2009 Vol.22(3)
Display Mode： |
2009, 23(3).
Abstract:
Underactuated mechanical system has less independent inputs than the degrees of freedom(DOF) of the mechanism. The energy efficiency of this class of mechanical systems is an essential problem in practice. On the basis of the sufficient and necessary condition that concludes a single input nonlinear system is differentially flat, it is shown that the flat output of the single input underactuated mechanical system can be obtained by finding a smooth output function such that the relative degree of the system equals to the dimension of the state space. If the flat output of the underactuated system can be solved explicitly, and by constructing a smooth curve with satisfying given boundary conditions in flat output space, an energy efficiency optimization method is proposed for the motion planning of the differentially flat underactuated mechanical systems. The inertia wheel pendulum is used to verify the proposed optimization method, and some numerical simulations show that the presented optimal motion planning method can efficaciously reduce the energy cost for given control tasks.
Underactuated mechanical system has less independent inputs than the degrees of freedom(DOF) of the mechanism. The energy efficiency of this class of mechanical systems is an essential problem in practice. On the basis of the sufficient and necessary condition that concludes a single input nonlinear system is differentially flat, it is shown that the flat output of the single input underactuated mechanical system can be obtained by finding a smooth output function such that the relative degree of the system equals to the dimension of the state space. If the flat output of the underactuated system can be solved explicitly, and by constructing a smooth curve with satisfying given boundary conditions in flat output space, an energy efficiency optimization method is proposed for the motion planning of the differentially flat underactuated mechanical systems. The inertia wheel pendulum is used to verify the proposed optimization method, and some numerical simulations show that the presented optimal motion planning method can efficaciously reduce the energy cost for given control tasks.
Acquisition and Active Navigation of Knowledge Particles throughout Product Variation Design Process
2009, 23(3).
Abstract:
The variation design of complex products has such features as multivariate association, weak theory coupling and implicit knowledge iteration. However, present CAD soft wares are still restricted to making decisions only according to current design status in dynamic navigation which leads to the huge drain of the knowledge hidden in design process. In this paper, a method of acquisition and active navigation of knowledge particles throughout product variation design process is put forward. The multi-objective decision information model of the variation design is established via the definition of condition attribute set and decision attribute set in finite universe. The addition and retrieval of the variation semantics is achieved through bidirectional association between the transplantable structures and variation design semantics. The mapping relationships between the topology lapping geometry elements set and constraint relations set family is built by means of geometry feature analysis. The acquisition of knowledge particles is implemented by attribute reduction based on rough set theory to make multi-objective decision of variation design. The topology lapping status of transplantable substructures is known from DOF reduction. The active navigation of knowledge particles is realized through embedded event-condition-action(ECA) rules. The independent prototype system taking Alan, Charles, Ian’s system(ACIS) as kernel has been developed to verify the proposed method by applying variation design of complex mechanical products. The test results demonstrate that the navigation decision basis can be successfully extended from static isolated design status to dynamic continuous design process so that it more flexibly adapts to the different designers and various variation design steps. It is of profound significance for enhancing system intelligence as well as improving design quality and efficiency.
The variation design of complex products has such features as multivariate association, weak theory coupling and implicit knowledge iteration. However, present CAD soft wares are still restricted to making decisions only according to current design status in dynamic navigation which leads to the huge drain of the knowledge hidden in design process. In this paper, a method of acquisition and active navigation of knowledge particles throughout product variation design process is put forward. The multi-objective decision information model of the variation design is established via the definition of condition attribute set and decision attribute set in finite universe. The addition and retrieval of the variation semantics is achieved through bidirectional association between the transplantable structures and variation design semantics. The mapping relationships between the topology lapping geometry elements set and constraint relations set family is built by means of geometry feature analysis. The acquisition of knowledge particles is implemented by attribute reduction based on rough set theory to make multi-objective decision of variation design. The topology lapping status of transplantable substructures is known from DOF reduction. The active navigation of knowledge particles is realized through embedded event-condition-action(ECA) rules. The independent prototype system taking Alan, Charles, Ian’s system(ACIS) as kernel has been developed to verify the proposed method by applying variation design of complex mechanical products. The test results demonstrate that the navigation decision basis can be successfully extended from static isolated design status to dynamic continuous design process so that it more flexibly adapts to the different designers and various variation design steps. It is of profound significance for enhancing system intelligence as well as improving design quality and efficiency.
2009, 23(3).
Abstract:
For the purpose of solving the engineering constrained discrete optimization problem, a novel discrete particle swarm optimization(DPSO) is proposed. The proposed novel DPSO is based on the idea of normal particle swarm optimization(PSO), but deals with the variables as discrete type, the discrete optimum solution is found through updating the location of discrete variable. To avoid long calculation time and improve the efficiency of algorithm, scheme of constraint level and huge value penalty are proposed to deal with the constraints, the stratagem of reproducing the new particles and best keeping model of particle are employed to increase the diversity of particles. The validity of the proposed DPSO is examined by benchmark numerical examples, the results show that the novel DPSO has great advantages over current algorithm. The optimum designs of the 100−1 500 mm bellows under 0.25 MPa are fulfilled by DPSO. Comparing the optimization results with the bellows in-service, optimization results by discrete penalty particle swarm optimization(DPPSO) and theory solution, the comparison result shows that the global discrete optima of bellows are obtained by proposed DPSO, and confirms that the proposed novel DPSO and schemes can be used to solve the engineering constrained discrete problem successfully.
For the purpose of solving the engineering constrained discrete optimization problem, a novel discrete particle swarm optimization(DPSO) is proposed. The proposed novel DPSO is based on the idea of normal particle swarm optimization(PSO), but deals with the variables as discrete type, the discrete optimum solution is found through updating the location of discrete variable. To avoid long calculation time and improve the efficiency of algorithm, scheme of constraint level and huge value penalty are proposed to deal with the constraints, the stratagem of reproducing the new particles and best keeping model of particle are employed to increase the diversity of particles. The validity of the proposed DPSO is examined by benchmark numerical examples, the results show that the novel DPSO has great advantages over current algorithm. The optimum designs of the 100−1 500 mm bellows under 0.25 MPa are fulfilled by DPSO. Comparing the optimization results with the bellows in-service, optimization results by discrete penalty particle swarm optimization(DPPSO) and theory solution, the comparison result shows that the global discrete optima of bellows are obtained by proposed DPSO, and confirms that the proposed novel DPSO and schemes can be used to solve the engineering constrained discrete problem successfully.
2009, 23(3).
Abstract:
In metal cutting industry it is a common practice to search for optimal combination of cutting parameters in order to maximize the tool life for a fixed minimum value of material removal rate(MRR). After the advent of high-speed milling(HSM) process, lots of experimental and theoretical researches have been done for this purpose which mainly emphasized on the optimization of the cutting parameters. It is highly beneficial to convert raw data into a comprehensive knowledge-based expert system using fuzzy logic as the reasoning mechanism. In this paper an attempt has been presented for the extraction of the rules from fuzzy neural network(FNN) so as to have the most effective knowledge-base for given set of data. Experiments were conducted to determine the best values of cutting speeds that can maximize tool life for different combinations of input parameters. A fuzzy neural network was constructed based on the fuzzification of input parameters and the cutting speed. After training process, raw rule sets were extracted and a rule pruning approach was proposed to obtain concise linguistic rules. The estimation process with fuzzy inference showed that the optimized combination of fuzzy rules provided the estimation error of only 6.34 m/min as compared to 314 m/min of that of randomized combination of rules.
In metal cutting industry it is a common practice to search for optimal combination of cutting parameters in order to maximize the tool life for a fixed minimum value of material removal rate(MRR). After the advent of high-speed milling(HSM) process, lots of experimental and theoretical researches have been done for this purpose which mainly emphasized on the optimization of the cutting parameters. It is highly beneficial to convert raw data into a comprehensive knowledge-based expert system using fuzzy logic as the reasoning mechanism. In this paper an attempt has been presented for the extraction of the rules from fuzzy neural network(FNN) so as to have the most effective knowledge-base for given set of data. Experiments were conducted to determine the best values of cutting speeds that can maximize tool life for different combinations of input parameters. A fuzzy neural network was constructed based on the fuzzification of input parameters and the cutting speed. After training process, raw rule sets were extracted and a rule pruning approach was proposed to obtain concise linguistic rules. The estimation process with fuzzy inference showed that the optimized combination of fuzzy rules provided the estimation error of only 6.34 m/min as compared to 314 m/min of that of randomized combination of rules.
2009, 23(3).
Abstract:
Among the proposed techniques for delivering drugs to specific sites within the human body, magnetic targeting drug delivery surpasses due to its non-invasive character and its high targeting efficiency. Although there have been some analyses theoretically for magnetic drug targeting, very few researchers have addressed the hydrodynamic models of magnetic fluids in the blood vessel of human body. This paper presents a mathematical model to describe the hydrodynamics of ferrofluids as drug carriers flowing in a blood vessel under the applied magnetic field. A 3D flow field of magnetic particles in a blood vessel model is numerically simulated in order to further understand clinical application of magnetic targeting drug delivery. Simulation results show that magnetic nanoparticles can be enriched in a target region depending on the applied magnetic field intensity. Magnetic resonance imaging confirms the enrichment of ferrofluids in a desired body tissue of Sprague-Dawley rats. The simulation results coincide with those animal experiments. Results of the analysis provide the important information and can suggest strategies for improving delivery in favor of the clinical application.
Among the proposed techniques for delivering drugs to specific sites within the human body, magnetic targeting drug delivery surpasses due to its non-invasive character and its high targeting efficiency. Although there have been some analyses theoretically for magnetic drug targeting, very few researchers have addressed the hydrodynamic models of magnetic fluids in the blood vessel of human body. This paper presents a mathematical model to describe the hydrodynamics of ferrofluids as drug carriers flowing in a blood vessel under the applied magnetic field. A 3D flow field of magnetic particles in a blood vessel model is numerically simulated in order to further understand clinical application of magnetic targeting drug delivery. Simulation results show that magnetic nanoparticles can be enriched in a target region depending on the applied magnetic field intensity. Magnetic resonance imaging confirms the enrichment of ferrofluids in a desired body tissue of Sprague-Dawley rats. The simulation results coincide with those animal experiments. Results of the analysis provide the important information and can suggest strategies for improving delivery in favor of the clinical application.
2009, 23(3).
Abstract:
When the decrease in the space between magnetic head and disk arrived at 10 nm or less, which is much lower than the mean free path of gas molecules, the gas flow presents distinctive features against the macro features because of the rarefied effects. The modified Reynolds equation considering rarefied gas effect is used to calculate the rarefied region of a negative pressure magnetic head working in the distance of 10 nm. Inverse Knudsen number was adopted to calculating the ratio of the rarefied area. According to the numerical results, discussions and analyses are then presented to reveal the rarefied effect on the working performances of a magnetic head. The results show that the magnetic head works in the slip-flow and transition regions and moves to the transition region with the increase in velocity. Furthermore, the maximum rarefied effects occur at the side edges where the flying height is thinner and pressure is lower, rather than in the minimum flying height on the rear. The results also show that with considering the rarefied effects, the load-carrying capacity of the magnetic head and the maximum pressure decrease significantly, but the minimum pressure slightly changes.
When the decrease in the space between magnetic head and disk arrived at 10 nm or less, which is much lower than the mean free path of gas molecules, the gas flow presents distinctive features against the macro features because of the rarefied effects. The modified Reynolds equation considering rarefied gas effect is used to calculate the rarefied region of a negative pressure magnetic head working in the distance of 10 nm. Inverse Knudsen number was adopted to calculating the ratio of the rarefied area. According to the numerical results, discussions and analyses are then presented to reveal the rarefied effect on the working performances of a magnetic head. The results show that the magnetic head works in the slip-flow and transition regions and moves to the transition region with the increase in velocity. Furthermore, the maximum rarefied effects occur at the side edges where the flying height is thinner and pressure is lower, rather than in the minimum flying height on the rear. The results also show that with considering the rarefied effects, the load-carrying capacity of the magnetic head and the maximum pressure decrease significantly, but the minimum pressure slightly changes.
2009, 23(3).
Abstract:
Fatigue behaviour has important implications for engineering composite structures in sectors ranging from automotive to aerospace. Optical sensing technology displays excellent performance in these fields for monitoring. In this paper, temperature and residual strain during fatigue of a carbon fiber reinforced polymer(CFRP) are investigated. Four autoclaved CFRP beam specimens, with fiber Bragg grating(FBG) sensors and thermocouples embedded at selected locations, are subjected to three-point bending cyclic loading on the BOSE testing machine for fatigue testing. Thermocouples are used to measure the temperature while FBGs can sense the temperature and strain as well. Seven tests in total are conducted at different frequencies, and each test lasts for several days. From the experimental results, transient steep peaks of temperature increases (up to 2.3 ℃) are discovered at the beginning of the load. The following constant temperature increments are around 1.0 ℃, which is not relevant to frequencies from 0.1 Hz to 20 Hz and suspected due to fatigue. Residual strains of 1×10−5–2×10−5 during fatigue, fading away rapidly when unloading, are also reported. Embedded FBGs here are validated to sense temperature and strains in composite structures, which demonstrates promising potentials in structure monitoring fields. CFRP are verified to have an excellent performance during fatigue with low temperature increase and residual strain.
Fatigue behaviour has important implications for engineering composite structures in sectors ranging from automotive to aerospace. Optical sensing technology displays excellent performance in these fields for monitoring. In this paper, temperature and residual strain during fatigue of a carbon fiber reinforced polymer(CFRP) are investigated. Four autoclaved CFRP beam specimens, with fiber Bragg grating(FBG) sensors and thermocouples embedded at selected locations, are subjected to three-point bending cyclic loading on the BOSE testing machine for fatigue testing. Thermocouples are used to measure the temperature while FBGs can sense the temperature and strain as well. Seven tests in total are conducted at different frequencies, and each test lasts for several days. From the experimental results, transient steep peaks of temperature increases (up to 2.3 ℃) are discovered at the beginning of the load. The following constant temperature increments are around 1.0 ℃, which is not relevant to frequencies from 0.1 Hz to 20 Hz and suspected due to fatigue. Residual strains of 1×10−5–2×10−5 during fatigue, fading away rapidly when unloading, are also reported. Embedded FBGs here are validated to sense temperature and strains in composite structures, which demonstrates promising potentials in structure monitoring fields. CFRP are verified to have an excellent performance during fatigue with low temperature increase and residual strain.
2009, 23(3).
Abstract:
In order to overcome many limitations of the conventional power supplies, such as ponderosity, big wastage, and simplex output characteristic, a dual-inverter power supply is designed to meet the different requirements of micro-arc oxidation. The main circuit structure and principle of the dual-inverter power supply for micro-arc oxidation is described, the control system and the control adjustment method are also introduced. The dual-inverter technology is adopted in micro-arc oxidation power supply. The limited bipolar control mode is applied in the power inverter circuit for adjusting the voltage, and various voltage waveform can be obtained by controlling the chopper circuit. Meanwhile, the control accuracy and response speed are improved greatly because of the higher inverter frequency. The power supply can output direct current(DC) waveform, DC pulse waveform, symmetry alternating current(AC) waveform, asymmetry AC waveform, and so on. Besides, the parameters such as pulse width, range, frequency, duty cycle can be adjusted. The experimental result shows that the power supply has many advantages, such as stable output，wonderful waveform consistency and obvious advantage in technique, and it can meet the requirements of micro-arc oxidation process fully.
In order to overcome many limitations of the conventional power supplies, such as ponderosity, big wastage, and simplex output characteristic, a dual-inverter power supply is designed to meet the different requirements of micro-arc oxidation. The main circuit structure and principle of the dual-inverter power supply for micro-arc oxidation is described, the control system and the control adjustment method are also introduced. The dual-inverter technology is adopted in micro-arc oxidation power supply. The limited bipolar control mode is applied in the power inverter circuit for adjusting the voltage, and various voltage waveform can be obtained by controlling the chopper circuit. Meanwhile, the control accuracy and response speed are improved greatly because of the higher inverter frequency. The power supply can output direct current(DC) waveform, DC pulse waveform, symmetry alternating current(AC) waveform, asymmetry AC waveform, and so on. Besides, the parameters such as pulse width, range, frequency, duty cycle can be adjusted. The experimental result shows that the power supply has many advantages, such as stable output，wonderful waveform consistency and obvious advantage in technique, and it can meet the requirements of micro-arc oxidation process fully.
2009, 23(3).
Abstract:
Due to the narrowness of space and the complexity of structure, the assembly of aircraft cabin has become one of the major bottlenecks in the whole manufacturing process. To solve the problem, at the beginning of aircraft design, the different stages of the lifecycle of aircraft must be thought about, which include the trial manufacture, assembly, maintenance, recycling and destruction of the product. Recently, thanks to the development of the virtual reality and augmented reality, some low-cost and fast solutions are found for the product assembly. This paper presents a mixed reality-based interactive technology for the aircraft cabin assembly, which can enhance the efficiency of the assemblage in a virtual environment in terms of vision, information and operation. In the mixed reality-based assembly environment, the physical scene can be obtained by a camera and then generated by a computer. The virtual parts, the features of visual assembly, the navigation information, the physical parts and the physical assembly environment will be mixed and presented in the same assembly scene. The mixed or the augmented information will provide some assembling information as a detailed assembly instruction in the mixed reality-based assembly environment. Constraint proxy and its match rules help to reconstruct and visualize the restriction relationship among different parts, and to avoid the complex calculation of constraint’s match. Finally, a desktop prototype system of virtual assembly has been built to assist the assembly verification and training with the virtual hand.
Due to the narrowness of space and the complexity of structure, the assembly of aircraft cabin has become one of the major bottlenecks in the whole manufacturing process. To solve the problem, at the beginning of aircraft design, the different stages of the lifecycle of aircraft must be thought about, which include the trial manufacture, assembly, maintenance, recycling and destruction of the product. Recently, thanks to the development of the virtual reality and augmented reality, some low-cost and fast solutions are found for the product assembly. This paper presents a mixed reality-based interactive technology for the aircraft cabin assembly, which can enhance the efficiency of the assemblage in a virtual environment in terms of vision, information and operation. In the mixed reality-based assembly environment, the physical scene can be obtained by a camera and then generated by a computer. The virtual parts, the features of visual assembly, the navigation information, the physical parts and the physical assembly environment will be mixed and presented in the same assembly scene. The mixed or the augmented information will provide some assembling information as a detailed assembly instruction in the mixed reality-based assembly environment. Constraint proxy and its match rules help to reconstruct and visualize the restriction relationship among different parts, and to avoid the complex calculation of constraint’s match. Finally, a desktop prototype system of virtual assembly has been built to assist the assembly verification and training with the virtual hand.
2009, 23(3).
Abstract:
In order to solve the problem of trajectory tracking for a class of novel serial-parallel hybrid humanoid arm(HHA), which has parameters uncertainty, frictions, disturbance, abrasion and pulse forces derived from motors, a multistep dynamics modeling strategy is proposed and a robust controller based on neural network(NN)-adaptive algorithm is designed. At the first step of dynamics modeling, the dynamics model of the reduced HHA is established by Lagrange method. At the second step of dynamics modeling, the parameter uncertain part resulting mainly from the idealization of the HHA is learned by adaptive algorithm. In the trajectory tracking controller, the radial basis function(RBF) NN, whose optimal weights are learned online by adaptive algorithm, is used to learn the upper limit function of the total uncertainties including frictions, disturbances, abrasion and pulse forces. To a great extent, the conservatism of this robust trajectory tracking controller is reduced, and by this controller the HHA can impersonate mostly human actions. The proof and simulation results testify the validity of the adaptive strategy for parameter learning and the neural network-adaptive strategy for the trajectory tracking control.
In order to solve the problem of trajectory tracking for a class of novel serial-parallel hybrid humanoid arm(HHA), which has parameters uncertainty, frictions, disturbance, abrasion and pulse forces derived from motors, a multistep dynamics modeling strategy is proposed and a robust controller based on neural network(NN)-adaptive algorithm is designed. At the first step of dynamics modeling, the dynamics model of the reduced HHA is established by Lagrange method. At the second step of dynamics modeling, the parameter uncertain part resulting mainly from the idealization of the HHA is learned by adaptive algorithm. In the trajectory tracking controller, the radial basis function(RBF) NN, whose optimal weights are learned online by adaptive algorithm, is used to learn the upper limit function of the total uncertainties including frictions, disturbances, abrasion and pulse forces. To a great extent, the conservatism of this robust trajectory tracking controller is reduced, and by this controller the HHA can impersonate mostly human actions. The proof and simulation results testify the validity of the adaptive strategy for parameter learning and the neural network-adaptive strategy for the trajectory tracking control.
2009, 23(3).
Abstract:
Magneto-rhelological(MR) dampers are devices that employ rheological fluids to modify their mechanical properties. Their mechanical simplicity, high dynamic range, lower power requirements, large force capacity, robustness and safe manner of operation in cases of failure have made them attractive devices for semi-active real-time control in civil, aerospace and automotive applications. Time response characteristic is one of the most important technical performances of MR dampers, and response time directly affects the control frequency, application range and the actual effect of MR dampers．In this study, one kind of finite difference solution for predicting the response time of magneto-rheological dampers from “off-state” to “on-state” is put forward. A laminar flow model is used to describe the flow in the MR valve, and a bi-viscous fluid flow model is utilized to describe the relationship of shear stress and shear rate of MR fluid. An explicit difference format is used to discretize the Novior-Stoks equation, and stability condition of this algorithm is built by Von-Neumann stability criterion. The pressure gradient along the flow duct is solved by a dichotomy algorithm with iteration, and the changing curve of the damping force versus time of MR damper is obtained as well. According to the abovementioned numerical algorithm, the damping forces versus time curves from “off-state” to “on-state” of a cylindrical piston type MR damper are computed. Moreover, the MR damper is installed in a material test system(MTS), the magnetic field in the wire circles of the MR damper is “triggered” when the MR damper is imposed to do a constant speed motion, and the damping force curves are recorded. The comparison between numerical results and experimental results indicates that this finite difference algorithm can be used to estimate the response time delay of MR dampers.
Magneto-rhelological(MR) dampers are devices that employ rheological fluids to modify their mechanical properties. Their mechanical simplicity, high dynamic range, lower power requirements, large force capacity, robustness and safe manner of operation in cases of failure have made them attractive devices for semi-active real-time control in civil, aerospace and automotive applications. Time response characteristic is one of the most important technical performances of MR dampers, and response time directly affects the control frequency, application range and the actual effect of MR dampers．In this study, one kind of finite difference solution for predicting the response time of magneto-rheological dampers from “off-state” to “on-state” is put forward. A laminar flow model is used to describe the flow in the MR valve, and a bi-viscous fluid flow model is utilized to describe the relationship of shear stress and shear rate of MR fluid. An explicit difference format is used to discretize the Novior-Stoks equation, and stability condition of this algorithm is built by Von-Neumann stability criterion. The pressure gradient along the flow duct is solved by a dichotomy algorithm with iteration, and the changing curve of the damping force versus time of MR damper is obtained as well. According to the abovementioned numerical algorithm, the damping forces versus time curves from “off-state” to “on-state” of a cylindrical piston type MR damper are computed. Moreover, the MR damper is installed in a material test system(MTS), the magnetic field in the wire circles of the MR damper is “triggered” when the MR damper is imposed to do a constant speed motion, and the damping force curves are recorded. The comparison between numerical results and experimental results indicates that this finite difference algorithm can be used to estimate the response time delay of MR dampers.
2009, 23(3).
Abstract:
In recent years, more attention has been paid on artificial life researches. Artificial life(AL) is a research on regulating gene parameters of digital organisms under complicated problematic environments through natural selections and evolutions to achieve the final emergence of intelligence. Most recent studies focused on solving certain real problems by artificial life methods, yet without much address on the AL life basic mechanism. The real problems are often very complicated, and the proposed methods sometimes seem too simple to handle those problems. This study proposed a new approach in AL research, named “generalized artificial life structure(GALS)”, in which the traditional “gene bits” in genetic algorithms is first replaced by “gene parameters”, which could appear anywhere in GALS. A modeling procedure is taken to normalize the input data, and AL “tissue” is innovated to make AL more complex. GALS is anticipated to contribute significantly to the fitness of AL evolution. The formation of “tissue” begins with some different AL basic cells, and then tissue is produced by the casual selections of one or several of these cells. As a result, the gene parameters, represented by “tissues”, could become highly diversified. This diversification should have obvious effects on improving gene fitness. This study took the innovative method of GALS in a stock forecasting problem under a carefully designed manipulating platform. And the researching results verify that the GALS is successful in improving the gene evolution fitness.
In recent years, more attention has been paid on artificial life researches. Artificial life(AL) is a research on regulating gene parameters of digital organisms under complicated problematic environments through natural selections and evolutions to achieve the final emergence of intelligence. Most recent studies focused on solving certain real problems by artificial life methods, yet without much address on the AL life basic mechanism. The real problems are often very complicated, and the proposed methods sometimes seem too simple to handle those problems. This study proposed a new approach in AL research, named “generalized artificial life structure(GALS)”, in which the traditional “gene bits” in genetic algorithms is first replaced by “gene parameters”, which could appear anywhere in GALS. A modeling procedure is taken to normalize the input data, and AL “tissue” is innovated to make AL more complex. GALS is anticipated to contribute significantly to the fitness of AL evolution. The formation of “tissue” begins with some different AL basic cells, and then tissue is produced by the casual selections of one or several of these cells. As a result, the gene parameters, represented by “tissues”, could become highly diversified. This diversification should have obvious effects on improving gene fitness. This study took the innovative method of GALS in a stock forecasting problem under a carefully designed manipulating platform. And the researching results verify that the GALS is successful in improving the gene evolution fitness.
2009, 23(3).
Abstract:
For the electro-hydraulic servo vibrating system(ESVS) with the characteristics of non-linearity and repeating motion, a novel method, PI-type iterative learning control(ILC), is proposed on the basis of traditional PID control. By using memory ability of computer, the method keeps last time’s tracking error of the system and then applies the error information to the next time’s control process. At the same time, a forgetting factor and a D-type learning law of feedforward fuzzy-inferring referenced displacement error under the optimal objective are employed to enhance the systemic robustness and tracking accuracy. The results of simulation and test reveal that the algorithm has a trait of high repeating precision, and could restrain the influence of nonlinear factors like leaking, external disturbance, aerated oil, etc. Compared with traditional PID control, it could better meet the requirement of nonlinear electro-hydraulic servo vibrating system.
For the electro-hydraulic servo vibrating system(ESVS) with the characteristics of non-linearity and repeating motion, a novel method, PI-type iterative learning control(ILC), is proposed on the basis of traditional PID control. By using memory ability of computer, the method keeps last time’s tracking error of the system and then applies the error information to the next time’s control process. At the same time, a forgetting factor and a D-type learning law of feedforward fuzzy-inferring referenced displacement error under the optimal objective are employed to enhance the systemic robustness and tracking accuracy. The results of simulation and test reveal that the algorithm has a trait of high repeating precision, and could restrain the influence of nonlinear factors like leaking, external disturbance, aerated oil, etc. Compared with traditional PID control, it could better meet the requirement of nonlinear electro-hydraulic servo vibrating system.
2009, 23(3).
Abstract:
When adaptive robust control(ARC) strategy based on backstepping design is applied in pneumatic servo control, accurate pressure tracking in motion is especially necessary for both force and position trajectories tracking of rodless pneumatic cylinders, and therefore an adaptive robust pressure controller is developed in this paper to improve the tracking accuracy of pressure trajectory in the chamber when the pneumatic cylinder is moving. In the proposed adaptive robust pressure controller, off-line fitting of the orifice area and on-line parameter estimation of the flow coefficient are utilized to have improved model compensation, and meanwhile robust feedback and Kalman filter are used to have strong robustness against uncertain nonlinearities, parameter fluctuations and noise. Research results demonstrate that the adaptive robust pressure controller could not only track various pressure trajectories accurately even when the pneumatic cylinder is moving, but also obtain very smooth control input, which indicates the effectiveness of adaptive model compensation. Especially when a step pressure trajectory is tracked under the condition of the movement of a rodless pneumatic cylinder, maximum tracking error of ARC is 4.46 kPa and average tracking error is 0.99 kPa, and steady-state error of ARC could achieve 0.84 kPa, which is very close to the measurement accuracy of pressure transducer.
When adaptive robust control(ARC) strategy based on backstepping design is applied in pneumatic servo control, accurate pressure tracking in motion is especially necessary for both force and position trajectories tracking of rodless pneumatic cylinders, and therefore an adaptive robust pressure controller is developed in this paper to improve the tracking accuracy of pressure trajectory in the chamber when the pneumatic cylinder is moving. In the proposed adaptive robust pressure controller, off-line fitting of the orifice area and on-line parameter estimation of the flow coefficient are utilized to have improved model compensation, and meanwhile robust feedback and Kalman filter are used to have strong robustness against uncertain nonlinearities, parameter fluctuations and noise. Research results demonstrate that the adaptive robust pressure controller could not only track various pressure trajectories accurately even when the pneumatic cylinder is moving, but also obtain very smooth control input, which indicates the effectiveness of adaptive model compensation. Especially when a step pressure trajectory is tracked under the condition of the movement of a rodless pneumatic cylinder, maximum tracking error of ARC is 4.46 kPa and average tracking error is 0.99 kPa, and steady-state error of ARC could achieve 0.84 kPa, which is very close to the measurement accuracy of pressure transducer.
2009, 23(3).
Abstract:
Since the traditional Grübler-Kutzbach criterion fails in many overconstrained mechanisms, developing a general mobility formula is a hot topic lasting for more than 150 years in mechanisms. GOGU systematically investigated various mobility methods, and pointed that the methods were not fit for two kinds of paradoxical overconstrained mechanisms. The mobility on the two kinds of mechanisms is regarded as “Gogu problem”. The Modified Grübler-Kutzbach criterion has solved the mobility of the second kind of mechanisms in “Gogu problem”, and has developed into a systematic mobility methodology. Myard 5R linkage is one of the single-loop mechanisms involved in “Gogu problem”, its joint axes are distributed in space with special geometric conditions, which increases the difficulty of mobility analysis. The study is to calculate the global mobility of the Myard 5R linkage using the mobility methodology. Firstly, the mobility methodology based on screw theory is briefly introduced. Secondly, some homogeneous transforms are performed according to the D-H parameters and the invariance of the linkage plane symmetry is revealed, which provides an idea to judge a plane-symmetric loop. The special geometric features of the axes distribution are discussed as well. Finally, the global mobility of the Myard 5R linkage is determined by the Modified Grübler-Kutzbach criterion. The results show that the methodology can be applied to more paradoxical mechanisms.
Since the traditional Grübler-Kutzbach criterion fails in many overconstrained mechanisms, developing a general mobility formula is a hot topic lasting for more than 150 years in mechanisms. GOGU systematically investigated various mobility methods, and pointed that the methods were not fit for two kinds of paradoxical overconstrained mechanisms. The mobility on the two kinds of mechanisms is regarded as “Gogu problem”. The Modified Grübler-Kutzbach criterion has solved the mobility of the second kind of mechanisms in “Gogu problem”, and has developed into a systematic mobility methodology. Myard 5R linkage is one of the single-loop mechanisms involved in “Gogu problem”, its joint axes are distributed in space with special geometric conditions, which increases the difficulty of mobility analysis. The study is to calculate the global mobility of the Myard 5R linkage using the mobility methodology. Firstly, the mobility methodology based on screw theory is briefly introduced. Secondly, some homogeneous transforms are performed according to the D-H parameters and the invariance of the linkage plane symmetry is revealed, which provides an idea to judge a plane-symmetric loop. The special geometric features of the axes distribution are discussed as well. Finally, the global mobility of the Myard 5R linkage is determined by the Modified Grübler-Kutzbach criterion. The results show that the methodology can be applied to more paradoxical mechanisms.
2009, 23(3).
Abstract:
Increasing frame torsional stiffness of off-road vehicle will lead to the decrease of body torsional deformation, but the increase of torsional loads of frame and suspension system and the decrease of wheel adhesive weight. In severe case, a certain wheel will be out of contact with road surface. Appropriate matching of body, frame and suspension torsional stiffnesses is a difficult problem for off-road vehicle design. In this paper, these theoretically analytic models of the entire vehicle, body, frame and suspension torsional stiffness are constructed based on the geometry and mechanism of a light off-road vehicle’s body, frame and suspension. The body and frame torsional stiffnesses can be calculated by applying body CAE method, meanwhile the suspension’s rolling angle stiffness can be obtained by the bench test of the suspension’s elastic elements. Through fixing the entire vehicle, using sole timber to raise wheels to simulate the road impact on a certain wheel, the entire vehicle torsional stiffness can be calculated on the geometric relation and loads of testing. Finally some appropriate matching principles of the body, frame and suspension torsional stiffness are summarized according to the test and analysis results. The conclusion can reveal the significance of the suspension torsional stiffness on off-road vehicle’s torsion-absorbing capability. The results could serve as a reference for the design of other off-road vehicles.
Increasing frame torsional stiffness of off-road vehicle will lead to the decrease of body torsional deformation, but the increase of torsional loads of frame and suspension system and the decrease of wheel adhesive weight. In severe case, a certain wheel will be out of contact with road surface. Appropriate matching of body, frame and suspension torsional stiffnesses is a difficult problem for off-road vehicle design. In this paper, these theoretically analytic models of the entire vehicle, body, frame and suspension torsional stiffness are constructed based on the geometry and mechanism of a light off-road vehicle’s body, frame and suspension. The body and frame torsional stiffnesses can be calculated by applying body CAE method, meanwhile the suspension’s rolling angle stiffness can be obtained by the bench test of the suspension’s elastic elements. Through fixing the entire vehicle, using sole timber to raise wheels to simulate the road impact on a certain wheel, the entire vehicle torsional stiffness can be calculated on the geometric relation and loads of testing. Finally some appropriate matching principles of the body, frame and suspension torsional stiffness are summarized according to the test and analysis results. The conclusion can reveal the significance of the suspension torsional stiffness on off-road vehicle’s torsion-absorbing capability. The results could serve as a reference for the design of other off-road vehicles.
2009, 23(3).
Abstract:
The turbo air classifier is widely used powder classification equipment in a variety of fields. The flow field characteristics of the turbo air classifier are important basis for the improvement of the turbo air classifier’s structural design. The flow field characteristics of the rotor cage in turbo air classifiers were investigated under different operating conditions by laser Doppler velocimeter(LDV), and a measure diminishing the axial velocity is proposed. The investigation results show that the tangential velocity of the air flow inside the rotor cage is different from the rotary speed of the rotor cage on the same measurement point due to the influences of both the negative pressure at the exit and the rotation of the rotor cage. The tangential velocity of the air flow likewise decreases as the radius decreases in the case of the rotor cage’s low rotary speed. In contrast, the tangential velocity of the air flow increases as the radius decreases in the case of the rotor cage’s high rotary speed. Meanwhile, the vortex inside the rotor cage is found to occur near the pressure side of the blade when the rotor cage’s rotary speed is less than the tangential velocity of air flow. On the contrary, the vortex is found to occur near the blade suction side once the rotor cage’s rotary speed is higher than the tangential velocity of air flow. Inside the rotor cage, the axial velocity could not be disregarded and is largely determined by the distances between the measurement point and the exit.
The turbo air classifier is widely used powder classification equipment in a variety of fields. The flow field characteristics of the turbo air classifier are important basis for the improvement of the turbo air classifier’s structural design. The flow field characteristics of the rotor cage in turbo air classifiers were investigated under different operating conditions by laser Doppler velocimeter(LDV), and a measure diminishing the axial velocity is proposed. The investigation results show that the tangential velocity of the air flow inside the rotor cage is different from the rotary speed of the rotor cage on the same measurement point due to the influences of both the negative pressure at the exit and the rotation of the rotor cage. The tangential velocity of the air flow likewise decreases as the radius decreases in the case of the rotor cage’s low rotary speed. In contrast, the tangential velocity of the air flow increases as the radius decreases in the case of the rotor cage’s high rotary speed. Meanwhile, the vortex inside the rotor cage is found to occur near the pressure side of the blade when the rotor cage’s rotary speed is less than the tangential velocity of air flow. On the contrary, the vortex is found to occur near the blade suction side once the rotor cage’s rotary speed is higher than the tangential velocity of air flow. Inside the rotor cage, the axial velocity could not be disregarded and is largely determined by the distances between the measurement point and the exit.
2009, 23(3).
Abstract:
Metal oxide films prepared by thin film technology have been reported for the potential applications on thin solid electrolyte layers for solid oxide fuel cells(SOFCs). Gadolinia-doped ceria(GDC) thin films and Al2O3 layers on SiO2/Si substrates are successively deposited by RF reactive magnetron sputtering from a cerium-gadolinium (90:10 at.%) alloy target and Al target in O2/Ar gas mixture and then perform post-thermal treatments at 300–700 ℃ and 900 ℃ for 2 h, respectively. Materials characteristics and chemical compositions of GDC films and Al2O3 layers are investigated by X-ray photoelectron spectroscopy(XPS), cross-sectional scanning electron microscopy(SEM), X-ray diffraction(XRD), and atomic force microscopy(AFM). Stoichiometric Al2O3 layers with polycrystalline structures are firstly prepared onto SiO2/Si substrates. A cubic fluorite structure with columnar crystallites of GDC films is successfully deposited on Al2O3/SiO2/Si systems. The chemical composition of 700 ℃-annealed GDC films is (Ce0.91Gd0.09)O1.94 and possesses a higher film density of 7.257 g/cm3. As a result, GDC thin films prepared by RF reactive magnetron sputtering and post-thermal treatments can be used as thin solid electrolyte layers for intermediate temperature SOFCs system as compared to the well-known yttria-stabilized zirconia(YSZ).
Metal oxide films prepared by thin film technology have been reported for the potential applications on thin solid electrolyte layers for solid oxide fuel cells(SOFCs). Gadolinia-doped ceria(GDC) thin films and Al2O3 layers on SiO2/Si substrates are successively deposited by RF reactive magnetron sputtering from a cerium-gadolinium (90:10 at.%) alloy target and Al target in O2/Ar gas mixture and then perform post-thermal treatments at 300–700 ℃ and 900 ℃ for 2 h, respectively. Materials characteristics and chemical compositions of GDC films and Al2O3 layers are investigated by X-ray photoelectron spectroscopy(XPS), cross-sectional scanning electron microscopy(SEM), X-ray diffraction(XRD), and atomic force microscopy(AFM). Stoichiometric Al2O3 layers with polycrystalline structures are firstly prepared onto SiO2/Si substrates. A cubic fluorite structure with columnar crystallites of GDC films is successfully deposited on Al2O3/SiO2/Si systems. The chemical composition of 700 ℃-annealed GDC films is (Ce0.91Gd0.09)O1.94 and possesses a higher film density of 7.257 g/cm3. As a result, GDC thin films prepared by RF reactive magnetron sputtering and post-thermal treatments can be used as thin solid electrolyte layers for intermediate temperature SOFCs system as compared to the well-known yttria-stabilized zirconia(YSZ).
2009, 23(3).
Abstract:
The harmonic wavelet transform(HWT) and its fast realization based on fast Fourier transform(FFT) are introduced. Its ability to maintain the same amplitude-frequency feature is revealed. A new method to construct the time-frequency(TF) spectrum of HWT is proposed, which makes the HWT TF spectrum able to correctly reflect the time-frequency-amplitude distribution of the signal. A new way to calculate the HWT coefficients is proposed. By zero padding the data taken out, the non-decimated coefficients of HWT are obtained. Theoretical analysis shows that the modulus of the coefficients obtained by the new calculation way and living at a certain scale are the envelope of the component in the corresponding frequency band. By taking the cross section of the new TF spectrum, the demodulation for the component at a certain frequency band can be realized. A comparison with the Hilbert demodulation combined with band-pass filtering is done, which indicates for multi-components, the method proposed here is more suitable since it realizes ideal band-pass filtering and avoids pass band selecting. In the end, it is applied to bearing and gearbox fault diagnosis, and the results reflect that it can effectively extract the fault features in the signal.
The harmonic wavelet transform(HWT) and its fast realization based on fast Fourier transform(FFT) are introduced. Its ability to maintain the same amplitude-frequency feature is revealed. A new method to construct the time-frequency(TF) spectrum of HWT is proposed, which makes the HWT TF spectrum able to correctly reflect the time-frequency-amplitude distribution of the signal. A new way to calculate the HWT coefficients is proposed. By zero padding the data taken out, the non-decimated coefficients of HWT are obtained. Theoretical analysis shows that the modulus of the coefficients obtained by the new calculation way and living at a certain scale are the envelope of the component in the corresponding frequency band. By taking the cross section of the new TF spectrum, the demodulation for the component at a certain frequency band can be realized. A comparison with the Hilbert demodulation combined with band-pass filtering is done, which indicates for multi-components, the method proposed here is more suitable since it realizes ideal band-pass filtering and avoids pass band selecting. In the end, it is applied to bearing and gearbox fault diagnosis, and the results reflect that it can effectively extract the fault features in the signal.
2009, 23(3).
Abstract:
The hot bulk deformation processes (such as extrusion, forging and rolling) are efficient ways to produce fine microstructure. The effects of extrusion parameters on the evolved microstructure of directly extruded AZ 31B magnesium alloy were investigated. Extrusion processes were carried out at five different combinations with ram speed ranging from 2 to 8 mm•s–1 and billet temperature ranging from 350 to 450 ℃. The experimental results show that the peak extrusion force decreases with increase in billet temperature and decreases in ram speed. During all the extrusion the profile temperature and die temperature rise continuously. Small particles of secondary phase (β-Mg17Al12) are uniformly distributed near the edge of the extruded profiles whereas their distribution is nonuniform in the centre of the extrudates. The size of secondary phase particles present in the central region of the specimens was found to increase with billet temperature and extrusion speed. All the specimens showed mixed microstructure―In the central region of the specimen, low volume fraction of dynamically recrystallized fine grains presented at the grain boundaries of original coarse grains; but near the edge region, the microstructure consisted nearly equiaxed fine recrystallized grains.
The hot bulk deformation processes (such as extrusion, forging and rolling) are efficient ways to produce fine microstructure. The effects of extrusion parameters on the evolved microstructure of directly extruded AZ 31B magnesium alloy were investigated. Extrusion processes were carried out at five different combinations with ram speed ranging from 2 to 8 mm•s–1 and billet temperature ranging from 350 to 450 ℃. The experimental results show that the peak extrusion force decreases with increase in billet temperature and decreases in ram speed. During all the extrusion the profile temperature and die temperature rise continuously. Small particles of secondary phase (β-Mg17Al12) are uniformly distributed near the edge of the extruded profiles whereas their distribution is nonuniform in the centre of the extrudates. The size of secondary phase particles present in the central region of the specimens was found to increase with billet temperature and extrusion speed. All the specimens showed mixed microstructure―In the central region of the specimen, low volume fraction of dynamically recrystallized fine grains presented at the grain boundaries of original coarse grains; but near the edge region, the microstructure consisted nearly equiaxed fine recrystallized grains.
2009, 23(3).
Abstract:
For building the analytical model of mean temperature in rail universal rolling, the cross-section of workpieces and the profile of horizontal roll and vertical roll are simplified rationally. The mean temperature of the web of rail, the top of rail and the base of rail are considered individually. The temperature rises for plastic deformation and friction incorresponding deformation zone, the temperature drop for contact is calculated on the base of variation principle and energy conservation law. Then the mean temperature is obtained. For verifying the theoretical model, the 18 kg/m light rail universal rolling experiments are accomplished in Yanshan University Rolling Laboratory, China and the surface temperature is measured. The surface temperature is not exact enough to express the true temperature and the mean temperature can show the status of the true temperature basically. So the mean temperature can be used to express the true temperature and this theoretical model and its results can be applied as an important reference to control the temperature of rail universal rolling and the heat treatment of the rolled rail.
For building the analytical model of mean temperature in rail universal rolling, the cross-section of workpieces and the profile of horizontal roll and vertical roll are simplified rationally. The mean temperature of the web of rail, the top of rail and the base of rail are considered individually. The temperature rises for plastic deformation and friction incorresponding deformation zone, the temperature drop for contact is calculated on the base of variation principle and energy conservation law. Then the mean temperature is obtained. For verifying the theoretical model, the 18 kg/m light rail universal rolling experiments are accomplished in Yanshan University Rolling Laboratory, China and the surface temperature is measured. The surface temperature is not exact enough to express the true temperature and the mean temperature can show the status of the true temperature basically. So the mean temperature can be used to express the true temperature and this theoretical model and its results can be applied as an important reference to control the temperature of rail universal rolling and the heat treatment of the rolled rail.
E-mail Alerts
