems, electro-hydraulic systems, etc.) configured to controllably position each of the plurality of slidable plates along respective tracks, without going beyond the scope of the present disclosure. The actuating system (200) described herein is therefore a non-limiting example. As shown in Fig. 4 and Fig. 5, the actuating system (200) may include a stepper motor (140) for each slidable plate (120), coupled to allow relatively small adjustments to the position of the slidable plate (120) along a corresponding track (84). A circular motion of a linear-motion pin (148) driven by the stepper motor (140) may be translated into a linear movement of bars (144) by a cam mechanism (142). The cam mechanism (142) may include the linear-motion pin (148) engaged with a slotted plate (146). The bars (144) connect a corresponding slidable plate (120) to the slotted plate (146), such that linear motion of the slotted plate (146) in the first transverse direction (82) causes the bars (144) to drive the slidable plate in linear movement along a corresponding track (84) parallel to the first transverse direction. A guiding plate (150) having a plurality of apertures may be provided for guiding the linear movement of the bars (144). A second seal (119a) may be provided between the nozzle body (110) and the guiding plate (150) to prevent significant leakage of materials out of the channel (112). Part of the actuating system (200) may be disposed in a modular housing (130). Opposing sides of the modular housing (130) may be spaced apart to accommodate the slotted plates (146). The opposing sides of the modular housing (130) may be configured with guiding slots (132), such that opposing ends of each slotted plate (146) are received in the corresponding guiding slots (132) and prevented from tilting during movement. Each guiding slot (132) may provide abutment walls (133) to act as displacement limits for the slotted plates (146). The guiding slots (132) are oriented in the first transverse direction (82) so that the slotted plates (146) and the sliding plates (120) are constrained to move in linear or translational motion in the first transverse direction (82). The slidable plates (120) may thus be independently positioned or collectively positioned by controlling the stepper motors (140). A sensor assembly (160) may be provided to detect the respective positions of the slidable plates (120), that is, to determine the respective positions or displacements of the first end surfaces relative to the interior wall (114). The sensor assembly (160) may include a plurality of position sensors disposed at modular housing (130). Alternatively, the position sensors (162) may be configured to detect the positions of the slotted plates (146), and thereby determine the respective positions or displacements of the first end surfaces (122) relative to the interior wall (114). The sensor assembly (160) may be configured to determine the respective positions of the plurality of slidable plates (120) with reference to a zero position (90) as shown in Fig. 6A and Fig. 6B. The zero position (90) of a slidable plate (120) may be defined as one in which the first end surface (122) is substantially flushed with the rest of the adjacent interior wall (114). The zero position (90) may alternatively be defined as one in which the slidable plate 120 is retracted into the nozzle body (110) or the side opening (118) until the slotted plate (146) abuts the abutment wall (133). Alternatively, a zero-position state may be described as the configuration or nozzle shape in which the channel (112) has the largest possible width dimensions.

[0028] Further, the nozzle (100) may be configured to be symmetrical about a longitudinal axis (80) of the nozzle (100), such that more than one surface of the extrudate layer (90) may be shaped by the variable-geometry section (121), such as shown in Fig. 6A. The nozzle (100) may include more than one side opening (118) disposed in the nozzle body (110), with each of the side openings (118) being in slidable engagement with a corresponding stack (124) of slidable plates, that is, with a corresponding plurality of slidable plates (120). Each of the plurality of slidable plates is configured to be positionable at selected positions (125) along respective tracks (84). In one example, two side openings (118) are disposed substantially opposite one another. Actuators (140), such as stepper motors or linear motors, may be provided and operatively coupled to respective slidable plates (120) to move the slidable plates (120). Each of the plurality of slidable plates (120) may be configured to be positionable at selected positions (125) along respective tracks, such that the slidable plates (120) may be independently positioned or collectively positioned. The tracks (84) may be substantially parallel to the first transverse direction (82).

[0029] Examples of the nozzle shape (129) definable by the slidable plates (120) in different positions are schematically illustrated in Fig. 6A and Fig. 6B. In these non limiting examples of a rectangular nozzle body, the inner wall may be described as having a leading face (114a) and a trailing face (114b), relative to a printing direction (71). Making reference also to Fig. 3A, in a situation where the nozzle (100) is moved in a printing direction (71), the leading face (114a) travels ahead of the trailing face (114b) to deposit the extrudate layer (90). The material defined by the leading face (114a) corresponds to a first surface (94a) of the extrudate layer (90), and the material defined by the trailing face (114b) corresponds to a second surface (94b) of the extrudate layer (90). The first surface (94a) can be in contact with a previously deposited extrudate layer. A thickness (95) of the extrudate layer (90) can be defined between the first surface (94a) and the second surface (94b). The nozzle (100) used in a vertical deposition process can be configured such that material that is shaped by the plurality of slidable plates (120) forms corresponding surfaces of the extrudate layer (90), and thereby the corresponding surfaces of the object formed. The nozzle (100) may also be used to define at least one surface of the extrudate layer (90). With reference to a configuration in which all the slidable plates are at the zero position, the nozzle shape (129) at the variable-geometry section may be other than rectangular in shape. The nozzle shape (129) may alternatively be configured with a circular cross- section, a square cross-section, a polygonal cross-section, etc. Accordingly, the nozzle (100) may be configured with more than two side openings (118), in which each side opening is provided with a corresponding plurality of plates (120). The outlet lip (116) may also be configured in different shapes, and preferably no smaller than the nozzle shape (129) at the variable-geometry section, such that the outlet lip does not interfere with the profile or shape of the material as it passes through the outlet lip.

[0030] According to another aspect, embodiments of the present disclosure include a method (400) (Fig. 7) of forming a three-dimensional object in which the method can be performed by a processor configured to execute instructions embodied by a computer- readably memory coupled to the processor. Referring also to Fig. 8A to Fig. 8C, the method (400) includes slicing (410) a model (600) of the object into a plurality of primary slices (610) using a plurality of primary slicing planes (612). The model (600) represents a target surface geometry (such as an outer surface geometry) of a three-dimensional object to be fabricated by 3D printing. Each primary slice (610) (defined between two neighboring primary slicing planes) represents a single printing layer obtained in one pass of the nozzle, that is, an extrudate layer (90). Primary slicing planes (612) are defined as parallel planes with adjacent primary slicing planes spaced apart by a primary slice distance equivalent to a thickness of the extrudate layer, such that, each of the plurality of primary slices has a primary slice thickness (614) corresponding to a thickness (95) of the extrudate layer (90), which in this case also corresponds to the collective thickness (164) of a stack (124) of the slidable plates. For each extrudate layer to be printed, the corresponding primary slice is further sliced into thinner secondary slices (620). The method includes slicing (420) a selected primary slice (610) into a plurality of secondary slices (620) according to a plurality of secondary slicing planes (622), in which the selected primary slice (610) is selected from the plurality of primary slices. Each of the plurality of secondary slices (620) has a secondary slice thickness (624), where the plurality of secondary slice thickness (624) collectively corresponds to the primary slice thickness (614). The method further includes defining (430) a target extrudate profile (650) of the selected primary slice such that the target extrudate profile (650) corresponds to a cross-section of the extrudate layer (90). The target extrudate profile is defined by a plurality of intersections (660) between the plurality of secondary slicing planes (622) and a cross-section (673) of the selected primary slice. The target extrudate profile (650) can be used as a basis for controllably adjusting the nozzle shape (129) at the variable-geometry section (121) of the nozzle. In some cases, the plurality of primary slices (610) and the plurality of secondary slices (620) may be substantially parallel to a transverse plane (60), in which the transverse plane (60) is substantially parallel to the printing path or printing trajectories of the same primary slice (610).

[0031] The method may further include determining multiple trajectory points (670) for the extrudate layer (90), in which each of the multiple trajectory points corresponds to an intersection between an outer surface of the selected primary slice (or a surface geometry as described by the model) and a cross-section plane (672). The method includes acquiring the target extrudate profile (650) for at least one trajectory point selected from the multiple trajectory points (670). The cross-section plane (672) is defined as a plane that is substantially perpendicular to the plurality of primary slices. The cross-section plane (672) at a trajectory point is also defined as a plane that is substantially perpendicular to the nozzle’s direction of movement at the trajectory point. The cross-section plane (672) may be defined with reference to coordinates of the trajectory point (670) and a normal vector (674) pointing in the direction of travel of the nozzle. The intersection of the cross- section plane (672) and the outer surface of the selected primary slice (610) defines a corresponding target extrudate profile (650) associated with the trajectory point (670). The method may include defining the target extrudate profile (650) for at least one trajectory point selected from the multiple trajectory points.

[0032] In an example where the surface of the object is curved, the “ideal” or “exact” cross-section geometry (690) of the extrudate layer (90) will have a correspondingly curved profile since it is based on the model. The term “target extrudate profile” refers to an approximation of the “ideal” or “exact” cross-sectional geometry. In particular, the target extrudate profile (650) can be acquired by using a stepped or “staircase” profile to approximate a curved profile. In one example, for a nozzle in which the plurality of slidable plates (120) consists of five such adjustable elements, each primary slice (610) is further sliced into a corresponding five secondary slices (620). A reference point (intersection) (660) is taken from each intersection of the primary slice geometry (690) and the extrudate cross-section plane (672). An approximation of the exact cross- sectional geometry of the extrudate layer is derived from the reference points (660). According to embodiments of this method, one extrudate layer (90) deposited for a curved surface is expected to have a side surface configured with steps. There is no layer interface between adjacent steps since the steps are formed as part of the same extrudate layer. A stepped profile is traditionally avoided when the desired surface geometry is curved. However, according to embodiments of the present disclosure, the target extrudate profile (650) is intentionally defined as a stepped profile by using discrete width variations to approximate the exact cross-sectional geometry. [0033] The method may include generating a printing path from the multiple trajectory points (670) for all of the plurality of primary slices (600) required to form the object. The method may include storing the printing path such that each of the multiple trajectory points (670) is associated with the corresponding target extrudate profile (650). The method may include correlating the target extrudate profile (650) with a target nozzle shape (700). The correlation may be based on a machine learning model. The machine learning model may be configured such that it is trained to provide the target extrudate profile (650) based on input parameters associated with the target nozzle shape (700) and a flow ratio of a selected material. Examples of input parameters include environmental factors such as temperature and humidity, selected material property such as viscosity and composition, etc. The method may include acquiring a target nozzle shape (700) for the nozzle, based on the target extrudate profile (650), in which the nozzle has a nozzle shape that is adjustable to conform with the target nozzle shape (700). The target nozzle shape (700) may be acquired based on a database and/or calculations or analysis.

[0034] According to another aspect, embodiments of the present disclosure includes a method (500) of forming a three-dimensional object. The method may be performed by a processor configured to execute instructions embodied by a computer- readably memory coupled to the processor. Referring to Fig. 9 and Fig. 10, the method (500) includes acquiring (510) a target extrudate profile (650) for a nozzle having a nozzle shape (such as by the method described above), and predicting (520) a target nozzle shape (700) correlated with the target extrudate profile (650). The method includes adjusting (530) the nozzle shape such that the nozzle shape adaptively conforms with the target nozzle shape (700) as the nozzle travels along a printing path to deposit an extrudate layer. As illustrated in Fig. 10, if the target extrudate profile is different for different extrudate layers, the target nozzle shape can be varied accordingly for the different extrudate layers. The resulting object can thus be formed by extrudate layers in which the actual extrudate profile differs from one extrudate layer to another extrudate layer. The target nozzle shape can also be varied from one trajectory point to another trajectory point for the same extrudate layer. The resulting object can thus be formed by at least one extrudate layer in which the actual extrudate profile varies along the same extrudate layer. [0035] The method may further include depositing an extrudate layer (90) characterised by a stepped surface (98), the stepped surface defining different widths along a thickness (95) of the extrudate layer such that the stepped surface (98) approximates a curved surface, in which the curved surface is characterised by different curvatures along the printing path.

[0036] The method may further include actuating a plurality of slidable plates (120) configured to vary respective transverse widths (127) of the channel cross-section, such that the extrudate layer is characterised by different widths along a thickness (t) of the extrudate layer, in which the thickness (t) of the extrudate layer corresponds to a collective thickness (W2) of the plurality of slidable plates.

[0037] In a situation where the nozzle (100) is moved along the printing path by the nozzle positioning system (310), a current position of the nozzle (100) may be determined, for example, by sensing and/or calculations. Embodiments of the method includes adjusting the nozzle shape (129) at the variable-geometry section (121) at the same time as the nozzle (100) is travelling along the printing path. The method may include determining a nearest trajectory point (670) relative to the current location of the nozzle, and acquiring a predictive target extrudate profile (650) associated with the nearest trajectory point (670), such that the target nozzle shape (700) acquired is one correlated to the predictive target extrudate profile (650). For example, the current position of the nozzle may be one that does not exactly coincide with any of the multiple trajectory points stored. The method may then involve using the target extrudate profile (650) associated with the nearest trajectory point as the basis for adjusting the nozzle shape. In some examples, the method may use the closest trajectory point yet to be traversed by the nozzle as the basis for predicting a target extrudate profile (650).

[0038] The use of cementitious materials in 3D printing is notoriously challenging. Comparison was made with reference to a nozzle such as one shown schematically in Fig. 11. It was observed that the nozzle of Fig. 11 produced extrudate layers (90) in which all the extrudate layers have the same extrudate profile. As a result, the object has a surface configuration formed with relatively large degrees of non-compliance with the model, with layer interfaces showing significant gaps (hl/h2) from the surface profile of the model (600). The resulting object of Fig. 11 showed less compliance with the “ideal” or modelled extrudate profile. In contrast, using a method and apparatus of the present disclosure, experiments conducted using a cementitious material have demonstrated obvious improvements in the surface quality. Quantitative measures of surface quality were measured, including the surface roughness factor Rt (sum of the height of the largest profile peak height) and the Rq parameter (root mean square value of the ordinate values within the sampling length). It was found that, in terms of Rt, the surface roughness improved by 34.3%, while surface quality Rq improved by 45%, using an example of a nozzle system (300) that is configured to operate with one example of the nozzle (100) described above.

[0039] Referring to Fig. 12, the nozzle system (300) includes a computing device having at least one processor (302) and a computer-readable memory (304) coupled to the at least one processor, in which the computer-readable memory is configured to embody instructions executable by the processor. The nozzle system (300) may be coupled with a nozzle positioning system (310) such that the nozzle positioning system can move the nozzle (100) along the printing path. The nozzle system further includes an actuating system (200) coupled to control the adjustable elements of the variable-geometry section and to configure the nozzle shape. The nozzle system is configured such that the nozzle positioning system (310) and the actuating system (200) work cooperatively and simultaneously when the nozzle system is depositing an extrudate to form an object. A nozzle system (900) is configured to perform a method, in which the method includes: i) acquiring a target extrudate profile for a primary slice of the model, the target extrudate profile being approximated based on intersections between a plurality of secondary slicing planes and a cross-section of the primary slice of the model; ii) based on the target extrudate profile, acquiring a target nozzle shape from a machine learning model; and iii) positioning the plurality of slidable plates at respective selected positions along the respective tracks such that the nozzle shape corresponds to the target nozzle shape; and forming a corresponding extrudate layer. The number of secondary slicing planes is selected to produce a number of secondary slices corresponding to a number of the slidable plates. The method may also include: iv) for each of multiple trajectory points along the printing path, acquiring and storing the target extrudate profile; and v) sending commands to the actuating system, wherein the commands are configured to position the plurality of slidable plates to provide the nozzle shape corresponding to each of the multiple trajectory points. Further, the method may also include: vi) locating a current position of the nozzle; and controllably positioning the plurality of slidable plates to provide the nozzle shape corresponding to the target extrudate profile associated with a trajectory point nearest to the current position.

[0040] As an example, Fig. 13 is a workflow diagram of a working prototype, according to embodiments of the present disclosure. A model of an object may be developed in the form of a computer-aided drawing (CAD) model (902). The nozzle system (900) is configured to define both the printing paths and the target extrudate geometry at multiple trajectory points. The model is first sliced using a number of spaced apart primary planes, and each primary plane is further sliced using a plurality of secondary planes. In this example, the primary planes are spaced 15 millimeters (mm) apart, and the secondary planes are spaced 3 mm part (3 mm resolution), with the primary planes and the secondary planes being horizontally disposed. The number of primary planes and secondary planes used, and the respective spacing, are defined to correspond to the physical configuration of the nozzle. In this example, the variable-geometry section of the nozzle includes two side openings, each of which is slidably engaged with a stack of five slidable plates. The result is a nozzle with ten degrees of freedom for the configuration of the nozzle shape. The leading face and the trailing face of the channel are spaced 15 mm apart such that the thickness of one extrudate layer is correspondingly 15 mm, with a maximum channel width of 38 mm. Based on the data obtained from slicing the model (sliced data, 904), the printing paths and the target extrudate profiles are generated for the model (912, 950). The printing paths are loaded to a robot controller (922) of a robotic arm (924) which forms part of the nozzle positioning system (310). The target extrudate profiles (950) are loaded to a computing device which stores a nozzle-extrudate correlation database (940). The nozzle- extrudate correlation database may be compiled through training a machine learning model. The nozzle-extrudate correlation database is configured to associate target extrudate profiles with corresponding nozzle shapes.

[0041] During printing, the robot controller (922) controls the robotic arm (924) such that the nozzle is moved along the printing path. The nozzle may be coupled to the robotic arm by an end-effector of the robotic arm. A real-time position of the end-effector (930) may be recorded by position sensors (926) and sent as feedback to the robot controller (922). Part of the nozzle system may reside in a remote computing device connected to the robot controller by an ethernet port, such that the real-time position can be published via a server to the processor (970). In response to receiving or acquiring the real-time position of the end-effector, the nozzle system calculates a current position of the nozzle. The nozzle system (300) is thus configurable for use with different types of nozzle positioning systems. The nozzle system is configured to acquire a target extrudate shape based on the current position of the nozzle. This may include determining the current position of the nozzle with respect to the traj ectory points, and performing a look-up in the nozzle-extrudate correlation database to acquire a target extrudate shape. The nozzle-extrudate correlation database may reside at a local processor, such as one coupled to the actuating system. The nozzle system may be configured to find a target nozzle shape (960) corresponding to a best approximation of the desired extrudate profile. The target nozzle shape is converted into data and/or commands, and the commands are sent to the motor controller (972) of the actuating system. The nozzle shape (channel cross-section) is adjusted accordingly (974). This process is repeated automatically during the printing process.

[0042] Reference throughout this specification to “one embodiment”, “another embodiment” or “an embodiment” (or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment. As used herein, the singular “a” and “an” may be construed as including the plural “one or more” unless clearly indicated otherwise.

[0043] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that the various embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, some or all known structures, materials, or operations may not be shown or described in detail to avoid obfuscation. [0044] This disclosure has been presented for purposes of illustration and description but is not intended to be exhaustive or limiting. Many modifications and variations will be apparent to those of ordinary skill in the art. The example embodiments were chosen and described in order to explain principles and practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated. Thus, although illustrative example embodiments have been described herein with reference to the accompanying figures, it is to be understood that this description is not limiting and that various other changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the disclosure.

Claims

1. A nozzle configured to travel along a printing path, the nozzle comprising: a nozzle body having an interior wall, the interior wall extending in a longitudinal direction to define a channel terminating at an outlet lip, the outlet lip being disposed in a first transverse plane substantially parallel to the printing path and substantially perpendicular to the longitudinal direction; a side opening disposed at the nozzle body and longitudinally spaced apart from the first transverse plane; and a plurality of slidable plates in slidable engagement with the side opening, each of the plurality of slidable plates including a first end surface disposed to form a part of the interior wall defining a nozzle shape, wherein each of the plurality of slidable plates is in slidable contact with at least one other of the plurality of slidable plates.

2. The nozzle as recited in claim 1, further comprising a dynamic seal disposed between the side opening and the plurality of slidable plates.

3. The nozzle as recited in claim 2, wherein each of the plurality of slidable plates is slidable along a first transverse direction independently of one another.

4. The nozzle as recited in claim 3, wherein the plurality of slidable plates is configured to be positionable at selected positions along respective tracks, the tracks being substantially parallel to the first transverse direction, such that the first end surface of each of the plurality of slidable plates defines a corresponding variable channel width in the first transverse direction.

5. The nozzle as recited in claim 4, wherein the first end surface defines a rectangle having longer edges and shorter edges, and wherein the plurality of slidable plates are disposed such that the longer edges are substantially parallel to the longitudinal direction.

6. The nozzle as recited in claim 2, further comprising: more than one side opening disposed in the nozzle body; and a plurality of slidable plates in slidable engagement with each of the side openings, wherein each of the plurality of slidable plates is configured to be positionable at selected positions along respective tracks.

7. A nozzle system operable with a nozzle positioning system to deposit an extrudate to form an object based on a model, the nozzle system comprising: a nozzle, the nozzle including a variable-geometry section spaced apart from an outlet lip, the nozzle being coupled to the nozzle positioning system such that the nozzle positioning system is configured to move the nozzle along a printing path defined by the nozzle system; an actuating system operably coupled to controllably position a plurality of slidable plates along respective tracks, the plurality of slidable plates being slidably disposed at the variable-geometry section to define a nozzle shape; at least one processor; and a computer-readable memory coupled to the at least one processor, the computer-readable memory embodying instructions executable by the at least one processor to perform a method comprising: acquiring a target extrudate profile for a primary slice of the model, the target extrudate profile being approximated based on intersections between a plurality of secondary slicing planes and a cross-section of a primary slice of the model; based on the target extrudate profile, predicting a target nozzle shape based on a machine learning model; and positioning the plurality of slidable plates at respective selected positions along the respective tracks such that the nozzle shape corresponds to the target nozzle shape.

8. The nozzle system as recited in claim 7, wherein the number of secondary slicing planes is selected to produce a number of secondary slices corresponding to a number of the slidable plates.

9. The nozzle system as recited in claim 8, further comprising: for each of multiple trajectory points along the printing path, acquiring and storing the target extrudate profile; and sending commands to the actuating system, wherein the commands are configured to position the plurality of slidable plates to provide the nozzle shape corresponding to each of the multiple trajectory points.

10. The nozzle system as recited in claim 9, further comprising: locating a current position of the nozzle; and controllably positioning the plurality of slidable plates to provide the nozzle shape corresponding to the target extrudate profile associated with a trajectory point nearest to the current position.

11. A method of forming a three-dimensional object, the method being performable by a processor configured to execute instructions embodied by a computer-readable memory coupled to the processor, the method comprising: slicing a model of the object into a plurality of primary slices, each of the plurality of primary slices having a primary slice thickness corresponding to a thickness of an extrudate layer; slicing a selected primary slice into a plurality of secondary slices according to a plurality of secondary slicing planes, the selected primary slice being selected from the plurality of primary slices; and defining a target extrudate profile of the selected primary slice such that the target extrudate profile corresponds to a cross-section of the extrudate layer, wherein the target extrudate profile is defined by a plurality of intersections between the plurality of secondary slicing planes and a cross-section of the selected primary slice.

12. The method as recited in claim 11, wherein the plurality of primary slices and the plurality of secondary slices are substantially parallel to a transverse plane.

13. The method as recited in claim 11, further comprising: determining multiple trajectory points for the extrudate layer, each of the multiple trajectory points corresponding to an intersection between an outer surface of the selected primary slice and an extrudate cross-section plane, the extrudate cross-section plane being substantially perpendicular to the plurality of primary slices; and defining the target extrudate profile for at least one trajectory point selected from the multiple trajectory points.

14. The method as recited in claim 13, further comprising: generating a printing path from the multiple trajectory points for all of the plurality of primary slices required to form the object; and storing the printing path such that each of the multiple trajectory points is associated with the corresponding target extrudate profile.

15. The method as recited in claim 13, further comprising: based on a machine learning model, correlating the target extrudate profile with a target nozzle shape, wherein the machine learning model is trained to provide the target extrudate profile based on input parameters associated with the target nozzle shape and a flow ratio of a selected material.

16. The method as recited in claim 13, further comprising: based on the target extrudate profile, acquiring a target nozzle shape for a nozzle, the nozzle having a nozzle shape that is adjustable to conform with the target nozzle shape.

17. A method of forming a three-dimensional object, the method being performable by a processor configured to execute instructions embodied by a computer-readable memory coupled to the processor, the method comprising: acquiring a target extrudate profile for a nozzle having a nozzle shape; predicting a target nozzle shape correlated with the target extrudate profile; and adjusting the nozzle shape such that the nozzle shape adaptively conforms with the target nozzle shape as the nozzle travels along a printing path to deposit an extrudate layer.

18. The method as recited in claim 17, further comprising: actuating a plurality of slidable plates configured to vary respective transverse widths of the nozzle shape, such that the extrudate layer is characterised by different widths along a thickness of the extrudate layer, the thickness of the extrudate layer corresponding to a collective thickness of the plurality of slidable plates.

19. The method as recited in claim 17, further comprising: determining a nearest trajectory point relative to a current location of the nozzle; and acquiring a predictive target extrudate profile associated with the nearest trajectory point, such that the target nozzle shape acquired is one correlated to the predictive target extrudate profile.

20. The method as recited in claim 17, further comprising: depositing an extrudate layer characterised by a stepped surface, the stepped surface defining different widths along a thickness of the extrudate layer such that the stepped surface approximates a curved surface characterised by different curvatures along the printing path.