Static characteristics and calculation model of air spring with vertical variable stiffness for mattress

Abstract

Stiffness property of mattress significantly affects the spinal alignment and the pressure relief of human-mattress interface. Therefore, the variable stiffness mattress can theoretically provide personalized and adjustable support for users. However, the existing mattresses in the market are commonly equipped with a fixed stiffness spring layer, which cannot meet the needs of personalized support and the change of sleeping posture. In addition, some mattresses use air bags with adjustable stiffness as bedding layer, but existing studies have shown that bedding layer of the mattress mainly affects the pressure distribution at the mattress interface, which has little relation with the shape of the spine. Changing bedding layer hardness can only change the surface layer hardness of mattress and cannot change the core layer hardness of mattress. Therefore, to overcome the existing mattress stiffness problems, it is desired to develop mattresses with adjustable stiffness of core layer. In order to study the variable stiffness spring layer of mattress, a kind of air spring with vertical variable stiffness was designed and manufactured with thermoplastic polyurethane coating fabric composite materials. Through quasi-static uniaxial compression experiments, the mechanical properties and the relationship between the stiffness and the initial volume, initial internal pressure and material density were studied. Finally, the mechanical calculation model of air spring was established by polynomial fitting. The results showed that the stiffness and internal pressure increased non-linearly with the increase of air spring compression. There was a nonlinear negative correlation between the stiffness of the air spring and the initial volume, and a positive correlation between the initial internal pressure and material density. It was concluded that the air spring and its engineering control calculation model made the design of variable stiffness mattress possible, which can provide the basic theory basis of variable stiffness spring. As the basis of the study on the softness adjustable mattress, this study proves that the air spring can adjust the softness and hardness of mattress. On this basis, the influence of the air spring assembly on the mechanical properties and support characteristics of the mattress will be further studied.