A new profile model based on multi-scale asperities is developed and contact error is cal- culated. After stratified sampling, the model can get the distribution law of entity points on each cross section. Asperity ra...A new profile model based on multi-scale asperities is developed and contact error is cal- culated. After stratified sampling, the model can get the distribution law of entity points on each cross section. Asperity radius of curvature is estimated by the relationship between circle radius and the section interval. Contact error is related to surface form error. A model equation of contact error plane is calculated through a method based on static equilibrium theory. Three contact asperities which determine the contact error plane on the rough surface are studied. The simulation results show that contact error can be accurately calculated according to the profile error model.展开更多
This paper proposes a new approach to design pinion machine tool-settings for spiral bevel gears by controlling contact path and transmission errors. It is based on the satisfaction of contact condition of three given...This paper proposes a new approach to design pinion machine tool-settings for spiral bevel gears by controlling contact path and transmission errors. It is based on the satisfaction of contact condition of three given control points on the tooth surface. The three meshing points are controlled to be on a predesigned straight contact path that meets the pre-designed parabolic function of transmission errors. Designed separately, the magnitude of transmission errors and the orientation of the contact path are subjected to precise control. In addition, in order to meet the manufacturing requirements, we suggest to modify the values of blank offset, one of the pinion machine tool-settings, and redesign pinion ma- chine tool-settings to ensure that the magnitude and the geometry of transmission errors should not be influenced apart from minor effects on the predesigned straight contact path. The proposed approach together with its ideas has been proven by a numerical example and the manufacturing practice of a pair of spiral bevel gears.展开更多
Straight bevel gears are widely applied in automotive, aerospace, chemical and many other fields as one of the most common type of gears. Currently, the researches on straight bevel gears have focused on the fields of...Straight bevel gears are widely applied in automotive, aerospace, chemical and many other fields as one of the most common type of gears. Currently, the researches on straight bevel gears have focused on the fields of fatigue, wear, noise and vibration, while little attention is paid to the effect of multiple alignment errors on the gear tooth wear. To study the influence of alignment errors on the gear tooth wear, a simulated model of a straight bevel gear pair is established. Then, the contact pressure on the tooth surface is analyzed under the various alignment errors according to the Archard wear relationship. The main combinations of alignment errors played vital roles on the tooth wear are investigated. The result shows that under the single alignment error, the contact pressure moves to the tooth heel and increases greatly at here when ？P=0.1 or ？G=0.1; when ？E=–0.03, the contact pressure greatly increases at the tooth heel, but it obviously increases at the tooth toe when ？E=0.03; the alignment error ？γ=1 has little effect on the contact pressure on the tooth surface. Moreover, the combination of ？P, ？G, ？E〈0 and ？γ is the most dangerous type among the multiple alignment errors. This research provides valuable guidelines for predicting the tooth wear under various alignment errors.展开更多
In order to analyze the influence of setting error of tool on both tooth profile and contact characteristic of orthogonal face gear drive,the coordinate systems with and without setting error are established.Moreover,...In order to analyze the influence of setting error of tool on both tooth profile and contact characteristic of orthogonal face gear drive,the coordinate systems with and without setting error are established.Moreover,the equations of tooth profile and contact points of face gear drive are derived by envelope principle.According to the equations,the change of tooth profile and the contact points position on face gear are analyzed.The tooth surface and contact points are obtained by numerical simulation.Results show that the tooth profile and contact characteristic of face gear drive are not sensitive to the setting error of tool.展开更多
In order to find out the contact pressure intensity distribution and its effects on the workepiece flatness error in plane polishing with retaining ring,the contact model and the boundary conditions are built up based...In order to find out the contact pressure intensity distribution and its effects on the workepiece flatness error in plane polishing with retaining ring,the contact model and the boundary conditions are built up based on the axial symmetric elastic contact theory.The pressure intensity distribution is calculated and analyzed with the help of the Hankel transform theory and the constructing solution method of Chebyshev orthogonal polynomials.And then,the effects of the dimensionless ring-workpiece gap,the load ratio of the retaining ring and the dimensionless ring width on the contact pressure intensity distribution are obtained.Finally,based on the distribution theory of material removal volume,the effects of the pressure intensity distributions on the flatness errors of polished workpiece are also investigated experimentally.The results show that the contact pressure intensity distribution becomes more uniform and the better profile of polished workpiece can also be obtained,if the dimensionless ring-workpiece gap is reduced,the load ratio is selected as 0.6 to 0.85,and the dimensionless ring width is taken as 0.13 to 0.40.展开更多
Monte Carlo method was adopted to calculate the meshing error considering the manufacture error and assembly error of the meshing point along the time-varying contact line for helical gear pair. The flexural-torsion-a...Monte Carlo method was adopted to calculate the meshing error considering the manufacture error and assembly error of the meshing point along the time-varying contact line for helical gear pair. The flexural-torsion-axis dynamic model coupled was established under the tooth friction force and solved by the perturbation method to compute real dynamic tooth load. The change laws of the friction force and friction torque were obtained in a meshing period. The transmission error formulation was analyzed to introduce meshing excitations. The maximum dynamic transmission error, the maximum meshing force and the maximum dynamic factor were calculated under different speeds, external loads and damping factors. The conclusions can provide theoretical basis for the gear design especially in tooth profile correction.展开更多
The influences of machining and misalignment errors play a very critical role in the performance of the anti-backlash double-roller enveloping hourglass worm gear(ADEHWG).However,a corresponding efficient method for e...The influences of machining and misalignment errors play a very critical role in the performance of the anti-backlash double-roller enveloping hourglass worm gear(ADEHWG).However,a corresponding efficient method for eliminating or reducing these errors on the tooth profile of the ADEHWG is seldom reported.The gear engagement equation and tooth profile equation for considering six different errors that could arise from the machining and gear misalignment are derived from the theories of differential geometry and gear meshing.Also,the tooth contact analysis(TCA) is used to systematically investigate the influence of the machining and misalignment errors on the contact curves and the tooth profile by means of numerical analysis and three-dimensional solid modeling.The research results show that vertical angular misalignment of the worm wheel(Δβ) has the strongest influences while the tooth angle error(Δα) has the weakest influences on the contact curves and the tooth profile.A novel efficient approach is proposed and used to minimize the effect of the errors in manufacturing by changing the radius of the grinding wheel and the approaching point of contact.The results from the TCA and the experiment demonstrate that this tooth profile design modification method can indeed reduce the machining and misalignment errors.This modification design method is helpful in understanding the manufacturing technology of the ADEHWG.展开更多
The propagation of variations, such as fixture errors and datum errors resulting from assembly and machining processes, has been extensively studied. However, only a few studies that focus on form error propagation in...The propagation of variations, such as fixture errors and datum errors resulting from assembly and machining processes, has been extensively studied. However, only a few studies that focus on form error propagation in assembly systems have been implemented. Machining errors, especially form errors, have great impact on assembly accuracy and accuracy stability of precision mechanical systems. With form errors being the research object, a method for calculating mating variation and specifying mating coordinate is proposed to improve the accuracy of the variation propagation model. Taking into account the form error of mating surfaces, the assembly variation propagation of a precision mechanical system is analyzed, and the brief derivation procedure of the variation propagation model is introduced afterwards. The variation propagation model involves a new concept of mating variation specified by the two mating surfaces. An innovative method, the difference surface search based method, is proposed to calculate the mating variation amongst the mating surfaces. The obtained mating variation is then utilized to specify the mating coordinate in the variation propagation model. Moreover, FEM is employed to simulate the contact state of the two mating surfaces to demonstrate effectiveness of the proposed method. Meanwhile, the mating variation and mating coordinate obtained are incorporated into the assembly variation propagation model, which is then verified by a following case study through a comparison between the calculated results and the experimental results. The comparing results indicate that the established model improves the prediction of assembly accuracy. The developed model enables the investigation of various fundamental issues in variation reduction, including variation analysis, process monitoring, accuracy prediction, and accuracy control.展开更多
AIM： To compare the lifetime and annual economic burden of spectacles, contact lenses, and refractive surgery in correction of refractive errors.METHODS： This is a cross-sectional study with convenience sampling whi...AIM： To compare the lifetime and annual economic burden of spectacles, contact lenses, and refractive surgery in correction of refractive errors.METHODS： This is a cross-sectional study with convenience sampling which 120 patients were interviewed in a tertiary referral hospital in the Iranian health care system. The bottom-up based cost of illness approach was estimated using a face-to-face interview to assess the direct and indirect cost of different refractive errors correction of any correction technologies. RESULTS： Correction with spectacle imposes a total direct cost of US dollar （US$） 342.5 （±8.41） per year and US$9373.5 （±230.1） per lifetime to each patient. These figures for the contact lenses were obtained US$198.3 （±0.12） and US$5203.1 （±256.3） and for refractive surgery were obtained US$19.1 （±1.2） and US$568.1 （±64.6）, respectively. Overall, based on age-adjusted prevalence rates, astigmatism had the highest share of refractive errors economic burden with a lifetime direct cost of slightly less than US$5.49 billion, while hyperopia and myopia imposed less than US$5.24 and 4.2 billion on patients, respectively. The annually imposed cost on each individual Iranian patient with refractive errors is US$308.5. CONCLUSION： Based on 18mo post refractive surgery course observation, which is generalized to whole life, refractive surgery significantly imposed much less cost compared with spectacles and contact lenses. Refractive errors among Iranians result in considerable economic burden. Using the refractive surgery instead of other two correction methods has the ability to reduce this economic loss in the future.展开更多
Based on elementary group theory, the block pivot methods for solving two-dimensional elastic frictional contact problems are presented in this paper. It is proved that the algorithms converge within a finite number o...Based on elementary group theory, the block pivot methods for solving two-dimensional elastic frictional contact problems are presented in this paper. It is proved that the algorithms converge within a finite number of steps when the friction coefficient is ''relative small''. Unlike most mathematical programming methods for contact problems, the block pivot methods permit multiple exchanges of basic and nonbasic variables.展开更多
The adaptive element techniques of contact problem are studied by means of penalty method, and the error estimators are discussed. Based on error estimators, algorithm of the adaptive element techniques is developed, ...The adaptive element techniques of contact problem are studied by means of penalty method, and the error estimators are discussed. Based on error estimators, algorithm of the adaptive element techniques is developed, then the Gauss - Newton iterations are used which allow the nonlinear problem to be transformed into a sequence of linear sub- problems then easily solved. In addition, the algorithm can be applied into the simulation of de -bonding of fiber - reinforced composites.展开更多
基金Supported by the National Natural Science Foundation of China(5107503551127004)
文摘A new profile model based on multi-scale asperities is developed and contact error is cal- culated. After stratified sampling, the model can get the distribution law of entity points on each cross section. Asperity radius of curvature is estimated by the relationship between circle radius and the section interval. Contact error is related to surface form error. A model equation of contact error plane is calculated through a method based on static equilibrium theory. Three contact asperities which determine the contact error plane on the rough surface are studied. The simulation results show that contact error can be accurately calculated according to the profile error model.
基金National Natural Science Foundation of China (50475148)Aeronautical Science Foundation of China (04C53015)Areonautical Sci-tech Innovation Foundation of China (07B53004)
文摘This paper proposes a new approach to design pinion machine tool-settings for spiral bevel gears by controlling contact path and transmission errors. It is based on the satisfaction of contact condition of three given control points on the tooth surface. The three meshing points are controlled to be on a predesigned straight contact path that meets the pre-designed parabolic function of transmission errors. Designed separately, the magnitude of transmission errors and the orientation of the contact path are subjected to precise control. In addition, in order to meet the manufacturing requirements, we suggest to modify the values of blank offset, one of the pinion machine tool-settings, and redesign pinion ma- chine tool-settings to ensure that the magnitude and the geometry of transmission errors should not be influenced apart from minor effects on the predesigned straight contact path. The proposed approach together with its ideas has been proven by a numerical example and the manufacturing practice of a pair of spiral bevel gears.
基金Supported by National Natural Science Foundation of China(Grant No.51105287)Innovative Research Team Development Program of Ministry of Education of China(Grant No.IRT13087)
文摘Straight bevel gears are widely applied in automotive, aerospace, chemical and many other fields as one of the most common type of gears. Currently, the researches on straight bevel gears have focused on the fields of fatigue, wear, noise and vibration, while little attention is paid to the effect of multiple alignment errors on the gear tooth wear. To study the influence of alignment errors on the gear tooth wear, a simulated model of a straight bevel gear pair is established. Then, the contact pressure on the tooth surface is analyzed under the various alignment errors according to the Archard wear relationship. The main combinations of alignment errors played vital roles on the tooth wear are investigated. The result shows that under the single alignment error, the contact pressure moves to the tooth heel and increases greatly at here when ？P=0.1 or ？G=0.1; when ？E=–0.03, the contact pressure greatly increases at the tooth heel, but it obviously increases at the tooth toe when ？E=0.03; the alignment error ？γ=1 has little effect on the contact pressure on the tooth surface. Moreover, the combination of ？P, ？G, ？E〈0 and ？γ is the most dangerous type among the multiple alignment errors. This research provides valuable guidelines for predicting the tooth wear under various alignment errors.
基金Supported by the National Natural Science Foundation of China(51105194)the Scientific Research Funding of Nanjing University of Aeronautics and Astronautics(NP2011014)
文摘In order to analyze the influence of setting error of tool on both tooth profile and contact characteristic of orthogonal face gear drive,the coordinate systems with and without setting error are established.Moreover,the equations of tooth profile and contact points of face gear drive are derived by envelope principle.According to the equations,the change of tooth profile and the contact points position on face gear are analyzed.The tooth surface and contact points are obtained by numerical simulation.Results show that the tooth profile and contact characteristic of face gear drive are not sensitive to the setting error of tool.
基金Sponsored by the National Nature Science Foundation of China (50875179)
文摘In order to find out the contact pressure intensity distribution and its effects on the workepiece flatness error in plane polishing with retaining ring,the contact model and the boundary conditions are built up based on the axial symmetric elastic contact theory.The pressure intensity distribution is calculated and analyzed with the help of the Hankel transform theory and the constructing solution method of Chebyshev orthogonal polynomials.And then,the effects of the dimensionless ring-workpiece gap,the load ratio of the retaining ring and the dimensionless ring width on the contact pressure intensity distribution are obtained.Finally,based on the distribution theory of material removal volume,the effects of the pressure intensity distributions on the flatness errors of polished workpiece are also investigated experimentally.The results show that the contact pressure intensity distribution becomes more uniform and the better profile of polished workpiece can also be obtained,if the dimensionless ring-workpiece gap is reduced,the load ratio is selected as 0.6 to 0.85,and the dimensionless ring width is taken as 0.13 to 0.40.
基金Supported by National Basic Research Program of China("973"Program,No.2013CB632305)
文摘Monte Carlo method was adopted to calculate the meshing error considering the manufacture error and assembly error of the meshing point along the time-varying contact line for helical gear pair. The flexural-torsion-axis dynamic model coupled was established under the tooth friction force and solved by the perturbation method to compute real dynamic tooth load. The change laws of the friction force and friction torque were obtained in a meshing period. The transmission error formulation was analyzed to introduce meshing excitations. The maximum dynamic transmission error, the maximum meshing force and the maximum dynamic factor were calculated under different speeds, external loads and damping factors. The conclusions can provide theoretical basis for the gear design especially in tooth profile correction.
基金supported by National Natural Science Foundation of China(Grant Nos. 50775190No.51275425)+2 种基金Spring Sunshine Plan of Ministry of Education of China(Grant No. 10202258)Talent Introduction of Xihua UniversityChina(Grant No. Z1220217)
文摘The influences of machining and misalignment errors play a very critical role in the performance of the anti-backlash double-roller enveloping hourglass worm gear(ADEHWG).However,a corresponding efficient method for eliminating or reducing these errors on the tooth profile of the ADEHWG is seldom reported.The gear engagement equation and tooth profile equation for considering six different errors that could arise from the machining and gear misalignment are derived from the theories of differential geometry and gear meshing.Also,the tooth contact analysis(TCA) is used to systematically investigate the influence of the machining and misalignment errors on the contact curves and the tooth profile by means of numerical analysis and three-dimensional solid modeling.The research results show that vertical angular misalignment of the worm wheel(Δβ) has the strongest influences while the tooth angle error(Δα) has the weakest influences on the contact curves and the tooth profile.A novel efficient approach is proposed and used to minimize the effect of the errors in manufacturing by changing the radius of the grinding wheel and the approaching point of contact.The results from the TCA and the experiment demonstrate that this tooth profile design modification method can indeed reduce the machining and misalignment errors.This modification design method is helpful in understanding the manufacturing technology of the ADEHWG.
基金supported by National Natural Science Foundation of China (Grant No. 51075035)National Major Scientific Instruments and Equipments Special Project of China (Grant No. 51127004)National Natural Science Foundation of China (Grant No. 51105036)
文摘The propagation of variations, such as fixture errors and datum errors resulting from assembly and machining processes, has been extensively studied. However, only a few studies that focus on form error propagation in assembly systems have been implemented. Machining errors, especially form errors, have great impact on assembly accuracy and accuracy stability of precision mechanical systems. With form errors being the research object, a method for calculating mating variation and specifying mating coordinate is proposed to improve the accuracy of the variation propagation model. Taking into account the form error of mating surfaces, the assembly variation propagation of a precision mechanical system is analyzed, and the brief derivation procedure of the variation propagation model is introduced afterwards. The variation propagation model involves a new concept of mating variation specified by the two mating surfaces. An innovative method, the difference surface search based method, is proposed to calculate the mating variation amongst the mating surfaces. The obtained mating variation is then utilized to specify the mating coordinate in the variation propagation model. Moreover, FEM is employed to simulate the contact state of the two mating surfaces to demonstrate effectiveness of the proposed method. Meanwhile, the mating variation and mating coordinate obtained are incorporated into the assembly variation propagation model, which is then verified by a following case study through a comparison between the calculated results and the experimental results. The comparing results indicate that the established model improves the prediction of assembly accuracy. The developed model enables the investigation of various fundamental issues in variation reduction, including variation analysis, process monitoring, accuracy prediction, and accuracy control.
基金Supported partially by Hormoz Chams Research Chair in Public Health Ophthalmology,Allama Tabatabaei Award,National Elite Foundation(http://bmn.ir/)
文摘AIM： To compare the lifetime and annual economic burden of spectacles, contact lenses, and refractive surgery in correction of refractive errors.METHODS： This is a cross-sectional study with convenience sampling which 120 patients were interviewed in a tertiary referral hospital in the Iranian health care system. The bottom-up based cost of illness approach was estimated using a face-to-face interview to assess the direct and indirect cost of different refractive errors correction of any correction technologies. RESULTS： Correction with spectacle imposes a total direct cost of US dollar （US$） 342.5 （±8.41） per year and US$9373.5 （±230.1） per lifetime to each patient. These figures for the contact lenses were obtained US$198.3 （±0.12） and US$5203.1 （±256.3） and for refractive surgery were obtained US$19.1 （±1.2） and US$568.1 （±64.6）, respectively. Overall, based on age-adjusted prevalence rates, astigmatism had the highest share of refractive errors economic burden with a lifetime direct cost of slightly less than US$5.49 billion, while hyperopia and myopia imposed less than US$5.24 and 4.2 billion on patients, respectively. The annually imposed cost on each individual Iranian patient with refractive errors is US$308.5. CONCLUSION： Based on 18mo post refractive surgery course observation, which is generalized to whole life, refractive surgery significantly imposed much less cost compared with spectacles and contact lenses. Refractive errors among Iranians result in considerable economic burden. Using the refractive surgery instead of other two correction methods has the ability to reduce this economic loss in the future.
基金The project supported by the National Natural Science Foundation of China
文摘Based on elementary group theory, the block pivot methods for solving two-dimensional elastic frictional contact problems are presented in this paper. It is proved that the algorithms converge within a finite number of steps when the friction coefficient is ''relative small''. Unlike most mathematical programming methods for contact problems, the block pivot methods permit multiple exchanges of basic and nonbasic variables.
文摘The adaptive element techniques of contact problem are studied by means of penalty method, and the error estimators are discussed. Based on error estimators, algorithm of the adaptive element techniques is developed, then the Gauss - Newton iterations are used which allow the nonlinear problem to be transformed into a sequence of linear sub- problems then easily solved. In addition, the algorithm can be applied into the simulation of de -bonding of fiber - reinforced composites.
