Control Aspects of Prosthetics and Orthotics. Proceedings of by R. M. Campbell

By R. M. Campbell

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If the knee torque became flexive during stance, a conventional prosthesis would collapse. Fig. 1C shows power requirements for the knee· Prosthetic knee power is zero while the knee is locked in stance. The two dissipatiye peaks in the last half of the cycle depend upon the damping provided by the prosthesis and can be similar to normal. If knee power is integrated through time over a cycle, the net energy is negative for both normal subjects and amputees wearing conventional prostheses. For the prosthesis there is no energy required, only energy dissipated.

The three locomotion modes are level walking, stair climbing, and ramp climbing. These three locomotion modes were chosen to test the multi-mode concept and take advantage of the active capabilities of the electrohydraulic system. During most of the stance phase of each of these locomotion modes, echo control will be used. During the swing phase of these locomotion modes, the prosthesis is controlled to simulate a pendulum with springs and dampers. Two supplemental modes, stand-still and stumble, were added to make the system safer and easier to use.

During level walking, the knee is close to full extension at heel contact but then undergoes a flexion and re-extension pattern through the stance phase. This process may contribute to minimizing the vertical displacement of the body center of gravity (Grimes, Flowers, and Donnath, 1977; Saunders, Dec, Inman and Eberhart, 1953) and allows the knee to dissipate some energy over the first part of the cycle. Over the second half of the cycle, knee power is essentially all dissipative; the knee acts only as a damped pendulum over the last half of the cycle.

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