2011 Vol.24(5)
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2011, 25(5).
Abstract:
The existing research of sequential zoning system and simultaneous zoning system mainly focuses on some optimization problems such as workload balance, product assignment and simulation for each system separately. But there is little research on comparative study between sequential zoning and simultaneous zoning. In order to help the designers to choose the suitable zoning policy for picker-to-parts system reasonably and quickly, a systemic selection method is presented. Essentially, both zoning and batching are order clustering, so the customer order sheet can be divided into many unit grids. After the time formulation in one-dimensional unit was defined, the time models for each zoning policy in two-dimensional space were established using filling curves and sequence models to link the one-dimensional unit grids. In consideration of “U” shaped dual tour into consideration, the subtraction value of order picking time between sequential zoning and simultaneous zoning was defined as the objective function to select the suitable zoning policy based on time models. As it is convergent enough, genetic algorithm is adopted to find the optimal value of order picking time. In the experimental study, 5 different kinds of order/stock keeping unit(SKU) matrices with different densities d and quantities q following uniform distribution were created in order to test the suitability of sequential zoning and simultaneous zoning to different kinds of orders. After parameters setting, experimental orders inputting and iterative computations, the optimal order picking time for each zoning policy was gotten. By observing whether the delta time between them is greater than 0 or not, the suitability of zoning policies for picker-to-parts system were obtained. The significant effect of batch size b, zone number z and density d on suitability was also found by experimental study. The proposed research provides a new method for selection between sequential zoning and simultaneous zoning for picker-to-parts system, and improves the rationality and efficiency of selection process in practical design.
The existing research of sequential zoning system and simultaneous zoning system mainly focuses on some optimization problems such as workload balance, product assignment and simulation for each system separately. But there is little research on comparative study between sequential zoning and simultaneous zoning. In order to help the designers to choose the suitable zoning policy for picker-to-parts system reasonably and quickly, a systemic selection method is presented. Essentially, both zoning and batching are order clustering, so the customer order sheet can be divided into many unit grids. After the time formulation in one-dimensional unit was defined, the time models for each zoning policy in two-dimensional space were established using filling curves and sequence models to link the one-dimensional unit grids. In consideration of “U” shaped dual tour into consideration, the subtraction value of order picking time between sequential zoning and simultaneous zoning was defined as the objective function to select the suitable zoning policy based on time models. As it is convergent enough, genetic algorithm is adopted to find the optimal value of order picking time. In the experimental study, 5 different kinds of order/stock keeping unit(SKU) matrices with different densities d and quantities q following uniform distribution were created in order to test the suitability of sequential zoning and simultaneous zoning to different kinds of orders. After parameters setting, experimental orders inputting and iterative computations, the optimal order picking time for each zoning policy was gotten. By observing whether the delta time between them is greater than 0 or not, the suitability of zoning policies for picker-to-parts system were obtained. The significant effect of batch size b, zone number z and density d on suitability was also found by experimental study. The proposed research provides a new method for selection between sequential zoning and simultaneous zoning for picker-to-parts system, and improves the rationality and efficiency of selection process in practical design.
2011, 25(5).
Abstract:
With jumping mechanisms, soft landing motion is important to protect loads and the mechanisms. This study proposes a leg mechanism for soft landing based on biological motion. Human jumping motion with a load suggests a unique motion for soft landing. The landing model consists of two periods. Jerk is minimized in the first period and force is minimized in the second period. In comparison with other landing models, this model is specialized for soft landing motion protecting an objective part. Given all mechanisms have mass, such model is useful in practical application. For the purpose of realizing soft landing motion, this study proposes a new leg mechanism. The mechanism achieves quick variable transmission with cam and wire. Design process of the cam is explained with dynamics and computation. With the calculated cam shape, the leg mechanism can be driven by constant input voltage for simple control. Robustness against height change is also verified with landing simulation. With 50mm falling experiment, prototype leg mechanism performed soft landing without bounce motion and large sound. The acceleration profile of the body also agrees with the proposed soft landing model.
With jumping mechanisms, soft landing motion is important to protect loads and the mechanisms. This study proposes a leg mechanism for soft landing based on biological motion. Human jumping motion with a load suggests a unique motion for soft landing. The landing model consists of two periods. Jerk is minimized in the first period and force is minimized in the second period. In comparison with other landing models, this model is specialized for soft landing motion protecting an objective part. Given all mechanisms have mass, such model is useful in practical application. For the purpose of realizing soft landing motion, this study proposes a new leg mechanism. The mechanism achieves quick variable transmission with cam and wire. Design process of the cam is explained with dynamics and computation. With the calculated cam shape, the leg mechanism can be driven by constant input voltage for simple control. Robustness against height change is also verified with landing simulation. With 50mm falling experiment, prototype leg mechanism performed soft landing without bounce motion and large sound. The acceleration profile of the body also agrees with the proposed soft landing model.
2011, 25(5).
Abstract:
By using high-power and high-efficiency propulsion systems, current hybrid electric vehicles(HEVs) in market can achieve excellent fuel economy and kinetic performance. However, it is the cost of current HEVs that hinders HEVs coming into widespread use. A novel hybrid electric propulsion system is designed to balance HEV cost and performance for developing markets. A batterysupercapacitor-based hybrid energy storage system(HESS) is used to improve energy conversion efficiency and reduce battery size and cost. An all-in-one-controller(AIOC) which integrates engine electronic control unit(ECU), motor ECU, and HESS management system is developed to save materials and energy, and reduce the influence of distribution parameters on circuit. As for the powertrain configuration, four schemes are presented: belt-driven starter generator(BSG) scheme, four-wheel drive HEV scheme, full HEV scheme, and ranger-extender electric vehicle(EV) scheme. Component selection and parameter matching for the propulsion system are performed, and an energy management strategy is developed based on powertrain configuration and selected components. Forward-facing simulation models are built, comprehending the control strategy based on the optimal engine torque for the low-cost hybrid electric propulsion system. Co-simulation of AVL CRUISE and Matlab/Simulink is presented and the best scheme is selected. The simulation results indicate that, for the best design, fuel consumption in urban driving condition is 4.11 L(100 km) and 0–50 kmh accelerating time is 10.95 s. The proposed research can realize low-cost concept for HEV while achieving satisfactory fuel economy and kinetic performance, and help to improve commercialization of HEVs.
By using high-power and high-efficiency propulsion systems, current hybrid electric vehicles(HEVs) in market can achieve excellent fuel economy and kinetic performance. However, it is the cost of current HEVs that hinders HEVs coming into widespread use. A novel hybrid electric propulsion system is designed to balance HEV cost and performance for developing markets. A batterysupercapacitor-based hybrid energy storage system(HESS) is used to improve energy conversion efficiency and reduce battery size and cost. An all-in-one-controller(AIOC) which integrates engine electronic control unit(ECU), motor ECU, and HESS management system is developed to save materials and energy, and reduce the influence of distribution parameters on circuit. As for the powertrain configuration, four schemes are presented: belt-driven starter generator(BSG) scheme, four-wheel drive HEV scheme, full HEV scheme, and ranger-extender electric vehicle(EV) scheme. Component selection and parameter matching for the propulsion system are performed, and an energy management strategy is developed based on powertrain configuration and selected components. Forward-facing simulation models are built, comprehending the control strategy based on the optimal engine torque for the low-cost hybrid electric propulsion system. Co-simulation of AVL CRUISE and Matlab/Simulink is presented and the best scheme is selected. The simulation results indicate that, for the best design, fuel consumption in urban driving condition is 4.11 L(100 km) and 0–50 kmh accelerating time is 10.95 s. The proposed research can realize low-cost concept for HEV while achieving satisfactory fuel economy and kinetic performance, and help to improve commercialization of HEVs.
2011, 25(5).
Abstract:
The adjacency matrix operations, which connect with configuration transformation correspondingly, can be used for analysis of configuration transformation of metamorphic mechanisms and the corresponding algorithm can easily be simulated by computer. But the adjacency matrix based on monochrome topological graph is not suitable for the topological representation of mechanisms with multiple joints. The method of adjacency matrix operations has its own limitations for analysis of configuration transformation of metamorphic mechanisms because it can only be used in the topological representation of mechanisms with single joints. In order to overcome the drawback of the adjacency matrix, a kind of new matrix named as extended adjacency matrix is proposed to express topological structures of all mechanisms. The extended adjacency matrix is not only suitable for the topological representation of mechanisms with single joints, but also can be used in that of mechanisms with multiple joints. On this basis, a method of matrix operations based on the extended adjacency matrix is proposed to analyze the configuration transformation of metamorphic mechanisms. The method is not only suitable for configuration analysis of metamorphic mechanisms with single joints as well as metamorphic mechanisms with multiple joints. The method is evaluated by calculating two examples representing metamorphic mechanisms with single joint and multiple joints respectively. It can be concluded that the method is effective and correct for analysis of configuration transformation of all metamorphic mechanisms. The proposed method is simple and easy to be achieved by computer programming. It provides a basis for structural synthesis of all metamorphic mechanisms.
The adjacency matrix operations, which connect with configuration transformation correspondingly, can be used for analysis of configuration transformation of metamorphic mechanisms and the corresponding algorithm can easily be simulated by computer. But the adjacency matrix based on monochrome topological graph is not suitable for the topological representation of mechanisms with multiple joints. The method of adjacency matrix operations has its own limitations for analysis of configuration transformation of metamorphic mechanisms because it can only be used in the topological representation of mechanisms with single joints. In order to overcome the drawback of the adjacency matrix, a kind of new matrix named as extended adjacency matrix is proposed to express topological structures of all mechanisms. The extended adjacency matrix is not only suitable for the topological representation of mechanisms with single joints, but also can be used in that of mechanisms with multiple joints. On this basis, a method of matrix operations based on the extended adjacency matrix is proposed to analyze the configuration transformation of metamorphic mechanisms. The method is not only suitable for configuration analysis of metamorphic mechanisms with single joints as well as metamorphic mechanisms with multiple joints. The method is evaluated by calculating two examples representing metamorphic mechanisms with single joint and multiple joints respectively. It can be concluded that the method is effective and correct for analysis of configuration transformation of all metamorphic mechanisms. The proposed method is simple and easy to be achieved by computer programming. It provides a basis for structural synthesis of all metamorphic mechanisms.
2011, 25(5).
Abstract:
The regrinding error is the main factor affecting the eligible length of hob tooth, how to decrease the regrinding error is a hot issue in the research area of hob grinding. At present, researches focus on changing the trajectory of relief moving, because of no unified relief grinding path planning method, the research result is restricted in the practical application. For solving the problem, the calculation model of the hob relief angle is established with the Archimedes relieving motion to analyze the interaction between the increasing relief angle of the hob and the accelerating tooth profile errors. Based on it, the improved relief grinding method of gear hob is proposed with equal relief angle (ERA). Furthermore, the relief grinding method with ERA is developed with the following two steps. Firstly, the convergence numerical solution algorithm of the tooth top curve is designed to form the wheel motion path which is compared with that of traditional grinding. The second step is to establish the solution model of ERA grinding wheel. In order to verify the effect of the method, hob grinding simulation system of 3D solid was built under the AutoCAD environment. The regrinding errors is analyzed by intercepting the hob axial profiles of the various regrinding angles with Boolean operations and further converting it to basic rack tooth, then the simulation example of zero rake straight flute hob is used to compare the regrinding errors between ERA grinding and traditional grinding. Finally, the experiments were implemented on the five-axis CNC relief grinder with the relief motion of ERA grinding driven by cam. The results of experiments show that the method can effectively reduce the regrinding errors of hob and grind expediently gear hob of AA rank and over. This research provide an effective model of relief moving path plan reducing regrinding error, and have practicable value in CNC relief grinder.
The regrinding error is the main factor affecting the eligible length of hob tooth, how to decrease the regrinding error is a hot issue in the research area of hob grinding. At present, researches focus on changing the trajectory of relief moving, because of no unified relief grinding path planning method, the research result is restricted in the practical application. For solving the problem, the calculation model of the hob relief angle is established with the Archimedes relieving motion to analyze the interaction between the increasing relief angle of the hob and the accelerating tooth profile errors. Based on it, the improved relief grinding method of gear hob is proposed with equal relief angle (ERA). Furthermore, the relief grinding method with ERA is developed with the following two steps. Firstly, the convergence numerical solution algorithm of the tooth top curve is designed to form the wheel motion path which is compared with that of traditional grinding. The second step is to establish the solution model of ERA grinding wheel. In order to verify the effect of the method, hob grinding simulation system of 3D solid was built under the AutoCAD environment. The regrinding errors is analyzed by intercepting the hob axial profiles of the various regrinding angles with Boolean operations and further converting it to basic rack tooth, then the simulation example of zero rake straight flute hob is used to compare the regrinding errors between ERA grinding and traditional grinding. Finally, the experiments were implemented on the five-axis CNC relief grinder with the relief motion of ERA grinding driven by cam. The results of experiments show that the method can effectively reduce the regrinding errors of hob and grind expediently gear hob of AA rank and over. This research provide an effective model of relief moving path plan reducing regrinding error, and have practicable value in CNC relief grinder.
2011, 25(5).
Abstract:
Engine spark ignition is an important source for diagnosis of engine faults. Based on the waveform of the ignition pattern, a mechanic can guess what may be the potential malfunctioning parts of an engine with his/her experience and handbooks. However, this manual diagnostic method is imprecise because many spark ignition patterns are very similar. Therefore, a diagnosis needs many trials to identify the malfunctioning parts. Meanwhile the mechanic needs to disassemble and assemble the engine parts for verification. To tackle this problem, an intelligent diagnosis system was established based on ignition patterns. First, the captured patterns were normalized and compressed. Then wavelet packet transform (WPT) was employed to extract the representative features of the ignition patterns. Finally, a classification system was constructed by using multi-class support vector machines (SVM) and the extracted features. The classification system can intelligently classify the most likely engine fault so as to reduce the number of diagnosis trials. Experimental results show that SVM produces higher diagnosis accuracy than the traditional multilayer feedforward neural network. This is the first trial on the combination of WPT and SVM to analyze ignition patterns and diagnose automotive engines.
Engine spark ignition is an important source for diagnosis of engine faults. Based on the waveform of the ignition pattern, a mechanic can guess what may be the potential malfunctioning parts of an engine with his/her experience and handbooks. However, this manual diagnostic method is imprecise because many spark ignition patterns are very similar. Therefore, a diagnosis needs many trials to identify the malfunctioning parts. Meanwhile the mechanic needs to disassemble and assemble the engine parts for verification. To tackle this problem, an intelligent diagnosis system was established based on ignition patterns. First, the captured patterns were normalized and compressed. Then wavelet packet transform (WPT) was employed to extract the representative features of the ignition patterns. Finally, a classification system was constructed by using multi-class support vector machines (SVM) and the extracted features. The classification system can intelligently classify the most likely engine fault so as to reduce the number of diagnosis trials. Experimental results show that SVM produces higher diagnosis accuracy than the traditional multilayer feedforward neural network. This is the first trial on the combination of WPT and SVM to analyze ignition patterns and diagnose automotive engines.
2011, 25(5).
Abstract:
Based on feature compression with orthogonal locality preserving projection(OLPP), a novel fault diagnosis model is proposed in this paper to achieve automation and high-precision of fault diagnosis of rotating machinery. With this model, the original vibration signals of training and test samples are first decomposed through the empirical mode decomposition(EMD), and Shannon entropy is constructed to achieve high-dimensional eigenvectors. In order to replace the traditional feature extraction way which does the selection manually, OLPP is introduced to automatically compress the high-dimensional eigenvectors of training and test samples into the low-dimensional eigenvectors which have better discrimination. After that, the low-dimensional eigenvectors of training samples are input into Morlet wavelet support vector machine(MWSVM) and a trained MWSVM is obtained. Finally, the low-dimensional eigenvectors of test samples are input into the trained MWSVM to carry out fault diagnosis. To evaluate our proposed model, the experiment of fault diagnosis of deep groove ball bearings is made, and the experiment results indicate that the recognition accuracy rate of the proposed diagnosis model for outer race crack、inner race crack and ball crack is more than 90%. Compared to the existing approaches, the proposed diagnosis model combines the strengths of EMD in fault feature extraction, OLPP in feature compression and MWSVM in pattern recognition, and realizes the automation and high-precision of fault diagnosis.
Based on feature compression with orthogonal locality preserving projection(OLPP), a novel fault diagnosis model is proposed in this paper to achieve automation and high-precision of fault diagnosis of rotating machinery. With this model, the original vibration signals of training and test samples are first decomposed through the empirical mode decomposition(EMD), and Shannon entropy is constructed to achieve high-dimensional eigenvectors. In order to replace the traditional feature extraction way which does the selection manually, OLPP is introduced to automatically compress the high-dimensional eigenvectors of training and test samples into the low-dimensional eigenvectors which have better discrimination. After that, the low-dimensional eigenvectors of training samples are input into Morlet wavelet support vector machine(MWSVM) and a trained MWSVM is obtained. Finally, the low-dimensional eigenvectors of test samples are input into the trained MWSVM to carry out fault diagnosis. To evaluate our proposed model, the experiment of fault diagnosis of deep groove ball bearings is made, and the experiment results indicate that the recognition accuracy rate of the proposed diagnosis model for outer race crack、inner race crack and ball crack is more than 90%. Compared to the existing approaches, the proposed diagnosis model combines the strengths of EMD in fault feature extraction, OLPP in feature compression and MWSVM in pattern recognition, and realizes the automation and high-precision of fault diagnosis.
2011, 25(5).
Abstract:
The hydraulic caliper disc brake system with air-over-oil is widely adopted at present for heavy vehicles, which makes use of air pressure system propelling the hydraulic pressure system acting on friction plates divided and combined for braking. There are some disadvantages such as pneumatic components failure, dust polluted and produce lots of heat in hydraulic caliper disc brake system. Moreover, considering the demands of the high speed, heavy weight, heavy load and fast brake of heavy vehicles, the full power hydraulic brake system based on double pipelines for heavy vehicles is designed and analyzed in this paper. The scheme of the full power hydraulic brake system, in which the triloculare cylinder is controlled by dual brake valve, is adopted in the brake system. The full power hydraulic brake system can accomplish steering brake, parking brake and emergent brake for heavy vehicles. Furthermore, electronic control system that is responsible for coordinating the work of hydraulic decelerator and hydraulic brake system is developed for different speed brakes. Based on the analysis of the influence of composed unit and connecting pipeline on braking performance, the nonlinear mathematic model is established for the full power hydraulic brake system. The braking completion time and braking pressure in braking performance of the double-pipeline steering brake and parking brake are discussed by means of simulation experiments based on Matlab/Simulink, and the simulation results prove that the braking performance of steering brake and parking brake meets the designing requirement of the full power hydraulic brake system. Moreover, the test-bed experiments of the brake system for heavy vehicles are carried out. The experimental data prove that the braking performance achieves the goal of the design, and that the full power hydraulic brake system based on double pipelines can effectively enhance braking performance, ensure braking reliability and security for heavy vehicles.
The hydraulic caliper disc brake system with air-over-oil is widely adopted at present for heavy vehicles, which makes use of air pressure system propelling the hydraulic pressure system acting on friction plates divided and combined for braking. There are some disadvantages such as pneumatic components failure, dust polluted and produce lots of heat in hydraulic caliper disc brake system. Moreover, considering the demands of the high speed, heavy weight, heavy load and fast brake of heavy vehicles, the full power hydraulic brake system based on double pipelines for heavy vehicles is designed and analyzed in this paper. The scheme of the full power hydraulic brake system, in which the triloculare cylinder is controlled by dual brake valve, is adopted in the brake system. The full power hydraulic brake system can accomplish steering brake, parking brake and emergent brake for heavy vehicles. Furthermore, electronic control system that is responsible for coordinating the work of hydraulic decelerator and hydraulic brake system is developed for different speed brakes. Based on the analysis of the influence of composed unit and connecting pipeline on braking performance, the nonlinear mathematic model is established for the full power hydraulic brake system. The braking completion time and braking pressure in braking performance of the double-pipeline steering brake and parking brake are discussed by means of simulation experiments based on Matlab/Simulink, and the simulation results prove that the braking performance of steering brake and parking brake meets the designing requirement of the full power hydraulic brake system. Moreover, the test-bed experiments of the brake system for heavy vehicles are carried out. The experimental data prove that the braking performance achieves the goal of the design, and that the full power hydraulic brake system based on double pipelines can effectively enhance braking performance, ensure braking reliability and security for heavy vehicles.
2011, 25(5).
Abstract:
Fourier Descriptors (FD) has been widely used in image analysis and computer vision for shape recognition as they can be made independent of translation, rotation, as well as scaling. They have also been used for developing methods for the analysis and synthesis of four-bar linkages for path generation. This paper focuses on a comparative study of Fourier descriptors derived from various shape signatures of planar closed curves. This includes representations based on Cartesian coordinates, centroid distance, cumulative angle, and curvature. The comparison is conducted not only using commonly used criteria for shape representation and identification but also in the context of shape based retrieval of kinematic constraints for task centered mechanism design. Examples are provided to seek to extract geometric constraints such as circle, circular arc, ellipse and line-segment from a given motion.
Fourier Descriptors (FD) has been widely used in image analysis and computer vision for shape recognition as they can be made independent of translation, rotation, as well as scaling. They have also been used for developing methods for the analysis and synthesis of four-bar linkages for path generation. This paper focuses on a comparative study of Fourier descriptors derived from various shape signatures of planar closed curves. This includes representations based on Cartesian coordinates, centroid distance, cumulative angle, and curvature. The comparison is conducted not only using commonly used criteria for shape representation and identification but also in the context of shape based retrieval of kinematic constraints for task centered mechanism design. Examples are provided to seek to extract geometric constraints such as circle, circular arc, ellipse and line-segment from a given motion.
2011, 25(5).
Abstract:
The laser provides a controllable means of supplying localized energy for solder joint formation and is a valuable tool in electronics manufacture. Diode laser soldering for fine pitch QFP devices were carried out with Sn-Ag-Cu lead-free solder and Sn-Pb solder respectively, and the mechanical properties of micro-joints of the QFP devices were tested and studied by STR-1000 micro-joints tester. The results indicate that sound QFP micro-joints without bridging or solder ball are gained by means of diode laser soldering method with appropriate laser processing parameters, and the pitch of the QFP devices is as fine as to 0.4mm. Tensile strength of QFP micro-joints increases gradually with the increase of laser output power, the maximum tensile strength presents when the laser output power increase to a certain value. The results also indicate that the mechanical properties of QFP micro-joints soldered by diode laser soldering system are better than those of QFP micro-joints soldered by IR reflow soldering method. The experimental results may provide a theory guide for investigation of diode laser soldering.
The laser provides a controllable means of supplying localized energy for solder joint formation and is a valuable tool in electronics manufacture. Diode laser soldering for fine pitch QFP devices were carried out with Sn-Ag-Cu lead-free solder and Sn-Pb solder respectively, and the mechanical properties of micro-joints of the QFP devices were tested and studied by STR-1000 micro-joints tester. The results indicate that sound QFP micro-joints without bridging or solder ball are gained by means of diode laser soldering method with appropriate laser processing parameters, and the pitch of the QFP devices is as fine as to 0.4mm. Tensile strength of QFP micro-joints increases gradually with the increase of laser output power, the maximum tensile strength presents when the laser output power increase to a certain value. The results also indicate that the mechanical properties of QFP micro-joints soldered by diode laser soldering system are better than those of QFP micro-joints soldered by IR reflow soldering method. The experimental results may provide a theory guide for investigation of diode laser soldering.
2011, 25(5).
Abstract:
Thermally Grown Oxide (TGO) is a dominating component in controlling the effectiveness of thermal barrier coating. During the growth of TGO, whether we could homogeneously distribute Al atom on the TGO and the intermediate metal layer will be the key factor in forming TGO with continuous, uniform and single-ingredient (Al2O3). In this experiment, we bombarded particles on to the metallic bound layer. We studied the influence of supersonic particle bombardment on the diffusion of Al. We hope to control the growth of TGO by monitoring the diffusion of Al. Thermal barrier coating (TBC), which consists of a NiCoCrAlY bond coat and a ZrO2-8Y2O3 (wt. %) topcoat (TC), is fabricated on the nickel-base superalloy by air plasma spray (APS). NiCoCrAlY bond coat is treated by supersonic fine particles bombarding (SFPB). The morphology, oxidation behavior of TBC and phase are characterized by scanning electron microscope (SEM) equipped with an energy dispersive spectromrter (EDS) and X-ray diffractometer (XRD). The influence of supersonic fine particles bombarding technique on the service life of thermal barrier coating is studied. The results show that SFPB technique improves the flaw of excessive surface undulation in the as-sprayed bond coat. A continuous, uniform and single-ingredient (Al2O3) TGO can quickly form in the SFPB TBC during high temperature oxidation process. The thickening of TGO is relatively slow. These will effectively suppress the formation of other non-protective oxides. Therefore, SFPB technique reduces the growth stress level generated by the continuous growth of TGO, and also avoids the stress concentration induced by formation of the large particle spinal oxide. Thermal barrier coating still remains well after 350 thermal cycles. The service life of TBC is improved. The proposed research provides theoretical basis and technical references to further improve and enhance the SFPB technique.
Thermally Grown Oxide (TGO) is a dominating component in controlling the effectiveness of thermal barrier coating. During the growth of TGO, whether we could homogeneously distribute Al atom on the TGO and the intermediate metal layer will be the key factor in forming TGO with continuous, uniform and single-ingredient (Al2O3). In this experiment, we bombarded particles on to the metallic bound layer. We studied the influence of supersonic particle bombardment on the diffusion of Al. We hope to control the growth of TGO by monitoring the diffusion of Al. Thermal barrier coating (TBC), which consists of a NiCoCrAlY bond coat and a ZrO2-8Y2O3 (wt. %) topcoat (TC), is fabricated on the nickel-base superalloy by air plasma spray (APS). NiCoCrAlY bond coat is treated by supersonic fine particles bombarding (SFPB). The morphology, oxidation behavior of TBC and phase are characterized by scanning electron microscope (SEM) equipped with an energy dispersive spectromrter (EDS) and X-ray diffractometer (XRD). The influence of supersonic fine particles bombarding technique on the service life of thermal barrier coating is studied. The results show that SFPB technique improves the flaw of excessive surface undulation in the as-sprayed bond coat. A continuous, uniform and single-ingredient (Al2O3) TGO can quickly form in the SFPB TBC during high temperature oxidation process. The thickening of TGO is relatively slow. These will effectively suppress the formation of other non-protective oxides. Therefore, SFPB technique reduces the growth stress level generated by the continuous growth of TGO, and also avoids the stress concentration induced by formation of the large particle spinal oxide. Thermal barrier coating still remains well after 350 thermal cycles. The service life of TBC is improved. The proposed research provides theoretical basis and technical references to further improve and enhance the SFPB technique.
2011, 25(5).
Abstract:
Fuze micro-electro-mechanical system(MEMS) has become a popular subject in recent years. Studies have been done for the application of MEMS-based fuze safety and arm devices. The existing researches mainly focused on reducing the cost and volume of the fuze safety device. The reduction in volume allows more payload and, thus, makes small-caliber rounds more effective and the weapon system more affordable. At present, MEMS-based fuze safety devices are fabricated mainly by using deep reactive ion ething or LIGA technology, and the fabrication process research on the fuze MEMS safety device is in the exploring stage. In this paper, a new micro fabrication method of metal-based fuze MEMS safety device is presented based on ultra violet(UV)-LIGA technology. The method consists of SU-8 thick photoresist lithography process, micro electroforming process, no back plate growing process, and SU-8 photoresist sacrificial layer process. Three kinds of double-layer moveable metal devices have been fabricated on metal substrates directly with the method. Because UV-LIGA technology and no back plate growing technology are introduced, the production cycle is shortened and the cost is reduced. The smallest dimension of the devices is 40 m, which meets the requirement of size. To evaluate the adhesion property between electroforming deposit layer and substrate qualitatively, the impact experiments have been done on the device samples. The experimental result shows that the samples are still in good condition and workable after undergoing impact pulses with 20 kg peak and 150 s duration and completely met the requirement of strength. The presented fabrication method provides a new option for the development of MEMS fuze and is helpful for the fabrication of similar kinds of micro devices.
Fuze micro-electro-mechanical system(MEMS) has become a popular subject in recent years. Studies have been done for the application of MEMS-based fuze safety and arm devices. The existing researches mainly focused on reducing the cost and volume of the fuze safety device. The reduction in volume allows more payload and, thus, makes small-caliber rounds more effective and the weapon system more affordable. At present, MEMS-based fuze safety devices are fabricated mainly by using deep reactive ion ething or LIGA technology, and the fabrication process research on the fuze MEMS safety device is in the exploring stage. In this paper, a new micro fabrication method of metal-based fuze MEMS safety device is presented based on ultra violet(UV)-LIGA technology. The method consists of SU-8 thick photoresist lithography process, micro electroforming process, no back plate growing process, and SU-8 photoresist sacrificial layer process. Three kinds of double-layer moveable metal devices have been fabricated on metal substrates directly with the method. Because UV-LIGA technology and no back plate growing technology are introduced, the production cycle is shortened and the cost is reduced. The smallest dimension of the devices is 40 m, which meets the requirement of size. To evaluate the adhesion property between electroforming deposit layer and substrate qualitatively, the impact experiments have been done on the device samples. The experimental result shows that the samples are still in good condition and workable after undergoing impact pulses with 20 kg peak and 150 s duration and completely met the requirement of strength. The presented fabrication method provides a new option for the development of MEMS fuze and is helpful for the fabrication of similar kinds of micro devices.
2011, 25(5).
Abstract:
In the current research for parachute flow field nowadays, the size of parachutes in previous research are so large compared with their carriers that the effects of the carriers wake flow to parachute are always neglected. Different from such large parachutes, the parachute size in this paper is on the same magnitude with the carrier, thus, the carrier can obviously affect the parachute flow field. In this paper, flow field characteristics of small parachute for projectile decelerating are researched through two approaches, namely, computational fluid dynamics (CFD) simulation and wind tunnel tests. Three parachutes with various sizes are chosen for study. Firstly, the CFD simulation of flow field around these parachutes is carried out, and then the CFD simulation of parachute-projectile systems is executed. According to the simulation results, the phenomenon is observed that in the simulations of parachutes there are two vortex-rings at the wind shadow of parachutes, however, in the second simulations of parachute-projectile systems, two additional vortex-rings emerge inside the parachutes. Due to these two inner vortex-rings, the pressure inside parachutes decreases. As a result, the drag of parachute in simulation of parachute-projectile systems is about 20% smaller compared with the prior one. In order to verify the numerical results of CFD simulations, wind tunnel tests are employed. In terms of the data of the wind tunnel tests, the CFD simulation for flow field characteristics is reasonable and feasible. The results of both CFD simulation and wind tunnel tests demonstrated the influence of projectile wake flow to parachute drag can not be neglected if the parachute size is on the same magnitude with projectile. The influence to parachute drag from the ratio of projectile diameter to parachute diameter is also analyzed both in CFD simulations and wind tunnel tests. The approach combined CFD simulation and wind tunnel tests proposed can be used to guide the design of such parachute whose size is on the same magnitude with carrier.
In the current research for parachute flow field nowadays, the size of parachutes in previous research are so large compared with their carriers that the effects of the carriers wake flow to parachute are always neglected. Different from such large parachutes, the parachute size in this paper is on the same magnitude with the carrier, thus, the carrier can obviously affect the parachute flow field. In this paper, flow field characteristics of small parachute for projectile decelerating are researched through two approaches, namely, computational fluid dynamics (CFD) simulation and wind tunnel tests. Three parachutes with various sizes are chosen for study. Firstly, the CFD simulation of flow field around these parachutes is carried out, and then the CFD simulation of parachute-projectile systems is executed. According to the simulation results, the phenomenon is observed that in the simulations of parachutes there are two vortex-rings at the wind shadow of parachutes, however, in the second simulations of parachute-projectile systems, two additional vortex-rings emerge inside the parachutes. Due to these two inner vortex-rings, the pressure inside parachutes decreases. As a result, the drag of parachute in simulation of parachute-projectile systems is about 20% smaller compared with the prior one. In order to verify the numerical results of CFD simulations, wind tunnel tests are employed. In terms of the data of the wind tunnel tests, the CFD simulation for flow field characteristics is reasonable and feasible. The results of both CFD simulation and wind tunnel tests demonstrated the influence of projectile wake flow to parachute drag can not be neglected if the parachute size is on the same magnitude with projectile. The influence to parachute drag from the ratio of projectile diameter to parachute diameter is also analyzed both in CFD simulations and wind tunnel tests. The approach combined CFD simulation and wind tunnel tests proposed can be used to guide the design of such parachute whose size is on the same magnitude with carrier.
2011, 25(5).
Abstract:
Recent literature on walking robots deals predominantly with multi-degrees-of-freedom leg mechanisms and machines capable of adopting several gaits. This paper explores the other end of the spectrum suggesting mechanisms derived from a four bar coupler curve for a one degree of freedom walking robot. Simulation of the walk indicates that body of the robot is able to move with low variation in velocity. The best strategy for changing the gait to enable the robot to walk over obstacles and the effect of change in length of different links are explored to open up the possibility of a two degree of freedom walking robot with the capability of changing its gait, suitable as a low cost unit for several applications. Such rugged units would permit the use of an IC engine as the primary source of power and could be of utility in installations where electronics may not be functional. In simple walking machines the foot of a leg is usually required to trace a D shaped curve with respect to the chassis. In this paper we begin with a Hoecken mechanism capable of tracing such a curve. The foot is required to move parallel to itself and the same could be achieved using a six or eight link mechanism. A few such devices have been synthesized in this paper and their motion properties compared. The study also covers the possibility of providing adjustments to vary the step length and height of the foots movement.
Recent literature on walking robots deals predominantly with multi-degrees-of-freedom leg mechanisms and machines capable of adopting several gaits. This paper explores the other end of the spectrum suggesting mechanisms derived from a four bar coupler curve for a one degree of freedom walking robot. Simulation of the walk indicates that body of the robot is able to move with low variation in velocity. The best strategy for changing the gait to enable the robot to walk over obstacles and the effect of change in length of different links are explored to open up the possibility of a two degree of freedom walking robot with the capability of changing its gait, suitable as a low cost unit for several applications. Such rugged units would permit the use of an IC engine as the primary source of power and could be of utility in installations where electronics may not be functional. In simple walking machines the foot of a leg is usually required to trace a D shaped curve with respect to the chassis. In this paper we begin with a Hoecken mechanism capable of tracing such a curve. The foot is required to move parallel to itself and the same could be achieved using a six or eight link mechanism. A few such devices have been synthesized in this paper and their motion properties compared. The study also covers the possibility of providing adjustments to vary the step length and height of the foots movement.
2011, 25(5).
Abstract:
Nowadays, how to enhance the maneuverability of autonomous underwater vehicles (AUVs) is an important issue in the domain of international navigation in that most AUVs just have a single function of underwater navigation or submarine movement, while the design of thrusters is the key of solving the problem. The multi-moving state autonomous underwater vehicle in this paper can achieve four functions, such as wheels, legs, thrust, and course control depend on the characteristics of spatial deflexion and continual circumgyratetion of the flexible transmission shaft. A new wheel propeller for the multi-moving state autonomous underwater vehicle is presented through analyzing the mechanical characteristics of the ducted propeller and the contracted and loaded tip (CLT) propeller. Then the computational fluid dynamics (CFD) method is used to simulate numerically different propellers open-water performance by using the Reynolds-averaged Navier-Stokes (RANS) equations and Reynolds stress model (RSM) based on sub-domains hybrid meshes. The predicted thrust coefficients, torque coefficients and pressure of the propellers agree well with the experimental data of their open-water performance. The good consistency shows that the numerical method has good accuracy in the prediction of propeller open-water performance, which guides to design the wheel propeller. Moreover, for the sake of ensuring the security and stability of the AUV when it is moving on the ground, finite element method is used to simulate numerically the intensity and vibration characteristics. The proposed final wheel propeller D4-70 (WPD4-70) has preferable open-water performance and intensity characteristics, which can realize the agile maneuverability of the multi-moving state autonomous underwater vehicle.
Nowadays, how to enhance the maneuverability of autonomous underwater vehicles (AUVs) is an important issue in the domain of international navigation in that most AUVs just have a single function of underwater navigation or submarine movement, while the design of thrusters is the key of solving the problem. The multi-moving state autonomous underwater vehicle in this paper can achieve four functions, such as wheels, legs, thrust, and course control depend on the characteristics of spatial deflexion and continual circumgyratetion of the flexible transmission shaft. A new wheel propeller for the multi-moving state autonomous underwater vehicle is presented through analyzing the mechanical characteristics of the ducted propeller and the contracted and loaded tip (CLT) propeller. Then the computational fluid dynamics (CFD) method is used to simulate numerically different propellers open-water performance by using the Reynolds-averaged Navier-Stokes (RANS) equations and Reynolds stress model (RSM) based on sub-domains hybrid meshes. The predicted thrust coefficients, torque coefficients and pressure of the propellers agree well with the experimental data of their open-water performance. The good consistency shows that the numerical method has good accuracy in the prediction of propeller open-water performance, which guides to design the wheel propeller. Moreover, for the sake of ensuring the security and stability of the AUV when it is moving on the ground, finite element method is used to simulate numerically the intensity and vibration characteristics. The proposed final wheel propeller D4-70 (WPD4-70) has preferable open-water performance and intensity characteristics, which can realize the agile maneuverability of the multi-moving state autonomous underwater vehicle.
2011, 25(5).
Abstract:
The currently prevalent machine performance degradation assessment techniques involve estimating a machines current condition based upon the recognition of indications of failure features, which entail complete data collected in different conditions. However, failure data are always hard to acquire, thus making those techniques hard to be applied. In this paper, a novel method which does not need failure history data is introduced. Wavelet packet decomposition(WPD) is used to extract features from raw signals, principal component analysis(PCA) is utilized to reduce feature dimensions, and Gaussian mixture model(GMM) is then applied to approximate the feature space distributions. Single-channel confidence value(SCV) is calculated by the overlap between GMM of the monitoring condition and that of the normal condition, which can indicate the performance of single-channel. Furthermore, multi-channel confidence value(MCV), which can be deemed as the overall performance index of multi-channel, is calculated via logistic regression(LR) and that the task of decision-level sensor fusion is also completed. Both SCV and MCV can serve as the basis on which proactive maintenance measures can be taken, thus preventing machine breakdown. The method has been adopted to assess the performance of the turbine of a centrifugal compressor in a factory of Petro-China, and the result shows that it can effectively complete this task. The proposed method has engineering significance for machine performance degradation assessment.
The currently prevalent machine performance degradation assessment techniques involve estimating a machines current condition based upon the recognition of indications of failure features, which entail complete data collected in different conditions. However, failure data are always hard to acquire, thus making those techniques hard to be applied. In this paper, a novel method which does not need failure history data is introduced. Wavelet packet decomposition(WPD) is used to extract features from raw signals, principal component analysis(PCA) is utilized to reduce feature dimensions, and Gaussian mixture model(GMM) is then applied to approximate the feature space distributions. Single-channel confidence value(SCV) is calculated by the overlap between GMM of the monitoring condition and that of the normal condition, which can indicate the performance of single-channel. Furthermore, multi-channel confidence value(MCV), which can be deemed as the overall performance index of multi-channel, is calculated via logistic regression(LR) and that the task of decision-level sensor fusion is also completed. Both SCV and MCV can serve as the basis on which proactive maintenance measures can be taken, thus preventing machine breakdown. The method has been adopted to assess the performance of the turbine of a centrifugal compressor in a factory of Petro-China, and the result shows that it can effectively complete this task. The proposed method has engineering significance for machine performance degradation assessment.
2011, 25(5).
Abstract:
As the differences of sensors precision and some random factors are difficult to control, the actual measurement signals are far from the target signals that affect the reliability and precision of rotating machinery fault diagnosis. The traditional signal processing methods, such as classical inference and weighted averaging algorithm usually lack dynamic adaptability that is easy for trends to cause the faults to be misjudged or left out. To enhance the measuring veracity and precision of vibration signal in rotary machine multi-sensor vibration signal fault diagnosis, a novel data level fusion approach is presented on the basis of correlation function analysis to fast determine the weighted value of multi-sensor vibration signals. The approach doesn’t require knowing the prior information about sensors, and the weighted value of sensors can be confirmed depending on the correlation measure of real-time data tested in the data level fusion process. It gives greater weighted value to the greater correlation measure of sensor signals, and vice versa. The approach can effectively suppress large errors and even can still fuse data in the case of sensor failures because it takes full advantage of sensors own-information to determine the weighted value. Moreover, it has good performance of anti-jamming due to the correlation measures between noise and effective signals are usually small. Through the simulation of typical signal collected from multi-sensors, the comparative analysis of dynamic adaptability and fault tolerance between the proposed approach and traditional weighted averaging approach is taken. Finally, the rotor dynamics and integrated fault simulator is taken as an example to verify the feasibility and advantages of the proposed approach, it is shown that the multi-sensor data level fusion based on correlation function weighted approach is better than the traditional weighted average approach with respect to fusion precision and dynamic adaptability. Meantime, the approach is adaptable and easy to use, can be applied to other areas of vibration measurement.
As the differences of sensors precision and some random factors are difficult to control, the actual measurement signals are far from the target signals that affect the reliability and precision of rotating machinery fault diagnosis. The traditional signal processing methods, such as classical inference and weighted averaging algorithm usually lack dynamic adaptability that is easy for trends to cause the faults to be misjudged or left out. To enhance the measuring veracity and precision of vibration signal in rotary machine multi-sensor vibration signal fault diagnosis, a novel data level fusion approach is presented on the basis of correlation function analysis to fast determine the weighted value of multi-sensor vibration signals. The approach doesn’t require knowing the prior information about sensors, and the weighted value of sensors can be confirmed depending on the correlation measure of real-time data tested in the data level fusion process. It gives greater weighted value to the greater correlation measure of sensor signals, and vice versa. The approach can effectively suppress large errors and even can still fuse data in the case of sensor failures because it takes full advantage of sensors own-information to determine the weighted value. Moreover, it has good performance of anti-jamming due to the correlation measures between noise and effective signals are usually small. Through the simulation of typical signal collected from multi-sensors, the comparative analysis of dynamic adaptability and fault tolerance between the proposed approach and traditional weighted averaging approach is taken. Finally, the rotor dynamics and integrated fault simulator is taken as an example to verify the feasibility and advantages of the proposed approach, it is shown that the multi-sensor data level fusion based on correlation function weighted approach is better than the traditional weighted average approach with respect to fusion precision and dynamic adaptability. Meantime, the approach is adaptable and easy to use, can be applied to other areas of vibration measurement.
2011, 25(5).
Abstract:
An extensive research activity has been focused on the upper and lower limbs of humanoid robots. However, due to mechanical design difficulties and complex control of multi-body system, the torso of humanoid robot is somehow a neglected or simplified design part. In this paper, operation performance of a new waist-trunk system as torso for humanoid robots is presented through results of lab experimental tests. The proposed waist-trunk system is composed of two 3 DOFs (degrees of freedom) parallel manipulators, which are connected in a serial chain architecture. A prototype is built by using two prototypes of CaPaMan (Cassino Parallel Manipulator), which are convenient stiff architectures with easy-operation characteristics. Experimental tests are carried out with the aims to imitate lateral-bending and transverse-rotation movements of human torso. Operation performances like displacements, accelerations, and actuation torque are measured for a performance evaluation and design characterization of the used manipulator solution imitating human torso. Experimental test results are illustrated and discussed to show the practical operation feasibility of the proposed architecture and the operation characteristics of the built prototype.
An extensive research activity has been focused on the upper and lower limbs of humanoid robots. However, due to mechanical design difficulties and complex control of multi-body system, the torso of humanoid robot is somehow a neglected or simplified design part. In this paper, operation performance of a new waist-trunk system as torso for humanoid robots is presented through results of lab experimental tests. The proposed waist-trunk system is composed of two 3 DOFs (degrees of freedom) parallel manipulators, which are connected in a serial chain architecture. A prototype is built by using two prototypes of CaPaMan (Cassino Parallel Manipulator), which are convenient stiff architectures with easy-operation characteristics. Experimental tests are carried out with the aims to imitate lateral-bending and transverse-rotation movements of human torso. Operation performances like displacements, accelerations, and actuation torque are measured for a performance evaluation and design characterization of the used manipulator solution imitating human torso. Experimental test results are illustrated and discussed to show the practical operation feasibility of the proposed architecture and the operation characteristics of the built prototype.
2011, 25(5).
Abstract:
The vibration signals of machinery with various faults often show clear nonlinear characteristics. Currently, fractal dimension analysis as the common useful method for nonlinear signal analysis, is a kind of single fractal form, which only reflects the overall irregularity of signals, but cannot describe its local scaling properties. For comprehensive revealing of internal properties, a combinatorial method based on band-phase-randomized(BPR) surrogate data and multifractal is introduced. BPR surrogate data method is effective to eliminate nonlinearity in specified frequency band for a fault signal, which can be utilized to detect nonlinear degree in whole fault signal by nonlinear titration method, and the overall nonlinear distribution of fault signal is displayed in nonlinear characteristic curve that can be used to analyze the fault signal qualitatively. Then multifractal theory as a quantitative analysis method is used to describe geometrical characteristics and local scaling properties, and asymmetry coefficient of multifractal spectrum and multifractal entropy for fault signals are extracted as new criterions to diagnose machinery faults. Several typical faults include rotor misalignment, transversal crack, and static-dynamic rubbing fault are analyzed, and the results indicate that those faults can be distinguished by the proposed method effectively, which provides a qualitative and quantitative analysis way in the field of machinery fault diagnosis.
The vibration signals of machinery with various faults often show clear nonlinear characteristics. Currently, fractal dimension analysis as the common useful method for nonlinear signal analysis, is a kind of single fractal form, which only reflects the overall irregularity of signals, but cannot describe its local scaling properties. For comprehensive revealing of internal properties, a combinatorial method based on band-phase-randomized(BPR) surrogate data and multifractal is introduced. BPR surrogate data method is effective to eliminate nonlinearity in specified frequency band for a fault signal, which can be utilized to detect nonlinear degree in whole fault signal by nonlinear titration method, and the overall nonlinear distribution of fault signal is displayed in nonlinear characteristic curve that can be used to analyze the fault signal qualitatively. Then multifractal theory as a quantitative analysis method is used to describe geometrical characteristics and local scaling properties, and asymmetry coefficient of multifractal spectrum and multifractal entropy for fault signals are extracted as new criterions to diagnose machinery faults. Several typical faults include rotor misalignment, transversal crack, and static-dynamic rubbing fault are analyzed, and the results indicate that those faults can be distinguished by the proposed method effectively, which provides a qualitative and quantitative analysis way in the field of machinery fault diagnosis.
2011, 25(5).
Abstract:
Numerical solutions could not perform rapid system-level simulation of the behavior of micro-electro-mechanical systems (MEMS) and analytic solutions for the describing partial differential equations are only available for simple geometries. Model order reduction (MOR) can extract approximate low-order model from the original large scale system. Conventional model order reduction algorithm is based on first-order system model, however, most structure mechanical MEMS systems are naturally second-order in time. For the purpose of solving the above problem, a direct second-order system model order reduction approach based on Krylov subspace projection for the coupled dynamic study of electrostatic torsional micromirrors is presented. The block Arnoldi process is applied to create the orthonormal vectors to construct the projection matrix, which enables the extraction of the low order model from the discretized system assembled through finite element analysis. The transfer functions of the reduced order model and the original model are expanded to demonstrate the moment-matching property of the second-order model reduction algorithm. The torsion and bending effect are included in the finite element model, and the squeeze film damping effect is considered as well. An empirical method considering relative error convergence is adopted to obtain the optimal choice of the order for the reduced model. A comparison research between the full model and the reduced model is carried out. The modeling accuracy and computation efficiency of the presented second-order model reduction method are confirmed by the comparison research results. The research provides references for MOR of MEMS.
Numerical solutions could not perform rapid system-level simulation of the behavior of micro-electro-mechanical systems (MEMS) and analytic solutions for the describing partial differential equations are only available for simple geometries. Model order reduction (MOR) can extract approximate low-order model from the original large scale system. Conventional model order reduction algorithm is based on first-order system model, however, most structure mechanical MEMS systems are naturally second-order in time. For the purpose of solving the above problem, a direct second-order system model order reduction approach based on Krylov subspace projection for the coupled dynamic study of electrostatic torsional micromirrors is presented. The block Arnoldi process is applied to create the orthonormal vectors to construct the projection matrix, which enables the extraction of the low order model from the discretized system assembled through finite element analysis. The transfer functions of the reduced order model and the original model are expanded to demonstrate the moment-matching property of the second-order model reduction algorithm. The torsion and bending effect are included in the finite element model, and the squeeze film damping effect is considered as well. An empirical method considering relative error convergence is adopted to obtain the optimal choice of the order for the reduced model. A comparison research between the full model and the reduced model is carried out. The modeling accuracy and computation efficiency of the presented second-order model reduction method are confirmed by the comparison research results. The research provides references for MOR of MEMS.
2011, 25(5).
Abstract:
This paper focuses on the development of an optimized photovoltaic tracking system involving low-cost, relative simple mechanisms, with linear actuators able to insure strokes comparable with those resulted when using gear rotary actuators. Starting with a rhombus linkage, with a linear actuator on the diagonal used for the elevation motion till 90°, a new performance solution is generated. This new linkage allows large angular strokes by using an asymmetric rhombus and an eccentrically positioned linear actuator. The paper can be divided in three main parts. Firstly the kinematical modeling of the new linkage is addressed, which permits the establishing of the linkage dimensions according to two adjustable parameters (k2, k5). Using the resulted correlations, in the second part the linkage synthesis algorithm is developed; the steps followed in this algorithm are presented in a numerical application considering a tracked PV platform, where the azimuthal vertical movement is obtained with the new proposed rhomboidal linkage. In the last part of the paper an analysis is done with the aim of determining the PV platform tracking efficiency (which represents the ratio between the received and the available beam solar energy) using the new linkage, in the meteorological conditions of Braşov, Romania implementation site.
This paper focuses on the development of an optimized photovoltaic tracking system involving low-cost, relative simple mechanisms, with linear actuators able to insure strokes comparable with those resulted when using gear rotary actuators. Starting with a rhombus linkage, with a linear actuator on the diagonal used for the elevation motion till 90°, a new performance solution is generated. This new linkage allows large angular strokes by using an asymmetric rhombus and an eccentrically positioned linear actuator. The paper can be divided in three main parts. Firstly the kinematical modeling of the new linkage is addressed, which permits the establishing of the linkage dimensions according to two adjustable parameters (k2, k5). Using the resulted correlations, in the second part the linkage synthesis algorithm is developed; the steps followed in this algorithm are presented in a numerical application considering a tracked PV platform, where the azimuthal vertical movement is obtained with the new proposed rhomboidal linkage. In the last part of the paper an analysis is done with the aim of determining the PV platform tracking efficiency (which represents the ratio between the received and the available beam solar energy) using the new linkage, in the meteorological conditions of Braşov, Romania implementation site.
2011, 25(5).
Abstract:
Portable electronics is usually powered by battery, which is not sustainable not only to the longtime outdoor use but also to our living environment. There is rich kinetic energy in footstep motion during walking, so it is ideal to harvest the kinetic energy from human footstep motion as power source for portable electronic devices. In this paper, a novel mechanism based on dual-oscillating mode is designed to harvest the kinetic energy from footstep motion. The harvester contains two oscillating sub-mechanisms: one is spring-mass oscillator to absorb the vibration from external excitation, i.e., the footstep motion, and the other is cantilever beam with tip mass for amplifying the vibration. Theoretic analysis shows that the dual-oscillating mechanism can be more effectively harness the foot step motion. The energy conversion sub-mechanism is based on the electromagnetic induction, where the wire coils fixed at the tip end of the cantilever beam serves as the slider and permanent magnets and yoke form the changing magnetic field. Simulation shows that the harvester, with total mass 70 g, can produce about 100 mW of electricity at the walking speed of 2 steps per second.
Portable electronics is usually powered by battery, which is not sustainable not only to the longtime outdoor use but also to our living environment. There is rich kinetic energy in footstep motion during walking, so it is ideal to harvest the kinetic energy from human footstep motion as power source for portable electronic devices. In this paper, a novel mechanism based on dual-oscillating mode is designed to harvest the kinetic energy from footstep motion. The harvester contains two oscillating sub-mechanisms: one is spring-mass oscillator to absorb the vibration from external excitation, i.e., the footstep motion, and the other is cantilever beam with tip mass for amplifying the vibration. Theoretic analysis shows that the dual-oscillating mechanism can be more effectively harness the foot step motion. The energy conversion sub-mechanism is based on the electromagnetic induction, where the wire coils fixed at the tip end of the cantilever beam serves as the slider and permanent magnets and yoke form the changing magnetic field. Simulation shows that the harvester, with total mass 70 g, can produce about 100 mW of electricity at the walking speed of 2 steps per second.
2011, 25(5).
Abstract:
The hybrid dynamics of multi-rigid-body and multi-flexible-body system becomes the mainstream of multi-body dynamics. Currently there lacks a compact approach to model the hybrid dynamics, especially in modern machine tool application, due to the difficulty of solving the hybrid equations or the limitation of current software when dealing with the hybrid dynamics. The extended transfer matrix method (E-TMM), which extends elements in three-dimensional space with higher matrixes, is proposed to simplify the modeling process of the hybrid dynamics. The E-TMM modeling approaches of 3 basic elements including 3D vibrant rigid body, joint and flexible body are studied in details. A parallel mill-turn tool spindle head unit driven by dual-linear motors is chosen as a plant to demonstrate the E-TMM modeling process. By using E-TMM, the spindle head unit is simplified as a topological network consisting of the three types of element, i.e., 3D vibrant rigid body, joint and flexible body, including 11 rigid bodies, 14 joints and 1 3D-Timoshenko beam. Then the dynamic model of the system can be easily obtained by deducing the element-network by means of state vector transformation. The dynamic characteristics of the spindle head, such as natural frequencies, dynamic flexibility, etc. can be predicted by solving the obtained model. Experiment verification indicates that the E-TMM is valid with enough accuracy in the dynamic analysis of the parallel mill-turn tool spindle head. The E-TMM is capable of modeling the dynamics of machine tool structure with no requirements of deducing and solving the sophisticated differential equations. Moreover, the E-TMM provides a simple and elegant tool for hybrid dynamic analysis in future dynamic design of machine tools.
The hybrid dynamics of multi-rigid-body and multi-flexible-body system becomes the mainstream of multi-body dynamics. Currently there lacks a compact approach to model the hybrid dynamics, especially in modern machine tool application, due to the difficulty of solving the hybrid equations or the limitation of current software when dealing with the hybrid dynamics. The extended transfer matrix method (E-TMM), which extends elements in three-dimensional space with higher matrixes, is proposed to simplify the modeling process of the hybrid dynamics. The E-TMM modeling approaches of 3 basic elements including 3D vibrant rigid body, joint and flexible body are studied in details. A parallel mill-turn tool spindle head unit driven by dual-linear motors is chosen as a plant to demonstrate the E-TMM modeling process. By using E-TMM, the spindle head unit is simplified as a topological network consisting of the three types of element, i.e., 3D vibrant rigid body, joint and flexible body, including 11 rigid bodies, 14 joints and 1 3D-Timoshenko beam. Then the dynamic model of the system can be easily obtained by deducing the element-network by means of state vector transformation. The dynamic characteristics of the spindle head, such as natural frequencies, dynamic flexibility, etc. can be predicted by solving the obtained model. Experiment verification indicates that the E-TMM is valid with enough accuracy in the dynamic analysis of the parallel mill-turn tool spindle head. The E-TMM is capable of modeling the dynamics of machine tool structure with no requirements of deducing and solving the sophisticated differential equations. Moreover, the E-TMM provides a simple and elegant tool for hybrid dynamic analysis in future dynamic design of machine tools.
2011, 25(5).
Abstract:
Hybrid technology has been widely developed for various vehicles in recent years. However, due to the limitation of size and space, it is difficult to apply the technology in the small two-wheeled vehicles, especially scooters. For scooters, the hybrid system could be with small capacity, and must be simple and affordable. The Purpose of this study is to analyze and develop the conceptual designs of fuel-electric hybrid systems especially for scooters. Firstly, the graph called “function power graph (FPG)” is defined, which transforms traditional mechanical schematic diagrams into simplified graphs, and makes the characteristics of hybrid systems can be identified clearly. Based on the FPG, a systematic method for synthesizing all possible arrangements of hybrid systems, then, is developed, and the hybrid system arrangements with one internal combustion engine (ICE), one electric machine (M/G), and some mechanical clutch units are all enumerated. In order to evaluate the applicability of these design concepts for Scooters, twelve system functions and three system complexities are defined, and this evaluation process can be automated numerically by using a computer program, which is Matlab in this study. With the systematic design and analysis methods developed, the function capability and characteristics of current hybrid systems can be easily identified, and also, new and useful hybrid systems are found for future possible applications.
Hybrid technology has been widely developed for various vehicles in recent years. However, due to the limitation of size and space, it is difficult to apply the technology in the small two-wheeled vehicles, especially scooters. For scooters, the hybrid system could be with small capacity, and must be simple and affordable. The Purpose of this study is to analyze and develop the conceptual designs of fuel-electric hybrid systems especially for scooters. Firstly, the graph called “function power graph (FPG)” is defined, which transforms traditional mechanical schematic diagrams into simplified graphs, and makes the characteristics of hybrid systems can be identified clearly. Based on the FPG, a systematic method for synthesizing all possible arrangements of hybrid systems, then, is developed, and the hybrid system arrangements with one internal combustion engine (ICE), one electric machine (M/G), and some mechanical clutch units are all enumerated. In order to evaluate the applicability of these design concepts for Scooters, twelve system functions and three system complexities are defined, and this evaluation process can be automated numerically by using a computer program, which is Matlab in this study. With the systematic design and analysis methods developed, the function capability and characteristics of current hybrid systems can be easily identified, and also, new and useful hybrid systems are found for future possible applications.
2011, 25(5).
Abstract:
The current research of the 5-axis tool positioning algorithm mainly focuses on searching the local optimal tool position without gouging and interference at a cutter contact(CC) point, while not considering the smoothness and continuity of a whole tool path. When the surface curvature varies significantly, a local abrupt change of tool paths will happen. The abrupt change has a great influence on surface machining quality. In order to keep generated tool paths smooth and continuous, a five-axis tool positioning algorithm based on smooth tool paths is presented. Firstly, the inclination angle, the tilt angle and offset distance of the tool at a CC point are used as design variables, and the machining strip width is used as an objective function, an optimization model of a local tool positioning algorithm is thus established. Then, a vector equation of tool path is derived by using the above optimization model. By analyzing the equation, the main factors affecting the tool path quality are obtained. Finally, a new tool position optimization model is established, and the detailed process of tool position optimization is also given. An experiment is conducted to machine an aircraft turbine blade by using the proposed algorithm on a 5-axis blade grinding machine, and the machined blade surface is measured with a coordinate measuring machine(CMM). Experimental and measured results show that the proposed algorithm can ensure tool paths are smooth and continuous, improve the tool path quality, avoid the local abrupt change of tool paths, and enhance machining quality and machining efficiency of sculptured surfaces.
The current research of the 5-axis tool positioning algorithm mainly focuses on searching the local optimal tool position without gouging and interference at a cutter contact(CC) point, while not considering the smoothness and continuity of a whole tool path. When the surface curvature varies significantly, a local abrupt change of tool paths will happen. The abrupt change has a great influence on surface machining quality. In order to keep generated tool paths smooth and continuous, a five-axis tool positioning algorithm based on smooth tool paths is presented. Firstly, the inclination angle, the tilt angle and offset distance of the tool at a CC point are used as design variables, and the machining strip width is used as an objective function, an optimization model of a local tool positioning algorithm is thus established. Then, a vector equation of tool path is derived by using the above optimization model. By analyzing the equation, the main factors affecting the tool path quality are obtained. Finally, a new tool position optimization model is established, and the detailed process of tool position optimization is also given. An experiment is conducted to machine an aircraft turbine blade by using the proposed algorithm on a 5-axis blade grinding machine, and the machined blade surface is measured with a coordinate measuring machine(CMM). Experimental and measured results show that the proposed algorithm can ensure tool paths are smooth and continuous, improve the tool path quality, avoid the local abrupt change of tool paths, and enhance machining quality and machining efficiency of sculptured surfaces.
2011, 25(5).
Abstract:
Centrifugal pumps always work under steady conditions, and many researches focus on the steady operation. But transient conditions, such as sudden startup and shutdown, are inevitable. The researches on the inner flow of centrifugal pumps under transient conditions have been done, and they show that the transient operation is different from the steady operation. In order to research the evolution of unsteady flow in a centrifugal pump under transient conditions, and to investigate the mechanism of transient effects by analyzing the unsteady flow in a centrifugal pump, the external characteristic experiment and the internal flow numerical calculation of the centrifugal pump with an open impeller during startup is presented. The relationships of the rotation speed, capacity and head between start-time are obtained by the external characteristics experiment. The numerical calculations under startup process are carried out by using the k- model and N-S equation. The distribution of velocity and pressure in the inner channel of the tested pump was obtained by choosing fourteen start-time points and twelve geometrical points in the impeller channel during startup. The calculation results show that the velocity and the pressure increase linearly with the start-time before rotation’s speed gets steady, then changes almost horizontally after rotation speed becomes steady, then fluctuates until being steady. The internal flow characteristics are in good agreement with the external characteristic experimental results and numerical calculation. The simulation methods and results make the basis for the diagnosis and optimization of under flow in the centrifugal pump during transient operation.
Centrifugal pumps always work under steady conditions, and many researches focus on the steady operation. But transient conditions, such as sudden startup and shutdown, are inevitable. The researches on the inner flow of centrifugal pumps under transient conditions have been done, and they show that the transient operation is different from the steady operation. In order to research the evolution of unsteady flow in a centrifugal pump under transient conditions, and to investigate the mechanism of transient effects by analyzing the unsteady flow in a centrifugal pump, the external characteristic experiment and the internal flow numerical calculation of the centrifugal pump with an open impeller during startup is presented. The relationships of the rotation speed, capacity and head between start-time are obtained by the external characteristics experiment. The numerical calculations under startup process are carried out by using the k- model and N-S equation. The distribution of velocity and pressure in the inner channel of the tested pump was obtained by choosing fourteen start-time points and twelve geometrical points in the impeller channel during startup. The calculation results show that the velocity and the pressure increase linearly with the start-time before rotation’s speed gets steady, then changes almost horizontally after rotation speed becomes steady, then fluctuates until being steady. The internal flow characteristics are in good agreement with the external characteristic experimental results and numerical calculation. The simulation methods and results make the basis for the diagnosis and optimization of under flow in the centrifugal pump during transient operation.
2011, 25(5).
Abstract:
The roller-scraper tribosystem of automatic teller machine (ATM) plays an important role in reliable cash requests. However, the abrasive wear of the polymer tribosystem becomes a prominent problem when operating in sandy environment. The wear behavior of the tribosystem in a simulated sandy environment has been experimentally studied previously. However the abrasive wear mechanism of roller-scraper tribosystems is still unknown to new design. The wear rates of polymer rollers were examined comprehensively and several jumping variations were found in the full data extent. Three wear stages were classified by the magnitude of wear rates, and different dominant wear mechanisms corresponding with different particle diameter were found by examining the worn surfaces. Accordingly a presumption was proposed that wear mechanisms in different stages were correlated with sand particles of different diameter. In a verification experiment, three typical wear mechanisms including cutting, ploughing, and wedging were found corresponding with different wear stages by scanning electron microscope(SEM) examination. A theoretical analysis was carried out with a simplified sphere particle intrusion model and the transfer conditions for different wear mechanisms were studied referring to the slip-field theory. As a main result, three typical wear models versus friction coefficient of particle/roller, and particle radius were mapped with variant hardness of the polymer roller and ratio of contact shear stress to bulk shear stress. The result illuminated the abrasive wear mechanism during particle intrusion. Particularly，the critical transition conditions gave the basis for improving the wear performance of roller-scraper tribosystems in a sandy environment.
The roller-scraper tribosystem of automatic teller machine (ATM) plays an important role in reliable cash requests. However, the abrasive wear of the polymer tribosystem becomes a prominent problem when operating in sandy environment. The wear behavior of the tribosystem in a simulated sandy environment has been experimentally studied previously. However the abrasive wear mechanism of roller-scraper tribosystems is still unknown to new design. The wear rates of polymer rollers were examined comprehensively and several jumping variations were found in the full data extent. Three wear stages were classified by the magnitude of wear rates, and different dominant wear mechanisms corresponding with different particle diameter were found by examining the worn surfaces. Accordingly a presumption was proposed that wear mechanisms in different stages were correlated with sand particles of different diameter. In a verification experiment, three typical wear mechanisms including cutting, ploughing, and wedging were found corresponding with different wear stages by scanning electron microscope(SEM) examination. A theoretical analysis was carried out with a simplified sphere particle intrusion model and the transfer conditions for different wear mechanisms were studied referring to the slip-field theory. As a main result, three typical wear models versus friction coefficient of particle/roller, and particle radius were mapped with variant hardness of the polymer roller and ratio of contact shear stress to bulk shear stress. The result illuminated the abrasive wear mechanism during particle intrusion. Particularly，the critical transition conditions gave the basis for improving the wear performance of roller-scraper tribosystems in a sandy environment.
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