The existing research of the electro-hydraulic vibrator mainly focuses on system stability,working frequency width and output waveform distortion.However,this high frequency performance of the electro-hydraulic vibrat...The existing research of the electro-hydraulic vibrator mainly focuses on system stability,working frequency width and output waveform distortion.However,this high frequency performance of the electro-hydraulic vibrator is difficult to be improved greatly due to fast insufficiently frequency response of the servo valve itself and limited compensation capability of the control structure in the vibrator system.In this paper,to realize high frequency vibration,an improved two-dimensional valve(here within defined as a2D valve)as a main control component is adopted to the parallel connection with a servo valve to control the electro-hydraulic vibrator.Because the output waveforms of this electro-hydraulic vibrator are incapable to be verified through timely feedback as in the conventional electro-hydraulic servo system,the analysis to the output waveform becomes crucial to the design and control of the electro-hydraulic vibrator.The mathematical models of hydraulic actuation mechanism and the orifice area of the parallel valves connection are established first.And then the vibration process is divided into two sections in terms of the direction of the flow,the analytical expression of the excited waveform is solved.Based on the analytical results,the vibration boundary positions and the relationships exist between working states and the control parameters are derived.Finally an experimental system was built to validate the theoretical analysis.It is verified that this electro-hydraulic vibration system could achieve high working frequency,up to 2 000 Hz.The excited waveform is similar to the sinusoidal waveform.And the ascent and decent slopes of the waveforms are somewhat asymmetrical.This asymmetry is not only caused by the change of the direction of the elastic force but also dependent on the bias position of the vibration.Consequently the distortion of effective working waveform is less than 10%.This electro-hydraulic vibrator controlled by the multiple valves could not only greatly enhance the working frequency but also precisely control the vibration characteristic variables such as waveform shape.展开更多
The existing articulated arm coordinate measuring machines(AACMM) with one measurement model are easy to cause low measurement accuracy because the whole sampling space is much bigger than the result in the unstable c...The existing articulated arm coordinate measuring machines(AACMM) with one measurement model are easy to cause low measurement accuracy because the whole sampling space is much bigger than the result in the unstable calibration parameters. To compensate for the deficiency of one measurement model, the multiple measurement models are built by the Denavit-Hartenberg's notation, the homemade standard rod components are used as a calibration tool and the Levenberg-Marquardt calibration algorithm is applied to solve the structural parameters in the measurement models. During the tests of multiple measurement models, the sample areas are selected in two situations. It is found that the measurement errors' sigma value(0.083 4 mm) dealt with one measurement model is nearly two times larger than that of the multiple measurement models(0.043 1 mm) in the same sample area. While in the different sample area, the measurement errors' sigma value(0.054 0 mm) dealt with the multiple measurement models is about 40% of one measurement model(0.137 3 mm). The preliminary results suggest that the measurement accuracy of AACMM dealt with multiple measurement models is superior to the accuracy of the existing machine with one measurement model. This paper proposes the multiple measurement models to improve the measurement accuracy of AACMM without increasing any hardware cost.展开更多
The optimal attitude control of an underactuat-ed spacecraft is investigated in this paper.The flywheels ofthe spacecraft can somehow only provide control inputs intwo independent directions.The dynamic equations are ...The optimal attitude control of an underactuat-ed spacecraft is investigated in this paper.The flywheels ofthe spacecraft can somehow only provide control inputs intwo independent directions.The dynamic equations are for-mulated for the spacecraft under a nonholonomic constraintresulting from the constant time-rate of the total angularmomentum of the system.The reorientation of such underac-tuated spacecraft is transformed into an optimal control prob-lem.A genetic algorithm is proposed to derive the controllaws of the two flywheels angle velocity inputs.The controllaws are approximated by the discrete orthogonal wavelets.The numerical simulations indicate that the genetic algorithmwith the wavelet approximation is an effective approach todeal with the optimal reorientation of underactuatedspacecraft.展开更多
To fulfill the demands for higher quality,efficiency and flexibility in aviation industry,a multi-functional end effector is designed to automate the drilling and riveting processes in assembling carbon fiber reinforc...To fulfill the demands for higher quality,efficiency and flexibility in aviation industry,a multi-functional end effector is designed to automate the drilling and riveting processes in assembling carbon fiber reinforced polymer(CFRP)and aluminum components for a robotic aircraft assembly system.To meet the specific functional requirements for blind rivet installation on CFRP and aluminum materials,additional modules are incorporated on the end effector aside of the basic processing modules for drilling.And all of these processing modules allow for a onestep-drilling-countersinking process,hole inspection,automatic rivet feed,rivet geometry check,sealant application,rivet insertion and installation.Besides,to guarantee the better quality of the hole drilled and joints riveted,several online detection and adjustment measures are applied to this end effector,including the reference detection and perpendicular calibration,which could effectively ensure the positioning precision and perpendicular accuracy as demanded.Finally,the test result shows that this end effector is capable of producing each hole to a positioning precision within ±0.5 mm,aperpendicular accuracy within 0.3°,a diameter tolerance of H8,and a countersink depth tolerance of±0.01 mm.Moreover,it could drill and rivet up to three joints per minute,with acceptable shearing and tensile strength.展开更多
The production process plan design and configurations of reconfigurable machine tool (RMT) interact with each other. Reasonable process plans with suitable configurations of RMT help to improve product quality and red...The production process plan design and configurations of reconfigurable machine tool (RMT) interact with each other. Reasonable process plans with suitable configurations of RMT help to improve product quality and reduce production cost. Therefore, a cooperative strategy is needed to concurrently solve the above issue. In this paper, the cooperative optimization model for RMT configurations and production process plan is presented. Its objectives take into account both impacts of process and configuration. Moreover, a novel genetic algorithm is also developed to provide optimal or near-optimal solutions: firstly, its chromosome is redesigned which is composed of three parts, operations, process plan and configurations of RMTs, respectively; secondly, its new selection, crossover and mutation operators are also developed to deal with the process constraints from operation processes (OP) graph, otherwise these operators could generate illegal solutions violating the limits; eventually the optimal configurations for RMT under optimal process plan design can be obtained. At last, a manufacturing line case is applied which is composed of three RMTs. It is shown from the case that the optimal process plan and configurations of RMT are concurrently obtained, and the production cost decreases 6.28% and nonmonetary performance increases 22%. The proposed method can figure out both RMT configurations and production process, improve production capacity, functions and equipment utilization for RMT.展开更多
An attempt is made to measure three direction forces using octagonal ring dynamometer in the 2024 aluminum alloy friction stir joining(FSJ)process.A test is made to measure the specific area stress and stress distribu...An attempt is made to measure three direction forces using octagonal ring dynamometer in the 2024 aluminum alloy friction stir joining(FSJ)process.A test is made to measure the specific area stress and stress distributions in the specific area of the workpiece are obtained.The workpiece stresses in the FSJ process are analyzed by numerical simulation method.It is found that,in the downward stage of the process,feed force and lateral force in the tool are small,almost zero,and the maximum axial force can reach 12.5kN.In the stable joining stage,the forces acting on the tool become stabilized.Compared with the low speed,high feed speed results in small feed force and small lateral force,but large feed force in the stable joining stage.The stresses in three directions of feed direction,direction that perpendicular to butt face and direction perpendicular to the surface are obtained.The simulation stress value of measure point is obtained.Test and numerical simulation can authenticate each other.Both experimental stress values and numerical simulation stress values are credible.展开更多
Under certain growth conditions for systems with a film/substrate lattice misfit, the deposited material is known to aggregate into island-like shapes. We have obtained an analytical expression of the total free energ...Under certain growth conditions for systems with a film/substrate lattice misfit, the deposited material is known to aggregate into island-like shapes. We have obtained an analytical expression of the total free energy, which consists of strain energy, surface energy and interfacial energy of a coherent island/substrate system, and the change of equilibrium aspect ratio versus the volume of the island and the misfit of lattices in the system, which provides a broad perspective on island behaviour. These then were used to study the equilibrium shapes of the system. The results show that in order to minimize the total free energy, a coherent island will have a particular height-to-width aspect ratio, called equilibrium aspect ratio, that is a function of the island volume and misfit. The aspect ratio is increased with increasing island volume at a fixed misfit, and with increasing misfit strain between the island and substrate at a fixed island volume. Moreover, the effect of misfit dislocation on the equilibrium shape of the island is also examined. The results obtained are in good agreement with experiment of observations and thus can serve as a basis for interpreting the experiments.展开更多
The dynamic properties of rolling mill are significantly influenced by many coupling factors. According to the coupled mechanical and electric dynamics theory, the global coupled equations for the dynamic analysis of ...The dynamic properties of rolling mill are significantly influenced by many coupling factors. According to the coupled mechanical and electric dynamics theory, the global coupled equations for the dynamic analysis of planishing mill CM04 of Shanghai Baosteel Group Corporation were derived, by using finite element methods. These elasto-dynamic equations establish the coupling relations among the stand vibration system, torsional vibration system, driving motors, etc. It provides theoretical basis to a certain extent for globally dynamic simulation, analysis of stability of motion, prediction of abnormal operating mode, globally optimum design and control, etc.展开更多
The concentration of elements in molten metal of AZ31 magnesium alloy after long pulsed Nd:YAG laser processing was quantitatively analyzed by using calibration-free laser-induced breakdown spectroscopy(CF-LIBS). The ...The concentration of elements in molten metal of AZ31 magnesium alloy after long pulsed Nd:YAG laser processing was quantitatively analyzed by using calibration-free laser-induced breakdown spectroscopy(CF-LIBS). The composition change in AZ31 magnesium alloy under different laser pulse width was also investigated. The experimental results showed that CF-LIBS can obtain satisfactory quantitative or semi-quantitative results for matrix or major elements,while only qualitative analysis was possible for minor or trace elements. Moreover, it is found that the chemical composition of molten metal will change after laser processing. The concentration of magnesium in molten metal is lower than that present in the base metal. The Mg loss increases with an increase of pulse width in the laser processing. This result shows that the selective vaporization of different elements is affected by the pulse width during laser processing.展开更多
Natural language processing has got great progress recently. Controlling robots with spoken natural language has become expectable. With the reliability problem of this kind of control in mind a confirmation process o...Natural language processing has got great progress recently. Controlling robots with spoken natural language has become expectable. With the reliability problem of this kind of control in mind a confirmation process of natural language instruction should be included before carried out by the robot autonomously and the prototype dialog system was designed thus the standardization problem was raised for the natural and understandable language interaction. In the application background of remotely navigating a mobile robot inside a building with Chinese natural spoken language considering that as an important navigation element in instructions a place name can be expressed with different lexical terms in spoken language this paper proposes a model for substituting different alternatives of a place name with a standard one (called standardization). First a CRF (Conditional Random Fields) model is trained to label the term required be standardized then a trained word embedding model is to represent lexical terms as digital vectors. In the vector space similarity of lexical terms is defined and used to find out the most similar one to the term picked out to be standardized. Experiments show that the method proposed works well and the dialog system responses to confirm the instructions are natural and understandable.展开更多
Magneto-rheological (MR) fluid-based dampers are currently being explored for their potential implementation in intelligent vehicle suspension designs. Due to inherent hysteretic force properties of the MR dampers, an...Magneto-rheological (MR) fluid-based dampers are currently being explored for their potential implementation in intelligent vehicle suspension designs. Due to inherent hysteretic force properties of the MR dampers, analyzing and suppressing the MR-damper hysteresis effects, therefore, impose a great challenge. A quarter-vehicle MR-suspension model is formulated in conjunction with proposed hysteretic and mean MR-damper models, and the passive and semi-actively controlled MR-suspension systems are focused to investigate the influence of MR-damper force hysteresis. The semi-actively controlled MR-suspension employs the “on-off” control law in response to direction of the damper velocity, so as to generate the asymmetric damping force property form the symmetric MR-damper design. The results show that the MR-damping hysteresis yields serious transients and oscillations in responses for the semi-actively controlled MR-suspension than the passive MR-suspension due to the current-switching discontinuity, and would thus deteriorate the suspension performance. The undesired strong transients and oscillations in responses can be effectively suppressed by employing the proposed smooth technique without phase shift for modulating the command current discontinuity.展开更多
This paper attempts to solve the complexity of scheduling problems and meet the requirement of the ever-changing manufacturing environment. In this paper, a new Workflow-Based Scheduling System (WBSS) is proposed. The...This paper attempts to solve the complexity of scheduling problems and meet the requirement of the ever-changing manufacturing environment. In this paper, a new Workflow-Based Scheduling System (WBSS) is proposed. The integration of Workflow Management System (WfMS) and rule-based scheduler provides us an effective way of generating a task-sheet according to the states of system and the scheduled objects. First, the definition of workflow model for scheduling is proposed, and following are the architecture and mechanism of the proposed WBSS. At last, an application is given to show how the established system works.展开更多
Diabetic retinopathy(DR) is one of the most important causes of visual impairment. Automatic recognition of DR lesions, like hard exudates(EXs), in retinal images can contribute to the diagnosis and screening of the d...Diabetic retinopathy(DR) is one of the most important causes of visual impairment. Automatic recognition of DR lesions, like hard exudates(EXs), in retinal images can contribute to the diagnosis and screening of the disease. To achieve this goal, an automatically detecting approach based on improved FCM(IFCM) as well as support vector machines(SVM) was established and studied. Firstly, color fundus images were segmented by IFCM, and candidate regions of EXs were obtained. Then, the SVM classifier is confirmed with the optimal subset of features and judgments of these candidate regions, as a result hard exudates are detected from fundus images. Our database was composed of 126 images with variable color, brightness, and quality. 70 of them were used to train the SVM and the remaining 56 to assess the performance of the method. Using a lesion based criterion, we achieved a mean sensitivity of 94.65% and a mean positive predictive value of 97.25%. With an image-based criterion, our approach reached a 100% mean sensitivity, 96.43% mean specificity and 98.21% mean accuracy. Furthermore, the average time cost in processing an image is 4.56 s. The results suggest that the proposed method can efficiently detect EXs from color fundus images and it could be a diagnostic aid for ophthalmologists in the screening for DR.展开更多
With the development of electric power technology, information technology and military technology, the impact of cyber attack on electric power infrastructure has increasingly become a hot spot issue which calls both ...With the development of electric power technology, information technology and military technology, the impact of cyber attack on electric power infrastructure has increasingly become a hot spot issue which calls both domestic and foreign attention. First, main reasons of the impact on power infrastructure caused by cyber attack are analyzed from the following two aspects: 1) The dependence of electric power infrastructure on information infrastructure makes cyber attack issues in information field likely to affect electric power field. 2) As regards to the potential threat sources, it will be considerably profitable to launch cyber attacks on electric power infrastructure. On this basis, this paper gives a classified elaboration on the characteristics and the possibilities of cyber attacks on electrical infrastructures. Finally, the recently published actual events of cyber attacks in respect of threat sources, vulnerabilities and assaulting modes are analyzed and summarized.展开更多
Modified adaptive observer based backstepping control system for dynamic positioning of ship is proposed.As an improvement,the adaptive observer takes the first-order wave frequency model and the bias term which repre...Modified adaptive observer based backstepping control system for dynamic positioning of ship is proposed.As an improvement,the adaptive observer takes the first-order wave frequency model and the bias term which represent the slowly varying environmental disturbances and the unmodeled dynamics.Thus,the wave-frequency motions are filtered out,and only the reconstructed low-frequency motions are sent as inputs of the controller.Furthermore,as the ship dynamics parameters are unknown,the adaptive estimation law is designed for both the unknown ship dynamics and the unmeasured state variables.Based on the estimated states and parameters,backstepping controller considering the integral action is designed.Global exponential stability(GES) for the total system is proved using Lyapunov direct method.Simulation results show a good performance of the observer and control system.展开更多
In order to improve ride comfort and handling performance of the vehicle, an adaptive hybrid control algorithm is proposed for semi-active suspension systems. The virtues of sky-hook is combined with ground-hook contr...In order to improve ride comfort and handling performance of the vehicle, an adaptive hybrid control algorithm is proposed for semi-active suspension systems. The virtues of sky-hook is combined with ground-hook control strategies and a more suitable compromise for the suspension systems is chosen. The hybrid coefficient is tuned according to the longitudinal and lateral acceleration so as to improve the vehicle stability especially in high speed conditions. Damping continuous adjustable absorber is used to continuously control the damping force so as to eliminate the damping force jerk instead of traditional on-off control policy. Based on suspension stroke measured by sensors, unscented Kalman filter is designed to estimate the suspension states in real-time for the realization of hybrid control, which improves the robustness of the control strategy and is adaptive to different types of road profiles. Finally, the proposed control algorithm is validated under the following two typical road profiles: half-sine speed bump road and the random road. The simulation results indicate that the hybrid control algorithm could offer a good coordination between ride comfort and handling of the vehicle.展开更多
基金supported by National Natural Science Foundation of China(Grant No.50675204)Zhejiang Provincial Natural Science Foundation of China(Grant No.D1080667)
文摘The existing research of the electro-hydraulic vibrator mainly focuses on system stability,working frequency width and output waveform distortion.However,this high frequency performance of the electro-hydraulic vibrator is difficult to be improved greatly due to fast insufficiently frequency response of the servo valve itself and limited compensation capability of the control structure in the vibrator system.In this paper,to realize high frequency vibration,an improved two-dimensional valve(here within defined as a2D valve)as a main control component is adopted to the parallel connection with a servo valve to control the electro-hydraulic vibrator.Because the output waveforms of this electro-hydraulic vibrator are incapable to be verified through timely feedback as in the conventional electro-hydraulic servo system,the analysis to the output waveform becomes crucial to the design and control of the electro-hydraulic vibrator.The mathematical models of hydraulic actuation mechanism and the orifice area of the parallel valves connection are established first.And then the vibration process is divided into two sections in terms of the direction of the flow,the analytical expression of the excited waveform is solved.Based on the analytical results,the vibration boundary positions and the relationships exist between working states and the control parameters are derived.Finally an experimental system was built to validate the theoretical analysis.It is verified that this electro-hydraulic vibration system could achieve high working frequency,up to 2 000 Hz.The excited waveform is similar to the sinusoidal waveform.And the ascent and decent slopes of the waveforms are somewhat asymmetrical.This asymmetry is not only caused by the change of the direction of the elastic force but also dependent on the bias position of the vibration.Consequently the distortion of effective working waveform is less than 10%.This electro-hydraulic vibrator controlled by the multiple valves could not only greatly enhance the working frequency but also precisely control the vibration characteristic variables such as waveform shape.
基金Supported by National Natural Science Foundation of China(Grant No.51265017)Jiangxi Provincial Science and Technology Planning Project,China(Grant No.GJJ12468)Science and Technology Planning Project of Ji’an City,China(Grant No.20131828)
文摘The existing articulated arm coordinate measuring machines(AACMM) with one measurement model are easy to cause low measurement accuracy because the whole sampling space is much bigger than the result in the unstable calibration parameters. To compensate for the deficiency of one measurement model, the multiple measurement models are built by the Denavit-Hartenberg's notation, the homemade standard rod components are used as a calibration tool and the Levenberg-Marquardt calibration algorithm is applied to solve the structural parameters in the measurement models. During the tests of multiple measurement models, the sample areas are selected in two situations. It is found that the measurement errors' sigma value(0.083 4 mm) dealt with one measurement model is nearly two times larger than that of the multiple measurement models(0.043 1 mm) in the same sample area. While in the different sample area, the measurement errors' sigma value(0.054 0 mm) dealt with the multiple measurement models is about 40% of one measurement model(0.137 3 mm). The preliminary results suggest that the measurement accuracy of AACMM dealt with multiple measurement models is superior to the accuracy of the existing machine with one measurement model. This paper proposes the multiple measurement models to improve the measurement accuracy of AACMM without increasing any hardware cost.
基金supported by the National Natural Science Foundation of China (10772020)
文摘The optimal attitude control of an underactuat-ed spacecraft is investigated in this paper.The flywheels ofthe spacecraft can somehow only provide control inputs intwo independent directions.The dynamic equations are for-mulated for the spacecraft under a nonholonomic constraintresulting from the constant time-rate of the total angularmomentum of the system.The reorientation of such underac-tuated spacecraft is transformed into an optimal control prob-lem.A genetic algorithm is proposed to derive the controllaws of the two flywheels angle velocity inputs.The controllaws are approximated by the discrete orthogonal wavelets.The numerical simulations indicate that the genetic algorithmwith the wavelet approximation is an effective approach todeal with the optimal reorientation of underactuatedspacecraft.
基金supported by the National Natural Science Foundations of China(Nos.5157051626,51475225)
文摘To fulfill the demands for higher quality,efficiency and flexibility in aviation industry,a multi-functional end effector is designed to automate the drilling and riveting processes in assembling carbon fiber reinforced polymer(CFRP)and aluminum components for a robotic aircraft assembly system.To meet the specific functional requirements for blind rivet installation on CFRP and aluminum materials,additional modules are incorporated on the end effector aside of the basic processing modules for drilling.And all of these processing modules allow for a onestep-drilling-countersinking process,hole inspection,automatic rivet feed,rivet geometry check,sealant application,rivet insertion and installation.Besides,to guarantee the better quality of the hole drilled and joints riveted,several online detection and adjustment measures are applied to this end effector,including the reference detection and perpendicular calibration,which could effectively ensure the positioning precision and perpendicular accuracy as demanded.Finally,the test result shows that this end effector is capable of producing each hole to a positioning precision within ±0.5 mm,aperpendicular accuracy within 0.3°,a diameter tolerance of H8,and a countersink depth tolerance of±0.01 mm.Moreover,it could drill and rivet up to three joints per minute,with acceptable shearing and tensile strength.
基金supported by National Natural Science Foundation of China (Grant Nos. 51005169, 50875187, 50975209)Shanghai Municipal Natural Science Foundation of China (Grant No. 10ZR1432300)+1 种基金International Science & Technology Cooperation Program of China (Grant No. 2012DFG72210)Zhejiang Provincial Key International Science & Technology Cooperation Program of China (Grant No. 2011C14025)
文摘The production process plan design and configurations of reconfigurable machine tool (RMT) interact with each other. Reasonable process plans with suitable configurations of RMT help to improve product quality and reduce production cost. Therefore, a cooperative strategy is needed to concurrently solve the above issue. In this paper, the cooperative optimization model for RMT configurations and production process plan is presented. Its objectives take into account both impacts of process and configuration. Moreover, a novel genetic algorithm is also developed to provide optimal or near-optimal solutions: firstly, its chromosome is redesigned which is composed of three parts, operations, process plan and configurations of RMTs, respectively; secondly, its new selection, crossover and mutation operators are also developed to deal with the process constraints from operation processes (OP) graph, otherwise these operators could generate illegal solutions violating the limits; eventually the optimal configurations for RMT under optimal process plan design can be obtained. At last, a manufacturing line case is applied which is composed of three RMTs. It is shown from the case that the optimal process plan and configurations of RMT are concurrently obtained, and the production cost decreases 6.28% and nonmonetary performance increases 22%. The proposed method can figure out both RMT configurations and production process, improve production capacity, functions and equipment utilization for RMT.
基金supported by the National Natural Science Foundation of China(51175255)the Funding of Jiangsu Innovation Program for Graduate Education(CXZZ13_0152)the Fundamental Research Funds for the Central Universities in P.R.China
文摘An attempt is made to measure three direction forces using octagonal ring dynamometer in the 2024 aluminum alloy friction stir joining(FSJ)process.A test is made to measure the specific area stress and stress distributions in the specific area of the workpiece are obtained.The workpiece stresses in the FSJ process are analyzed by numerical simulation method.It is found that,in the downward stage of the process,feed force and lateral force in the tool are small,almost zero,and the maximum axial force can reach 12.5kN.In the stable joining stage,the forces acting on the tool become stabilized.Compared with the low speed,high feed speed results in small feed force and small lateral force,but large feed force in the stable joining stage.The stresses in three directions of feed direction,direction that perpendicular to butt face and direction perpendicular to the surface are obtained.The simulation stress value of measure point is obtained.Test and numerical simulation can authenticate each other.Both experimental stress values and numerical simulation stress values are credible.
基金Project supported by the National Natural Science Foundation of China (Grant No 90101004)
文摘Under certain growth conditions for systems with a film/substrate lattice misfit, the deposited material is known to aggregate into island-like shapes. We have obtained an analytical expression of the total free energy, which consists of strain energy, surface energy and interfacial energy of a coherent island/substrate system, and the change of equilibrium aspect ratio versus the volume of the island and the misfit of lattices in the system, which provides a broad perspective on island behaviour. These then were used to study the equilibrium shapes of the system. The results show that in order to minimize the total free energy, a coherent island will have a particular height-to-width aspect ratio, called equilibrium aspect ratio, that is a function of the island volume and misfit. The aspect ratio is increased with increasing island volume at a fixed misfit, and with increasing misfit strain between the island and substrate at a fixed island volume. Moreover, the effect of misfit dislocation on the equilibrium shape of the island is also examined. The results obtained are in good agreement with experiment of observations and thus can serve as a basis for interpreting the experiments.
基金Project supported by the National Natural Science Foundation of China (Grant No 90101004) and by the National Basic Research Program of China (Grant No G2000067102).
文摘The dynamic properties of rolling mill are significantly influenced by many coupling factors. According to the coupled mechanical and electric dynamics theory, the global coupled equations for the dynamic analysis of planishing mill CM04 of Shanghai Baosteel Group Corporation were derived, by using finite element methods. These elasto-dynamic equations establish the coupling relations among the stand vibration system, torsional vibration system, driving motors, etc. It provides theoretical basis to a certain extent for globally dynamic simulation, analysis of stability of motion, prediction of abnormal operating mode, globally optimum design and control, etc.
基金supported by National Natural Science Foundation of China(Nos.61405147,51375348)the Scientific Research Fund of Zhejiang Provincial Education Department,China(No.Y201430387)
文摘The concentration of elements in molten metal of AZ31 magnesium alloy after long pulsed Nd:YAG laser processing was quantitatively analyzed by using calibration-free laser-induced breakdown spectroscopy(CF-LIBS). The composition change in AZ31 magnesium alloy under different laser pulse width was also investigated. The experimental results showed that CF-LIBS can obtain satisfactory quantitative or semi-quantitative results for matrix or major elements,while only qualitative analysis was possible for minor or trace elements. Moreover, it is found that the chemical composition of molten metal will change after laser processing. The concentration of magnesium in molten metal is lower than that present in the base metal. The Mg loss increases with an increase of pulse width in the laser processing. This result shows that the selective vaporization of different elements is affected by the pulse width during laser processing.
基金Sponsored by the Basic Research Development Program of China ( Grant No. 2013CB03554)the Fundamental Research Funds for Universities, Central South University (Grant No. 2017zzts394).
文摘Natural language processing has got great progress recently. Controlling robots with spoken natural language has become expectable. With the reliability problem of this kind of control in mind a confirmation process of natural language instruction should be included before carried out by the robot autonomously and the prototype dialog system was designed thus the standardization problem was raised for the natural and understandable language interaction. In the application background of remotely navigating a mobile robot inside a building with Chinese natural spoken language considering that as an important navigation element in instructions a place name can be expressed with different lexical terms in spoken language this paper proposes a model for substituting different alternatives of a place name with a standard one (called standardization). First a CRF (Conditional Random Fields) model is trained to label the term required be standardized then a trained word embedding model is to represent lexical terms as digital vectors. In the vector space similarity of lexical terms is defined and used to find out the most similar one to the term picked out to be standardized. Experiments show that the method proposed works well and the dialog system responses to confirm the instructions are natural and understandable.
文摘Magneto-rheological (MR) fluid-based dampers are currently being explored for their potential implementation in intelligent vehicle suspension designs. Due to inherent hysteretic force properties of the MR dampers, analyzing and suppressing the MR-damper hysteresis effects, therefore, impose a great challenge. A quarter-vehicle MR-suspension model is formulated in conjunction with proposed hysteretic and mean MR-damper models, and the passive and semi-actively controlled MR-suspension systems are focused to investigate the influence of MR-damper force hysteresis. The semi-actively controlled MR-suspension employs the “on-off” control law in response to direction of the damper velocity, so as to generate the asymmetric damping force property form the symmetric MR-damper design. The results show that the MR-damping hysteresis yields serious transients and oscillations in responses for the semi-actively controlled MR-suspension than the passive MR-suspension due to the current-switching discontinuity, and would thus deteriorate the suspension performance. The undesired strong transients and oscillations in responses can be effectively suppressed by employing the proposed smooth technique without phase shift for modulating the command current discontinuity.
文摘This paper attempts to solve the complexity of scheduling problems and meet the requirement of the ever-changing manufacturing environment. In this paper, a new Workflow-Based Scheduling System (WBSS) is proposed. The integration of Workflow Management System (WfMS) and rule-based scheduler provides us an effective way of generating a task-sheet according to the states of system and the scheduled objects. First, the definition of workflow model for scheduling is proposed, and following are the architecture and mechanism of the proposed WBSS. At last, an application is given to show how the established system works.
基金Supported by the National High Technology Research and Development Program of China(863 Program)(No.2006AA020804)Fundamental Research Funds for the Central Universities(No.NJ20120007)+2 种基金Jiangsu Province Science and Technology Support Plan(No.BE2010652)Program Sponsored for Scientific Innovation Research of College Graduate in Jangsu Province(No.CXLX11_0218)Shanghai University Scientific Selection and Cultivation for Outstanding Young Teachers in Special Fund(No.ZZGCD15081)
文摘Diabetic retinopathy(DR) is one of the most important causes of visual impairment. Automatic recognition of DR lesions, like hard exudates(EXs), in retinal images can contribute to the diagnosis and screening of the disease. To achieve this goal, an automatically detecting approach based on improved FCM(IFCM) as well as support vector machines(SVM) was established and studied. Firstly, color fundus images were segmented by IFCM, and candidate regions of EXs were obtained. Then, the SVM classifier is confirmed with the optimal subset of features and judgments of these candidate regions, as a result hard exudates are detected from fundus images. Our database was composed of 126 images with variable color, brightness, and quality. 70 of them were used to train the SVM and the remaining 56 to assess the performance of the method. Using a lesion based criterion, we achieved a mean sensitivity of 94.65% and a mean positive predictive value of 97.25%. With an image-based criterion, our approach reached a 100% mean sensitivity, 96.43% mean specificity and 98.21% mean accuracy. Furthermore, the average time cost in processing an image is 4.56 s. The results suggest that the proposed method can efficiently detect EXs from color fundus images and it could be a diagnostic aid for ophthalmologists in the screening for DR.
文摘With the development of electric power technology, information technology and military technology, the impact of cyber attack on electric power infrastructure has increasingly become a hot spot issue which calls both domestic and foreign attention. First, main reasons of the impact on power infrastructure caused by cyber attack are analyzed from the following two aspects: 1) The dependence of electric power infrastructure on information infrastructure makes cyber attack issues in information field likely to affect electric power field. 2) As regards to the potential threat sources, it will be considerably profitable to launch cyber attacks on electric power infrastructure. On this basis, this paper gives a classified elaboration on the characteristics and the possibilities of cyber attacks on electrical infrastructures. Finally, the recently published actual events of cyber attacks in respect of threat sources, vulnerabilities and assaulting modes are analyzed and summarized.
基金financially supported by the National Natural Science Foundation of China(Grant No.51609120)the Qingdao Applied Basic Research Project(Grant No.14-2-4-116-jch)
文摘Modified adaptive observer based backstepping control system for dynamic positioning of ship is proposed.As an improvement,the adaptive observer takes the first-order wave frequency model and the bias term which represent the slowly varying environmental disturbances and the unmodeled dynamics.Thus,the wave-frequency motions are filtered out,and only the reconstructed low-frequency motions are sent as inputs of the controller.Furthermore,as the ship dynamics parameters are unknown,the adaptive estimation law is designed for both the unknown ship dynamics and the unmeasured state variables.Based on the estimated states and parameters,backstepping controller considering the integral action is designed.Global exponential stability(GES) for the total system is proved using Lyapunov direct method.Simulation results show a good performance of the observer and control system.
基金Projects(51375046,51205021)supported by the National Natural Science Foundation of China
文摘In order to improve ride comfort and handling performance of the vehicle, an adaptive hybrid control algorithm is proposed for semi-active suspension systems. The virtues of sky-hook is combined with ground-hook control strategies and a more suitable compromise for the suspension systems is chosen. The hybrid coefficient is tuned according to the longitudinal and lateral acceleration so as to improve the vehicle stability especially in high speed conditions. Damping continuous adjustable absorber is used to continuously control the damping force so as to eliminate the damping force jerk instead of traditional on-off control policy. Based on suspension stroke measured by sensors, unscented Kalman filter is designed to estimate the suspension states in real-time for the realization of hybrid control, which improves the robustness of the control strategy and is adaptive to different types of road profiles. Finally, the proposed control algorithm is validated under the following two typical road profiles: half-sine speed bump road and the random road. The simulation results indicate that the hybrid control algorithm could offer a good coordination between ride comfort and handling of the vehicle.
基金Project(2012AA062104)supported by the National High Technology Research and Development Program of ChinaProject(51704178)supported by the National Natural Science Foundation of China+1 种基金Project(ZR2017MEE034)supported by Natural Science Foundation of Shandong Province,ChinaProject(2018T110700)supported by China Postdoctoral Science Foundation