Nowadays falls are a serious problem for elderly people with the coming of aged society in the world. According to statistics,hip fracture accounts for the most of the deaths and costs of all the fall-induced injury. This paper presented an airbag system of hip protection, which included air source, sensors, microcontroller, gas circuit and airbags. A six-axial inertial sensor module that integrated an embedded three-axis MEMS accelerometer and three-axis MEMS gyroscope was used to collect human motion data, and a one-axis obliquity sensor was used to collect human angle data. The microcontroller was employed to recognize the activities of daily living (ADL) and falls based on fall detection algorithm and the collected data from sensors. The gas circuit was triggered once the event that the fall would be inevitable was confirmed by the microcontroller, then the compressed gas would fill into airbags through the gas circuit rapidly. Therefore, a buffer would appear between the human body and the ground before the body impacting the ground, which would reduce the impact of the human body. Compressed CO2 was selected as the air source after we tested several kinds of gas. A 16g CO2 pressurized cylinder could provide enough pressure and volume to inflate quickly the airbags. In order to improve the reliability of the gas circuit, a needle valve was optimized from the several designed structures by the experimental optimization methods. Finally, the airbag system was tested in various designed trials. The results indicated that the system gained the satisfaction for the design requirements and would be potential to apply to the protection of hip joint in the fall high-risk people in the future.
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