Three ways to get ThinThree ways to get Thin
August 20, 2001
As tough as it can be to shoehorn a mobile computer's electronics into the familiar "clamshell" form factor, IBM engineers faced a far more difficult packaging task when they created the new ThinkPad TransNote. Wrapped in a flexible elastomer cover, this computer could masquerade as a simple portfolio-the kind normally stuffed with legal pads and reams of paper. But TransNote flips opens to reveal a high-tech heart. A thin mobile computer sits side-by-side with a "digital notepad," which sends handwritten notes from a pad of paper to the computer.
Squeezing these two computing components into a 1.3 inch-thick portfolio package intensified the need to design for thinness, according to Dr. John Karidis, the IBM Distinguished Engineer who developed the TransNote design in collaboration with IBM industrial designer Ron Smith. The ultra-thin computer, which features a Pentium III processor, a 10.4 inch color touchscreen, a 10 GB hard drive, and a keyboard, measures just 18.8 mm thick. "Considered alone, it's one of the thinnest mobile computers on the market," he says. And at just 9 mm thick, the digital notepad doesn't take up much room either.
Other packaging hurdles arose from the kinds of movement implicit in a portfolio design. "The TransNote required provisions for all kinds of motion and articulation that a traditional notebook computer doesn't have," says Dr. Randy Moulic, an IBM electrical engineer and senior manager for mobile computing. Like a portfolio, TransNote opens flat, giving users simultaneous access to the computer and the digital notepad. It also folds to allow either one of the two sides to be used independently, while the other side remains hidden away.
More than just a way to close the computer, this folding provision helps the TransNote meet the very usability goals that provided the impetus for integrating a mobile computer and digitizer in the first place. As Karidis explains, the TransNote lets users put pen to paper-or to the touchscreen-without fully opening the portfolio or extending the computer's display. "This ability to use the pen on a flat surface breaks down some of the social barriers to using the computer to take notes at a meeting," he says. What's more, the folding minimizes the TransNote's footprint on the user's desktop or in that cramped computing locale known as the coach airline seat.
Further complicating the mechanical design, the TransNote also had to be ambidextrous. The standard configuration opens with the mobile computer on the left and the digital notepad on the right. For lefties, the same TransNote components can be arranged in the opposite configuration. Happy lefties notwithstanding, this capability imposed design constraints on the TransNote's computer enclosure, which features an aluminum base plate and a carbon-fiber-reinforced PC/ABS cover. The need to swap components from left to right meant that the housing required mirror-image redundancy with respect to many fastener and connector locations. The same went for the digitizer enclosure, which has a top made from unfilled PC/ASA with a separate glass reinforced stiffener bonded to selected areas underneath.
To come up with the TransNote's thin, articulating, switch-hitting package, IBM engineers applied three broad design strategies:
1. Rethink the layout
Lots of mobile computers are slender, but the TransNote's portfolio form factor required what Karidis describes, with more than a hint of understatement, as "an extremely constrained planar layout." To pack the TransNote components into its portfolio cover, IBM engineers first reshuffled the elements of a conventional mobile computer, particularly the display.
If attached like a clamshell-at simple hinges along the computers rear edge-even the thinnest display adds a few millimeters to the computer's overall thickness. So IBM engineers instead mounted the display further forward in the center of the enclosures top. When fully closed, the TransNote's display nestles above the keyboard. Occupying just the front half of the enclosure, the keyboard and closed display together match the thickness of the enclosure's boxier rear half, which houses the computer's processor, cooling fan, and other internal components.
The display opens with a distinctive two-axis articulation made possible by a double hinge made from diecast magnesium alloy with stainless steel pins. The bottom section of the hinge allows the display to rise straight up from the enclosure top, while the upper section lets the display tilt toward the user. "A lot of engineering went into that hinge," Moulic says, noting that it had to pass 36-inch drop tests with the screen open to various positions.
The screen articulation also aided the usability goals, according to Karidis. The hinge keeps the screen face up even when closed, enabling user as a pen-based computer. Or they can keep the screen low and flat while using the keyboard. The hinge also allows the whole display to tilt completely away from the user for presentations. And best of all for anyone who flies in the cheap seats, the hinge allows users to position the open display over the keyboard to avoid reclining airline seats.
A creative layout also helped conserve space on the TransNote's other side too. Unlike IBM's earlier standalone digitizers, the TransNote's digital notepad has its bulkiest electronic components on the same plane as the pad of paper. "Our challenge was to find electronics that were small enough not to grow the form factor and thin enough to fit within the same thickness as a pad of paper," says Karidis.
To find skinny electronic components and fine-tune the TransNote's component and board layouts, Karidis turned to engineers at IBM Research and IBM Yamato in Japan. "The Yamato team has more experience than any other team in the world at creating thin, light computer packages," he says. "They are the experts at sizing, mechanical design and board layout." That expertise came in handy as the TransNote evolved from a concept to the final design. "At first, we were overly aggressive in sizing the components," Karidis says, noting that he and industrial designer Ron Smith initially shot for a 17-mm thick computer. Yamato's engineers ultimately provided a reality-check complete with the real-world sizing constraints. They also handled the final board layouts, which further contributed to thickness reductions. "Board layout is tightly coupled with overall thickness," Karidis notes.
2. Wrap it up
A unique cover design with carefully placed living hinges and fasteners helped solve both the usability and space problems, in addition to providing a protective and aesthetic covering for the TransNote. "The cover was a huge challenge," recalls Karidis. In addition to a pair of book-style living hinges at its spine, IBM's patent-pending "FlexFold" design also features vertical bending points halfway across each of its sides. Screws secure the computer and digital notepad to metal frames within the cover, but the frames attach the computer components only along their outer edges so that they can partially detach from the flexible cover.
This arrangement of bending points and partial fastening allows either side of the TransNote to be stacked on top of the other in a "lift and fold" action that keeps both components in a top-up orientation. A pure portfolio cover, one that bends only about its spine, would have placed the display screen and keyboard face down during solo digitizer use. "We had concerns about perceived and real damage from the display resting on a hard surface," he says.
3. Share the power.
In another space-saving gambit, the TransNote's two sides share a single power source. A power cable hidden within the cover connects the digitizer to a lithium ion battery in the computer. Specialized power management software lets the devices run together or separately. More important, the software preserves 8-10 hours of power for the digitizer even after the notebook power powers down. "To the user, the system seems to have two batteries," Karidis says.
The shared battery highlights one of the big technical-as opposed to usability-advantages of integrating two computing products that already exist in standalone versions. As Karidis points out, "You avoid a lot of complexity once you eliminate separate batteries, connectors, and cables." The shared single power source also influenced the communication method between the computer and digitizer. Since a power cable was already present, the design team used a relatively simple serial connection between the two sides, rather than a more complicated wireless link.
The only problem with the shared-battery approach cropped up when it came time to specify a copper cable to connect the two sides. The design team couldn't find a small cable that would reliably wrap into a tight radius at the bends in the TransNote's cover. "We had started to look at some emerging technologies to connect the two side," Karidis recalls. Ultimately, however, design team worked with undisclosed vendors in Japan to produce a slim copper cabling capable of withstanding bend radii of "a couple of millimeters," he says.
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