滑模方法在分布式电动车容错控制上的应用

分布式电动车是一种由轮毂电机驱动的新型车辆.针对其驱动系统部分失效的情况下车辆发生跑偏等的问题,设计了一种基于滑模变结构控制的被动容错控制方法,该控制方法不需要精确的故障估计信息便能够对车辆进行有效控制.首先,讨论了可能发生的失效,建立了所需的车辆模型.而后,使用二自由度车辆模型作为参考模型,建立了基于横摆角速度、质心...     

A method for manufacturing a probe for a combined scanning tunneling and atomic-force microscope on the basis of a quartz tuning fork with a supersharp metal tip

A method for manufacturing a probe for a combined scanning tunneling and atomic-force microscope on the basis of a quartz tuning fork with a metal tip, which is equipped with an independent conductor, is described. When the probe is manufactured, the billet for a tip has the form of a rather small (in order not to change the frequency and quality factor of the quartz tuning fork) metal cone, which is glued to the end of the beam of the quartz resonator-tuning fork together with a carbon fiber as a conductor. A spark is used to form a melted ball at the vertex of the cone. The thickness of the cone near the ball is reduced to a diameter of <0.5 μm by the electrochemical technique, and the ball is then mechanically detached. The main advantage of this method is that it allows manufacturing a high-quality-factor force detector with a single super sharp and clean tip, which is made of platinum (or platinum alloys) and tungsten, with a yield of ≥80%.     

电机离心开关断开瞬时转速测量仪

离心开关断开转速是单相电动机的一个关键技术指标?由于电动机的起动过程很短，一般中小型电动机的起动时间都在1～3s内，所以在离心开关断开前后，电机转速变化很快。测量的难点是：(1)获得离心开关断开瞬时，既无时延又无稳定的信号；(2)准确的瞬时转速测量方法：该测量仪采用单片机为核心器件，当电机起动时，直接监测离心开关两端的电压来得到离心开关断开的瞬时信号；同时使用光电旋转编码器获取电机瞬时转动脉冲信号，经过光耦隔离后送单片机，测量电机瞬时转速.     

Protrusion recognition from solid model using orthogonal bounding factor

Feature recognition is important for describing shapes in many applications taking advantage of solid modeling. Graph-based feature recognition methods search from solid models the unique patterns of features that are represented as a graph. A typical example of such patterns is a loop of concave edges. When the loop is an inner loop on a single face, it is a strong hint of the existence of protrusion feature and recognition of protrusion faces is straightforward. However, when a protrusion feature lies on multiple faces, it is bounded by a loop of concave edges that are not on a single face. Consequently, the rule of inner loop is no more available and recognition of protrusion faces becomes unclear. To address this problem, a new quantitative measure, orthogonal bounding factor (OBF), is introduced. OBF is defined as the sum of cross products of two consecutive vectors normal to a set of faces, and it physically represents the possibility of being a protrusion in a solid model. The formal definition of orthogonal bounding factor is established and a method to recognize protrusion features using OBF is presented. Examples are also shown to demonstrate the effectiveness of the method for feature recognition.     

Finite element analysis for temperature distributions in a cold forging

In this research, the finite element method is utilized to predict the temperature distributions in a cold-forging process for a cambolt. The cambolt is mainly used as a part of a suspension system of a vehicle. The cambolt has an off-centered lobe that manipulates the vertical position of the knuckle and wheel to a slight degree. The cambolt requires certain mechanical properties, such as strength and endurance limits. Moreover, temperature is also an important factor to realize mass production and improve efficiency. However, direct measurement of temperature in a forging process is infeasible with existing technology; therefore, there is a critical need for a new technique. Accordingly, in this study, a thermo-coupled finite element method is developed for predicting the temperature distribution. The rate of energy conversion to heat for the workpiece material is determined, and the temperature distribution is analyzed throughout the forging process for a cambolt. The temperatures associated with different punch speeds are also studied, as well as the relationships between load, temperature, and punch speed. Experimental verification of the technique is presented.     

点在平面多边形内外的判断方法

在诸多研究领域中,判断点是否在多边形内是一个非常基本的问题。首先分析了解决这一问题的传统方法, 然后提出一种边界代数跟踪法对多边形进行栅格化,在此基础上设计出Flooding操作和轮廓腐蚀算法进行多边形内外点的判断。试验结果表明该方法具有健壮性好、适用于任意复杂多边形而无需对奇异情况进行单独处理等优点。     

A kinematic calibration method of a 3-DOF secondary mirror of the giant magellan telescope based on least square algorithm

Because of manufacturing and assembly errors in the geometric parameters of parallel robots, calibrating the parameters is necessary for improving the positioning accuracy. The objective of this study is a 3-DOF secondary mirror of the giant Magellan telescope, which is operated by a 3-DOF parallel robot. In this paper, a kinematic calibration method is presented. In this method, a moving platform is commanded to execute a sinusoidal movement by the cooperation of three piezoelectric actuators, and experimental data is obtained using capacitive sensors. The inverse kinematic and forward kinematic equations for the local system are illustrated in this paper. Furthermore, importantly, a least square algorithm is implemented to reduce the residual between the experimental values and expected values. Additionally, a simulation model is developed for supervising the movement of the system. Results of experiment show that the method used in this paper is effective and efficient.     

从“高深学问”到“大学文化”

高深学问及其构成的学科（专业）是大学存在的知识和组织基础。大学文化既是一种存在更是一种信仰,二者既有深刻联系又有质的区别。任何社会思潮是特定时代的产物,当大学文化缺失问题,特别是大学精神衰微现象成为时代关注的焦点并逐步进入到哲学领域时,大学文化哲学便产生了。从＂高深学问＂到＂大学文化＂是一个质的飞跃,以＂大学文化＂为逻辑起点,从整体上构建一个以＂大学文化既是一种存在更是一种信仰＂为核心的大学文化哲学的基本理论框架,是当今时代的强烈呼唤。其核心内涵是：大学的本质是一种以传承和创新文化为己任的功能独特的文化组织;大学更重要的是一种文化存在和精神存在;人文关怀和追求真理是大学应当坚守的＂永恒之魂＂;和谐文化的本质是一种信仰。当今我国大学的崇高使命是：坚持＂中国特色,综合创新＂的文化发展道路,创新和高扬当代中国大学精神,全面加强大学文化建设,大力增强我国大学核心竞争力,为实现中国特色大学理想和建设中国特色文化强国而奋斗。     

The effect of base replacement on the dynamic load carrying capacity of robotic manipulators

The problem of establishing the load carrying capacity of mobile base manipulators operated by limited force or torque actuators is presented. It is shown the maximum allowable load on a given load trajectory, is a function of base position. The load workspace is defined as the union of places where the base can be located on them and it carries a load by the manipulator on a desired trajectory. The load workspace is discretised into some grid points, and the base is positioned on each grid point. The recursive Newton-Euler method is used to compute the dynamic effects of the load and manipulator on each joint actuator, then the load carrying capacity of the mobile manipulator at each base location is computed by considering the manipulator joints and actuator torque constraints. By applying a simple procedure, a smaller subspace of the load workspace is selected, so that the load carrying capacity is near to a maximum. This procedure is repeated until the optimum base location is found so that the load carrying of the manipulator is a global maximum in the load workspace for the desired dynamic trajectory. Finally, the effect of base mobility on optimising the dynamic load carrying capacity for different robotic arms is investigated in separate case studies.     

汽车轮胎动力学特性研究

运用非线性动力学理论和Matlab 6．1对分别采用轮胎非线性模型和线性模型的汽车悬架的运动特性进行比较，结果表明轮胎的非线性特性对汽车悬架的动力学特性有很大影响，在高速运动、较大路面不平度过程中汽车悬架系统应采用非线性模型。     

Plate tearing by a cone

The present paper is concerned with steady-state plate tearing by a cone. This is a scenario where a cone is forced through a ductile metal plate with a constant lateral tip penetration in a motion in the plane of the plate. The considered process could be an idealisation of the damage, which develops in a ship bottom raking accident or a collision with a floating object. The deformation involves a complex mixture of large plastic deformations, fracture and friction. The observed mode of deformation is idealised by a simplified, kinematically admissible deformation mode, and the rate of internal energy dissipation in plasticity, fracture and friction is quantified accordingly by analytical expressions. The idealised mode has two free parameters which are determined from the postulate that they adjust to give the least rate of energy dissipation. The theory is compared to a series of measurements. The coefficient of friction was not measured, so the calculations are presented for different realistic values and it is shown that, for a coefficient of friction of about 0.2, there is a reasonably good agreement between theory and measurements for the in-plane resistance force as well as for the out-of-plane reaction force.     

Measuring the Quantitative Characteristics of Local Vortices on a Plane of a Deformed Material

A problem for determining the center, size, and spatial distribution of displacements of a vortex on the basis of a plane vector field is under consideration. A seed algorithm is proposed instead of typical contour scanning, and specific circulation is used as a criterion for determining the center of a vortex flow. In order to increase the stability of this algorithm, a parameter playing the role of a threshold is introduced. A Monte-Carlo method is used to study the influence of measurement errors on the accuracy in determining the coordinates of a hard rotation center, and the relationship between the false alarm probability and the threshold level is established. The use of the least squares method for calculating the spatial distribution of displacements is shown. This approach is demonstrated on the example of a real vector field measured in the vicinity of a main crack tip.     

Multimodel PD-control of a pneumatic actuator under variable loads

In this paper, a multimodel controller is designed and implemented to a variably loaded pneumatic actuator. A particular design of the pneumatic system with one PWM-driven switching valve is utilized which has a quasilinear input–output behavior under constant load conditions. Therefore, under a constant load, position control is properly accomplished by a linear PD-controller. In order to use the system in variable load applications such as robot actuators, a multimodel controller is designed based on the PD-controllers. For this purpose, a number of constant loads are considered and corresponding to each load, a linear model is identified and a PD-controller is tuned for the system. Then, a switching algorithm is applied which determines the best model and selects the corresponding controller in any load condition. Also, for the realization of the D-action in PD-controllers, a Kalman filter is designed to observe the velocity instead of direct differentiation of the output position. Experimental results indicate the high performances of the multimodel controller under variable load conditions.     

软件滤波器的快速设计

传统的数字滤波器的设计过程复杂,计算工作量大,滤波特性调整困难,影响了它的应用.本文介绍一种利用MATLAB辅助设计快速的方法,对于滤波器性能要求不是很高的情况下,能快速地设计出满足需要的滤波器.本文还介绍了如何使用C语言实现滤波器的功能.     

Robust and nominal stability conditions for a simplified model predictive controller

A new condition is derived that guarantees robust stability for a set of stable, linear time-invariant plants controlled by using a simplified model predictive control algorithm (SMPC). Discrete single-input-single-output control systems are considered in this paper. Uncertainty is treated in the time domain by considering the stabilization of a set of pulse response functions. The method presented is suitable for stabilizing a set of plants that are not necessarily related. Central to this method is a bounding function, which is a function of the model and controller parameters. The bounding function is designed to have a larger magnitude than all of the pulse response functions in the set of plants to be stabilized. Using this method, it was found that the bounding function is monotonically decreasing when a first-order plus dead-time model is used to design the controller. This allows the coincidence point used in SMPC to be employed directly as a tuning "knob" for robustness, and also simplifies the analysis for dead-time uncertainty. In addition, a comparison of two nominal stability conditions is provided.     

A precision frequency synthesizer with direct digital synthesis for a low-field magnetic-resonance imager

A frequency synthesizer of the microwave spectrometer of a magnetic-resonance imager (MRI) with a 0.06-T intensity of the basic magnetic field is described. The synthesizer is based on a programmable logic integrated circuit and a direct digital synthesis microcircuit. The synthesizer is capable of operating in a range up to 70 MHz with a 3-μHz tuning step, allowing one to use it in MRI systems with a basic magnetic intensity of up to 1.5 T. The unit is intended to store up to 16348 frequency values in its random-access memory, and the switching is carried out by a logic signal, the source of which can be, e.g., a pulse train programmer of the microwave spectrometer. The frequency switching rate is 1 kHz and higher. The synthesizer is loaded through a USB 2.0 standard interface.     

Post-buckling stability of orthotropic, linear elastic, rectangular plates under biaxial loads

The potential energy function in a neighborhood of the buckling point for a biaxially loaded, linear elastic, orthotropic, simply supported, rectangular plate is obtained from a perturbation analysis. The perfect system has two independent bifurcation parameters, the loads. The postbuckling behavior is stable, and a good estimate is found for the post-buckling deflection of the plate in terms of the loads. The orthotropic constitutive equation interacts with the biaxial loading to cause a bimodal buckling point for certain combinations of loads; this point is also stable. Away from the bimodal point, the equilibrium surface is described as a cusp cylinder. At the bimodal point, the equilibrium surface is a double cusp.     

Simulation on the motion of crankshaft with a slant crack in crankpin

A new model for vibration analysis of a crankshaft with a slant crack in crankpin is proposed, and the influence of crack depth on the transient response of a cracked crankshaft is investigated. A slant cracked shaft element is developed by deducing the local flexibility due to a slant crack. The frequently occurred slant crack in crankpin is studied, and a new finite element model of crankshaft including the slant crack in crankpin, which combines the slant cracked shaft element and Timoshenko beam elements, is derived. The support of engine block and the switching behaviour of the crack are considered, and the non-linear equation of motion for cracked crankshaft-bearing system is set up in a rotating coordinate system. The motion of a crankshaft of a four in-line cylinder engine with and without an initial crack is simulated. The influence of the crack depth on the transient response is investigated. The numerical simulation demonstrates that the current model is valid for simulating the motion of cracked crankshaft system. The results show that a useful foundation is laid for crack detection of crankshaft.     

Crack detection, localization and estimation of the depth in a turbo rotor

The goal of this paper is to describe an advanced method of a crack detection: a new way to localize position and to estimate depth of a crack on rotating shaft. As a first step, the shaft is physically modelled with a finite element method and the dynamic mathematical model is derived using the Hamilton principle; thus, the system is represented by various subsystems. The equations of motion of the shaft with a crack are established by adapting the local stiffness change through breathing and gaping from the crack to an undamaged shaft. This is the reference system for the given system. Based on a model for transient behavior induced from vibration measured at the bearings, a nonlinear state observer is designed to detect cracks on the shaft. This is the elementary NL-observer (Beo). Using the observer, an Estimator (Observer Bank) is established and arranged at the certain position on the shaft. When a crack position is localized, the procedure for estimating of the depth is engaged.