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This paper focuses on the finite-time tracking control with external disturbance for active suspension systems. In order to compensate unknown disturbance efficiently, a disturbance compensator with finite-time convergence property is studied. By analyzing the discontinuous phenomenon of classical disturbance compensation techniques, this study presents a simple approach to construct a continuous compensator satisfying the finite-time disturbance rejection performance. According to the finite-time separation principle, the design procedures of the nominal controller for the suspension system without disturbance and the disturbance compensator can be implemented in a completely independent manner. Therefore, the overall control law for the closed-loop system is continuous, which offers some distinct advantages over the existing discontinuous ones. From the perspective of practical implementation, the continuous controller can avoid effectively the unexpected chattering in active suspension control. Comparative experimental results are presented and discussed to illustrate the advantage and effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

In this paper, reliability analysis of dynamic structural system is introduced into chatter vibration prediction of a turning process system. Chatter reliability is defined to represent the probability of stability (no chatter occurs) for a turning process system. Probability model (reliability model) of chatter vibration is established to predict turning chatter vibration, in which structural parameters m , c , k and spindle speed Ω are considered as random variables. Choosing chatter frequency ω c as an intermediate variable, reliability model is developed from a model impossible to solve to a new model related to chatter frequency, and the new model can be solved. The first-order second-moment, fourth moment method are adopted to solve the turning process system reliability model and obtain the reliability probability of the system. An example is used to demonstrate the feasibility of the proposed method. The reliability probability of turning chatter system was calculated using the FOSM method, fourth moment and compared with that calculated by Monte Carlo simulation method. The results using the three methods were consistent. Reliability lobe diagram (RLD) is proposed to identify the chatter and no chatter regions for chatter prediction instead of stability lobe diagram (SLD). Comparing with the traditional SLD method, chatter reliability and RLD can be used to judge the probability of stability of turning process system. The RLD and the index of chatter reliability have better prospects in workshop application. [ABSTRACT FROM AUTHOR]

[Display omitted] • The coupling effect between the spindle-tool system and the workpiece system with similar characteristics is analyzed. • Stability of the spindle-tool-workpiece (STW) system proves to be weaker than that of the spindle-tool or workpiece system. • The necessity of chatter control based on the STW coupling system instead of the spindle-tool system is verified. • Two active chatter control strategies for the STW system are proposed and experimentally verified. • The maximum material removal rate is significantly improved under control. 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. [ABSTRACT FROM AUTHOR]

Abstract: Based on cross fourth-order cumulants, a total least square ESPRIT approach to jointly estimating harmonic parameters in hybrid colored noises is presented, which is applied to investigate the harmonic retrieval of regenerative machining chatter responses. Taking into consideration the multiple-regenerative effect, the delayed machining dynamics under the excitation of stochastic noises is modeled, and a recursive algorithm of the solution to the delayed machining dynamics is proposed. The harmonic parameter estimation of regenerative chatter responses is detailed, which include the harmonic frequencies, cross powers, and phase shifts between successive cuts. The results demonstrate that the presented harmonic parameter estimation approach can eliminate the hybrid colored noises, retrieve the harmonic parameters with excellent estimation performance, and extract the evolution features of regenerative machining chatter. [Copyright &y& Elsevier]

Abstract: This paper is focused on the optimal selection of the parameters of a passive dynamic vibration absorber (DVA) attached to a boring bar. The boring bar was modeled as an Euler–Bernoulli cantilever beam and the stability of the system was analyzed in terms of the bar and the absorber characteristics. To obtain the optimum parameters of the absorber, a classical method for unconstrained optimization problems has been used. The selection criterion consisted of the maximization of the minimum values of the stability lobe diagram. Empirically fitted expressions for the frequency and damping ratio of the DVA (which permit to obtain its stiffness and damping) are proposed. These expressions are fully applicable when the damping ratio of the boring bar is non-null as it is in practical operations. The computed results show a clear improvement in the stability performance regarding other methodologies previously used. [Copyright &y& Elsevier]

Abstract: A nonlinear differentiator being fit for rapid convergence is presented, which is based on singular perturbation technique. The differentiator design can not only sufficiently reduce the chattering phenomenon of derivative estimation by introducing a continuous power function, but the dynamical performances are also improved by adding linear correction terms to the nonlinear ones. Moreover, strong robustness ability is obtained by integrating nonlinear items and the linear filter. The merits of the rapid-convergent differentiator include the excellent dynamical performances, restraining noises sufficiently, avoiding the chattering phenomenon and being not based on system model. The theoretical results are confirmed by computer simulations and an experiment. [Copyright &y& Elsevier]

Abstract: Hysteresis is a property of systems that do not instantly follow the forces applied to them, but react slowly, or do not return completely to their original state. A velocity based active vibration control, along with a special class of hysteretic models using passive functions are presented in this paper. This hysteretic model is based on a modification of the Bouc–Wen model, where a nonlinear term is replaced by a passive function. The proposed class retains the rate-independence property of the original Bouc–Wen model, and it is able to reproduce several kinds of hysteretic loops that cannot be reproduced with the original Bouc–Wen model. Using this class of hysteretic models, a chattering velocity-based active vibration control scheme is developed to mitigate seismic perturbations on hysteretic base-isolated structures. Our hysteretic model is used because of its simplicity in proving the stability of the closed-loop system; i.e., a controller is designed using the proposed model, and its performance is tested on the original hysteretic system, modeled with Bouc–Wen. Numerical experiments show the robustness and efficiency of the proposed control algorithm. [Copyright &y& Elsevier]

Abstract: The paper concerns self-excited chatter vibration during high speed slender ball-end milling. Non-stationary cutting process, with inclusion of various approaches towards dynamic characteristics of the process, is described. Dynamic analysis of the milling process is performed and dynamics of controlled closed loop system with time-delay is presented. In order to reduce vibration level, instantaneous change in the spindle speed appears as a control command, and thus—the method of vibration surveillance by the spindle speed optimal-linear control is developed. Presented cutting models have been applied for the proposed method and procedure of the chatter vibration surveillance with a use of variable spindle speed has been developed. Computer simulations are performed for selected cases of ball-end milling at constant and variable spindle speed. The results of them are successfully confirmed by experimental investigations on the Alcera Gambin 120CR milling machine equipped with the S2M high speed electrospindle. [Copyright &y& Elsevier]

Abstract: Forced harmonic vibration of a non-uniform elastic beam with attached dynamic vibration absorbers (DVA) is studied. Analytical approximation of the solution is obtained by the functional perturbation method (FPM). The problem has application to cutting tools operations where the resistance of the tool holder against regenerative chatter can be enhanced by optimizing the real part of the frequency response function (FRF). A test case of a beam with step-like heterogeneity and single DVA at the tip shows that the FPM solution is very accurate for up to ∼40 percent deviation in both stiffness and mass density. Using the analytical results and Sims approach, optimal DVA tuning is found for each set of beam heterogeneity parameters by solving a set of nonlinear algebraic equations numerically. It is found that the optimum can be further improved by searching for the best step location. The system optimization is then expanded to a general heterogeneous beam with a DVA at its tip. The mass and stiffness distribution is optimized by applying the Lagrange variation method on the FPM solution yielding Fredholm integral equations. The optimized morphology is found to be approximately linear and far from the “intuitive” step-like one (Rivin and Kang, 1992) and yields better chatter-resistance. [Copyright &y& Elsevier]

Abstract: The present study introduces the concept of statistical quality control in automotive wheel bearings manufacturing processes. Defects on products under analysis can have a direct influence on passengers’ safety and comfort. At present, the use of vibration analysis on machine tools for quality control purposes is not very extensive in manufacturing facilities. Noise and vibration are common quality problems in bearings. These failure modes likely occur under certain operating conditions and do not require high vibration amplitudes but relate to certain vibration frequencies. The vibration frequencies are affected by the type of surface problems (chattering) of ball races that are generated through grinding processes. The purpose of this paper is to identify grinding process variables that affect the quality of bearings by using statistical principles in the field of machine tools. In addition, an evaluation of the quality results of the finished parts under different combinations of process variables is assessed. This paper intends to establish the foundations to predict the quality of the products through the analysis of self-induced vibrations during the contact between the grinding wheel and the parts. To achieve this goal, the overall self-induced vibration readings under different combinations of process variables are analysed using statistical tools. The analysis of data and design of experiments follows a classical approach, considering all potential interactions between variables. The analysis of data is conducted through analysis of variance (ANOVA) for data sets that meet normality and homoscedasticity criteria. This paper utilizes different statistical tools to support the conclusions such as chi squared, Shapiro–Wilks, symmetry, Kurtosis, Cochran, Hartlett, and Hartley and Krushal–Wallis. The analysis presented is the starting point to extend the use of predictive techniques (vibration analysis) for quality control. This paper demonstrates the existence of predictive variables (high-frequency vibration displacements) that are sensible to the processes setup and the quality of the products obtained. Based on the result of this overall vibration analysis, a second paper will analyse self-induced vibration spectrums in order to define limit vibration bands, controllable every cycle or connected to permanent vibration-monitoring systems able to adjust sensible process variables identified by ANOVA, once the vibration readings exceed established quality limits. [Copyright &y& Elsevier]

The regenerative-chatter resistance of a viscoelastic cantilever beam is analyzed and compared to the common dynamic vibration absorber (DVA) system. The beam represents a tool holder for turning operation in machining. The optimum structural parameters are found by maximizing the most negative real part of the frequency response function (FRF). The FRF is found analytically by using an appropriate Green''s function. Keeping the cantilever static stiffness constant, further increase in the optimal resistance is achieved by changing the ratio between the two elastic moduli in the 3-parameter solid viscoelastic material model. Three additional chatter resistance indicators are also investigated: the most positive real part of the FRF, the magnitude of the FRF and the resonant frequency. It is found that in contrast to the DVA system, the chatter resistance of the viscoelastic beam is optimal with respect to the above indicators for approximately unique set of the same material parameters. [Copyright &y& Elsevier]

Dynamic vibration absorbers are used to reduce the undesirable vibrations in many applications such as electrical transmission lines, helicopters, gas turbines, engines, bridges, etc. Tuneable vibration absorbers (TVA) are also used as semi-active controllers. In this paper, the application of a TVA for suppression of chatter vibrations in the boring manufacturing process is presented. The boring bar is modeled as a cantilever Euler–Bernoulli beam and the TVA is composed of mass, spring and dashpot elements. In addition, the effect of spring mass is considered in this analysis. After formulation of the problem, the optimum specifications of the absorber such as spring stiffness, absorber mass and its position are determined using an algorithm based on the mode summation method. The analog-simulated block diagram of the system is developed and the effects of various excitations such as step, ramp, etc. on the absorbed system are simulated. In addition, chatter stability is analyzed in dominant modes of boring bar. Results show that at higher modes, larger critical widths of cut and consequently more material removal rate (MRR) can be achieved. In the case of self-excited vibration, which is associated with a delay differential equation, the optimum absorber suppresses the chatter and increases the limit of stability. [Copyright &y& Elsevier]

Abstract: Regenerative chatter is a self-excited vibration that can occur during milling and other machining processes. It leads to a poor surface finish, premature tool wear, and potential damage to the machine or tool. Variable pitch and variable helix milling tools have been previously proposed to avoid the onset of regenerative chatter. Although variable pitch tools have been considered in some detail in previous research, this has generally focussed on behaviour at high radial immersions. In contrast there has been very little work focussed on predicting the stability of variable helix tools. In the present study, three solution processes are proposed for predicting the stability of variable pitch or helix milling tools. The first is a semi-discretisation formulation that performs spatial and temporal discretisation of the tool. Unlike previously published methods this can predict the stability of variable pitch or variable helix tools, at low or high radial immersions. The second is a time-averaged semi-discretisation formulation that assumes time-averaged cutting force coefficients. Unlike previous work, this can predict stability of variable helix tools at high radial immersion. The third is a temporal-finite element formulation that can predict the stability of variable pitch tools with a constant uniform helix angle, at low radial immersion. The model predictions are compared to previously published work on variable pitch tools, along with time-domain model simulations. Good agreement is found with both previously published results and the time-domain model. Furthermore, cyclic-fold bifurcations were found to exist for both variable pitch and variable helix tools at lower radial immersions. [Copyright &y& Elsevier]

Abstract: In turning operations, a common problem that can drastically degrade the quality of a machined part is regenerative chatter. Proper machine design, such as increased stiffness and damping of the machine tool structure can broaden the range of stable operating conditions. However, the inherent geometry of the tool and workpiece can sometimes severely limit the range of stable cutting. In this case, active control is needed in order to allow for a sufficiently broad range of stability. This work investigates turning relatively compliant workpieces, therefore it is the body that undergoes the bulk of the motion during chatter. Since it is highly impractical to instrument the workpiece, a Neural Network trained with Particle Swarm Optimization is used to transform a radial displacement measurement made at the cutting tool to an estimation of the radial displacement of the workpiece. This could serve as an observer in a real time control system that could mitigate chatter by appropriately actuating an active toolholder such as a fast tool servo. The workpiece displacement was predicted with an average RMSE of 1.41 and 1.70μm for the two testing datasets. This current approach differs from other chatter detection investigations because with the direct displacement measurement of the toolholder and the output from the Neural Network observer, there is information about both bodies’ motions. In this way, direct conclusions can be made about the stability of cutting in a chatter detection scheme. In addition, the nature of the transition from stable cutting to chatter is investigated by experimentally measuring the variation in uncut chip thickness over time. [Copyright &y& Elsevier]

Abstract: The development of a chatter detection system for application in industrial conditions was investigated. Several sensors—rotating dynamometer, accelerometers, acoustic emission and electrical power sensors—were compared to determine which signals are most sensitive to chatter onset. The signal characteristics both in time and frequency domain were condensed into a set of chatter indicators, which were further elaborated by means of statistical basic concepts, in order to obtain a chatter identification system. Single-sensor systems and multisensor systems were compared both in terms of accuracy and robustness against malfunctions. Among single sensor systems, the cutting torque signal proved to be a superior signal for chatter identification. Multisensors systems composed of three or four sensors are the most promising solution for reliable and robust chatter identification. The best results were obtained by the multisensor system composed of the axial force sensor and accelerometers. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to demonstrate the effect of active damping on regenerative chatter instability for a turning operation. Two approaches are used for this purpose. In the first approach, the traditional stability analysis technique in Altintas [Manufacturing Automation, Cambridge University Press, Cambridge, 2000. ] and other works is adopted and a correlation between the chip shape (which is dependent on the spindle speed) and the system damping is presented. It is shown that different spindle speeds cause changes in the system damping, resulting in different levels of stability limits at different spindle speeds. A second approach involves plotting of the root locus of the system poles with increasing axial width of cut. This study presents a different perspective to the problem. It is shown that the low and high stability regions of the stability lobe diagram are due to different relative positions of the poles and zeros of the system. Active damping is proposed as a strategy to enhance the stability limits of the system. The effect of active damping is studied by the two approaches, mentioned above, both showing that active damping can successfully enhance the stability limits, particularly in the low stability regions. [Copyright &y& Elsevier]