停车设备型材组合机床控制系统的设计与实现

为提高停车设备型材加工效率及加工精度,针对停车设备型材组合机床设计中钻削、铣削和等离子切割的要求,开发了一套基于EtherMAC实时工业以太网总线平台的21轴组合机床控制系统。文章分析了控制系统硬件和软件需求,并阐述了系统方案的构建及功能实现过程。实际应用中,可加工型材最大长度达7.5m,钻削、铣削、等离子切割可同时进行,效率明显提高,实现了预期加工要求,为停车设备型材的自动加工提供了一个新的可行的方案。     

Geometric and force errors compensation in a 3-axis CNC milling machine

This paper proposes a new off line error compensation model by taking into accounting of geometric and cutting force induced errors in a 3-axis CNC milling machine. Geometric error of a 3-axis milling machine composes of 21 components, which can be measured by laser interferometer within the working volume. Geometric error estimation determined by back-propagation neural network is proposed and used separately in the geometric error compensation model. Likewise, cutting force induced error estimation by back-propagation neural network determined based on a flat end mill behavior observation is proposed and used separately in the cutting force induced error compensation model. Various experiments over a wide range of cutting conditions are carried out to investigate cutting force and machine error relation. Finally, the combination of geometric and cutting force induced errors is modeled by the combined back-propagation neural network. This unique model is used to compensate both geometric and cutting force induced errors simultaneously by a single model. Experimental tests have been carried out in order to validate the performance of geometric and cutting force induced errors compensation model.     

基于PC的开放式数控系统的开发

基于PC＋MPC02运动控制器开发了一套开放式数控铣床系统,该系统具有图形自动编程、加工仿真、实时监控机床加工等功能。本文介绍了该系统软、硬件组成和实现方法。     

雕铣机运动部件温度动态检测及误差补偿系统

热变形是影响机床精度的主要因素之一.本文采用了将高速雕铣机丝杠的热变形误差值加入到执行数据中,通过修改G代码而实现热变形误差的补偿.经实际生产应用表明:该方法既不影响机床的高速性能,又能使机床的精度得到较大幅度的提高.     

Geometric adaptive straightness control system for the peripheral end milling process with large error sources

An off-line Geometric Adaptive Control (GAC) scheme is proposed to compensate for machining straightness errors due to the machine tool's inaccuracy and those arising as a result of the metal cutting process during the finish peripheral end milling process. In the milling process, the workpiece travels along the guideway while the spindle system remains fixed. The scheme is based on the exponential smoothing of post-process measurements of relative machining errors due to the tool and bed deflections. Without a priori knowledge of the variations of the cutting parameters, the time-varying parameters are estimated by an Exponentially Weighted Recursive Least Squares (EWRLS) method. This method is able to incorporate a straightedge which is not necessarily accurate to identify the guideway errors. To reduce the drift of the cutting parameters, a single parameter adaptation method is introduced. Experimental results show that the location error is controlled within the range of the fixing error of the milling bed on the guideway. Further, the waviness error is reduced to less than 10 μm in the machining of a 508-mm long prismatic workpiece regardless of the machining conditions.     

Analytical models for high performance milling. Part I: Cutting forces, structural deformations and tolerance integrity

Milling is one of the most common manufacturing processes in industry. Despite recent advances in machining technology, productivity in milling is usually reduced due to the process limitations such as high cutting forces and stability. If milling conditions are not selected properly, the process may result in violations of machine limitations and part quality, or reduced productivity. The usual practice in machining operations is to use experience-based selection of cutting parameters which may not yield optimum conditions. In this two-part paper, milling force, part and tool deflection, form error and stability models are presented. These methods can be used to check the process constraints as well as optimal selection of the cutting conditions for high performance milling. The use of the models in optimizing the process variables such as feed, depth of cut and spindle speed are demonstrated by simulations and experiments.     

XK714/1数控铣床螺距误差补偿

数控机床的定位精度是影响其高精度性能的一个重要方面,因而也是数控机床验收和检测的重要指标之一。螺距误差是影响定位精度的重要因素,通过螺距误差补偿能够有效改善机床的定位精度和加工精度,对数控机床的使用和维护具有重要意义。对数控机床反向间隙补偿和螺距误差补偿的原理及测量方法进行深入研究,并针对XK714/1数控铣床FANUC 0M系统的螺距误差进行补偿,取得了良好的补偿效果,说明对滚珠丝杆传动机构的反向偏差与螺距误差进行补偿是恢复和提高机床精度的一种重要手段。     

基于PLC的切割机运动轨迹控制系统的设计

在实际应用中,很多切割机不能满足加工精度要求,精度高的切割机又十分紧缺,因此发展高精度的切割机很有必要。另一方面,很多切割机自动化水平不高,尤其是手动操作的切割机在操作时很不方便。故采用可编程终端、PLC、运动控制单元、伺服驱动系统等成熟的控制部件构建切割机运动轨迹控制系统。详细设计此系统的各个模块单元,介绍各个部件之间的数据通信和软件设计步骤,并以一个简单的例子说明了其操作过程。采用此运动系统能使加工工件的质量、机床的自动化程度、可操作性都得到大幅度的提高。     

Runout effects in milling: Surface finish, surface location error, and stability

This paper investigates the effect of milling cutter teeth runout on surface topography, surface location error, and stability in end milling. Runout remains an important issue in machining because commercially-available cutter bodies often exhibit significant variation in the teeth/insert radial locations; therefore, the chip load on the individual cutting teeth varies periodically. This varying chip load influences the machining process and can lead to premature failure of the cutting edges. The effect of runout on cutting force and surface finish for proportional and non-proportional tooth spacing is isolated here by completing experiments on a precision milling machine with 0.1 μm positioning repeatability and 0.02 μm spindle error motion. Experimental tests are completed with different amounts of radial runout and the results are compared with a comprehensive time-domain simulation. After verification, the simulation is used to explore the relationships between runout, surface finish, stability, and surface location error. A new instability that occurs when harmonics of the runout frequency coincide with the dominant system natural frequency is identified.     

铣削残余应力离散性实验研究

为了了解铣削加工表面残余应力的离散特征,对45钢在干切削和浇注润滑状态下分别进行粗/精铣削加工实验;采用数理统计方法对试样加工残余应力的离散性进行研究。实验结果表明:铣削残余应力有着明显的离散性,比车削残余应力大;铣削残余应力离散性主要来源于切削过程热力耦合的随机变化和铣削的刀具-工件复杂运动;工艺条件可以在一定范围内影响铣削残余应力离散性,粗加工的离散性比精加工大,浇注润滑离散性比干切削小。     

In-process prediction of cutting depths in end milling

In geometric adaptive control systems for the end milling process, the surface error is usually predicted from the cutting force owing to the close relationship between them, and the easiness of its measurement. Knowledge of the cutting depth improves the effectiveness of this approach, since different cutting depths result in different surface errors even if the measured cutting forces are the same. This work suggests an algorithm for estimating the cutting depth based on the pattern of cutting force. The cutting force pattern, rather than its magnitude, better reflects the change of the cutting depth, because while the magnitude is influenced by several cutting parameters, the pattern is affected mainly by the cutting depth. The proposed algorithm can be applied to extensive cutting circumstances, such as presence of tool wear, change of work material hardness, etc.     

Adaptive two-degree-of-freedom control of feed drive systems

Feed drive systems are widely used in industrial applications, and many efforts for improving their precision control have been made thus far. One of the basic approaches for improving the control accuracy of feed drive systems is to design a controller based on the internal model principle, which states that for a control system to track a reference signal without a steady state error, it needs to include a generator of the reference signal. Feed-forward controllers, such as the zero phase error tracking controller (ZPETC) proposed by Tomizuka, are also employed for improving control performance. However, prior knowledge of plant dynamics and/or reference signal properties is required for both the internal model principle and the feed-forward controller based designs. For precision control, plant dynamics should be identified in real time because feed drive dynamics are affected by varying conditions, such as frictional and thermal effects. This paper presents a new type of adaptive control for arbitrary reference tracking, which requires neither plant dynamics nor reference signal properties for controller design. This type of controller can also reduce the effect of unknown disturbances. The control system is designed using a discrete-time plant model and consists of adaptive feed-forward and feedback controllers. This design is then applied to a feed drive system with a ball screw drive. The effectiveness of the proposed design is demonstrated by simulation and experimental results, which was obtained by applying the proposed control system to an unknown reference signal whose property is varied during control.     

X80钢油气管道的钻铣切管机设计

围绕X80高强度油气管道的切割问题,分析了这一领域的国内外技术现状,介绍了钻铣切管机的组成及工作原理,设计了液压驱动方案。通过现场试验,得出了用钻铣切管机切割高强度油气管道具有在线切管不夹刀、切管时间短、能切割X80高强度油气管道的结论。     

Design and implementation of tuned viscoelastic dampers for vibration control in milling

Passive means of vibration attenuation have been employed successfully and efficiently in machining systems such as turning and milling. Traditional approach to controlling vibration in a milling system is to develop control mechanisms for cutting tools or machine spindles. However, due to the nature of milling operations where the cutting tools rotate at high speed, the passive vibration control methods find very limited application with the traditional approach. In order to utilise the potential of the passive vibration control methodology in milling applications, the milling operation should be viewed as a system comprising an elastic structure and operation parameters. Dynamics of this closed-loop system should improve with improvement in dynamics of any of the system components, especially within the elastic structure that comprises the cutting tool, the machine tool, the workholding system and the workpiece. Although the level of improvement will vary depending on which component of the elastic chain is targeted for this purpose. This paper presents the development and testing of tuned viscoelastic dampers (TVDs) for vibration control through their application on a workpiece in milling operations. This work targets workpiece held on a palletised workholding system for the control of unwanted vibration and thus deviates from the traditional approach where cutting tool and/or machine spindles are targeted for vibration control strategies. Palletised workholding systems, due to their compact design, offer an opportunity to design passive damping mechanisms that are easier to implement in the case of a milling system. The TVD developed through this research is based on a commercially available viscoelastic damping polymer. Advantage of such materials is their high damping performance over a wide range of excitation frequencies. The TVD design process has used a unique combination of analytical modelling with experimental FRF data. Modal impact testing showed that the application of the TVD reduced the amplitude of vibration acceleration by 20 dB for the target mode. Since the target mode corresponded to torsional vibration, the TVD was effective in two planar coordinates, i.e. X and Y. In addition, the TVD also significantly reduced the amplitude of a vibration mode far from the mode it was designed for. The system has been tested experimentally to demonstrate significant reduction in vibration amplitudes during a milling process. The milling tests with different combinations of cutting parameters show that multi-TVD approach is always valid regardless of the parameters being used. The only requirement for TVDs to function effectively is that the natural frequency of the system, for which the TVDs are designed, is excited during the milling process.     

高精密数控机床的非线性误差分析、控制及补偿

误差控制及补偿是提高数控机床精度的重要手段,因此误差模型的建立与分析显得至关重要.本文详细阐述了数控机床几何误差、热误差、切削力误差和控制误差的基本概念、起因、建模及参数辨识,综述了误差研究现状,并对今后的研究方向进行了展望.对减小误差的控制策略和误差综合软件补偿两个方面进行了探讨.为提高数控机床的加工精度提出了可行的思路.     

End milling tool breakage detection using lifting scheme and Mahalanobis distance

In this paper, a novel method based on lifting scheme and Mahalanobis distance (MD) is proposed for detection of tool breakage via acoustic emission (AE) signals generated in end milling process. The method consists of three stages. First, by investigating the specialty of AE signals, a biorthogonal wavelet with impact property is constructed using lifting scheme, and wavelet transform is carried out to separate AE components from the original signals. Second, Hilbert transform is adopted to demodulate signal envelope on wavelet coefficients and salient features indicating the tool state (i.e., normal conditions, slight breakage, and serious breakage) are extracted. Finally, tool conditions are identified directly through the recognition of these features by means of MD. Practical application results on a CNC vertical milling machine tool show that the proposed method is accurate for feature extraction and efficient for condition monitoring of cutting tools in end milling process.     

基于ZPETC和CCC的直驱XY平台高精度控制

针对直接驱动XY平台轮廓加工中存在的电气--机械延迟、系统参数不确定性及两轴驱动系统参数不匹配等因素的影响,提出了将零相位误差跟踪控制器(ZPETC)与交叉耦合控制器(CCC)相结合的控制策略对两轴的运动进行协调控制,实现跟踪误差与轮廊误差同时减小.ZPETC作为前馈跟踪控制器,克服了伺服滞后,使系统实现准确跟踪,减小了跟踪误差;CCC作用于两轴之间,用以增加两轴间的匹配程度,以减小轮廓误差.仿真和实验结果表明所提出的控制方案具有较好的跟踪性和鲁棒性,进而大大提高了跟踪精度和轮廓精度.     

水下单壁桩钻铣切割机设计及验证

针对水下单壁钢桩切割作业需求，设计并制造水下液压钻铣切割机，以立铣刀为切割工具，使用液压缸进给、液压马达驱动铣刀钻铣及回转切割，完成切割作业。对设备的设计依据及设备的组成进行了详细描述，分析钻铣刀、驱动马达、传动系统等参数的选用，并根据设计方案制造样机。通过对水下液压钻铣切割样机的海上及车间测试，验证设备可靠性，得出样机切割效率、铣刀消耗参数等数据。实际测试表明：该设备运行可靠，且该设备加工、使用及维护成本低，适合水下单壁钢桩切割推广使用。     

A ballscrew drive mechanism with piezo-electric nut for preload and motion control

This work reports the development of a ballscrew drive mechanism equipped with a piezo-electric nut for active ballscrew preload and fine motion control. This mechanism is intended for a motion stage of long-stroke, high-speed and ultra-precision applications. Motion of the piezo-electric nut ballscrew drive system consists of a high-speed coarse positioning and an ultra-fine positioning. Coarse positioning is done by a conventional servo motor and ballscrew where the piezo-electric nut exerts a light ballscrew preload in order to reduce the friction torque and wear at high speed motion. After the coarse positioning, a fine position adjustment is actuated by three piezo-electric actuators to get very precise positioning. Test results show that the positioning error can be fine-adjusted to the nanometer level. The low speed stability of the ballscrew drive mechanism has also been improved using the piezo-electric actuators by applying a dither signal to the ballscrew preload. The dither action can smooth and reduce the ballscrew friction force and consequently reduce the stick–slip phenomenon at low speed motion.     

Optimized feed scheduling in three axes machining. Part I: Fundamentals of the optimized feed scheduling strategy

An optimized feed scheduling strategy is proposed in this paper to maximize the metal removal rate in 3-axis machining while guaranteeing the machining accuracy. The tool path is assumed defined by a cubic parametric form. In part I of this paper, the fundamentals of this strategy are presented. This strategy integrates the feed drive dynamics, described by the acceleration/deceleration (Acc/Dec) profile, with the minimum-time trajectory planning in order to achieve the desired feed rate at the appropriate position. An optimum use of the feed drive capabilities is considered to track the changes in the cutting geometry along the tool path and to ensure an acceptable contour error. Therefore, this strategy combines different constraints and various criteria in modifying the feed rate to maintain a near-constant cutting force resulting in a highly non-linear problem. The constraints include the cutting force magnitude, the feed rate boundaries, the contour error and the characteristics of the (Acc/Dec) profile of the different feed drive systems. The criteria are the maximum production rate, the machining accuracy and safety. In part II of this paper, the effectiveness of this strategy is demonstrated using ball end mill operation on a workpiece that provides variable cutting geometry along a non-linear tool path. The performance of this strategy in terms of productivity, machining safety, and machining accuracy, is compared to a feed scheduling strategy based on control points as well as to milling with constant feed rate.