New Technology For Reducing Ladder Slips

[tweetmeme]Ladder slips account for more than one third of all ladder-related fall incidents.  NIOSH has announced it is collaborating with SRI International, an independent nonprofit research and development institute, to develop a prototype device that will enhance extension ladder stability.  The device will use an innovative electroadhesion technology invented and developed at SRI.

A prototype of a robot using electroadhesion climbs a wall at SRI headquarters. (photo: SRI International)

Electroadhesion provides a means to electrically attach a ladder to a variety of building surfaces using considerable force, thereby providing increased traction and resistance to slip. Applying electroadhesion technology to ladders has the potential to improve their stability on variety of materials with smooth, rough, and dusty surfaces.

Here’s how it works:

SRI’s wall-climbing robot features a loop of plastic film that runs on rollers.  The machine uses a battery to charge electrodes on the polymer, positively on one side, negatively on the other.

When the robot is brought near a wall, the surface naturally develops opposite charges from the part of the film closest to it.  As you may recall from high school science class, opposites attract.  The robot thus clings to the wall or, when the rollers are engaged, climbs up or down it.

The battery multiplies the natural effect of static electricity; in effect vigorously and continually rubbing the film across a head of hair (i.e., the balloon example).  The other key advance is the flexibility of the film, allowing it to closely adhere to the specific shape of the surface, more so than the rounded side of the balloon.

Harsha Prahlad is the senior research engineer at SRI International who is leading the development efforts at the famed research institute focused on electroadhesion.  “Static electricity is generally a weak phenomenon, because the distances involved are large,” Prahlad said.  “Flexible materials conform around the roughness or texture of whatever you’re trying to clamp to, and the forces become quite strong.”

It requires mere milliwatts of energy per pound to work.  That’s one thousandth of a watt, orders of magnitude lower than your typical 60-watt incandescent light bulb.

Theoretically, the weight that can be supported is limited only by surface area.  At present, the technology can hold 1/2 to 1 pound of weight for every square inch on most surfaces, and the team has built pads that can support more than 75 pounds.

Scaling buildings

As the technology is improved and scaled up, there’s every reason to believe that applications that could allow humans to scale buildings is possible.

Sadly, for every Spider-Man fan out there, the most practical approach would be a sort of moving ledge, rather than a superhero suit.  Because of the surface area requirements, the hand and feet pads would have to be cumbersomely large to actually work.

An added practical benefit to the ledge?  Humans lacking the strength of a radioactive spider wouldn’t actually have to exert any physical effort.

To market

Historically, SRI has brought its innovations to the world by licensing or selling its technology, or spinning off its research teams into full-fledged companies.  Prahlad said all those options are on the table.

NIOSH and the CDC awarded SRI a contract to use the technology to build ladders that won’t slip, the cause of thousands of accidents and dozens of deaths in the United States each year.

Meanwhile, the research institute is in early discussions with construction oversight bodies about utilizing the wall-climbing robots to inspect bridges and other projects, and in advanced talks with companies about employing the gripping tools for factories.

SRI isn’t, however, the only organization working on revolutionary approaches to the problem of sticking to walls.

Points of contact

Researchers at both UC Berkeley and Stanford University are exploring technology that employs the same natural forces that allow geckos to scramble across ceilings.  Millions of microscopic hairs on the lizard’s feet essentially multiply the effect of weak attractions between molecules called van der Waals forces, by vastly increasing the points of contact.

Scientists at Stanford have replicated this effect by building a robot known as Stickybot that can climb glass walls, while the Cal researchers have created a gecko-inspired tape that firmly sticks and easily unsticks depending on the direction from which it’s pulled.

Ronald Fearing, the UC Berkeley professor leading those efforts, said a big advantage of the tape over electroadhesion is that it doesn’t require a continual flow of electricity.  That gives it a leg up in small and cheap applications, like shoes that don’t slip, bandages that can be painlessly removed and picture frames that don’t require nailing a hole in your landlord’s wall.

Still, Fearing was complimentary of electroadhesion, saying its ability to work across a wide array of surfaces is a major plus.

“It looks promising within the space of climbing robots,” he said.

“We’re actively looking into business strategies to roll this out into the commercial marketplace.”

Source: The San Francisco Chronicle (California), November 29, 2010 edition

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