In October 2020, Epson's invention entitled "Laser projector with no flicker" won the Japan Patent Attorneys Association President's Award at the association's Kanto Region Invention Awards. The award is given to engineers and R&D professionals who produce outstanding inventions, ideas, or designs in each of eight regions in Japan (Hokkaido, Tohoku, Kanto, Chubu, Kinki, Chugoku, Shikoku, and Kyushu).
Laser projectors have boosted demand for projector applications, not only in offices and classrooms, but also for uses like projection mapping at event halls. We asked Takashi Toyooka and Makoto Zakoji, two developers of Epson's laser projectors, about the technology that brings out such beautiful expression without flicker and the new possibilities for visual communication that this provides.
VP Planning & Design Department Manager
VP Planning & Design Department
ToyookaOur first objective was to build a brighter projector.
The ELP-3000, which, started selling in 1994, was connected to a PC and created the culture of big-screen presentations in meeting rooms. Brightness is measured in lumens. The product put out 250 lumens, but the meeting room had to be darkened to use it.
Later, as we made progress on various technologies, projectors quickly became brighter, first 1000 lumens, then 3000. At a brightness of 3000 lumens, you no longer have to darken the room. That improved the meeting environment, because participants could easily look at handouts and take memos even while the projector was in use.
Before long, projectors found new uses. Previously, the most common uses of projectors were for projecting reference information in meeting rooms and video in home theaters. But starting in the 2010s, users were looking for products that could project to large screens in event halls and auditoriums, as well as products that could project very bright and large images for special events, with applications like projection mapping.
At first, we dealt with the brightness issue by inserting multiple large lamps. But that made the projector itself quite large. And there were other problems too. Lamps had a certain life span and had to be replaced regularly, and sometimes a lamp would burn out unexpectedly in the middle of an event.
The solution we settled on to ensure appropriate projector brightness and size and lamp life was to use a laser light source. We started developing a laser projector in about 2000. Around that time, laser light sources were very expensive and the three primary colors (red, green, and blue) that you need to display images were just not bright enough. But the technology progressed in a number of fields, like semiconductors. That was the trigger that led to big strides in realizing a laser projector.
The ELP-3000 liquid crystal business projector realized high brightness and resolution
ToyookaThe problem is not actually limited to the type of light source. It's not unusual for projectors themselves to have a problem with flicker. Even some projectors that used lamps had a flicker problem. So early on in the effort to develop a laser projector, we started testing flicker solutions.
Originally, we supposed that combining a laser light source with the 3LCD (liquid crystal display) technology that generates the image would cause flicker. That's because there was flicker when we combined the light source with liquid crystal displays in lamp projectors.
But the combination of light sources with liquid crystal displays was not the only cause of flicker in laser projectors.
ZakojiOur laser projectors use blue laser diode as a light source. There are several reasons we chose blue. For example, the laser diode (elements) of a blue laser can generate a brighter light source at lower power than other colors can. But blue lasers cannot be used on their own as a light source for projectors. A 3LCD projector requires all three primary colors: blue, red, and green. You need those other two primary colors in a 3LCD projector. So then we tried using a phosphor, such as is used in devices like white LEDs. We combined the blue laser light and the yellow light returned by irradiating the phosphor to generate white light.
If you illuminate a phosphor with a laser, the laser energy heats up the substance. And if you keep the laser on a single point, the phosphor gets even hotter. Eventually the substance gets so hot that it degrades. As the substance continues to degrade, it reflects back less light and the projector loses its brightness. So at Epson we tried putting a phosphor in a circular manner on a rotating disk to make a phosphor wheel. This way, the laser was always focused on a different part. The parts of the phosphor wheel could cool down while the laser was not on them, and that helped control temperature increase.
ToyookaPart of the reason for flicker in our laser projectors was that the phosphor was rotating like this.
The thickness of the phosphor could be slightly uneven, or the disk might be warped, or there might be variation in how the phosphor was bonded to the disk. So as the disk rotated and the laser beam moved over the phosphor wheel, these slight errors in the phosphor wheel caused fluctuations in the intensity of the yellow light reflected back. That caused the light to blink in the same pattern. Any time you try to make something, there will be very tiny errors. You can minimize them, but it's very hard to eliminate them completely. It's the same with phosphor wheels.
Another thing is that we adjust the brightness of laser projectors by controlling the laser elements with a slight pulse, which causes blinking. We can subtly control the relative brightness of the image not only by controlling the intensity of the laser beam itself but by modulating the pulse width to control blinking.
If there is interference between the blinking cycle of the light reflected back from the phosphor wheel and the blinking cycle of the laser element under some conditions, the low-frequency component occurs during the blink, making it visible to the eye. This causes flicker in laser projectors. After a lot of analysis, we realized that flicker occurs when the difference between the frequency of the disk rotation and that of the laser light source's pulse is less than 20 Hz.
The frequency at which the light reflected from the phosphor wheel blinks depends on the disk's speed of rotation. The frequency at which the light reflected from the phosphor wheel blinks depends on the disk's speed of rotation. So we controlled the frequency of the laser light source's pulse width modulation and the frequency of the speed of rotation of the phosphor wheel's disk so that the gap between the disk's speed of rotation and the laser light source's pulse would always be at least 20 Hz.
The result was that the laser projector could project images that are easy to view, with no flicker.
Zakoji The brightness, compactness, and long service life of laser projectors are making them more popular, and their uses are expanding substantially. They are no longer limited to meeting rooms and home theaters. In places like shopping complexes you can see new forms of image expression like projection mapping and digital art.
(Products built with the technology and examples of their use)
ToyookaThere is an exhibition called "MORI Building DIGITAL ART MUSEUM: EPSON teamLab Borderless" in Odaiba, Tokyo. There are about 500 projectors with this technology completely covering a space of 10,000 m2 with images. This is a whole new world of expression. At an exhibition of this scale, the many projectors used at the same time have to project images at uniform brightness. If not, the images will not have continuity, the big screen will not look dynamic, and the immersive experience of being surrounded by images at all 360° will be lost. The high-precision variable light control of the laser light source has an important role to play in a setting like this.
EPSON teamLab Borderless, Tokyo © teamLab
ZakojiUnlike conventional lamp projectors, laser projectors can be placed in any position. The lamp in a lamp projector can only be placed in certain positions. With a laser projector, on the other hand, the position of the laser element does not matter, so there are no limits on the angle at which the projector sits. So now we can project images at any angle, even the floor or ceiling, which was not easy to do before. This is an advantage that is vital to event production.
Epson has also been running the Fantas Aquarium at facilities like hospitals and special-needs school around Japan since 2015. The rooms of the facilities used as the venues have different conditions such as brightness, structure, and size. In addition, there are various features such as ceilings, walls, and floors that are easy for viewers to see. Using a laser projector is one of the solutions to this. It's possible to project bright, high-contrast and clear images even in a bright room where it is difficult to block out light. In addition, the flexible installation angle makes it possible to easily project onto the ceiling, walls, floor, etc., in rooms of any size, and at an angle that matches the viewer's line of sight.
Using laser projectors has made it possible to provide a richer video experience.
ZakojiProjectors first created a culture of large-screen presentations in the office. Then schools started using them, and projectors have helped provide learning environments that give every student a fair opportunity to learn. As the applications expanded, they found use in home theaters. But projectors aren't stopping there. They are increasingly being used for presentations in large halls, digital art delivered by projection mapping in shopping complexes, and digital signage, among others. In these applications, projectors can amaze and entertain large crowds of people. The backstory to those projectors includes the development of light sources, as we've talked about in this interview, but there's also been a constant cycle of R&D to enhance convenience and reliability and efforts to make the equipment smaller and lighter.
Heading into the future, we want to develop new applications in addition to home, office, and shopping complexes. There are already "lighting model" products on the market, for example, that use projection to make stores and products look more attractive. We want to use image experiences in all aspects of life like this to delight people and make the new normal more colorful.
That's another reason why we want to further elevate Epson's already strong microdisplay and projection technologies and get into markets where we will be second to none.