Application of acoustic emission sensing to slip detection in robot grippers

This paper discusses the application of acoustic emission signal analysis as a sensing tool for the detection of contact and slip related motion between a workpiece and an end effector. Some results from past work in this area are first reviewed. Different modes of slip motion (rotational and translational) are then discussed. The ability to distinguish between these slip modes is important since it enables the robot to assess the gripping stability and recover positional control of the workpiece. Experimental results are presented to demonstrate the sensitivity of the detected acoustic emission signal to these different modes of slip motion. The effects of the gripping force on the detected acoustic emission is also discussed.     

药筒筒体旋压工艺参数影响分析

通过数值模拟方法,分析了错距值、压下量等旋压工艺参数对药筒筒体加工质量的影响.采用弹塑性材料模型和库伦摩擦模型,以旋轮的径向旋压力、工件变形速率和内径胀缩量为研究对象,得到了径向旋压力,内径尺寸胀缩量和变形速率在不同错距值和径向力均方差下的变化规律.模拟结果表明,错距值与压下量的不同匹配,对旋轮径向力影响很大,工件内径胀缩量随错距值增大呈U形变化,径向力均方差在0.95 mm时,变形速率最大.     

凸轮型面摆动磨削残余应力有限元建模及分析

为分析摆动磨削工艺参数对表面残余应力的影响规律,基于热-力顺序耦合理论,建立基于温度场的凸轮残余应力有限元仿真模型,研究摆动频率、摆动幅度、砂轮线速度、磨削深度、工件转速、砂轮宽度、砂轮直径等工艺参数对凸轮型面残余应力的影响规律。结果表明：残余应力随工件转速、磨削深度、砂轮线速度的增加而增加,随砂轮宽度的增加先增加然后趋于平缓,随砂轮直径的增加而减少,随摆动频率与摆动幅度的增加而缓慢增加。     

振动式滚磨光整加工过程中的受力测试与分析

目的测试不同加工参数对振动式滚磨光整加工过程中作用力的影响,对实际加工过程中加工参数的选择提供一定的数值指导。方法通过改变偏心块夹角、固定工件埋入深度及固定工件装夹角度,应用动态式压力传感器测试每种加工参数对加工作用力的影响。结果偏心块夹角不同时,磨料的运动形态及运动轨迹差异明显,且偏心块夹角大小对工件的作用力影响显著,偏心块夹角为90°时磨料螺旋运动显著,加工效果好。固定工件埋入深度越深,其所受作用力越大;超过一定范围时,作用力陡增。通过改变固定工件装夹角度,观察磨料流态并测试工件不同装夹角下所受作用力,分析得到在装夹角为20°时磨料会以工件为中心聚集,工件所受作用力最大。结论偏心块夹角不同,磨料的运动流态及对工件的作用力不同,偏心块夹角为90°时光整加工效果最好。埋入深度对工件作用力影响显著,加工过程中应根据工件的加工要求确定合适的埋入深度。固定工件装夹角度不同,磨料流态变化明显,固定工件装夹角为20°时工件所受作用力最大,需根据实际加工要求确定装夹的具体角度。     

机器人气动夹持力的CNN-LSTM建模估计方法

由于气动系统具有迟滞、强非线性特性，难以直接依据气压信号实现气动夹持力的有效控制，因此采用建模估计夹持力是实现无力传感器低成本控制的有效途径。为此，提出一种基于卷积神经网络(CNN)优化的长短期记忆神经网络(LSTM)低成本气动夹持力估计方法。根据工业机器人末端气爪夹持力与气路历史输入/输出有关的特点，采用了具有记忆特性的LSTM网络建立无传感器气压/压力估计模型;针对直接采用LSTM网络进行建模存在误差大的问题，利用CNN提取输入信息中气压和夹持力的非线性关系，进一步对LSTM网络结构进行优化，提高模型描述气压和夹持力之间多值对应特性与非线性迟滞特性的能力，实现气爪的夹持力有效估计。实验结果表明：相比LSTM预测模型，所提模型的建模估计与验证估计均方根误差分别减少77.14%和70.83%，最大误差分别减少79.80%和78.84%,证明了所提建模估计方法的有效性。     

TC4钛合金钻削力和钻削温度仿真研究

为了提高TC4钛合金的可钻削性,采用有限元分析软件AdvantEdge建立TC4钛合金铣削加工有限元模型,分析工件和刀具上的温度分布规律,获得了钻削加工过程中钻削参数对钻削力和钻削温度的影响规律。结果表明：钻削TC4钛合金时最高温度出现在切屑上;钻削力随着主轴转速和进给量的增加而增大,随着钻头直径的增大而减小;钻削温度随着主轴转速、进给量和钻头直径的增加而增大。     

Dimensional errors in longitudinal turning based on the unified generalized mechanics of cutting approach.: Part II: Machining process analysis and dimensional error estimate

The model presented in the first part of this work is used here to estimate the diameter error in the most common turning operations. In fact, the diameter error is considered as a variable depending on the deflections of the tool, workpiece holder and workpiece, which are considered the main factors responsible for the machining accuracy. The proposed model has been applied to the three most common turning schemes related to workpiece fixturing, where the workpiece is clamped in a chuck, or supported between two centers, or clamped in a chuck at the spindle and supported on a center at the tailstock. Some numerical examples have been computed using the proposed model to predict the diameter error along the workpiece and the cutting force along the workpiece axis, as well as the influence of the cutting force components on the error prediction. The results provide additional insight into error formation in the turning process. Finally, some experimental tests have been carried out in order to validate the developed model. Good agreement has been obtained between numerical and experimental results. The proposed model represents a first step towards accuracy control in machining operations and, thus, towards optimization of the manufacturing process.     

管件电磁成形电磁力分布特性分析

本文基于安培力定理建立了管件电磁成形时径向和轴向电磁力的计算公式 ,直观描述了线圈 -工件系统几何参数与电磁力幅值的对应关系 ,阐述了轴向电磁力对提高材料成形性能的作用 ,用数值方法分析了径向和轴向电磁力的分布特性。分析表明 ,细管较粗管成形困难 ,轴向电磁力在管端最大 ,忽略轴向电磁力会导致终态变形分析值小于实际值。     

Comparative study of small scale and ‘large scale’ resistance spot welding

Abstract

An incrementally coupled electrical–thermal–mechanical model is developed to simulate small scale resistance spot welding (SSRSW) using the finite element method. This numerical model is then employed to study the differences between SSRSW and ‘large scale’ resistance spot welding (LSRSW). The variations in contact area, current distribution, and temperature profile at the workpiece/workpiece interfaces are compared. The computation shows that the difference in electrode force could be the essential reason for other differences between SSRSW and LSRSW. Compared with LSRSW, a much lower electrode force (pressure) applied in SSRSW results in a relatively small contact area and hence a much higher current density, which in turn leads to a greater heating rate and higher temperature at the workpiece/workpiece interface. This small contact area also results in a relatively small nugget diameter in SSRSW, which is only about 30% of the electrode tip diameter. In contrast, the nugget diameter in LSRSW is comparable to the electrode tip diameter. The predicted nugget diameters in both SSRSW and LSRSW of mild steel sheets compare well with experimental results.     

大厚度工件电火花线切割加工多次切割腰鼓度成因研究

为研究往复走丝电火花线切割加工在大厚度工件多次切割时形成腰鼓度的成因,对厚度为185 mm的工件进行了多次切割实验,通过改变工作液电导率、电极丝走丝速度、修刀补偿量和电极丝直径等条件,对加工形成的腰鼓度进行了测试及分析。结果表明:大厚度切割过程中,两极之间的脉冲放电爆炸力是产生腰鼓度的主要原因,通过增加电极丝直径以提高电极丝截面惯矩,可减小因放电爆炸力对电极丝形成的挠度,从而减小腰鼓度误差值。     

Research on gripping conditions in profile ring rolling of raceway groove

Ring gripping means that under the pressure of roll and friction, ring grips the rolling gap and produces rotating rolling motion, thus ring thickness receives equal rolling and the outer diameter expands equally, and this is a sufficient condition for ring rolling forming. In this paper, gripping course in profile ring rolling of raceway groove is analyzed based on ring rolling principle and static theory. The gripping mechanical model for profile ring rolling of raceway groove is established, and gripping conditions are researched according to the geometrical relationship in rolling. The results indicate that ring could be ensured to continuously grip the gap in rolling by controlling feed per revolution and preventing it from exceeding the maximum feed per revolution allowed by ring gripping. Furthermore, influencing factors of gripping conditions are analyzed. At last, the experiments and the FE simulation for profile ring rolling of raceway groove are performed to testify the validity of gripping conditions. Both the experimental and simulation results show that when feed satisfies gripping conditions, ring can continuously grip the gap and be formed by rolling. Otherwise, ring cannot grip the gap and is squashed between the rolls. The results of this research provide a theoretical basis for design of technological parameters of profile ring rolling of raceway groove.     

永磁体磁场对铝合金电阻点焊力学性能及微观组织的影响

文中采用永磁体作为磁场源,研究了外加稳定磁场对铝合金电阻点焊的熔核尺寸、焊点力学性能、断裂模式以及微观组织的影响.文中还对熔核直径与峰值载荷之间的关系进行了研究.结果表明,永磁铁的工作距离对熔核直径大小具有重要影响.距离越近,外磁场促进熔核直径增加的效果越明显.外加磁场能够有效增加焊点熔核直径、提高点焊接头的剪切拉伸强度、促进断裂模式由界面断裂向纽扣断裂转变.在不同工艺参数下,熔核直径增长在3.5%~14.1%,剪切拉伸力可提高4%~25%.外加磁场可促进点焊熔核内等轴晶的形成和细化.峰值载荷与熔核尺寸、工件厚度、母材极限抗拉强度的乘积具有良好的线性关系.     

动力卡盘的设计与计算

文章介绍了三爪动力卡盘的工作原理及其设计计算.通过力的平衡方程,得出夹紧力与推拉力的关系.讨论了夹紧力和极限转速是卡盘设计的理论基础.     

Integrated model for assessment of electromagnetic force field due to arc welding

Abstract

Computation of the electromagnetic force over a wide range of consumable arc welding parameters is difficult with available models because of the need for experimentally evaluated electrode extension for every individual set of parameters. This becomes more complicated in case of submerged are welding, because the welding arc remains buried beneath flux. This study presents a new approach of integrating mechanistic model of electrode extension with the computational model of electromagnetic force, wherein the apparent electrode extension is obtained by solving the electrode melting rate equation. The proposed approach is demonstrated through a case on submerged arc welding. The effect of current, voltage, electrode diameter, contact tip to workpiece distance and polarity, on the electromagnetic force, is determined and analysed. This investigation shows that detrimental effects of welding electromagnetic force can be restricted without compromising productivity because after initial rapid increase, no considerable change in melting rate is caused by the force under consideration.     

Optimization of parameters and study of joint microstructure of resistance spot welding of magnesium alloy

Experimental investigations on the DC spot welding of Mg alloy AZ31B are presented. Experiments are carried out to study the influence of spot welding parameters （ electrode force, welding heat input and welding time） on the tensile shear load and the diameter of nugget, based on an orthogonal test and analysis method. The optimum parameters are as follows： electrode force is 2 000 N, welding heat input is 80% and welding time is 6 cycles. The microstrueture of spot weld is single fine equiaxed crystals in the nugget, of which the structure is β-Mg17Al12 precipitated on α-Mg boundaries induced by nonequilibrium freezing. And the surface condition of the workpiece has great influence on the joint quality.     

金刚石薄锯片高速锯切花岗石过程中的锯切力特性

本文对金刚石薄锯片高速锯切花岗石过程中的锯切力特性进行试验研究,在较宽的参数范围下,通过测量水平力、垂直力和主轴功率来计算切向力和法向力.对锯切力、力比、单颗金刚石承受的平均载荷进行了分析.结果显示,提高锯片的线速度使锯切力、力比和单颗金刚石磨粒承受平均载荷减小;在高速锯切时,锯切力随着锯切深度和进给速度的增加而增加,而进给速度对锯切力的明显影响要小于锯切深度,应选择小切深大进给的工艺参数组合;锯切力比随锯切深度的增加而增加,随进给速度的增加而减小;单颗金刚石磨粒承受平均载荷随着单颗粒金刚石最大未变形切削厚度的增大而线性增大.     

改进的单向磨料流加工效果及轴向力测量研究

由合金材料制成的结构复杂工件内通道及相交部位的毛刺难以有效去除,而采用磨料流(AFM)加工工艺可以有效抛光零件复杂表面、提高工件加工质量。基于此,对不同工作压力的单向磨料流作用下,工件的表面粗糙度和扩展直径进行研究,介绍一种适用于单向AFM轴向力在线测量的装置,分析了不同加工压力和流体通道长度对轴向力和体积流量的影响。研究结果表明:4.0 MPa加工压力下的AFM加工可以有效降低工件表面粗糙度,同时使工件获得更均匀的表面粗糙度,但是4.0 MPa条件下的加工时长远大于7.0 MPa;流体通道长度越短,体积流量相对于轴向力来说随着加工压力的增加而明显增加;而对于最长的流体通道,加工压力的增加导致轴向力的增加更为显著。     

航空薄壁件铣削加工铣削力预测方法研究

铣削加工中铣削力是导致加工变形的直接原因,而航空薄壁件加工中,加工变形是加工误差产生的主要因素.本文以航空薄壁件铣削加工过程的铣削力为研究对象,通过确定铣削力模型和切削系数参数,建立了刚性和考虑刀具工件变形耦合的柔性预测两种模型.在柔性模型中,采用预扭Timoshenko梁单元的刀具/工件独立建模的方法建立有限元模型,利用Python语言在通用有限元软件Abaqus下迭代求解.实验验证表明预测模型具有很高的准确性和有效性.     

烧结金刚石串珠绳锯切花岗石的锯切力研究

本文对烧结金刚石串珠绳在锯切花岗石过程中,锯切力及锯切后工件表面的轮廓进行了跟踪检测,研究了锯切过程中,锯切力随锯切参数的变化,以及锯切力与工件表面轮廓的相互关系。实验结果表明：锯切过程中,工件上所承受的锯切力Fh和Fv随着线速度Vs的提高而减低,随着进给速度吩的提高而增加。垂直力与水平力之间存在着良好的对应关系,垂直力与水平力比约为4．18。加工后工件轮廓偏差量随着工件所承受的垂直力的增加而增加,两者之间呈指数关系。     

小直径砂轮超声振动磨削SiC陶瓷的表面质量研究

用小直径砂轮超声振动磨削和普通磨削加工SiC陶瓷零件,对比研究砂轮线速度、工件进给速度、磨削深度和超声振幅对其磨削表面质量的影响。结果表明:与普通磨削相比,超声振动磨削的磨粒轨迹相互交叉叠加,工件表面形貌更均匀,表面质量更好。由于超声振动时的磨粒划痕交叉会使磨粒产生空切削,因而降低了其磨削力,使磨削过程更加稳定。超声振动磨削的表面粗糙度和磨削力随砂轮线速度和超声振幅的增加而降低,随工件进给速度和磨削深度的减小而降低。且砂轮线速度、工件进给速度较小时,超声振动磨削的效果更明显。