2004 Vol.17(3)
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FAULT DIAGNOSIS BASED ON INTE-GRATION OF CLUSTER ANALYSIS, ROUGH SET METHOD AND FUZZY NEURAL NETWORK
2004, 18(3).
Abstract:
In order to increase the efficiency and decrease the cost of machinery diagnosis, a hybrid system of computational intelligence methods is presented. Firstly, the continuous attributes in diagnosis decision system are discretized with the self-organizing map (SOM) neural network. Then, dynamic reducts are computed based on rough set method, and the key conditions for diagnosis are found according to the maximum cluster ratio. Lastly, according to the optimal reduct, the adaptive neuro-fuzzy inference system (ANFIS) is designed for fault identification. The diagnosis of a diesel verifies the feasibility of engineering applications.
In order to increase the efficiency and decrease the cost of machinery diagnosis, a hybrid system of computational intelligence methods is presented. Firstly, the continuous attributes in diagnosis decision system are discretized with the self-organizing map (SOM) neural network. Then, dynamic reducts are computed based on rough set method, and the key conditions for diagnosis are found according to the maximum cluster ratio. Lastly, according to the optimal reduct, the adaptive neuro-fuzzy inference system (ANFIS) is designed for fault identification. The diagnosis of a diesel verifies the feasibility of engineering applications.
2004, 18(3).
Abstract:
The 5-axis NC machining offers the potential of efficient and accurate machining. However, the present CAM system for 5-axis control is still an unsolved problem due to interference between tool and surrounding objects. A new method is presented. There are two steps in this procedure. First, it detects the interference by calculating the shortest distance between the tool-axis and the surrounding surfaces. Then upon the maximum gouging, the interference-free tool posture for 5-axis NC cylindrical milling free-form surfaces is obtained by adjusting tool. The validity of the proposed method has been confirmed by machining an impel-ler.
The 5-axis NC machining offers the potential of efficient and accurate machining. However, the present CAM system for 5-axis control is still an unsolved problem due to interference between tool and surrounding objects. A new method is presented. There are two steps in this procedure. First, it detects the interference by calculating the shortest distance between the tool-axis and the surrounding surfaces. Then upon the maximum gouging, the interference-free tool posture for 5-axis NC cylindrical milling free-form surfaces is obtained by adjusting tool. The validity of the proposed method has been confirmed by machining an impel-ler.
2004, 18(3).
Abstract:
Building an Internet based tele-robotic system requires the developers being proficient in computer theory, network technology, control theory, etc. A flexible, open structured and module based framework for tele-control system is proposed on the basis of abstraction and analysis of existing Internet-based control systems. This framework is designed following the peer to peer (P2P) distributed computing model. As a key to the system, the XML based ontology of resources/modules/peers is discussed, so do the model for dynamically allocating of resources, based on which the coordination among modules or peers can then be implemented. The experiment system and its experimental results prove the feasibility of the framework and its ease to use.
Building an Internet based tele-robotic system requires the developers being proficient in computer theory, network technology, control theory, etc. A flexible, open structured and module based framework for tele-control system is proposed on the basis of abstraction and analysis of existing Internet-based control systems. This framework is designed following the peer to peer (P2P) distributed computing model. As a key to the system, the XML based ontology of resources/modules/peers is discussed, so do the model for dynamically allocating of resources, based on which the coordination among modules or peers can then be implemented. The experiment system and its experimental results prove the feasibility of the framework and its ease to use.
2004, 18(3).
Abstract:
The 3-D traction field in the pressure screw-pair of a 3 500 heavy and medium plate mill press down system is successfully calculated by applying the 3-D frictional contact multipole-BEM and the corresponding program that has been developed. The computing results show the medium diameter orientation is unreliable, especially under the interference of an outer force couple. Under such working conditions, the circumferential traction distribution on the screw teeth is extremely uneven, which is the main reason for the destruction and short life time of screw-pairs. When utilizing the same precision (the relative tolerance is 10×10–5), the multipole-BEM uses almost the same CPU time as used by the FEM, but the needed computer memory size is only one eightieth of that needed by the FEM (10 MB vs. 800 MB). The multipole-BEM is well suited for computing large-scale engineering problems.
The 3-D traction field in the pressure screw-pair of a 3 500 heavy and medium plate mill press down system is successfully calculated by applying the 3-D frictional contact multipole-BEM and the corresponding program that has been developed. The computing results show the medium diameter orientation is unreliable, especially under the interference of an outer force couple. Under such working conditions, the circumferential traction distribution on the screw teeth is extremely uneven, which is the main reason for the destruction and short life time of screw-pairs. When utilizing the same precision (the relative tolerance is 10×10–5), the multipole-BEM uses almost the same CPU time as used by the FEM, but the needed computer memory size is only one eightieth of that needed by the FEM (10 MB vs. 800 MB). The multipole-BEM is well suited for computing large-scale engineering problems.
2004, 18(3).
Abstract:
Combining with the characteristic of the fuzzy control and the neural network control(NNC), a new kind of the fuzzy neural network controller is proposed, and the synthesis design method of the control law and fast speed learning algorithm of the parameters of networks are put forward. The output of the controller is composed of two parts, part one is derived on basis of the principle of sliding control, the lower order model and the estimated parameters of the plant are only required, part two is derived on basis FNN, it is used to compensate the uncertainties of the systems. Because new type of FNN controller extracts from the advantages of the intelligent control and model based sliding mode control, the numbers of adjusting parameters and the structure of FNN are simplified at large, and the practical significance and variation range are attached to each layer of the network and its connected weights, the control performance and learning speed are increased at large. The rightness of the conclusions is verified by the experiment of an electro-hydraulic position servo system of the mold of the continuous casting machinery.
Combining with the characteristic of the fuzzy control and the neural network control(NNC), a new kind of the fuzzy neural network controller is proposed, and the synthesis design method of the control law and fast speed learning algorithm of the parameters of networks are put forward. The output of the controller is composed of two parts, part one is derived on basis of the principle of sliding control, the lower order model and the estimated parameters of the plant are only required, part two is derived on basis FNN, it is used to compensate the uncertainties of the systems. Because new type of FNN controller extracts from the advantages of the intelligent control and model based sliding mode control, the numbers of adjusting parameters and the structure of FNN are simplified at large, and the practical significance and variation range are attached to each layer of the network and its connected weights, the control performance and learning speed are increased at large. The rightness of the conclusions is verified by the experiment of an electro-hydraulic position servo system of the mold of the continuous casting machinery.
2004, 18(3).
Abstract:
Applying the rule of laminar flow in the gap between two parallel disks, the theoretical model of a new type MR damper is established, the damping characteristic and structural characteristic of the MR damper are analyzed. Experimental results show that the model can reflect the fundamental characteristics of the disk-gap MR damper.
Applying the rule of laminar flow in the gap between two parallel disks, the theoretical model of a new type MR damper is established, the damping characteristic and structural characteristic of the MR damper are analyzed. Experimental results show that the model can reflect the fundamental characteristics of the disk-gap MR damper.
2004, 18(3).
Abstract:
A high efficiency sliding screw driver is introduced. It can improve driving efficiency obviously. As the material strength of the nut in this structure is low and the nut is the most dangerous part, so it is important to master the structure's characters of deformation and stress. The deformation and stress of this structure are researched by finite element method(FEM), and the changing law of stress concentration coefficient of the structure is gained. So the exact stress of nut teeth with highest load can be calculated directly based on this result.
A high efficiency sliding screw driver is introduced. It can improve driving efficiency obviously. As the material strength of the nut in this structure is low and the nut is the most dangerous part, so it is important to master the structure's characters of deformation and stress. The deformation and stress of this structure are researched by finite element method(FEM), and the changing law of stress concentration coefficient of the structure is gained. So the exact stress of nut teeth with highest load can be calculated directly based on this result.
2004, 18(3).
Abstract:
Intelligent virtual control (IVC) is an intelligent measurement instrument unit with the function of actual measurement instruments, and the unit can be used as basic building block for a variety of more complex virtual measurement instruments on a PC. IVC is a further advancement from virtual instrument (VI), and it fuses the function modules and the controls modules so that the relationship between the functions and controls of an instrument is imbedded in one or more units. The design, implementation and optimization methods of IVCs are introduced. The computer software representation of IVCs is discussed. An example of an actual VI constructed with the building blocks of IVCs is given.
Intelligent virtual control (IVC) is an intelligent measurement instrument unit with the function of actual measurement instruments, and the unit can be used as basic building block for a variety of more complex virtual measurement instruments on a PC. IVC is a further advancement from virtual instrument (VI), and it fuses the function modules and the controls modules so that the relationship between the functions and controls of an instrument is imbedded in one or more units. The design, implementation and optimization methods of IVCs are introduced. The computer software representation of IVCs is discussed. An example of an actual VI constructed with the building blocks of IVCs is given.
2004, 18(3).
Abstract:
Adaptive control of a flexible beam system preceded by an unknown dead-zone in the driving motor is investigated in state space form. By introducing an important lemma for simplifying error equation between the flexible beam model and the matching reference model, a robust adaptive control scheme is developed by involving the dead-zone inverse terms. The new adaptive control law ensures global stability of the entire system and achieves desired tracking precision even when the slopes of the dead-zone are not equal. Simulations performed on a typical flexible beam system illustrate and clarify the validity of this approach.
Adaptive control of a flexible beam system preceded by an unknown dead-zone in the driving motor is investigated in state space form. By introducing an important lemma for simplifying error equation between the flexible beam model and the matching reference model, a robust adaptive control scheme is developed by involving the dead-zone inverse terms. The new adaptive control law ensures global stability of the entire system and achieves desired tracking precision even when the slopes of the dead-zone are not equal. Simulations performed on a typical flexible beam system illustrate and clarify the validity of this approach.
2004, 18(3).
Abstract:
Based on theory of mechanical dynamics, meshing characteristic as well as the dynamic model of double circular arc helical gearing, an analysis approach and a computer program have been developed for studying the state of dynamic load and factor of dynamic load of the gearing, the changing situation of dynamic load and dynamic load factor vs some affecting factors such as gear width, helix angle and accuracy grade etc are investigated. A series of conclusions are obtained: ①With the increasing in the values of gear width, the dynamic load factor appears slow decreasing tendency in most region of gear width. ② When the accuracy grades of the gearing are improved, the values of dynamic load factor decrease. ③ The value of dy-namic load factor appears a decreasing tendency with the increasing of value of helix angle at the same ratio of critical rotational speed.
Based on theory of mechanical dynamics, meshing characteristic as well as the dynamic model of double circular arc helical gearing, an analysis approach and a computer program have been developed for studying the state of dynamic load and factor of dynamic load of the gearing, the changing situation of dynamic load and dynamic load factor vs some affecting factors such as gear width, helix angle and accuracy grade etc are investigated. A series of conclusions are obtained: ①With the increasing in the values of gear width, the dynamic load factor appears slow decreasing tendency in most region of gear width. ② When the accuracy grades of the gearing are improved, the values of dynamic load factor decrease. ③ The value of dy-namic load factor appears a decreasing tendency with the increasing of value of helix angle at the same ratio of critical rotational speed.
2004, 18(3).
Abstract:
In order to recognize various metal transfer modes, by the creation of a pattern recognition system for metal transfer mode, five kinds of spectrum signal in gas metal arc welding (MIG, MAG and CO2) are collected and taken as training samples. These samples are pretreated by computer. Several key characteristic parameters of the spectrum signal are creatively extracted, and a corresponding recognition function and a minimum-distance-classifier are constructed. The results show that using this method, the pattern recognition of several kinds of metal transfer mode for the metal gas arc welding can be done successfully. It has good accuracy and recognition precision, basis for controlling the metal gas arc welding metal transfer automatically, and relative important parameters in welding process, such as the frequency of droplet transfer and the approximate diameter of each droplet, can also be obtained.
In order to recognize various metal transfer modes, by the creation of a pattern recognition system for metal transfer mode, five kinds of spectrum signal in gas metal arc welding (MIG, MAG and CO2) are collected and taken as training samples. These samples are pretreated by computer. Several key characteristic parameters of the spectrum signal are creatively extracted, and a corresponding recognition function and a minimum-distance-classifier are constructed. The results show that using this method, the pattern recognition of several kinds of metal transfer mode for the metal gas arc welding can be done successfully. It has good accuracy and recognition precision, basis for controlling the metal gas arc welding metal transfer automatically, and relative important parameters in welding process, such as the frequency of droplet transfer and the approximate diameter of each droplet, can also be obtained.
2004, 18(3).
Abstract:
The forming principle and deformation analysis of NC incremental sheet metal forming process as well as the process planning, experiment and key process parameters of vertical wall square box forming are presented. Because the deformation of sheet metal only occurs around the tool head and the deformed region is subjected to stretch deformation, the deformed region of sheet metal thins, and surface area increases. Sheet metal forming stepwise is to lead to the whole sheet metal deformation. The forming half-apex angle θ and corner radius R are the main process parameters in NC incremental forming of vertical wall square box. According to sine law, a vertical wall square box can't be formed by NC incremental sheet metal forming process in a single process, rather, it must be formed in multi processes. Thus, the parallel line type tool path process method is presented to form the vertical wall square box, and the experiment and analysis are made to verify it.
The forming principle and deformation analysis of NC incremental sheet metal forming process as well as the process planning, experiment and key process parameters of vertical wall square box forming are presented. Because the deformation of sheet metal only occurs around the tool head and the deformed region is subjected to stretch deformation, the deformed region of sheet metal thins, and surface area increases. Sheet metal forming stepwise is to lead to the whole sheet metal deformation. The forming half-apex angle θ and corner radius R are the main process parameters in NC incremental forming of vertical wall square box. According to sine law, a vertical wall square box can't be formed by NC incremental sheet metal forming process in a single process, rather, it must be formed in multi processes. Thus, the parallel line type tool path process method is presented to form the vertical wall square box, and the experiment and analysis are made to verify it.
2004, 18(3).
Abstract:
Time synchronous averaging of vibration data is a fundament technique for gearbox diagnosis. Currently, this technique relies on hardware tachometer to give phase synchronous information. Empirical mode decomposition (EMD) is introduced to replace time synchronous averaging of gearbox vibration signal. With it, any compli-cated dataset can be decomposed into a finite and often small number of intrinsic mode functions (IMF). The key problem is how to assure that vibration signals deduced by gear defects could be sifted out by EMD. The characteristic vibration signals of gear defects are proved IMFs, which makes it possible to utilize EMD for the diagnosis of gearbox faults. The method is validated by data from recordings of the vibration of a single-stage spiral bevel gearbox with fatigue pitting. The results show EMD is powerful to extract characteristic information from noisy vibration signals.
Time synchronous averaging of vibration data is a fundament technique for gearbox diagnosis. Currently, this technique relies on hardware tachometer to give phase synchronous information. Empirical mode decomposition (EMD) is introduced to replace time synchronous averaging of gearbox vibration signal. With it, any compli-cated dataset can be decomposed into a finite and often small number of intrinsic mode functions (IMF). The key problem is how to assure that vibration signals deduced by gear defects could be sifted out by EMD. The characteristic vibration signals of gear defects are proved IMFs, which makes it possible to utilize EMD for the diagnosis of gearbox faults. The method is validated by data from recordings of the vibration of a single-stage spiral bevel gearbox with fatigue pitting. The results show EMD is powerful to extract characteristic information from noisy vibration signals.
2004, 18(3).
Abstract:
It has been postulated that, with tensile loading conditions, micro-cracks on thin hard film act as stress concentrators enhancing plastic deformation of the substrate material in their vicinity. Under favorable conditions the localized plastic flow near the cracks may turn into macroscopic plastic strain thus affects the plasticity behaviors of the substrate. This phenomenon is analyzed quantitatively with finite element method with special attention focused on the analysis and discussion of the effects of plastic work hardening rate, film thickness and crack depth on maximum plastic strain, critical loading stress and the size of the local plastic deformation zone. Results show that micro-cracks on thin hard film have unnegligible effects on the plasticity behaviors of the substrate material under tensile loading.
It has been postulated that, with tensile loading conditions, micro-cracks on thin hard film act as stress concentrators enhancing plastic deformation of the substrate material in their vicinity. Under favorable conditions the localized plastic flow near the cracks may turn into macroscopic plastic strain thus affects the plasticity behaviors of the substrate. This phenomenon is analyzed quantitatively with finite element method with special attention focused on the analysis and discussion of the effects of plastic work hardening rate, film thickness and crack depth on maximum plastic strain, critical loading stress and the size of the local plastic deformation zone. Results show that micro-cracks on thin hard film have unnegligible effects on the plasticity behaviors of the substrate material under tensile loading.
2004, 18(3).
Abstract:
Aiming at the discontinuous traction on contact elements of roller bearing, new concepts of sub- and micro-element are put forward. In the sub-element and micro-element, traction influence coefficient has been modified, which is calculated by the former boundary element method (BEM) with roller bearing load. Hence, three-dimensional distribution of load on roller bearing is calculated accurately. In practice, it has been proved that this method has higher calculation accuracy. An effective numerical method is offered for analyzing load characteristics of roller bearing to improve service longevity of roller bearing and operation efficiency of rolling mill.
Aiming at the discontinuous traction on contact elements of roller bearing, new concepts of sub- and micro-element are put forward. In the sub-element and micro-element, traction influence coefficient has been modified, which is calculated by the former boundary element method (BEM) with roller bearing load. Hence, three-dimensional distribution of load on roller bearing is calculated accurately. In practice, it has been proved that this method has higher calculation accuracy. An effective numerical method is offered for analyzing load characteristics of roller bearing to improve service longevity of roller bearing and operation efficiency of rolling mill.
2004, 18(3).
Abstract:
Deformation is a powerful tool for geometric modeling and design. Such a tool can be used to create a new shape from existing shape without restarting whole design process. A new mathematical model for producing controllable periodic deformations is proposed. By introducing cosine extension functions construct a shape operator matrix and then use the matrix to transform the position vector of some points on the object surface so as to create the deformation effects. Because the cosine extension functions have a number of variable parameters with different properties, the method has corresponding interactive control means. The user can manipulate those parameters to get desirable periodic deformation effects. Experimental results show that the method is feasible and applicable to engineering and research fields such as sheet metal forming by stamping and CAD.
Deformation is a powerful tool for geometric modeling and design. Such a tool can be used to create a new shape from existing shape without restarting whole design process. A new mathematical model for producing controllable periodic deformations is proposed. By introducing cosine extension functions construct a shape operator matrix and then use the matrix to transform the position vector of some points on the object surface so as to create the deformation effects. Because the cosine extension functions have a number of variable parameters with different properties, the method has corresponding interactive control means. The user can manipulate those parameters to get desirable periodic deformation effects. Experimental results show that the method is feasible and applicable to engineering and research fields such as sheet metal forming by stamping and CAD.
2004, 18(3).
Abstract:
A GPC (generalized predictive control) law is developed to control the power of a turbine, after transforming the nonlinear mathematical model of the power regulation system into a CARIMA(controlled auto-regressive integrated moving average) form. The effect of the new control law is compared with a traditional PID (proportional, integral and differential) control law by numerical simulation. The simulation results verify the effectiveness, the correctness and the advantage of the new control scheme.
A GPC (generalized predictive control) law is developed to control the power of a turbine, after transforming the nonlinear mathematical model of the power regulation system into a CARIMA(controlled auto-regressive integrated moving average) form. The effect of the new control law is compared with a traditional PID (proportional, integral and differential) control law by numerical simulation. The simulation results verify the effectiveness, the correctness and the advantage of the new control scheme.
2004, 18(3).
Abstract:
Experimental investigations are made on the effects of operating conditions on the flow characteristics of throttle when tap water is used as the working media. The researched throttles include cone poppet valve, ball valve, disc valve and dumping orifice. Operating condition includes poppet lift, working media, back pressure, medium temperature, etc. Because the vapourous pressure of water is much higher than that of oil, cavitation is easier to occur in water hydraulic elements and systems, so the effects of operating conditions on the cavitation characteristics of throttle are also researched.
Experimental investigations are made on the effects of operating conditions on the flow characteristics of throttle when tap water is used as the working media. The researched throttles include cone poppet valve, ball valve, disc valve and dumping orifice. Operating condition includes poppet lift, working media, back pressure, medium temperature, etc. Because the vapourous pressure of water is much higher than that of oil, cavitation is easier to occur in water hydraulic elements and systems, so the effects of operating conditions on the cavitation characteristics of throttle are also researched.
2004, 18(3).
Abstract:
A new heuristic algorithm is proposed for the problem of finding the minimum makespan in the job-shop scheduling problem. The new algorithm is based on the principles of particle swarm optimization (PSO). PSO employs a collaborative population-based search, which is inspired by the social behavior of bird flocking. It combines local search (by self experience) and global search (by neighboring experience), possessing high search efficiency. Simulated annealing (SA) employs certain probability to avoid becoming trapped in a local optimum and the search process can be controlled by the cooling schedule. By reasonably combining these two different search algorithms, a general, fast and easily implemented hybrid optimization algorithm, named HPSO, is developed. The effectiveness and efficiency of the proposed PSO-based algorithm are demonstrated by applying it to some benchmark job-shop scheduling problems and comparing results with other algorithms in literature. Com-paring results indicate that PSO-based algorithm is a viable and effective approach for the job-shop scheduling problem.
A new heuristic algorithm is proposed for the problem of finding the minimum makespan in the job-shop scheduling problem. The new algorithm is based on the principles of particle swarm optimization (PSO). PSO employs a collaborative population-based search, which is inspired by the social behavior of bird flocking. It combines local search (by self experience) and global search (by neighboring experience), possessing high search efficiency. Simulated annealing (SA) employs certain probability to avoid becoming trapped in a local optimum and the search process can be controlled by the cooling schedule. By reasonably combining these two different search algorithms, a general, fast and easily implemented hybrid optimization algorithm, named HPSO, is developed. The effectiveness and efficiency of the proposed PSO-based algorithm are demonstrated by applying it to some benchmark job-shop scheduling problems and comparing results with other algorithms in literature. Com-paring results indicate that PSO-based algorithm is a viable and effective approach for the job-shop scheduling problem.
2004, 18(3).
Abstract:
To investigate the effect of dynamic loading on fracture behavior of welded joints of structural steel Q235B and 16Mn in common use and compare the earthquake resistances of the two kinds of materials, dynamic tension and fracture toughness tests are carried out at room temperature. On the basis of the tests, the stress-strain fields near the crack tip of the compact specimens are analyzed by three-dimensional finite element model. The test results and finite element analysis results show that, the fracture toughness of welds and base metal of 16Mn steel increases with the increment of loading rate. Compared with 16Mn steel, Q235B steel is more sensitive to dynamic loading. The fracture toughness of welds of Q235B is comparatively low under static loading and dynamic loading at room temperature. Compared with the static loading, the fracture toughness of Q235B parent metal under dynamic loading decreases by about four times. Therefore, it can be concluded that compared with 16Mn steel, the earthquake resistances of weld and parent metal of Q235B are rather poor.
To investigate the effect of dynamic loading on fracture behavior of welded joints of structural steel Q235B and 16Mn in common use and compare the earthquake resistances of the two kinds of materials, dynamic tension and fracture toughness tests are carried out at room temperature. On the basis of the tests, the stress-strain fields near the crack tip of the compact specimens are analyzed by three-dimensional finite element model. The test results and finite element analysis results show that, the fracture toughness of welds and base metal of 16Mn steel increases with the increment of loading rate. Compared with 16Mn steel, Q235B steel is more sensitive to dynamic loading. The fracture toughness of welds of Q235B is comparatively low under static loading and dynamic loading at room temperature. Compared with the static loading, the fracture toughness of Q235B parent metal under dynamic loading decreases by about four times. Therefore, it can be concluded that compared with 16Mn steel, the earthquake resistances of weld and parent metal of Q235B are rather poor.
2004, 18(3).
Abstract:
A new construction of the relief valve is presented with pilot G-p bridge hydraulic resistances network. The design theory of G-p bridge relief valve is studied and the formulas for designing the relief valve with zero static pressure override are obtained. The static performances of the relief valve are experimentally investigated. The theoretical and experimental results show that the static pressure override of the developed relief valve can be zero, I.e. when the overflow increases the control pressure is kept constant.
A new construction of the relief valve is presented with pilot G-p bridge hydraulic resistances network. The design theory of G-p bridge relief valve is studied and the formulas for designing the relief valve with zero static pressure override are obtained. The static performances of the relief valve are experimentally investigated. The theoretical and experimental results show that the static pressure override of the developed relief valve can be zero, I.e. when the overflow increases the control pressure is kept constant.
2004, 18(3).
Abstract:
The reflecting Schmidt plate system of the large sky area multi-object fiber spectroscopic telescope (LAMOST) serves active optical correction with a reflecting surface of segmented mirror. An azimuth-altitude mounting is adopted with two self-aligning ball bearings for altitude axis and hydrostatic bearings for azimuth. With static and modal analyses, finite element modeling of the full Schmidt plate system is discussed. Conventional seismic response spectrum has been adapted for particular application for telescope engineering before a seismic response spectrum analysis is performed, and results have confirmed that the design of the reflecting Schmidt plate manifests good performance and can survive the seismic intensity of up to 7 magnitude specified by technical requirements.
The reflecting Schmidt plate system of the large sky area multi-object fiber spectroscopic telescope (LAMOST) serves active optical correction with a reflecting surface of segmented mirror. An azimuth-altitude mounting is adopted with two self-aligning ball bearings for altitude axis and hydrostatic bearings for azimuth. With static and modal analyses, finite element modeling of the full Schmidt plate system is discussed. Conventional seismic response spectrum has been adapted for particular application for telescope engineering before a seismic response spectrum analysis is performed, and results have confirmed that the design of the reflecting Schmidt plate manifests good performance and can survive the seismic intensity of up to 7 magnitude specified by technical requirements.
2004, 18(3).
Abstract:
To improve the dynamic tracking ability of spot welding manipulator with heavy payload, a new programmable motion controller, which can provide software and hardware supports for several kinds of control algorithms, is developed first. Then, a decentralized adaptive control algorithm is used to compensate the coupling between the manipulator joints, and the algorithm is easy to implement based on the motion controller. Finally, experiments demonstrate that, compared with the traditional PID, the dynamic tracking ability of the manipulator can be obviously improved with this algorithm.
To improve the dynamic tracking ability of spot welding manipulator with heavy payload, a new programmable motion controller, which can provide software and hardware supports for several kinds of control algorithms, is developed first. Then, a decentralized adaptive control algorithm is used to compensate the coupling between the manipulator joints, and the algorithm is easy to implement based on the motion controller. Finally, experiments demonstrate that, compared with the traditional PID, the dynamic tracking ability of the manipulator can be obviously improved with this algorithm.
2004, 18(3).
Abstract:
A new method named orthogonal two-way link-shift here has been proposed. Based on the method and a standard involute gear hob, a specific gear tooth profile (including an arbitrary gear tooth profile and a modified involute gear tooth profile) can be generated on a CNC(computer numerical control) hobbing machine. Computer simulation has been carried out, and the results prove that the method is right and practicable. So, the fabrication costs can be greatly decreased than before. The new method has momentous significance to realize gear's optimized modification under different work conditions.
A new method named orthogonal two-way link-shift here has been proposed. Based on the method and a standard involute gear hob, a specific gear tooth profile (including an arbitrary gear tooth profile and a modified involute gear tooth profile) can be generated on a CNC(computer numerical control) hobbing machine. Computer simulation has been carried out, and the results prove that the method is right and practicable. So, the fabrication costs can be greatly decreased than before. The new method has momentous significance to realize gear's optimized modification under different work conditions.
2004, 18(3).
Abstract:
The uncertainty of time, quantity and quality of recycling products leads to the bad stability and flexibility of remanufacturing logistics networks, and general design only covered the minimizing logistics cost, thus, robust design is presented here to solve the uncertainty. The mathematical model of remanufacturing logistics networks is built based on stochastic distribution of uncontrollable factors, and robust objectives are presented. The integration of mathematical simulation and design of experiment method is performed to do sensitive analysis. The influence of each factor and level on the system is investigated, and the main factors and optimum combination are studied. The numbers of factors, level of each factor and design process of experiment are investigated as well. Finally, the process of robust design based on design of experiment is demonstrated by a detailed example.
The uncertainty of time, quantity and quality of recycling products leads to the bad stability and flexibility of remanufacturing logistics networks, and general design only covered the minimizing logistics cost, thus, robust design is presented here to solve the uncertainty. The mathematical model of remanufacturing logistics networks is built based on stochastic distribution of uncontrollable factors, and robust objectives are presented. The integration of mathematical simulation and design of experiment method is performed to do sensitive analysis. The influence of each factor and level on the system is investigated, and the main factors and optimum combination are studied. The numbers of factors, level of each factor and design process of experiment are investigated as well. Finally, the process of robust design based on design of experiment is demonstrated by a detailed example.
2004, 18(3).
Abstract:
Current measurement method for unknown free-form surface has low efficiency. To acquire given precision, a lot of null points are measured. Based on change surface curvature, a new measurement planning is put forward. Sample step is evaluated from the change curvature and the locally-bounded character of extrapolating curve. Two coefficients, maximum error coefficient and local camber coefficient, are used to optimize sampling step. The first coefficient is computed to avoid sampling-point exceeding the measurement range and the second control sampling precision. Compared with the other methods, the proposed planning method can reduce the number of the measuring-point efficiently for the given precision. Measuring point distributes adaptively by the change surface curvature. The method can be applied to improve measurement efficiency and accuracy.
Current measurement method for unknown free-form surface has low efficiency. To acquire given precision, a lot of null points are measured. Based on change surface curvature, a new measurement planning is put forward. Sample step is evaluated from the change curvature and the locally-bounded character of extrapolating curve. Two coefficients, maximum error coefficient and local camber coefficient, are used to optimize sampling step. The first coefficient is computed to avoid sampling-point exceeding the measurement range and the second control sampling precision. Compared with the other methods, the proposed planning method can reduce the number of the measuring-point efficiently for the given precision. Measuring point distributes adaptively by the change surface curvature. The method can be applied to improve measurement efficiency and accuracy.
2004, 18(3).
Abstract:
Vibration acceleration signals are often measured from case surface of a running machine to monitor its condition. If the measured vibration signals display to have periodic impulse components with a certain frequency, there may exist a corresponding local fault in the machine, and if further extracting the periodic impulse components from the vibration signals, the severity of the local fault can be estimated and tracked. However, the signal-to-noise ratios (SNRs) of the vibration acceleration signals are often so small that the periodic impulse components are submersed in much background noises and other components, and it is difficult or inconvenient for us to detect and extract the periodic impulse components with the current common analyzing methods for vibration signals. Therefore, another technique, called singular value decomposition (SVD), is tried to be introduced to solve the problem. First, the principle of detecting and extracting the signal periodic components using singular value decomposition is summarized and discussed. Second, the infeasibility of the direct use of the existing SVD based detecting and extracting approach is pointed out. Third, the approach to construct the matrix for SVD from the signal series is improved largely, which is the key program to improve the SVD technique; Other associated improvement is also proposed. Finally, a simulating application example and a real-life application example on detecting and extracting the periodic impulse components are given, which showed that the introduced and improved SVD technique is feasible.
Vibration acceleration signals are often measured from case surface of a running machine to monitor its condition. If the measured vibration signals display to have periodic impulse components with a certain frequency, there may exist a corresponding local fault in the machine, and if further extracting the periodic impulse components from the vibration signals, the severity of the local fault can be estimated and tracked. However, the signal-to-noise ratios (SNRs) of the vibration acceleration signals are often so small that the periodic impulse components are submersed in much background noises and other components, and it is difficult or inconvenient for us to detect and extract the periodic impulse components with the current common analyzing methods for vibration signals. Therefore, another technique, called singular value decomposition (SVD), is tried to be introduced to solve the problem. First, the principle of detecting and extracting the signal periodic components using singular value decomposition is summarized and discussed. Second, the infeasibility of the direct use of the existing SVD based detecting and extracting approach is pointed out. Third, the approach to construct the matrix for SVD from the signal series is improved largely, which is the key program to improve the SVD technique; Other associated improvement is also proposed. Finally, a simulating application example and a real-life application example on detecting and extracting the periodic impulse components are given, which showed that the introduced and improved SVD technique is feasible.
2004, 18(3).
Abstract:
Robot programming by demonstration (PBD) system for task in which object requires contact with environment is built based on the controlling skill model. The skill is described in three aspects: contact state classifier, acquirement of contact states sequence and controlling transition between states. The classifier is developed with the support vector machine by using force sense. Sequence of states is obtained from the force signal of demonstration by the event trigger. The velocity command of transition is achieved by linearization method. The PBD system is successfully built with robot controller with open architecture.
Robot programming by demonstration (PBD) system for task in which object requires contact with environment is built based on the controlling skill model. The skill is described in three aspects: contact state classifier, acquirement of contact states sequence and controlling transition between states. The classifier is developed with the support vector machine by using force sense. Sequence of states is obtained from the force signal of demonstration by the event trigger. The velocity command of transition is achieved by linearization method. The PBD system is successfully built with robot controller with open architecture.
2004, 18(3).
Abstract:
The automotive industry is seeking new concepts for a continuously variable transmission (CVT) in the driveline. One possible solution for a CVT design is half toroidal traction drive, providing a high torque capacity with quick ratio change. An analytical study on the contact points of the half toroidal CVT has been detailed. The shapes of the contact areas among the input disk, power roller and output disk are con-sidered ellipses. Mathematical equations for estimating the torque capacity, power loss due to spin action, and contact efficiency of the elliptical contacts of the half toroidal CVT are formulated and expressed in the form of integrals which can be readily evaluated by numerical scheme. The contact efficiency calculations of the half toroidal CVT have been developed for the proper spin point locations under the effect of system parameters. Numerical results are presented in graphical forms for considered parameters, which can help the designer to select the proper system parameters to minimize the undesirable spin effects.
The automotive industry is seeking new concepts for a continuously variable transmission (CVT) in the driveline. One possible solution for a CVT design is half toroidal traction drive, providing a high torque capacity with quick ratio change. An analytical study on the contact points of the half toroidal CVT has been detailed. The shapes of the contact areas among the input disk, power roller and output disk are con-sidered ellipses. Mathematical equations for estimating the torque capacity, power loss due to spin action, and contact efficiency of the elliptical contacts of the half toroidal CVT are formulated and expressed in the form of integrals which can be readily evaluated by numerical scheme. The contact efficiency calculations of the half toroidal CVT have been developed for the proper spin point locations under the effect of system parameters. Numerical results are presented in graphical forms for considered parameters, which can help the designer to select the proper system parameters to minimize the undesirable spin effects.
2004, 18(3).
Abstract:
“N-2-1” principle is widely recognized in the fixture design for deformable sheet metal workpieces, where N, the locators on primary datum, is the key to sheet metal fixture design. However, little research is done on how to determine the positions and the number of N locators. In practice, the N locators are frequently designed from experience, which is often unsatisfactory for achieving the precision requirement in fixture design. A new method to lay out the N locators for measuring fixture of deformable sheet metal workpiece is presented, given the fixed number of N. Finite-element method is used to model and analysis the deformation of different locator layouts. A knowledge based genetic algorithm (KBGA) is applied to identify the optimum locator layout for measuring fixture design. An example of a door outer is used to verify the optimization approach.
“N-2-1” principle is widely recognized in the fixture design for deformable sheet metal workpieces, where N, the locators on primary datum, is the key to sheet metal fixture design. However, little research is done on how to determine the positions and the number of N locators. In practice, the N locators are frequently designed from experience, which is often unsatisfactory for achieving the precision requirement in fixture design. A new method to lay out the N locators for measuring fixture of deformable sheet metal workpiece is presented, given the fixed number of N. Finite-element method is used to model and analysis the deformation of different locator layouts. A knowledge based genetic algorithm (KBGA) is applied to identify the optimum locator layout for measuring fixture design. An example of a door outer is used to verify the optimization approach.
2004, 18(3).
Abstract:
Some dynamic factors, such as inertial forces and friction, may affect the robot trajectory accuracy. But these effects are not taken into account in robot motion control schemes. Dynamic control methods, on the other hand, require the dynamic model of robot and the implementation of new type controller. A method to improve robot trajectory accuracy by dynamic compensation in robot motion control system is proposed. The dynamic compensation is applied as an additional velocity feedforward and a multilayer neural network is employed to realize the robot inverse dynamics. The complicated dynamic parameter identification problem becomes a learning process of neural network connecting weights under supervision. The finite Fourier series is used to activate each actuator of robot joints for obtaining training samples. Robot control system, consisting of an industrial computer and a digital motion controller, is implemented. The system is of open architecture with velocity feedforward function. The proposed method is not model-based and combines the advantages of close-loop position control and computed torque control. Experimental results have shown that the method is validatities to improve the robot trajectory accuracy.
Some dynamic factors, such as inertial forces and friction, may affect the robot trajectory accuracy. But these effects are not taken into account in robot motion control schemes. Dynamic control methods, on the other hand, require the dynamic model of robot and the implementation of new type controller. A method to improve robot trajectory accuracy by dynamic compensation in robot motion control system is proposed. The dynamic compensation is applied as an additional velocity feedforward and a multilayer neural network is employed to realize the robot inverse dynamics. The complicated dynamic parameter identification problem becomes a learning process of neural network connecting weights under supervision. The finite Fourier series is used to activate each actuator of robot joints for obtaining training samples. Robot control system, consisting of an industrial computer and a digital motion controller, is implemented. The system is of open architecture with velocity feedforward function. The proposed method is not model-based and combines the advantages of close-loop position control and computed torque control. Experimental results have shown that the method is validatities to improve the robot trajectory accuracy.
2004, 18(3).
Abstract:
Differed from the existed applications of generalized stochastic Petri net (GSPN) theory in machine-tool manufacturing system, reliability computation of FMS, testability parameters determination and fault analysis, a new idea of applying GSPN to model and performance analysis for the serial and parallel production system is proposed. And one typical discrete event dynamic system (DEDS), turner-unit of palletizing system, is taken as a real case to research. Based upon the established GSPN models, the working performances of serial and parallel layout are compared. Furthermore, their differences of working mechanisms including feeding mechanism, coordinating mechanism and monitoring mechanism are discussed. Thus the theoretical basis which is helpful to appraise layout plan and its reasonableness is provided. Meanwhile, the research results show that parallel layout is more advantageous to greatly improve the operational speed of production system than serial one.
Differed from the existed applications of generalized stochastic Petri net (GSPN) theory in machine-tool manufacturing system, reliability computation of FMS, testability parameters determination and fault analysis, a new idea of applying GSPN to model and performance analysis for the serial and parallel production system is proposed. And one typical discrete event dynamic system (DEDS), turner-unit of palletizing system, is taken as a real case to research. Based upon the established GSPN models, the working performances of serial and parallel layout are compared. Furthermore, their differences of working mechanisms including feeding mechanism, coordinating mechanism and monitoring mechanism are discussed. Thus the theoretical basis which is helpful to appraise layout plan and its reasonableness is provided. Meanwhile, the research results show that parallel layout is more advantageous to greatly improve the operational speed of production system than serial one.
2004, 18(3).
Abstract:
Application of the multiobjective evolutionary algorithms to the aerodynamic optimization design of a centrifugal impeller is presented. The aerodynamic performance of a centrifugal impeller is evaluated by using the three-dimensional Navier-Stokes solutions. The typical centrifugal impeller is redesigned for maximization of the pressure rise and blade load and minimization of the rotational total pressure loss at the given flow conditions. The Bézier curves are used to parameterize the three-dimensional impeller blade shape. The present method obtains many reasonable Pareto optimal designs that outperform the original centrifugal impeller. Detailed observation of the certain Pareto optimal design demonstrates the feasibility of the present multiobjective optimization method tool for turbomachinery design.
Application of the multiobjective evolutionary algorithms to the aerodynamic optimization design of a centrifugal impeller is presented. The aerodynamic performance of a centrifugal impeller is evaluated by using the three-dimensional Navier-Stokes solutions. The typical centrifugal impeller is redesigned for maximization of the pressure rise and blade load and minimization of the rotational total pressure loss at the given flow conditions. The Bézier curves are used to parameterize the three-dimensional impeller blade shape. The present method obtains many reasonable Pareto optimal designs that outperform the original centrifugal impeller. Detailed observation of the certain Pareto optimal design demonstrates the feasibility of the present multiobjective optimization method tool for turbomachinery design.
2004, 18(3).
Abstract:
The measurement of the middle-convex and varying ellipse profile of a piston skirt is a key technology because of its complex profile and high precision. Generally, a piston is measured on special device after it is machined. High accuracy can be achieved through this off-line measurement, but the result diverges from the actual dimension. Therefore, a no-contact in-site measurement system is proposed. A laser displacement meter is used to measure the profile of the piston skirt. A computer connected to the meter is used to process the measured data. A regression analysis method is used to process the ellipse section data. The method of moving average is used to process the middle-convex curve data. By using the given system, high measurement accuracy can be gained, and the production requirement is met.
The measurement of the middle-convex and varying ellipse profile of a piston skirt is a key technology because of its complex profile and high precision. Generally, a piston is measured on special device after it is machined. High accuracy can be achieved through this off-line measurement, but the result diverges from the actual dimension. Therefore, a no-contact in-site measurement system is proposed. A laser displacement meter is used to measure the profile of the piston skirt. A computer connected to the meter is used to process the measured data. A regression analysis method is used to process the ellipse section data. The method of moving average is used to process the middle-convex curve data. By using the given system, high measurement accuracy can be gained, and the production requirement is met.
2004, 18(3).
Abstract:
In the robotic community more and more hands are developed. Based on the experience of HIT Hand and DLR Hand II, a smaller and easier manufactured dexterous robot hand with multisensory function and high integration is jointly developed. The prototype of the hand is successfully built. It has 4 fingers in total 13-DOFs (degree of freedom). Each finger has 3-DOFs and 4 joints, the last 2 joints are mechanically coupled by means of four-bar linkage mechanism. It also has an additional DOF to realize motion of the thumb relative to the palm. The fingertip force can reach up to 10 N. Full integration of mechanical body, actuation system, multisensory system and electronics is a significant feature. DSP based control system is implemented in PCI bus architecture and the serial communica-tion between the hand and DSP needs only 2 lines.
In the robotic community more and more hands are developed. Based on the experience of HIT Hand and DLR Hand II, a smaller and easier manufactured dexterous robot hand with multisensory function and high integration is jointly developed. The prototype of the hand is successfully built. It has 4 fingers in total 13-DOFs (degree of freedom). Each finger has 3-DOFs and 4 joints, the last 2 joints are mechanically coupled by means of four-bar linkage mechanism. It also has an additional DOF to realize motion of the thumb relative to the palm. The fingertip force can reach up to 10 N. Full integration of mechanical body, actuation system, multisensory system and electronics is a significant feature. DSP based control system is implemented in PCI bus architecture and the serial communica-tion between the hand and DSP needs only 2 lines.
2004, 18(3).
Abstract:
Emprical mode decomposition(EMD) is a method and principle of decomposing signal dealing with Hilbert-Huang transform (HHT) in signal analysis, while directly-mean EMD is an improved EMD method presented by N.E.Huang, the inventor of HHT, which is aimed at solving the problems of EMD principle. Although the directly-mean EMD method is very remarkable with its advantages and N. E. Huang has given a method to realize it, he did not find the theoretic evidence of the method so that the feasibility of the idea and correctness of realizing the directly-mean EMD method is still indeterminate. For this a deep research on the forming process of complex signal is made and the involved stationary point principle and asymptotic stationary point principle are demonstrated, thus some theoretic evidences and the correct realizing way of directly-mean EMD method is firstly presented. Some simulation examples for demonstrating the idea presented are given.
Emprical mode decomposition(EMD) is a method and principle of decomposing signal dealing with Hilbert-Huang transform (HHT) in signal analysis, while directly-mean EMD is an improved EMD method presented by N.E.Huang, the inventor of HHT, which is aimed at solving the problems of EMD principle. Although the directly-mean EMD method is very remarkable with its advantages and N. E. Huang has given a method to realize it, he did not find the theoretic evidence of the method so that the feasibility of the idea and correctness of realizing the directly-mean EMD method is still indeterminate. For this a deep research on the forming process of complex signal is made and the involved stationary point principle and asymptotic stationary point principle are demonstrated, thus some theoretic evidences and the correct realizing way of directly-mean EMD method is firstly presented. Some simulation examples for demonstrating the idea presented are given.
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