Chatter Analysis Research Articles

Chattering analysis of an electro-hydraulic backstepping velocity controller

This paper focuses on the chattering analysis in a backstepping controller used to drive an electro-hydraulic servo system. The chattering phenomenon, well known in sliding mode control, strongly reduces operating performance while causing premature wear of the system. Four cases are studied to highlight the factors influencing the chattering in the backstepping control. In the first case, the effect of the unmodeled fast servo valve dynamics is analysed by comparing a reduced-order backstepping controller with a full-order controller. The second case analyses the sensitivity to the tuning gains of the backstepping controller. The third case emphasises the influence of the parameter of sign function approximation. The last case analyses the sensitivity of the parameter of the time derivative of the virtual controls. The simulation results in the Matlab/Simulink show that the chattering is mitigated by an appropriate gains tuning but above all an appropriate calculation of the derivatives of the virtual controls, particularly for high-order systems.

Dynamic Modeling for Chatter Analysis in Micro-Milling by Integrating Effects of Centrifugal Force, Gyroscopic Moment, and Tool Runout.

During micro-milling, regenerative chatter will decrease the machining accuracy, destabilize the micro-milling process, shorten the life of the micro-mill, and increase machining failures. Establishing a mathematical model of chatter vibration is essential to suppressing the adverse impact of chatter. The mathematical model must include the dynamic motions of the cutting system with the spindle-holder-tool assembly and tool runout. In this study, an integrated model was developed by considering the centrifugal force induced by rotational speeds, the gyroscopic effect introduced by high speeds, and the tool runout caused by uncertain factors. The tool-tip frequency-response functions (FRFs) obtained by theoretical calculations and the results predicted by simulation experiments were compared to verify the developed model. And stability lobe diagrams (SLDs) and time-domain responses are depicted and analyzed. Furthermore, experiments on tool-tip FRFs and micro-milling were conducted. The results validate the effectiveness of the integrated model, which can calculate the tool-tip FRFs, SLDs, and time responses to analyze chatter stability by considering the centrifugal force, gyroscopic effect, and tool runout.

Frequency monitoring analysis of milling edge chatter in composites using WPD for frequency band selection

In the milling process of composite materials, the initial chatter frequency is not obvious and is easily swamped by the rest of the signals, making frequency monitoring difficult, so the study proposes a chatter frequency monitoring method based on frequency cancellation algorithms and wavelet packet decomposition. The results of the experiments shown that the frequency cancellation algorithm can successfully remove invalid signals, such as spindle rotation frequency and cutter tooth frequency, and only keep the necessary signals, at which point the chattering frequency may be observed at a frequency of roughly 1333 Hz. The influence of the frequency bands s5, s9, s10, s12, and s13 after de-frequency removal should be avoided because they all have a low energy share of roughly 23 %, 0.9 %, 5 %, 10 %, and 16 %, respectively, and are less sensitive to chatter. For milling edge depths of 0.5 mm, 2 mm, and 4 mm, the average chatter thresholds were around 3.27, 2.9, and 2.89, respectively. It was challenging to pinpoint the chatter of the system because the empirical modal decomposition observed an average chatter energy entropy of just 1.55 and found that its fluctuations at the milling edge depth junction were insignificant. On the other hand, the chattering could be plainly seen since the energy entropy experienced a substantial and dramatic fluctuation at the intersection of the milling edge depth when it was about 2.9, 2.6, and 2.5, respectively. The experimental findings demonstrated that the frequency cancellation technique and wavelet packet decomposition-based chattering frequency monitoring approach can precisely track the chattering state of the system.

Study of optimization of blade non-uniform allowance process and chatter stability domain

In addressing the phenomenon of chatter during the machining of thin-walled components, a machining strategy involving the implementation of a continuous non-uniform toolpath has been proposed as a remedy for chatter suppression. The methodology commences with a meticulous determination of machining allowances, accomplished by utilizing fitting functions. Subsequently, the stiffness coefficients and natural frequencies inherent to the workpiece-tool system are extracted through modal analysis. A stability lobes diagram is formulated, employing the principles of regenerative chatter analysis. This diagram encompasses both uniform toolpath scenarios and non-uniform continuous toolpath scenarios, with the latter established via the least squares method. The resultant stability lobes diagram effectively delineates the boundaries within which chatter remains stable, under varying depths of cut. The stability lobes diagrams substantiate the effectiveness of the non-uniform continuous toolpath constructed via the least squares method in significantly augmenting the inherent stiffness coefficient of the workpiece-tool system, thereby mitigating chatter. This approach serves as a valuable guide for the manufacturing of intricate curved thin-walled components.

Experimental analysis of chatter in grooving with slender blades

This paper reports on experiments that offer new insights on chatter in grooving with slender blades. Experiments reveal two distinct blade modes cause two types of chatter: diametrical chatter that is of the regenerative kind and snaking chatter on the side walls that is of the mode-coupling type. We find that diametrical chatter can be avoided by using damped blades designed for the purpose. However, since no such blades are available to damp snaking chatter, we show that by cutting in the low-speed process damping region snaking chatter too can be avoided.

Chatter reliability of high speed cylindrical grinding with uncertain parameters

Cylindrical grinding is commonly used as the final process of machining, but its quality and efficiency are often limited by chatter phenomenon. Many research show that the result from conventional chatter analysis by using the deterministic parameters is not consistent with the practical working condition and the chatter reliability prediction in high speed cylindrical grinding with uncertain parameters is studied in this paper. The dynamic model of the cylindrical grinding system is established, and uncertain parameters such as mass, stiffness and damping coefficient are introduced, and the stability lobe diagrams with uncertain parameters were obtained. The reliability model of the grinding system was established, and the reliability was solved by using the Monte Carlo simulation method, the improved first-order second-moment method and the second-order second-moment method, respectively. Then, the chatter-free reliability of the system was predicted by using the reliability lobe diagram. The accuracy of the grinding reliability prediction results is verified by the experiment results. Furthermore, the Monte Carlo sensitivity analysis method is used to study the influence of random parameters on the grinding system, and the results show that the variation of modal mass has the greatest influence on the reliability of the grinding system.

A framework for multi-faceted content analysis of social media chatter regarding non-medical use of prescription medications

BackgroundSubstance use, including the non-medical use of prescription medications, is a global health problem resulting in hundreds of thousands of overdose deaths and other health problems. Social media has emerged as a potent source of information for studying substance use-related behaviours and their consequences. Mining large-scale social media data on the topic requires the development of natural language processing (NLP) and machine learning frameworks customized for this problem. Our objective in this research is to develop a framework for conducting a content analysis of Twitter chatter about the non-medical use of a set of prescription medications.MethodsWe collected Twitter data for four medications—fentanyl and morphine (opioids), alprazolam (benzodiazepine), and Adderall® (stimulant), and identified posts that indicated non-medical use using an automatic machine learning classifier. In our NLP framework, we applied supervised named entity recognition (NER) to identify other substances mentioned, symptoms, and adverse events. We applied unsupervised topic modelling to identify latent topics associated with the chatter for each medication.ResultsThe quantitative analysis demonstrated the performance of the proposed NER approach in identifying substance-related entities from data with a high degree of accuracy compared to the baseline methods. The performance evaluation of the topic modelling was also notable. The qualitative analysis revealed knowledge about the use, non-medical use, and side effects of these medications in individuals and communities.ConclusionsNLP-based analyses of Twitter chatter associated with prescription medications belonging to different categories provide multi-faceted insights about their use and consequences. Our developed framework can be applied to chatter about other substances. Further research can validate the predictive value of this information on the prevention, assessment, and management of these disorders.

Theoretical and Experimental Analysis of Grinding Stability of Beam Workpiece

Grinding chatter is a kind of self-excited vibration in which the grinding system continuously absorbs energy from the grinding machine, increasing the mechanical energy of the system. Grinding chatter can damage the surface of the workpiece and accelerate the abrasion of the grinding wheel. The theoretical analysis of the grinding chatter for the beam surface was launched based on the behavior of a single abrasive grain, whose cutting thickness is a key factor affecting grinding stability. The dynamic grinding force model has been developed, which is the interaction interface between the grinding wheel and the workpiece. In this paper, rail beam grinding was taken as an example. The vibration performance of the rail beam was described with the Timoshenko beam. The characteristics of the frequency domain of the grinding wheel-workpiece system were observed, and the condition of the stability at any position in the longitudinal direction of the beam was gained, which could be quantitatively characterized with the stability limit curve. The grinding experiments of the rail beam surface demonstrated that as chatter developed, the chatter marks could be investigated on the surface of the rail, and the energy of the chatter signal was mainly concentrated around the chatter frequency, which was higher than the natural frequency of the grinding wheel.

The Early Detection of Fraudulent COVID-19 Products From Twitter Chatter: Data Set and Baseline Approach Using Anomaly Detection.

Social media has served as a lucrative platform for spreading misinformation and for promoting fraudulent products for the treatment, testing, and prevention of COVID-19. This has resulted in the issuance of many warning letters by the US Food and Drug Administration (FDA). While social media continues to serve as the primary platform for the promotion of such fraudulent products, it also presents the opportunity to identify these products early by using effective social media mining methods. Our objectives were to (1) create a data set of fraudulent COVID-19 products that can be used for future research and (2) propose a method using data from Twitter for automatically detecting heavily promoted COVID-19 products early. We created a data set from FDA-issued warnings during the early months of the COVID-19 pandemic. We used natural language processing and time-series anomaly detection methods for automatically detecting fraudulent COVID-19 products early from Twitter. Our approach is based on the intuition that increases in the popularity of fraudulent products lead to corresponding anomalous increases in the volume of chatter regarding them. We compared the anomaly signal generation date for each product with the corresponding FDA letter issuance date. We also performed a brief manual analysis of chatter associated with 2 products to characterize their contents. FDA warning issue dates ranged from March 6, 2020, to June 22, 2021, and 44 key phrases representing fraudulent products were included. From 577,872,350 posts made between February 19 and December 31, 2020, which are all publicly available, our unsupervised approach detected 34 out of 44 (77.3%) signals about fraudulent products earlier than the FDA letter issuance dates, and an additional 6 (13.6%) within a week following the corresponding FDA letters. Content analysis revealed misinformation, information, political, and conspiracy theories to be prominent topics. Our proposed method is simple, effective, easy to deploy, and does not require high-performance computing machinery unlike deep neural network-based methods. The method can be easily extended to other types of signal detection from social media data. The data set may be used for future research and the development of more advanced methods.

Analysis of chattering in homogenous sliding mode controllers using the locus of a perturbed relay system

AbstractThis work investigates the use of the locus of a perturbed relay system (LPRS) method for the analysis of chattering and other possible oscillations in discontinuous homogenous Sliding Mode Controllers (SMC). Particularly these homogeneous SMCs are considered as linear input‐to‐state and nonlinear separable state‐to‐output dynamics of Wiener type. The existence of non‐vanishing oscillations in these sliding mode control systems, when parasitic dynamics are present, is shown. This supports the claim that the finite‐time convergence for homogenous SMCs only occurs in the absence of any parasitic dynamics which is an ideal and non‐realizable condition. We investigate the chattering and other possible oscillations using the LPRS for the controllers proposed in the study by Ding et al. The undertaken analysis reveals multiple periodic solutions for the plants of relative degrees 2 through 4. The LPRS, originally developed for linear plants, is extended to linear input‐to‐state and nonlinear separable state‐to‐output dynamics. To investigate chattering, the parasitic dynamics are included in this analysis through a second‐order actuator model. The proposed approach to analysis provides exact values of the frequency and amplitude of chattering, as well as categorization of the obtained periodic solutions into orbitally stable and orbitally unstable. The analytical results are supported by simulations.

THEORETICAL STUDY OF NONLINEAR CHATTER STABILITY ANALYSIS BASED ON SYNTHESIS OF LINEARIZATIONS IN OPERATING POINTS FOR DIFFERENT TURNING CONDITIONS

This paper deals with an approach to study nonlinear chatter analysis, which is based on the synthesis of linear theory for different turning conditions. Mainly, contact nonlinearities play a crucial role in the behavior of the machine tool and the stability of turning operation. However, the analysis of nonlinear systems is challenging because nonlinear system analyzes are often limited to a linearized solution, which may be insufficient to reveal the stability lobe diagram. The presented study proposes a theoretical approach which is based on a synthesis of linearization in the operating point. This approach provides several solutions of stability lobe diagrams which are strongly depending on the loading conditions of the nonlinear system and all solutions are integrated to the final stability lobe diagram. The presented method is applied to a simplified 2D structure between two supports with nonlinear contact stiffness. Resulted analysis of the lobe diagram are compared with results of the time-domine simulations and it shows a good match. This paper shows that the presented approach offers an effective solution for refining the stability estimate for nonlinear mechanical systems.

Numerical study on stability of composite cutter bar milling system in rotating coordinate frame

This paper studies the chatter stability of composite cutter bar milling system in rotating coordinate frame. The main contribution of this paper is establishing a continuous distributed chatter analysis model for a composite cutter bar milling system in rotating coordinate frame. The stability of the milling system with a rotary symmetric dynamic cutter bar is predicted using the semi-discrete time domain method. The effects such as internal damping, external damping, and symmetrical and asymmetric laminates on the stability of the milling system were analysed, and the results were compared between rotating and fixed coordinate frames. The results are consistent for symmetrical cutter bars in both the rotating and fixed coordinate frames. A new chatter instability zone appears at high rotating speeds due to the material internal damping of the rotating composite cutter bar.

Study on Bandwidth Analyzed Adaptive Boosting Machine Tool Chatter Diagnosis System

This paper presents an Adaboost algorithm based cutting data analysis for chatter detection. This offline chatter analysis uses the vibration data collected by accelerometers attached to the spindle housing. A comparison of the accuracy achieved with support vector machine, Random Forest, 1D Convolutional Neural Networks and Multilayer Perceptron algorithm is also made. In this paper, the accelerometer data are transformed into bandwidth. Time-accelerometer and time-spectral bandwidth learning models are built in order to realize chatter detection and automated machine learning. A comparison of the models is made. The results of cross validation indicate that an accuracy of 98% is achieved, which is made possible by using the bandwidth signals that are transformed from accelerometer data. Experimental results show that applying the Adaboost algorithm to analyze the spectral data transformed from vibration signals and using them to detect chatters has higher reliability and accuracy compared to other algorithms and analyzing other transform signals.

Analysis of chattering in step down converter via sliding mode reaching law

The reaching law approach is broadly used for chattering repression, minimization of steady state error and reaching pace kept minimsed. The reasons of chattering, in this paper proposes sliding mode reaching law. In one hand, they assurance the scheme arrives at the sliding face swiftly and stay on it, in another way they deteriorate the chattering inefficiently, even matchless certainties and disturbances. This proposed reaching law gives uniqueness of the response. The reaching law is compared with Gao’s reaching law. Sliding mode reaching laws gives the efficacy in reducing the chattering of the variable structure control (VSC). This reaching law also reduces the losses in the switching diplomacy. In turns efficiency of the step-down converter increases. Simulation results give significant decrease of chattering and extremely fewer receptive in supply and load variation.

Themes, communities and influencers of online probiotics chatter: A retrospective analysis from 2009-2017.

We build on recent examinations questioning the quality of online information about probiotic products by studying the themes of content, detecting virtual communities and identifying key influencers in social media using data science techniques. We conducted topic modelling (n = 36,715 tweets) and longitudinal social network analysis (n = 17,834 tweets) of probiotic chatter on Twitter from 2009-17. We used Latent Dirichlet Allocation (LDA) to build the topic models and network analysis tool Gephi for building yearly graphs. We identified the top 10 topics of probiotics-related communication on Twitter and a constant rise in communication activity. However the number of communities grew consistently to peak in 2014 before dipping and levelling off by 2017. While several probiotics industry actors appeared and disappeared during this period, the influence of one specific actor rose from a hub initially to an authority in the latter years. With multi-brand advertising and probiotics promotions mostly occupying the Twitter chatter, scientists, journalists, or policymakers exerted minimal influence in these communities. Consistent with previous research, we find that probiotics-related content on social media veers towards promotions and benefits. Probiotic industry actors maintain consistent presence on Twitter while transitioning from hubs to authorities over time; scientific entities assume an authoritative role without much engagement. The involvement of scientific, journalistic or regulatory stakeholders will help create a balanced informational environment surrounding probiotic products.

과도상태 밀링에서 시간영역 채터 시뮬레이션

Chatter between the end mill and thin aircraft components reduces tool life and surface quality. This paper presents a time-domain chatter analysis that simulates the peripheral milling of thin aluminum plates. Peak forces and tool deformations were predicted in the time domain by simulation software written in C++. The maximum forces at various cutting depths and spindle speeds were predicted, and the stability lobe diagram was drawn in the frequency domain. The software was validated in comparison with the results of Professor Y. C. Shin’s experiments and was used to analyze the relationship between chatter and runout, number of teeth, and feed rate in virtual space. The chatter in transient state was simulated to predict the side effect of feed rate control.

Time-varying dynamics updating method for chatter prediction in thin-walled part milling process

The dynamics of thin-walled parts vary in time with the feed of tool and the removal of material in the milling process, which is a non-negligible phenomenon related to chatter. A new thin-walled parts time-varying dynamics updating method based on a degree of freedom (DOF) reduction model is proposed in this paper for milling chatter prediction. First, to establish the DOF-reduced model, the in-process thin-walled part is divided into two substructures, namely, the substructure with material to be removed and the substructure with finished part, according to the entire removed material. The finite element (FE) model of the substructure with finished part is directly reduced by using the free-interface method since it remains unchanged in the milling process. The FE model of the substructure with material to be removed is reduced by using a combination of the free-interface method and the structural dynamic modification technique. In this way, the changed dynamics of the thin-walled part are updated only in the DOF-reduced model of the substructure with material to be removed. DOF-reduced FE models of the two substructures are coupled by using interface compatibility conditions to establish the DOF-reduced FE model of the entire thin-walled part. Then, the time-varying dynamics of the thin-walled part are obtained by solving the eigenvalue problem of the reduced thin-walled part. Compared to the existing methods, the proposed method updates the time-varying dynamics with high efficiency. Finally, the proposed time-varying dynamics updating method for thin-walled parts is merged into a milling dynamic model to predict chatter. A series of milling experiments are carried out to verify the correctness of the proposed method. The experimental results agree with the simulation results, indicating that the proposed method can be used to predict the time-varying dynamics of the thin-walled parts for chatter analysis.

Comparative analysis of chatter in micro end milling operations

The advancement in microfabrication in pursuit of miniaturization is cutting a dynamic role for micro-milling. Micro-milling is a fast and cost-efficient threedimensional fabrication method with the ability to achieve good accuracy, low surface roughness and extraordinary material removal rate (MRR) compared to some other micro manufacturing processes. Given the need for components with high dimensional integrity, identification of appropriate machining conditions is very vital to getting good surface finish. It is also required to couple different complex dynamics which are associated with this machining technique. Chatter during milling and micro-milling process bring adverse effects in surface quality, dimensional accuracy and in tool life. There is need for versatile modelling of micro end-milling dynamics in order to understand how chatter affects the micro end milling operation and to advance the synthetic application of several chatter stability parameters to overcome the limitation imposed by the single chatter stability criterion. This study performs a linear and non-linear analysis of chatter in micro end milling based on the major influential parameters. In addition, a detailed time domain simulation for micro end milling was performed to predict the force a displacement resulting from variable cutter geometries. This dynamic simulation results have significant impact on the actual micro milling process towards the manufacturing of miniaturized parts.

Analysis of Chatter and Turning Errors of Basalt Fiber Reinforced Polymer Concrete Lathe

In order to improve the turning accuracy of the lathe, a basalt fiber reinforced polymer concrete lathe bed was designed. In the light of theory, the turning error model of the lathe, the vibration of the lathe-workpiece system and the average amplitude calculation model of turning error are established. The Runge-Kutta method is used to calculate the vibration of the lathe-workpiece. The influence of the workpiece radius and turning parameters on the average amplitude of the turning error is studied. The results shows that average amplitude of the turning error is significantly influenced by feed rate, workpiece radius, back engagement and spindle speed from large to small.

Chatter analysis and mitigation of milling of the pocket-shaped thin-walled workpieces with viscous fluid

This article presents a theoretical method to analyze the dynamic behavior of the milling process of the pocket-shaped thin-walled workpieces, which are filled with viscous fluid to suppress the chatter vibrations. Dynamic models of both the spindle-tool system and the pocket-shaped thin-walled workpiece with the viscous fluid are derived by extending the principles of the fluid-structure interaction dynamics theory and structural mechanics. The in-process dynamical parameters of the tool and the workpiece, i.e. natural frequency and modal shape, are solved by comprehensively integrating the effects of the viscous fluid, material removals, and tool position changes. Based on the built models, a method for analyzing the machining stability of this kind of workpieces after using the viscous fluid in the milling process is carried out and the avoidance principle of chatter vibrations is established by reasonably selecting the cutting parameters. A series of simulation and experimental tests are conducted on a typical pocket-shaped thin-walled workpiece to verify the reliability and effectiveness of the proposed methods for the suppression of chatter during the whole milling process.