Considering the problem of residual noise and spurious modes in the complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN), a rolling element bearing malfunction diagnostic method based on improved CEEMDAN (ICEEMDAN) is proposed. First, different from the CEEMDAN, which directly adds Gaussian white noise with a mean of zero, the proposed method adds the kth component obtained from white noise decomposed by empirical mode decomposition (EMD) to the vibration signal, and then the ICEEMDAN is employed to decompose the signal into several intrinsic mode functions (IMFs). Second, aiming at the uncertainty problem of entropy estimation in multi-scale fuzzy entropy (MFE), a refined composite multi-scale fuzzy entropy (RCMFE) is proposed to obtain the characteristic from the selected IMFs. Finally, smoothing factor of PNN is determined by fruit fly optimization algorithm (FOA), and the extracted features are input into the FOA-PNN model to achieve condition identification. Experimental results illustrate that the identification accuracy is more than 99%, which indicates its high effectiveness and superiority.

五轴数控机床由于能实现各轴之间的联动,且精度较高,被用于加工各种复杂曲面和精密部件,在航天、船舶、军事装备等方面都有重要应用。随着制造水平的提升,对机床加工精度的要求也更高,机床正朝着高精度的方向发展,而误差补偿是提高机床加工精度的有效方法。几何误差对机床加工精度影响较大,且测量耗时耗力,因此本文分析几何误差建模过程,提出快速测量与辨识几何误差的方法,分析加工过程中几何误差的敏感度,研究误差补偿方法,论文的主要研究内容如下:①基于旋量理论建立双转台五轴数控机床几何误差模型。将旋量理论引入到机床几何误差建模过程中,用指数矩阵表示刚体间的运动变换矩阵,推导出表示机床运动学的指数积公式;分析机床各运动轴的几何误差,推导几何误差模型。②基于球杆仪快速测量辨识五轴数控机床直线轴和旋转轴的几何误差。用球杆仪对直线轴几何误差进行测量,分别在XY、YZ、ZX平面内执行一次测量,即可辨识出直线轴的21项几何误差;通过A轴和C轴轴向和径向测量模式辨识旋转轴位置无关几何误差,将球杆仪测量数据拟合圆圆心偏差与几何误差联系起来,克服了在测量结果中取特殊位置点进行辨识的缺陷,提高了辨识精度;提出锥形测量法测量旋转轴位置相关几何误差,推导几何误差与球杆仪杆长变化量的矩阵关系式,结合测量结果,即可得到误差值,使辨识过程更高效。③分析圆锥台试件加工过程中几何误差对空间误差的敏感度,识别出关键几何误差项。基于Sobol法对几何误差模型进行方差分析,推导出敏感度系数的计算公式;在圆锥台试件加工过程中取若干加工位置点,计算加工点处几何误差对空间位置和姿态误差的一阶和全局敏感度系数,识别出工件加工过程中影响空间误差的关键几何误差项,为几何误差补偿提供理论基础。④提出一种五轴数控机床几何误差补偿策略。构造机床位置误差和姿态误差的雅克比矩阵,先补偿姿态误差再补偿位置误差,计算得到直线轴和旋转轴的补偿量;在华中数控HMU20型五轴数控机床上,执行本文所提出的几何误差建模、测量、辨识和补偿方法,并对补偿结果进行验证;结合圆锥台试件加工过程中敏感度分析的结果,有侧重性地进行补偿,对比补偿所有误差与仅补偿关键误差的效果,根据补偿效果对误差模型进行修正,简化补偿过程,提高建模和补偿效率。

Considering the uncertainty of entropy value estimation in multi-scale fuzzy entropy (MFE), and the difficulty of determining the smoothing parameter of probabilistic neural network (PNN). The rolling element bearing fault diagnostics method on the basis of improved MFE and improved PNN is proposed. Firstly, variational mode decomposition (VMD) is employed to decompose rolling bearing vibration signal into several intrinsic mode functions (IMF). Secondly, aiming at the uncertainty problem of entropy estimation in MFE, refined composite multi-scale fuzzy entropy (RCMFE) method is proposed to obtain characteristic from the selected IMF. Finally, smoothing factor of PNN are determined by whale optimization algorithm (WOA), and the extracted features are input into the WOA-PNN model to achieve condition identification. Experimental results illustrate that the identification accuracy is 98.75%, which indicates its high superiority. © 2023 IEEE.

For realizing the precision dressing of worm grinding wheel of face gear, this paper studies the over-cutting phenomenon of worm grinding wheel in forming dressing and puts forward the solution. Combined with the forming principle of face gear worm and forming dressing method, the influence of the continuous dressing method on the grinding wheel helix and the relative position between the dresser and the worm are expounded. Based on the numerical simulation model and the actual machining phenomenon, two kinds of over-cutting phenomenon are discovered. To ensure the surface integrity of grinding wheel in continuous processing, the reasons and laws of over-cutting are deeply analyzed. The first kind of over-cutting can be eliminated by increasing the angle between the extended line and the axis on the dresser, and a method of estimating the minimum angle is proposed for a more reasonable design of the dresser. The second kind of over-cutting can be eliminated by choosing proper dressing interval while ensuring the utilization efficiency of worm, and the selection criteria of dressing interval in continuous dressing are put forward. To verify the proposed methods, digital model, Vericut, and SolidWorks are applied, and the results show that the proposed method can effectively solve the over-cutting problem.

本项目针对齿面蜗杆砂轮磨削加工误差溯源机理及等效补偿的关键科学难题开展研究。建立基于齿面误差测点的误差曲面拟合模型，研究齿面误差评定方法；基于蜗杆砂轮磨齿的数字化计算原理，建立叠加刀具—轨迹—工件误差的齿面创成耦合模型，揭示齿面误差与创成运动误差的映射规律；研究齿面误差解耦方法，分离蜗杆砂轮磨削加工过程中的刀具误差及轴运动误差，实现等效误差补偿；研制蜗杆砂轮磨削加工误差补偿系统并进行仿真与实验验证，并通过误差补偿系统的研制实现了研究成果转化。依托本项目，正式发表EI/SCI论文13篇,CSCD论文2篇，网络出版SCI论文1篇，授权发明专利5项，公开发明专利6项，授权软件著作权2项，出版学术专著1本。项目研究为蜗杆砂轮磨齿加工误差补偿提供了运动几何学原理与方法支撑，对于打破国外高端磨齿机垄断，提升我国高端齿轮制造水平，具有重要的社会和经济价值。

For a crossed beveloid gear pair with approximate line contact, the macroscopic geometric parameter is a dominant factor that affects meshing characteristics. However, geometric parameter design and reliability under misalignment are of great difficulty. To deal with these issues, an enhanced design method for a beveloid gear with approximate line contact is firstly proposed. Based on this, a robust optimization model of geometric parameters for crossed beveloid gear pairs with approximate line contact is developed. Three evaluation items are considered, namely the maximum contact pressure, contact trace offset distance and contact ratio. To reduce the calculation time, the influence coefficient method is applied to calculate the contact pressure. Considering the characteristics of installation deviation uncertainty and distribution, the mean maximum contact pressure, contact trace offset distance and ratio are considered as objective functions, formulated as a robust design optimization problem. Finally, robust optimization of a crossed beveloid gear pair based on a fast elitist nondominated sorting genetic algorithm (NSGA-II) is applied to solve the model to obtain the Pareto front of the macroscopic geometric parameters. A numerical example is provided to demonstrate the effectiveness of the proposed method.

Exact contact pressure and load distribution are key evaluation indices for beveloid gear design. A numerical calculation approach of contact pressure and load distribution for crossed beveloid gears is proposed, as opposed to the traditional method based on a finite element modeling software package. To acquire the flexibility properties of beveloid gear tooth surfaces, an accurate finite element (FE) model about a beveloid gear tooth with root fillets is first built. A solution model for crossed beveloid gears is developed using the influence coefficients technique. An enhanced solving approach is presented to improve the robustness of the solving model by addressing the limitation of the influence coefficients method. In addition, a unique contact pressure is presented. The numerical example proposed can be used to test the proposed methodology.

Continuous generating grinding has become an important gear processing method owing to its high efficiency and precision. In this study, an adaptive design model is proposed for the continuous generation of beveloid gears in common gear grinding machines. Based on this model, a method for determining the installation position and grinding kinematics is developed alongside an analytical meshing model for grinding contact trace and derivation of key grinding parameters. By combining these aspects, a general mathematical model for the continuous generation of beveloid gears is presented, comprising the entire grinding process from worm wheel dressing to the evaluation of grinding deviation. The effects of the worm and dressing wheel parameters on the grinding deviation were analysed, facilitating the development of an approach to improve the grinding accuracy. The presented procedure represents a novel design method for the continuous generation of beveloid gears in common gear grinding machines, facilitating the appropriate selection of worm and dressing wheel parameters.