Development Of Wearable Inertial Switches Of Security Detection For The Elderly

With the intensification of China's aging population,the extension of life expectancy and the increase of empty-nest families,the physical and mental health of the elderly are concerned by the community and the government.Due to the decline in physical fitness,not only does the elderly falling cause great physical and mental harm to them,but also brings a heavy financial burden to their family.At present,wearable devices based on human falling have decent market application prospects owing to their characteristics of being portable,protecting personal privacy,unrestricted detection area and high falling detection rate.This thesis develops a space-omnidirectional wearable inertial switch based on the the elderly falling detection environment.According to the research on the elderly falling,the design index of the switch is determined in the thesis.In terms of the physical model of the switch,the thesis analyzes and figures out the natural frequency range of the switch in the condition of the given excitation signal pulse width.By analyzing the structure of each part of the switch and the performance of the switch,i.e.response time,contact time,threshold,etc.,the thesis completes the structural design of it.The inertial switch adopts Archimedes spiral springs to support the circular proof mass as a “Spring-Mass” system,with the contact radial electrodes uniformly distributed around the proof mass,and a semi-circular axial electrode above the proof mass.The switch can respond well to the space-omnidirectional excitation signal,and meanwhile its contact time can be extended by the flexible electrode,which facilitates the processing of succeeding circuit signals.In addition,the stop post and the radial electrode are integrated into one,which can protect the switch in an overload environment.Based on the designed switch,the ANSYS software is used for dynamic simulation analysis.The modal simulation determines the working mode of the switch.Besides,the transient simulation analyzes the omnidirectionality,response contact time and adaptability of the switch.The space threshold acceleration of the inertial switch is between 2.9g and 4.24 g and the switch has good contact performance with over 200μs contact time in any direction.Based on the UV-LIGA technology,the switch is completed on the metal substrate.The thesis analyzes the source of the scale error in the production process and determines the compensation size of the switch,that is,to increase the critical size of the mask during production.The manufactured switch has the overall size of 5.8mm×5.8mm×0.25 mm,andis encapsulated.Eventually,the dynamic and static parameters of the switch are tested using a centrifuge device and a dropping hammer device test.The test results show that the switch threshold is too large but the space threshold difference is little,and the contact performance with over 100μs of the switch in all directions is stable.