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Robotic ‘Exoskeletons’ Could Help Soldiers Bear Heavier Loads 

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by Joe Pappalardo 

Researchers are edging closer to fielding a gas-powered system that will permit soldiers to effortlessly carry hundreds of pounds of equipment on the battlefield.

The program, sponsored by the Defense Advanced Research Projects Agency (DARPA), is paving the way for robotically enhanced soldiers, but not necessarily futuristic front-line warriors, caution scientists.

Contractors and the program manager of the exoskeletons for human performance augmentation (EHPA) said that, while the option for battle-ready, wearable robotic suits remains open, the system that is being currently pursued is aimed at allowing soldiers to tote enormous loads.

“This thing is useful for carrying payload,” said DARPA project manager John Main. “It could be 200 pounds of food, or it could be 200 pounds of body armor.”

The overall goal of EHPA is to develop devices that increase the speed, strength and endurance of soldiers in combat environments. When EHPA was launched in 2000, visions of massive power suits that propelled wearers over buildings and through walls—mainly products of the fertile imagination of science fiction writer Robert Heinlein—leapt into people’s minds. The reality may be more mundane, but the challenge remains enormous.

“This is a fairly boring transportation program,” Main said, with a small grin. “We’re not jumping over buildings. We’re getting into rough terrain that is denied to Humvees.”

In 2001, six contractors were left to pursue the development of self-powered, controlled, and wearable strength augmentation systems. The first challenge was proving that actuators—machine muscle—and high-density, man-portable energy sources were feasible.

In the fall of 2003, two contractors—the University of California-Berkeley and Sarcos Research Corp.—were chosen to create the system. Locust USA Inc. of Miami and TIAX LLC, of Cambridge, Mass., are working on the power source.

The words off-the-shelf are not used much in the exoskeleton program, Main said, since everything is being built and optimized specifically for the product. “Every part going into the exoskeleton needs to be designed from the ground up,” he said.

It may be too early to plan around real-world applications, but military personnel are watching the development of the project. Those who handle logistics envision exoskeletons loading trucks, while infantry commanders see the extra weight dedicated to shielding, Main noted.

“If you think about this in terms of airplanes, we’re about at a Wright flier,” Main said. “Three years ago no one thought it would walk.”

Two teams of researchers late last year proved that the idea behind EHPA was technically possible. Last August, a research team at University of California-Berkeley’s robotics engineering lab operated their Berkeley lower extremity exoskeleton (BLEXX) from a tether. The prototype weighs 90 pounds and allows a soldier to carry 80 extra pounds without feeling it. Sarcos soon followed with an untethered prototype that could handle 125 pounds.

The two projects are approaching the systems problems in different ways. At Sarcos, sensors in the foot respond to force and apply a counter-force that nullifies it and quickly tells actuators in the joints to bear the load. That way the EHPA wearer does not feel the greater weight, and does not have to think about operating the system.

The exoskeleton system at Berkeley responds to what the body is doing and adjusts its behavior accordingly. For example, the leg acts differently while the foot is raised in mid-air as opposed to on the ground. Fast computer processing matches the machine with the human body’s changing states.

The head of the Berkeley effort, Homi Kazerooni, told National Defense his team is leaving the future uses for military engineers. For him the true challenge is to seamlessly integrate and synchronize the movements of man and machine, not to create a man-shaped battle tank. “We are not thinking of the exoskeleton as a suit of armor,” he said. “We’re looking at the exoskeleton as a mobile platform, good for carrying mission-critical systems. This is a lot different than the movies, or what science fiction authors write about.”

The key is to make a robotic system that can keep up with split-second demands of human operators. With positive-definite points of contact at the feet, back and shoulders, coupled with other compliant sensors at the hip or leg, the system relies on the scores of linked nodes, placed close to sensors and actuators, to bond the system in a moveable local area network. The nodes are arranged in rings—one for each leg, and an additional ring for any mission-critical electronics gear unrelated to the exoskeleton.

“Agility is a function of the computer and the hardware itself,” Kazerooni summed up. The goal, he added, is to create a machine that’s “transparent,” one that a wearer can use without feeling it, as with a garment.

“Exoskeletons have the number one most difficult problems in robotics,” said Kazerooni. “We’re taking on those problems on a systematic level.

Power supply is as important to exoskeleton systems as design, Main said. “During the last three or four years, we’ve winnowed down to three engines,” he said. “They have to last a minimum of 1,000 hours…The challenge you have is to make a power system that does what muscles does: convert fuel directly into work.”

Given the parameters of military missions, there is a premium on conserving power. Actuators that mimic muscle cannot waste fuel while idling, but also must be ready for action in microseconds.

Kazerooni conceded that robotic enhancements worthy of combat were feasible, given a system design that could keep up with soldiers’ reflexes. “Can the machine shadow our reflexes? These are not voluntary, and sometimes 200 microseconds is not fast enough.”

Kazerooni said that upper body enhancements, focused on arm strength and automated gripping, are better suited for logistical support rather than combat since soldiers want their hands free. “We don’t know what to do with upper body extremities except logistics,” Kazerooni said. “Soldiers never want to lose the weapons from their hands.”

For prototype testing, DARPA turns to the ergonomics experts at the Army’s Natick Soldier Center in Massachusetts. By bringing the human factor into the development of the EHPA system, designers hope to circumvent design problems early and ensure that the system is as transparent as hoped.

“What better time is there than when you’re building the equipment?” said Jack Obusek, team leader for the ergonomics team at Natick. “We can make quantifiable measurements in movement patterns and changes in the force on the body of the wearer.” Unpowered prototypes from Sarcos and Berkeley already have been tested at Natick, and powered tests are scheduled for early next year. While there, lab scientists will don the leg gear and perform a series of incremental tests as Natick personnel collect data on the changes in force patterns on the wearers and examine any biomechanical shifts induced by the system.

He said that the next round of tests would be very lab-based, but that the future could hold involve obstacle courses and harsh terrain.

Still, no one understands the challenges of making a combat-ready robotic enhancement system like a PhD. in biomechanics, and Obusek said he doubts the exoskeleton system will be used to knock down walls or pound down doors in urban combat since any force exerted must be matched in the opposite direction—the soldier in the suit. “You’ve got to remember the laws of physics,” he said.

Still, he said EHPA could provide the framework for improved ballistic armor or medical evacuation equipment, applications that could find a home in a combat environment.

The fuel issues are equally unique to EHPA. The concept of the internal combustion engine is being reworked by researchers to be more compact, efficient and quiet.

“Efficiency gets you power density,” said John Bowman, senior manager in charge of the exoskeleton program for TIAX. “Technology is pushing things to much higher efficiencies from small-scale engines.”

The system features a two-stroke, linear-free piston engine that drives hydraulic fluids at high pressures. The final product will have a six-inch diameter and is 12 inches long, and meets another key EHPA requirement by running quietly. Bowman declined to discuss how his team keeps engine noise to a minimum. As far as fuel, prototypes run on propane but his team is advancing into gaseous fuels that are “more appropriate to the military,” Bowman said.

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