The problem of linear time-varying（LTV） system modal analysis is considered based on time-dependent state space representations, as classical modal analysis of linear time-invariant systems and current LTV system mo...The problem of linear time-varying（LTV） system modal analysis is considered based on time-dependent state space representations, as classical modal analysis of linear time-invariant systems and current LTV system modal analysis under the ＂frozen-time＂ assumption are not able to determine the dynamic stability of LTV systems. Time-dependent state space representations of LTV systems are first introduced, and the corresponding modal analysis theories are subsequently presented via a stabilitypreserving state transformation. The time-varying modes of LTV systems are extended in terms of uniqueness, and are further interpreted to determine the system＇s stability. An extended modal identification is proposed to estimate the time-varying modes, consisting of the estimation of the state transition matrix via a subspace-based method and the extraction of the time-varying modes by the QR decomposition. The proposed approach is numerically validated by three numerical cases, and is experimentally validated by a coupled moving-mass simply supported beam exper- imental case. The proposed approach is capable of accurately estimating the time-varying modes, and provides anew way to determine the dynamic stability of LTV systems by using the estimated time-varying modes.展开更多
The milling-head machine tool is a sophisticated and high-quality machine tool of which the spindle system is made up of special multi-element structure. Two special mechanical configurations make the cutting performa...The milling-head machine tool is a sophisticated and high-quality machine tool of which the spindle system is made up of special multi-element structure. Two special mechanical configurations make the cutting performance of the machine tool decline. One is the milling head spindle supported on two sets of complex bearings. The mechanical dynamic rigidity of milling head structure is researched on designed digital prototype with finite element analysis（FEA） and modal synthesis analysis （ MSA ） for identifying the weak structures. The other is the ram structure hanging on milling head. The structure is researched to get dynamic performance on cutting at different ram extending positions. The analysis results on spindle and ram are used to improve the mechanical configurations and structure in design. The machine tool is built up with modified structure and gets better dynamic rigidity than it was before.展开更多
Technological progress has led to increased demand for small components with tiny features, which cannot be achieved through conventional machining. Industrial application of processes based on microcutting is limited...Technological progress has led to increased demand for small components with tiny features, which cannot be achieved through conventional machining. Industrial application of processes based on microcutting is limited by some issues concerning the geometrical scale. The process performance is significantly affected by milling machine, tool holder, tool, workpiece material microstructure, workpiece fixtures, and process parameters. At present, an ultimate micromachining assessment procedure is not available. This study aims to propose and conduct an experiment on a testing procedure for micromilling. The set up to be implemented and the output to be considered are defined and described. Three major stages are identified: estimation of the effective bandwidth of the load cell–tool holder system, the milling machine natural frequency measurement, and micromilling test execution. The entire procedure is performed, and its robustness is demonstrated.展开更多
In this paper, we investigate the empirical likelihood diagnosis of modal linear regression models. The empirical likelihood ratio function based on modal regression estimation method for the regression coefficient is...In this paper, we investigate the empirical likelihood diagnosis of modal linear regression models. The empirical likelihood ratio function based on modal regression estimation method for the regression coefficient is introduced. First, the estimation equation based on empirical likelihood method is established. Then, some diagnostic statistics are proposed. At last, we also examine the performance of proposed method for finite sample sizes through simulation study.展开更多
To provide a good machining method in remanufacturing for the repaired parts with various forms, the design method of reconfigurable multi-process combined machining system and its implementation technology for remanu...To provide a good machining method in remanufacturing for the repaired parts with various forms, the design method of reconfigurable multi-process combined machining system and its implementation technology for remanufacturing are systematically proposed. The key technologies include reconfigurable structure design method of multi-process combined machining, man-machine coordination parameter programming and control system technology with self-maintenance function. A turn-milling machine tool based on this design method is developed. Natural frequency and corresponding vibration modes of the machine tool were analyzed by using both FEA and vibration test. Stiffness tests and machining experiments show that the rapid machining of most processes for the repaired work pieces can be successfully realized.展开更多
基金Supported by the China Scholarship Council,National Natural Science Foundation of China(Grant No.11402022)the Interuniversity Attraction Poles Programme of the Belgian Science Policy Office(DYSCO)+1 种基金the Fund for Scientific Research–Flanders(FWO)the Research Fund KU Leuven
文摘The problem of linear time-varying（LTV） system modal analysis is considered based on time-dependent state space representations, as classical modal analysis of linear time-invariant systems and current LTV system modal analysis under the ＂frozen-time＂ assumption are not able to determine the dynamic stability of LTV systems. Time-dependent state space representations of LTV systems are first introduced, and the corresponding modal analysis theories are subsequently presented via a stabilitypreserving state transformation. The time-varying modes of LTV systems are extended in terms of uniqueness, and are further interpreted to determine the system＇s stability. An extended modal identification is proposed to estimate the time-varying modes, consisting of the estimation of the state transition matrix via a subspace-based method and the extraction of the time-varying modes by the QR decomposition. The proposed approach is numerically validated by three numerical cases, and is experimentally validated by a coupled moving-mass simply supported beam exper- imental case. The proposed approach is capable of accurately estimating the time-varying modes, and provides anew way to determine the dynamic stability of LTV systems by using the estimated time-varying modes.
基金supported by Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipality,China.
文摘The milling-head machine tool is a sophisticated and high-quality machine tool of which the spindle system is made up of special multi-element structure. Two special mechanical configurations make the cutting performance of the machine tool decline. One is the milling head spindle supported on two sets of complex bearings. The mechanical dynamic rigidity of milling head structure is researched on designed digital prototype with finite element analysis（FEA） and modal synthesis analysis （ MSA ） for identifying the weak structures. The other is the ram structure hanging on milling head. The structure is researched to get dynamic performance on cutting at different ram extending positions. The analysis results on spindle and ram are used to improve the mechanical configurations and structure in design. The machine tool is built up with modified structure and gets better dynamic rigidity than it was before.
文摘Technological progress has led to increased demand for small components with tiny features, which cannot be achieved through conventional machining. Industrial application of processes based on microcutting is limited by some issues concerning the geometrical scale. The process performance is significantly affected by milling machine, tool holder, tool, workpiece material microstructure, workpiece fixtures, and process parameters. At present, an ultimate micromachining assessment procedure is not available. This study aims to propose and conduct an experiment on a testing procedure for micromilling. The set up to be implemented and the output to be considered are defined and described. Three major stages are identified: estimation of the effective bandwidth of the load cell–tool holder system, the milling machine natural frequency measurement, and micromilling test execution. The entire procedure is performed, and its robustness is demonstrated.
文摘In this paper, we investigate the empirical likelihood diagnosis of modal linear regression models. The empirical likelihood ratio function based on modal regression estimation method for the regression coefficient is introduced. First, the estimation equation based on empirical likelihood method is established. Then, some diagnostic statistics are proposed. At last, we also examine the performance of proposed method for finite sample sizes through simulation study.
基金Supported by the Technology Innovation Project of BIT(CX02016)
文摘To provide a good machining method in remanufacturing for the repaired parts with various forms, the design method of reconfigurable multi-process combined machining system and its implementation technology for remanufacturing are systematically proposed. The key technologies include reconfigurable structure design method of multi-process combined machining, man-machine coordination parameter programming and control system technology with self-maintenance function. A turn-milling machine tool based on this design method is developed. Natural frequency and corresponding vibration modes of the machine tool were analyzed by using both FEA and vibration test. Stiffness tests and machining experiments show that the rapid machining of most processes for the repaired work pieces can be successfully realized.
