Volume Additive Manufacturing Method and Equipment with Digital Distortion Compensation

Abstract

The present invention relates to a method for digitally compensating for beam ray distortion in tomography-based additive manufacturing, wherein the tomography-based additive manufacturing involves projecting a light pattern from multiple angles into a container (22) containing a light-responsive material, by simulating the light path passing through the container (22) and the light-responsive material; and digitally compensating the light projection based on the simulated light path to obtain a corrected light projection. The present invention also relates to a method and an apparatus for manufacturing an object (24) in tomography-based additive manufacturing using the distortion compensation method.

Description

Technical Field

[0001] The present invention relates to methods and apparatus for volumetric additive manufacturing of three-dimensional objects from light-responsive materials. In particular, the present invention relates to, but is not limited to, manufacturing systems in which light distortion induced by the cylindrical walls of a container is compensated for. Background Art

[0002] In tomographic-based additive manufacturing methods, a large amount of light-responsive material (resin), typically contained within a container, usually a cylindrical container, is irradiated from multiple angles with calculated light patterns in order to fabricate a three-dimensional object. The main advantage of this method compared to existing methods is its very rapid fabrication time (as low as a few tens of seconds). For a detailed description of this method, reference may be made to the published documents in the following paragraph.

[0003] State-of-the-art tomographic printers typically include a refractive-index matching liquid bath surrounding the resin container (see, for example, US2018 / 0326666A1; "Volumetric additive manufacturing via tomographic reconstruction", B. E. Kelly, I. Bhattacharya, H. Heidari, M. Shusteff, C. M. Spadaccini, and H. K. Taylor; Science Vol. 363, Issue 6431, pp. 1075-1079 (08 Mar 2019); "Volumetric Bioprinting of Complex Living-Tissue Constructs within Seconds", P. N. Bernal, P. Delrot, D. Loterie, Y. Li, J. Malda, C. Moser, and R. Levato, Advanced Materials, 19 August 2019). The refractive-index matching liquid bath minimizes the lens effect caused by the cylindrical shape of the light-responsive material container (as in US2018 / 0326666A1). In order to calculate the light patterns using standard tomographic algorithms such as the Radon transform, the lens effect must be mitigated.

[0004] However, for a variety of reasons, the use of a refractive-index matching liquid bath is not desirable. First, it is not always possible to find a liquid that precisely matches the properties of the resin, while also being safe to operate and easy to clean up in the event of an overflow.

[0005] Instead of using a refractive index matching liquid bath, a compensation lens as previously disclosed (see WO2019 / 043529A1) can also be used. This solution avoids using a refractive index matching liquid, but the lens needs to be adapted to the optical properties of the container. For example, each time the container has a different size or material, the compensation lens should also be replaced.

[0006] Therefore, there is a need for a tomographic additive manufacturing method that can be easily adapted to different resins and containers without changing the printing equipment. Summary of the Invention

[0007] The present invention relates to a method for digitally compensating for beam ray distortion in tomographic additive manufacturing, wherein the tomographic additive manufacturing involves projecting a light pattern into a container containing a light-responsive material from multiple angles, and the method includes the following steps:

[0008] - Simulating the path of light rays passing through the container and the light-responsive material;

[0009] - Digitally compensating the light projection based on the simulated path of the light rays to obtain a corrected light projection;

[0010] The present invention also relates to a method for preparing an object in tomographic additive manufacturing, wherein the tomographic additive manufacturing involves projecting a light pattern into a container containing a light-responsive material from multiple angles, and the method includes the following steps:

[0011] - Providing the container containing the light-responsive material;

[0012] - Implementing the distortion compensation method described above to obtain a corrected light projection;

[0013] - Projecting the corrected light projection into the container containing the light-responsive material, thereby creating an object without distortion.

[0014] The present invention also relates to an apparatus for digitally compensating for beam ray distortion and preparing an object in tomographic additive manufacturing, the apparatus including:

[0015] - A resin container for providing a resin to be polymerized, wherein the resin container is rotatable;

[0016] - A unit for providing a beam of light to be projected into the resin container;

[0017] - A processing unit for performing the distortion compensation method preferably as described above.

[0018] Wherein the apparatus does not include a physical compensation component between the unit for providing the beam of light and the container, such as a refractive index matching liquid bath surrounding the container or a lens, for example. Description of the Drawings

[0019] The present invention can be better understood by a detailed description of non - limiting preferred embodiments and with reference to the non - limiting drawings, wherein:

[0020] Figure 1A is a perspective view of an embodiment of a volumetric additive manufacturing apparatus with a resin bath and a refractive index matching fluid bath according to the prior art.

[0021] Figure 1B is Figure 1A a top view of the apparatus, in which the light rays have been traced to show the light projection path in this embodiment.

[0022] Figure 2A is a perspective view of an embodiment of a volumetric additive manufacturing apparatus without a compensation element according to the present invention.

[0023] Figure 2B is Figure 2A a top view of the apparatus, in which the light rays have been traced to show the light projection path in this embodiment. The light ray path extends beyond the container to show that the light rays do not all intersect at the same point.

[0024] Figure 2C is Figure 2A a perspective view of the apparatus in which the actual path of the light rays is compared with the path expected in a parallel beam projection algorithm.

[0025] Figure 3 is a schematic diagram of the light ray state required for applying the fan - beam algorithm. Detailed Description of the Invention

[0026] In tomographic volumetric additive manufacturing, a volume of light - responsive material is irradiated with light patterns from multiple directions. These light patterns are calculated using algorithms similar to those used in X - ray computed tomography (also known as a medical CT scanner). These algorithms are known to those skilled in the art. Apparatuses for tomographic additive manufacturing have been described in detail in, for example, WO2019 / 043529A1 or US2018 / 0326666A1.

[0027] So far, all tomographic - based volumetric additive manufacturing systems have used physical compensation methods for the distortion caused by the cylindrical shape of the light - responsive material container, such as using a refractive index matching fluid bath ( Figure 1A shown and as described in US2018 / 0326666 A1) or compensation lenses. These compensation elements mitigate the lens effect caused by the cylindrical shape of the light - responsive material container and allow the light rays to pass straight through the light - responsive material (as Figure 1BAs shown). Straight light is required to calculate the light pattern using standard parallel beam tomography algorithms (e.g., Radon transform and its inverse transform).

[0028] Figure 1A This configuration is shown, where the light beam 11 first enters the refractive index matching liquid bath 12 and then enters the container 13 with the light-responsive material. The container 13 is fixed to a rotating gantry (platform) 14 to irradiate the light-responsive material with the light pattern 11 from multiple angles, thereby fabricating the object 15.

[0029] As Figure 1B shown in the top view, the light beam 11 (represented here as separate multiple light rays) passes through the refractive index matching liquid bath 12 and the container 13 with negligible distortion in this configuration. In Figure 1B the simulated light ray trajectories, the refractive indices of the resin and the refractive index matching liquid are assumed to be 1.53, while the refractive index of the fused silica container is 1.47.

[0030] Unfortunately, compensation elements such as refractive index matching liquid baths or compensating lenses must be matched to the geometry and materials employed for each specific light-responsive material container. This means that physical changes to the printing device are required when the container or the light-responsive material or both are changed. Additionally, refractive index matching liquids are cumbersome to handle, and compensating lenses also require precise alignment.

[0031] Figure 2A A volume printing device according to the present invention is shown, which does not include a compensation element. Here, the light beam 21 directly enters the light-responsive material container 22. The container is attached to a rotating platform 23 as in the device Figure 1A shown above to irradiate the resin from multiple angles and fabricate the object 24.

[0032] Figure 2B With Figure 2A the top view of the device showing the light path through such a device. The light rays of the light beam 21 now change direction when they enter the container 22 of the light-responsive medium. By virtually extending these light rays outside the container, it can be observed that the light rays do not all converge to a single point. However, the focus depends on the lateral offset of each light ray before it enters the container, for example, the light rays intersecting at points 251, 252, and 253. In summary, without using a compensation element, different light rays will have different directions and the light rays will not all intersect at the same point. This means that the light pattern cannot be calculated by parallel beam tomography algorithms (as Figure 1B shown) nor by fan beam tomography algorithms because this requires the light rays to converge to a point (as Figure 3 shown), which are algorithms known to those skilled in the art.

[0033] According to the present invention, a method for digitally compensating for light ray distortion of a light beam in tomography-based additive manufacturing is disclosed, wherein the tomography-based additive manufacturing involves projecting a light pattern from multiple angles into a container containing a light-responsive material, and the method comprises the following steps:

[0034] - Simulating the light ray path through the container and the light-responsive material;

[0035] - Digitally compensating the light projection based on the simulated light ray path to obtain a corrected light projection.

[0036] Digital compensation can be implemented, for example, by resampling:

[0037] - Calculating the light projection at each angle using a parallel beam tomography algorithm, thereby ignoring any distortion caused by the light beam in the actual printing device.

[0038] The parallel beam tomography algorithm (see, for example, A.H. Delaney; Y. Bresler; A fast and accurate Fourier algorithm for iterative parallel-beam tomography, IEEE Transactions on Image Processing, Volume 5, Issue 5, May 1996, 740-753) is known in the art.

[0039] This results in a three-dimensional data set containing two-dimensional light projections at multiple angles. This data set is mathematically represented as I 平行 (x, y, θ), where x and y represent two spatial coordinates, and θ is each projection angle.

[0040] - Comparing the position and direction of the light rays presented by the parallel beam algorithm with the position and direction of the light rays obtained by simulating the light propagation through the container and the light-responsive material. Figure 2C As shown in: The path of light ray 271 is simulated until the mid-section 26 of the light-responsive material container 22 and compared with the path 272 that the light ray might have taken without being deflected. This results in a coordinate mapping between the light ray positions and angles assumed by the parallel beam algorithm (x, y, θ) and the simulated light ray positions and angles described as x’, y’, θ’. This coordinate mapping can be mathematically represented as a function:

[0041] (x, y, θ) = (x’, y’, θ’)

[0042] - Then resampling the light projection calculated using the parallel beam with the simulated coordinates (for example, by linear interpolation):

[0043] I 补偿 = I 平行 (x’,y’,θ’)

[0044] Using the distortion compensation method, different objects can be generated in a time-saving and cost-reducing manner in a tomography-based additive manufacturing method without any physical modification to the equipment components used to perform the method.

[0045] Specifically, the present invention also relates to a method for preparing an object in tomography-based additive manufacturing, wherein the tomography-based additive manufacturing involves projecting a light pattern from multiple angles into a container containing a light-projection material, and the method comprises the following steps:

[0046] - Providing the container containing the light-responsive material;

[0047] - Implementing the above distortion compensation method to obtain a corrected light projection.

[0048] - Projecting the corrected light projection into the container containing the light-responsive material, thereby creating an object without distortion.

[0049] Methods for preparing objects in tomography-based additive manufacturing are known in the art, for example, from WO2019 / 043529A1 or US2018 / 0326666A1. However, the method of the present invention is characterized in that the corrected light projection obtained from the above distortion compensation method is projected without passing through a physical compensation component, such as a refractive index matching liquid bath or a lens.

[0050] The present invention also relates to a method for digitally compensating for ray distortion of a light beam and preparing an object in tomography-based additive manufacturing, and the device comprises:

[0051] - A resin container for providing a resin to be polymerized, wherein the resin container is rotatable;

[0052] - A unit for providing a light beam to be projected into the resin container;

[0053] - A processing unit for performing the distortion compensation method preferably as described above,

[0054] wherein the device does not include a physical compensation component between the unit for providing the light beam and the container, such as a refractive index matching liquid bath surrounding the container or a lens, for example.

[0055] Devices for preparing objects in tomography-based additive manufacturing are known in the art, for example from WO2019 / 043529A1 or US2018 / 0326666A1. However, the device according to the invention is characterized in that it does not have physical compensation components, such as a bath with a liquid having a refractive index match or a lens, for example.

[0056] Since the device according to the invention does not include a physical compensation component (such as a refractive index matching liquid bath surrounding the container or a lens, for example) between the unit for providing the beam and the container, but digitally compensates for any distortion of the rays of the beam, the device according to the invention does not have to be adapted to different resins and containers by changing the printing device, for example by replacing the refractive index matching liquid or the compensation lens.

[0057] According to a preferred embodiment, the resin container is attached to a rotating platform. Thereby, the irradiation of the light-responsive material with a light pattern projected from multiple angles is implemented by rotating the container containing the light-responsive material relative to the unit for providing the beam.

Claims

1. A method for digitally compensating for light beam ray distortion in tomography-based additive manufacturing, wherein the tomography-based additive manufacturing involves projecting a light pattern into a container (22) containing a light-responsive material from multiple angles, the method comprises the following steps: - Simulating the path of light rays passing through the container (22) and the light-responsive material; - Digitally compensating the light projection based on the simulated light ray path to obtain a corrected light projection, wherein digitally compensating the light projection based on the simulated light ray path is implemented by using a resampling algorithm, which includes the following steps: - Calculating the light projection using a parallel beam tomography algorithm; - Calculating the coordinate mapping between the position and direction of the light rays presented by the parallel beam tomography algorithm and the position and direction of the light rays obtained by simulating the light propagation through the container (22) and the light-responsive material; - Resampling the light projection using the coordinate mapping.

2. The method according to claim 1, wherein resampling is performed by linear interpolation.

3. A method for fabricating an object (24) in tomography-based additive manufacturing, wherein the tomography-based additive manufacturing involves projecting a light pattern into a container (22) containing a light-responsive material from multiple angles, the method comprises the following steps: - Providing the container (22) containing the light-responsive material; - Implementing the method for digitally compensating for light beam ray distortion in tomography-based additive manufacturing according to any one of claims 1 to 2 to obtain a corrected light projection; - Projecting the corrected light projection into the container (22) containing the light-responsive material, thereby creating the object (24) without distortion.

4. The method according to claim 3, wherein the corrected light projection is projected without passing through a physical compensation component.

5. The method according to claim 4, wherein the physical compensation component is a bath or a lens with a refractive index matching liquid.

6. An apparatus for digitally compensating for light beam ray distortion and fabricating an object (24) in tomography-based additive manufacturing, the apparatus comprises: - A container (22) for providing a resin to be polymerized, wherein the container (22) is rotatable; - A unit for providing a light beam (21) to be projected into the container (22); - A processing unit for performing the method for digitally compensating for light beam ray distortion in tomography-based additive manufacturing according to any one of claims 1 to 2; wherein the apparatus does not include a physical compensation component between the unit for providing the light beam (21) and the container (22).

7. The apparatus according to claim 6, wherein the physical compensation component is a bath or a lens with a refractive index matching liquid.

8. The apparatus according to claim 6, wherein the container (22) is attached to a rotating platform (23).

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