As a newly invented parallel kinematic machine（PKM）, Exechon has found its potential application in machining and assembling industries due to high rigidity and high dynamics. To guarantee the overall performance, t...As a newly invented parallel kinematic machine（PKM）, Exechon has found its potential application in machining and assembling industries due to high rigidity and high dynamics. To guarantee the overall performance, the loading conditions and deflections of the key components must be revealed to provide basic mechanic data for component design. For this purpose, a kinetostatic model is proposed with substructure synthesis technique. The Exechon is divided into a platform subsystem, a fixed base subsystem and three limb subsystems according to its structure. By modeling the limb assemblage as a spatial beam constrained by two sets of lumped virtual springs representing the compliances of revolute joint, universal joint and spherical joint, the equilibrium equations of limb subsystems are derived with finite element method（FEM）. The equilibrium equations of the platform are derived with Newton＇s 2nd law. By introducing deformation compatibility conditions between the platform and limb, the governing equilibrium equations of the system are derived to formulate an analytical expression for system＇s deflections. The platform＇s elastic displacements and joint reactions caused by the gravity are investigated to show a strong position-dependency and axis-symmetry due to its kinematic and structure features. The proposed kinetostatic model is a trade-off between the accuracy of FEM and concision of analytical method, thus can predict the kinetostatics throughout the workspace in a quick and succinct manner. The proposed modeling methodology and kinetostatic analysis can be further expanded to other PKMs with necessary modifications, providing useful information for kinematic calibration as well as component strength calculations.展开更多
Continuum robots actuated by flexible rods have large potential applications,such as detection and operation tasks in confined environments,since the push and pull actuation of flexible rods withstand tension and comp...Continuum robots actuated by flexible rods have large potential applications,such as detection and operation tasks in confined environments,since the push and pull actuation of flexible rods withstand tension and compressive force,and increase the structure's rigidity.In this paper,a generalized kinetostatics model for multi-module and multi-segment continuum robots considering the effect of friction based on the Cosserat rod theory is established.Then,the model is applied to a two-module rod-driven continuum robot with winding ropes to analyze its deformation and load characteristics.Four different in-plane configurations under the external load term as S1,S2,C1,and C2 are defined.Taking a bending plane as an example,the tip deformation along thex-axis of these shapes is simulated and compared,which shows that the load capacity of C1 and C2 is generally larger than that of S1 and S2.Furthermore,the deformation experiments and simulations show that the maximum error ratio without external loads relative to the total length is no more than 3%,and it is no more than 4.7%under the external load.The established kinetostatics model is proven sufficient to accurately analyze the rod-driven continuum robot with the consideration of internal friction.展开更多
Being di erent from avoidance of singularity of closed-loop linkages, this paper employs the kinematic singularity to construct compliant mechanisms with expected nonlinear sti ness characteristics to enrich the metho...Being di erent from avoidance of singularity of closed-loop linkages, this paper employs the kinematic singularity to construct compliant mechanisms with expected nonlinear sti ness characteristics to enrich the methods of compliant mechanisms synthesis. The theory for generating kinetostatic nonlinear sti ness characteristic by the kinematic limb-singularity of a crank-slider linkage is developed. Based on the principle of virtual work, the kinetostatic model of the crank-linkage with springs is established. The influences of spring sti ness on the toque-position angle relation are analyzed. It indicates that corresponding spring sti ness may generate one of four types of nonlinear sti ness characteristics including the bi-stable, local negative-sti ness, zero-sti ness or positive-sti ness when the mechanism works around the kinematic limb-singularity position. Thus the compliant mechanism with an expected sti ness characteristic can be constructed by employing the pseudo rigid-body model of the mechanism whose joints or links are replaced by corresponding flexures. Finally, a tri-symmetrical constant-torque compliant mechanism is fabricated,where the curve of torque-position angle is obtained by an experimental testing. The measurement indicates that the compliant mechanism can generate a nearly constant-torque zone.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
The pose accuracy of parallel manipulators(PMs)is a key index to measure their performance.Establishing the grav-ity-based kinetostatic model of a parallel robot provides an important basis for its error composition a...The pose accuracy of parallel manipulators(PMs)is a key index to measure their performance.Establishing the grav-ity-based kinetostatic model of a parallel robot provides an important basis for its error composition and accuracy improvement.In this paper,a kinetostatic modeling approach that takes real gravity distribution into consideration is proposed to analyze the influence of gravity on the infinitesimal twist and actuator forces of PMs.First,the duality of the twist screw and constraint wrenches are used to derive the gravity-attached constraint wrenches independent of the external load and the limb stiffness matrix corresponding to the kinematics-based constraint wrenches.Sec-ond,the gravity model of the mechanism is established based on the screw theory and the principle of virtual work.Finally,the analytical formulas of the infinitesimal twist and the actuator force of PMs are obtained,and the influences of the external load,platform gravity,and rod gravity on the stiffness of the mechanism are decoupled.The non-overconstrained 3RPS and overconstrained 2PRU-UPR PMs are taken as examples to verify the proposed method.This research proposes a methodology to analyze the infinitesimal deformation of the mechanism under the influence of gravity.展开更多
In-situ maintenance is of great significance for improving the efficiency and ensuring the safety of aero-engines.The cable-driven continuum robot(CDCR)with twin-pivot compliant mechanisms,which is enabled with flexib...In-situ maintenance is of great significance for improving the efficiency and ensuring the safety of aero-engines.The cable-driven continuum robot(CDCR)with twin-pivot compliant mechanisms,which is enabled with flexible deformation capability and confined space accessibility,has emerged as a novel tool that aims to promote the development of intelligence and efficiency for in-situ aero-engine maintenance.The high-fidelity model that describes the kinematic and morphology of CDCR lays the foundation for the accurate operation and control for in-situ maintenance.However,this model was not well addressed in previous literature.In this study,a general kinetostatic modeling and morphology characterization methodology that comprehensively contains the effects of cable-hole friction,gravity,and payloads is proposed for the CDCR with twin-pivot compliant mechanisms.First,a novel cable-hole friction model with the variable friction coefficient and adaptive friction direction criterion is proposed through structure optimization and kinematic parameter analysis.Second,the cable-hole friction,all-component gravities,deflection-induced center-of-gravity shift of compliant joints,and payloads are all considered to deduce a comprehensive kinetostatic model enabled with the capacity of accurate morphology characterization for CDCR.Finally,a compact continuum robot system is integrated to experimentally validate the proposed kinetostatic model and the concept of in-situ aero-engine maintenance.Results indicate that the proposed model precisely predicts the morphology of CDCR and outperforms conventional models.The compact continuum robot system could be considered a novel solution to perform in-situ maintenance tasks of aero-engines in an invasive manner.展开更多
Reducing the peak actuating force(PAF)and parasitic displacement is of high significance for improving the performance of compliant parallel mechanisms(CPMs).In this study,a 2-DOF 4-4R compliant parallel pointing mech...Reducing the peak actuating force(PAF)and parasitic displacement is of high significance for improving the performance of compliant parallel mechanisms(CPMs).In this study,a 2-DOF 4-4R compliant parallel pointing mechanism(4-4R CPPM)was used as the object,and the actuating force of the mechanism was optimized through redundant actuation.This was aimed at minimizing the PAF and parasitic displacement.First,a kinetostatic model of the redundantly actuated 4-4R CPPM was established to reveal the relationship between the input forces/displacements and the output displacements of the mobile platform.Subsequently,based on the established kinetostatic model,methods for optimizing the actuating force distribution with the aim of minimizing the PAF and parasitic displacement were introduced successively.Second,a simulated example of a mobile platform’s spatial pointing trajectory validated the accuracy of the kinetostatic model.The results show a less than 0.9%relative error between the analytical and finite element(FE)results,and the high consistency indicates the accuracy of the kinetostatic model.Then,the effectiveness of the method in minimizing the PAF and parasitic displacement was validated using two simulated examples.The results indicate that compared with the non-redundant actuation case,the PAF of the mechanism could be reduced by up to 50%,and the parasitic displacement was reduced by approximately three-four orders of magnitude by means of redundant actuation combined with the optimal distribution of the actuating force.As expected,with the reduction in parasitic displacement,the FE-results of the output angular displacements(θ_(x) andθ_(z))of the mobile platform were closer to the target oscillation trajectory.This further verified that the reduction in parasitic displacement is indeed effective in improving the motion accuracy of the mechanism.The advantage of this proposed method is that it reduces the PAF and parasitic displacement from the perspective of the actuating force control strategy,without the requirement of structural changes to the original mechanism.展开更多
This study addresses the challenges of tendon-driven continuum robots in terms of high-performance joint design,high-accuracy and-efficiency mechanical modeling,and inverse kinetostatic-based control.First,a general d...This study addresses the challenges of tendon-driven continuum robots in terms of high-performance joint design,high-accuracy and-efficiency mechanical modeling,and inverse kinetostatic-based control.First,a general design framework for rigid–flexible coupled continuum robots is proposed inspired by the Freedom and Constraint Topology theory.Based on this framework,a novel claw-type continuum robot with high torsion resistance,high-precision positioning,and excellent anti-buckling performance is developed.Consequently,a novel kinetostatic model named the separated beam equilibrium model(SBEM)is proposed by solving the equilibrium equations for each unit individually rather than recursively,which achieves high modeling accuracy and efficiency.Finally,an iterative inverse kinetostatic-based control method involving mechanic factors is proposed.Comparative experimental results demonstrate that the claw-type continuum robot outperforms the twin-pivot continuum robot in terms of torsion resistance by more than 300 times.Moreover,the SBEM achieves high morphology estimation accuracy with errors less than 2.91%of manipulator length and high efficiency with more than 20 times improvement for computation reduction compared with the conventional chained beam constraint model.Furthermore,the iterative inverse kinetostatic model-based control obtains a tip error less than 3.70%of manipulator length by only using the open-loop method.The proposed design,modeling,and control method exhibits vast potential for continuum robots when tackling challenging tasks such as inspection,maintenance,and medical surgery in confined and unstructured environments including engine flow paths,nuclear conduits,and human body cavities.展开更多
Parallel continuum robots(PCRs) have attracted increasing attention in the robotics community due to their simplicity in structure,inherence with compliance, and easiness of realization. Over the past decade, a variet...Parallel continuum robots(PCRs) have attracted increasing attention in the robotics community due to their simplicity in structure,inherence with compliance, and easiness of realization. Over the past decade, a variety of novel designs have been reported to enrich their diversity. However, there is a lack of systematic review of these emerging robots. To this end, this paper conducts a comprehensive survey on the mechanism design, kinetostatic modeling and analysis, and performance evaluation. For these robots, kinetostatic modeling plays a fundamental role throughout the design, analysis, and control stages. A systematic review of the existing approaches for kinetostatic modeling and analysis is provided, and a comparison is made to distinguish their differences. As well, a classification is made according to the characteristics of structure and actuation. In addition, performance evaluation on the workspace, stability, and singularity is also overviewed. Finally, the scenarios of potential applications are elaborated, and future research prospects are discussed. We believe that the information provided in this paper will be particularly useful for those who are interested in PCRs.展开更多
基金Supported by State Key Laboratory for Manufacturing Systems Engineering,Xi’an Jiaotong University(Grant No.sklms2015004)Open Research Fund of Key Laboratory of High Performance Complex Manufacturing,Central South University(Grant No.Kfkt2013-12)+2 种基金Open Fund of Shanghai Key Laboratory of Digital Manufacture for Thin-walled Structures(Grant No.2014001)Innovation Research Fund for Postgraduates of Anhui University of Technology(Grant No.2014054)Engineering and Physical Science Research Council in the United Kingdom(Grant No.EP/K004964/1)
文摘As a newly invented parallel kinematic machine（PKM）, Exechon has found its potential application in machining and assembling industries due to high rigidity and high dynamics. To guarantee the overall performance, the loading conditions and deflections of the key components must be revealed to provide basic mechanic data for component design. For this purpose, a kinetostatic model is proposed with substructure synthesis technique. The Exechon is divided into a platform subsystem, a fixed base subsystem and three limb subsystems according to its structure. By modeling the limb assemblage as a spatial beam constrained by two sets of lumped virtual springs representing the compliances of revolute joint, universal joint and spherical joint, the equilibrium equations of limb subsystems are derived with finite element method（FEM）. The equilibrium equations of the platform are derived with Newton＇s 2nd law. By introducing deformation compatibility conditions between the platform and limb, the governing equilibrium equations of the system are derived to formulate an analytical expression for system＇s deflections. The platform＇s elastic displacements and joint reactions caused by the gravity are investigated to show a strong position-dependency and axis-symmetry due to its kinematic and structure features. The proposed kinetostatic model is a trade-off between the accuracy of FEM and concision of analytical method, thus can predict the kinetostatics throughout the workspace in a quick and succinct manner. The proposed modeling methodology and kinetostatic analysis can be further expanded to other PKMs with necessary modifications, providing useful information for kinematic calibration as well as component strength calculations.
基金Supported by National Natural Science Foundation of China(Grant No.51875033)Fundamental Research Funds for the Central Universities of China(Grant No.2021YJS137).
文摘Continuum robots actuated by flexible rods have large potential applications,such as detection and operation tasks in confined environments,since the push and pull actuation of flexible rods withstand tension and compressive force,and increase the structure's rigidity.In this paper,a generalized kinetostatics model for multi-module and multi-segment continuum robots considering the effect of friction based on the Cosserat rod theory is established.Then,the model is applied to a two-module rod-driven continuum robot with winding ropes to analyze its deformation and load characteristics.Four different in-plane configurations under the external load term as S1,S2,C1,and C2 are defined.Taking a bending plane as an example,the tip deformation along thex-axis of these shapes is simulated and compared,which shows that the load capacity of C1 and C2 is generally larger than that of S1 and S2.Furthermore,the deformation experiments and simulations show that the maximum error ratio without external loads relative to the total length is no more than 3%,and it is no more than 4.7%under the external load.The established kinetostatics model is proven sufficient to accurately analyze the rod-driven continuum robot with the consideration of internal friction.
基金Supported by National Natural Science Foundation of China(Grant No.51605006)Research Foundation of Key Laboratory of Manufacturing Systems and Advanced Technology of Guangxi Province,China(Grant No.17-259-05-013K)
文摘Being di erent from avoidance of singularity of closed-loop linkages, this paper employs the kinematic singularity to construct compliant mechanisms with expected nonlinear sti ness characteristics to enrich the methods of compliant mechanisms synthesis. The theory for generating kinetostatic nonlinear sti ness characteristic by the kinematic limb-singularity of a crank-slider linkage is developed. Based on the principle of virtual work, the kinetostatic model of the crank-linkage with springs is established. The influences of spring sti ness on the toque-position angle relation are analyzed. It indicates that corresponding spring sti ness may generate one of four types of nonlinear sti ness characteristics including the bi-stable, local negative-sti ness, zero-sti ness or positive-sti ness when the mechanism works around the kinematic limb-singularity position. Thus the compliant mechanism with an expected sti ness characteristic can be constructed by employing the pseudo rigid-body model of the mechanism whose joints or links are replaced by corresponding flexures. Finally, a tri-symmetrical constant-torque compliant mechanism is fabricated,where the curve of torque-position angle is obtained by an experimental testing. The measurement indicates that the compliant mechanism can generate a nearly constant-torque zone.
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Supported by National Natural Science Foundation of China(Grant No.52275036)Key Research and Development Project of Jiaxing Science and Technology Bureau of China(Grant No.2022BZ10004).
文摘The pose accuracy of parallel manipulators(PMs)is a key index to measure their performance.Establishing the grav-ity-based kinetostatic model of a parallel robot provides an important basis for its error composition and accuracy improvement.In this paper,a kinetostatic modeling approach that takes real gravity distribution into consideration is proposed to analyze the influence of gravity on the infinitesimal twist and actuator forces of PMs.First,the duality of the twist screw and constraint wrenches are used to derive the gravity-attached constraint wrenches independent of the external load and the limb stiffness matrix corresponding to the kinematics-based constraint wrenches.Sec-ond,the gravity model of the mechanism is established based on the screw theory and the principle of virtual work.Finally,the analytical formulas of the infinitesimal twist and the actuator force of PMs are obtained,and the influences of the external load,platform gravity,and rod gravity on the stiffness of the mechanism are decoupled.The non-overconstrained 3RPS and overconstrained 2PRU-UPR PMs are taken as examples to verify the proposed method.This research proposes a methodology to analyze the infinitesimal deformation of the mechanism under the influence of gravity.
基金sponsored by the National Natural Science Foundation of China(Grant Nos.52105117,52375125,and 52105118).
文摘In-situ maintenance is of great significance for improving the efficiency and ensuring the safety of aero-engines.The cable-driven continuum robot(CDCR)with twin-pivot compliant mechanisms,which is enabled with flexible deformation capability and confined space accessibility,has emerged as a novel tool that aims to promote the development of intelligence and efficiency for in-situ aero-engine maintenance.The high-fidelity model that describes the kinematic and morphology of CDCR lays the foundation for the accurate operation and control for in-situ maintenance.However,this model was not well addressed in previous literature.In this study,a general kinetostatic modeling and morphology characterization methodology that comprehensively contains the effects of cable-hole friction,gravity,and payloads is proposed for the CDCR with twin-pivot compliant mechanisms.First,a novel cable-hole friction model with the variable friction coefficient and adaptive friction direction criterion is proposed through structure optimization and kinematic parameter analysis.Second,the cable-hole friction,all-component gravities,deflection-induced center-of-gravity shift of compliant joints,and payloads are all considered to deduce a comprehensive kinetostatic model enabled with the capacity of accurate morphology characterization for CDCR.Finally,a compact continuum robot system is integrated to experimentally validate the proposed kinetostatic model and the concept of in-situ aero-engine maintenance.Results indicate that the proposed model precisely predicts the morphology of CDCR and outperforms conventional models.The compact continuum robot system could be considered a novel solution to perform in-situ maintenance tasks of aero-engines in an invasive manner.
基金Supported by Key Project of Hubei Provincial Department of Education Research Program(Grant No.D20211401).
文摘Reducing the peak actuating force(PAF)and parasitic displacement is of high significance for improving the performance of compliant parallel mechanisms(CPMs).In this study,a 2-DOF 4-4R compliant parallel pointing mechanism(4-4R CPPM)was used as the object,and the actuating force of the mechanism was optimized through redundant actuation.This was aimed at minimizing the PAF and parasitic displacement.First,a kinetostatic model of the redundantly actuated 4-4R CPPM was established to reveal the relationship between the input forces/displacements and the output displacements of the mobile platform.Subsequently,based on the established kinetostatic model,methods for optimizing the actuating force distribution with the aim of minimizing the PAF and parasitic displacement were introduced successively.Second,a simulated example of a mobile platform’s spatial pointing trajectory validated the accuracy of the kinetostatic model.The results show a less than 0.9%relative error between the analytical and finite element(FE)results,and the high consistency indicates the accuracy of the kinetostatic model.Then,the effectiveness of the method in minimizing the PAF and parasitic displacement was validated using two simulated examples.The results indicate that compared with the non-redundant actuation case,the PAF of the mechanism could be reduced by up to 50%,and the parasitic displacement was reduced by approximately three-four orders of magnitude by means of redundant actuation combined with the optimal distribution of the actuating force.As expected,with the reduction in parasitic displacement,the FE-results of the output angular displacements(θ_(x) andθ_(z))of the mobile platform were closer to the target oscillation trajectory.This further verified that the reduction in parasitic displacement is indeed effective in improving the motion accuracy of the mechanism.The advantage of this proposed method is that it reduces the PAF and parasitic displacement from the perspective of the actuating force control strategy,without the requirement of structural changes to the original mechanism.
基金supported by the National Natural Science Foundation of China(Grant Nos.52475129,52105117,and 52375125).
文摘This study addresses the challenges of tendon-driven continuum robots in terms of high-performance joint design,high-accuracy and-efficiency mechanical modeling,and inverse kinetostatic-based control.First,a general design framework for rigid–flexible coupled continuum robots is proposed inspired by the Freedom and Constraint Topology theory.Based on this framework,a novel claw-type continuum robot with high torsion resistance,high-precision positioning,and excellent anti-buckling performance is developed.Consequently,a novel kinetostatic model named the separated beam equilibrium model(SBEM)is proposed by solving the equilibrium equations for each unit individually rather than recursively,which achieves high modeling accuracy and efficiency.Finally,an iterative inverse kinetostatic-based control method involving mechanic factors is proposed.Comparative experimental results demonstrate that the claw-type continuum robot outperforms the twin-pivot continuum robot in terms of torsion resistance by more than 300 times.Moreover,the SBEM achieves high morphology estimation accuracy with errors less than 2.91%of manipulator length and high efficiency with more than 20 times improvement for computation reduction compared with the conventional chained beam constraint model.Furthermore,the iterative inverse kinetostatic model-based control obtains a tip error less than 3.70%of manipulator length by only using the open-loop method.The proposed design,modeling,and control method exhibits vast potential for continuum robots when tackling challenging tasks such as inspection,maintenance,and medical surgery in confined and unstructured environments including engine flow paths,nuclear conduits,and human body cavities.
基金supported by the National Key R&D Program of China(Grant No. 2022YFB4701200)the National Natural Science Foundation of China(NSFC)(Grant Nos. 52022056 and 51875334)the Innovation Foundation of the Manufacturing Engineering Technology Research Center of Commercial Aircraft Corporation of China(Grant No. COMAC-SFGS-2023-41)。
文摘Parallel continuum robots(PCRs) have attracted increasing attention in the robotics community due to their simplicity in structure,inherence with compliance, and easiness of realization. Over the past decade, a variety of novel designs have been reported to enrich their diversity. However, there is a lack of systematic review of these emerging robots. To this end, this paper conducts a comprehensive survey on the mechanism design, kinetostatic modeling and analysis, and performance evaluation. For these robots, kinetostatic modeling plays a fundamental role throughout the design, analysis, and control stages. A systematic review of the existing approaches for kinetostatic modeling and analysis is provided, and a comparison is made to distinguish their differences. As well, a classification is made according to the characteristics of structure and actuation. In addition, performance evaluation on the workspace, stability, and singularity is also overviewed. Finally, the scenarios of potential applications are elaborated, and future research prospects are discussed. We believe that the information provided in this paper will be particularly useful for those who are interested in PCRs.
