汽车ABS滑移率的模糊滑模控制研究

汽车防抱死系统(ABS)是汽车制动过程中的一项基本安全措施,滑移率控制是汽车防抱死控制的重要部分。汽车制动时路况时时变化,汽车滑移率的动力学模型是一个时变、非线性、不确定系统。针对这一特点,将滑模控制运动到汽车防抱死制动控制中,设计了汽车滑移率的等效滑模控制器。为了消除滑模控制切换项带来的抖振,使切换控制项在保证鲁棒性能的同时尽可能小,利用模糊规则,对切换项进行模糊化,建立基于模糊切换控制的等效滑模控制器。仿真结果表明,滑模控制方法具有很好的鲁棒性能,加入模糊规则的等效滑模方法能很好的消除抖振现象。     

一种基于模糊边界层的转台伺服系统滑模控制器设计

针对飞行模拟转台位置伺服系统中存在的非线性摩擦环节,设计了一种补偿摩擦的模糊边界层滑模变结构控制器.在常规的准滑模变结构控制中引入模糊控制,利用模糊控制器来动态调整滑模边界层的厚度.通过MATLAB仿真,结果表明该控制器较好地协调了常规固定边界层滑模控制鲁棒性与平滑控制抖振之间的矛盾,有效地抑制了摩擦力矩的影响,保证了系统的快速性和鲁棒性,实现了高精度的位置跟踪.     

汽车AMT离合器的非线性滑模控制

汽车离合器的减振器具有分段非线性的弹性和阻尼特性，给机构式自动变速系统的控制带来困难。针对离合器接合过程，建立系统的单输入单输出非线性动力学模型，应用基于微分几何的反馈线性化方法，将原非线性系统等价为具有零动力学的线性化模型，然后设计滑模变结构控制器，仿真结果表明，非线性滑模控制跟踪精度高，鲁棒性好。     

基于滑模变结构控制的多轮独立电驱动车辆驱动防滑控

车辆在低附着路面起步或加速时,车轮极易发生滑转,严重影响车辆行驶动力性和稳定性。针对多轮独立电驱动车辆的驱动防滑控制问题,基于滑模变结构控制理论,设计了防滑控制算法,并设置平滑切换函数,减小转矩切换引起系统输出的抖振,通过滑模变结构控制器调节电机转矩,使车轮滑转率跟踪最优滑转率。在ADAMS/View与MATLAB/Simulink中分别建立车辆动力学模型和防滑控制器模型。机电联合仿真实验结果表明:该控制算法能够在车辆起步阶段或加速行驶时有效控制车轮滑转率,达到了提高车辆动力性的目的。     

滑模控制在气动伺服系统中的应用

分析了气动伺服控制系统中存在的非线性摩擦特性,并设计实验台,测定低速环境下基于直缸的气动伺服系统中的摩擦特性;将其作为全局滑模控制中的外干扰,通过改变控制器结构或调整控制参数来抑制干扰,使系统在响应的全过程都具有鲁棒性。数字仿真表明：滑模变结构控制方案较PD策略具有更好的动、静态特性及对参数变化和外界干扰的鲁棒性。通过在台面球XY轨迹气动控制系统中的实验研究,验证了滑模变结构控制器具有可行性和理想的轨迹跟踪性能。     

数控机床用磁悬浮系统非线性时变滑模变结构控制

为实现数控机床横梁磁悬浮系统悬浮气隙的精确控制,采用了非线性时变滑模变结构控制策略。首先,通过设计一种带有指数项的滑模面,使系统在任意初始状态下的状态变量都直接处于系统的滑模面上,实现对参数摄动和外部干扰的全局鲁棒性;然后,在此基础上设计了一种时变滑模控制器,并通过李亚普诺夫定理证明了该控制律的稳定性。仿真实验结果表明,非线性时变滑模变结构控制方法在保证系统全局稳定的前提下提高了滑模面的收敛速度,有效地削弱了抖振。     

采用分数阶趋近律的汽车ABS积分滑模控制研究

为研究和评价ABS性能,以单轮车辆模型为基础,建立了单轮车辆动力学模型、轮胎模型及滑移率与附着系数的数学模型。在此基础上,提出了一种采用分数指数趋近律的汽车防抱死制动系统滑模变结构控制策略。这里主要采用含积分的滑模函数来设计切换函数,并结合分数阶指数微分方程、F-函数定义与性质,设计了分数阶指数趋近律。然后以实现高精度的滑模控制为目标,推导得到控制器总的等效控制输出。同时,在Matlab/Simulink中进行系统建模和仿真实验。结果表明:相比整数阶的汽车防抱死滑模控制系统滑移率能够更快、更准的跟踪达到期望值,制动时间和制动距离明显降低。     

基于干扰观测器的时滞非线性切换系统滑模控制方法

为实现更加精准的时滞非线性切换系统滑模控制,应用干扰观测器设计一种新的系统滑模控制方法。构建时滞非线性切换系统模型,针对系统在发生结构变化时会产生复合干扰变化的情况,设计了一种非线性切换干扰观测器,实施系统不连续干扰的估计。通过 Backstepping 方法结合干扰观测器,设计一种切换滑模控制器,依据标量非线性特性打造一个滑模面,通过滑模控制器算法使时滞非线性切换系统能够满足滑模面的实际可达性条件,完成切换滑模控制器设计,实现系统的滑模控制。对设计的滑模控制方法进行测试,实验中选择的时滞非线性切换系统为一种变后掠翼 NSV 。实验结果表明,该设计方法能够实现较为准确地切入信号跟踪,表现出了很好的切换复合干扰估计性能。     

基于PSO的某稳瞄系统滑模变结构控制研究

针对某坦克瞄准镜稳定控制系统,考虑到其中二分之一传动机构间隙和上反射镜固定轴导致的黏性摩擦所引起的非线性时变特征,提出基于粒子群算法的模糊滑模变结构控制方法,旨在优化稳定控制系统滑模控制器的参数,增强系统鲁棒性,并有效弱化抖振。仿真结果表明,该设计可有效提高瞄控系统稳态精度,为坦克稳瞄系统的控制提供了一种切实可行的控制方案。     

机床横梁磁悬浮系统的动态积分滑模变结构控制器的设计

设计了控制悬浮高度的滑模变结构控制器和动态积分滑模控制器.动态积分滑模控制器可保持悬浮高度的稳定性,并能够有效降低滑模控制器抖振的发生.仿真研究结果表明,通过动态积分滑模控制器和传统的滑模控制器相比较可以得出,动态积分滑模控制器能够更好地实现稳定悬浮,具有很强的抗扰性并能够使系统具有较高刚度.     

液体润滑剂的黏度对边界滑移影响的实验研究

为了了解微纳米间隙中流体的流动特性,采用原子力显微镜对微纳米间隙中的固体和液体边界滑移进行了实验研究,主要研究了液体润滑剂的黏度对边界滑移的影响。实验中采用的固体样品为SiO2,液体样品为两种不同黏度的季戊四醇油酸酯,分子式为C77H140O8,黏度分别为32mm2/s和150mm2/s。采用相对速度法对实验数据进行了处理,结果表明,不同黏度的季戊四醇油酸酯和SiO2表面作用时都会发生边界滑移,黏度大,产生的滑移大。其原因是,随着黏度升高,邻近固体表面的液体分子与和固体表面相接触的液体分子之间的剪切力增大,可更加容易地克服固液界面间的作用力,更加容易产生边界滑移。     

A dual-purpose positioner-fixture for precision six-axis positioning and precision fixturing: Part II. Characterization and calibration

The kinematics, stiffness, and repeatability of a moving groove, dual-purpose positioner-fixture were determined experimentally. A dual-purpose positioner-fixture is an alignment device that may be operated in a fixture mode or a six-axis nanopositioning mode. When operated in fixture mode, experiments show standard deviation in repeatability of 11, 11, and 38 nm in x, y, and z; and 0.7, 0.3, and 0.3 μrad in θ_x, θ_y, and θ_z. The stiffness characteristics were shown to match predictions within 5%. When operated in nanopositioner mode, the device demonstrated 4 nm resolution and a range, of 40 μm × 40 μm × 80 μm in translation and 800 μrad × 800 μrad × 400 μrad in rotation. The fixture possesses a load capacity of 450 N and a natural frequency of 200 Hz when the fixture is preloaded to 225 N.     

A Further Discussion on Trends in the Development of Advanced Manufacturing Technology

This paper is a supplement to “Trends in the Development of Advanced Manufacturing Technology” (Yang and Wu in Chin. J. Mech. Eng., 39: 73, 2003) but delves deeper into it. It first points out the strategic status of manufacturing industry in state development. Then, a detailed analysis is given on the features and trends in the development of advanced manufacturing technology in a total of 12 points from three aspects: “precision,” “extreme,” and “culture” from the aspect of the product itself; “green,” “rapidness,” “saving,” and “efficiency” during the manufacturing process; and “digit,” “auto,” “integration,” “networking,” and “intelligence” in view of the manufacturing method. In addition, it emphasizes that all the above aspects should be based on two base points: “manufacture” and “machinery.” Finally, it puts forth the guiding ideologies for the development of advanced manufacturing technology and the aspects China should give priority to in development, while stressing on the principles of independence, innovation and “human orientation.”     

Loading strategies for a class of just-in-time manufacturing system

In this paper, based on the group technology and the just-in-time manufacturing concepts, two loading models for optimal utilisation of the processing capabilities of an integrated manufacturing system consisting of a set of heterogeneous workstations are developed. These loading models are developed to integrate and utilise the available information from both the bill of materials and the process plans. The objective functions for these models are: the maximum tardiness and the makespan. In these models, the production quantity of each customer order for any part or product always equals its corresponding demand quantity; each part requires a finite number of aggregated stages of operation; job splitting is allowed; and the processing priorities of all the jobs during the planning time horizon are specified based on a desirable dispatching rule. The proposed mathematical programming models are fixed charge problems which are solved by compatible mixed integer programming algorithms. Finally, to provide additional decision-making capabilities, based on these models and their corresponding solution algorithms, a compatible decision support system is suggested.Notation l(1 toL) the product index - t(1 toN) the component (e.g., job type) index - i(1 toN) the job type priority index - j(1 toM) the workstation index - r(1 toR) the processing stage priority index - k(1 toK) the due date priority index - J _i,j,r,k the job with the job type priority indexi of the customer with the processing stage priority indexr and the due date priority indexk which has to be processed at the workstationj - L _i,r,k the number of units of the job with the job type priority indexi of the customer with processing stage priority indexr and the due date priority indexk (e.g. demand quantities) - t _i,j,r the required time to perform the processing stage priority indexr of each unit of the job with the job type priority indexi at the workstationj - D _i,r,k the due date of the job with the job type priority indexi of the customer with the processing stage priority indexr and the due date priority indexk - s _i,j,r the required time for setting up the workstationj for processing the job with the processing stage priority indexr, and the job type priority indexi - X _i,j,r,k the number of units of the job with job type priority indexi of the customer with the processing stage priority indexr, and the due date priority indexk to be produced at the workstationj - l _i,j,r,k the idle time at the workstationj prior to processing the job with the job type priority indexi and the processing stage priority indexr with the due date priority indexk - V the maximum tardiness - W the makespan of the operation - Y _i,j,r,k=1 ifX _i,j,r,k>0 - Y _i,j,r,k=0 ifX _i,j,r,k=0 - _i,j,r,k a sufficiently large constant (e.g. _i,j,r,kL _i,r,k)     

Preparation of ultrafine α -Al2O3 using precipitation-azeotropic distillation method

Ammonium aluminum carbonate hydroxide (AACH) was prepared by a precipitation-azeotropic distillation method, which uses aluminum sulfate as the Al source and ammonium carbonate as the precipitant. Then, AACH was calcined into ultrafine α-Al₂O₃ powder. The factors that influence the dispersion property of ultrafine α-Al₂O₃ powder are discussed in this paper, such as the methods of adding materials, surfactant, and drying methods. The changes of the structure and property of ultrafine alumina in the thermal treatment process are also studied. The morphological structure and properties of AACH are characterized by DTA/TGA, SEM, XRD, and ICP measurements. The results show that ultrafine α-Al₂O₃ powder with a uniform particle size and well-distributed property can be synthesized only after aluminum sulfate atomizes into ammonium carbonate, proper amount of PEG1000 is added as the dispersant, and the product is treated by azeotropic distillation. The phase transformation of alumina during the calcination process can be described as amorphous Al₂O₃→γ-Al₂O₃→ϑ-Al₂O₃→α-Al₂O₃. The crystal grain size and density of ultrafine alumina powder increase with the increase of the calcination temperature. After AACH has been calcined at 1200°C for 2 h, the ultrafine α-Al₂O₃ with uniform particle size, spherical shape, and more than 99.97% purity is obtained and its powder is well dispersed. __________ Translated from Journal of Hunan University of Science & Technology (Natural Science Edition), 2007, 22(2): 35–39 [译自: 湖南科技大学学报(自然科学版)]     

高速数控加工中NURBS曲线拟合及插补技术的研究

通过分析现代数控系统中自由曲面插补算法的特点,提出了基于最小二乘法的NURBS曲线拟合算法和基于弧长参数补偿的NURBS插补技术。采用最小二乘法拟合NURBS曲线,能获得光滑的刀具加工路径,并且在一定范围内能复原曲线的设计轮廓。参数补偿的NURBS插补方法,以泰勒展开法得到的插补参数作为临时插补点,利用该插补法能显著减小速度波动,可将速度控制在理想的范围内,可进一步提高加工精度并减小数控机床的振动。仿真实验表明：该算法简明高效、易于实现,能够满足现代数控系统的要求。     

Studies of high temperature sliding wear of metallic dissimilar interfaces II: Incoloy MA956 versus Stellite 6

The development of wear surfaces formed during limited debris retention sliding wear of Incoloy MA956 against Stellite 6 between room temperature and 750 °C, and sliding speeds of 0.314 and 0.905 m s⁻¹ (7 N applied load, 4522 m sliding distance) were investigated. At 0.314 m s⁻¹, mild oxidational wear was observed at all temperatures, due to oxidation of Stellite 6-sourced debris and transfer to the Incoloy MA956; this debris separated the Incoloy MA956 and Stellite 6 wear surfaces. Between room temperature and 450 °C, the debris mainly took the form of loose particles with limited compaction, whilst between 510 °C and 750 °C the debris were compacted and sintered together to form a Co–Cr-based, wear protective ‘glaze’ layer. The behaviour was identical to that previously observed on sliding Nimonic 80A versus Stellite 6 at 0.314 m s⁻¹.At 0.905 m s⁻¹, mild oxidational wear was only observed at room temperature and 270 °C and dominated by Incoloy MA956-sourced debris. At 390 and 450 °C, the absence of oxide debris allowed ‘metal-to-metal’ contact and resulted in intermediate temperature severe wear; losses in the form of ejected metallic debris were almost entirely Incoloy MA956-sourced. This severe wear regime was also observed from 510 up to 630 °C, but increasingly restricted to the early stages of wear by development of a wear protective Incoloy MA956-sourced ‘glaze’ layer. This ‘glaze’ layer formed so rapidly at 690 °C and 750 °C, that severe wear was all but eliminated and wear levels were kept low.The behaviour observed for Incoloy MA956 versus Stellite 6 at 0.905 m s⁻¹ contrasts sharply with that previously observed for Nimonic 80A versus Stellite 6, in that the Incoloy MA956-sourced high Fe–Cr debris formed a protective oxide ‘glaze’, whilst the Nimonic 80A-sourced Ni and Cr oxides formed an abrasive oxide that at high sliding speeds assisted wear. The data indicates that the tendency of oxide to form a ‘glaze’ is readily influenced by the chemistry of the oxides generated.     

基于敏感参数分析的变矩器叶片参数研究

运用试验设计技术,研究了叶片进出口角、液流偏离角和损失系数等液力变矩器敏感参数,综合考虑这些敏感参数对最高效率、启动变矩比系数和力矩系数的影响,得到了它们之间的影响趋势,确定了影响因素的特定范围。改变泵轮的入口角度后,通过相关试验验证了效率变化的趋势。     

Antimicrobial effect,frictional resistance,and surface roughness of stainless steel orthodontic brackets coated with nanofilms of silver and titanium oxide: a preliminary study

Nano‐silver and nano‐titanium oxide films can be coated over brackets in order to reduce bacterial aggregation and friction. However, their antimicrobial efficacy, surface roughness, and frictional resistance are not assessed before. Fifty‐five stainless‐steel brackets were divided into 5 groups of 11 brackets each: uncoated brackets, brackets coated with 60 µm silver, 100 µm silver, 60 µm titanium, and 100 µm titanium. Coating was performed using physical vapor deposition method. For friction test, three brackets from each group were randomly selected and tested. For scanning electron microscopy and atomic‐force microscopy assessments, one and one brackets were selected from each group. For antibacterial assessment, six brackets were selected from each group. Of them, three were immediately subjected to direct contact with S. mutans. Colonies were counted 3, 6, 24, and 48 h of contact. The other three were stored in water for 3 months. Then were subjected to a similar direct contact test. Results pertaining to both subgroups were combined. Groups were compared statistically. Mean (SD) friction values of the groups 'control, silver‐60, silver‐100, titanium‐60, and titanium‐100' were 0.55 ± 0.14, 0.77 ± 0.08, 0.82 ± 0.11, 1.52 ± 0.24, and 1.57 ± 0.41 N, respectively (p = .0004, Kruskal–Wallis). Titanium frictions were significantly greater than control (p < .05), but silver groups were not (p > .05, Dunn). In the uncoated group, colony count increased exponentially within 48 h. The coated groups showed significant reductions in colony count (p < .05, two‐way‐repeated‐measures ANOVA). In conclusions, all four explained coatings reduce surface roughness and bacterial growth. Nano‐titanium films are not suitable for friction reduction. Nano‐silver results were not conclusive and need future larger studies.