基于刀具姿态控制的指令点插补算法

为克服五轴数控加工中忽略刀具姿态控制所带来的旋转轴速度和加速度不连续等问题,提出一种基于刀具姿态控制的五轴数控加工指令点插补算法。该算法根据给定的数控加工程序确定刀尖点位置集合和刀轴矢量集合,分别采用样条曲线对离散刀尖点和刀轴矢量进行拟合,得到刀尖点曲线和刀具姿态曲线,在此基础上进行指令点插补。实验结果表明,该算法能够将离散刀轴矢量拟合成位于单位球面的二阶连续曲线,保证旋转轴速度和加速度的连续性。     

新型石板材上下料装置的结构设计与轨迹规划

为提高石板材研磨生产线的自动化水平,改善石板材上下料装置的适应性、稳定性和工作效率,在现有的石板材上下料装置基础上,设计新型石板材上下料装置,并根据轨迹规划方法,在直角坐标空间中对末端执行器进行了轨迹规划。采用有过渡圆弧的门字路径以避免末端执行器在拐角处抖动,分别对三个平动和一个转动采用修正梯形加速度模式,使末端执行器的位移、速度、加速度随时间连续变化,平滑过渡。在Adams和Matlab中进行运动仿真,结果表明:采用有过渡圆弧的门字路径和修正梯形加速度模式的轨迹规划方案,装置运行平稳,动力特性好,工作效率高。     

基于向量的圆弧插补和加减速算法研究

提出基于向量的圆弧插补算法,通过速度和圆弧半径求出相邻两个插补点的角度差,然后通过当前插补点与圆心的一个向量来求出下一个插补点的向量值,最后进行向量差计算,从而得到需要的x和y方向的速度值。该算法不需要对所处象限进行分析,同时加工精度可以得到保证。还提出了离散型S曲线加减速控制的新方法,以单位加速度为基础,根据当前速度和加速度从而求出下一点的加速度与速度,使加速度、速度、位移的计算更为简单。实验结果表明:该算法保证了速度、加速度的连续,提高了系统的柔性。     

基于圆弧过渡的五段S型加减速算法

为提高加工速度,提出基于圆弧过渡的改进五段S型加减速算法,该算法包括五个运动阶段,并且加加速度分段线性连续变化,速度、加速度连续变化;基于圆弧的平滑过渡模型能使机床在微段间高速转接,提高加工效率,同时减小对机床的冲击。实验结果表明,该算法简单高效,能够使微小线段高速平滑衔接,延长机床寿命,提高系统的柔性。     

基于Cardinal样条曲线的自适应前瞻插补算法

数控加工中的连续微小直线段的加工,主要是通过微段间连接处的速度来制约加工速度,在满足加工精度和加速度的前提下,要尽可能提高加工速度。为了减少加速度震荡,采用Cardinal样条曲线过渡的方式,通过建立拐角曲线过渡矢量模型,得出弦高误差、相邻线段长度和夹角以及过渡曲线弧长和最大曲率之间的关系,从而确定满足条件的拐角过渡曲线,并通过弦高误差和机床机械特性以及曲率确定所允许的最大加工速度。同时给出了一种基于S型加减速的自适应前瞻算法,从而实现了微段间速度的高速衔接。仿真结果表明,该算法能够提高相邻线段间的转接速度,实现速度和加速度的平滑过渡。     

基于五次B样条的机械手关节空间平滑轨迹规划

为实现机械手作业轨迹平滑,关节轨迹的速度、加速度、加加速度保持连续,起始和停止的速度、加速度和加加速度可以任意配置,采用5次B样条曲线插值方法构造关节轨迹。推导了B样条曲线插值轨迹算法;通过VC++6.0开发平台,基于MFC框架类和OpenGL图形库仿真出机械手的运动过程,并绘制出各关节的位置、速度、加速度时间曲线图。仿真结果表明,该方法使机械手关节调整平滑且运动平稳,运动性能显著优于传统的三次样条轨迹规划。     

一种高效的机器人自由曲线运动位姿同步规划方法

针对机器人在自由曲线运动中位姿难以同步的问题,提出一种机器人自由曲线运动的位姿规划方法。该方法采用抛物线边界的三次非均匀B样条曲线拟合任意数目的示教点位置,同时采用四次四元数样条曲线拟合示教点姿态。根据示教点将自由曲线分段,以获得速度规划降速点,减少机器振动。对分段位置曲线及姿态曲线采用复化的辛普森积分求得曲线长度及姿态转角;对位置曲线进行七段S形速度规划,并利用位置规划所得的时间对姿态曲线进行速度规划,从而得到速度连续且时间同步的位置及姿态。实验表明该方法可行、高效。     

搬运机器人的轨迹规划

用五段三次多项式方法对一种搬运机器人的运行轨迹进行规划,并利用Matlab工具对该方法进行仿真分析.结果表明该方法能使运动轨迹的位置和速度都连续,尤其是加速度也连续,并且能够使机器人按照规定路径运动,保证机器人运行平稳不抖动,顺利避开障碍物,满足设计要求.     

高速数控机床平滑路径规划分析

高速数控机床切削速度大于60 m/min,加速度大于2g,对于小曲率及不连续切线加工,易导致冲击尖峰,产生机械振动,降低切削质量,缩短设备寿命。目前,通过路径平滑技术可消除刀具路径的不连续性,但该技术仅限于线性刀具路径。提出基于双回旋曲线倒角的路径平滑方法,该方法可将任意直线、弧组成路径转换为曲率连续路径,通过路径的弧长参数化,简化插值。通过数控激光切削机床测试可知,平滑圆角可在圆弧与圆弧之间或圆弧与直线之间拟合。与贝塞尔曲线圆角比较分析可知,该方法提高了进给速度,缩短了循环时间,且所得曲率轮廓更平滑。     

基于NURBS算法的工业机器人轨迹规划研究

轨迹规划是工业机器人研究领域的重要内容之一。为解决使用直线与圆弧逼近不规则曲线方法带来较大误差的问题,提出使用NURBS拟合自由曲线,并使用S形速度曲线来控制机器人末端的运动速度和加速度,使各个插补点的位置、速度和加速度能够连续,将之反推到关节空间可以得到各个关节的角度、角速度和角加速度。最后以IRB2600工业机器人为仿真本体,通过MATLAB仿真证明:NURBS和S形速度曲线相结合的方法可以得到在关节空间连续、平稳的运行轨迹、速度曲线、加速度曲线,减弱了因各关节角度、角速度、角加速度突变带来的冲击影响,优化了机器人运行轨迹。     

Corner rounding of linear five-axis tool path by dual PH curves blending

The widespread linear five-axis tool path (G01 blocks) is usually described by two trajectories. One trajectory describes the position of the tool tip point, and the other one describes the position of the second point on the tool axis. The inherent disadvantages of linear tool path are tangential and curvature discontinuities at the corners in five-axis tool path, which will result in feedrate fluctuation and decrease due to the kinematic constraints of the machine tools. In this paper, by using a pair of quintic PH curves, a smoothing method is proposed to round the corners. There are two steps involved in our method. Firstly, according to the accuracy requirements of the tool tip contour and tool orientation tolerances, the corner is rounded with a pair of PH curves directly. Then, the control polygon lengths of PH curves are adjusted simply to guarantee the continuous variation of the tool orientation at the junctions between the transition curves and the remainder linear segments. Because the PH curves for corner rounding can be constructed without any iteration, and those two rounded trajectories are synchronized linearly in interpolation, which makes this smoothing method can be applied in a high efficiency way. Its high computational efficiency allows it to be implemented in real-time applications. This method has been integrated into a CNC system with an open architecture to implement on-line linear five-axis tool path smoothing. Simulations and experiments validate its practicability and reliability.     

Closed form formulation of cutting forces for ball and flat end mills

In this paper, a set of basis functions for the calculation of cutting forces in milling are introduced. It is shown that the cutting force at any tool position can be determined by the linear combination of the force basis functions. The method is based on the projection of the chip load area onto the reference coordinate planes. Due to the analytical integration of the cutting forces along the cutter edge, the developed closed form equations provide a fast means of calculating the cutting forces. The validity of the method is experimentally verified for both flat and ball end mills.     

TB9钛合金车削系统振动特性与表面粗糙度关系的试验研究

目的 通过车削加工TB9钛合金试验,定量研究不同位置的振动特性对表面粗糙度的影响规律,并建立基于振动参数的表面粗糙度预测模型。方法 选用涂层硬质合金刀具对TB9钛合金线材进行车削加工。通过8704B25和3333A2加速度传感器对试验过程中不同位置的切削振动进行检测。运用Matlab对振动加速度信号进行处理和分析。采用TR2000高精度表面粗糙度仪测量工件表面粗糙度。结果 车削系统不同位置的振动特性均与表面粗糙度存在线性关系。车削系统中刀具振动加速度均方根值、主轴振动加速度均方根值以及后导向振动加速度均方根值与表面粗糙度的Pearson相关系数分别为0.379 93、0.331 90、0.181 95。表面粗糙度预测模型的预测平均百分比误差小于3%。结论 车削加工时刀具、主轴以及后导向的车削振动均对表面粗糙度有一定影响。车削系统不同位置的振动特性对表面粗糙度的影响次序为刀具>主轴>后导向,可见距离切削位置越近的振动对车削加工表面粗糙度的影响越大。基于振动参数的表面粗糙度预测模型的准确度较高,可作为表面粗糙度的预测模型。     

Statistical analysis of the effects of machining parameters and workpiece hardness on the surface finish of machined medium carbon steel

The objective of this study is to ascertain the effect of machining parameters and workpiece hardness on surface roughness of machined components and to develop a better understanding of the effect of process parameters on the machined surface. Such an understanding can provide insight into the problems of controlling the finish of machined surfaces when the process parameters are adjusted to obtain a certain surface finish. The collected data were analyzed using parametric analyses of variance (ANOVA) with surface finish as the dependent variable and hardness of the workpiece material, cutting tool position from the surface of the clamping device (chuck), depth of cut, cutting velocity, and cutting feed as independent variables. The results showed that surface roughness is significantly affected by the workpiece hardness, cutting feed, cutting speed, depth of cut, cutting tool position from the chuck, and their interactions with each other. The results suggest that feed rate and cutting speed can be adjusted to produce a certain surface finish when the position of the cutting tool from the surface of a clamping device or the hardness of the workpiece is changed.     

A method for direct evaluation of the dynamic 3D path accuracy of NC machine tools

Fast and high-quality machining operations require high dynamic path accuracy of the machine tool in use. Complementary to the work done on NC path planning and mechatronic simulation, in this paper a device is introduced for direct 3D measurements of dynamic path deviations at the tool center point (TCP). With it, linear as well as rotary axes can be tested in one setup, thus dynamic parameters such as jerk and acceleration limits can be set homogeneously for obtaining the required dynamic path accuracy. Relevant Eigenfrequencies of the machine can be identified. Measurement method, uncertainty estimation and result evaluation are explained in this paper.     

Mechanism of minimum quantity lubrication in high-speed milling of hardened steel

The rapid wear rate of cutting tools due to high cutting temperature is a critical problem to be solved in high-speed machining (HSM) of hardened steels. Near-dry machining such as minimum quantity lubrication (MQL) is regarded as one of the solutions to this difficulty. However, the function of MQL in HSM is still uncertain so far which prevents MQL from widely being utilized in the machining of hardened steels. In this paper, the mechanism of MQL in HSM of hardened steel is investigated more comprehensively. Comparing with dry cutting, the tool performance can be enhanced by MQL under all cutting speeds in this study. It is found that MQL can provide extra oxygen to promote the formation of a protective oxide layer in between the chip–tool interface. This layer is basically quaternary compound oxides of Fe, Mn, Si, and Al, and is proved to act as diffusion barriers effectively. Hence, the strength and wear resistance of a cutting tool can be retained which leads to a significant improvement of tool life. It is found that there exists an optimal cutting speed at which a stable protective oxide layer can be formed. When cutting speed is lower than this speed, there is less oxide layer and the improvement of tool life is less apparent. As the cutting speed is far beyond the optimal value, the protective layer is absent and the thermal cracks are apt to occur at the cutting edge due to large fluctuation of temperature. Resultantly, application of MQL is inappropriate in the extreme high-speed cutting condition irrespective of its little increase in tool life. Based on this study, it is concluded that the tool life can be effectively improved by MQL in HSM of NAK80 hardened steels when cutting parameters are chosen properly.     

Virtual Design and Optimization of Machine Tool Spindles

An integrated digital model of spindle, tool holder, tool and cutting process is presented. The spindle is modeled using an in-house developed Finite Element system. The preload on the bearings and the influence of gyroscopic and centrifugal forces from all rotating parts due to speed are considered. The bearing stiffness, mode shapes, Frequency Response Function at any point on the spindle can be predicted. The static and dynamic deflections along the spindle shaft as well as contact forces on the bearings can be predicted with simulated cutting forces before physically building and testing the spindles. The spacing of the bearings are optimized to achieve either maximum dynamics stiffness or maximum chatter free depth of cut at the desired speed region for a given cutter geometry and work-piece material. It is possible to add constraints to model mounting of the spindle on the machine tool, as well as defining local springs and damping elements at any nodal point on the spindle. The model is verified experimentally.     

整体翅片管的劈切—挤压加工

提出了一种新的本翅片管的机械加工方法,即劈切－挤压加工,实验观察发现,翅片的形成包括切入、挤压和成形3个阶段,实验结果表明,影响翅片形成的主要有刀具几何参数、挤压深度,进给量和劈切－挤压速度;对某一刀具,在选定挤压速度时,一定的挤压深度对应一个极限进人量,一定的进给量对应一个极限挤压深度。选择合理的参数可保证翅片加工的连续性和获得接近最佳形状的翅片。劈切－挤坟加工在普通车床上进行,设备简单易,翅片一次成形,材料利用率高,是一种能降低加工技术,提高生产率的加工方式。     

Tool condition monitoring in turning using fuzzy set theory

This paper presents a study on tool condition monitoring in turning using the fuzzy set theory. The tool conditions considered include tool breakage, several states of tool wear, and chatter. Force, vibration, and power sensors are used in this study to monitor the three components of the cutting force, i.e. acceleration of the tool holder in two perpendicular directions, and the spindle motor current respectively. A total of 11 monitoring indices (signature features) are selected to describe the signature characteristics of various tool conditions. A linear fuzzy equation is proposed to describe the relationship between the tool conditions and the monitoring indices. The proposed methodology is verified experimentally using a total of 396 cutting tests performed at 52 different cutting conditions. The proposed methodology is also compared with that of several classification schemes, including the K-mean and the Fisher's pattern recognition methods, the nearest neighbor method and the fuzzy C-mean method. The results indicate an overall 90% reliability of the proposed methodology for detecting tool conditions regardless of the variation in cutting conditions.     

S曲线加减速控制新方法的研究

直线加减速方法由于加速度不连续易造成冲击,传统的S曲线加减速实现方法可克服这一不足,但分段较多,程序实现较复杂。针对上述问题,提出了S曲线加减速控制的新方法,将加减速过程划分为五个阶段,并给出其加加速度、加速度、速度、位移的计算表达式,根据路径段长度进一步建立了S曲线加减速控制算法。仿真结果表明,该方法能保证速度、加速度的连续,有效提高了系统的柔性,同时简化了算法的实现。