Jianwei Wu

This paper presents the design, analysis, fabrication, and testing of a series of two degrees of freedom (2-DOF) Remote Center of Motion (RCM) flexure hinges. These hinges are constructed using planner generalized cross-spring pivots according to the building block approach. Load–rotation relationships for the flexure hinge are established through the beam constraint method, with finite element analysis confirming theoretical predictions and elucidating parametric dependencies of critical dimensions. An illustrative application of the flexure hinge is presented, showcasing its capability to transform planar linear motion into spatial 2-DOF RCM movements. Experimental validation substantiates the functionality and efficacy of the designed mechanism, reinforcing its potential practical applications.

The slip mechanism between the chunk and wafer during high-speed dynamic scanning of the extreme ultraviolet lithography (EUV) motion stage remains unclear. Considering real-machined roughness, molecular dynamics (MD) simulations were performed to investigate the nanotribological behavior of 6H-SiC sliders on single-crystal silicon substrates. The effects of sinusoidal asperity parameters and normal loads on wear and slip were systematically analyzed. Results indicate that, for friction between sinusoidal asperities and ideal flat surfaces, the amplitude of surface parameters exhibits negligible influence on friction. In contrast, reduced normal loads and lower periods significantly increase both friction force and coefficient of friction (COF).

Leaf spring-type flexible hinges serve as critical transmission components in kilogram quantization energy balance systems. Investigating their bending behavior is crucial for enhancing measurement accuracy and ensuring structural reliability. This work employs molecular dynamics simulations to analyze the mechanical properties and deformation characteristics of such hinges under varying bending rates. The findings reveal a significant correlation between the bending rate and the hinges’ plastic deformation and microstructural evolution, indicating the presence of a critical bending rate. When the bending rate is below the critical threshold, the hinges exhibit excellent structural stability, characterized by low dislocation density, reduced von Mises stress, and limited temperature rise, making them suitable for long-term use. Conversely, when the bending rate exceeds the critical threshold, the hinges undergo significant plastic deformation, including notable increases in stress and temperature concentration, as well as microstructural alterations. Specifically, the initially stable crystal structure is disrupted, leading to the formation of numerous defect structures. These changes result in localized instability and elevate the risk of fatigue damage. This work comprehensively elucidates the mechanical responses and failure mechanisms of flexible hinges, providing valuable data and guidance for their optimized design and application.

Aerostatic thrust bearings are widely used in advanced equipment such as lithography machines due to their excellent lubrication performance. In this study, computational fluid dynamics (CFD) was employed for the analysis of errors in the calculation of static characteristics of bearings based on the pressure behind the orifice. We put forth an analytical model for calculating the static characteristics of bearings utilizing the average pressure (P_dAVE) within the area surrounded by orifice. By analyzing the influence of various structural parameters, film thickness, and gas supply pressure on P_dAVE in aerostatic bearings, we derived an approximate expression for the average pressure coefficient, which was subsequently verified through experiments. The findings demonstrate that the analytical model for aerostatic bearings, formulated using P_dAVE, can accurately predict the static characteristics of the bearings. The working range corresponding to the optimal stiffness of the bearings is entirely consistent, and the prediction error of the bearing capacity within the optimal working range is less than 5%. This provides a more precise and effective performance prediction model for rectangular aerostatic thrust bearings in engineering design.

The positioning accuracy of the end effector is the core index that affects the robot’s performance. However, to achieve lightweight and functional requirements, the construction of end effectors is becoming more complex. Lightweight design through slotting is becoming more common. This leads to the fact that the traditional mathematical model cannot accurately characterize the vibration of the end effector. This study proposed the multi-stepwise beam model. It employed the separation of variables and element transmitting method to obtain the mathematical model of the modal shape functions and the natural frequencies. Meanwhile, the vibration response of the end effector under fixed-end excitation was analyzed, and the conclusions were made through experimental research. The direct inverse controller was presented to achieve vibration suppression. The experimental results indicate that the amplitude suppression rate reaches 50%. The system’s equations of motion were solved numerically to analyze the exact relationships for the response and excitation of the beam considered.

Optical probes are the preferred choice for high-precision surface metrology, necessitating improved flexibility and a broader range of motion to adapt to the increasing complexity of surfaces. This study introduces an interferometric probe designed for measuring aspheric surfaces, utilizing a wave-plate-array detection component. By integrating splitter elements into the detector, the probe improves integration and dynamic scanning performance, while maintaining high-precision measurement capability. The system design and working principle are explored, and comprehensive nonlinear models based on the Jones matrix theory are established. These models focus on the nonlinear errors arising from alignment errors in various cases. Moreover, rigorous numerical simulations and optical experiments are conducted to validate the proposed models. When the alignment error reaches 10°, it results in a maximum nonlinear error of 3.02 nm. The experimental results demonstrate the effectiveness of the models in capturing nonlinear errors induced by alignment errors, providing a theoretical foundation for error reduction and compensation.

The aerodynamic properties of rotor systems operating within low Reynolds number flow field conditions are profoundly influenced by their geometric and flight parameters. Precise estimation of optimal airfoil parameters at different angles of attack is indispensable for enhancing these aerodynamic properties. This study presents a technique for optimizing the airfoil parameters of a Mars helicopter by employing machine learning methods in conjunction with computational fluid dynamics (CFD) simulations, thereby circumventing the need for expensive experiments and simulations. The effectiveness of diverse machine learning algorithms for prediction is evaluated, and the resultant models are utilized for airfoil optimization. Ultimately, the aerodynamic properties of the optimized airfoil are experimentally validated. The experimental findings exhibit agreement with the simulated predictions, indicating the successful optimization of the aerodynamic properties. This research offers valuable insights into the influence of airfoil parameters on the aerodynamic properties of the Mars helicopter, along with guidance for airfoil optimization.

In ultra-precision positioning equipment, the positioning accuracy is affected by the friction characteristics, especially the pre-slip stage. At present, the research on friction mainly includes contact theory and the dynamic friction process. There is no time variable in contact theory models, so they only apply to the stage of static contact, while the establishment of a friction dynamics model depends on parameter identification and cannot reflect the influence of a rough morphology and load. Therefore, neither theory can elucidate the ultra-precise slip mechanism. In this paper, maximum static friction force, tangential stiffness, and tangential damping models of contact surfaces were deduced through fractal contact theory. By substituting the contact parameters into the modified LuGre model, a dynamic slip model of the mask was established. Finally, the above model was verified by a reticle dynamic slip measurement system. The experimental results showed that in the pre-slip stage of the reticle, with an increase in the normal external load, the slippage of the reticle decreased. The theoretical value calculated by the model was basically consistent with the experimental value, and the slippage of the reticle mainly originated from the tangential deformation and relative sliding of the contact surface. With the increase in the normal external load, the proportion of the tangential deformation in the sliding of the entire contact surface was larger. For the change in slippage during different motion stages, the theoretical value was close to the experimental value after eliminating system errors such as vibration and fiber bending, which proved the correctness of the model in this paper.