数控车床实验系统的主轴变频调速系统设计分析

主要针对要求高精度、快响应的数控车床主轴调速系统的设计要求,通过对变频调速的基本原理和变频方式的分析,提出了变频电机与变频器组合的调速方案.根据数控车床实验系统的运行条件,计算车床的切削力和主轴电机的功率,为选择实验系统的主轴变频调速电机提供依据.根据选定的变频电机的特性,提出了变频器的选择原则,进而选择了额定容量和额...     

Drilling torque control using spindle motor current and its effect on tool wear

Drilling torque was estimated using the spindle motor current and controlled through feedrate manipulation for the reduction of drill wear. A PID controller was used to control the cutting torque measured indirectly from the spindle motor current. The effect of cutting torque control on drill flank wear was also investigated. Experimental results showed that the drilling torque was well-regulated at a given reference level and the risk of drill failure and drill flank wear were reduced remarkably through cutting torque control. Moreover, the suggested cutting torque control system does not disturb the cutting process and is practical in an industrial environment.Nomenclature I _rms Root mean square value of spindle motor current (ampere) - I _u,v,w U, V, and W phase current of the spindle motor (ampere) - I _rms,c Spindle motor current due to cutting (ampere) - I _rms,t Tare current of the spindle motor (ampere) - T _c Cutting torque (Nm) - T _s Sampling rate (Hz) - N _r Number of revolution - N _d Number of data per revolution - K _I Spindle motor current gain (ampere N^–1m^–1) - _d Time constant of the spindle system (sec)     

Indirect Cutting Force Measurement Considering Frictional Behaviour in a Machining Centre Using Feed Motor Current

In machine tools, friction exists between the table and the guideways, and in ballscrews. In this paper, feed motor current is measured by a hall effect current sensor. It is used to calculate the motor torque which, in turn, is the frictional torque at steady state. Some frictional phenomena are studied in feed drive systems of a horizontal machining centre, such as the relationship between feedrate and frictional torque, the relationship between frictional torque and table feed position, and the slideway cover effects on frictional torque. Considering all these frictional phenomena, the relationship between the feed force and the feed motor current is obtained. Feed force can be estimated well from the feed motor current considering frictional behaviour. The relationship between the cutting force and the feed motor current is slightly different during up milling and down milling, because y(vertical) directional cutting force changes the frictional force.     

电主轴系统的最佳预紧力研究

高速电主轴是高性能机床的核心部件,它将主轴电动机内置于机床主轴中,两者"合二为一",因而具有结构紧凑、质量轻、惯性小、振动小、噪音低、响应快、易于实现主轴定位和准停等突出优点.新一代高速电主轴的工况特点是低速大转矩和高速大功率,预紧力可控是很有技术发展前途的新方向.确定最佳预紧力,实现电主轴在包含低速大转矩与高速大功率整个工作范围内动力学品质全局兼优是预紧力可控的基础.因此,本文对电主轴系统的最佳预紧力进行了研究.     

Cutting torque and tangential cutting force coefficient identification from spindle motor current

This article presents an enhanced methodology for cutting torque prediction from the spindle motor current, readily available in modern machine tool controllers. This methodology includes the development of the spindle power model which takes into account all mechanical and electrical power losses in a spindle motor for high-speed milling. The predicted cutting torque is further used to identify tangential cutting force coefficients in order to predict accurately the cutting forces and chatter-free regions for milling process planning purposes. The developed model is compared with other studies available in the literature, and it demonstrates significant improvements in terms of the completeness and accuracy achieved. The developed model is also validated experimentally, and the obtained results show good compliance between the predicted and the measured cutting torque. The developed enhanced procedure is very appealing for industrial implementation for cutting torque/force monitoring and tangential cutting force coefficient identification.     

在数控机床上通过监视主轴电机负荷实时监控刀具寿命

金属切削刀具的磨损和损坏直接影响到加工质量,因此有必要在生产实践中对刀具进行实时监控。刀具磨损或损坏时,切削力会发生变化,主轴电动机负荷也会发生变化,因此,可以根据主轴电动机负荷判断切削刀具是否到达寿命。本文探索了一种在数控机妹上通过监视主轴电动机负荷实时监控刀具寿命的方法,并给出了具体的实现技术及PLC和CNC程序。     

Real-Time Prediction of Workpiece Errors for a CNC Turning Centre, Part 3. Cutting Force Estimation Using Current Sensors

This paper presents a new method for measurement of cutting force using reliable and inexpensive current sensors. The relationship between the various factors which affect the performance of the spindle and feed drive systems are analysed, together with models of the spindle and feed drive system. The tangential (Ft) and axial cutting forces (Fa) are measured, using a neuro-fuzzy technique, with inexpensive current sensors installed on the a.c. servomotors of a CNC turning centre. The normal cutting pressure (Kn) and effective friction coefficient (Kf ) are calculated using the model of the cutting force and the two cutting forces measured by motor current, then the radial cutting force (Fr) can be calculated based on the model of cutting force. Experimental results show that the method can measure tangential, axial and radial cutting forces within errors of 10%, 5% and 25%, respectively, so the need for controlling or monitoring the cutting processes can be met in practice.     

普及型数控车床主轴控制的设计

对普及型数控车床的主轴变速控制和恒速切削控制进行了分析和研究，介绍利用VVVF实现的主轴变速系统在STAR—3T数控系统中的应用及新的设计，解决了经济型NC车床主轴实现无级变速问题。     

坡口机恒负载切削控制系统的设计与研究

针对坡口机的现状,提出了由触摸屏、伺服单元、PLC和主轴动力单元组成的一种坡口机恒负载控制系统,将模糊控制应用到坡口加工过程中,在主轴电机转速不变的情况下,通过伺服电机的智能进给,实现恒负载切削的目的,以满足提高设备寿命和加工性能的需求.     

高速加工理论在普通数控机床上的应用

高速加工在切削速度、材料去除率以及表面加工质量等方面较普通数控加工具有明显优势。在工艺研究中,将高速加工切削理论应用在现有的普通数控设备上,在主轴转速不变或相应提高的情况下,提高切削移动速度同时减小切削深度进给量,从而达到提高切削效率、减小切削应力以及改善加工表面质量的目的。     

力矩电动机驱动双摆头的结构设计

力矩电动机直接驱动双摆头是实现五轴联动数控机床高速化的新形式。介绍了双摆头系统的组成,提出了机械结构设计中强电、弱电、冷却水、气等的在相对运动间的耦合问题的解决方案。     

盘形成形铣刀的刀具磨损故障诊断方法研究

通过分析高速铣齿机的盘形成形铣刀及其铣削过程的特殊性、刀具磨损的信号采集和处理方法.选用电流法监测数控铣齿机的主轴电动机电流,采用BP神经网络方法对信号进行处理,最后实现对盘形成形铣刀的刀具磨损诊断.经实验证明,该铣刀的电流监测和基于BP神经网络数据处理的方法具有良好的诊断性能.     

Design of a Drilling Torque Controller for a Machining Center

In the drilling process, cutting torque control through feedrate manipulation has significant benefits in prevention of tool breakage and reduction of machine tool vibration and tool wear. In this paper, a PID torque controller was designed for real time drilling torque control in a machining centre. The drilling torque was estimated from the spindle motor current and regulated by feedrate control. The plant including the feed drive system, cutting process, and spindle system was modelled for controller design. For a certain cutting condition, the Ziegler-Nichols method was used to determine the proportional gain and derivative and integral control action times of the controller. Also, the root locus plot was used to tune the proportional gain of the controller. A simple method was also suggested to obtain the tuned controller gain instead of the Ziegler-Nichols method and the root locus plot for an arbitrary cutting condition. Experimental works have been performed to verify the performance of the proposed controller. It is shown that the gain tuning is essential for enhancement of the controller performance and the designed controller can regulate the drilling torque well at a given reference level.Nomenclature G_fc(s) transfer function of combined system of feed drive and cutting process - G_s(s) transfer function of spindle system - G_p(s) transfer function of plant - G_CL(s) transfer function of closed loop system - G_con(s) transfer function of controller - _fc1, _fc2 time constants of combined system of feed drive and cutting process - _s time constant of spindle system - K controller gain - K_c cutting process gain - K_s spindle motor current gain - K_plant plant gain - K_cr critical gain - K_p proportional gain of controller - K_{p_tune} tuned proportional gain of controller - I_s spindle motor current - I_u,v,w u, v, and w phase current of spindle motor - I_idle idling current of spindle motor - damping ratio - T oscillation period of system response - T_c cutting torque - T_m motor torque - T_idle idling torque of spindle motor - T_i integral control action time - T_d derivative control action time     

基于主轴电流信号多特征融合的刀具磨损状态监测

为实现在正常生产条件下进行刀具磨损的长期在线监测,提出了基于主轴电流信号和粒子群优化支持向量机模型(PSO-SVM)的刀具磨损状态间接监测方法。首先对数控机床主轴电机电流信号进行分析,将与刀具磨损相关的主轴电流信号多个特征参数和EMD能量熵进行特征融合作为输入特征向量;其次,通过粒子群寻优算法(PSO)对支持向量机模型(SVM)参数进行优化,建立基于主轴电流信号融合特征和PSO-SVM理论的刀具磨损状态识别模型;最后,通过实验采集某立式加工中心主轴在刀具不同磨损状态下电流信号进行验证,并与传统SVM模型、BP神经网络模型进行了对比分析。结果表明,所提出的方法具有较高的准确率和较好的泛化能力。能够实现正常生产条件下对刀具磨损的长期在线监测。     

Analysis of CNC machining based on characteristics of thermal errors and optimal design of experimental programs during actual cutting process

The compensation of thermal errors plays a critical role in developing the machine tools of intelligent computer numerically controlled (CNC). According to the international standards, the testing, modeling, and compensation of thermal error of CNC machine tools are carried out only in a so-called idling state where the spindle is free running without any workload. However, in practical applications, machine tools are often applied in the actual cutting state with more influence factors, such as cutting parameters, cooling liquid, and cutting force. Subsequently, the thermal characteristics at idling state and actual cutting state are compared and analyzed in this paper. It was found that the thermal error compensation model under idling state is not precise enough to be applied in actual cutting state. Also, further research finds that different combinations of cutting parameters, such as spindle speed and feed rate, also have influences on the accuracy of prediction and robustness of thermal error model under actual cutting state. Therefore, the cutting parameters of spindle speed, feed rate, depth of cut, and ambient temperature are studied with the usage of the Taguchi method. Through calculating signal-to-noise ratio (SN) of each combination through residual standard deviation of thermal error model, the combination of optimal cutting parameters can be obtained. The resultant analysis shows that the thermal error model under the combination of optimal cutting parameters demonstrates higher accuracy of prediction and better robustness.     

电机软启动器启动时间的计算

以电机软启动器时间计算研究为主,通过对电启动机在从最开始的运转到运行结束每个阶段的运动速度以及运动时间、力矩等,计算出电机在每段时间内加速运行的时间。结果证明在知道一端电压、电机力矩、负载力度的情况下,能够得到电机在运转过程中的平均电压,然后在通过电压与加速力矩,得到电机在某一时间内的运行速度,将这些运行速度相加,直到电机的运动结束为止,得到电机在整个启动过程中的时间。通过这些计算,我们可以知道,电机软启动器时间计算所涉及的内容很多,电厂中软启动器时间计算的精确度要求是相当高的。     

数控机床伺服进给系统无传感器检测技术

提出一种基于光栅尺与编码器信号的机床伺服进给系统定位精度检测方法;深入研究电流、扭矩、润滑特性之间关系,获取伺服电动机电流并据此对机床润滑状态进行分析和监测.在全闭环和半闭环条件下进行单轴直线和两轴联动圆测试,实验表明位置、瞬时速度等光栅尺、编码器信息可以用于机床伺服进给系统精度评定和控制特性评估;进行了不同进给速度下的恒速、润滑特性测试,试验分析表明机床润滑特性符合Stribeck摩擦效应,能够实现对机床润滑和运行状态进行监测.     

BCD码控制车床主轴分级调速系统

介绍数控车床主轴电机驱动调速系统的控制原理，二位ＢＣＤ码控制调速的软件及变速机构设计方法。     

Integration of cutting force control and chatter suppression control into automatic cutting feed adjustment system design

Abstract

This study designed an automatic cutting feed adjustment system for computer numerical control (CNC) turning machine tools, which integrate the operational characteristics of cutting force control and chatter suppression control to shorten the machining time and maintain the quality of workpieces. The setting of appropriate machining conditions (such as cutting feed, spindle speed and depth of cut) to consider both machining quality and efficiency often causes difficulties for machine tool operators. Therefore, this study uses cutting force control to design an automatic cutting feed adjustment method for cutting tools, and then, the chatter suppression control design is used to modify the cutting force command to suppress cutting chatter. The experimental results of the CNC turning machine tool show that the use of the cutting force control to adjust the cutting feed can shorten the machining time; however, the cutting chatter results in larger surface waviness on the workpiece surface. When the cutting force command is properly modified by actuating the chatter suppression control, the workpiece shows better surface roughness with prolonged machining time. Therefore, the cutting tests demonstrate that the proposed system is feasible for satisfying the machining requirements of the manufacturing processes of mechanical parts for high speed and high accuracy.     

复合型超声波电机在数控机床中的应用研究

复合型超声波电机是一种新型摩擦驱动器，具有低转速大转矩、可用于直接驱动、断电时具有高自锁力矩、高转角分辨率、小型轻量、响应速度快、运行平稳等特点。基于这些特点探索了复合型超声波电机在数控机床的转角坐标中的应用，为解决超声波电机在精密定位控制中的强非线性影响，提出了一种新型的脉冲法精密定位方法，介绍了定位方法的原理及其相应系统的设计、总体结构和实现过程，并对控制参数的选择进行了探讨和实验研究。实验结果表明，采用该方法对任意转角的重复定位精度在0．010之内，表明了这一方法的有效性和高精度。