Micro-milling technology is widely applied in micro manufacturing,particularly for the fabrication of miniature and micro components.However,the chatters and machining dynamics related issues in micro-milling are ofte...Micro-milling technology is widely applied in micro manufacturing,particularly for the fabrication of miniature and micro components.However,the chatters and machining dynamics related issues in micro-milling are often the main challenges restricting its machining quality and productivity.Many research works have rendered that the machining dynamics and chatters in micro-milling are more complex compared with the conventional macro-milling process,likely because of the size effect and rigidity of the micro-milling system including the tooling,workpiece,process variables,materials involved,and the high-speed milling machines,and further their collective dynamic effects.Therefore,in this paper,the state of the art focusing on micro-milling chatters and dynamics related issues over the past years are comprehensively and critically reviewed to provide some insights for potential researchers and practitioners.Firstly,typical applications and the problems caused by the machining dynamics and chatters in micro-milling have been put forward in this paper.Then,the research on the underlying micro-cutting mechanics and dynamics,stability analysis,chatters detection,and chatter suppression are summarized critically.Furthermore,the underlying scientific and technological challenges are discussed particularly against typical precision engineering applications.Finally,the possible future directions and trends in research and development of micro-milling have been discussed.展开更多
Thin-walled parts have been widely employed as critical components in high-performance equipment due to the high specific strength and light weight.However,owing to their relatively weak rigidity and poor damping prop...Thin-walled parts have been widely employed as critical components in high-performance equipment due to the high specific strength and light weight.However,owing to their relatively weak rigidity and poor damping properties,chatter vibration is likely to occur during the milling process,which severely deteriorates surface quality and decreases machining productivity.Therefore,chatter suppression is essential for improving the dynamic machinability of thin-walled structures and has attracted extensive attention over the past few decades.This paper reviews the current state of the art in research concerning chatter suppression during the milling of thin-walled workpieces.In consideration of the dynamic characteristics of this process,the challenges in design and application of chatter attenuation methods are highlighted.Moreover,various chatter suppression techniques,involving passive,active,and semi-active methods,are comprehensively discussed in terms of basic concepts,working mechanism,optimal design,and application.Finally,future research opportunities in chatter mitigation technology for thin-wall milling are recommended.展开更多
Low-frequency structural vibrations caused by poor rigidity are one of the main obstacles limiting the machining efficiency of robotic milling.Existing vibration suppression strategies primarily focus on passive vibra...Low-frequency structural vibrations caused by poor rigidity are one of the main obstacles limiting the machining efficiency of robotic milling.Existing vibration suppression strategies primarily focus on passive vibration absorption at the robotic end and feedback control at the joint motor.Although these strategies have a certain vibration suppression effect,the limitations of robotic flexibility and the extremely limited applicable speed range remain to be overcome.In this study,a Magnetorheological Joint Damper(MRJD)is developed.The joint-mounted feature ensures machining flexibility of the robot,and the millisecond response time of the Magnetorheological Fluid(MRF)ensures a large effective spindle speed range.More importantly,the evolution law of the damping performance of MRJD was revealed based on a low-frequency chatter mechanism,which guarantees the application of MRJD in robotic milling machining.To analyze the influence of the robotic joint angle on the suppression effect of the MRJD,the joint braking coefficient and end braking coefficient were proposed.Parallel coordinate plots were used to visualize the joint range with the optimal vibration suppression effect.Finally,a combination of different postures and cutting parameters was used to verify the vibration suppression effect and feasibility of the joint angle optimization.The experimental results show that the MRJD,which directly improves the joint vibration resistance,can effectively suppress the low-frequency vibration of robotic milling under a variety of cutting conditions.展开更多
Sliding mode control(SMC)is a widely adopted control technology known for its robustness and simplicity.The essence of SMC is to use discontinuous control to drive a system into a pre-defined motion,called the sliding...Sliding mode control(SMC)is a widely adopted control technology known for its robustness and simplicity.The essence of SMC is to use discontinuous control to drive a system into a pre-defined motion,called the sliding mode,which is designed with desirable dynamical properties.In the sliding mode,the controlled system is insensitive to the matched uncertainties and disturbances.Most SMC theory and methods have been developed based on the dynamical systems in the continuous-time domain,where switching functions play a critical role.Ideal switching is supposed to be instantaneous,activating as soon as the switching condition is met.However,in practice,switching mechanisms are affected by imperfections such as time delays,unmodeled dynamics,defects,digitization effects,and actuation limitations,which can degrade the salient properties of SMC.Understanding these effects and developing mitigation strategies are essential for industrial applications.Furthermore,the advent of networked control environments presents new challenges like limited communication bandwidth,latency and cyberattack,which have seen the emergence of the event-triggered SMC recently.Despite these significant advances,there is a lack of comprehensive studies which examine the commonalities and distinctions of utilizing switching in SMC across the continuous-time and discrete-time domains and beyond.This paper investigates the role of switching in SMC from a spatio-temporal perspective,considering both state-space and time aspects.The aim is to facilitate better understanding of its effects and misbehaviors,and to unlock its full potential for future applications.The interplay between SMC methods in the continuous-time and discrete-time domains is analyzed,and their shared principles and unique challenges are identified.Furthermore,important technical issues relating to switching across these time domains are explored,and several myths and pitfalls in their theory and applications are depicted.The relationships of SMC with other switching-based control systems such as switched control systems,fuzzy control systems,and event-triggered control systems are discussed.The impact of networked control environments on SMC in the continuous-time and discrete-time domains is also examined.Finally,key challenges and opportunities are outlined for future work in SMC and beyond.展开更多
The possibility of the electric-hydraulic chattering technology and its application in the cold extrusion were presented.The conventional and electric-hydraulic chattering assisted backward extrusion processes were pe...The possibility of the electric-hydraulic chattering technology and its application in the cold extrusion were presented.The conventional and electric-hydraulic chattering assisted backward extrusion processes were performed on 6061 aluminum alloy billets at room temperature.The experimental results showed that 5.65% reduction in the extrusion load was attained if the die and ejector were vibrated at a frequency of 100 Hz and amplitude of 0.013 mm in the longitudinal direction.The friction coefficient at the billet and tool system interface determined from the finite element analysis（FEA） decreased from 0.2 without chattering to 0.1 with application of electric-hydraulic chattering.The higher values of instantaneous velocity and direction change of material flow were achieved during the chattering assisted backward extrusion process.The strain distribution of the chattering assisted backward extrusion billet revealed lower maximum strain and smoother strain distribution in comparison with that produced by the conventional extrusion method.展开更多
Considering the self-excited and forced vibrations in high-speed milling processes, a novel method for dynamic optimization of system stability is used to determine the cutting parameters and structural parameters by ...Considering the self-excited and forced vibrations in high-speed milling processes, a novel method for dynamic optimization of system stability is used to determine the cutting parameters and structural parameters by increasing the chatter free material removal rate （CF-MRR） and surface finish. The method is hased on the theory of the chatter stability and the semi-bandwidth of the resonant region. The objective function of the method is material removal rate（MRR）,the constraints are chatter stability and surface finish, and the optimizing variables are cutting and structural parameters. The optimization procedure is stated. The method is applied to a milling system and CF-MRR is increased 18.86%. It is shown that the influences of the chatter stability and the resonance are simultaneously considered in the dynamic optimization of the milling system for increasing CF-MRR and the surface finish.展开更多
Considering the deficiency in milling process parameters selection, based on the modelling of dynamic milling force and the deduction of chatter stability limits, the chatter stability lobes simulation program for mil...Considering the deficiency in milling process parameters selection, based on the modelling of dynamic milling force and the deduction of chatter stability limits, the chatter stability lobes simulation program for milling is developed with MAT- LAB. The simulation optimization application software of dynamics was designed using engineering simulation software Visio Basic. The chatter stability lobes for milling, which can be used as an instruction guide for the selection of process parameters, are simulated with frequency response functions （FRFs） gained by hammer test. The validation and accuracy of the simulation algorithm are verified by experiments. The simulation method has been used in a factory with an excellent application effect.展开更多
A new method for suppressing cutting chatter is studied by adjusting servo parameters of the numerical control （NC） machine tool and controlling the limited cutting width. A model of the cutting system of the NC mac...A new method for suppressing cutting chatter is studied by adjusting servo parameters of the numerical control （NC） machine tool and controlling the limited cutting width. A model of the cutting system of the NC machine tool is established. It includes the mechanical system, the servo system and the cutting chatter system. Interactions between every two systems are shown in the model. The cutting system stability is simulated and relation curves between the limited cutting width and servo system parameters are described in the experiment. Simulation and experimental results show that there is a mapping relation between the limited cutting width and servo parameters of the NC machine tool, and the method is applicable and credible to suppress chatter.展开更多
An applicable method to control regenerative cutting chatter automatically based on the optimal regulation of spindle speed is introduced. The optimal value of the phase shift angle of the regenerative chatter signal ...An applicable method to control regenerative cutting chatter automatically based on the optimal regulation of spindle speed is introduced. The optimal value of the phase shift angle of the regenerative chatter signal between the two successive cuts is 270°. The cutting process can be adjusted from the unstable region to stable one whenever regenerative chatter occurs if the phase shift angle is kept 270° by the optimal regulation of spindle speed. The theoretical analysis and the experimental results prove that the optimal regulation of spindle speed can effectively control regenerative cutting chatter. In addition, a reliablelly optimal control system of reliable spindle speed is presented. There is no need for system identification of the machine tool, and it is easy to put this regenerative chatter control method into practice, so the method has excellent application prospect.展开更多
A mathematical model of the computer numerical control (CNC) heavy cuttingservo system including chatter in cutting courses was constructed for the chatter in CNC heavycutting. The theoretical analysis, computer simul...A mathematical model of the computer numerical control (CNC) heavy cuttingservo system including chatter in cutting courses was constructed for the chatter in CNC heavycutting. The theoretical analysis, computer simulation and orthogonal tests on this model show thatincreasing the gain of position K_(pp) can improve the rapid tracking performance of machine tools,and decreasing the delay time of speed loop τ_s can quickly eliminate the static error in thesystem, but the limited cutting width b_(lim) will descend correspondingly; excessively large orexcessively small gain of speed loop K_(ps) can result in decreasing b_(lim); optimizing K_(pp),τ_s and K_(ps) can improve the dynamic and static performance of the system and increase b_(lim).It is easy and feasible to optimize the servo parameters by the orthogonal test. This method caneffectively improve the system's stability and limited cutting width and it is suitable for the CNCheavy cutting of heavy-duty machine tools.展开更多
Chatter is a self-excited vibration of parts in machining systems. It is widely present across a range of cutting processes, and has an impact upon both efficiency and quality in production processing. A great deal of...Chatter is a self-excited vibration of parts in machining systems. It is widely present across a range of cutting processes, and has an impact upon both efficiency and quality in production processing. A great deal of research has been dedicated to the development of technologies that are able to predict and detect chatter. The purpose of these technologies is to facilitate the avoidance of chatter during cutting processes, which leads to better surface precision, higher productivity,and longer tool life. This paper summarizes the current state of the art in research regarding the problems of how to arrive at stable chatter prediction, chatter identification, and chatter control/-suppression, with a focus on milling processes. Particular focus is placed on the theoretical relationship between cutting chatter and process damping, tool runout, and gyroscopic effect, as well as the importance of this for chatter prediction. The paper concludes with some reflections regarding possible directions for future research in this field.展开更多
Grinding chatter is a self?induced vibration which is unfavorable to precision machining processes. This paper proposes a forecasting method for grinding state identification based on bivarition empirical mode decompo...Grinding chatter is a self?induced vibration which is unfavorable to precision machining processes. This paper proposes a forecasting method for grinding state identification based on bivarition empirical mode decomposition(BEMD) and least squares support vector machine(LSSVM), which allows the monitoring of grinding chatter over time. BEMD is a promising technique in signal processing research which involves the decomposition of two?dimen?sional signals into a series of bivarition intrinsic mode functions(BIMFs). BEMD and the extraction criterion of its true BIMFs are investigated by processing a complex?value simulation chatter signal. Then the feature vectors which are employed as an amplification for the chatter premonition are discussed. Furthermore, the methodology is tested and validated by experimental data collected from a CNC guideway grinder KD4020 X16 in Hangzhou Hangji Machine Tool Co., Ltd. The results illustrate that the BEMD is a superior method in terms of processing non?stationary and nonlinear signals. Meanwhile, the peak to peak, real?time standard deviation and instantaneous energy are proven to be e ec?tive feature vectors which reflect the di erent grinding states. Finally, a LSSVM model is established for grinding status classification based on feature vectors, giving a prediction accuracy rate of 96%.展开更多
Thin-walled parts are widely used in the aerospace industry owing to their light weight and high specific strength.However,due to the low rigidity of thin-walled parts,elastic deformation and chatter easily occur,whic...Thin-walled parts are widely used in the aerospace industry owing to their light weight and high specific strength.However,due to the low rigidity of thin-walled parts,elastic deformation and chatter easily occur,which seriously affect the machining accuracy and workpiece surface quality.To solve this problem,several supporting technologies have been reported in recent years.This paper reviews the recent research progress of flexible supporting technologies in the aerospace field by classifying them based on different principles and characteristics.The principle,progress,advantages,and limitations of the technologies are expounded by systematic comparison and summarized.Finally,the challenges and future development trends of flexible supporting technology,which will provide guidelines for further research,are discussed.展开更多
This paper proposes a finite-time robust flight controller, targeting for a reentry vehicle with blended aerodynamic surfaces and a reaction control system（RCS）. Firstly, a novel finite-time attitude controller is p...This paper proposes a finite-time robust flight controller, targeting for a reentry vehicle with blended aerodynamic surfaces and a reaction control system（RCS）. Firstly, a novel finite-time attitude controller is pointed out with the introduction of a nonsingular finite-time sliding mode manifold. The attitude tracking errors are mathematically proved to converge to zero within finite time which can be estimated. In order to improve the performance, a second-order finite-time sliding mode controller is further developed to effectively alleviate chattering without any deterioration of robustness and accuracy. Moreover, an optimization control allocation algorithm, using linear programming and a pulse-width pulse-frequency（PWPF） modulator, is designed to allocate torque commands for all the aerodynamic surface deflections and on–off switching-states of RCS thrusters.Simulations are provided for the reentry vehicle considering uncertain parameters and external disturbances for practical purposes, and the results demonstrate the effectiveness and robustness of the attitude control system.展开更多
Milling of the thin-walled workpiece in the aerospace industry is a critical process due to the high flexibility of the workpiece. In this paper, a flexible fixture based on the magnetorheological (MR) fluids is desig...Milling of the thin-walled workpiece in the aerospace industry is a critical process due to the high flexibility of the workpiece. In this paper, a flexible fixture based on the magnetorheological (MR) fluids is designed to investigate the regenerative chatter suppression during the machining. Based on the analysis of typical structural components in the aerospace industry, a general complex thin-walled workpiece with fixture and damping constraint can be equivalent as a rectangular cantilever beam. On the basis of the equivalent models, natural frequency and mode shape function of the thin-walled workpiece is obtained according to the Euler-Bernoulli beam assumptions. Then, the displacement response function of the bending vibration of the beam is represented by the product of all the mode shape function and the generalized coordinate. Furthermore, a dynamic equation of the workpiece-fixture system considering the external damping factor is proposed using the Lagrangian method in terms of all the mode shape function and the generalized coordinate, and the response of system under the dynamic cutting force is calculated to evaluate the stability of the milling process under damping control. Finally, the feasibility and effectiveness of the proposed approach are validated by the impact hammer experiments and several machining tests. (C) 2016 Production and hosting by Elsevier Ltd. on behalf of Chinese Society of Aeronautics and Astronautics.展开更多
To alleviate the chattering problem, a new type of fuzzy global sliding mode controller （FGSMC） is presented. In this controller, the switching gain is estimated by fuzzy logic system based on the reachable conditio...To alleviate the chattering problem, a new type of fuzzy global sliding mode controller （FGSMC） is presented. In this controller, the switching gain is estimated by fuzzy logic system based on the reachable conditions of sliding mode controller（SMC）, and genetic algorithm （GA） is used to optimize scaling factor of the switching gain, thus the switch chattering of SMC can be alleviated. Moreover, global sliding mode is realized by designing an exponential dynamic sliding surface. Simulation and real-time application for flight simulator servo system with Lugre friction are given to indicate that the proposed controller can guarantee high robust performance all the time and can alleviate chattering phenomenon effectively.展开更多
In order to build high accuracy integral dynamic models of cold rolling mill system, by analyzing the vibration process of cold rolling, the dynamic model of 4-h mill, including the rolling process model, the mill rol...In order to build high accuracy integral dynamic models of cold rolling mill system, by analyzing the vibration process of cold rolling, the dynamic model of 4-h mill, including the rolling process model, the mill roll stand structure model and the hydraulic servo system model is built. These three models are coupled and linearized, then the multiple input and multiple output （MIMO） linear transfer function model of single stand 4-h cold mill system is obtained. The model with the proposed data proves its validity, meanwhile the effects of different working conditions on the stability of cold rolling mill system have been discussed. Simulation resulsts show that the model accords with former models and has its own advancement. It contributes to the further study and supression of coupling vibraiton.展开更多
Chatter has been a primary obstacle to the successful implementation of high speed machining.The frequency response function（FRF） of the tool point is crucial for identification of chatter free cutting conditions.In...Chatter has been a primary obstacle to the successful implementation of high speed machining.The frequency response function（FRF） of the tool point is crucial for identification of chatter free cutting conditions.In order to quickly acquire the FRF of the different components combinations of machine tool,the assembly of machine tool was always decomposed into several parts,where the fluted portion of tool,however,was always treated as a uniform beam,and the associated discrepancy was ignored.This paper presents a new method to predict the dynamic response of the machine-spindle-holder-tool assembly using the receptance coupling substructure analysis technique,where the assembly is divided into three parts：machine-spindle,holder and tool shank,and tool＇s fluted portion.Impact testing is used to measure the receptance of machine-spindle,the Timoshenko beam model is employed to analyze the dynamics of holder and tool shank,and the finite element method（FEM） is used to calculate the receptance of the tool＇s fluted portion.The approximation of the fluted portion cross section using an equivalent diameter is also addressed.All the individual receptances are coupled by using substructure method.The predicted assembly receptance is experimentally verified for three different tool overhang lengths.The results also show that the equivalent diameter beam model reaches an acceptable accuracy.The proposed approach is helpful to predict the tool point dynamics rapidly in industry.展开更多
Milling the free-end of cylindrical parts, which are vertically fixed on the machine table,often suffers from large chatter vibrations. This kind of phenomenon is harmful to the cutting process. Therefore, it is of gr...Milling the free-end of cylindrical parts, which are vertically fixed on the machine table,often suffers from large chatter vibrations. This kind of phenomenon is harmful to the cutting process. Therefore, it is of great importance to develop means to suppress these undesirable chatters.This paper proposes a new idea for designing a tunable mass damper(TMD) to reduce vibrations in milling of cylindrical parts. Frequency response function(FRF) of the milling system is derived to comprehensively reveal the influence of both the dynamic response of the machine tools and the TMD. Critical axial depth of cut, which is usually used to characterize the process stability, is formulated by considering the FRFs of both the milling system itself and the TMD. Maximization of critical axial depth of cut is taken as objective function, while kernel dynamic parameters of TMD,which are involved in the derived expression of critical axial depth of cut, are extracted as designable variables. Optimization procedure is carried out to adjust the parameters of TMD by using sequential quadratic programming algorithm. A series of experiments with a designed passive TMD validate that the design has a good performance in reducing vibrations and improving stability of milling process.展开更多
An analytical model for chatter aero-engine casings is presented in this paper stability prediction in bull-nose end milling of And the mechanics and dynamics variations due to the complex cutter and workpiece geomet...An analytical model for chatter aero-engine casings is presented in this paper stability prediction in bull-nose end milling of And the mechanics and dynamics variations due to the complex cutter and workpiece geometry are considered by analyzing the effects of the lead angle on the milling process. Firstly, the tool-workpiece engagement region is obtained by using a previously developed method and divided into several disk elements along the tool-axis direction. Secondly, a 3D dynamic model for stability limit calculation is developed and simplified into a 1D model in normal direction considering only the dominant mode of the workpiece. Then the cutting force coefficients, the start and exit angles corresponding to each disk element are determined. And the total stability lobe diagram is calculated using an iterative algorithm. Finally, several experimental tests are carried out to validate the feasibility and effectiveness of the proposed ~rediction approach.展开更多
基金supported by the National Natural Science Foundation of China(No.52075129).
文摘Micro-milling technology is widely applied in micro manufacturing,particularly for the fabrication of miniature and micro components.However,the chatters and machining dynamics related issues in micro-milling are often the main challenges restricting its machining quality and productivity.Many research works have rendered that the machining dynamics and chatters in micro-milling are more complex compared with the conventional macro-milling process,likely because of the size effect and rigidity of the micro-milling system including the tooling,workpiece,process variables,materials involved,and the high-speed milling machines,and further their collective dynamic effects.Therefore,in this paper,the state of the art focusing on micro-milling chatters and dynamics related issues over the past years are comprehensively and critically reviewed to provide some insights for potential researchers and practitioners.Firstly,typical applications and the problems caused by the machining dynamics and chatters in micro-milling have been put forward in this paper.Then,the research on the underlying micro-cutting mechanics and dynamics,stability analysis,chatters detection,and chatter suppression are summarized critically.Furthermore,the underlying scientific and technological challenges are discussed particularly against typical precision engineering applications.Finally,the possible future directions and trends in research and development of micro-milling have been discussed.
基金supported by the National Natural Science Foundation of China(Grant No.U22A20202)。
文摘Thin-walled parts have been widely employed as critical components in high-performance equipment due to the high specific strength and light weight.However,owing to their relatively weak rigidity and poor damping properties,chatter vibration is likely to occur during the milling process,which severely deteriorates surface quality and decreases machining productivity.Therefore,chatter suppression is essential for improving the dynamic machinability of thin-walled structures and has attracted extensive attention over the past few decades.This paper reviews the current state of the art in research concerning chatter suppression during the milling of thin-walled workpieces.In consideration of the dynamic characteristics of this process,the challenges in design and application of chatter attenuation methods are highlighted.Moreover,various chatter suppression techniques,involving passive,active,and semi-active methods,are comprehensively discussed in terms of basic concepts,working mechanism,optimal design,and application.Finally,future research opportunities in chatter mitigation technology for thin-wall milling are recommended.
基金supported by the National Natural Science Foundation of China(No.U20A20294)the National Natural Science Foundation of China(No.52322511)the National Natural Science Foundation of China(No.52188102).
文摘Low-frequency structural vibrations caused by poor rigidity are one of the main obstacles limiting the machining efficiency of robotic milling.Existing vibration suppression strategies primarily focus on passive vibration absorption at the robotic end and feedback control at the joint motor.Although these strategies have a certain vibration suppression effect,the limitations of robotic flexibility and the extremely limited applicable speed range remain to be overcome.In this study,a Magnetorheological Joint Damper(MRJD)is developed.The joint-mounted feature ensures machining flexibility of the robot,and the millisecond response time of the Magnetorheological Fluid(MRF)ensures a large effective spindle speed range.More importantly,the evolution law of the damping performance of MRJD was revealed based on a low-frequency chatter mechanism,which guarantees the application of MRJD in robotic milling machining.To analyze the influence of the robotic joint angle on the suppression effect of the MRJD,the joint braking coefficient and end braking coefficient were proposed.Parallel coordinate plots were used to visualize the joint range with the optimal vibration suppression effect.Finally,a combination of different postures and cutting parameters was used to verify the vibration suppression effect and feasibility of the joint angle optimization.The experimental results show that the MRJD,which directly improves the joint vibration resistance,can effectively suppress the low-frequency vibration of robotic milling under a variety of cutting conditions.
基金supported in part by the Australian Research Council(DP240100830)。
文摘Sliding mode control(SMC)is a widely adopted control technology known for its robustness and simplicity.The essence of SMC is to use discontinuous control to drive a system into a pre-defined motion,called the sliding mode,which is designed with desirable dynamical properties.In the sliding mode,the controlled system is insensitive to the matched uncertainties and disturbances.Most SMC theory and methods have been developed based on the dynamical systems in the continuous-time domain,where switching functions play a critical role.Ideal switching is supposed to be instantaneous,activating as soon as the switching condition is met.However,in practice,switching mechanisms are affected by imperfections such as time delays,unmodeled dynamics,defects,digitization effects,and actuation limitations,which can degrade the salient properties of SMC.Understanding these effects and developing mitigation strategies are essential for industrial applications.Furthermore,the advent of networked control environments presents new challenges like limited communication bandwidth,latency and cyberattack,which have seen the emergence of the event-triggered SMC recently.Despite these significant advances,there is a lack of comprehensive studies which examine the commonalities and distinctions of utilizing switching in SMC across the continuous-time and discrete-time domains and beyond.This paper investigates the role of switching in SMC from a spatio-temporal perspective,considering both state-space and time aspects.The aim is to facilitate better understanding of its effects and misbehaviors,and to unlock its full potential for future applications.The interplay between SMC methods in the continuous-time and discrete-time domains is analyzed,and their shared principles and unique challenges are identified.Furthermore,important technical issues relating to switching across these time domains are explored,and several myths and pitfalls in their theory and applications are depicted.The relationships of SMC with other switching-based control systems such as switched control systems,fuzzy control systems,and event-triggered control systems are discussed.The impact of networked control environments on SMC in the continuous-time and discrete-time domains is also examined.Finally,key challenges and opportunities are outlined for future work in SMC and beyond.
基金Project(51275475)supported by the National Natural Science Foundation of ChinaProject(2014BY001)supported by the Department of Education in Zhejiang Province,ChinaProject(2014EP0110)supported by the Key Laboratory of Special Purpose Equipment and Advanced Manufacturing Technology,Ministry of Education and Zhejiang Province,China
文摘The possibility of the electric-hydraulic chattering technology and its application in the cold extrusion were presented.The conventional and electric-hydraulic chattering assisted backward extrusion processes were performed on 6061 aluminum alloy billets at room temperature.The experimental results showed that 5.65% reduction in the extrusion load was attained if the die and ejector were vibrated at a frequency of 100 Hz and amplitude of 0.013 mm in the longitudinal direction.The friction coefficient at the billet and tool system interface determined from the finite element analysis（FEA） decreased from 0.2 without chattering to 0.1 with application of electric-hydraulic chattering.The higher values of instantaneous velocity and direction change of material flow were achieved during the chattering assisted backward extrusion process.The strain distribution of the chattering assisted backward extrusion billet revealed lower maximum strain and smoother strain distribution in comparison with that produced by the conventional extrusion method.
基金Supported by the National Key Basic Research Program of China("973"Project)(2009CB724401)the China Postdoctoral Science Foundation(20070420208)the Postdoctoral Innovation Foundation of Shandong Province(200702023)~~
文摘Considering the self-excited and forced vibrations in high-speed milling processes, a novel method for dynamic optimization of system stability is used to determine the cutting parameters and structural parameters by increasing the chatter free material removal rate （CF-MRR） and surface finish. The method is hased on the theory of the chatter stability and the semi-bandwidth of the resonant region. The objective function of the method is material removal rate（MRR）,the constraints are chatter stability and surface finish, and the optimizing variables are cutting and structural parameters. The optimization procedure is stated. The method is applied to a milling system and CF-MRR is increased 18.86%. It is shown that the influences of the chatter stability and the resonance are simultaneously considered in the dynamic optimization of the milling system for increasing CF-MRR and the surface finish.
基金Tianjin Municipal Association of Higher Vocational&Technical Education Projects(No.XIV412)
文摘Considering the deficiency in milling process parameters selection, based on the modelling of dynamic milling force and the deduction of chatter stability limits, the chatter stability lobes simulation program for milling is developed with MAT- LAB. The simulation optimization application software of dynamics was designed using engineering simulation software Visio Basic. The chatter stability lobes for milling, which can be used as an instruction guide for the selection of process parameters, are simulated with frequency response functions （FRFs） gained by hammer test. The validation and accuracy of the simulation algorithm are verified by experiments. The simulation method has been used in a factory with an excellent application effect.
文摘A new method for suppressing cutting chatter is studied by adjusting servo parameters of the numerical control （NC） machine tool and controlling the limited cutting width. A model of the cutting system of the NC machine tool is established. It includes the mechanical system, the servo system and the cutting chatter system. Interactions between every two systems are shown in the model. The cutting system stability is simulated and relation curves between the limited cutting width and servo system parameters are described in the experiment. Simulation and experimental results show that there is a mapping relation between the limited cutting width and servo parameters of the NC machine tool, and the method is applicable and credible to suppress chatter.
文摘An applicable method to control regenerative cutting chatter automatically based on the optimal regulation of spindle speed is introduced. The optimal value of the phase shift angle of the regenerative chatter signal between the two successive cuts is 270°. The cutting process can be adjusted from the unstable region to stable one whenever regenerative chatter occurs if the phase shift angle is kept 270° by the optimal regulation of spindle speed. The theoretical analysis and the experimental results prove that the optimal regulation of spindle speed can effectively control regenerative cutting chatter. In addition, a reliablelly optimal control system of reliable spindle speed is presented. There is no need for system identification of the machine tool, and it is easy to put this regenerative chatter control method into practice, so the method has excellent application prospect.
文摘A mathematical model of the computer numerical control (CNC) heavy cuttingservo system including chatter in cutting courses was constructed for the chatter in CNC heavycutting. The theoretical analysis, computer simulation and orthogonal tests on this model show thatincreasing the gain of position K_(pp) can improve the rapid tracking performance of machine tools,and decreasing the delay time of speed loop τ_s can quickly eliminate the static error in thesystem, but the limited cutting width b_(lim) will descend correspondingly; excessively large orexcessively small gain of speed loop K_(ps) can result in decreasing b_(lim); optimizing K_(pp),τ_s and K_(ps) can improve the dynamic and static performance of the system and increase b_(lim).It is easy and feasible to optimize the servo parameters by the orthogonal test. This method caneffectively improve the system's stability and limited cutting width and it is suitable for the CNCheavy cutting of heavy-duty machine tools.
基金supported by Projects of International Cooperation and Exchanges NSFC (51720105009)the National Natural Science Foundation of China (No. 51575147)the Youth Talent Support Program of Harbin University of Science and Technology (201507)
文摘Chatter is a self-excited vibration of parts in machining systems. It is widely present across a range of cutting processes, and has an impact upon both efficiency and quality in production processing. A great deal of research has been dedicated to the development of technologies that are able to predict and detect chatter. The purpose of these technologies is to facilitate the avoidance of chatter during cutting processes, which leads to better surface precision, higher productivity,and longer tool life. This paper summarizes the current state of the art in research regarding the problems of how to arrive at stable chatter prediction, chatter identification, and chatter control/-suppression, with a focus on milling processes. Particular focus is placed on the theoretical relationship between cutting chatter and process damping, tool runout, and gyroscopic effect, as well as the importance of this for chatter prediction. The paper concludes with some reflections regarding possible directions for future research in this field.
基金National Natural Science Foundation of China(Grant No.51475432)Zhejiang Provincial National Natural Science Foundation of China(Grant No.LZ13E050003)State Key Program of National Natural Science of China(Grant Nos.U1234207,U1709210)
文摘Grinding chatter is a self?induced vibration which is unfavorable to precision machining processes. This paper proposes a forecasting method for grinding state identification based on bivarition empirical mode decomposition(BEMD) and least squares support vector machine(LSSVM), which allows the monitoring of grinding chatter over time. BEMD is a promising technique in signal processing research which involves the decomposition of two?dimen?sional signals into a series of bivarition intrinsic mode functions(BIMFs). BEMD and the extraction criterion of its true BIMFs are investigated by processing a complex?value simulation chatter signal. Then the feature vectors which are employed as an amplification for the chatter premonition are discussed. Furthermore, the methodology is tested and validated by experimental data collected from a CNC guideway grinder KD4020 X16 in Hangzhou Hangji Machine Tool Co., Ltd. The results illustrate that the BEMD is a superior method in terms of processing non?stationary and nonlinear signals. Meanwhile, the peak to peak, real?time standard deviation and instantaneous energy are proven to be e ec?tive feature vectors which reflect the di erent grinding states. Finally, a LSSVM model is established for grinding status classification based on feature vectors, giving a prediction accuracy rate of 96%.
基金supported by National Natural Science Foundation of China(No.51975096,No.51905075)China Postdoctoral Science Foundation(No.2019M661090)Liao Ning Revitalization Talents Program(No.XLYC1807230)。
文摘Thin-walled parts are widely used in the aerospace industry owing to their light weight and high specific strength.However,due to the low rigidity of thin-walled parts,elastic deformation and chatter easily occur,which seriously affect the machining accuracy and workpiece surface quality.To solve this problem,several supporting technologies have been reported in recent years.This paper reviews the recent research progress of flexible supporting technologies in the aerospace field by classifying them based on different principles and characteristics.The principle,progress,advantages,and limitations of the technologies are expounded by systematic comparison and summarized.Finally,the challenges and future development trends of flexible supporting technology,which will provide guidelines for further research,are discussed.
基金co-supported by the National Basic Research Program of China(No.2012CB720000)the National Natural Science Foundation of China(No.61104153)the Research Fund for the Doctoral Program of Higher Education of China(No.20091101110025)
文摘This paper proposes a finite-time robust flight controller, targeting for a reentry vehicle with blended aerodynamic surfaces and a reaction control system（RCS）. Firstly, a novel finite-time attitude controller is pointed out with the introduction of a nonsingular finite-time sliding mode manifold. The attitude tracking errors are mathematically proved to converge to zero within finite time which can be estimated. In order to improve the performance, a second-order finite-time sliding mode controller is further developed to effectively alleviate chattering without any deterioration of robustness and accuracy. Moreover, an optimization control allocation algorithm, using linear programming and a pulse-width pulse-frequency（PWPF） modulator, is designed to allocate torque commands for all the aerodynamic surface deflections and on–off switching-states of RCS thrusters.Simulations are provided for the reentry vehicle considering uncertain parameters and external disturbances for practical purposes, and the results demonstrate the effectiveness and robustness of the attitude control system.
基金supported by the National Basic Research Program of China (Grant No. 2013CB035802)the 111 Project of China (Grant No. B13044)
文摘Milling of the thin-walled workpiece in the aerospace industry is a critical process due to the high flexibility of the workpiece. In this paper, a flexible fixture based on the magnetorheological (MR) fluids is designed to investigate the regenerative chatter suppression during the machining. Based on the analysis of typical structural components in the aerospace industry, a general complex thin-walled workpiece with fixture and damping constraint can be equivalent as a rectangular cantilever beam. On the basis of the equivalent models, natural frequency and mode shape function of the thin-walled workpiece is obtained according to the Euler-Bernoulli beam assumptions. Then, the displacement response function of the bending vibration of the beam is represented by the product of all the mode shape function and the generalized coordinate. Furthermore, a dynamic equation of the workpiece-fixture system considering the external damping factor is proposed using the Lagrangian method in terms of all the mode shape function and the generalized coordinate, and the response of system under the dynamic cutting force is calculated to evaluate the stability of the milling process under damping control. Finally, the feasibility and effectiveness of the proposed approach are validated by the impact hammer experiments and several machining tests. (C) 2016 Production and hosting by Elsevier Ltd. on behalf of Chinese Society of Aeronautics and Astronautics.
基金This project is supported by Aeronautics Foundation of China (No. 00E51022)
文摘To alleviate the chattering problem, a new type of fuzzy global sliding mode controller （FGSMC） is presented. In this controller, the switching gain is estimated by fuzzy logic system based on the reachable conditions of sliding mode controller（SMC）, and genetic algorithm （GA） is used to optimize scaling factor of the switching gain, thus the switch chattering of SMC can be alleviated. Moreover, global sliding mode is realized by designing an exponential dynamic sliding surface. Simulation and real-time application for flight simulator servo system with Lugre friction are given to indicate that the proposed controller can guarantee high robust performance all the time and can alleviate chattering phenomenon effectively.
基金Item Sponsored by National Natural Science Foundation of China(60374032)Beijing Municipal Education Commission Key Discipline Control Theory and Control Engineering of China(XK100080537)
文摘In order to build high accuracy integral dynamic models of cold rolling mill system, by analyzing the vibration process of cold rolling, the dynamic model of 4-h mill, including the rolling process model, the mill roll stand structure model and the hydraulic servo system model is built. These three models are coupled and linearized, then the multiple input and multiple output （MIMO） linear transfer function model of single stand 4-h cold mill system is obtained. The model with the proposed data proves its validity, meanwhile the effects of different working conditions on the stability of cold rolling mill system have been discussed. Simulation resulsts show that the model accords with former models and has its own advancement. It contributes to the further study and supression of coupling vibraiton.
基金supported by National Basic Research Program of China (973 Program,Grant No. 2009CB724407)National Natural Science Foundation of China (Grant No. 51005175)Chinese Scholarship Council (University of Florida)
文摘Chatter has been a primary obstacle to the successful implementation of high speed machining.The frequency response function（FRF） of the tool point is crucial for identification of chatter free cutting conditions.In order to quickly acquire the FRF of the different components combinations of machine tool,the assembly of machine tool was always decomposed into several parts,where the fluted portion of tool,however,was always treated as a uniform beam,and the associated discrepancy was ignored.This paper presents a new method to predict the dynamic response of the machine-spindle-holder-tool assembly using the receptance coupling substructure analysis technique,where the assembly is divided into three parts：machine-spindle,holder and tool shank,and tool＇s fluted portion.Impact testing is used to measure the receptance of machine-spindle,the Timoshenko beam model is employed to analyze the dynamics of holder and tool shank,and the finite element method（FEM） is used to calculate the receptance of the tool＇s fluted portion.The approximation of the fluted portion cross section using an equivalent diameter is also addressed.All the individual receptances are coupled by using substructure method.The predicted assembly receptance is experimentally verified for three different tool overhang lengths.The results also show that the equivalent diameter beam model reaches an acceptable accuracy.The proposed approach is helpful to predict the tool point dynamics rapidly in industry.
基金supported by the National Natural Science Foundation of China(No.51675440 and 51705427)National Key Research and Development Program of China(No.2017YFB1102800)the Fundamental Research Funds for the Central Universities of China(No.3102018gxc025)
文摘Milling the free-end of cylindrical parts, which are vertically fixed on the machine table,often suffers from large chatter vibrations. This kind of phenomenon is harmful to the cutting process. Therefore, it is of great importance to develop means to suppress these undesirable chatters.This paper proposes a new idea for designing a tunable mass damper(TMD) to reduce vibrations in milling of cylindrical parts. Frequency response function(FRF) of the milling system is derived to comprehensively reveal the influence of both the dynamic response of the machine tools and the TMD. Critical axial depth of cut, which is usually used to characterize the process stability, is formulated by considering the FRFs of both the milling system itself and the TMD. Maximization of critical axial depth of cut is taken as objective function, while kernel dynamic parameters of TMD,which are involved in the derived expression of critical axial depth of cut, are extracted as designable variables. Optimization procedure is carried out to adjust the parameters of TMD by using sequential quadratic programming algorithm. A series of experiments with a designed passive TMD validate that the design has a good performance in reducing vibrations and improving stability of milling process.
基金supported by the National Basic Research Program of China(No.2013CB035802)the 111 Project of China(No.B13044)
文摘An analytical model for chatter aero-engine casings is presented in this paper stability prediction in bull-nose end milling of And the mechanics and dynamics variations due to the complex cutter and workpiece geometry are considered by analyzing the effects of the lead angle on the milling process. Firstly, the tool-workpiece engagement region is obtained by using a previously developed method and divided into several disk elements along the tool-axis direction. Secondly, a 3D dynamic model for stability limit calculation is developed and simplified into a 1D model in normal direction considering only the dominant mode of the workpiece. Then the cutting force coefficients, the start and exit angles corresponding to each disk element are determined. And the total stability lobe diagram is calculated using an iterative algorithm. Finally, several experimental tests are carried out to validate the feasibility and effectiveness of the proposed ~rediction approach.
