  This paper presents a comprehensive analysis of the contact force profile of
a single-cell bidirectional soft pneumatic actuator, specifically designed to
aid in the abduction and adduction of the shoulder for pediatric exosuits. The
actuator was embedded in an infant-scale test rig featuring two degrees of
freedom: an actuated revolute joint supporting shoulder abduction/adduction and
a passive (but lockable) revolute joint supporting elbow flexion/extension.
Integrated load cells and an encoder within the rig were used to measure the
force applied by the actuator and the shoulder joint angle, respectively. The
actuator's performance was evaluated under various anchoring points and elbow
joint angles. Experimental results demonstrate that optimal performance,
characterized by maximum range of motion and minimal force applied on the torso
and upper arm, can be achieved when the actuator is anchored at two-thirds the
length of the upper arm, with the elbow joint positioned at a 90-degree angle.
The force versus pressure and joint angle graphs reveal nonlinear and
hysteresis behaviors. The findings of this study yield insights about optimal
anchoring points and elbow angles to minimize exerted forces without reducing
the range of motion.
