Control Chattering Research Articles

Application of Permanent Magnets for Chatter Control in End Milling of Titanium Alloy Ti-6Al-4V

Machining of metals is generally accompanied by a violent relative vibration between work and tool, known as chatter. Chatter is undesirable due to its adverse effects on product quality, operation cost, machining accuracy, tool life, and productivity. This paper presents an innovative approach to chatter control during end milling of titanium alloy Ti-6Al-4V using ferrite permanent magnets to reduce the unwanted vibrations. A special fixture was fabricated and mounted on a Vertical Machining Center‘s spindle for holding the permanent magnet bars, used in suppressing the vibration amplitudes. DASY Lab 5.6 was used for signal analysis and processing to compare the intensity of chatter under normal and magnet application conditions. Fast Fourier Transform (FFT) was subsequently used to transform the vibration data to a function of frequency domain. The experiments focused on monitoring the vibration amplitudes and analysis of chip formation process during metal cutting. It was observed that the magnetic fields contributed to reduction of chatter amplitudes. It was apparent that a reduction of chatter amplitude would result in improved surface finish of the work-piece and lead to uniform chip formation.

Chatter control in the milling process of composite materials

In this paper, a model of the milling process of fibre reinforced composite material is shown. This classical one degree of freedom model of the milling process is adjusted for composite materials by variable specific cutting forces, which describe the fibre resistance. The stability lobe diagrams are determined numerically. Additionally, to eliminate the chatter vibration, small relative oscillations between the workpiece and the tool are introduced. Basing on numerical simulations the range of amplitude and the frequency of excitation is found for chatter reduction.

Robust Active Chatter Control in the High-Speed Milling Process

Chatter is an instability phenomenon in machining processes which limits productivity and results in inferior workpiece quality, noise and rapid tool wear. The increasing demand for productivity in the manufacturing community motivates the development of an active control strategy to shape the chatter stability boundary of manufacturing processes. In this work a control methodology for the high-speed milling process is developed that alters the chatter stability boundary such that the area of chatter-free operating points is increased and a higher productivity can be attained. The methodology developed in this paper is based on a robust control approach using -synthesis. Hereto, the most important process parameters (depth of cut and spindle speed) are treated as uncertainties to guarantee the robust stability (i.e., no chatter) in an a priori specified range of these process parameters. Effectiveness of the proposed methodology is demonstrated by means of illustrative examples.

Research on Dynamic Characteristics Based on Roll-Bite Model in Metal Elastic-Plastic Deformation Process

The main issue in cold rolling is the control of rolling chatter, the deformation of the metal sheet roll-bite is ideally homogeneous and elastic-plastic. In addition, only the vertical interactions of the work roll and the roll-bite are considered. The sheet force resulted from the elastic-plastic deformation of the roll-bite is established to be the dominant factor affecting the dynamic response of the work roll. Although the developed rolling system is highly nonlinear, however, the induced instability and chatter in response to various types of sheet force excitations are either modal excitation or resonance-like beating, both of which are characteristically linear. This article establishes the fundamental knowledge base required for the understanding of the characteristics and mechanism of the third and the fifth octave rolling chatters, and thus provides the essential basis for effective control of rolling instability and chatter-free roll mill design.

Coupling Dynamic Model and Control of Chatter in Cold Rolling

The dynamic model of 4-h mill, which couples with the rolling process model, the mill roll stand structure model, and the hydraulic servo system model, is built by analyzing the vibration process of cold rolling. By linearization, the multiple input multiple output linear transfer function matrix model of single stand 4-h cold mill system is obtained. With the consideration of strip quality, the model of strip thickness control system is established in a simplified form. Meanwhile, the robust controller based on quantitative feedback theory is designed for the gauge control model. A comparison with PID controller shows that the controller has better disturbance attenuation performance for parameter uncertainty and external disturbance.

Adaptive Fuzzy-Neural-Network Design for Voltage Tracking Control of a DC–DC Boost Converter

In this study, an adaptive fuzzy-neural-network control (AFNNC) scheme is designed for the voltage tracking control of a conventional dc–dc boost converter. First, the description of the circuit framework of a conventional boost converter and system modeling is introduced. Then, a total sliding-mode control (TSMC) strategy without the reaching phase in the conventional SMC is developed for enhancing system robustness during the transient response of the voltage control. In order to alleviate the control chattering phenomena caused by the sign function in the TSMC design and relax the requirement of detailed system dynamics, an AFNNC scheme is further investigated to imitate the TSMC law for the boost converter. In the AFNNC scheme, online learning algorithms are derived in the sense of Lyapunov stability theorem and projection algorithm to ensure the stability of the controlled system without the requirement of auxiliary compensated controllers despite the existence of uncertainties. The output of the AFNNC scheme can be easily supplied to the duty cycle of the power switch in the boost converter without strict constraints on control parameters selection in conventional control strategies. In addition, the effectiveness of the proposed AFNNC scheme is verified by realistic experimentations, and its advantages are indicated in comparison with the TSMC strategy.

Multi-Level Dynamics in Deep Milling of Flexible Workpiece

Chatter is the most obscuring phenomenon and significant amount of research has been documented regarding prediction, control and elimination of chatter. The present study has been undertaken in order to investigate the effects of multilevel dynamics in the dynamic stability prediction of deep end milling of the flexible parts. In the course of development of stability lobes diagram (SLD), input parameter of structure dynamics plays a vital role on the precision of SLD. In the present study CutPro is used to develop SLD for deep end milling of flexible workpiece after considering two cases of frequency response function (FRF) identification of flexible workpiece. It is shown that for deep end milling of flexible workpiece it is not enough to just identify the FRF of the workpiece only at one free end of the workpiece. To develop the exact and precise SLD it is necessary to identify the FRF of the flexible workpiece at more than one point along the axial depth depending upon how deep the workpiece is being milled.

Active Control of Milling Chatter Based on the Built-in Force Actuator

Chatter not only causes poor surface finish,but gives rise to electric spindle spindle,cutter and parts damage in a high speed machining,so there is great significance on online control of electric spindle chatter in milling.In order to effectively control electric spindle chatter in milling,the high speed induction electric spindle with a built-in force actuator based on bearingless induction motor with double-winding is presented.The finite-element-based electric spindle-tools dynamic,the dynamic milling and the electric spindle with double windings are modeled.After the electromagnetic force which is worked on the high-speed induction electric spindle with built-in actuator decoupled,the active chatter control scheme for electric spindle-tools is proposed.The influence of the controller main parameters on the stability characteristics of the milling system is investigated.The simulation results show the controller parameters can improve the stability region of milling and the proposed control scheme has obvious effect on suppressing the electric spindle chatter in milling.

Fuzzy Variable Structure Control for Uncertain Systems with Disturbance

This paper focuses on the fuzzy variable structure control for uncertain systems with disturbance. Specifically, the fuzzy control is introduced to estimate the control disturbance, the switching control is included to compensate for the approximation error, and they possess the characteristic of simpleness in design and effectiveness in attenuating the control chattering. Some typical numerical examples are presented to demonstrate the effectiveness and advantage of the fuzzy variable structure controller proposed.

Robust Control Based on Velocity Filter of Free-floating Dual-arm Space Robot System in Inertial Space

针对末端所持载荷参数未知的自由漂浮双臂空间机器人系统, 提出了基于速度滤波器的鲁棒控制方法. 利用拉格朗日方法进行运动学及动力学分析, 建立了双臂空间机器人系统欠驱动形式的动力学模型. 借助于增广变量法, 证明了可将空间机器人系统的增广广义Jacobi矩阵及动力学方程表示为一组组合惯性参数的线性函数. 在此基础上引入速度滤波器, 设计了双臂空间机器人基于速度滤波器的惯性空间轨迹跟踪鲁棒控制方案. 该速度滤波器可利用实测位置误差生成末端爪手的伪速度信号, 有效避免了相关速度信号的实时测量与反馈. 该方案的显著优点在于, 不需要测量、反馈末端爪手的移动速度和加速度, 同时有效消除了控制过程中的抖振现象. 平面自由漂浮双臂空间机器人系统的数值仿真验证了算法的有效性.

Robust Nonlinear Control of a Hypersonic Aircraft Based on Sliding Mode Control

For the characteristic of the longitudinal model of a hypersonic aircraft containing strong coupling and uncertainty, a sliding mode controller with an improved approach exponential law, using feedback linear model was designed. The controller can solve the strong coupling and uncertainty of the longitudinal model, track the velocity step input and height step input with zero tracking error, and eliminate the control chattering. The control system has nice robustness.

Numerical Solution of Tuned Mass Dampers for Optimum Milling Chatter Suppression

The most common tunings for the TMD in the field of vibration suppression areH∞andH2. However, regenerative machine tool chatter is a complex problem with many variations, which therefore requires a new tuning for the optimum chatter suppression. The real part based tuning is investigated numerically by employing the minimax numerical approach, which aims to maximize the minimum real part of the primary structure under the harmonic excitation. The performances of multiple TMDs system are discussed. A face milling case is employed to verify the benefits of multiple TMDs in increasing the chatter free depth of cut. It is concluded that multiple TMDs configuration are more effective than single TMD in chatter control.

Influence of Helix Angle in Low Immersion Milling Forces and Stability Analysis: down-Milling, up-Milling and Slotting

Chatter is the most obscuring phenomenon and significant amount of research has been documented regarding prediction, control and elimination of chatter. Chatter is still a main hindrance in achieving good surface finish and productivity. This paper presents the influence of helix angle of milling cutter in down-milling, up-milling and slotting operation. Altintas multi-frequency solution (MFS) is advanced by adding the impact of helix angle in milling forces. A comparison is made for stability lobes diagram based on the helix angle model for different helix angles against the Altintas multi-frequency solution model (MFS) and zero order approximation (ZOA) model. The comparison shows that for small helix angle the stability lobes follow the Altintas (MFS) model and for high helix angle the stability lobes follow the Altintas (ZOA) model. The experimental results prove the simulations. Introduction

Design of Chatter Measurement and Control System Based on Virtual Instrument

The technique to suppress regenerative chatter is to regulate the spindle speed around the mean speed to disturb the regenerative mechanism. According to the technique, it builds a platform to collect, process the machine working information and output control instruction. On the platform, some advanced algorithms are applied to analyze and finish the control task.

Design of Chatter Measurement and Control System Based on Virtual Instrument

The technique to suppress regenerative chatter is to regulate the spindle speed around the mean speed to disturb the regenerative mechanism. According to the technique, it builds a platform to collect, process the machine working information and output control instruction. On the platform, some advanced algorithms are applied to analyze and finish the control task.

Method for early detection of the regenerative instability in turning

Nowadays, approaches in chatter detection and control are based on chatter prediction, by using a machining system dynamic model, or on chatter detection by different techniques, but after chatter onset. They are not efficient because the models are complicated and specific (in the first case) respectively because of chatter unwanted consequences occurrence (in the second case). This paper presents a method for early detection of the process regenerative instability state (as a specific process current dynamical state), based on cutting force monitoring. Using the cutting force records, the process current dynamical state is assessed. Appropriate cutting force signal features are defined, based on signal statistic processing, signal chaotic modeling or signal harmonic analysis, and used on this purpose. The process dynamical state evolution is modeled aiming the features values prediction. Two types of models were used in this purpose: linear and neural. The instability regenerative mechanism is identified by using either dedicated features or input variable selection. The method was conceived and experimentally implemented in the case of turning process. The results show the method reliability and the possibility of using it in developing an intelligent system for stability control.

The design of smooth switching control with application to V/STOL aircraft dynamics under input and output constraints

This paper presents a smooth switching gain-scheduled control approach for linear parameter varying (LPV) system dynamics, indexed by a scalar varying parameter. The proposed approach is demonstrated by application to the planar vertical/short takeoff and landing (V/STOL) aircraft dynamics subject to input and output constraints. In the design of switching control, the switch logic determines the switching process between control laws. The usual switching logics use the instantaneous switching manner, which can cause discontinuous chattering control signal. By performing convex weightings between two individual control laws for neighboring subsystems, the proposed smooth switching gain-scheduled control approach can provide improved performance but does not arouse control signal chattering. For the studied application, the nonlinear aircraft dynamics are represented in the form of LPV systems with parameter dependence on attitude angle. The resulting design is verified by the obtained relative stability and time response simulations. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

Swarm Coordination Under Conflict and Use of Enhanced Lyapunov Control

We consider hostile conflicts between two multi-agent swarms. First, we investigate the complex nature of a single pursuer attempting to intercept a single evader (1P-1E), and establish some rudimentary rules of engagement. The stability repercussions of these rules are investigated using a Lyapunov-based stability analysis. Second, we extend the modeling and stability analysis to interactions between multi-agent swarms of pursuers and evaders. The present document considers only swarms with equal membership strengths for simplicity. This effort is based on a set of suggested momenta deployed on individual agents. The control of group pursuit is divided into two phases: the approach phase during which the two swarms act like individuals in the 1P-1E interaction, and the assigned pursuit phase, where each pursuer follows an assigned evader. A simple, single-step dissipative control strategy, which results in undesirable control chatter, is considered first. A distributed control logic is then introduced, in order to ameliorate the chatter problems. In this new logic, the dissipative control action is spread out over a time window. A wide range of case studies is tested in order to quantify the parametric effects of the new strategy.

Fuzzy Sliding Mode Control for 6-DOF Parallel Robot Based on Support Vector Machines

To realize the trajectory tracking control for six degrees of freedom parallel robot, a fuzzy sliding mode control strategy based on support vector machines is presented. Sliding mode control algorithm has complete adaptability to system disturbance and siring in sliding mode, which is used to automatically track the uncertainty of system parameters and external disturbance. Fuzzy algorithm is applied to improve the sliding mode control performance. Fuzzy support vector machines have strong treatment of non-linear signal and generalization ability, which is used to reduce the chattering in sliding mode control. The parameters of fuzzy support machines controller are optimized by hybrid learning algorithm, which combines least square algorithm with improved genetic algorithm, to get the optimal control performance for the object. The simulation results demonstrated that the control strategy designed gets tracking effect with high precision and speed, as well as reduces chattering of control under the condition of model error and external disturbance.

Performance Optimization and Comparison of TMD, MTMD and DTMD for Machining Chatter Control

This paper investigates and analyzes the performances of several types of tuned mass damper (TMD) including common single TMD(STMD), multiple tuned mass dampers (MTMD) and dual tuned mass dampers (DTMD) on the machining chatter control. Considering the special nature of the machining stability problem, the optimal design parameters of the dampers are defined as those that minimize the magnitude of the real part of the FRF of the damped machining system. This paper demonstrates the performance of the optimally designed different TMDs for machining stability improvement by calculating the stability diagrams for the turning processes. The calculation results show that a more than 60% improvement in the critical limiting cutting depth can be obtained for the optimally designed MTMD (2 TMDs) compared to the optimally designed STMD, and a more than20% improvement for the optimally designed DTMD compared to the optimally designed MTMD(2 TMDs).