A Continuous 3D Printing Control Method and Printing Device Based on Dynamic Light Intensity

Abstract

The present application relates to a continuous 3D printing control method and a printing device based on dynamic light intensity. The method includes: Step 1), calling a sliced image of a three-dimensional model to be printed; Step 2), configuring a dynamically changing printing speed v for each frame of the sliced image; Step 3), configuring a corresponding dynamic light intensity P for each frame of the sliced image according to the printing speed v v , and the dynamic light intensity P v increases as the printing speed v increases and decreases as the printing speed v decreases; the projection device continuously exposes the forming surface with the dynamic light intensity P v so that the projection device can adjust the exposure intensity of each pixel point on each frame of the sliced image of the three-dimensional model in coordination with the adjustment of the printing speed, thereby obtaining a three-dimensional model with a continuous and smooth surface and controllable precision.

Description

Technical Field

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

[0002] In the field of photocuring, according to the light source system of photocuring forming, 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. 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 cures layer by layer through many frames of images and can form a single format at a time. Therefore, 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). 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 forms an uncured area by making the irradiated and cured surface not adhere to the release film, such as using a film with a polymerization inhibitor component, or an oxygen-permeable film, or a flowing interface, etc., so that the resin is always cured and formed above the uncured area. Therefore, the peeling action in the traditional printing process is eliminated, and continuous, smooth, and fast forming is realized. Compared with the traditional layer-by-layer printing method (such as DLP), the continuous 3D printing technology can realize the rapid printing of complex objects. However, in the continuous printing method, the forming principle at the physical level will change greatly, the process is very complex, and the accuracy is more difficult to control. At a fixed printing speed, the photosensitive resin materials around the three-dimensional model have different filling speeds due to different slice entity areas. Insufficient filling will cause the model to have patterns or even breakage; slowing down the speed will reduce the printing efficiency; the dynamic speed will cause uneven exposure of the material, resulting in problems such as the thickening, thinning, and surface undulation of the three-dimensional model. Therefore, how to ensure stable and sufficient exposure of the material during continuous printing, how to obtain a flat and smooth printing surface in the continuous printing method; how to dynamically match the best parameters for the continuous 3D printing device are the technical problems to be solved by the present invention. Summary of the Invention

[0005] The purpose of this application is to provide a continuous 3D printing control method and a printing device based on dynamic light intensity, so that the energy received by the photosensitive resin at each position during continuous printing is kept consistent, thereby making the surface of the printed model continuous and smooth without becoming thick or thin.

[0006] To achieve the above-mentioned invention purpose, the present invention adopts the following technical solutions: A continuous 3D printing control method based on dynamic light intensity, comprising the following steps:

[0007] Step 1), call the sliced image of the three-dimensional model to be printed;

[0008] Step 2), configure a dynamically changing printing speed v for each frame of the sliced image;

[0009] Step 3), configure a corresponding dynamic light intensity Pv for each frame of the sliced image according to the printing speed v, and this dynamic light intensity P v increases as the printing speed v increases and decreases as the printing speed v decreases.

[0010] In an embodiment of the present application, the relationship between the dynamic light intensity P v and the printing speed v is as follows:

[0011] wherein,

[0012] P v represents the dynamic light intensity when the printing speed is v;

[0013] v represents the printing speed;

[0014] E c represents the critical exposure amount of the photosensitive resin;

[0015] τ represents the light transmittance of the photosensitive resin under unit thickness;

[0016] h c represents the lateral distance between the actual curing boundary and the theoretical curing boundary;

[0017] Δd is the unit thickness, that is, the shortest distance between two adjacent sliced images;

[0018] T represents the exposure time.

[0019] In an embodiment of the present application, the actual dynamic light intensity P v ' of the corresponding pixel points on the sliced image is α × P v , where α is an adjustment coefficient and 0.8 ≤ α ≤ 1.2.

[0020] In an embodiment of the present application, -0.1 mm ≤ h c ≤ 0.3 mm.

[0021] In one embodiment of the present application, the step 2) further includes:

[0022] Comparing the maximum wall thickness S in the slice image with a given threshold S0 of the wall thickness;

[0023] If the maximum wall thickness S of the current slice image is less than the given threshold S0, configure the printing speed of this frame of slice image according to the maximum printable speed V0 of the current photosensitive resin material, v = V0;

[0024] If the maximum wall thickness S of the current slice image is greater than the given threshold S0, v < V0.

[0025] In one embodiment of the present application, the printing speed v satisfies the condition v = max(1.0, min(S0 / S, 1)×V0).

[0026] In one embodiment of the present application, S0 is 0.5 - 4 millimeters.

[0027] Another technical solution of the present invention is: a continuous 3D printing device, including 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, and the processor is configured to execute the control method.

[0028] Compared with the prior art, the present invention has the following beneficial effects: The present invention adjusts the dynamic light intensity of each pixel point on the three-dimensional model through dynamic printing speed. When the printing speed decreases, the light intensity is reduced, and when the printing speed increases, the light intensity is increased, ultimately enabling the printing contour thickness hc of the three-dimensional model to always remain constant, thereby obtaining a three-dimensional model with a continuous and smooth surface and controllable precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Attached Figure 1 is a schematic structural diagram of a 3D printing device in an embodiment of the present application;

[0030] Attached Figure 2 is Figure 1 the curing principle diagram of the 3D printing device in

[0031] Attached Figure 3 shows the decay relationship of light intensity in the photosensitive resin;

[0032] Attached Figure 4 shows the light intensity received by a point at a distance h from the periphery of the three-dimensional model at time t;

[0033] Attached Figure 5 shows the established curing area, diffusion curing area, and under-curing area;

[0034] 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. Detailed implementation mode

[0035] 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 drawings.

[0036] In the continuous printing mode, the printing accuracy is affected by various factors, mainly including: (1) The material around the model may be cured due to long-term irradiation. Since it is necessary to make the light diffusion range far exceed the thickness of the uncured area 300, so as to realize the gradual curing of the photosensitive resin material above the uncured area 300, the photosensitive resin material used for continuous printing has a higher light transmittance, and a higher light intensity is required. Moreover, during the continuous printing process, the action of continuously and slowly lifting the printing platform is difficult to eliminate the accumulation of the exposure amount of the photosensitive resin around the three-dimensional model. Once the energy exceeds the critical exposure amount, the curing phenomenon will be triggered. (2) Changing the printing speed will result in different exposure amounts. Traditional DLP replenishes materials by lifting the printing platform, so theoretically it can form slices of any area. In continuous printing, the material can only slowly flow in through the tiny gaps of the uncured area. Therefore, once a large-area solid area is encountered, it is necessary to dynamically change the speed of lifting the z-axis (that is, the printing speed v) by the method of claim 6 so that the photosensitive resin material can flow in sufficiently. And the slower the printing speed v, the longer the photosensitive resin material is exposed to light, and the easier it is to cure. Therefore, adjusting the printing speed will inevitably cause uneven diffusion and curing thickness.

[0037] Therefore, the present application proposes a continuous 3D printing device and its control method. Refer to Figure 1 As shown in FIG. -2, the continuous 3D printing device includes a frame, a material tank 102 for containing photosensitive resin, a printing platform 105 that is vertically liftable above the material tank, 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 liftably arranged above the horizontal workbench, a Z-axis lifting mechanism 104 is arranged at the rear of the frame, and the printing platform 105 realizes vertical up and down 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. The photosensitive resin stops the polymerization reaction at this interface, so that there is always a 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] Before printing, start the 3D printing device. The printing platform 105 descends above the uncured area 300 driven by the Z-axis lifting mechanism 104, and a maximum printing speed V0 is preset. V0 is related to the initial forming strength, light sensitivity (content of photoinitiator), light transmittance and viscosity of the material and is a fixed value. For example, V0 is set to 10 mm / min for harder materials and V0 is set to 5 mm / min for softer materials.

[0040] The following is an example to illustrate the control method of the continuous 3D printing device of the present application, including the following steps:

[0041] Step 1: Call the sliced image of the three-dimensional model to be printed currently;

[0042] Step 2: Configure a dynamically changing printing speed v for each frame of the sliced image, satisfying the condition v = max(1.0, min(S0 / S, 1)×V0);

[0043] Step 21): Compare the maximum wall thickness S in the sliced image with the given threshold S0 of the wall thickness; among them, the maximum wall thickness S of the sliced image can be understood as when an image erosion operation with an edge distance of S0 / 2 is performed, the image is just completely eroded. If the wall thickness exceeds S0, then there will be residues when eroding according to S0 / 2. The more residues, the larger the entity area, which is also called the "large-area entity" area.

[0044] Read the sliced image frame by frame. Calculate the corresponding number of pixels x according to a length of 0.25 mm, and perform an erosion operation of x pixels on the sliced image. If there is no residue after erosion, the maximum wall thickness S of the sliced image is less than 0.5 mm; if there is a residue in the image, continue to perform an erosion operation on the remaining sliced image at a certain step length (such as 0.1 mm) until there is no residue in the sliced image;

[0045] If the maximum wall thickness S of the current sliced image is less than the given threshold S0, configure the printing speed of this frame of sliced image according to the maximum printable speed V0 of the current photosensitive resin material, v = V0;

[0046] If the maximum wall thickness S of the current sliced image is greater than the given threshold S0, v < V0, and v = max(1.0, min(S0 / S, 1) × V0);

[0047] Step 3: Configure the dynamic light intensity P corresponding to each pixel point in each frame of the sliced image based on the dynamically changing printing speed v v , and this dynamic light intensity P v increases as the printing speed v increases and decreases as the printing speed v decreases;

[0048] Step 4: Generate the projection parameters of the projection device, where the projection parameters include the light intensity corresponding to each pixel point on the sliced image of the three-dimensional model;

[0049] Step 5: Start the optical machine, project the sliced images frame by frame according to the projection parameters, and at the same time, the printing platform 105 rises at the dynamic printing speed v until the printing is completed to obtain a complete three-dimensional model.

[0050] In an embodiment of the present application, the maximum wall thickness reference S0 is generally set to 0.5 - 4 millimeters.

[0051] Generally speaking, the printing speed v is greater than or equal to 0.5 mm / min, and the printing speed v ≤ V0. The maximum printing speed V0 is determined by the material of the photosensitive resin. When the printing device prints at the maximum printing speed, the corresponding light intensity will also reach the peak. Continuing to increase the speed cannot ensure the full curing of the photosensitive resin. The minimum speed of the dynamic printing speed is not lower than 0.5 mm / min. This printing speed is already the upper limit printing speed of a traditional stereolithography (DLP) printer. Therefore, the continuous 3D printing device of the present application is a high-speed 3D printing device.

[0052] Next, we analyze the key physical factors affecting the continuous curing process and find out what relationship the change between the printing speed and the light intensity received by each pixel point satisfies.

[0053] See Figure 3 as shown, the decay relationship of ultraviolet light in the photosensitive resin satisfies:

[0054]

[0055] 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 received by the photosensitive resin at point d d is related to the light transmittance of the material and the distance, and decreases exponentially.

[0056] Figure 3 Pτ in 0 represents the light intensity at the pixel point located in the photocuring window. Pτ 1 represents the light intensity at the pixel point one unit thickness away from the photocuring window, and so on. Pτ 4 represents the light intensity at the pixel point 4 unit thicknesses away from the photocuring window. The power of τ is the same as the number of unit lengths of the distance.

[0057] See Figure 4 As 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 lifts, getting farther away from the projection plane and gradually moving out of the illumination range.

[0058] As shown in the figure, for the photosensitive resin with a lateral distance h from the exposure edge of the printed part, the initial light intensity it receives is P h , and during the process of the platform printing upward at the printing speed v, the distance d between this point and the projection edge after t seconds is:

[0059]

[0060] Substituting Equation (2) into Equation (1), the light intensity near the point with an initial distance h from the exposure area at any time t can be obtained:

[0061]

[0062] Among them, h is the initial distance of the pixel point from the cross - sectional contour 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 one 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.

[0063] Next, we continue to calculate the accumulated exposure amount of the point with an initial distance h from the exposure area. As the printing platform continuously lifts 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 we integrate P th 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 .

[0064]

[0065] Among them, T is a sufficiently long time such that after moving for T seconds, the light intensity decays to a negligible level and cannot substantially change the integration result. Equation (4) indicates that for a point at a distance h outside the three-dimensional model contour, given the printing speed v, the total exposure E received 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 object contour to become thicker. Theoretically, we hope that h = 0, that is, we hope that the photosensitive resin outside the three-dimensional model contour cannot be cured. However, this is actually impossible to achieve. Therefore, we set h c to a fixed value to make it satisfy a relatively small value, and within this range, keep h c constant, so as to keep the outer contour of the three-dimensional model constant and obtain a three-dimensional model with a continuous and smooth surface that will not become thicker or thinner.

[0066] Remove the integral from the above Equation (4) to obtain a formula form that can be controlled in real time. First, simplify the calculation method of the distance d to:

[0067]

[0068] 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 Equation (4) becomes:

[0069]

[0070] Then integrate Equation (6) to obtain Equation (7).

[0071]

[0072] where 0 < τ < 1 and T is sufficiently large. Equation (7) can be used to determine whether the material at a distance h from the surface of the printed part will cure when continuously printing at speed v. As Figure 5 shown, during the gradual rising process of the three-dimensional model, its direct illumination area will gradually cure, which is called the established cured part D1. Due to the existence of a relatively high diffused light intensity near the body of the three-dimensional model, after time accumulation, it exceeds the critical exposure amount, generating a diffused cured area D2. In a farther place, because the diffused light intensity weakens, curing will not occur, and D3 is the under-cured area.

[0073] We can transform Equation (7) to obtain:

[0074]

[0075] where h c represents the lateral distance between the actual curing boundary and the theoretical curing boundary.

[0076] As described above, we hope to obtain h c A constant three-dimensional model, so that the printed product will not become thicker or thinner due to the change of printing speed. In order to make h c fixed, we can continue to transform Equation (8) to obtain the intensity P v of the light during the projection of the sliced image;

[0077]

[0078] Wherein,

[0079] P v represents the dynamic light intensity at the printing speed of v;

[0080] v represents the current printing speed;

[0081] E c represents the critical exposure of the photosensitive resin;

[0082] τ represents the light transmittance of the photosensitive resin per unit thickness;

[0083] h c represents the lateral distance between the actual curing boundary and the theoretical curing boundary, that is, the printing profile thickness;

[0084] Δd is the unit thickness, that is, the shortest distance between two adjacent sliced images;

[0085] T represents the exposure time.

[0086] It can be seen that when the desired h c is fixed, the dynamic light intensity P v is positively correlated with the printing speed v, and the two satisfy the relationship of Equation (9). When the printing speed v increases, P v will increase accordingly. When the printing speed v decreases, P v will decrease accordingly. The change rate of P v in the function is higher than that of v.

[0087] hc is a fixed value. Generally, the value of h c satisfies: -0.1 ≤ h c ≤ 0.3 mm.

[0088] Since there may be differences between the three-dimensional model obtained by printing according to Equation (9) and the model thickness h c in the theoretical design under different photosensitive resin materials and 3D printing devices, in an embodiment of the present application, we also introduce an adjustment coefficient α, and the actual dynamic light intensity P v ' corresponding to each pixel point on the sliced image = α × P v .

[0089] The adjustment coefficient α is positively correlated with the viscosity of the photosensitive resin and negatively correlated with the light transmittance τ of the photosensitive resin, and a reasonable value can be conveniently obtained through experiments. Preferably, in this application, 0.8 ≤ α ≤ 1.2.

[0090] In summary, the continuous 3D printing device of this application will dynamically calculate according to the area of the entity projection region in the current sliced image. If the area ratio of the entity region is large, the device will gradually reduce the printing speed v, and calculate the dynamic light intensity P of any pixel point according to the dynamic printing speed v. v , so as to ensure that the lateral distance hc between the actual curing boundary and the theoretical curing boundary remains constant, and then obtain a three-dimensional model with a continuous and smooth surface and controllable precision.

[0091] 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 by the above embodiments. The above embodiments and the descriptions in the specification only illustrate 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 required by the present invention is defined by the appended claims, the specification and their equivalents.

Claims

1. A continuous 3D printing control method based on dynamic light intensity, characterized in that Including the following steps: Step 1), calling the slice image of the three-dimensional model to be printed; Step 2), configuring a dynamically changing printing speed v for each frame of the slice image; Step 3), configure the dynamic light intensity P corresponding to each frame of sliced image according to the printing speed v v , and this dynamic light intensity P v increases as the printing speed v increases and decreases as the printing speed v decreases; The dynamic light intensity P v and the printing speed v satisfy the following relationship: Among them, P v represents the dynamic light intensity at a printing speed of v; 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; h c represents the lateral distance between the actual solidification boundary and the theoretical solidification boundary; Δd is the unit thickness, that is, the shortest distance between two adjacent frames of slice images; T represents the exposure time.

2. The control method according to claim 1, characterized in that: The actual dynamic light intensity P of each corresponding pixel point on the sliced image v ’ = α × P v , where α is an adjustment coefficient, and 0.8 ≤ α ≤ 1.

2.

3. The control method according to claim 1, characterized in that: -0.1 mm ≤ h c ≤ 0.3 mm。 4. The control method according to claim 1, characterized in that, Step 2) further includes: comparing the maximum wall thickness S in the slice image with a given threshold S0 of the wall thickness; If the maximum wall thickness S of the current slice image is less than the given threshold S0, configure the printing speed of this frame of slice image according to the maximum printable speed V0 of the current photosensitive resin material, v = V0; If the maximum wall thickness S of the current slice image is greater than the given threshold S0, v < V0.

5. The control method according to claim 4, wherein: The printing speed v satisfies the condition v = max(1.0, min(S0 / S, 1)×V0).

6. The control method according to claim 4, characterized in that: S0 is 0.5 - 4 millimeters.

7. 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 control method described in any one of claims 1 - 6.

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