  This paper presents an analysis of parametric characterization of a motor
driven tendon-sheath actuator system for use in upper limb augmentation for
applications such as rehabilitation, therapy, and industrial automation. The
double tendon sheath system, which uses two sets of cables (agonist and
antagonist side) guided through a sheath, is considered to produce smooth and
natural-looking movements of the arm. The exoskeleton is equipped with a single
motor capable of controlling both the flexion and extension motions. One of the
key challenges in the implementation of a double tendon sheath system is the
possibility of slack in the tendon, which can impact the overall performance of
the system. To address this issue, a robust mathematical model is developed and
a comprehensive parametric study is carried out to determine the most effective
strategies for overcoming the problem of slack and improving the transmission.
The study suggests that incorporating a series spring into the system's tendon
leads to a universally applicable design, eliminating the need for individual
customization. The results also show that the slack in the tendon can be
effectively controlled by changing the pretension, spring constant, and size
and geometry of spool mounted on the axle of motor.
