Biomedical Engineering Reference
In-Depth Information
FIGURE 10-59
Construction of the
MR Rheo knee from
Össur. (a) Prosthesis
hardware.
(b) Identification of
individual
components
(c) Schematic
showing how the
rheological
mechanism
operates. (Herr and
Wilkenveld 2003.)
to the knee from the ground in the direction of the longitudinal axis when the signals are
added. Subtracting the strain gauge signals provides a measure of the knee torque.
Five critical states were identified, and a state machine was developed to determine the
requirements for transition between the states, as shown in Figure 10-60 and Figure 10-61.
State 1: Stance flexion (0-16%):
The prosthetic knee applies a high level of damping
to inhibit the knee from buckling under the user's weight. Initially this starts out at the
maximum to ensure that buckling does not occur, but it is progressively reduced to a value
proportional to the peak axial force during the stance period.
State 2: Stance extension (16-41%):
High damping is applied to damp knee extension to
stop the knee hitting its extension end stop. Flexion and extension damping is dependent
on the size of the amputee. Initially this starts out low to ensure that the knee extends
completely, but it is progressively increased to a value proportional to the peak axial force
as in State 1.
