This paper aims to experimentally and numerically probe fatigue behaviours and lifetimes of 3D4D(three-dimensional four-directional)braided composite I-beam under four-point flexure spectrum loading.New fatigue damage...This paper aims to experimentally and numerically probe fatigue behaviours and lifetimes of 3D4D(three-dimensional four-directional)braided composite I-beam under four-point flexure spectrum loading.New fatigue damage models of fibre yarn,matrix and fibre–matrix interface are proposed,and fatigue failure criteria and PFDA(Progressive Fatigue Damage Algorithm)are thus presented for meso-scale fatigue damage modelling of 3D4D braided composite I-beam.To validate the aforementioned model and algorithm,fatigue tests are conducted on the 3D4D braided composite I-beam under four-point flexure spectrum loading,and fatigue failure mechanisms are analyzed and discussed.Novel global–local FE(Finite Element)model based on the PFDA is generated for modelling progressive fatigue failure process and predicting fatigue life of 3D4D braided composite I-beam under four-point flexure spectrum loading.Good agreement has been achieved between experimental results and predictions,demonstrating the effective usage of new model.It is shown that matrix cracking and interfacial debonding initially initiates on top surface of top flange of I-beam,and then gradually propagates from the side surface of top flange to the intermediate web along the braiding angle,and considerable fiber breakage finally causes final fatigue failure of I-beam.展开更多
A flexure hinge is a major component in designing compliant mechanisms that o ers unique possibilities in a wide range of application fields in which high positioning accuracy is required. Although various flexure hin...A flexure hinge is a major component in designing compliant mechanisms that o ers unique possibilities in a wide range of application fields in which high positioning accuracy is required. Although various flexure hinges with di erent configurations have been successively proposed, they are often designed based on designers' experiences and inspirations. This study presents a systematic method for topological optimization of flexure hinges by using the level set method. Optimization formulations are developed by considering the functional requirements and geometrical constraints of flexure hinges. The functional requirements are first constructed by maximizing the compliance in the desired direction while minimizing the compliances in the other directions. The weighting sum method is used to construct an objective function in which a self-adjust method is used to set the weighting factors. A constraint on the symmetry of the obtained configuration is developed. Several numerical examples are presented to demonstrate the validity of the proposed method. The obtained results reveal that the design of a flexure hinge starting from the topology level can yield more choices for compliant mechanism design and obtain better designs that achieve higher performance.展开更多
The thin-walled tube flexure（TWTF） hinges have important potential application value in the deployment mechanisms of satellite and solar array, but the optimal design of the TWTF hinges haven＇t been completely solv...The thin-walled tube flexure（TWTF） hinges have important potential application value in the deployment mechanisms of satellite and solar array, but the optimal design of the TWTF hinges haven＇t been completely solved, which restricts their applications. An optimal design method for the qusai-static folding and deploying of TWTF hinges with double slots is presented based on the response surface theory. Firstly, the full factorial method is employed to design of the experiments. Then, the finite element models of the TWTF hinges with double slots are constructed to simulate the qusai-static folding and deploying non-linear analysis. What＇s more, the mathematical model of the TWTF flexure hinge quasi-static folding and deploying properties are derived by the response surface method. Considering of small mass and high stability, the peak moment of quasi-static folding and deploying as well as the lightless are set as the objectives to get the optimal performances. The relative errors of the objectives between the optimal design results and the FE analysis results are less than 7%, which demonstrates the precision of the surrogate models. Lastly, the parameter study shows that both the slots length and the slots width both have significant effects to the peak moment of quasi-static folding and deploying of TWTF hinges with double slots. However, the maximum Mises stress of quasi-static folding is more sensitive to the slots length than the slots width. The proposed research can be applied to optimize other thin-walled flexure hinges under quasi-static folding and deploying, which is of great importance to design of flexure hinges with high stability and low stress.展开更多
Large-deflection flexure pivot is widely used in high precision rotation application, but there are less flexure configurations and simple and convenient design methods, This paper presents a novel large-deflection cu...Large-deflection flexure pivot is widely used in high precision rotation application, but there are less flexure configurations and simple and convenient design methods, This paper presents a novel large-deflection curved-compliant annulus-shaped flexure pivot composed of six curved beam flexure elements. It can offer more than lO^angular stroke theoretically. Firstly, main-motion pseudo-rigid-body method is introduced to establish the flexure pivot model. Although pseudo-rigid-body method can be used to analyze the large-deformation flexure pivot performance, the method is definitely a laborious and difficult task for designing this novel flexure pivot. In order to simply the designing process, dimension-design graphs based on the parametric models and finite element analysis is presented. Using the dimension-design method as a tool, the designers can determine the optimal geometry rapidly, based on the stiffness and rotation demands of an annulus-shaped flexure pivot. Finally, dimension-design graph examples are given whose primary design aims to achieve a rotation stroke of annulus-shaped flexure pivot. The finite element analysis results show that the relative designing error between anticipative rotation stroke and graph design result is less than 4%. The dimensionless method used in designing annulus-shaped flexure pivot can reduce design process in both time and complexity. The novel annulus-shaped flexure pivot and dimension-design method are helpful supplement to configuration and design method of large-deflection flexure pivot.展开更多
Conventional flexible joints generally have limited range of motion and high stress concentration. To overcome these shortcomings, corrugated flexure beam（CF beam） is designed because of its large flexibility obtain...Conventional flexible joints generally have limited range of motion and high stress concentration. To overcome these shortcomings, corrugated flexure beam（CF beam） is designed because of its large flexibility obtained from longer overall length on the same span. The successful design of compliant mechanisms using CF beam requires manipulation of the stiffnesses as the design variables. Empirical equations of the CF beam stiffness components, except of the torsional stiffness, are obtained by curve-fitting method. The application ranges of all the parameters in each empirical equation are also discussed. The ratio of off-axis to axial stiffness is considered as a key characteristic of an effective compliant joint. And parameter study shows that the radius of semi-circular segment and the length of straight segment contribute most to the ratio. At last, CF beam is used to design translational and rotational flexible joints, which also verifies the validity of the empirical equations. CF beam with large flexibility is presented, and empirical equations of its stiffness are proposed to facilitate the design of flexible joint with large range of motion.展开更多
Flexure mechanisms with decoupled characteristics have been widely utilized in precision positioning applications.However,these mechanisms suffer from either slow response or low load capability.Furthermore,asymmetric...Flexure mechanisms with decoupled characteristics have been widely utilized in precision positioning applications.However,these mechanisms suffer from either slow response or low load capability.Furthermore,asymmetric design always leads to thermal error.In order to solve these issues,a novel 2-DOF decoupled mechanism is developed by monolithically manufacturing sets of statically indeterminate symmetric（SIS） flexure structures in parallel.Symmetric design helps to eliminate the thermal error and Finite Element Analysis（FEA） results show that the maximum coupling ratio between X and Y axes is below 0.25% when a maximum pretension force of 200 N is applied.By ignoring the mass effect,all the SIS flexure structures are simplified to ＂spring-damper＂ components,from which the static and dynamics model are derived.The relation between the first resonant frequency of the mechanism and the load is investigated by incorporating the load mass into the proposed dynamics model.Analytical results show that even with a load of 0.5 kg,the first resonant frequency is still higher than 300 Hz,indicating a high load capability.The mechanism＇s static and dynamic performances are experimentally examined.The linear stiffnesses of the mechanism at the working platform and at the driving point are measured to be 3.563 0 N·μm-1 and 3.362 1 N·μm-1,respectively.The corresponding estimation values from analytical models are 3.405 7 N·μm-1 and 3.381 7 N·μm-1,which correspond to estimation errors of-4.41% and 0.6%,respectively.With an additional load of 0.16 kg,the measured and estimated first resonant frequencies are 362 Hz and 365 Hz,respectively.The estimation error is only 0.55%.The analytical and experimental results show that the developed mechanism has good performances in both decoupling ability and load capability;its static and dynamic performance can be precisely estimated from corresponding analytical models.The proposed mechanism has wide potentials in precision positioning applications.展开更多
The current research of kinetostatic characteristics in flexure mechanisms mainly focus on the improvement of accuracy. To reduce or eliminate the parasitic motion is considered as an approach by using the common know...The current research of kinetostatic characteristics in flexure mechanisms mainly focus on the improvement of accuracy. To reduce or eliminate the parasitic motion is considered as an approach by using the common knowledge of symmetry. However, there is no study on designing the flexure mechanisms with symmetrical features as many as possible for better kinetostatic performance, when considering the resulting cost by the symmetry. In this paper, the concept of degree of symmetry(DoS) is proposed for the first time, which is committed to symmetry design in the phase of conceptual design. A class of flexure mechanisms with 0?DoS, 1?DoS, 2?DoS and 3?DoS are synthesized respectively based on the Freedom and Constraint Topology method. Their overall compliance matrices in an analytical form formulated within the framework of the screw theory are used to analyze and compare the effect of different number of DoS on the kinetostatic characteristics for flexure mechanisms. The finite element analysis(FEA) simulations are implemented to verify the analytical results. These results show that the higher the DoS is, the smaller the parasitic motion error will be. The flexure model with 3?DoS is optimized according to the overall compliance matrix and then tested by using the FEA simulation. The testing result shows that with the best combination parameters, the parasitic motion error for 3?DoS mechanism is almost eliminated. This research introduces a design principle which can alleviate the unwanted parasitic motion for better accuracy.展开更多
A novel 6-PSS flexible parallel mechanism was presented,which employed wide-range flexure hinges as passive joints.The proposed mechanism features micron level positioning accuracy over cubic centimeter scale workspac...A novel 6-PSS flexible parallel mechanism was presented,which employed wide-range flexure hinges as passive joints.The proposed mechanism features micron level positioning accuracy over cubic centimeter scale workspace.A three-layer back-propagation(BP) neural network was utilized to the kinematics analysis,in which learning samples containing 1 280 groups of data based on stiffness-matrix method were used to train the BP model.The kinematics performance was accurately calculated by using the constructed BP model with 19 hidden nodes.Compared with the stiffness model,the simulation and numerical results validate that BP model can achieve millisecond level computation time and micron level calculation accuracy.The concept and approach outlined can be extended to a variety of applications.展开更多
This paper presents a precise solution to predict the behavior of steel fiber reinforced concrete(SFRC) under the four point bending test(FPBT).All the force components at the beam section(before and after cracking) a...This paper presents a precise solution to predict the behavior of steel fiber reinforced concrete(SFRC) under the four point bending test(FPBT).All the force components at the beam section(before and after cracking) are formulated by applying these assumptions:a realistic stress-strain model is used for concrete behavior in compression,a linear response is considered for the uncracked tension region in a concrete constitutive model,and an exponential relationship is proposed as a stress-crack opening in the crack region which requires two parameters.Then the moment capacity of the critical cracked section is calculated by using these forces and satisfying equilibrium law at the section.Parametric studies are done on the behavior of SFRC to assess the sensitivity of the solution.Finally,this solution is validated with some existing experimental data.The result shows the proposed solution is able to estimate the behavior of SFRC under FPBT.展开更多
This paper presents the design, development, and control of a large range beam flexure-based nano servo system for the micro-stereolithography （MSL） process. As a key enabler of high accuracy in this process, a comp...This paper presents the design, development, and control of a large range beam flexure-based nano servo system for the micro-stereolithography （MSL） process. As a key enabler of high accuracy in this process, a compact desktop-size beam flexure-based nanopositioner was designed with millimeter range and nanometric motion quality. This beam flexure-based motion system is highly suitable for harsh operation conditions, as no assembly or maintenance is required during the operation. From a mechanism design viewpoint, a mirror-symmetric arrangement and appropriate redundant constraints are crucial to reduce undesired parasitic motion. Detailed finite element analysis （FEA） was conducted and showed satisfactory mechanical features. With the identified dynamic models of the nanopositioner, real-time control strategies were designed and implemented into the monolithically fabricated prototype system, demonstrating the enhanced tracking capability of the MSL process. The servo system has both a millimeter operating range and a root mean square （RMS） tracking error of about 80 nm for a circular traiectorv.展开更多
The alignment accuracy of the strap-down inertial navigation system （SINS） of airborne weapon is greatly degraded by the dynamic wing flexure of the aircraft. An adaptive Kalman filter uses innovation sequences base...The alignment accuracy of the strap-down inertial navigation system （SINS） of airborne weapon is greatly degraded by the dynamic wing flexure of the aircraft. An adaptive Kalman filter uses innovation sequences based on the maximum likelihood estimated criterion to adapt the system noise covariance matrix and the measurement noise covariance matrix on line, which is used to estimate the misalignment if the model of wing flexure of the aircraft is unknown. From a number of simulations, it is shown that the accuracy of the adaptive Kalman filter is better than the conventional Kalman filter, and the erroneous misalignment models of the wing flexure of aircraft will cause bad estimation results of Kalman filter using attitude match method.展开更多
BACKGROUND Situs inversus totalis(SIT)is a rare group of congenital developmental malformations in the clinical setting,with all organs in the chest and abdomen existing in a mirror image reversal of their normal posi...BACKGROUND Situs inversus totalis(SIT)is a rare group of congenital developmental malformations in the clinical setting,with all organs in the chest and abdomen existing in a mirror image reversal of their normal positions.Few reports have described laparoscopic surgery for colorectal cancer in patients with SIT,and it is considered difficult even for an experienced surgeon because of the mirror positioning.We present a case report of laparoscopic radical resection of a colonic splenic flexure carcinoma in a patient with SIT.CASE SUMMARY A 72-year-old male was referred to our hospital with colonic splenic flexure carcinoma,and computed tomography showed that all the organs in the chest and abdomen were inverted.Laparoscopic hemicolectomy with complete mesocolic excision was safely performed.The operating surgeon stood on the patient’s left side,which is opposite of the normal location.CONCLUSION Abdominal computed tomography is an effective method for diagnosing SIT preoperatively in patients with colonic splenic flexure carcinomas.Laparoscopic radical resection is difficult,but it is well established and safe.The surgeon should stand in the opposite position and perform backhand operations.展开更多
The effects of ply orientation angle of composite flexures on stability of hingeless rotor blade system are studied.The composite hingeless rotor blade system is simplified as a hub,a flap flexure and a lag flexure.pi...The effects of ply orientation angle of composite flexures on stability of hingeless rotor blade system are studied.The composite hingeless rotor blade system is simplified as a hub,a flap flexure and a lag flexure.pitch bearing and main blade.The kinematics formulations are inferred by employing the moderate deflection beam theory.The shear deformation and warping related to torsion are considered.The quasi-steady strip theory with dynamic inflow effects is applied to obtain the aerodynamic loads acting on the blade.Based on these.the set of finite element formulations of a hingeless rotor blade system is worked out.The numerical results show that the ply angle of the composite flexures has great effects on the aeroelastic stability of rotor blade.展开更多
A large workspace flexure parallel positioner system is developed, which can attain sub-micron scale accuracy over cubic centimeter motion range for utilizing novel wide-range flexure hinges instead of the conventiona...A large workspace flexure parallel positioner system is developed, which can attain sub-micron scale accuracy over cubic centimeter motion range for utilizing novel wide-range flexure hinges instead of the conventional mechanism joints. Flexure hinges eliminate backlash and friction, but on the other hand their deformation caused by initial loads influences the positioning accuracy greatly, so discussions about loads＇ influence analysis on this flexure parallel positioner is very necessary. The stiffness model of the whole mechanism is presented via stiffness assembly method based on the stiffness model of individual flexure hinge, And the analysis results are validated by the finite element analysis （FEA） simulation and experiment tests, which provide essential data to the practical application of this positioner system.展开更多
A new type of air bearing with flexure structure is introduced. The new bearing is designed for precision mechanical engineering devices such as mechanical watch movement. The new design uses the flexure structure to ...A new type of air bearing with flexure structure is introduced. The new bearing is designed for precision mechanical engineering devices such as mechanical watch movement. The new design uses the flexure structure to provide 3D damping to absorb shocks from all directions. Two designs are presented： one has 12 T-shape slots in the radian direction while the other has 8 spiral slots in the radian direction. Both designs have flexure mountings on the axial directions. Based on the finite element analysis （FEA）, the new bearing can reduce the vibration （displacement） by as much as 8.37% and hence, can better protect the shafts.展开更多
In design of flexure mechanism, diminishing the parasitic-motion is a key point to improve the accuracy. However, most of existing topics concentrate on improving the accuracy of linear-motion flexure mechanisms via c...In design of flexure mechanism, diminishing the parasitic-motion is a key point to improve the accuracy. However, most of existing topics concentrate on improving the accuracy of linear-motion flexure mechanisms via compensating the parasitic error, but few research the multi-dimensional flexure mechanisms. A general design principle and method for high-precision flexure mechanisms based on the parasitic-motion compensation is presented, and the proposed method can compensate the parasitic rotation in company with translation, or the parasitic translation in company with rotation, or both. The crucial step for the method is that the parasitic motion of a flexure mechanism is formulated and evaluated in terms of its compliance. The overall compliance matrix of a general flexure mechanism is formulated by using screw theory firstly, then the criteria for the parasitic motions is introduced by analyzing the characteristics of the resultant compliance matrix as well as with aid of the concept of instantaneous rotation center. Subsequently, a compliance-based compensation approach for reducing parasitic-motion is addressed as the most important part. The design principles and procedure are further discussed to help with improving the accuracy of flexure mechanisms, and case studies are provided to illustrate this method. Finally, an analytical verification is provided to demonstrate that the symmetry design philosophy widely used in flexure design can effectively improve accuracy in terms of the proposed method. The proposed compensation method can be well used to diminish the parasitic-motion of multi-dimensional flexure mechanisms.展开更多
The purpose of this thesis is to derive the flexibility formula of the corner-filleted flexure hinge easily and conveniently and use it to design a micro-rotation compliant mechanism. Firstly,we get the corner-fillete...The purpose of this thesis is to derive the flexibility formula of the corner-filleted flexure hinge easily and conveniently and use it to design a micro-rotation compliant mechanism. Firstly,we get the corner-filleted flexure hinge flexibility formula by methods of symmetry transformation and coordinates translation. The correctness of this formula is validated on the basis of the finite element method and under the premise that the effects of shear stress are taken into consideration. Then a micro-rotation compliant mechanism is designed in accordance with the corner-filleted flexure hinge,and the deduction and analysis of its working moment/rigidity are conducted. Moreover,this theoretical formula is proved to be accurate and reliable through the finite element analysis and the experimental verification,based on which the structural design and optimization can be made on the rotating part of a micro adjustment device. The results illustrate that designing and optimizing the structures by the analysis model is convenient and reliable so that complicated 3D modeling and finite element analysis are not needed.展开更多
Beam flexure hinges can achieve accurate motion and force control through the elastic deformation. This paper presents a nonlinear model for uniform and circular cross-section spatial beam flexure hinges which are com...Beam flexure hinges can achieve accurate motion and force control through the elastic deformation. This paper presents a nonlinear model for uniform and circular cross-section spatial beam flexure hinges which are commonly employed in compliant parallel mechanisms. The proposed beam model takes shear deformations into consideration and hence is applicable to both slender and thick beam flexure hinges. Starting from the first principles, the nonlinear strain measure is derived using beam kinematics and expressed in terms of translational displacements and rotational angles. Second-order approximation is employed in order to make the nonlinear strain within acceptable accuracy. The natural boundary conditions and nonlinear governing equations are derived in terms of rotational Euler angles and subsequently solved for combined end loads. The resulting end load-displacement model, which is compact and closed-form, is proved to be accurate for both slender and thick beam flexure using nonlinear finite element analysis. This beam model can provide designers with more design insight of the spatial beam flexure and thus will benefit the structural design and optimization of compliant manipulators.展开更多
基金supported by the National Natural Science Foundation of China(No.12472340).
文摘This paper aims to experimentally and numerically probe fatigue behaviours and lifetimes of 3D4D(three-dimensional four-directional)braided composite I-beam under four-point flexure spectrum loading.New fatigue damage models of fibre yarn,matrix and fibre–matrix interface are proposed,and fatigue failure criteria and PFDA(Progressive Fatigue Damage Algorithm)are thus presented for meso-scale fatigue damage modelling of 3D4D braided composite I-beam.To validate the aforementioned model and algorithm,fatigue tests are conducted on the 3D4D braided composite I-beam under four-point flexure spectrum loading,and fatigue failure mechanisms are analyzed and discussed.Novel global–local FE(Finite Element)model based on the PFDA is generated for modelling progressive fatigue failure process and predicting fatigue life of 3D4D braided composite I-beam under four-point flexure spectrum loading.Good agreement has been achieved between experimental results and predictions,demonstrating the effective usage of new model.It is shown that matrix cracking and interfacial debonding initially initiates on top surface of top flange of I-beam,and then gradually propagates from the side surface of top flange to the intermediate web along the braiding angle,and considerable fiber breakage finally causes final fatigue failure of I-beam.
基金Supported by National Natural Science Foundation of China(Grant Nos.51605166,51820105007)Fundamental Research Funds for the Central Universities of China
文摘A flexure hinge is a major component in designing compliant mechanisms that o ers unique possibilities in a wide range of application fields in which high positioning accuracy is required. Although various flexure hinges with di erent configurations have been successively proposed, they are often designed based on designers' experiences and inspirations. This study presents a systematic method for topological optimization of flexure hinges by using the level set method. Optimization formulations are developed by considering the functional requirements and geometrical constraints of flexure hinges. The functional requirements are first constructed by maximizing the compliance in the desired direction while minimizing the compliances in the other directions. The weighting sum method is used to construct an objective function in which a self-adjust method is used to set the weighting factors. A constraint on the symmetry of the obtained configuration is developed. Several numerical examples are presented to demonstrate the validity of the proposed method. The obtained results reveal that the design of a flexure hinge starting from the topology level can yield more choices for compliant mechanism design and obtain better designs that achieve higher performance.
基金supported by National Natural Science Foundation ofChina(Grant No.50935002)
文摘The thin-walled tube flexure（TWTF） hinges have important potential application value in the deployment mechanisms of satellite and solar array, but the optimal design of the TWTF hinges haven＇t been completely solved, which restricts their applications. An optimal design method for the qusai-static folding and deploying of TWTF hinges with double slots is presented based on the response surface theory. Firstly, the full factorial method is employed to design of the experiments. Then, the finite element models of the TWTF hinges with double slots are constructed to simulate the qusai-static folding and deploying non-linear analysis. What＇s more, the mathematical model of the TWTF flexure hinge quasi-static folding and deploying properties are derived by the response surface method. Considering of small mass and high stability, the peak moment of quasi-static folding and deploying as well as the lightless are set as the objectives to get the optimal performances. The relative errors of the objectives between the optimal design results and the FE analysis results are less than 7%, which demonstrates the precision of the surrogate models. Lastly, the parameter study shows that both the slots length and the slots width both have significant effects to the peak moment of quasi-static folding and deploying of TWTF hinges with double slots. However, the maximum Mises stress of quasi-static folding is more sensitive to the slots length than the slots width. The proposed research can be applied to optimize other thin-walled flexure hinges under quasi-static folding and deploying, which is of great importance to design of flexure hinges with high stability and low stress.
基金supported by National Natural Science Foundation of China(Grant No. 50675007)Program for New Century Excellent Talents in University of China (Grant No. NCET-06-0165)
文摘Large-deflection flexure pivot is widely used in high precision rotation application, but there are less flexure configurations and simple and convenient design methods, This paper presents a novel large-deflection curved-compliant annulus-shaped flexure pivot composed of six curved beam flexure elements. It can offer more than lO^angular stroke theoretically. Firstly, main-motion pseudo-rigid-body method is introduced to establish the flexure pivot model. Although pseudo-rigid-body method can be used to analyze the large-deformation flexure pivot performance, the method is definitely a laborious and difficult task for designing this novel flexure pivot. In order to simply the designing process, dimension-design graphs based on the parametric models and finite element analysis is presented. Using the dimension-design method as a tool, the designers can determine the optimal geometry rapidly, based on the stiffness and rotation demands of an annulus-shaped flexure pivot. Finally, dimension-design graph examples are given whose primary design aims to achieve a rotation stroke of annulus-shaped flexure pivot. The finite element analysis results show that the relative designing error between anticipative rotation stroke and graph design result is less than 4%. The dimensionless method used in designing annulus-shaped flexure pivot can reduce design process in both time and complexity. The novel annulus-shaped flexure pivot and dimension-design method are helpful supplement to configuration and design method of large-deflection flexure pivot.
基金Supported by National Natural Science Foundation of China(Grant Nos.51205134,91223201)Doctoral Fund of Ministry of Education of China(Grant No.20120172120001)Research Project of State Key Laboratory of Mechanical System and Vibration,China(Grant No.MSV201405)
文摘Conventional flexible joints generally have limited range of motion and high stress concentration. To overcome these shortcomings, corrugated flexure beam（CF beam） is designed because of its large flexibility obtained from longer overall length on the same span. The successful design of compliant mechanisms using CF beam requires manipulation of the stiffnesses as the design variables. Empirical equations of the CF beam stiffness components, except of the torsional stiffness, are obtained by curve-fitting method. The application ranges of all the parameters in each empirical equation are also discussed. The ratio of off-axis to axial stiffness is considered as a key characteristic of an effective compliant joint. And parameter study shows that the radius of semi-circular segment and the length of straight segment contribute most to the ratio. At last, CF beam is used to design translational and rotational flexible joints, which also verifies the validity of the empirical equations. CF beam with large flexibility is presented, and empirical equations of its stiffness are proposed to facilitate the design of flexible joint with large range of motion.
基金supported by National Natural Science Foundation of China (Grant No. 51175372)National Key Special Project of Science and Technology of China (Grant No. 2011ZX04016-011)
文摘Flexure mechanisms with decoupled characteristics have been widely utilized in precision positioning applications.However,these mechanisms suffer from either slow response or low load capability.Furthermore,asymmetric design always leads to thermal error.In order to solve these issues,a novel 2-DOF decoupled mechanism is developed by monolithically manufacturing sets of statically indeterminate symmetric（SIS） flexure structures in parallel.Symmetric design helps to eliminate the thermal error and Finite Element Analysis（FEA） results show that the maximum coupling ratio between X and Y axes is below 0.25% when a maximum pretension force of 200 N is applied.By ignoring the mass effect,all the SIS flexure structures are simplified to ＂spring-damper＂ components,from which the static and dynamics model are derived.The relation between the first resonant frequency of the mechanism and the load is investigated by incorporating the load mass into the proposed dynamics model.Analytical results show that even with a load of 0.5 kg,the first resonant frequency is still higher than 300 Hz,indicating a high load capability.The mechanism＇s static and dynamic performances are experimentally examined.The linear stiffnesses of the mechanism at the working platform and at the driving point are measured to be 3.563 0 N·μm-1 and 3.362 1 N·μm-1,respectively.The corresponding estimation values from analytical models are 3.405 7 N·μm-1 and 3.381 7 N·μm-1,which correspond to estimation errors of-4.41% and 0.6%,respectively.With an additional load of 0.16 kg,the measured and estimated first resonant frequencies are 362 Hz and 365 Hz,respectively.The estimation error is only 0.55%.The analytical and experimental results show that the developed mechanism has good performances in both decoupling ability and load capability;its static and dynamic performance can be precisely estimated from corresponding analytical models.The proposed mechanism has wide potentials in precision positioning applications.
基金Supported by National Natural Science Foundation of China(Grant No.51575017)
文摘The current research of kinetostatic characteristics in flexure mechanisms mainly focus on the improvement of accuracy. To reduce or eliminate the parasitic motion is considered as an approach by using the common knowledge of symmetry. However, there is no study on designing the flexure mechanisms with symmetrical features as many as possible for better kinetostatic performance, when considering the resulting cost by the symmetry. In this paper, the concept of degree of symmetry(DoS) is proposed for the first time, which is committed to symmetry design in the phase of conceptual design. A class of flexure mechanisms with 0?DoS, 1?DoS, 2?DoS and 3?DoS are synthesized respectively based on the Freedom and Constraint Topology method. Their overall compliance matrices in an analytical form formulated within the framework of the screw theory are used to analyze and compare the effect of different number of DoS on the kinetostatic characteristics for flexure mechanisms. The finite element analysis(FEA) simulations are implemented to verify the analytical results. These results show that the higher the DoS is, the smaller the parasitic motion error will be. The flexure model with 3?DoS is optimized according to the overall compliance matrix and then tested by using the FEA simulation. The testing result shows that with the best combination parameters, the parasitic motion error for 3?DoS mechanism is almost eliminated. This research introduces a design principle which can alleviate the unwanted parasitic motion for better accuracy.
基金Project(2002AA422260) supported by the National High Technology Research and Development Program of ChinaProject(2011-6) supported by CAST-HIT Joint Program,ChinaProject supported by Harbin Institute of Technology (HIT) Overseas Talents Introduction Program,China
文摘A novel 6-PSS flexible parallel mechanism was presented,which employed wide-range flexure hinges as passive joints.The proposed mechanism features micron level positioning accuracy over cubic centimeter scale workspace.A three-layer back-propagation(BP) neural network was utilized to the kinematics analysis,in which learning samples containing 1 280 groups of data based on stiffness-matrix method were used to train the BP model.The kinematics performance was accurately calculated by using the constructed BP model with 19 hidden nodes.Compared with the stiffness model,the simulation and numerical results validate that BP model can achieve millisecond level computation time and micron level calculation accuracy.The concept and approach outlined can be extended to a variety of applications.
文摘This paper presents a precise solution to predict the behavior of steel fiber reinforced concrete(SFRC) under the four point bending test(FPBT).All the force components at the beam section(before and after cracking) are formulated by applying these assumptions:a realistic stress-strain model is used for concrete behavior in compression,a linear response is considered for the uncracked tension region in a concrete constitutive model,and an exponential relationship is proposed as a stress-crack opening in the crack region which requires two parameters.Then the moment capacity of the critical cracked section is calculated by using these forces and satisfying equilibrium law at the section.Parametric studies are done on the behavior of SFRC to assess the sensitivity of the solution.Finally,this solution is validated with some existing experimental data.The result shows the proposed solution is able to estimate the behavior of SFRC under FPBT.
基金The authors would like to acknowledge support from the Open Foundation of the State Key Laboratory of Tribology ＆ Institute of Manufacturing Engineering （SKL2016B05）, and the National Natural Science Foundation of China （NSFC） （61327003）.
文摘This paper presents the design, development, and control of a large range beam flexure-based nano servo system for the micro-stereolithography （MSL） process. As a key enabler of high accuracy in this process, a compact desktop-size beam flexure-based nanopositioner was designed with millimeter range and nanometric motion quality. This beam flexure-based motion system is highly suitable for harsh operation conditions, as no assembly or maintenance is required during the operation. From a mechanism design viewpoint, a mirror-symmetric arrangement and appropriate redundant constraints are crucial to reduce undesired parasitic motion. Detailed finite element analysis （FEA） was conducted and showed satisfactory mechanical features. With the identified dynamic models of the nanopositioner, real-time control strategies were designed and implemented into the monolithically fabricated prototype system, demonstrating the enhanced tracking capability of the MSL process. The servo system has both a millimeter operating range and a root mean square （RMS） tracking error of about 80 nm for a circular traiectorv.
文摘The alignment accuracy of the strap-down inertial navigation system （SINS） of airborne weapon is greatly degraded by the dynamic wing flexure of the aircraft. An adaptive Kalman filter uses innovation sequences based on the maximum likelihood estimated criterion to adapt the system noise covariance matrix and the measurement noise covariance matrix on line, which is used to estimate the misalignment if the model of wing flexure of the aircraft is unknown. From a number of simulations, it is shown that the accuracy of the adaptive Kalman filter is better than the conventional Kalman filter, and the erroneous misalignment models of the wing flexure of aircraft will cause bad estimation results of Kalman filter using attitude match method.
基金Supported by Chongqing medical scientific research project(Joint project of Chongqing Health Commission and Science and Technology Bureau),No.2021MSXM309.
文摘BACKGROUND Situs inversus totalis(SIT)is a rare group of congenital developmental malformations in the clinical setting,with all organs in the chest and abdomen existing in a mirror image reversal of their normal positions.Few reports have described laparoscopic surgery for colorectal cancer in patients with SIT,and it is considered difficult even for an experienced surgeon because of the mirror positioning.We present a case report of laparoscopic radical resection of a colonic splenic flexure carcinoma in a patient with SIT.CASE SUMMARY A 72-year-old male was referred to our hospital with colonic splenic flexure carcinoma,and computed tomography showed that all the organs in the chest and abdomen were inverted.Laparoscopic hemicolectomy with complete mesocolic excision was safely performed.The operating surgeon stood on the patient’s left side,which is opposite of the normal location.CONCLUSION Abdominal computed tomography is an effective method for diagnosing SIT preoperatively in patients with colonic splenic flexure carcinomas.Laparoscopic radical resection is difficult,but it is well established and safe.The surgeon should stand in the opposite position and perform backhand operations.
文摘The effects of ply orientation angle of composite flexures on stability of hingeless rotor blade system are studied.The composite hingeless rotor blade system is simplified as a hub,a flap flexure and a lag flexure.pitch bearing and main blade.The kinematics formulations are inferred by employing the moderate deflection beam theory.The shear deformation and warping related to torsion are considered.The quasi-steady strip theory with dynamic inflow effects is applied to obtain the aerodynamic loads acting on the blade.Based on these.the set of finite element formulations of a hingeless rotor blade system is worked out.The numerical results show that the ply angle of the composite flexures has great effects on the aeroelastic stability of rotor blade.
基金This project is supported by National Hi-tech Research and Development Program of China(863 Program, No.2002AA422260).
文摘A large workspace flexure parallel positioner system is developed, which can attain sub-micron scale accuracy over cubic centimeter motion range for utilizing novel wide-range flexure hinges instead of the conventional mechanism joints. Flexure hinges eliminate backlash and friction, but on the other hand their deformation caused by initial loads influences the positioning accuracy greatly, so discussions about loads＇ influence analysis on this flexure parallel positioner is very necessary. The stiffness model of the whole mechanism is presented via stiffness assembly method based on the stiffness model of individual flexure hinge, And the analysis results are validated by the finite element analysis （FEA） simulation and experiment tests, which provide essential data to the practical application of this positioner system.
基金Selected from Proceedings of the 7th International Conference on Frontiers of DesignManufacturing(ICFDM'2006)This project is partially sup-ported by the Research Grant from the Hong Kong Watch Manufacturers Association the Federation of Hong Kong Watch TradeIndustry Technology Commission China(No.ITS/001/05).
文摘A new type of air bearing with flexure structure is introduced. The new bearing is designed for precision mechanical engineering devices such as mechanical watch movement. The new design uses the flexure structure to provide 3D damping to absorb shocks from all directions. Two designs are presented： one has 12 T-shape slots in the radian direction while the other has 8 spiral slots in the radian direction. Both designs have flexure mountings on the axial directions. Based on the finite element analysis （FEA）, the new bearing can reduce the vibration （displacement） by as much as 8.37% and hence, can better protect the shafts.
基金Supported by National Natural Science Foundation of China(Grant No.51305022)the Fundamental Research Funds for the Central Universities,China(Grant No.FRF-TP-13-013A)National Science Foundation for Post-doctoral Scientists of China(Grant No.2012M520163)
文摘In design of flexure mechanism, diminishing the parasitic-motion is a key point to improve the accuracy. However, most of existing topics concentrate on improving the accuracy of linear-motion flexure mechanisms via compensating the parasitic error, but few research the multi-dimensional flexure mechanisms. A general design principle and method for high-precision flexure mechanisms based on the parasitic-motion compensation is presented, and the proposed method can compensate the parasitic rotation in company with translation, or the parasitic translation in company with rotation, or both. The crucial step for the method is that the parasitic motion of a flexure mechanism is formulated and evaluated in terms of its compliance. The overall compliance matrix of a general flexure mechanism is formulated by using screw theory firstly, then the criteria for the parasitic motions is introduced by analyzing the characteristics of the resultant compliance matrix as well as with aid of the concept of instantaneous rotation center. Subsequently, a compliance-based compensation approach for reducing parasitic-motion is addressed as the most important part. The design principles and procedure are further discussed to help with improving the accuracy of flexure mechanisms, and case studies are provided to illustrate this method. Finally, an analytical verification is provided to demonstrate that the symmetry design philosophy widely used in flexure design can effectively improve accuracy in terms of the proposed method. The proposed compensation method can be well used to diminish the parasitic-motion of multi-dimensional flexure mechanisms.
基金Sponsored by the National High-tech R&D Progrom(Grant No.2011AA12A103)the Equipment Development Fund(Grant No.08001SA050)
文摘The purpose of this thesis is to derive the flexibility formula of the corner-filleted flexure hinge easily and conveniently and use it to design a micro-rotation compliant mechanism. Firstly,we get the corner-filleted flexure hinge flexibility formula by methods of symmetry transformation and coordinates translation. The correctness of this formula is validated on the basis of the finite element method and under the premise that the effects of shear stress are taken into consideration. Then a micro-rotation compliant mechanism is designed in accordance with the corner-filleted flexure hinge,and the deduction and analysis of its working moment/rigidity are conducted. Moreover,this theoretical formula is proved to be accurate and reliable through the finite element analysis and the experimental verification,based on which the structural design and optimization can be made on the rotating part of a micro adjustment device. The results illustrate that designing and optimizing the structures by the analysis model is convenient and reliable so that complicated 3D modeling and finite element analysis are not needed.
基金supported by the National Natural Science Foundation of China (No. 51305013)
文摘Beam flexure hinges can achieve accurate motion and force control through the elastic deformation. This paper presents a nonlinear model for uniform and circular cross-section spatial beam flexure hinges which are commonly employed in compliant parallel mechanisms. The proposed beam model takes shear deformations into consideration and hence is applicable to both slender and thick beam flexure hinges. Starting from the first principles, the nonlinear strain measure is derived using beam kinematics and expressed in terms of translational displacements and rotational angles. Second-order approximation is employed in order to make the nonlinear strain within acceptable accuracy. The natural boundary conditions and nonlinear governing equations are derived in terms of rotational Euler angles and subsequently solved for combined end loads. The resulting end load-displacement model, which is compact and closed-form, is proved to be accurate for both slender and thick beam flexure using nonlinear finite element analysis. This beam model can provide designers with more design insight of the spatial beam flexure and thus will benefit the structural design and optimization of compliant manipulators.
