Nowadays,free-form surfaces have been widely used in various industrial fields.They are usually machined by CNC machine tools,but recently have also begun to be manufactured by industrial robotic arm manipulators,than...Nowadays,free-form surfaces have been widely used in various industrial fields.They are usually machined by CNC machine tools,but recently have also begun to be manufactured by industrial robotic arm manipulators,thanks to low cost,large operation reaching space and high machining flexibility of robot.So far,various methodologies have been proposed to improve efficiency and quality of free-form surface machining,thus this paper aims at providing a state-ofthe-art review on research advances in free-form surface machining.In this review,tool path generation,feedrate scheduling in Cartesian space and trajectory planning in joint space are focused for both CNC machining and robot machining,and their research statues,existing difficulties and key issues are discussed in detail.Finally,the feasible routes,breakthrough points and future development trend are also expounded.展开更多
Although significant progress has been made in precision machining of free-form surfaces recently, inspection of such surfaces remains a difficult problem. In order to solve the problem that no specific standards for ...Although significant progress has been made in precision machining of free-form surfaces recently, inspection of such surfaces remains a difficult problem. In order to solve the problem that no specific standards for the verification of free-form surface profile are available, the profile parameters of free-form surface are proposed by referring to ISO standards regarding form tolerances and considering its complexity and non-rotational symmetry. Non-uniform rational basis spline（NURBS） for describing free-form surface is formulated. Crucial issues in surface inspection and profile error verification are localization between the design coordinate system（DCS） and measurement coordinate system（MCS） for searching the closest points on the design model corresponding to measured points. A quasi particle swarm optimization（QPSO） is proposed to search the transformation parameters to implement localization between DCS and MCS. Surface subdivide method which does the searching in a recursively reduced range of the parameters u and v of the NURBS design model is developed to find the closest points. In order to verify the effectiveness of the proposed methods, the design model is generated by NURBS and the measurement data of simulation example are generated by transforming the design model to arbitrary position and orientation, and the parts are machined based on the design model and are measured on CMM. The profile errors of simulation example and actual parts are calculated by the proposed method. The results verify that the evaluation precision of freeform surface profile error by the proposed method is higher 10%-22% than that by CMM software. The proposed method deals with the hard problem that it has a lower precision in profile error evaluation of free-form surface.展开更多
An essential step for the realization of free-form surface structures is to create an efficient structural gird that satisfies not only the architectural aesthetics,but also the structural performance.Employing the ma...An essential step for the realization of free-form surface structures is to create an efficient structural gird that satisfies not only the architectural aesthetics,but also the structural performance.Employing the main stress trajectories as the representation of force flows on a free-form surface,an automatic grid generation approach is proposed for the architectural design.The algorithm automatically plots the main stress trajectories on a 3D free-form surface,and adopts a modified advancing front meshing technique to generate the structural grid.Based on the proposed algorithm,an automatic grid generator named "St-Surmesh" is developed for the practical architectural design of free-form surface structure.The surface geometry of one of the Sun Valleys in Expo Axis for the Expo Shanghai 2010 is selected as a numerical example for validating the proposed approach.Comparative studies are performed to demonstrate how different structural grids affect the design of a free-form surface structure.展开更多
3D solid models for parts with regular-form surfaces (PRFSs) are effectively generated using traditional parametric design techniques. A new model is obtained by changing some parameters defining the model. The parts ...3D solid models for parts with regular-form surfaces (PRFSs) are effectively generated using traditional parametric design techniques. A new model is obtained by changing some parameters defining the model. The parts with free-form surfaces (PFFSs), however, cannot be defined by several parameters. Usually they are defined by some geometric elements like profile curves. The traditional parametric design approaches have not easily dealt with the PFFSs. A method for generating a solid model and an engineering drawing for PFFSs is proposed in this paper: First, the new profiles are generated from input point data. Second, the profile information is extracted from the existing model. Last, the old profiles are replaced with the new profiles. This method can preserve the associative information of the existing model and automatically generate the drawing including views, dimen- sions, and annotations. The proposed method has been implemented using a commercial CAD/CAM system, Unigraphics, and API functions written in C-language, and were applied to the blades of a turbine generator. Some illustrative examples are pro- vided in order to show the effectiveness of the proposed method.展开更多
Current measurement method for unknown free-form surface has low efficiency.To acquire given precision, a lot of null points are measured. Based on change surface curvature, anew measurement planning is put forward. S...Current measurement method for unknown free-form surface has low efficiency.To acquire given precision, a lot of null points are measured. Based on change surface curvature, anew measurement planning is put forward. Sample step is evaluated from the change curvature and thelocally-bounded character of extrapolating curve. Two coefficients, maximum error coefficient andlocal camber coefficient, are used to optimize sampling step. The first coefficient is computed toavoid sampling-point exceeding the measurement range and the second control sampling precision.Compared with the other methods, the proposed planning method can reduce the number of themeasuring-point efficiently for the given precision. Measuring point distributes adaptively by thechange surface curvature. The method can be applied to improve measurement efficiency and accuracy.展开更多
A new method is put forward combining computer vision with computer aidedgeometric design (CAGD) to resolve the problem of free-form surface reconstruction. The surface isfirst subdivided into N-sided Gregory patches,...A new method is put forward combining computer vision with computer aidedgeometric design (CAGD) to resolve the problem of free-form surface reconstruction. The surface isfirst subdivided into N-sided Gregory patches, and a stereo algorithm is used to reconstruct theboundary curves. Then, the cross boundary tangent vectors are computed through reflectance analysis.At last, the whole surface can be reconstructed jointing these patches with G^1 continuity(tangentcontinuity). Examples on synthetic images are given.展开更多
Carrying out experiments and researches on tool bre ak age and undercut of work-piece of free-form surface by using wavelet analysis, both the fault features can be extracted in a special frequency segment of wave let...Carrying out experiments and researches on tool bre ak age and undercut of work-piece of free-form surface by using wavelet analysis, both the fault features can be extracted in a special frequency segment of wave let decompose. According to the feature of transient fault, the author proposes for the first time the automatic determination technology of the threshold by us e of the adaptive filter characteristic of wavelet transform. Based on profound researches on steady fault feature, this dissertation makes an effective token o f steady fault feature by using wavelet energy method, and proposes the new idea to identify cut-in case and cut-out case, thereby successfully gives an uniqu e description quantitatively on the characterization of the variation of fault a nd cutting condition in the monitoring system.展开更多
The methodology of 5-axis cutter selection to avert collision for free-form surface machining by flat-end cutters is presented. The combination of different cutters is adopt aiming at short machining time and high pre...The methodology of 5-axis cutter selection to avert collision for free-form surface machining by flat-end cutters is presented. The combination of different cutters is adopt aiming at short machining time and high precision. The optimal small cutter is determined based on the geometric information of the points where a cutter most probably collide with the machined surface. Several larger cutters are selected to machine the surface in order to find the interference-free area. The difference of machining time for this area between the optimal small cutter and the large cutters is calculated. The functional relationship between the machining time and the radius of a cutter is established, by which the optimal number of cutters is obtained. The combination of cutters, which possesses the minimum overall machining time, is selected as the optimal cutter sizes. A case study has demonstrated the validity of the proposed methodology and algorithms.展开更多
In CNC machining, two essential components decide the accuracy and machining time for a sculptured surface: one is the step-size interval, the other is the tool-path interval. Due to the limitation of the conventional...In CNC machining, two essential components decide the accuracy and machining time for a sculptured surface: one is the step-size interval, the other is the tool-path interval. Due to the limitation of the conventional method for calculating the tool-path interval, it cannot satisfy the machining requirement for high-speed and high-resolution machining. Accordingly, for high-speed and high-resolution machining, the current study proposes a new tool-path interval algorithm, plus a variable step-size algorithm for NURBS. Furthermore, a new type cutter, which can improve the cutting efficiency, is investigated in the paper. The transversal equation of the torus cutter onto the flat plan is given in this paper. The tool-path interval is calculated with the transversal equation and the proposed algorithm. The illustrated example shows that the redundant tool paths can be reduced because an accurate tool-path interval could be calculated.展开更多
A non contact three dimensional measurement method is presented in this paper.This system consists of a laser triangulation probe,a probe head and a coordinate measuring machine (CMM).The measurement principle of th...A non contact three dimensional measurement method is presented in this paper.This system consists of a laser triangulation probe,a probe head and a coordinate measuring machine (CMM).The measurement principle of the system is discussed,and a system calibration method employing a reference ball is proposed.The geometric model involving four frames is established to calculate the data points based on the reading of the laser probe and position information from the CMM.A measuring experiment for gesso free form surface using this system is carried out.展开更多
With an elastic negative pole being driven by ultra so nic vibration and being moved along the surface of work-piece compliantly by ro bot, a new kind of effective EDM, the compliant EDM, cuts the electrically condu c...With an elastic negative pole being driven by ultra so nic vibration and being moved along the surface of work-piece compliantly by ro bot, a new kind of effective EDM, the compliant EDM, cuts the electrically condu ctive materials away and polishes work-piece of free-form surface. The study o f the contact force between the end of polishing tool and the surface of work-p iece is the key for the compliant EDM to study its cutting mechanism and to make better use of it. This paper makes a model for the contact force and verifies i t by experiments and simulation based on the theory of elastic body kinetics and dynamic stress concentration. The research work shows that this contact force i s caused by both the electrical impulsion of EDM and the mechanical force of ult rasonic vibration, the discharge frequency of compliant EDM has a much more clos er connection with the vibration frequency of polishing tool rather than the fre quency of ultrasonic vibration.展开更多
Visual method is now broadly used in reverse engineering for 3D reconstruction. The traditional computer vision methods are feature-based, i.e., they require that the objects must reveal features owing to geometry or ...Visual method is now broadly used in reverse engineering for 3D reconstruction. The traditional computer vision methods are feature-based, i.e., they require that the objects must reveal features owing to geometry or textures. For textureless free-form surfaces, dense feature points are added artificially. In this paper, a new method is put forward combining computer vision with CAGD. The surface is subdivided into N-side Gregory patches using marked curves, and a stereo algorithm is used to reconstruct the curves. Then, the cross boundary tangent vector is computed through reflectance analysis. At last, the whole surface can be reconstructed by jointing these patches with 1Gcontinuity.展开更多
Taking the construction project of National Network Security Talents and Innovation Base Exhibition Center as an example,the application of building information model in the construction process of free-form surface s...Taking the construction project of National Network Security Talents and Innovation Base Exhibition Center as an example,the application of building information model in the construction process of free-form surface steel structure is analyzed in this paper.The results show that the application of Building Information Modeling(BIM)technology to the construction of free-form surface structure improves the work efficiency of the construction team in multi-disciplinary collaboration,surface component manufacturing,and construction process design,and subsequently improves the construction speed and construction quality.展开更多
This paper treats adaptation to the machining precision and productivity of compound free-form surfaces. The principle of a mixed NC machining method (surface direct interpolating (SDI[1])and discrete NC programming) ...This paper treats adaptation to the machining precision and productivity of compound free-form surfaces. The principle of a mixed NC machining method (surface direct interpolating (SDI[1])and discrete NC programming) is introduced- Three adaptive procedures are discussed : ( 1 ) adaptivedivision of the machining areas, (2) adaptive triangulation for generating interference-free tool pathsfrom compound surfaces, (3) machining along surface/surface intersection (SSI ) curves with anadaptive step length. They upgrade the intelligence of machining compound surfaces.展开更多
Hydrogen peroxide(H_(2)O_(2))oxidation and reduction reactions(HPOR/HPRR)are pivotal in various innovative electrochemical energy conversion devices.A comprehensive understanding of these mechanisms is critical for ca...Hydrogen peroxide(H_(2)O_(2))oxidation and reduction reactions(HPOR/HPRR)are pivotal in various innovative electrochemical energy conversion devices.A comprehensive understanding of these mechanisms is critical for catalyst design and performance improvement in these applications.In this work,we systematically investigate the HPOR/HPRR mechanisms on low-index Pt surfaces,specifically Pt(111),Pt(100)and Pt(110),through density functional theory(DFT)calculations combined with the computational hydrogen electrode(CHE)model.For HPOR,all the low-index Pt surfaces exhibit a unified potential-determining step(PDS)involving the electrochemical oxidation of hydroperoxyl intermediates(HOO*).The binding free energy of HOO*(Δ_(GHOO*))emerges as an activity descriptor,with Pt(110)exhibiting the highest HPOR activity.The HPRR mechanism follows a chem-electrochemical(C-EC)pathway.The rate-determining step(RDS)of HPRR is either the cleavage of the HO-OH bond(chemical)or the reduction of HO(electrochemical),depending on their respective activation energies.These activation energies are functions of the HO*binding free energy,Δ_(GHO*),establishingΔ_(GHO*)as the descriptor for HPRR activity prediction.Pt(111)and Pt(100)are identified as the most active HPRR catalysts among the studied metal surfaces,although they still experience a significant overpotential.The scaling relationship betweenΔ_(GHOO*)andΔ_(GHO*)reveals a thermodynamic coupling of HPOR and HPRR,explaining their occurrence on Pt surfaces.These findings provide important insights and activity descriptors for both HPOR and HPRR,providing valuable guidance for the design of electrocatalysts in H_(2)O_(2)-related energy applications and fuel cells.展开更多
BACKGROUND Dry eye disease(DED)is a multifactorial ocular surface disorder with rising prevalence.It is closely related to systemic health and psychological factors,such as sleep and mood disorders,which significantly...BACKGROUND Dry eye disease(DED)is a multifactorial ocular surface disorder with rising prevalence.It is closely related to systemic health and psychological factors,such as sleep and mood disorders,which significantly impact the quality of life of patients.AIM To explore the correlations between ocular surface function,sleep quality,and anxiety/depression in patients with DED.METHODS This was a cross-sectional investigative study that included 358 patients with DED between January 2022 and January 2025.Ocular surface was assessed using the ocular surface disease index(OSDI),tear film break-up time,fluorescein staining score,and Schirmer I test.The Pittsburgh Sleep Quality Index(PSQI),Self-Rating Anxiety Scale(SAS),and Self-Rating Depression Scale(SDS)were used to evaluate sleep quality and anxiety/depression levels.Correlation and linear regression analyses were used to explore the relationships.RESULTS The mean PSQI score of the patients was 9.94±2.18;the mean SAS score was 47.30±4.90,and the mean SDS score was 50.08±5.52.These suggested a prevalence of sleep and psychological abnormalities.There was a significant correlation between the indicators of ocular surface function(OSDI,tear film break-up time,fluorescein staining,and Schirmer I test)and PSQI,SAS,and SDS scores(P<0.05).Moreover,multiple regression revealed that age≥50 years(β=1.55,P=0.029),PSQI scores(β=0.58,P<0.001),SAS scores(β=0.17,P=0.017),and SDS scores(β=0.15,P=0.019)were independent predictors of the OSDI scores.CONCLUSION Ocular surface function in patients with DED is closely related to sleep quality and anxiety/depression,emphasizing the need for holistic clinical management.展开更多
The atmospheric surface layer of the tropical coastal ocean is commonly very unstable and experiences weakwind conditions.How the latent(LE)and sensible(H)heat fluxes behave under such conditions are unclear because o...The atmospheric surface layer of the tropical coastal ocean is commonly very unstable and experiences weakwind conditions.How the latent(LE)and sensible(H)heat fluxes behave under such conditions are unclear because of the lack of observation stations in the tropics.Thus,this study aims to analyze LE and H and the microclimate parameters influencing them.The authors deployed an eddy covariance system in a tropical coastal region for seven months.The microclimate parameters investigated were wind speed(U),vapor pressure deficit(Δe),temperature difference(ΔT),wind-vapor pressure deficit(UΔe),wind-temperature difference(UΔT),and atmospheric stability(z/L),where z is height and L is the Monin–Obukhov length.On the daily time scale,the results show that LE was more associated with U thanΔe,while H was more related toΔT than U.Cross-wavelet analysis revealed the strong coherence in the LE-U relationship for periods between one and two days,and for H–ΔT,0.5 to 1 day.Correlation and regression analyses confirmed the time series analyses results,where strong positive correlation coefficients(r)were obtained between LE and U(r=0.494)and H andΔT(r=0.365).Compared to other water bodies,the transfer coefficient of moisture(CE N)was found to be small(=0.40×10^(-3))and independent of stability;conversely,the transfer coefficient of heat(CH N)was closer to literature values(=1.00×10^(-3))and a function of stability.展开更多
Undesired ice accumulation on infrastructure and transportation systems leads to catastrophic events and significant economic losses.Although various anti-icing surfaces with photothermal effects can initially prevent...Undesired ice accumulation on infrastructure and transportation systems leads to catastrophic events and significant economic losses.Although various anti-icing surfaces with photothermal effects can initially prevent icing,any thawy droplets remaining on the horizontal surface can quickly re-freezing once the light diminishes.To address these challenges,we have developed a self-draining slippery surface(SDSS)that enables the thawy droplets to self-remove on the horizontal surface,thereby facilitating real-time anti-icing with the aid of sunlight(100 m W cm^(-2)).This is achieved by sandwiching a thin pyroelectric layer between slippery surface and photothermal film.Due to the synergy between the photothermal and pyroelectric layers,the SDSS not only maintains a high surface temperature of 19.8±2.2℃at the low temperature(-20.0±1.0℃),but also generates amount of charge through thermoelectric coupling.Thus,as cold droplets dropped on the SDSS,electrostatic force pushes the droplets off the charged surface because of the charge transfer mechanism.Even if the surface freezes overnight,the ice can melt and drain off the SDSS within 10 min of exposure to sunlight at-20.0±1.0℃,leaving a clean surface.This work provides a new perspective on the anti-icing system in the real-world environments.展开更多
Global warming induced by increased CO_(2) has caused marked changes in the ocean.Previous estimates of ocean salinity change in response to global warming have considerable ambiguity,largely attributable to the diver...Global warming induced by increased CO_(2) has caused marked changes in the ocean.Previous estimates of ocean salinity change in response to global warming have considerable ambiguity,largely attributable to the diverse sensitivities of surface fluxes.This study utilizes data from the Flux-Anomaly-Forced Model Intercomparison Project to investigate how ocean salinity responds to perturbations of surface fluxes.The findings indicate the emergence of a sea surface salinity(SSS)dipole pattern predominantly in the North Atlantic and Pacific fresh pools,driven by surface flux perturbations.This results in an intensification of the“salty gets saltier and fresh gets fresher”SSS pattern across the global ocean.The spatial pattern amplification(PA)of SSS under global warming is estimated to be approximately 11.5%,with surface water flux perturbations being the most significant contributor to salinity PA,accounting for 8.1% of the change after 70 years in experiments since pre-industrial control(piControl).Notably,the zonal-depth distribution of salinity in the upper ocean exhibits lighter seawater above the denser water,with bowed isopycnals in the upper 400 m.This stable stratification inhibits vertical mixing of salinity and temperature.In response to the flux perturbations,there is a strong positive feedback due to consequent freshening.It is hypothesized that under global warming,an SSS amplification of 7.2%/℃ and a mixed-layer depth amplification of 12.5%/℃ will occur in the global ocean.It suggests that the salinity effect can exert a more stable ocean to hinder the downward transfer of heat,which provides positive feedback to future global warming.展开更多
基金partially supported by the National Natural Science Foundation of China(Nos.91948203,51975097)the National Key Research and Development Project(No.2020YFA0713702)to Dalian University of Technology。
文摘Nowadays,free-form surfaces have been widely used in various industrial fields.They are usually machined by CNC machine tools,but recently have also begun to be manufactured by industrial robotic arm manipulators,thanks to low cost,large operation reaching space and high machining flexibility of robot.So far,various methodologies have been proposed to improve efficiency and quality of free-form surface machining,thus this paper aims at providing a state-ofthe-art review on research advances in free-form surface machining.In this review,tool path generation,feedrate scheduling in Cartesian space and trajectory planning in joint space are focused for both CNC machining and robot machining,and their research statues,existing difficulties and key issues are discussed in detail.Finally,the feasible routes,breakthrough points and future development trend are also expounded.
基金supported by National Natural Science Foundation of China(Grant No. 51075198)Jiangsu Provincial Natural Science Foundation of China(Grant No. BK2010479)+1 种基金Jiangsu Provincial Project of 333 Talents Engineering of ChinaJiangsu Provincial Project of Six Talented Peak of China
文摘Although significant progress has been made in precision machining of free-form surfaces recently, inspection of such surfaces remains a difficult problem. In order to solve the problem that no specific standards for the verification of free-form surface profile are available, the profile parameters of free-form surface are proposed by referring to ISO standards regarding form tolerances and considering its complexity and non-rotational symmetry. Non-uniform rational basis spline（NURBS） for describing free-form surface is formulated. Crucial issues in surface inspection and profile error verification are localization between the design coordinate system（DCS） and measurement coordinate system（MCS） for searching the closest points on the design model corresponding to measured points. A quasi particle swarm optimization（QPSO） is proposed to search the transformation parameters to implement localization between DCS and MCS. Surface subdivide method which does the searching in a recursively reduced range of the parameters u and v of the NURBS design model is developed to find the closest points. In order to verify the effectiveness of the proposed methods, the design model is generated by NURBS and the measurement data of simulation example are generated by transforming the design model to arbitrary position and orientation, and the parts are machined based on the design model and are measured on CMM. The profile errors of simulation example and actual parts are calculated by the proposed method. The results verify that the evaluation precision of freeform surface profile error by the proposed method is higher 10%-22% than that by CMM software. The proposed method deals with the hard problem that it has a lower precision in profile error evaluation of free-form surface.
基金Project(51378457)supported by the National Natural Science Foundation of China
文摘An essential step for the realization of free-form surface structures is to create an efficient structural gird that satisfies not only the architectural aesthetics,but also the structural performance.Employing the main stress trajectories as the representation of force flows on a free-form surface,an automatic grid generation approach is proposed for the architectural design.The algorithm automatically plots the main stress trajectories on a 3D free-form surface,and adopts a modified advancing front meshing technique to generate the structural grid.Based on the proposed algorithm,an automatic grid generator named "St-Surmesh" is developed for the practical architectural design of free-form surface structure.The surface geometry of one of the Sun Valleys in Expo Axis for the Expo Shanghai 2010 is selected as a numerical example for validating the proposed approach.Comparative studies are performed to demonstrate how different structural grids affect the design of a free-form surface structure.
文摘3D solid models for parts with regular-form surfaces (PRFSs) are effectively generated using traditional parametric design techniques. A new model is obtained by changing some parameters defining the model. The parts with free-form surfaces (PFFSs), however, cannot be defined by several parameters. Usually they are defined by some geometric elements like profile curves. The traditional parametric design approaches have not easily dealt with the PFFSs. A method for generating a solid model and an engineering drawing for PFFSs is proposed in this paper: First, the new profiles are generated from input point data. Second, the profile information is extracted from the existing model. Last, the old profiles are replaced with the new profiles. This method can preserve the associative information of the existing model and automatically generate the drawing including views, dimen- sions, and annotations. The proposed method has been implemented using a commercial CAD/CAM system, Unigraphics, and API functions written in C-language, and were applied to the blades of a turbine generator. Some illustrative examples are pro- vided in order to show the effectiveness of the proposed method.
基金This project is supported by Provincial Key Project of Science and Technology of Zhejiang (No.2003C21031).
文摘Current measurement method for unknown free-form surface has low efficiency.To acquire given precision, a lot of null points are measured. Based on change surface curvature, anew measurement planning is put forward. Sample step is evaluated from the change curvature and thelocally-bounded character of extrapolating curve. Two coefficients, maximum error coefficient andlocal camber coefficient, are used to optimize sampling step. The first coefficient is computed toavoid sampling-point exceeding the measurement range and the second control sampling precision.Compared with the other methods, the proposed planning method can reduce the number of themeasuring-point efficiently for the given precision. Measuring point distributes adaptively by thechange surface curvature. The method can be applied to improve measurement efficiency and accuracy.
基金National Natural Science Foundation of China(No.59975057).
文摘A new method is put forward combining computer vision with computer aidedgeometric design (CAGD) to resolve the problem of free-form surface reconstruction. The surface isfirst subdivided into N-sided Gregory patches, and a stereo algorithm is used to reconstruct theboundary curves. Then, the cross boundary tangent vectors are computed through reflectance analysis.At last, the whole surface can be reconstructed jointing these patches with G^1 continuity(tangentcontinuity). Examples on synthetic images are given.
文摘Carrying out experiments and researches on tool bre ak age and undercut of work-piece of free-form surface by using wavelet analysis, both the fault features can be extracted in a special frequency segment of wave let decompose. According to the feature of transient fault, the author proposes for the first time the automatic determination technology of the threshold by us e of the adaptive filter characteristic of wavelet transform. Based on profound researches on steady fault feature, this dissertation makes an effective token o f steady fault feature by using wavelet energy method, and proposes the new idea to identify cut-in case and cut-out case, thereby successfully gives an uniqu e description quantitatively on the characterization of the variation of fault a nd cutting condition in the monitoring system.
基金Funded by the Doctorate Degree Program Foundation of the Ministry of Education (No. 2000061120)
文摘The methodology of 5-axis cutter selection to avert collision for free-form surface machining by flat-end cutters is presented. The combination of different cutters is adopt aiming at short machining time and high precision. The optimal small cutter is determined based on the geometric information of the points where a cutter most probably collide with the machined surface. Several larger cutters are selected to machine the surface in order to find the interference-free area. The difference of machining time for this area between the optimal small cutter and the large cutters is calculated. The functional relationship between the machining time and the radius of a cutter is established, by which the optimal number of cutters is obtained. The combination of cutters, which possesses the minimum overall machining time, is selected as the optimal cutter sizes. A case study has demonstrated the validity of the proposed methodology and algorithms.
文摘In CNC machining, two essential components decide the accuracy and machining time for a sculptured surface: one is the step-size interval, the other is the tool-path interval. Due to the limitation of the conventional method for calculating the tool-path interval, it cannot satisfy the machining requirement for high-speed and high-resolution machining. Accordingly, for high-speed and high-resolution machining, the current study proposes a new tool-path interval algorithm, plus a variable step-size algorithm for NURBS. Furthermore, a new type cutter, which can improve the cutting efficiency, is investigated in the paper. The transversal equation of the torus cutter onto the flat plan is given in this paper. The tool-path interval is calculated with the transversal equation and the proposed algorithm. The illustrated example shows that the redundant tool paths can be reduced because an accurate tool-path interval could be calculated.
基金Supported by"863"High Technology Development Comittee ofChina (No."863"- 51 1 - 942 - 0 2 4 ) National Natural Science Foun-dation of China (No.50 0 750 64)
文摘A non contact three dimensional measurement method is presented in this paper.This system consists of a laser triangulation probe,a probe head and a coordinate measuring machine (CMM).The measurement principle of the system is discussed,and a system calibration method employing a reference ball is proposed.The geometric model involving four frames is established to calculate the data points based on the reading of the laser probe and position information from the CMM.A measuring experiment for gesso free form surface using this system is carried out.
文摘With an elastic negative pole being driven by ultra so nic vibration and being moved along the surface of work-piece compliantly by ro bot, a new kind of effective EDM, the compliant EDM, cuts the electrically condu ctive materials away and polishes work-piece of free-form surface. The study o f the contact force between the end of polishing tool and the surface of work-p iece is the key for the compliant EDM to study its cutting mechanism and to make better use of it. This paper makes a model for the contact force and verifies i t by experiments and simulation based on the theory of elastic body kinetics and dynamic stress concentration. The research work shows that this contact force i s caused by both the electrical impulsion of EDM and the mechanical force of ult rasonic vibration, the discharge frequency of compliant EDM has a much more clos er connection with the vibration frequency of polishing tool rather than the fre quency of ultrasonic vibration.
文摘Visual method is now broadly used in reverse engineering for 3D reconstruction. The traditional computer vision methods are feature-based, i.e., they require that the objects must reveal features owing to geometry or textures. For textureless free-form surfaces, dense feature points are added artificially. In this paper, a new method is put forward combining computer vision with CAGD. The surface is subdivided into N-side Gregory patches using marked curves, and a stereo algorithm is used to reconstruct the curves. Then, the cross boundary tangent vector is computed through reflectance analysis. At last, the whole surface can be reconstructed by jointing these patches with 1Gcontinuity.
基金The Hubei provincial building technology project in 2021(Project No:43).
文摘Taking the construction project of National Network Security Talents and Innovation Base Exhibition Center as an example,the application of building information model in the construction process of free-form surface steel structure is analyzed in this paper.The results show that the application of Building Information Modeling(BIM)technology to the construction of free-form surface structure improves the work efficiency of the construction team in multi-disciplinary collaboration,surface component manufacturing,and construction process design,and subsequently improves the construction speed and construction quality.
文摘This paper treats adaptation to the machining precision and productivity of compound free-form surfaces. The principle of a mixed NC machining method (surface direct interpolating (SDI[1])and discrete NC programming) is introduced- Three adaptive procedures are discussed : ( 1 ) adaptivedivision of the machining areas, (2) adaptive triangulation for generating interference-free tool pathsfrom compound surfaces, (3) machining along surface/surface intersection (SSI ) curves with anadaptive step length. They upgrade the intelligence of machining compound surfaces.
基金Supported by the Shanxi Province Grant(202203021212007,2023SHB003).
文摘Hydrogen peroxide(H_(2)O_(2))oxidation and reduction reactions(HPOR/HPRR)are pivotal in various innovative electrochemical energy conversion devices.A comprehensive understanding of these mechanisms is critical for catalyst design and performance improvement in these applications.In this work,we systematically investigate the HPOR/HPRR mechanisms on low-index Pt surfaces,specifically Pt(111),Pt(100)and Pt(110),through density functional theory(DFT)calculations combined with the computational hydrogen electrode(CHE)model.For HPOR,all the low-index Pt surfaces exhibit a unified potential-determining step(PDS)involving the electrochemical oxidation of hydroperoxyl intermediates(HOO*).The binding free energy of HOO*(Δ_(GHOO*))emerges as an activity descriptor,with Pt(110)exhibiting the highest HPOR activity.The HPRR mechanism follows a chem-electrochemical(C-EC)pathway.The rate-determining step(RDS)of HPRR is either the cleavage of the HO-OH bond(chemical)or the reduction of HO(electrochemical),depending on their respective activation energies.These activation energies are functions of the HO*binding free energy,Δ_(GHO*),establishingΔ_(GHO*)as the descriptor for HPRR activity prediction.Pt(111)and Pt(100)are identified as the most active HPRR catalysts among the studied metal surfaces,although they still experience a significant overpotential.The scaling relationship betweenΔ_(GHOO*)andΔ_(GHO*)reveals a thermodynamic coupling of HPOR and HPRR,explaining their occurrence on Pt surfaces.These findings provide important insights and activity descriptors for both HPOR and HPRR,providing valuable guidance for the design of electrocatalysts in H_(2)O_(2)-related energy applications and fuel cells.
文摘BACKGROUND Dry eye disease(DED)is a multifactorial ocular surface disorder with rising prevalence.It is closely related to systemic health and psychological factors,such as sleep and mood disorders,which significantly impact the quality of life of patients.AIM To explore the correlations between ocular surface function,sleep quality,and anxiety/depression in patients with DED.METHODS This was a cross-sectional investigative study that included 358 patients with DED between January 2022 and January 2025.Ocular surface was assessed using the ocular surface disease index(OSDI),tear film break-up time,fluorescein staining score,and Schirmer I test.The Pittsburgh Sleep Quality Index(PSQI),Self-Rating Anxiety Scale(SAS),and Self-Rating Depression Scale(SDS)were used to evaluate sleep quality and anxiety/depression levels.Correlation and linear regression analyses were used to explore the relationships.RESULTS The mean PSQI score of the patients was 9.94±2.18;the mean SAS score was 47.30±4.90,and the mean SDS score was 50.08±5.52.These suggested a prevalence of sleep and psychological abnormalities.There was a significant correlation between the indicators of ocular surface function(OSDI,tear film break-up time,fluorescein staining,and Schirmer I test)and PSQI,SAS,and SDS scores(P<0.05).Moreover,multiple regression revealed that age≥50 years(β=1.55,P=0.029),PSQI scores(β=0.58,P<0.001),SAS scores(β=0.17,P=0.017),and SDS scores(β=0.15,P=0.019)were independent predictors of the OSDI scores.CONCLUSION Ocular surface function in patients with DED is closely related to sleep quality and anxiety/depression,emphasizing the need for holistic clinical management.
基金supported by a PETRONAS-Academia Collabora-tion Dialogue 2022 Grant[Grant number PACD 2022]from PETRONAS Research Sdn.Bhd。
文摘The atmospheric surface layer of the tropical coastal ocean is commonly very unstable and experiences weakwind conditions.How the latent(LE)and sensible(H)heat fluxes behave under such conditions are unclear because of the lack of observation stations in the tropics.Thus,this study aims to analyze LE and H and the microclimate parameters influencing them.The authors deployed an eddy covariance system in a tropical coastal region for seven months.The microclimate parameters investigated were wind speed(U),vapor pressure deficit(Δe),temperature difference(ΔT),wind-vapor pressure deficit(UΔe),wind-temperature difference(UΔT),and atmospheric stability(z/L),where z is height and L is the Monin–Obukhov length.On the daily time scale,the results show that LE was more associated with U thanΔe,while H was more related toΔT than U.Cross-wavelet analysis revealed the strong coherence in the LE-U relationship for periods between one and two days,and for H–ΔT,0.5 to 1 day.Correlation and regression analyses confirmed the time series analyses results,where strong positive correlation coefficients(r)were obtained between LE and U(r=0.494)and H andΔT(r=0.365).Compared to other water bodies,the transfer coefficient of moisture(CE N)was found to be small(=0.40×10^(-3))and independent of stability;conversely,the transfer coefficient of heat(CH N)was closer to literature values(=1.00×10^(-3))and a function of stability.
基金supported by the National Natural Science Foundation of China(52273101,51922018,and 21875011)the Fundamental Research Funds for the Central Universities(KG21015201 and KG21020801)China Postdoctoral Science Foundation(2025M77422)。
文摘Undesired ice accumulation on infrastructure and transportation systems leads to catastrophic events and significant economic losses.Although various anti-icing surfaces with photothermal effects can initially prevent icing,any thawy droplets remaining on the horizontal surface can quickly re-freezing once the light diminishes.To address these challenges,we have developed a self-draining slippery surface(SDSS)that enables the thawy droplets to self-remove on the horizontal surface,thereby facilitating real-time anti-icing with the aid of sunlight(100 m W cm^(-2)).This is achieved by sandwiching a thin pyroelectric layer between slippery surface and photothermal film.Due to the synergy between the photothermal and pyroelectric layers,the SDSS not only maintains a high surface temperature of 19.8±2.2℃at the low temperature(-20.0±1.0℃),but also generates amount of charge through thermoelectric coupling.Thus,as cold droplets dropped on the SDSS,electrostatic force pushes the droplets off the charged surface because of the charge transfer mechanism.Even if the surface freezes overnight,the ice can melt and drain off the SDSS within 10 min of exposure to sunlight at-20.0±1.0℃,leaving a clean surface.This work provides a new perspective on the anti-icing system in the real-world environments.
基金supported by the Laoshan Laboratory[grant number LSKJ202202403]the National Natural Science Foundation of China[grant number 42030410]+1 种基金additionally supported by the Startup Foundation for Introducing Talent of NUISTJiangsu Innovation Research Group[grant number JSSCTD202346]。
文摘Global warming induced by increased CO_(2) has caused marked changes in the ocean.Previous estimates of ocean salinity change in response to global warming have considerable ambiguity,largely attributable to the diverse sensitivities of surface fluxes.This study utilizes data from the Flux-Anomaly-Forced Model Intercomparison Project to investigate how ocean salinity responds to perturbations of surface fluxes.The findings indicate the emergence of a sea surface salinity(SSS)dipole pattern predominantly in the North Atlantic and Pacific fresh pools,driven by surface flux perturbations.This results in an intensification of the“salty gets saltier and fresh gets fresher”SSS pattern across the global ocean.The spatial pattern amplification(PA)of SSS under global warming is estimated to be approximately 11.5%,with surface water flux perturbations being the most significant contributor to salinity PA,accounting for 8.1% of the change after 70 years in experiments since pre-industrial control(piControl).Notably,the zonal-depth distribution of salinity in the upper ocean exhibits lighter seawater above the denser water,with bowed isopycnals in the upper 400 m.This stable stratification inhibits vertical mixing of salinity and temperature.In response to the flux perturbations,there is a strong positive feedback due to consequent freshening.It is hypothesized that under global warming,an SSS amplification of 7.2%/℃ and a mixed-layer depth amplification of 12.5%/℃ will occur in the global ocean.It suggests that the salinity effect can exert a more stable ocean to hinder the downward transfer of heat,which provides positive feedback to future global warming.
