A robust controller method for flexible joint robot considering the effect caused by nonlinear friction was presented.The nonlinear friction was denoted as inverse additive output uncertainty relative to the nominal m...A robust controller method for flexible joint robot considering the effect caused by nonlinear friction was presented.The nonlinear friction was denoted as inverse additive output uncertainty relative to the nominal model in our work,based on which the describing function was analyzed in frequency domain,and the weighting function of nonlinear friction was further calculated as well. By combining the friction uncertainty,the mixed sensitivity H∞optimization was proposed as the benchmark for controller design, which also leaded to good performance of robustness. Furthermore,unstructured perturbation to the system was analyzed so that the stability was guaranteed. Simulation results show that the proposed controller can provide excellent tracking and regulation performance.展开更多
In order to alleviate the steady-state position error and the destabilizing effect of the nonlinear friction, a novel compensation method is presented, which modified the traditional Southward's compensation metho...In order to alleviate the steady-state position error and the destabilizing effect of the nonlinear friction, a novel compensation method is presented, which modified the traditional Southward's compensation method. Estimated the nonlinear friction model using an identification method, the effect caused by its nonlinear component can be compensated, and an enhanced tracking performance is verified on a selectively compliant articulated robot arm(SCARA) robot.展开更多
For a pneumatic actuator,precise positioning is difficult to obtain because of the compressibility of air and the static friction and Coulomb friction.This paper develops a nonlinear friction compensation scheme for p...For a pneumatic actuator,precise positioning is difficult to obtain because of the compressibility of air and the static friction and Coulomb friction.This paper develops a nonlinear friction compensation scheme for precise positioning of a pneumatic system.This Scheme is tested by simulation and experiment and is shown to be effective.展开更多
In semiconductor precision packaging and other applications involving alignment of automated equipment,the nonlinear motion caused by structural characteristics and friction effects on torque-type rotating motion stag...In semiconductor precision packaging and other applications involving alignment of automated equipment,the nonlinear motion caused by structural characteristics and friction effects on torque-type rotating motion stages seriously affects output accuracy and stability.To solve this problem,the motion characteristics of a rotating stage and the mechanism by which friction nonlinearity influences accuracy are analyzed in detail.In addition,a compound control strategy based on a kinematic model and the Stribeck friction model is designed.A friction disturbance observer based on output position feedback is improved for simple parameter tuning.Finally,an experimental system is constructed to carry out validation tests,including identification of nonlinear characteristics and performance comparisons.The experimental results show that the linear tracking error of the torque-type rotating stage is less than 1.47µm after adoption of the proposed model-based composite control strategy,and the corresponding rotary angle deviation is less than 0.0153°.The linearity of output motion is increased to 97.59%and the error compensation effect is improved by 51.6%compared with the PID control method.The experimental results confirm that the analysis method adopted here and the proposed compensation strategy can effectively reduce frictional nonlinearity and improve motion accuracy.The proposed method can also be applied to other precision electromechanical systems.展开更多
This article focuses on the problem of how to accurately calculate the joint control torques when the explosion-proof robot performs collision detection without sensors and gives a complete solution.Nonlinear joint fr...This article focuses on the problem of how to accurately calculate the joint control torques when the explosion-proof robot performs collision detection without sensors and gives a complete solution.Nonlinear joint frictions are incorporated into the dynamic model of a robotic manip-ulator to improve calculation accuracy.A genetic algorithm is used to optimise the excitation trajectories to fully stimulate the robot dynamic characteristics.Effective and applicable data filtering and smoothing methods are proposed and the Iteratively Reweighted Least-Squares method based on the error term is applied to identify the robot dynamic parameters.Compared with Ordinary Least-Squares method,the proposed algorithm improves the accuracy of joint control torques estimation.展开更多
A Jeffery-Hamel （J-H） flow model of the non-Newtonian fluid type inside a convergent wedge （inclined walls） with a wall friction is derived by a nonlinear ordinary differential equation with appropriate boundary c...A Jeffery-Hamel （J-H） flow model of the non-Newtonian fluid type inside a convergent wedge （inclined walls） with a wall friction is derived by a nonlinear ordinary differential equation with appropriate boundary conditions based on similarity relationships. Unlike the usual power law model, this paper develops nonlinear viscosity based only on a tangential coordinate function due to the radial geometry shape. Two kinds of solutions are developed, i.e., analytical and semi-analytical （numerical） solutions with suitable assumptions. As a result of the parametric examination, it has been found that the Newtonian normalized velocity gradually decreases with the tangential direction progress. Also, an increase in the friction coefficient leads to a decrease in the normalized Newtonian velocity profile values. However, an increase in the Reynolds number causes an increase in the normalized velocity function values. Additionally, for the small values of wedge semi-angle, the present solutions are in good agreement with the previous results in the literature.展开更多
This paper presents a refined parabolic approximation model of the mild slope equation to simulate the combination of water wave refraction and diffraction in the large coastal region. The bottom friction and weakly n...This paper presents a refined parabolic approximation model of the mild slope equation to simulate the combination of water wave refraction and diffraction in the large coastal region. The bottom friction and weakly nonlinear term are included in the model. The difference equation is established with the Crank-Nicolson scheme. The numerical test shows that some numerical prediction results will be inaccurate in complicated topography without considering weak nonlinearity; the bottom friction will make wave height damping and it can not be neglected for calculation of wave field in large areas.展开更多
Reinforced concrete （r.c.） framed buildings designed in compliance with inadequate seismic classifi- cations and code provisions present in many cases a high vulnerability and need to be retrofitted. To this end, th...Reinforced concrete （r.c.） framed buildings designed in compliance with inadequate seismic classifi- cations and code provisions present in many cases a high vulnerability and need to be retrofitted. To this end, the insertion of a base isolation system allows a considerable reduction of the seismic loads transmitted to the super- structure. However, strong near-fault ground motions, which are characterised by long-duration horizontal pulses, may amplify the inelastic response of the superstructure and induce a failure of the isolation system. The above considerations point out the importance of checking the effectiveness of different isolation systems for retrofitting a r.c. framed structure. For this purpose, a numerical inves- tigation is carried out with reference to a six-storey r.c. framed building, which, primarily designed （as to be a fixed-base one） in compliance with the previous Italian code （DM96） for a medium-risk seismic zone, has to be retrofitted by insertion of an isolation system at the base for attaining performance levels imposed by the current Italian code （NTC08） in a high-risk seismic zone. Besides the （fixed-base） original structure, three cases of base isolation are studied： elastomeric bearings acting alone （e.g. HDLRBs）; in-parallel combination of elastomeric and friction bearings （e.g. high-damping-laminated-rubber beatings, HDLRBs and steel-PTFE sliding bearings, SBs）; friction bearings acting alone （e.g. friction pendulum bearings, FPBs）. The nonlinear analysis of the fixed-base and base-isolated structures subjected to horizontal com- ponents of near-fault ground motions is performed for checking plastic conditions at the potential critical （end） sections of the girders and columns as well as critical conditions of the isolation systems. Unexpected high val- ues of ductility demand are highlighted at the lower floors of all base-isolated structures, while re-centring problems of the base isolation systems under near-fault earthquakes are expected in case of friction beatings acting alone （i.e. FPBs） or that in combination （i.e. SBs） with HDLRBs.展开更多
基金National Natural Science Foundation of China(No.61273339)
文摘A robust controller method for flexible joint robot considering the effect caused by nonlinear friction was presented.The nonlinear friction was denoted as inverse additive output uncertainty relative to the nominal model in our work,based on which the describing function was analyzed in frequency domain,and the weighting function of nonlinear friction was further calculated as well. By combining the friction uncertainty,the mixed sensitivity H∞optimization was proposed as the benchmark for controller design, which also leaded to good performance of robustness. Furthermore,unstructured perturbation to the system was analyzed so that the stability was guaranteed. Simulation results show that the proposed controller can provide excellent tracking and regulation performance.
文摘In order to alleviate the steady-state position error and the destabilizing effect of the nonlinear friction, a novel compensation method is presented, which modified the traditional Southward's compensation method. Estimated the nonlinear friction model using an identification method, the effect caused by its nonlinear component can be compensated, and an enhanced tracking performance is verified on a selectively compliant articulated robot arm(SCARA) robot.
文摘For a pneumatic actuator,precise positioning is difficult to obtain because of the compressibility of air and the static friction and Coulomb friction.This paper develops a nonlinear friction compensation scheme for precise positioning of a pneumatic system.This Scheme is tested by simulation and experiment and is shown to be effective.
基金funded by the European Union’s Horizon 2020 Research and Innovation Program under the Marie Sklodowska-Curie Grant Agreement(Grant No.101026104)by the National Natural Science Foundation of China(Grant No.U20A6004)in part by the State Key Laboratory of Precision Electronics Manufacturing Technology and Equipment(Grant No.JMDZ202314).
文摘In semiconductor precision packaging and other applications involving alignment of automated equipment,the nonlinear motion caused by structural characteristics and friction effects on torque-type rotating motion stages seriously affects output accuracy and stability.To solve this problem,the motion characteristics of a rotating stage and the mechanism by which friction nonlinearity influences accuracy are analyzed in detail.In addition,a compound control strategy based on a kinematic model and the Stribeck friction model is designed.A friction disturbance observer based on output position feedback is improved for simple parameter tuning.Finally,an experimental system is constructed to carry out validation tests,including identification of nonlinear characteristics and performance comparisons.The experimental results show that the linear tracking error of the torque-type rotating stage is less than 1.47µm after adoption of the proposed model-based composite control strategy,and the corresponding rotary angle deviation is less than 0.0153°.The linearity of output motion is increased to 97.59%and the error compensation effect is improved by 51.6%compared with the PID control method.The experimental results confirm that the analysis method adopted here and the proposed compensation strategy can effectively reduce frictional nonlinearity and improve motion accuracy.The proposed method can also be applied to other precision electromechanical systems.
基金supported by the National Key Research and Development Program:[Grant Number 2018YFB1305700].
文摘This article focuses on the problem of how to accurately calculate the joint control torques when the explosion-proof robot performs collision detection without sensors and gives a complete solution.Nonlinear joint frictions are incorporated into the dynamic model of a robotic manip-ulator to improve calculation accuracy.A genetic algorithm is used to optimise the excitation trajectories to fully stimulate the robot dynamic characteristics.Effective and applicable data filtering and smoothing methods are proposed and the Iteratively Reweighted Least-Squares method based on the error term is applied to identify the robot dynamic parameters.Compared with Ordinary Least-Squares method,the proposed algorithm improves the accuracy of joint control torques estimation.
文摘A Jeffery-Hamel （J-H） flow model of the non-Newtonian fluid type inside a convergent wedge （inclined walls） with a wall friction is derived by a nonlinear ordinary differential equation with appropriate boundary conditions based on similarity relationships. Unlike the usual power law model, this paper develops nonlinear viscosity based only on a tangential coordinate function due to the radial geometry shape. Two kinds of solutions are developed, i.e., analytical and semi-analytical （numerical） solutions with suitable assumptions. As a result of the parametric examination, it has been found that the Newtonian normalized velocity gradually decreases with the tangential direction progress. Also, an increase in the friction coefficient leads to a decrease in the normalized Newtonian velocity profile values. However, an increase in the Reynolds number causes an increase in the normalized velocity function values. Additionally, for the small values of wedge semi-angle, the present solutions are in good agreement with the previous results in the literature.
基金National Natural Science Foundation of China(Grant No.19732004)
文摘This paper presents a refined parabolic approximation model of the mild slope equation to simulate the combination of water wave refraction and diffraction in the large coastal region. The bottom friction and weakly nonlinear term are included in the model. The difference equation is established with the Crank-Nicolson scheme. The numerical test shows that some numerical prediction results will be inaccurate in complicated topography without considering weak nonlinearity; the bottom friction will make wave height damping and it can not be neglected for calculation of wave field in large areas.
基金financed by Re.L.U.I.S.(Italian network of university laboratories of earthquake engineering),under the project "Convenzione D.P.C.-Re.L.U.I.S. 2014-2016,WPI,Isolation and Dissipation"
文摘Reinforced concrete （r.c.） framed buildings designed in compliance with inadequate seismic classifi- cations and code provisions present in many cases a high vulnerability and need to be retrofitted. To this end, the insertion of a base isolation system allows a considerable reduction of the seismic loads transmitted to the super- structure. However, strong near-fault ground motions, which are characterised by long-duration horizontal pulses, may amplify the inelastic response of the superstructure and induce a failure of the isolation system. The above considerations point out the importance of checking the effectiveness of different isolation systems for retrofitting a r.c. framed structure. For this purpose, a numerical inves- tigation is carried out with reference to a six-storey r.c. framed building, which, primarily designed （as to be a fixed-base one） in compliance with the previous Italian code （DM96） for a medium-risk seismic zone, has to be retrofitted by insertion of an isolation system at the base for attaining performance levels imposed by the current Italian code （NTC08） in a high-risk seismic zone. Besides the （fixed-base） original structure, three cases of base isolation are studied： elastomeric bearings acting alone （e.g. HDLRBs）; in-parallel combination of elastomeric and friction bearings （e.g. high-damping-laminated-rubber beatings, HDLRBs and steel-PTFE sliding bearings, SBs）; friction bearings acting alone （e.g. friction pendulum bearings, FPBs）. The nonlinear analysis of the fixed-base and base-isolated structures subjected to horizontal com- ponents of near-fault ground motions is performed for checking plastic conditions at the potential critical （end） sections of the girders and columns as well as critical conditions of the isolation systems. Unexpected high val- ues of ductility demand are highlighted at the lower floors of all base-isolated structures, while re-centring problems of the base isolation systems under near-fault earthquakes are expected in case of friction beatings acting alone （i.e. FPBs） or that in combination （i.e. SBs） with HDLRBs.
