Abstract
Perhaps more than anything, amputees want to engage in normal activities of daily
living without attracting attention to their disability. Their best hope of achieving
this is with a lifelike prosthesis that operates by means of naturally occurring control
signals. Experiments have shown that the currently available elbow prostheses with
proportional myocontrol and high joint stiffness provide significant drawbacks to
this goal.
Abul-Haj and Hogan argued that for slow, large-amplitude movements, the relationship
between the level of muscle activity and the angular joint velocity is nonlinear in
intact limbs. They replaced the proportional relationship with relationships that
more closely mimic characteristics of the intact neuromuscular limb system Like a
human joint, their system also provides final position estimation and uses co-contraction
to modulate the stiffness of the prosthetic joint. Applied to an elbow prosthesis
emulator, their "natural control" scheme showed superior performance over the curriently
available prostheses, particularly during interaction with other objects.
Variable joint stiffness can play a particularly crucial role in an amputee's success
with a prosthesis For example, a high elbow stiffness is essential for amputees in
such tasks as holding a glass of water or writing with a pen, whereas a low elbow
stiffness is desired during interaction with constrained objects, such as a steering
wheel, or to reduce the impact fiom an unexpected obstruction. With only very high
or minimal joint stiffness in the current prostheses, many amputees have been required
to use significant "body english" to complete certain tasks. Such requirements may
lead to prosthesis rejection, as amputees tend to avoid activities that require unnatural
movements.
This paper describes an attempt to develop an adaptation to the Boston Elbow to accommodate
variable joint stiffness.
Citation
From "MEC 97," Proceedings of the 1997 MyoElectric Controls/Powered Prosthetics Symposium
Fredericton, New Brunswick, Canada: August, 1997. Copyright University of New Brunswick.
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