Underdetermined direction of arrival estimation with nonuniform linear motion sampling based on a small unmanned aerial vehicle platform

Uniform linear array(ULA)radars are widely used in the collision-avoidance radar systems of small unmanned aerial vehicles(UAVs).In practice,a ULA's multi-target direction of arrival(DOA)estimation performance suffers from significant performance degradation owing to the limited number of physical elements.To improve the underdetermined DOA estimation performance of a ULA radar mounted on a small UAV platform,we propose a nonuniform linear motion sampling underdetermined DOA estimation method.Using the motion of the UAV platform,the echo signal is sampled at different positions.Then,according to the concept of difference co-array,a virtual ULA with multiple array elements and a large aperture is synthesized to increase the degrees of freedom(DOFs).Through position analysis of the original and motion arrays,we propose a nonuniform linear motion sampling method based on ULA for determining the optimal DOFs.Under the condition of no increase in the aperture of the physical array,the proposed method obtains a high DOF with fewer sampling runs and greatly improves the underdetermined DOA estimation performance of ULA.The results of numerical simulations conducted herein verify the superior performance of the proposed method.

Exploration on 2D DOA Estimation of Linear Array Motion:Uniform Linear Motion

Generally,due to the limitation of the dimension of the array aperture,linear arrays cannot achieve two-dimensional(2D)direction of arrival(DOA)estimation.But the emergence of array motion provides a chance for that.In this paper,a generalized motion scheme and a novel method of 2D DOA estimation are proposed by exploring the linear array motion.To be specific,the linear arrays are controlled to move along an arbitrary direction at a constant velocity and snap per fixed time delay.All the received signals are processed to synthesize the comprehensive observation vector for an extended 2D virtual aperture.Subsequently,since most of 2D DOA estimation methods are not universal to our proposed motion scheme and the reduced-dimensional(RD)method fails to handle the case of the coupled parameters,a decoupled reduced-complexity multiple signals classification(DRC MUSIC)algorithm is designed specifically.Simulation results demonstrate that:a)our proposed scheme can achieve underdetermined 2D DOA estimation just by the linear arrays;b)our designed DRC MUSIC algorithm has the good properties of high accuracy and low complexity;c)our proposed motion scheme with the DRC method has better universality in the motion direction.

Development of a New Flux Switching Transverse Flux Machine with the Ability of Linear Motion

This paper proposes a new rotary flux switching transverse flux machine with the ability of linear motion(FSTFMaLM),in which both the stator and the rotor cores are made by using soft magnetic composite(SMC)materials.With the special design pattern,for the rotary motion model,the proposed machine can combine both the advantages of the flux switching permanent magnet machine(FSPMM)and the transverse flux machine(TFM).It can output with relatively high torque density,and as there is no windings or the magnets on the rotor cores,the proposed machine can operate in the high speed region to improve the output power.With the adoption of the SMC materials,the manufacturing of this machine can be quite easy.By stacking the rotor core together and prolong it with the determined length in the axial direction,in addition with the special control algorithm,the proposed machine can have the ability of the linear motion.In this paper,the operation principle of this machine has been explained and the design methods are also presented.To seek the better performance,the main dimension of the machine is optimized,and for the performance evaluation,the finite element method(FEM)is adopted.The proposed machine can be used for the electric driving systems,robotic systems or other applications where the linear motion ability is required.

NEW TYPE OF LINEAR ULTRASONIC MOTOR WITH TWO DEGREES OF FREEDOM USING LONGITUDINAL AND BENDING MODE

A new type of linear ultrasonic motor with two degrees of freedom (DOF) motion is presented. The concept of the new typical motor is based on the combination of a longitudinal and two bending modes. The construction and the operational principle of motor are described, and the elliptical motion of the driving point of the actuator is proved. Meanwhile, a prototype linear motor is designed by using the finite element method (FEM) and is constructed for experiments. The vibration modes are tested with the laser doppler vibrometer (PSV-300F), and the experimental results prove that the design requirements on the mode shape of the actuator and nature frequency are satisfied. The test run of the motor indicates that the operational principle of the motor and the design results are correct, and the output properties are also tested.

LINEAR ULTRASONIC MOTOR WITH 2-DOF USING LONG-ITUDINAL AND BENDING VIBRATION MODES

A two-degree-of-freedom（2-DOF） linear ultrasonic motor （USM） consists of a cylinder-shaped stator and a slider. Two bending vibration modes with orthogonality and one longitudinal vibration mode are excited in the stator by three groups of piezoelectric ceramic elements. The combinations of any one bending mode and the longitudinal mode mentioned above push the slider to move linearly in direction x or y. Some key issues for improving the motor output properties and efficiency are given. They include selection of the vibration modes, consistency of the modal frequencies, placement of the piezoelectric ceramic elements and the supporting plane, setting of pre-pressure, and influence of interfering modes.

船舶动力定位非线性模型预测控制

针对受船舶运动状态和推力饱和约束影响的动力定位控制问题,本文提出了一种非线性模型预测控制方法。依据多面体描述理论建立了船舶动力定位多面体描述偏差模型,针对上述模型采用线性矩阵不等式设计非线性模型预测控制器中的终端要素,并证明了闭环系统的稳定性。仿真结果表明:设计的控制器能在满足约束条件和受环境干扰条件下快速控制船舶稳定在计划航向和计划船位,验证了控制器的有效性和本质鲁棒性。

Decoupling Analysis for a Powertrain Mounting System with a Combination of Hydraulic Mounts

The existing torque roll axis(TRA) decoupling theories for a powertrain mounting system assume that the stiffness and viscous damping properties are constant. However, real-life mounts exhibit considerable spectrally varying stiffness and damping characteristics, and the influence of the spectrally-varying properties of the hydraulic mounts on the powertrain system cannot be ignored. To overcome the deficiency, an analytical quasi-linear model of the hydraulic mount and the coupled properties of the powertrain and hydraulic mounts system are formulated. The influence of the hydraulic mounts on the TRA decoupling of a powertrain system is analytically examined in terms of eigensolutions, frequency, and impulse responses, and then a new analytical axiom is proposed based on the TRA decoupling indices. With the experimental setup of a fixed decoupler hydraulic mount in the context of non-resonant dynamic stiffness testing procedure, the quasi-linear model of the hydraulic mount is verified by comparing the predictions with the measurement. And the quasi-linear formulation of the coupled system is also verified by comparing the frequency responses with the numerical results obtained by the direct inversion method. Finally, the mounting system with a combination of hydraulic mounts is redesigned in terms of the stiffness, damping and mount locations by satisfying the new axiom. The frequency and time domain results of the redesigned system demonstrate that the torque roll axis of the redesigned powertrain mounting system is indeed decoupled in the presence of hydraulic mounts (given oscillating torque or impulsive torque excitation). The proposed research provides an important basis and method for the research on a powertrain system with spectrally-varying mount properties, especially for the TRA decoupling.

Review of Linear Switched Reluctance Motor Designs for Linear Propulsion Applications

Linear switched reluctance motor(LSRM)and its applications in different industries have been an interesting research topic for the past few years.LSRMs have proved to be a suitable alternative in a variety of applications requiring linear motion.However,its use is not that popular which instigated an active interest in the evolution of newer LSRM configurations.Enhancement in its propulsion force along with the reduction in force ripples,weight,acoustic noise,and vibration have been the main objectives in recently proposed LSRM designs.In this paper,recently proposed LSRM designs are reviewed and analyzed.The paper presents a one-stop introduction and a complete update to the designs,both in terms of qualitative and quantitative parameters.In addition,it takes into account the challenges in the implementation of these designs.Based on a detailed comparison of these designs as presented in this paper,an appropriate design can be chosen for a given application.

Finite-time stability and stabilization of Markovian switching stochastic systems with impulsive effects

Many practical systems in physics, biology, engineer- ing and information science exhibit impulsive dynamical behaviors due to abrupt changes at certain instants during the dynami- cal processes. The problems of finite-time stab!lity analysis are investigated for a class of Markovian switching stochastic sys- tems, in which exist impulses at the switching instants. Multiple Lyapunov techniques are used to derive sufficient conditions for finite-time stochastic stability of the overall system. Furthermore, a state feedback controller, which stabilizes the closed loop sys- tems in the finite-time sense, is then addressed. Moreover, the controller appears not only in the shift part but also in the diffu- sion part of the underlying stochastic subsystem. The results are reduced to feasibility problems involving linear matrix inequalities （LMIs）. A numerical example is presented to illustrate the proposed methodology.

Extreme Dynamics on Electronic Cam Linear Drive

One of the requirements for modem production machine is versatility and easy reconfiguration to produce new products. The production machines use fixed gearing and mechanical cams in history. The cams were used for specific stokes and cam switches were used for commissioning of technological process. This solution has disadvantages in lower production speed and no flexibility of production. This article summaries practical steps for machine modernization and highlight practical problems in modernization of older production machine. The electronic cam with direct linear drive was used for traversal motion with high peak acceleration. This paper discusses cam stoke curve design, redesign and fitting.

直线电机运动系统输入到状态稳定性分析

直线电机是一种典型的直接驱动系统,具有高速度、高精度和大推力的优点,适用于各种高端装备中的精密直线运动场合。然而,直线电机运动系统的“零传动”特性,使得负载变化、非线性摩擦力、推力波动等扰动因素直接作用于系统,进而严重影响系统的性能和运动精度。为了分析扰动对系统状态的影响,针对直线电机运动系统进行建模并研究系统的输入到状态稳定性分析问题,提出一种基于李雅普诺夫方法的直线电机运动系统输入到状态稳定性分析方法,建立控制器增益与系统输入到状态稳定性之间的关系,为控制器增益的选取提供理论支持。

基于直线运动机构的大变倍比红外变焦成像系统

针对同时兼顾大范围搜索和精确识别目标的迫切需求,研制了一种大变倍比红外变焦成像系统,设计两片独立运动的变倍镜及一片补偿镜,通过两个变倍镜级联的方式获得大变倍比。结合系统运动镜片多及变焦曲线复杂的特点,采用直线运动机构实现镜片变焦运动,使用集成编码器及螺纹丝杆的直线电机作为驱动。通过有限元仿真开展了系统力学分析,所设计镜片最大位移为3.04×10^(-3)mm。成像系统适用于中波红外制冷式640×512焦平面阵列探测器,变倍比达到55倍。实验室成像及外场实景成像的结果表明,系统在焦距由6 mm至330 mm连续变化的过程中成像清晰、像质良好,验证了系统的连续变焦成像性能,该设计合理可靠。研究成果在搜索、跟踪、侦察、监视等方面有广阔的应用前景。

波浪能装置设计模型及其解析求解

本文通过对波浪能装置设计模型进行简化,得出一种快速且准确地提升波浪能转化效率的解决方案.首先,从分析波浪能装置在海水中的垂荡运动出发,将该装置简化为多自由度线性系统,通过分别对浮子和振子进行受力分析、建立微分方程,利用数值模拟的方式求解,给出浮子和振子从静止到进行垂荡运动各时刻的运动状态;然后,通过调节阻尼器阻尼系数的形式及其数值,计算出使得PTO系统平均输出功率最大的阻尼系数;最后,通过对弹簧刚度的稳定性检验说明该模型可拓展至其他不同的情况,具有普适性.本文模型对于提高波浪能装置的能量转换效率具有指导意义.

高速直线运动系统非线性摩擦力建模研究

在分析摩擦力非线性特性的基础上,针对高速直线运动系统建立了一种简单有效的空间摩擦力模型,引入附加摩擦力的概念描述了工作状态下扰动因素引起的摩擦力。分析并仿真了工作负载、移动单元质心偏移和运动耦合等扰动因素对摩擦力的影响,仿真与实验结果基本一致。提出的摩擦力模型更接近实际,拓宽了模型的应用范围,有望在高速直线运动系统轨迹跟踪控制中取得更好的效果。

基于运动序列分割的运动捕获数据关键帧提取

采用线性时不变系统把高维运动数据映射到低维状态空间;在低维状态空间中,定义了姿态之间的相似性度量;并采用误差平方和准则对时序的低维数据点集进行运动分割,分割点上的运动姿态被定义为关键帧.实验结果表明:该算法能够较好地提取出运动序列中的关键帧,并且这些关键帧能够很好地概括原始运动序列的内容.

图像法识别运动目标技术

讨论了图像法识别物体运动参数的基本原理和过程.通过分析,比较了每一个子过程中采用的图像处理方法的优劣,指出了图像法识别运动物体在目前存在的主要问题是目标样本库太大以及线性成像系统带来的对原始输入信号的干扰,影响了对运动目标的实时响应处理和智能化识别.

自由活塞式内燃发电机仿真研究

建立了自由活塞式内燃发电机模型,所建模型主要由自由活塞式内燃机与直线发电机两部分组成。在MATLAB/Simulink仿真环境下,将通过有限元验证的直线发电机数学模型嵌入到自由活塞式内燃发电机仿真模型中。分析讨论了耦合系统的运动特征,阐明了它与传统内燃机运动规律的差异;研究了活塞质量、负载、初始进气压力等参数对该耦合系统运动规律的作用。仿真结果表明,自由活塞在每个循环的上止点附近加速度远大于传统内燃机的加速度,且上止点随活塞质量、负载、初始进气压力等参数而变化,可以很容易地实现高压缩比。该仿真模型有利于进一步掌握自由活塞式内燃发电机的特性,并为自由活塞式内燃发电机的实际样机设计提供了理论依据。

转子与定子几何不对中引起的碰摩分析

研究一类与定子几何不对中的转子的碰摩模型。通过碰摩映射的建立，将非光滑运动的研究转化为该映射的动力学研究。从几何角度分析了转子碰摩的机理，并通过数值模拟发现该类转子碰摩具有非线性系统特有的分岔和混沌等现象。

机械系统运动稳定性分析的Routh-Hurwitz法

对机械运动中多自由度线性自治系统的运动稳定性分析有多种方法 ,但是这些方法不是受到使用条件的限制就是数学分析繁杂。本文利用劳斯 -赫尔维茨判据 (Routh -HurwitzCriterion)对上述系统的运动稳定性问题进行了研究探讨。给出的算例表明该方法较为简捷、实用。

磁悬浮微进给机构的PID控制

利用磁悬浮技术实现了微进给机构的运动部件与运行导轨之间的无接触支撑,消除了摩擦与磨损,克服了摩擦产生的金属粉尘污染问题。采用主动可控电磁阻尼系统,控制线圈的电流即可控制系统的阻尼,可根据实际应用场合,确定采用恒定阻尼还是时变阻尼。对磁悬浮微进给机构实施PID控制,并进行了仿真试验。结果表明:当阻尼恒定不变时,应使C_2=0.5～1.0,机构的位移控制超调量≤0.933％,绝对稳态误差值≤1.77～2.30μm;当采用时变阻尼系统时,位移控制超调量≤3.617％,绝对稳态误差值≤0.033μm,运动控制达到纳米级准确度。