FDM 3D打印模型表面阶梯效应的分析

3D打印模型表面的阶梯效应是常见的表面缺陷。在概述FDM 3D打印的原理基础上,以简化的三维锥体模型的3D打印加工为研究对象,分析了模型表面阶梯效应的形成原理,论述了阶梯效应与成型层厚及成型模型面角度的关系,同时也与铣削加工进行了对比。提出了改善FDM 3D打印阶梯效应的方法,为探索和提高FDM 3D打印表面的质量,减小阶梯效应,提供了有益的参考。     

碳纤维长纤3D打印的路径跳转处理

针对碳纤维长纤3D打印复杂模型的路径跳转问题,以三维模型切片处理后的G代码文件为基础,对其进行3D打印跳转点识别;基于三维路径坐标与远端切断装置间的距离关系,实现打印跳转点与纤维切断点的精确匹配,进行连续性纤维远端切断处理。通过不同打印路径的三维模型跳转点与断点的仿真分析,以及碳纤维长纤3D打印系统对单层及多层模型的3D打印测试,验证了路径跳转处理方法对连续纤维复杂模型3D打印成型的可行性。算法为碳纤维长纤3D打印的实现提供基础。     

FDM技术中基于层轮廓特征的路径规划方法研究

通过对3D打印技术中目前主流的路径规划方式的研究的基础上,提出了基于层轮廓特征的路径规划方法,即对同一三维模型分层处理后针对不同层截面轮廓特征采用不同的路径规划。运用G代码仿真和3D打印实验验证方法,得到如下结论:采用Hilbert曲线路径规划可提高制件的打印精度;采用三角形分形路径规划可提高制件的打印效率;采用并行栅格路径规划、普通蜂巢路径规划在充盈度、饱满度比较差的截面上可提高成型质量。经过实验数据分析,所选用的路径规划提高了打印精度与打印效率,对熔融沉积成型合理选用路径规划具有借鉴意义。     

基于熔融沉积成型3D打印模型表面质量的研究

由于FDM技术本身的工作原理,3D打印模型表面不可避免地存在阶梯效应。研究分析了模型表面阶梯效应的形成机理,以具有2种不同截面的三维试验模型为研究对象,验证了系统分层厚度d和模型成型方向夹角α对表面粗糙度系数δ的影响,试验实测数据基本与理论计算数据保持一致。提出了改善模型表面阶梯效应的措施和方法,为提高3D打印模型表面质量提供了有效地解决方案。     

增减材复合制造加工FDM薄壁样件研究

研究了增减材复合制造加工熔融沉积成型(fused deposition modeling, FDM)薄壁零件的方法。结合增材制造和减材制造,改造传统独立双喷头3D打印机,修改右侧喷头为数控铣刀,在3D打印模型切片时对模型外轮廓进行识别和处理,生成数控加工代码,自动集成到3D打印G代码中,可对薄壁零件进行直接打印,并获得高精度的表面质量。对于薄壁复杂结构塑料零件的加工,通过改造的增减材打印机可以全自动生成复合加工G代码,大大提高了增减材复合制造的效率。     

3D打印机G代码预处理优化算法

为了突破现有3D打印机控制系统原有的文件处理模式的限制,提出将G代码程序在PC端先行预处理的方法。在程序预处理过程中,同时对多段微小线段进行前瞻控制和速度规划;预处理结束后,再将处理结果输入3D打印机执行打印操作。该方法减少了3D打印机处理器负担,且通过PC端预处理可以得到更优化的计算结果。实验测量数据证明：G代码预处理方法与传统G代码处理方法相比,节省了打印机处理器处理时间,同时提高了打印品质。     

基于自动计算车削节点软件的边界轮廓提取

为设计一套价格低廉、效率高的专门面向木质零件加工的自动计算车削节点软件,从AUTOCAD图形是由数据结构储存、阶梯轴都是由普通回转体构成和G71/G72切屑循环指令给出轮廓的全部节点信息出发用编程的方法进行描述,设计了回转体的数据结构和阶梯轴数据结构等,依据上述数据结构对G代码中包含的回转体边界参数数据进行插补节点转化,提出一种从G代码提取边界轮廓的方法。实例验证,该方法性能良好,提取后的边界效果很好。     

利用3D打印技术实现骨盆骨折手术导板的设计制造

目的使用3D打印技术设计制造手术导板,辅助手术操作,降低骨盆骨折手术的难度。方法基于数字化骨盆模型的重构流程,针对CT断层图像的台阶效应,提出了层间插值算法,通过层间插值算法优化后,提高了骨盆模型重构精度。然后利用优化后的三维骨盆模型设计制造手术导板,并将其应用于手术。结果术中所见与术前模拟完全一致,术后CT复查显示克氏针位置正确,术后效果满意。3D打印技术的应用使手术时间由两小时缩短为十分钟,避免了术中透视,提高了定位精度,降低了手术难度。     

几何参数对3D打印零件轮廓精度影响的研究

提出用表面轮廓平均偏差作为评价3D打印零件由于台阶效应引起的表面轮廓偏差与表面粗糙度的统一指标,推导出表面轮廓平均偏差的计算公式及其与表面粗糙度指标Ra的关系。研究表明,3D打印零件的轮廓精度和表面质量与该表面的角度、曲面半径、打印层厚均有关系;对于形状简单的工件,可通过调整打印时的摆放方向来获得更优的轮廓精度与表面质量;对于形状复杂的工件,采用较小的打印层厚是提高打印零件表面轮廓精度与表面质量最有效的方法;对于常规尺寸的零件,打印层厚为0.030mm时即可获得较好的轮廓精度与表面质量,而采用更小的层厚来提高打印质量效果将不明显。     

多轴3D打印技术研究进展

3D打印技术通过逐层堆积的方式成型，克服了零件制造的几何限制，受到了学术界和工业界的广泛关注。但这种定向构建方式会导致零件存在阶梯效应，强度不足且需要添加支撑结构等一系列问题。为了解决传统层式打印存在的问题，研究人员开发了多轴3D打印技术。多轴3D打印技术使用多自由度机器人对零件进行动态构建，克服了传统层式打印的限制，显示出了极高的零件制造灵活性。鉴于此，对多轴3D打印技术进行了回顾，首先分析了传统3D打印存在的一些问题，然后综述了多轴3D打印技术的研究进展，包括多轴3D打印技术在路径规划、零件力学性改善、去支撑化、消除阶梯效应以及大尺寸打印上的研究概况。最后探讨了多轴3D打印技术目前存在的问题和未来可能发展的方向。     

三绕组变压器的双绕组等效建模及在Matpower中的应用

针对实际电网存在着大量的三绕组变压器,但国际上一些著名商业软件,如BPA仿真软件、Matpower这一权威潮流计算开源软件,均只提供双绕组变压器模型,限制了其在具有三绕组变压器的电力系统中的应用的问题,潮流计算是自主开发的电力系统各种应用软件的核心模块,因此依托国际权威开源程序进行二次开发,是一种较好的选择。对Matpower要求的数据格式进行了归纳,对变压器的一般的等值电路及带理想变压器的等值电路和带标幺值的等值电路进行了分析研究,提出了三绕组变压器转换为双绕组等效模型的建模方法,使得原先只适应双绕组变压器的潮流计算软件可以适用于三绕组变压器电网的潮流计算;最后以Matpower软件为例进行了案例计算,并用PSASP仿真软件进行对比验证。研究结果证明,所提出的建模方法是有效的。     

On the Relation of Load to Average Gap in the Contact Between Surfaces with Longitudinal Roughness

A computer simulation model for the contact between longitudinally-oriented rough surfaces has been formulated. This model closely duplicates the actual surf ace contact deformation behavior by taking into account the elastic interactions between the asperities. There were no assumptions made about the shapes, or any deformation behavior of the asperities, except for their obeying the laws of elasticity. The plastic deformations on the high asperity peaks were taken into account by setting a ceiling on their contact pressures at the material hardness value. The simulations used real surface profiles which were digitized from unworn circumferentially ground steel surfaces. Each pair of these profiles was mathematically combined to form an equivalent rough profile pressing against an infinitely rigid flat and having the appropriately adjusted elastic modulus. A total of 28 different pairs of profiles were used in the simulations. Each contacting pair was subjected to 30 different load levels and the local contact pressures and deformations were calculated. The contact simulations yielded some important mathematical relationships between parameters, such as the real area of contact, average gap, and average asperity load through statistical curve fitting. Two analytical functions were generated to relate the average load to average gap and the real area of contact to load.     

电站锅炉模糊风险评价方法研究与应用

针对电站锅炉风险等级评价问题,将模糊综合评价技术应用到电站锅炉风险等级评价中。开展了电站锅炉失效影响因素及模糊评价因素的重要程度分析,建立了一套科学合理适于在线评价的电站锅炉风险评价体系,提出了模糊综合评价技术与改进的模糊层次分析法相结合的模糊风险评价方法,利用改进的模糊层次分析法计算了指标体系中各层指标权重。对某一台电站锅炉的实际运行工况影响子因素进行了模糊风险评价,采用模糊合成算子进行模糊综合运算得到电了站锅炉运行工况影响子因素的评价向量。研究结果表明:电站锅炉的运行工况影响子因素的风险评价等级为第6级,失效可能性等级为小,该电站锅炉运行工况良好。     

交通荷载作用下桥梁结构参数识别方法

应用动力节点加载法,将作用在桥梁上的交通荷载转化为等效节点荷载,再用两步构造法识别结构物理参数.第1步,用Newmark-β方法变换结构运动方程,并用结构的加速度响应求得变换空间内的位移、速度和加速度响应;第2步,基于最小二乘原理,构造出变换空间内求解结构参数的递推式,进行结构物理参数识别.数值模拟结果表明,在交通荷载作用下,该方法能够快速、准确地进行桥梁结构参数识别.     

RLS and LMS blind adaptive multi-user detection method and comparison in acoustic communication

RLS and LMS blind adaptive multi-user detection algorithm and multi-user detector was proposed to solve the problem of multi-user signal detection problem encountered in underwater acoustic communication networks.In simulation analysis,RLS and the LMS blind adaptive multi-user detector were designed and tested for synchronous and asynchronous multi-user communication process.The results of SIR comparison and MMSE comparison show that,both of the two methods can realize blind adaptive detection when any user change in multi-user communication,during this process,the training communication sequences are not needed.The RLS algorithm has about 5 dB higher in SIR compared with LMS algorithm,and the convergence velocity of RLS algorithm is also higher than LMS algorithm when the communication users change.RLS algorithm has better ability in multi-user detection than that of LMS algorithm,and it has great attraction and guiding significance for solving the problem of multiple access interference(MAI) in multi-user communication.     

Robust Impedance Control of Robots Using an Adaptive Interaction Force Observer

For robot interaction control,the interaction force between the robot and the manipulated object or environment should be monitored.Impedance control is a type ...     

Research on key techniques of expendable conductivity temperature depth measuring system

This paper analysis the developing of expendable conductivity temperature depth measuring system(XCTD)and introduce its principle of measuring about temperature,salinity and depth of ocean.Some key techniques are put forward.According to the real needs of XCTD,conductivity sensor with high sensitivity is designed by principle of electromagnetic induce,the ocean conductivity from induced electromotive force has been calculated.Adding temperature correction circuit would help to reduce error of conductivity measurement because of sharply changing temperature.Advanced temperature measuring circuit of high precision and the constant current source is used to weaken effect of self-heating of resistance and fluctuation of the source.On respect of remote data transmission,LVDS is a good choice for the purpose of guarantee the quality of data transmitted and the transmission distance is reaching to thousand meters in the seawater.Modular programming method is also brought into this research aimed at improve the stability,reliability and maintainability of the whole measuring system.In February,2015,the trials in South China Sea demonstrate that the developed XCTD realize effective measurement at a speed of 6 knots and detection depth at 800 m.The consistency coefficient of the acquired data is greater than 0.99 and the success rate of probe launching is above 90%.     

CHARACTERISTCS OF FLUID FILM IN OPTIMIZED SPIRAL GROOVE MECHANICAL SEAL

In order to investigate the sealing performance variation resulted from the thermal deformation of the end faces, the equations to calculate the fluid film pressure distribution, the bearing force and the leakage rate are derived, for the fluid film both in parallel gap and in wedgy gap. The geometrical parameters of the sealing members are optimized by means of heat transfer analysis and complex method. The analysis results indicate that the shallow spiral grooves can generate hydrodynamic pressure while the rotating ring rotates and the bearing force of the fluid film in spiral groove end faces is much larger than that in the flat end faces. The deformation increases the bearing force of the fluid film in flat end faces, but it decreases the hydrodynamic pressure of the fluid film in spiral groove end faces. The gap dimensions which determine the characteristics of the fluid film is obtained by coupling analysis of the frictional heat and the thermal deformation in consideration of the equilibrium condition of the bearing force and the closing force. For different gap dimensions, the relationship between the closing force and the leakage rate is also investigated, based on which the leakage rate can be controlled by adjusting the closing force.     

Quantum Cooperative Robotics and Autonomy

The intersection of Quantum Technologies and Robotics Autonomy is explored in the present paper.The two areas are brought together in establishing an interdisci...     

OPTIMIZATION METHOD ON IMPELLER MERIDIONAL CONTOUR AND 3D BLADE

An optimization method for 3D blade and meridional contour of centrifugal or mixed-flow impeller based on the 3D viscous computational fluid dynamics (CFD) analysis is proposed. The blade is indirectly parameterized using the angular momentum and calculated by inverse design method. The design variables are separated into two categories: the meridional contour design variables and the blade design variables. Firstly, only the blade is optimized using genetic algorithm with the meridional contour remained constant. The artificial neural network (ANN) techniques with the training sample data schemed according to design of experiment theory are adopted to construct the response relation between the blade design variables and the impeller performance. Then, based on the ANN approximated relation between the meridional contour design variables and impeller performance, the meridional contour is optimized. Fewer design variables and less calculation effort is required in this method that may be widely used in the optimization of three-dimension impellers. An optimized impeller in a mixed-flow pump, where the head and the efficiency are enhanced by 12.9% and 4.5% respectively, confirms the validity of this newly proposed method.