不同载荷工况下机床主轴预紧力选取的数值分析方法

为研究预紧力对机床主轴的影响,提出在不同载荷工况下机床主轴预紧力选取的数值分析方法.计算得到预紧力与轴承刚度的关系,在轴系结构有限元模型中设置不同预紧力下的轴承刚度值,通过静力学分析求解轴系变形和刚度;计算得到预紧力与轴承发热量的关系,在轴系热分析有限元模型中设置轴承热源,通过传热分析求解主轴温升.计算结果表明,该方法...     

基于横向场激励的高频压电超声换能器

介绍了一种基于横向场激励模式的高频压电超声换能器及其设计、分析和制作过程。采用扩展的Christoffel-Bech-mann方法对LiNbO3、LiTaO3和PMN-33PT三种不同压电材料的a模式横向场压电耦合系数进行了计算,发现这三种材料中LiNbO3具有最大的LFE a模式压电耦合系数,为28%。采用具有最大压电耦合系数的X切LiNbO3设计并制作了基于横向场激励的高频超声换能器,并采用传统的Pulse-Echo方法测试了该超声换能器的中心频率和带宽。实验测得该LFE高频超声换能器的中心频率为34MHz,-6dB带宽为14.4%。从理论和实验上证明了横向场激励模式可以应用于高频超声换能器。     

静电刚度式谐振微加速度计设计

运用梁的横向振动特性分析了梁振动频率与平行板电容形成的静电刚度的关系,并以此设计了静电刚度式谐振微加速度计。在加速度作用下,检测质量产生的惯性力使电容器极板发生位移来改变电容结构的间隙大小,从而使谐振频率发生变化,通过检测频率变化量来测量输入加速度的大小。根据加速度计的工作原理说明检测过程中梁的机械刚度保持不变,只与产生静电刚度的电容间隙变化相关,减小了检测信号对机械误差与残余应力的依赖性。运用加工参数进行理论计算得出加速度计的灵敏度为21．17Hz／gn,在CoventorWare2005中进行仿真表明：加速度计的固有频率为23．94kHz,灵敏度约为20Hz／gn,与理论设计值相近。     

Vibration analysis of cable-driven parallel manipulators

A cable-driven parallel manipulator is a manipulator whose end-effector is driven by a number of parallel cables instead of rigid links. Since cables always have more flexibility than rigid links, a cable manipulator bears a concern of possible vibration. Thus, investigation of vibration of cable manipulators caused by cable flexibility is important for applications requiring high system stiffness or bandwidth. This paper provides a vibration analysis of general 6-DOF cable-driven parallel manipulators. Based on the analysis of the natural frequencies of the multibody system, the study demonstrates that a cable manipulator can be designed stiff enough for special applications like the cable-manipulator based hardware-in-the-loop simulation of contact dynamics. Moreover, under an excitation, a cable may vibrate not only in its axial direction, but also in its transversal direction. The paper also analyzes the vibration of cable manipulators caused by cable flexibilities in both axial and transversal directions. It is shown that the vibration of a cable manipulator due to the transversal vibration of cables can be ignored comparing to that due to the axial flexibility of cables.     

Viscoelastic material design with negative stiffness components using topology optimization

An application of topology optimization to design viscoelastic composite materials with elastic moduli that soften with frequency is presented. The material is a two-phase composite whose first constituent is isotropic and viscoelastic while the other is an orthotropic material with negative stiffness but stable. A concept for this material based on a lumped parameter model is used. The performance of the topology optimization approach in this context is illustrated using three examples.     

光电转台轻量化几何形状优化研究

对光电转台进行轻量化,首先需要进行几何形状进行优化.筋板如何布置才能使转台的动态刚度达到最优,在设计中一直是一个难点.基于此,通过对转台的连接部件、止推轴承及径向轴承进行有效简化,建立起了光电转台的动力学模型,结合模型.对转台内部的筋板布置形式进行了详尽的研究比较.研究结果表明,要想获得满意的动态刚度,单纯地增加筋板数量并不能达到要求,而应该根据其具体的振动情况来选择合理的筋板布置形式,并且在平行于振型方向的筋板上,开孔时的动刚度效果相对地比未开孔时的动刚度效果要好.     

Toward Flexible Embodied Energy: Scale-Inspired Overlapping Lithium-Ion Batteries with High-Energy-Density and Variable Stiffness

High performance flexible batteries are essential ingredients for flexible devices. However, general isolated flexible batteries face critical challenges in developing multifunctional embodied energy systems, owing to the lack of integrative design. Herein, inspired by scales in creatures, overlapping flexible lithium-ion batteries (FLIBs) consisting of energy storage scales and connections using LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) and graphite electrodes are presented. The scale-dermis structure ensures a high energy density of 374.4 Wh L⁻¹ as well as a high capacity retention of 93.2% after 200 charge/discharge cycles and 40 000 bending times. A variable stiffness property is revealed that can be controlled by battery configurations and deformation modes. Furthermore, the overlapping FLIBs can be housed directly into the architecture of several flexible devices, such as robots and grippers, allowing to create multifunctionalities that go far beyond energy storage and include load-bearing and variable flexibility. This study broadens the versatility of FLIBs toward energy storage structure engineering of flexible devices.     

Bioinspired Intervertebral Disc with Multidirectional Stiffness Prepared via Multimaterial Additive Manufacturing

Degenerative disc disease (DDD) has become a significant public health issue worldwide. This can result in loss of spinal function affecting patient health and quality of life. Artificial total disc replacement (A-TDR) is an effective approach for treating symptomatic DDD that compensates for lost functionality and helps patients perform daily activities. However, because current A-TDR devices lack the unique structure and material characteristics of natural intervertebral discs (IVDs), they fail to replicate the multidirectional stiffness needed to match physiological motions and characterize anisotropic behavior. It is still unclear how the multidirectional stiffness of the disc is affected by structural parameters and material characteristics. Herein, a bioinspired intervertebral disc (BIVD-L) based on a representative human lumbar segment is developed. The proposed BIVD-L reproduces the multidirectional stiffness needed for the most common physiological kinematic behaviors. The results demonstrate that the multidirectional stiffness of the BIVD-L can be regulated by structural and material parameters. The results of this research deepen knowledge of the biomechanical behavior of the human lumbar disc and may provide new inspirations for the design and fabrication of A-TDR devices for both engineering and functional applications.     

Lateral WSe2 Homojunction through Metal Contact Doping: Excellent Self-powered Photovoltaic Photodetector

Here an IR-heating chemical vapor deposition (CVD) approach enabling fast 2D-growth of WSe₂ thin films is reported, and the great potential of metal contact doping in building CVD-grown WSe₂-based lateral homojunction is demonstrated by contacting with TiN/Ni metals in favor of holes/electrons injection. Shortening nanosheet channel to ≈2 µm leads to pronounced enhancement in the performance of diode. The fabricated WSe₂-based diode exhibits high rectification ratios without the need of gate modulation and can work efficiently as photovoltaic cell, with maximum open circuit voltage reaching up to 620 mV and a high power conversion efficiency over 15%, empowering it as superb self-powered photodetector for visible to near-infrared lights, with photoresponsivity over 0.5 A W⁻¹ and a fast photoresponse speed of 10 µs under 520 nm illumination. It is of practical significance to achieve well-performed photovoltaic devices with CVD-grown WSe₂ using fab-friendly metals and simple processing, which will help pave the way toward future mass production of optoelectronic chips.     

Non-Hierarchical Architected Materials with Extreme Stiffness and Strength

Stretch-dominated truss and plate microstructures are contenders in the quest for realizing architected materials with extreme stiffness and strength. In the low volume fraction limit, closed-cell isotropic plate microstructures meet theoretical upper bounds on stiffness but have low buckling strength, whereas open-cell truss microstructures have high buckling strength at the cost of significantly reduced stiffness. At finite volume fractions, the picture becomes less clear but both are outperformed by hollow truss lattice and hierarchical microstructures in terms of buckling strength. Despite significant advances in manufacturing methods, hollow and multi-scale hierarchical microstructures are still challenging to build. The question is if there exist realizable microstructures providing stiffness and strength matching or even beating hard-to-realize hollow or hierarchical microstructures? Herein, single-scale non-hierarchical (first order) microstructures that beat the buckling strength of hollow truss lattice structures by a factor of 2.4 and first- and second-order plate microstructures by factors of 5 and 1.4, respectively, are systematically designed, built, and tested. Stiffness of the microstructures is within 40% of theoretical bounds and beats both truss and second order plate microstructures. The microstructures are realized with 3D printing. Experiments validate theoretical predictions and additional insight is provided through numerical modeling of a CT-scanned sample.