Active Chatter Control Research Articles

Analysis of virtual inerter-based passive absorber for active chatter control

This paper presents a novel approach to active chatter control in milling operations using a new concept called the virtual inerter-based dynamic vibration absorber (VIDVA). While passive control methods, such as tuned mass damper (TMDs), have their merits, they may not provide optimal performance and adaptability in certain scenarios. Moreover, the realisation of an idealised inerter-based absorber as a localisation addition can be a difficult task to achieve. In response of these challenges, the integration of the inerter concept into virtual passive absorber (VPA) control to improve chatter stability performance is proposed. Four IDVAs are numerically evaluated to enhance the absolute chatter stability limit, and the numerical results are experimentally validated using cutting tests with a proof-mass actuator providing the control force. The study also includes robustness and actuator saturation analysis to provide a comprehensive evaluation of the proposed virtual IDVA. The findings demonstrate that the virtual IDVA offers improved chatter suppression performance, making it a promising solution for active chatter control and application of IDVAs in milling operations.

Active control of milling chatter considering the coupling effect of spindle-tool and workpiece systems

Chatter occurred in the machining process can seriously limit the processing efficiency and reduce the surface quality of the machined workpiece, which urgently needs to be controlled. Aiming at milling of flexible workpieces with similar characteristics to the spindle-tool system, two active chatter control strategies are proposed in this work. Firstly, considering the coupling effect of the spindle-tool system and the workpiece system, the milling force is developed based on the regenerative effect. And the 3D stability lobe diagram along the tool path is constructed. Then, an active chatter control structure is designed by integrating piezoelectric actuators and displacement sensors into the spindle-tool-workpiece (STW) system. Next, based on the developed milling force and active control structure, two chatter control strategies with different feedback signals are proposed using the model predictive control method. Finally, numerical simulations and milling experiments are carried out under different cutting conditions. The results show that milling chatter of the STW system can be effectively controlled by the proposed strategies. The maximum material removal rate is also significantly improved.

Fractional Calculus-Based Energy Efficient Active Chatter Control of Milling Process Using Small Size Electromagnetic Actuators

Abstract For a larger depth of cutting above a certain critical value, self-excited vibrations occur in case of milling operations. This phenomenon of unstable milling tool vibrations is called chatter and is the main cause of the workpiece surface finish deterioration. The working life of the milling tool decreases substantially if the chatter is ignored. Active chatter control technique using the fractional order control methodology is investigated in the present work. Controller parameters are optimized by using the pattern search optimization technique. Electromagnetic actuators are used to generate the required control forces. The proposed technique is compared with the optimal loop shaping (LS) robust controller and optimal traditional proportional-derivative controller. It has been observed that the chatter can be avoided with relatively much less amplitude of control forces using the proposed controller. This aspect not only reduces the size of the required actuators but substantially reduces the control energy required to maintain stability. With the proposed controller, there is 168% saving in the control energy compared with the widely used robust control strategy. The robustness properties of the proposed controller are comparable with the loop shaping robust controller. Experimental results verify the efficiency and robustness of the proposed method.

Active chatter control in turning processes with input constraint

Regenerative chatter is an annoying dynamic phenomenon in machining processes. In this paper, an adaptive sliding mode controller (SMC) is developed for turning chatter mitigation in the presence of control input constraint, parameter uncertainties, and external disturbances. Adaptive laws are employed to estimate parameter uncertainties and disturbances, while a SMC, fulfilling the control input constraint, is designed to mitigate chatter. One unique feature of the developed adaptive approach is that it guarantees chatter suppression even in the presence of control input constraint. Theoretical analyses and experimental investigations are performed, and results demonstrate that the developed SMC with chosen controller parameters guarantees chatter mitigation in the tested examples.

Feasibility analysis of active chatter control for stationary and revolving bar boring operations based on magnitude of control forces using fractional order PDλ controller

Due to the factors of limited rigidity and small inherent damping of boring bars, very small depths of cutting can be applied for chatter free machining. Stability lobe diagrams can truly represent that limit. Boring operations are categorized based on the relative motion between the boring bar and workpiece. Modelling of each category is presented in detail using a 3-DOF model. The dynamics of such systems can be successfully represented using ordinary delay differential equations and time periodic delay differential equations. The open loop stability of each type of boring operation is numerically investigated. It has been observed that the stable depth of cut is much more for revolving bar (RB) as compared to stationary bar (SB) boring process. Active chatter control (ACC) techniques can enhance the material removal rates and surface finish of the workpiece. The feasibility of active chatter control for each category is investigated in detail. It is further observed that RB boring process is not a suitable candidate for ACC because much higher harmonic control forces are required for minor improvement in critical depth of cut.

Active Control of Regenerative Chatter in Turning by Compensating the Variable Cutting Force

During metal cutting operations performed by conventional machine tools (turning, milling…) often appear vibrations due to the emergence of a variable force generated by the so-called regenerative effect. Such vibrations, known as regenerative chatter, may not be prevented at the machine design stage and often limit productivity severely. Therefore, a lot of effort has been put into developing solutions for this problem in the past. To compare the performance of such solutions, it is interesting to realistically reproduce in the laboratory the mentioned regenerative effect in a reliable, repeatable way and covering general machining conditions. With this objective, the paper presents an improvement of a Hardware-in-the-loop chatter simulator that creates this type of vibration for turning machines on a specifically designed mechanical structure. This simulator completely corrects the effects that the delay, introduced by the used equipment (by actuator and controller, mainly), has on the vibration and, moreover, it is capable of imposing general behaviors for any machine with a certain damping factor. Later, by installing inertial actuators on the mentioned structure, the operation of various active chatter control systems may be compared. In this work, the effort made to accurately create the variable machining force is harnessed to try its compensation, by generating with the inertial actuator an approximately inverse control action. In this context, the performance of the novel controller, based on the cancelation of the whole variable cutting force, is analyzed.

Chatter suppression technologies for metal cutting

Background. The cutting process is carried out in a closed elastic technological machining system and is always accompanied by vibrations. Vibrations arising during cutting, depending on the amplitude, can very slightly affect the machining result, and can lead to a catastrophic loss of stability of the whole process. In any case, all researchers agree that vibration is the factor that ultimately determines the productivity of the cutting process and the quality of the machined surface.Objective. The aim of this study is to develop new technologies for selecting parameters for controlling the cutting speed to suppress chatter by passive methods, as well as to control the drive of the forming motion to suppress chatter by active methods.Methods. The goal is achieved by creating new technologies aimed at the study of dynamic processes occurring in the cutting. It is noted that the mathematical model of the cutting process should be built taking into account the loop closed of the elastic technological machining system and the function of the delayed argument, which represents machining “on the trail”. When studying the cutting process, four main groups of factors that influence its mathematical representation are taken into account, and three approaches are used to determine the stability diagram: frequency analysis, root analysis of the characteristic equation of motion of the system and the numerical method. The numerical method using the amplitude-frequency characteristics according to the corresponding stability criterion is considered to be the most effective.Results. The results of theoretical studies are used in practice in the form of technologies for passive and active chatter reduction during cutting. A technology has been developed to suppress vibrations during face milling when controlling the spindle speed according to a harmonic law. An application program for simulating a process for determining the parameters of the control law is presented. For active control, a new technology is proposed, based on the use of a CNC machine drive with an additional closed system, introducing a harmonious signal into the channel of the shaping movement, the amplitude and phase of which are automatically adjusted using the coordinate-wise descent algorithm according to the criterion of the minimum amplitude of the motor current.Conclusions. The technology of chatter suppression during face milling by controlling the spindle speed according to the harmonic law is limited by the speed of the spindle drive and its inertial characteristics. The active chatter control system uses a standard servo drive of the CNC machine, which has an additional closed loop for automatically searching for the amplitude and phase of the compensating control signal

Efficient active chatter mitigation for boring operation by electromagnetic actuator using optimal fractional order PDλ controller

Abstract Due to the factor of limited rigidity of boring bars, small depths of cutting are normally applied for chatter free machining. Stability lobe diagrams can truly represent that limit. However, due to the presence of manufacturing inaccuracies like ovality and eccentricity, these limits are considerably changed. Hence, considering these during modelling the cutting process, stability analysis and controller design is a novel idea, hence implemented in the present work. Dynamic modelling of boring process is presented in detail using a 3-DOF model. Dynamics of such systems is represented using delay differential equations with time periodic coefficients. The system stability is enhanced with active control techniques. The closed loop system considering fractional order PDλ in the loop is a nonlinear time periodic delay differential equation system. Any systematic controller synthesis process for such systems is rarely available in literature. It is observed that a fractional order PDλ controller designed by using combination of pseudo spectral and response optimization techniques is highly efficient in terms of the requirement of low amplitude of the peak force and simplicity of implementation. Transient vibrations can also be quenched in a limited period of time by using this controller. Different control techniques available in literature (H∞ Loop shaping and PD control) are tested and compared to the proposed controller for enhancing the material removal rates and surface finish of the workpiece. By using the active chatter control, the chatter can be efficiently reduced and the material removal rate can be increased. The critical depth of cut is increased from 0.2 mm (open loop) to 0.6 mm (closed loop) with a limited actuator size in the case study.

An Active Control Method for Chatter Suppression in Thin Plate Turning

This paper presents an active control method, consisting of an adaptive sliding-mode controller (ASMC) and a displacement field reconstruction (DFR) method, for chatter suppression in turning of thin-walled workpieces (such as compressor disks and casings in aircraft engines) where low workpiece stiffness renders machining with potential regenerative chatter. Due to the presence of multi-modal dynamics, variant modal parameters, and measurement difficulties, active chatter control of thin plate turning has been challenging. Unlike existing controls based on a lumped-parameter single degree-of-freedom cutting model, a distributed-parameter dynamic model of a rotating thin plate with multiple vibration modes is used to analyze the machining stability with the designed controller. Moreover, model parameters of the plate are not needed to construct the controller. The DFR is employed to capture the plate dynamic behavior for feedback to the ASMC during turning, overcoming the long existing difficulties to measure plate vibration at the cutting point. A fast tool servo is utilized in the control implementation. Theoretical analyses, numerical simulations, and experimental evaluation on a lathe demonstrate that chatter in thin plate turning can be effectively attenuated with the proposed active control method.

Improving the cutting rate in turning operations of flexible stepped shafts with a linear parameter-varying controller using the electromagnetic actuator

The stability requirement in turning operations of uniform and stepped shafts limits the cutting depth to avoid chatter. There is no solution so far for the problem. The recent trend is to generate stability lobe diagrams and the depth of cut is selected in such a manner the chatter regions are avoided. Hence, the cutting rates are very low due to the limited depth of cut. Normally, the workpiece is considered rigid and active chatter control techniques are applied to reduce vibrations of flexible cutting tools. In our work, both the workpiece and cutting tool are considered flexible in appropriate directions. The novelty of the work is the combination of theory and practical applications. As the material is removed during cutting, natural frequencies of the shaft are changed. Fixed parameter controllers lose their effectiveness under these changing conditions. Linear parameter-varying controller has been designed and implemented so that the cutting stability can be maintained in the total range of parameters. Due to non-contact nature of electromagnetic actuators, control forces can be applied from a distance and hence stability can be maintained. Theoretical solutions are investigated for feasibility of the control process through simulation. The productivity of the process is improved as the cutting depth has been increased from 72 to 250 μm in a case study.

Model predictive control based active chatter control in milling process

Abstract In high-speed milling process, chatter is often encountered due to the self-excitation mechanism, which not only limits the productivity, but also results in inferior work piece quality, shorter tool life, cutting noise and so on. In order to control chatter, an active chatter control method based on model predictive control is proposed in this work. Firstly, an active control structure is designed by integrating the specific tool holder, piezoelectric actuators and sensors into the spindle. Then, a time-varying model integrating the chatter dynamics is developed comprehensively considering the designed structure and the milling process. The model is then transformed into a linear time invariant (LTI) approximate model through zero order approximation (ZOA) and Pade approximation. Next, on the base of the model, a model predictive controller is designed to control only the chatter dynamics caused by regenerative effect. Finally, both simulation analysis and milling experiments are carried out to verify the effectiveness of the active chatter control method. The results show that the chatter is effectively controlled in the milling process and the milling stability is improved using the proposed active control method.

Discrete Time-Delay Optimal Control Method for Experimental Active Chatter Suppression and Its Closed-Loop Stability Analysis

Abstract Chatter is a self-excited and unstable vibration phenomenon during machining operations, which affects the workpiece surface quality and the production efficiency. Active chatter control has been intensively studied to mitigate chatter and expand the boundary of machining stability. This paper presents a discrete time-delay optimal control method for chatter suppression. A dynamical model incorporating the time-periodic and time-delayed characteristic of active chatter suppression during the milling process is first formulated. Next, the milling system is represented as a discrete linear time-invariant (LTI) system with state-space description through averaging and discretization. An optimal control strategy is then formulated to stabilize unstable cutting states, where the balanced realization method is applied to determine the weighting matrix without trial and error. Finally, a closed-loop stability lobe diagram (CLSLD) is proposed to evaluate the performance of the designed controller based on the proposed method. The CLSLD can provide the stability lobe diagram with control and evaluate the performance and robustness of the controller cross the tested spindle speeds. Through many numerical simulations and experimental studies, it demonstrates that the proposed control method can make the unstable cutting parameters stable with control on, reduce the control force to 21% of traditional weighting matrix selection method by trial and error in simulation, and reduce the amplitude of chatter frequency up to 78.6% in experiment. Hence, the designed controller reduces the performance requirements of actuators during active chatter suppression.

A chatter mitigation technique in milling based on H∞-ADDPMS and piezoelectric stack actuators

Chatter is a kind of self-excited vibration which may occur in the milling process and has several negative effects such as poor surface quality and severe tool wear. This paper presents an active chatter control method based on H∞ almost disturbance decoupling problem with measurement feedback and with internal stability (H∞-ADDPMS) and piezoelectric stack actuators. First, a milling process model considering regenerative effect is constructed to find out the milling conditions when chatter occurs. Then, the whole active control system and constructing procedure of an active controller based on H∞-ADDPMS is proposed. Next, the milling process is simulated and the H∞-ADDPMS controller is calculated based on cutting force coefficient identification, frequency response experiments, and modal analysis technique. Finally, the active control experiment is carried out on a computer numerical control (CNC) milling machine to verify the feasibility and effectiveness of the proposed active control strategy.

Robust Active Chatter Control in Milling Processes With Variable Pitch Cutters

Milling chatters caused by the regenerative effect is one of the major limitations in increasing the machining efficiency and accuracy of milling operations. This paper studies robust active chatter control for milling processes with variable pitch cutters whose dynamics are governed by multidelay nonlinear differential equations. We propose a state feedback controller based on linear matrix inequality (LMI) approach that can enlarge multiple stability domains in the stability lobe diagram (SLD) while the controller gain is minimized. Numerical simulations of active magnetic bearing systems demonstrate the effectiveness of the proposed method.

Active chatter control in high speed milling processes based on H∞ almost disturbance decoupling problem

High speed milling is commonly used to improve the cutting efficiency. However, chatter is still an obstacle limiting the performance of high speed milling. In this work, an active chatter control strategy is proposed based on H∞ almost disturbance decoupling problem. Firstly, a cutting force model is introduced to simulate the milling force under given milling conditions. Then, the cutting force model is coupled with transfer functions of the original system to simulate the whole milling process and the regenerative chatter. Next, the controller is calculated based on H∞ almost disturbance decoupling problem and the closed-loop bode diagram is compared with the open-loop bode diagram. Finally, the vibration responses with and without control are compared and the effect of controller parameter adjustment is presented.

Robust controller design for turning operations based on measured frequency response functions

One of the most significant limitation of the productivity of machining operations is the regenerative machine tool vibration, also called machine tool chatter, which is a self-excited vibration between the tool and the workpiece induced by the chip formation mechanism. Extension of the chatter-free parameters is possible by active chatter control techniques. The design of the controller requires the identification of the dynamic properties of the system. Uncertainties in the system parameters may result in an inappropriate control performance. Robust control design is therefore a necessary step during the optimization of machining operations. In this paper, a fast and efficient method is presented to determine the region of control gains in the presence of uncertainties in the measured frequency response functions. The method is based on the concept of structured singular values.

Intelligent Fixtures for Active Chatter Control in Milling

The mitigation of chatter vibrations in milling has collected the interest of several researches in the last decades. One of the most industrially oriented alternatives is represented by active fixtures, complex mechatronic devices capable of actuating the workpiece during machining operations, with the purpose of stabilizing the process by generating counteracting vibrations. Most of the previous works show different fixture architecture and model based control techniques. This paper deals with the development and testing of such an active fixture, presenting the main design aspects and the features of the black-box control-logic used. Experimental tests are presented to show the achievable chatter mitigation.

Investigating Actuation Strategies in Active Fixtures for Chatter Suppression

Active fixtures represent one of the most industrially relevant alternatives among active chatter control techniques in milling, even though control logics and actuation strategies could directly reflect on their effectiveness. Closed-loop controls targeted in the chatter frequency range are commonly adopted for this purpose, but this approach lacks of applicability when chatter frequency exceeds the achievable actuation bandwidth. The purpose of this work is to investigate the effectiveness of potential low-frequency actuation strategies in suppressing chatter vibrations. A dedicated time-domain simulation model, developed and validated by authors, is used to test different actuation strategies in order to highlight the most relevant factors in assessing actuation effectiveness. The simulation results demonstrated that employing actuation frequencies close to the first half-harmonic of the tooth-pass frequency could disrupt the regenerative effect. This allows the mitigation and suppression of chatter phenomenon, increasing the critical axial depth of cut, as discussed in the paper.

Fixed‐structure robust controller design for chatter mitigation in high‐speed milling

SummaryChatter is an instability phenomenon in high‐speed milling that limits machining productivity by the induction of tool vibrations, inferior machining accuracy, noise, and wear of machine components. In this paper, a fixed‐structure active chatter control design methodology is proposed, which enables dedicated shaping of the chatter stability boundary such that working points of higher machining productivity become feasible while avoiding chatter. The control design problem is cast into a nonsmooth optimization problem, which is solved using bundle methods. Using this approach, fixed‐structure dynamic (delayed) output feedback controllers can be synthesized. Distinct benefits of this approach are the a priori fixing of the controller order, the limitation of the control action, and the fact that no finite‐dimensional model approximations and online chatter estimation techniques are required. All these benefits are important in milling practice. Representative examples illustrate the power of the proposed methodology in terms of increasing the chatter‐free depth of cut, thereby enabling significant increases in machining productivity. Copyright © 2014 John Wiley & Sons, Ltd.

Research of Active Chatter Control for the Piezoelectric Intelligent Boring Bar with Distribution Quality

Seen as a cantilever beam with distributed mass system, the boring bar model and its state -space equation is built. On the basis of the dynamic model, a stability diagram of the boring system of the type of regenerative chatter is obtained. According to the stability diagram of the system, we get main analysis and comparison of the system stability near the fundamental frequency. In this paper, piezoelectric smart flutter suppression is carried out on a boring system with distributed mass, which improved the stability of the boring system