Based on the characteristics of integrated virtual prototype technology, the mechanical system sub-model, the hydraulic system sub-model and the control system sub-model of a forging manipula- tor system have been bui...Based on the characteristics of integrated virtual prototype technology, the mechanical system sub-model, the hydraulic system sub-model and the control system sub-model of a forging manipula- tor system have been built using a variety of software, and a forging manipulator mtrltidisciplinary co- simulation model has been also built using a method of simulation models interface. Then the simu- lation and experiment are finished, and the result of the experiment is in good agreement with the re- sult of the simulation. It shows that the co-simulation model established can simulate accurately pa- rameter changes in real time during the moving of the forging manipulator such as displacement, ve- locity and pressure flow, which is of important significance for the optimized design of the forging manipulator system to establish the models.展开更多
The existing research on rescue robots has focused mainly on reconnaissance,detection,and firefighting,and a small number of robots that can achieve human rescue have problems such as poor safety and stability and ins...The existing research on rescue robots has focused mainly on reconnaissance,detection,and firefighting,and a small number of robots that can achieve human rescue have problems such as poor safety and stability and insufficient carrying capacity.This article addresses the above issues and cleverly combines the advantages of soft robotic arms,underactuated robotic arms,and suction cups based on the principles of bionics.A new design for a robotic arm was proposed,and its working principle was explained.Then,the human rescue process was divided into two stages,and the grasping force of the robotic arm in each stage was analyzed separately.Finally,a prototype of the principle was developed,and the feasibility of the design principle of the robotic arm was verified through grasping experiments on a cross-sectional contour model of the human chest.At the same time,grasping experiments were conducted on different objects to demonstrate the potential application of the robotic arm in grasping ground objects.This research proposes a stress envelope adsorption rescue robot arm inspired by the adhesion ability of the Drosera plant and the stress envelope effect,which can apply force to the entire surface of the human body,reduce local force on the human body,ensure load-bearing capacity and adaptability,and improve the safety and stability of rescue grasping.展开更多
The complexity of the kinematics and dynamics of a manipulator makes it necessary to simplify the modeling process.However,the traditional representations cannot achieve this because of the absence of coordinate invar...The complexity of the kinematics and dynamics of a manipulator makes it necessary to simplify the modeling process.However,the traditional representations cannot achieve this because of the absence of coordinate invariance.Therefore,the coordinate invariant method is an important research issue.First,the rigid-body acceleration,the time derivative of the twist,is proved to be a screw,and its physical meaning is explained.Based on the twist and the rigid-body acceleration,the acceleration of the end-effector is expressed as a linear-bilinear form,and the kinematics Hessian matrix of the manipulator（represented by Lie bracket）is deduced.Further,Newton-Euler＇s equation is rewritten as a linear-bilinear form,from which the dynamics Hessian matrix of a rigid body is obtained.The formulae and the dynamics Hessian matrix are proved to be coordinate invariant.Referring to the principle of virtual work,the dynamics Hessian matrix of the parallel manipulator is gotten and the detailed dynamic model is derived.An index of dynamical coupling based on dynamics Hessian matrix is presented.In the end,a foldable parallel manipulator is taken as an example to validate the deduced kinematics and dynamics formulae.The screw theory based method can simplify the kinematics and dynamics of a manipulator,also the corresponding dynamics Hessian matrix can be used to evaluate the dynamical coupling of a manipulator.展开更多
High strength aluminum alloy plate has a low elongation at room temperature, which leads to the forming of its components need a high temperature. Liquid or gas is used as the pressure-transfer medium in the existing ...High strength aluminum alloy plate has a low elongation at room temperature, which leads to the forming of its components need a high temperature. Liquid or gas is used as the pressure-transfer medium in the existing flexible mould forming process, the heat resistance of the medium and pressurizing device makes the application of aluminum alloy plate thermoforming restricted. To solve this problem, the existing medium is replaced by the heat-resisting solid granules and the general pressure equipments are applied. Based on the pressure-transfer performance test of the solid granules medium, the feasibility that the assumption of the extended Drucker-Prager linear model can be used in the finite element analysis is proved. The constitutive equation, the yield function and the theoretical forming limit diagram（FLD） of AA7075 sheet are established. Through the finite element numerical simulation of hot granules medium pressure forming（HGMF） process, not only the influence laws of the process parameters, such as forming temperature, the blank-holder gap and the diameter of the slab, on sheet metal forming performance are discussed, but also the broken area of the forming process is analyzed and predicted, which are coincided with the technological test. The conical part whose half cone angle is 15° and relative height H/d0 is 0.57, is formed in one process at 250℃. The HGMF process solves the problems of loading and seal in the existing flexible mould forming process and provides a novel technology for thermoforming of light alloy plate, such as magnesium alloy, aluminium alloy and titanium alloy.展开更多
It is desired to require a walking robot for the elderly and the disabled to have large capacity,high stiffness,stability,etc.However,the existing walking robots cannot achieve these requirements because of the weight...It is desired to require a walking robot for the elderly and the disabled to have large capacity,high stiffness,stability,etc.However,the existing walking robots cannot achieve these requirements because of the weight-payload ratio and simple function.Therefore,Improvement of enhancing capacity and functions of the walking robot is an important research issue.According to walking requirements and combining modularization and reconfigurable ideas,a quadruped/biped reconfigurable walking robot with parallel leg mechanism is proposed.The proposed robot can be used for both a biped and a quadruped walking robot.The kinematics and performance analysis of a 3-UPU parallel mechanism which is the basic leg mechanism of a quadruped walking robot are conducted and the structural parameters are optimized.The results show that performance of the walking robot is optimal when the circumradius R,r of the upper and lower platform of leg mechanism are 161.7 mm,57.7 mm,respectively.Based on the optimal results,the kinematics and dynamics of the quadruped walking robot in the static walking mode are derived with the application of parallel mechanism and influence coefficient theory,and the optimal coordination distribution of the dynamic load for the quadruped walking robot with over-determinate inputs is analyzed,which solves dynamic load coupling caused by the branches’ constraint of the robot in the walk process.Besides laying a theoretical foundation for development of the prototype,the kinematics and dynamics studies on the quadruped walking robot also boost the theoretical research of the quadruped walking and the practical applications of parallel mechanism.展开更多
The multi-roller straightening process of section steel is analyzed by the springback theory of small curva- ture plane bending. The theoretical analysis results prove the curvature unification in straightening proces...The multi-roller straightening process of section steel is analyzed by the springback theory of small curva- ture plane bending. The theoretical analysis results prove the curvature unification in straightening process and clear- ly reveal the principle of the multi-roller straightening process. The principle can be described as~ the initial curva- tures are reduced by several times anti-bendingl meanwhile the initial curvature differences are diminished and the residual curvatures are unified~ finally, the member after curvature unification is straightened by the last anti-ben- ding. With the plastic region ratios becoming larger, the initial curvatures are more easily unified in straightening process. Based on the plastic region ratios and the required number of roller systems for unifying the initial curva- tures, the large deformation straightening strategy and the small deformation straightening strategy are redefined. The new definition provides an important theoretical basis for setting reliable reduction rules. Through the theoretical analysis results, a new straightener design philosophy is proposed to improve the straightening quality and further increase the adjustment precision as well as the flexibility of the last roller system. The adjustable end roller emerges as the times required, achieving a good effect in practical application.展开更多
The influence of the MnS plastic inclusion on the accumulation of internal damage was considered, and the Gurson– Tvergaard–Needleman (GTN) model was calibrated based on the finite element inverse method and image a...The influence of the MnS plastic inclusion on the accumulation of internal damage was considered, and the Gurson– Tvergaard–Needleman (GTN) model was calibrated based on the finite element inverse method and image analysis method using ABAQUS and GTN models. The modified GTN damage model was used to simulate the initiation and propagation of cracks in an as-cast 304 stainless steel with MnS inclusions at 900 C. The simulation results agreed well with the experimental results, indicating that the model can be effectively applied to examine the high-temperature fracture behavior of MnS inclusions. The simulation and high-temperature tensile test results revealed that MnS inclusions increased the number of holes initiation and the probability of hole polymerization, reduced the crack propagation resistance, accelerated the occurrence of material fracture behavior, and were closely related to the stress state at high temperatures. When the stress triaxiality was low, the plastic strain in the metal matrix was high, and the MnS plastic inclusions accelerated the polymerization of the pores, making metal fracture failure more likely. On the other hand, when the stress triaxiality was high, the stress state in the metal matrix was biased to the tensile state, the plastic strain in the metal matrix was low, and the influence of MnS plastic inclusions on the fracture behavior was not evident.展开更多
Dynamic modeling of a parallel manipulator（PM） is an important issue. A complete PM system is actually composed of multiple physical domains. As PMs are widely used in various fields, the importance of modeling the ...Dynamic modeling of a parallel manipulator（PM） is an important issue. A complete PM system is actually composed of multiple physical domains. As PMs are widely used in various fields, the importance of modeling the global dynamic model of the PM system becomes increasingly prominent. Currently there lacks further research in global dynamic modeling. A unified modeling approach for the multi-energy domains PM system is proposed based on bond graph and a global dynamic model of the 3-UPS/S parallel stabilized platform involving mechanical and electrical-hydraulic elements is built. Firstly, the screw bond graph theory is improved based on the screw theory, the modular joint model is modeled and the normalized dynamic model of the mechanism is established. Secondly, combined with the electro-hydraulic servo system model built by traditional bond graph, the global dynamic model of the system is obtained, and then the motion, force and power of any element can be obtained directly. Lastly, the experiments and simulations of the driving forces, pressure and flow are performed, and the results show that, the theoretical calculation results of the driving forces are in accord with the experimental ones, and the pressure and flow of the first limb and the third limb are symmetry with each other. The results are reasonable and verify the correctness and effectiveness of the model and the method. The proposed dynamic modeling method provides a reference for modeling of other multi-energy domains system which contains complex PM.展开更多
The experimental die apparatus of the solid granules medium forming on sheet metal was designed and manufactured.Typical parts,such as conical,parabolic,cylindrical and square-box-shaped components,were successfully t...The experimental die apparatus of the solid granules medium forming on sheet metal was designed and manufactured.Typical parts,such as conical,parabolic,cylindrical and square-box-shaped components,were successfully trial-produced as well.According to the analysis of the changing trends of the cross-section shape and the wall thickness during the process,it can be found that the shape of the free deformation zone of the sheet metal,which is the most critical thinning area,can be described as an approximately spherical cap.According to this forming feature,back pressure deep drawing technology with solid granules medium on sheet metal was proposed to restrain drastic thinning at the bottom of the part through the joint friction effect of solid granules medium,the back pressure tringle and the sheet metal.Therefore,the deep drawing limit of the sheet metal is significantly improved.In order to fabricate thin-walled rotary parts with great drawing ratio and complex cross-sections,a finite element model based on the material property test of the solid granules medium was established to optimize the scheme of the back pressure deep drawing.The effects on the forming performance of sheet metal from back pressure load and the approach of blank holding control were analyzed through this model.展开更多
The compressive deformation behaviors of 300M high strength steel were investigated over a wide range of temperatures （850- 1200 C） and strain rates （0. 001- 10 s^- 1 ） on a Gleeble-3800 thermo-mechanical simulato...The compressive deformation behaviors of 300M high strength steel were investigated over a wide range of temperatures （850- 1200 C） and strain rates （0. 001- 10 s^- 1 ） on a Gleeble-3800 thermo-mechanical simulator. The measured flow stress was modified by the corrections of the friction and the temperature compensations, which nicely reflect negative effects of the friction and temperature on the flow stress. The corrected stress-strain curves were the dynamic recrystallization type on the conditions of higher deformation temperature and lower strain rate. Flow stress increases with the increase of strain rate at the same deformation temperature and strain. By contrast, flow stress decreases with the increase of temperature at the same strain rate and strain. Dependence of the peak stress on temperature and strain rate for 300M steel is described by means of the conventional hyperbolic sine equation. By re gression analysis, the activation energy （Q） in the whole range of deformation temperature is determined to be 367. 562 kJ/mol. The effects of the temperature and the strain rate on mierostructural evolution are obvious. With the increase of the deformation temperature and the decrease of the strain rate, the original austenite grain sizes of 300M steel increase. At the same time, the corrected flow stress curves more accurately determine the evolution of the microstrueture.展开更多
Hot compression experiments conducted on a Gleeble-3500thermo-mechanical simulator and metallographic observation tests were employed to study the critical conditions of dynamic recrystallization（DRX）of 316 LN auste...Hot compression experiments conducted on a Gleeble-3500thermo-mechanical simulator and metallographic observation tests were employed to study the critical conditions of dynamic recrystallization（DRX）of 316 LN austenitic stainless steel.The true stress-true strain curves of 316 LN were obtained at deformation temperatures ranging from 900℃to 1 200℃and strain rates ranging from 0.001s-1 to 10s-1.Based on the above tests,the critical conditions of DRX were determined and compared with those obtained from work-hardening theory and the Cingara-McQueen flow stress model.Furthermore,the microstructure was observed to validate the calculated results.The ratio of critical strain to peak strain（εc/εp）for 316 LN was determined,and the quantitative relationship between the critical strain and the deformation parameters of 316 LN was elucidated.The results demonstrated that the onset of DRX corresponds to the constant normalized strain hardening rate（Γ）,namely,the critical strain hardening rateΓcfor316LN is equal to 0.65.展开更多
The static recrystallization of 316LN austenitic stainless steel was studied by double-pass hot compression tests on a Gleeble 3500 thermomechanical simulator. The specimens were compressed at the deformation tempera-...The static recrystallization of 316LN austenitic stainless steel was studied by double-pass hot compression tests on a Gleeble 3500 thermomechanical simulator. The specimens were compressed at the deformation tempera- tures of 950, 1050, 1150 ℃, strain rates of 0.01, 0.1, 1 s^- 1, strains of 0.1, 0.15, 0.2, and intervals of 1-100 s. The results show that the volume fraction of static recrystallization of 316LN increases with the increase of deforma- tion temperature, strain rate, strain and interval, which indicates that static recrystallization occurs easily under the conditions of higher deformation temperature, higher strain rate and larger strain. Deformation temperature has sig- nificant influence on static recrystallization of 316LN. The volume fraction of static recrystallization could easily reach 1000% at higher deformation temperatures. By microstructure analysis, it can be concluded that the larger the volume fraction of static recrystallization, the more obvious the grain refinement. The static recrystallization activation energy of 317 882 J/mol and the exponent n of 0.46 were obtained. The static recrystallization kinetics was established. The predicted volume fraction of static recrystallization is in good agreement with the experimental results.展开更多
It is significant to develop a robot hand with high rigidity by a 6-DOF parallel manipulator（PM）.However,the existing6-DOF PMs include spherical joint which has less capability of pulling force bearing,less rotation...It is significant to develop a robot hand with high rigidity by a 6-DOF parallel manipulator（PM）.However,the existing6-DOF PMs include spherical joint which has less capability of pulling force bearing,less rotation range and lower precision under alternately heavy loads.A novel 6-DOF PM with three planar limbs and equipped with three fingers is proposed and its kinematics and statics are analyzed systematically.A 3-dimension simulation mechanism of the proposed manipulator is constructed and its structure characteristics is analyzed.The kinematics formulae for solving the displacement,velocity,acceleration of the platform,the active legs and the fingers are established.The statics formulae are derived for solving the active forces of PM and the finger mechanisms.An analytic example is given for solving the kinematics and statics of proposed manipulator and the analytic solved results are verified by the simulation mechanism.It is proved from the error analysis of analytic solutions and simulation solutions that the derived analytic formulae are correct and provide the theoretical and technical foundations for its manufacturing,control and application.展开更多
The two-rotational-degrees-of-freedom（2R） parallel mechanism（PM） with two continuous rotational axes（CRAs） has a simple kinematic model.It is therefore easy to implement trajectory planning,parameter calibration...The two-rotational-degrees-of-freedom（2R） parallel mechanism（PM） with two continuous rotational axes（CRAs） has a simple kinematic model.It is therefore easy to implement trajectory planning,parameter calibration,and motion control,which allows for a variety of application prospects.However,no systematic analysis on structural constraints of the 2R-PM with two CRAs has been performed,and there are only a few types of 2R-PM with two CRAs.Thus,a theory regarding the type synthesis of the 2R-PM with two CRAs is systematically established.First,combining the theories of reciprocal screw and space geometry,the spatial arrangement relationships of the constraint forces applied to the moving platform by the branches are explored,which give the 2R-PM two CRAs.The different distributions of the constraint forces in each branch are also studied.On the basis of the obtained structural constraints of branches,and considering the geometric relationships of constraint forces in each branch,the appropriate kinematic chains are constructed.Through the reasonable configuration of branch kinematic chains corresponding to every structural constraint,a series of new 2R-PMs with two CRAs are finally obtained.展开更多
A high-Ti 6061 alloy was rolled with strains up to 0. 8 - 2. 0 and at 350 - 550 ℃ . Microstructures that developed during deformation and subsequent solution heat treatment (SHT) were observed by using optical and tr...A high-Ti 6061 alloy was rolled with strains up to 0. 8 - 2. 0 and at 350 - 550 ℃ . Microstructures that developed during deformation and subsequent solution heat treatment (SHT) were observed by using optical and transmission electron microscopy. Microstructure evolution during SHT depends mainly on the initial rolling temperature,and it was found that the higher this temperature is,the coarser the grains are. After rolling at 400 ℃ ,well-defined cells and subgrains were formed, which induced further sites for recrystallization nucleation during subsequent SHT. The recrystallization mechanism was found to be subgrain rotation,with a final grain size smaller than 200 μm. Increasing the rolling temperature to 500 ℃ results in a low density of dislocations distributed uniformly in the deformed matrix and fewer nucleation sites during subsequent SHT. The recrystallization mechanism is grain boundary bulging,while the final grain size approaches several millimeters. Finally,a hot forming process of high-Ti 6061 alloy for inhibiting grain coarsening was proposed,and verified by experiments.展开更多
Hot granule medium pressure forming （HGMF） process is a new process in which granule medium replaces the medium in existing flexible-die hot forming process, such as liquids, gases or viscous medium. Hot forming of ...Hot granule medium pressure forming （HGMF） process is a new process in which granule medium replaces the medium in existing flexible-die hot forming process, such as liquids, gases or viscous medium. Hot forming of light alloy sheet parts can be realized based on the properties of granule medium, such as withstanding high temperature and pressure, filling well, sealing and loading easily. In this work, the forming of AA7075 cylindrical parts by HGMF process is taken as an example to establish the constitutive relation and forming limit diagram （FLD） of AA7075 sheet which is related to temperature by hot uniaxial tensile test of sheet metal. Based on the assumption that granule medium is applied to extended Drucker-Prager linear material model, the finite element model of HGMF process is established and the effect of technological parameters, such as forming temperature, blank-holder gap and drawing ratio, on the sheet metal formability, is studied. The limit drawing ratio curve of AA7075 cylindrical parts at forming temperature of 175-300 ℃ is obtained by HGMF process test, and the limit drawing ratio reaches the maximum value of 1.71 at 250 ℃. The results of numerical simulation are consistent with the results of process test, and the forming force, distribution of wall thichness and form of instability are predicted correctly, which provides reference for the application of HGMF process.展开更多
Currently,two rotations and one translation(2R1T)three-degree-of-freedom(DOF)parallel mechanisms(PMs)are widely applied in five-DOF hybrid machining robots.However,there is a lack of an effective method to evaluate th...Currently,two rotations and one translation(2R1T)three-degree-of-freedom(DOF)parallel mechanisms(PMs)are widely applied in five-DOF hybrid machining robots.However,there is a lack of an effective method to evaluate the configuration stiffness of mechanisms during the mechanism design stage.It is a challenge to select appropriate 2R1T PMs with excellent stiffness performance during the design stage.Considering the operational status of 2R1T PMs,the bending and torsional stiffness are considered as indices to evaluate PMs'configuration stiffness.Subsequently,a specific method is proposed to calculate these stiffness indices.Initially,the various types of structural and driving stiffness for each branch are assessed and their specific values defined.Subsequently,a rigid-flexible coupled force model for the over-constrained 2R1T PM is established,and the proposed evaluation method is used to analyze the configuration stiffness of the five 2R1T PMs in the entire workspace.Finally,the driving force and constraint force of each branch in the whole working space are calculated to further elucidate the stiffness evaluating results by using the proposed method above.The obtained results demonstrate that the bending and torsional stiffness of the 2RPU/UPR/RPR mechanism along the x and y-directions are larger than the other four mechanisms.展开更多
The phase diagram of an Nb- and V-containing 18Mnl8Cr0.5N steel was investigated using thermodynam ic calculation. The compositions and characteristics of precipitates were investigated by scanning electron microsco- ...The phase diagram of an Nb- and V-containing 18Mnl8Cr0.5N steel was investigated using thermodynam ic calculation. The compositions and characteristics of precipitates were investigated by scanning electron microsco- py, energy dispersive spectrometry, X-ray diffraction, and differential scanning calorimetry. Under equilibrium con- ditions, MX precipitates at 1 350 ℃. MX is a substitutional solid solution of Nb4 N3.38, and its composition （at. %） is approximately.. Nb 40, N 40, V 8, and Fe, Cr, and Mn balance. The precipitates, with shapes including irregular bulk, rod, and ellipsoid, are primarily distributed at grain boundaries and triple junctions, and their size is approxi- mately 5 10 μm. Finally, the microalloying of high nitrogen CrMn austenite steels, control of precipitate size, and the effect of precipitate on hot formin~ were discussed.展开更多
To develop a robot system for minimally invasive surgery is significant,however the existing minimally invasive surgery robots are not applicable in practical operations,due to their limited functioning and weaker per...To develop a robot system for minimally invasive surgery is significant,however the existing minimally invasive surgery robots are not applicable in practical operations,due to their limited functioning and weaker perception.A novel wire feeder is proposed for minimally invasive vascular interventional surgery.It is used for assisting surgeons in delivering a guide wire,balloon and stenting into a specific lesion location.By contrasting those existing wire feeders,the motion methods for delivering and rotating the guide wire in blood vessel are described,and their mechanical realization is presented.A new resistant force detecting method is given in details.The change of the resistance force can help the operator feel the block or embolism existing in front of the guide wire.The driving torque for rotating the guide wire is developed at different positions.Using the CT reconstruction image and extracted vessel paths,the path equation of the blood vessel is obtained.Combining the shapes of the guide wire outside the blood vessel,the whole bending equation of the guide wire is obtained.That is a risk criterion in the delivering process.This process can make operations safer and man-machine interaction more reliable.A novel surgery robot for feeding guide wire is designed,and a risk criterion for the system is given.展开更多
The cylindrical part of sheet metal based on hot-granule medium-pressure forming (HGMF) technology was investigated.The stress functions of the free deformation zone and the fracture instability theory were combined t...The cylindrical part of sheet metal based on hot-granule medium-pressure forming (HGMF) technology was investigated.The stress functions of the free deformation zone and the fracture instability theory were combined to establish the analytical expression of the critical pressure of punch. The results show that the active friction between the granule medium and the sheet metal, as well as the non-uniform internal pressure presented by the solid granule medium, can obviously improve the forming performance of the sheet metal. The critical pressure of punch increases with the increment of the friction coefficient between the granule medium and sheet metal, as well as the plastic strain ratio, whereas it decreases with the increase of the material-hardening exponent. Furthermore, the impact on the critical pressure from high to low order is the plastic strain ratio, the friction coefficient,and material-hardening exponent. The deep-drawing experiment with HGMF technology on AZ31B magnesium alloy sheet verified the instability theory.Key words: hot-granule展开更多
基金Supported by the National Natural Science Foundation of China(No.51575471)Collaborative Innovation Program Topics of Heavy Machinery of Yanshan University(2011 Program,No.ZX01-20140400-01)
文摘Based on the characteristics of integrated virtual prototype technology, the mechanical system sub-model, the hydraulic system sub-model and the control system sub-model of a forging manipula- tor system have been built using a variety of software, and a forging manipulator mtrltidisciplinary co- simulation model has been also built using a method of simulation models interface. Then the simu- lation and experiment are finished, and the result of the experiment is in good agreement with the re- sult of the simulation. It shows that the co-simulation model established can simulate accurately pa- rameter changes in real time during the moving of the forging manipulator such as displacement, ve- locity and pressure flow, which is of important significance for the optimized design of the forging manipulator system to establish the models.
基金Supported by National Natural Science Foundation of China(Grant No.52475032)Central Government Guides Local Science and Technology Development Fund Projects(Grant No.246Z2001G)Hebei Provincial Natural Science Foundation Key Projects(Grant No.E2021203125).
文摘The existing research on rescue robots has focused mainly on reconnaissance,detection,and firefighting,and a small number of robots that can achieve human rescue have problems such as poor safety and stability and insufficient carrying capacity.This article addresses the above issues and cleverly combines the advantages of soft robotic arms,underactuated robotic arms,and suction cups based on the principles of bionics.A new design for a robotic arm was proposed,and its working principle was explained.Then,the human rescue process was divided into two stages,and the grasping force of the robotic arm in each stage was analyzed separately.Finally,a prototype of the principle was developed,and the feasibility of the design principle of the robotic arm was verified through grasping experiments on a cross-sectional contour model of the human chest.At the same time,grasping experiments were conducted on different objects to demonstrate the potential application of the robotic arm in grasping ground objects.This research proposes a stress envelope adsorption rescue robot arm inspired by the adhesion ability of the Drosera plant and the stress envelope effect,which can apply force to the entire surface of the human body,reduce local force on the human body,ensure load-bearing capacity and adaptability,and improve the safety and stability of rescue grasping.
基金Supported by National Natural Science Foundation of China(Grant Nos.51375420,51105322)
文摘The complexity of the kinematics and dynamics of a manipulator makes it necessary to simplify the modeling process.However,the traditional representations cannot achieve this because of the absence of coordinate invariance.Therefore,the coordinate invariant method is an important research issue.First,the rigid-body acceleration,the time derivative of the twist,is proved to be a screw,and its physical meaning is explained.Based on the twist and the rigid-body acceleration,the acceleration of the end-effector is expressed as a linear-bilinear form,and the kinematics Hessian matrix of the manipulator（represented by Lie bracket）is deduced.Further,Newton-Euler＇s equation is rewritten as a linear-bilinear form,from which the dynamics Hessian matrix of a rigid body is obtained.The formulae and the dynamics Hessian matrix are proved to be coordinate invariant.Referring to the principle of virtual work,the dynamics Hessian matrix of the parallel manipulator is gotten and the detailed dynamic model is derived.An index of dynamical coupling based on dynamics Hessian matrix is presented.In the end,a foldable parallel manipulator is taken as an example to validate the deduced kinematics and dynamics formulae.The screw theory based method can simplify the kinematics and dynamics of a manipulator,also the corresponding dynamics Hessian matrix can be used to evaluate the dynamical coupling of a manipulator.
基金Supported by National Natural Science Foundation of China(Grant Nos.51305386,51305385)Hebei Provincial Natural Science Foundation of China(Grant No.E2013203093)
文摘High strength aluminum alloy plate has a low elongation at room temperature, which leads to the forming of its components need a high temperature. Liquid or gas is used as the pressure-transfer medium in the existing flexible mould forming process, the heat resistance of the medium and pressurizing device makes the application of aluminum alloy plate thermoforming restricted. To solve this problem, the existing medium is replaced by the heat-resisting solid granules and the general pressure equipments are applied. Based on the pressure-transfer performance test of the solid granules medium, the feasibility that the assumption of the extended Drucker-Prager linear model can be used in the finite element analysis is proved. The constitutive equation, the yield function and the theoretical forming limit diagram（FLD） of AA7075 sheet are established. Through the finite element numerical simulation of hot granules medium pressure forming（HGMF） process, not only the influence laws of the process parameters, such as forming temperature, the blank-holder gap and the diameter of the slab, on sheet metal forming performance are discussed, but also the broken area of the forming process is analyzed and predicted, which are coincided with the technological test. The conical part whose half cone angle is 15° and relative height H/d0 is 0.57, is formed in one process at 250℃. The HGMF process solves the problems of loading and seal in the existing flexible mould forming process and provides a novel technology for thermoforming of light alloy plate, such as magnesium alloy, aluminium alloy and titanium alloy.
基金supported by National Natural Science Foundation of China(Grant No.61075099)
文摘It is desired to require a walking robot for the elderly and the disabled to have large capacity,high stiffness,stability,etc.However,the existing walking robots cannot achieve these requirements because of the weight-payload ratio and simple function.Therefore,Improvement of enhancing capacity and functions of the walking robot is an important research issue.According to walking requirements and combining modularization and reconfigurable ideas,a quadruped/biped reconfigurable walking robot with parallel leg mechanism is proposed.The proposed robot can be used for both a biped and a quadruped walking robot.The kinematics and performance analysis of a 3-UPU parallel mechanism which is the basic leg mechanism of a quadruped walking robot are conducted and the structural parameters are optimized.The results show that performance of the walking robot is optimal when the circumradius R,r of the upper and lower platform of leg mechanism are 161.7 mm,57.7 mm,respectively.Based on the optimal results,the kinematics and dynamics of the quadruped walking robot in the static walking mode are derived with the application of parallel mechanism and influence coefficient theory,and the optimal coordination distribution of the dynamic load for the quadruped walking robot with over-determinate inputs is analyzed,which solves dynamic load coupling caused by the branches’ constraint of the robot in the walk process.Besides laying a theoretical foundation for development of the prototype,the kinematics and dynamics studies on the quadruped walking robot also boost the theoretical research of the quadruped walking and the practical applications of parallel mechanism.
基金Item Sponsored by National Natural Science Foundation of China(51178452)
文摘The multi-roller straightening process of section steel is analyzed by the springback theory of small curva- ture plane bending. The theoretical analysis results prove the curvature unification in straightening process and clear- ly reveal the principle of the multi-roller straightening process. The principle can be described as~ the initial curva- tures are reduced by several times anti-bendingl meanwhile the initial curvature differences are diminished and the residual curvatures are unified~ finally, the member after curvature unification is straightened by the last anti-ben- ding. With the plastic region ratios becoming larger, the initial curvatures are more easily unified in straightening process. Based on the plastic region ratios and the required number of roller systems for unifying the initial curva- tures, the large deformation straightening strategy and the small deformation straightening strategy are redefined. The new definition provides an important theoretical basis for setting reliable reduction rules. Through the theoretical analysis results, a new straightener design philosophy is proposed to improve the straightening quality and further increase the adjustment precision as well as the flexibility of the last roller system. The adjustable end roller emerges as the times required, achieving a good effect in practical application.
基金This research was supported by the National Natural Science Foundation of China (Grant Nos. 51575475 and 51675465).
文摘The influence of the MnS plastic inclusion on the accumulation of internal damage was considered, and the Gurson– Tvergaard–Needleman (GTN) model was calibrated based on the finite element inverse method and image analysis method using ABAQUS and GTN models. The modified GTN damage model was used to simulate the initiation and propagation of cracks in an as-cast 304 stainless steel with MnS inclusions at 900 C. The simulation results agreed well with the experimental results, indicating that the model can be effectively applied to examine the high-temperature fracture behavior of MnS inclusions. The simulation and high-temperature tensile test results revealed that MnS inclusions increased the number of holes initiation and the probability of hole polymerization, reduced the crack propagation resistance, accelerated the occurrence of material fracture behavior, and were closely related to the stress state at high temperatures. When the stress triaxiality was low, the plastic strain in the metal matrix was high, and the MnS plastic inclusions accelerated the polymerization of the pores, making metal fracture failure more likely. On the other hand, when the stress triaxiality was high, the stress state in the metal matrix was biased to the tensile state, the plastic strain in the metal matrix was low, and the influence of MnS plastic inclusions on the fracture behavior was not evident.
基金Supported by National Natural Science Foundation of China(Grant Nos.51275438,51405421)Hebei Provincial Natural Science Foundation of China(Grant No.E2015203101)
文摘Dynamic modeling of a parallel manipulator（PM） is an important issue. A complete PM system is actually composed of multiple physical domains. As PMs are widely used in various fields, the importance of modeling the global dynamic model of the PM system becomes increasingly prominent. Currently there lacks further research in global dynamic modeling. A unified modeling approach for the multi-energy domains PM system is proposed based on bond graph and a global dynamic model of the 3-UPS/S parallel stabilized platform involving mechanical and electrical-hydraulic elements is built. Firstly, the screw bond graph theory is improved based on the screw theory, the modular joint model is modeled and the normalized dynamic model of the mechanism is established. Secondly, combined with the electro-hydraulic servo system model built by traditional bond graph, the global dynamic model of the system is obtained, and then the motion, force and power of any element can be obtained directly. Lastly, the experiments and simulations of the driving forces, pressure and flow are performed, and the results show that, the theoretical calculation results of the driving forces are in accord with the experimental ones, and the pressure and flow of the first limb and the third limb are symmetry with each other. The results are reasonable and verify the correctness and effectiveness of the model and the method. The proposed dynamic modeling method provides a reference for modeling of other multi-energy domains system which contains complex PM.
基金Project(50775197) supported by the National Natural Science Foundation of China
文摘The experimental die apparatus of the solid granules medium forming on sheet metal was designed and manufactured.Typical parts,such as conical,parabolic,cylindrical and square-box-shaped components,were successfully trial-produced as well.According to the analysis of the changing trends of the cross-section shape and the wall thickness during the process,it can be found that the shape of the free deformation zone of the sheet metal,which is the most critical thinning area,can be described as an approximately spherical cap.According to this forming feature,back pressure deep drawing technology with solid granules medium on sheet metal was proposed to restrain drastic thinning at the bottom of the part through the joint friction effect of solid granules medium,the back pressure tringle and the sheet metal.Therefore,the deep drawing limit of the sheet metal is significantly improved.In order to fabricate thin-walled rotary parts with great drawing ratio and complex cross-sections,a finite element model based on the material property test of the solid granules medium was established to optimize the scheme of the back pressure deep drawing.The effects on the forming performance of sheet metal from back pressure load and the approach of blank holding control were analyzed through this model.
基金Sponsored by Technology Major Projects of "High-end CNC Machine Tools and Basic Manufacturing Equipment"(2012ZX04010081)Natural Science Research Foundation Program for Distinguished Young Scholars in Higher EducationInstitutions of Hebei Province of China(Y2012034)
文摘The compressive deformation behaviors of 300M high strength steel were investigated over a wide range of temperatures （850- 1200 C） and strain rates （0. 001- 10 s^- 1 ） on a Gleeble-3800 thermo-mechanical simulator. The measured flow stress was modified by the corrections of the friction and the temperature compensations, which nicely reflect negative effects of the friction and temperature on the flow stress. The corrected stress-strain curves were the dynamic recrystallization type on the conditions of higher deformation temperature and lower strain rate. Flow stress increases with the increase of strain rate at the same deformation temperature and strain. By contrast, flow stress decreases with the increase of temperature at the same strain rate and strain. Dependence of the peak stress on temperature and strain rate for 300M steel is described by means of the conventional hyperbolic sine equation. By re gression analysis, the activation energy （Q） in the whole range of deformation temperature is determined to be 367. 562 kJ/mol. The effects of the temperature and the strain rate on mierostructural evolution are obvious. With the increase of the deformation temperature and the decrease of the strain rate, the original austenite grain sizes of 300M steel increase. At the same time, the corrected flow stress curves more accurately determine the evolution of the microstrueture.
基金Item Sponsored by National Natural Science Foundation of China(51101136)Scientific and Technological Research Foundation for Outstanding Young Talents of Hebei Provincial Universities of China(Y2012034)College Innovation Team Leader Training Program of Hebei Province of China(LJRC012)
文摘Hot compression experiments conducted on a Gleeble-3500thermo-mechanical simulator and metallographic observation tests were employed to study the critical conditions of dynamic recrystallization（DRX）of 316 LN austenitic stainless steel.The true stress-true strain curves of 316 LN were obtained at deformation temperatures ranging from 900℃to 1 200℃and strain rates ranging from 0.001s-1 to 10s-1.Based on the above tests,the critical conditions of DRX were determined and compared with those obtained from work-hardening theory and the Cingara-McQueen flow stress model.Furthermore,the microstructure was observed to validate the calculated results.The ratio of critical strain to peak strain（εc/εp）for 316 LN was determined,and the quantitative relationship between the critical strain and the deformation parameters of 316 LN was elucidated.The results demonstrated that the onset of DRX corresponds to the constant normalized strain hardening rate（Γ）,namely,the critical strain hardening rateΓcfor316LN is equal to 0.65.
基金Sponsored by National Natural Science Foundation of China(51005198)Technology Major Projects of High-End CNC Machine Tools and Basic Manufacturing Equipment of China(2012ZX04010081)
文摘The static recrystallization of 316LN austenitic stainless steel was studied by double-pass hot compression tests on a Gleeble 3500 thermomechanical simulator. The specimens were compressed at the deformation tempera- tures of 950, 1050, 1150 ℃, strain rates of 0.01, 0.1, 1 s^- 1, strains of 0.1, 0.15, 0.2, and intervals of 1-100 s. The results show that the volume fraction of static recrystallization of 316LN increases with the increase of deforma- tion temperature, strain rate, strain and interval, which indicates that static recrystallization occurs easily under the conditions of higher deformation temperature, higher strain rate and larger strain. Deformation temperature has sig- nificant influence on static recrystallization of 316LN. The volume fraction of static recrystallization could easily reach 1000% at higher deformation temperatures. By microstructure analysis, it can be concluded that the larger the volume fraction of static recrystallization, the more obvious the grain refinement. The static recrystallization activation energy of 317 882 J/mol and the exponent n of 0.46 were obtained. The static recrystallization kinetics was established. The predicted volume fraction of static recrystallization is in good agreement with the experimental results.
基金Supported by National Natural Science Foundation of China(Grant No.51175447)Key Planned Project of Hebei Province,China(Grant No.11962127D)
文摘It is significant to develop a robot hand with high rigidity by a 6-DOF parallel manipulator（PM）.However,the existing6-DOF PMs include spherical joint which has less capability of pulling force bearing,less rotation range and lower precision under alternately heavy loads.A novel 6-DOF PM with three planar limbs and equipped with three fingers is proposed and its kinematics and statics are analyzed systematically.A 3-dimension simulation mechanism of the proposed manipulator is constructed and its structure characteristics is analyzed.The kinematics formulae for solving the displacement,velocity,acceleration of the platform,the active legs and the fingers are established.The statics formulae are derived for solving the active forces of PM and the finger mechanisms.An analytic example is given for solving the kinematics and statics of proposed manipulator and the analytic solved results are verified by the simulation mechanism.It is proved from the error analysis of analytic solutions and simulation solutions that the derived analytic formulae are correct and provide the theoretical and technical foundations for its manufacturing,control and application.
基金Supported by National Natural Science Foundation of China(Grant No.51405425)Hebei Provincial Natural Science Foundation of China(Grant No.E2014203255)Independent Research Program Topics of Young Teachers in Yanshan University,China(Grant No.13LGA001)
文摘The two-rotational-degrees-of-freedom（2R） parallel mechanism（PM） with two continuous rotational axes（CRAs） has a simple kinematic model.It is therefore easy to implement trajectory planning,parameter calibration,and motion control,which allows for a variety of application prospects.However,no systematic analysis on structural constraints of the 2R-PM with two CRAs has been performed,and there are only a few types of 2R-PM with two CRAs.Thus,a theory regarding the type synthesis of the 2R-PM with two CRAs is systematically established.First,combining the theories of reciprocal screw and space geometry,the spatial arrangement relationships of the constraint forces applied to the moving platform by the branches are explored,which give the 2R-PM two CRAs.The different distributions of the constraint forces in each branch are also studied.On the basis of the obtained structural constraints of branches,and considering the geometric relationships of constraint forces in each branch,the appropriate kinematic chains are constructed.Through the reasonable configuration of branch kinematic chains corresponding to every structural constraint,a series of new 2R-PMs with two CRAs are finally obtained.
基金Sponsored by the Project of High-level Talent of Hebei Province (Post-Doctoral Research Project of Hebei Province)
文摘A high-Ti 6061 alloy was rolled with strains up to 0. 8 - 2. 0 and at 350 - 550 ℃ . Microstructures that developed during deformation and subsequent solution heat treatment (SHT) were observed by using optical and transmission electron microscopy. Microstructure evolution during SHT depends mainly on the initial rolling temperature,and it was found that the higher this temperature is,the coarser the grains are. After rolling at 400 ℃ ,well-defined cells and subgrains were formed, which induced further sites for recrystallization nucleation during subsequent SHT. The recrystallization mechanism was found to be subgrain rotation,with a final grain size smaller than 200 μm. Increasing the rolling temperature to 500 ℃ results in a low density of dislocations distributed uniformly in the deformed matrix and fewer nucleation sites during subsequent SHT. The recrystallization mechanism is grain boundary bulging,while the final grain size approaches several millimeters. Finally,a hot forming process of high-Ti 6061 alloy for inhibiting grain coarsening was proposed,and verified by experiments.
基金Projects(5130538651305385)supported by the National Natural Science Foundation of ChinaProject(E2013203093)supported by the Natural Science Foundation of Hebei Province,China
文摘Hot granule medium pressure forming （HGMF） process is a new process in which granule medium replaces the medium in existing flexible-die hot forming process, such as liquids, gases or viscous medium. Hot forming of light alloy sheet parts can be realized based on the properties of granule medium, such as withstanding high temperature and pressure, filling well, sealing and loading easily. In this work, the forming of AA7075 cylindrical parts by HGMF process is taken as an example to establish the constitutive relation and forming limit diagram （FLD） of AA7075 sheet which is related to temperature by hot uniaxial tensile test of sheet metal. Based on the assumption that granule medium is applied to extended Drucker-Prager linear material model, the finite element model of HGMF process is established and the effect of technological parameters, such as forming temperature, blank-holder gap and drawing ratio, on the sheet metal formability, is studied. The limit drawing ratio curve of AA7075 cylindrical parts at forming temperature of 175-300 ℃ is obtained by HGMF process test, and the limit drawing ratio reaches the maximum value of 1.71 at 250 ℃. The results of numerical simulation are consistent with the results of process test, and the forming force, distribution of wall thichness and form of instability are predicted correctly, which provides reference for the application of HGMF process.
基金Supported by National Natural Science Foundation of China (Grant Nos.51875495,U2037202)Hebei Provincial Science and Technology Project (Grant No.206Z1805G)。
文摘Currently,two rotations and one translation(2R1T)three-degree-of-freedom(DOF)parallel mechanisms(PMs)are widely applied in five-DOF hybrid machining robots.However,there is a lack of an effective method to evaluate the configuration stiffness of mechanisms during the mechanism design stage.It is a challenge to select appropriate 2R1T PMs with excellent stiffness performance during the design stage.Considering the operational status of 2R1T PMs,the bending and torsional stiffness are considered as indices to evaluate PMs'configuration stiffness.Subsequently,a specific method is proposed to calculate these stiffness indices.Initially,the various types of structural and driving stiffness for each branch are assessed and their specific values defined.Subsequently,a rigid-flexible coupled force model for the over-constrained 2R1T PM is established,and the proposed evaluation method is used to analyze the configuration stiffness of the five 2R1T PMs in the entire workspace.Finally,the driving force and constraint force of each branch in the whole working space are calculated to further elucidate the stiffness evaluating results by using the proposed method above.The obtained results demonstrate that the bending and torsional stiffness of the 2RPU/UPR/RPR mechanism along the x and y-directions are larger than the other four mechanisms.
基金Item Sponsored by Natural Science Foundation of Hebei Province for Distinguished Young Scholars of China(E2011203131)Natural Science Foundation-Steel and Iron Foundation of Hebei Province of China(E2013203110)
文摘The phase diagram of an Nb- and V-containing 18Mnl8Cr0.5N steel was investigated using thermodynam ic calculation. The compositions and characteristics of precipitates were investigated by scanning electron microsco- py, energy dispersive spectrometry, X-ray diffraction, and differential scanning calorimetry. Under equilibrium con- ditions, MX precipitates at 1 350 ℃. MX is a substitutional solid solution of Nb4 N3.38, and its composition （at. %） is approximately.. Nb 40, N 40, V 8, and Fe, Cr, and Mn balance. The precipitates, with shapes including irregular bulk, rod, and ellipsoid, are primarily distributed at grain boundaries and triple junctions, and their size is approxi- mately 5 10 μm. Finally, the microalloying of high nitrogen CrMn austenite steels, control of precipitate size, and the effect of precipitate on hot formin~ were discussed.
基金Supported by National Hi-tech Research and Development Program of China(863 Program,Grant No.2010AA044001)Hebei Provincial Natural Science Foundation of China(Grant No.E2015203405)
文摘To develop a robot system for minimally invasive surgery is significant,however the existing minimally invasive surgery robots are not applicable in practical operations,due to their limited functioning and weaker perception.A novel wire feeder is proposed for minimally invasive vascular interventional surgery.It is used for assisting surgeons in delivering a guide wire,balloon and stenting into a specific lesion location.By contrasting those existing wire feeders,the motion methods for delivering and rotating the guide wire in blood vessel are described,and their mechanical realization is presented.A new resistant force detecting method is given in details.The change of the resistance force can help the operator feel the block or embolism existing in front of the guide wire.The driving torque for rotating the guide wire is developed at different positions.Using the CT reconstruction image and extracted vessel paths,the path equation of the blood vessel is obtained.Combining the shapes of the guide wire outside the blood vessel,the whole bending equation of the guide wire is obtained.That is a risk criterion in the delivering process.This process can make operations safer and man-machine interaction more reliable.A novel surgery robot for feeding guide wire is designed,and a risk criterion for the system is given.
基金Projects(51305385,51305386)supported by the National Natural Science Foundation of ChinaProject(QN20131080)supported by the Science Research Youth Foundation of Hebei Province Universities,China
文摘The cylindrical part of sheet metal based on hot-granule medium-pressure forming (HGMF) technology was investigated.The stress functions of the free deformation zone and the fracture instability theory were combined to establish the analytical expression of the critical pressure of punch. The results show that the active friction between the granule medium and the sheet metal, as well as the non-uniform internal pressure presented by the solid granule medium, can obviously improve the forming performance of the sheet metal. The critical pressure of punch increases with the increment of the friction coefficient between the granule medium and sheet metal, as well as the plastic strain ratio, whereas it decreases with the increase of the material-hardening exponent. Furthermore, the impact on the critical pressure from high to low order is the plastic strain ratio, the friction coefficient,and material-hardening exponent. The deep-drawing experiment with HGMF technology on AZ31B magnesium alloy sheet verified the instability theory.Key words: hot-granule
