Conical Kresling origami and its applications to curvature and energy programming

Kresling origami has recently been widely used to design mechanical metamaterials, soft robots and smart devices, benefiting from its bistability and compression-twist coupling deformation. However, previous studies mostly focus on the traditional parallelogram Kresling patterns which can only be folded to cylindrical configurations. In this paper, we generalize the Kresling patterns by introducing free-form quadrilateral unit cells, leading to diverse conical folded configurations. The conical Kresling origami is modelled with a truss system, by which the stable states and energy landscapes are derived analytically. We find that the generalization preserves the bistable nature of parallelogram Kresling patterns, while enabling an enlarged design space of geometric parameters for structural and mechanical applications. To demonstrate this, we develop inverse design frameworks to employ conical Kresling origami to approximate arbitrary target surfaces of revolution and achieve prescribed energy landscapes. Various numerical examples obtained from our framework are presented, which agree well with the paper models and the finite-element simulations. We envision that the proposed conical Kresling pattern and inverse design framework can provide a new perspective for applications in deployable structures, shape-morphing devices, multi-modal robots and multistable metamaterials.

Characteristic analysis of a micro-/nanopositioning stage with coupling errors by the gravity

The piezo-actuated micro-/nanopositioning stages are often used in the current precision engineering applications, and the coupling deformation under the gravity of the stage is critical to error analysis. Considering the torsional deformation and bending deformation of the flexure hinges, the coupling error’s analytical model of the positioning stage along the Z-axis is derived by using the virtual work principle and the elastic beam theory. The performance of the proposed theoretical model is analyzed and verified by the comparison between two common materials, and the quantities of the piezoelectric actuators are also analyzed with the impact on the coupling deformation of the stage along the Z-axis. Through the comparison and analysis of theoretical results, simulation results and experimental results, the maximum error between finite element analysis and experimental results is 11.43%, with the rest fluctuates within 10%, which proves the correctness of the theoretical model. It is concluded that gravity generated by the workload and the stage does have an influence on the coupling deformation along the Z-axis of the micro-/nanopositioning stage. It cannot be ignored in the analysis and consideration of the positioning stage.

Thermal-fluid-solid coupling deformation of hydrostatic thrust bearing friction pairs

Purpose The purpose of this paper is to study thermal-fluid-solid coupling deformation and friction failure mechanism of bearing friction pairs under the working conditions of high speed and heavy load. Design/methodology/approach The deformation is simulated based on thermal-fluid-solid coupling method, its deformation distribution law is revealed and the relationships of deformation of friction pairs, rotational speed and bearing weight are obtained. Findings The results prove that the oil film temperature rises sharply, the lubricating oil viscosity decreases rapidly, the film thickness becomes thinner, the deformation increases, the whole deformation is uneven and the boundary lubrication or dry friction are caused with the increase in rotational speed and bearing load. Originality/value The conclusions provide theoretical method for deformation solution and friction failure mechanism of hydrostatic thrust bearing.

Fluid-solid coupling characteristics analysis for tripod sliding universal joints

Fluid-solid coupling theory is introduced into tripod sliding universal joint design. The geometric models of the tripod sliding universal joint and lubricant film are established respectively and meshed. Fluid-solid coupling analyses of tripod sliding universal joints in unidirectional and bidirectional scenarios are performed to investigate sleeve and lubricant film coupling as well as sliding pin and lubricant film coupling under various differential pressures and frequencies. In the condition of unidirectional and bidirectional coupling, sleeve and sliding pin deformation and stress increase gradually with differential pressure and frequency. Under various differential pressures and frequencies, tripod sliding universal joint bidirectional coupling deformation and stress are greater than those of unidirectional coupling. The theory of fluid-solid coupling is combined with the tripod sliding universal joint for the first time in this paper. The fluid-solid coupling analysis results are of great significance and benefit to the design, application and marketing of tripod sliding universal joints.