Three-dimensional printing principle and technology

In the field of printing, the three-dimensional printing of three-dimensional objects to reproduce the three-dimensional printing of three-dimensional images, has become an important part of the special printing industry, the following talk about the technical features and development prospects in this regard.

<The principle and characteristics of three-dimensional printing

The principle of three-dimensional printing is to simulate the distance between two eyes of a person and shoot from different angles. The left and right pixels are recorded on the photosensitive material. When viewed, the left eye sees the left pixel and the right eye sees the right pixel. The printed matter produced according to this principle is called For three-dimensional printing.

Three-dimensional printing has the following characteristics: (1) It can realistically reproduce objects with a strong three-dimensional effect. Product images are clear, rich in levels, vivid in image and profound in artistic conception; (2) The manuscripts of three-dimensional printing are often made of design or scenery, and the printed matter is generally selected from high-quality coated paper and high-temperature resistant ink, so the gloss is good. Bright colors, not fading; (3) printed product surface covered with a concave and convex cylindrical mirror grating board, you can directly view the three-dimensional effect of the panoramic picture. From the perspective of people's stereoscopic vision of objects, the stereoscopic vision produced by objects is mainly based on human physiological factors, experience, and psychological factors. In fact, stereo vision is the stereoscopic information formed by the integration of the complex factors of appeal in the visual process. In terms of physiological factors, there are parallax (parallax in both eyes and parallax in monocular movement), convergence, and adjustment. Specifically, binocular parallax is a fundamental factor for people to obtain stereoscopic vision. In everyday life, when people observe objects, due to the perspective between the two eyes, the images of the objects seen by the left and right eyes will be different. Parallax, it gives people three-dimensionality.

The effect of stereoscopic images must be reflected by display technology. The stereoscopic display here refers to the reproduction of stereoscopic information in the three-dimensional space of an image, which is another basic condition for obtaining stereoscopic vision. There are two main ways to achieve stereoscopic display, namely two-way display method and multi-directional display method.

(1) Two-way display method. Can be divided into three-dimensional mirror method, two-color filter method, polarizing filter method and alternating division method. Regardless of the method used, stereopsis is obtained by using the binocular parallax and left and right eyes to observe the image separately. Stereoscopic method: The basic principle of the stereoscopic method is to use a stereoscopic mirror to observe the left and right graphics and create a three-dimensional sense. This method has been widely adopted since the advent of the 19th century, but special stereoscopes must be used, otherwise there would be no stereo vision. Two-color filter method: the left and right images are respectively printed on the same plane with red and blue inks, and the printed images are observed through red and blue filters. Since the color filter and the ink are complementary to each other, the image observed through the color filter is not red and blue but black. Therefore, this method is limited to black-and-white photographs and is not suitable for color prints. In addition, light of different wavelengths enters into both eyes, and it is easy to make eyes fatigued. Therefore, this method is rarely used except for air maps. Polarized filter method: The left and right images are respectively projected on the same plane by the polarized filters that are orthogonal to each other, and the left and right eyes are also observed by the same polarizing filter. Although this method requires special glasses, it has been widely used in stereoscopic movies and stereoscopic televisions. Alternate splitting method: The left and right images are alternately presented on the same plane and the unnecessary parts of the same period are masked to create a three-dimensional effect. Since the afterimage effect causes flashes, masking glasses are expensive, so this method has not been popular so far.

(2) Multi-directional display method. There are parallax shielding methods and cylindrical lens methods. Parallax Shielding Method: Parallax Shielding Method, also known as parallax slit method, was invented by FELves in 1930. Its working principle is to divide the left-eye image and right-eye image by slits and exposure on the film, and then develop, Shaiban and printing. If you place it in the same position at the time of photography, and both eyes are placed at the position where the image is placed, stereo images can be seen. Using the parallax slit method, parallax stereo images can be obtained by combining two images. If the aperture ratio of the slit is reduced and the synthesis of a plurality of images can be completed, a parallax panoramic image can be obtained. The parallax slit method is essentially an inescapable reduction in the amount of light. Therefore, it is rarely used except for the cylindrical lens method. Cylindrical lens method: A cylindrical lens can be viewed as a lens Plate composed of a plurality of convex lens pieces side by side, which has an imaging effect. The back of this lens coincides with the focal plane. Due to the separation of the lens, the images A, B, C, and D in each direction can be separated into a, b, c, and d and recorded on the focal plane, as long as the left and right eyes are placed on the B and C. Position, you can see stereo images.

Three-dimensional printing process and points

Three-dimensional printing photography method

As described above, the cylindrical lens method for stereoscopic printing requires an image of an object to be viewed from various directions. Photography methods include (1) circular arc movement method. This method takes a certain point on the subject as the center of the circle. The distance from this point to the camera is the arc radius. The camera moves along the arc and shoots continuously or intermittently. (2) Parallel movement method. Move the lens parallel to the centerline of the object. When this method is used for shooting, the accuracy is not easy to grasp; (3) Straight line shaking method. Shooting images can be a bit offensive. However, if you do not require higher accuracy, this is a simple method.

In addition, the cylindrical lens is not used for photography, and it is photographed while moving as with a normal camera, and then the images in each direction are synthesized by a cylindrical lens. Therefore, images in all directions (6-9) cannot be continuous. It mainly has instant photography. Cameras with multiple (6-9) lenses are best suited for outdoor photography, especially for moving objects, due to their ease of portability. However, stereoscopic photographs cannot be formed without post-composition, and there is the advantage that the size can be enlarged when the images are synthesized. Ordinary camera movement method: The ordinary camera is mounted on an electric chute and photographed while sliding. This has no outstanding advantages compared to the instant photography method described above, except that it does not require a special camera. The method of using a cylindrical lens for photography can continuously photograph within an effective angle. A stereoscopic image can be obtained at one time, but it is very difficult to enlarge the image after shooting, and the exposure time is too long to capture a moving object, and the camera is large in size and should not be carried. The object moving method is the opposite of the moving camera in that the object to be illuminated rotates and moves linearly.

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At present, there are two methods commonly used for photographing three-dimensional printing manuscripts, that is, arc stereography and shutter movement. Circular motion shooting: The cylindrical lens plate is directly attached to the front of the photosensitive sheet and is photographed with a camera. The optical axis of the camera always faces the center of the subject. The total distance of the camera movement is based on the requirements of the reconstructed image, generally controlled at an angle of 3° to 10°. The grating plate in front of the camera photographic plate and the photosensitive plate move randomly and synchronously. Each exposure is focused to one pixel under each half cylinder of the grating plate. When the camera finishes shooting at a predetermined distance, the pixels fill the entire pitch. After washing can get a three-dimensional photo. Shutter movement shooting: When shooting, the distance of the shutter from one end of the lens to the other is 60mm, which is equivalent to the distance between two eyes. At the same time, the grid plate immediately in front of the photosensitive sheet also moves accordingly, and the moving distance is a pitch of 0.6 mm.

Platemaking and printing process

Due to the fineness of the stereo image pixels and the magnification of the lenticular lens grating, the number of plate-making screen lines must be 120 lines/cm or more. Stereoscopic printing and general color printing have different screening angles, and green and black versions use the same mesh angle. In addition, three-dimensional prints with different grid pitches must have different combinations of yellow, magenta, cyan, and black grid lines to avoid interference fringes. Nowadays, the screen angle used by general manufacturers at home and abroad is: 0.6 pitch/cm, 100 line/cm color separation, then the degree of screen angle is Y81, M36, C66, K66; 0.44 pitch/cm, 58 line/ For color separation of cm, the degree of screen angle is Y50, M20, C65, K65; color separation of 0.31 pitch/cm, and 81 line/cm, and the degree of screen angle is Y66, M22, C51, K51.

Since the three-dimensional manuscript is composed of a closely-arranged pixel, after the plate-making and printing, the lenticular plate is compounded. Therefore, besides the moiré formed between the screens, the network line angle must be considered. The screen angle forms a moiré pattern formed by the pixel lines and the lenticular lines.

For example, three-dimensional printing should not choose 0 degrees, because the horizontal network line is the most obvious, and 0 degrees and the pixel line, cylindrical lens line orthogonality, interfere with the clarity and depth of the image. The three-dimensional printing in the blue and black version of the same screen angle is determined by its own characteristics. Because the three-dimensional prints are finally composited with plastic plates, the lenticular plates are mostly with a certain grayscale, and because the three-dimensional printing uses a very fine 300-line screen, it only needs to be 8.5 to 9 or 9 when printing. Into the point, otherwise it is easy to paste version when printing, so you need to increase the amount of dark tone in the area, in order to achieve 9-9.5 into the effect. Therefore, the three-dimensional printing is more dense than the solid color density of the four-color printing on the plane. Generally: lithographic offset: Y: 1-1.1, M: 1.4-1.5, C: 1.5-1.6; three-dimensional printing: Y: 1.33-1.35, M: 1.31-1.33, C: 2. If the three-color printing ink is close to neutral gray after overprinting, in order to reduce the error caused by the fourth overprint, it is not necessary to print the black version again, and the black and green versions can be taken the same angle for flexibility. In the small area even when the sun, due to the temperature of the exposure light source will cause the film to shrink, resulting in changes in the pitch of the front and rear width, affecting the accuracy of the print position, so the separation of the separation film made into the whole film for the best print.

When copying the positive image, it is necessary to make a line that is equal in width and pitch between the negative film and the photosensitive film. The printing plate should be printed with a PS plate with a better level of expression. The printing method selected for the three-dimensional printing shall ensure that there is no loss of three-dimensionality due to printing, and the accuracy of overprinting is good, and a large number of printings are preferable. Lithographic Offset: Platemaking, printing overprint accuracy, resistance to printing force are better, printed products better three-dimensional, plate making stable, and mass production; Photogravure: plate making, printing overprint accuracy is not good, good resistance to India, India The product has a good three-dimensional effect, but the multi-color printing effect is not good; the Milo version: the plate-making modulation is unstable, the printing-resistant force is low, the printing accuracy of the printing product is good, and the three-dimensional feeling is better, but it is not suitable for mass production. Stereo printing is generally printed using a lithographic offset process. The quality of three-dimensional printing is good and has obvious influence on the visual effect of three-dimensional pictures. Due to the focusing and obstruction of the grating, the network cable is required to be clear and overprinting is accurate. The trapping error must not exceed 0.02 mm, and the ink must be bright and clean without fading. The use of high-precision four-color printer printing, the rules line must meet strictly, and the workshop must have constant temperature and humidity conditions. With regard to the above comparison of conditions, stereographs are generally used for offset printing. The stereoscopic negative film taken was separated by electronic color separation or direct screening.

Three-dimensional printing materials and technologies

(1) Paper. Paper for printing needs to be compact, smooth, smooth, and less stretchable; usually coated paper or cardboard is used.

(2) grating sheet material. There are mainly rigid plastic lenticular films. Polystyrene raw material was processed into an lenticular mirror-like grating by injection molding. Polystyrene is colorless and transparent (transparency 88%-92%), refractive index 1.59-1.6, non-ductile, flammable. Because of this high refractive index it gives it a good sheen. The birefringence stress on the transparent plastic processing - light