Fuzzy logic for constant force control of end milling

The machining condition usually has significant variation resulting from the change of cutting depth and the intrinsic property of the workpiece. In order to maintain the performance of a classical proportional integral derivative control system, the tool life and machining quality, conservative feedrate, and cutting depth change are prespecified as the limitations of computer numerically controlled operators. Therefore, constant cutting force control is proposed as a useful approach for increasing the metal removal rate and the tool life. However, the model-based controller cannot handle the nonlinearity of a force control system due to cutting condition variations. Here, a fuzzy controller with learning ability was employed to improve both the system performance and the adaptability. This control approach vias implemented on a retrofit old-fashioned milling machine for the end milling process. The experimental results show that this control strategy has smooth feedrate and good cutting force dynamic responses     

Recording of real cutting forces along the milling of complex parts

In this paper, a data acquisition system that simultaneously allows the recording of cutting forces and cutting tool position (coordinates X, Y and Z) is presented. Thus, the geometry of the surface being machined and the values of the cutting forces generated during the surface milling can be correlated. In this manner, two usual problems in milling experimentation are solved. First, those derive from the continuous changes in the feed rate value due to the special look ahead functions (being on-line applied by the numerical control in all high-speed milling centres), which affects the correlation between part geometry and forces. Second, those originate by the presence of unexpected stocks coming from previous semi-finishing operations, which changes the value of cutting forces respect to those calculated taking into account the theoretical tool engagement into the part.The objective of this work is the development of a diagnostics tool for allowing the detection of potential milling problems by researchers, making more profitable the performance of machining test on real complex parts. This tool can be used in the optimization of the milling of test-parts, machining real geometries that incorporate problems different from those observed in the linear tests at constant linear feeds (in end-milling conditions).The final goal of the system is the generation of cutting forces maps as a function of the geometry of real workpieces, which is an advance respect the usual forces recording in function of time or tool rotation typical of linear machining tests. In order to do that, the system incorporates a dynamometric plate for the measurement of the three components of the cutting force, as well as an acquisition card connected to the analog output of the position control loops. After machining, the file containing position and force data is post-processed and chromatic and vector maps are generated.The force analysis utility has been applied to three cases, in order to assess its feasibility in machining research projects. The first example shows a reduction of the number of tests and therefore machining time (even by 18 times) in the validation of a mechanistic cutting force model. Second example is focused on the detection of unexpected tool engagement conditions in complex parts. And the last one addresses to the milling of thin walls, for investigation of static and dynamic milling problems.     

Hyperworks在床身动静态分析及优化中的应用

床身刚度是影响高速机床加工精度的一个重要因素。针对床身刚度是否满足加工精度要求的问题,以双直线电机高速进给的铣床床身为研究对象,采用有限元方法建立床身的动力学模型,并利用有限元软件Hyperworks对床身进行动静态分析,找出该床身的动静态性能薄弱部位,利用Hyperworks的Optistruct拓扑模块对床身进行结构优化。优化后的结果表明,3个方向静刚度平均提高了1 000 N·μm-1,固有频率提高了约30 Hz,x和z向频率响应的振幅约减小50%,为同类型结构设计提供一定的参考。     

Tool breakage monitoring using motor current signals for machine tools with linear motors

In recent years, a number of machining centers have been built using linear motors. These machining centers have great potential for precision and high-speed machining. Nevertheless, a number of problems remain unsolved, such as monitoring and control. This paper presents a new tool breakage monitoring method for this type of machining center using the current signal of the linear motor. First, the relationship between the cutting force and the motor current is analyzed. Then, the new tool breakage method is presented. From a mathematical point of view, the new method uses a nonlinear energy operator to capture the abrupt changes of the motor current signal, which is directly related to the tool breakage. The experiment validation is included.     

Current-sensor-based feed cutting force intelligent estimation andtool wear condition monitoring

Tool wear condition monitoring has the potential to play a critical role in ensuring the dimensional accuracy of the workpiece and prevention of damage to cutting equipment. It could also help in automating cutting processes. In this paper, the feed cutting force estimated with the aid of an inexpensive current sensor installed on the AC servomotor of a computerized numerical control tuning center is used to monitor tool wear condition. To achieve this, the feed drive system is modeled, using neuro-fuzzy techniques, to provide the framework for estimating the feed cutting force based on the feed motor current measured. Functional dependence of the feed cutting force on tool wear and cutting parameters are then expressed in the form of a difference equation relating variation in the feed cutting force to tool wear rate. The computerized system automatically compares successive feed cutting force estimates and determines the onset of accelerated tool wear in order to issue a request for tool replacement. Experimental results show that the tool wear condition monitoring is effective and industrially applicable     

Detection of tool deflection in milling by a sensory axis slide for machine tools

Previous publications regarding the project Gentelligent Components for Machine Tools of the Collaborative Research Center 653 presented the design of a new sensory z-slide for a 5-axis machining center. Equipped with several strain sensors, the new slide is able to feel the machining process by measuring the process forces and vibrations. Here, a challenge is the detection of mechanical strains in the slide without degrading its high global stiffness. The application of micro strain gages in small notches on the slide represents a promising approach for the improvement of the sensitivity as well as the integration of sensors into the slide. This paper presents the utilization of the sensing axis-slide in a manufacturing environment. For this purpose, a first prototype of the slide is build and integrated into a milling center DMG HSC 55 linear. In this test machine, the dynamic characteristics of the integrated slide are identified with frequency response function measurements. Based on force measurements with a dynamometer, force calibration matrices are computed to calculate the forces in the machine coordinate system at the tool center point from the measured strain signals during milling processes. The force sensing with the slide allows furthermore the identification of tool characteristics such as the static tool stiffness. This parameter is estimated from the ratio of the measured contact forces and the set collision distance when moving the tool smoothly into the work piece. The known tool stiffness enables the detection of the static tool deflection from the force signals during a milling process. To compare the detected tool deflection with the real tool deflection, reference measurements on the work piece are performed using a perthometer. For further monitoring applications of the tool deflection in more complex 2.5D milling an approach to transform the measured forces from the stationary machine coordinate system into the moving tool coordinate system is presented.     

斜角裁切机切边送料系统的开发与研制

介绍了在斜角裁切机切边送料系统开发与研制过程中,如何实现定长送料和纠偏的工艺过程。通过采用电机带动同步带结构和上下橡胶辊以及上下同步移动气缸相结合的传动结构设计了定长送料机构,保证了偏光片定长送料的精度。通过采用纠偏电机和纠偏控制器以及超声波传感器等设计了送料纠偏机构,保证了送料的精度,同时提高了送料的效率。     

A smart boring tool for process control

A mechatronic metal cutting tool has been developed to improve the accuracy and flexibility of line boring machining in the automotive industry. Laser position sensors and piezoelectric actuator were integrated into the rotating body of the boring tool. To compensate the boring bar droop and effects of cutting forces, a fast tool servo utilizing feedback control of the boring tool insert position was designed and embedded in the rotating tool assembly. In addition to position control, a self-monitoring algorithm that utilizes disturbance estimator has been put together in the controller. Experimental results demonstrated that the developed cutting process controller improves the accuracy of the boring tool as well as reliably detects the process failures, such as tool tip breakage, without additional monitoring equipment.     

液压碳石墨密封环激光辅助车削的加工性能研究

为了实现液压碳石墨密封环的高效车削加工,采用激光辅助加工方法,进行了碳石墨密封环材料的激光辅助车削加工研究.考虑到碳石墨密封环材料具有高强度、高硬度等特点,利用激光束对工件进行局部加热,以提高加工效率、减小切削力和刀具磨损.针对碳石墨M104密封环的车削加工过程,进行了常规切削和激光辅助切削的对比实验研究.设计了激光辅助加工的实验流程,并进行了工艺参量的合理选择,得到了较高的切削效率.结果表明,激光辅助切削的主切削力和径向力分别比常规切削下降了23.5%和19.9%;激光辅助切削的切削区温度分布与常规切削相近;刀具磨损和破损的程度较小,能获得较好的表面加工质量.     

模糊理论在数控铣床加工中的应用研究

基于对数控铣床加工过程智能优化与提高加工效率的目的,改变传统的数控铣床加工过程中加工参数一成不变情况。本文从加工过程中,人的思维逻辑作用出发,选定模糊理论作为调整加工参数的方法设计一个能够自动调整伺服电机进给速度的模糊控制器,实现伺服电机的恒功率加工,提高铣削加工效率。并结合仿真手段对模糊控制器的控制作用进行仿真分析。找到一个合适的进给速度,对模糊控制器在数控铣床实际加工中的应用提供一个参数指导。     

Multiphase Power Converter Drive for Fault-Tolerant Machine Development in Aerospace Applications

This paper describes an experimental tool to evaluate and support the development of fault-tolerant machines designed for aerospace motor drives. Aerospace applications involve essentially safety-critical systems which should be able to overcome hardware or software faults and therefore need to be fault tolerant. A way of achieving this is to introduce variable degrees of redundancy into the system by duplicating one or all of the operations within the system itself. Looking at motor drives, multiphase machines, such as multiphase brushless dc machines, are considered to be good candidates in the design of fault-tolerant aerospace motor drives. This paper introduces a multiphase two-level inverter using a flexible and reliable field-programmable gate-array/digital-signal-processor controller for data acquisition, motor control, and fault monitoring to study the fault tolerance of such systems.      

50 μm级D形硬质合金微铣刀铣削纯铜试验研究

针对折叠波导慢波结构的微型化和高精度要求,采用自研的μEM-200CDS2组合高精度加工机床,通过线电极电火花磨削技术,制备出直径为50 μm级的D形微铣刀。在纯铜工件上开展工艺试验,研究微槽的表面质量。使用白光干涉仪、超景深显微镜、扫描电镜等仪器来观察微槽的变化情况,获得了微槽表面形貌、粗糙度等随铣削距离的变化规律,并对微铣削过程中的表面质量变化及毛刺形成的现象进行了分析。结果表明,槽底刀具的旋转轨迹纹路先是集中在刀具切出方向,随着刀具磨损,转为刀具进给方向;微槽顺铣侧毛刺多于逆铣侧,并随着铣削距离的增加而增多;微槽槽底粗糙度以线性增长趋势不断上升。     

X62W铣床PLC系统改造

X62W77能铣床是一种高效率的加工机械,在机械加工和机械修理中得到广泛的应用．万能铣床的操作是通过机械手柄N时操作电气与机械,已达到机电紧密配合完成预定的操作．是机械与电气结构联合动作的典型控制,是自动化程度较高的组合机床。继电器接触式控制系统,由于电气控制线路触点多、线路复杂、故障率高、检修周期长,给生产与维护带来诸多不便。将X62W万能铣床电气控制线路改造为可编程控制器控制,既可以提高整个电气控制系统的工作性能．又减少维护、维修的工作量。PLC控制系统无论是硬件还是软件,控制稳定可靠,具有极高的可靠性与灵活性。     

A new method based on Fiber Bragg grating sensor for the milling force measurement

Milling force is an important parameter to describe the mechanical processing chip removal process, and it has a direct influence on generation of heat, tool wear or failure, quality of machined surface and accuracy of the work piece. Its accurate measurement is a significant basis for judging process state and improving the reliability of machining system. In this study, through analyzing the variation rule of ring diameter, a new method that using Fiber Bragg grating sensors and variation rule of ring diameter to measure the milling force has been proposed, and the basic structure of annulus has also been designed. A dynamometer has also been constructed, and the preliminary verification test was done. Through the analysis of experimental data, the dynamometer based on annulus elastic body can be used in milling force test, and it owns high sensitivity.     

雷达精密深腔壳体零件数控加工动力学研究

为了确定合理的精密深腔薄壁零件铣削加工工艺参数，借助动力学仿真的数控加工工艺参数优化方法，通过建立铣削过程动力学系统实验模态分析测试平台，测试具体加工机床和不同长径比刀具的动力学特性，再应用“切削过程动力学仿真优化系统”获取特定机床不同刀具特性、不同加工阶段加工系统的切削稳定域和优化的切削参数。从而有效提高零件材料的去除效率，抑制细长刀具的切削颤振现象，较好地解决精密深腔薄壁壳体零件铣削加工时侧壁产生切削振纹的难题。     

Fuzzy Logic-Based Torque Control System for Milling Process Optimization

This paper focuses on the design and implementation of a fuzzy-logic-based torque control system, embedded in an open-architecture computer numerical control (CNC), in order to provide an optimization function for the material removal rate. The control system adjusts the feed rate and spindle speed simultaneously as needed, to regulate the cutting torque using the CNC's own resources without requiring additional hardware overheads. The control system consists of two inputs (i.e., torque error and change of error), two outputs (i.e., the feed rate and spindle speed increment) fuzzy controller, and a self-tuning mechanism, all of which are embedded within the kernel of a standard open control. The self-tuning strategy is based on the measured peaks in the torque error signal of the closed-loop system response. The self-tuning fuzzy controller is applied to the milling process in a production environment in order to demonstrate the improvements in performance and effectiveness. Two approaches are tested, and their performance is assessed using several performance measurements. These approaches are the two-input/two-output for the fuzzy controller and a single-output fuzzy controller (i.e., only feed-rate modification), with and without the self-tuning mechanism. The results demonstrate that the proposed control strategy provides better transient performance, accuracy, and machining cycle time than the others, thus, increasing the metal removal rate.     

Adaptronic gantry machine tool with piezoelectric actuator for active error compensation of structural oscillations at the tool centre point

In modern high dynamic gantry type machine tools rotary motors for feed axes have been replaced by linear direct motors. Thus, the limiting parameter in terms of the dynamic response is now the mechanical structure itself. Current design wisdom to improve the cutting accuracy is to increase the rigidity of essential machine components. This detrimentally results in either higher masses to be moved or sophisticated reinforcements being applied to the cross-arm or both. The adaptronic gantry concept proposed in this paper overcomes the need for stiffer machine structures but incorporates a light weight cross-arm. The occurring cross-arm’s structural oscillations are actively compensated by means of an additional piezo actuator that is attached between the cutting head, that moves along the cross-arm, and the tool. The piezo command is obtained from an observer that utilises additionally sensed acceleration information.     

Variable flux control of permanent magnet synchronous motor drivesfor constant torque operation

In this paper, a small signal model of permanent magnet synchronous machines is developed which includes both components of torque, i.e., magnet torque and reluctance torque. The effects of flux variations on the torque are analyzed by the use of the developed model. The off-line torque compensation method proposed for induction machines is then adapted to permanent magnet motor drives to achieve a constant torque, variable flux operation of the drives. A sensitivity analysis is performed to show that the off-line method is influenced considerably by machine parameter variations. Therefore the concept of forced compensation is introduced and an on-line torque compensation controller is proposed. Simulation results are presented to show the effectiveness of the proposed controller. An experimental vector controlled permanent magnet motor drive including the on-line torque compensation controller is implemented based on a TMS320C31 DSP to evaluate the method. The experimental results also confirm a desirable variable flux control of the motor drive under constant torque operation     

Cutting force control of milling machine

In metal cutting processes, an effective control system, which depends on a suitably developed scheme or set of algorithms can maintain machine tools in good condition. In this paper, an approach is developed for cutting force control of CNC machine. Several linear models are identified based on different working conditions. A dominant model plus uncertain terms is derived from these model set, to yield the necessary and key information from the system. Subsequently, it is used as a state estimator, and robust control is carried out by using the observed variables and cutting force. The developed approach is applied to a milling machine center. Examples taken from experimental tests shown that the developed approach is effective for the uncertain CNC machine.     

Performance optimization of a fast tool servo for single-pointdiamond turning machines

This paper describes a new, fast tool servo system designed for fabrication of nonrotationally symmetric components using single-point diamond turning machines. A prototype device, designed for flexible interfacing to typical machine tool controllers, is described, along with performance testing data of tilted flat and off-axis conic sections. Techniques for controlling the piezoelectric actuator to less than 1% error are discussed. The performance of a standard integral controller shows a significant error due to hysteresis in the actuator. The effects of the hysteresis were reduced by implementing two control schemes, an optimized PID controller and a technique that utilizes a dynamic compensator module in conjunction with the linear controller. The compensator samples the hysteretic voltage/displacement relationship in real time and modifies the effective gain accordingly. Experimental implementation results in an 80% reduction in the motion error caused by hysteresis, but peak-to-valley errors are limited by side effects from the compensation