EP4688389A1

EP4688389A1 - Print volume upscaling using multiple projectors in tomographic volumetric 3d printing

Info

Publication number: EP4688389A1
Application number: EP24718128.2A
Authority: EP
Inventors: Yi Yang
Original assignee: Danmarks Tekniske Universitet
Current assignee: Danmarks Tekniske Universitet
Priority date: 2023-04-05
Filing date: 2024-04-05
Publication date: 2026-02-11
Also published as: CN120936480A; JP2026511360A; WO2024209034A1

Abstract

The present disclosure relates to a method for producing a three-dimensional object comprising: computing a plurality of subsinograms, wherein the subsinograms are derived from at least one sinogram describing the three-dimensional object to be formed from different orientation angles; providing a build volume comprising a photosensitive component capable of initiating a photochemical reaction upon irradiation by light of an activation wavelength; irradiating the build volume, by each of a plurality of projection units, with a projection of a series of patterns of light corresponding to one of the subsinograms, at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength, and wherein each projection unit irradiates the build volume with a series of patterns of light that is derived from a different subsinogram, such that the build volume is irradiated by a resulting series of patterns of light corresponding to the sinogram at the corresponding orientation angles.

Description

Print volume upscaling using multiple projectors in tomographic volumetric 3D printing

Technical field

The present disclosure relates to a system and a method for tomographic vat photopolymerization for 3D printing of objects with increased resolution, including the spatial resolution (horizontal and/or vertical) and/or the temporal resolution by means of multiple projection units arranged to irradiate a build volume.

Background

Additive manufacturing (AM) is a technique for fabricating a wide range of structures and complex geometries based on three-dimensional model data. The process relies on the printing of successive layers of materials on top of each other. The technology was originally developed in a process known as stereolithography (SLA).

SLA typically uses UV light to initiate a chain reaction on a layer of resin or monomer solution, for example acrylic or epoxy-based. The monomers are UV-active and convert to polymer chains after activation (radicalization). The polymerization leads to the generation of a pattern inside the resin layer that is solidified, and that can hold the subsequent layers. Following printing, the unreacted resin is removed. Additionally, depending on the material and the desired mechanical properties, post-process treatments such as heating or photo-curing may be applied to the printed object.

While SLA is a versatile method that has gained widespread use, mainly attributing to its success in rapid and cheap prototyping, it suffers from slow printing speeds. This property is inherent to SLA, as it is a layer-by-layer processing method. Once a layer is irradiated and cured, a new layer of uncured material must be provided above or below the solid layer, depending on the build direction. Most commonly, the uncured material is provided by mechanically recoating of the surface, which, in addition to increasing the printing time, may act to distort the formed parts.

Another, more recent, technology is tomographic vat photopolymerization (TVP) wherein a build volume comprising a photosensitive component is irradiated from multiple angles in order to rapidly produce complex materials. The technology thus relies on a completely different approach as compared to layer-by-layer technologies, as it physically reverses the principle of computed tomography (CT) to realize highspeed, auxiliary-free 3D printing.

WO2018/208378 discloses a method of forming an object comprising providing a volume of photo-curable resin contained within an optically transparent resin container, and simultaneously directing optical projections from a plurality of angles about a z-axis extending through the volume of photo-curable resin. The projections act over a fixed temporal exposure period, during which the net exposure dose is sufficient to cure select portions of the volume of photo-curable resin, and to leave other portions uncured.

Tomographic vat photopolymerization is still in its infancy and holds great prospects for the future. However, a significant drawback is the limited resolution attainable, making it difficult to achieve three-dimensional objects having for example small features or sharp corners.

Summary

The present inventors have realized that while the technological field of tomographic vat polymerization (TVP) tomographic has built upon knowledge gained from computed tomography (CT), in that tomographic vat polymerization physically reverses the principle of CT, tomographic vat polymerization is limited by the currently available projection units, which acts to limit the resolution of three-dimensional objects formed by tomographic vat photopolymerization. Further, the present inventors have realized that multiple projection units can be combined in a way such that the resolution (e.g. spatial resolution and/or temporal resolution) offered by each individual projection unit can be combined in order to increase the maximum resolution attainable.

Thus, in a first aspect, the present disclosure relates to a method for producing a three- dimensional object comprising:

• computing a plurality of sets of subsinograms, wherein each set of subsinograms is derived from a set of sinograms, wherein each sinogram describes a layer of the three-dimensional object to be formed from different orientation angles; • providing a build volume comprising a photosensitive component capable of initiating a photochemical reaction upon irradiation by light of an activation wavelength;

• irradiating the build volume with light comprising the activation wavelength, by each of a plurality of projection units, with a projection of a series of patterns of light corresponding to one of the sets of subsinograms, at the corresponding orientation angles, and wherein each projection unit irradiates the build volume with a series of patterns of light that is derived from a different set of subsinograms, such that in total the build volume is irradiated with a resulting series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles.

Typically, the resulting irradiation of the build volume is of a higher resolution than the maximum resolution of any of the individual projection units. The increase in resolution may for example be an increase in the spatial resolution (e.g. horizontal and/or vertical), additionally or alternatively, the resolution increase may be an increase in the temporal resolution.

Another effect of the presently disclosed method is that the three-dimensional object may be produced faster, since the build volume is irradiated with a power that is the sum of the contribution of each projection unit.

Thus, in order to overcome the resolution constraints associated with conventional tomographic vat polymerization, the present inventors have realized that sinograms can be divided in subsinograms such that a three-dimensional object can be manufactured by irradiating a photosensitive component with light patterns from multiple orientation angles and projection units, wherein each subsinogram has an associated projection unit. Thus, each subsinogram may be associated with a different projection unit.

Thereby, the three-dimensional object may be physically reproduced in a resolution (e.g. spatial and/or temporal) that is higher than the maximum resolution of any of the individual projection units. Thus, each projection unit is typically arranged to irradiate, preferably simultaneously or at least partly simultaneously (such that the irradiations overlap in time), the build volume with a series of patterns of light at corresponding angles, typically with light of the same wavelength, wherein the patterns of each projection unit correspond to the subsinogram of the specific projection unit. The resulting irradiation of the build volume typically corresponds to what would only be attainable by a projection unit having a resolution that is higher than any of the individual projection units.

In this way, the resolution of the sinogram, and/or the object, would not be limited by the number of pixels of a single projection unit. Typically, the resolution limit would instead be limited by the chemical reaction of the photosensitive component and/or diffraction limitations of the optical system used to generate the series of patterns of light.

In the general sense, the present disclosure is not limited to a certain number of projection units, and the present disclosure may thus allow for a resolution increase by combining the resolution offered by any number of projection units, for example by virtually stitching of the subsinograms in order to maximize the number of pixels that they could offer to the sinogram, and/or the resulting irradiation of the build volume.

In an further aspect, the present disclosure relates to a method for producing a three- dimensional object comprising:

• computing a set of sinograms describing the three-dimensional object to be formed from different orientation angles;

• providing a build volume comprising a photosensitive component capable of initiating a photochemical reaction upon irradiation by light of an activation wavelength; irradiating the build volume, by each of a plurality of projection units with a projection of a series of patterns of light, such that the build volume is irradiated with a resulting series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles, and wherein the irradiating light comprises the activation wavelength, wherein the projection units have one or more depth of fields that are shorter than the distance of the three-dimensional object, such as along an optical axis, and wherein the focal plane of each projection unit is selected such that the resulting combined depth of field, of all projections units, spans the distance of the three- dimensional object, such as along an optical axis.

In a further aspect, the present disclosure relates to a method for producing a three- dimensional object comprising:

• providing a build volume comprising a photosensitive component capable of initiating a photochemical reaction upon irradiation by light of an activation wavelength;

• irradiating the build volume, by each of a plurality of projection units having the same refresh rate f, with a projection of a series of patterns of light corresponding to the set of sinograms, at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength, wherein at least one of the projection units is arranged to irradiate the build volume with the projection at the corresponding orientation angles with a delay, with respect to the other projection unit(s), that is given by 1/(f nj, wherein n is a natural number.

In this way the temporal resolution may be increased. Typically, n is the number of projection units used to irradiate the build volume with the series of patterns of light. The projection units may for example be arranged to have a delay that is given by l-i f-n and wherein / is a different natural number for each projection unit in the interval [1 ,n],

As such, one of said projection units may have a delay of 0, while each other projection unit has a delay that increases by 1/(fn) for each projection unit.

• computing a set of sinograms describing the three-dimensional object to be formed from different orientation angles; • providing a build volume comprising a photosensitive component capable of initiating a photochemical reaction upon irradiation by light of an activation wavelength;

• irradiating the build volume, by each of a plurality of projection units, with a projection of a series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength.

Thus, each projection unit may be arranged to illuminate the build volume with a series of patterns of light that correspond to the sinogram. However, the use of multiple projects may for example lead to a faster production time, as the power applied to the build volume during the step of irradiation is equal to the sum of the contribution of each projection unit. The projection units don’t have to be synchronized, and may have different refresh rates, but may be arranged to start and/or stop irradiation of the build volume at the same time.

In a further aspect, the present disclosure relates to a system for producing a three- dimensional object, the system comprising:

• a processing unit configured for computing a plurality of sets of subsinograms, wherein each set of subsinograms is derived from a set of sinograms, wherein each sinogram describes a layer of the three- dimensional object to be formed from different orientation angles;

• a build volume comprising a photosensitive component capable of a photochemical reaction upon irradiation by light of an activation wavelength;

• a projection system comprising a plurality of projection units capable of irradiating the build volume by a series of patterns of light comprising said activation wavelength;

• a direction adjustment unit for controllably varying a direction of incidence of light of the projection units relative to said build volume; and

• a controller configured for controlling the direction adjustment unit and the projection system such that the build volume is irradiated with light comprising the activation wavelength, by each of a plurality of projection units, with a projection of a series of patterns of light corresponding to one of the sets of subsinograms, at the corresponding orientation angles, and wherein each projection unit irradiates the build volume with a series of patterns of light that is derived from a different set of subsinograms, such that in total the build volume is irradiated with a resulting series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles.

• a processing unit configured for computing a set of sinograms describing the three-dimensional object to be formed from different orientation angles;

• a build volume comprising a photosensitive component capable of a photochemical reaction upon irradiation by light comprising an activation wavelength;

• a projection system comprising a plurality of projection units having the same refresh rate and capable of irradiating the build volume by a series of patterns of light comprising the activation wavelength;

• a controller configured for controlling the direction adjustment unit and the projection system such that the build volume is irradiated, with a projection of a series of patterns of light corresponding to the set of sinograms, at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength, wherein at least one of the projection units is arranged to irradiate the build volume with the projection at the corresponding orientation angles with a delay, with respect to the other projection unit(s), that is given by 1/(f nj, wherein n is a natural number.

In a further aspect, the present disclosure relates to a system for producing a three- dimensional object, the system comprising: • a processing unit configured for computing a set of sinograms describing the three-dimensional object to be formed from different orientation angles;

• a projection system comprising a plurality of projection units capable of irradiating the build volume by a series of patterns of light comprising the activation wavelength;

• a controller configured for controlling the direction adjustment unit and the projection system such that the build volume is irradiated, with a projection of a series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength.

Typically, the build volume is irradiated with a resolution that is higher than the maximum resolution of any of the individual projection units. A further possible effect is that the three-dimensional object may be produced faster, since the build volume is irradiated with a power that is the sum of the contribution of each projection unit.

The increase in resolution may for example be an increase in the spatial resolution (e.g. horizontal and/or vertical), additionally or alternatively, the resolution increase may be an increase in the temporal resolution.

The presently disclosed systems are preferably configured to carry out the methods for producing a three-dimensional object, as disclosed elsewhere herein.

Advantageously, the methods disclosed herein allows for an increase of the resolution of tomographic vat photopolymerization, such as the resolution of the sinogram describing the three-dimensional object to be formed from multiple orientation angles, including one or more of the horizontal resolution, the vertical resolution and/or the temporal resolution. Horizontal and vertical resolution increase relies on the use of multiple projection units, and by dividing the sinogram among the different projection units in order to reach the maximum number of pixels allowable with that specific setup. Horizontal and vertical resolution may be increased simultaneously; the virtual stitching is thus carried out both in the horizontal plane and the vertical plane.

In addition, the temporal resolution may be increased by synchronizing the projection of multiple projection units. This is done by having multiple projection units that have an overlapping virtual alignment of their fields of projections. While a single projector has a finite temporal resolution, e.g. 60 Hz, the temporal resolution of multiple projection units are given by 1/(f n) where f is the refresh rate and n the number of projection units.

Thus, the irradiation may be arranged such that the build volume is irradiated in a temporal resolution that is higher than any of the temporal resolutions (i.e. the refresh rates) of the individual projection units, and/or at a temporal resolution of up to the sum of the maximum refresh rate of all the projection units. Thus, each projection unit is arranged to irradiate the build volume with a series of patterns of light corresponding to one individual subsinogram, at the respective corresponding orientations, such that the build volume is illuminated with a series of patterns of light corresponding to the sinogram.

Thereby, this approach allows for an increase in the power output (e.g. in Mw/cm²) to shorten the printing time by an overlapping virtual alignment of the field of projections from multiple projection units. However, to increase the power output to shorten the printing time no synchronization is needed.

Description of Drawings

In the following embodiments, the examples will be described in greater detail with reference to the accompanying drawings:

Fig.1 shows a schematic illustration of a system comprising multiple projection units, according to an embodiment of the present disclosure . Fig. 2 shows a sinogram and the virtual alignment of fields of projections, for example for increasing the horizontal resolution, according to an embodiment of the present disclosure.

Fig. 3 shows the sinogram of 2A divided into multiple subsinograms, according to radial indices, and wherein the angular indices of the subsinograms are shifted to compensate for the relative orientation of the different projection units, according to an embodiment of the present disclosure.

Fig. 4 shows a virtual alignment for increasing the horizontal and vertical resolution, as compared to a single projection unit, according to an embodiment of the present disclosure.

Fig. 5 shows the increase in output power achieved by the use of multiple projection units, according to an embodiment of the present disclosure.

Fig. 6 shows a schematic illustration of a system for increasing the temporal resolution by synchronization of several projection units, according to an embodiment of the present disclosure.

Fig. 7 shows a flowchart outlining a method for producing a multi-material three- dimensional object according to a specific embodiment of the present disclosure.

Fig. 8 shows a flowchart outlining a method for producing a multi-material three- dimensional object according to a specific embodiment of the present disclosure.

Fig. 9 shows a flowchart outlining a method for producing a multi-material three- dimensional object according to a specific embodiment of the present disclosure.

Fig. 10 shows a tomographic vat photopolymerization system for producing a three- dimensional object from a build volume according to a specific embodiment of the present disclosure. Fig. 11 shows an example of a system of the present disclosure comprising a plurality of projection units, wherein the focal plane of each projection unit is shifted with respect to the center of the build volume.

Fig. 12 shows a schematic illustration of resulting virtual alignment of the focal planes of Fig. 11, resulting in multiple projection units having a combined depth of field that spans the workpiece.

Fig.13 shows a schematic illustration of a system comprising multiple projection units, according to an embodiment of the present disclosure, and a sinogram divided into subsinograms by the angular index.

Detailed description

As used herein, the singular forms “a”, “an” and “the” include plural referents unless the context clearly states otherwise.

The term “some embodiments” can include one, or more than one embodiment.

As employed herein "plurality" means at least two. However in many instances at least four and sometimes at least ten or up to an indefinite number of projection units are used.

In a first aspect, the present disclosure relates to a method for producing a three- dimensional.

Sinogram

In CT and SPECT imaging, a sinogram is generated by rotating detectors around a patient, and storing the detected projection profiles at each angle in the sinogram. Tomographic vat polymerization can be said to reverse this process, in that a series of patterns of light, corresponding to the sinogram, is projected onto the build volume in order to form a three-dimensional object. The sinogram may however be modified in order to more correctly produce the three-dimensional object, as may also be done in CT/SPECT imaging when performing a back projection in order to accurately reconstruct the three-dimensional object. For example the sinogram may be modified in order to comprise negative intensity values in order to more accurately reproduce the three-dimensional object.

In order to describe a three-dimensional object to be formed from multiple orientation angles, a set of sinograms/subsinograms are typically needed, as each individual sinogram typically only describes a single layer of said object, from multiple orientation angles. The height of each layer, as described by the sinogram, typically corresponds to the height of the voxels of the build volume. Thus, the thickness of the layer described by a sinogram is typically the thickness of the voxels of said layer, typically perpendicular to the orientation angles of the sinograms. Typically, the sinograms describe the object in the horizontal plane. The rotation of the build volume (and/or the projection units) are carried out with an axis of rotation that is typically perpendicular to the plane at which the sinograms describe the object from. Thus, typically, the sinograms describe the object from multiple orientation angles in a horizontal plane, and the axis of rotation is vertical and typically through the center of the build volume.

Virtual alignment, as used herein, refers to the use of multiple projection units to create a resulting high resolution pattern of light, as given by a set of sinograms, by the use of multiple projections units wherein each projection unit is assigned a set of subsinograms. The set of sinograms corresponds to a series of patterns of light from multiple orientation angles, necessary to produce the three-dimensional object. As an example, by just considering the pattern of light corresponding to a single angular index of the set of sinograms. This pattern can be created by aligning the patterns of light of multiple projection units. As the different projection units have different orientation angles with respect to the build volume, the timing of the different projection units have been shifted, and thus the patterns of light can be said to be virtually aligned.

In order to overcome the resolution constraints associated with tomographic vat polymerization, one or more sinograms can be divided into subsinograms, such that a three-dimensional object can be manufactured by irradiating a photosensitive component with light patterns from multiple angles and projection units.

A two-dimensional object may be described by a sinogram, while a three-dimensional object may be described by a set of sinograms. For example, each layer of the three- dimensional object may be represented by a different sinogram, of the set of sinograms. Furthermore, a sinogram may be divided into two or more subsinograms. Similarly, a set of sinograms may be divided into two or more sets of subsinograms. In specific examples, a set of sinograms may be used to describe a three-dimensional object to be formed, from corresponding orientation angles. Said sets of sinograms may be divided into two or more sets of subsinograms, that together describe the three-dimensional object to be formed, from corresponding orientation angles. Each set of subsinograms may for example describe different spatial or temporal parts of the three-dimensional object to the formed. Furthermore, the set of subsinograms may be used to modify the depth of field as described herein.

Typically, the projection units are arranged to irradiate the build volume (i.e. the photosensitive component of the build volume) at least partly simultaneously, e.g. such that at least part of the irradiations from the plurality of projections overlap in time. It is also a preference that each sinogram is associated with a single wavelength, or at least a narrow spectral band, typically a wavelength/band at which the photosensitive component is sensitive to light, e.g. such that it may form a polymerization of a monomer of the build volume at this wavelength(s). Thus, the series of patterns of lights, used to irradiate the build volume, should be irradiated at this specific wavelength(s). In specific examples of the present disclosure, multiple sinograms are used in order to represent the three-dimensional volume. In such cases each sinogram may be associated with a separate wavelength(s) and wherein each wavelength is chosen such that it activates a separate photosensitive compound of the build volume. Thus, in such a case, the build volume may comprise multiple different photosensitive materials/components. For example in order to generate a three-dimensional object of different material as disclosed in W02022/090318. However, in the present disclosure, each sinogram is used to derive a plurality of subsinograms, where each subsinogram is associated with a separate projection unit, as disclosed herein.

A sinogram includes any two-dimensional array of numerical values in which one index is radial (i.e. a radial index, (16) in Fig. 2A), and the other index is angular (i.e. an angular index, (17) in Fig. 2B).

Typically, each line of the sinogram, i.e. the same angular index, may comprise values, such as an intensity value, that may vary according to their radial index. Thus, the sinogram may determine the pixel values of a projection unit, e.g. for a single line of pixels. Further, a set of sinograms may be used, wherein each sinogram of the set has a different vertical index. The series of patterns of light irradiated by a projection unit may be given by irradiating the build volume with a pattern of light that is given by the values of the radial, angular and vertical indices. I.e. the radial indices may describe the intensity values along a plane such as a horizontal plane, the vertical indices may describe the intensity values along another plane such as a vertical plane. I.e. radial and vertical indices may correspond to the x and y axis of a pattern of light. The angular indices represent the corresponding orientation angles between the projection unit and a plane of the build volume.

As the build volume rotates with respect to the projection units, each pattern of light, of the series of patterns of light may be given by a different angular index. Thus, for other embodiments, wherein the build volume does not rotate with respect to the projection units, e.g. in case of multiple stationary projection units, e.g. one or more digital micromirror devices, the relative orientation angle between the projection unit and the build volume determines the pattern of light that is to be irradiated onto the build volume by said projection unit. The orientation angle is therefore linked to the angular index of the sinogram.

Thus, in one example, the intensity values at a particular angular index of each sinogram within a set of sinogram, may determine the intensity values along a first axis of a pattern of light that irradiates the build volume. The different sinograms of the set may be used to create a projection, as each sinogram may correspond to a single line of said projection. Thus, each value of a set of sinograms, may be assigned a radial index, an angular index, and a vertical index, wherein each sinogram of said set has a different vertical index.

Further, as disclosed elsewhere herein, each sinogram of said set of sinograms may be divided by their radial index and assigned to a different projection unit. In this way, each projection unit may be arranged to only illuminate a part of the build volume (e.g. a part of the workpiece). The angular index of each set of subsinograms are typically shifted to compensate for the different relative orientation angles of the projection units, such as if they are positioned at different orientations with respect to the build volume. Examples of a sinogram include a collection of projections, a collection of radially filtered projections, and a collection of synthetic-aperture-radar (SAR) data that has been radially-inverse-Fourier-transformed, and the like.

In one embodiment of the present disclosure, the method disclosed herein comprises a step of computing a number of subsinograms describing a three-dimensional object to be formed from different orientation angles of said object. The method may for example comprise computing a sinogram and thereafter generating the subsinograms.

The subsinograms may for example be derived by subdividing the sinogram into a plurality of subsinograms describing the sinogram of said object to be formed by the plurality of projection units. Thus, the subsinograms may be parts of the sinograms, wherein said parts have been modified by an angular shift in order to compensate for the position of the projection unit with respect to the build volume. The number of subsinograms may thus be a multiple of the number of sinograms.

The subsinograms may be used to illuminate a series of patterns of light onto the build volume. In some embodiments the projection of the projection unit is arranged such that each horizontal line of pixels corresponds to one pattern (i.e. of a corresponding orientation angle) of one subsinogram. However, the projection may comprise one such pattern for each horizontal line, thus each projection unit may be arranged to illuminate the build volume by multiple patterns of lights, each based on a subsinogram associated with the specific projection unit. Thus, typically, the projection unit has a number of pixels in the horizontal direction (i.e. the horizontal resolution of the projection unit) that is used to illuminate the build volume with a series of patterns of light based on a subsinogram, at the corresponding orientation angles. Further, the projection unit typically has a number of pixels in the vertical direction (i.e. as defined by the vertical resolution of the projection unit). Each horizontal row may, as stated above, be assigned to illuminate the build volume with a series of patterns of light corresponding to a subsinogram, at the corresponding orientation angles.

In some embodiments of the present disclosure, the sinograms are computed using any one of the following list: a Radon-transform followed by a tomographic reconstruction filter; a fan-beam algorithm followed by a tomographic reconstruction filter; and/or a cone-beam algorithm followed by a tomographic reconstruction filter. The sinograms may for example be formed by the application of a Radon-transform followed by a tomographic reconstruction filter. The resulting projections may be two- dimensional patterns that each have a corresponding orientation angle. Irradiation of the build volume may be carried out by the use of multiple projection units, which may irradiate the build volume from different angles, or a single light source may be used. It is however a preference that the light patterns irradiate the build volume at a similar wavelength distribution.

In some embodiments of the present disclosure, said sinograms are computed, at least in part, by using any one of the following projection algorithms: a Radon-transform; a fan-beam algorithm; a cone-beam algorithm, a tomographic reconstruction filter; an iterative reconstruction technique; an algebraic reconstruction technique; and/or a diffractive tomography algorithm, or a combination thereof.

Consequently, the computation may comprise the application of a Radon-transform followed by a tomographic reconstruction filter; a fan-beam algorithm followed by a tomographic reconstruction filter; a cone-beam algorithm followed by a tomographic reconstruction filter; an iterative reconstruction technique; an algebraic reconstruction technique; or a diffractive tomography algorithm, or a combination thereof. In an embodiment of the present disclosure, the sinograms are obtained by application of at least one projection algorithm to a computer-based model. The method may therefore be seen as a method for producing a three-dimensional object that is a reproduction of said computer-based model. In an embodiment of the present disclosure, the method is a computer-implemented method or a processor-implemented method.

In some embodiments of the present disclosure, the sinogram is divided into subsinograms. Typically, each subsinogram has a number of pixels in the axial direction similar or equivalent to the number of pixels of the associated projection unit (the projection unit used to illuminate the build volume with a series of patterns of light corresponding to this specific subsinogram), typically in the same axial direction.

In some embodiments of the present disclosure, all projection units are arranged to initiate irradiation of the build volume at the same time. Typically, wherein each projection unit is arranged to irradiate the build volume at different orientations with respect to the build volume, as shown for example in Figure 1. The projection units may be positioned at an off-centered position, and/or the projection units may be provided with optical focusing means, such that the patterns provided by each projection unit are virtually aligned across the build volume, as can be seen in Figure 2B. In this example, each pattern of light/field of projection, has been provided at a specific incidence angle, depending on the position of the projection unit in relation to the focal plane of said unit and the area of said focal plane that the specific projection unit is arranged to irradiate. However, one or more, such as all of the projection units may be arranged to irradiate their assigned field (as shown in Figure 2B) of the focal plane perpendicular to the focal plane. In such a case, the patterns would not be provided at an angle with respect to the focal plane. However, as can be seen in Figure 2B, provided the patterns at an angle with respect to the focal plane, may contribute to increasing the spatial resolution even further, as each projection unit irradiates each respective focal plane with a higher number of pixels.

In some embodiments of the present disclosure, each subsinogram needs to be shifted vertically, according to the difference between its projecting orientation and a reference plane. In this way, a virtual alignment of the projection units, according to for example Figure 2B may be generated.

In some embodiments of the present disclosure, the reference plane is the focal plane of one of the projection units. Typically the reference plane and/or focal plane intersects with the centre of rotation of the build volume, and/or the centre of rotation of the projection units around the build volume. Typically, the centre of rotation is the physical centre of the build volume, such as in the horizontal plane when the axis of rotation is a vertical axis. However, in other embodiments, the focal planes of a plurality of projection units may be arranged at different positions in the build volume, for example, the focal planes may be arranged at different distances with respect to the centre of the build volume. In this way, a plurality of projection units may be arranged to have a focal plane along different distances of an optical axis, e.g. at different positions with respect to the centre of the build volume.

In some embodiments of the present disclosure, the output curves of the projection units are unified. Calibration is needed when calculating printing patterns for various projection units. The correlation between gray value and output power is in general different for each projector (especially if not from the same brand). The desired gray value I2’ of the projection unit 2 is calculated so that a light pattern would produce exactly the same outputs with different projection units (Projectors 1 and 2), even though their “Gray Value - Output Power” correlations differ. This is calculated by I'₂ =

Projection units

The number of projection units, which can be used to generate the three-dimensional object, can in theory be indefinite. In some embodiments, the different projection units can be different types of projectors, such as DLP, LEP, LCD and/or other types of projection units such as digital micromirror devices. The projection units may therefore have the same or different resolutions, i.e. spatial and/or temporal resolution. Further, the projection units may have different irradiation power. As such, the projection units may be different models and/or brands of projection units.

As used herein the term projection system refers to a system comprising multiple projection units. The projection units of the projection system are typically located separate from each other, but arranged to irradiate the build volume, in order to produce the three-dimensional object. Typically, wherein the build volume is irradiated while being rotated.

In some embodiments of the present disclosure, the patterns are irradiated by a projection unit. Any type of system that is capable of irradiating the build volume with a series of patterns of light may be used as a projection unit. Typical examples of a projection unit are DLP projectors, LED Projectors, LCD projectors, Laser projectors, spatial light modulators and optoelectromechanical systems, such as digital micromirror devices, that may be coupled with a light source. Further, the projection unit may be a light source, such as a LED, covered with a microlens. Further, the projection unit may be a part of a projection system, wherein the projection system comprises an array of light sources, such as an OLED array covered by microlenses. Other projection units are known to the skilled person.

In some embodiments of the present disclosure, the series of patterns of light are irradiated by a projection unit, such as wherein the projection unit is a DLP projector. In a DLP projector, such as a conventional 3-color channel DLP projector with red, green, and blue color channels, each pixel in an image or image frame has intensity values for the red, green, and blue components that together form the pixel. To achieve the intensity values for each component, each of the mirrors of the array of micromirrors of DMD are controlled to rapidly turn on and off (i.e. turned toward or away from the projection environment) to create light pulses which together form the desired intensity. The process of rapidly controlling the on/off state of the micromirrors is sometimes referred to as a pulse sequence or mirror flip sequence.

In some embodiments of the present disclosure, the series of patterns of light are irradiated by a projection unit, such as wherein the projection unit is an LED Projector. In operation, the LED projector of the present subject matter may operate in one or more projection modes. A projection mode may be understood as a configuration of the LED projector used for projection of data.

In some embodiments of the present disclosure, the series of patterns of light are irradiated by a projection unit, such as wherein the projection unit is an LCD projector.

In some embodiments of the present disclosure, the patterns are irradiated by a projection unit, such as wherein the projection unit is a Laser projector. A laser projector may have various laser light sources, which may include: at least one laser transmitter, wherein the laser light source is able to emit light of at least one color. Generally, the laser light source may also include: a fluorescent wheel (also referred to as a fluorescence color wheel), which may serve as a wavelength transformation device. The laser light source may be a monochromatic laser light source (i.e., include one kind of laser transmitter which generates one color), and may also be a dual-color laser light source (i.e., include two kind of laser transmitters which each generate one color), so as to emit laser of one or two colors. The fluorescent wheel is provided with fluorescent powder which may be excited to generate fluorescence of corresponding colors, which jointly forms three primary colors along with the color of the laser emitted by the laser transmitter, thus acting as a projection light source for providing lighting to optical parts. The light source parts of the laser projector include at least a laser transmitter and a fluorescent wheel. The optical parts of the laser projector include at least an imaging element and a projection lens, wherein the imaging element can be a DMD element or a LCOS element.

In some embodiments of the present disclosure, the plurality of projection units are located separate from each other. In some embodiments of the present disclosure, the focal planes of the projection units are aligned. In some embodiments of the present disclosure, the number of projection units is unlimited. In some embodiments of the present disclosure, the number of projection units is at least 2, such as at least 5, such as at least 10, such as at least 100, such as at least 1000. In theory the number of projection units is indefinite.

In some embodiments of the present disclosure, each projection unit is configured for projecting light at an activation wavelength, preferably wherein said activation wavelength comprises an activation wavelength of the photosensitive components, such as the activation wavelength of a photoinitiator. In some embodiments, wavelength includes a spectral range of wavelengths, such as a spectral peak having a 25 nm, 50 nm, 75 nm, 100 nm, 125 nm, 200 nm range on both sides of the spectral peak. In some embodiments of the present disclosure, each projection unit irradiates the build volume with the same wavelength. In some embodiments of the present disclosure, each projection unit irradiates the build volume with a different wavelength, such as at least 1 nm difference, such as at least 5 nm difference, such as at least 50 nm difference, such as at least 100 nm difference, such as at least 500 nm difference. In some embodiments of the present disclosure, each projection unit irradiates the build volume with a different wavelength, such as at less than 500 nm difference, such as less than 100 nm difference, such as less than 50 nm difference, such as less than 5 nm difference, such as less than 1 nm difference.

In some embodiments of the present disclosure, the activation wavelength is in the UV (ultraviolet) range. In some embodiments of the present disclosure, the activation wavelength is in the visible light range.

In some embodiments of the present disclosure, the step of irradiating comprises:

• irradiating the build volume, individually by each of a plurality of projection units, with a number of patterns of light that are defined by the subsinogram allocated to the corresponding projection unit; wherein each projection unit is located separate from each other, such as wherein each projection unit is arranged with a different orientation angle with respect to the build volume (such as the centre of the build volume). The build volume may be arranged to rotate around an axis of rotation that intersects the centre of the build volume. Typically the axis of rotation is perpendicular to the plane of the projection units, however one or more of the projection units, such as all, may be located outside of said plane. For example, one or more of the projection units, such as all, may be located in different planes, such as planes that are perpendicular to the relative axis of rotation with respect to the build volume. Alternatively, or additionally, the projection units may be arranged to revolve/rotate around the build volume.

In some embodiments of the present disclosure, the patterns of light are irradiated in a mask-less process, such as without a photomask.

Resolution

Resolution of the projection units refers to the number of pixels available for projection onto the build volume. By combining the resolution of multiple projection units according to the present disclosure, the total resolution of the system increases. As a result, also the resolution of the sinogram can be increased, and further the resolution of the object to be formed (the number of voxels).

Thus, the projection units of the present disclosure may have a certain resolution. Depending on the desired characteristics of the object to be formed, specific parts of the objects may be irradiated with a higher number density of pixels (pixels per area) than others. In such instances, one or more of the projects may be arranged to irradiate parts where a higher number density of pixels are desired while one or more other projection units are arranged to irradiate another part of the object to be formed with a lower number density of pixels.

Increasing the resolution would thus result in 1) an increase in the total volume, if the size of each pixel and/or voxel is kept constant, and/or 2) an increase in the total number of voxels used for defining the three-dimensional object, if the total volume is kept constant.

In some embodiments of the present disclosure, the spatial resolution can be increased by keeping the size of each voxel while increasing the total volume. In some embodiments of the present disclosure, the spatial resolution can be increased by keeping the total volume while increasing the total number of voxels it contains.

As used herein, the term voxels refer to each of an array of elements of volume that constitute a notional three-dimensional space, especially each of an array of discrete elements into which a representation of a three-dimensional object is divided, such as a three-dimensional object. The voxel size is typically determined by the printing resolution. Smaller voxels (i.e. a higher printing resolution) typically allow for a higher degree of details being reproduced, and a higher printing accuracy. The size of the voxel may be the resolution of the method, as the properties of the three-dimensional object are defined for each voxel of said object. Contrary to this, points, or pixels, typically refers to discrete points, such as the smallest addressable discrete element.

In some embodiments of the present disclosure, each projection unit has a maximum resolution.

In some embodiments of the present disclosure, the spatial resolution can be increased in the vertical direction and/or the horizontal direction. Figure 4A shows an embodiment of the present disclosure wherein the virtual alignment has been arranged such that both the vertical and the horizontal resolution increases. In this example, four projection units are used, having different aspect ratios, and wherein each projection unit is arranged to irradiate a different part of the focal plane. The virtual alignment also includes overlapping parts, which can either be used to increase the resolution of the object at the corresponding parts, which can be suppressed by blocking at least part of the light from one or more projectors in the overlapping areas.

In some embodiments of the present disclosure, the spatial resolution is limited by the size of the photosensitive component.

In some embodiments of the present disclosure, the three-dimensional object is reproduced in a number of voxels of the build volume, and wherein the step of computing comprises defining subsinograms of the sinogram and allocate each subsinogram to one projection unit. Deriving the subsinograms may be based on the positions and/or orientations of the projection units with respect to the centre of the build volume. In one example a sinogram, as used for a simple system comprising a single projection unit to irradiate a build volume, is divided into multiple subsinograms, wherein each subsinogram is associated with a projection unit, and wherein the radial angle is shifted based on the position of the projection unit. However, the subsinograms may further be modified based on whether the projection unit is out of plane and/or the orientation with respect to the centre of the build volume. In some embodiments of the present disclosure, the spatial resolution of each point of the reproduced three-dimensional object is defined by the sum of the resolution of each projection unit. In some embodiments of the present disclosure, the horizontal resolution of each point of the reproduced three-dimensional object is defined by the sum of the resolution of each projection unit. In some embodiments of the present disclosure, the vertical resolution of each point of the reproduced three-dimensional object is defined by the sum of the resolution of each projection unit.

Refresh rate

Theoretically, the temporal resolution is indefinite if the number of projection units is indefinite. In some embodiments, temporal resolution is increased by synchronizing the irradiation of multiple projection units, thereby resulting in a virtual frame rate that is higher than the frame rate of each individual projection unit. Each projection unit typically is typically individually arranged to irradiate a series of patterns of light, corresponding to the subsinogram of each individual projection unit, wherein the subsinograms have been radially shifted to compensate for the position and/or orientation of the specific projection unit (thereby forming a virtual radial alignment of the projection units). However, in addition each projection unit may be arranged to irradiate the build volume with a specific delay, that is typically given by the refresh rate of the projection units divided by the number of projection units. In this way, the resulting irradiation may correspond to using a single projection unit that has a refresh rate that is equal to the sum of the refresh rates of the projection units of the aforementioned example. Thus, by increasing the temporal resolution of the system (i.e. the frame rate) A better temporal resolution is able to better

Further, the use of multiple projection units leads to an increased power output (e.g. in Mw/cm²) allowing for a decreased printing time. In such an instance, it may not be necessary to synchronize the irradiation of the projection units.

In some embodiments of the present disclosure, the spatial and temporal resolution of each point of the reproduced three-dimensional object is increased.

In some embodiments of the present disclosure, each projection unit has a maximum refresh rate. In some embodiments of the present disclosure, the temporal resolution of each point of the reproduced three-dimensional object, is defined by the sum of the refresh rates of each projection unit.

In some embodiments of the present disclosure, the projection of each projection unit is delayed by 1/fn, wherein f is the refresh rate and n the number of projection units.

In some embodiments of the present disclosure, the total power output provided to the build volume is the sum of the power output of each individual projection unit.

Depth of field

TVP's ultra-high 3D-printing speed is conditioned on a sufficient power output of the projection units used to irradiate the build volume. The larger the aperture of a projection unit, the greater the output power. At the same time, it is advantageous to irradiate with a depth of field that is greater than a dimension of a workpiece, e.g. in order to ensure the same fabrication precision throughout the entire workpiece.

Thus, for a single projection unit system, in order to have a depth of field that is at least the length, such as along an optical axis, of the workpiece, the aperture size may pose a limit on the output power used to irradiate the build volume. Thereby leading to e.g. increased print times, in case the aperture is sufficiently small such that the depth of field is at least the distance of the workpiece/object to the formed, as mentioned above.

As disclosed elsewhere herein, in order to counteract this, it is possible to combine multiple projection units in such a way, that their individual irradiation results in the same three-dimensional energy distribution. Thus, the power output/intensity provided by each projection unit to irradiate the build volume is added up in order to decrease the printing time.

Further, alternatively to using multiple projection units each having a depth of field that is at least the distance, along the optical axis, of the workpiece, the build volume may be irradiated with a plurality of projection units that each has a larger aperture and consequently larger power output, but as a result shorter depth of field. By virtually aligning said projection units, such that they, collectively, have a depth of field that spans the distance of the workpiece, e.g. along the optical axis, the printing times may be reduced, as shown in Fig. 11-12. Photosensitive component

As used herein, the term photosensitive component is a material that changes its properties when exposed to electromagnetic radiation, typically light in the visible and/or ultraviolet region. These changes are often manifested structurally, for example hardening of the material occurs as a result of cross-linking when exposed to light. The material may comprise a photoinitiator, and/or a photosensitizer, in order to be activated by said electromagnetic radiation. Activation may lead to polymerization of other parts of the photosensitive component, such as a monomer and/or a prepolymer.

As used herein, the term prepolymer refers to a monomer, or system of monomers, that have been reacted to an intermediate molecular mass state, that is capable of polymerization, or further polymerization, by reactive groups to a higher molecular weight state.

In some embodiments of the present disclosure, the prepolymers are selected from the list including acrylate monomers, epoxy monomers, or a combination thereof. In some embodiments of the present disclosure, the prepolymers are acrylate monomers. In some embodiments of the present disclosure, the prepolymers epoxy monomers.

In an embodiment of the present disclosure the photosensitive component comprises a prepolymer, such as a monomer; and a photoactivator such as a photosensitizer, a photoinitiator, or a mixture thereof. Preferably the photosensitive component is configured such that it is activated by irradiation of light, and wherein said activation leads to a polymerization of the prepolymer. The activation is typically generated through activation of the photoactivator that in turn generates, typically through catalysis, polymerization of the prepolymer. Commonly, the photoactivator is susceptible to activation in a specific wavelength range/wavelength distribution. For photoinitiation to proceed efficiently the absorption bands of the photoinitiator must overlap with the emission spectrum of the source, i.e. the wavelength distribution used for polymerization of that specific photosensitive component, and there should preferably be minimal competing absorption by the components of the formulation at the wavelengths corresponding to photoinitiator excitation.

In some embodiments of the present disclosure, the photosensitive component is capable of a photochemical reaction upon irradiation of light at an activation wavelength. The activation wavelength, and/or the irradiation wavelength, may comprise or consist of a wavelength distribution that each consist of a single wave, or multiple wavelengths, such as a wavelength band/wavelength range or multiple separate wavelengths.

As used herein, the term photoinitiator refers to a molecule that absorbs photons (typically of a certain wavelength(s)) upon irradiation with light and forms reactive species out of the excited state, which initiate consecutive reactions. The initiating species may be radicals, cations, or anions. Different photoinitiators are distinguished by the wavelength range in which they present high-energy absorption, and are thus readily described by their unique absorption spectra. The choice of excitation light source wavelength and photoinitiator composition are thus typically inextricably linked to one another.

In some embodiments of the present disclosure, the photoinitiators are selected from the list including free radical photoinitiators, cationic photoinitiators, or a combination thereof. In some embodiments of the present disclosure, the photoinitiators are free radical photoinitiators. In some embodiments of the present disclosure, the photoinitiators are cationic photoinitiators.

Photoinitiators are molecules that are sensitive to light. Upon light absorption they undergo photochemical cleavage to produce reactive species (either free radicals or a Bronsted or Lewis acid) that will interact with the active components in formulations. There are 2 classes of photoinitiators: Type I and Type II, wherein Type I photoinitiators are those that undergo unimolecular bond cleavage after absorption of light to render the reactive species. No other species are necessary in order for these photoinitiators to work. Type II photoinitiators undergo a bimolecular reaction. After absorption of light, the photoinitiator reaches an excited state from which it reacts with another molecule (co-initiator or synergist) to create the reactive species. A photosensitizer is a molecule that produces a chemical change in another molecule in a photochemical process.

As used herein, the term polymerization is a process of reacting prepolymer and/or monomer molecules together in a chemical reaction to form polymer chains or three- dimensional networks. Photopolymerization reactions are typically chain-growth polymerizations which are initiated by the absorption of visible or ultraviolet light. The light may be absorbed either directly by the reactant monomer (direct photopolymerization), or by a photosensitizer or a photoinitiator.

In some embodiments of the present disclosure, the photochemical reaction leads to polymerization of the build volume at the irradiated voxels.

In one embodiment of the present disclosure, the photosensitive component(s) comprises:

• a prepolymer, such as a monomer; and

• a photoinitiator that is activated upon irradiation by light with the activation wavelength, wherein activation of the photoinitiator polymerizes the prepolymer.

Relative angle

It is a preference that the orientation and/or the position of at least one of the build volume and the projection unit is modified during irradiation of the build volume. For example, the projection unit may revolve around the build volume, with the projection constantly pointed towards a center, such as the horizontal center, of the build volume, while the build volume is stationary. Alternatively, the build volume may rotate, typically with a rotation axis that is perpendicular to the plane of projection. Several configurations of the positioning and/or the orientation of the build volume and the projection unit is possible to reconstruct a three-dimensional object, as known by a person skilled in the art. In some embodiments, multiple projection units are used, wherein the projection units are positioned at separate positions, for example, each projection unit may be positioned at the corresponding position of each projection.

As mentioned, multiple configurations of the projection unit and the build volume are possible, and are known to the skilled person within the field of tomographic vat photopolymerization. In some embodiments of the present disclosure the build volume is rotating around a vertical rotational axis that intersects the center of said build volume. In some embodiments of the present disclosure, the patterns of light are generated by a projection unit that is projecting said patterns of light substantially parallel to a plane of rotation of the build volume. In some embodiments of the present disclosure the patterns of light are generated by a projection unit that is projecting said patterns of light substantially perpendicular to a plane of rotation of the build volume. In some embodiments of the present disclosure the patterns of light are generated by a projection unit that is revolving around the build volume and projecting said patterns of light towards said build volume.

Application

Printing technologies can be used to create three-dimensional objects from data output of a computerized modeling source. For example, one can design a three-dimensional object using a computer program, and the computer can output the data of the design to a system capable of forming the solid three-dimensional object, such as the system of the present disclosure.

In some embodiments of the present disclosure, the build volume comprises cells, and wherein the system may be arranged such that upon irradiation of the build volume, the cells are incorporated into the three-dimensional object.

In some embodiments of the present disclosure, the three-dimensional object is an artificial tissue, such as for in vitro drug screening or in vivo grafting.

In some embodiments of the present disclosure, the build volume comprises cells, such as undifferentiated stem cells, for example iPS cells.

In some embodiments of the present disclosure, the three-dimensional object is a personalized earmold for hearing-aid or music buds.

In some embodiments of the present disclosure, the three-dimensional object is a custom sealing for swimming glasses.

In some embodiments of the present disclosure, the three-dimensional object is a microfluidic device.

In some embodiments of the present disclosure, the three-dimensional object is a lab- on-a-chip device or an organ-on-a-chip device.

In some embodiments of the present disclosure, the patterns of light are produced and/or irradiated by a DLP projector, LED Projector, LCD projector and/or a Laser projector. It is in general a preference that the patterns are irradiated onto the build volume in a mask-less process, such as without the use of a photo-mask. In some embodiments of the present disclosure, the patterns are produced by a DLP projector. In some embodiments of the present disclosure, the patterns are produced by a LED Projector. In some embodiments of the present disclosure, the patterns are produced by LCD projector. In some embodiments of the present disclosure, the patterns are produced by a Laser projector. In some embodiments of the present disclosure, the patterns are irradiated by a DLP projector. In some embodiments of the present disclosure, the patterns are irradiated by a LED Projector. In some embodiments of the present disclosure, the patterns are irradiated by a LCD projector. In some embodiments of the present disclosure, the patterns are irradiated by a Laser projector.

In some embodiments of the present disclosure, the method is a computer- implemented method or a processor-implemented method.

System

In some embodiments of the present disclosure, the system is configured for carrying out the method for producing a three-dimensional object, as disclosed elsewhere herein.

As used herein, the term direction adjustment unit refers to a system that is configured for controlling the relative orientation of the build volume and/or the projection units. For example, the direction adjustment unit may comprise a direction adjustment unit configured for rotating the build volume, such as while the projection units are stationary, thereby irradiating the build volume from multiple orientations. Alternatively or additionally, the projection units may revolve around the build volume. Typically, the revolutions and/or rotations are in a horizontal plane, however they may be in any plane.

In a further aspect, the present disclosure relates to a system for producing a three- dimensional object.

In some embodiments of the present disclosure, the projection system comprises multiple projection units selected from the list including: a spatial light modulator, a digital micromirror device, a galvanometer-scanner, or an acousto-optic deflector.

In some embodiments of the present disclosure, the projection system comprises a spatial light modulator. In some embodiments of the present disclosure, the projection system comprises a digital micromirror device. In some embodiments of the present disclosure, the projection system comprises a galvanometer-scanner. In some embodiments of the present disclosure, the projection system comprises an acoustooptic deflector. In some embodiments of the present disclosure, the projection system comprises a light source, or a light source for each projection unit.

In some embodiments of the present disclosure, the light source comprises one or more incandescent lamps, such as a halogen lamp, or one or more luminescent lamps, such as a laser, an LED, or an electric discharge lamp. In some embodiments of the present disclosure, the light source comprises a halogen lamp. In some embodiments of the present disclosure, the light source comprises one or more luminescent lamps. In some embodiments of the present disclosure, the light source comprises a laser. In some embodiments of the present disclosure, the light source comprises an LED. In some embodiments of the present disclosure, the light source comprises an electric discharge lamp.

Further, in some embodiments of the present disclosure, the patterns are irradiated by a projection unit. Any type of system that is capable of irradiating the build volume with a series of patterns of light may be used as a projection unit. Typical examples of a projection unit are DLP projectors, LED Projectors, LCD projectors, Laser projectors, spatial light modulators and optoelectromechanical systems, such as digital micromirror devices, that may be coupled with a light source. Further, the projection unit may be a light source, such as a LED, covered with a microlens. Further, the projection unit may be a part of a projection system, wherein the projection system comprises an array of light sources, such as an OLED array covered by microlenses. Other projection units are known to the skilled person. Other types of projection units are disclosed elsewhere herein.

In some embodiments of the present disclosure, the direction adjustment unit is configured to either rotate the build volume within the field of irradiation of the projection units, and/or to rotate the projection units relative to the build volume.

In some embodiments of the present disclosure, the system comprises a direction adjustment unit. Preferably, the direction adjustment unit is configured for controllably varying a direction of incidence of said patterns of light relative to said build volume. The direction adjustment unit may be rotating the build volume and/or the projection system. Preferably, said rotation is configured such that the patterns of light are projected onto the build volume at multiple angles during the irradiating step. The direction adjustment unit may further comprise movement of mirrors and/or lenses, and wherein the irradiating source of the projection units and the build volume are fixed in position and not rotating, however said direction adjustment unit may comprise a number of lenses configured such that the number of patterns of light are projected onto the build volume at the corresponding angles and at the corresponding wavelengths, such as defined in a computation step by a processing unit.

In some embodiments of the present disclosure, the system comprises a controller. Preferably, said controller is configured for controlling the direction adjustment unit and/or the projection unit. It is a further preference that the controller is configured to control the projection unit and the direction adjustment unit such that the build volume is irradiated with the controlled patterns of light at an activation wavelength, from directions corresponding to the different orientation angles. The controller may be a computer, and said computer may further comprise the processing unit.

In some embodiments of the present disclosure, the system comprises a receptacle, such as a vessel, for containing the build volume and wherein said vessel is optically transparent to the patterns of light. Preferably, the receptacle is cylindrical, but may have a multifaceted shape. For example, the receptacle may be a vertically extruded polygon, such as a pentagon or decagon. In such cases, the system may comprise one projection unit arranged to irradiate each face of the multifaceted receptacle.

In some embodiments of the present disclosure, the processing unit is configured to compute the projections, the materials to use, and/or the corresponding orientation angles. In some embodiments of the present disclosure, the processing unit is configured for controlling the controller. In some embodiments of the present disclosure, the processing unit is configured to compute the projections. In some embodiments of the present disclosure, the processing unit is configured to compute the materials to use. In some embodiments of the present disclosure, the processing unit is configured to compute the corresponding orientation angles.

In some embodiments of the present disclosure, the method comprises providing a build volume. The build volume typically comprises a number of components that, when exposed to light, such as light of a specific wavelength, polymerizes into an object.

It should be noted that the embodiments disclosed herein may be modified or combined without departing from the inventive concept.

For example, the horizontal and/or vertical resolution may be increased, by virtual alignment of the projection units (i.e. virtual alignment of the irradiation of the projection units), as shown in e.g. Figs. 1-4. Such horizontal and/or vertical resolution increase may be combined with an increase in temporal resolution, relying on the timing of the projection units, as disclosed elsewhere herein, e.g. in Fig. 6. Further, the horizontal and/or vertical resolution increase, and/or the temporal resolution increase may be combined with the use of multiple partially or fully overlapping projection units (e.g. fully overlapping and identical irradiation patterns) in order to maintain or decrease the printing time. Alternatively, or additionally, the resolution increase may be combined with the use of a plurality of projection units arranged to have a focal plane at different distances along an optical axis (e.g. at different distances with respect to the centre of the build volume) such that the combined depth of field is larger than the distance, along the optical axis, across the build volume (e.g. as shown in Fig. 11-12).

Thus, the present disclosure relates to several different strategies for improving the resolution (e.g. spatial, such as vertical and/or horizontal, or temporal) while maintaining and/or decreasing the printing time by aligning multiple projection units, for example wherein multiple overlapping projection units are arranged to irradiate the build volume with an identical focal plane, thereby increasing the intensity of the irradiation provided to the build volume. Alternatively, or additionally, multiple projects may be arranged with a focal plane that is shifted along the optical axis, along different positions through the build volume. In this way, projection units having a larger aperture, and shorter depth of field, can be used while, collectively, having a depth of field that is identical or exceeds the length of the build volume along the optical axis, or at least the size of the object to be formed along said optical axis.

Detailed description of drawings

The invention will in the following be described in greater detail with reference to the accompanying drawings. The drawings are exemplary and are intended to illustrate some of the features of the presently disclosed methods and systems for producing a three-dimensional object, and are not to be construed as limiting to the presently disclosed invention.

Fig. 1 shows an example of a system of the present disclosure comprising multiple projection units (1-4). The projection units are irradiating the photosensitive component (14) in the build volume (13) from different orientation angles (9-12) typically perpendicular to the respective focal plane. Each projector (1-4) projects onto a different focal plane (5-8). Each projector can have different resolutions and refresh rates. The projection units are arranged such that the build volume is irradiated with light comprising an activation wavelength of the photosensitive component, by each of the plurality of projection units, with a projection of a series of patterns of light corresponding to one of a sets of subsinograms, at the corresponding orientation angles, and wherein each projection unit irradiates the build volume with a series of patterns of light that is derived from a different set of subsinograms, such that in total the build volume is irradiated with a resulting series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles. Thereby, the irradiation may lead to the formation of the three-dimensional object (15).

Fig. 2 shows the virtual alignment of fields of projections of multiple projection units. Specifically, Fig. 2A shows how the present disclosed method, and the related system, may be used in order to increase the spatial resolution of an object to the formed (e.g. the number of voxels and/or the number of pixels used by the projection units in order to form said object). A high resolution sinogram (18) is computed comprising 11 ,619 pixels per row in horizontal resolution (16). The number of pixels exceeds the resolution of any of the projection units. Thus, none of the used projection units has sufficient pixels to project this sinogram. As shown in Fig. 2B, four projection units (1-4) are used to irradiate the build volume with a resulting series of patterns of light corresponding to the sinograms at the corresponding orientation angles. It should be noted that the sinogram typically corresponds to only a single (vertical) layer of the build volume, thus the projection units are typically arranged to irradiate the build volume with a series of patterns of light corresponding to a set of sinograms, wherein each sinogram of said set corresponds to a single layer of said build volume, such as wherein the layer thickness defines the (vertical) size of a voxel. In this example, the projection units (1-4) contribute with 2203, 4406, 1280 and 3730 pixels, respectively. Each projection (39-42) is done by irradiating the build volume with a series of patterns on light corresponding to a set of subsinograms. The set of subsinograms may for example be obtained by dividing a set of sinograms, wherein each sinogram and set of sinograms correspond to a layer of the object.

The projections (39-42) are aligned on their respective focal plane (5-8 of Fig. 1) such that they irradiate different, or partly overlapping, parts of the virtual focal plane (37). The object is defined between the ends (38) of the illuminated area. In this way, the projection units (1-4) are aligned along an imaginary focal plane (37) resulting in an increased resolution.

Fig. 3 shows the physical alignments of the four projection units of the present example. Fig. 3A) shows that one sinogram, i.e. one layer, (11,619 horizontal pixels) is split into four subsinograms (19). The horizontal resolution of the subsinograms are, from left to right, 3730 pixels, 1280 pixels, 4406 pixels and 2203 pixels, and will be projected using Projection units 4, 3, 2, 1 , respectively. In order to be able to project a series of patterns of light corresponding to a set of subsinograms for the formation of the object, the subsinograms (and/or the sets of subsinograms) have to be compensated for the orientation angle of each projection unit. Thus by shifting the angular index of each subsinogram (and/or sets of subsinograms) by a degree that reflects the difference between the projecting direction (0) and a reference plane (e.g. the focal plane), the contribution of each projection unit during the step of irradiation of the build volume may correspond to having a single projection unit with a sufficient resolution to accurately project the set of sinograms (i.e. the entire object at full resolution). Here the focal plane (37) is used as the reference plane. The angular index (17) is shifted and adjusted. Fig. 3C shows that, physically, on each focal plane (5-8), there is only one projection, however as explained above, each projection provides a contribution to the virtual focal plane in order to generate a three-dimensional object of higher resolution.

Fig. 4 shows an example of the virtual alignment of multiple projections, each based on a set of subsinograms, for increasing the horizontal and vertical resolution by using multiple projection units, four in this example. Fig. 4A shows a schematic illustration of the build volume, perpendicular to the axis of rotation. The projections (39-42), each comprising a series of patterns of light corresponding to a set of subsinograms, of the four projection units are combined in such a way as to increase the spatial resolution. As can be seen, projection units may be arranged both to increase the vertical resolution (by being arranged to irradiate different horizontal layers of the build volume) and/or to increase the horizontal resolution by, as mentioned above, being arranged to irradiate different parts of a virtual focal plane. The projection units may be arranged such that both the virtual and the horizontal resolution is increased. Further, the projections may, as can be seen in the figure, overlap one another. In those areas, it may be advantageous to compensate the power output of the projection units such that all areas are provided with an accurate irradiation dosage for formation of the three- dimensional object. Alternatively, as can be seen in Fig. 4B, a single projection unit may be arranged to illuminate these areas.

Fig. 5 shows a calibration according to an embodiment of the present disclosure, which may be needed when calculating printing patterns for various projection units. The correlation between the gray value (20) and output power (25) is in general different for each projector (especially if not from the same brand) (21-24). The desired gray value I2’ of the projection unit 2 is calculated so that a light pattern would produce exactly the same outputs with different projection units (Projectors 1 and 2), even though their “Gray Value - Output Power” correlations differ. This is calculated by I'₂ = The patterns of lights of each projection unit are preferably compensated for these discrepancies between the projection units, such that the three-dimensional object may be accurately formed.

Fig. 6 shows a schematic illustration of how the temporal resolution may be increased in tomographic vat polymerization by the synchronization of a plurality of projection units (1-4). The number of projection units may be at least two, but there is no upper theoretical limit to the number of projection units. Further, each of the projection units may have any orientation angle, as this may be compensated for, for example by shifting the sets of sinograms, as explained for Fig. 3. Preferably all projection units have the same refresh rate, for example 60 Hz, and the projection of each subsequent projection unit after the first is delayed by 1/fn, wherein f is the refresh rate and n is the number of projection units. Thus, by having four projection units with a refresh rate of 60 Hz, projection unit 2 may have a delay of 1/240 s, projection unit 3 may have a delay of 2/240 s, and projection unit 3 may have a delay of 3/240 s. In this way, the irradiation of the build volume would correspond to that of a projection unit with a refresh rate of 240 Hz. The method and system of the present disclosure for increasing the temporal resolution may be combined with methods and systems for increasing the spatial resolution. However, the temporal resolution may be increased by using projection units that each is arranged to illuminate the build volume with a series of patterns of lights that correspond to the sets of sinograms, from the respective corresponding orientation angles (9-12).

Fig. 7 shows a flowchart outlining a method for producing a multi-material three- dimensional object according to a specific embodiment of the present disclosure. The method may comprise a step of computing (26), comprising computing a plurality of sets of subsinograms, wherein each set of subsinograms is derived from a set of sinograms, wherein each sinogram describes a layer of the three-dimensional object to be formed from different orientation angles. The method may further comprise a step of providing (27), comprising providing a build volume comprising a photosensitive component capable of initiating a photochemical reaction upon irradiation by light of an activation wavelength. The method may further comprise a step of irradiating (28), comprising irradiating the build volume with light comprising the activation wavelength, by each of a plurality of projection units, with a projection of a series of patterns of light corresponding to one of the sets of subsinograms, at the corresponding orientation angles, and wherein each projection unit irradiates the build volume with a series of patterns of light that is derived from a different set of subsinograms, such that in total the build volume is irradiated with a resulting series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles.

Fig. 8 shows a flowchart outlining a method for producing a multi-material three- dimensional object according to a specific embodiment of the present disclosure. The method may comprise a step of computing (29), comprising computing a set of sinograms describing the three-dimensional object to be formed from different orientation angles. The method may further comprise a step of providing (30), comprising providing a build volume comprising a photosensitive component capable of initiating a photochemical reaction upon irradiation by light of an activation wavelength. The method may further comprise a step of irradiating (31), comprising irradiating the build volume, by each of a plurality of projection units having the same refresh rate f, with a projection of a series of patterns of light corresponding to the set of sinograms, at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength, wherein at least one of the projection units is arranged to irradiate the build volume with the projection at the corresponding orientation angles with a delay, with respect to the other projection unit(s), that is given by 1/(fn), wherein n is a natural number.

Fig. 9 shows a flowchart outlining a method for producing a multi-material three- dimensional object according to a specific embodiment of the present disclosure. The method may comprise a step of computing (43), comprising computing a set of sinograms describing the three-dimensional object to be formed from different orientation angles. The method may further comprise a step of providing (44), comprising providing a build volume comprising a photosensitive component capable of initiating a photochemical reaction upon irradiation by light of an activation wavelength. The method may further comprise a step of irradiating (45), comprising irradiating the build volume, by each of a plurality of projection units, with a projection of a series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength.

Fig. 10 shows a tomographic vat photopolymerization system for producing a three- dimensional object from a build volume according to a specific embodiment of the present disclosure. The figure shows a system wherein a build volume is contained by a receptacle (33). The exemplary system comprises a projection system comprising two projection units (34 and 36), i.e. a first projection unit and a second projection unit. As shown, the system may comprise optics (35), such as lenses, between the projector and the receptacle. The receptacle, while fixed in position, is suspended from a direction adjustment unit (32), herein exemplified as a rotation stage. Thereby, the build volume is capable of rotating, while the projector units irradiate a number of patterns of light at their respective corresponding orientations.

Fig. 11 shows an example of a system of the present disclosure comprising a plurality of projection units (1-4). While the shown system comprises four projectors, any number of projector is possible, as disclosed elsewhere herein. The projection units are arranged to irradiate a photosensitive component (14) of the build volume (13). Each projector (1-4) projects onto a different focal plane (5-8). Thus, a first projector (1) has a first focal plane (5), a second projector (2) has a second focal plane (6), a third projector (3) has a third focal plane (7), a fourth projector (4) has a fourth focal plane (8). As disclosed elsewhere herein, the projection units may have different resolutions and/or refresh rates, and may be arranged on different planes in the vertical direction, i.e. a different position along the viewing axis of the figure. It should be noted, that while the figure shows the projectors having different orientation angles with respect to the build volume, this is not a requirement. In fact, a subset of the projectors, or even all of the projectors could have the same orientation angle with respect to the build volume. The projectors could for example, be stacked on top of each other, and thus have the same (radial) orientation angle with respect to the build volume.

In one example the projectors have different focal planes, i.e. the focal planes are arranged differently in the build volume.

The projection units (1-4) may be arranged to have a depth of field which spans the workpiece (i.e. the object to be formed, or alternatively the build volume), typically along an optical axis of the projection unit. As disclosed elsewhere herein, a common way to increase the depth of field is to decrease the aperture of the projection unit. This is however associated with the drawback that the output power is reduced. To compensate for this, a plurality of projection units, each having a depth of field that spans the workpiece, may be virtually aligned such that they each, as a result of their respective irradiation, results in a similar or identical three dimensional energy distribution. The projection units may for example be arranged to each have a depth of field that spans the workpiece or even the build volume. The projection units may for example be arranged to irradiate the build volume, and each may have a focal plane that intersects the centre of rotation, and/or the centre of the build volume (e.g. as shown in Fig. 1). Thus, the projection units may be arranged to produce the same three-dimensional object, but by virtually aligning them (or in this case virtually overlapping their series of patterns of light), the printing time is reduced.

However, alternatively, the projection units (1-4) may be arranged such that each projection unit has a focal plane that is shifted with respect to the others. For example, the projection units may have focal planes (1-4) that are selected such that, taking into account the depth of fields of the projection units, the resulting depth of field spans the workpiece and/or the build volume, such as along an optical axis. The projection units may have one or more, e.g. different, depth of fields that are shorter than the distance of the three-dimensional object. By virtually aligning the focal plane, the build volume can be irradiated by a plurality of projection units, wherein the resulting combined depth of field, of all projections units, spans the distance of the three-dimensional object, such as along an optical axis. Thus, each projection unit can be said to contribute to a distance of the three-dimensional object, such as from each respective orientation angle. The total depth of field, of all projection units may span the three-dimensional unit, such as along an optical axis of each projection unit.

As can be seen in Fig. 11, the focal planes are shifted along the projection units virtual optical axis. Wherein the fourth focal plane (4) is at a nearest position with respect to the projection units, the second focal plane (2) is at a second nearest position, the first focal plane is at a third nearest position, and the third focal plane is at a fourth nearest position. In this way, the focal planes are arranged such that the depth of fields of the projection units, collectively, spans the entire workpiece and/or the build volume, such as along an optical axis.

Fig. 12, further illustrates the effective depth of field (48) of a plurality of projection units, wherein the individual depth of fields (47) and individual focal planes (5-8) have been selected such that the effective depth of field spans the entire workpiece and/or the entire build volume, such as along an optical axis. In this way, printing times can be decreased, and/or projection units having a shorter depth of field can be used for efficient printing of a workpiece that is larger than the depth of field of an individual projection unit. Thus, the focal planes are virtually aligned, such that they each have an effective depth of field (47) that, collectively, spans the workpiece and/or the build volume, such as along the optical axis of the projection units.

Fig. 13A shows an example of a system of the present disclosure comprising a plurality of projection units (1-3). While the shown system comprises three projectors, any number of projector is possible, as disclosed elsewhere herein. The projection units are arranged to irradiate a photosensitive component (14) of the build volume (13). Each projector (1-3) projects onto a different focal plane (5-7). Thus, a first projector (1) has a first focal plane (5), a second projector (2) has a second focal plane (6), a third projector (3) has a third focal plane (7). In the shown example, a plurality of sets of subsinograms has been computed from a set of sinograms, wherein each projector unit is arranged to irradiate the build volume with a different set of subsinogram. Thus, it can be said that the set of subsinograms has been derived by equally dividing the set of sinograms between the projection units, such that the each projection unit is arranged to irradiate the build volume from corresponding orientation angles that defines a sector of 2-n/n, wherein n is the number of projection units. In this way, the three-dimensional object can be produced faster and more accurately. For example, a first projection unit (1) may be arranged to irradiate the build volume from a first sector (49), a second projection unit (2) may be arranged to irradiate the build volume from a second sector (50), a third projection unit (3) may be arranged to irradiate the build volume from a third sector (51). Each sector may, in this example, be 2n7n, where n is the number of projection units, e.g. 3. Fig. 13B shows subsinograms (18) derived from a sinogram. The subsinogram may describe a single layer of a three-dimensional structure. The subsinograms have been derived by dividing the sinogram by the angular index, such that each subsinogram has an angular index range of 2TTIV\. Thus, in this example, a first projection unit (1) may be arranged to irradiate the build volume with a series of patterns of light derived from a first subsinogram (52), the second projection unit (2) from a second subsinogram (53), and a third projection unit (3) from a third subsinogram (54).

Items

1. A method for producing a three-dimensional object comprising:

• computing a plurality of sets of subsinograms, wherein each set of subsinograms is derived from a set of sinograms, wherein each sinogram describes a layer of the three-dimensional object to be formed from different orientation angles;

• irradiating the build volume with light comprising the activation wavelength, by each of a plurality of projection units, with a projection of a series of patterns of light corresponding to one of the sets of subsinograms, at the corresponding orientation angles, and wherein each projection unit irradiates the build volume with a series of patterns of light that is derived from a different set of subsinograms, such that the build volume is irradiated with a resulting series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles. 2. The method according to any of the preceding items, wherein the sets of subsinograms are derived by dividing the set of sinograms, such as one or a plurality of times.

3. The method according to item 2, wherein the sets of subsinograms are derived by dividing the set of sinograms according to one or more radial indices and/or one or more angular indices, and/or one or more vertical indices.

4. The method according to any of the preceding items, wherein the set of sinograms is divided into the same number of sets of subsinograms as the number of projection units used for irradiating the build volume, such as the same number of sets of subsinograms as the number of projection units.

5. The method according to any of the preceding items, wherein the set of sinograms is divided into the sets of subsinograms based on the number of pixels and/or the aspect ratio of the projection units.

6. The method according to any of the preceding items, wherein the projection units are arranged to have a focal plane that intersects the centre of the build volume.

7. The method according to any of the preceding items, wherein the projection units are arranged to be virtually aligned, such that they irradiate different parts of their respective focal plane, and wherein said parts are connected or partially overlapping, when the respective focal planes are overlaid, such as wherein the spatial resolution is increased along the focal plane.

8. The method according to any of the preceding items, wherein the projection units are arranged to irradiate different parts of the build volume, for the formation of the three-dimensional object, and wherein said parts are connected, or partly overlapping, and wherein the radial position with respect to an axis of rotation across the build volume, and/or the vertical position between said parts differ. 9. The method according to any one of the preceding claims, wherein the series of patterns of light irradiated by the different projections units have a different number of pixels per unit length along a distance of their respective focal plane.

10. The method according to any of the preceding items, wherein the projections of the different projection units have a different number of pixels in the horizontal and/or vertical direction per length at the focal plane, such as wherein parts of the three-dimensional object that is desired to be more well-defined is assigned to have a higher number of pixels per length.

11. The method according to any one of items 1-5, wherein the projection units are arranged to have a focal plane that intersects with the center of the build volume, and/or the center of rotation, and wherein the depth of field of the projection units are adapted such that they span the length of the three- dimensional object/workpiece, such as along an optical axis.

12. The method according to any one of items 1-5, wherein the depth of field of the projection units are shorter than the distance of the three-dimensional object such as along an optical axis, and wherein the focal planes of the projection units are selected such that the resulting combined depth of field spans the three-dimensional object such as along an optical axis.

13. The method according to item 12, wherein the focal plane of each projection unit is shifted along an optical axis.

14. The method according to item 12-13, wherein each projection unit is arranged to have a focal plane arranged at a different distance with respect to the centre of the build volume, such as along an optical axis.

15. The method according to any of the preceding items, wherein the set of sinograms is divided into the sets of subsinograms, by dividing the set of sinograms by the radial index, such that at least two sets of subsinograms have different corresponding orientation angles. 16. The method according to item 15, wherein the angular indices of the sets of subsinograms are shifted to compensate for the relative angular orientation of the projection units, such as with respect to the build volume.

17. The method according to any one of the preceding items, wherein the step of irradiating comprises:

• irradiating the build volume, by each of a plurality of projection units, with a number of patterns of light that are defined by the set of subsinograms allocated to the corresponding projection unit; wherein each projection unit is located separate from each other, and wherein the build volume rotates relative to the projection units, wherein said rotation has an axis of rotation that is parallel to the focal plane of the projection units.

18. The method according to any one of the preceding items, wherein the three- dimensional object is reproduced in a number of voxels of the build volume, and wherein the step of computing comprises defining the sets of subsinograms of the set of sinograms and allocate each set of subsinograms to one projection unit.

19. The method according to any of the preceding items, wherein each set of subsinograms is derived by shifting the set of subsinograms vertically, according to the difference between the orientation angle of the focal planes of the projection units.

20. The method according to any one the preceding items, wherein the three- dimensional object to be formed is described by the set of sinograms such that one sinogram describes a layer of the three-dimensional object, such as wherein the thickness of said layer is the size of a voxel, such as the vertical size of a voxel.

21. A method for producing a three-dimensional object comprising:

• irradiating the build volume, by each of a plurality of projection units having the same refresh rate f, with a projection of a series of patterns of light corresponding to the set of sinograms, at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength.

22. The method according to item 21 , wherein at least one of the projection units is arranged to irradiate the build volume with the projection at the corresponding orientation angles with a delay, with respect to the other projection unit(s), that is given by (fn), wherein n is a natural number.

23. The method according to item 22, wherein n is the number of projection units used to irradiate the build volume with the series of patterns of light.

24. The method according to any one of items 21-23, wherein each of said plurality of projection units is arranged to have a delay that is given by l-i f-n and wherein / is a different natural number for each projection unit in the interval [1 ,n],

25. A method for producing a three-dimensional object comprising:

• irradiating the build volume, by each of a plurality of projection units, with a projection of a series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength. The method according to any of the preceding items, wherein the power provided to the build volume during the step of irradiating equals the sum of the power output of the projection units. The method according to any one of the preceding items, wherein multiple sinograms are used to describe the three-dimensional object to be formed, typically one sinogram for each vertical voxel of said object, such as each voxel of said object perpendicular to an axis of rotation of the build volume and/or the projection units. The method according to any one of the preceding items, wherein the photochemical reaction leads to polymerization of the build volume at the irradiated voxels. The method according to any one of the preceding items wherein the method comprises a step of computing the sinogram, such as by a Radon-transform followed by a tomographic reconstruction filter, a fan-beam algorithm followed by a tomographic reconstruction filter, and/or a cone-beam algorithm followed by a tomographic reconstruction filter. The method according to any one of the preceding items wherein said sinograms are computed using any one of the following list: a Radon-transform followed by a tomographic reconstruction filter; a fan-beam algorithm followed by a tomographic reconstruction filter; a cone-beam algorithm followed by a tomographic reconstruction filter; an iterative reconstruction technique; an algebraic reconstruction technique; or a diffractive tomography algorithm. The method according to any of the preceding items, wherein the projection units are arranged to initiate irradiation of the build volume at substantially the same time, and/or wherein the projection units are arranged to terminate irradiation of the build volume at substantially the same time. The method according to any one of the preceding items, wherein the photosensitive component comprise: • a prepolymer, such as a monomer; and

• a photoinitiator that is activated upon irradiation by light with the activation wavelength, wherein activation of the photoinitiator polymerizes the prepolymer. The method according to any one of the preceding items, wherein the photoinitiators are selected from the list including free radical photoinitiators, cationic photoinitiators, or a combination thereof. The method according to any one of the preceding items, wherein the photosensitive component is configured such that it is activated by irradiation of light, and wherein said activation leads to a polymerization of the prepolymer. The method according to any one of the preceding items, wherein the prepolymers are selected from the list including acrylate monomers or epoxy monomers. The method according to any one of the preceding items, wherein the activation wavelength is in the UV range. The method according to any one of the preceding items, wherein the activation wavelength is in the visible light range. The method according to any one of the preceding items, wherein the patterns of light are generated by a projection unit that is projecting said patterns of light substantially parallel to a plane of rotation of the build volume. The method according to any one of the preceding items, wherein the patterns of light are generated by a projection unit that is projecting said patterns of light substantially perpendicular to a plane of rotation of the build volume. The method according to any one of the preceding items, wherein the patterns of light are generated by a projection unit that is revolving around the build volume and projecting said patterns of light towards said build volume. The method according to any one of the preceding items, wherein the build volume comprises cells, and wherein the cells are arranged such that upon irradiation of the build volume, the cells are incorporated into the three- dimensional object. The method according to any one of the preceding items, wherein the three- dimensional object is an artificial tissue, such as for in vitro drug screening or in vivo grafting. The method according to any one of the preceding items, wherein the build volume comprises cells, such as undifferentiated stem cells, for example iPS cells. The method according to any one of the preceding items, wherein the method is used to print personalized earmolds for hearing-aid or music buds. The method according to any one of the items, wherein the three-dimensional object is a custom sealing, such as for swimming glasses, a microfluidic device, a lab-on-a-chip device and/or an organ-on-a-chip device. The method according to any one of the preceding items, wherein the projection units are selected from the list including: a DLP projector, an LED Projector, an LCD projector, a Laser projector, a spatial light modulator and/or an optoelectromechanical system, such as a digital micromirror device. The method according to any one of the preceding items, wherein the patterns are irradiated in a mask-less process. A system for producing a three-dimensional object, the system comprising:

• a processing unit configured for computing a plurality of sets of subsinograms, wherein each set of subsinograms is derived from a set of sinograms, wherein each sinogram describes a layer of the three- dimensional object to be formed from different orientation angles; • a build volume comprising a photosensitive component capable of a photochemical reaction upon irradiation by light of an activation wavelength;

• a controller configured for controlling the direction adjustment unit and the projection system such that the build volume is irradiated with light comprising the activation wavelength, by each of a plurality of projection units, with a projection of a series of patterns of light corresponding to one of the sets of subsinograms, at the corresponding orientation angles, and wherein each projection unit irradiates the build volume with a series of patterns of light that is derived from a different set of subsinograms, such that in total the build volume is irradiated with a resulting series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles. stem for producing a three-dimensional object, the system comprising:

• a controller configured for controlling the direction adjustment unit and the projection system such that the build volume is irradiated, with a projection of a series of patterns of light corresponding to the set of sinograms, at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength, wherein at least one of the projection units is arranged to irradiate the build volume with the projection at the corresponding orientation angles with a delay, with respect to the other projection unit(s), that is given by 1/(fnj, wherein n is a natural number. stem for producing a three-dimensional object, the system comprising:

• a controller configured for controlling the direction adjustment unit and the projection system such that the build volume is irradiated, with a projection of a series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength. stem for producing a three-dimensional object, the system comprising:

• a projection system comprising a plurality of projection units capable of irradiating the build volume by a series of patterns of light comprising the activation wavelength, wherein the projection units each have a depth of field that is longer than the three-dimensional object and/or the build volume, such as along an optical axis, and wherein the focal planes of each projection unit is arranged to intersect with the center of rotation and/or the center of the build volume;

• a controller configured for controlling the direction adjustment unit and the projection system such that the build volume is irradiated, by each of said plurality of projection units, with a projection of a series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength. stem for producing a three-dimensional object, the system comprising:

• a projection system comprising a plurality of projection units capable of irradiating the build volume by a series of patterns of light comprising the activation wavelength, wherein the projection units have a depth of field that is shorter than the three-dimensional object and/or the build volume, such as along an optical axis, and wherein the focal planes of each projection unit is arranged such that the depth of fields spans the length of the three-dimensional object and/or the build volume, such as along an optical axis;

• a controller configured for controlling the direction adjustment unit and the projection system such that the build volume is irradiated, by each of said plurality of projection units, with a projection of a series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength. The system according to any one of items 48-53, wherein said system is configured to carry out the method according to any one of items 1-47.

Claims

1. A method for producing a three-dimensional object comprising:

• irradiating the build volume with light comprising the activation wavelength, by each of a plurality of projection units, with a projection of a series of patterns of light corresponding to one of the sets of subsinograms, at the corresponding orientation angles, and wherein each projection unit irradiates the build volume with a series of patterns of light that is derived from a different set of subsinograms, such that the build volume is irradiated with a resulting series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles.

2. The method according to claim 1 , wherein the sets of subsinograms are derived in a process comprising dividing the set of sinograms into the same number of sets of subsinograms as the number of projection units used for irradiating the build volume.

3. The method according to any one of the preceding claims, wherein the sets of subsinograms are derived in a process comprising dividing the set of sinograms, at least once, according to a radial index.

4. The method according to any one of the preceding claims, wherein the sets of subsinograms are derived in a process comprising dividing the set of sinograms, at least once, such that the sets of subsinograms describe different layers, such as in the vertical direction, of the three-dimensional object to be formed from different orientation angles.

5. The method according to any one of the preceding claims, wherein the sets of subsinograms are derived in a process comprising shifting the orientation angles of at least one set of subsinograms, according to a difference in the angles of the focal planes of the projection units.

6. The method according to any one of the preceding claims, wherein the series of patterns of light irradiated by the different projections units have a different number of pixels per unit length along a distance of their respective focal plane.

7. The method according to any one of the preceding claims, wherein each projection unit is arranged to have a focal plane that intersects with the centre of the build volume, and wherein the projection units are arranged to be virtually aligned such that they irradiate different parts, and/or partially overlapping parts, of their respective focal plane.

8. The method according to any one of the preceding claims, wherein the projection units are arranged to have a focal plane that intersects with the center of the build volume, and/or the center of rotation, and wherein the depth of field of the projection units are adapted such that they span the length of the three-dimensional object/workpiece, such as along an optical axis.

9. The method according to any one of claims 1-6, wherein the projection units have one or more depth of fields that are shorter than the distance of the three- dimensional object, such as along an optical axis, and wherein the focal planes of the projection units are selected such that the resulting combined depth of field spans the distance of the three-dimensional object, such as along an optical axis.

10. The method according to claim 9, wherein the focal plane of each projection unit is at a different position, such as along the optical axis.

11. The method according to claim 9-10, wherein each projection unit is arranged to have a focal plane arranged at a different distance with respect to the centre of the build volume, such as along the optical axis.

12. The method according to any one of the preceding claims, wherein the step of irradiating comprises:

• irradiating the build volume, by each of a plurality of projection units, with a number of patterns of light that is defined by the set of subsinograms allocated to the corresponding projection unit.

13. The method according to claim 11 , wherein the projection units are located at different orientation angles, such as with respect to the center of the build volume.

14. The method according to any one of the preceding claims, wherein the build volume rotates relative to the projection units.

15. A method for producing a three-dimensional object comprising:

• irradiating the build volume, by each of a plurality of projection units with a projection of a series of patterns of light, such that the build volume is irradiated with a resulting series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles, and wherein the irradiating light comprises the activation wavelength, wherein the projection units have one or more depth of fields that are shorter than the distance of the three-dimensional object, such as along an optical axis, and wherein the focal plane of each projection unit is selected such that the resulting combined depth of field, of all projections units, spans the distance of the three-dimensional object, such as along an optical axis.

16. The method according to claim 15, wherein the focal plane of each projection unit is at a different position, such as along the optical axis.

17. The method according to claim 15-16, wherein each projection unit is arranged to have a focal plane arranged at a different distance with respect to the centre of the build volume, such as along the optical axis.

18. The method according to any one of the preceding claims, wherein the build volume rotates relative to the projection units.

19. A method for producing a three-dimensional object comprising:

• irradiating the build volume, by each of a plurality of projection units with a projection of a series of patterns of light, such that the build volume is irradiated with a resulting series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles, and wherein the irradiating light comprises the activation wavelength.

20. The method according to claim 19, wherein each projector unit irradiates the build volume with the same series of patterns of light.

21. The method according to claim 19, wherein the method further comprises a step of computing a plurality of sets of subsinograms from the set of sinograms, and wherein the step of irradiating comprises irradiating the build volume, by each of a plurality of projection units with a projection of a series of patterns of light corresponding to one of the sets of subsinograms, such that the build volume is irradiated with a resulting series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles.

22. The method according to claim 21 , wherein the plurality of sets of subsinograms is derived by dividing equally the set of sinograms between the plurality of projection units, such that the each projection unit is arranged to irradiate the build volume from corresponding orientation angles that defines a sector of 2n7n, wherein n is the number of projection units.

23. The method according to claim 19, wherein the projection units have an identical refresh rate f, and wherein at least one of the projection units is arranged to irradiate the build volume with the projection at the corresponding orientation angles with a delay, with respect to the other projection unit(s), that is given by (fn), wherein n is a natural number.

24. The method according to claim 23, wherein n is the number of projection units used to irradiate the build volume with the series of patterns of light, and wherein each of said plurality of projection units is arranged to have a delay that is given by l-i f-n and wherein / is a different natural number for each projection unit in the interval [1 ,n],

25. A system for producing a three-dimensional object, the system comprising:

• a processing unit configured for computing a set of sinograms, wherein each sinogram describes a layer of the three-dimensional object to be formed from different orientation angles;

• a build volume arranged for containing a photosensitive component capable of a photochemical reaction upon irradiation by light of an activation wavelength;

• a controller configured for controlling the projection system such that the build volume is irradiated with light comprising the activation wavelength, by each of a plurality of projection units, with a projection of a series of patterns of light corresponding to one of the sets of sinograms, at the corresponding orientation angles.

26. A system for producing a three-dimensional object, the system comprising:

27. A system for producing a three-dimensional object, the system comprising:

• a controller configured for controlling the direction adjustment unit and the projection system such that the build volume is irradiated, by each of said plurality of projection units, with a projection of a series of patterns of light corresponding to the set of sinograms at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength.

28. The system according to claim 27, wherein said controller is configured for controlling the direction adjustment unit and the projection system such that the build volume is irradiated, with a projection of a series of patterns of light corresponding to the set of sinograms, at the corresponding orientation angles, wherein the irradiating light comprises the activation wavelength, wherein at least one of the projection units is arranged to irradiate the build volume with the projection at the corresponding orientation angles with a delay, with respect to the other projection unit(s), that is given by 1/(fnj, wherein n is a natural number.

29. A system for producing a three-dimensional object, the system comprising:

• a projection system comprising a plurality of projection units capable of irradiating the build volume by a series of patterns of light comprising the activation wavelength, wherein the projection units have a depth of field that is longer than the three-dimensional object, such as along an optical axis, and wherein the focal planes of each projection unit is arranged to intersect with the center of rotation and/or the center of the build volume;

30. A system for producing a three-dimensional object, the system comprising:

• a projection system comprising a plurality of projection units capable of irradiating the build volume by a series of patterns of light comprising the activation wavelength, wherein the projection units have a depth of field that is shorter than the three-dimensional object, such as along an optical axis, and wherein the focal planes of each projection unit is arranged such that the depth of fields spans the length of the three- dimensional object, such as along an optical axis;

31 . The system according to any one of claims 25-30, wherein the system is arranged to carry out the method of any one of claims 1-24.