2003 Vol.16(2)
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2003, 17(2).
Abstract:
The main purpose of reverse engineering is to convert discrete data points into piecewise smooth, continuous surface models. Before carrying out model reconstruction it is significant to extract geometric features because the quality of modeling greatly depends on the representation of features. Some fitting techniques of natural quadric surfaces with least-squares method are described. And these techniques can be directly used to extract quadric surfaces features during the process of segmentation for point cloud.
The main purpose of reverse engineering is to convert discrete data points into piecewise smooth, continuous surface models. Before carrying out model reconstruction it is significant to extract geometric features because the quality of modeling greatly depends on the representation of features. Some fitting techniques of natural quadric surfaces with least-squares method are described. And these techniques can be directly used to extract quadric surfaces features during the process of segmentation for point cloud.
2003, 17(2).
Abstract:
Based on the elastic-plastic large deformation finite element formulation as well as the shell element combined discrete Kirchhoff theoretical plate element (DKT) with membrane square element, deep-drawing bending springback of typical U-pattern is studied. At the same time the springback values of the drawing of patterns' unloading and trimming about the satellite aerial reflecting surface are predicted and also compared with those of the practical punch. Above two springbacks all obtain satisfactory results, which provide a kind of effective quantitative pre-prediction of springback for the practical engineers.
Based on the elastic-plastic large deformation finite element formulation as well as the shell element combined discrete Kirchhoff theoretical plate element (DKT) with membrane square element, deep-drawing bending springback of typical U-pattern is studied. At the same time the springback values of the drawing of patterns' unloading and trimming about the satellite aerial reflecting surface are predicted and also compared with those of the practical punch. Above two springbacks all obtain satisfactory results, which provide a kind of effective quantitative pre-prediction of springback for the practical engineers.
2003, 17(2).
Abstract:
It is important for robotic hands to obtain optimal grasping performance in the meanwhile balancing external forces and maintaining grasp stability. The problem of force optimization of grasping is solved in the space of joint torques. A measure of grasping performance is presented to protect joint actuators from working in heavy payloads. The joint torques are calculated for the optimal performance under the frictional constraints and the physical limits of motor outputs. By formulating the grasping forces into the explicit function of joint torques, the frictional constraints imposed on the grasping forces are transformed into the constraints on joint torques. Without further simplification, the nonlinear frictional constraints can be simply handled in the process of optimization. Two numerical examples demonstrate the simplicity and effectiveness of the approach.
It is important for robotic hands to obtain optimal grasping performance in the meanwhile balancing external forces and maintaining grasp stability. The problem of force optimization of grasping is solved in the space of joint torques. A measure of grasping performance is presented to protect joint actuators from working in heavy payloads. The joint torques are calculated for the optimal performance under the frictional constraints and the physical limits of motor outputs. By formulating the grasping forces into the explicit function of joint torques, the frictional constraints imposed on the grasping forces are transformed into the constraints on joint torques. Without further simplification, the nonlinear frictional constraints can be simply handled in the process of optimization. Two numerical examples demonstrate the simplicity and effectiveness of the approach.
2003, 17(2).
Abstract:
Four methods aiming at measuring rotary machine axis center trace are discussed in detail. The comparative analysis is made on some aspects such as measurement accuracy, on-machine characteristics, feasibility, practical operation convenience and the integrity of measurement information. In order to simplify measurement, the axis profile error is ignored in traditional condition, while the measurement accuracy will be reduced. The 3-point method that the axis profile error is firstly separated has better real time character, at the same time, not only the axis motion error but also the axis profile error can be measured. All of those information can be used to diagnose the fault origin. The analysis result is proved to be correct by the experiment.
Four methods aiming at measuring rotary machine axis center trace are discussed in detail. The comparative analysis is made on some aspects such as measurement accuracy, on-machine characteristics, feasibility, practical operation convenience and the integrity of measurement information. In order to simplify measurement, the axis profile error is ignored in traditional condition, while the measurement accuracy will be reduced. The 3-point method that the axis profile error is firstly separated has better real time character, at the same time, not only the axis motion error but also the axis profile error can be measured. All of those information can be used to diagnose the fault origin. The analysis result is proved to be correct by the experiment.
2003, 17(2).
Abstract:
By defining the static stable area for foot placement, a new approach to analysis of quadruped robot stability is presented. Unlike conventionally, the method avoids solving complicated direct kinematics of quadruped robot and shows the information on the robot stability and the selection of swing leg. Especially, the proposed algorithm can be used as real-time operation for on-line gait generation and control for quadruped robots. The effectiveness of the proposed approach is shown through a practical crawling experiment of the quadruped robot TITAN-VIII.
By defining the static stable area for foot placement, a new approach to analysis of quadruped robot stability is presented. Unlike conventionally, the method avoids solving complicated direct kinematics of quadruped robot and shows the information on the robot stability and the selection of swing leg. Especially, the proposed algorithm can be used as real-time operation for on-line gait generation and control for quadruped robots. The effectiveness of the proposed approach is shown through a practical crawling experiment of the quadruped robot TITAN-VIII.
2003, 17(2).
Abstract:
A much better substitutional means is discussed to calculate the flame temperature field with the application of digital image processing technology. Three non-contacting temperature meas-urements are used and compared. Such as the traditional two-color temperature measurement,the CCD filtering two-color temperature measurement and the monochromatic temperature measurement. It is indicated that the CCD two-color temperature measurement is not a fully correct means because of its poor theoretical basis. The monochromatic temperature measurement acquires a relatively ideal temperature field distribution in spite of needing a reference temperature. It should be noted that the Abel transformation applied in the plasma diagnosis is for the first time introduced to solve the problem of three-dimensional flame brightness piling.
A much better substitutional means is discussed to calculate the flame temperature field with the application of digital image processing technology. Three non-contacting temperature meas-urements are used and compared. Such as the traditional two-color temperature measurement,the CCD filtering two-color temperature measurement and the monochromatic temperature measurement. It is indicated that the CCD two-color temperature measurement is not a fully correct means because of its poor theoretical basis. The monochromatic temperature measurement acquires a relatively ideal temperature field distribution in spite of needing a reference temperature. It should be noted that the Abel transformation applied in the plasma diagnosis is for the first time introduced to solve the problem of three-dimensional flame brightness piling.
2003, 17(2).
Abstract:
A simple, efficient, automatic and universal method to fulfill displacement analysis of a great deal of mechanisms regenerated by Yan's mechanism creative theory has been developed. For a regenerated mechanism, at first, the method identifies its type and structure and changes it into a rigid structure by fixing the ground link and the input link. And then this rigid structure is decomposed into a set of basic kinematic chains (BKCs). By matching the type of BKC, the displacement analysis equations can be set up, and all possible configurations, in which positions of all movable links are considered, can be given out.
A simple, efficient, automatic and universal method to fulfill displacement analysis of a great deal of mechanisms regenerated by Yan's mechanism creative theory has been developed. For a regenerated mechanism, at first, the method identifies its type and structure and changes it into a rigid structure by fixing the ground link and the input link. And then this rigid structure is decomposed into a set of basic kinematic chains (BKCs). By matching the type of BKC, the displacement analysis equations can be set up, and all possible configurations, in which positions of all movable links are considered, can be given out.
2003, 17(2).
Abstract:
Direct algorithm of wavelet transform (WT) is the numerical algorithm obtained from the integral formula of WT by directly digitization. Some problems on realizing the algorithm are studied. Some conclusions on the direct algorithm of discrete wavelet transform (DWT), such as discrete convolution operation formula of wavelet coefficients and wavelet components, sampling principle and technology to wavelets, deciding method for scale range of wavelets, measures to solve edge effect problem, etc, are obtained. The realization of direct algorithm of continuous wavelet transform (CWT) is also studied. The computing cost of direct algorithm and Mallat algorithm of DWT are still studied, and the computing formulae are obtained. These works are beneficial to deeply understand WT and Mallat algorithm. Examples in the end show that direct algorithm can also be applied widely.
Direct algorithm of wavelet transform (WT) is the numerical algorithm obtained from the integral formula of WT by directly digitization. Some problems on realizing the algorithm are studied. Some conclusions on the direct algorithm of discrete wavelet transform (DWT), such as discrete convolution operation formula of wavelet coefficients and wavelet components, sampling principle and technology to wavelets, deciding method for scale range of wavelets, measures to solve edge effect problem, etc, are obtained. The realization of direct algorithm of continuous wavelet transform (CWT) is also studied. The computing cost of direct algorithm and Mallat algorithm of DWT are still studied, and the computing formulae are obtained. These works are beneficial to deeply understand WT and Mallat algorithm. Examples in the end show that direct algorithm can also be applied widely.
2003, 17(2).
Abstract:
The design method of a 6-axis force robot's transducer based on the Stewart platform is detailed. For this purpose, the sensitivity isotropy evaluation criteria of the transducer are defined, and by the aid of computer, the relationships between the criteria and the parameters of all the transducers based on the Stewart platform are investigated within the geometric model of the solution space, which can provide the theoretical background for the optimal construction design of the 6-axis force transducer related to the sensitivity isotropy.
The design method of a 6-axis force robot's transducer based on the Stewart platform is detailed. For this purpose, the sensitivity isotropy evaluation criteria of the transducer are defined, and by the aid of computer, the relationships between the criteria and the parameters of all the transducers based on the Stewart platform are investigated within the geometric model of the solution space, which can provide the theoretical background for the optimal construction design of the 6-axis force transducer related to the sensitivity isotropy.
2003, 17(2).
Abstract:
One of the important trends in precision machining is the development of real-time error compensation technique. The error compensation for multi-axis CNC machine tools is very difficult and attractive. The modeling for the geometric error of five-axis CNC machine tools based on multi-body systems is proposed. And the key technique of the compensation—identifying geometric error parameters—is developed. The simulation of cutting workpiece to verify the modeling based on the multi-body systems is also considered.
One of the important trends in precision machining is the development of real-time error compensation technique. The error compensation for multi-axis CNC machine tools is very difficult and attractive. The modeling for the geometric error of five-axis CNC machine tools based on multi-body systems is proposed. And the key technique of the compensation—identifying geometric error parameters—is developed. The simulation of cutting workpiece to verify the modeling based on the multi-body systems is also considered.
2003, 17(2).
Abstract:
Based on the Sanders thin shell theory and Reddy's higher order shell theory, a general refined shell theory is developed for the analysis of stresses and deformations of pneumatic radial tires of composite construction. For easy and efficient simulation of the tire a piecewise Rayleigh-Ritz technique is proposed and applied to get a numerical solution to the nonlinear structural problem. Bezier polynomials are used to approximate both the geometry of the surface of reference and displacement fields of the tires. Stress distributions and deformations of the tires subjected to uniform inflation pressure are computed and discussed in details. From comparison of the present results with the numerical predictions by 3D finite element method, it has been shown that the present solution procedure is accurate and applicable to much complicated time-consuming nonlinear analysis for the high quality tire.
Based on the Sanders thin shell theory and Reddy's higher order shell theory, a general refined shell theory is developed for the analysis of stresses and deformations of pneumatic radial tires of composite construction. For easy and efficient simulation of the tire a piecewise Rayleigh-Ritz technique is proposed and applied to get a numerical solution to the nonlinear structural problem. Bezier polynomials are used to approximate both the geometry of the surface of reference and displacement fields of the tires. Stress distributions and deformations of the tires subjected to uniform inflation pressure are computed and discussed in details. From comparison of the present results with the numerical predictions by 3D finite element method, it has been shown that the present solution procedure is accurate and applicable to much complicated time-consuming nonlinear analysis for the high quality tire.
2003, 17(2).
Abstract:
A new algorithm of structure random response numerical characteristics, named as matrix algebra algorithm of structure analysis is presented. Using the algorithm, structure random response numerical characteristics can easily be got by directly solving linear matrix equations rather than structure motion differential equations. Moreover, in order to solve the corresponding linear matrix equations, the numerical integration fast algorithm is presented. Then according to the results, dynamic design and life-span estimation can be done. Besides, the new algorithm can solve non-proportion damp structure response.
A new algorithm of structure random response numerical characteristics, named as matrix algebra algorithm of structure analysis is presented. Using the algorithm, structure random response numerical characteristics can easily be got by directly solving linear matrix equations rather than structure motion differential equations. Moreover, in order to solve the corresponding linear matrix equations, the numerical integration fast algorithm is presented. Then according to the results, dynamic design and life-span estimation can be done. Besides, the new algorithm can solve non-proportion damp structure response.
2003, 17(2).
Abstract:
Based on the principle of laminated machining, the method of auto-programming in the electro discharge milling (ED-milling) process is drawn out. With the help of IGES formatted files, the process slicing and the machining locus can be programmed well. The program adopts three-parameter convergence as the basic way to slice the geometry mold and divide the non-uniform rational B-spline curve (NURBS) surface. With the great mount of discrete points, a given arithmetic is drawn out to order them, and then is carried out the interpolation of bi-arc. In the process, according to the character of the EDM process, the zigzag track of machining is accepted to remove the volume of work piece and shape the contour along the contour line of the slicing segments, including multi-connection. As a result, some correla-tive experiments are accomplished.
Based on the principle of laminated machining, the method of auto-programming in the electro discharge milling (ED-milling) process is drawn out. With the help of IGES formatted files, the process slicing and the machining locus can be programmed well. The program adopts three-parameter convergence as the basic way to slice the geometry mold and divide the non-uniform rational B-spline curve (NURBS) surface. With the great mount of discrete points, a given arithmetic is drawn out to order them, and then is carried out the interpolation of bi-arc. In the process, according to the character of the EDM process, the zigzag track of machining is accepted to remove the volume of work piece and shape the contour along the contour line of the slicing segments, including multi-connection. As a result, some correla-tive experiments are accomplished.
2003, 17(2).
Abstract:
The patternless casting manufacturing(PCM) technique adopts a new method of double scanning which combines the principle of discreteness and deposition with the resin-bonded sand technique. Two main factors, the liquid penetration regularities in the space between particles and the shape and dimension of the agglomeration unit body, are studied qualitatively and quantitatively. This provides the theoretical basis for selecting the forming technical parameters. The experiments verify the analysis.
The patternless casting manufacturing(PCM) technique adopts a new method of double scanning which combines the principle of discreteness and deposition with the resin-bonded sand technique. Two main factors, the liquid penetration regularities in the space between particles and the shape and dimension of the agglomeration unit body, are studied qualitatively and quantitatively. This provides the theoretical basis for selecting the forming technical parameters. The experiments verify the analysis.
2003, 17(2).
Abstract:
Automatic straightening process is a nonlinear process, and affected by many factors. The straightening technology CAM system has been designed and built up to straighten shafts, which mainly consists of the straightening technology's database and the model of stroke-controlled precise straightening calculation model. The operational test of the CAM system has been passed.
Automatic straightening process is a nonlinear process, and affected by many factors. The straightening technology CAM system has been designed and built up to straighten shafts, which mainly consists of the straightening technology's database and the model of stroke-controlled precise straightening calculation model. The operational test of the CAM system has been passed.
2003, 17(2).
Abstract:
A genetic algorithm (GA)-based method is proposed to solve the nonlinear optimization problem of minimum zone cylindricity evaluation. First, the background of the problem is introduced. Then the mathematical model and the fitness function are derived from the mathematical definition of dimensioning and tolerancing principles. Thirdly with the least squares solution as the initial values, the whole implementation process of the algorithm is realized in which some key techniques, for example, variables representing, population initializing and such basic operations as selection, crossover and mutation, are discussed in detail. Finally, examples are quoted to verify the proposed algorithm. The computation results indicate that the GA-based optimization method performs well on cylindricity evaluation. The outstanding advantages conclude high accuracy, high efficiency and capabilities of solving complicated nonlinear and large space problems.
A genetic algorithm (GA)-based method is proposed to solve the nonlinear optimization problem of minimum zone cylindricity evaluation. First, the background of the problem is introduced. Then the mathematical model and the fitness function are derived from the mathematical definition of dimensioning and tolerancing principles. Thirdly with the least squares solution as the initial values, the whole implementation process of the algorithm is realized in which some key techniques, for example, variables representing, population initializing and such basic operations as selection, crossover and mutation, are discussed in detail. Finally, examples are quoted to verify the proposed algorithm. The computation results indicate that the GA-based optimization method performs well on cylindricity evaluation. The outstanding advantages conclude high accuracy, high efficiency and capabilities of solving complicated nonlinear and large space problems.
2003, 17(2).
Abstract:
According to traditional phenomenological fatigue methodology and modern continuum damage mechanics theory, dual fatigue cumulative damage rules to predict fatigue damage formation and propagation lives of the notched composite laminates are presented. A 3-dimensional damage constitutive equation of anisotropic composites is also established. Damage strain energy release rate is interpreted as a driving force of the fatigue delamination damage propagation. A new damage evolution equation and a damage propagation ?a–?m–N? surface (stress amplitude-mean stress-life surface) are derived. Hence, using the method above, the fatigue life of composite components can be predicted. Finally, theoretically predicted results are compared with experimental data. It is found that the deviation of theoretic prediction from experimental results is about 22%.
According to traditional phenomenological fatigue methodology and modern continuum damage mechanics theory, dual fatigue cumulative damage rules to predict fatigue damage formation and propagation lives of the notched composite laminates are presented. A 3-dimensional damage constitutive equation of anisotropic composites is also established. Damage strain energy release rate is interpreted as a driving force of the fatigue delamination damage propagation. A new damage evolution equation and a damage propagation ?a–?m–N? surface (stress amplitude-mean stress-life surface) are derived. Hence, using the method above, the fatigue life of composite components can be predicted. Finally, theoretically predicted results are compared with experimental data. It is found that the deviation of theoretic prediction from experimental results is about 22%.
2003, 17(2).
Abstract:
Premature failure of coated tool often results from a poor adhesion of coating-substrate and shortens the lifetime of the tool. The results of increasing the adhesion strength of thin film coatings on cutting tool inserts by pretreating the inserts with sandblasting technique to obtain a desirable surface morphology of the inserts are presented. A geometric model representing the ideal surface morphology is established to enhance the nucleation density and adhesion strength of coating-substrate. Thin film coating experiment is conducted on the substrates of four different sample groups. Indentation and wear tests are performed on coated inserts to evaluate the effect of sandblasting on the adhesion strength of the coatings. A theoretical analysis is provided on the formation and growth of atom clusters in terms of the contact angle and the thermodynamic barrier of a substrate to predict thin film nucleation.
Premature failure of coated tool often results from a poor adhesion of coating-substrate and shortens the lifetime of the tool. The results of increasing the adhesion strength of thin film coatings on cutting tool inserts by pretreating the inserts with sandblasting technique to obtain a desirable surface morphology of the inserts are presented. A geometric model representing the ideal surface morphology is established to enhance the nucleation density and adhesion strength of coating-substrate. Thin film coating experiment is conducted on the substrates of four different sample groups. Indentation and wear tests are performed on coated inserts to evaluate the effect of sandblasting on the adhesion strength of the coatings. A theoretical analysis is provided on the formation and growth of atom clusters in terms of the contact angle and the thermodynamic barrier of a substrate to predict thin film nucleation.
2003, 17(2).
Abstract:
A novel pilot stage valve called simplified 2D valve, which utilizes both rotary and linear motions of a single spool, is presented. The rotary motion of the spool incorporating hydraulic resistance bridge, formed by a damper groove and a crescent overlap opening, is utilized as pilot to actuate linear motion of the spool. A criterion for stability is derived from the linear analysis of the valve. Special experiments are designed to acquire the mechanical stiffness, the pilot leakage and the step response. It is shown that the sectional size of the spiral groove affects the dynamic response and the stiffness contradictorily and is also very sensitive to the pilot leakage. Therefore, it is necessary to establish a balance between the static and dynamic characteristics in deciding the structural parameters. Nevertheless, it is possible to sustain the dynamic response at a fairly high level, while keeping the leakage of the pilot stage at an ac-ceptable level.
A novel pilot stage valve called simplified 2D valve, which utilizes both rotary and linear motions of a single spool, is presented. The rotary motion of the spool incorporating hydraulic resistance bridge, formed by a damper groove and a crescent overlap opening, is utilized as pilot to actuate linear motion of the spool. A criterion for stability is derived from the linear analysis of the valve. Special experiments are designed to acquire the mechanical stiffness, the pilot leakage and the step response. It is shown that the sectional size of the spiral groove affects the dynamic response and the stiffness contradictorily and is also very sensitive to the pilot leakage. Therefore, it is necessary to establish a balance between the static and dynamic characteristics in deciding the structural parameters. Nevertheless, it is possible to sustain the dynamic response at a fairly high level, while keeping the leakage of the pilot stage at an ac-ceptable level.
2003, 17(2).
Abstract:
A neural-network-based adaptive variable structure control methodology is proposed for the tracking problem of nonlinear discrete-time input-output systems. The unknown dynamics of the system are approximated via radial basis function neural networks. The control law is based on sliding modes and simple to implement. The discrete-time adaptive law for tuning the weight of neural networks is presented using the adaptive filtering algorithm with residue upper-bound compensation. The application of the proposed controller to engine idle speed control design is discussed. The results indicate the validation and effectiveness of this approach.
A neural-network-based adaptive variable structure control methodology is proposed for the tracking problem of nonlinear discrete-time input-output systems. The unknown dynamics of the system are approximated via radial basis function neural networks. The control law is based on sliding modes and simple to implement. The discrete-time adaptive law for tuning the weight of neural networks is presented using the adaptive filtering algorithm with residue upper-bound compensation. The application of the proposed controller to engine idle speed control design is discussed. The results indicate the validation and effectiveness of this approach.
2003, 17(2).
Abstract:
A new approach, namely, "defining protrusion-feature with depression-parameter" is advanced, which focuses on the shortcomings of protrusion-feature alteration method; The full depression-feature model is built up, and a basic converse reasoning iterative algorithm for machining process is given. The detailed examination has been implemented on the feature-based modeling system for light industry product (QJFMS) and the converse reasoning on fixture-based machining process is achieved.
A new approach, namely, "defining protrusion-feature with depression-parameter" is advanced, which focuses on the shortcomings of protrusion-feature alteration method; The full depression-feature model is built up, and a basic converse reasoning iterative algorithm for machining process is given. The detailed examination has been implemented on the feature-based modeling system for light industry product (QJFMS) and the converse reasoning on fixture-based machining process is achieved.
2003, 17(2).
Abstract:
To improve roll system stability of aluminum foil mills, roll system stability of 2200 high-speed aluminum foil mill is analyzed with energy stable method. Two different restrictive conditions which gaps between chock of work roll and window of stand whether exist or not, are studied respectively. A new concept of roll system with open /closed compound pair comes up with as well for renewably synthesizing restrictive mechanism of aluminum foil mills' chock. Through these studies, the conflict, whether reserving the gap for the roller replacement or eliminating the gap for roller's normal work, is successfully settled. This concept and analyzed result give the actual mechanism with open/closed compound restriction and the method of realizing high-speed rolling and prolonging longevity of end thrust bearing on work roll. It has important theoretical meaning and engineering value for modern technical reform of aluminum foil mills and plate strip mills.
To improve roll system stability of aluminum foil mills, roll system stability of 2200 high-speed aluminum foil mill is analyzed with energy stable method. Two different restrictive conditions which gaps between chock of work roll and window of stand whether exist or not, are studied respectively. A new concept of roll system with open /closed compound pair comes up with as well for renewably synthesizing restrictive mechanism of aluminum foil mills' chock. Through these studies, the conflict, whether reserving the gap for the roller replacement or eliminating the gap for roller's normal work, is successfully settled. This concept and analyzed result give the actual mechanism with open/closed compound restriction and the method of realizing high-speed rolling and prolonging longevity of end thrust bearing on work roll. It has important theoretical meaning and engineering value for modern technical reform of aluminum foil mills and plate strip mills.
2003, 17(2).
Abstract:
In the industrial process situation, principal component analysis (PCA) is a general method in data reconciliation. However, PCA sometime is unfeasible to nonlinear feature analysis and limited in application to nonlinear industrial process. Kernel PCA (KPCA) is extension of PCA and can be used for nonlinear feature analysis. A nonlinear data reconciliation method based on KPCA is proposed. The basic idea of this method is that firstly original data are mapped to high dimensional feature space by nonlinear function, and PCA is implemented in the feature space. Then nonlinear feature analysis is implemented and data are reconstructed by using the kernel. The data reconciliation method based on KPCA is applied to ternary distillation column. Simulation results show that this method can filter the noise in measurements of nonlinear process and reconciliated data can represent the true information of nonlinear process.
In the industrial process situation, principal component analysis (PCA) is a general method in data reconciliation. However, PCA sometime is unfeasible to nonlinear feature analysis and limited in application to nonlinear industrial process. Kernel PCA (KPCA) is extension of PCA and can be used for nonlinear feature analysis. A nonlinear data reconciliation method based on KPCA is proposed. The basic idea of this method is that firstly original data are mapped to high dimensional feature space by nonlinear function, and PCA is implemented in the feature space. Then nonlinear feature analysis is implemented and data are reconstructed by using the kernel. The data reconciliation method based on KPCA is applied to ternary distillation column. Simulation results show that this method can filter the noise in measurements of nonlinear process and reconciliated data can represent the true information of nonlinear process.
2003, 17(2).
Abstract:
A study of bispectral analysis in gearbox condition monitoring is presented. The theory of bispectrum and quadratic phase coupling (QPC) is first introduced, and then equations for computing bispectrum slices are obtained. To meet the needs of online monitoring, a simplified method of computting bispectrum diagonal slice is adopted. Industrial gearbox vibration signals measured from normal and tooth cracked conditions are analyzed using the above method. Experiments results indicate that bispectrum can effectively suppress the additive Gaussian noise and characterize the QPC phenomenon. It is also shown that the 1-D bispectrum diagonal slice can capture the non-Gaussian and nonlinear feature of gearbox vibration when crack occurred, hence, this method can be employed to gearbox real time monitoring and early diagnosis.
A study of bispectral analysis in gearbox condition monitoring is presented. The theory of bispectrum and quadratic phase coupling (QPC) is first introduced, and then equations for computing bispectrum slices are obtained. To meet the needs of online monitoring, a simplified method of computting bispectrum diagonal slice is adopted. Industrial gearbox vibration signals measured from normal and tooth cracked conditions are analyzed using the above method. Experiments results indicate that bispectrum can effectively suppress the additive Gaussian noise and characterize the QPC phenomenon. It is also shown that the 1-D bispectrum diagonal slice can capture the non-Gaussian and nonlinear feature of gearbox vibration when crack occurred, hence, this method can be employed to gearbox real time monitoring and early diagnosis.
2003, 17(2).
Abstract:
The bearing is described by constrain matrix, and the spindle system of a NC surface grinding machine is simplified as elastic-coupling beam, then modal synthesis method is used to establish the dynamic model of beam. Moreover, the response of the end of rotor is analyzed, and the natural frequency, principle mode and other dynamic characteristics of the coupling system are studied, the law of bearing stiffness to coupling frequency and amplitude of rotor is also found. Finally, according to the actual condition, a dynamic absorber is designed. The simulation and experimental results show that the amplitude of spindle can be declined effectively when the dynamic absorber is attached.
The bearing is described by constrain matrix, and the spindle system of a NC surface grinding machine is simplified as elastic-coupling beam, then modal synthesis method is used to establish the dynamic model of beam. Moreover, the response of the end of rotor is analyzed, and the natural frequency, principle mode and other dynamic characteristics of the coupling system are studied, the law of bearing stiffness to coupling frequency and amplitude of rotor is also found. Finally, according to the actual condition, a dynamic absorber is designed. The simulation and experimental results show that the amplitude of spindle can be declined effectively when the dynamic absorber is attached.
2003, 17(2).
Abstract:
Wet steam condensing flow in low-pressure steam turbine leads to efficiency losses and blade erosions. In order to investigate this problem by numerical approach, an Eulerian/Eulerian model has been developed, in which the wet steam is regarded as mixture comprising two coupled systems: the vapor phase and the liquid phase. These two systems are both described by conservation equations. High resolution TVD scheme is employed to capture condensing phenomena in wet steam flow. This model has been validated by numerical simulations of condensing flows in 1D and 2D nozzles. Compared with experimental data, a good agreement is observed. This Eulerian/Eulerian model can be extended to 3D calculation of condensing flow.
Wet steam condensing flow in low-pressure steam turbine leads to efficiency losses and blade erosions. In order to investigate this problem by numerical approach, an Eulerian/Eulerian model has been developed, in which the wet steam is regarded as mixture comprising two coupled systems: the vapor phase and the liquid phase. These two systems are both described by conservation equations. High resolution TVD scheme is employed to capture condensing phenomena in wet steam flow. This model has been validated by numerical simulations of condensing flows in 1D and 2D nozzles. Compared with experimental data, a good agreement is observed. This Eulerian/Eulerian model can be extended to 3D calculation of condensing flow.
2003, 17(2).
Abstract:
In the multi-robots system, it's important for a robot to acquire adaptive navigation rules for reaching the goal and avoiding other robots and obstacles and in the real-time environment. An efficient approach to collision-avoidance in multi-robots system is suggested. It is based on velocity information of moving objects and the distances between the robots and the obstacles in three specified directions and makes the robot navigate adaptively without collision with each other in a complicated situation. The effectiveness of algorithm is proved by the several simple examples in the physical world.
In the multi-robots system, it's important for a robot to acquire adaptive navigation rules for reaching the goal and avoiding other robots and obstacles and in the real-time environment. An efficient approach to collision-avoidance in multi-robots system is suggested. It is based on velocity information of moving objects and the distances between the robots and the obstacles in three specified directions and makes the robot navigate adaptively without collision with each other in a complicated situation. The effectiveness of algorithm is proved by the several simple examples in the physical world.
2003, 17(2).
Abstract:
The variation of casting hot spot with proceeding of solidification and components of casting-mold system is studied by the technique of numerical simulation of solidification. The result shows that the thickest part of casting is not exactly the last part of solidification in the casting, while the last part of solidification is not exactly casting hot spot at the early stage of solidification. The location, size, shape and number of casting hot spot change with geomitric, physical and technological factors of the casting-mold system such as thickness of the casting secondary wall and with the passage of time in the course of the solidification. The former is known as the systematic property of hot spot and the latter, dynamic property. Only when the properties of hot spot are grasped completely and accurately, can it be fed more effectively. By doing so, not only sound castings can be obtained, but also riser efficiency can be improved.
The variation of casting hot spot with proceeding of solidification and components of casting-mold system is studied by the technique of numerical simulation of solidification. The result shows that the thickest part of casting is not exactly the last part of solidification in the casting, while the last part of solidification is not exactly casting hot spot at the early stage of solidification. The location, size, shape and number of casting hot spot change with geomitric, physical and technological factors of the casting-mold system such as thickness of the casting secondary wall and with the passage of time in the course of the solidification. The former is known as the systematic property of hot spot and the latter, dynamic property. Only when the properties of hot spot are grasped completely and accurately, can it be fed more effectively. By doing so, not only sound castings can be obtained, but also riser efficiency can be improved.
2003, 17(2).
Abstract:
In recent years, hybrid devices have increasingly received more research. However, few of researchers studied the dynamic analysis. The inverse dynamic analysis of a novel hybrid machine tool designed in Tsinghua University is presented. The hybrid machine tool under consideration consists of parallel and serial structures, which is based on a new 2-DOF parallel platform and serial orientations. The kinematics and the dynamic equations are studied first for the parallel structure through Newton-Euler approach. And then, the dynamic analysis for serial structures is conducted. Finally, a closed-form inverse dynamic formulation is derived by using some elimination techniques. Some simulation results are also given.
In recent years, hybrid devices have increasingly received more research. However, few of researchers studied the dynamic analysis. The inverse dynamic analysis of a novel hybrid machine tool designed in Tsinghua University is presented. The hybrid machine tool under consideration consists of parallel and serial structures, which is based on a new 2-DOF parallel platform and serial orientations. The kinematics and the dynamic equations are studied first for the parallel structure through Newton-Euler approach. And then, the dynamic analysis for serial structures is conducted. Finally, a closed-form inverse dynamic formulation is derived by using some elimination techniques. Some simulation results are also given.
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