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Conventional mattresses can not adjust precisely according to the individualized spinal alignment. In addition, there is no theoretical basis for quantitative design and adjustment of mattresses firmness. The purpose of this paper is to overcome deficiency of traditional air chambers for research of ergonomic mattresses in accordance with spinal alignment. A novel variable stiffness air spring was designed and static experiments were conducted to analyze its mechanical properties and its influence factors. An analytical model based on geometric parameters and initial internal pressure was established. The results showed that the air spring has nonlinear stiffness during the working process. Furthermore, the model can predict the load of the air spring accurately at any equilibrium position with an average error of 6.96%. The initial stiffness, volume and assembly height could be predicted by means of geometric parameters and initial internal pressure. The conclusions are that the novel air spring can obtain predictable stiffness compared with cubic and the rod-shaped air chambers, which provides a theoretical basis and possible solution for the study of stiffness adaptive ergonomic mattress according to spinal alignment.

To investigate the nonlinear stiffness characteristics and the model of an air spring for mattresses on arbitrary working conditions, a finite element model of an air spring is established, modified by response surface method and verified by uniaxial compression experiment on conditions of different initial inner pressure. Then the static stiffness characteristics on arbitrary working conditions are analyzed by finite element analysis in ABAQUS. In addition, the model for engineering control is established and the stiffness characteristics are analyzed by numerical method under working conditions. The results demonstrate the nonlinear stiffness of an air spring is positively correlated with the inner pressure and compression displacement. Additionally, a finite element model is established with average relative error ratio of 0.059 and 0.074 on conditions of compression by 20 and 30 mm, respectively, satisfying engineering requirement. Moreover, the stiffness model of an air spring on any working conditions is established by fitting surfacecontaining compression displacement and inner pressure at equilibrium position then calculating its partial derivative with respect to compression displacement. The present study suggests the nonlinear stiffness prediction model of an air spring is applicable to any working conditions, only requiring inner pressure at initial and equilibrium conditions.

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As one of largest optical units used in high-power laser inertial confinement fusion facility, the large-aperture transport mirror's misalignment error can have a very negative impact on the targeting performance of laser beams. In this article, we have carried out a fundamental analysis on the mounting and misalignment errors of transport mirror. An integrated simulated assembly station is proposed to align the mirror precisely, and the design of transport mirror unit is optimized to satisfy the stringent specifications. Finally, methods that integrated theoretical modeling, numerical simulation, and field experiments are used to evaluate the mirror's alignment, and the results indicate a more robust and precise alignment performance of new design.