| The simulation of the mechanical characters of human chest, a core technique of the Cardiopulmonary Resuscitation (CPR) manikins, was studied in this dissertation. An expression of simplified Gruben Model (SGM) about the force-sternal displacement relationship was obtained according to the mechanical of human chest. Based on this expression, a variable-stiffness springs group-damper system was introduced to simulate the human chest. The spring-damper system else with the sample manikin were tested by a experimental system designed and manufactured for manual CPR compression test, then design parameters were perfected until the force-sternal displacement relationship was simulated precisely and a CPR manikin sample was built up.Basic knowledge of CPR, the anatomy of the thorax about CPR, compression-hemodynamic theories, and the general situation of CPR manikins were introduced briefly in this dissertation. Researches on human thorax's mechanical characters under CPR compression were particularized with emphasis, including three models deduced on force-sternal displacement relationship. Modeling work had showed that the thorax's compression force-sternal displacement relationship was a hystereesis curve. Then simulation works including special structures simulated the human chest such as a single linear spring, a cube of low density polyurethane foam, a bellows structure, and so on shared an introduction in detail. But in experiments on the compression character of the manikins, differences between human chest and them were shown as following: (1) manikins'force-sternal displacement relationship is rather linear, while it is non-linear in the human thorax; (2) the damper coefficient in manikins are less than that in human chest. So it is necessary to study the model of the human chest's mechanical character and its realization, which is the main problem studied in this paper. A variable-stiffness springs group-damper system was introduced to simulate the human chest with a route of modeling, simulation, realization, and experimentation.A SGM was proposed and simulated based on the anatomy structure, material's physical character and physiology. According to the discussions on Gruben Model including the process of the modeling, the importance of the model, and the reason why it has to be simplified, using the Boltzmann stacking theory and Voiget Model of viscoelastic medium, hypothesis were founded on the anatomy structure of human chest. Then the thorax was regarded as a spring-damper structure composed of a group of linear springs whose distortion were not equal to each other considering the ribs as linear springs. The force-displacement function was displayed and a simple formula was deduced. Then experimental data were extracted using an image processing arithmetic based on intensity of pixel, and parameters of the SMG on the data were computed by Lemke arithmetic. The remained error analysis, simulation, and examination of were executed, with the coefficient of determination was 0.9816, proving the validity of the model. At last the'typical human'parameters of SMG were presented using function approaching arithmetic. It is ease for the SMG, which has an expression of 3 terms less than Gruben Model, to direct the realization.According to the SGM, the variable-stiffness spring (spring's group) and hydraulic damper were introduced and formed a parallel connection to simulate the human chest. Based on the variable-stiffness spring (spring's group) techniques, the process of designing variable-stiffness springs group was created. After studying the linear spring designing theory and the characters of the spring's group, 4 groups of varied distortion parallel type compression springs with varied spring amount and two varied picth cylindrically coiled compression springs, which simulated the elasticity of human chest, were designed and manufactured. A type of hydraulic damper AC2050-1 was chosen based on analysis of the structure and technique of damper, and was improved by adding max displacement to 60 mm, rejecting the recovering spring and so on. Then AC2060 suiting the human chest's damping was designed and manufactured. The variable-stiffness spring (spring's group) and the hydraulic damper formed a parallel connection and then the spring-damper structure was formed as the core of the manikin's chest.Based on virtual instrument technology, an experimental system for the dynamic mechanical test under CPR compression was designed and realized. According to the discussion of existing experimental equipments, especially Gruben's experiment system, the compressing gantry was designed based on the need of the experiment, while the excellences were absorbed and the shortcomings were avoided. Both the verticality of loading and the fixing of transducers were studied to ensure the measuring veracity. Dynamic force and displacement signals were measured by transducers chosen, collected by collection card NI-USB6229, and then processed in computer. A collection and processing software with an interface was developed by LabVIEW to collect, process, and analyze the signals. After the experiment system was built up, a contrast experiment using INSTRON-5865 strength tester to calibrate this system was designed and performed. The relative errors of force and displacement were 1.27% and 0.75%, respectively, showing that the system had a high precision to satisfy the needs of experiment.The elasticity and damping were revised according to the static and dynamic mechanical tests results and a CPR manikin sample was accomplished. The relative error of elasticity was less than 1%, and damping coefficient was 2.10 Ns/cm. There were hysterisis curve shown in the results of dynamic mechanical test on CPR manikin sample with a variable-stiffness springs group-damper system in it. Compared to'typical human', the relative errors of all parameters of the CPR manikin sample were less than 9%, with 8.45%, 8.56%, 7.33% of work of elastic force, elasticity curve and damping coefficient (3.191 Ns/cm), respectively. Much greater relative errors were shown in same experiments on other manikins existing, for example, relative errors of Leardel Ressci Anny's work of elastic force, elasticity curve and damping coefficient were 13.85%, 44.20%, 59.91%, respectively. Through comparing and analyzing of the experiment results on integer, detail and process of the mechanical characters, namely the work of the elastic force, elasticity curve, the damping coefficient, it was obvious that the CPR manikin sample using the variable-stiffness spring-damper system as resistant cell had more adjacent work of elastic force, elasticity curve and damping coefficient to'typical human', which represented the average mechanical characters of human chest, than other manikins.Through the process of modeling, simulation, realization, and experimentation, the mechanical characters of the human chest were understood deeper, and the CPR manikin sample whose mechanical characters were superior to other manikins existing was created. The idea of modeling guided the realization method of nonlinear spring group; meanwhile, the realization validated the model. Lemke arithmetic was used during modeling and simulation. An image extracting arithmetic based on intensity of pixel which could be used in other fields was original through that, too. A method of designing varied distortion- paralleled- compressing springs group based on height compensate was created during the realization. The experimental system synthesized the virtual instrument technique especially the software LabVIEW and mechanism designing technique, and could be used in materials dynamic mechanical test. The experiments ensured the precision of the springs and damper, validated the feasibility, and established the value of the idea in realization through the comparing with other manikins. The results of this dissertation may enhance the CPR manikin technique, and may improve the effect of CPR training. |
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