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Home > Members > Members Only > Engineering Case Study
Consulting Practices Engineering Case Study
Application:
Lower Extremity Enhancer Exoskeleton
PATCA member:
George Anwar
Consulting Project Goal:
Design of the electronic hardware architecture for control and data acquisition
Do you need help walking? Probably not but some people might, for example firefighters rescuing people from a burning forest, soldiers marching with a heavy load or a person in physical therapy to rebuild strength.
UC Berkeley researchers are developing a robotic exoskeleton that can enhance human strength and endurance. New robotics research has produced a prototype self-powered exoskeleton to effectively help people haul heavy packs across miles of rugged terrain or up 50 flights of stairs.
"We set out to create an exoskeleton that combines a human control system with robotic muscle," said Homayoon Kazerooni, professor of mechanical engineering and director of UC Berkeley’s Robotics and Human Engineering Laboratory. "We’ve designed
this system to be ergonomic, highly maneuverable and technically robust so the wearer can walk, squat, bend and swing from side to side without noticeable reductions in agility. The human pilot can also step over and under obstructions while carrying equipment and supplies."
 The Berkeley Lower Extremity Exoskeleton (BLEEX) helps lighten the load for the human user. (UC Berkeley photo)
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The exoskeleton, as it’s officially called, consists of mechanical metal leg braces that are connected rigidly to the user at the feet, and, in order to prevent abrasion, more compliantly elsewhere. The device includes a power unit and a backpack-like frame used to carry a large load.
Such a machine could become an invaluable tool for anyone who needs to travel long distances by foot with a heavy load. The exoskeleton could eventually be used by army medics to carry injured soldiers off a battlefield, firefighters to haul their gear up dozens of flights of stairs to put out a high-rise blaze, or rescue workers to bring in food and first-aid supplies to areas where vehicles cannot enter.
"The fundamental technology developed here can also be developed to help people with limited muscle ability to walk optimally," said Kazerooni.
The researchers point out that the human pilot does not need a joystick, button or special keyboard to "drive" the device. Rather, the machine is designed so that the pilot becomes an integral part of the exoskeleton, thus requiring no special training to use it. In the UC Berkeley experiments, the human pilot moved about a room wearing the 100-pound exoskeleton and a 70-pound backpack while feeling as if he were lugging a mere 5 pounds.
The project, funded by the Defense Advanced Research Projects Agency, or DARPA, began in 2000.
For the current model, the user steps into a pair of modified Army boots that are then attached to the exoskeleton. A pair of metal legs frames the outside of a person’s legs to facilitate ease of movement. The wearer then dons the exoskeleton’s vest that is attached to the backpack frame and engine. If the machine runs out of fuel, the exoskeleton legs can be easily removed so that the device converts to a large backpack.
More than 40 sensors and hydraulic actuators form a local area network (LAN) for the exoskeleton and function much like a human nervous system. The sensors, including some that are embedded within the shoe pads, are constantly providing the central computer brain information so that it can adjust the load based upon what the human is doing. When it is turned on, the exoskeleton is constantly calculating what it needs to do to distribute the weight so little to no load is imposed on the wearer.
George Anwar, of Integrated Motions, and PATCA member, is consulting for the project to design a platform for real-time multivariable control. The control system had to be modular, compact and be able to accommodate distributed sensors and actuators. The greatest challenge was the management of over 210 wires required to carry power and all of the sensor and actuator signals. The reduction of wires, which is a general problem for most robotic applications, forced us to go to a
network system. The resulting design is a highly flexible system capable of sampling the sensor data at 10 KHz. The real time control is done on a 650 MHz Pentium Class PC104+ single board computer. The entire highly nonlinear control for the six axis actuators are updated every 100 microseconds. In the end, the networked real-time control platform was able to carry all of the required sensor information back to the centralized computing unit through only 24 wires. The development and advancement
of the Internet clearly made the exoskeleton possible today, and would have been impossible five years ago. "We are taking great pains to make this as practical and robust as possible for the wearer," said Kazerooni. "Several engineers around the world are working on motorized exoskeletons that can enhance human strength, but we’ve advanced our design to the point where a ‘pilot’ could strap on the external metal frame and walk in figure eights around a room. No one else has done that."
One significant challenge for the researchers was to design a fuel-based power source and actuation system that would provide the energy needed for a long mission. The UC Berkeley researchers are using an engine that delivers hydraulic power for locomotion and electrical power for the computer. The engine provides the requisite energy needed to power the exoskeleton while affording the ease of refueling in the field.
The current prototype allows a person to travel over flat terrain and slopes, but work on the exoskeleton is ongoing, with the focus turning to miniaturization of its components. The UC Berkeley engineers are also developing a quieter, more powerful engine, and a faster, more intelligent controller, that will enable the exoskeleton to carry loads up to 120 pounds within the next six months. In addition, the researchers are studying what it takes to enable pilots to run and jump with the exoskeleton legs.
The engineers point out that while the exoskeleton does the heavy lifting, the human contributes to the balance. "The pilot is not ‘driving’ the exoskeleton," said Kazerooni. "Instead, the control algorithms in the computer are constantly calculating how to move the exoskeleton so that it moves in concert with the human."
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