2011 Vol.24(6)
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2011, 25(6).
Abstract:
With sustaining change of production mode, layout planning is no longer a thing built once for all. Cellular layout (CL) is becoming a hotspot in the research field of manufacturing system layout. Traditional researches on layout planning are mainly concentrating on aspects of layout arithmetic, style and evaluation, etc. Relatively seldom efforts are paid to CL and its specific problems as cell formation (CF), equipment sharing and CL analysis. Through problem analyzing of layout in cellular manufacturing system (CMS), research approach of cell formation, interactive layout and layout analysis threaded with process interconnection relationship (PIR) is proposed. Typical key technologies in CL like CF technology based on similarity analysis of part processes, interactive visual layout technology, layout evaluation technology founded on PIR analysis and algorithm of cell equipment sharing are put forward. Against the background of one enterprise which encounters problems of low utility of key equipments and disperse material logistic, an example of four-cell layout is given. The CL adjustment and analysis results show that equipment with high level of sharing degree should be disposed around the boundary of its main cell, and be near to other sharing cells as possible; process route should be centralized by all means, so equipment adjustment is to be implemented along direction that route intersection can be decreased; giving consideration to the existence of discrete cell, logistic route and its density should be centralized to cells formed. The proposed research can help improve equipment utility and material logistic efficiency of CL, and can be popularized to other application availably.
With sustaining change of production mode, layout planning is no longer a thing built once for all. Cellular layout (CL) is becoming a hotspot in the research field of manufacturing system layout. Traditional researches on layout planning are mainly concentrating on aspects of layout arithmetic, style and evaluation, etc. Relatively seldom efforts are paid to CL and its specific problems as cell formation (CF), equipment sharing and CL analysis. Through problem analyzing of layout in cellular manufacturing system (CMS), research approach of cell formation, interactive layout and layout analysis threaded with process interconnection relationship (PIR) is proposed. Typical key technologies in CL like CF technology based on similarity analysis of part processes, interactive visual layout technology, layout evaluation technology founded on PIR analysis and algorithm of cell equipment sharing are put forward. Against the background of one enterprise which encounters problems of low utility of key equipments and disperse material logistic, an example of four-cell layout is given. The CL adjustment and analysis results show that equipment with high level of sharing degree should be disposed around the boundary of its main cell, and be near to other sharing cells as possible; process route should be centralized by all means, so equipment adjustment is to be implemented along direction that route intersection can be decreased; giving consideration to the existence of discrete cell, logistic route and its density should be centralized to cells formed. The proposed research can help improve equipment utility and material logistic efficiency of CL, and can be popularized to other application availably.
2011, 25(6).
Abstract:
Local flexibility of crack plays an important role in crack identification of structures. Analytical methods on local flexibility in a cracked beam with simple geometric crossing sections, such as rectangle, circle, have been made, but there are some difficulties in calculating local flexibility in a cracked beam with complex crossing section, such as pipe and I-beam. In this paper, an analytical method to calculate the local flexibility and rotational spring stiffness due to crack in I-beam is proposed. The local flexibility with respect to various crack depths can be calculated by dividing a cracked I-beam into a series of thin rectangles. The forward and inverse problems in crack detection of I-beam are studied. The forward problem comprises the construction of crack model exclusively for crack section and the construction of a numerically I-beam model to gain crack detection database. The inverse problem consists of the measurement of modal parameters and the detection of crack parameters. Two experiments including measurement of rotational spring stiffness and prediction of cracks in I-beam are conducted. Experimental results based on the current methods indicate that relative error of crack location is less than 3%, while the error of crack depth identification is less than 6%. Crack identification of I-beam is expected to contribute to the development of automated crack detection techniques for railway lines and building skeletons.
Local flexibility of crack plays an important role in crack identification of structures. Analytical methods on local flexibility in a cracked beam with simple geometric crossing sections, such as rectangle, circle, have been made, but there are some difficulties in calculating local flexibility in a cracked beam with complex crossing section, such as pipe and I-beam. In this paper, an analytical method to calculate the local flexibility and rotational spring stiffness due to crack in I-beam is proposed. The local flexibility with respect to various crack depths can be calculated by dividing a cracked I-beam into a series of thin rectangles. The forward and inverse problems in crack detection of I-beam are studied. The forward problem comprises the construction of crack model exclusively for crack section and the construction of a numerically I-beam model to gain crack detection database. The inverse problem consists of the measurement of modal parameters and the detection of crack parameters. Two experiments including measurement of rotational spring stiffness and prediction of cracks in I-beam are conducted. Experimental results based on the current methods indicate that relative error of crack location is less than 3%, while the error of crack depth identification is less than 6%. Crack identification of I-beam is expected to contribute to the development of automated crack detection techniques for railway lines and building skeletons.
2011, 25(6).
Abstract:
Recently automotive nets are adopted to solve increasing problems in automotive electronic systems. Technologies of automotive local area network from CAN and LIN can solve the problems of the increasing of wire bunch weight and lack in module installation space. However, the multilayer automotive nets software becomes more and more complex, and the development expense is difficult to predict and to keep in check. In this paper, the modeling method of hierarchical automotive nets and the substitution operation based on object-oriented colored Petri net (OOCPN) are proposed. The OOCPN model which analyzes the software structure and validates the collision mechanism of CANLIN bus can speed the automobile system development. First, the subsystems are divided and modeled by object-oriented Petri net (OOPN). According to the sets of message sharing relations, the message ports among them are set and the communication gate transitions are defined. Second, the OOPN model is substituted step by step until the inner objects in the automotive body control modules (BCM) are indivisible and colored by colored Petri net (CPN). And the color subsets mark the node messages for the collision mechanism. Third, the OOCPN model of the automotive body CANLIN nets is assembled, which keeps the message sets and the system can be expanded. The proposed model is used to analyze features of information sharing among the objects, and it is also used to describe each subsystem real-time behavior of processing messages and implemental device controllers operating, and puts forward a reasonable software framework for the automotive body control subsystem. The research can help to design the communication model in the automotive body system effectively and provide a convenient and rapid way for developing the logical hierarchy software.
Recently automotive nets are adopted to solve increasing problems in automotive electronic systems. Technologies of automotive local area network from CAN and LIN can solve the problems of the increasing of wire bunch weight and lack in module installation space. However, the multilayer automotive nets software becomes more and more complex, and the development expense is difficult to predict and to keep in check. In this paper, the modeling method of hierarchical automotive nets and the substitution operation based on object-oriented colored Petri net (OOCPN) are proposed. The OOCPN model which analyzes the software structure and validates the collision mechanism of CANLIN bus can speed the automobile system development. First, the subsystems are divided and modeled by object-oriented Petri net (OOPN). According to the sets of message sharing relations, the message ports among them are set and the communication gate transitions are defined. Second, the OOPN model is substituted step by step until the inner objects in the automotive body control modules (BCM) are indivisible and colored by colored Petri net (CPN). And the color subsets mark the node messages for the collision mechanism. Third, the OOCPN model of the automotive body CANLIN nets is assembled, which keeps the message sets and the system can be expanded. The proposed model is used to analyze features of information sharing among the objects, and it is also used to describe each subsystem real-time behavior of processing messages and implemental device controllers operating, and puts forward a reasonable software framework for the automotive body control subsystem. The research can help to design the communication model in the automotive body system effectively and provide a convenient and rapid way for developing the logical hierarchy software.
2011, 25(6).
Abstract:
Three-dimensional (3-D) free-form shape measurement，a challenging task pursued by computer vision, is mainly characterized with single view acquisition and multiple view registration. Most of the conventional scanning systems are less flexibility and difficult to realize engineering applications for employing sequential registration tactic. To develop portable scanning system and engineering registration method overcoming problems of error accumulation and propagation is the research direction. In this paper, one 3-D free-form shape measuring system using unconstrained range sensor is designed. A quasi-active stereo binocular visual sensor embedded within a scanning mechanism is used as the range sensor. Error compensation is performed by residual amendment according to camera calibration lattice. Artificial control points are designed and adhered on object and one camera is introduced to shot these control points from different positions and orientations. Then ray bundle adjustment (BA) method is used to calculate the space coordinates of all the control points, so as to set up a global control net work. Registration can be completed by mapping at least 3 control points observed by range sensor in single view acquisition into the global control network. In this system, no calibration for laser plane is required and the motion of range sensor is completely free. The overlapping of neighboring region is unessential for registration. Therefore, the working range of the system can be easily extended. The measuring precision mainly depends on the quality of global control network. The sequential distances of coding control points are observed by electronic theodolites and then compared with those obtained according to BA result. Experimental results show that relative distance error of control points is no more than 0.2%. The proposed measuring system is portable, provides good capacity for global error control, and contributes to the engineering application of 3-D free-form shape measurement.
Three-dimensional (3-D) free-form shape measurement，a challenging task pursued by computer vision, is mainly characterized with single view acquisition and multiple view registration. Most of the conventional scanning systems are less flexibility and difficult to realize engineering applications for employing sequential registration tactic. To develop portable scanning system and engineering registration method overcoming problems of error accumulation and propagation is the research direction. In this paper, one 3-D free-form shape measuring system using unconstrained range sensor is designed. A quasi-active stereo binocular visual sensor embedded within a scanning mechanism is used as the range sensor. Error compensation is performed by residual amendment according to camera calibration lattice. Artificial control points are designed and adhered on object and one camera is introduced to shot these control points from different positions and orientations. Then ray bundle adjustment (BA) method is used to calculate the space coordinates of all the control points, so as to set up a global control net work. Registration can be completed by mapping at least 3 control points observed by range sensor in single view acquisition into the global control network. In this system, no calibration for laser plane is required and the motion of range sensor is completely free. The overlapping of neighboring region is unessential for registration. Therefore, the working range of the system can be easily extended. The measuring precision mainly depends on the quality of global control network. The sequential distances of coding control points are observed by electronic theodolites and then compared with those obtained according to BA result. Experimental results show that relative distance error of control points is no more than 0.2%. The proposed measuring system is portable, provides good capacity for global error control, and contributes to the engineering application of 3-D free-form shape measurement.
2011, 25(6).
Abstract:
Lower limb injures are frequently observed in passenger car traffic accidents. Previous studies of the injuries focus on long bone fractures by using either cadaver component tests or simulations of the long bone kinematics, which lack in-depth study on the fractures in stress analysis. This paper aims to investigate lower limb impact biomechanics in real-world car to pedestrian accidents and to predict fractures of long bones in term of stress parameter for femur, tibia, and fibula. For the above purposes, a 3D finite element (FE) model of human body lower limb (HBM-LL) is developed based on human anatomy. The model consists of the pelvis, femur, tibia, fibula, patella, foot bones, primary tendons, knee joint capsule, meniscus, and ligaments. The FE model is validated by comparing the results from a lateral impact between simulations and tests with cadaver lower limb specimens. Two real-world accidents are selected from an in-depth accident database with detailed information about the accident scene, car impact speed, damage to the car, and pedestrian injuries. Multi-body system (MBS) models are used to reconstruct the kinematics of the pedestrians in the two accidents and the impact conditions are calculated for initial impact velocity and orientations of the car and pedestrian during the collision. The FE model is used to perform injury reconstructions and predict the fractures by using physical parameters, such as von Mises stress of long bones. The calculated failure level of the long bones is correlated with the injury outcomes observed from the two accident cases. The reconstruction result shows that the HBM-LL FE model has acceptable biofidelity and can be applied to predict the risk of long bone fractures. This study provides an efficient methodology to investigate the long bone fracture suffered from vehicle traffic collisions.
Lower limb injures are frequently observed in passenger car traffic accidents. Previous studies of the injuries focus on long bone fractures by using either cadaver component tests or simulations of the long bone kinematics, which lack in-depth study on the fractures in stress analysis. This paper aims to investigate lower limb impact biomechanics in real-world car to pedestrian accidents and to predict fractures of long bones in term of stress parameter for femur, tibia, and fibula. For the above purposes, a 3D finite element (FE) model of human body lower limb (HBM-LL) is developed based on human anatomy. The model consists of the pelvis, femur, tibia, fibula, patella, foot bones, primary tendons, knee joint capsule, meniscus, and ligaments. The FE model is validated by comparing the results from a lateral impact between simulations and tests with cadaver lower limb specimens. Two real-world accidents are selected from an in-depth accident database with detailed information about the accident scene, car impact speed, damage to the car, and pedestrian injuries. Multi-body system (MBS) models are used to reconstruct the kinematics of the pedestrians in the two accidents and the impact conditions are calculated for initial impact velocity and orientations of the car and pedestrian during the collision. The FE model is used to perform injury reconstructions and predict the fractures by using physical parameters, such as von Mises stress of long bones. The calculated failure level of the long bones is correlated with the injury outcomes observed from the two accident cases. The reconstruction result shows that the HBM-LL FE model has acceptable biofidelity and can be applied to predict the risk of long bone fractures. This study provides an efficient methodology to investigate the long bone fracture suffered from vehicle traffic collisions.
2011, 25(6).
Abstract:
The existing design of the pumping systems mainly focuses on the approximate computational formulae and procedures, which are developed based on the analytic approaches of conventional oilgas fields. The calculation of polished rod loads usually just concerns about the static and inertial loads. And the computation of gearbox torque generally uses empirical formulae and correction factors. The above modeling procedures, if applied to the coalbed methane(CBM) wells, can not give the desired accuracy of the system design and its pertinent analysis. In this paper, based on the kinematic and dynamic analysis of the pumping system, the kinematic relation of polished rod is analyzed, and the variation of the total loads of polished rod is developed with the limits of CBM well conditions along the string. The gearbox torque calculation model is established by combining the counterbalance effect with the calculated dynamometer cards and torque factors. The application characteristics of this model are demonstrated by the example of ZH002-4 well in Qinshui basin. The interpretations of results show that the cranks of beam units should rotate in a counter clockwise direction viewed with the wellhead to the right. Compared with oilgas fields, the dynamic and friction to polished rod load ratios are relatively high and the computation of polished rod loads should involve the static and inertial loads, as well as vibration and friction loads. And the dynamic load ratio decreases rapidly during the production. Besides, the total deformation of the string is small in CBM wells. As for balanced operation, the gearbox torque load usually has two approximately equal peaks and the magnitudes of instantaneous torque are just within 50% of unbalanced gearbox loadings. The proposed research improves efficiency of the pumping system, loads the pumping unit more uniformly, and provides the reasonable basis for selecting the units.
The existing design of the pumping systems mainly focuses on the approximate computational formulae and procedures, which are developed based on the analytic approaches of conventional oilgas fields. The calculation of polished rod loads usually just concerns about the static and inertial loads. And the computation of gearbox torque generally uses empirical formulae and correction factors. The above modeling procedures, if applied to the coalbed methane(CBM) wells, can not give the desired accuracy of the system design and its pertinent analysis. In this paper, based on the kinematic and dynamic analysis of the pumping system, the kinematic relation of polished rod is analyzed, and the variation of the total loads of polished rod is developed with the limits of CBM well conditions along the string. The gearbox torque calculation model is established by combining the counterbalance effect with the calculated dynamometer cards and torque factors. The application characteristics of this model are demonstrated by the example of ZH002-4 well in Qinshui basin. The interpretations of results show that the cranks of beam units should rotate in a counter clockwise direction viewed with the wellhead to the right. Compared with oilgas fields, the dynamic and friction to polished rod load ratios are relatively high and the computation of polished rod loads should involve the static and inertial loads, as well as vibration and friction loads. And the dynamic load ratio decreases rapidly during the production. Besides, the total deformation of the string is small in CBM wells. As for balanced operation, the gearbox torque load usually has two approximately equal peaks and the magnitudes of instantaneous torque are just within 50% of unbalanced gearbox loadings. The proposed research improves efficiency of the pumping system, loads the pumping unit more uniformly, and provides the reasonable basis for selecting the units.
2011, 25(6).
Abstract:
Currently the extruded effect, roughness to the lubricant shear thinning, temperature changes and other factors or some combination of a single factor mainly considered in the lubrication study of piston ring-cylinder. In the study of the energy equation, the oil viscosity-temperature properties, adsorption layer characteristics are usually not considered. So the theoretical research is different from the actual situation of engineering. The lubrication of piston ring-cylinder liner system in internal combustion (IC) engines is studied here based on the theory of thermal flow. An unsteady and compressible hydrodynamic lubrication model with an equivalent viscosity based on shear and extruded flow factor is derived by employing the viscosity-temperature relationship, meanwhile, characteristics such as lubricating oil’s density varying with pressure and temperature, thickness of adsorbent layer and oil film’s geometry are also considered in this model. While setting up the energy equation, the effect of lubricating oil’s volume expansion and viscous dissipation on temperature, the heat conduction along oil film’s thickness direction are considered. Finite difference equation is formed by using a first-order difference scheme in time scale and second-order difference scheme in space scale. A common diesel engine is introduced as an instance to predict the distribution of the minimum oil film thickness in the piston ring-cylinder liner system. The results of simulation calculation show that the minimum oil film thickness will decrease especially around the top dead center when the oil’s volume expansion, viscous dissipation and heat conduction are considered, which implies that: it is essential to take the thermal flow idea into account during investigating piston ring-cylinder liner system’s lubrication. A more complete piston ring - cylinder liner lubrication theory was established according to thermal fluids from the perspective of research. It is more helpful to guide the practical application of engineering to improve the accuracy of forecasting the minimum film thickness. On the other hand, distribution of the minimum oil film thickness shows a nonlinear property if the thickness of piston rings and cylinder liner adsorbent layer are involved in the analysis. It may be feasible to increase the minimum oil film thickness by varying surface roughness and material properties of piston rings and cylinder liner.
Currently the extruded effect, roughness to the lubricant shear thinning, temperature changes and other factors or some combination of a single factor mainly considered in the lubrication study of piston ring-cylinder. In the study of the energy equation, the oil viscosity-temperature properties, adsorption layer characteristics are usually not considered. So the theoretical research is different from the actual situation of engineering. The lubrication of piston ring-cylinder liner system in internal combustion (IC) engines is studied here based on the theory of thermal flow. An unsteady and compressible hydrodynamic lubrication model with an equivalent viscosity based on shear and extruded flow factor is derived by employing the viscosity-temperature relationship, meanwhile, characteristics such as lubricating oil’s density varying with pressure and temperature, thickness of adsorbent layer and oil film’s geometry are also considered in this model. While setting up the energy equation, the effect of lubricating oil’s volume expansion and viscous dissipation on temperature, the heat conduction along oil film’s thickness direction are considered. Finite difference equation is formed by using a first-order difference scheme in time scale and second-order difference scheme in space scale. A common diesel engine is introduced as an instance to predict the distribution of the minimum oil film thickness in the piston ring-cylinder liner system. The results of simulation calculation show that the minimum oil film thickness will decrease especially around the top dead center when the oil’s volume expansion, viscous dissipation and heat conduction are considered, which implies that: it is essential to take the thermal flow idea into account during investigating piston ring-cylinder liner system’s lubrication. A more complete piston ring - cylinder liner lubrication theory was established according to thermal fluids from the perspective of research. It is more helpful to guide the practical application of engineering to improve the accuracy of forecasting the minimum film thickness. On the other hand, distribution of the minimum oil film thickness shows a nonlinear property if the thickness of piston rings and cylinder liner adsorbent layer are involved in the analysis. It may be feasible to increase the minimum oil film thickness by varying surface roughness and material properties of piston rings and cylinder liner.
2011, 25(6).
Abstract:
The material characteristics of a structure will change with temperature variation, and will induce stress within the structure. Currently, the optimal design for the topology of compliant mechanisms is mainly performed in single physical field. However, when compliant mechanisms work in high temperature environments, their displacement outputs are generated not only by mechanical load, but also by the temperature variation which may become the prominent factor. Therefore, the influence of temperature must be considered in the design. In this paper, a novel optimization method for multi-objective topology of thermo-mechanical compliant mechanisms is presented. First, the thermal field is analyzed with finite-element method, where the thermal strain is taken into account in the constitutive relation, and the equivalent nodal thermal load is derived with the principle of virtual work. Then the thermal load is converted into physical loads in elastic field, and the control equation of the thermo-mechanical compliant mechanism is obtained. Second, the mathematical model of the multi-objective topology optimization is built by incorporating both the flexibility and stiffness. Meanwhile, the coupling sensitivity function and the sensitivity analysis equations of thermal steady-state response are derived. Finally, optimality criteria algorithm is employed to obtain numerical solution of the multi-objective topology optimization. Numerical examples show that the compliant mechanisms have better performance and are more applicable if the temperature effect is taken into account in the design process. The presented modeling and analysis methods provide a new idea and an effective approach to topology optimization of compliant mechanisms in electrothermic coupling field and multiphysics fields.
The material characteristics of a structure will change with temperature variation, and will induce stress within the structure. Currently, the optimal design for the topology of compliant mechanisms is mainly performed in single physical field. However, when compliant mechanisms work in high temperature environments, their displacement outputs are generated not only by mechanical load, but also by the temperature variation which may become the prominent factor. Therefore, the influence of temperature must be considered in the design. In this paper, a novel optimization method for multi-objective topology of thermo-mechanical compliant mechanisms is presented. First, the thermal field is analyzed with finite-element method, where the thermal strain is taken into account in the constitutive relation, and the equivalent nodal thermal load is derived with the principle of virtual work. Then the thermal load is converted into physical loads in elastic field, and the control equation of the thermo-mechanical compliant mechanism is obtained. Second, the mathematical model of the multi-objective topology optimization is built by incorporating both the flexibility and stiffness. Meanwhile, the coupling sensitivity function and the sensitivity analysis equations of thermal steady-state response are derived. Finally, optimality criteria algorithm is employed to obtain numerical solution of the multi-objective topology optimization. Numerical examples show that the compliant mechanisms have better performance and are more applicable if the temperature effect is taken into account in the design process. The presented modeling and analysis methods provide a new idea and an effective approach to topology optimization of compliant mechanisms in electrothermic coupling field and multiphysics fields.
2011, 25(6).
Abstract:
Feature recognition aims at extracting manufacturing features with geometrical information from solid model and is considered to be an efficient way of changing the interactive NC machining programming mode. Existing recognition methods have some disadvantages in practical applications. They can essentially handle prismatic components with regular shapes and are difficult to recognize the intersecting features and curved surfaces. Besides, the robustness of them is not strong enough. A new feature recognition approach is proposed based on the analysis of aircraft integral panels’ geometry and machining characteristics. In this approach, the aircraft integral panel is divided into a number of local machining domains. The machining domains are extracted and recognized first by finding the principal face of machining domain and extracting the sides around the principal face. Then the machining domains are divided into various features in terms of the face type. The main sections of the proposed method are presented including the definition, classification and structure of machining domain, the relationship between machining domain and principal face loop, the rules of machining domains recognition, and the algorithm of machining feature recognition. In addition, a robotic feature recognition module is developed for aircraft integral panels and tested with several panels. Test results show that the strategy presented is robust and valid. Features extracted can be post processed and linked to various downstream applications. The approach is able to solve the difficulties in recognizing the aircraft integral panel’s features and automatic obtaining the machining zone in NC programming, and can be used to further develop the automatic programming of NC machining.
Feature recognition aims at extracting manufacturing features with geometrical information from solid model and is considered to be an efficient way of changing the interactive NC machining programming mode. Existing recognition methods have some disadvantages in practical applications. They can essentially handle prismatic components with regular shapes and are difficult to recognize the intersecting features and curved surfaces. Besides, the robustness of them is not strong enough. A new feature recognition approach is proposed based on the analysis of aircraft integral panels’ geometry and machining characteristics. In this approach, the aircraft integral panel is divided into a number of local machining domains. The machining domains are extracted and recognized first by finding the principal face of machining domain and extracting the sides around the principal face. Then the machining domains are divided into various features in terms of the face type. The main sections of the proposed method are presented including the definition, classification and structure of machining domain, the relationship between machining domain and principal face loop, the rules of machining domains recognition, and the algorithm of machining feature recognition. In addition, a robotic feature recognition module is developed for aircraft integral panels and tested with several panels. Test results show that the strategy presented is robust and valid. Features extracted can be post processed and linked to various downstream applications. The approach is able to solve the difficulties in recognizing the aircraft integral panel’s features and automatic obtaining the machining zone in NC programming, and can be used to further develop the automatic programming of NC machining.
2011, 25(6).
Abstract:
The mobility of the vectored thruster AUV in different environment is the important premise of control system design. The new type of autonomous underwater vehicle (AUV) equipped with rudders and vectored thrusters which are combined to control the course is studied. Firstly, Euler angles representation and quaternion method are applied to establish six-DOF kinematic model respectively, then Newton second law and Lagrangian approach are used to deduce the vectored thruster AUV’s nonlinear dynamic equations with six degrees of freedom (DOF) respectively in complex sea conditions based on the random wave theory according to the structural and kinetic characteristics of the vectored thruster AUV in this paper. The kinematic models and dynamic models based on different theories have the same expression and conclusion, which shows that the kinematic models and dynamic models of the vectored thruster AUV are accurate. The Runge-Kutta arithmetic is used to solve the dynamic equations, which not only can simulate the motions such as cruise and hover but also can describe the vehicle’s low-frequency and high-frequency motion. The results of computation show that the mobility of the vectored thruster AUV in interference-free environment and the integrated signals including low-frequency motion signal and high-frequency motion signal in environmental disturbance accord with practical situation, which not only solve the problem of especial singularities when the pitch angle θ ±90° but also clears up the difficulties of computation and display of the coupled nonlinear motion equations in complex sea conditions. Moreover, the high maneuverability of the vectored thruster AUV equipped with rudders and vectored thrusters is validated, which lays a foundation for the control system design.
The mobility of the vectored thruster AUV in different environment is the important premise of control system design. The new type of autonomous underwater vehicle (AUV) equipped with rudders and vectored thrusters which are combined to control the course is studied. Firstly, Euler angles representation and quaternion method are applied to establish six-DOF kinematic model respectively, then Newton second law and Lagrangian approach are used to deduce the vectored thruster AUV’s nonlinear dynamic equations with six degrees of freedom (DOF) respectively in complex sea conditions based on the random wave theory according to the structural and kinetic characteristics of the vectored thruster AUV in this paper. The kinematic models and dynamic models based on different theories have the same expression and conclusion, which shows that the kinematic models and dynamic models of the vectored thruster AUV are accurate. The Runge-Kutta arithmetic is used to solve the dynamic equations, which not only can simulate the motions such as cruise and hover but also can describe the vehicle’s low-frequency and high-frequency motion. The results of computation show that the mobility of the vectored thruster AUV in interference-free environment and the integrated signals including low-frequency motion signal and high-frequency motion signal in environmental disturbance accord with practical situation, which not only solve the problem of especial singularities when the pitch angle θ ±90° but also clears up the difficulties of computation and display of the coupled nonlinear motion equations in complex sea conditions. Moreover, the high maneuverability of the vectored thruster AUV equipped with rudders and vectored thrusters is validated, which lays a foundation for the control system design.
2011, 25(6).
Abstract:
As few or no failures occur during accelerated life test, it is difficult to assess reliability for long-life products with traditional life tests. Reliability assessment using degradation data of product performance over time becomes a significant approach. Aerospace electrical connector is researched in this paper. Through the analysis of failure mechanism, the performance degradation law is obtained and the statistical model for degradation failure is set up; according to the research on statistical analysis methods for degradation data, accelerated life test theory and method for aerospace electrical connector based on performance degradation is proposed by improving time series analysis method, and the storage reliability is assessed for Y11X series of aerospace electrical connector with degradation data from accelerated degradation test. The result obtained is basically consistent with that obtained from accelerated life test based on failure data, and the two estimates of product’s characteristic life only have a difference of 8.7%, but the test time shortens about a half. As a result, a systemic approach is proposed for reliability assessment of highly reliable and long-life aerospace product.
As few or no failures occur during accelerated life test, it is difficult to assess reliability for long-life products with traditional life tests. Reliability assessment using degradation data of product performance over time becomes a significant approach. Aerospace electrical connector is researched in this paper. Through the analysis of failure mechanism, the performance degradation law is obtained and the statistical model for degradation failure is set up; according to the research on statistical analysis methods for degradation data, accelerated life test theory and method for aerospace electrical connector based on performance degradation is proposed by improving time series analysis method, and the storage reliability is assessed for Y11X series of aerospace electrical connector with degradation data from accelerated degradation test. The result obtained is basically consistent with that obtained from accelerated life test based on failure data, and the two estimates of product’s characteristic life only have a difference of 8.7%, but the test time shortens about a half. As a result, a systemic approach is proposed for reliability assessment of highly reliable and long-life aerospace product.
2011, 25(6).
Abstract:
Due to large workspace, heavy-duty and over-constrained mechanism, a small deformation is caused and the precision of the 2-DOF planar parallel manipulator is affected. The kinematic calibration cannot compensate the end-effector errors caused by the small deformation. This paper presents a method combined step kinematic calibration and linear forecast real-time error compensation in order to enhance the precision of a two degree-of-freedom (DOF) planar parallel manipulator of a hybrid machine tool. In the step kinematic calibration phase of the method, the end-effector errors caused by the errors of major constant geometrical parameters is compensated. The step kinematic calibration is based on the minimal linear combinations (MLCs) of the error parameters. All simple and feasible measurements in practice are given, and identification analysis of the set of the MLCs for each measurement is carried out. According to identification analysis results, both measurement costs and observability are considered, and a step calibration including step measurement, step identification and step error compensation is determined. The linear forecast real-time error compensation is used to compensate the end-effector errors caused by other parameters after the step kinematic calibration. Taking the advantages of the step kinematic calibration and the linear forecast real-time error compensation, a method for improving the precision of the 2-DOF planar parallel manipulator is developed. Experiment results show that the proposed method is robust and effective, so that the position errors are kept to the same order of the measurement noise. The presented method is attractive for the 2-DOF planar parallel manipulator and can be also applied to other parallel manipulators with fewer than six DOFs.
Due to large workspace, heavy-duty and over-constrained mechanism, a small deformation is caused and the precision of the 2-DOF planar parallel manipulator is affected. The kinematic calibration cannot compensate the end-effector errors caused by the small deformation. This paper presents a method combined step kinematic calibration and linear forecast real-time error compensation in order to enhance the precision of a two degree-of-freedom (DOF) planar parallel manipulator of a hybrid machine tool. In the step kinematic calibration phase of the method, the end-effector errors caused by the errors of major constant geometrical parameters is compensated. The step kinematic calibration is based on the minimal linear combinations (MLCs) of the error parameters. All simple and feasible measurements in practice are given, and identification analysis of the set of the MLCs for each measurement is carried out. According to identification analysis results, both measurement costs and observability are considered, and a step calibration including step measurement, step identification and step error compensation is determined. The linear forecast real-time error compensation is used to compensate the end-effector errors caused by other parameters after the step kinematic calibration. Taking the advantages of the step kinematic calibration and the linear forecast real-time error compensation, a method for improving the precision of the 2-DOF planar parallel manipulator is developed. Experiment results show that the proposed method is robust and effective, so that the position errors are kept to the same order of the measurement noise. The presented method is attractive for the 2-DOF planar parallel manipulator and can be also applied to other parallel manipulators with fewer than six DOFs.
2011, 25(6).
Abstract:
Ultrasonic vibration feeding (UVF) method which can quantitatively feed and precisely deposit fine powder is a potential technique for micro feeding. The excitation sources transmit vibration to capillary though the third medium for most UVF devices. The vibrator is directly touched with the capillary can transmit mechanical energy on the capillary as much as possible, and the powder feeding can be controlled more precise. However, there are few reports about it. A direct UVF system which integrates the function of micro feeding, process observing, and powder forming was developed in this work. In order to analyze the effect of the system factors on feeding, a group of L9(33) orthogonal experiments are selected to confirm the effect of level change of factors. The three factors are capillary nozzle diameter, amplitude and signal. The flow rate was stable for each combined factors, and the optimum combination for the minimum flow rate are choosing small capillary, small amplitude, and triangular wave orderly. The whole process of feeding includes start point, middle stage and stop stage. Starting of feeding was synchronized to vibration when the amplitude of capillary nozzle is larger than critical amplitude. Then, the feeding process enters the middle stage, the feeding state is observed by the CCD, and it is very stable in the middle stage. Overflow of feeding can’t be eliminated during the stop stage. The features of the deposited powder lines are analyzed; the overflow can be diminished by choosing small capillary and appropriate ratio of the capillary nozzle diameter to the particle size. Chinese characters lattices were deposited to validate the ability of quantitatively feeding and fixed feeding of UVF. Diameters of all powder dots show normal distribution, and more than 60% dots are concentrated from 550 μm to 650 μm, and the average diameter for all the dots is 597 μm. Most dots positions are well approached to their scheduled positions, and the maximum deviation is 0.27 mm. The new direct UVF system is used to implement experiments, which confirms the precise controllable of feeding. According improve the feeding technique, it suits well for rapid prototyping, chemistry, pharmaceutics and many other fields, which require precise measurement and feed minim powder.
Ultrasonic vibration feeding (UVF) method which can quantitatively feed and precisely deposit fine powder is a potential technique for micro feeding. The excitation sources transmit vibration to capillary though the third medium for most UVF devices. The vibrator is directly touched with the capillary can transmit mechanical energy on the capillary as much as possible, and the powder feeding can be controlled more precise. However, there are few reports about it. A direct UVF system which integrates the function of micro feeding, process observing, and powder forming was developed in this work. In order to analyze the effect of the system factors on feeding, a group of L9(33) orthogonal experiments are selected to confirm the effect of level change of factors. The three factors are capillary nozzle diameter, amplitude and signal. The flow rate was stable for each combined factors, and the optimum combination for the minimum flow rate are choosing small capillary, small amplitude, and triangular wave orderly. The whole process of feeding includes start point, middle stage and stop stage. Starting of feeding was synchronized to vibration when the amplitude of capillary nozzle is larger than critical amplitude. Then, the feeding process enters the middle stage, the feeding state is observed by the CCD, and it is very stable in the middle stage. Overflow of feeding can’t be eliminated during the stop stage. The features of the deposited powder lines are analyzed; the overflow can be diminished by choosing small capillary and appropriate ratio of the capillary nozzle diameter to the particle size. Chinese characters lattices were deposited to validate the ability of quantitatively feeding and fixed feeding of UVF. Diameters of all powder dots show normal distribution, and more than 60% dots are concentrated from 550 μm to 650 μm, and the average diameter for all the dots is 597 μm. Most dots positions are well approached to their scheduled positions, and the maximum deviation is 0.27 mm. The new direct UVF system is used to implement experiments, which confirms the precise controllable of feeding. According improve the feeding technique, it suits well for rapid prototyping, chemistry, pharmaceutics and many other fields, which require precise measurement and feed minim powder.
2011, 25(6).
Abstract:
It is difficult to weld the material and structure of implantable neuro-stimulator such as pure medical titanium and irregular outside shield by conventional arc welding methods. Currently there are few reports on the neuro stimulator sealing technology, and none of them have simultaneously considered the quality control methods. In order to develop the sealing procedure and quality control methods, an investigation of applying Nd: YAG laser welding to implantable neuro-stimulator components is carried out. Firstly, the automatic Nd: YAG laser welding system equipped with proper fixture configuration is introduced. A special fixture structure is illustrated and the key point for the device is to reduce the fit-up gap between the two shields. Then, a novel welding process technique is proposed to satisfy the engineering requirements. The optimized process parameters for titanium shell, feedthrough and fastener are provided and concluded by an orthogonal experiment. Finally, different quality control measures such as visual inspection, X-ray detecting and leakage testing, are presented on the final products. The results show that the Nd: YAG laser welding applied on the implanted neuro-stimulator under optimized parameters can prevent welding defects and improve the weld joints quality. Combination of various quality control methods will guarantee the sealing performance and mechanical properties of the products. It is confirmed that the processing procedure and quality methods can not only resolve the process technology on welding ultra-thin structure of medical device, but also provide the reference for other implantable device.
It is difficult to weld the material and structure of implantable neuro-stimulator such as pure medical titanium and irregular outside shield by conventional arc welding methods. Currently there are few reports on the neuro stimulator sealing technology, and none of them have simultaneously considered the quality control methods. In order to develop the sealing procedure and quality control methods, an investigation of applying Nd: YAG laser welding to implantable neuro-stimulator components is carried out. Firstly, the automatic Nd: YAG laser welding system equipped with proper fixture configuration is introduced. A special fixture structure is illustrated and the key point for the device is to reduce the fit-up gap between the two shields. Then, a novel welding process technique is proposed to satisfy the engineering requirements. The optimized process parameters for titanium shell, feedthrough and fastener are provided and concluded by an orthogonal experiment. Finally, different quality control measures such as visual inspection, X-ray detecting and leakage testing, are presented on the final products. The results show that the Nd: YAG laser welding applied on the implanted neuro-stimulator under optimized parameters can prevent welding defects and improve the weld joints quality. Combination of various quality control methods will guarantee the sealing performance and mechanical properties of the products. It is confirmed that the processing procedure and quality methods can not only resolve the process technology on welding ultra-thin structure of medical device, but also provide the reference for other implantable device.
2011, 25(6).
Abstract:
To cope with the market demand dynamically, enterprise needs to obtain the production status of work in process real-timely, but the information of machining progress has feature of uncertainty and can not reflect the status of production field effectively. In this work, to overcome the ineffectiveness of computer numerical control (CNC) machining progress information extraction and its application restriction in practice because of heterogeneous system of CNC machine, based on information fusion by analyzing multi-sources information, estimating CNC machining status and predicting the machining progress through tracking tool coordinates, a CNC machining progress monitoring method is presented. The multi-sources heterogeneous information includes machining path, real-time spindle power information, manual input data and tool position. On the method of obtaining this multi-sources heterogeneous information, the method which helps explore numerical control (NC) program, monitor spindle power of CNC, collect human-computer interaction(HCI) information, obtain real-time tool coordinates and express the knowledge concerned in this field is analyzed; The decision rule of CNC machining status in the way of fusing multi-sources information in manufacturing process is summarized, as well as the machining progress tracking method in accordance with real-time tool coordinates and machining path is presented. Finally, the method discussed is proved feasible by the verification of machining progress tracking through simulation experiment. The proposed research realizes the effective integration of CNC machining progress information, and enables enterprises an efficient way to share CNC information and configure CNC resources optimally.
To cope with the market demand dynamically, enterprise needs to obtain the production status of work in process real-timely, but the information of machining progress has feature of uncertainty and can not reflect the status of production field effectively. In this work, to overcome the ineffectiveness of computer numerical control (CNC) machining progress information extraction and its application restriction in practice because of heterogeneous system of CNC machine, based on information fusion by analyzing multi-sources information, estimating CNC machining status and predicting the machining progress through tracking tool coordinates, a CNC machining progress monitoring method is presented. The multi-sources heterogeneous information includes machining path, real-time spindle power information, manual input data and tool position. On the method of obtaining this multi-sources heterogeneous information, the method which helps explore numerical control (NC) program, monitor spindle power of CNC, collect human-computer interaction(HCI) information, obtain real-time tool coordinates and express the knowledge concerned in this field is analyzed; The decision rule of CNC machining status in the way of fusing multi-sources information in manufacturing process is summarized, as well as the machining progress tracking method in accordance with real-time tool coordinates and machining path is presented. Finally, the method discussed is proved feasible by the verification of machining progress tracking through simulation experiment. The proposed research realizes the effective integration of CNC machining progress information, and enables enterprises an efficient way to share CNC information and configure CNC resources optimally.
2011, 25(6).
Abstract:
The exist researches of the magneto-rheological semi-active suspension(MSAS) control mainly focus on the design of control laws, which aim at obtaining an optimal control strategy to improve the ride comfort and handling stability. In the controller design, the stability of the MSAS system cannot be confirmed owing to the control input time delay considered little. In this paper, a quarter vehicle MSAS model with time-delay is built. Therefore, through formulating the sprung mass acceleration suitably as the optimization object, suspension deflection and tyre dynamic load and coulomb damping force as the constraint objects, with considering the control input time-delay, a delay-dependent state feedback H2H∞ controller is designed. According to Lyapunov-Krasovskii functional theory, the sufficient conditions for asymptotic stability and the existence of delay-dependent H2H∞ controller are obtained, and the controller design is transformed into the minimization problem for linear function through linear matrix inequality(LMI). Random road excitation simulations and experiments are carried out. The simulation and experiment results show that the design can preserve the closed-loop stability and achieve the performances for MSAS system in spite of the existence of the control input time-delay. The present study can provide an important basis and method for research on time-delay problem in MSAS and other chassis subsystems.
The exist researches of the magneto-rheological semi-active suspension(MSAS) control mainly focus on the design of control laws, which aim at obtaining an optimal control strategy to improve the ride comfort and handling stability. In the controller design, the stability of the MSAS system cannot be confirmed owing to the control input time delay considered little. In this paper, a quarter vehicle MSAS model with time-delay is built. Therefore, through formulating the sprung mass acceleration suitably as the optimization object, suspension deflection and tyre dynamic load and coulomb damping force as the constraint objects, with considering the control input time-delay, a delay-dependent state feedback H2H∞ controller is designed. According to Lyapunov-Krasovskii functional theory, the sufficient conditions for asymptotic stability and the existence of delay-dependent H2H∞ controller are obtained, and the controller design is transformed into the minimization problem for linear function through linear matrix inequality(LMI). Random road excitation simulations and experiments are carried out. The simulation and experiment results show that the design can preserve the closed-loop stability and achieve the performances for MSAS system in spite of the existence of the control input time-delay. The present study can provide an important basis and method for research on time-delay problem in MSAS and other chassis subsystems.
2011, 25(6).
Abstract:
There are two kinds of internationally recognized approaches in terms of lightweight design. One is based on fatigue accumulated damage theory to achieve better reliability by optimal structural design; another is to use high performance lightweight materials. The former method takes very few considerations on the structural strengthening effects caused by the massive small loads in service. In order to ensure safety, the design is usually conservative, but the strength potential of the component is not fully exerted. In the latter method, cost is the biggest obstacle to lightweight materials in automotive applications. For the purpose of light weighting design on a fuel cell vehicle, the new design method is applied on drive shafts. The method is based on the low amplitude load strengthening characteristics of the material, and allows the stress, corresponding to test load, to enter into the strengthened range of the material. Under this condition, the light weighting design should assure that the reliability of the shaft is not impaired, even maximizes the strength potential of machine part in order to achieve the weight reduction and eventually to reduce the cost. At last, the feasibility of the design is verified by means of strength analysis and modal analysis based on the CAD model of light weighted shaft. The design applies to the load case of half shaft in independent axle, also provides technological reference for the structural lightweight design of vehicles and other machineries.
There are two kinds of internationally recognized approaches in terms of lightweight design. One is based on fatigue accumulated damage theory to achieve better reliability by optimal structural design; another is to use high performance lightweight materials. The former method takes very few considerations on the structural strengthening effects caused by the massive small loads in service. In order to ensure safety, the design is usually conservative, but the strength potential of the component is not fully exerted. In the latter method, cost is the biggest obstacle to lightweight materials in automotive applications. For the purpose of light weighting design on a fuel cell vehicle, the new design method is applied on drive shafts. The method is based on the low amplitude load strengthening characteristics of the material, and allows the stress, corresponding to test load, to enter into the strengthened range of the material. Under this condition, the light weighting design should assure that the reliability of the shaft is not impaired, even maximizes the strength potential of machine part in order to achieve the weight reduction and eventually to reduce the cost. At last, the feasibility of the design is verified by means of strength analysis and modal analysis based on the CAD model of light weighted shaft. The design applies to the load case of half shaft in independent axle, also provides technological reference for the structural lightweight design of vehicles and other machineries.
2011, 25(6).
Abstract:
The nonuniform irradiation in the standard photovoltaic (PV) cells causes their relatively high series resistance, which results in a considerably lowered efficiency of PV cells. Currently the concentrator of uniform irradiation designed for concentrator photovoltaic is rare in China and lack sufficient theoretical research. In this paper, a systematic research on the solar reflective concentrator is conducted. A novel structure for a solar reflective concentrator is designed with the application of a flat mirror matrix to concentrate the sunlight for concentrator photovoltaic (CPV) systems. Sunlight beams are focused through the reflection of the mirror array on the solar cell to generate electricity. The concentrator is capable of producing much more uniform sunlight with a certain concentration ratio. The design scheme includes laying out the flat mirrors, optimizing the optical pathway and the parameters of each mirror. The prototype of the CPV system was installed at Nanjing, China. In the configuration of the prototype, it is composed of 24 pieces parallelogram flat mirrors, which are arranged into a total reflective array of 5 rows and 5 columns. In comparison with the parabolic trough concentrator, the experimental measurements verify such design has high efficiency. The concentrator model of a flat mirror matrix and the proposed new design method will lay a solid foundation for designing the concentrator of uniform irradiation.
The nonuniform irradiation in the standard photovoltaic (PV) cells causes their relatively high series resistance, which results in a considerably lowered efficiency of PV cells. Currently the concentrator of uniform irradiation designed for concentrator photovoltaic is rare in China and lack sufficient theoretical research. In this paper, a systematic research on the solar reflective concentrator is conducted. A novel structure for a solar reflective concentrator is designed with the application of a flat mirror matrix to concentrate the sunlight for concentrator photovoltaic (CPV) systems. Sunlight beams are focused through the reflection of the mirror array on the solar cell to generate electricity. The concentrator is capable of producing much more uniform sunlight with a certain concentration ratio. The design scheme includes laying out the flat mirrors, optimizing the optical pathway and the parameters of each mirror. The prototype of the CPV system was installed at Nanjing, China. In the configuration of the prototype, it is composed of 24 pieces parallelogram flat mirrors, which are arranged into a total reflective array of 5 rows and 5 columns. In comparison with the parabolic trough concentrator, the experimental measurements verify such design has high efficiency. The concentrator model of a flat mirror matrix and the proposed new design method will lay a solid foundation for designing the concentrator of uniform irradiation.
2011, 25(6).
Abstract:
The existing research about ductile grinding of fused silica glass was mainly focused on how to carry out ductile regime material removal for generating very “smoothed” surface and investigate the machining-induced damage in the grinding in order to reduce or eliminate the subsurface damage. The brittle/ductile transition behavior of optical glass materials and the wear of diamond wheel are the most important factors for ductile grinding of optical glass. In this paper, the critical brittle/ductile depth, the influence factors on brittle/ductile transition behavior, the wear of diamond grits in diamond grinding of ultra pure fused silica (UPFS) are investigated by means of micro/nano indentation technique, as well as single grit diamond grinding on an ultra-stiff machine tool, Tetraform “C”. The single grit grinding processes are in-process monitored using acoustic emission (AE) and force dynamometer simultaneously. The wear of diamond grits, morphology and subsurface integrity of the machined groves are examined with atomic force microscope (AFM) and scanning electron microscope (SEM). The critical brittle/ductile depth of more than 0.5 m is achieved. When compared to the using roof-like grits, by using pyramidal diamonds leads to higher critical depths of scratch with identical grinding parameters. However, the influence of grit shapes on the critical depth is not significant as supposed. The grinding force increased linearly with depth of cut in the ductile removal regime, but in brittle removal regime, there are large fluctuations instead of forces increase. The SEM photographs of the cross-section profile show that the median cracks dominate the crack patterns beneath the single grooves. Furthermore, The SEM photographs show multi worn patterns of diamond grits, indicating an inhomogeneous wear mechanism of diamond grits in grinding of fused silica with diamond grinding wheels. The proposed research provides the basal technical theory for improving the ultra-precision grinding of UPFS.
The existing research about ductile grinding of fused silica glass was mainly focused on how to carry out ductile regime material removal for generating very “smoothed” surface and investigate the machining-induced damage in the grinding in order to reduce or eliminate the subsurface damage. The brittle/ductile transition behavior of optical glass materials and the wear of diamond wheel are the most important factors for ductile grinding of optical glass. In this paper, the critical brittle/ductile depth, the influence factors on brittle/ductile transition behavior, the wear of diamond grits in diamond grinding of ultra pure fused silica (UPFS) are investigated by means of micro/nano indentation technique, as well as single grit diamond grinding on an ultra-stiff machine tool, Tetraform “C”. The single grit grinding processes are in-process monitored using acoustic emission (AE) and force dynamometer simultaneously. The wear of diamond grits, morphology and subsurface integrity of the machined groves are examined with atomic force microscope (AFM) and scanning electron microscope (SEM). The critical brittle/ductile depth of more than 0.5 m is achieved. When compared to the using roof-like grits, by using pyramidal diamonds leads to higher critical depths of scratch with identical grinding parameters. However, the influence of grit shapes on the critical depth is not significant as supposed. The grinding force increased linearly with depth of cut in the ductile removal regime, but in brittle removal regime, there are large fluctuations instead of forces increase. The SEM photographs of the cross-section profile show that the median cracks dominate the crack patterns beneath the single grooves. Furthermore, The SEM photographs show multi worn patterns of diamond grits, indicating an inhomogeneous wear mechanism of diamond grits in grinding of fused silica with diamond grinding wheels. The proposed research provides the basal technical theory for improving the ultra-precision grinding of UPFS.
2011, 25(6).
Abstract:
Violent axial vibration of a vehicle engine crankshaft might lead to multiple defects to the engine. Much research on mechanism and control measures has been done on engines, such as using the dynamic stiffness matrix method, rayleigh differential method, and system matrix method. But the source of axial vibration has not been identified clearly because there are many excitation factors for the axial vibration of a crankshaft, such as coupled torsional-axial vibration and coupled bending- axial vibration, etc. In order to improve the calculation reliability and identify the excitation source of axial vibration of in vehicle engine crankshafts, this paper presents a method to identify the axial vibration excitation source of crankshafts for high speed diesel engines based on an auto-regressive and moving average (ARMA) model. Through determining initial moving average variables and measuring axial /bending/ torsional vibrations of a crankshaft at the free-end of a 4-cylinder diesel engine, autoregressive spectrum analysis is applied to the measured vibration signal. The results show that the axial vibration of the crankshaft is mainly excited by coupled bending vibration at high speed. But at low speed, the axial vibration in some frequencies is excited primarily by torsional excitation. Through investigation of axial vibration source of engine crankshafts, calculation accuracy of vibration can be improved significantly.
Violent axial vibration of a vehicle engine crankshaft might lead to multiple defects to the engine. Much research on mechanism and control measures has been done on engines, such as using the dynamic stiffness matrix method, rayleigh differential method, and system matrix method. But the source of axial vibration has not been identified clearly because there are many excitation factors for the axial vibration of a crankshaft, such as coupled torsional-axial vibration and coupled bending- axial vibration, etc. In order to improve the calculation reliability and identify the excitation source of axial vibration of in vehicle engine crankshafts, this paper presents a method to identify the axial vibration excitation source of crankshafts for high speed diesel engines based on an auto-regressive and moving average (ARMA) model. Through determining initial moving average variables and measuring axial /bending/ torsional vibrations of a crankshaft at the free-end of a 4-cylinder diesel engine, autoregressive spectrum analysis is applied to the measured vibration signal. The results show that the axial vibration of the crankshaft is mainly excited by coupled bending vibration at high speed. But at low speed, the axial vibration in some frequencies is excited primarily by torsional excitation. Through investigation of axial vibration source of engine crankshafts, calculation accuracy of vibration can be improved significantly.
2011, 25(6).
Abstract:
Titanium alloys are very chemically reactive and, therefore, have a tendency to weld to the cutting tool during machining. The deterioration in the tool life caused by adhesion is a serious problem when titanium alloys are cut using carbide tools. The chemical reactivity of titanium alloys with carbide tool materials and their consequent welding by adhesion onto the cutting tool during dry cutting leads to excessive chipping, premature tool failure, and poor surface finish. In the present study, dry turning and milling tests were carried out on Ti-6Al-4V alloys with WCCo carbide tools. The adhesion on the tool rake and flank face was explored, the adhesive joint interface between the workpiece materials and tools were observed. SEM observation showed that adhesion can be observed both on the rake and the flank face, and was more pronounced in rake face than in flank face. There was evidence of element diffusion from the tool rake face to the adhering layer (vice versa) through the adhesive joint interface, which leads to the tool element loss and microstructure change. While the adhering materials at the flank face can be easily separated from the joint interface owing to the lower temperature and less pressure at the flank face, the adhesive wear attack results in an abrasive wear in the flank face. Moreover, adhesion is more notable in turning than in milling. The proposed research provides references for studying the adhesion between the workpiece materials and the tools, the adhesion mechanisms and their effect on the tool wear.
Titanium alloys are very chemically reactive and, therefore, have a tendency to weld to the cutting tool during machining. The deterioration in the tool life caused by adhesion is a serious problem when titanium alloys are cut using carbide tools. The chemical reactivity of titanium alloys with carbide tool materials and their consequent welding by adhesion onto the cutting tool during dry cutting leads to excessive chipping, premature tool failure, and poor surface finish. In the present study, dry turning and milling tests were carried out on Ti-6Al-4V alloys with WCCo carbide tools. The adhesion on the tool rake and flank face was explored, the adhesive joint interface between the workpiece materials and tools were observed. SEM observation showed that adhesion can be observed both on the rake and the flank face, and was more pronounced in rake face than in flank face. There was evidence of element diffusion from the tool rake face to the adhering layer (vice versa) through the adhesive joint interface, which leads to the tool element loss and microstructure change. While the adhering materials at the flank face can be easily separated from the joint interface owing to the lower temperature and less pressure at the flank face, the adhesive wear attack results in an abrasive wear in the flank face. Moreover, adhesion is more notable in turning than in milling. The proposed research provides references for studying the adhesion between the workpiece materials and the tools, the adhesion mechanisms and their effect on the tool wear.
2011, 25(6).
Abstract:
It is a fact that acoustic emission (AE) signals contain potentially valuable information for tool wear and breakage monitoring and detection. However, AE stress waves produced in the cutting zone are distorted by the transmission path and the measurement systems, it is difficult to obtain a reliable result by these raw AE data. It is generally known that the process of tool wear belongs to detect weak singularity signals in strong noise. The objective of this paper is to combine Newland Harmonic wavelet and Richman-Moorman (2000) sample entropy for detecting weak singularity signals embedded in strong signals. First, the raw AE signal is decomposed by harmonic wavelet and transformed into the three-dimensional time-frequency mesh map of the harmonic wavelet, at the same time, the contours of the mesh map with log space is induced. Second, the profile map of the three-dimensional time-frequency mesh map is offered, which corresponds to decomposed level on harmonic wavelets. Final, by computing sample entropy in each level, the weak singularity signal can be easily extracted from strong noise. Machining test was carried out on HL-32 NC turning center. This lathe does not have a tailstock. Tungsten carbide finishing tool was used to turn free machining mild steel. The work material was chosen for ease of machining, allowing for generation of surfaces of varying quality without the use of cutting fluids. In turning experiments, the feasibility for tool condition monitoring is demonstrated by 27 kinds of cutting conditions with the sharp tool and the worn tool, 54 group data are sampled by AE. The sample entropy of each level of wavelet decomposed for each one of 54 AE datum is computed, wear tool and shaper tool can be distinguished obviously by the sample entropy value at the 12th level, this is a criterion. The proposed research provides a new theoretical basis and a new engineering application on the tool condition monitoring.
It is a fact that acoustic emission (AE) signals contain potentially valuable information for tool wear and breakage monitoring and detection. However, AE stress waves produced in the cutting zone are distorted by the transmission path and the measurement systems, it is difficult to obtain a reliable result by these raw AE data. It is generally known that the process of tool wear belongs to detect weak singularity signals in strong noise. The objective of this paper is to combine Newland Harmonic wavelet and Richman-Moorman (2000) sample entropy for detecting weak singularity signals embedded in strong signals. First, the raw AE signal is decomposed by harmonic wavelet and transformed into the three-dimensional time-frequency mesh map of the harmonic wavelet, at the same time, the contours of the mesh map with log space is induced. Second, the profile map of the three-dimensional time-frequency mesh map is offered, which corresponds to decomposed level on harmonic wavelets. Final, by computing sample entropy in each level, the weak singularity signal can be easily extracted from strong noise. Machining test was carried out on HL-32 NC turning center. This lathe does not have a tailstock. Tungsten carbide finishing tool was used to turn free machining mild steel. The work material was chosen for ease of machining, allowing for generation of surfaces of varying quality without the use of cutting fluids. In turning experiments, the feasibility for tool condition monitoring is demonstrated by 27 kinds of cutting conditions with the sharp tool and the worn tool, 54 group data are sampled by AE. The sample entropy of each level of wavelet decomposed for each one of 54 AE datum is computed, wear tool and shaper tool can be distinguished obviously by the sample entropy value at the 12th level, this is a criterion. The proposed research provides a new theoretical basis and a new engineering application on the tool condition monitoring.
2011, 25(6).
Abstract:
Unmanned vehicle has attracted wide attention and interests throughout the world since it first deputed in the 1960s. However, the experimental methods for unmanned vehicle’s intelligent behavior, such as semi-physical simulation and motion subsystem, have not been widely explored. First, the requirements of the motion subsystem in unmanned vehicle semi-physical facility are analyzed, and a six DOF parallel manipulator is selected to reproduce the pose of the vehicle. The link lengths of the motion subsystem are worked out under the given rotational angles of the vehicle. According to the geometric properties of tetrahedron, three joint positions of the top platform are determined, and the rest are obtained from the first three position vectors. Six constraint equations are set up based on the vertices on the top platform and the link lengths. In order to solve the six angle variables, a numerical algorithm built on the Newton-Raphson iterative method is presented, which is based on Taylor series expansion of six constraint equations. The pose of the top platform is ultimately calculated. The eigenvalues of the top platform are solved to obtain the natural frequencies of the motion subsystem. The coordinates of six joint centers on the top platform and six constraint equations can be realized by simple algebraic manipulation, which allows significant abbreviation in the formulation and provides a systematic way of obtaining the kinematic solution of the parallel manipulator. A numerical example is given and its efficacy is demonstrated by the inverse kinematics. The computation strategy based on tetrahedron method and Newton-Raphson iterative method provide a simple and cost-effective method for solving forward kinematics of six DOF parallel manipulators, and this method sheds light on other parallel manipulators.
Unmanned vehicle has attracted wide attention and interests throughout the world since it first deputed in the 1960s. However, the experimental methods for unmanned vehicle’s intelligent behavior, such as semi-physical simulation and motion subsystem, have not been widely explored. First, the requirements of the motion subsystem in unmanned vehicle semi-physical facility are analyzed, and a six DOF parallel manipulator is selected to reproduce the pose of the vehicle. The link lengths of the motion subsystem are worked out under the given rotational angles of the vehicle. According to the geometric properties of tetrahedron, three joint positions of the top platform are determined, and the rest are obtained from the first three position vectors. Six constraint equations are set up based on the vertices on the top platform and the link lengths. In order to solve the six angle variables, a numerical algorithm built on the Newton-Raphson iterative method is presented, which is based on Taylor series expansion of six constraint equations. The pose of the top platform is ultimately calculated. The eigenvalues of the top platform are solved to obtain the natural frequencies of the motion subsystem. The coordinates of six joint centers on the top platform and six constraint equations can be realized by simple algebraic manipulation, which allows significant abbreviation in the formulation and provides a systematic way of obtaining the kinematic solution of the parallel manipulator. A numerical example is given and its efficacy is demonstrated by the inverse kinematics. The computation strategy based on tetrahedron method and Newton-Raphson iterative method provide a simple and cost-effective method for solving forward kinematics of six DOF parallel manipulators, and this method sheds light on other parallel manipulators.
Experimental Investigation on Vibration Control of Rotor-bearing System with Active Magnetic Exciter
2011, 25(6).
Abstract:
Vibration control is an efficient way to minimize a rotating machine’s vibration level so that its vibration fault-free can be realized. While，several factors, such as unbalance, misalignment and instability, contribute to the serious vibration of rotating machines. It is necessary that one apparatus can depress vibration caused by two or more reasons. The fault self-recovery(FSR) mechanism is introduced and investigated. Strategies of vibration control are investigated theoretically using numerical method firstly. Active magneticelectric exciter(AME) are selected as the actuator of a FSR device because it can provide suitable force by varying the control current in the exciters depending upon a proportional and derivative control law. By numerical study, it is indicate that only a small control force is needed to improve stability margins of the compressor and prevent subsynchronous vibration fault efficiently. About synchronous vibration, three control strategies, searching in whole circle, fast optimizing control (FOC), and none mistaking control, are investigated to show which of the control strategy can realize the fault self-recovery in the shortest time. Experimental study is conducted on a test rig with variable rotating speed. Results of the test indicate that the non-mistake control strategy can minimize synchronous vibration in less than three seconds. The proposed research can provide a new insight for subsynchronous and synchronous vibration restraining about centrifugal compressor.
Vibration control is an efficient way to minimize a rotating machine’s vibration level so that its vibration fault-free can be realized. While，several factors, such as unbalance, misalignment and instability, contribute to the serious vibration of rotating machines. It is necessary that one apparatus can depress vibration caused by two or more reasons. The fault self-recovery(FSR) mechanism is introduced and investigated. Strategies of vibration control are investigated theoretically using numerical method firstly. Active magneticelectric exciter(AME) are selected as the actuator of a FSR device because it can provide suitable force by varying the control current in the exciters depending upon a proportional and derivative control law. By numerical study, it is indicate that only a small control force is needed to improve stability margins of the compressor and prevent subsynchronous vibration fault efficiently. About synchronous vibration, three control strategies, searching in whole circle, fast optimizing control (FOC), and none mistaking control, are investigated to show which of the control strategy can realize the fault self-recovery in the shortest time. Experimental study is conducted on a test rig with variable rotating speed. Results of the test indicate that the non-mistake control strategy can minimize synchronous vibration in less than three seconds. The proposed research can provide a new insight for subsynchronous and synchronous vibration restraining about centrifugal compressor.
2011, 25(6).
Abstract:
Particle coagulation by Brownian motion is an important but difficult research topic. When particle volume concentration is larger than 0.1%, the classic SMOLUCHOWSKI equation is not applicative anymore. The high concentration coagulation, with HEINE’s correction, source terms for the Taylor-series expansion method of moments (TEMOM) are firstly driven in this paper. Ultra-fine particle (d0100 mm) with initial volume fraction f1% coagulation in a planar jet turbulence flow is simulated via the large eddy simulation (LES). The instantaneous and time-averaged particle distributions and the high concentration enhancement are given out. The particle number concentration distribution results show that the coagulation is more intense comparing to dilute case in previous research, especially near the nozzle exit. After jet flow is fully developed, the effect is much more obvious at the region between vortexes. The time-averaged (the high concentration enhance factor) distributes sharply and symmetrically about the jet centerline at the upstream, but becomes broad and flat at downstream where the cross-stream averaged fluctuates drastically. As a new attempt, this paper shows Brownian coagulation with high concentration also can be calculated via TEMOM appropriately, and the coagulation at the region between vortexes is about 1.38 times intensive of the dilute result calculated by the classic Smoluchowski theory.
Particle coagulation by Brownian motion is an important but difficult research topic. When particle volume concentration is larger than 0.1%, the classic SMOLUCHOWSKI equation is not applicative anymore. The high concentration coagulation, with HEINE’s correction, source terms for the Taylor-series expansion method of moments (TEMOM) are firstly driven in this paper. Ultra-fine particle (d0100 mm) with initial volume fraction f1% coagulation in a planar jet turbulence flow is simulated via the large eddy simulation (LES). The instantaneous and time-averaged particle distributions and the high concentration enhancement are given out. The particle number concentration distribution results show that the coagulation is more intense comparing to dilute case in previous research, especially near the nozzle exit. After jet flow is fully developed, the effect is much more obvious at the region between vortexes. The time-averaged (the high concentration enhance factor) distributes sharply and symmetrically about the jet centerline at the upstream, but becomes broad and flat at downstream where the cross-stream averaged fluctuates drastically. As a new attempt, this paper shows Brownian coagulation with high concentration also can be calculated via TEMOM appropriately, and the coagulation at the region between vortexes is about 1.38 times intensive of the dilute result calculated by the classic Smoluchowski theory.
2011, 25(6).
Abstract:
The existing researches on the damping wheel mainly focus on investigating the influence of damping structure change on the vibro-acoustic control. The changes include the geometric size of the damping structure, the damping material parameters, and the placement, and so on. In order to further understand the mechanism in reducing the acoustic radiation of railway wheel with layer damping treatment, in this paper, the wheel is simply modified by a full-sized circular plate. The circle plate side has stuck circumference constrained damping ridges and radial constrained damping ridges on it. Based on a hybrid finite element method-boundary element method (FEM-BEM), the paper develops a vibro-acoustic radiation model for such a distributed constrained damping structure. The vibration and acoustic radiation of the circular plate is analyzed. In the analysis, the dynamic response of the system is obtained by using the 3D finite model superposition method. The obtained vibration response is used as the initial boundary condition in solving Helmholtz boundary integral equation for the sound radiation analysis. In the procedure, firstly, the modal analysis of the circular plate is performed to get the distribution of the system modal strain energy. Secondly, the vibro-acoustic radiation characteristics of the plate with different kinds of circumference damping ridges and radial damping ridges are compared in order to try to find the best effective damping ridge structure. Thirdly, using the distribution of the plate modal strain energy investigates the effect of the ridge distribution locations on the circular plate on its vibro-acoustic radiation. The calculation and analysis research results show that, the sticking circumference and radial damping ridges on the plate can control the vibro-acoustic radiation of the plate effectively in different frequency range. The distribution of the constrained damping ridge has an effect on reduction in vibro-acoustic radiation of the circular plate. The present research is very useful in the design of railway wheel with low noise level.
The existing researches on the damping wheel mainly focus on investigating the influence of damping structure change on the vibro-acoustic control. The changes include the geometric size of the damping structure, the damping material parameters, and the placement, and so on. In order to further understand the mechanism in reducing the acoustic radiation of railway wheel with layer damping treatment, in this paper, the wheel is simply modified by a full-sized circular plate. The circle plate side has stuck circumference constrained damping ridges and radial constrained damping ridges on it. Based on a hybrid finite element method-boundary element method (FEM-BEM), the paper develops a vibro-acoustic radiation model for such a distributed constrained damping structure. The vibration and acoustic radiation of the circular plate is analyzed. In the analysis, the dynamic response of the system is obtained by using the 3D finite model superposition method. The obtained vibration response is used as the initial boundary condition in solving Helmholtz boundary integral equation for the sound radiation analysis. In the procedure, firstly, the modal analysis of the circular plate is performed to get the distribution of the system modal strain energy. Secondly, the vibro-acoustic radiation characteristics of the plate with different kinds of circumference damping ridges and radial damping ridges are compared in order to try to find the best effective damping ridge structure. Thirdly, using the distribution of the plate modal strain energy investigates the effect of the ridge distribution locations on the circular plate on its vibro-acoustic radiation. The calculation and analysis research results show that, the sticking circumference and radial damping ridges on the plate can control the vibro-acoustic radiation of the plate effectively in different frequency range. The distribution of the constrained damping ridge has an effect on reduction in vibro-acoustic radiation of the circular plate. The present research is very useful in the design of railway wheel with low noise level.
2011, 25(6).
Abstract:
There are two kinds of piezoelectric pumps: check valve pumps and valve-less pumps. Whether to use a check valve or not depends upon the application occasion. To achieve large backpressure for higher flow rates, the pump with check valve is desirable. However, adding check valves implies more complex structure and higher probability of valve blocking, etc. In order to solve the problem, effective driving and transport mechanics with compact construction and reliable service are being sought. In this paper, using the second-order longitudinal vibration mode of a bar-shaped piezoelectric vibrator for driving fluid, a piezoelectric pump is successfully made. The proposed piezoelectric pump consists of coaxial cylindrical shells and a bar-shaped piezoelectric vibrator, which has a disk part and a cone part. The lead zirconium titanate ceramic rings fixed in the vibrator are polarized along the thickness direction. When the second-order longitudinal vibration of the vibrator along its axis is excited, the disk part of the vibrator changes periodically the volume of the chamber and the cone part acts as a pin valve, driving the fluid from the inlet port to the outlet port. Finite elements analysis on the proposed pump model is carried out to verify its operation principle and design by the commercial FEM software ANSYS. Components of the piezoelectric pump were manufactured, assembled, and tested for flow rate and backpressure to validate the concepts of the proposed pump and confirm the simulation results of modal and harmonic analyses. The test results show that the performance of the proposed piezoelectric pump is about 910 mL/min in flow rate with a highest pressure level of 1.5 kPa under 400 V peak-to-peak voltage and 51.7 kHz operating frequency. It is confirmed that this bar-shaped piezoelectric transducer can be effectively applied in fluid transferring mechanism of pump through this research.
There are two kinds of piezoelectric pumps: check valve pumps and valve-less pumps. Whether to use a check valve or not depends upon the application occasion. To achieve large backpressure for higher flow rates, the pump with check valve is desirable. However, adding check valves implies more complex structure and higher probability of valve blocking, etc. In order to solve the problem, effective driving and transport mechanics with compact construction and reliable service are being sought. In this paper, using the second-order longitudinal vibration mode of a bar-shaped piezoelectric vibrator for driving fluid, a piezoelectric pump is successfully made. The proposed piezoelectric pump consists of coaxial cylindrical shells and a bar-shaped piezoelectric vibrator, which has a disk part and a cone part. The lead zirconium titanate ceramic rings fixed in the vibrator are polarized along the thickness direction. When the second-order longitudinal vibration of the vibrator along its axis is excited, the disk part of the vibrator changes periodically the volume of the chamber and the cone part acts as a pin valve, driving the fluid from the inlet port to the outlet port. Finite elements analysis on the proposed pump model is carried out to verify its operation principle and design by the commercial FEM software ANSYS. Components of the piezoelectric pump were manufactured, assembled, and tested for flow rate and backpressure to validate the concepts of the proposed pump and confirm the simulation results of modal and harmonic analyses. The test results show that the performance of the proposed piezoelectric pump is about 910 mL/min in flow rate with a highest pressure level of 1.5 kPa under 400 V peak-to-peak voltage and 51.7 kHz operating frequency. It is confirmed that this bar-shaped piezoelectric transducer can be effectively applied in fluid transferring mechanism of pump through this research.
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