  In this paper we give a new control model based on the so called
computed-torque method for the control of a 2 degrees of freedom orthosis for
the rehabilitation of the lower limb, the AIRGAIT exoskeleton's leg orthosis.
The actuation of the AIRGAIT is made through self-made pneumatic muscles. For
this reason this work starts with the static and dynamic characterization of
our pneumatic muscles. The followed approach is based on the analytical
description of the system. For this, we describe the pneumatic muscles
behaviour with an easy-invertible polynomial fit function in order to model its
non-linear trend. We give a geometrical model of the mechanical system to
compute the length between the attachments of the pneumatic muscles to the
structure for every angles assumed by the two joints. We evaluate through
Newton-Euler equation the couples at the joints for each values of the angles.
At last we show some validation tests in order to characterize the functioning
of the proposed control model on the actuation of the orthosis.
