Electronic Design

Adidas Designs A Winner With "Smart" Running Shoes

I'm not a runner, and I typically wouldn't consider spending $250 on sports shoes. But I found myself at the mall yesterday in the hopes of testing out the new adidas_1 "smart" shoes. After three years in the laboratory, Adidas officially launched the electronics-enabled shoes this month. If first-wave sales are an indicator (my local stores are sold out and don't expect more shoes until May), the company has a major success on its hands.

"Smart shoes" may sound gimmicky. But adaptive cushioning makes sense, and the design engineering behind the shoes is impressive. The shoe constantly adapts its shock-absorbing characteristics to customize its value to the individual runner, depending on running style, pace, body weight, and running surface. The shoe uses a magnetic sensing system to measure cushioning level, which is adjusted via a DSP that controls a motor-driven cable system.

A Hall effect sensor is positioned at the top of the "cushioning element," and the magnet is placed at the bottom of the element. As the cushioning compresses on each impact, the sensor measures the distance from top to bottom of mid-sole (accurate to 0.1 mm). About 1000 readings per second are taken and relayed to the shoe's microprocessor.

The MPU is positioned under the arch of the shoe. It runs an algorithm that compares the compression messages received from the sensor to a preset range of proper cushioning levels, so it understands if the shoe is too soft or too firm.

Then the MPU sends a command to a micromotor, housed in the mid-foot. The micromotor turns a lead screw to lengthen or shorten a cable secured to the walls of a plastic-cushioning element. When the cable is shortened, the cushioning element is pulled taut and compresses very little. A longer cable allows for a more cushioned feel. A replaceable 3-V battery powers the motor and lasts for about 100 hours of running.

The Portland, Ore.-based Adidas Innovation Team that developed the shoe was led by Christian DiBenedetto. It also included electromechanical engineer Mark Oleson, as well as a footwear developer and two industrial designers. Oleson explains that the team chose a magnetic sensor because it could measure the amount of compression in addition to the time it took to reach full compression.

Gathering sensor data, he says, meant little without building a comparative "running context." So one of the first steps in developing the MPU algorithms was building this database. Runners wore test shoes that gathered information about various compression levels during a run. Then the runners were interviewed to learn their thoughts about the different cushion levels. "When the two matched up, that helped validate our sensor," says Oleson.

IN THE "COMPRESSION" ZONE
The development team found that most people prefer about the same amount of compression, so the focus was on building a system that could keep the shoe in a preferred compression zone, no matter the runners' speed, weight, or surface they were on.

According to Oleson, getting the algorithm right meant poring over reams of compression data, uploading the algorithm program onto the processor, testing it, correlating the results, and then testing again, adjusting not only the algorithm but also the adaptation mechanism.

Adaptations in the cushioning element account for the change of running surface and pace of the runner, and they're made gradually over an average of four running steps. The goal is for the runner not to feel any sudden changes. Adaptations are made during the "swing" phase rather than the "stance" phase of the stride (i.e., when the foot is off the ground).

If the shoe's owner prefers a more cushioned or a firmer "ride," adjustments can be made via "+" and "­" buttons that also activate the intelligent functions of the shoe. LED indicators confirm when the electronics are turned on. (The lights do not remain on when the shoes are in use.) If the shoes aren't turned on, they operate like old-fashioned "manual" running shoes. The shoes turn off if their owner is either inactive or at a walking pace for 10 minutes.

The shoes also come with a "demonstration key" that lets users experience all the capabilities of the shoe. With the DemoKey, users can try the shoe in the softest setting and then quickly reset the shoe to the firmest setting to get a feel for the range of settings.

Kudos to Adidas for the thoughtful engineering behind these shoes. The company could have just thrown in some electronics for the sake of creating "intelligent" shoes. But that would have been a setback to the future of "smart clothing," what may soon be an important new market for electronic design.

TAGS: Digital ICs
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