Active chatter suppression in turning by band-limited force control

The suppression of chatter vibration is required to enhance the machined surface quality and to increase tool life. In this study, a new, conceptually active approach for chatter suppression in machining is proposed. The hybrid control method developed by applying sensorless force control with a disturbance observer enables the simultaneous and independent control of the position trajectory and band-limited forces. The proposed method is introduced to the carriage of a prototype desktop-sized turning machine, and the ability to suppress chatter is evaluated by end-face cutting tests. The results demonstrate that actively controlling a band-limited force leads to the avoidance of chatter.     

Model-based controller design for machine tool direct feed drives

This paper presents a controller design methodology for machine tool direct feed drives. The methodology is applied to a linear motor (LM) and a piezoelectric actuator (PA). The structure of each plant model is obtained from physical laws and its parameters are obtained using system identification. A single transfer function (TF) model is shown to accurately predict the response of the LM. For the PA, multiple local models are required to accurately represent its dynamics. Next, a procedure for designing a model-based two degrees-of-freedom (2DOF) controller with anti-windup protection is presented for the single model and multiple model cases. With the LM, friction compensation, force ripple compensation and a disturbance observer are added to improve the tracking performance. Experimental results for both drives are included for step, ramp and sinusoidal reference inputs. For the LM, the rise time for a 1000 μm step input is reduced from 25 to 3.5 ms in comparison to a proportional-integral-derivative (PID) controller. For the PA, the rise time for a 10 μm step is reduced from 6 to 1.5 ms.     

On-line control of machine tool vibration in turning

This paper presents a system developed for on-line vibration control on a turning lathe. Relative vibration between the workpiece and the cutting tool is sensed with the help of a bifurcated bunch of optical fibres which is then phase shifted, amplified and fed back to a specially designed piezoelectric vibrator supporting the tool. Whenever a vibration occurs, leading the machine tool-cutting process system to instability, the close-dloop feedback contour, with the help of the vibrator-exciter, generates an equal and opposite force to stabilize the vibration. Results obtained by mathematical modelling and experimental investigations indicate a significant improvement in the dynamic characteristics of the machine tool resulting in considerably higher productivity, accuracy and finish.     

Machine tool feed drives

This paper reviews the design and control of feed drive systems used in machine tools. Machine tool guides designed using friction, rolling element, hydrostatic and magnetic levitation principles are reviewed. Mechanical drives based on ball-screw and linear motors are presented along with their compliance models. The electrical motors and sensors used in powering and measuring the motion are discussed. The control of both rigid and flexible drive systems is presented along with active damping strategies. Virtual modeling of feed drives is discussed. The paper presents the engineering principles and current challenges in the design, analysis and control of feed drives.     

变频器在机床电力拖动中的应用问题

本文分析了机床拖动的特点,变频调速对电动机及变频器的要求,分析了变频器应用中的干扰问题及采取的抑制措施。     

Analysis of acoustic emission in chatter vibration with tool wear effect in turning

The progressive wear of cutting tools and occurrence of chatter vibration often pose limiting factors on the achievable productivity in machining processes. An effective in-process monitoring system for tool wear and chatter therefore offers the unique advantage of relaxing the process parameter constraints and optimizing the machining production rate. This research presents a dynamic model of the cutting RMS acoustic emission (AE) signal when chatter occurs in turning, and it determines how this motion is related to the RMS AE signal in the presence of tool flank wear. The tool wear effect on acoustic emission generated in turning is expressed as an explicit function of the cutting parameters and tool/workpiece geometry. The AE generated from the sliding contact on the flank wear flat during chatter is investigated based on the energy dissipation principle. This model offers an explanation of the phenomenon of chatter vibration in the neighborhood of the chatter frequency of the tool. It also sheds light on the variation of the RMS AE signal power in close correlation to the characteristic of the state of wear. Cutting tests were conducted to determine the amplitude relationship between RMS AE and cutting parameters. It is shown that RMS AE is quite sensitive to the dynamic incremental changes in the friction and the wear flat mechanism active in machining processes.     

Motion control for linear motor feed drives in advanced machine tools

Minimum-time path optimization (MTPO) and minimum-time tracking control (MTTC) have previously been introduced as effective strategies for controlling high-speed machine tools [D. Renton, M.A. Elbestawi, High speed seruo control of multi-axis machine tools, Int. J. Machine Tools Manuf. 40 (2000) 539–559]. It has been argued that the effectiveness of these strategies is due to their ability to accommodate the dominating saturation effects in control of high-speed machine tools. In this paper the application of MTPO and MTTC to linear-motor-driven machines is examined. It is found that the attention paid to saturation limits by MTPO and MTTC strategies provides significant performance improvements for linear-motor-driven machines. Issues such as improved stiffness to periodic disturbances, improving holding torque through heat-reducing commutation methods and improved sensor feedback are also examined.     

A novel cascade control principle for feed drives of machine tools

Most feed drives in machine tools are designed using ball screw drives. The bandwidth of such drives with conventional PPI control principle is limited by the first natural frequency of mechanical transmission elements. A novel feedback control principle is presented to improve feed drive dynamics. It is cascade structured and consists of a weakly set motor speed controller, a disturbance observer with the feedback velocity of machine table and a PD position controller. This principle increases the bandwidth of the position loop over 200% without any extra sensor or actuator. Experimental results validate the effectiveness and robustness of this principle.     

Programming spindle speed variation for machine tool chatter suppression

This paper presents a novel method for programming spindle speed variation for machine tool chatter suppression. This method is based on varying the spindle speed for minimum energy input by the cutting process. The work done by the cutting force during sinusoidal spindle speed variation S³V is solved numerically over a wide range of spindle speeds to study the effect of S³V on stable and unstable systems and to generate charts by which the optimum S³V amplitude ratio can be selected. For on-line application, a simple criterion for computing the optimal S³V amplitude ratio is presented. Also, a heuristic criterion for selecting the frequency of the forcing speed signal is developed so that the resulting signal ensures fast stabilization of the machining process. The proposed criteria are suitable for on-line chatter suppression, since they only require knowledge of the chatter frequency and spindle speed. The effectiveness of the developed S³V programming method is verified experimentally.     

Hybrid modelling of machine tool axis drives

The x-axis dynamics of a milling machine where the workpiece and saddle are mounted on supporting slides is considered. A permanent magnet motor, lead screw, ball nut and bearings are employed as the machine, traverse actuator mechanism. Hybrid, distributed–lumped parameter methods are used to model the machine tool x-axis drive system. Inclusion of the spatial configuration of the drive generates the incident, travelling and reflected vibration signature of the system. Lead screw interactive torsion and tension loading, which is excited by cutting and input disturbance conditions, is incorporated in the modelling process. Measured and results from simulation exercises are presented in comparative studies enabling the dynamic characteristics of the machine to be identified under, no load and with the application of cyclic, cutting force disturbances. The effect of the lead screw length, cutting speed and hence the load disturbance frequency are examined and the resulting performance accuracy is commented upon.     

模糊自适应PID在数控进给伺服系统的应用

数控机床的进给伺服控制是复杂的机电耦合系统,因其存在参数时变、负载扰动以及电机的非线性等缺点,很难为其建立准确的模型。模糊Fuzzy控制具有无需建立被控对象的数学模型、鲁棒性好等优点但稳态精度差,将模糊控制和PID控制相结合,设计了模糊自适应PID控制器,并将此应用于数控伺服系统的控制中,该控制器具有较完善的控制性能。仿真实验的结果表明,采用该模糊自适应PID控制器具有较高的稳定精度,较强的鲁棒性。     

A new perspective and analysis for regenerative machine tool chatter

The paper contains a practical perspective on regenerative machine tool chatter. Chatter is a well known phenomenon, occurrence of which is undesired in manufacturing. Aggressive machining conditions, in the sense of removing more metal rapidly, usually cause chatter. In most cases, these conditions can be determined a priori to the operation. A chatter stability study and its reasoning based on root locus plot analysis of time delayed systems is presented as a new and practical perspective in the field. At the junction of root locus and chatter concepts an area of particular interest to the authors arises: a new method for active vibration suppression, the Delayed Resonator. It is an active vibration absorber tuning of which is achieved utilizing a simple time delayed feedback. The cross linking between the Delayed Resonator study and the subject matter, machine tool chatter, is exciting to share. This is the primary motivation in pursuing this study. One of the highlights of the work appears at the phenomenon called Dual Frequency Delayed Resonator. This feature has been conjectured in the literature using the well known “stability lobes”, but never discussed with detail.     

Optimization of multiple tuned mass dampers to suppress machine tool chatter

Chatter is more detrimental to machining due to its instability than forced vibrations. This paper presents design and optimal tuning of multiple tuned mass dampers (TMDs) to increase chatter resistance of machine tool structures. Chatter free critical depth of cut of a machine is inversely proportional to the negative real part of frequency response function (FRF) at the tool–workpiece interface. Instead of targeting reduction of magnitude, the negative real part of FRF of the machine is reduced by designing single and multiple TMD systems. The TMDs are designed to have equal masses, and their damping and stiffness values are optimized to improve chatter resistance using minimax numerical optimization algorithm. It is shown that multiple TMDs need more accurate tuning of stiffness and natural frequency of each TMD, but are more robust to uncertainties in damping and input dynamic parameters in comparison with single TMD applications. The proposed tuned damper design and optimization strategy is experimentally illustrated to increase chatter free depth of cuts.     

A comprehensive chatter prediction model for face turning operation including tool wear effect

This paper presents a three-dimensional mechanistic frequency domain chatter model for face turning processes, that can account for the effects of tool wear including process damping. New formulations are presented to model the variation in process damping forces along nonlinear tool geometries such as the nose radius. The underlying dynamic force model simulates the variation in the chip cross-sectional area by accounting for the displacements in the axial and radial directions. The model can be used to determine stability boundaries under various cutting conditions and different states of flank wear. Experimental results for different amounts of wear are provided as a validation for the model.     

结合PLC对X5032机床的变频调速改造

本文阐述了X5032的变频调速改造方案,介绍了如何通过PLC来控制变频调速的频率和其他复杂顺序加工程序.重点说明了利用BPTS系列变频器对该机床主轴的调速改造过程,最后给出了改造后机床运行的性能状况.     

Numerical simulation of non-linear chatter vibration in turning

In this paper, basic relationships and algorithms for numerical simulation of non-linear, self-excited vibrations in single degree-of-freedom cutting systems are presented. Non-linearities due to the tool leaving the cut, as well as interference between the cutting tool clearance face and cutting surface waviness, were taken into consideration. Examples of vibration simulation results are shown.     

机床主轴、进给电动机控制线路的设计

本文阐述了用继电接触器及PLC控制机床主轴、进给电动机控制线路的设计方法和思路.本程序适合于三菱系列的PLC.     

Feed drive control tuning considering machine dynamics and chatter stability

In large machine tools, where structural dynamics significantly influences the cutting stability, judicious selection of the servo control parameters can increase the damping, thereby improving the chatter stability. This paper presents a new strategy for feed drive controller tuning, which takes this effect into consideration. The proposed strategy generalizes successfully to machine tool structures with high order dynamics, and integrates model-free frequency domain estimation and analysis techniques with model-based root locus design, the latter which is achieved through an efficient and accurate identification approach. The proposed strategy has been tested in machining stability tests, demonstrating up to 30% increase in productivity.     

Adaptive turning force control with optimal robustness and constrained feed rate

In rough cutting operations, the typical economic objective is to maximize the metal removal rate by the highest possible feed rate under the constraint of tool breakage. This type of control strategy is called adaptive constraint control. However, the strategy has a poor industrial acceptance record because of the potential problems of controller instability and tool breakage resulting from the sudden change of cutting depth or spindle speed. In this paper, an adaptive turning force controller that has optimal robustness under the constraint of feed rate is presented. The experimental results for the sudden change of cutting depth are demonstrated. The proposed controller may be a promising method for the industrial application of turning force control.     

台达PLC通过RS485网络控制变频器在铣边机床上的应用

本文介绍了在专用卧式铣边机床电气系统设计中,台达PLC作为主站与多台VFD—B矢量变频器通过RS485网络通信进行凋速控制应用,充分体现了台达变频器与PLC的通信功能及便利性,说明了变频器与PLC的结合应用是目前控制电动机调速方面既先进又经济的一种方法：