基于修正等速运动规律的自由曲面多轴加工刀轴序列优化方法

针对自由曲面多轴加工中起始位置处刀具相对工件速度、加速度不为零导致的一定程度刚性冲击现象,提出了一种基于修正等速运动规律的刀轴序列优化方法,通过控制工件坐标系中决定刀具姿态的两个约束角,使之变化遵循修正等速运动规律,获得了切削行上平稳变化的刀轴序列,避免了由于起始位置处刀具相对工件速度、加速度不为零导致刀具不能精准到达后续加工位置的现象。算例分析表明,该方法能产生平稳且光滑的刀轴序列,可一定程度改善机床运动性能,提高加工表面质量。     

Enhancing nugget size and weldable current range of ultra-high-strength steel using multi-pulse resistance spot welding

ABSTRACT

This paper presents an innovative approach that uses a pulse-profile to improve the welding quality of CP1180 steel in resistance spot welding process. Three pulses with two cooling times were used in the developed multi-pulse welding (MPW) schedule. The experimental results show that the first pulse increases the contact area between the sheets to improve the current flow pattern. The second pulse was designed to extend the sheet-to-sheet contact area and corona bond for preventing rapid nugget growth. Using these designs, the nugget size was maximised through the third pulse. The maximum nugget size using the designed MPW schedule was 18.5% greater than that of the single-pulse welding schedule and the weldable current range was extended by 130%.     

一种Chirplet神经网络自动目标识别算法

针对飞机目标的自动识别问题,提出一种联合特征提取与分类的Chirplet神经网络方法,实现一维高分辨率距离像的识别。Chirplet神经网络将Chirplet原子变换用于多层前馈神经网络结构的输入层,替换传统的激励函数对距离像序列进行特征提取;网络的分类部分由隐层和输出层组成。在训练过程中调整神经网络权值的同时,完成对Chirplet原子时频参数的自动调整,协调优化特征参数和分类器参数,使Chirplet神经网络同时实现特征提取和目标分类。对4类飞机目标的仿真测试结果表明,相比时频变换和Gabor原子网络等方法,具有四特征参数的Chirplet神经网络方法具有较高的识别率和抗噪性能。     

Durable,Sensitive, and Wide‐Range Wearable Pressure Sensors Based on Wavy‐Structured Flexible Conductive Composite Film

Flexible pressure sensors have potential applications in human motion monitoring and electronic skins. To satisfy the practical applications, pressure sensors with a high sensitivity, a low detection limit, a broad response range, and an excellent stability are highly needed. Here, a piezoresistive pressure sensor based on wavy‐structured single‐walled carbon nanotube/graphite flake/thermoplastic polyurethane (SWCNT/GF/TPU) composite film is fabricated by a prestretching process. Due to the random wavy structure, high conductivity, and good flexibility, the prepared sensor displays a low detection limit of 2 Pa, a wide sensing range of 0–60 kPa, and a high sensitivity of 5.49 kPa^?1 for 0–50 Pa. Furthermore, the sensor shows a remarkable repeatability of over 1.1 × 10⁴, 9.0 × 10³, and 2.0 × 10³ pressure loading/unloading cycles at 50 Pa, 500 Pa, and 30 kPa, respectively, and a fast responsibility of 100–150 ms of loading response time and 400–600 ms of relaxation time. Therefore, the pressure sensor is successfully adopted to monitor both the large‐scale human activities (e.g., walk and jump) and the small‐scale signals (e.g., wrist pulse). Furthermore, a sensor array is assembled to map the weight and shape of an object, indicating its various potential applications including human–machine interactions, human health monitoring, and other wearable electronics.     

地表移动带范围内建构筑物安全可靠性分析

地表建构筑物位于在生产矿山地表开采移动范围内，如果按照一般圈定地表移动范围原则判断建构筑物的安全可靠性，结果是不安全或者预留保安矿柱可保证安全。为分析地表移动带范围内建构筑物安全可靠性，采用FLAC3D软件建立数值模拟模型，对矿区地表移动进行分析研究，并结合建构筑物的破坏等级评判标准，可以更加合理地判断地表移动范围内建构筑物的安全可靠性，对存在相似条件的矿山具有一定的借鉴意义。     

Effect of Solute Elements and Cooling Rate on Strain in Brittle Temperature Range of Continuously Cast Strand

A micro-segregation model of solute elements in mushy zone withδ/γtransformation during solidification was established based on the regular hexagon transverse cross section of dendrite shape proposed by finite difference method under the non-equilibrium solidification condition.The model was used to calculate the non-equilibrium pseudo binary Fe-C phase diagram and the strain of steels induced by variation of temperature in brittle temperature range.On the basis of the phase diagram and the strain,the strain curve in brittle temperature range as a function of carbon content for continuously cast strand was introduced and obtained.Solute elements change the position of the strain curve.And cooling rate changes the position and the shape of the strain curve.The comprehensive formula of the strain as functions of solute elements and cooling rate in brittle temperature range has been obtained by nonlinear fitting program.     

High-resolution ISAR imaging of fast rotating targets based on pattern-coupled Bayesian strategy for multiple measurement vectors

Very high resolution inverse synthetic aperture radar (ISAR) imaging of fast rotating targets is a complicated task. There may be insufficient pulses or may introduce migration through range cells (MTRC) during the coherent processing interval (CPI) when we use the conventional range Doppler (RD) ISAR technique. With compressed sensing (CS) technique, we can achieve the high-resolution ISAR imaging of a target with limited number of pulses. Sparse representation based method can achieve the super resolution ISAR imaging of a target with a short CPI, during which the target rotates only a small angle and the range migration of the scatterers is small. However, traditional CS-based ISAR imaging method generally faced with the problem of basis mismatch, which may degrade the ISAR image. To achieve the high resolution ISAR imaging of fast rotating targets, this paper proposed a pattern-coupled sparse Bayesian learning method for multiple measurement vectors, i.e. the PC-MSBL algorithm. A multi-channel pattern-coupled hierarchical Gaussian prior is proposed to model the pattern dependencies among neighboring range cells and correct the MTRC problem. The expectation-maximization (EM) algorithm is used to infer the maximum a posterior (MAP) estimate of the hyperparameters. Simulation results validate the effectiveness and superiority of the proposed algorithm.     

Modeling for the electromagnetic properties and EMI shielding of Cf/mullite composites in the gigahertz range

The electromagnetic properties and EMI shielding effectiveness of C_f/mullite composites via the spark plasma sintering were intensively investigated in the gigahertz range (8.2–12.4 GHz). Experimental results have revealed excellent electromagnetic properties and a high value of EMI shielding effectiveness (nearly 40 dB) for C_f/mullite composites with 1.65 vol% carbon fillers at thickness of 2 mm. We quantitatively characterize the contributions of microstructural features to overall EMI shielding effectiveness using a micromechanics-based homogenization model. The EMI shielding effectiveness enhances with respect to the C_f volume concentration before the threshold. The increasing trend of EMI shielding effectiveness with respect to AC (alternating current) frequency can be attributed to enhanced conductivity at high gigahertz range. It is demonstrated that filler and frequency dependent interface effects are essential to obtain excellent electromagnetic properties of C_f/mullite composite. The present research can provide guidances for the design of ceramic-based composites applied in high-temperature EMI shielding devices.     

基于船载卫星通信三轴天线的跟踪搜索技术

针对船载卫星通信三轴天线跟踪系统,介绍了船载三轴天线的系统组成,提出了一种基于捷联惯导的船载三轴天线跟踪搜索技术。天线以目标地理角为中心,通过坐标转换将目标地理角转换为天线的目标甲板角,调整AEC三轴使其及时准确地跟随目标甲板角。目前,该方法已经成功应用于多种船载三轴天线。实践表明,该方法能够快速准确地搜索到目标卫星,并实现对目标卫星的稳定跟踪。