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Small-modulus gears, which are essential for motion transmission in precision instruments, present a measurement challenge due to their minuscule gear gaps. A high-precision measurement method under the influence of positioning errors is proposed, enabling precise evaluation of the machining quality of small-modulus gears. Firstly, a compound measurement platform for small-modulus gears is developed. Using a 3D model of the measurement system, the mathematical relationships governing motion transmission between various components are analyzed. Secondly, the formation mechanism of gear positioning error is revealed and its important influence on measurement accuracy is discussed. An optimization method for spatial coordinate transformation matrices under positioning errors of gears is proposed. Thirdly, the study focuses on small-sized gears with a modulus of 0.1 mm and a six-level accuracy. Based on the aforementioned measurement system, the tooth profile measurement points are collected in the actual workpiece coordinate system. Then, gear error parameters are extracted based on the established models for tooth profile deviation and pitch deviation. Finally, the accuracy and effectiveness of the proposed measurement method are verified by comparing the measurement results of the P26 gear measuring center. [ABSTRACT FROM AUTHOR]

Contact stiffness and backlash in the harmonic drive significantly impact a robot's positioning accuracy and vibration characteristics. The height of the harmonic drive tooth pair is typically less than 1 mm, making the measurement and modeling of backlash and contact stiffness inherently complex. This paper proposes a contact stiffness and backlash model by establishing a correlation between fractal parameters and tooth contact load. To obtain the fractal roughness parameters of the real machined tooth surface, a combination of a noncontact optical profiler and the RMS method is employed. Subsequently, the study explores the influence of rough tooth surface and contact force fractal parameters on contact stiffness and gear backlash. The results demonstrate the substantial impact of surface topography parameters and contact force on contact stiffness and backlash. Specifically, an increase in the fractal dimension correlates with a reduction in gear backlash and contact stiffness. Conversely, the fractal roughness parameter exhibits the opposite effect. Notably, an increase in contact force enhances contact stiffness. [ABSTRACT FROM AUTHOR]

This study aims to analyze the impact of uniform and eccentric load conditions on the performance of internal feedback hydrostatic thrust and journal bearing. Two distinct models are established: a three-degrees-of-freedom uniform load model and a five-degrees-of-freedom eccentric load model. The support stiffness, overturning stiffness, and flow rate for both thrust and journal bearings are calculated. Additionally, numerical analysis is conducted to examine the influence of oil film thickness, inlet pressure, and restrictor size on the operational characteristics of the bearings, revealing the interplay between an eccentric load and journal bearing speed. The validity of the theoretical algorithm is verified through finite element simulation. The research outcomes hold significant guiding implications for the design and application of internal feedback hydrostatic bearings. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive exploration of the operational mechanism of an internal feedback hydrostatic turntable. It employs a self‐compensating gap restrictor mechanism, resulting in heightened load capacity and stiffness. In this paper, the concept of internal flow is innovatively introduced. Subsequently, the Reynolds equation is solved using the finite difference method. This methodology offers a more precise and efficient assessment of the load‐bearing performance of the oil pad within the turntable. Then this paper further investigates the influence of the internal flow coefficient and pressure ratio on oil pad performance, encompassing aspects like load capacity, stiffness, and flow rate. Ultimately, optimal parameters are selected to improve the structure of the gap restrictor, considering various operational scenarios. In conclusion, the method adopted in this study not only improves the calculation accuracy and efficiency but also improves the structure and performance of the oil pad. [ABSTRACT FROM AUTHOR]

Flange connections are widely used in various mechanical components. The most important purpose of tightening for flanged bolts is to achieve designed clamping force for the maintenance of overall performance. In this work, a multi-bolt tightening algorithm is proposed based on elastic interaction coefficient and gasket creep relaxation. Firstly, dispersion of the individual bolt clamping forces for torque control method is considered in the algorithm. Relationship between the nut factors of the flange bolts in multi-pass tightening is established through experiment. Subsequently, the elastic interaction coefficient matrix was updated during the multi-pass tightening process to reduce the error. Two cases, without gasket and silicone gasket, are considered in the multi-bolt tightening experiment. Without gasket, the elastoplastic deformation at the initial stage after tightening will also cause a loss of clamping force. When using gasket, the clamping force loss due to gasket creep relaxation is more pronounced. Through experimental verification, the proposed multi-bolt tightening algorithm are able to achieve the target range of designed clamping forces and reduce its dispersion. Finally, the main influencing factors of the multi-bolt tightening are analyzed to provide a reference for the design of flange connections. [ABSTRACT FROM AUTHOR]

The performance of the milling head is affected by the machining and assembly process of the parts. The key to improving machining accuracy and reliability of swing angle milling head is to establish the precision prediction model. Therefore, a precision prediction model of swing angle milling head under the influence of multiple errors' sources is built. The transmission and accumulation of machining and assembly errors along the assembly sequence path for the transmission system are carried out. All essential components on the assembly sequence path are considered. In addition, the secondary impact of the bearing seat hole is also taken into account. The source of the gear assembly errors is explained. The predicted range of transmission error based on the coupling relationship between assembly errors and transmission error is obtained. A precision experiment is carried out, and the result is within the predicted range. This research demonstrates that the errors' coupling relationship considered in this paper does exist and has an effect on transmission error, which provides a new idea for calculating transmission error of other gear systems. [ABSTRACT FROM AUTHOR]

Adjustable lubrication aims to achieve active control of the relative motion of the friction interface, providing a new idea for intelligent operation. A new phenomenon of sudden changes of friction coefficient (COF) in the poly(vinylphosphoric acid) (PVPA) superlubricity system by mixing different lubricants, was found in this study. It was found that anions were the critical factor for the COF change. The change degrees of the COF were investigated by a universal micro tribometer (UMT). A quartz crystal microbalance (QCM)-D was used to analyze the adsorption quantity of anions on the PVPA surface. The hydratability of the PVPA interface was controlled by changing the anionic properties (the amount of charge and structure), thus regulating the COF. The adsorption difference of anions is an important reasoning of how anionic properties can regulate the hydratability. It was analyzed by molecular dynamics simulation. For anions carrying different numbers of charges or double bonds, the adsorption quantity of anions was mainly affected by the adsorption degree on the PVPA surface, while the adsorption quantity of anions with different molecular configuration was synergistically regulated by the adsorption degree and adsorption area of anions on the PVPA surface. This work can be used to develop smart surfaces for applications. [ABSTRACT FROM AUTHOR]

The two main failure modes of harmonic reducers are wear and contact friction between the tooth profile of the circular spline (CS) and the flexible spline (FS). The sliding speed of the meshing point is a key factor affecting friction and wear processes of the CS and FS and should therefore be accurately determined. Herein, envelope theory is used to deduce the FS trajectory and the envelope track is divided into two segments according to whether or not the meshing point is outside the top circle of the CS. The velocity of the meshing point in the second meshing stage is essentially the vector sum of the FS velocity in three directions. When the CS is fixed, the relative sliding velocity is the instantaneous velocity of the FS along the tangential direction of the enveloped tooth profile. To verify the proposed model, the finite element method (FEM) and laser sensor experiments were performed and a relationship between the angle of rotation of the wave generator (WG) and the velocity of the FS was established. The results show that the sliding speed is sensitive to the radial displacement coefficient and has a linear relationship with the rotational speed of the WG. [ABSTRACT FROM AUTHOR]

In actual engineering, material properties, load effects, and other factors of mechanical structures change due to long‐term use. In order to understand the operation of a mechanical structure in real time, it is crucial to obtain the dynamic trajectory of its reliability. Considering the time variability of a mechanical structure over time, uncertain random variables are introduced to express the uncertainty of various parameters of structures, and the Wiener process is used to describe the strength degradation process of structures so as to solve the calculation problem of time‐varying reliability of mechanical structures. Based on the advanced first‐order and second moment method (AFOSM), the proposed linearized Nataf change is used to complete the transformation from related nonnormal variables to independent standard normal variables in order to simplify the calculation process of reliability solution and solve the reliability calculation problem of random parameters subjected to arbitrary distribution. The deduced random variable sensitivity factor indicates the degree of influence of different random variables on the reliability of the mechanical structure, providing a theoretical basis for the optimal design and maintenance of a mechanical structure. The proposed method is analyzed using the cantilever beam and compared with the nonlinear Nataf transform and verified by the Monte Carlo simulation results. The results show that the proposed method can effectively solve the reliability sensitivity problem of structural system strength degradation. [ABSTRACT FROM AUTHOR]

In order to improve the printing quality, this study focused on the thermo-fluid-solid coupling process of ink roller-ink. One of the highlights of this study is to consider the influence of temperature on the rubber hyperelastic parameters, viscoelastic parameters, and ink viscosity. The other highlight is to improve the elastohydrodynamic lubrication theory and Hertz contact theory through the rubber elastic modulus, which is determined by the relaxation curve considering the temperature and working conditions. Furthermore, based on the improved theory, the thermo-fluid-solid coupling model of ink roller-ink was established. Finally, the effect of temperature on the coupling process was analyzed. The results show that under the working conditions, with increasing temperature from 20 °C to 40 °C, the contact half-width increases from 4.2335 mm to 4.4701 mm, and the minimum ink film thickness decreases from 0.5097 mm to 0.1410 mm, and the maximum ink pressure decreases from 0.6802 MPa to 0.6618 MPa. [ABSTRACT FROM AUTHOR]

Ball screw mechanisms (BSMs) are used as accuracy transmission components in a wide range of industries and are characterized by their high accuracy. More specifically, the positioning accuracy of BSM has a significant effect on the accuracy of machine tool. Based on the macro-micro multiscale method, an exponential prediction model for the BSM positioning accuracy was developed considering time-varying working conditions (load and rotational speed) and feed modes. Since the accuracy degradation is mainly caused by wear, a microscopic approach was proposed to describe the positioning accuracy retention and the microscopic wear process was investigated. The sliding contact of the asperities between the ball and raceway was analyzed, and the microscopic wear behavior of the asperities was determined. Considering the time-varying working conditions, the BSM positioning accuracy characteristics were obtained under the normal feed mode by conducting suitable tests. The exponential wear model used the wear index to describe the wear status based on the positioning accuracy measurement. The accuracy loss value and the prediction index of positioning accuracy were determined based on an exponential model, and the effective lifetime of the BSM was predicted. Finally, the exponential prediction model was used in negative/positive skew feed distribution, and the effective lifetime determined. [ABSTRACT FROM AUTHOR]