3D Overprinting Apparatus and Method

Abstract

The present invention discloses a 3D overprinting device that overprints a three-dimensional shape on an existing structure, the device including: a water tank that contains a photocurable material; a drive unit that can fix the existing structure and move it up and down one step at a time within the water tank; and an optical unit that contacts the existing structure and projects UV light from multiple directions from above the surface of the photocurable material toward a surface of the photocurable material exposed at the top, thereby photocuring an area to be cured on the surface of the photocurable material, the optical unit having a mirror structure and a projector that divides an image of a shape to be cured on the surface of the photocurable material contained in the water tank into multiple areas according to the projection direction, converts the images and projects them simultaneously with the projector. The 3D overprinting device operates in such a way that when each divided image is reflected by the mirror structure and projected from multiple directions and combined, the combined image becomes the shape to be cured.

Description

Technical Field

[0001] The present invention relates to a 3D over-printing apparatus and method for over-printing a three-dimensional shape on an existing structure. More specifically, the present invention relates to a 3D over-printing apparatus and method in which divided images are simultaneously projected onto the surface of a UV curable substance from a plurality of directions using a mirror and then photocured.

Background Art

[0002] An over-printing type 3D printing apparatus and method for outputting a new shape on an existing structure using a polymer substance or a material added with a polymer substance have been proposed.

[0003] Among them, in Prior Patent 1 (Korean Patent No. 10-2106102) filed by the present applicant, a single projector is rotated outside a water tank containing a photocurable substance while the existing structure completely immersed in the photocurable substance, and UV light images are sequentially projected from various directions, or a plurality of projectors are used to simultaneously project UV light images from a plurality of directions, so that light energy increases in the region where the UV light overlaps inside the photocurable substance and photocuring occurs. A 3D over-printing apparatus and method using such a method are disclosed.

[0004] However, such a method has a limitation in that it cannot be applied when a photocuring material such as resin is opaque or has a high absorption rate, because UV light cannot penetrate to the inside of the resin in which the existing structure is completely immersed.

[0005] To solve such a problem, in the case of an opaque resin, since the region where photocuring can occur by UV light is the surface of the resin, the existing SLA and Vat photopolymerization methods where photocuring occurs on the surface of the resin can be considered. Among them, as schematically shown in FIG. 1, the Vat photopolymerization method includes a bottom-up method of projecting a UV image onto a transparent window under the resin water tank and a top-down method of projecting it onto the surface of the resin from above the water tank. Both methods are suitable for directly forming a new structure without an existing structure.

[0006] Because in the case of the bottom-up method, it is a method of photocuring the resin in contact with the bottom surface of the resin container while gradually raising the distance between the light-receiving surface and the bottom surface of the resin water tank in a close contact state one step at a time. If there is an existing structure, it is impossible to output because it is impossible to make both sides in close contact or adjust the distance between both sides. In the case of the top-down method, as schematically shown in FIG. 2, although photocuring occurs on the upper surface of the resin, if there is an existing structure, there is a problem that a shadow region is generated depending on the shape of the structure and the irradiation direction of the UV light, and correct output cannot be achieved.

[0007] Therefore, there is still a need for a groundbreaking study on an apparatus and method that can easily overprint and manufacture a shaped body of the same or different materials on an existing structure made of the same or different materials.

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention has been made to solve the problems in such prior art. The object is to configure an optical unit so that a partial region of UV light projected from one projector is inverted in each projection direction using a plurality of mirrors and projected onto an existing structure simultaneously from a plurality of directions, thereby eliminating the problem of shadow region generation due to the shape of the existing structure and the projection direction, and to provide a 3D overprinting apparatus and method.

[0009] Another object of the present invention is to provide a 3D overprinting apparatus and method capable of overprinting a three-dimensional shape on an existing structure even with a photocurable material that is opaque or has a high light absorption rate by sequentially photocuring the surface region of the photocurable material housed in an aquarium.

[0010] The problems to be solved by the present invention are not limited to the above-described technical problems, and other technical problems not described above will be clearly understood by those having ordinary knowledge in the technical field to which the present invention pertains from the following description.

Means for Solving the Problems

[0011] In order to achieve the above object, a 3D overprinting apparatus for overprinting a three-dimensional shape on an existing structure according to an embodiment of the present invention is a 3D overprinting apparatus for overprinting a three-dimensional shape on an existing structure, including: an aquarium containing a photocurable material; a driving unit for fixing the existing structure and moving it up and down step by step in the aquarium; and an optical unit having a projector and a mirror structure that projects UV light from above the surface of the photocurable material in contact with the existing structure and exposed at the upper part simultaneously from a plurality of directions toward the surface of the photocurable material to photocure the area to be cured on the surface of the photocurable material. The optical unit divides the shape image to be cured on the surface of the photocurable material housed in the aquarium into a plurality of regions according to the projection direction, converts it, and when it is simultaneously projected by the projector, each divided image is reflected by the mirror structure and projected from a plurality of directions and combined so as to form an image having the shape to be cured.

[0012] In the above embodiment, it is preferable that the optical unit includes one projector and a mirror structure having two or more mirrors perpendicular or parallel to each other.

[0013] Also, in the above embodiment, it is preferable that the optical unit includes two projectors and a mirror structure having two or more mirrors perpendicular or parallel to each other.

[0014] Also, in the above embodiment, it is preferable that the optical unit includes one projector and a mirror structure having four mirrors.

[0015] Also, in the above embodiment, it is preferable that the optical unit includes two projectors and a mirror structure having four mirrors.

[0016] Also, in the above embodiment, it is preferable to further include heating means for heating the surface area of the photocurable substance contained in the water tank to lower the viscosity.

[0017] Also, in the above embodiment, it is preferable that the drive unit can drive the existing structure to move up and down and tilt left and right.

[0018] Also, in the above embodiment, it is preferable to further include a water level sensor for automatically adjusting the water level of the photocurable substance contained in the water tank.

[0019] On the one hand, a 3D overprinting method for overprinting a three-dimensional shape on an existing structure according to an embodiment of the present invention is a method for overprinting a three-dimensional shape on an existing structure using a 3D overprinting apparatus as described above, including the steps of positioning an existing structure that requires overprinting in a water tank containing a photocurable material, and an overprinting step of overprinting the existing structure in a top-down manner by sequentially photocuring the layer of the photocurable material exposed at the top while lowering the existing structure step by step in the water tank. The overprinting step includes dividing a shape image to be cured on the surface of the photocurable material accommodated in the water tank into a plurality of regions according to the projection direction, converting the divided image, and projecting it onto the projector. Each divided image is reflected by the mirror structure and projected from a plurality of directions and combined to form an image that is photocured to have the shape to be cured. This is an overprinting step that is sequentially performed while lowering the existing structure step by step.

[0020] In the above embodiment, the overprinting step preferably includes, for each overprinting step, generating a slice image of the area to be overprinted on the existing structure, dividing the projection direction into a plurality of directions to define an image area for each direction, dividing the slice image into images corresponding to each divided area, converting each divided image in consideration of image inversion by the mirror and image distortion, etc., and combining them into one projection image, loading the combined projection image into the projector and projecting it, and projecting the divided images reflected by each mirror surface onto each divided surface of the overprinting area to form the shape to be cured.

[0021] Also, in the above embodiment, the overprinting step preferably includes a step of dividing an image according to the direction in which light projected from a projector is reflected by a mirror surface and projected onto the surface of a photocurable material using one projector and a mirror structure having two or more mirrors perpendicular or parallel to each other.

[0022] Also, in the above embodiment, the lamination step preferably includes a step of dividing an image according to the direction in which light projected from a projector is reflected by a mirror surface and projected onto the surface of a photocurable material, using two projectors and a mirror structure having two or more mirrors perpendicular or parallel to each other.

[0023] Also, in the above embodiment, the lamination step preferably includes a step of dividing the projection direction into eight directions, using one projector and a mirror structure having four mirrors.

[0024] Also, in the above embodiment, the lamination step preferably includes a step of dividing the projection direction into ten directions, using two projectors and a mirror structure having four mirrors.

[0025] Also, in the above embodiment, the lamination step preferably further includes a step of heating the surface region of the photocurable material so as to lower the viscosity of the photocurable material when forming a layer to be newly cured, by lowering the existing structure step by step.

[0026] Also, in the above embodiment, the lamination step preferably further includes a step of driving the existing structure in a manner that mixes the ascending, descending, and tilting operations in the left and right directions of the existing structure when forming a layer to be newly cured, by lowering the existing structure step by step.

Advantages of the Invention

[0027] When using a 3D overprinting device for overprinting a three-dimensional shape on an existing structure according to the present invention having the above-described configuration, problems such as the generation of shadow regions due to the complex shape of the existing structure and the projection direction can be prevented in advance, and a three-dimensional shape can be easily overprinted on the existing structure.

[0028] In addition, the present invention can overprint a three-dimensional shape onto an existing structure even with a photocurable substance that is opaque or has a high light absorption rate by sequentially photocuring the surface region of the photocurable substance housed in the water tank.

Brief Description of the Drawings

[0029]

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Embodiments for Carrying Out the Invention

[0030] First, as a method for solving the shadow area generation problem that occurs during overprinting by the above-described conventional top-down method, it is conceivable to project from a plurality of directions. For example, as schematically shown in FIG. 3, while rotating one projector around an existing structure, an image that matches the cured shape in each direction is projected from all directions, or a plurality of projectors are installed in different directions from each other to simultaneously project respective images that match the cured shape in each direction from a plurality of directions.

[0031] However, in the method of rotating one projector, since it is necessary to have a drive mechanism for rotating the optical system or the water tank containing the photocurable resin 360 degrees around the existing structure, the configuration of the mechanism part becomes complicated, and the time required to photocure a single layer on the surface becomes as long as the rotation time. And in the method of installing a plurality of projectors, due to the size of the projectors, there is a limit to the number of projectors that can be installed, so the number of directions in which projection can be performed simultaneously is limited, and the size of the entire system increases by the number of projectors to be configured, the configuration becomes complicated, and the cost increases. Therefore, it is necessary to develop a system that can project light simultaneously from a plurality of directions at a small cost without the system being too large or too complicated, eliminating the need for 360-degree rotation and shortening the output time.

[0032] In view of such a situation, the present inventors devised a method of realizing projection from a plurality of directions using a plurality of mirrors in order to improve the above-described shadow area problem. For example, as schematically shown in FIG. 4, a partial area of the UV light projected from one projector is inverted in each projection direction using two or more mirrors, and the projector and the mirrors are arranged so as to be simultaneously projected onto the existing structure from a plurality of directions.

[0033] The method of combining a projector and mirrors can be configured by using one projector and two, three, or four mirrors that are perpendicular or parallel to each other, or by using two projectors and two or more mirrors that are perpendicular or parallel to each other, or by using three mirrors for each projector, or by using two projectors and four mirrors, as exemplarily shown in FIG. 5.

[0034] Among these, taking the case of using one projector and four mirrors as an example, the four directions that are reflected by the four mirror surfaces and immediately projected onto the resin surface, and the four directions of the corner portions that are continuously reflected twice by adjacent mirror surfaces and projected onto the resin surface, can divide the area into a total of eight directions. The conceptual diagram of the image division area and the projection direction in this case is as shown in FIG. 6.

[0035] Also, when using two projectors and four mirrors, for each projector, the three directions that are reflected by the three nearby mirror surfaces and immediately projected onto the resin surface, and the two directions of the corner portions that are continuously reflected twice by adjacent mirror surfaces and projected onto the resin surface, etc., can divide the area into five directions each, for a total of ten directions.

[0036] When the offset of the projector is close to zero, since the incident angle is large in the up, down, left, and right directions of the projected image, when four mirrors are arranged and reflected, it is possible to obtain the projection light with a large incident angle in eight directions from the four directions of each mirror and the four directions of the corners orthogonal to the mirrors towards the center of the image.

[0037] However, when using a projector with an offset as large as about 100% to obtain a larger incident angle, a large incident angle can be obtained in three directions: the left - right direction and the upward direction of the projected image. However, in the downward direction, the incident angle becomes smaller as it approaches 0. Therefore, by arranging mirrors on three sides: left / right / up on one projector, a projection beam with a large incident angle in five directions can be obtained, which is from the three directions of the mirror surfaces and the two directions of the corners between the mirrors towards the center. Since the combination of one projector and three mirrors described above has an asymmetric structure without projection light incident from the downward direction, if another combination of the same one projector and three mirrors is arranged symmetrically, projection light can be obtained that is incident symmetrically from five directions from each of the two projectors, for a total of ten directions.

[0038] When the shape image to be cured on the surface of the photocurable resin is divided into a plurality of regions according to the projection direction, and this is converted and projected onto a projector, each divided image is reflected by a mirror and projected onto the surface of the resin from a plurality of directions and combined into an image that is the shape to be cured.

[0039] Hereinafter, a 3D overprint apparatus according to an embodiment of the present invention for realizing the above - described principle will be described in detail.

[0040] As schematically shown in FIG. 7, a 3D overprint apparatus according to an embodiment of the present invention includes a water tank 10 containing a photocurable substance for selectively curing a photocurable polymer substance on an existing structure by irradiating it with UV light, a drive unit 20 for fixing the existing structure and being able to move it up and down one step at a time in the water tank, and an optical unit 30 having a projector and a mirror structure so that UV light can be projected simultaneously from a plurality of directions. Hereinafter, the installation and operation methods of each component will be described.

[0041] First, in order to support each of the above - mentioned components, it includes a base plate on the bottom surface and a main body frame 60 extending upward therefrom. Inside and outside this main body frame 60, each component is fixedly or movably installed.

[0042] The water tank portion 10 includes a water tank 12 with an open upper portion for containing a photocurable resin, a resin supply tank 14 and a resin discharge tank 16 for storing the resin supplied or discharged inside and outside the water tank 12. The resin supply tank 14 and the resin discharge tank 16 are respectively arranged in the vertical direction of the water tank 12 and are connected to the water tank 12 through pipes equipped with on-off valves capable of controlling the resin flow.

[0043] Preferably, it also includes a configuration for automatically adjusting the water level of the resin in the water tank 12. This includes a water level sensor 18 installed on the upper part or side surface of the water tank 12, and a control unit for appropriately opening and closing the on-off valve according to the measurement signal from the water level sensor 18.

[0044] The drive unit 20 includes a structure holder 22 having a structure pedestal for supporting existing structures and output objects, and a drive mechanism capable of moving the structure holder 22 up and down step by step. Further, it can further include a drive mechanism capable of moving up and down a water tank pedestal 24 for supporting the water tank 12. The drive mechanism can be arranged and installed inside the main body frame 60.

[0045] The optical unit 30 includes a projector 32 arranged above the water tank 12 and horizontally attached to the upper end of the main body frame 60, a fold mirror 36 for reflecting the image projected from the projector 32 vertically downward through a lens 34, and a mirror structure 38 arranged below the fold mirror 36.

[0046] When the shape image to be cured on the surface of the resin contained in the water tank 12 is divided into a plurality of regions according to the projection direction, converted, and projected by the projector 32, each divided image is reflected by a plurality of mirrors of the mirror structure 38 and projected onto the surface of the resin from a plurality of directions and combined to form an image that is the shape to be cured.

[0047] At this time, with reference to the exemplary implementation examples shown in FIGS. 5 and 6, the projector 32 and the mirror structure 38 can be appropriately arranged and installed by being composed of a combination of one projector and a plurality of mirrors, or a combination of a plurality of projectors and a plurality of mirrors, in order to efficiently improve the occurrence of regions that are not photocured due to the shadow generated according to the light irradiation direction and the shape of the existing structure.

[0048] The projector 32 is a component for providing a light source necessary for curing to the photocurable substance accommodated in the water tank 12, and any one of a digital light processing projector (DLP projector) or other image generation optical systems can be used. Any optical system can be used as long as it can create a 1D or 2D optical image or projection toward the photocurable substance.

[0049] On the other hand, if the incident angle of the UV light projected by the projector is large, it is possible to overprint on the inclined portion of the existing structure without generating a shadow, so a projector with a small throw ratio (preferably 1.0 or less as much as possible) is preferable (see FIG. 8).

[0050] Also, as schematically shown in FIG. 9, when the offset of the projector is close to 0%, the projection direction is close to being symmetric, so it is composed of one projector and a plurality of mirrors. When the offset is large, such as 100% or more, the incident angle is asymmetric, that is, one end has a large incident angle, but the other side is close to 0 (perpendicular incidence). Therefore, it is preferable to arrange a mirror on the side where the incident angle of the projection light of each projector is large, and finally form a symmetric projection light distribution using a plurality of such projectors.

[0051] When the structure holder 22 is lowered for step - by - step lamination in the top - down method and a new resin layer covers the output layer, if the viscosity of the resin is high, the resin does not flow well, making it difficult to uniformly form a new layer and it may take a long time. To lower the viscosity by raising the surface temperature of the resin so that the resin flows smoothly and a new layer is formed within a short time, it is preferable to install a heating mechanism 50 along the upper edge of the resin water tank 12 on the upper part or side surface of the water tank 12 (see Fig. 10).

[0052] Also, in order to be able to utilize it together with or independently of the heating mechanism 50 so that a new resin layer is formed well, when driving the structure support of the structure holder, it is preferably configured to be able to tilt not only vertically but also in the left - right direction. Fig. 11 illustrates a driving procedure of such a structure support.

[0053] Hereinafter, an embodiment of a method of overprinting on an existing structure using a 3D overprinting apparatus for overprinting a three - dimensional shape on the existing structure according to an embodiment of the present invention configured as described above will be described in detail.

[0054] A 3D overprinting method according to an embodiment of the present invention includes the steps of positioning an existing structure that requires overprinting in a water tank containing a photocurable substance, and an overprinting lamination step of overprinting on the existing structure in a top - down method in which the existing structure is sequentially lowered in the water tank while sequentially photocuring the layer of the photocurable substance exposed at the top.

[0055] First, an existing structure that requires overprinting is positioned on a structure holder 22 that can be moved vertically step - by - step in a water tank 10 containing a photocurable resin.

[0056] The existing structure that requires overprinting of the same or different materials on at least a part of its outer surface may be a structure of various shapes combined with concave or convex shapes, and may be made of a transparent or opaque material such as metal.

[0057] The existing structure can be manufactured by various methods known to date. Its surface is preferably roughened in advance in order to increase the bonding force with the substance to be photocured or bonded thereon. As means therefor, various methods such as chemical etching, sand blasting, and laser surface treatment can be used.

[0058] The existing structure needs to be fixed so as to be positioned on the structure pedestal of the structure holder 22 without shaking, and fixing means of various methods can be appropriately used as needed.

[0059] The photocurable resin may be a transparent resin or an opaque resin.

[0060] In the lamination step, the shape image to be cured on the surface of the photocurable substance accommodated in the water tank is divided into a plurality of regions according to the projection direction, and when this is converted and projected by the projector, each divided image is reflected by the mirror structure and projected from a plurality of directions and combined. The laminated step is a step in which the existing structure is sequentially lowered step by step while being photocured so that the combined image has the shape to be cured.

[0061] Such an overprint lamination step will be described in more detail with reference to the explanatory diagram illustrated in FIG. 12. FIG. 12 shows, as an example, the case of overprinting a three-dimensional shape of a cross-sectional star shape indicated in yellow on an existing structure having a cross-sectional shape protruding in four directions of up, down, left, and right.

[0062] First, (1) for each lamination step, a slice image of the region to be overprinted is generated on the existing structure using a modeling and slicing program. Various programs known to date can be used.

[0063] Next, (2) the directions in which the light is reflected and projected by each mirror surface of the mirror structure are divided into a plurality of directions, for example, 2 to 10 directions, and image regions for each direction are defined, and the slice image is divided into images corresponding to each divided region. FIG. 12 shows an example of division into 8 directions.

[0064] Next, (3) considering image inversion by the mirror, image distortion, etc., each divided image is transformed and combined into one projected image. When using two or more projectors, the steps of dividing, transforming, and combining the projected images may be performed for each projector.

[0065] Next, (4) the projected image thus combined is loaded into each projector and projected. Then, (5) the divided images reflected by each mirror surface gather in the direction (center) of the existing structure on the resin surface and are projected onto each divided surface of the overprint region to create the overall shape.

[0066] For this purpose, an appropriate arrangement example may be selected and used from the arrangement states of the projector exemplarily shown in FIG. 5 and the mirror structure having a plurality of mirrors. When dividing the projection direction into 8 directions, it is preferable to configure an optical unit having one projector and four mirrors. When dividing the projection direction into 10 directions, it is preferable to configure an optical unit having two projectors and four mirrors.

[0067] When the lamination of one layer is completed as described above, the existing structure is lowered one step into the water tank, a new resin layer is formed on the output layer, and the lamination step is repeated again.

[0068] At this time, the lamination step may further include a step of heating the surface region of the resin in order to lower the viscosity of the resin and induce the flow of the resin quickly and stably when forming a resin layer to be newly cured by lowering the existing structure step by step into the water tank. The heating in the heating step is preferably performed by heating means arranged above or outside the upper edge portion of the water tank.

[0069] In addition, the lamination step can further include a driving step of driving the existing structure in a manner that mixes the upward, downward, and left - right tilting movements of the existing structure into the resin when forming a resin layer to be newly cured by lowering the existing structure step - by - step into the water tank. For example, as shown in FIG. 11, by continuously driving the existing structure in the order of tilting to the left, descending, ascending, tilting to the right, and descending, the formation of a new resin layer can be smoothly induced. Such a driving step of the existing structure can be performed simultaneously with or independently of the heating step of the resin surface area described above.

[0070] The above - described lamination step may be repeated until the final overprint shape is completed. After that, after taking out the final output overprinted on the existing structure from the water tank, finishing processing is performed.

Claims

1. A 3D overprinting apparatus for overprinting a three-dimensional shape onto an existing structure, comprising: a water tank containing an opaque photocurable material; a driving unit for fixing the existing structure and capable of moving it step by step up and down in the water tank; an optical unit having a projector and a mirror structure, the optical unit being in contact with the existing structure and simultaneously projecting UV light from a plurality of directions onto the upper surface of the photocurable material exposed at the upper part, so as to photocure the area to be cured on the surface of the photocurable material; the optical unit divides the shape image to be cured on the surface of the photocurable material contained in the water tank into a plurality of regions according to the projection direction, converts it, and when simultaneously projecting it with the projector, each divided image is reflected by the mirror structure and projected from a plurality of directions and combined into an image that forms the shape to be cured; the projector and the mirror structure of the optical unit are arranged to invert the partial regions of the UV light projected from the projector using a plurality of mirrors and project them simultaneously from a plurality of directions, and the plurality of mirrors are configured such that the angles between their respective reflecting surfaces are perpendicular or parallel to each other. The 3D overprinting apparatus.

2. The 3D overprinting apparatus according to claim 1, wherein the optical unit includes one projector and a mirror structure having two or more mirrors perpendicular or parallel to each other.

3. The 3D overprinting apparatus according to claim 1, wherein the optical unit includes two projectors and a mirror structure having two or more mirrors perpendicular or parallel to each other.

4. The 3D overprinting apparatus according to claim 1, wherein the optical unit includes one projector and a mirror structure having four mirrors.

5. The 3D overprinting apparatus according to claim 1, wherein the optical unit includes two projectors and a mirror structure having four mirrors.

6. The 3D overprinting apparatus according to claim 1, further comprising heating means for heating the surface region of the photocurable material contained in the water tank to reduce its viscosity.

7. The 3D overprinting apparatus according to claim 1, wherein the driving unit can drive the existing structure to move up and down and tilt left and right.

8. The 3D overprinting apparatus according to claim 1, further comprising a water level sensor for automatically adjusting the water level of the photocurable substance contained in the water tank.

9. A 3D overprinting method for overprinting a three-dimensional shape on an existing structure using the 3D overprinting apparatus according to any one of claims 1 to 8, positioning an existing structure that requires overprinting in a water tank containing a photocurable substance; a lamination step of overprinting on the existing structure in a top-down manner in which the layer of the photocurable substance exposed at the upper part is sequentially photocured while lowering the existing structure step by step in the water tank, In the lamination step, when the shape image to be cured on the surface of the photocurable substance contained in the water tank is divided into a plurality of regions according to the projection direction, converted, and projected onto the projector, each divided image is reflected by the mirror structure and projected from a plurality of directions and combined so that the image is in the shape to be cured. The 3D overprinting method is a lamination step that is sequentially performed while lowering the existing structure step by step.

10. The lamination step includes: generating a slice image of the area to be overprinted on the existing structure for each lamination step; dividing the projection direction into a plurality of directions to define image regions for each direction, and dividing the slice image into images corresponding to each divided region; converting each divided image and combining them into one projection image in consideration of image inversion and image distortion by the mirror; loading the combined projection image into a projector and projecting it; The 3D overprinting method according to claim 9, further comprising a step in which the divided images reflected by each mirror surface are projected onto each divided surface of the overprinting area to form the shape to be cured.

11. The lamination step includes a step of dividing an image according to the direction in which light projected from a projector is reflected by a mirror surface and projected onto the surface of a photocurable substance, using one projector and a mirror structure having two or more mirrors perpendicular or parallel to each other. The 3D overprinting method according to claim 9.

12. The lamination step includes, using two projectors and a mirror structure having two or more mirrors perpendicular or parallel to each other, dividing an image according to the direction in which light projected from the projectors is reflected by the mirror surfaces and projected onto the surface of the photocurable material. The 3D overprinting method according to claim 9.

13. The lamination step includes, using one projector and a mirror structure having four mirrors, dividing the projection direction into eight directions. The 3D overprinting method according to claim 9.

14. The lamination step includes, using two projectors and a mirror structure having four mirrors, dividing the projection direction into ten directions. The 3D overprinting method according to claim 9.

15. The lamination step further includes heating a surface region of the photocurable material to lower the viscosity of the photocurable material when forming a layer to be newly cured by lowering the existing structure step by step. The 3D overprinting method according to claim 9.

16. The lamination step further includes driving the existing structure in a manner that mixes the ascending, descending, and tilting motions in the left and right directions of the existing structure when forming a layer to be newly cured by lowering the existing structure step by step. The 3D overprinting method according to claim 9.

Images