Touch Technology for Ereaders
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frontline technology Touch Technology for eReaders Four touch technologies are currently used in eReaders: analog resistive, electromagnetic pen digitizer, scanned infrared, and projected capacitive. None of these meet 100% of the user and system requirements for optimum touch in eReaders. by Geoff Walker WITH MORE THAN 500 million touch screens with very high transmissivity. reducing surface reflectivity is very expen- people using smartphones and tablets equipped Low reflectivity of the touch screen is also sive. Resistive requires a relatively heavy with projected-capacitive touch technology, a very important, since reflected light reduces touch, but works well with a passive stylus – de facto standard has arisen for what users the image contrast. except that the lack of palm rejection makes expect on any touch-capable mobile device – Additional system-level requirements for touch annotation difficult. Resistive as used in including eReaders. The key requirements of screens in eReaders include the following: eReaders today provides single-touch only. this standard include the following: • Very low power consumption (like that Resistive is available in an “almost-flush • Extremely light touch for EPDs) bezel” form in which the touch-screen’s • Fast response • Light weight, ideally achieved with no plastic cover sheet is extended to cover the • High accuracy for selection added glass layer entire top surface of the product. • Multi-touch for zoom (with images • Durable surface for annotations. Scanned Infrared: Infrared (sometimes stored at higher resolution) called “optical”) touch technology has not • Flush bezel for a high-tech look. Four Current Touch Technologies historically been used in mobile products. There are four touch technologies currently However, one company (Neonode in Sweden) The touch usage model of eReaders adds has made significant progress in miniaturizing another requirement: annotation capability. used in eReaders (see Fig. 1), as follows in order of decreasing popularity: infrared touch components over the past half- At the minimum, this means high-resolution dozen years, with the result that it is currently digital ink for good readability; ideally, it • Analog resistive (e.g., in the Sony the only supplier of infrared touch in eReaders. includes handwriting recognition for automat- PRS-600 and many others) (Neonode’s patent portfolio provides a signifi- ically converting ink annotations into text. • Scanned infrared (e.g., in the Kindle cant barrier to entry for other suppliers.) The primary characteristic that differenti- Touch, the Nook Simple Touch, the Sony Infrared’s major advantage in an eReader is ates a dedicated eReader from a tablet is the PRS-950, and a number of others) the lack of need for a substrate. This is ideal use of an electrophoretic display, often • Electromagnetic pen digitizer (e.g., in for use with a reflective EPD, since no light is referred to as an “electronic-paper display” the Onyx Boox M90, the Hanlin V90, the lost. On the other hand, sensing touch with (EPD). EPDs are reflective displays, so the Hanvon WISEreader E920, which adds infrared requires breaking a matrix of light light that produces the image seen by the user finger touch, and several others) beams that are present above the surface of must travel twice through whatever layers are • Projected capacitive (e.g., in the Pixelar the display, so a flush bezel is not possible. on top of the display. This puts a premium on MReaders, the Hanlin V60T/V61T/A6/ Conventional infrared is relatively low resolu- A9, the Kogan Reader, and a few others) tion, so annotation with a stylus typically is Geoff Walker is the Owner & Principal Analog Resistive: While resistive is com- not very satisfying, and multi-touch is gener- Consultant at Walker Mobile, LLC, and monly used in touch eReaders because of its ally limited to two not-very-robust touches. Principal Analyst for Touch at IMS Research. low cost, it is actually the worst choice. Infrared is susceptible to unintended touches He has been Information Display’s Guest Transmissivity is typically in the 80–90% from contaminants (or if the user forgets to Editor for Touch since 2007 and is a range, which means that up to 40% of the turn off the device before putting it in a brief- recognized touch-industry expert. He can light can be lost during its two trips through case) and from ambient IR radiation. be reached at 408/945-1221 or geoff@ the touch screen. Because there are four Electromagnetic Pen Digitizer: Pen digi- walkermobile.com. reflective surfaces in a resistive touch screen, tizers have been used in mobile products for 30 Information Display 2&3/12 0362-0972/03/2012-030$1.00 + .00 © SID 2012 Fig. 1: Four 6-in. eReaders are shown, one with each touch technology (left to right): Sony’s PRS-600 (resistive), Amazon’s Kindle Touch (infrared), Hanvon’s N618 (electromagnetic pen digitizer), and Jinke’s Hanlin A6 (projected capacitive). Most eReader manufacturers offer only one or two touch technologies; Jinke in China is the only one that offers all four. Source: Manufacturers. over 20 years, so it is not surprising that they a major issue with pro-cap, since transmissiv- ments is Hanvon’s Dual Touch pen digitizer. are used in some eReaders. Like infrared, this ity is in the 95–98% range. However, limiting Hanvon achieves finger touch by adding some technology’s major advantage is its lack of a the reflectivity of the touch screen’s top low-cost components to the digitizer sensor need for a substrate (the digitizer’s sensor surface adds even more cost. Two of the three behind the EPD; if Hanvon can meet its goal goes behind the EPD, so no light is lost). sample eReader suppliers listed under pro-cap of supporting touch with multiple fingers, the Since there is no touch-screen substrate, the on the previous page use the SiPix/AUO EPD; only remaining negative will be the electronic possibility of a flush bezel depends on the this form of pro-cap uses two patterned- (but batteryless) stylus. design and construction of the EPD. Pen electrode films laminated on top of the EPD Another technology that has a good chance digitizers are typically very high resolution during manufacturing and is covered with a of meeting all the requirements is waveguide (often as high as 1000 dpi) with inherent palm hard coat (i.e., no glass). While the cost of infrared. Created by RPO in Australia and rejection, which makes them very well-suited this form is relatively low, future stylus branded “Digital Waveguide Touch” (DWT), for annotation. However, with the exception support seems unlikely. it is essentially a lower-cost and higher- of Hanvon’s “Dual-Touch” technology (which performance version of scanned infrared. supports both pen and single-touch finger), Power Consumption Unfortunately, RPO shut down due to lack of pen digitizers are pen-only. Power consumption in an eReader is domi- funding during 2011 and its extensive patent Projected Capacitive: “Pro-cap,” as it is nated by page-turns; i.e., by changing the portfolio is currently for sale. It is possible often called, is the touch technology used in image on the EPD. The power consumption that the technology (which was very close to most smartphones and tablets today. How- of all four of the touch technologies described mass production) may be purchased and made ever, it is relatively expensive (a 9-in. pro-cap in this article is orders of magnitude less available by another touch supplier. touch screen is typically 3× the cost of resis- than that of the EPD. While some power- There is one additional touch technology tive), so it is less frequently used in eReaders. consumption differences do exist between the that has at least some chance of meeting all Pro-cap’s advantages are its very light touch, technologies, experience has shown that the the requirements once it becomes more multi-touch, and flush-bezel capability – all of quality of the power-management algorithms mature. The technology is TE Connectivity’s which are characteristics of the de facto stan- used to control the touch screen is actually (Elo TouchSystems’) Acoustic Pulse Recogni- dard, so usage is likely to increase despite the much more significant than the differences tion (APR). APR is capable of pen and finger cost. Currently, it is finger-only, so annota- between technologies. touch with nothing added in front of the tion is not possible (although some pro-cap display. E Ink has done some prototyping touch-screen suppliers will start supporting Emerging and Future Solutions of APR integrated into its EPD, but it is too both active and passive styli during 2012). As noted earlier, none of the four touch tech- early to determine the potential. I When stylus support arrives, pro-cap is capa- nologies described here meet 100% of the ble of providing good palm rejection, so the user and system requirements listed in the user’s annotation experience can be almost as beginning of this article. Of the four, the one good as with a pen digitizer. Light loss is not that is the closest to meeting all the require- Information Display 2&3/12 31.