3D PRINTING MACHINE AND MANUFACTURING METHOD

Abstract

A multi-head 3D printing machine has first and second common guides for a plurality of deposition heads and provides a relative displacement between the deposition heads along a third guide, the first, second and third guides identifying a reference frame. The 3D printing machine further includes a control unit programmed to process a sequence of discretized position information within the reference frame and deposition information so as to deposit non-replica, non-mirrored segments while the deposition heads simultaneously operate.

Claims

1. A multi-head additive manufacturing machine comprising: a first common guide aligned to a first direction; a second common guide aligned to a second direction; a multi-deposition unit comprising at least a first deposition device and a second deposition device, wherein the first deposition device and the second deposition device are independently actuatable to provide different quantities of deposition material; a multi-head unit (MHU) movable with respect to the first common guide and the second common guide and comprising at least a first motorized deposition head and a second motorized deposition heads movable with respect to one another along a third guide aligned to a third direction, the first direction, the second direction and the third direction defining a three-dimensional reference frame for deposition; wherein the first motorized deposition head and the second motorized deposition heads comprise a first opening and a second opening, respectively, wherein the deposition material is deposited through the first opening and the second opening, respectively; an electronic control unit (ECU) programmed to:  control a movement of the first motorized deposition head and the second motorized deposition head via actuators within the three-dimensional reference frame by processing at least a discretized sequence of coordinate value sets within the three-dimensional reference frame representing a pre-defined first deposition path and a pre-defined second deposition paths for the first motorized deposition head and the second motorized deposition head as a plurality of points;  provide, via a pre-defined first deposition quantity information for the first motorized deposition head and a second deposition quantity information for the second motorized deposition head, each of the pre-defined first deposition quantity information and the second deposition quantity information being associated to the plurality of points, a pre-defined quantity of material to be deposited along the pre-defined first deposition path and the pre-defined second deposition path via the first opening and the second opening and a deposition system;  wherein the first motorized deposition head and the second motorized deposition head are controlled with identical movements along the first direction and the second direction,  wherein the coordinate values further include first position information along the third direction for the first motorized deposition head and second position information along the third direction for the second motorized deposition head such that, for at least a section of the discretized sequence where the first motorized deposition head and the second motorized deposition head simultaneously deposit, the pre-defined first deposition path and the pre-defined second deposition path describe a first segment and a second segment, wherein the first segment and the second segment are arbitrarily different, non-mirrored, non-replica, and the first segment and the second segment having, for a first span along the first direction and for a second span along the second direction, a corresponding first length associated to the first motorized deposition head and a corresponding second length associated to the second motorized deposition head so that a length of the first segment is different from a length of the second segment,  the electronic control unit coordinating the first motorized deposition head and the second motorized deposition head by operating the actuators and the deposition system so that, when the first motorized deposition head and the second motorized deposition head simultaneously operate based on the section, each coordinate value set of the discretized sequence having identical coordinate values along the first direction and the second direction and different values along the third direction and for first deposition information and second deposition information, is simultaneously reached by the first motorized deposition head and the second motorized deposition head so that the first segment and the second segment are synchronously deposited over a same time interval by having a first travelling speed of the first motorized deposition head lower than a second travelling speed of the second motorized deposition head when the first segment is shorter than the second segment.

2. The multi-head additive manufacturing machine according to claim 1, wherein the discretized sequence processed by the electronic control unit is configured to define a first pre-defined discretization step along the first direction and a second pre-defined discretization step along the second direction between adjacent coordinate value sets and wherein at least one of a plurality of pre-defined first discretization steps and a plurality of pre-defined second discretization steps have non-constant discretization step values along the section, the plurality of pre-defined first discretization steps and the plurality of pre-defined second discretization steps being applied together to the pre-defined first deposition path and the pre-defined second deposition path so that the pre-defined first deposition path and the pre-defined second deposition path have a same discretization along the first direction and the second direction.

3. The multi-head additive manufacturing machine according to claim 1, wherein the electronic control unit is programmed so that, when two or more stratified layers of each printed object or sub-part are at least partially defined by the pre-defined first deposition path and the pre-defined second deposition path, the pre-defined first deposition path of the first motorized deposition head of a lower layer is not overlapped by the pre-defined second deposition path of the second motorized deposition head of a higher layer and the pre-defined second deposition path of the lower layer is not overlapped by the pre-defined first deposition path of the higher layer.

4. The multi-head additive manufacturing machine according to claim 1, wherein at least within the section each point of the discretized sequence is defined by at least six degrees of freedom including first position information along the first direction, second position information along the second direction, third position information of the first deposition head along the third direction, fourth position information of the second deposition head along the third direction, the first deposition information and the second deposition information and wherein the electronic control unit is programmed to: check if an inputted preferred speed value including deposition rates of the first motorized deposition head and the second motorized deposition head is compatible with a set of pre-defined speed values, each pre-defined speed value being associated to a respective degree of freedom; when an inputted speed is, along at least an axis or for the deposition system, higher than a relative pre-defined speed value or deposition rate, choose the relative pre-defined speed or deposition rate as a maximum speed or rate along a relative direction or associated to the first motorized deposition head and the second motorized deposition head; and calculate other speed values along other axes or remaining deposition rate so that the first motorized deposition head and the second motorized deposition head simultaneously reach a target point.

5. The multi-head additive manufacturing machine according to claim 1, wherein the first deposition information and the second deposition information are different so that, between adjacent points of the discretized sequence, the electronic control unit causes a first width of material deposited at a given time by the first motorized deposition head for the first segment to be different from a second width of material deposited for the second segment by the second motorized deposition head so that a first area covered by the first segment is different from a second area covered by the second segment in width and/or in length.

6. The multi-head additive manufacturing machine according to claim 1, wherein the first deposition information and the second deposition information are different so that the electronic control unit causes the first motorized deposition head to be deactivated from deposition while the second motorized deposition head is depositing and causes the first motorized deposition head to deposit again while the second motorized deposition head is depositing, wherein a thickness for the deposited material of the first motorized deposition head is obtained and higher than a thickness for the deposited material of the second motorized deposition head.

7. A manufacturing method for two or more objects or sub-parts with a multi-head additive manufacturing machine, wherein the multi-head additive manufacturing machine comprises: a first common guide aligned to a first direction; a second common guide aligned to a second direction; a multi-deposition unit comprising at least of a first deposition device and a second deposition device, wherein the first deposition device and the second deposition device are independently actuatable to provide different quantities of deposition material; and a multi-head unit (MHU) movable with respect to the first common guide and the second common guide and comprising at least a first motorized deposition head and a second motorized deposition heads movable with respect to one another along a third guide aligned to a third direction, the first direction, the second direction and the third direction defining a three-dimensional reference frame for deposition; wherein the first motorized deposition head and the second motorized deposition heads comprise a first opening and a second opening, respectively, wherein the deposition material is deposited through the first opening and the second opening, respectively; the manufacturing method comprising steps of: via an electronic control unit (ECU), receiving at least a discretized sequence of coordinate value sets within the three-dimensional reference frame representing pre-defined first and second deposition paths for the first motorized deposition head and the second motorized deposition head as a plurality of points; providing, via a pre-defined first deposition quantity information for the first motorized deposition head and a second deposition quantity information for the second motorized deposition head, each of the pre-defined first deposition quantity information and the second deposition quantity information being associated to the plurality of points, a pre-defined quantity of material to be deposited along the first and second deposition paths via the first opening and the second opening and a deposition system; and controlling predetermined movements within the three-dimensional reference frame of the first motorized deposition head and the second motorized deposition head along the third direction to implement the first and second deposition paths, wherein the first motorized deposition head and the second motorized deposition head are controlled with identical movements along the first direction and the second direction, wherein the coordinate values further include first position information along the third direction for the first motorized deposition head and second position information along the third direction for the second motorized deposition head such that, for at least a section of the discretized sequence where the first motorized deposition head and the second motorized deposition head simultaneously deposit, the first and second deposition paths describe a first segment and a second segment, wherein the first segment and the second segment are arbitrarily different, non-mirrored, non-replica, and the first segment and the second segment having, for a first span along the first direction and for a second span along the second direction, a corresponding first length associated to the first motorized deposition head and a corresponding second length associated to the second motorized deposition head so that a length of the first segment is different from a length of the second segment, the electronic control unit coordinating the first motorized deposition head and the second motorized deposition head by operating the actuators and the deposition system so that, when the first motorized deposition head and the second motorized deposition head simultaneously operate based on the section, each coordinate value set of the discretized sequence having identical coordinate values along the first direction and the second direction and different values along the third direction and for first deposition information and second deposition information, is simultaneously reached by the first motorized deposition head and the second motorized deposition head so that the first segment and the second segment are synchronously deposited over a same time interval by having a first travelling speed of the first motorized deposition head lower than a second travelling speed of the second motorized deposition head when the first segment is shorter than the second segment.

8. The manufacturing method according to claim 7, comprising the step of generating, on the plane of a first axis and a second axis, a first projection and a second projection of respective first and second 3D computational models of a relative object or a sub-part, the relative object or the sub-part is to be deposited by the first motorized deposition head or the second motorized deposition head; calculating a parameter indicative of overlapping between the first projection and the second projection; changing a relative orientation between the first and second 3D computational models within the three-dimensional reference frame until a target orientation is found such a parameter reaches a predefined threshold; generating the discretized sequence based on the target orientation to define a portion of each of the relative object or the sub-part, the deposition of the relative object or the sub-part is operated with the first motorized deposition head and the second motorized deposition head depositing at a same time via sequences generating the first segment and the second segments.

9. The manufacturing method according to claim 7, further comprising steps of: receiving a single or plurality of first discretized toolpaths originated by a decomposition of a first computational model of one of the at least two objects and a single or plurality of second discretized toolpaths originated by the decomposition of a second computational model of another of the at least two objects, a common discretization step pattern being applied between adjacent points of a first discretized toolpath and a second discretized toolpath where the first motorized deposition head and the second motorized deposition head simultaneously deposit; pairing at least one of the first discretized toolpaths with at least one of the second discretized toolpaths in ordered sequential pairs based on the common discretization step pattern, for each of the ordered sequential pairs, defining a common direction of travel along the first direction and the second direction to generate the discretized sequence.

10. The manufacturing method according to claim 7, wherein the at least two objects are paired objects and the at least two objects and sub-parts are wearable by an individual and comprising the step of generating a first 3D computational model and a second 3D computational model of one or more body portions of the individual based on an output by a biometric device and generating and or selecting a proper sequence based on the first 3D computational model and the second 3D computational model.

11. The multi-head additive manufacturing machine according to claim 2, wherein the electronic control unit is programmed so that, when two or more stratified layers of each printed object or sub-part are at least partially defined by the pre-defined first deposition path and the pre-defined second deposition path, the pre-defined first deposition path of the first motorized deposition head of a lower layer is not overlapped by the pre-defined second deposition path of the second motorized deposition head of a higher layer and the pre-defined second deposition path of the lower layer is not overlapped by the pre-defined first deposition path of the higher layer.

12. The multi-head additive manufacturing machine according to claim 2, wherein at least within the section each point of the discretized sequence is defined by at least six degrees of freedom including first position information along the first direction, second position information along the second direction, third position information of the first deposition head along the third direction, fourth position information of the second deposition head along the third direction, the first deposition information and the second deposition information and wherein the electronic control unit is programmed to: check if an inputted preferred speed value including deposition rates of the first motorized deposition head and the second motorized deposition head is compatible with a set of pre-defined speed values, each pre-defined speed value being associated to a respective degree of freedom; when an inputted speed is, along at least an axis or for the deposition system, higher than a relative pre-defined speed value or deposition rate, choose the relative pre-defined speed or deposition rate as a maximum speed or rate along a relative direction or associated to the first motorized deposition head and the second motorized deposition head; and calculate other speed values along other axes or remaining deposition rate so that the first motorized deposition head and the second motorized deposition head simultaneously reach a target point.

13. The multi-head additive manufacturing machine according to claim 3, wherein at least within the section each point of the discretized sequence is defined by at least six degrees of freedom including first position information along the first direction, second position information along the second direction, third position information of the first deposition head along the third direction, fourth position information of the second deposition head along the third direction, the first deposition information and the second deposition information and wherein the electronic control unit is programmed to: check if an inputted preferred speed value including deposition rates of the first motorized deposition head and the second motorized deposition head is compatible with a set of pre-defined speed values, each pre-defined speed value being associated to a respective degree of freedom; when an inputted speed is, along at least an axis or for the deposition system, higher than a relative pre-defined speed value or deposition rate, choose the relative pre-defined speed or deposition rate as a maximum speed or rate along a relative direction or associated to the first motorized deposition head and the second motorized deposition head; and calculate other speed values along other axes or remaining deposition rate so that the first motorized deposition head and the second motorized deposition head simultaneously reach a target point.

14. The multi-head additive manufacturing machine according to claim 2, wherein the first deposition information and the second deposition information are different so that, between adjacent points of the discretized sequence, the electronic control unit causes a first width of material deposited at a given time by the first motorized deposition head for the first segment to be different from a second width of material deposited for the second segment by the second motorized deposition head so that a first area covered by the first segment is different from a second area covered by the second segment in width and/or in length.

15. The multi-head additive manufacturing machine according to claim 3, wherein the first deposition information and the second deposition information are different so that, between adjacent points of the discretized sequence, the electronic control unit causes a first width of material deposited at a given time by the first motorized deposition head for the first segment to be different from a second width of material deposited for the second segment by the second motorized deposition head so that a first area covered by the first segment is different from a second area covered by the second segment in width and/or in length.

16. The multi-head additive manufacturing machine according to claim 4, wherein the first deposition information and the second deposition information are different so that, between adjacent points of the discretized sequence, the electronic control unit causes a first width of material deposited at a given time by the first motorized deposition head for the first segment to be different from a second width of material deposited for the second segment by the second motorized deposition head so that a first area covered by the first segment is different from a second area covered by the second segment in width and/or in length.

17. The multi-head additive manufacturing machine according to claim 2, wherein the first deposition information and the second deposition information are different so that the electronic control unit causes the first motorized deposition head to be deactivated from deposition while the second motorized deposition head is depositing and causes the first motorized deposition head to deposit again while the second motorized deposition head is depositing, wherein a thickness for the deposited material of the first motorized deposition head is obtained and higher than a thickness for the deposited material of the second motorized deposition head.

18. The multi-head additive manufacturing machine according to claim 3, wherein the first deposition information and the second deposition information are different so that the electronic control unit causes the first motorized deposition head to be deactivated from deposition while the second motorized deposition head is depositing and causes the first motorized deposition head to deposit again while the second motorized deposition head is depositing, wherein a thickness for the deposited material of the first motorized deposition head is obtained and higher than a thickness for the deposited material of the second motorized deposition head.

19. The multi-head additive manufacturing machine according to claim 4, wherein the first deposition information and the second deposition information are different so that the electronic control unit causes the first motorized deposition head to be deactivated from deposition while the second motorized deposition head is depositing and causes the first motorized deposition head to deposit again while the second motorized deposition head is depositing, wherein a thickness for the deposited material of the first motorized deposition head is obtained and higher than a thickness for the deposited material of the second motorized deposition head.

20. The multi-head additive manufacturing machine according to claim 5, wherein the first deposition information and the second deposition information are different so that the electronic control unit causes the first motorized deposition head to be deactivated from deposition while the second motorized deposition head is depositing and causes the first motorized deposition head to deposit again while the second motorized deposition head is depositing, wherein a thickness for the deposited material of the first motorized deposition head is obtained and higher than a thickness for the deposited material of the second motorized deposition head.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

[0039] FIG. 1 is a sketch showing an example of a machine according to the present invention wherein the second direction, i.e. Y-direction, is perpendicular to X- and Z-axes;

[0040] FIG. 2 is a sketch of the machine of FIG. 1 in a plane showing Y- and X-axes;

[0041] FIG. 3 is a sketch showing a preferred discretization of a first and second deposition paths;

[0042] FIGS. 4 and 5 show sketches about a suitable orientation of 3D geometrical or numeric models of the objects/sub-parts to be printed;

[0043] FIGS. 6 to 8 show sketches of deposition paths;

[0044] FIGS. 9 and 10 are flow-charts in a more general and two-head configuration for the calculation of operating parameters such as speed of the heads during printing; and

[0045] FIG. 11 is a vectorial decomposition of a quantity discussed in FIGS. 9 and 10.

DETAILED DESCRIPTION OF THE INVENTION

[0046] FIG. 1 shows a preferred and not limiting embodiment of a printing machine according to the present invention wherein a multi-head unit (MHU) comprises first, second and third (or more) printing heads 1, 2, 3, 4 . . . N, that move independently but without colliding along a single X direction, the direction being defined by a preferably rectilinear guiding beam 4.

[0047] The printing machine further comprises another guide, preferably a rectilinear guide 5 (shown in FIG. 2), along which multi-head unit MHU travels parallel to a Y-direction and a printing bed 6 that receives a filament material extruded or otherwise deposited from a nozzle 7 of each head 1, 2, N. Multi-head unit MHU is configured to move with respect to bed 6 along a Z-direction, which defines with X- and Y-direction a reference frame to express a 3D deposition or deposition path of the material via a triplet of coordinates. Preferably X- Y- and Z-axes are rectilinear and mutually orthogonal but the present invention applies to other reference frames, e.g. for polar or spherical coordinates, depending on the case. Furthermore, according to the embodiment of FIG. 1, bed 6 moves along suitable guides but it is also possible that multi-head unit MHU move along the Z-direction and bed 6 be fixed.

[0048] The printing machine further comprises actuators, e.g. electric rotary motors, to move heads 1, 2, N in the reference frame, a multi-deposition unit 8 that can process a single deposition material or a plurality of materials e.g. a material X can be fed in nozzle 7 of head 1 and an elastic material Y can be fed to nozzle 7 of head 2, which can be as well different in size, e.g. one with orifice of 0.5 mm other with 0.8 mm, with a filament-like deposition material in a softened or partially melted condition to favor shaping and deposition and an electronic control unit ECU to control, e.g. via suitable circuitry and sensors, position within the reference frame of heads 1, 2, N via the actuators and a quantity of material to each head 1, 2, N. In particular, the deposition system comprises actuators to provide a diversified deposition rate for each head. A control parameter of such actuators may be used to indicate an amount and/or rate of deposition material processed by each head, e.g. in case of extrusion, the angular position and motion of a feeding screw that feeds the respective deposition head.

[0049] As shown in FIG. 1, each head 1, 2, N prints its own object or sub-part so that material deposited by one printing head do not overlap with material deposited by another printing head.

[0050] Furthermore, FIG. 1 shows objects having different slicing. This can be obtained by e.g. having head 1 depositing every other layer and head 2 depositing every layer. When head 1 does not deposit, the relative deposition data (E1 in FIG. 3) for the given z-coordinate of the sequence where head 2 does deposit is zero. Deposition data of head 1 for the subsequent layer shall take into account the higher volume of material to be deposited in order to have a different slicing than that of head 2. More generally, while one deposition head does deposit, the non-depositing head may move or not.

[0051] FIG. 2 shows examples of deposition paths in the non-limiting embodiment where layers are substantially planar and deposited on a geometric horizontal plane perpendicular to the Z-direction. According to an important aspect of the invention, paths A and B show different geometries that are compatible with contemporaneous deposition of both heads 1 and 2. Deposition path C has a region R that is incompatible with a contemporaneous deposition with one or both of paths A, B: in such a region only head 3 is active and deposits whilst deposition from heads 1, 2 is temporarily stopped.

[0052] As shown in FIG. 2, the toolpaths of the first and second deposition heads shall have a certain degree of similarity in order to be processed by the machine. For example, it is not possible to process a toolpath for e.g. deposition head 1 that, at a given step of the relative array, requires a negative displacement along the y axis together with another toolpath for e.g. deposition head 2, that requires a positive displacement along the y axis. FIG. 2 (and FIGS. 6 to 8) shows how coordinates along the Z and Y axis are identical between toolpath and coordinates along the X axis are different so as to generate a non-replica, non-mirrored figures or segments.

[0053] FIG. 3 shows a detail to describe a preferred programming of electronic control unit (ECU) for the definition of exemplary deposition path 1 and 2. According to a preferred embodiment, each deposition path is identified by a pre-defined input array or sequence comprising a first section with the triplets of coordinates of each point of an arbitrary spatial discretization applied to the preferred deposition path. As shown in FIG. 3, for heads 1 and 2 coordinates z and y are the same because the latter are provided by movements along the common guides 5 and bed 6.

[0054] Input array or sequence of FIG. 3 also comprises a section about a quantity of deposition material, preferably expressed as a volume of material, to be deposited when travelling from a starting point to and adjacent point by the relative head 1, 2.

[0055] Each row of the array includes position and, preferably, non-position information, e.g. quantity of material to be deposited, speed at a given point in space. Furthermore, array of FIG. 3 is a single sequence for both heads but it is possible to provide an array for each head, wherein, for a given row, Y and Z coordinates are identical and X coordinates as well as other non-position information are different.

[0056] Array may include both position and non-position absolute space coordinates or displacements with sign. In the latter case it is very easy to spot an inconsistency of toolpaths because it is not possible to have, at a given step of the array i.e. at a give y-coordinate, displacements of different signs for head 1 and head 2. If the array contains absolute coordinates, it is a simple algebraic step to calculate the displacement and therefore compatibility of toolpaths.

[0057] FIGS. 4 and 5 show a preferred embodiment of the invention wherein two shapes are oriented e.g oriented at an angle about Z-axis in order to maximize the condition for contemporary deposition of heads 1 and 2. According to a preferred embodiment, orientation of the pair of shapes to be printed is calculated as follows: [0058] Calculation of centroids of first and second 3D model of the shapes to be printed, whereas a centroid is defined as a point whose position is the average or mean position of all points constituting the object. [0059] Orientation of local xyz reference frame centered in each centroid is operated, local reference frames being ‘parallel’ to machine reference frame. [0060] Iterative rotations about the centroids and axes of local reference frames by a preset finite angle are applied to each 3D model and respective projections on a plane defined by the first and second common directions of the deposition heads, i.e. Y-Z plane are collected (FIGS. 4a, 4b). [0061] All projections from first object are compared to all projections from second object on a 1-to-1 basis, by a brute force algorithm, while having their centroids aligned along X axis. [0062] As an output and final solution of the brute force algorithm is provided the pair of projections of first and second object that have the biggest common/overlapping area of YZ projections. [0063] In a case of multiple solutions that have equal or similar common area, the final solution is selected as the one having the objects in such orientation that minimize the Z coordinate.

[0064] Orienting may be either calculated onboard of the manufacturing machine, or by an external electronic device, in which case arrays take into account the optimized orientation.

[0065] FIG. 5 shows in greater detail, within the slicing plane, a possible starting orientation of 3D models projections and a better orientation in which the synchronisation of deposition is improved (or potentially optimized). More generally, orientation is such that a parameter indicative of simultaneous deposition of two printing heads, e.g. percentage of overlapping area with respect to total area, is kept above a predefined level.

[0066] FIGS. 6 to 8 show different approaches for defining deposition path. In particular, once an optimal orientation has been defined for both of the objects, they are sliced with a horizontal plane (XY) perpendicular to the plane defined by first and second common direction (YZ). An iterative slicing between the horizontal plane (XY) and different Z height identifies the layers for which toolpaths need to be developed for example for Z=const. The height difference between the intersections defines the layer height. In particular, FIG. 6 shows how discretization step pattern has variable step values in order to provide a better definition to the shape having higher complexity. Such step pattern is common to both layers so that synchronism is maximized. As an alternative, a more general decomposition of the object is automatically operated to generate a continuous serpentine, e.g. non-constant Z coordinate, toolpath for the object as a whole. In this way, a stratification of layers having no constant Z takes place and the deposition interruptions required by constant Z layers are avoided.

[0067] In FIG. 6a, the layers of two objects A and B are shown. In this embodiment, the toolpaths are developed by first locating the Ymax and Ymin coordinate that in this example are equal for both of the objects. In a following step, the external contours of the layers obtained by the slicing in a preceding phase are split into left and right toolpaths, hereby denoted as a0 and a1 from object A and b0 and b1 from object B. The following toolpaths can be obtained by planar offset of these two toolpaths in the horizontal plane. Once the toolpaths have been developed, they are coupled in pairs for simultaneous execution, according to their Ymax and Ymin coordinates, denoted with Ymax2, Ymin2, Ymax3, Ymin3 etc. For example, a suitable pair for toolpath a0 could be found by analysing the respective Ymax and Ymin coordinates of all toolpaths from Object B and selecting the toolpath with most similar or identical Ymax and Ymin to the ones from a0, thus minimising the average error between corresponding extreme coordinates, resulting in both b0 and b1 as a possible solution in the example shown in FIG. 6a. In such a case of multiple solutions, an applicable criterion for pairing is to pair left offset toolpaths of Object A, obtained as a result from offsetting a0 to left offset toolpaths of Object B, obtained as a result from offsetting b0. This is presented in FIG. 6a, where the toolpaths have been paired in the following way: [a0,b0], [a1,b1],[a2,b2],[a3,b3] etc. During the manufacturing phase using this method, a simultaneous deposition of two deposition heads will take place in such way that deposition head 1 will follow the toolpaths belonging to Object A from the pairs, while deposition head 2 will follow the toolpaths belonging to Object B from the pairs. Furthermore, such figure shows how deposition heads 1, 2 deposit in a coordinated, continuous and simultaneous manner.

[0068] When using this multi-deposition method, an additional parameter of direction of Y axis (common direction) needs to be defined. In this example the pair [a0,b0] is being executed with a direction of movement of the common Y axis from Ymax to Ymin as indicated by the arrow, followed by a direction of movement from Ymin to Ymax of the common axis during execution of the second pair of toolpaths [a1,b1] as indicated by the arrows, thus causing a counterclockwise motion on both deposition head 1 and deposition head 2, maximising the relative distance between them, and consequently their thermal and airflow independence. In another example, where the toolpaths are paired as first pair [a0,b1] and second pair [a1, b0], while maintaining the same common direction from Ymax to Ymin for the first pair, and from Ymin to Ymax for the second pair, the motion of deposition head 2 would be clockwise, conversely to the counterclockwise motion of deposition head 1, thus countering its inertial forces, ultimately resulting in a dynamically more balanced system of the entire apparatus. These thermal or mechanical dynamics of the apparatus as described in this invention can be used as further criteria for defining the specific combination of toolpath pairs and common direction for process execution. The process of toolpath generation and pairing and/or common direction selection is then repeated, according to a given criteria similar to the ones described above, until a desired infill percentage of the layer is obtained. In some examples, the developed toolpaths can only consist of a certain number of contour offsets (also known as walls) without filling the rest of the layer.

[0069] Besides the preparation of the toolpaths in such a way that would enable execution using the multi-head deposition method, the process needs to be strictly controlled and synchronised in order to guarantee the correct geometrical deposition of the required toolpaths, while satisfying the constraints that common Y direction is shared for both of the deposition heads.

[0070] It is important that the control unit ensures correct interpolation of the required curves in a coordinated and synchronous way. In one example, this synchronicity can be achieved by a linear interpolation of points obtained by required sampling of the said curves. In such an example, every sampling point on any of the curves would require a sampling point on the other toolpath from the corresponding pair. Sampling points are collected in arrays as described above e.g. about FIG. 3.

[0071] For example, reference can be made to FIG. 6b where for an accurate representation of curve a0, three points Pa1, Pa2 and Pa3 would suffice. However, for accurate representation of the other curve in the corresponding pair, b0, more points might be necessary: Pb1, Pb2, Pb3, Pb4 etc. . . . . In such an example, the toolpath (or better CAM preparation) would need to also find suitable sampling points of curve a0, by for example a projection algorithm and locate points: Pa4, Pa5, Pa6 in order to specify the movement of the deposition heads in every point necessary for either of the curves.

[0072] It should be noted that such additional sampling points might not always be necessary due to accurate geometrical representation, but also due to examples where the material deposition needs to be controlled as for example, in areas where the deposition on one of the deposition heads needs to be stopped or initiated.

[0073] In another embodiment represented in FIG. 7a, cross sections of Object A and Object B can be decomposed in suitable toolpaths following more complex algorithms for curve generation. In such an example, a mid-line toolpath has been generated by connecting the Ymax and Ymin points of each cross section of the corresponding objects, denoted as a2 and b2 in FIG. 7a. The rest of the toolpaths can then be generated according to algorithms for morph curve (also known as tween curve) given a specific distance based on infill density, where the newly generated curves are generated as a weighted average of boundary curves, and where the weight is the distance from the boundary curves. For example, b3 and b4 are morph curves when using curves b1 and b2 curves as boundaries, and curves a3 and a4 are morph (tween) curves when using a1 and a2 as boundaries. FIG. 7a shows how, according to the invention, corresponding segments a4 and b4 have different lengths and are deposited in the same time interval, i.e. are non-replica segments.

[0074] In such an example, the distance between adjacent toolpaths varies, so it can, for example, be particularly advantageous to provide deposition data relative to a varying filament width on a segment-to-segment basis, based on such toolpath distance, by controlling the amount of material deposited along the toolpaths, represented by the areas in pattern, depicted in FIG. 7b. Such figure shows how corresponding segments, S1 and S2 are deposited synchronously during the same time interval to cover respectively different areas by a variation of the filament width. The control over width is beneficial as a further degree of freedom for the designer in order to extend the number of non-replica geometries that can be printed by the machine.

[0075] In yet another example, the geometry of some toolpaths may not be related to the geometry of the cross-section with such a high level of similarity, but might be obtained by populating the cross-section of the object by toolpaths from a pre-made database of toolpaths, depending on the area that needs to be infilled by toolpaths, and adjusting it to that infill area. For example, in FIG. 8 toolpath a4 has been obtained by using a template zig-zag curve a′, where all right hand control points of that curve have been extended in X direction until intersection with the infill area.

[0076] The above described examples of different types of toolpaths and toolpath pairs between various objects can be combined in the deposition of layers.

[0077] It is important to note that speed of heads during deposition can be calculated by the control unit in a number of different ways. For example, an initial speed is assigned to each deposition head and such speed is maintained until the array specifies a different value in case such speed is always less than a maximum speed of the machine. Otherwise, the array further comprises a specific column for the speed to be kept at each step, i.e. between adjacent points along the deposition path. It is important to note that speed of a deposition head is defined by kinematic constraints, e.g. performances of actuators dedicated to move the head in the space or along a plane parallel to the deposition plane.

[0078] In FIGS. 9 and 10, an algorithm or dataflow is given as example on how to manage the speed for all of the separate axes based on the array data, specifically the relative value between two points in the array, the speed specified by the designer or user and the maximum capabilities in terms of permitted speeds for each of the axes of the apparatus. In particular, a maximum speed for each direction may be either a nominal speed of the relative actuator or a maximum speed stored as such in the electronic control unit.

[0079] FIG. 11 shows the multi-dimensional reference frame wherein ‘displacement’ vector P and ‘speed’ vector F are defined and whose length or norm is mentioned in FIG. 9. Such vectors comprise the combination of position information and non-position information, e.g. a numerical parameter indicative of the quantity of material to be deposited by each printing head for the given step of deposition defined by adjacent point in the array E1, E2. Such parameter may be a length [mm] of filament-like material to be deposited between two adjacent points of the array, an angle of rotation of a filament-like material feeding device or the like. Each row of the array defines a mono-dimensional component that combines with other mono-dimensional components to generate multi-dimensional vector P. Therefore any row of the array provides information to generate a multi-dimensional vector P.

[0080] Vector F is set by the designer in various manners, e.g. is assigned at the beginning of a layer and kept constant or changes every e.g. 10 rows of the array etc. and vector P includes the operating position coordinates between a starting point and a target point of deposition heads along the respective toolpath, the starting and target points being adjacent along the array of coordinates and material deposition parameters.

[0081] According to an embodiment, both P and F shall be expressed by the same formula, for example the norm. Dividing norm of vector P by norm of vector F provides a time that shall be common to all actuators along the axes and deposition system to guarantee a simultaneous motion. Dividing the difference between the position coordinates and material quantity of the target point and the starting point by such common time provides the speed along each axis and deposition rates for each deposition head. In case one of such values is higher than a pre-set maximum value for a given axis or deposition system, such pre-set value is chosen by the control unit as the actual speed or rate value (left branch in flowcharts of FIGS. 9 and 10) and the speed along the remaining axes and rates of the remaining deposition heads is calculated, in particular decreased, to satisfy the condition to simultaneously reach the coordinates of the target point. According to a preferred embodiment this is achieved by calculating a new time based on the actual (maximum) speed or rate and, with such new time, calculate the speeds along those axes or the deposition rates of the heads that were not above the pre-set value.