A continuous 3D printing method and printing device based on dynamic rendering

Abstract

The present application relates to a continuous 3D printing method and printing device based on dynamic rendering. The method includes the following steps: obtaining a plurality of sliced images based on a three-dimensional model to be printed, each of the sliced images having an original exposure boundary, and dynamically configuring a printing speed v; calculating a theoretical deviation value h of the printing contour of the three-dimensional model according to the printing speed v c and an actual deviation value Δh, and correcting each sliced image based on the actual deviation value Δh to obtain a corrected exposure boundary, that is, the corrected exposure boundary is equal to the distance obtained by horizontally increasing or decreasing the original exposure boundary by Δh; exposing pixels within the corrected exposure boundary. The present application can dynamically change the contour of the sliced images of the three-dimensional model according to the change of the printing speed, and by increasing or decreasing the thickness of the contour, reversely compensate for the change of the contour thickness caused by the speed change, and finally obtain a three-dimensional model with accurate printing size, coherent and smooth contour.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocuring 3D printing, and particularly relates to a continuous 3D printing method and a printing device. Background Art

[0002] In the field of photocuring, according to the light source system of photocuring forming, the photocuring 3D printing technology is divided into laser point light source (SLA) and surface light source digital light projection (DLP). The process of photocuring is to use ultraviolet light to irradiate and cure the photosensitive resin layer by layer. After the energy received by the irradiated photosensitive resin exceeds the critical value Ec, a polymerization reaction will occur and it will be cured.

[0003] The DLP 3D printing system cures layer by layer through many frames of images and can form a format at one time. Therefore, it is a faster 3D printing method. In the traditional DLP technology, the layer thickness of each slice is fixed and the exposure time is fixed (usually slightly overexposed). Therefore, macroscopically, it can be considered that the discrete exposure amount received by each point of the model is uniform. Although the resin materials around each slice will receive some diffused light, the up and down movement of the printing platform in the z-axis will quickly mix these lightly exposed materials with other materials, continuously eliminating the accumulation of resin exposure amount around the printed part. Therefore, traditional DLP printers only need to cooperate with simple xy size scaling to unify the accuracy.

[0004] The continuous liquid surface printing technology realizes continuous, smooth and rapid forming by making the irradiated and cured surface not adhere to the release film, for example, establishing a non-curing area so that the resin is always cured and formed above the non-curing area. Compared with the traditional layer-by-layer printing method (such as DLP), the continuous liquid surface 3D printing technology can realize the rapid printing of complex objects. However, in the continuous printing method, there are large solid areas in some printing layers that need to be exposed. In order to allow the photosensitive resin to flow in, the printing speed will be reduced. However, if the printing speed is reduced, the exposure amount of the photosensitive material near the three-dimensional model will increase, and the contour thickness (the lateral distance between the actual cured boundary and the ideal cured boundary) will increase. And if the printing speed is increased, the exposure amount of the photosensitive resin will decrease and the printed object will become thinner. Summary of the Invention

[0005] The purpose of the present application is to provide a continuous 3D printing method and a printing device that can obtain a three-dimensional model with precise dimensions and smooth contours.

[0006] In order to achieve the above-mentioned invention purpose, the present invention adopts the following technical solution: A continuous 3D printing method based on dynamic rendering, including the following steps:

[0007] Obtain a plurality of slice images based on the three-dimensional model to be printed, each of the slice images has an original exposure boundary, and dynamically configure the printing speed v for each frame of slice image;

[0008] Calculate the theoretical deviation value h between the printing profile of the three-dimensional model and the standard model according to the dynamically changing printing speed v c , and correct each of the sliced images based on the actual deviation value Δh to obtain a corrected exposure boundary, that is, the corrected exposure boundary is equal to the original exposure boundary increased or decreased by a distance of Δh laterally;

[0009] Expose the pixels within the corrected exposure boundary.

[0010] In an embodiment of the present application, a corrected area is formed between the corrected exposure boundary and the original exposure boundary, and the width of the corrected area covers m circles of pixels, where n circles of pixels are all black pixels with a gray level of 0 or all white pixels with a gray level of 255, and the remaining pixels are gray pixels with a gray level greater than 0 and less than 255, m≥n, and n is an integer.

[0011] In an embodiment of the present application, when the speed v is slow and causes Δh>0, the printing profile of the three-dimensional model becomes thicker, and the n circles of pixels are all black pixels with a gray level of 0; when the speed v is fast and causes Δh<0, the printing profile of the three-dimensional model becomes thinner, and the n circles of pixels are all white pixels with a gray level of 255.

[0012] In an embodiment of the present application, n = |[Δh / d]|, where d is the pixel size of the 3D printing device.

[0013] In an embodiment of the present application, Δh = α×h c , where α is an adjustment coefficient.

[0014] In an embodiment of the present application, the theoretical deviation value h of the printing profile of the three-dimensional model c satisfies the following relationship, where,

[0015] P represents the light intensity;

[0016] v represents the printing speed;

[0017] E c represents the critical exposure amount of the photosensitive resin;

[0018] τ represents the light transmittance of the photosensitive resin under unit thickness;

[0019] Δd is the unit thickness;

[0020] T represents the exposure time.

[0021] In an embodiment of the present application, 0.5≤α≤1.2.

[0022] In one embodiment of the present application, m = n + 1, and the corrected exposure boundary further increases or decreases by one circle of gray pixels relative to the original exposure boundary. When Δh > 0, the gray value of this circle of gray pixels is: Gray n+1 = 255×(1 - f / d); when Δh < 0, the gray value of this circle of gray pixels is Gray n+1 = 255×f / d, where t = [Δh mod d].

[0023] Another technical solution of the present application is:

[0024] A continuous 3D printing device is provided, including a material tank for containing photosensitive resin, a printing platform that is vertically movable above the material tank along the Z-axis, a projection device, a memory, and a processor. The processor is configured to execute the printing method as described above.

[0025] Compared with the prior art, the present invention has the following beneficial effects: The present application can dynamically change the contour of the sliced image of the three-dimensional model according to the change of the printing speed. By increasing or decreasing the thickness of the contour, it compensates for the change in the contour thickness caused by the speed change in reverse, and finally obtains a three-dimensional model with accurate printing size, coherent and smooth contour. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG Figure 1 is a schematic structural diagram of a 3D printing device in an embodiment of the present application;

[0027] FIG Figure 2 is Figure 1 the schematic diagram of the 3D printing device in;

[0028] FIG Figure 3 shows the decay relationship of light intensity in the photosensitive resin;

[0029] FIG Figure 4 shows the light intensity received by a point at a distance h from the periphery of the original exposure boundary of the three-dimensional model at time t;

[0030] FIG Figure 5 shows the established curing area, diffusion curing area, and under-curing area;

[0031] FIG Figure 6 shows, in an embodiment of the present application, the ideal exposure area and the original exposure boundary;

[0032] FIG Figure 7 shows Figure 6 in the embodiment shown, the corrected exposure area and the corrected exposure boundary;

[0033] FIG Figure 8 shows Figure 6In the illustrated embodiment, the brightness and darkness of the pixels of the original exposure boundary before correction;

[0034] Appendix Figure 9 shows Figure 6 In the illustrated embodiment, the brightness and darkness of the pixels near the corrected exposure boundary.

[0035] Wherein: 101, optical machine; 102, material tank; 103, photosensitive resin; 104, Z-axis lifting mechanism; 105, printing platform; 106, three-dimensional model; 200, release film; 300, uncured area. Specific embodiments

[0036] To describe in detail the technical content, structural features, achieved objectives and effects of the invention, the following will be described in detail in conjunction with embodiments and with reference to the accompanying drawings. Appendix Figure 1 The upward direction in the appendix is the "Z-axis" direction and the optical axis direction described in this specification.

[0037] This application proposes a continuous 3D printing method and printing device based on dynamic rendering. Refer to Figure 1 , 2 As shown, the continuous 3D printing device includes a frame, a material tank 102 for containing photosensitive resin, a printing platform 105 arranged above the material tank and liftable along the Z-axis, a projection device, a memory, and a processor. A horizontal workbench extending along the x-y plane is provided in the middle of the frame, and the material tank 102 is fixedly arranged on the horizontal workbench. The projection device in this embodiment is an optical machine 101. The optical machine 101 is fixedly installed below the horizontal workbench, the printing platform 105 is arranged above the horizontal workbench in a liftable manner, and a Z-axis lifting mechanism 104 is arranged at the rear of the frame. The printing platform 105 realizes vertical upward or downward movement through the Z-axis lifting mechanism 104. A release element, such as a release film, is arranged at the bottom of the material tank 102.

[0038] When the continuous 3D printing device is working, the projection light emitted upward by the optical machine 101 passes through the release film 200 and cures the photosensitive resin 103 above the release film 200 to form a three-dimensional model 106. The upper part of the three-dimensional model 106 adheres to the printing platform 105 and moves upward with the printing platform 105. The lower part of the three-dimensional model 106 is immersed in the photosensitive resin. There is an interface between the photosensitive resin 103 and the release film 200, and the photosensitive resin stops the polymerization reaction at this interface, so that there is always liquid photosensitive resin between the three-dimensional model 106 and the release film 200, reducing the adhesion force between the three-dimensional model and the release film, and thus realizing continuous high-speed 3D printing.

[0039] In one embodiment, a computer program is stored in the memory of the continuous 3D printing device of this application, and the processor is configured to execute the following printing method:

[0040] Step 1: Start the printing program. The printing platform descends above the non-curing area 300 driven by the Z-axis lifting mechanism 104, and the light machine is started.

[0041] Step 2: Call a number of sliced images of the 3D model to be printed currently. Each sliced image has an original exposure boundary, which is the ideal printing boundary calculated through the original 3D model design. Configure the dynamic printing speed v for the 3D model.

[0042] During the actual continuous light exposure process, as the speed changes, the integral of the light exposure changes, and the printed 3D model may become thicker or thinner compared to the designed model. Therefore, there will be a theoretical deviation value h for the printing contour. c ,h c represents the horizontal lateral distance between the ideal printing boundary and the actual curing boundary, and h c changes with the printing speed v.

[0043] Step 3: Calculate the theoretical deviation value h of the 3D model according to the current printing speed v c ,and calculate the actual deviation value Δh according to the theoretical deviation value h c ,and then etch or dilate the sliced image according to Δh.

[0044] Among them,

[0045] P represents the light intensity;

[0046] v represents the printing speed;

[0047] E c represents the critical exposure amount of the photosensitive resin;

[0048] τ represents the light transmittance of the photosensitive resin under unit thickness, and is also written as tau;

[0049] Δd is the unit thickness;

[0050] T represents the exposure time.

[0051] The actual deviation value Δh is corrected according to the selected photosensitive resin material. Δh = α × h c ,where α is the adjustment coefficient for fine-tuning in actual engineering, to correct the original exposure boundary of each sliced image by expanding or shrinking. Δh is the distance that needs to correct the original exposure boundary to thicken or reduce, so as to obtain the corrected exposure boundary.

[0052] Step 4: Expose the pixels within the corrected exposure boundary until the printing is completed to obtain a complete 3D model.

[0053] In this embodiment, the correction of the 3D model printing boundary is carried out along with the printing process. In other embodiments of the present application, the above step of correcting the boundary of the sliced image can also be carried out during the 3D model design process or during the printing preparation stage. Simply adjusting the order of the steps does not affect the implementation of the technical solution of the present application.

[0054] The printing speed v of the 3D printing device can be a dynamically changing printing speed curve set manually based on the sliced shape of the printed part and the material viscosity. During the printing process, the printing speed V changes dynamically according to the curve. For example, for a certain photosensitive resin material with a standard printing speed of 2.5 mm / min, the printing speed v can be set around 2.5 mm / min, with the slowest being 1.5 mm / min and the fastest being 3 mm / min, and it is iteratively adjusted in a timely manner according to the actual printing situation.

[0055] The setting of the printing speed satisfies the following relationship: 1 ≤ v ≤ v0, where v0 is the standard printing speed of the material. Generally, for viscous photosensitive resin materials, the standard printing speed v0 = 2 - 4 mm / min, and for thin photosensitive resin materials, the standard printing speed is 5 - 10 mm / min. If the printing speed is a bit faster, h c will be small or even negative. If the printing speed is a bit slower, h c will be positive.

[0056] h c can be obtained through theoretical calculation, and the detailed calculation process will be introduced below. α is selected according to the photosensitive resin material. Generally, the more viscous the photosensitive resin material, the smaller the actual thickening value of the printing contour compared to the theoretically calculated h c should be, so α should be a bit smaller, such as 0.85; the thinner the photosensitive resin material, the closer the actual thickening value is to the theoretical deviation value h c and α is close to 1.

[0057] Specifically, in step 3, if the current printing speed v causes h c to increase, and h c is positive, it means that the current printing speed will make the thickness of the printing contour larger and the 3D model thicker. Therefore, in the correction process, the original exposure boundary is reduced by Δh to obtain the corrected exposure boundary. If h c is negative, it means that the current printing speed v will make the printing contour smaller and the 3D model thinner. Therefore, in the correction process, the original exposure boundary needs to be increased by Δh. The area formed between the corrected exposure boundary and the original exposure boundary is the correction area, which is a strip-shaped area parallel to the original exposure boundary, and its horizontal coverage width is Δh (the horizontal direction refers to the direction in the X - Y plane).

[0058] Convert the width of the correction area into the pixel size on the projection plane. Δh can cover m circles of pixels. Under the width of m circles of pixels, some circles of pixels are completely black (gray level is 0) or completely white pixels (gray level is 255), and some circles of pixels are gray pixels for smooth transition. The gray pixels have a gray level greater than 0 and less than 255, m≥n, and both m and n are integers.

[0059] When Δh is a positive number, the printing contour of the three-dimensional model becomes thicker. When correcting, it is necessary to reduce the exposure of some pixels. Therefore, it is necessary to change n circles of pixels into completely black pixels with a gray level of 0, that is, reduce the exposure of n circles of pixels in the correction area to make the exposure boundary shrink inward; when Δh is a negative number, the printing contour of the three-dimensional model becomes thinner. When correcting, it is necessary to increase the exposure of some pixels. Therefore, it is necessary to change n circles of pixels into completely white pixels with a gray level of 255, that is, increase the exposure of n circles of pixels in the correction area to make the exposure boundary expand outward. Generally, the characteristics of the photosensitive material are fixed and the light intensity is fixed. Usually, the speed v that exceeds the standard printing speed too much will not be set. Therefore, Δh is generally a positive number, that is, it is necessary to correct by shrinking the image contour.

[0060] Furthermore, n = |[Δh / d]|, where n is the absolute value of the integer function of Δh / d. Here, d is the pixel size of the 3D printer, and Δh = α×h c , α is an adjustment coefficient. Generally speaking, 0.5≤α≤1.2. When Δh can be divided evenly by d, the number of circles of gray pixels is 0, and m = n.

[0061] When Δh cannot be divided evenly by d, m = n + 1. The corrected exposure boundary increases or shrinks by 1 circle of gray pixels relative to the original exposure boundary, and the gray level of the nth circle of gray pixels is: when Δh>0, it is necessary to shrink the boundary, Gray n+1 = 255×(1 - f / d), when Δh<0, it is necessary to expand the boundary, Gray n+1 = 255×f / d, where f is the remainder of Δh / d, f = [Δh mod d]. Suppose it is necessary to expand the original exposure boundary by 4.01d, that is, 4 circles of completely white pixels + 0.01×255 gray pixels, and the last circle is a little white; if it is to shrink the original exposure boundary by 4.01d, that is, 4 circles of completely black pixels + 0.99×255 gray pixels, and the last circle is a little black.

[0062] The following uses Figures 6 - 9 The following embodiments are used to illustrate the printing method of the present application by way of example:

[0063] (1) When the current printing speed v is large, calculate the theoretical deviation value h of the printing contour corresponding to this printing speed c , which will cause h c to become smaller, and the overall model becomes thinner.

[0064] (2) Set Δh = α × h c , where α is taken as 1.0.

[0065] (3) Determine how many pixel widths Δh covers on the projection plane. The pixel size is d = screen × length / × pixel value. For example, for a 4K screen with a length of 192 mm and a resolution of 3840 pixels, one pixel represents an actual d = 0.05 mm. Use Δh / d to obtain the quotient and remainder. For example, if h c is -0.17 mm, α = 1.0, Δh = 1.0 × -0.17, Δh / d = -3 remainder 0.02, n = 3, and m is taken as 4, that is, the corrected exposure boundary needs to be expanded, and 4 circles of pixels will be modified.

[0066] (4) The integer part of the quotient is 3, corresponding to expanding the original slice image by 3 pixels along the edge for the corrected exposure boundary.

[0067] (5) The remainder 0.02 is used to determine the proportion f of gray pixels. For example, f = 0.02 / 0.05 = 40%, and then change the brightness of the 4th circle of pixels from 255 to 255 × 40% = 102, so as to achieve the effect of blurring the edge. See Figure 9 .

[0068] Next, the calculation method of the theoretical deviation value h c of the printing contour will be described in detail.

[0069] See Figure 3 as shown, the decay relationship of ultraviolet light in the photosensitive resin satisfies:[[]]

[0070]

[0071] where d is the shortest straight-line distance from any point in the photosensitive resin to the projection image; τ is the light transmittance per unit thickness of the photosensitive resin (also written as tau), that is, for every Δd unit thickness, the ratio of the transmitted light flux to the incident light flux is τ. The more light dispersant added to the photosensitive resin, the smaller τ. Therefore, the diffused light intensity P d received by the photosensitive resin at point d is related to the light transmittance of the material and the distance, and decreases exponentially.

[0072] Figure 3 The Pτ 0 in 1 represents the light intensity at the pixel point in the photocuring window, and Pτ 4 represents the light intensity at the pixel point one unit thickness away from the photocuring window, and so on. Pτ

[0073] See Figure 4As shown, during continuous printing, when the z-axis moves upward, the uncured material on the surface of the printed part will rise as the platform is lifted, gradually moving away from the projection plane and gradually out of the illumination range.

[0074] As shown in the figure, for the photosensitive resin that is horizontally at a distance h from the original exposure boundary of the printed part, the initial light intensity it receives is P h , during the process of the platform printing upward at the printing speed v, after t seconds, the distance d between this point and the projection edge is:

[0075]

[0076] Substituting Formula 2 into Formula 1, the light intensity near the point with an initial distance of h from the exposure area at any time t can be obtained.

[0077]

[0078] Among them, h is the initial distance of the pixel point from the original exposure boundary (ideal printing boundary) of the cross-section of the three-dimensional model, t is the illumination time, and v is the printing speed (i.e., the lifting speed of the z-axis). Generally, it is considered that v does not change in a short period of time. Here, the short period of time refers to the printing time within a unit thickness of Δd. The speed is updated 10 - 30 times per second, but the speed v is related to the current image, and the image changes smoothly within a certain period of time. Therefore, the change of the speed v within 1 second or within a unit distance is very, very small.

[0079] Next, we continue to calculate the accumulated exposure amount of the point with an initial distance of h from the original exposure boundary. As the printing platform continuously rises at the speed v and the printing time t increases, the uncured resin will gradually move away from the exposure surface, and the illumination intensity received by the surrounding materials will become smaller and smaller. When the total exposure amount E of a certain point of the resin material accumulates to a certain extent, it will solidify. If for P th is integrated with respect to time t in the time period [0, T], then its curing condition is that the total exposure amount E T is greater than the critical exposure amount E c .

[0080]

[0081] Among them, T is a sufficiently long time so that after moving for T seconds, the light intensity decays to a negligible level and cannot substantially change the integration result. Formula 4 shows that for a point at a distance h outside the original exposure boundary of the three-dimensional model, when the printing speed v is given, the total exposure amount E T is also fixed. Once E T > E c, the photosensitive resin at this position will cure on the surface of the three-dimensional model, causing the outline of the object to become thicker. In theory, we hope that h = 0, that is, we hope that the photosensitive resin outside the original exposure boundary of the three-dimensional model cannot be cured. However, in practice, this cannot be achieved. Therefore, we hope that h c remains constant, so that the outer contour of the three-dimensional model is constant, and a three-dimensional model with a continuous and smooth surface, without becoming thicker or thinner, can be obtained.

[0082] Remove the integral from the above formula four to obtain a formula form that can be controlled in real time. First, simplify the calculation method of the distance d as:

[0083]

[0084] In the initial stage of exposure, h has a greater influence. In the later stage of exposure, the speed v has a greater influence. After approximate transformation, the integral of formula four becomes:

[0085]

[0086] Integrate formula six again to obtain formula seven,

[0087]

[0088] where 0 < τ < 1 and T is large enough. Formula seven can be used to determine whether the material at a distance of h will cure when continuously printed at a speed v. As Figure 5 shown, during the gradual rising process of the three-dimensional model, its directly illuminated area will gradually cure, which is called the established cured part D1. Due to the existence of a relatively high diffusion light intensity near the body of the three-dimensional model, after time accumulation, it exceeds the critical exposure amount, generating a diffusion cured area D2. Further away, due to the weakening of the diffusion light intensity, curing will not occur. D3 is the under-cured area.

[0089] We can transform formula seven to get:

[0090]

[0091] Substitute parameters such as the light intensity P, printing speed v, critical exposure amount Ec, light transmittance, and exposure time into formula eight, and the value of h c can be calculated. Then, calculate Δh based on h c Finally, obtain the number of circles and gray levels of the pixels that need to be adjusted. To sum up, through the present application, by dynamically changing the contour of the three-dimensional model during slice image / real-time rendering, increasing or decreasing the thickness of the contour, and reversely compensating for the h c thickness change caused by the speed change, a three-dimensional model with accurate printing size and stable contour thickness can be finally obtained.

[0092] The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements. The scope of protection claimed by the present invention is defined by the appended claims, the specification and their equivalents.

Claims

1. A continuous 3D printing method based on dynamic rendering, characterized in that, Including the following steps: Obtain a plurality of slice images based on a three-dimensional model to be printed, each of the slice images having an original exposure boundary, and dynamically configure a printing speed v for each frame of slice image; Calculate the theoretical deviation value h of the printing profile of the three-dimensional model according to the dynamically changing printing speed v c and the actual deviation value Δh, and correct each of the sliced images based on the actual deviation value Δh to obtain a corrected exposure boundary, that is, the corrected exposure boundary is equal to the distance obtained by horizontally increasing or decreasing the original exposure boundary by Δh; Expose the pixels within the corrected exposure boundary.

2. The printing method according to claim 1, wherein: A corrected area is formed between the corrected exposure boundary and the original exposure boundary, and the width of the corrected area covers m circles of pixels, where n circles of pixels are all-black pixels with a gray level of 0 or all-white pixels with a gray level of 255, and the remaining pixels are gray-scale pixels with a gray level greater than 0 and less than 255, m≥n, and n is an integer.

3. The printing method according to claim 2, wherein: When Δh>0, the n circles of pixels are all-black pixels with a gray level of 0; when Δh<0, the n circles of pixels are all-white pixels with a gray level of 255.

4. The printing method according to claim 2, characterized in that: n = |[Δh / d]|, where d is the pixel size of the 3D printing device.

5. The printing method according to claim 1 or 4, characterized in that: Δh = α × h c , where α is the adjustment coefficient.

6. The printing method according to claim 5, characterized in that: The theoretical deviation value h of the printing contour of the three-dimensional model c satisfies the following relationship where P represents light intensity; v represents the printing speed; E c represents the critical exposure of the photosensitive resin; τ represents the light transmittance of the photosensitive resin per unit thickness; Δd is the unit thickness; T represents the exposure time.

7. The printing method according to claim 5, characterized in that: 0.5≤α≤1.2。 8. The printing method according to claim 2, characterized in that: m = n + 1. The corrected exposure boundary is increased or decreased by one circle of gray pixels relative to the original exposure boundary. When Δh > 0, the gray value of this circle of gray pixels is: Gray n+1 = 255×(1 - f / d); When Δh < 0, the gray level of the gray pixels in this circle is Gray n+1 = 255 × f / d, where f = [Δh mod d].

9. A continuous 3D printing device, comprising a material tank for containing photosensitive resin, a printing platform arranged above the material tank and capable of lifting along the Z axis, a projection device, a memory, and a processor, characterized in that, The processor is configured to execute the printing method according to any one of claims 1-8.

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