Optimization of stiffness and dampipng properties of below-knee prosthesis
Tutor / Supervisor
Berbyuk, Viktor
Student
Serrancolí, Gil
Document type
Master thesis (pre-Bologna period)
Date
2009
rights
Open Access
Publisher
Chalmers Tekniska Högskola
UPCommons
Abstract
Nowadays, prosthetic manufacturers have developed new designs of below-knee
prosthesis which are anthropomorphic and safe. But more research should be done.
This project tries to find out optimized parameters of below-knee prosthesis to walk
with as low energy as possible.
A biomechanical optimal problem is formulated to find out suitable stiffness and
damping properties of below-knee prosthesis. These properties mean the relation
between the torque on the ankle joint of the prosthetic leg with ankle angle and its
velocity. The criterion used has been minimizing energy of both on the healthy part of
the body as well as external energy with which the prosthesis battery is supplied.
In order to state the optimal problem, firstly an anthropomorphic human gait has been
looked for by using computer simulations. It has been chosen a mechanical human
model that consist of two legs (with thigh and shank), the trunk and with joints: at
ankle, knee and hip. Foot has been modeled as footprint. The system has 7 degrees of
freedom. The motion has been parameterized by using polynomial and Fourier series
and their parameters have been chosen so that the motion was anthropomorphic.
Control torques at joints and ground reaction forces have been determined by using
Lagrange equations.
After that, the optimization problem has been considered using energy of the healthy
part of the body as cost function, while energy consumed by the prosthesis has been
calculated in each variance. Algorithm of solution of optimization problem has been
implemented in MATLAB so that optimized kinematic parameters of the gait as well
as stiffness and damping parameters of the below-knee prosthesis are determined
automatically. fmincon function is used to solve the optimal problem and ode45
function to solve the differential equation to find out kinematics of the trunk.
The analyses of the obtained optimized values of stiffness and damping parameters of
a below-knee prosthesis as well as kinematics of the optimized gait are presented.
Future work within the project topic is outlined.
Participating teacher
- Berbyuk, Viktor