Fig. 5 Comparison between the previous system (left) and the improved system (right).
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.
Conclusion: 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.
Acknowledgments: This study was funded by the Korea National Research Foundation of the Korean Government (No. NRF-2017M3A0E2063105).