2011 Vol.24(3)
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2011, 25(3).
Abstract:
The historical records of mechanical fault contain great amount of important information which is useful to identify the similar fault. The current fault diagnosis methods using historical records are inefficient to deal with intuitive application and multicomponent multiphase fault diagnosis. Towards the problem, the rapid and intelligent fault diagnosis method based on system-phenomenon-fault (SPF) tree is proposed. The method begins with the physical system of the fault system, conceives the fault causes as leaves, the fault causes as leaves and the frequentness of fault as the interrelationship, and finally forms the fault tree with structural relationship of administrative subordination and flexible multi-granularity components. Firstly, the forming method of SPF tree is discussed; Secondly some basic definitions as synonymous branch, the tough degree of the branch, the dominant leaf, and the virtual branch are defined; and then, the performances including the merger of the dominant branches keeping dominant, the merger of the synonymous branches keeping dominant were proved. Furthermore, the merging, optimizing and calculating of virtual branch of SPF tree are proposed, the self-learning mechanism including the procedure and the related parameter calculation is presented, and the fault searching method and main fault statistics calculation are also presented based on SPF tree. Finally, the method is applied in the fault diagnosis of the certain type of embedded terminal to demonstrate fault information searching in the condition of the synonymous branch, the virtual branch merging and visual presentation of search results. The application shows that the proposed method is effective to narrow down the scope of searching fault and reduce the difficulty of computing. The proposed method is a new way to resolve the intelligent fault diagnosis problem of complex systems by organizing the disordering fault records and providing intuitive expression and intelligent computing capabilities
The historical records of mechanical fault contain great amount of important information which is useful to identify the similar fault. The current fault diagnosis methods using historical records are inefficient to deal with intuitive application and multicomponent multiphase fault diagnosis. Towards the problem, the rapid and intelligent fault diagnosis method based on system-phenomenon-fault (SPF) tree is proposed. The method begins with the physical system of the fault system, conceives the fault causes as leaves, the fault causes as leaves and the frequentness of fault as the interrelationship, and finally forms the fault tree with structural relationship of administrative subordination and flexible multi-granularity components. Firstly, the forming method of SPF tree is discussed; Secondly some basic definitions as synonymous branch, the tough degree of the branch, the dominant leaf, and the virtual branch are defined; and then, the performances including the merger of the dominant branches keeping dominant, the merger of the synonymous branches keeping dominant were proved. Furthermore, the merging, optimizing and calculating of virtual branch of SPF tree are proposed, the self-learning mechanism including the procedure and the related parameter calculation is presented, and the fault searching method and main fault statistics calculation are also presented based on SPF tree. Finally, the method is applied in the fault diagnosis of the certain type of embedded terminal to demonstrate fault information searching in the condition of the synonymous branch, the virtual branch merging and visual presentation of search results. The application shows that the proposed method is effective to narrow down the scope of searching fault and reduce the difficulty of computing. The proposed method is a new way to resolve the intelligent fault diagnosis problem of complex systems by organizing the disordering fault records and providing intuitive expression and intelligent computing capabilities
2011, 25(3).
Abstract:
The early fatigue damage in the van-body of the semi-trailer is often caused by the unique mechanical characteristics and the dynamic impact of the loads. The traditional finite element method with static strength analysis cannot support the fatigue design of van-body; thus, the dynamics analysis should be adopted for the endurance performance. The accurate dynamics model to describe the transient impacts of all kinds of uneven road and the proper system transfer functions to calculate the load transfer effects from tire to van-body are two critical factors for transient dynamics analysis. In order to evaluate the dynamic performance, the dynamics model of the trailer with the air suspension is brought forward. Then the analysis method of the power spectral density (PSD) is set up to study the transient responses of the road dynamic impacts. The transient responses transferred from axles to van-body are calculated, such as dynamic stress, dynamic RMS acceleration, and dynamic load factors. Based on the above dynamic responses, the fatigue life of van-body is predicted with the finite element analysis (FEA) method. Applying the test parameters of the trailer with air suspension, the simulation system with Matlab/Simulink is constructed to describe the dynamic responses of the impacts of the tested PSD of the vehicle axles, and then the fatigue life is predicted with FEA method. The simulated results show that the vibration level of the van-body with air suspension is reduced and the fatigue life is improved. The real vehicle tests on different roads are carried out, and the test results validate the accuracy of the simulation system. The proposed fatigue life prediction method is effective for the virtual design of auto-body.
The early fatigue damage in the van-body of the semi-trailer is often caused by the unique mechanical characteristics and the dynamic impact of the loads. The traditional finite element method with static strength analysis cannot support the fatigue design of van-body; thus, the dynamics analysis should be adopted for the endurance performance. The accurate dynamics model to describe the transient impacts of all kinds of uneven road and the proper system transfer functions to calculate the load transfer effects from tire to van-body are two critical factors for transient dynamics analysis. In order to evaluate the dynamic performance, the dynamics model of the trailer with the air suspension is brought forward. Then the analysis method of the power spectral density (PSD) is set up to study the transient responses of the road dynamic impacts. The transient responses transferred from axles to van-body are calculated, such as dynamic stress, dynamic RMS acceleration, and dynamic load factors. Based on the above dynamic responses, the fatigue life of van-body is predicted with the finite element analysis (FEA) method. Applying the test parameters of the trailer with air suspension, the simulation system with Matlab/Simulink is constructed to describe the dynamic responses of the impacts of the tested PSD of the vehicle axles, and then the fatigue life is predicted with FEA method. The simulated results show that the vibration level of the van-body with air suspension is reduced and the fatigue life is improved. The real vehicle tests on different roads are carried out, and the test results validate the accuracy of the simulation system. The proposed fatigue life prediction method is effective for the virtual design of auto-body.
2011, 25(3).
Abstract:
The manufacturing accuracy of ultra-precision master gears signifies the technological capability of the ultra-precision gear. Currently, there is little report about the manufacturing technologies of ultra-precision master gears at home and aboard. In order to meet the requirement of grinding ultra precision master gear, the gear grinder with flat-faced wheel Y7125 is chosen as the object machine tool and the geometric model of its precision generating part, the involute cam, is established. According to the structure of the involute cam, the effective working section and its adjustable range of the cam are determined, and the mathematical expressions of the effects of comprehensive eccentricity of the involute cam on gear profile deviations are derived. According to the primary harmonic trends of the deviation curve, it is shown that gear profile form and slope deviations in different work generating sections of the involute cam are different which the latter changes with the cam eccentricity obviously. Then, the issues of extreme values and methods of error compensation are studied and the conclusion that large adjustable range is benefit to search the optimal involute-cam section which is responding to the minimum gear profile deviations is obtained. A group of examples are calculated by choosing master gears with d120 mm and m26 mm and an involute cam with base diameter djcam117 mm. And it is found that the maximum gear profile deviation counts for no more than 5% of the cam eccentricity after error compensation. A gear-grinding experiment on the master gear with m2 mm is conducted by choosing different sections of the involute cam and the differences of gear profile deviations then the existence of the cam eccentricity are verified. The research discloses the rule of gear profile deviations caused by the comprehensive eccentricity of the involute cam and provides the theoretical guidance and the processing methods for grinding profile of the ultra precision master gear.
The manufacturing accuracy of ultra-precision master gears signifies the technological capability of the ultra-precision gear. Currently, there is little report about the manufacturing technologies of ultra-precision master gears at home and aboard. In order to meet the requirement of grinding ultra precision master gear, the gear grinder with flat-faced wheel Y7125 is chosen as the object machine tool and the geometric model of its precision generating part, the involute cam, is established. According to the structure of the involute cam, the effective working section and its adjustable range of the cam are determined, and the mathematical expressions of the effects of comprehensive eccentricity of the involute cam on gear profile deviations are derived. According to the primary harmonic trends of the deviation curve, it is shown that gear profile form and slope deviations in different work generating sections of the involute cam are different which the latter changes with the cam eccentricity obviously. Then, the issues of extreme values and methods of error compensation are studied and the conclusion that large adjustable range is benefit to search the optimal involute-cam section which is responding to the minimum gear profile deviations is obtained. A group of examples are calculated by choosing master gears with d120 mm and m26 mm and an involute cam with base diameter djcam117 mm. And it is found that the maximum gear profile deviation counts for no more than 5% of the cam eccentricity after error compensation. A gear-grinding experiment on the master gear with m2 mm is conducted by choosing different sections of the involute cam and the differences of gear profile deviations then the existence of the cam eccentricity are verified. The research discloses the rule of gear profile deviations caused by the comprehensive eccentricity of the involute cam and provides the theoretical guidance and the processing methods for grinding profile of the ultra precision master gear.
2011, 25(3).
Abstract:
Multidisciplinary collaborative simulation (MCS) is an important area of research in the domain of multidisciplinary design optimization (MDO). Although previous research for MCS has to some extent addressed some issues like using of multiple tools, integration stability, control of step size, data synchronization, etc, further work is still necessary to study how to achieve improved precision. A theoretical model is formulated to describe and analyze the integration process of MCS. A basic algorithm with equal major steps is proposed based on the model, along with two methods of implementation for the model, namely the serial method and the parallel method. A further algorithm based on convergent integration step is proposed, which has a more flexible strategy for run-time integration. The influence of interpolation techniques on simulation performance is studied as well. Simulations of the performance of various algorithms with different interpolation techniques are performed for both a simple numerical example and a complex mechatronic product. The novel algorithm based on convergent integration step, when used with a high-order interpolation technique, has better performance in terms of precision and efficiency. The innovation of this paper is mainly on the validation of high precision of the proposed convergent integration step algorithm.
Multidisciplinary collaborative simulation (MCS) is an important area of research in the domain of multidisciplinary design optimization (MDO). Although previous research for MCS has to some extent addressed some issues like using of multiple tools, integration stability, control of step size, data synchronization, etc, further work is still necessary to study how to achieve improved precision. A theoretical model is formulated to describe and analyze the integration process of MCS. A basic algorithm with equal major steps is proposed based on the model, along with two methods of implementation for the model, namely the serial method and the parallel method. A further algorithm based on convergent integration step is proposed, which has a more flexible strategy for run-time integration. The influence of interpolation techniques on simulation performance is studied as well. Simulations of the performance of various algorithms with different interpolation techniques are performed for both a simple numerical example and a complex mechatronic product. The novel algorithm based on convergent integration step, when used with a high-order interpolation technique, has better performance in terms of precision and efficiency. The innovation of this paper is mainly on the validation of high precision of the proposed convergent integration step algorithm.
2011, 25(3).
Abstract:
Mastering the influence laws of parameters on the solution structure of nonlinear systems is the basis of carrying out vibration isolation and control. Many researches on solution structure and bifurcation phenomenon in parameter spaces are carried out broadly in many fields, and the research on nonlinear gear systems has attracted the attention of many scholars. But there is little study on the solution domain boundary of nonlinear gear systems. For a periodic non-autonomous nonlinear dynamic system with several control parameters, a solution domain boundary analysis method of nonlinear systems in parameter spaces is proposed, which combines the cell mapping method based on Poincaré point mapping in phase spaces with the domain decomposition technique of parameter spaces. The cell mapping is known as a global analysis method to analyze the global behavior of a nonlinear dynamic system with finite dimensions, and the basic idea of domain decomposition techniques is to divide and rule. The method is applied to analyze the solution domain boundaries in parameter spaces of a nonlinear gear system. The distribution of different period domains, chaos domain and the domain boundaries between different period domains and chaotic domain are obtained in control parameter spaces constituted by meshing damping ratio with excitation frequency, fluctuation coefficient of meshing stiffness and average exciting force respectively by calculation. The calculation results show that as the meshing damping increases, the responses of the system change towards a single motion, while the variations of the excitation frequency, meshing stiffness and exciting force make the solution domain presenting diversity. The proposed research contribution provides evidence for vibration control and parameter design of the gear system, and confirms the validity of the solution domain boundary analysis method.
Mastering the influence laws of parameters on the solution structure of nonlinear systems is the basis of carrying out vibration isolation and control. Many researches on solution structure and bifurcation phenomenon in parameter spaces are carried out broadly in many fields, and the research on nonlinear gear systems has attracted the attention of many scholars. But there is little study on the solution domain boundary of nonlinear gear systems. For a periodic non-autonomous nonlinear dynamic system with several control parameters, a solution domain boundary analysis method of nonlinear systems in parameter spaces is proposed, which combines the cell mapping method based on Poincaré point mapping in phase spaces with the domain decomposition technique of parameter spaces. The cell mapping is known as a global analysis method to analyze the global behavior of a nonlinear dynamic system with finite dimensions, and the basic idea of domain decomposition techniques is to divide and rule. The method is applied to analyze the solution domain boundaries in parameter spaces of a nonlinear gear system. The distribution of different period domains, chaos domain and the domain boundaries between different period domains and chaotic domain are obtained in control parameter spaces constituted by meshing damping ratio with excitation frequency, fluctuation coefficient of meshing stiffness and average exciting force respectively by calculation. The calculation results show that as the meshing damping increases, the responses of the system change towards a single motion, while the variations of the excitation frequency, meshing stiffness and exciting force make the solution domain presenting diversity. The proposed research contribution provides evidence for vibration control and parameter design of the gear system, and confirms the validity of the solution domain boundary analysis method.
2011, 25(3).
Abstract:
The steady state and dynamic characteristics of pressure output of a hydraulic power unit are important to the hydraulic system behavior. Because of the compact structure, the B-half bridge resistance network is widely used in the pilot controlled pressure relief valves. However the steady-state pressure error might be unacceptably big in those pressure control systems. A constant pressure power unit is typically assumed in analysis of steady state and dynamic behavior of hydraulic systems. The flow-pressure relationship seems to be much complex, in particular when big flow variation takes place. In this paper, the bridge hydraulic resistance network pilot stage is designed in order to get better flow-pressure characteristics. Based on the similarity of electrical circuits, the main factors influencing flow-pressure characteristics are analyzed. Moreover, the optimum diameters of both constant hydraulic resistor and dynamic resistor are proposed. Flow-pressure characteristics are compared with different constant hydraulic resistors, dynamic resistor and spring stiffness by simulations and experiments. Results of simulations and experiments show that flow-pressure characteristics depend very little on the spring stiffness in whole flow range. Good controlled pressure characteristics can be achieved with suitable constant resistors. Overshoot can be reduced with the small diameter of the dynamic resistor. Flow-pressure characteristics of pressure relief valve can be improved with a bridge pilot stage. The proposed pressure control method will provide some positive guidelines and be helpful to design a high performance hydraulic system with large flow.
The steady state and dynamic characteristics of pressure output of a hydraulic power unit are important to the hydraulic system behavior. Because of the compact structure, the B-half bridge resistance network is widely used in the pilot controlled pressure relief valves. However the steady-state pressure error might be unacceptably big in those pressure control systems. A constant pressure power unit is typically assumed in analysis of steady state and dynamic behavior of hydraulic systems. The flow-pressure relationship seems to be much complex, in particular when big flow variation takes place. In this paper, the bridge hydraulic resistance network pilot stage is designed in order to get better flow-pressure characteristics. Based on the similarity of electrical circuits, the main factors influencing flow-pressure characteristics are analyzed. Moreover, the optimum diameters of both constant hydraulic resistor and dynamic resistor are proposed. Flow-pressure characteristics are compared with different constant hydraulic resistors, dynamic resistor and spring stiffness by simulations and experiments. Results of simulations and experiments show that flow-pressure characteristics depend very little on the spring stiffness in whole flow range. Good controlled pressure characteristics can be achieved with suitable constant resistors. Overshoot can be reduced with the small diameter of the dynamic resistor. Flow-pressure characteristics of pressure relief valve can be improved with a bridge pilot stage. The proposed pressure control method will provide some positive guidelines and be helpful to design a high performance hydraulic system with large flow.
2011, 25(3).
Abstract:
58SiMn steel can be used as a kind of material for projectile-like barrel parts. During producing barrel parts, the microstructure of the barrel parts will be changed due to its hot deformation at certain high temperature, which resulted in the variety of the parts mechanical properties. It is necessary to optimize the parameters for recrystallization process by prediction and simulation. The double-pass hot compression tests were conducted using Gleeble 1500 System at different deformation temperature, strain rate and pre-strain. Effect of pre-strain, deformation temperature on the curve of stress-strain has been analyzed. The static recrystallization fraction of double-pass hot deformation was computed and analyzed using compensation test. The actual grain size was measured by metallographic method using oxidation process, which overcomes the difficulty in revealing grain size of 58SiMn steel. The oxidation process was the method of heating the martensite in very fast speed and use of its microstructure inherent characteristic and regarding the size of austenite grain as the maximum of martensite plate. Using regression of the experimental data, the mathematical model of static recrystallization is set up. The average grain size of 58SiMn steel during hot deformation was calculated by deform-3D software and verified by experiment. The results show that the rate of static recrystallization was in direct proportional to the pre-strain of the steel. The grain size decreased with the increase of holding time at low deformation temperature 1 173 K and pre-strain 0.10. The mathematical model proposed could be used for predicting the static recrystallization behaviors of 58SiMn steel.
58SiMn steel can be used as a kind of material for projectile-like barrel parts. During producing barrel parts, the microstructure of the barrel parts will be changed due to its hot deformation at certain high temperature, which resulted in the variety of the parts mechanical properties. It is necessary to optimize the parameters for recrystallization process by prediction and simulation. The double-pass hot compression tests were conducted using Gleeble 1500 System at different deformation temperature, strain rate and pre-strain. Effect of pre-strain, deformation temperature on the curve of stress-strain has been analyzed. The static recrystallization fraction of double-pass hot deformation was computed and analyzed using compensation test. The actual grain size was measured by metallographic method using oxidation process, which overcomes the difficulty in revealing grain size of 58SiMn steel. The oxidation process was the method of heating the martensite in very fast speed and use of its microstructure inherent characteristic and regarding the size of austenite grain as the maximum of martensite plate. Using regression of the experimental data, the mathematical model of static recrystallization is set up. The average grain size of 58SiMn steel during hot deformation was calculated by deform-3D software and verified by experiment. The results show that the rate of static recrystallization was in direct proportional to the pre-strain of the steel. The grain size decreased with the increase of holding time at low deformation temperature 1 173 K and pre-strain 0.10. The mathematical model proposed could be used for predicting the static recrystallization behaviors of 58SiMn steel.
2011, 25(3).
Abstract:
The weldability of copper-bearing aging steel is evaluated using calculated cracking susceptibility index Pcm, oblique Y-groove cracking test, heat-affected zone (HAZ) maximum hardness measurement, submerged arc welding (SAW) test and gas metal arc welding (GMAW) test. The results show that this copper-bearing aging steel has low hardenability and cold cracking susceptibility. SAW test of 40 mm thick plate with WS03 wire matched by CHF101 flux reveals that the welded joints obtain high strength and good impact toughness at low temperature. The HAZ has no hardening but there exists a slightly softening phenomenon. Thus, line energy should be limited or controlled strictly to avoid softening behavior in HAZ during SAW. GMAW tests of 12mm and 24mm thick plates using WER70NH wire show that the tensile strength of joints reaches 720MPa, higher than the stipulated strength requirement of base metal. The average impact energy at 40℃ in the welded joints is more than 140J exceeding minimum stipulated requirement by a wide margin. There are no hardening and softening behaviors in the heat-affected zones of GMAW. All weld metals exhibit acicular ferrite (AF) plus small amount of proeutectoid ferrite (PF) structure, of which the former can significantly improve impact toughness of weld metal. The predominant microstructure in coarse grain HAZ is bainite.
The weldability of copper-bearing aging steel is evaluated using calculated cracking susceptibility index Pcm, oblique Y-groove cracking test, heat-affected zone (HAZ) maximum hardness measurement, submerged arc welding (SAW) test and gas metal arc welding (GMAW) test. The results show that this copper-bearing aging steel has low hardenability and cold cracking susceptibility. SAW test of 40 mm thick plate with WS03 wire matched by CHF101 flux reveals that the welded joints obtain high strength and good impact toughness at low temperature. The HAZ has no hardening but there exists a slightly softening phenomenon. Thus, line energy should be limited or controlled strictly to avoid softening behavior in HAZ during SAW. GMAW tests of 12mm and 24mm thick plates using WER70NH wire show that the tensile strength of joints reaches 720MPa, higher than the stipulated strength requirement of base metal. The average impact energy at 40℃ in the welded joints is more than 140J exceeding minimum stipulated requirement by a wide margin. There are no hardening and softening behaviors in the heat-affected zones of GMAW. All weld metals exhibit acicular ferrite (AF) plus small amount of proeutectoid ferrite (PF) structure, of which the former can significantly improve impact toughness of weld metal. The predominant microstructure in coarse grain HAZ is bainite.
2011, 25(3).
Abstract:
Turbopump condition monitoring is a significant approach to ensure the safety of liquid rocket engine (LRE). Because of lack of fault samples, a monitoring system cannot be trained on all possible condition patterns. Thus it is important to differentiate abnormal or unknown patterns from normal pattern with novelty detection methods. One-class support vector machine (OCSVM) that has been commonly used for novelty detection cannot deal well with large scale samples. In order to model the normal pattern of the turbopump with OCSVM and so as to monitor the condition of the turbopump, a monitoring method that integrates OCSVM with incremental clustering is presented. In this method, the incremental clustering is used for sample reduction by extracting representative vectors from a large training set. The representative vectors are supposed to distribute uniformly in the object region and fulfill the region. And training OCSVM on these representative vectors yields a novelty detector. By applying this method to the analysis of the turbopump’s historical test data, it shows that the incremental clustering algorithm can extract 91 representative points from more than 36 000 training vectors, and the OCSVM detector trained on these 91 representative points can recognize spikes in vibration signals caused by different abnormal events such as vane shedding, rub-impact and sensor faults. This monitoring method does not need fault samples during training as classical recognition methods. The method resolves the learning problem of large samples and is an alternative method for condition monitoring of the LRE turbopump.
Turbopump condition monitoring is a significant approach to ensure the safety of liquid rocket engine (LRE). Because of lack of fault samples, a monitoring system cannot be trained on all possible condition patterns. Thus it is important to differentiate abnormal or unknown patterns from normal pattern with novelty detection methods. One-class support vector machine (OCSVM) that has been commonly used for novelty detection cannot deal well with large scale samples. In order to model the normal pattern of the turbopump with OCSVM and so as to monitor the condition of the turbopump, a monitoring method that integrates OCSVM with incremental clustering is presented. In this method, the incremental clustering is used for sample reduction by extracting representative vectors from a large training set. The representative vectors are supposed to distribute uniformly in the object region and fulfill the region. And training OCSVM on these representative vectors yields a novelty detector. By applying this method to the analysis of the turbopump’s historical test data, it shows that the incremental clustering algorithm can extract 91 representative points from more than 36 000 training vectors, and the OCSVM detector trained on these 91 representative points can recognize spikes in vibration signals caused by different abnormal events such as vane shedding, rub-impact and sensor faults. This monitoring method does not need fault samples during training as classical recognition methods. The method resolves the learning problem of large samples and is an alternative method for condition monitoring of the LRE turbopump.
2011, 25(3).
Abstract:
Highly accurate manufacture in machining industry can only be obtained with precise temperature control of the coolant (oil or water). Machine tool with more accurate, stable and advanced the precision of the working component cannot be developed without appropriate cooling. However, the machine tool coolers are facing the control hunting of cooling temperature and the dramatic variation of heat load in high-accuracy machining. The main objective of this study is to evaluate the influence of the hot-gas by-pass scheme and suction regulation for capacity control of a machine tool cooler system. In this study, experimental investigation on both hot-gas by-pass scheme and suction valve regulation for capacity control has been proposed. Effects of using capillary tube and thermostatic expansion valve along with different capacity control scheme have been investigated extensively in an environmental testing room. Cooling performance and power consumption of the cooler system have been measured and analyzed as well by comparing with different opening percentage of throttling valve under specific coolant temperature. The experimental results reveal that the power consumption will reduce slightly by capacity control using the hot-gas by-pass scheme but the coefficient of performance (COP) of the overall system will decrease. Lower coolant temperature will result in higher compressor power consumption as well. While conducting suction valve regulating for capacity control, energy-saving at 10%–12% can be obtained by using thermostatic expansion valve under different evaporator load. It also reveals that suction valve regulation along with adequate choice of thermostatic expansion valve can provide alternative choice for steady capacity control and substantial energy-saving. The proposed cooler systems with different capacity control schemes are not only more cost-effective than inverter driven system, but also can perform energy-saving and precise temperature control specific for high-accuracy machine tool cooling.
Highly accurate manufacture in machining industry can only be obtained with precise temperature control of the coolant (oil or water). Machine tool with more accurate, stable and advanced the precision of the working component cannot be developed without appropriate cooling. However, the machine tool coolers are facing the control hunting of cooling temperature and the dramatic variation of heat load in high-accuracy machining. The main objective of this study is to evaluate the influence of the hot-gas by-pass scheme and suction regulation for capacity control of a machine tool cooler system. In this study, experimental investigation on both hot-gas by-pass scheme and suction valve regulation for capacity control has been proposed. Effects of using capillary tube and thermostatic expansion valve along with different capacity control scheme have been investigated extensively in an environmental testing room. Cooling performance and power consumption of the cooler system have been measured and analyzed as well by comparing with different opening percentage of throttling valve under specific coolant temperature. The experimental results reveal that the power consumption will reduce slightly by capacity control using the hot-gas by-pass scheme but the coefficient of performance (COP) of the overall system will decrease. Lower coolant temperature will result in higher compressor power consumption as well. While conducting suction valve regulating for capacity control, energy-saving at 10%–12% can be obtained by using thermostatic expansion valve under different evaporator load. It also reveals that suction valve regulation along with adequate choice of thermostatic expansion valve can provide alternative choice for steady capacity control and substantial energy-saving. The proposed cooler systems with different capacity control schemes are not only more cost-effective than inverter driven system, but also can perform energy-saving and precise temperature control specific for high-accuracy machine tool cooling.
2011, 25(3).
Abstract:
For the purpose of improving the precision of the inertial guidance system, it is necessary to enhance the accuracy of the accelerometer. Combining the micro-fabrication processes with resonant sensor technology, a high-resolution inertial-grade novel micro resonant accelerometer is studied. Based on the detecting theory of the resonant sensors, the accelerometer is designed, fabricated, and tested. The accelerometer consists of one proofmass, two micro leverages and two double-ended-tuning-fork (DETF) resonators. The sensing principle of this accelerometer is based on that the natural frequency of the DETF resonator shifts with its axial load which is caused by inertial force. The push-pull configuration of the DETF is for temperature compensation. The two-stage micro leverage mechanisms are employed to amplify the force and increase the sensitivity of the accelerometer. The micro leverage and the resonator are modeled for static analysis and nonlinear modal analysis via theory method and finite element method (FEM), respectively. The geometrical parameters of them are optimized. The amplification factor of the leverage is 102, and the sensitivity of the resonator on theory is about 62 Hzg. The samples of the accelerometer are fabricated with deep reactive ion etching (DRIE) technology which can get a high-aspect ratio structure for contributing a greater sensing-capacitance. The measuring results of the samples by scanning electron microscopy (SEM) show that the process is feasible, because of the complete structure, the sound combs and micro leverages, and the acceptable errors. The frequency of the resonator and the sensitivity of the accelerometer are tested via printed circuit board (PCB), respectively. The result of the test shows that the frequency of the push-resonator is about 54 530 Hz and the sensitivity of the accelerometer is about 55 Hzg. The amplification factor of the leverage is calculated more accurately because the coupling of the two stages leverage is considered during derivation of the analysis formula. In addition, the novel differential structure of the accelerometer can greatly improve the sensitivity of the accelerometers.
For the purpose of improving the precision of the inertial guidance system, it is necessary to enhance the accuracy of the accelerometer. Combining the micro-fabrication processes with resonant sensor technology, a high-resolution inertial-grade novel micro resonant accelerometer is studied. Based on the detecting theory of the resonant sensors, the accelerometer is designed, fabricated, and tested. The accelerometer consists of one proofmass, two micro leverages and two double-ended-tuning-fork (DETF) resonators. The sensing principle of this accelerometer is based on that the natural frequency of the DETF resonator shifts with its axial load which is caused by inertial force. The push-pull configuration of the DETF is for temperature compensation. The two-stage micro leverage mechanisms are employed to amplify the force and increase the sensitivity of the accelerometer. The micro leverage and the resonator are modeled for static analysis and nonlinear modal analysis via theory method and finite element method (FEM), respectively. The geometrical parameters of them are optimized. The amplification factor of the leverage is 102, and the sensitivity of the resonator on theory is about 62 Hzg. The samples of the accelerometer are fabricated with deep reactive ion etching (DRIE) technology which can get a high-aspect ratio structure for contributing a greater sensing-capacitance. The measuring results of the samples by scanning electron microscopy (SEM) show that the process is feasible, because of the complete structure, the sound combs and micro leverages, and the acceptable errors. The frequency of the resonator and the sensitivity of the accelerometer are tested via printed circuit board (PCB), respectively. The result of the test shows that the frequency of the push-resonator is about 54 530 Hz and the sensitivity of the accelerometer is about 55 Hzg. The amplification factor of the leverage is calculated more accurately because the coupling of the two stages leverage is considered during derivation of the analysis formula. In addition, the novel differential structure of the accelerometer can greatly improve the sensitivity of the accelerometers.
2011, 25(3).
Abstract:
Low pressure sheet molding compound (LPMC, 1.0–3.0 MPa, 95–103 ℃) is a new kind of thermosetting material with crystalline polyester as a physical thickenner. LPMC is different from conventional SMC using an earth oxide thickening agent (e.g. MgO) as chemical thickenner, it relies on the physical thickening of crystalline polyester. Crystalline polyester resin is the key material to mold LPMC parts. Currently there was no report about the thickening mechanism of crystalline polyester in LPMC. In this article, crystalline polyester resins, whose melting points were between 45 ℃ and 89 ℃, were synthesized by a two-step esterification. The melt points of crystalline polyesters are controlled by regulating the mol ratio of the two glycols and the two acids. And by means of varying the content of crystalline polyester resin, the thickening effect on resin paste is investigated. In addition, the thickening mechanism of crystalline polyester in LPMC was investigated by FTIR and DSC analysis. The effects of the diameters and viscosity of crystalline polyester on the rheological property and fiber distribution of LPMC sheets were studied, too. Results show that the thickening effect is excellent when the weight content of crystalline polyester resin is 3%. And there exists three kinds of functions acting in the process of thickening: swelling, hydrogen bonds and induction crystallization. During the preparing process of resin paste in LPMC, the temperature of resin paste must be kept at 90 ℃. In addition, crystalline polyester make LPMC have a perfect fluid property. When the viscosity of LPMC sheet is beyond 1 kPa • s, the fiber orientation is not obvious. But when the viscosity of LPMC sheet is about 500 Pa • s, the fiber shows a certain degree of orientation. Moreover the study of physical and chemical thickening mechanism of crystalline polyester and the rheological discipline of LPMC sheets in the hot mould will provide the researchers and enterprises with theory guidance.
Low pressure sheet molding compound (LPMC, 1.0–3.0 MPa, 95–103 ℃) is a new kind of thermosetting material with crystalline polyester as a physical thickenner. LPMC is different from conventional SMC using an earth oxide thickening agent (e.g. MgO) as chemical thickenner, it relies on the physical thickening of crystalline polyester. Crystalline polyester resin is the key material to mold LPMC parts. Currently there was no report about the thickening mechanism of crystalline polyester in LPMC. In this article, crystalline polyester resins, whose melting points were between 45 ℃ and 89 ℃, were synthesized by a two-step esterification. The melt points of crystalline polyesters are controlled by regulating the mol ratio of the two glycols and the two acids. And by means of varying the content of crystalline polyester resin, the thickening effect on resin paste is investigated. In addition, the thickening mechanism of crystalline polyester in LPMC was investigated by FTIR and DSC analysis. The effects of the diameters and viscosity of crystalline polyester on the rheological property and fiber distribution of LPMC sheets were studied, too. Results show that the thickening effect is excellent when the weight content of crystalline polyester resin is 3%. And there exists three kinds of functions acting in the process of thickening: swelling, hydrogen bonds and induction crystallization. During the preparing process of resin paste in LPMC, the temperature of resin paste must be kept at 90 ℃. In addition, crystalline polyester make LPMC have a perfect fluid property. When the viscosity of LPMC sheet is beyond 1 kPa • s, the fiber orientation is not obvious. But when the viscosity of LPMC sheet is about 500 Pa • s, the fiber shows a certain degree of orientation. Moreover the study of physical and chemical thickening mechanism of crystalline polyester and the rheological discipline of LPMC sheets in the hot mould will provide the researchers and enterprises with theory guidance.
2011, 25(3).
Abstract:
The solder joint reliability of quad flat non-lead (QFN) package, which has become very popular over the past few years, has received intense interest. The finite element method (FEM) is essential to evaluate the reliability of QFN device. In this paper, Garofalo-Arrheninus model was implemented to simulate the deformation of QFN soldered joints. Equivalent creep strain of the soldered joints was calculated by means of finite element analyses, and was used to evaluate the reliability of QFN packages. It is found that the critical soldered joint of QFN is located the package corner while the maximum creep strain is obtained at the top interface of peripheral soldered joint. The creep strain is provided with periodicity and additivity as the thermal cycling. Nonlinear analysis of QFN package with different lead counts was presented as well, in which the phenomenon that the value of induced creep strain arise as the package size decreasing is noted. Moreover, SnPb and two lead-free solders, namely, Sn3.5AgSn3.8Ag0.7Cu, were both taken into consideration. Simulated results indicate that the creep strain value of lead-free soldered joints is lower than that of SnPb soldered joints, which can be attributed to the difference of stiffness and coefficient of thermal expansion among three solders. Garofalo-Arrheninus model is used to calculate the creep strain of the QFN device for the first time in this study. The results provide an important basis for evaluating the reliability of QFN package.
The solder joint reliability of quad flat non-lead (QFN) package, which has become very popular over the past few years, has received intense interest. The finite element method (FEM) is essential to evaluate the reliability of QFN device. In this paper, Garofalo-Arrheninus model was implemented to simulate the deformation of QFN soldered joints. Equivalent creep strain of the soldered joints was calculated by means of finite element analyses, and was used to evaluate the reliability of QFN packages. It is found that the critical soldered joint of QFN is located the package corner while the maximum creep strain is obtained at the top interface of peripheral soldered joint. The creep strain is provided with periodicity and additivity as the thermal cycling. Nonlinear analysis of QFN package with different lead counts was presented as well, in which the phenomenon that the value of induced creep strain arise as the package size decreasing is noted. Moreover, SnPb and two lead-free solders, namely, Sn3.5AgSn3.8Ag0.7Cu, were both taken into consideration. Simulated results indicate that the creep strain value of lead-free soldered joints is lower than that of SnPb soldered joints, which can be attributed to the difference of stiffness and coefficient of thermal expansion among three solders. Garofalo-Arrheninus model is used to calculate the creep strain of the QFN device for the first time in this study. The results provide an important basis for evaluating the reliability of QFN package.
2011, 25(3).
Abstract:
Due to potential wide applications, the problem of utilizing an unmanned helicopter to track a ground target has become one of the most active research directions in related areas. However, in most cases, it is possible for a dynamic target to implement evasive actions with strong maneuverability, such as a sudden turn during high-speed movement, to flee from the tracker, which then brings much difficulty for the design of tracking control systems. Currently, most research on this field focuses on utilizing a ground mobile robot to track a high-speed target. Unfortunately, it is very difficult to extend those developed methods to airborne applications due to much more complex dynamices of UAV-target relative motion. This study investiages thoroughly for the problem of using an unmanned helicopter to track a ground target, with particular emphasis on the avoidance of tracking failure caused by the evasive maneuvers of dynamic targets. Specifically, a novel control scheme, which consists of an innovative target tracking controller and a classical flight controller, is proposed for the helicopter-target tracking problem. Wherein, the tracking controller, whose design is the focus of the paper, aims to utilize the motion information of the helicopter and the dynamic target to construct a suitable trajectory for the helicopter, so that when it flies along this trajectory, the relative pose between the helicopter and the dynamic target will be kept consant. When designing the target tracking controller, a novel coordinate transformation is firstly introduced to convert the tracking system into a more compact form convenient for control law design, the desired velocities for the helicopter is then proposed with consideration of the dynamic constraint. The stability of the closed-loop system is finally analyzed by Lyapunov techniques. Based on Matlab/Simulink environment, two groups of simulation are conducted for the helicopter-target tracking control system where the target moves along a linear path and takes a sudden turn during high-speed movement, respectively. As shown by the simulation results, both the distance error and the pointing error are bounded during the tracking process, and they are convergent to zero when the target moves straightly. Moreover, the tracking performance can be adjusted properly to avoid tracking failure due to evasive maneuvers of the target, so as to guarantee superior tracking performance for all kinds of dynamic targets.
Due to potential wide applications, the problem of utilizing an unmanned helicopter to track a ground target has become one of the most active research directions in related areas. However, in most cases, it is possible for a dynamic target to implement evasive actions with strong maneuverability, such as a sudden turn during high-speed movement, to flee from the tracker, which then brings much difficulty for the design of tracking control systems. Currently, most research on this field focuses on utilizing a ground mobile robot to track a high-speed target. Unfortunately, it is very difficult to extend those developed methods to airborne applications due to much more complex dynamices of UAV-target relative motion. This study investiages thoroughly for the problem of using an unmanned helicopter to track a ground target, with particular emphasis on the avoidance of tracking failure caused by the evasive maneuvers of dynamic targets. Specifically, a novel control scheme, which consists of an innovative target tracking controller and a classical flight controller, is proposed for the helicopter-target tracking problem. Wherein, the tracking controller, whose design is the focus of the paper, aims to utilize the motion information of the helicopter and the dynamic target to construct a suitable trajectory for the helicopter, so that when it flies along this trajectory, the relative pose between the helicopter and the dynamic target will be kept consant. When designing the target tracking controller, a novel coordinate transformation is firstly introduced to convert the tracking system into a more compact form convenient for control law design, the desired velocities for the helicopter is then proposed with consideration of the dynamic constraint. The stability of the closed-loop system is finally analyzed by Lyapunov techniques. Based on Matlab/Simulink environment, two groups of simulation are conducted for the helicopter-target tracking control system where the target moves along a linear path and takes a sudden turn during high-speed movement, respectively. As shown by the simulation results, both the distance error and the pointing error are bounded during the tracking process, and they are convergent to zero when the target moves straightly. Moreover, the tracking performance can be adjusted properly to avoid tracking failure due to evasive maneuvers of the target, so as to guarantee superior tracking performance for all kinds of dynamic targets.
2011, 25(3).
Abstract:
The recent research on stability of gas bearing-rotor systems still mostly adopts the same method as in oil-lubricated bearing-rotor systems. The dynamic coefficients of gas bearings in the case that the perturbation frequencies are same as the rotating speed are used to carry out the stability analysis of rotor systems. This method does not contact the frequency characteristics of dynamic stiffness and damping coefficients of gas bearings with the dynamical behaviors of rotor systems. Furthermore, the effects of perturbation frequencies on the stability of systems are not taken into account. In this paper, the dynamic stiffness and damping coefficients of tilting-pad gas bearings are calculated by the partial derivative method. On the base of solution of dynamic coefficients, two computational models are produced for stability analysis on rotor systems supported by tilting-pad gas bearings according to whether the degrees of the freedom of pads tilting motions are included in the equations of motion or not. In the condition of considering the frequency effects of dynamic coefficients of tilting-pad gas bearings, the corresponding eigenvalues of the rigid and first five vibration modes of the system with the working speeds of 830 krmin are computed through iteratively solving the equations of motion of rotor-system by using two computational models, respectively. According to the obtained eigenvalues, the stability of rotor system is analyzed. The results indicate that the eigenvalues and the stability of rotor system obtained by these two computational models are well agreement each other. They all can more accurately analyze the stability of rotor systems supported by tilting-pad gas bearings. This research has important meaning for perfecting the stability analysis method of rotor systems supported by gas bearings.
The recent research on stability of gas bearing-rotor systems still mostly adopts the same method as in oil-lubricated bearing-rotor systems. The dynamic coefficients of gas bearings in the case that the perturbation frequencies are same as the rotating speed are used to carry out the stability analysis of rotor systems. This method does not contact the frequency characteristics of dynamic stiffness and damping coefficients of gas bearings with the dynamical behaviors of rotor systems. Furthermore, the effects of perturbation frequencies on the stability of systems are not taken into account. In this paper, the dynamic stiffness and damping coefficients of tilting-pad gas bearings are calculated by the partial derivative method. On the base of solution of dynamic coefficients, two computational models are produced for stability analysis on rotor systems supported by tilting-pad gas bearings according to whether the degrees of the freedom of pads tilting motions are included in the equations of motion or not. In the condition of considering the frequency effects of dynamic coefficients of tilting-pad gas bearings, the corresponding eigenvalues of the rigid and first five vibration modes of the system with the working speeds of 830 krmin are computed through iteratively solving the equations of motion of rotor-system by using two computational models, respectively. According to the obtained eigenvalues, the stability of rotor system is analyzed. The results indicate that the eigenvalues and the stability of rotor system obtained by these two computational models are well agreement each other. They all can more accurately analyze the stability of rotor systems supported by tilting-pad gas bearings. This research has important meaning for perfecting the stability analysis method of rotor systems supported by gas bearings.
2011, 25(3).
Abstract:
Target tracking control for wheeled mobile robot (WMR) need resolve the problems of kinematics model and tracking algorithm. High-order sliding mode control is a valid method used in the nonlinear tracking control system, which can eliminate the chattering of sliding mode control. Currently there lacks the research of robustness and uncertain factors for high-order sliding mode control. To address the fast convergence and robustness problems of tracking target, the tracking mathematical model of WMR and the target is derived. Based on the finite-time convergence theory and second order sliding mode method, a nonlinear tracking algorithm is designed which guarantees that WMR can catch the target in finite time. At the same time an observer is applied to substitute the uncertain acceleration of the target, then a smooth nonlinear tracking algorithm is proposed. Based on Lyapunov stability theory and finite-time convergence, a finite time convergent smooth second order sliding mode controller and a target tracking algorithm are designed by using second order sliding mode method. The simulation results verified that WMR can catch up the target quickly and reduce the control discontinuity of the velocity of WMR.
Target tracking control for wheeled mobile robot (WMR) need resolve the problems of kinematics model and tracking algorithm. High-order sliding mode control is a valid method used in the nonlinear tracking control system, which can eliminate the chattering of sliding mode control. Currently there lacks the research of robustness and uncertain factors for high-order sliding mode control. To address the fast convergence and robustness problems of tracking target, the tracking mathematical model of WMR and the target is derived. Based on the finite-time convergence theory and second order sliding mode method, a nonlinear tracking algorithm is designed which guarantees that WMR can catch the target in finite time. At the same time an observer is applied to substitute the uncertain acceleration of the target, then a smooth nonlinear tracking algorithm is proposed. Based on Lyapunov stability theory and finite-time convergence, a finite time convergent smooth second order sliding mode controller and a target tracking algorithm are designed by using second order sliding mode method. The simulation results verified that WMR can catch up the target quickly and reduce the control discontinuity of the velocity of WMR.
2011, 25(3).
Abstract:
Axiomatic design(AD) is a popular design method, and satisfying the independence axiom is the basis of AD. However, AD doesn’t provide methods to decompose functions then keep them independent and to handle coupled design. A few of ways of handling coupled design are mainly passive resolutions when coupled design exists, but not efficient to each product design. Hence, this paper presents an innovative approach to design and decompose functions of complex products based on functional connections, aiming at actively avoiding functional coupling. By contrasting with component networks, four kinds of relations among functions are identified, including spatial, energy, material, and information connection. Then the definitions of these relations and the dominant connection are given. Based on the definitions, the principles of functional decomposition and design are developed, in which each non-leaf function is broken into sub functions centered on its dominant connection with avoidance of functional cross and coupling, and sequentially satisfies the independence axiom. Then the operational flow of the proposed approach is constructed. Determining the dominant connection of a function, decomposing the function into sub functions in terms of the dominant connection and reverse examination and optimization are planed as the core steps in each zigzagging. Input process output(IPO) analysis is introduced to obtain the dominant connection of a function, some rules for examining and optimizing the decomposition results reversely according to oriented object theory are presented as well. An illustrative example about the pouring function of squeeze casting equipments presented demonstrates how to use the proposed approach, and indicates its effectiveness. The proposed approach expands the principles of AD, constructs a guidance policy for independent functional design of complex products based on AD, and can help decrease or actively avoid coupled design and improve design efficiency.
Axiomatic design(AD) is a popular design method, and satisfying the independence axiom is the basis of AD. However, AD doesn’t provide methods to decompose functions then keep them independent and to handle coupled design. A few of ways of handling coupled design are mainly passive resolutions when coupled design exists, but not efficient to each product design. Hence, this paper presents an innovative approach to design and decompose functions of complex products based on functional connections, aiming at actively avoiding functional coupling. By contrasting with component networks, four kinds of relations among functions are identified, including spatial, energy, material, and information connection. Then the definitions of these relations and the dominant connection are given. Based on the definitions, the principles of functional decomposition and design are developed, in which each non-leaf function is broken into sub functions centered on its dominant connection with avoidance of functional cross and coupling, and sequentially satisfies the independence axiom. Then the operational flow of the proposed approach is constructed. Determining the dominant connection of a function, decomposing the function into sub functions in terms of the dominant connection and reverse examination and optimization are planed as the core steps in each zigzagging. Input process output(IPO) analysis is introduced to obtain the dominant connection of a function, some rules for examining and optimizing the decomposition results reversely according to oriented object theory are presented as well. An illustrative example about the pouring function of squeeze casting equipments presented demonstrates how to use the proposed approach, and indicates its effectiveness. The proposed approach expands the principles of AD, constructs a guidance policy for independent functional design of complex products based on AD, and can help decrease or actively avoid coupled design and improve design efficiency.
2011, 25(3).
Abstract:
Fine dust particles (diameter is less than 2.5 m) generated during machining processes, especially dry cutting, are harmful to operators, because they remain suspended in the air for long time and have marked concentration gradients in workshop. Hence studies about cutting dust source states and indoor air quality prediction have been developed. However, few researches focus on the distribution state of the cutting dust, dynamic status of fine dust particles, and environment estimating of the machining workshop. The machining workshops have diversified architectural structures, complex working conditions, so the dust emission is sensitive dynamic. According to these features, after analysis of the static and dynamic influence factors, this paper proposes a method and establishes a model to estimate the fine dust particles distribution based on COwZ (COMIS (conjunction of multizone infiltration specialists) with sub-zones) model when only dry cutting is processed just needing various working parameters. And two key technologies are discussed: the description of the machine tools using sub-zones of COwZ model considering the local obstacle effects of machine tools themselves; description and implementation of dynamic process of cutting dust emission with a new concept of equivalent source strengths. At last, multi-point experiments in a hybrid ventilation machining workshop prove the method is practical. Good agreement was observed between the estimation results and the experimental measurements for the investigated conditions. The proposed method can supply reference data for green manufacturing.
Fine dust particles (diameter is less than 2.5 m) generated during machining processes, especially dry cutting, are harmful to operators, because they remain suspended in the air for long time and have marked concentration gradients in workshop. Hence studies about cutting dust source states and indoor air quality prediction have been developed. However, few researches focus on the distribution state of the cutting dust, dynamic status of fine dust particles, and environment estimating of the machining workshop. The machining workshops have diversified architectural structures, complex working conditions, so the dust emission is sensitive dynamic. According to these features, after analysis of the static and dynamic influence factors, this paper proposes a method and establishes a model to estimate the fine dust particles distribution based on COwZ (COMIS (conjunction of multizone infiltration specialists) with sub-zones) model when only dry cutting is processed just needing various working parameters. And two key technologies are discussed: the description of the machine tools using sub-zones of COwZ model considering the local obstacle effects of machine tools themselves; description and implementation of dynamic process of cutting dust emission with a new concept of equivalent source strengths. At last, multi-point experiments in a hybrid ventilation machining workshop prove the method is practical. Good agreement was observed between the estimation results and the experimental measurements for the investigated conditions. The proposed method can supply reference data for green manufacturing.
2011, 25(3).
Abstract:
Chatter has been a primary obstacle to the successful implementation of high speed machining. The frequency response function(FRF) of the tool point is crucial for identification of chatter free cutting conditions. In order to quickly acquire the FRF of the different components combinations of machine tool, the assembly of machine tool was always decomposed into several parts, where the fluted portion of tool, however, was always treated as a uniform beam, and the associated discrepancy was ignored. This paper presents a new method to predict the dynamic response of the machine-spindle-holder-tool assembly using the receptance coupling substructure analysis technique, where the assembly is divided into three parts: machine-spindle, holder and tool shank, and tool’s fluted portion. Impact testing is used to measure the receptance of machine-spindle, the Timoshenko beam model is employed to analyze the dynamics of holder and tool shank, and the finite element method(FEM) is used to calculate the receptance of the tool’s fluted portion. The approximation of the fluted portion cross section using an equivalent diameter is also addressed. All the individual receptances are coupled by using substructure method. The predicted assembly receptance is experimentally verified for three different tool overhang lengths. The results also show that the equivalent diameter beam model reaches an acceptable accuracy. The proposed approach is helpful to predict the tool point dynamics rapidly in industry.
Chatter has been a primary obstacle to the successful implementation of high speed machining. The frequency response function(FRF) of the tool point is crucial for identification of chatter free cutting conditions. In order to quickly acquire the FRF of the different components combinations of machine tool, the assembly of machine tool was always decomposed into several parts, where the fluted portion of tool, however, was always treated as a uniform beam, and the associated discrepancy was ignored. This paper presents a new method to predict the dynamic response of the machine-spindle-holder-tool assembly using the receptance coupling substructure analysis technique, where the assembly is divided into three parts: machine-spindle, holder and tool shank, and tool’s fluted portion. Impact testing is used to measure the receptance of machine-spindle, the Timoshenko beam model is employed to analyze the dynamics of holder and tool shank, and the finite element method(FEM) is used to calculate the receptance of the tool’s fluted portion. The approximation of the fluted portion cross section using an equivalent diameter is also addressed. All the individual receptances are coupled by using substructure method. The predicted assembly receptance is experimentally verified for three different tool overhang lengths. The results also show that the equivalent diameter beam model reaches an acceptable accuracy. The proposed approach is helpful to predict the tool point dynamics rapidly in industry.
2011, 25(3).
Abstract:
Nonlinear dynamic equation is a common engineering model. There is not precise analytical solution for most of nonlinear differential equations. These nonlinear differential equations should be solved by using approximate methods. Classical perturbation methods such as LP method, KBM method, multi-scale method and the averaging method on weakly nonlinear vibration system is effective, while the strongly nonlinear system is difficult to apply. Approximate solutions of primary resonance for forced Duffing equation is investigated by means of homotopy analysis method (HAM). Different from other approximate computational method, the HAM is totally independent of small physical parameters, and thus is suitable for most nonlinear problems. The HAM provides a great freedom to choose base functions of solution series, so that a nonlinear problem may be approximated more effectively. The HAM provides us a simple way to adjust and control the convergence region of the series solution by means of an auxiliary parameter ħ and the auxiliary function. Therefore, HAM not only may solve the weakly non-linear problems but also may be suitable for the strong non-linear problem. Through the approximate solution of forced Duffing equation with cubic non-linearity, the HAM and fourth order Runge-Kutta method of numerical solution were compared, the results show that the HAM not only can solve the steady state solution, but also can calculate the unsteady state solution, and has the good computational accuracy.
Nonlinear dynamic equation is a common engineering model. There is not precise analytical solution for most of nonlinear differential equations. These nonlinear differential equations should be solved by using approximate methods. Classical perturbation methods such as LP method, KBM method, multi-scale method and the averaging method on weakly nonlinear vibration system is effective, while the strongly nonlinear system is difficult to apply. Approximate solutions of primary resonance for forced Duffing equation is investigated by means of homotopy analysis method (HAM). Different from other approximate computational method, the HAM is totally independent of small physical parameters, and thus is suitable for most nonlinear problems. The HAM provides a great freedom to choose base functions of solution series, so that a nonlinear problem may be approximated more effectively. The HAM provides us a simple way to adjust and control the convergence region of the series solution by means of an auxiliary parameter ħ and the auxiliary function. Therefore, HAM not only may solve the weakly non-linear problems but also may be suitable for the strong non-linear problem. Through the approximate solution of forced Duffing equation with cubic non-linearity, the HAM and fourth order Runge-Kutta method of numerical solution were compared, the results show that the HAM not only can solve the steady state solution, but also can calculate the unsteady state solution, and has the good computational accuracy.
2011, 25(3).
Abstract:
Shot peening can improve fatigue strength of materials by creating compressive residual stress field in their surface layers, and offers a protection against crack initiation and propagation, corrosion, etc. And fatigue fracture and stress corrosion cracking of NAK80 steel parts are improved effectively. Currently there lacks in-depth research in which the beneficial effect of the residual stress may be offset by the surface damage associated with shot peening, especially in terms of the research on the effective control of shot peening intensity. In order to obtain the surface residual stress field of NAK80 steel after shot peening, the samples are shot peened by pneumatic shot peening machine with different rules. The residual stress in the precipitation-hardening layer of NAK80 steel is measured before and after a shot peening treatment by X-ray diffraction method. In order to obtain true residual stress field, integral compensation method is used to correct results. By setting up analytical model of the residual stress in the process of shot peening, the surface residual stress is calculated after shot peening, and mentioning the reason of errors occurred between calculated and experimental residual stresses, which is mainly caused by the measurement error of the shoot arc height. At the same time, micro hardness, microstructure and roughness in the precipitation-hardening layer of NAK80 steel before and after shot peening were measured and surveyed in order to obtain the relation between shot peening strength and surface quality in the precipitation-hardening layer. The results show that the surface quality of NAK80 steel is significantly improved by shot peening process. The over peening effect is produced when the shot peening intensity is too high, it is disadvantageous to improve samples surface integrity, and leading to reduce the fatigue life. When arc high value of optimal shot peening is 0.40 mm, the surface quality is the best, and the depth of residual stress in the precipitation-hardening layer reaches to about 450 m. Numerical calculation is very useful to define the process parameters when a specific residual stress profile is intended, either to quantify the benefits on a specific property like fatigue life or to help on modeling a forming process like shot peen forming. In particular, the proposed parameter optimization in the progress of shot peening and effective control of the surface texture provide new rules for the quantitative evaluations of shot peening surface modification of NAK80 steel.
Shot peening can improve fatigue strength of materials by creating compressive residual stress field in their surface layers, and offers a protection against crack initiation and propagation, corrosion, etc. And fatigue fracture and stress corrosion cracking of NAK80 steel parts are improved effectively. Currently there lacks in-depth research in which the beneficial effect of the residual stress may be offset by the surface damage associated with shot peening, especially in terms of the research on the effective control of shot peening intensity. In order to obtain the surface residual stress field of NAK80 steel after shot peening, the samples are shot peened by pneumatic shot peening machine with different rules. The residual stress in the precipitation-hardening layer of NAK80 steel is measured before and after a shot peening treatment by X-ray diffraction method. In order to obtain true residual stress field, integral compensation method is used to correct results. By setting up analytical model of the residual stress in the process of shot peening, the surface residual stress is calculated after shot peening, and mentioning the reason of errors occurred between calculated and experimental residual stresses, which is mainly caused by the measurement error of the shoot arc height. At the same time, micro hardness, microstructure and roughness in the precipitation-hardening layer of NAK80 steel before and after shot peening were measured and surveyed in order to obtain the relation between shot peening strength and surface quality in the precipitation-hardening layer. The results show that the surface quality of NAK80 steel is significantly improved by shot peening process. The over peening effect is produced when the shot peening intensity is too high, it is disadvantageous to improve samples surface integrity, and leading to reduce the fatigue life. When arc high value of optimal shot peening is 0.40 mm, the surface quality is the best, and the depth of residual stress in the precipitation-hardening layer reaches to about 450 m. Numerical calculation is very useful to define the process parameters when a specific residual stress profile is intended, either to quantify the benefits on a specific property like fatigue life or to help on modeling a forming process like shot peen forming. In particular, the proposed parameter optimization in the progress of shot peening and effective control of the surface texture provide new rules for the quantitative evaluations of shot peening surface modification of NAK80 steel.
2011, 25(3).
Abstract:
Parallel kinematic machines (PKMs) have the advantages of a compact structure, high stiffness, a low moving inertia, and a high load/weight ratio. PKMs have been intensively studied since the 1980s, and are still attracting much attention. Compared with extensive researches focus on their type/dimensional synthesis, kinematic/dynamic analyses, the error modeling and separation issues in PKMs are not studied adequately, which is one of the most important obstacles in its commercial applications widely. Taking a 3-PRS parallel manipulator as an example, this paper presents a separation method of source errors for 3-DOF parallel manipulator into the compensable and non-compensable errors effectively. The kinematic analysis of 3-PRS parallel manipulator leads to its six-dimension Jacobian matrix, which can be mapped into the Jacobian matrix of actuations and constraints, and then the compensable and non-compensable errors can be separated accordingly. The compensable errors can be compensated by the kinematic calibration, while the non-compensable errors may be adjusted by the manufacturing and assembling process. Followed by the influence of the latter, i.e., the non-compensable errors, on the pose error of the moving platform through the sensitivity analysis with the aid of the Monte-Carlo method, meanwhile, the configurations of the manipulator are sought as the pose errors of the moving platform approaching their maximum. The compensable and non-compensable errors in limited-DOF parallel manipulators can be separated effectively by means of the Jacobian matrix of actuations and constraints, providing designers with an informative guideline to taking proper measures for enhancing the pose accuracy via component tolerancing and/or kinematic calibration, which can lay the foundation for the error distinguishment and compensation.
Parallel kinematic machines (PKMs) have the advantages of a compact structure, high stiffness, a low moving inertia, and a high load/weight ratio. PKMs have been intensively studied since the 1980s, and are still attracting much attention. Compared with extensive researches focus on their type/dimensional synthesis, kinematic/dynamic analyses, the error modeling and separation issues in PKMs are not studied adequately, which is one of the most important obstacles in its commercial applications widely. Taking a 3-PRS parallel manipulator as an example, this paper presents a separation method of source errors for 3-DOF parallel manipulator into the compensable and non-compensable errors effectively. The kinematic analysis of 3-PRS parallel manipulator leads to its six-dimension Jacobian matrix, which can be mapped into the Jacobian matrix of actuations and constraints, and then the compensable and non-compensable errors can be separated accordingly. The compensable errors can be compensated by the kinematic calibration, while the non-compensable errors may be adjusted by the manufacturing and assembling process. Followed by the influence of the latter, i.e., the non-compensable errors, on the pose error of the moving platform through the sensitivity analysis with the aid of the Monte-Carlo method, meanwhile, the configurations of the manipulator are sought as the pose errors of the moving platform approaching their maximum. The compensable and non-compensable errors in limited-DOF parallel manipulators can be separated effectively by means of the Jacobian matrix of actuations and constraints, providing designers with an informative guideline to taking proper measures for enhancing the pose accuracy via component tolerancing and/or kinematic calibration, which can lay the foundation for the error distinguishment and compensation.
2011, 25(3).
Abstract:
Full-field measurement techniques such as the scanning laser Doppler vibrometer (LDV) and the electronic speckle pattern interferometry systems can provide a dense and accurate vibration measurement on structural operating deflection shape (ODS) on a relatively short period of time. The possibility of structural damage detection and localization using the ODS looks likely more attractive than when using traditional measurement techniques which address only a small number of discrete points. This paper discusses the decomposition method of the structural ODSs in the time history using principal component analysis to provide a novel approach to the structural health monitoring and damage detection. The damage indicator is proposed through comparison of structural singular vectors of the ODS variation matrixes between the healthy and damaged stages. A plate piece with a fix-free configuration is used as an example to demonstrate the effectiveness of the damage detection and localization using the proposed method. The simulation results show that: (1) the dominated principal components and the corresponding singular vectors obtained from the decomposition of the structural ODSs maintain most of all vibration information of the plate, especially in the case of harmonic force excitations that the 1st principal component and its vectors mostly dominated in the system; (2) the damage indicator can apparently flag out the damage localization in the case of the different sinusoidal excitation frequencies that may not be close to any of structural natural frequencies. The successful simulation indicates that the proposed method for structural damage detection is novel and robust. It also indicates the potentially practical applications in industries.
Full-field measurement techniques such as the scanning laser Doppler vibrometer (LDV) and the electronic speckle pattern interferometry systems can provide a dense and accurate vibration measurement on structural operating deflection shape (ODS) on a relatively short period of time. The possibility of structural damage detection and localization using the ODS looks likely more attractive than when using traditional measurement techniques which address only a small number of discrete points. This paper discusses the decomposition method of the structural ODSs in the time history using principal component analysis to provide a novel approach to the structural health monitoring and damage detection. The damage indicator is proposed through comparison of structural singular vectors of the ODS variation matrixes between the healthy and damaged stages. A plate piece with a fix-free configuration is used as an example to demonstrate the effectiveness of the damage detection and localization using the proposed method. The simulation results show that: (1) the dominated principal components and the corresponding singular vectors obtained from the decomposition of the structural ODSs maintain most of all vibration information of the plate, especially in the case of harmonic force excitations that the 1st principal component and its vectors mostly dominated in the system; (2) the damage indicator can apparently flag out the damage localization in the case of the different sinusoidal excitation frequencies that may not be close to any of structural natural frequencies. The successful simulation indicates that the proposed method for structural damage detection is novel and robust. It also indicates the potentially practical applications in industries.
2011, 25(3).
Abstract:
Hot dip aluminizing is one of the most effective methods of surface protection for steels and is gradually gaining popularity. Although the pulling speed is one of the most important parameters to control the coating thickness of aluminizing products, however, there are few publications on the mathematical modeling of pulling speed during the hot dip process. In order to describe the correlation among the pulling speed, coating thickness and solidification time, the principle of mass and heat transfer during the aluminizing process is investigated in this paper. The mathematical models are based on Navier-Stokes equation and heat transfer analysis. Experiments using the self-designed equipment are carried out to validate the mathematical models. Specifically, aluminum melt is purified at 730 ℃. The Cook-Norteman method is used for the pretreatment of Q235 steel plates. The temperature of hot dip aluminizing is set to 690 ℃ and the dipping time is set to 3 min. A direct current motor with stepless speed variation is used to adjust the pulling speed. The temperature change of the coating is recorded by an infrared thermometer, and the coating thickness is measured by using image analysis. The validate experiment results indicate that the coating thickness is proportional to the square root of pulling speed for the Q235 steel plate, and that there is a linear relationship between coating thickness and solidification time when the pulling speed is lower than 0.11 ms. The prediction of the proposed model fits well with the experimental observations of the coating thickness.
Hot dip aluminizing is one of the most effective methods of surface protection for steels and is gradually gaining popularity. Although the pulling speed is one of the most important parameters to control the coating thickness of aluminizing products, however, there are few publications on the mathematical modeling of pulling speed during the hot dip process. In order to describe the correlation among the pulling speed, coating thickness and solidification time, the principle of mass and heat transfer during the aluminizing process is investigated in this paper. The mathematical models are based on Navier-Stokes equation and heat transfer analysis. Experiments using the self-designed equipment are carried out to validate the mathematical models. Specifically, aluminum melt is purified at 730 ℃. The Cook-Norteman method is used for the pretreatment of Q235 steel plates. The temperature of hot dip aluminizing is set to 690 ℃ and the dipping time is set to 3 min. A direct current motor with stepless speed variation is used to adjust the pulling speed. The temperature change of the coating is recorded by an infrared thermometer, and the coating thickness is measured by using image analysis. The validate experiment results indicate that the coating thickness is proportional to the square root of pulling speed for the Q235 steel plate, and that there is a linear relationship between coating thickness and solidification time when the pulling speed is lower than 0.11 ms. The prediction of the proposed model fits well with the experimental observations of the coating thickness.
2011, 25(3).
Abstract:
Ultrasonic guided wave inspection is an effective non-destructive testing method which can be used for stress level evaluation in steel strands. Unfortunately the propagation velocity of ultrasonic guided waves changes due to temperature shift making the prestress measurement of steel strands inaccurate and even sometimes impossible. In the course of solving the problem, this paper reports on quantitative research on the temperature dependence of ultrasonic longitudinal guided wave propagation in long range steel strands. In order to achieve the generation and reception of a chosen longitudinal mode in a steel strand with a helical shaped surface, a new type of magnetostrictive transducer was developed, characterized by a group of thin clips and three identical permanent magnets. Excitation and reception of ultrasonic guided waves in a steel strand were performed experimentally. Experimental results shows that in the temperature range from –4 ℃ to 34 ℃, the propagation velocity of the L(0, 1) mode at 160 kHz linearly decreased with increasing temperature and its temperature dependent coefficient was (m•s–1•(℃)–1) which is very close to the theoretical prediction. The effect of dimension deviation between the helical and center wires and the effect of the thermal expansion of the steel strand on ultrasonic longitudinal guided wave propagation were also analyzed. It was found that these effects could be ignored compared with the change in the material mechanical properties of the steel strands due to temperature shift. It was also observed that the longitudinal guided wave mode was somewhat more sensitive to temperature changes compared with conventional ultrasonic waves theoretically. Therefore, it is considered that the temperature effect on ultrasonic longitudinal guided wave propagation in order to improve the accuracy of stress measurement in prestressed steel strands. Quantitative research on the temperature dependence of ultrasonic guided wave propagation in steel strands provides an important basis for the compensation of temperature effects in stress measurement in steel strands by using ultrasonic guided wave inspection.
Ultrasonic guided wave inspection is an effective non-destructive testing method which can be used for stress level evaluation in steel strands. Unfortunately the propagation velocity of ultrasonic guided waves changes due to temperature shift making the prestress measurement of steel strands inaccurate and even sometimes impossible. In the course of solving the problem, this paper reports on quantitative research on the temperature dependence of ultrasonic longitudinal guided wave propagation in long range steel strands. In order to achieve the generation and reception of a chosen longitudinal mode in a steel strand with a helical shaped surface, a new type of magnetostrictive transducer was developed, characterized by a group of thin clips and three identical permanent magnets. Excitation and reception of ultrasonic guided waves in a steel strand were performed experimentally. Experimental results shows that in the temperature range from –4 ℃ to 34 ℃, the propagation velocity of the L(0, 1) mode at 160 kHz linearly decreased with increasing temperature and its temperature dependent coefficient was (m•s–1•(℃)–1) which is very close to the theoretical prediction. The effect of dimension deviation between the helical and center wires and the effect of the thermal expansion of the steel strand on ultrasonic longitudinal guided wave propagation were also analyzed. It was found that these effects could be ignored compared with the change in the material mechanical properties of the steel strands due to temperature shift. It was also observed that the longitudinal guided wave mode was somewhat more sensitive to temperature changes compared with conventional ultrasonic waves theoretically. Therefore, it is considered that the temperature effect on ultrasonic longitudinal guided wave propagation in order to improve the accuracy of stress measurement in prestressed steel strands. Quantitative research on the temperature dependence of ultrasonic guided wave propagation in steel strands provides an important basis for the compensation of temperature effects in stress measurement in steel strands by using ultrasonic guided wave inspection.
2011, 25(3).
Abstract:
Returning home is the most important process of a parallel kinematic machine (PKM) with incremental encoders. Currently, most corresponding articles focus on the accuracy of homing process, and there lacks the investigation of the operations safety. For a 4RRR PKM, all servoaxes would be independently driven to their zero positions at the same time based on the traditional homing mode, and that can bring serious interfere of the kinematic chains. This paper systemically investigates this 4RRR PKMs safety of homing process. A homing strategy usually contains three parts which are the home switches locations, the platforms initial moving space, and each links homing direction, and all of them can influence the safety of homing operation. For the purpose of evaluating and describing the safety of the homing strategy, some important parameters are introduced as follows: Safely homing ratio (SHR) is used to evaluate the probability of a machines successfully returning home from an initial moving space; Synchronal rotational angle (SRA) is the four links largest synchronal rotational angle with given directions from a given pose. Whether a machine can safely return home from a given pose can be judged by comparing the SRA with all four home switches mounting angles. By meshing the initial moving space and checking the safeties of returning home from all the initial poses on the nodes, the SHR of this initial moving space can be calculate. For the sake of convenience, the platforms initial moving space should be as large as possible, and in this 4RRR PKM, a square zone in the center of the workspace with a giving initial rotation range is selected as the platforms initial moving space. The forward direction is selected as each links homing direction according to custom, and the platforms initial rotational angle is selected as larger than 0 based on this 4RRR PKMs kinematic characteristics. The platforms initial moving space can be defined only by the side length of the initial moving square. By setting a probable searching step and calculating the SHR of the initial moving square, an optimal procedure of searching for the largest side length of the platforms initial moving square is proposed. The homing strategy proposed is based on a systemic research on the safety of homing process for PKM, and the two new indexes SHR and SRA can clearly describe the safety of homing operation. The homing operation based on this strategy is fast and safe, and the method can also be used in other PKMs with the situation of serious components interference.
Returning home is the most important process of a parallel kinematic machine (PKM) with incremental encoders. Currently, most corresponding articles focus on the accuracy of homing process, and there lacks the investigation of the operations safety. For a 4RRR PKM, all servoaxes would be independently driven to their zero positions at the same time based on the traditional homing mode, and that can bring serious interfere of the kinematic chains. This paper systemically investigates this 4RRR PKMs safety of homing process. A homing strategy usually contains three parts which are the home switches locations, the platforms initial moving space, and each links homing direction, and all of them can influence the safety of homing operation. For the purpose of evaluating and describing the safety of the homing strategy, some important parameters are introduced as follows: Safely homing ratio (SHR) is used to evaluate the probability of a machines successfully returning home from an initial moving space; Synchronal rotational angle (SRA) is the four links largest synchronal rotational angle with given directions from a given pose. Whether a machine can safely return home from a given pose can be judged by comparing the SRA with all four home switches mounting angles. By meshing the initial moving space and checking the safeties of returning home from all the initial poses on the nodes, the SHR of this initial moving space can be calculate. For the sake of convenience, the platforms initial moving space should be as large as possible, and in this 4RRR PKM, a square zone in the center of the workspace with a giving initial rotation range is selected as the platforms initial moving space. The forward direction is selected as each links homing direction according to custom, and the platforms initial rotational angle is selected as larger than 0 based on this 4RRR PKMs kinematic characteristics. The platforms initial moving space can be defined only by the side length of the initial moving square. By setting a probable searching step and calculating the SHR of the initial moving square, an optimal procedure of searching for the largest side length of the platforms initial moving square is proposed. The homing strategy proposed is based on a systemic research on the safety of homing process for PKM, and the two new indexes SHR and SRA can clearly describe the safety of homing operation. The homing operation based on this strategy is fast and safe, and the method can also be used in other PKMs with the situation of serious components interference.
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