行波超声马达摩擦材料的研究

行波超声马达是一种靠摩擦力直接驱动的新型驱动器。其中摩擦材料的优劣对于行波超声马达的工作性能和使用寿命有直接的影响。该文提出了一种以超高分子量聚乙烯为基体的摩擦材料，并掺入多种无机徽粒和高分子化合物改善其性能，对制得的摩擦材料样品进行了摩擦学分析和应用于马达的对比实验，从理论和实验的角度提出了行波超声马达用摩擦材料对各摩擦学参数的要求。     

硅灰石／海泡石纤维混杂增强摩擦材料的摩擦学行为

摩擦材料主要用于汽车、火车、飞机、坦克等交通运输工具及工程机械中，随着交通工具及工程机械的高速发展，摩擦材料的发展大致经历了几个阶段。由石棉摩擦材料发展到了半金属摩擦材料，然而由于半金属摩擦材料的制动噪音及在潮湿的环境里金属纤维易发生锈蚀等不足，现在无石棉混杂纤维增强摩擦材料成为摩擦材料的主要发展方向。我国非金属矿行业近年生产的硅灰石、海泡石等针状非金属矿物材料在摩擦材料增强改性方面显示出较好的性能，对人体无害。硅灰石的单相摩擦性能和抗热衰退性能好于石棉，但其耐磨性低于石棉材料，硅灰石与钢纤维复合增强的盘式衬片有比较稳定的摩擦系数。海泡石是一种富镁纤维状硅酸盐粘土矿物，具有良好的耐高温性能。本文以耐高温酚醛树脂为粘结剂，以量广价廉的天然矿物纤维如海泡石、硅灰石纤维等作为增强材料制备摩擦材料，并分析了其摩擦学行为。     

扭纵复合驻波超声马达驱动相位的实验研究

采用两路相位差可调的电源,对扭纵复合驻波超声马达表面质点扭振、纵振相位进行调整,发现当定子表面扭振、纵振的相位差为π／２时,马达不转动;当相位差为０或π时,该马达输出驱动力矩大,运行性能良好。另外,我们观测了两种摩擦材料的马达转动力矩与相位差的关系。还通过金相显微镜拍摄了定子表面粒子的运动轨迹     

超声马达的应用和发展动向

在简明阐述超声马达基本原理及性能特点的基础上,重点介绍了目前超声马达的应用情况,并展望了超声马达的研究和发展方向。     

直线超声马达研究进展

简述了近十年来直线超声马达的研究进展,分析了超声马达在结构设计和摩擦驱动等方面的关键问题。分析表明,开发新型原理的超声马达方兴未艾,但接触型马达为目前直线马达的主要发展方向。本体结构简化、驱动性能增强、工作效率及稳定性提高,是超声马达结构设计时应考虑的目标和任务。但接触型直线马达正常工作过程就是定/动子间的高频冲击磨损过程,定动子间摩擦学设计至关重要。另外,装配预紧力、接触间隙和磨损过程等引起的非线性问题,在马达设计制造和使用维护中应给予关注。最后,探讨了马达使用性能及运行寿命的影响因素,并总结了直线超声马达工作过程中的能量损失缘由和噪声产生机理。     

两种矿物纤维增强摩擦材料的摩擦学特性和磨屑分析

汽车用摩擦材料主要是制动摩擦片和离合器片。它们既是保安件、又是易损件，在汽车用材中占有特殊重要的地位，且非石棉低噪声摩擦材料的研究开发是一门涉及多学科的高新技术。许多无石棉摩擦材料能满足某些使用要求，但尚没有一类新型摩擦材料能够完全满足汽车工业发展的需求，且在性能提高的同时，成本也大幅度降低。所以降低成本、全面提高新型摩擦材料的性能仍是各国亟待解决的一项任务。采用混杂纤维作为增强纤维，有利于发挥每一种纤维的优点，弥补相互之间的缺陷，获得的材料配方性能更加优异。我国是一个矿物资源大国，有着丰富的天然矿物资源。因此，我们采用来源稳定的硅灰石纤维与海泡石纤维混杂使用来增强酚醛树脂基摩擦材料，并对其摩擦学特性和磨屑特征进行了分析。     

基于复合材料超声直线电机振子的有限元分析

用有限元数值分析法,研究了一种利用各向异性的复合材料作为振动体的超声直线电机模型.首先,在各向异性复合材料振动体的振动解析基础上,建立碳纤维增强型复合材料(CFRP)振动体的数值分析模型;然后,研究复合材料超声直线电机的多种振动模态;最后,分析CFRP纤维角不同时对电机性能的影响.结果表明,电机在B(1,1)振型下具有最简振动模态,CFRP的纤维角为45°时电机工作性能最好.表明有限元法是研究复合材料超声直线电机的有效方法.     

复合型超声马达的数值研究

利用等效电路，对复合型超声马达进行了数值分析．为该型马达的性能分析和设计提供了理论依据．     

一种旋转方向可控的驻波超声马达

利用移动定子中驻波振动模式空间位置的方法，该文提出一种旋转方向可控的驻波超声马达设计方案。对样机的试验表明，方案是可行的，正反方向旋转时力矩和转速等性能基本一致。     

纵扭复合型超声马达共振频率的研究

对夹心式纵扭复合型超声马达的共振频率进行了研究.研究分析表明,负载因子同超声马达的共振频率有密切的关系,负载因子越大,超声马达工作时的共振频率下降的越多.因此,超声马达工程设计中应尽量选用声阻抗大的材料作为超声马达定子以确保其共振频率最小程度的受负载的影响.纵扭复合型超声马达共振频率的理论值与测试值基本符合.     

Control of a 2-DOF ultrasonic piezomotor stage for grommet insertion

The treatment of a common disease called “Otitis Media with Effusion (OME)” involves the surgeon inserting a grommet in the eardrum to bypass the Eustachian tube for draining fluid when medication fails. In this paper, a novel device for myringotomy and grommet insertion is first designed and introduced. Due to the advantages of high precision and fast response, a 2-DOF ultrasonic piezomotor (USM) stage is chosen to provide the motion sequences of the device, especially a precise path tracking during the grommet insertion. This paper briefly presents the mechanical design of the device and the configuration and control of the 2-DOF USM stage. The model of the USM consisting of a linear and nonlinear term is built. A PID controller is used as the main controller and tuned with the help of LQR technique. Since there are nonlinear dynamics caused by friction and hysteresis existing in the system, a nonlinear compensation including a sign function and sliding mode control is designed to reject the nonlinearity. Moreover, a decoupling controller is designed to eliminate the coupling effects between the two USM stages. The experimental results show that the LQR-assisted PID controller with compensation can achieve very good system performance and the decoupling controller can further improve the performance.     

陶瓷刀具表面微织构激光加工工艺的实验研究

较好的刀具表面微织构可以改善刀具摩擦磨损性能,提升刀具切削性能,延长刀具使用寿命。针对光纤激光在陶瓷刀具表面加工微织构的过程中,激光功率、频率、扫描速度和扫描次数对微沟槽尺寸和形貌的影响进行了实验研究。确定了使用1064 nm波长光纤激光器在陶瓷刀具表面加工微织构的合理参数。选用不同形貌微织构和无织构刀具进行摩擦磨损实验并进行对比。实验结果表明,微织构可以降低陶瓷刀具表面摩擦系数,提高其抗磨损性能。微织构沟槽深度或宽度较大时作用效果较差。     

Plane-wave shielding properties of anisotropic laminated compositecylindrical shells

The plane-wave shielding properties of advanced composite cylindrical shells are analyzed. Based on a rigorous theory that clearly displays the propagating nature of the electromagnetic field in an anisotropic, multi-layered, and lossy cylindrical shell structure. In this study, numerical results are presented for graphite/epoxg fiber-reinforced composite shells. In particular, the parameters that influence the shielding effectiveness, such as material properties, cylinder configuration, fiber orientation, and incident wave polarization, are investigated in detail. For design purposes, an empirical formula is also proposed to estimate the shielding effectiveness in the lower frequency range. Finally, a sharp reduction of shielding performance due to resonance is also examined     

如何选择扬声器纸盆专用植物纤维

植物纤维材料仍是扬声器纸盆用料的主流.介绍了几种特种植物纤维以其独特的电声物理性能在高档扬声器音盆中有特殊的电声效果.说明了原料相同但不同的制浆提纯方法得到的纤维材料在电声性能上的表现是不一样的.     

同轴水密电缆用金属化纤维材料的性能研究

随着海洋装备技术的发展,对同轴水密电缆的轻量化和耐弯曲性能提出了较高的要求。通过研究镀银芳纶纤维、镀银维克特纶纤维和镀银柴隆纤维三类不同类型的金属化纤维及其编织屏蔽的性能以及对同轴水密电缆的减重性能、屏蔽性能、抗压性能、温度相位稳定性的影响,认为目前同轴水密电缆较为理想的金属化纤维编织屏蔽材料是镀银柴隆纤维。     

Speed control of ultrasonic motors using neural network

The ultrasonic motor (USM) is a newly developed motor, and it has excellent performance and many useful features, therefore, it has been expected to be of practical use. However, the driving principle of USM is different from that of other electromagnetic-type motors, and the mathematical model is complex to apply to motor control. Furthermore, the speed characteristics of the motor have heavy nonlinearity and vary with driving conditions. Hence, the precise speed control of USM is generally difficult. This paper proposes a new speed-control scheme for USM using a neural network. The proposed controller can approximate the nonlinear input-output mappings of the motor using a neural network and can compensate the characteristic variations by on-line learning using the error backpropagation algorithm. Then, the trained network finally makes an inverse model of the motor. The usefulness and validity of the proposed control scheme are examined in experiments     

Tough Lessons From Bone: Extreme Mechanical Anisotropy at the Mesoscale

Bone is mechanically and structurally anisotropic with oriented collagen fibrils and nanometer‐sized mineral particles aggregating into lamellar or woven bone.[1] Direct measurements of anisotropic mechanical properties of sublamellar tissue constituents are complicated by the existence of an intrinsic hierarchical architecture. Methods such as nanoindentation provide insight into effective modulus values; however, bulk material properties cannot sufficiently be characterized since such measurements represent properties of near‐surface volumes and are partially averaged over fibril orientations.[2–5] In this study, we focus on the material properties of bone at one single level of hierarchy. By measuring properties of individual parallel‐fibered units of fibrollamellar bone under tension under controlled humidity conditions, an unusually high anisotropy is found. Here, we clearly demonstrate ratios as large as 1:20 in elastic modulus and 1:15 in tensile strength between orientations perpendicular and parallel to the main collagen fiber orientation in native wet bone; these ratios reduce to 1:8 and 1:7, respectively, under dry conditions. This extreme anisotropy appears to be caused by the existence of periodic, weak interfaces at the mesoscopic length scale. These interfaces are thought to be relevant to the proper mechanical and physiological performance of bone.     

Composite Three‐Dimensional Woven Scaffolds with Interpenetrating Network Hydrogels to Create Functional Synthetic Articular Cartilage

The development of synthetic biomaterials that possess mechanical properties mimicking those of native tissues remains an important challenge to the field of materials. In particular, articular cartilage is a complex nonlinear, viscoelastic, and anisotropic material that exhibits a very low coefficient of friction, allowing it to withstand millions of cycles of joint loading over decades of wear. Here, a three‐dimensionally woven fiber scaffold that is infiltrated with an interpenetrating network hydrogel can build a functional biomaterial that provides the load‐bearing and tribological properties of native cartilage. An interpenetrating dual‐network “tough‐gel” consisting of alginate and polyacrylamide was infused into a porous three‐dimensionally woven poly(?‐caprolactone) fiber scaffold, providing a versatile fiber‐reinforced composite structure as a potential acellular or cell‐based replacement for cartilage repair.     

Adjustable speed control of ultrasonic motors by adaptive control

The driving principle of the ultrasonic motor (USM) is different from those of the electro-magnetic type motors. Some mathematical models for the USM have been reported; however, these models are very complex to apply for speed control of the USM. Therefore, the speed controllers have been designed using PI controllers or fuzzy controllers and it is necessary to develop a simple and convenient mathematical model for the USM in order to achieve a high-performance speed control. In this paper, a mathematical model for the USM is proposed which is simple and useful for speed control. The speed controller is designed based on the model using adaptive control theory. Adaptive control is attractive for control of the USM because the speed characteristics of the USM vary with drive conditions. The application of this control scheme to speed control for the USM is attempted first. The effectiveness of proposed control is demonstrated by experimental     

Theoretical, Numerical, and Experimental Analysis of Optical Fiber Tapering

An optical fiber taper is fabricated by heating and stretching a fiber. The resulting taper shape is important as it strongly affects optical performance. In this paper, the tapering process of solid optical fiber is modeled and analyzed under several heating and stretching conditions. The fiber material is assumed to be of non-Newtonian inelastic type. The results show that for a given heating profile, the shape of a tapered fiber is independent of the material properties and the stretching conditions applied at the fiber ends, and a section of uniform waist can be formed as long as the extensional deformation rate in a section of the heating zone is position-independent. Different shapes of fiber tapers can only be achieved by using different heating profiles. Therefore, spatially uniform heating of the fiber within the heating zone is of critical importance for producing a taper with a uniform waist. This is particularly true if the fiber material has a low deformation temperature