关节铰接双面接触摩擦对医用机械臂影响分析

以医用机械臂为研究对象,同时考虑关节旋转铰接圆柱面及端面２处的摩擦,提出端面接触系数,利用达朗伯定理对医用机械臂进行动静力学分析求得两接触面处的法向接触力,并基于库仑摩擦模型求得两接触面摩擦力矩,结合拉格朗日方程建立了不包含摩擦及包含摩擦的２种动力学模型,通过仿真求解分析得出对于所研究的医用机械臂及结构相类似的机械臂,铰接端面处的摩擦对机械臂关节输出扭矩及末端位置影响大于圆柱面处摩擦的影响,端面接触程度越高造成能量损失越大,机械臂末端位置轨迹越混乱。     

Modeling and simulation of joint clearance effects on mechanisms having rigid and flexible links

In this study, kinematic and dynamic characteristics of a planar four-bar mechanism having joint clearance and link flexibility are investigated. Assuming that joint clearance as a virtual massless link, artificial clearances are developed at crank-coupler and coupler-follower joints. Contact model in joints with clearance is established using the nonlinear spring-damper model and the friction effect is considered using the Coulomb friction model. Then the simulation is implemented and the kinematic and dynamic characteristics of model mechanism are investigated. The computational methodology can predict the effects of clearance on planar mechanism having rigid and flexible links. The results are evaluated for the case of stationary phase, and naturally show that extreme values occur in output of the mechanism with clearances. Due primarily to the suspension effect of the flexible link, values of these peaks in the flexible mechanism decrease relative to that of the rigid mechanism. In addition, the flexibility has a significant effect on the vibration response of the mechanism with joint clearance.     

考虑摩擦因素影响的结合面切向接触阻尼分形预估模型及其仿真

为准确计入结合面表面微观形貌对结合面的影响,提出结合面的“固-隙-固”接触模型。基于该接触模型和接触分形理论以及赫兹理论,建立考虑摩擦因素影响的结合面切向接触阻尼的分形预估模型,并通过数值仿真研究揭示有关参数对结合面切向接触阻尼的影响,为后续结合面动力学建模和动力学特性分析做准备。仿真分析结果表明：结合面的切向接触阻尼随结合面实际接触面积的增大而增大;随结合面法向载荷的增大而减小;随结合面间摩擦因数的增大而趋于恒定;实际接触面积影响cte*-μ曲线转折点(即临界摩擦因数μc)的位置,随着实际接触面积的增大,临界摩擦因数μc亦同时增大;不同的分形维数取值,尤其是分形维数取值在临界值(D=1.55)的两侧时,结合面间的接触行为存在较大差异。     

具有谐波减速器柔性关节摩擦力辨识及控制

为了减轻关节重量,提高关节输出力矩,在关节内部集成谐波减速器等部件。然而,谐波减速器的加入,不仅增加关节柔性,而且导致关节内部摩擦力复杂。针对具有谐波减速器的柔性关节,提出了摩擦力辨识方法,并且的得到关节摩擦力模型与Strbeck摩擦力模型相似的结论。搭建了柔性关节试验平台,利用辨识的摩擦力模型有效的补偿了关节内部摩擦力的影响,提高了关节的控制精度。     

Tribomechanical method of computing coefficient of lateral pressure at compacting dispersed materials with cohesive bonding

A method has been developed for computing coefficient of lateral pressure arising at compacting dispersed materials. The method takes into account a joint effect of cohesive bonding (shear strength), interparticle and external friction, as well as the pressure applied at compacting. The coefficient was subjected to design estimates within a broad variation range of critical values.     

皮肤-纺织品的摩擦特性试验研究

为了定量研究纺织品与人体皮肤之间的摩擦特性,采用微观摩擦试验机对4种织物与20位男女手臂前臂皮肤之间的摩擦因数进行测试。结果表明:皮肤-织物的平均摩擦因数在0.30~0.50之间,其中男性皮肤-织物的平均摩擦因数在0.30~0.36之间,女性皮肤-织物的平均摩擦因数在0.40~0.50之间。织物表面特征,如表面形状、纹理特点、组织结构、平整度、致密度和弹性等,以及纤维本身的表面特征,是织物表面摩擦特性存在差异的根本原因。4种织物的平均摩擦因数由高到低分别为全毛绒面呢、羊皮、真丝绸和本色平纹棉布,其中丝绸和平纹棉布的平均摩擦因数比较接近;在与不同纺织品摩擦时,女性皮肤-织物的平均摩擦因数普遍比男性高。     

Tribomechanical calculation method of the lateral pressure coefficient for brittle dispersed materials

A calculation procedure is proposed to analyze the lateral pressure coefficient of brittle dispersed materials with account of the joint effect of the interparticle and external (wall or boundary) friction modes The measurement range of this coefficient is defined as the ratio of the interparticle friction coefficient to the external (boundary) friction one.     

A Biphasic Model for Hip-Joint Replacement

The ball-and-socket geometry of the hip joint makes kinematic analysis of the joint motion relatively straightforward in comparison to other joints. The load-carrying surfaces of both ball and socket are covered with tough viscoelastic material known as cartilage. A number of lubrication theories have been proposed in the literature to account for the low coefficient of friction and low wear observed in healthy joints. The actual mechanism by which joints are capable of sustaining large repetitive loads with virtually no wear and with very little friction has not been fully understood. Therefore, analytical studies are presented for the understanding of the lubrication mechanism occurring in hip-joint replacements under restricted motion during standing or in the supporting phase during walking. The viscoelastic fluid has been considered to represent the synovial fluid in the fluid-film region. The problem described here has been analyzed in two regions (the porous matrix and the fluid-film region) separately along with suitable matching and boundary conditions at the interface. It has been concluded that the effect of the viscoelastic parameter for a particular gap is to increase the load capacity, indicating positive effects of the increase in concentration of suspended particles in the lubricant region. It has been observed that the coefficient of friction decreases with increasing values of the viscoelestic parameter. This is due to the fact that as the viscoelastic parameter increases, the concentration of hyaluronic acid molecules increases. It may also be noted from the results that the coefficient of friction decreases with increasing values of slip parameter. This shows that the slip velocity occurring at the porous boundary helps in maintaining normal functioning of human joints.     

聚氨酯弹性体摩擦衬垫材料的摩擦特性研究

本文研究了聚氨酯弹性体摩擦衬垫材料的摩擦特性,发现聚氨酯弹性体材料的动摩擦系数是和滑动速度有关的,在0．0l-0．4mm／s的速度范围内,速度提高摩擦系数上升,在更高的速度下摩擦系数还会下降。聚氨酯弹性体材料的静摩擦系数是比较难以确定的,本文建议把滑动量较小而滑动速度又很低的这一时期的摩擦称为“初期摩擦”,它是界于静摩擦与动摩擦之间的一种特殊的摩擦状态。文中还分析了粘着摩擦机理,提出了接点化学粘接机理。并根据这种机理对实验结果进行了分析和讨论。     

人工髋关节球形凹坑微织构表面摩擦学性能研究*

为改善人工髋关节表面的摩擦学性能,在人工髋关节表面设计球形凹坑微织构;建立人工髋关节微织构表面的流体动压润滑模型,利用CFD软件ANSYS Fluent对微织构表面流体动压进行数值分析,得到摩擦副表面相对滑动时产生的油膜平均承载力以及摩擦因数,并分析表面微织构参数对摩擦学性能的影响。结果表明:在给定的织构参数范围内,平均承载力随深径比的增加呈现出先降低后升高再降低的趋势,随面积密度的增加呈先升高再降低的趋势;摩擦因数随深径比和面积密度增加的变化趋势与平均承载力相反;织构的最优参数分别为深径比0.06,面积密度25%。因此,在人工髋关节表面设置合适参数的球形凹坑微织构可以提高油膜平均承载力和降低摩擦因数,从而起到减小关节的摩擦磨损提高人工关节使用寿命的作用。     

Experimental estimate of tribological characteristics of epilam-coated materials that operate in threaded joints under dry friction

Friction in the threaded joint of a screw and nut, the surfaces of which are treated by an epilam, is experimentally studied and an analytical engineering calculation of the coefficient of friction in this threaded joint is presented. Results of the study show the efficiency of the method for depositing a molecular film of the fluorine-containing surfactant (epilam) in order to reduce the friction losses in the screw-nut joint. It is shown that the coefficients of dynamic and static friction in the threaded joint are substantially smaller than those for the material without an epilam coating. The wear resistance of the epilam-coated materials increases due to the formation of a solid lubricant on the surfaces of the materials in contact. The results of the study show that the ultrathin epilam film prevents the occurrence of seizures in the threaded joint. The thermal tests have demonstrated that, after heating the epilam-coated material to a temperature of over 300°C, the coating loses its unique antifriction properties.     

Investigation of the friction effect at pin joints for the five-point double-toggle clamping mechanisms of injection molding machines

In this study, an analytical formulation for the necessary thrust of the crosshead of the five-point double-toggle clamping mechanism during real-mold clamping operation is proposed in order to investigate the effect of the friction at pin joints. The friction is considered to be a Coulomb friction. The inertia effects are not considered.Numerical examples are studied for different values of coefficient of friction to investigate the effects of friction at pin joints. In order to estimate the kinetic friction coefficient at pin joints, the motor torques required for real-mold clamping obtained by the present study are adjusted by using different values of coefficient of friction and mechanical efficiency to fit the experimental data.     

四轮独立驱动汽车多工况路面附着系数识别研究

四轮独立驱动（Four-wheel independent drive, 4WID）电动汽车具有较好的动力学稳定性协调控制潜力,轮胎-路面附着系数的识别是汽车操纵性能控制的基础。基于视觉传感器的路面识别方案成本高,传统卡尔曼滤波算法观测精度低且难以适应含有时变结构的非线性系统。众多研究已详细介绍均一路面附着系数的估计方法,尚未充分考虑对接和对开路面的观测方案。本研究将强跟踪理论（Strong tracking theory, STT）引入无迹卡尔曼滤波（Unscented Kalman filter, UKF）算法,构造强跟踪无迹卡尔曼滤波（Strong tracking unscented Kalman filter, STUKF）观测器,提高识别算法的识别精度,以及对时变附着系数的适应能力。考虑多重渐消因子计算过程的复杂性,本研究降低四轮路面识别模型的维数,构造两个含单重渐消因子矩阵的二维观测器,实时观测四个轮胎-路面附着系数。仿真和试验结果表明,与传统四维UKF算法相比,改进的并联STUKF算法能够更加有效地追踪转向或直行工况下均一路面、对接路面和对开路面的四轮附着系数。     

Friction coefficient for hexagonal boron nitride surfaces from ab initio calculations

The friction coefficient for two hexagonal boron nitride (h-BN) sheets was estimated on the basis of ab initio calculations. Several models, both cluster and periodic one, were applied to describe h-BN and the interactions between its dimers. In all cases, the gauche orientation is favoured, the interaction energies being virtually independent of the size of the model. The friction coefficient values, in contrast, converge towards the values from periodic calculations. At the lower limit of the periodic system, the friction coefficients vary between 0.226 and 0.265 depending on the orientations of the dimers. The calculations are in good agreement with an experimental study of the friction [Saito and Honda, Wear 237 (2000) 253], which suggested a friction coefficient of 0.23–0.25 for h-BN.     

蛇形机器人蜿蜒运动的摩擦机理及推进条件

针对带有从动轮的蛇形机器人,考虑实际结构中从动轮在蛇形机器人关节连杆上的安装位置,建立蛇形机器人蜿蜒运动的动力学模型。提出一种库伦-粘滞混合摩擦力模型,整体的库伦摩擦力特性和临界点处的粘滞摩擦力特性,避免了库伦摩擦力模型本身的非光滑性,以提高动力学模型的求解效率与计算稳定性。基于改进的动力学与摩擦力模型,利用摩擦系数比来表征法向与切向摩擦力的各向异性程度,通过对蜿蜒运动的仿真分析,讨论了摩擦系数比对前向运动速度与推进效率的影响规律,并对运动过程中蛇形机器人各个关节模块的速度和摩擦力变化进行了分析,明确了蛇形机器人蜿蜒运动的摩擦学机理,解释了蛇的蜿蜒抬起运动能够有效减少摩擦阻力而适用于高速运动的原因。最后通过带从动轮的蛇形机器人样机实验,对实现蜿蜒运动的摩擦学推进条件进行了验证。研究对于实现蛇形机器人的结构优化,步态规划与运动控制具有重要的理论意义与实际指导价值。     

Finite element analysis for friction noise of simplified hip joint and its experimental validation

In a hip joint system, squeak noise often occurs due to friction between the ball and hemispherical cup. To analyze the dynamic instability induced by friction in the hip joint system, the dynamic ball joint model was constructed by using the finite element method. The results from stability analysis revealed that the mode-coupling type instability occurred for one bending mode and its adjacent composite mode with the axial and transverse displacements with the increase of friction coefficient. The vitro squeak test and vibration modal tests confirmed that squeak arose near the frequency of the mode pair.     

考虑摩擦的结合面法向刚度分形模型及仿真

为了获得微动结合面较精确的法向接触刚度模型,研究影响接触刚度的因素,基于经典的G-W (greenwood-williamson)统计模型和分形模型,建立了考虑摩擦因素的结合面的接触刚度分形模型,并推导出了相应的刚度公式.通过数值仿真探讨了分形维数、摩擦系数、接触载荷、结合面积等4个因素对结合面法向接触刚度的影响.研究表明,所推导出的法向接触刚度模型能够有效模拟具有摩擦作用的结合面,结合面间的摩擦系数对法向接触刚度的影响与结合面的尺寸有很大的关系,结合面之间的分形维数、接触载荷、结合面积对法向接触刚度有很大的影响.     

Frictional characteristics of the beetle head-joint material

Frictional properties of the head part in the beetle head–thorax articulation were studied in two beetle species, Pachnoda marginata and Geotrupes stercorarius (Coleoptera, Scarabaeoidea). Using the microtribometer, the head part of the joint was brought into contact with the flat glass and slid along a distance of 120 μm. The friction experiment was carried out with two conditions of the head material: fresh and air-dried. The tribosystem, consisting of the sapphire sphere in contact with flat glass, was used for comparison. Frictional coefficient of the joint material on glass was significantly lower than that of the sapphire sphere on glass. The material of the joint cuticle is rather stiff and the surface is hydrophobic (the contact angle of distilled water was 88.3°). It is suggested here that the high stiffness of the joint material and hydrophobicity of the joint surface are parts of the mechanism minimizing friction in insect joints.     

Precision radial turning of AISI D2 steel

This paper compares finite element model (FEM) simulations with experimental and analytical findings concerning precision radial turning of AISI D2 steel. FEM machining simulation employs a Lagrangian finite element-based machining model applied to predict cutting and thrust forces, cutting temperature and plastic strain distribution. The results show that the difference between the experimental and simulated cutting force is near 20%, irrespectively of the friction coefficient used in the simulation work (approximately 19.8% for a friction of 0.25% and 18.4% for the Coulomb approach). Concerning the thrust force, differences of about 22.4% when using a friction coefficient of μ?=?0.25 and about 56.9% when using the Coulomb friction coefficient (μ?=?0.378) were found. The maximum cutting temperature obtained using the analytical model is 494.07°C and the difference between experimentation and simulation methods is 15.2% when using a friction coefficient of 0.25 and when using the Coulomb friction only 3.1%. Regarding the plastic strain, the differences between analytical calculations and FEM simulations (for the presented friction values) suggest that the finite element method is capable of predictions with reasonable precision.     

Performance Characteristics at the Rib Roller End Contact in Tapered Roller Bearings

Analytical and experimental work is presented to determine the nature of the coefficient of friction at the large rib roller end of a tapered roller bearing. The analytical work considers the dynamic equilibrium of a roller, and it is shown that for normal bearing speeds the inertial forces have negligible effect on the performance at the rib contact. Mathematical expressions for the frictional torque on a detached rib have been derived for the case of axially applied bearing loads.

Experimental work has been carried out to obtain the rib torque values for the detached rib of a tapered roller bearing. Experimental information has been presented to show the variation in the value of the coefficient of friction with the sliding speed and the Hertzian stress at the rib contact. It is observed that the condition of lubrication is an important factor influencing the performance at the rib and that for the hydrodynamic condition of lubrication, the value of the rib torque is very low.