柱销式双螺母行星滚柱丝杠预紧机理研究

为了实现行星滚柱丝杠正反转双向精密驱动,迫切需要开展含预紧的行星滚柱丝杠传动研究。构建了一种柱销式双螺母行星滚柱丝杠无背隙传动构型。它利用双螺母的相对转角提供预紧力,并使用柱销固定该转角从而维持预紧力。建立了包含有双螺母、双滚柱以及丝杠螺纹双向受载状态的静力学模型。提出了仅受预紧力与考虑外载荷时,柱销式双螺母行星滚柱丝杠的受力和变形计算方法。通过与有限元模型载荷分布和预紧力计算结果的对比,验证了所建模型的正确性。分析了初始预紧力对螺母相对转角和柱销剪切力的影响,以及不同外载荷作用下,螺母预紧力、柱销剪切力和螺纹载荷分布的变化。结果表明,较小的螺母相对转角便会产生较大的初始预紧力,柱销剪切力远小于初始预紧力或外载荷。当外载荷增加时,螺母#1所受预紧力和柱销剪切力均会增加,螺母#2所受预紧力会减小。使得螺母#2预紧力消失时的外载荷远大于初始预紧力。     

滚珠丝杠副载荷分布与轴向刚度分析

基于赫兹接触理论,建立了相邻滚珠间接触变形的相互关系,并考虑滚珠丝杠副支承形式、载荷条件和螺母间相互耦合的影响,建立单螺母和双螺母滚珠载荷分布的数学模型,以双螺母垫片预紧滚珠丝杠副为例进行了计算和分析。研究结果表明不同支承形式和载荷条件下的滚珠载荷分布不同,并给出了根据轴向载荷的大小和方向确定支承形式和轴向载荷作用点的方法。     

Effective transmission screw nuts of steel backing/self-lubricating composite lining fabricated by injection molding

To increase transmission efficiencies and bearing abilities of sliding screw pairs, a new type of screw nuts and their fabricating method were put forward. The nuts have the structure of steel backing/self-lubricating composite lining with the advantages of high bearing capacity and low friction coefficient. The lining material was composed of epoxy as the matrix and some additives: carbon fiber, graphite, MoS₂, firming agents and coupling agents etc. A suitable formulation was determined by experiments to meet lining requirements: high bounding strength, sufficient mechanical properties and good tribological properties. An injection molding set for fabricating the nut linings was designed and made to achieve even lining thickness along the thread surfaces during molding. Lubrication grooves on the nut thread surfaces were created during molding. In comparison with bronze ZQSn6-6-3, the friction coefficient of the composite nuts was reduced by 35% and the transmission efficiency increased by 30%.     

高效重载螺旋传动技术的研究开发综述

综述了目前高效、重载螺旋副研究开发的三个发展方向:减摩耐磨合金螺母、聚合物自润滑整体螺母、钢背衬复合材料螺母这三种。铜基、锌基等减摩耐磨合金螺母可以有效提高螺旋传动的工作性能,但采用切削加工难以形成有效的润滑油道;尼龙和酚醛树脂等非金属聚合物自润滑整体螺母具有良好的减摩性能,但承载能力低。钢背衬碳纤维织物/树脂复合材料螺母兼具高的承载能力和良好的减摩耐磨性能,具有良好的发展和应用前景。     

Performance analytical study of the dual screws actuation mechanism

This paper presents a dual screw actuation mechanism (DSAM) wherein two screws actuate the common sliding platform by connecting two screw nuts with a gear pair. Two dimensionless parameters, namely, the gear ratio between two gears and the pitch ratio between the two screws, are defined to describe the structural characteristics of the DSAM. This study investigates the performance characteristics of a DSAM with respect to gear ratio and pitch ratios. The load distribution between the two screws, which is important in planning the contributions of the two inputs during operation, is discussed. The load capacity is deduced according to the load limits of the two screws with the actuator. The analytical expression for the overall mechanical efficiency of the DSAM is derived from the normal operational power flow mode (two-input-one-output). Based on the Lagrangian formulation, the dynamic coupling term that evaluates the extent to which the inertia torque of one input is affected by the motion variations of the other input is obtained. This performance study provides the fundamental guidelines for the design and operation of a DSAM.     

Acceleration-Dependent Analysis of Vertical Ball Screw Feed System without Counterweight

The distinguishing feature of a vertical ball screw feed system without counterweight is that the spindle system weight directly acts on the kinematic joints.Research into the dynamic characteristics under acceleration and decel-eration is an important step in improving the structural performance of vertical milling machines.The magnitude and direction of the inertial force change significantly when the spindle system accelerates and decelerates.Therefore,the kinematic joint contact stiffness changes under the action of the inertial force and the spindle system weight.Thus,the system transmission stiffness also varies and affects the dynamics.In this study,a variable-coefficient lumped parameter dynamic model that considers the changes in the spindle system weight and the magnitude and direc-tion of the inertial force is established for a ball screw feed system without counterweight.In addition,a calculation method for the system stiffness is provided.Experiments on a vertical ball screw feed system under acceleration and deceleration with different accelerations are also performed to verify the proposed dynamic model.Finally,the influence of the spindle system position,the rated dynamic load of the screw-nut joint,and the screw tension force on the natural frequency of the vertical ball screw feed system under acceleration and deceleration are studied.The results show that the vertical ball screw feed system has obviously different variable dynamics under acceleration and deceleration.The influence of the rated dynamic load and the spindle system position on the natural frequency under acceleration and deceleration is much greater than that of the screw tension force.     

热管滚珠丝杠热性能仿真和实验

针对传统液冷散热滚珠丝杠存在的丝杠表面温度梯度及温度波动性较大、达到热平衡时间较长等问题,设计了内置热管的新型滚珠丝杠。选择热管丝杠充液介质并计算其结构尺寸参数;为验证热管丝杠热性能,提出了含管壁层、冷凝回流层、蒸气腔层的热管丝杠分层等效模型并对其进行仿真;分析螺母位于不同位置时丝杠表面的温度分布,并与传统液冷丝杠散热性能进行对比分析;采用沸腾排气法制备热管丝杠,搭建实验台,测试热管丝杠表面温度并与仿真结果进行对比。研究结果表明,相对传统的液冷散热丝杠,热管丝杠表面具有较小的温度梯度,温度均匀性良好,且达到热平衡的时间短,仿真与实验结果一致,验证了仿真方法的有效性。     

On the natural frequencies of helical compression springs

The linearized disturbance equations governing the resonant frequencies of a helical spring subjected to a static axial compressive load are solved numerically using the transfer matrix method for clamped ends and circular cross-section to produce frequency design charts. The effect of varying the number of turns of the spring is investigated, and in the limit of large numbers of turns, our results validate earlier work on the vibration of helical compression springs in which the helix was modeled as an elastic beam with rigidities corresponding to those of unclosed circular rings.     

基于UHMWPE/纳米ZnO复合材料的滑动摩擦磨损机制

用热压成型法制备了超高分子量聚乙烯(UHMWPE)纳/米ZnO复合材料,采用销盘式摩擦磨损试验机考察了载荷和相对滑动线速度对复合材料摩擦学性能的影响;采用扫描电子显微镜观察了复合材料磨损表面形貌。结果表明:在低载荷试验条件下磨损机制为粘着磨损,在高载荷试验条件下磨损机制为粘着磨损和疲劳磨损。而在一定载荷试验条件下,无论相对滑动线速度高或低,复合材料的磨损机制主要表现为粘着磨损,只是在高速情况下粘着磨损程度加大,局部还出现了表面撕裂的痕迹。     

Increasing the load capacity and rigidity of roller–screw mechanisms by adjusting the screw surfaces

A method is proposed for increasing the load capacity and rigidity of roller–screw mechanisms by adjusting the screw surfaces. That permits the design of compact mechanisms such as automobile steering assemblies.     

交错互通微通道多孔网格板的力学性能研究

为了增大交错互通微通道多孔网格板的机械强度,研究了网格板在拉伸、压缩以及弯曲情况下的力学性能,并建立了相应的理论模型,还对网格板在拉伸、压缩以及弯曲情况下的应力分布情况进行了仿真分析。结果表明,无论是拉伸、压缩还是弯曲,在同样受力F作用时网格板上的最大应力都比同等尺寸致密金属板的应力要大,网格板的机械强度相对致密金属板变小,并且网格板机械强度随着微通道宽度、深度的增大而减小;交错互通微通道多孔网格板在仅受力而未有力矩作用的情况下没有出现应力集中现象,在仅受力矩作用的情况下稍微出现应力集中现象,在同时受到力与力矩的双重作用时出现十分明显的应力集中现象;网格板在微通道宽度较小时更易产生应力集中。     

Cyclic loading of beams based on the Prager and Frederick–Armstrong kinematic hardening models

The kinematic hardening theory of plasticity based on the Prager and Frederick–Armstrong models are used to evaluate the cyclic loading behavior of a beam under the axial, bending, and thermal loads. The beam material is assumed to follow non-linear strain hardening property. The material's strain hardening curves in tension and compression are assumed to be both identical for the isotropic material and different for the anisotropic material. A numerical iterative method is used to calculate the stresses and plastic strains in the beam due to cyclic loadings. The results of the analysis are checked with the known experimental tests. It is concluded that the Prager kinematic hardening theory under deformation controlled conditions, excluding creep, results into reversed plasticity. The load controlled cyclic loading under the Prager kinematic hardening model with isotropy assumption results into reversed plasticity. Under anisotropy assumption of tension/compression curve, this model predicts ratcheting. On the other hand, the Frederick–Armstrong model predicts ratcheting behavior of the beam under load controlled cyclic loading with non-zero mean load. This model predicts reversed plasticity under the load controlled cyclic loading with zero mean load, and deformation controlled cyclic loading.     

外弯矩下螺栓法兰连接紧密性研究

为准确分析螺栓法兰连接系统的紧密性,利用当量内压法﹑当量轴向力法和变形协调方程,研究外弯矩作用下螺栓法兰连接中的垫片压紧应力。分析结果表明:若利用当量内压法来计算,外弯矩等同于内压,相当于增大了系统的内压,但并不能体现出外弯矩作用下垫片应力在螺栓法兰连接系统分布的不均匀性;而利用当量轴向力法来计算,可以体现出整个系统在承受外弯矩作用导致的垫片应力沿管道圆周方向按余弦分布的不均匀性,并且垫片受拉侧和受压侧的压紧应力相差增大,其中受拉侧垫片应力减小,受压侧垫片应力增大,因此螺栓法兰连接的紧密性需重点考虑受拉侧的垫片应力。     

滚珠丝杠副返向器反相位布置方式分析

多列布置的滚珠丝杠副会由于各列载荷分布不均出现滚道磨损问题,对于重载滚珠丝杠副这一问题尤为突出.通过对螺母上返向器反相位布置方式的介绍和原因分析,提出返向器反相位布置后使得各列滚珠所受栽荷更加均匀,丝杠、螺母受力情况得到改善,特别有利于滚珠丝杠副存在安装误差时的受力平衡.也分析了采用返向器反相位布置方式时螺母尺寸的影响...     

复合材料机械联接接头的寿命估算

以机械联接接头应力分布的解析解为基础，以单向板纵向拉拉ＳＮ曲线为依据，按照孔边一定范围内逐层逐单元损伤直至破坏的物理本质，从宏观唯象观点出发，提出了一种寿命估算方法。同时，文中还给出了孔的永久变形与循环次数之间的拟合关系式。     

轧机压下螺纹副承载特性测试研究

依据相似准则，制作3500mm中厚板轧机电动压下传动螺纹副1／3的测试模型，采用电测法获取悬臂螺牙弯曲应变值，模拟实际轧制力和过平衡力作用下螺纹副螺牙各层载荷大小及分布。螺纹副测试结果和边界元、有限元法数值计算结果相比，螺牙层载荷大小和分布规律基本吻合，证明电测法可行、直观且可靠。通过测定数据，证实了轻重两种载荷工况的不同承载特性，还发现螺母与丝杆轴线错移或倾斜的微尺度行为对载荷大小及分布影响极大的重要现象，为提高压下传动螺纹副寿命及可靠性提供了重要思路。     

Relationship Between the Friction and Microscopic Contact Behavior of a Medical Compression Stocking at Different Strains

The contact and friction behavior of a medical compression stocking (MCS) under different strains was investigated in friction and compression experiments against a mechanical skin model. In addition, the 3D topography of the MCS surfaces was analyzed in order to study the relationship between macroscopic friction and microscopic surface properties. The load dependence of friction coefficients was found to be in accordance with the adhesion friction model. The surface structure of MCS samples was considerably changed when varying the strain state, while friction coefficients remained comparable, indicating real contact areas independent of strain on the microscopic level. The experimental findings could be confirmed and explained on the basis of the microscopic surface analyses, when interpreting the fabric surfaces to be composed of numerous individual round asperities obeying the Hertz contact model.     

Specific Features of the Behavior of the Coercive Force in Low-Carbon Plastically Deformed Steels

The relationship between the coercive force in low-carbon steels under plastic extension and compression and the values of deformation and actual and residual stresses are studied. This relationship is investigated for both “ slow” loading (when an equilibrium deformation is attained for each load value) and “fast” loading (when such equilibrium is not attained). It is shown that (i) a comparatively small increase in the coercive force in a loaded condition is due only to an increase in the density of dislocations in the process of plastic extension; (ii) a significant steep increase in the coercive force accompanying removal of the load from a plastically stretched specimen is fully due to residual compression stresses; (iii) the values of the coercive force under “slow” and “fast” loading are significantly different in the region of small deformations less than 2.5%; (iv) these values are close to each other in the loaded state for all deformations up to 10%; (v) a relief of the compression stress that creates plastic deformations causes a steep decrease in the coercive force that is as large as its increase following relief of plastic extension; this is explained by the emergence of a significant residual tension stress. The obtained results are of importance for the use of the method based on measuring the coercive force to test steel structures under the conditions when plastic deformations develop.__________Translated from Defektoskopiya, Vol. 41, No. 5, 2005, pp. 24–38.Original Russian Text Copyright © 2005 by Kuleev, Tsar’kova, Nichipuruk.     

R134a应用于中间补气螺杆压缩机制冷系统的数值分析与研究

分析了中间补气的螺杆压缩机制冷系统的工作原理,并对系统的循环进行分析,在不同工况下,对使用R134a的中间补气的螺杆压缩机制冷系统的性能进行了理论分析。研究表明:对于应用R134a的中间补气螺杆压缩机系统,制冷量和电功率均随一级压缩内容积比的增大而减小,而性能系数COP值随一级压缩内容积比的增大而增大。因此,在满足所需制冷量的前提下,要选取适当的补气口开设位置,才能获得较好的性能。     

楔铁式调平机构的设计

为满足仪器在大的垂直负载和方位扭矩下的精密调平和精度保持,设计了楔铁式调平机构.利用静摩擦平衡方位扭矩,通过增大楔铁工作面来满足大的垂直负载,应用斜面机构和螺旋机构的速比大和自锁的特点实现精密调平和精度的保持.根据该机构的使用要求,提出了设计的4项准则.以此,设计计算了在垂直负载15 t,方位扭矩10 000 N·m,调平角度不小于1°,调平精度1"条件的楔铁式调平机构.