Modelling Motor Control Paradigms - Computational Neuroscience: A Comprehensive Approach - page 541

external disturbance

dX

1

2

K

3

dF

elbow

restoring
force

F

4

y

X

100N/m

y

x

shoulder

x

Figure 17.9
Conceptual scheme for the measurement of the hand mechanical impedance. As
shown in the left panel, a grasped handle transmits to the hand small and quick dis-
turbance vectors dX by means of a computer controlled robotic arm, starting from
a given resting position. The restoring force vectors dF are measured and the re-
sponse patterns, for many directions of dX , are fitted by a spring-mass-damper sys-
tem, yielding a set of polar plots. In particular, the polar plot of the elastic coefficient
(i.e., the stiffness) is shown in the right panel, for different positions of the hand in
the workspace.