24 January 2012

E-paper displays find industrial applications

Electrophoretic displays have been developed by companies such as E Ink to replicate, as closely as possible, the appearance of text on paper. Not surprisingly, these displays have been the enabling technology for e-readers such as Amazon's Kindle and Kobo's Touch.

The approach has a number of attractive features for the consumer world. One benefit is that electrophoretic displays, or EPDs, do not require backlighting. Instead, the devices rely on reflected light in the same way as you need a reading light when it gets dark. But another plus point for EPDs is they are bistable; even if you turn the power off, the image remains visible, providing there is enough light.

EPDs are one of a number of approaches to the development of e-paper. The technology was developed originally by MIT academic Joseph Jacobson, who later moved to commercialise the idea by establishing E Ink.

Each EPD comprises microcapsules, each containing positively charged white particles and negatively charged black particles suspended in a clear fluid. To form the display, the particles are coated onto a sheet of plastic film that is laminated to a layer of circuitry. The circuitry forms a pattern of pixels that can then be controlled by a display driver. The microcapsules are suspended in a liquid 'carrier medium', allowing them to be coated using existing coating processes. The final laminate can be applied to most surfaces, which allows for the production of displays with some degree of flexibility.

While most applications for EPDs have come in the consumer world, there is growing interest in their use in broader applications, including harsh environments.

Sri Peruvemba, chief marketing officer for E Ink, said: "We see a lot of interest for EPDs for various industrial, medical – even military – applications. E Ink has partnered with companies such as Neolux, Pervasive Displays and others to build display module solutions for various industrial applications, including shelf labels and point of purchase signage, as well as applications that have yet to be announced."

Another company seeing interest in EPDs from the industrial sector is Densitron Displays. Elijah Ebo, technical director for Europe and Asia, said: "We are seeing interest, but one thing which customers do not always understand is that EPDs will not be suited to every application. That means we're having to do some education."

Torsten Mindach, product marketing manager with Gleichmann Electronics, widened the scope. "Most customers we talk with are interested in using EPDs as status displays. But we're also seeing interest from those developing home automation applications and medical devices." Mindach added that transportation could be another target market. "There are interesting possibilities here; for example, bus timetables in rural locations could be updated with actual timings." The advantage here would be the bistable nature of EPDs; once the display is updated, it would consume no more power until the next change is required.

Ebo pointed out another consideration for those looking at EPDs. "You could be forgiven for thinking that industrial applications aren't as cost sensitive as consumer products, but you'd be wrong; these product developers don't want to throw money away." And the reason is that EPDs are the most expensive of the display options available – at least for the moment.

Mindach sees EPDs as being suited to industrial applications. "They offer a combination of low power consumption, good reliability and no need for backlighting. They are thin and are readable in most conditions."

With EPDs already being considered for retail use, Ebo believes image retention will be important in more obvious industrial applications. "The ability to retain an image when there's no power is important. For instance, the last image could have read 'danger'; EPDs will retain that message."

Peruvemba claimed the primary benefit for EPDs in industrial applications is their low power consumption. "Battery operated devices can last for a very long time compared to conventional displays. In addition, E Ink displays are plastic based, so offer a new solution to product designers where they need a level of ruggedness not possible with glass." Another benefit, said Peruvemba, is the display can be cut into irregular shapes, allowing greater freedom in product design.

Refresh rate remains an issue with EPDs, although they can run more quickly than they do in e-readers. "It can be a problem," Ebo admitted, "as refreshes take longer than, say, a tft. But it could update twice as fast as an e-reader."

But if you are thinking about using EPDs, beware; it's not just a matter of unplugging a tft and replacing it. Mindach noted: "There's a difference between the two technologies. EPDs need different interfacing and a specific waveform to stabilise the image. If you don't do it correctly, you won't have a stable image. We're working with companies such as Epson to develop controllers that will allow our customers to do this more readily."

Gleichmann is distributing products developed by Pervasive Displays, which has recently added area colour and monocolour to its EPD products, allowing users to emphasise important information.

Called Beacon, the approach allows multiple colours to be assigned to a particular area on the module and the information displayed in this area to be displayed in different colours, according to status. In addition to black and white, the monocolour option allows any third colour to be added.

Potential applications include picking systems, Kanban cards, automatic conveyer systems and retail, where special offers can be highlighted.

Greater ruggedness is another goal. Damon Hess, vp of business development for Pervasive Displays, noted: "Pervasive Displays is committed to furthering the use of electronic paper beyond the eReader and we know that the addition of ruggedisation and colour options will make electronic paper solutions viable for a myriad of additional industries.

"Pervasive Displays' Armor options are a huge step toward advancing PDI's mature, reliable and innovative solutions in the most demanding applications and environments."

Asked how E Ink's EPD technology is developing, Peruvemba said: "We are making progress on a number of fronts and have worked in collaboration with our chip partners – Freescale, Texas Instruments, Epson and Marvell – to launch new devices which enable EPDs to show animation and video. We have built tiled E Ink displays up to 2.4m in size and we have created devices up to 40in diagonal on a single substrate with no tiling. The recently launched Triton colour display is in mass production and under consideration for a variety of industrial applications."

Developers are also considered blending tft and EPD technologies to bring an effective 'best of both worlds' to industrial applications. EPDs would be used to display static data, while the tft could be used to display graphics when appropriate. "This would enable moving images," Ebo said, "a solution that would save power and have better legibility."

Peruvemba agreed: "EPDs can indeed collaborate with other display technologies, particularly oleds and lcds. Some of our customers have developed devices with lcd and E Ink displays and we definitely see that as a possibility in the future."

Author
Graham Pitcher

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