Non-contact electromagnetic exciter design with linear control method

A non-contact type force actuator is necessary for studying the dynamic performance of a high-speed spindle system owing to its high-speed operating conditions. A non-contact electromagnetic exciter is designed for identifying the dynamic coefficients of journal bearings in high-speed grinding spindles. A linear force control method is developed based on PID controller. The influence of amplitude and frequency of current, misalignment and rotational speed on magnetic field and excitation force is investigated based on two-dimensional finite element analysis. The electromagnetic excitation force is measured with the auxiliary coils and calibrated by load cells. The design is validated by the experimental results. Theoretical and experimental investigations show that the proposed design can accurately generate linear excitation force with sufficiently large amplitude and higher signal to noise ratio. Moreover, the fluctuations in force amplitude are reduced to a greater extent with the designed linear control method even when the air gap changes due to the rotor vibration at high-speed conditions. Besides, it is possible to apply various types of excitations: constant, synchronous, and non-synchronous excitation forces based on the proposed linear control method. This exciter can be used as linear-force exciting and controlling system for dynamic performance study of different high-speed rotor-bearing systems.     

考虑结合面和轴向力的主轴系统动力学特性

汽车覆盖件淬硬钢模具由于硬度高,在铣削过程中动态铣削力大,易发生颤振,而主轴系统动力学特性直接影响铣削稳定性。为了准确建立主轴系统动力学模型,考虑主轴系统铣削状态下产生的轴向铣削力和离心力对主轴结合面接触刚度的影响。通过分析得到,轴向铣削力对主轴结合面接触刚度有强化作用,使主轴系统固有频率有微小的增加;而离心力对结合面接触刚度有软化作用,随着主轴转速升高,系统的固有频率减小,尤其高转速时主轴系统的动力学特性偏差较大,对比而言离心力的软化作用多于轴向铣削力的强化作用,故主轴系统在铣削过程中动力学特性相比静止无载状态下仍是软化现象;分析结合面预紧力、刀具参数等因素对主轴系统动力学特性的影响规律,为准确分析主轴系统动力学特性和预测铣削稳定性提供理论参考。     

高精度动态切削力自感知智能刀具的研究

切削状态监测是高档数控机床实现智能加工的必备功能,而切削力测量是进行切削状态监测最直接、有效的方法。目前商业化的切削力测力仪由于体积大、价格贵、兼容性差等原因,难以满足实际工业生产的应用要求。针对机械加工过程中动态切削力的准确测量这一研究目标,提出了一种具有切削力自感知功能的智能刀具,该智能刀具以刀杆作为弹性敏感元件、以半导体应变计作为信号转换元件;通过理论计算和有限元仿真,确定了封装半导体应变计的最佳应力区域以及传感器测量电路的设计方案。所研制的智能刀具结构紧凑、兼容性好、精度高、动态特性好,试验结果显示主切削力F_c方向的静态精度为1.799%、横向交叉干扰为2.610%,进给力F_f方向的静态精度为1.628%、横向交叉干扰为0.694%,智能刀具的固有频率为1 778.98 Hz,可以满足在机床主轴转速不超过26 685 r/min的高速切削过程中准确测量动态切削力的应用需求。     

高速主轴过盈联结特性研究

高速主轴是高速切削技术的核心部件，其与电动机转子间的过盈量的大小是影响主轴的几何精度、运动精度、加工精度的关键因素。高速主轴与转子间的联结特性不仅受到初始装配公差的影响．还受到离心力的影响，且随着转速的提高。离心力的影响也越来越大。因此．设计过盈联结时．必须综合考虑接触应力、扭矩和转速对联结特性的影响。文章研究了高速主轴过盈联结的特性，分别推导出了高速主轴在静态和动态条件下过盈量和接触应力的理论公式。上述公式的推导有助于高速主轴过盈联结的设计。提高主轴的运动特性和加工特性。     

基于开放式控制器的铣削颤振在线抑制

为实现在线抑制铣削颤振,对颤振领域常用的传感器监控技术,尤其是三向切削力和振动加速度传感器的各向分量在颤振监控过程中的时域和频域敏感信号特征进行试验研究。针对监控的颤振敏感信号频域特性,研究快速傅里叶变换技术对信号有效信息的在线提取技术。对自激颤振的机理进行分析,建立颤振频率与主轴转速间的关系模型,为实现变主轴转速抑制自激颤振提供理论基础。对集成在线参数采集、反馈控制的全软件型模块化铣削控制器进行设计,将在线抑制颤振的相关变主轴转速算法嵌入开放式控制器中,并设计控制参数数据流在控制器模块间的实现流程。对连续变切削深度铝合金工件进行在线颤振抑制加工试验,试验验证开放式智能铣削控制器在线抑制颤振相关技术的正确性。     

Electromagnetic actuator for determining frequency response functions of dynamic modal testing on milling tool

Machine tools are the main driving forces of industrialization of a country. However, poor machinability because of chatter vibration results in poor surface quality, excessive noise, and reduced material removal rate. Modal testing is a useful method to investigate dynamic properties of a cutting tool system and improve material removal rate. However, at present, modal testing using impact hammer is limited by certain problems. This paper developed a non-contacting electromagnetic actuator (EMA) to determine frequency response functions (FRFs) under amplitude and speed dependencies of cutting milling tools. The geometry was designed using magnetic circuit analysis and generalized machined theory before finite element analysis was conducted using magnetostatic-ansys software. Next, EMA was used as a contacting and non-contacting exciter of a conventional milling machine to determine the FRFs and dynamic properties of milling tool with amplitude and speed dependencies including comparison with static FRFs. Subsequently, dynamic properties and FRFs are used to establish stability lobe diagram. Stability lobe diagram also shows an improvement of up to 5% of depth of cut at lower spindle speed. In conclusion, by generating force that applies to static and dynamic modal testing, an EMA can determine dynamic properties and stability lobe diagram for increasing material removal rate and production rate.     

Estimation of the cutting torque without a speed sensor during CNC turning

In this paper, the cutting torque of a CNC machine tool during machining is monitored through the internet. To estimate the cutting torque precisely, the spindle driving system is divided into two parts: electrical induction motor part and mechanical part. A magnetized current is calculated from the measured three-phase stator currents and used for the total torque estimation generated by a spindle motor. Slip angular velocity is calculated from the magnetized current directly, which gets rid of the necessity of a spindle speed sensor. Since the frictional torque changes according to the cutting torque and the spindle rotational speed, an experiment is adopted to obtain the frictional torque as a function of the cutting torque and the spindle rotation speed. Then the cutting torque can be calculated by solving a 2^nd order difference equation at a given cutting condition. A graphical programming method is used to implement the torque monitoring system developed in this study to the computer and at the same time monitor the torque of the spindle motor in real time through the internet. The cutting torque of the CNC lathe is estimated well within an about 3% error range in average in various cutting conditions.     

永磁同步型磨削电主轴偏心振动分析及实验*

电主轴是将旋转主轴与电机转子集成为一体的主轴单元,结构复杂,由于加工或装配误差等原因,电主轴转子会存在着一定的偏心量,为探求由于电主轴偏心所导致的转子振动特性,建立了电主轴转子偏心模型,采用Maxwell应力张量法计算了偏心造成的不平衡磁拉力(UMP),将UMP解析式代入Jeffcott转子模型,得到了转子偏心振动方程。以某磨床的永磁同步电主轴为研究对象,利用有限元方法分析了UMP,发现作用于转子的UMP始终指向气隙最小的方向,研究了不同转速下转子在质量偏心离心力和UMP作用下的振动响应。研究结果表明,电主轴在低速运行时,UMP为转子振动的主要来源;随着转速的增加,质量偏心离心力对转子振动的影响更加明显,而UMP大小保持不变,其频率随转速增加而增大,对转子振动的作用随之减弱。对某机床厂所研发永磁同步型磨削电主轴在试运行时产生的振动问题进行了实验,对主轴振动频谱分析后判断实验电主轴存在静态偏心,测得主轴轴心轨迹对前述分析进行了验证。     

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.     

Counterbalance of cutting force for advanced milling operations

The goal of this work is to concurrently counterbalance the dynamic cutting force and regulate the spindle position deviation under various milling conditions by integrating active magnetic bearing (AMB) technique, fuzzy logic algorithm and an adaptive self-tuning feedback loop. Since the dynamics of milling system is highly determined by a few operation conditions, such as speed of spindle, cut depth and feedrate, therefore the dynamic model for cutting process is more appropriate to be constructed by experiments, instead of using theoretical approach. The experimental data, either for idle or cutting, are utilized to establish the database of milling dynamics so that the system parameters can be on-line estimated by employing the proposed fuzzy logic algorithm as the cutting mission is engaged. Based on the estimated milling system model and preset operation conditions, i.e., spindle speed, cut depth and feedrate, the current cutting force can be numerically estimated. Once the current cutting force can be real-time estimated, the corresponding compensation force can be exerted by the equipped AMB to counterbalance the cutting force, in addition to the spindle position regulation by feedback of spindle position. On the other hand, for the magnetic force is nonlinear with respect to the applied electric current and air gap, the characteristics of the employed AMB is investigated also by experiments and a nonlinear mathematic model, in terms of air gap between spindle and electromagnetic pole and coil current, is developed. At the end, the experimental simulations on realistic milling are presented to verify the efficacy of the fuzzy controller for spindle position regulation and the capability of the dynamic cutting force counterbalance.     

A study on the development of a new conceptual automatic variable preload system for a spindle bearing

In machine-tool spindle systems, rolling bearings are generally the most widely used type of bearing, offering high stiffness and a large load capacity. The performance of bearings is greatly affected by the applied preload. This paper suggests a new automatic variable preload system that uses an eccentric mass device applied to the bearings of a spindle system. A spindle sustains centrifugal force when rotating. The eccentric mass device converts the radial direction force caused by the centrifugal force into axial force using an eccentric mass device. The eccentric mass device applies a small amount of force to the bearing when the spindle rotates at a low speed and applies large force to the bearing when the spindle rotates at a high speed. In this design, the device maintains a large preload at low speeds and lowers the preload at high speeds. Depending on the increase in the spindle rpm, the force that the eccentric mass device delivers to the axial direction will also increase. In addition, the preload applied to the bearings will be reduced. A finite element analysis was conducted to predict the shape of the eccentric mass device and changes of the preload. Based on the analysis results, a prototype was fabricated. According to the results of experiments conducted on the prototype, it was confirmed that the automatic variable preload device with the suggested structure operated satisfactorily. Also, vibration and noise of the prototype were measured and analyzed. The approach suggested in this study is expected to allow reduced manufacturing and operating costs, as the complex devices for hydraulic pressure or electricity required in existing variable preload devices can be eliminated.     

磁悬浮铣削电主轴转子-刀具变质量不平衡系统动态特性研究

针对磁悬浮铣削电主轴在切削过程中因切屑进入刀具容屑槽中而导致“刀具-主轴”系统质量变化,进而引起系统回转精度不稳定的问题,以变质量质点理论为依据建立“切屑-刀具-主轴”系统的变质量动力学模型。分析系统的不平衡质量变化时所引起的系统振动,进而导致磁悬浮轴承定/转子间气隙磁场不均所产生不平衡磁拉力,并利用等效磁路法建立不平衡磁拉力模型。利用Riccati传递矩阵法求解磁悬浮铣削电主轴转子-刀具系统的稳态动力学模型,得到系统的模态参数和初始偏心质量影响下的不平衡响应。考虑铣削力、变质量力、切屑质量不平衡离心力和不平衡磁拉力等因素,采用Newmark-β算法求解磁悬浮铣削电主轴转子-刀具变质量系统的瞬态动力学模型。对系统从起动到切削过程的动态响应进行仿真分析,结果表明,质量不平衡是影响磁悬浮铣削电主轴转子-刀具系统稳态响应的主要因素;在切削过程中,变质量力是影响系统瞬态响应的主要因素;不平衡磁拉力对系统响应的影响与系统的稳定性成负相关与系统的振幅成正相关。     

Spindle vibration suppression for advanced milling process by using self-tuning feedback control

The goal of this work is to concurrently counterbalance the dynamic cutting force and regulate the spindle position deviation under various milling conditions by integrating active magnetic bearing (AMB) technique, fuzzy logic algorithm, and an adaptive self-tuning feedback loop. The experimental data, either for idle or cutting, are utilized to establish the database of milling dynamics so that the system parameters can be on-line estimated by employing the proposed fuzzy logic algorithm as the cutting mission is engaged. Based on the estimated milling system model and preset operation conditions, i.e., spindle speed, cut depth, and feed rate, the current cutting force can be numerically estimated. Once the current cutting force can be real time estimated, the corresponding compensation force can be exerted by the equipped AMB to counterbalance the cutting force, in addition to the spindle position regulation by feedback of spindle position. At the end, the experimental simulations on realistic milling are presented to verify the efficacy of the fuzzy controller for spindle position regulation and the capability of the dynamic cutting force counterbalance.     

Real‐Time Monitoring of Tool Fracture in Turning Using Sensor Fusion

The sensor fusion method using both an acoustic emission (AE) sensor and a built-in force sensor is introduced for on-line tool condition monitoring during turning. The cutting force was measured by a built-in piezoelectric force sensor, which was inserted in the tool turret housing of an NC lathe. FEM analysis was carried out to locate the most sensitive position for the sensor. A burst of AE signal was used as a triggering signal to inspect the cutting force. A significant drop in cutting force indicated tool breakage. The algorithm was implemented in a DSP board and the monitoring system was installed on a CNC lathe in an FMS line for in-process tool-breakage detection. The proposed system showed an excellent monitoring capability.     

高速喷漆涡轮转子轴疲劳寿命分析

通过对高速喷漆涡轮转子轴质量等效,将涡轮系统复杂振动转化为简单的单自由度振动问题。在此基础上,论述了等幅应力下有限疲劳寿命分析方法,推算出高速喷漆涡轮转子轴有限疲劳寿命,分析了该转子轴直径、悬臂长、振动幅值及偏心距对疲劳寿命的影响规律。为转子轴的维修和制造奠定基础。     

Chatter prevention for milling process by acoustic signal feedback

This paper presents how real-time chatter prevention can be realized by feedback of acoustic cutting signal, and the efficacy of the proposed adaptive spindle speed tuning algorithm is verified as well. The conventional approach to avoid chatter is to select a few appropriate operating points according to the stability lobes by experiments and then always use these preset cutting conditions. For most cases, the tremble measurement, obtained by accelerometers or dynamometers, is merely to monitor spindle vibration or detect the cutting force, respectively. In fact, these on-line measures can be more useful, instead of always being passive. Furthermore, most of these old-fashioned methodologies are invasive, expensive, and cumbersome at the milling stations. On the contrary, the acoustic cutting signal, which is fed into the data acquisition interface, Module DS1104 by dSPACE, so that an active feedback loop for spindle speed compensation can be easily established in this research, is non-invasive, inexpensive, and convenient to facilitate. In this research, both the acoustic chatter signal index (ACSI) and spindle-speed compensation strategy (SSCS) are proposed to quantify the acoustic signal and compensate the spindle speed, respectively. By converting the acoustic feedback signal into ACSI, an appropriate spindle speed compensation rate (SSCR) can be determined by SSCS based on real-time chatter level. Accordingly, the compensation command, referred to as added-on voltage (AOV), is applied to actively tune the spindle motor speed. By employing commercial software MATLAB/Simulink and DS1104 interface module to implement the intelligent controller, the proposed chatter prevention algorithm is practically verified by intensive experiments. By inspection on the precision and quality of the workpiece surface after milling, the efficacy of the real-time chatter prevention strategy via acoustic signal feedback is further examined and definitely assured.     

航空钛合金高效插铣加工实验与多目标优化研究

钛合金整体叶盘是航空发动机的重要零部件,结构复杂,加工难度大。插铣加工因其轴向承受能力强和刚性大等特性,非常适合加工钛合金整体叶盘这类难加工、结构复杂的零部件。针对钛合金插铣加工效率的问题,采用响应曲面法设计插铣实验,建立切削力经验模型,以切削力和材料去除率为目标,采用NSGA-II算法进行多目标优化获得Pareto最优解。研究表明:切削力随主轴转速的增加而缓慢减小,随切削宽度、切削步距和每齿进给量的上升而增加;与实验初始参数组合相比,优化后的材料去除率提高了81.19%,而切削力减小了23.68%,达到了本研究的高效加工目标。     

Analysis of cutting force coefficients in high-speed ball end milling at varying rotational speeds

In high-speed ball end milling, cutting forces influence machinability, dimensional accuracy, tool failure, tool deflection, machine tool chatter, vibration, etc. Thus, an accurate prediction of cutting forces before actual machining is essential for a good insight into the process to produce good quality machined parts. In this article, an attempt has been made to determine specific cutting force coefficients in ball end milling based on a linear mechanistic model at a higher range of rotational speeds. The force coefficients have been determined based on average cutting force. Cutting force in one revolution of the cutter was recorded to avoid the cutter run-out condition (radial). Milling experiments have been conducted on aluminum alloy of grade Al2014-T6 at different spindle speeds and feeds. Thus, the dependence of specific cutting force coefficients on cutting speeds has been studied and analyzed. It is found that specific cutting force coefficients change with change in rotational speed while keeping other cutting parameters unchanged. Hence, simulated cutting forces at higher range of rotational speed might have considerable errors if specific cutting force coefficients evaluated at lower rotational speed are used. The specific cutting force coefficients obtained analytically have been validated through experiments.     

基于磁悬浮轴承高速电主轴的法向磨削力检测方法

利用磁悬浮轴承高速电主轴作为检测器件解决高速磨削法向磨削力实时在线测量困难的问题。通过对磁悬浮轴承高速电主轴转子的动力学分析,得到法向磨削力与电主轴转子位移的两阶导数和转子受到的电磁力的关系。转子的位移数据可由磁悬浮轴承电主轴中的位移传感器的输出得到。为了精确求取电磁力,气隙磁通密度采用图解法求出,消除线性化引入的系统误差;气隙宽度由遍历搜索法标定,消除系统加工装配误差对电磁力测量带来的影响;引入修正系数对由漏磁、磁滞和边缘效应带来的测量误差进行补偿,修正系数由三层神经网络动态实时求出。通过静态和动态试验对电磁力和动态磨削力的检测结果进行验证,试验结果证明基于磁悬浮轴承高速电主轴的法向磨削力检测方法的有效性和准确性。     

基于球对称环型阵列传感器的扭矩测量系统

针对恶劣环境下机械转轴扭矩动态测量问题,利用交流电磁感应原理,采用球对称环型阵列器件和专门的磁电式检测器,构造一种新型的非接触扭矩测量传感器。文章设计了传感器的结构并对测量原理进行了分析,给出了测量系统框架结构。通过磁性钢球作切割磁力线运动,引起感应信号的周期性变化,实现位移信号到电信号的转换,得到了两路具有相位差的扭矩信号,对信号进行了放大、调相和整形处理,并给出了相应的方法和处理电路。