<div>Fig. 5 <i>Comparison between the previous system (left) and the
improved system (right).</i></div><div>The volume of the vest actuator, as shown in Fig. 5, was also reduced by
refining to the backpack type, and became easier to wear. The optimized
AFO system is more feasible than the previous system.</div><div><i>Conclusion:</i> A portable pneumatic AFO system was optimized to
improve wearability. The cast of the AFO was re-formed at the insole to
improve comfort. Simultaneously, the Velcro strap was revised to the BOA
Fit System to enhance wearability. Thus, the volume of the AFO was
significantly reduced and hidden in the pants of the wearer. In total,
120 g of weight was removed from the AFO. Based on the required piston
head force and flow rate of the AFO from the kinematic model of the
crankshaft mechanism, the combination of the DC motor and planetary gear
was refined. When the gear ratio was reduced from 66:1 to 26:1 and a DC
motor with a higher nominal torque of 0.177 Nm was used, the noise level
decreased 60%, and the efficiency of the system increased 13.3%. The
modified compressor satisfied the criterion for generating the required
air pressure and flow rate of the AFO. Finally, optimizing the
arrangement of the compressor, PCB, pneumatic fitting, and battery in
the backpack and implementing both the inlet and outlet eliminated the
overheating issue in the previous design by maintaining the temperature
of each component at 40°C. The optimal positions of both fans for low
power consumption were experimentally verified. The installation of fans
in the backpack comprising the portable compressor and corresponding
components made the long-term operation of the compressor possible and
increased the wearability by impeding the overheating of the system. As
a result of the optimization process, one can expect practical use of
the AFO system not only for daily living of drop foot patients but also
as a new AFO system design reference.</div><div><i>Acknowledgments:</i> This study was funded by the Korea National
Research Foundation of the Korean Government (No. NRF-2017M3A0E2063105).</div>