五轴联动机床的误差补偿与优化研究

以五轴联动精密卧式加工中心为研究对象,首先阐述了五轴联动机床的圆度测试过程,对可能出现的测试结果给出分析与解决方法;从而得到具体的检测步骤以及相应的机床数据;最后讨论了同步龙门轴的调整问题.实验结果表明了所述方法的有效性.     

Thermal error mode analysis and robust modeling for error compensation on a CNC turning center

In this paper a novel concept of thermal error mode analysis is proposed in order to develop a better understanding of the thermal deformation on a turning center. The thermal error of the machine can be treated as the superposition of a series of thermal error modes with corresponding mode shapes and time constants. The selection of sensor location can then be improved based on the thermal error mode analysis. A robust modeling approach is also proposed to minimize the errors due to temperature measuring noise and the adverse effect of environmental changes. Through the use of thermal error mode analysis and the robust modeling approach, the number of thermal sensors has been reduced from 16 to four. The thermal error compensation system has been applied to a turning center in daily production for more than two years and it has kept year-round accuracy. The thermal drift in workpiece diameter on the turning center has been reduced from 35 μm to 6 μm from its center of tolerance.     

Thermally induced positioning error modelling and compensation based on thermal characteristic analysis

To decrease the thermally induced positioning error of machine tools, a novel approach for modelling and compensation is proposed in this study. The cause of this error is determined to be dynamic pitch error, and its manifestations are discussed in this study. The thermal expansion of a screw shaft under the influence of friction heat is analysed theoretically, and a mathematical model of the transient temperature of the screw with regard to time is developed. A temperature calculation method in the cases of cooling in the process of warming up and warming up after cooling is also introduced. To solve the problem of heat unevenly distributed of the entire screw shaft, the screw shaft is divided into several evenly distributed heat regions, and the established model is fit for each region. The synthetic model is established by superposition of all models of the regions. In addition, an external error compensation system is developed based on a function called external mechanical origin offset in Fanuc CNC systems. Six test pieces are machined to validate the accuracy of the model and the effectiveness of the error compensation system. The result indicates that the accuracy of the pieces is significantly improved compared with that obtained without error compensation. The synthetic model of the entire screw shaft is demonstrated to be an effective approach to improve the accuracy of machine tools.     

普及型数控系统直线误差的研究与应用

通过分析普及型半闭环数控系统的直线误差,指出传动系统的反向间隙和螺距误差是影响定位精度和重复定位精度的主要原因.阐述了数控系统反向间隙补偿和螺距误差补偿的原理,提出了发挥数控系统软件功能,控制直线误差,是提高行业加工精度的经济而有效的方法.研究了反向间隙测量方法和螺距误差补偿原点设置的原则.以GSK数控系统为例,详细介绍了反向间隙补偿、螺距误差补偿相关的误差测量方法、数控系统参数设置、变量设置等内容,并列举了具体操作实例.     

数控机床三维空间误差建模及补偿技术研究

为了提高数控机床的加工精度,解决由机床三维空间误差引起的工件加工质量降低的问题,在研究多体系统理论误差建模技术的基础上,提出离线补偿和嵌入式补偿两种补偿策略。离线补偿是基于数控加工程序的修正补偿,将机床三维空间误差映射到数控加工程序,通过修改加工程序实现对机床的三维空间误差补偿;嵌入式补偿是基于数控系统的在线补偿,将机床三维空间误差融合到数控系统中,通过修正数控系统中的数据流实现对机床的三维空间误差补偿。实验表明,在不影响机床可靠性的前提下,两种补偿策略均显著提高了数控机床的加工精度。     

Accuracy enhancement of five-axis machine tool based on differential motion matrix: Geometric error modeling,identification and compensation

This paper presents the precision enhancement of five-axis machine tools according to differential motion matrix, including geometric error modeling, identification and compensation. Differential motion matrix describes the relationship between transforming differential changes of coordinate frames. Firstly, differential motion matrix of each axis relative to tool is established based on homogenous transformation matrix of tool relative to each axis. Secondly, the influences of errors of each axis on accuracy of tool are calculated with error vector of each axis. The sum of these influences is integration of error components of machine tool in coordinate system of tool. It endows the error modeling clear physical meaning. Moreover, integrated error components are transformed to coordinate frame of working table for integrated error transformation matrix of machine tools. Thirdly, constructed Jacobian is established using differential motion matrix of each axis without extra calculation to compensate the integrated error components of tool. It makes compensation easy and convenient with reuse of intermediate. Fourthly, six-circle method of ballbar is developed based on differential motion matrix to identify all ten error components of each rotary axis. Finally, the experiments are carried out on SmartCNC500 five-axis machine tool to testify the effectiveness of proposed accuracy enhancement with differential motion matrix.     

基于球杆仪的数控机床误差识别与补偿

论述了数控机床几何误差的球杆仪识别及软件补偿技术。提出了从Renishaw球杆仪测量数控机床的联动误差数据中识别反向间隙、直线度、垂直度、定位误差的一种方法;建立了机床结构的每个误差元和切削刀具相对工件位置误差相联系的通用数学模型;用球杆仪在数控机床上进行补偿前后加工轨迹的测量实验表明该方法效率高、效果显著。