Optimal Design of the Modular Joint Drive Train for Enhancing Cobot Load Capacity and Dynamic Performance

Automation advancements prompts the extensive integration of collaborative robot(cobot)across a range of industries.Compared to the commonly used design approach of increasing the payload-to-weight ratio of cobot to enhance load capacity,equal attention should be paid to the dynamic response characteristics of cobot during the design process to make the cobot more flexible.In this paper,a new method for designing the drive train parameters of cobot is proposed.Firstly,based on the analysis of factors influencing the load capacity and dynamic response characteristics,design criteria for both aspects are established for cobot with all optimization design criteria normalized within the design domain.Secondly,with the cobot in the horizontal pose,the motor design scheme is discretized and it takes the joint motor diameter and gearbox speed ratio as optimization design variables.Finally,all the discrete values of the optimization objectives are obtained through the enumeration method and the Pareto front is used to select the optimal solution through multi-objective optimization.Base on the cobot design method proposed in this paper,a six-axis cobot is designed and compared with the commercial cobot.The result shows that the load capacity of the designed cobot in this paper reaches 8.4 kg,surpassing the 5 kg load capacity commercial cobot which is used as a benchmark.The minimum resonance frequency of the joints is 42.70 Hz.

Joint Return Value Estimation of Significant Wave Heights and Wind Speeds with Bivariate Copulas

The joint design criteria of significant wave heights and wind speeds are quite important for the structural reliability of fixed offshore platforms.However,the design method that regards different ocean environmental variables as independent is conservative.In the present study,we introduce a bivariate sample consisting of the maximum wave heights and concomitant wind speeds of the threshold by using the peak-over-threshold and declustering methods.After selecting the appropriate bivariate copulas and univariate distributions and blocking the sample into years,the bivariate compound distribution of annual extreme wave heights and concomitant wind speeds is constructed.Two joint design criteria,namely,the joint probability density method and the conditional probability method,are applied to obtain the joint return values of significant wave heights and wind speeds.Results show that(28.5±0.5)m s^(-1)is the frequently obtained wind speed based on the Atlantic dataset,and these joint design values are more appropriate than those calculated by univariate analysis in the fatigue design.

Joint Transceiver Designs for Full-Duplex MIMO SWIPT Systems Based on MSE Criterion

For the simultaneous wireless information and power transfer(SWIPT), the full-duplex MIMO system can achieve simultaneous transmission of information and energy more efficiently than the half-duplex. Based on the mean-square-error(MSE) criterion, the optimization problem of joint transceiver design with transmitting power constraint and energy harvesting constraint is formulated. Next, by semidefinite relaxation(SDR) and randomization method, the SDRbased scheme is proposed. In order to reduce the complexity, the closed-form scheme is presented with some simplified measures. Robust beamforming is then studied considering the practical condition. The simulation results such as MSE versus signal-noise-ratio(SNR), MSE versus the iteration number, well prove the performance of the proposed schemes for the system model.

Subsection method of fatigue design for welded joints treated by ultrasonic peening

Concerning the notable difference between the S-N curve slope of welded joints treated by ultrasonic peening treatment （UPT） and that of as-welded joints, the subsection method is put forward for fatigue design of welded joints treated by UPT, using the design method of nominal S-N curves. Results show that, in medium life zone, strength grade of the fatigue design curves for UPT welded joints is two grades higher than that for as-welded joints. Furthermore, in medium life zone, strength grade of the fatigue design curves for UPT welded joints is three grades lower than that in long life zone. Conclusion of the comparison is that as for different joint types in different life zones, fatigue design should be processed according to different S-N curves respectively.

Joint Transceiver Design for OFDM Systems

Orthogonal Frequency Division Multiplexing(OFDM) is an effective technique to deal with a frequency selective channel since it can convert the channel into some flat fading subchannels.However,very different output SNR values of the subchannels will lead to poor bit error performance when a linear equalizer and Equal Bit Allocation(EBA) are adopted in OFDM systems.So,we proposed three novel nonlinear Joint Transceiver(JT) schemes based on Zero-Forcing(ZF) criterion and Minimum Mean Square Error(MMSE) criterion respectively,which can transform all subchannels of an OFDM system into subchannels with identical channel gain.Thus,EBA is equivalent to the Optimum Bit Allocation(OBA) for these subchannels.Numerical analysis helps us to obtain the theoretical approximate BER values of the JT scheme.Simulation results verify the numerical analysis and confirm that the performance of our proposed JT scheme greatly outperforms the traditional linear equalizer with EBA at moderate and high SNR values.

Nonlinear Finite Element Analysis and Optimum Design of Spot-Welded Joints and Weld-Bonded Joints

Resistance spot welding and hybrid weld bonding have wide applications in the body work construction within the automobile industry. The integrity of the spot welds and applied adhesives determines the body assembly rigidity and dynamic performance. Incorporating contact nonlinearity and geometric nonlinearity, finite element analysis (FEA) have been carried out to investigate the structural stiffness and strength of both spot-welded and weld-bonded assemblies. Topology optimization has been performed to reveal the distributions of material effectiveness in the overlap regions and suggest a feasible method for removing underutilized material for weight reduction. Design optimization has been conducted with an aim to reduce the maximum von Mises stress in the assembly to minimum by choosing optimum values for a set of design variables, including the weld spacing, weld diameter and overlap width.

Design of a Modified Cassegrain System Used in Joint Transform Correlator

In order to detect and recognize infrared target with joint transform correlator,a modified Cassegrain optical system is designed.The main advantages of the system are large field-of-view,infrared dual-band common optical path and compact structure.In the modified Cassegrain optical system,the working wavelengths are 3.7~4.8μm and 8~12μm,the field-of-view is 4° and the aperture is 240mm.The paraboloidal primary mirror and hyperboloidal secondary mirror are all replaced by spherical surfaces.So the problems of high machining accuracy and alignment become much easier.In order to balance the aberrations,three compensating lenses are used in the system.The total length of the system is 183mm,and the ratio of the total length to focal length is 0.68.Moreover,the system has a good performance of athermalization between negative 40℃ and positive 60℃.The design results of the system show that the MTF value of each field is greater than 0.72 when the cut-off frequency is 11lp/mm.Due to the excellent image quality of the modified optical system,the ability of Joint transform correlator(JTC)applied in target tracking and identification has been improved for further.

Shape design of the reinforcement for bending load-carrying capacity of under-matched butt joint under four-point bending load

To improve the bending load-carrying capacity （ BLCC） of under-matched butt joint under four-point bending load in the elastic stage, the shape design of the reinforcement is studied based on the theoretics of mechanics of materials. The concept, criterion, realization condition and design proposal of equal bending load-carrying capacity （EBLCC） are put forward. The theoretical analysis results have been verified by the finite element method. The simulation results are coincident basically with the ones of theoretical analysis. The research results show that the shape design of the reinforcement of EBLCC can improve BLCC of under-matched butt joint and the unilateral-side type reinforcement can replace double-side symmetry

Design and Analysis of Tapered Stress Joint for Top Tensioned Riser System

Stress Joint （SJ） plays a key role in the Top Tensioned Riser （TTR） system for deep water engineering. A preliminary design method of tapered SJ is proposed in the paper, which could help designers obtain accurate design data. After a further sensitive analysis is carried out, the related parameters choice and control methods are recommended in the engineering practice. By taking the extreme environment conditions into consideration, the effects of bending stress reduction and curve control are analyzed, and the 3-D FE models are established by ABQOUS for numerical evaluation to verify the correctness of design results. At last, dynamic analysis and fatigue analysis, based on actual project, are carried out with designed stress joint. The analysis results prove the feasibility and guidance of this method in the practical engineering applications.

Study on solder joint reliability of ceramic ball grid array component based on design of experiment method

Four process parameters, pad diameter, stencil thickness, ball diameter and stand-off were chosen as four control factors. By using an L25 （5^6 ） orthogonal array the ceramic ball grid array （ CBGA ） solder joints which have 25 different combinations of process parameters were designed. The numerical models of all the 25 CBGA solder joints were developed using the Sugrace Evolver. Utilizing the sugrace coordinate exported from the 25 CBGA solder joints numerical models, the finite element analysis models were set up and the nonlinear finite element analysis of the CBGA solder joints under thermal cycles were pegrormed by ANSYS. The thermal fatigue life of CBGA solder joint was calculated using Coffin-Manson equation. Based on the calculated thermal fatigue life results, the range analysis and the variance analysis were pegrormed. The results show that the fatigue life of CBGA solder joint is affected by the pad diameter, the stencil thickness, the ball diameter and the stand-off in a descending order, the best combination of process parameters results in the longest fatigue life is 0.07 mm stand-off, 0.125 mm stencil thickness of, 0.85 mm ball diameter and 0. 89 mm pad diameter. With 95% confidence the pad diameter has a significant effect on the reliability of CBGA solder joints whereas the stand-off, the stencil thickness and the ball diameter have little effect on the reliability of CBGA solder joints.

公路隧道二衬钢筋装配化螺栓的接头设计

针对公路隧道二衬钢筋现场焊接、绑扎效率低、质量控制难度大的弊端,基于直线型混凝土软化本构模型及钢筋应力应变关系,推导得到钢筋混凝土衬砌截面的极限承载力计算式.结合螺栓连接面极限承载力,以应力分布系数作为控制因素,将轴心压缩状态、大小偏心分界点以及纯弯状态时的最危险截面作为特征截面,控制钢筋混凝土截面极限承载力以及螺栓连接面极限承载力在特征截面处的大小,得到连接面处螺栓的设计方法 .选取某隧道隧址围岩参数及其断面尺寸、支护参数,运用得到的螺栓设计方法进行螺栓选型并设计连接面处的螺栓分布,给出钢筋预制节段的划分方案,通过数值模拟验证了二衬钢筋装配化螺栓的接头设计的合理性.研究结果表明:钢筋骨架采用螺栓装配化预制连接后,二衬结构的应力进行了重分布,应力与变形的增长速率放缓,并逐渐稳定.最终,左拱肩和左拱脚处的应力分别降低58%和53%,位移量同样有不同程度的降低;在拱底螺栓连接面,应力相较提高,但由于螺栓的高承载性能,隆起量反而有所降低,充分发挥了螺栓的性能,实现了结构优化.

台风作用下轻钢屋面自攻钉节点的静力-疲劳统一设计模型

对已受疲劳损伤的V125型屋面板自攻钉节点进行静力拉伸试验,获得该类节点在不同幅值疲劳加载作用后的剩余承载力,并分析其在受静载作用下的损伤演化过程,提出了风致疲劳作用下的承载力折减及退化系数计算方法,建立了静力-疲劳统一设计模型.根据实验结果,推导拟合了风速与风致疲劳折减系数的相关关系.根据我国沿海11个城市的台风风速概率信息,给出了适用于相应城市的V125型自攻钉节点的静力-疲劳承载力退化模型.结果表明:V125型自攻钉节点的疲劳极限为其静力极限承载力的20%;在风致疲劳作用下,中国台北的轻钢屋面自攻钉节点的疲劳损伤折减系数最大,上海地区自攻钉节点的疲劳损伤折减系数最小.

创建行动导向下美丽乡村联创联建的规划设计方法探索

伴随着浙江省乡村发展愿景从“千万工程”到“美丽乡村”再到共同富裕的纵深推进,以单个行政村为单元的美丽乡村创建模式已经难以适应新的发展诉求。基于自然资源禀赋或基础设施地理空间连续性的美丽乡村联创联建工作,是破解各行政村独立发展的多重瓶颈的创新性尝试。针对具有明确的目标、资金、时间约束的美丽乡村创建行动,基于“产业-空间协同发展”的总体思路,试图探讨一种面向美丽乡村联创联建的规划设计方法,即“二阶三心法”。这一方法从乡村地区的存量资源切入,旨在系统性、创造性地回应创建行动目标,开展面向产业-空间复合型目标的空间规划干预:一是基于“土地矛盾最小化原则”进行空间节点设计,二是基于“空间投入-融合效益最大化原则”形成特色主线,三是基于“优先塑造-示范带动原则”打造示范样板。进一步的,结合湖州市道场乡菰城片区规划设计工作,探讨了该方法在产业策划和空间设计层面落地应用的关键问题和解决策略,为中国先发地区美丽乡村联创联建的规划设计工作提供经验借鉴。

基于通感融合的无人机预编码及飞行轨迹设计

无人机(UAVs)具有机动性强,低成本及易部署等特性,通过搭载通信及感知设备,支持通信与感知技术的高效资源共享,无人机可作为融合通信与传感技术的高性能空中平台。该文针对多输入多输出(MIMO)无人机使能的联合通信、感知场景,综合考虑无人机飞行能量、多天线传输及用户业务需求等限制条件,建模无人机通信、感知预编码及飞行轨迹联合优化问题为多目标优化问题,以实现通信用户最低速率最大化及目标最小发现概率最大化。由于通信用户最低速率最大化问题为非凸优化问题,难以直接求解,将原优化问题分解为通信预编码设计子问题及无人机轨迹设计子问题,并采用交替迭代法依次求解两个子问题直至算法收敛,其中,对于通信预编码设计子问题,提出一种基于迫零(ZF)算法的求解策略;对于无人机轨迹设计子问题,提出一种基于连续凸逼近(SCA)算法的求解策略。基于所得到的无人机最优轨迹,将无人机感知位置选择问题建模为加权距离和最小化问题,进而应用泛搜索算法优化确定目标感知位置,并设计基于ZF算法的通信感知预编码联合优化策略,以实现通信感知性能的联合优化。最后通过仿真验证了该文所提算法的有效性。

考虑多种作用效应的表面防渗聚脲涂层非线性分析及设计

聚脲与聚氨酯相比,具有绿色环保、耐久性好、力学性能优异、施工面适应性强等优势,聚脲基防渗层被广泛应用于水工结构中。鉴于防渗聚脲尚无成型的结构设计计算理论,惯常采用的经验性设计可能会导致不安全、不合理、不经济的设计结果,本研究通过探讨聚脲基表面防渗涂层非线性分析的关键理论,基于有限单元法建立了非线性数值模型。在涂层基面开裂、水压荷载作用、伸缩缝变形等不同受力工况下,通过对材料的受力变形行为、剥离行为、破坏模式等分析,总结了涂层受力变形规律,并基于分析结果,提出表面防渗聚脲设计流程。研究表明:对于水压作用下的涂层基面开裂工况,涂层最大应力随水压荷载、粘结强度增大而增大,随开裂宽度变化不显著,涂层剥离长度随粘结强度增大而减小,随开裂宽度增大而增大;对于伸缩缝变形工况,涂层剥离长度均随涂层厚度增大而增大,涂层剥离长度随伸缩缝变形量增大而增大,随粘结强度增大而减小,剥离长度随水压荷载变化趋势不显著;涂层最大应力随涂层厚度增大而减小,随粘结强度增大而增大,随水压荷载增大而逐渐增大。最终基于数值分析结果提出了考虑伸缩缝变形工况下的聚脲涂层结构设计方法,形成设计流程并计算机软件化。

四川大学博物馆结构设计重难点分析研究

四川大学博物馆采用钢框架结构体系,并设置屈曲约束支撑改善结构的抗震性能。介绍了四川大学博物馆的结构设计参数及抗震性能目标。针对结构设计中的重难点,开展了屈曲约束支撑的工作机理分析、框架柱计算长度与穿层柱分析、东侧大悬挑空间的相关分析。利用反应谱分析及时程分析探究了屈曲约束支撑工作机理,分析结果表明,屈曲约束支撑能够有效改善钢结构产生塑性铰的状况,起到保护主体钢框架的作用。针对东侧大悬挑空间的功能要求,设计采用了屋顶桁架结合钢拉杆吊挂东侧大楼梯的结构形式,通过结构防连续倒塌分析、楼板应力分析、楼盖舒适度分析、关键节点有限元分析等确保该部位结构设计安全合理。对整体结构受力机理和薄弱部位进行了研究,提出了重点部位的设计原则和加强措施。

高超声速喷管流场不均匀性分析与改进

飞行器的发展,对风洞不同模拟条件下气动和操稳特性的准确预测提出了更高需求。风洞流场品质是影响试验数据精准度的主要因素之一,本文以某风洞马赫数5.5喷管为研究对象,开展喷管出口流场不均匀性研究。通过数值计算捕捉喷管内部微弱波系结构,分析喷管型面设计方法、型面加工精度和型面拼接处阶差等因素对喷管出口流场品质的影响,并与风洞流场校测结果进行对比分析,得出目前影响喷管出口流场品质的主要因素是拼接处阶差,并针对该因素提出了改进策略,通过对喷管合理分段减少波系对试验区域影响,以进一步提升风洞流场品质。

基于数据失真的雷达通信一体化OFDM波形设计方法

正交频分复用(OFDM)波形设计是实现雷达通信一体化的物理层关键技术之一。OFDM波形通常存在峰均功率比(PAPR)高,以及波形自相关旁瓣电平高的问题。该文针对现有联合降低PAPR和自相关旁瓣方法存在的通信速率下降问题,提出了一种基于数据失真的一体化波形设计方法。该文还将通信数据的误差矢量幅度作为优化目标之一,降低了数据失真引起的通信误码率。首先,构建了PAPR约束下最小化积分旁瓣比和误差矢量幅度的优化模型。其次,根据调制星座图特点,通过外围星座调制的数据失真和所有调制数据失真,将多目标高维非凸优化问题转化为两个单目标优化子问题,分别采取凸松弛操作和交替方向乘子法(ADMM)求解简化后的子问题,得到低积分旁瓣比波形和PAPR约束下的低误差矢量幅度波形。仿真结果表明该方法设计的一体化波形可满足PAPR要求,同时具有良好的感知和通信性能。

超大跨度张弦结构多索索夹偏心节点设计及有限元分析

对于超大跨度张弦结构,其撑杆下端的索夹节点是影响张弦结构成型的关键因素。由于外圈环向索的受力较大,超大直径拉索的捻制成型工艺尚未成熟,外圈环向索需采取并排多索的形式才能满足其受力要求,索夹节点相连构件数量多且受力大。基于贵阳奥林匹克体育中心(二期)主体育馆项目大跨度弦支穹顶结构,分析多索索夹节点的设计重难点,通过综合对比多种索槽布置方式,提出适用于超大跨度张弦结构的多索索夹偏心节点,并对该偏心节点进行整体受力和节点有限元分析。结果表明,多索索夹偏心节点对结构索力分布影响较小;该偏心节点设计符合计算假定,具有较高的承载力和抗滑移能力,有效解决了多索索夹节点连接、索夹安装及拉索更换等问题。