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To prevent lower back pain (LBP) in the industrial workplace, various powered back support exoskeletons (BSEs) have been developed. However, conventional kinematics-triggered assistance (KA) strategies induce latency, degrading assistance efficiency. Therefore, we proposed and experimentally evaluated a surface electromyography (sEMG)-triggered assistance (EA) strategy. Nine healthy subjects participated in the lifting experiments: 1) external loads test, 2) extra latency test, and 3) repetitive lifting test. In the external loads test, subject performed lifting with four different external loads (0 kg, 7.5 kg, 15 kg, and 22.5 kg). The assistance was triggered earlier by EA compared to KA from 114 ms to 202 ms, 163 ms to 269 ms for squat and stoop lifting respectively, as external loads increased from 0 kg to 22.5 kg. In the extra latency test, the effects of extra latency (manual switch, 0 ms, 100 ms and 200 ms) in EA on muscle activities were investigated. Muscle activities were minimized in the fast assistance (0 ms and 100 ms) condition and increased with extra latency. In the repetitive lifting test, the EA strategy significantly reduced L1 muscle fatigue by 70.4% in stoop lifting, compared to KA strategy. Based on the experimental results, we concluded that fast assistance triggered by sEMG improved assistance efficiency in BSE and was particularly beneficial in heavy external loads situations. The proposed assistive strategy can be used to prevent LBP by reducing back muscle fatigue and is easily applicable to various industrial exoskeleton applications.

Pneumatic active ankle foot orthosis (AFO) for drop foot correction has the advantages of inherent compliance and remote force control. However, pneumatic AFOs that use heavy stationary air compressors as the energy source have limitations for outdoor use. Although a portable air-compressor-powered pneumatic AFO has been developed recently, it is difficult to operate in practical applications owing to the bulky design of the AFO and excessive power sources with overheating issues. In this study, the AFO system was optimized to improve wearability. The weight of the AFO was decreased from 720 to 600 g. A Bluetooth module was installed instead of a 1.2-m cable between the master and slave boards. The efficiency of the portable pneumatic actuator increased 12.4%, whereas its volume decreased 11%. The internal temperature was reduced from 100°C to 40°C using two cooling fans. Throughout the optimization process, the wearability of the AFO system was improved for real-life use.