2011 Vol.24(1)
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2011, 25(1).
Abstract:
A dry-gas seal system is a non-contact seal technology that is widely used in different industrial applications. Spiral-groove dry-gas seal utilizes fluid dynamic pressure effects to realize the seal and lubrication processes, while forming a high pressure gas film between two sealing faces due to the deceleration of the gas pumped in or out. There is little research into the effects and the influence on seal performance, if the grooves and the gas film are at the micro-scale. This paper investigates the micro-scale effects on spiral-groove dry-gas seal performance in a numerical solution of a corrected Reynolds equation. The Reynolds equation is discretized by means of the finite difference method with the second order scheme and solved by the successive-over-relaxation(SOR) iterative method. The Knudsen number of the flow in the sealing gas film is changed from 0.005 to 0.120 with a variation of film depth and sealing pressure. The numerical results show that the average pressure in the gas film and the sealed gas leakage increase due to micro-scale effects. The open force is enlarged, while the gas film stiffness is significantly decreased due to micro-scale effects. The friction torque and power consumption remain constant, even in low sealing pressure and spin speed conditions. In this paper, the seal performance at different rotor face spin speeds is also described. The proposed research clarifies the micro-scale effects in a spiral-groove dry-gas seal and their influence on seal performance, which is expected to be useful for the improvement of the design of dry-gas seal systems operating in the slip flow regime.
A dry-gas seal system is a non-contact seal technology that is widely used in different industrial applications. Spiral-groove dry-gas seal utilizes fluid dynamic pressure effects to realize the seal and lubrication processes, while forming a high pressure gas film between two sealing faces due to the deceleration of the gas pumped in or out. There is little research into the effects and the influence on seal performance, if the grooves and the gas film are at the micro-scale. This paper investigates the micro-scale effects on spiral-groove dry-gas seal performance in a numerical solution of a corrected Reynolds equation. The Reynolds equation is discretized by means of the finite difference method with the second order scheme and solved by the successive-over-relaxation(SOR) iterative method. The Knudsen number of the flow in the sealing gas film is changed from 0.005 to 0.120 with a variation of film depth and sealing pressure. The numerical results show that the average pressure in the gas film and the sealed gas leakage increase due to micro-scale effects. The open force is enlarged, while the gas film stiffness is significantly decreased due to micro-scale effects. The friction torque and power consumption remain constant, even in low sealing pressure and spin speed conditions. In this paper, the seal performance at different rotor face spin speeds is also described. The proposed research clarifies the micro-scale effects in a spiral-groove dry-gas seal and their influence on seal performance, which is expected to be useful for the improvement of the design of dry-gas seal systems operating in the slip flow regime.
2011, 25(1).
Abstract:
Conical cam mechanism has been widely used in modern machinery and equipment. However, the commonly used planar expansion methods for the design of spatial cam contour produce significant errors, because these methods incorrectly use the distance from the axis of the follower to the main conical cam to replace the corresponding arc length on the conical cam. HSIEH, et al, used analytical methods to achieve higher accuracy, but these analytical methods have their own drawbacks since they are too complicated for practical use. Through the analysis of the errors created during the generation of conical cam contour using the existing expansion methods, this paper proposes to include diverge angle in the calculation of conical cam rotation angle in the equation of conical cam contour expansion. This correction eliminates the error generated by the commonly used methods. Based on the expression of the follower’s 3D trajectory and the spatial geometry of conical cam, this paper has deduced the planar polar curve equation for determining polar coordinates for the curve of planar expansion outline. Furthermore, this paper provides an example of conical cam contour design based on sinusoidal acceleration variation. According to polar coordinates and the movement of curve equation function expression, this paper applies MATLAB software to solve coordinates for the cam expansion curve and uses AutoCAD software to generate conical cam expansion contour that meets the requirement of the law of motion. The proposed method provides a design process that is simple, intuitive and easy to master and implement. It also avoids the design error in the traditional methods for generating contour of conical cam with oscillating follower that requires high precision
Conical cam mechanism has been widely used in modern machinery and equipment. However, the commonly used planar expansion methods for the design of spatial cam contour produce significant errors, because these methods incorrectly use the distance from the axis of the follower to the main conical cam to replace the corresponding arc length on the conical cam. HSIEH, et al, used analytical methods to achieve higher accuracy, but these analytical methods have their own drawbacks since they are too complicated for practical use. Through the analysis of the errors created during the generation of conical cam contour using the existing expansion methods, this paper proposes to include diverge angle in the calculation of conical cam rotation angle in the equation of conical cam contour expansion. This correction eliminates the error generated by the commonly used methods. Based on the expression of the follower’s 3D trajectory and the spatial geometry of conical cam, this paper has deduced the planar polar curve equation for determining polar coordinates for the curve of planar expansion outline. Furthermore, this paper provides an example of conical cam contour design based on sinusoidal acceleration variation. According to polar coordinates and the movement of curve equation function expression, this paper applies MATLAB software to solve coordinates for the cam expansion curve and uses AutoCAD software to generate conical cam expansion contour that meets the requirement of the law of motion. The proposed method provides a design process that is simple, intuitive and easy to master and implement. It also avoids the design error in the traditional methods for generating contour of conical cam with oscillating follower that requires high precision
2011, 25(1).
Abstract:
Electro-hydraulic screw down servo system(HSDS) is widely used in seamless tube rolling mill in western companies. But in Chinese companies, mechanical screw down system(MSDS) is popularly equipped and has a serious disadvantage that the roller would often be locked when it is overloaded. For the purpose of designing the first set of domestic twin-roller, four-cylinder and six-framework electro-hydraulic HSDS of seamless tube rolling mill, an experiment system that can simulate the process of seamless tube rolling is constructed. A digital simulation model of the experiment system is built with AMESim software and validated by comparing the simulation results with experiment results. The sudden load response of the screw piston position is studied with the built model and the experiment system. To improve the HSDS’s positioning accuracy with large load, a hybrid control scheme of combining load disturbance feedforward compensation(LDFC) method based on servo valve’s pressure-stroke feature and anti-saturation integral control(ASIC) is proposed. Both results of simulation and experiment indicate that the transient response time of the single-roller HSDS with the proposed scheme decreases from 0.65 s to less than 0.2 s without static error. To improve the system dynamic stiffness and production qualified rate, a flow rate feedforward compensation(FFC) control strategy based on oil compressibility to dynamic position error is proposed. This FFC strategy is validated with experiments in which the transient error caused by sudden load is reduced to less than 25% of that without FFC. By extending the simulation model to HSDS of a twin-roller, four-cylinder rolling mill, analyzing the mill deformation, and applying the LDFC, ASIC and FFC to the HSDS, the dynamic performance and positioning accuracy of compensated multi-roller HSDS at biting moment are predicted. The research results provide a theoretical and experimental basis for the design of HSDS of seamless steel tube rolling mill.
Electro-hydraulic screw down servo system(HSDS) is widely used in seamless tube rolling mill in western companies. But in Chinese companies, mechanical screw down system(MSDS) is popularly equipped and has a serious disadvantage that the roller would often be locked when it is overloaded. For the purpose of designing the first set of domestic twin-roller, four-cylinder and six-framework electro-hydraulic HSDS of seamless tube rolling mill, an experiment system that can simulate the process of seamless tube rolling is constructed. A digital simulation model of the experiment system is built with AMESim software and validated by comparing the simulation results with experiment results. The sudden load response of the screw piston position is studied with the built model and the experiment system. To improve the HSDS’s positioning accuracy with large load, a hybrid control scheme of combining load disturbance feedforward compensation(LDFC) method based on servo valve’s pressure-stroke feature and anti-saturation integral control(ASIC) is proposed. Both results of simulation and experiment indicate that the transient response time of the single-roller HSDS with the proposed scheme decreases from 0.65 s to less than 0.2 s without static error. To improve the system dynamic stiffness and production qualified rate, a flow rate feedforward compensation(FFC) control strategy based on oil compressibility to dynamic position error is proposed. This FFC strategy is validated with experiments in which the transient error caused by sudden load is reduced to less than 25% of that without FFC. By extending the simulation model to HSDS of a twin-roller, four-cylinder rolling mill, analyzing the mill deformation, and applying the LDFC, ASIC and FFC to the HSDS, the dynamic performance and positioning accuracy of compensated multi-roller HSDS at biting moment are predicted. The research results provide a theoretical and experimental basis for the design of HSDS of seamless steel tube rolling mill.
2011, 25(1).
Abstract:
Micro-tubes manufactured by hydro-forming techniques have now been widely used in medical and microelectronics applications. One of the difficulties in forming such parts is the control of localized necking in the initial stages of the deformationforming process. A lack of microstructural information causes conventional macro-mechanics finite element(FE) tools to break down when used to investi-gate the localized microstructure evolution and necking encountered in micro-forming. An effort has been made to create an integrated crystal plasticity finite element(CPFE) system that enables micro-forming process simulations to be carried out easily, with the important features in forming micro-parts captured by the model. Based on Voronoi tessellation and probability theory, a virtual GRAIN(VGRAIN) system is created for generating grains and grain boundaries for micro-materials. Numerical procedures are developed to link the physical parameters of a material to the control variables in a Gamma distribution. A script interface is developed so that the virtual microstructure can be input to the commercial FE code, ABAQUS, for mesh generation. A simplified plane strain CPFE modeling technique is developed and used to capture localized thinning and failure features for hydro-forming of micro-tubes. Grains within the tube workpiece, their distributions and orientations are generated automatically by using the VGRAIN system. A set of crystal viscoplasticity constitutive equations are implemented in ABAQUSExplicit by using the user-defined material subroutine, VUMAT. Localized thinning is analyzed for different microstructures and deformation conditions of the material using the CPFE modeling tech-nique. The research results show that locations of thinning in forming micro-tubes can be random, which are related to microstructure and grain orientations of the material. The proposed CPFE technique can be used to predict the locations of thinning in forming micro-tubes.
Micro-tubes manufactured by hydro-forming techniques have now been widely used in medical and microelectronics applications. One of the difficulties in forming such parts is the control of localized necking in the initial stages of the deformationforming process. A lack of microstructural information causes conventional macro-mechanics finite element(FE) tools to break down when used to investi-gate the localized microstructure evolution and necking encountered in micro-forming. An effort has been made to create an integrated crystal plasticity finite element(CPFE) system that enables micro-forming process simulations to be carried out easily, with the important features in forming micro-parts captured by the model. Based on Voronoi tessellation and probability theory, a virtual GRAIN(VGRAIN) system is created for generating grains and grain boundaries for micro-materials. Numerical procedures are developed to link the physical parameters of a material to the control variables in a Gamma distribution. A script interface is developed so that the virtual microstructure can be input to the commercial FE code, ABAQUS, for mesh generation. A simplified plane strain CPFE modeling technique is developed and used to capture localized thinning and failure features for hydro-forming of micro-tubes. Grains within the tube workpiece, their distributions and orientations are generated automatically by using the VGRAIN system. A set of crystal viscoplasticity constitutive equations are implemented in ABAQUSExplicit by using the user-defined material subroutine, VUMAT. Localized thinning is analyzed for different microstructures and deformation conditions of the material using the CPFE modeling tech-nique. The research results show that locations of thinning in forming micro-tubes can be random, which are related to microstructure and grain orientations of the material. The proposed CPFE technique can be used to predict the locations of thinning in forming micro-tubes.
2011, 25(1).
Abstract:
Reduction of drag torque is one of important potentials to improve transmission efficiency. Existing mathematical model of drag torque was not accurate to predict the decrease after oil film shrinking because of the difficulty in modeling the flow pattern between two plates. Flow pattern was considered as laminar flow and full oil film in the gap between two plates in traditional model. Subsequent equivalent circumferential degree model presented an improvement in oil film shrinking due to centrifugal force, but was also based on full oil film in the gap, which resulted difference between model prediction and experimental data. The objective of this paper is to develop an accurate mathematical model for the above problem by using experimental verification. An experimental apparatus was set up to test drag torque of disengaged wet clutch consisting of single friction and separate plate. A high speed camera was used to record the flow pattern through transparent quartz disk plate. The visualization of flow pattern in the clearance was investigated to evaluate the characteristics of oil film shrinking. Visual test results reveal that the oil film begins to shrink from outer radius to inner radius at the stationary plate and only flows along the rotating plate after shrinking. Meanwhile, drag torque decreases sharply due to little contact area between the stationary plate and the oil. A three-dimensional Navier-Stokes (N-S) equation based on laminar flow is presented to model the drag torque. Pressure distributions in radial and circumferential directions as well as speed distributions are deduced. The model analysis reveals that the acceleration of flow in radial direction caused by centrifugal force is the key reason for the shrinking at the constant feeding flow rate. An approach to descript flow pattern was presented on the basis of visual observation. The drag torque predicted by the model agrees well with test data for non-grooved wet clutch. The proposed model enhances the precision for predicting drag torque, and lays down a framework on which some subsequent models are developed.
Reduction of drag torque is one of important potentials to improve transmission efficiency. Existing mathematical model of drag torque was not accurate to predict the decrease after oil film shrinking because of the difficulty in modeling the flow pattern between two plates. Flow pattern was considered as laminar flow and full oil film in the gap between two plates in traditional model. Subsequent equivalent circumferential degree model presented an improvement in oil film shrinking due to centrifugal force, but was also based on full oil film in the gap, which resulted difference between model prediction and experimental data. The objective of this paper is to develop an accurate mathematical model for the above problem by using experimental verification. An experimental apparatus was set up to test drag torque of disengaged wet clutch consisting of single friction and separate plate. A high speed camera was used to record the flow pattern through transparent quartz disk plate. The visualization of flow pattern in the clearance was investigated to evaluate the characteristics of oil film shrinking. Visual test results reveal that the oil film begins to shrink from outer radius to inner radius at the stationary plate and only flows along the rotating plate after shrinking. Meanwhile, drag torque decreases sharply due to little contact area between the stationary plate and the oil. A three-dimensional Navier-Stokes (N-S) equation based on laminar flow is presented to model the drag torque. Pressure distributions in radial and circumferential directions as well as speed distributions are deduced. The model analysis reveals that the acceleration of flow in radial direction caused by centrifugal force is the key reason for the shrinking at the constant feeding flow rate. An approach to descript flow pattern was presented on the basis of visual observation. The drag torque predicted by the model agrees well with test data for non-grooved wet clutch. The proposed model enhances the precision for predicting drag torque, and lays down a framework on which some subsequent models are developed.
2011, 25(1).
Abstract:
What is pursued by multi-product type and variant volume(MPTVV) production is rapid response and quick switching, so that structure of transferring line in manufacturing system is no longer unalterable. Cell formation(CF) algorithm is the key technology of cellular manufacturing system(CMS). Currently, CF methods are mainly extended on the idea of group technology(GT) that covers a lot on analysis of resource capability matching and its algorithm. Various constraints are considered, but seldom utilized comprehensively. Aimed to the problem of manufacturing cell(MC) formation under MPTVV production mode, integrated formation technologies for typical MC as group type of cell(GC), flow type of cell(FC) and inherited cell(IC) are presented based on technical analysis of CF. Oriented to practical production constraints like delivery time, product batch, equipment ability, key machine, key part and machine sharing, etc, an integrated formation model is constructed and internal interrelations of these constraints are analyzed synthetically. Ulteriorly, formation goals of types of MCs and their formation procedures under joint effect of formation constraints and rules are spread. In case study, three highly balanced GC are formed first; then FC formation are implemented based on the same data which indicate good balancing effect of cell load and flow-style production for key tasks; When task is adjusted, a new scheme is constructed on the result of FC configuration by using IC formation method, and more optimal performance of flow-style production is manifested. The proposed comparative study of different type of cells strongly explains the validation of integrated MC formation in support of rapid manufacturing resource transformation under MPTVV production mode.
What is pursued by multi-product type and variant volume(MPTVV) production is rapid response and quick switching, so that structure of transferring line in manufacturing system is no longer unalterable. Cell formation(CF) algorithm is the key technology of cellular manufacturing system(CMS). Currently, CF methods are mainly extended on the idea of group technology(GT) that covers a lot on analysis of resource capability matching and its algorithm. Various constraints are considered, but seldom utilized comprehensively. Aimed to the problem of manufacturing cell(MC) formation under MPTVV production mode, integrated formation technologies for typical MC as group type of cell(GC), flow type of cell(FC) and inherited cell(IC) are presented based on technical analysis of CF. Oriented to practical production constraints like delivery time, product batch, equipment ability, key machine, key part and machine sharing, etc, an integrated formation model is constructed and internal interrelations of these constraints are analyzed synthetically. Ulteriorly, formation goals of types of MCs and their formation procedures under joint effect of formation constraints and rules are spread. In case study, three highly balanced GC are formed first; then FC formation are implemented based on the same data which indicate good balancing effect of cell load and flow-style production for key tasks; When task is adjusted, a new scheme is constructed on the result of FC configuration by using IC formation method, and more optimal performance of flow-style production is manifested. The proposed comparative study of different type of cells strongly explains the validation of integrated MC formation in support of rapid manufacturing resource transformation under MPTVV production mode.
2011, 25(1).
Abstract:
High pressure is an important development orientation in pneumatic field, since it can not only improve dynamic characteristics of pneumatic system but also decrease the size of components and mounting space. Due to the advantages of high energy density and high instant expansibility, high pressure gas has been widely used in many applications. However, systematic researches are lacked especially in pressure characteristics which are very important in pneumatic system at present. In a high pressure pneumatic system, the pressure of a fixed cavity with annular clearance needs to be controlled within a wide range, so a single stage proportional slide valve is proposed to satisfy the requirements of high pressure and low flow rate. First, working principle and structure of the pressure assembly and the slide valve are introduced. Then mathematical model of the high pressure pneumatic system is built up; controllable pressure range is simulated, and influence of uncertain factors, such as fit clearance of the pressure valve and the cavity on controllable pressure, is discussed. Finally, a test bench of the pressure assembly is built up, and the controllable pressure and step response experiments are carried out. Both simulation and experimental results show that the designed slide valve can satisfy the requirements well. The proposed clearance presumption method based on simulation and experimental results is valuable for indirect measurement of processing tolerance.
High pressure is an important development orientation in pneumatic field, since it can not only improve dynamic characteristics of pneumatic system but also decrease the size of components and mounting space. Due to the advantages of high energy density and high instant expansibility, high pressure gas has been widely used in many applications. However, systematic researches are lacked especially in pressure characteristics which are very important in pneumatic system at present. In a high pressure pneumatic system, the pressure of a fixed cavity with annular clearance needs to be controlled within a wide range, so a single stage proportional slide valve is proposed to satisfy the requirements of high pressure and low flow rate. First, working principle and structure of the pressure assembly and the slide valve are introduced. Then mathematical model of the high pressure pneumatic system is built up; controllable pressure range is simulated, and influence of uncertain factors, such as fit clearance of the pressure valve and the cavity on controllable pressure, is discussed. Finally, a test bench of the pressure assembly is built up, and the controllable pressure and step response experiments are carried out. Both simulation and experimental results show that the designed slide valve can satisfy the requirements well. The proposed clearance presumption method based on simulation and experimental results is valuable for indirect measurement of processing tolerance.
2011, 25(1).
Abstract:
With the development of technology and the change of market demands, the trend in middle and high grade bicycle manufacturing is developed toward small-volume, multi-species, and customer-oriented production. Therefore, human element should be fully considered in design so that the bicycle has the best cycling performance for the specific rider. Currently, customized design is difficult to achieve since feature parameters of the rider are not included in the design. The design of bicycle frame is the most important in bicycle design. The relative positions among the saddle, handlebar and central axis are defined as the bicycle three-pivot, they are the main parameters in bicycle frame design. In conventional bicycle design, frame parameters are merely relevant to bicycle types. On the basis of the principles of biomechanics and ergonomics knowledge, this paper presents a design method for bicycle three-pivot considering feature parameters of the rider by dynamic simulation. Firstly, a dynamic model of rider-bicycle system is built for a special rider, and a serial of simulation experiments is designed by uniform test method. Then, a mathematical model is built between the three-pivot position and the square of lower limb muscle stress by using simulation and regression analysis of the rider-bicycle system. The optimal three-pivot position parameters are obtained by setting the minimal of the square of the lower limb muscle stress as the objective. Therefore, the optimal parameters are gained for the specific rider. Finally, various results are gained for different riders based on the same design process. The function between feature parameters of the rider and the optimum three-pivot position parameters is built by regression. Bicycle design considering biomechanics can be divided into three main steps: calculating the three-pivot position, designing the geometrical structure of the bicycle frame and analyzing frame strength, and selecting appropriate parts and assembling the bicycle. Bicycle design considering biomechanics changes the conventional bicycle design and realizes customized design by considering human element in the design process.
With the development of technology and the change of market demands, the trend in middle and high grade bicycle manufacturing is developed toward small-volume, multi-species, and customer-oriented production. Therefore, human element should be fully considered in design so that the bicycle has the best cycling performance for the specific rider. Currently, customized design is difficult to achieve since feature parameters of the rider are not included in the design. The design of bicycle frame is the most important in bicycle design. The relative positions among the saddle, handlebar and central axis are defined as the bicycle three-pivot, they are the main parameters in bicycle frame design. In conventional bicycle design, frame parameters are merely relevant to bicycle types. On the basis of the principles of biomechanics and ergonomics knowledge, this paper presents a design method for bicycle three-pivot considering feature parameters of the rider by dynamic simulation. Firstly, a dynamic model of rider-bicycle system is built for a special rider, and a serial of simulation experiments is designed by uniform test method. Then, a mathematical model is built between the three-pivot position and the square of lower limb muscle stress by using simulation and regression analysis of the rider-bicycle system. The optimal three-pivot position parameters are obtained by setting the minimal of the square of the lower limb muscle stress as the objective. Therefore, the optimal parameters are gained for the specific rider. Finally, various results are gained for different riders based on the same design process. The function between feature parameters of the rider and the optimum three-pivot position parameters is built by regression. Bicycle design considering biomechanics can be divided into three main steps: calculating the three-pivot position, designing the geometrical structure of the bicycle frame and analyzing frame strength, and selecting appropriate parts and assembling the bicycle. Bicycle design considering biomechanics changes the conventional bicycle design and realizes customized design by considering human element in the design process.
2011, 25(1).
Abstract:
The existing researches on quartz gyroscope mainly focus on the structure design of the tuning fork, which aim at obtaining a better vibration characterization. However, the fabrication of complicated structure is a challenge for present processes, and the imperfect fabrication process seriously affects the performances of the sensors. In this paper, a novel quartz cross-fork structure micromachined gyroscope is proposed. The sensor has a simple structure in x-y plane of quartz crystal. Unlike other quartz gyroscopes, the proposed gyroscope is based on shear stress detection to sense Coriolis’ force rather than normal stress detection. This feature can simplify the sensing electrode patterns and miniaturize the structure easily. Then the mechanical analysis of the structure is discussed. In order to obtain high sensitivities and uniform characteristics between different structures, the sensing beam is designed to be tapered, and the taper should be appreciably greater than 1°. This scheme is validated by finite element analysis software. The dynamic characteristic of the structure is analyzed by lumped parameter model. The dynamic stress in the beam and the detection sensitivity are deduced to optimize the structure parameter of gyroscope. Finally, the gyroscope is fabricated by quartz anisotropic wet etching. The prototype is characterized as follows. The drive mode frequency is 13.38 kHz, and the quality factor is about 900 in air. The scale factor is 1.45 mV((°) • s–1) and the nonlinearity is 3.6% in the dynamic range of 200°s. Process and test results show that the proposed quartz gyroscope can achieve a high performance at atmosphere pressure. The research can simplify the fabrication of the quartz gyroscope, and is taken as a novel method for the design of quartz gyroscope.
The existing researches on quartz gyroscope mainly focus on the structure design of the tuning fork, which aim at obtaining a better vibration characterization. However, the fabrication of complicated structure is a challenge for present processes, and the imperfect fabrication process seriously affects the performances of the sensors. In this paper, a novel quartz cross-fork structure micromachined gyroscope is proposed. The sensor has a simple structure in x-y plane of quartz crystal. Unlike other quartz gyroscopes, the proposed gyroscope is based on shear stress detection to sense Coriolis’ force rather than normal stress detection. This feature can simplify the sensing electrode patterns and miniaturize the structure easily. Then the mechanical analysis of the structure is discussed. In order to obtain high sensitivities and uniform characteristics between different structures, the sensing beam is designed to be tapered, and the taper should be appreciably greater than 1°. This scheme is validated by finite element analysis software. The dynamic characteristic of the structure is analyzed by lumped parameter model. The dynamic stress in the beam and the detection sensitivity are deduced to optimize the structure parameter of gyroscope. Finally, the gyroscope is fabricated by quartz anisotropic wet etching. The prototype is characterized as follows. The drive mode frequency is 13.38 kHz, and the quality factor is about 900 in air. The scale factor is 1.45 mV((°) • s–1) and the nonlinearity is 3.6% in the dynamic range of 200°s. Process and test results show that the proposed quartz gyroscope can achieve a high performance at atmosphere pressure. The research can simplify the fabrication of the quartz gyroscope, and is taken as a novel method for the design of quartz gyroscope.
2011, 25(1).
Abstract:
The existence of inclusion influences the properties of aluminum alloy castings, from which the castings will face scrapping under severe condition. Great efforts on the inclusions in aluminum alloy were made and many inclusion assessment methods were put forward. However, most of the current methods are characterized by time consuming and expensive equipment cost, which limits the application in aluminum industry. Since the aluminum properties are sensitive to the inclusion, this paper tries to establish a new kind of inclusion assessment method. The inclusions were introduced to aluminum melts by adding aluminum scraps. The samples with different inclusion contents were prepared. The microstructure contained inclusions was observed. The inclusion was automatically identified with an image analyzer by setting different grey threshold value, and the inclusion content was obtained. The image analysis shows that inclusions wreck the continuity of the alloy matrix seriously, and the inclusion area percentage increases with the increasing of aluminum scraps. The high and low polarization measurements were conducted in 3.5 wt% NaCl aqueous solution at the temperature of 25 ℃. The electrochemical parameters of the testing materials, such as corrosion potential Ek, corrosion current density Ik and the linear polarization resistance Rp, were obtained. The polarization measurement results show that the linear polarization resistances decrease, the corrosion potentials move towards more negative direction, and the corrosion current densities increase with the increasing of inclusion content. The theoretical analysis of the inclusion content and the corrosion current density was performed. The existence of inclusions makes the microstructure form corrosion microcells between the alloy matrix and inclusions. The impressed current can accelerate the current velocity or corrosion current density. The regression model of the inclusion contents vs. the corrosion current density was obtained. This model can be used to quantitatively analyze the inclusion content in aluminum alloys on the basis of inclusion sensitivity to the inclusion content. It is confirmed that the electrochemical method for inclusion assessment (EcMIA) is simple and reliable, which can provide a new solution for inclusion assessment in aluminum alloy.
The existence of inclusion influences the properties of aluminum alloy castings, from which the castings will face scrapping under severe condition. Great efforts on the inclusions in aluminum alloy were made and many inclusion assessment methods were put forward. However, most of the current methods are characterized by time consuming and expensive equipment cost, which limits the application in aluminum industry. Since the aluminum properties are sensitive to the inclusion, this paper tries to establish a new kind of inclusion assessment method. The inclusions were introduced to aluminum melts by adding aluminum scraps. The samples with different inclusion contents were prepared. The microstructure contained inclusions was observed. The inclusion was automatically identified with an image analyzer by setting different grey threshold value, and the inclusion content was obtained. The image analysis shows that inclusions wreck the continuity of the alloy matrix seriously, and the inclusion area percentage increases with the increasing of aluminum scraps. The high and low polarization measurements were conducted in 3.5 wt% NaCl aqueous solution at the temperature of 25 ℃. The electrochemical parameters of the testing materials, such as corrosion potential Ek, corrosion current density Ik and the linear polarization resistance Rp, were obtained. The polarization measurement results show that the linear polarization resistances decrease, the corrosion potentials move towards more negative direction, and the corrosion current densities increase with the increasing of inclusion content. The theoretical analysis of the inclusion content and the corrosion current density was performed. The existence of inclusions makes the microstructure form corrosion microcells between the alloy matrix and inclusions. The impressed current can accelerate the current velocity or corrosion current density. The regression model of the inclusion contents vs. the corrosion current density was obtained. This model can be used to quantitatively analyze the inclusion content in aluminum alloys on the basis of inclusion sensitivity to the inclusion content. It is confirmed that the electrochemical method for inclusion assessment (EcMIA) is simple and reliable, which can provide a new solution for inclusion assessment in aluminum alloy.
Real-time Feed-forward Force Compensation for Active Magnetic Bearings System Based on H∞ Controller
2011, 25(1).
Abstract:
There are two kinds of unbalance vibrations—force vibration and displacement vibration due to the existence of unbalance excitation in active magnetic bearings(AMB) system. And two unbalance compensation methods—closed-loop feedback and open loop feed-forward are presented to reduce the force vibration. The transfer function order of the control system directly influencing the system stability will be increased when the closed-loop method is adopted, which makes the real-time compensation not easily achieved. While the open loop method would not increase the primary transfer function order, it provides conditions for real-time compensation. But the real-time compensation signals are not easy to be obtained in the open loop method. To implement real-time force compensation, a new method is proposed to reduce the force vibration caused by the rotor unbalance on the basis of AMB active control. The method realizes real-time and on-line force auto-compensation based on H∞ controller and one novel feed-forward compensation controller, which makes the rotor rotate around its inertia axis. The time-variable feed-forward compensatory signal is provided by a modified adaptive variable step-size least mean square(VSLMS) algorithm. And the relevant least mean square(LMS) algorithm parameters are used to solve the H∞ controller weighting functions. The simulation of the new method to compensate some frequency-variable and sinusoidal signals is completed by MATLAB programming, and real-time compensation is implemented in the actual AMB experimental system. The simulation and experiment results show that the compensation scheme can improve the robust stability and the anti-interference ability of the whole AMB system by using H∞ controller to achieve close-loop control, and then real-time force unbalance compensation is implemented. The proposed research provides a new control strategy containing real-time algorithm and H∞ controller for the force compensation of AMB system. And the stability of the control system is finally improved.
There are two kinds of unbalance vibrations—force vibration and displacement vibration due to the existence of unbalance excitation in active magnetic bearings(AMB) system. And two unbalance compensation methods—closed-loop feedback and open loop feed-forward are presented to reduce the force vibration. The transfer function order of the control system directly influencing the system stability will be increased when the closed-loop method is adopted, which makes the real-time compensation not easily achieved. While the open loop method would not increase the primary transfer function order, it provides conditions for real-time compensation. But the real-time compensation signals are not easy to be obtained in the open loop method. To implement real-time force compensation, a new method is proposed to reduce the force vibration caused by the rotor unbalance on the basis of AMB active control. The method realizes real-time and on-line force auto-compensation based on H∞ controller and one novel feed-forward compensation controller, which makes the rotor rotate around its inertia axis. The time-variable feed-forward compensatory signal is provided by a modified adaptive variable step-size least mean square(VSLMS) algorithm. And the relevant least mean square(LMS) algorithm parameters are used to solve the H∞ controller weighting functions. The simulation of the new method to compensate some frequency-variable and sinusoidal signals is completed by MATLAB programming, and real-time compensation is implemented in the actual AMB experimental system. The simulation and experiment results show that the compensation scheme can improve the robust stability and the anti-interference ability of the whole AMB system by using H∞ controller to achieve close-loop control, and then real-time force unbalance compensation is implemented. The proposed research provides a new control strategy containing real-time algorithm and H∞ controller for the force compensation of AMB system. And the stability of the control system is finally improved.
2011, 25(1).
Abstract:
Research of thermal characteristics has been a key issue in the development of high-speed feed system. Most of the work carried out thus far is based on the principle of directly mapping the thermal error against the temperature of critical machine elements irrespective of the operating conditions. But recent researches show that different sets of operating parameters generated significantly different error values even though the temperature of the machine elements generated was similar. As such, it is important to develop a generic thermal error model which is capable of evaluating the positioning error induced by different operating parameters. This paper ultimately aims at the development of a comprehensive prediction model that can predict the thermal characteristics under different operating conditions (feeding speed, load and preload of ballscrew) in a feed system. A novel wavelet neural network based on feedback linearization autoregressive moving averaging (NARMA-L2) model is introduced to predict the temperature rise of sensitive points and thermal positioning errors considering the different operating conditions as the model inputs. Particle swarm optimization(PSO) algorithm is brought in as the training method. According to ISO230-2 Positioning Accuracy Measurement and ISO230-3 Thermal Effect Evaluation standards, experiments under different operating conditions were carried out on a self-made quasi high-speed feed system experimental bench HUST-FS-001 by using Pt100 as temperature sensor, and the positioning errors were measured by Heidenhain linear grating scale. The experiment results show that the recommended method can be used to predict temperature rise of sensitive points and thermal positioning errors with good accuracy. The work described in this paper lays a solid foundation of thermal error prediction and compensation in a feed system based on varying operating conditions and machine tool characteristics.
Research of thermal characteristics has been a key issue in the development of high-speed feed system. Most of the work carried out thus far is based on the principle of directly mapping the thermal error against the temperature of critical machine elements irrespective of the operating conditions. But recent researches show that different sets of operating parameters generated significantly different error values even though the temperature of the machine elements generated was similar. As such, it is important to develop a generic thermal error model which is capable of evaluating the positioning error induced by different operating parameters. This paper ultimately aims at the development of a comprehensive prediction model that can predict the thermal characteristics under different operating conditions (feeding speed, load and preload of ballscrew) in a feed system. A novel wavelet neural network based on feedback linearization autoregressive moving averaging (NARMA-L2) model is introduced to predict the temperature rise of sensitive points and thermal positioning errors considering the different operating conditions as the model inputs. Particle swarm optimization(PSO) algorithm is brought in as the training method. According to ISO230-2 Positioning Accuracy Measurement and ISO230-3 Thermal Effect Evaluation standards, experiments under different operating conditions were carried out on a self-made quasi high-speed feed system experimental bench HUST-FS-001 by using Pt100 as temperature sensor, and the positioning errors were measured by Heidenhain linear grating scale. The experiment results show that the recommended method can be used to predict temperature rise of sensitive points and thermal positioning errors with good accuracy. The work described in this paper lays a solid foundation of thermal error prediction and compensation in a feed system based on varying operating conditions and machine tool characteristics.
2011, 25(1).
Abstract:
It is a complicated problem for the bottom-to-top adaptive conceptual design of complicated products between structure and function. Reliable theories demand to be found in order to determine whether the structure accords with the requirement of design. For the requirement generally is dynamic variety as time passes, new requirements will come, and some initial requirements can no longer be used. The number of product requirements, the gene length expressing requirements, the structure of the product, and the correlation matrix are varied with individuation of customer requirements of the product. By researching on the calculation mechanisms of dynamic variety, the approaches of gene expression and variable length gene expression are proposed. According to the diversity of structure selection in conceptual design and mutual relations between structure and function as well as structure and structure, the correlation matrixes between structure and function as well as structure and structure are defined. By the approach of making the sum of the elements of correlation matrix maximum, the mathematical models of multi-object optimization for structure design are provided based on variable requirements. An improved genetic algorithm called segment genetic algorithm is proposed based on optimization preservation simple genetic algorithm. The models of multi-object optimization are calculated by the segment genetic algorithm and hybrid genetic algorithm. An example for the conceptual design of a washing machine is given to show that the proposed method is able to realize the optimization structure design fitting for variable requirements. In addition, the proposed approach can provide good Pareto optimization solutions, and the individuation customer requirements for structures of products are able to be resolved effectively.
It is a complicated problem for the bottom-to-top adaptive conceptual design of complicated products between structure and function. Reliable theories demand to be found in order to determine whether the structure accords with the requirement of design. For the requirement generally is dynamic variety as time passes, new requirements will come, and some initial requirements can no longer be used. The number of product requirements, the gene length expressing requirements, the structure of the product, and the correlation matrix are varied with individuation of customer requirements of the product. By researching on the calculation mechanisms of dynamic variety, the approaches of gene expression and variable length gene expression are proposed. According to the diversity of structure selection in conceptual design and mutual relations between structure and function as well as structure and structure, the correlation matrixes between structure and function as well as structure and structure are defined. By the approach of making the sum of the elements of correlation matrix maximum, the mathematical models of multi-object optimization for structure design are provided based on variable requirements. An improved genetic algorithm called segment genetic algorithm is proposed based on optimization preservation simple genetic algorithm. The models of multi-object optimization are calculated by the segment genetic algorithm and hybrid genetic algorithm. An example for the conceptual design of a washing machine is given to show that the proposed method is able to realize the optimization structure design fitting for variable requirements. In addition, the proposed approach can provide good Pareto optimization solutions, and the individuation customer requirements for structures of products are able to be resolved effectively.
2011, 25(1).
Abstract:
In high-speed cutting, natural thermocouple, artificial thermocouple and infrared radiation temperature measurement are usually adopted for measuring cutting temperature, but these methods have difficulty in measuring transient temperature accurately of cutting area on account of low response speed and limited cutting condition. In this paper, NiCrNiSi thin-film thermocouples(TFTCs) are fabricated according to temperature characteristic of cutting area in high-speed cutting by means of advanced twinned microwave electro cyclotron resonance(MW-ECR) plasma source enhanced radio frequency(RF) reaction non-balance magnetron sputtering technique, and can be used for transient cutting temperature measurement. The time constants of the TFTCs with different thermo-junction film width are measured at four kinds of sampling frequency by using Ultra-CFR short pulsed laser system that established. One-dimensional unsteady heat conduction model is constructed and the dynamic performance is analyzed theoretically. It can be seen from the analysis results that the NiCrNiSi TFTCs are suitable for measuring transient temperature which varies quickly, the response speed of TFTCs can be obviously improved by reducing the thickness of thin-film, and the area of thermo-junction has little influence on dynamic response time. The dynamic calibration experiments are made on the constructed dynamic calibration system, and the experimental results confirm that sampling frequency should be larger than 50 kHz in dynamic measurement for stable response time, and the shortest response time is 0.042 ms. Measurement methods and devices of cutting heat and cutting temperature measurement are developed and improved by this research, which provide practical methods and instruments in monitoring cutting heat and cutting temperature for research and production in high-speed machining.
In high-speed cutting, natural thermocouple, artificial thermocouple and infrared radiation temperature measurement are usually adopted for measuring cutting temperature, but these methods have difficulty in measuring transient temperature accurately of cutting area on account of low response speed and limited cutting condition. In this paper, NiCrNiSi thin-film thermocouples(TFTCs) are fabricated according to temperature characteristic of cutting area in high-speed cutting by means of advanced twinned microwave electro cyclotron resonance(MW-ECR) plasma source enhanced radio frequency(RF) reaction non-balance magnetron sputtering technique, and can be used for transient cutting temperature measurement. The time constants of the TFTCs with different thermo-junction film width are measured at four kinds of sampling frequency by using Ultra-CFR short pulsed laser system that established. One-dimensional unsteady heat conduction model is constructed and the dynamic performance is analyzed theoretically. It can be seen from the analysis results that the NiCrNiSi TFTCs are suitable for measuring transient temperature which varies quickly, the response speed of TFTCs can be obviously improved by reducing the thickness of thin-film, and the area of thermo-junction has little influence on dynamic response time. The dynamic calibration experiments are made on the constructed dynamic calibration system, and the experimental results confirm that sampling frequency should be larger than 50 kHz in dynamic measurement for stable response time, and the shortest response time is 0.042 ms. Measurement methods and devices of cutting heat and cutting temperature measurement are developed and improved by this research, which provide practical methods and instruments in monitoring cutting heat and cutting temperature for research and production in high-speed machining.
2011, 25(1).
Abstract:
The direct use of the determinant of Jacobian matrix being equal to zero for the singularity analysis is generally difficult which is due to complexity of the Jacobian matrix of 6-DOF parallel manipulators, especially for Stewart platform. Recently, several scholars make their great contribution to the effective solution of this problem, but neither of them find the right answer. This paper gives a brief analysis of the kinematics of the Stewart platform and derives the Jacobian matrices of the system through the velocity equation. On the basis of the traditional classification of singularities, the second type of singularity is investigated. An assumption of any three of the six variables of the Stewart platform as constant is made, then the analytical expression of singularity locus equation of the second type singularity which contains another three pose variables is obtained. The singularity locus is represented in the three-dimensional space through the derived equation. The correctness and validity of the proposed method are verified through examples. Finally, the singularity analysis of an electric Stewart platform in its desired workspace and reachable workspace is implemented. Thus, one can easily identify whether singularity exists in a given workspace of a Stewart platform and determine whether the existed singularity can be avoided through the proposed method. The proposed method also provides theoretical principle for the design and application of the Stewart platform and has great significance for the trajectory planning and control.
The direct use of the determinant of Jacobian matrix being equal to zero for the singularity analysis is generally difficult which is due to complexity of the Jacobian matrix of 6-DOF parallel manipulators, especially for Stewart platform. Recently, several scholars make their great contribution to the effective solution of this problem, but neither of them find the right answer. This paper gives a brief analysis of the kinematics of the Stewart platform and derives the Jacobian matrices of the system through the velocity equation. On the basis of the traditional classification of singularities, the second type of singularity is investigated. An assumption of any three of the six variables of the Stewart platform as constant is made, then the analytical expression of singularity locus equation of the second type singularity which contains another three pose variables is obtained. The singularity locus is represented in the three-dimensional space through the derived equation. The correctness and validity of the proposed method are verified through examples. Finally, the singularity analysis of an electric Stewart platform in its desired workspace and reachable workspace is implemented. Thus, one can easily identify whether singularity exists in a given workspace of a Stewart platform and determine whether the existed singularity can be avoided through the proposed method. The proposed method also provides theoretical principle for the design and application of the Stewart platform and has great significance for the trajectory planning and control.
2011, 25(1).
Abstract:
Spot weld models are widely used in finite element analysis(FEA) of automotive body in white(BIW) to predict static, dynamic, durability and other characteristics of automotive BIW. However, few researches are done on evaluation of the validity of these spot weld models in structural dynamic analysis of BIW. To evaluate the validity and accuracy of spot weld models in structural dynamic analysis of BIW, two object functions, error function and deviation function, are introduced innovatively. Modal analysis of Two-panel and Double-hat structures, which are the dominated structures in BIW, is conducted, and the values of these two object functions are obtained. Based on the values of object functions, the validity of these spot weld models are evaluated. It is found that the area contact method(ACM2) and weld element connection(CWELD) can give more precise prediction in modal analysis of these two classical structures, thus are more applicable to structural dynamic analysis of automotive BIW. Modal analysis of a classical BIW is performed, which further confirms this evaluation. The error function and deviation function proposed in this research can give guidance on the adaptability of spot weld models in structural dynamic analysis of BIW. And this evaluation method can also be adopted in evaluation of other finite element models in static, dynamic and other kinds of analysis for automotive structures.
Spot weld models are widely used in finite element analysis(FEA) of automotive body in white(BIW) to predict static, dynamic, durability and other characteristics of automotive BIW. However, few researches are done on evaluation of the validity of these spot weld models in structural dynamic analysis of BIW. To evaluate the validity and accuracy of spot weld models in structural dynamic analysis of BIW, two object functions, error function and deviation function, are introduced innovatively. Modal analysis of Two-panel and Double-hat structures, which are the dominated structures in BIW, is conducted, and the values of these two object functions are obtained. Based on the values of object functions, the validity of these spot weld models are evaluated. It is found that the area contact method(ACM2) and weld element connection(CWELD) can give more precise prediction in modal analysis of these two classical structures, thus are more applicable to structural dynamic analysis of automotive BIW. Modal analysis of a classical BIW is performed, which further confirms this evaluation. The error function and deviation function proposed in this research can give guidance on the adaptability of spot weld models in structural dynamic analysis of BIW. And this evaluation method can also be adopted in evaluation of other finite element models in static, dynamic and other kinds of analysis for automotive structures.
2011, 25(1).
Abstract:
Gap debris as discharge product is closely related to machining process in electrical discharge machining(EDM). A lot of recent researches have focused on the relationship among debris size, surfaces texture, remove rate, and machining stability. The study on statistical distribution of debris size contributes to the research, but it is still superficial currently. In order to obtain the distribution law of the debris particle size, laser particle size analyzer(LPSA) combined with scanning electron microscope(SEM) is used to analyze the EDM debris size. Firstly, the heating dried method is applied to obtain the debris particles. Secondly, the measuring range of LPSA is determined as 0.5–100 m by SEM observation, and the frequency distribution histogram and the cumulative frequency distribution scattergram of debris size are obtained by using LPSA. Thirdly, according to the distribution characteristic of the frequency distribution histogram, the statistical distribution functions of lognormal, exponentially modified Gaussian(EMG), Gamma and Weibull are chosen to achieve curve fitting of the histogram. At last, the distribute law of the debris size is obtained by fitting results. Experiments with different discharge parameters are carried out on an EDM machine designed by the authors themselves, and the machining conditions are tool electrode of red-copper material, workpiece of ANSI 1045 material and working fluid of de-ionized water. The experimental results indicate that the debris sizes of all experiment sample truly obey the Weibull distribution. The obtained distribution law is significantly important for all the models established based on the debris particle size.
Gap debris as discharge product is closely related to machining process in electrical discharge machining(EDM). A lot of recent researches have focused on the relationship among debris size, surfaces texture, remove rate, and machining stability. The study on statistical distribution of debris size contributes to the research, but it is still superficial currently. In order to obtain the distribution law of the debris particle size, laser particle size analyzer(LPSA) combined with scanning electron microscope(SEM) is used to analyze the EDM debris size. Firstly, the heating dried method is applied to obtain the debris particles. Secondly, the measuring range of LPSA is determined as 0.5–100 m by SEM observation, and the frequency distribution histogram and the cumulative frequency distribution scattergram of debris size are obtained by using LPSA. Thirdly, according to the distribution characteristic of the frequency distribution histogram, the statistical distribution functions of lognormal, exponentially modified Gaussian(EMG), Gamma and Weibull are chosen to achieve curve fitting of the histogram. At last, the distribute law of the debris size is obtained by fitting results. Experiments with different discharge parameters are carried out on an EDM machine designed by the authors themselves, and the machining conditions are tool electrode of red-copper material, workpiece of ANSI 1045 material and working fluid of de-ionized water. The experimental results indicate that the debris sizes of all experiment sample truly obey the Weibull distribution. The obtained distribution law is significantly important for all the models established based on the debris particle size.
2011, 25(1).
Abstract:
The configuration selection for reconfigurable manufacturing systems(RMS) have been tackled in a number of studies by using analytical or simulation models. The simulation models are usually based on fewer assumptions than the analytical models and therefore are more wildly used in modeling complex RMS. But in the absence of an efficient gradient analysis method of the objective function, it is time-consuming in solving large-scale problems by using a simulation model coupled with a meta-heuristics algorithm. In this paper, a new approach by means of characteristic state space is presented to improve the efficiency of the configuration selection for an RMS. First, a characteristic state equation is set up to represent the input and the output resources of each basic activity in an RMS. A production process model in terms of matrix equations is established by iterating the equations of basic activities according to the resource flows. This model introduces the production process into a characteristic state space for further analysis. Second, the properties of the characteristic state space are presented. On the basis of these properties, the configuration selection in an RMS is considered as a path-planning problem, and the gradient of the objective function is computed. Modified simulated annealing(SA) is also presented, in which neighborhood generation is guided by the gradient to accelerate convergence and reduce the run time of the optimization procedure. Finally, several case studies on the configuration selection for some actual reconfigurable assembly job-shops are presented and compared to the classical SA. The comparison shows relatively positive results. This study provides a more efficient configuration selection approach by using the gradient of the objective function and presents the relevant theories on which it is based.
The configuration selection for reconfigurable manufacturing systems(RMS) have been tackled in a number of studies by using analytical or simulation models. The simulation models are usually based on fewer assumptions than the analytical models and therefore are more wildly used in modeling complex RMS. But in the absence of an efficient gradient analysis method of the objective function, it is time-consuming in solving large-scale problems by using a simulation model coupled with a meta-heuristics algorithm. In this paper, a new approach by means of characteristic state space is presented to improve the efficiency of the configuration selection for an RMS. First, a characteristic state equation is set up to represent the input and the output resources of each basic activity in an RMS. A production process model in terms of matrix equations is established by iterating the equations of basic activities according to the resource flows. This model introduces the production process into a characteristic state space for further analysis. Second, the properties of the characteristic state space are presented. On the basis of these properties, the configuration selection in an RMS is considered as a path-planning problem, and the gradient of the objective function is computed. Modified simulated annealing(SA) is also presented, in which neighborhood generation is guided by the gradient to accelerate convergence and reduce the run time of the optimization procedure. Finally, several case studies on the configuration selection for some actual reconfigurable assembly job-shops are presented and compared to the classical SA. The comparison shows relatively positive results. This study provides a more efficient configuration selection approach by using the gradient of the objective function and presents the relevant theories on which it is based.
2011, 25(1).
Abstract:
There are very few researches on the shape standard curve currently, and they merely remain on the level of description of the general concept and production experiences, lacking of the in-depth theoretical analysis, and the concrete principle, method and steps for determining the shape standard curve are not put forward, therefore, they are not applicable in industrial production. This is the weakest spot in the research on the basic shape theory. In this paper, the basic shape standard curve and the transverse distribution curve of the exit thickness are attained with stepwise optimization, which is based on the theoretical calculation method of the shape standard curve of strip mills proposed by authors. By calculating the shape discrimination model and the shape forecast model separately, the simultaneous iterative calculation by the previous method is avoided, and the speed and stability of calculation are improved. The compensation models of the transverse temperature difference of the strip, the shape detection roller deflection and the shape of the strip coil are established, respectively, meantime, the basic shape standard curves are compensated, and the relatively perfect theoretical establishment method of the shape standard curve is formed. The simulation and calculation are done on a 1 220 mm five-stand cold strip tandem mill. The simulation and calculation result shows that the principle, method and steps for determining the shape standard curve are correct and feasible, and the correctness of theoretical analysis and calculation is verified. This paper proposes an idea and a method for the establishment of the shape standard curve in the rolling processes of cold strip mills, which develop the theory and model of the shape standard curve and improve the quality and efficiency of the shape control in the rolling processes of cold strip mills.
There are very few researches on the shape standard curve currently, and they merely remain on the level of description of the general concept and production experiences, lacking of the in-depth theoretical analysis, and the concrete principle, method and steps for determining the shape standard curve are not put forward, therefore, they are not applicable in industrial production. This is the weakest spot in the research on the basic shape theory. In this paper, the basic shape standard curve and the transverse distribution curve of the exit thickness are attained with stepwise optimization, which is based on the theoretical calculation method of the shape standard curve of strip mills proposed by authors. By calculating the shape discrimination model and the shape forecast model separately, the simultaneous iterative calculation by the previous method is avoided, and the speed and stability of calculation are improved. The compensation models of the transverse temperature difference of the strip, the shape detection roller deflection and the shape of the strip coil are established, respectively, meantime, the basic shape standard curves are compensated, and the relatively perfect theoretical establishment method of the shape standard curve is formed. The simulation and calculation are done on a 1 220 mm five-stand cold strip tandem mill. The simulation and calculation result shows that the principle, method and steps for determining the shape standard curve are correct and feasible, and the correctness of theoretical analysis and calculation is verified. This paper proposes an idea and a method for the establishment of the shape standard curve in the rolling processes of cold strip mills, which develop the theory and model of the shape standard curve and improve the quality and efficiency of the shape control in the rolling processes of cold strip mills.
Sliding Wear of the Hybrid Kevlar/PTFE Fabric Reinforced Phenolic Composite Filled with Nano-titania
2011, 25(1).
Abstract:
The Kevlar/polytetrafluroethylene(Kevlar/PTFE) fabric composite can be used as a self-lubricating liner of the self-lubricating bearing. Many types of nano-particles can improve the tribological performance of the polymer-based composite. Unfortunately, up to now, published work on the effect of nano-particles on the tribological performance of the fabric composite which can be used as a self-lubricating liner is quite scarce. Therefore, for the purpose of exploring a way to significantly improve the tribological performance of the fabric composite, the tribological performance of the Kevlar/PTFE fabric composite filled with nano-titania is evaluated by using the block-on-ring wear tester. The scanning electron microscopy is utilized to observe the morphologies of worn surfaces of the fabric composites and the counterparts. The tensile properties of the composites are evaluated on the universal material testing machine. The test results show that the addition of nano-titania at a proper mass fraction of the matrix resin improves the wear resistance and the tensile strength, decreases the friction coefficient, and makes the wear volume of the composite reach a relative steady state more quickly; plastic deformation and microcutting are important for the wear of the fabric composite; a lubricating layer is formed on the worn surface of the composite during sliding, and the lubricating layer is critical for the tribological performance of the composite; the formation and properties of the lubricating layer are influenced by the nano-titania particles. The proposed study on the effect of nano-titania on the tribological performance of the Kevlar/PTFE fabric composite, especially on the evolution of the worn surface of the composite, provides the basis for further understanding of the influence mechanism of the nano-particles on the tribological performance of the composite and explores a method of improving the tribological performance of the composite.
The Kevlar/polytetrafluroethylene(Kevlar/PTFE) fabric composite can be used as a self-lubricating liner of the self-lubricating bearing. Many types of nano-particles can improve the tribological performance of the polymer-based composite. Unfortunately, up to now, published work on the effect of nano-particles on the tribological performance of the fabric composite which can be used as a self-lubricating liner is quite scarce. Therefore, for the purpose of exploring a way to significantly improve the tribological performance of the fabric composite, the tribological performance of the Kevlar/PTFE fabric composite filled with nano-titania is evaluated by using the block-on-ring wear tester. The scanning electron microscopy is utilized to observe the morphologies of worn surfaces of the fabric composites and the counterparts. The tensile properties of the composites are evaluated on the universal material testing machine. The test results show that the addition of nano-titania at a proper mass fraction of the matrix resin improves the wear resistance and the tensile strength, decreases the friction coefficient, and makes the wear volume of the composite reach a relative steady state more quickly; plastic deformation and microcutting are important for the wear of the fabric composite; a lubricating layer is formed on the worn surface of the composite during sliding, and the lubricating layer is critical for the tribological performance of the composite; the formation and properties of the lubricating layer are influenced by the nano-titania particles. The proposed study on the effect of nano-titania on the tribological performance of the Kevlar/PTFE fabric composite, especially on the evolution of the worn surface of the composite, provides the basis for further understanding of the influence mechanism of the nano-particles on the tribological performance of the composite and explores a method of improving the tribological performance of the composite.
2011, 25(1).
Abstract:
Nano assembly and manipulation technologies are the basis for nano-electro-mechanical systems(NEMS). Atomic force microscope(AFM) is widely used to manipulate nanotubes to assemble NEMS. Manipulating nanotubes with AFM is a challenging and difficult task. One of the major reasons is the deficiency of visual information during the manipulation process. To address these difficulties, this research aims to put forward novel virtual tools and assembly strategies to improve the efficiency, accuracy and ease of the assembly process of NEMS. This paper begins by the discussion of the principles and implementation of a virtual nano-assembly simulator, which serves as a benchmark to test the proposed NEMS assembly techniques and virtual tools. Then, a general framework of nanotube-based NEMS assembly is proposed. Several nano-assembly strategies and virtual tools, such as automated path planning for NEMS assembly, a four-step scheme of nanotube manipulation, virtual fixtures for assembly finalization and safe manipulation, are introduced. These virtual tools and methods are experimented for justification. An assembly task of moderate complexity was performed in our virtual nano-assembly simulator with and without the help of the proposed toolkit. Experimental results suggest that the proposed methods tend to greatly enhance the efficiency and accuracy of nanotube-based NEMS assembly. In general, the proposed virtual reality toolkit not only ensures the safety, but also enhances the accuracy and efficiency of the assembly of nanotube-based NEMS.
Nano assembly and manipulation technologies are the basis for nano-electro-mechanical systems(NEMS). Atomic force microscope(AFM) is widely used to manipulate nanotubes to assemble NEMS. Manipulating nanotubes with AFM is a challenging and difficult task. One of the major reasons is the deficiency of visual information during the manipulation process. To address these difficulties, this research aims to put forward novel virtual tools and assembly strategies to improve the efficiency, accuracy and ease of the assembly process of NEMS. This paper begins by the discussion of the principles and implementation of a virtual nano-assembly simulator, which serves as a benchmark to test the proposed NEMS assembly techniques and virtual tools. Then, a general framework of nanotube-based NEMS assembly is proposed. Several nano-assembly strategies and virtual tools, such as automated path planning for NEMS assembly, a four-step scheme of nanotube manipulation, virtual fixtures for assembly finalization and safe manipulation, are introduced. These virtual tools and methods are experimented for justification. An assembly task of moderate complexity was performed in our virtual nano-assembly simulator with and without the help of the proposed toolkit. Experimental results suggest that the proposed methods tend to greatly enhance the efficiency and accuracy of nanotube-based NEMS assembly. In general, the proposed virtual reality toolkit not only ensures the safety, but also enhances the accuracy and efficiency of the assembly of nanotube-based NEMS.
2011, 25(1).
Abstract:
Nowadays validation of anti-lock braking systems(ABS) relies mainly on a large amount of road tests. An alternative means with higher efficiency is employing the hardware-in-the-loop simulation(HILS) system to substitute part of road tests for designing, testing, and tuning electronic control units(ECUs) of ABS. Most HILS systems for ABS use expensive digital signal processor hardware and special purpose software, and some fail-safe functions with regard to wheel speeds cannot be evaluated since artificial wheel speed signals are usually provided. In this paper, a low-cost ABS HILS test bench is developed and used for validating the anti-lock braking performance and tuning control parameters of ABS controllers. Another important merit of the proposed test bench is that it can comprehensively evaluate the fail-safe functions with regard to wheel speed signals since real tone rings and sensors are integrated in the bench. A 5-DOF vehicle model with consideration of longitudinal load transfer is used to calculate tire forces, wheel speeds and vehicle speed. Each of the four real-time wheel speed signal generators consists of a servo motor plus a ring gear, which has sufficient dynamic response ability to emulate the rapid changes of the wheel speeds under strict braking conditions of very slippery roads. The simulation of braking tests under different road adhesion coefficients using the HILS test bench is run, and results show that it can evaluate the anti-lock braking performance of ABS and partly the fail-safe functions. This HILS system can also be used in such applications as durability test, benchmarking and comparison between different ECUs. The test bench developed not only has a relatively low cost, but also can be used to validate the wheel speed-related ECU design and all its fail-safe functions, and a rapid testing and proving platform with a high efficiency for research and development of the automotive ABS is therefore provided.
Nowadays validation of anti-lock braking systems(ABS) relies mainly on a large amount of road tests. An alternative means with higher efficiency is employing the hardware-in-the-loop simulation(HILS) system to substitute part of road tests for designing, testing, and tuning electronic control units(ECUs) of ABS. Most HILS systems for ABS use expensive digital signal processor hardware and special purpose software, and some fail-safe functions with regard to wheel speeds cannot be evaluated since artificial wheel speed signals are usually provided. In this paper, a low-cost ABS HILS test bench is developed and used for validating the anti-lock braking performance and tuning control parameters of ABS controllers. Another important merit of the proposed test bench is that it can comprehensively evaluate the fail-safe functions with regard to wheel speed signals since real tone rings and sensors are integrated in the bench. A 5-DOF vehicle model with consideration of longitudinal load transfer is used to calculate tire forces, wheel speeds and vehicle speed. Each of the four real-time wheel speed signal generators consists of a servo motor plus a ring gear, which has sufficient dynamic response ability to emulate the rapid changes of the wheel speeds under strict braking conditions of very slippery roads. The simulation of braking tests under different road adhesion coefficients using the HILS test bench is run, and results show that it can evaluate the anti-lock braking performance of ABS and partly the fail-safe functions. This HILS system can also be used in such applications as durability test, benchmarking and comparison between different ECUs. The test bench developed not only has a relatively low cost, but also can be used to validate the wheel speed-related ECU design and all its fail-safe functions, and a rapid testing and proving platform with a high efficiency for research and development of the automotive ABS is therefore provided.
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