3D printing control method and printing device based on thermal integrated light intensity correction

Abstract

This application relates to a 3D printing control method and printing device based on thermal integral light intensity correction. The method includes: A. Establishing the mapping relationship between temperature k and the critical exposure amount E of photosensitive resin c ; B. Reading the sliced images of the 3D model to be printed frame by frame, dividing the printing area into several blocks, and calculating the heat integral ratio I of each block at any moment based on the exposure area in the sliced images t ; C. Calculating the dynamic temperature k of the photosensitive resin in each block at any moment according to the heat integral ratio, and determining the critical exposure amount E of the photosensitive resin corresponding to the block at any moment according to the mapping relationship between temperature and the critical exposure amount E of photosensitive resin t ; D. Determining the dynamic light intensity correction value P corresponding to the block at any moment based on the critical exposure amount of the block, and configuring the projection parameters corresponding to the block according to the dynamic light intensity correction value P c ; D. Determining the dynamic light intensity correction value P corresponding to the block at any moment based on the critical exposure amount of the block, and configuring the projection parameters corresponding to the block according to the dynamic light intensity correction value P ck ; D. Determining the dynamic light intensity correction value P corresponding to the block at any moment based on the critical exposure amount of the block, and configuring the projection parameters corresponding to the block according to the dynamic light intensity correction value P k ; and D. Determining the dynamic light intensity correction value P corresponding to the block at any moment based on the critical exposure amount of the block, and configuring the projection parameters corresponding to the block according to the dynamic light intensity correction value P k .

Description

Technical Field

[0001] The present invention belongs to the technical field of photocuring 3D printing, and in particular relates to a 3D printing control method and a printing device based on thermal integrated light intensity correction. Background Art

[0002] In the field of photocuring, the photocuring 3D printing technology is divided into laser point light source (SLA) and surface light source digital light projection (DLP) according to the light source system of photocuring molding. The photocuring process uses ultraviolet rays to irradiate and cure photosensitive resin in layers. When 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 solidifies layer by layer through many frames of images, and can form one format at a time, so it is a faster 3D printing method. In traditional DLP technology, the layer thickness of each slice is fixed, and the exposure time is fixed (usually slightly overexposed), so it can be considered that the discrete exposure amount received by each point of the model is uniform and consistent from a macro perspective. Although the resin material around each layer of the slice will be exposed to some diffuse light, the up and down movement of the printing platform on the z-axis will quickly mix these lightweight exposed materials with other materials, continuously eliminating the accumulation of resin exposure around the print. Therefore, traditional DLP printers only need to cooperate with simple xy size scaling to achieve uniform accuracy.

[0004] The continuous liquid surface printing technology is to make the surface after irradiation and curing not stick to the release film, for example, to establish a non-curing area, so that the resin is always cured and formed above the non-curing area, so as to achieve continuous, smooth and rapid molding. Compared with the traditional layer-by-layer printing method (such as DLP), the continuous liquid surface 3D printing technology can achieve rapid printing of complex objects. The curing process of photosensitive resin is accompanied by a large amount of exothermic reaction. In the process of continuous 3D printing, since the printing platform does not move up and down, heat is easy to accumulate locally. After the heat is increased, the photosensitive resin is easier to be cured. Therefore, in the early and late stages of 3D printing, using a fixed value of light intensity to irradiate the photosensitive resin will obtain different three-dimensional models, which will cause the print to be distorted, or the three-dimensional model to become coarse and the surface to be rough. Summary of the invention

[0005] The purpose of this application is to provide a 3D printing control method and printing device based on thermal integrated light intensity correction, so that the light intensity in the continuous printing process can be corrected as the temperature changes, thereby making the accuracy of the printed model controllable.

[0006] In order to achieve the above-mentioned one invention object, the present invention adopts the following technical solution: a 3D printing control method based on thermal integrated light intensity correction, comprising the following steps:

[0007] A. Establishing the temperature k and the critical exposure amount E of the photosensitive resinc The mapping relationship of

[0008] B. Read the slice image of the 3D model to be printed frame by frame, divide the printing area into several blocks, and calculate the corresponding heat integral ratio I of each block at any time based on the exposure area in the slice image. t ;

[0009] C. Calculate the dynamic temperature k of the photosensitive resin in each block at any time according to the heat integral ratio t , and according to the temperature and the critical exposure amount E of the photosensitive resin c The mapping relationship is used to determine the critical exposure amount E of the photosensitive resin corresponding to the block at any time. ck ;

[0010] D. Determine the dynamic light intensity correction value P corresponding to the block at any time based on the critical exposure of the block k , and according to the dynamic light intensity correction value P k Configure the projection parameters corresponding to this block.

[0011] In one embodiment of the present application, in step B, the printing area is divided into m×n blocks, and the heat integral ratio I corresponding to each block over time is t =(1-r)×I t-1 +r×R t , where I represents the heat integral ratio, r represents the thermal conductivity, and R t Represents the heat release area ratio of the block at the current time t, R t =W / S, S represents the area of ​​each block, and W represents the area of ​​the exposure region in the block.

[0012] In one embodiment of the present application, 0<r≤1.

[0013] In one embodiment of the present application, in step C, the dynamic temperature K t Satisfy the relationship: k t =k0+(k max -k0)×I t , where k0 is the ambient room temperature, k max is the highest temperature that photosensitive resin can withstand, I t is the heat integral ratio at the current moment, 0 t <1.

[0014] In one embodiment of the present application, the light intensity correction value P k Satisfies the following relationship:

[0015] in,

[0016] E​ck Represents the photosensitive resin at dynamic temperature k t The critical exposure at ;

[0017] v represents the printing speed;

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

[0019] h c Represents the lateral distance between the actual solidification boundary and the theoretical solidification boundary;

[0020] Δd is the unit thickness;

[0021] T represents the exposure integration time.

[0022] In one embodiment of the present application, h c It is a fixed value and satisfies -0.1mm≤h c ≤0.3mm.

[0023] In one embodiment of the present application, in step A, a plurality of photosensitive resin materials and temperatures k and a critical exposure amount E of the photosensitive resin are established. ck The mapping relationship.

[0024] Another technical solution of the present application is to provide a 3D printing device based on thermal integrated light intensity correction, including a material trough for holding photosensitive resin, a printing platform arranged above the material trough to be liftable along the Z axis, a projection device for projecting the slice image frame by frame onto the printing area, a memory and a processor, wherein the processor is configured to execute the aforementioned control method.

[0025] Compared with the prior art, the present invention achieves the following beneficial effects: the present invention accumulates the temperatures of each printing area and matches the appropriate light intensity with the critical exposure at the temperature, thereby well controlling the photosensitive resin curing process of the printing area and ensuring that the thickness of the cured material outside the printing area is constant, thereby obtaining a three-dimensional printed model with controllable accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Attached Figure 1 A schematic diagram of the structure of a 3D printing device in one embodiment of the present application;

[0027] Attached Figure 2 for Figure 1 Schematic diagram of the 3D printing device in;

[0028] Attached Figure 3 The decay relationship of light intensity in photosensitive resin is shown;

[0029] Attached Figure 4 It shows the light intensity of a point at a distance h from the periphery of the three-dimensional model at time t;

[0030] Attached Figure 5 Shows established cure areas, diffuse cure areas, and under-cure areas;

[0031] Attached Figure 6 The temperature-critical exposure curve of the photosensitive resin material is shown;

[0032] Wherein: 101, optical machine; 102, material trough; 103, photosensitive resin; 104, Z-axis lifting mechanism; 105, printing platform; 106, three-dimensional model; 200, release film; 300, non-curing area. DETAILED DESCRIPTION

[0033] In order to explain the technical content, structural features, objectives and effects of the invention in detail, the following will be described in detail with reference to the embodiments and the accompanying drawings.

[0034] To this end, the present application proposes a continuous 3D printing device and a control method thereof. Figure 1 , 2 As shown, the continuous 3D printing device includes a frame, a material trough 102 for holding photosensitive resin, a printing platform 105 which is arranged above the material trough and can be lifted along the Z axis, a projection device, a memory and a processor. A horizontal workbench extending along the xy plane is provided in the middle of the frame, and the material trough 102 is fixedly provided 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, and the printing platform 105 is arranged above the horizontal workbench and can be lifted. A Z-axis lifting mechanism 104 is provided at the rear of the frame, and the printing platform 105 is vertically lifted or lowered by the Z-axis lifting mechanism 104. The bottom of the material trough 102 is provided with the release element, such as a release film.

[0035] 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 solidifies 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 is attached 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. The photosensitive resin stops the polymerization reaction at the interface (non-curing area 300), so that there is always liquid photosensitive resin between the three-dimensional model 106 and the release film 200, reducing the adhesion between the three-dimensional model and the release film, thereby realizing continuous high-speed 3D printing.

[0036] The memory of the continuous 3D printing device of the present application stores a computer program, and the processor is configured to execute the computer program to implement the following control method:

[0037] A. Establish the photosensitive resin, temperature k and critical exposure E of the photosensitive resin c The mapping relationship is to create a heat release database;

[0038] B. Read the slice image of the 3D model to be printed frame by frame, divide the printing area into m×n blocks, and calculate the corresponding heat integral ratio I of each block at any time based on the exposure area in the slice image. t , I t =(1-r)×I t-1 +r×R t , R t Represents the heat release area ratio of the block at the current time t, R t =W / S, S represents the total area of ​​the block, W represents the area of ​​the exposure area in the block, r is the thermal conductivity of the photosensitive resin material, 0<r≤1;

[0039] C. Calculate the dynamic temperature k of the photosensitive resin in each block at any time according to the heat integral ratio t , k t =k0+(k max -k0)×I t , where k0 is the ambient room temperature (3D printing generally requires a constant temperature and humidity environment, k0 is usually set to 26°C), k max is the highest temperature that the photosensitive resin can withstand (e.g. 75°C), I t is the heat integral ratio at the current moment, 0 t <1, and according to the dynamic temperature k t Determine the critical exposure amount E of the photosensitive resin corresponding to the block at any time in the above heat release database ck ;

[0040] D. Determine the dynamic light intensity correction value P corresponding to the block at any time based on the critical exposure of the block k , and according to the dynamic light intensity correction value P k Configure the projection parameters corresponding to this block.

[0041] In this embodiment, the final exposure intensity required for the block is the dynamic intensity correction value P k .

[0042] The thermal conductivity is related to the thermal conductivity of the photosensitive resin material. The larger the r, the stronger the heat absorption and heat dissipation ability of the photosensitive resin. t The faster the curve changes. In the laboratory, the value of r can be obtained by locally irradiating a small area with a high-precision temperature gun.

[0043] In one embodiment, the entire screen is divided into m×n blocks, for example, 160×90=14400 areas. ​

[0044] The total area S of each small block can be expressed by the number of pixels. For example, a 4k screen is 3840×2160, and the total area S of a small block contains 24×24=576 pixels.

[0045] The area W of the exposure region in each small block can be represented by the number of white pixels, that is, the illumination diagram at the current time t. The number of white pixels in this small block represents the area W of the exposure region.

[0046] The heat release area ratio R of each small block at the current time t t =W / S, R t Between 0-1 (0 represents no exposure, 1 represents full exposure).

[0047] Generally speaking, pure polymer materials have poor thermal conductivity. For example, when the calculation iteration interval is t = 1 second, r = 0.01. Then the heat integral ratio of the small block at time t is I t =0.99×I t-1 +0.01×R t . According to I t The dynamic temperature k can be calculated t , and find the corresponding E ck .

[0048] E ck Substitute the following formula to calculate the dynamic light intensity correction value P k :

[0049]

[0050] in:

[0051] E ck Represents the photosensitive resin at dynamic temperature k t The critical exposure at ;

[0052] v represents the printing speed, that is, the lifting speed of the printing platform;

[0053] τ represents the light transmittance of photosensitive resin per unit thickness;

[0054] h c represents the lateral distance between the actual solidification boundary and the theoretical solidification boundary. Ideally, h c is a fixed value, and the printed 3D model is uniform in thickness and accurate in size;

[0055] Δd is the unit thickness,

[0056] T represents the exposure time.

[0057] In one embodiment of the present application, -0.1 mm ≤ hc ≤0.3mm.

[0058] The following focuses on the relationship between light intensity, temperature and speed changes.

[0059] See also Figure 3 As shown, the decay relationship of ultraviolet light in photosensitive resin satisfies:

[0060]

[0061] Where d is the shortest straight line distance from any point in the photosensitive resin to the projected image; τ is the light transmittance per unit thickness of the photosensitive resin (also written as tau), that is, the ratio of the transmitted light flux to the incident light flux per unit thickness of Δd is τ. The more light dispersants are added to the photosensitive resin, the smaller τ is. Therefore, the diffuse light intensity P received by the photosensitive resin at point d is d It is related to the light transmittance of the material and the distance, and decreases exponentially.

[0062] Figure 3 Pτ 0 Represents the light intensity at the pixel point in the light curing window, Pτ 1 Represents the light intensity of a pixel at a unit thickness away from the light curing window. Similarly, Pτ 4 It represents the light intensity of a pixel at 4 unit thickness away from the light curing window. The distance in unit length is the power of τ.

[0063] See also Figure 4 As shown, in continuous printing, when the z axis ( Figure 1 When the platform moves upward (in the up and down directions), the uncured material on the surface of the print will rise as the platform rises, gradually moving away from the projection surface and out of the illumination range.

[0064] As shown in the figure, the photosensitive resin with a lateral distance h from the exposed edge of the print is subjected to an initial light intensity of P h , when the platform prints upward at a printing speed v, the distance d between the point and the projection edge after t seconds is:

[0065]

[0066] Substituting Formula 2 into Formula 1, we can get the light intensity near a point at an initial distance h from the exposure area at any time t:

[0067]

[0068] Among them, h is the initial distance between the pixel point and the cross-sectional profile of the 3D model, t is the illumination time, and v is the printing speed (i.e. the speed of the z-axis lifting). It is generally believed that v does not change in a short time. The short time here refers to the printing time of a unit thickness of Δd. The speed update will be executed 10-30 times per second, but the speed v is related to the current image. The image changes smoothly over a period of time, so the speed v changes very little within 1 second or per unit distance.

[0069] Next, we continue to calculate the accumulated exposure amount of a point at a distance h from the initial exposure area. As the printing platform is continuously raised at a speed v, as the printing time t increases, the uncured resin will gradually move away from the exposure surface, and the light intensity of the surrounding materials will become smaller and smaller. When the total exposure amount E at a certain point of the resin material accumulates to a certain extent, it will cure. If P th According to the time t, the integral is carried out in the time period [0, T], and the curing condition is the total exposure E T Greater than critical exposure E c .

[0070]

[0071] Where T is a long enough time that after T seconds of movement, the light intensity decays to a negligible level and does not substantially change the integral result. Formula 4 shows that for a point at a distance h outside the contour of the 3D model, when the printing speed v is given, the total amount of exposure E T It is also fixed. Once E T >E c , the photosensitive resin at this position will solidify on the surface of the 3D model, causing the outline of the object to become thicker. Theoretically, we hope that h = 0, that is, we hope that the photosensitive resin outside the outline of the 3D model cannot be solidified, but in reality it is impossible to do so. Therefore, we set h c Set to a fixed value to satisfy a smaller value within this range. c Keep it constant so that the outer contour of the 3D model is constant, and obtain a 3D model with a continuous and smooth surface that does not become thicker or thinner.

[0072] Remove the integral from the above formula 4 to obtain a formula form that can be controlled in real time. First, simplify the calculation method of distance d to:

[0073]

[0074] In the early stage of exposure, h has a greater impact, and in the later stage of exposure, speed v has a greater impact. After approximate transformation, the integral of company 4 becomes:

[0075]

[0076] Then integrate formula 6 to get formula 7:

[0077]

[0078] Where 0<τ<1, T is large enough. Formula 7 can be used to determine whether the material at a distance h from the print surface will solidify when printing continuously at speed v. Figure 5 As shown, as the three-dimensional model gradually rises, its directly illuminated area will gradually solidify, which is called the established solidified part D1. Due to the high diffuse light intensity near the main body of the three-dimensional model, it exceeds the critical exposure after accumulation over time, resulting in a diffuse solidified area D2. Further away, due to the weakened diffuse light intensity, no solidification will occur, and D3 is the insufficiently cured area.

[0079] We can transform formula 7 to get:

[0080]

[0081] Among them, h c Represents the lateral distance between the actual solidification boundary and the theoretical solidification boundary.

[0082] As mentioned above, ideally, we want to obtain h c Constant 3D model, the printed product will not become thicker or thinner due to changes in printing speed, making h c Take a fixed value, the range is: -0.1mm≤hc≤0.3mm. This requires adjusting the irradiation intensity P to maintain h c Fixed, and we know that the curing process of photosensitive resin is accompanied by a large amount of heat release. After the heat is increased, the activity of the photosensitive resin material increases, and the critical exposure E c The critical exposure amount E of each photosensitive resin material c The relationship between the change in temperature and the exposure time can be measured experimentally, so that the critical exposure value E of any photosensitive resin material can be established. ck The relationship curve or mapping relationship with the temperature k, such as Figure 6 This is a curve diagram of the relationship between the critical exposure amount and temperature change of a photosensitive resin material.

[0083] In the actual printing process, the critical exposure E c When the h c It will increase (the ln value is a negative number), that is, the hotter the resin is, the thicker it will cure under the same conditions.

[0084] Next, the printing area is divided into m×n blocks, and the heat of each block is integrated to calculate the temperature in the block. Finally, the critical exposure E of the photosensitive resin material can be calculated based on the established critical exposure-temperature change relationship curve.ck , and then by transforming formula 8, we get the light intensity correction value based on temperature change:

[0085]

[0086] When other parameters remain unchanged, according to I t Calculate k t , according to k t Check the heat release database to get E ck , we get P k , and the light intensity correction value P corresponding to each block is obtained k Afterwards, by adjusting the brightness of the mask of the current small block, the light intensity of the local part can be suppressed or increased accordingly to achieve the purpose of morphological stability.

[0087] The present invention accumulates the temperature of each printing area and matches the appropriate light intensity with the critical exposure at the temperature, thereby well controlling the photosensitive resin curing process of the printing area and ensuring a constant thickness of the cured material outside the printing area, thereby obtaining a three-dimensional printed model with controllable accuracy.

[0088] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and the scope of protection of the present invention is defined by the attached claims, description and their equivalents.

Claims

1. A 3D printing control method based on thermal integrated light intensity correction, characterized in that: The steps include: A. Establishing the temperature k and the critical exposure amount E of the photosensitive resin c The mapping relationship; B. Read the slice image of the 3D model to be printed frame by frame, divide the printing area into several blocks, and calculate the corresponding heat integral ratio I of each block at any time based on the exposure area in the slice image. t ; C. Calculate the dynamic temperature k of the photosensitive resin in each block at any time according to the heat integral ratio t , and according to the temperature and the critical exposure amount E of the photosensitive resin c The mapping relationship is used to determine the critical exposure amount E of the photosensitive resin corresponding to the block at any time. ck ; D. Determine the dynamic light intensity correction value P corresponding to the block at any time based on the critical exposure of the block k , and according to the dynamic light intensity correction value P k Configure the projection parameters corresponding to this block.

2. The control method according to claim 1, characterized in that: In step B, the printing area is divided into m×n blocks, and the heat integral ratio I corresponding to each block over time is t =(1-r)×I t-1 +r×R t , where I represents the heat integral ratio, r represents the thermal conductivity, and R t Represents the heat release area ratio of the block at the current time t, R t =W / S, S represents the area of ​​each block, and W represents the area of ​​the exposure region in the block.

3. The control method according to claim 2, characterized in that: 0＜r≤1。 4. The control method according to claim 1, characterized in that: In step C, the dynamic temperature K t Satisfy the relationship: k t =k0+(k max -k0)×I t , where k0 is the ambient room temperature, k max is the highest temperature that photosensitive resin can withstand, I t is the heat integral ratio at the current moment, 0 t <1.​ 5. The control method according to claim 1, characterized in that: The light intensity correction value P k Satisfies the following relationship: Among them, E ck Represents the photosensitive resin at dynamic temperature k t The critical exposure corresponding to ; v represents the printing speed; τ represents the light transmittance of photosensitive resin per unit thickness; h c Represents the lateral distance between the actual solidification boundary and the theoretical solidification boundary; Δd is the unit thickness; T represents the exposure integration time.

6. The control method according to claim 5, characterized in that: h c It is a fixed value and satisfies -0.1mm≤h c ≤0.3mm.

7. The control method according to claim 1, characterized in that: In the step A, a plurality of photosensitive resin materials and temperatures k and a critical exposure amount E of the photosensitive resin are established. ck The mapping relationship.

8. A 3D printing device, comprising a material tank for holding a photosensitive resin, a printing platform arranged above the material tank in a manner that can be raised and lowered along the Z axis, a projection device for projecting a slice image frame by frame onto a printing area, a memory, and a processor, characterized in that: The processor is configured to execute the control method as claimed in claims 1-7.

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