Page 56 - ITU KALEIDOSCOPE, ATLANTA 2019

2019 ITU Kaleidoscope Academic Conference

5. MODULE STRUCTURE AND ITS
STANDARDIZATION

One main reason why existing powered prosthetics are so
expensive is that the prosthetic market is not open in terms
of standards. A few manufacturers provide prosthetics to
replace a foot, leg and hip as an integrated device. These are
selected and adopted to each patient accordingly. However,
the components that comprise each prosthetic are not
compatible with those of other manufacturers.
Figure 10 – EMG sensors placement By introducing a module structure and standardized
interfaces between module parts, third-party manufacturers
could produce individual components, significantly reducing
the overall price of prosthetics.

5.1 Module structure

From analyzing existing powered foot prosthetics, shown in
Figures 1, 2 and 3, we propose a standardized foot prosthetic
that comprises the following ten modules as shown in Figure
12:
- socket: connecting the leg to a prosthetic;
- ankle joint: connecting the socket to the foot with
rotational connector;
(1) Person with walking disability #1 - foot: the same as a typical foot on which a battery
and control board are mounted:
- instep push/pull: enabling a foot to be raised and
lowered;
- heel-up spring: absorbing shock when landing on a
hard surface and raising the heel (optional);
- toe: triggers walking to start from a standing position,
and connects to a hard surface when walking with
wide strides (optional);
- battery: driving a single cylinder module and toe
module;
(2) Person with walking disability #2
- control board: controlling a single cylinder module
and a toe module in accordance with signals from a
Figure 11 – iEMG data when heel was raised central terminal;
- heel sensor: sensing the motion of a healthy foot;
It is clear that the proposed shoe compensates for muscle - central terminal: sending signals to a control board
weakness. However, most evaluators including authors felt to raise or lower a foot and toe (smartphone).
the timing to generate a spring reaction force is too early to
walk smoothly; the timing at which the knee comes out in As described in section 4, a shoe with a built-in coil spring
front of the ankle is best. compensates for muscle weakness. However, we believe that
this is insufficient to raise the foot module of a prosthetic in
The solid-ankle cushion heel (SACH) has been provided to the same way as a person would raise a healthy foot.
the foot prosthetic, and popularly used [10]. Most of them Therefore, we believe the instep push/pull is needed to raise
are made with rubber, and inserted as the heel part of the or lower a foot module in addition to the heel-up spring. An
prosthetic foot. It assists foot prosthetic users to walk easily, ankle joint module is necessary to connect the leg socket to
not walking disabilities. Its compensation principle would be the foot module in the same way as an actual ankle joint.
the same as the proposed shoe. Since SACHs are made with
rubber, a period of compensation effect is limited. They have In existing powered foot prosthetics, sensors have been
to be exchanged periodically. However, since metal springs incorporated into the prosthetic control board to raise or
are used in the proposed shoe, these would not need lower the foot part. However, there are differences between
exchange. a foot prosthetic and a healthy foot in motion. A computer
built into the prosthetic gradually compensates for such
The proposed shoe has a toe roller. However, as it is difficult differences. The proposed foot prosthetic is based on the idea
to have a person with walking disabilities intentionally trip that both legs and feet move in essentially the same way, but
over an obstacle, we could not quantitatively evaluate it. the motion cycle of each leg and foot is offset by half a cycle.

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