Portable pneumatic back support exoskeleton and assistive strategy for lifting assistance

Abstract

Several back support exoskeletons have been developed and implemented for lifting assistance to reduce the possibility of lower back pain (LBP). Although pneumatic power transmission is attractable due to the inherent compliance and backdrivability, the portability of the pneumatic system is highly limited due to the bulky air compressors that provide compressed air to the system. Moreover, previously developed assistive strategies are not capable of reflecting various lifting conditions. Therefore, we aimed to develop a fully-portable pneumatic back support exoskeleton and assistive strategy which reflects lifting kinematics and object condition. First of all, design requirements were defined based on the previous studies on back support exoskeletons and lifting biomechanics. Then the modeling parameters of developed mechanism were identified. The microcompressor and pneumatic reservoir were designed by modeling the compressed air consumption and generation. The developed exoskeleton weighs about 9.2kg and was completely stand-alone and provides 80 Nm of maximum extension torque for 6 liftings per minute (6 l/m). Finally, the experiments were performed to validate the physical assistance of the developed exoskeleton system. The back muscles (TES/LES) activation were significantly reduced with the assistance compared to no exoskeleton condition. On the other hand, lifting detection algorithm is necessary to assist user effectively. However, conventional kinematics-based detection algorithm induces time delay. In this study, the sEMG-based fast lifting detection algorithm was developed and validated with experiments. The developed algorithm detected about 200ms earlier than the conventional kinematics-based algorithm. In addition, fast lifting detection reduced peak back muscle activation. The effect of assist torque magnitude on metabolic energy consumption was investigated. For three subjects, the metabolic rate was decreased about 14.6% with assistance compared to no assistance condition. For one subject, wider range of assist torque was examined and the metabolic rate was saturated as the assist torque magnitude increased.