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Robotics Technology Advances Artificial Legs

Recent advances in robotics technology enables prosthetics that can dramatically improve the mobility of lower-limb amputees, allowing them to negotiate stairs and slopes and uneven ground, and significantly reducing their risk of falling, say a team of engineers at Vanderbilt University’s Center for Intelligent Mechatronics, Nashville, TN.

For the last decade, they have been doing pioneering research in lower-limb prosthetics, and developed the first robotic prosthesis with both powered knee and ankle joints. The design became the first artificial leg controlled by thought when researchers at the Rehabilitation Institute of Chicago created a neural interface for it.

Some of the technological advances that have made robotic prostheses viable include lithium-ion batteries that can store more electricity, powerful brushless electric motors with rare-Earth magnets, miniaturized sensors built into semiconductor chips, particularly accelerometers and gyroscopes, and low-power computer chips.

The size and weight of these components is small enough so that they can be combined into a package comparable to that of a biological leg and they can duplicate all of its basic functions. Electric motors play the role of muscles. The batteries store enough power so the robot legs can operate for a full day on a single charge. The sensors serve the function of the nerves in the peripheral nervous system, providing vital information such as the angle between the thigh and lower leg and the force being exerted on the bottom of the foot, etc. The microprocessor provides the coordination function normally provided by the central nervous system. And, in the most advanced systems, a neural interface enhances integration with the brain.

Robotic legs must recognize a user’s intent to change from one activity to another, such as moving from walking to stair climbing. Identifying intent requires some connection with the central nervous system. Currently, there are several different approaches to establishing this connection that vary greatly in invasiveness. The least invasive method uses physical sensors that divine the user’s intent from his or her body language. Another method, the electromyography interface, uses electrodes implanted into the user’s leg muscles. The most invasive techniques involve implanting electrodes directly into a patient’s peripheral nerves or directly into his or her brain. They say that the jury is still out on which of these approaches will prove to be best.

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