The imaging principle of the three-piece LCD projector takes the optical path of the LCD projector as an example: first, the light passes through the filter to filter out infrared rays, ultraviolet rays and other invisible lights that are harmful to the LCD. The light is homogenized by two multi-lens lenses, and the cone light generated by UHP lamp is corrected into rectangular light similar to the projected image. The prism between the two mirrors is used to pre-polarize the light, which can reduce the loss of light compared with the asymmetric light box without prism. Next, the light is divided into three primary colors of red, green and blue by the beam splitter, and reflected to the corresponding liquid crystal panel. Before reaching the LCD panel, the light also needs to pass through the convex lens and polarizer. The convex lens is used to collect light, and the polarizing plate further polarizes the light and makes it vibrate in the same direction, which can be controlled by the liquid crystal panel. Finally, the light passes through the liquid crystal panel and is driven by the circuit board, and each pixel on the liquid crystal panel is turned on and off in turn to generate an image, and rich colors are generated through the adjustment of each primary color light. Finally, the three rays finally converge and are projected by the lens.
Speaking of liquid crystal technology, it has long been eliminated by the world. The last international brand that produced this technology projector was Sharp PN 500 projector for entertainment, which was also produced by Sharp in 2003. The parameter is 640*480, 120ANSI lumens.
At the same time, in China, companies such as Multidimensional Electronics, Ruicheng Technology and ATV Technology have produced similar LCD single-chip projectors, using HID gas discharge lamps as light sources, and the service life can actually reach about 6,000 hours. Most display devices use second-hand disassembled LCD screens, most of which are Sharp 320*240 resolution LCD screens. Then in 2005, LCD screens with 800*480 resolution, such as Toshiba's TF070B070F and Hitachi's LQ series LCD screens, began to be widely used. Until 2007, PVI of Yuantai Company produced a backless LCD screen with a resolution of 800*600, and began to become a relatively professional LCD screen in the industry. In 20 1 1 year, Yuantai Company produced the 5.8-inch 1280*768 resolution LCD projection screen of PM058 series, and Lysine took the lead in launching the LED projector ESP300HD with this LCD screen that year, reaching the peak of domestic LCD single-chip projectors. Since then, projectors with this technical framework have gradually withdrawn from the market. Compared with DLP and 3LCD technologies adopted by international brands, this type of projector has some problems, such as poor color, only 256,000 colors, low contrast (only 500: 1), no off-axis, blurred image after keystone correction (only Rexain adopts electronic keystone correction without this shortcoming), etc. No matter what kind of light source is used, this kind of products have been out of consumers' sight in domestic and foreign markets.
Digital optical processing
Taking the resolution of 1024×768 as an example, there are 1024×768 small mirrors on a DMD, each mirror represents a pixel, and each small mirror has the ability to control light independently. The angle of the light reflected by the small mirror is controlled by the video signal, which is modulated by the digital light processor DLP, and the video signal is modulated into a pulse width modulation signal with equal amplitude, and the opening and closing time of the light path of the small mirror is controlled by the pulse width, so that gray images with different brightness are generated on the screen. DMD projectors can be divided into single-chip, double-chip and three-chip according to the number of reflective lenses. Taking a single chip as an example, DLP can produce colors because the color wheel (composed of three groups of red, green and blue) placed in the light path of the light source generates three primary colors of RGB through the light emitted by the light source through the condenser lens to the color filter. A DMD chip containing thousands of micromirrors projects light from a light source onto the surface of a microchip DMD embedded with an array of micromirrors through fast-rotating red, green and blue filters. These micromirrors rotate at a speed of 5000 times per second and reflect incident light.
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DMD is the core device of digital light processing technology (DLP) of Texas Instruments. On this matchbox-sized chip, there are 800,000 to 6,543.38+0,000 small mirrors densely arranged, and each small mirror can independently flip 654.38+00 degrees, and can flip 65,000 times per second. The light source is reflected on the screen through these small mirrors to form an image directly. Therefore, DLP projection technology abandons the traditional optical convergence, can change the focal length at will, is very convenient to adjust, and the optical path is quite simple and smaller.
Take Rexain's movie series as an example. The projector is only the size of a palm, but it can play all kinds of digital media and is compatible with all video formats. It also has the functions of TV, electronic keystone correction and multimedia playing PMP. And the excellent optical design ability ensures that 100% is off-axis, so it has enough use and practical value.
Its LED technology is sequential RGB technology, which ensures that the color is real, vivid and not exaggerated, reaching 100%NTSC color gamut.
LCOS
LCOS(Liquid Crystal on Silicon) is a new reflective micro LCD projection technology, which uses CMOS integrated circuit chip coated with liquid crystal silicon as the substrate of reflective LCD. Polishing with advanced technology, aluminum plating as a reflective layer to form a CMOS substrate, then bonding the CMOS substrate to a glass substrate with transparent electrodes, and then injecting liquid crystal for packaging. LCOS puts the control circuit behind the display device, which can improve the light transmittance, thus achieving greater light output and higher resolution.
LCOS can also be regarded as a kind of LCD. Traditional LCD is made on glass substrate, while LCOS is made on silicon wafer. The former usually adopts the way of penetrating projection, the light utilization efficiency is only about 3%, and the resolution is not easy to improve; LCOS adopts reflective projection, and the light utilization efficiency can reach more than 40%. With the rapid refinement of semiconductor manufacturing process, the resolution can be gradually improved. On the other hand, the high-temperature polysilicon LCD needs separate equipment, which is a special process and the cost is not easy to reduce. The structure of LCOS panel is somewhat similar to TFT LCD. Spacers are distributed between the upper and lower substrates to isolate them, and then liquid crystals are filled between the substrates to form a light valve. The switch of the circuit drives the liquid crystal molecules to rotate, which determines the brightness of the picture. The upper substrate of LCOS panel is ITO conductive glass, and the lower substrate is CMOS substrate coated with liquid crystal silicon. The biggest feature of LCOS panel is that the lower substrate is monocrystalline silicon, so the electron mobility is good, and monocrystalline silicon can form thinner lines. Therefore, compared with the existing LCD and DLP projection panels, LCOS is a new projection technology that can easily achieve high resolution.
Light Emitting Diode(LED)
As we all know, the projector bulb is an expensive consumable and has a certain service life. If used for a long time, the light bulb will age. Replacing light bulbs is a problem that projector users must consider, which is also a big disadvantage of projection compared with LCD TV. Over the years, major projector manufacturers have been committed to developing light bulbs with longer service life. The emergence of LED projection technology has opened up a new situation for the development of projectors. Compared with the traditional projector, the biggest advantage of LED projector with LED light source is that it doesn't need to change the bulb frequently, and its bulb life is 10000-20000 hours or even longer, so users don't have to worry about the loss of the projector bulb at all.
However, although LED light source is called cold light source, it is particularly afraid of heat. If the heat generated by the chip itself cannot be eliminated or dissipated in time, the temperature will rise higher and higher. When the chip temperature exceeds 100 degrees Celsius, the luminous efficiency of LED chips will be greatly reduced, resulting in light attenuation. When the temperature exceeds 150 degrees Celsius, the LED chip can be burned instantly. Therefore, only with good heat dissipation can the long-life characteristics of LED light sources be truly exerted. Otherwise, the LED chip will decay sharply in a short time, and its life may be worse than that of the traditional metal halide lamp. Heat pipe heat dissipation and heat sink technology is an inevitable choice. Referring to Rexain's patented technology, we can find that only this technology can guarantee the long life of LED.
As the LED is a cold light source, it will not generate a lot of heat like a metal halogen lamp, which simplifies the complex light path structure required by the original light source, thus reducing the requirements for the projector cooling system and making it much smaller than the original one. From a small point of view, LED projectors are generally kept below 1 kg, and some even weigh only about 0.5 kg, which is easy to carry and move. And the noise is much less.