Authors:
Joseph Mizrahi
1
;
Navit Roth
1
and
Rahamim Seliktar
2
Affiliations:
1
Israel Institute of Technology, Israel
;
2
Drexel University, United States
Keyword(s):
Mechanical Impedance, Muscle Activation, Motor Control, Manual-grasping, Balanced Walking, End-effector, Joint Constraints.
Abstract:
The design of spring-based artificial and robotic arm joints presents a challenge in problems of transportation
of manually-held objects during walking. For maintaining stability of these objects, stiffness and damping of
the arm joints have to be adjusted by continuously tuning muscle activation. This necessitates knowledge
about the mechanisms by which stiffness and damping (mechanical impedance) are being modulated in
walking movement. The paradigm employed in this study consisted of modeling the impedance adjustments
from input data obtained in simultaneously controlled grasping and walking experiments. While walking on
a treadmill, tested subjects held a cup filled with liquid and were asked to aim at minimizing liquid spillage.
Monitoring liquid spillage served to quantify stability of the hand as the end-effector of the upper limb.
Kinematic data were obtained for the shoulder, elbow and wrist joints. Accelerometer data were obtained for
the wrist and for the knee. Electro-myo
graphy (EMG) data were collected for the wrist flexor and extensor
muscles. Based on the measured data, regressive functions were used to express stiffness and damping as a
function of angle and angular velocity. The joints of the upper limb were thereafter successively constrained
to study the effect of joint immobilization on joint impedance and muscle activation. The obtained results
indicate the nonlinearity of the joint impedances as required in tasks of manual grasping of objects during
locomotion, with and without joint constraints.
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